Preparation method of zinc-based coating hot-formed steel part and part

Abstract

The invention provides a preparation method of a zinc-based coating hot forming steel part and the part, and belongs to the field of automobile steel. The method comprises the steps that continuous three-stage heating is conducted on the zinc-based coating hot forming steel, and steel to be stamped is obtained; wherein the temperature of the first heating section is 750-830 DEG C, the temperature of the second heating section is 880-950 DEG C, and the temperature of the third heating section is 800-900 DEG C; and the steel to be stamped is subjected to hot stamping and sand blasting treatment, and the part is obtained. Continuous three-stage heating is carried out on the zinc-based coating hot forming steel, and the three-stage heating comprises low-temperature area heating in the first stage, high-temperature area heating in the second stage and medium-temperature area heating in the third stage. And the Fe element in the substrate is diffused into the plating layer through the low-temperature area, so that the melting and evaporation of the zinc-based plating layer are effectively reduced, and the degree of the plating layer adhering to the ceramic roller can be reduced. Therefore, the technical problem that the corrosion resistance of the hot-formed steel part with the zinc-based coating is poor is solved.

Description

Technical Field

[0001] The present application relates to the technical field of automobile steel, and in particular to a preparation method and parts of zinc-based coated hot-formed steel parts. Background Art

[0002] The hot forming process is to stamp at high temperature to avoid cracking. The formed parts have good dimensional accuracy and ultra-high strength. At the same time, the zinc-based coating has good corrosion resistance due to the presence of zinc. The zinc-based hot-formed steel has excellent welding performance, processing performance, coating performance, good aesthetics and cathodic protection. It is an ideal coating for hot-formed automotive parts.

[0003] However, due to the low melting point of zinc, it will melt and evaporate during the hot forming heating process, thus affecting the corrosion resistance of the coating after forming. Therefore, it is urgent to develop a method for improving the corrosion resistance of zinc-based coated hot-formed steel parts. Summary of the invention

[0004] The present application provides a preparation method and parts of a zinc-based coated hot-formed steel part, so as to solve the technical problem of poor corrosion resistance of zinc-based coated hot-formed steel parts in the prior art.

[0005] In a first aspect, the present application provides a method for preparing a zinc-based coated hot-formed steel part, the method comprising:

[0006] The zinc-based coated hot-formed steel is continuously heated in three stages to obtain the steel to be stamped; wherein the temperature of the first heating stage is 750°C to 830°C, the temperature of the second heating stage is 880°C to 950°C, and the temperature of the third heating stage is 800°C to 900°C; and

[0007] The steel to be stamped is subjected to hot stamping and sandblasting to obtain parts.

[0008] Optionally, the time t1 of the first heating section and the total time t of the continuous three-stage heating satisfy the following relationship: t1 = (0.1-0.2) t; and / or

[0009] The time t2 of the second heating stage and the total time t of the continuous three-stage heating satisfy the following relationship: t2 = (0.4-0.7) t; and / or

[0010] The time t3 of the third heating section and the total time t of the continuous three-stage heating satisfy the following relationship: t3=(0.1-0.5)t.

[0011] Optionally, the total time t of the continuous three-stage heating satisfies the following relationship:

[0012] If the thickness of the zinc-based coated hot-formed steel is less than 1.2 mm, then 210 ≤ t ≤ 250 s;

[0013] If the thickness of the zinc-based coated hot-formed steel is 1.2 mm to 2.0 mm, then 250 < t ≤ 320 s;

[0014] If the thickness of the zinc-based coated hot-formed steel is greater than 2.0 mm and less than or equal to 3.0 mm, then 320<t≤400s.

[0015] Optionally, in the first heating section, the Fe content in the zinc-based coating of the zinc-based coating hot-formed steel is 30% to 40% by mass; and / or

[0016] In the second heating section, the Fe content in the zinc-based coating of the zinc-based coating hot-formed steel is 50% to 70% by mass.

[0017] Optionally, the zinc-based coated hot-formed steel comprises:

[0018] steel base,

[0019] A metal pre-plating layer covering at least a portion of the surface of the steel substrate, wherein the metal pre-plating layer comprises one or more of Ni, Cu, Cr and Fe, and

[0020] A zinc-based coating covering at least a portion of the surface of the metal pre-coating has a thickness of 5 μm to 20 μm and is a pure zinc coating, an alloy coating, a Zn-Ni coating or an electroplated zinc coating.

[0021] Optionally, the chemical composition of the steel matrix includes, by mass fraction: C: 0.1%-0.4%, Si: 0.2%-1.5%, Mn: 2%-5%, Al: 0.05%-0.5%, Ti: 0.01%-0.1%, V: 0.01%-0.15%, Cr: 0.2%-0.5%, B: 0.001%-0.004%, P: ≤0.005%, S: ≤0.005%, N: ≤0.005%, and the balance is Fe and unavoidable impurities.

[0022] Optionally, the step of hot stamping and sandblasting the steel to be stamped to obtain a part comprises:

[0023] The steel to be stamped is transferred to a hot stamping device, and cooled during the transfer process, and then hot stamped using the hot stamping device to obtain a hot stamped part, wherein the cooling rate is ≥25°C / s;

[0024] The hot stamping part is sandblasted to obtain a part.

[0025] Optionally, the process parameters of the hot stamping include: a stamping temperature of 550°C to 750°C, a cooling rate of press-holding quenching of ≥20°C / s, and a die-out temperature of ≤200°C.

[0026] Optionally, the sand particle size of the sand blasting treatment is ≤300 mesh, and the sand blasting depth is ≤5 μm.

[0027] In the second aspect, the present application provides a zinc-based coated hot-formed steel part prepared by the method described in any one of the embodiments of the first aspect, wherein the coating thickness of the part is 8μm to 35μm, and the part satisfies at least one of the following properties: surface roughness Ra≤2.0, peak number RPc≥80, LME crack depth≤5μm, corrosion potential of -0.6V to -0.3V, corrosion current of 2.5μA to 5μA, and salt spray corrosion time to the steel substrate is ≥650h.

[0028] The above technical solution provided by the embodiment of the present application has the following advantages compared with the prior art:

[0029] The present application provides a method for preparing zinc-based coated hot-formed steel parts, by heating the zinc-based coated hot-formed steel in three consecutive stages, including heating in the low-temperature zone in the first stage, heating in the high-temperature zone in the second stage, and heating in the medium-temperature zone in the third stage. The low-temperature zone allows the Fe element in the substrate to diffuse into the coating, effectively reducing the melting and evaporation of the zinc-based coating and reducing the degree of adhesion of the coating to the ceramic roller; in the high-temperature zone, the substrate is completely austenitized to ensure the mechanical properties of the parts after forming; in the medium-temperature zone, austenitization can continue to be carried out to ensure that the internal structure of the material is a uniform full-austenite structure, while pre-solidifying the coating and reducing the requirements for the cooling rate after leaving the furnace. This solves the technical problem of poor corrosion resistance of zinc-based coated hot-formed steel parts. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the present application and, together with the description, serve to explain the principles of the present application.

[0031] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0032] Figure 1 A schematic flow chart of a method for preparing a zinc-based coated hot-formed steel part provided in an embodiment of the present application;

[0033] Figure 2 A cross-sectional view of a zinc-based coated hot-formed steel part provided in Example 1 of the present application. DETAILED DESCRIPTION

[0034] In order to make the purpose, technical solution and advantages of the embodiments of the present application clearer, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application.

[0035] Various embodiments of the present application may be presented in the form of a range; it should be understood that the description in the form of a range is only for convenience and brevity, and should not be understood as a rigid limitation on the scope of the present application; therefore, the range description should be considered to have specifically disclosed all possible sub-ranges and single numerical values ​​within the range. For example, the range description from 1 to 6 should be considered to have specifically disclosed sub-ranges, such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., as well as single numbers within the range, such as 1, 2, 3, 4, 5 and 6, which apply regardless of the range. In addition, whenever a numerical range is indicated herein, it is meant to include any cited number (fractional or integer) within the indicated range.

[0036] In addition, in the description of the specification of the present application, the terms "including", "comprising", etc. mean "including but not limited to". In this article, relational terms such as "first" and "second", etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. In this article, "and / or" describes the association relationship of associated objects, indicating that three relationships may exist. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. Wherein A and B can be singular or plural. In this article, "at least one" means one or more, and "plurality" means two or more. "At least one", "the following at least one item (items)" or similar expressions refer to any combination of these items, including any combination of single items (items) or plural items (items). For example, "at least one of a, b, or c", or "at least one of a, b and c", can both mean: a, b, c, ab (i.e. a and b), ac, bc or abc, where a, b, c can be single or plural, respectively.

[0037] Unless otherwise specified, various raw materials, reagents, instruments and equipment used in this application can be purchased from the market or prepared by existing methods.

[0038] Figure 1 A schematic flow chart of a method for preparing a zinc-based coated hot-formed steel part provided in an embodiment of the present application.

[0039] See also Figure 1 The present application provides a method for preparing a zinc-based coated hot-formed steel part, the method comprising:

[0040] S1. The zinc-based coated hot-formed steel is continuously heated in three stages to obtain steel to be stamped; wherein the temperature of the first heating section is 750°C to 830°C, the temperature of the second heating section is 880°C to 950°C, and the temperature of the third heating section is 800°C to 900°C;

[0041] Specifically, in an embodiment of the present application, when hot stamping is performed on the zinc-based coated hot-formed steel, the zinc-based coated hot-formed steel needs to be heated first. At present, the heating equipment of the hot stamping production line is mainly roller-hearth furnace. When heating with a roller-hearth furnace, the robot clamps the aluminum-silicon coated hot-formed steel and puts it in from one end of the furnace mouth. The aluminum-silicon coated hot-formed steel moves to the other end in the roller-hearth furnace, and then comes out of the furnace from the other end. Then the robot clamps the heated aluminum-silicon coated hot-formed steel and transfers it to the hot stamping die for hot stamping. The roller-hearth furnace heating process is divided into three stages (that is, divided into three zones in sequence), which are divided into the first heating section, the second heating section, and the third heating section in chronological order.

[0042] In the embodiment of the present application, the first heating section is for heating in the low temperature zone, the second heating section is for heating in the high temperature zone, and the third heating section is for heating in the medium temperature zone. In the low temperature zone, the Fe element in the substrate is diffused into the coating, which can effectively reduce the melting of the coating and reduce the degree of adhesion of the coating to the ceramic roller; in the high temperature zone, the substrate is ensured to be completely austenitized to ensure the mechanical properties of the parts after forming. The medium temperature zone mainly plays the role of heat preservation and pre-cooling the coating. The positive effect of controlling the heating temperature of the medium temperature zone to 800℃~900℃ is: the material can continue to be austenitized in the medium temperature zone, ensuring that the internal structure of the material is a uniform full austenite structure. At the same time, the coating is pre-solidified to reduce the requirements for the cooling rate after leaving the furnace. If the temperature in the medium temperature zone is higher than 900℃, it cannot play the role of pre-cooling, which will aggravate the melting of the coating and reduce the corrosion resistance of the material after forming. If the temperature in the medium temperature zone is lower than 800℃, it will affect the austenitization of the material, resulting in the mechanical properties of the material after forming being affected. Exemplarily, the temperature of the first heating section can be 750°C, 760°C, 770°C, 780°C, 790°C, 800°C, 820°C, 830°C, etc., the temperature of the second heating section can be 880°C, 900°C, 910°C, 920°C, 940°C, 950°C, etc., and the temperature of the third heating section is 800°C, 820°C, 840°C, 860°C, 870°C, 880°C, 890°C, 900°C, etc.

[0043] In some embodiments, the time t1 of the first heating stage and the total time t of the three-stage continuous heating satisfy the following relationship: t1 = (0.1-0.2) t; and / or

[0044] The time t2 of the second heating stage and the total time t of the continuous three-stage heating satisfy the following relationship: t2 = (0.4-0.7) t; and / or

[0045] The time t3 of the third heating section and the total time t of the continuous three-stage heating satisfy the following relationship: t3=(0.1-0.5)t.

[0046] In the implementation manner of the present application, the above-mentioned time setting can improve the heating efficiency, reduce the total heating time, and play a role in energy conservation and emission reduction.

[0047] In some embodiments, the total time t of the continuous three-stage heating satisfies the following relationship:

[0048] If the thickness of the zinc-based coated hot-formed steel is less than 1.2 mm, then 210 ≤ t ≤ 250 s;

[0049] If the thickness of the zinc-based coated hot-formed steel is 1.2 mm to 2.0 mm, then 250 < t ≤ 320 s;

[0050] If the thickness of the zinc-based coated hot-formed steel is greater than 2.0 mm and less than or equal to 3.0 mm, then 320<t≤400s.

[0051] In the implementation manner of the present application, different heating times are used for zinc-based coated hot-formed steels of different thicknesses, which can improve production efficiency and ensure the performance of the zinc-based coated hot-formed steel after hot forming.

[0052] In some embodiments, in the first heating section, the Fe content in the zinc-based coating of the zinc-based coating hot-formed steel is 30% to 40% by mass; and / or

[0053] In the second heating section, the Fe content in the zinc-based coating of the zinc-based coating hot-formed steel is 50% to 70% by mass.

[0054] In the first heating section, the positive effect of controlling the Fe content in the zinc-based coating to 30% to 40% is to ensure that the Fe content in the coating is 30% to 40%, thereby increasing the melting point of the coating to above 700°C, which can effectively reduce the melting of the coating and reduce the degree of adhesion of the coating to the ceramic roller. Exemplarily, the Fe content in the zinc-based coating in the heating section is 30%, 32%, 34%, 36%, 38%, 39%, 40%, etc.

[0055] In the second heating section, the positive effects of the Fe content in the zinc-based coating being 50% to 70% are: (1) ensuring the Zn element content in the coating, thereby improving the corrosion resistance of the coating after forming. (2) preventing the coating thickness from exceeding the control range, thereby causing problems such as cracking during stamping. (3) preventing the formation of a large amount of ɑ-Fe (Zn) phase in the coating. Due to the poor plasticity of the ɑ-Fe (Zn) phase, a large amount of ɑ-Fe (Zn) phase is prone to form a large number of cracks during the stamping process, thereby affecting the performance of the coating. Exemplarily, the Fe content in the zinc-based coating in this heating section is 50%, 52%, 55%, 58%, 60%, 65%, 68%, 70%, etc.

[0056] In some embodiments, the zinc-based hot-formed steel comprises: a steel substrate, a metal pre-plating layer covering at least a portion of the surface of the steel substrate, the metal pre-plating layer comprising one or more of Ni, Cu, Cr and Fe, and a zinc-based coating covering at least a portion of the surface of the metal pre-plating layer, the zinc-based coating having a thickness of 5 μm to 20 μm, and the zinc-based coating is a pure zinc coating, an alloy coating, a Zn-Ni coating or an electroplated zinc coating.

[0057] The zinc-based coating has good corrosion resistance when the thickness is within this range. For example, the thickness of the zinc-based coating may be 5 μm, 8 μm, 10 μm, 12 μm, 14 μm, 15 μm, 18 μm, 20 μm, etc.

[0058] In some embodiments, the chemical composition of the steel matrix includes, by mass fraction: C: 0.1% to 0.4%, Si: 0.2% to 1.5%, Mn: 2% to 5%, Al: 0.05% to 0.5%, Ti: 0.01% to 0.1%, V: 0.01% to 0.15%, Cr: 0.2% to 0.5%, B: 0.001% to 0.004%, P: ≤0.005%, S: ≤0.005%, N: ≤0.005%, and the balance is Fe and unavoidable impurities.

[0059] The positive effect of controlling the C content to 0.1% to 0.4% is that the C element is the main strengthening element in steel. When the C content is less than 0.1%, the substrate strength is low and cannot meet the strength requirements of users; when the C content is greater than 0.4%, the welding performance and plasticity of the substrate will be greatly reduced. For example, the C content is 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, etc.

[0060] The positive effect of controlling the Si content to 0.2% to 1.5% is that the Si element is added mainly to reduce the formation of carbides during the heating process. When the Si content is less than 0.2%, the formation of carbides cannot be reduced; when the Si content is greater than 1.5%, the hot-dip performance of the substrate will deteriorate, affecting the quality of the coating. Exemplarily, the Si content is 0.2%, 0.3%, 0.4%, 0.6%, 0.8%, 1.0%, 1.2%, 1.4%, 1.5%, etc.

[0061] The positive effect of controlling the Mn content to 2% to 5% is that the Mn element is added mainly to expand the austenite phase region of the substrate and increase the forming process window. When the Mn% content is less than 2, the austenite phase region cannot be effectively expanded; when the Mn% content is greater than 5, it will cause element segregation in the substrate and affect the forming performance of the material. Exemplarily, the Mn content is 2%, 2.5%, 3.0%, 3.5%, 4.0%, 4.5%, 5%, etc.

[0062] The positive effect of controlling the Al content to 0.05% to 0.5% is that the Al element is added mainly to play a role in deoxidation during the steelmaking process. When the Al content is less than 0.05%, deoxidation cannot be effectively performed; when the Al element exceeds 0.5%, the plasticity of the substrate will be reduced. Exemplarily, the Al content is 0.05%, 0.10%, 0.15%, 0.20%, 0.25%, 0.30%, 0.40%, 0.5%, etc.

[0063] The positive effect of controlling the Ti content to 0.01% to 0.1% is that the Ti element is added to fix the N element in the substrate. When the Ti content is less than 0.01%, the N element cannot be effectively fixed. When the Ti content is greater than 0.1%, a large amount of TiC will be generated, resulting in reduced plasticity of the substrate. For example, the Ti content is 0.01%, 0.03%, 0.05%, 0.07%, 0.09%, 0.1%, etc.

[0064] The positive effect of controlling the V content to 0.01% to 0.15% is that the addition of V element mainly plays the role of refining the grains, thereby improving the cold bending performance of the material. When the V content is less than 0.01%, the grains cannot be effectively refined; when the V content is greater than 0.15%, the effect on improving the cold bending performance is limited. Exemplarily, the V content is 0.01%, 0.03%, 0.05%, 0.08%, 0.10%, 0.12%, 0.15%, etc.

[0065] The positive effect of controlling the Cr content to 0.2% to 0.5% is that the Cr element is added mainly to improve the hardness and wear resistance of the substrate. When the Cr content is less than 0.2%, the hardness cannot be effectively improved; when the Cr content exceeds 0.5%, the austenitizing temperature will be greatly increased, causing the heating temperature to be too high. For example, the Cr content can be 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, 0.45%, 0.5%, etc.

[0066] The positive effect of controlling the B content to 0.001% to 0.004% is that the B element is added mainly to improve the hardenability of the substrate. When the B content is less than 0.001%, the hardenability cannot be effectively improved; when the B content is greater than 0.004%, the B element will gather at the grain boundary and cause the substrate to become brittle. For example, the B content can be 0.001%, 0.002%, 0.003%, 0.004%, etc.

[0067] S2. Hot stamping and sandblasting the steel to be stamped to obtain parts.

[0068] In some embodiments, the step of hot stamping and sandblasting the steel to be stamped to obtain a part comprises:

[0069] The steel to be stamped is transferred to a hot stamping device, and cooled during the transfer process, and then hot stamped using the hot stamping device to obtain a hot stamped part, wherein the cooling rate is ≥25°C / s;

[0070] The hot stamping part is sandblasted to obtain a part.

[0071] Specifically, in an embodiment of the present application, after the zinc-based hot-formed steel is heated, the zinc-based hot-formed steel is taken out of the furnace, and then the aluminum-silicon-coated hot-formed steel is quickly clamped by the machine and transferred to the hot stamping die, and then stamping is performed. After stamping, pressure holding and quenching are performed. The pressure holding quenching process is mainly to convert the austenite of the zinc-based hot-formed steel into martensite. In order to ensure the cooling rate of the hot stamping parts, corresponding cooling water channels will be designed in the hot stamping die, and water cooling will be performed during the production process. After the pressure holding quenching of the parts, the mold is opened, and then the manipulator clamps the parts and moves them out of the hot stamping mold. Usually, the manipulator places the parts on a conveyor belt, and the conveyor belt sends them to the workbench. The workers inspect and analyze the parts. The main forming qualities tested include cracking, thinning, and part performance.

[0072] In the embodiment of the present application, the synchronous cooling method after the furnace is mainly used to ensure that the coating has been completely solidified during the stamping process, thereby further reducing the risk of LME. Exemplarily, the cooling rate can be 25°C / s, 26°C / s, 28°C / s, 29°C / s, 30°C / s, 32°C / s, 35°C / s, etc.

[0073] In some embodiments, the process parameters of the hot stamping include: a stamping temperature of 550°C to 750°C, a cooling rate of press-holding quenching of ≥20°C / s, and a die-out temperature of ≤200°C.

[0074] The positive effect of controlling the stamping temperature to 550℃~750℃: within this range, the stamping temperature can avoid causing serious liquid cracks and serious solid cracks, and reduce the cooling time to increase production efficiency. The stamping temperature is 550℃, 580℃, 600℃, 620℃, 650℃, 680℃, 700℃, 720℃, 750℃, etc.

[0075] The positive effect of controlling the cooling rate of press quenching ≥ 20°C / s: In order to convert the austenite of the aluminum-silicon coated hot-formed steel into martensite. Exemplarily, the cooling rate of the press quenching can be 20°C / s, 25°C / s, 26°C / s, 28°C / s, 29°C / s, 30°C / s, 32°C / s, 35°C / s, etc.

[0076] The positive effect of controlling the demoulding temperature ≤ 200℃ is to avoid the self-tempering of the material, thereby reducing the mechanical properties of the material. The demoulding temperature can be 50℃, 100℃, 120℃, 140℃, 150℃, 160℃, 180℃, 200℃, etc.

[0077] In some embodiments, the sand particle size of the sand blasting is ≤300 mesh, and the sand blasting depth is ≤5 μm.

[0078] In the embodiment of the present application, sandblasting is used instead of traditional shot peening after forming. After experimental research by the inventor, the thickness of the surface oxide layer of zinc-based coated hot-formed steel after hot forming is 1μm to 5μm, so in order to ensure the integrity of the coating, the sandblasting depth should be ≤5μm. In addition, if the shot peening process is used, the aluminum oxide on the surface of the coating will not be completely removed, thus affecting the subsequent coating process. Controlling the sand particle size ≤300 mesh is to ensure that the oxide on the surface of the coating is completely removed and the surface of the coating is smooth. Exemplarily, the sand particle size of the sand blasting treatment can be 150 mesh, 200 mesh, 210 mesh, 220 mesh, 250 mesh, 280 mesh, 300 mesh, and the sand blasting depth can be 1μm, 2μm, 3μm, 4μm, 5μm, etc.

[0079] Based on a general inventive concept, the present application provides a zinc-based coated hot-formed steel part, the coating thickness of the part is 8μm~35μm, and the part meets at least one of the following properties: surface roughness Ra≤2.0, peak number RPc≥80, LME crack depth≤5μm, corrosion potential of -0.6V~-0.3V, corrosion current of 2.5μA~5μA, and salt spray corrosion time to steel substrate ≥650h.

[0080] The zinc-based hot-formed steel parts have fewer cracks and stronger corrosion resistance. For example, the coating thickness of the parts can be 8μm, 35μm

[0081] The zinc-based hot-formed steel part is realized based on the preparation method of the zinc-based hot-formed steel part mentioned above. The specific steps of the preparation method of the zinc-based hot-formed steel part can refer to the above embodiment. Since the zinc-based hot-formed steel part adopts part or all of the technical solutions of the above embodiment, it has at least all the beneficial effects brought by the technical solutions of the above embodiment, which will not be repeated here one by one.

[0082] Examples 1 to 4 of the present application and comparative examples 1 to 4 provide a method for preparing a zinc-based coated hot-formed steel part, comprising the following steps:

[0083] S11, continuously heating the zinc-based coated hot-formed steel in three stages to obtain steel to be stamped; wherein the temperature of the first heating section is 750°C to 830°C, the temperature of the second heating section is 880°C to 950°C, and the temperature of the third heating section is 800°C to 900°C;

[0084] S21, hot stamping and sandblasting the steel to be stamped to obtain parts, wherein the stamping temperature used in Examples 1 to 4 and Comparative Examples 1 to 4 is 700° C. and the demolding temperature is 200° C. The chemical composition and thickness of the steel substrate of the zinc-based hot-formed steel are shown in Table 1, the coating name and thickness of the zinc-based hot-formed steel are shown in Table 2, and the process parameters for preparing zinc-based hot-formed steel parts are shown in Table 3.

[0085] Table 1 Chemical composition (wt%) and thickness of steel substrates of Examples 1 to 4 and Comparative Examples 1 to 4

[0086]

[0087]

[0088] Table 2 Coating name and coating thickness of Examples 1 to 4 and Comparative Examples 1 to 4

[0089] Group Coating Type Zn / wt% Al / wt% Ni / wt% Coating thickness on one side / μm Example 1 GI 99.8 0.2 - 15 Example 2 GA 99.88 0.12 - 10 Example 3 Electrogalvanizing 100 - - 5 Example 4 Zn-Ni 88 - 12 6 Comparative Example 1 GI 99.8 0.2 - 15 Comparative Example 2 GA 99.88 0.12 - 10 Comparative Example 3 Electrogalvanizing 100 - - 5 Comparative Example 4 Zn-Ni 88 - 12 6

[0090] Table 3 Process parameters for preparing zinc-based hot-formed steel parts of Examples 1 to 4 and Comparative Examples 1 to 4

[0091]

[0092] The stamped parts of Examples 1 to 4 and Comparative Examples 1 to 4 were subjected to a neutral salt spray test according to the international standard ISO 3768-1976, and then the cross-section of the corroded samples was observed to measure the time until the corrosion reached the substrate. Electrochemical experiments were conducted according to the national standard GB / T24196-2009 to measure the corrosion potential and corrosion current of the hot stamped parts, and the LME crack depth and corrosion performance are shown in Table 4.

[0093] Table 4 LME crack depth and corrosion resistance of parts after hot forming of Example 1-4

[0094] Group LME crack depth / μm Corrosion potential / V Corrosion current / μA Salt spray corrosion time to substrate / h Example 1 3 -0.41 4.12 720 Example 2 5 -0.55 4.78 672 Example 3 2 -0.32 3.33 768 Example 4 4 -0.29 2.86 840 Comparative Example 1 10 -0.86 6.38 480 Comparative Example 2 8 -0.93 7.89 432 Comparative Example 3 18 -1.23 9.65 240 Comparative Example 4 25 -1.50 12.43 96

[0095] It can be obtained from Comparative Example 1 that when the cooling rate after leaving the furnace is less than 25°C / s, the LME crack depth of the formed part increases, resulting in a decrease in the corrosion resistance of the material. It can be obtained from Comparative Example 2 that when the material is heated in the low temperature zone for too long, the coating will cause serious sticking to the roller, and the Fe content in the coating will increase after forming, resulting in a decrease in the corrosion resistance of the part. It can be obtained from Comparative Example 3 that when the material is heated in the high temperature zone for too long, the Fe content in the coating will increase and the plasticity will decrease, resulting in an increase in the crack depth of the part, and then the corrosion resistance will decrease. It can be obtained from Comparative Example 4 that if zone heating is not used during the heating process, the coating will melt and evaporate seriously, and the crack depth of the coating will increase significantly after forming, resulting in a serious decrease in the corrosion resistance of the part.

[0096] Figure 2 A cross-sectional view of a zinc-based coated hot-formed steel part provided in Example 1 of the present application.

[0097] Depend on Figure 2 It can be seen that the bright area in the picture is a zinc-rich phase. After hot forming, the coating is complete, has a high zinc content, and has excellent corrosion resistance.

[0098] The above description is only a specific implementation of the present application, so that those skilled in the art can understand or implement the present application. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to the embodiments shown herein, but will conform to the widest range consistent with the principles and novel features applied for herein.

Claims

1. A method for preparing a zinc-based coated hot-formed steel part, characterized in that: The method comprises: The zinc-based coated hot-formed steel is continuously heated in three stages to obtain the steel to be stamped; wherein the temperature of the first heating stage is 750°C to 830°C, the temperature of the second heating stage is 880°C to 950°C, and the temperature of the third heating stage is 800°C to 900°C; and The steel to be stamped is subjected to hot stamping and sandblasting to obtain parts.

2. The method according to claim 1, characterized in that The time t1 of the first heating stage and the total time t of the continuous three-stage heating satisfy the following relationship: t1 = (0.1-0.2) t; and / or The time t2 of the second heating stage and the total time t of the continuous three-stage heating satisfy the following relationship: t2 = (0.4-0.7) t; and / or The time t3 of the third heating section and the total time t of the continuous three-stage heating satisfy the following relationship: t3=(0.1-0.5)t.

3. The method according to claim 2, characterized in that The total time t of the continuous three-stage heating satisfies the following relationship: If the thickness of the zinc-based coated hot-formed steel is less than 1.2 mm, then 210 ≤ t ≤ 250 s; If the thickness of the zinc-based coated hot-formed steel is 1.2 mm to 2.0 mm, then 250 < t ≤ 320 s; If the thickness of the zinc-based coated hot-formed steel is greater than 2.0 mm and less than or equal to 3.0 mm, then 320<t≤400s.

4. The method according to claim 1, characterized in that In the first heating section, the Fe content in the zinc-based coating of the zinc-based coating hot-formed steel is 30% to 40% by mass; and / or In the second heating section, the Fe content in the zinc-based coating of the zinc-based coating hot-formed steel is 50% to 70% by mass.

5. The method according to claim 1, characterized in that The zinc-based coated hot-formed steel comprises: steel base, A metal pre-plating layer covering at least a portion of the surface of the steel substrate, wherein the metal pre-plating layer comprises one or more of Ni, Cu, Cr and Fe, and A zinc-based coating covering at least a portion of the surface of the metal pre-coating has a thickness of 5 μm to 20 μm and is a pure zinc coating, an alloy coating, a Zn-Ni coating or an electroplated zinc coating.

6. The method according to claim 5, characterized in that Measured by mass fraction, the chemical composition of the steel matrix includes: C: 0.1%-0.4%, Si: 0.2%-1.5%, Mn: 2%-5%, Al: 0.05%-0.5%, Ti: 0.01%-0.1%, V: 0.01%-0.15%, Cr: 0.2%-0.5%, B: 0.001%-0.004%, P: ≤0.005%, S: ≤0.005%, N: ≤0.005%, and the balance is Fe and unavoidable impurities.

7. The method according to claim 1, characterized in that The method of subjecting the steel to be stamped to hot stamping and sandblasting to obtain a part comprises: The steel to be stamped is transferred to a hot stamping device, and cooled during the transfer process, and then hot stamped using the hot stamping device to obtain a hot stamped part, wherein the cooling rate is ≥25°C / s; The hot stamping part is sandblasted to obtain a part.

8. The method according to claim 7, characterized in that The process parameters of the hot stamping include: a stamping temperature of 550°C to 750°C, a cooling rate of press-holding quenching of ≥20°C / s, and a die-out temperature of ≤200°C.

9. The method according to claim 7, characterized in that The sand particle size of the sand blasting treatment is ≤300 mesh, and the sand blasting depth is ≤5 μm.

10. A zinc-based coated hot-formed steel part prepared by the method according to any one of claims 1 to 9, characterized in that: The coating thickness of the part is 8μm to 35μm, and the part meets at least one of the following properties: surface roughness Ra≤2.0, peak number RPc≥80, LME crack depth≤5μm, corrosion potential of -0.6V to -0.3V, corrosion current of 2.5μA to 5μA, and salt spray corrosion time to steel substrate ≥650h.

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