High-strength outer plate with excellent flanging forming performance and preparation method

Abstract

The invention relates to a high-strength outer plate with excellent flanging forming performance and a preparation method, and belongs to the technical field of steel manufacturing. The high-strength outer plate comprises the following chemical components in percentage by mass: 0.05%-0.14% of C, 0.1%-0.4% of Si, 0.8%-1.4% of Mn, less than or equal to 0.01% of P, less than or equal to 0.005% of S, 0.5%-1.0% of Al, 0.01%-0.04% of Ti and a matrix element Fe, the microstructure of the high-strength outer plate comprises, by area ratio, 80%-90% of ferrite, 5%-15% of martensite and 2%-5% of retained austenite. By designing chemical components and microstructures, ferrite provides good elongation and deformability, martensite improves the strength of the material, and the element Ti realizes grain refinement by forming a precipitated phase, so that not only is the requirement on the waviness of the outer plate favorably realized, but also the hole expansion rate of the material can be improved. According to the obtained high-strength outer plate, the balance of various mechanical properties such as strength, ductility and hole expansion rate is achieved while the surface quality is met, and the forming and performance requirements of the outer plate are met.

Description

Technical Field

[0001] The present application relates to the technical field of steel manufacturing, and in particular to a high-strength outer plate with excellent flanging forming performance and a preparation method thereof. Background Art

[0002] With the rapid development of the automobile industry, especially the growing strength of the new energy automobile industry, the lightweighting of automobile bodies has received more and more attention. In recent years, a large amount of high-strength steel has been used in structural parts and reinforcements such as A-pillars and B-pillars, making outstanding contributions to the high strength and lightweighting of automobiles. In addition, the weight of the external covering parts such as the side panels, roof, hood, and door panels of the automobile body in white accounts for more than 25% of the body in white. Due to the large size of the parts and the high weight ratio, if the above-mentioned external covering parts are reduced in weight, the lightweighting effect will be very significant.

[0003] With the increasing requirements for lightweight body and complex parts design, some automobile companies, especially new energy automobile companies, have designed a front and rear door outer panel with hidden door handles, which has the advantages of reducing wind resistance and aesthetics. Since such door handles require high flanging forming requirements, they are currently generally produced using low-strength grade materials such as soft steel and BH steel, but their weight reduction and dent resistance are limited. As the lightweighting of outer panels is increasingly valued, it is necessary to develop a high-strength outer panel with higher strength and flanging and hole expansion performance to meet the needs of forming and lightweighting. Summary of the invention

[0004] The present application provides a high-strength outer plate with excellent flanging forming performance and a preparation method thereof, in order to solve the following technical problem: how to improve the flanging forming performance of the high-strength outer plate while satisfying a relatively high surface quality.

[0005] In a first aspect, an embodiment of the present application provides a high-strength outer plate with excellent flanging forming performance, wherein the chemical composition of the high-strength outer plate includes, by mass fraction: C: 0.05% to 0.14%, Si: 0.1% to 0.4%, Mn: 0.8% to 1.4%, P≤0.01%, S≤0.005%, Al: 0.5% to 1.0%, Ti: 0.01% to 0.04%, and matrix element Fe;

[0006] Calculated by area ratio, the microstructure of the high-strength outer plate includes: ferrite: 80% to 90%, martensite: 5% to 15%, and retained austenite: 2% to 5%.

[0007] Optionally, the high-strength outer plate satisfies at least one of the following properties: tensile strength of 500MPa to 600MPa, yield strength of 280MPa to 400MPa, hole expansion rate of 40% to 60%, elongation after fracture A80 ≥ 30%, and BH value ≥ 30MPa.

[0008] Optionally, the corrugation degree Wsa1-5 of the high-strength outer plate after flanging is ≤0.30μm.

[0009] In a second aspect, an embodiment of the present application provides a method for preparing a high-strength outer plate with excellent flanging forming performance as described in the first aspect, the method comprising:

[0010] Obtaining a casting billet having the chemical composition;

[0011] The ingot is heated and hot-rolled in sequence to obtain a hot-rolled plate;

[0012] The hot-rolled sheet is pickled, cold-rolled and hot-dip galvanized in sequence to obtain a galvanized sheet; wherein the hot-dip galvanizing comprises: a heating section, a first cooling section, a second cooling section, a galvanizing section and a third cooling section;

[0013] The galvanized sheet is subjected to skin finishing to obtain a finished high-strength outer sheet.

[0014] Optionally, the heating temperature is 1200° C. to 1280° C., and the heating insulation time is 2 h to 4 h.

[0015] Optionally, the final rolling temperature of the hot rolling is 870°C to 920°C, and the coiling temperature of the hot rolling is 640°C to 700°C.

[0016] Optionally, the cold rolling reduction rate is 50% to 80%.

[0017] Optionally, the heating rate of the heating section is 2°C / s to 5°C / s, the termination temperature of the heating section is 800°C to 840°C, and the insulation time of the heating section is 40s to 80s.

[0018] Optionally, the cooling rate of the first cooling section is 10°C / s to 20°C / s, and the termination temperature of the first cooling section is 650°C to 730°C.

[0019] Optionally, the cooling rate of the second cooling section is 20°C / s to 40°C / s, and the termination temperature of the second cooling section is 455°C to 465°C.

[0020] Optionally, the cooling rate of the third cooling section is 15°C / s to 25°C / s, and the termination temperature of the third cooling section is 180°C to 240°C.

[0021] Optionally, the elongation of the finishing is 0.5% to 1.0%.

[0022] The above technical solution provided by the embodiment of the present application has the following advantages compared with the prior art:

[0023] The embodiment of the present application provides a high-strength outer plate with excellent flanging forming performance. The chemical composition of the high-strength outer plate includes, by mass fraction, C: 0.05% to 0.14%, Si: 0.1% to 0.4%, Mn: 0.8% to 1.4%, P≤0.01%, S≤0.005%, Al: 0.5% to 1.0%, Ti: 0.01% to 0.04%, and matrix element Fe; by area ratio, the microstructure of the high-strength outer plate includes: ferrite: 80% to 90%, martensite: 5% to 15%, and residual austenite: 2% to 5%. By designing the chemical composition and microstructure, ferrite provides good elongation and deformation ability, martensite improves the strength of the material, and the element Ti forms a precipitated phase to achieve grain refinement, which not only helps to achieve the requirements of the corrugation of the outer plate, but also can improve the hole expansion rate of the material. The obtained high-strength outer plate achieves a balance of various mechanical properties such as strength, elongation, and hole expansion rate while meeting the surface quality requirements, meeting the outer plate forming and performance requirements. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] 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.

[0025] In order to more clearly illustrate the technical solutions in the embodiments of the present application or 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.

[0026] Figure 1 A schematic flow chart of a method for preparing a high-strength outer plate with excellent flanging forming performance provided in an embodiment of the present application;

[0027] Figure 2 Microstructure photos of high-strength outer plates with excellent flange forming performance provided in the embodiments of the present application;

[0028] Figure 3 The door handle position forming state after the high-strength outer panel provided in the embodiment of the present application is actually stamped and formed. DETAILED DESCRIPTION

[0029] 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.

[0030] 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, it should be considered that the range description has specifically disclosed all possible sub-ranges and single numerical values ​​within the range; for example, it should be considered that the range description from 1 to 6 has 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 applies regardless of the range; in addition, whenever a numerical range is indicated in this document, it is meant to include any cited numbers (fractions or integers) within the indicated range.

[0031] In this document, the terms including "including" and "including" mean "including but not limited to". Relational terms such as "first" and "second" 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. "And / or" describes the association relationship of associated objects, indicating that there can be three relationships. For example, A and / or B can mean: A exists alone, A and B exist at the same time, and B exists alone; where A and B can be singular or plural. "At least one" means one or more, and "plurality" means two or more; "at least one", "at least one of the following" or similar expressions refer to any combination of these items, including any combination of single or plural items; for example, "at least one of a, b, or c", or "at least one of a, b, and c" can all mean: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can be single or multiple. "Parts" such as parts by weight and parts by mass indicate the proportional relationship between the components. In the proportional relationship involved in this article, the parameters that need to be described by proportion should be understood as the first term of the proportional formula in the order of description, and the proportional numbers should be understood as the second term of the proportional formula. For example, if the mass ratio of substance A, substance B and substance C is 1:2:3, then substance A, substance B and substance C should correspond to the proportional numbers in the proportional formula in the order of description, that is, the mass of substance A: the mass of substance B: the mass of substance C = 1:2:3.

[0032] Unless otherwise specified, various raw materials, reagents, instruments and equipment used in this article can be purchased from the market or prepared by existing methods.

[0033] In a first aspect, an embodiment of the present application provides a high-strength outer plate with excellent flanging forming performance, wherein the chemical composition of the high-strength outer plate includes, by mass fraction: C: 0.05% to 0.14%, Si: 0.1% to 0.4%, Mn: 0.8% to 1.4%, P≤0.01%, S≤0.005%, Al: 0.5% to 1.0%, Ti: 0.01% to 0.04%, and matrix element Fe;

[0034] Element C is one of the most important strengthening elements of steel products, which can make the material reach a strength level of 500MPa. However, if the mass fraction of C is too high, it will significantly affect the plasticity and toughness of the material, which is not conducive to its use as an outer plate stamping material. Therefore, this application sets the mass fraction of C to 0.05% to 0.14%. For example, the mass fraction of C can be 0.05%, 0.07%, 0.09%, 0.11%, 0.13%, 0.14%, etc.

[0035] Element Si, as a ferrite-forming element, can purify ferrite and improve elongation. However, if the mass fraction of Si is too high, it will be enriched on the surface, causing defects such as plating leakage and pitting on the coating surface, reducing the surface quality and making it impossible to use as an outer plate. Therefore, this application sets the mass fraction of Si to 0.1% to 0.4%. For example, the mass fraction of Si can be 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, etc.

[0036] The element Mn can improve the strength of the material. When the mass fraction of Mn is too low, the strength cannot meet the requirements. When the mass fraction of Mn is too high, it is easy to segregate and combine with sulfur to form MnS inclusions, which reduces the forming performance. Therefore, this application sets the mass fraction of Mn to 0.8% to 1.4%. For example, the mass fraction of Mn can be 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, etc.

[0037] P and S are harmful elements in steel. P tends to segregate at grain boundaries, seriously damaging the plasticity and toughness of the steel plate; S combines with elements such as manganese in steel to form MnS inclusions, which is detrimental to the plasticity and toughness of the steel, so the mass fractions of P and S should be as low as possible. This application sets the upper limit of P at 0.01% and the upper limit of S at 0.005%. Exemplarily, the mass fraction of P can be 0.002%, 0.004%, 0.006%, 0.008%, 0.01%, etc.; Exemplarily, the mass fraction of S can be 0.001%, 0.002%, 0.003%, 0.004%, 0.005%, etc.

[0038] The element Al can promote the enrichment of austenite stabilizing elements into austenite and enhance the stability of austenite. Too high a mass fraction of Al will lead to non-metallic inclusions in molten steel and cause nozzle blockage during casting. Therefore, the mass fraction of Al is set at 0.5% to 1.0% in this application. For example, the mass fraction of Al can be 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, etc.

[0039] Ti can form a titanium compound precipitate phase with N and C to achieve grain refinement, and obtain a ferrite grain size of less than 10μm, so that the product has a small deformation (5%) condition of Wsa1-5≤0.30μm, meets the corrugation requirements of the outer plate, and increases the hole expansion rate to 40% to 60%. The present application sets the mass fraction of Ti to 0.01% to 0.04%. For example, the mass fraction of Ti can be 0.01%, 0.02%, 0.03%, 0.04%, etc.

[0040] Fe is a matrix element. The specific content / content range of Fe can be obtained by the upper and lower limit formula of the component, that is:

[0041] The sum of the percentages of the contents of each component in a composition should be equal to 100%, and the content ranges of several components should meet the following conditions: the upper limit value of a component + the lower limit value of other components ≤ 100; the lower limit value of a component + the upper limit value of other components ≥ 100.

[0042] Calculated by area ratio, the microstructure of the high-strength outer plate includes: ferrite: 80% to 90%, martensite: 5% to 15%, and retained austenite: 2% to 5%.

[0043] In the embodiment of the present application, the microstructure of the high-strength outer plate includes 80% to 90% ferrite, 5% to 15% martensite, 2% to 5% residual austenite, and a small amount of Ti precipitation phase. Ferrite can provide good elongation and deformation ability, but too high ferrite content will lead to insufficient tensile strength of the material, so it is set to 80% to 90%. Exemplarily, the area ratio of ferrite can be 80%, 82%, 84%, 86%, 90%, etc. Martensite controls the strength of the material above 500MPa, but excessive martensite content can easily cause excessive hardness difference between ferrite and martensite phases, reduce the material expansion rate, so it is set to 5% to 15%; at the same time, the two-phase organization of ferrite and martensite can achieve a BH value ≥ 30MPa, improving the overall dent resistance. Exemplarily, the area ratio of martensite can be 5%, 8%, 11%, 14%, 15%, etc. The presence of retained austenite will help to further improve the elongation of the material and meet the requirements of outer plate forming. For example, the area ratio of retained austenite can be 2%, 3%, 4%, 5%, etc. The Ti precipitate phase can achieve the outer plate free of the corrugation requirements of the intermediate product by refining the grains, and on the other hand, it will be conducive to the improvement of the hole expansion rate.

[0044] In some embodiments, the high-strength outer plate satisfies at least one of the following properties: tensile strength of 500MPa to 600MPa, yield strength of 280MPa to 400MPa, hole expansion rate of 40% to 60%, elongation after fracture A80 ≥ 30%, and BH value ≥ 30MPa.

[0045] Tensile strength: The tensile strength of high-strength outer plates ranges from 500MPa to 600MPa. This means that the material can withstand considerable stress without breaking when subjected to tensile forces. This high-strength property is particularly important for applications that need to withstand large external loads or impacts.

[0046] Yield Strength: Yield strength is the maximum stress that a material can withstand before plastic deformation. In this embodiment, the yield strength of the high-strength outer plate is between 280MPa and 400MPa. This means that before the yield point, the material can maintain its original shape and size and is not prone to permanent deformation.

[0047] Hole expansion rate: Hole expansion rate is an important indicator to measure the deformation ability of materials during flanging or hole expansion. The hole expansion rate of high-strength outer plate is between 40% and 60%, indicating that it has good flanging forming performance and can adapt to large hole diameter changes without cracking or severe deformation.

[0048] Elongation after fracture A80: Elongation after fracture reflects the plastic deformation ability of the material before fracture. The elongation after fracture A80 of the high-strength outer plate is greater than or equal to 30%, indicating that it has good ductility and toughness and can maintain integrity when subjected to large deformation.

[0049] BH value (bake hardening value): BH value is an indicator to measure the degree of hardening of the material during the baking process. The BH value of high-strength outer plate is greater than or equal to 30MPa, which means that during the baking process, the strength of the material will be further improved, thereby enhancing its resistance to dents and wear.

[0050] In summary, the mechanical properties of these high-strength outer panels in their implementation make them ideal for automotive manufacturing, building structures, and other applications that require high strength and good formability. Through reasonable component design and preparation process, it can be ensured that these panels have good plasticity and toughness while maintaining high strength to meet the needs of different application scenarios.

[0051] In some embodiments, the corrugation degree Wsa1-5 of the high-strength outer plate after flanging is ≤0.30 μm.

[0052] The corrugation Wsa1-5 is an important parameter to measure the microscopic roughness of the material surface. It reflects the changes in the surface morphology of the material during the processing. For high-strength outer plates, the corrugation after flanging directly affects its appearance quality and performance. If the corrugation is too large, it may cause problems such as cracks and deformation of the material during subsequent processing or use, thereby affecting the overall quality and reliability of the product. The high-strength outer plate in the embodiment of the present application has excellent flanging forming performance, and the corrugation Wsa1-5 after flanging forming is ≤0.30μm, which means that during the flanging forming process, the high-strength outer plate can maintain good shape stability and surface quality.

[0053] Figure 1 A schematic flow chart of a method for preparing a high-strength outer plate with excellent flanging forming performance provided in an embodiment of the present application.

[0054] See also Figure 1 In a second aspect, an embodiment of the present application provides a method for preparing a high-strength outer plate with excellent flanging forming performance as described in the first aspect, the method comprising:

[0055] S1, obtaining a casting billet having the chemical composition;

[0056] Ingot preparation is one of the key links in the production of high-strength outer plates. First of all, the raw materials must be strictly screened and accurately proportioned to ensure that the chemical composition of the ingot meets the product specifications. At the same time, it is crucial to control the cooling rate and temperature of the ingot to avoid defects such as cracks and segregation to ensure the quality of the ingot.

[0057] S2, heating and hot rolling the ingot in sequence to obtain a hot-rolled plate;

[0058] The heated ingot enters the hot rolling process. Through multiple rolling passes and appropriate temperature control, the structure of the ingot undergoes recrystallization and phase change, improving its mechanical properties and processing performance.

[0059] In some embodiments, the heating temperature is 1200° C. to 1280° C., and the heating insulation time is 2 h to 4 h.

[0060] Insulation can make the tissue more uniform. For example, the heating temperature can be 1200°C, 1220°C, 1240°C, 1260°C, 1280°C, etc.; the heating insulation time can be 2h, 2.5h, 3h, 3.5h, 4h, etc.

[0061] In some embodiments, the final rolling temperature of the hot rolling is 870°C to 920°C, and the coiling temperature of the hot rolling is 640°C to 700°C.

[0062] The above-mentioned final rolling temperature is in the full austenite region, and the austenite phase has good plasticity and toughness. Therefore, when the final rolling temperature is in the full austenite region, the plastic deformation ability of the metal material is enhanced, which is conducive to the smooth progress of the hot rolling process and reduces the occurrence of cracks and fractures. Exemplarily, the final rolling temperature of hot rolling can be 870°C, 880°C, 890°C, 900°C, 900°C, 920°C, etc.

[0063] By adopting high temperature coiling, a hot rolled structure of ferrite + cementite can be obtained, which is helpful for controlling the rolling force of subsequent cold rolling and obtaining a more uniform structure. For example, the coiling temperature of hot rolling can be 640°C, 650°C, 660°C, 670°C, 680°C, 690°C, 700°C, etc.

[0064] S3, sequentially pickling, cold rolling and hot-dip galvanizing the hot-rolled sheet to obtain a galvanized sheet; wherein the hot-dip galvanizing includes: a heating section, a first cooling section, a second cooling section, a galvanizing section and a third cooling section;

[0065] After hot rolling, the steel plate needs to be pickled to remove the surface oxide scale and oil stains to provide a clean surface for subsequent cold rolling. During the cold rolling process, further plastic deformation and work hardening can further improve the strength and hardness of the steel plate to meet the requirements of high-strength outer plates. In order to improve the corrosion resistance of high-strength outer plates, hot-dip galvanizing is usually used for surface treatment.

[0066] In some embodiments, the cold rolling reduction ratio is 50% to 80%.

[0067] The hot-rolled plate is cold-rolled after pickling, and the cold-rolling reduction rate is 50% to 80%. This choice can not only meet the thickness requirements of the outer plate, but also increase the deformation storage energy to a certain extent, providing favorable conditions for the subsequent annealing process. At the same time, this reduction rate also avoids the situation where the equipment is damaged due to excessive rolling force. Exemplarily, the cold rolling reduction rate can be 50%, 55%, 60%, 65%, 70%, 75%, 80%, etc.

[0068] In some embodiments, the heating rate of the heating section is 2°C / s to 5°C / s, the termination temperature of the heating section is 800°C to 840°C, and the holding time of the heating section is 40s to 80s.

[0069] The temperature of the heating section is within the ferrite-austenite two-phase region. If the temperature is too low, the austenite content is insufficient, and sufficient martensite cannot be obtained, resulting in insufficient strength; if the temperature is too high, there is more austenite, and more martensite is formed, resulting in too high strength while reducing the elongation and hole expansion rate of the material. Exemplarily, the termination temperature of the heating section can be 800°C, 810°C, 820°C, 830°C, 840°C, etc.

[0070] In some embodiments, the cooling rate of the first cooling section is 10°C / s to 20°C / s, and the termination temperature of the first cooling section is 650°C to 730°C.

[0071] The above cooling temperature can promote the transformation of a part of austenite into phase transformation ferrite, improve the elongation of the material, and promote the enrichment of austenite stabilizing elements to the remaining austenite, thereby improving the stability of austenite. Exemplarily, the cooling rate of the first cooling section can be 10°C / s, 12°C / s, 14°C / s, 16°C / s, 18°C / s, 20°C / s, etc.; the termination temperature of the first cooling section can be 650°C, 660°C, 670°C, 680°C, 690°C, 700°C, 710°C, 720°C, 730°C, etc.

[0072] In some embodiments, the cooling rate of the second cooling section is 20°C / s to 40°C / s, and the termination temperature of the second cooling section is 455°C to 465°C.

[0073] The second cooling section is cooled to 455°C to 465°C at a rate of 20°C / s to 40°C / s for hot-dip galvanizing. This process obtains a good Zn coating on the surface of the steel plate and improves the corrosion resistance of the material. Exemplarily, the cooling rate of the second cooling section can be 20°C / s, 24°C / s, 28°C / s, 32°C / s, 36°C / s, 40°C / s, etc.

[0074] In some embodiments, the cooling rate of the third cooling section is 15°C / s to 25°C / s, and the termination temperature of the third cooling section is 180°C to 240°C.

[0075] The galvanized steel strip is cooled to 180°C to 240°C at a rate of 15°C / s to 25°C / s, and then cooled to room temperature. The termination temperature of the third cooling section is lower than the martensite start transformation temperature, and the austenite is transformed into martensite to obtain sufficient tensile strength. Exemplarily, the termination temperature of the third cooling section can be 180°C, 190°C, 200°C, 210°C, 220°C, 230°C, 240°C, etc.

[0076] S4, performing skin finishing on the galvanized sheet to obtain a finished high-strength outer sheet.

[0077] Skin finishing is aimed at improving the surface quality and glossiness of steel plates.

[0078] In some embodiments, the elongation of the finishing is 0.5% to 1.0%.

[0079] Finishing can obtain the required surface roughness and improve the surface oil film storage capacity, which is beneficial to the subsequent stamping. At the same time, finishing can eliminate the yield platform and avoid the appearance of stretch marks during the stamping process. For example, the elongation of finishing can be 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, etc.

[0080] The present application is further described below in conjunction with specific examples. The experimental methods in the following examples where specific conditions are not specified are usually measured in accordance with national standards / industry standards; if there are no corresponding national standards / industry standards, they are measured in accordance with common international standards, conventional conditions or conditions recommended by the manufacturer.

[0081] The ingots of Examples 1 to 6 and Comparative Examples 1 to 2 were obtained, and the chemical compositions of the ingots are shown in Table 1.

[0082] Table 1 Chemical composition of the ingot (wt%)

[0083]

[0084]

[0085] Based on the chemical composition of the ingots of the embodiment and the comparative example, this embodiment also provides a method for preparing a high-strength outer plate with excellent flanging forming performance, comprising the following steps:

[0086] Obtaining a casting billet having the chemical composition;

[0087] The ingot is heated and hot-rolled in sequence to obtain a hot-rolled plate;

[0088] The hot-rolled sheet is pickled, cold-rolled and hot-dip galvanized in sequence to obtain a galvanized sheet; wherein the hot-dip galvanizing comprises: a heating section, a first cooling section, a second cooling section, a galvanizing section and a third cooling section;

[0089] The galvanized sheet is subjected to skin finishing to obtain a finished high-strength outer sheet. The preparation process parameters are shown in Table 2.

[0090] Table 2

[0091]

[0092] The products obtained from the above examples and comparative examples were subjected to mechanical property tests and hole expansion rate tests, and the obtained data are shown in Table 3.

[0093] Table 3 Mechanical properties and hole expansion ratio of high-strength outer plate

[0094]

[0095]

[0096] Among them, Rp0.2 represents the stress when the non-proportional elongation of the gauge length of the specimen reaches 0.2% of the original gauge length; the tensile test standard is GB / T228-2002.

[0097] It can be seen from Tables 1-3 that the embodiments of the present application have obtained high-strength outer panels with a yield strength of 329-365MPa, a tensile strength of 537-560MPa, an elongation A80 ≥ 30%, and a hole expansion rate ≥ 40% through a specific chemical composition design and process combination. The product has improved strength and forming performance on the basis of meeting the surface quality requirements, and is particularly suitable for the production needs of door outer panel parts that require the flanging of hidden door handles. In contrast, the elongation, hole expansion rate or surface quality of the products prepared in Comparative Examples 1-2 cannot meet the target requirements at the same time.

[0098] Attached Figure 2-3 Detailed description:

[0099] Figure 2 The microstructure photograph of the high-strength outer plate with excellent flange forming performance provided in the embodiment of the present application; Figure 2 As shown, the gray is the ferrite structure and the white is the martensite-retained austenite structure.

[0100] Figure 3 The door handle position forming state after the high-strength outer panel provided in the embodiment of the present application is actually stamped and formed.

[0101] One or more technical solutions in the embodiments of the present invention have at least the following technical effects or advantages:

[0102] The product obtained by the embodiment of the present invention has good surface quality, hole expansion rate and strength, and meets the production requirements of lightweight and highly strengthened outer panel parts.

[0103] 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. It will be apparent to those skilled in the art that various modifications to these embodiments are possible, and the general principles defined in the present application 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 in the present application, but will conform to the widest range consistent with the principles and novel features applied for by the present application.

Claims

1. A high-strength outer plate with excellent flange forming performance, wherein the chemical composition of the high-strength outer plate comprises, by mass fraction: C： 0.05%~0.14%, Si: 0.1%~0.4%, Mn: 0.8%~1.4%, P≤0.01%, S≤0.005%, Al: 0.5%~1.0%, Ti: 0.01%~0.04%, and matrix element Fe; Calculated by area ratio, the microstructure of the high-strength outer plate includes: ferrite: 80% to 90%, martensite: 5% to 15%, and retained austenite: 2% to 5%.

2. The high-strength outer plate according to claim 1, characterized in that: The high-strength outer plate meets at least one of the following properties: tensile strength of 500MPa-600MPa, yield strength of 280MPa-400MPa, hole expansion rate of 40%-60%, elongation after fracture A80≥30%, and BH value≥30MPa.

3. The high-strength outer plate according to claim 1, characterized in that: The corrugation degree Wsa1-5 of the high-strength outer plate after flanging is ≤0.30 μm.

4. A method for preparing the high-strength outer plate according to any one of claims 1 to 3, the method comprising: Obtaining a casting billet having the chemical composition; The ingot is heated and hot-rolled in sequence to obtain a hot-rolled plate; The hot-rolled sheet is pickled, cold-rolled and hot-dip galvanized in sequence to obtain a galvanized sheet; wherein the hot-dip galvanizing comprises: a heating section, a first cooling section, a second cooling section, a galvanizing section and a third cooling section; The galvanized sheet is subjected to skin finishing to obtain a finished high-strength outer sheet.

5. The method according to claim 4, characterized in that The heating temperature is 1200° C. to 1280° C., and the heating insulation time is 2 h to 4 h; and / or, The hot rolling finishing temperature is 870°C to 920°C, the hot rolling coiling temperature is 640°C to 700°C; and / or, The cold rolling reduction ratio is 50% to 80%.

6. The method according to claim 4, characterized in that The heating rate of the heating section is 2°C / s to 5°C / s, the termination temperature of the heating section is 800°C to 840°C, and the heat preservation time of the heating section is 40s to 80s.

7. The method according to claim 4, characterized in that The cooling rate of the first cooling section is 10°C / s to 20°C / s, and the termination temperature of the first cooling section is 650°C to 730°C.

8. The method according to claim 4, characterized in that The cooling rate of the second cooling section is 20°C / s to 40°C / s, and the termination temperature of the second cooling section is 455°C to 465°C.

9. The method according to claim 4, characterized in that The cooling rate of the third cooling section is 15°C / s to 25°C / s, and the termination temperature of the third cooling section is 180°C to 240°C.

10. The method according to claim 4, characterized in that The elongation of the finishing is 0.5% to 1.0%.

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