500MPa grade aluminum alloy coated hot-formed steel sheet and its production method, hot-formed steel components and applications

Abstract

This invention provides a hot-formed aluminum alloy coated steel sheet with a tensile strength of 500 MPa, its production method, hot-formed steel components, and applications. The composition is: C 0.03–0.12%, Si ≤0.30%, Mn 1.00–2.00%, Cr ≤0.30%, P ≤0.05%, S ≤0.05%, Al 0.01–0.10%, Ti 0.01–0.10%, Nb 0.01–0.10%, N ≤0.01%, 100C / (Mn+Cr+Si) ≥2.50, with the remainder being Fe and unavoidable impurities. Compared with existing technologies, this invention controls the oxidation state of the substrate surface and the thickness fluctuation of the FeAlSi inhibition layer before hot forming through chemical composition and production process control. Ultimately, it controls the size and number of Kirkendall holes after hot forming, ensuring that the hot-formed steel components have excellent coating corrosion resistance and weldability.

Description

Technical Field

[0001] This invention belongs to the field of metallurgical technology and relates to hot-formed steel plates with aluminum alloy coatings and production methods for steel plates with a tensile strength of 500MPa, as well as hot-formed steel components and their applications. Background Technology

[0002] With the rapid development of my country's economy, the acceleration of urbanization, and the increasing urgency of global energy shortages and environmental protection requirements, lightweighting of automobiles has become the future development direction of automobiles. Hot forming technology, utilizing the characteristics of high temperature and easy forming, and possessing high strength after hot forming, is one of the mainstream lightweighting technologies.

[0003] Aluminum-silicon coated hot-formed steel is currently the mainstream material for hot forming due to its excellent high-temperature oxidation resistance and corrosion resistance. Laser-welded hot-formed door rings further improve the level of lightweighting from a structural design perspective. Generally, door rings use materials of different strength levels, such as 500MPa, 1000MPa, and 1500MPa, depending on the different performance requirements of different parts.

[0004] Arcelor-Mittal's laser-welded thermoformed door ring, codenamed Ductibor500, boasts a typical yield strength of 408 MPa, a tensile strength of 657 MPa, and an elongation (A80) of 18.9% after thermoforming. Arcelor-Mittal employs an aluminum-silicon coating thickness between 20 and 33 μm. Because aluminum degrades the weld performance of laser-welded seams, the process involves first partially or completely stripping the aluminum-silicon coating before laser welding, with or without filler wire.

[0005] Yucaitang (Suzhou) Materials Technology Co., Ltd. has proposed that reducing the thickness of the aluminum-silicon coating can improve the impact of aluminum on weld performance, allowing for direct laser welding using filler wire. Their patent CN108588612A, published on September 28, 2018, discloses a hot-stamped forming component, a pre-coated steel sheet for hot stamping, and a hot-stamping forming process, specifying a coating thickness of 3–19 μm before hot stamping for the thin-coated steel sheet. Furthermore, another patent CN111394679A, published on July 10, 2020, discloses a coated steel sheet with a thin aluminum alloy coating and its coating method. This patent, based on a thin coating (5–14 μm), further controls the number and size of Kirkendal pores within 2 μm of the interface between the FeAlSi inhibition layer and the base steel, which helps to further suppress the formation of large-sized pores during hot stamping, thereby improving the resistance spot welding performance of the subsequent hot-stamped forming component.

[0006] However, regardless of whether it is a conventional aluminum-silicon coating (20-33μm) or a thin aluminum-silicon coating (3-19μm), even if the raw material does not have obvious Kirkendal pores, it is difficult to guarantee that large-sized pores will not be formed after hot stamping. However, the above-mentioned existing technologies do not disclose how to solve the problem of Kirkendal pores. Summary of the Invention

[0007] The purpose of this invention is to provide a hot-formed steel sheet with an aluminum alloy coating and a production method for a tensile strength of 500MPa. By controlling the chemical composition of the raw material matrix and the production process, the oxidation state of the matrix surface and the thickness fluctuation of the FeAlSi inhibition layer before hot forming can be controlled, and finally the size and number of Kirkendal holes after hot forming can be controlled.

[0008] Another objective of this invention is to provide hot-formed steel components obtained by hot-forming the aforementioned aluminum alloy coated hot-formed steel sheet with a tensile strength of 500MPa. When the pre-coating layer is thin, the size and number of Kirkendall holes in the aforementioned steel sheet can be controlled after hot forming, ensuring that the hot-formed steel components have good coating corrosion resistance and welding performance.

[0009] Another object of the present invention is to provide applications of hot-formed steel components for automotive parts, especially high-strength automotive parts.

[0010] The specific technical solution of this invention is as follows:

[0011] A hot-formed steel sheet with an aluminum alloy coating and a tensile strength of 500 MPa, comprising a base steel sheet and an aluminum alloy coating, wherein the base steel sheet comprises the following components by weight percentage:

[0012] C: 0.03–0.12%, Si: ≤0.30%, Mn: 1.00–2.00%, Cr: ≤0.30%, P: ≤0.05%, S: ≤0.05%, Al: 0.01–0.10%, Ti: 0.01–0.10%, Nb: 0.01–0.10%, N: ≤0.01%, with the remainder being Fe and unavoidable impurities.

[0013] Preferably, the 500MPa grade aluminum alloy coated hot-formed steel sheet comprises the following components by mass percentage: C: 0.05-0.10%, Si: ≤0.25%, Mn: 1.45-1.80%, Cr: ≤0.30%, P: ≤0.015%, S: ≤0.01%, Al: 0.035-0.060%, Ti: 0.035-0.060%, Nb: 0.01-0.06%, N: ≤0.01%, with the remainder being Fe and unavoidable impurities.

[0014] The steel composition of the aluminum alloy coated hot-formed steel sheet with a tensile strength of 500MPa also meets the following requirement: 100×C / (Mn+Cr+Si)≥2.50;

[0015] When calculating using the above formulas, multiply the content of each element by 100 and substitute it into the formula.

[0016] The aluminum alloy coating of the hot-formed steel sheet with a tensile strength of 500MPa includes a FeAl alloy layer, a FeAlSi suppression layer, and an Al alloy layer; from the base steel sheet to the surface layer, the layers are FeAl alloy layer (thickness <1μm), FeAlSi suppression layer, and Al alloy layer on the outer side thereof.

[0017] The hot-formed steel sheet with aluminum alloy coating has a tensile strength of 500MPa, an aluminum alloy coating thickness of 7-19μm, no oxidation on the surface within 5μm of the base steel sheet, and an FeAlSi inhibition layer thickness of 3-7μm; the FeAlSi inhibition layer thickness fluctuation is ≤40%.

[0018] The design principles for key alloying elements and their contents, using the base steel plate as the substrate, are as follows:

[0019] 0.03% ≤ C ≤ 0.12%: Carbon (C) is the most important element for ensuring strength after hot forming. When the C content is between 0.03% and 0.15%, suitable mechanical strength after hot forming can be guaranteed. Generally, the microstructure of 500MPa hot-formed steel after hot forming is ferrite + martensite + bainite. When the C content is below 0.03%, the hardenability is insufficient during hot forming and cooling, resulting in a larger amount of ferrite structure after hot forming, causing a significant reduction in mechanical strength, and the tensile strength cannot reach 500MPa. When the C content is above 0.12%, a larger amount of martensite structure is formed after hot forming, resulting in higher strength, but a sharp decrease in toughness. Therefore, the C content is determined to be between 0.03% and 0.12%.

[0020] Si ≤ 0.30%: When the Si content is higher than 0.30%, a certain amount of Si oxidation and enrichment will occur on the surface layer (including the surface) of the hot-formed steel substrate during hot rolling and annealing, resulting in incomplete plating or the formation of large Kirkendal voids after hot forming. These problems are particularly pronounced when the hot rolling coiling temperature, annealing temperature, or dew point is too high. Therefore, the Si content is determined to be 0–0.30%.

[0021] 1.00% ≤ Mn ≤ 2.00%, Cr ≤ 0.30%: Mn and Cr elements will also oxidize and enrich on the surface layer (including the surface) of the matrix during hot rolling and annealing. This oxidation enrichment phenomenon is particularly pronounced when the Mn content is higher than 2.00% or the Cr content is higher than 0.30%. Furthermore, Mn and Cr play a role in ensuring hardenability and mechanical strength after hot forming. When the Mn content is lower than 1.00%, hardenability is insufficient during cooling after hot forming, and mechanical strength is significantly reduced. When the Cr content is higher than 0.30%, the above effects are no longer significant. Therefore, the Mn content is determined to be 1.00–2.00%, and the Cr content is determined to be 0–0.30%.

[0022] 100C / (Mn+Cr+Si)≥2.50: The inventors discovered that Mn, Cr, and Si are particularly prone to oxidation enrichment on the surface of the steel matrix during hot rolling and annealing. This phenomenon is exacerbated when the hot rolling temperature, coiling temperature, annealing temperature, or dew point is too high. Subsequent hot-dip galvanizing results in poor surface wettability, leading to incomplete galvanizing and significant porosity defects after hot forming, reducing the corrosion resistance and weldability of the hot-formed parts. However, the degree of oxidation enrichment of Mn, Cr, and Si on the matrix surface is affected by the C content of the matrix. During hot rolling and annealing, decarburization and oxidation enrichment of Mn, Cr, and Si occur simultaneously. If the C, Mn, Cr, and Si content of the matrix satisfies: 100×C / (Mn+Cr+Si)≥2.50, the degree of decarburization on the matrix surface increases, which can significantly reduce the degree of oxidation enrichment of Mn, Cr, and Si on the matrix surface. Therefore, the present invention ensures that the contents of C, Mn, Cr and Si satisfy: 100×C / (Mn+Cr+Si)≥2.50.

[0023] P≤0.05%, S≤0.05%: Excessive sulfur and phosphorus lead to decreased toughness. The P content is 0-0.05%, and the S content is 0-0.05%.

[0024] 0.01% ≤ Al ≤ 0.10%: Al has deoxidizing and nitrogen-precipitating effects. Al is a ferrite stabilizing element. When the Al content is higher than 0.10%, steel is prone to forming δ-ferrite in the high-temperature zone during hot rolling. During hot forming, the δ-ferrite is preserved, deteriorating product performance. In this invention, the Al content is determined to be 0.01% to 0.10%.

[0025] 0.01% ≤ Ti ≤ 0.10%: The main function of adding Ti to steel is to fix nitrogen (N). When the Ti content is below 0.01%, N cannot be sufficiently fixed. When the Ti content is above 0.10%, a large number of large Ti carbides, nitrides, or carbonitrides are formed in the steel, which is detrimental to the toughness of the product. Therefore, the Ti content is determined to be 0.01%–0.10%.

[0026] 0.01% ≤ Nb ≤ 0.10%: Nb improves the uniformity of microstructure, refines grains, and enhances strength and toughness. When the Nb content is below 0.01%, these effects are not significant. When the Nb content is above 0.10%, the effect on improving strength and toughness tends to saturate, and at this point, a large number of large-sized Nb carbides, nitrides, or carbonitrides are formed in the steel. These carbides, nitrides, or carbonitrides are detrimental to the toughness of the product.

[0027] N ≤ 0.01%: When the N content is higher than 0.01%, it easily forms numerous and large-sized Ti and Nb nitrides or carbonitrides, which is detrimental to the toughness of the product. Therefore, the N content is determined to be 0–0.01%.

[0028] The production method of aluminum alloy coated hot-formed steel sheet with a tensile strength of 500MPa provided by the present invention includes the following process flow: steelmaking → continuous casting → hot rolling → pickling and cold rolling → substrate cleaning → annealing → coating → finishing → coiling.

[0029] The steelmaking process is carried out according to the above-mentioned formula and composition.

[0030] The continuous casting process involves injecting refined molten steel into a tundish, which then distributes the molten steel into various crystallizers. After the casting is formed and crystallized, it is pulled out and cut into slabs of a certain length.

[0031] The hot rolling process involves heating the slab in a furnace, rolling it after it exits the furnace, and then coiling it up at a temperature between 350 and 600°C.

[0032] It should be noted that hot rolling temperature control is one of the key processes to prevent significant Si, Mn, and Cr oxidation enrichment on the surface of the steel substrate. This invention, by limiting the Si, Mn, and Cr content in the steel substrate, specifies an upper limit for the hot rolling temperature, significantly reducing the tendency for Si, Mn, and Cr oxidation enrichment on the steel substrate surface, thus ensuring good coating corrosion resistance and weldability of the final product. Furthermore, the coiling temperature should not be lower than 350℃. Below 350℃, a large amount of hard martensite and bainite phases will be generated in the hot-rolled coil, significantly increasing its strength and making subsequent acid rolling difficult.

[0033] When oxidation occurs on the surface of the substrate, the oxidized area is generally concentrated within 5 μm of the surface. Through energy dispersive spectroscopy or glow discharge spectroscopy, obvious enrichment regions or points of O, Si, Mn, and Cr elements are found in this oxidized area. The content of O, Si, Mn, and Cr elements in the enriched regions or points is significantly higher than that in the unoxidized area in the center of the substrate. The content of Si, Mn, and Cr elements in the unoxidized area in the center of the substrate is controlled according to the present invention: Si: ≤0.30%, Mn: 1.00~2.00%, Cr: ≤0.30%.

[0034] The pickling and cold rolling process is characterized by a cold rolling reduction rate of ≤60%; preferably, the cold rolling reduction rate is controlled at 50-60%.

[0035] Hot-rolled steel sheets are further pickled and cold-rolled to obtain pickled and cold-rolled steel sheets. This process removes the iron oxide scale generated on the surface of the steel sheet during hot rolling. To ensure good surface quality after plating, the residual oil content on one side of the hard-rolled coil must be ≤250mg / m² after pickling and cold rolling. 2 Residual iron content ≤100mg / m³ 2 Due to temperature differences across different parts of the steel plate surface during hot rolling, the thickness of the oxide scale formed in different areas is uneven, resulting in an uneven surface after pickling. If there is a certain degree of alloy element oxidation enrichment in the substrate surface layer at this time, pickling cannot completely remove the alloy element oxides from the substrate surface. After pickling, pits form on the surface of the alloy element oxidation areas of the substrate surface. The greater the pickling reduction rate, the more pits there are. The unevenness between the pitted and normal areas, coupled with the presence of alloy elements that were not pickled away in the pitted areas, leads to differences in the Fe-Al reaction rate between the pitted and normal areas during hot-dip galvanizing. This results in a significant difference in the thickness of the FeAlSi inhibitory layer between the pitted and normal areas during hot-dip galvanizing. The large fluctuation in the FeAlSi inhibitory layer thickness causes differences in the degree of diffusion in different parts during hot forming, exacerbating the formation of Kirkendal voids.

[0036] The substrate cleaning process includes: alkaline washing → alkaline brushing → alkaline washing → water brushing → electrolytic cleaning → rinsing → drying. To ensure good surface quality after plating, the residual oil content on one side of the steel plate after cleaning is ≤20mg / m². 2 Single-sided residual iron ≤10mg / m 2 .

[0037] The annealing process, as described in this invention, involves controlling the annealing temperature at 700-850℃, which includes the heating zone temperature and the soaking zone temperature. In this invention, the heating temperature of the annealing zone does not exceed 850℃, the soaking zone temperature does not exceed 850℃, and the temperatures of both the heating and soaking zones should not be lower than 700℃. Furthermore, the annealing furnace controls the dew point inside the furnace to ≤5℃ by adjusting the amount of steam introduced, meaning the dew point of the annealing heating and soaking zones does not exceed 5℃. The atmosphere inside the annealing furnace is N2 and H2, with H2 accounting for 5-10% by volume and the remainder being N2. Introducing 5-10% H2 into the furnace can reduce iron oxides generated by Fe reacting with H2O, O2, etc., thereby ensuring good coating quality before hot forming. Additionally, the oxygen content in the heating and soaking zones is controlled below 50ppm to further reduce the oxidation of the steel substrate.

[0038] The main purpose of the annealing process is to allow the hard-rolled coil to recrystallize, eliminate residual stress, and control the microstructure and properties of the finished coil. The heating and homogenization temperatures should not be lower than 700℃. If the heating and homogenization temperatures are too low, the recrystallization of the hard-rolled coil will be insufficient, which is detrimental to the performance of the finished coil. It should be noted that the annealing process control in this invention is also one of the key processes to prevent the formation of significant Si, Mn, and Cr oxide enrichment on the surface of the steel substrate. This invention, based on limiting the content of Si, Mn, and Cr elements in the steel substrate, specifies the heating temperature, homogenization temperature, dew point, and upper limit of oxygen content, further reducing the tendency of Si, Mn, and Cr oxide enrichment on the surface of the steel substrate, and ensuring good coating corrosion resistance and weldability of the final product.

[0039] The coating process typically involves a plating solution composition of 5–11% Si, 2–4% Fe, with the balance being Al and unavoidable impurities. The hot-dip plating solution temperature is between 600 and 680°C. The substrate temperature should be kept as consistent as possible with the hot-dip plating solution temperature when immersed to minimize steel strip dissolution and aluminum dross formation. The immersion time is 2–10 seconds. After hot-dip plating, nitrogen or compressed air is used to purge the coating thickness, which is controlled to be 7–19 μm on one side. The average thickness of the pre-coating layer is ≥7 μm. The FeAlSi inhibition layer thickness is 3–7 μm. The FeAlSi inhibition layer thickness fluctuation is ≤40%, where the FeAlSi inhibition layer thickness fluctuation = |maximum or minimum thickness - average thickness| / average thickness × 100%, and the average thickness = (maximum thickness + minimum thickness) / 2.

[0040] This invention controls the hot-dip galvanizing bath temperature between 600 and 680°C, preferably 650-680°C. When the hot-dip galvanizing bath temperature exceeds 680°C, the thickness fluctuation of the FeAlSi inhibitory layer formed between the bath and the steel substrate during hot-dip galvanizing increases significantly. This large fluctuation in the FeAlSi inhibitory layer thickness causes differences in the diffusion degree in different parts during hot forming, exacerbating the formation of Kirkendal voids. Furthermore, the melting point of aluminum-silicon alloy is approximately 600°C, and the hot-dip galvanizing bath temperature should not be lower than 600°C. The FeAlSi inhibitory layer thickness fluctuation of this invention is ≤40%. It should be noted that, in order to achieve a FeAlSi suppression layer thickness fluctuation of ≤40%, this invention not only requires controlling the hot-dip plating bath temperature to ≤680℃ and the cold rolling reduction rate to ≤60%, but also that the oxidation and enrichment of alloying elements on the substrate surface can cause excessive fluctuations in the FeAlSi suppression layer thickness after hot-dip plating. To ensure that the FeAlSi suppression layer thickness fluctuation is ≤40% after hot-dip plating, this invention controls the hot rolling coiling temperature to ≤600℃, the annealing temperature to ≤850℃, and the annealing dew point to ≤5℃.

[0041] In this invention, the thickness of the pre-coating layer after hot-dip plating should not be less than 7 μm. The inventors discovered that the thinner the initial coating, the more pronounced the Kirkendal voids become. This is because a thinner initial coating shortens the diffusion path between Fe and Al, increasing the diffusion rate. However, the thinner coating reduces the relative Al content in the coating, decreasing the amount of Al available to fill Fe vacancies, thus exacerbating the formation of large Kirkendal voids. Furthermore, a pre-coating thickness of less than 7 μm easily leads to incomplete plating defects.

[0042] The finishing process involves finishing the coated steel strip to improve the shape of the sheet and control the surface roughness of the coating.

[0043] The winding process involves winding and unwinding the steel strip.

[0044] The hot-formed steel component provided by the present invention is obtained by hot forming of the above-mentioned aluminum alloy coated hot-formed steel sheet with a tensile strength of 500MPa; the specific process includes: blanking → heat treatment → hot stamping.

[0045] The blanking process involves punching or cutting the 500MPa grade aluminum alloy coated hot-formed steel sheet into a blank of the required shape for the hot-formed part.

[0046] The heat treatment involves placing the billet in a heating furnace and heating and holding it at a temperature of 840–970°C. The furnace atmosphere is either air or nitrogen, and the billet remains in the furnace for 2–10 minutes.

[0047] Currently, commonly used heating furnaces include box-type heating furnaces and roller bottom heating furnaces. When using a box-type heating furnace, heating is carried out at a fixed temperature, while when using a roller bottom heating furnace, heating is carried out in sections. In this case, the heating furnace temperature mentioned above refers to the highest heating temperature of the roller bottom heating furnace.

[0048] The hot stamping process involves rapidly transferring the heat-treated blank into a mold for stamping and cooling. The transfer time is no more than 15 seconds, the stamping holding time is 5 to 15 seconds, the cooling and demolding temperature is no more than 250°C, and the cooling rate is ≥30°C / s.

[0049] In the hot-formed steel component, the number of Kirkendal pores with a diameter of 1.0 μm or more in the interdiffusion layer does not exceed 15 per 100 μm;

[0050] Preferably, in the hot-formed steel component, the number of Kirkendal pores with a diameter of 1.0 μm or more in the interdiffusion layer does not exceed 10 per 100 μm;

[0051] More preferably, in the hot-formed steel component, the number of Kirkendal pores with a diameter of 1.0 μm or more in the interdiffusion layer does not exceed 7 per 100 μm;

[0052] After being coated (phosphating, electrophoresis), hot-formed steel components undergo scratch corrosion testing. The maximum corrosion spread width is no more than 4 mm. The number of weld points with a fusion diameter of no less than 5.0 mm is ≥500, and the tensile strength of the hot-formed steel components is ≥500 MPa.

[0053] The application of the hot-formed steel components provided by this invention is in automotive parts, especially high-strength automotive parts.

[0054] The design concept of this invention is as follows:

[0055] The inventors have discovered that regardless of whether it is a conventional aluminum-silicon coating (20–33 μm) or a thin aluminum-silicon coating (3–19 μm), even if the raw material does not have obvious Kirkendal pores, it is difficult to guarantee that large-sized pores will not form after hot stamping. Furthermore, the thinner the coating, the greater the tendency to form large-sized pores after hot stamping. When a large number of large-sized pores form after hot stamping, the corrosion resistance and weldability of the hot-stamped parts will significantly decrease.

[0056] The inventors have discovered that during the heating process of hot-formed steel with aluminum alloy coatings, the significant difference in diffusion rates between Fe and Al easily leads to the formation of Kirkendal voids on the substrate surface. Furthermore, when the substrate surface (including the outer layer) is oxidized before hot forming, the presence of Kirkendal voids (size and number) is significantly aggravated. This is likely because the interdiffusion of Fe and Al is hindered at oxidized areas, making it more difficult for Al to fill the vacancies created by Fe diffusion. Additionally, as the coating thins, the interdiffusion path of Fe and Al shortens and the interdiffusion rate accelerates. However, due to the reduced Al content in the coating, less Al is available to fill Fe vacancies, further exacerbating the formation of large-sized Kirkendal voids. The inventors also found that during the hot forming heating process, the interdiffusion between the steel substrate and the FeAlSi inhibition layer near the substrate is most intense. The uniformity of the FeAlSi inhibition layer thickness in the pre-coated Al-Si coating also significantly affects the formation of Kirkendal voids. When the thickness of the FeAlSi inhibition layer in the pre-coating fluctuates greatly, the diffusion rate varies in different parts of the coating, further intensifying the formation of large-sized Kirkendal voids. In other words, when the pre-coating layer is thin, to ensure that the hot-formed aluminum alloy coated parts have good coating corrosion resistance and weldability, the size and number of Kirkendal holes need to be strictly controlled. At this time, it is necessary to comprehensively control the oxidation state of the substrate surface before hot forming and the thickness fluctuation of the FeAlSi inhibition layer. Among them, the oxidation state of the substrate surface before hot forming is mainly related to the chemical composition of the substrate, the hot rolling process, and the annealing process. The thickness fluctuation of the FeAlSi inhibition layer is not only related to the hot rolling process and the annealing process, but also to the pickling and cold rolling process and the hot-dip galvanizing temperature.

[0057] Compared with existing technologies, this invention controls the oxidation state of the substrate surface and the thickness fluctuation of the FeAlSi inhibition layer before hot forming by controlling the chemical composition of the raw material matrix and the production process. Finally, it controls the size and number of Kirkendal holes after hot forming, ensuring that the hot-formed steel components have good coating corrosion resistance and welding performance. Attached Figure Description

[0058] Figure 1 Example 2: Oxidation state of the steel substrate surface and fluctuation of FeAlSi inhibition layer thickness before hot forming;

[0059] Figure 2 The diagram shows the oxidation state of the steel substrate surface and the thickness fluctuation of the FeAlSi inhibition layer before hot forming in Comparative Example 1.

[0060] Figure 3 This is a diagram showing the state of the Kirkendal holes after thermoforming, as shown in Comparative Example 1. Detailed Implementation

[0061] To further illustrate the invention, a detailed explanation is provided with reference to specific examples.

[0062] The present invention provides a method for producing hot-formed aluminum alloy coated steel sheets with a tensile strength of 500MPa. The specific process is as follows: steelmaking → continuous casting → hot rolling → pickling and cold rolling → substrate cleaning → annealing → coating → finishing → coiling.

[0063] 1) Steelmaking: The steelmaking composition is controlled by mass as follows: C: 0.03~0.12%, Si: ≤0.30%, Mn: 1.00~2.00%, Cr: ≤0.30%, P: ≤0.05%, S: ≤0.05%, Al: 0.01~0.10%, Ti: 0.01~0.10%, Nb: 0.01~0.10%, N: ≤0.01%, and 100C / (Mn+Cr+Si)≥2.50, with the remainder being Fe and unavoidable impurities.

[0064] As an example, the composition of the base steel is shown in Table 1. To control the oxidation and enrichment of Mn, Cr, and Si on the surface of the steel matrix during hot rolling and annealing, this invention specifically limits the content of the three elements and the ratio of C to Mn+Cr+Si: Mn: 1.00–2.00%, Cr: ≤0.30%, Si: ≤0.30%, and 100×C / (Mn+Cr+Si) ≥ 2.50. Specifically, Embodiment Steel 1 and Embodiment Steel 2 are the compositions of this invention. In Comparative Steel 1, the Mn content exceeds the upper limit of this invention, and the 100×C / (Mn+Cr+Si) ratio is lower than the lower limit of this invention. In Comparative Steel 2, the 100×C / (Mn+Cr+Si) ratio is lower than the lower limit of this invention.

[0065] Table 1. Composition of the base steel (wt%)

[0066]

[0067] 2) Continuous casting: The refined molten steel is poured into the tundish, which then distributes the molten steel to each crystallizer. After the casting is formed and crystallized, the casting is pulled out and cut into slabs of a certain length.

[0068] 3) Hot rolling: The slab is heated in a heating furnace, rolled after exiting the furnace, and then coiled at a temperature between 350 and 600°C.

[0069] It should be noted that hot rolling temperature control is one of the key processes to prevent significant Si, Mn, and Cr oxidation enrichment on the surface of the steel substrate. This invention, by limiting the Si, Mn, and Cr content in the steel substrate, specifies an upper limit for the hot rolling temperature, significantly reducing the tendency for Si, Mn, and Cr oxidation enrichment on the steel substrate surface, thus ensuring good coating corrosion resistance and weldability of the final product. Furthermore, the coiling temperature should not be lower than 350℃. Below 350℃, a large amount of hard martensite and bainite phases will be generated in the hot-rolled coil, significantly increasing its strength and making subsequent acid rolling difficult.

[0070] When oxidation occurs on the surface of the substrate, the oxidized area is generally concentrated within 5 μm of the surface. Through energy dispersive spectroscopy or glow discharge spectroscopy, obvious enrichment regions or points of O, Si, Mn, and Cr elements are found in this oxidized area. The content of O, Si, Mn, and Cr elements in the enriched regions or points is significantly higher than that in the unoxidized area in the center of the substrate. The content of Si, Mn, and Cr elements in the unoxidized area in the center of the substrate is controlled according to the present invention: Si: ≤0.30%, Mn: 1.00~2.00%, Cr: ≤0.30%.

[0071] 4) Pickling and Cold Rolling: Hot-rolled steel sheets are further pickled and cold rolled to obtain pickled and cold-rolled steel sheets. This process removes the iron oxide scale generated on the surface of the steel sheet during hot rolling. To ensure good surface quality after plating, the residual oil content on one side of the hard-rolled coil must be ≤250mg / m² after pickling and cold rolling. 2 Residual iron content ≤100mg / m³ 2Due to temperature differences across different parts of the steel plate surface during hot rolling, the thickness of the oxide scale formed in different areas is uneven, resulting in an uneven surface after pickling. If there is a certain degree of alloy element oxidation enrichment in the substrate surface layer at this time, pickling cannot completely remove the alloy element oxides from the substrate surface. After pickling, pits form on the surface of the alloy element oxidation areas of the substrate surface. The greater the pickling reduction rate, the more pits there are. The unevenness between the pitted and normal areas, coupled with the presence of alloy elements that were not pickled away in the pitted areas, leads to differences in the Fe-Al reaction rate between the pitted and normal areas during hot-dip galvanizing. This results in a significant difference in the thickness of the FeAlSi inhibitory layer between the pitted and normal areas during hot-dip galvanizing. The large fluctuation in the FeAlSi inhibitory layer thickness causes differences in the degree of diffusion in different parts during hot forming, exacerbating the formation of Kirkendal voids. This invention achieves an acid rolling reduction rate of ≤60% and a FeAlSi suppression layer thickness fluctuation of ≤40% after hot-dip plating. The FeAlSi suppression layer thickness fluctuation is defined as: |maximum or minimum thickness - average thickness| / average thickness × 100%, where average thickness = (maximum thickness + minimum thickness) / 2. It should be noted that oxidation enrichment of alloying elements on the substrate surface can also cause excessive fluctuations in the FeAlSi suppression layer thickness after hot-dip plating. To ensure that the FeAlSi suppression layer thickness fluctuation is ≤40% after hot-dip plating, this invention controls the hot-rolling coiling temperature to ≤600℃, the annealing temperature to ≤850℃, and the annealing dew point to ≤5℃.

[0072] 5) Substrate Cleaning: Substrate cleaning includes: alkaline washing → alkaline brushing → alkaline washing → water brushing → electrolytic cleaning → rinsing → drying. To ensure good surface quality after plating, the residual oil content on one side of the steel plate after cleaning should be ≤20mg / m². 2 Single-sided residual iron ≤10mg / m 2 .

[0073] 6) Annealing: The main purpose of the annealing process is to restore recrystallization of the hard-rolled coil, eliminate residual stress, and control the microstructure and properties of the finished coil. The heating and homogenization temperatures should not be lower than 700℃. If the heating and homogenization temperatures are too low, the hard-rolled coil will not fully restore recrystallization, which is detrimental to the properties of the finished coil. In this invention, the annealing temperature is controlled between 700-850℃, and the annealing temperature includes the heating section temperature and the homogenization section temperature. In this invention, the heating temperature of the annealing section does not exceed 850℃, the temperature of the homogenization section does not exceed 850℃, and the temperatures of the heating section and the homogenization section should not be lower than 700℃. In addition, the dew point inside the annealing furnace is controlled to be ≤5℃ by adjusting the amount of steam introduced, that is, the dew point of the annealing heating section and the homogenization section does not exceed 5℃. In addition, the dew point inside the annealing furnace is controlled by adjusting the amount of steam introduced. The dew point in the heating section and the soaking section does not exceed 5°C. The atmosphere inside the annealing furnace is N2+H2, with H2 accounting for 5-10% by volume. Introducing 5-10% H2 into the furnace can reduce the iron oxides generated by Fe with H2O, O2, etc., thereby ensuring good coating quality before hot forming. Furthermore, the oxygen content in the heating section and the soaking section is controlled below 50ppm to further reduce the oxidation of the steel substrate.

[0074] It should be noted that the annealing process control in this invention is also one of the key processes to prevent significant oxidation enrichment of Si, Mn, Cr, etc. on the surface of the steel substrate. Based on limiting the content of elements such as Si, Mn, and Cr in the steel substrate, this invention specifies the heating temperature, soaking temperature, dew point, and upper limit of oxygen content, further reducing the tendency of oxidation enrichment of Si, Mn, Cr, etc. on the surface of the steel substrate, and ensuring the good coating corrosion resistance and weldability of the final product.

[0075] 7) Coating: The plating solution consists of aluminum alloy and unavoidable impurities. A typical plating solution includes 5-11% Si and 2-4% Fe by mass, with the balance being Al and unavoidable impurities. The hot-dip plating solution temperature is between 600 and 680°C. The substrate temperature should be kept as consistent as possible with the hot-dip plating solution temperature when it is immersed in the solution to reduce the dissolution of the steel strip and the formation of aluminum dross. The immersion time is 2-10 seconds. After hot-dip plating, nitrogen or compressed air is used to purge the coating thickness. The coating thickness is controlled at 7-19 μm on one side, the average thickness of the pre-coating is ≥7 μm, and the FeAlSi inhibition layer thickness is 3-7 μm; the FeAlSi inhibition layer thickness fluctuation is ≤40%.

[0076] The hot-dip galvanizing bath temperature is ≤680℃. When the hot-dip galvanizing bath temperature exceeds 680℃, the thickness fluctuation of the FeAlSi suppression layer formed between the galvanizing bath and the steel substrate during hot-dip galvanizing increases significantly. This large fluctuation in the FeAlSi suppression layer thickness causes differences in the diffusion degree in different parts during hot forming, exacerbating the formation of Kirkendal voids. In this invention, the FeAlSi suppression layer thickness fluctuation is ≤40%. Furthermore, the melting point of aluminum-silicon alloy is approximately 600℃, and the hot-dip galvanizing bath temperature must not be lower than 600℃. It should be noted that to achieve a FeAlSi suppression layer thickness fluctuation of ≤40%, this invention requires not only controlling the hot-dip galvanizing bath temperature to ≤680℃, but also controlling the hot rolling coiling temperature to ≤600℃, the acid rolling reduction rate to ≤60%, the annealing temperature to ≤850℃, and the annealing dew point to ≤5℃.

[0077] The pre-coating thickness should not be less than 7 μm. The inventors have discovered that the thinner the initial coating, the more pronounced the Kirkendal voids become. This is because a thinner initial coating shortens the interdiffusion path of Fe and Al, accelerating the interdiffusion rate. However, the thinner coating reduces the relative Al content in the coating, decreasing the Al available to fill Fe vacancies, thus further exacerbating the formation of large-sized Kirkendal voids. Furthermore, a pre-coating thickness of less than 7 μm easily leads to incomplete plating defects.

[0078] 8) Finishing: The coated steel strip is finished to improve the shape of the strip and control the surface roughness of the coating.

[0079] 9) Winding: Winding and unwinding the steel strip.

[0080] Hot-formed steel components are made from aluminum alloy coated hot-formed steel sheets with a tensile strength of 500MPa. The specific process is as follows: blanking → heat treatment → hot stamping.

[0081] The blanking process involves punching or cutting the aforementioned 500MPa grade pre-coated aluminum alloy hot-formed steel sheet into a blank of the required shape for the hot-formed part. The typical thickness of the steel sheet in this invention is 1.4mm, and the steel sheet is processed into a template with dimensions of 150×300mm.

[0082] The heat treatment involves placing the billet in a heating furnace and heating and holding it at a temperature of 840–970°C. The furnace atmosphere is either air or nitrogen, and the billet remains in the furnace for 2–10 minutes.

[0083] Currently, commonly used heating furnaces include box-type heating furnaces and roller hearth heating furnaces. When using a box-type heating furnace, heating is performed at a fixed temperature, while when using a roller hearth heating furnace, segmented heating is employed. In this case, the heating furnace temperature mentioned above refers to the highest heating temperature of the roller hearth heating furnace. This invention example uses a box-type resistance heating furnace to heat a pre-coated steel plate, employing a typical heating process, namely a heating temperature of 930℃ and a heating time of 5 minutes.

[0084] The hot stamping process involves rapidly transferring the heat-treated billet into a mold for stamping and cooling. The transfer time is no more than 15 seconds, the stamping holding time is 5–15 seconds, the cooling and demolding temperature is no more than 250°C, and the cooling rate is ≥30°C / s. In this invention, the heat-treated steel plate is placed on a flat quenching mold, pressed, and held under pressure for a certain time. Cooling water is circulated inside the mold to cool the steel plate.

[0085] Pre-coated aluminum alloy-coated hot-formed steel sheets and hot-formed steel components were prepared according to the above process flow. The production process parameters, pre-coating thickness and FeAlSi thickness fluctuation are shown in Table 2.

[0086] The typical plating solution composition used in each embodiment and comparative example is 8-10% Si, 2-4% Fe, with the balance being Al and unavoidable impurities.

[0087] Table 2 Production process parameters, pre-coating thickness, and FeAlSi thickness fluctuation

[0088]

[0089] The oxidation state, coating thickness, and FeAlSi layer thickness of the pre-coated aluminum alloy hot-formed steel plate substrate were observed and analyzed. The porosity of the hot-formed steel components was observed and analyzed. Scratch corrosion tests were performed on the hot-formed steel components after coating. The welding performance and mechanical properties of the hot-formed steel components were also tested.

[0090] The oxidation state of the substrate surface, coating thickness, and FeAlSi layer thickness before thermoforming were mainly observed using scanning electron microscopy. The focus was on the oxidation state within 5 μm of the substrate surface, as this area strongly affects the porosity after thermoforming. When oxidation is present, it is mainly concentrated near the substrate grain boundaries. The composition of this area was analyzed using an energy dispersive spectroscopy (EDS) analyzer. When oxidation is severe, it can even form a crack-like morphology.

[0091] The porosity of hot-formed steel components was observed and analyzed using a scanning electron microscope (SEM). The porosity was mainly found within the interdiffusion layer, which is connected to the steel substrate and is generally composed of αFe + Fe3Al, with an Fe content of not less than 80%. Large-sized porosity, such as those with a diameter greater than 1.0 μm, requires special attention, as these porosity significantly affect the corrosion resistance of coatings and weldability. This invention statistically analyzes the number of large-sized porosity within the interdiffusion layer. The porosity diameter is determined by measuring the longest and shortest diameters of the porosity under the same field of view, and taking half of their sum as the porosity diameter. The number of porosity is determined by counting porosity within a 100 μm range along the surface of the substrate steel within the SEM field of view. It is important to note that when the surface of the raw material substrate is severely oxidized, the pores in the coating may connect after thermoforming, forming a pore area. In this case, the number of pores can be determined by: statistically analyzing the area of ​​the pore area within a 100 μm length along the surface of the steel substrate in the field of view of a scanning electron microscope. The pore area / 1 μm 2 That is, the number of holes.

[0092] After coating, the hot-formed steel components underwent scratch corrosion testing. The coating process included phosphating and electrophoresis. The coating was then subjected to scratch corrosion testing to evaluate paint adhesion and corrosion resistance (a maximum corrosion spread width of no more than 4 mm was considered satisfactory). This invention selected three hot-formed steel plates under the same conditions for scratch corrosion testing, and the average of the maximum corrosion spread widths was used to evaluate paint adhesion and corrosion resistance. The phosphating agents and test parameters listed in Table 3 were used to phosphate the hot-formed samples. Subsequently, the resulting phosphated plates were subjected to electrophoresis (electrophoresis paint model: Kansai HT-8000C), with a dry film thickness of approximately 18 μm. Subsequently, a cyclic corrosion method was used. Each cycle consisted of 8 hours of ambient temperature maintenance (25±3℃, during which 4 sprays of salt solution were performed for 3 minutes each, with the salt solution composition being: 0.9wt% NaCl, 0.1wt% CaCl2, and 0.075wt% NaHCO3), followed by 8 hours of wet heat treatment (49±2℃, 100% RH), and finally 8 hours of drying (60±2℃, <30% RH). A total of 26 cycles were performed to evaluate corrosion resistance.

[0093] Table 3 Phosphating process parameters

[0094]

[0095]

[0096] The welding performance test of hot-formed steel components adopts the GWS-5A standard to evaluate the number of weld points with a fusion diameter of not less than 5.0 mm. Generally, a number of weld points of not less than 500 is considered to meet the requirements.

[0097] Mechanical property testing of hot-formed steel components shall be conducted in accordance with the standard GB / T228.1-2010.

[0098] The results of the oxidation state, porosity, scratch corrosion test, weldability, and mechanical property tests are shown in Table 4.

[0099] Table 4. Results of Oxidation State, Porosity, Scratch Corrosion Tests, Weldability, and Mechanical Properties Tests

[0100]

[0101] This invention controls the oxidation state of the substrate surface and the thickness fluctuation of the FeAlSi inhibition layer before hot forming by controlling the chemical composition of the raw material matrix and the production process. Ultimately, it controls the size and number of Kirkendal pores after hot forming, ensuring that the hot-formed steel components have good coating corrosion resistance and weldability. Specifically:

[0102] (1) Matrix Chemical Composition: To control the oxidation and enrichment of Mn, Cr, and Si on the surface of the steel matrix during hot rolling and annealing, this invention specifically limits the content of the three elements and the ratio of C to Mn+Cr+Si: Mn: 1.00~2.00%, Cr: ≤0.30%, Si: ≤0.30%, and 100×C / (Mn+Cr+Si)≥2.50. Specifically, Implemented Steel 1 and Implemented Steel 2 are the compositions of this invention. In Comparative Steel 1, the Mn content exceeds the upper limit of this invention, and 100×C / (Mn+Cr+Si) is lower than the lower limit of this invention. In Comparative Steel 2, 100C / (Mn+Cr+Si) is lower than the lower limit of this invention. Production process control mainly includes hot rolling coiling temperature ≤600℃, pickling reduction rate ≤60%, annealing temperature ≤850℃, annealing dew point ≤5℃, and hot-dip galvanizing bath temperature ≤680℃. Through the above controls, it is ensured that there is no obvious oxidation on the surface of the raw material matrix, and the thickness fluctuation of the FeAlSi inhibition layer is controlled to be ≤40% (total thickness 7~19μm). In the interdiffusion layer after hot forming, the number of Kirkendal pores with a diameter of 1.0μm or more does not exceed 15 / 100μm. After the hot-formed steel components are coated (phosphating, electrophoresis), scratch corrosion tests are performed, and the maximum corrosion expansion width is not greater than 4mm. The number of weld points with a fusion diameter of not less than 5.0mm in the hot-formed steel components is ≥500.

[0103] It can be seen that when the matrix composition of the present invention is used, namely Examples 1, 2, 3, 4, 5 and Comparative Examples 1, 2, 3, and Examples 1, 2, 5, and the production process of the present invention (hot rolling, pickling, annealing, hot-dip galvanizing) is adopted, it ensures that there is no obvious oxidation on the surface of the raw material matrix and controls the thickness fluctuation of the FeAlSi inhibition layer to ≤40% (see Figure 1Example 2: No oxidation on the substrate surface (FeAlSi suppression layer thickness fluctuation 33%). After final hot forming, the number of Kirkendal pores with a diameter of 1.0 μm or more in the interdiffusion layer does not exceed 15 per 100 μm. After the hot-formed steel component is coated (phosphating, electrophoresis), a scratch corrosion test is performed, and the maximum corrosion expansion width is not greater than 4 mm. The number of weld points with a fusion diameter of not less than 5.0 mm in the hot-formed steel component is ≥500. In contrast, Comparative Examples 1 / 2 / 3 did not employ the production process of this invention. The surface of the raw material matrix showed obvious oxidation (Comparative Examples 1 and 3) or the thickness fluctuation of the FeAlSi inhibition layer was >40% (Comparative Examples 1, 2, and 3). After final hot forming, the number of Kirkendal pores with a diameter of 1.0 μm or more in the interdiffusion layer exceeded 15 per 100 μm. After the hot-formed steel components were coated (phosphating and electrophoresis), scratch corrosion tests were conducted, and the maximum corrosion expansion width was greater than 4 mm. The number of weld points with a fusion diameter of not less than 5.0 mm in the hot-formed steel components was less than 500.

[0104] When the matrix composition of this invention is not used, i.e., comparative examples 4 and 5 (using comparative steels 1 and 2), even if the production process of this invention is used, the surface of the raw material matrix still has obvious oxidation and the thickness fluctuation of the FeAlSi inhibition layer is >40%. This results in more than 15 Kirkendal pores with a diameter of more than 1.0 μm in the interdiffusion layer after hot forming, and the maximum corrosion expansion width is greater than 4 mm after the hot-formed steel component is coated (phosphating, electrophoresis). The number of weld points with a fusion diameter of not less than 5.0 mm in the hot-formed steel component is less than 500.

[0105] In addition, the hot-formed steel using the matrix composition of the present invention has good hardenability and mechanical strength after hot forming, with a tensile strength ≥500MPa after hot forming.

[0106] (2) Production Process: Controlling the hot rolling and annealing processes is crucial to preventing significant oxidation enrichment of Si, Mn, Cr, etc., on the surface of the steel substrate. Specifically, in the hot rolling process, the coiling temperature should be ≤600℃, and in the annealing process, the annealing temperature should be ≤850℃, with an annealing dew point ≤5℃. Controlling the FeAlSi suppression layer thickness fluctuation is related not only to the above processes but also to the acid rolling reduction rate and the hot-dip galvanizing bath temperature; the acid rolling reduction rate should be ≤60%, and the galvanizing bath temperature ≤680℃.

[0107] It can be seen that the matrix composition of this invention was used, but the production process of this invention was not used, namely Comparative Examples 1, 2, and 3. Specifically, the hot rolling coiling temperature of Comparative Example 1 was too high (650℃ > 600℃), and the dew point temperature of Comparative Example 3 was too high (10℃ > 5℃), resulting in obvious oxidation on the surface of the raw material matrix and a FeAlSi inhibition layer thickness fluctuation of >40% (see Comparative Examples 1, 2, and 3). Figure 2Comparative Example 1 shows the energy dispersive spectroscopy (EDS) analysis points / regions 1, 2, and 3 on the oxidized surface of the substrate, and point / region 4 on the unoxidized surface of the substrate (the composition analysis results are shown in Table 5). Comparative Example 2, however, exhibited excessively high acid rolling reduction (63% > 60%) and excessively high plating bath temperature (688℃ > 680℃), resulting in a FeAlSi inhibition layer thickness fluctuation of >40%. Therefore, in Comparative Examples 1, 2, and 3, the number of Kirkendal pores with a diameter greater than 1.0 μm in the interdiffusion layer after thermoforming exceeded 15 per 100 μm (see Table 5). Figure 3 Comparative Example 1): After the hot-formed steel components are coated (phosphating, electrophoresis), a scratch corrosion test is performed. The maximum corrosion spread width is greater than 4 mm, and the number of weld points with a fusion diameter of not less than 5.0 mm is less than 500.

[0108] Table 5 Comparative Example 1 Figure 2 Energy dispersive spectroscopy (EDS) results

[0109]

[0110]

[0111] In summary, for pre-coated aluminum alloy hot-formed steel sheets, the matrix chemical composition and production process of this invention ensure that there is no obvious oxidation on the surface of the raw material matrix, and the FeAlSi inhibition layer thickness fluctuation is ≤40%. In the final hot-formed interdiffusion layer, the number of Kirkendal pores with a diameter of 1.0 μm or more does not exceed 15 per 100 μm. After the hot-formed steel components are coated (phosphating, electrophoresis), the maximum corrosion spread width is not greater than 4 mm. The number of weld points with a fusion diameter of not less than 5.0 mm in the hot-formed steel components is ≥500, and the tensile strength of the hot-formed steel components is ≥500 MPa.

[0112] The above embodiments have described in detail the purpose and effects of the present invention. It should be understood that the above embodiments are only specific embodiments of the present invention, and the present invention is not limited to the above methods. All modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention or using the technical concept and technical solution of the present invention are within the protection scope of the present invention.

Claims

1. A hot-formed steel sheet with an aluminum alloy coating and a tensile strength of 500 MPa, characterized in that, The 500MPa grade aluminum alloy coated hot-formed steel sheet includes a base steel sheet and an aluminum alloy coating. The base steel plate comprises the following components by weight percentage: C: 0.03~0.12%, Si: ≤0.30%, Mn: 1.00~2.00%, Cr: ≤0.30%, P: ≤0.05%, S: ≤0.05%, Al: 0.01~0.10%, Ti: 0.01~0.10%, Nb: 0.01~0.10%, N: ≤0.01%, with the remainder being Fe and unavoidable impurities; The composition of the base steel plate also satisfies: 100×C / (Mn+Cr+Si)≥2.50; The aluminum alloy coating has a thickness of 7~19μm, and the thickness fluctuation of the FeAlSi suppression layer in the aluminum alloy coating is ≤40%. The 500MPa grade aluminum alloy coated hot-formed steel sheet is hot-formed to obtain hot-formed steel components. After hot forming, the number of Kirkendall holes with a diameter of 1.0μm or more in the interdiffusion layer does not exceed 15 per 100μm.

2. The hot-formed aluminum alloy coated steel sheet with a tensile strength of 500 MPa according to claim 1, characterized in that, The base steel plate comprises the following components by weight percentage: C: 0.05~0.10%, Si: ≤0.25%, Mn: 1.45~1.80%, Cr: ≤0.30%, P: ≤0.015%, S: ≤0.01%, Al: 0.035~0.060%, Ti: 0.035~0.060%, Nb: 0.01~0.06%, N: ≤0.01%, with the remainder being Fe and unavoidable impurities.

3. A method for producing a hot-formed aluminum alloy coated steel sheet with a tensile strength of 500 MPa as described in any one of claims 1-2, characterized in that, The production method includes the following process flow: steelmaking → continuous casting → hot rolling → pickling and cold rolling → substrate cleaning → annealing → coating → finishing → coiling. The hot rolling process involves coiling the rolls at a temperature of 350~600℃. The pickling and cold rolling process shall control the pickling reduction rate to ≤60%. The annealing is carried out at a temperature of 700~850℃ and the annealing dew point is ≤5℃. The coating process involves a plating solution temperature of 600~680℃.

4. A hot-formed steel component, characterized in that, It is obtained by hot forming of aluminum alloy coated hot-formed steel sheet with a tensile strength of 500MPa as described in any one of claims 1-2.

5. The hot-formed steel component according to claim 4, characterized in that, In the hot-formed steel component, the number of Kirkendal pores with a diameter of 1.0 μm or more in the interdiffusion layer after hot forming does not exceed 15 per 100 μm.

6. The hot-formed steel component according to claim 4 or 5, characterized in that, After being coated, the hot-formed steel components undergo a scratch corrosion test. The maximum corrosion spread width is no more than 4 mm. The number of weld points with a fusion diameter of not less than 5.0 mm is ≥500. The tensile strength of the hot-formed steel components is ≥500 MPa.

7. An application of the hot-formed steel component according to any one of claims 4-6, characterized in that, Used in automotive parts.

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