Preparation process of high-toughness 301 stainless steel

Abstract

This invention relates to the field of metal material processing technology and discloses a preparation process for high-strength and high-toughness 301 stainless steel. Through multi-stage synergistic regulation of microstructure via warm rolling and deep cryogenic rolling, the microstructure evolution of 301 stainless steel during deformation and phase transformation is precisely controlled, promoting the formation of fine-grained austenite and ultrafine martensite. This ensures high strength while maintaining excellent ductility, achieving a significant improvement in strength-ductility product. Furthermore, the process is directly adaptable to existing mainstream rolling production lines and is suitable for large-scale industrial production.

Description

Technical Field

[0001] This invention relates to the field of metal material processing technology, specifically to a preparation process for high-strength and high-toughness 301 stainless steel. Background Technology

[0002] 301 stainless steel is widely used in rail transportation, aerospace, and other fields due to its excellent corrosion resistance, high strength, and work hardening ability. Traditional manufacturing processes often employ cold rolling, but during cold rolling, austenite (γ phase) undergoes stress-induced transformation into martensite (α' phase). While martensite improves strength, its hard and brittle properties significantly reduce the material's ductility and formability, leading to cracking or fracture failure during subsequent processing. Existing technologies often use annealing to restore the material's plasticity, but high-temperature annealing causes martensite decomposition and grain growth, sacrificing material strength and failing to meet the high-strength requirements of advanced equipment. Some studies have used cryogenic treatment to optimize the microstructure of 301 stainless steel, but conventional cryogenic treatment only modifies the post-rolling microstructure and has limited effect on grain refinement, making it difficult to achieve a synergistic improvement in strength and plasticity. Therefore, developing a novel rolling process that can effectively suppress excessive martensite formation and achieve grain refinement and a synergistic balance between strength and plasticity is of significant scientific and engineering importance. Summary of the Invention

[0003] To address the shortcomings of existing technologies, this invention provides a manufacturing process for high-strength and high-toughness 301 stainless steel. Through multi-stage synergistic control of microstructure via warm rolling and deep cryogenic rolling, excellent ductility is maintained while ensuring high material strength, achieving a significant improvement in strength-ductility product. Furthermore, the process is directly adaptable to existing mainstream rolling production lines, making it suitable for large-scale industrial production.

[0004] To achieve the above objectives, the present invention provides the following technical solution: a preparation process for high-strength and high-toughness 301 stainless steel, comprising the following steps: (1) Annealing pretreatment: Hold the original 301 stainless steel sheet at 1180-1220℃ for 8-12 minutes to make the sheet completely austenitized; (2) Warm rolling pre-control: After the austenitized plate is heated to 180-220℃ and held for a period of time, it is rolled in multiple passes with a total deformation of 40%-60% to obtain a warm rolled plate with twinned austenite as the main structure. (3) Deep cold rolling strengthening: The warm rolled plate is pre-immersed in liquid nitrogen for cooling. During the rolling process, a liquid nitrogen spraying system is used to dynamically cool the contact area between the roll and the plate in real time, and the rolling interface temperature is controlled to be stable at -180--150℃. The total deformation is 30%-50%, which induces the transformation of twinned austenite to ultrafine martensite. (4) Low temperature structure stabilization treatment: The plate after cryogenic rolling is heated to 40-60℃ to eliminate rolling internal stress and promote recrystallization to refine the grains. It is then naturally cooled to room temperature to obtain high strength and toughness 301 stainless steel.

[0005] Preferably, the heat preservation time in step (2) is 10-30 min, and the single-pass reduction rate in the warm rolling process is controlled at 5%-15%. This temperature range can promote the formation of a large amount of twinned austenite while inhibiting the premature precipitation of martensite and avoiding the deterioration of the final performance by coarse-grained martensite.

[0006] Preferably, in step (3), the liquid nitrogen injection flow rate is 0.3-1.0 L / min, and the cooling area covers 85%-95% of the contact surface between the roll and the plate. This dynamic cooling method can offset the frictional heat and deformation heat generated during the rolling process in real time, ensuring that the rolling interface temperature is always maintained within the target range and improving the uniformity of the martensitic phase transformation.

[0007] Preferably, after the cryogenic rolling in step (3) is completed, the average grain size of the generated ultrafine martensite is ≤200nm.

[0008] Preferably, the microstructure of the 301 stainless steel prepared by the high-strength and tough 301 stainless steel preparation process consists of two phases: 40%-60% by volume of residual austenite, mainly fine-grained austenite separated by twin boundaries, with an average grain size of 0.5-2 μm; and 40%-60% by volume of ultrafine martensite, which is a diffusely distributed nanoscale lath structure, with a coherent interface formed between the two phases.

[0009] In summary, this application includes at least one of the following beneficial technical effects: Collaborative innovation in processes: For the first time, a three-stage process route of "warm rolling pre-control - deep cryogenic rolling strengthening - low temperature stabilization" was proposed. In the warm rolling stage, high-density twinned austenite is generated in advance as a "precursor" for martensitic phase transformation. In the deep cryogenic stage, a controllable phase transformation is achieved to generate ultrafine martensite, breaking through the performance bottleneck of "strength improvement is inevitably accompanied by plasticity decrease" in traditional processes. The final material strength-plasticity product can reach 37.8 GPa·

[0010] Breakthrough in dynamic temperature control technology: To address the interface temperature rise caused by deformation heat and frictional heat during cryogenic rolling, liquid nitrogen dynamic spray cooling is adopted in real time. This can control the temperature fluctuation of the rolling interface within ±5℃, ensuring the uniformity of martensitic phase transformation, avoiding the formation of local coarse-grained martensite, and improving the consistency of product performance.

[0011] Low energy consumption and high adaptability: The process route has good engineering adaptability, requiring no complex equipment or extremely high energy consumption. Liquid nitrogen cooling and low-temperature heat treatment have controllable costs, making it suitable for large-scale production. This process provides a new approach for the green preparation of high-strength and tough stainless steel, which helps to promote the material upgrading of industries such as high-end equipment manufacturing and transportation, improve product performance and service life, and is in line with the high-quality development direction of the manufacturing industry. It has profound significance for social energy transformation and sustainable development. Attached Figure Description

[0012] Figure 1 SEM image of the microstructure of 301 stainless steel prepared by traditional cold rolling process; Figure 2 This is a SEM image of the microstructure of 301 stainless steel prepared in Example 1 of the present invention. Detailed Implementation

[0013] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are described clearly and completely. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0014] To better understand the above technical solutions, the following will provide a detailed description of the technical solutions in conjunction with the accompanying drawings and specific embodiments.

[0015] Example 1 The preparation process of high-strength and high-toughness 301 stainless steel in this embodiment includes the following steps: (1) Select a 2mm thick 301 stainless steel raw plate and place it in a box-type heat treatment furnace at 1200℃ for 10 minutes to make it completely austenitic. (2) The austenitized sheet was transferred to a box furnace at 200℃ and kept warm for 20 minutes. Then, it was warm rolled using a four-roll mill with a single pass reduction rate of 10% and a total deformation of 50%, to obtain a warm rolled sheet with a thickness of 1 mm. (3) The warm-rolled plate was immersed in liquid nitrogen for cooling, and then deep-cold rolling was carried out. During the rolling process, liquid nitrogen was sprayed into the contact area between the roll and the plate at a flow rate of 0.5L / min. The cooling coverage rate was 85%, the rolling interface temperature was controlled at -160±5℃, the total deformation was 30%, and a deep-cold rolled plate with a thickness of 0.7mm was obtained. (4) Heat the cryogenic rolled plate to 50°C to eliminate internal stress, and then let it cool naturally to room temperature to obtain the finished product.

[0016] Mechanical property tests were performed on the finished product of this embodiment: tensile strength was 1350 MPa, elongation at break was 28%, and strength-ductility product was 37.8 GPa·s. 10 mm × 10 mm samples were cut from the stamped part using wire cutting. The samples were progressively ground with different grades of sandpaper up to 2000#, followed by polishing and etching. Microscopic characterization of the samples was performed using SEM, and the characterization results are as follows: Figure 2 .

[0017] Example 2 The preparation process of high-strength and high-toughness 301 stainless steel in this embodiment includes the following steps: (1) Select a 2mm thick 301 stainless steel raw plate and place it in a box-type heat treatment furnace at 1200℃ for 10 minutes to make it completely austenitic. (2) The austenitized sheet was transferred to a box furnace at 200℃ and kept warm for 20 minutes. Then, it was warm rolled using a four-roll mill with a single pass reduction rate of 10% and a total deformation of 50%, to obtain a warm rolled sheet with a thickness of 1 mm. (3) The warm-rolled plate was immersed in liquid nitrogen for cooling, and then deep-cold rolling was carried out. During the rolling process, liquid nitrogen was sprayed into the contact area between the roll and the plate at a flow rate of 0.6L / min. The cooling coverage rate was 85%, the rolling interface temperature was controlled at -170±5℃, and the total deformation was 40%, resulting in a deep-cold rolled plate with a thickness of 0.6mm. (4) Heat the cryogenic rolled plate to 50°C to eliminate internal stress, and then let it cool naturally to room temperature to obtain the finished product.

[0018] Mechanical properties of the finished product in this embodiment were tested: tensile strength was 1300 MPa, elongation at break was 25%, and strength-ductility product was 32.5 GPa·s.

[0019] Example 3 The preparation process of high-strength and high-toughness 301 stainless steel in this embodiment includes the following steps: (1) Select a 2mm thick 301 stainless steel raw plate and place it in a box-type heat treatment furnace at 1200℃ for 10 minutes to make it completely austenitic. (2) The austenitized sheet was transferred to a box furnace at 200℃ and kept warm for 20 minutes. Then, it was warm rolled using a four-roll mill with a single pass reduction rate of 10% and a total deformation of 50%, to obtain a warm rolled sheet with a thickness of 1 mm. (3) The warm-rolled plate was immersed in liquid nitrogen for 8 minutes to cool it down, and then deep-cold rolling was carried out. During the rolling process, liquid nitrogen was sprayed into the contact area between the roll and the plate at a flow rate of 0.7L / min. The cooling coverage rate was 85%, the rolling interface temperature was controlled at -175±5℃, and the total deformation was 50%, resulting in a deep-cold rolled plate with a thickness of 0.5mm. (4) Heat the cryogenic rolled plate to 50°C to eliminate internal stress, and then let it cool naturally to room temperature to obtain the finished product.

[0020] Mechanical properties of the finished product in this embodiment were tested: tensile strength was 1320 MPa, elongation at break was 26%, and strength-ductility product was 34.32 GPa·s.

[0021] Comparative Example 1 301 stainless steel was prepared using a traditional cold rolling process as a control: a 2mm thick original sheet was austenitized by holding it at 1200℃ for 10 minutes, and then subjected to multiple cold rolling passes at room temperature with a total deformation of 75% to obtain a finished product with a thickness of 0.5mm. Subsequently, it was annealed at 200℃ to relieve stress.

[0022] Mechanical properties of the finished product in this comparative example were tested: tensile strength was 1100 MPa, elongation at break was 18%, and strength-ductility product was 19.8 GPa·s.

[0023] It should be noted that, in this document, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Unless otherwise specified, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0024] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

[0025] Those skilled in the art should understand that the above descriptions are merely several specific embodiments of the present invention, and not all embodiments. It should be noted that many modifications and improvements can be made by those skilled in the art, and all modifications or improvements not exceeding the scope of the claims should be considered within the protection scope of the present invention.

Claims

1. A preparation process for high-strength and high-toughness 301 stainless steel, characterized in that, Includes the following steps: (1) Annealing pretreatment: Hold the original 301 stainless steel sheet at 1180-1220℃ for 8-12 minutes to make the sheet completely austenitized; (2) Warm rolling pre-control: After the austenitized plate is heated to 180-220℃ and held for a period of time, it is rolled in multiple passes with a total deformation of 40%-60% to obtain a warm rolled plate with twinned austenite as the main structure. (3) Deep cold rolling strengthening: The warm rolled plate is pre-immersed in liquid nitrogen for cooling. During the rolling process, a liquid nitrogen spraying system is used to dynamically cool the contact area between the roll and the plate in real time, and the rolling interface temperature is controlled to be stable at -180--150℃. The total deformation is 30%-50%, which induces the transformation of twinned austenite to ultrafine martensite. (4) Low temperature structure stabilization treatment: The plate after cryogenic rolling is heated to 40-60℃ to eliminate rolling internal stress and promote recrystallization to refine the grains. It is then naturally cooled to room temperature to obtain high strength and toughness 301 stainless steel.

2. The preparation process of high-strength and high-toughness 301 stainless steel according to claim 1, characterized in that, In step (2), the holding time is 10-30 min, and the single-pass reduction rate of the warm rolling process is controlled at 5%-15%. This temperature range can promote the formation of a large amount of twinned austenite while inhibiting the early precipitation of martensite and avoiding the deterioration of the final performance by coarse-grained martensite.

3. The preparation process of high-strength and high-toughness 301 stainless steel according to claim 1, characterized in that, In step (3), the liquid nitrogen injection flow rate is 0.3-1.0 L / min, and the cooling area covers 85%-95% of the contact surface between the roll and the plate. This dynamic cooling method can offset the frictional heat and deformation heat generated during the rolling process in real time, ensuring that the rolling interface temperature is always maintained within the target range and improving the uniformity of the martensitic phase transformation.

4. The preparation process of high-strength and high-toughness 301 stainless steel according to claim 1, characterized in that, After the deep cold rolling in step (3) is completed, the average grain size of the generated ultrafine martensite is ≤200nm.

5. The preparation process of high-strength and high-toughness 301 stainless steel according to claim 1, characterized in that, The microstructure of the prepared 301 stainless steel consists of two phases: 40%-60% retained austenite by volume, mainly fine-grained austenite separated by twin boundaries, with an average grain size of 0.5-2 μm; and 40%-60% ultrafine martensite by volume, which is a diffusely distributed nanoscale lath structure, with a coherent interface between the two phases.

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