Austenitic stainless steel for cold rolling and preparation method thereof

Abstract

The invention belongs to the technical field of steel and iron materials, and provides austenitic stainless steel for cold rolling and a preparation method of the austenitic stainless steel for cold rolling, by optimizing the content of core elements of Cr, Ni, Mn and N. The content of the element Ni is reduced, meanwhile, the austenitic structure is stabilized through the synergistic effect of Mn, N and Cr, and meanwhile the problem of material brittleness caused by mismatching of the content of Mn and the content of N is avoided. A trace amount of Nb and Ti is introduced, crystal grains are effectively refined, carbide precipitation is inhibited, the strength, toughness and corrosion resistance of the material are enhanced, meanwhile, the cold rolling machining performance of the material is remarkably improved, meanwhile, the preparation method is adjusted, and the problems that existing nickel-saving austenitic stainless steel is large in cold rolling difficulty and prone to cracking after rolling are solved.

Description

Technical Field

[0001] This invention belongs to the field of steel materials technology, specifically an austenitic stainless steel for cold rolling and its preparation method. Background Technology

[0002] Stainless steel is widely used in construction, chemical, automotive, and pipeline industries due to its excellent corrosion resistance, mechanical properties, and processing performance. Among them, austenitic stainless steel, with its good toughness and weldability, has become a commonly used material in the pipe manufacturing industry. However, traditional 300 series austenitic stainless steel has a high nickel content (usually above 8 wt%). As nickel is a scarce and precious metal, its price fluctuates greatly, resulting in high production costs for 300 series stainless steel.

[0003] To reduce production costs, nickel-saving austenitic stainless steel has emerged. This type of stainless steel uses manganese and nitrogen to replace some of the nickel, thus stabilizing the austenitic microstructure. The 200 series stainless steel is a typical example. Currently, 200 series stainless steel for pipe manufacturing suffers from problems such as difficulty in cold rolling and susceptibility to cracking after rolling due to an unreasonable manganese and nitrogen substitution ratio and a lack of effective synergistic control of alloying elements. This severely affects the product's processing qualification rate and performance, hindering the further promotion and application of nickel-saving austenitic stainless steel in the pipe manufacturing field.

[0004] Therefore, in view of the above situation, there is an urgent need to provide an austenitic stainless steel for cold rolling and its preparation method to overcome the shortcomings in current practical applications. Summary of the Invention

[0005] The purpose of this invention is to provide an austenitic stainless steel for cold rolling and a method for preparing the same, effectively solving the problems in the background art.

[0006] According to a first aspect of the present invention, the present invention provides the following technical solution: An austenitic stainless steel for cold rolling, comprising, by weight percentage: C 0.06~0.12%, Si 0.3~0.6%, Mn 8~11%, P≤0.035%, S≤0.030%, Cr 16.5~18.5%, Ni 2.0~3.5%, N 0.20~0.30%, Nb 0.005~0.015%, Ti 0.003~0.008%, with the balance being Fe and unavoidable impurities.

[0007] As a preferred embodiment of the austenitic stainless steel for cold rolling according to the present invention, the composition of the austenitic stainless steel for cold rolling further satisfies: 18.5≤2 / 3Mn+1 / 2Cr+5N+Ni≤20.5.

[0008] As a preferred embodiment of the austenitic stainless steel for cold rolling according to the present invention, the composition of the austenitic stainless steel for cold rolling further satisfies: 30≤Mn / N≤50.

[0009] As a preferred embodiment of the austenitic stainless steel for cold rolling according to the present invention, the austenitic stainless steel for cold rolling has a yield strength ≥250MPa, a tensile strength ≥520MPa, an elongation ≥40%, corrosion resistance that meets the requirement of no obvious corrosion after 1000h of neutral salt spray test, and no cracking after cold rolling reduction ≥60%.

[0010] According to a second aspect of the present invention, the present invention provides the following technical solution: A method for preparing the above-mentioned austenitic stainless steel for cold rolling includes the following steps: S1: Melting to obtain nickel-saving austenitic stainless steel billets; S2: Heating the billet to perform austenitization treatment; S3: The heated billet is hot rolled in multiple passes, with water cooling during the hot rolling process, and then rapidly cooled to room temperature after hot rolling to obtain a hot-rolled plate; S4: After annealing, hot-rolled plates are pickled to obtain austenitic stainless steel for cold rolling.

[0011] In a preferred embodiment of the method for preparing cold-rolled austenitic stainless steel according to the present invention, in step S2, the billet is first heated to 800-850°C at a rate of 5-8°C / min and held for 1-1.5 hours, and then heated to 1150-1250°C at a rate of 3-5°C / min and held for 2-3 hours to ensure uniform billet temperature and full austenitization of the microstructure.

[0012] In a preferred embodiment of the method for preparing cold-rolled austenitic stainless steel according to the present invention, in step S3, the heated billet is fed into a hot rolling mill for rolling. The initial rolling temperature is 1100~1150℃, and multi-pass rolling is adopted. The reduction rate of the first pass is 25~30%, and the reduction rate of each subsequent pass is 10~15%. The final rolling temperature is 850~900℃, and the total reduction rate is 60~70%.

[0013] In a preferred embodiment of the method for preparing austenitic stainless steel for cold rolling according to the present invention, in step S3, the temperature of the rolls is controlled at 180~220℃ during the rolling process.

[0014] In a preferred embodiment of the method for preparing cold-rolled austenitic stainless steel according to the present invention, in step S4, the annealing temperature is 1050~1100℃.

[0015] The present invention has the following technical effects: This invention proposes an austenitic stainless steel for cold rolling and its preparation method. By optimizing the content of core elements Cr, Ni, Mn, and N, the Ni content is reduced while the synergistic effect of Mn, N, and Cr stabilizes the austenitic structure, thus avoiding the material brittleness problem caused by the mismatch of Mn and N contents. The introduction of trace amounts of Nb and Ti effectively refines the grains, inhibits carbide precipitation, and enhances the material's strength, toughness, and corrosion resistance. It also significantly improves the material's cold rolling performance. Furthermore, the adjusted preparation method solves the problems of high difficulty in cold rolling and easy cracking after rolling in existing nickel-saving austenitic stainless steels. Detailed Implementation

[0016] The technical solutions described below in conjunction with the embodiments will be clearly and completely described. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the 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.

[0017] An austenitic stainless steel for cold rolling, comprising, by weight percentage: C 0.06~0.12%, Si 0.3~0.6%, Mn 8~11%, P≤0.035%, S≤0.030%, Cr 16.5~18.5%, Ni 2.0~3.5%, N 0.20~0.30%, Nb 0.005~0.015%, Ti 0.003~0.008%, with the balance being Fe and unavoidable impurities.

[0018] While existing technologies have achieved cost reduction by replacing some nickel with manganese and nitrogen, current nickel-saving austenitic stainless steels suffer from challenges in cold rolling and are prone to cracking after rolling due to unreasonable manganese and nitrogen substitution ratios and a lack of effective alloying element synergy. The applicant's research has found that not only the content and ratio of manganese and nitrogen affect the performance of nickel-saving austenitic stainless steel, but chromium and nickel content also influence its performance indicators. Research has determined that the composition of the austenitic stainless steel used for cold rolling should also satisfy: 30 ≤ Mn / N ≤ 50. Manganese and nitrogen levels above this range lead to significant cracking enhancement, while levels below this range result in insufficient strength. Preferably, Mn / N can be, for example, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, or 50. The range of any one or any two of the following; at the same time, the applicant's research also found that inappropriate chromium and nickel content can also lead to cracking during cold rolling of nickel-saving austenitic stainless steel into tubes, and will also affect the toughness, plasticity and corrosion resistance of nickel-saving austenitic stainless steel. After research, it was determined that the composition of the austenitic stainless steel used for cold rolling should also meet the following: 18.5≤2 / 3Mn+1 / 2Cr+5N+Ni≤20.5, so as to ensure that the yield strength of the austenitic stainless steel used for cold rolling is ≥250MPa, the tensile strength is ≥520MPa, the elongation is ≥40%, the corrosion resistance meets the requirement of no obvious corrosion after 1000h neutral salt spray test, and no cracking occurs when the cold rolling reduction rate is ≥60%. Specifically, 2 / 3Mn+1 / 2Cr+5N+Ni can be any one or any combination of the following values: 18.5, 18.6, 18.7, 18.8, 18.9, 19, 19.1, 19.2, 19.3, 19.4, 19.5, 19.6, 19.7, 19.8, 19.9, 20, 20.1, 20.2, 20.3, 20.4, 20.5. Furthermore, this invention incorporates trace amounts of niobium and titanium. These minimal amounts of niobium and titanium effectively refine the grain size, suppress carbide precipitation, and further enhance the material's strength, toughness, and corrosion resistance.

[0019] A method for preparing the above-mentioned austenitic stainless steel for cold rolling includes the following steps: S1: Melting to obtain nickel-saving austenitic stainless steel billets; S2: Heating the billet to perform austenitization treatment; S3: The heated billet is hot rolled in multiple passes, with water cooling during the hot rolling process, and then rapidly cooled to room temperature after hot rolling to obtain a hot-rolled plate; S4: After annealing, hot-rolled plates are pickled to obtain austenitic stainless steel for cold rolling.

[0020] Preferably, in step S2, the billet is first heated to 800-850°C at a rate of 5-8°C / min and held for 1-1.5 hours, and then heated to 1150-1250°C at a rate of 3-5°C / min and held for 2-3 hours to ensure uniform billet temperature and full austenitization of the microstructure.

[0021] Preferably, in step S3, the heated billet is fed into a hot rolling mill for rolling. The initial rolling temperature is 1100~1150℃, and multi-pass rolling is adopted. The reduction rate of the first pass is 25~30%, the reduction rate of each subsequent pass is 10~15%, the final rolling temperature is 850~900℃, and the total reduction rate is 60~70%.

[0022] In a preferred embodiment of the method for preparing austenitic stainless steel for cold rolling according to the present invention, in step S3, the temperature of the rolls is controlled at 180~220℃ during the rolling process.

[0023] Preferably, in step S4, the annealing temperature is 1050~1100℃.

[0024] The technical solution of the present invention will be further described below with reference to specific embodiments.

[0025] Example 1 An austenitic stainless steel for cold rolling comprises, by weight percentage: C 0.07%, Si 0.5%, Mn 8.5%, P 0.031%, S 0.028%, Cr 16.8%, Ni 3.3%, N 0.28%, Nb 0.013%, Ti 0.005%, with the balance being Fe and unavoidable impurities; wherein: Mn / N = 30.36, 2 / 3Mn + 1 / 2Cr + 5N + Ni = 18.77; The above-mentioned method for preparing austenitic stainless steel for cold rolling includes the following steps: S1: Melting to obtain nickel-saving austenitic stainless steel billets; S2: First, heat the billet to 850℃ at a rate of 5℃ / min and hold for 1 hour, then heat it to 1150℃ at a rate of 3℃ / min and hold for 3 hours to ensure uniform billet temperature and full austenitization of the microstructure.

[0026] S3: The heated billet is fed into a hot rolling mill for rolling. The initial rolling temperature is 1100℃, and multi-pass rolling is used. The first pass has a reduction rate of 25%, and the reduction rates of subsequent passes are 10%. The final rolling temperature is 850℃, and the total reduction rate is 60%. After hot rolling, the billet is rapidly cooled to room temperature to obtain a hot-rolled plate. The roll temperature is controlled at 180℃ during the rolling process.

[0027] S4: After annealing the hot-rolled plate, pickling is performed at a temperature of 1050℃ to obtain austenitic stainless steel for cold rolling.

[0028] Example 2 An austenitic stainless steel for cold rolling comprises, by weight percentage: C 0.11%, Si 0.57%, Mn 10.8%, P 0.031%, S 0.022%, Cr 18.3%, Ni 2.8%, N 0.23%, Nb 0.007%, Ti 0.008%, with the balance being Fe and unavoidable impurities; wherein: Mn / N = 46.96, 2 / 3Mn + 1 / 2Cr + 5N + Ni = 20.3; The above-mentioned method for preparing austenitic stainless steel for cold rolling includes the following steps: S1: Melting to obtain nickel-saving austenitic stainless steel billets; S2: First, heat the billet to 850℃ at a rate of 8℃ / min and hold for 1 hour, then heat it to 1250℃ at a rate of 5℃ / min and hold for 2 hours to ensure uniform billet temperature and full austenitization of the microstructure.

[0029] S3: The heated billet is fed into a hot rolling mill for rolling. The initial rolling temperature is 1150℃, and multi-pass rolling is used. The first pass has a reduction rate of 30%, and the reduction rates of subsequent passes are 15%. The final rolling temperature is 900℃, and the total reduction rate is 70%. After hot rolling, the billet is rapidly cooled to room temperature to obtain a hot-rolled plate. The roll temperature is controlled at 220℃ during the rolling process.

[0030] S4: After annealing the hot-rolled plate, pickling is performed at an annealing temperature of 1100℃ to obtain austenitic stainless steel for cold rolling.

[0031] Example 3 An austenitic stainless steel for cold rolling comprises, by weight percentage: C 0.10%, Si 0.5%, Mn 9.8%, P 0.030%, S 0.030%, Cr 17.6%, Ni 2.9%, N 0.26%, Nb 0.009%, Ti 0.004%, with the balance being Fe and unavoidable impurities; wherein: Mn / N = 37.69, 2 / 3Mn + 1 / 2Cr + 5N + Ni = 19.53; The above-mentioned method for preparing austenitic stainless steel for cold rolling includes the following steps: S1: Melting to obtain nickel-saving austenitic stainless steel billets; S2: First, heat the billet to 820℃ at a rate of 6℃ / min and hold for 1 hour. Then, heat it to 1200℃ at a rate of 4℃ / min and hold for 2.5 hours to ensure uniform billet temperature and full austenitization of the microstructure.

[0032] S3: The heated billet is fed into a hot rolling mill for rolling. The initial rolling temperature is 1130℃, and multi-pass rolling is used. The first pass has a reduction rate of 27%, and the reduction rates of subsequent passes are 12%. The final rolling temperature is 880℃, and the total reduction rate is 68%. After hot rolling, the billet is rapidly cooled to room temperature to obtain a hot-rolled plate. The roll temperature is controlled at 200℃ during the rolling process.

[0033] S4: After annealing the hot-rolled plate, pickling is performed at a temperature of 1080℃ to obtain austenitic stainless steel for cold rolling.

[0034] Comparative Example 1 The difference from Example 3 is that it does not contain Nb or Ti.

[0035] Comparative Example 2 The difference from Example 3 is that Mn is 12% and Ni is 0.15%.

[0036] Comparative Example 3 The difference from Example 3 is that Mn 8%, Cr 16.8%, Ni 2.2%, N 0.29%, where: Mn / N=27.59, 2 / 3Mn+1 / 2Cr+5N+Ni=17.38.

[0037] Comparative Example 4 The difference from Example 3 is that step S2 is not performed.

[0038] Comparative Example 5 The difference from Example 3 is that step S4 is not performed.

[0039] Comparative Example 6 The difference from Example 3 is that in step S3, the reduction rate for each pass is 27%.

[0040] The stainless steel products prepared in Examples 1-3 and Comparative Examples 1-6 were subjected to performance tests. The test items included mechanical properties (yield strength, tensile strength, elongation), corrosion resistance (neutral salt spray test, 1000h), cold rolling processing performance (whether cracking occurs when the cold rolling reduction rate is 60%), and production cost. The test results are shown in Table 1.

[0041] Table 1 Product Performance Test Table The above description is merely a preferred embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural transformations made using the contents of the present invention under the inventive concept of the present invention, or direct / indirect applications in other related technical fields, are included within the patent protection scope of the present invention.

Claims

1. An austenitic stainless steel for cold rolling, characterized in that, Its composition, by mass percentage, includes: C 0.06~0.12%, Si 0.3~0.6%, Mn 8~11%, P≤0.035%, S≤0.030%, Cr 16.5~18.5%, Ni 2.0~3.5%, N 0.20~0.30%, Nb 0.005~0.015%, Ti 0.003~0.008%, with the balance being Fe and unavoidable impurities.

2. The austenitic stainless steel for cold rolling according to claim 1, characterized in that, The composition of the austenitic stainless steel used for cold rolling also satisfies: 18.5≤2 / 3Mn+1 / 2Cr+5N+Ni≤20.

5.

3. The austenitic stainless steel for cold rolling according to claim 1, characterized in that, The composition of the austenitic stainless steel used for cold rolling also satisfies: 30≤Mn / N≤50.

4. The austenitic stainless steel for cold rolling according to claim 1, characterized in that, The austenitic stainless steel used for cold rolling has a yield strength ≥250MPa, a tensile strength ≥520MPa, and an elongation ≥40%.

5. The austenitic stainless steel for cold rolling according to claim 1, characterized in that, The corrosion resistance of the austenitic stainless steel used for cold rolling meets the requirements of no significant corrosion after 1000 hours of neutral salt spray testing, and no cracking when the cold rolling reduction rate is ≥60%.

6. A method for preparing cold-rolled austenitic stainless steel according to any one of claims 1-5, characterized in that, Includes the following steps: S1: Melting to obtain nickel-saving austenitic stainless steel billets; S2: Heating the billet to perform austenitization treatment; S3: The heated billet is hot rolled in multiple passes, with water cooling during the hot rolling process, and then rapidly cooled to room temperature after hot rolling to obtain a hot-rolled plate; S4: After annealing, hot-rolled plates are pickled to obtain austenitic stainless steel for cold rolling.

7. The method for preparing cold-rolled austenitic stainless steel according to claim 6, characterized in that, In step S2, the billet is first heated to 800-850℃ at a rate of 5-8℃ / min and held for 1-1.5h, then heated to 1150-1250℃ at a rate of 3-5℃ / min and held for 2-3h.

8. The method for preparing cold-rolled austenitic stainless steel according to claim 6, characterized in that, In step S3, the heated billet is fed into a hot rolling mill for rolling. The initial rolling temperature is 1100~1150℃, and multi-pass rolling is adopted. The reduction rate of the first pass is 25~30%, and the reduction rate of each subsequent pass is 10~15%. The final rolling temperature is 850~900℃, and the total reduction rate is 60~70%.

9. The method for preparing cold-rolled austenitic stainless steel according to claim 6, characterized in that, In step S3, the temperature of the rolls is controlled at 180~220℃ during the rolling process.

10. The method for preparing cold-rolled austenitic stainless steel according to claim 6, characterized in that, In step S4, the annealing temperature is 1050~1100℃.

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