Hot Stamping Parts

Abstract

The present invention provides a hot stamped part having a drilled portion formed therein, the hot stamped part comprising: a base material; an interdiffusion layer disposed on the base material; and a plating layer disposed on the interdiffusion layer; wherein the hot stamped part comprises a sheared surface formed on the edge of the drilled portion, the sheared surface comprising a roll-over surface, a sheared surface, and a fractured surface, and the thickness th1 of the fractured surface and the thickness th2 of the sheared surface satisfy Equation 1 (th1 / th2≦0.6).

Description

[Technical Field]

[0001] The present invention relates to hot stamped parts. [Background technology]

[0002] As environmental and fuel economy regulations become stricter worldwide, the need for lighter vehicle materials is increasing, which has led to active research and development into ultra-high strength steels and hot stamping steels.

[0003] Hot stamping is a process of manufacturing high-strength parts by heating steel sheets to high temperatures in a heating furnace and then quenching them in a press. A drilling process can also be performed to cut / machine holes in the high-strength parts.

[0004] The drilling process uses a laser device or a press die, but when using a laser device, the processing time increases, and when using a press die, the quality of the sheared surface may decrease.

[0005] Related technologies include Korean Patent Publication No. 10-2020-0080721 (Title of the invention: Hot stamping part manufacturing apparatus and hot stamping part manufacturing method using the same). Summary of the Invention [Problem to be solved by the invention]

[0006] The problem to be solved by the present invention is to provide a hot stamped part that has excellent resistance to hydrogen embrittlement. [Means for solving the problem]

[0007] One embodiment of the present invention provides a hot stamped part having a drilled portion formed therein, the hot stamped part comprising: a base material; an interdiffusion layer disposed on the base material; and a plating layer disposed on the interdiffusion layer; wherein the hot stamped part comprises a sheared surface formed on an edge of the drilled portion, the sheared surface comprising a roll-over surface, a sheared surface, and a fractured surface, and a thickness th1 of the fractured surface and a thickness th2 of the sheared surface satisfy the following formula 1:

[0008] <Expression 1> th1 / th2≦0.6

[0009] In this embodiment, the roll-over surface, the shear surface, and the fracture surface may be provided sequentially in the thickness direction of the hot stamping part.

[0010] In this embodiment, the thickness of the sheared surface is also the sum of the thickness of the fracture surface, the thickness of the sheared surface, and the thickness of the roll-over surface.

[0011] In this embodiment, the thickness of the fracture surface is also the shortest distance in the thickness direction of the hot stamped part from the start point of the fracture surface to the end point of the fracture surface.

[0012] In this embodiment, the thickness of the sheared surface is also the shortest distance in the thickness direction of the hot stamped part from the start of the roll-over surface to the end of the fracture surface.

[0013] In this embodiment, the hot stamped part may further include a plating layer-removed surface where at least a portion of the upper surface of the intermixed layer is exposed.

[0014] In this embodiment, the width w1 of the plating layer removal surface and the width w2 of the rollover surface satisfy the following formula 2.

[0015] <Expression 2> w1 / w2≦0.6

[0016] In this embodiment, at least two or more perforating portions may be provided.

[0017] Other aspects, features, and advantages beyond those described above will become apparent from the following detailed description of the invention, the claims, and the drawings. [Effects of the Invention]

[0018] According to one embodiment of the present invention, a hot stamped part having excellent resistance to hydrogen embrittlement can be provided, although it goes without saying that the scope of the present invention is not limited to such an effect. [Brief explanation of the drawings]

[0019] [Figure 1] 1 is a perspective view showing a schematic diagram of a hot stamped part according to an embodiment of the present invention; FIG. [Figure 2] 1 is a cross-sectional view showing a schematic diagram of a hot stamped part according to an embodiment of the present invention; [Figure 3] 3 is an enlarged view of part A in FIG. 2. [Figure 4A] 1 is a side view of a punched portion of a hot stamped part according to an embodiment of the present invention; [Figure 4B] 1 is a front view of a punched portion of a hot stamped part according to an embodiment of the present invention; [Figure 4C] 4B is an enlarged view of a portion of FIG. 4A. [Figure 5A] 1 is a side view of a hole formed in a hot stamped part according to a comparative example. [Figure 5B] 1 is a front view of a hole formed in a hot stamped part according to a comparative example. [Figure 5C] 5B is an enlarged view of a portion of FIG. 5A. [Figure 6] 1 is a flow chart that schematically illustrates a method for manufacturing a hot stamped part according to an embodiment of the present invention. [Figure 7]1 is a flow chart that schematically illustrates the preparatory steps of a method for manufacturing a hot stamped part according to an embodiment of the present invention. [Figure 8] FIG. 1 is a plan view schematically illustrating a blank according to an embodiment of the present invention. [Figure 9] 1 is a flow chart that schematically illustrates a heating stage of a method for manufacturing a hot stamped part according to an embodiment of the present invention. [Figure 10] 1 is a view illustrating a heating furnace having multiple sections in a heating step of a method for manufacturing a hot stamped part according to an embodiment of the present invention; [Figure 11] 2 is a cross-sectional view illustrating the forming / punching stage of the manufacturing process of a hot stamped part according to one embodiment of the present invention. FIG. [Figure 12] 2 is a cross-sectional view illustrating the forming / punching stage of the manufacturing process of a hot stamped part according to one embodiment of the present invention. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0020] The present invention can be embodied in various forms and in various modifications, and specific embodiments are illustrated in the drawings and described in detail in the detailed description. The advantages and features of the present invention, as well as methods for achieving them, will become clearer with reference to the following detailed description of the embodiments together with the drawings. However, the present invention is not limited to the embodiments disclosed below, and may be embodied in various forms.

[0021] In the following examples, terms such as first and second are not used in a limiting sense but are used to distinguish one component from another.

[0022] In the following examples, the singular expression includes the plural expression unless the context clearly indicates otherwise.

[0023] In the following examples, terms such as "comprise" or "have" mean the presence of a feature or component described in the specification, but do not preclude the possibility of adding one or more other features or components.

[0024] In the drawings, the size of components may be exaggerated or reduced for the sake of convenience of explanation. For example, the size and thickness of each component shown in the drawings are arbitrarily shown for the sake of convenience of explanation, and the present invention is not necessarily limited to what is shown in the drawings.

[0025] When an embodiment can be implemented differently, the order of certain steps may be performed differently than described. For example, two steps described in succession may be performed substantially simultaneously or in the reverse order of the steps described.

[0026] In this specification, "A and / or B" refers to A, B, or A and B. And "at least one of A and B" refers to A, B, or A and B.

[0027] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. When describing with reference to the drawings, identical or corresponding components will be designated by the same reference numerals, and duplicate descriptions thereof will be omitted.

[0028] FIG. 1 is a perspective view that schematically illustrates a hot stamped part according to one embodiment of the present invention.

[0029] 1 , a hot stamped part 10 according to an embodiment of the present invention may include a punching portion 110. In one embodiment, the hot stamped part 10 may include two punching portions 110. The punching portion 110 may include a first punching portion 110a and a second punching portion 110b. However, the present invention is not limited thereto. The hot stamped part 10 may include one punching portion 110 or three or more punching portions 110.

[0030] Although not shown, the hot stamped part 10 may include additional drilling portions in addition to the drilling portion 110. In this case, the drilling portion 110 is formed by hot drilling, and the additional drilling portions may be formed by cold drilling or laser drilling. The hot stamped part 10 may be provided with one or more additional drilling portions.

[0031] In one embodiment, perforation 110 may be used to form additional perforations, as will be described in more detail below.

[0032] Although not shown, the hot stamped part 10 may also include an end portion. In this case, the end portion of the hot stamped part 10 may refer to a surface extending along the long side of the hot stamped part 10.

[0033] Fig. 2 is a cross-sectional view schematically illustrating a hot stamped part according to one embodiment of the present invention, and Fig. 3 is an enlarged view of part A in Fig. 2. Specifically, Fig. 2 is a cross-sectional view schematically illustrating a punched portion of a hot stamped part according to one embodiment of the present invention.

[0034] 2 and 3, a hot stamped part 10 according to an embodiment may include a base material 200, an interdiffusion layer 210, and a plating layer 220. The base material 200, the interdiffusion layer 210, and the plating layer 220 may be sequentially provided in a thickness direction of the hot stamped part 10. In this regard, the thickness direction of the hot stamped part 10 is defined as a vertical direction, and a direction intersecting the thickness direction of the hot stamped part 10 is defined as a horizontal direction.

[0035] In one embodiment, the hot stamped component 10 may include a sheared surface 300 formed on the edge of the punched portion 110. The sheared surface 300 may include a rolled-over surface 301, a sheared surface 302, and a fractured surface 303.

[0036] In one embodiment, the rollover surface 301 is a surface where sagging or indentations occur. As will be described later, during shearing (or hot punching), the blank is deformed by the downward movement of the punch, causing sagging, which may cause curvature in the top surface of the preform 200, which forms the top surface in the horizontal direction. In this case, the surface where the curvature occurs on the top surface of the preform 200 may correspond to the rollover surface 301. The rollover surface 301 may correspond to the area from where the curvature begins to occur on the top surface of the preform 200 to where the shear plane 302 begins.

[0037] In one embodiment, the shear surface 302 is a surface extending vertically or at a predetermined angle to the vertical. As will be described later, as the punch continues to cut in the vertical direction, the sagging of the blank ends, and the punch and the blank come into direct contact to proceed with shearing (or perforation). As the shearing (or perforation) proceeds, the shear surface 302 may be formed along the vertical direction. For example, the curvature that occurred on the top surface of the base material 200 disappears, and a linear shear surface 302 may be formed along the vertical direction or a direction that forms a predetermined angle with the vertical direction. The shear surface 302 may correspond to the area from the end point of the rollover surface 301 to the start point of the fracture surface 303.

[0038] In one embodiment, the fracture surface 303 is also a surface formed by breaking the blank. As described below, the fracture surface 303 may be formed by breaking at least a portion of the blank as the punch descends vertically. Since the fracture surface 303 is formed by breaking at least a portion of the blank, it may be irregular compared to the shear surface 302. Compared to the shear surface 302, the fracture surface 303 may correspond to the point where the irregular formation begins to the point where the fracture surface 303 ends or the point where the base material 200 ends.

[0039] In one embodiment, the shear surface 302 is a portion that is directly rubbed against the punch, and in a front view, the shear surface 302 may have a glossy surface due to direct friction with the punch. Furthermore, the fracture surface 303 is a portion where the blank has been irregularly removed, and may have a rough surface. Therefore, since the shear surface 302 has a smooth surface and the fracture surface 303 has an irregular surface, it is easy to distinguish the boundary between the shear surface 302 and the fracture surface 303.

[0040] In one embodiment, the plating layer removal surface 304 is also a surface from which at least a portion of the plating layer 220 has been removed. During the hot stamping heat treatment, the interdiffusion layer 210 may be formed by alloying the base material 200 and the plating layer 220. At this time, during hot drilling, at least a portion of the plating layer 220 disposed on the upper surface of the interdiffusion layer 210 may be removed (or eliminated). The plating layer removal surface 304 may be defined as a surface from which at least a portion of the plating layer 220 disposed on the upper surface of the interdiffusion layer 210 has been removed (or eliminated). The plating layer removal surface 304 may correspond to a region from a point where the upper surface of the interdiffusion layer 210, exposed by removing at least a portion of the plating layer 220, meets the plating layer 220 to a start point of the shear surface 302.

[0041] In one embodiment, the thickness th1 of the fracture surface 303 may be defined as the shortest vertical distance from the boundary between the shear surface 302 and the fracture surface 303 to the end point of the base material 200. That is, the thickness th1 of the fracture surface 303 may be defined as the shortest distance between a first imaginary line (or a first imaginary plane) extending horizontally through the boundary between the shear surface 302 and the fracture surface 303 and a second imaginary line (or a second imaginary plane) extending horizontally through the end point of the base material 200. In this case, the end point of the base material 200 may refer to the end point of the fracture surface 303.

[0042] In one embodiment, the thickness th3 of the shear plane 302 may be defined as the shortest vertical distance from the boundary between the rollover surface 301 and the shear plane 302 to the boundary between the shear plane 302 and the fracture surface 303. In other words, the thickness th3 of the shear plane 302 may be defined as the shortest distance between a third imaginary line (or a second imaginary plane) extending horizontally through the start point of the shear plane 302 and a fourth imaginary line (or a fourth imaginary plane) extending horizontally through the boundary between the shear plane 302 and the fracture surface 303.

[0043] In one embodiment, the thickness th4 of the rollover surface 301 may be defined as the shortest vertical distance from the start point of the curvature of the base material 200 to the start point of the shear plane 302. In other words, the thickness th4 of the rollover surface 301 may be defined as the shortest distance between a fifth imaginary line (or a fifth imaginary plane) that is tangent to the top surface of the base material 200 and extends horizontally, and a sixth imaginary line (or a sixth imaginary plane) that extends horizontally through the point where the shear plane 302 begins.

[0044] In one embodiment, the thickness th2 of the sheared surface 300 may be defined as the shortest vertical distance from the start point of the curvature of the base material 200 to the end point of the base material 200. In other words, the thickness th2 of the sheared surface 300 may be defined as the shortest distance between a fifth imaginary line (or a fifth imaginary plane) that is tangent to the top surface of the base material 200 and extends horizontally, and a second imaginary line (or a second imaginary plane) that extends horizontally through the end point of the base material 200. For example, the thickness th2 of the sheared surface 300 is also the sum of the thickness th1 of the fracture surface 303, the thickness th3 of the sheared surface 302, and the thickness th4 of the roll-over surface 301.

[0045] In one embodiment, the width w1 of the plating layer removal surface 304 may be defined as the shortest horizontal distance from a point where the upper surface of the interdiffusion layer 210, exposed by removing at least a portion of the plating layer 220, meets the plating layer 220 to the start of the shear plane 302. That is, the width w1 of the plating layer removal surface 304 may be defined as the shortest horizontal distance between a seventh imaginary line (or a seventh imaginary plane) extending vertically through a point where the upper surface of the interdiffusion layer 210, exposed by removing at least a portion of the plating layer 220, meets the plating layer 220, and an eighth imaginary line (or an eighth imaginary plane) extending vertically through the start of the shear plane 302.

[0046] In one embodiment, the width w2 of the rollover surface 301 may be defined as the shortest horizontal distance from the start point of the curvature of the base material 200 to the start point of the shear plane 302. In other words, the width w2 of the rollover surface 301 may be defined as the shortest distance between a ninth imaginary line (or a ninth imaginary plane) extending vertically through the start point of the curvature of the base material 200 and an eighth imaginary line (or an eighth imaginary plane) extending vertically through the start point of the shear plane 302.

[0047] If the temperature of the blank increases, the flow stress decreases, and if the stress acting on the blank decreases, the resistance to hydrogen embrittlement can be improved.

[0048] In one embodiment, as described below, hot drilling at a relatively high temperature compared to cold drilling, where shearing is performed at approximately 30°C (e.g., room temperature), reduces the shear stress acting on the blank, which may improve resistance to hydrogen embrittlement.

[0049] FIG. 4A is a side view of a drilling portion of a hot stamped part according to one embodiment of the present invention, FIG. 4B is a front view of a drilling portion of a hot stamped part according to one embodiment of the present invention, and FIG. 4C is an enlarged view of a portion of FIG. 4A.

[0050] FIG. 5A is a side view of the perforation of a hot stamped part according to a comparative example, FIG. 5B is a front view of the perforation of a hot stamped part according to a comparative example, and FIG. 5C is an enlarged view of a portion of FIG. 5A.

[0051] Specifically, FIGS. 4A, 4B, and 4C correspond to the case where hot drilling is performed, and FIGS. 5A, 5B, and 5C correspond to the case where cold drilling is performed.

[0052] 4A, 4B, 4C, 5A, 5B, and 5C, it can be seen that the width w2 of the roll-over surface 301 when hot drilling is performed is larger than the width w2' of the roll-over surface 301' when cold drilling is performed. It can also be seen that the width w1 of the coating layer removal surface 304 when hot drilling is performed is smaller than the width w1' of the coating layer removal surface 304' when cold drilling is performed. Therefore, when hot drilling is performed, the width w2 of the roll-over surface 301 may increase and the width w1 of the coating layer removal surface 304 may decrease compared to when cold drilling is performed. That is, when drilling is performed when the blank temperature is high, the width w2 of the roll-over surface 301 increases and the width w1 of the coating layer removal surface 304 decreases compared to when drilling is performed when the blank temperature is low.

[0053] It can be seen that when hot drilling is performed, the shear surface fraction is larger and the fracture surface fraction is smaller than when cold drilling is performed. Specifically, it can be seen that the thickness th3 of the shear surface 302 when hot drilling is performed is larger than the thickness th3' of the shear surface 302' when cold drilling is performed. It can also be seen that the thickness th1 of the fracture surface 303 when hot drilling is performed is smaller than the thickness th1' of the fracture surface 303' when cold drilling is performed. This confirms that when hot drilling is performed, the proportion of the shear surface 302 is larger and the proportion of the fracture surface 303 is smaller in the sheared surface 300 than when cold drilling is performed.

[0054] It can be seen that when hot drilling is performed, the ratio of the roll-over surface 301 to the sheared surface 300 is larger than when cold drilling is performed. Specifically, it can be seen that the thickness th4 of the roll-over surface 301 when hot drilling is performed is larger than the thickness th4' of the roll-over surface 301' when cold drilling is performed. As a result, it can be seen that the thickness th4 of the roll-over surface 301 is increased when hot drilling is performed compared to when cold drilling is performed.

[0055] As the shear stress acting on the blank 100 during drilling increases, the proportion of the fracture surface 303 in the sheared surface 300 may increase. Specifically, as the shear stress acting on the blank 100 increases, the thickness th1 of the fracture surface 303 may increase and the thickness th3 of the sheared surface 302 may decrease. A large thickness th1 of the fracture surface 303 means that the shear stress acting on the blank is large, and the large shear stress may induce hydrogen embrittlement in the drilled portion 110. Therefore, in order to improve the hydrogen embrittlement resistance of the hot stamped component 10, it is necessary to reduce the thickness th1 of the fracture surface 303 below a certain level.

[0056] Furthermore, as the shear stress acting on the blank increases, the width w1 of the coating layer removal surface 304 increases and the width w2 of the roll-over surface 301 decreases. Therefore, in order to improve the hydrogen embrittlement resistance of the hot stamped component 10, it is necessary to decrease the width w1 of the coating layer removal surface 304 and increase the width w2 of the roll-over surface 301.

[0057] Therefore, the inventors conducted extensive experiments and derived Equations 1 and 2 that provide the hot stamped component 10 with excellent hydrogen embrittlement resistance. In one embodiment, the hot stamped component 10 satisfies Equations 1 and 2. Specifically, in the hot stamped component 10, the thickness th1 of the fracture surface 303 and the thickness th2 of the sheared surface 300 satisfy Equation 1, and in the hot stamped component 10, the width w1 of the plating layer removal surface 304 and the width w2 of the roll-over surface 301 satisfy Equation 2.

[0058] <Expression 1> th1 / th2≦0.6 <Expression 2> w1 / w2≦0.6

[0059] In one embodiment, the value of the thickness th1 of the fracture surface 303 / thickness th2 of the sheared surface 300 is the average value of the values ​​of the thickness th1 of the fracture surface 303 / thickness th2 of the sheared surface 300 measured at a minimum of four or more points at equal angles from the center of the drilling portion 110.

[0060] In one embodiment, the value of the width w1 of the plating layer removal surface 304 / the width w2 of the roll-over surface 301 is the average value of the values ​​of the width w1 of the plating layer removal surface 304 / the width w2 of the roll-over surface 301 measured at at least four or more points at equal angles from the center of the perforation portion 110.

[0061] In the case of cold drilling, if the clearance decreases, the percentage of fractured surfaces may also decrease. That is, in the case of cold drilling, if the clearance decreases, the ratio of the thickness th1 of the fractured surface 303 to the thickness th2 of the sheared surface 300 may decrease. However, if the clearance decreases, the shear stress acting on the blank may increase. Therefore, the shear stress and the percentage of fractured surfaces are inversely proportional to each other.

[0062] In the case of hot drilling, drilling is performed at a relatively higher temperature than in cold drilling, so the shear stress acting on the blank is reduced and the fraction of fracture surfaces can also be reduced.

[0063] Furthermore, if drilling is performed at a high temperature, the length of the plating layer 220 that peels off around the drilled portion 110 may decrease. Furthermore, as the temperature of the blank increases and the clearance increases, the stress acting on the blank decreases, which increases the area of ​​the rollover surface 301 and the width w1 of the rollover surface 301.

[0064] If the fraction of fracture surface 303 is large, it is believed that a large shear stress acts on drilled portion 110 during hot drilling, and if a large shear stress acts on drilled portion 110, hydrogen embrittlement may occur in a portion adjacent to drilled portion 110 of hot stamped component 10. That is, if the thickness th1 of fracture surface 303 is large, it is believed that a large shear stress acts on drilled portion 110 during hot drilling, and if a large shear stress acts on drilled portion 110, hydrogen embrittlement may occur in a portion adjacent to drilled portion 110.

[0065] If the thickness th1 of the fracture surface 303 of the hot stamped part 10 and the thickness th2 of the sheared surface do not satisfy Equation 1, hydrogen embrittlement may occur in the area adjacent to the drilled portion 110. Specifically, if the value of the thickness th1 of the fracture surface 303 / the thickness th2 of the sheared surface 300 of the hot stamped part 10 exceeds 0.6, this means that the proportion of the fracture surface 303 in the sheared surface 300 is large, which means that a large shear stress acts on the drilled portion 110 during drilling, and this may cause hydrogen embrittlement in the area adjacent to the drilled portion 110 of the hot stamped part 10.

[0066] Therefore, when the thickness th1 of the fracture surface 303 and the thickness th2 of the sheared surface 300 of the hot stamped part 10 satisfy Equation 1, hydrogen embrittlement in the area adjacent to the drilled portion 110 can be prevented or minimized.

[0067] If the shear stress applied to the blank during drilling increases, hydrogen embrittlement may occur around the drilled portion 110. Furthermore, if the shear stress applied to the blank during drilling increases, the amount of peeled plating layer 220 around the drilled portion 110 may increase, and the length (or area) of the roll-over surface 301 may decrease. Specifically, if the shear stress applied to the blank during drilling increases, the width w1 of the plating layer removal surface 304 may increase, and the width w2 of the roll-over surface 301 may decrease.

[0068] If the width w1 of the coating removal surface 304 and the width w2 of the roll-over surface 301 of the hot stamped component 10 do not satisfy Equation 2, hydrogen embrittlement may occur in the area adjacent to the drilled portion 110. Specifically, in order for the ratio of the width w1 of the coating removal surface 304 to the width w2 of the roll-over surface 301 of the hot stamped component 10 to exceed 0.6, the width w1 of the coating removal surface 304 must be increased or the width w2 of the roll-over surface 301 must be decreased. An increase in the width w1 of the coating layer removal surface 304 or a decrease in the width w2 of the roll-over surface 301 indicates that a large shear stress has acted on the drilled portion 110. Therefore, if the value of the width w1 of the coating layer removal surface 304 / the width w2 of the roll-over surface 301 of the hot stamped part 10 exceeds 0.6, this indicates that a large shear stress has acted on the drilled portion 110 during drilling, and as a result, hydrogen embrittlement may occur in the portion of the hot stamped part 10 adjacent to the drilled portion 110.

[0069] Therefore, when the width w1 of the plating layer removal surface 304 and the width w2 of the roll-over surface 301 of the hot stamped part 10 satisfy Equation 2, hydrogen embrittlement in the area adjacent to the drilled portion 110 can be prevented or minimized.

[0070] The method for manufacturing a hot stamped part will now be described.

[0071] FIG. 6 is a flow chart that schematically illustrates a method for manufacturing a hot stamped part according to one embodiment of the present invention.

[0072] Referring to FIG. 6, a method for manufacturing a hot stamped part according to an embodiment may include a preparation step (S100), a heating step (S200), a transfer step (S300), and a forming / punching step (S400).

[0073] FIG. 7 is a flow chart that schematically illustrates the preparatory steps of a method for manufacturing a hot stamped part according to an embodiment of the present invention, and FIG. 8 is a plan view that schematically illustrates a blank according to an embodiment of the present invention.

[0074] 7 and 8, the preparation step (S100) is also a step of preparing a blank 100 for hot stamping. In one embodiment, the preparation step (S100) may include a hot rolling step (S110), a cooling / coiling step (S120), a cold rolling step (S130), an annealing step (S140), a plating step (S150), and a cutting step (S160).

[0075] First, a steel slab reheating step may be performed. In this step, the steel slab obtained through the continuous casting process is reheated to a predetermined temperature to redissolve elements that segregated during casting. In one embodiment, the slab reheating temperature (SRT) is approximately 1,200°C to 1,400°C. If the SRT is lower than approximately 1,200°C, elements that segregated during casting are not sufficiently redissolved, resulting in a less effective homogenization of alloy elements and a less effective dissolution of titanium (Ti). A higher SRT is more advantageous for homogenization, but if the SRT exceeds approximately 1,400°C, the austenite grain size increases, making it difficult to ensure strength, and the excessive heating process may increase the manufacturing costs of the steel sheet.

[0076] In the hot rolling step (S110), the reheated sheet material can be hot-rolled at a predetermined finish rolling temperature. A hot-rolled steel sheet can be manufactured through the hot rolling step (S110). In one embodiment, the finish delivery temperature (FDT) is about 880°C to 950°C. If the FDT is lower than about 880°C, it may be difficult to ensure workability of the steel sheet due to the generation of a duplex structure caused by abnormal region rolling, and workability may be reduced due to non-uniform microstructure. Furthermore, a rapid phase change may cause problems with sheet threadability during hot rolling. If the FDT exceeds about 950°C, austenite grains may become coarse and TiC precipitates may become coarse, resulting in reduced performance of the hot stamped part.

[0077] In the cooling / coiling step (S120), the hot-rolled steel sheet may be cooled to a predetermined coiling temperature (CT) and then coiled. In one embodiment, the coiling temperature in the cooling / coiling step (S120) is about 550°C to 800°C. The coiling temperature affects carbon redistribution. If the coiling temperature is less than about 550°C, the low-temperature fraction increases due to overcooling, resulting in increased strength, and the rolling load during cold rolling may become severe, resulting in a sudden decrease in softness. Conversely, if the coiling temperature exceeds about 800°C, abnormal or excessive grain growth may occur, resulting in deterioration of formability and strength.

[0078] In the cold rolling step (S130), the coiled hot-rolled steel sheet may be uncoiled, pickled, and then cold-rolled. Here, the pickling may be performed to remove scale from the coiled hot-rolled steel sheet, i.e., the hot-rolled coil manufactured through the hot rolling process. A cold-rolled steel sheet may be manufactured through the cold rolling step (S130).

[0079] The annealing step (S140) may involve annealing the cold-rolled steel sheet at a temperature of about 700°C or higher. For example, the annealing step (S140) may include heating the cold-rolled steel sheet and cooling the heated cold-rolled steel sheet at a predetermined cooling rate. In the annealing step (S140), the cold-rolled steel sheet may be annealed. The annealing step (S140) may be performed in an annealing furnace.

[0080] In one embodiment, the annealing temperature of the cold-rolled steel sheet is about 750°C to 900°C. If the annealing temperature of the cold-rolled steel sheet is less than about 750°C, the desired structure will not be obtained and recrystallization will not be fully completed. On the other hand, if the annealing temperature of the cold-rolled steel sheet exceeds about 900°C, the annealing temperature will be too high and the efficiency of the manufacturing process may decrease. Therefore, if the annealing temperature of the cold-rolled steel sheet satisfies the range of about 750°C to 900°C, the desired structure will be obtained, recrystallization will be fully completed, and the efficiency of the manufacturing process may be improved.

[0081] The plating step (S150) is also a step of forming a plating layer on the annealed cold-rolled steel sheet. In one embodiment, a plating layer may be formed on the annealed cold-rolled steel sheet through the plating step (S150). In this case, the plating layer may include a zinc (Zn)-based plating layer or an aluminum (Al)-based plating layer.

[0082] Specifically, in the plating step (S150), the annealed cold-rolled steel sheet may be immersed in a plating bath. At this time, the plating bath may be maintained at a temperature of about 400°C to 700°C. The coating weight is about 40 g / m2 on both sides of the base material of the cold-rolled steel sheet. 2 ~200g / m 2 After the plating step (S150), the cold-rolled steel sheet on which the plating layer is formed may be wound into a coil.

[0083] 7 illustrates that the cold rolling step (S130), the annealing step (S140), and the coating step (S150) are performed after the cooling / coiling step (S120), but the present invention is not limited thereto. At least one of the cold rolling step (S130), the annealing step (S140), and the coating step (S150) may be omitted. For example, the cold rolling step (S130) and the annealing step (S140) may be omitted. In this case, after the coating step (S150), the hot-rolled steel sheet on which the coating layer is formed may be wound into a coil.

[0084] In the subsequent cutting step (S160), a coiled steel sheet (e.g., a cold-rolled steel sheet or a hot-rolled steel sheet) may be uncoiled, and then the steel sheet may be cut into blanks 100 using a laser or a cold press die. In this case, the blank 100 may include an outer periphery (or edge) of a coil. For example, the blank 100 may include an outer periphery (or edge) of a steel sheet.

[0085] 6, after the preparation step (S100) of preparing the blank 100, a heating step (S200) of heating the blank 100 may be performed. The heat source method in the heating step (S200) may be direct heating or indirect heating. The heat source method in the heating step (S200) may be one of direct heating and indirect heating, or a combination of direct heating and indirect heating.

[0086] In one embodiment, in the heating step (S200), the blank 100 may be heated in a heating furnace. The heating furnace may have one section with one temperature range (or a single temperature), or may have multiple sections with different temperature ranges. When the heating furnace has one section with one temperature range, the blank 100 may be heated to a target temperature in the heating furnace. In this case, the target temperature is Ac3 to 1,000°C. That is, the blank 100 may be heated in a heating furnace having a temperature range of Ac3 to 1,000°C until the temperature of the blank 100 reaches Ac3 to 1,000°C.

[0087] On the other hand, if the heating furnace is provided with a plurality of sections having different temperature ranges, the blank 100 can be heated to a target temperature in the heating furnace in different temperature ranges.

[0088] FIG. 9 is a flowchart illustrating a heating step of a method for manufacturing a hot stamped part according to an embodiment of the present invention, and FIG. 10 is a diagram illustrating a heating furnace having multiple sections in the heating step of a method for manufacturing a hot stamped part according to an embodiment of the present invention.

[0089] 9 and 10, in the heating step (S200), the blank 100 (see FIG. 8) may be heated in a heating furnace having multiple sections with different temperature ranges. As shown in FIG. 9, the heating step (S200) may include a multi-stage heating step (S210) and a soaking heating step (S220). The multi-stage heating step (S210) and the soaking heating step (S220) are also steps in which the blank 100 is heated by passing through multiple sections provided in the heating furnace.

[0090] In one embodiment, the temperature of the entire furnace is about 680°C to 1,000°C. Specifically, the temperature of the entire furnace in which the multi-stage heating step (S210) and the soaking heating step (S220) are performed is about 680°C to 1,000°C. In this case, the temperature of the furnace in which the multi-stage heating step (S210) is performed is about 680°C to Ac3, and the temperature of the furnace in which the soaking heating step (S220) is performed is about Ac3 to 1,000°C.

[0091] In the multi-stage heating step (S210), the blank 100 may be heated (or heated) in stages as it passes through multiple sections provided in the heating furnace. There may be multiple sections in which the multi-stage heating step (S210) is performed among the multiple sections provided in the heating furnace, and the temperature may be set for each section so that the temperature increases from the entrance of the heating furnace where the blank 100 is inserted toward the exit of the heating furnace where the blank 100 is removed, thereby heating (or raising the temperature) the blank 100 in stages.

[0092] After the multi-stage heating step (S210), a soaking heating step (S220) may be performed. In the soaking heating step (S220), the multi-stage heated blank may be heated (or soaked) by passing through a section of a heating furnace set at a temperature of about Ac3 to 1,000°C. The soaking heating step (S220) is performed in at least one section among the multiple sections provided in the heating furnace.

[0093] According to an embodiment, the heating furnace may include multiple zones having different temperature ranges. Specifically, the heating furnace may include a first zone P1 having a first temperature range T1, a second zone P2 having a second temperature range T2, a third zone P3 having a third temperature range T3, a fourth zone P4 having a fourth temperature range T4, a fifth zone P5 having a fifth temperature range T5, a sixth zone P6 having a sixth temperature range T6, and a seventh zone P7 having a seventh temperature range T7.

[0094] In one embodiment, in the multi-stage heating step (S210), the blank may be heated in stages by passing through first to fourth sections P1 to P4 defined in a heating furnace. In addition, in the soaking heating step (S220), the blank that has been multi-stage heated in the first to fourth sections P1 to P4 may be soaked by passing through fifth to seventh sections P5 to P7.

[0095] The first through seventh sections P1 through P7 may be arranged sequentially within the heating furnace. The first section P1 having the first temperature range T1 may be adjacent to the entrance of the heating furnace where the blanks are inserted, and the seventh section P7 having the seventh temperature range T7 may be adjacent to the exit of the heating furnace where the blanks are removed. Therefore, the first section P1 having the first temperature range T1 is the first section of the heating furnace, and the seventh section P7 having the seventh temperature range T7 is the last section of the heating furnace.

[0096] The temperatures of the multiple sections within the heating furnace, for example, the temperatures of the first section P1 through the seventh section P7, may increase from the entrance where the blanks are inserted to the exit where the blanks are removed. However, the temperatures of the fifth section P5, the sixth section P6, and the seventh section P7 are the same. In addition, the temperature difference between two adjacent sections among the multiple sections within the heating furnace is greater than 0°C and less than 100°C. For example, the temperature difference between the first section P1 and the second section P2 is greater than 0°C and less than 100°C.

[0097] The furnace temperature in the soaking step (S220) is Ac3 to 1,000°C. If the furnace temperature in the soaking step (S220) is less than Ac3, the hot stamped part produced will not have the desired properties. On the other hand, if the furnace temperature in the soaking step (S220) is more than about 1,000°C, carbide-forming elements and nitride-forming elements in the blank 100, such as Ti, V, Nb, and Mo, will dissolve in the base material, making it difficult to suppress grain coarsening.

[0098] 10, the furnace according to one embodiment is shown to have seven zones with different temperature ranges, but the present invention is not limited thereto. The furnace may have five, six, eight, or other zones with different temperature ranges.

[0099] In one embodiment, the heating step (S200) is comprised of a multi-stage heating step (S210) and a soaking heating step (S220), so that the temperature of the heating furnace can be set in stages, thereby improving the energy efficiency of the heating furnace.

[0100] In one embodiment, the heating furnace may have a length of approximately 20 to 40 meters along the transfer path of the blank 100. The heating furnace may include multiple sections having different temperature ranges, and the ratio of the length of the section in which the blank is heated in multiple stages to the length of the section in which the blank is soaked satisfies approximately 1:1 to 4:1. If the length of the section in which the blank is soaked in the heating furnace increases so that the ratio of the length of the section in which the blank is soaked to the length of the section in which the blank is soaked exceeds approximately 1:1, the amount of hydrogen permeating into the blank in the soaking section may increase, resulting in an increased risk of delayed fracture. On the other hand, if the length of the section in which the blank is soaked decreases so that the ratio of the length of the section in which the blank is soaked to the length of the section in which the blank is soaked is less than approximately 4:1, the soaking section (or time) may not be sufficiently secured, resulting in uneven strength of the produced hot stamped part. For example, the length of the soaking section among the multiple sections provided in the heating furnace may be approximately 20 to 50% of the overall length of the heating furnace.

[0101] In one embodiment, the total heating time for the heating step (S200) is about 2 to 20 minutes. That is, the total time the blank remains in the heating furnace is about 2 to 20 minutes. If the total heating time for the heating step (S200) is about 2 minutes or less, the heating time is insufficient, and the resulting hot stamped part does not have the desired material properties. On the other hand, if the total heating time for the heating step (S200) is about 20 minutes or more, the heating time is too long, resulting in a decrease in production speed and reduced economic efficiency. Therefore, if the total heating time for the heating step (S200) is about 2 to 20 minutes, the resulting hot stamped part will have the desired material properties, and a decrease in the economic efficiency of the manufacturing process can be prevented or minimized.

[0102] 6, after the heating step (S200), a transfer step (S300) may be performed. In the transfer step (S300), the heated blank 100 may be transferred to a press die 400 (see FIG. 11). For example, the heated blank 100 may be removed from a heating furnace and then transferred to the press die 400.

[0103] In the transfer step (S300), the heated blank 100 may be cooled to ambient temperature (or room temperature). That is, the heated blank 100 may be air-cooled at ambient temperature during transfer. If the heated blank 100 is not air-cooled, the mold entry temperature (e.g., the forming start temperature) may become high, and wrinkles (or bends) may occur on the surface of the manufactured hot stamped part. In addition, since the use of a coolant may affect subsequent processes (hot stamping), it is desirable to air-cool the heated blank 100 during transfer.

[0104] 11 and 12 are cross-sectional views illustrating the forming / punching step of the manufacturing process of the hot stamped part according to one embodiment of the present invention. Specifically, Fig. 11 is a cross-sectional view of the blank and the press die before the forming / punching step is performed, and Fig. 12 is a cross-sectional view of the blank and the press die during the forming / punching step.

[0105] 6, 11, and 12, after the transfer step S300, a forming / punching step S400 may be performed. The forming / punching step S400 is a step of hot-forming the transferred blank 100 into the shape of a hot stamping part and forming a punched portion 110 in the transferred blank 100.

[0106] In one embodiment, the forming / punching step (S400) may be performed using a press die 400. The press die 400 may include a lower die 410, an upper die 420, and a punch 430. The lower die 410 may have a shape corresponding to the bottom surface of the hot stamping part. The upper die 420 faces the lower die 410 and may have a shape corresponding to the top surface of the hot stamping part. The press die 400 may include at least one punch 430, preferably at least two punches 430. In one embodiment, the punches 430 may include a first punch and a second punch. However, the present invention is not limited thereto. For example, the press die 400 may include one punch 430, or three or more punches 430.

[0107] Although not shown, if the press die 400 is equipped with only one punch 430, one foam bead may be formed on the edge of the blank 100 when the blank 100 is formed.

[0108] For example, as described below, a laser process or a cold drilling process may be performed using the perforation portion 110 formed through hot drilling. Specifically, the blank 100 may be placed on a jig using the perforation portion 110 formed through hot drilling as a guide pattern (or reference point), and then a subsequent process may be performed. Therefore, at least two perforation portions 110 may be formed in the blank 100 through hot drilling.

[0109] In one embodiment, the clearance between the punch 430 and the die (e.g., the lower die 410 and / or the upper die 420) is between about 5% and about 15%. If the clearance is less than about 5%, the punch 430 may be pinched between the dies due to thermal expansion of the dies. On the other hand, if the clearance is more than about 15%, the punch 430 may vibrate too violently, resulting in uneven quality, including grain flows on the sheared surfaces. For example, the uniformity of the grain flows may be reduced, such as grain flows being formed only in certain parts of the sheared surfaces. Therefore, if the clearance between the punch 430 and the die (e.g., the lower die 410 and / or the upper die 420) is about 5% to 15%, the punch 430 may be prevented from being pinched between the dies due to thermal expansion, and grain flows may be formed uniformly around the sheared surfaces.

[0110] In one embodiment, the blank 100 may be hot-formed in the forming / punching step (S400). The transferred (or heated) blank 100 may be hot-formed into the shape of the hot stamped part using a press die 400 including a lower die 410 and an upper die 420. Specifically, the blank 100 may be formed into the shape of the hot stamped part by pressing (e.g., hot pressing) the lower die 410, which has the shape of the bottom surface of the hot stamped part, with the upper die 420, which has the shape of the top surface of the hot stamped part.

[0111] In one embodiment, in the forming / punching step (S400), hot forming and hot punching may be performed simultaneously or sequentially. In one embodiment, in the forming / punching step (S400), hot punching may be performed on the blank 100 after hot forming of the blank 100 is completed (or started). Specifically, during hot forming of the blank 100 (or after hot forming is completed), a punch 430 included in the press die 400 may descend to perform hot punching on the blank 100, thereby forming the punched portion 110 in the hot stamped part 10 (or blank 100). For example, after the upper die 420 reaches the bottom dead center and hot forming of the blank 100 is completed (or after hot forming is started), the punch 430 may descend to perform hot punching on the blank 100, thereby forming the punched portion 110 in the hot stamped part 10 (or blank 100). That is, hot punching can be performed after hot forming is completed (or initiated), or hot forming and hot punching can be performed simultaneously.

[0112] Although not shown, the punch 430 may be raised and lowered by a hydraulic cylinder, although the present invention is not limited thereto.

[0113] In one embodiment, the forming start temperature at which the blank 100 begins to be hot-formed in the forming / punching step (S400) is between the Ms temperature and 750°C. If the blank 100 is hot-formed below the Ms temperature, a large load may be generated during hot forming, damaging the press die 400 and reducing the formability of the blank 100. The resulting hot-stamped part may not have the desired structure and physical properties. On the other hand, if the forming start temperature exceeds about 750°C, wrinkles (or warping) may occur on the surface of the resulting hot-stamped part. In addition, the coating layer may be burned onto the die. Therefore, if the forming start temperature is between about the Ms temperature and about 750°C, the formability of the hot-stamped steel sheet is improved, the resulting hot-stamped part has the desired structure and physical properties, and wrinkles (or warping) on ​​the surface of the resulting hot-stamped part may be prevented or minimized.

[0114] In one embodiment, the temperature of the blank 100 when hot punching is performed on the blank 100 in the forming / punching step (S400) is between about 200°C and about 700°C. If the temperature of the blank 100 during hot punching is less than about 200°C, a large load may be generated during hot punching, which may damage the press die 400 and / or punch 430. Meanwhile, since the heated blank 100 is air-cooled when it is removed from the heating furnace and transferred to the press die 400, the temperature of the blank 100 before hot punching is about 700°C or less. Furthermore, since hot punching is performed after hot forming of the heated blank 100 is completed (or started), the temperature of the blank 100 when hot punching is performed is lower than the temperature of the blank 100 when hot forming is performed. Therefore, when hot punching is performed in the forming / punching step (S400) when the temperature of the blank 100 is between about 200°C and about 700°C, the punched portion 110 can be formed in the blank 100 without damaging the press die 400 and / or punch 430.

[0115] In one embodiment, when the blank 100 is hot-formed using the press die 400, a first punch and a second punch included in the press die 400 may descend to form at least two perforations 110a and 110b in the blank 100. Specifically, during the process of hot-forming the blank 100 by pressing the lower die 410 and the blank 100 with the upper die 420, the first punch and the second punch may descend to form the first perforation 110a and the second perforation 110b in the hot-stamped part 10.

[0116] 11 and 12 show that the punch 430 included in the press die 400 descends to form the hole 110 in the blank 100, but the present invention is not limited thereto. Although not shown, the hole 110 may be formed in the blank 100 through a separately provided external device.

[0117] In one embodiment, the blank 100 may be cooled while being formed into a final part shape using the press die 400 (or during hot forming). The press die 400 may include cooling channels 440 through which a coolant circulates. For example, the lower die 410 and the upper die 420 may each include a cooling channel 440. Specifically, the cooling channels 440 may be disposed within the lower die 410 and the upper die 420 along the surfaces of the lower die 410 and the upper die 420. The heated blank 100 may be quenched by the coolant circulating through the cooling channels 440 provided in the press die 400. In this case, to prevent springback of the sheet material and maintain the desired shape, quenching may be performed while the press die 400 is closed and pressurized. During the forming and cooling operations, the heated blank 100 may be cooled to the martensite finish temperature at an average cooling rate of at least 10°C / s. Desirably, the cooling rate is at least 20°C / s or more.

[0118] The blank 100 may be held in the press die 400 for 3 to 20 seconds. For example, the press die 400 may be held in an engaged state for 3 to 20 seconds. If the holding time in the press die 400 is less than 3 seconds, the blank 100 may not be sufficiently cooled, and residual heat and temperature variations between regions may cause thermal deformation, resulting in reduced dimensional quality. On the other hand, if the holding time in the press die 400 exceeds 20 seconds, the holding time in the press die 400 may be too long, resulting in reduced productivity.

[0119] In one embodiment, the hot forming of the blank 100 and the cooling of the blank 100 are performed with the press die 400 in a closed state (or engaged state), and after a certain time has passed, the hot punching of the blank 100 may be performed.

[0120] In one embodiment, hot forming, hot punching, and cooling of the heated blank 100 occur simultaneously within the press die 400. For example, hot forming, hot punching, and cooling of the blank 100 may be performed simultaneously (or together) with the press die 400 in a closed (or interlocked) state.

[0121] Although not shown, a trimming step may be performed after the forming / punching step (S400). The trimming step is also a step of cutting off the outer periphery of the formed hot stamped part 10 using at least two punching portions 110a, 110b formed in the formed hot stamped part 10. That is, the trimming step is also a step of cutting off the outer periphery of the hot stamped part 10 using the two punching portions 110a, 110b formed in the hot stamped part 10 through hot punching.

[0122] In one embodiment, in the trimming step, the edge of the hot stamped component 10 may be cut using the at least two perforations 110a, 110b formed through hot punching as reference points (or guide patterns). That is, the hot stamped component 10 may be placed on a jig using the at least two perforations 110a, 110b formed in the molded hot stamped component 10, and the edge of the hot stamped component 10 may be cut. For example, after inserting fixing pins into the at least two perforations 110a, 110b formed in the hot stamped component 10, the outer periphery of the hot stamped component 10 may be cut.

[0123] In one embodiment, the trimming step may be performed using a laser or a press die (eg, a cold press die).

[0124] In a method for manufacturing a hot stamped part according to an embodiment of the present invention, after forming a hole 110 in a blank 100 through hot punching, an outer portion of the hot stamped part 10 may be cut off through cold trimming or laser trimming. That is, in a method for manufacturing a hot stamped part according to an embodiment of the present invention, a hot punching process may be performed on the blank 100, and after the blank 100 is cooled, cold trimming or laser trimming may be performed.

[0125] In one embodiment, a second drilling step may be performed after the forming / punching step (S400). The second drilling step is also a step of forming an additional drilling portion in the hot stamped component 10 using at least two drilling portions 110a, 110b formed in the hot stamped component 10. That is, the second drilling step is also a step of forming an additional drilling portion (e.g., an additional drilling portion) in the hot stamped component 10 using the two drilling portions 110a, 110b formed in the hot stamped component 10 through hot drilling.

[0126] In one embodiment, the second drilling step may be performed during the trimming step. For example, the second drilling step and the trimming step may be performed simultaneously. Alternatively, the second drilling step may be performed before or after the trimming step. For example, the second drilling step and the trimming step may be performed sequentially.

[0127] In a method for manufacturing a hot stamped part according to an embodiment of the present invention, after forming a hole 110 in the hot stamped part 10 through hot punching, a further hole (e.g., an additional hole) may be formed in the hot stamped part 10 through cold punching or laser punching. That is, in a method for manufacturing a hot stamped part according to an embodiment of the present invention, a hot punching process may be performed on a blank 100, and after the blank 100 has been subjected to the hot punching process, a cold punching process or a laser punching process may be performed.

[0128] In one embodiment, a portion of the outer periphery of the produced hot stamped part is also an edge of the coil blank, i.e., a portion of the outer periphery of the produced hot stamped part is also an edge of the coil blank in an uncut state.

[0129] In one embodiment, after the trimming step and / or the second punching step, a step of removing burrs formed on the blank may be performed, thereby removing burrs formed during processes such as hot punching, cold punching, and cold trimming.

[0130] Experimental Example The present invention will be described in more detail with reference to the following experimental examples. However, the following experimental examples are intended to further explain the present invention, and the scope of the present invention is not limited to 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.

[0131] [Table 1]

[0132] [Table 2]

[0133] [Table 3]

[0134] In Examples 1 to 11 and Comparative Examples 1 to 12, blanks were manufactured from slabs having the compositions shown in Table 1 under the following conditions: slab reheating temperature (SRT): 1,230°C, finish rolling temperature (FDT): 900°C, hot rolling reduction: 95%, coiling temperature (CT): 700°C, annealing heat treatment temperature: 780°C, and galvanizing immersion temperature: 660°C. The blanks were then heated at 950°C for 270 seconds, followed by hot forming, hot piercing, and cooling in a press die. In Tables 2 and 3, th1 is the thickness of the fracture surface 303, th2 is the thickness of the sheared surface 300, w1 is the width of the coating layer removal surface 304, and w2 is the width of the roll-over surface 301. In Tables 2 and 3, the values ​​(th1 / th2) of Equation 1 and the values ​​(w1 / w2) of Equation 2 are also the average values ​​measured at a minimum of four points at equal angles from the center of the perforation part 110. Also, in Table 3, room temperature may mean 30°C.

[0135] The hydrogen embrittlement evaluation was performed on the hot stamped parts (e.g., specimens) of Examples 1 to 11 and Comparative Examples 1 to 12 using a 4-point bending test in accordance with ASTM G39-99. The 4-point bending test is a test method in which a specimen is fabricated by simulating a condition in which the specimen is exposed to a corrosive environment, and stress below the elastic limit is applied to specific points on the specimen to check for the occurrence of stress corrosion cracking. In this case, stress corrosion cracking refers to cracking that occurs when corrosion and sustained tensile stress act simultaneously. Specifically, the hydrogen embrittlement evaluation results in Tables 2 and 3 were obtained by applying a stress of 1,000 MPa to each specimen in air for 100 hours and checking for the occurrence of fracture.

[0136] Referring to Table 2, it can be confirmed that no fracture occurs during hydrogen embrittlement evaluation when the value of thickness th1 of fracture surface 303 / thickness th2 of sheared surface 300 is 0.6 or less and simultaneously the value of width w1 of coating layer removed surface 304 / width w2 of rolled-over surface 301 is 0.6 or less. In other words, it can be confirmed that no fracture occurs during hydrogen embrittlement evaluation when the thickness th1 of fracture surface 303 and the thickness th2 of sheared surface 300 satisfy Equation 1 (th1 / th2≦0.6) and the width w1 of coating layer removed surface 304 and the width w2 of rolled-over surface 301 satisfy Equation 2 (w1 / w2≦0.6).

[0137] However, referring to Table 3, if the value of thickness th1 of fracture surface 303 / thickness th2 of sheared surface 300 exceeds 0.6 or the value of width w1 of coating layer removed surface 304 / width w2 of rolled-over surface 301 exceeds 0.6, it can be confirmed that fracture has occurred during hydrogen embrittlement evaluation. In other words, if the thickness th1 of fracture surface 303 and the thickness th2 of sheared surface 300 do not satisfy Equation 1 (th1 / th2≦0.6) or the width w1 of coating layer removed surface 304 and the width w2 of rolled-over surface 301 do not satisfy Equation 2 (w1 / w2≦0.6), it can be confirmed that fracture has not occurred during hydrogen embrittlement evaluation.

[0138] Therefore, when the ratio of the thickness th1 of the fracture surface 303 to the thickness th2 of the sheared surface 300 of the hot stamped part 10 is 0.6 or less and the ratio of the width w1 of the coating layer removal surface 304 to the width w2 of the rolled-over surface 301 is 0.6 or less, no fracture occurs during the hydrogen embrittlement evaluation, confirming that the part has excellent hydrogen embrittlement resistance. In other words, when the thickness th1 of the fracture surface 303 and the thickness th2 of the sheared surface 300 satisfy Equation 1 (th1 / th2≦0.6) and the width w1 of the coating layer removal surface 304 and the width w2 of the rolled-over surface 301 satisfy Equation 2 (w1 / w2≦0.6), no fracture occurs during the hydrogen embrittlement evaluation, confirming that the part has excellent hydrogen embrittlement resistance.

[0139] Although the present invention has been described based on the embodiments shown in the drawings, these are merely illustrative, and those skilled in the art will recognize that various modifications and equivalent embodiments are possible. Therefore, the true technical scope of the present invention should be determined by the technical spirit of the claims.

Claims

1. A hot stamped part having a hole formed therein, A base material and an interdiffusion layer disposed on the base material; a plating layer disposed on the interdiffusion layer, The hot stamped component includes a sheared surface formed on an edge of the punched portion, The sheared surface includes a rollover surface, a shear surface, and a fracture surface; A hot stamped part, wherein the thickness th1 of the fracture surface and the thickness th2 of the sheared surface satisfy the following formula 1. <Formula 1> th1 / th2≦0.6

2. The hot stamped part according to claim 1 , wherein the roll-over surface, the shear surface, and the fracture surface are provided sequentially in a thickness direction of the hot stamped part.

3. The hot stamped part of claim 1 , wherein the thickness of the sheared surface is the sum of the thickness of the fracture surface, the thickness of the sheared surface, and the thickness of the roll-over surface.

4. 2. The hot stamped component of claim 1, wherein the thickness of the fracture surface is the shortest distance in the thickness direction of the hot stamped component from the start of the fracture surface to the end of the fracture surface.

5. 2. The hot stamped component of claim 1, wherein the thickness of the sheared surface is the shortest distance in the thickness direction of the hot stamped component from the start of the rollover surface to the end of the fracture surface.

6. The hot stamped component according to claim 1 , further comprising a plated layer-removed surface where at least a portion of the upper surface of the intermixed layer is exposed.

7. 7. The hot stamped part according to claim 6, wherein the width w1 of the plating layer removal surface and the width w2 of the roll-over surface satisfy the following formula 2: <Formula 2> w1 / w2≦0.6

8. The hot stamped part according to claim 1 , wherein the number of the holes is at least two.

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