High cold bend tensile strength 1000mpa grade al alloy coated hot formed steel sheet and production method, hot formed steel component and application

Abstract

The application provides a high-cold-bending tensile strength 1000MPa-grade aluminum alloy coated hot forming steel plate and a production method, a hot forming steel component and an application. The composition comprises C 0.05-0.15%, Si≤0.50%, Mn 1.00-2.50%, Cr≤0.50%, P≤0.05%, S≤0.05%, Al 0.01-0.10%, Ti 0.01-0.10%, B 0.001-0.01%, N≤0.01%, Nb 0.01-0.06%, Mo≤0.30%, and the rest is Fe and inevitable impurities. Compared with the prior art, the chemical composition and the production process are controlled, thereby the surface layer oxidation state of the substrate before hot forming, the thickness fluctuation of the FeAlSi inhibition layer are controlled, and finally the size and quantity of the Cottrell holes after hot forming are controlled, so that the cold bending performance, the coating corrosion resistance and the welding performance of the hot forming steel component are ensured.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of metallurgy, and relates to a 1000MPa-grade high-cold-bending tensile strength Al-Si coating hot forming steel plate and a production method, a hot forming steel component and application. BACKGROUND

[0002] To meet the requirements of automobile lightweight, fuel consumption reduction, pollutant emission reduction and automobile collision safety improvement, the proportion of high-strength steel plates used in automobiles is increasing. Generally, the formability of steel decreases with the increase of strength, and the contradiction between strength and formability can be solved by separating forming and strengthening into two steps. Hot forming technology is a new technology for realizing high-strength automobile parts by heating stamping and then cooling and strengthening.

[0003] At present, the material for hot forming is mainly the Al-Si coating hot forming steel developed by ArcelorMittal, and according to different application scenarios, ArcelorMittal and domestic steel enterprises have developed Al-Si coating hot forming steels of different strength grades, covering 500-2000MPa.

[0004] For the 1000MPa-grade Al-Si coating hot forming steel, in the prior art, on November 1, 2022, Baosteel Co., Ltd. disclosed a patent with the publication number CN115261742A, which disclosed a tensile strength 1000MPa hot stamping part and a manufacturing method thereof, mainly adopting a low-carbon micro-alloying design idea, improving the hardenability through C solid solution strengthening and C / Mn complex to ensure the strength requirement of the hot stamping part, adding trace amounts of Nb, Ti, B and other micro-alloying elements, and controlling 0.24%≤C+Mn / 6≤0.45%, 0.05%≤Nb+Ti+B×10≤0.15%, significantly refining the grain size of the hot stamping part, ensuring that the average grain size of the original austenite of the hot stamping part is ≤10μm, improving the toughness of the high-strength hot stamping part, and the VDA cold bending angle is ≥80°.

[0005] In addition, ArcelorMittal developed a 1000MPa-grade Al-Si coating hot forming steel, product code 1000, the yield strength after hot stamping can reach 800MPa or more, the compressive strength can reach 1000MPa or more, and the VDA cold bending angle is ≥80°.

[0006] However, the cold bending angle of the mainstream 1000MPa-grade Al-Si coating hot forming steel on the market after hot forming is difficult to be stably controlled at 80° or more, which seriously affects the safety performance of automobiles. More importantly, when the hot forming steel is pre-coated with an Al-Si coating, Kirkendall holes are easily formed between the coating and the substrate after hot forming, and a large number of Kirkendall holes obviously deteriorate the corrosion resistance and welding performance of the hot forming after coating. SUMMARY

[0007] The present application provides a high cold bending tensile strength 1000MPa grade aluminum alloy coated hot formed steel sheet and a production method, when the pre-coating is thin, the present application controls the base material substrate chemical composition, production process, thereby controlling the base substrate surface layer oxidation state before hot forming of the 1000MPa grade pre-coated aluminum alloy coated hot formed steel sheet, the thickness fluctuation of the FeAlSi inhibition layer, finally controlling the size and quantity of the Cordenal holes after hot forming, ensuring that the hot formed steel member has good cold bending performance, coating corrosion resistance and welding performance.

[0008] The present application also has a purpose to provide a hot formed steel member obtained by hot forming the above-mentioned high cold bending tensile strength 1000MPa grade aluminum alloy coated hot formed steel sheet.

[0009] The present application also has a purpose to provide the application of the hot formed steel member to automobile parts.

[0010] The specific technical solutions of the present application are as follows:

[0011] The high cold bending tensile strength 1000MPa grade aluminum alloy coated hot formed steel sheet comprises a substrate steel sheet and an aluminum alloy coating layer.

[0012] The substrate steel sheet comprises the following mass percentage components:

[0013] C: 0.05-0.15%, Si: ≤0.50%, Mn: 1.00-2.50%, Cr: ≤0.50%, P: ≤0.05%, S: ≤0.05%, Al: 0.01-0.10%, Ti: 0.01-0.10%, B: 0.001-0.01%, N: ≤0.01%, Nb: 0.01-0.06%, Mo: ≤0.30%, and the rest is Fe and inevitable impurities.

[0014] Preferably, the substrate steel sheet comprises the following mass percentage components:

[0015] C: 0.07-0.12%, Si: 0.15%-0.40%, Mn: 1.30-1.90%, Cr: ≤0.40%, P: ≤0.05%, S: ≤0.05%, Al: 0.01-0.06%, Ti: 0.01-0.06%, B: 0.001-0.005%, N: ≤0.01%, Nb: 0.02-0.06%, Mo: ≤0.30%, and the rest is Fe and inevitable impurities.

[0016] The composition of the base steel sheet of the high cold-bending tensile strength 1000 MPa grade aluminum alloy coated hot-formed steel sheet also satisfies: 100xC / (Mn+Cr+Si)≥3.00;

[0017] The aluminum alloy coating comprises a FeAl alloy layer, a FeAlSi barrier layer and an Al alloy layer; from the base steel sheet to the surface layer, there are the FeAl alloy layer (thickness <1 μm), the FeAlSi barrier layer and the Al alloy layer outside the FeAlSi barrier layer.

[0018] The high cold-bending tensile strength 1000 MPa grade aluminum alloy coated hot-formed steel sheet has no oxidation in the surface layer within 5 μm from the surface of the base steel sheet, and the thickness fluctuation of the FeAlSi barrier layer is ≤40%;

[0019] The thickness of the FeAlSi barrier layer is controlled to be 3-7 μm;

[0020] The key alloying elements in the steel sheet substrate and the design principle of the content are as follows:

[0021] 0.05%≤C≤0.15%: C is the most important strength guarantee element after hot forming, when the content of C is between 0.05% and 0.15%, the good hardenability during hot forming cooling and the mechanical strength after hot forming can be ensured. When the content of C is lower than 0.05%, the hardenability during hot forming cooling is insufficient, and a large amount of ferrite structure is generated after hot forming, which causes the mechanical strength to decrease obviously, and the tensile strength cannot reach 1000 MPa. When the content of C is higher than 0.15%, a large amount of martensite structure is generated after hot forming, and the toughness of the steel sheet decreases sharply. Therefore, the content of C is determined to be 0.05%-0.15%.

[0022] Si≤0.50%: when the content of Si is higher than 0.50%, there is a certain Si oxidation enrichment in the surface layer (including the surface) of the hot-formed steel substrate during hot rolling and annealing, which causes the plating to be leaked or holes to be generated after hot forming. Especially when the hot rolling heating temperature is too high, the coiling temperature is too high, or the annealing temperature is too high, or the dew point is too high, the above problems are more obvious. Therefore, the content of Si is determined to be 0-0.50%.

[0023] 1.00%≤Mn≤2.50%, Cr≤0.50%: Mn and Cr elements are also oxidized and enriched in the surface layer (including the surface) of the substrate during hot rolling and annealing. When the content of Mn is higher than 2.50% or the content of Cr is higher than 0.50%, the above oxidation enrichment phenomenon is particularly obvious. In addition, Mn and Cr have the effect of ensuring the hardenability and the mechanical strength after hot forming, when the content of Mn is lower than 1.00%, the hardenability during hot forming cooling is insufficient, and the mechanical strength decreases obviously, when the content of Cr is higher than 0.50%, the above effect is no longer obvious. Therefore, the content of Mn is determined to be 1.00%-2.50%, and the content of Cr is determined to be 0-0.50%.

[0024] 0.01%≤Nb≤0.06%, Mo≤0.30%: the higher the strength of the hot forming steel, the worse the toughness of the material, the cold bending angle of the mainstream 1000MPa Al-Si coated hot forming steel in the market is difficult to be stably controlled above 80° after hot forming. The present application adds micro-alloying elements Nb and Mo to generate fine and dispersed precipitates in the steel, which has the effect of refining grains and improving strength and toughness. When the content of Nb is less than 0.01%, the effect of improving strength and toughness is not obvious, and when the content of Nb is higher than 0.06% or the content of Mo is higher than 0.30%, the effect of improving strength and toughness tends to be saturated, and at this time, the number of precipitates formed in the steel is large and the size is large, which is not conducive to the toughness of the product. Therefore, the content of Nb is determined to be 0.01-0.06%, and the content of Mo is determined to be 0-0.30%.

[0025] 100xC / (Mn+Cr+Si)≥3.00: the present inventors have found that Mn, Cr and Si are particularly prone to form oxidation enrichment of the above elements on the surface layer of the steel matrix during hot rolling and annealing, especially when the hot rolling heating temperature is too high, the coiling temperature is too high or the annealing temperature is too high, the dew point is too high, the above phenomenon is more obvious, the surface wettability is poor during subsequent hot dipping, causing plating failure, and causing obvious hole defects after hot forming, reducing the corrosion resistance and welding performance of the hot formed parts. But the degree of oxidation enrichment of Mn, Cr and Si on the surface layer of the matrix 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 on the surface layer of the matrix. Decarburization and oxidation of alloying elements are both processes of reacting with oxygen in the environment, and they compete with each other. Different C content and different Mn, Cr and Si content have different decarburization and oxidation enrichment reaction rates. For 1000MPa Al-Si coated hot forming steel, due to the low overall C content, the tendency of Mn, Cr and Si oxidation enrichment on the surface layer of the matrix is large. At this time, in order to inhibit the oxidation enrichment of Mn, Cr and Si on the surface layer of the matrix, the C, Mn, Cr and Si contents of the matrix should satisfy: 100xC / (Mn+Cr+Si)≥3.00, at this time, the decarburization degree of the matrix surface layer increases, which can obviously reduce the oxidation enrichment degree of Mn, Cr and Si on the surface layer of the matrix. Therefore, the present application ensures that the C, Mn, Cr and Si contents satisfy: 100xC / (Mn+Cr+Si)≥3.00.

[0026] P≤0.05%, S≤0.05%: excessive sulfur and phosphorus lead to a decrease in toughness, the P content is 0-0.05%, and the S content is 0-0.05%.

[0027] 0.01%≤Al≤0.10%: Al has the effect of deoxidation and nitrogen precipitation, Al is a ferrite stabilizing element, when Al element is higher than 0.10%, the steel is easy to form delta ferrite at high temperature zone in hot rolling, the delta ferrite is preserved in the hot forming process, which deteriorates the product performance. The Al content of the application is determined to be 0.01-0.10%.

[0028] 0.01%≤Ti≤0.10%: The addition of Ti in the steel is mainly to fix N, when the Ti content is lower than 0.01%, N cannot be fixed sufficiently. When the Ti content is higher than 0.10%, a large number of Ti carbides, nitrides or carbonitrides with large size are formed in the steel, which is not conducive to the toughness of the product. Therefore, the Ti content is determined to be 0.01-0.10%.

[0029] 0.001%≤B≤0.01%: B element improves the hardenability of the steel, when the B content is lower than 0.001%, it cannot fully play its role in improving the hardenability of the steel, when the B content is higher than 0.01%, its role in improving the hardenability of the steel no longer increases, and at this time the BN formed causes the decrease of the toughness of the product. Therefore, the B content is determined to be 0.001-0.01%.

[0030] N≤0.01%: when the N content is higher than 0.01%, it is easy to form a large number of Ti, Nb nitrides or carbonitrides with large size with Ti, Nb, which is not conducive to the toughness of the product. Therefore, the N content is determined to be 0-0.01%.

[0031] The application provides a production method of a high cold-bending tensile strength 1000MPa-grade aluminum alloy coated hot-formed steel plate, and the production process comprises the following steps: steelmaking, continuous casting, hot rolling, pickling and cold rolling, base plate cleaning, annealing, coating, finishing and coiling.

[0032] The steelmaking is performed according to the above-mentioned formula composition;

[0033] The continuous casting: after refining, the molten steel is injected into a tundish, the tundish then distributes the molten steel to each crystallizer, and after the casting is shaped and crystallized, the casting is pulled out and cut into a slab with a certain length.

[0034] The hot rolling: the slab is heated in a heating furnace, then rolled out of the furnace, and then coiled after rolling, and the coiling temperature is between 400-600℃.

[0035] It should be noted that the hot-rolled coiling temperature control is one of the key processes for preventing the formation of obvious Si, Mn and Cr oxidation enrichment on the surface layer of the steel matrix. The present application defines the upper limit of the hot-rolled coiling temperature on the basis of the limited Si, Mn and Cr element content of the steel matrix, significantly reduces the oxidation enrichment trend of Si, Mn and Cr on the surface layer of the steel matrix, and ensures the good cold bending performance, coating corrosion resistance and welding performance of the final product. In addition, the coiling temperature should not be lower than 400℃. If the coiling temperature is lower than 400℃, a large amount of martensite and bainite hard phases will be generated in the hot-rolled coil, which significantly increases the strength of the hot-rolled coil and causes subsequent difficulties in pickling and rolling.

[0036] When the substrate surface layer is oxidized, the oxidation zone is generally concentrated in the surface layer within 5μm from the surface. Through energy spectrum analysis or glow spectrum analysis, there are obvious O, Si, Mn and Cr element enrichment areas or points in the oxidation zone. The O, Si, Mn and Cr element content in the above enrichment areas or points is obviously higher than that in the unoxidized central zone of the substrate. The Si, Mn and Cr element content in the unoxidized central zone of the substrate is controlled according to the present application, i.e. Si:≤0.50%, Mn:1.00-2.50%, and Cr:≤0.50%.

[0037] The pickled cold-rolled steel plate is further pickled and cold-rolled to obtain a pickled cold-rolled steel plate. This process can remove the iron oxide scale generated on the surface of the steel plate during hot rolling. In order to ensure good surface quality after plating, the residual oil content on one side of the hard coil after pickling and cold rolling should be ≤250mg / m 2 , and the residual iron content should be ≤100mg / m 2Due to the temperature difference of different parts of the steel plate surface in the hot rolling process, the thickness of the oxide skin formed by different parts is uneven, and the surface of the steel plate after pickling is uneven. If there is a certain degree of alloy element oxidation enrichment in the surface layer of the substrate at this time, the pickling cannot completely remove the oxide of the alloy element in the surface layer of the substrate, and after the pickling and rolling, the surface of the alloy element oxidation area of the substrate surface forms a pit pattern. When the pickling and rolling reduction is greater, the number of pits is more. The pit area and the normal area itself are uneven, and in addition, the pit area has not been pickled off the alloy element, the pit area and the normal area have different Fe-Al reaction rates during hot dipping, which causes the thickness difference of the FeAlSi inhibition layer during hot dipping to be large, and the thickness fluctuation of the FeAlSi inhibition layer is large, which causes the difference in diffusion degree of different parts during hot forming, and aggravates the formation of Cordenal holes. The pickling and rolling reduction of the present application is ≤60%, which ensures that the thickness fluctuation of the FeAlSi inhibition layer after hot dipping is ≤40%; preferably, the cold rolling reduction is controlled to be 50-60%. It should be noted that the oxidation enrichment of the alloy element in the surface layer of the substrate will also cause the thickness fluctuation of the FeAlSi inhibition layer after hot dipping to be too large, in order to ensure that the thickness fluctuation of the FeAlSi inhibition layer after hot dipping is ≤40%, the present application controls the hot rolling coiling temperature to be ≤600℃, the annealing temperature to be ≤830℃, and the annealing dew point to be ≤5℃.

[0038] The substrate cleaning includes: alkali washing → alkali brushing → alkali washing → water brushing → electrolytic cleaning → rinsing → drying, in order to ensure good surface quality after plating, the residual oil amount of the steel plate after cleaning is ≤20mg / m 2 , the residual iron of one side is ≤10mg / m 2 .

[0039] The annealing temperature is controlled to be 700-830℃; the annealing temperature includes the annealing heating temperature and the soaking temperature, which are controlled according to this temperature range. The main purpose of the annealing process is to make the hard rolled coil recover and recrystallize, eliminate residual stress, and control the organization and performance of the finished coil. The heating and soaking temperatures should not be lower than 700℃, and the heating and soaking temperatures are too low, which is not conducive to the performance of the finished coil.

[0040] The heating temperature of the annealing section is not more than 830 DEG C, and the temperature of the soaking section is not more than 830 DEG C. In addition, the annealing furnace controls the dew point in the furnace by adjusting the amount of water vapor, wherein the annealing dew point temperature is less than or equal to 5 DEG C, that is, the dew point of the heating section and the soaking section is not more than 5 DEG C, the atmosphere in the annealing furnace is N2 and H2, wherein the volume percentage of H2 is 5-10%, and the 5-10% H2 introduced into the furnace can reduce the iron oxide generated by Fe and H2O, O2, etc., thereby ensuring good pre-thermal forming coating quality, and the oxygen content in the heating section and the soaking section is controlled to be less than or equal to 50 ppm, further reducing the oxidation of the steel substrate.

[0041] It should be noted that the annealing process control of the present application is also one of the key processes for preventing the formation of obvious Si, Mn, Cr and other oxidized enrichment on the surface layer of the steel substrate. On the basis of limiting the content of Si, Mn, Cr and other elements in the steel substrate, the present application specifies the upper limit of the heating temperature, the soaking temperature, the dew point and the oxygen content, further reduces the oxidation enrichment trend of Si, Mn, Cr and other elements on the surface layer of the steel substrate, and ensures the good cold bending performance, coating corrosion resistance and welding performance of the final product.

[0042] The plating solution is an aluminum alloy and unavoidable impurities, and a typical plating solution includes the following components by mass percentage: 5-11% Si, 2-4% Fe, and the balance of Al and unavoidable impurities. The hot-dip plating solution temperature is between 600-680 DEG C, preferably, the hot-dip plating solution temperature is 650-680 DEG C; the temperature of the substrate into the plating solution needs to be consistent with the hot-dip plating solution temperature as much as possible to reduce the dissolution of the steel strip and the formation of aluminum slag, the immersion plating time is 2-10 s, nitrogen or compressed air is used to control the coating thickness after hot-dip plating, the pre-coating thickness is controlled to be 7-19 microns on one side, the FeAlSi inhibition layer thickness after hot-dip plating is controlled to be 3-7 microns, and the FeAlSi inhibition layer thickness fluctuation is less than or equal to 40%.

[0043] The hot-dip plating solution temperature is between 600-680 DEG C. When the hot-dip plating solution temperature is higher than 680 DEG C, the FeAlSi inhibition layer thickness fluctuation formed by the plating solution and the steel substrate is significantly increased during hot-dip plating, the large FeAlSi inhibition layer thickness fluctuation causes the difference in diffusion degree in different parts during thermal forming, and aggravates the formation of Kirkendall holes. In addition, the melting point of aluminum-silicon alloy is about 600 DEG C, and the hot-dip plating solution temperature is not less than 600 DEG C. The pre-coating thickness of the present application is controlled to be 7-19 microns on one side, the FeAlSi inhibition layer thickness after hot-dip plating is controlled to be 3-7 microns, and the FeAlSi inhibition layer thickness fluctuation is less than or equal to 40%. It should be noted that in order to achieve the FeAlSi inhibition layer thickness fluctuation of less than or equal to 40%, it is necessary to control the hot-dip plating solution temperature to be less than or equal to 680 DEG C, the acid rolling reduction to be less than or equal to 60%, and the hot-rolled coiling temperature to be less than or equal to 600 DEG C, the annealing temperature to be less than or equal to 830 DEG C, and the annealing dew point to be less than or equal to 5 DEG C.

[0044] Pre-coating thickness should not be less than 7 microns. The present inventors found that the thinner the initial coating, the more obvious the Cottrell holes, because the thinner the initial coating, the shorter the Fe and Al mutual diffusion path, and the faster the mutual diffusion rate, but because the coating is thinned, the relative Al content in the coating is reduced, and the Al available to supplement Fe vacancies is reduced, which further exacerbates the formation of large-size Cottrell holes. In addition, when the coating thickness is less than 7 microns, plating defects are prone to occur.

[0045] Pre-coating thickness should not be greater than 19 microns. Too thick coating reduces the cold bending performance of the final product, and too thick coating increases production cost.

[0046] The finishing: the steel strip after coating is finished to improve the shape and control the surface roughness of the coating.

[0047] The coiling: the steel strip is coiled and offline.

[0048] The present application provides a hot-formed steel member, which is obtained by hot forming the high cold-bending tensile strength 1000 MPa grade aluminum alloy coated hot-formed steel sheet; the specific process flow comprises blanking, heat treatment and hot stamping.

[0049] The blanking: the high cold-bending tensile strength 1000 MPa grade aluminum alloy coated hot-formed steel sheet is punched or cut into a blank of the shape required by the hot-formed part.

[0050] The heat treatment: the blank is heated and held in a heating furnace, the heating furnace temperature is 840-970℃, the heating furnace atmosphere uses air or nitrogen, and the blank stays in the heating furnace for 2-10 minutes.

[0051] The commonly used heating furnace at present is a box-type heating furnace or a roller bottom heating furnace. When a box-type heating furnace is used, the heating is at a fixed temperature, and when a roller bottom heating furnace is used, the heating is in stages. At this time, the heating furnace temperature refers to the highest heating temperature of the roller bottom heating furnace.

[0052] The hot stamping: the blank after heat treatment is quickly transferred to the die for stamping and forming and cooling, wherein the transfer time is not more than 15 seconds, the stamping and forming pressure holding time is 5-15 seconds, the cooling ejection temperature is not more than 250℃, and the cooling speed is ≥30℃ / s.

[0053] The hot-formed steel member, after hot forming, has no more than 15 Cottrell holes with a diameter of 1.0 microns or more per 100 microns in the mutual diffusion layer;

[0054] Preferably, the hot-formed steel member has no more than 8 Cottrell holes with a diameter of 1.0 microns or more per 100 microns in the mutual diffusion layer;

[0055] More preferably, the hot-formed steel member has no more than 6 Cottrell holes per 100 μm of diameter in the inter-diffusion layer.

[0056] The hot-formed steel member has a cold-bending angle of ≥ 85° after baking, a maximum corrosion propagation width of no more than 4 mm after scratch corrosion testing, a weldability welding current range of ≥ 1 kA, and a tensile strength of ≥ 1000 MPa.

[0057] The application provides an application of the hot-formed steel member to an automobile part, in particular, a high-strength automobile part.

[0058] The inventors have found that when the hot-formed steel is pre-coated with an Al-Si coating, Cottrell holes are easily formed between the coating and the substrate after hot forming, and the size and number of the holes are closely related to the state of the raw material coating or steel substrate. When the coating is thinner, the tendency to form large-size holes after hot stamping is greater. More Cottrell holes affect the cold-bending performance of the product after hot forming, so the cold-bending angle of the mainstream 1000 MPa Al-Si coating hot-formed steel on the market after hot forming is difficult to be stably controlled to be greater than 80°, which seriously affects the safety performance of the automobile. More importantly, more Cottrell holes significantly deteriorate the corrosion resistance and welding performance of the hot-formed product after coating.

[0059] The inventors found that due to the large difference in diffusion speed of Fe and Al, Kirkendall holes are easily formed in the surface layer of the substrate during heating, and when there is a certain oxidation on the surface layer of the substrate before hot forming, the situation (size, number) of the Kirkendall holes is significantly aggravated, which may be due to the fact that the mutual diffusion of Fe and Al is blocked at the oxidation site, and after the diffusion of Fe forms vacancies, it is more difficult for Al to supplement the vacancies. In addition, after the coating is thinned, the diffusion distance of Fe and Al is shortened, and the mutual diffusion rate is accelerated, but due to the reduction of the relative Al content in the coating after the coating is thinned, the Al available for supplementing Fe vacancies is reduced, which further aggravates the formation of large-size Kirkendall holes. In addition, the inventors found that during the heating process of hot forming, the mutual diffusion between the steel substrate and the FeAlSi inhibition layer close to the substrate is the most intense, and the uniformity of the thickness of the FeAlSi inhibition layer in the pre-coating layer also has a significant influence on the formation of the Kirkendall holes. When the thickness of the FeAlSi inhibition layer in the pre-coating layer fluctuates greatly, the diffusion rates at different parts of the coating are different, which also aggravates the formation of large-size Kirkendall holes. Large-size Kirkendall holes significantly reduce the coating corrosion resistance and welding performance of the hot-formed part. In addition, Kirkendall holes also affect the cold bending performance of the hot-formed part. It should be noted that the holes may reduce the cold bending performance or improve the cold bending performance. When there are holes between the substrate and the coating after hot forming, decarburization occurs in the surface layer of the substrate during the heating process of hot forming, and the surface layer of the substrate after decarburization is lower in strength and better in plasticity and toughness than the non-decarburized area, but when the hole size is small and the number is small, the decarburized area is small, and the effect of decarburization on the improvement of the cold bending performance is not great, but due to the existence of the holes, the cracks in the hole area will rapidly expand from the coating to the substrate when subjected to stress bending, which significantly reduces the cold bending performance; but when the hole size is large and the number is large, especially when the holes are connected to form a large-area hole area, the surface layer of the hole area is significantly decarburized during the heating process of hot forming, and the large-area hole area can improve the cold bending performance, but the large-area hole area greatly deteriorates the coating corrosion resistance and welding performance of the hot-formed part.

[0060] That is, when the pre-coating layer is thin, in order to ensure that the aluminum alloy coated hot-formed part has stable cold bending performance, good coating corrosion resistance and welding performance, the size and number of Kirkendall holes need to be strictly controlled, and at this time, the oxidation state of the surface layer of the substrate before hot forming and the thickness fluctuation of the FeAlSi inhibition layer need to be comprehensively controlled. The oxidation state of the surface layer of the substrate before hot forming is mainly related to the chemical composition of the substrate and the production process, and the production process mainly includes hot rolling process and 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 related to the pickling process and the hot dipping temperature. In addition, the present application further improves the toughness of the material by adding micro-alloying elements Nb and Mo to refine the grains.

[0061] Compared with the prior art, the application controls the chemical composition of the raw material matrix, the production process, thereby controls the oxidation state of the matrix surface layer before hot forming, the thickness fluctuation of the FeAlSi inhibition layer, finally controls the size and quantity of the Cottrell holes after hot forming, and ensures that the hot-formed steel member has good cold bending performance, coating corrosion resistance and welding performance. In the interdiffusion layer after hot forming, the number of Cottrell holes with a diameter of 1.0 μm or more is not more than 15 per 100 μm, the cold bending angle of the hot-formed steel member after baking is ≥85°, the maximum corrosion propagation width of the hot-formed steel member after coating (phosphating, electrophoresis) and scratch corrosion test is not more than 4 mm, the weldability welding current range of the hot-formed steel member is ≥1 kA, and the tensile strength of the hot-formed steel member is ≥1000 MPa. BRIEF DESCRIPTION OF DRAWINGS

[0062] Figure 1 It is the FeAlSi layer thickness fluctuation graph of the steel matrix surface layer before hot forming of Example 1.

[0063] Figure 2 It is the steel matrix surface layer oxidation state graph before hot forming of Comparative Example 1.

[0064] Figure 3 It is the FeAlSi layer thickness fluctuation graph before hot forming of Comparative Example 2.

[0065] Figure 4 It is the Cottrell hole state graph after hot forming of Comparative Example 1. DETAILED DESCRIPTION

[0066] In order to further illustrate the application, the application will be described in detail in combination with cases.

[0067] The application provides a production method of a high-cold-bending tensile-strength 1000MPa-grade aluminum alloy coated hot-formed steel plate, and the specific process is as follows: steelmaking, continuous casting, hot rolling, pickling and cold rolling, base plate cleaning, annealing, coating, finishing and coiling.

[0068] 1) Steelmaking:

[0069] The preferred steel plate steelmaking composition is controlled as follows in terms of mass: C: 0.05-0.15%, Si: ≤0.50%, Mn: 1.00-2.50%, Cr: ≤0.50%, P: ≤0.05%, S: ≤0.05%, Al: 0.01-0.10%, Ti: 0.01-0.10%, B: 0.001-0.01%, N: ≤0.01%, Nb: 0.01-0.06%, Mo: ≤0.30%, and 100xC / (Mn+Cr+Si)≥3.00, and the rest is Fe and inevitable impurities.

[0070] As an example, the base steel composition is shown in Table 1. The present application controls the oxidation enrichment of Mn, Cr, and Si in the surface layer of the steel base during hot rolling and annealing, and particularly limits the contents of the three elements and the ratio of C to Mn+Cr+Si, i.e., Mn: 1.00-2.50%, Cr: ≤0.50%, Si: ≤0.50%, and 100xC / (Mn+Cr+Si)≥3.00. Among them, the steel 1, steel 2, and steel 3 are the compositions of the present application, and 100xC / (Mn+Cr+Si)≥3.00. In the comparative steel 1, 100xC / (Mn+Cr+Si) is lower than the lower limit 3.00 of the present application.

[0071] Table 1 Base steel composition (wt%)

[0072]

[0073]

[0074] In the base steel composition in Table 1, P: ≤0.05%, and S: ≤0.05%.

[0075] 2) Continuous casting: the refined molten steel is poured into a tundish, the tundish then distributes the molten steel into each crystallizer, and after the casting is shaped and crystallized, the casting is drawn out and cut into a certain length of slab.

[0076] 3) Hot rolling: the slab is heated in a heating furnace, and after being discharged, it is rolled and coiled at a temperature of 400-600°C.

[0077] It should be noted that the hot rolling coiling temperature control is one of the key processes for preventing the formation of obvious Si, Mn, and Cr oxidation enrichment in the surface layer of the steel base. Based on the limitation of the Si, Mn, and Cr element contents of the steel base, the present application specifies the upper limit of the hot rolling coiling temperature, significantly reduces the oxidation enrichment trend of Si, Mn, and Cr in the surface layer of the steel base, and ensures the good cold bending performance, coating corrosion resistance, and welding performance of the final product. In addition, the coiling temperature should not be lower than 400°C. If the coiling temperature is lower than 400°C, a large amount of hard phase of martensite and bainite will be generated in the hot rolling coil, significantly increasing the strength of the hot rolling coil and causing difficulty in subsequent pickling rolling.

[0078] When the surface layer of the base is oxidized, the oxidation zone is generally concentrated in the surface layer within 5 μm from the surface. Through energy spectrum analysis or glow spectrum analysis, there are obvious O, Si, Mn, and Cr element enrichment regions or points in the oxidation zone. The contents of O, Si, Mn, and Cr in the above enrichment regions or points are obviously higher than those in the unoxidized zone of the center of the base. The contents of Si, Mn, and Cr in the unoxidized zone of the center of the base are limited to Si: ≤0.50%, Mn: 1.00-2.50%, and Cr: ≤0.50% according to the present application.

[0079] 4) Pickling cold rolling:

[0080] The hot-rolled steel plate is further pickled and cold-rolled to obtain a pickling cold-rolled steel plate, which can remove the iron oxide scale generated on the surface of the steel plate during the hot-rolling process. In order to ensure good surface quality after plating, the residual oil amount on one side of the steel plate after pickling and cold rolling should be ≤250 mg / m 2 , and the residual iron amount should be ≤100 mg / m 2 . Due to the temperature difference between different parts of the steel plate during the hot-rolling process, the thickness of the iron oxide scale formed at different parts is uneven, and the surface of the steel plate after pickling is uneven. If there is a certain degree of oxidation and enrichment of alloying elements on the surface layer of the substrate at this time, the oxidation of the alloying elements on the surface layer of the substrate cannot be completely removed by pickling, and after acid rolling, a concave morphology is formed on the surface of the oxidation area of the alloying elements on the surface layer of the substrate. The greater the cold rolling reduction, the more the number of concaves. The concave area and the normal area are inherently uneven, and in addition, the concave area has un-pickled alloying elements, so there is a difference in the Fe-Al reaction rate between the concave area and the normal area during hot-dip plating, resulting in a large difference in the thickness of the FeAlSi inhibition layer between the concave area and the normal area during hot-dip plating, and a large fluctuation in the thickness of the FeAlSi inhibition layer, which causes a difference in the diffusion degree between different parts during hot forming, and aggravates the formation of Kirkendall holes. The cold rolling reduction of the present application is ≤60%, which ensures that the thickness fluctuation of the FeAlSi inhibition layer after hot-dip plating is ≤40%. The thickness fluctuation of the FeAlSi inhibition layer is | maximum thickness or minimum thickness - average thickness | / average thickness x 100%, and the average thickness is (maximum thickness + minimum thickness) / 2. It should be noted that the oxidation and enrichment of alloying elements on the surface layer of the substrate will also cause a large fluctuation in the thickness of the FeAlSi inhibition layer after hot-dip plating. In order to ensure that the thickness fluctuation of the FeAlSi inhibition layer after hot-dip plating is ≤40%, the present application controls the hot-rolled coiling temperature to be ≤600℃, the annealing temperature to be ≤830℃, and the annealing dew point to be ≤5℃.

[0081] 5) Substrate cleaning:

[0082] The substrate cleaning includes: alkaline cleaning → alkaline brushing → alkaline cleaning → water brushing → electrolytic cleaning → rinsing → drying. In order to ensure good surface quality after plating, the residual oil amount on one side of the steel plate after cleaning should be ≤20 mg / m 2 , and the residual iron amount should be ≤10 mg / m 2 .

[0083] 6) Annealing: The annealing temperature is controlled in the range of 700-830℃; the annealing temperature includes the annealing heating temperature and the soaking temperature, which are both controlled in the range of 700-830℃.

[0084] The main purpose of the annealing process is to make the hard-rolled coil recover and recrystallize, eliminate residual stress, and control the structure and performance of the finished coil. The heating and soaking temperatures should not be lower than 700℃, and if they are too low, the hard-rolled coil will not recover and recrystallize sufficiently, which is not conducive to the performance of the finished coil.

[0085] The heating temperature of the annealing section is not more than 830 DEG C, and the temperature of the soaking section is not more than 830 DEG C. In addition, the annealing furnace controls the dew point in the furnace by adjusting the amount of water vapor, and the dew point temperature of the annealing is less than or equal to 5 DEG C, that is, the dew point of the heating section and the soaking section is not more than 5 DEG C, the atmosphere in the annealing furnace is N2+H2, and the volume percentage of H2 is 5-10%, the 5-10% H2 introduced into the furnace can reduce the iron oxide generated by Fe and H2O, O2, etc., so as to ensure the good quality of the pre-coating for hot forming, and the oxygen content in the heating section and the soaking section is controlled to be less than or equal to 50 ppm, which further reduces the oxidation of the steel matrix.

[0086] It should be noted that the annealing process control is one of the key processes for preventing the formation of obvious Si, Mn, Cr and other oxidized enrichment on the surface layer of the steel matrix. On the basis of limiting the content of Si, Mn, Cr and other elements in the steel matrix, the upper limit of the heating temperature, the soaking temperature, the dew point and the oxygen content is specified, which further reduces the oxidation enrichment trend of Si, Mn, Cr and other elements on the surface layer of the steel matrix, and ensures the good cold bending performance, coating corrosion resistance and welding performance of the final product.

[0087] 7) Coating: the coating solution is an aluminum alloy and inevitable impurities, the target control of the coating solution is 8-10% Si, 2-4% Fe, and the balance is Al and inevitable impurities. The hot dip coating solution temperature is between 600-680 DEG C, the temperature of the substrate into the coating solution needs to be consistent with the hot dip coating solution temperature as much as possible to reduce the dissolution of the steel strip and the formation of aluminum slag, the immersion coating time is 2-10 s, nitrogen or compressed air is used to control the coating thickness after hot dip coating, the coating thickness is controlled to be 7-19 mu m on a single side, the FeAlSi suppression layer thickness after hot dip coating is controlled to be 3-7 mu m, and the thickness fluctuation of the FeAlSi suppression layer is less than or equal to 40%.

[0088] The hot dip coating solution temperature is between 600-680 DEG C. When the hot dip coating solution temperature is higher than 680 DEG C, the thickness fluctuation of the FeAlSi suppression layer formed by the coating solution and the steel matrix is obviously increased during hot dip coating, the large thickness fluctuation of the FeAlSi suppression layer causes the difference in the diffusion degree of different parts during hot forming, and aggravates the formation of Cottrell holes. In addition, the melting point of aluminum-silicon alloy is about 600 DEG C, and the hot dip coating solution temperature is not less than 600 DEG C. The thickness fluctuation of the FeAlSi suppression layer is less than or equal to 40% according to the present application. It should be noted that in order to realize the thickness fluctuation of the FeAlSi suppression layer being less than or equal to 40%, it is necessary to control the hot dip coating solution temperature to be less than or equal to 680 DEG C, and also need to control the oxidation enrichment of alloy elements on the surface layer of the substrate, therefore, it is necessary to control the hot rolling coiling temperature to be less than or equal to 600 DEG C, the pickling reduction rate to be less than or equal to 60%, the annealing temperature to be less than or equal to 830 DEG C, and the annealing dew point to be less than or equal to 5 DEG C.

[0089] The thickness fluctuation of the FeAlSi suppression layer is less than or equal to 40%.

[0090] Pre-coating thickness should not be less than 7μm. The inventors found that the thinner the initial coating, the more obvious the Cottrell holes, because the thinner the initial coating, the shorter the mutual diffusion distance of Fe and Al, and the faster the mutual diffusion rate, but because the coating is thinned, the relative Al content in the coating is reduced, and the Al available to supplement Fe vacancies is reduced, which further exacerbates the formation of large-size Cottrell holes. In addition, when the coating thickness is less than 7μm, plating defects are prone to occur.

[0091] Pre-coating thickness should not be greater than 19μm. Too thick coating reduces the cold bending performance of the final product, and too thick coating increases production cost.

[0092] 8) Finishing: the steel strip is finished after coating to improve the shape and control the surface roughness of the coating.

[0093] 9) Coiling: the steel strip is coiled and offline.

[0094] A hot-formed steel member is prepared from the high-cold-bending tensile strength 1000MPa grade aluminum alloy coated hot-formed steel sheet produced by the above process, and the specific process is: blanking → heat treatment → hot stamping.

[0095] The blanking:

[0096] The above-mentioned one tensile strength 1000MPa grade pre-coated aluminum alloy coated hot-formed steel sheet is punched or cut into a blank of the shape required for the hot-formed part. The thickness of the steel sheet is selected as a typical value of 1.4mm, and the steel sheet is processed into a sample plate with a size of 150×300mm.

[0097] The heat treatment:

[0098] The blank is heated and held in a heating furnace, the heating furnace temperature is 840-970℃, the heating furnace atmosphere uses air or nitrogen, and the blank stays in the heating furnace for 2-10min.

[0099] The commonly used heating furnace at present is a box-type heating furnace or a roller bottom heating furnace. When a box-type heating furnace is used, it is heated at a fixed temperature, and when a roller bottom heating furnace is used, it is heated in stages. At this time, the above-mentioned heating furnace temperature refers to the highest heating temperature of the roller bottom heating furnace. The inventors use a box-type resistance heating furnace to heat the pre-coated steel sheet, and use a typical heating process, i.e. heating temperature 930℃, heating time 5min.

[0100] The hot stamping:

[0101] The hot treated blank is quickly transferred into a die for stamping forming and cooling, wherein the transfer time is not more than 15s, the stamping forming pressure maintaining time is 5-15s, the cooling ejection temperature is not more than 250℃, and the cooling speed is ≥30℃ / s. The hot treated steel plate is pressed and pressure maintained for a certain time on a flat plate quenching die, and the steel plate is cooled by cooling water in the die.

[0102] The pre-coated aluminum alloy coated hot forming steel plate and hot forming steel member are prepared according to the above process flow, the production process parameters, pre-coating thickness and FeAlSi thickness fluctuation are shown in Table 2.

[0103] Table 2 Production process parameters, pre-coating thickness, FeAlSi thickness fluctuation

[0104]

[0105]

[0106] The above pre-coated aluminum alloy coated hot forming steel plate substrate surface layer oxidation state, coating thickness, FeAlSi layer thickness are observed and analyzed, the hot forming steel member hole condition is observed and analyzed, the cold bending performance of the hot forming steel member is tested, the scratch corrosion test is carried out after the hot forming steel member is coated, and the welding performance and mechanical properties of the hot forming steel member are tested.

[0107] Among them, the substrate surface layer oxidation state, coating thickness and FeAlSi layer thickness before hot forming are mainly observed and analyzed by scanning electron microscope, and the oxidation state within 5μm of the substrate surface layer is focused on, because this part of the area strongly affects the hole condition after hot forming, when oxidation exists, the oxidation is mainly concentrated near the substrate grain boundary, the composition analysis of this area is carried out by energy spectrum analyzer, when the oxidation is serious, even a crack-like morphology is formed.

[0108] The hole condition of the hot-formed steel member is observed and analyzed by a scanning electron microscope. The holes mainly exist in the interdiffusion layer, wherein the interdiffusion layer is connected with the steel matrix and is generally composed of αFe+Fe3Al, and the content of Fe is not less than 80%. It is necessary to focus on the large-size holes, such as the holes with a diameter greater than 1.0 μm, which have a greater impact on the coating corrosion resistance and welding performance. The present application counts the number of large-size holes in the interdiffusion layer, and the determination method of the diameter of the hole is as follows: in the same field of view, the longest diameter and the shortest diameter of the hole are measured, and half of the sum of the two is taken as the diameter of the hole. The determination method of the number of holes is as follows: in the field of view of the scanning electron microscope, the holes in the range of 100 μm along the surface of the base steel are counted. It should be noted that when the surface layer of the raw material base is seriously oxidized, the coating holes after hot forming may be connected to form a hole area. At this time, the determination method of the number of holes is as follows: in the field of view of the scanning electron microscope, the area of the hole region in the range of 100 μm along the surface of the base steel is counted, and the hole area / 1 μm 2 That is, the number of holes.

[0109] The hot-formed steel member is subjected to a baking process in a simulated automobile paint spraying process, the baking temperature is 170℃, the baking time is 20 min, and the cold bending performance of the hot-formed steel member after baking is tested, and the test standard adopts VDA238-100.

[0110] The hot-formed steel member is subjected to scratch corrosion test after coating, the coating includes phosphating and electrophoresis, and the scratch corrosion test is performed on the coating after coating to evaluate the paint adhesion and corrosion resistance (when the maximum corrosion expansion width is not greater than 4 mm, the requirement is met). The present application selects three hot-formed steel plates under the same conditions to perform scratch corrosion test, and the average value of the maximum corrosion expansion width is taken to evaluate the paint adhesion and corrosion resistance. The hot-formed sample is subjected to phosphating treatment by using the phosphating agent and test parameters in Table 3, and then the obtained phosphating plate is subjected to electrophoresis (electrophoretic paint type: Kosei HT-8000C), and the dry film thickness of the electrophoresis is about 18 μm. Then, the corrosion resistance is evaluated by using a cyclic corrosion method, and a single cycle includes 8 h of normal temperature maintenance (25±3℃), 4 times of spraying of salt solution for 3 min each time during the period, the composition of the salt solution is: 0.9wt% of NaCl, 0.1wt% of CaCl2, and 0.075wt% of NaHCO3, then 8 hours of wet heat (49±2℃, 100% RH), and finally 8 hours of drying (60±2℃, <30% RH), a total of 26 cycles.

[0111] Table 3: Phosphating process parameters

[0112]

[0113]

[0114] The hot-formed steel member welding performance test is tested by GWS-5A standard, and the corresponding welding current range is measured at three welding times (240s, 270s, 300s), and only when the welding current range at the three times is greater than or equal to 1kA, the requirement is met.

[0115] The hot-formed steel member mechanical property test is tested by GB / T228.1-2010.

[0116] The above oxidation state, hole, cold bending performance, scratch corrosion test, welding performance, mechanical property test results are shown in Table 4.

[0117] Table 4 Oxidation state, hole, scratch corrosion test, welding performance, mechanical property test results

[0118]

[0119] The present application controls the chemical composition of the raw material matrix, the production process, thereby controls the oxidation state of the matrix surface layer before hot forming, the thickness fluctuation of the FeAlSi inhibition layer, finally controls the size and number of Cokendal holes after hot forming, ensures that the hot-formed steel member has good cold bending performance, coating corrosion resistance and welding performance, in particular:

[0120] 1) The chemical composition of the matrix: the preferred steelmaking composition is controlled as follows in mass: C: 0.05-0.15%, Si: ≤0.50%, Mn: 1.00-2.50%, Cr: ≤0.50%, P: ≤0.05%, S: ≤0.05%, Al: 0.01-0.10%, Ti: 0.01-0.10%, B: 0.001-0.01%, N: ≤0.01%, Nb: 0.01-0.06%, Mo: ≤0.30%, and 100C / (Mn+Cr+Si)≥3.00, the rest is Fe and unavoidable impurities.

[0121] The present application is to control the oxidation enrichment of Mn, Cr and Si in the surface layer of the steel matrix during hot rolling and annealing, and the content of the three elements and the ratio of C and Mn+Cr+Si are particularly limited, Mn: 1.00-2.50%, Cr: ≤0.50%, Si: ≤0.50%, and 100C / (Mn+Cr+Si)≥3.00. Among them, the steel 1, the steel 2 and the steel 3 are the components of the present application, and 100C / (Mn+Cr+Si)≥3.00, and the 100C / (Mn+Cr+Si) in the comparative steel 1 is lower than the lower limit 3.00 of the present application. The production process control mainly includes hot rolling coiling temperature ≤600℃, pickling reduction rate ≤60%, annealing temperature ≤830℃, annealing dew point ≤5℃, hot dip plating liquid temperature ≤680℃. Through the above control, it is ensured that the surface layer of the raw material matrix has no obvious oxidation, and the thickness fluctuation of the FeAlSi inhibition layer is controlled to be ≤40%, the thickness of the FeAlSi inhibition layer after hot dip plating is controlled to be 3-7μm, the total thickness of the pre-coating layer is 7-19μm, the number of Cottrell holes with a diameter of more than 1.0μm in the interdiffusion layer after hot forming is not more than 15 / 100μm, the cold bending angle of the hot formed steel member after baking is ≥85°, the maximum corrosion expansion width of the hot formed steel member after coating (phosphating, electrophoresis) is not more than 4mm, and the weldability welding current range of the hot formed steel member is ≥1kA.

[0122] It can be seen that when the matrix component of the present application is used, i.e. examples 1, 2, 3, 4, 5, 6 and comparative examples 1, 2, 3, 4, 5, examples 1, 2, 3, 4, 5, 6 use the production process (hot rolling, pickling, annealing, hot dip plating) of the present application, it is ensured that the surface layer of the raw material matrix has no obvious oxidation, and the thickness fluctuation of the FeAlSi inhibition layer is controlled to be ≤40% (see Figure 1 , example 1, the surface layer of the matrix is 5μm without oxidation, the thickness of the FeAlSi inhibition layer is 4-6μm, the thickness fluctuation of the FeAlSi inhibition layer is 20%), the number of Cottrell holes with a diameter of more than 1.0μm in the interdiffusion layer after hot forming is not more than 15 / 100μm, the cold bending angle of the hot formed steel member after baking is ≥85°, the maximum corrosion expansion width of the hot formed steel member after coating (phosphating, electrophoresis) is not more than 4mm, and the weldability welding current range of the hot formed steel member is ≥1kA. While comparative examples 1, 2, 3, 4, 5 do not use the production process of the present application, the thickness of the pre-coating layer, the number of Cottrell holes with a diameter of more than 1.0μm in the interdiffusion layer after hot forming is more than 15 / 100μm, the cold bending angle of the hot formed steel member after baking cannot be stabilized at more than 80°, the maximum corrosion expansion width of the hot formed steel member after coating (phosphating, electrophoresis) is more than 4mm, and the weldability welding current range of the hot formed steel member is less than 1kA.

[0123] When the base component of the present application is not used, i.e. Comparative Example 6 (Comparative Steel 1), in which 100C / (Mn+Cr+Si) is 2.21, lower than the lower limit of the present application 3.00, even if the production process of the present application and the pre-coating thickness are used, there is still obvious oxidation on the surface layer of the raw material base, and the thickness fluctuation of the FeAlSi inhibition layer exceeds 40%, resulting in that after hot forming, the number of Cottrell holes with a diameter of 1.0 μm or more in the interdiffusion layer is more than 15 per 100 μm, the maximum corrosion propagation width of the hot-formed steel member after coating (phosphating, electrophoresis) is greater than 4 mm, and the weldability welding current range of the hot-formed steel member is less than 1 kA.

[0124] At the same time, the hot-formed steel using the base component of the present application has good hardenability and mechanical strength after hot forming, and the tensile strength after hot forming is ≥1000 MPa.

[0125] 2) Production process: the hot rolling process and annealing process control are the key processes for preventing obvious oxidation and enrichment of Si, Mn, Cr, etc. on the surface layer of the steel base. Among them, in the hot rolling process, the coiling temperature is ≤600℃, in the annealing process, the annealing temperature is ≤830℃, and the annealing dew point is ≤5℃. Controlling the thickness fluctuation of the FeAlSi inhibition layer is related to the above processes, and also related to the pickling reduction and hot dip plating bath temperature, in which the pickling reduction is ≤60%, and the plating bath temperature is ≤680℃.

[0126] It can be seen that the base component of the present application is used, but the production process of the present application is not used, i.e. Comparative Examples 1, 2, 3, 4, specifically, the hot rolling coiling temperature of Comparative Example 1 is too high (655℃>600℃), the annealing temperature of Comparative Example 2 is too high (850℃>830℃), the annealing dew point of Comparative Example 3 is too high (10℃>5℃), resulting in that there is obvious oxidation on the surface layer of the raw material base (see Figure 2 , the composition analysis results of the energy spectrum analysis points / areas 25, 26, 27 on the oxidized surface layer of Comparative Example 1 and the energy spectrum analysis point / area 28 on the unoxidized base are shown in Table 5), and the thickness fluctuation of the FeAlSi inhibition layer exceeds 40% (see Figure 3 , and the pickling reduction of Comparative Example 4 is too high (65%>60%), and the plating bath temperature is too high (695℃>680℃), resulting in that the thickness fluctuation of the FeAlSi inhibition layer exceeds 40%, therefore, the number of Cottrell holes with a diameter of 1.0 μm or more in the interdiffusion layer after hot forming of Comparative Examples 1, 2, 3, 4 is more than 15 per 100 μm (see Figure 4Comparative Example 1: The number of Kirkendal pores with a diameter of 1.0 μm or more is 16 per 100 μm. The cold bending angle of the hot-formed steel component after baking cannot be stabilized above 80°. The maximum corrosion spread width of the hot-formed steel component after coating (phosphating, electrophoresis) is greater than 4 mm. The weldability current range of the hot-formed steel component is less than 1 kA.

[0127] 3) Pre-coating thickness: The coating thickness of this invention is controlled at 7–19 μm on a single side, and the coating thickness should not be less than 7 μm. The inventors have found 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, due to the reduced Al content in the coating, the amount of Al available to fill Fe vacancies decreases, further exacerbating the formation of large-sized Kirkendal voids. Furthermore, a coating thickness less than 7 μm is prone to incomplete plating defects.

[0128] It can be seen that, although the surface of the raw material matrix of Comparative Example 5 is not obviously oxidized and the thickness fluctuation of the FeAlSi inhibition layer is controlled to be ≤40%, the pre-coating thickness of Comparative Example 5 is too thin (6μm<7μm). After hot forming, the number of Kirkendal pores with a diameter of more than 1.0μm in the interdiffusion layer exceeds 15 / 100μm. The cold bending angle of the hot-formed steel component after baking is <80°. After the hot-formed steel component is coated (phosphating, electrophoresis), the maximum corrosion expansion width is greater than 4mm. The weldability current range of the hot-formed steel component is less than 1kA.

[0129] Table 5 Comparative Example 1 Figure 2 Energy dispersive spectroscopy (EDS) results

[0130]

[0131] In summary, by employing the raw material matrix chemical composition, production process, and pre-coating thickness of this invention, the oxidation state of the matrix surface and the fluctuation of the FeAlSi inhibition layer thickness are controlled before hot forming. Ultimately, the size and number of Kirkendal pores after hot forming are controlled, ensuring that the hot-formed steel components possess excellent cold bending performance, coating corrosion resistance, and weldability. Specifically, within the interdiffusion layer after hot forming, the number of Kirkendal pores with a diameter greater than 1.0 μm does not exceed 15 per 100 μm; the cold bending angle of the hot-formed steel component after baking is ≥85°; after coating (phosphating, electrophoresis), the maximum corrosion spread width of the hot-formed steel component is not greater than 4 mm during scratch corrosion testing; the weldability current range of the hot-formed steel component is ≥1 kA; and the tensile strength of the hot-formed steel component is ≥1000 MPa.

[0132] The above embodiments have described the purposes and implementation effects of the present application in detail, and it should be understood that the above embodiments are only specific embodiments of the present application, and the present application is not limited by the above embodiments, and various modifications, equivalent replacements, improvements, etc. within the spirit and principles of the present application or using the technical concepts and technical solutions of the present application are within the protection scope of the present application.

Claims

1. A hot-formed steel sheet with aluminum alloy coating and high cold bending tensile strength of 1000MPa, characterized in that, The high cold bending tensile strength grade 1000MPa 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: 0.05~0.15%, Si: ≤0.50%, Mn: 1.00~2.50%, Cr: ≤0.50%, P: ≤0.05%, S: ≤0.05%, Al: 0.01~0.10%, Ti: 0.01~0.10%, B: 0.001~0.01%, N: ≤0.01%, Nb: 0.01~0.06%, Mo: ≤0.30%, with the remainder being Fe and unavoidable impurities; The composition of the base steel plate also satisfies: 100×C / (Mn+Cr+Si)≥3.30; The thickness fluctuation of the FeAlSi suppression layer in the aluminum alloy coating of the high cold bending tensile strength 1000MPa grade aluminum alloy coated hot-formed steel sheet is ≤40%. The high cold bending tensile strength 1000MPa grade aluminum alloy coated hot-formed steel sheet is hot-formed to obtain hot-formed steel components. After hot forming, the number of Kirkendal pores with a diameter of more than 1.0μm in the interdiffusion layer does not exceed 15 per 100μm.

2. The high cold bending tensile strength 1000MPa grade aluminum alloy coated hot-formed steel sheet according to claim 1, characterized in that, The base steel plate comprises the following components by weight percentage: C: 0.07~0.12%, Si: 0.15%~0.40%, Mn: 1.30~1.90%, Cr: ≤0.40%, P: ≤0.05%, S: ≤0.05%, Al: 0.01~0.06%, Ti: 0.01~0.06%, B: 0.001~0.005%, N: ≤0.01%, Nb: 0.02~0.06%, Mo: ≤0.30%, with the remainder being Fe and unavoidable impurities.

3. The high cold bending tensile strength 1000MPa grade aluminum alloy coated hot-formed steel sheet according to claim 1, characterized in that, The high cold bending tensile strength grade 1000MPa aluminum alloy coated hot-formed steel sheet has an aluminum alloy coating thickness of 7~19μm.

4. A method for producing a high cold bending tensile strength of 1000MPa grade aluminum alloy coated hot-formed steel sheet as described in any one of claims 1-3, characterized in that, The production process is as follows: steelmaking → continuous casting → hot rolling → pickling and cold rolling → substrate cleaning → annealing → coating → finishing → coiling.

5. The production method according to claim 4, characterized in that, The hot rolling process involves coiling the rolled material at a temperature of 400~600℃.

6. The production method according to claim 4, characterized in that, The pickling and cold rolling process involves a pickling reduction rate of ≤60%.

7. The production method according to claim 4, characterized in that, The annealing is performed at a temperature of 700~830℃, and the annealing dew point is ≤5℃.

8. The production method according to claim 4, characterized in that, The coating process involves a plating solution temperature between 600 and 680°C.

9. A hot-formed steel component, characterized in that, The hot-formed steel component is obtained by hot-forming a high cold bending tensile strength of 1000MPa grade aluminum alloy coated hot-formed steel sheet as described in any one of claims 1-3.

10. The hot-formed steel component according to claim 9, characterized in that, In the hot-formed steel component, the number of Kirkendall pores with a diameter of 1.0 μm or more in the interdiffusion layer after hot forming does not exceed 15 per 100 μm.

11. The hot-formed steel component according to claim 9 or 10, characterized in that, After baking, the cold bending angle of the hot-formed steel component is ≥85°. After coating, the hot-formed steel component undergoes a scratch corrosion test, and the maximum corrosion spread width is not greater than 4mm. The weldability of the hot-formed steel component is within the welding current range of ≥1kA, and the tensile strength of the hot-formed steel component is ≥1000MPa.

12. An application of the hot-formed steel component according to any one of claims 9-11, characterized in that, Used in automotive parts.

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