Hot stamping part and method for manufacturing the same

Abstract

The present invention provides a hot stamping part comprising: a base material; a zinc-based plating layer disposed on at least one surface of the base material; and a surface layer disposed on the plating layer and comprising a zinc-based oxide, wherein the flatness of the zinc-based oxide satisfies the relationship (1 < C / S < 1.118).

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 surface flatness 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 zinc-based plating layer disposed on at least one surface of the base material, and a surface layer disposed on the plating layer and comprising a zinc-based oxide, wherein the flatness of the zinc-based oxide satisfies the relationship (1 < C / S < 1.118).

[0010] In this embodiment, the average thickness of the zinc-based oxide may be less than 3 μm.

[0011] In this embodiment, the surface layer may further include a surface treatment portion.

[0012] In this embodiment, the zinc-based plating layer is gamma phase (Γ-Fe3Zn 10 It may include ) and alpha iron (α-Fe(Zn)).

[0013] One embodiment of the present invention provides a method for manufacturing a hot stamping part, comprising the steps of: manufacturing a hot stamping steel plate having a plating layer and a surface treatment layer formed sequentially on a base material; heating the hot stamping steel plate at a target temperature of Ac3 to 910°C; transferring the heated hot stamping steel plate to a press mold; and pressing the transferred hot stamping part to the press mold to form a molded body and cooling the formed molded body, wherein a zinc-based oxide is formed on the surface of the hot stamping part and the flatness of the zinc-based oxide satisfies the relationship (1 < C / S < 1.118).

[0014] In this embodiment, the thickness of the zinc-based oxide may be less than 3 μm.

[0015] In the present embodiment, the step of manufacturing the steel plate for hot stamping may include the step of forming the plating layer on the base material and the step of forming the surface treatment layer on the plating layer.

[0016] In this embodiment, the surface treatment layer may include an inorganic surface treatment agent bonded with silicon (Si).

[0017] In this embodiment, a step of alloying the plating layer may be further included between the step of forming the plating layer and the step of forming the surface treatment layer.

[0018] In this embodiment, the surface treatment layer may include an inorganic surface treatment agent bonded with silicon (Si).

[0019] 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

[0020] According to one embodiment of the present invention as described above, a hot stamping part with improved surface flatness 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

[0021] 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 diagram illustrating a method for measuring the flatness of a zinc-based oxide according to an embodiment of the present invention. FIG. 3 is a cross-sectional view schematically illustrating a steel plate for hot stamping according to one embodiment of the present invention. FIG. 4 is a schematic diagram illustrating a method for manufacturing a hot stamping part according to one embodiment of the present invention. FIG. 5 is a schematic diagram illustrating a method for manufacturing a steel plate for hot stamping according to one embodiment of the present invention. FIG. 6 is a schematic diagram showing a cross-section of a hot stamping part manufactured by hot stamping a steel plate for hot stamping that does not have a surface treatment layer formed on the plating layer. Specific details for implementing the invention

[0022] 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.

[0023] 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.

[0024] In the following examples, singular expressions include plural expressions unless the context clearly indicates otherwise.

[0025] 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.

[0026] 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.

[0027] 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.

[0028] 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.

[0029] 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.

[0030] 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.

[0031] FIG. 1 is a cross-sectional view schematically illustrating a hot stamping part according to one embodiment of the present invention.

[0032] 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).

[0033] 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.

[0034] 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.

[0035] The plating layer (200) is gamma phase (e.g., Γ-Fe3Zn 10 It can be composed of ) and alpha iron (e.g., α-Fe(Zn)).

[0036] 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.

[0037] A surface layer (300) may be disposed on the plating layer (200). The surface layer (300) may include a zinc-based oxide. The surface of the surface layer (300) may refer to the surface of the hot stamping part (10).

[0038] Zinc oxide can 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 average thickness of the zinc oxide may be less than 3 μm. Zinc oxide is formed during the hot stamping heating process, and if the average thickness of the zinc oxide is 3 μm or more, the dynamic resistance may increase and cause spatter to occur, which may result in poor spot weldability.

[0039] In one embodiment, the zinc oxide can be formed in a flatter shape. In this case, the flatness of the zinc oxide can be quantified by measuring the minimum straight length (S) between any two points and the length (C) of the curved zinc oxide between the two points in a continuous cross-sectional image of the zinc oxide.

[0040] FIG. 2 is a diagram illustrating a method for measuring the flatness of a zinc-based oxide according to an embodiment of the present invention.

[0041] Referring to FIG. 2, the ratio of the length (C) of the zinc oxide between any two points in a continuous zinc oxide to the minimum straight length (S) can be defined as the flatness ratio (F=C / S). In this case, length measurements can be performed only on the region where the length of the zinc oxide in the horizontal direction is secured to be at least 10 μm. Additionally, the flatness (F) of the zinc oxide can satisfy the following relationship.

[0042] <Relationship>

[0043] 1 < C / S < 1.118

[0044] In the relationship, C is the length of the curved zinc oxide between any two points in the continuous zinc oxide on the microscope cross-section (in μm), and S is the minimum straight line length between any two points in the continuous zinc oxide on the microscope cross-section (in μm).

[0045] Since zinc oxide is formed in a serpentine shape, the length of the zinc oxide between any two points is greater than the straight distance between any two points, so the flatness (F) can be greater than 1. If the flatness (F) is 1.118 or higher, the zinc oxide is formed too serpentinely, so the surface quality and spot weldability may be inferior. Therefore, if the flatness (F) satisfies the relationship, the surface quality and spot weldability may be excellent.

[0046] In one embodiment, the surface layer (300) may further include a surface treatment section. 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. 3) of the steel plate (10') for hot stamping, and components diffused from the plating layer (200') and the base material (100'). For example, the surface treatment section may be a mixture of 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.

[0047] 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).

[0048] 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.

[0049] The surface treatment section is formed on the plating layer (200) to suppress and minimize the formation of zinc oxide by combining with oxygen in the zinc (Zn) of the plating layer (200') of the hot stamping steel plate (10'). The surface treatment section can suppress the formation of zinc oxide that hinders binding with the coating layer, and by inducing the formation of silicon oxide that improves binding with the coating layer, it can ultimately improve the coating adhesion of the hot stamping part (10).

[0050] The average thickness of the surface treatment portion may be smaller than the average thickness of the zinc oxide. The area fraction of the surface treatment portion on the surface of the surface layer (300) may be 20% or more and 70% or less relative to the total area fraction of the surface layer. If the area fraction of the surface treatment portion is less than 20%, the coating thickness may be reduced, and as a result, the corrosion resistance of the coating may be reduced.

[0051] FIG. 3 is a cross-sectional view schematically illustrating a steel plate for hot stamping according to one embodiment of the present invention.

[0052] Referring to FIG. 3, 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').

[0053] 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.

[0054] The plating layer (200') may include zinc (Zn) and iron (Fe). However, the present invention is not limited thereto. The plating layer (200') is 15 g / m² on one surface of the steel plate (100). 2 Up to 100 g / m² 2 (30~200 g / m² based on double-sided) 2 It can be plated with an amount of ) and the thickness of the plating layer (200') can be 4㎛ to 30㎛.

[0055] 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 / m²2 5,000 mg / m² or higher 2 It may be less than.

[0056] 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, making it difficult to ensure the flatness of the zinc-based oxide of the hot stamping part (10, see FIG. 1). On the other hand, if the thickness of the surface treatment layer (300') exceeds 2 μm, the additional effect may be minimal, and it may not dry uniformly over the entire area, which may result in reduced physical properties and operability.

[0057] FIG. 4 is a schematic diagram illustrating a method for manufacturing a hot stamping part according to one embodiment of the present invention, and FIG. 5 is a schematic diagram illustrating a method for manufacturing a steel plate for hot stamping according to one embodiment of the present invention.

[0058] Referring to FIGS. 4 and 5, 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.

[0059] A hot stamping steel plate (10', see FIG. 3) 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. 3) is a molten zinc plating layer, the alloying step (S120) may be omitted.

[0060] In the plating step (S110), a plating layer (200') can be formed on a base material (100', see FIG. 3). 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.

[0061] 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.

[0062] The temperature of the plating bath in the plating step (S110) may be 400°C to 700°C.

[0063] In one embodiment, the plating layer (200') is 15 g / m² on one surface of the steel plate (100). 2 Up to 100 g / m² 2 30 g / m² (based on double-sided) 2 Up to 200 g / m² 2 It can be plated with an amount of ) and the thickness of the plating layer (200') can be 4㎛ to 30㎛.

[0064] 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. 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. 3) may be formed on the plating layer (200').

[0065] In one embodiment, in the surface treatment step (S130), 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.

[0066] 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. In addition, the thickness of the surface treatment layer (300') after drying may be 0.05㎛ to 2㎛.

[0067] 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).

[0068] Referring again to FIG. 4, 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°C. For example, the target temperature may be 820°C to 910°C. Additionally, in the heating step (S200), the hot stamping steel plate (10') may be heated while staying in the furnace for 120 seconds to 600 seconds.

[0069] 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.

[0070] 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.

[0071] 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.

[0072] 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.

[0073] 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.

[0074] 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 550°C to 750°C. If the forming start temperature is less than 550°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 750°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.

[0075] 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 maintained at a minimum of 10°C / s or more until the martensite end temperature is reached.

[0076] 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.

[0077] When manufacturing hot stamping parts using a steel sheet for hot stamping that includes a zinc-based plating layer, zinc-based oxide may be formed on the surface of the material during the heating step.

[0078] FIG. 6 is a schematic diagram showing a cross-section of a hot stamping part manufactured by hot stamping a steel plate for hot stamping that does not have a surface treatment layer formed on the plating layer.

[0079] Referring to FIG. 6, the generated zinc-based oxide can be formed in a wavy, swollen shape based on cross-section, and the thickness of the zinc-based oxide can be 3 μm to 5 μm.

[0080] Zinc oxides can easily detach in the form of dust during the pressing process in hot stamping and accumulate within the press mold, requiring frequent cleaning and maintenance. Furthermore, due to the form of the zinc oxides, they can negatively affect the spot weldability required during the vehicle body assembly process. For example, dynamic resistance may increase, and spatter may occur.

[0081] In the present invention, by forming an inorganic surface treatment layer in which silicon (Si) is bonded to the surface of a zinc-based plating layer and then performing a hot stamping process (e.g., hot stamping heating), the thickness of the zinc-based oxide formed on the surface of the material can be reduced to less than 3 μm, and the zinc-based oxide can be formed in a flatter shape. At this time, the flatness (F, C / S) of the zinc-based oxide can be greater than 1 and less than 1.118. In addition, by reducing the thickness of the zinc-based oxide formed on the surface of the material and forming the zinc-based oxide in a flat shape, the cleaning and maintenance cycle of the press mold can be extended, thereby increasing production efficiency, improving the spot weldability of the hot stamped part manufactured without additional post-processing (e.g., sand-blasting or shot-blasting), and reducing manufacturing costs.

[0082] Experimental Example

[0083] The present invention will be explained in more detail below through experimental examples. However, the following experimental examples are intended to explain the present invention more specifically, and the scope of the present invention is not limited by the following experimental examples. The following experimental examples may be appropriately modified or changed by those skilled in the art within the scope of the present invention.

[0084] Table 1 below shows the component content of the slabs used in the experimental examples of the present invention. The specimens of the examples and comparative examples were prepared by the following method.

[0085] A steel plate composed of the components shown in Table 1 and the remainder being iron (Fe) and unavoidable impurities was immersed in a plating bath set at 500°C, and then passed through the plating bath at a line speed of 120 mpm to deposit molten zinc on both the upper and lower surfaces of the steel plate, after which it was charged into an alloying furnace at 530°C to form an alloyed molten zinc plating layer. At this time, the average thickness of the plating layer was controlled to 20 μm.

[0086] Subsequently, in the case of the example, an inorganic surface treatment agent was applied onto the plating layer and dried at a temperature of 110°C for 5 seconds to form a surface treatment layer. At this time, the inorganic surface treatment agent was a Si-based inorganic surface treatment agent composed of 15 wt% or more and 50 wt% or less silicon (Si), 5 wt% or more and 50 wt% or less zinc (Zn), more than 0 wt% and 15 wt% or less iron (Fe), more than 0 wt% and 15 wt% or less manganese (Mn), and 10 wt% or more and 75 wt% or less oxygen (O), at a concentration of 3 g / m² 2 It was applied with the amount of coating. In the case of the comparative example, a surface treatment layer was not formed.

[0087] Afterwards, a hot stamping steel plate was introduced into a heating furnace and heated for 270 seconds in a heating furnace with a maximum temperature of 870℃, and then the heated steel plate was transferred to a press mold to form a molded body, and at the same time, rapidly cooled to 150℃ at a cooling rate of 25℃ / s to manufacture a hot stamping part.

[0088] Flatness measurement

[0089] The flatness of the zinc oxide of a hot stamping part was measured using a microscope. Specifically, after selecting any two points of continuous zinc oxide on the microscope cross-sectional image, the minimum straight-line length (S) between the two points and the actual length of the zinc oxide (C) between the two points were measured, and the flatness (C / S) of the zinc oxide was derived. At this time, the flatness (C / S) of the zinc oxide was measured 10 times at each random location. In addition, since some parts may be damaged or detached during microscopic observation and sample processing, measurements were performed in an area where the zinc oxide was continuous in the horizontal direction for at least 10 μm or more, and cross-sectional processing was carried out using an ion beam to prevent the detachment of surface oxide during the sample processing.

[0090] Ingredients (wt%) C Si Mn P S B 0.28 0.15 1.3 0.01 0.002 0.002

[0091] No. Examples Comparative example 1 1.016 1.318 2 1.027 1.461 3 1.117 1.164 4 1.116 1.260 5 1.110 1.436 6 1.043 1.290 7 1.106 1.118 8 1.011 1.281 9 1.062 1.127 10 1.069 1.412

[0092] Referring to Table 2, it can be seen that when a surface treatment layer is formed on a zinc-plated steel sheet prior to the hot stamping process, the flatness (C / S) of the zinc oxide formed on the surface of the hot stamped part is greater than 1 and less than 1.118. However, when a surface treatment layer is not formed on the zinc-plated steel sheet, it can be seen that the flatness (C / S) of the zinc oxide formed on the surface of the hot stamped part is 1.118 or higher.

[0093] Therefore, it can be confirmed that when a surface treatment layer is formed on a zinc-plated steel sheet prior to hot stamping, the surface flatness of the hot-stamped part decreases.

[0094] 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

[0095] 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 zinc-based plating layer disposed on at least one surface of the base material; and a surface layer disposed on the plating layer and comprising a zinc-based oxide, wherein the flatness of the zinc-based oxide satisfies the following relationship. <Relationship> 1 < C / S < 1.118 In the above relationship, C is the length of a curved zinc-based oxide between any two points in a continuous zinc-based oxide on a cross-section (in μm), and S is the minimum straight length between any two points in a continuous zinc-based oxide on a cross-section (in μm). Claim 2 A hot stamping part according to claim 1, wherein the average thickness of the zinc-based oxide is less than 3㎛. Claim 3 A hot stamping part according to claim 1, wherein the surface layer further comprises a surface treatment portion. Claim 4 In claim 1, the zinc-based plating layer is gamma phase (Γ-Fe3Zn 10 Hot stamping part comprising ) and alpha iron (α-Fe(Zn)). Claim 5 A method for manufacturing a hot stamping part comprises the steps of: manufacturing a hot stamping steel plate having a plating layer and a surface treatment layer formed sequentially on a base material; heating the hot stamping steel plate at a target temperature of Ac3 to 910°C; transferring the heated hot stamping steel plate to a press mold; and pressing the transferred hot stamping part to the press mold to form a molded body and cooling the formed molded body; wherein a zinc-based oxide is formed on the surface of the hot stamping part, and the flatness of the zinc-based oxide satisfies the following relationship. <Relationship> 1 < C / S < 1.118 In the above relationship, C is the length of a curved zinc-based oxide between any two points in a continuous zinc-based oxide on a cross-section (in μm units), and S is the minimum straight length between any two points in a continuous zinc-based oxide on a cross-section (in μm units). Claim 6 A method for manufacturing a hot stamping part according to claim 5, wherein the thickness of the zinc-based oxide is less than 3㎛. Claim 7 A method for manufacturing a hot stamping part according to claim 5, wherein the step of manufacturing the hot stamping steel plate comprises: a step of forming the plating layer on the base material; and a step of forming the surface treatment layer on the plating layer. Claim 8 A method for manufacturing a hot stamping part, wherein the surface treatment layer comprises an inorganic surface treatment agent bonded with silicon (Si) in claim 7. Claim 9 A method for manufacturing a hot stamping part according to claim 7, further comprising a step of alloying the plating layer between the step of forming the plating layer and the step of forming the surface treatment layer. Claim 10 A method for manufacturing a hot stamping part according to claim 9, wherein the surface treatment layer comprises an inorganic surface treatment agent bonded with silicon (Si).

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