A method for preparing a gradient martensite distributed ultrafine grain 301 stainless steel

Abstract

The present application belongs to the technical field of high-strength steel, and particularly relates to a preparation method of ultra-fine grain 301 stainless steel with gradient martensite distribution, comprising the following steps: high differential speed ratio hot rolling: selecting a plate, heating the plate to an appropriate temperature, keeping the plate at temperature for a certain period of time, then transferring the plate to a hot rolling unit, setting an appropriate upper and lower roller speed ratio, rolling with an appropriate reduction, then rapidly cooling the plate to room temperature; cold rolling: transferring the rolled plate to a cold rolling unit, cold rolling, and rolling the plate to an appropriate thickness; tempering: heating the cold-rolled plate to an appropriate temperature, keeping the plate at temperature for a certain period of time, then rapidly cooling the plate to room temperature; the present application introduces a gradient structure into the plate through high differential speed ratio rolling technology, and produces a gradient distribution of grain size in the thickness direction of the plate through the cooperation of the ingenious hot rolling process and cold rolling process, thereby improving the mechanical properties of the plate and solving the problem of improving the mechanical properties of the existing 301 stainless steel plate.

Description

Technical Field

[0001] This invention belongs to the field of high-strength steel technology, specifically relating to a method for preparing ultrafine-grained 301 stainless steel with gradient martensite distribution. Background Technology

[0002] 301 stainless steel strip is a metastable austenitic stainless steel, possessing a fully austenitic structure under sufficient solution treatment. Among austenitic stainless steels, 301 stainless steel is the easiest to cold-work strengthened; cold working can improve the steel's strength and hardness while retaining sufficient plasticity and toughness. This steel also exhibits good rust resistance under atmospheric conditions. However, current research on improving the performance of 301 stainless steel often reveals a "strength-toughness inversion" relationship in traditional manufacturing processes and microstructure design strategies, which limits further improvements in the performance of 301 stainless steel. In the process of "learning from nature," it was discovered that bamboo has a typical gradient structure. The density of bamboo's vascular bundle structure gradually decreases from the outside to the inside, and its core has good flexibility while maintaining overall strength and stiffness. Currently, the gradient structure has been successfully replicated in various metal materials, and its mechanical properties have been systematically studied. Related research shows that gradient structure metal materials can, to a certain extent, break the inverse relationship between the material's strength and plasticity, and obtain excellent strength and plasticity. Therefore, the design of the gradient structure provides a reference for solving the existing problem of the inverse relationship between the strength and toughness of 301 stainless steel. Currently, the most mature process for preparing gradient layered structures in metallic materials is surface gradient plastic deformation, such as surface mechanical grinding, surface mechanical milling, and surface mechanical pressing. This method can only achieve microstructure gradient changes on the material surface, and the thickness of the gradient layer is limited by the material's plasticity and size. Traditional preparation methods have limitations for the preparation of 301 stainless steel plates, and there is a bottleneck in improving the mechanical properties of 301 stainless steel plates.

[0003] Therefore, it is necessary to provide a method for preparing ultrafine-grained 301 stainless steel with gradient martensite distribution that can introduce a gradient martensite structure into the preparation of 301 stainless steel plates. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing ultrafine-grained 301 stainless steel with gradient martensite distribution, so as to solve the technical problem of martensite distribution in different thickness layers of 301 stainless steel plates.

[0005] To solve the above-mentioned technical problems, the present invention provides a method for preparing ultrafine-grained 301 stainless steel with gradient martensite distribution, comprising the following steps: Step 1, high differential speed ratio hot rolling: Select a plate, heat the plate to an appropriate temperature, hold the plate at that temperature for a certain period of time, then transfer the plate to a hot rolling mill, set an appropriate upper and lower roll speed ratio, perform rolling with an appropriate reduction, and then rapidly cool the plate to room temperature; Step 2, cold rolling: Transfer the plate rolled in Step 1 to a cold rolling mill for cold rolling to a suitable thickness; Step 3, tempering: Heat the plate cold-rolled in Step 2 to an appropriate temperature, hold it at that temperature for a certain period of time, and then rapidly cool it to room temperature.

[0006] Furthermore, in step one, the thickness of the sheet is 5mm-15mm, the rolling speed ratio is ≥2, and the proportion of sheet reduction is 50-80%.

[0007] Furthermore, in step one, the heating temperature of the plate is 500℃~600℃, and the heat preservation time of the plate is 5min-10min.

[0008] Furthermore, in step one, the plate is protected by protective gas throughout the entire process.

[0009] Furthermore, in step two, the rolling thickness of the sheet material is 0.05~0.5mm.

[0010] Furthermore, in step three, the heating temperature of the plate is 600℃~900℃.

[0011] Furthermore, in step three, the heat preservation time of the board is 60-180 seconds.

[0012] Furthermore, an ultrafine-grained 301 stainless steel with gradient martensite distribution was prepared using the above-described method for preparing ultrafine-grained 301 stainless steel with gradient martensite distribution.

[0013] Furthermore, the present invention provides a method for testing the performance of the ultrafine-grained 301 stainless steel with gradient martensite distribution. The heat-treated ultrafine-grained 301 stainless steel with gradient martensite distribution is processed into hot tensile specimens according to ASTM-E8-E8M standards and along the rolling direction using a wire cutting device, and then tensile performance tests are performed at a tensile rate of 1 mm / min.

[0014] Furthermore, the present invention provides a method for microscopic characterization testing of the ultrafine-grained 301 stainless steel with gradient martensite distribution. A 10mm×10mm heat-treated sample of the ultrafine-grained 301 stainless steel with gradient martensite distribution is prepared by using a wire cutting device. The sample is ground stepwise to 2000# with different grades of sandpaper, and then polished and etched. The microstructure of the sample is then observed.

[0015] The beneficial effects of this invention: 1. This invention introduces a gradient structure into 301 stainless steel sheet through high differential speed ratio rolling technology. By combining hot rolling and cold rolling processes, a gradient distribution of grain size is generated in the thickness direction of 301 stainless steel sheet. The gradient structure and gradient martensitic phase transformation are realized in stages during the preparation of 301 stainless steel sheet, and finally the martensite in 301 stainless steel sheet is gradient distributed. 2. This invention utilizes a gradient structure design, combined with novel methods and processes, to improve the mechanical properties of 301 stainless steel sheets, solving the problem of improving the mechanical properties of existing 301 stainless steel sheets. This invention has excellent effects on the preparation of gradient structures and the improvement of mechanical properties of 301 stainless steel sheets; 3. This invention, through its gradient structure design, greatly increases the tensile strength and elongation of 301 stainless steel sheet. Attached Figure Description

[0016] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0017] Figure 1 This is a schematic diagram of the microstructure of the ultrafine-grained 301 stainless steel with gradient martensite distribution according to the present invention. Figure 2 This is a graph showing the performance test data of the ultrafine-grained 301 stainless steel with gradient martensite distribution according to the present invention. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings. 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.

[0019] This invention provides a method for preparing ultrafine-grained 301 stainless steel with a gradient martensitic distribution, comprising the following steps: Step 1, high differential speed ratio hot rolling: Select a plate, heat the plate to an appropriate temperature, hold the plate at that temperature for a certain period of time, then transfer the plate to a hot rolling mill, set an appropriate upper and lower roll speed ratio, perform rolling with an appropriate reduction, and then rapidly cool the plate to room temperature; Step 2, cold rolling: Transfer the plate rolled in Step 1 to a cold rolling mill for cold rolling to a suitable thickness; Step 3, tempering: Heat the cold-rolled plate from Step 2 to an appropriate temperature, hold it at that temperature for a certain period of time... The plate is dried for a short time and then rapidly cooled to room temperature. In step one, the initial microstructure of the plate rolled at a high differential speed ratio is austenite, and after sufficient solution treatment and cooling, the microstructure of the plate is a gradient distribution of austenite + martensite. In step two, cold rolling promotes the martensitic transformation of the plate. Since austenite has different grains, the degree of martensitic transformation during cold rolling varies in the thickness direction of the plate, resulting in different martensite contents in the thickness direction, exhibiting a gradient distribution. In step three, the tempering process can greatly reduce the internal stress of the plate and improve its ductility and toughness. By performing high differential speed ratio rolling in the medium temperature range, shear deformation is introduced into the preparation process of the sheet metal, resulting in a gradient distribution of grain size in the thickness direction of the sheet metal. Secondly, the heating temperature in step one has two functions: 1. It can prevent the sheet metal from entering the two-phase region and introducing ferrite, which would affect the mechanical properties of the sheet metal; 2. The heating temperature is higher than the martensitic transformation temperature, which can prevent the sheet metal from undergoing martensitic phase transformation during deformation and avoid the formation of martensite. In the cold rolling process in step two, cold deformation is used to induce martensitic phase transformation in the metastable austenite of the sheet metal, thereby improving the strength and hardness of the sheet metal. Due to the gradient analysis of grains during high differential speed ratio rolling, the resistance of grains of different thicknesses to cold deformation varies during cold rolling, resulting in different degrees of martensitic phase transformation in different thickness layers. This leads to varying martensite content along the thickness direction, thereby utilizing the unique performance advantages of the gradient structure to improve the mechanical properties of the sheet material. This invention introduces a gradient structure into the sheet material through high differential speed ratio rolling technology, and through a clever combination of hot rolling and cold rolling processes, the gradient structure and gradient martensitic phase transformation are realized in stages during the sheet material preparation process, ultimately achieving a gradient distribution of martensite in the sheet material. This invention utilizes gradient structure design and combines novel methods and processes to improve the mechanical properties of the sheet material, solving the problem of improving the mechanical properties of existing 301 stainless steel sheets. This invention has a good effect on the preparation of gradient microstructure and the improvement of mechanical properties of 301 stainless steel sheets. Through gradient structure design, this invention greatly increases the tensile strength and elongation of 301 stainless steel sheets.

[0020] In step one, the thickness of the sheet is 5mm-15mm, the rolling speed ratio is ≥2, and the sheet reduction ratio is 50-80%.

[0021] In step one, the heating temperature of the plate is 500℃~600℃, and the heat preservation time of the plate is 5min-10min.

[0022] In step one, the board is protected by a protective gas throughout the process; the protective gas is preferably argon, which can effectively prevent the oxidation of the board.

[0023] In step two, the rolling thickness of the sheet material is 0.05~0.5mm.

[0024] In step three, the heating temperature of the plate is 600℃~900℃.

[0025] In step three, the heat preservation time of the board is 60-180 seconds.

[0026] The ultrafine-grained 301 stainless steel with gradient martensite distribution was prepared using the above-described method for preparing ultrafine-grained 301 stainless steel with gradient martensite distribution.

[0027] This invention provides a method for testing the performance of ultrafine-grained 301 stainless steel with gradient martensite distribution. The heat-treated ultrafine-grained 301 stainless steel with gradient martensite distribution is processed into hot tensile specimens according to ASTM-E8-E8M standards and along the rolling direction using a wire cutting device, and then tensile performance is tested at a tensile rate of 1 mm / min.

[0028] This invention provides a method for microscopic characterization testing of the ultrafine-grained 301 stainless steel with gradient martensite distribution. A 10mm×10mm heat-treated sample of the ultrafine-grained 301 stainless steel with gradient martensite distribution is prepared using a wire cutting device. The sample is ground stepwise to 2000# using sandpaper of different grades, followed by polishing and etching, and the microstructure of the sample is observed.

[0029] The following detailed description of the preparation method of pseudoboehmite provided by the present invention, in conjunction with the embodiments, should not be construed as limiting the scope of protection of the present invention. Example

[0030] Step 1: Select a 5mm thick plate and heat it to 500℃. Hold the plate at this temperature for 5 minutes. Then transfer the plate to a hot rolling mill, set the upper and lower roll speed ratio to 2, and roll it with a reduction of 50%. Then cool it to room temperature at a cooling rate of 50℃ / s.

[0031] Step 2: Transfer the sheet material rolled in Step 1 to the cold rolling mill for cold rolling, and finally roll the sheet material to a thickness of 0.05 mm.

[0032] Step 3: Heat the cold-rolled sheet material from Step 2 to 600℃, hold for 60s, and then cool the sheet material to room temperature at a cooling rate of 50℃ / s to complete the preparation of the gradient martensite-distributed ultrafine-grained 301 stainless steel.

[0033] like Figure 2 As shown, the method for testing the performance of the ultrafine-grained 301 stainless steel with gradient martensite distribution was used. The results showed that in this embodiment, the tensile strength of the prepared ultrafine-grained 301 stainless steel with gradient martensite distribution was 2000 MPa and the elongation was 11%. Example

[0034] Step 1: Select a 15mm thick plate and heat it to 900℃. Hold the plate at this temperature for 10 minutes. Then transfer the plate to a hot rolling mill, set the upper and lower roll speed ratio to 3, and roll it with a reduction of 50%. Then cool it to room temperature at a cooling rate of 50℃ / s.

[0035] Step 2: Transfer the sheet material rolled in Step 1 to the cold rolling mill for cold rolling, and finally roll the sheet material to a thickness of 0.5 mm.

[0036] Step 3: Heat the cold-rolled sheet material from Step 2 to 900℃, hold for 180s, and then cool the sheet material to room temperature at a cooling rate of 60℃ / s to complete the preparation of the gradient martensite distribution ultrafine grain 301 stainless steel.

[0037] like Figure 2 As shown, the method for testing the performance of the ultrafine-grained 301 stainless steel with gradient martensite distribution was described. The results showed that, in this embodiment, the tensile strength of the prepared ultrafine-grained 301 stainless steel with gradient martensite distribution was 2105 MPa, and the elongation was 10%. Example

[0038] Step 1: Select a 12mm thick plate and heat it to 900℃. Hold the plate at this temperature for 10 minutes. Then transfer the plate to a hot rolling mill, set the upper and lower roll speed ratio to 3, and roll it with a reduction of 80%. Then cool it to room temperature at a cooling rate of 70℃ / s.

[0039] Step 2: Transfer the sheet material rolled in Step 1 to the cold rolling mill for cold rolling, and finally roll the sheet material to a thickness of 0.2 mm.

[0040] Step 3: Heat the cold-rolled sheet material from Step 2 to 700℃, hold for 150s, and then cool the sheet material to room temperature at a cooling rate of 50℃ / s to complete the preparation of the gradient martensite distribution ultrafine grain 301 stainless steel.

[0041] like Figure 2 As shown, the method for testing the performance of the ultrafine-grained 301 stainless steel with gradient martensite distribution was used. The results showed that in this embodiment, the tensile strength of the prepared ultrafine-grained 301 stainless steel with gradient martensite distribution was 2084 MPa and the elongation was 10.3%. Example

[0042] like Figure 1 As shown, the microstructure of the ultrafine-grained 301 stainless steel with gradient martensite distribution was characterized using the microstructure testing method described above. The results show that, after processing by this process, the microstructure of the ultrafine-grained 301 stainless steel with gradient martensite distribution exhibits a clear gradient structure layer, which meets the process requirements.

[0043] Based on the above-described preferred embodiments of the present invention, and through the foregoing description, those skilled in the art can make various changes and modifications without departing from the inventive concept. The technical scope of this invention is not limited to the contents of the specification, but must be determined according to the scope of the claims.

Claims

1. A method for preparing ultrafine-grained 301 stainless steel with gradient martensite distribution, characterized in that, Includes the following steps: Step 1, high differential speed ratio hot rolling: Select a plate, heat the plate to an appropriate temperature, keep the plate at that temperature for a certain period of time, then transfer the plate to a hot rolling mill, set an appropriate upper and lower roll speed ratio, roll with an appropriate reduction, and then quickly cool the plate to room temperature; Step 2, cold rolling: The sheet material rolled in Step 1 is transferred to a cold rolling mill for cold rolling to achieve an appropriate thickness. Step 3, tempering: Heat the cold-rolled sheet from Step 2 to a suitable temperature, hold it at that temperature for a certain period of time, and then quickly cool it to room temperature; In step one, the thickness of the sheet material is 5mm-15mm, the rolling speed ratio is ≥2, and the sheet material reduction ratio is 50-80%. In step one, the heating temperature of the plate is 500℃-600℃, and the heat preservation time of the plate is 5min-10min. In step one, the plate is protected by protective gas throughout the entire process; In step two, the rolling thickness of the sheet metal is 0.05-0.5 mm; In step three, the heating temperature of the plate is 600℃-900℃; In step three, the heat preservation time of the board is 60-180 seconds.

2. The method for preparing ultrafine-grained 301 stainless steel with gradient martensite distribution as described in claim 1, characterized in that, Ultrafine-grained 301 stainless steel with gradient martensite distribution was prepared using this method.

3. The method for preparing ultrafine-grained 301 stainless steel with gradient martensite distribution as described in claim 2, characterized in that, The performance testing method for ultrafine-grained 301 stainless steel with gradient martensite distribution is as follows: The heat-treated ultrafine-grained 301 stainless steel with gradient martensite distribution was processed into hot tensile specimens according to ASTM-E8-E8M standards and along the rolling direction using a wire cutting device, and then tensile properties were tested at a tensile rate of 1 mm / min.

4. The method for preparing ultrafine-grained 301 stainless steel with gradient martensite distribution as described in claim 3, characterized in that, The microscopic characterization test method for ultrafine-grained 301 stainless steel with gradient martensite distribution is as follows: A 10mm × 10mm heat-treated sample of the ultrafine-grained 301 stainless steel with gradient martensite distribution was prepared using a wire cutting device. The sample was ground stepwise to 2000# using different grades of sandpaper, and then polished and etched. The microstructure of the sample was then observed.

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