Method for improving surface quality of GA ultrahigh-strength steel, GA ultrahigh-strength steel and automobile plate

Abstract

The invention relates to a method for improving the surface quality of GA ultrahigh-strength steel, the GA ultrahigh-strength steel and an automobile sheet, and belongs to the technical field of steel preparation. The method comprises the steps that a casting blank of the GA ultrahigh-strength steel is obtained; the casting blank is heated; the heated casting blank is rolled, the dephosphorization pass and the dephosphorization pressure of rolling are controlled, and hot-rolled strip steel is obtained; the hot-rolled strip steel is subjected to acid rolling, the emulsion concentration, the roller diameter and the roller roughness are controlled, and a cold hard coil is obtained; and zinc plating is conducted on the cold hard coil, the production scheduling mode of zinc plating and the dew point of furnace nose humidification are controlled, and the GA ultrahigh-strength steel is obtained. Through process optimization of surface quality re-control point positions of all procedures such as hot rolling heating, a descaling process, an acid rolling process and a galvanizing process, the occurrence rate of alloying spots and zinc ash defects is reduced, the quality effect of the galvanized surface is guaranteed, and the ideal GA ultrahigh-strength steel surface quality requirement is met.

Description

Technical Field

[0001] This application relates to the technical field of steel preparation, and particularly to a method for improving the surface quality of GA ultra-high strength steel, GA ultra-high strength steel, and automotive sheets. Background Art

[0002] With the advancement of lightweighting in the automotive industry and the increasing requirements of safety standards year by year, the usage ratio of high-strength steel and ultra-high strength steel sheets will continue to increase. Japanese automotive factories have put forward high-end requirements for GA ultra-high strength steel automotive sheets. The demand for ultra-high strength steel of 780 and above levels in Japanese GA products increases month by month, and users require that there should be no obvious defects visible to the naked eye on the surface. However, with the increase in production volume, defects such as surface stripes, alloying traces, and zinc ash on ultra-high strength steel have deteriorated. These defects not only affect the aesthetics of the product but may also pose potential threats to the corrosion resistance, fatigue resistance, and even overall safety of the material.

[0003] Alloying traces usually occur in the galvanizing process. Due to excessive local temperature or too long time during the alloying process of the steel sheet surface, uneven reactions occur between the zinc layer and the steel sheet substrate, forming visible spots or stripes. Zinc ash is an oxide impurity formed on the surface of the galvanizing solution. If not effectively removed, it will leave gray or black granular traces on the steel sheet surface. To solve these problems, manufacturers have continuously explored and optimized the process control of each link in production practice. Traditionally, to improve alloying traces, some manufacturers have tried to adjust the atmosphere in the galvanizing furnace by turning on the furnace nose humidification system. Although this approach can alleviate alloying traces to a certain extent, it may exacerbate the generation of zinc ash problems. Closing the furnace nose humidification system can improve alloying traces by changing the oxidation method (from external oxidation to internal oxidation), but long-term closing will lead to the deterioration of zinc ash problems, forming a dilemma. Summary of the Invention

[0004] This application provides a method for improving the surface quality of GA ultra-high strength steel, GA ultra-high strength steel, and GA ultra-high strength steel automotive sheets to solve the following technical problem: how to improve the surface quality of GA ultra-high strength steel.

[0005] In a first aspect, an embodiment of this application provides a method for improving the surface quality of GA ultra-high strength steel, the method comprising:

[0006] Obtaining a continuous casting billet of GA ultra-high strength steel;

[0007] Heating the continuous casting billet;

[0008] Rolling the heated continuous casting billet and controlling the descaling passes and descaling pressure of the rolling to obtain a hot-rolled strip;

[0009] The hot-rolled strip steel is pickled and cold-rolled, and the emulsion concentration, roll diameter and roll roughness are controlled to obtain a cold-hardened coil.

[0010] The cold-hardened coil is galvanized, and the production scheduling method of the galvanizing and the dew point of the furnace nose humidification are controlled to obtain GA ultra-high strength steel.

[0011] Optionally, the tapping temperature of the heating is 1260 °C to 1290 °C, and the residence time in the furnace of the heating is 160 min to 200 min.

[0012] Optionally, the rolling includes rough rolling and finish rolling. The descaling passes of the rough rolling mill R2 are ≥3, and the descaling pressure of the rough rolling is ≥17 MPa.

[0013] Optionally, the descaling pressure of the finish rolling is ≥22 MPa.

[0014] Optionally, the emulsion cooling and lubrication system for the pickling and cold-rolling includes: No. 1 emulsion tank, No. 2 emulsion tank and No. 3 emulsion tank.

[0015] Optionally, the concentration of the No. 2 emulsion tank is 2.0% to 3.5%, and the concentration of the No. 3 emulsion tank is 0.2% to 1.5%.

[0016] Optionally, the equipment for the pickling and cold-rolling has 5 stands F1 to F5. Among them, the roll diameters of stands F1 to F4 are ≤500 mm, and the roll roughness of stand F5 is 4.1 μm to 4.5 μm.

[0017] Optionally, the production scheduling method of the galvanizing includes: closing the furnace nose humidification, producing the GA ultra-high strength steel for no more than 4 hours, adding at least 2 slag-skimming coils to treat zinc ash, and then opening the furnace nose humidification to produce other steel grades for at least 3 hours.

[0018] Optionally, the dew point of the furnace nose humidification is -35 °C to -50 °C.

[0019] In a second aspect, an embodiment of the present application provides a GA ultra-high strength steel, and the GA ultra-high strength steel is prepared by the method described in the first aspect.

[0020] In a third aspect, an embodiment of the present application provides a GA ultra-high strength steel automotive sheet, and the GA ultra-high strength steel automotive sheet is prepared from the GA ultra-high strength steel described in the second aspect.

[0021] The above technical solutions provided by the embodiments of the present application have the following advantages compared with the prior art:

[0022] An embodiment of the present application provides a method for improving the surface quality of GA ultra-high strength steel. The method includes: obtaining a continuous casting billet of GA ultra-high strength steel; heating the continuous casting billet; rolling the heated continuous casting billet and controlling the descaling passes and descaling pressure during the rolling to obtain a hot-rolled strip; subjecting the hot-rolled strip to acid rolling and controlling the emulsion concentration, roll diameter, and roll roughness to obtain a cold-rolled and hardened coil; galvanizing the cold-rolled and hardened coil and controlling the production scheduling mode of the galvanizing and the dew point of the furnace nose humidification to obtain GA ultra-high strength steel. By optimizing the hot-rolling heating and descaling processes, the surface quality of the hot-rolled coil is improved; by reasonably using the acid rolling emulsion and rolls, the defect ratio of the cold-rolled and hardened coil strip is reduced; by stabilizing the furnace nose humidification dew point and optimizing the production scheduling mode, the incidence of alloying traces and zinc ash defects is reduced, ensuring the quality effect of the galvanized surface and meeting the ideal surface quality requirements of GA ultra-high strength steel. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The accompanying drawings herein are incorporated into the specification and form a part of the specification, showing embodiments consistent with the present application and used together with the specification to explain the principles of the present application.

[0024] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the accompanying drawings required for describing the embodiments or the prior art. Obviously, for those of ordinary skill in the art, other accompanying drawings can also be obtained based on these drawings without creative efforts.

[0025] Figure 1 It is a schematic flow chart of a method for improving the surface quality of GA ultra-high strength steel provided by an embodiment of the present application. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0026] To make the objectives, technical solutions, and advantages of the embodiments of the present application clearer, the following will clearly and completely describe the technical solutions in the embodiments of the present application with reference to the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are some but not all of the embodiments of the present application. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present application without creative efforts belong to the scope of protection of the present application.

[0027] Various embodiments of the present application may exist in the form of a range; it should be understood that the description in the form of a range is only for convenience and brevity, and should not be construed as a rigid limitation on the scope of the present application; therefore, it should be considered that the described range description has specifically disclosed all possible sub-ranges and individual values within that range; for example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and individual numbers within the range, such as 1, 2, 3, 4, 5, and 6, and this applies regardless of the range; in addition, whenever a numerical range is indicated herein, it means including any cited number (fraction or integer) within the indicated range.

[0028] In this document, terms including "comprising" and the like mean "including but not limited to". Relative terms such as "first" and "second" are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. "And / or" describes the associated relationship of associated objects and indicates that three relationships can exist. For example, A and / or B can represent: A exists alone, A and B exist simultaneously, and B exists alone; where A and B can be singular or plural. "At least one" means one or more, and "a plurality" means two or more; "at least one kind", "at least one of the following items (pieces)" or similar expressions refer to any combination of these items, including any combination of single items (pieces) or plural items (pieces); for example, "at least one of a, b, or c", or "at least one of a, b, and c" can both represent: a, b, c, a - b (i.e., a and b), a - c, b - c, or a - b - c, where a, b, and c can be single or multiple respectively. "Parts representation method" such as parts by weight, parts by mass, etc. represents the proportional relationship between each component. In the proportional relationships involved in this document, the parameters that need to be described by proportion should be understood as the antecedents of the proportion formula in the order of description, and the proportional numbers should be understood as the consequents of the proportion formula. For example, if the mass ratio of substance A, substance B, and substance C is 1:2:3, then substance A, substance B, and substance C should correspond one by one with the proportional numbers in the proportion formula in the order of description, that is, the mass of substance A: the mass of substance B: the mass of substance C = 1:2:3.

[0029] Unless otherwise specifically stated, various raw materials, reagents, instruments, equipment, etc. used in this document can be obtained through market purchase or can be prepared by existing methods.

[0030] Figure 1 It is a schematic flow diagram of a method for improving the surface quality of GA ultra-high-strength steel provided for the embodiments of the present application.

[0031] AsFigure 1 As shown in Figure 1 , in a first aspect, an embodiment of the present application provides a method for improving the surface quality of GA ultra-high strength steel, and the method includes:

[0032] S1. Obtain a continuous casting billet of GA ultra-high strength steel;

[0033] First, obtain a continuous casting billet of GA ultra-high strength steel as the starting material. GA ultra-high strength steel, namely Galvanized Alloyed ultra-high strength steel, is a special steel mainly used in fields such as automobiles and aerospace. Its main characteristics are extremely high yield strength and tensile strength, and at the same time, it has good toughness and formability.

[0034] S2. Heat the continuous casting billet;

[0035] Heating the continuous casting billet is to soften the material for subsequent rolling operations. The heating process may need to be adjusted according to specific material compositions and expected product properties.

[0036] In some embodiments, the tapping temperature of the heating is 1260°C to 1290°C, and the residence time in the furnace of the heating is 160 min to 200 min.

[0037] The continuous casting billet is first heated in the furnace. This process is not only to soften the material for subsequent rolling, but also to form a uniform and good oxide film to protect the surface of the continuous casting billet from further oxidation, so as to control the scale formed in the furnace and ensure the surface quality of the continuous casting billet. Controlling the tapping temperature between 1260°C and 1290°C ensures the sufficient heating of the continuous casting billet and appropriate microstructure transformation. Setting the residence time in the furnace to 160 min to 200 min helps to form a stable and dense oxide layer, which has an important impact on the subsequent descaling process and the quality of the final product.

[0038] S3. Roll the heated continuous casting billet and control the descaling passes and descaling pressure of the rolling to obtain hot-rolled strip steel;

[0039] When rolling the heated continuous casting billet, precisely control the descaling passes (i.e., the number of times to remove the oxide scale or scale on the surface of the continuous casting billet) and the descaling pressure to ensure the surface cleanliness and smoothness of the hot-rolled strip steel. Optimizing this step helps to improve the surface quality of the hot-rolled coil and reduce surface defects.

[0040] In the embodiment of the present application, a high-speed steel roll with a uniform and good oxide film on the surface is used to roll the heated continuous casting billet.

[0041] In some embodiments, the rolling includes rough rolling and finish rolling. The descaling passes of the rough rolling mill R2 are ≥3, and the descaling pressure of the rough rolling is ≥17 MPa.

[0042] In some embodiments, the descaling pressure in finish rolling is ≥ 22 MPa.

[0043] In the embodiments of the present application, double rows are opened in finish rolling, that is, in the finish rolling process, two coils of steel are simultaneously fed into the finishing mill for rolling.

[0044] Strip defects are relatively concealed in hot coil products and are difficult to directly detect in the hot rolling stage due to the iron scale covering the surface. These defects usually become apparent after the pickling process, presenting an obvious stripe morphology. After cold rolling, these strip defects may further evolve, showing more obvious surface unevenness or alloying traces. By controlling the descaling passes (≥ 3 times) and descaling pressure (≥ 17 MPa) of the rough rolling mill R2, as well as the descaling pressure (≥ 22 MPa) in finish rolling, the scale on the surface of the slab can be effectively removed, avoiding the formation of strip defects in subsequent processes. The setting of these parameters is based on an in-depth understanding of material properties and the process to ensure the best surface quality of the hot rolled strip.

[0045] S4. Acid rolling is performed on the hot rolled strip, and the emulsion concentration, roll diameter, and roll roughness are controlled to obtain a cold rolled hard coil;

[0046] During acid rolling, by controlling the concentration of the emulsion, the cooling and lubrication effects can be effectively adjusted, thereby affecting the surface quality and dimensional accuracy of the strip. Reasonable selection of the roll diameter and roughness helps to reduce scratches and wear of the strip during rolling, further reducing the defect ratio of the cold rolled hard coil strip.

[0047] In some embodiments, the emulsion cooling and lubrication system for acid rolling includes: No. 1 emulsion tank, No. 2 emulsion tank, and No. 3 emulsion tank.

[0048] In some embodiments, the concentration of the No. 2 emulsion tank is 2.0% - 3.5%, and the concentration of the No. 3 emulsion tank is 0.2% - 1.5%.

[0049] Emulsion plays a crucial role in metal processing. It can not only provide better lubrication effects, reduce friction and wear between tools and workpieces, improve processing efficiency and quality, but also absorb and carry away the heat generated during processing to prevent the workpiece from overheating and deforming. The concentration of the emulsion directly affects the performance and effect of the emulsion. Too high a concentration may lead to excessive foaming, high cost, and poor cooling performance; too low a concentration may result in poor rust prevention, bacteriostatic ability, and lubricity. Therefore, precisely controlling the concentration of the emulsion is crucial.

[0050] In the embodiments of the present application, the concentration of the No. 2 emulsion tank is 2.0% - 3.5%, and it is controlled according to the upper-middle limit; the concentration of the No. 3 emulsion tank is 0.2% - 1.5%, and it is controlled according to the upper-middle limit. Controlling according to the upper-middle limit means that in actual operation, a concentration value close to but not exceeding the upper limit of the concentration range will be selected. That is to say, in the No. 2 emulsion tank, the concentration of the emulsion is set to a higher value within this range to ensure sufficient lubrication and cooling effects. Similarly, in the No. 3 emulsion tank, the concentration of the emulsion is also set to a higher value within the specified range. Such a control strategy helps to maintain the stability and performance of the emulsion, while reducing the adverse effects that may be brought by excessive dilution.

[0051] In some embodiments, the equipment of the acid rolling contains 5 stands F1 - F5. Among them, the roll diameters of the rolls of stands F1 - F4 are ≤500 mm, and the roll roughness of stand F5 is 4.1 μm - 4.5 μm.

[0052] In the embodiments of the present application, the rolling tonnage of stand F5 is ≤1500 tons, and the rolling tonnage refers to the weight of the material that the rolling mill can withstand and process under specific conditions.

[0053] In the acid rolling process, the concentration of the emulsion and the selection of the rolls have a direct impact on the surface quality of the product. By controlling the concentration ranges of the No. 2 and No. 3 emulsion tanks, as well as the roll diameters of stands F1 - F4 and the roll roughness of stand F5, the surface quality of the cold rolled and hardened coil can be further optimized. The setting of these parameters aims to reduce friction and wear during the rolling process, while keeping the roll surface clean and smooth, so as to obtain a cold rolled and hardened coil with good surface quality.

[0054] S5. Galvanize the cold rolled and hardened coil, and control the production scheduling method of the galvanizing and the dew point of the furnace nose humidification to obtain GA ultra-high strength steel.

[0055] By optimizing the production scheduling method of the galvanizing production line, a continuous and stable production process can be ensured, and quality problems caused by production interruptions or switches can be reduced. Stabilizing the dew point of the furnace nose humidification helps to control the temperature and humidity conditions during the galvanizing process, thereby reducing the occurrence of alloying stains and zinc ash defects and ensuring the quality effect of the galvanized surface.

[0056] The galvanizing process is the last step in the preparation of GA ultra-high strength steel. In this step, alloying streaks and zinc ash defects are two issues that require special attention. By exploring the occurrence patterns of alloying streaks and zinc ash defects and taking appropriate measures to balance their occurrence rates, galvanized strip steel with stable quality can be obtained. The method of closing the furnace nose humidification can effectively control alloying streaks, while opening the furnace nose humidification helps reduce the floating of zinc ash. By adopting a production scheduling method of 4+2+3, that is, trying to produce for a period of time after closing the furnace nose humidification, then opening the furnace nose humidification to treat zinc ash and arranging the production of other steel grades, the occurrence rates of these two defects during the production of GA ultra-high strength steel can be effectively controlled.

[0057] In galvanizing production, high-temperature zinc liquid in the furnace nose will generate zinc vapor, and these zinc vapors will condense into zinc ash on the relatively cooler furnace grate cavity walls. If the zinc ash falls onto the strip steel surface, it will affect the surface quality of the strip steel and cause quality problems such as missing plating. Therefore, it is necessary to control the temperature and humidity in the furnace nose to reduce the generation of zinc ash. By humidifying, the dew point in the furnace nose can be lowered, thereby forming an extremely thin zinc oxide protective film on the surface of the zinc liquid to inhibit the volatilization of zinc vapor.

[0058] In some embodiments, the dew point of the furnace nose humidification is -35°C to -50°C.

[0059] The dew point, also known as the dew point temperature, refers to the temperature at which the water vapor in the air reaches the saturation state under a certain pressure. During the steel production process, the temperature and humidity environment in the furnace nose has a significant impact on the microstructure and properties of the product. By controlling the humidification dew point of the furnace nose between -35°C and -50°C, an environment conducive to improving the quality of steel can be created. The temperature and humidity conditions within this range can reduce problems such as cracks and inclusions that may occur during the cooling process of the steel, thereby improving the strength and toughness of the steel.

[0060] In some embodiments, the production scheduling method for galvanizing includes: closing the furnace nose humidification, producing the GA ultra-high strength steel for no more than 4 hours, adding at least 2 slag-removing coils to treat zinc ash, and then opening the furnace nose humidification and producing other steel grades for at least 3 hours.

[0061] The production scheduling method refers to the method by which an enterprise determines the specific arrangements and sequences of production tasks according to factors such as order requirements, production capacity, and resource status during the production process. Different production scheduling methods are applicable to different production environments and requirements, and have important impacts on aspects such as production efficiency, cost control, and delivery date. In the embodiments of this application, first arrange to produce the GA ultra-high strength steel for no more than 4 hours (closing the humidification), then put in at least 2 slag-removing coils to treat zinc ash, and then produce other steel grades that require humidification for at least 3 hours to inhibit the floating of zinc ash. This periodic production scheduling mode helps to balance the relationship between production efficiency and product quality.

[0062] During the production of GA ultra-high strength steel, humidification is turned off to prevent excessive moisture from entering the furnace and affecting the properties of the steel. GA ultra-high strength steel has high requirements for the uniformity and purity of its microstructure. Turning off humidification helps maintain the stability of the furnace environment and reduces the impact of adverse factors on the quality of the steel. Subsequently, at least 2 slag skimming rolls are put into operation to handle zinc ash in order to prevent the accumulation of zinc ash in the furnace. Zinc ash is a by-product generated during the steel production process. If not properly treated, it will adhere to the surface of the steel, affecting the appearance quality and performance of the product. By using the slag skimming rolls to remove slag, the zinc ash in the furnace can be cleaned in a timely manner, ensuring the smooth progress of subsequent production. Finally, the humidification of the furnace nose is turned on, and other steel grades are produced for at least 3 hours to inhibit the floating of zinc ash. In a humid environment, water vapor can react with zinc ash to form compounds that are easier to clean. At the same time, humidification also helps improve the temperature distribution and humidity conditions in the furnace, providing a more stable environment for the production of other steel grades.

[0063] This "4 + 2 + 3" production scheduling method can not only effectively control the occurrence of two major defects, namely alloying traces and zinc ash, but also improve the flexibility and efficiency of the production line. By reasonably arranging the production sequence and time of different steel grades, production resources can be utilized to the maximum extent, reducing production interruptions and waste. In addition, this production scheduling method also helps to improve the consistency of product quality. Through a periodic production scheduling mode, it can ensure that each steel grade is produced under similar environmental conditions, thereby reducing quality fluctuations caused by environmental differences.

[0064] In summary, controlling the dew point of the furnace nose humidification between -35°C and -50°C and adopting the "4 + 2 + 3" production scheduling method is an effective production strategy. It can not only significantly control the occurrence of two major defects, namely alloying traces and zinc ash, but also improve production efficiency and the consistency of product quality, providing strong support for the sustainable development of steel enterprises and the enhancement of their market competitiveness.

[0065] In a second aspect, an embodiment of the present application provides a GA ultra-high strength steel, which is prepared by the method described in the first aspect.

[0066] In a third aspect, an embodiment of the present application provides a GA ultra-high strength steel automotive sheet, which is made of the GA ultra-high strength steel described in the second aspect.

[0067] The following further elaborates on the present application in conjunction with specific embodiments. For the experimental methods without specific conditions indicated in the following embodiments, they are generally determined in accordance with national standards / industry standards; if there are no corresponding national standards / industry standards, they are carried out in accordance with general international standards, conventional conditions, or the conditions recommended by the manufacturer.

[0068] A method for improving the surface quality of GA ultra-high strength steel provided by an embodiment of the present application includes:

[0069] Obtaining a continuous casting billet of GA ultra-high strength steel;

[0070] Heating the continuous casting billet;

[0071] Rolling the heated continuous casting billet and controlling the descaling passes and descaling pressure of the rolling to obtain a hot-rolled strip;

[0072] Acid rolling the hot-rolled strip and controlling the emulsion concentration, roll diameter, and roll roughness to obtain a cold-rolled coil;

[0073] Galvanizing the cold-rolled coil and controlling the production scheduling method of the galvanizing and the dew point of the furnace nose humidification to obtain GA ultra-high strength steel. Specific process parameters are shown in Tables 1-2.

[0074] Table 1

[0075]

[0076] Table 2

[0077]

[0078] About 1000 tons of GA ultra-high strength steel products produced in Examples 1-4 and Comparative Examples 1-2 above were statistically compared and analyzed for alloying traces and the quality degradation rate of zinc ash defects. The results are shown in Table 3.

[0079] Table 3

[0080] Group Total production weight (tons) Defective weight (tons) Defect rate (%) Example 1 1007 7 0.70％ Example 2 1010 16 1.58％ Example 3 1023 9 0.88％ Example 4 982 18 1.83％ Comparative Example 1 1029 68 6.61％ Comparative Example 2 1036 83 8.01％

[0081] As can be seen from Tables 1-3, the preparation process parameters of the examples are all within the required range of the present invention, and the defect incidence rate is reduced to less than 2%, thereby improving the surface quality of the strip, while the defect rates of Comparative Examples 1-2 are about 7%.

[0082] One or more technical solutions in the embodiments of the present invention at least further have the following technical effects or advantages:

[0083] The GA ultra-high strength steel provided by the embodiments of the present invention has a defect incidence rate of less than 2% and good surface quality.

[0084] The above are only specific embodiments of the present application, enabling those skilled in the art to understand or implement the present application. Various modifications to these embodiments will be obvious to those skilled in the art, and the general principles defined in the present application can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to these embodiments shown in the present application, but rather to the broadest scope consistent with the principles and novel features claimed in the present application.

Claims

1. A method for improving the surface quality of GA ultra-high strength steel, the method comprising: Obtaining a GA ultra-high strength steel ingot; heating the ingot; Rolling the heated ingot, and controlling the dephosphorization pass and dephosphorization pressure of the rolling to obtain hot-rolled steel strip; Acid rolling is performed on the hot-rolled steel strip, and the concentration of the emulsion, the diameter of the roll and the roughness of the roll are controlled to obtain a chilled coil; The cold hardened coil is galvanized, and the production scheduling mode of the galvanizing and the dew point of the furnace nose humidification are controlled to obtain GA ultra-high strength steel.

2. The method according to claim 1, characterized in that The heating furnace exit temperature is 1260° C. to 1290° C., and the heating furnace time is 160 min to 200 min.

3. The method according to claim 1, characterized in that The rolling includes rough rolling and finish rolling, the dephosphorization pass of the rolling mill R2 of the rough rolling is ≥3, and the dephosphorization pressure of the rough rolling is ≥17MPa; and / or, The dephosphorization pressure of the finishing rolling is ≥22MPa.

4. The method according to claim 1, characterized in that: The acid rolling emulsion cooling and lubrication system comprises: a No. 1 emulsion tank, a No. 2 emulsion tank and a No. 3 emulsion tank.

5. The method according to claim 4, characterized in that The concentration of the No. 2 emulsion tank is 2.0% to 3.5%, and the concentration of the No. 3 emulsion tank is 0.2% to 1.5%.

6. The method according to claim 1, characterized in that The acid rolling equipment comprises five stands F1 to F5, wherein the roll diameters of the stands F1 to F4 are ≤500 mm, and the roll roughness of the stand F5 is 4.1 μm to 4.5 μm.

7. The method according to claim 1, characterized in that The production scheduling method of galvanizing includes: turning off the furnace nose humidification, producing the GA ultra-high strength steel for no more than 4 hours, adding at least 2 slag rolls to treat the zinc ash, and then turning on the furnace nose humidification to produce other steel grades for at least 3 hours.

8. The method according to claim 1, characterized in that: The dew point of the furnace nose humidification is -35°C to -50°C.

9. A GA ultra-high strength steel, wherein the GA ultra-high strength steel is produced by the method according to any one of claims 1 to 8.

10. A GA ultra-high strength steel automobile sheet, wherein the GA ultra-high strength steel automobile sheet is made of the GA ultra-high strength steel according to claim 9.

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