Forming method of automobile ultrahigh-strength steel hot stamping part

Abstract

The invention discloses a forming method of an automobile ultrahigh-strength steel hot stamping part, which adopts the design of equal-thickness and unequal-width symmetrical blank cross sections, and the unequal-width symmetrical blank structure enables the deformation of different-width areas in the stamping process to be more uniform, so that the stripping of a plating layer and a base material caused by local stress concentration is avoided, and the forming quality of the automobile ultrahigh-strength steel hot stamping part is improved. According to the technical characteristics that the hot stamping heat preservation temperature is calculated and controlled in a partitioned mode according to the shape of a formed component, the thermodynamic requirements of all parts in the forming process are precisely matched, coating oxidation or phase change caused by uneven temperature is reduced, and therefore the interlayer bonding strength of a coating and a base material is directly improved, meanwhile, the risk of corrosive medium permeation is reduced, and the service life of the coating is prolonged. Through collaborative optimization of structural design and temperature control, the corrosion resistance of the plating layer is further enhanced, the service life of the hot stamping part in a complex environment is prolonged, and the problem that the interlayer bonding strength and corrosion of the aluminum-silicon plating layer are reduced is effectively solved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of hot stamping, in particular to a forming method of an automobile ultrahigh-strength steel hot stamping part. BACKGROUND

[0002] In the field of automobile manufacturing, in order to meet the comprehensive needs of safety, lightweight and durability of vehicles, automobile parts need to have high strength and excellent processing performance. Ultrahigh-strength steel hot stamping parts become key components for improving the safety of vehicle body structures because they can achieve very high strength levels. Aluminum-silicon coated sheet metal, as a raw material for hot stamping, is used because of the special requirements of the hot stamping process: during the high-temperature heating and rapid cooling forming process, the steel substrate is prone to surface deterioration such as oxidation and decarburization, which affects the mechanical properties and appearance quality of the final part. The aluminum-silicon coating can form a stable composite structure with the substrate at high temperatures, effectively isolating oxygen from direct contact with the substrate and inhibiting oxidation and decarburization, thereby ensuring the surface integrity and intrinsic performance of the part after hot stamping. At the same time, the coating can adapt well to the process requirements in subsequent processing steps such as welding and painting, without affecting the welding strength and quality, and providing additional corrosion protection for the part, extending its service life. Therefore, aluminum-silicon coated sheet metal is an ideal raw material choice for producing ultrahigh-strength steel hot stamping parts in the automobile industry, taking into account process feasibility, part performance and production efficiency.

[0003] The hot stamping process requires heating the sheet metal to high temperatures, at which time the coating and substrate are in an active physical and chemical state. The aluminum-silicon coating may diffuse or react with the substrate at high temperatures, forming an alloy layer. If the thickness or uniformity of the alloy layer is not properly controlled, it may weaken the bonding force between the coating and the substrate, or even cause local peeling or cracking, thereby reducing the bonding strength. During the stamping forming stage, the material undergoes plastic deformation at high temperatures. If the ductility of the coating does not match that of the substrate, or if the stress is uneven during the deformation process, microcracks or delamination may occur in the coating or at the interface between the coating and the substrate. These defects not only directly weaken the bonding strength, but also may become a channel for the invasion of corrosive media, affecting corrosion resistance.

[0004] Therefore, it is necessary to improve the process of the automobile ultrahigh-strength steel hot stamping part in the prior art. SUMMARY

[0005] The present application overcomes the shortcomings of the prior art and provides a forming method of an automobile ultrahigh-strength steel hot stamping part, aiming to solve the problem of reduced aluminum-silicon coating interlayer bonding strength and corrosion resistance caused by the process of the automobile ultrahigh-strength steel hot stamping part in the prior art.

[0006] To achieve the above-mentioned purpose, the technical scheme adopted by the present application is as follows: a forming method of an automobile ultrahigh-strength steel hot stamping part, comprising the following steps: S1: aluminum-silicon plated sheet material is made into a hot stamping blank, the cross section of the hot stamping blank is an equal-thickness non-equal-width symmetric figure; S2: the width of each part of the hot stamping blank is calculated according to the heat stamping holding temperature, and the heat stamping holding temperature of each part of the hot stamping blank is obtained, the hot stamping forming member is a shape with a narrow middle part and wide ends along the length direction, and the width range of the hot stamping blank is 120-200 mm; S3: the hot stamping blank is heated according to the heat stamping holding temperature of each part of the hot stamping blank; S4: the heated hot stamping blank is moved to a hot stamping device for stamping forming, and an automobile ultra-high strength steel hot stamping part is obtained.

[0007] In a preferred embodiment of the present application, the aluminum-silicon plated sheet material in S1 comprises a steel body and an aluminum-silicon plated layer, the thickness of the steel body is 1.5-3 mm, and the thickness of the aluminum-silicon plated layer is 8-20 μm.

[0008] In a preferred embodiment of the present application, the composition and mass percentage of the steel body are as follows: C: 0.22-0.25%, Mn: 1.2-1.4%, B: 0.0005-0.0032%, Cr: 0.10-0.20%, and the rest is Fe; the composition and mass percentage of the aluminum-silicon plated layer are as follows: Si: 8-12%, Al: 5-10%, Mg: 0.5-1.5%, Zn: 0.5-2%, and the rest is Fe.

[0009] In a preferred embodiment of the present application, the length and cross-sectional area ratio of the hot stamping blank in S1 is between 5-12, the unit of length is mm, and the unit of cross-sectional area is mm 2 .

[0010] In a preferred embodiment of the present application, the heat stamping holding temperature in S2 comprises a first stamping holding temperature and a second stamping holding temperature, and the first stamping holding temperature is less than the second stamping holding temperature.

[0011] In a preferred embodiment of the present application, the first stamping holding temperature is 700-750℃, the temperature of the two ends of the hot stamping blank along the length direction in the second stamping holding temperature is 950-970℃, and the temperature of the middle part of the hot stamping blank along the length direction in the second stamping holding temperature is 780-820℃.

[0012] In a preferred embodiment of the present application, the widths of the two ends and the middle part of the hot stamping blank are consistent respectively, and a transition section with uniform width change is arranged between the two ends and the middle part, and the second stamping holding temperature is uniformly changed in the temperature of the transition section.

[0013] In a preferred embodiment of the present application, the oxygen content during heating of the hot stamping blank in S3 is 0.5-1.5%.

[0014] In a preferred embodiment of the present application, a die is arranged in the hot stamping equipment in S4, and the surface temperature of the die before stamping is 25-100℃.

[0015] In a preferred embodiment of the present application, the stamping speed during stamping forming in S4 is 70-80mm / s, the flow rate of the cooling water is 1.0-1.2m / s, the pressure holding time is 10-15s, and the cooling rate of the hot stamping blank after stamping forming is 30-40℃ / s.

[0016] The present application solves the defects in the background art, and has the following beneficial effects: (1) In the present application, by adopting the design of an equal-thickness non-equal-width symmetrical blank cross section, the non-equal-width symmetrical blank structure makes the deformation of different width regions more uniform during stamping, avoiding the peeling of the plating layer from the base material due to local stress concentration. Combined with the technical features of calculating and controlling the hot stamping holding temperature according to the shape partition of the formed component, the thermodynamic requirements of each part during forming are accurately matched, the oxidation or phase change of the plating layer caused by uneven temperature is reduced, compared with the prior art, thereby directly improving the interlayer bonding strength of the plating layer and the base material, and reducing the risk of penetration of corrosive medium. Through the synergistic optimization of structural design and temperature control, the corrosion resistance of the plating layer is further enhanced, and the service life of the hot stamping part in a complex environment is prolonged.

[0017] (2) In the present application, the appropriate C and Mn in the steel body ensure the basic strength and hardenability, the B element refines the grains to improve the toughness, and the high proportion of Si and Al in the aluminum-silicon plating layer forms a stable oxide layer during heating. Compared with the prior art, the plating layer and the base material are more closely combined, and the corrosive medium is difficult to penetrate through the plating layer defects, thereby significantly improving the interlayer bonding strength and overall corrosion resistance. Through precise design of the composition, the probability of occurrence of bonding defects and corrosion is reduced from the material essence, the service life of the hot stamping part in a complex environment is prolonged, and the protection of the plating layer on the base material is more durable. It provides a material basis for the reliable application of ultra-high strength steel in automobile structural parts requiring high corrosion resistance.

[0018] (3) In the present application, the high temperature at both ends in the second temperature promotes the diffusion bonding of the aluminum-silicon coating layer and the base material, and the intermediate low temperature inhibits excessive oxidation or grain coarsening of the coating layer, and the uniform change of the transition section temperature matches the uniform change of the width, compared with the prior art, further reducing the damage risk of the heat stress concentration to the interface between the coating layer and the base material, the bonding between the aluminum-silicon coating layer and the steel body is more closely, and the interface peeling tendency is significantly reduced, and the dense oxide layer formed in the high temperature zone and the coating layer integrity reserved in the low temperature zone jointly block the penetration of the corrosion medium.

[0019] (4) In the present application, through the cooperation of temperature zoning control and structure design, the possibility of coating failure is reduced from the heat treatment link, compared with the prior art, the corrosion resistance of the hot stamped part in the complex environment is improved, and the protection effect of the coating layer on the base material is more durable, which provides process guarantee for the reliable application of ultra-high strength steel in automobile structural parts requiring high corrosion resistance. BRIEF DESCRIPTION OF DRAWINGS

[0020] 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 below. Obviously, the drawings described below are only some embodiments of the present application, and for those skilled in the art, other drawings can be obtained without creative labor on the basis of these drawings. Figure 1 is a method step diagram of the preferred embodiment of the present application. DETAILED DESCRIPTION

[0021] The technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only some embodiments of the present application, not all embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0022] In the following description, many specific details are set forth in order to provide a thorough understanding of the present application, but the present application can also be implemented in other ways different from those described herein, therefore, the scope of protection of the present application is not limited by the specific embodiments disclosed below.

[0023] As shown in Figure 1 A forming method of an automobile ultra-high strength steel hot stamped part, comprising the following steps: S1: aluminum-silicon coating layer plate is made into a hot stamped part blank, and the cross section of the hot stamped part blank is an equal-thickness non-equal-width symmetric figure; S2: Calculate the heat stamping holding temperature of each part of the hot stamping blank according to the shape of the hot stamping forming member, obtain the heat stamping holding temperature of each part of the hot stamping blank, the shape of the hot stamping forming member is narrow in the middle and wide at both ends along the length direction, and the width of the hot stamping blank ranges from 120 to 200 mm; S3: Heat the hot stamping blank according to the heat stamping holding temperature of each part of the hot stamping blank respectively; S4: Move the heated hot stamping blank to the hot stamping equipment for stamping forming to obtain a kind of automobile ultra-high strength steel hot stamping part.

[0024] By adopting the equal-thickness non-equal-width symmetrical blank cross-section design, the non-equal-width symmetrical blank structure makes the deformation of different width areas more uniform during stamping, avoiding the peeling of the coating from the substrate caused by local stress concentration, combining with the technical features of calculating and controlling the heat stamping holding temperature according to the shape of the forming member, the thermodynamic demand of each part during forming is accurately matched, the oxidation or phase change of the coating caused by uneven temperature is reduced, thereby directly improving the interfacial bonding strength of the coating and the substrate, and reducing the risk of corrosion medium penetration, through the synergistic optimization of structure design and temperature control, the corrosion resistance of the coating is further enhanced, and the service life of the hot stamping part in complex environment is prolonged, effectively solving the problems of interfacial bonding strength and corrosion resistance of aluminum-silicon coating.

[0025] When the stamping part bears the collision load, the middle narrow part can preferentially occur controllable plastic deformation, guide the energy to transfer along the predetermined path and absorb, avoid the problem of low energy absorption efficiency caused by deformation dispersion of traditional equal-width structure, the energy absorption capacity of unit mass material is improved, the energy absorption is more concentrated and effective during collision, the energy absorption process is accurately regulated through shape optimization, further improving the safety of vehicle in collision accident, meeting the strict requirements of high-strength lightweight parts on energy absorption performance.

[0026] In S1, the aluminum-silicon coated plate includes a steel body and an aluminum-silicon coating, the thickness of the steel body is 1.5-3 mm, and the thickness of the aluminum-silicon coating is 8-20 μm.

[0027] The composition and mass percentage of the steel body are: C: 0.22-0.25%, Mn: 1.2-1.4%, B: 0.0005-0.0032%, Cr: 0.10-0.20%, and the rest is Fe; the composition and mass percentage of the aluminum-silicon coating are: Si: 8-12%, Al: 5-10%, Mg: 0.5-1.5%, Zn: 0.5-2%, and the rest is Fe.

[0028] The length and cross-sectional area ratio of the hot stamping blank is between 5 and 12, the unit of length is mm, and the unit of cross-sectional area is mm 2 .

[0029] The steel body thickness of the aluminum-silicon plated plate is set to 1.5-3mm, the aluminum-silicon plating layer thickness is 8-20μm, and is combined with the equal-thickness non-equal-width symmetric blank design and the zoned heat preservation process, effectively solving the problems of interlayer bonding strength and corrosion reduction of the aluminum-silicon plating layer.

[0030] The steel body thickness in this range not only ensures the strength basis of the ultra-high strength steel, but also provides enough space for plastic deformation during hot stamping, avoiding insufficient deformation caused by too thin base material or forming difficulty caused by too thick base material; the aluminum-silicon plating layer thickness of 8-20μm balances the protection of the base material by the plating layer and the demand for its own ductility, neither losing the corrosion protection function due to being too thin, nor generating too much internal stress during heating due to being too thick.

[0031] During hot stamping, the reasonable thickness ratio controls the thermal expansion difference between the plating layer and the base material, reducing the risk of interface peeling, and the zoned heat preservation temperature further optimizes the thermal stress distribution of each region, the interlayer bonding strength between the aluminum-silicon plating layer and the steel body is significantly improved, and the plating layer can still adhere tightly to the surface of the base material after forming, effectively blocking the penetration of corrosion media such as moisture and salt mist.

[0032] Through precise matching of thickness parameters, the probability of generating bonding defects is reduced from the material design level, the corrosion resistance of the hot stamped part is enhanced, and local corrosion caused by plating layer peeling is not easy to occur during long-term use, prolonging the service life of the part in complex environments, and providing a reliable guarantee for the application of ultra-high strength steel in automobile structural parts requiring high corrosion resistance.

[0033] The steel body thickness ensures that the material has sufficient strength and toughness to absorb energy through plastic deformation during a collision; the structural design of the narrow middle part causes controllable compression deformation in this area when stressed, guiding the transfer and consumption of impact energy along the predetermined path, while the wide ends maintain the overall structural integrity through a more stable deformation mode.

[0034] The moderate thickness of the aluminum-silicon plating layer reduces the risk of plating layer rupture during deformation, avoiding the intrusion of corrosion media caused by plating layer damage, thereby maintaining the surface integrity of the energy absorption area, and the hot stamped part can more efficiently absorb impact energy during a collision, improving the energy absorption efficiency per unit mass of material, while the deformation process is more controllable, avoiding the problem of insufficient energy absorption caused by the dispersion of traditional equal-width structures.

[0035] Through the coordinated design of thickness and shape, both energy absorption performance and corrosion resistance are improved. Further effects are that the vehicle can more effectively protect the passenger compartment structure during a collision, reducing the collision damage, while the lightweight potential of the hot stamped part is further released, promoting the wider application of ultra-high strength steel in automobile safety components.

[0036] The appropriate amount of C and Mn in the steel body ensures the basic strength and hardenability, the B element refines the grain to improve toughness, and the Cr element enhances the corrosion resistance of the base material through solid solution strengthening and passivation, reducing the penetration of corrosive media to the interface between the coating and the base material; the high proportion of Si and Al in the aluminum-silicon coating forms a stable oxide layer when heated, and the addition of Mg and Zn further inhibits the interfacial reaction between the coating and the base material, reducing the risk of interlayer peeling caused by thermal stress.

[0037] The combination of the coating and the base material is more compact, and the corrosive medium is difficult to penetrate through the coating defects, thereby significantly improving the interlayer bonding strength and overall corrosion resistance. Through precise design of the composition, the probability of defects and corrosion is reduced from the essence of the material, the service life of the hot stamped part in complex environments is extended, and the protective effect of the coating on the base material is more durable, providing a material basis for the reliable application of ultra-high strength steel in automobile structural parts with high corrosion resistance requirements.

[0038] The Cr element in the steel body improves the corrosion resistance of the base material, avoiding performance degradation caused by corrosion and ensuring that the material can stably absorb energy during a collision; the Zn element in the aluminum-silicon coating oxidizes preferentially during deformation, forming a dense corrosion product layer and reducing the impact of coating rupture on the surface integrity of the energy-absorbing area. The structural design of the middle narrow part causes controlled plastic deformation in this area when stressed, guiding the impact energy along a predetermined path and dissipating it, while the wide parts at both ends maintain the overall structural integrity through a more stable deformation mode.

[0039] The hot stamped part can more efficiently absorb impact energy in a collision, improving the energy absorption efficiency of the material per unit mass, while the deformation process is more controllable, avoiding the problem of insufficient energy absorption caused by deformation dispersion in traditional equal-width structures. Through the coordinated design of composition and shape, both energy absorption performance and structural stability are improved, the vehicle can more effectively protect the passenger compartment structure during a collision, reducing the impact of the collision, while the lightweight potential of the hot stamped part is further released, promoting the wider application of ultra-high strength steel in automotive safety components.

[0040] The length and cross-sectional area ratio of the hot stamped part blank ensures the uniformity of the temperature distribution during heating, avoiding local overheating caused by excessive length or small cross-sectional area, or insufficient heating caused by excessive length or large cross-sectional area, thereby reducing the thermal stress difference between the coating and the base material.

[0041] The Cr element in the steel body improves the corrosion resistance of the base material through solid solution strengthening and passivation. The Zn element in the aluminum-silicon coating forms a dense oxide layer when heated, further blocking the penetration of corrosive media. The coating and the base material are more tightly combined, the risk of interface peeling is significantly reduced, and the corrosive medium is difficult to penetrate through the coating defects. The overall corrosion resistance is improved.

[0042] Through the synergistic effect of ratio optimization and material composition, the probability of defects and corrosion is reduced from the process parameters and material essence. The service life of hot stamped parts in complex environments is extended, and the protection of the coating on the base material is more durable. It provides a double guarantee of process and material for the reliable application of ultra-high strength steel in automobile structural parts with high corrosion resistance requirements.

[0043] The ratio range makes the blank deformation more concentrated during stamping. The narrow middle part preferentially undergoes controlled plastic deformation under stress, guiding the impact energy along the predetermined path and consuming it. The wide ends maintain the overall structural integrity through a more stable deformation mode. The appropriate amount of C and Mn in the steel body ensures the basic strength and hardenability, and the B element refines the grain to improve toughness, ensuring that the material can stably absorb energy during a collision.

[0044] The high proportion of Si and Al in the aluminum-silicon coating forms a stable oxide layer when heated, reducing the impact of coating rupture on the surface integrity of the energy-absorbing area. The hot stamped part can more efficiently absorb impact energy during a collision, improving the energy-absorbing efficiency of unit mass material, and the deformation process is more controllable, avoiding the problem of insufficient energy absorption caused by dispersed deformation in traditional equal-width structures.

[0045] Through the synergistic effect of ratio optimization and shape design, both energy-absorbing performance and structural stability are improved. The vehicle can more effectively protect the passenger compartment structure during a collision, reducing collision damage, while the lightweight potential of hot stamped parts is further released, promoting the wider application of ultra-high strength steel in automotive safety components.

[0046] The hot stamping holding temperature in S2 includes a first stamping holding temperature and a second stamping holding temperature, and the first stamping holding temperature is less than the second stamping holding temperature.

[0047] The first stamping holding temperature is 700-750℃, the temperature of the two ends of the hot stamped part blank along the length direction in the second stamping holding temperature is 950-970℃, and the temperature of the middle part of the hot stamped part blank along the length direction in the second stamping holding temperature is 780-820℃.

[0048] The widths of the two ends and the middle part of the hot stamped part blank are consistent, and a transition section with uniform width change is provided between the two ends and the middle part. The transition section temperature in the second stamping holding temperature changes uniformly. The transition section temperature change rate is C / mm, wherein a is a variation parameter value, the value of a ranges from 1.4 to 1.8, t is the length of the transition section, the value of t ranges from 50 to 100, and the unit is mm.

[0049] By setting the first and second stamping holding temperatures, and in combination with the features that the width of the blank at both ends is consistent with the width in the middle and the width of the transition section changes uniformly, the problems of reduced interlayer bonding strength and corrosion resistance of the aluminum-silicon coating are effectively solved.

[0050] The high temperature at both ends in the second temperature promotes the diffusion bonding of the aluminum-silicon coating and the base material, and the low temperature in the middle inhibits the excessive oxidation or grain coarsening of the coating, thereby reducing the interface stress difference caused by uneven temperature. The uniform change in the temperature of the transition section matches the uniform change in the width, further reducing the risk of damage to the interface between the coating and the base material caused by thermal stress concentration.

[0051] The bonding between the aluminum-silicon coating and the steel body is more compact, and the interface peeling tendency is significantly reduced. At the same time, the dense oxide layer formed in the high temperature zone and the coating integrity retained in the low temperature zone jointly block the penetration of corrosive media. Through the synergy of temperature zoning control and structural design, the possibility of coating failure is reduced from the heat treatment link, the corrosion resistance of the hot stamped part in a complex environment is improved, and the protection of the coating on the base material is more durable, providing process support for the reliable application of ultra-high strength steel in automobile structural parts that require high corrosion resistance.

[0052] Through the differential design of high temperature at both ends and low temperature in the middle in the second stamping holding temperature, in combination with the shape of the formed component with narrow width in the middle along the length direction, the performance of the ultra-high strength steel hot stamped part in energy absorption is significantly improved.

[0053] The high temperature at both ends makes the material in this region more prone to plastic deformation during stamping, preferentially absorbing collision energy; the low temperature in the middle maintains the strength of the steel body, ensuring that deformation is concentrated in the predetermined area and avoiding overall structural instability. The uniform change in the temperature of the transition section matches the uniform change in the width, making the deformation process smoothly transition from both ends to the middle, reducing unintended deformation caused by stress concentration.

[0054] The hot stamped part can more efficiently guide the energy to be transmitted and consumed along the narrow middle part in a collision accident, improving the energy absorption efficiency per unit mass of material, and enhancing the controllability of the deformation path. Through the synergy of temperature zoning and shape design, precise regulation of the energy absorption process is achieved.

[0055] The oxygen content when heating the blank of the hot stamped part in S3 is 0.5-1.5%.

[0056] By controlling the oxygen content in the range of 0.5-1.5% during the heating of the hot stamping blank, and combining with the composition ratio of the aluminum-silicon coating and the design of the zoned holding temperature, the problems of reducing the interlayer bonding strength and corrosion resistance of the aluminum-silicon coating are effectively solved. This oxygen range not only avoids the problem of excessive oxidation of the coating due to excessive oxygen content, which forms a loose oxide layer and reduces the bonding strength, but also prevents the problem of insufficient reaction of the coating and the substrate interface due to insufficient oxygen, which results in insufficient bonding.

[0057] The Si and Al elements in the aluminum-silicon coating react with oxygen to form a dense oxide film during heating, the addition of Mg and Zn further inhibits the formation of interfacial brittle phases, and the appropriate oxygen content ensures the uniformity and appropriateness of the oxidation reaction, reducing the interfacial stress concentration caused by uneven oxidation.

[0058] The bonding between the aluminum-silicon coating and the steel body is more compact, the oxide layer not only provides sufficient adhesion strength, but also blocks the penetration of corrosive media, thereby significantly improving the interlayer bonding strength and overall corrosion resistance. By precisely controlling the oxygen content, the probability of defects and corrosion is reduced from the heating process, the service life of the hot stamping part in complex environments is extended, and the protection of the coating on the substrate is more durable, providing process support for the reliable application of ultra-high strength steel in automobile structural parts that require high corrosion resistance.

[0059] The appropriate oxygen content allows the aluminum-silicon coating to form a uniform and dense oxide layer during heating, reducing the risk of coating rupture or peeling during stamping, and maintaining the integrity of the energy-absorbing area, thereby ensuring controllable deformation and stable energy absorption path.

[0060] The design of the intermediate narrow structure allows the region to preferentially undergo controlled plastic deformation under stress, guiding the transfer and consumption of impact energy along the predetermined path, while the wide ends maintain the overall structural integrity through a more stable deformation mode; the high temperature at both ends in the zoned holding temperature promotes material softening and improves deformation ability, while the low temperature in the middle maintains strength and avoids premature instability, which further optimizes the efficiency of the energy-absorbing process in cooperation with the control of oxygen content.

[0061] The hot stamping part can more efficiently absorb impact energy in a collision accident, and the energy absorption efficiency of unit mass material is improved, while the controllability of the deformation path is enhanced, avoiding the problem of low energy absorption efficiency caused by coating damage or uneven temperature in traditional processes.

[0062] Through the coordinated design of oxygen content and process parameters, precise control of energy absorption performance is achieved, the vehicle can more effectively protect the passenger compartment structure during a collision, reducing the damage of the collision, while the lightweight potential of the hot stamping part is further released, promoting the wider application of ultra-high strength steel in automobile safety parts.

[0063] The surface temperature of the die in the hot stamping device in S4 is 25-100℃.

[0064] The stamping speed during stamping forming in S4 is 70-80mm / s, the flow rate of the cooling water is 1.0-1.2m / s, the pressure maintaining time is 10-15s, and the cooling rate of the hot stamping piece blank after stamping forming is 30-40℃ / s.

[0065] By controlling the surface temperature of the die in the hot stamping device to be 25-100℃, and combining the aluminum-silicon coating composition ratio and the zoned heat preservation process, the problems of reducing the interlayer bonding strength and corrosion of the aluminum-silicon coating are effectively solved. In the traditional process, the die temperature is relatively high, and the coating is easy to produce intense heat exchange with the high-temperature die during stamping, which leads to a large thermal stress at the interface between the coating and the substrate due to rapid cooling, causing the coating to peel off or brittle phase to be generated.

[0066] The low-temperature die reduces the heat exchange rate between the coating and the die during stamping, reduces the accumulation of interfacial thermal stress, and at the same time, inhibits the excessive reaction of the coating and the substrate at high temperature, avoiding the formation of brittle phase. The bonding between the aluminum-silicon coating and the steel body is more compact, and the interface peeling tendency is significantly reduced. Moreover, the coating can still maintain a dense structure after stamping, effectively blocking the penetration of corrosive media such as moisture and salt mist.

[0067] By precise control of the die temperature, the risk of interface failure is reduced from the stamping link, the corrosion resistance of the hot stamped part is improved, and the protective effect of the coating on the substrate is more durable, providing process support for the reliable application of ultra-high strength steel in automobile structural parts requiring high corrosion resistance.

[0068] The low-temperature die helps to control the cooling speed of the stamped part, making the deformation more concentrated in the middle narrow part, guiding the impact energy to be transmitted and consumed along the predetermined path. The structural design of the middle narrow part makes this area preferentially undergo controllable plastic deformation when stressed, while the wide parts at both ends maintain the overall structural integrity through a more stable deformation mode; the low-temperature die further reduces the residual stress within the material, avoiding cracks or fractures caused by stress concentration during deformation, and the hot stamped part can more efficiently absorb impact energy in a collision accident, improving the energy absorption efficiency per unit mass of material, while the controllability of the deformation path is enhanced.

[0069] The stamping speed in this range balances the deformation rate and heat transfer efficiency, avoiding the problems of too short contact time between the material and the die, local uneven cooling, or excessive heating of the material, excessive reaction of the coating and the substrate interface due to too slow speed; the cooling water flow rate of 1.0-1.2m / s ensures uniform heat exchange between the die and the hot stamped part, reduces the concentration of thermal stress caused by local temperature difference, and inhibits the peeling tendency of the coating due to rapid cooling; The pressure maintaining time 10-15s makes the material fully set after stamping, the coating and the base material are further closely combined under the action of pressure, meanwhile, the shape springback or interface separation caused by insufficient pressure maintaining is avoided; and the cooling rate 30-40℃ / s quickly locks the martensite structure of the steel body, improves the strength of the base material, and meanwhile, the brittle phase generation of the coating and the base material at high temperature is inhibited, and the interface bonding defects are reduced.

[0070] The combination between the aluminum-silicon coating and the steel body is more close, the oxide layer not only maintains sufficient adhesive strength, but also blocks the penetration of corrosive medium, so that the interlayer bonding strength and overall corrosion resistance are significantly improved, through accurate matching of process parameters, the occurrence probability of bonding defects and corrosion is reduced from the stamping link, the service life of the hot stamped part in a complex environment is prolonged, the protection of the coating on the base material is more durable, and process guarantee is provided for reliable application of the ultra-high strength steel in automobile structural parts requiring high corrosion resistance.

[0071] The stamping speed 70-80mm / s ensures the controllability of the deformation process, so that stable plastic deformation of the intermediate narrow part is preferentially generated when stressed, the impact energy is guided to transfer and consume along the predetermined path; the cooling water flow rate 1.0-1.2m / s reduces the residual stress in the material through uniform cooling, and avoids cracks or fractures caused by stress concentration in the deformation process; the pressure maintaining time 10-15s makes the shape of the stamped part stable, and the two wide parts maintain the overall structural integrity through a more stable deformation mode; and the cooling rate 30-40℃ / s quickly forms the martensite structure, which improves the strength and toughness of the base material, and ensures that the material can efficiently absorb energy when colliding.

[0072] The application of the present application is a cross beam body of an automobile front anti-collision beam.

[0073] Embodiment 1: The present embodiment provides a forming method of an automobile ultra-high strength steel hot stamped part, comprising the following steps: S1: an aluminum-silicon coated plate is made into a hot stamped part blank, the cross section of the hot stamped part blank is an equal-thickness non-equal-width symmetric figure, the aluminum-silicon coated plate comprises a steel body and an aluminum-silicon coating layer, the thickness of the steel body is 2mm, and the thickness of the aluminum-silicon coating layer is 16μm; the composition and mass percentage of the steel body are as follows: C: 0.24%, Mn: 1.2%, B: 0.00%, Cr: 0.10%, and the rest is Fe; the composition and mass percentage of the aluminum-silicon coating layer are as follows: Si: 10%, Al: 8%, Mg: 1.0%, Zn: 0.5%, and the rest is Fe; S2: the hot stamping holding temperature of each part of the hot stamped part blank is calculated according to the shape of the hot stamped part forming component, the hot stamping holding temperature of each part of the hot stamped part blank is obtained, the hot stamped part forming component is a shape with wide ends and a narrow middle part along the length direction, the width of the two ends of the hot stamped part blank is 200mm, and the width range of the middle part is 160mm. The hot stamping holding temperature comprises a first stamping holding temperature and a second stamping holding temperature, and the first stamping holding temperature is less than the second stamping holding temperature.

[0074] The first stamping holding temperature is 750℃, the temperature of the two ends of the hot stamping blank along the length direction in the second stamping holding temperature is 950℃, and the temperature of the middle part of the hot stamping blank along the length direction in the second stamping holding temperature is 810℃.

[0075] The widths of the two ends and the middle part of the hot stamping blank are consistent respectively, a transition section with uniform width change is arranged between the two ends and the middle part, the temperature of the transition section in the second stamping holding temperature changes uniformly, the length of the transition section is 100mm, and the temperature change rate of the transition section is 1.2℃ / mm.

[0076] S3: heating the hot stamping blank according to the hot stamping holding temperature of each part of the hot stamping blank respectively, and the oxygen content when the hot stamping blank is heated is 1.0%; S4: moving the heated hot stamping blank to a hot stamping device for stamping forming, a die is arranged in the hot stamping device, the surface temperature of the die before stamping is 100℃, the stamping speed when the hot stamping blank is stamped is 70mm / s, the flow rate of the cooling water is 1.0m / s, the holding time is 10s, the cooling rate of the hot stamping blank after stamping forming is 35℃ / s, and a hot stamping part of an automobile ultra-high strength steel is obtained.

[0077] Embodiment 2: The difference between this embodiment and embodiment 1 is that the temperature change rate of the transition section is 1.4℃ / mm, and the rest is consistent.

[0078] Embodiment 3: The difference between this embodiment and embodiment 1 is that the temperature change rate of the transition section is 1.6℃ / mm, and the rest is consistent.

[0079] Embodiment 4: The difference between this embodiment and embodiment 1 is that the temperature change rate of the transition section is 1.8℃ / mm, and the rest is consistent.

[0080] Embodiment 5: The difference between this embodiment and embodiment 1 is that the temperature change rate of the transition section is 2.0℃ / mm, and the rest is consistent.

[0081] Embodiment 6: The difference between this embodiment and embodiment 3 is that the stamping speed when the hot stamping blank is stamped is 65mm / s, and the rest is consistent.

[0082] Embodiment 7: The difference between this embodiment and embodiment 3 is that the stamping speed when the hot stamping blank is stamped is 75mm / s, and the rest is consistent.

[0083] Embodiment 8: The difference between this embodiment and embodiment 3 is that the stamping speed when the hot stamping blank is stamped is 80mm / s, and the rest is consistent.

[0084] Example 9: The difference between this example and Example 3 is that the stamping speed during stamping forming is 85 mm / s, and the rest is the same.

[0085] Comparative Example 1: This comparative example provides a forming method of an automobile ultra-high strength steel hot stamped part, comprising the following steps: S1: An aluminum-silicon plated sheet is made into a hot stamped part blank, the cross section of the hot stamped part blank is an equal-thickness non-equal-width symmetric figure, the aluminum-silicon plated sheet comprises a steel body and an aluminum-silicon plating layer, the thickness of the steel body is 2 mm, and the thickness of the aluminum-silicon plating layer is 16 μm; the composition of the steel body and the mass percentage thereof are as follows: C: 0.24%, Mn: 1.2%, B: 0.00%, Cr: 0.10%, and the rest is Fe; the composition of the aluminum-silicon plating layer and the mass percentage thereof are as follows: Si: 10%, Al: 8%, Mg: 1.0%, Zn: 0.5%, and the rest is Fe; S2: The temperature of the hot stamped part blank is heated to 950℃, and the oxygen content during heating of the hot stamped part blank is 1.0%; S4: The heated hot stamped part blank is moved to a hot stamping device for stamping forming, a die is arranged in the hot stamping device, the surface temperature of the die before stamping is 100℃, the stamping speed during stamping forming is 70 mm / s, the flow rate of the cooling water is 1.0 m / s, the pressure holding time is 10 s, the cooling rate of the hot stamped part blank after stamping forming is 35℃ / s, and an automobile ultra-high strength steel hot stamped part is obtained.

[0086] The hot stamped parts of the ultra-high strength steel of Examples 1-9 and Comparative Example 1 are respectively tested for plating layer bonding strength and corrosion resistance, and the test data are shown in Table 1.

[0087] Table 1: Plating layer bonding strength and corrosion resistance test data of Examples 1-9 and Comparative Example 1

[0088] As can be seen from Table 1, the plating layer bonding strength and corrosion resistance of Examples 1-9 are greater than those of Comparative Example 1, and the present application has advantages.

[0089] In Examples 1-5, as the temperature gradient of the transition section increases, the coating bonding strength and corrosion resistance both increase first and then decrease. When the temperature gradient is small, the element diffusion power at the interface between the transition section coating and the base material is insufficient, the Fe-Al alloy layer grows slowly and discontinuously. At this time, the alloy layer is thin and there is an unreacted area, resulting in weak metallurgical bonding between the coating and the base material and low bonding strength. The low temperature gradient causes the residual stress caused by the difference in the thermal expansion coefficient between the coating and the base material to be uniformly distributed along the transition section, but the insufficient interface reaction limits the release of stress through metallurgical bonding, and the bonding strength is still limited. The temperature uniformity of the transition section is high, but the slow cooling allows sufficient time for the oxidation reaction on the surface of the coating, but the oxidation layer has coarse grains and internal holes or cracks, and the corrosion medium easily penetrates, so the corrosion resistance is general.

[0090] A moderate temperature gradient promotes the balance between the element diffusion power and the reaction time at the interface between the coating and the base material. The Fe-Al alloy layer grows continuously and uniformly along the transition section, forming a dense metallurgical bonding layer, which significantly enhances the bonding strength between the coating and the base material. The temperature gradient causes the transition section to produce a gradually decreasing residual stress distribution from both ends to the middle. The high stress area at both ends is partially released through the martensitic transformation of the base material, and the low stress area in the middle is strengthened by metallurgical bonding, and the overall stress state is conducive to inhibiting the cracking or peeling of the coating. The moderate cooling rate allows the oxidation reaction on the surface of the coating to be sufficient, the iron oxide grains are refined and closely arranged, and a dense oxidation layer is formed. This oxidation layer effectively blocks the penetration of corrosive media, and the corrosion resistance is significantly improved.

[0091] An excessive temperature gradient causes rapid cooling at both ends of the transition section, and the element diffusion time at the interface is insufficient, the Fe-Al alloy layer is reduced in thickness and discontinuous, and even unreacted coating areas appear. At this time, the bonding between the coating and the base material is mainly mechanical interlocking, and the metallurgical bonding is weakened, resulting in a decrease in bonding strength. The high temperature gradient significantly increases the residual tensile stress at both ends of the transition section, while the stress in the middle part is low. Stress concentration easily causes micro-cracks in the coating, and even local peeling, further reducing the bonding strength. Rapid cooling causes insufficient oxidation reaction on the surface of the coating, and the iron oxide layer has holes or cracks, and the corrosion medium penetrates to the interface through the defects, accelerating local corrosion. At the same time, high residual stress promotes stress corrosion cracking, and the corrosion resistance decreases sharply. The preferred embodiment is Example 3.

[0092] In Example 3 and Examples 6-9, as the stamping speed during the stamping forming gradually increases, the plating layer bonding strength and the corrosion resistance both first increase and then decrease, because the stamping speed has a trend of first increasing and then decreasing on the plating layer bonding strength and the corrosion resistance in the hot stamping forming process, and this phenomenon is due to the comprehensive regulation of the stamping speed on the interface mechanical interlocking, metallurgical bonding and the quality of the oxidation layer: when the stamping speed is low, the contact time of the die and the sheet metal is long, but the insufficient strain rate leads to insufficient mechanical interlocking of the plating layer and the substrate interface, at the same time, the fast heat dissipation makes the interface element diffusion power insufficient, it is difficult to form a continuous metallurgical bonding layer, and the oxidation layer on the surface of the plating layer is coarse and has defects due to the uniform temperature, resulting in low bonding strength and general corrosion resistance; as the stamping speed increases to the medium range, the strain rate and the deformation time reach a balance, the interface mechanical interlocking is enhanced, at the same time, the sufficient temperature promotes the Fe-Al interdiffusion, forming a continuous and dense metallurgical bonding layer, and the oxidation layer is densified due to the matching of the reaction time and temperature conditions, effectively blocking the penetration of corrosive media, at this time, the bonding strength and the corrosion resistance both reach the peak; however, when the stamping speed is too high, the high strain rate leads to local stress concentration of the plating layer due to rapid deformation, which easily causes micro-cracks or peeling, at the same time, the rapid decline of the interface temperature inhibits the element diffusion, the metallurgical bonding layer is reduced in thickness and discontinuous, and the oxidation layer has holes or cracks due to the insufficient reaction time, the penetration of corrosive media accelerates local corrosion, finally leading to a sharp decline in the bonding strength and the corrosion resistance. The preferred embodiment is Example 7.

[0093] The above is based on the ideal embodiment of the present application, through the above description, relevant personnel can make various changes and modifications without deviating from the technical idea of the present application. The technical scope of the present application is not limited to the contents of the specification, and the technical scope must be determined according to the scope of the claims.

Claims

1. A forming method for automotive ultra-high strength steel hot stamping parts, characterized in that, Includes the following steps: S1: The aluminum-silicon coated sheet is made into a hot stamping blank, and the cross-section of the hot stamping blank is a symmetrical shape with equal thickness but not equal width; S2: Calculate the hot stamping heat preservation temperature of each part of the hot stamping blank according to the shape of the hot stamping forming component, and obtain the hot stamping heat preservation temperature of each part of the hot stamping blank. The hot stamping forming component is a shape that is wide at both ends and narrow in the middle along the length direction. The width range of the hot stamping blank is 120-200mm. S3: Heat the hot stamping blank according to the hot stamping heat preservation temperature of each part of the hot stamping blank; S4: The heated hot stamping blank is transferred to a hot stamping machine for stamping to obtain an automotive ultra-high strength steel hot stamping part.

2. The forming method of a hot-stamped automotive ultra-high strength steel part according to claim 1, characterized in that: The aluminum-silicon coated sheet in S1 includes a steel body and an aluminum-silicon coating. The thickness of the steel body is 1.5-3 mm, and the thickness of the aluminum-silicon coating is 8-20 μm.

3. The forming method of a hot-stamped automotive ultra-high strength steel part according to claim 2, characterized in that: The composition and mass percentage of the steel body are as follows: C: 0.22-0.25%, Mn: 1.2-1.4%, B: 0.0005-0.0032%, Cr: 0.10-0.20%, with the remainder being Fe; the composition and mass percentage of the aluminum-silicon coating are as follows: Si: 8-12%, Al: 5-10%, Mg: 0.5-1.5%, Zn: 0.5-2%, with the remainder being Fe.

4. The forming method of a hot-stamped automotive ultra-high strength steel part according to claim 1, characterized in that: The length-to-cross-sectional area ratio of the S1 hot-stamped part blank is between 5 and 12, with the length in mm and the cross-sectional area in mm. 2 .

5. The forming method of a hot-stamped automotive ultra-high strength steel part according to claim 1, characterized in that: The hot stamping insulation temperature in S2 includes a first stamping insulation temperature and a second stamping insulation temperature, wherein the first stamping insulation temperature is lower than the second stamping insulation temperature.

6. The forming method of a hot-stamped automotive ultra-high strength steel part according to claim 5, characterized in that: The first stamping heat preservation temperature is 700-750℃, the temperature at both ends of the hot stamping blank along the length direction in the second stamping heat preservation temperature is 950-970℃, and the temperature of the middle part of the hot stamping blank along the length direction in the second stamping heat preservation temperature is 780-820℃.

7. The forming method of a hot-stamped automotive ultra-high strength steel part according to claim 6, characterized in that: The widths of the two ends and the middle portion of the hot stamping blank are the same, and a transition section with a uniformly varying width is provided between the two ends and the middle portion. The second stamping heat preservation temperature varies uniformly in the temperature of the transition section.

8. The forming method of a hot-stamped automotive ultra-high strength steel part according to claim 1, characterized in that: The oxygen content during the heating of the hot stamping blank in step S3 is 0.5-1.5%.

9. The forming method of a hot-stamped automotive ultra-high strength steel part according to claim 1, characterized in that: The hot stamping equipment in S4 is equipped with a mold, and the surface temperature of the mold before stamping is 25-100℃.

10. The forming method of a hot-stamped automotive ultra-high strength steel part according to claim 1, characterized in that: The stamping speed during the stamping process in S4 is 70-80 mm / s, the cooling water flow rate is 1.0-1.2 m / s, the holding time is 10-15 s, and the cooling rate of the hot stamped part blank after stamping is 30-40 ℃ / s.

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