Austenitic stainless steel and production process thereof

Abstract

The invention provides austenitic stainless steel and a production process thereof. The austenitic stainless steel comprises the following chemical components in percentage by mass: 0.03%-0.08% of C, 1.0%-1.5% of Mn, less than or equal to 0.03% of P, less than or equal to 0.006% of S, 18.1%-18.6% of Cr, 8.0%-9.0% of Ni, 0.03%-0.06% of N, Si and the balance of iron and inevitable impurities. The relationship between the Si content and the S content meets the condition that Si is greater than or equal to 37.5 * S + 0.335%. The invention further provides a production process of the austenitic stainless steel, and the production process comprises the steps of controlling the tapping temperature to be 1650 DEG C or below and carrying out high-pressure water dephosphorization in hot rolling. According to the chemical composition and the production process of the stainless steel, the surface color difference problem of the cold-rolled stainless steel can be obviously improved, and the obtained austenitic stainless steel has excellent surface quality.

Description

Technical Field

[0001] The present invention relates to the technical field of austenitic stainless steel manufacturing, and particularly to an austenitic stainless steel and its production process. Background Art

[0002] Surface color difference is a stubborn defect in cold-rolled stainless steel products. In severe cases, the incidence rate can reach more than 30%, seriously affecting product quality. Currently, during production, surface grinding of continuous casting slabs, cold rolling after hot annealing coil grinding, and increasing the cold rolling reduction rate are often used to alleviate the surface color difference problem. However, whether it is continuous casting slab or hot annealing coil grinding, it will take a large amount of production time and reduce the yield. And increasing the cold rolling reduction rate can generally only be used for thinner materials. Affected by production equipment, especially cold rolling mills, some thicker materials cannot achieve a large cold rolling reduction rate.

[0003] Therefore, a production process with simple operation is needed to significantly improve the surface color difference problem of cold-rolled stainless steel. Summary of the Invention

[0004] In order to overcome the above problems, the purpose of the present invention is to provide an austenitic stainless steel and its production process. This production process can significantly improve the surface color difference problem of cold-rolled stainless steel, and the austenitic stainless steel obtained thereby has excellent surface quality.

[0005] To achieve the above purpose, the present invention provides an austenitic stainless steel. In terms of mass percentage, the chemical composition of this austenitic stainless steel includes: C: 0.03% - 0.08%, Mn: 1.0% - 1.5%, P ≤ 0.03%, S ≤ 0.006%, Cr: 18.1% - 18.6%, Ni: 8.0% - 9.0%, N: 0.03% - 0.06%, Si, and the rest are iron and unavoidable impurities; wherein, the relationship between the Si content and the S content satisfies: Si ≥ 37.5 × S + 0.335% (it can be understood that in this relational expression, Si and S respectively represent the percentage contents of silicon and sulfur in the stainless steel, with the unit of %, for example, if the S content is 0.001%, then 0.001% is substituted into the formula to obtain that the Si content is greater than or equal to 0.3725%).

[0006] In the above austenitic stainless steel, the sum of the masses of each component is 100%.

[0007] The present invention can improve the surface quality of austenitic stainless steel and avoid the problem of surface color difference by controlling the contents of each component in the stainless steel, especially the relationship between the Si content and the S content.

[0008] According to a specific embodiment of the present invention, the mass content of silicon Si in the austenitic stainless steel can be further controlled to be 0.40% - 0.80%, for example, specific values such as 0.40%, 0.45%, 0.50%, 0.55%, 0.60%, 0.65%, 0.70%, 0.75%, 0.80% and ranges with any two of the above specific values as endpoints.

[0009] According to a specific embodiment of the present invention, the mass content of carbon C in the austenitic stainless steel is generally 0.03% - 0.08%, and specifically can be specific values such as 0.03%, 0.04%, 0.05%, 0.06%, 0.07%, 0.08% and ranges with any two of the above specific values as endpoints.

[0010] According to a specific embodiment of the present invention, the mass content of manganese Mn in the austenitic stainless steel is generally 1.0% - 1.5%, and specifically can be specific values such as 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5% and ranges with any two of the above specific values as endpoints.

[0011] According to a specific embodiment of the present invention, the mass content of chromium Cr in the austenitic stainless steel is generally 18.1% - 18.6%, and specifically can be specific values such as 18.1%, 18.2%, 18.3%, 18.4%, 18.5%, 18.6% and ranges with any two of the above specific values as endpoints.

[0012] According to a specific embodiment of the present invention, the mass content of nickel Ni in the austenitic stainless steel is generally 8.0% - 9.0%, and specifically can be specific values such as 8.0%, 8.1%, 8.2%, 8.3%, 8.4%, 8.5%, 8.6%, 8.7%, 8.8%, 8.9%, 9.0% and ranges with any two of the above specific values as endpoints.

[0013] According to a specific embodiment of the present invention, the mass content of nitrogen N in the austenitic stainless steel is generally 0.03% - 0.06%, and specifically can be specific values such as 0.03%, 0.035%, 0.04%, 0.045%, 0.05%, 0.055%, 0.06% and ranges with any two of the above specific values as endpoints.

[0014] According to a specific embodiment of the present invention, the mass content of sulfur S in the austenitic stainless steel is generally below 0.0060%, for example, it can be 0.0012% - 0.0060%.

[0015] The present invention also provides a production process for austenitic stainless steel, and this production process includes:

[0016] S1. Subject the steelmaking raw materials to electric furnace melting and AOD refining, tap the steel, ladle the molten steel into a ladle for secondary refining, and then carry out continuous casting; wherein, the tapping temperature is less than or equal to 1650 °C.

[0017] S2. Reheat the continuous casting billet in a heating furnace and then carry out hot rolling to obtain a black skin coil; wherein, the hot rolling process includes the operation of descaling with high-pressure water.

[0018] S3. Uncoil the black skin coil, carry out hot annealing and pickling to obtain a white skin coil; carry out cold rolling, cold annealing and pickling on the white skin coil to obtain an austenitic stainless steel coil with a 2B surface.

[0019] The austenitic stainless steel produced by the above production process includes the above austenitic stainless steel provided by the present invention.

[0020] In S1 of the above production process, in terms of mass percentage, the chemical composition of the steelmaking raw materials is generally obtained by proportioning with the chemical composition of the above austenitic stainless steel as the target.

[0021] S1 of the above production process includes the processes of smelting and continuous casting. The smelting specifically includes electric furnace melting, AOD refining, tapping, and secondary refining. The tapping temperature is generally controlled below 1650 °C, for example, it can be specific values such as 1620 °C, 1625 °C, 1630 °C, 1635 °C, 1640 °C, 1645 °C, 1650 °C, etc. and ranges with any two of the above specific values as endpoints.

[0022] In S1 of the above production process, the process of electric furnace melting includes: subjecting the steelmaking raw materials to electric arc furnace melting (EAF) to form a molten bath.

[0023] In S1 of the above production process, the AOD refining includes: feeding the molten bath formed by electric furnace melting into a refining furnace (AOD) for refining. The molten bath undergoes oxidation-reduction reactions in the AOD furnace. During this period, adjust the basicity of the refining slag and add ferroalloy to adjust the composition. When the composition meets the requirements, tap the steel. Among them, before feeding the molten bath into the refining furnace AOD, generally control the mass content of S in the molten bath below 0.050%. This S content range can match the basicity of the refining slag. If the S content is too high, the basicity of the refining slag will also increase correspondingly, which is not conducive to controlling the purity of the molten steel. The basicity of the refining slag is generally controlled at 1.20 - 1.75. In the above AOD refining, the oxidation-reduction reaction is generally carried out by blowing oxygen for oxidation and adding ferrosilicon for reduction.

[0024] In S1 of the above production process, the tapping temperature is generally below 1650 °C; in S2, the operation of descaling with high-pressure water is usually carried out during hot rolling. By controlling the tapping temperature and carrying out descaling with high-pressure water during hot rolling, the formation of surface color difference of the stainless steel can be avoided.

[0025] In S1 of the above production process, the process of secondary refining includes: loading molten steel into a ladle, completely skimming the slag on the surface of the ladle, and then adding lime, heat preservation agent, covering agent, etc. to protect the molten steel from oxidation and keep it warm; making fine adjustments to the composition of the ladle in secondary refining (LF) to meet the control requirements, and adjusting the temperature to complete secondary refining.

[0026] In S1 of the above production process, during the secondary refining process, the temperature of the molten steel is generally controlled at 1500 - 1520 °C, such as specific values of 1500 °C, 1505 °C, 1510 °C, 1515 °C, 1520 °C, etc. and ranges with any two of the above specific values as endpoints.

[0027] In S1 of the above production process, the ladle after secondary refining is sent to the continuous casting workbench for continuous casting. The continuous casting generally adopts full protection casting. The specific process of the continuous casting may include: using a long nozzle from the ladle to the tundish, closing the tundish with a protective gas (such as argon), covering the mold with a special protective slag, controlling the continuous casting speed to carry out continuous casting, and obtaining continuous casting billets.

[0028] In S1 of the above production process, the speed of the continuous casting is generally controlled at 1.0 - 1.5 m / min, specifically it can be specific values such as 1.0 m / min, 1.1 m / min, 1.2 m / min, 1.3 m / min, 1.4 m / min, 1.5 m / min, etc. and ranges with any two of the above specific values as endpoints.

[0029] In S2 of the above production process, the soaking temperature of the heating furnace is generally controlled at 1240 - 1280 °C, specifically it can be specific values such as 1240 °C, 1250 °C, 1260 °C, 1270 °C, 1280 °C, etc. and ranges with any two of the above specific values as endpoints.

[0030] In S2 of the above production process, the pressure of high-pressure water descaling is generally controlled at 24 - 26 MPa, specifically it can be specific values such as 24 MPa, 24.5 MPa, 25 MPa, 25.5 MPa, 26 MPa, etc. and ranges with any two of the above specific values as endpoints.

[0031] In S2 of the above production process, the process of hot rolling includes rough rolling and finish rolling. The high-pressure water descaling is generally carried out in the first pass of rough rolling, the second pass of rough rolling, and each pass of finish rolling. Specifically, the pressure of high-pressure water descaling carried out in the first pass and the second pass of rough rolling is generally 24 - 26 MPa; the pressure of high-pressure water descaling carried out in each pass of finish rolling is generally 24 - 26 MPa.

[0032] In S2 of the above production process, the temperature of rough rolling is generally controlled at 1200 - 1260°C, specifically it can be specific values such as 1200°C, 1210°C, 1220°C, 1230°C, 1240°C, 1250°C, 1260°C, etc. and ranges with any two of the above specific values as endpoints.

[0033] In S2 of the above production process, the temperature of finish rolling is generally controlled at 970 - 1030°C, specifically it can be specific values such as 970°C, 980°C, 990°C, 1000°C, 1010°C, 1020°C, 1030°C, etc. and ranges with any two of the above specific values as endpoints.

[0034] In the above production process, after hot rolling, a black skin steel strip is obtained. S2 further includes coiling the black skin steel strip while controlling the temperature to obtain a stainless steel black belt. In some specific embodiments, generally the temperature of the black skin steel strip is controlled at 600 - 800°C for coiling.

[0035] In S3 of the above production process, the conditions for hot annealing are: soaking zone temperature 1030 - 1070°C, specifically it can be specific values such as 1030°C, 1040°C, 1050°C, 1060°C, 1070°C, etc. and ranges with any two of the above specific values as endpoints; soaking time 2.5 min - 3.5 min, specifically it can be specific values such as 2.5 min, 2.6 min, 2.7 min, 2.8 min, 2.9 min, 3.0 min, 3.1 min, 3.2 min, 3.3 min, 3.4 min, 3.5 min, etc. and ranges with any two of the above specific values as endpoints. After hot annealing (i.e., soaking) is completed, it is cooled (water-cooled) to room temperature for pickling.

[0036] In S3 of the above production process, the reduction ratio of cold rolling is generally greater than or equal to 80%.

[0037] In S3 of the above production process, the conditions for cold annealing are generally: soaking zone temperature 1180 - 1220°C, specifically it can be specific values such as 1180°C, 1190°C, 1200°C, 1210°C, 1220°C, etc. and ranges with any two of the above specific values as endpoints; soaking time 1.75 min - 2.25 min, specifically it can be specific values such as 1.75 min, 2.00 min, 2.25 min, etc. and ranges with any two of the above specific values as endpoints. After soaking in cold annealing is completed, it is cooled (water-cooled) to room temperature for pickling.

[0038] The beneficial effects of the present invention include:

[0039] 1. By simply controlling the composition of austenitic stainless steel and conducting other production process controls with simple operations, the present invention can significantly improve the surface color difference problem of cold-rolled stainless steel. The austenitic stainless steel produced thereby has excellent surface quality.

[0040] 2. The production process control provided by the present invention is simple and low in cost, avoiding a large amount of grinding work on continuous casting slabs and hot-rolled white coils, and eliminating the need for complex process control requirements such as large cold rolling reduction rates. The improvement effect of the surface quality of stainless steel is obvious, which is conducive to promotion. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 It is a diagram showing the influence results of the contents of silicon and sulfur elements on the surface quality of stainless steel. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0042] For a clearer understanding of the technical features, objectives, and beneficial effects of the present invention, the technical solutions of the present invention will be described in detail below, but it should not be construed as a limitation on the scope of implementation of the present invention.

[0043] Examples 1 to 5

[0044] Examples 1 to 5 each provide an austenitic stainless steel, and the chemical compositions (mass percentages) of the stainless steels are shown in Table 1.

[0045] The production process of the austenitic stainless steel in the above examples includes:

[0046] S1. Melting the steelmaking raw materials into a molten bath in an electric arc furnace (EAF), charging the molten bath into an argon oxygen decarburization furnace (AOD) for refining. Before charging the molten bath into the AOD furnace, control the S content to be less than 0.050%. Conduct an oxidation (oxygen blowing)-reduction reaction (adding ferrosilicon) on the molten bath in the AOD furnace. During this period, adjust the basicity of the refining slag to be controlled between 1.20 and 1.75, add alloy iron to adjust the composition, and tap the steel when the composition meets the requirements. Control the tapping temperature to be less than or equal to 1650°C; Pour the molten steel into a ladle, completely remove the slag on the surface of the ladle, and then add lime, heat preservation agent, covering agent, etc. to protect the molten steel from oxidation and keep it warm; Conduct composition micro-adjustment and temperature adjustment on the ladle in ladle furnace (LF) to make the composition fully meet the control requirements, and control the molten steel temperature at 1500 - 1520°C; Then lift the ladle to the continuous casting workbench for continuous casting operation;

[0047] For continuous casting, full protection casting is adopted. A long nozzle is used from the ladle to the tundish, the tundish is sealed with argon, and the mold is covered with a special protective slag; Control the continuous casting speed at 1.0 - 1.5 m / min. The molten steel obtains continuous casting billets through continuous casting.

[0048] S2. Reheat the continuous casting billet obtained in S1 in a heating furnace and then hot-roll it to obtain a black skin coil (also known as a black skin steel strip). The hot rolling includes rough rolling and finish rolling. Among them, the soaking temperature of the heating furnace is controlled at 1260 ± 20 °C, the rough rolling temperature is 1230 ± 30 °C, high-pressure water descaling is carried out in the first and second passes of rough rolling, and the pressure of high-pressure water descaling is 25 ± 1 MPa; the finish rolling temperature is 1000 ± 30 °C, high-pressure water descaling is carried out in each pass of finish rolling, and the pressure of high-pressure water descaling is 25 ± 1 MPa. After finish rolling, the black skin steel strip is cooled by laminar flow to control the strip temperature at 600 - 800 °C for coiling to obtain a stainless steel black skin coil (also known as a stainless steel black belt).

[0049] S3. Uncoil the black skin coil obtained by hot rolling, perform hot annealing and pickling to obtain a white skin coil. Among them, the soaking zone temperature of hot annealing is 1050 ± 20 °C, the soaking time is 3 ± 0.5 min, and after soaking and water cooling to room temperature, pickling is carried out;

[0050] The white skin coil is cold-rolled, cold-annealed and pickled to obtain a stainless steel coil with a 2B surface. Among them, the cold rolling reduction rate is controlled at more than 80%, the soaking zone temperature of cold annealing is 1200 ± 20 °C, the soaking time is 2 ± 0.25 min, and after soaking and water cooling to room temperature, pickling is carried out.

[0051] The composition of the steelmaking raw materials in each example is formulated according to the chemical composition of the target stainless steel.

[0052] Comparative Examples 1 to 4

[0053] Comparative Examples 1 to 4 each provide an austenitic stainless steel. The chemical composition (mass percentage) of each stainless steel is shown in Table 1. The production processes of the austenitic stainless steels in each comparative example are similar to those of Examples 1 to 5, and the key process parameters are shown in Table 1.

[0054] Figure 1 It is a graph showing the influence of silicon and sulfur element contents on the surface quality of stainless steel. Figure 1 For the shown stainless steel chemical composition, except for the Si and S contents, the contents of other elements meet the following percentage contents: C: 0.03% - 0.08%, Mn: 1.0% - 1.5%, P ≤ 0.03%, Cr: 18.1% - 18.6%, Ni: 8.0% - 9.0%, N: 0.03% - 0.06%.

[0055] From Figure 1 it can be seen that the surface color difference situation of austenitic stainless steel is significantly related to the Si and S contents. When the Si and S element contents meet Si ≥ 37.5 × S + 0.335% (i.e., Figure 1 the situation above the critical line in Figure 1In the case where it is below the critical line on the lower right, there is a color difference on the surface of the austenitic stainless steel. The above results show that by controlling the silicon and sulfur contents in the stainless steel, the present invention can significantly improve the surface color difference of the stainless steel and improve the surface quality of the stainless steel.

[0056] The surface color differences of the austenitic stainless steels in the above examples and comparative examples were evaluated, and the evaluation results are shown in Table 1. The color difference rating has a total of 5 levels: 0, 1, 2, 3, and 4. Levels 0, 1, and 2 indicate qualified, and levels 3 and 4 indicate unqualified.

[0057] Table 1

[0058]

[0059] *In Table 1, Equation 1 is: Si≥37.5×S + 0.335%. The units of Si and S are %.

[0060] Although the component content of the stainless steel in Comparative Example 1 meets the stainless steel components provided by the present invention, but no high-pressure water descaling is carried out, resulting in a color difference on the surface of the stainless steel and an unqualified color difference rating.

[0061] Although the component content of the stainless steel in Comparative Example 2 meets the stainless steel components provided by the present invention, but the tapping temperature is higher than 1650 °C and does not meet the production process provided by the present invention, resulting in a color difference on the surface of the stainless steel and an unqualified color difference rating.

[0062] The stainless steel components in Comparative Example 3 do not meet the requirements of the stainless steel components of the present invention, especially do not meet the relationship between the Si content and the S content, and the tapping temperature of Comparative Example 3 is too high, higher than 1650 °C, resulting in a color difference on the surface of the stainless steel and an unqualified color difference rating.

[0063] Although the production process of the stainless steel in Comparative Example 4 meets the production process provided by the present invention, but the stainless steel component content does not meet the stainless steel components provided by the present invention, especially does not meet the relationship between the Si content and the S content, resulting in a color difference on the surface and an unqualified color difference rating.

[0064] The stainless steels produced in Examples 1 to 5 not only meet the stainless steel components provided by the present invention (including meeting the relationship between the Si content and the S content), but also meet the stainless steel production process provided by the present invention. Therefore, the produced stainless steel has no color difference on the surface and excellent quality.

[0065] Based on the above comprehensive results, it shows that by controlling the component content of the stainless steel (especially the Si and S contents), and at the same time adjusting the production process of the stainless steel (including controlling the tapping temperature and carrying out high-pressure water descaling), the present invention can effectively improve the surface color difference defect of the stainless steel and improve the surface quality.

Claims

1. An austenitic stainless steel, wherein the chemical composition of the austenitic stainless steel comprises, by mass percentage: C： 0.03%-0.08%, Mn: 1.0%-1.5%, P≤0.03%, S≤0.006%, Cr: 18.1%-18.6%, Ni: 8.0%-9.0%, N: 0.03%-0.06%, Si, the rest is iron and unavoidable impurities; The relationship between Si content and S content satisfies: Si≥37.5×S+0.335%.

2. The austenitic stainless steel according to claim 1, wherein: The mass content of Si in austenitic stainless steel is 0.40%-0.80%.

3. The austenitic stainless steel according to claim 1, wherein: The mass content of S in austenitic stainless steel is 0.0012%-0.0060%.

4. A production process for austenitic stainless steel, the production process comprising: S1. Smelting the steelmaking raw materials in an electric furnace, refining with AOD, tapping the steel, and putting the molten steel into a ladle for refining outside the furnace and continuous casting; wherein the tapping temperature is less than or equal to 1650° C.; S2, reheating the continuous casting billet in a heating furnace and hot rolling to obtain a black coil; wherein the hot rolling process includes a high-pressure water dephosphorization operation; S3. Uncoiling, heat annealing and pickling the black coil to obtain a white coil; cold rolling, cold annealing and pickling the white coil to obtain an austenitic stainless steel coil with a 2B surface, wherein the austenitic stainless steel includes the austenitic stainless steel according to any one of claims 1 to 3.

5. The production process according to claim 4, wherein: In S1, during the AOD refining process, the basicity of the refined slag is controlled to be 1.20-1.

75.

6. The production process according to claim 4, wherein: In S1, during the refining process outside the furnace, the temperature of the molten steel is controlled to be 1500-1520°C.

7. The production process according to claim 4, wherein: In S2, the heating furnace has a soaking temperature of 1240-1280°C; And / or, the pressure of the high-pressure water dephosphorization is 24-26 MPa.

8. The production process according to claim 4, wherein: In S2, the hot rolling process includes rough rolling and finish rolling, and the high-pressure water dephosphorization is performed in the first pass of rough rolling, the second pass of rough rolling and each pass of finish rolling; Wherein, the temperature of the rough rolling is 1200-1260°C, and the temperature of the finish rolling is 970-1030°C.

9. The production process according to claim 4, wherein: In S3, the conditions of the thermal annealing are: the soaking zone temperature is 1030-1070° C., and the soaking time is 2.5 min-3.5 min.

10. The production process according to claim 4, wherein: In S3, the cold rolling reduction ratio is ≥80%; The cold annealing conditions are: soaking zone temperature 1180-1220° C., soaking time 1.75 min-2.25 min.

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