Hot-Stamped Component

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.

The present disclosure relates to a hot-stamped component.

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.

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.

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

Referring to, a hot-stamped componentaccording to an embodiment of the present disclosure may include pierced portions. In an embodiment, the hot-stamped componentmay include two pierced portions. The pierced portionsmay include a first pierced portionand a second pierced portion. However, the present disclosure is not limited thereto. The hot-stamped componentmay include one pierced portion, or three or more pierced portions.

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

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

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

is a cross-sectional view schematically illustrating a hot-stamped component according to an embodiment of the present disclosure, andis an enlarged view of portion A of. In detail,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, in an embodiment, the hot-stamped componentmay include a base material, an interdiffusion layer, and a plating layer. The base material, the interdiffusion layer, and the plating layermay be sequentially arranged in a thickness direction of the hot-stamped component. Here, the thickness direction of the hot-stamped componentmay 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 componentmay include a shearing-processed surfaceformed at an edge of the pierced portion. The shearing-processed surfacemay include a rollover surface, a shear surface, and a fracture surface.

In an embodiment, the rollover surfacemay 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 materialthat forms the upper surface in the horizontal direction. Here, the surface having the curvature formed on the uppermost surface of the base materialmay correspond to the rollover surface. The rollover surfacemay extend from the point where the curvature begins to form on the uppermost surface of the base materialto the point where the shear surfacebegins.

In an embodiment, the shear surfacemay 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 surfacemay be formed in the vertical direction. For example, the curvature on the uppermost surface of the base materialmay disappear, and a linear shear surfacemay be formed in the vertical direction or a direction at a certain angle with respect to the vertical direction. The shear surfacemay extend from the point where the rollover surfaceends to the point where the fracture surfacebegins. In an embodiment, the fracture surfacemay 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 surfacemay be formed as at least a portion of the blank breaks away. The fracture surfaceis formed by the fracture of at least a portion of the blank, and thus may be irregular compared to the shear surface. The fracture surfacemay extend from the point where the irregularity compared to the shear surfacebegins, to an end point of the fracture surfaceor an end point of the base material.

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

In an embodiment, a plating layer delamination surfacemay be a surface from which at least a portion of the plating layerhas been removed. During a hot-stamping heat treatment, the interdiffusion layermay be formed by the alloying of the base materialand the plating layer. Here, during hot piercing, at least a portion of the plating layerarranged on the upper surface of the interdiffusion layermay be delaminated (or removed). The plating layer delamination surfacemay be defined as a surface from which at least a portion of the plating layerarranged on the upper surface of the interdiffusion layerhas been delaminated (or removed). The plating layer delamination surfacemay extend from the point where the plating layermeets the upper surface of the interdiffusion layerthat is exposed as at least a portion of the plating layerhas been removed, to the point where the shear surfacebegins.

In an embodiment, a thickness thof the fracture surfacemay be defined as the shortest distance in the vertical direction from the boundary between the shear surfaceand the fracture surfaceto an end point of the base material. In other words, the thickness thof the fracture surfacemay be defined as the shortest distance between a first virtual line (or a first virtual plane), which passes through the boundary between the shear surfaceand the fracture surfaceand extends in the horizontal direction, and a second virtual line (or a second virtual plane), which passes through the end point of the base materialand extends in the horizontal direction. Here, the end point of the base materialmay refer to the point where the fracture surfaceends.

In an embodiment, a thickness thof the shear surfacemay be defined as the shortest distance in the vertical direction from the boundary between the rollover surfaceand the shear surfaceto the boundary between the shear surfaceand the fracture surface. In other words, the thickness thof the shear surfacemay 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 surfaceand extends in the horizontal direction, and a fourth virtual line (or a fourth virtual plane), which passes through the boundary between the shear surfaceand the fracture surfaceand extends in the horizontal direction.

In an embodiment, a thickness thof the rollover surfacemay be defined as the shortest distance in the vertical direction from the point where the curvature of the base materialbegins to the point where the shear surfacebegins. In other words, the thickness thof the rollover surfacemay 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 materialand extends in the horizontal direction, and a sixth virtual line (or a sixth virtual plane), which passes through the point where the shear surfacebegins, and extends in the horizontal direction.

In an embodiment, a thickness thof the shearing-processed surfacemay be defined as the shortest distance in the vertical direction from the point where the curvature of the base materialbegins to the end point of the base material. In other words, the thickness thof the shearing-processed surfacemay 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 materialand extends in the horizontal direction, and the second virtual line (or the second virtual plane), which passes through the end point of the base materialand extends in the horizontal direction. For example, the thickness thof the shearing-processed surfacemay be the sum of the thickness thof the fracture surface, the thickness thof the shear surface, and the thickness thof the rollover surface.

In an embodiment, a width wof the plating layer delamination surfacemay be defined as the shortest distance in the horizontal direction from the point where the plating layermeets the upper surface of the interdiffusion layerthat is exposed as at least a portion of the plating layerhas been removed, to the point where the shear surfacebegins. In other words, the width wof the plating layer delamination surfacemay be defined as the shortest distance between a seventh virtual line (or a seventh virtual plane), which passes through the point where the plating layermeets the upper surface of the interdiffusion layerthat is exposed as at least a portion of the plating layerhas 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 surfacebegins, and extends in the vertical direction.

In an embodiment, a width wof the rollover surfacemay be defined as the shortest distance in the horizontal direction from the point where the curvature of the base materialbegins to the point where the shear surfacebegins. In other words, the width wof the rollover surfacemay 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 materialbegins, and extends in the vertical direction, and the eighth virtual line (or the eighth virtual plane), which passes through the point where the shear surfacebegins, 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.

is a side view of a pierced portion of a hot-stamped component according to an embodiment of the present disclosure,is a front view of a pierced portion of a hot-stamped component according to an embodiment of the present disclosure, andis an enlarged view of a portion of.

In addition,is a side view of a pierced portion of a hot-stamped component according to a comparative example,is a front view of a pierced portion of a hot-stamped component according to a comparative example, andis an enlarged view of a portion of.

In detail,correspond to a case in which hot piercing is performed, andcorrespond to a case in which cold piercing is performed.

Referring to, it may be seen that the width wof the rollover surfacein the case of hot piercing is greater than a width w′ of a rollover surface′ in the case of cold piercing. In addition, it may be seen that the width wof the plating layer delamination surfacein the case of hot piercing is less than a width w′ of a plating layer delamination surface′ in the case of cold piercing. Thus, when hot piercing is performed, compared to when cold piercing is performed, the width wof the rollover surfacemay increase, and the width wof the plating layer delamination surfacemay 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 wof the rollover surfacemay be greater, and the width wof the plating layer delamination surfacemay 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 thof the shear surfacein the case of hot piercing is greater than a thickness th′ of a shear surface′ in the case of cold piercing. In addition, it may be seen that the thickness thof the fracture surfacein the case of hot piercing is less than a thickness th′ of a fracture surface′ in the case of cold piercing. From this, it may be seen that, in the case of hot piercing, the proportion of the shear surfacewithin the shearing-processed surfaceis greater, and the proportion of the fracture surfaceis less, than in the case of cold piercing.

It may be seen that, in the case of hot piercing, the proportion of the rollover surfacewithin the shearing-processed surfaceis greater than in the case of cold piercing. In detail, it may be seen that the thickness thof the rollover surfacein the case of hot piercing is greater than a thickness th′ of the rollover surface′ in the case of cold piercing. From this, it may be seen that the thickness thof the rollover surfacein the case of hot piercing increases compared to the case of cold piercing.

As the shear stress acting on a blankduring piercing increases, the proportion of the fracture surfacewithin the shearing-processed surfacemay increase. In detail, as the shear stress acting on the blankincreases, the thickness thof the fracture surfacemay increase, and the thickness thof the shear surfacemay decrease. A large thickness thof the fracture surfacemay indicate that the shear stress acting on the blank is large, and the large shear stress may induce hydrogen embrittlement in the pierced portion. Thus, to enhance the resistance to hydrogen embrittlement of the hot-stamped component, it is necessary to reduce the thickness thof the fracture surfaceto a certain level or less.

In addition, as the shear stress acting on the blank increases, the width wof the plating layer delamination surfacemay increase, and the width wof the rollover surfacemay decrease. Thus, to enhance the resistance to hydrogen embrittlement of the hot-stamped component, it is necessary to decrease the width wof the plating layer delamination surfaceand increase the width wof the rollover surface.

Accordingly, the present inventor, through extensive experimentation, has derived Equation 1 and Equation 2, which allow the hot-stamped componentto have excellent resistance to hydrogen embrittlement. In an embodiment, the hot-stamped componentmay satisfy Equation 1 and Equation 2. In detail, for the hot-stamped component, the thickness thof the fracture surfaceand the thickness thof the shearing-processed surfacemay satisfy Equation 1, and the width wof the plating layer delamination surfaceand the width wof the rollover surfacemay satisfy Equation 2.

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

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

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 thof the fracture surfacewithin the thickness thof the shearing-processed surfacemay 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 layerdelaminating around the pierced portionmay 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 surfaceand the width wof the rollover surfacemay also increase.

A large fraction of the fracture surfacemay indicate that a large shear stress has acted on the pierced portionduring hot piercing, and when a large shear stress acts on the pierced portion, hydrogen embrittlement may occur in a portion of the hot-stamped componentadjacent to the pierced portion. That is, a large thickness thof the fracture surfacemay indicate that a large shear stress has acted on the pierced portionduring hot piercing, and when a large shear stress acts on the pierced portion, hydrogen embrittlement may occur in a portion adjacent to the pierced portion.

When the thickness thof the fracture surfaceand the thickness thof the shearing-processed surface of the hot-stamped componentdo not satisfy Equation 1, hydrogen embrittlement may occur in a portion adjacent to the pierced portion. In detail, that the value of (thickness thof fracture surface/thickness thof shearing-processed surface) in the hot-stamped componentis greater than 0.6 may mean that the fraction of the fracture surfacewithin the shearing-processed surfaceis large, which means that a large shear stress has acted on the pierced portionduring piercing, and this may cause hydrogen embrittlement in a portion of the hot-stamped componentadjacent to the pierced portion.