CN109055864B - High-strength toughness low-yield specific heat simmered steel plate for simmering and its production method - Google Patents

Abstract

The invention provides a wide and thick steel plate for simmering elbows with high strength and toughness and low yield strength specific heat and a production method thereof. Mn: 1.76% to 1.95%, Nb: 0.051% to 0.080%, Ti: 0.010% to 0.025%, V: 0.09% to 0.13%, Cr: 0.25% to 0.45%, Mo: 0.20% to 0.35%, Ni< 0.25%, Cu<0.25%, Al: 0.010%～0.035%, P≤0.010%, S≤0.002%, N: 0.001%～0.004%, of which (Mo+Ni+Cr+Cu): 0.6%～1.0% , CE _IIW is controlled at 0.50% to 0.55%, CE _Pcm is controlled at 0.19% to 0.23%, and the balance is iron and inevitable impurities. The production methods include molten iron pretreatment, converter smelting, out-of-furnace refining, continuous casting, heating, Rolling, cooling and heat treatment; the microstructure of the present invention is a composite structure of bainite and ferrite, and the performance meets the requirements of making X90 grade hot simmering elbows with ultra-wide and thick walls in a low temperature environment.

Description

High-strength toughness low-yield specific heat simmered steel plate for simmering and its production method

technical field

The invention belongs to the field of low-carbon and low-alloy steel, and in particular relates to an X90-grade high-strength, high-toughness, low-yield-ratio hot-rolled wide-thick steel plate with a thickness of ≥22 mm and a width of >4300 mm for hot simmering bent pipes in a low temperature environment and a production method thereof.

Background technique

In order to improve the transportation efficiency of oil and gas pipelines, the transportation pressure and the diameter of the pipeline are continuously increasing; in order to take into account the safety of pipeline operation, the corresponding steel for oil and gas pipelines is required to develop in the direction of high strength, thick wall and large plate width. At the same time, with the continuous extension of oil and gas pipeline construction to remote, cold, geologically active areas and the increase in the demand for pipeline steel in special environments such as low-temperature stations, the low-temperature toughness and plasticity resistance (high plasticity, low yield-strength ratio) of steel for oil and gas pipelines ) and other technical indicators have been paid more and more attention. Therefore, products with high strength, high toughness, low yield ratio, width and thickness specifications are an important direction for the development of pipeline steel.

The hot simmering elbow is an important structural part in the oil and gas pipeline, which plays the role of changing the direction of the pipeline, buffering strain and torque, and over-matching protection. Its use conditions are more complicated than that of the main line pipe. Thicker than the main line pipe, and has excellent overall performance. The thickness of the wide and thick steel plate for hot simmering elbows of the present invention is greater than or equal to 22 mm, and the width is greater than 4300 mm. Thick-walled features make accelerated cooling less effective, tissue refinement and homogenization control near the center of the thickness more difficult; thus, ultimately significantly increasing the difficulty of performance control; at the same time, with increasing width, under the same implementation conditions and equipment capabilities The rolling deformation capacity of the steel plate is severely restricted, and the difficulty of grain refinement and control is doubled. Therefore, for the steel plate used in the low temperature environment for thick-walled and large-width hot simmering pipes, how to deform and cool the process is restricted. It is one of the key problems to be solved by the present invention to obtain good comprehensive performance and shape of the steel plate under the circumstance of the present invention. In addition, since the hot simmering elbow has to undergo a heat treatment process during the forming process, the steel used for the hot simmering elbow also needs to have good heat resistance to ensure that it still has good comprehensive properties after heat treatment.

The technical indicators of X90 grade wide and thick steel plate for hot simmering elbow in low temperature environment include transverse and longitudinal yield strength ≥ 625MPa, transverse and longitudinal tensile strength ≥ 740MPa, transverse and longitudinal elongation ≥ 20%, transverse and longitudinal yield ratio ≤ 0.87, -55°C transverse V-notch Charpy impact energy ≥120J; at the same time, it has the dimensional characteristics of thick wall and large plate width.

At present, there are some studies on steel plates for oil and gas transportation elbows at home and abroad, and some relevant patents and literatures have been found through search, but the recorded content is related to the technical scheme of the present invention and the product category, composition, process and performance, etc. There are obvious differences in aspects, which do not affect the inventiveness and novelty of the present invention.

The existing related inventions and documents are as follows:

The invention "a preparation method of X90 steel grade elbow and pipe fittings" (publication number: CN102161148A) discloses an X90 hot simmering elbow and pipe fittings. %~0.50%) design, low temperature toughness is not high and control is difficult, it needs to be supplemented with a large amount of elements such as Ni, Mo, and the yield-strength ratio of the product is high.

The invention "Rolling Process for High Toughness Hot Simmer Bending Steel" (Publication No.: CN107385340A) discloses a rolling process of X80 grade hot simmering bend steel, the width of which is less than 2600mm. , can not meet the requirements of manufacturing large-diameter hot simmering elbows; the composition uses more precious alloys such as Ni: 0.60% ~ 0.70%, Mo: 0.28% ~ 0.32%, etc., the production cost is high; large pass deformation is used in the process High efficiency and ultra-fast cooling put forward strict requirements on equipment capacity, and are not suitable for the production of ultra-wide and thick-walled steel for hot simmering bends.

Invention "A preparation method of X100 steel grade elbow and pipe fittings" (publication number: CN102127698A). Provided is an X100 hot simmering elbow and pipe fittings, which are also designed with high C (0.12%-0.20%) and high Si (0.30%-0.50%) in composition, and have the problems of insufficient low-temperature toughness and high yield-strength ratio.

The invention "A Ultra-High Strength Elbow with Good Low Temperature Toughness" (Publication No.: JP2005350724(A)) discloses a X100-X120 grade elbow, which also uses Ni, Mo and other precious alloys to improve performance and has a high yield-strength ratio .

The document "Influence of Whole Heating and Local Heating on the Microstructure and Properties of X90 High-strength Steel Hot Simmering Bend" ("Welded Pipe", Vol. 39, No. 6, 2016, Guo Youtian, Chen Zhongjun, Chen Xuan, etc.), the paper mainly introduces a kind of X90 The influence of the hot simmering elbow and the heat treatment process on it, the hot simmering elbow is designed with high Mo (>0.40%), the alloy cost is high, and the low temperature toughness is low, and the yield-strength ratio is high.

To sum up, the research on the wide and thick specification high-strength hot simmering elbow steel for low temperature environment is still insufficient in the prior art.

SUMMARY OF THE INVENTION

The purpose of the present invention is to overcome the above problems and deficiencies and provide a kind of steel plate for hot simmering pipe bends in a low temperature environment, which has high strength, low temperature toughness, plastic deformation resistance, stable heat treatment performance, thickness ≥ 22mm, width > 4300mm X90 class ultra-wide , Thick-walled, high-strength, high-toughness, low-yield-strength-ratio, high-plasticity wide and thick steel plate for hot simmer bend and its production method.

The object of the present invention is achieved in this way:

The thickness of the wide and thick steel plate for simmering elbows with high strength and toughness and low yield strength specific heat according to the present invention is greater than 22mm and width is greater than 4300mm; the composition design is based on low C and low Mn, and focuses on using V and Cr elements to partially or completely replace valuable Mo, Nb, Ni and other elements are used to ensure the strength and toughness of the material; the use of V, Nb and other elements in the process of deformation and heat treatment to refine grains and precipitation strengthen, promote the refinement and homogenization of the structure, improve the strength and toughness, heat resistance properties and welding performance; with targeted smelting, heating, rolling, cooling and unique heat treatment and other production processes to obtain ultra-wide, thick-walled, high strength, low yield ratio, high plasticity and good low temperature toughness. Comprehensive index of steel plate for hot simmering elbow and ideal microstructure.

A wide and thick steel plate for simmering and bending pipes with high strength and toughness and low yield strength is provided. Nb: 0.051% to 0.080%, Ti: 0.010% to 0.025%, V: 0.09% to 0.13%, Cr: 0.25% to 0.45%, Mo: 0.20% to 0.35%, Ni<0.25%, Cu<0.25%, Al: 0.010%～0.035%, P≤0.010%, S≤0.002%, N: 0.001%～0.004%, of which (Mo+Ni+Cr+Cu): 0.6%～1.0%, CE _IIW controlled at 0.50%～ 0.55%, CE _Pcm is controlled at 0.19% ~ 0.23%, the balance is iron and inevitable impurities, where CE _IIW =C+Mn/6+(Cr+Mo)/5+(Ni+Cu)/15;

CE _Pcm =C+Si/30+(Mn+Cu+Cr)/20+Ni/60+Mo/15+V/10+5B.

Further, the microstructure of the steel sheet is a composite structure of bainite and ferrite, and the grain size reaches grade 11 and above, wherein the volume percentage of ferrite is 10% to 30%.

Further, the thickness of the wide and thick steel plate for simmering elbows with high strength and toughness and low yield strength is ≥22mm, width>4300mm, transverse and longitudinal yield strength ≥630MPa, transverse and longitudinal tensile strength ≥750MPa, transverse and longitudinal elongation ≥35% , transverse and longitudinal yield ratio ≤ 0.83, -60 ℃ transverse impact energy average ≥ 220J.

The reasons for the composition design of the present invention are as follows:

C is an effective strengthening element, which can form interstitial solid solution, improve hardenability and strength after heat treatment; it can also act with Nb, V, Ti and other elements to form fine carbides, which are precipitated in the process of heating, deformation and heat treatment of steel plates. Play the role of hindering the growth of grains and refining the structure; at the same time, the precipitation phase can hinder the movement of dislocations and effectively improve the strength. Therefore, the carbon content should not be too low; however, considering that the increase in carbon content is unfavorable to weldability and toughness, especially It is to deteriorate the low temperature toughness, so the carbon content should not be too high. The present invention considers that it is appropriate to control the carbon at 0.055% to 0.080%.

In the present invention, Si mainly plays the role of solid solution strengthening, improves the hardenability, and has a positive effect on improving the strength of controlled rolling and controlled cold state and heat treatment state; however, if its content is too high, the plasticity and toughness of the steel will be reduced, and it is easy to cause cold brittleness. , and its suitable range is 0.16% to 0.30%.

Mn has the effect of solid solution strengthening, which can improve the hardenability, which is beneficial to ensuring the strength after heat treatment; it can also increase the stability of austenite, reduce the austenite transformation temperature, and inhibit the phase transformation and grain growth of the steel plate before accelerated cooling. , to play the role of grain refinement; however, too high manganese content is easy to induce segregation, deteriorate the microstructure uniformity and thickness center toughness of the thick-walled steel plate, and is not conducive to welding.

Nb has obvious solid solution and precipitation strengthening effects. The present invention makes full use of the precipitation pinning ability of Nb before rolling, accelerated cooling and during heat treatment to effectively refine grains, increase strength and improve toughness. At the same time, Nb can inhibit Austenite is recrystallized, and the recrystallization rolling temperature is increased, thereby effectively reducing the rolling force, and improving the rolling pass deformation rate of the steel plate for the ultra-wide and thick-walled hot simmer bend of the present invention, reaching the expected fineness. In addition, Nb can also reduce the mixed crystal problem of thick-walled pipeline steel due to the temperature difference in the thickness direction during rolling. However, excessive Nb content will significantly increase the production cost, and will promote precipitates. Growing up, on the contrary, is not conducive to exerting a strengthening effect, and has an adverse effect on the toughness. The present invention believes that it is more appropriate to control the Nb content to 0.051% to 0.080%.

Ti can exert the effect of nitrogen fixation and form the precipitation phase mainly composed of TiN, which can inhibit the grain growth of austenite under high temperature conditions, which is beneficial to refine the microstructure of the slab and the steel plate, and can also improve the toughness of the heat affected zone after welding; At the same time, the formation of precipitation phase by Ti at high temperature will reduce the concentration of N and C, inhibit the precipitation of elements such as Nb and V at high temperature, and make it easy to form fine precipitation phase at lower temperature, which is more conducive to improving performance. The present invention considers that it is appropriate to control the Ti content to 0.010% to 0.025%.

V has the effect of solid solution and precipitation, which can effectively improve the strength during solid solution; and its precipitation temperature is lower than the precipitation phase dominated by Nb and Ti, and can combine with C and N to form fine precipitation during rolling, cooling and heat treatment. , In particular, it has a secondary hardening effect during heat treatment, which increases the tempering resistance and ensures the performance after heat treatment. The present invention focuses on using the above two characteristics of V to effectively improve the comprehensive performance. However, if the V content is too high, the toughness of the steel sheet and the hot zone will be affected. Therefore, the present invention controls the V content to be 0.09% to 0.13%.

Cr can improve the stability and hardenability of austenite, reduce the austenite transformation temperature, refine grains, ensure the performance after heat treatment, and play a good role in improving the strength of thick-walled steel plates and improving the uniformity of the thickness direction; Cr also It has the effect of solid solution strengthening, which is beneficial to ensure the strength; at the same time, Cr can reduce the diffusion ability of C, improve the stability of heat treatment performance, and promote the refinement of Nb and V precipitation phases; moreover, Cr element is highly economical and can partially replace Mo, Ni and other precious alloying elements; the present invention makes full use of the above characteristics of Cr to effectively improve the comprehensive performance of the product; but too high Cr content is unfavorable for weldability, and the plasticity also tends to deteriorate, so it is appropriate to control the Cr content to 0.25% to 0.45% .

Mo can increase the stability of austenite, significantly improve the hardenability, promote the microstructure transformation at medium and low temperature, increase the strength, and can also optimize the microstructure and properties of the steel plate and HAZ area. , it will increase the hardening phase such as M/A in the structure and reduce the toughness. Therefore, its content should be controlled at 0.20% to 0.35%.

Ni plays the role of solid solution strengthening, which is conducive to improving low temperature toughness; it can also promote the formation of medium temperature transformation structure and reduce the limit of cooling rate of thick steel plate; but the price of nickel is high, so it is appropriate to control its content at <0.25%.

Cu can play the role of solid solution strengthening, at the same time, it can reduce the diffusivity of C and improve the stability of heat treatment performance. Cu can also improve corrosion resistance, but too high content of Cu can easily induce cracks and damage weldability. It is more appropriate to control the content at <0.25%.

Al is a deoxidizing element, and also has a strong tendency to combine with N. AlN can improve the toughness of the welding hot zone; however, if the Al content is too high, it will promote the increase of inclusions.

P and S are harmful impurity elements in the present invention, and the lower the content, the better; among them, P has obvious adverse effects on low temperature toughness, the present invention controls P to be less than or equal to 0.010%, and the increase of S content will promote the formation of inclusions and Grows up and deteriorates performance, therefore, S≤0.002%.

N can combine with Nb, V, Ti and other elements to form precipitates, which play a significant role in inhibiting grain growth during slab heating. At the same time, it can play a role in precipitation strengthening during rolling, cooling and heat treatment. Therefore, in steel The presence of a certain amount of N is beneficial to the performance, but too high a content will deteriorate the toughness of the base metal and the welding heat-affected zone, and its content should be controlled at 0.001% to 0.004%.

Mo, Ni, Cr and Cu all have a strengthening effect, increase the stability of austenite, which is beneficial to improve hardenability and performance after heat treatment. Too low Mo+Ni+Cr+Cu is not conducive to performance and microstructure control, and too high content Affects weldability and economy, therefore, in the present invention, (Mo+Ni+Cr+Cu): 0.6%-1.0%.

In the present invention, CEIIW is controlled at 0.50%-0.55%, and CEPcm is controlled at 0.19%-0.23%, which can not only ensure the strength and toughness of the steel plate, but also make the steel plate have suitable weldability.

The second technical solution of the present invention is to provide a method for producing wide and thick steel plates for simmering elbows with high strength and toughness and low yield specific heat, including molten iron pretreatment, converter smelting, out-of-furnace refining, continuous casting, heating, rolling, cooling, and heat treatment. ;

(1) Continuous casting: After refining molten steel, the sedation time of argon blowing before continuous casting is not less than 10min, the casting superheat degree of continuous casting is 15~35℃, the pulling speed of continuous casting is 0.6m/min-1.0m/min, and the continuous casting Thickness/thickness of finished steel plate is controlled at 7-14; argon blowing sedation before continuous casting can improve the uniformity of molten steel temperature and composition, which is beneficial to the floating removal of inclusions; the control of pouring superheat and continuous casting billet pulling speed can effectively reduce The quality of the slab is defective; the compression ratio from the continuous casting slab to the finished steel plate is conducive to grain refinement.

(2) Heating: The continuous casting billet is cleaned and heated in a furnace, and a two-stage heating method is adopted. Among them, the temperature of the high-temperature heating section is 1210-1240 °C, the temperature of the soaking section is 1200-1230 °C, and the time of the high-temperature heating section + soaking section is not Less than 150min; continuous casting billet cleaning can effectively reduce surface defects, the design of heating process is mainly to ensure the solid solution of alloy elements, so that it can play an ideal role in subsequent production, and at the same time, effectively control the growth of austenite grains; The heating time can ensure the heating effect and temperature uniformity.

(3) Rolling: the starting temperature of rough rolling is 1120-1170 °C, the final rolling temperature of rough rolling is 1000-1050 °C, and the horizontal and vertical rolling method is adopted. Ensure that the pass deformation rate of at least the last 2 passes is greater than 15% and the pass interval does not exceed 15s; the rolling speed of rough rolling is 1.2m/s-2.0m/s; the rolling temperature and deformation process of the rough rolling stage make the Austrian The intenite grains are recrystallized. The large reduction and short interval process at the end of the rough rolling and longitudinal rolling can better exert the deformation superposition effect under the premise of taking into account the equipment capacity and rolling load, and promote the recrystallization of austenite to achieve The grain refinement goal is more suitable for the production of the ultra-wide and thick-walled steel plate of the present invention. The control of the rough rolling speed can promote the penetration of the rolling deformation to the thickness center, and refine the thickness center grains, which is beneficial to improve the pipeline steel with large wall thickness. of cardiac tissue.

The thickness of the intermediate billet to be warmed is 3.1t ~ 5.0t, where t is the thickness of the finished steel plate, the starting temperature of finishing rolling is 810 ~ 900 ℃, and the final rolling temperature of finishing rolling is 720 ~ 750 ℃; On the one hand, the low finishing rolling temperature can ensure the deformation of austenite and accumulate deformation energy; grains; furthermore, it can also promote the nucleation of fine ferrite.

(4) Cooling: After rolling, the steel sheet is accelerated by water cooling, the initial cooling temperature is 710-740°C, the final cooling temperature is 340-460°C, the water-cooling cooling rate is 8-20°C/s, and the water-cooling cooling time is not less than 15s. Since Cr, Mn, Mo, Cu and other elements can reduce the austenite transformation temperature, a lower starting cooling temperature can be used, which is beneficial to the refinement of grains and the formation of fine precipitates; In order to improve the hardenability, a lower cooling rate and a longer cooling time can be used, thereby increasing the cooling uniformity in the thickness direction of the thick-walled steel plate and reducing the internal stress of the steel plate, which can meet the performance and reduce the influence on the shape of the plate.

(5) Heat treatment: During heat treatment, the quenching temperature should be controlled at 840-890°C, and the quenching holding time should be 0.5min/mm-1.0min/mm. The low-temperature heating process for quenching can obtain the composite structure of polygonal ferrite + austenite at the same time. Effectively inhibit the growth of grains; quenching cooling rate ≥ 15℃/s, cool to room temperature to obtain polygonal ferrite + bainite, M/A hard phase; tempering temperature 350 ~ 500℃, tempering holding time 1.6min/mm～3.0min/mm, promote precipitation strengthening and tempering hardening, improve yield strength, reduce residual stress, at the same time, prevent excessive desolubilization of elements and growth of bainite grains, and ensure strength.

After heat treatment, the microstructure of the steel plate is a composite structure of bainite + ferrite, and the grain size is above grade 11. Among them, the volume percentage of ferrite is 10% to 30%, and the steel plate has ultra-wide, thick-walled, high-strength , Low yield ratio, high plasticity and good low temperature toughness, at the same time, the weldability and formability meet the requirements of making ultra-wide and thick-walled X90 grade hot simmering elbows.

The invention provides a method for producing a wide and thick steel plate for simmering elbows with high strength and toughness and low yield strength specific heat. Grain, control the precipitation phase, thus, relying on tissue heredity and appropriate heat treatment process to refine and control the organization and structure after heat treatment, to ensure the performance after heat treatment.

The beneficial effects of the present invention are:

(1) The composition design of the present invention is based on low C and low Mn, and focuses on the use of V, Cr elements to partially or fully replace the precious elements such as Mo, Nb, Ni, etc., to ensure the strength and toughness of the material; the use of V, Nb and other elements to reduce During the heat treatment process, the grain refinement and precipitation strengthening effect promotes the refinement and homogenization of the structure, and improves the strength, toughness, heat resistance and welding performance. The steel plate for simmering elbow has ideal microstructure, fine grains, excellent comprehensive properties and good shape.

(2) The carbon equivalents CEIIW and CEPcm of the present invention are suitable to ensure that the material has good strength and weldability.

(3) The refining and continuous casting process scheme of the present invention effectively improves the quality of the slab, thereby improving the performance of the final product.

(4) The present invention utilizes the unique low-temperature, low-speed, short-interval rolling + low-temperature and long-time uniform cooling after rolling + low-temperature quenching and tempering process to give full play to alloying elements to reduce phase transformation temperature, improve hardenability, precipitate fine grains and strengthen Equal effect and the heredity of the organization, the compound matching effect of multiple organizations, obtain products with good matching of strength, plasticity and toughness, at the same time, increase the cooling uniformity, reduce the internal stress and organizational stress, and effectively control the shape of the steel plate.

(5) The thickness of the wide and thick steel plate for simmering elbows with high strength and toughness and low yield specific heat according to the present invention is ≥22mm, width>4300mm, transverse and longitudinal yield strength ≥630MPa, transverse and longitudinal tensile strength ≥750MPa, transverse and longitudinal Longitudinal elongation ≥ 35%, transverse and longitudinal yield ratio ≤ 0.83, -60 ℃ transverse impact energy average ≥ 220J, microstructure is a composite structure of bainite + ferrite, of which the volume percentage of polygonal ferrite is 10 %～30%, the grain size reaches grade 11 and above, which meets the requirements of making X90 grade hot simmering elbows with ultra-wide and thick walls in low temperature environment.

Description of drawings

FIG. 1 is a microstructure metallographic diagram of Example 2 of the present invention.

Detailed ways

The present invention will be further illustrated by the following examples.

In the embodiment of the present invention, molten iron pretreatment, converter smelting, out-of-furnace refining, continuous casting, heating, rolling, cooling, and heat treatment are performed according to the component distribution ratio of the technical solution.

(1) Continuous casting: After refining molten steel, the sedation time of argon blowing before continuous casting is not less than 10min, the casting superheat degree of continuous casting is 15~35℃, the pulling speed of continuous casting is 0.6m/min-1.0m/min, and the continuous casting Thickness/finished steel plate thickness is controlled at 7-14;

(2) Heating: The continuous casting billet is cleaned and heated in a furnace, and a two-stage heating method is adopted. Among them, the temperature of the high-temperature heating section is 1210-1240 °C, the temperature of the soaking section is 1200-1230 °C, and the time of the high-temperature heating section + soaking section is not less than 150min;

(3) Rolling: the starting temperature of rough rolling is 1120-1170 °C, the final rolling temperature of rough rolling is 1000-1050 °C, and the horizontal and vertical rolling method is adopted. Ensure that the pass deformation rate of at least the last 2 passes is greater than 15% and the pass interval does not exceed 15s; the rolling speed of rough rolling is 1.2m/s-2.0m/s;

The thickness of the intermediate billet to be warmed is 3.1t～5.0t, where t is the thickness of the finished steel plate, the finishing rolling temperature is 810～900℃, and the finishing rolling temperature is 720～750℃;

(4) Cooling: After rolling, the steel sheet is accelerated by water cooling, the initial cooling temperature is 710-740°C, the final cooling temperature is 340-460°C, the water-cooling cooling rate is 8-20°C/s, and the water-cooling cooling time is not less than 15s;

(5) Heat treatment: quenching temperature 840～890℃, quenching holding time 0.5min/mm～1.0min/mm, quenching cooling rate ≥15℃/s, cooled to room temperature; tempering temperature 350～500℃, tempering holding time 1.6min/mm～3.0min/mm.

The composition of the steel in the embodiment of the present invention is shown in Table 1. The smelting and continuous casting process and slab heating parameters of the steel in the embodiment of the present invention are shown in Table 2. The rough rolling process of the steel in the embodiment of the present invention is shown in Table 3. The finishing rolling and cooling process of the steel in the embodiment of the present invention are shown in Table 4. The heat treatment process of the steel of the embodiment of the present invention is shown in Table 5. Table 6 of the properties of the steel of the embodiment of the present invention. Table 7 shows the microstructure of the steel in the embodiment of the present invention.

Table 1 Composition (wt%) of the steel according to the embodiment of the present invention

Example 1 2 3 4 5 6 C 0.071 0.065 0.058 0.066 0.056 0.062 Si 0.22 0.26 0.18 0.25 0.27 0.20 Mn 1.79 1.91 1.76 1.82 1.87 1.77 P 0.008 0.007 0.008 0.006 0.005 0.006 S 0.0013 0.0017 0.0014 0.0013 0.0016 0.0014 Nb 0.065 0.076 0.058 0.064 0.073 0.055 Ti 0.017 0.021 0.013 0.015 0.012 0.013 Cr 0.31 0.40 0.38 0.28 0.34 0.42 V 0.09 0.10 0.12 0.09 0.10 0.11 Mo 0.24 0.22 0.31 0.32 0.28 0.22 Ni 0.13 0 0.16 0 0.21 0.12 Cu 0 0 0.14 0.08 0 0.19 al 0.030 0.021 0.027 0.019 0.033 0.031 N 0.0031 0.0018 0.0025 0.0018 0.0026 0.0036 CE_IIW 0.506 0.527 0.533 0.513 0.526 0.528 CE_Pcm 0.211 0.214 0.213 0.214 0.208 0.215

Table 2 The smelting continuous casting and slab heating process parameters of the steel of the embodiment of the present invention

The rough rolling process of table 3 embodiment steel of the present invention

Finish rolling and cooling process of table 4 embodiment steel of the present invention

Table 5 The heat treatment process of the embodiment steel of the present invention

Example Quenching temperature, ℃ Quenching holding time, min/mm Tempering temperature, ℃ Tempering holding time, min/mm 1 860 0.8 380 2.9 2 840 0.9 410 2.4 3 880 0.6 440 1.7 4 860 0.8 370 1.9 5 840 0.9 390 1.6 6 860 0.7 360 2.1

The performance of table 6 embodiment steel of the present invention

Note: The tensile sample is a full-thickness rectangular sample, and the plate width of the parallel test section is 38.1mm; the size of the impact sample is 10*55*55mm

Table 7 The microstructure of the steel of the embodiment of the present invention

As can be seen from the above, the thickness of the high-strength toughness and low-yield specific heat simmering steel plate for wide and thick steel plates obtained by applying the technical solution disclosed in the present invention is ≥ 22mm, width > 4300mm, transverse and longitudinal yield strength ≥ 630MPa, transverse and longitudinal tensile strength ≥750MPa, transverse and longitudinal elongation ≥35%, transverse and longitudinal yield ratio ≤0.83, average transverse impact energy at -60°C ≥220J, microstructure mainly composed of bainite + ferrite composite structure, among which, multilateral The volume percentage of ferrite is 10% to 30%, and the grain size reaches grade 11 and above, which meets the requirements for making ultra-wide and thick-walled X90 grade hot-simmered pipes in low-temperature environments.

In order to describe the present invention, the present invention has been properly and fully described through the examples above. The above embodiments are only used to illustrate the present invention, rather than to limit the present invention. In the case of the spirit and scope of the invention, various changes and modifications can also be made, and any modifications, equivalent replacements, improvements, etc., should be included in the protection scope of the present invention, and the patent protection scope of the present invention should be determined by Claims limited.

Claims (3)

1. A wide and thick steel plate for simmering elbows with high strength and toughness and low yield strength specific heat, characterized in that the composition of the steel plate is as follows by weight: C: 0.056% to 0.080%, Si: 0.16% to 0.30%, Mn: 1.76% to 1.95%, Nb: 0.051% to 0.080%, Ti: 0.010% to 0.025%, V: 0.09% to 0.13%, Cr: 0.25% to 0.45%, Mo: 0.20% to 0.35%, Ni<0.25% , Cu<0.25%, Al: 0.010%～0.035%, P≤0.010%, S≤0.002%, N: 0.001%～0.004%, of which (Mo+Ni+Cr+Cu): 0.62%～1.0%, CE _IIW is controlled at 0.50%~0.55%, CE _Pcm is controlled at 0.19%~0.23%, the balance is iron and inevitable impurities, where CE _IIW =C+Mn/6+(Cr+Mo)/5+(Ni+ Cu)/15; CE _Pcm =C+Si/30+(Mn+Cu+Cr)/20+Ni/60+Mo/15+V/10+5B; the high-strength toughness low-yield specific heat simmering bend Production methods for wide and thick steel plates, including molten iron pretreatment, converter smelting, out-of-furnace refining, continuous casting, heating, rolling, cooling, and heat treatment; (1) Continuous casting: After molten steel is refined, the quenching time of argon blowing before continuous casting is not less than 10 minutes. Thickness/finished steel plate thickness is controlled at 7-14; (2) Heating: After the continuous casting slab is cleaned, it is heated in a furnace, and a two-stage heating method is adopted. The temperature of the high-temperature heating section is 1210-1240°C, the temperature of the soaking section is 1201-1230°C, and the time of the high-temperature heating section + soaking section is not less than 150min; (3) Rolling: The starting temperature of rough rolling is 1120-1170°C, the finishing temperature of rough rolling is 1000-1050°C, adopting the method of horizontal and vertical rolling, wherein the starting temperature of longitudinal rolling is not higher than 1090°C, Ensure that the pass deformation rate of at least the last two passes is greater than 15% and the pass interval does not exceed 15s; the rough rolling speed is 1.2m/s-2.0m/s; The thickness of the billet to be warmed in the middle is 3.1t-5.0t, where t is the thickness of the finished steel plate, the starting temperature of finish rolling is 810-900°C, and the temperature of finishing rolling is 720-750°C; (4) Cooling: After rolling, the steel plate is subjected to accelerated water cooling, the initial water cooling temperature is 710-740°C, the final cooling temperature is 340-460°C, the water-cooling cooling rate is 8-20°C/s, and the water-cooling cooling time is not less than 15s; (5) Heat treatment: Quenching temperature 840～890℃, quenching holding time 0.5min/mm～1.0min/mm, quenching cooling rate ≥15℃/s, cool to room temperature; tempering temperature 350～440℃, tempering holding time 1.6min/mm～3.0min/mm. 2. A kind of wide and thick steel plate for high-strength toughness and low-yield specific heat simmering pipe bending according to claim 1, characterized in that, the microstructure of the steel plate is a composite structure of bainite+ferrite, and the grain size reaches Grade 11 and above, wherein the volume percentage of ferrite is 10% to 30%. 3. A kind of wide and thick steel plate for high-strength toughness and low yield strength specific heat bending pipe according to claim 1, characterized in that, the thickness of the wide and thick steel plate for high strength toughness and low yield strength specific heat bending pipe is ≥ 22mm, and the width > 4300mm, transverse and longitudinal yield strength ≥ 630MPa, transverse and longitudinal tensile strength ≥ 750MPa, transverse and longitudinal elongation ≥ 35%, transverse and longitudinal yield ratio ≤ 0.83, -60°C average transverse impact energy ≥ 220J.