500MPa-grade hot-rolled high-strength steel without color difference on surface and preparation method thereof

Abstract

The invention discloses 500MPa-grade hot-rolled high-strength steel free of surface chromatic aberration and a preparation method thereof.The surface chromatic aberration of 500MPa-grade hot-rolled strip steel is controlled by controlling a hot rolling process and an acid pickling process, and the preparation method specifically comprises the following steps that a continuous casting steel billet is subjected to hot rolling and finish rolling, then a dispersed cooling mode is adopted, coiling is conducted, and a hot rolled steel coil is obtained; the hot rolled steel coil is subjected to acid pickling, oxide scale is removed through shallow slot turbulent flow acid pickling, the withdrawal and straightening elongation is controlled according to different thicknesses, the insertion amount of a working roller is set according to the withdrawal and straightening elongation, then three-stage acid pickling is conducted through an acid pickling tank, five-stage rinsing is conducted through a rinsing tank, and the hot-rolled high-strength steel is obtained. According to the method disclosed by the invention, the limitation that the surface quality is controlled by depending on a single process traditionally is broken through by carrying out optimization design on the process technical parameters of the whole process and multiple processes, a control thought of multi-process coupling type design is provided, and effective control on the color difference of the acid-pickled surface of the 500MPa-grade hot-rolled strip steel is realized.

Description

Technical Field

[0001] The present invention relates to the fields of materials and metallurgy, and more specifically, to a 500 MPa grade hot-rolled high-strength steel with no surface color difference and a preparation method thereof. Background Art

[0002] With the continuous development of modern industrial technology, the steel industry has increasingly higher requirements for the quality and performance of steel. As an important steel product, hot-rolled strip is widely used in many fields such as automobiles, construction, and machinery. However, during the production process, color difference problems often occur on the surface of hot-rolled strip, which not only affects the aesthetics of the steel, but may also have an adverse impact on its performance and service life. Especially in the production of 500 MPa grade high-strength hot-rolled strip, due to the particularity of the material and the complexity of the production process, the color difference problem is more prominent. Research shows that the surface color difference defects of 500 MPa grade hot-rolled high-strength steel are mainly manifested as black-gray strip-shaped defects on the surface of the finished strip, concentrated in the middle of the strip, and there is no obvious tactile sensation. The formation mechanism is due to the mismatch of the hot-rolling process design, resulting in differences in the thickness and bonding force of the surface scale. During the pickling process, part of the scale and the silicon-manganese enrichment layer remain, thus forming color difference defects.

[0003] At present, the control methods for the surface color difference problem of hot-rolled strip in the market have problems such as limited effect of single-process control methods, unstable effects, complex operations, and high costs, and it is difficult to meet the increasingly strict quality control requirements of steel enterprises. Chinese Patent with Publication No. CN117305850A discloses a method for controlling the acid tank scratch defects of hot-rolled pickled sheets / coils in a continuous pickling process, and does not carry out pickling process design for surface color difference defects according to the strength level and alloy composition. Chinese Patent with Publication No. CN114535313A discloses a method for eliminating the grid defects on the surface of thin-gauge hot-rolled pickled sheets, but the key optimization of this technical solution is the grid-like surface defects caused by Lüders bands, and it is not designed for color difference defects. Chinese Patents with Publication Nos. CN104226683A and CN101618406A have the problem of limited effect of single-process control methods, and are not applicable to high-strength grade strips designed with high silicon and high manganese either.

[0004] Therefore, it is of great significance to develop a method that can effectively control the pickling surface color difference of 500 MPa grade hot-rolled strip, which can not only improve the surface quality of the steel, enhance the market competitiveness of the product, but also reduce the production cost and improve the economic benefits of the enterprise. Summary of the Invention

[0005] The object of the present invention is to overcome the above-mentioned defects existing in the prior art, and to provide a 500 MPa grade hot-rolled high-strength steel with no color difference on the surface and a preparation method thereof. In view of the limited effect of the control method for a single process, the present invention is based on a full-process process coupling design for suppression. Specifically, the present invention realizes precise control of the color difference on the surface of the hot-rolled strip by optimizing the hot-rolling process and pickling process parameters. The multi-dimensional control method can not only reduce the subsequent processing quality problems caused by the surface color difference problem, but also improve production efficiency, reduce energy consumption and waste emissions, and realize green production, which is of great significance for improving the quality of 500 MPa grade hot-rolled strips.

[0006] To achieve the above object, the technical solution of the present invention is as follows:

[0007] A preparation method of a 500 MPa grade hot-rolled high-strength steel with no color difference on the surface controls the color difference on the surface of the 500 MPa grade hot-rolled strip by controlling the hot-rolling process and pickling process, and specifically includes the following steps:

[0008] The molten steel is obtained by smelting, and the continuous casting billet is obtained by continuous casting of the molten steel; the continuous casting billet includes the following components in mass percentage: C: 0.05% - 0.15%, Si: 0.10% - 0.15%, Mn: 1.00% - 2.00%, P≤0.050%, S≤0.010%, Als: 0.015% - 0.055%, and the balance is Fe and unavoidable impurities;

[0009] The continuous casting billet is hot-rolled, the finish rolling temperature is 850 °C - 900 °C, and after finish rolling, it is coiled in a dispersed cooling mode to obtain a hot-rolled steel coil;

[0010] The hot-rolled steel coil is pickled, the scale is removed by shallow-tank turbulent pickling, the tension leveling elongation is controlled according to different thicknesses, and the working roll insertion amount is set according to the tension leveling elongation, and then it is subjected to three-stage pickling in a pickling tank and five-stage rinsing in a rinsing tank to obtain the hot-rolled high-strength steel; wherein, the range of the tension leveling elongation is 0.6% - 1.2%.

[0011] Optionally, in the dispersed cooling mode, the coiling temperature within the range of 20 m at the head and 20 m at the tail of the steel strip is controlled to be 600 °C - 650 °C, the coiling temperature at the middle position of the strip is 550 °C - 600 °C, the coiling temperature difference between the range of 20 m at the head and 20 m at the tail of the steel strip and the middle position of the strip is 50 °C, and after coiling, it is air-cooled to room temperature.

[0012] Optionally, in the three-stage pickling, the new acid inlet flow rate ≥ 3.5 m 3 / h, and the pickling speed ≤ 100 m / min.

[0013] Optionally, in the five-stage rinsing, the fresh water flow rate ≥ 10 m3 / h, when the pickling speed < 20 m 3 / h, turn on the shutdown spray water, and the temperature of the rinsing water is 50°C to 60°C.

[0014] Optionally, the work rolls include a first bending roll, a second bending roll, and a leveling roll.

[0015] Optionally, when the thickness ≤ 2.0 mm and the tension leveling elongation is 1.0% - 1.2%, the insertion amount of the first bending roll is set to 25 mm - 27 mm, the insertion amount of the second bending roll is set to 28 mm - 30 mm, and the insertion amount of the leveling roll is 36 mm - 40 mm.

[0016] Optionally, when the thickness is 2.0 mm - 3.0 mm and the tension leveling elongation is 0.9% - 1.1%, the insertion amount of the first bending roll is set to 23 mm - 26 mm, the insertion amount of the second bending roll is set to 26 mm - 29 mm, and the insertion amount of the leveling roll is 34 mm - 38 mm;

[0017] Optionally, when the thickness is 3.0 mm - 4.0 mm and the tension leveling elongation is 0.8% - 1.0%, the insertion amount of the first bending roll is set to 21 mm - 24 mm, the insertion amount of the second bending roll is set to 24 mm - 27 mm, and the insertion amount of the leveling roll is 32 mm - 36 mm.

[0018] Optionally, when the thickness ≥ 4.0 mm and the tension leveling elongation is 0.6% - 0.9%, the insertion amount of the first bending roll is set to 18 mm - 21 mm, the insertion amount of the second bending roll is set to 21 mm - 24 mm, and the insertion amount of the leveling roll is 28 mm - 32 mm.

[0019] Optionally, in the three-stage pickling, the pickling solution is hydrochloric acid with a concentration of 5% - 20%; it consists of 3 pickling tanks in series. The inlet acid circulation flow rate of the No. 1 tank ≥ 90 m 3 / h, and the pickling temperature is 82°C - 88°C; the outlet acid circulation flow rate of the No. 1 tank ≥ 90 m 3 / h, and the pickling temperature is 80°C - 85°C; the inlet acid circulation flow rate of the No. 2 tank ≥ 90 m 3 / h, and the pickling temperature is 75°C - 80°C; the outlet acid circulation flow rate of the No. 2 tank ≥ 85 m 3 / h, and the pickling temperature is 72°C - 78°C; the inlet acid circulation flow rate of the No. 3 tank ≥ 90 m 3 / h, and the pickling temperature is 70°C - 80°C; the outlet acid circulation flow rate of the No. 3 tank ≥ 85 m 3 / h, and the pickling temperature is 65°C - 70°C.

[0020] Optionally, when the pickling speed < 20 m / min, the acid circulation flow rate is 50 m 3 / h to 60 m 3 / h.

[0021] The present invention also discloses a 500 MPa grade hot-rolled high-strength steel with a colorless surface, which is prepared by the above-mentioned preparation method; the hot-rolled high-strength steel comprises the following components by mass percentage: C: 0.05% - 0.15%, Si: 0.10% - 0.15%, Mn: 1.00% - 2.00%, P ≤ 0.050%, S ≤ 0.010%, Als: 0.015% - 0.055%, and the balance is Fe and inevitable impurities.

[0022] Optionally, the hot-rolled high-strength steel has a tensile strength ≥ 500 MPa, a yield strength ≥ 350 MPa, an elongation ≥ 10%, and a color difference △E ≤ 1.5.

[0023] Optionally, the thickness of the hot-rolled high-strength steel is 1.6 mm - 6.0 mm.

[0024] Implementing the embodiments of the present invention will have the following beneficial effects:

[0025] The present invention proposes a multi-dimensional control method based on hot rolling and cold rolling processes. By optimizing the process technical parameters of the whole process and multiple processes, it breaks through the limitation of relying on a single process to control the surface quality traditionally, proposes a control idea of multi-process coupling design, and realizes the effective control of the pickling surface color difference of 500 MPa grade hot-rolled strip steel. This method does not require additional auxiliary equipment or special process equipment, has the characteristics of low cost and high efficiency, can be directly applied to industrial production, and simplifies the process flow.

[0026] By optimizing the hot rolling process and pickling process parameters, the present invention can achieve precise control of the surface color difference of hot-rolled strip steel. This can not only reduce the quality problems caused by surface color difference in subsequent processing and use, but also improve production efficiency, reduce energy consumption and waste emissions, and contribute to green production. Description of the Drawings

[0027] Figure 1 It is a morphology diagram of the 500 MPa grade hot-rolled high-strength steel of Embodiment 1 of the present invention. Detailed Embodiments

[0028] The following further illustrates the present invention with specific embodiments, but does not limit the present invention in any way.

[0029] The color difference defect of the present invention is a black-gray strip-shaped defect covering the surface of the finished strip steel, mainly concentrated in the middle of the strip steel along the width direction, without obvious tactile sensation. Through further analysis of the defect, it can be found that the formation mechanism of the defect is as follows: Due to the mismatch in the hot rolling process design of 500 MPa grade hot-rolled high-strength steel, there are differences in the thickness and bonding force of the surface scale, and there is a small amount of scale residue and silicon-manganese enrichment layer residue during the pickling process, resulting in color difference defects on the strip steel surface.

[0030] Based on this, the present invention discloses a preparation method for 500 MPa grade hot-rolled high-strength steel with a colorless surface, which controls the surface color difference of 500 MPa grade hot-rolled strip steel by controlling the hot rolling process and pickling process, and specifically includes the following steps:

[0031] S1. Obtain molten steel through smelting, and perform continuous casting on the molten steel to obtain a continuous casting billet; the continuous casting billet includes the following components in mass percentage: C: 0.05% - 0.15%, Si: 0.10% - 0.15%, Mn: 1.00% - 2.00%, P ≤ 0.050%, S ≤ 0.010%, Als: 0.015% - 0.055%, and the balance is Fe and inevitable impurities.

[0032] S2. Perform hot rolling on the continuous casting billet, and suppress the color difference defect by suppressing the growth of scale during the hot rolling process. The final rolling temperature of hot rolling is 850 °C - 900 °C, and after final rolling, it is coiled using a dispersed cooling mode to obtain a hot-rolled steel coil.

[0033] S3. Pickle the hot-rolled steel coil, use a shallow tank turbulent flow pickling to remove the scale, control the tension leveling elongation according to different thicknesses, and set the working roll insertion amount according to the tension leveling elongation. Subsequently, suppress the color difference defect by improving the scale removal efficiency during the pickling process. After passing through the pickling tank for three-stage pickling and the rinsing tank for five-stage rinsing, obtain hot-rolled high-strength steel; among them, the range of the tension leveling elongation is 0.6% - 1.2%.

[0034] In a specific embodiment, in the dispersed cooling mode, control the coiling temperature within the range of 600 °C - 650 °C for the first 20 m and the last 20 m of the steel strip, and the coiling temperature at the middle position of the strip is 550 °C - 600 °C. The temperature difference between the first 20 m and the last 20 m of the steel strip and the middle position of the strip is 50 °C, and after coiling, it is air-cooled to room temperature.

[0035] In a specific embodiment, in the three-stage pickling, the new acid inlet flow rate ≥ 3.5 m 3 / h, and the pickling speed ≤ 100 m / min.

[0036] In a specific embodiment, in the five-stage rinsing, the new water flow rate ≥ 10 m 3 / h, when the pickling speed < 20 m3 When it is [h], turn on the shutdown spray water to prevent color difference caused by long-term accumulation of chloride ions on the strip surface. The temperature of the rinsing water is 50°C to 60°C.

[0037] In a specific embodiment, the work roll includes a first bending roll, a second bending roll, and a leveling roll.

[0038] In a specific embodiment, when the thickness ≤ 2.0 mm and the tension leveling elongation is 1.0% - 1.2%, the insertion amount of the first bending roll is set to 25 mm - 27 mm, the insertion amount of the second bending roll is set to 28 mm - 30 mm, and the insertion amount of the leveling roll is 36 mm - 40 mm.

[0039] In a specific embodiment, when the thickness is 2.0 mm - 3.0 mm and the tension leveling elongation is 0.9% - 1.1%, the insertion amount of the first bending roll is set to 23 mm - 26 mm, the insertion amount of the second bending roll is set to 26 mm - 29 mm, and the insertion amount of the leveling roll is 34 mm - 38 mm.

[0040] In a specific embodiment, when the thickness is 3.0 mm - 4.0 mm and the tension leveling elongation is 0.8% - 1.0%, the insertion amount of the first bending roll is set to 21 mm - 24 mm, the insertion amount of the second bending roll is set to 24 mm - 27 mm, and the insertion amount of the leveling roll is 32 mm - 36 mm.

[0041] In a specific embodiment, when the thickness ≥ 4.0 mm and the tension leveling elongation is 0.6% - 0.9%, the insertion amount of the first bending roll is set to 18 mm - 21 mm, the insertion amount of the second bending roll is set to 21 mm - 24 mm, and the insertion amount of the leveling roll is 28 mm - 32 mm.

[0042] In a specific embodiment, in the three-stage pickling, the pickling solution is hydrochloric acid with a concentration of 5% - 20%; it consists of 3 serially connected pickling tanks. The inlet acid circulation flow rate of the No. 1 tank ≥ 90 m 3 / h, and the pickling temperature is 82°C - 88°C; the outlet acid circulation flow rate of the No. 1 tank ≥ 90 m 3 / h, and the pickling temperature is 80°C - 85°C; the inlet acid circulation flow rate of the No. 2 tank ≥ 90 m 3 / h, and the pickling temperature is 75°C - 80°C; the outlet acid circulation flow rate of the No. 2 tank ≥ 85 m 3 / h, and the pickling temperature is 72°C - 78°C; the inlet acid circulation flow rate of the No. 3 tank ≥ 90 m 3 / h, and the pickling temperature is 70°C - 80°C; the outlet acid circulation flow rate of the No. 3 tank ≥ 85 m 3 / h, and the pickling temperature is 65°C - 70°C.

[0043] In a specific embodiment, when the pickling speed < 20 m / min, the acid circulation flow rate is 50 m 3 / h to 60 m 3 / h.

[0044] Specifically, in the production process of 500 MPa grade hot-rolled high-strength steel, conventional processes are adopted in smelting, continuous casting and other processes, which will not be elaborated here.

[0045] The present invention also discloses a 500 MPa grade hot-rolled high-strength steel with colorless surface, which is prepared by the preparation method of any embodiment of the present invention; the hot-rolled high-strength steel comprises the following components in mass percentage: C: 0.05% - 0.15%, Si: 0.10% - 0.15%, Mn: 1.00% - 2.00%, P ≤ 0.050%, S ≤ 0.010%, Als: 0.015% - 0.055%, and the balance is Fe and inevitable impurities.

[0046] In a specific embodiment, the tensile strength of the hot-rolled high-strength steel is ≥500 MPa, the yield strength is ≥350 MPa, the elongation is ≥10%, and the color difference △E ≤ 1.5.

[0047] In a specific embodiment, the thickness of the hot-rolled high-strength steel is 1.6 mm - 6.0 mm.

[0048] The following are specific embodiments

[0049] Examples 1 - 8

[0050] The preparation method of the 500 MPa grade hot-rolled high-strength steel with colorless surface in Examples 1 - 8 specifically comprises the following steps:

[0051] S1. Obtain molten steel through smelting, and perform continuous casting on the molten steel to obtain a continuous casting billet.

[0052] S2. Hot-roll the continuous casting billet, and suppress the color difference defects by suppressing the growth of scale during the hot-rolling process stage. After finish rolling, adopt a dispersed cooling mode and coiling to obtain a hot-rolled steel coil.

[0053] S3. Pickle the hot-rolled steel coil, remove the scale by using shallow-tank turbulent pickling, control the tension leveling elongation according to different thicknesses, and set the working roll insertion amount according to the tension leveling elongation. Subsequently, suppress the color difference defects by improving the scale removal efficiency during the pickling process. Perform three-stage pickling in the pickling tank and five-stage rinsing in the rinsing tank. The pickling uses hydrochloric acid with a concentration of 17% to obtain the hot-rolled high-strength steel.

[0054] Among them, the hot rolling process parameters of Examples 1-8 are shown in Table 1, the straightening process parameters of Examples 1-8 are shown in Table 2, the pickling process parameters of Examples 1-8 are shown in Table 3, the acid tank process parameters of Examples 1-8 are shown in Table 4, and the chemical composition and mechanical properties of Examples 1-8 are shown in Table 5.

[0055] Table 1 Hot rolling process parameters of Examples 1-8

[0056]

[0057] Table 2 Tensile Leveling Process Parameters for Examples 1-8

[0058]

[0059]

[0060] Table 3 Other pickling process parameters of Examples 1-8

[0061] Serial number <![CDATA[New acid feed rate m 3 / h]]> Pickling speed m / min New water flow rate of the 5# rinsing tank m3 / h Rinsing water temperature °C 1# 3.6 84 11.3 50 2# 4 82 11 52 3# 3.7 84 11 54 4# 4 84 11.2 50 5# 3.8 86 10.8 57 6# 3.7 92 10.6 51 7# 3.7 82 11.6 50 8# 3.8 84 10.6 60

[0062] Table 4 Acid tank process parameters for Examples 1-8

[0063]

[0064] Table 5 Chemical composition and mechanical properties of Examples 1-8

[0065]

[0066]

[0067] It can be seen from the above embodiments that the color difference defect control method of the present invention can achieve a 500MPa grade hot-rolled high-strength steel product with no color difference defects on the surface, greatly improving the yield rate and surface quality of the product.

[0068] The above-described embodiments merely represent several implementation methods of the present invention. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent application. It should be noted that a person skilled in the art would be able to make various modifications and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the patent for this invention shall be determined by the appended claims.

Claims

1. A preparation method of a 500MPa grade hot-rolled high-strength steel with a colorless surface difference, characterized in that, Controlling the surface color difference of hot-rolled strip steel of 500 MPa grade by controlling the hot rolling process and pickling process, which specifically includes the following steps: Obtaining molten steel through smelting, and continuously casting the molten steel to obtain a continuously cast billet; the continuously cast billet includes the following components by mass percentage: C: 0.05% - 0.15%, Si: 0.10% - 0.15%, Mn: 1.00% - 2.00%, P ≤ 0.050%, S ≤ 0.010%, Als: 0.015% - 0.055%, and the balance is Fe and inevitable impurities; Hot rolling the continuously cast billet, the final rolling temperature is 850°C - 900°C, and after final rolling, it is coiled in a dispersed cooling mode to obtain a hot-rolled steel coil; Pickling the hot-rolled steel coil, using shallow-tank turbulent pickling to remove scale, controlling the tension leveling elongation according to different thicknesses, and setting the working roll insertion amount according to the tension leveling elongation, and then performing three-stage pickling in the pickling tank and five-stage rinsing in the rinsing tank to obtain the hot-rolled high-strength steel; among them, the range of the tension leveling elongation is 0.6% - 1.2%.

2. The preparation method of the 500MPa grade hot-rolled high-strength steel with colorless surface according to claim 1, characterized in that In the dispersed cooling mode, control the coiling temperature within the range of 600°C - 650°C for the head 20 m and the tail 20 m of the steel strip, and the coiling temperature at the mid-strip position is 550°C - 600°C. The coiling temperature difference between the head 20 m and the tail 20 m of the steel strip and the mid-strip position is 50°C, and after coiling, it is air-cooled to room temperature.

3. The preparation method of the 500MPa grade hot-rolled high-strength steel with a colorless surface according to claim 1, characterized in that, In the three-stage pickling, the amount of fresh acid fed ≥ 3.5 m 3 / h, and the pickling speed ≤ 100 m / min.

4. The preparation method of the 500MPa grade hot-rolled high-strength steel with a colorless surface according to claim 1, characterized in that In the five-stage rinsing, the fresh water flow rate ≥ 10 m 3 / h. When the pickling speed < 20 m 3 / h, the shutdown spray water is turned on, and the temperature of the rinsing water is 50°C to 60°C.

5. The preparation method of the 500MPa grade hot-rolled high-strength steel with a colorless surface according to claim 1, characterized in that, The working roll includes a first bending roll, a second bending roll, and a straightening roll; When the thickness ≤ 2.0 mm and the tension leveling elongation is 1.0% - 1.2%, the insertion amount of the first bending roll is set to 25 mm - 27 mm, the insertion amount of the second bending roll is set to 28 mm - 30 mm, and the insertion amount of the straightening roll is 36 mm - 40 mm; When the thickness is 2.0 mm - 3.0 mm and the tension leveling elongation is 0.9% - 1.1%, the insertion amount of the first bending roll is set to 23 mm - 26 mm, the insertion amount of the second bending roll is set to 26 mm - 29 mm, and the insertion amount of the straightening roll is 34 mm - 38 mm; When the thickness is 3.0 mm - 4.0 mm and the tension leveling elongation is 0.8% - 1.0%, the insertion amount of the first bending roll is set to 21 mm - 24 mm, the insertion amount of the second bending roll is set to 24 mm - 27 mm, and the insertion amount of the straightening roll is 32 mm - 36 mm; When the thickness ≥ 4.0 mm and the tension leveling elongation is 0.6% - 0.9%, the insertion amount of the first bending roll is set to 18 mm - 21 mm, the insertion amount of the second bending roll is set to 21 mm - 24 mm, and the insertion amount of the straightening roll is 28 mm - 32 mm.

6. The preparation method of the 500MPa grade hot-rolled high-strength steel with colorless surface according to claim 1, characterized in that, In the three-stage pickling, the pickling solution is hydrochloric acid with a concentration of 5% to 20%; it consists of 3 pickling tanks connected in series. The inlet acid circulation flow rate of the No. 1 tank is ≥90 m 3 / h, and the pickling temperature is 82°C to 88°C; the outlet acid circulation flow rate of the No. 1 tank is ≥90 m 3 / h, and the pickling temperature is 80°C to 85°C; the inlet acid circulation flow rate of the No. 2 tank is ≥90 m 3 / h, and the pickling temperature is 75°C to 80°C; the outlet acid circulation flow rate of the No. 2 tank is ≥85 m 3 / h, and the pickling temperature is 72°C to 78°C; the inlet acid circulation flow rate of the No. 3 tank is ≥90 m 3 / h, and the pickling temperature is 70°C to 80°C; the outlet acid circulation flow rate of the No. 3 tank is ≥85 m 3 / h, and the pickling temperature is 65°C to 70°C.

7. The preparation method of the 500MPa grade hot-rolled high-strength steel with colorless surface according to claim 1, characterized in that When the pickling speed < 20 m / min, the acid circulation flow rate is 50 m 3 / h to 60 m 3 / h.

8. A 500 MPa grade hot-rolled high-strength steel with a colorless surface, characterized in that, The hot-rolled high-strength steel is prepared by the preparation method described in any one of claims 1 - 7; the hot-rolled high-strength steel includes the following components by mass percentage: C: 0.05% to 0.15%, Si: 0.10% to 0.15%, Mn: 1.00% to 2.00%, P ≤ 0.050%, S ≤ 0.010%, Als: 0.015% to 0.055%, and the balance is Fe and unavoidable impurities.

9. The 500 MPa grade hot-rolled high-strength steel with colorless surface according to claim 8, characterized in that, The hot-rolled high-strength steel has a tensile strength ≥ 500 MPa, a yield strength ≥ 350 MPa, and an elongation ≥ 10%. The color difference △E ≤ 1.

5.

10. The 500 MPa grade hot-rolled high-strength steel with colorless surface according to claim 8, characterized in that, The thickness of the hot-rolled high-strength steel is 1.6 mm to 6.0 mm.

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