KR102308021B1 - Hot stamping member for vehicle and method of manufacturing the same - Google Patents

Abstract

The present invention provides a hot stamping component for a vehicle, which achieves crashworthiness and weight lightening of the vehicle at the same time. According to one embodiment of the present invention, the hot stamping component for a vehicle comprises: a first member having a first hardness and a first elongation; and a second member which is welded on the first member and has a second hardness, lower than the first hardness, and a second elongation, higher than the first elongation. A weld part formed by welding of the second member on the first member is slanted at a predetermined angle on a horizontal line extended in parallel with an end part of one among the first member or the second member.

Description

Hot stamping member for vehicle and method of manufacturing the same

The present invention relates to a vehicle component, and more particularly, to a vehicle hot stamping component that simultaneously achieves collision stability and vehicle weight reduction, and a method for manufacturing the same.

Recently, the automobile industry is demanding strict body crash performance to enhance passenger safety. In addition, as the awareness of the environment increases, fuel efficiency standards according to exhaust gas regulations are strengthened, and accordingly, the need for weight reduction of the vehicle body is continuously increasing. The application of high-strength steel sheet to the car body is continuously increasing as part of an effort to simultaneously satisfy the demands of improving collision performance and reducing weight. When manufacturing a car body, high-strength parts are applied to reduce damage caused by a crash, because it plays a very important role in securing the driver's survival space in the event of a crash.

Among these automobile parts, a center pillar is a body part that is installed in the left and right central portions of the vehicle to support the roof and hold the door. However, since the conventional center pillar is manufactured using only one material having high rigidity, the ability to resist a strong impact is good, but it has a disadvantage of having high brittleness. Accordingly, the center pillar may be fractured after a collision with the collision blank, which causes the collision blank to break the center pillar and then rush to the driver's seat to cause injury to the driver. In order to prevent such a problem, when reinforcing materials are added to the center pillar, it is disadvantageous to lightening the vehicle.

Korean Patent Publication No. 2016-0061560

The technical problem to be achieved by the technical idea of the present invention is to provide a hot stamping part for a vehicle capable of achieving both collision stability and vehicle weight reduction, and a method for manufacturing the same.

However, these tasks are exemplary, and the technical spirit of the present invention is not limited thereto.

According to one aspect of the present invention, there is provided a hot stamping part for a vehicle that can achieve both crash stability and vehicle weight reduction.

According to an embodiment of the present invention, the hot stamping part for a vehicle includes: a first member having a first strength and a first elongation; and a second member welded to the first member and having a second strength lower than the first strength and a second elongation higher than the first elongation, wherein the first member and the second member are The welded portion formed by welding may be inclined at a predetermined angle with respect to a horizontal line extending parallel to an end of any one of the first member or the second member.

According to an embodiment of the present invention, the welding portion may form an angle of greater than 0 degrees and less than or equal to 60 degrees with respect to the horizontal line.

According to an embodiment of the present invention, the first member, by weight, carbon (C): 0.20% to 0.50%, silicon (Si): 0.05% to 1.00%, manganese (Mn): 0.10% to 2.50% , Phosphorus (P): More than 0% to 0.015% or less, Sulfur (S): More than 0% to 0.005% or less, Chromium (Cr): 0.05% to 1.00%, Boron (B): 0.001% to 0.009%, Titanium (Ti): 0.01% to 0.09% and the balance may include iron (Fe) and unavoidable impurities.

According to an embodiment of the present invention, the first member may have a tensile strength (TS): 1200 MPa to 1500 MPa, and may have a martensitic single-phase structure.

According to an embodiment of the present invention, the second member, by weight, carbon (C): 0.04% to 0.06%, silicon (Si): 0.4% to 0.6%, manganese (Mn): 1.7% to 1.9% , Phosphorus (P): more than 0% to 0.018% or less, Sulfur (S): more than 0% to 0.003% or less, Chromium (Cr): 0.1% to 0.3%, Boron (B): 0.0015% to 0.0025%, Titanium (Ti): 0.05% to 0.07%, niobium (Nb): 0.04% to 0.06%, and the remainder may include iron (Fe) and unavoidable impurities.

According to an embodiment of the present invention, the second member, tensile strength (TS): 900 MPa to 1100 MPa, yield strength (YS): 700 MPa to 900 MPa, and elongation (El): 8% to 10% , has a bending angle of 90 degrees to 120 degrees, and may have a dual phase structure of bainite and martensite.

According to an embodiment of the present invention, the hot stamping part for a vehicle may include a center pillar, a front side member, a rear side member, or a roof side member.

According to one aspect of the present invention, there is provided a method of manufacturing a hot stamping part for a vehicle capable of achieving both collision stability and vehicle weight reduction.

According to an embodiment of the present invention, the method for manufacturing a hot stamping part for a vehicle includes: forming a molded body by hot stamping a cutting material cut by welding a first blank and a second blank; and hot stamping the bonding cutting material to form a molded body. and cooling the molded body to form a hot stamping part for a vehicle.

According to an embodiment of the present invention, the hot stamping part for a vehicle may include: a first member formed from the first blank and having a first strength and a first elongation; a second member formed from the second blank and welded to the first member, the second member having a second strength lower than the first strength and a second elongation higher than the first elongation; The welded portion of the member and the second member may be formed inclined at a predetermined angle with respect to a horizontal line extending in parallel with respect to an end of any one of the first member and the second member.

According to an embodiment of the present invention, the bonding cutting material may be manufactured by cutting the welding portion to be formed by being inclined at a predetermined angle with respect to the horizontal line.

According to an embodiment of the present invention, the second blank, heating the steel slab to a reheating temperature (SRT): 1200 ℃ ~ 1250 ℃ conditions; Finishing hot rolling the reheated steel slab at a finish rolling temperature (FDT): 860° C. to 920° C.; winding the finish hot-rolled blank by cooling to a coiling temperature (CT): 620° C. to 660° C.; uncoiling and cold rolling the wound blank; and performing annealing heat treatment of the cold-rolled blank.

According to the technical idea of the present invention, it is possible to reduce the weight of the vehicle body by applying a different blank compared to the conventional local softening application material, and to secure a high level of assembly quality by minimizing the distortion inside the part according to the cooling rate after heating. have. In addition, by using 150K-class ultra-high strength material compared to conventional hot stamping materials, it is possible to absorb a large amount of collision energy compared to deformation, prevent material breakage during a collision, and minimize the amount of intrusion into the vehicle body due to deformation. The above-described effects of the present invention have been described by way of example, and the scope of the present invention is not limited by these effects.

1 is a schematic diagram illustrating a state in which hot stamping parts for a vehicle installed on a vehicle body are installed on a vehicle body according to an embodiment of the present invention.
2 and 3 are schematic diagrams illustrating a hot stamping part for a vehicle according to an embodiment of the present invention.
4 is a flowchart illustrating a method of manufacturing a hot stamping part for a vehicle according to an embodiment of the present invention.
5 and 6 are schematic views illustrating a method of manufacturing the hot stamping part for a vehicle of FIG. 4 according to an embodiment of the present invention according to a process sequence.
7 shows a rear collision analysis result when a hot stamping part for a vehicle according to an embodiment of the present invention is applied to a rear side member.
8 shows a result of deformation of a fuel tank space when the hot stamping part for a vehicle according to an embodiment of the present invention is applied to a rear side member.
9 shows the deformation mode results when the hot stamping part for a vehicle according to an embodiment of the present invention is applied to the center pillar.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. The embodiments of the present invention are provided to more completely explain the technical idea of the present invention to those of ordinary skill in the art, and the following examples may be modified in various other forms, The scope of the technical idea is not limited to the following examples. Rather, these embodiments are provided so as to more fully and complete the present disclosure, and to fully convey the technical spirit of the present invention to those skilled in the art. In the present specification, the same reference numerals refer to the same elements throughout. Furthermore, various elements and regions in the drawings are schematically drawn. Accordingly, the technical spirit of the present invention is not limited by the relative size or spacing drawn in the accompanying drawings.

1 is a schematic diagram illustrating a state in which hot stamping parts for a vehicle installed on a vehicle body are installed on a vehicle body according to an embodiment of the present invention.

Referring to FIG. 1 , various hot stamping parts for a vehicle installed on a vehicle body are illustrated. The hot stamping parts for the vehicle include a center pillar 200 , a front side member 300 , and a rear side member 400 . However, this is exemplary and the technical spirit of the present invention is not limited thereto. The center pillar 200 includes a high-strength region 210 disposed on an upper side and a high-flexibility region 220 disposed on a lower side. The frontside member 300 includes a high-strength region 310 disposed on the inside and a high-flexibility region 320 disposed on the outside. The rear side member 400 includes a high-strength region 410 disposed on the inside and a high-flexibility region 420 disposed on the outside. The high-strength regions 210 , 310 , and 410 are portions having relatively high strength and low elongation, and may prevent an external impact body from entering the vehicle body by its own elastic force. The high ductility regions 220 , 320 , and 420 are portions having relatively low strength and high elongation, and local deformation is easy to prevent brittle fracture caused by high strength.

When a vehicle collides, the collision energy is transferred and converted into inertial kinetic energy and absorbed energy. When the weight of the vehicle increases, the inertial kinetic energy decreases and the absorbed energy increases, resulting in vehicle body deformation. In particular, if the mid-to-large class vehicle is composed of hot stamping parts having the same strength as a whole, the crash performance is disadvantageous. If only parts with high tensile strength of 1.5 GPa are applied, the thickness should be increased in order to transmit the collision energy transmitted to the vehicle body as kinetic energy and to minimize the deformation of the vehicle body. Therefore, it is effective to form an energy absorbing region in the vehicle body in which partial deformation occurs locally in response to the front and rear and side collisions of the vehicle. As such, hot stamping parts for vehicles that need to have an energy absorbing region for locally reducing tensile strength include the above-described center pillar, frontside member, rearside member, and roofside member.

In order to form such an energy absorption region, a local softening technique, a tailored rolled blank (TRB) technique, and a Taylor welded blank (TWB) technique may be applied.

The local softening technique locally converts mechanical properties by changing the heat treatment conditions applied to a part of the same material. Therefore, deformation occurs in the low-strength part and thus the deformation of the main part of the vehicle can be minimized, but since the material has the same thickness as a whole, it is difficult to reduce the weight, and since the material deviation caused by the cooling difference of the mold is used, the vehicle assembly It is difficult to process, and even parts can be discarded because they are not manufactured properly. In addition, since the TRB technology must additionally secure a cold rolling facility, parts manufacturing cost and facility investment cost are increased. Accordingly, interest in the TWB technology is increasing.

The object of the present invention is to secure the material and toughness by improving the tensile strength of the energy absorbing part in the range of 780 MPa to 1100 MPa by applying TWB technology using different steel materials, thereby securing a bending angle of 70 degrees or more as a result of the VDA 238-100 bending test By doing so, it is to develop a hot stamping part for a vehicle that maximizes reaction force and induces stable deformation and has good crash rupture property.

When the TWB technology is applied according to the technical idea of the present invention, the shock absorbing ability can be improved by connecting blanks having different mechanical properties to form high-strength vehicle parts in which the high-strength region and the high-ductility region are separated. Protection and driver protection can be implemented simultaneously.

2 and 3 are schematic diagrams illustrating a hot stamping part 100 for a vehicle according to an embodiment of the present invention.

2 and 3 , a center pillar is illustrated as an example of the hot stamping part 100 for a vehicle. The hot stamping part 100 for a vehicle includes a first member 110 disposed at an upper side and a second member 120 disposed at a lower side. The first member 110 corresponds to the high-strength regions 210 , 310 , and 410 of FIG. 1 , and the second member 120 corresponds to the high-ductility regions 220 , 320 , 420 of FIG. 1 .

The first member 110 may have a first strength and a first elongation. The second member 120 may be welded to the first member 110 . The second member 120 may have a second strength lower than the first strength and a second elongation higher than the first elongation. Accordingly, the first member 110 may be made of high-strength steel, and the second member 120 may be made of high-ductility steel.

The welding portion WL formed by welding the first member 110 and the second member 120 may be an oblique line inclined at a predetermined angle with respect to the horizontal line HL. The horizontal line HL may refer to a line extending parallel to the end of the first member 110 or the second member 120 . The weld WL may form a predetermined angle θ with respect to the horizontal line HL, for example, may form an angle greater than 0 degrees and less than or equal to 90 degrees, for example, an angle greater than 0 degrees and less than or equal to 60 degrees. may be achieved, for example, an angle of 20 to 50 degrees may be achieved, for example, an angle of 45 degrees may be achieved.

FIG. 2 shows a case in which the welding part WL is directed downward to the left of the hot stamping part 100 , and FIG. 3 shows a case in which the welding part WL is directed downward to the right of the hot stamping part 100 .

As described above. The hot stamping part 100 such as a center pillar is composed of a first member 110 disposed on the upper portion and supporting a collision, and a second member 120 disposed on the lower portion and absorbing an impact, the first member 110 . And the second member 120 is manufactured by combining steel materials of different strengths, welding the two steel materials, and forming the steel materials.

The first member 110, for example, has a tensile strength in the range of 1200 MPa to 1500 MPa and is composed of 150K class ultra-high strength steel having a martensitic single-phase structure, and the second member 120 in which the stress is concentrated has an impact absorbing performance By composing this excellent blank, it is possible to improve the shock absorption ability in the event of a vehicle collision.

The shock absorbing part formed through the conventional hot stamping process has a dual phase of ferrite and martensite (Ferrite-Martensite) and has been developed as a 70K grade steel having a tensile strength of about 700 MPa. When these 70K-class steels are welded with 150K-class steels to form a TWB and then hot-stamped, problems may occur due to material deviation between different materials. In other words, 150K grade steel implements a single-phase martensitic structure through the hot stamping process and the material deviation according to process conditions during the hot stamping process is not large, whereas in the case of 70K grade steel, various variables of the hot stamping process, such as For example, there is a disadvantage in that the material changes rapidly depending on the transfer time it takes to transfer the steel to the hot stamping mold after heating it, or the cooling rate of the blank or mold. Therefore, when hot stamping is performed by welding the 70K class steel material with the 150K class super-strength steel material to form a bonding material, it is very difficult to control the material deviation between different types of steel that occurs during the process, and in some cases, problems such as torsion may occur. have. Therefore, the hot stamping part manufactured in this way is not suitable as an automobile crash member.

In order to solve this problem, in the present invention, after hot stamping as a shock absorber, a steel material having a bainite and martensite dual phase and a tensile strength of about 1000 MPa or more is used to reduce material deviation from 150K steel. It is possible to solve the problem in the case of using the conventional 70K grade steel. In addition, the first member 110 corresponding to the shock support part and the second member 120 corresponding to the shock absorption part are welded to be inclined at a predetermined angle,

In the case of the center pillar applied in this way, a physical boundary line due to the difference in material strength and thickness is generated by the weld WL. The weld WL becomes a central axis of bending deformation of the center pillar when a lateral load of the side impact is applied. This bending deformation mode may increase the amount of vehicle body deformation, and in severe cases, may act as a starting point for component failure. Therefore, when the weld WL is applied diagonally, the geometrical TWB boundary is enlarged and does not act as an axis of the bending center for lateral load, and the bending resistance increases, thus material properties between 1.5 GPa and 1 GPa As a result, it is possible to reduce vehicle body deformation.

In the case of a rearside member or frontside member, it is a major component that protects the vehicle body against longitudinal loads, such as a partial head-on collision or a rear-end collision according to Federal Motor Vehicle Safety Standard 301 (FMVSS301). The second member 120 may be applied to the front of the members so that energy is absorbed well, and the impact support part at the rear of the members may be designed to apply the first member 110 . In the collision mode of the members, since only a part of the vehicle body overlaps, a large bending load is applied. When the welding portion WL of the members is vertically applied, the members whose collision deformation is completed are bent, thereby deforming the vehicle body or the fuel tank. This is a major cause of lowering the crash safety of the vehicle body. Therefore, when the welding portion WL is applied diagonally so that the first member 110, which is a high-strength material, is applied to the inside of the cross-section and the second member 120 having relatively low strength is applied to the outside, the strength at the time of collision is increased. Bending occurs towards the lower second member 120 . That is, the members are deformed outwardly, so that the members do not affect the vehicle body and the fuel tank.

The first member 110, by weight, carbon (C): 0.20% to 0.50%, silicon (Si): 0.05% to 1.00%, manganese (Mn): 0.10% to 2.50%, phosphorus (P): 0 % to 0.015% or less, sulfur (S): more than 0% to 0.005% or less, chromium (Cr): 0.05% to 1.00%, boron (B): 0.001% to 0.009%, titanium (Ti): 0.01% to 0.09% and the balance iron (Fe) and unavoidable impurities.

The first member 110 has a tensile strength (TS): 1200 MPa to 1500 MPa, and may have a martensitic single-phase structure.

The second member 120 is, by weight, carbon (C): 0.04% to 0.06%, silicon (Si): 0.4% to 0.6%, manganese (Mn): 1.7% to 1.9%, phosphorus (P): 0 % to 0.018% or less, Sulfur (S): 0% to 0.003% or less, Chromium (Cr): 0.1% to 0.3%, Boron (B): 0.0015% to 0.0025%, Titanium (Ti): 0.05% to 0.07 %, niobium (Nb): 0.04% to 0.06% and the balance contains iron (Fe) and unavoidable impurities.

The second member 120, tensile strength (TS): 900 MPa to 1100 MPa, yield strength (YS): 700 MPa to 900 MPa, and elongation (El): 8% to 10%, bending angle (VDA238-100) ) may have mechanical properties of 90 degrees to 120 degrees. The second member 120 may have a dual phase structure of bainite and martensite.

The role of each component constituting the second member 120 and the content thereof will be described as follows.

carbon (C)

Carbon (C) is a major element that determines the strength and hardness of steel, and is added after the hot stamping (or hot pressing) process to secure the tensile strength of the steel. In one embodiment, carbon (C) is preferably added in an amount of 0.04 wt% to 0.06 wt% based on the total weight of the second member 120 . When carbon (C) is added in an amount of less than 0.04% by weight, it is difficult to achieve the mechanical strength of the present invention, and when it is added in excess of 0.06% by weight, the toughness of the steel may be reduced.

silicon( Si )

Silicon (Si) is added for the purpose of securing a soft low-temperature phase during heat treatment. Silicon (Si) is preferably added in a content ratio of 0.4 wt% to 0.6 wt% of the second member 120 . When the content of silicon (Si) is less than 0.4% by weight, it is difficult to secure a soft low-temperature phase during heat treatment.

Manganese (Mn)

Manganese (Mn) is added to increase hardenability and strength during heat treatment. Manganese (Mn) is preferably added in a content ratio of 1.7 wt% to 1.9 wt% of the second member 120 . When the content of manganese (Mn) is less than 1.7 wt%, the effect of refining the grains is insufficient. Conversely, when the content of manganese (Mn) exceeds 1.9 wt %, there is a problem in that toughness is deteriorated due to segregation in the center and disadvantageous in terms of cost.

Phosphorus (P)

The phosphorus (P) is an element that segregates well and inhibits the toughness of steel. Phosphorus (P) is preferably added in a content ratio of greater than 0% by weight to 0.018% by weight or less of the second member 120 . When included in the above range, it is possible to prevent deterioration of toughness. When the phosphorus is included in an amount exceeding 0.018% by weight, cracks may be caused during the process, and an iron phosphide compound may be formed, thereby reducing toughness.

Sulfur (S)

Sulfur (S) is an element that inhibits processability and physical properties. Sulfur (S) is preferably added in a content ratio of greater than 0 wt% to 0.003 wt% or less of the second member (120). When the sulfur is included in an amount exceeding 0.003% by weight, the hot workability is deteriorated, and surface defects such as cracks may occur due to the generation of large inclusions.

chrome( Cr )

Chromium (Cr) is added for the purpose of improving the hardenability and strength of the steel. Chromium (Cr) is preferably added in a content ratio of 0.1 wt% to 0.3 wt% of the second member 120 . When the content of chromium (Cr) is less than 0.1 wt%, the effect of improving hardenability and strength is insufficient. Conversely, when the content of chromium (Cr) exceeds 0.3 wt%, there is a problem in that toughness is lowered.

Boron (B)

Boron (B) is added for the purpose of securing soft martensite hardenability and refining crystal grains. Boron (B) is preferably added in a content ratio of 0.0015% by weight to 0.0025% by weight of the second member 120 . When the content of boron (B) is less than 0.0015% by weight, the effect of improving hardenability is insufficient. Conversely, when the content of boron (B) exceeds 0.0025 wt %, there is a problem in that the risk of inferior elongation is increased.

titanium( Ti )

Titanium (Ti) is added for the purpose of increasing strength and toughness according to a decrease in the martensite packet size. Titanium (Ti) is preferably added in a content ratio of 0.05 wt% to 0.07 wt% of the second member 120 . When the content of titanium (Ti) is less than 0.05% by weight, the effect of refining the grains is insufficient. Conversely, when the content of titanium (Ti) exceeds 0.07% by weight, toughness may be deteriorated.

Niobium ( Nb )

Niobium (Nb) is added for the purpose of increasing strength and toughness according to a decrease in martensite packet size. In addition, niobium (Nb) contributes to the improvement of the elongation of the steel material through the stabilization of the ferrite region. In one embodiment, niobium (Nb) is added in an amount of 0.04 wt% to 0.06 wt% of the second member 120 . When niobium (Nb) is added in an amount of less than 0.04% by weight, the effect of refining the grains of the steel in the hot rolling and cold rolling process is insignificant, and when it is added in excess of 0.06% by weight, coarse precipitates in steelmaking may be generated, and the steel elongation This decreases, which is disadvantageous in terms of cost.

Hereinafter, a case in which the first member 110 and the second member 120 are plated steel sheets will be exemplarily described.

The first member 110 and the second member 120 may be an aluminum plated steel sheet or an aluminum alloy plated steel sheet. When the first member 110 and the second member 120 are welded, aluminum constituting the plating layer may be mixed into the base steel sheet. In this case, after performing hot stamping, the strength of the weld is lowered, and there is a risk of fracture in the weld, and accordingly, the ability to absorb collision energy in the weld may be reduced. The plating layer may be formed by immersing the base steel sheet in molten aluminum or molten aluminum alloy at 600° C. to 800° C., and cooling it at an average rate of 1° C./sec to 50° C./sec. After the base steel sheet is immersed, air or gas is sprayed on the surface to wipe the hot-dip plating layer, and the amount of plating adhesion on the base steel sheet can be adjusted by controlling the spray pressure. The plating adhesion amount is preferably ^{20 g/m 2} to 100 g/m ² on at least one surface of the base steel sheet. If it is less than 20 g/m ² , the corrosion resistance is lowered, and ^{when it exceeds 100 g/m 2} , the amount of Al mixed into the welding part when joining the plated steel sheet increases, and the strength of the welding part after hot stamping is decreased.

The plating layer includes aluminum or an aluminum alloy, is formed on the surface of the base steel sheet and includes an Al-Fe to Al-Fe-Si intermetallic compound, and an alloying having an iron (Fe) content of 20 wt% to 50 wt% a layer and a surface layer having an aluminum content of at least 80% by weight and an average thickness of 10 μm to 40 μm. When the average thickness is less than 10 μm, corrosion resistance is lowered, and when the average thickness is 40 μm or more, the amount of Al mixed into the welding part during bonding increases, and the mechanical properties of the welding part after hot stamping are deteriorated.

A filler wire may be used during welding in order to prevent a decrease in the strength of the welded portion due to the incorporation of aluminum in the plating layer, particularly the surface layer. The welding may include laser welding, and preferably may be performed only by laser welding. The filler wire may include an austenite stabilizing element such as carbon and manganese, and may be made of a component system in which ferrite is not formed at 800°C to 980°C. In the case of welding using such a filler wire, the welding portion WL after performing hot stamping may include aluminum mixed in the plating layer.

In one embodiment, the filler wire may include 0.3 wt% to 1.0 wt% of carbon and 0.3 wt% to 1.2 wt% of manganese (Mn). Preferably, the filler wire may contain 0.5 wt% to 0.8 wt% of carbon and 0.4 wt% to 1.0 wt% of manganese. For example, the filler wire may include 0.62 wt% carbon and 0.45 wt% manganese.

Aluminum included in the base steel sheet of the first member 110 and the second member 120 and aluminum included in the plating layer may include a total of 0.1 wt% to 2.0 wt%. Here, each of the first member 110 and the second member 120 may contain less than 0.1 wt% of aluminum. In order for the aluminum content to be less than 0.2 wt%, the process cost increases because the plating layer must be removed when the blank is joined. and strength may be reduced. Preferably, the content of aluminum may be 0.1 wt% to 1.0 wt%. When the content of aluminum is 1.0 wt% or more, there is a risk that a large amount of oxide film is formed in the subsequent portion.

The microstructure of the welded portion WL may contain 90% by weight or more of martensite, or preferably the whole may be composed of martensite.

Hereinafter, a method of manufacturing a hot stamping part according to an embodiment of the present invention will be described in detail.

4 is a flowchart illustrating a method ( S100 ) of manufacturing a hot stamping part for a vehicle according to an embodiment of the present invention.

Referring to FIG. 4 , the method of manufacturing a hot stamping part for a vehicle ( S100 ) includes preparing a first blank and a second blank ( S110 ); forming a bonding material by welding the first blank and the second blank (S120); Cutting the bonding material to form a bonding cutting material (S130); forming a molded body by hot stamping the bonding cutting material (S140); and cooling the molded body to form a hot stamping part for a vehicle (S150).

5 and 6 are schematic views illustrating a method of manufacturing the hot stamping part for a vehicle of FIG. 4 according to an embodiment of the present invention according to a process sequence. A center pillar is illustrated as an example of the hot stamping part for the vehicle.

4 and 5 , the step of preparing the first blank 111 and the second blank 121 ( S110 ) is performed. The step (S110) is a step of preparing a different type of blank, and a first blank 111 forming a first member 110 functioning as a collision support part and a second member 120 functioning as a shock absorption part are prepared. A second blank 121 to be formed is prepared.

The first blank 111 is a material constituting the collision support part of the center pillar, and in order to protect the driver by securing a survival space for the driver in the event of a vehicle collision, for example, a tensile strength of 1200 MPa to 1500 MPa after hot stamping. It is made of ultra-high strength steel with single phase martensite.

The first blank 111 is a reheating temperature (SRT) of the steel slab: reheating to a temperature of 1200 ℃ ~ 1250 ℃; Finishing hot rolling the reheated slab at a finish rolling temperature (FDT): 900° C. to 950° C.; winding the finish hot-rolled blank by cooling to a coiling temperature (CT): 680° C. to 800° C.; uncoiling and cold rolling the wound blank; and annealing the cold-rolled blank at 740°C to 820°C.

The second blank 121 is a material constituting the shock absorbing part of the center pillar, and preferably has appropriate strength to protect the driver in case of a vehicle collision, but has ductility to protect the driver by absorbing the shock in the case of a collision. For example, the second blank 121 has a tensile strength (TS): 900 MPa to 1100 MPa, a yield strength (YS): 700 MPa to 900 MPa, and an elongation (El): 8% to 10% after hot stamping treatment , has a bending angle of 90 degrees to 120 degrees, and may have a dual phase structure of bainite and martensite.

The second blank 121, heating the steel slab to a reheating temperature (SRT): 1200 ℃ ~ 1250 ℃ condition; Finishing hot rolling the reheated steel slab at a finish rolling temperature (FDT): 860° C. to 920° C.; winding the finish hot-rolled blank by cooling to a coiling temperature (CT): 620° C. to 660° C.; uncoiling and cold rolling the wound blank; and performing annealing heat treatment of the cold-rolled blank.

The second blank 121 may be provided to be thicker than the first blank 111 . For example, if the first blank 111 is provided with a thickness of about 1.1 mm to 1.3 mm, the second blank 121 may be provided with a thickness of about 1.5 mm to 1.7 mm. Accordingly, in the case of the center pillar as the hot stamping part 100 for a vehicle of FIG. 1 , the first member 110 processed into the first blank 111 has a thickness of about 1.1 mm to 1.3 mm, and the second blank 121 ), the processed second member 120 may be configured to have a thickness of about 1.5 mm to 1.7 mm. However, this is exemplary, and the present invention is not limited thereto. For example, a case in which the thickness of the first blank 111 is greater than that of the second blank 121 or a case in which the thickness is the same is also included in the technical concept of the present invention.

Then, the step of forming the bonding material 113 by welding the first blank 111 and the second blank 121 (S120) is performed. For example, the first blank 111 is disposed to be a collision support part of the upper part of the center pillar, and the second blank 121 is disposed to be an impact absorption part of the lower part of the center pillar, and, for example, laser welding is performed. It can be welded by a butt method using friction stir welding or the like.

Next, the step (S130) of cutting the bonding material 113 to form the bonding cutting material 115 is performed. The cutting (S130) may be performed using a laser, and may be performed simultaneously with the above-described welding. In the cutting step S130 , the bonding cutting material 115 may be cut so that the welding portion WL is an oblique line having a predetermined angle with respect to the horizontal line HL. The bonding cutting material 115 may include a first blank portion 112 cut from the first blank 111 and a second blank portion 122 cut from the second blank 121 .

4 and 6, the step (S140) of forming a molded body by hot stamping the bonding cutting material 115 is performed. The bonding cutting material 115 is softened by heating in the heating furnace 10 at a temperature of Ac3 or higher, preferably at a temperature of 800°C to 980°C. For example, the heating may be performed at a temperature of 950° C. for about 5 minutes. Then, the heated bonding cutting material 115 is transferred to the press mold 20 . In this case, a transfer time of about 5 to 20 seconds may be required. The bonding cutting material 115 is press-worked in the press mold 20 to form a molded body 117 having a final part shape.

Then, a step (S150) of cooling the molded body 117 to form a hot stamping part for a vehicle is performed. The molded body 117 is rapidly cooled to a temperature of 300° C. or less at an average cooling rate of about 20° C./sec to 120° C./sec to form the hot stamping part 100 for a vehicle. Such cooling may be performed simultaneously with molding in the press mold 20 . The press mold 20 may be provided with a cooling channel 22 through which a refrigerant circulates therein. It is possible to rapidly cool the heated molded body 117 by circulation by the refrigerant supplied through the provided cooling channel 22 . At this time, it is possible to maintain a state in which the cooling water of about 20 ℃ is supplied to the cooling channel 22 of the mold 20 . In order to prevent a spring back phenomenon of the molded body 117 and maintain a desired shape, rapid cooling may be performed while the press mold is closed and pressurized. For example, the molding of the bonding cutting material 115 in the mold 20 may be completed within about 5 seconds, and the molded body 117 may be rapidly cooled for about 30 seconds.

By the hot stamping, the bonding cutting material 115 is heated to a high temperature to soften it, so that it can be press-worked easily, and the mechanical strength of the steel is increased by quenching by cooling after forming. However, since the steel is heated to a high temperature of 800° C. or higher, iron (Fe) on the surface of the steel is oxidized and oxide (scale) is generated. Therefore, after the annealing heat treatment described above, a predetermined coating can be performed on the first blank 111 and the second blank 121, and aluminum (Al) having a higher melting point than organic coating or zinc (Zn) coating. )-based metal coating, for example, aluminum (Al)-silicon (Si)-based plating treatment may be performed. When the aluminum (Al)-silicon (Si) is plated, corrosion is prevented and the generation of scale on a hot surface when moving to a press can be prevented.

According to an embodiment of the present invention, a method of manufacturing a hot stamping part for a vehicle includes: forming a molded body by hot stamping a cutting material cut by welding a first blank and a second blank; and hot stamping the bonding cutting material to form a molded body. and cooling the molded body to form a hot stamping part for a vehicle. The bonding cutting material may be manufactured by cutting the welding portion to be formed inclined at a predetermined angle with respect to the horizontal line.

According to an embodiment of the present invention, a bonding material for hot stamping parts for a vehicle includes: a first blank having a first strength and a first elongation; a second blank welded to the first blank and having a second strength lower than the first strength and a second elongation higher than the first elongation; and a welding part formed by welding the first blank and the second blank, wherein the welding part has a predetermined angle with respect to a horizontal line extending in parallel with respect to an end of any one of the first blank and the second blank. It can be formed inclined to

According to an embodiment of the present invention, a hot stamping part for a vehicle is formed by cutting a bonding material for a vehicle hot stamping component to form a bonding cutting material, hot stamping the bonding cutting material to form a molded body, and cooling the molding to form a vehicle A hot stamping part, the hot stamping part for a vehicle comprising: a first member formed from the first blank and having a first strength and a first elongation; a second member formed from the second blank, welded to the first blank, and having a second strength lower than the first strength and a second elongation higher than the first elongation; The welding portion formed by welding the member and the second member may be formed inclined at a predetermined angle with respect to a horizontal line extending in parallel with respect to an end of any one of the first member and the second member.

Hereinafter, the mechanical properties in the case of applying the hot stamping parts for vehicles according to the technical spirit of the present invention will be described.

7 is a rear collision analysis result when the hot stamping part for a vehicle according to an embodiment of the present invention is applied to the rear side member. am. 7 (a) and (b) is a comparative example, a case in which the angle of the welding portion with respect to the horizontal line is 0 degree, that is, the first blank and the second blank are formed by laser welding in parallel with two lines. 7( c ) and 7 ( d ) show a case in which the welding part is formed by laser welding with the angle of the welding part with respect to the horizontal line oblique to 45 degrees as an embodiment.

Referring to FIG. 7 , it can be seen that the blue region indicating a high degree of deformation is increased in the embodiment compared to the comparative example, and accordingly, the embodiment increases the deformation of the rear portion of the rear side member.

8 shows a result of deformation of a fuel tank space when the hot stamping part for a vehicle according to an embodiment of the present invention is applied to a rear side member.

Referring to FIG. 8 , as compared to the comparative example, in the example, the amount of deformation was greatly reduced at the measurement position 3 and increased at the measurement position 6 and the measurement position 7 . That is, in the case of the embodiment, it is possible to provide an effect of improving the vehicle body deformation amount in the fuel tank space by 22.1 mm by about 23.5% by controlling the vehicle body deformation mode during a rear collision. Therefore, in the case of the embodiment, it is possible to locally strengthen the material and control the vehicle body deformation mode, and it is possible to minimize the problem of undesirable local fracture caused by brittle fracture.

9(b) shows the deformation mode results according to the IIHS side collision standard when the hot stamping part for a vehicle according to an embodiment of the present invention is applied to the center pillar. As a comparative example, the result of the deformation mode of the center pillar manufactured by the local softening technique is shown in FIG. 9(a).

Referring to FIGS. 9A and 9B , compared to the Comparative Example, the local deformation was significantly reduced in the central portion of the center pillar, which is the area A of the blue dotted line. On the other hand, the local deformation was increased in the central part of the center pillar, which is the area B of the red dotted line. That is, it is analyzed that the deformation occurred in the B region so that the deformation occurring in the A region is suppressed. Therefore, it can be seen that the embodiment of the present invention can ensure stability by reducing the deformation of area A, which is highly likely to injure the driver. By reducing the thickness of the region B where the deformation is induced to 1.2t or less and increasing the lower deformation, the upper load can be reduced, and through this, additional weight reduction of the vehicle body can be achieved.

The technical spirit of the present invention described above is not limited to the above-described embodiments and the accompanying drawings, and it is the technical spirit of the present invention that various substitutions, modifications and changes are possible without departing from the technical spirit of the present invention. It will be apparent to those of ordinary skill in the art to which this belongs.

10: heating furnace, 20: press mold,
22: cooling channel, 100: hot stamping part;
110: a first member, 120: a second member,
111: a first blank, 112: a first blank portion;
113: bonding material, 115: bonding cutting material,
117: molded body, 121: second blank,
122: second blank portion, 200: center pillar,
210, 310, 410: high intensity region;
220, 320, 420: high ductility area;
300: front side member, 400: rear side member,
WL: Weld, HL: Horizontal,

Claims (12)

a first member having a first strength and a first elongation; and
a second member welded to the first member and having a second strength lower than the first strength and a second elongation higher than the first elongation;
A welding portion formed by welding the first member and the second member is formed inclined at a predetermined angle with respect to a horizontal line extending parallel to an end of any one of the first member and the second member,
Hot stamping parts for vehicles. The method of claim 1,
wherein the angle has a range greater than 0 degrees and less than or equal to 60 degrees with respect to the horizontal line,
Hot stamping parts for vehicles. The method of claim 1,
The first member, by weight, carbon (C): 0.20% to 0.50%, silicon (Si): 0.05% to 1.00%, manganese (Mn): 0.10% to 2.50%, phosphorus (P): more than 0% ~ 0.015% or less, sulfur (S): more than 0% ~ 0.005% or less, chromium (Cr): 0.05% to 1.00%, boron (B): 0.001% to 0.009%, titanium (Ti): 0.01% to 0.09% and the balance of iron (Fe) and unavoidable impurities,
Hot stamping parts for vehicles. The method of claim 1,
The second member, by weight, carbon (C): 0.04% to 0.06%, silicon (Si): 0.4% to 0.6%, manganese (Mn): 1.7% to 1.9%, phosphorus (P): more than 0% ~ 0.018% or less, sulfur (S): more than 0% ~ 0.003% or less, chromium (Cr): 0.1% to 0.3%, boron (B): 0.0015% to 0.0025%, titanium (Ti): 0.05% to 0.07% , niobium (Nb): 0.04% to 0.06% and the balance containing iron (Fe) and unavoidable impurities,
Hot stamping parts for vehicles. The method of claim 1,
The first member, tensile strength (TS): having a range of 1200 MPa ~ 1500 MPa,
Hot stamping parts for vehicles. The method of claim 1,
The second member has a tensile strength (TS): 900 MPa to 1100 MPa, a yield strength (YS): 700 MPa to 900 MPa, and an elongation (El): 8% to 10%, a bending angle of 90° to 120° branch,
Hot stamping parts for vehicles. The method of claim 1,
The first member has a martensitic single-phase structure,
Hot stamping parts for vehicles. The method of claim 1,
The second member has a dual phase structure of bainite and martensite,
Hot stamping parts for vehicles. The method of claim 1,
The hot stamping part for the vehicle includes a center pillar, a front side member, a rear side member, or a roof side member,
Hot stamping parts for vehicles. forming a molded body by hot stamping the cut joint cutting material by welding the first blank and the second blank; and
Including; cooling the molded body to form a hot stamping part for a vehicle;
The hot stamping part for a vehicle may include: a first member formed from the first blank and having a first strength and a first elongation; a second member formed from the second blank, welded to the first blank, and having a second strength lower than the first strength and a second elongation higher than the first elongation;
The welding portion of the first member and the second member is formed inclined at a predetermined angle with respect to a horizontal line extending parallel to the end of any one of the first member and the second member,
A method of manufacturing hot stamping parts for vehicles. 11. The method of claim 10,
The joint cutting material is manufactured by cutting so that the welding part is formed inclined at a predetermined angle with respect to the horizontal line,
A method of manufacturing hot stamping parts for vehicles. 11. The method of claim 10,
The second blank,
Reheating the steel slab temperature (SRT): heating to 1200 ℃ ~ 1250 ℃ conditions;
Finishing hot rolling the reheated steel slab at a finish rolling temperature (FDT): 860° C. to 920° C.;
winding the finish hot-rolled blank by cooling to a coiling temperature (CT): 620° C. to 660° C.;
uncoiling and cold rolling the wound blank; and
Formed by performing an annealing heat treatment of the cold-rolled blank,
A method of manufacturing hot stamping parts for vehicles.

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