Stainless clad steel plate and producing method thereof

Abstract

To provide a high strength stainless clad steel plate excellent in stress corrosion cracking resistance and low temperature toughness and a producing method thereof.SOLUTION: A stainless clad steel plate comprises a base material and a laminating material formed on the base material, wherein the laminating material has a specific composition, the base material has a specific composition, a yield strength of 620 MPa or more, a tensile strength of 700 MPa or more, and an absorbed energy of 47 J or more when a Charpy impact test is conducted at -40°C, and the clad steel sheet has a shear strength of SH: 0.87×((t+T)×YSC-T×YSB) / t or more, a yield strength of 620 MPa or more, and a tensile strength of 700 MPa or more.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a high-strength stainless clad steel plate suitable for use in cryogenic tanks, particularly to a high-strength stainless clad steel plate of 700 MPa class or higher used for large liquefied ammonia tanks and the like, and a method for producing the same. [Background technology]

[0002] The use of ammonia is expanding in response to carbon neutrality. Traditionally, ammonia was mainly used as a fertilizer raw material, but its use as a hydrogen carrier or directly as a fuel is on the rise. As the use of ammonia expands, the tanks used to store it are also becoming larger, with progress being made in the design and construction of large tanks up to around 100,000 tons, up from the conventional 10,000-20,000 ton class. In order to increase the size of the tanks, it is necessary to increase the thickness of the steel plates used or to increase the strength of the steel plates, and in particular, it is hoped that higher strength will be promoted in order to reduce the weight of the steel.

[0003] Ammonia liquefies when cooled to -35°C or below or under high pressure, and is usually stored in a liquefied state in tanks. However, liquefied ammonia is known to corrode steel and cause stress corrosion cracking, and the higher the strength of the steel, the greater the susceptibility to this stress corrosion cracking. This makes it difficult to increase the strength of the steel plates used for the aforementioned liquefied ammonia tanks, and 400 MPa-class steel plates (JIS G3126:2021 SLA325A, etc.) are mainly used.

[0004] Therefore, studies have been conducted on steel plates that are resistant to stress corrosion cracking caused by liquefied ammonia. For example, Patent Document 1 discloses a method for producing steel plates that have a strength of 400 MPa or more, low-temperature toughness at -60°C, and excellent toughness in the heat-affected zone of high-heat-input welds, by reducing the amount of C in the steel and optimally controlling the amounts of Ti and N. Patent Document 2 discloses a method for producing a steel plate having a strength of 530 MPa or more while realizing a low yield ratio by reducing the amount of C in the steel and applying accelerated cooling. Furthermore, Patent Document 3 discloses a method for producing a steel sheet having a strength of 570 MPa or more while suppressing an increase in hardness in the surface layer of the steel sheet by reducing the amount of C in the steel and applying accelerated cooling. In addition, in Patent Document 4, a decarburized layer is formed on the surface of a steel sheet, and the resulting strength is 590 MPa or more (60 kgf / mm 2 The present invention discloses a method for manufacturing a steel sheet that has a strength of 1000 MPa or more and also ensures excellent stress corrosion cracking resistance. Furthermore, Patent Document 5 discloses a method for manufacturing a steel sheet that ensures excellent stress corrosion cracking resistance by subjecting the surface of the steel sheet to a softening treatment to reduce the surface hardness to 190 or less in Vickers hardness. Patent Documents 6 and 7 disclose methods for manufacturing steel sheets that ensure stress corrosion cracking resistance by optimally controlling the ferrite structure fraction and crystal grain size of the steel sheets and controlling the yield strength to 440 MPa or less. Patent Document 8 discloses a method for manufacturing a steel plate that ensures stress corrosion cracking resistance by optimizing the ferrite structure fraction in the center of the steel plate thickness while suppressing the hardness of the surface layer of the steel plate to 210 or less. Patent Document 9 discloses a method for manufacturing a steel plate that ensures stress corrosion cracking resistance by optimizing the morphology of the surface layer of the steel plate and optimizing the ferrite structure fraction in the center of the steel plate thickness. Patent Document 10 discloses a method for manufacturing a steel plate suitable for a tank for transporting liquefied ammonia, in which the yield ratio of the steel plate is reduced by minimizing the structure of ferrite and the like at the quarter thickness position of the steel plate. Furthermore, Patent Document 11 discloses a method for producing a steel plate that ensures excellent stress corrosion cracking resistance by rapidly cooling the steel plate in two stages during quenching or direct quenching to generate a soft ferrite structure. Furthermore, Patent Document 12 discloses a method for manufacturing a clad steel plate that ensures excellent stress corrosion cracking resistance by joining a clad material having a low carbon and manganese content to the surface of the steel plate by cast cladding or overlay welding. In Patent Document 13, the yield strength of the weld heat affected zone is 440 MPa or less (45 kgf / mm 2 The present invention discloses a method for manufacturing a clad steel plate that ensures excellent stress corrosion cracking resistance by joining clad steel sheets (hereinafter referred to as "clad steel sheets") together.

[0005] On the other hand, it is known that stainless steel plates with a low carbon content do not suffer from stress corrosion cracking when exposed to liquefied ammonia, and because stainless steel plates themselves are expensive, clad steel plates are sometimes used in which inexpensive low-alloy steel plates are used as the base material and stainless steel plates are attached as clad materials. Patent Document 14 discloses a method for manufacturing clad steel plates in which duplex stainless steel plates used for storage tanks for chemicals and the like are used as clad materials. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 11-131178 [Patent Document 2] Japanese Patent Application Publication No. 10-195533 [Patent Document 3] Japanese Patent Application Laid-Open No. 2001-115233 [Patent Document 4] Japanese Patent Application Publication No. 61-279631 [Patent Document 5] Japanese Patent Application Publication No. 50-085516 [Patent Document 6] Patent No. 7323090 [Patent Document 7] Patent No. 7323091 [Patent Document 8] Patent No. 7323088 [Patent Document 9] International Publication No. 2021 / 106368 [Patent Document 10] Patent Publication No. 2021-88753 [Patent Document 11] Japanese Patent Publication No. 156228 / 1983 [Patent Document 12] Japanese Patent Application Publication No. 57-149425 [Patent Document 13] Japanese Patent Application Publication No. 50-085546 [Patent Document 14] Japanese Patent Publication No. 2023-82763 Summary of the Invention [Problem to be solved by the invention]

[0007] However, the techniques described in Patent Documents 1 to 4 are aimed at strengths up to 590 MPa, which is insufficient for manufacturing large tanks, which are in demand these days. Furthermore, Patent Document 5 does not take into consideration the low temperature toughness of the base material at all. The techniques described in Patent Documents 6 to 10 are based on the premise that the steel sheet contains a soft ferrite structure, and are therefore unable to produce the high-strength steel sheet for large tanks that is the subject of the present invention. The technique described in Patent Document 11 uses two-stage cooling, which requires special water cooling equipment. The technique described in Patent Document 12 requires cast cladding or overlay welding, which requires special equipment and has problems in productivity. The technology described in Patent Document 13 can suppress stress corrosion cracking in the weld heat affected zone. However, when rolling and heat treatment conditions are selected to increase the strength of the clad base material in order to manufacture a large tank, the hardness of the clad material before welding increases, and stress corrosion cracking performance cannot be suppressed outside the weld heat affected zone.

[0008] The technology described in Patent Document 14 can suppress stress corrosion cracking, but does not disclose a method for increasing the strength required for manufacturing large tanks, and does not provide a solution to the problems that arise when the tank is used as a low-temperature tank, such as improving the toughness of the base material or suppressing peeling due to shrinkage between the laminated stainless steel plate and the base material of low-alloy steel.

[0009] As described above, none of the methods proposed so far has disclosed a manufacturing method that can ensure excellent stress corrosion cracking resistance in high-strength steel plates exceeding 590 MPa, which are used for large tanks, without using special equipment. Furthermore, no method other than Patent Document 1 has been disclosed for ensuring the toughness at temperatures of −35° C. or below, which is necessary when storing liquefied ammonia. Furthermore, even in the case of preventing stress corrosion cracking by using a clad steel plate with a stainless steel clad material, no method for increasing strength for manufacturing large tanks has been disclosed, and no solution has been disclosed for improving the toughness of the base material or suppressing delamination caused by shrinkage between the stainless steel clad material and the low-alloy steel base material, which are problems when used as low-temperature tanks.

[0010] In view of the above-mentioned problems of the conventional technology, the present invention aims to provide a steel plate having a high strength exceeding 590 MPa for use in large tanks and having excellent stress corrosion cracking resistance and low temperature toughness; specifically, to provide a stainless clad steel plate having a yield strength of 620 MPa or more, a tensile strength of 700 MPa or more, and having excellent stress corrosion cracking resistance and low temperature toughness, and a method for manufacturing the same.

[0011] Here, the yield strength and tensile strength are the yield strength and tensile strength of the clad steel plate and the base material of the clad steel plate measured in accordance with JIS Z 2241:2022. In addition, excellent stress corrosion cracking resistance means that a 5mm thick x 15mm x 115mm test piece taken from the surface side of the clad material is ultrasonically degreased in acetone for 5 minutes, and then a stress of 80% of the yield strength of the clad steel plate is applied by four-point bending.The load is applied so that the two-point bending side with the shorter span of the four-point bending jig faces the clad material, and the test piece is placed in a test cell filled with a solution of 12.5g of ammonium carbamate and 1L of liquid ammonia.A potentiostat is then used to control the flow of +2.0V vs Pt to the test piece, and the test piece is immersed at room temperature (25°C) for 168 hours, after which no cracks are observed in the clad material. In addition, excellent low-temperature toughness refers to a base material having an absorbed energy of 47J or more when a Charpy impact test is conducted at -40°C in accordance with JIS Z 2242:2018. [Means for solving the problem]

[0012] As a result of intensive research to solve the above problems, the present inventors have discovered the following: First, it was found that in order to suppress stress corrosion cracking due to contact with liquefied ammonia, it is necessary to use stainless steel sheets with a C content of 0.030% or less as cladding materials.

[0013] Next, when a low-temperature tank is manufactured with a clad steel plate made of low-alloy steel as the base material and a stainless steel plate as the clad material on the inside, the clad material tends to shrink significantly during operation due to differences in thermal expansion coefficients, which can cause tensile residual stress equivalent to the yield stress on the clad material side, potentially leading to separation at the interface of the clad steel plate. Therefore, after examining the conditions for preventing separation of the clad steel plate, it was found that the shear strength must be maintained at or above SH, as shown in formula (2), in the shear test specified in JIS G 0601:2012.

[0014] The present invention was completed through further investigation based on the above findings, and the gist of the present invention is as follows. [1] A clad steel plate having a base material and a clad material formed on the base material, The cladding material is, in mass%, C: 0.001 to 0.030%, Si: 0.05 to 1.00%, Mn: 0.30 to 2.00% P: 0.040% or less, S: 0.030% or less, Cr: 11.0~28.0%, N: 0.002 to 0.300% and the balance being Fe and unavoidable impurities, The base material is, in mass%, C: 0.05~0.15%, Si: 0.01 to 0.60%, Mn: 1.00~2.20%, P: 0.020% or less, S: 0.005% or less, Al: 0.001 to 0.060% Contains Pcm represented by the following formula (1) is 0.20 or more and 0.32 or less, The balance is Fe and unavoidable impurities, and The base material has a yield strength of 620 MPa or more, a tensile strength of 700 MPa or more, and a Charpy impact absorption energy at -40°C of 47 J or more, The clad steel plate is The shear strength obtained in the shear test specified in JIS G 0601:2012 is equal to or greater than SH of the following formula (2), The yield strength is 620 MPa or more, Stainless steel clad plate with a tensile strength of 700 MPa or more. Here, Pcm is defined by the following equation (1). Pcm=C+Si / 30+Mn / 20+Cu / 20+Ni / 60+Cr / 20+Mo / 15+V / 10+5B...(1) In formula (1), the element symbols indicate the content (mass%) of each element in the composition, and elements that are not contained are represented as 0. Here, SH is defined by the following equation (2). SH=0.87×((t+T)×YSC-T×YSB) / t...(2) t: thickness of cladding material (mm), T: thickness of base material (mm), YSC: Yield strength of clad steel plate (MPa), YSB: Yield strength of base material (MPa) [2] The component composition of the cladding material is further, in mass%, Cu: 1.00% or less, Ni: 15.0% or less, Mo: 2.50% or less Nb: 0.10% or less, V: 0.10% or less, Ti: 0.10% or less, B: 0.0050% or less, Ca: 0.005% or less, Mg: 0.005% or less The stainless clad steel plate according to [1] above, containing one or more selected from the following: [3] The composition of the base material is, in mass%, Cu: 1.00% or less, Ni: 2.50% or less, Cr: 1.00% or less, Mo: 1.00% or less Nb: 0.10% or less, V: 0.10% or less, Ti: 0.10% or less, B: 0.0050% or less, Ca: 0.005% or less, Mg: 0.005% or less The stainless clad steel plate according to [1] or [2], containing one or more selected from the following: [4] A method for producing a stainless clad steel plate according to any one of [1] to [3], The base material and cladding material are stacked and welded together to form a slab, which is then heated to a temperature of 1000°C to 1200°C. Next, hot rolling is performed at a finishing temperature of 700°C to 1000°C, a first treatment of accelerated cooling from 650°C to 400°C at an average cooling rate of 10°C / s or more to a cooling stop temperature of 200°C to 400°C; A method for manufacturing stainless clad steel plate, which comprises either air-cooling to room temperature, then heating to 850°C or higher and 1050°C or lower, and a second treatment of accelerated cooling from 650°C to 400°C at an average cooling rate of 10°C / s or higher to a cooling stop temperature of 20°C or higher and 400°C or lower. [5] The method for producing a stainless clad steel plate according to [4], wherein after the first treatment or the second treatment, tempering is performed at 500°C or higher and 680°C or lower. [Effects of the Invention]

[0015] According to the present invention, it is possible to provide a high-strength stainless clad steel plate having excellent stress corrosion cracking resistance and low-temperature toughness, which is suitable for large cryogenic tanks for storing liquefied ammonia and the like. DETAILED DESCRIPTION OF THE INVENTION

[0016] The stainless clad steel plate of the present invention will be specifically described. The clad steel plate of the present invention has a base material and a clad material formed on the base material, and the base material and the clad material have the following chemical compositions. The clad material is stainless steel. Specifically, in the stainless clad steel sheet of the present invention, the cladding material has a composition, by mass%, of C: 0.001 to 0.030%, Si: 0.05 to 1.00%, Mn: 0.30 to 2.00%, P: 0.040% or less, S: 0.030% or less, Cr: 11.0 to 28.0%, N: 0.002 to 0.300%, with the balance being Fe and unavoidable impurities; The base metal contains, in mass%, C: 0.05 to 0.15%, Si: 0.01 to 0.60%, Mn: 1.00 to 2.20%, P: 0.020% or less, S: 0.005% or less, and Al: 0.001 to 0.060%, and has a component composition in which Pcm, represented by the following formula (1), is 0.20 or more and 0.32 or less, with the remainder being Fe and unavoidable impurities. Here, Pcm is defined by the following equation (1). Pcm=C+Si / 30+Mn / 20+Cu / 20+Ni / 60+Cr / 20+Mo / 15+V / 10+5B...(1) In formula (1), the element symbols indicate the content (mass%) of each element in the composition, and elements that are not contained are represented as 0. First, the reasons for limiting the composition of the steel (base material and cladding material) in the present invention will be explained for each component. Note that "%" regarding the composition means "mass %" unless otherwise specified.

[0017] [Component composition of cladding material] C: 0.001 to 0.030% C is one of the elements that inevitably exists in steel, but if the C content exceeds 0.030%, significant carbide precipitation occurs, causing stress corrosion cracking when the steel comes into contact with liquefied ammonia. Therefore, the C content is set to 0.03% or less. The C content is preferably 0.025% or less. On the other hand, if the C content is too low, the grain boundaries become brittle and the toughness deteriorates, so the lower limit of the C content is set to 0.001%, and the C content is preferably 0.005% or more.

[0018] Si: 0.05 to 1.00% Silicon is an industrially useful element for deoxidation, and is contained in an amount of 0.05% or more. The Si content is preferably 0.08% or more. However, if the Si content exceeds 1.00%, toughness and weldability deteriorate. Therefore, the Si content is set to 1.00% or less. The Si content is preferably 0.80% or less.

[0019] Mn: 0.30 to 2.00% Mn is an element that improves strength and toughness. It is also an industrially useful element for deoxidation. For this reason, it is preferable to actively add Mn, and the Mn content is set to 0.30% or more. The Mn content is preferably 0.70% or more, and more preferably 0.80% or more. On the other hand, if the Mn content exceeds 2.00%, the weldability is significantly deteriorated. Also, the stress corrosion cracking resistance is deteriorated. Therefore, the upper limit of the Mn content is set to 2.00%. The Mn content is preferably 1.80% or less, and more preferably 1.50% or less.

[0020] P:0.040% or less Since P deteriorates toughness and weldability, the P content is set to 0.040% or less, and preferably 0.030% or less. Although there is no particular lower limit, since reducing P increases refining costs, the preferred lower limit for the P content is set to 0.001%.

[0021] S: 0.030% or less S is a harmful element that deteriorates the toughness and weldability of steel, so it is desirable to reduce its content as much as possible. In particular, if the S content exceeds 0.030%, the base material toughness and weld toughness will deteriorate significantly. Therefore, the S content is set to 0.030% or less. The S content is preferably set to 0.015% or less. Although there is no particular lower limit, since reducing S increases refining costs, the preferred lower limit for the S content is set to 0.0001%.

[0022] Cr: 11.0~28.0% Cr is an essential element for ensuring the basic corrosion resistance of stainless steel, and in order to suppress stress corrosion cracking caused by liquefied ammonia, the Cr content must be 11.0% or more, and preferably 13.0% or more. On the other hand, if the Cr content exceeds 28.0%, the toughness of the duplex stainless steel and the corrosion resistance of the welded joint deteriorate. Therefore, the Cr content is set to the range of 11.0 to 28.0%. The Cr content is preferably 25.0% or less.

[0023] N: 0.002 to 0.300% N is an important element for improving strength and corrosion resistance, and to achieve this effect, an N content of 0.002% or more is required. The N content is preferably 0.005% or more. However, if the N content exceeds 0.300%, it will cause a significant decrease in weldability. Therefore, the N content is set to 0.002 to 0.300%. The N content is preferably 0.250% or less.

[0024] The clad steel plate cladding material of the present invention has the basic composition as described above, but may further contain one or more elements selected from the group consisting of Cu: 1.00% or less, Ni: 15.0% or less, Mo: 2.50% or less, Nb: 0.10% or less, V: 0.10% or less, Ti: 0.10% or less, B: 0.0050% or less, Ca: 0.005% or less, and Mg: 0.005% or less, as necessary, in order to ensure tensile strength throughout the entire thickness and improve weldability.

[0025] Cu: 1.00% or less Cu is an element that improves corrosion resistance, and from the viewpoint of corrosion resistance, the Cu content is preferably 0.10% or more, and more preferably 0.20% or more. If the Cu content exceeds 1.00%, the hot workability will be significantly deteriorated. Therefore, if Cu is contained, the Cu content should be 1.00% or less.

[0026] Ni: 15.0% or less Ni is an element that stabilizes the austenite phase of stainless steel and improves corrosion resistance to various acids as well as toughness. To achieve this effect, it is preferable to add 0.1% or more of Ni. The Ni content is more preferably 0.2% or more, and even more preferably 3.0% or more. However, Ni is an expensive metal, and in stainless clad steel, excessive Ni content is undesirable from the viewpoint of alloy cost. Therefore, when Ni is contained, the Ni content is set to 15.0% or less. The Ni content is preferably 14.0% or less.

[0027] Mo: 2.50% or less Mo is an element that improves corrosion resistance, particularly pitting corrosion resistance, and from the viewpoint of pitting corrosion resistance, it is preferable that the content be 0.05% or more. If the Mo content exceeds 2.50%, for example, in the case of a duplex stainless steel sheet, sigma phase precipitation is promoted, resulting in a deterioration in corrosion resistance. Furthermore, Mo deteriorates weldability, and since Mo is an expensive metal, excessive Mo content is undesirable from the viewpoint of alloy cost. Therefore, if Mo is contained, the Mo content is set to 2.50% or less. The Mo content is preferably 1.20% or less.

[0028] Nb: 0.10% or less Nb has the property of easily bonding with C, and when contained in an alloy, it is harmful to corrosion resistance. 23 It is possible to delay the precipitation of carbides such as C6. From this viewpoint, the Nb content is preferably 0.01% or more, and more preferably 0.02% or more. On the other hand, even if the Nb content exceeds 0.10%, the effect is not improved and the alloy cost increases. Therefore, if Nb is contained, the Nb content is set to 0.10% or less.

[0029] V: 0.10% or less V has the property of easily bonding with C, and when contained in an alloy, it is harmful to corrosion resistance. 23 It is possible to delay the precipitation of carbides such as C6. From this viewpoint, it is preferable to contain 0.01% or more of V. The V content is more preferably 0.02% or more. On the other hand, if the V content exceeds 0.10%, the effect is not improved and the alloy cost increases. Therefore, if V is contained, the V content is set to 0.10% or less.

[0030] Ti: 0.10% or less Ti has the property of easily bonding with C, and when contained in an alloy, it is harmful to corrosion resistance. 23 It is possible to delay the precipitation of carbides such as C6. From this viewpoint, it is preferable that the Ti content is 0.01% or more. The Ti content is more preferably 0.02% or more. On the other hand, if the Ti content exceeds 0.10%, the effect is not improved and the alloy cost increases. Therefore, if Ti is contained, the Ti content is set to 0.10% or less.

[0031] B: 0.0050% or less B has the effect of increasing the hardenability and strength of the laminated material. To realize this effect, the B content is preferably 0.0005% or more. Since excessive B content leads to a deterioration in toughness, the upper limit of the B content is preferably set to 0.0050%. Therefore, when B is contained, the B content is set to 0.0050% or less. The B content is preferably 0.0030% or less.

[0032] Ca: 0.005% or less Ca is an element that suppresses the formation of MnS and improves the internal quality of the steel sheet, and in order to obtain this effect, the Ca content is preferably 0.001% or more. On the other hand, if the Ca content exceeds 0.005%, Ca clusters and deteriorates the internal quality of the steel sheet, so the upper limit of the Ca content is set to 0.005%. Therefore, if Ca is contained, the Ca content is set to 0.005% or less. Furthermore, the Ca content is preferably set to 0.003% or less.

[0033] Mg: 0.005% or less Mg is an element that suppresses the formation of MnS and improves the internal quality of the steel sheet, and in order to obtain this effect, the Mg content is preferably 0.001% or more. On the other hand, if the Mg content exceeds 0.005%, Mg clusters and deteriorates the internal quality of the steel sheet, so the upper limit of the Mg content is set to 0.005%. Therefore, if Mg is contained, the Mg content should be 0.005% or less. Furthermore, the Mg content is preferably 0.003% or less.

[0034] The cladding material used in the clad steel plate of the present invention contains the above-mentioned composition, with the balance being Fe and unavoidable impurities.

[0035] [Base material composition] C: 0.05 to 0.15% C is the element that has the greatest effect on the strength and toughness of the base material. That is, if the C content exceeds 0.15%, the base material toughness deteriorates, so the C content is set to 0.15% or less. Preferably, the C content is 0.14% or less. On the other hand, if the C content is less than 0.05%, the desired base metal strength cannot be achieved, so the C content is set to 0.05% or more, and preferably 0.06% or more.

[0036] Si: 0.01 to 0.60% Since Si is an element that is inevitably contained in pig iron and a large amount thereof reduces the toughness and weldability of the base material, the Si content is set to 0.60% or less, and preferably 0.55% or less. On the other hand, reducing the Si content to less than 0.01% would require significant steelmaking costs, so a Si content of 0.01% or more is allowed. Therefore, the Si content is set to 0.01% or more. Furthermore, the Si content is preferably 0.05% or more.

[0037] Mn: 1.00 to 2.20% Mn is an element that is inevitably contained in pig iron, and if contained in large amounts, it reduces the toughness and weldability of the base material, so the Mn content is set to 2.20% or less, and preferably 2.00% or less. On the other hand, if the Mn content is less than 1.00%, the desired base metal strength cannot be obtained, so the lower limit of the Mn content is set to 1.00%.The preferred range of the Mn content is 1.10% or more.

[0038] P:0.020% or less P is an element that has a large embrittlement effect, and if contained in large amounts, it reduces the ductility and toughness of steel. Therefore, the P content is set to 0.020% or less. Furthermore, the P content is preferably set to 0.015% or less. On the other hand, since the less P the better, there is no particular lower limit for the P content. However, since an excessively low P content increases the refining time and costs, the P content is preferably 0.001% or more.

[0039] S: 0.005% or less S is an element that has a large embrittlement effect, and if contained in large amounts, it reduces the ductility and toughness of steel. Therefore, the S content is set to 0.005% or less. Furthermore, the S content is preferably set to 0.003% or less. On the other hand, since the less S there is, the better, there is no particular lower limit for the S content. However, since excessively low S content increases the refining time and costs, the S content is preferably 0.0001% or more.

[0040] Al: 0.001 to 0.060% Al is effective as a deoxidizer. To obtain this effect, the Al content must be 0.001% or more. Therefore, the Al content is set to 0.001% or more. The Al content is preferably set to 0.005% or more. On the other hand, if the Al content exceeds 0.060%, the cleanliness of the steel material or steel plate decreases, resulting in decreased ductility and toughness. Therefore, the Al content is set to 0.060% or less. The Al content is preferably 0.055% or less.

[0041] Pcm: 0.20 or more and 0.32 or less Pcm is an index for evaluating the limit of weld cold cracking, and is highly correlated with the base material strength and toughness. If Pcm exceeds 0.32, the base material toughness and weldability deteriorate, so the upper limit of Pcm is set to 0.32. Pcm is preferably 0.28 or less. On the other hand, if Pcm is less than 0.20, the desired strength cannot be obtained, so the lower limit of Pcm is set to 0.20, and Pcm is more preferably 0.22 or more.

[0042] The base material of the clad steel plate of the present invention has the basic composition as described above, but in order to ensure tensile strength throughout the entire thickness and improve weldability, it may further contain one or more elements selected from the group consisting of Cu: 1.00% or less, Ni: 2.50% or less, Cr: 1.00% or less, Mo: 1.00% or less, Nb: 0.10% or less, V: 0.10% or less, Ti: 0.10% or less, B: 0.0050% or less, Ca: 0.005% or less, and Mg: 0.005% or less, as necessary.

[0043] Cu: 1.00% or less Cu is an element that improves strength. To obtain this effect, the Cu content is preferably 0.10% or more, and more preferably 0.15% or more. On the other hand, if the Cu content exceeds 1.00%, scratches occur on the surface of the steel sheet, so when Cu is contained, the upper limit is set to 1.00%.Furthermore, the Cu content is preferably set to 0.30% or less.

[0044] Ni: 2.50% or less Ni is an element that improves strength and toughness. To obtain this effect, the Ni content is preferably 0.10% or more, and more preferably 0.15% or more. On the other hand, if the Ni content exceeds 2.50%, scratches occur on the surface of the steel sheet, so when Ni is contained, the upper limit of the Ni content is set to 2.50%.Furthermore, the Ni content is preferably set to 0.30% or less.

[0045] Cr:1.00% or less Cr is an element that improves strength. To obtain this effect, the Cr content is preferably 0.10% or more, and more preferably 0.15% or more. On the other hand, if the Cr content exceeds 1.00%, the toughness and weldability of the base material decrease, so when Cr is contained, the upper limit is set to 1.00%.Furthermore, the Cr content is preferably set to 0.50% or less.

[0046] Mo: 1.00% or less Mo is an element that improves strength. To obtain this effect, the Mo content is preferably 0.05% or more, and more preferably 0.15% or more. On the other hand, if the Mo content exceeds 1.00%, the toughness and weldability of the base material decrease, so when Mo is contained, the upper limit is set to 1.00%.Moreover, the Mo content is preferably set to 0.50% or less.

[0047] Nb: 0.10% or less Nb is an element that improves strength and toughness, and in order to obtain this effect, the Nb content is preferably 0.01% or more. On the other hand, if the Nb content exceeds 0.10%, the base material toughness and weldability deteriorate, so when Nb is contained, the upper limit of the Nb content is set to 0.10%. The Nb content is preferably set to 0.06% or less.

[0048] V: 0.10% or less V is an element that improves strength. To obtain this effect, the V content is preferably 0.01% or more, and more preferably 0.02% or more. On the other hand, if the V content exceeds 0.10%, the base material toughness and weldability decrease, so when V is contained, the upper limit of the V content is set to 0.10%. The V content is preferably set to 0.05% or less.

[0049] Ti: 0.10% or less Ti is an element that improves surface defects and strength, and to obtain this effect, the Ti content is preferably 0.01% or more. On the other hand, if the Ti content exceeds 0.10%, TiC precipitates, reducing the toughness of the base material, so when Ti is contained, the upper limit of the Ti content is set to 0.10%. The Ti content is preferably 0.05% or less, and more preferably 0.03% or less.

[0050] B: 0.0050% or less B significantly improves the hardenability of the steel sheet and improves its strength and toughness. To obtain this effect, the B content is preferably 0.0005% or more. On the other hand, if the B content exceeds 0.0050%, BN precipitates, reducing the toughness of the base material, so when B is contained, the upper limit of the B content is set to 0.0050%. The B content is preferably set to 0.0020% or less.

[0051] Ca: 0.005% or less Ca is an element that suppresses the formation of MnS and improves the internal quality and weldability of the steel sheet. To obtain this effect, the Ca content is preferably 0.001% or more. On the other hand, if the Ca content exceeds 0.005%, Ca clusters and deteriorates the internal quality and weldability of the steel sheet, so when Ca is contained, the upper limit of the Ca content is set to 0.005%, and the Ca content is preferably set to 0.003% or less.

[0052] Mg: 0.005% or less Mg is an element that suppresses the formation of MnS and improves the internal quality and weldability of the steel sheet. To obtain this effect, the Mg content is preferably 0.001% or more. On the other hand, if the Mg content exceeds 0.005%, Mg clusters and deteriorates the internal quality and weldability of the steel sheet, so the upper limit of the Mg content is set to 0.005%. The Mg content is preferably set to 0.003% or less.

[0053] The base material used in the clad steel plate of the present invention contains the above-mentioned composition, with the balance being Fe and unavoidable impurities.

[0054] [Mechanical properties of base material] Yield strength: 620 MPa or more, tensile strength: 700 MPa or more The large-scale liquefied ammonia tank that is the primary target of this invention is assumed to be a PC tank in the 90,000 to 110,000 ton class. The strength required for this large-scale liquefied ammonia tank, when a tensile test is conducted on a cut-out base material portion alone, requires a yield strength of 620 MPa or more and a tensile strength of 700 MPa or more. Preferably, the yield strength is 665 MPa or more and the tensile strength is 760 MPa or more. More preferably, the yield strength is 680 MPa or more and the tensile strength is 780 MPa or more. In tank strength design, there are cases where the strength and plate thickness of the entire clad thickness are used, and cases where the strength and plate thickness of only the clad base material and only the base material are used. Therefore, in this invention, both are satisfied.

[0055] Absorbed energy when conducting Charpy impact test at -40℃: 47J or more Ammonia liquefies at -35°C under normal pressure. Therefore, the low-temperature toughness of steel must be evaluated at temperatures lower than -35°C, and testing is conducted at -40°C. The test temperature is preferably -50°C, and even more preferably -55°C. The absorbed energy is 47J or greater, consistent with JIS G 3115:2022, the primary standard used for high-strength tanks, and is the average value obtained from three test specimens. The absorbed energy is preferably 47J average, with individual test values ​​of 27J or greater. While no special impact test method is specified, the same method as JIS G 3115:2022, the primary standard used for high-strength tanks, is typically used, with test specimens taken from 1 / 4 the thickness of the base material, perpendicular to the rolling direction. The 1 / 4 thickness of the base material is defined as the point originating from the surface opposite the surface joined to the clad material.

[0056] [Thickness of clad steel plate] Clad steel plate thickness: 8mm or more (optimal conditions) In the case of large liquefied ammonia tanks, which are the main target of the present invention, the thickness of the steel plate used for the tank will not be less than 8 mm, so the lower limit of the thickness of the clad steel plate when used for the tank is 8 mm. The thickness of the clad steel plate is more preferably 9 mm or more and 60 mm or less. Although not particularly limited, the thickness of the cladding material is preferably 1 mm or more, and more preferably 5 mm or less. Although not particularly limited, the thickness of the base material is preferably 6 mm or more, and more preferably 60 mm or less.

[0057] [Mechanical properties of clad steel plates] Yield strength: 620 MPa or more, tensile strength: 700 MPa or more The large-scale liquefied ammonia tank that is the primary target of this invention is assumed to be a PC tank in the 90,000 to 110,000 ton class. The strength required for this large-scale liquefied ammonia tank, when a tensile test is conducted across the entire thickness of the clad steel plate, requires a yield strength of 620 MPa or more and a tensile strength of 700 MPa or more. Preferably, the yield strength is 665 MPa or more and the tensile strength is 760 MPa or more. More preferably, the yield strength is 680 MPa or more and the tensile strength is 780 MPa or more. In terms of tank strength design, there are cases where the strength and plate thickness of the entire clad thickness are used, and cases where the strength and plate thickness of only the clad base material are used. Therefore, in this invention, both are satisfied.

[0058] Shear strength of clad steel plate: SH or higher When a cryogenic tank is manufactured with a clad steel plate made of low-alloy steel as the inner clad material and a stainless steel clad plate as the base material, the clad steel tends to shrink significantly during operation due to differences in thermal expansion coefficients. This causes tensile residual stress equivalent to the yield stress on the clad steel side, which may cause peeling at the clad steel plate interface. The clad steel plate is subjected to a shear test specified in JIS G 0601:2012. If the shear strength is SH or higher, peeling will not occur, and the shear strength is considered to be SH or higher. The shear strength is preferably SH + 50 MPa or higher. Here, SH is defined by the following equation (2). SH=0.87×((t+T)×YSC-T×YSB) / t...(2) t: thickness of cladding material (mm), T: thickness of base material (mm), YSC: Yield strength of clad steel plate (MPa), YSB: Yield strength of base material (MPa)

[0059] [Manufacturing method] Next, a method for producing a clad steel plate according to the present invention will be described. A slab is used that is integrated by overlapping and welding the cladding material and the base material. The hot rolling conditions for producing the base material and cladding material are not particularly specified. Clad steel plates are produced using either a sandwich clad method, in which two slabs of clad and base materials are stacked together, with a release agent applied between the two slabs to allow for separation after hot rolling. Alternatively, a sacrificial clad method is used, in which a slab of clad and base materials is stacked together with a steel plate (sacrificial material) that will not be used in the final product. A release agent is applied between the two slabs to allow for separation after hot rolling. In sandwich clad and sacrificial clad, the width and length of the clad material are slightly smaller than the base material. A steel plate called a spacer is inserted to fill the gap between the clad material and the base material, and the spacer is then welded to the base material. Welding must be performed in a high vacuum, using either electron beam welding or laser welding.

[0060] In the manufacturing method of stainless clad steel plate of the present invention, a slab formed by overlapping and welding a base material having the aforementioned chemical composition and a cladding material having the aforementioned chemical composition is heated to a temperature of 1000°C or higher and 1200°C or lower, and subsequently hot-rolled at a finishing temperature of 700°C or higher and 1000°C or lower, followed by accelerated cooling from 650°C to 400°C at an average cooling rate of 10°C / s or higher to a cooling stop temperature of 200°C to 400°C or lower (a first process), or air-cooling to room temperature, followed by heating to 850°C to 1050°C or lower, and accelerated cooling from 650°C to 400°C at an average cooling rate of 10°C / s or higher to a cooling stop temperature of 20°C to 400°C or lower (a second process). Hereinafter, in the present invention, the temperature refers to the surface temperature of the slab or steel plate unless otherwise specified.

[0061] Reheating temperature: 1000℃ or higher and 1200℃ or lower The reheating temperature of the slab affects the toughness of the base material and the bondability of the clad interface. If the reheating temperature is below 1000°C, poor bonding occurs at the clad interface. In addition, the strength of the base material decreases. Therefore, the lower limit of the reheating temperature is set at 1000°C. On the other hand, if the reheating temperature exceeds 1200°C, the toughness of the base metal decreases, so the upper limit of the reheating temperature is set to 1200°C. The reheating temperature is preferably 1050 to 1200°C.

[0062] Hot rolling finishing temperature: 700℃ to 1000℃ The finishing temperature of hot rolling (hot rolling end temperature) affects the toughness of the base material and the bondability of the clad interface. If the finishing temperature is below 700°C, poor bonding occurs at the clad interface. In addition, the strength of the base material decreases. Therefore, the lower limit of the finishing temperature is set to 700°C. The finishing temperature is preferably 750°C or higher. If the finishing temperature exceeds 1000° C., the toughness of the base material decreases, so the upper limit of the finishing temperature is set to 1000° C. The finishing temperature is preferably 950° C. or lower.

[0063] After hot rolling, either (1) the first treatment, in which accelerated cooling is performed immediately after hot rolling, or (2) the second treatment, in which accelerated cooling is performed after hot rolling by air cooling to room temperature, reheating, and then accelerated cooling. The accelerated cooling is performed using water.

[0064] (1) First treatment Accelerated cooling rate: Average cooling rate from 650°C to 400°C (average cooling rate in the thickness direction): 10°C / s or more The cooling rate of the accelerated cooling carried out immediately after hot rolling affects the strength of the steel sheet. The cooling rate correlated with these performance characteristics is defined as the average cooling rate from 650°C to 400°C (average cooling rate in the plate thickness direction). The average cooling rate is determined by heat conduction calculations based on the relationship between the actual cooling start temperature (650°C) and cooling stop temperature (400°C) and the time between them. If the average cooling rate is below 10°C / s, the desired steel plate strength cannot be obtained, so the lower limit of the average cooling rate is set to 10°C / s. The average cooling rate is preferably 15°C / s or higher. Although there is no particular upper limit, the average cooling rate may be 100°C / s or less. In the first treatment, "accelerated cooling is carried out immediately after hot rolling" means that accelerated cooling is carried out without air-cooling to room temperature after hot rolling.

[0065] Accelerated cooling stop temperature: 200°C to 400°C The cooling stop temperature of accelerated cooling performed immediately after hot rolling affects the strength and toughness of the base material. The cooling stop temperature is the temperature at which the plate is reheated to a degree that makes the temperature distribution in the thickness direction uniform by air cooling after accelerated cooling. If the cooling stop temperature is below 200°C, the toughness of the base material cannot be ensured, so the lower limit of the cooling stop temperature is set to 200°C. The cooling stop temperature is preferably 220°C or higher. On the other hand, if the cooling stop temperature exceeds 400°C, the strength of the base material cannot be ensured, so the upper limit of the cooling stop temperature is set to 400°C. The cooling stop temperature is preferably 380°C or lower. After accelerated cooling, the material may be air-cooled to room temperature or immediately tempered to the desired temperature.

[0066] (2) Secondary processing Heating temperature after cooling to room temperature: 850℃ to 1050℃ After hot rolling, the steel is cooled (air cooling: 0.01 to 1°C / s) to room temperature (-5 to 50°C), and the heating temperature of the subsequent heat treatment affects the strength and toughness of the base material. If the heating temperature is below 850°C, the desired base material strength cannot be obtained, so the lower limit of the heating temperature is set to 850°C. The heating temperature is preferably 880°C or higher. If the heating temperature exceeds 1050°C, the base material toughness cannot be obtained, so the upper limit of the heating temperature is set to 1050°C. The heating temperature is preferably 1000°C or lower.

[0067] Accelerated cooling rate after reheating: Average cooling rate from 650°C to 400°C: 10°C / s or more After the heating (reheating), accelerated cooling is immediately carried out, preferably within 300 seconds after heating. The cooling rate after air cooling and reheating following hot rolling affects the strength of the base material. The cooling rate that correlates with these performance characteristics is defined as the average cooling rate in the thickness direction from 650°C to 400°C. The average cooling rate is determined by heat conduction calculations based on the relationship between the actual cooling start temperature (650°C) and cooling stop temperature (400°C) and the time between them. If the average cooling rate is below 10°C / s, the desired base material strength cannot be obtained, so the lower limit of the average cooling rate is set to 10°C / s. The average cooling rate is preferably 15°C / s or higher. Although there is no particular upper limit, the average cooling rate may be 100°C / s or less.

[0068] Accelerated cooling stop temperature: 20℃ to 400℃ The cooling stop temperature after air cooling and reheating after hot rolling affects the strength and toughness of the base material. The cooling stop temperature is the temperature at which the plate is reheated to a level where the temperature distribution in the thickness direction becomes uniform through air cooling after accelerated cooling. If the cooling stop temperature is below 20°C, the toughness of the base material cannot be ensured, so the lower limit of the cooling stop temperature is set to 20°C. On the other hand, if the cooling stop temperature exceeds 400° C., the strength of the base material cannot be ensured, so the upper limit of the cooling stop temperature is set to 400° C. The cooling stop temperature is preferably 20 to 300° C. After accelerated cooling, the material may be air-cooled to room temperature, or immediately tempered to the desired temperature.

[0069] The steel sheet that has been subjected to accelerated cooling or reheating followed by cooling (the steel sheet that has been subjected to the first treatment or the second treatment) can be further subjected to tempering treatment.

[0070] Tempering temperature: 500℃ or higher and 680℃ or lower The tempering temperature affects the strength and toughness of the base material. If the tempering temperature is below 500°C, the desired base material strength may not be obtained, so the lower limit of the tempering temperature is set to 500°C. The tempering temperature is preferably 550°C or higher. If the tempering temperature exceeds 680°C, the base material toughness may not be obtained, so the upper limit of the tempering temperature is set to 680°C. The tempering temperature is preferably 650°C or lower. Tempering may be performed by reheating using a method such as induction heating immediately after cooling is stopped, or by air-cooling to room temperature after cooling is stopped and then reheating in a heating furnace, etc. In the case of induction heating, the surface of the steel sheet is heated rapidly, and the temperature at which the temperature becomes uniform in the thickness direction after heating is completed is the tempering temperature. [Example]

[0071] Next, the present invention will be described in more detail based on examples. The following examples are intended to illustrate preferred examples of the present invention, and the present invention is not limited to these examples in any way.

[0072] First, by continuous casting, slabs for cladding materials having the chemical compositions shown in Table 1 and slabs for base materials having the chemical compositions shown in Table 2 were produced. The blank spaces in Tables 1 and 2 indicate that the element is not contained or is contained as an unavoidable impurity.

[0073] [Table 1]

[0074] [Table 2]

[0075] Next, the obtained slabs for the base material and the cladding material were used to produce base material materials and cladding material materials of various thicknesses by hot rolling. These base material materials and cladding material materials were cut to the same length and width, and the surface scale was removed by polishing. The base material materials and cladding material materials thus obtained were stacked to be assembled using either the sacrificial clad or sand clad method. Then, the materials were placed in a vacuum chamber of 10 -4 ~10 -5 The interface between the base material and the cladding material was welded with an electron beam around the entire periphery in a Torr chamber to form an integrated slab. Note that in Table 3, when a sacrificial clad material was used, it is listed as "sacrificial material," and when a sand clad material was used, it is listed as "sand." The obtained slabs were then used to produce clad steel plates under the conditions shown in Table 3. Specifically, the produced slabs were reheated and hot-rolled, and then some of the steel plates were immediately subjected to accelerated cooling (first treatment: in Table 3, the timing of accelerated cooling is indicated as "immediately after hot-rolling"). In addition, some of the steel plates were air-cooled to room temperature (25°C), then reheated and subjected to accelerated cooling (second treatment: in Table 3, the timing of accelerated cooling is indicated as "after air-cooling to room temperature").

[0076] Some of the steel sheets were tempered after accelerated cooling (water cooling). In Table 3, the tempering method is indicated as "induction heating immediately after cooling was stopped" for steel sheets that were reheated by induction heating immediately after cooling was stopped, and as "air-cooled to room temperature, then furnace heating" for steel sheets that were reheated in a heating furnace after cooling was stopped.

[0077] [Table 3]

[0078] For the manufactured steel plates, the following material test pieces were taken from the base material and the entire clad thickness and tested. The results are summarized in Table 4.

[0079] [Base material yield strength, tensile strength] Test pieces were taken from the center positions in the longitudinal and width directions of the obtained clad steel plate, the cladding material was removed by milling, and JIS Z 2241:2022 No. 5 tensile test pieces were machined from only the base metal portion. The test pieces were taken perpendicular to the rolling direction. Tensile tests were conducted on the taken test pieces to determine the yield strength and tensile strength. The upper yield point was taken as the yield strength, and if the upper yield point could not be obtained, the 0.2% proof stress was taken as the yield strength.

[0080] [Impact test of base material] Test pieces were taken from the center positions in the longitudinal and transverse directions of the obtained clad steel plate, and the cladding material was removed by milling. 2 mm V-notch Charpy impact test pieces according to JIS Z 2242:2018 were machined from only the base metal portion. The test pieces were taken perpendicular to the rolling direction and from a position at or close to 1 / 4 of the thickness in the plate thickness direction. 10 mm x 10 mm test pieces were used when the base metal thickness was 12 mm or more, and 10 mm x 7.5 mm test pieces were used when the base metal thickness was less than 12 mm. The test was conducted at -40°C, and the absorbed energy was measured.

[0081] [Yield strength and tensile strength of clad steel plate throughout its thickness] Test pieces were taken from the center positions in the longitudinal and transverse directions of the obtained clad steel plate, and processed into No. 5 tensile test pieces according to JIS Z 2241:2022. The test pieces were taken perpendicular to the rolling direction. A tensile test was conducted on the taken test pieces to measure the yield strength and tensile strength. The upper yield point was taken as the yield strength, and if the upper yield point could not be obtained, the 0.2% proof stress was taken as the yield strength.

[0082] [Shear strength of clad steel plate] The shear strength of the obtained clad steel plate was determined by the shear strength test standardized in JIS G0601:2012.

[0083] [Liquid ammonia stress corrosion cracking resistance of clad steel plates (stress corrosion cracking resistance)] The liquefied ammonia stress corrosion cracking resistance (stress corrosion cracking resistance) was evaluated by an accelerated test (stress corrosion cracking test) in which a four-point bending test was performed in a test solution and constant-potential anodic electrolysis was performed to accelerate corrosion.

[0084] Specifically, the following steps were performed:

[0085] Test specimens measuring 5 mm thick x 15 mm x 115 mm were taken from the clad surface of the steel plates and ultrasonically degreased in acetone for 5 minutes. Then, a stress equivalent to 80% of the yield strength of each clad steel plate was applied by four-point bending. Because the clad material was thinner than 5 mm, the test specimen included the base material. However, the load was applied so that the shorter span of the two-point bending jig was facing the clad material, so that stress was applied to the back side of the bend. The four-point bending test specimens were placed in a test cell and filled with a solution containing 12.5 g of ammonium carbamate and 1 L of liquid ammonia. The potentiostat was used to control the flow of +2.0 V vs. Pt through the test specimens, and the specimens were immersed at room temperature (25°C). If no cracks were found in the cladding material after 168 hours of immersion, the liquefied ammonia stress corrosion cracking resistance (ammonia SCC resistance) was judged to be "good", and if cracks were found in the cladding material, the liquefied ammonia stress corrosion cracking resistance (ammonia SCC resistance) was judged to be "poor".

[0086] [Table 4]

[0087] It was found that the clad steel plates of the present invention had high strength, with both the base material and the clad steel plates having a yield strength of 620 MPa or more and a tensile strength of 700 MPa or more. Furthermore, the clad steel plates of the examples of the present invention were evaluated as "good" in terms of liquefied ammonia stress corrosion cracking resistance (stress corrosion cracking resistance), demonstrating that they have excellent stress corrosion cracking resistance. Furthermore, when the clad steel plate of the present invention was subjected to a Charpy impact test at -40°C, the absorbed energy of the base material was 47 J or more, demonstrating excellent low-temperature toughness. On the other hand, it was found that the clad steel plates of the comparative examples were inferior in at least one of strength, stress corrosion cracking resistance, and low-temperature toughness.

Claims

1. A clad steel plate having a base material and a clad material formed on the base material, The cladding material is, in mass %, C: 0.001-0.030%, Si: 0.05-1.00%, Mn: 0.30-2.00%, P: 0.040% or less, S: 0.030% or less, Cr: 11.0-28.0%, N: 0.002-0.300% and the balance being Fe and unavoidable impurities, The base material comprises, in mass %, C: 0.05-0.15%, Si: 0.01-0.60%, Mn: 1.00-2.20%, P: 0.020% or less, S: 0.005% or less, Al: 0.001-0.060% Contains Pcm represented by the following formula (1) is 0.20 or more and 0.32 or less, The remainder is Fe and unavoidable impurities, and The base material has a yield strength of 620 MPa or more, a tensile strength of 700 MPa or more, and a Charpy impact absorption energy at −40° C. of 47 J or more, The clad steel plate is The shear strength obtained in the shear test specified in JIS G 0601:2012 is equal to or greater than SH of the following formula (2), The yield strength is 620 MPa or more, A stainless clad steel plate having a tensile strength of 700 MPa or more. Here, Pcm is defined by the following equation (1). Pcm=C+Si / 30+Mn / 20+Cu / 20+Ni / 60+Cr / 20+Mo / 15+V / 10+5B...(1) In formula (1), the element symbols indicate the content (mass%) of each element in the composition, and elements that are not contained are represented as 0. Here, SH is defined by the following equation (2). SH=0.87×((t+T)×YSC-T×YSB) / t...(2) t: thickness of cladding material (mm), T: thickness of base material (mm), YSC: yield strength of clad steel plate (MPa), YSB: yield strength of base material (MPa)

2. The component composition of the cladding material is further, in mass%, Cu: 1.00% or less, Ni: 15.0% or less, Mo: 2.50% or less, Nb: 0.10% or less, V: 0.10% or less, Ti: 0.10% or less, B: 0.0050% or less, Ca: 0.005% or less, Mg: 0.005% or less The stainless clad steel plate according to claim 1, comprising one or more selected from the following:

3. The composition of the base material is, in mass%, Cu: 1.00% or less, Ni: 2.50% or less, Cr: 1.00% or less, Mo: 1.00% or less, Nb: 0.10% or less, V: 0.10% or less, Ti: 0.10% or less, B: 0.0050% or less, Ca: 0.005% or less, Mg: 0.005% or less The stainless clad steel plate according to claim 1, comprising one or more selected from the following:

4. The composition of the base material is, in mass%, Cu: 1.00% or less, Ni: 2.50% or less, Cr: 1.00% or less, Mo: 1.00% or less, Nb: 0.10% or less, V: 0.10% or less, Ti: 0.10% or less, B: 0.0050% or less, Ca: 0.005% or less, Mg: 0.005% or less The stainless clad steel plate according to claim 2, comprising one or more selected from the following:

5. The method for producing a stainless clad steel plate according to any one of claims 1 to 4, The slab, which is formed by overlapping and welding the base material and the cladding material together, is heated to a temperature of 1000°C or more and 1200°C or less; Subsequently, hot rolling is performed at a finishing temperature of 700°C or more and 1000°C or less, and then A first treatment in which the average cooling rate from 650°C to 400°C is 10°C / s or more and accelerated cooling is performed to a cooling stop temperature of 200°C to 400°C, and A method for manufacturing stainless clad steel plate, which comprises either air-cooling to room temperature, then heating to 850°C or higher and 1050°C or lower, and a second treatment of accelerated cooling from 650°C to 400°C at an average cooling rate of 10°C / s or higher to a cooling stop temperature of 20°C to 400°C.

6. The method for producing a stainless clad steel plate according to claim 5, wherein tempering is performed at 500°C or higher and 680°C or lower after the first treatment or the second treatment.

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