Continuous production method of high-strength and high-toughness austenitic stainless steel plate with 3D full-gradient structure

Abstract

The invention provides a continuous production method of a high-strength and high-toughness austenitic stainless steel plate with a 3D full-gradient structure, and belongs to the technical field of stainless steel plate production. According to the method, an austenitic stainless steel plate is subjected to cold rolling and cutting, the size specification and the surface quality of the austenitic stainless steel plate are controlled, and then the rolled austenitic stainless steel plate is subjected to austenitizing treatment; or the austenitic stainless steel plate is firstly subjected to hot rolling to control the size specification, then rapid cooling is conducted, and the coarse-grain single-phase austenite structure is obtained. And then, reciprocating torsional deformation is conducted on the coarse-grain single-phase austenitic stainless steel plate, on the basis that the macroscopic size specification of the coarse-grain single-phase austenitic stainless steel plate is not changed, combination of the strength and the toughness of the coarse-grain single-phase austenitic stainless steel plate is greatly improved, and finally the plate is rolled into a The size specification and the surface quality of the plate are accurately controlled by adjusting a rolling process; and meanwhile, controllable construction of a 3D full-gradient structure is achieved by regulating and controlling reciprocating torsion technological parameters, and therefore cooperation of high strength and high toughness is achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of stainless steel plate production, and in particular to a method for continuously producing a high-strength and high-toughness 3D full-gradient structure austenitic stainless steel plate. Background Art

[0002] Rolling is the main technology for producing austenitic stainless steel sheets. Austenitic stainless steel sheets produced by traditional hot rolling or cold rolling technology have relatively uniform structure, but their performance advantages are usually relatively single, and they can usually only choose between strength or toughness. Therefore, it is difficult to achieve one-time forming and continuous production of austenitic stainless steel sheets with both high strength and high toughness through low-cost processes.

[0003] The synergy of high strength and high toughness is a necessary condition for the widespread application of metal sheets. The yield strength of austenitic stainless steel sheets produced by traditional hot rolling technology is usually low (<300MPa), which limits its application in high-strength fields; and although austenitic stainless steel sheets produced by traditional cold rolling technology have high yield strength, their plasticity and toughness are poor, which cannot ensure the safety and reliability of high-strength sheets, thus limiting their scope of application, and usually require subsequent heat treatment to improve toughness. Therefore, it is of great significance to achieve low-cost production of austenitic stainless steel sheets with both high strength and high toughness, but it still faces technical challenges. Summary of the invention

[0004] The purpose of the present invention is to provide a method for continuous production of high-strength and high-toughness 3D full-gradient structure austenitic stainless steel plates, which is used to solve the technical problem that stainless steel plates produced by traditional rolling processes can only obtain a single property of high strength or high toughness, but cannot simultaneously meet the requirements of high strength and high toughness.

[0005] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0006] The present invention provides a method for continuously producing a high-strength and high-toughness 3D full-gradient structure austenitic stainless steel plate, comprising the following steps:

[0007] 1) cold rolling and austenitizing the austenitic stainless steel sheet in sequence; or hot rolling and cooling the austenitic stainless steel sheet in sequence to control its size and surface quality, to obtain a coarse-grained single-phase austenitic stainless steel sheet with a controlled thickness of 0.3 to 3 mm and a width of 5 to 1000 mm;

[0008] 2) The coarse-grained single-phase austenitic stainless steel plate is subjected to reciprocating torsional deformation, and then the plate is rolled into a round shape;

[0009] The reciprocating torsional deformation has an angle of 5 to 50°, a number of passes of 15 to 60 times, and a speed of 30 to 60° / min.

[0010] Furthermore, the cold rolling temperature is 20-40°C, and the hot rolling temperature is 1000-1300°C.

[0011] Furthermore, the reduction ratios of the cold rolling and the hot rolling are independently 50 to 70%.

[0012] Furthermore, the temperature of the austenitizing treatment is 800-1000° C., and the time of the austenitizing treatment is 0.5-2 h.

[0013] Furthermore, the cooling rate is 200-500° C. / min.

[0014] Furthermore, the reciprocating torsional deformation does not change the macroscopic size specifications of the coarse-grained single-phase austenitic stainless steel plate.

[0015] Furthermore, the rolling speed is 3 to 10 m / min.

[0016] Beneficial effects of the present invention:

[0017] 1) The present invention can accurately control the macroscopic size and surface quality of austenitic stainless steel plates by combining rolling with reciprocating torsional deformation technology;

[0018] 2) The present invention can realize the controllable regulation of the new 3D full gradient structure while keeping the macroscopic size specifications of the austenitic stainless steel plate unchanged, and significantly improve its comprehensive mechanical properties;

[0019] 3) The present invention can realize one-time forming and continuous production of austenitic stainless steel plates of various sizes and specifications under low cost conditions.

[0020] The technology of the present invention combines traditional rolling with reciprocating torsional deformation. On the basis of effectively controlling the size and surface quality of the plate, a new 3D full gradient structure is constructed to achieve the synergy of high yield strength (350-700MPa) and high toughness (elongation 45-60%). Compared with the austenitic stainless steel plates (yield strength ~200MPa, elongation ~55%) used in existing projects, the present invention increases the yield strength by 1 to 2 times while retaining high toughness, thereby achieving an excellent balance between high strength and high toughness of austenitic stainless steel plates, and supporting low-cost one-time forming and continuous production of stainless steel plates of different specifications and sizes. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a schematic diagram of the production method of the present invention;

[0022] Figure 2 This is a tensile mechanical property curve diagram of the reciprocating torsion stainless steel plate of Example 1 of the present invention;

[0023] Figure 3 This is a microhardness distribution diagram of the cross section of the reciprocating torsion stainless steel plate in Example 1 of the present invention;

[0024] Figure 4 EBSD phase diagrams and grain boundary diagrams of different positions of the cross section of the reciprocatingly torsion stainless steel plate in Example 1 of the present invention;

[0025] Figure 5 This is a TEM image of the surface layer of the reciprocatingly torsion stainless steel plate in Example 1 of the present invention;

[0026] Figure 6 This is a diagram of the tensile loading-unloading-reloading (LUR) test and heterogeneous deformation induced (HDI) stress results of the reciprocating torsion stainless steel plate in Example 1 of the present invention. DETAILED DESCRIPTION

[0027] The present invention provides a method for continuously producing a high-strength and high-toughness 3D full-gradient structure austenitic stainless steel plate, comprising the following steps:

[0028] 1) cold rolling and austenitizing the austenitic stainless steel sheet in sequence; or hot rolling and cooling the austenitic stainless steel sheet in sequence to control its size and surface quality, to obtain a coarse-grained single-phase austenitic stainless steel sheet with a controlled thickness of 0.3 to 3 mm and a width of 5 to 1000 mm;

[0029] 2) The coarse-grained single-phase austenitic stainless steel plate is subjected to reciprocating torsional deformation, and then the plate is rolled into a round shape;

[0030] The reciprocating torsional deformation has an angle of 5 to 50°, a number of passes of 15 to 60 times, and a speed of 30 to 60° / min.

[0031] In the present invention, the angle of the reciprocating torsional deformation is preferably 10 to 40°, more preferably 20 to 30°; the number of reciprocating torsional deformation is preferably 20 to 60 times, more preferably 50 to 60 times; the rate of the reciprocating torsional deformation is preferably 30 to 50° / min, more preferably 30 to 40° / min.

[0032] In the present invention, the temperature of the cold rolling is 20-40°C, preferably 25-35°C, and more preferably 25-30°C; the temperature of the hot rolling is 1000-1300°C, preferably 1000-1200°C.

[0033] In the present invention, the reduction ratios of the cold rolling and the hot rolling are independently 50 to 70%, preferably 60%.

[0034] In the present invention, the temperature of the austenitizing treatment is 800-1000° C., preferably 850-950° C., and more preferably 900° C.; the time of the austenitizing treatment is 0.5-2 h, and preferably 1 h.

[0035] In the present invention, the cooling rate is 200-500°C / s, preferably 250-400°C / s.

[0036] In the present invention, the reciprocating torsional deformation does not change the macroscopic size specifications of the coarse-grained single-phase austenitic stainless steel plate.

[0037] In the present invention, the rolling speed is 3 to 10 m / min, preferably 3 to 8 m / min.

[0038] The present invention reciprocates and twists the coarse-grained single-phase austenitic stainless steel sheet to greatly improve the combination of its strength and toughness without changing its macroscopic size specifications, and finally rolls the sheet into a circle. By adjusting the rolling process, the size specifications and surface quality of the sheet can be accurately controlled; at the same time, by adjusting the reciprocating torsion process parameters and the rolling rate, the controllable construction of the 3D full gradient structure can be achieved, thereby achieving the synergy of high strength and high toughness. The present invention supports the low-cost continuous production of austenitic stainless steel sheets.

[0039] The technical solutions provided by the present invention are described in detail below in conjunction with the embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0040] Example 1

[0041] This embodiment is a 304 austenitic stainless steel plate, and its chemical composition is Fe-0.04C-0.38Si-1.16Mn-18.24Cr-8.02Ni-0.029P-0.005N (wt.%).

[0042] Production method:

[0043] 1) rolling a 304 austenitic stainless steel sheet at 25°C from 5 mm to 2 mm, then austenitizing at 900°C for 1 hour, and quenching to room temperature to obtain a coarse-grained single-phase austenitic stainless steel sheet with an average grain size of about 16.5 μm;

[0044] 2) The size of the coarse-grained single-crystal austenitic stainless steel plate is controlled to be 5 mm in width and 2 mm in thickness, and it is subjected to reciprocating torsion deformation with a torsion angle of 30°, a torsion rate of 60° / min, and 60 torsion passes. The plate size specifications remain unchanged, and then the plate is rolled at a rate of 5 m / min.

[0045] The tensile properties and cross-sectional microhardness tests were performed on the 304 austenitic stainless steel plate after reciprocating torsion deformation in Example 1, and EBSD and TEM microstructure characterizations were performed at different positions along the cross section.

[0046] Example 2

[0047] The austenitic stainless steel plate is the same as that in Example 1;

[0048] Production method:

[0049] 1) The 304 austenitic stainless steel sheet was hot rolled at 1200°C from 3 mm to 1 mm, and then cooled to room temperature at a rate of 300°C / min to obtain a coarse-grained single-phase austenitic stainless steel sheet with an average grain size of about 23 μm;

[0050] 2) The size of the coarse-grained single-crystal austenitic stainless steel plate is controlled to be 10 mm in width and 1 mm in thickness, and it is subjected to reciprocating torsion deformation with a torsion angle of 40°, a torsion rate of 30° / min, and 30 torsion passes. The plate size specifications remain unchanged, and then the plate is rolled at a rate of 3 m / min.

[0051] Example 3

[0052] The austenitic stainless steel plate is the same as that in Example 1;

[0053] Production method:

[0054] 1) rolling a 304 austenitic stainless steel sheet at 25°C from 6 mm to 2 mm, then austenitizing at 1000°C for 0.5 hours, and quenching to room temperature to obtain a coarse-grained single-phase austenitic stainless steel sheet with an average grain size of about 30 μm;

[0055] 2) The size of the coarse-grained single-crystal austenitic stainless steel plate is controlled to be 10 mm in width and 2 mm in thickness, and it is subjected to reciprocating torsion deformation with a torsion angle of 20°, a torsion rate of 45° / min, and a torsion pass of 50, while the plate size specifications remain unchanged.

[0056] Example 4

[0057] The austenitic stainless steel plate is the same as that in Example 1;

[0058] Production method:

[0059] 1) The 304 austenitic stainless steel sheet was hot rolled at 1100°C from 6 mm to 3 mm, and then cooled to room temperature at a rate of 300°C / min to obtain a coarse-grained single-phase austenitic stainless steel sheet with an average grain size of about 25 μm;

[0060] 2) The size of the coarse-grained single-crystal austenitic stainless steel plate is controlled to be 8 mm in width and 3 mm in thickness, and it is subjected to reciprocating torsion deformation with a torsion angle of 35°, a torsion rate of 60° / min, and 15 torsion passes, while the plate size specifications remain unchanged.

[0061] Test results:

[0062] Example 1 After 30°, 60 times of reciprocating torsion deformation treatment, the tensile performance test results are as follows Figure 2 As shown. The yield strength of 304 austenitic stainless steel sheet is increased to about 464.4MPa, the tensile strength is increased to about 905.4MPa, while maintaining a uniform elongation of about 51.8%. Compared with the coarse-grained 304 austenitic stainless steel sheet (yield strength of about 270.4MPa, tensile strength of about 858.2MPa, and uniform elongation of about 56.2%), the yield strength is increased by 71.7%, and the high uniform elongation of 92.2% of the coarse grain is retained, successfully achieving an excellent combination of high strength and high toughness.

[0063] Cross-sectional Vickers microhardness test ( Figure 3 ) shows that the hardness distribution on the cross section of austenitic stainless steel plate at 30° and 60 reciprocating torsion is very uneven, and changes continuously along multiple dimensions and paths in a gradient. EBSD and TEM characterization results (such as Figure 4 and Figure 5 ) shows that during the reciprocating torsional deformation, different regions experienced different degrees of strain-induced martensitic phase transformation, and the dislocation density between regions was significantly different. By comparing the EBSD results with the hardness distribution results, it can be found that the hardness increase is consistent with the direction of the increase in martensitic phase content and dislocation density. In addition, there are also differences in the organization and properties between austenite and α′ martensite. Therefore, reciprocating torsional deformation forms a new 3D full gradient structure covering the entire plate in the 304 austenitic stainless steel plate, that is, the α′ martensite content and dislocation density change continuously along multiple paths in 3D space.

[0064] The introduction of α′ martensite with higher hardness and a large number of dislocations, as well as the heterogeneous deformation induced (HDI) strengthening stimulated by the 3D full gradient structure, significantly improves the yield strength of 304 austenitic stainless steel sheet. The multi-stage work hardening behavior triggered by multiple deformation mechanisms is the main reason for its high toughness. Specifically, under different regions and strain conditions, the reverse martensitic phase transformation (α′→γ), the forward martensitic phase transformation (γ→α′) and the nano-twins occur non-uniformly and continuously and work together. The combination of 3D full gradient structure (3D-GGS), martensitic phase transformation and nano-twins effectively promotes the heterogeneous deformation induced (HDI) work hardening effect (such as Figure 6 ), thus achieving continuous strain hardening in the uniform plastic deformation stage.

[0065] It can be seen from the above embodiments that the present invention provides a method for continuous production of high-strength and high-toughness 3D full gradient structure austenitic stainless steel plates. The present invention uses a new technology that combines rolling with reciprocating torsional deformation to control the size specifications and surface quality of the austenitic stainless steel plates while constructing a new 3D full gradient structure covering the entire plate. Compared with commercial 304 austenitic stainless steel plates with coarse-grained structure, the present invention increases the yield strength by more than 70%, while retaining more than 90% of the uniform elongation, achieving excellent synergy of high strength and high toughness. Therefore, the present invention can achieve one-time forming and continuous production of high-strength and high-toughness synergistic austenitic stainless steel plates by constructing a new 3D full gradient structure.

[0066] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for continuous production of high-strength and high-toughness 3D full-gradient structure austenitic stainless steel sheet, characterized in that: The following steps are involved: 1) cold rolling and austenitizing the austenitic stainless steel sheet in sequence; or hot rolling and cooling the austenitic stainless steel sheet in sequence to control its size and surface quality, to obtain a coarse-grained single-phase austenitic stainless steel sheet with a controlled thickness of 0.3 to 3 mm and a width of 5 to 1000 mm; 2) The coarse-grained single-phase austenitic stainless steel plate is subjected to reciprocating torsional deformation, and then the plate is rolled into a round shape; The reciprocating torsional deformation has an angle of 5 to 50°, a number of passes of 15 to 60 times, and a speed of 30 to 60° / min.

2. The continuous production method of a high-strength and high-toughness 3D full-gradient structure austenitic stainless steel sheet according to claim 1 is characterized in that: The cold rolling temperature is 20-40°C, and the hot rolling temperature is 1000-1300°C.

3. The continuous production method of a high-strength and high-toughness 3D full-gradient structure austenitic stainless steel sheet according to claim 1 or 2, characterized in that: The reduction ratios of the cold rolling and the hot rolling are independently 50 to 70%.

4. The continuous production method of a high-strength and high-toughness 3D full-gradient structure austenitic stainless steel sheet according to claim 3 is characterized in that: The temperature of the austenitizing treatment is 800-1000° C., and the time of the austenitizing treatment is 0.5-2 hours.

5. The continuous production method of a high-strength and high-toughness 3D full-gradient structure austenitic stainless steel sheet according to claim 1, 2 or 4, characterized in that: The cooling rate is 200-500°C / min.

6. The continuous production method of a high-strength and high-toughness 3D full-gradient structure austenitic stainless steel sheet according to claim 1 is characterized in that: The reciprocating torsional deformation does not change the macroscopic size specifications of the coarse-grained single-phase austenitic stainless steel plate.

7. The continuous production method of a high-strength and high-toughness 3D full-gradient structure austenitic stainless steel sheet according to claim 1, 4 or 6, characterized in that: The rolling speed is 3-10 m / min.

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