A crack-proof heat treatment process for martensitic stainless steel bending or rolling workpieces

Abstract

The present invention discloses a heat treatment process for preventing cracking of a martensitic stainless steel bending or rolling workpiece, and belongs to the field of heat treatment technology. The present invention prevents cracking of martensitic stainless steel during bending or rolling by annealing heat treatment according to the mechanical properties of the martensitic stainless steel plate or the matching degree between the martensitic stainless steel plate and the welding wire during welding before bending or rolling the martensitic stainless steel plate, or bending or rolling the martensitic stainless steel plate first and then welding the martensitic stainless steel bending or rolling workpiece; the process parameters of the annealing heat treatment are: the holding temperature is 720~770℃, the holding time is (T / 25)h and at least 1h, and the furnace temperature after the heat treatment is completed is not higher than 300℃. The present invention eliminates the internal stress of the martensitic stainless steel material itself and reduces the yield strength ratio through annealing heat treatment, thereby reducing the possibility of fracture during bending or rolling.

Description

Technical Field

[0001] The invention relates to the technical field of heat treatment of martensitic stainless steel, and in particular to a crack-proof heat treatment process for a martensitic stainless steel bent or rolled workpiece. Background Art

[0002] Martensitic stainless steel has good corrosion resistance, high temperature oxidation resistance, good low temperature performance and excellent machining performance, so it is widely used in chemical, petroleum, power, nuclear engineering, aerospace, ocean, medicine, light industry, textile and other fields.

[0003] Martensitic stainless steel materials usually contain a large amount of chromium, and the higher the chromium content, the higher the carbon content required for the steel to ensure the formation of martensitic structure during heat treatment, which makes martensitic stainless steel have great hardenability. In the actual production process, when bending or rolling martensitic stainless steel plates or martensitic stainless steel welded plates, cold bending process is usually used, which is easy to break from the plate bending part. If the martensitic stainless steel plate is bent or rolled before welding, it is also easy to break from the weld during the rounding process; if the hot bending process is used, small workpieces are easier to operate, but hot bending of large workpieces is not easy to achieve, because the workpiece volume is large, the required plate size is large, and an additional heating furnace is required for heating before bending or rolling, and bending or rolling needs to be performed immediately after heating, but the next batch of plates may not be heated yet, resulting in discontinuous production; and after heating, the high-temperature plate needs to be transferred from the heating furnace to the bending equipment, and then the bending equipment is used to perform corresponding operations on the high-temperature plate, which also increases the safety risk during the operation, and the operator's working environment temperature is high and the working environment is harsh. Summary of the invention

[0004] In order to solve the above technical problems, the present invention provides a crack prevention heat treatment process for a martensitic stainless steel bent or rolled workpiece, which can reduce the possibility of fracture during the production process of the martensitic stainless steel bent or rolled workpiece.

[0005] The technical solution adopted by the present invention is:

[0006] A heat treatment process for preventing cracking of a martensitic stainless steel bending or rolling workpiece, wherein before bending or rolling a martensitic stainless steel sheet, or before first bending or rolling a martensitic stainless steel sheet and then welding it to prepare a martensitic stainless steel bending or rolling workpiece, an annealing heat treatment is performed to prevent the martensitic stainless steel from cracking during bending or rolling;

[0007] The process parameters of annealing heat treatment are: holding temperature of 720~770℃, holding time of (T / 25)h and at least 1h, furnace temperature not higher than 300℃, and air cooling to room temperature after furnace; where T is thickness, mm.

[0008] Preferably, during the annealing heat treatment, the furnace temperature does not exceed 300°C, the heating rate does not exceed (5500 / T)°C / h and does not exceed 220°C / h; the cooling rate does not exceed (5500 / T)°C / h and does not exceed 280°C / h.

[0009] Preferably, before preparing the martensitic stainless steel bending or coiling workpiece, it is necessary to determine whether annealing heat treatment is required based on the mechanical properties of the martensitic stainless steel sheet or the matching degree between the martensitic stainless steel sheet and the welding wire during welding, specifically:

[0010] When bending or rolling martensitic stainless steel sheets to prepare bent or rolled workpieces, first test the mechanical properties of the martensitic stainless steel sheets and calculate the yield strength ratio. If the yield strength ratio is greater than 0.8, perform annealing heat treatment before bending or rolling, and perform bending or rolling after the annealing heat treatment is completed and the temperature is lowered to room temperature.

[0011] When a martensitic stainless steel plate is first bent or rolled and then welded to prepare a martensitic stainless steel bent or rolled workpiece, the mechanical properties of the martensitic stainless steel plate are first detected, and the yield strength ratio is calculated. If the yield strength ratio is greater than 0.8, annealing heat treatment is performed before bending or rolling, and bending or rolling is performed after the annealing heat treatment is completed and the temperature is lowered to room temperature; then, it is determined whether the welding wire used in welding is highly matched with the martensitic stainless steel plate. If the welding wire is highly matched with the martensitic stainless steel plate, annealing heat treatment is required after welding, and rounding is performed after the annealing heat treatment is completed and the temperature is lowered to room temperature. Otherwise, the mechanical properties of the weld area of ​​the martensitic stainless steel bent or rolled welded workpiece are continuously detected, and the yield strength ratio is calculated. If the yield strength ratio is greater than 0.8, annealing heat treatment is required after welding, and rounding is performed after the annealing heat treatment is completed and the temperature is lowered to room temperature.

[0012] Preferably, when a martensitic stainless steel plate is first bent or rolled and then welded to prepare a martensitic stainless steel bent or rolled workpiece, a welding groove needs to be opened at the joint of the martensitic stainless steel plate before bending or rolling, and the welding groove is a double-sided double V-shaped groove, and the double-sided double V-shaped groove includes two symmetrically arranged double V-shaped grooves, and each double V-shaped groove includes a first V-shaped groove close to the center of the groove and a second V-shaped groove away from the center of the groove.

[0013] Preferably, the groove surface angle of the first V-shaped groove is 10°~15°, and the groove surface angle of the second V-shaped groove is 45°~60°.

[0014] Preferably, the martensitic stainless steel bent or rolled workpiece comprises the following alloy components in mass percentage: C 0.10%~0.25%, Si≤1.0%, Mn 0.3%~1.0%, P≤0.04%, S≤0.03%, Ni≤0.6%, Cr 11.5%~14.0%, and the balance is Fe and unavoidable impurities.

[0015] Preferably, the material of the martensitic stainless steel bending or rolling workpiece is 12Cr13 or 20Cr13.

[0016] Preferably, the method for judging whether the welding wire used in welding is highly matched with the martensitic stainless steel plate is: judging according to the material of the welding wire;

[0017] The chemical composition of the welding wire that is highly matched with the martensitic stainless steel plate is: in mass percentage, C≤0.06%, Si≤0.5%, Mn≤0.6%, P≤0.03%, S≤0.03%, Ni≤4.0%~5.0%, Cr≤11%~12.5%, Mo≤0.4%~0.7%, and the balance is Fe.

[0018] Preferably, the welding wire that is highly matched with the martensitic stainless steel plate is ER410NiMo welding wire.

[0019] The beneficial effects of the present invention are:

[0020] (1) The present invention provides a production process for preventing cracking of a martensitic stainless steel bent or rolled workpiece. When a martensitic stainless steel sheet is bent or rolled, or when a martensitic stainless steel sheet is first bent or rolled and then welded to prepare a martensitic stainless steel bent or rolled workpiece, cracking of the martensitic stainless steel bent or rolled workpiece is prevented by annealing heat treatment according to the mechanical properties of the martensitic stainless steel sheet or the matching degree between the martensitic stainless steel sheet and the welding wire during welding. The annealing heat treatment can eliminate the internal stress of the martensitic stainless steel material itself and reduce the yield strength ratio, thereby reducing the possibility of fracture during bending or rolling.

[0021] (2) The annealing heat treatment process adopted by the present invention can not only reduce the yield strength ratio of the martensitic stainless steel sheet, but also does not change the supply status of the martensitic stainless steel workpiece, thereby ensuring that its mechanical properties meet the supply requirements, and there is no need to perform heat treatment again in the later stage to restore its mechanical properties; in addition, after the martensitic stainless steel is annealed and heat treated, it can be bent, rolled or rounded in a cooling state, without the need to perform operations immediately after heat treatment, which is convenient for work task arrangement and is not only suitable for the production of small workpieces, but also suitable for the production of large workpieces. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0023] Figure 1 This is a schematic diagram of the structure of the welding groove of Example 3 of the present invention.

[0024] Markings in the figure: 1, first V-shaped groove; 2, second V-shaped groove. DETAILED DESCRIPTION

[0025] The present invention provides a crack prevention heat treatment process for a martensitic stainless steel bending or rolling workpiece. In order to make the purpose, technical solution and effect of the present invention clearer and more specific, the present invention is further described in detail below. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0026] The present invention provides a crack prevention heat treatment process for a martensitic stainless steel bent or rolled workpiece. The martensitic stainless steel used for preparing the bent or rolled workpiece comprises the following alloy components in parts by weight: C 0.10%-0.25%, Si≤1.0%, Mn 0.3%-1.0%, P≤0.04%, S≤0.03%, Ni≤0.6%, Cr 11.5%-14.0%, and the balance is Fe and unavoidable impurities; preferably, the material of the martensitic stainless steel bent or rolled workpiece is 12Cr13 or 20Cr13.

[0027] When the martensitic stainless steel with the above alloy composition is used to prepare a bent or rolled workpiece, it has high hardenability and is prone to cracking at the bend or weld. To solve this problem, the present invention, before bending or rolling the martensitic stainless steel sheet, or first bending or rolling the martensitic stainless steel sheet and then welding it to prepare the martensitic stainless steel bent or rolled workpiece, determines whether annealing heat treatment is required to prevent the martensitic stainless steel from cracking during the bending or rolling process according to the mechanical properties of the martensitic stainless steel sheet or the matching degree between the martensitic stainless steel sheet and the welding wire during welding; specifically:

[0028] When bending or rolling martensitic stainless steel sheets to prepare bent or rolled workpieces, first test the mechanical properties of the martensitic stainless steel sheets and calculate the yield strength ratio. If the yield strength ratio is greater than 0.8, perform annealing heat treatment before bending or rolling, and perform bending or rolling after the annealing heat treatment is completed and the temperature is lowered to room temperature; if the yield strength ratio is ≤0.8, grind the edge of the sheet into a fillet before bending or rolling, and the fillet radius R is 4~10mm, and no annealing heat treatment is required;

[0029] When martensitic stainless steel sheets are first bent or rolled and then welded to prepare martensitic stainless steel bent or rolled workpieces, the mechanical properties of the martensitic stainless steel sheets are first tested and the yield strength ratio is calculated. If the yield strength ratio is greater than 0.8, annealing heat treatment is performed before rolling, and the sheet is rolled after the annealing heat treatment is completed and cooled to room temperature. If the yield strength ratio is ≤0.8, the edge of the sheet is ground into a fillet before bending or rolling, and the fillet radius R is 4~10mm, and no annealing heat treatment is required; then determine whether the welding wire used in welding is highly matched with the martensitic stainless steel sheet. If the welding wire is highly matched with the martensitic stainless steel sheet, If the martensitic stainless steel plate is highly matched, annealing heat treatment is required after welding, and rounding is performed after the annealing heat treatment is completed and cooled to room temperature. Otherwise, continue to detect the mechanical properties of the weld area of ​​the martensitic stainless steel bending or coil welding workpiece, and calculate the yield strength ratio. If the yield strength ratio is greater than 0.8, annealing heat treatment is required after welding, and rounding is performed after the annealing heat treatment is completed and cooled to room temperature. Otherwise, annealing heat treatment is not required after welding, but the edges of the martensitic stainless steel bending or coil welding workpiece are ground into fillets and then rounded, and the fillet radius R is 4~10mm.

[0030] The above annealing heat treatment is mainly used to eliminate the internal stress of the martensitic stainless steel material itself and reduce the yield strength ratio to reduce the possibility of fracture during bending or rolling.

[0031] The above-mentioned rounded corners are mainly used to reduce stress concentration during bending or rolling, so as to reduce the possibility of fracture caused by stress concentration during bending or rolling.

[0032] Specifically, the method for judging whether the welding wire used in welding is highly matched with the martensitic stainless steel plate in the present invention is: judging according to the material of the welding wire;

[0033] The chemical composition of the welding wire that is highly matched with the martensitic stainless steel plate is: by mass percentage, C≤0.06%, Si≤0.5%, Mn≤0.6%, P≤0.03%, S≤0.03%, Ni≤4.0%~5.0%, Cr≤11%~12.5%, Mo≤0.4%~0.7%, and the balance is Fe;

[0034] The chemical composition of the welding wire that is low-matched with the martensitic stainless steel plate is: in mass percentage, C≤0.12%, Si≤0.5%, Mn≤0.6%, P≤0.03%, S≤0.03%, Ni≤0.6%, Cr≤11.5%~13.5%, and the balance is Fe.

[0035] In a preferred embodiment of the present invention, the welding wire that is highly matched with the martensitic stainless steel plate is an ER410NiMo welding wire; and the welding wire that is moderately matched with the martensitic stainless steel plate is an ER410 welding wire.

[0036] Specifically, the process parameters of the annealing heat treatment in the present invention are:

[0037] The holding temperature is 720~770℃, the holding time is (T / 25)h and at least 1h; the furnace exit temperature is not higher than 300℃, and it is air-cooled to room temperature after being taken out of the furnace; and during the annealing heat treatment, the furnace entry temperature does not exceed 300℃, the heating rate does not exceed (5500 / T)℃ / h and does not exceed 220℃ / h, and the cooling rate does not exceed (5500 / T)℃ / h and does not exceed 280℃ / h; where T is the thickness, mm.

[0038] The present invention mainly transforms the residual quenched martensite in the martensitic stainless steel plate or the quenched martensite structure in the weld area into a tempered martensite structure through an annealing heat treatment process. For the quenched martensite structure, the lattice distortion is large, there are large pinning dislocations between the lattices, the dislocations are difficult to move, and the quenching stress is large. Therefore, the present invention transforms the uneven lattice with large distortion into a uniform equiaxed lattice through annealing heat treatment, the pinning dislocations between the lattices are reduced, the lattice distortion is small, thereby reducing the internal stress and the yield strength ratio, so that the material undergoes plastic deformation first when subjected to external force, and avoids brittle fracture. In addition, the holding temperature range is set to 720-770°C in the present invention. Below the phase transformation start temperature of martensitic stainless steel of 780-830°C, if the holding temperature exceeds the phase transformation temperature, the martensite and other structures in the martensitic stainless steel begin to transform into austenite structures. The austenite structure has coarse grains, few grain boundaries, and small grain boundary energy, which will cause the strength of the material to drop sharply, thereby affecting the mechanical properties of the material; the starting transformation temperature point of the quenched martensitic structure to the tempered martensitic structure is 710°C, and the cut-off temperature point is 780°C. If the holding temperature is lower than 720°C, the amount of the quenched martensitic structure transformed into the tempered martensitic structure is less, thereby retaining more quenched martensitic structures, and failing to improve the material structure properties and reduce the internal stress and yield strength ratio of the material itself.

[0039] The annealing heat treatment process provided by the present invention can reduce the yield strength ratio of the martensitic stainless steel sheet without changing the supply status of the martensitic stainless steel workpiece, thereby ensuring that its mechanical properties meet the supply requirements and that there is no need to perform heat treatment again to restore its mechanical properties.

[0040] In addition, when a martensitic stainless steel plate is first bent or rolled and then welded to prepare a martensitic stainless steel bent or rolled workpiece, the present invention also opens a double-sided double V-shaped groove at the joint of the martensitic stainless steel plate before bending or rolling, and the double-sided double V-shaped groove includes two symmetrically arranged double V-shaped grooves, and each double V-shaped groove includes a first V-shaped groove close to the center of the groove and a second V-shaped groove away from the center of the groove; wherein the groove surface angle of the first V-shaped groove is 10°~15°, and the groove surface angle of the second V-shaped groove is 45°~60°.

[0041] The first V-shaped groove adopts a small groove, which can reduce the welding amount, and the groove surface angle of the second V-shaped groove close to the outside is increased to more than 45°, which can reduce stress concentration and further prevent fracture during the rounding process after welding. If a common V-shaped groove is used, in order to reduce stress concentration, when the groove surface angle reaches 45°, the martensitic stainless steel plate needs to have a larger welding groove, and the welding amount of the welding groove is much greater than the welding amount of the double V-shaped groove of the present invention.

[0042] Example 1

[0043] This embodiment mainly studies the influence of different annealing heat treatment processes on the mechanical properties and bending properties of martensitic stainless steel plates and martensitic stainless steel welded plates, by preparing several samples for different heat treatments and testing the corresponding mechanical and bending properties.

[0044] The samples in this embodiment use 20Cr13 martensitic stainless steel plates from the same batch, the sample thickness is 25 mm, and two martensitic stainless steel plates are welded with ER410 welding wire and ER410NiMo welding wire with the same welding parameters, and the martensitic stainless steel plate (i.e., parent material), ER410 welding plate, and ER410NiMo welding plate are processed into several samples, and then heat treated according to the following annealing heat treatment scheme, and in each scheme, 2 samples are set for the martensitic stainless steel parent material, ER410 welding plate, and ER410NiMo welding plate.

[0045] Annealing heat treatment scheme:

[0046] Option 1: Heat treatment temperature is 630℃, holding time is 1h;

[0047] Option 2: Heat treatment temperature is 660℃, holding time is 1h;

[0048] Scheme 3: heat treatment temperature is 690℃, holding time is 1h;

[0049] Scheme 4: heat treatment temperature is 720℃, holding time is 1h;

[0050] Scheme 5: Heat treatment temperature is 750℃, holding time is 1h;

[0051] Option 6: Heat treatment temperature is 780℃ and holding time is 1h.

[0052] In the above schemes 1 to 6, the temperature entering the furnace is room temperature, the heating rate is 220°C / h, the cooling rate is 220°C / h, the temperature exiting the furnace is 300°C, and it is naturally cooled to room temperature after exiting the furnace.

[0053] Annealing heat treatment was carried out according to the above scheme. After the heat treatment was completed and cooled to room temperature, the mechanical properties were tested, as shown in Table 1. Groups 1, 2, and 3 in Table 1 correspond to martensitic stainless steel base material, ER410 welding plate, and ER410NiMo welding plate, respectively. Supply requirements for 20Cr13 martensitic stainless steel workpieces: tensile strength ≥520MPa, yield strength ≥225MPa, and elongation ≥18%.

[0054] Table 1 Mechanical properties and bending properties of martensitic stainless steel base material and welded plate under different annealing heat treatment processes

[0055]

[0056] From Table 1 above, it can be seen that: when the heat treatment temperature is 630~690℃, the yield strength ratio does not decrease significantly, still greater than 0.8, and the bending test is prone to fracture; when the heat treatment temperature is 720~780℃, the yield strength ratio decreases significantly, the bending test is qualified, and when the heat treatment temperature is 720~780℃, the mechanical properties of the sample can basically meet the supply requirements. Only at 780℃, a group of martensitic stainless steel tensile strength does not meet the requirements, slightly lower than the supply requirements. In actual production, in order to ensure that the mechanical properties of the workpiece can meet the supply requirements, the heat treatment temperature can be set to 720~770℃, and more preferably set to 720~750℃.

[0057] Example 2

[0058] In this embodiment, a martensitic stainless steel plate is used to prepare a bent workpiece. The martensitic stainless steel plate is specifically 20Cr13, and its alloy composition is C 0.2%, Si 0.38%, Mn 0.52%, P 0.022%, S 0.003%, Cr 13.13%, Ni0.06%, and the remainder is Fe and unavoidable impurities. The thickness is 25 mm.

[0059] The above martensitic stainless steel plate was sampled for mechanical property testing, and the tensile strength was 715MPa, the yield strength was 586MPa, and the yield strength ratio was 0.82.

[0060] The yield strength ratio of the martensitic stainless steel sheet is greater than 0.8, and it is first subjected to annealing heat treatment and then bent. Specifically, the martensitic stainless steel sheet is placed in an annealing furnace, and the martensitic stainless steel sheet sample is placed in the furnace. The furnace temperature is room temperature, the heating rate is 220℃ / h, the insulation temperature is 750℃, and the insulation time is 1h. After the insulation is completed, the temperature is reduced to 300℃ at a cooling rate of 220℃ / h and then taken out of the furnace. After being taken out of the furnace, it is naturally cooled to room temperature; after cooling, it is bent, and no fracture occurs during bending.

[0061] In addition, the mechanical properties of the samples heat treated in the furnace during the above annealing heat treatment were tested, and the tensile strength was 630MPa, the yield strength was 410MPa, and the yield strength ratio was 0.65. The mechanical property requirements of the 20Cr13 martensitic stainless steel supply are tensile strength ≥520MPa and yield strength ≥225MPa. The martensitic stainless steel bent parts prepared in this embodiment meet the requirements and do not break during the bending process.

[0062] Example 3

[0063] In this embodiment, a martensitic stainless steel plate is used to prepare a rolled workpiece, and welding is performed after the roll is rolled. The martensitic stainless steel plate specifically uses 12Cr13, and its alloy composition is C 0.14%, Si 0.47%, Mn 0.38%, P 0.019%, S 0.002%, Cr 11.73%, Ni 0.06%, and the thickness is 45 mm.

[0064] The above martensitic stainless steel plate was sampled for mechanical property testing, and the tensile strength was 609 MPa, the yield strength was 443 MPa, and the yield strength ratio was 0.73.

[0065] The yield strength ratio of the martensitic stainless steel sheet is less than 0.8, and it is first subjected to annealing heat treatment, and then rolled, welded, and rounded. Specifically, the martensitic stainless steel sheet is placed in an annealing furnace, and a martensitic stainless steel sheet sample is placed in the furnace. The furnace temperature is room temperature, the heating rate is 122℃ / h, the insulation temperature is 740℃, and the insulation time is 1.8h. After the insulation is completed, the temperature is cooled to 300℃ at a cooling rate of 100℃ / h and the furnace is naturally cooled to room temperature after being taken out of the furnace. After cooling, the martensitic stainless steel sheet and the martensitic stainless steel sheet sample in the furnace are rolled to obtain a martensitic stainless steel rolled workpiece and a martensitic stainless steel rolled sample. No fracture occurs during the rolling process; then E R410NiMo welding wire is used to weld the martensitic stainless steel coil workpiece and the martensitic stainless steel coil sample. The welding parameters are the same. After welding, the martensitic stainless steel coil welding workpiece and the martensitic stainless steel coil welding sample are annealed again. The furnace entry temperature is room temperature, the heating rate is 122℃ / h, the insulation temperature is 750℃, and the insulation time is 1.8h. After the insulation is completed, the temperature is cooled to 200℃ at a cooling rate of 100℃ / h and then taken out of the furnace. After being taken out of the furnace, it is naturally cooled to room temperature. After cooling, it is rounded. No weld fracture occurs during the rounding process.

[0066] Mechanical properties testing was performed on the weld area of ​​the martensitic stainless steel coil welding sample after the second annealing heat treatment after the above welding. The tensile strength was 786 MPa, the yield strength was 571 MPa, the yield strength ratio was 0.726, and no fracture occurred during the rounding process.

[0067] The mechanical properties of the base material area of ​​the martensitic stainless steel coil welding sample after the second annealing heat treatment after the above welding were tested, and the tensile strength was 575MPa and the yield strength was 390MPa. The mechanical properties of the 12Cr13 martensitic stainless steel supply require a tensile strength of ≥450MPa and a yield strength of ≥205MPa. The martensitic stainless steel coil welding workpiece prepared in this embodiment meets the requirements, and no fracture occurs during the coiling process and the rounding process.

[0068] It should be noted that, in this embodiment, the yield strength ratio of the martensitic stainless steel sheet is 0.73, and it may not be heat treated before being rolled, but the edges of both sides of the martensitic stainless steel sheet are rounded, and the rounded radius R is 6 mm, and then rolled. In this embodiment, heat treatment is performed before rolling to further reduce the yield strength ratio of the base material, but after welding with a highly matched ER410NiMo welding wire, fracture still occurs during the rounding process. Therefore, even if the yield strength ratio of the base material is reduced by heat treatment, heat treatment is still required after subsequent welding with a highly matched ER410NiMo welding wire.

[0069] In addition, refer to Figure 1 In this embodiment, before the roll is rolled, a welding groove is provided at the joint of the martensitic stainless steel plate. The welding groove is a double-sided double V-shaped groove, which includes two symmetrically arranged double V-shaped grooves, and each double V-shaped groove includes a first V-shaped groove 1 close to the groove center and a second V-shaped groove 2 far from the groove center; wherein the groove surface angle of the first V-shaped groove 1 is 10°, and the groove surface angle of the second V-shaped groove 2 is 45°. In this embodiment, the first V-shaped groove has a small angle, which can reduce the welding amount, and the groove surface angle of the second V-shaped groove close to the outside is increased to more than 45°, which can reduce stress concentration and further prevent fracture during the rounding process after welding.

[0070] Example 4

[0071] In this embodiment, a martensitic stainless steel plate is used to prepare a rolled workpiece. The martensitic stainless steel plate is specifically 12Cr13, and its alloy composition is C 0.13%, Si 0.46%, Mn 0.36%, P 0.022%, S 0.001%, Cr 11.54%, Ni 0.06%, and the thickness is 40 mm.

[0072] The above martensitic stainless steel plate was sampled for mechanical property testing, and its tensile strength was 648MPa, yield strength was 480MPa, and yield strength ratio was 0.74.

[0073] The above martensitic stainless steel sheet was directly rolled without heat treatment, and there were slight cracks around the edge of the cylinder. The edges of both sides of the martensitic stainless steel sheet were rounded in advance, and the radius R of the rounded corners was 6mm, and then rolled, and no small cracks were generated.

[0074] Example 5

[0075] In this embodiment, the crack-free rolled workpiece prepared in Example 4 is welded. ER410 welding wire is used for welding. The tensile strength of the weld area is 530 MPa, the yield strength is 378 MPa, and the yield strength ratio is 0.71. The edges of the rolled workpiece are rounded with a fillet radius R of 10 mm. Rounding is performed directly without heat treatment, and no cracks or fractures occur.

[0076] Comparative Example 1

[0077] This comparative example uses the same martensitic stainless steel plate as in Example 2, but does not undergo annealing heat treatment and is directly bent (cold bent), resulting in fracture.

[0078] Comparative Example 2

[0079] This comparative example uses the same martensitic stainless steel plate as in Example 3, which is subjected to the same annealing heat treatment as in Example 3 before being rolled, but the rolled workpiece is not subjected to annealing heat treatment after welding, but is directly rounded after welding, during which fracture occurs in the weld area.

[0080] This comparative example also carries out mechanical property testing on the weld area which has not been annealed and heat treated, and the tensile strength is 896MPa, the yield strength is 822MPa, and the yield strength ratio is 0.917. The yield strength ratio is large after welding, and it is easy to break during roundness calibration.

[0081] Comparative Example 3

[0082] The difference between this comparative example and comparative example 2 is that, in this comparative example, after the roll workpiece is welded, the edge of the roll workpiece is ground and rounded with a radius of 5 mm, and then rounding is performed, during which the weld area is fractured.

[0083] Comparative Example 4

[0084] The difference between this comparative example and Example 3 is that in this comparative example, the welding groove is Figure 1 The double-sided double V-shaped groove shown in the embodiment has a groove surface angle of 10° for the first V-shaped groove 1 and a groove surface angle of 35° for the second V-shaped groove 2. The rest is the same as that of the embodiment 3.

[0085] During the rounding process of this comparative example 4, part of the weld area broke.

[0086] It should be noted that some parts not described in the present invention can be implemented by adopting or drawing on existing technologies.

[0087] Of course, the above description is not a limitation of the present invention, and the present invention is not limited to the above examples. Changes, modifications, additions or substitutions made by technicians in this technical field within the essential scope of the present invention should also fall within the protection scope of the present invention.

Claims

1. A crack prevention heat treatment process for a martensitic stainless steel bending or rolling workpiece, characterized in that: Before bending or rolling the martensitic stainless steel sheet, or before bending or rolling the martensitic stainless steel sheet and then welding it to prepare a martensitic stainless steel bent or rolled workpiece, annealing heat treatment is performed to prevent the martensitic stainless steel from cracking during bending or rolling; The process parameters of annealing heat treatment are: holding temperature of 720~770℃, holding time of (T / 25)h and at least 1h, furnace temperature not higher than 300℃, air cooling to room temperature after furnace; where T is thickness, mm; Before preparing martensitic stainless steel bending or coiling workpieces, it is necessary to determine whether annealing heat treatment is required based on the mechanical properties of the martensitic stainless steel sheet or the matching degree between the martensitic stainless steel sheet and the welding wire during welding. Specifically: When bending or rolling martensitic stainless steel sheets to prepare bent or rolled workpieces, first test the mechanical properties of the martensitic stainless steel sheets and calculate the yield strength ratio. If the yield strength ratio is greater than 0.8, perform annealing heat treatment before bending or rolling, and perform bending or rolling after the annealing heat treatment is completed and the temperature is lowered to room temperature. When a martensitic stainless steel plate is first bent or rolled and then welded to prepare a martensitic stainless steel bent or rolled workpiece, the mechanical properties of the martensitic stainless steel plate are first detected, and the yield strength ratio is calculated. If the yield strength ratio is greater than 0.8, annealing heat treatment is performed before bending or rolling, and bending or rolling is performed after the annealing heat treatment is completed and the temperature is lowered to room temperature; then, it is determined whether the welding wire used in welding is highly matched with the martensitic stainless steel plate. If the welding wire is highly matched with the martensitic stainless steel plate, annealing heat treatment is required after welding, and rounding is performed after the annealing heat treatment is completed and the temperature is lowered to room temperature; otherwise, the mechanical properties of the weld area of ​​the martensitic stainless steel bent or rolled welded workpiece are continuously detected, and the yield strength ratio is calculated. If the yield strength ratio is greater than 0.8, annealing heat treatment is required after welding, and rounding is performed after the annealing heat treatment is completed and the temperature is lowered to room temperature; The martensitic stainless steel bending or rolling workpiece includes the following alloy components by mass percentage: C 0.10%~0.25%, Si≤1.0%, Mn 0.3%~1.0%, P≤0.04%, S≤0.03%, Ni≤0.6%, Cr 11.5%~14.0%, and the balance is Fe and unavoidable impurities; The method for judging whether the welding wire used in welding is highly matched with the martensitic stainless steel plate is: judging according to the material of the welding wire; The chemical composition of the welding wire that is highly matched with the martensitic stainless steel plate is: in mass percentage, C≤0.06%, Si≤0.5%, Mn≤0.6%, P≤0.03%, S≤0.03%, Ni≤4.0%~5.0%, Cr≤11%~12.5%, Mo≤0.4%~0.7%, and the balance is Fe.

2. The anti-cracking heat treatment process for a martensitic stainless steel bent or rolled workpiece according to claim 1, characterized in that: During the annealing heat treatment process, the furnace temperature shall not exceed 300°C, the heating rate shall not exceed (5500 / T)°C / h and shall not exceed 220°C / h; the cooling rate shall not exceed (5500 / T)°C / h and shall not exceed 280°C / h.

3. The anti-cracking heat treatment process for a martensitic stainless steel bent or rolled workpiece according to claim 1, characterized in that: When a martensitic stainless steel bent or rolled workpiece is prepared by first bending or rolling a martensitic stainless steel sheet and then welding it, a welding groove needs to be opened at the joint of the martensitic stainless steel sheet before bending or rolling. The welding groove is a double-sided double V-shaped groove, and the double-sided double V-shaped groove includes two symmetrically arranged double V-shaped grooves, and each double V-shaped groove includes a first V-shaped groove close to the center of the groove and a second V-shaped groove away from the center of the groove.

4. The anti-cracking heat treatment process for a martensitic stainless steel bent or rolled workpiece according to claim 3, characterized in that: The groove surface angle of the first V-shaped groove is 10°~15°, and the groove surface angle of the second V-shaped groove is 45°~55°.

5. The anti-cracking heat treatment process for a martensitic stainless steel bent or rolled workpiece according to claim 1, characterized in that: The material of the martensitic stainless steel bending or rolling workpiece is 12Cr13 or 20Cr13.

6. The anti-cracking heat treatment process for a martensitic stainless steel bent or rolled workpiece according to claim 1, characterized in that: The welding wire that is highly matched with martensitic stainless steel plate is ER410NiMo welding wire.

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