Hot forming steel, preparation method thereof and automobile part

Abstract

The invention provides hot forming steel, a preparation method thereof and an automobile part. The preparation method comprises the following steps that a steel ingot is rolled, and rolled hard steel is prepared; a chromium layer is formed on the surface of the rolled hard steel through electroplating, then annealing treatment is conducted, a chromium-iron alloy layer is formed, and hot forming steel is obtained; wherein in the chromium-iron alloy layer, the mass ratio of chromium is greater than or equal to 15%. According to the preparation method, the hot forming steel with high-temperature oxidation corrosion resistance and good weldability can be obtained.

Description

Technical Field

[0001] The present invention relates to the technical field of alloys, and in particular to hot-formed steel and a preparation method thereof, and automobile parts. Background Art

[0002] In order to meet the increasingly stringent emission regulations and collision safety requirements, the body design of the automobile manufacturing industry must use thinner and higher-strength materials to ensure the safety of passengers while reducing the weight of the body. Hot-formed steel has become an ideal solution for lightweighting automobiles with its ultra-high strength and good forming performance. With the popularization of hot stamping technology and the reduction of costs, the proportion of hot-formed parts used in the body has increased significantly. At present, the mainstream hot stamping materials are divided into cold-rolled AL-Si coated plates and cold-rolled bare plates. Among them, the surface of the parts of the AL-Si coated plates has no iron oxide scale, does not require shot blasting, has good corrosion resistance, but poor welding performance. Laser welding requires additional weld de-plating treatment, which increases the production process and cost. In addition, the AL-Si coating will produce crack sources after hot pressing, and the cold bending performance is weak. At the same time, the material price is relatively expensive. The price of ordinary bare plate materials is low, and the cold bending performance of the material after hot pressing is good, but the parts need to be shot blasted. The iron oxide scale on the surface of the parts affects the quality of the parts and the service life of the mold. The parts are deformed after shot blasting, and the dimensional accuracy of large parts is difficult to guarantee.

[0003] Therefore, how to obtain hot-formed steel that is resistant to high-temperature oxidation and corrosion and at the same time has good weldability is a technical problem that still needs to be solved, and traditional technology still needs to be improved. Summary of the invention

[0004] Based on this, the present application provides a hot-formed steel and a preparation method thereof, and automotive parts. The preparation method can obtain hot-formed steel that has both resistance to high-temperature oxidation and corrosion and good weldability.

[0005] The technical solution of this application is as follows.

[0006] In a first aspect of the present application, a method for preparing hot-formed steel is provided, comprising the following steps:

[0007] The steel ingot is subjected to a rolling process to prepare hardened steel;

[0008] Electroplating a chromium layer on the surface of the rolled hardened steel, and then performing annealing to form a chromium-iron alloy layer to obtain hot-formed steel;

[0009] Wherein, in the chromium-iron alloy layer, the mass proportion of chromium is greater than or equal to 15%.

[0010] In the above method, a chromium layer is formed by electroplating on the surface of the hardened steel. During the subsequent annealing process, the hardened steel is recrystallized and softened, and the chromium layer and the hardened steel are diffused and alloyed. The chromium in the chromium layer forms a chromium-iron alloy with the iron element in the hardened steel, thereby forming a chromium-iron alloy layer on the surface of the hot-formed steel. The mass proportion of chromium is greater than or equal to 15%, which is higher than the Cr content in general stainless steel. It has excellent corrosion and oxidation resistance, meets the surface quality requirements of the material without shot blasting after hot stamping, and Cr and Fe are alloy elements that can be infinitely dissolved. Brittle structures similar to Zn-plated plates and Al-Si-plated plates will not be produced in the weld / weld point area. It has good weldability and can be directly laser welded. When producing laser-welded one-piece hot stamping parts, the steps of pre-deplating and wire welding are omitted, which greatly reduces the manufacturing cost and production cycle of parts.

[0011] In some embodiments, the thickness of the chromium layer is 5 micrometers to 10 micrometers; and / or

[0012] The thickness of the rolled hardened steel is 1 mm to 2.5 mm.

[0013] The chromium content of the formed chromium-iron alloy layer can be regulated by regulating the thickness of the chromium layer.

[0014] In some embodiments, the chromium-iron alloy layer has a thickness of 15 micrometers to 30 micrometers.

[0015] In some embodiments, the annealing treatment is performed at a temperature of 620° C. to 720° C. for 10 to 30 hours; and / or

[0016] The annealing treatment adopts hood annealing.

[0017] In some embodiments, the rolling process includes a hot rolling process and a pickling cold rolling process performed sequentially; wherein the hot rolling process includes the following steps:

[0018] The steel ingot is heated to 1150° C. to 1250° C., and then rolled and coiled, wherein the final rolling temperature is 860° C. to 930° C., and the coiling temperature is 550° C. to 650° C.;

[0019] During the pickling and cold rolling process, the relative reduction rate is controlled to be 35% to 70%.

[0020] In some embodiments, the steel ingot is made by continuous casting of refined molten steel;

[0021] Wherein, in terms of mass percentage, the components of the refined molten steel include the following:

[0022] 0.2%~0.25% C, 0<Si≤0.5%, 1.%-1.5% Mn, P≤0.025%, S≤0.01%, 0.01%~0.06% Al, 0.02%-0.050% Ti, 0.0015%~0.004% B, N≤0.008% and the balance Fe.

[0023] In some of the embodiments, the continuous casting process conditions include: the continuous casting tundish temperature is 1500° C. to 1550° C., and the casting speed is ≥1 m / min.

[0024] In some of the embodiments, after the annealing step, there is also a step of flattening the hot-formed steel that has undergone the annealing step; in the flattening step, the flattening elongation is controlled to be 0.8% to 1.5%.

[0025] According to a second aspect of the present application, a hot-formed steel is provided. The hot-formed steel is produced by the method for producing hot-formed steel according to the first aspect.

[0026] The hot-formed steel produced by the above method has excellent high-temperature oxidation resistance and rust resistance, and has good adaptability to hot stamping conditions. Under the hot stamping process conditions, there is no iron oxide scale falling off the surface of the parts, which meets the processing requirements of direct painting and welding. The chromium-iron alloy layer on the surface makes it have good weldability and can be directly laser welded. It is especially suitable for the manufacture of large hot stamping parts such as laser welded integrated stamped door rings.

[0027] According to a third aspect of the present application, an automobile component is provided. The automobile component comprises the hot-formed steel according to the second aspect.

[0028] The above-mentioned hot-formed steel has excellent high-temperature oxidation resistance and rust resistance, which can prevent the scratches caused by the friction between the sheet and the part during the hot stamping process from exceeding the corrosion-resistant layer, so that the parts have stable surface quality and corrosion resistance. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is a physical picture of the parts obtained in Example 1;

[0030] Figure 2 This is a physical picture of the parts prepared in Example 2. DETAILED DESCRIPTION

[0031] For ease of understanding of the present application, the present application will be described more fully below, and preferred embodiments of the present application are provided. However, the present application can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the understanding of the disclosure of the present application more thorough and comprehensive.

[0032] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those generally understood by those skilled in the art to which the present application belongs. The terms used herein in the specification of the present application are only for the purpose of describing specific embodiments and are not intended to limit the present application. The term "and / or" used herein includes any and all combinations of one or more of the related listed items.

[0033] In the description of the embodiments of the present application, the technical terms "first", "second", etc. are only used to distinguish different objects, and cannot be understood as indicating or implying relative importance or implicitly indicating the number, specific order or primary and secondary relationship of the indicated technical features. In the description of the embodiments of the present application, the meaning of "multiple" is two or more, unless otherwise clearly and specifically defined.

[0034] The "range" disclosed in the present application can be defined in the form of a lower limit and an upper limit, and a given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundaries of a particular range. The range defined in this way can be inclusive or exclusive of the end values, and any end value can be included or excluded independently, and can be arbitrarily combined, that is, any lower limit can be combined with any upper limit to form a range. For example, if a range of 60 to 120 and 80 to 110 is listed for a specific parameter, it is understood that the range of 60 to 110 and 80 to 120 is also expected. In addition, if the minimum range values ​​1 and 2 are listed, and if the maximum range values ​​3, 4 and 5 are also listed, the following ranges can all be expected: 1 to 3, 1 to 4, 1 to 5, 2 to 3, 2 to 4 and 2 to 5. In the present application, unless otherwise specified, the numerical range "a to b" represents an abbreviation of any real number combination between a and b, where a and b are both real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" are listed in this document, and "0-5" is just an abbreviation of these numerical combinations. In addition, when a parameter is expressed as an integer ≥ 2, it is equivalent to listing the parameter as, for example, integers 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc. For example, when a parameter is expressed as an integer selected from "2-10", it is equivalent to listing the integers 2, 3, 4, 5, 6, 7, 8, 9 and 10.

[0035] In this application, "optionally", "optional", and "optional" mean optional, that is, any one of the two parallel schemes of "yes" or "no". If there are multiple "options" in a technical solution, unless otherwise specified and there is no contradiction or mutual restriction, each "option" is independent.

[0036] Reference to "embodiments" herein means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment of the present application. The appearance of the phrase in various locations in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0037] An embodiment of the present application provides a method for preparing hot-formed steel, comprising the following steps S1 to S2.

[0038] S1: The steel ingot is rolled to prepare hardened steel.

[0039] S2: A chromium layer is formed by electroplating on the surface of the rolled hardened steel, and then annealing is performed to form a chromium-iron alloy layer to obtain hot-formed steel.

[0040] Wherein, in the chromium-iron alloy layer, the mass proportion of chromium is greater than or equal to 15%.

[0041] In the above method, a chromium layer is formed by electroplating on the surface of the hardened steel. During the subsequent annealing process, the hardened steel is recrystallized and softened, and the chromium layer and the hardened steel are diffused and alloyed. The chromium in the chromium layer forms a chromium-iron alloy with the iron element in the hardened steel, thereby forming a chromium-iron alloy layer on the surface of the hot-formed steel. The mass proportion of chromium is greater than or equal to 15%, which is higher than the Cr content in general stainless steel. It has excellent corrosion and oxidation resistance and meets the surface quality requirements of the material without shot blasting after hot stamping. Cr and Fe are alloy elements that can be infinitely dissolved in solid solution, and will not produce brittle structures similar to Zn-plated plates and Al-Si-plated plates in the weld / weld point area. It has good weldability and can be directly laser welded. When producing laser-welded one-piece hot stamping parts, the requirements for pre-deplating and wire welding are omitted, which greatly reduces the manufacturing cost and production cycle of parts.

[0042] It should be noted that the main elements in the chromium-iron alloy layer are chromium and iron, but they are not completely limited to these two elements. Other elements in the hardened steel may be mixed in, depending on the composition of the hardened steel. However, the other elements mixed in do not affect the chromium-iron alloy layer to exert its excellent corrosion resistance and oxidation resistance, as well as good weldability.

[0043] In some embodiments, the chromium layer has a thickness of 5 micrometers to 10 micrometers.

[0044] The chromium content of the formed chromium-iron alloy layer can be regulated by regulating the thickness of the chromium layer.

[0045] Optionally, the thickness of the chromium layer may be 5 microns, 7 microns, or 10 microns.

[0046] In some of the embodiments, the chromium-iron alloy layer has a thickness of 15 micrometers to 30 micrometers.

[0047] Optionally, the thickness of the chromium-iron alloy layer is 15 micrometers, 20 micrometers, 25 micrometers, or 30 micrometers.

[0048] In some of the embodiments, in the chromium-iron alloy layer, the mass proportion of chromium may be 15% to 50%, and may further be 15%, 20%, 25%, 30%, 40%, or 50%.

[0049] In some embodiments, the annealing temperature is 620° C. to 720° C., and the annealing time is 10 to 30 hours.

[0050] In some embodiments, the annealing process is performed by hood annealing.

[0051] In some embodiments, the rolling process includes a hot rolling process and a pickling cold rolling process performed sequentially; wherein the hot rolling process includes the following steps:

[0052] The steel ingot is heated to 1150°C to 1250°C and then rolled and coiled. The final rolling temperature is 860°C to 930°C, and the coiling temperature is 550°C to 650°C.

[0053] In some of the embodiments, during the pickling and cold rolling process, the relative reduction rate is controlled to be 35% to 70%.

[0054] In some of the embodiments, the refined molten steel is obtained by continuous casting.

[0055] Among them, the components of refined molten steel include, by mass percentage: 0.2%~0.25% C, 0<Si≤0.5%, 1.%-1.5% Mn, P≤0.025%, 0≤S≤0.01%, 0.01%~0.06% Al, 0.02%-0.050% Ti, 0.0015%~0.004% B, N≤0.008% and the balance Fe.

[0056] It can be understood that the composition of refined molten steel can also be regarded as the composition of steel ingot.

[0057] In some of the embodiments, the continuous casting process conditions include: the continuous casting tundish temperature is 1500° C. to 1550° C., and the casting speed is ≥1 m / min.

[0058] In some of the embodiments, after the annealing step, there is also a step of flattening the annealed hot-formed steel, and in the flattening step, the flattening elongation is controlled to be 0.8% to 1.5%.

[0059] In some of the embodiments, after the flattening step, conventional operations in the art such as re-coiling / cross-cutting → cold rolling of finished coils / plates are also included.

[0060] Another embodiment of the present application provides a hot-formed steel, which is produced by the above-mentioned method for producing hot-formed steel.

[0061] The hot-formed steel produced by the above method has excellent high-temperature oxidation resistance and rust resistance, and has good adaptability to hot stamping conditions. Under the hot stamping process conditions, there is no iron oxide scale falling off the surface of the parts, which meets the processing requirements of direct painting and welding. The chromium-iron alloy layer on the surface makes it have good weldability and can be directly laser welded. It is especially suitable for the manufacture of large hot stamping parts such as laser welded integrated stamped door rings.

[0062] Another embodiment of the present application provides an automobile component, which includes the above-mentioned hot-formed steel.

[0063] The above-mentioned hot-formed steel has excellent high-temperature oxidation resistance and rust resistance, which can prevent the scratches caused by the friction between the sheet and the part during the hot stamping process from exceeding the corrosion-resistant layer, so that the parts have stable surface quality and corrosion resistance.

[0064] In some of the embodiments, automobile parts include, but are not limited to: high-strength structural parts and collision safety parts such as automobile A and B pillars, center channels, front and rear anti-collision beams, etc., and are particularly suitable for large parts such as laser-welded one-piece hot-stamped door rings and double door rings, which can greatly reduce the welding costs.

[0065] The present application will be described below in conjunction with specific embodiments, but the present application is not limited to the following embodiments. It should be understood that the attached claims summarize the scope of the present application. Under the guidance of the concept of the present application, technical personnel in the field should realize that certain changes made to the various embodiments of the present application will be covered by the spirit and scope of the claims of the present application.

[0066] The following are specific embodiments.

[0067] Example 1

[0068] (1) Continuously casting, hot rolling, pickling and cold rolling refined molten steel to obtain hardened steel; wherein, in terms of mass percentage, the refined molten steel comprises: 0.25% C, 0.5% Si, 1.% Mn, 0.0025% P, 0.001% S, 0.06% Al, 0.02% Ti, 0.0015% B, 0.008% N and the balance Fe; the temperature of the continuous casting tundish is 1500°C to 1550°C, the pulling speed is 1 m / min, and the hot rolling process comprises the following steps: heating the steel ingot to 1150°C and then rolling and coiling, the final rolling temperature of the rolling is 860°C, and the coiling temperature is 650°C; in the pickling and cold rolling process, the relative reduction ratio is controlled to be 50%.

[0069] (2) The hardened steel obtained above is degreased and cleaned, and then electroplated with C to obtain a 7-μm-thick chromium layer, and then annealed in a bell-type furnace at 700°C for 20 h to form a chromium-iron alloy layer with a Cr content of 25% and a thickness of 20 μm, and then flattened to obtain hot-formed steel.

[0070] (3) The hot-formed steel is directly sent to the hot stamping factory for the following steps: blanking → heating → hot stamping → laser cutting to obtain the hot-formed parts: the B-pillar of the car, as shown in the actual picture Figure 1 shown.

[0071] from Figure 1 It can be seen that after hot stamping and laser cutting, the surface of the parts is smooth and no oxide falls off, indicating that the hot-formed steel prepared above has good resistance to high-temperature corrosion and oxidation.

[0072] Example 2

[0073] Example 2 is basically the same as Example 2, except that: in step (3), the hot-formed steel is directly sent to the hot stamping factory and then subjected to the following steps: blanking → laser welding → heating → hot stamping → laser cutting to obtain an integrally formed hot-formed part: a car door knocker, as shown in the actual picture. Figure 2 shown.

[0074] from Figure 2 It can be seen that after hot stamping and laser welding, the surface of the parts is free of oxides and remains smooth, and there is no defective structure in the weld / weld point area, indicating that the hot-formed steel prepared above has good resistance to high-temperature corrosion and oxidation, as well as good weldability, which can save the steps of pre-plating and wire filling welding, greatly reducing the manufacturing cost and production cycle of parts.

[0075] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0076] The above embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the patent application. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of this patent shall be subject to the attached claims.

Claims

1. A method for preparing hot-formed steel, characterized in that: The steps include: The steel ingot is subjected to a rolling process to prepare hardened steel; Electroplating a chromium layer on the surface of the rolled hardened steel, and then performing annealing to form a chromium-iron alloy layer to obtain hot-formed steel; Wherein, in the chromium-iron alloy layer, the mass proportion of chromium is greater than or equal to 15%.

2. The method for preparing hot-formed steel according to claim 1, characterized in that: The thickness of the chromium layer is 5 micrometers to 10 micrometers; and / or The thickness of the rolled hardened steel is 1 mm to 2.5 mm.

3. The method for preparing hot-formed steel according to claim 1, characterized in that: The thickness of the chromium-iron alloy layer is 15 micrometers to 30 micrometers.

4. The method for preparing hot-formed steel according to any one of claims 1 to 3, characterized in that: The annealing treatment is performed at a temperature of 620° C. to 720° C. for 10 to 30 hours; and / or The annealing treatment adopts hood annealing.

5. The method for preparing hot-formed steel according to any one of claims 1 to 3, characterized in that: The rolling process includes a hot rolling process and a pickling cold rolling process performed sequentially; wherein the hot rolling process includes the following steps: The steel ingot is heated to 1150° C. to 1250° C., and then rolled and coiled, wherein the final rolling temperature is 860° C. to 930° C., and the coiling temperature is 550° C. to 650° C.; During the pickling and cold rolling process, the relative reduction rate is controlled to be 35% to 70%.

6. The method for preparing hot-formed steel according to any one of claims 1 to 3, characterized in that: The steel ingot is made by continuous casting of refined molten steel; Wherein, the components of the refined molten steel include the following in terms of mass percentage: C: 0.2%~0.25%, Si≤0.5%, Mn: 1.0%-1.5%, P≤0.025%, S≤0.01%, Al: 0.01%~0.06%, Ti: 0.02%-0.050%, B: 0.0015%~0.004%, N≤0.008% and the balance Fe.

7. The method for preparing hot-formed steel according to claim 6, characterized in that: The conditions of the continuous casting process include: the temperature of the continuous casting tundish is 1500° C. to 1550° C., and the casting speed is ≥1 m / min.

8. The method for preparing hot-formed steel according to any one of claims 1 to 3, characterized in that: After the annealing step, the method further includes a step of flattening the hot-formed steel after the annealing step; in the flattening step, the flattening elongation is controlled to be 0.8% to 1.5%.

9. A hot-formed steel, characterized in that: The hot-formed steel is produced by the method for producing hot-formed steel according to any one of claims 1 to 8.

10. An automobile component, characterized in that: The automobile component comprises the hot-formed steel according to claim 9.

Images