A production method of a thick zinc layer high surface hot-dip galvanizing super deep drawing plate for an automobile outer plate

Abstract

This invention discloses a method for producing thick zinc-coated, high-surface-coating hot-dip galvanized extra-deep-drawing steel sheets for automotive exterior panels. The invention uses Ti-IF steel and controls the processes of steelmaking, hot rolling, pickling, and hot-dip galvanizing. Firstly, by controlling the process of producing pure steel in the steelmaking process, the source of inclusions is reduced. Simultaneously, in the hot rolling process, the heating process in the heating furnace is controlled to reduce the occurrence of peeling. Furthermore, the pickling, reduction rate, and hot-dip galvanizing process parameters in the cold rolling process are controlled to reduce the impact of peeling defects. This results in a steel for producing thick zinc-coated, high-surface-coating hot-dip galvanized automotive exterior panels, which has a high surface zinc coating thickness and good formability, meeting the complex forming and high surface requirements of automotive exterior panels. After coating, the surface is free of point defects and has excellent surface finish. The process is simple, requires no additional investment in equipment upgrades, and is easy to industrialize.

Description

Technical Field

[0001] This invention relates to the field of iron and steel metallurgy, and specifically to a method for producing thick zinc-coated, high-surface hot-dip galvanized extra-deep-drawn steel sheets for automotive exterior panels. Background Technology

[0002] With the rapid development of modern automotive technology, my country has become the world's largest automobile producer and consumer, and the demand for cold-rolled automotive steel sheets is increasing both domestically and internationally. Hot-dip galvanized steel sheets are widely used in automobile bodies due to their beautiful appearance, uniform coating, good mechanical properties, and excellent paintability. The production process of hot-dip galvanized outer sheets is very complex, placing high demands on equipment, hot-dip galvanizing processes, and overall production management. With continuous advancements in production technology, automobile companies have increasingly higher requirements for the surface quality and corrosion resistance of automotive outer sheets supplied by steel companies, leading to a growing demand for thicker zinc-coated outer sheets. Thicker zinc layers offer better corrosion resistance; when electrochemical corrosion occurs, the zinc coating acts as the anode, protecting the iron substrate, which acts as the cathode. Therefore, the thicker the coating, the longer its service life. However, issues such as uneven zinc layer weight control, thick edges, and small black spots on the surface of thick-zinc hot-dip galvanized products affect their market promotion. In particular, the small black spots on the surface after hot-dip galvanizing affect subsequent stamping and painting. Unresolved point defects cannot meet customer requirements, posing increasingly higher challenges to the actual production control of automotive outer sheets. The ability to consistently produce hot-dip galvanized automotive exterior panels that combine excellent surface quality and corrosion resistance is of practical significance for market promotion and corporate competitiveness.

[0003] By searching domestic and foreign literature resources, a total of 11 articles related to this research project were found. Among the publicly published articles searched, there are two reports on thick zinc layer high surface hot-dip galvanized automotive outer panels. (1) Publication (Announcement) No. CN103627957B: A CR4 hot-dip galvanized automotive steel, the chemical composition by mass percentage is: C: 0.0008-0.0015%, Mn: 0.08-0.18%, Si: ≤0.010%, P: ≤0.010%, S: ≤0.008%, Als: 0.025-0.06%, N: ≤0.004%, B: 0.0006~0.0012%, Ti: 0.03~0.07%, the remainder being Fe and unavoidable impurities. The production method of CR4 hot-dip galvanized automotive steel provided by this invention, through adjusting the content of C, Si, Mn, P, and B and comprehensively optimizing the hot rolling, continuous annealing and hot-dip galvanizing processes, produces CR4 hot-dip galvanized automotive steel sheets with high deep drawing performance, extremely low secondary processing brittle transition temperature and O5 grade automotive outer panels, meeting the requirements of high-end automotive users and bringing considerable economic benefits. (2) Publication (Announcement) No. CN112159926A: An economical hot-dip galvanized automotive outer panel steel with excellent comprehensive mechanical properties and its production method, belonging to the technical field of hot-dip galvanized automotive steel. The main chemical element composition and mass percentage content of the steel used for hot-dip galvanized automotive outer panels are as follows: C: 0.001~0.005%, Si: 0.09~0.15%, Mn: 0.40~0.55%, Ti: 0.05~0.07%, Als: 0.02~0.06%, P: 0.035~0.055%, S≤0.015%, N≤0.005%, Nb: 0.001~0.006%, B≤0.0015%, with the balance being Fe and unavoidable impurities. Hot-dip galvanized automotive outer panel steel has excellent formability, excellent comprehensive mechanical properties, good performance stability, high surface quality, and low production cost. It has achieved stable large-scale industrial production, resulting in good economic benefits for enterprises. However, none of the above-mentioned hot-dip galvanized automotive steel panels meets the requirement of a thick zinc layer (≥60 / 60g / m). 2 High surface quality (surface sorting degree 1000) requirement. Summary of the Invention

[0004] The purpose of this invention is to provide a method for producing a high-surface-area hot-dip galvanized extra-deep-drawing steel sheet with a thick zinc layer for automotive outer panels. The resulting steel sheet has a high surface-area-thick zinc layer and good formability, which meets the complex forming and high surface requirements of automotive outer panels. After coating, the surface is free of point defects and has an excellent surface finish.

[0005] To achieve the above-mentioned technical objectives, the present invention adopts the following technical solution:

[0006] A method for producing thick zinc-coated, high-surface-surface hot-dip galvanized extra-deep-drawn steel sheets for automotive exterior panels is provided. The specific process includes hot metal desulfurization, converter smelting, RH vacuum treatment, continuous casting, hot rolling, pickling, cold rolling, and hot-dip galvanizing. The specific steps are as follows:

[0007] Steelmaking process: The slabs obtained by continuous casting of molten steel are cleaned by flame cleaning, and the surface quality of the slabs after machine cleaning is improved by grinding. The chemical composition of the molten steel, by weight percentage, is C≤0.002%, Si≤0.020%, Mn:0.06-0.12%, P≤0.015%, S≤0.010%, Als:0.02-0.06%, Ti:0.045-0.06%, B:0.0002-0.0006%, N≤0.003%, with the remainder being Fe and unavoidable impurities.

[0008] Hot rolling process: The continuously cast slab adopts the cold billet charging method. After the slab enters the furnace, the first heating temperature of the slab is controlled to be ≤1050℃, the excess air coefficient is -8~-12%, the second heating temperature is ≤1150℃, and the slab exiting the furnace temperature range is 1220-1280℃. The speed of the roughing descaling mill is controlled at 0.7-0.8m / min to improve the descaling effect. Then, after primary rolling and final rolling, the slab is coiled.

[0009] Pickling and rolling process: The pickling speed is controlled at 160-270mpm, and 5 passes are rolled using a cold continuous rolling mill with a reduction rate of 81-93%.

[0010] Hot-dip galvanizing process: The temperature of the P6 plate in the hot-dip galvanizing unit is controlled at 463-467℃, the temperature of the zinc bath is controlled at 458-462℃, the dew point of the furnace nose is -5-10℃, and the zinc layer on the upper / lower surfaces is 60-63g / m². 2 .

[0011] According to the above scheme, starting from the desulfurization of molten iron, after smelting in a converter, the molten steel is subjected to vacuum treatment, and then the steel billet is continuously cast.

[0012] According to the above scheme, in the hot rolling process, the initial rolling temperature is controlled at 1030-1090℃, the Ar3 point of Ti-IF steel is generally around 900℃, the final rolling temperature is controlled at 900-940℃ to avoid rolling in the two-phase region, and the coiling temperature is controlled at 660-700℃.

[0013] According to the above scheme, in the hot-dip galvanizing process, the speed of the hot-dip galvanizing unit is controlled at 100-120 mpm, and the substrate P2 / P3 plate temperature is controlled at 840-850℃. Among them, P6, P2, and P3 are all conventional process parameters for hot-dip galvanizing; the P6 plate temperature refers to the plate temperature before entering the zinc pot after annealing; the P2 and P3 plate temperatures refer to the annealing homogenization temperature.

[0014] According to the above scheme, in the hot-dip galvanizing process, the aluminum content of the zinc liquid in the zinc pot is 0.25-0.3%.

[0015] A hot-dip galvanized extra-deep drawing sheet obtained by the above production method is provided.

[0016] According to the above scheme, the thickness of the hot-dip galvanized extra-deep drawing plate is 0.50-1.0mm, the grain size is 7.5-8, the yield strength is 140-165MPa, the tensile strength is 270-330MPa, the elongation is ≥42%, the average R value is ≥1.8, and the N90 is ≥0.21.

[0017] According to the above scheme, the zinc layer thickness in the hot-dip galvanized extra-deep drawing sheet is ≥60 / 60g / m. 2 Surface sorting degree 1000. Zinc layer thickness ≥ 60 g / m. 2 This refers to a zinc coating thickness of ≥60g / m² on both sides. 2 .

[0018] This invention provides an application of the aforementioned hot-dip galvanized extra-deep drawing sheet in automotive outer panel steel with a thick zinc layer and high surface area, wherein the thick zinc layer refers to a zinc layer thickness ≥ 60 / 60 g / m. 2 High surface area refers to a surface sorting degree of 1000.

[0019] The beneficial effects of this invention are as follows:

[0020] This invention utilizes Ti-IF steel and controls the processes of steelmaking, hot rolling, pickling, and hot-dip galvanizing. Firstly, by controlling the process of producing pure steel during steelmaking, the source of inclusions is reduced. Simultaneously, in the hot rolling process, heating furnace control reduces the occurrence of peeling, and the pickling, reduction rate, and hot-dip galvanizing process parameters during cold rolling are controlled to minimize the impact of peeling defects. The result is a steel for producing high-surface-weight hot-dip galvanized automotive exterior panels. This steel possesses a high surface-weight zinc layer and excellent formability, meeting the complex forming requirements and high surface finish of automotive exterior panels. After coating, the surface is free of point defects and exhibits excellent surface quality. The process is simple, requires no additional investment in equipment upgrades, and is easy for industrial application. Attached Figure Description

[0021] Figure 1 This is a surface morphology diagram of the pickled hot-rolled plate in Embodiment 1 of the present invention.

[0022] Figure 2 This is a surface morphology diagram of the pickled hot-rolled plate of Comparative Example 1 of the present invention. Detailed Implementation

[0023] The technical solution of the present invention will be further explained and illustrated below through specific embodiments.

[0024] Example 1:

[0025] A method for producing thick zinc-coated, high-surface hot-dip galvanized extra-deep-drawing steel sheet for automotive exterior panels is provided. The chemical composition of the steel sheet by weight percentage is: C: 0.002%, Si: 0.004%, Mn: 0.12%, P: 0.011%, S: 0.010%, Als: 0.02%, Ti: 0.05%, B: 0.0005%, N: 0.0025%, with the remainder being Fe and unavoidable impurities.

[0026] The specific implementation process includes the following steps:

[0027] Steelmaking process: Starting with desulfurization of molten iron, after smelting in a converter, the molten steel is vacuum treated and then continuously cast into steel billets. Flame cleaning is used to clean the surface of the billets to eliminate the influence of inclusions within 3mm below the surface. At the same time, grinding measures are taken to improve the surface quality of the billets after machine cleaning, and to avoid burrs or protrusions caused by uneven local conditions during the machine cleaning process from forming machine cleaning "peeling" defects after multiple rolling processes.

[0028] Hot rolling process: To avoid surface peeling caused by continuous casting defects during hot rolling, the hot rolling mill uses a cold billet charging method for continuously cast steel billets. After the billet enters the furnace, the first heating temperature is controlled at 1050℃ with an air excess coefficient of -10%, the second heating temperature at 1150℃, and the billet exit temperature range is 1280℃. By controlling the first and second heating temperatures, the billet is heated at a slow and suitable temperature to avoid excessive heating and surface peeling; the exit temperature ensures complete austenitization of the grains. The roughing mill descaling speed is controlled at 0.8 m / min to improve descaling efficiency. The initial rolling temperature is controlled at 1090℃, while the Ar3 point of Ti-IF steel is generally around 900℃. The final rolling temperature is controlled at 940℃ to avoid rolling in the two-phase region, and the coiling temperature is controlled at 700℃.

[0029] Pickling process: The hot-rolled steel strip is pickled to ensure that the iron oxide scale on the surface of the strip is cleaned and not over-pickled. The pickling speed is 270mpm. The strip is then cold-rolled using a five-stand continuous rolling mill with a reduction rate of 85%.

[0030] Hot-dip galvanizing process: The continuous hot-dip galvanizing unit speed is controlled at 110 mpm, the substrate temperature of P2 / P3 is controlled at 850℃, the P6 substrate temperature is controlled at 465℃, the zinc bath temperature is controlled at 460℃, the aluminum content is 0.3%, the furnace nose dew point is 5℃, and the zinc layer on the upper / lower surfaces is 63 g / m². 2 After finishing, a cold-rolled steel sheet with a thickness of 1.0 mm is obtained, with a grain size of 7.5, a yield strength of 145 MPa, a tensile strength of 280 MPa, an elongation of 45%, an average R value of 2.2, and an N90 value of 0.23. This also meets the requirements for use in thick zinc coatings (≥60 / 60 g / m²). 2 High surface area (surface sorting degree 1000) automotive exterior panels.

[0031] Example 2:

[0032] A method for producing thick zinc-coated, high-surface hot-dip galvanized extra-deep-drawing steel sheet for automotive exterior panels is provided. The chemical composition of the steel sheet by weight percentage is: C: 0.0015%, Si: 0.005%, Mn: 0.10%, P: 0.010%, S: 0.008%, Als: 0.03%, Ti: 0.05%, B: 0.0005%, N: 0.0030%, with the remainder being Fe and unavoidable impurities.

[0033] The specific implementation process includes the following steps:

[0034] Steelmaking process: Starting with desulfurization of molten iron, the molten steel is smelted in a converter and then vacuum-treated. It is then continuously cast into steel billets, and the surface of the billets is cleaned by flame cleaning. At the same time, grinding measures are taken to improve the surface quality of the billets after machine cleaning.

[0035] Hot rolling process: Continuously cast steel billets are charged into the furnace using a cold billet loading method. After the billets enter the furnace, the first heating temperature is controlled at 1030℃ with an excess air coefficient of -9%, the second heating temperature at 1130℃, and the billet exiting the furnace at a temperature range of 1250℃. The roughing mill descaling speed is controlled at 0.8 m / min, the initial rolling temperature is controlled at 1050℃, the final rolling temperature at 930℃, and the coiling temperature at 680℃.

[0036] Pickling and rolling process: The hot-rolled steel strip is pickled at a speed of 250 mpm and then cold-rolled using a five-stand continuous rolling mill with a reduction rate of 81%.

[0037] Hot-dip galvanizing process: The continuous hot-dip galvanizing unit speed is controlled at 110 mpm, the substrate temperature of P2 / P3 is controlled at 845℃, the P6 substrate temperature is controlled at 465℃, the zinc bath temperature is controlled at 462℃, the aluminum content is 0.28%, the furnace nose dew point is 2℃, and the zinc layer on the upper / lower surfaces is 62 g / m². 2 After finishing, a cold-rolled steel sheet with a thickness of 1.0 mm is obtained, with a grain size of 7.5, a yield strength of 155 MPa, a tensile strength of 300 MPa, an elongation of 46%, an average R value of 2.2, and an N90 value of 0.23. This also meets the requirements for use in thick zinc coatings (≥60 / 60 g / m²). 2 High surface area (surface sorting degree 1000) automotive exterior panels.

[0038] Example 3:

[0039] A method for producing thick zinc-coated, high-surface hot-dip galvanized extra-deep-drawing steel sheet for automotive exterior panels is provided. The chemical composition of the steel sheet by weight percentage is: C: 0.0018%, Si: 0.006%, Mn: 0.12%, P: 0.013%, S: 0.006%, Als: 0.06%, Ti: 0.05%, B: 0.0006%, N: 0.003%, with the remainder being Fe and unavoidable impurities.

[0040] The specific implementation process includes the following steps:

[0041] Steelmaking process: Starting with desulfurization of molten iron, the molten steel is smelted in a converter and then vacuum-treated. It is then continuously cast into steel billets, and the surface of the billets is cleaned by flame cleaning. At the same time, grinding measures are taken to improve the surface quality of the billets after machine cleaning.

[0042] Hot rolling process: Continuously cast steel billets are charged into the furnace using a cold billet loading method. After the billets enter the furnace, the first heating temperature is controlled at 1020℃ with an excess air coefficient of -11%, the second heating temperature at 1120℃, and the billet exiting the furnace at a temperature range of 1230℃. The roughing mill descaling speed is controlled at 0.8 m / min, the initial rolling temperature is controlled at 1030℃, the final rolling temperature at 920℃, and the coiling temperature at 670℃.

[0043] Pickling and rolling process: The hot-rolled steel strip is pickled at a speed of 230 mpm and then cold-rolled using a five-stand continuous rolling mill with a reduction rate of 86%.

[0044] Hot-dip galvanizing process: The continuous hot-dip galvanizing unit speed is controlled at 110 mpm, the substrate temperature of P2 / P3 is controlled at 848℃, the P6 substrate temperature is controlled at 465℃, the zinc bath temperature is controlled at 460℃, the aluminum content is 0.27%, the furnace nose dew point is -1℃, and the zinc layer on the upper / lower surfaces is 61 g / m². 2 After finishing, a cold-rolled steel sheet with a thickness of 0.65 mm is obtained, with a grain size of 7.5, a yield strength of 158 MPa, a tensile strength of 302 MPa, an elongation of 47%, an average R value of 2.3, and an N90 value of 0.22. This also meets the requirements for use in thick zinc coatings (≥60 / 60 g / m²). 2 High surface area (surface sorting degree 1000) automotive exterior panels.

[0045] Example 4:

[0046] A method for producing thick zinc-coated, high-surface hot-dip galvanized extra-deep-drawing steel sheet for automotive exterior panels is provided. The chemical composition of the steel sheet by weight percentage is: C: 0.0014%, Si: 0.005%, Mn: 0.11%, P: 0.011%, S: 0.007%, Als: 0.04%, Ti: 0.055%, B: 0.0006%, N: 0.0025%, with the remainder being Fe and unavoidable impurities.

[0047] The specific implementation process includes the following steps:

[0048] Steelmaking process: Starting with desulfurization of molten iron, the molten steel is smelted in a converter and then vacuum-treated. It is then continuously cast into steel billets, and the surface of the billets is cleaned by flame cleaning. At the same time, grinding measures are taken to improve the surface quality of the billets after machine cleaning.

[0049] Hot rolling process: Continuously cast steel billets are charged into the furnace using a cold billet loading method. After the billets enter the furnace, the first heating temperature is controlled at 1010℃ with an excess air coefficient of -12%, the second heating temperature at 1110℃, and the billet exiting the furnace at a temperature range of 1220℃. The roughing mill descaling speed is controlled at 0.8 m / min, the initial rolling temperature is controlled at 1040℃, the final rolling temperature at 910℃, and the coiling temperature at 660℃.

[0050] Pickling and rolling process: The hot-rolled steel strip is pickled at a speed of 220 mpm and then cold-rolled using a five-stand continuous rolling mill with a reduction rate of 88%.

[0051] Hot-dip galvanizing process: The continuous hot-dip galvanizing unit speed is controlled at 110 mpm, the substrate temperature of P2 / P3 is controlled at 847℃, the P6 substrate temperature is controlled at 465℃, the zinc bath temperature is controlled at 458℃, the aluminum content is 0.24%, the furnace nose dew point is 2℃, and the zinc layer on the upper / lower surfaces is 60 g / m². 2 After finishing, a cold-rolled steel sheet with a thickness of 0.55 mm is obtained, with a grain size of 7.5, a yield strength of 160 MPa, a tensile strength of 310 MPa, an elongation of 44%, an average R value of 2.1, and an N90 value of 0.21. This also meets the requirements for use in thick zinc coatings (≥60 / 60 g / m²). 2 High surface area (surface sorting degree 1000) automotive exterior panels.

[0052] Example 5:

[0053] A method for producing thick zinc-coated, high-surface hot-dip galvanized extra-deep-drawing steel sheet for automotive exterior panels is provided. The steel sheet has the following chemical composition by weight percentage: C: 0.0016%, Si: 0.005%, Mn: 0.11%, P: 0.008%, S: 0.005%, Als: 0.05%, Ti: 0.05%, B: 0.0003%, N: 0.0028%, with the remainder being Fe and unavoidable impurities.

[0054] The specific implementation process includes the following steps:

[0055] Steelmaking process: Starting with desulfurization of molten iron, the molten steel is smelted in a converter and then vacuum-treated. It is then continuously cast into steel billets, and the surface of the billets is cleaned by flame cleaning. At the same time, grinding measures are taken to improve the surface quality of the billets after machine cleaning.

[0056] Hot rolling process: Continuously cast steel billets are charged into the furnace using a cold billet loading method. After the billets enter the furnace, the first heating temperature is controlled at 1040℃ with an excess air coefficient of -8%, the second heating temperature at 1140℃, and the billet exiting the furnace at a temperature range of 1240℃. The roughing mill descaling speed is controlled at 0.8 m / min, the initial rolling temperature is controlled at 1040℃, the final rolling temperature at 930℃, and the coiling temperature at 680℃.

[0057] Pickling and rolling process: The hot-rolled steel strip is pickled and then cold-rolled using a five-stand continuous rolling mill. The pickling speed is 200 mpm and the reduction rate is 85%.

[0058] Hot-dip galvanizing process: The continuous hot-dip galvanizing unit speed is controlled at 110 mpm, the substrate temperature of P2 / P3 is controlled at 845℃, the P6 substrate temperature is controlled at 465℃, the zinc bath temperature is controlled at 460℃, the aluminum content is 0.28%, the furnace nose dew point is 1℃, and the zinc layer on the upper / lower surfaces is 60 g / m². 2 After finishing, a cold-rolled steel sheet with a thickness of 0.75 mm is obtained, with a grain size of 7.5, a yield strength of 148 MPa, a tensile strength of 282 MPa, an elongation of 45%, an average R value of 2.3, and an N90 value of 0.22. This also meets the requirements for use in thick zinc coatings (≥60 / 60 g / m²). 2 High surface area (surface sorting degree 1000) automotive exterior panels.

[0059] Example 6:

[0060] A method for producing thick zinc-coated, high-surface hot-dip galvanized extra-deep-drawing steel sheet for automotive exterior panels is provided. The chemical composition of the steel sheet by weight percentage is: C: 0.0018%, Si: 0.004%, Mn: 0.12%, P: 0.008%, S: 0.005%, Als: 0.05%, Ti: 0.05%, B: 0.0004%, N: 0.0026%, with the remainder being Fe and unavoidable impurities.

[0061] The specific implementation process includes the following steps:

[0062] Steelmaking process: Starting with desulfurization of molten iron, the molten steel is smelted in a converter and then vacuum-treated. It is then continuously cast into steel billets, and the surface of the billets is cleaned by flame cleaning. At the same time, grinding measures are taken to improve the surface quality of the billets after machine cleaning.

[0063] Hot rolling process: Continuously cast steel billets are charged into the furnace using a cold billet loading method. After the billets enter the furnace, the first heating temperature is controlled at 1030℃ with an air excess coefficient of -10%, the second heating temperature at 1120℃, and the billet exiting the furnace at a temperature range of 1260℃. The roughing mill descaling speed is controlled at 0.8 m / min, the initial rolling temperature is controlled at 1030℃, the final rolling temperature at 930℃, and the coiling temperature at 680℃.

[0064] Pickling and rolling process: The hot-rolled steel strip is pickled at a speed of 230 mpm and then cold-rolled using a five-stand continuous rolling mill with a reduction rate of 83%.

[0065] Hot-dip galvanizing process: The continuous hot-dip galvanizing unit speed is controlled at 110 mpm, the substrate temperature of P2 / P3 is controlled at 848℃, the P6 substrate temperature is controlled at 465℃, the zinc bath temperature is controlled at 460℃, the aluminum content is 0.29%, the furnace nose dew point is 0℃, and the zinc layer on the upper / lower surfaces is 62 g / m². 2 After finishing, a cold-rolled steel sheet with a thickness of 0.85 mm is obtained, with a grain size of 7.5, a yield strength of 148 MPa, a tensile strength of 282 MPa, an elongation of 46%, an average R value of 2.3, and an N90 value of 0.22. This also meets the requirements for use in thick zinc coatings (≥60 / 60 g / m²). 2 High surface area (surface sorting degree 1000) automotive exterior panels.

[0066] Comparative Example 1:

[0067] The chemical composition by weight percentage is: C: 0.04%, Si: 0.005%, Mn: 0.19%, P: 0.008%, S: 0.005%, Als: 0.025%, with the remainder being Fe and unavoidable impurities. The specific implementation process begins with desulfurization of the molten iron, followed by converter smelting, argon blowing at an argon station, and then continuous casting into steel billets. Without machine cleaning, the continuously cast billets are hot-rolled into steel strips. The hot-rolled steel strips are then pickled, and under a reduction rate of 79%, they are cold-rolled using a five-stand continuous rolling mill. Finally, after a conventional hot-dip galvanizing process, a cold-rolled steel sheet with a thickness of 0.8 mm is obtained. Tests revealed that the grain size was 10.5, the yield strength was 162 MPa, the tensile strength was 294 MPa, the elongation was 40.3%, the average R value was 1.8, the N90 value was 0.20, the zinc layer on the upper and lower surfaces was 62 g / m2, and there were numerous small black spots on the surface. Both the surface and performance did not meet the requirements.

[0068] Comparative Example 2:

[0069] The chemical composition by weight percentage is: C: 0.035%, Si: 0.005%, Mn: 0.23%, P: 0.008%, S: 0.005%, Als: 0.025%, with the remainder being Fe and unavoidable impurities. The specific implementation process begins with desulfurization of the molten iron. After converter smelting, the molten steel undergoes vacuum treatment, followed by continuous casting into steel billets. Without machine cleaning, the continuously cast billets are hot-rolled into steel strips. The hot-rolled steel strips are then pickled, and under a reduction rate of 91%, they are cold-rolled using a five-stand continuous rolling mill. After ordinary hot-dip galvanizing, they are finished to obtain a cold-rolled steel sheet with a thickness of 0.8 mm. Testing revealed that its grain size was grade 10, yield strength was 175 MPa, tensile strength was 312 MPa, elongation was 39.3%, average R value was 1.9, N90 value was 0.20, zinc layer on the upper / lower surfaces was 60 g / m2, and there were numerous small black spots on the surface. Both the surface and performance did not meet the requirements.

[0070] Comparative Example 3:

[0071] The chemical composition by weight percentage is: C: 0.0027%, Si: 0.005%, Mn: 0.15%, P: 0.008%, S: 0.005%, Als: 0.03%, Ti: 0.05%, N: 0.0026%, with the remainder being Fe and unavoidable impurities. The specific implementation process begins with desulfurization of the molten iron. After converter smelting, the molten steel undergoes vacuum treatment, followed by continuous casting into steel billets. Without machine cleaning, the continuously cast billets are hot-rolled into steel strips. The hot-rolled steel strips are then pickled, and under a reduction rate of 80%, they are cold-rolled using a five-stand continuous rolling mill. After ordinary hot-dip galvanizing, they are finished to obtain a cold-rolled steel sheet with a thickness of 0.8 mm. Tests showed that its grain size was grade 9, yield strength was 148 MPa, tensile strength was 298 MPa, elongation was 44.3%, average R value was 2.3, N90 value was 0.22, and the zinc layer on the upper / lower surfaces was 61 g / m2, which met the performance requirements. However, the surface had a large number of small black spots, which did not meet the requirements for the outer panel.

[0072] As can be seen from the above embodiments, the hot-dip galvanized sheet produced by the present invention has a thickness of 0.50-1.0 mm, a grain size of 7.5-8, a yield strength of 140-165 MPa, a tensile strength of 270-330 MPa, an elongation of ≥42%, an average R value of ≥1.8, and an N90 of ≥0.21, while also meeting the requirements for use in thick zinc layers (≥60 / 60 g / m²). 2 High surface area (surface sorting degree 1000) automotive exterior panels.

[0073] Figure 1 This is a surface morphology diagram of the pickled hot-rolled plate in Embodiment 1 of the present invention. Figure 2 This is a surface morphology diagram of the pickled hot-rolled steel plate used in Comparative Example 1 of the invention. The diagram shows: Figure 1 The surface is smooth and flat, with excellent surface finish; Figure 2 The surface has many wrinkles, which can easily develop into peeling after pickling.

[0074] It should be understood that those skilled in the art can make improvements or modifications based on the above description, and all such improvements and modifications should fall within the protection scope of the appended claims.

Claims

1. A method for producing thick zinc-coated, high-surface hot-dip galvanized extra-deep-drawn sheet for automotive exterior panels, characterized in that, Including the following: Steelmaking process: The slab obtained by continuous casting of molten steel is cleaned by flame cleaning and then ground; wherein, by weight percentage, the chemical composition of the molten steel is C≤0.002%, Si≤0.020%, Mn:0.06-0.12%, P≤0.015%, S≤0.010%, Als:0.02-0.06%, Ti:0.045-0.06%, B:0.0002-0.0006%, N≤0.003%, with the remainder being Fe and unavoidable impurities; Hot rolling process: The continuously cast slab adopts the cold billet charging method. After the slab enters the furnace, the first heating temperature of the slab is controlled to be ≤1050℃, the excess air coefficient is -8~-12%, the second heating temperature is ≤1150℃, and the slab exiting the furnace temperature range is 1220-1280℃; the speed of the roughing descaling mill is controlled at 0.7-0.8m / min, and then after primary rolling and final rolling, it is coiled. Pickling and rolling process: Pickling speed is controlled at 160-270mpm, and 5 passes are rolled using a cold continuous rolling mill with a reduction rate of 81-93%; Hot-dip galvanizing process: The temperature of the P6 plate in the hot-dip galvanizing unit is controlled at 463-467℃, the temperature of the zinc liquid is controlled at 458-462℃, and the dew point of the furnace nose is -5-10℃.

2. The production method according to claim 1, characterized in that, In the steelmaking process, starting with the desulfurization of molten iron, the molten steel is smelted in a converter, then vacuum-treated, and finally continuously cast into slabs.

3. The production method according to claim 1, characterized in that, In the hot rolling process, the initial rolling temperature is controlled at 1030-1090℃, the final rolling temperature is controlled at 900-940℃, and the coiling temperature is controlled at 660-700℃.

4. The production method according to claim 1, characterized in that, In the hot-dip galvanizing process, the speed of the hot-dip galvanizing unit is controlled at 100-120 mpm, and the temperature of the substrate P2 / P3 is controlled at 840-850℃.

5. The production method according to claim 1, characterized in that, In the hot-dip galvanizing process, the aluminum content of the zinc bath is 0.25-0.3%.

6. The production method according to claim 1, characterized in that, In the hot-dip galvanizing process, the zinc layer thickness on the upper / lower surfaces is 60-63 g / m. 2 .

7. Hot-dip galvanized extra-deep drawing sheet obtained by the production method according to any one of claims 1-6.

8. The hot-dip galvanized extra-deep drawing sheet according to claim 7, characterized in that, The hot-dip galvanized extra-deep drawing plate has a thickness of 0.50~1.0mm, a grain size of 7.5-8, a yield strength of 140-165MPa, a tensile strength of 270-330MPa, an elongation of ≥42%, an average R value of ≥1.8, and an N90 of ≥0.

21.

9. The hot-dip galvanized extra-deep drawing sheet according to claim 7, characterized in that, In the hot-dip galvanized extra-deep drawing sheet, the zinc layer thickness is ≥60 / 60g / m. 2 Surface sorting degree 1000.

10. The application of the hot-dip galvanized extra-deep-drawn sheet of claim 7 in automotive exterior steel with a thick zinc layer and high surface area, characterized in that, The thick zinc layer refers to a zinc layer thickness ≥ 60 / 60 g / m. 2 High surface area refers to a surface sorting degree of 1000.

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