A hot deformation method for high alloy martensitic stainless steel and stainless steel

Abstract

The invention provides a hot deformation method for high-alloy martensitic stainless steel, which comprises: homogenizing a high-alloy martensitic stainless steel ingot; performing fast forging on the homogenized ingot, wherein the start forging temperature is not less than 1050°C, the final forging temperature is not less than 900°C, the fast forging deformation is controlled at 50-70%, and the forging is annealed after slow cooling; performing fine forging on the forging after the fast forging, wherein the start forging temperature is not less than 1050°C, the final forging temperature is not less than 900°C, the fine forging deformation is controlled at 50-70%, and the forging is annealed after cooling; rolling the forging after the fine forging, wherein the start rolling temperature is not less than 1050°C, the final rolling temperature is not less than 900°C, the rolling deformation is controlled at 80-95%, cooling after rolling, and then annealing or normalizing. The method can obtain a material with fine grains and uniform structure by comprehensively controlling the homogenization treatment, forging and rolling operations of the ingot. The invention also provides a high-alloy martensitic stainless steel prepared by the hot deformation method.

Description

Technical Field

[0001] The invention belongs to the technical field of stainless steel hot working deformation, and particularly relates to a hot deformation method of high alloy martensitic stainless steel and the stainless steel prepared by the method. Background Art

[0002] In order to meet the demand for structural materials in the rapid development of the aviation industry, a new type of high-alloy ultra-high strength steel has been developed. Ultra-high strength steel is widely used in the manufacture of various parts used in aerospace due to its high strength and toughness. For high-strength martensitic stainless steel, due to the addition of high content of alloy elements such as Cr, Mo, and V, the complex alloy ratio makes it easy for the steel ingot to produce element segregation during the solidification process, and at the same time, the solidification forms an equiaxed crystal area-columnar crystal area-coarse equiaxed crystal area structure, which makes it easy to produce cracks and uneven grain size during thermal deformation, thereby affecting the comprehensive performance of the material.

[0003] In industrial production, hot working deformation is often used to change the size of ingots, control the internal structure of materials, and eliminate metallurgical defects. However, for martensitic stainless steel with high Cr, Mo, and V alloy content, due to the high content of alloy elements added inside the material, the material is prone to form precipitation phases during heating, and dynamic recrystallization occurs inside the material during hot deformation. If the hot working process is not set properly, it will cause problems such as uneven internal structure of the finished steel product and hot deformation cracking.

[0004] Therefore, the process technology for hot deformation of high alloy martensitic stainless steel grades still needs to be improved. Summary of the invention

[0005] In order to solve the existing technical problems, the present invention proposes a hot deformation method for high-alloy martensitic stainless steel, which can obtain a material with fine grains and uniform structure by comprehensively controlling the homogenization treatment, forging and rolling operations of the ingot. The present invention also provides a high-alloy martensitic stainless steel prepared by the hot deformation method.

[0006] According to one aspect of the present invention, a method for hot deformation of high alloy martensitic stainless steel is provided, the method comprising the following steps:

[0007] homogenizing a high alloy martensitic stainless steel ingot;

[0008] The homogenized ingot is subjected to rapid forging treatment, the starting forging temperature is not less than 1050°C, the final forging temperature is not less than 900°C, the forging deformation is controlled at 50-70%, and the forging is annealed after slow cooling;

[0009] The forgings after rapid forging are subjected to fine forging treatment, the starting forging temperature is not less than 1050°C, the final forging temperature is not less than 900°C, the forging deformation is controlled at 50-70%, and the forgings are annealed after cooling;

[0010] The forgings after fine forging are rolled, the starting rolling temperature is not less than 1050°C, the final rolling temperature is not less than 900°C, the rolling deformation is controlled at 80-95%, and after rolling, they are cooled and then annealed or normalized.

[0011] According to one embodiment of the present invention, the composition system of high alloy martensitic stainless steel includes, by mass percentage: C: 0.10-0.15, Cr: 10.0-15.0, Co: 10.0-14.0, Mo: 4.0-8.0, Ni: 1.5-3.0, V: 0.50-1.0, Nb: 0.01-0.05, and the rest is Fe and unavoidable impurities.

[0012] According to one embodiment of the present invention, the homogenization treatment comprises: heating the high alloy martensitic stainless steel ingot to 1050-1200° C. and keeping the temperature therefor for not less than 72 hours.

[0013] According to one embodiment of the present invention, the method further includes heating the homogenized ingot to 1150-1200°C for insulation before subjecting the homogenized ingot to rapid forging treatment, and the insulation time is not less than 5 hours; and heating the forging to 1150-1200°C for insulation before subjecting the rapid forging to fine forging treatment, and the insulation time is controlled within 3-5 hours.

[0014] According to one embodiment of the present invention, the rapid forging process includes the following operations:

[0015] The initial forging temperature of the first fire is set at 1050-1150℃, the deformation is controlled at 70-90%, and the furnace is kept warm for no less than 2 hours;

[0016] The second forging temperature is set at 1080-1150℃, the deformation is controlled at 70-90%, and the furnace is kept warm for no less than 2 hours;

[0017] The forging is stretched in the third fire, the initial forging temperature is set at 1080-1150°C, and the deformation is controlled at 50-65%.

[0018] Thermal simulation shows that the high alloy martensitic stainless steel involved in the present invention has good high temperature thermoplasticity in the temperature range of 900-1200°C, so forging within this temperature range can prevent forging cracks.

[0019] According to one embodiment of the present invention, the forging after rapid forging is slowly cooled to a temperature not higher than 100°C and then annealed, and the annealing temperature is controlled at 500-650°C.

[0020] According to one embodiment of the present invention, the precision forging process comprises performing multiple forging passes on the forging, wherein the deformation amount of each pass is controlled within a range of 10 to 30%, and the total deformation amount is controlled within a range of 50 to 70%.

[0021] According to one embodiment of the present invention, the rolling comprises performing multiple rolling passes on the forging, the deformation amount of each pass is controlled within 15-30%, and the total deformation amount is controlled within 80-95%.

[0022] According to one embodiment of the present invention, the ingot is produced by a double vacuum melting process combining vacuum induction and vacuum self-consumption, and the ingot diameter is 300-510 mm. The double vacuum smelting technology is used to control the impurity elements such as S, P, gas and five harmful elements in the steel at an extremely low level, while ensuring that the inclusions are small in size, small in number and evenly distributed.

[0023] According to one embodiment of the present invention, before rolling the forged piece after the fine forging treatment, the forged piece is heated to 1130-1180° C. and kept warm for 2-6 hours.

[0024] According to one embodiment of the present invention, after the fine forging process, the forging is cooled to room temperature and then annealed.

[0025] According to one embodiment of the present invention, after rolling, the forging is cooled to room temperature and then annealed or normalized.

[0026] According to one embodiment of the present invention, the annealing temperature of the annealing treatment in the method is 500-650°C.

[0027] According to one embodiment of the present invention, the normalizing temperature of the normalizing treatment in the method is 900-1000°C.

[0028] According to another aspect of the present invention, a high-alloy martensitic stainless steel is provided. The high-alloy martensitic stainless steel is subjected to heat deformation treatment by the heat treatment method described in any one of the above embodiments, wherein the grain size of the high-alloy martensitic stainless steel is not less than level 7 and the grain size difference is not higher than level 1.

[0029] By adopting the above technical scheme, through the reasonable control of process parameters such as hot working time, temperature and deformation, the high alloy martensitic stainless steel is subjected to multiple high temperature and large deformation treatments. Under the condition of a small forging ratio, the billet as a whole is deformed to a certain extent and the core is guaranteed to have a large deformation, so as to prevent the forging from having uneven structures such as coarse grains and mixed grains. After forging and rolling deformation, the high alloy martensitic stainless steel has a uniform structure without low-magnification defects such as looseness, shrinkage, and cracks. At the same time, its grain size is guaranteed to be ≥7 levels, and the grain size difference is ≤1 level, with high structural uniformity. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 is a flow chart of a hot deformation method of high alloy martensitic stainless steel according to the present invention;

[0031] Figure 2 The microstructure metallographic diagram of the high alloy martensitic stainless steel according to Example 2 of the present invention;

[0032] Figure 3 is the microstructure metallographic diagram of the martensitic stainless steel in Comparative Example 1;

[0033] Figure 4 This is the microstructure metallographic diagram of the martensitic stainless steel in Comparative Example 2. DETAILED DESCRIPTION

[0034] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with embodiments. 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.

[0035] The present invention provides a method for hot deformation of high alloy martensitic stainless steel and high alloy martensitic stainless steel prepared by the method. The composition system of the high alloy martensitic stainless steel includes, by mass percentage, C: 0.10-0.15, Cr: 10.0-15.0, Co: 10.0-14.0, Mo: 4.0-8.0, Ni: 1.5-3.0, V: 0.50-1.0, Nb: 0.01-0.05, and the rest is Fe and unavoidable impurities. For this type of martensitic stainless steel with high Cr, Mo, and V alloy content, due to the high content of alloy elements added inside the material, the material forms a precipitate phase during heating and temperature rise, and dynamic recrystallization occurs inside the material during the hot deformation process. If the hot processing process is not properly set, it will cause problems such as uneven internal structure of the finished steel product and hot deformation cracking. The present invention targets such martensitic stainless steel with high Cr, Mo and V alloy contents, and performs multiple high-temperature large deformation treatments on the martensitic stainless steel by reasonably controlling the process parameters such as the processing sequence, time, temperature and deformation amount of the hot deformation. Under the condition of a relatively small forging ratio, the blank is deformed as a whole and the core is ensured to have a relatively large deformation amount, so as to prevent the forging from having uneven structures such as coarse grains and mixed grains. After forging and rolling deformation, the structure is uniform without low-magnification defects such as looseness, shrinkage cavities and cracks, and at the same time, the grain size is ensured to be ≥7 levels, and the grain size difference is ≤1 level, with high structural uniformity.

[0036] Figure 1 A flow chart showing a hot deformation method of high alloy martensitic stainless steel according to the present invention is shown.

[0037] As shown in the figure, in step S1, the high alloy martensitic stainless steel ingot is homogenized. The specific operation of the homogenization treatment is to heat the ingot to 1050-1200°C for insulation, and the insulation time is not less than 72 hours. Homogenization of the ingot before forging can make the composition and organization distribution of the ingot more uniform and alleviate the situation of component segregation.

[0038] In step S2, the homogenized ingot is subjected to rapid forging. The starting forging temperature of the rapid forging treatment is not less than 1050°C, the final forging temperature is not less than 900°C, the forging deformation is controlled at 50-70%, and the forging is slowly cooled to room temperature and then heated to 500-650°C for insulation annealing. For high-alloy martensitic stainless steel, the forging method of multiple upsetting and then drawing can effectively break the structure in the ingot at the heating temperature to obtain a fine and uniform grain structure. The purpose of the first upsetting is to ensure that the billet size and stress state required for the second upsetting are ensured, so that the steel ingot is fully forged through and the basic task of the main deformation is completed. The purpose of the second upsetting is to ensure that the billet reaches the size required for the forging; to keep the billet in the best stress and strain state at all times, so as to avoid the defects of the forging during the first upsetting being pulled apart or new forging defects being generated; the above process steps are adopted to make the billet as a whole have a certain deformation and ensure that the core has a large deformation, so as to prevent the forging from having uneven structures such as coarse grains and mixed grains.

[0039] In some embodiments of the present invention, the rapid forging process may include multiple forgings. In the first forging, the initial forging temperature is set at 1050-1150°C, the deformation is controlled at 70-90%, and the furnace is kept warm for not less than 2 hours; the initial forging temperature is set at 1080-1150°C, the deformation is controlled at 70-90%, and the furnace is kept warm for not less than 2 hours; the forging is stretched in the third forging, the initial forging temperature is set at 1080-1150°C, and the deformation is controlled at 50-60%. Thermal simulation shows that the high-alloy martensitic stainless steel involved in the present invention has good high-temperature thermoplasticity in the temperature range of 900-1100°C, so forging within this temperature range can prevent the forging from cracking.

[0040] In step S3, the forging after rapid forging is subjected to fine forging. The start forging temperature of the fine forging is not less than 1050°C, the final forging temperature is not less than 900°C, the forging deformation is controlled at 50-70%, and the forging is heated to 500-650°C for insulation annealing after cooling to room temperature. During the fine forging process, the forging is subjected to multiple forging passes, and the deformation of each pass is controlled at 10-30%, and the total deformation is controlled at 50-70%. The rapid forging process causes a large deformation in the core of the forging, but the deformation on the surface of the forging is small. When only the rapid forging process is used, the structure of the forging close to the surface is relatively coarse. The fine forging process can improve the organizational morphology of the forging close to the surface, so that the grains on the surface become fine and uniform. Moreover, the shape and size of the forging can be processed to meet the required requirements through fine forging.

[0041] In step S4, the forgings after fine forging are rolled. The starting rolling temperature is not less than 1050°C, the final rolling temperature is not less than 900°C, the rolling deformation is controlled at 80-95%, and the forging is cooled to room temperature after rolling, and then annealing or normalizing is performed. The annealing temperature of the annealing treatment is 500-650°C, and the normalizing temperature of the normalizing treatment is 900-1000°C. The rolling may include multiple passes of the forging, with the deformation of each pass controlled at 15-30%, and the total deformation controlled at 80-95%.

[0042] In some embodiments of the present invention, the homogenized ingot is heated to 1150-1200° C. and kept warm for not less than 5 hours before being subjected to rapid forging.

[0043] In some embodiments of the present invention, before the forgings after rapid forging are subjected to finish forging, the forgings are heated to 1150-1200° C. for insulation, and the insulation time is controlled to be 3-5 hours.

[0044] In some embodiments of the present invention, before rolling the forging after the fine forging treatment, the forging is heated to 1130-1180° C. and kept warm for 2 hours.

[0045] In some embodiments of the present invention, the ingot is produced by a double vacuum melting process combining vacuum induction and vacuum self-consumption, and the ingot diameter is 300-510 mm. The double vacuum smelting technology is used to control the impurity elements such as S, P, gas and five harmful elements in the steel at an extremely low level, while ensuring that the inclusions are small in size, small in number and evenly distributed.

[0046] The following are specific examples of the thermal processing method according to the present invention.

[0047] Example 1

[0048] In this embodiment, the high alloy martensitic stainless steel composition system includes, by mass percentage, C: 0.10, Cr: 10.0, Co: 10.0, Mo: 4.0, Ni: 1.5, V: 0.50, Nb: 0.01, and the rest is Fe and unavoidable impurities. The materials of the above composition are melted by vacuum induction + vacuum consumable to obtain a martensitic stainless steel ingot with a diameter of 508 mm. The above ingot is hot-worked in the following manner:

[0049] (1) Homogenization treatment: The martensitic stainless steel ingot is heated to 1100°C and kept warm for 80 hours;

[0050] (2) Preheating before forging: After high-temperature homogenization is completed, the furnace temperature is reduced to 1050°C, kept at this temperature for 1 hour, and then raised to 1150±10°C, kept at this temperature for 6 hours before being taken out of the furnace for forging;

[0051] (3) Fast forging: First fire, the start forging temperature is 1050℃, the final forging temperature is 900℃, the first fire deformation is controlled at 70%, and then returned to the furnace for 2h, the furnace temperature is 1150±10℃;

[0052] The second fire, the start forging temperature is 1080℃, the final forging temperature is 900℃, the deformation of the second fire is controlled at 90%, and then returned to the furnace for 2h, the furnace temperature is 1150±10℃;

[0053] The third fire, the start forging temperature is 1080℃, the final forging temperature is 900℃, slowly cooled to 100℃ and then annealed, the third fire deformation is 60%, and the annealing temperature is 500℃;

[0054] (4) Finish forging: Heat the forging to 1150±20℃, keep it warm for 4h and then forge it out of the furnace. The starting forging temperature is 1050℃ and the final forging temperature is 900℃. Perform four deformations, and the deformation of each pass is controlled at about 10%. The total deformation is about 50%. Slowly cool it to room temperature and then anneal it. The annealing temperature is 520℃.

[0055] (5) Rolling: Heat the forging to 1150±20℃, keep it warm for 2h, start rolling at 1050℃, and finish rolling at 900℃. The diameter of the bar after rolling is 60mm. After cooling to room temperature, anneal at 550℃.

[0056] After adopting the high temperature and large deformation process combining the above-mentioned rapid forging, precision forging and rolling, the rolled bar has uniform structure, no low-magnification defects such as looseness, shrinkage holes, cracks, etc., the grain size is 7.5, and the grain size difference is 1 level.

[0057] Mechanical properties after heat treatment: tensile strength 1922MPa, yield strength 1222MPa, impact toughness 60J.

[0058] Example 2

[0059] In this embodiment, the high alloy martensitic stainless steel composition system includes, by mass percentage, C: 0.12, Cr: 13.0, Co: 12.0, Mo: 6.0, Ni: 2.5, V: 0.80, Nb: 0.03, and the rest is Fe and unavoidable impurities. The materials of the above composition are melted by vacuum induction + vacuum consumable to obtain a martensitic stainless steel ingot with a diameter of 508 mm. The above ingot is hot-worked in the following manner:

[0060] (1) Homogenization treatment: The martensitic stainless steel ingot is heated to 1050°C and kept warm for 96 hours;

[0061] (2) Preheating before forging: After high-temperature homogenization is completed, the homogenized ingot is placed in a heating furnace and heated to 1180±10℃. After keeping the temperature for 5 hours, it is taken out of the furnace for forging;

[0062] (3) Fast forging: First fire, start forging temperature is 1100℃, final forging temperature is 900℃, first fire deformation is 90%, then return to the furnace for 3h, furnace temperature is 1150±10℃;

[0063] Second fire, the starting forging temperature is 1100℃, the final forging temperature is 900℃, the second fire deformation is 70%, and then it is returned to the furnace for insulation for 3h, and the furnace temperature is 1150±10℃;

[0064] The third fire, the start forging temperature is 1100℃, the final forging temperature is 900℃, slowly cooled to 100℃ and then annealed, the third fire deformation is 60%, and the annealing temperature is 550℃;

[0065] (4) Finish forging: Heat the forging to 1150±20℃, keep it warm for 2h and then forge it out of the furnace. The starting forging temperature is 1050℃, the final forging temperature is 900℃, and four deformation passes are performed. The deformation of each pass is controlled at about 17%, and the total deformation is about 68%. After slowly cooling to room temperature, annealing is performed at 600℃.

[0066] (5) Rolling: Heat the forging to 1150±20℃ and keep it for 4h. The starting rolling temperature is 1100℃ and the final rolling temperature is 950℃. The diameter of the bar after rolling is 60mm. After cooling to room temperature, anneal it at 550℃.

[0067] After adopting the high temperature large deformation process combining rapid forging, precision forging and rolling, the rolled bar structure is as follows: Figure 2 As shown, the rod has uniform structure, no low-magnification defects such as looseness, shrinkage holes, cracks, etc., the grain size is level 7, and the grain size difference is level 1.

[0068] Mechanical properties after heat treatment: tensile strength 1830MPa, yield strength 1290MPa, impact toughness 70J.

[0069] Example 3

[0070] In this embodiment, the high alloy martensitic stainless steel composition system includes, by mass percentage, C: 0.15, Cr: 15.0, Co: 14.0, Mo: 8.0, Ni: 3.0, V: 1.0, Nb: 0.05, and the rest is Fe and unavoidable impurities. The materials of the above composition are melted by vacuum induction + vacuum consumable to obtain a martensitic stainless steel ingot with a diameter of 508 mm. The above ingot is hot-worked in the following manner:

[0071] (1) Homogenization treatment: The martensitic stainless steel ingot is heated to 1200°C and kept warm for 72 hours;

[0072] (2) Preheating before forging: After high-temperature homogenization is completed, the furnace temperature is reduced to 1050°C, kept at this temperature for 1 hour, and then raised to 1200°C, kept at this temperature for 5 hours before being taken out of the furnace for forging;

[0073] (3) Fast forging: First fire, start forging temperature is 1150℃, final forging temperature is 950℃, first fire deformation is 80%, then return to the furnace for 3h, furnace temperature is 1200℃;

[0074] The second fire, the start forging temperature is 1150℃, the final forging temperature is 900℃, the second fire deformation is 80%, and then it is returned to the furnace for 2h, and the furnace temperature is 1200℃;

[0075] The third fire, the start forging temperature is 1150℃, the final forging temperature is 900℃, slowly cooled to 100℃ and then annealed, the third fire deformation is 55%, and the annealing temperature is 650℃;

[0076] (4) Finish forging: Heat the forging to 1200°C, keep it warm for 3 hours and then forge it out of the furnace. The starting forging temperature is 1050°C and the final forging temperature is 900°C. Perform three deformations, with the deformation of each pass controlled at about 20% and the total deformation of about 60%. Slowly cool it to room temperature and then anneal it at a temperature of 550°C.

[0077] (5) Rolling: The forging is heated to 1150°C and kept at this temperature for 2 h. The starting rolling temperature is 1100°C and the final rolling temperature is 900°C. The diameter of the bar after rolling is about 50 mm. After cooling to room temperature, annealing is performed at 580°C.

[0078] After adopting the high temperature and large deformation process combining the above-mentioned rapid forging, precision forging and rolling, the rolled bar has uniform structure, no low-magnification defects such as looseness, shrinkage holes, cracks, etc., the grain size is 8 levels, and the grain size difference is 1 level.

[0079] Mechanical properties after heat treatment: tensile strength 1850MPa, yield strength 1280MPa, impact toughness 75J.

[0080] Comparative Example 1

[0081] The composition ratio of the martensitic stainless steel used in this comparative example is the same as that in Example 2, that is, the high alloy martensitic stainless steel composition system includes, by mass percentage, C: 0.15, Cr: 15.0, Co: 14.0, Mo: 8.0, Ni: 3.0, V: 1.0, Nb: 0.05, and the rest is Fe and unavoidable impurities. The materials of the above composition are melted by vacuum induction + vacuum consumable to obtain a martensitic stainless steel ingot with a diameter of 508 mm. The above ingot is hot-worked in the following manner:

[0082] (1) Homogenization treatment: The martensitic stainless steel ingot is heated to 1050°C and kept warm for 72 hours;

[0083] (2) Preheating before forging: After high-temperature homogenization is completed, the homogenized ingot is placed in a heating furnace and heated to 1180±10℃. After keeping the temperature for 5 hours, it is taken out of the furnace for forging;

[0084] (3) Fast forging: First fire, start forging temperature is 1100℃, final forging temperature is 900℃, first fire deformation is 70%, then return to the furnace for 3h, furnace temperature is 1150±10℃;

[0085] Second fire, the starting forging temperature is 1100℃, the final forging temperature is 900℃, the second fire deformation is 90%, then return to the furnace for 3h, the furnace temperature is 1150±10℃;

[0086] For the third fire, the starting forging temperature is 1100℃, the final forging temperature is 900℃, and it is annealed after slow cooling to 100℃. The deformation of the third fire is 50% and the annealing temperature is 550℃.

[0087] Figure 3 The microstructure metallographic diagram of the high alloy martensitic stainless steel obtained by the above-mentioned hot working method is shown. It can be seen from the figure that after deformation, there are still problems such as mixed crystals and uneven structure in the structure, and the grain size is uneven and the size difference is significant.

[0088] Comparative Example 2

[0089] The composition ratio of the martensitic stainless steel used in this comparative example is the same as that in Example 2, that is, the high alloy martensitic stainless steel composition system includes, by mass percentage, C: 0.15, Cr: 15.0, Co: 14.0, Mo: 8.0, Ni: 3.0, V: 1.0, Nb: 0.05, and the rest is Fe and unavoidable impurities. The materials of the above composition are melted by vacuum induction + vacuum consumable to obtain a martensitic stainless steel ingot with a diameter of 508 mm. The above ingot is hot-worked in the following manner:

[0090] (1) Homogenization treatment: The martensitic stainless steel ingot is heated to 1050°C and kept warm for 72 hours;

[0091] (2) Preheating before forging: After high-temperature homogenization is completed, the homogenized ingot is placed in a heating furnace and heated to 1180±10℃. After keeping the temperature for 5 hours, it is taken out of the furnace for forging;

[0092] (3) Fast forging: First fire, start forging temperature is 1100℃, final forging temperature is 900℃, first fire deformation is 80%, then return to the furnace for 3h, furnace temperature is 1150±10℃;

[0093] Second fire, the starting forging temperature is 1100℃, the final forging temperature is 900℃, the second fire deformation is 70%, then return to the furnace for 3h, the furnace temperature is 1150±10℃;

[0094] The third fire, the start forging temperature is 1100℃, the final forging temperature is 900℃, slowly cooled to 100℃ and then annealed, the third fire deformation is 60%, and the annealing temperature is 550℃;

[0095] (4) Finish forging: Heat the forging to 1150±20℃, keep it warm for 2h and then forge it out of the furnace. The start forging temperature is 1050℃ and the final forging temperature is 900℃. Perform four deformation passes, and the deformation of each pass is controlled at about 12%. The total deformation is about 48%. Slowly cool it to room temperature and then anneal it at 600℃.

[0096] Figure 4 The microstructure of the high alloy martensitic stainless steel obtained by the above heat treatment method is shown in Figure 1. As can be seen from the figure, the microstructure after the above heat treatment is relatively uniform, but the grain size is large and the problem of mixed crystals still exists.

[0097] Therefore, the hot deformation method of the present invention can be used to obtain a high-alloy martensitic stainless steel material with fine grains and uniform structure.

[0098] The above embodiments only express the implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the present invention. It should be pointed out that, for those of ordinary skill in the art, several modifications and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the present invention patent shall be subject to the attached claims.

Claims

1. A method for hot deformation of high alloy martensitic stainless steel, characterized in that: The following steps are involved: The high alloy martensitic stainless steel ingot is homogenized, wherein the high alloy martensitic stainless steel composition system comprises, by mass percentage, C: 0.10-0.15, Cr: 10.0-15.0, Co: 10.0-14.0, Mo: 4.0-8.0, Ni: 1.5-3.0, V: 0.50-1.0, Nb: 0.01-0.05, and the rest is Fe and unavoidable impurities; The homogenized ingot is subjected to rapid forging treatment, the start forging temperature is not less than 1050°C, the final forging temperature is not less than 900°C, the forging deformation is controlled at 50-70%, and the forging is annealed after slow cooling. The rapid forging treatment includes the following operations: The initial forging temperature of the first fire is set at 1050~1150℃, the deformation is controlled at 70~90%, and the furnace is kept warm for no less than 2 hours; The second forging temperature is set at 1080~1150℃, the deformation is controlled at 70~90%, and the furnace is kept warm for no less than 2 hours; The forging is stretched in the third fire, the initial forging temperature is set at 1080~1150℃, and the deformation is controlled at 50%~65%; The forgings after quick forging are subjected to fine forging treatment, the starting forging temperature is not less than 1050℃, the final forging temperature is not less than 900℃, the forging deformation is controlled at 50~70%, and the forgings are annealed after cooling; The forgings after fine forging are rolled, the starting rolling temperature is not less than 1050℃, the final rolling temperature is not less than 900℃, the rolling deformation is controlled at 80~95%, and after rolling, they are cooled and then annealed or normalized.

2. The method according to claim 1, characterized in that The homogenization treatment comprises: heating the high alloy martensitic stainless steel ingot to 1050-1200° C. and keeping the temperature for not less than 72 hours.

3. The method according to claim 1, characterized in that It further includes heating the homogenized ingot to 1150-1200°C for insulation before the rapid forging treatment, and the insulation time is not less than 5 hours, and heating the forging after rapid forging to 1150-1200°C for insulation before the fine forging treatment, and the insulation time is controlled within 3h-5h.

4. The method according to claim 1, characterized in that: After the rapid forging treatment, the forging is slowly cooled to a temperature not higher than 100° C. and then annealed. The annealing temperature is controlled at 500-650° C.

5. The method according to claim 1, characterized in that The precision forging process comprises performing multiple forging passes on the forging, wherein the deformation amount of each pass is controlled within 10-30%, and the total deformation amount is controlled within 50-70%.

6. The method according to claim 1, characterized in that The rolling comprises rolling the forging piece in multiple passes, wherein the deformation of each pass is controlled within 15-30%, and the total deformation is controlled within 80-95%.

7. The method according to claim 1, characterized in that The ingot is produced by a double vacuum melting process combining vacuum induction and vacuum self-consumption, and the ingot diameter is 300-510 mm.

8. A high alloy martensitic stainless steel, characterized in that: The high alloy martensitic stainless steel is subjected to hot deformation treatment by the hot deformation method according to any one of claims 1 to 7, wherein the grain size of the high alloy martensitic stainless steel is not less than grade 7 and the grain size difference is not higher than grade 1.

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