Preparation method for improving strength and plasticity of martensitic stainless steel

Abstract

The invention discloses a preparation method for improving the strength and plasticity of martensitic stainless steel, which comprises the following steps: heating martensitic steel to the temperature above Ac3, preserving heat for a period of time to completely austenitize the structure, and then quickly spraying water to cool the austenitized martensitic steel to a metastable austenite area; warm rolling is conducted on the heated martensitic steel; after warm rolling, rapidly cooling to a temperature lower than the martensite transformation initial temperature; the quenched steel is subjected to partition treatment, and the material is reheated; and cooling to room temperature after the partitioning treatment is finished, thereby obtaining the product. The purpose is achieved mainly through a warm rolling-quenching-partitioning process, according to the process, warm rolling machining is carried out in a metastable austenite area, grains are remarkably refined, the dislocation density in a matrix is improved, effective distribution of carbon elements is promoted in the subsequent quenching and partitioning stages, and finally a certain amount of retained austenite is reserved in a structure.

Description

Technical Field

[0001] The invention relates to a metal material processing method, in particular to a hot processing method for improving the strength and plasticity of martensitic stainless steel. Background Art

[0002] Martensitic stainless steel is widely used in the manufacture of various mechanical parts and tools due to its high hardness, strength and good corrosion resistance, especially in situations where certain wear resistance and corrosion resistance are required, such as knives, valves and bearings. However, although martensitic steel excels in high hardness and corrosion resistance, its toughness is relatively low, and it is more prone to brittle fracture, especially under low temperature conditions. For this reason, the application of this type of steel is limited in certain fields with high toughness requirements. Although traditional heat treatment methods (such as quenching + tempering) can increase the hardness of the material, the plasticity decreases significantly, making it difficult to balance strength and ductility. Therefore, the optimization of the mechanical properties of martensitic steel has become an urgent problem to be solved in the industry.

[0003] In recent years, studies have found that by controlling the microstructure, such as refining grains, introducing residual austenite, and increasing dislocation density, it is possible to achieve a simultaneous improvement in strength and plasticity. Warm rolling combined with a quenching-partitioning process can introduce a high-density dislocation structure into the steel, refine the grains, and retain a certain amount of residual austenite in the structure, thereby improving the overall performance of the material. However, there is currently a gap in the research and application of using this process to optimize the performance of martensitic steel. Based on this theory, the present invention proposes an innovative process route that significantly improves the strength-plasticity matching of martensitic steel through a warm rolling-quenching-partitioning process. Summary of the invention

[0004] Purpose of the invention: In view of the shortcomings of the prior art, the present invention provides a preparation method for improving the strength and plasticity of martensitic stainless steel. The main process of the method includes a warm rolling-quenching-partitioning method, which can effectively control the austenite content under low-carbon conditions, and improve the strength and toughness of the material by refining the grains and increasing the dislocation density, thereby overcoming the shortcomings of the prior art and having important technical significance and practical application value.

[0005] Technical solution: The preparation method for improving the strength and plasticity of martensitic stainless steel according to the present invention specifically comprises the following steps:

[0006] (1) The martensitic steel is heated to a temperature above Ac3, kept at this temperature for a period of time to completely austenitize the structure, and then the austenitized martensitic steel is rapidly cooled by spraying water to the metastable austenite region;

[0007] (2) warm rolling the heated martensitic steel;

[0008] (3) After warm rolling, it is rapidly cooled to a temperature below the martensitic transformation start temperature;

[0009] (4) Partitioning the quenched steel and reheating the material;

[0010] (5) After the distribution process is completed, cool to room temperature to obtain the product.

[0011] Furthermore, in step (1), A c3 The insulation time above the temperature is 30-50 minutes.

[0012] Furthermore, in the step (1), the austenitized martensitic steel is then rapidly cooled to 700°C-750°C by spraying water.

[0013] Furthermore, in the step (2), the warm rolling deformation is 70%-90%.

[0014] Furthermore, in step (3), the martensitic transformation starting temperature is 200°C-300°C.

[0015] Furthermore, the heating temperature in step (4) is 350° C.-400° C., and the insulation time is 5-30 min.

[0016] Furthermore, the rapid cooling method adopts water cooling, and the cooling rate is greater than 50°C / s.

[0017] Furthermore, the tensile strength of the finally prepared martensitic steel is ≥1280.9 MPa; and the total elongation is ≥9.8%.

[0018] Furthermore, the chemical composition of martensitic stainless steel mainly includes C (≤0.15), Cr (12%-13%), Si (≤0.5%), and Mn (≤1%).

[0019] The plan is detailed as follows:

[0020] 1. Material selection

[0021] The basic material is martensitic steel, and its chemical composition mainly includes C (≤0.15), Cr (12%-13%), Si (≤0.5%), Mn (≤1%), etc.

[0022] 2. Warm rolling process

[0023] The martensitic steel is heated to A c3 The temperature is kept above 950-1150℃ for a period of time to make the structure completely austenitized, and then the austenitized martensitic steel is quickly sprayed with water to cool the metastable austenite zone (about 700℃-750℃). Then warm rolling is carried out, and the deformation is controlled at 70%-90%. High-density dislocations are generated during warm rolling, and the austenite grains are refined, laying the foundation for subsequent processes.

[0024] 3.Quenching process

[0025] After warm rolling, it is rapidly cooled to a temperature below the martensite transformation start temperature (M s , about 200℃-300℃) to form a structure mainly composed of martensite and a small amount of retained austenite. The cooling rate must be fast enough to avoid pearlite precipitation.

[0026] 4. Distribution process

[0027] The quenched material is heated to the partitioning temperature (350℃-400℃) and kept at this temperature for a period of time (5-30min). The partitioning process promotes the diffusion of carbon in the martensite into the residual austenite, which improves the stability of the austenite. At the same time, the partitioning temperature controls the degree of carbide precipitation to maintain the uniformity of the dislocation structure.

[0028] 5. Cooling treatment

[0029] After partitioning is completed, the material is water-cooled to room temperature to form a stable multiphase structure, maintain a high proportion of retained austenite and maintain an appropriate dislocation density.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] 1. Improve the comprehensive mechanical properties of materials: This process adopts the treatment method of warm rolling-quenching-partitioning. Through the pre-warm rolling plastic deformation, the grains are significantly refined, and high-density dislocations are introduced into the material to achieve dislocation strengthening and fine grain strengthening, which effectively improves the strength of martensitic steel.

[0032] 2. Improve the plasticity and ductility of the material: Stabilize the retained austenite through partitioning treatment, so that the material has high strength and excellent plasticity and ductility, thereby expanding the application range of the material.

[0033] 3. High process controllability: This process ensures the controllability of process parameters and high repeatability of the production process by precisely controlling temperature, holding time and deformation, thus ensuring the stable quality of the final product.

[0034] 4. Reduce the tendency of cracks in production: Combining rapid cooling and partitioning treatment effectively reduces the occurrence of stress concentration during quenching, reduces the tendency of materials to crack, and significantly improves the overall reliability of the product.

[0035] 5. Enhance the wear resistance and fatigue resistance of materials: By refining the grains and stabilizing the residual austenite phase structure, the wear resistance of the material is improved, the stress concentration effect is reduced, thereby improving the fatigue resistance of the material and extending the service life. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1It is a process diagram of the method of the present invention, showing the specific process steps of the warm rolling-quenching-partitioning process;

[0037] Figure 2 (a) is a microscopic photograph of the microstructure of the martensitic steel (1Cr13) after partitioning in Example 1, showing the distribution of retained austenite and martensite;

[0038] Figure 3 The microstructure micrograph (b) of the martensitic steel (1Cr13) after partitioning in Example 2 shows the distribution of retained austenite and martensite;

[0039] Figure 4 This is a mechanical property test curve, which shows the improvement effect of this process on tensile strength and ductility. DETAILED DESCRIPTION

[0040] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described in combination with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, other embodiments obtained by ordinary technicians in this field without creative work are all within the scope of protection of the present invention.

[0041] The method for preparing martensitic stainless steel to improve its strength and plasticity in the embodiment comprises the following steps:

[0042] (1) Heat the martensitic steel to A c3 The temperature is kept above 100°C for a period of time to make the structure completely austenitized, and then the austenitized martensitic steel is quickly sprayed with water to cool to the metastable austenite region;

[0043] (2) warm rolling the heated martensitic steel;

[0044] (3) After warm rolling, it is rapidly cooled to a temperature below the martensitic transformation start temperature;

[0045] (4) Partitioning the quenched steel and reheating the material;

[0046] (5) After the distribution process is completed, cool to room temperature to obtain the product.

[0047] The parameters are set as follows:

[0048] Embodiment 1:

[0049] See also Figure 1 The preparation method for improving the strength and plasticity of martensitic stainless steel provided in the embodiment of the present invention specifically comprises the following steps:

[0050] 1.1Cr13 steel plate (C-0.124%, Si-0.474%, Cr-12.37%, Mn-1%, Mo-0.042%, A1-0.032%)

[0051] 2. Warm rolling conditions: 1000℃ for 45min, then quickly cooled to 750℃ by water spraying, rolling deformation 80%

[0052] 3. Quenching conditions: Rapid salt bath cooling to 240°C and keep warm for 1 minute

[0053] 4. Distribution conditions: 400°C for 10 minutes

[0054] 5. Cooling conditions: After the partitioning is completed, water quenching to room temperature

[0055] 6.Performance test: tensile strength 1290.5MPa, total elongation 11.8%

[0056] Compared with the original sample, the tensile strength increased by nearly 270MPa and the elongation increased by 3.2 times

[0057] Embodiment 2:

[0058] 1.1Cr13 steel plate (C-0.099%, Si-0.267%, Cr-12.19%, Mn-0.81%, Mo-0.049%, A1-0.033%)

[0059] 2. Warm rolling conditions: 1000℃ for 45min, then quickly cooled to 750℃ by water spraying, rolling deformation 90%

[0060] 3. Quenching conditions: Rapid salt bath cooling to 240°C and keep warm for 1 minute

[0061] 4. Distribution conditions: 400°C for 5 minutes

[0062] 5. Cooling conditions: After the partitioning is completed, water quenching to room temperature

[0063] 6.Performance test: tensile strength 1366.3MPa, total elongation 10.1%

[0064] Compared with the original sample, the tensile strength increased by nearly 350MPa and the elongation increased by 2.8 times

[0065] Example 3

[0066] 1.1Cr13 plate (C-0.15%, Si-0.342%, Cr-12.79%, Mn-0.727%, Mo-0.046%, Al-0.031%)

[0067] 2. Warm rolling conditions: 950℃ for 50min, then quickly spray water to cool to 700℃, rolling deformation 80%

[0068] 3. Quenching conditions: Rapid salt bath cooling to 240°C and keep warm for 1 minute

[0069] 4. Distribution conditions: 350°C for 5 minutes

[0070] 5. Cooling conditions: Cool to room temperature after distribution

[0071] 6. Performance test: tensile strength 1328.6MPa, total elongation 9.8%

[0072] Compared with the original sample, the tensile strength increased by nearly 310MPa and the elongation increased by 2.7 times

[0073] Example 4

[0074] 1.1Cr13 plate (C-0.118%, Si-0.5%, Cr-12.99%, Mn-0.84%, Mo-0.041%, A1-0.035%)

[0075] 2. Warm rolling conditions: 1150℃ for 30min, then quickly cooled to 750℃ by water spraying, rolling deformation 70%

[0076] 3. Quenching conditions: Rapid salt bath cooling to 240°C and keep warm for 1 minute

[0077] 4. Distribution conditions: 400°C for 30 minutes

[0078] 5. Cooling conditions: water cooling to room temperature after distribution

[0079] 6. Performance test: tensile strength 1280.9MPa, total elongation 10.3%

[0080] Compared with the original sample, the tensile strength increased by nearly 260MPa and the elongation increased by nearly 2.9 times.

[0081] The present invention is theoretically applicable to all martensitic steels for the following reasons:

[0082] 1. The warm rolling process significantly refines the grains and introduces high-density dislocations. The residual austenite is stabilized by carbon diffusion in the partitioning stage, thereby improving strength and toughness. These mechanisms are applicable to all martensitic steels.

[0083] 2. The warm rolling-quenching-partitioning process parameters (such as warm rolling temperature, quenching temperature and partitioning conditions) can be adjusted according to the composition and performance requirements of different martensitic steels. Through grain refinement, dislocation strengthening and residual austenite stabilization, the brittleness can be effectively reduced and the comprehensive performance can be optimized. It is suitable for various types of martensitic steels.

[0084] The above is only a preferred embodiment of the present invention and does not limit the present invention in any way. Any technician in the relevant technical field, without departing from the scope of the technical solution of the present invention, makes any form of equivalent replacement or modification to the technical solution and technical content disclosed in the present invention, which does not depart from the content of the technical solution of the present invention and still falls within the protection scope of the present invention.

Claims

1. A preparation method for improving the strength and plasticity of martensitic stainless steel, characterized in that: The following steps are involved: (1) Heat the martensitic steel to A c3 The temperature is kept above 100°C for a period of time to make the structure completely austenitized, and then the austenitized martensitic steel is quickly sprayed with water to cool to the metastable austenite region; (2) warm rolling the heated martensitic steel; (3) Rapid cooling after warm rolling to a temperature below the martensitic transformation start temperature; (4) Partitioning the quenched steel and reheating the material; (5) After the distribution process is completed, cool to room temperature to obtain the product.

2. The method for improving the strength and plasticity of martensitic stainless steel according to claim 1, characterized in that: In the step (1), A c3 The insulation time above the temperature is 30-50 minutes.

3. According to the preparation method for improving the strength and plasticity of martensitic stainless steel as described in claim 1, in the step (1), the austenitized martensitic steel is then rapidly cooled to 700°C-750°C by spraying water.

4. The method for improving the strength and plasticity of martensitic stainless steel according to claim 1, characterized in that: In the step (2), the warm rolling deformation is 70%-90%.

5. The method for improving the strength and plasticity of martensitic stainless steel according to claim 1, characterized in that: In the step (3), the martensitic transformation starting temperature is 200°C-300°C.

6. The method for improving the strength and plasticity of martensitic stainless steel according to claim 1, characterized in that: The heating temperature in step (4) is 350° C.-400° C., and the insulation time is 5-30 minutes.

7. The method for improving the strength and plasticity of martensitic stainless steel according to claim 1, characterized in that: The rapid cooling method adopts water cooling, and the cooling rate is greater than 50°C / s.

8. The method for improving the strength and plasticity of martensitic stainless steel according to claim 1, characterized in that: The tensile strength of the finally prepared martensitic steel is ≥1280.9MPa; and the total elongation is ≥9.8%.

9. The method for improving the strength and plasticity of martensitic stainless steel according to claim 1, characterized in that: The chemical composition of martensitic stainless steel mainly includes C (≤0.15), Cr (12%-14%), Si (≤1%), and Mn (≤1%).

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