A steel sheet, hot-stamped part, and method for manufacturing and use thereof

Abstract

The application discloses a kind of steel plate, hot stamping part and its preparation method and application, belong to alloy material technical field, hot stamping part includes oxide layer, alloy layer and steel matrix, alloy layer is between oxide layer and steel matrix;The phase ratio of the phase with Fe content of 45 wt.%-95 wt.% in alloy layer is greater than or equal to 80%, and the frequency of the coincidence site lattice grain boundary Sigma 3 of the phase with Fe content of 45 wt.%-95 wt.% is greater than or equal to 1%.In addition, the application also discloses the composition of the steel plate of the hot stamping part, the preparation method and the hot forming process of the hot stamping part.The application can improve the Fe content of the alloy layer while ensuring the improvement of the LME resistance, control the crystal configuration of the coating, improve the frequency of the coincidence site lattice grain boundary Sigma 3 of the phase with Fe content of 45 wt.%-95 wt.% in zinc-iron alloy layer, and utilize the good intergranular corrosion resistance of the coincidence site lattice structure, which can improve the corrosion resistance of the hot forming part while ensuring the LME resistance.

Description

Technical Field

[0001] This application belongs to the field of alloy materials technology, specifically relating to a steel plate, hot-stamped parts, their preparation methods and applications. Background Technology

[0002] The development of low-carbon technologies demands lightweight, high-strength steel sheets used in the automotive industry, along with excellent deformability. While cold-formed high-strength steel boasts high strength, its deformation is limited and it suffers from springback issues. Hot-formed steel, possessing both high strength and excellent deformability, has garnered significant attention in the automotive steel sheet market. Hot-formed steel undergoes a high-temperature austenitizing process during forming, followed by rapid cooling to obtain a high-strength martensitic structure. It is typically used for lower body structural components and safety parts. Notably, in addition to high strength, lower body components must also meet the essential requirement of corrosion resistance.

[0003] Mainstream hot-formed steels rely on aluminum-silicon coatings to resist corrosion. However, these coatings offer only physical protection and are relatively weak. Therefore, researchers have high hopes for zinc-based coatings, which provide electrochemical protection. However, zinc can cause liquid metal embrittlement (LME) during high-temperature stamping, leading to microcracks and safety risks. Existing technology CN116590640A uses zinc-based coated steel sheets with a continuous lamellar or granular FeAl alloy layer. It controls coating cracking through a two-stage heating and direct hot stamping method, combined with mold closing speed and cooling rate. However, it does not consider the impact of coating changes during stamping on corrosion resistance. Existing technologies also address LME by limiting the proportion of the Γ phase (a zinc-iron alloy phase), but reducing the Γ phase leads to decreased corrosion resistance.

[0004] CN115125439B addresses the control and corrosion resistance of LME cracks, but the method for controlling corrosion resistance is to reduce zinc evaporation through prolonged preheating. However, excessively long hot stamping heating times are detrimental to industrial forming efficiency and increase production line costs. Furthermore, due to excessively low preheating temperatures, the alloying effect of the coating is poor, resulting in insufficient effectiveness in resolving LME. Existing technology CN118696146A attempts to enhance the corrosion resistance of hot-stamped parts by improving the composition and thickness of the surface oxide layer. However, this may adversely affect the weldability of the parts, and the effectiveness of this technical solution in resolving LME may be limited.

[0005] How to control LME cracking while maintaining good corrosion resistance of the coating, resolving the contradiction between good corrosion resistance and LME resistance, and improving solderability remains a major problem in this field. Summary of the Invention

[0006] The technical problem to be solved by this application is to overcome the problem that good corrosion resistance and LME resistance of hot-formed parts cannot be achieved simultaneously in the prior art, thereby providing a steel plate, hot-stamped parts, their preparation method and application.

[0007] Therefore, this application provides the following technical solution:

[0008] According to one aspect of this application, a hot-stamped component is provided, comprising an oxide layer, an alloy layer, and a steel substrate, wherein the alloy layer is located between the oxide layer and the steel substrate;

[0009] The proportion of phases with Fe content of 45 wt.%-95 wt.% in the alloy layer is ≥80%, and the frequency of occurrence of the lattice grain boundary Σ3 of the phase with Fe content of 45 wt.%-95 wt.% is ≥1%.

[0010] LME formation is caused by three factors: an aggressive liquid metal (such as Zn, Ga, Bi); a susceptible material (such as Fe with an FCC structure); and external tensile or internal tensile stresses. In the hot stamping process, the LME susceptibility of zinc-based hot-stamped parts is directly affected by the melting point of the alloy layer phase on the surface of the hot-stamped part. The phase with an Fe content of 45 wt.%-95 wt.% is an iron-rich phase, with a melting point higher than other iron-poor zinc-iron alloy phases and pure zinc phases. LME cracking occurs because the liquid metal penetrates along the stress into the matrix grain boundaries. Reducing the amount of liquid metal can effectively suppress LME cracking. Through extensive experiments, the inventors discovered that limiting the proportion of the iron-rich phase to no less than 80%, i.e., reducing the proportion of the Zn-rich phase, can reduce the probability of unsolidified liquid metal, thereby reducing the risk of LME formation.

[0011] However, in existing technologies, the Fe content is rarely ≥80% (45 wt.%-95 wt.%), because this reduces the electrochemical potential difference between the coating and the substrate, decreasing the preferential reaction tendency of the zinc-iron coating in corrosive environments, which leads to poor corrosion resistance. Therefore, it is necessary to improve corrosion resistance while reducing the risk of LME (Liquid Metal Electrode).

[0012] In fact, the corrosion protection of the substrate by the coating relies not only on the sacrifice of the coating itself, but also on the long-term corrosion resistance of the coating itself. Unrestricted by theory, researchers have discovered through numerous experiments that the fundamental reason for poor corrosion resistance in this situation may be the randomness of the high-temperature formation of the zinc-iron alloy, leading to disordered crystal structure in the coating and resulting in high grain boundary energy. Corrosion of the coating itself typically begins at grain boundaries with high grain boundary energy. Crystal engineering shows that low grain boundary energy is thermodynamically more stable than high grain boundary energy, reducing chemical inhomogeneity at grain boundaries and thus reducing the occurrence of grain boundary corrosion. Simultaneously, a low grain boundary energy structure also implies fewer intercrystalline dislocations and atomic segregations, reducing the number of corrosion-prone sites in the coating. This invention, by significantly increasing the proportion of iron-rich phase and effectively controlling the grain boundaries of the heavy-point lattice, yields hot-stamped components that both reduce the risk of LME formation and enhance corrosion resistance.

[0013] Specifically, it is necessary to control the frequency of occurrence of Σ3 grain boundaries, particularly in the phase with Fe content of 45 wt.%–95 wt.%. A Σ3 grain boundary refers to a three-dimensional periodic superlattice formed by the partial overlap of lattice points of two interpenetrating crystal lattices under a specific orientation. The overlap of Σ3 grain boundaries can be quantified by the Σ value, which is the ratio of the size of the overlapping lattice unit cell to the size of the standard unit cell. Researchers compared the corrosion resistance effects of different Σ values ​​and found that low Σ3 grain boundaries (Σ3 means that one of every three original lattice positions overlaps) have high atomic overlap, ordered crystal orientation, and low grain boundary energy, thus exhibiting significantly better corrosion resistance than ordinary grain boundaries. When the frequency of occurrence of Σ3 grain boundaries in the phase with Fe content of 45 wt.%–95 wt.% is ≥1%, the alloy layer exhibits good corrosion resistance.

[0014] In this application, the frequencies of Σ3 grain boundaries at the lattice of heavy lattice points are statistically analyzed using EBSD (electron backscatter diffraction). EBSD determines the crystallographic orientation of each grain by analyzing the Kikuchi pattern generated by the interaction of the electron beam with the crystal on the sample surface. Furthermore, the coincidence density (1 / Σ) can be directly calculated using the accompanying CHANNEL5 software to quantify the lattice grain boundary characteristics of a specific phase. This invention involves preparing cross-sectional metallographic samples and performing EBSD characterization on the sample coating. Specifically, EBSD images of the coating at 1000x magnification are selected, and the frequencies of Σ3 grain boundaries at the lattice of heavy lattice points for phases with Fe content ranging from 45 wt.% to 95 wt.% are statistically analyzed using the accompanying software. Ten views are randomly selected from each sample, and the average value of the Σ3 frequencies statistically analyzed from the ten views is calculated.

[0015] Furthermore, the frequency of occurrence of the Σ3 lattice grain boundary in the phase with Fe content of 45 wt.%-95 wt.% as defined in this application is ≥2%. A frequency above 2% indicates better periodicity matching of the grain boundary, lower interfacial energy, and better corrosion resistance.

[0016] Furthermore, the occurrence frequency of Σ3 lattice grain boundaries in phases with Fe content of 45 wt.%–95 wt.% at 2%–10% is most favorable for controlling corrosion resistance. This is because when the frequency exceeds 10%, the atomic arrangement at the grain boundaries is more compact, leading to a reduction in dislocation slip and plastic deformation capacity at the grain boundaries, which affects the ductility and formability of the material.

[0017] Optionally, the phase ratio of the phase with Fe content of 45 wt.%-95 wt.% in the alloy layer can be 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, higher, and any value between them.

[0018] Optionally, the frequency of occurrence of the lattice grain boundary Σ3 of the phase with Fe content of 45 wt.%-95 wt.% can be 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, and any value between them.

[0019] The present invention defines "the phase ratio of the phase with Fe content of 45 wt.%-95 wt.% in the alloy layer as ≥80%". This invention lists the following control methods, or their combined use, but does not limit these methods. For example: it can be achieved by optimizing the hot forming process and setting stepped heating (optimizing the temperature and time of hot forming); it can be achieved by reducing the thickness of the zinc layer to reduce the alloying time from a kinetic perspective; it can be achieved by controlling the galvanizing process during steel plate production, such as increasing the hot-dip galvanizing temperature and appropriately extending the annealing time to make the iron distribution in the coating more uniform; it can be achieved by creating a concentration difference of Al element between the coating and the substrate to regulate the role of the Fe2Al5 barrier layer in alloy diffusion.

[0020] The frequency of occurrence of Σ3 lattice grain boundaries at the heavy point is ≥1%, which can be achieved by the following control methods or by using them in combination, and the following methods are not limited. For example: (1) The Al content of the substrate is 0.01%~0.21%, the Al content of the coating is 0.25%~0.30%, and the Al content of the coating is greater than the Al content of the substrate. When the heating temperature Tn ≥ 850℃ during heat treatment, the corresponding heating time tn satisfies 270000℃·s ≤ ≤450000℃·s (n is selected from integers from 1 to 10); wherein, the heating process is stepped heating, which includes at least two heating stages with different temperatures. The present invention will continue to heat for a preset time at at least two constant temperatures. The concentration difference design of the coating Al content being greater than the substrate Al content is closely combined with the specific stepped heating process and works synergistically. (2) When the substrate Al content is 0.01%~0.21% and the coating Al content is 0.22%~0.35%, and the heating temperature Tn ≥ 850℃ during the heating process, the corresponding heating time tn satisfies 102000℃·s≤ ≤510000℃·s (n is selected from integers from 1 to 10); wherein, the heating process is stepped heating, which includes at least two heating stages at different temperatures. The present invention will continue to heat for a preset time at at least two constant temperatures. The concentration difference design of the coating Al content being greater than the substrate Al content is closely combined with the specific stepped heating process and works synergistically. (3) Adding elements such as B and Zr to the zinc pot can fill grain boundary vacancies and reduce grain boundary free energy during the heating process; etc. Any method that can obtain the frequency of Σ3 grain boundary occurrence of the present invention ≥1% is acceptable. The present invention does not have any special limitations.

[0021] Unrestricted by theory, this invention controls the proportion of the phase with Fe content of 45 wt.%-95 wt.% in the alloy layer to ≥80%, and controls the frequency of the occurrence of Σ3 lattice grain boundaries to ≥1%. This significantly reduces the risk of LME (Liquid Metal Erosion) and provides good corrosion resistance. The reason is likely that the melting point of the phase with Fe content of 45 wt.%-95 wt.% is higher than that of the iron-poor and zinc phases. Increasing the content of this phase in the coating to ≥80% effectively controls the liquid metal during the hot forming heating process. LME cracks occur because liquid metal penetrates along stress into the matrix grain boundaries; reducing the amount of liquid metal effectively suppresses LME cracks. Simultaneously, due to the complex phase structure in the coating, a high proportion of iron-poor and pure zinc phases will, to some extent, disrupt the grain growth of the iron-rich phase, hindering the increase of the frequency of Σ3 lattice grain boundaries. Therefore, the content of the phase with Fe content of 45 wt.%-95 wt.% needs to be ≥80%. When the frequency of Σ3 lattice grain boundaries in the iron-rich phase is ≥1%, there is a lower grain boundary energy, resulting in greater thermodynamic stability between grains and reduced chemical inhomogeneity at the grain boundaries, thus reducing grain boundary corrosion. Simultaneously, the low grain boundary energy structure also implies fewer intergranular dislocations and atomic segregations, reducing sites prone to corrosion and thus improving corrosion resistance. Furthermore, the increased iron-rich phase reduces the alloying reaction between the copper electrode and the zinc plating during resistance spot welding, extending the service life of the spot welding electrode.

[0022] When the proportion of iron-rich phase is insufficient, LME is prone to germination, which limits the service life of spot welding electrodes. When the iron-rich phase is ≥80% but the frequency of occurrence of heavy lattice grain boundaries Σ3 is less than 1%, although LME can be effectively controlled, the coating has poor corrosion resistance, which limits the application of the product.

[0023] Preferably, in this application, the average thickness of the alloy layer is 6-30 μm, and can be 6 μm, 8 μm, 10 μm, 12 μm, 14 μm, 16 μm, 18 μm, 20 μm, 22 μm, 25 μm, 27 μm, 30 μm, or any value between them. If the alloy layer thickness is less than 6 μm, its corrosion resistance will deteriorate. If the alloy layer thickness exceeds 30 μm, it will increase manufacturing costs and hinder market application.

[0024] Preferably, in this application, the method for defining the average thickness of all coatings is to prepare a cross-sectional metallographic image, take 3 measurement points under a 200x field of view, select a total of 10 100x fields of view, and average the 30 measurement values.

[0025] Furthermore, the average thickness of the oxide layer in this application is 0.1~6 μm, and can be 0.1μm, 0.5μm, 1μm, 1.5μm, 2μm, 2.5μm, 3μm, 3.5μm, 4μm, 4.5μm, 5μm, 5.5μm, 6μm, or any value between them. Hot-formed steel is in an air atmosphere during high-temperature austenitization, and the surface inevitably reacts with oxygen in the air, resulting in an oxide layer of 0.1 μm. If the surface oxide layer exceeds 6 μm in thickness, it will be detrimental to subsequent welding and painting of the component.

[0026] Furthermore, the average thickness of the oxide layer is 0.1~4 μm, and the thickness of the oxide layer can be controlled to be as thin as possible to expand the solderable area.

[0027] In this application, the chemical elements of the alloy layer include Zn and Fe, with Zn derived from the zinc-based coating of the hot-formed steel sheet itself. During the high-temperature austenitization process, the Fe element in the substrate and the Zn element in the coating will undergo mutual diffusion and combination, fully diffusing to form a phase with a high melting point Fe content of 45 wt.%-95 wt.%, reducing the Zn-rich phase and the pure Zn phase, which is key to controlling LME.

[0028] Furthermore, within the half-thickness range of the alloy layer closest to the steel substrate, the Zn / Fe atomic ratio is 0.3~0.85, and can be 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, or any value between them. When the Zn / Fe atomic ratio is higher than 0.85, Zn and Fe diffusion is insufficient, posing a risk of LME (Limited Metallic Effluent). When the Zn / Fe ratio is lower than 0.3, it will coarsen the austenitic grains of the substrate and reduce toughness.

[0029] Furthermore, the oxide layer includes one or more of Mn oxide, Al oxide, Zn oxide, and Fe oxide. During the heat treatment, element migration occurs. The Mn, Al, and Fe elements that migrate to the surface, along with the Zn elements in the coating, will react with oxygen at the interface to generate the corresponding oxides.

[0030] The hot-stamped components in this application have the following chemical composition of steel matrix by mass percentage: Fe, C: 0.1%~0.4%, Si: 0.1%~0.8%, Mn: 1.0%~3.0%, Al: 0.01%~0.21%, B: 0.0005%~0.01%, Cr: 0.0005%~0.4%, Ti: 0.0005%~0.1%.

[0031] In this application, the content and selection of each element in the steel matrix are limited to ensure that the mechanical strength of the matrix after hot forming is greater than 500 MPa and that it has good transformation properties during austenitization, which are necessary requirements for hot-formable steel. At the same time, the content of elements such as Al in the matrix is ​​limited to meet the requirements of LME resistance and corrosion resistance after alloying.

[0032] Al, as a deoxidizing element, can refine the grains of steel and improve its strength and toughness. Therefore, it is best for steel to contain more than 0.01% Al. However, adding excessive Al to steel can lead to difficulties in steelmaking. In this invention, to ensure that the frequency of the lattice grain boundary Σ3 of the Fe content phase (45 wt.%-95 wt.%) is ≥1%, key measures include a close combination and synergistic effect of a concentration difference design where the Al content in the coating is greater than that in the substrate, and a specific stepped heating process. In this way, during the high-temperature austenitization process of hot forming, the higher Al content in the coating compensates for the Al consumption of the barrier layer at high temperatures through gradient-driven diffusion, preventing a sudden drop or enrichment of Al at the interface, thus ensuring a uniform alloying reaction of Fe and Zn. At the same time, the diffusion inertness of Al in the substrate avoids its interference with the interface reaction, ensuring that the alloying process is dominated only by the gradient of Al in the coating. Therefore, in this invention, it is necessary to control the Al content to be higher than 0.01% but lower than the Al content (0.22%) in the coating. Thus, the Al content of the substrate is controlled between 0.01% and 0.21%, and can be 0.01%, 0.02%, 0.03%, 0.04%, 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, 0.1%, 0.11%, 0.12%, 0.13%, 0.14%, 0.15%, 0.16%, 0.17%, 0.18%, 0.19%, 0.20%, 0.21%, and any value between them.

[0033] Carbon (C) plays a decisive role in martensitic phase transformation and material strength. Too low a C content will reduce yield strength. Too high a C content will easily lead to the formation of coarse carbides in the weld heat-affected zone, resulting in weld embrittlement. Therefore, the C content in this application is controlled between 0.1% and 0.4%, and can be 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, or any value between them.

[0034] Si can improve the strength of steel and inhibit cementite formation to maintain plasticity. If the Si content is too low, the yield strength will decrease. In this invention, an excessively high Si content increases the thickness of the surface oxide layer during hot forming, deteriorating weldability. Therefore, the Si content in this application is controlled at 0.1% to 0.8%, and can be 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, 0.45%, 0.5%, 0.55%, 0.6%, 0.65%, 0.7%, 0.75%, 0.8%, and any value between them.

[0035] Mn not only improves the strength and hardness of steel but also increases its hardenability; therefore, the Mn content in this invention is not less than 1.0%. However, excessive Mn content can cause Mn segregation, reducing the toughness of the steel and deteriorating its weldability and formability. Therefore, in this invention, the Mn content is controlled between 1.0% and 3.0%, which can be 1%, 1.5%, 2%, 2.5%, 3%, or any value between them.

[0036] Boron (B), an important element in hot-formed steel, plays a role in improving the hardenability of the steel. However, once B reaches saturation, its effect on increasing hardenability becomes less significant. Therefore, in this invention, the B content is controlled between 0.0005% and 0.01%, and can be 0.0005%, 0.001%, 0.002%, 0.003%, 0.004%, 0.005%, 0.006%, 0.007%, 0.008%, 0.009%, 0.01%, or any value between them.

[0037] Cr increases the hardness, strength, and wear resistance of steel, while also improving its hardenability. However, excessive chromium content can reduce the steel's plasticity. Notably, Cr can increase corrosion resistance; therefore, many inventions use increased Cr content to improve the quality of the oxide layer on the surface of hot-stamped parts. For example, in publication CN116837296A, Cr is 0.6%~1.5%, and in CN117265225A, Cr is 0.5%~1.6%. The difference is that this invention primarily relies on controlling the frequency of occurrence of the Σ3 lattice grain boundaries of the 45 wt.%-95 wt.% phase, without requiring large amounts of Cr. Its content is controlled between 0.0005% and 0.4%, and can be 0.0005%, 0.001%, 0.005%, 0.01%, 0.05%, 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, or any value between them.

[0038] Ti is an important alloying element in steel, playing a role in solid solution strengthening and reacting with C and N to form compounds that refine grains and reduce hydrogen embrittlement. However, excessive Ti content will consume the effective carbon equivalent, and coarse TiCN can become crack initiation sites. Therefore, this invention controls the Ti content to 0.0005%~0.1%, which can be 0.0005%, 0.001%, 0.005%, 0.01%, 0.05%, 0.1%, or any value between them.

[0039] Furthermore, the steel matrix in this application may also contain at least one of the following: V: 0~0.3%, Mo: 0~0.3%, Ni: 0~0.3%, and Nb: 0~0.3%. The reasons for the role and content limitation of each element are as follows:

[0040] Vitamin V can precipitate and strengthen materials, improving their strength. However, excessively high V content leads to excessively high precipitate density, resulting in decreased toughness. Controlling the V content between 0% and 0.3%, specifically 0%, 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, or any value in between, allows for both strengthening and improved toughness.

[0041] Mo can improve high-temperature resistance to softening, but excessive amounts can increase the Ac3 point, leading to increased energy consumption in hot forming. Controlling the Mo content to 0-0.3%, which can be 0, 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, or any value in between, can improve high-temperature performance while avoiding energy consumption issues.

[0042] Ni can improve low-temperature toughness, but it is a cost-sensitive component. Controlling the Ni content to 0-0.3%, which can be 0, 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, or any value in between, allows for improved low-temperature performance while controlling costs.

[0043] Nitrogen (Nb) can refine the original austenite grains, but requires higher heating temperatures. Controlling the Nb content to 0-0.3% (0, 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, and any value in between) allows for grain refinement while avoiding excessively high heating temperatures.

[0044] In this application, the chemical composition of the steel matrix may also include: Mg: 0~0.02%, Ca: 0~0.025%, Ce: 0~0.03%, Sn: 0~0.035%, Cu: 0~0.03%, Zr: 0~0.02%, W: 0~0.02%, La: 0~0.002%. The roles and content limits of each element are explained below:

[0045] Mg can control sulfide morphology, but excessive amounts can lead to the risk of nodule formation in continuous casting nozzles. Controlling the Mg content to 0-0.02%, which can be 0, 0.005%, 0.01%, 0.015%, 0.02%, or any value in between, can optimize sulfide morphology while avoiding nodule formation.

[0046] Ca can modify oxide inclusions and plasticize them, but excessive amounts can form a hard CaS phase, which impairs fatigue life. Controlling the Ca content to 0–0.025%, which can be 0, 0.005%, 0.01%, 0.015%, 0.02%, 0.025%, or any value between them, can optimize inclusions while ensuring fatigue life.

[0047] Ce can purify molten steel and refine dendrites, but excessive amounts can cause rare earth oxide cluster defects. Controlling the Ce content to 0-0.03%, which can be 0, 0.005%, 0.01%, 0.015%, 0.02%, 0.025%, 0.03%, or any value in between, can purify the molten steel while avoiding defects.

[0048] Even trace amounts of Sn can significantly improve the atmospheric corrosion resistance of steel substrates by forming a dense oxide film, thus reducing the rate of environmental erosion. However, excessive amounts can induce mid-temperature brittleness. Therefore, the Sn content should be controlled within the range of 0~0.035%, which can be 0, 0.005%, 0.01%, 0.015%, 0.02%, 0.025%, 0.03%, 0.035%, or any value between them.

[0049] Cu can enhance the surface hardening tendency of steel, and when added in combination with Ni, it can suppress the hot-rolling red brittleness phenomenon. Excessive Cu tends to accumulate on the surface during high-temperature oxidation, forming a low-melting-point phase and causing hot-rolling cracking. Therefore, the Cu content should be controlled between 0 and 0.03%, which can be 0, 0.005%, 0.01%, 0.015%, 0.02%, 0.025%, 0.03%, or any value between them.

[0050] Zr can refine austenite grains, but excessive amounts will generate ZrCN, which impairs fracture toughness. Controlling the Zr content to 0~0.02%, which can be 0, 0.005%, 0.01%, 0.015%, 0.02%, or any value in between, can refine the grains while maintaining toughness.

[0051] W can improve high-temperature tempering resistance, but excessive amounts will increase heating energy consumption. Controlling the W content to 0-0.02%, which can be 0, 0.005%, 0.01%, 0.015%, 0.02%, or any value in between, can improve high-temperature performance while avoiding energy consumption issues.

[0052] The addition of ultrafine La can refine the coagulated structure, but in excess, La's high chemical reactivity can lead to the formation of coarse rare earth inclusions. Controlling the La content to 0-0.002%, which can be 0, 0.0005%, 0.001%, 0.0015%, 0.002%, or any value in between, can refine the structure while avoiding other problems.

[0053] Furthermore, the chemical composition of the steel matrix consists of Fe and unavoidable impurities. Among the unavoidable impurities, P ≤ 0.3%, S ≤ 0.1%, and N ≤ 0.1%.

[0054] The steel sheet for the hot-stamped component of this application includes a substrate and a plating layer on the surface of the substrate.

[0055] Furthermore, the average thickness of the coating is 3-15µm, and can be 3µm, 4µm, 5µm, 6µm, 7µm, 8µm, 9µm, 10µm, 11µm, 12µm, 13µm, 14µm, 15µm, or any value between them. If the average thickness is less than 3µm, the corrosion resistance effect is limited. If the average thickness exceeds 15µm, the manufacturing cost is high, which is not conducive to practical applications.

[0056] Furthermore, the chemical composition of the coating, in parts by mass, includes:

[0057] Zn: 95%~99.78%, Fe: 0~4%;

[0058] The chemical composition of the coating also includes a second mass content of Al.

[0059] Preferably, the second mass content of Al is greater than the first mass content of Al contained in the substrate.

[0060] Optionally, the Zn mass percentage content in the coating can be 95%, 95.5%, 96%, 96.5%, 97%, 97.5%, 98%, 98.5%, 99%, 99.5%, 99.78%, and any value between them.

[0061] Optionally, the mass percentage of Fe in the coating can be 0, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, and any value between them.

[0062] Optionally, the second mass content of Al in the coating can be 0.22%, 0.23%, 0.24%, 0.25%, 0.26%, 0.27%, 0.28%, 0.29%, 0.3%, 0.31%, 0.32%, 0.33%, 0.34%, 0.35%, and any value between them.

[0063] When the Zn content in the coating of this invention is less than 95%, the coating will exhibit problems such as uneven appearance and easy peeling, affecting the coating quality. When the Fe content is higher than 4%, zinc dross will increase, increasing zinc pot loss and also affecting the appearance quality. Therefore, the Zn mass percentage in the coating of this invention is 95%~99.5%, and the Fe mass percentage is 0~4%.

[0064] In the coating, Al reacts with the steel substrate (Fe) at the interface to form a dense intermetallic compound (mainly Fe2Al5). This compound forms a "barrier layer" that inhibits the interdiffusion of Fe and Zn. To form this barrier layer, the Al content in the coating typically needs to be greater than 0.2%. However, simply controlling the Al content to the lower limit of 0.2% is insufficient. While it can initially form a barrier layer, it is difficult to maintain its integrity stably during the complex hot stamping process, and it cannot actively control the crystal structure of the alloy layer. The key to this invention is that it not only increases the Al content in the coating to ≥0.22%, but more importantly, it ensures that the second mass content of Al is greater than the first mass content of Al (0.01%~0.21%) in the substrate, thereby creating a clear Al concentration gradient between the coating and the substrate. This concentration difference design is closely integrated with a specific stepped heating process and works synergistically.

[0065] Specifically, during the hot forming austenitization process, when the heating temperature Tn ≥ 850℃, the corresponding heating time tn is precisely controlled, so that the accumulated heat input ( The temperature range is within a specific window of 102,000℃·s to 510,000℃·s. This gradient heating regime provides a continuous and directional diffusion driving force for Al atoms, enabling the high concentration of Al in the coating to be continuously and uniformly transported to the interface. This dynamically compensates for the consumption of Al in the Fe2Al5 barrier layer at high temperatures, effectively preventing the barrier layer from breaking down and failing due to rapid Al depletion at the interface, which could lead to severe local Fe diffusion or the formation of coarse compounds due to Al enrichment. This process, driven by concentration difference and precisely empowered by gradient heating, ensures that the alloying reaction between Fe and Zn proceeds smoothly in a controlled and uniform environment.

[0066] Meanwhile, the diffusion inertness of the low Al content in the substrate can avoid interference with the interfacial reaction, ensuring that the alloying process is dominated only by the Al gradient of the coating. A uniform alloying reaction promotes closer alignment of phases with Fe content ranging from 45 wt.% to 95 wt.%, ultimately resulting in a frequency of Σ3 grain boundaries appearing at a density of ≥1%. However, the Al content in the coating should not be too high, and must be controlled at ≤0.35% to avoid increased iron loss and zinc dross in the zinc pot and defects such as incomplete coating.

[0067] In this invention, the mass content of coating elements is determined according to standard GB / T 24514-2009.

[0068] Those skilled in the art will understand that hot-stamped parts are made from steel plates. Although some migration and exchange of elements may occur in the substrate and coating of the steel plate during the manufacturing process, it is generally believed in the art that the composition of the steel substrate of the resulting hot-stamped parts is basically consistent with the composition of the substrate in the steel plate.

[0069] This application also provides a method for preparing a hot-stamped part, comprising the following steps: S1, blanking or welding a steel plate to obtain a blank, and then heat-treating it; S2, transferring the heat-treated blank to a mold, and then simultaneously cooling and stamping it.

[0070] This invention illustrates that the following control methods can be used to achieve the desired results, but do not limit the specific methods employed. For example, the heating process can be a stepped heating process. Stepped heating includes at least two heating stages at different temperatures, where the heating temperature T of each stage is between 680℃ and 930℃, and the total heating time t of each stage is between 300s and 600s. Wherein, when the heating temperature Tn of a heating stage is not lower than 850℃, the corresponding heating time tn satisfies 102000℃·s ≤ ≤510000℃·s, where n is the number of heating stages with a heating temperature not lower than 850℃, and n is an integer selected from 1 to 10.

[0071] It should be noted that the heating stage in the heat treatment process of this invention refers to continuously heating the billet at a preset temperature for a preset time, that is, continuously holding the billet at a preset constant temperature for a preset period of time, rather than allowing the billet to reach the preset temperature during a continuous heating process. Step heating includes at least two heating stages at different temperatures, meaning that this invention will continuously heat at at least two preset temperatures for a preset time.

[0072] It is understood that the objective of this invention is not merely to heat the material to a specific temperature, but rather to complete a series of crucial physicochemical reactions, such as element diffusion and grain growth, at that specific temperature. These reactions require time and are extremely sensitive to temperature. Specifically, the heat treatment in the hot stamping process has two main purposes: First, to austenitize the steel substrate, preparing it for subsequent quenching into martensite. Second, to promote sufficient and uniform interdiffusion and alloying reactions of Fe, Zn, and Al elements in the coating, forming specific phase structures and grain boundaries, providing a functional surface. Both the austenitization transformation and the diffusion and reaction of atoms are kinetic processes, dependent on temperature and time. Simply heating the material to the target temperature (e.g., 850°C) is insufficient; it must be maintained at that temperature for a sufficient time to provide the atoms with enough energy and time to move, thus completing the desired microstructural transformation.

[0073] Furthermore, the heating temperature T during the heating stage is between 680℃ and 930℃, and the total heating time t during the heating stage is between 300s and 600s. The reasons for setting this temperature and time window are as follows: If the heating temperature is below 680℃, the process of heating to austenitization is slow, resulting in low energy utilization. Furthermore, when the heating temperature exceeds 680℃, the relatively dense δ phase (a Zn / Fe alloy phase) can exist briefly or as a metastable phase. After this process of combination, the subsequent Fe / Zn diffusion is more uniform. If the heating temperature is above 930℃, the overall temperature of the steel plate is too high, the proportion of the coating in the molten state increases, and the risk of LME (Liquid Metallization) during subsequent deformation increases. If the heating time is less than 300s, the matrix austenitization is insufficient, leading to lower mechanical properties. If the heating time is greater than 600s, the grain size of the substrate is too large, reducing toughness.

[0074] Furthermore, through extensive experiments, the applicant discovered that when the stepped heating temperature Tn ≥ 850℃, the corresponding heating time tn must satisfy 102000℃·s ≤ ≤510000℃·s. A temperature of 102,000 °C·s or higher is required for Fe and Zn elements to diffuse sufficiently, promoting grain boundary migration in the Fe-containing phase (45 wt.%–95 wt.%) of the alloy layer and inducing similar grain orientations. However, while high temperatures promote grain boundary migration and twin nucleation, excessive grain coarsening must be avoided; therefore, it is necessary to limit... ≤510000℃·s. The combination of the two can promote the occurrence frequency of Σ3 lattice grain boundaries of phases with Fe content of 45 wt.%-95 wt.% ≥1%, thereby improving corrosion resistance.

[0075] The stepped heating process of this invention is designed based on the synergistic control of the alloying kinetics of the coating and the phase transformation process of the substrate. Compared with single-temperature heating, the stepped heating of this invention aims to drive grain boundary migration through temperature steps, and in conjunction with the Al concentration difference between the substrate and the coating (substrate Al: 0.01 wt%~0.21 wt% < coating Al: 0.22 wt%~0.35 wt%), promotes sufficient and uniform pre-diffusion of Zn, Fe, and Al elements in the coating at the initial temperature, and promotes the uniform thinning of the Fe2Al5 barrier layer. This avoids the non-uniform structure caused by excessive thickness or cracking of the barrier layer, and lays the compositional and structural foundation for the subsequent uniform alloying reaction at high temperature, thereby ensuring that the Fe content in the alloy layer is ≥80% (45 wt.%-95 wt%). Under this premise, the diffusion rate of Fe / Zn elements at the interface between the coating and the substrate is guaranteed, and the high-temperature heat input during the heating stage is controlled ( This process drives a full Fe-Zn interdiffusion reaction at the interface, and through specific grain boundary migration kinetics, induces the preferential formation of low-energy grain boundaries (especially Σ3 twin boundaries) in the iron-rich phase (Fe content 45 wt.%-95 wt%). This significantly increases the frequency of Σ3 twin boundaries (≥1%) in the iron-rich phase, achieving synergistic optimization of LME resistance and corrosion resistance. This temperature-zone control mechanism effectively avoids problems such as local overmelting of the coating, uneven element diffusion, and disordered grain boundary structure that are easily caused by rapid heating at a single high temperature, and is the key to achieving a high Σ3 grain boundary frequency ≥1%.

[0076] Understandably, 850℃ is set as the dividing line because this temperature is the critical temperature threshold for the austenitization of the steel matrix and the achievement of efficient Zn-Fe alloying. A temperature ≥850℃ is a necessary condition to ensure the high hardenability required for the matrix to achieve complete martensitic transformation.

[0077] This invention defines n as the number of stages in stepped heating with a temperature not lower than 850℃, where n is an integer selected from 1 to 10. This invention must ensure that at least one heating stage has a temperature ≥ 850℃ (i.e., n ≥ 1) to ensure sufficient austenitization of the steel matrix. Simultaneously, since stepped heating requires at least two heating stages with different temperatures, when n = 1, there must be another process segment with a heating temperature between 680℃ and 850℃ (excluding 850℃). This intermediate temperature segment provides the initial momentum for uniform thinning of the barrier layer, facilitating uniform and sufficient diffusion of Fe / Zn in the subsequent stage. When n > 1, the absence of a heating segment in the 680℃ to 850℃ range is permissible. From a kinetic perspective, the stepped temperature of the first stage (temperature greater than or equal to 850℃) and subsequent higher temperatures can both achieve uniform thinning of the barrier layer, with a faster thinning rate. However, the surface oxidation caused by the initial high temperature must be fully considered. Furthermore, considering the limitations of heating furnace equipment and process efficiency in actual industrial applications, the total number of steps should not be too high, so the upper limit of n is set to 10.

[0078] Specifically, the design logic for the ladder combination is as follows:

[0079] First, adopt the "one-stage medium temperature (680℃~850℃) + one-stage high temperature (≥850℃)" mode (n=1): This combination focuses on coating optimization.

[0080] In the mid-temperature range below 850℃, an energy barrier is first provided for the Fe2Al5 barrier layer composed of Al elements to begin uniform thinning, promoting the initial and uniform diffusion of Fe / Zn at the interface; simultaneously, a thin zinc oxide (ZnO) layer is formed on the coating surface. The boiling point of this ceramic phase zinc oxide is higher than that of pure zinc, which can effectively suppress the excessive generation of zinc vapor during subsequent heating, reduce coating loss, and provide a basis for optimizing the grain size of the alloy layer.

[0081] After entering the high-temperature stage of ≥850℃, the main process is to fully austenitize the steel substrate and drive the coating to achieve final alloying and grain boundary structure optimization, inducing the formation of low-energy Σ3 twin boundaries.

[0082] This method balances process reliability and coating quality, and is suitable for components with high requirements for corrosion resistance and LME resistance.

[0083] Second, adopting a "multi-stage high temperature (≥850℃)" mode (n>1): This combination focuses more on matrix properties and industrial production rhythm. While ensuring austenitization quality, it controls the high-temperature heat input by adjusting the combination of different high-temperature stages (≥850℃). The application method is used to dominate the two key processes of uniform element diffusion and grain boundary optimization, thereby guiding the phase transformation dynamics of the coating alloy layer in a directional manner while avoiding excessive grain coarsening, and finally achieving a high-proportion, crystallographically ordered iron-rich phase structure.

[0084] It should be noted that while a dedicated mid-temperature range is not required in this mode, a stepped temperature regime must still be established through at least two high-temperature phases, following the principle of "diffusion first, optimization later." Specifically, at least one relatively low temperature phase, but still above 850℃ (e.g., 850℃~890℃), can be set, with a relatively long holding time. The main purpose of this stage is to promote the uniform consumption of the Fe2Al5 barrier layer, while providing sufficient thermal activation energy to drive Fe, Zn, and Al atoms to undergo sufficient and uniform bulk diffusion and grain boundary diffusion, so that the alloying reaction tends to be in equilibrium, ensuring the formation of a high proportion of iron-rich phase (Fe content 45wt.%-95 wt%), and laying a uniform compositional foundation for subsequent grain boundary structure optimization. If the temperature is too high in this stage, the diffusion will be too rapid, easily leading to compositional inhomogeneity or local overmelting.

[0085] After diffusion is largely complete, a short heating stage at a higher temperature (e.g., 900℃~930℃) can be introduced. The core objective of this stage is to significantly enhance grain boundary mobility by utilizing the higher temperature, building upon the already homogenized composition. High grain boundary mobility facilitates grain growth by engulfing surrounding unfavorable grains, preferentially forming low-energy coherent grain boundaries (e.g., Σ3 twin boundaries) in the process. The short-duration operation aims to minimize the overall grain coarsening tendency and other unwanted phase transitions while achieving grain boundary optimization.

[0086] The synergistic advantage of this optimized multi-stage combination lies in its decomposition of a complex heat treatment objective into multiple sub-processes. This stepwise strategy of "diffusion first, optimization later" is more efficient and controllable than attempting to achieve all objectives simultaneously at a single, fixed high temperature. By flexibly adjusting the temperature-time combination of these two (or more) stages, the high-temperature heat input (…) can be precisely controlled. It is allocated to the specific physical processes that require it most, thereby enabling the formation of the final microstructure (especially the Σ3 grain boundary frequency).

[0087] This mode can also achieve grain optimization and has higher production efficiency, making it suitable for production lines with tight schedules. However, it is necessary to fully consider that excessively high initial temperatures may lead to accelerated surface oxidation. If the parts have high requirements for coating performance, subsequent surface treatment processes such as shot blasting can be used.

[0088] By adjusting the combination of different high-temperature ranges (such as different combinations of temperature and time), high-temperature heat input can be achieved. Precise control of the process ensures the quality of austenitization while regulating the crystal structure of the alloy layer. Whether or not a heating stage in the 680℃~850℃ range is included in this combination depends on the initial coating condition and production goals, but the core requirements must meet the total heat input constraints of the high-temperature stage.

[0089] Furthermore, when there is a heating section in the range of 680℃ to 850℃, the cumulative heating time in the temperature range of 680℃ to 850℃ can be no less than 60s, so that Fe, Zn and Al elements in the coating can be fully pre-diffused and the Fe2Al5 barrier layer can be stably thinned, laying a uniform composition and structural foundation for the subsequent high-temperature alloying reaction; while in the heating section in the range of 850℃ to 930℃, the minimum duration of each heating stage should be no less than 10s, so as to avoid the adverse effects of drastic temperature fluctuations on the integrity of the coating structure and the diffusion kinetics process.

[0090] Furthermore, the atmosphere during the heat treatment process is dry air, or a mixture of dry air and certain combustible gases (such as methane), with the volume ratio of air to other combustible gases in the mixture greater than 9:1. The atmosphere of the heat treatment in this application affects the oxidation of the coating surface. If the oxygen content in the gas is high, surface oxidation is severe, which will degrade the weld. If the oxygen content in the gas is low, the oxide layer on the surface forms slowly, and zinc evaporation loss is severe; therefore, the volume of air must occupy at least 9 / 10 of the coating. By introducing combustible gases and utilizing the reactivity of combustible gases with oxygen, the oxygen content of the atmosphere can be controlled.

[0091] This method does not introduce additional highly corrosion-resistant elements (which may increase manufacturing costs and welding difficulty) or use more cumbersome indirect hot forming or pre-cooling hot forming. Instead, while ensuring the increased Fe content in the alloy layer resists LME, it controls the crystal structure of the coating, increasing the frequency of the Σ3 grain boundary of the lattice phase with Fe content of 45 wt.%-95 wt.% in the zinc-iron alloy layer. By utilizing the good intergranular corrosion resistance of the lattice structure, it not only resists LME but also ensures the corrosion resistance of the hot-formed parts and good weldability, which is beneficial to extending the life of resistance welding electrodes.

[0092] Furthermore, in S2, the actual thinning rate of the blank during the stamping process ranges from 0% to 20%, and can be 0, 2%, 5%, 8%, 10%, 12%, 15%, 18%, 20%, or any value between them. Controlling the actual thinning rate range provides sufficient plastic deformation space for flexible forming of the product shape, while strictly controlling the strain and internal stress during the stamping process below the critical value, thereby effectively avoiding plating cracking or substrate damage that may be caused by excessive deformation.

[0093] Furthermore, in S2, the die-closing rate during the stamping process ranges from 5 mm / s to 90 mm / s, and can be any value between 5 mm / s, 10 mm / s, 20 mm / s, 30 mm / s, 40 mm / s, 50 mm / s, 60 mm / s, 70 mm / s, 80 mm / s, and 90 mm / s. Controlling the die-closing rate range allows for more coordinated plastic flow between the coating and the substrate at high temperatures, effectively alleviating stress concentration and thus suppressing the initiation and propagation of liquid metal brittle (LME) cracks. Simultaneously, this range also ensures sufficient production efficiency and guarantees that the final part achieves a uniform martensitic structure and the required mechanical properties by controlling the heat exchange process.

[0094] This application also provides the application of hot-stamped parts or hot-stamped parts obtained by the same manufacturing method in transportation vehicles, household appliances, and construction. Attached Figure Description

[0095] To more clearly illustrate the technical solutions in the specific embodiments of this application or the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0096] Figure 1 This is an EBSD cross-sectional view of the hot-stamped component in Embodiment 1 of this application;

[0097] Figure 2This is an EBSD cross-sectional view of the hot-stamped component of Comparative Example 4 of this application;

[0098] Figure 3 Metallographic images of the same sampling locations of the hot-stamped parts in Embodiment 1 and Comparative Example 3 of this application. Detailed Implementation

[0099] The following embodiments are provided to better understand this application and are not limited to the preferred embodiments described herein. They do not constitute a limitation on the content and scope of protection of this application. Any product that is the same as or similar to this application, derived by anyone under the guidance of this application or by combining features of this application with other prior art, falls within the scope of protection of this application.

[0100] For experiments not specifically described in the examples, the procedures or conditions should be followed according to the conventional experimental procedures described in the literature in this field. Reagents or instruments whose manufacturers are not specified are all commercially available conventional reagent products.

[0101] The present application will be further described in detail below with reference to specific embodiments, which should not be construed as limiting the scope of protection claimed in the present application.

[0102] Examples and Comparative Examples

[0103] This embodiment or comparative example provides a hot-stamped component, the composition of which and its manufacturing process are as follows:

[0104] (1) Steelmaking, casting, hot rolling, pickling, cold rolling, annealing, and coating are performed on the substrate to obtain a steel plate. The parameters of each step in this process are conventional in the field. This embodiment and comparative example do not have specific limitations, but only need to comply with the elemental composition control in Table 1. Table 1 provides the chemical elemental composition of the steel plate substrate in each embodiment and comparative example. The rest are Fe and unavoidable impurities.

[0105] To ensure consistency, both the examples and comparative examples used hot-dip galvanizing to prepare the zinc layer. This process required controlling the plating bath temperature between 420℃ and 480℃, and the Al mass fraction in the plating bath between 0.10% and 0.25%. The hot-dip galvanizing temperature, Al content in the plating bath, and the composition and thickness of the zinc layer after plating are shown in Table 2.

[0106] (2) Cut the steel plate into blanks and / or weld them together to obtain sheet metal.

[0107] (3) Heating the sheet material. A roller hearth furnace is used for heating. The roller hearth furnace has multiple temperature distribution zones, and the temperature of each zone can be set independently and adjusted according to process requirements. This application uses stepped heating, with a heating temperature T of 680℃~930℃ and a heating time t of 300s~600s. nFor temperatures above 850℃, the corresponding heating time is t. n Satisfying 102000℃·s≤ ≤510000℃·s, where n is an integer selected from 1 to 10. The atmosphere in the heating furnace is dry air or a mixture of dry air and certain combustible gases (such as methane), wherein the volume ratio of air to other combustible gases in the mixture is greater than 9:1.

[0108] (4) Transfer the blank to the mold for hot stamping. To ensure the strength of the hot stamped part, the cooling rate of the blank during the stamping process is >30℃ / s. The actual thinning rate of the blank during the stamping process is in the range of 10%~18%; the mold closing rate during the stamping process is in the range of 60mm / s.

[0109] The key parameters for heat treatment control are shown in Table 3.

[0110] Table 1 Substrate composition (wt%)

[0111]

[0112] Continued from Table 1

[0113]

[0114] Table 2 Main parameters of plating solution and coating

[0115]

[0116] Table 3 Main parameters of heat treatment

[0117]

[0118] Continued from Table 3

[0119]

[0120] Test case

[0121] The hot-stamped parts obtained in the above embodiments and comparative examples were tested.

[0122] Corrosion resistance evaluation: Tested according to standard VDA621-415, and rated according to corrosion depth and width, with level 5 being the highest corrosion resistance and level 1 being the worst corrosion resistance.

[0123] LME Evaluation: The embodiments and comparative examples of this application were formed using the corresponding hot stamping process. Metallographic samples were prepared from at least ten typical deformation locations of the formed parts. These generally include locations such as the upper radius corner, sidewall, lower radius corner, and flat surface. The presence of cracks extending beyond the alloy layer into the substrate (LME cracks) was observed. The length from the interface between the alloy layer and the substrate to the crack termination point on the substrate was measured; this length is the crack length.

[0124] Welding electrode life evaluation: Measured according to ISO 18594 method, the welding electrode is placed in contact with the surface of the component, or the upper and lower surfaces of the component, and continuous welding operation is performed under standard welding parameters. The number of times the electrode is used during the welding process is directly recorded as an indicator of electrode life.

[0125] The specific test results are shown in Table 4.

[0126] Table 4 Test Results

[0127]

[0128] As shown in Table 4, the hot-stamped components of Examples 1-9 were all prepared according to the method described in this invention. The frequency of Σ3 lattice grain boundaries of the phase with Fe content of 45 wt.%-95 wt.% in the alloy layer was ≥1%, which effectively improved corrosion resistance, while LME was well controlled. The corrosion resistance rating was ≥4, and the maximum LME crack was 8.6 μm (less than 10 μm). In addition, the welding electrode life of the examples was generally excellent, indicating that the present invention significantly improved welding performance and extended electrode life while improving corrosion resistance and LME resistance. Examples 1, 3-7, and 9 were all prepared according to a more preferred method of this invention. The frequency of Σ3 lattice grain boundaries of the phase with Fe content of 45 wt.%-95 wt.% in the alloy layer was 2%~10%, which effectively improved corrosion resistance, while LME was well controlled. The corrosion resistance rating was 5, and the maximum LME crack was 5.6 μm (less than 10 μm). Meanwhile, the welding electrode lifespan reached over 750 cycles, indicating that the high Σ3 frequency not only benefits corrosion resistance but also has a positive impact on the durability of the welding electrode.

[0129] Figure 1 The image shown is the EBSD diagram of the hot-stamped component of Example 1 of this application. No LME cracks were found. The phase structure of the coating with Fe content of 45 wt.%-95 wt.% is orderly arranged, and the corresponding Σ3 frequency of the heavy point lattice grain boundary is 5.5%. It has good corrosion resistance and a corrosion resistance rating of 5.

[0130] Figure 2 The image shown is the EBSD diagram of the hot-stamped part in Comparative Example 4 of this application, revealing cracks in the coating. The zinc-iron alloy phase in the coating has a relatively small grain size. Figure 1 The number of grains in the medium is significantly reduced, and their arrangement is disordered, making them prone to intergranular corrosion. Statistical analysis shows that the Σ3 frequency of the lattice grain boundaries of the phase with Fe content of 45 wt.%-95 wt.% in the coating is 0.75%, corresponding to a corrosion resistance rating of 3.

[0131] Figure 3Metallographic images of the same sampling locations of the hot-stamped parts in Example 1 and Comparative Example 3 of this application are shown. No LME cracks were observed in Example 1, while obvious LME cracks were found in Comparative Example 3, with the longest reaching 65 μm.

[0132] It should be noted that the combination of technical features in this application is not limited to the combinations described above. All technical features described in this application can be freely combined or combined in any way, unless they contradict each other. Obviously, the above embodiments are merely examples for clear illustration and are not intended to limit the implementation. For those skilled in the art, other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all implementation methods here. However, obvious variations or modifications derived therefrom are still within the protection scope of this invention.

Claims

1. A hot-stamped component, characterized in that, It includes an oxide layer, an alloy layer, and a steel substrate, wherein the alloy layer is located between the oxide layer and the steel substrate; In the alloy layer, the proportion of the phase with Fe content of 45 wt.%-95 wt.% is ≥80%, and the frequency of occurrence of the lattice grain boundary Σ3 of the phase with Fe content of 45 wt.%-95 wt.% is ≥1%; The elemental composition of the steel matrix, by mass percentage, includes: Fe, C: 0.1%~0.4%, Si: 0.1%~0.8%, Mn: 1.0%~3.0%, B: 0.0005%~0.01%, Cr: 0.0005%~0.4%, Ti: 0.0005%~0.1%; It also includes at least one of the following elements: V: 0~0.3%, Mo: 0~0.3%, Ni: 0~0.3%, Nb: 0~0.3%; It also includes a first mass content of Al, the alloy layer being formed by hot stamping of a coating, the coating including a second mass content of Al, the first mass content being less than the second mass content; The first mass content ranges from 0.01% to 0.21%, and the second mass content ranges from 0.22% to 0.35%.

2. The hot-stamped component according to claim 1, characterized in that, The proportion of the phase with Fe content of 45 wt.%-95 wt.% in the alloy layer is ≥85%.

3. The hot-stamped component according to claim 2, characterized in that, The proportion of the phase with Fe content of 45 wt.%-95 wt.% in the alloy layer is ≥90%.

4. The hot-stamped component according to claim 1, characterized in that, The frequency of occurrence of Σ3 lattice grain boundaries of phases with Fe content of 45 wt.%-95 wt.% is ≥2%.

5. The hot-stamped component according to claim 4, characterized in that, The frequency of Σ3 lattice grain boundaries in phases with Fe content of 45 wt.%-95 wt.% is 2%~10%.

6. The hot-stamped component according to claim 1, characterized in that, The average thickness of the alloy layer is 6~30 μm.

7. The hot-stamped component according to claim 1, characterized in that, The alloy layer contains Zn and Fe as chemical elements, and the atomic ratio of Zn / Fe is 0.3 to 0.85 in the half-thickness range of the alloy layer closest to the steel substrate.

8. The hot-stamped component according to claim 1, characterized in that, The steel matrix, by mass percentage, further comprises at least one of the following elements: Mg: 0~0.02%, Ca: 0~0.025%, Ce: 0~0.03%, Sn: 0~0.035%, Cu: 0~0.03%, Zr: 0~0.02%, W: 0~0.02%, La: 0~0.002%.

9. The hot-stamped component according to claim 1, characterized in that, The elemental composition of the steel matrix is ​​composed of Fe and unavoidable impurities. Among the unavoidable impurities, P ≤ 0.3%, S ≤ 0.1%, and N ≤ 0.1%.

10. A steel sheet for preparing the hot-stamped component according to any one of claims 1 to 9, characterized in that, The steel plate includes a substrate and a plating layer on the surface of the substrate; The average thickness of the coating is 3~15µm.

11. The steel plate according to claim 10, characterized in that, The chemical composition of the coating, by weight percentage, includes: Zn: 95%~99.78%, Fe: 0~4%; It also includes a second mass content of Al, which is greater than the first mass content of Al contained in the substrate.

12. The steel plate according to claim 11, characterized in that, The chemical composition of the substrate, by mass percentage, includes: Fe, C: 0.1%~0.4%, Si: 0.1%~0.8%, Mn: 1.0%~3.0%, B: 0.0005%~0.01%, Cr: 0.0005%~0.4%, Ti: 0.0005%~0.1%; It also includes at least one of the following elements: V: 0~0.3%, Mo: 0~0.3%, Ni: 0~0.3%, Nb: 0~0.3%; It also includes a first mass content of Al, which is less than a second mass content.

13. The steel plate according to claim 12, characterized in that, The first mass content ranges from 0.01% to 0.21%; And / or, the second mass content ranges from 0.22% to 0.35%.

14. The steel plate according to claim 12, characterized in that, The chemical composition of the substrate, by mass percentage, further includes at least one of the following elements: Mg: 0~0.02%, Ca: 0~0.025%, Ce: 0~0.03%, Sn: 0~0.035%, Cu: 0~0.03%, Zr: 0~0.02%, W: 0~0.02%, La: 0~0.002%.

15. The steel plate according to claim 12, characterized in that, The substrate composition contains Fe and unavoidable impurities in the remainder. Among the unavoidable impurities, P ≤ 0.3%, S ≤ 0.1%, and N ≤ 0.1%.

16. A method for preparing a hot-stamped component according to any one of claims 1 to 9, characterized in that, Includes the following steps: S1, steel plates are cut or welded together to obtain billets, which are then heat-treated; S2, the heat-treated blank is transferred to the mold, and then cooled and stamped at the same time.

17. The method for preparing a hot-stamped component according to claim 16, characterized in that, The heating process is a stepped heating process, which includes at least two heating stages with different temperatures. The heating temperature T of each heating stage is between 680℃ and 930℃, and the total heating time t of each heating stage is between 300s and 600s. Where the heating temperature Tn during the heating stage is not lower than 850℃, the corresponding heating time tn satisfies 102000℃·s≤ ≤510000℃·s, where n is the number of heating stages with a heating temperature not lower than 850℃, and n is an integer selected from 1 to 10.

18. The method for preparing a hot-stamped component according to claim 16, characterized in that, In S1, the atmosphere during the heating process is dry air, or a mixture of dry air and combustible gas; The volume ratio of air to combustible gas in the mixed gas is greater than 9:

1.

19. The method for preparing a hot-stamped component according to claim 16, characterized in that, In S2, the actual thinning rate of the blank during the stamping process ranges from 0% to 20%. And / or, in S2, the die closing rate during the stamping process ranges from 5 mm / s to 90 mm / s.

20. The application of a hot-stamped component according to any one of claims 1 to 9 or a hot-stamped component prepared by the preparation method according to any one of claims 16 to 19 in the fields of transportation vehicles, household appliances, and construction.

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