CN116287964A - A preparation method of super duplex stainless steel with PREN≥42 and seamless pipe - Google Patents

Abstract

The invention discloses a preparation method of super duplex stainless steel with PREN not less than 42 and a seamless pipe, which are characterized in that the super duplex stainless steel with PREN not less than 42 and the seamless pipe with high strength and high corrosion resistance is finally obtained by optimizing alloy components and adopting the processes of electric furnace smelting, electroslag remelting, forging cogging, extrusion pipe making, solution heat treatment and cold rolling.

Description

A preparation method of super duplex stainless steel with PREN≥42 and seamless pipe

technical field

The invention belongs to the field of duplex stainless steel, and in particular relates to a preparation method of a super duplex stainless steel with PREN≥42 and a seamless pipe. The super duplex stainless steel seamless pipe is mainly used for the transportation and treatment of dangerous goods, and the drilling of offshore oil and natural gas and other special industries.

Background technique

Today's petrochemical industry is developing rapidly, but the regional development of my country's petrochemical industry is unbalanced. Most of the chemical industry clusters based on oil and natural gas are distributed in the west, while the sales places of their output products and downstream deep processing enterprises are mostly concentrated in the east. In coastal areas, more than 95% of chemical raw materials need to be transported; "separation of production and sales" determines the tightness of "dangerous chemical logistics" transportation, so the steel used to manufacture dangerous goods transportation equipment must not only have high strength, but also be resistant to various Form of corrosion, but also resistant to seawater corrosion, currently people widely use duplex stainless steel, super duplex stainless steel to manufacture related transportation equipment. Due to the continuous improvement of the corrosion resistance requirements of super duplex stainless steel for transportation equipment, the super duplex stainless steel with PREN=Cr%+3.3Mo%+16N% of 40-41 can no longer meet the requirements, and people began to ask for the super duplex stainless steel with PREN≥42 The compositional design and manufacturing methods of duplex stainless steels have put forward demands; this is also the pursuit of equipment such as umbilical cables and transmission tubing for offshore oil and gas drilling and acquisition industries.

Since the alloy content of super duplex stainless steel with PREN ≥ 42 is higher than that of conventional super duplex stainless steel (PREN is in the range of 40-41), and the N content is also higher than conventional, it often brings unexpected problems to smelting and production. difficulty. In order to solve the problems and bottlenecks encountered in smelting and production, the present invention proposes to use electric furnace + electroslag for smelting/remelting of PREN ≥ 42 super duplex stainless steel, and through alloy composition design, to avoid forging and subsequent hot processing Precipitation of harmful phases.

At present, there are relatively few patents on the electroslag remelting process for the production of super duplex stainless steel products. Liu Haiding et al. (CN201711374347.2) of Chongqing Materials Research Institute Co., Ltd. invented a super duplex stainless steel (UNSS32750, S32760, S32707, S32907, S33207, etc.) electroslag remelting slag system: CaF ₂ :55-74 %, CaO: 5-20%, Al ₂ O3: 5-20%, MgO: 5-15%, SiO ₂ : 1-15%, so that the purity of super duplex stainless steel is improved, the harmful impurity elements are reduced, and the electrode rod structure Optimization, greatly improving the processing performance of stainless steel and increasing the yield of thermal processing. Hu Huajun and others (CN201310271485.3) of Jiangyin Hengye Forging Co., Ltd. proposed a forging method for super duplex stainless steel large-scale tube sheet forgings. The slag is remelted into an electroslag ingot with a diameter of 1750 mm, but the patent does not specify the electroslag condition. Du Xiaoliang (CN201010281943.8) of Jiangsu Lixin Alloy Industry Corporation involved the electroslag remelting process in his proposed production method of a super duplex stainless steel welding material, mainly the proportion of electroslag slag: aluminum powder 25g, alumina powder 230g, lime 100g, magnesium powder 100g, fluorite powder 1240g, titanium dioxide 25g. Electroslag applies a voltage of 42 volts and a current of 2200-2800A. Liao Yunhu et al. (CN201611105338.9) of Sichuan Liuhe Forging Co., Ltd. used electroslag remelting to further reduce the content of impurity elements in super duplex stainless steel. The steps and process parameters are that the slag system is CaF ₂ : Al ₂ O ₃ : CaO:MgO=60:25:10:5; power system: voltage 56V±2V, current 7500±300A.

Contents of the invention

In view of the above-mentioned defects existing in the prior art, the object of the present invention is to provide a preparation method of super duplex stainless steel and seamless pipe with PREN ≥ 42, optimize the alloy composition from the aspects of harmful phase suppression and strength improvement, and adopt electric The characteristics of the slag remelting process make the electroslag ingots free of nitrogen pores, ensure the smooth progress of the forging process, effectively reduce the amount of surface grinding of the tube billet, improve the yield of the final product, and prepare a steel pipe with excellent mechanical properties and PREN ≥ 42. Super duplex stainless steel seamless pipes meet the needs of special industries such as transportation and handling of dangerous goods, offshore oil and natural gas drilling, etc.

To achieve the above object, the present invention adopts the following technical solutions:

The first aspect of the present invention provides a super duplex stainless steel with PREN≥42, including the following components by weight percentage: C: 0.022-0.030%, Si: 0.10-0.80%, Mn: 0.10-1.20%, P≤0.022 %, S≤0.003%, Al≤0.030%, Cu≤0.50%, N: 0.265～0.295%, Cr: 25.7～26.0%, Ni: 6.0～8.0%, Mo: 3.66～3.75%, B: 0.002～0.005% %, the balance is Ni and unavoidable impurities.

Preferably, the pitting resistance index PREN of the super duplex stainless steel with PREN≥42 satisfies:

PREN=Cr+3.3×Mo+16×N≥42%; and/or

The critical temperature for the precipitation of the harmful phase σ phase of the super duplex stainless steel with PREN≥42 satisfies:

T _σ =1000×(4.17-0.338×Cr+5.16×Mo) ^(1/11.2) -273≤1000°C; and/or

The critical temperature for the precipitation of the harmful phase Cr2N phase of the super duplex stainless steel with PREN ≥ 42 satisfies:

T _Cr2N = 1000×(-61.1+40.4×C+1.97×Cr+2.49×Mo+59.6×N) ^(1/9.6) -273≤1080°C.

The second aspect of the present invention provides a super duplex stainless steel seamless pipe with PREN≥42 prepared based on the super duplex stainless steel with PREN≥42 described in the first aspect of the present invention, and the super duplex stainless steel with PREN≥42 The room temperature tensile strength of the stainless steel seamless pipe is ≥800MPa, the yield strength is ≥650MPa, and the elongation is ≥30%.

The third aspect of the present invention provides a method for preparing a super duplex stainless steel seamless pipe with PREN≥42, comprising the following steps:

S1, smelting, according to the composition ratio raw material of the super duplex stainless steel with PREN≥42 according to claim 1, the raw material is smelted in an electric furnace and electroslag remelted to obtain an electroslag ingot;

S2, forging and blanking, heating the electroslag ingot, and then forging and blanking to obtain a tube blank;

S3, extruding the pipe, processing the pipe blank through extrusion, and obtaining a blank pipe after water cooling;

S4, solution heat treatment, after performing solution heat treatment on the waste tube, water cooling;

S5, cold rolling, cutting the raw pipe, pickling, and then performing multi-pass cold rolling to obtain a super duplex stainless steel seamless pipe with PREN≥42.

Preferably, in the step S1:

During the smelting process of the electric furnace, nitrogen is used for stirring, and argon is used for protective pouring when the molten steel is tapped, the flow rate of the argon is 2-5Nm ³ /h, and the casting temperature is 1600-1650°C; and/or

In the electroslag remelting process, the composition of the electroslag system used is as follows: CaF ₂ : Al ₂ O ₃ : CaO: MgO=65～75:15～22:3～7:3～7; and/or

During the electroslag remelting process, the electroslag steady-state melting rate is 6.0-7.0 kg/min.

Preferably, in the step S2:

During the heat treatment process, the heating temperature is 1220-1250°C, and the holding time is (110-130min) × electroslag ingot thickness mm/100mm; and/or

During the forging blanking process, the forging start temperature is ≥ 1100°C, and the forging stop temperature is ≥ 1000°C; and/or

During the forging billet opening process, the temperature of the surface of the electroslag ingot is made to be greater than or equal to 1000° C. by returning to the furnace and heating.

Preferably, in the step S2, during the forging billet opening process, the furnace heating temperature is 1220-1250° C., and the holding time is 40-60 minutes.

Preferably, in the step S3, during the extrusion tube making process, the extrusion temperature is 1150-1200°C.

Preferably, in the step S4, in the solution heat treatment, the solution temperature is 1080-1150° C., and the treatment time is 20-40 minutes.

Preferably, in the step S5:

In the cold rolling process, degreasing, solution annealing heat treatment and straightening are performed after each pass of cold rolling; and/or

The room temperature tensile strength of the super duplex stainless steel seamless pipe with PREN ≥ 42 is ≥ 800 MPa, the yield strength is ≥ 650 MPa, and the elongation is ≥ 30%.

The principle of composition design of the super duplex stainless steel with PREN≥42 of the present invention is as follows:

C: A strong austenite forming element, which can stabilize the austenite structure. Its increase can improve the mechanical properties of the steel, but when the content is too high, it will combine with the Cr element in the steel to form M23C6 carbides, resulting in The surrounding matrix is poor in chromium, resulting in reduced intergranular corrosion resistance. In the present invention, the carbon content is limited within the range of 0.022 to 0.030 wt%.

Si: ferrite forming element, on the one hand, it is a deoxidizer in the smelting process, on the other hand, it can be used as an element to adjust the content of ferrite phase. Excessive silicon content will promote the precipitation of intermetallic compounds in duplex stainless steel, resulting in reduced performance. In the present invention, the silicon content is limited within the range of 0.10-0.80wt%.

Mn: an element that forms and stabilizes austenite, and is also a deoxidizer in the smelting process. In addition, it has a relatively strong affinity with nitrogen, and its addition will significantly increase the nitrogen solubility of steel. However, excessive manganese will reduce the acid corrosion resistance of duplex stainless steel, resulting in accelerated corrosion. In the present invention, the manganese content is limited within the range of 0.10-1.20 wt%.

Cr: Ferrite phase forming element is also the most important element for duplex stainless steel to obtain corrosion resistance, which can significantly improve the pitting corrosion resistance and intergranular corrosion resistance of steel. It has a relatively strong affinity with nitrogen, and is also an important element for improving the nitrogen solubility of duplex stainless steel. Therefore, its addition can adjust the ferrite content of duplex stainless steel and improve the corrosion resistance of steel. However, it is also a key element for the formation of Sigma phase and intermetallic compounds in steel, so the content of chromium in the present invention is limited within the range of 25.70-26.00wt%.

Ni: Austenite forming and stabilizing element, improving the acid corrosion resistance of stainless steel. However, since its content determines the cost and price of the steel, its content needs to be controlled. In the present invention, the nickel content is limited within the range of 6.00-8.00%.

Mo: Ferrite forming element, together with nitrogen, can significantly improve the corrosion resistance of steel and promote the corrosion resistance of chromium in steel. However, molybdenum is also a key element in the formation of σ phase and intermetallic compounds in steel, and is expensive, too high will increase the cost of the alloy. The content of molybdenum in the present invention is limited in the range of 3.66-3.75wt%.

B: As a high-temperature grain boundary strengthening element, it can improve the thermoplasticity of steel at high temperature. However, if it is too much, low-melting-point phases are likely to be formed on the grain boundaries in duplex stainless steel, so that high-temperature hot workability deteriorates. In the present invention, the boron content is limited in the range of 0.002-0.005wt%.

N: It is one of the important elements of duplex stainless steel. It is a strong austenite-forming element like carbon and can replace the austenitization of nickel with manganese; it cooperates with molybdenum to significantly improve duplex Stainless steel pitting corrosion resistance and crevice corrosion resistance in chloride ion environment. It can also increase the strength of duplex stainless steels without reducing toughness. However, when the nitrogen content is too high, it will be precipitated from the molten steel in the form of nitrogen pores during smelting, causing the product to be scrapped, and it will also increase the deformation resistance during hot working, making hot working difficult. In the present invention, the nitrogen content is limited within the range of 0.265-0.295wt%.

P, S: P, S are harmful elements of the alloy of the present invention, too high content will deteriorate the hot workability of the alloy, and easily lead to microsegregation, the lower the content, the better, comprehensively considering the manufacturing cost of the alloy, the It is controlled within the ranges of P≤0.022wt%, S≤0.003wt%.

The beneficial effects of the preparation method of the super duplex stainless steel with PREN≥42 and the seamless pipe provided by the present invention:

The preparation method of the super duplex stainless steel with PREN≥42 and the seamless pipe provided by the present invention optimizes the alloy composition from the aspects of harmful phase suppression and strength improvement, and adopts the characteristics of the electroslag remelting process so that nitrogen does not appear in the electroslag ingot Holes ensure the smooth progress of the forging process, effectively reduce the amount of surface grinding of the tube blank, improve the yield of the final product, and prepare a super duplex stainless steel seamless tube with excellent mechanical properties and PREN ≥ 42, which meets the requirements of dangerous goods transportation and Processing, offshore oil and gas drilling and other special industry needs.

Detailed ways

In order to better understand the above-mentioned technical solution of the present invention, the technical solution of the present invention will be further described below in conjunction with examples.

The super duplex stainless steel with PREN≥42 provided by the present invention comprises the following components by weight percentage: C: 0.022-0.030%, Si: 0.10-0.80%, Mn: 0.10-1.20%, P≤0.022%, S≤ 0.003%, Al≤0.030%, Cu≤0.50%, N: 0.265～0.295%, Cr: 25.7～26.0%, Ni: 6.0～8.0%, Mo: 3.66～3.75%, B: 0.002～0.005%, balance For Ni and unavoidable impurities.

The pitting resistance index PREN of the above-mentioned PREN≥42 super duplex stainless steel satisfies:

PREN=Cr+3.3×Mo+16×N≥42%; and/or

The critical temperature for the precipitation of the harmful phase σ phase of the super duplex stainless steel with PREN ≥ 42 satisfies:

T _σ =1000×(4.17-0.338×Cr+5.16×Mo) ^(1/11.2) -273≤1000°C; and/or

The critical temperature for the precipitation of the harmful phase Cr2N phase of the super duplex stainless steel with PREN ≥ 42 satisfies:

T _Cr2N = 1000×(-61.1+40.4×C+1.97×Cr+2.49×Mo+59.6×N) ^(1/9.6) -273≤1080°C.

Based on the above-mentioned super duplex stainless steel of PREN ≥ 42, a super duplex stainless steel seamless pipe of PREN ≥ 42 can be made, with room temperature tensile strength ≥ 800 MPa, yield strength ≥ 650 MPa, and elongation ≥ 30%.

The above-mentioned process flow of the preparation method of the super duplex stainless steel seamless pipe with PREN≥42 is: electric furnace smelting→electroslag remelting→forging billet cutting→extrusion preparation pipe→solution heat treatment→cold rolling, specifically including the following steps:

S1, smelting, according to the above-mentioned super duplex stainless steel composition ratio raw material of PREN ≥ 42, the raw material is smelted in an electric furnace and electroslag remelted to obtain an electroslag ingot;

The specific process is as follows: firstly, according to the ratio of raw materials of super duplex stainless steel with PREN≥42, the raw materials are low-phosphorus, low-copper scrap steel, etc.; use ≥6 tons of electric furnace melting to smelt the raw materials with good ratio into electrode rods , in which nitrogen stirring is used during the electric furnace smelting process, and argon gas protection pouring is used when the molten steel is tapped. The flow rate of argon gas is controlled at 2-5Nm ³ /h, and the pouring temperature is 1600-1650°C; followed by electroslag remelting to obtain electroslag Ingot, through the electroslag remelting process with a relatively fast cooling rate during solidification, on the one hand, the purity of the steel is improved, and on the other hand, the formation of nitrogen pores in the electroslag ingot is reduced. The electroslag used in the electroslag remelting process The composition of the slag system is as follows: CaF ₂ : Al ₂ O ₃ : CaO: MgO=65～75:15～22:3～7:3～7, and the electroslag steady state melting rate is 6.0～7.0kg/min.

S2, forging and blanking, heating the electroslag ingot, and then forging and blanking to obtain a tube blank;

The specific process is: heating the electroslag ingot, excessive ferrite will appear if the heating temperature is too high or the holding time is too long, resulting in the loss of the advantages of super duplex stainless steel in steel properties, and the occurrence of high temperature δ phase, so the heating temperature is controlled at 1220-1250°C, as far as possible to the upper limit, preferably 1250°C, the surface temperature of the electroslag ingot should be uniform before forging, so the holding time follows 110-130min/100mm (thickness of the electroslag ingot ), that is, the holding time is (110～130min)×thickness of electroslag ingot mm/100mm; followed by forging and blanking,

Because the as-cast thermoplasticity of the steel is poor, the first fire forging uses a light hammer to control the deformation ≤ 5%, with the purpose of breaking the as-cast structure, and the subsequent fires can appropriately increase the deformation. During the forging process, it is necessary to Pay attention to uniform deformation to prevent surface cracks. During the forging process, the surface temperature of the electroslag ingot should be ≥ the critical temperature for the precipitation of the harmful phase σ phase T _σ (T _σ ＝1000×(4.17-0.338×Cr+5.16×Mo) ^{(1/ 11.2)} -273≤1000℃), that is, the surface temperature of the electroslag ingot should be ≥1000℃ during the forging process. The heating temperature of returning to the furnace is 1220-1250 ℃, and the holding time is 40-60 minutes. Clean up surface defects during forging and after forging to prevent tip cracks from developing along the grain, especially some slender cracks that are consistent with the striking direction (perpendicular to the deformation direction) ) Surface defects should be cleaned immediately after forging, and polished immediately or directly after carbon planing. Among them, in the process of forging billet opening, the forging start temperature is ≥1100°C, the forging stop temperature is ≥1000°C,

S3, extruding the pipe, processing the pipe blank through extrusion, and obtaining a blank pipe after water cooling;

The specific process is as follows: the tube blank obtained in the forging process is cut into a steel bar with a conventional size of Φ236±5mm×450-800m, and then the steel bar is extruded, and the extrusion temperature is controlled at 1150-1200°C. Water cooling after pressing to obtain a waste tube of Φ114±5mm×12±0.5mm;

S4, solution heat treatment, after performing solution heat treatment on the waste tube, water cooling;

The specific process is: carry out solid solution heat treatment to the waste pipe, and prevent the precipitation of the harmful phase Cr2N phase during this process, so the solution heat treatment temperature should be ≥ the critical temperature for the precipitation of the harmful phase Cr2N phase T _Cr2N (T _Cr2N = 1000 × (-61.1+ 40.4×C+1.97×Cr+2.49×Mo+59.6×N) ^(1/9.6) -273≤1080°C), so the solution heat treatment is controlled at 1080-1150°C, the treatment time is 20-40min, and then water-cooled.

S5, cold rolling, cutting the raw pipe, pickling, and then performing multi-pass cold rolling to obtain a super duplex stainless steel seamless pipe with PREN≥42.

The specific process is as follows: cut the waste pipe, pickle it, and then perform multi-pass cold rolling according to the size of the waste pipe and the final product size to obtain a boron-containing super duplex stainless steel seamless pipe, such as 4 to 5 times of cold rolling; After each pass of cold rolling, degreasing treatment, solution annealing heat treatment and straightening are required. During the solution annealing heat treatment, the treatment temperature is 1080-1150°C, and the treatment time is 20-40 minutes.

According to the performance test of the finished product, the room temperature tensile strength of the super duplex stainless steel seamless pipe with PREN ≥ 42 is ≥ 800 MPa, the yield strength is ≥ 650 MPa, and the elongation is ≥ 30%.

The super duplex stainless steel with PREN≥42, the seamless pipe and the preparation method of the present invention will be further introduced in combination with specific examples below.

Example 1

1) Electric Furnace Melting

Using a 40-ton electric furnace for smelting, according to the composition and raw materials of super duplex stainless steel with PREN≥42, the electrode rod with the following composition (weight percentage) is smelted:

C: 0.025%, Si: 0.50%, Mn: 0.60%, P: 0.018%, S: 0.003%, Al: 0.012%, Cu: 0.30%, N: 0.28%, Cr: 25.85%, Ni: 7.0%, Mo: 3.705%, B: 0.003%, and the rest are nickel and unavoidable impurities.

The principle of raw material selection is: low-phosphorus, low-copper clean scrap steel, etc. as raw materials; electric furnace smelting uses argon protection pouring, and the pouring temperature is 1630°C. Pouring into a Φ422mm electrode rod.

2) Electroslag remelting

The electroslag system used is CaF ₂ :Al ₂ O ₃ :CaO:MgO=70:16:7:7, the electroslag steady-state melting rate is controlled at 6.0-7.0kg/min, and the capping time is 40 minutes.

3) Forging blank

Selection of heating temperature and holding time: the heating temperature is 1240°C; the temperature of the electroslag ingot for forging should be uniform. The holding time follows 120min/100mm (the thickness of the electroslag ingot), that is, the holding time is 120min×the thickness of the electroslag ingot mm/100mm;

Forging process: start forging temperature: 1110°C, stop forging temperature: 1000°C. During the forging billet opening process, the heating temperature of the furnace (returning chamber furnace) is 1220°C and the temperature is kept for 60 minutes.

Clean up surface defects during and after forging to prevent tip cracks from developing and cracking along the grain, especially some surface defects that are consistent with the striking direction (slender cracks perpendicular to the deformation direction) should be immediately stopped forging and cleaned, and polished or directly after carbon planing. polished.

4) extrusion tube

Preparation:

Cut the billet after hot forging into a steel bar with a conventional size of Φ236mm×750mm, and carry out surface coloring inspection to show the forging cracks on the surface of the steel bar; then use the surface grinding method to remove the fine cracks on the surface of the steel bar, otherwise It will affect the smooth progress and quality of pipe threading;

Extruded tube:

The above-mentioned steel rods were subjected to extrusion processing at an extrusion temperature of 1180° C., and the finally obtained blank pipe had a size of Φ114×12 mm.

3) Solution heat treatment

Solid solution heat treatment for waste tube: 1080℃×30min, water cooling.

4) cold rolling

Carry out pipe cutting and pickling for the blank pipe; then carry out multi-pass cold rolling according to the size of the blank pipe and the final product size, and perform degreasing, solution annealing heat treatment (1080°C×40min) and straightening after each pass of cold rolling; The final size of the finished product is Φ38×4mm.

The performance test and tissue test of the super duplex stainless steel seamless pipe with PREN ≥ 42 are carried out, and the results are shown in Table 1 and Table 2.

Example 2

1) Electric Furnace Melting

Using a 40-ton electric furnace for smelting, according to the composition and raw materials of super duplex stainless steel with PREN≥42, the electrode rod with the following composition (weight percentage) is smelted:

C: 0.030%, Si: 0.80%, Mn: 1.20%, P: 0.016%, S: 0.003%, Al: 0.012%, Cu: 0.50%, N: 0.295%, Cr: 26.0%, Ni: 8.0%, Mo: 3.75%, B: 0.005%, and the rest are nickel and unavoidable impurities.

The principle of raw material selection is: low-phosphorus, low-copper clean scrap steel, etc. as raw materials; electric furnace smelting uses argon protection pouring, and the pouring temperature is 1610°C. Pouring into a Φ422mm electrode rod.

2) Electroslag remelting

The electroslag system used is CaF ₂ :Al ₂ O ₃ :CaO:MgO=73:17:5:5, the electroslag steady-state voltage is 58-62V, the current is 10000-11500A, and the electroslag steady-state melting rate is controlled at 6.0～7.0kg/min, capping time is 43 minutes.

3) Forging blank

Selection of heating temperature and holding time: the heating temperature is 1230°C; the temperature of the electroslag ingot for forging should be uniform. The holding time follows 120min/100mm (the thickness of the electroslag ingot), that is, the holding time is 120min×the thickness of the electroslag ingot mm/100mm;

Forging process: start forging temperature: 1130°C, stop forging temperature: 1040°C. During the forging billet opening process, the heating temperature of the furnace (returning chamber furnace) is 1240°C and the temperature is kept for 60 minutes.

Clean up surface defects during and after forging to prevent tip cracks from developing and cracking along the grain, especially some surface defects that are consistent with the striking direction (slender cracks perpendicular to the deformation direction) should be immediately stopped forging and cleaned, and polished or directly after carbon planing. polished.

4) extrusion tube

Preparation:

Cut the hot-forged billet car into a steel bar with a conventional size of Φ236mm×800mm, and carry out surface coloring flaw detection to show forging cracks on the surface of the steel bar; then use surface grinding to remove the fine cracks on the surface of the steel bar, otherwise It will affect the smooth progress and quality of pipe threading;

Extruded tube:

The above-mentioned steel rods were subjected to extrusion processing at an extrusion temperature of 1180° C., and the finally obtained blank pipe had a size of Φ114×12 mm.

3) Solution heat treatment

Solid solution heat treatment for waste tube: 1080℃×30min, water cooling.

4) cold rolling

Carry out cutting and pickling of the blank pipe; then carry out multi-pass cold rolling according to the size of the blank pipe and the final product size, and perform degreasing, solution annealing heat treatment (1150°C×20min) and straightening after each pass of cold rolling; The final size of the finished product is Φ57×5.7mm.

The performance test and tissue test of the super duplex stainless steel seamless pipe with PREN ≥ 42 are carried out, and the results are shown in Table 1 and Table 2.

Example 3

1) Electric Furnace Melting

Using a 40-ton electric furnace for smelting, according to the composition and raw materials of super duplex stainless steel with PREN≥42, the electrode rod with the following composition (weight percentage) is smelted:

C: 0.022%, Si: 0.10%, Mn: 0.10%, P: 0.020%, S: 0.002%, Al: 0.013%, Cu: 0.10%, N: 0.265%, Cr: 25.7%, Ni: 6.0%, Mo: 3.66%, B: 0.002%, and the rest are nickel and unavoidable impurities.

The principle of raw material selection is: low-phosphorus, low-copper clean scrap steel, etc. as raw materials; electric furnace smelting uses argon protection pouring, and the pouring temperature is 1630°C. Pouring into a Φ422mm electrode rod.

2) Electroslag remelting

The electroslag system used is CaF ₂ :Al ₂ O ₃ :CaO:MgO=70:18:6:6, the electroslag steady-state voltage is 58-62V, the current is 10000-11500A, and the electroslag steady-state melting rate is controlled at 6.0～7.0kg/min, capping time is 42 minutes.

3) Forging blank

Selection of heating temperature and holding time: the heating temperature is 1240°C; the temperature of the electroslag ingot for forging should be uniform. The holding time follows 120min/100mm (the thickness of the electroslag ingot), that is, the holding time is 120min×the thickness of the electroslag ingot mm/100mm;

Forging process: start forging temperature: 1130°C, stop forging temperature: 1020°C. During the forging billet opening process, the heating temperature of the furnace (returning chamber furnace) is 1220°C and the temperature is kept for 60 minutes.

Clean up surface defects during and after forging to prevent tip cracks from developing and cracking along the grain, especially some surface defects that are consistent with the striking direction (slender cracks perpendicular to the deformation direction) should be immediately stopped forging and cleaned, and polished or directly after carbon planing. polished.

4) extrusion tube

Preparation:

Cut the billet after hot forging into a steel bar with a conventional size of Φ236mm×700mm, and carry out surface coloring flaw detection to show the forging cracks on the surface of the steel bar; then use the surface grinding method to remove the fine cracks on the surface of the steel bar, otherwise It will affect the smooth progress and quality of pipe threading;

Extruded tube:

The above-mentioned steel rods were subjected to extrusion processing at an extrusion temperature of 1180° C., and the finally obtained blank pipe had a size of Φ114×12 mm.

3) Solution heat treatment

Solid solution heat treatment for waste tube: 1080℃×30min, water cooling.

4) cold rolling

Carry out pipe cutting and pickling for the blank pipe; then carry out multi-pass cold rolling according to the size of the blank pipe and the final product size, and perform degreasing, solution annealing heat treatment (1100°C×30min) and straightening after each pass of cold rolling; The final size of the finished product is Φ38×4mm.

The performance test and tissue test of the super duplex stainless steel seamless pipe with PREN ≥ 42 are carried out, and the results are shown in Table 1 and Table 2.

Table 1 Mechanical properties of super duplex stainless steel seamless pipes with PREN≥42

Table 2 Non-metallic inclusion levels of super duplex stainless steel seamless pipes with PREN≥42

Combining with Table 1, it can be seen that the room temperature tensile strength of the super duplex stainless steel seamless pipe with PREN≥42 of the present invention is 800MPa, yield strength≥650MPa, elongation≥30%, pitting resistance index PREN≥42, and harmful phase σ phase precipitation critical The temperature satisfies: T _σ ≤ 1000°C, the critical temperature for the precipitation of harmful phase Cr2N satisfies: T _Cr2N ≤ 1080°C, and the critical temperature for the precipitation of harmful phase M23C6 satisfies: T _M23C6 ≥ 880°C. It can be seen from Table 2 that the super duplex stainless steel seamless pipe with PREN≥42 of the present invention has less non-metallic inclusions.

Those of ordinary skill in the art should recognize that the above embodiments are only used to illustrate the present invention, rather than as a limitation to the present invention, as long as within the scope of the spirit of the present invention, the above-described embodiments Changes and modifications will fall within the scope of the claims of the present invention.

Claims (10)

1. A super duplex stainless steel with PREN≥42, characterized in that it comprises the following components by weight percentage: C: 0.022～0.030%, Si: 0.10～0.80%, Mn: 0.10～1.20%, P≤0.022% , S≤0.003%, Al≤0.030%, Cu≤0.50%, N: 0.265～0.295%, Cr: 25.7～26.0%, Ni: 6.0～8.0%, Mo: 3.66～3.75%, B: 0.002～0.005% , the balance being Ni and unavoidable impurities. 2. The super duplex stainless steel of PREN≥42 according to claim 1, characterized in that, The pitting resistance index PREN of the super duplex stainless steel with PREN≥42 satisfies: PREN=Cr+3.3×Mo+16×N≥42%; and/or The critical temperature for the precipitation of the harmful phase σ phase of the super duplex stainless steel with PREN≥42 satisfies: T _σ =1000×(4.17-0.338×Cr+5.16×Mo) ^(1/11.2) -273≤1000°C; and/or The critical temperature for the precipitation of the harmful phase Cr2N phase of the super duplex stainless steel with PREN ≥ 42 satisfies: T _Cr2N = 1000×(-61.1+40.4×C+1.97×Cr+2.49×Mo+59.6×N) ^(1/9.6) -273≤1080°C. 3. A super duplex stainless steel seamless pipe of PREN ≥ 42 prepared based on the super duplex stainless steel of PREN ≥ 42 according to claim 1 or 2, characterized in that the super duplex stainless steel of PREN ≥ 42 has no The room temperature tensile strength of the seam tube is ≥800MPa, the yield strength is ≥650MPa, and the elongation is ≥30%. 4. A method for preparing a super duplex stainless steel seamless pipe with PREN≥42, comprising the following steps: S1, smelting, according to the composition ratio raw material of the super duplex stainless steel with PREN≥42 according to claim 1, the raw material is smelted in an electric furnace and electroslag remelted to obtain an electroslag ingot; S2, forging and blanking, heating the electroslag ingot, and then forging and blanking to obtain a tube blank; S3, extruding the pipe, processing the pipe blank through extrusion, and obtaining a blank pipe after water cooling; S4, solution heat treatment, after performing solution heat treatment on the waste tube, water cooling; S5, cold rolling, cutting the raw pipe, pickling, and then performing multi-pass cold rolling to obtain a super duplex stainless steel seamless pipe with PREN≥42. 5. The preparation method of the super duplex stainless steel seamless pipe with PREN≥42 according to claim 4, characterized in that, in the step S1: During the smelting process of the electric furnace, nitrogen is used for stirring, and argon is used for protective pouring when the molten steel is tapped, the flow rate of the argon is 2-5Nm ³ /h, and the casting temperature is 1600-1650°C; and/or In the electroslag remelting process, the components of the electroslag system used are as follows: CaF ₂ : Al ₂ O ₃ : CaO: MgO=65～75:15～22:3～7:3～7; and/or During the electroslag remelting process, the electroslag steady-state melting rate is 6.0-7.0 kg/min. 6. The preparation method of the super duplex stainless steel seamless pipe with PREN≥42 according to claim 5, characterized in that, in the step S2: During the heat treatment process, the heating temperature is 1220-1250°C, and the holding time is (110-130min)×electroslag ingot thickness mm/100mm; and/or During the forging blanking process, the forging start temperature is ≥ 1100°C, and the forging stop temperature is ≥ 1000°C; and/or During the forging billet opening process, the temperature of the surface of the electroslag ingot is made to be greater than or equal to 1000° C. by returning to the furnace and heating. 7. The preparation method of super duplex stainless steel seamless pipe with PREN≥42 according to claim 6, characterized in that, in the step S2, during the forging billet opening process, the furnace heating temperature is 1220~ 1250°C, the holding time is 40-60 minutes. 8. The preparation method of super duplex stainless steel seamless pipe with PREN≥42 according to claim 4, characterized in that, in the step S3, during the extrusion pipe making process, the extrusion temperature is 1150-1200 ℃. 9. The method for preparing a super duplex stainless steel seamless pipe with PREN≥42 according to claim 4, characterized in that, in the step S4, in the solution heat treatment, the solution temperature is 1080-1150°C, The processing time is 20-40 minutes. 10. The preparation method of the super duplex stainless steel seamless pipe with PREN≥42 according to claim 4, characterized in that, in the step S5: In the cold rolling process, degreasing, solution annealing heat treatment and straightening are performed after each pass of cold rolling; and/or The room temperature tensile strength of the super duplex stainless steel seamless pipe with PREN ≥ 42 is ≥ 800 MPa, the yield strength is ≥ 650 MPa, and the elongation is ≥ 30%.