Cold rolling production method for eliminating shading on the surface of ferritic stainless steel

Abstract

The invention discloses a cold rolling production method for eliminating shading on the surface of ferritic stainless steel, comprising: hot-rolling a steel coil to form a hot-rolled white coil; performing a first rolling process on the hot-rolled white coil; grinding the rolled surface; pickling the ground surface with mixed acid; performing a second rolling process on the pickled steel coil, wherein the roughness of the rolling working roll is 0.1-0.3 μm, and the rolling speed of the last pass is controlled to be no more than 200 mpm; performing bright annealing on the steel coil in an intermediate rolling process, and the annealing furnace temperature is controlled to be 950-1110° C.; performing a third rolling process on the steel coil after the bright annealing, wherein the roughness of the rolling working roll is 0.05-0.2 μm, and the rolling speed of the last pass is controlled to be no more than 150 mpm; performing bright annealing on the steel coil in a finished product rolling process, and the annealing furnace temperature is 20° C. lower than the annealing furnace temperature of the intermediate rolling process; and leveling the steel coil three times after the bright annealing. Through the present invention, the surface shading of ferritic stainless steel is completely eliminated, the surface brightness is effectively improved, and the surface roughness is significantly reduced, which fully meets the application requirements in the field of high-end decoration.

Description

Technical Field

[0001] The invention belongs to the technical field of ferritic stainless steel production, and more particularly relates to a cold rolling production method for eliminating shading on the surface of ferritic stainless steel. Background Art

[0002] High-end decorative applications require materials with high image quality and low reflective haze. Due to its body-centered cubic structure, ferrite stainless steel is prone to developing skin-like lines on its surface, known as shading. This shading causes image edges to jitter along these lines, affecting image clarity. Therefore, high-end decorative applications currently typically use 304 stainless steel or chrome-plated ferrite to mask the shading.

[0003] Common ultra-pure ferritic stainless steels such as 441, SUS436L, and TTS443M have corrosion resistance no less than that of 304, as well as good economic efficiency. In order for ferritic stainless steel to be used in the high-end decoration industry, the main indicators that need to be controlled include reflective haze HAZE <12, imaging quality RIQ >98, peak reflectivity RSPEC >900, and gloss GU >1000. In terms of surface quality, this means eliminating surface shading, improving surface brightness, and reducing surface roughness. To meet the above index requirements, it is necessary to develop a new cold rolling production process that can eliminate ferritic stainless steel shading. By controlling the shading defects of ferritic stainless steel through the cold rolling process, ferritic stainless steel can directly replace 304 stainless steel in the high-end decoration industry, thereby improving economic efficiency. Summary of the Invention

[0004] In order to solve the technical problems existing in the above-mentioned prior art, the present invention provides a cold rolling production method for eliminating shading on the surface of ferritic stainless steel, comprising the following steps:

[0005] Step 1: After annealing, flattening, and pickling, the ferritic stainless steel hot-rolled coil is formed into a hot-rolled white coil with a NO.1 surface. The surface roughness of the hot-rolled white coil is controlled to be Ra = 3.0-3.5 μm;

[0006] Step 2: In the first rolling process, the hot rolled white steel coil is rolled on a 20-high Sendkimer mill, and the total deformation rate of the rolled thickness is controlled to be 15-30%;

[0007] Step 3: Use 240# abrasive belt to grind the rolled surface;

[0008] Step 4: Use mixed acid to pickle the ground surface. The mixed acid is nitric acid + hydrofluoric acid. The concentration of nitric acid is 100-140g / l and the concentration of hydrofluoric acid is 10-15g / l.

[0009] Step 5: In the second rolling process, the pickled steel coil is rolled on a 20-roll Sendkimir mill. The total deformation rate of the rolling thickness is controlled to 50-60%, and the deformation rate of each pass does not exceed 10%. The roughness of the rolling work rolls is 0.1-0.3 μm. The roughness of the work rolls used in each pass in the second rolling process is gradually reduced, and each work roll is used no more than two passes. After the rolling starts smoothly, the AFC system and the AGC system are fully put into use. The rolling oil flow rate is controlled to 1500-2000 L / min, and both sets of scraper rollers of the rolling mill are put into use, and the scraper roller pressure is controlled to 60 bar. The rolling speed of the last pass is controlled to no more than 200 mpm.

[0010] Step 6: The rolled steel coil is subjected to intermediate bright annealing in a bright annealing furnace. The hydrogen content in the bright annealing furnace is controlled to be no less than 85%, the dew point is ≤-50°C, and the oxygen content is ≤15ppm. The intermediate annealing furnace temperature is controlled to be 950-1110°C.

[0011] Step 7: In the third rolling pass, the bright annealed steel coil is rolled on a 20-roll Sendkimer mill. The total deformation rate of the rolling thickness is controlled to 60-70%, and the deformation rate of each pass does not exceed 10%. The roughness of the rolling work rolls is 0.05-0.2 μm. The roughness of the work rolls used in each pass in the third rolling pass is gradually reduced, and each work roll is used no more than two passes. After the rolling starts smoothly, the AFC system and the AGC system are fully put into use. The rolling oil flow rate is controlled to 1500-2000 L / min, and both sets of oil scraper rolls of the rolling mill are fully put into use, with the oil scraper roll pressure controlled to 60 bar. The rolling speed of the last pass is controlled to no more than 150 mpm.

[0012] Step 8: The rolled steel coil is subjected to a bright annealing furnace for a finished product rolling process. The hydrogen content in the bright annealing furnace is controlled to be not less than 85%, the dew point is ≤-50°C, and the oxygen content is ≤15ppm. The temperature of the finished product rolling process annealing furnace is 20°C lower than the temperature of the intermediate rolling process annealing furnace in step 6.

[0013] Step 9: After bright annealing, the finished steel coil is leveled three times.

[0014] Furthermore, the above-mentioned cold rolling production method for eliminating the surface shading of ferritic stainless steel can be used for the production of ferritic stainless steel with grades SUS436L, 441, and TTS443M, with a raw material thickness of 4.0 to 6.0 mm, a finished product thickness of 0.4 to 0.6 mm, and a finished product width of 1000 to 1255 mm.

[0015] Furthermore, in the above-mentioned cold rolling production method for eliminating the shading on the surface of ferritic stainless steel, the intermediate rolling process annealing furnace temperatures of ferritic stainless steels with grades SUS436L, 441, and TTS443M are respectively: 960°C for TTS443M steel, 980°C for SUS436L steel, and 1020°C for 441 steel; the finished rolling process annealing furnace temperatures of ferritic stainless steels with grades SUS436L, 441, and TTS443M are respectively: 940°C for TTS443M steel, 960°C for SUS436L steel, and 1000°C for 441 steel.

[0016] As an embodiment, in the above-mentioned cold rolling production method for eliminating shading on the surface of ferritic stainless steel of the present invention, the grade of the ferritic stainless steel hot-rolled coil is SUS436L, and its chemical composition by mass percentage is: C: 0.011%, Si: 0.237%, Mn: 0.094%, P: 0.021%, S: 0.001%, Cr: 17.159%, Mo: 0.845%, Nb: 0.281%, N: 0.014%, and the rest is Fe and other inevitable impurities. The nominal specifications of the ferritic stainless steel hot-rolled coil are: thickness 4.0 mm, width 1253 mm, and the nominal thickness of the finished product of the target product is 0.5 mm, wherein:

[0017] In step 1: the surface roughness of the hot-rolled white coil formed by the hot-rolled steel coil is Ra=3.14 μm;

[0018] In step 2, the thickness of the finished product in the first rolling process is set to 3.0 mm, and the rolling is performed in one pass;

[0019] In step 5, the thickness of the finished product of the second rolling process is set to 1.5 mm, the rolling oil flow rate is controlled to 1830 L / min, and the rolling process parameters of the second rolling process are controlled according to the following table:

[0020]

[0021] In step 6, during the intermediate rolling bright annealing, the hydrogen content is controlled to be 88%, the dew point is -51°C, the oxygen content is 12ppm, and the intermediate rolling annealing furnace temperature is controlled to be 980°C;

[0022] In step 7, the thickness of the finished product of the third rolling process is set to 0.5 mm, the rolling oil flow rate is controlled to 1710 L / min, and the rolling process parameters of the third rolling process are controlled according to the following table:

[0023]

[0024]

[0025] In step 8, during bright annealing of the finished product, the hydrogen content is controlled to be 92%, the dew point is -51°C, the oxygen content is 11 ppm, and the annealing furnace temperature of the finished product is controlled to be 960°C.

[0026] The cold rolling production method for eliminating ferritic stainless steel surface shading of the present invention has the following advantages and beneficial effects: through the design of process route, rolling deformation rate, rolling process, roller use, bright annealing, surface grinding and other technical measures, the surface shading is completely eliminated, the surface brightness is effectively improved, and the surface roughness is significantly reduced. The ferritic stainless steel product produced by the cold rolling production method for eliminating ferritic stainless steel surface shading of the present invention has a surface roughness Ra≤0.15μm, a grain size≥level 7, and a surface brightness of more than 1000GU. In addition, after actual testing, HAZE<12, imaging quality RIQ>98, peak reflectivity RSPEC>900, and glossiness GU>1000, which fully meets the application requirements in the high-end decoration field. Therefore, ferritic stainless steel can directly replace 304 stainless steel in the high-end decoration industry, significantly improving economic efficiency. DETAILED DESCRIPTION

[0027] To make the objectives, technical solutions, and advantages of the present invention more clear, the technical solutions of the present invention will be clearly and completely described below in conjunction with specific embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0028] The cold rolling production method for eliminating shading on the surface of ferritic stainless steel of the present invention comprises the following steps:

[0029] Step 1: After annealing, flattening, and pickling, the ferritic stainless steel hot-rolled coil is formed into a hot-rolled white coil with a NO.1 surface. The surface roughness of the hot-rolled white coil is controlled to be Ra = 3.0 ~ 3.5μm. The specific production process is not described in detail in this article.

[0030] Step 2: In the first rolling process, the hot rolled white coil is rolled on a 20-roll Sendkimer mill, and the total deformation rate of the rolling thickness is controlled at 15-30% to ensure the flatness of the plate.

[0031] Step 3: Use 240# abrasive belt to grind the rolled surface.

[0032] Step 4: Use mixed acid to pickle the ground surface. The mixed acid uses nitric acid + hydrofluoric acid. The concentration of nitric acid is 100-140g / l, and the concentration of hydrofluoric acid is 10-15g / l.

[0033] Step 5: In the second rolling process, the steel coil after pickling is rolled on a twenty-roll Sendkimir mill, and the total deformation rate of the rolling thickness is controlled to be 50-60%, and the deformation rate of each pass does not exceed 10%; the roughness of the rolling work roll is 0.1-0.3 μm, and the roughness of the working roll used in each pass in the second rolling process gradually decreases, and each working roll is used no more than 2 times; after the rolling starts smoothly, the AFC system and the AGC system are fully put into use to ensure the plate shape level and thickness tolerance; the rolling oil flow is controlled to 1500-2000 L / min, and the two sets of scraper rollers of the rolling mill are all put into use, and the scraper roller pressure is controlled to 60 bar to improve the scraping effect; the rolling speed of the last pass is controlled to not exceed 200 mpm.

[0034] Step 6: The rolled coils undergo intermediate bright annealing in a bright annealing furnace. The hydrogen content in the bright annealing furnace is controlled to be no less than 85%, the dew point ≤ -50°C, and the oxygen content ≤ 15 ppm. The intermediate annealing furnace temperature is controlled between 950°C and 1110°C. More specifically, the intermediate annealing furnace temperatures for common ferritic steel grades are: 960°C for TTS443M steel, 980°C for SUS436L steel, and 1020°C for 441 steel.

[0035] Step 7: In the third rolling process, after bright annealing, the steel coil is rolled on a twenty-roll Sendkimer mill, and the total deformation rate of the rolling thickness is controlled to be 60-70%, and the deformation rate of each pass does not exceed 10%; the roughness of the rolling work rolls is 0.05-0.2μm, and the roughness of the working rolls used in each pass in the third rolling process gradually decreases, and each working roll is used no more than 2 times; after the rolling starts smoothly, the AFC system and the AGC system are fully put into use to ensure the plate shape level and thickness tolerance; the rolling oil flow is controlled to 1500-2000L / min, and the two sets of scraper rollers of the rolling mill are all put into use, and the scraper roller pressure is controlled to 60bar to improve the scraping effect; the rolling speed of the last pass is controlled to not exceed 150mpm.

[0036] Step 8: The rolled coils undergo a final-pass bright annealing in a bright annealing furnace. The hydrogen content in the bright annealing furnace is controlled to be no less than 85%, the dew point ≤ -50°C, and the oxygen content ≤ 15 ppm. The final-pass annealing furnace temperature is 20°C lower than the intermediate-pass annealing furnace temperature in Step 6. More specifically, the final-pass annealing furnace temperatures for common ferritic steel grades are: 940°C for TTS443M steel, 960°C for SUS436L steel, and 1000°C for 441 steel.

[0037] Step 9: After bright annealing of the finished product, the steel coil is flattened three times to ensure that the plate shape is straight and the surface brightness reaches above 1000GU.

[0038] In the cold rolling production method for eliminating shading on the surface of ferritic stainless steel of the present invention, by means of technical means such as rolling pass allocation, roll use, flow control, and rolling oil control in steps 5 and 7, the surface roughness of the ferritic stainless steel strip can be reduced to Ra ≤ 0.15 μm, and the shading of the ferritic stainless steel can be eliminated at the naked eye level.

[0039] In the cold rolling production method for eliminating shading on the surface of ferritic stainless steel of the present invention, the intermediate rolling process bright annealing in step 6 and the finished product rolling process bright annealing in step 8 can prevent the surface of the ferritic stainless steel strip from turning yellow due to oxidation, and can ensure a grain size of ≥ level 7, thereby ensuring imaging clarity in high-end decorative applications.

[0040] In the cold rolling production method for eliminating shading on the surface of ferritic stainless steel of the present invention, by leveling the steel coil three times in step 9, the surface brightness of the ferritic stainless steel strip can reach above 1000 GU.

[0041] The ferritic stainless steel product produced by the cold rolling production method for eliminating the surface shading of ferritic stainless steel of the present invention has a surface roughness Ra≤0.15μm, a grain size≥level 7, a surface brightness of more than 1000GU, the surface shading is completely eliminated, the surface brightness is effectively improved, and the surface roughness is significantly reduced. After actual testing, the HAZE is less than 12, the imaging quality RIQ is greater than 98, the peak reflectivity RSPEC is greater than 900, and the glossiness GU is greater than 1000, which fully meets the application requirements in the high-end decoration field.

[0042] As a specific embodiment, the cold rolling production method for eliminating shading on the surface of ferritic stainless steel of the present invention is applicable to the production of common grades of ferritic stainless steel such as SUS436L, 441, TTS443M, etc. The raw material thickness can be 4.0 to 6.0 mm, the finished product thickness can be 0.4 to 0.6 mm, and the finished product width can be 1000 to 1255 mm.

[0043] The cold rolling production method for eliminating shading on the surface of ferritic stainless steel of the present invention is described in detail below with reference to specific embodiments.

[0044] Example 1

[0045] In Example 1 of the present invention, an ultrapure ferritic hot-rolled steel coil of grade SUS436L is used as raw material. The chemical composition thereof, by mass percentage, is as follows: C: 0.011%, Si: 0.237%, Mn: 0.094%, P: 0.021%, S: 0.001%, Cr: 17.159%, Mo: 0.845%, Nb: 0.281%, and N: 0.014%. The remainder is Fe and other unavoidable impurities. The nominal specifications of the ferritic stainless steel hot-rolled steel coil are: thickness 4.0 mm, width 1253 mm, and the finished product nominal thickness of the target product is 0.5 mm.

[0046] The cold rolling production method for eliminating shading on the surface of ferritic stainless steel of Example 1 comprises the following steps:

[0047] Step 1: After annealing, flattening and pickling, the hot-rolled steel coil is formed into a NO.1 hot-rolled white coil. The actual thickness of the hot-rolled white coil is 3.88 mm and the surface roughness is Ra = 3.14 μm. The specific production process is not repeated here.

[0048] Step 2: In the first rolling process, the hot rolled white steel coil is cold rolled on a 20-high Sendkimer mill. The finished product thickness of the first rolling process is set to 3.0 mm, and the total deformation rate of the rolling thickness is 22.68%. The rolling process parameters of the first rolling process are shown in Table 1:

[0049] Table 1 Rolling process parameters of the first rolling process

[0050] path Raw material thickness / mm Finished product thickness in the first rolling process / mm Deformation rate 1 3.88 3.0 22.68％

[0051] Step 3: Use the upper grinding machine to improve the surface defects. Use four sets of upper grinding heads, 240# sand belt, speed 14mpm, and grind both surfaces once each.

[0052] Step 4: Cold line mixed acid pickling to further clean the surface. The mixed acid is nitric acid + hydrofluoric acid, with a nitric acid concentration of 131g / l and a hydrofluoric acid concentration of 11.2g / l.

[0053] Step 5: In the second rolling pass, the pickled coils were cold-rolled on a 20-high Sendkimir mill. The finished thickness of the second rolling pass was set to 1.5 mm, and the total deformation rate was 50%. Once the rolling process stabilized, the AFC and AGC systems were fully operational, with the rolling oil flow controlled at 1830 L / min. Both sets of scraper rollers were operational, and the scraper pressure was controlled at 60 bar. The rolling process parameters for the second rolling pass are shown in Table 2:

[0054] Table 2 Rolling process parameters of the second rolling process

[0055]

[0056] Step 6: After rolling, the steel coil is subjected to intermediate rolling bright annealing. The hydrogen content in the bright annealing furnace is controlled to 88%, the dew point is -51°C, the oxygen content is 12ppm, and the intermediate rolling annealing furnace temperature is controlled to 980°C.

[0057] Step 7: In the third rolling pass, the bright annealed coils were cold rolled on a 20-high Sendkimir mill. The finished thickness of the third rolling pass was set to 0.5 mm, and the total deformation rate was 66.67%. Once the rolling process stabilized, the AFC and AGC systems were fully activated, with the rolling oil flow rate controlled at 1710 L / min. Both sets of scraper rollers were fully activated, and the scraper roller pressure was controlled at 60 bar. The rolling process parameters for the third rolling pass are shown in Table 3:

[0058] Table 3 Rolling process parameters of the third rolling process

[0059]

[0060]

[0061] Step 8: After rolling, the steel coil is subjected to bright annealing of the finished rolling process. The hydrogen content in the bright annealing furnace is controlled to 92%, the dew point is -51°C, the oxygen content is 11ppm, and the temperature of the finished rolling process annealing furnace is controlled to 960°C.

[0062] Step 9: After bright annealing of the finished product, the steel coil is leveled three times to ensure that the plate shape is straight and the surface brightness reaches 1123GU.

[0063] In summary, the cold rolling production method for eliminating the surface shading of ferritic stainless steel of the present invention is achieved through technical measures such as designing process routes, rolling deformation rate, rolling process, use of rolling rollers, bright annealing, and surface grinding, so that the surface shading is completely eliminated, the surface brightness is effectively improved, and the surface roughness is significantly reduced. The ferritic stainless steel products produced by the cold rolling production method for eliminating the surface shading of ferritic stainless steel of the present invention have a surface roughness Ra≤0.15μm, a grain size≥level 7, and a surface brightness of more than 1000GU. In addition, after actual testing, HAZE<12, imaging quality RIQ>98, peak reflectivity RSPEC>900, and glossiness GU>1000, which fully meet the application requirements in the field of high-end decoration. Therefore, ferritic stainless steel can directly replace 304 stainless steel in the high-end decoration industry, significantly improving economic efficiency.

[0064] It should be noted that, in this article, the term "comprise" or any other variation thereof is intended to cover non-exclusive inclusion, so that an article or device that includes a series of elements includes not only those elements, but also includes other elements that are not explicitly listed, or also includes elements that are inherent to such article or device.

[0065] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A cold rolling production method for eliminating shading on the surface of ferritic stainless steel, characterized in that: The steps include: Step 1: After annealing, flattening, and pickling, the ferritic stainless steel hot-rolled coil is formed into a hot-rolled white coil with a NO.1 surface. The surface roughness of the hot-rolled white coil is controlled to be Ra = 3.0-3.5 μm; Step 2: In the first rolling process, the hot rolled white steel coil is rolled on a 20-high Sendkimer mill, and the total deformation rate of the rolled thickness is controlled to be 15-30%; Step 3: Use 240# abrasive belt to grind the rolled surface; Step 4: Use mixed acid to pickle the ground surface. The mixed acid is nitric acid + hydrofluoric acid. The concentration of nitric acid is 100-140g / l and the concentration of hydrofluoric acid is 10-15g / l. Step 5: In the second rolling process, the pickled steel coil is rolled on a 20-roll Sendkimir mill. The total deformation rate of the rolling thickness is controlled to 50-60%, and the deformation rate of each pass does not exceed 10%. The roughness of the rolling work rolls is 0.1-0.3 μm. The roughness of the work rolls used in each pass in the second rolling process is gradually reduced, and each work roll is used no more than two passes. After the rolling starts smoothly, the AFC system and the AGC system are fully put into use. The rolling oil flow rate is controlled to 1500-2000 L / min, and both sets of scraper rollers of the rolling mill are put into use, and the scraper roller pressure is controlled to 60 bar. The rolling speed of the last pass is controlled to no more than 200 mpm. Step 6: The rolled steel coil is subjected to intermediate bright annealing in a bright annealing furnace. The hydrogen content in the bright annealing furnace is controlled to be no less than 85%, the dew point is ≤-50°C, and the oxygen content is ≤15ppm. The intermediate annealing furnace temperature is controlled to be 950-1110°C. Step 7: In the third rolling pass, the bright annealed steel coil is rolled on a 20-roll Sendkimer mill. The total deformation rate of the rolling thickness is controlled to 60-70%, and the deformation rate of each pass does not exceed 10%. The roughness of the rolling work rolls is 0.05-0.2 μm. The roughness of the work rolls used in each pass in the third rolling pass is gradually reduced, and each work roll is used no more than two passes. After the rolling starts smoothly, the AFC system and the AGC system are fully put into use. The rolling oil flow rate is controlled to 1500-2000 L / min, and both sets of oil scraper rolls of the rolling mill are fully put into use, with the oil scraper roll pressure controlled to 60 bar. The rolling speed of the last pass is controlled to no more than 150 mpm. Step 8: The rolled steel coil is subjected to a bright annealing furnace for a finished product rolling process. The hydrogen content in the bright annealing furnace is controlled to be not less than 85%, the dew point is ≤-50°C, and the oxygen content is ≤15ppm. The temperature of the finished product rolling process annealing furnace is 20°C lower than the temperature of the intermediate rolling process annealing furnace in step 6. Step 9: After bright annealing, the finished steel coil is leveled three times.

2. The cold rolling production method for eliminating shading on the surface of ferritic stainless steel according to claim 1 is used for the production of ferritic stainless steel with grades SUS436L, 441, and TTS443M, wherein: The raw material thickness is 4.0~6.0mm, the finished product thickness is 0.4~0.6mm, and the finished product width is 1000~1255mm.

3. The cold rolling production method for eliminating shading on the surface of ferritic stainless steel according to claim 2, characterized in that: The intermediate rolling process annealing furnace temperatures of ferritic stainless steels with grades of SUS436L, 441, and TTS443M are: 960°C for TTS443M steel, 980°C for SUS436L steel, and 1020°C for 441 steel; the finished rolling process annealing furnace temperatures of ferritic stainless steels with grades of SUS436L, 441, and TTS443M are: 940°C for TTS443M steel, 960°C for SUS436L steel, and 1000°C for 441 steel.

4. The cold rolling production method for eliminating shading on the surface of ferritic stainless steel according to claim 1, characterized in that: The ferritic stainless steel hot-rolled coil is SUS436L, and its chemical composition by mass percentage is: C: 0.011%, Si: 0.237%, Mn: 0.094%, P: 0.021%, S: 0.001%, Cr: 17.159%, Mo: 0.845%, Nb: 0.281%, N: 0.014%, and the remainder is Fe and other inevitable impurities. The nominal specifications of the ferritic stainless steel hot-rolled coil are: thickness 4.0 mm, width 1253 mm, and the nominal thickness of the finished product of the target product is 0.5 mm, wherein: In step 1: the surface roughness of the hot-rolled white coil formed by the hot-rolled steel coil is Ra=3.14 μm; In step 2, the thickness of the finished product in the first rolling process is set to 3.0 mm, and the rolling is performed in one pass; In step 5, the thickness of the finished product of the second rolling process is set to 1.5 mm, the rolling oil flow rate is controlled to 1830 L / min, and the rolling process parameters of the second rolling process are controlled according to the following table: In step 6, during the intermediate rolling bright annealing, the hydrogen content is controlled to be 88%, the dew point is -51°C, the oxygen content is 12ppm, and the intermediate rolling annealing furnace temperature is controlled to be 980°C; In step 7, the thickness of the finished product of the third rolling process is set to 0.5 mm, the rolling oil flow rate is controlled to 1710 L / min, and the rolling process parameters of the third rolling process are controlled according to the following table: In step 8, during bright annealing of the finished product, the hydrogen content is controlled to be 92%, the dew point is -51°C, the oxygen content is 11 ppm, and the annealing furnace temperature of the finished product is controlled to be 960°C.

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