High-corrosion-resistance hot air bulging forming steel member and preparation method thereof

Abstract

The invention relates to a high-corrosion-resistance hot air bulging forming steel component and a preparation method, and belongs to the technical field of component production. The steel member comprises a steel base body and a plating layer attached to at least part of the surface of the steel base body. Wherein the steel matrix comprises the following chemical components in percentage by mass: more than or equal to 0.15% of C, less than or equal to 0.40% of Si, less than or equal to 0.50% of Al, 0.10-0.30% of Cr, less than or equal to 0.20% of Mo, less than or equal to 0.40% of Ni, 0.0001-0.0050% of B, less than or equal to 0.02% of P, less than or equal to 0.005% of S, less than or equal to 0.01% of N, less than or equal to 0.003% of O and a matrix element Fe; the chemical components of the steel matrix simultaneously meet the following conditions: the sum of the mass fractions of Cr, Mo and Ni is 0.20-0.80%, and the sum of the mass fractions of Al and Si is 0.30-0.60%; a microscopic structure of the steel matrix comprises martensite, and the volume fraction of the martensite is larger than or equal to 80%. An aluminum element is introduced into hot dipping to form an inhibition layer to enhance the binding force of a plating layer, and an alloying process is dynamically regulated and controlled based on the thickness of a steel plate, so that sufficient austenitizing of a matrix is synchronously realized to guarantee the hot forming strength, and the plating layer structure of a gamma (Fe3Zn10) phase is optimized.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of component production, in particular to a high-corrosion-resistance hot gas bulging forming steel component and a preparation method thereof. BACKGROUND

[0002] Automobile lightweighting and passive safety requirements continue to drive the progress of hot stamping technology, among which the "hot gas bulging forming combined die quenching" process has attracted much attention because it can produce ultra-high strength tubular beam components (such as vehicle door impact beams and A / B pillars). The new energy vehicle field particularly needs components with ultra-high strength, high plasticity and toughness, and long-term corrosion resistance, which depends on the design of a martensite-dominated complex microstructure. Although existing zinc-based plating technology can simultaneously achieve high-temperature oxidation prevention and electrochemical protection, it still has a significant process adaptability bottleneck in complex tubular gas bulging forming, which is particularly embodied in the heating link.

[0003] With the complexity of tubular beam configuration, the traditional process needs to pre-bend the tube to form a spatial profile and then go through multiple processes of heating, bulging, and quenching, significantly increasing the process difficulty. There are two major problems in the current tube blank heating: 1) self-resistance heating causes local overburning and zinc layer oxidation failure due to the coupling of skin effect and uneven wall thickness of the bent tube; 2) the efficiency of the radiation furnace is low and cannot meet the mass production demand. What is particularly critical is that existing technologies have not recognized the synergistic defects of tube bending variation and heating methods, and there is a lack of systematic solutions, which seriously restricts the reliable manufacturing of complex tubular beams and the integrity of the plating layer. Therefore, it is urgent to develop a synergistic process that integrates plating protection and efficient and uniform heating to fundamentally improve the plating layer integrity and mass production stability while ensuring the geometric accuracy of complex tubular beam components. SUMMARY

[0004] The application provides a high-corrosion-resistance hot gas bulging forming steel component and a preparation method thereof to solve the following technical problem: how to synergistically solve the dual contradictions of zinc layer oxidation failure caused by uneven heating due to pre-bending of the tube and low efficiency of traditional heating. In a first aspect, the embodiments of the application provide a high-corrosion-resistance hot gas bulging forming steel component, which comprises a steel base body and a plating layer attached to at least part of the surface of the steel base body. In the steel base body, the chemical composition is as follows: C≥0.15%, Si≤0.40%, Al≤0.50%, Cr: 0.10%~0.30%, Mo≤0.20%, Ni≤0.40%, B: 0.0001%~0.0050%, P≤0.02%, S≤0.005%, N≤0.01%, O≤0.003%, and the base element Fe.

[0005] Optionally, the chemical composition of the steel substrate satisfies simultaneously: the sum of mass fractions of Cr, Mo and Ni is 0.20%-0.80%, and the sum of mass fractions of Al and Si is 0.30%-0.60%.

[0006] Optionally, the microstructure of the steel substrate comprises martensite, and the volume fraction of the martensite is ≥80%.

[0007] Optionally, the plating layer is a zinc-based plating layer, and the zinc-based plating layer comprises a first layer and a second layer: the first layer is a layer of iron-rich α-Fe(Zn) phase, and the second layer is a mixed layer of iron-rich α-Fe(Zn) phase and zinc-rich Γ(Fe3Zn 10 ) intermetallic phase. In the zinc-based plating layer, the mass fraction of Zn is ≥40%, the mass fraction of Zn in the iron-rich α-Fe phase is ≥20%, and the mass fraction of Zn in the zinc-rich Γ(Fe3Zn 10 ) intermetallic phase is ≥65%.

[0008] Optionally, the single-side weight of the zinc-based plating layer is 30g / m 2 ~80g / m 2 .

[0009] Optionally, the volume fraction of the iron-rich α-Fe(Zn) phase in the first layer is ≥90%, and the zinc-rich Γ(Fe3Zn 10 ) intermetallic phase is isolated from the steel substrate by the first layer.

[0010] Optionally, the total thickness of the zinc-based plating layer is 7μm-25μm, and the ratio p of the average thickness of the first layer to the average thickness of the second layer is 0.3-3.0.

[0011] Optionally, the chemical composition of the steel substrate further comprises, in terms of mass fraction, any two or three of Ti: 0.01%-0.06%, Nb: 0.01%-0.06%, and V: 0.01%-0.10%; wherein 0.04%≤Ti+4Nb+4V<0.60% and Ti / 2(Nb+V)≤1.0%, and Ti, Nb and V each represent the mass fraction of the corresponding element in the steel substrate.

[0012] Optionally, the chemical composition of the steel substrate further satisfies, in terms of mass fraction: when the mass fraction of C is 0.15%-0.25%, the mass fraction of Mn is 1.50%-2.50%; when the mass fraction of C is 0.25%-0.40%, the mass fraction of Mn is 1.0%-1.5%.

[0013] Optionally, the steel member satisfies at least one of the following properties: tensile strength: 1300 MPa to 2400 MPa, and elongation at break ≥4%.

[0014] In a second aspect, the embodiments of the present application provide a method for preparing the steel member in the first aspect, and the method comprises the following steps: obtaining a steel strip having the chemical composition according to any one of claims 1 to 4; carrying out hot-dip galvanizing and alloy annealing on the steel strip in sequence to obtain a coated steel strip; carrying out heating, hot gas bulging and quenching on the coated steel strip in sequence to obtain the steel member.

[0015] Optionally, the temperature of the hot-dip galvanizing is 400℃ to 500℃.

[0016] Optionally, the temperature of the alloy annealing is 700℃ to 900℃.

[0017] Optionally, the heating is multi-stage heating, and the multi-stage heating comprises a first stage and a second stage. wherein the heating temperature T1 of the first stage is ≤760℃, and the heating temperature T2 of the second stage is 840℃ to 900℃.

[0018] Optionally, the heating speed V1 of the first stage is 5℃ / s to 30℃ / s, and when V1≥10℃ / s, the coated steel strip is subjected to soaking at a temperature of 600℃ to 760℃, and the soaking time is ≤40s.

[0019] Optionally, the heating speed V2 of the second stage is 5℃ / s to 15℃ / s.

[0020] Optionally, the total time of the heating is 40s to 200s.

[0021] Optionally, the gas pressure of the hot gas bulging is 20MPa to 150MPa, and the pressure holding time of the hot gas bulging is 5s to 20s.

[0022] Optionally, the cooling rate of the quenching is 20℃ / s to 100℃ / s, and the final cooling temperature of the quenching is 50℃ to 200℃.

[0023] The above technical solution provided by the embodiments of the present application has the following advantages compared with the prior art: The embodiment of the present application provides a high corrosion-resistant hot gas expansion forming steel member, the steel member comprising a steel base body and a plating layer attached to at least part of the surface of the steel base body; wherein the chemical composition of the steel base body, in terms of mass fraction, is: C >= 0.15%, Si <= 0.40%, Al <= 0.50%, Cr: 0.10%-0.30%, Mo <= 0.20%, Ni <= 0.40%, B: 0.0001%-0.0050%, P <= 0.02%, S <= 0.005%, N <= 0.01%, O <= 0.003%, and base element Fe; the chemical composition of the steel base body simultaneously satisfies: the sum of the mass fractions of Cr, Mo and Ni is 0.20%-0.80%, and the sum of the mass fractions of Al and Si is 0.30%-0.60%; the microstructure of the steel base body comprises martensite, and the volume fraction of the martensite is >= 80%. By synergistically regulating the grain size and the martensite-bainite complex phase structure through micro-alloying, the mechanical properties of the part are ensured, the heat treatment process is simultaneously optimized, and the plating layer structure and thickness are accurately controlled to realize long-term corrosion resistance. BRIEF DESCRIPTION OF DRAWINGS

[0024] The drawings incorporated in the specification and forming a part thereof illustrate embodiments consistent with the present application and, together with the description, serve to explain the principles of the application.

[0025] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments or the prior art description will be briefly introduced as follows. Obviously, those skilled in the art can obtain other drawings according to these drawings without any creative effort.

[0026] Figure 1 A flowchart of a high corrosion-resistant hot gas expansion forming steel member provided by the embodiment of the present application is provided. Figure 2 A plating layer microstructure diagram provided by the embodiment 1 of the present application is provided. Figure 3 A plating layer microstructure diagram provided by the embodiment 2 of the present application is provided. Figure 4 A microstructure diagram provided by the comparative example 1 of the present application is provided. Figure 5 A plating layer SEM diagram and EDS component spectrum diagram provided by the embodiment 5 of the present application are provided. Figure 6 A surface oxidation powder comparison diagram of the embodiment 1 and the comparative example 3 of the present application is provided. DETAILED DESCRIPTION

[0027] In order to make the objects, technical solutions and advantages of the embodiments of the present application clearer, the following will be combined with the accompanying drawings for the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are some but not all of the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by a person of ordinary skill in the art without creative work fall within the protection scope of the present application.

[0028] The range descriptions described herein, such as numerical range, ratio range, etc., include all possible subranges and single values within the range, for example, the range description of "1 to 6" or "1~6" covers all subranges (such as 1 to 3, 2 to 5, etc.) and single numbers (such as 1, 2, 3, 4, 5, 6) between 1 and 6. Unless otherwise specified, the terms "include", "contain" and the like used herein mean "including but not limited to"; the relationship terms "first", "second" and the like are only used to distinguish different entities or operations, and do not imply actual sequence or relationship. "And / or" means that multiple situations can exist independently or simultaneously. "At least one", "multiple", "at least one" and the like refer to any combination of the corresponding objects, including single or multiple combinations of objects. The proportional relationship involved herein, such as mass ratio, molar ratio, etc., should be understood as the corresponding relationship between the front and the rear in the proportional form according to the description order. The raw materials, reagents, instruments and equipment used herein can be purchased or prepared by existing methods.

[0029] In a first aspect, the embodiments of the present application provide a high-corrosion-resistant hot gas forming steel member, which comprises a steel base body and a plating layer attached to at least part of the surface of the steel base body. In the steel base body, the chemical composition in terms of mass fraction is: C≥0.15%, Si≤0.40%, Al≤0.50%, Cr: 0.10%~0.30%, Mo≤0.20%, Ni≤0.40%, B: 0.0001%~0.0050%, P≤0.02%, S≤0.005%, N≤0.01%, O≤0.003%, and base element Fe.

[0030] The positive effect of limiting the mass fraction of C to≥0.15%: C, as the most economical and effective solid solution strengthening element, can guarantee the strength requirement of the hot stamping steel. However, if the mass fraction of C is≥0.40%, the toughness and plasticity matching will be deteriorated, resulting in too high strength and weakening the impact energy absorption performance, and increasing the welding difficulty of safety components. Exemplarily, the mass fraction of C can be 0.15%, 0.20%, 0.25%, 0.30%, etc.

[0031] Positive effects of limiting the mass fraction of Si to be ≤0.40%: Si, as a ferrite-forming element, is dissolved in ferrite phase during the holding period of austenitization of hot stamping steel, and its dissolution significantly increases the activity of C atoms, driving the diffusion of C from ferrite to austenite. This diffusion process increases the carbon content of austenite, thereby improving its stability, but too high a mass fraction of Si will cause embrittlement risk. For example, the mass fraction of Si can be 0.05%, 0.10%, 0.15%, 0.20%, 0.25%, 0.30%, 0.35%, 0.40%, etc.

[0032] Positive effects of limiting the mass fraction of Al to be ≤0.50%: Al can improve the plasticity of steel by increasing the driving force of austenite to bainite transformation, significantly accelerating the kinetics of bainite phase transformation. This process simultaneously increases the activity of C atoms in ferrite and inhibits the precipitation of cementite; but the mass fraction of Al needs to be controlled to avoid excessive risk of nozzle clogging during continuous casting. For example, the mass fraction of Al can be 0.10%, 0.15%, 0.20%, 0.25%, 0.30%, 0.35%, 0.40%, 0.45%, 0.50%, etc.

[0033] Positive effects of limiting the mass fraction of Cr to be 0.10%-0.30%: Cr can significantly improve the hardenability of steel and inhibit high-temperature surface oxidation, which is beneficial to obtaining a cold-rolled base material with high surface quality; but as a strong carbide-forming element, excessive Cr will excessively promote bainite generation, so the upper limit of the mass fraction needs to be controlled. For example, the mass fraction of Cr can be 0.10%, 0.15%, 0.20%, 0.25%, 0.30%, etc.

[0034] Positive effects of limiting the mass fraction of Mo to be ≤0.20%: Mo can significantly improve the hardenability of steel, with an effect between Cr and Mn; at the same time, it can achieve precise control of the size of precipitated phases by solid solution strengthening of ferrite and stabilization of carbides, thereby synergistically enhancing the effects of precipitation strengthening and hydrogen embrittlement resistance. But the upper limit of the mass fraction of Mo needs to be controlled to avoid hindering the implementation of hot forming process due to the sharp increase in deformation resistance during hot working. For example, the mass fraction of Mo can be 0.05%, 0.10%, 0.15%, 0.20%, etc.

[0035] Positive effects of limiting the mass fraction of Ni to be ≤0.40%: Ni can improve the strength of steel while maintaining excellent plasticity and toughness, and significantly improve the low-temperature service performance of the material by lowering the ductile-brittle transition temperature. For example, the mass fraction of Ni can be 0.05%, 0.10%, 0.15%, 0.20%, 0.25%, 0.30%, 0.35%, 0.40%, etc.

[0036] The positive effect of limiting the mass fraction of B to 0.0001% to 0.0050% is that the hardenability can be significantly improved, the grain boundary can be strengthened, and the brittle phase precipitation can be inhibited, while the alloy cost is reduced. For example, the mass fraction of B can be 0.0010%, 0.0020%, 0.0030%, 0.0040%, 0.0050%, etc.

[0037] The positive effect of limiting the mass fraction of P to ≤0.02% is that the grain boundary segregation brittleness and hydrogen trap density can be effectively inhibited, the toughness and plasticity of the steel material can be significantly improved, and the risk of hydrogen-induced delayed fracture can be reduced, thereby ensuring the service reliability of the component. For example, the mass fraction of P can be 0.01%, 0.02%, etc.

[0038] The positive effect of limiting the mass fraction of S to ≤0.005% is that the MnS inclusion coarsening and grain boundary segregation can be effectively inhibited, the purity and toughness of the steel material can be significantly improved, and the hydrogen diffusion channel density can be reduced, thereby ensuring the fatigue resistance and brittle fracture resistance of the dynamic load component. For example, the mass fraction of S can be 0.001%, 0.002%, 0.003%, 0.004%, 0.005%, etc.

[0039] The positive effect of limiting the mass fraction of N to ≤0.01% is that the nitride grain refinement and hydrogen trap effects can be maximized, and the brittleness risk caused by nitrogen grain boundary segregation can be effectively inhibited, thereby ensuring the synergistic improvement of the strength and toughness of the material and the delayed fracture resistance. For example, the mass fraction of N can be 0.002%, 0.004%, 0.006%, 0.008%, 0.010%, etc.

[0040] The positive effect of limiting the mass fraction of O to ≤0.003% is that the number and size of oxide inclusions can be significantly reduced, the cleanliness, fatigue life, and cold forming surface quality of the steel material can be significantly improved, and the brittle fracture resistance under dynamic load can be simultaneously optimized. For example, the mass fraction of O can be 0.001%, 0.002%, 0.003%, etc.

[0041] Fe is the base element, and the specific content / content range of Fe can be obtained by the upper and lower limit formula of the components, that is: The sum of the content percentages of each component in a composition should be equal to 100%, and the content range of several components should meet the following conditions: the upper limit value of a certain component + the lower limit value of other components ≤100; the lower limit value of a certain component + the upper limit value of other components ≥100. In addition, the specific content of Fe is supplemented to 100% by the actual detection value of the above-mentioned other chemical components and unlisted active elements and / or impurities, and Fe as the base element accounts for an absolute proportion.

[0042] In some embodiments, the chemical composition of the steel substrate satisfies both: the sum of mass fractions of Cr, Mo and Ni is 0.20%-0.80%, and the sum of mass fractions of Al and Si is 0.30%-0.60%.

[0043] The sum of mass fractions of Cr, Mo and Ni is 0.20%-0.80%, and the sum of mass fractions of Al and Si is 0.30%-0.60%, which can synergistically ensure the hardenability, high-temperature oxidation resistance and plating adhesion of the steel material, and simultaneously optimize the matching of strength and toughness and the feasibility of mass production process. For example, the sum of mass fractions of Cr, Mo and Ni can be 0.20%, 0.30%, 0.40%, 0.50%, 0.60%, 0.70%, 0.80%, etc.; the sum of mass fractions of Al and Si can be 0.30%, 0.40%, 0.50%, 0.60%, etc.

[0044] In some embodiments, the microstructure of the steel substrate includes martensite, and the volume fraction of the martensite is ≥80%.

[0045] The microstructure of the steel substrate includes martensite, and the volume fraction of the martensite is ≥80%, which can ensure that the martensite forms a continuous strengthening framework as the dominant phase, endows the material with super-high strength characteristics, and at the same time retains a proper amount of toughness phase dispersed distribution to maintain the plastic deformation ability and crack inhibition function under impact working conditions. For example, the volume fraction of the martensite can be 80%, 85%, 90%, etc.

[0046] In some embodiments, the plating layer is a zinc-based plating layer, which includes a first layer and a second layer: the first layer is a layer of iron-rich α-Fe(Zn) phase, and the second layer is a mixed layer of iron-rich α-Fe(Zn) phase and zinc-rich Γ(Fe3Zn 10 ) intermetallic phase. In the zinc-based plating layer, the mass fraction of Zn is ≥40% in total, the mass fraction of Zn in the iron-rich α-Fe phase is ≥20%, and the mass fraction of Zn in the zinc-rich Γ(Fe3Zn 10 ) intermetallic phase is ≥65%.

[0047] The first layer is a layer of iron-rich α-Fe(Zn) phase, which serves as a substrate transition layer, enhances the plating adhesion by high Fe content and delays the initial corrosion rate, and provides a basic protective barrier for the part. The second layer is a mixed layer of iron-rich α-Fe(Zn) phase and zinc-rich Γ(Fe3Zn 10) intermetallic phases, the gradient zinc-rich design coordinates the sacrificial anode activity and long-term corrosion resistance, the Γ phase preferentially corrodes to protect the substrate, and the α phase supports the structural integrity. The mass fraction of Zn ensures a continuous sacrificial anode protection network, avoiding the spread of substrate corrosion caused by local protection failure. Exemplarily, in the zinc-based coating, the mass fraction of Zn can be 40%, 45%, 50%, 55%, 60%, etc.; in the iron-rich α-Fe phase, the mass fraction of Zn can be 20%, 25%, 30%, 35%, 40%, etc.; in the zinc-rich Γ (Fe3Zn 10 ) intermetallic phase, the mass fraction of Zn can be 65%, 70%, 75%, etc.

[0048] In some embodiments, the single-sided weight of the zinc-based coating is 30 g / m 2 ~80 g / m 2 .

[0049] The single-sided weight of the zinc-based coating is between 30 g / m 2 ~80 g / m 2 , the lower limit ensures continuous coating coverage to provide basic sacrificial anode protection, and the upper limit prevents the coating from being too thick, causing forming cracking and cost soaring, while synergistically regulating the coating thickness to achieve the optimal solution of long-term corrosion protection and process stability. Exemplarily, the single-sided weight of the zinc-based coating can be 30 g / m 2 , 40 g / m 2 , 50 g / m 2 , 60 g / m 2 , 70 g / m 2 , 80 g / m 2 , etc.

[0050] In some embodiments, the volume fraction of the iron-rich α-Fe (Zn) phase in the first layer is ≥90%, and the zinc-rich Γ (Fe3Zn 10 ) intermetallic phase is isolated from the steel substrate by the first layer.

[0051] By isolating the Γ phase from direct contact with the steel substrate through a high-purity α phase (≥90%) isolation layer, the generation of brittle Fe-Zn alloy phases is effectively inhibited, and the penetration of corrosion current into the substrate is simultaneously delayed, achieving synergistic optimization of long-term corrosion protection and interface integrity. Exemplarily, the volume fraction of the iron-rich α-Fe (Zn) phase in the first layer can be 90%, 91%, 92%, 93%, 94%, 95%, etc.

[0052] In some embodiments, the total thickness of the zinc-based coating is 7 μm~25 μm, and the ratio p of the average thickness of the first layer to the average thickness of the second layer is 0.3~3.0.

[0053] The total thickness of the zinc-based plating layer is between 7 μm and 25 μm, the lower limit of the plating layer thickness is precisely controlled to ensure the formation of a continuous corrosion barrier, the upper limit avoids the risk of forming cracks caused by stress concentration at the interface, and the corrosion resistance and process stability are simultaneously optimized. For example, the total thickness of the zinc-based plating layer can be 7 μm, 11 μm, 15 μm, 19 μm, 23 μm, etc. The ratio p of the average thickness of the first layer to the average thickness of the second layer is 0.3 to 3.0, and the p value range is limited to balance the sacrificial anode activity and long-term corrosion resistance, p≥0.3 to maintain sufficient Γ phase to provide electrochemical protection, and p≤3.0 to ensure that the α phase barrier function inhibits corrosion propagation. For example, the ratio p of the average thickness of the first layer to the average thickness of the second layer can be 0.3, 0.7, 1.1, 1.5, 1.9, 2.3, 2.7, etc.

[0054] In some embodiments, the chemical composition of the steel substrate further includes, in mass fraction, any two or three of Ti: 0.01% to 0.06%, Nb: 0.01% to 0.06%, and V: 0.01% to 0.10%; wherein 0.04%≤Ti+4Nb+4V<0.60% and Ti / 2(Nb+V)≤1.0%, Ti, Nb, and V each refer to the mass fraction of the corresponding element in the steel substrate.

[0055] By synergistically adding Nb, Ti, and V micro-alloying elements, the triple synergistic gain is achieved by using the nanoscale precipitated phase (NbC / VC / TiN) formed by them and carbon and nitrogen: Nb dominates austenite grain refinement, V promotes ultra-fine precipitate strengthening, and Ti provides economic complement. The composite addition index is strictly controlled to be 0.04%≤Ti+4Nb+4V<0.60% (atomic weight ratio coefficient balance), the lower limit ensures the density of the precipitated phase to strengthen the grain boundary pinning effect, the precipitate strength, and the hydrogen trap density, and the upper limit avoids the risk of coarsening and deactivation; simultaneously, the element ratio Ti / 2(Nb+V)≤1.0% is limited to prevent excessive Ti from causing coarse phase wrapping Nb / V and weakening the micro-alloying effect, and finally the optimal synergy of fine-grain strengthening, precipitate strengthening, and hydrogen embrittlement resistance is achieved. For example, the mass fraction of Ti can be 0.01%, 0.02%, 0.03%, 0.04%, 0.05%, 0.06%, etc.; the mass fraction of Nb can be 0.01%, 0.02%, 0.03%, 0.04%, 0.05%, 0.06%, etc.; the mass fraction of V can be 0.02%, 0.04%, 0.06%, 0.08%, 0.10%, etc.; the mass fraction of Ti+4Nb+4V can be 0.10%, 0.20%, 0.30%, 0.40%, 0.50%, 0.60%, etc.; and the mass fraction of Ti / 2(Nb+V) can be 0.2%, 0.4%, 0.6%, 0.8%, 1.0%, etc.

[0056] In some embodiments, the chemical composition of the steel base further satisfies, in terms of mass fraction: When the mass fraction of C is 0.15% to 0.25%, the mass fraction of Mn is 1.50% to 2.50%. When the mass fraction of C is 0.25% to 0.40%, the mass fraction of Mn is 1.0% to 1.5%.

[0057] When the mass fraction of C is 0.15% to 0.25%, the mass fraction of Mn is 1.50% to 2.50%, the positive effect is: through the low mass fraction of C to ensure weldability and ductile plasticity, while the high mass fraction of Mn compensates for the hardenability and stabilizes the residual austenite, realizing the high strength and high collision energy absorption demand of lightweight thin-walled parts. For example, when the mass fraction of C is 0.15% to 0.25%, the mass fraction of Mn can be 1.50%, 2.00%, 2.50%, etc.

[0058] When the mass fraction of C is 0.25% to 0.40%, the mass fraction of Mn is 1.0% to 1.5%, the positive effect is: using the high mass fraction of C to improve the strength and hardness of the base, and controlling the lower limit of Mn to avoid incomplete martensitic transformation caused by excessive austenite stability, meeting the deep hardenability and compression strength of thick-walled parts. For example, when the mass fraction of C is 0.25% to 0.40%, the mass fraction of Mn can be 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, etc.

[0059] In some embodiments, the steel member satisfies at least one of the following properties: tensile strength: 1300MPa to 2400MPa, fracture elongation ≥4%.

[0060] Tensile strength: the maximum engineering stress that the material can withstand before tensile fracture. Fracture elongation: the percentage of plastic deformation and original length of the material at the time of fracture. For example, the tensile strength can be 1300MPa, 1500MPa, 1700MPa, 1900MPa, 2100MPa, 2300MPa, etc.; the fracture elongation can be 4%, 5%, 6%, etc.

[0061] Figure 1 A flow chart of a high-corrosion-resistant hot gas expansion forming steel member and a preparation method provided by the embodiments of the present application.

[0062] Please refer to Figure 1 , in a second aspect, the present application provides a preparation method of the steel member in the first aspect, the method comprises: S1, obtaining a steel strip having the chemical composition according to any one of claims 1 to 4; S2, sequentially hot-dip galvanizing and alloying annealing the steel strip to obtain a coated steel strip; S3, sequentially heating, hot gas forming and quenching the coated steel strip to obtain a steel component.

[0063] In some embodiments, the temperature of the hot-dip galvanizing is 400-500℃.

[0064] The temperature of the hot-dip galvanizing is between 400-500℃, the zinc liquid fluidity and reaction kinetics are controlled through the medium temperature range, the uniform and dense coating is realized, and the excessive growth of brittle intermetallic phase is inhibited, so as to guarantee the initial bonding strength and surface integrity of the coating. For example, the temperature of the hot-dip galvanizing can be 400℃, 420℃, 440℃, 460℃, 480℃, 500℃, etc.

[0065] In some embodiments, the temperature of the alloying annealing is 700-900℃.

[0066] The temperature of the alloying annealing is between 700-900℃, the zinc-iron interdiffusion and matrix austenitization are simultaneously driven through the high temperature range, the gradient alloying coating is formed at the same time, the matrix structure is strengthened, and the integration of corrosion resistance and mechanical properties is achieved. For example, the temperature of the alloying annealing can be 700℃, 750℃, 800℃, 850℃, 900℃, etc.

[0067] In some embodiments, the heating is multi-stage heating, and the multi-stage heating includes a first stage and a second stage. In the first stage, the heating temperature T1 is ≤760℃, and in the second stage, the heating temperature T2 is 840-900℃.

[0068] The heating is by resistance heating or induction heating, and the temperature is monitored in real time by a thermocouple or a pyrometer. In the first stage, the heating temperature T1 is ≤760℃, the evaporation and oxidation of the coating elements are preferentially inhibited through low-temperature slow heating, the temperature is uniformly preheated to avoid thermal deformation of the thin-walled pipe, and stable interface conditions are created for high-temperature phase change. For example, the heating temperature T1 in the first stage can be 700℃, 720℃, 740℃, 760℃, etc. In the second stage, the heating temperature T2 is between 840-900℃, rapid austenitization is implemented after the activation of the coating protection mechanism, the matrix is completely phase-changed and the micro-alloying elements are diffused and dissolved, and the target structure regulation and coating alloying reaction are achieved. For example, the heating temperature T2 in the second stage can be 840℃, 860℃, 880℃, 900℃, etc.

[0069] In some embodiments, the heating rate V1 of the first stage is 5-30 °C / s, and when V1≥10 °C / s, the coated steel strip is soaked at a temperature of 600-760 °C, and the soaking time is ≤40 s.

[0070] The heating rate V1 of the first stage is 5-30 °C / s, which balances production efficiency and thermal shock control through medium-high speed heating, and when a faster rate is used, a soaking procedure is triggered to eliminate the pipe blank cross-section temperature difference to inhibit the coating cross-section temperature difference to inhibit the risk of coating thermal shock cracking. For example, the heating rate V1 of the first stage can be 5 °C / s, 10 °C / s, 15 °C / s, 20 °C / s, 25 °C / s, 30 °C / s, etc. When V1≥10 °C / s, the coated steel strip is soaked at a temperature of 600-760 °C to establish a thermal equilibrium platform in the critical temperature window, promote the homogenization of heat conduction inside the pipe wall, and stabilize the coating structure, laying a low stress foundation for subsequent high temperature phase change. For example, the soaking temperature can be 600 °C, 650 °C, 700 °C, 750 °C, etc.; and the soaking time can be 20 s, 25 s, 30 s, 35 s, 40 s, etc.

[0071] In some embodiments, the heating rate V2 of the second stage is 5-15 °C / s.

[0072] The heating rate V2 of the second stage is 5-15 °C / s, which precisely controls the austenite phase change process and coating alloying reaction kinetics through medium-low speed heating, synchronously achieving the uniform refinement of the base body structure and the stable formation of the coating gradient structure, and avoiding the risks of coating peeling and abnormal grain coarsening caused by thermal stress. For example, the heating rate V2 of the second stage can be 5 °C / s, 10 °C / s, 15 °C / s, etc.

[0073] In some embodiments, the total heating time is 40-200 s.

[0074] The total heating time is 40-200 s, which through the lower limit ensures the completion of the base body phase change and coating alloying reaction, and the upper limit inhibits grain coarsening and excessive oxidation of the coating, achieving the process balance of structure and performance control and coating integrity. For example, the total heating time can be 50 s, 100 s, 150 s, 200 s, etc.

[0075] In some embodiments, the gas pressure of the hot gas expansion is 20-150 MPa, and the holding time of the hot gas expansion is 5-20 s.

[0076] The gas pressure of hot gas bulging is between 20 MPa and 150 MPa, the technology of injecting high-pressure gas to make it expand into shape, inert gas (such as nitrogen) is pressurized, so that the pipe fitting is attached to the inner wall of the mold to achieve the purpose of forming and rapid cooling. For example, the gas pressure of hot gas bulging can be 20 MPa, 40 MPa, 60 MPa, 80 MPa, 100 MPa, 120 MPa, 140 MPa, etc. The holding time of hot gas bulging is between 5 s and 20 s, which ensures the dimensional accuracy of the part. For example, the holding time of hot gas bulging can be 5 s, 10 s, 15 s, 20 s, etc.

[0077] In some embodiments, the cooling rate of quenching is 20℃ / s~100℃ / s, and the final cooling temperature of quenching is 50℃~200℃.

[0078] The cooling rate of quenching is 20℃ / s~100℃ / s, and the final cooling temperature of quenching is between 50℃ and 200℃, so as to obtain a structure mainly of martensite. If the cooling rate is too low, it is difficult to achieve complete martensitic transformation, resulting in a high opening temperature and a decrease in the dimensional accuracy of the part, and the holding time needs to be prolonged to cool the part to near room temperature. While a too high cooling rate will cause excessive thermal stress in the martensite matrix, thereby degrading the elongation performance of the part. For example, the cooling rate of quenching can be 20℃ / s, 40℃ / s, 60℃ / s, 80℃ / s, 100℃ / s, etc.; the final cooling temperature of quenching can be 50℃, 100℃, 150℃, 200℃, etc.

[0079] The product prepared by the method for preparing the steel member is the steel member described above. Since the method for preparing the steel member adopts part or all of the technical solutions of the steel member embodiment, it at least has all the beneficial effects brought by the technical solutions of the above embodiments, which will not be repeated here.

[0080] The application will be further described below in conjunction with specific examples. The experimental methods in the following examples are not specified, and are usually determined according to national standards / industry standards / the content disclosed herein; if there is no corresponding national standard / industry standard / the content disclosed herein, the general international standard, conventional conditions or the conditions recommended by the manufacturer are used.

[0081] The chemical composition of the steel base body of the examples and comparative examples (mass percentage / %) is shown in Tables 1 and 2.

[0082] Table 1

[0083] Table 2

[0084] Based on the chemical composition of the ingots in the examples and comparative examples, this embodiment also provides a method for preparing high corrosion-resistant hot gas expansion forming steel components, including the following steps: A steel strip having the chemical composition described in any one of claims 1 to 4 is obtained; The steel strip is subjected to hot-dip galvanizing and alloying annealing in sequence to obtain coated steel strip material; The coated steel strip is sequentially heated, expanded, and quenched to obtain the steel component. The process parameters are shown in Tables 3 and 4.

[0085] The process parameters for the examples and comparative examples are shown in Table 3.

[0086] Table 3

[0087] The hot stamping process parameters for the embodiments and comparative examples are shown in Table 4.

[0088] Table 4

[0089] The coating thickness, corrosion potential after thermoforming, and cyclic corrosion weight loss results of the examples and comparative examples are shown in Table 5.

[0090] Table 5

[0091] The mechanical properties and volume fractions of each tissue in the examples and comparative examples are shown in Table 6.

[0092] Table 6

[0093] The data tables above provide a clear comparison of the differences between various embodiments and comparative examples. The following conclusions can be drawn: As can be seen from the data in Tables 5 and 6, the steel components provided in the embodiments of this application have a corrosion potential of -0.875V to -0.763V, a yield strength of 401MPa to 1361MPa, a tensile strength of 691MPa to 2108MPa, and an elongation at break of 4% to 18%.

[0094] As can be seen from Examples 1-6 and Comparative Examples 1-3, the zinc-based coating after thermal expansion has good corrosion resistance, that is, it has a low potential, which plays a role in cathodic protection, and avoids the rapid weight loss caused by excessively low potential.

[0095] Appendix Figures 2-6 Detailed explanation: Figure 2 This is a diagram of the coating structure provided in Embodiment 1 of this application. According to... Figure 2It can be known that the plating layer has a clear two-layer structure, the first layer is a continuous iron-rich alpha-Fe (Zn) phase layer, and the second layer is a layered structure uniformly mixed with alpha-Fe (Zn) and zinc-rich Gamma (Fe3Zn 10 ) phase.

[0096] Figure 3 The plating layer microstructure diagram provided for Example 2 of the application is shown in Figure 2. Figure 3 It can be known that the plating layer still maintains the clear two-layer structure characteristics: the first layer is a continuous iron-rich alpha-Fe (Zn) phase transition layer, and the second layer is a mixed layer of alpha-Fe (Zn) and zinc-rich Gamma (Fe3Zn 10 ) phase, but the distribution of the second layer mixed phase is more irregular.

[0097] Figure 4 The microstructure diagram provided for Comparative Example 1 of the application is shown in Figure 3. Figure 4 It can be known that the plating layer structure is discontinuous, there are multiple cracks (length of 17 μm~23.7 μm), and the clear two-layer protective structure in the example is not formed, and the integrity of the plating layer is seriously damaged.

[0098] Figure 5 The plating layer SEM diagram and EDS composition spectrum provided for Example 5 of the application are shown in Figure 5. Figure 5 It can be known that the cross section of the plating layer and the steel substrate presents a gradient element distribution characteristic that the Fe content gradually decreases and the Zn content gradually increases from the substrate side to the surface of the plating layer.

[0099] Figure 6 The surface oxidation powder contrast diagram of Example 1 and Comparative Example 3 of the application is shown in Figure 6. Figure 6 It can be known that the surface oxidation powder of Example 1 is significantly less than that of Comparative Example 3, and the surface is smoother.

[0100] The one or more technical solutions in the embodiments of the application have at least the following technical effects or advantages: The high corrosion-resistant hot gas expansion forming steel member provided by the embodiments of the application balances long-term corrosion resistance and interface integrity through the design of the plating layer gradient structure; through the optimization of process parameters, the defects such as plating layer cracking and grain coarsening are effectively suppressed, and the synergy of the substrate strength and toughness is ensured; at the same time, the synergistic composition design of the micro-alloying element improves the strength of the steel while maintaining good formability, and both high performance and process feasibility are considered.

[0101] The foregoing detailed description of the application has been presented for purposes of illustration and description. Various modifications to the description will be readily apparent to those skilled in the art, and the generic principles defined herein can be applied to other implementations without departing from the spirit or scope of the application. Accordingly, the application is not intended to be limited to the implementations described herein but is to be accorded the widest scope consistent with the principles and novel features to the application.

Claims

1. A high corrosion-resistant hot gas-expanded steel component, characterized in that, The steel component includes a steel substrate and a coating attached to at least a portion of the surface of the steel substrate; The chemical composition of the steel matrix, by mass fraction, is as follows: C ≥ 0.15%, Si ≤ 0.40%, Al ≤ 0.50%, Cr: 0.10%~0.30%, Mo ≤ 0.20%, Ni ≤ 0.40%, B: 0.0001%~0.0050%, P ≤ 0.02%, S ≤ 0.005%, N ≤ 0.01%, O ≤ 0.003%, and Fe as the matrix element; The chemical composition of the steel matrix simultaneously satisfies the following conditions: the sum of the mass fractions of Cr, Mo, and Ni is 0.20%~0.80%, and the sum of the mass fractions of Al and Si is 0.30%~0.60%. The microstructure of the steel matrix includes martensite, and the volume fraction of the martensite is ≥80%. The coating is a zinc-based coating, comprising a first layer and a second layer: the first layer is an iron-rich α-Fe(Zn) phase layer, and the second layer is an iron-rich α-Fe(Zn) phase and a zinc-rich Γ(Fe3Zn) phase. 10 A mixed layer of intermetallic phases; Wherein, the overall Zn mass fraction of the zinc-based coating is ≥40%, and the Zn mass fraction in the iron-rich α-Fe phase is ≥20%; the zinc-rich Γ(Fe3Zn) 10 The mass fraction of Zn in the intermetallic phase is ≥65%; The zinc-based coating has a single-sided weight of 30g / m². 2 ~80g / m 2 ; The volume fraction of the iron-rich α-Fe(Zn) phase in the first layer is ≥90%, and the zinc-rich Γ(Fe3Zn) phase is ≥90%. 10 The metallic phase is isolated from the steel substrate through the first layer; The total thickness of the zinc-based coating is 7μm to 25μm, wherein the ratio p of the average thickness of the first layer to the average thickness of the second layer is 0.3 to 3.

0.

2. The steel component according to claim 1, characterized in that, The chemical composition of the steel matrix, by mass fraction, further includes any two or three of the following: Ti: 0.01%~0.06%, Nb: 0.01%~0.06%, and V: 0.01%~0.10%. Wherein, 0.04%≤Ti+4Nb+4V<0.60% and Ti / 2(Nb+V)≤1.0%, and Ti, Nb, and V all refer to the mass fraction of the corresponding elements in the steel matrix.

3. The steel component according to claim 1, characterized in that, The chemical composition of the steel matrix, by mass fraction, also satisfies: When the mass fraction of C is 0.15%~0.25%, the mass fraction of Mn is 1.50%~2.50%. When the mass fraction of C is 0.25%~0.40%, the mass fraction of Mn is 1.0%~1.5%.

4. The steel component according to claim 1, characterized in that, The steel component meets at least one of the following properties: tensile strength: 1300MPa~2400MPa, elongation at break ≥4%.

5. A method for preparing a steel component according to any one of claims 1 to 4, characterized in that, The method includes: A steel strip having the chemical composition described in any one of claims 1 to 4 is obtained; The steel strip is subjected to hot-dip galvanizing and alloying annealing in sequence to obtain coated steel strip material; The coated steel strip is sequentially heated, hot-gas expanded and quenched to obtain a steel component.

6. The method according to claim 5, characterized in that, The hot-dip galvanizing temperature is 400℃~500℃.

7. The method according to claim 5, characterized in that, The alloying annealing temperature is 700℃~900℃.

8. The method according to claim 5, characterized in that, The heating is multi-stage heating, which includes a first stage and a second stage. Wherein, the heating temperature T1 in the first stage is ≤760℃, and the heating temperature T2 in the second stage is 840℃~900℃; and / or, The heating rate V1 in the first stage is 5℃ / s to 30℃ / s. When V1 ≥ 10℃ / s, the coated steel strip is subjected to uniform heat treatment at a temperature of 600℃ to 760℃ for a duration ≤ 40s; and / or, The heating rate V2 in the second stage is 5℃ / s to 15℃ / s; and / or, The total heating time is 40s to 200s.

9. The method according to claim 5, characterized in that, The gas pressure for hot gas expansion is 20MPa~150MPa, and the pressure holding time for hot gas expansion is 5s~20s.

10. The method according to claim 5, characterized in that, The quenching cooling rate is 20℃ / s to 100℃ / s, and the final cooling temperature of the quenching is 50℃ to 200℃.

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