HOT-STAMPED COMPONENT

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of International Application No. PCT/KR2023/003607 filed on Mar. 17, 2023, which claims under 35 U.S.C. § 119 (a) the benefit of Korean Patent Application No. 10-2022-0190990 filed on Dec. 30, 2022, the entire contents of which applications are incorporated by reference herein.

FIELD

The present disclosure relates to a hot-stamped component.

BACKGROUND

As environmental regulations and fuel efficiency regulations have become stricter worldwide, the need for lighter vehicle materials has increased. Accordingly, research and development of ultra-high-strength steel and hot stamping steel have been actively conducted.

Hot stamping includes heating a steel sheet to a high temperature in a furnace and then simultaneously forming and rapidly cooling the steel sheet in a press to manufacture a high-strength component. In addition, a piercing process may be performed to form/process a hole in the high-strength component.

The piercing process is performed using equipment such as a laser device or a press die, however, the use of a laser device may increase the processing time and the use of a press die may result in degradation of the quality of a shear surface.

SUMMARY

In aspects, embodiments of the present disclosure may provide a hot-stamped component with excellent resistance to hydrogen embrittlement.

In aspects, an embodiment of the present disclosure provides a hot-stamped component having a pierced portion formed therein, the hot-stamped component including: a base material; an interdiffusion layer arranged on the base material; and a plating layer arranged on the interdiffusion layer, wherein the hot-stamped component includes a shearing-processed surface formed at an edge of the pierced portion, the shearing-processed surface includes a rollover surface, a shear surface, and a fracture surface, and a thickness th1 of the fracture surface and a thickness th2 of the shearing-processed surface satisfy the following Equation 1:

th ⁢ 1 / th ⁢ 2 ≤ 0 . 6 . < Equation ⁢ 1 >

In the present embodiment, the rollover surface, the shear surface, and the fracture surface suitably may be sequentially arranged in a thickness direction of the hot-stamped component.

In an embodiment, the thickness of the shearing-processed surface suitably may be a sum of the thickness of the fracture surface, a thickness of the shear surface, and a thickness of the rollover surface.

In an embodiment, the thickness of the fracture surface suitably may be a shortest distance in the thickness direction of the hot-stamped component from a starting point of the fracture surface to an end point of the fracture surface.

In an embodiment, the thickness of the shearing-processed surface suitably may be a shortest distance in the thickness direction of the hot-stamped component from a starting point of the rollover surface to an end point of the fracture surface.

In an embodiment, the hot-stamped component suitably may further include a plating layer delamination surface on which at least a portion of an upper surface of the interdiffusion layer is exposed.

In an embodiment, a width w1 of the plating layer delamination surface and a width w2 of the rollover surface suitably may satisfy the following Equation 2:

w ⁢ 1 / w ⁢ 2 ≤ 0 . 6 . < Equation ⁢ 2 >

In an embodiment, the pierced portion suitably may include at least two pierced portions.

Other aspects, features, and advantages than those described above will become clear from the following detailed description, claims, and drawings for carrying out the present disclosure.

According to an embodiment of the present disclosure as described above, a hot-stamped component having excellent resistance to hydrogen embrittlement may be provided. However, the scope of the present disclosure is not limited by the above effects.

BRIEF DESCRPTION OF THE DRAWINGS

FIG. 1 is a perspective view schematically illustrating a hot-stamped component according to an embodiment of the present disclosure.

FIG. 2 is a cross-sectional view schematically illustrating a hot-stamped component according to an embodiment of the present disclosure.

FIG. 3 is an enlarged view of portion A of FIG. 2.

FIG. 4A is a side view of a pierced portion of a hot-stamped component according to an embodiment of the present disclosure.

FIG. 4B is a front view of a pierced portion of a hot-stamped component according to an embodiment of the present disclosure.

FIG. 4C is an enlarged view of a portion of FIG. 4A.

FIG. 5A is a side view of a pierced portion of a hot-stamped component according to a comparative example.

FIG. 5B is a front view of a pierced portion of a hot-stamped component according to a comparative example.

FIG. 5C is an enlarged view of a portion of FIG. 5A.

FIG. 6 is a flowchart schematically illustrating a method of manufacturing a hot-stamped component, according to an embodiment of the present disclosure.

FIG. 7 is a flowchart schematically illustrating a preparation operation of a method of manufacturing a hot-stamped component, according to an embodiment of the present disclosure.

FIG. 8 is a plan view schematically illustrating a blank according to an embodiment of the present disclosure.

FIG. 9 is a flowchart schematically illustrating a heating operation of a method of manufacturing a hot-stamped component, according to an embodiment of the present disclosure.

FIG. 10 is a diagram for describing a heating furnace having a plurality of sections for a heating operation of a method of manufacturing a hot-stamped component, according to an embodiment of the present disclosure.

FIGS. 11 and 12 are cross-sectional views for describing a forming/piercing operation of a process of manufacturing a hot-stamped component, according to an embodiment of the present disclosure.

DETAILED DESCRIPTION

As the present disclosure allows for various changes and numerous embodiments, particular embodiments will be illustrated in the drawings and described in detail. Advantages and features of the present disclosure and a method of achieving the same should become clear with embodiments described below in detail with reference to the drawings. However, the present disclosure is not limited to the embodiments disclosed below, but may be implemented in various forms.

In the following embodiments, terms such as “first,” “second,” etc., are used only to distinguish one component from another, and such components must not be limited by these terms.

In the following embodiments, the singular expression also includes the plural meaning as long as it is not inconsistent with the context.

In the following embodiments, the terms “comprises,” “includes,” “has”, and the like used herein specify the presence of stated features or components, but do not preclude the presence or addition of one or more other features or components.

For convenience of descriptions, the magnitude of components in the drawings may be exaggerated or reduced. For example, because the size and thickness of each component illustrated in the drawings are arbitrarily shown for convenience of descriptions, the present disclosure is not necessarily limited to those illustrated in the drawing.

In a case in which a particular embodiment is realized otherwise, a particular process may be performed out of the order described. For example, two processes, which are successively described herein, may be substantially simultaneously performed, or may be performed in a process sequence opposite to a described process sequence.

In the present specification, “A and/or B” indicates A, B, or both A and B. In addition, “at least one of A and B” indicates A, B, or both A and B.

Hereinafter, embodiments of the present disclosure will be described in detail with reference to the accompanying drawings, and the same or corresponding components will be denoted by the same reference numerals when described with reference to the accompanying drawings, and thus, their descriptions that are already provided will be omitted.

FIG. 1 is a perspective view schematically illustrating a hot-stamped component according to an embodiment of the present disclosure.

Referring to FIG. 1, a hot-stamped component 10 according to an embodiment of the present disclosure may include pierced portions 110. In an embodiment, the hot-stamped component 10 may include two pierced portions 110. The pierced portions 110 may include a first pierced portion 110a and a second pierced portion 110b. However, the present disclosure is not limited thereto. The hot-stamped component 10 may include one pierced portion 110, or three or more pierced portions 110.

Although not illustrated, the hot-stamped component 10 may include an additional pierced portion, in addition to the pierced portions 110. In this case, the pierced portions 110 may be formed by hot piercing, and the additional pierced portion may be formed by cold piercing or laser piercing. The hot-stamped component 10 may include one or more additional pierced portions.

In an embodiment, an additional pierced portion may be formed by using the pierced portion 110. This will be described in more detail below.

In addition, although not illustrated, the hot-stamped component 10 may include an edge portion. In this case, the edge portion of the hot-stamped component 10 may refer to a surface extending along a long side of the hot-stamped component 10.

FIG. 2 is a cross-sectional view schematically illustrating a hot-stamped component according to an embodiment of the present disclosure, and FIG. 3 is an enlarged view of portion A of FIG. 2. In detail, FIG. 2 is a cross-sectional view schematically illustrating a pierced portion of a hot-stamped component according to an embodiment of the present disclosure.

Referring to FIGS. 2 and 3, in an embodiment, the hot-stamped component 10 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 arranged in a thickness direction of the hot-stamped component 10. Here, the thickness direction of the hot-stamped component 10 may be defined as a vertical direction, and a direction intersecting the thickness direction may be defined as a horizontal direction.

In an embodiment, the hot-stamped component 10 may include a shearing-processed surface 300 formed at an edge of the pierced portion 110. The shearing-processed surface 300 may include a rollover surface 301, a shear surface 302, and a fracture surface 303.

In an embodiment, the rollover surface 301 may be a surface on which a droop or an impression has occurred. As will be described below, during a shearing process (or during hot piercing), the descent of a punch may cause a blank to be plastically deformed, resulting in a droop, and this may, in turn, form a curvature on the uppermost surface of the base material 200 that forms the upper surface in the horizontal direction. Here, the surface having the curvature formed on the uppermost surface of the base material 200 may correspond to the rollover surface 301. The rollover surface 301 may extend from the point where the curvature begins to form on the uppermost surface of the base material 200 to the point where the shear surface 302 begins.

In an embodiment, the shear surface 302 may be a surface extending in the vertical direction or at a certain angle with respect to the vertical direction. As will be described below, as the punch continuously descends in the vertical direction, the droop of the blank may end, and the punch and the blank may come into direct contact with each other to initiate shearing (or piercing), and as the shearing (or piercing) proceeds, the shear surface 302 may be formed in the vertical direction. For example, the curvature on the uppermost surface of the base material 200 may disappear, and a linear shear surface 302 may be formed in the vertical direction or a direction at a certain angle with respect to the vertical direction. The shear surface 302 may extend from the point where the rollover surface 301 ends to the point where the fracture surface 303 begins. In an embodiment, the fracture surface 303 may be a surface formed by the fracture of the blank. As will be described below, as the punch descends in the vertical direction, the fracture surface 303 may be formed as at least a portion of the blank breaks away. The fracture surface 303 is formed by the fracture of at least a portion of the blank, and thus may be irregular compared to the shear surface 302. The fracture surface 303 may extend from the point where the irregularity compared to the shear surface 302 begins, to an end point of the fracture surface 303 or an end point of the base material 200.

In an embodiment, the shear surface 302 is a portion that directly rubs against the punch, and due to this direct friction, the shear surface 302 may form a glossy surface when viewed from the front. In addition, the fracture surface 303 is a portion where the blank has been irregularly broken off, and may have a rough surface. Thus, because the shear surface 302 has a smooth surface while the fracture surface 303 has an irregular surface, the boundary between the shear surface 302 and the fracture surface 303 may be readily distinguished.

In an embodiment, a plating layer delamination surface 304 may be a surface from which at least a portion of the plating layer 220 has been removed. During a hot-stamping heat treatment, the interdiffusion layer 210 may be formed by the alloying of the base material 200 and the plating layer 220. Here, during hot piercing, at least a portion of the plating layer 220 arranged on the upper surface of the interdiffusion layer 210 may be delaminated (or removed). The plating layer delamination surface 304 may be defined as a surface from which at least a portion of the plating layer 220 arranged on the upper surface of the interdiffusion layer 210 has been delaminated (or removed). The plating layer delamination surface 304 may extend from the point where the plating layer 220 meets the upper surface of the interdiffusion layer 210 that is exposed as at least a portion of the plating layer 220 has been removed, to the point where the shear surface 302 begins.

In an embodiment, a thickness th1 of the fracture surface 303 may be defined as the shortest distance in the vertical direction from the boundary between the shear surface 302 and the fracture surface 303 to an end point of the base material 200. In other words, the thickness th1 of the fracture surface 303 may be defined as the shortest distance between a first virtual line (or a first virtual plane), which passes through the boundary between the shear surface 302 and the fracture surface 303 and extends in the horizontal direction, and a second virtual line (or a second virtual plane), which passes through the end point of the base material 200 and extends in the horizontal direction. Here, the end point of the base material 200 may refer to the point where the fracture surface 303 ends.

In an embodiment, a thickness th3 of the shear surface 302 may be defined as the shortest distance in the vertical direction from the boundary between the rollover surface 301 and the shear surface 302 to the boundary between the shear surface 302 and the fracture surface 303. In other words, the thickness th3 of the shear surface 302 may be defined as the shortest distance between a third virtual line (or a second virtual plane), which passes through the starting point of the shear surface 302 and extends in the horizontal direction, and a fourth virtual line (or a fourth virtual plane), which passes through the boundary between the shear surface 302 and the fracture surface 303 and extends in the horizontal direction.

In an embodiment, a thickness th4 of the rollover surface 301 may be defined as the shortest distance in the vertical direction from the point where the curvature of the base material 200 begins to the point where the shear surface 302 begins. In other words, the thickness th4 of the rollover surface 301 may be defined as the shortest distance between a fifth virtual line (or a fifth virtual plane), which is tangent to the upper surface of the base material 200 and extends in the horizontal direction, and a sixth virtual line (or a sixth virtual plane), which passes through the point where the shear surface 302 begins, and extends in the horizontal direction.

In an embodiment, a thickness th2 of the shearing-processed surface 300 may be defined as the shortest distance in the vertical direction from the point where the curvature of the base material 200 begins to the end point of the base material 200. In other words, the thickness th2 of the shearing-processed surface 300 may be defined as the shortest distance between the fifth virtual line (or the fifth virtual plane), which is tangent to the upper surface of the base material 200 and extends in the horizontal direction, and the second virtual line (or the second virtual plane), which passes through the end point of the base material 200 and extends in the horizontal direction. For example, the thickness th2 of the shearing-processed surface 300 may be the sum of the thickness th1 of the fracture surface 303, the thickness th3 of the shear surface 302, and the thickness th4 of the rollover surface 301.

In an embodiment, a width w1 of the plating layer delamination surface 304 may be defined as the shortest distance in the horizontal direction from the point where the plating layer 220 meets the upper surface of the interdiffusion layer 210 that is exposed as at least a portion of the plating layer 220 has been removed, to the point where the shear surface 302 begins. In other words, the width w1 of the plating layer delamination surface 304 may be defined as the shortest distance between a seventh virtual line (or a seventh virtual plane), which passes through the point where the plating layer 220 meets the upper surface of the interdiffusion layer 210 that is exposed as at least a portion of the plating layer 220 has been removed, and extends in the vertical direction, and an eighth virtual line (or an eighth virtual plane), which passes through the point where the shear surface 302 begins, and extends in the vertical direction.

In an embodiment, a width w2 of the rollover surface 301 may be defined as the shortest distance in the horizontal direction from the point where the curvature of the base material 200 begins to the point where the shear surface 302 begins. In other words, the width w2 of the rollover surface 301 may be defined as the shortest distance between a ninth virtual line (or a ninth virtual plane), which passes through the point where the curvature of the base material 200 begins, and extends in the vertical direction, and the eighth virtual line (or the eighth virtual plane), which passes through the point where the shear surface 302 begins, and extends in the vertical direction.

When the temperature of the blank increases, flow stress may decrease, and when stress acting on the blank decreases, resistance to hydrogen embrittlement may be enhanced.

In an embodiment, as will be described below, compared to cold piercing performed at about 30° C. (e.g., room temperature), performing hot piercing at a relatively high temperature may reduce the shear stress acting on the blank, thereby enhancing the resistance to hydrogen embrittlement.

FIG. 4A is a side view of a pierced portion of a hot-stamped component according to an embodiment of the present disclosure, FIG. 4B is a front view of a pierced portion of a hot-stamped component according to an embodiment of the present disclosure, and FIG. 4C is an enlarged view of a portion of FIG. 4A.

In addition, FIG. 5A is a side view of a pierced portion of a hot-stamped component according to a comparative example, FIG. 5B is a front view of a pierced portion of a hot-stamped component according to a comparative example, and FIG. 5C is an enlarged view of a portion of FIG. 5A.

In detail, FIGS. 4A, 4B, and 4C correspond to a case in which hot piercing is performed, and FIGS. 5A, 5B, and 5C correspond to a case in which cold piercing is performed.

Referring to FIGS. 4A, 4B, 4C, 5A, 5B, and 5C, it may be seen that the width w2 of the rollover surface 301 in the case of hot piercing is greater than a width w2′ of a rollover surface 301′ in the case of cold piercing. In addition, it may be seen that the width w1 of the plating layer delamination surface 304 in the case of hot piercing is less than a width w1′ of a plating layer delamination surface 304′ in the case of cold piercing. Thus, when hot piercing is performed, compared to when cold piercing is performed, the width w2 of the rollover surface 301 may increase, and the width w1 of the plating layer delamination surface 304 may decrease. That is, compared to a case in which piercing is performed when the blank is at a low temperature, in a case in which piercing is performed when the blank is at a high temperature, the width w2 of the rollover surface 301 may be greater, and the width w1 of the plating layer delamination surface 304 may be less.

It may be seen that the shear surface fraction is larger and the fracture surface fraction is smaller in the case of hot piercing than in the case of cold piercing. In detail, it may be seen that the thickness th3 of the shear surface 302 in the case of hot piercing is greater than a thickness th3′ of a shear surface 302′ in the case of cold piercing. In addition, it may be seen that the thickness th1 of the fracture surface 303 in the case of hot piercing is less than a thickness th1′ of a fracture surface 303′ in the case of cold piercing. From this, it may be seen that, in the case of hot piercing, the proportion of the shear surface 302 within the shearing-processed surface 300 is greater, and the proportion of the fracture surface 303 is less, than in the case of cold piercing.

It may be seen that, in the case of hot piercing, the proportion of the rollover surface 301 within the shearing-processed surface 300 is greater than in the case of cold piercing. In detail, it may be seen that the thickness th4 of the rollover surface 301 in the case of hot piercing is greater than a thickness th4′ of the rollover surface 301′ in the case of cold piercing. From this, it may be seen that the thickness th4 of the rollover surface 301 in the case of hot piercing increases compared to the case of cold piercing.

As the shear stress acting on a blank 100 during piercing increases, the proportion of the fracture surface 303 within the shearing-processed surface 300 may increase. In detail, 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 shear surface 302 may decrease. A large thickness th1 of the fracture surface 303 may indicate that the shear stress acting on the blank is large, and the large shear stress may induce hydrogen embrittlement in the pierced portion 110. Thus, to enhance the resistance to hydrogen embrittlement of the hot-stamped component 10, it is necessary to reduce the thickness th1 of the fracture surface 303 to a certain level or less.

In addition, as the shear stress acting on the blank increases, the width w1 of the plating layer delamination surface 304 may increase, and the width w2 of the rollover surface 301 may decrease. Thus, to enhance the resistance to hydrogen embrittlement of the hot-stamped component 10, it is necessary to decrease the width w1 of the plating layer delamination surface 304 and increase the width w2 of the rollover surface 301.

Accordingly, the present inventor, through extensive experimentation, has derived Equation 1 and Equation 2, which allow the hot-stamped component 10 to have excellent resistance to hydrogen embrittlement. In an embodiment, the hot-stamped component 10 may satisfy Equation 1 and Equation 2. In detail, for the hot-stamped component 10, the thickness th1 of the fracture surface 303 and the thickness th2 of the shearing-processed surface 300 may satisfy Equation 1, and the width w1 of the plating layer delamination surface 304 and the width w2 of the rollover surface 301 may satisfy Equation 2.

th ⁢ 1 / th ⁢ 2 ≤ 0.6 < Equation ⁢ 1 > w ⁢ 1 / w ⁢ 2 ≤ 0.6 < Equation ⁢ 2 >

In an embodiment, the value of (thickness th1 of fracture surface 303/thickness th2 of shearing-processed surface 300) may be an average of values of (thickness th1 of fracture surface 303/thickness th2 of shearing-processed surface 300) measured at four or more points at equiangular intervals from the center of the pierced portion 110.

In an embodiment, the value of (width w1 of plating layer delamination surface 304/width w2 of rollover surface 301) may be an average of values of (width w1 of plating layer delamination surface 304/width w2 of rollover surface 301) measured at four or more points at equiangular intervals from the center of the pierced portion 110.

In cold piercing, as the clearance decreases, the fracture surface fraction may also decrease. That is, in cold piercing, as the clearance decreases, the proportion of the thickness th1 of the fracture surface 303 within the thickness th2 of the shearing-processed surface 300 may decrease. However, when the clearance decreases, the shear stress acting on the blank may increase. Thus, the shear stress and the fracture surface fraction may be inversely proportional.

In the case of hot piercing, because piercing is performed at a relatively higher temperature than in cold piercing, the shear stress acting on the blank may be reduced, and the fracture surface fraction may also be reduced.

In addition, when piercing is performed at a high temperature, the length of the plating layer 220 delaminating around the pierced portion 110 may be reduced. In addition, as the temperature of the blank increases and as the clearance increases, the stress acting on the blank may decrease, and accordingly, the area of the rollover surface 301 and the width w1 of the rollover surface 301 may also increase.

A large fraction of the fracture surface 303 may indicate that a large shear stress has acted on the pierced portion 110 during hot piercing, and when a large shear stress acts on the pierced portion 110, hydrogen embrittlement may occur in a portion of the hot-stamped component 10 adjacent to the pierced portion 110. That is, a large thickness th1 of the fracture surface 303 may indicate that a large shear stress has acted on the pierced portion 110 during hot piercing, and when a large shear stress acts on the pierced portion 110, hydrogen embrittlement may occur in a portion adjacent to the pierced portion 110.

When the thickness th1 of the fracture surface 303 and the thickness th2 of the shearing-processed surface of the hot-stamped component 10 do not satisfy Equation 1, hydrogen embrittlement may occur in a portion adjacent to the pierced portion 110. In detail, that the value of (thickness th1 of fracture surface 303/thickness th2 of shearing-processed surface 300) in the hot-stamped component 10 is greater than 0.6 may mean that the fraction of the fracture surface 303 within the shearing-processed surface 300 is large, which means that a large shear stress has acted on the pierced portion 110 during piercing, and this may cause hydrogen embrittlement in a portion of the hot-stamped component 10 adjacent to the pierced portion 110.

Thus, when the thickness th1 of the fracture surface 303 and the thickness th2 of the shearing-processed surface 300 of the hot-stamped component 10 satisfy Equation 1, the occurrence of hydrogen embrittlement in a portion adjacent to the pierced portion 110 may be prevented or minimized.

When the shear stress applied to the blank during piercing increases, hydrogen embrittlement may occur around the pierced portion 110. In addition, when the shear stress applied to the blank during piercing increases, the delamination of the plating layer 220 around the pierced portion 110 may increase, and the length (or area) of the rollover surface 301 may decrease. In detail, when the shear stress applied to the blank during piercing increases, the width w1 of the plating layer delamination surface 304 may increase, and the width w2 of the rollover surface 301 may decrease.

When the width w1 of the plating layer delamination surface 304 and the width w2 of the rollover surface 301 of the hot-stamped component 10 do not satisfy Equation 2, hydrogen embrittlement may occur in a portion adjacent to the pierced portion 110. In detail, for the value of (width w1 of plating layer delamination surface 304/width w2 of rollover surface 301) in the hot-stamped component 10 to be greater than 0.6, the width w1 of the plating layer delamination surface 304 needs to increase, or the width w2 of the rollover surface 301 needs to decrease. An increase in the width w1 of the plating layer delamination surface 304 or a decrease in the width w2 of the rollover surface 301 means that a large shear stress has acted on the pierced portion 110, and thus, that the value of (width w1 of plating layer delamination surface 304/width w2 of rollover surface 301) in the hot-stamped component 10 is greater than 0.6 means that a large shear stress has acted on the pierced portion 110 during piercing, and accordingly, hydrogen embrittlement may occur in a portion of the hot-stamped component 10 adjacent to the pierced portion 110.

Thus, when the width w1 of the plating layer delamination surface 304 and the width w2 of the rollover surface 301 of the hot-stamped component 10 satisfy Equation 2, the occurrence of hydrogen embrittlement in a portion adjacent to the pierced portion 110 may be prevented or minimized.

Hereinafter, a method of manufacturing a hot-stamped component will be described.

FIG. 6 is a flowchart schematically illustrating a method of manufacturing a hot-stamped component, according to an embodiment of the present disclosure.

Referring to FIG. 6, a method of manufacturing a hot-stamped component according to an embodiment may include a preparation operation S100, a heating operation S200, a transfer operation S300, and a forming/piercing operation S400.

FIG. 7 is a flowchart schematically illustrating a preparation operation of a method of manufacturing a hot-stamped component, according to an embodiment of the present disclosure, and FIG. 8 is a plan view schematically illustrating a blank according to an embodiment of the present disclosure.

Referring to FIGS. 7 and 8, the preparation operation S100 may be an operation of preparing the blank 100 for hot stamping. In an embodiment, the preparation operation S100 may include a hot rolling operation S110, a cooling/coiling operation S120, a cold rolling operation S130, an annealing operation S140, a plating operation S150, and a cutting operation S160.

First, an operation of reheating a steel slab may be performed. In the operation of reheating the steel slab, the steel slab obtained through a continuous casting process may be reheated at a certain temperature such that components segregated during casting may be re-dissolved. In an embodiment, a slab reheating temperature (SRT) may be about 1,200° C. to about 1,400° C. When the SRT is less than about 1,200° C., it may be difficult to achieve significant homogenization of alloying elements or significant dissolution of titanium (Ti), because the elements segregated during casting may not be sufficiently re-dissolved. Although a higher SRT is advantageous for homogenization, when the SRT is greater than about 1,400° C., it may be difficult to achieve desired strength due to an increase in austenite grain size, and the manufacturing cost of the steel sheet may also increase due to an excessive heating process.

In the hot rolling operation S110, the reheated steel sheet may be hot-rolled at a certain finishing delivery temperature. A hot-rolled steel sheet may be manufactured through the hot rolling operation S110. In an embodiment, a finishing delivery temperature (FDT) may be about 880° C. to about 950° C. Here, when the FDT is less than about 840° C., it may be difficult to secure the workability of the steel sheet due to the occurrence of a duplex grain structure due to rolling over an abnormal area, the workability may deteriorate due to microstructural non-uniformity, and a passing ability issue may occur during hot rolling due to a rapid phase change. When the FDT is greater than about 950° C., austenite grains may be coarsened, and TiC precipitates may be coarsened, which may degrade the performance of the hot-stamped component.

In the cooling/coiling operation S120, the hot-rolled steel sheet may be cooled to a certain coiling temperature (CT) and then coiled. In an embodiment, the CT in the cooling/coiling operation S120 may be about 550° C. to about 800° C. The CT affects the redistribution of carbon, and when the CT is less than about 550° C., the strength may increase due to a high fraction of a low-temperature phase caused by overcooling, the rolling load during cold rolling may be intensified, and the ductility may be rapidly degraded. On the contrary, when the coiling temperature is greater than about 800° C., deterioration of formability and strength may occur due to abnormal grain growth or excessive grain growth.

In the cold rolling operation S130, the coiled hot-rolled steel sheet may be uncoiled, pickled, and then cold-rolled. Here, the pickling may be performed for the purpose of removing scale from the coiled hot-rolled steel sheet, that is, a hot-rolled coil manufactured through the hot rolling process. A cold-rolled steel sheet may be manufactured through the cold rolling operation S130.

In the annealing operation S140, the cold-rolled steel sheet may be annealed at a temperature of about 700° C. or higher. For example, the annealing operation S140 may include an operation of heating the cold-rolled steel sheet and cooling the heated cold-rolled steel sheet at a certain cooling rate. In the annealing operation S140, the cold-rolled steel sheet may be annealed. The annealing operation S140 may be performed in an annealing furnace.

In an embodiment, the annealing temperature for the cold-rolled steel sheet may be about 750° C. to about 900° C. When the annealing temperature for the cold-rolled steel sheet is less than about 750° C., a desired structure may not be obtained, and recrystallization may not be sufficiently completed. On the contrary, when the annealing temperature for the cold-rolled steel sheet is greater than about 900° C., the efficiency of the manufacturing process may be degraded because the annealing temperature is too high. Thus, when the annealing temperature for the cold-rolled steel sheet is about 750° C. to about 900° C., a desired structure may be obtained, recrystallization may be sufficiently completed, and the efficiency of the manufacturing process may be improved.

The plating operation S150 may be an operation of forming a plating layer on the annealed cold-rolled steel sheet. In an embodiment, a plating layer may be formed on the annealed cold-rolled steel sheet through the plating operation S150. Here, the plating layer may include a zinc (Zn)-based plating layer or an aluminum (AI)-based plating layer.

In detail, in the plating operation S150, the annealed cold-rolled steel sheet may be immersed in a plating bath. Here, the plating bath may be maintained at a temperature of about 400° C. to about 700° C. The plating adhesion amount of the plating layer may be about 40 g/m² to about 200 g/m² per opposite sides of the cold-rolled steel sheet. After the plating operation S150, the cold-rolled steel sheet on which the plating layer has been formed may be coiled into a coil shape.

Although FIG. 7 illustrates that the cold rolling operation S130, the annealing operation S140, and the plating operation S150 are performed after the cooling/coiling operation S120, the present disclosure is not limited thereto. At least one of the cold rolling operation S130, the annealing operation S140, and the plating operation S150 may be omitted. For example, the cold rolling operation S130 and the annealing operation S140 may be omitted. In this case, after the plating operation S150, the hot-rolled steel sheet on which the plating layer has been formed may be coiled into a coil shape.

Subsequently, in the cutting operation S160, the coiled steel sheet (e.g., a cold-rolled steel sheet or a hot-rolled steel sheet) may be uncoiled and then cut into the blank 100 by using a laser or a cold press die. Here, the blank 100 may include an outer portion (or an edge) of the coil. For example, the blank 100 may include an outer portion (or an edge) of the steel sheet.

Referring to FIG. 6, after the preparation operation S100 of preparing the blank 100, the heating operation S200 of heating the blank 100 may be performed. The heating method in the heating operation S200 may be direct heating or indirect heating. The heating operation S200 may use any one of direct heating and indirect heating, or a combination thereof.

In an embodiment, in the heating operation S200, the blank 100 may be heated in a heating furnace. The heating furnace may be provided with a single section with a single temperature range (or a single temperature), or with a plurality of sections with different temperature ranges. In a case in which the heating furnace is provided with a single section with a single temperature range, the blank 100 may be heated to a target temperature within the single temperature range in the heating furnace. Here, the target temperature may be Ac3 to about 1,000° C. That is, the blank 100 may be heated in a heating furnace with a temperature range of Ac3 to about 1,000° C. until the temperature of the blank 100 reaches Ac3 to about 1,000° C.

On the contrary, in a case in which the heating furnace is provided with a plurality of sections with different temperature ranges, the blank 100 may be heated to a target temperature across the different temperature ranges in the heating furnace.

FIG. 9 is a flowchart schematically illustrating a heating operation of a method of manufacturing a hot-stamped component, according to an embodiment of the present disclosure, and FIG. 10 is a diagram for describing a heating furnace having a plurality of sections for a heating operation of a method of manufacturing a hot-stamped component, according to an embodiment of the present disclosure.

Referring to FIGS. 9 and 10, in the heating operation S200, the blank 100 (see FIG. 8) may be heated in a heating furnace having a plurality of sections with different temperature ranges. As illustrated in FIG. 9, the heating operation S200 may include a multi-stage heating operation S210 and a soaking operation S220. The multi-stage heating operation S210 and the soaking operation S220 may be operations in which the blank 100 is heated while passing through the plurality of sections provided in the heating furnace.

In an embodiment, the overall temperature of the heating furnace may be about 680° C. to about 1,000° C. In detail, the overall temperature of the heating furnace in which the multi-stage heating operation S210 and the soaking operation S220 are performed may be from about 680° C. to about 1,000° C. Here, the temperature of the heating furnace at which the multi-stage heating operation S210 is performed may be about 680° C. to about Ac3, and the temperature of the heating furnace at which the soaking operation S220 is performed may be about Ac3 to about 1,000° C.

In the multi-stage heating operation S210, the blank 100 may be heated stepwise (or may increase in temperature) while passing through the plurality of sections provided in the heating furnace. Among the plurality of sections provided in the heating furnace, there may be a plurality of sections in which the multi-stage heating operation S210 is performed, and the temperature of each section may be set such that the temperature increases from the inlet of the heating furnace into which the blank is fed, toward the outlet of the heating furnace from which the blank is discharged, and thus, the blank may be heated (or may increase in temperature) in stages.

The soaking operation S220 may be performed after the multi-stage heating operation S210. In the soaking operation S220, the blank that has undergone multi-stage heating may be heated (or soaked) while passing through sections of the heating furnace that are set to a temperature of about Ac3 to about 1,000° C. Among the plurality of sections provided in the heating furnace, there may be at least one section in which the soaking operation S220 is performed.

A heating furnace according to an embodiment may include a plurality of sections having different temperature ranges. In detail, the heating furnace may include a first section P₁ having a first temperature range T₁, a second section P₂ having a second temperature range T₂, a third section P₃ having a third temperature range T₃, a fourth section P₄ having a fourth temperature range T₄, a fifth section P₅ having a fifth temperature range T₅, a sixth section P₆ having a sixth temperature range T₆, and a seventh section P₇ having a seventh temperature range T₇.

In an embodiment, in the multi-stage heating operation S210, the blank may be heated in stages while passing through the first section P₁ to the fourth section P₄ that are defined in the heating furnace. In addition, in the soaking operation S220, the blank that has undergone multi-stage heating through the first section P₁ to the fourth section P₄, may be soaked while passing through the fifth section P₅ to the seventh section P₇.

The first section P₁ to the seventh section P₇ may be arranged sequentially within the heating furnace. The first section P₁ having the first temperature range T₁ may be adjacent to the inlet of the heating furnace into which the blank is fed, and the seventh section P₇ having the seventh temperature range T₇ may be adjacent to the outlet of the heating furnace from which the blank is discharged. Thus, the first section P₁ having the first temperature range T₁ may be the first section of the furnace, and the seventh section P₇ having the seventh temperature range T₇ may be the last section of the furnace.

The temperatures of the plurality of sections provided in the heating furnace, for example, the temperatures of the first section P₁ to the seventh section P₇, may increase from the inlet of the heating furnace into which the blank is fed, toward the outlet of the heating furnace from which the blank is discharged. However, the fifth section P₅, the sixth section P₆, and the seventh section P₇ may have the same temperature. In addition, the temperature difference between two adjacent sections among the plurality of sections provided in the heating furnace may be greater than 0° C. but less than or equal to 100° C. For example, the temperature difference between the first section P₁ and the second section P₂ may be greater than 0° C. but less than or equal to 100° C.

The temperature of the heating furnace in the soaking operation S220 may be Ac3 to about 1,000° C. When the temperature of the heating furnace in the soaking operation S220 is less than Ac3, the manufactured hot-stamped component may not have a desired material quality. On the contrary, when the temperature of the heating furnace in the soaking operation S220 is greater than about 1,000° C., carbide-forming elements or nitride-forming elements, such as T₁, V, Nb, or Mo, in the blank 100 are dissolved into the base material, making it difficult to suppress grain coarsening.

Although FIG. 10 illustrates that the heating furnace according to an embodiment includes seven sections with different temperature ranges, the present disclosure is not limited thereto. The heating furnace may include five, six, or eight sections having different temperature ranges.

In an embodiment, as the heating operation S200 includes the multi-stage heating operation S210 and the soaking operation S220, the temperature of the heating furnace may be set in stages, which may enhance the energy efficiency of the heating furnace.

In an embodiment, the heating furnace may have a length of about 20 m to about 40 m along a transfer path for the blank 100. The heating furnace may include a plurality of sections having different temperature ranges, and the ratio of the length of sections from among the plurality of sections, in which the blank is multi-stage-heated, to the length of sections from among the plurality of sections, in which the blank is soaked, may be within the range of about 1:1 to about 4:1. In a case in which the length of the sections of the heating furnace in which the blank is soaked increases such that the ratio of the length of the sections in which the blank is multi-stage-heated, to the length of the sections in which the blank is soaked is greater than about 1:1, the amount of hydrogen penetrating into the blank in the soaking sections increases, which may increase delayed fracture.

On the contrary, in a case in which the length of the sections in which the blank is soaked decreases such that the ratio of the length of the sections in which the blank is multi-stage-heated, to the length of the sections in which the blank is soaked is less than about 4:1, the soaking section (or time) is not sufficiently secured, and thus, the strength of the manufactured hot-stamped component may be non-uniform. For example, the length of the soaking sections among the plurality of sections provided in the heating furnace may be about 20% to about 50% of the total length of the heating furnace.

In an embodiment, a total heating time during which the heating operation S200 is performed may be about 2 min to about 20 min. That is, the total time during which the blank remains in the heating furnace may be about 2 minutes to about 20 minutes. In a case in which the total heating time during which the heating operation S200 is performed is less than about 2 min, the manufactured hot-stamped component may not have the desired material quality due to insufficient heating time. On the contrary, in a case in which the total heating time during which the heating operation S200 is performed is about 20 min or longer, the heating time may be too long, which may lower the production rate and thus reduce economic feasibility. Thus, in a case in which the total heating time during which the heating operation S200 is performed is within the range of about 2 min to about 20 min, the manufactured hot-stamped component may have the desired material quality, while preventing or minimizing a deterioration in the economic feasibility of the manufacturing process.

Referring to FIG. 6, after the heating operation S200, the transfer operation S300 may be performed. In the transfer operation S300, the heated blank 100 may be transferred to a press die 400 (see FIG. 11). For example, after being discharged from the heating furnace, the heated blank 100 may be transferred to the press die 400.

In the transfer operation S300, the heated blank 100 may be cooled at an ambient temperature (or room temperature). That is, the heated blank 100 may be air-cooled at an ambient temperature during the transfer. When the heated blank 100 is not air-cooled, a die entry temperature (e.g., a forming start temperature) may increase, which may cause wrinkles (or bends) to form on the surface of the manufactured hot-stamped component. In addition, because the use of a coolant may affect a subsequent process (hot stamping), it may be preferable for the heated blank 100 to be air-cooled during the transfer.

FIGS. 11 and 12 are cross-sectional views for describing a forming/piercing operation of a process of manufacturing a hot-stamped component, according to an embodiment of the present disclosure. In detail, FIG. 11 is a cross-sectional view of a blank and a press die before the forming/piercing operation is performed, and FIG. 12 is a cross-sectional view of the blank and the press die while the forming/piercing operation is being performed.

Referring to FIGS. 6, 11, and 12, after the transfer operation S300, the forming/piercing operation S400 may be performed. The forming/piercing operation S400 may be an operation of hot-forming the transferred blank 100 into the shape of a hot-stamped component, and forming the pierced portion 110 in the transferred blank 100.

In an embodiment, the forming/piercing operation S400 may be performed in the 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 the shape of a lower surface of the hot-stamped component. The upper die 420 may face the lower die 410 and may have the shape of an upper surface of the hot-stamped component. The press die 400 may include at least one punch 430, and preferably, at least two punches 430. In an embodiment, the punches 430 may include a first punch and a second punch. However, the present disclosure is not limited thereto. For example, various modifications are possible, such as the press die 400 including only one punch 430, or including three or more punches 430.

Although not illustrated, in a case in which the press die 400 includes only one punch 430, a single form bead may be formed at an edge of the blank 100 during the forming of the blank 100.

For example, as will be described below, a laser process or a cold piercing process may be performed by using the pierced portion 110 formed through hot piercing. In detail, a subsequent process may be performed after the blank 100 is seated on a jig by using the pierced portions 110, which are formed through hot piercing, as a guide pattern (or reference points). Thus, there may be at least two pierced portions 110 formed in the blank 100 through hot piercing.

In an embodiment, a clearance between the punch 430 and the die (e.g., the lower die 410 and/or the upper die 420) may be about 5% to about 15%. When the clearance is less than about 5%, an issue may occur in which the punch 430 gets stuck in the die due to thermal expansion of the die. On the contrary, when the clearance is greater than about 15%, there is a risk that the quality, including flow lines on the shear surface, may become non-uniform due to severe wobble of the punch 430. For example, the uniformity of the flow lines may be degraded, such as by many flow lines being formed on only one part of the shear surface. Thus, when 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 about 15%, seizure of the punch 430 in the die due to thermal expansion may be prevented, and flow lines may be uniformly formed around the shear surface.

In an embodiment, in the forming/piercing operation S400, the blank 100 may be hot-formed. By using the press die 400, which includes the lower die 410 and the upper die 420, the transferred (or heated) blank 100 may be hot-formed into the shape of the hot-stamped component. In detail, the blank 100 may be formed into the shape of the hot-stamped component by pressing (e.g., hot-pressing) the blank 100 with the lower die 410, which has the shape of the lower surface of the hot-stamped component, against the upper die 420, which has the shape of the upper surface of the hot-stamped component.

In an embodiment, in the forming/piercing operation S400, hot forming and hot piercing may be performed simultaneously or sequentially. In an embodiment, in the forming/piercing operation S400, hot piercing may be performed on the blank 100 after a time point at which hot forming of the blank 100 is completed (or initiated). In detail, while the blank 100 is being hot-formed (or after the hot forming is completed), the punch 430 included in the press die 400 may descend to perform hot piercing on the blank 100, thereby forming the pierced portion 110 in the hot-stamped component 10 (or the blank 100). For example, after the upper die 420 reaches a bottom dead center and the hot forming of the blank 100 is completed (or after the hot forming is initiated), the punch 430 may descend to perform hot piercing on the blank 100, thereby forming the pierced portion 110 in the hot-stamped component 10 (or the blank 100). That is, hot piercing may be performed after hot forming is completed (or started). Alternatively, hot forming and hot piercing may be performed simultaneously.

Although not illustrated, the punch 430 may be raised and lowered by a hydraulic cylinder. However, the present disclosure is not limited thereto.

In an embodiment, in the forming/piercing operation S400, the forming start temperature for the blank 100 at which the forming of the blank 100 is initiated when the blank 100 is hot-formed may be an Ms temperature to 750° C. When the blank 100 is hot-formed at a temperature lower than the Ms temperature, a large load may be generated during hot forming, and thus, the press die 400 may be damaged, the formability of the blank 100 may be degraded, and the manufactured hot-stamped component may not have a desired structure and material properties. On the contrary, when the forming start temperature is greater than about 750° C., wrinkles (or bends) may form on the surface of the manufactured hot-stamped component. In addition, the plating layer may be sintered in the die. Thus, when the forming start temperature is about the Ms temperature to about 750° C., the formability of the hot stamping steel sheet may be enhanced, the manufactured hot-stamped component may have the desired structure and material properties, and the formation of wrinkles (or bends) on the surface of the manufactured hot-stamped component may be prevented or minimized.

In an embodiment, in the forming/piercing operation S400, the temperature of the blank 100 when hot piercing is performed on the blank 100 may be about 200° C. to about 700° C. When the temperature of the blank 100 during hot piercing is less than about 200° C., a large load may be generated during hot piercing, which may cause damage to the press die 400 and/or the punch 430. On the contrary, because the blank 100 is air-cooled while being discharged from the heating furnace and transferred to the press die 400, the temperature of the blank 100 before hot piercing is performed may be about 700° C. or less. In addition, because hot piercing is performed after the hot forming of the heated blank 100 is completed (or initiated), the temperature of the blank 100 when hot piercing is performed may be less than the temperature of the blank 100 when hot forming is performed. Thus, when hot piercing is performed in the forming/piercing operation S400 while the temperature of the blank 100 is about 200° C. to about 700° C., the pierced portion 110 may be formed in the blank 100 without damage to the press die 400 and/or the punch 430.

In an embodiment, when hot-forming the blank 100 by using the press die 400, the first punch and the second punch included in the press die 400 may descend to form at least two pierced portions 110a and 110b in the blank 100. In detail, in the process of hot-forming the blank 100 by pressing the blank 100 with the upper die 420 against the lower die 410, the first punch and the second punch may descend to form a first pierced portion 110a and a second pierced portion 110b in the hot-stamped component 10.

Although FIGS. 11 and 12 illustrate that the pierced portion 110 is formed in the blank 100 by the descent of the punch 430 included in the press die 400, the present disclosure is not limited thereto. Although not illustrated, the pierced portion 110 may be formed in the blank 100 by a separately provided external device.

In an embodiment, the blank 100 may be cooled in the press die 400 simultaneously with being formed into a final component shape (or during hot forming). The press die 400 may include a cooling channel 440 through which a coolant circulates. For example, cooling channels 440 may be provided inside each of the lower die 410 and the upper die 420. In detail, the cooling channels 440 may be arranged inside 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 circulation of the coolant supplied through the cooling channel 440 provided in the press die 400. Here, to prevent a spring-back phenomenon of the steel sheet and maintain the desired shape, quenching may be performed while applying pressure with the press die 400 closed. In forming and cooling the heated blank 100, the blank may be cooled to the martensite finish temperature at an average cooling rate of at least 10° C./s. Preferably, the blank 100 may be cooled at a rate of at least 20° C./s.

The blank 100 may be held in the press die 400 for 3 seconds to 20 seconds. For example, the engaged state of the press die 400 may be maintained for 3 seconds to 20 seconds. When the holding time in the press die 400 is less than 3 seconds, sufficient cooling of the blank 100 may not be achieved, and accordingly, thermal deformation may occur due to residual heat and regional temperature deviation, degrading the dimensional quality. On the contrary, when the holding time in the press die 400 is greater than 20 seconds, the productivity may be degraded because the holding time is too long.

In an embodiment, while the press die 400 is in a closed state (or an engaged state), hot forming and cooling of the blank 100 may be performed, and after a certain amount of time has passed, hot piercing may be performed on the blank 100.

In an embodiment, hot forming, hot piercing, and cooling of the heated blank 100 may be performed simultaneously in the press die 400. For example, hot forming, hot piercing, and cooling of the blank 100 may be performed simultaneously (or together) while the press die 400 is in a closed state (or an engaged state).

Although not illustrated, a trimming operation may be performed after the forming/piercing operation S400. The trimming operation may be an operation of cutting an outer portion of the formed hot-stamped component 10 by using at least two pierced portions 110a and 110b formed in the hot-stamped component 10. In other words, the trimming operation may be an operation of cutting an outer portion of the hot-stamped component 10 by using the two pierced portions 110a and 110b formed in the hot-stamped component 10 through hot piercing.

In an embodiment, in the trimming operation, edges of the hot-stamped component 10 may be cut by using the at least two pierced portions 110a and 110b formed through hot piercing, as reference points (or a guide pattern). In other words, the hot-stamped component 10 may be seated on a jig by using the at least two pierced portions 110a and 110b formed in the hot-stamped component 10, and then the edges of the hot-stamped component 10 may be cut. For example, after inserting fixing pins respectively into the at least two pierced portions 110a and 110b formed in the hot-stamped component 10, an outer portion of the hot-stamped component 10 may be cut.

In an embodiment, the trimming operation may be performed by using a laser or a press die (e.g., a cold press die).

In the method of manufacturing a hot-stamped component according to an embodiment of the present disclosure, the pierced portion 110 may be in the blank 100 through hot piercing, and an outer portion of the hot-stamped component 10 may be additionally cut through cold trimming or laser trimming. That is, in the method of manufacturing a hot-stamped component according to an embodiment of the present disclosure, a hot piercing process may be performed on the blank 100, then the blank 100 may be cooled, and then cold trimming or laser trimming may be performed.

In an embodiment, a second piercing operation may be performed after the forming/piercing operation S400. The second piercing operation may be an operation of forming an additional pierced portion in the hot-stamped component 10 by using the at least two pierced portions 110a and 110b formed in the hot-stamped component 10. In other words, the second piercing operation may be an operation of additionally forming a pierced portion (e.g., an additional pierced portion) in the hot-stamped component 10 by using the two pierced portions 110a and 110b formed in the hot-stamped component 10 through hot piercing.

In an embodiment, the second piercing operation may be performed during the trimming operation. For example, the second piercing operation and the trimming operation may be performed simultaneously. Alternatively, the second piercing operation may be performed before the trimming operation, or may be performed after the trimming operation. For example, the second piercing operation and the trimming operation may be performed sequentially.

In the method of manufacturing a hot-stamped component according to an embodiment of the present disclosure, after forming the pierced portion 110 in the hot-stamped component 10 through hot piercing, a pierced portion (e.g., an additional pierced portion) may be additionally formed in the hot-stamped component 10 through cold piercing or laser piercing. That is, in the method of manufacturing a hot-stamped component according to an embodiment of the present disclosure, a hot piercing process may be performed on the blank 100, then the blank 100 on which the hot piercing process has been performed may be cooled, and then a cold piercing process or a laser piercing process may be performed.

In an embodiment, a part of an outer portion of the manufactured hot-stamped component may be an edge of a raw coil material. That is, a part of the outer portion of the manufactured hot-stamped component may be an edge of the raw coil material without being cut.

In an embodiment, after the trimming operation and/or the second piercing operation is performed, an operation of removing burrs formed on the blank may be performed. Through this, burrs formed in processes such as hot piercing, cold piercing, or cold trimming may be removed.

Experimental Examples

Hereinafter, the present disclosure will be described in more detail through experimental examples. However, the experimental examples are intended to describe the present disclosure in more detail, and the scope of the present disclosure is not limited by the following experimental example. The following experimental examples may be appropriately modified and changed by those skilled in the art within the scope of the present disclosure.

TABLE 1
Component (wt %)

C	Si	Mn	P	S	Cr	B	Ti
0.22	0.3	1.5	0.02	0.015	0.25	0.0025	0.05

	TABLE 2
			Blank
			temperature			Hydrogen
	Blank		during			embrittlement
	Thickness	Clearance	piercing			evaluation
	(mm)	(%)	(° C.)	th1/th2	w1/w2	result

Embodi-	1.2	5	600	0.228	0.058	No fracture
ment 1
Embodi-	1.2	5	400	0.231	0.054	No fracture
ment 2
Embodi-	1.2	5	200	0.225	0.043	No fracture
ment 3
Embodi-	1.2	10	600	0.273	0.153	No fracture
ment 4
Embodi-	1.2	10	400	0.255	0.123	No fracture
ment 5
Embodi-	1.2	10	200	0.218	0.125	No fracture
ment 6
Embodi-	1.2	15	600	0.231	0.196	No fracture
ment 7
Embodi-	1.2	15	400	0.263	0.125	No fracture
ment 8
Embodi-	1.2	15	200	0.286	0.073	No fracture
ment 9
Embodi-	2	12	700	0.329	0.078	No fracture
ment 10
Embodi-	2	12	400	0.448	0.171	No fracture
ment 11

	TABLE 3
			Blank
			temperature			Hydrogen
	Blank		during			embrittlement
	Thickness	Clearance	piercing			evaluation
	(mm)	(%)	(° C.)	th1/th2	w1/w2	result

Comparative	1.2	5	190	0.264	0.612	Fractured
example 1
Comparative	1.2	5	100	0.652	0.591	Fractured
example 2
Comparative	1.2	5	Room	0.770	1.315	Fractured
example 3			temperature
Comparative	1.2	10	190	0.494	0.718	Fractured
example 4
Comparative	1.2	10	100	0.657	0.856	Fractured
example 5
Comparative	1.2	10	Room	0.784	2.752	Fractured
example 6			temperature
Comparative	1.2	15	100	0.726	0.332	Fractured
example 7
Comparative	1.2	15	Room	0.724	0.733	Fractured
example 8			temperature
Comparative	2	4	190	0.301	4.365	Fractured
example 9
Comparative	2	4	Room	0.800	3.250	Fractured
example 10			temperature
Comparative	2	12	190	0.694	2.249	Fractured
example 11
Comparative	2	12	Room	0.778	2.695	Fractured
example 12			temperature

Examples 1 to 11 and Comparative examples 1 to 12 are specimens that were prepared by manufacturing blanks from a slab having the composition shown in Table 1 under conditions including a slab reheating temperature (SRT) of 1,230° C., a finishing delivery temperature (FDT) of 900° C., a reduction ratio during hot rolling of 95%, a coiling temperature (CT) of 700° C., an annealing heat treatment temperature of 780° C., and a plating immersion temperature of 660° C., then heating the manufactured blanks at 950° C. for 270 seconds, and then performing hot forming, hot piercing, and cooling on the blanks in a press die. In Tables 2 and 3, th1 denotes the thickness of the fracture surface 303, th2 denotes the thickness of the shearing-processed surface 300, w1 denotes the width of the plating layer delamination surface 304, and w2 denotes the width of the rollover surface 301. In Tables 2 and 3, the value of Equation 1 (th1/th2) and the value of Equation 2 (w1/w2) may each be an average of values measured at four or more points at equiangular intervals from the center of the pierced portion 110. In addition, in Table 3, the room temperature may refer to 30° C.

The hydrogen embrittlement evaluation was performed on the hot-stamped components (e.g., specimens) of Examples 1 to 11 and Comparative examples 1 to 12 through a 4-point bending test according to the ASTM G39-99 standard. The 4-point bending test refers to a test method for checking for the occurrence of stress corrosion cracking by applying stress at a level lower than or equal to the elastic limit to a particular point on a specimen that is manufactured while the specimen is exposed to a corrosive environment. Here, stress corrosion cracking refers to cracking that occurs when corrosion and continuous tensile stress act simultaneously. In detail, the hydrogen embrittlement evaluation results in Tables 2 and 3 are results of checking for the occurrence of fracture after applying a stress of 1,000 MPa for 100 hours in air to the respective specimens.

Referring to Table 2, it may be seen that, when the value of (thickness th1 of fracture surface 303/thickness th2 of shearing-processed surface 300) was 0.6 or less, and the value of (width w1 of plating layer delamination surface 304/width w2 of rollover surface 301) was 0.6 or less, no fracture occurred in the hydrogen embrittlement evaluation. That is, it may be seen that, when the thickness th1 of the fracture surface 303 and the thickness th2 of the shearing-processed surface 300 satisfied Equation 1 (th1/th2≤0.6), and the width w1 of the plating layer delamination surface 304 and the width w2 of the rollover surface 301 satisfied Equation 2 (w1/w2≤0.6), no fracture occurred in the hydrogen embrittlement evaluation.

However, referring to Table 3, it may be seen that, when the value of (thickness th1 of fracture surface 303/thickness th2 of shearing-processed surface 300) was greater than 0.6, or the value of (width w1 of plating layer delamination surface 304/width w2 of rollover surface 301) was greater than 0.6, fracture occurred in the hydrogen embrittlement evaluation. That is, it may be seen that, when the thickness th1 of the fracture surface 303 and the thickness th2 of the shearing-processed surface 300 did not satisfy Equation 1 (th1/th2≤0.6), or the width w1 of the plating layer delamination surface 304 and the width w2 of the rollover surface 301 did not satisfy Equation 2 (w1/w2 ≤0.6), fracture occurred in the hydrogen embrittlement evaluation.

Thus, it may be seen that, in the hot-stamped component 10, when the value of (thickness th1 of fracture surface 303/thickness th2 of shearing-processed surface 300) was 0.6 or less, and the value of (width w1 of plating layer delamination surface 304/width w2 of rollover surface 301) was 0.6 or less, no fracture occurred in the hydrogen embrittlement evaluation, indicating excellent resistance to hydrogen embrittlement. That is, it may be seen that, when the thickness th1 of the fracture surface 303 and the thickness th2 of the shearing-processed surface 300 satisfied Equation 1 (th1/th2≤0.6), and the width w1 of the plating layer delamination surface 304 and the width w2 of the rollover surface 301 satisfied Equation 2 (w1/w2≤0.6), no fracture occurred in the hydrogen embrittlement evaluation, indicating excellent resistance to hydrogen embrittlement.

Although the present disclosure has been described with reference to the embodiments illustrated in the drawings, they are merely exemplary, and it will be understood by one of skill in the art that various modifications and equivalent embodiments may be made therefrom. Therefore, the true technical protection scope of the present disclosure should be determined by the appended claims.