CN117363977A

CN117363977A - High-strength high-toughness 1500 MPa-level aluminum alloy coating hot-formed steel plate, production method, hot-formed steel member and application

Info

Publication number: CN117363977A
Application number: CN202311238445.9A
Authority: CN
Inventors: 周世龙; 崔磊; 邓宗吉; 谷海容; 郑笑芳
Original assignee: Maanshan Iron and Steel Co Ltd
Current assignee: Maanshan Iron and Steel Co Ltd
Priority date: 2023-09-25
Filing date: 2023-09-25
Publication date: 2024-01-09

Abstract

The invention provides a high-strength high-toughness 1500 MPa-level aluminum alloy coating hot-formed steel plate, a production method, a hot-formed steel member and application, wherein the components are as follows: c:0.19 to 0.25 percent, si:0.15 to 0.40 percent, mn:1.00 to 1.50 percent, cr:0.10 to 0.40 percent, P: less than or equal to 0.05 percent, S: less than or equal to 0.05 percent, al:0.01 to 0.10 percent, ti:0.01 to 0.10 percent, B:0.001 to 0.01 percent, N: less than or equal to 0.01 percent, and the balance of Fe and unavoidable impurities; compared with the prior art, the method controls the chemical components and the production process of the matrix, thereby controlling the oxidation state of the surface layer of the matrix before thermoforming and the thickness fluctuation of the FeAlSi inhibition layer, and finally controlling the size and the number of the Kendall holes after thermoforming, and ensuring that the thermoformed steel member has good cold bending performance, coating corrosion resistance and welding performance.

Description

High-strength high-toughness 1500 MPa-level aluminum alloy coating hot-formed steel plate, production method, hot-formed steel member and application

Technical Field

The invention belongs to the technical field of metallurgy, and particularly relates to a high-strength high-toughness 1500 MPa-level aluminum alloy coating hot-formed steel plate, a production method, a hot-formed steel member and application.

Background

In 2000, the automobile industry develops into a fast traffic lane, the output of automobiles is rapidly increased, but problems such as oil consumption, haze and safety are generated, and energy conservation and emission reduction of automobiles and improvement of safety of automobiles are not sustained. The high-strength steel is a necessary way for realizing energy conservation, emission reduction and safety improvement. The hot stamping forming technology utilizes good formability of materials in a high-temperature state, can effectively reduce rebound, can ensure the service life of a die, and has ultrahigh strength after forming and quenching, so the hot stamping forming technology is an advanced forming technology for realizing the weight reduction and the safety of automobiles.

Steel for hot stamping is classified into a bare plate and a coated steel plate, and since the coated hot stamped steel plate can dispense with shot blasting after hot stamping relative to the bare plate, attention is being paid more and more to the hot forming steel with al—si coating, which is mainly used at present. Typical Al-Si coatings consist of 10% Si+90% Al, the hot forming process requires heating the steel plate above the austenitizing temperature, and when the Al-Si coated steel plate is heated, fe atoms in the matrix diffuse into the Al-Si coating, and the final texture and properties of the coating have a large influence on the cold bending properties, coating corrosion resistance and welding properties of the final hot formed part.

At present, the 1500 MPa-grade Al-Si coating hot forming steel has the most application, but the cold bending angle after hot forming is difficult to be stably controlled to be more than 55 degrees, so that the safety performance of an automobile is greatly reduced.

In order to solve the problems, the patent with publication number CN108588612A published by the material science and technology Co., ltd., 9 th and 28 th, 2018 discloses a hot stamping member, a pre-coated steel plate for hot stamping and a hot stamping process, and proposes to reduce the thickness of an Al-Si pre-coating to 3-19 μm, and reduce the C enrichment degree between the coating and a substrate, thereby improving the cold bending angle of a hot-stamped part by 1-7 degrees.

The patent with publication number of CN111041370A published in 21 of 4 months 2020 discloses a Cr-Al-Si alloy system coated steel plate with a wide hot forming heating process window and a preparation and hot stamping forming process thereof, and the patent proposes that after a small amount of Cr element is added into an aluminum-silicon coating liquid, the coating surface layer has higher roughness and good coating performance even if a small amount of incompletely alloyed Al exists under the condition of shorter heating time, the hot forming process window can be effectively enlarged, and compared with the traditional Al or Al alloy system coated steel plate, the hot forming heat preservation time can be reduced by 0.5-2min; meanwhile, the hardness of the surface layer of the coating is low, and the abrasion of a welding joint in the spot welding process can be effectively reduced.

However, when the hot-formed steel is precoated with an al—si coating, the formation of the kemel pores between the coating and the substrate after hot forming is extremely easy, and when the coating is thinner, the tendency of forming large-size pores after hot stamping is greater. More Kendall holes affect cold bending performance of a product after hot forming, so that the cold bending angle of the 1500 MPa-grade Al-Si coated hot formed steel after hot forming is difficult to be controlled to be more than 55 degrees stably. More importantly, the greater number of kendall pores significantly worsen post-thermoforming coating corrosion resistance and welding performance.

Disclosure of Invention

The invention aims to provide a high-strength high-toughness 1500 MPa-level aluminum alloy coating hot-formed steel plate and a production method thereof, when a precoat is thinner, the high-strength high-toughness 1500 MPa-level aluminum alloy coating hot-formed steel plate is obtained through the designed components and the matched production method, the size and the number of the Kendall holes after hot forming are controlled, and the hot-formed steel member is ensured to have good cold bending performance, coating corrosion resistance and welding performance.

The invention also aims to provide a hot-formed steel member, which is obtained by hot forming the high-strength high-toughness 1500 MPa-level aluminum alloy coated hot-formed steel plate and has good cold bending performance, coating corrosion resistance and welding performance.

It is also an object of the present invention to provide the use of a thermoformed steel article for automotive parts.

The specific technical scheme of the invention is as follows:

the high-strength high-toughness 1500 MPa-level aluminum alloy coating hot-formed steel plate comprises a base steel plate and an aluminum alloy coating;

the matrix steel plate comprises the following components in percentage by mass:

c:0.19 to 0.25 percent, si:0.15 to 0.40 percent, mn:1.00 to 1.50 percent, cr:0.10 to 0.40 percent, P: less than or equal to 0.05 percent, S: less than or equal to 0.05 percent, al:0.01 to 0.10 percent, ti:0.01 to 0.10 percent, B:0.001 to 0.01 percent, N: less than or equal to 0.01 percent, and the balance of Fe and unavoidable impurities.

Preferably, the matrix steel plate comprises the following components in percentage by mass:

c:0.19 to 0.23 percent, si:0.15 to 0.30 percent, mn:1.20 to 1.50 percent, cr:0.15 to 0.40 percent, P: less than or equal to 0.05 percent, S: less than or equal to 0.05 percent, al:0.01 to 0.06 percent, ti:0.01 to 0.06 percent, B:0.001 to 0.005 percent, N: less than or equal to 0.01 percent, and the balance of Fe and unavoidable impurities.

The components of the matrix steel plate also satisfy the following conditions: mn+Cr+Si is less than or equal to 2.00%.

The aluminum alloy coating comprises a FeAl alloy layer, a FeAlSi inhibition layer and an Al alloy layer; the base steel sheet comprises a FeAl alloy (thickness < 1 μm), a FeAlSi inhibitor layer and an Al alloy layer on the outer side thereof in this order from the surface layer.

The high-strength high-toughness 1500 MPa-level aluminum alloy coating thermoformed steel plate is free from oxidation from the surface layer within 5 mu m from the surface of the base steel plate, the thickness of the FeAlSi inhibition layer is controlled to be 3-7 mu m, and the thickness fluctuation of the FeAlSi inhibition layer is less than or equal to 40%.

The key alloy elements and the content design principle in the high-strength high-toughness 1500 MPa-level aluminum alloy coating hot-formed steel plate substrate are as follows:

c is more than or equal to 0.19 percent and less than or equal to 0.25 percent: c is used as the most important element for ensuring the strength after hot forming, and when the content of C is between 0.19 and 0.25 percent, the steel plate can ensure good hardenability during hot forming and cooling and mechanical strength after hot forming. When the C content is lower than 0.19%, the hardenability is insufficient during hot forming and cooling, and more ferrite tissues are generated after hot forming, so that the mechanical strength is obviously reduced, and the tensile strength is less than 1500MPa. When the C content is more than 0.25%, the toughness of the steel sheet after hot forming is drastically reduced. Therefore, the C content is determined to be 0.19 to 0.25%.

Si is more than or equal to 0.15 percent and less than or equal to 0.40 percent: si plays a role in deoxidizing in liquid steel, when the Si content is lower than 0.15%, the deoxidizing effect is not obvious, but when the Si content is higher than 0.40%, a certain Si oxidation enrichment exists on the surface layer (including the surface) of the hot-formed steel matrix in the hot rolling process and the annealing process, so that plating leakage or holes after hot forming are caused. The above problems are more pronounced especially when the hot rolling heating temperature is too high, the coiling temperature is too high or the annealing temperature is too high, and the dew point is too high. Therefore, the Si content is determined to be 0.15 to 0.40%.

Mn is more than or equal to 1.00 percent and less than or equal to 1.50 percent: mn also plays a very important role in ensuring hardenability and mechanical strength after thermoforming. When the Mn content is less than 1.00%, the hardenability is insufficient during hot forming and cooling, the mechanical strength is obviously reduced, and the tensile strength is less than 1500MPa. In addition, mn also has the effect of a deoxidizer, and when the Mn content is less than 1.00%, the deoxidizing effect is not obvious. However, when the Mn content is too high, such as above 1.50%, a certain Mn oxidation enrichment exists on the surface layer (including the surface) of the hot-formed steel matrix during the hot rolling and annealing, and thus, the coating is omitted or holes are formed after the hot forming. The above problems are more pronounced especially when the hot rolling heating temperature is too high, the coiling temperature is too high or the annealing temperature is too high, and the dew point is too high. Therefore, the Mn content is determined to be 1.00 to 1.50%.

Cr is more than or equal to 0.10 percent and less than or equal to 0.40 percent: besides the effect of ensuring hardenability and mechanical strength after hot forming, cr also has the effect that when the Cr content is less than 0.10%, the effect of improving the hardenability of the material is not great, and when the Cr content is more than 0.40%, the effect of improving the hardenability of the material is not obvious. In addition, when the Cr content is higher than 0.40%, a certain Cr oxidation enrichment exists on the surface layer (including the surface) of the hot-formed steel matrix during the hot rolling and annealing processes, so that the coating is omitted or holes are formed after the hot forming. The above problems are more pronounced especially when the hot rolling heating temperature is too high, the coiling temperature is too high or the annealing temperature is too high, and the dew point is too high. Therefore, the Cr content is determined to be 0.10 to 0.40%.

Mn+Cr+Si is less than or equal to 2.00 percent: the research shows that three elements Mn, cr and Si are particularly easy to form oxidation enrichment of the elements on the surface layer of the steel matrix in the hot rolling process and the annealing process, especially when the hot rolling heating temperature is too high, the coiling temperature is too high or the annealing temperature is too high and the dew point is too high, the phenomenon is more obvious, the surface wettability is poor during subsequent hot dip plating, the plating omission is caused, obvious hole defects are caused after hot forming, and the coating corrosion resistance and the welding performance of a hot formed part are reduced. The research shows that the oxidation enrichment degree of three elements Mn, cr and Si on the surface layer of the matrix is influenced by the content of C in the matrix, and in the hot rolling and annealing processes, decarburization on the surface layer of the matrix and oxidation enrichment of Mn, cr and Si occur simultaneously, and decarburization and oxidation of alloy elements are the processes of reacting with oxygen in the environment and compete with each other. The decarburization and oxidation enrichment reaction rates of different C contents and different Mn, cr and Si contents are different, for low-strength grade hot forming steel such as 500MPa and 1000MPa, the C content is lower, the oxidation enrichment tendency of the surface layer of Mn, cr and Si matrixes is larger, but in order to ensure higher strength, the Mn content is generally added, such as more than 1.5%, the C content is higher than 0.19-0.25, C is the most important element for ensuring the strength after hot forming, at the moment, less Mn is generally added, and the Mn content is 1.00-1.50%, at the moment, the oxidation enrichment tendency of Mn on the surface layer of the matrixes is smaller. However, the inventor researches and discovers that for 1500 MPa-level hot forming steel, when the Mn content is low, si and Cr in a matrix are more easy to enrich and form a surface layer, and at the moment, in order to reduce the enrichment degree of the surface layer of the alloy element matrix, the overall content of Si and Cr needs to be controlled, and the content needs to be satisfied: mn+Cr+Si is less than or equal to 2.00%.

P is less than or equal to 0.05 percent, S is less than or equal to 0.05 percent: the excessive sulfur and phosphorus cause the toughness to be reduced, the P content is 0-0.05%, and the S content is 0-0.05%.

Al is more than or equal to 0.01% and less than or equal to 0.10%: al has deoxidizing and nitrogen precipitating effects, al is a ferrite stabilizing element, and when Al is more than 0.10%, steel is liable to form delta ferrite in a high temperature region during hot rolling, deteriorating product properties. The Al content of the invention is determined to be 0.01-0.10%.

Ti is more than or equal to 0.01% and less than or equal to 0.10%: ti is added into the steel to play a role of fixing N, so that BN is prevented from being formed by B element and N, and the effect of B element in the aspect of improving hardenability can be fully exerted. When the Ti content is less than 0.01%, N cannot be sufficiently fixed. When the Ti content is more than 0.10%, a large amount of Ti carbide, nitride or carbonitride of a large size is formed in the steel, which is disadvantageous in terms of toughness of the product. Therefore, the Ti content is determined to be 0.01 to 0.10%.

B is more than or equal to 0.001% and less than or equal to 0.010%: the B element remarkably improves the hardenability of the steel, and when the B content is less than 0.001%, the effect of the B element on improving the hardenability of the steel cannot be fully exerted, and when the B content is more than 0.010%, the effect of the B element on improving the hardenability of the steel is not increased. Therefore, the B content is determined to be 0.001 to 0.010%.

N is less than or equal to 0.01 percent: when the N content is higher than 0.01%, a nitride or carbonitride of Ti with a large number and a large size is easily formed with Ti, which is disadvantageous to the toughness of the product, and in addition, excessive N and B form a large amount of BN, which is disadvantageous to the toughness of the product, and the effect of B in improving the hardenability is reduced. Therefore, the N content is determined to be 0 to 0.01%.

The invention provides a production method of a high-strength high-toughness 1500 MPa-level aluminum alloy coating hot-formed steel plate, which comprises the following steps of: steelmaking, continuous casting, hot rolling, pickling and cold rolling, substrate cleaning, annealing, coating, finishing and coiling.

The steelmaking is carried out according to the formula components;

and the continuous casting is carried out, refined molten steel is injected into a tundish, the tundish distributes the molten steel into each crystallizer, and after the casting is formed and crystallized, the casting is pulled out and cut into slabs with certain lengths.

And (3) hot rolling, namely placing the slab in a heating furnace for heating, discharging, rolling, coiling after rolling, and enabling the coiling temperature to be 450-580 ℃.

The hot rolling coiling temperature control is one of key processes for preventing the surface layer of the steel matrix from forming obvious oxidation enrichment of Si, mn and Cr, and on the basis of limiting the content of Si, mn and Cr elements of the steel matrix, the upper limit of the hot rolling coiling temperature is regulated, the oxidation enrichment trend of Si, mn and Cr on the surface layer of the steel matrix is obviously reduced, and the good cold bending performance, coating corrosion resistance and welding performance of a final product are ensured. In addition, the coiling temperature is not lower than 450 ℃, the coiling temperature is lower than 450 ℃, more martensite and bainite hard phases can be generated in the hot rolled coil, the strength of the hot rolled coil is obviously increased, and the subsequent acid rolling is difficult.

When the surface layer of the matrix is oxidized, the oxidized area is generally concentrated on the surface layer within 5 mu m from the surface, and through energy spectrum analysis or glow spectrum analysis, an obvious O, si, mn, cr element enriched area or enriched point exists in the oxidized area, wherein the element content of the enriched area or enriched point O, si, mn, cr is obviously higher than that of a central unoxidized area of the matrix, and the element content of Si, mn and Cr in the central unoxidized area of the matrix is controlled by referring to the invention: 0.15 to 0.40 percent, mn:1.00 to 1.50 percent, cr:0.10 to 0.40 percent.

The pickling cold-rolled steel plate is further subjected to pickling cold-rolling to obtain a pickling cold-rolled steel plate, and oxide scales generated on the surface of the steel plate in the hot-rolling process can be removed in the pickling cold-rolling process. To ensure good surface quality after plating, the residual oil quantity of one side of the rolled hard coil after pickling and cold rolling is less than or equal to 250mg/m ² The residual iron content is less than or equal to 100mg/m ² . As the temperature difference exists at different parts of the surface of the steel plate in the hot rolling process, the thickness of the oxide scale formed at different parts is uneven, and the surface of the steel plate after pickling is uneven. If the alloy element oxidation enrichment exists on the surface layer of the matrix to a certain extent, the alloy element oxide on the surface layer of the matrix cannot be completely removed by acid washing, and after acid rolling, pit morphology is formed on the surface of the alloy element oxidation area on the surface layer of the matrix. Pit when acid rolling reduction is larger The greater the number. The pit area and the normal area are uneven, and in addition, alloy elements which are not pickled exist in the pit area, and the reaction rate of Fe-Al is different between the pit area and the normal area during hot dip plating, so that the thickness difference of FeAlSi inhibition layers of the pit area and the normal area during hot dip plating is larger, the diffusion degree difference of different parts during the hot forming process is caused by larger fluctuation of the thickness of the FeAlSi inhibition layers, and the formation of Kendall holes is aggravated. The acid rolling reduction rate is less than or equal to 60 percent, and is preferably controlled to be 50 to 60 percent; the thickness of the FeAlSi inhibition layer after hot dip plating is controlled to be 3-7 mu m, and the thickness fluctuation of the FeAlSi inhibition layer is less than or equal to 40%. Wherein the FeAlSi suppresses layer thickness fluctuation= |maximum thickness or minimum thickness-average thickness|/average thickness×100%, average thickness= (maximum thickness+minimum thickness)/2. It should be noted that oxidation enrichment of alloy elements on the surface layer of the substrate also causes overlarge thickness fluctuation of the FeAlSi inhibition layer after hot dip plating, and in order to ensure that the thickness fluctuation of the FeAlSi inhibition layer after hot dip plating is less than or equal to 40%, the hot rolling coiling temperature is less than or equal to 580 ℃, the annealing temperature is less than or equal to 810 ℃ and the annealing dew point is less than or equal to 0 ℃.

The substrate cleaning, the substrate cleaning includes: alkali cleaning, alkali scrubbing, alkali cleaning, water scrubbing, electrolytic cleaning, rinsing and drying, wherein the single-side residual oil amount of the cleaned steel plate is less than or equal to 20mg/m for ensuring good surface quality after plating ² The single-sided residual iron is less than or equal to 10mg/m ² 。

The annealing temperature is controlled between 700 ℃ and 810 ℃, and the annealing temperature comprises the temperature of an annealing heating section and the temperature of a soaking section, which are controlled according to the temperature. The annealing dew point is controlled to be less than or equal to 0 ℃, namely the dew point of the heating section and the soaking section is not more than 0 ℃. The annealing process mainly aims at recovering and recrystallizing the rolled hard coil, eliminating residual stress, controlling the structure and performance of the finished coil, and controlling the heating and soaking temperature to be not lower than 700 ℃, wherein the heating and soaking temperature is too low, the recovering and recrystallizing of the rolled hard coil is insufficient, and the performance of the finished coil is unfavorable.

The heating temperature of the annealing section is not more than 810 ℃, and the temperature of the soaking section is not more than 810 ℃. In addition, the annealing furnace controls the dew point in the furnace by adjusting the inflow amount of water vapor, wherein the dew point of the heating section and the soaking section is not more than 0 ℃, and the atmosphere in the annealing furnace is N ₂ +H ₂ Wherein H is ₂ The volume percentage of the furnace is 5-10%, 5-10% H is introduced into the furnace ₂ Reducible Fe and H ₂ O、O ₂ And the generated iron oxide is used for ensuring good coating quality before hot forming, and the oxygen content of a heating section and a soaking section is controlled below 50ppm, so that the oxidation of a steel matrix is further reduced.

It should be noted that the control of the annealing process is also one of the key processes for preventing the surface layer of the steel matrix from forming obvious oxidation enrichment of Si, mn, cr and the like. On the basis of limiting the contents of elements such as Si, mn, cr and the like in the steel matrix, the upper limit of heating temperature, soaking temperature, dew point and oxygen content is regulated, so that the oxidation enrichment trend of Si, mn, cr and the like on the surface layer of the steel matrix is further reduced, and the good cold bending performance, coating corrosion resistance and welding performance of the final product are ensured.

The coating and plating solution is aluminum alloy and unavoidable impurities, and the typical plating solution comprises the following components in percentage by mass: 5-11% of Si, 2-4% of Fe and the balance of Al and unavoidable impurities. The temperature of the hot dip plating solution is 600-680 ℃, the temperature needs to be kept as consistent as possible with the temperature of the hot dip plating solution when the substrate is put into the plating solution, so as to reduce the dissolution of steel strips and the formation of aluminum slag, the dip plating time is 2-10 s, an air knife is adopted to purge nitrogen or compressed air to control the thickness of the coating after the hot dip plating, the thickness of the precoat is controlled to be 7-19 mu m on one side, the thickness of the FeAlSi inhibition layer is controlled to be 3-7 mu m, and the thickness fluctuation of the FeAlSi inhibition layer is controlled to be less than or equal to 40%.

Wherein the temperature of the hot dip plating solution is 600-680 ℃. When the temperature of the hot dip plating solution is higher than 680 ℃, the thickness fluctuation of the FeAlSi inhibition layer formed by the plating solution and the steel matrix is obviously increased, and the difference of the diffusion degree of different parts in the hot forming process is caused by the larger thickness fluctuation of the FeAlSi inhibition layer, so that the formation of the Kendall holes is aggravated. In addition, the melting point of the aluminum-silicon alloy is about 600 ℃, and the temperature of the hot dip plating solution is not lower than 600 ℃. The thickness fluctuation of the FeAlSi inhibition layer is less than or equal to 40 percent. In order to realize that the thickness fluctuation of FeAlSi inhibition layers is less than or equal to 40 percent, the temperature of hot dip plating solution is less than or equal to 680 ℃ and the acid rolling reduction is less than or equal to 60 percent, and the oxidation enrichment of alloy elements on the surface layer of a substrate is also required to be controlled, so that the hot rolling coiling temperature is less than or equal to 580 ℃, the annealing temperature is less than or equal to 810 ℃ and the annealing dew point is less than or equal to 0 ℃.

The precoat layer thickness is not preferably < 7. Mu.m. The inventors found that the thinner the initial coating, the more pronounced the Kendall pores are, because the thinner the initial coating, the shorter the Fe, al interdiffusion travel, and the faster the interdiffusion rate, but because of the reduced relative Al content in the coating-thinned coating, the reduced Al content available to supplement Fe vacancies, which in turn exacerbates the formation of large-sized Kendall pores. In addition, the thickness of the precoat is less than 7 mu m, and the plating leakage defect is easy to occur.

The thickness of the precoat is not more than 19 mu m, the coating is too thick, the cold bending performance of the final product is reduced, the coating is too thick, and the production cost is increased.

The steel strip is polished after being coated to improve the plate shape and control the surface roughness of the coating.

And the coiling is carried out, and the steel belt is coiled and is off-line.

The invention provides a hot-formed steel member, which is obtained by hot-forming the high-strength high-toughness 1500 MPa-level aluminum alloy coated hot-formed steel plate;

the number of Kendall holes with the diameter of more than 1.0 mu m in the interdiffusion layer after hot forming is not more than 15/100 mu m,

preferably, the number of Kendall holes with a diameter of more than 1.0 μm in the interdiffusion layer of the hot formed steel member is not more than 10/100 μm;

More preferably, the number of Kendall holes with a diameter of 1.0 μm or more in the interdiffusion layer of the hot formed steel member is not more than 6/100 μm;

the hot formed steel member is subjected to scratch corrosion test after being coated (phosphating and electrophoresis) at a cold bending angle of more than or equal to 55 degrees after being baked, the maximum corrosion expansion width is not more than 4mm, the number of welding spots with the fusion diameter of not less than 5.0mm of the hot formed steel member is more than or equal to 500, and the tensile strength of the hot formed steel member is more than or equal to 1450MPa.

The specific process for producing the hot formed steel member comprises the following steps: blanking, heat treatment and hot stamping.

And blanking, namely blanking or cutting the high-strength high-toughness 1500 MPa-level aluminum alloy coating hot-formed steel plate into a blank with a shape required by a hot-formed part.

And (3) the heat treatment, namely placing the blank into a heating furnace for heating and preserving heat, wherein the temperature of the heating furnace is 840-970 ℃, the atmosphere of the heating furnace adopts air or nitrogen, and the blank stays in the heating furnace for 2-10 min.

The conventional heating furnaces comprise a box type heating furnace and a roller bottom heating furnace, when the box type heating furnace is adopted, the roller bottom heating furnace is heated at a fixed temperature, and when the roller bottom heating furnace is adopted, the sectional heating is adopted, and the temperature of the heating furnace refers to the highest heating temperature of the roller bottom heating furnace.

And (3) hot stamping, namely rapidly transferring the blank subjected to heat treatment into a die for stamping forming and cooling, wherein the transfer time is not more than 15 seconds, the stamping forming dwell time is 5-15 seconds, the cooling die stripping temperature is not more than 250 ℃, and the cooling speed is not less than 30 ℃/s.

The application of the hot formed steel member provided by the invention is used for high-strength automobile parts.

The inventor researches that when the hot-formed steel is precoated with an Al-Si coating, the coating and a matrix are extremely easy to form Kendall holes after hot forming, and the size and the number of the holes are closely related to the state of the raw material coating or the steel matrix. The thinner the coating, the greater the propensity for large-size holes to form after hot stamping. More Kendall holes affect cold bending performance of a product after hot forming, so that the cold bending angle of the 1500 MPa-grade Al-Si coated hot formed steel after hot forming is difficult to be controlled to be more than 55 degrees stably. More importantly, the greater number of kendall pores significantly worsen post-thermoforming coating corrosion resistance and welding performance. The inventor also found that the diffusion speed difference of Fe and Al is larger in the heating process of the aluminum alloy coating hot forming steel, the surface layer of the matrix is easy to form the Kendall holes, and when certain oxidation exists on the surface layer (including the surface) of the matrix before hot forming, the situation (size and quantity) of the Kendall holes is obviously aggravated, which is probably due to the fact that the mutual diffusion of Fe and Al at the oxidation part is blocked, and after Fe diffuses to form vacancies, al is more difficult to supplement to the vacancies. In addition, after the coating is thinned, the inter-diffusion travel of Fe and Al is shortened, and the inter-diffusion rate is accelerated, but due to the fact that the relative Al content in the coating thinned coating is reduced, the Al which can be used for supplementing Fe vacancies is reduced, and the formation of large-size Kendall holes is further aggravated. Moreover, the inventor researches and discovers that the interdiffusion of the steel matrix and the FeAlSi inhibition layer close to the matrix is most severe in the hot forming and heating process, and the thickness uniformity of the FeAlSi inhibition layer in the precoated Al-Si coating layer also has obvious influence on the formation of Kendall holes. When the thickness fluctuation of the FeAlSi inhibition layer in the precoat layer is large, the diffusion rates of different parts of the coating layer are different, and the formation of large-size Kendall holes is also aggravated. The large-sized Kendall pores significantly reduce the coating corrosion resistance and welding performance of the thermoformed part. In addition, the Kendall cavity may also have an effect on the cold bending properties of the thermoformed part. It should be noted that the holes may reduce the cold bending performance or improve the cold bending performance. When holes exist between the hot formed substrate and the coating, decarburization occurs on the surface layer of the substrate in the hole area in the hot forming heating process, the surface layer of the substrate after the decarburization has lower strength and better plasticity than that of the surface layer of the substrate after the decarburization, but when the size and the quantity of the holes are smaller, the area of the decarburization area is smaller, the decarburization effect on the cold bending performance is not large, but at the moment, due to the existence of the holes, when the stress is bent, cracks in the hole area can be rapidly expanded from the coating to the substrate, and the cold bending performance is obviously reduced; however, when the size of the holes is large and the number of the holes is large, especially the holes are connected with each other to form a large-area hole sheet area, obvious decarburization occurs on the surface layer of the matrix of the hole sheet area in the thermoforming heating process, and at the moment, the area of the decarburization area is large, so that the cold bending performance can be improved, but the coating corrosion resistance and welding performance of the thermoformed part are greatly deteriorated by the large-area hole sheet area.

That is, when the precoat layer is thinner, in order to ensure that the aluminum alloy coated thermoformed part has stable cold bending performance, good coating corrosion resistance and welding performance, the size and the number of the Kendall holes are strictly controlled, and at this time, the oxidation state of the surface layer of the substrate and the thickness fluctuation of the FeAlSi inhibition layer before thermoforming are comprehensively controlled. Wherein, the oxidation state of the surface layer of the matrix before thermoforming is mainly related to the chemical composition of the matrix and the production process, the production process mainly comprises a hot rolling process and an annealing process, and the thickness fluctuation of the FeAlSi inhibition layer is mainly related to the acid rolling process and the hot dip plating temperature.

Compared with the prior art, the method controls the chemical composition and the production process of the raw material matrix, so as to control the oxidation state of the surface layer of the matrix before hot forming and the thickness fluctuation of the FeAlSi inhibition layer, and finally control the size and the number of the Kendall holes after hot forming, thereby ensuring that the hot formed steel member has good cold bending performance, coating corrosion resistance and welding performance.

Drawings

FIG. 1 is a diagram showing the thickness fluctuation of the FeAlSi inhibitor layer in the oxidized state of the steel substrate surface layer before hot forming in example 1;

FIG. 2 is a graph showing the thickness fluctuation of the FeAlSi inhibitor layer in the oxidized state of the steel substrate surface layer before hot forming in comparative example 3;

FIG. 3 is a diagram showing the state of the Kendall cavity after thermoforming in example 1;

FIG. 4 is a graph of the state of the Kendall cavity after thermoforming of comparative example 3;

FIG. 5 is a graph showing the scratch etching development after thermoforming in example 1.

Detailed Description

The invention will be described in detail with reference to examples for the purpose of further explaining the invention.

The invention provides a production method of a high-strength high-toughness 1500 MPa-level aluminum alloy coating hot-formed steel plate, which comprises the following specific procedures: steelmaking, continuous casting, hot rolling, pickling and cold rolling, substrate cleaning, annealing, coating, finishing and coiling.

Specific:

1) Steelmaking: the preferable steelmaking components are controlled by mass: c:0.19 to 0.25 percent, si:0.15 to 0.40 percent, mn:1.00 to 1.50 percent, cr:0.10 to 0.40 percent, P: less than or equal to 0.05 percent, S: less than or equal to 0.05 percent, al:0.01 to 0.10 percent, ti:0.01 to 0.10 percent, B:0.001 to 0.01 percent, N: less than or equal to 0.01 percent, less than or equal to 2.00 percent of Mn+Cr+Si, and the balance of Fe and unavoidable impurities.

By way of example, the matrix steel composition is shown in Table 1. The invention controls the oxidation enrichment of three elements Mn, cr and Si on the surface layer of the steel matrix in the hot rolling process and the annealing process, and particularly limits the contents of the three elements Mn:1.00 to 1.50 percent, cr:0.10 to 0.40 percent, si:0.15 to 0.40 percent, and Mn+Cr+Si is less than or equal to 2.00 percent. Wherein, the steel 1 and the steel 2 are components of the invention, mn+Cr+Si is less than or equal to 2.00 percent, the Cr content in the steel 1 exceeds the upper limit of the invention by 0.40 percent, mn+Cr+Si=2.10, and exceeds the upper limit of the invention by 2.00 percent.

TABLE 1 matrix Steel composition (wt%)

2) Continuous casting

Pouring the refined molten steel into a tundish, distributing the molten steel into each crystallizer by the tundish, forming and crystallizing the castings, and then pulling out the castings and cutting the castings into slabs with certain lengths.

3) Hot rolling

And heating the slab in a heating furnace, discharging, rolling, and coiling at 450-580 ℃.

5) Pickling cold rolling

The hot-rolled steel plate is further subjected to pickling and cold rolling to obtain a pickling cold-rolled steel plate, and the process can remove iron scales generated on the surface of the steel plate in the hot rolling process. To ensure good surface quality after plating, the residual oil quantity of one side of the rolled hard coil after pickling and cold rolling is less than or equal to 250mg/m ² The residual iron content is less than or equal to 100mg/m ² . As the temperature difference exists at different parts of the surface of the steel plate in the hot rolling process, the thickness of the oxide scale formed at different parts is uneven, and the surface of the steel plate after pickling is uneven. If the alloy element oxidation enrichment exists on the surface layer of the matrix to a certain extent, the alloy element oxide on the surface layer of the matrix cannot be completely removed by acid washing, and after acid rolling, pit morphology is formed on the surface of the alloy element oxidation area on the surface layer of the matrix. The greater the acid rolling reduction, the greater the pit number. The pit area and the normal area are uneven, and in addition, alloy elements which are not pickled exist in the pit area, and the reaction rate of Fe-Al is different between the pit area and the normal area during hot dip plating, so that the thickness difference of FeAlSi inhibition layers of the pit area and the normal area during hot dip plating is larger, the diffusion degree difference of different parts during the hot forming process is caused by larger fluctuation of the thickness of the FeAlSi inhibition layers, and the formation of Kendall holes is aggravated. The acid rolling reduction rate is less than or equal to 60%, and the thickness fluctuation of the FeAlSi inhibition layer after hot dip plating is less than or equal to 40%. Wherein the FeAlSi suppresses layer thickness fluctuation= |maximum thickness or minimum thickness-average thickness|/average thickness×100%, average thickness= (maximum thickness+minimum thickness)/2. It should be noted that oxidation enrichment of alloy elements on the surface layer of the substrate also causes overlarge thickness fluctuation of the FeAlSi inhibition layer after hot dip plating, and in order to ensure that the thickness fluctuation of the FeAlSi inhibition layer after hot dip plating is less than or equal to 40%, the hot rolling coiling temperature is less than or equal to 580 ℃, the annealing temperature is less than or equal to 810 ℃ and the annealing dew point is less than or equal to 0 ℃.

5) Substrate cleaning

The substrate cleaning includes: alkali cleaning, alkali scrubbing, alkali cleaning, water scrubbing, electrolytic cleaning, rinsing and drying, wherein the single-side residual oil amount of the cleaned steel plate is less than or equal to 20mg/m for ensuring good surface quality after plating ² The single-sided residual iron is less than or equal to 10mg/m ² 。

6) Annealing

The annealing process mainly aims at recovering and recrystallizing the rolled hard coil, eliminating residual stress, controlling the structure and performance of the finished coil, and controlling the heating and soaking temperature to be not lower than 700 ℃, wherein the heating and soaking temperature is too low, the recovering and recrystallizing of the rolled hard coil is insufficient, and the performance of the finished coil is unfavorable.

The heating temperature of the annealing section is not more than 810 ℃, and the temperature of the soaking section is not more than 810 ℃. In addition, the annealing furnace controls the dew point in the furnace by adjusting the inflow amount of water vapor, wherein the dew point of the heating section and the soaking section is not more than 0 ℃, and the atmosphere in the annealing furnace is N ₂ +H ₂ Wherein H is ₂ The volume percentage of the furnace is 5-10%, 5-10% H is introduced into the furnace ₂ Reducible Fe and H ₂ O、O ₂ And the generated iron oxide is used for ensuring good coating quality before hot forming, and the oxygen content of a heating section and a soaking section is controlled below 50ppm to further reduce the oxidation of a steel matrix.

It should be noted that the control of the annealing process is also one of the key processes for preventing the surface layer of the steel matrix from forming obvious oxidation enrichment of Si, mn, cr and the like. On the basis of limiting the contents of elements such as Si, mn, cr and the like in the steel matrix, the upper limit of heating temperature, soaking temperature, dew point and oxygen content is regulated, so that the oxidation enrichment trend of Si, mn, cr and the like on the surface layer of the steel matrix is further reduced, and the good cold bending performance, coating corrosion resistance and weldability of the final product are ensured.

7) Coating and plating

The plating solution is aluminum alloy and unavoidable impurities, the target of the plating solution is controlled to be 8-10% of Si, 2-4% of Fe, and the balance is Al and unavoidable impurities. The temperature of the hot dip plating solution is between 600 and 680 ℃, the temperature of the substrate needs to be kept as consistent as possible with the temperature of the hot dip plating solution when the substrate is put into the plating solution, so as to reduce the dissolution of steel strips and the formation of aluminum slag, the dip plating time is 2 to 10 seconds, an air knife is adopted to purge nitrogen or compressed air to control the thickness of the coating after the hot dip plating, the thickness of the coating is controlled to be 7 to 19 mu m on one side, and the thickness of a FeAlSi inhibition layer is 3 to 7 mu m; the thickness fluctuation of the FeAlSi inhibition layer is less than or equal to 40 percent.

The thickness fluctuation of the FeAlSi inhibition layer is less than or equal to 40 percent.

The coating thickness is not suitable to be less than 7 μm. The inventors found that the thinner the initial coating, the more pronounced the Kendall pores are, because the thinner the initial coating, the shorter the Fe, al interdiffusion travel, and the faster the interdiffusion rate, but because of the reduced relative Al content in the coating-thinned coating, the reduced Al content available to supplement Fe vacancies, which in turn exacerbates the formation of large-sized Kendall pores. In addition, the thickness of the coating is less than 7 mu m, and the coating is easy to have a missing plating defect.

The thickness of the coating is not more than 19 mu m, the coating is too thick, the cold bending performance of the final product is reduced, the coating is too thick, and the production cost is increased.

8) Finishing process

The coated steel strip is finished to improve the plate shape and control the surface roughness of the coating.

9) Coiling

And coiling and offline the steel strip.

The hot formed steel member is prepared by adopting the high-strength high-toughness 1500 MPa-level aluminum alloy coating hot formed steel plate, and the specific process comprises the following steps of: blanking, heat treatment and hot stamping.

And (3) blanking:

and blanking or cutting the high-strength high-toughness 1500 MPa-level aluminum alloy coating hot-formed steel plate into blanks with shapes required by hot-formed parts. The thickness of the steel plate of the invention is selected to be a typical value of 1.4mm, and the steel plate is processed into a sample plate with the size of 150 multiplied by 300 mm.

The heat treatment:

heating the blank in a heating furnace at 840-970 deg.c for 2-10 min in air or nitrogen.

The conventional heating furnaces comprise a box type heating furnace and a roller bottom heating furnace, when the box type heating furnace is adopted, the roller bottom heating furnace is heated at a fixed temperature, and when the roller bottom heating furnace is adopted, the sectional heating is adopted, and the temperature of the heating furnace refers to the highest heating temperature of the roller bottom heating furnace. The invention adopts a box-type resistance heating furnace to heat the precoated steel plate, and adopts a typical heating process, namely, the heating temperature is 930 ℃ and the heating time is 5min.

The hot stamping:

and rapidly transferring the blank subjected to heat treatment into a die for stamping forming and cooling, wherein the transfer time is not more than 15s, the stamping forming dwell time is 5-15 s, the cooling demolding temperature is not more than 250 ℃, and the cooling speed is not less than 30 ℃/s. The invention puts the steel plate after heat treatment on a flat quenching die for pressing and maintaining the pressure for a certain time, and cooling water is introduced into the die for cooling the steel plate.

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

TABLE 2 production process parameters, precoat thickness, feAlSi thickness fluctuation

And observing and analyzing the oxidation state, the coating thickness and the FeAlSi layer thickness of the surface layer of the pre-coated aluminum alloy coating thermoformed steel plate, observing and analyzing the hole condition of the thermoformed steel member, and testing scratch corrosion test, welding performance and mechanical property of the coated thermoformed steel member.

The oxidation state of the surface layer of the substrate before thermoforming is mainly observed through a scanning electron microscope, and the oxidation state in the surface layer 5 mu m of the substrate is mainly focused on because the part of the region strongly influences the hole condition after thermoforming, when oxidation exists, the oxidation is mainly concentrated near the grain boundary of the substrate, the region is subjected to component analysis through an energy spectrum analyzer, and even a crack-like morphology is formed when the oxidation is serious.

The condition of the holes of the hot formed steel member is observed and analyzed by a scanning electron microscope, the holes mainly exist in an interdiffusion layer, wherein the interdiffusion layer is connected with a steel substrate and is generally formed by alpha Fe+Fe ₃ Al composition, fe content not less than 80%. The method for determining the diameters of the holes by counting the number of the large-size holes in the interdiffusion layer is characterized in that the large-size holes are required to be focused, for example, the diameters of the holes are larger than 1.0 mu m, the influences of the holes on the corrosion resistance and the welding performance of the coating are larger, and the method for determining the diameters of the holes comprises the following steps: and under the same field of view, measuring the longest diameter and the shortest diameter of the holes, taking half of the sum of the longest diameter and the shortest diameter as the hole diameter, and determining the number of the holes by the following steps: in the field of view of the scanning electron microscope, holes in the range of 100 μm in length were counted along the surface of the base steel. It should be noted that, when the surface layer of the raw material matrix is severely oxidized, the holes of the coating may be connected to form a hole area after thermoforming, and the method for determining the number of holes is as follows: in the field of view of the scanning electron microscope, the area of the hole area in the range of 100 mu m in length is counted along the surface of the matrix steel, and the area of the hole area is/1 mu m ² I.e. as the number of holes.

The hot formed steel member was subjected to scratch corrosion testing after coating, including phosphating, electrophoresis, and the coated coating was subjected to scratch corrosion testing to evaluate paint adhesion and corrosion resistance (meeting the requirements when the maximum corrosion spread width was not more than 4 mm). According to the invention, 3 hot-formed steel plates under the same condition are selected for scratch corrosion test, and the average value of the maximum corrosion expansion width is used for evaluating the paint adhesion and corrosion resistance. Phosphorus as in Table 3Phosphating the thermoformed sample with the aid of a phosphating agent and test parameters, and then electrophoresing the resulting phosphating plate (type of electrophoretic paint: guangxi HT-8000C), with a dry film thickness of about 18. Mu.m. Then, a cyclic etching method was used, and a single cycle was carried out including 8 hours of normal temperature maintenance (25.+ -. 3 ℃ C., 4 spraying saline solutions each for 3 minutes, the saline solution composition was 0.9% by weight of NaCl, 0.1% by weight of CaCl) ₂ 0.075wt% NaHCO ₃ ) Then, the mixture was subjected to damp heat (49.+ -. 2 ℃ C., 100% RH) for 8 hours, and finally, the mixture was dried (60.+ -. 2 ℃ C.,<30% rh) for a total of 26 cycles.

TABLE 3 parameters of the phosphating process

And (3) testing the welding performance of the hot formed steel member, and evaluating the number of welding spots with the fusion diameter not smaller than 5.0mm by adopting a GWS-5A standard, wherein the number of welding spots is generally not smaller than 500, and the welding spots are considered to meet the requirements.

And (3) testing mechanical properties of the hot formed steel member, wherein GB/T228.1-2010 is adopted as a test standard.

The oxidation state, holes, scratch corrosion test, welding performance and mechanical property test results are shown in Table 4.

TABLE 4 oxidation state, cavitation, scratch Corrosion test, welding Property, mechanical Property test results

According to the invention, the chemical components and the production process of the raw material matrix are controlled, so that the oxidation state of the surface layer of the matrix before hot forming and the thickness fluctuation of the FeAlSi inhibition layer are controlled, and finally the size and the number of the Kendall holes after hot forming are controlled, thereby ensuring that the hot formed steel member has good cold bending performance, coating corrosion resistance and welding performance. The chemical composition of the matrix is controlled, and the contents of three elements of Mn, cr and Si are mainly limited, mn:1.00 to 1.50 percent, cr:0.10 to 0.40 percent, si:0.15 to 0.40 percent, and Mn+Cr+Si is less than or equal to 2.00 percent; the production process control mainly comprises hot rolling coiling temperature less than or equal to 580 ℃, acid rolling reduction rate less than or equal to 60%, annealing temperature less than or equal to 810 ℃, annealing dew point less than or equal to 0 ℃ and hot dip plating bath temperature less than or equal to 680 ℃. Through the control, the surface layer of the raw material matrix is ensured to have no obvious oxidation, the thickness fluctuation of the FeAlSi inhibition layer is controlled to be less than or equal to 40 percent, and the thickness of the FeAlSi inhibition layer is controlled to be 3-7 mu m; the total thickness of the precoat layer is 7-19 mu m, the number of Kendall holes with the diameter of more than 1.0 mu m in an inter-diffusion layer after hot forming is finally formed, the number of Kendall holes with the diameter of more than 1.0 mu m is not more than 15/100 mu m, the cold bending angle of the hot formed steel member after baking is not less than 55 degrees, the hot formed steel member is subjected to scratch corrosion test after being coated (phosphating and electrophoresis), the maximum corrosion expansion width is not more than 4mm, and the number of welding spots with the fusion diameter of not less than 5.0mm of the hot formed steel member is not less than 500.

In the invention, the following components are added:

1) Chemical components of the matrix: the preferable steelmaking components of the invention are controlled by mass: c:0.19 to 0.25 percent, si:0.15 to 0.40 percent, mn:1.00 to 1.50 percent, cr:0.10 to 0.40 percent, P: less than or equal to 0.05 percent, S: less than or equal to 0.05 percent, al:0.01 to 0.10 percent, ti:0.01 to 0.10 percent, B:0.001 to 0.01 percent, N: less than or equal to 0.01 percent, less than or equal to 2.00 percent of Mn+Cr+Si, and the balance of Fe and unavoidable impurities.

The invention controls the oxidation enrichment of three elements Mn, cr and Si on the surface layer of the steel matrix in the hot rolling process and the annealing process, and particularly limits the contents of the three elements Mn:1.00 to 1.50 percent, cr:0.10 to 0.40 percent, si:0.15 to 0.40 percent, and Mn+Cr+Si is less than or equal to 2.00 percent. Wherein, the steel 1 and the steel 2 are components of the invention, mn+Cr+Si is less than or equal to 2.00 percent, the Cr content in the steel 1 exceeds the upper limit of the invention by 0.40 percent, mn+Cr+Si=2.10, and exceeds the upper limit of the invention by 2.00 percent.

Specifically, when the matrix composition of the present invention, i.e. the example 1/2/3/4/5 and the comparative examples 1/2/3/4, the production process (hot rolling, acid rolling, annealing, hot dip plating) of the example 1/2/3/4/5 is adopted, no obvious oxidation of the surface layer of the raw material matrix is ensured, the FeAlSi inhibition layer thickness fluctuation is controlled to be less than or equal to 40% (see fig. 1, example 1), the number of the Kendall holes after final hot forming is no more than 15/100 μm in the interdiffusion layer after final hot forming, the cold bending angle of the hot formed steel member is no less than 55 degrees after baking, the maximum corrosion expansion width is no more than 4mm, and the number of welding spots with the fusion diameter of the hot formed steel member no less than 5.0mm is no less than 500. In the comparative example 1/2/3/4, the production process of the invention is not adopted, the surface layer of the raw material matrix has obvious oxidation (comparative example 3/4) or FeAlSi inhibition layer thickness fluctuation is more than 40% (comparative example 1/2/3/4), the diameter in the interdiffusion layer after final hot forming is more than 15 Kendall holes/100 mu m, the cold bending angle of the hot formed steel member can not be stabilized to be more than 55 DEG after baking, the hot formed steel member is subjected to scratch corrosion test after being coated (phosphating and electrophoresis), the maximum corrosion expansion width is more than 4mm, and the fusion diameter of the hot formed steel member is not less than 5.0mm, and the number of welding spots is less than 500.

When the matrix composition of the present invention, i.e., comparative example 5, was not employed, the Cr content exceeded the upper limit of the present invention by 0.40%, and the mn+cr+si=2.10 exceeded the upper limit of the present invention by 2.00, the surface layer of the raw material matrix was still significantly oxidized, and the FeAlSi suppressed layer thickness fluctuation was > 40%, resulting in the number of kekokakodak holes exceeding 15/100 μm in diameter in the interdiffusion layer after hot forming, at which time the number of weld spots of not less than 5.0mm was < 500 in spite of the baking of the hot-formed steel member, because a large number of hole sheet regions resulted in decarburization softening of the surface layer of the matrix, and the hot-formed steel member was subjected to scratch corrosion test after coating (phosphating, electrophoresis) by a maximum corrosion expansion width of more than 4 mm.

Moreover, the hot-formed steel adopting the matrix composition has good hardenability and mechanical strength after hot forming, and the tensile strength after hot forming is more than or equal to 1450MPa.

2) The production process comprises the following steps: the control of the hot rolling process and the annealing process is a key process for preventing the surface layer of the steel matrix from forming obvious oxidation enrichment of Si, mn, cr and the like. Wherein, in the hot rolling process, the coiling temperature is less than or equal to 580 ℃, in the annealing process, the annealing temperature is less than or equal to 810 ℃ and the annealing dew point is less than or equal to 0 ℃. The control of FeAlSi inhibition layer thickness fluctuation is related to the process, the acid rolling reduction and the hot dip plating bath temperature, wherein the acid rolling reduction is less than or equal to 60 percent, and the bath temperature is less than or equal to 680 ℃.

It can be seen that, with the matrix composition of the present invention, the production process of the present invention was not adopted, namely, comparative example 1/2/3/4, specifically, the acid rolling reduction of comparative example 1 was too high (65% > 60%), the plating bath temperature of comparative example 2 was too high (700 ℃ > 680 ℃), at which time, although there was no significant oxidation of the raw material matrix surface layer, the cakener's hole number was > 40%, in addition, the coiling temperature of comparative example 3 was too high (665 ℃ > 580 ℃), the annealing dew point of comparative example 4 was too high (5 ℃ > 0 ℃), causing significant oxidation of the raw material matrix surface layer and the FeAlSi inhibition layer thickness fluctuation was > 40% (see FIG. 2, comparative example 3, the spectrum analysis point/region 1 at the oxidized place of matrix surface layer and the unoxidized place in the matrix was found in the analyzed point/region 3, the composition analysis result was found in Table 5), and therefore, in the interdiffusion layer after the hot forming of comparative example 1/2/3/4, the number of Kekener holes was more than 15/100 μm in diameter above 1.0 μm diameter, the hot formed steel member could not be stabilized at the cold bending angle (55 ℃ C. 7 mm) and the cold-formed steel member was subjected to cold-formed corrosion resistance was increased by the largest expansion of the hot-rolled steel sheet, the largest size was measured by the largest expansion resistance of the weld surface layer was measured at the weld surface layer width of the largest scale (see FIG. 2. 5 mm, the largest scale, and the weld formed steel sheet was not subjected to the expansion).

TABLE 5 results of spectral analysis at comparative example 3 (FIG. 2)

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In summary, the chemical composition, the production process and the precoat thickness of the raw material matrix are adopted to control the oxidation state of the surface layer of the matrix before hot forming and the thickness fluctuation of the FeAlSi inhibition layer, and finally control the size and the number of the Kendall holes after hot forming, so that the hot formed steel member has good cold bending performance, coating corrosion resistance and welding performance. Specifically, in the interdiffusion layer after hot forming, the number of Kendall holes with the diameter of more than 1.0 μm is not more than 15/100 μm, the cold bending angle of the hot formed steel member is not less than 55 degrees after baking, the hot formed steel member is subjected to scratch corrosion test after coating (phosphating and electrophoresis), the maximum corrosion expansion width is not more than 4mm, the number of welding spots with the fusion diameter of not less than 5.0mm of the hot formed steel member is not less than 500, and the tensile strength of the hot formed steel member is not less than 1450MPa.

The foregoing embodiments have been described in some detail for purposes of clarity of understanding, it will be appreciated that the foregoing embodiments are merely illustrative of the invention, and that the invention is not limited to the details of construction and practice of the invention, but is to be accorded the full scope of the invention.

Claims

1. The high-strength high-toughness 1500 MPa-level aluminum alloy coating hot-formed steel plate is characterized by comprising a base steel plate and an aluminum alloy coating;

2. The high-strength high-toughness 1500 MPa-level aluminum alloy coated hot-formed steel sheet according to claim 1, wherein the base steel sheet comprises the following components in mass percent:

3. The high strength and high toughness 1500 MPa-level aluminum alloy coated hot-formed steel sheet according to claim 1 or 2, wherein the composition of the base steel sheet further satisfies: mn+Cr+Si is less than or equal to 2.00%.

4. A high strength and high toughness 1500 MPa-level aluminum alloy coated hot formed steel sheet according to any one of claims 1-3, wherein the thickness of the aluminum alloy coating is 7-19 μm, and the thickness fluctuation of the FeAlSi suppressed layer in the aluminum alloy coating is not more than 40%.

5. A method for producing a high-strength high-toughness 1500 MPa-level aluminum alloy coated hot-formed steel sheet according to any one of claims 1 to 4, characterized in that the production method comprises the following process steps: steelmaking, continuous casting, hot rolling, pickling and cold rolling, substrate cleaning, annealing, coating, finishing and coiling.

6. The method according to claim 5, wherein the hot rolling is followed by coiling at a coiling temperature of 450 to 580 ℃.

7. The method according to claim 5, wherein the cold-rolled reduction ratio by pickling is 60% or less.

8. The method according to claim 5, wherein the annealing temperature is 700 to 810 ℃ and the annealing dew point is not more than 0 ℃.

9. The method according to claim 5, wherein the plating solution temperature is 600 to 680 ℃.

10. A hot-formed steel member, characterized in that it is obtained by hot-forming a hot-formed steel sheet using the high-strength high-toughness 1500 MPa-grade aluminum alloy-coated steel sheet according to any one of claims 1 to 4.

11. The hot-formed steel member according to claim 10, wherein the number of kekokadak pores having a diameter above 1.0 μm in the hot-formed inter-diffusion layer does not exceed 15/100 μm.

12. The hot-formed steel member according to claim 10 or 11, wherein the cold bending angle of the hot-formed steel member after baking is not less than 55 °, the hot-formed steel member is subjected to scratch corrosion test after being coated, the maximum corrosion expansion width is not more than 4mm, the number of welding spots of the hot-formed steel member fusion diameter is not less than 5.0mm is not less than 500, and the tensile strength of the hot-formed steel member is not less than 1450MPa.

13. Use of a thermoformed steel component according to any one of claims 10 to 12 for automotive components.