Production method of austenitic stainless steel composite plate

Abstract

The invention relates to a production method of an austenitic stainless steel composite board, a base material is carbon steel SA-533B Cl. 1, a covering material is austenitic stainless steel SA-240 304L, the thickness of the produced composite board is 40-70mm, and a process route is adopted as follows: assembling, composite blank heating, controlled rolling, quenching and tempering. The composite board produced through the method is good in shape, the binding rate is 100%, the delivery state and die welding state performance is good and uniform, the shear strength is larger than or equal to 350 MPa, the yield strength is larger than or equal to 345 MPa, the tensile strength is 550-690 MPa, the elongation A is larger than or equal to 18%, the 150-DEG C high-temperature tensile yield strength is larger than or equal to 315 MPa, the tensile strength is larger than or equal to 500 MPa, the 10-DEG C impact absorption energy is larger than or equal to 120 J, the side expansion value is larger than or equal to 1.0 mm, and the non-plastic transition (NDT) temperature is smaller than or equal to-21 DEG C; the coating austenitic stainless steel has good intergranular corrosion resistance and completely meets the technical requirements of the austenitic stainless steel composite plate for the nuclear power safety injection tank.

Description

Technical Field

[0001] This invention belongs to the field of composite plate manufacturing technology, and relates to a production method of austenitic stainless steel composite plate, particularly suitable for stainless steel composite plates used in nuclear power plant safety injection boxes. Background Technology

[0002] Nuclear power, as an important low-carbon energy source, has long played a crucial role in the global energy structure. Against the backdrop of the "dual-carbon" goal and global energy transition, the development prospects of nuclear power are very broad. Nuclear safety has always been a significant factor restricting the development of nuclear power, and the nuclear safety injection tank (safety water injection tank) is the core equipment of the safety injection system in pressurized water reactor nuclear power plants. In the event of a loss-of-coolant accident, it can quickly inject boron-containing cooling water into the reactor core to prevent core meltdown. Therefore, strict requirements are placed on the core structural materials used in the manufacture of the nuclear safety injection tank. Currently, austenitic stainless steel composite plates are mainly used, balancing structural strength and corrosion resistance, and at a lower cost than solid stainless steel plates. The base layer is usually made of high-strength low-alloy steel such as SA-533B Cl.1, providing the main structural strength and toughness; the cladding is usually made of stainless steel such as SA-240 304L, providing excellent resistance to boron water corrosion.

[0003] The main technical requirements for austenitic stainless steel composite plates widely used in nuclear power plant safety injection boxes are as follows: ① The composite steel plates should be delivered in a quenched and tempered condition; ② Room temperature tensile properties (Rp0.2 ≥ 345 MPa, 550 MPa ≤ Rm ≤ 690 MPa, elongation A ≥ 18%) in both the delivered and mold-welded states; ③ High temperature tensile properties (Rp0.2 ≥ 315 MPa, Rm ≥ 500 MPa) in both the delivered and mold-welded states; ④ Impact properties (10℃ impact absorption energy ≥ 68 J, lateral expansion ≥ 0.90 mm) in both the delivered and mold-welded states; ⑤ Non-plastic transformation (NDT) temperature ≤ -21℃; ⑥ Shear strength ≥ 310 MPa; ⑦ The clad austenitic stainless steel should conform to ASTM A262. Method E is used to conduct intergranular corrosion tests, and no cracks are caused by intergranular corrosion; ⑧ The heat treatment process for mold welding is held at a temperature of 595~620℃ for at least 24 hours. When the sample enters the furnace, the furnace temperature should not be higher than 425℃, and the heating and cooling rates above 425℃ should not exceed 55℃ / h.

[0004] Previously, austenitic stainless steel composite plates for nuclear power plant safety injection boxes were mainly produced using explosive bonding. However, due to the low production efficiency, high cost, significant environmental impact, and poor surface quality and shape of explosive bonding, rolling bonding is gradually being adopted. Austenitic stainless steel composite plates for nuclear power plant safety injection boxes must undergo quenching and tempering treatment. Because of the significant difference in the coefficients of thermal expansion and thermal conductivity between carbon steel and stainless steel, quenching deformation is large, which not only easily damages the quenching equipment but also affects the uniformity and consistency of the product. New technologies are urgently needed to solve this technical problem. Summary of the Invention

[0005] The purpose of this invention is to provide a method for producing austenitic stainless steel composite plates, particularly suitable for stainless steel composite plates used in nuclear power plant safety injection tanks, to obtain austenitic stainless steel composite plates for nuclear power plant safety injection tanks with good plate shape and whose shear strength, mechanical properties of the substrate, and corrosion resistance of the cladding all meet the technical requirements.

[0006] The technical solution of the present invention: A method for producing an austenitic stainless steel composite plate, characterized in that: the produced composite plate has a thickness of 40-70mm, the base material is carbon steel SA-533B Cl.1, and its chemical composition by mass percentage is C≤0.25%, Si:0.15%-0.40%, Mn:1.15%-1.50%, P≤0.012%, S≤0.015%, Al:0.020%-0.040%, Nb≤0.02%, V≤0.05%, Ti≤0.03%, Cr≤0.25%, Mo:0.45%-0.60%, Ni:0.40%-0.70%, Cu≤0.10%, Co≤0.25%, with the balance being Fe and unavoidable impurities; the cladding material is austenitic stainless steel SA-240. 304L, its chemical composition by mass percentage is: C≤0.030%, Si≤0.75%, Mn≤2.00%, P≤0.035%, S≤0.010%, Cr: 18.00%~20.00%, Ni: 8.00%~12.00%, Co≤0.05%, N≤0.10%, with the balance being Fe and unavoidable impurities; the process steps include: (1) Assembly: The symmetrical assembly is adopted. The surfaces where the substrate and the cover are joined are cleaned and a release agent is applied to both the cover and the contact surface of the cover. The substrate → cover → cover → substrate are stacked from bottom to top. Then the composite blank is welded and sealed around and vacuumed. The vacuum degree is ≤0.01Pa and the vacuuming time is ≥1 hour. The gas inside the composite blank is completely removed.

[0007] (2) Heating of composite billet: The process of limited temperature heating + sufficient heat preservation is adopted to limit the furnace temperature to ≤1220℃ and control the tapping temperature at 1200~1220℃. The heating time in the furnace is calculated according to the thickness of the composite billet (mm) at 1.5~1.7min / mm to ensure uniform heating of the composite billet.

[0008] (3) Controlled rolling: The first stage rolling temperature is ≥1050℃ and the final rolling temperature is ≥980℃. The first pass reduction in the first stage is ≤30mm and the last pass reduction rate is ≤10%. Other passes adopt a large reduction system with a pass reduction of ≥35mm or a pass reduction rate of ≥15%. The second stage rolling temperature is 870~950℃ and the final rolling temperature is 790~850℃. The second stage adopts a multi-pass small reduction system with a reduction rate of ≤10% per pass.

[0009] (4) Quenching and tempering treatment: ① Quenching: The composite plate is heated in a roller hearth furnace with the cladding layer on top and the base layer on the bottom. The upper furnace temperature is set at 860℃ and the lower furnace temperature at 920℃. The furnace time is controlled at [(1.4~1.6)×H1+(4.4~4.6)×H2]min / mm, where H1 and H2 are the base layer thickness (mm) and the cladding layer thickness (mm), respectively. The surface temperature of the composite plate after exiting the furnace is 860±10℃ and the lower surface temperature is 920±10℃. Then, controlled cooling is performed with a water flow rate of 1800~2300m³ / h in the high-pressure zone. 3 / h, roller speed 0.15~0.25m / s, water output / water output ratio 0.4~0.8, water flow rate in low pressure zone 3400~3800m³ / h 3 The ratio of water flow rate to water supply rate is 0.4–0.8, and the material is oscillating and cooled to room temperature; this allows the cladding and base layer of the composite panel to deform in tandem during the cooling process. ② Tempering: Tempering temperature 690±10℃, holding time is H×2.0~H×2.5min / mm; H is the thickness of the composite board in mm.

[0010] Furthermore, the characteristic of step (3) is to control the rolling: in the first stage, the first pass reduction is controlled to be ≤30mm, the last pass reduction rate is ≤10%, and the other passes reduction is ≥35mm or the pass reduction rate is ≥15%; in the second stage, a multi-pass small reduction system is adopted and the pass reduction rate is ≤10%.

[0011] Further, step (4) quenching and tempering treatment: by heating the composite plate by temperature difference between the top and bottom and cooling the composite plate by high temperature fast cooling + low temperature slow cooling + small water ratio, austenitic stainless steel composite plate for nuclear power safety injection boxes with good plate shape, uniform performance, and shear strength, mechanical properties of the base material and corrosion resistance of the cladding material all meet the technical requirements.

[0012] The main innovations of this invention are: symmetrical billet assembly, with stainless steel isolated from air in the middle of the composite billet, preventing oxidation and burn-off, reducing costs, and enabling one-time production of both upper and lower composite plates with high efficiency; the use of a temperature-limited heating + sufficient heat preservation process, by limiting furnace temperature and controlling heating time in the furnace, homogenizes the austenite in the carbon steel substrate and inhibits austenite grain growth, while ensuring sufficient solid solution of the cladding stainless steel; a two-stage controlled rolling process is employed, with the first stage using appropriate pass reduction to ensure complete composite of the base layer and cladding; the second stage controls the appropriate final rolling temperature and uses a small reduction to refine the carbon steel grains in the base layer while reducing strain-induced precipitation of the second phase in the cladding stainless steel, and reducing stress caused by inconsistent deformation resistance between the base layer and cladding; quenching employs differential heating and a combination of high-temperature rapid cooling + low-temperature slow cooling + low water ratio cooling, along with a suitable tempering process, to obtain a composite plate with good shape and uniform and consistent properties.

[0013] The beneficial effects of the present invention are as follows: the austenitic stainless steel composite plate for nuclear power plant safety injection boxes produced by the method of the present invention has good plate shape, high shear strength, and the mechanical properties of the base material and the corrosion resistance of the cladding material all meet the technical requirements for austenitic stainless steel composite plates for nuclear power plant safety injection boxes. Detailed Implementation

[0014] The present invention will be further described below with reference to the embodiments. Example 1

[0015] A method for producing an austenitic stainless steel composite plate for nuclear power plant safety injection boxes, wherein the base material is carbon steel SA-533BCl.1 and the cladding material is austenitic stainless steel SA-240 304L, and the thickness of the produced composite plate is (62+7) mm. The base material, carbon steel SA-533B Cl.1, has a chemical composition (by weight percentage) of C=0.12%, Si=0.21%, Mn=1.31%, P=0.008%, S=0.001%, Al=0.035%, Nb=0.016%, V=0.003%, Ti=0.008%, Cr=0.05%, Mo=0.51%, Ni=0.62%, Cu=0.04%, Co=0.006%, with the balance being Fe and unavoidable impurities. The cladding material, austenitic stainless steel SA-240 304L, has a chemical composition (by weight percentage) of C=0.011%, Si=0.39%, Mn=1.68%, P=0.02%, S=0.001%, Cr=18.44%, Ni=8.16%, Co=0.05%, N=0.055%, with the balance being Fe and unavoidable impurities. Key process steps include: (1) Assembly: Two carbon steel billets SA-533B Cl.1 and two stainless steel billets SA-240 304L are selected for symmetrical assembly. The dimensions of the carbon steel billet SA-533B Cl.1 are 222mm thick × 2140mm wide × 2920mm long, and the dimensions of the stainless steel billet SA-240 304L are 26mm thick × 1860mm wide × 2640mm long. The dimensions of the composite billet after assembly are 496mm thick × 2140mm wide × 2920mm long. Before assembly, the surfaces where the substrate and the cladding are joined, as well as the two surfaces of the cladding, must be cleaned of iron oxide scale, oil stains and other foreign matter. A release agent is evenly applied to the surfaces where the stainless steel is in contact with the stainless steel. Then, the substrate → cladding → cladding → substrate are stacked from bottom to top. The composite billet is then welded and sealed around its perimeter and vacuumed: vacuum degree 0.01Pa, vacuuming time 1 hour.

[0016] (2) Composite billet heating: The composite billet is heated in a walking beam furnace. The process of limited temperature heating + sufficient heat preservation is adopted to ensure uniform heating inside and outside the composite billet. The furnace temperature is limited to 1220℃, the actual tapping temperature is 1207℃, and the heating time in the furnace is 812min.

[0017] (3) Controlled rolling: The first stage rolling temperature is 1159℃, the final rolling temperature is 1030℃, the first pass reduction is 26mm, the second / third / fourth pass reductions are 41mm, 41mm and 40mm respectively, and the last pass reduction rate is 9.1%; the second stage rolling temperature is 882℃, the final rolling temperature is 823℃, and the pass reduction rate is within 10%.

[0018] (4) Quenching and tempering treatment: ① Quenching: The composite board, with the cladding layer on top and the base layer on the bottom, is heated in a roller hearth quenching furnace using a differential heating method. The furnace temperature is set at 860℃ for the upper part and 920℃ for the lower part. Actual temperatures measured after the composite board exiting the furnace were 867℃ for the upper surface and 915℃ for the lower surface, with a furnace time of 126 minutes. The composite board is then directly transferred to a roller quenching machine for quenching. Quenching cooling parameters are: high-pressure zone flow rate of 2070 m³ / h, roller speed of 0.2 m / s, and water ratio (lower water / upper water) of 0.5; low-pressure zone flow rate of 3630 m³ / h, water ratio (lower water / upper water) of 0.5; and oscillating cooling to room temperature. The board shape is good after exiting the quenching machine.

[0019] ② Tempering: The tempering furnace temperature is set at 690℃, the actual temperature of the composite board exiting the furnace is 687℃, and the holding time is 145min.

[0020] Table 1-1 Mechanical properties of the base layer and corrosion resistance of the coating of the composite board in Example 1 .

[0021] The (62+7) mm thick SA-533B Cl.1+SA-240 304L composite board produced in Example 1 has a 100% bonding rate, good board shape, and uniform performance. The mechanical properties of the base layer and the corrosion resistance of the coating in various parts of the composite board are shown in Table 1. The sample mold welding heat treatment process was as follows: the holding temperature was 610±10℃, the holding time was 24 hours, the sample entry and exit temperatures were ≤425℃, and the heating and cooling rates above 425℃ were ≤55℃ / h.

[0022] Table 1-2 Mechanical properties of the base layer and corrosion resistance of the coating of the composite board in Example 1 .

[0023] Table 1-3 Mechanical properties of the base layer and corrosion resistance of the coating of the composite board in Example 1 . Example 2

[0024] A method for producing an austenitic stainless steel composite plate for nuclear power plant safety injection boxes, wherein the base material is carbon steel SA-533BCl.1 and the cladding material is austenitic stainless steel SA-240 304L, and the thickness of the produced composite plate is (56+6) mm. The base material, carbon steel SA-533B Cl.1, has the following chemical composition by mass percentage: C=0.12%, Si=0.25%, Mn=1.34%, P=0.009%, S=0.0014%, Al=0.027%, Nb=0.015%, V=0.004%, Ti=0.006%, Cr=0.06%, Mo=0.51%, Ni=0.63%, Cu=0.03%, Co=0.0065%, with the balance being Fe and unavoidable impurities. The cladding material, austenitic stainless steel SA-240 304L, has the following chemical composition by mass percentage: C=0.021%, Si=0.41%, Mn=0.67%, P=0.019%, S=0.001%, Cr=18.27%, Ni=8.16%, Co=0.04%, N=0.070%, with the balance being Fe and unavoidable impurities. Key process steps include: (1) Assembly: Two carbon steel billets SA-533B Cl.1 and two stainless steel billets SA-240 304L are selected for symmetrical assembly. The dimensions of the carbon steel billet SA-533B Cl.1 are 219mm thick × 1990mm wide × 3035mm long, and the dimensions of the stainless steel billet SA-240 304L are 24mm thick × 1710mm wide × 2755mm long. The dimensions of the composite billet after assembly are 486mm thick × 1990mm wide × 3035mm long. Before assembly, the surfaces where the substrate and the cladding are joined, as well as the two surfaces of the cladding, must be cleaned of iron oxide scale, oil stains and other foreign matter. A release agent is evenly applied to the surfaces where the stainless steel is in contact with the stainless steel. Then, the substrate → cladding → cladding → substrate are stacked from bottom to top. The composite billet is then welded and sealed around its perimeter and vacuumed: vacuum degree 0.01Pa, vacuuming time 1 hour.

[0025] (2) Composite billet heating: The composite billet is heated in a walking beam furnace. The process of limited temperature heating + sufficient heat preservation is adopted to ensure uniform heating inside and outside the composite billet. The furnace temperature is limited to 1220℃, the actual tapping temperature is 1204℃, and the heating time in the furnace is 776min.

[0026] (3) Controlled rolling: The first stage rolling temperature is 1154℃, the final rolling temperature is 1035℃, the first pass reduction is 25mm, the second / third / fourth pass reductions are 40mm, 39mm and 39mm respectively, and the last pass reduction rate is 9.5%; the second stage rolling temperature is 885℃, the final rolling temperature is 828℃, and the pass reduction rate is within 10%.

[0027] (4) Quenching and tempering treatment: ① Quenching: The composite board, with the cladding layer on top and the base layer on the bottom, is heated in a roller hearth quenching furnace using a differential heating method. The furnace temperature is set at 860℃ for the upper part and 920℃ for the lower part. Actual temperatures measured after the composite board exiting the furnace were 868℃ for the upper surface and 912℃ for the lower surface, with a furnace time of 111 minutes. The composite board is then directly transferred to a roller quenching machine for quenching. Quenching cooling parameters are: high-pressure zone flow rate 1980 m³ / h, roller speed 0.2 m / s, water ratio (bottom water / top water) 0.5; low-pressure zone flow rate 3465 m³ / h, water ratio (bottom water / top water) 0.5; and oscillating cooling to room temperature. The board shape is good after exiting the quenching machine.

[0028] ② Tempering: The tempering furnace temperature is set at 690℃, the actual temperature of the composite board exiting the furnace is 685℃, and the holding time is 136 minutes.

[0029] The (56+6) mm thick SA-533B Cl.1+SA-240 304L composite board produced in Example 2 has a 100% bonding rate, good board shape, and uniform performance. The mechanical properties of the base layer and the corrosion resistance of the coating in various parts of the composite board are shown in Table 2. The sample mold welding heat treatment process was as follows: the holding temperature was 610±10℃, the holding time was 24 hours, the sample entry and exit temperatures were ≤425℃, and the heating and cooling rates above 425℃ were ≤55℃ / h.

[0030] Table 2-1 Mechanical properties of the base layer and corrosion resistance of the coating of the composite board in Example 2 .

[0031] Table 2-2 Mechanical properties of the base layer and corrosion resistance of the coating of the composite board in Example 2 .

[0032] Table 2-3 Mechanical properties of the base layer and corrosion resistance of the coating in Example 2 .

[0033] As can be seen from the results of Examples 1 and 2, the austenitic stainless steel composite plate for nuclear power safety injection tanks produced by the method of the present invention has a 100% bonding rate, good plate shape, high shear strength, and the mechanical properties of the substrate and the corrosion resistance of the cladding material meet the technical requirements for austenitic stainless steel composite plates for nuclear power safety injection tanks. In particular, the overall plate performance is uniform and has small fluctuations, which fully meets the requirements of the nuclear power industry for material uniformity and consistency.

Claims

1. A method for producing an austenitic stainless steel composite plate, characterized in that: The stainless steel composite plates produced have a thickness of 40-70mm. The base material is carbon steel SA-533B Cl.1, with the following chemical composition by mass percentage: C≤0.25%, Si: 0.15%-0.40%, Mn: 1.15%-1.50%, P≤0.012%, S≤0.015%, Al: 0.020%-0.040%, Nb≤0.02%, V≤0.05%, Ti≤0.03%, Cr≤0.25%, Mo: 0.45%-0.60%, Ni: 0.40%-0.70%, Cu≤0.10%, Co≤0.25%, with the balance being Fe and unavoidable impurities. The cladding material is austenitic stainless steel SA-240. 304L, its chemical composition by mass percentage is: C≤0.030%, Si≤0.75%, Mn≤2.00%, P≤0.035%, S≤0.010%, Cr: 18.00%~20.00%, Ni: 8.00%~12.00%, Co≤0.05%, N≤0.10%, with the balance being Fe and unavoidable impurities; the process steps include: (1) Assembly: The symmetrical assembly is adopted. The surfaces where the substrate and the cover are joined are cleaned and a release agent is applied to both the cover and the contact surface of the cover. The substrate → cover → cover → substrate are stacked from bottom to top. Then the composite blank is welded and sealed around and vacuumed. The vacuum degree is ≤0.01Pa and the vacuuming time is ≥1 hour. The gas inside the composite blank is completely removed. (2) Heating of composite billet: The process of limited heating + sufficient heat preservation is adopted to limit the furnace temperature to ≤1220℃ and control the tapping temperature at 1200~1220℃. The heating time in the furnace is calculated at 1.5~1.7min / mm based on the thickness of the composite billet in mm to ensure uniform heating of the composite billet; (3) Controlled rolling: The initial rolling temperature of the first stage is ≥1050℃, the final rolling temperature is ≥980℃, the reduction of the first pass in the first stage is ≤30mm, the reduction rate of the last pass is ≤10%, and other passes adopt a large reduction system with a reduction of ≥35mm or a reduction rate of ≥15%; The initial rolling temperature of the second stage is 870~950℃, the final rolling temperature is 790~850℃, and the second stage adopts a multi-pass small reduction system with a reduction rate of ≤10% per pass; (4) Quenching and tempering treatment: ① Quenching: The composite plate is heated in a roller hearth furnace with the cladding layer on top and the base layer on the bottom. The upper furnace temperature is set at 860℃ and the lower furnace temperature at 920℃. The furnace time is controlled at [(1.4~1.6)×H1+(4.4~4.6)×H2] min / mm, where H1 and H2 are the base layer thickness (mm) and the cladding layer thickness (mm), respectively. The surface temperature of the composite plate after exiting the furnace is 860±10℃ and the lower surface temperature is 920±10℃. Then, controlled cooling is performed with a water flow rate of 1800~2300m³ / h in the high-pressure zone. 3 / h, roller speed 0.15~0.25m / s, water output / water output ratio 0.4~0.8, water flow rate in low pressure zone 3400~3800m³ / h 3 The water flow rate is 0.4 to 0.8 per hour, and the water is oscillating and cooled to room temperature; this allows the cladding and base layer of the composite panel to deform in tandem during the cooling process. ② Tempering: Tempering temperature 690±10℃, holding time is H×2.0~H×2.5min / mm; H is the thickness of the composite board in mm.

2. The method for producing an austenitic stainless steel composite plate according to claim 1, characterized in that... Step (3) Control rolling: In the first stage, the first pass reduction is ≤30mm, the last pass reduction is ≤10%, and the other passes reduction is ≥35mm or the pass reduction is ≥15%; in the second stage, a multi-pass small reduction system is adopted and the pass reduction is ≤10%.

3. The method for producing an austenitic stainless steel composite plate according to claim 1, characterized in that... Step (4) Quenching and tempering treatment: By heating the composite plate with temperature difference between the top and bottom and cooling with high temperature fast cooling + low temperature slow cooling + small water ratio, austenitic stainless steel composite plate for nuclear power safety injection boxes with good plate shape, uniform performance, and shear strength, mechanical properties of the base material and corrosion resistance of the cladding material all meet the technical requirements.