Control method for high surface quality of 600MPa-grade hot-dip galvanized double-phase high-strength strip steel
Through the heat treatment process of segmented pickling and gas atmosphere control, the surface defects of 600MPa grade hot-dip galvanized dual-phase high-strength strip steel are solved, high surface quality and low-cost production are achieved, and zinc layer bonding and surface uniformity are improved.
Patent Information
- Application Number
- CN202510457120.2
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-04-13
- Publication Date
- 2025-08-01
AI Technical Summary
The existing 600MPa grade hot-dip galvanized biphasic high-strength strip steel is prone to surface defects such as "cross surface", "color difference" and "poor adhesion (dezincification)" during the production process, which leads to amplification of defects during subsequent surface treatment and increases smelting costs.
The turbulent pickling technology with decreasing segmented free acid concentration is adopted, combined with specific gas atmosphere and heat treatment parameters, including dew point control in the preheating, heating and homogenizing stages, combined with high-pressure water descaling and optimized galvanizing technology, the layered peeling and precise control of the iron oxide sheet is achieved, and the surface activation uniformity of the strip steel and the adhesion of the zinc layer are ensured.
The surface quality of 600MPa grade hot-dip galvanized dual-phase high-strength strip steel is significantly improved, the lint surface and color difference defects are reduced, the acid consumption and waste acid treatment load are reduced, the thickness and adhesion of the zinc layer inhibition layer are improved, and the smelting cost is reduced.
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Abstract
Description
Technical Field
[0001] The present invention relates to the field of metallurgical technology. Specifically, it relates to a method for controlling the high surface quality of 600 MPa grade hot-dip galvanized dual-phase high-strength strip steel. Background Art
[0002] The 600 MPa grade hot-dip galvanized dual-phase high-strength strip steel has the advantages of good formability and excellent corrosion resistance. It is widely used in the manufacture of automotive parts, which can achieve vehicle weight reduction, reduce energy consumption, improve safety performance and the overall vehicle life. The proportion of high-strength steel in some vehicles reaches more than 70%.
[0003] However, the existing 600 MPa grade hot-dip galvanized dual-phase high-strength strip steel is extremely prone to surface defects such as "pitted surface", "color difference", "poor adhesion (zinc removal)", and pinhole non-galvanizing during the production process. The reasons for the appearance of such surface defects include high residual iron content in pickling and poor surface quality of the galvanized finished product. When subsequent surface treatments such as electrophoresis and painting are carried out, not only can these defects not be eliminated, but they will also be magnified. Once products with the above surface defects are found, they need to be downgraded, resulting in great steel losses and increasing the smelting cost.
[0004] Therefore, it is of crucial significance to improve the surface quality of 600 MPa grade hot-dip galvanized dual-phase high-strength strip steel. Summary of the Invention
[0005] The present invention provides a method for controlling the high surface quality of 600 MPa grade hot-dip galvanized dual-phase high-strength strip steel, which solves the problem of poor surface quality of 600 MPa grade hot-dip galvanized dual-phase high-strength strip steel in the related art.
[0006] The technical solution of the present invention is as follows: The present invention provides a method for controlling the high surface quality of 600 MPa grade hot-dip galvanized dual-phase high-strength strip steel, including the following steps: S1. Hot-rolling, cooling, pickling, cold-rolling, and heat-treating the steel billet to obtain a heat-treated strip steel; S2. Galvanizing the heat-treated strip steel to obtain 600 MPa grade hot-dip galvanized dual-phase high-strength strip steel; The pickling includes three-stage pickling. The free acid concentration in the first-stage pickling is 170 - 190 g / L, the free acid concentration in the second-stage pickling is 100 - 120 g / L, and the free acid concentration in the third-stage pickling is 50 - 60 g / L.
[0007] As a further technical solution, the strip steel is composed of elements in the following mass percentages: carbon 0.1% - 0.12%, silicon 0.25% - 0.45%, manganese 1.5% - 1.7%, aluminum 0.025% - 0.045%, chromium 0.1% - 0.2%, phosphorus 0.002% - 0.012%, sulfur 0.001% - 0.008%, and the remaining components are iron.
[0008] In the present invention, the thickness of the 600 MPa grade hot-dip galvanized dual-phase high-strength strip steel is 0.5 - 2.5 mm, the width is 1000 - 1800 mm, and the metallographic structure is a ferrite + martensite dual-phase structure.
[0009] As a further technical solution, during the pickling process, the first-stage pickling, the second-stage pickling, and the third-stage pickling are each independently turbulent pickling; During the pickling process, the turbulent flow velocities of the first-stage pickling, the second-stage pickling, and the third-stage pickling are each independently 2.5 - 3.5 m / s; During the pickling process, the pickling speeds of the first-stage pickling, the second-stage pickling, and the third-stage pickling are each independently 100 - 120 m / s.
[0010] In the present invention, through the dynamic matching of the pickling speed of the 600 MPa grade hot-dip galvanized dual-phase high-strength strip steel and the turbulent flow velocity of the free acid, the balance between mass transfer efficiency and substrate protection is achieved. The high flow velocity of the acid solution under the turbulent flow state destroys the boundary layer on the surface of the iron oxide scale, accelerates the diffusion of H⁺ and the removal of reaction products, significantly improves the dissolution rate of the iron oxide scale. At the same time, the precise control of the pickling speed not only fully removes the iron oxide scale but also avoids excessive dissolution of the substrate. In addition, the optimization of the turbulent flow velocity reduces the risk of acid solution retention and local corrosion, extends the service life of the key components of the pickling equipment, and reduces the maintenance cost.
[0011] As a further technical solution, the heat treatment includes a preheating stage, a heating stage, and a soaking stage; During the heating stage, the gas atmosphere is composed of components in the following volume percentages: hydrogen 4.0% - 4.5%, carbon monoxide 15.0% - 18.5%, and the rest is nitrogen.
[0012] In the present invention, by controlling the gas atmosphere during the heating stage to be hydrogen 4.0% - 4.5%, carbon monoxide 15.0% - 18.5%, and the remaining components are nitrogen, while ensuring the adhesion of the zinc layer, the thickness of the zinc layer inhibition layer of the 600 MPa grade hot-dip galvanized dual-phase high-strength strip steel is increased; During the heating stage, the volume fraction of hydrogen gas in the gas atmosphere can be 4.0%, 4.1%, 4.2%, 4.3%, 4.4%, 4.5%, and the volume fraction of carbon monoxide can be 15.2%, 15.4%, 15.6%, 15.8%, 16.0%, 16.2%, 16.4%, 16.6%, 16.8%, 17.0%, 17.2%, 17.4%, 17.6%, 17.8%, 18.0%, 18.2%, 18.4%, 18.5%, and the rest is nitrogen.
[0013] As a further technical solution, the temperature in the soaking stage is 450 - 455 °C.
[0014] As a further technical solution, during the preheating stage, the dew point value is -25 to -15 °C; The dew point values in the heating stage and the soaking stage are independently -50 to -35 °C.
[0015] In the present invention, compressed air is introduced during the preheating stage to increase the dew point value of the preheating section, and the dew point value of the preheating section is controlled to be -25 to -15 °C. In view of the difference in hydrogen embrittlement sensitivity of ferritic-martensitic duplex steel, segmented dew point control realizes the coordination of martensite hydrogen capture inhibition and ferrite hydrogen diffusion blocking: the preheating section is moderately dried by controlling the dew point value within a specific range, removing the free water on the strip surface to avoid hydrogen production from the decomposition of water vapor during heating; the dew point values in the heating section and the soaking section are further reduced, and deep drying inhibits the adsorption of hydrogen by martensite, overall reducing the hydrogen diffusion coefficient of ferrite and reducing the hydrogen capture rate of martensite, eliminating the hidden danger of hydrogen-induced cracking from the source.
[0016] As a further technical solution, during hot rolling, it includes heating, rolling, coiling, and descaling.
[0017] As a further technical solution, during heating, the temperature is 1160 - 1200 °C and the time is 150 - 180 min; During rolling, the finish rolling temperature is 850 - 870 °C.
[0018] In the present invention, heating at 1160 - 1200 °C ensures the full dissolution of carbides, providing a solid solution carbon basis for subsequent martensite strengthening; short-time heating inhibits the excessive growth of austenite grains and refines the original grain size. The overall parameter optimization balances the material properties and production economy, laying a foundation for the tissue uniformity of duplex steel.
[0019] As a further technical solution, during coiling, the temperature is 500 - 540 °C.
[0020] In the present invention, the co-control of the continuity of ferrite and the dispersion of martensite is achieved by designing the coiling temperature at 500 - 540°C: this temperature range avoids the pearlite transformation region (pearlite is likely to form at temperatures above 550°C), promotes the preferential precipitation of ferrite at the austenite grain boundaries, and the remaining austenite transforms into martensite during cooling. The precise control of the coiling temperature refines the ferrite grains and reduces the diameter of the martensite islands. This microstructure not only retains the high plasticity of ferrite but also enhances the properties of 600 MPa grade hot-dip galvanized dual-phase high-strength strip steel through the dispersion strengthening of martensite.
[0021] In the present invention, by using a lower heating temperature and avoiding long-time heating, the removability of the slab scale is improved, and the residue of primary scale is reduced. The residue of primary scale is extremely difficult to remove in subsequent processes after being rolled through multiple passes and is likely to cause strip-shaped color difference defects.
[0022] In the present invention, compared with the conventional process, lower finishing rolling and coiling temperatures are adopted, reducing the thickness of the hot-rolled raw material scale and increasing the proportion of Fe3O4 in the scale, thereby reducing the cleaning difficulty of the subsequent scale and greatly reducing surface defects such as scale residue.
[0023] During the heating stage, it is ensured that the carbides are fully dissolved. The finishing rolling temperature controls the austenite grain size. The coiling process inhibits the formation of harmful phases. The descaling process preliminarily removes the scale. Through multi-step coordination, the tissue segregation and surface residue are avoided, providing a uniform and clean substrate for subsequent pickling, cold rolling, and galvanizing.
[0024] As a further technical solution, during descaling, high-pressure water descaling is used, and the pressure is 220 - 240 dbar.
[0025] In the present invention, through high-pressure water descaling, the surface cleanliness is significantly improved and the roughness is optimized, providing an ideal substrate for subsequent galvanizing. The microscopic rough structure formed by high-pressure water enhances the bonding force between the galvanized layer and the steel substrate, effectively reducing the defective coating and extending the corrosion resistance life of the coating. Compared with the traditional process, high-pressure water descaling greatly reduces water consumption and the use of chemical agents, reduces the pollution treatment cost, and at the same time avoids excessive damage to the surface of the steel strip, ensuring the stability of the mechanical properties of the material.
[0026] As a further technical solution, during galvanizing, with the upper edge of the galvanizing pot as the horizontal line, the liquid level height of the zinc liquid is -67~-63mm; The liquid level height of the zinc liquid is 3 - 6mm higher than the overflow tank; The temperature of the zinc liquid is 448 - 452°C; The zinc liquid is composed of the following elements by mass percentage: aluminum 0.25% - 0.3%, iron 0.01% - 0.02%, lead 0.001% - 0.002%, and the remaining component is zinc.
[0027] In the present invention, zinc is added 1 hour before hot-dip galvanizing of the strip steel during heat treatment, and the aluminum content is controlled to be 0.25% - 0.3% to selectively inhibit the iron-zinc reaction of ferrite.
[0028] The working principle and beneficial effects of the present invention are as follows: In the present invention, through the design of decreasing free acid concentration in segments, the delamination and precise control of scale are realized: the high-concentration acid in the first segment quickly breaks the dense oxide layer, the medium-concentration acid in the middle segment penetrates and peels the intermediate layer, and the low-concentration acid in the last segment is used for cleaning residues, avoiding the problem of high pickling residue iron in traditional single-segment pickling. The three-segment pickling enhances the dynamic contact between the acid solution and the strip steel, significantly improving the surface activation uniformity, providing ideal micro-anchor points for subsequent galvanizing, fundamentally reducing surface defects such as pitted surface and color difference, improving the surface quality of 600 MPa grade hot-dip galvanized dual-phase high-strength strip steel, and at the same time reducing acid solution consumption and waste acid treatment load, taking into account both efficiency and environmental protection. BRIEF DESCRIPTION OF THE DRAWINGS
[0029] The present invention will be further described in detail below with reference to the drawings and specific embodiments.
[0030] Figure 1 It is a photograph of 600 MPa grade hot-dip galvanized dual-phase high-strength strip steel obtained in Example 3 of the present invention; Figure 2 It is a photograph of 600 MPa grade hot-dip galvanized dual-phase high-strength strip steel obtained in Example 5 of the present invention; Figure 3 It is a photograph of 600 MPa grade hot-dip galvanized dual-phase high-strength strip steel obtained in Comparative Example 6 of the present invention; Figure 4 It is a photograph of 600 MPa grade hot-dip galvanized dual-phase high-strength strip steel obtained in Comparative Example 7 of the present invention; Figure 5 It is a photograph of 600 MPa grade hot-dip galvanized dual-phase high-strength strip steel obtained in Comparative Example 8 of the present invention. SPECIFIC EMBODIMENTS
[0031] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts fall within the scope of the present invention.
[0032] Example 1 A method for controlling the high surface quality of 600 MPa grade hot-dip galvanized dual-phase high-strength strip steel includes the following steps: S1. Hot-rolling, cooling, pickling, cold-rolling, and heat-treating the steel billet to obtain the heat-treated strip steel; S2. Galvanize the heat-treated strip steel to obtain a 600 MPa grade hot-dip galvanized dual-phase high-strength strip steel; The strip steel is composed of the following elements by mass percentage: carbon 0.12%, silicon 0.45%, manganese 1.7%, aluminum 0.045%, chromium 0.2%, phosphorus 0.012%, sulfur 0.008%, and the remaining components are iron; During hot rolling, the heating temperature is 1200 °C, the time is 150 min, the finishing rolling temperature is 870 °C, and the coiling temperature is 540 °C. When descaling, high-pressure water descaling is used, and the pressure is 240 dbar; The pickling includes three-stage turbulent pickling. The free acid concentration in the first-stage pickling is 190 g / L, the free acid concentration in the second-stage pickling is 120 g / L, and the free acid concentration in the third-stage pickling is 60 g / L. The turbulent flow velocity in all three stages of pickling is 3.5 m / s, and the pickling speed in all three stages is 120 m / s; During heat treatment, the preheating stage is advanced by 1 h, and compressed air is introduced. The dew point value in the preheating stage is -15 °C, the dew point value in the heating stage is -35 °C, the dew point value in the soaking stage is -35 °C, the temperature in the soaking stage is 455 °C, and the gas atmosphere in the heating stage is composed of the following components by volume percentage: hydrogen 4.0%, and the rest is nitrogen; During galvanizing, taking the upper edge of the zinc pot as the horizontal line, the liquid level height of the zinc liquid is controlled at -63 mm, the liquid level of the zinc liquid is 6 mm higher than the overflow tank, the temperature of the zinc liquid is 452 °C, and the zinc liquid is composed of the following elements by mass percentage: aluminum 0.3%, iron 0.02%, lead 0.002%, and the remaining components are zinc.
[0033] Example 2 A method for controlling the high surface quality of a 600 MPa grade hot-dip galvanized dual-phase high-strength strip steel includes the following steps: S1. Hot roll, cool, pickle, cold roll, and heat treat the steel billet to obtain a heat-treated strip steel; S2. Galvanize the heat-treated strip steel to obtain a 600 MPa grade hot-dip galvanized dual-phase high-strength strip steel; The strip steel is composed of the following elements by mass percentage: carbon 0.1%, silicon 0.25%, manganese 1.5%, aluminum 0.025%, chromium 0.1%, phosphorus 0.002%, sulfur 0.001%, and the remaining components are iron; During hot rolling, the heating temperature is 1160 °C, the time is 180 min, the finishing rolling temperature is 850 °C, and the coiling temperature is 500 °C. When descaling, high-pressure water descaling is used, and the pressure is 220 dbar; The pickling includes three-stage turbulent pickling. The free acid concentration in the first-stage pickling is 170 g / L, the free acid concentration in the second-stage pickling is 100 g / L, and the free acid concentration in the third-stage pickling is 50 g / L. The turbulent flow velocity in all three stages of pickling is 2.5 m / s, and the pickling speed in all three stages is 100 m / s; During heat treatment, the preheating stage is advanced by 1 h, and compressed air is introduced. The dew point value in the preheating stage is -25°C, the dew point value in the heating stage is -50°C, the dew point value in the soaking stage is -50°C, the temperature in the soaking stage is 450°C, and the gas atmosphere in the heating stage consists of the following components by volume percentage: hydrogen 4.0%, and the rest is nitrogen; During galvanizing, with the upper edge of the zinc pot as the horizontal line, the liquid level height of the zinc liquid is controlled at -67 mm, the liquid level of the zinc liquid is 3 mm higher than the overflow tank, the temperature of the zinc liquid is 448°C, and the zinc liquid consists of the following elements by mass percentage: aluminum 0.25%, iron 0.01%, lead 0.001%, and the rest is zinc.
[0034] Example 3 A method for controlling the high surface quality of 600 MPa grade hot-dip galvanized dual-phase high-strength strip steel includes the following steps: S1. Hot-roll, cool, pickling, cold-roll, and heat-treat the steel billet to obtain the heat-treated strip steel; S2. Galvanize the heat-treated strip steel to obtain 600 MPa grade hot-dip galvanized dual-phase high-strength strip steel; The strip steel consists of the following elements by mass percentage: carbon 0.11%, silicon 0.35%, manganese 1.6%, aluminum 0.035%, chromium 0.15%, phosphorus 0.008%, sulfur 0.006%, and the rest is iron; During hot rolling, the heating temperature is 1180°C, the time is 160 min, the final rolling temperature is 860°C, the coiling temperature is 520°C. During descaling, high-pressure water descaling is used, and the pressure is 230 dbar; Pickling includes three-stage turbulent pickling. The free acid concentration in the first-stage pickling is 180 g / L, the free acid concentration in the second-stage pickling is 110 g / L, the free acid concentration in the third-stage pickling is 55 g / L. The turbulent flow velocity during the three-stage pickling is 3.0 m / s, and the pickling speed of the three stages is 110 m / s; During heat treatment, the preheating stage is advanced by 1 h, and compressed air is introduced. The dew point value in the preheating stage is -20°C, the dew point value in the heating stage is -45°C, the dew point value in the soaking stage is -45°C, the temperature in the soaking stage is 453°C, and the gas atmosphere in the heating stage consists of the following components by volume percentage: hydrogen 4.0%, and the rest is nitrogen; During galvanizing, with the upper edge of the zinc pot as the horizontal line, the liquid level height of the zinc liquid is controlled at -65 mm, the liquid level of the zinc liquid is 5 mm higher than the overflow tank, the temperature of the zinc liquid is 450°C, and the zinc liquid consists of the following elements by mass percentage: aluminum 0.28%, iron 0.015%, lead 0.0015%, and the rest is zinc.
[0035] Example 4 The difference between this example and Example 3 is only that the gas atmosphere in the heat treatment heating stage of this example consists of the following components by volume percentage: 4.0% hydrogen, 15.0% carbon monoxide, and the rest nitrogen.
[0036] Example 5 The difference between this example and Example 3 is only that the gas atmosphere in the heat treatment heating stage of this example consists of the following components by volume percentage: 4.5% hydrogen, 18.5% carbon monoxide, and the rest nitrogen.
[0037] Comparative Examples 1 - 8 The difference between Comparative Examples 1 - 8 and Example 3 is only that the free acid concentrations in each section of pickling in Comparative Examples 1 - 8 are different. The free acid concentrations in each section of pickling in Comparative Examples 1 - 8 are shown in Table 1.
[0038] Table 1 Free acid concentrations in each section of pickling for Comparative Examples 1 - 8
[0039] Experimental Example 1 In the control methods for high surface quality of 600 MPa grade hot - dip galvanized dual - phase high - strength strip steel in Examples 1 - 3 and Comparative Examples 1 - 8, after pickling, the steel billets were taken to test the residual iron content in pickling according to the method specified in YB / T 4302 - 2012 "Determination Method for Residual Oil and Residual Iron Content on the Surface of Cold - Rolled Steel Sheets and Strips", and the high surface quality of 600 MPa grade hot - dip galvanized dual - phase high - strength strip steel was observed. The photos of the 600 MPa grade hot - dip galvanized dual - phase high - strength strip steel prepared in Example 3 are shown in Figure 1 , the photos of the 600 MPa grade hot - dip galvanized dual - phase high - strength strip steel prepared in Example 5 are shown in Figure 2 , the photos of the 600 MPa grade hot - dip galvanized dual - phase high - strength strip steel prepared in Comparative Example 6 are shown in Figure 3 , the photos of the 600 MPa grade hot - dip galvanized dual - phase high - strength strip steel prepared in Comparative Example 7 are shown in Figure 4 , the photos of the 600 MPa grade hot - dip galvanized dual - phase high - strength strip steel prepared in Comparative Example 8 are shown in Figure 5 . The test results are shown in Table 2.
[0040] Table 2 Test results of residual iron content in pickling and observation results
[0041] As can be seen from Table 2, the control method for high surface quality of 600 MPa grade hot - dip galvanized dual - phase high - strength strip steel proposed in the present invention reduces the residual iron content in pickling of 600 MPa grade hot - dip galvanized dual - phase high - strength strip steel and improves the surface quality of 600 MPa grade hot - dip galvanized dual - phase high - strength strip steel by limiting the free acid concentrations in each section of a specific three - stage turbulent pickling. And, as Figures 1 to 5 can be seen, surface defects such as pitted surface and color difference are avoided.
[0042] Experimental Example 2 The 600 MPa grade hot-dip galvanized dual-phase high-strength steel strips prepared in Examples 3 to 5 were observed and measured for the thickness of the zinc layer inhibition layer using a Thermo Scientific Apreo 2 CSEM electron microscope, and the adhesion of the zinc layer was evaluated according to the 180° bending test in GB / T 39130-2020 "Test Method for Adhesion of Zinc Coating on Galvanized Products". The test results are shown in Table 3.
[0043] Table 3 Test Results of Zinc Layer Inhibition Layer Thickness and Zinc Layer Adhesion
[0044] As can be seen from Table 3, the method for controlling the high surface quality of the 600 MPa grade hot-dip galvanized dual-phase high-strength steel strip proposed in the present invention can endow the 600 MPa grade hot-dip galvanized dual-phase high-strength steel strip with good zinc layer inhibition layer thickness and zinc layer adhesion by controlling the gas atmosphere during the galvanizing heating stage.
[0045] Experimental Example 3 The 600 MPa grade hot-dip galvanized dual-phase high-strength steel strips prepared in Examples 3 to 5 were used to measure the color difference with an X-Rite Ci64. The test results are shown in Table 4.
[0046] Table 4 Test Results of Color Difference
[0047] As can be seen from Table 4, the 600 MPa grade hot-dip galvanized dual-phase high-strength steel strip prepared in the present invention has a small color difference and meets the actual production requirements.
[0048] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.
Claims
1. A control method for high surface quality of 600 MPa grade hot-dip galvanized dual-phase high-strength strip steel, characterized in that, It includes the following steps: S1. Hot-roll, cool, pickling, cold-roll, and heat-treat the steel billet to obtain a heat-treated strip steel; S2. Galvanize the heat-treated strip steel to obtain a 600 MPa grade hot-dip galvanized dual-phase high-strength strip steel; The pickling includes three-stage pickling. The free acid concentration in the first-stage pickling is 170 - 190 g / L, the free acid concentration in the second-stage pickling is 100 - 120 g / L, and the free acid concentration in the third-stage pickling is 50 - 60 g / L.
2. The control method for high surface quality of a 600 MPa grade hot-dip galvanized dual-phase high-strength strip steel according to claim 1, characterized in that, During the pickling, the first-stage pickling, the second-stage pickling, and the third-stage pickling are each independently turbulent flow pickling; During the pickling, the pickling speed in the first-stage pickling, the second-stage pickling, and the third-stage pickling are each independently 100 - 120 m / s.
3. A method for controlling the high surface quality of a 600 MPa grade hot-dip galvanized dual-phase high-strength strip steel according to claim 1, characterized in that, The heat treatment includes a preheating stage, a heating stage, and a soaking stage; During the heating stage, the gas atmosphere is composed of the following components by volume percentage: hydrogen 4.0% - 4.5%, carbon monoxide 15.0% - 18.5%, and the rest is nitrogen.
4. A method for controlling the high surface quality of a 600 MPa grade hot-dip galvanized dual-phase high-strength strip steel according to claim 3, characterized in that, The temperature of the soaking stage is 450 - 455 °C.
5. The control method for high surface quality of a 600 MPa grade hot-dip galvanized dual-phase high-strength strip steel according to claim 3, characterized in that, During the preheating stage, the dew point value is -25 - -15 °C; The dew point values during the heating stage and the soaking stage are each independently -50 - -35 °C.
6. The control method for high surface quality of a 600MPa grade hot-dip galvanized dual-phase high-strength strip steel according to claim 1, characterized in that, During the hot rolling, it includes heating, rolling, coiling, and descaling.
7. A control method for high surface quality of a 600 MPa grade hot-dip galvanized dual-phase high-strength strip steel according to claim 6, characterized in that, During the heating, the temperature is 1160 - 1200 °C and the time is 150 - 180 min; During the rolling, the final rolling temperature is 850 - 870 °C.
8. The control method for high surface quality of a 600 MPa grade hot-dip galvanized dual-phase high-strength strip steel according to claim 6, characterized in that, During the coiling, the temperature is 500 - 540 °C.
9. The control method for high surface quality of a 600MPa grade hot-dip galvanized dual-phase high-strength strip steel according to claim 6, characterized in that, During the descaling, high-pressure water descaling is used and the pressure is 220 - 240 dbar.
10. The control method for high surface quality of 600 MPa grade hot-dip galvanized dual-phase high-strength strip steel according to claim 1, characterized in that, During the galvanizing, with the upper edge of the zinc pot as the horizontal line, the liquid level height of the zinc liquid is -67 - -63 mm; The liquid level height of the zinc liquid is 3 - 6 mm higher than the overflow tank; The temperature of the zinc liquid is 448 - 452 °C; The zinc liquid is composed of the following elements by mass percentage: aluminum 0.25% - 0.3%, iron 0.01% - 0.02%, lead 0.001% - 0.002%, and the rest is zinc.