Hot stamping part and method for manufacturing the same

Abstract

The present invention provides a hot stamping part comprising a base material, a plating layer disposed on at least one surface of the base material, and a surface layer disposed on the plating layer and including an oxide portion and a surface treatment portion, wherein the area fraction of the oxide portion on the surface of the hot stamping part is greater than 0% and less than or equal to 35%.

Description

Technology Field

[0001] The present invention relates to a hot stamping part and a method for manufacturing a hot stamping part. Background Technology

[0002] High-strength steel is used in automotive parts to ensure lightweighting and stability. However, while high-strength steel can secure high strength-to-weight ratio characteristics, press formability deteriorates as strength increases. This leads to material fracture or springback during processing, making it difficult to form products with complex and precise shapes.

[0003] Hot stamping is a method to address these issues, and as interest in it grows, research on materials for hot stamping is also actively being conducted. For example, as disclosed in Korean Patent Publication No. 10-2017-0076009, hot stamping is a forming technology that manufactures high-strength parts by heating a steel plate for hot stamping to a high temperature and then forming and rapidly cooling it simultaneously within a press mold.

[0004] Related technologies include Korean Patent Publication No. 10-2018-0095757 (Title of Invention: Method for Manufacturing Hot Stamping Parts).

[0005] Meanwhile, steel sheets for hot stamping have a problem in that the surface of the steel sheet can oxidize and form scale when heated, which degrades the surface characteristics and paintability of the product and also results in corrosion resistance being inferior to that of plated materials. Therefore, scale is removed through post-treatment such as sandblasting or shotblasting after product forming. In addition, to prevent the above problems, a method has been used to increase the corrosion resistance of the steel sheet by using an Al-based plating layer to suppress the oxidation reaction on the surface of the steel sheet and induce the formation of an Al passivation film. However, in the case of such Al-plated materials, although heat resistance is excellent, there is a problem in that corrosion resistance is inferior compared to Zn-plated materials and manufacturing costs increase.

[0006] However, in the case of Zn-plated materials, zinc oxides are formed due to the oxidation of Zn during hot stamping heat treatment, which degrades the appearance and spot weldability. To solve this, surface quality and weldability can be improved by removing zinc oxides through post-treatment methods such as sand-blasting or shot-blasting after the hot stamping process, but this may reduce productivity by incurring additional costs and processes. Prior art literature

[0007] No. 10-2017-0076009 No. 10-2018-0095757 The problem to be solved

[0008] Embodiments of the present invention aim to provide a hot stamping part with improved spot weldability and a method for manufacturing the same. means of solving the problem

[0009] One embodiment of the present invention provides a hot stamping part comprising a base material, a plating layer disposed on at least one surface of the base material, and a surface layer disposed on the plating layer and including an oxide portion and a surface treatment portion, wherein the area fraction of the oxide on the surface of the hot stamping part is greater than 0% and less than or equal to 35%.

[0010] In this embodiment, the oxide portion may include zinc-based oxide and manganese-based oxide.

[0011] In this embodiment, the plating layer may include gamma phase and α-Fe(Zn).

[0012] In this embodiment, the area fraction of the gamma phase within the plating layer may be 25% to 60%.

[0013] In this embodiment, the surface treatment portion may include 15 wt% or more and 50 wt% silicon (Si), aluminum (Al) or calcium (Ca), 5 wt% or more and 50 wt% zinc (Zn), more than 0 wt% and 15 wt% iron (Fe), more than 0 wt% and 15 wt% manganese (Mn), and 10 wt% or more and 75 wt% oxygen (O).

[0014] One embodiment of the present invention provides a method for manufacturing a hot stamping part, comprising: a step of manufacturing a hot stamping steel plate in which a first plating layer and a surface treatment layer are sequentially formed on a first base material; a heating step of heating the hot stamping steel plate at a heating temperature of Ac3 to 910°C; a transfer step of transferring the heated hot stamping steel plate to a press mold; and a forming and cooling step of pressing the transferred hot stamping steel plate to the press mold to form a formed body and cooling the formed body, wherein the heating time in the heating step satisfies Equation 1 (50*t + 70 ≤ HT ≤ 150*t + 210).

[0015] In the present embodiment, the hot stamping part comprises a second base material, a second plating layer disposed on at least one surface of the second base material, and a surface layer disposed on the second plating layer and including an oxide portion and a surface treatment portion, and the area fraction of the oxide portion on the surface of the hot stamping part may be greater than 0% and less than or equal to 35%.

[0016] In this embodiment, the oxide portion may include zinc-based oxide and manganese-based oxide.

[0017] In this embodiment, the second plating layer may include gamma phase and α-Fe(Zn).

[0018] In this embodiment, the area fraction of the gamma phase in the second plating layer may be 25% to 60%.

[0019] In the present embodiment, the step of manufacturing a steel plate for hot stamping may include the step of immersing the steel plate in a molten zinc plating bath to form a molten zinc plating layer on the steel plate, the step of alloying the steel plate on which the molten zinc plating layer is formed to form an alloyed molten zinc plating layer on the steel plate, and the step of forming a surface treatment layer on the alloyed molten zinc plating layer.

[0020] In this embodiment, the surface treatment layer can be formed by applying an inorganic surface treatment agent and then drying it.

[0021] Other aspects, features, and advantages other than those described above will become clear from the specific details, claims, and drawings for implementing the invention below. Effects of the invention

[0022] According to one embodiment of the present invention as described above, a hot stamping part with improved spot weldability and a method for manufacturing the hot stamping part can be provided. Of course, the scope of the present invention is not limited by these effects. Brief explanation of the drawing

[0023] FIG. 1 is a cross-sectional view schematically illustrating a hot stamping part according to one embodiment of the present invention. FIG. 2 is a cross-sectional view schematically illustrating a steel plate for hot stamping according to one embodiment of the present invention. FIG. 3 is a schematic diagram illustrating a method for manufacturing a hot stamping part according to one embodiment of the present invention. FIG. 4 is a schematic diagram illustrating a method for manufacturing a steel plate for hot stamping according to one embodiment of the present invention. Figure 5 is a drawing showing zinc-based oxide and manganese-based oxide formed on the surface of a hot stamping part in an amount of more than 35%. Figure 6 is a drawing showing zinc-based oxide and manganese-based oxide formed on the surface of a hot stamping part at 35% or less. Specific details for implementing the invention

[0024] The present invention will be described in detail below. However, in describing the present invention, if it is determined that a detailed description of related known technologies or configurations may unnecessarily obscure the essence of the present invention, such detailed description will be omitted.

[0025] In the following embodiments, terms such as first, second, etc. are used not in a limiting sense, but for the purpose of distinguishing one component from another component.

[0026] In the following examples, singular expressions include plural expressions unless the context clearly indicates otherwise.

[0027] In the following embodiments, when various components such as layers, films, regions, and plates are described as being "on" another component, this includes not only cases where they are "directly on" another component, but also cases where another component is interposed between them.

[0028] In the drawings, the size of components may be exaggerated or reduced for convenience of explanation. For example, the size and thickness of each component shown in the drawings are depicted arbitrarily for convenience of explanation, and therefore the present invention is not necessarily limited to what is illustrated.

[0029] In the following embodiments, terms such as "include" or "have" mean that the features or components described in the specification are present, and do not preclude the possibility that one or more other features or components may be added.

[0030] In this specification, "A and / or B" indicates the case where it is A, B, or both A and B. Additionally, in this specification, "at least one of A and B" indicates the case where it is A, B, or both A and B.

[0031] Unless otherwise defined, all terms used herein, including technical and scientific terms, have the same meaning as generally understood by those skilled in the art to which this invention pertains. Terms defined in commonly used dictionaries are further interpreted to have meanings consistent with relevant technical literature and the present disclosure, and are not interpreted in an ideal or highly formal sense unless otherwise defined.

[0032] Hereinafter, embodiments of the present invention are described in detail so that those skilled in the art can easily implement the invention. However, the present invention may be embodied in various different forms and is not limited to the embodiments described herein.

[0033] FIG. 1 is a cross-sectional view schematically illustrating a hot stamping part according to one embodiment of the present invention.

[0034] Referring to FIG. 1, a hot stamping part (10) according to one embodiment may include a base material (100), a plating layer (200), and a surface layer (300).

[0035] In one embodiment, a plating layer (200) may be disposed on a base material (100). The plating layer (200) may be formed by mutual diffusion of the components of the base material (100', see FIG. 3) of the hot stamping steel plate (10', see FIG. 3) and the plating layer (200', see FIG. 3). For example, the plating layer (200) may be an alloyed plating layer in which the iron (Fe) of the base material (100') of the hot stamping steel plate (10') and the zinc (Zn) of the plating layer (200') of the hot stamping steel plate (10') are alloyed.

[0036] The plating layer (200) may include at least one of Zn, Fe, Al, Mn, and Si. The plating layer (200) may include iron (Fe): 10% to 70%, aluminum (Al): greater than 0 and less than or equal to 5%, manganese (Mn): greater than 0 and less than or equal to 5%, silicon (Si): greater than 0 and less than or equal to 5%, and the remainder being zinc (Zn) and other unavoidable impurities. However, the present invention is not limited thereto.

[0037] The plating layer (200) can be formed with a thickness of 5㎛ to 50㎛. If the thickness of the plating layer (200) is less than 5㎛, corrosion resistance may be reduced, and if the thickness exceeds 50㎛, productivity may be reduced.

[0038] The plating layer (200) is composed of alpha iron (e.g., α-Fe(Zn)) (210) and gamma phase (e.g., Γ-Fe3Zn 10It can be made of )(220). In one embodiment, the area fraction of the gamma phase (220) in the plating layer (200) in the cross-sectional view may be 25% to 60%. If the area fraction of the gamma phase (220) in the plating layer (200) is less than 25%, sufficient bonding strength within the weldment cannot be secured, and the spot weldability of the hot stamping part may be inferior. Specifically, as described below, the present invention forms a surface treatment layer (300', see FIG. 2) by applying an inorganic surface treatment agent on the plating layer (200', see FIG. 2) of a steel plate (10', see FIG. 2) for hot stamping, and then performs a hot stamping process, thereby securing bonding strength in the weldment and thereby securing spot weldability. However, if the area fraction of the gamma phase (220) in the plating layer (200) is less than 25%, the bonding strength of the weldment may be insufficient, and spot weldability may be reduced. If the area fraction of the gamma phase (220) in the plating layer (200) exceeds 60%, the LME phenomenon caused by zinc (Zn) penetrating along the austenite grain boundaries may occur during the hot stamping process. Therefore, if the area fraction of the gamma phase (220) in the plating layer (200) satisfies between 25% and 60%, the deterioration of spot weldability and the occurrence of the LME phenomenon can be prevented.

[0039] A surface layer (300) may be disposed on the plating layer (200). The surface layer (300) may include an oxide portion and a surface treatment portion.

[0040] The oxide portion may include zinc-based oxide and / or manganese-based oxide. The zinc-based oxide may be formed by the oxidation of zinc in the plating layer (200') of the steel plate (10') for hot stamping during the hot stamping heating process. The manganese-based oxide may be formed by the oxidation of manganese in the base material (100') and / or the plating layer (200') of the steel plate (10') for hot stamping during the hot stamping heating process.

[0041] In one embodiment, the area fraction of zinc-based oxide and manganese-based oxide on the surface of the hot stamping part (10) may be greater than 0% and less than or equal to 35%. It is preferable to have less zinc-based oxide and manganese-based oxide on the surface of the hot stamping part (10), but it may be difficult to make the zinc-based oxide and manganese-based oxide on the surface of the hot stamping part (10) 0%. Specifically, if the heating time in the heating step (S200, see FIG. 3) is increased, the area fraction of the surface oxide may increase, and the area fraction of the gamma phase (220) in the plating layer (200) may decrease. Since the LME phenomenon may occur if the area fraction of the gamma phase (220) in the plating layer (200) exceeds 60%, it is necessary to increase the heating time to reduce the area fraction of the gamma phase (220) in the plating layer (200) to 60% or less. However, in this case, if the heating time is increased, the area fraction of the surface oxide increases, so that the zinc-based oxide and manganese-based oxide on the surface of the hot stamping part (10) may exceed 0%.

[0042] If the area fraction of zinc-based oxide and manganese-based oxide on the surface of the hot stamping part (10) exceeds 35%, the area fraction of oxide on the surface of the hot stamping part (10) is too high, which may reduce weldability and lower the bonding strength.

[0043] The average thickness of the oxide layer may be less than 3㎛. The oxide layer is formed during the hot stamping heating process, and if the average thickness of the oxide layer is 3㎛ or more, the dynamic resistance may increase and cause spatter to occur, which may result in poor spot weldability.

[0044] The surface treatment section may include an inorganic surface treatment agent. For example, the inorganic surface treatment agent may be a Si-based inorganic surface treatment agent, an Al-based inorganic surface treatment agent, or a Ca-based inorganic surface treatment agent. The surface treatment section may further include oxides such as SiO, AlO, or CaO, in which Si, Al, or Ca are oxidized relative to the surface treatment layer (300', see FIG. 2) of the steel plate (10') for hot stamping, and components diffused from the plating layer (200') and the base material (100'). For example, the components of the base material (100'), the plating layer (200'), and the surface treatment layer (300') of the steel plate (10') for hot stamping may be mixed in the surface treatment section.

[0045] The surface treatment portion may include at least one of SiO, AlO, or CaO; Zn, Fe, and Mn. Specifically, the surface treatment portion may include 15 wt% or more and 50 wt% of silicon (Si), aluminum (Al) or calcium (Ca), 5 wt% or more and 50 wt% of zinc (Zn), more than 0 wt% and 15 wt% of iron (Fe), more than 0 wt% and 15 wt% of manganese (Mn), and 10 wt% or more and 75 wt% of oxygen (O).

[0046] The average zinc content of the surface treatment portion may be smaller than the average zinc content of the plating layer (200). Additionally, the average zinc content of the surface treatment portion may be smaller than the average silicon content.

[0047] The surface treatment section is formed on the plating layer (200) and can suppress and minimize the formation of oxides by combining zinc (Zn) or manganese (Mn) with oxygen. The surface treatment section can suppress the formation of oxides that hinder binding with the coating layer and can ultimately improve the coating adhesion of the hot stamping part (10) by inducing the formation of silicon oxides that improve binding with the coating layer.

[0048] FIG. 2 is a cross-sectional view schematically illustrating a steel plate for hot stamping according to one embodiment of the present invention.

[0049] Referring to FIG. 2, a hot stamping steel plate (10') according to one embodiment may include a base material (100'), a plating layer (200') disposed on at least one side of the base material (100'), and a surface treatment layer (300') disposed on the plating layer (200').

[0050] In one embodiment, a plating layer (200') may be disposed on at least one surface of a base material (100'). The plating layer (200') may be a zinc (Zn)-based plating layer. For example, the plating layer (200') may be an alloyed molten zinc plating layer formed by thermal diffusion of the base material (100') and zinc (Zn), or a molten zinc plating layer.

[0051] The plating layer (200') may include zinc (Zn) and iron (Fe). However, the present invention is not limited thereto. The plating layer (200') has a thickness of 130 g / m² on both sides. 2 Up to 180 g / m² 2 It can be plated with a coating amount of 130 g / m². 2 In the case of less, the area fraction of the gamma phase (220, see FIG. 1) of the plating layer (200, see FIG. 1) may be less than 25%. The plating deposition amount is 180 g / m² 2 If exceeded, the LME phenomenon may occur during the hot stamping process.

[0052] A surface treatment layer (300') may be disposed on the plating layer (200'). The surface treatment layer (300') may include an inorganic surface treatment agent. For example, the inorganic surface treatment agent may be a Si-based inorganic surface treatment agent, an Al-based inorganic surface treatment agent, or a Ca-based inorganic surface treatment agent. The application amount of the inorganic surface treatment agent is 500 mg / m² 2 5,000 mg / m² or higher 2 It may be less than.

[0053] The thickness of the surface treatment layer (300') may be 0.05 μm to 2 μm. If the thickness of the surface treatment layer (300') is less than 0.05 μm, the thickness of the surface treatment layer (300') is too thin, and a thick zinc-based oxide may be formed on the surface of the hot stamping part (10, see FIG. 1). On the other hand, if the thickness of the surface treatment layer (300') is greater than 2 μm, the additional effect may be negligible, and it may not dry uniformly over the entire area, which may result in reduced physical properties and operability.

[0054] FIG. 3 is a schematic diagram illustrating a method for manufacturing a hot stamping part according to one embodiment of the present invention, and FIG. 4 is a schematic diagram illustrating a method for manufacturing a steel plate for hot stamping according to one embodiment of the present invention.

[0055] Referring to FIGS. 3 and 4, a method for manufacturing a hot stamping part according to one embodiment may include a step of manufacturing a steel plate for hot stamping (S100), a heating step (S200), a transfer step (S300), and a forming / cooling step (S400). Through the method for manufacturing a hot stamping part, a hot stamping part (10, see FIG. 1) described through FIG. 1 can be manufactured.

[0056] A hot stamping steel plate (10', see FIG. 2) can be manufactured through a hot stamping steel plate manufacturing step (S100). The hot stamping steel plate manufacturing step (S100) may include a plating step (S110), an alloying step (S120), and a surface treatment step (S130). Additionally, if the plating layer (200', see FIG. 2) is a molten zinc plating layer, the alloying step (S120) may be omitted.

[0057] In the plating step (S110), a plating layer (200') can be formed on a base material (100', see FIG. 2). At this time, the base material (100') may be a hot-rolled steel sheet or a cold-rolled steel sheet. For example, the base material (100') may be a hot-rolled steel sheet or a cold-rolled steel sheet manufactured by preparing a slab having a known composition for hot stamping, performing at least one of hot rolling and cold rolling on the slab by a known method, and then performing annealing heat treatment.

[0058] In the plating step (S110), the base material (100') can be immersed in a plating bath to form a plating layer (200') on at least one surface of the base material (100'). At this time, the plating bath may have zinc (Zn) as the main component and may additionally include aluminum (Al), iron (Fe), etc. The temperature of the plating bath may be 400°C to 700°C.

[0059] In one embodiment, the plating layer (200') is 130 g / m² on both sides of the base material (100'). 2 Up to 180 g / m² 2 It can be plated with an amount of coating. The reason for limiting the amount of plating is as explained above.

[0060] An alloying step (S120) may be performed after the plating step (S110). In the alloying step (S120), the plating layer (200') may be heated at a predetermined temperature to induce a phase change in the plating layer. The alloying temperature in the alloying step (S120) may be 500°C to 600°C.

[0061] A surface treatment step (S130) may be performed after the alloying step (S120). In the surface treatment step (S130), a surface treatment layer (300', see FIG. 2) may be formed on the plating layer (200').

[0062] In one embodiment, in the surface treatment step (S120), an inorganic surface treatment agent may be applied to the plating layer (200') and then dried to form a surface treatment layer (300') on the plating layer (200'). The inorganic surface treatment agent may comprise 15 wt% or more and 50 wt% of silicon (Si), aluminum (Al) or calcium (Ca), 5 wt% or more and 50 wt% of zinc (Zn), more than 0 wt% and 15 wt% of iron (Fe), more than 0 wt% and 15 wt% of manganese (Mn), and 10 wt% or more and 75 wt% of oxygen (O). At this time, drying may be performed at a temperature of 70 ℃ to 150 ℃ for 1 second to 10 seconds.

[0063] The application amount in the surface treatment step (S130) is 500 mg / m² 2 5,000 mg / m² or higher 2 It may be less than or equal to 0.05㎛. In addition, the thickness of the surface treatment layer (300') after drying may be 0.05㎛ to 2㎛.

[0064] The surface treatment layer (300') may contain, in weight percent, 15 weight percent or more and 50 weight percent or less silicon (Si), aluminum (Al) or calcium (Ca), 5 weight percent or more and 50 weight percent or less zinc (Zn), more than 0 weight percent and 15 weight percent or less iron (Fe), more than 0 weight percent and 15 weight percent or less manganese (Mn), and 10 weight percent or more and 75 weight percent or less oxygen (O).

[0065] Referring again to FIG. 3, a heating step (S200) may be performed after the hot stamping steel plate manufacturing step (S100). In the heating step (S200), the hot stamping steel plate (10') may be introduced into a heating furnace and heated. In the heating step (S200), the hot stamping steel plate (10') may be heated in the heating furnace to a target temperature, and the target temperature may be Ac3 to 910℃. For example, the target temperature may be 820℃ to 910℃.

[0066] In one embodiment, the heating time in the heating step (S200) may be 50*t + 70s to 150*t + 210s. Here, t may be the thickness (mm) of the steel plate for hot stamping (or, hot stamping part). For example, if the thickness of the steel plate for hot stamping (or, hot stamping part) is 1mm, the heating time may be 120s to 360s, and if the thickness of the steel plate for hot stamping (or, hot stamping part) is 2mm, the heating time may be 170s to 510s.

[0067] As the heating time in the heating step (S200) increases, the area fraction of alpha iron (e.g., α-Fe(Zn)) (210, see FIG. 1) in the plating layer (200, see FIG. 1) may increase, and the area fraction of gamma phase (220, see FIG. 1) may decrease. If the heating time is less than 50*t + 70s, the area fraction of gamma phase (220) in the plating layer (200) may exceed 60%, and the LME phenomenon may occur. On the other hand, if the heating time exceeds 150*t + 210s, the area fraction of gamma phase (220) in the plating layer (200) may be formed at less than 25%, resulting in insufficient bonding strength of the weld and reduced spot weldability. Additionally, as the heating time in the heating step (S200) increases, the area fraction of oxide formed on the surface of the hot stamping part (10, see FIG. 1) (e.g., plating layer (200)) may increase. For example, as the heating time in the heating step (S200) increases, the area fraction of oxide on the surface of the surface layer (300, see FIG. 1) may increase. If the heating time exceeds 150*t + 210s, the area fraction of oxide formed on the surface may exceed 35%, which may reduce weldability and lower bonding strength.

[0068] In one embodiment, in the heating step (S200), the steel plate (10') for hot stamping can be heated through single heating. For example, in the heating step (S200), the steel plate (10') for hot stamping can be heated in a drawer-type heating furnace consisting of multiple layers.

[0069] In one embodiment, in the heating step (S200), multi-stage heating and / or crack heating may be performed. For example, the heating step (S200) may include a multi-stage heating step and a crack heating step. The multi-stage heating step may be a step of heating a steel plate in stages, and the crack heating step may be a step of heating a steel plate that has been multi-stage heated to a crack temperature (e.g., a target temperature). In the multi-stage heating step, the steel plate may be heated in stages as it passes through a plurality of sections provided within the furnace. Among the plurality of sections provided within the furnace, there may be multiple sections where the multi-stage heating step is performed, and the temperature may be set for each section so that the steel plate is heated in stages from the inlet of the furnace into which the steel plate is fed to the outlet of the furnace from which the steel plate is ejected. A crack heating step may be performed after the multi-stage heating step. In the crack heating step, the multi-stage heated steel plate may be heat-treated as it passes through a section of the furnace set to a temperature of Ac3 to 910 ℃ (e.g., 820 ℃ to 910 ℃). In addition, among the plurality of sections provided within the furnace, there may be at least one section where the crack heating step is performed.

[0070] During the heating step (S200), the components of the base material (100'), the components of the plating layer (200'), and the components of the surface treatment layer (300') can be mutually diffused.

[0071] A transfer step (S300) may be performed after the heating step (S200). The transfer step (S300) may be a step of transferring the heated hot stamping steel plate (10') from the heating furnace to the press mold. At this time, during the transfer step (S300), the heated hot stamping steel plate (10') may be cooled at ambient temperature (or room temperature). That is, the heated hot stamping steel plate (10') may be air-cooled during transfer. If the heated hot stamping steel plate (10') is not air-cooled, the mold entry temperature (e.g., forming start temperature) may rise, causing wrinkles (or bends) to occur on the surface of the manufactured hot stamping part (10). Additionally, since the use of a refrigerant may affect the subsequent process (hot stamping), it may be desirable for the heated hot stamping steel plate (10') to be air-cooled during transfer.

[0072] A forming / cooling step (S400) may be performed after the transfer step (S300). In the forming / cooling step (S400), the transferred hot stamping steel plate (10') may be hot stamped to form a formed body, and at the same time, the hot stamping steel plate (or formed body) may be cooled.

[0073] In the forming / cooling step (S400), a steel plate (10') for hot stamping can be pressed with a press mold to form a molded body. In one embodiment, the forming start temperature may be 500°C to 700°C. If the forming start temperature is less than 500°C, the forming start temperature is too low, which may reduce the formability of the hot stamping part, and the manufactured hot stamping part (20) may not have the target structure and physical properties. On the other hand, if the forming start temperature exceeds 700°C, the durability may be reduced due to the occurrence of cracks of 10 μm or more on the sidewalls of the manufactured hot stamping part caused by the Liquid Metal Embrittlement (LME) phenomenon. Additionally, the plating layer may adhere to the mold.

[0074] In addition, in the forming / cooling step (S400), a steel plate for hot stamping can be pressed with a press mold to form a formed body, and at the same time, the steel plate for hot stamping (or the formed body) can be cooled. Specifically, a hot stamping part can be formed by forming the steel plate for hot stamping into the shape of a hot stamping part in a press mold and simultaneously cooling the formed body. The press mold may be equipped with a cooling channel through which a refrigerant circulates. The steel plate for hot stamping (or the formed body) can be rapidly cooled by the circulation of the refrigerant supplied through the cooling channel provided in the press mold. At this time, in order to prevent the springback phenomenon of the sheet metal and maintain the desired shape, rapid cooling can be performed while applying pressure with the mold closed. When performing forming and cooling operations on the formed body, the average cooling rate can be exceeded 20℃ / s to the martensite end temperature.

[0075] In one embodiment, the cooling end temperature at which the cooling of the hot stamping part (or, molded body) ends may be 300°C or lower. If the cooling end temperature exceeds 300°C, warping may occur in the hot stamping part (10) as the manufactured hot stamping part (10) is air-cooled at room temperature, and it may be difficult to secure the target material.

[0076] When manufacturing hot stamping parts using a steel sheet for hot stamping that includes a zinc-based plating layer, zinc-based oxides and / or manganese-based oxides may be formed on the surface of the hot stamping part during the heating step.

[0077] FIG. 5 is a drawing showing zinc-based oxide and manganese-based oxide formed on the surface of a hot stamping part at a concentration of more than 35%, and FIG. 6 is a drawing showing zinc-based oxide and manganese-based oxide formed on the surface of a hot stamping part at a concentration of 35% or less. Specifically, FIG. 5 corresponds to the case where the area fraction of zinc-based oxide and manganese-based oxide on the surface of a hot stamping part is 44.5%, and FIG. 6 corresponds to the case where the area fraction of zinc-based oxide and manganese-based oxide on the surface of a stamping part is 28.2%.

[0078] Referring to FIGS. 5 and 6, when zinc-based oxide and manganese-based oxide are formed on the surface of a hot stamping part (10, see FIG. 1) in an area fraction of more than 35%, weldability may be reduced and joint strength may be lowered. When zinc-based oxide and manganese-based oxide are formed in an area fraction of 35% or less, the hot stamping part may have a flat surface, which can lower the initial dynamic resistance during resistance spot welding (RSW), secure welding current, reduce spatter generation, and secure welding strength.

[0079] The present invention has been described with reference to the embodiments illustrated in the drawings, but this is merely illustrative, and those skilled in the art will understand that various modifications and equivalent alternative embodiments are possible therefrom. Accordingly, the true technical scope of protection of the present invention should be determined by the technical spirit of the appended claims. Explanation of the symbols

[0080] 10: Hot stamping parts 10': Steel plate for hot stamping 100, 100': Base material 200, 200': Plating layer 300: Surface layer 300': Surface treatment layer

Claims

Claim 1 A hot stamping part comprising: a base material; a plating layer disposed on at least one surface of the base material; and a surface layer disposed on the plating layer and comprising an oxide portion and a surface treatment portion; wherein the area fraction of the oxide on the surface of the hot stamping part is greater than 0% and less than or equal to 35%. Claim 2 A hot stamping part according to claim 1, wherein the oxide portion comprises zinc-based oxide and manganese-based oxide. Claim 3 A hot stamping part according to claim 1, wherein the plating layer comprises a gamma phase and α-Fe(Zn). Claim 4 A hot stamping part according to paragraph 3, wherein the area fraction of the gamma phase in the plating layer is 25% to 60%. Claim 5 A hot stamping part according to claim 1, wherein the surface treatment portion comprises 15 wt% or more and 50 wt% or less silicon (Si), aluminum (Al) or calcium (Ca), 5 wt% or more and 50 wt% or less zinc (Zn), greater than 0 and 15 wt% or less iron (Fe), greater than 0 and 15 wt% or less manganese (Mn), and 10 wt% or more and 75 wt% or less oxygen (O). Claim 6 A method for manufacturing a hot stamping part, comprising: a step of manufacturing a hot stamping steel plate in which a first plating layer and a surface treatment layer are sequentially formed on a first base material; a heating step of heating the hot stamping steel plate at a heating temperature of Ac3 to 910°C; a transfer step of transferring the heated hot stamping steel plate to a press mold; and a forming and cooling step of pressing the transferred hot stamping steel plate to the press mold to form a formed body and cooling the formed body; wherein the heating time in the heating step satisfies the following Equation 1. <Equation 1> 50*t + 70 ≤ HT ≤ 150*t + 210 In the above Equation 1, HT is the heating time (s), and t is the thickness (in mm) of the hot stamping steel plate (or, hot stamping part). Claim 7 A method for manufacturing a hot stamping part according to claim 6, wherein the hot stamping part comprises: a second base material; a second plating layer disposed on at least one surface of the second base material; and a surface layer disposed on the second plating layer and comprising an oxide portion and a surface treatment portion; wherein the area fraction of the oxide portion on the surface of the hot stamping part is greater than 0% and less than or equal to 35%. Claim 8 A method for manufacturing a hot stamping part according to claim 7, wherein the oxide part comprises zinc-based oxide and manganese-based oxide. Claim 9 A method for manufacturing a hot stamping part according to claim 7, wherein the second plating layer comprises a gamma phase and α-Fe(Zn). Claim 10 A method for manufacturing a hot stamping part according to claim 9, wherein the area fraction of the gamma phase in the second plating layer is 25% to 60%. Claim 11 In claim 6, the step of manufacturing a steel plate for hot stamping comprises: a step of immersing the steel plate in a molten zinc plating bath to form a molten zinc plating layer on the steel plate; a step of alloying the steel plate on which the molten zinc plating layer is formed to form an alloyed molten zinc plating layer on the steel plate; and a step of forming a surface treatment layer on the alloyed molten zinc plating layer; a method for manufacturing a hot stamping part. Claim 12 A method for manufacturing a hot stamping part according to claim 11, wherein the surface treatment layer is formed by applying an inorganic surface treatment agent and then drying.

Images