High strength hot press parts with high cold bending performance and manufacturing method thereof

Abstract

The present invention discloses a high-strength hot-pressed part with high cold bending performance and a manufacturing method thereof, which includes the following steps: (1) producing a steel plate for hot pressing; (2) pre-processing of the part; (3) heat treatment, transfer and pressing of the part: the part semi-finished product is placed into a heat treatment furnace, and the heat treatment temperature is controlled to 750-960°C, and the total heat treatment time is controlled to 1.5-10min, in which the time when the heat treatment temperature is 880°C or higher is 1.2min or more; the semi-finished product after heat treatment is transferred to a mold for mold clamping pressing, and the temperature of the semi-finished product when it leaves the heat treatment furnace is ≧900°C; where, when the steel plate thickness of the part to be produced is ≦1.5mm, the transfer time is controlled to 11-20s, and when the steel plate thickness of the part to be produced is >1.5mm, the transfer time is controlled to 13-25s; (4) post-pressing treatment: the part is kept warm and homogenized, and then machined to obtain a finished product. Accordingly, the method can produce parts with a strength-strain product ≧10 GPa·%, a cold bending angle ≧60 degrees, and a maximum three-point bending load ≧13 KN.

Description

[Technical field]

[0001] The present invention relates to a manufacturing method of a high-strength part, and more particularly to a high-strength hot-pressed part having high cold bending performance and a manufacturing method thereof. [Background technology]

[0002] In recent years, with the rapid development of the automobile industry, the market and users' requirements for vehicles are also increasing, and weight reduction has become a development trend of the automobile industry in the future.

[0003] In order to meet the requirement of vehicle weight reduction, currently hot-stamped steel is often used in the manufacture of automotive structural parts and safety parts, which can realize vehicle weight reduction and improvement of vehicle safety performance. Among them, 1500MPa-class hot-stamped steel has been applied on a large scale in the automotive industry, and 1800MPa and 2000MPa hot-stamped steel have also been successively used.

[0004] However, research has shown that the higher the strength of hot-pressed steel with a fully martensite structure, the lower the toughness of the steel, and the greater the risk of brittle fracture during impact and delayed cracking during practical use. This problem directly leads to the difficulty of current hot-pressed steels in achieving both high strength and excellent toughness.

[0005] To solve this problem, many scientists and engineers have made useful attempts in recent years: A Chinese patent document with publication number CN110799659A and publication date of February 14, 2020, entitled "Method for manufacturing high-strength steel part with improved ductility and part obtained by the method", discloses a high-strength steel part with improved ductility and a method for manufacturing the same, in which a high-strength steel part with good ductility is obtained by mainly controlling the Ni content and its distribution, and controlling the Ni content in the matrix to 0.25% or more.

[0006] A Chinese patent document entitled "Steel material for hot press forming, hot press forming process and hot press formed part" with publication number CN106399837A and publication date February 15, 2017 discloses a fine grain hot press steel. This technical solution is mainly for obtaining a steel material for hot press forming with fine grains by adding V element to the matrix, and also discloses a hot pressing process. In the hot pressing process of this technical solution, it is necessary to control the surface temperature of the mold below 200℃, and control the cooling rate of the steel material in the mold to 10℃ / s or more.

[0007] A Chinese patent document with publication number CN111876676A and publication date of November 3, 2020, titled "Method for manufacturing 1800 MPa class cold rolled steel for hot press forming", discloses a method for manufacturing 1800 MPa class cold rolled steel for hot press forming. This technical solution is based on the premise of low cost and no addition of any trace elements, to obtain 1800 MPa class hot press forming steel. However, the toughness of this hot press forming steel, especially the cold bending performance, is insufficient.

[0008] A Chinese patent document with publication number CN101583486A, publication date November 18, 2009, entitled "Coated steel strip, manufacturing method thereof, use method thereof, pressed billet produced thereby, pressed product produced thereby, and finished products including such pressed products", reports a method of hot pressing coated steel, in which the elapsed time from when the billet leaves a heat treatment furnace to when pressing begins is limited to 10 seconds or less, and the cooling rate from when the billet leaves the furnace to 400°C is controlled to 50°C / s or more, but the toughness of the material is not considered in this technical solution.

[0009] A Chinese patent document entitled "Hot press forming parts, pre-coated steel sheet for hot press forming and hot press forming process" with publication number CN108588612A and publication date September 28, 2018, discloses a pre-coated hot press steel and its hot pressing method. The technical solution mentions that the temperature when the steel sheet is transferred to the mold is 550℃ or higher, but the patent improves the problem of poor cold bending performance pointed out in patent CN101583486B by reducing the coating thickness.

[0010] From this, it can be seen that in the current prior art, those skilled in the art have little research on high-strength hot press-formed steel with good cold bending performance. Among the above technical solutions, only the patent document with publication number CN110799659A has considered the cold bending performance of the material while ensuring that the hot press-formed steel has high strength.

[0011] According to a study, the larger the cold bending angle of hot press forming steel, the more energy it can absorb under the same conditions, and the longer the fracture failure time can be. Therefore, the present inventor believes that it is particularly important to study the cold bending performance of high strength hot press steel and its feasible manufacturing method, and based on this, the present invention hopes to obtain a manufacturing method for high strength hot press parts with high cold bending performance. Summary of the Invention [Problem to be solved by the invention]

[0012] One of the objectives of the present invention is to provide a method for producing high-strength hot-pressed parts with high cold bending performance, which is convenient and feasible, can efficiently produce high-strength hot-pressed parts with high cold bending performance, and has good prospects for popularization and application effects. [Means for solving the problem]

[0013] In order to achieve the above object, the present invention provides a method for producing a high strength hot pressed part with high cold bending performance, the method comprising the following steps: (1) Producing steel plates for hot pressing; (2) Pre-machining of parts; (3) Parts heat treatment, transfer and pressing: The parts semi-finished products processed into a predetermined shape are placed into a heat treatment furnace, the heat treatment temperature is controlled to 750-960°C, and the total heat treatment time is controlled to 1.5-10min, of which the time when the heat treatment temperature is 880°C or higher is 1.2min or more; The semi-finished products after heat treatment are transferred to a mold and pressed by mold clamping, and the temperature of the semi-finished products when they leave the heat treatment furnace is ≧900°C; Here, when the steel plate thickness of the parts to be manufactured is ≦1.5mm, the transfer time is controlled to 11-20s, and when the steel plate thickness of the parts to be manufactured is >1.5mm, the transfer time is controlled to 13-25s; (4) Post-press processing: The parts are kept warm and homogenized, and then machined to obtain the finished product.

[0014] In the above technical solution of the present invention, the inventors optimize the design of the heat treatment, transfer and pressing processes of the part in step (3). In particular, heat treatment, transfer and pressing are three important and complementary factors for the performance of the part described in the present invention. The heat treatment process is very important for the forming of the part, transfer is very important for the cold bending and strength of the part, and pressing is very important for the forming and strength of the part.

[0015] The temperature and time of the heat treatment process can be flexibly adjusted according to the thickness specification and size of the part, mainly to ensure complete austenitization and surface characteristics. The optimized transformation process is the core of the technical solution of the present invention. In the past, in order to ensure high strength of hot-formed parts, the faster the transformation process, the better, and it is basically required to be completed within 10 seconds. However, according to the research of the present invention, by combining with the turning point of the phase transformation temperature of the hot-pressed steel plate substrate, the transformation time can be controlled within an appropriate range, which can improve the cold bending performance while ensuring high strength.

[0016] In the present invention, when specifically implemented, the heat treatment temperature is within the above-mentioned temperature range of 750°C to 960°C, which may be in a stepwise different temperature zone or in a single temperature range, the heat treatment temperature may be freely increased or decreased or a combination thereof, the total heat treatment time is controlled between 1.5 to 10 min, the time when the heat treatment temperature is 880°C or higher is 1.2 min or more, and the temperature when the semi-finished product leaves the heat treatment furnace is ≧900°C (for example, between 900°C to 960°C), otherwise austenitization may be incomplete and affect the strength and elongation product. Here, the heat treatment time refers to the total time at all heat treatment temperatures.

[0017] Therefore, in step (4) described in the present invention, the post-press treatment process can further eliminate the residual stress from the forming process, solve the problems of uneven structure and hydrogen diffusion, and further improve the cold bending performance of the parts.

[0018] In the present invention, the manufacturing in step (1) may be a conventional manufacturing method in the industry, and includes manufacturing a base steel strip through processes such as steelmaking, hot rolling, cold rolling, and annealing according to the desired elements. The obtained base steel strip may be used as a steel sheet for hot pressing as it is, or the base steel strip may be further plated to become a steel sheet for hot pressing. The plating layer may be any of an aluminum silicon plating layer, an aluminum silicon zinc magnesium plating layer, an aluminum silicon magnesium plating layer, a zinc plating layer, and a zinc iron alloy plating layer. To form a steel sheet having the above-mentioned various plating layers on the surface of the base steel strip, a method well known in the industry may be adopted.

[0019] For example, a steel sheet having an aluminum silicon plating layer on its surface is manufactured by immersing a steel strip at 630 to 680°C in a plating solution containing 7 to 10% Si, 2 to 4% Fe, the balance Al and unavoidable impurities by mass percent. For example, a steel sheet having a zinc iron alloy plating layer on its surface is manufactured by immersing a steel strip at 420 to 700°C in a plating solution containing 8 to 12% Zn, 2 to 4% Fe, the balance Al and unavoidable impurities by mass percent. For example, a steel sheet having an aluminum silicon magnesium plating layer on its surface is manufactured by immersing a steel strip at 630 to 700°C in a plating solution containing 6 to 10% Si, 0.5 to 3% Mg, the balance Al and unavoidable impurities by mass percent. For example, a steel sheet having a zinc plating layer on its surface is manufactured by immersing a steel strip at 420 to 700°C in a plating solution containing 0.08 to 0.3% Al, the balance Zn and unavoidable impurities by mass percent. For example, a steel strip is immersed in a plating solution containing, by mass percent, 6-10% Si, 0.5-2% Mg, 8-12% Zn, the balance being Al and unavoidable impurities at 420-700°C to produce a steel sheet having an aluminum-silicon-zinc-magnesium plating layer on its surface.

[0020] In the present invention, the part pre-processing described in step (2) refers to processing the part into a desired shape. Depending on the required part shape, the part can be processed into the required shape by one-step or multi-step laser or shearing, or by combining two or more steel sheets with different shapes and different thicknesses by methods such as tailored blank welding, patch welding, etc. Of course, the part pre-processing process described in the present invention is not limited to the above operations, and may include similar or equivalent operations in some other embodiments.

[0021] In addition, when the product obtained in step (2) is a tailored blank part or a patch welded part, if one of the thicknesses is 1.5 mm or less and the other thickness is 1.5 mm or more, the transition time of the part needs to balance both, and can be selected to be, for example, 13 to 20 s.

[0022] Furthermore, in the method for producing a high-strength hot-pressed part with high cold bending performance described in the present invention, the steel sheet for hot pressing includes at least one of an unplated steel sheet, an aluminum-silicon plated layer steel sheet, an aluminum-silicon-zinc-magnesium plated layer steel sheet, an aluminum-silicon-magnesium plated layer steel sheet, a hot-dip galvanized steel sheet, and a zinc-iron alloy plated layer steel sheet.

[0023] Furthermore, in the method for producing a high-strength hot-pressed part with high cold bending performance described in the present invention, the chemical component weight percentage composition of the substrate of the steel plate for hot pressing is C: 0.2-0.4%, Mn: 1.0-2.0%, Si: 0.1-0.5%, Al: 0.01-0.1%, Ti: 0.01-0.1%, B: 0.0005-0.01%, Cr: 0.1-0.5%, and Nb+Mo+Ni: 0.3-0.6%, with the proviso that the mass percentage content of any of Nb, Mo, and Ni is 0.3% or less.

[0024] In the substrate of the hot press steel plate according to the present invention, the design principles of each chemical element are as follows: C: In the substrate described in the present invention, adding an appropriate amount of C element to the substrate can ensure the strength of the steel material and ensure the strength of the hot press parts. Therefore, it is not preferable that the content of C element in the steel is too low, and if the content of C element in the steel is less than 0.2%, the strength is not guaranteed; the content of C element in the steel should not be too high, and if the content of C element in the steel is more than 0.4%, the strength is too high and the welding performance of the steel material is deteriorated. Based on this, and taking into account the performance of the substrate, the mass percent content of C element in the substrate described in the present invention is controlled to be between 0.2% and 0.4%.

[0025] Mn: In the substrate described in the present invention, Mn element is added to ensure the strength of hot press parts, similar to C element, and Mn element can further supplement the toughness of substrate steel. If the content of Mn element in steel is less than 1.0%, the strength of steel cannot be ensured; if the content of Mn element in steel is more than 2.0%, element segregation and production cost will increase. Based on this, in order to exert the beneficial effect of Mn element, the mass percent content of Mn element is controlled between 1.0% and 2.0% in the substrate described in the present invention.

[0026] Si: Adding an appropriate amount of Si element to the substrate described in the present invention not only increases the strength of hot-pressed parts, but also serves as an important deoxidizer in the steelmaking process. If the content of Si element in steel is too high, oxidation during the manufacturing process will be severe, making it difficult to ensure good product surface quality. Therefore, in the substrate described in the present invention, the mass percent content of Si element is controlled between 0.1% and 0.5%.

[0027] Al: In the substrate described in the present invention, Al element is also a deoxidizer, and adding an appropriate amount of Al element can also improve the impact toughness of steel material. Therefore, considering the effect of Al element on the performance of steel material, the mass percent content of Al element in the substrate described in the present invention is controlled to be between 0.01% and 0.1%.

[0028] B: Adding an appropriate amount of B element to the substrate described in the present invention improves the hardenability of the steel material and ensures sufficient hardenability at each position of the hot press part. Therefore, in the substrate described in the present invention, the mass percent content of B element is controlled to be between 0.0005% and 0.01%.

[0029] Ti: In the substrate described in the present invention, Ti is an element that strengthens C and N. Adding an appropriate amount of Ti element to steel can improve the strength and toughness of the substrate, and further improve the strength and toughness of the hot press part. At the same time, Ti element can interact with B element, and better exert the hardenability by B. Based on this, in order to exert the beneficial effect of Ti element, the mass percent content of Ti element is controlled between 0.01%-0.1% in the substrate described in the present invention.

[0030] Cr: Adding an appropriate amount of Cr element to the substrate described in the present invention can improve the hardenability of the steel material and ensure sufficient hardenability at each position of the hot-pressed part. Therefore, the mass percent content of Cr element in the substrate described in the present invention is controlled to be between 0.1% and 0.5%.

[0031] The substrate described in the present invention further contains an appropriate amount of Nb, Mo, and Ni elements, among which Nb and Mo elements both can refine the crystal grains and improve the toughness of the parts after hot pressing; Ni element also plays a role in improving the toughness of the hot pressing parts, and at the same time, Ni improves hydrogen diffusion. Therefore, in the substrate described in the present invention, the mass percent content of Nb, Mo, and Ni elements is controlled between Nb+Mo+Ni:0.3-0.01%. However, the mass percent content of any of Nb, Mo, and Ni is 0.3% or less. In some embodiments, the mass percent content of Nb is 0.0001%-0.25%. In some embodiments, the mass percent content of Mo is 0.1%-0.25%. In some embodiments, the mass percent content of Ni is 0.05%-0.25%, for example, 0.08%-0.2%.

[0032] Furthermore, in the method for producing a high-strength hot-pressed part with high cold bending performance described in the present invention, in step (3), the total time of the heat treatment is controlled to 1.5 to 8 minutes.

[0033] Furthermore, in the method for producing a high-strength hot-pressed part with high cold bending performance described in the present invention, in step (3), the press speed is controlled to 40 to 80 mm / s and maintained for 2 to 30 s.

[0034] Further, in the method for producing a high strength hot pressed part with high cold bending performance described in the present invention, in step (3), the temperature of the mold during the pressing process is always less than 200° C. In some embodiments, the temperature of the mold during the pressing process is in the range of 25 to 190° C.

[0035] Furthermore, in the method for producing a high-strength hot-pressed part with high cold bending performance described in the present invention, in step (4), the temperature of the heat-holding homogenization is 150-250° C., and the time is 10-30 minutes.

[0036] Further, in the method for producing a high strength hot pressed part with high cold bending performance described in the present invention, in step (4), the machining includes at least one of cutting, trimming, punching, and welding.

[0037] Furthermore, in the method for producing a high strength hot pressed part with high cold bending performance described in the present invention, the part forms a martensite structure with a volume fraction of 95% or more in step (3).

[0038] According to the method of the present invention, a high-strength hot-pressed part with high cold bending performance and a strength elongation product ≧10 GPa·%, a cold bending angle ≧60 degrees, and a three-point bending maximum load of the high-strength hot-pressed part ≧13 KN can be produced. In some embodiments, the high-strength hot-pressed part produced by the method of the present invention has a tensile strength ≧1500 MPa and an elongation after break ≧5.5%. In some embodiments, the high-strength hot-pressed part produced by the method of the present invention has a tensile strength between 1500 and 1700 MPa, an elongation after break between 6.0 and 7.0%, and a strength elongation product ≧10 GPa·%. In some embodiments, the high-strength hot-pressed part produced by the method of the present invention has a tensile strength between 1800 and 2100 MPa, an elongation after break between 5.5 and 6.0%, and a strength elongation product ≧10.5 GPa·%.

[0039] Therefore, another object of the present invention is to provide a high-strength hot-pressed part, which has high strength and high cold bending performance at the same time, is widely applicable, can be effectively applied in the automobile industry, and exhibits good front impact resistance and side impact resistance during automobile collision.

[0040] In order to achieve the above object, the present invention provides a high-strength hot-pressed part having a strength elongation product ≧10 GPa·% and a cold bending angle ≧60°. In some embodiments, the high-strength hot-pressed part has a three-point bending maximum load ≧13 KN. In some embodiments, the high-strength hot-pressed part described in the present invention has a strength elongation product between 10-12 GPa·%, a cold bending angle between 60-75°, and a three-point bending maximum load between 13-20 KN. In some embodiments, the high-strength hot-pressed part described in the present invention has a diffused hydrogen content between 0.01-0.06 ppm. In some embodiments, the high-strength hot-pressed part has a tensile strength ≧1500 MPa and an elongation after break ≧5.5%. In some embodiments, the high-strength hot-pressed part has a tensile strength between 1500-1700 MPa, an elongation after break between 6.0-7.0%, and a strength elongation product ≧10 GPa·%. In some embodiments, the high strength hot pressed part has a tensile strength between 1800-2100 MPa, an elongation after break between 5.5-6.0%, and a strength-strain product >= 10.5 GPa %. In some embodiments, the hot pressed part is made by a method according to any of the embodiments of the present invention.

[0041] Compared with the prior art, the method for producing high strength hot pressed parts with high cold bending performance according to the present invention, the hot pressed parts have the following advantages and beneficial effects: In the present invention, the inventors have rationally optimized the design of the manufacturing method for high-strength hot-pressed parts, and optimized and controlled the three processes of heat treatment, transformation and pressing, thereby achieving high strength while ensuring good toughness and cold bending performance.

[0042] In the method for producing high strength hot pressing parts with high cold bending performance described in the present invention, the parts can form more than 95% martensite structure during heat treatment and pressing, and have high strength. At the same time, in the precise transformation control of the parts, the present invention utilizes the difference in cooling between the surface and the core to form gradient transformation control on the surface of the parts, which is very helpful in improving the toughness and cold bending performance of the parts.

[0043] The performance of the high-strength hot-pressed part manufactured by the above-mentioned method of the present invention is quite excellent, with a strength-strain product of ≧10 GPa·%, a cold bending angle of ≧60 degrees, and preferably a maximum three-point bending load of ≧13 KN. The applicability of this high-strength hot-pressed part is very wide, and it can be effectively applied in the automotive industry, showing good frontal and side impact resistance during automobile collisions. [Brief description of the drawings]

[0044] [Figure 1] 1 is a photograph of a cross-sectional microstructure of a plating layer of a high-strength hot-pressed part of Example 2. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0045] The method for producing a high-strength hot-pressed part with high cold bending performance and the hot-pressed part according to the present invention will be further explained and described below based on specific examples, but the explanation and interpretation are not intended to unduly limit the technical solution of the present invention.

[0046] Examples 1 to 9 Table 1 shows the mass percentage blending of each chemical element in the substrate of the steel sheets for hot press use in Examples 1 to 9 and the relationship between each chemical element.

[0047] [Table 1]

[0048] In the present invention, the high-strength hot-pressed parts of Examples 1 to 9 are all manufactured by the following steps: (1) A base steel strip was produced by processes such as steelmaking, hot rolling, cold rolling, and annealing according to the mass percentage composition of each chemical element shown in Table 1. However, the obtained base steel strip may be used as a steel sheet for hot pressing as it is, or the base steel strip may be further plated to produce a steel sheet for hot pressing.

[0049] (2) Parts pre-processing: According to the required part shape, blanking can be completed by one-step or multi-step laser or shearing, or it can be completed by combining two or more steel plates with different shapes and different thicknesses by methods such as tailored blank welding, patch welding, etc.

[0050] (3) Heat treatment, transfer and pressing of parts: The part semi-finished product processed into a predetermined shape is placed into a heat treatment furnace, the heat treatment temperature is controlled to 750-960°C, the total heat treatment time is controlled to 1.5-10min, preferably 1.5-8min, and the time when the heat treatment temperature is 880°C or more is 1.2min or more; The semi-finished product after the heat treatment is transferred to a mold and pressed by mold clamping, and the temperature of this semi-finished product when it leaves the heat treatment furnace is ≧900°C; The upper and lower molds are clamped by a press machine, the pressing speed is controlled to 40-80mm / s, and kept for 2-30s, and the temperature of the mold is always less than 200°C during pressing; Here, when the steel plate thickness of the part to be manufactured is ≦1.5mm, the transfer time is controlled to 11-20s, and when the steel plate thickness of the part to be manufactured is >1.5mm, the transfer time is controlled to 13-25s; (4) Post-pressing treatment: The parts are homogenized by heat preservation, the temperature of heat preservation is 150-250℃, and the time is 10-30min. Then, the parts are machined to obtain the finished products; however, the machining includes cutting, trimming, punching and welding.

[0051] In step (1) of the above-mentioned manufacturing method, the hot-pressed steel sheet may be an uncoated steel sheet or a coated steel sheet. When the hot-pressed steel sheet is a coated steel sheet, it may be specifically an aluminum-silicon coated layer steel sheet, an aluminum-silicon-zinc-magnesium coated layer steel sheet, an aluminum-silicon-magnesium coated layer steel sheet, a hot-dip galvanized layer steel sheet, or a zinc-iron alloy coated layer steel sheet.

[0052] In the present invention, the specific processes of Examples 1 to 9 in the above step (1) and step (2) are as follows: Example 1: A 1.2 mm substrate steel strip was obtained through steelmaking, hot rolling, cold rolling, and annealing according to the mass percentage composition of each chemical element shown in Table 1 above. The 1.2 mm substrate steel strip was molten aluminum silicon plated at 650°C to obtain an aluminum silicon plated layer steel sheet, of which the plating solution components were 9% Si, 2.3% Fe, and the remainder was Al and unavoidable impurities. In the pre-processing of parts, the aluminum silicon plated layer steel sheet was continuously blanked to become a part of a certain shape.

[0053] Example 2: According to the mass percentage composition of each chemical element shown in Table 1, 1.5mm and 1.8mm substrate steel strips were obtained through steelmaking, hot rolling, cold rolling, and annealing. The 1.5mm and 1.8mm substrate steel strips were molten aluminum silicon plated at 650℃ to obtain aluminum silicon plated layer steel sheets, of which the plating solution components were 9% Si, 2.3% Fe, and the remainder was Al and unavoidable impurities. In the pre-processing of the parts, the aluminum silicon plated layer steel sheets were laser blanked to become parts of a certain shape, and the two parts were connected by tailored blank welding to obtain parts of a certain shape.

[0054] Example 3: A 1.8 mm substrate steel strip was obtained through steelmaking, hot rolling, cold rolling, and annealing according to the mass percentage composition of each chemical element shown in Table 1 above. The 1.8 mm substrate steel strip was molten aluminum silicon plated at 660°C to obtain an aluminum silicon plated layer steel sheet, of which the plating solution components were 8.5% Si, 2.5% Fe, and the remainder was Al and unavoidable impurities. In the pre-processing of parts, the aluminum silicon plated layer steel sheet was continuously blanked to become a billet of a certain shape, and localized positions of the billet were patched by spot welding (patch welding from two 1.8 mm thick substrates) to obtain a part of a certain shape.

[0055] Example 4: A 2.0 mm steel strip was obtained as a hot press steel sheet through steelmaking, hot rolling, cold rolling and annealing according to the mass percentage composition of each chemical element shown in Table 1. In the pre-processing for parts, the steel strip was continuously blanked to form a billet of a certain shape.

[0056] Example 5: A 2.3 mm steel strip was obtained as a hot press steel sheet through steelmaking, hot rolling, cold rolling and annealing according to the mass percentage composition of each chemical element shown in Table 1. In the pre-processing for parts, the steel strip was continuously blanked to form a billet of a certain shape.

[0057] Example 6: A 1.4 mm substrate steel strip was obtained through steelmaking, hot rolling, cold rolling and annealing according to the mass percentage composition of each chemical element shown in Table 1 above. The 1.4 mm substrate steel strip was subjected to hot dip galvanizing and alloying at 680°C to obtain a zinc-iron alloy plated steel sheet, of which the plating solution components were 9% Zn, 2.3% Fe, and the balance was Al and unavoidable impurities. In the pre-processing of parts, the zinc-iron alloy plated steel sheet was laser blanked to form a billet of a certain shape.

[0058] Example 7: A 2.5 mm substrate steel strip was obtained through steelmaking, hot rolling, cold rolling, and annealing according to the mass percentage composition of each chemical element shown in Table 1 above. The 2.5 mm substrate steel strip was molten aluminum silicon magnesium plated at 680°C to obtain an aluminum silicon magnesium plated layer steel sheet, the plating solution components of which were 8.5% Si, 1% Mg, and the remainder was Al and unavoidable impurities. In the pre-processing of parts, the aluminum silicon magnesium plated layer steel sheet was laser blanked to form a billet of a certain shape.

[0059] Example 8: A 0.9 mm substrate steel strip was obtained through steelmaking, hot rolling, cold rolling, and annealing according to the mass percentage composition of each chemical element shown in Table 1 above. The 0.9 mm substrate steel strip was hot-dipped at 680°C to obtain a hot-dip galvanized layer steel sheet, of which the plating solution components were 0.13% Al, the remainder being Zn and unavoidable impurities. In the pre-processing of parts, the hot-dip galvanized layer steel sheet was laser blanked to form a billet of a certain shape.

[0060] Example 9: A 3.0 mm substrate steel strip was obtained through steelmaking, hot rolling, cold rolling, and annealing according to the mass percentage composition of each chemical element shown in Table 1 above. The 3.0 mm substrate steel strip was hot-dip plated at 680°C to obtain an aluminum silicon zinc magnesium plated layer steel sheet, of which the plating solution components were 8.5% Si, 1% Mg, 10% Zn, and the balance was Al and unavoidable impurities. In the pre-processing of the part, the aluminum silicon zinc magnesium plated layer steel sheet was laser blanked to form a billet of a certain shape.

[0061] In the present invention, the chemical composition designs and related processes of the steel sheets for hot press of the high-strength hot press parts of Examples 1 to 9 all satisfy the requirements of the design criteria of the present invention.

[0062] Tables 2-1 and 2-2 show process parameters relating to the manufacturing methods of high-strength hot-pressed parts of Examples 1-9.

[0063] [Table 2-1] TIFF2025512864000004.tif38170

[0064] [Table 2-2]

[0065] In addition, in the above Table 2-1, the heat treatment temperatures in the heat treatment process of step (3) in Examples 1 to 9 are all range values ​​rather than a single point value. This is because a heat treatment furnace is usually controlled in stages, so the temperature of each stage can be controlled individually and the temperature of each stage may be different. The temperature range of the heat treatment temperature in the present invention is the distribution range of all temperatures of each stage.

[0066] In addition, in Examples 1 to 9, when carrying out the above manufacturing process, in step (3), after the parts are heat-treated, transformed, and pressed as designed in Examples 1 to 9, the parts of Examples 1 to 9 are sampled and the microstructure of the parts of each Example is inspected to obtain the percentage of martensite structure in the parts of Examples 1 to 9, and the inspection results are shown in Table 3 below. Measurement of the percentage content of martensite in the parts by metallography: After inserting the sample, mechanical polishing, buffing, and corrosion were performed, and the collected image was processed using metallography image analysis software to obtain the percentage content of martensite structure.

[0067] [Table 3]

[0068] The high-strength hot-pressed parts of Examples 1 to 9, which were finally obtained through the above process steps as finished products, were each sampled and performance tests were carried out on each example sample. The performance test results are shown in Table 4 below.

[0069] In the present invention, the performance testing means adopted are as follows: (1) Strength and elongation product: Strength and elongation product is a comprehensive performance index that indicates the level of toughness of metal materials. In the present invention, the strength and elongation product of each example sample is obtained by using the product of the tensile strength and the elongation after break of the part. According to the metal tensile test method GB / T228.1, the tensile strength and the elongation after break of the part are obtained by tensile testing.

[0070] (2) Cold bending test: A cold bending test is carried out according to the VDA-238 standard to obtain the cold bending angles of the samples of Examples 1 to 9. Here, the larger the cold bending angle, the better the toughness of the material; the smaller the cold bending angle, the lower the toughness of the material.

[0071] (3) Three-point bending test and drop weight test: In the three-point bending test and drop weight test, the hot pressed parts of the examples are set in a bending device, the span is adjusted, and a load is applied to the parts until they break, and the maximum load at which breakage occurs is recorded. In the drop weight test, a 30 kg drop weight is dropped in a free fall mode from a height of 50 cm, and the degree of cracking of the sample members of each example is observed.

[0072] (4) Measurement of diffusive hydrogen content: Obtain samples from the parts by wire cutting, punching, or a water-cooled saw blade method, ultrasonically clean them with acetone, and measure the diffusive hydrogen content in the samples of each example at 300 to 400 °C using a hydrogen analyzer.

[0073] Table 4 shows the relevant performance test results of the high-strength hot-pressed part samples of Examples 1 to 9.

[0074] [Table 4]

[0075] In addition, Example 2 is a tailored blank welded part, and Example 3 is a patch welded part, both of which involve welding and are affected by welding, so the drop weight test cannot be evaluated; in addition, the maximum load test is also affected by the weld line and cannot be evaluated. Therefore, neither Example 2 nor Example 3 was subjected to a three-point bending test or a drop weight test.

[0076] As is clear from Table 4, the high-strength hot-pressed parts of Examples 1 to 9 have high strength and are also excellent in toughness and cold bending performance. In the present invention, the high-strength hot-pressed parts of Examples 1 to 9 have a strength-strain product between 10 and 12 GPa %, a cold bending angle between 60 and 75 degrees, and a maximum three-point bending load between 13 and 20 KN.

[0077] Furthermore, referring to Table 4, when a drop weight test was conducted using the high-strength hot-pressed parts of Examples 1 to 9 used as bumper beam parts, it was found that none of the high-strength hot-pressed parts of Examples 1 to 9 developed cracks and had excellent strength-elongation product and toughness; on the other hand, the diffused hydrogen content of the high-strength hot-pressed parts of Examples 1 to 9 was 0.01 to 0.06 ppm, indicating excellent hydrogen embrittlement resistance.

[0078] FIG. 1 is a photograph of the cross-sectional microstructure of the plating layer of the high-strength hot-pressed part of Example 2. As shown in Fig. 1, the high-strength hot-pressed part of Example 2 has an aluminum silicon plating layer, which includes a substrate A and a plating layer b. Among them, there is an obvious interface layer C between the plating layer A and the substrate B.

[0079] Furthermore, the combinations of the technical features in this application are not limited to the combinations described in the claims of this application or the combinations described in the specific examples, and all technical features described in this application can be freely combined or combined in any form, as long as they are not mutually contradictory.

[0080] In addition, it should be noted that the above-mentioned embodiments are merely specific embodiments of the present invention. The present invention is not limited to the above-mentioned embodiments, and it is clear that any similar changes or modifications that can be directly derived or easily conceived by those skilled in the art from the disclosure of the present invention are included in the protection scope of the present invention.

Claims

1. A method for producing a high strength hot stamped part with high cold bending performance, comprising the steps of: (1) Producing steel plates for hot pressing; (2) Pre-processing of parts; (3) Heat treatment, transfer and pressing of parts: the part semi-finished product processed into a predetermined shape is placed into a heat treatment furnace, the heat treatment temperature is controlled at 750-960°C, and the total heat treatment time is controlled at 1.5-10 min, in which the time when the heat treatment temperature is 880°C or higher is 1.2 min or more; the semi-finished product after heat treatment is transferred to a mold for mold clamping pressing, and the temperature of this semi-finished product when it leaves the heat treatment furnace is ≧900°C; here, when the steel plate thickness of the manufactured part is ≦1.5 mm, the transfer time is controlled at 11-20 s, and when the steel plate thickness of the manufactured part is >1.5 mm, the transfer time is controlled at 13-25 s; (4) Post-press processing: The parts are kept warm and homogenized, and then machined to obtain the finished product.

2. 2. The method for producing a high-strength hot-pressed part with high cold bending performance according to claim 1, wherein the hot-press steel sheet includes at least one of an uncoated steel sheet, an aluminum-silicon-plated steel sheet, an aluminum-silicon-zinc-magnesium-plated steel sheet, an aluminum-silicon-magnesium-plated steel sheet, a hot-dip galvanized steel sheet, and a zinc-iron alloy-plated steel sheet.

3. The method for producing a high-strength hot-pressed part with high cold bending performance according to claim 1, characterized in that the chemical component weight percentage composition of the substrate of the hot-press steel plate is C: 0.2-0.4%, Mn: 1.0-2.0%, Si: 0.1-0.5%, Al: 0.01-0.1%, Ti: 0.01-0.1%, B: 0.0005-0.01%, Cr: 0.1-0.5%, and Nb+Mo+Ni: 0.3-0.6%, with the mass percentage content of any of Nb, Mo, and Ni being 0.3% or less; preferably, the mass percentage content of Nb is 0.0001%-0.25%, the mass percentage content of Mo is 0.1%-0.25%, and the mass percentage content of Ni is 0.05%-0.25%, for example, 0.08%-0.2%.

4. The method for producing a high-strength hot-pressed part with high cold bending performance according to claim 1, characterized in that in step (3), the total time of the heat treatment is controlled to be 1.5-8 min.

5. The method for producing high strength hot pressed parts with high cold bending performance according to claim 1, characterized in that in step (3), the press speed is controlled at 40-80 mm / s and held for 2-30 s.

6. The method for producing a high strength hot pressed part with high cold bending performance according to claim 1 or 5, characterized in that in step (3), during the pressing process, the temperature of the mold is always less than 200°C.

7. The method for producing a high-strength hot-pressed part with high cold bending performance as claimed in claim 1, characterized in that in step (4), the temperature of the heat-insulating homogenization is 150-250°C, and the time is 10-30 minutes.

8. The method for producing a high strength hot pressed part with high cold bending performance according to claim 1, characterized in that in step (4), the machining includes at least one of cutting, trimming, punching, and welding.

9. 2. The method for producing a high strength hot pressed part with high cold bending performance according to claim 1, wherein the part forms a martensite structure with a volume fraction of 95% or more in step (3).

10. The method for producing a high-strength hot-pressed part with high cold bending performance, as described in claim 1, characterized in that the strength-elongation product of the hot-pressed part is ≧10 GPa%, the cold bending angle is ≧60 degrees; preferably, the three-point bending maximum load of the hot-pressed part is ≧13 KN; preferably, the tensile strength of the hot-pressed part is ≧1500 MPa; preferably, the elongation after fracture of the hot-pressed part is ≧5.5%.

11. A hot pressed part manufactured by the method according to any one of claims 1 to 10.

12. The chemical component weight percentage composition of the substrate of the hot pressed part is C: 0.2-0.4%, Mn: 1.0-2.0%, Si: 0.1-0.5%, Al: 0.01-0.1%, Ti: 0.01-0.1%, B: 0.0005-0.01%, Cr: 0.1-0.5%, and Nb+Mo+Ni: 0.3-0.6%, with the mass percent content of any of Nb, Mo, and Ni being 0.3% or less; and the hot pressed part has a strength elongation product ≧10 GPa·%, and a cold bending angle ≧60 degrees.

13. 13. The hot pressed part according to claim 12, characterized in that the mass percentage content of Nb is 0.0001% to 0.25%, the mass percentage content of Mo is 0.1% to 0.25%, and the mass percentage content of Ni is 0.05% to 0.25%, for example 0.08% to 0.2%.

14. 14. The hot-pressed part according to claim 12 or 13, further comprising a plating layer on a surface of the substrate; preferably, the plating layer is selected from an aluminum-silicon plating layer, an aluminum-silicon-zinc-magnesium plating layer, an aluminum-silicon-magnesium plating layer, a hot-dip galvanizing layer, and a zinc-iron alloy plating layer.

15. The hot pressed part according to claim 12, 13 or 14, characterized in that the three-point bending maximum load of the hot pressed part is ≧13 KN, and / or the diffused hydrogen content of the hot pressed part is between 0.01 and 0.06 ppm, and / or the tensile strength of the hot pressed part is ≧1500 MPa, and / or the elongation after break of the hot pressed part is ≧5.5%.

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