A method for preparing a high-strength high-nitrogen austenitic stainless steel plate

Abstract

The application discloses a preparation method of high-strength high-nitrogen austenitic stainless steel plate material, and the high-nitrogen austenitic stainless steel plate material is subjected to solid solution treatment in a heating furnace at 1150±50 DEG C for 6-8 hours, and then is water-cooled to rapidly reduce the temperature to room temperature; after the solid solution treatment is completed, the high-nitrogen austenitic stainless steel plate material is first placed into a heating furnace at 300 DEG C for heat preservation for 10 minutes, and then is placed into the heating furnace at 300 DEG C for heat preservation for 5 minutes before each pass rolling, and the cumulative reduction is 40-75%. The warm rolling process is used, the rolling force required by the warm rolling process is smaller than that required by room temperature rolling, the strength of the obtained material is equivalent to that of the material rolled at room temperature, and the processing is easier to carry out.

Description

Technical Field

[0001] This invention belongs to the field of austenitic stainless steel sheet manufacturing, specifically relating to a method for preparing high-strength sheets by warm rolling after solution treatment of high-nitrogen austenitic stainless steel. Background Technology

[0002] High-nitrogen austenitic stainless steel possesses excellent toughness, creep resistance, strong resistance to pitting corrosion, and non-magnetic properties. Nitrogen is dissolved in austenitic stainless steel as interstitial atoms, occupying octahedral interstitial positions in the face-centered cubic structure. This causes lattice distortion and pins dislocations, and nitrogen can also replace nickel to stabilize austenite. Furthermore, it improves the corrosion resistance of austenitic steel. These superior properties make high-nitrogen austenitic stainless steel widely applicable in transportation, biomedicine, energy and chemical industries, and national defense. Although the yield strength of high-nitrogen steel (around 465 MPa) is higher than that of 316L (around 250 MPa), further strength enhancement is needed to meet the requirements of more demanding service conditions. Therefore, specific processing techniques are required to improve its strength.

[0003] Austenitic stainless steel commonly utilizes plastic deformation treatment to improve its strength, with rolling being one of the most frequently used methods. However, due to the strong work hardening ability of high-nitrogen austenitic stainless steel, the rolling force required for room temperature rolling is enormous, placing high demands on the rolling mill and resulting in significant energy loss. When rolling with large deformation amounts, the rolling mill is prone to overload and affecting the service life of the equipment, making large-scale industrial production difficult. Figure 1 The figures show the work hardening rate versus true stress and true stress-strain curves of high-nitrogen austenitic stainless steel at different temperatures. It can be observed that the work hardening rate is very high at room temperature, far exceeding that at 300℃ and 600℃. Simultaneously, the yield strength of high-nitrogen austenitic stainless steel at room temperature is 465 MPa, while the yield strength at 300℃ and 600℃ is only 252 MPa, representing a decrease of approximately two times. Therefore, pre-heating high-nitrogen austenitic stainless steel to reduce its deformation resistance could potentially reduce the rolling difficulty of high-nitrogen austenitic stainless steel, providing a new approach for the production of high-strength, high-nitrogen steel. Summary of the Invention

[0004] To address the aforementioned problems, this invention provides a method for preparing high-strength, high-nitrogen austenitic stainless steel sheets using a warm rolling process. The sheets obtained by this method exhibit a yield strength ≥ 1430 MPa, a tensile strength ≥ 1525 MPa, and a uniform elongation of approximately 0.03.

[0005] The technical solution to achieve the purpose of this invention is as follows: The high-strength, high-nitrogen austenitic stainless steel plate of this invention has the following alloy composition by mass percentage: C ≤ 0.068, Si ≤ 0.42, Ni ≤ 1.48, Cr ≤ 21.74, Mn ≤ 15.12, N ≤ 0.85, with the remainder being Fe.

[0006] Preferably, by mass percentage, its alloy composition is: C 0.05-0.07, Si 0.40-0.45, Ni 1.40-1.5, Cr 20-22, Mn 15-15.5, N 0.77-0.85, with the remainder being Fe.

[0007] More preferably, by mass percentage, its alloy composition is: C 0.068, Si 0.42, Ni 1.48, Cr 21.74, Mn 15.12, N 0.85, with the remainder being Fe.

[0008] The preparation method of the above-mentioned high-strength, high-nitrogen austenitic stainless steel sheet includes the following steps:

[0009] (1) Weigh the corresponding high-purity metal powder according to the alloy composition of the high-strength high-nitrogen austenitic stainless steel plate, wherein the nitrogen element is introduced by high-purity chromium nitride, and steel ingots are obtained by smelting in a pressurized vacuum induction furnace, and then the plates with a thickness of 15-20 mm are obtained by continuous rolling at 1000-1100℃.

[0010] (2) Solution treatment: The obtained plate is solution treated in a heating furnace at 1150±50 ℃ for 6-8 h, and then water-cooled to rapidly reduce the temperature to room temperature to obtain a single-phase high-nitrogen austenitic stainless steel plate with a single austenitic structure.

[0011] (3) Warm rolling: After the solution treatment is completed, the above single-phase high-nitrogen austenitic stainless steel sheet is warm rolled.

[0012] Preferably, the specific process of warm rolling is as follows: First, the high-nitrogen austenitic stainless steel sheet is placed in a heating furnace at 300 ℃ and held for 10 min. Then, before each rolling pass, it is placed in a heating furnace at 300 ℃ and held for 5 min, with a cumulative reduction of 40-75%.

[0013] The present invention has the following significant advantages compared with the prior art:

[0014] (1) The present invention uses a warm rolling process, which requires less rolling force than room temperature rolling, while the strength of the obtained material is comparable to that of room temperature rolled material, and the processing is easier;

[0015] (2) The equipment used in this invention is simple, easy to operate, and conducive to large-scale industrial production;

[0016] (3) The high-nitrogen austenitic stainless steel prepared by the present invention has a yield strength ≥ 1430 MPa, a tensile strength ≥ 1525 MPa, and a uniform elongation of about 0.03. Attached Figure Description

[0017] Figure 1 The tensile property curves of high-nitrogen austenitic stainless steel at different temperatures are shown; (a) is the work hardening rate-true stress curve, and (b) is the true stress-strain curve.

[0018] Figure 2 This is a schematic diagram of the processing flow.

[0019] Figure 3 These are optical micrographs of the tissue after solution treatment in Example 1, taken at different magnifications.

[0020] Figure 4 The light microstructures of the room temperature rolled and warm rolled samples are shown in (a) and (b), respectively, which are 40% room temperature rolled in Comparative Example 1 and 75% room temperature rolled in Comparative Example 3; (c) and (d) are 45% warm rolled at 300°C in Example 1 and 75% warm rolled at 300°C in Example 3.

[0021] Figure 5 The tensile test results of the plates after treatment in Examples 1, 2, 3 and Comparative Examples 1, 2, 3 are engineering stress-strain curves.

[0022] Figure 6 This is the Hull-corrected diagram of the Schaeffler tissue transformation. Detailed Implementation

[0023] The present invention will be further described in detail below with reference to the embodiments.

[0024] The design principle of the alloy element composition of this invention is as follows:

[0025] Ni is a powerful austenite stabilizer in existing commercially available austenitic stainless steels, and like N, it can expand the austenite phase region. However, due to the limited resources of Ni and its status as a precious metal, as well as the fact that Ni can easily cause allergic reactions in humans, the application of Ni-containing austenitic stainless steels in the food and medical fields is limited.

[0026] Carbon (C) is one of the austenite-forming elements, and its stabilizing effect is stronger than that of nickel (Ni). It also exists in stainless steel in the form of interstitial solid solutions, thus providing solid solution strengthening. However, the presence of C easily leads to the formation of carbide precipitation during thermomechanical processing of stainless steel, severely affecting its mechanical properties.

[0027] Nitrogen (N) plays three main roles in austenitic stainless steel: (1) It improves the stability of the austenitic structure, expands the austenitic phase region, and can partially or completely replace the role of Ni. (2) It improves the yield strength and tensile strength of steel through solid solution strengthening, grain boundary strengthening, and precipitation strengthening. (3) It improves the local corrosion resistance of austenitic stainless steel, especially its resistance to pitting and crevice corrosion. A stable austenitic structure can be obtained while reducing the production cost of stainless steel by reducing the nickel content and adding sufficient nitrogen.

[0028] The excellent corrosion resistance of austenitic stainless steel is achieved by adding a high content of chromium (Cr). However, Cr has a strong effect on ferrite formation, significantly shrinking the austenite phase region and hindering the formation of austenitic microstructure. Increasing the Cr content leads to a greater tendency for the formation of harmful intermetallic compounds (σ phase) during thermomechanical treatment. In high-nitrogen austenitic stainless steel, Cr also reacts with nitrogen to form compounds such as CrN and Cr2N; when the carbon content is high, Cr also reacts with carbon to form M... 23 C6 and other carbides. The precipitation of these intermetallic compounds and carbonitrides reduces the corrosion resistance and mechanical properties of the material.

[0029] Mn is also a typical austenite stabilizing element, but its austenite stabilizing ability is weaker than that of N. In Fe-Cr-Mn alloys, if the Cr content exceeds 14%, a single austenitic structure cannot be obtained by Mn alone. At the same time, excessively high manganese content will have an adverse effect on the corrosion resistance of the steel.

[0030] In oxidizing solutions, silicon (Si) accumulates on the surface of stainless steel, forming SiO2, which increases the pitting potential of the stainless steel. However, excessive addition of silicon will degrade the mechanical properties of stainless steel.

[0031] When designing the alloy composition of high-nitrogen austenitic stainless steel, it is necessary to consider not only the independent effects of each alloying element but also the synergistic effects between them to obtain high-quality high-nitrogen austenitic stainless steel. Based on the Hull-modified Schaeffler microstructure transformation diagram (see...), Figure 6 The alloy composition of the above-mentioned high-strength high-nitrogen austenitic stainless steel sheet was determined by formulas (1) and (2).

[0032] (1)

[0033] (2)

[0034] The following embodiments and Figure 2 The preparation process of the high-strength, high-nitrogen austenitic stainless steel sheet of the present invention is given.

[0035] Example 1

[0036] (1) Weigh the raw materials according to the alloy composition of the high-strength high-nitrogen austenitic stainless steel plate, wherein the nitrogen element is introduced by high-purity chromium nitride, and steel ingots are obtained by smelting in a pressurized vacuum induction furnace, and then the plates with a thickness of 15-20 mm are obtained by continuous rolling at 1000-1100℃.

[0037] (2) Solution treatment: The material was placed in a furnace at 1150 ℃ for solution treatment for 8 h, followed by water cooling. The oxide scale on the surface of the material was removed, and the material was processed into a 10 mm thick plate. After solution treatment, a homogeneous single-phase high-nitrogen austenitic stainless steel plate was obtained, with a microstructure as shown in the optical microscopy diagram. Figure 3 As shown;

[0038] (3) Warm rolling: The material is first placed in a heating furnace at 300 ℃ and held for 10 min, then held in the heating furnace for 5 min before each rolling pass. The plate thickness is rolled to approximately 5.5 mm in 6 passes, with a total rolling yield of approximately 45%. The microstructure of the sample is as follows: Figure 4 As shown in c;

[0039] (4) In this example, the high-nitrogen austenitic stainless steel sheet obtained by the above method has a yield strength of 1430 MPa, a tensile strength of 1525 MPa, and a uniform elongation of 0.03. The engineering stress-strain curve of the sheet after treatment is shown below. Figure 5 As shown.

[0040] Example 2

[0041] (1) Weigh the raw materials according to the alloy composition of the high-strength high-nitrogen austenitic stainless steel plate, wherein the nitrogen element is introduced by high-purity chromium nitride, and steel ingots are obtained by smelting in a pressurized vacuum induction furnace, and then the plates with a thickness of 15-20 mm are obtained by continuous rolling at 1000-1100℃.

[0042] (2) Solution treatment: The plate was placed in a heating furnace at 1150 °C for solution treatment for 8 h, followed by water cooling. The oxide scale on the surface of the material was removed, and the material was processed into a 10 mm thick plate. After solution treatment, a single-phase high-nitrogen austenitic stainless steel plate with uniform microstructure was obtained, and its microstructure was the same as that in Example 1.

[0043] (3) Warm rolling: First, place the material in a heating furnace at 300 ℃ and hold for 10 min. Then, hold it in the heating furnace for 5 min before each rolling pass. Roll the plate thickness to approximately 4 mm in 9 passes, with a total rolling yield of approximately 60%.

[0044] (4) In this example, the high-nitrogen austenitic stainless steel sheet obtained by the above method has a yield strength of 1592 MPa, a tensile strength of 1764 MPa, and a uniform elongation of 0.03. The engineering stress-strain curve of the sheet after treatment is shown below. Figure 5 As shown.

[0045] Example 3

[0046] (1) Weigh the raw materials according to the alloy composition of the high-strength high-nitrogen austenitic stainless steel plate, wherein the nitrogen element is introduced by high-purity chromium nitride, and steel ingots are obtained by smelting in a pressurized vacuum induction furnace, and then the plates with a thickness of 15-20 mm are obtained by continuous rolling at 1000-1100℃.

[0047] (2) Solution treatment: The plate was placed in a heating furnace at 1150 °C for solution treatment for 8 h, followed by water cooling. The oxide scale on the surface of the material was removed, and the material was processed into a 10 mm thick plate. After solution treatment, a single-phase high-nitrogen austenitic stainless steel plate with uniform microstructure was obtained, and its microstructure was the same as that in Example 1.

[0048] (3) Warm rolling: The material is first placed in a heating furnace at 300 ℃ and held for 10 min, then held in the heating furnace for 5 min before each rolling pass. The plate thickness is rolled to approximately 2.5 mm in 12 passes, with a total rolling yield of approximately 75%. The microstructure of the sample is as follows. Figure 4 As shown in d;

[0049] (4) In this example, the high-nitrogen austenitic stainless steel sheet obtained by the above method has a yield strength of 1613 MPa, a tensile strength of 1788 MPa, and a uniform elongation of 0.03. The engineering stress-strain curve of the sheet after treatment is shown below. Figure 5 As shown.

[0050] Comparative Example 1

[0051] (1) Obtain a 10 mm thick, uniformly structured single-phase high-nitrogen austenitic stainless steel sheet by following the first and second steps described in Example 1.

[0052] (2) Room temperature rolling: The plate thickness was rolled to approximately 6 mm in 8 passes at room temperature, with a total rolling amount of approximately 40%. The microstructure of the sample is as follows. Figure 4 As shown in a;

[0053] (3) The high-nitrogen austenitic stainless steel sheet obtained by the above method in this comparative example has a yield strength of 1370 MPa, a tensile strength of 1534 MPa, and a uniform elongation of 0.03. The engineering stress-strain curve of the sheet after treatment is shown below. Figure 5 As shown.

[0054] Comparative Example 2

[0055] (1) Obtain a 10 mm thick, uniformly structured single-phase high-nitrogen austenitic stainless steel sheet by following the first and second steps described in Example 2.

[0056] (2) Room temperature rolling: The plate thickness is rolled to about 4 mm in 12 passes at room temperature, with a total rolling amount of about 60%.

[0057] (3) The high-nitrogen austenitic stainless steel sheet obtained by the above method in this comparative example has a yield strength of 1594 MPa, a tensile strength of 1706 MPa, and a uniform elongation of 0.025. The engineering stress-strain curve of the sheet after treatment is shown below. Figure 5 As shown.

[0058] Comparative Example 3

[0059] (1) Obtain a 10 mm thick, uniformly structured single-phase high-nitrogen austenitic stainless steel sheet by following the first and second steps described in Example 1.

[0060] (2) Room temperature rolling: The plate thickness was rolled to approximately 2.5 mm in 16 passes at room temperature, with a total rolling yield of approximately 75%. The microstructure of the sample is as follows. Figure 4 As shown in b;

[0061] (3) The high-nitrogen austenitic stainless steel sheet obtained by the above method in this comparative example has a yield strength of 1688 MPa, a tensile strength of 1830 MPa, and a uniform elongation of 0.025. The engineering stress-strain curve of the sheet after treatment is shown below. Figure 5 As shown.

[0062] Comparative Example 4

[0063] (1) Obtain a 10 mm thick, uniformly structured single-phase high-nitrogen austenitic stainless steel sheet by following the first and second steps described in Example 1.

[0064] (2) Warm rolling: First, place the material in a heating furnace at 600 ℃ and hold for 10 min. Then, hold it in the heating furnace for 5 min before each rolling pass. Roll the plate to a thickness of about 6 mm in 6 passes, with a total rolling amount of about 40%.

[0065] (3) The high-nitrogen austenitic stainless steel plate obtained by the above method in this example has a yield strength of 1262 MPa, a tensile strength of 1413 MPa, and a uniform elongation of 0.034.

[0066] Comparative Example 5

[0067] (1) Obtain a 10 mm thick, uniformly structured single-phase high-nitrogen austenitic stainless steel sheet by following the first and second steps described in Example 2.

[0068] (2) Warm rolling: The material is first placed in a heating furnace at 600 ℃ and held for 10 min, and then held in the heating furnace for 5 min before each rolling pass. The plate thickness is rolled to about 4 mm in 9 passes, with a total rolling amount of about 60%.

[0069] (3) The high-nitrogen austenitic stainless steel plate obtained by the above method in this example has a yield strength of 1369 MPa, a tensile strength of 1515 MPa, and a uniform elongation of 0.03.

[0070] Comparative Example 6

[0071] (1) Obtain a 10 mm thick, uniformly structured single-phase high-nitrogen austenitic stainless steel sheet by following the first and second steps described in Example 3.

[0072] (2) Warm rolling: The material is first placed in a heating furnace at 600 ℃ and held for 10 min, and then held in the heating furnace for 5 min before each rolling pass. The plate thickness is rolled to about 3 mm in 12 passes, with a total rolling yield of about 70%.

[0073] (3) The high-nitrogen austenitic stainless steel plate obtained by the above method in this example has a yield strength of 1530 MPa, a tensile strength of 1625 MPa, and a uniform elongation of 0.03.

Claims

1. A high-strength, high-nitrogen austenitic stainless steel sheet, characterized in that, By mass percentage, its alloy composition is: C 0.05-0.07, Si 0.40-0.45, Ni 1.40-1.5, Cr 20-22, Mn 15-15.5, N 0.77-0.85, with the remainder being Fe; The preparation method of the austenitic stainless steel sheet includes: after the solution treatment of the sheet, the obtained single-phase high-nitrogen austenitic stainless steel sheet is warm rolled. The specific process of warm rolling is as follows: First, the high-nitrogen austenitic stainless steel sheet is placed in a heating furnace at 300 ±5℃ and held for 10 minutes. Then, before each rolling pass, it is placed in a heating furnace at 300 ±5℃ and held for 5 minutes, with a cumulative reduction of 40-75%.

2. The austenitic stainless steel sheet as described in claim 1, characterized in that, The alloy composition by mass percentage is: C 0.068, Si 0.42, Ni 1.48, Cr 21.74, Mn 15.12, N 0.85, with the remainder being Fe.

3. The method for preparing austenitic stainless steel sheet according to any one of claims 1-2, characterized in that, It includes the following steps: (1) Weigh the corresponding high-purity metal powder according to the alloy composition of the austenitic stainless steel plate, wherein the nitrogen element is introduced by high-purity chromium nitride, and steel ingots are obtained by smelting in a pressure vacuum induction furnace, and then the plates with a thickness of 15-20 mm are obtained by continuous rolling at 1000-1100℃. (2) Solution treatment: The obtained plate is solution treated in a heating furnace at 1150±50℃ for 6-8 h, and then water-cooled to rapidly cool it to room temperature to obtain a single-phase high-nitrogen austenitic stainless steel plate with a single austenitic structure. (3) Warm rolling: After the solution treatment is completed, the above-mentioned single-phase high-nitrogen austenitic stainless steel sheet is warm rolled. The specific process of warm rolling is as follows: First, the high-nitrogen austenitic stainless steel sheet is placed in a heating furnace at 300±5℃ and held for 10 minutes. Then, before each rolling pass, it is placed in a heating furnace at 300±5℃ and held for 5 minutes, with a cumulative reduction of 40-75%.

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