Low-thermal-expansion anisotropic stainless steel sheet and preparation method thereof

Abstract

The invention discloses a low-thermal-expansion anisotropic stainless steel sheet and a preparation method thereof. The low-thermal-expansion anisotropic stainless steel sheet comprises the following chemical components: less than or equal to 0.03% of C, less than or equal to 1.00% of Si, less than or equal to 0.60% of Mn, less than or equal to 0.020% of P, less than or equal to 0.015% of S, 17.50%-18.50% of Cr, 0.1%-0.4% of Al, 0.10%-0.40% of Ti, 0.30%-0.55% of Nb, 0.01%-0.03% of B, 0.04%-0.08% of Ce and the balance of iron and inevitable impurities. Wherein the mass percentage contents of Nb, Ti, Al, B and Ce meet the relational expression that Ti + Nb + Al is larger than or equal to 0.6% and smaller than or equal to 1.0%, and B + Ce is smaller than or equal to 0.1%; the preparation method comprises the procedures of smelting, hot rolling, cold rolling and multi-stage annealing. According to the method, the anisotropy of the stainless steel sheet in thermal expansion performance is reduced, and the use stability of the stainless steel sheet is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of metal material processing, and particularly relates to a low thermal expansion anisotropic stainless steel thin plate and a preparation method thereof. Background Art

[0002] Ferritic stainless steel is widely used in many fields due to its unique properties, such as corrosion resistance, low cost, high temperature oxidation resistance, etc., such as automotive exhaust / fuel systems, thin plates for household appliances and kitchenware, chemical and energy equipment components, etc. During the production and preparation process of ferritic stainless steel thin plates, anisotropy will inevitably occur, resulting in performance differences in different directions, such as mechanical properties, thermal expansion properties, etc. Among them, the inconsistency of thermal expansion performance may affect the application of products in high temperature environments. For example, in the automotive or aerospace fields, it may cause component deformation or failure; during the thin plate welding process, the thermal expansion differences in different directions may cause residual stress at the welding joint, resulting in deformation or cracks (especially under high temperature cyclic conditions); in high temperature service environments, such as in automotive exhaust systems, frequent thermal cycling will cause local stress concentration due to anisotropy, accelerating fatigue failure; in the application scenarios of precision components, in occasions where dimensional stability is required (such as sensor brackets), anisotropy may cause uncontrollable deformation.

[0003] The current production and preparation process of ferritic stainless steel thin plates is prone to cause grain orientation, resulting in anisotropy of mechanical / thermal expansion properties, and it is difficult to completely eliminate it with existing technologies (such as single annealing). The industry lacks a systematic combined control solution for composition - hot rolling - cold rolling - heat treatment, and fails to effectively reduce the anisotropy of thin plates. Summary of the Invention

[0004] The purpose of the present invention is to provide a low thermal expansion anisotropic stainless steel thin plate and a preparation method thereof. Through the cooperation of alloying elements, rolling process, and heat treatment process, the anisotropy of the thin plate in thermal expansion performance is reduced, and its use stability is improved.

[0005] To achieve the above purpose, the technical solution provided by the present invention is as follows:

[0006] A low thermal expansion anisotropic stainless steel thin plate, whose chemical composition and mass percentage are as follows: C ≤ 0.03%, Si ≤ 1.00%, Mn ≤ 0.60%, P ≤ 0.020%, S ≤ 0.015%, Cr 17.50% - 18.50%, Al 0.1% - 0.4%, Ti 0.10% - 0.40%, Nb 0.30% - 0.55%, B 0.01% - 0.03%, Ce 0.04% - 0.08%, and the balance is iron and inevitable impurities; among them, the mass percentages of Nb, Ti, Al, B, and Ce elements satisfy the relational expression: 0.6% ≤ Ti + Nb + Al ≤ 1.0%, B + Ce ≤ 0.1%.

[0007] Furthermore, for the low anisotropic thermal expansion stainless steel thin plate of the present invention, its thickness is 1 - 2 mm.

[0008] Furthermore, for the low anisotropic thermal expansion stainless steel thin plate of the present invention, the ratio of the average thermal expansion coefficients in the rolling direction and the transverse direction within room temperature to 800 °C is 0.98 ≤ α X:RT-800 / α Y:RT-800 ≤ 1.03, and the ratio of the average thermal expansion coefficients in the rolling direction and the transverse direction within 700 - 800 °C is 0.97 ≤ α X:700-800 / α Y:700-800 ≤ 1.04. The α X:RT-800 is the average thermal expansion coefficient in the rolling direction of the steel plate within room temperature to 800 °C, and α Y:RT-800 is the average thermal expansion coefficient in the transverse direction of the steel plate within room temperature to 800 °C; the α X:700-800 is the average thermal expansion coefficient in the rolling direction of the steel plate within 700 - 800 °C, and α Y:700-800 is the average thermal expansion coefficient in the transverse direction of the steel plate within 700 - 800 °C.

[0009] Furthermore, for the low anisotropic thermal expansion stainless steel thin plate of the present invention, its preparation method includes smelting, hot rolling, cold rolling, and multi-stage annealing processes.

[0010] Furthermore, for the hot rolling process of the present invention: three-stage temperature control rolling is adopted: ① Initial rolling stage: the rolling temperature is 1100 - 1150 °C, and the reduction ratio ≥ 50%; ② Middle rolling stage: the rolling temperature is 950 - 1000 °C, multi-pass rolling, and the pass reduction ratio is 15% - 20%; ③ Final rolling stage: controlled rolling at 850 - 900 °C, water-cooled to below 600 °C after final rolling, and finally rolled to 4.5 - 5 mm; ④ The hot rolled plate is annealed, with the temperature of 1000 - 1050 °C and the time of 8 - 10 min.

[0011] Furthermore, for the cold rolling process of the present invention: two-stage cold rolling is adopted: ① In the first stage, the single-pass reduction rate is 20% - 25%, cold rolled to 2.5 - 3 mm, annealed at 950 ± 5 °C for 5 - 10 min; ② In the second stage, the single-pass reduction rate is 15% - 20%, and the reduction rate of the last pass does not exceed 10%, cold rolled to 1.5 - 2 mm.

[0012] Furthermore, for the multi-stage annealing process of the present invention: ① Primary annealing: the annealing temperature is 950 - 980 °C, and the time is 5 - 10 min. ② Secondary annealing: the annealing temperature is 850 - 880 °C, and the time is 5 - 10 min.

[0013] The invention principle and beneficial technical effects of the technical solution of the present invention are as follows:

[0014] Through the cooperation of alloy elements, rolling process, and heat treatment process, the present invention effectively reduces the anisotropy of the thin plate in thermal expansion performance. The mechanism of action is as follows:

[0015] (1) In terms of the steel plate composition, on the basis of 441 stainless steel, Al, B, and Ce are added, and the contents of Nb and Ti elements are adjusted.

[0016] Nb, Ti, and Al can all improve the service performance of stainless steel at high temperatures. When Nb is added as a strengthening element to stainless steel, it can significantly improve the strength at room temperature and high temperatures, and at the same time improve the high-temperature creep resistance; in addition, Nb can fix carbon and nitrogen, avoid the precipitation of Cr, and refine the recrystallized structure. The Ti element improves the creep rupture strength and creep resistance of stainless steel through precipitation strengthening and stabilizing carbides. Titanium (Ti) and niobium (Nb) act as stabilizing elements in stainless steel. By preferentially combining with carbon to form carbides (TiC, NbC), they prevent the precipitation of chromium carbides, thereby avoiding intergranular corrosion. Al is an alloy element that is relatively economical and can improve the oxidation resistance of stainless steel. If the total content of Ti, Nb, and Al is too high, it will deteriorate the hot working performance, weaken the corrosion resistance, and exacerbate the brittleness and anisotropy of the material. In the present invention, the sum of the above three elements satisfies 0.6% ≤ Ti + Nb + Al ≤ 1.0%, which can ensure the improvement of the high-temperature performance of stainless steel while reducing the anisotropy and the harm caused by excessive amounts.

[0017] The B element can segregate at the grain boundaries, prevent grain boundary migration, refine the grain structure, improve the intergranular toughness and corrosion resistance of stainless steel, and at the same time, the refinement of the grain structure will also reduce the anisotropy; Ce reacts with elements such as sulfur S and oxygen O in the steel to form rare earth sulfides with high melting points (such as Ce2O2S, CeS) or oxides (such as Ce2O3), thereby changing the morphology and distribution of inclusions. The synergistic effect of the two can reduce the anisotropy caused by factors such as abnormal grains and inclusion distribution.

[0018] (2) The hot rolling process adopts a three-stage temperature control rolling method to reduce abnormal grain growth and mixed crystal phenomena during hot working, and further reduce anisotropy.

[0019] (3) The cold rolling process adopts a two-stage cold rolling + intermediate annealing process to reduce anisotropy during cold working.

[0020] (4) After cold rolling, a multi-stage annealing process is adopted. While eliminating the residual stress of the cold-rolled sheet, the grain size is controlled by recrystallization, thereby further eliminating anisotropy.

[0021] The method of the present invention effectively reduces the anisotropy of the thin sheet in terms of thermal expansion performance. For the prepared stainless steel thin sheet, the ratio of the average thermal expansion coefficients in the rolling direction and the transverse direction is 0.98 ≤ α X:RT-800 / α Y:RT-800 ≤ 1.03 within the temperature range of room temperature to 800 °C, and the ratio of the average thermal expansion coefficients in the rolling direction and the transverse direction is 0.97 ≤ α X:700-800 / α Y:700-800 ≤ 1.04 within the temperature range of 700 - 800 °C. Specific embodiments

[0022] The present invention will be described in more detail below through embodiments. These embodiments are only descriptions of the best implementation modes of the present invention and do not limit the scope of the present invention in any way.

[0023] Examples 1 - 6

[0024] The chemical compositions of the stainless steel thin sheets in each example are shown in Table 1.

[0025] Table 1 Chemical compositions of the stainless steel thin sheets in each example (mass fraction, %)

[0026] Example C Si Mn P S Cr Al Ti Nb B Ce 1 0.022 0.81 0.31 0.009 0.015 17.6 0.12 0.13 0.36 0.023 0.049 2 0.014 0.98 0.37 0.006 0.013 17.9 0.11 0.39 0.43 0.021 0.078 3 0.024 0.21 0.59 0.012 0.004 17.8 0.26 0.11 0.49 0.028 0.051 4 0.028 0.47 0.41 0.015 0.011 18.5 0.21 0.23 0.31 0.021 0.067 5 0.009 0.45 0.32 0.020 0.007 18.2 0.17 0.17 0.54 0.015 0.072 6 0.006 0.73 0.47 0.018 0.005 18.1 0.39 0.19 0.42 0.011 0.041

[0027] In Table 1, the balance is iron and unavoidable impurities.

[0028] The preparation methods of the stainless steel thin sheets in each example include smelting, hot rolling, cold rolling, and multi-stage annealing, which are specifically as follows:

[0029] (1) Hot rolling: Adopt three-stage temperature control rolling: ① Initial rolling stage: The rolling temperature is 1100 - 1150 °C, and the reduction rate ≥ 50%; ② Intermediate rolling stage: The rolling temperature is 950 - 1000 °C, multi-pass rolling, and the reduction rate per pass is 15% - 20%; ③ Final rolling stage: Controlled rolling at 850 - 900 °C, water-cooled to below 600 °C after final rolling, and finally rolled to 4.5 - 5 mm; ④ The hot-rolled sheet is annealed at a temperature of 1000 - 1050 °C for 8 - 10 min.

[0030] The parameters of the hot rolling process in each example are shown in Table 2.

[0031] Table 2 Hot Rolling Process Parameters of Each Example

[0032]

[0033] (2) Cold Rolling: Two-stage cold rolling is adopted: ① In the first stage, the single-pass reduction rate is 20% - 25%, cold rolled to 2.5 - 3 mm, annealed at 950 ± 5 °C for 5 - 10 min; ② In the second stage, the single-pass reduction rate is 15% - 20%, and the last pass does not exceed 10%, cold rolled to 1.5 - 2 mm.

[0034] (3) Multi-stage Annealing: ① Primary Annealing: Annealing temperature is 950 - 980 °C, time is 5 - 10 min. ② Secondary Annealing: Annealing temperature is 850 - 880 °C, time is 5 - 10 min.

[0035] The cold rolling and multi-stage annealing process parameters of each example are shown in Table 3.

[0036] Table 3 Cold Rolling and Multi-stage Annealing Process Parameters of Each Example

[0037]

[0038] Comparative Example 1

[0039] The chemical composition of the stainless steel sheet is: C 0.026%, Si 0.53%, Mn 0.37%, Cr 17.8%, Ni 0.21%, P 0.022%, S 0.009%, Nb + Ti 0.52%, and the balance is Fe and inevitable impurity elements; its production process includes hot rolling, cold rolling and annealing, specifically as follows:

[0040] (1) Hot Rolling: The initial rolling temperature is 1125 °C, and the final rolling stage: 880 °C, the reduction rate is 22%; the annealing temperature of the hot rolled sheet is 976 °C, and the time is 6 min.

[0041] (2) Cold Rolling: The reduction rate is 18%, cold rolled to 1.8 mm.

[0042] (3) Annealing: The annealing temperature is 860 °C, and the time is 8 min.

[0043] The ratios of the average thermal expansion coefficients in the rolling direction and the transverse direction of the stainless steel sheets prepared in each example and Comparative Example 1 are shown in Table 4.

[0044] Table 4 Ratios of Average Thermal Expansion Coefficients of Stainless Steel Sheets in Each Example and Comparative Example 1

[0045] <![CDATA[α X:RT-800 / α Y:RT-800 > <![CDATA[α X:700-800 / α Y:700-800 > Example 1 1.017 1.038 Example 2 1.027 1.035 Example 3 1.002 1.034 Example 4 1.023 0.972 Example 5 0.996 0.998 Example 6 0.983 1.008 Comparative Example 1 0.938 1.211

[0046] As can be seen from Table 4, for the stainless steel thin sheet provided by the present invention, the ratio of the average thermal expansion coefficients in the rolling direction and the transverse direction within the range of room temperature to 800 °C is 0.98 to 1.03, and within the range of 700 to 800 °C, the ratio of the average thermal expansion coefficients in the rolling direction and the transverse direction is 0.97 to 1.04. The anisotropy of its thermal expansion performance is relatively low, improving the use stability of the stainless steel thin sheet.

Claims

1. A low thermal expansion anisotropic stainless steel thin sheet, characterized in that, The chemical composition and mass percentage content are as follows: C ≤ 0.03%, Si ≤ 1.00%, Mn ≤ 0.60%, P ≤ 0.020%, S ≤ 0.015%, Cr 17.50% - 18.50%, Al 0.1% - 0.4%, Ti 0.10% - 0.40%, Nb 0.30% - 0.55%, B 0.01% - 0.03%, Ce 0.04% - 0.08%, and the balance is iron and inevitable impurities; among them, the mass percentage contents of Nb, Ti, Al, B, and Ce elements satisfy the relational expression: 0.6% ≤ Ti + Nb + Al ≤ 1.0%, B + Ce ≤ 0.1%.

2. The anisotropic stainless steel thin sheet with low thermal expansion according to claim 1, wherein Its thickness is 1 - 2 mm.

3. The anisotropic stainless steel thin sheet with low thermal expansion according to claim 1, characterized in that, The ratio of the average thermal expansion coefficients in the rolling direction and the transverse direction within the range of room temperature to 800 °C is 0.98 - 1.03, and the ratio of the average thermal expansion coefficients in the rolling direction and the transverse direction within the range of 700 - 800 °C is 0.97 - 1.

04.

4. A preparation method of the low thermal expansion anisotropic stainless steel thin plate according to claim 1, characterized in that, It includes smelting, hot rolling, cold rolling, and multi-stage annealing processes.

5. The preparation method of a low thermal expansion anisotropic stainless steel thin sheet according to claim 4, characterized in that, In the said hot rolling process, three-stage temperature control rolling is adopted: ① Initial rolling stage: The rolling temperature is 1100 - 1150 °C, and the reduction ratio ≥ 50%; ② Intermediate rolling stage: The rolling temperature is 950 - 1000 °C, multi-pass rolling, and the reduction ratio per pass is 15% - 20%; ③ Final rolling stage: Controlled rolling at 850 - 900 °C, water-cooled to below 600 °C after final rolling, and finally rolled to 4.5 - 5 mm; ④ The hot-rolled plate is annealed at a temperature of 1000 - 1050 °C for 8 - 10 min.

6. The preparation method of a low thermal expansion anisotropic stainless steel sheet according to claim 4, characterized in that, In the said cold rolling process, two-stage cold rolling is adopted: ① The first stage, the single-pass reduction ratio is 20% - 25%, cold-rolled to 2.5 - 3 mm, and annealed at 950 ± 5 °C for 5 - 10 min; ② The second stage, the single-pass reduction ratio is 15% - 20%, and the reduction ratio of the last pass does not exceed 10%, cold-rolled to 1.5 - 2 mm.

7. The preparation method of a low thermal expansion anisotropic stainless steel thin sheet according to claim 4, characterized in that, In the said multi-stage annealing process, ① Primary annealing: The annealing temperature is 950 - 980 °C, and the time is 5 - 10 min; ② Secondary annealing: The annealing temperature is 850 - 880 °C, and the time is 5 - 10 min.

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