Method for designing high-strength martensitic stainless steel based on phase change toughening

Abstract

The invention provides a method for designing high-strength martensitic stainless steel based on phase change toughening, and relates to the technical field of martensitic stainless steel performance regulation and control. The method for designing the high-strength martensitic stainless steel based on phase change toughening comprises the steps of raw material weighing and smelting, homogenizing heat treatment-oil quenching treatment, solid solution treatment-oil quenching treatment, subzero treatment for controlling the temperature and aging treatment for adjusting the content of reversed austenite. The high-strength martensitic stainless steel comprises the following components in percentage by mass: 10-12% of Cr, 7-9% of Ni, 4-6% of Co, 2-4% of Mo, Mn, V, Si, C, other elements and the balance of Fe and inevitable impurities. The method is simple and easy to operate, environmentally friendly, low in cost, short in process, high in efficiency and beneficial to industrial large-scale production and popularization.

Description

Technical Field

[0001] The invention relates to the technical field of martensitic stainless steel performance regulation, and in particular to a method for designing high-strength martensitic stainless steel based on phase transformation toughening. Background Art

[0002] Martensitic stainless steel is an advanced high-strength steel whose performance is regulated by heat treatment. It is characterized by acid resistance and corrosion resistance. It usually has a chromium content of ≥10.5% and a carbon content of ≤1.2%. The basic characteristic is that the structure of the stainless steel is mainly martensitic during use. The high dislocation density of the martensitic matrix gives it the basic characteristics of high strength and high hardness. It also has good wear resistance, heat resistance and good plasticity and toughness. It currently shows considerable application value in the fields of petrochemicals, military equipment and automobile manufacturing. With the increasing complexity of the service environment of modern materials, higher requirements are placed on the performance of steel materials. As the representative steel of the first generation of advanced high-strength steel, martensitic stainless steel has ultra-high strength, which makes it widely used in extreme environments and high-load fields, and has attracted extensive research by scholars from various countries.

[0003] At present, the standardized heat treatment process for maraging steel ingots is solid solution + aging. While the martensitic matrix provides ultra-high strength for martensitic stainless steel, it also brings the defect of insufficient plasticity and toughness, which limits its application range.

[0004] Chinese patent CN114921717A discloses a 2000MPa grade high plasticity, toughness and corrosion resistance martensitic aged stainless steel and its preparation method. The method not only requires multiple smelting, but also requires hot working and heat treatment to be prepared in coordination. Therefore, the process is long, energy consumption is high, and operation is difficult, resulting in high preparation cost and low efficiency. Although homogenization treatment is adopted, its purpose is for subsequent hot working rather than the subsequent heat treatment. Moreover, the high temperature quenching treatment adopts a 0°C ice-water mixture, which is different from the mechanism and effect of oil quenching treatment. Moreover, its deep cryogenic treatment temperature is difficult to predict.

[0005] Chinese patent CN118932150A discloses a heat treatment method for additively manufactured maraging steel and high-strength and tough maraging steel. The additively manufactured maraging steel needs to be subjected to aging treatment and annealing treatment to obtain the product; although the strength is not low, the elongation is not high, and the strength and plasticity are not synergistically improved; and it is aimed at additively manufactured maraging steel, and the aging treatment temperature needs to be calculated by software, which is not suitable for industrial large-scale preparation.

[0006] Chinese patent CN114752741A discloses a method for improving the mechanical properties of 12Cr13 martensitic stainless steel, which requires combining quenching treatment with cold rolling deformation processing and tempering. Although the toughness can be improved, the improvement is not large, and its strength and plasticity are not high. Summary of the invention

[0007] In order to solve the problem that the strength and plasticity of martensitic stainless steel in the prior art are generally improved by combining composition improvement, hot working and heat treatment, however, there are technical defects such as high alloy cost, hot working will change the casting structure so that it does not have the superiority of casting structure, the selection of quenching liquid composition and deep cold treatment temperature during heat treatment is not suitable, difficult to control, and subsequent aging treatment, annealing and tempering treatment cannot effectively improve the strength and plasticity or the improvement is not large; the present invention proposes a method for designing high-strength martensitic stainless steel based on phase transformation toughening that can solve the above technical defects. The technical scheme is as follows:

[0008] A method for designing high-strength martensitic stainless steel based on phase transformation toughening, the method for designing high-strength martensitic stainless steel based on phase transformation toughening comprising the following steps:

[0009] S1. Raw material weighing and smelting: The composition content of high-strength martensitic stainless steel is designed, and the raw materials are weighed according to the chemical composition content. Then, the weighed raw materials are added into a vacuum induction furnace for smelting, and the smelted molten steel is cast to obtain an ingot;

[0010] S2, homogenization heat treatment-oil quenching treatment: after heating the S1 ingot, perform homogenization heat treatment, and then perform oil quenching treatment to obtain a steel ingot with uniform structure;

[0011] S3, solution treatment-oil quenching treatment: the steel ingot with uniform structure in S2 is heated for solution treatment, and then oil quenching is performed to obtain a solution steel ingot;

[0012] S4, temperature-controlled cryogenic treatment: subjecting the S3 solid solution steel ingot to liquid nitrogen cryogenic treatment to obtain a cryogenic steel ingot;

[0013] S5. Aging treatment for adjusting the reverse transformation austenite content: The S4 deep-cold steel ingot is subjected to aging treatment to adjust the reverse transformation austenite content, and air-cooled to room temperature to obtain high-strength and plastic martensitic stainless steel.

[0014] Optionally, the composition content of the high-strength martensitic stainless steel in S1 is as follows by mass percentage: Cr 10-12%, Ni 7-9%, Co 4-6%, Mo 2-4%, and also contains Mn, V, Si, C and other elements, and the rest is Fe and unavoidable impurities.

[0015] Optionally, the total content of Mn, V, Si, C and other elements in S1 is 0.6-0.8%.

[0016] Optionally, the heating rate of the homogenization heat treatment in S2 is 3-5°C / min, the temperature is 950-1050°C, and the holding time is 60min; the oil temperature of the oil quenching treatment is 50-80°C, and the time of the oil quenching treatment is 3-5min.

[0017] Optionally, the heating rate of the solution treatment in S3 is 3-5°C / min, the temperature is 750-800°C, and the holding time is 60min; the oil temperature of the oil quenching treatment is 50-80°C, and the time of the oil quenching treatment is 2-3min.

[0018] Optionally, the temperature of the liquid nitrogen cryogenic treatment in S4 is minus 73° C., and the treatment time is 100-140 minutes.

[0019] Optionally, the heating rate of the aging treatment in S5 is 3-5°C / min, the temperature is 300-600°C, and the holding time is 2-8h; the high-strength and plastic martensitic stainless steel is in the shape of a block with a size of 40-44×6-10×6-9mm; room temperature performance: hardness of 370.5HV-419.1HV, tensile strength of 1227.3-1363.0MPa, yield strength of 802.6-1242.1MPa, yield strength ratio of 0.746-0.911, elongation at break of 20.1-27.6%, cross-sectional shrinkage of 68.9-84.9%, and strength-plasticity product of 25.220-33.874GPa·%.

[0020] Optionally, the volume percentage of reversed austenite in the S5 medium-high strength and ductility martensitic stainless steel is 30.9-53.5%, and the volume percentage of reversed austenite is 46.5-69.1%.

[0021] Optionally, when the content of precipitated reverse transformed austenite in S5 is less than 53.5%, the strength will increase with the increase of austenite content, and when the content of precipitated reverse transformed austenite is greater than 53.5%, the strength will decrease with the increase of reverse transformed austenite content.

[0022] Optionally, when S5 is heat treated at 300°C for 8h, the reverse transformed austenite content is 23.2%, and the room temperature properties are: hardness of 386.9HV, tensile strength of 1254.7MPa, yield strength of 936.2MPa, yield strength ratio of 0.746, elongation at break of 20.1%, cross-sectional shrinkage of 68.9%, and strength-ductility product of 25.220GPa·%.

[0023] Optionally, when S5 is heat treated at 400°C for 4h, the reverse transformed austenite content is 30.9%, and the room temperature properties are: hardness of 419.1HV, tensile strength of 1358.3MPa, yield strength of 1195.4MPa, yield strength ratio of 0.880, elongation at break of 20.8%, cross-sectional shrinkage of 74.3%, and strength-ductility product of 28.253GPa·%.

[0024] Optionally, when S5 is heat treated at 500°C for 4h, the reverse transformed austenite content is 53.5%, and the room temperature properties are: hardness of 418.7HV, tensile strength of 1363.0MPa, yield strength of 1242.1MPa, yield strength ratio of 0.911, elongation at break of 21.7%, cross-sectional shrinkage of 76.2%, and strength-ductility product of 29.578GPa·%.

[0025] Optionally, when S5 is heat treated at 500℃ for 6h, the reverse transformed austenite content is 62.2%, and the room temperature properties are: hardness of 414.1HV, tensile strength of 1317.2MPa, yield strength of 1169.4MPa, yield strength ratio of 0.888, elongation at break of 20.5%, cross-sectional shrinkage of 72.1%, and strength-ductility product of 27.003GPa·%

[0026] Optionally, when S5 is heat treated at 600°C for 2h, the reverse transformed austenite content is 92.2%, and the room temperature properties are: hardness of 370.5HV, tensile strength of 1127.3MPa, yield strength of 802.6MPa, yield strength ratio of 0.806, elongation at break of 27.6%, cross-sectional shrinkage of 84.9%, and strength-ductility product of 33.874GPa·%.

[0027] Technical principle of the present invention:

[0028] The present invention is a method for improving strength and plasticity by regulating the reverse transformation austenite content in FeCrNiCoMo martensitic stainless steel based on the phase transformation behavior of martensitic stainless steel during the tensile process. The method studies the influence of different reverse transformation austenite contents on the tensile strength and elongation at break of FeCrNiCoMo. As the reverse transformation austenite content increases, the tensile strength shows a trend of first rising and then falling, while the elongation at break shows a trend of steadily rising. Based on this discovery, the content of reverse transformation austenite can be changed by heat treatment process design to achieve the design of strength and plasticity of FeCrNiCoMo martensitic stainless steel. The method is applicable to martensitic stainless steel that can be strengthened by heat treatment, and the main components are about 11% Cr, 8% Ni, 5% Co, and 3% Mo. In addition, alloy elements such as Mn, V, Si, and C are also present in steel. According to the method, the content of reverse transformation austenite in martensitic stainless steel can be changed by adjusting the heat treatment process, thereby providing a reasonable idea reference for the toughening design of martensitic stainless steel.

[0029] The process flow adopted by the present invention to achieve the above-mentioned purpose is: heat treatment of the sample → regulating the precipitation of reverse transformed austenite in the martensitic stainless steel → strengthening and plasticizing through phase transformation.

[0030] Heat treatment of the sample: FeCrNiCoMo martensitic stainless steel is a steel material that can be strengthened by aging treatment. Different aging temperatures are selected: above 700℃, it belongs to chemically stable austenite, not reverse transformation austenite. In addition, the reverse transformation austenite of martensitic stainless steel under this composition system begins to precipitate at nearly 400℃, so the temperature range is 300-600℃, and the aging time range is 2-8h. This method is suitable for martensitic stainless steel that can be phase-transformed and strengthened under the Fe11Cr8Ni5Co3Mo composition system.

[0031] Regulating the precipitation of reverse transformed austenite in martensitic stainless steel: This method first homogenizes the martensitic stainless steel at 1000°C for 1 hour and then oil quenches it to promote the complete diffusion of alloy elements. It then solution treats it at 760°C for 1 hour and then oil quenches it to increase the dislocation density in the reverse transformed austenite. It then undergoes a deep cryogenic treatment at -73°C for 2 hours to promote complete martensitic transformation. Finally, it undergoes an aging treatment at 300-600°C for 2-8 hours and then air cools it to obtain a reverse transformed austenite with a volume fraction of about 23.2-92.2%, which makes organizational preparation for the TRIP (transformation induced plasticity) effect of the reverse transformed austenite during the stretching process.

[0032] Enhanced plasticization through phase transformation: This method uses tensile strength as the strength measure of FeCrNiCoMo martensitic stainless steel, and uses elongation at break as the plasticity measure of FeCrNiCoMo martensitic stainless steel. For strength regulation, the transformation of reverse-transformed austenite to martensite during stretching is mainly used to squeeze the nearby martensite phase, increase dislocation density and thus increase strength. For plasticity regulation, the phase transformation behavior of reverse-transformed austenite to martensite during stretching absorbs energy and thus improves plasticity. In general, strong plasticity design is based on the TRIP effect of austenite during stretching to improve strength and increase plasticity.

[0033] The theoretical basis of the present invention is that cast martensitic stainless steel is first prepared, and then FeCrNiCoMo martensitic stainless steel after different aging process treatments is designed. The phase compositions under each process are: 300°C heat treatment for 8h: martensitic stainless steel containing 23.2% reverse transformation austenite, 400°C heat treatment for 4h: martensitic stainless steel containing 30.9% reverse transformation austenite, 500°C heat treatment for 4h: martensitic stainless steel containing 53.5% reverse transformation austenite, 500°C heat treatment for 6h: martensitic stainless steel containing 62.2% reverse transformation austenite, 600°C heat treatment for 2h: martensitic stainless steel containing 92.2% reverse transformation austenite. Since the reverse transformation austenite of the material further inherits the high dislocation density of martensite after solid solution treatment, and the material undergoes stress-induced martensitic phase transformation during the stretching process, resulting in lattice distortion, introducing a large number of dislocations, and significantly improving the strength of the material. Solid solution strengthening Since the degree of lattice distortion caused by substitutional solid solution strengthening is small and the carbon content is low, the contribution of interstitial solid solution strengthening to martensitic stainless steel is relatively limited. In addition, the focus of the heat treatment process is to generate martensite through phase transformation and increase dislocation density. Therefore, this type of steel mainly relies on phase transformation strengthening and dislocation strengthening mechanisms. Since there is a certain degree of mutual exclusion between strength and plasticity in high-strength steel, high plasticity will hinder the improvement of strength. According to the experimental results, with the increase of aging temperature and aging time, more reverse transformation austenite will precipitate. When aged at 300℃, most of the phases are martensite, with high strength but poor plasticity. The content of soft austenite is the highest when heat treated at 600℃ for 2h, and the plasticity is also the highest at this time, but the strength is lower than that of a large proportion of martensite structure aged at 300℃. After aging treatment at 400℃ and 500℃, part of the martensite undergoes phase transformation into austenite. While the plasticity is improved, the strength is also improved by the TRIP effect of the reverse transformed austenite during the tensile process. The final strength is higher than that of the sample with most of the martensite phase at 300℃, indicating that under this process, the reverse transformed austenite exerts the TRIP effect to the maximum extent through stress-induced martensite phase transformation. It will not limit the effect of phase transformation on mechanical properties due to the small volume fraction of austenite, nor will the residual softer austenite phase after the phase transformation limit the high strength.

[0034] The present invention is characterized in that after the above heat treatment is performed on FeCrNiCoMo martensitic stainless steel, it is found that the reverse austenite undergoes phase transformation during the stretching process. With the increase of the reverse austenite content, the tensile strength first increases and then decreases, while the elongation at break presents a trend of steady growth. There is a certain degree of mutual exclusion between strength and plasticity in FeCrNiCoMo martensitic stainless steel. When the aging temperature is 600°C, the austenite content reaches more than 90%, the elongation exceeds 76%, but the strength decreases by about 100MPa. When aging at 400°C for 4h and 500°C for 4h, 30.9% and 53.5% of the reverse austenite are generated. These reverse austenites undergo phase transformation during the stretching process to produce the TRIP effect, which increases the strength of the martensitic stainless steel while improving the plasticity, so it has higher strength and better plasticity, the tensile strength reaches 1358.3MPa and 1363.0MPa, and the elongation at break reaches 20.8% and 21.7%.

[0035] Brief description of the solution of the present invention:

[0036] 1) Heat treatment of the sample. First, FeCrNiCoMo martensitic stainless steel was prepared. In order to obtain higher strength and hardness, it needed to be heat treated. First, it was homogenized at 1000℃ for 1h and then oil quenched to ensure complete recrystallization of austenite and promote the full diffusion of alloy elements. Then, it was solution treated at 760℃ for 1h and then oil quenched to increase the dislocation density of reverse transformed austenite. After deep cryogenic treatment at -73℃ for 2h, the complete transformation of martensite was promoted, which made organizational preparations for the subsequent precipitation process of reverse transformed austenite.

[0037] 2) Regulate the precipitation of reverse austenite in martensitic stainless steel. Through an aging process at 300-600℃ for 2-8h, martensitic stainless steel with different reverse austenite contents was precipitated. During the stretching process, these reverse austenites will undergo phase transformation after a certain degree of stress is applied due to their different stability, changing the phase distribution in the steel and ultimately affecting the performance of martensitic stainless steel. By summarizing the effect of the content of reverse austenite on the strength and plasticity of martensitic stainless steel, the strength and plasticity of FeCrNiCoMo martensitic stainless steel were regulated.

[0038] 3) Enhance plasticization through phase transformation. If it is necessary to design FeCrNiCoMo martensitic stainless steel with higher strength and plasticity, the aging process can be adjusted so that the precipitation of reverse transformed austenite reaches 30.9-53.5%. If it is necessary to design martensitic stainless steel with higher plasticity, the aging process can be adjusted so that the precipitation of reverse transformed austenite reaches more than 90%.

[0039] Compared with the prior art, the above technical solution has at least the following beneficial effects:

[0040] The above scheme proposes a method for designing high-strength martensitic stainless steel based on phase transformation toughening, which can solve the problem that the strength and plasticity of martensitic stainless steel in the prior art are generally improved by combining composition improvement, hot working and heat treatment, but there are technical defects such as high alloy cost, hot working will change the casting structure so that it does not have the superiority of the casting structure, the composition selection of the quenching liquid and the deep cold treatment temperature during the heat treatment process are not suitable and difficult to control, and the subsequent aging treatment and annealing, tempering treatment cannot make a synergistic improvement or the improvement is not large.

[0041] The present invention obtains steel ingots through raw material design, weighing and smelting, ensures good metallurgical quality, provides uniform chemical composition, and helps to enhance the stability of phase transformation during subsequent heat treatment. It avoids deviations in the content of alloy elements that may adversely affect strength and plasticity, ensures consistency in the composition and structure of the steel ingot, and ensures quality reliability and repeatability of large-scale process production.

[0042] The present invention can fully diffuse the alloy elements through homogenization heat treatment-oil quenching treatment, reduce segregation to obtain fully recrystallized austenite, ensure uniform phase transformation of the steel ingot, and avoid strength and hardness differences caused by local structural unevenness in the subsequent oil quenching process. Compared with water quenching, oil quenching has a slower cooling rate, which reduces cracks and deformation that may exist during rapid cooling. Oil quenching makes the cooling rate and transformation behavior more controllable, and improves the consistency and stability of the production process.

[0043] The present invention can make austenite inherit part of the dislocation density of the martensite matrix and the grain orientation of the original austenite through solution treatment-oil quenching treatment, thus making organizational preparation for aging treatment. Compared with water quenching, oil quenching is more gentle, reduces the internal stress and deformation caused by excessive temperature gradient, improves the overall stability of the ingot, retains part of the organizational toughness, and greatly reduces the performance fluctuation caused by water quenching. Ensure the performance consistency of each batch of products during large-scale production.

[0044] The present invention can promote martensitic transformation at low temperature, strengthen the microstructure of the steel ingot, and improve the low-temperature performance of the steel ingot by controlling the temperature of the deep cryogenic treatment. After the low-temperature deep cryogenic treatment, the structure of the steel ingot is more stable, and the performance will not decline after long-term service, thereby ensuring the consistency of the performance of the steel ingot during long-term use.

[0045] The present invention can transform austenite into martensite under the action of stress-induced phase transformation through aging treatment to adjust the content of reverse transformed austenite, thereby optimizing the phase transformation process of the steel ingot; the precipitated reverse transformed austenite can exert the TRIP (transformation induced plasticity) effect, absorb the energy required for the phase transformation from austenite to martensite, increase the toughness of the steel ingot, and delay the necking phenomenon, improve the uniformity of strain, and enhance the plasticity of the steel ingot.

[0046] The high-strength and plastic martensitic stainless steel of the present invention is in the shape of a block with a size of 40-44×6-10×6-9 mm; room temperature performance: hardness of 370.5HV-419.1HV, tensile strength of 1227.3-1363.0MPa, yield strength of 802.6-1242.1MPa, yield strength ratio of 0.746-0.911, elongation at break of 20.1-27.6%, cross-sectional shrinkage of 68.9-84.9%, and strength-plasticity product of 25.220-33.874GPa·%.

[0047] In summary, compared with other traditional methods, the method of the present invention prepares high-strength and plastic martensitic stainless steel through raw material design, weighing and smelting, homogenization heat treatment-oil quenching treatment, solution treatment-oil quenching treatment, temperature-controlled deep cold treatment and aging treatment for adjusting the reverse transformation austenite content; the method is simple and easy to operate, green and environmentally friendly, low in cost, short in process, high in efficiency, and is conducive to large-scale industrial production and promotion. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0049] Figure 1 It is a comparison diagram of X-ray diffraction of high-strength martensitic stainless steels designed based on phase transformation toughening according to Examples 1-5 of the present invention after being heat treated for 2-8 hours with different processes;

[0050] Figure 2 This is an electron backscattered diffraction pattern of a sample of the high-strength martensitic stainless steel designed based on phase transformation toughening according to Example 1 of the present invention after heat treatment at 300° C. for 8 hours;

[0051] Figure 3 This is an electron backscattered diffraction pattern of a sample of high-strength martensitic stainless steel designed based on phase transformation toughening according to Example 2 of the present invention after heat treatment at 400° C. for 4 hours;

[0052] Figure 4This is an electron backscattered diffraction pattern of a sample of high-strength martensitic stainless steel designed based on phase transformation toughening according to Example 3 of the present invention after heat treatment at 500° C. for 4 hours;

[0053] Figure 5 This is an electron backscattered diffraction pattern of a sample of high-strength martensitic stainless steel designed based on phase transformation toughening according to Example 4 of the present invention after heat treatment at 500° C. for 6 hours;

[0054] Figure 6 This is an electron backscattered diffraction pattern of a sample of high-strength martensitic stainless steel designed based on phase transformation toughening according to Example 5 of the present invention after heat treatment at 600° C. for 2 hours;

[0055] Figure 7 It is a comparison diagram of austenite content-heat treatment process curve of a sample of the high-strength martensitic stainless steel designed based on phase transformation toughening after heat treatment at 300-600°C for 2-8h;

[0056] Figure 8 It is a comparison diagram of true stress-strain curves of samples of high-strength martensitic stainless steel designed based on phase transformation toughening according to Examples 1-5 of the present invention after heat treatment at different temperatures for 2-8 hours;

[0057] Fig. 9 It is a statistical graph comparing the austenite content and mechanical properties of the samples of the high-strength martensitic stainless steel designed based on phase transformation toughening according to Examples 1-5 of the present invention after heat treatment at different temperatures for 2-8 hours. DETAILED DESCRIPTION

[0058] The technical solution of the present invention is described below in conjunction with the accompanying drawings.

[0059] In the embodiments of the present invention, words such as "exemplarily" and "for example" are used to indicate examples, illustrations or explanations. Any embodiment or design described as "example" in the present invention should not be interpreted as being more preferred or more advantageous than other embodiments or designs. Specifically, the use of the word "example" is intended to present the concept in a specific way. In addition, in the embodiments of the present invention, the meaning expressed by "and / or" can be both, or it can be either of the two.

[0060] In the embodiments of the present invention, "image" and "picture" may sometimes be used interchangeably. It should be noted that when the distinction between them is not emphasized, the meanings they intend to express are consistent.

[0061] In the embodiments of the present invention, sometimes the subscripts such as W 1 It may be written in non-subscript form such as W1. When the difference is not emphasized, the meaning is the same.

[0062] In order to make the technical problems, technical solutions and advantages to be solved by the present invention more clear, a detailed description will be given below with reference to the accompanying drawings and specific embodiments.

[0063] A method for designing high-strength martensitic stainless steel based on phase transformation toughening, the method for designing high-strength martensitic stainless steel based on phase transformation toughening comprising the following steps:

[0064] S1. Raw material weighing and smelting: The composition content of high-strength martensitic stainless steel is designed, and the raw materials are weighed according to the chemical composition content. Then, the weighed raw materials are added into a vacuum induction furnace for smelting, and the smelted molten steel is cast to obtain an ingot;

[0065] S2, homogenization heat treatment-oil quenching treatment: after heating the S1 ingot, perform homogenization heat treatment, and then perform oil quenching treatment to obtain a steel ingot with uniform structure;

[0066] S3, solution treatment-oil quenching treatment: the steel ingot with uniform structure in S2 is heated for solution treatment, and then oil quenching is performed to obtain a solution steel ingot;

[0067] S4, temperature-controlled cryogenic treatment: subjecting the S3 solid solution steel ingot to liquid nitrogen cryogenic treatment to obtain a cryogenic steel ingot;

[0068] S5. Aging treatment for adjusting the reverse transformation austenite content: The S4 deep-cold steel ingot is subjected to aging treatment to adjust the reverse transformation austenite content, and air-cooled to room temperature to obtain high-strength and plastic martensitic stainless steel.

[0069] In particular, the composition content of S1 medium-strength martensitic stainless steel is as follows by mass percentage: Cr 10-12%, Ni 7-9%, Co 4-6%, Mo 2-4%, and also contains Mn, V, Si, C and other elements, and the rest is Fe and inevitable impurities.

[0070] In particular, the total content of Mn, V, Si, C and other elements in S1 is 0.6-0.8%.

[0071] In particular, the heating rate of the homogenization heat treatment in S2 is 3-5°C / min, the temperature is 950-1050°C, and the holding time is 60min; the oil temperature of the oil quenching treatment is 50-80°C, and the time of the oil quenching treatment is 3-5min.

[0072] In particular, the heating rate of the solution treatment in S3 is 3-5°C / min, the temperature is 750-800°C, and the holding time is 60min; the oil temperature of the oil quenching treatment is 50-80°C, and the time of the oil quenching treatment is 2-3min.

[0073] In particular, the temperature of the liquid nitrogen cryogenic treatment in S4 is minus 73°C, and the treatment time is 100-140 minutes.

[0074] In particular, the heating rate of the aging treatment in S5 is 3-5℃ / min, the temperature is 300-600℃, and the holding time is 2-8h; the shape of the high-strength and plastic martensitic stainless steel is block-shaped, with a size of 40-44×6-10×6-9mm; room temperature performance: hardness is 370.5HV-419.1HV, tensile strength is 1227.3-1363.0MPa, yield strength is 802.6-1242.1MPa, yield strength ratio is 0.746-0.911, elongation at break is 20.1-27.6%, cross-sectional shrinkage is 68.9-84.9%, and strength-plasticity product is 25.220-33.874GPa·%.

[0075] In particular, the volume percentage of reversed austenite in S5 medium-high strength and ductility martensitic stainless steel is 30.9-53.5%, and the volume percentage of reversed austenite is 46.5-69.1%.

[0076] In particular, when the content of precipitated reversed austenite in S5 is less than 53.5%, the strength increases with the increase of austenite content, and when the content of precipitated reversed austenite is greater than 53.5%, the strength decreases with the increase of reversed austenite content.

[0077] In particular, when S5 is heat treated at 500℃ for 4h, the reverse transformed austenite content is 53.5%, and the room temperature properties are: hardness of 418.7HV, tensile strength of 1363.0MPa, yield strength of 1242.1MPa, yield strength ratio of 0.911, elongation at break of 21.7%, cross-sectional shrinkage of 76.2%, and strength-ductility product of 29.578GPa·%.

[0078] In particular, when S5 is heat treated at 300℃ for 8h, the reverse transformed austenite content is 23.2%, and the room temperature properties are: hardness of 386.9HV, tensile strength of 1254.7MPa, yield strength of 936.2MPa, yield strength ratio of 0.746, elongation at break of 20.1%, cross-sectional shrinkage of 68.9%, and strength-ductility product of 25.220GPa·%.

[0079] In particular, when S5 is heat treated at 400℃ for 4h, the reverse transformed austenite content is 30.9%, and the room temperature properties are: hardness of 419.1HV, tensile strength of 1358.3MPa, yield strength of 1195.4MPa, yield strength ratio of 0.880, elongation at break of 20.8%, cross-sectional shrinkage of 74.3%, and strength-ductility product of 28.253GPa·%.

[0080] In particular, when S5 is heat treated at 500℃ for 6h, the reverse transformed austenite content is 62.2%, and the room temperature properties are: hardness of 414.1HV, tensile strength of 1317.2MPa, yield strength of 1169.4MPa, yield strength ratio of 0.888, elongation at break of 20.5%, cross-sectional shrinkage of 72.1%, and strength-ductility product of 27.003Pa·%.

[0081] In particular, when S5 is heat treated at 600℃ for 2h, the reverse transformed austenite content is 92.2%, and the room temperature properties are: hardness of 370.5HV, tensile strength of 1227.3MPa, yield strength of 802.6MPa, yield strength ratio of 0.806, elongation at break of 27.6%, cross-sectional shrinkage of 84.9%, and strength-ductility product of 33.874GPa·%.

[0082] Example 1

[0083] A method for designing high-strength martensitic stainless steel based on phase transformation toughening, the method for designing high-strength martensitic stainless steel based on phase transformation toughening comprising the following steps:

[0084] S1. Raw material weighing and smelting: The component content of high-strength martensitic stainless steel is designed. In this embodiment, the component content of high-strength martensitic stainless steel is as follows: Cr 10.9%, Ni 8.18%, Co 5.37%, Mo 2.67%, C0.018%, and the rest is Fe and unavoidable impurities. The raw materials are weighed according to the chemical component content, and then the weighed raw materials are added to a vacuum induction furnace for smelting, and the smelted molten steel is cast to obtain an ingot;

[0085] S2, homogenization heat treatment-oil quenching treatment: after heating the S1 ingot, homogenization heat treatment is performed, the heating rate of the homogenization heat treatment is 5°C / min, the temperature is 1000°C, and the holding time is 60min; then oil quenching treatment is performed, the oil temperature of the oil quenching treatment is 60°C, and the oil quenching treatment time is 4min, to obtain a steel ingot with uniform structure;

[0086] S3, solution treatment-oil quenching treatment: the steel ingot with uniform structure of S2 is heated for solution treatment, the heating rate of the solution treatment is 5°C / min, the temperature is 760°C, and the holding time is 60min; then the oil quenching treatment is performed, the oil temperature of the oil quenching treatment is 60°C, and the oil quenching treatment time is 2min, to obtain a solution steel ingot;

[0087] S4, temperature-controlled cryogenic treatment: subjecting the S3 solid solution steel ingot to liquid nitrogen cryogenic treatment, the temperature of the liquid nitrogen cryogenic treatment being minus 73°C, the treatment time being 120 minutes, to obtain a cryogenic steel ingot;

[0088] S5. Aging treatment for adjusting the reverse transformation austenite content: The S4 deep-cold steel ingot is subjected to aging treatment to adjust the reverse transformation austenite content. The heating rate of the aging treatment is 5°C / min, the temperature is 300°C, and the insulation time is 8h; air cooling to room temperature obtains high-strength and plastic martensitic stainless steel.

[0089] The high-strength and ductile martensitic stainless steel prepared in this embodiment is in the shape of a block with a size of 40×6×9 mm; room temperature performance: hardness of 386.9 HV, tensile strength of 1254.7 MPa, yield strength of 936.2 MPa, yield strength ratio of 0.746, elongation at break of 20.1%, cross-sectional shrinkage of 68.9%, and strength-ductility product of 25.220 GPa·%.

[0090] Example 2

[0091] A method for designing high-strength martensitic stainless steel based on phase transformation toughening, the method for designing high-strength martensitic stainless steel based on phase transformation toughening comprising the following steps:

[0092] S1. Raw material weighing and smelting: The component content of high-strength martensitic stainless steel is designed. In this embodiment, the component content of high-strength martensitic stainless steel is as follows: Cr 10.9%, Ni 8.18%, Co 5.37%, Mo 2.67%, C0.018%, and the rest is Fe and unavoidable impurities. The raw materials are weighed according to the chemical component content, and then the weighed raw materials are added to a vacuum induction furnace for smelting, and the smelted molten steel is cast to obtain an ingot;

[0093] S2, homogenization heat treatment-oil quenching treatment: after heating the S1 ingot, homogenization heat treatment is performed, the heating rate of the homogenization heat treatment is 3°C / min, the temperature is 1000°C, and the holding time is 60min; then oil quenching treatment is performed, the oil temperature of the oil quenching treatment is 60°C, and the oil quenching treatment time is 3min, to obtain a steel ingot with uniform structure;

[0094] S3, solution treatment-oil quenching treatment: the steel ingot with uniform structure of S2 is heated for solution treatment, the heating rate of the solution treatment is 5°C / min, the temperature is 760°C, and the holding time is 60min; then the oil quenching treatment is performed, the oil temperature of the oil quenching treatment is 60°C, and the oil quenching treatment time is 2min, to obtain a solution steel ingot;

[0095] S4, temperature-controlled cryogenic treatment: subjecting the S3 solid solution steel ingot to liquid nitrogen cryogenic treatment, the temperature of the liquid nitrogen cryogenic treatment being minus 73°C, the treatment time being 120 minutes, to obtain a cryogenic steel ingot;

[0096] S5. Aging treatment for adjusting the reverse transformation austenite content: The S4 deep-cold steel ingot is subjected to aging treatment to adjust the reverse transformation austenite content. The heating rate of the aging treatment is 5°C / min, the temperature is 400°C, and the insulation time is 4h; air cooling to room temperature obtains high-strength and plastic martensitic stainless steel.

[0097] The high-strength and ductile martensitic stainless steel prepared in this embodiment is in the shape of a block with a size of 42×8×7.5 mm; room temperature performance: hardness of 419.1 HV, tensile strength of 1358.3 MPa, yield strength of 1195.4 MPa, yield strength ratio of 0.880, elongation at break of 20.8%, cross-sectional shrinkage of 74.3%, and strength-ductility product of 28.253 GPa·%.

[0098] Example 3

[0099] A method for designing high-strength martensitic stainless steel based on phase transformation toughening, the method for designing high-strength martensitic stainless steel based on phase transformation toughening comprising the following steps:

[0100] S1. Raw material weighing and smelting: The component content of high-strength martensitic stainless steel is designed. In this embodiment, the component content of high-strength martensitic stainless steel is as follows: Cr 10.9%, Ni 8.18%, Co 5.37%, Mo 2.67%, C0.018%, and the rest is Fe and unavoidable impurities. The raw materials are weighed according to the chemical component content, and then the weighed raw materials are added to a vacuum induction furnace for smelting, and the smelted molten steel is cast to obtain an ingot;

[0101] S2, homogenization heat treatment - oil quenching treatment: after heating the S1 ingot, homogenization heat treatment is performed, the heating rate of the homogenization heat treatment is 5°C / min, the temperature is 1000°C, and the holding time is 60min; then oil quenching treatment is performed, the oil temperature of the oil quenching treatment is 60°C, and the oil quenching treatment time is 3min, to obtain a steel ingot with uniform structure;

[0102] S3, solution treatment-oil quenching treatment: the steel ingot with uniform structure of S2 is heated for solution treatment, the heating rate of the solution treatment is 4°C / min, the temperature is 760°C, and the holding time is 60min; then the oil quenching treatment is performed, the oil temperature of the oil quenching treatment is 60°C, and the oil quenching treatment time is 2min, to obtain a solution steel ingot;

[0103] S4, temperature-controlled cryogenic treatment: subjecting the S3 solid solution steel ingot to liquid nitrogen cryogenic treatment, the temperature of the liquid nitrogen cryogenic treatment being minus 73°C, the treatment time being 120 minutes, to obtain a cryogenic steel ingot;

[0104] S5. Aging treatment for adjusting the reverse transformation austenite content: The S4 deep-cold steel ingot is subjected to aging treatment to adjust the reverse transformation austenite content. The heating rate of the aging treatment is 3°C / min, the temperature is 500°C, and the insulation time is 4h; air cooling to room temperature obtains high-strength and plastic martensitic stainless steel.

[0105] The high-strength and ductile martensitic stainless steel prepared in this embodiment is in the shape of a block with a size of 43×9×6 mm; room temperature performance: hardness of 418.7 HV, tensile strength of 1363.0 MPa, yield strength of 1242.1 MPa, yield strength ratio of 0.911, elongation at break of 21.7%, cross-sectional shrinkage of 76.2%, and strength-ductility product of 29.578 GPa•%.

[0106] Example 4

[0107] A method for designing high-strength martensitic stainless steel based on phase transformation toughening, the method for designing high-strength martensitic stainless steel based on phase transformation toughening comprising the following steps:

[0108] S1. Raw material weighing and smelting: The component content of high-strength martensitic stainless steel is designed. In this embodiment, the component content of high-strength martensitic stainless steel is as follows: Cr 10.9%, Ni 8.18%, Co 5.37%, Mo 2.67%, C0.018%, and the rest is Fe and unavoidable impurities. The raw materials are weighed according to the chemical component content, and then the weighed raw materials are added to a vacuum induction furnace for smelting, and the smelted molten steel is cast to obtain an ingot;

[0109] S2, homogenization heat treatment-oil quenching treatment: after heating the S1 ingot, homogenization heat treatment is performed, the heating rate of the homogenization heat treatment is 3°C / min, the temperature is 1000°C, and the holding time is 60min; then oil quenching treatment is performed, the oil temperature of the oil quenching treatment is 60°C, and the oil quenching treatment time is 3min, to obtain a steel ingot with uniform structure;

[0110] S3, solution treatment-oil quenching treatment: the steel ingot with uniform structure of S2 is heated for solution treatment, the heating rate of the solution treatment is 5°C / min, the temperature is 760°C, and the holding time is 60min; then the oil quenching treatment is performed, the oil temperature of the oil quenching treatment is 60°C, and the oil quenching treatment time is 2min, to obtain a solution steel ingot;

[0111] S4, temperature-controlled cryogenic treatment: subjecting the S3 solid solution steel ingot to liquid nitrogen cryogenic treatment, the temperature of the liquid nitrogen cryogenic treatment being minus 73°C, the treatment time being 120 minutes, to obtain a cryogenic steel ingot;

[0112] S5. Aging treatment for adjusting the reverse transformation austenite content: The S4 deep-cold steel ingot is subjected to aging treatment to adjust the reverse transformation austenite content. The heating rate of the aging treatment is 4°C / min, the temperature is 500°C, and the insulation time is 6h; air cooling to room temperature obtains high-strength and plastic martensitic stainless steel.

[0113] The high-strength and ductile martensitic stainless steel prepared in this embodiment is in the shape of a block with a size of 44×7×8 mm; room temperature performance: hardness of 424.1 HV, tensile strength of 1317.2 MPa, yield strength of 1169.4 MPa, yield strength ratio of 0.888, elongation at break of 20.5%, cross-sectional shrinkage of 72.1%, and strength-ductility product of 27.003 GPa·%.

[0114] Example 5

[0115] A method for designing high-strength martensitic stainless steel based on phase transformation toughening, the method for designing high-strength martensitic stainless steel based on phase transformation toughening comprising the following steps:

[0116] S1. Raw material weighing and smelting: The component content of high-strength martensitic stainless steel is designed. In this embodiment, the component content of high-strength martensitic stainless steel is as follows: Cr 10.9%, Ni 8.18%, Co 5.37%, Mo 2.67%, C0.018%, and the rest is Fe and unavoidable impurities. The raw materials are weighed according to the chemical component content, and then the weighed raw materials are added to a vacuum induction furnace for smelting, and the smelted molten steel is cast to obtain an ingot;

[0117] S2, homogenization heat treatment - oil quenching treatment: after heating the S1 ingot, homogenization heat treatment is performed, the heating rate of the homogenization heat treatment is 5°C / min, the temperature is 1000°C, and the holding time is 60min; then oil quenching treatment is performed, the oil temperature of the oil quenching treatment is 60°C, and the oil quenching treatment time is 3min, to obtain a steel ingot with uniform structure;

[0118] S3, solution treatment-oil quenching treatment: the steel ingot with uniform structure of S2 is heated for solution treatment, the heating rate of the solution treatment is 5°C / min, the temperature is 760°C, and the holding time is 60min; then the oil quenching treatment is performed, the oil temperature of the oil quenching treatment is 60°C, and the oil quenching treatment time is 2min, to obtain a solution steel ingot;

[0119] S4, temperature-controlled cryogenic treatment: subjecting the S3 solid solution steel ingot to liquid nitrogen cryogenic treatment, the temperature of the liquid nitrogen cryogenic treatment being minus 73°C, the treatment time being 120 minutes, to obtain a cryogenic steel ingot;

[0120] S5. Aging treatment for adjusting the reverse transformation austenite content: The S4 deep-cold steel ingot is subjected to aging treatment to adjust the reverse transformation austenite content. The heating rate of the aging treatment is 5°C / min, the temperature is 600°C, and the holding time is 2h; air cooling to room temperature is performed to obtain high-strength and plastic martensitic stainless steel.

[0121] The high-strength and ductile martensitic stainless steel prepared in this embodiment is in the shape of a block with a size of 43×10×6 mm; room temperature performance: hardness of 370.5 HV, tensile strength of 1227.3 MPa, yield strength of 802.6 MPa, yield strength ratio of 0.654, elongation at break of 27.6%, cross-sectional shrinkage of 84.9%, and strength-ductility product of 33.874 GPa·%.

[0122] Table 1 Mechanical properties data of martensitic stainless steel obtained in Example 1, Example 2 and Comparative Example 1, Comparative Example 2 (room temperature)

[0123] Example Hardness / HV Yield strength / MPa Tensile strength / MPa Elongation after fracture / % Strength and plasticity product / GPa·% Austenite volume fraction / % Example 1 386.9 936.2 1254.7 20.1 25.220 23.2 Example 2 419.1 1195.4 1358.3 20.8 28.253 30.9 Example 3 418.7 1242.1 1363.0 21.7 29.578 53.5 Example 4 414.1 1169.4 1317.2 20.5 27.003 62.2 Example 5 370.5 802.6 1227.3 27.6 33.874 92.2

[0124] From Table 1 and Figure 2 , Figure 3 , Figure 7 , Fig. 9 It can be seen that the volume fraction of austenite in the martensitic stainless steel obtained in Example 1 is 23.2%, and the volume fraction of austenite in the martensitic stainless steel obtained in Example 2 is 30.9%. The tensile strength of Example 1 is 1254.7MPa, and the tensile strength of Example 2 is 1358.3MPa. In comparison, the hard martensitic matrix of Example 1 is more than that of Example 2, but the strength of Example 2 is greater than that of Example 1. The reason is that the reverse transformation austenite undergoes stress-induced martensitic transformation during the tensile process, which disperses the stress distribution and improves the uniformity of deformation, thereby improving the plasticity. The austenite phase transforms to martensite while increasing the dislocation density, so the plasticity is improved while the strength is also increased. According to the comparison of the strength-plastic product of Example 1 and Example 2 in Table 1, it can also be seen that the comprehensive performance of Example 2 is also better than that of Example 1. Therefore, Example 2 of the present invention has better strength-plastic matching than Example 1. On the basis of Example 2, the heating temperature is further increased to 500°C, and the obtained Example 3 is improved in strength and plasticity compared with Example 2, and the hardness does not change much. This is similar to the fact that both strength and plasticity of Example 2 are improved compared to Example 1.

[0125] Compared with Example 5, Example 4 of the present invention has a volume fraction of austenite in the martensitic stainless steel obtained in Example 4 of 62.2%, and a volume fraction of reversed austenite in the martensitic stainless steel of Example 5 of 92.2. It can be found that most of the phases in Example 5 are softer austenite phases. Although the plasticity is increased from 20.5% in Example 4 to 27.6%, too much soft austenite phase reduces the strength. The high austenite volume fraction of Example 5 not only leads to its lower strength, but also performs worse under high stress environments. In contrast, Examples 3 and 4 are more outstanding in terms of strength and strength-plasticity product, indicating that they can maintain good plasticity while maintaining high strength, so that the material can still maintain good deformation capacity under high load conditions, increasing its adaptability under impact loads. It is suitable for application scenarios with high strength and high deformation resistance, and its applicability is wider.

[0126] like Figure 1-7 As shown, by comparing Examples 1-5, it is found that with the increase of heat treatment temperature and holding time, the content of reversed austenite increases, the elongation increases with the increase of the content of reversed austenite, and the tensile strength first increases and then decreases with the content of reversed austenite. The TRIP effect of reversed austenite in the tensile process during heat treatment improves the strength and plasticity, which has a strengthening effect on martensitic stainless steel. Therefore, Figure 2 , Figure 3 , Fig. 9 As shown, the strength of Example 2 is increased from 1254.7 MPa to 1358.3 MPa compared to that of Example 1. Figure 3 , Figure 4 , Figure 8 As shown, while ensuring that the strength of Example 3 is improved compared with Example 2, the plasticity is also improved to 21.7%, and the strength-plasticity product is 29.578 GPa·%, achieving a good match between strength and toughness, so that the material can withstand high loads while ensuring a certain deformation capacity, and can effectively relieve stress concentration under the action of external forces, prevent the occurrence of failure, and ensure the safety and reliability of the material when in use. Figure 4 , Figure 5 , Figure 6As shown, Example 4 further increases the holding time to 6h, and Example 5 further heat treats the temperature to 600℃, and the holding time is 2h. Although the plasticity reaches 27.6% at this time, the deformation capacity of the material after being subjected to force increases, avoiding fracture under a larger degree of deformation. However, the strength of the martensitic stainless steel at this time drops from 1363.0 in Example 3 to 1227.3MPa, which is even lower than the strength of Example 1, which is lower than the reverse transformation austenite, resulting in the material not having sufficient resistance when subjected to external force, especially the yield strength decreases by 300MPa, which may cause the material to yield earlier, reduce the fatigue life of the material, and even cause the material to fail under higher loads, thereby limiting its application field. The reason is that the increase in temperature at this time provides a greater driving force for the reverse transformation of austenite, and the nucleation and growth process of the reverse transformation austenite is relatively sufficient, and the volume fraction of austenite reaches 92.2%.

[0127] Only an appropriate volume fraction of austenite can help maintain good martensitic properties, thereby enhancing hardness and deformation resistance, while ensuring the safety of the structure during actual use, making martensitic stainless steel perform better in high stress and high deformation applications.

[0128] The above scheme proposes a method for designing high-strength martensitic stainless steel based on phase transformation toughening, which can solve the problem that the strength and plasticity of martensitic stainless steel in the prior art are generally improved by combining composition improvement, hot working and heat treatment, but there are technical defects such as high alloy cost, hot working will change the casting structure so that it does not have the superiority of the casting structure, the composition selection of the quenching liquid and the deep cold treatment temperature during the heat treatment process are not suitable and difficult to control, and the subsequent aging treatment and annealing, tempering treatment cannot make a synergistic improvement or the improvement is not large.

[0129] The present invention obtains steel ingots through raw material design, weighing and smelting, ensures good metallurgical quality, provides uniform chemical composition, and helps to enhance the stability of phase transformation during subsequent heat treatment. It avoids deviations in the content of alloy elements that may adversely affect strength and plasticity, ensures consistency in the composition and structure of the steel ingot, and ensures quality reliability and repeatability of large-scale process production.

[0130] The present invention can fully diffuse the alloy elements through homogenization heat treatment-oil quenching treatment, reduce segregation to obtain fully recrystallized austenite, ensure uniform phase transformation of the steel ingot, and avoid strength and hardness differences caused by local structural unevenness in the subsequent oil quenching process. Compared with water quenching, oil quenching has a slower cooling rate, which reduces cracks and deformation that may exist during rapid cooling. Oil quenching makes the cooling rate and transformation behavior more controllable, and improves the consistency and stability of the production process.

[0131] The present invention can make austenite inherit part of the dislocation density of the martensite matrix and the grain orientation of the original austenite through solution treatment-oil quenching treatment, thus making organizational preparation for aging treatment. Compared with water quenching, oil quenching is more gentle, reduces the internal stress and deformation caused by excessive temperature gradient, improves the overall stability of the ingot, retains part of the organizational toughness, and greatly reduces the performance fluctuation caused by water quenching. Ensure the performance consistency of each batch of products during large-scale production.

[0132] The present invention can promote martensitic transformation at low temperature, strengthen the microstructure of the steel ingot, and improve the low-temperature performance of the steel ingot by controlling the temperature of the deep cryogenic treatment. After the low-temperature deep cryogenic treatment, the structure of the steel ingot is more stable, and the performance will not decline after long-term service, thereby ensuring the consistency of the performance of the steel ingot during long-term use.

[0133] The present invention can transform austenite into martensite under the action of stress-induced phase transformation through aging treatment to adjust the content of reverse transformed austenite, thereby optimizing the phase transformation process of the steel ingot; the precipitated reverse transformed austenite can exert the TRIP (transformation induced plasticity) effect, absorb the energy required for the phase transformation from austenite to martensite, increase the toughness of the steel ingot, and delay the necking phenomenon, improve the uniformity of strain, and enhance the plasticity of the steel ingot.

[0134] The high-strength and plastic martensitic stainless steel of the present invention is in the shape of a block with a size of 40-44×6-10×6-9 mm; room temperature performance: hardness of 370.5HV-419.1HV, tensile strength of 1227.3-1363.0MPa, yield strength of 802.6-1242.1MPa, yield strength ratio of 0.746-0.911, elongation at break of 20.1-27.6%, cross-sectional shrinkage of 68.9-84.9%, and strength-plasticity product of 25.220-33.874GPa·%.

[0135] In summary, compared with other traditional methods, the method of the present invention prepares high-strength and plastic martensitic stainless steel through raw material design, weighing and smelting, homogenization heat treatment-oil quenching treatment, solution treatment-oil quenching treatment, temperature-controlled deep cold treatment and aging treatment for adjusting the reverse transformation austenite content; the method is simple and easy to operate, green and environmentally friendly, low in cost, short in process, high in efficiency, and is conducive to large-scale industrial production and promotion.

[0136] It should be understood that the term "and / or" in this article is only a description of the association relationship of associated objects, indicating that there can be three relationships. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. A and B can be singular or plural. In addition, the character " / " in this article generally indicates that the associated objects before and after are in an "or" relationship, but it may also indicate an "and / or" relationship. Please refer to the context for specific understanding.

[0137] In the present invention, "at least one" means one or more, and "plurality" means two or more. "At least one of the following" or similar expressions refers to any combination of these items, including any combination of single items or plural items. For example, at least one of a, b, or c can mean: a, b, c, ab, ac, bc, or abc, where a, b, and c can be single or multiple.

[0138] It should be understood that in various embodiments of the present invention, the size of the serial numbers of the above-mentioned processes does not mean the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present invention.

[0139] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art can easily think of changes or substitutions within the technical scope disclosed by the present invention, which should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A method for designing high-strength martensitic stainless steel based on phase transformation toughening, characterized in that: The method for designing high-strength martensitic stainless steel based on phase transformation toughening is as follows: S1. Raw material weighing and smelting: The composition content of high-strength martensitic stainless steel is designed, and the raw materials are weighed according to the chemical composition content. Then, the weighed raw materials are added into a vacuum induction furnace for smelting, and the smelted molten steel is cast to obtain an ingot; S2, homogenization heat treatment-oil quenching treatment: after heating the S1 ingot, perform homogenization heat treatment, and then perform oil quenching treatment to obtain a steel ingot with uniform structure; S3, solution treatment-oil quenching treatment: the steel ingot with uniform structure in S2 is heated for solution treatment, and then oil quenching is performed to obtain a solution steel ingot; S4, temperature-controlled cryogenic treatment: subjecting the S3 solid solution steel ingot to liquid nitrogen cryogenic treatment to obtain a cryogenic steel ingot; S5. Aging treatment for adjusting the reverse transformation austenite content: The S4 deep-cold steel ingot is subjected to aging treatment to adjust the reverse transformation austenite content, and air-cooled to room temperature to obtain high-strength and plastic martensitic stainless steel.

2. The method for designing high-strength martensitic stainless steel based on phase transformation toughening according to claim 1, characterized in that: The composition of S1 medium-high strength martensitic stainless steel is calculated by mass percentage as follows: Cr 10-12%, Ni 7-9%, Co 4-6%, Mo 2-4%, and it also contains Mn, V, Si, C and other elements, and the rest is Fe and unavoidable impurities.

3. The method for designing high-strength martensitic stainless steel based on phase transformation toughening according to claim 2, characterized in that: The total content of Mn, V, Si, C and other elements in S1 is 0.6-0.8%.

4. The method for designing high-strength martensitic stainless steel based on phase transformation toughening according to claim 1, characterized in that: The heating rate of the homogenization heat treatment in S2 is 3-5°C / min, the temperature is 950-1050°C, and the holding time is 60min; the oil temperature of the oil quenching treatment is 50-80°C, and the time of the oil quenching treatment is 3-5min.

5. The method for designing high-strength martensitic stainless steel based on phase transformation toughening according to claim 1, characterized in that: The heating rate of the solution treatment in S3 is 3-5°C / min, the temperature is 750-800°C, and the holding time is 60min; the oil temperature of the oil quenching treatment is 50-80°C, and the time of the oil quenching treatment is 2-3min.

6. The method for designing high-strength martensitic stainless steel based on phase transformation toughening according to claim 1, characterized in that: The temperature of liquid nitrogen cryogenic treatment in S4 is minus 73°C, and the treatment time is 100-140 minutes.

7. The method for designing high-strength martensitic stainless steel based on phase transformation toughening according to claim 1, characterized in that: The heating rate of aging treatment in S5 is 3-5℃ / min, the temperature is 300-600℃, and the holding time is 2-8h; the shape of high-strength and plastic martensitic stainless steel is block-shaped, and the size is 40-44×6-10×6-9mm; room temperature performance: hardness is 370.5HV-419.1HV, tensile strength is 1227.3-1363.0MPa, yield strength is 802.6-1242.1MPa, yield strength ratio is 0.746-0.911, elongation at break is 20.1-27.6%, cross-sectional shrinkage is 68.9-84.9%, and strength-plasticity product is 25.220-33.874GPa·%.

8. The method for designing high-strength martensitic stainless steel based on phase transformation toughening according to claim 1, characterized in that: When the content of precipitated reversed austenite in S5 is less than 53.5%, the strength will increase with the increase of austenite content. When the content of precipitated reversed austenite is greater than 53.5%, the strength will decrease with the increase of reversed austenite content.

9. The method for designing high-strength martensitic stainless steel based on phase transformation toughening according to claim 8, characterized in that: When S5 is heat treated at 500℃ for 4h, the reverse transformed austenite content is 53.5%. The room temperature properties are as follows: hardness is 418.7HV, tensile strength is 1363.0MPa, yield strength is 1242.1MPa, yield strength ratio is 0.911, elongation at break is 21.7%, cross-sectional shrinkage is 76.2%, and strength-ductility product is 29.578GPa·%.

10. The method for designing high-strength martensitic stainless steel based on phase transformation toughening according to claim 8, characterized in that: When S5 is heat treated at 400℃ for 4h, the reverse transformed austenite content is 30.9%. The room temperature properties are as follows: hardness is 419.1HV, tensile strength is 1358.3MPa, yield strength is 1195.4MPa, yield strength ratio is 0.880, elongation at break is 20.8%, cross-sectional shrinkage is 74.3%, and strength-ductility product is 28.253GPa·%.

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