CN112795847B

CN112795847B - Stainless steel seamless tube for sodium-cooled fast reactor and preparation method thereof

Info

Publication number: CN112795847B
Application number: CN202110046432.6A
Authority: CN
Inventors: 高虹; 翟丽丽; 陈泽民; 沈卫强; 高江君; 常春; 陆训卫
Original assignee: Individual
Current assignee: Gao Hong
Priority date: 2021-01-14
Filing date: 2021-01-14
Publication date: 2021-11-26
Anticipated expiration: 2041-01-14
Also published as: CN112795847A

Abstract

The invention discloses a stainless steel seamless tube for a sodium-cooled fast reactor, which is based on 316H stainless steel base material to carry out micro-alloying component fine adjustment, and comprises the following components in percentage by mass: 0.04 to 0.05 percent of C, less than or equal to 0.6 percent of Si, 1.00 to 2.00 percent of Mn, less than or equal to 0.030 percent of P, less than or equal to 0.003 percent of S, 17.0 to 18.0 percent of Cr, 11.5 to 12.5 percent of Ni, 2.50 to 2.70 percent of Mo, less than or equal to 0.10 percent of Cu, 0.05 to 0.07 percent of N, less than or equal to 0.0015 percent of B, less than or equal to 30ppm of O, less than or equal to 5.0ppm of H, the balance of Fe and impurities, and the content of ferrite is controlled to be less than or equal to 1 percent. A stainless steel seamless tube for sodium-cooled fast reactor is prepared through high-purity smelting, fine regulation of microalloying components, stainless steel casting, hot perforating and cold machining. Through the mode, the stainless steel seamless pipe for the sodium-cooled fast reactor and the preparation method can meet the use standard of nuclear safety high-temperature nano pipes, and have high toughness, corrosion resistance and durability.

Description

Stainless steel seamless tube for sodium-cooled fast reactor and preparation method thereof

Technical Field

The invention relates to the field of stainless steel seamless pipes, in particular to a stainless steel seamless pipe for a sodium-cooled fast reactor and a preparation method thereof.

Background

With the economic development and environmental deterioration pressure of all countries in the world, building nuclear power, utilizing and developing nuclear energy become one of the key points of future energy development. China has made great progress in nuclear power development and construction, the third generation nuclear power technology reaches the world advanced level, and the fourth generation nuclear power technology reaches the international advanced level. The sodium-cooled fast neutron reactor in the fourth generation nuclear power has high safety, reliability and proliferation capacity, and can improve the utilization rate of uranium resources to more than 60 percent, thereby reducing the generation amount of nuclear waste to the maximum extent, realizing the minimization of radioactive waste and the like, and being valued by countries in the world. Is one of the first-choice heap types of the fourth-generation advanced nuclear power system in the world, and represents the development direction of the fourth-generation advanced nuclear power construction. The method is also a key step for breakthrough of the four-generation nuclear power from the experimental reactor to the demonstration reactor technology in the aspect of sodium-cooled fast reactor in China.

As a sodium-cooled demonstration fast reactor of the fourth generation nuclear power, extremely strict requirements are put forward on the safety of the fast reactor, stainless steel seamless pipes such as 304, 316 and 321 are adopted in a nuclear safety high-temperature sodium pipeline, wherein the 316 stainless steel seamless pipe is the main steel grade of the nuclear safety sodium-cooled pipeline. Long-term service at high temperatures is required. Therefore, the method is greatly different from the conventional 316 austenitic stainless steel seamless tube, and almost has rigor requirements on the aspects of ferrite content, metal components, non-metallic inclusions, room temperature mechanical property, short-time high-temperature tensile property, grain size and grade difference, intergranular corrosion and the like.

The sodium-cooled fast reactor is a sodium-water three-loop heat transfer system, and a 316H stainless steel seamless pipe is used for a nuclear safety level two-level and level three-level high-temperature sodium pipeline, and the temperature of a reactor coolant outlet is 530-550 ℃, so that the temperature is higher than that of a third-generation nuclear power station, and the pressure is relatively small. The material is required to have higher high temperature resistance, and the 316H stainless steel seamless pipe inevitably has a certain ferrite content due to the components of ferrite forming elements such as Mo, Cr, Si and the like, so that the ferrite-containing body in the 316H stainless steel seamless pipe can generate the phenomenon of embrittlement at 475 ℃, and the brittle fracture tendency of the material is increased. Therefore, in order to ensure the safe operation of nuclear power in a service period, the ferrite content of the 316H stainless steel seamless pipe for the sodium-cooled pipeline is less than 1 percent, the service life of the nuclear power station can be effectively prolonged, and the safety is improved. Meanwhile, too high ferrite in steel affects hot workability of austenitic stainless steel seamless tubes, which is determined by the characteristic of poor ferrite ductility of the body-centered cubic crystal structure.

The sodium-cooled fast reactor 316H stainless steel seamless tube is operated in the environments of high temperature, corrosion, radiation and the like for a long time, is required to have higher room temperature tensile property and short-time high temperature tensile property, and also has obdurability, intergranular corrosion and durability. Specifically, the high-temperature sodium-cooled pipeline needs to operate in a high-temperature environment for a long time, has high-temperature creep resistance and enough endurance strength, has excellent plastic hardness and low carbon content of 316H, can improve high-temperature mechanical properties, has high toughness and intergranular corrosion resistance, and meets the performance index requirements of engineering design on materials by adding microalloy elements and controlling microstructure.

Referring to the technical conditions of sodium-cooled fast reactor, the formation mechanism of ferrite in a stainless steel tube blank needs to be clarified, and elimination strategies are provided, so that the preparation with the ferrite content less than 1% is realized. In order to ensure the structure performance of the stainless steel seamless tube for the nano-cooling pipeline, optimize the cold rolling processing and the solid solution process, and realize the control that the grain size of the stainless steel seamless tube is 5-grade and thinner, and the grain size difference in the full thickness direction is not more than 2-grade, the grain size of the cold rolling processing needs to be controlled. The intergranular corrosion resistance is required to improve the liquid metal corrosion resistance, and the stability of a fine crystal structure and the high-temperature mechanical property and corrosion resistance are ensured by controlling the dispersion distribution of fine carbides.

Disclosure of Invention

The invention mainly solves the technical problem of providing the stainless steel seamless pipe for the sodium-cooled fast reactor and the preparation method thereof, which can meet the use standard of nuclear safety high-temperature nano pipes and have high toughness, corrosion resistance and durability.

In order to solve the technical problems, the invention adopts a technical scheme that: the stainless steel seamless pipe for the sodium-cooled fast reactor is provided, and microalloying components are finely adjusted based on a 316H stainless steel base material, and the components comprise the following components in percentage by mass: 0.04 to 0.05 percent of C, less than or equal to 0.6 percent of Si, 1.00 to 2.00 percent of Mn, less than or equal to 0.030 percent of P, less than or equal to 0.003 percent of S, 17.0 to 18.0 percent of Cr, 11.5 to 12.5 percent of Ni, 2.50 to 2.70 percent of Mo, less than or equal to 0.10 percent of Cu, 0.05 to 0.07 percent of N, less than or equal to 0.0015 percent of B, less than or equal to 30ppm of O, less than or equal to 5.0ppm of H, and the balance of Fe and impurities, and the microalloy elements are regulated and controlled, and the ferrite content is controlled to be less than or equal to 1 percent.

In a preferred embodiment of the invention, the microalloying components are finely adjusted based on a 316H stainless steel base material, austenite forming elements of Ni, Mn, C, N, Cu, B, N, Mo, V and Co are added, the ferrite content is controlled by controlling the ratio of chromium equivalent to nickel equivalent, namely Creq/Nieq equivalent is controlled to be 1.10-1.25, the austenite mode is formed in advance by stainless steel crystallization, the ferrite content in the steel is obviously reduced, and the ferrite content is controlled to be below 1% by process control.

In a preferred embodiment of the present invention, the impurity component composition contains, in mass%, Al of 0.03% or less, Sb of 0.002% or less, Pb of 0.001% or less, Se of 0.015% or less, Sn of 0.005% or less, V of 0.05% or less, Zn of 0.01% or less, As of 0.01% or less, Co of 0.06% or less, and a low-melting harmful element of As + Sb + Bi + Sn + Pb of 0.15% or less.

In order to solve the technical problem, the invention adopts another technical scheme that: the preparation method of the stainless steel seamless tube for the sodium-cooled fast reactor comprises the following steps: a. the high-purity smelting process comprises the following steps: firstly, smelting and primary smelting by an electric furnace, wherein the tapping temperature is more than or equal to 1670 ℃, the components of molten steel are uniform, and qualified molten stainless steel is manufactured; then refining by an AOD furnace, and leading the Al to be less than or equal to 0.03 percent and the oxygen content to be less than or equal to 30ppm by the AOD furnace and a deoxidation process of adding aluminum powder on the slag surface; then, refining in an LF furnace, introducing weaker argon gas, stirring, and removing small-size impurities by using bubbles; b. fine adjustment of microalloying components: increasing austenite forming elements of Ni, Mn, C, N, Cu, B, N, Mo and V, controlling the ratio of chromium equivalent to nickel equivalent to be 1.10-1.2, adjusting the ferrite content of the final austenitic stainless steel seamless tube to be less than or equal to 1% by adjusting the chromium-nickel equivalent ratio, and obtaining a stainless steel solution for casting; c. the stainless steel casting process comprises the following steps: b, manufacturing a casting material by using the stainless steel melt obtained in the step b, and manufacturing a round pipe blank by adopting a continuous casting method or an ingot casting method; d. and (3) a hot perforation treatment process: carrying out hot piercing processing on the manufactured round pipe blank, regulating and controlling the process parameters of heating curvature, heat preservation time and cylinder turning times of each temperature section of the inclined hearth furnace on the round pipe blank, controlling the heating temperature to be 1160-1250 ℃, the heating time to be 150-900 minutes and the heat preservation time to be 15-150 minutes, carrying out deformation analysis and regulation on a stress strain field and a temperature field corresponding to large-grinding-angle inclined rolling piercing and controlling the temperature field in the top piercing process to form hot piercing and cooperatively control the tissue property, and producing a qualified pierced billet; e. and (3) a cold processing process of the intermediate product: rolling with large deformation, wherein the deformation elongation coefficient of a cold-rolled pipe is 1.3-1.9, the diameter reduction rate is controlled to be 31-48%, the wall reduction rate is 30-52%, the single-pass general elongation coefficient of intermediate expanding, drawing and rolling pipe passes is controlled to be 1.05-1.7, the diameter reduction rate is controlled to be 10-40%, the wall reduction rate is 5-46%, then carrying out process solution heat treatment, and controlling the temperature of the process solution heat treatment to be 1070-1100 ℃; f. and (3) cold processing of a finished product: detecting the grain size of the pipe before the finished product is rolled, accumulating deformation through the previous deformation rolling and cold expanding and drawing, controlling the deformation elongation coefficient of the cold rolled pipe to be 1.2-1.6 when the finished product is rolled, controlling the diameter reduction rate to be 11-30% and the wall reduction rate to be 12-32%, finally carrying out finished product solution heat treatment, controlling the temperature to be 1070-1090 ℃, and finally obtaining the finished product stainless steel seamless pipe for the sodium-cooled fast reactor.

In a preferred embodiment of the invention, in the step a, electric furnace smelting is carried out, the tapping temperature is more than or equal to 1670 ℃, the molten steel before tapping is completely dissolved, the Si content is controlled to be 0.5-0.6%, the molten steel components are uniform, qualified stainless steel melt is manufactured, Al is less than or equal to 0.03% and the oxygen content is less than or equal to 30ppm through an AOD furnace and a deoxidation process of adding aluminum powder on the slag surface, simultaneously, in order to reduce the S content, the slag melting point can be effectively reduced by adding Al2O3 into a binary alkalinity CaO/SiO2 slag system, the slag absorption of Al2O3 inclusion in the molten steel is promoted, after Al deoxidation, a large amount of Al2O3 inclusion with high melting point, high hardness and irregular shape is easy to exist in the molten steel, clustered Al2O3 can be continuously distributed along the rolling direction during rolling, the surface quality and the mechanical property can be seriously influenced, and the hard and undeformed Al2O3 inclusion is converted into low-melting-point plastic calcium aluminate through a Ca treatment process, the refining outside the LF furnace is mainly performed by weak argon stirring to promote the floating of the inclusion, because the molten steel circularly carries the inclusion at the bottom of the steel ladle and the slag involved in the molten steel to float for a certain time under deep molten pool in the furnace and strong stirring, the weak argon stirring is performed, blown argon bubbles can provide an adhesive matrix for particles which are not easy to discharge and are 10 mu m or smaller and are adhered to the surfaces of the bubbles to be discharged into the slag, so that the floating time of the inclusion is accelerated, the argon blowing pressure is controlled to be 2.0-2.5 kg/cm3, the flow is controlled to be 40-60L/min, the time is controlled to be 15-25 min, small-sized inclusions are removed through the bubbles, the small-sized inclusions are mutually aggregated, and the molten steel is subjected to high-temperature smelting and high-temperature smelting The collision is faster to form large-particle inclusion, so that the inclusion quickly floats upwards to be eliminated.

In a preferred embodiment of the present invention, the fine adjustment of the microalloying component in the step b increases the C content to form M at high temperature₂₃C₆Phase (1); the Cu-B element is added in a composite way, and a large amount of fine dispersed copper-rich phase is formed after the Cu is aged at high temperature and acts together with the B to strengthen precipitation strengthening; the N element has strong binding force at high temperature for long term, and can reduce the diffusion rate of Cr and C and inhibit M when being dissolved in the gamma matrix₂₃C₆Coarsening to play a role in solid solution strengthening; trace Mo, V and Co elements are added, and trace Mo is added as a strong carbide forming element, so that the heat strength and the pitting corrosion resistance can be improved, the solubility of C in gamma in steel is reduced, and the generation of M is accelerated₂₃C₆Phase (1); a small amount of Co is used as an austenite element to play a role in solid solution strengthening, and the heat resistance and the oxidation resistance are also improved; the V is added to pin dislocation in the deformation process, block dislocation movement, play a role in precipitation strengthening, and remarkably improve high-temperature endurance strength and creep resistance through multi-element composite strengthening.

In a preferred embodiment of the invention, in the step d, the diameter of the round steel is not more than 130mm, the whirling cutting amount is 1.5 mm-3 mm, the round steel with corresponding weight is sawed, a centering hole is drilled at one end, the outer surface of the round steel is polished, and the surface defects are removed; the diameter of the round steel is larger than 130mm, the round steel with corresponding weight is sawed, the turning amount on a lathe is 4 mm-12 mm, a centering hole is drilled at one end, the outer surface of the round steel is polished, and the surface defects are removed; in order to ensure the coaxiality of the round steel in the hot punching process, when the diameter of the round steel is larger than 300mm, a through hole is punched; heating temperature is 1160-1250 ℃ according to the specification of round steel, temperature deviation is +/-20 ℃, heating time is 150-900 minutes according to corresponding specification, heat preservation time is 15-150 minutes according to corresponding specification, steel turning frequency is increased, the consistency of the heating temperature of the stainless steel round steel is ensured, the phenomenon that the surface is too high and the interior does not reach the required temperature is avoided, temperature uniformity is improved, a conical long blank punching technology with small additional deformation is adopted, on the basis of adjusting parameters of hot punching top specification, guide plate spacing, roller spacing and top retraction amount corresponding to tube blanks with different outer diameters and wall thicknesses, the temperature rise curvature and time of each section heated by a furnace are optimized, and the temperature field change distribution characteristics in the large-grinding-angle oblique-rolling hot punching stress field, the temperature field and the top punching process are combined, so that the interaction and association rules among multiple elements in the hot forming punching process are analyzed, The thermal perforation stress-strain field and the temperature field change distribution characteristics in the process of piercing by the plug realize the high-quality thermal perforation of the thermal perforation molding and the cooperative control of the organization and the performance, so that the pierced billet is in a tension state after the perforation, simultaneously, the circumferential shear strain and the surface torsion strain are also reduced to the minimum, the high production efficiency and the high yield are realized, the external diameter specification of the produced pierced billet is from Æ 60-500 mm, for reducing the wall reduction amount of subsequent cold processing for the pierced billet with the diameter of more than 300mm, a secondary perforation process is adopted, because the roller rotating speed is high in the perforation process, the heat ratio of work conversion is relatively higher than that of the inner surface, the roller rotating speed is relatively lower, according to the fact that the speed of a roller of different perforating units and the perforating ratio are reduced by 22-38%, the angle of the roller is adjusted to be increased from 7 degrees to 15 degrees, in addition, the temperature of the outer surface of a pierced billet is regulated and controlled through spraying water, and temperature-controlled perforation of high-performance stainless steel is achieved.

In a preferred embodiment of the invention, the temperature-rotation speed matched hot piercing process technical parameters of the duplex stainless steel pierced billet with various specifications in the step d meet the following conditions that when the pierced billet specification is not more than phi 65mm, the outlet temperature of a heating furnace is controlled to be 1160-1200 ℃, the heating time is controlled to be 150-170 minutes, the heat preservation time is controlled to be 15-30 minutes, the corresponding deformation speed is controlled to be 89-92 revolutions per minute, when the pierced billet specification is phi 75-phi 130mm, the outlet temperature of the heating furnace is controlled to be 1170-1220 ℃, the heating time is controlled to be 190-330 minutes, the heat preservation time is controlled to be 26-70 minutes, the corresponding deformation speed is controlled to be 74-77 revolutions per minute, when the pierced billet specification is phi 160-phi 350mm, the outlet temperature of the heating furnace is controlled to be 1210-1260 ℃, the heating time is controlled to be 325-880 minutes, the heat preservation time is controlled to be 45-130 minutes, the corresponding deformation speed is controlled to be 51-55 revolutions per minute, and when the pierced billet specification is phi 350-500 mm, the outlet temperature of the heating furnace is controlled to be 1230-1270 ℃, the heating time is controlled to be 875-1100 minutes, the heat preservation time is controlled to be 80-180 minutes, the corresponding deformation speed is controlled to be 11-16 revolutions per minute, the volume of water in the cooling circulating water tank is 36-80 m3 according to different specifications of a perforating unit, sufficient cooling water circulation quantity is guaranteed in the perforating process, the water temperature of the cooling water tank is controlled to be not more than 30 ℃, pierced billet pipes quickly fall into the water tank for cooling after perforation, and the corresponding effect of solid solution heat treatment is achieved.

In a preferred embodiment of the invention, in the step e, large deformation amount rolling is adopted according to the grain size grade of the pierced billet, corresponding to a corresponding rolling deformation elongation coefficient of 1.3-1.9, grains are elongated into a fibrous shape along the deformation direction, the dislocation density is gradually increased, the distortion degree in the structure is increased, the compression or elongation degree of the grains is increased, the grain nucleation driving force and the growth driving force are obviously increased, the cold rolling deformation is sufficient, mixed crystals and coarse grains of a thick-wall pipe are avoided, the deformation elongation coefficient of the cold-rolled pipe is 1.3-1.9, the diameter reduction rate is controlled to be 31% -48%, the wall reduction rate is 30% -52%, the advantages of large deformation amount and flexible cold-expansion production of the cold-rolled pipe are exerted by combining with cold expansion and rolling, the size, morphology and the like of austenite grains are regulated and controlled by the accumulated large deformation amount of deformation, the elongation coefficient per pass is controlled to be 1.05-1.7, controlling the diameter reduction rate to 10-40 percent and the wall reduction rate to 10-46 percent, carrying out solution heat treatment in the process, controlling the temperature of the solution heat treatment to be 1070-1100 ℃, improving the yield ratio of the stainless steel by solution strengthening, eliminating the processing stress, obtaining supersaturated solid solution and proper grain size, further improving the structure, and preparing for subsequent cold rolling processing.

In a preferred embodiment of the invention, the grain size of the pipe before the finished pipe is rolled in step f is detected, and accumulated deformation amount is obtained through deformation rolling and cold-expanding drawing in the previous process, and other comprehensive performance requirements are met during rolling of the finished pipe, the deformation elongation coefficient of the cold-rolled pipe is relatively small, the deformation elongation coefficient of the cold-rolled pipe is 1.2-1.6, the diameter reduction rate is controlled to be 11-30%, the wall reduction rate is 12-32%, the total cold-working deformation elongation coefficient is 2.0-5.0, the grain size is controlled to be 5-7 levels, and the corresponding requirements of the outer diameter, the wall thickness and the tolerance are met; solution heat treatment of the finished product: the temperature is controlled to be between 1070 and 1090 ℃, under the condition of ensuring the consistency of the length of a pipe body and the temperature of a cross section, the cold processing stress is released, the stainless steel pipe is heated uniformly in a box type furnace, the pipe can be fully dissolved, crystal grains are effectively regulated and controlled, the work hardening is eliminated, the structure and the performance of the stainless steel pipe are recovered, the outer diameter is more than or equal to 200 mm, the thick-wall pipe with the ratio of the outer diameter to the wall thickness of 5 to 13.3 is heated uniformly, the solution temperature is controlled to be between 1070 and 1090 ℃, the heat preservation time of a product is controlled to be (1.5 to 2.5) multiplied by the wall thickness min, the heat preservation time of a finished product is controlled to be (1.0 to 1.5) multiplied by the wall thickness min, the time from discharging to draining is controlled to be less than or equal to 25S, the basic technological requirement of solution heat treatment is met, the roller-bottom continuous solution heat treatment process of the stainless steel pipe is adopted, the finished product is subjected to the bottom roller type solution heat treatment in a bottom roller type solution heat treatment furnace, the solid solution temperature is controlled to be 1070-1090 ℃, the temperature rise time is properly prolonged, the heat preservation time of a finished product is controlled to be (4-10) multiplied by the wall thickness min, and the heat preservation time of a finished product is controlled to be (4-8.8) multiplied by the wall thickness min.

The invention has the beneficial effects that: the stainless steel seamless pipe for the sodium-cooled fast reactor and the preparation method can meet the use standard of a nuclear safety high-temperature nano pipe, and have high toughness, corrosion resistance and durability.

Drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings needed to be used in the description of the embodiments are briefly introduced below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and other drawings can be obtained by those skilled in the art without inventive efforts, wherein:

FIG. 1 is a graph of thermal perforation stress-strain field and temperature field variation profiles;

FIG. 2 is a graph of temperature field variation distribution during piercing of a plug;

fig. 3 is a schematic diagram of cold rolled tube deformation.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

The invention provides a method for manufacturing an austenitic stainless steel seamless pipe for a sodium-cooled fast reactor, which is characterized in that the ferrite content is controlled to be below 1 percent, the medium-carbon content 316H stainless steel seamless pipe has obdurability, corrosion performance, durability and the like, the grain size difference in the thickness direction of the stainless steel seamless pipe is not more than 2 grade, and the austenitic stainless steel seamless pipe for a nuclear safety high-temperature nano pipeline is manufactured.

Therefore, as a stainless steel seamless tube for the fourth generation sodium-cooled fast reactor, the stainless steel seamless tube not only has the technical performance of the conventional 316H stainless steel seamless tube, but also has special requirements on fine adjustment of metal components, ferrite content not more than 1%, high-temperature mechanics, grain size and the like, the whole technical process of the metal components, smelting, casting, forging, hot piercing and cold working processes of the tube needs to be controlled, the ferrite forming mechanism in the manufacturing process of the stainless steel seamless tube is disclosed, elimination countermeasures are provided, the ferrite content is less than 1%, the precise control of alloy elements, the stainless steel hot working process of complete austenite structure and the cold rolling processing process of grain refinement are realized, the tube is ensured to have toughness, corrosion performance, durability and the like, and the requirements of engineering design on performance indexes of the material are met.

The present invention has been completed based on the above findings and has the following gist.

In order to achieve the above object, the chemical composition is preferable for the 316H stainless steel seamless pipe, and the content (%) of each element represents mass%.

On the basis of 316H stainless steel, the precise control technology of the metal components meeting the performance requirements.

On the basis of 316H stainless steel, the carbon content is properly reduced, the fine adjustment of metal component elements is realized, the purification and refining process of the stainless steel is considered, alloy elements such as N, Cu and B are added, the O, H content influencing the endurance strength and the fatigue strength is controlled, and the comprehensive performance of the steel is obviously improved through purification and smelting.

The chemical composition of the material determines the structure and the performance, and the chemical composition of the austenitic stainless steel is preferred, so that the precise control of the structure performance is realized.

C:0.04-0.05%, C is an interstitial element and is a strong austenite area enlarging element, the nickel equivalent is 30, the effect of C on increasing the strength of the austenitic stainless steel is very obvious, but the chromium carbide is generated by the combination of C and Cr very easily, the austenite grain boundary is poor in chromium, and the intergranular corrosion resistance is obviously reduced. Therefore, lowering the C content is the most effective measure for preventing intergranular corrosion. Meanwhile, through the improvement of the content of C in the austenitic stainless steel, the normal-temperature mechanical property, especially the high-temperature strength of the steel can be obviously improved after solid solution strengthening, austenite is formed and stabilized, and a gamma phase region is enlarged, so that the short-time high-temperature mechanical property and the lasting strength requirement are met. The influence of the fluctuation range of the C content on the austenitic stainless steel is large. The high-temperature strength is obviously improved by increasing the content of C, but the precipitation of a large amount of carbide is caused by excessively high content of carbon, so that the steel is embrittled in the long-term high-temperature service process. Therefore, the C content is set to be in the range of 0.04 to 0.10%, preferably in the range of 0.04 to 0.05%.

Si: not more than 0.6%, Si is a strong ferrite forming element, and the chromium equivalent thereof is 1.5. Has good deoxidation effect on the stainless steel liquid. The mechanical property of the steel is improved, and the strength of the austenitic stainless steel is stronger than that of Mn, Ni, Cr, W, Mo, V and the like; the elastic limit, the yield strength and the yield ratio of the steel are obviously improved, and the fatigue strength and the fatigue ratio are improved; meanwhile, Si02 particles which are finely dispersed and distributed are formed on the surface of the steel to hinder the diffusion of metal ions and improve the oxidation resistance. When Si is 1% or more, the corrosion resistance and workability of the steel are lowered in hot working. In the case where extremely high corrosion resistance and workability of steel are required, the content in the steel is generally controlled to 1.0% or less, the lower limit of Si is not necessarily specified, the content is 0%, and the Si content is set to a range of 0.8% or less, preferably 0.6% or less.

Mn:1.00-2.00%, Mn is an element for expanding and stabilizing austenite, and its nickel equivalent is 0.5. In austenitic stainless steel, the critical cooling speed of the stainless steel is reduced instead of forming austenite, the stability of an austenite structure is increased during cooling, the decomposition of austenite is inhibited, the austenite formed at high temperature can be kept to normal temperature, the ferrite content in the stainless steel is effectively reduced, and the effects of solid solution strengthening and austenite stabilizing are achieved. The solid solubility of N in steel is improved by adding Mn into stainless steel containing nitrogen. Therefore, the Mn content is set to a range of not more than 2.0%, preferably 1.00 to 2.00%.

Cr:17.0-18.0%, and typical ferrite-forming elements of Cr, which are also indispensable elements in stainless steel. The austenitic stainless steel is dissolved in a solid solution in an Fe matrix, thereby increasing the electrode potential of the matrix and improving the corrosion resistance of the austenitic stainless steel. Cr is a main element for resisting high-temperature oxidation and high-temperature corrosion in austenitic stainless steel, and a dense Cr2O3 protective film is formed at high temperature to block the outward diffusion of metal ions and the inward diffusion of oxygen atoms. In addition, a N retaining O-Cr 2O3 composite film can be formed in a certain temperature range, and the high-temperature oxidation resistance is further improved. However, Cr is a ferrite element, and Cr forms a continuous solid solution with Fe to narrow the austenite phase region. Therefore, the Cr content is set to a range of 16.5 to 19.5%, preferably 17.0 to 18.0%.

Ni:11.5 to 12.5%, and Ni is an element that strongly forms and stabilizes austenite and expands an austenite phase region, which can increase the potential and purification tendency of austenitic stainless steel. In order to control the ferrite content in the steel to be less than or equal to 1%, the solidification mode at high temperature is gradually changed to the all-austenite solidification mode with the increase of the nickel content. N in the steel retaining portion also suppresses the formation of the sigma phase, promoting the formation of the Cr2N phase to some extent. The Ni content is set to be in the range of 9.5 to 13.0%, preferably 11.5 to 12.5%.

Mo:2.50-2.70%, Mo is refractory metal, is stable ferrite element, and belongs to strong carbide forming element. Is beneficial to improving the high-temperature strength and can also improve the pitting corrosion resistance of the austenitic stainless steel. Mo can reduce the solubility of C in austenitic stainless steel and accelerate the generation of Cr23C 6. However, too much Mo promotes the precipitation of the σ phase at high temperatures, resulting in brittleness; also, since Mo is a precious metal, too high Mo content leads to increased costs. Therefore, the Mo content is set to a range of 1.5 to 3.5%, preferably a range of 2.50 to 2.70%.

P is less than or equal to 0.030 percent, S is less than or equal to 0.003 percent, P and S are all impurity elements inevitable in the stainless steel smelting process and have adverse effects on the performance of the stainless steel, the values of P and S are controlled to be lower, the contents of P and S are respectively set to be less than or equal to 0.0030 percent and less than or equal to 0.045 percent, and the preferable ranges are less than or equal to 0.0010 percent and less than or equal to 0.03 percent.

N:0.05-0.07%, N is a strong austenite region enlarging element, the nickel equivalent is 30, solid solution strengthening and stacking fault energy reduction can be achieved in steel, the stability of an austenite structure is improved, carbide precipitation is inhibited, and sigma (chi) phase folding is delayed. Can improve the hardness and corrosion resistance of the solid solution austenitic stainless steel and can also improve the creep deformation and high-temperature endurance strength of the steel. Nitrogen reduces the diffusivity of Cr and C in austenitic stainless steels and helps to inhibit Cr23C6 coarsening. However, an excessive N content forms a brittle phase, which lowers the hot workability of the steel. Therefore, the N content is set to a range of 0.12% or less, preferably 0.05 to 0.07%.

Cu: not more than 0.10 percent, Cu is an austenite stabilizing element, and the grain boundary corrosion capability and the corrosion resistance of the austenitic stainless steel can be improved by adding the Cu element. From the viewpoint of overall cost, the upper limit value is set to 0.3% and the lower limit value of the copper content is not required to be set to 0%, and the lower limit value is 0%.

B: less than or equal to 0.0015 percent, B is beneficial to improving the lasting creep property of austenitic stainless steel, and the addition of trace B can obviously improve the creep rupture life and simultaneously improve the plasticity indexes such as surface shrinkage, elongation and the like. B is the progress of remarkably stabilizing the carbide and suppressing the recovery process. The difference between the sizes of B atoms and Fe atoms is larger, the elastic combination of the B atoms with dislocation and grain boundaries is strong, the balanced segregation on the grain boundaries is easy, the precipitation speed and the quantity of Cr23C6 phases on the crystal valence are reduced, and the addition of the B atoms ensures that the Cr23C6 phase in the crystal is fine and stable. Therefore, the B content is set to a range of 0.0025% or less, preferably 0.0015% or less.

O: less than or equal to 30ppm, O is residual in the steel after the stainless steel is refined outside a furnace, the influence of the O on the performance of the steel is mainly related to the composition, the property, the distribution and the quantity of oxide inclusions, all the inclusions reduce the plasticity, the toughness and the fatigue strength of the steel to different degrees, and particularly, the steel is used under the condition of long service life and should be controlled as a harmful element. Therefore, the O content is set to a range of 50ppm or less, preferably 30ppm or less.

H: less than or equal to 5ppm, H is residual in the steel after the stainless steel is refined outside a furnace, is a harmful element, the H content in the steel is reduced as much as possible, various defects and performance reduction caused by H are prevented, and the influence on the service fatigue strength and the service life of the steel is large. Therefore, the H content is set to a range of 15ppm or less, preferably 5.0ppm or less.

Al: less than or equal to 0.03 percent, Al is aluminum which has strong affinity with oxygen and nitrogen, is a deoxidizing and nitrogen-fixing agent during steel making, and when the content of solid solution metal aluminum in steel exceeds a certain value, austenite grains are easy to grow and coarsen, and are inevitably strictly controlled. Therefore, the Al content is set to a range of 0.10% or less, preferably 0.03% or less.

V: less than or equal to 0.05 percent, V is a stable ferrite element, and a small amount of carbide particles, oxide particles or carbonitride particles of vanadium which are dispersed in the steel play a role in precipitation strengthening, so that the steel grains are refined, and the toughness is increased. However, excessive V and Fe form a continuous solid solution, and an austenite phase region is strongly reduced, so that the oxidation resistance of the steel is not good and must be strictly controlled. Therefore, the V content is set to a range of 0.15% or less, preferably 0.05% or less.

Sb: less than or equal to 0.002 percent, and Sb is an element for reducing an austenite phase region, is combined with Fe to form a low-melting-point compound and has a serious segregation tendency. Must be strictly controlled. Therefore, the Sb content is set to a range of 0.005% or less, and more preferably 0.002% or less.

Pb: less than or equal to 0.001 percent, Pb is not dissolved in steel, the boiling point of Pb is very low, most of Pb is converted into steam to escape in the smelting process, and lead contained in the steel greatly reduces the impact toughness. The external refining is strictly controlled. Therefore, the Pb content is set to a range of 0.0015% or less, more preferably 0.001% or less,

se: less than or equal to 0.015 percent, Se is a harmful element in the austenitic stainless steel, the ductility and the toughness of the steel are reduced, wherein the impact toughness is reduced most obviously, and the mass fraction of Se in the austenitic stainless steel is not over 0.04 percent. Therefore, the Se content is set to a range of 0.015% or less, preferably 0.015% or less

Sn: less than or equal to 0.005 percent, and Sn is a low melting point element, thereby greatly reducing the high-temperature mechanical property of the austenitic stainless steel, being harmful to the hot working performance, and the mass fraction of the austenitic stainless steel is not over 0.01 percent. Therefore, the Sn content is set to a range of 0.01% or less, preferably 0.005% or less

Zn: less than or equal to 0.01 percent, Zn is a low melting point element and enters steel as furnace charge during steel making, thereby reducing the metallographic structure and the performance of austenitic stainless steel. Therefore, the Zn content is set to a range of 0.05% or less, preferably 0.01% or less

As: not more than 0.01 percent, As is a low melting point element, and Fe is often used in steel₂As，Fe₃As₂FeAs and solid solutions thereof are present and tend to segregate seriously, and when the content is 0.2%, the brittleness and plasticity of steel increase. Therefore, the As content is set to a range of 0.10% or less, preferably 0.01% or less.

Co: less than or equal to 0.06 percent, and Co is an austenite forming element, so that the heat strength and the high-temperature oxidation resistance of the austenitic stainless steel can be obviously improved. Co60 generated after Co is irradiated by nuclear in nuclear power has a half-life period of more than 5 years, brings serious influence on the whole nuclear safety, and particularly influences the radiation damage to personnel in nuclear power station detection. Therefore, the Co content is controlled to be in the range of 0.10% or less, preferably 0.06% or less. The sum of (As + Sb + Bi + Sn + Pb) is less than or equal to 0.015 percent.

The total amount of low-melting point five-harmful elements (Sn, As, Sb, Bi and Pb) is remained in the steel after the stainless steel is refined outside the furnace, the high-temperature mechanical property of the steel is reduced, the high-temperature brittleness of the steel is increased, and the strict control is inevitably carried out. Therefore, the total of the low-melting-point five-harmful elements (As + Sb + Bi + Sn + Pb) is set to a range of 0.40% or less, and preferably 0.015% or less.

With respect to the composition control and optimization method, the metal composition determines the structure and properties of the stainless steel seamless tube.

The composition comprises the following components in percentage by mass: 0.04 to 0.05 percent of C, less than or equal to 0.6 percent of Si, 1.00 to 2.00 percent of Mn, less than or equal to 0.030 percent of S, less than or equal to 0.003 percent of P, 17.0 to 18.0 percent of Cr, 11.5 to 12.5 percent of Ni, 2.50 to 2.70 percent of Mo, less than or equal to 0.10 percent of Cu, 0.05 to 0.07 percent of N, less than or equal to 0.0015 percent of B, less than or equal to 30ppm of O and less than or equal to 5.0ppm of H. On the basis of 316H components, micro-alloy elements are regulated and controlled, the ferrite content is controlled to be less than or equal to 1 percent, and the problem of thermal aging embrittlement caused by long-term service is solved; the high-temperature durability and the corrosion resistance of the 316H alloy are improved, so that the key index of the service life of the pipe for the nano-cold fast reactor is improved. In order to improve the purity of the steel and the composition of inevitable impurities, the main control impurity elements are as follows: al is less than or equal to 0.03 percent, Sb is less than or equal to 0.002 percent, Pb is less than or equal to 0.001 percent, Se is less than or equal to 0.015 percent, Sn is less than or equal to 0.005 percent, V is less than or equal to 0.05 percent, Zn is less than or equal to 0.01 percent, As is less than or equal to 0.01 percent, and Co is less than or equal to 0.01 percent. Wherein the sum of harmful elements (As + Sb + Bi + Sn + Pb) with low melting point is less than or equal to 0.015 percent. And the balance of Fe and inevitable impurities, and the outer diameter of the stainless steel seamless steel pipe with the preset size is phi 10 mm-426 mm.

In order to solve the problem that the ferrite content needs to be controlled to be less than or equal to 1%, because the 316H austenitic stainless steel matrix structure comprises ferrite forming elements such as Mo, Cr, Si and the like and austenite forming elements such as Ni, Mn, C, N, Co, Cu and the like, generally, 316H stainless steel seamless pipes have a certain amount of ferrite (the delta ferrite content is 3% -15%), and the ferrite is a harmful phase in a high-temperature environment and is inevitably controlled according to the application context. When the austenitic stainless steel seamless pipe metal is solidified, the ferrite content is mainly controlled by controlling the ratio of chromium equivalent to nickel equivalent, namely Creq/Nieq, and the ferrite content of the final austenitic stainless steel seamless pipe is adjusted by adjusting components (chromium-nickel equivalent ratio).

Creq equivalent = 17.5% Cr +1.5 × 2.5% Mo +1.5 × 0.6% Si = 22.15%

Nieq equivalent = 12% Ni +2 × 1.5% Mn +30(0.045+ 0.06)% (C + N) +0.3 × 0.1% Cu = 18.18%

Creq/Nieq equivalence ratio =22.15/18.18= 1.21. The tissue prediction accuracy of the duplex stainless steel is effectively improved, and the Creq/Nieq equivalent is controlled to be 1.10-1.25, so that the method is used for determining the subsequent intermediate solution heat treatment and finished product solution heat treatment temperatures.

The 316H stainless steel adopts the fine adjustment of austenite forming elements to ensure that the crystallization mode of the stainless steel is an austenite-first mode, an austenite phase is generated firstly when molten steel is solidified to ensure that the austenite phase is crystallized and folded into a gamma austenite initial phase, then L + gamma + delta is generated, finally the gamma + delta is solidified into gamma + delta, and a delta ferrite structure is generated at a crystal boundary. The content of austenite forming elements is increased by micro-alloying regulation and fine regulation from the key metal components forming the austenite elements, so that the Creq/Nieq equivalence ratio is reduced, and the ferrite content in the steel is obviously reduced.

The temperature and the heat preservation time of the heat treatment of the finished product are regulated and controlled, so that the carbide is fully dissolved in the austenite structure at normal temperature, and the ferrite content is reduced. The ferrite content is controlled to be less than or equal to 1 percent.

Control of pipe impact toughness, room and high temperature endurance strength and corrosion resistance.

The high-temperature endurance strength is improved by regulating and controlling the metal components of the microalloy. The method adopts multi-element composite reinforcement and is based on a large amount of experiments and researches.

Moderate increase of C content at high temperature forms M₂₃C₆Phase (1); the Cu-B element is added in a composite way, and a large amount of fine dispersed copper-rich phase is formed after the Cu is aged at high temperature and acts together with the B to strengthen precipitation strengthening; the N element has strong binding force at high temperature for long term, and can reduce the diffusion rate of Cr and C and inhibit M when being dissolved in the gamma matrix₂₃C₆Coarsening to play a role in solid solution strengthening; trace Mo, V and Co elements are added. Adding trace Mo as strong carbide forming element can raise heat strength and pitting corrosion resistance, reduce C solubility in gamma and speed M formation₂₃C₆Phase (1); a small amount of Co is used as an austenite element to play a role in solid solution strengthening, and the heat resistance and the oxidation resistance are also improved; v is added to pin dislocation and block dislocation movement in the deformation process, plays a role in precipitation strengthening, and remarkably improves high-temperature holding capacity through multi-element composite strengtheningLong strength and creep resistance.

The room temperature and high temperature endurance strength performance is improved by a grain refinement and regulation method.

In the process from forging to finished product rolling, through compression deformation and solution heat treatment (grain boundary engineering treatment), from forging-hot piercing-intermediate product cold processing (large deformation cold rolling + process solution heat treatment) -finished product cold processing (cold rolling + finished product solution heat treatment integrated grain engineering treatment key technology), in-crystal twin crystal change and dislocation recovery mainly occur, grain refinement is easier from original coarse crystal, fine crystal can improve tensile strength, and fine crystal can improve the experiment and research of the characteristic that the solution heat treatment of CSL grain boundary in unit area after cold and hot rolled tube processing is easier to retain. The higher temperature of plastic processing in the hot working process is increased, crystal grains are coarsened, the crystal grains are controlled to be 3-5 grades through forging and hot perforation processing, the size and the morphology of the crystal grains are further regulated and controlled to be 5-7 grades through large-deformation cold rolling and solution heat treatment, and therefore the tensile strength at room temperature and high temperature is improved.

Through a large number of experiments and researches, the relationship between the solid solution heat treatment temperature and the impact toughness at different temperatures is obtained, the austenite structure with the solid solution heat treatment temperature of 1080 +/-20 ℃ is obtained, no harmful phase is precipitated, the crack initiation positions in the impact process are reduced, and the austenite with the net structure plays a good role in blocking impact cracks, so that the impact toughness of the steel is improved.

Through a large number of experiments and researches, the growth density of the surface oxide film has a great relationship to the crystal orientation, and the oxidation rate of different crystal faces is analyzed, so that the crystal grains with higher stacking density are oxidized more strongly. The dissolution rate of the steel is inversely proportional to the atom stacking density, the dissolution rate of the dense-packed surface is low, the growth rate of an oxide film on the dense-packed surface in the steel is higher, the size of crystal grains is thinned through the intermediate-pass large-deformation cold-rolled tube and solution heat treatment, the initial fine crystal grain size is formed through the processing of a finished cold-rolled tube on the basis, more morphological structures with the dense-packed surfaces parallel to the outer surface are formed after the heat treatment of the finished product, and the pitting corrosion resistance is improved.

Through a large number of experiments and researches, in order to meet the requirements of a 650 ℃ multiplied by 2h sensitization test of an intergranular corrosion sample, the basic requirements of the intergranular corrosion sensitization test are met through the control of small-deformation cold rolling and solution heat treatment processes under the condition that the nickel equivalent is in a range.

Regarding the manufacturing method: the high-purity smelting process technology ensures the quality of the tube blank.

Firstly, electric furnace smelting is carried out, the tapping temperature is more than or equal to 1670 ℃, molten steel before tapping is completely dissolved, the Si content is controlled to be 0.5-0.6%, the components of the molten steel are uniform, and qualified molten stainless steel is manufactured.

Ar-O₂A mixed gas bottom blowing decarburization furnace (AOD furnace) and a ladle refining furnace (LF furnace) adopt an Al intensified deoxidation process, and because the effect of effectively reducing the oxygen content of molten steel cannot be achieved due to insufficient addition of Al, the risk of generating AlN inclusions is caused due to excessive addition of Al. Through AOD furnace and deoxidation process of adding aluminium powder on slag surface, Al content is less than or equal to 0.03%, and oxygen content is less than or equal to 30 ppm. At the same time, in order to reduce the S content, CaO/SiO is added in a binary alkalinity₂Adding Al into the slag system₂O₃Can effectively reduce the melting point of the furnace slag and promote the furnace slag to adsorb Al in the molten steel₂O₃And (4) inclusion. After Al deoxidation, a large amount of Al with high melting point, high hardness and irregular shape is easy to exist in the molten steel₂O₃And (4) inclusion. Clustered Al₂O₃The steel can be continuously distributed along the rolling direction during rolling, and the surface quality and the mechanical property of the tube blank can be seriously influenced. By Ca treatment process, the hard non-deformable Al is treated₂O₃The inclusion is transformed into low melting point plastic calcium aluminate inclusion, 12CaO.7Al during refining₂O₃Is in a liquid state and is easy to grow up and float, thereby changing the shape of residual inclusion, fully desulfurizing and deoxidizing, reducing the effect of non-metallic inclusion and further improving the purity of steel.

LF external refining is mainly stirred by weak argon gas to promote the floating of impurities. Because the molten pool in the furnace is deep, impurities brought into the bottom of the steel ladle in the molten steel circulation and slag involved in the molten steel need to float for a certain time under strong stirring, at the moment, the argon gas is stirred weakly, and blown-in argon gas bubbles can provide adhesive matrixes for impurity particles which are not easy to discharge and are 10 mu m or smaller, so that the argon gas bubbles are adhered to the surfaces of the bubblesDischarging into slag to accelerate the floating time of inclusion, and controlling the argon blowing pressure at 2.0-2.5 kg/cm³The flow rate is controlled to be 40-60L/min, and the time is controlled to be 15-25 min. Small-size inclusions are removed through bubbles, and in addition, the small-size inclusions are aggregated and collided with each other to form large-particle inclusions more quickly, so that the inclusions quickly float upwards and are removed.

According to the three-step deoxidation process, the effective components of the covering slag are reasonably adjusted, the fluidity of the covering slag is ensured, and the oxygen content of the stainless steel tube blank is reduced to be below 30 ppm.

The steel is subjected to full degassing and argon stirring in the processes of primary smelting, AOD refining, LF refining and electroslag remelting in a stainless steel electric furnace, the degassing time is controlled to be more than or equal to 40 minutes, the appropriate slag amount, strong basicity and good ventilation are favorable for degassing, and hydrogen contained in the steel floats upwards and is removed while the slag floats upwards. And further blowing argon for stirring, wherein the blowing argon pressurization is controlled to be 2-2.5 kg/cm³And the flow rate is 30-50L/min, so that the molten steel churning furnace slag floats upwards, the hydrogen content of the stainless steel pipe blank is stably controlled to be lower, and the content is reduced to be below 5 ppm. Thereby improving the fatigue strength of the steel.

The microalloying metal component design is realized by regulating and controlling austenite forming elements such as Ni, C, N, Cu, Mn and the like, so that the nickel equivalent is obviously improved, and the ferrite content is regulated and controlled to be less than 1%. The impurity purification metallurgy technology has the advantages that the alloy components are accurately controlled, and the harmful elements are controlled within specified values.

The stainless steel casting control technology comprises the following steps: a cast material is produced from a molten stainless steel. And casting the steel bar into a strip-shaped steel block. Specifically, the cast material may be produced by a continuous casting method or an ingot casting method.

In the aspect of casting process control, the liquidus temperature of the molten steel of the 316H stainless steel is calculated, and the degree of superheat of casting is reasonably controlled;

in order to avoid secondary pollution caused by the casting process, slag spots, rust, cold steel, garbage and the like on the inner wall of the ingot mold are cleaned to ensure that the inner wall is smooth, a casting system adopts high-quality refractory materials, and cleaning work is well done; the pouring system is filled with argon in advance for protection, and after molten steel enters the mold, the slag ladle is protected from heat spreading, so that the situation of molten steel blocking can be effectively avoided, the molten steel quantity is controlled to stably rise, and the cap opening is fully fed in the molten steel cooling and solidifying process.

An electroslag remelting process is added, and the alloy is further refined during remelting. Firstly, an electrode ingot smelting stage: the adsorption effect of the low-alkalinity slag system on the DS impurities is utilized, the content of the DS impurities is obviously reduced, and the purity of the electrode ingot molten steel is improved; secondly, controlling the inclusion of the electroslag ingot: the adsorption effect of the high-alkalinity slag system on the B-type inclusions is utilized to reduce the oxygenation of the molten steel and the content of the B-type inclusions.

The inclusion floats upwards in the molten pool through slag washing, thereby improving the cast structure of the steel, reducing component segregation and obviously improving the purity of the steel. The nuclear-grade high-temperature nano pipeline requires higher purity, an electroslag remelting process is required to be added, 316H stainless steel is further refined during remelting, and impurities are removed through slag washing and floating in a molten pool, so that the purity of the steel is obviously improved. The feeding process is optimized, the head of the electroslag ingot is ensured to have enough molten steel supplement, shrinkage cavities are reduced, and the yield is improved. Electroslag remelting can improve the cast structure of steel and reduce component segregation, so that the purity of the steel is further improved.

The electroslag remelting generates a series of metallurgical reactions in the solidification process of forming liquid drops/slag washing by melting a consumable electrode, and under the condition of sequential solidification from top to bottom under a 316H stainless steel remelting process system, the uniform and compact crystal structure of a remelted ingot is ensured, the component control and the cleanliness are obviously improved, and particularly, nonmetallic inclusions are finely and dispersedly distributed. Improve solidification structure, reduce segregation, inhibit secondary phase precipitation and improve impact toughness.

And an argon protection device is adopted, and argon is introduced for protection in the whole smelting process, so that the burning loss of the easily-oxidized elements is effectively reduced.

In order to meet the requirement of higher purity of the steel and improve the cold and hot processing performance, the corrosion resistance and the chemical stability of the steel. The content of the TiN inclusions is controlled by purifying and refining, controlling the level of A, B, C, D-type nonmetallic inclusions and reasonably controlling the content of N elements; the requirements on the content of harmful element O, S in steel are strict, and the A-type fine system is required to be less than or equal to 1.0 grade; class B fine line is less than or equal to 1.0 grade; class C fine line is less than or equal to 1.0 grade; class D fine line is less than or equal to 1.0 grade; DS is less than or equal to 1.0 grade; the sum of the five classes is less than or equal to 2.0 grade. A. B, C, D the sum of the four coarse series is less than or equal to 1.0 grade.

The stainless steel forging control technology comprises the following steps: the cast material is hot worked to produce a round billet. And the small-size steel ingot is forged by a steel ingot, cogging is carried out to various specifications, the steel ingot is subsequently hot-rolled into a steel bar with a corresponding specification, and the large-size steel ingot is directly forged and rolled into a steel bar.

As the 316H structure is a stable austenite structure and has no isomerous transformation in the heating and cooling processes, the heating temperature and the deformation are controlled in the forging process, the compression ratio technical process control is improved, and the total compression ratio in forging is more than or equal to 3, so that a grain structure with fine grains and uniform distribution is obtained. The hot piercing processing performance is obviously improved, and the pierced billet yield is improved, so the following key control points are adopted in the forging process.

The ingot is heated in a chamber furnace with the diameter of 4m multiplied by 6m, and the bottom of the ingot is padded with refractory bricks to ensure that the ingot has a gap with the bottom of the furnace, thus the ingot can be heated more uniformly. A corresponding heating system is established for steel ingots with different specifications, the temperature is slowly increased in the heating process, and the consistency of the surface temperature and the central temperature of the ingot is improved. Meanwhile, the heating time and the heat preservation time are both prolonged.

The temperature is controlled, the optimal temperature of the 316H hot working plasticity is 1150-1250 ℃, the temperature drop, the deformation mode and the heating times are considered during forging, the final forging temperature is too low, incomplete recrystallization can be caused, and mixed grain structures with uneven grain sizes are caused, the initial forging temperature is controlled to be 1150-1250 ℃, the final forging temperature is more than or equal to 930 ℃ during forging, and the mixed grain structures with uneven grain sizes, which are caused by incomplete recrystallization due to too low temperature, are avoided; the crystal grain group is large due to the over-high temperature, otherwise, the crystal grains need to be re-melted in time.

In the hot forging deformation mode, an electroslag ingot needs to be tapped in the primary forging process, surface columnar crystals need to be quickly crushed by hammering and rolling, the deformation is mainly controlled by small deformation, the columnar crystals on the surface can be crushed by re-pressing after the deformation reaches 30 percent, and the forging deformation is increased under the condition of proper temperature. At this time, the round shape is forged into an octagonal shape, and both of the latter two fire forming are controlled by the octagonal shape, so that the low degree of deformation of one fire may fall into the critical deformation region, and the grain size may be uneven. And (4) rounding the final fire, wherein the critical deformation is controlled to be more than 15% to ensure uniform tissues.

The stainless steel bar is continuously rolled, and on the basis of large and medium bar wire cogging, a roughing mill group, a medium mill group and a bar reducing and sizing mill, a finishing mill, a reducing and sizing mill, online heat treatment, a bar cooling bed and a collecting device are adopted, so that the product size precision is improved, the tolerance and the ovality are reduced, the size precision of an outer diameter series is controlled within +/-0.1 mm- +/-0.2 mm, the ovality is 0.05 mm-0.15 mm, the surface defect depth of a large-diameter bar is generally 0.08-1.00 mm, the distribution uniformity of carbides is improved, the yield strength and the toughness are synchronously improved, a large number of dislocations are formed in the carbides, and the grain size control is more uniform.

The hot perforation key control technology comprises the following steps: and (4) carrying out hot piercing processing on the manufactured round pipe blank to manufacture a pierced billet.

The diameter of the round steel is not more than 130mm, the whirlwind cutting amount is 1.5 mm-3 mm, the round steel with corresponding weight is sawed, a centering hole is drilled at one end, the outer surface of the round steel is polished, and defects such as hairlines and cracks existing on the surface are removed.

The diameter of the round steel is larger than 130mm, the round steel is sawed into round steel with corresponding weight, the turning amount on a lathe is 4 mm-12 mm, a centering hole is formed at one end, the outer surface of the round steel is polished, and defects such as hairlines and cracks existing on the surface are removed. In order to ensure the coaxiality of the round steel in the hot punching process, when the diameter of the round steel is larger than 300mm, a through hole is punched.

Based on the driving of the structure performance requirement of the extreme application environment on the round steel hot perforation molding, the method aims at the technical characteristics of heating of round steel with different calibers. The process parameters such as heating curvature, heat preservation time and the like of each temperature section of the inclined hearth furnace are adjusted and controlled, and in the high-temperature heating stage, the heating and heat preservation time is properly prolonged, so that the temperature difference of the tube blank along the cross section and the length direction is reduced, the temperature field distribution of the whole tube blank is ensured to be uniform, and the conditions that the heating temperature is too high when the surface comes out and the temperature in the inner part does not reach the required temperature are avoided.

The heating temperature is 1160-1250 ℃ according to the specification of the round steel, the temperature deviation is +/-20 ℃, the heating time is 150-900 minutes according to the corresponding specification, and the heat preservation time is 15-150 minutes according to the corresponding specification. Meanwhile, the steel turnover frequency is increased, the consistency of the heating temperature of the stainless steel round steel of the processed batch number is ensured, the phenomenon that the heating temperature on the surface is too high and the temperature in the stainless steel round steel does not reach the requirement is avoided, and the temperature uniformity is improved.

The method is based on the adjustment of parameters such as hot piercing plug specifications, guide plate spacing, roller spacing, plug retraction amount and the like corresponding to pipe blanks with different outer diameters and wall thicknesses by adopting a conical long blank piercing technology with small additional deformation. Through optimizing the process parameters such as heating curvature and time of each section heated by the furnace, combining a large-rolling-angle cross rolling hot piercing stress strain field and a temperature field with the temperature field change distribution characteristics in the piercing process of the top head, analyzing and obtaining the interaction and association rules among multiple elements in the hot forming piercing process, the hot piercing stress-strain field and temperature field change distribution characteristics (shown in figure 1) and the temperature field change distribution characteristics (shown in figure 2) in the piercing process of the top head, realizing high-quality hot piercing of hot piercing forming, organization and performance cooperative control, enabling the pierced billet to be in a tensile state after piercing, simultaneously reducing the circumferential shear strain and the surface torsion strain to the minimum, and realizing high production efficiency and high yield. The diameter of the produced pierced billet is from Æ 60-500 mm.

For reducing the wall reduction amount of subsequent cold processing of pierced billets with the diameter of more than 300mm, a secondary piercing process is adopted, because the roller rotating speed is high in the piercing process, the heat ratio of work conversion is relatively higher than that of the inner surface, the roller rotating speed is relatively lower, the roller speed and the piercing ratio are reduced by 22-38% according to different piercing sets, the roller angle is adjusted to be increased from 7 degrees to 15 degrees, in addition, the temperature is regulated and controlled by spraying water on the outer surface of the pierced billets, and the temperature-controlled piercing of high-performance stainless steel is realized.

The technical parameters of the hot piercing process matched with the temperature and the rotating speed of the duplex stainless steel pierced billet with various specifications meet the following conditions.

When the specification of the pierced billet is less than or equal to phi 65mm, the outlet temperature of the heating furnace is controlled to be 1160-1200 ℃, the heating time is controlled to be 150-170 minutes, the heat preservation time is controlled to be 15-30 minutes, and the corresponding deformation speed is controlled to be 89-92 revolutions per minute.

When the specification of the pierced billet is phi 75-phi 130mm, the outlet temperature of the heating furnace is controlled to 1170-1220 ℃, the heating time is controlled to 190-330 minutes, the heat preservation time is controlled to 26-70 minutes, and the corresponding deformation speed is controlled to 74-77 revolutions per minute.

When the specification of the pierced billet is phi 160-phi 350mm, the outlet temperature of the heating furnace is controlled to be 1210-1260 ℃, the heating time is controlled to be 325-880 minutes, the heat preservation time is controlled to be 45-130 minutes, and the corresponding deformation speed is controlled to be 51-55 revolutions per minute.

When the specification of the pierced billet is phi 350-phi 500mm, the outlet temperature of the heating furnace is controlled to be 1230-1270 ℃, the heating time is controlled to be 875-1100 minutes, the heat preservation time is controlled to be 80-180 minutes, and the corresponding deformation speed is controlled to be 11-16 revolutions per minute.

The volume of the water in the cooling circulation water pool is 36-80 m according to different specifications of a perforating unit³Enough cooling water circulation quantity is ensured in the perforation process, and the water temperature of a cooling water pool is controlled to be less than or equal to 30 ℃. After perforation, the pierced billet falls into a water tank quickly to be cooled, and the corresponding effect of solution heat treatment is achieved.

The process for cooperatively controlling the grain size and carbide of the stainless steel cold machining forms a metallurgical rule and an optimal process schedule of large deformation rolling-solid solution integrated control cold machining.

The final delivery of the sodium-cooled pipeline is 316H stainless steel seamless pipe with phi of 10mm to phi 426mm, all the evaluation comprehensive performance indexes are based on the detection data of the pipe, the ferrite content is required to be controlled below 1%, the high endurance strength, creep property, toughness and fatigue property are required, the intergranular corrosion resistance is required to be achieved under the condition of medium carbon content, the grain size is 5-grade or finer, and the grade difference is not more than 2-grade, so that the control target of fine grains and uniform tissues is realized, and the performance index requirements of engineering design on the material are met.

In view of the above comprehensive index requirements, the cold rolling process and the solution heat treatment key process of the cold working process need to control the grain size and the carbide so as to meet the requirements of various performance indexes and realize the comprehensive balance among the indexes so as to ensure the stability of the fine crystal structure and improve the high-temperature mechanical property. The grain size and carbide are effectively regulated and controlled mainly through large-deformation cold rolling tubes and solution heat treatment.

Regarding the cold working process: rolling technology based on cooperative control of cold rolled tube grain size and carbide (intercrystalline corrosion resistance)

The cold rolled pipe is processed by cold drawing and cold rolling represented by a pilger mill. In the cold working process, cold rolling is mainly used, cold drawing is used as an auxiliary cold working process, compared with cold drawn pipes, the cold rolled pipes are fed while rotating, the cold rolled pipes play a role in wall equalization in pipe rolling, large strain is given to the pipes in axial stretching and circumferential compression, the cold drawn pipes only give axial tensile strain, the cold deformation is small, and the deformation of the rolled pipes is large.

According to the invention, through a large number of experiments and researches, the pipe body is uniformly deformed through a large-deformation cold-rolled pipe, the internal nucleation rate is improved, and the internal grain size is finer after the recrystallization through the solution heat treatment. When the cold rolling quantity is too large, recrystallization behavior is induced in the process of solution heat treatment, large-scale recrystallization behavior can generate more large-angle free crystal boundaries, newly generated large-angle crystal boundaries rapidly migrate in the process of high-temperature heating in a large scale, reaction with lattice dislocation inevitably occurs in the migration process, straight coherent twin crystal boundaries can be generated, coherent twin crystal energy is lower and stable, the large-angle crystal boundaries in an obvious network continuity shape bring negative influence on the characteristic distribution of the crystal boundaries, and surface intergranular corrosion is serious. The small-deformation cold-rolled tube has no random crystal boundary after solution heat treatment, and the small deformation can promote the migration of free crystal boundaries more, so that the crystal boundaries are thought to react with each other to generate a large amount of low-energy crystal boundaries, the grid connectivity is further dispersed, the crystal boundary characteristics are obviously optimized, and the intercrystalline corrosion resistance is improved. Therefore, when rolling a pipe, the relationship between rolling force and intergranular corrosion must be considered, and the elongation coefficient of the cold-rolled pipe is appropriate, and the grain is refined by the accumulation of multi-pass rolling, and the intergranular corrosion requirement is satisfied.

Based on the small-deformation cold rolling and carbide cooperative control technology, the process of cold rolling the tube by deformation with the elongation coefficient of 1.4-2.2 is adopted, a large amount of low-energy special crystal boundaries are formed after solution heat treatment, the free crystal boundaries with large angles are broken, the phenomena of intergranular carbide segregation and chromium depletion are obviously improved, and the resistance of the tube to intergranular corrosion is greatly improved by the low-energy special crystal boundaries. The deformation is accumulated through multi-pass rolling and solution heat treatment in the process of cold rolling the tube, so that the crystal grains are gradually refined, and the qualified intergranular corrosion meeting the sensitization test is ensured.

In the cold working process, cold drawing is only used for processing the size of a blank pipe before rolling the pipe which meets the corresponding hole pattern, and is only used for supplementing and adjusting the cold rolling process.

The 316H stainless steel seamless tube cold machining has multiple processes and circulations, and can meet the requirements of specifications and dimensions of finished products only by multiple process cycles (the processes of grinding, straightening, cold rolling, acid washing, solution heat treatment, head aligning (cutting), lubricating/baking and welding head (corresponding to the cold drawing process) are combined into the process cycles).

According to 316H stainless steel seamless tubes with different calibers and wall thicknesses and microstructure evolution rules and structure/performance relations under different cold-rolled tube deformation conditions, and considering the hardness effect, hardness gradient distribution and the transfer effect of the cold-rolled tubes in each pass, a key cold deformation regulation and control process integrating steel type, intermediate solution heat treatment and reasonable deformation distribution is established, so that the allowable deformation, a rolling forming pass function and a distribution rule in the preparation process of the stainless steel seamless tubes are obtained, and the processing deformation in each pass is reasonably distributed.

According to the processing characteristics, technical conditions and production conditions of the 316H material, the technological process comprises the steps of pipe material size, deformation mode and pass, deformation of each pass and the size of the deformed stainless steel pipe.

The diameter phi of the finished product pipe is 10mm to 406mm, the corresponding pierced billet specification and the rolling deformation of the pipe rolling mill are distributed by the multi-pass cold rolling mill, and the corresponding hole expanding pipe process, pipe drawing process and cold rolling mill process can be set according to the specific external diameter and wall thickness specification and size between two times of rolling, so that the original external diameter and wall thickness requirements of the finished product pipe are met.

According to the theory of cooperative control of deformation and carbide of the rolled pipe, the grain size detection is used as a support on the basis of the grain size detection of the pierced billet, so that the cooperative control of the grain size and the carbide is realized.

The first rolling can correspond to a corresponding rolling deformation elongation coefficient of 1.3-1.9 according to the grain size grade of a pierced billet, crystal grains are elongated into a fibrous shape along the deformation direction, the dislocation density is gradually increased, the distortion degree in the structure is improved, the compression or elongation degree of the crystal grains is improved, and the nucleation driving force and the growth driving force of the crystal grains are obviously increased. And the full cold rolling deformation avoids mixed crystals and coarse grains of the thick-wall pipe, and the deformation elongation coefficient of the cold-rolled pipe is 1.3-1.9. The diameter reduction rate is controlled to be 31-48 percent, and the wall reduction rate is controlled to be 30-52 percent.

On the basis of the previous rolling deformation, the advantages of large deformation of the cold-rolled pipe and flexible cold-expanding and drawing production are exerted by combining cold expanding and drawing and rolling, and the size, the shape and the like of austenite grains are regulated and controlled by accumulating larger deformation of the deformation. The elongation coefficient of each pass is controlled to be 1.05-1.7. The diameter reduction rate is controlled to reach 10-40%, and the wall reduction rate reaches 10-46%.

The grain size of the pipe is detected before the finished pipe is rolled, the deformation accumulated by the deformation rolling and cold expanding and drawing of the previous process is used, other comprehensive performance requirements are met during the rolling of the finished pipe, the deformation extension coefficient of the cold-rolled pipe is relatively small and thin, and the deformation extension coefficient of the cold-rolled pipe is 1.2-1.6. The diameter reduction rate is controlled to be 11-30%, and the wall reduction rate is controlled to be 12-32%.

The total elongation coefficient of the cold working deformation is 2.0 to 5.0. The grain size is controlled to be 5-7 grade, and the corresponding outer diameter and wall thickness sizes and tolerance requirements are met.

Controlling the diameter reduction rate to reach 35-55 percent and the wall reduction rate to reach 30-60 percent; the single-pass common elongation coefficient of the intermediate expanding, drawing and rolling tube pass is controlled to be 1.05-1.7. Controlling the diameter reduction rate to 10-20% and the wall reduction rate to 5-30%; the cold-rolled pipe of the finished pipe has a deformation elongation coefficient of 1.3-1.6. Controlling the diameter reduction rate to reach 13-30 percent and the wall reduction rate to reach 12-32 percent; the total elongation coefficient of the cold working deformation is 2.0 to 5.2.

Regarding the solution heat treatment: the solution heat treatment comprises the processes of solution heat treatment and finished product solution heat treatment.

Through a large number of experiments and researches, high-temperature short-time heating is more beneficial to the formation of low-energy grain boundaries than low-temperature long-time heating. Mainly, during high-temperature heating, the random grain boundary inevitably interacts with dislocation and other grain boundaries in the migration process and transfers to the low-energy grain boundary, the absorption rate of the dislocation of the low-energy grain boundary is much lower than that of the random grain boundary, and the low-energy grain boundary does not migrate before the dislocation is completely absorbed. The structure is stable. And the driving force of random grain boundary migration is small during low-temperature heating, the probability of the high-energy grain boundary contacting with other grain boundaries is reduced, the generation of new low-energy grain boundary fragments is reduced, and the low temperature is not favorable for the formation of the low-energy grain boundary for a long time. The proportion of low-energy grain boundaries generated at 1080 ℃ is the highest, and when the temperature is higher than 1080 ℃, although the high temperature can promote the formation of the low-energy grain boundaries, the further migration of random grain boundaries swallows the existing low-energy grain boundaries, so that the proportion is reduced. Also, low temperatures are not conducive to the formation of low energy grain boundaries.

The selection of the heat preservation time of the solution heat treatment is realized by regulating and controlling the heat preservation time of the solution heat treatment through a large number of experiments and researches, the requirements of the process characteristics of heat preservation and rapid cooling are met through different pipe outer diameters and wall thicknesses and different furnace types at the temperature of 1080 ℃, the fine carbides are completely redissolved and are kept in an austenite structure at normal temperature, and the fine carbides are dispersed and uniformly distributed, so that the lower intercrystalline corrosion sensitivity is obtained. At the same time, a uniform equiaxed crystal structure is obtained. The grain size and the carbide are controlled synergistically.

According to the method, the final crystal grain, the appearance and the like of the austenitic stainless steel can be influenced by the temperature and the heat preservation time of the solution heat treatment, on one hand, a large number of twin crystals are generated by the mutual association of the disappearance of microscopic grain boundary dislocation and the movement of the grain boundary through the deformation solution heat treatment of the cold rolled tube, the twin crystals grow gradually in the further solution heat treatment process, the local orientation of the original intragranular crystals is adjusted, low-energy grain boundaries are introduced into the high-angle free grain boundary grids, the content of special grain boundaries can be improved by the mutual interaction between the non-coherent twin grain boundaries, and more low-energy segments are introduced into the high-angle free grain boundary grids. The introduction of more low-energy fragments can enable the wide-angle grain boundary gridding to be distributed more dispersedly, thereby forming a low-energy grain boundary structure. The formation of the low-energy structure is caused by the movement of non-intrinsic grain boundary dislocation, thereby preventing carbide from expanding from the surface layer to the core part along the grain boundary grids, and improving the intergranular corrosion resistance of the pipe. Therefore, grain boundary dislocations are made to move with the grain boundaries in the solution heat treatment by the preceding small-deformation cold rolling in the solution heat treatment, disappear at triple points of the grain boundaries, and thereby the grain boundary energy is greatly reduced, more grain boundary energy is reduced and more low-energy grain boundary structures are formed. On the other hand, the crystal grains are gradually refined through accumulation of dislocation formed inside the multi-pass deformation cold-rolled tube. The crystal grains are refined, the local crystal orientation is changed, and the hardness of the pipe is obviously reduced while the mechanical property is maintained.

Solution heat treatment: through the previous rolling with large deformation, the temperature of the solution heat treatment is controlled to be 1070-1100 ℃, so that the yield ratio of the stainless steel is improved through solution strengthening on one hand, and on the other hand, the processing stress is eliminated, a supersaturated solid solution and a proper grain size are obtained, further, the structure is improved, and preparation is made for the subsequent cold rolling processing.

The solution heat treatment of the finished product is a key process related to the final performance of the product, and long-term tests and researches show that the recrystallization is insufficient when the solution heat treatment temperature is lower than 1020 ℃; when the solution heat treatment is carried out at a temperature higher than 1150 ℃, the temperature becomes too high, and the crystal grains become coarse.

Solution heat treatment of the finished product: the temperature is controlled between 1070 ℃ and 1090 ℃, and the cold machining stress is released under the condition of ensuring the consistency of the length and the section temperature of the pipe body, so that the stability of a fine crystal structure is improved, and the high-temperature mechanical property is improved. Meanwhile, based on the idea of carbide cooperative control, the method is used for eliminating sigma and M in steel₇C₃、M₂₃C₆The precipitated phases, which contain Cr, Mo and N elements and are main elements for ensuring corrosion resistance of steel, lower the surrounding pitting equivalent and lower the corrosion resistance. But also the ductility and toughness of the steel are reduced and the hardness is increased.

The stainless steel solution heat treatment roller hearth furnace and the box furnace are adopted according to different pipe diameters and wall thicknesses, so that the technical characteristic requirements of the solution heat treatment of the pipes are met.

The stainless steel pipe is heated uniformly in the box furnace, so that the pipe can be fully dissolved, crystal grains are effectively regulated and controlled, work hardening is eliminated, and the structure and the performance of the stainless steel pipe are recovered. The outer diameter is more than or equal to 200 mm, the ratio of the outer diameter to the wall thickness is 5-13.3, the solid solution temperature is controlled within the range of 1070-1090 ℃, the heat preservation time of the product is controlled within (1.5-2.5) multiplied by the wall thickness min, and the heat preservation time of the finished product is controlled within (1.0-1.5) multiplied by the wall thickness min. A special rapid launching device is configured, the time from the discharging to the launching is controlled to be less than or equal to 25S, and the basic technological requirements of the solid solution heat treatment are met.

And (3) carrying out solid solution treatment on a finished product on a roller-hearth type solid solution heat treatment furnace by adopting a stainless steel tube roller-hearth type continuous solid solution heat treatment process at the maximum heating temperature of less than or equal to 150mm small-caliber tubes and less than or equal to 600mm tubes with the wall thickness of less than or equal to 20 ℃, wherein the solid solution temperature is controlled between 1070 and 1090 ℃, and the temperature rise time is properly prolonged. The heat preservation time of the product is controlled to be (4-10) multiplied by the wall thickness min, and the heat preservation time of the finished product is controlled to be (4-8.8) multiplied by the wall thickness min.

By these methods, various conditions can be controlled, and the stainless steel seamless pipe at 316H forms comprehensive properties satisfying the above conditions.

Examples molten steel having a composition was melted in an electric furnace and cast into billets (steel pipe material) by die casting, and steels a and B are shown in table 1.

The microalloying of other elements in the steel and the control of harmful elements in the steel billets of steel a and steel B are shown in table 2.

TABLE 1

TABLE 2

Stainless steel billets of 316H different specifications are used as raw materials, pierced billets are manufactured through hot piercing, 100% of pierced billets are subjected to surface visual inspection and coping, various defects on the inner surface and the outer surface are removed, and requirements of the finished pierced billets on the outer diameter, the wall thickness and the like are shown in a table 3.

TABLE 3

The cold working mainly comprises cold rolling and solution heat treatment, the cold rolling mill is used for controlling the deformation to manufacture the steel pipe, the solution heat treatment is carried out, and the temperature and the time are controlled to manufacture the steel pipe with the same grain size as the finished product. The control is shown in table 4 for the cold working process embodiment.

TABLE 4

The finished stainless steel seamless pipe thus obtained was cut out at both ends of the pipe head and the end to obtain samples for observing the entire thickness structure, the samples were taken parallel to the longitudinal section of the steel pipe by a microscope at 200 to 400 times, and the actual field area was 0.056mm2 (square field 0.237 × 0.237) mm as measured by an image analyzer. Shown in table 5.

TABLE 5

From the above, samples of the finished stainless steel seamless pipe were taken at both ends of the pipe and were subjected to longitudinal and transverse room temperature tensile tests, short time high temperature tensile tests, charpy V-type impact tests and hardness tests, corrosion test hardness tests, and grain size tests for evaluation, as shown in table 6.

TABLE 6

And adopting pulse reflection type ultrasonic detection equipment to carry out longitudinal and transverse ultrasonic detection on the inner and outer surfaces according to NB/T20003, wherein the depth of the rectangular groove of the standard sample is 0.1-1.0 mm, the width is not more than 1.6mm, and the length is not more than 12.5 mm. The qualification rate of ultrasonic flaw detection is over 95 percent.

The finished stainless steel seamless pipe is subjected to a hydrostatic test according to the GB/T241 standard, the test pressure is calculated according to the formula P =2SR/D, and the qualification rate of the hydrostatic test exceeds 100%.

Adopting MAC175 digital eddy current inspection equipment, performing longitudinal and circumferential eddy current inspection tests according to NB/T20003 standard when the nominal outer diameter is less than 65mm, wherein the diameter of a through hole of a standard sample is not more than 1.5mm, the depth of a groove is not more than 0.1mm, the width is not more than 1.5mm, the length of the groove is not more than 25mm, and the eddy current inspection qualification rate reaches 100 percent

The above description is only an embodiment of the present invention, and not intended to limit the scope of the present invention, and all modifications of equivalent structures and equivalent processes, which are made by the present specification, or directly or indirectly applied to other related technical fields, are included in the scope of the present invention.

Claims

1. A preparation method of a stainless steel seamless tube for a sodium-cooled fast reactor is characterized in that the preparation method comprises the following steps of performing micro-alloying component fine adjustment based on a 316H stainless steel base material, wherein the components comprise the following components in percentage by mass: 0.04 to 0.05 percent of C, less than or equal to 0.6 percent of Si, 1.00 to 2.00 percent of Mn, less than or equal to 0.030 percent of P, less than or equal to 0.003 percent of S, 17.0 to 18.0 percent of Cr, 11.5 to 12.5 percent of Ni, 2.50 to 2.70 percent of Mo, less than or equal to 0.10 percent of Cu, 0.05 to 0.07 percent of N, less than or equal to 0.0015 percent of B, less than or equal to 30ppm of O, less than or equal to 5.0ppm of H, and the balance of Fe and impurities, and the microalloy elements are regulated and controlled, and the ferrite content is controlled to be less than or equal to 1 percent;

the method comprises the following steps:

a. the high-purity smelting process comprises the following steps: firstly, smelting and primary smelting by an electric furnace, wherein the tapping temperature is more than or equal to 1670 ℃, the components of molten steel are uniform, and qualified molten stainless steel is manufactured; then refining by an AOD furnace, and leading the Al to be less than or equal to 0.03 percent and the oxygen content to be less than or equal to 30ppm by the AOD furnace and a deoxidation process of adding aluminum powder on the slag surface; then, refining in an LF furnace, introducing weaker argon gas, stirring, and removing small-size impurities by using bubbles;

b. fine adjustment of microalloying components: increasing austenite forming elements of Ni, Mn, C, N, Cu, B, N, Mo and V, controlling the ratio of chromium equivalent to nickel equivalent to be 1.10-1.2, adjusting the ferrite content of the final austenitic stainless steel seamless tube to be less than or equal to 1% by adjusting the chromium-nickel equivalent ratio, and obtaining a stainless steel melt for casting;

c. the stainless steel casting process comprises the following steps: b, manufacturing a casting material by using the stainless steel melt obtained in the step b, and manufacturing a round pipe blank by adopting a continuous casting method or an ingot casting method;

d. and (3) a hot perforation treatment process: performing hot piercing processing on the manufactured round pipe blank, regulating and controlling the process parameters of heating curvature, heat preservation time and cylinder turning times of each temperature section of the inclined hearth furnace on the round pipe blank, controlling the heating temperature to be 1160-1250 ℃, the heating time to be 150-900 minutes and the heat preservation time to be 15-150 minutes, performing deformation analysis and regulation on a stress strain field and a temperature field corresponding to large-grinding-angle inclined rolling piercing and controlling the temperature field in the piercing process of the top head to form hot piercing and cooperatively control the tissue property, and producing a qualified pierced billet;

e. and (3) a cold processing process of the intermediate product: rolling with large deformation, wherein the deformation elongation coefficient of a cold-rolled pipe is 1.3-1.9, the diameter reduction rate is controlled to be 31-48%, the wall reduction rate is 30-52%, the single-pass elongation coefficient of intermediate expanding, drawing and rolling pipes is controlled to be 1.05-1.7, the diameter reduction rate is controlled to be 10-40%, the wall reduction rate is 5-46%, then carrying out solution heat treatment, and controlling the temperature of the solution heat treatment to be 1070-1100 ℃;

f. and (3) cold processing of a finished product: detecting the grain size of the pipe before the finished product is rolled, accumulating deformation through the previous deformation rolling and cold expanding and drawing, controlling the deformation elongation coefficient of the cold rolled pipe to be 1.2-1.6 when the finished product is rolled, controlling the diameter reduction rate to be 11-30% and the wall reduction rate to be 12-32%, finally performing finished product solution heat treatment, controlling the temperature to be 1070-1090 ℃, and finally obtaining the finished product stainless steel seamless pipe for the sodium-cooled fast reactor.

2. The method for preparing a stainless steel seamless tube for a sodium-cooled fast reactor according to claim 1, wherein the impurity components comprise, in mass%, not more than 0.03% of Al, not more than 0.002% of Sb, not more than 0.001% of Pb, not more than 0.015% of Se, not more than 0.005% of Sn, not more than 0.05% of V, not more than 0.01% of Zn, not more than 0.01% of As, not more than 0.01% of Co, and not more than 0.06% of low-melting-point harmful elements of As + Sb + Bi + Sn + Pb, not more than 0.15%.

3. The method for preparing the stainless steel seamless tube for the sodium-cooled fast reactor according to claim 1, wherein in the step a, electric furnace smelting is carried out, the tapping temperature is more than or equal to 1670 ℃, molten steel before tapping is completely melted down, the content of Si is controlled to be 0.5-0.6%, the components of the molten steel are uniform, and qualified molten stainless steel is manufactured; through the deoxidation process of adding aluminum powder into the AOD furnace and the slag surface, Al is less than or equal to 0.03 percent, oxygen content is less than or equal to 30ppm, and simultaneously, in order to reduce S content, CaO/SiO with binary alkalinity is used₂Adding Al into the slag system₂O₃Can effectively reduce the melting point of the furnace slag and promote the furnace slag to adsorb Al in the molten steel₂O₃Inclusion, after Al deoxidation, a large amount of Al with high melting point, high hardness and irregular shape is easy to exist in the molten steel₂O₃Inclusion, clustering of Al₂O₃The Al can be continuously distributed along the rolling direction during rolling, the surface quality and the mechanical property of a tube blank can be seriously influenced, and the hard non-deformable Al is treated by a Ca treatment process₂O₃The inclusion is changed into calcium aluminate inclusion with low melting point, and 12CaO 7Al is generated during refining₂O₃LF external refining mainly promotes the upward floating of inclusions through weak argon stirring, because the molten pool in the furnace is deep, under strong stirring, the inclusions brought into the bottom of a steel ladle and slag involved in the molten steel circularly need a certain time to float, weak argon stirring is performed at the moment, the insufflated particles with argon bubbles of 10 mu m or less and difficult to discharge provide adhesive substrates, and the adhered substrates are adhered to the surfaces of the bubbles and discharged into the slag, so that the upward floating time of the inclusions is accelerated, and the argon blowing pressure is controlled to be 2.0-2.5 kg/cm³The flow is controlled to be 40-60L/min, the time is controlled to be 15-25 min, small-size inclusions are removed through bubbles, the small-size inclusions are aggregated and collided with each other to form large-particle inclusions more quickly, and the inclusions are enabled to float upwards and be removed rapidly.

4. The sodium-cooled fast reactor of claim 1The preparation method of the stainless steel seamless pipe is characterized in that the microalloying components in the step b are finely adjusted to increase the content of C and form M at high temperature₂₃C₆Phase (1); the Cu-B element is added in a composite way, and a large amount of fine dispersed copper-rich phase is formed after the Cu is aged at high temperature and acts together with the B to strengthen precipitation strengthening; the N element has strong binding force at high temperature for long term, and can reduce the diffusion rate of Cr and C and inhibit M when being dissolved in the gamma matrix₂₃C₆Coarsening to play a role in solid solution strengthening; trace Mo, V and Co elements are added, and trace Mo is added as a strong carbide forming element, so that the heat strength and the pitting corrosion resistance can be improved, the solubility of C in gamma in steel is reduced, and the generation of M is accelerated₂₃C₆Phase (1); a small amount of Co is used as an austenite element to play a role in solid solution strengthening, and the heat resistance and the oxidation resistance are also improved; the V is added to pin dislocation in the deformation process, block dislocation movement, play a role in precipitation strengthening, and remarkably improve high-temperature endurance strength and creep resistance through multi-element composite strengthening.

5. The method for preparing the stainless steel seamless tube for the sodium-cooled fast reactor according to the claim 1, wherein the diameter of the round steel in the step d is not more than 130mm, the whirlwind cutting amount is 1.5 mm-3 mm, the round steel with the corresponding weight is sawed, a centering hole is drilled at one end, the outer surface of the round steel is polished, and the surface defects are removed; the diameter of the round steel is larger than 130mm, the round steel with corresponding weight is sawed, the turning amount on a lathe is 4 mm-12 mm, a centering hole is drilled at one end, the outer surface of the round steel is polished, and the surface defects are removed; in order to ensure the coaxiality of the round steel in the hot punching process, when the diameter of the round steel is larger than 300mm, a through hole is punched; heating temperature is 1160-1250 ℃ according to the specification of round steel, temperature deviation is +/-20 ℃, heating time is 150-900 minutes according to corresponding specification, heat preservation time is 15-150 minutes according to corresponding specification, steel turning frequency is increased, the consistency of the heating temperature of the stainless steel round steel is ensured, the phenomenon that the surface is too high and the interior does not reach the required temperature is avoided, temperature uniformity is improved, a conical long blank punching technology with small additional deformation is adopted, on the basis of adjusting parameters of hot punching top specification, guide plate spacing, roller spacing and top retraction amount corresponding to tube blanks with different outer diameters and wall thicknesses, the temperature rise curvature and time of each section heated by a furnace are optimized, and the temperature field change distribution characteristics in the large-grinding-angle oblique-rolling hot punching stress field, the temperature field and the top punching process are combined, so that the interaction and association rules among multiple elements in the hot forming punching process are analyzed, The thermal perforation stress-strain field and the temperature field change distribution characteristics in the process of piercing by the plug realize the high-quality thermal perforation of the thermal perforation molding and the cooperative control of the organization and the performance, so that the pierced billet is in a tension state after the perforation, meanwhile, the circumferential shear strain and the surface torsion strain are also reduced to the minimum, the high production efficiency and the high yield are realized, the external diameter specification of the produced pierced billet is from phi 60 to phi 500mm, for reducing the wall reduction amount of subsequent cold processing for the pierced billets with the diameter of more than 300mm, a secondary perforation process is adopted, because the roller rotating speed is high in the perforation process, the heat ratio of work conversion is relatively higher than that of the inner surface, the roller rotating speed is relatively lower, according to the fact that the speed of a roller of different perforating units and the perforating ratio are reduced by 22-38%, the angle of the roller is adjusted to be increased from 7 degrees to 15 degrees, in addition, the temperature of the outer surface of a pierced billet is regulated and controlled through spraying water, and temperature-controlled perforation of high-performance stainless steel is achieved.

6. The method for preparing the stainless steel seamless tube for the sodium-cooled fast reactor according to claim 1, characterized in that the hot perforation technological parameters matched with the temperature and the rotating speed of the double-phase stainless steel pierced tube with various specifications in the step d meet the following conditions that when the specification of the pierced tube is not more than 65mm, the outlet temperature of the heating furnace is controlled to be 1160-1200 ℃, the heating time is controlled to be 150-170 minutes, the heat preservation time is controlled to be 15-30 minutes, the corresponding deformation speed is controlled to be 89-92 revolutions per minute, when the specification of the pierced tube is 75-130 mm, the outlet temperature of the heating furnace is controlled to be 1170-1220 ℃, the heating time is controlled to be 190-330 minutes, the heat preservation time is controlled to be 26-70 minutes, the corresponding deformation speed is controlled to be 74-77 revolutions per minute, when the specification of the pierced tube is 160-350 mm, the outlet temperature of the heating furnace is controlled to be 1210-1260 ℃, the heating time is controlled to be 325-880 minutes, the heat preservation time is controlled to be 45-130 minutes, the corresponding deformation speed is controlled to be 51-55 revolutions per minute, when the specification of the pierced billet is phi 350-phi 500mm, the outlet temperature of the heating furnace is controlled to be 1230-1270 ℃, the heating time is controlled to be 875-1100 minutes, and the heat preservation time is controlled to be 80-18Controlling the corresponding deformation speed to be 11-16 rpm within 0 minute, and controlling the volume of the water in the cooling circulating water tank to be 36-80 m according to the perforating unit with different specifications³And enough cooling water circulation amount is ensured in the perforation process, the water temperature of a cooling water pool is controlled to be less than or equal to 30 ℃, and the pierced billet quickly falls into the water pool for cooling after perforation, so that the corresponding effect of solid solution heat treatment is achieved.

7. The method for preparing the stainless steel seamless tube for the sodium-cooled fast reactor according to claim 1, characterized in that large deformation amount rolling is adopted in the step e, according to the grain size grade of a pierced billet, corresponding to a corresponding rolling deformation elongation coefficient of 1.3-1.9, crystal grains are elongated into fibers along the deformation direction, the dislocation density is gradually increased, the distortion degree in the structure is improved, the compression or elongation degree of the crystal grains is improved, the grain nucleation driving force and the growth driving force are obviously increased, full cold rolling deformation is avoided, mixed crystals and coarse crystal grains are avoided for thick-wall tubes, the deformation elongation coefficient of the cold-rolled tube is 1.3-1.9, the diameter reduction rate is controlled to be 31-48%, the wall reduction rate is 30-52%, the advantages of large deformation amount of the cold-rolled tube and flexible cold-expansion production are exerted by combining with cold expansion and rolling, and the large deformation amount is accumulated, the austenite grain size deformation amount is adjusted, the deformation amount is adjusted, and the deformation amount is adjusted, Regulating and controlling the morphology and the like, wherein the coefficient of each pass is controlled to be 1.05-1.7, the diameter reduction rate is controlled to be 10-40%, the wall reduction rate is 10-46%, and the temperature of the solid solution heat treatment is controlled to be 1070-1100 ℃, so that the yield ratio of the stainless steel is improved by the solid solution strengthening, the processing stress is eliminated, the supersaturated solid solution and the proper grain size are obtained, the structure is further improved, and the preparation is made for the subsequent cold rolling processing.

8. The method for preparing the stainless steel seamless tube for the sodium-cooled fast reactor according to claim 1, wherein the grain size of the tube is detected before the finished tube is rolled in the step f, the accumulated deformation amount is obtained through previous deformation rolling and cold expanding and drawing, other comprehensive performance requirements are met when the finished tube is rolled, the deformation elongation coefficient of the cold-rolled tube is relatively small and thin, the deformation elongation coefficient of the cold-rolled tube is 1.2-1.6, the diameter reduction rate is controlled to be 11-30%, the wall reduction rate is controlled to be 12-32%, the total cold-working deformation elongation coefficient is 2.0-5.0, the grain size is controlled to be 5-7 levels, and the corresponding requirements on the outer diameter, the wall thickness and the tolerance are met; solution heat treatment of the finished product: controlling the temperature to be 1070-1090 ℃, releasing cold machining stress under the condition of ensuring the consistency of the length of a pipe body and the temperature of a cross section, heating a stainless steel pipe in a box furnace to be uniformly heated, fully dissolving the pipe in a solid solution, effectively regulating and controlling crystal grains, eliminating work hardening, recovering the structure and the performance of the stainless steel pipe, controlling the outer diameter to be more than or equal to 200 mm, controlling the thick-wall pipe with the ratio of the outer diameter to the wall thickness to be 5-13.3, controlling the solid solution temperature to be 1070-1090 ℃, controlling the heat preservation time of a product to be (1.5-2.5) x wall thickness min, controlling the heat preservation time of a finished product to be (1.0-1.5) x wall thickness min, controlling the time from discharging to draining to be less than or equal to 25s, meeting the basic technological requirements of the solid solution heat treatment, performing the solid solution heat treatment on a small-diameter pipe with the diameter of being less than or equal to 150mm, the pipe with the wall thickness of being less than or equal to 600mm, and the wall thickness of being less than or equal to 20mm, adopting a stainless steel pipe roller-bottom continuous solid solution heat treatment process, and performing the solid solution heat treatment on the finished product in a bottom roller-type solid solution heat treatment kiln, the solid solution temperature is controlled to be 1070-1090 ℃, the temperature rise time is properly prolonged, the heat preservation time of a finished product is controlled to be (4-10) multiplied by the wall thickness min, the heat preservation time of a finished product is controlled to be (4-8.8) multiplied by the wall thickness min, and the unit of the wall thickness is mm.