A manufacturing method for eliminating the longitudinal color difference between the head and tail of 180MPa yield strength phosphorus-containing IF steel hot-dip galvanized sheet

Abstract

The invention discloses a manufacturing method for eliminating longitudinal color difference between the head and tail of a phosphorus-containing IF steel hot-dip galvanized sheet with a yield strength of 180 MPa, belonging to the technical field of hot-dip galvanized steel sheets. By comprehensively controlling the rolling speed at different parts during hot rolling, the coiling temperature, the roughness of the last stand roll during acid continuous rolling, the dew point temperature during continuous annealing, the oxygen content in the heating section, and the Rpc value of the skin pass roll in the skin pass step, the produced GI galvanized sheet has a longitudinal color difference of ≤level 2, and the longitudinal color difference between the head and tail of the steel is basically invisible to the naked eye after oiling.

Description

Technical Field

[0001] The invention belongs to the technical field of hot-dip galvanized steel sheets, and particularly relates to a manufacturing method for eliminating longitudinal color difference between the head and tail of a phosphorus-containing IF steel hot-dip galvanized sheet with a yield strength of 180 MPa. Background Art

[0002] Pure zinc-coated steel sheets (GI steel sheets) offer excellent corrosion resistance and formability. With the continued push for lightweight vehicles, hot-dip galvanized high-strength IF steels with higher yield strength are finding widespread use in stamping parts such as door panels, fenders, and engine hood panels. Compared to standard IF steels, these steels offer superior stiffness and dent resistance.

[0003] Galvanized automotive hood panels, door panels, and fender parts have extremely strict surface quality requirements and a low tolerance for some subtle surface defects. Longitudinal color difference along the rolling direction is a typical defect. This defect is most likely to occur in the head and tail areas of the steel coil and has become one of the main defects that plague the stable production of this type of steel. Since high-strength IF steel is added with strengthening elements such as Mn, P, and B to increase its strength, these elements will change the microstructure evolution and iron oxide scale growth behavior during the rolling process, thereby affecting the final hot-dip galvanizing process, resulting in uneven diffuse reflection of light in the macroscopic morphology of the coating, that is, color difference. Therefore, it is necessary to invent a manufacturing method suitable for eliminating this type of steel to solve the above problems.

[0004] Chinese patent CN 116408358 A discloses a method for solving the color difference of the surface of electro-galvanized steel sheets. The method mainly involves finishing rolling the slab under set finishing inlet temperature and set finishing rolling rate conditions during the finishing rolling stage. The method only involves the hot rolling process and does not describe how to control the galvanizing annealing process to reduce the coating weight fluctuation.

[0005] Chinese patent CN 115558760 A discloses a method for reducing surface color deviation defects in electrogalvanized sheet. This method primarily involves controlling the heating temperature to a set temperature and the furnace heating time to a set time during the hot rolling stage. This method significantly reduces the thickness of the furnace-generated iron oxide scale, thereby avoiding the difference in light diffuse reflection caused by the directional growth of the zinc layer and the disordered growth of the surrounding zinc layer, thereby effectively improving the surface color deviation defects of electrogalvanized products. While this patent briefly summarizes the mechanism of longitudinal color deviation, it does not address the combined hot rolling and galvanizing process, and its guiding role in eliminating longitudinal color deviation in hot-dip galvanized products is limited. Summary of the Invention

[0006] The purpose of the present invention is to provide a manufacturing method for eliminating the longitudinal color difference between the head and tail of the 180MPa yield strength phosphorus-containing IF steel hot-dip galvanized sheet. The GI galvanized sheet produced by this manufacturing method has a longitudinal color difference of ≤2 levels, and the longitudinal color difference between the head and tail of the steel is basically invisible to the naked eye after oiling.

[0007] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0008] A manufacturing method for eliminating longitudinal color difference between the head and tail of a phosphorus-containing IF steel hot-dip galvanized sheet with a yield strength of 180 MPa, comprising the steps of hot rolling, acid continuous rolling, continuous annealing, hot-dip galvanizing, and skin-passing;

[0009] In the hot rolling step, the finishing rolling adopts a three-stage finishing rolling speed, the rolling speed within 50 meters of the head and tail is 30% higher than that of the middle part, and the coiling temperature is controlled at 630-670°C;

[0010] In the acid continuous rolling step, the roughness Ra of the last stand roll is controlled to be 2.0-2.2 μm;

[0011] In the continuous annealing step, the dew point of the heating section is set to -45~-60°C, and the oxygen content in the heating section is controlled at 1~5ppm to inhibit the enrichment and oxidation of elements such as phosphorus and boron at the edge of the strip and reduce color difference;

[0012] In the polishing step, high-pressure water is set at the polishing outlet to blow the strip surface, and the water pressure is controlled at 8~10 bar to reduce the head and tail color difference caused by the residual polishing liquid. The Rpc value of the polishing roller is controlled at 120~170.

[0013] Furthermore, in the hot rolling step, the heating temperature is controlled at 1180-1220°C, and the heating time is controlled at 180-240 min; during finish rolling, the rolling speed in the middle of the slab is 10-11 m / s, the finish rolling start temperature is controlled at 1050-1100°C, and the finish rolling outlet temperature is 910-950°C.

[0014] In the hot rolling step, edge heating is used during rolling; full-pass descaling is used during descaling, and secondary descaling water is added to the inlet and outlet of the finishing rolling F1 stand; and a front-stage intensive cooling process is used during controlled cooling.

[0015] In the hot rolling step, the thickness of the iron oxide scale at the edge and middle of the hot-rolled plate is controlled to be 5-10 μm, and the thickness deviation of the iron oxide scale at the middle and edge is ±1 μm.

[0016] In the acid continuous rolling step, the cold rolling reduction rate is controlled at 74-78.3%.

[0017] In the acid continuous rolling step, the roughness Ra of the strip entering the final stand is controlled to be 0.6-1.0 μm.

[0018] In the continuous annealing step, the annealing temperature is controlled at 780-800° C., and the annealing speed is controlled at 110-130 m / min.

[0019] During the continuous annealing step, a pre-oxidation process is used to reduce external oxidation of silicon, aluminum, and manganese on the surface. The pre-oxidation chamber temperature is 700-750°C, with an oxygen content of 1.8-2.4%. Compressed air is preheated to 350°C and maintained at a flow rate of ≥280 m³ / h to promote uniform internal oxidation of silicon, aluminum, and manganese. The tension in the heating section of the annealing furnace is controlled at 300-400 kN.

[0020] In the hot-dip galvanizing step, the steel strip is cooled to 470~480℃ and then enters a 460℃ zinc pot for galvanizing.

[0021] The chemical composition by weight percentage of the hot-dip galvanized phosphorus-containing IF steel with a yield strength of 180 MPa is as follows: C ≤ 0.003%, Si 0.03-0.09%, Mn 0.50-0.60%, Al 0.03-0.05%, Ti 0.025-0.035%, Nb 0.01-0.02%, P 0.032-0.047%, S ≤ 0.006%, N ≤ 0.003%, B 0.008-0.012%, and the balance is Fe and unavoidable impurities.

[0022] The metallographic structure of the phosphorus-containing IF steel with a yield strength of 180 MPa is single ferrite, and the average grain size is 8.5-9.0.

[0023] The hot-dip galvanized phosphorus-containing IF steel with a yield strength of 180 MPa has an elongation A80 of 34-44%, a work hardening rate n90 value of not less than 0.19, and a plastic strain ratio n90 of not less than 1.8, a yield strength of 180-240 MPa, and a tensile strength of 340-400 MPa.

[0024] The yield strength 180MPa grade hot dip galvanized sheet containing phosphorus IF steel is 0.6-0.7mm thick and has a coating weight of 40-60g / m 2 GI galvanized sheet.

[0025] In the manufacturing method for eliminating longitudinal color difference between the head and tail of phosphorus-containing IF steel hot-dip galvanized sheet with a yield strength of 180 MPa, provided herein, a three-stage strip threading speed control is employed during the hot rolling stage to prevent excessive temperature drop from the head to the tail, which could result in mixed crystals due to the temperature dropping to the FA two-phase region before entering the final finishing stand. For galvanized coils with a thickness of 0.6-0.7 mm, the rolling speed of the F7 stand within 50 meters of the head (Vh) and tail (Vt) is 30% higher than that of the remaining sections (denoted as Vm). Edge heaters are used during rolling to reduce heat loss at the edges. The slab heating temperature is controlled between 1180 and 1220°C to prevent incomplete dissolution of NbC, thereby increasing the number of ferrite nucleation sites during subsequent rolling and achieving a grain nucleation rate greater than the grain growth rate. To ensure uniform temperature between the core and surface of the slab, the heating time is controlled between 180 and 240 minutes, and the finishing exit temperature is maintained between 910 and 950°C to minimize the effects of increased deformation resistance caused by the addition of B. To control tertiary oxide scale thickness and ferrite grain growth, laminar cooling employs a front-end intensive cooling process, rapidly lowering the strip temperature to 630-670°C for coiling. After hot rolling, the oxide scale thickness at the edges and center of the hot-rolled plate is controlled to 5-10μm, with a center / edge thickness tolerance of ±1μm. This prevents uneven rolling forces caused by large thickness differences in certain areas after pickling.

[0026] During the acid continuous rolling, in order to reduce the surface tension of the steel plate, ensure that the thickness of the emulsion film is evenly distributed across the entire width of the plate during rolling in the final stand, and avoid local uneven rolling force caused by excessive changes in the emulsion flow direction in the plate width, the roughness Ra of the strip entering the final stand is controlled at 0.6~1.0μm, and the roughness Ra of the final stand roll is controlled at 2.0~2.2μm.

[0027] During the hot-dip galvanizing continuous annealing production, in order to prevent the ferrite grains from growing excessively and amplifying the grain size differences inherited from the hot coils, and to reduce the inharmonious deformation of the organization during the tensile deformation process, a rapid annealing process of 110~130m / min is adopted, the annealing heating temperature is controlled at 780~800℃, and the tension in the furnace is controlled at 300~400kN during heating to prevent the large grains in the organization from deforming too much during the thermal deformation process of the ferrite organization and the appearance of wasp waist-shaped undulations on the surface. The average ferrite grain size of the final product is controlled at 8.5~9.0μm, achieving a refined grain effect.

[0028] The 8~10bar high-pressure water at the exit of the skin-pass mill blows the strip surface to ensure that there is no residual skin-pass liquid on the strip surface. The Rpc value of the skin-pass roller is controlled at 120~170, further increasing the uniform reflectivity of the galvanized sheet surface to light.

[0029] The chemical composition of the phosphorus-containing IF steel with a yield strength of 180 MPa provided by the present invention has the following functions and controls:

[0030] C: For IF steel, the C content should be as low as possible. However, if the C content exceeds 0.003wt%, the product will contain too many interstitial C atoms, which will increase the amount of precious metals such as Nb and Ti that need to be added to fix the residual C. Furthermore, the product will contain too many Nb / Ti(C) precipitates, resulting in a high yield strength and poor stamping performance. Therefore, the appropriate C content range is ≤0.003wt%.

[0031] Al: Al is a common deoxidizer in steel. Too low an Al content increases coarse Mn and Si oxides, reducing the steel's purity. Too high an Al content increases aluminum oxide inclusions, impairing the steel's plasticity and increasing the difficulty of smelting and casting. Furthermore, AlN particles formed by combining with nitrogen can pin grain boundaries, contributing to grain refinement. The Al content in this invention is 0.03-0.05%.

[0032] Ti: In the steel described herein, Ti primarily serves to immobilize free nitrogen and sulfur atoms released during the smelting process. Too little Ti fails to fully immobilize nitrogen atoms, hindering aging performance. Too much Ti increases manufacturing costs and leads to higher yield strength. It also oxidizes during annealing, impacting wettability with zinc solution. The Ti content in this invention is 0.025-0.035%.

[0033] Nb: The Ti+Nb composite design utilizes Nb to combine with carbon atoms to form NbC, which disperses and precipitates during the hot-rolling coiling stage. Furthermore, TiN precipitated during the finishing rolling stage serves as nucleation sites for large-scale precipitation. This allows the ferrite nucleation rate to exceed its growth rate, thereby achieving refined and uniform ferrite grains. While adding Ti alone can also stabilize carbon and nitrogen, it is susceptible to oxidation and burnout, producing oxides that are detrimental to the surface quality of the hot-rolled coil. Excessive Nb addition increases costs. The present invention aims for a Nb content of 0.01-0.02 wt%.

[0034] P: P is a major solid solution strengthening element. To achieve the minimum yield strength requirement of 180 MPa, a certain amount of P must be added. Excessive addition will cause the yield strength to exceed the required range and degrade formability. The P content in this patented invention is controlled at 0.032-0.047%.

[0035] B: The main function of B is to reduce the segregation of phosphorus at grain boundaries and increase the strength of ferrite grain boundaries. However, the addition of B also increases the temperature of the FA two-phase region, resulting in increased deformation resistance during hot rolling in the F7 stand. B is also prone to oxidation and deteriorates surface quality, so it needs to be controlled at a low level. In the present invention, B is controlled at 0.008-0.012%.

[0036] S / N: S and N are unavoidable impurity elements. Excessive S will lead to embrittlement of hot-rolled grains and must be controlled at a low level. N will cause the aging properties of steel to deteriorate and should also be controlled at a low level. The present invention requires S≤0.006% and N≤0.003%.

[0037] Compared with the prior art, the present invention has the following beneficial effects:

[0038] The present invention provides a method for eliminating the longitudinal color difference between the head and tail of the hot-dip galvanized sheet with a yield strength of 180 MPa, for a thickness of 0.6-0.7 mm and a coating weight of 40-60 g / m 2 The longitudinal color difference of GI galvanized sheet changes from ≥4 levels to ≤2 levels, and is basically invisible to the naked eye after oiling.

[0039] The galvanized steel sheet produced has a single ferrite matrix with an average grain size of 8.5 to 9.0. The sheet exhibits an elongation (A80) of 34 to 44%, a work hardening rate (n90) of no less than 0.19, and a plastic strain ratio (n90) of no less than 1.8. The sheet also exhibits a yield strength of 180 to 240 MPa, a tensile strength of 340 to 400 MPa, and excellent formability. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 This is a micrograph of the phosphorus-containing IF steel in Comparative Example 1; the thickness of the oxide scale is 12.68 μm in the middle and 15 μm at the edge;

[0041] Figure 2 This is a micrograph of the phosphorus-containing IF steel in Comparative Example 3; the thickness of the oxide scale is 6.267 μm in the middle and 6.85 μm at the edge;

[0042] Figure 3 This is the microstructure of the phosphorus-containing IF steel hot-dip galvanized sheet in Example 1, showing that the substrate has uniform grain refinement and uniform coating cross-sectional thickness;

[0043] Figure 4 This is the microstructure of the phosphorus-containing IF steel hot-dip galvanized sheet in Comparative Example 3. The substrate has coarse grains and undulating grains, and the cross-section of the coating is uneven.

[0044] Figure 5 This is the metallographic structure diagram of the phosphorus-containing IF steel substrate in Example 1; its metallographic structure is fine and uniform, and the surface has no undulations;

[0045] Figure 6 This is the metallographic structure of the phosphorus-containing IF steel substrate in Comparative Example 3; its metallographic structure is coarse and uneven, and the surface is undulating;

[0046] Figure 7 The surface of the phosphorus-containing IF steel hot-dip galvanized sheet in Example 1 has no longitudinal color difference;

[0047] Figure 8 The surface of the phosphorus-containing IF steel hot-dip galvanized sheet in Comparative Example 3 has longitudinal color difference;

[0048] Figure 9 This is the surface of the phosphorus-containing IF steel hot-dip galvanized sheet in Comparative Example 7, which has longitudinal color difference. DETAILED DESCRIPTION

[0049] The present invention provides a method for eliminating longitudinal color difference between the head and tail of a hot-dip galvanized sheet of phosphorus-containing IF steel with a yield strength of 180 MPa, comprising the following steps:

[0050] 1) Steelmaking: After hot metal pretreatment → converter smelting → alloy fine-tuning station → RH → continuous casting, the basic chemical composition weight (wt) percentage is controlled as follows: C ≤ 0.003%, Si 0.03~0.09%, Mn 0.50~0.60%, Al 0.03~0.05%, Ti0.025~0.035%, Nb 0.01~0.02%, P 0.032~0.047%, S≤0.006%, N≤0.003%, B 0.008~0.012%, and the balance is Fe and unavoidable impurities to obtain the required composition slab.

[0051] 2) During the hot rolling process, the slab is first heated to 1180-1220°C. After dephosphorization and six passes of rough rolling, it undergoes seven passes of finishing rolling. The finishing rolling starts at a temperature of 1050-1100°C. A three-stage finishing speed is used. The rolling speeds at the head section (Vh) and tail section (Vt) are 30% higher than the rolling speeds at the middle section (Vm) within a 50-meter radius. The middle section rolling speed is 10-11 m / s. The F1 stand inlet and outlet are fully open for secondary descaling. The finishing outlet temperature is 910-950°C. Laminar flow is used to rapidly cool the slab to 630-670°C using a front-stage intensive cooling method. The slab is then coiled and air-cooled. The oxide scale thickness at the edges and center of the hot coil is controlled to 5-10 μm, with a center / edge oxide scale thickness tolerance of ±1 μm.

[0052] 3) After turbulent pickling, the steel is cold rolled with 5 stands at a total reduction of 74-78.3% to obtain a hard rolled coil with a thickness of 0.65 mm.

[0053] 4) The hard-rolled coils are cleaned and degreased, followed by continuous annealing and hot-dip galvanizing. The pre-oxidation chamber temperature is 700-750°C, with an oxygen content of 1.8-2.4%. Compressed air is preheated to 350°C and maintained at a flow rate of ≥280 m³ / h. The annealing temperature is 780-800°C, with a dew point in the heating section set at -45--60°C. The oxygen content in both the heating and cooling sections is controlled at 1-5 ppm. Cooling is performed in an atmosphere of 5% H₂ + 95% N₂ by volume to 480±10°C. During heating, the tension in the heating section of the furnace is controlled at 300-400 kN. The coils then pass through the furnace nose into the zinc bath for hot-dip galvanizing. The zinc bath temperature is maintained at 460±2°C, and a production speed of 110-130 m / min is used.

[0054] 5) The skin-pass working roll adopts a roughness roll with Ra=1.6-1.8μm, the Rpc value of the skin-pass roll is controlled at 120~170, the total skin-pass rolling force in the width direction of the plate is maintained at 300~400 tons, and the skin-pass elongation is set at 0.8-1.0% to ensure the plate shape and mechanical properties.

[0055] The present invention is described in detail below with reference to the embodiments.

[0056] The weight percentages of the chemical components of the phosphorus-containing IF steels in the examples and comparative examples are shown in Table 1. The remainder not shown in Table 1 is Fe and unavoidable impurities.

[0057]

[0058] The hot rolling processes of the phosphorus-containing IF steel in the examples and comparative examples are shown in Table 2.

[0059]

[0060] The cold rolling process, continuous annealing process, and hot-dip galvanizing process of the phosphorus-containing IF steel in the examples and comparative examples are shown in Table 3. The thickness of the substrate is 0.65 mm, and the coating weight is 55 g / m 2 .

[0061] .

[0062] Comparative Example 7

[0063] A phosphorus-containing IF steel hot-dip galvanized, its chemical composition and weight percentage are the same as those in Example 1.

[0064] The production method of hot-dip galvanizing the phosphorus-containing IF steel is carried out according to the production process of Example 1 in Chinese patent CN 116287976 A.

[0065] The longitudinal color difference grades of the finished products of the phosphorus-containing IF steel hot-dip galvanized sheets in the embodiments and comparative examples are shown in Table 4.

[0066] .

[0067] Note: The assessment standard for longitudinal color difference grade is: the steel plate is placed on a horizontal inspection table, the angle between the line of sight and the rolling direction of the steel plate is 45 degrees, and the distance is 30~50cm for visual observation. 2 ) The area ratio of the area with color difference in the steel plate area is graded, among which, level 1: the area ratio of the area with color difference per unit area of ​​the steel plate is 0, and there is no color difference; level 2: the area ratio of the area with color difference per unit area of ​​the steel plate area is 0-2%; level 3: the area ratio of the area with color difference per unit area of ​​the steel plate area is 2-3%; level 4: the area ratio of the area with color difference per unit area of ​​the steel plate area is ≥3%.

[0068] From the above content, it can be seen that the longitudinal color difference grade of the GI galvanized sheet produced according to the manufacturing method provided by the present invention is lower than grade 2.

[0069] In Comparative Examples 1-6, since the parameters required by the present invention were not controlled, the longitudinal color difference level of the GI galvanized sheet was too high.

[0070] In Comparative Example 7, when the production method of Example 1 in Chinese Patent CN 116287976 A is used for production, the phosphorus-containing IF steel hot-dip galvanized steel produced has obvious longitudinal color difference, such as Figure 9 shown.

[0071] The above-mentioned detailed description of a manufacturing method for eliminating the longitudinal color difference between the head and tail of the hot-dip galvanized sheet of phosphorus-containing IF steel with a yield strength of 180 MPa with reference to the embodiment is illustrative rather than restrictive. Several embodiments can be listed according to the limited scope. Therefore, changes and modifications without departing from the overall concept of the present invention should fall within the scope of protection of the present invention.

Claims

1. A method for eliminating longitudinal color difference between the head and tail of a hot-dip galvanized sheet of phosphorus-containing IF steel with a yield strength of 180 MPa, comprising the steps of hot rolling, continuous acid rolling, continuous annealing, hot-dip galvanizing, and skin-passing, characterized in that: 1) In the hot rolling step, the finishing rolling adopts a three-stage finishing rolling speed, the rolling speed within 50 meters of the head and tail is 30% higher than the rolling speed of the middle part, and the coiling temperature is controlled at 630-670°C; 2) In the acid continuous rolling step, the roughness Ra of the final stand roll is controlled within a range of 2.0 to 2.2 μm; 3) During the continuous annealing step, the dew point of the heating section is set to -45 to -60°C, and the oxygen content in the heating section is controlled to be 1 to 5 ppm; 4) During the polishing step, the water pressure at the polishing outlet is 8-10 bar, and the Rpc value of the polishing roller is controlled at 120-170; During the continuous annealing step, the pre-oxidation chamber temperature is 700-750°C, the oxygen content is 1.8-2.4%, and the compressed air is preheated to 350°C and maintained at a flow rate of ≥280m³ / h; The weight percentages of P and B in the phosphorus-containing IF steel with a yield strength of 180 MPa are: P 0.032-0.047%, B 0.008-0.012%.

2. The manufacturing method according to claim 1, characterized in that In the hot rolling step, the heating temperature is controlled at 1180-1220° C., and the heating time is controlled at 180-240 min. The finishing rolling start temperature is controlled at 1050-1100° C., and the finishing rolling outlet temperature is controlled at 910-950° C.

3. The manufacturing method according to claim 1, characterized in that In the hot rolling step, edge heating is used during rolling; full-pass descaling is used during descaling, and secondary descaling water is added to the inlet and outlet of the finishing rolling F1 stand; and a front-stage intensive cooling process is used during controlled cooling.

4. The manufacturing method according to claim 1, characterized in that In the hot rolling step, the thickness of the iron oxide scale at the edge and middle of the hot-rolled plate is controlled to be 5-10 μm, and the thickness deviation of the iron oxide scale at the middle and edge is ±1 μm.

5. The manufacturing method according to claim 1, characterized in that In the acid continuous rolling step, the roughness Ra of the strip entering the final stand is controlled to be 0.6-1.0 μm.

6. The manufacturing method according to claim 1, characterized in that In the continuous annealing step, the tension of the heating section in the annealing furnace is controlled at 300-400 kN.

7. The manufacturing method according to claim 1, characterized in that The chemical composition by weight percentage of phosphorus-containing IF steel with a yield strength of 180 MPa is: C ≤0.003%, Si 0.03~0.09%, Mn 0.50~0.60%, Al 0.03~0.05%, Ti0.025~0.035%, Nb 0.01~0.02%, P 0.032~0.047%, S≤0.006%, N≤0.003%, B 0.008~0.012%, and the balance is Fe and unavoidable impurities.

8. The manufacturing method according to claim 1, characterized in that The metallographic structure of phosphorus-containing IF steel with a yield strength of 180 MPa is a single ferrite with an average grain size of 8.5 to 9.

0.

9. The manufacturing method according to claim 1, characterized in that The 180MPa yield strength grade phosphorus-containing IF steel hot-dip galvanized sheet has an elongation A80 of 34-44%, a work hardening rate n90 value of not less than 0.19, a plastic strain ratio n90 of not less than 1.8, a yield strength of 180-240MPa, and a tensile strength of 340-400MPa.

10. The manufacturing method according to claim 1, characterized in that The yield strength 180MPa grade phosphorus-containing IF steel hot-dip galvanized sheet has a thickness of 0.6-0.7mm and a coating weight of 40-60g / m 2 GI galvanized sheet.

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