KR102089154B1 - Hot stamping component and method of manufacturing the same - Google Patents

Abstract

The present invention is carbon (C): 0.04 to 0.06% by weight, silicon (Si): 0.4 to 0.6% by weight, manganese (Mn): 1.7 to 1.9% by weight, phosphorus (P): more than 0 and 0.018% by weight or less, sulfur ( S): 0 to 0.003 wt% or less, Chromium (Cr): 0.1 to 0.3 wt%, Boron (B): 0.0015 to 0.0025 wt%, Titanium (Ti): 0.05 to 0.07 wt%, Niobium (Nb): 0.04 to A hot stamping part is provided, comprising 0.06% by weight and a balance of iron (Fe) and an inevitable impurity.

Description

Hot stamping component and method of manufacturing the same}

The present invention relates to a hot stamping part and a method for manufacturing the same, and more particularly, to a hot stamping part and a method for manufacturing the same, with improved elongation and performance as a shock absorber while minimizing material deviation according to process parameters of the hot stamping process. .

Recently, the automobile industry is demanding rigorous collision performance to enhance passenger safety. In addition, as the awareness of the environment increases, the fuel efficiency standards according to the exhaust gas regulations have been strengthened, and accordingly, the need for weight reduction of the vehicle body is continuously increasing. As part of an effort to simultaneously satisfy the demands of improving collision performance and reducing weight, the application of the body of a high-strength steel sheet is continuously increasing. When manufacturing a car body, high-strength parts are applied to reinforce side collisions because it plays a very important role in securing the driver's survival space during side collisions. In the case of 150K class high-strength steel mainly used as a collision member of a vehicle, due to a brittle fracture phenomenon that threatens the safety of the driver when the vehicle collides with the side, the Taylor Welded Blank (TWB) method is used in the lower part where brittleness occurs. The shock absorbing ability is improved by connecting other members.

A related technology is the Republic of Korea Patent Publication No. 2016-0061560 (published on June 1, 2016, Taylor Welded Blank manufacturing method).

The problem to be solved by the present invention is to provide a hot stamping part and a method for manufacturing the same, which can improve elongation and collision performance while minimizing material variation through control of alloy components and control of process conditions.

Hot stamping parts according to an embodiment of the present invention for achieving the above object is carbon (C): 0.04 ~ 0.06% by weight, silicon (Si): 0.4 ~ 0.6% by weight, manganese (Mn): 1.7 ~ 1.9% by weight , Phosphorus (P): more than 0 0.018 wt% or less, sulfur (S): more than 0 0.003 wt% or less, chromium (Cr): 0.1 to 0.3 wt%, boron (B): 0.0015 to 0.0025 wt%, titanium (Ti ): 0.05 to 0.07% by weight, niobium (Nb): 0.04 to 0.06% by weight, and the balance of iron (Fe) and steel materials composed of unavoidable impurities.

In the hot stamping part, the steel material may have a tensile strength (TS): 1000 MPa or more, a yield strength (YS): 880 MPa or more, and an elongation (El): 8% or more.

In the hot stamping part, the steel material may have a dual phase structure of bainite and martensite.

Method for producing a hot stamping part according to an embodiment of the present invention for achieving the above object is (a) carbon (C): 0.04 ~ 0.06% by weight, silicon (Si): 0.4 ~ 0.6% by weight, manganese (Mn) : 1.7 to 1.9% by weight, phosphorus (P): more than 0 to 0.018% by weight, sulfur (S): more than 0 to 0.003% by weight, chromium (Cr): 0.1 to 0.3% by weight, boron (B): 0.0015 to 0.0025 Weight percent, titanium (Ti): 0.05 to 0.07 weight percent, niobium (Nb): 0.04 to 0.06 weight percent, and the first blank using a steel slab containing the remaining iron (Fe) and unavoidable impurities, and the first blank Preparing a second blank by cutting the steel sheet provided separately from; (b) welding the first blank and the second blank in a Taylor welded blank method to form a joined steel; (c) forming a molded body by hot stamping the bonded steel material with a press mold; And (d) cooling the molded body to form a hot stamping part. It includes.

The step (a) of the method for manufacturing the hot stamping part includes: (a-1) heating the steel slab under conditions of reheating temperature (SRT): 1200 to 1250 ° C; (a-2) finishing hot rolling the reheated steel slab under the conditions of finishing rolling temperature (FDT): 860 to 920 ° C; (a-3) winding the finished hot-rolled sheet to a winding temperature (CT): 620 to 660 ° C; (a-4) uncoiling and cold rolling the wound plate; And (a-5) heat-treating the cold-rolled sheet material; It may include.

The step (c) of the method of manufacturing the hot stamping part includes: (c-1) heating the bonding steel to a temperature of 850 to 950 ° C; And (c-2) transferring the heated bonded steel material to the press mold at a transfer time of 9 to 11 seconds.

In step (d) of the method for manufacturing the hot stamping part, cooling of the molded body may be performed at a rate of 30 to 120 ° C / s.

According to an embodiment of the present invention, it is possible to implement a hot stamping component and a method for manufacturing the same, which can improve elongation and collision performance while minimizing material variation through control of alloy components and control of process conditions. Of course, the scope of the present invention is not limited by these effects.

1 is a process flow chart showing a method of manufacturing a hot stamping part according to an embodiment of the present invention.
2 is a process flow chart showing the steps of preparing a blank for hot stamping in the method of manufacturing a hot stamping part according to the embodiment of the present invention of FIG.
3 is a diagram illustrating the concept of microstructure phase transformation according to a temperature change during a hot stamping process in a method of manufacturing a hot stamping part according to an embodiment of the present invention and a comparative example.

Hereinafter, a method of manufacturing a steel material for line pipe according to an embodiment of the present invention will be described in detail. Terms to be described later are terms appropriately selected in consideration of functions in the present invention, and definitions of these terms should be made based on contents throughout the present specification.

B-pillars, which are important parts for vehicle collision members, are manufactured by welding two steels and forming them by combining steels of different strengths in the upper impact support and the lower shock absorber. At this time, the Taylor Welded Blank (TWB) method, which is mainly used, refers to a series of processes for manufacturing parts by cutting, welding, and pressing a different type of steel sheet of different thickness, strength, and material into a required shape. , It can be welded with different thickness and steel, so that it can have the required properties for each part. 120-150K grade ultra-high-strength steel is used, for example, at the upper impact support part of the B-pillar, and a shock absorbing performance member is connected to the lower part of the B-pillar where stress is concentrated by the TWB method to absorb shock during vehicle collision. The steel material used for the shock absorbing portion of the B-pillar is usually referred to as TWB steel, although improving the ability.

The currently developed steel for TWB has a dual phase of final ferrite and ferrite-martensite through a hot stamping process after hot rolling and cold rolling processes, and is being developed as a steel having a tensile strength of 70K. In order to form a B-pillar, the 70K-class TWB steel and, for example, 150K-class steel are welded by a TWB method and then hot stamped.

However, since the existing 150K grade steel obtains 100% martensite structure through a hot stamping process, there is no material change during the hot stamping process, but in the case of 70K class TWB steel, various variables of the hot stamping process, for example, steel There is a disadvantage in that the material rapidly changes depending on the transfer time taken to transfer to the hot stamping mold after heating, or the cooling rate of the blank or mold. Therefore, when the 70K-class TWB steel is welded with 150K-class steel to form a bonded steel, and hot stamping is performed on the bonded steel, the material variation of the hot stamping parts appears because the control of process variables is very difficult. It is not suitable as a crash member for automobiles. In order to improve this, the present invention is to provide a hot stamping component which is a steel material for 80 to 100K class TWB that can be welded with 150K class steel by controlling the component composition of the steel and minimizing the material deviation of the steel in a range of hot stamping process variables.

Steel for TWB

One aspect of the present invention relates to a hot stamping component as a steel for TWB that undergoes a hot stamping process. In one embodiment, the hot stamping part according to an aspect of the present invention, carbon (C): 0.04 ~ 0.06 wt%, silicon (Si): 0.4 ~ 0.6 wt%, manganese (Mn): 1.7 ~ 1.9 wt%, Phosphorus (P): more than 0 0.018 wt% or less, sulfur (S): more than 0 0.003 wt% or less, chromium (Cr): 0.1 to 0.3 wt%, boron (B): 0.0015 to 0.0025 wt%, titanium (Ti) : 0.05 to 0.07% by weight, niobium (Nb): 0.04 to 0.06% by weight, and the balance of iron (Fe) and unavoidable impurities.

The hot stamping part finally has a tensile strength (TS): 1000 MPa or more, a yield strength (YS): 880 MPa or more, and an elongation (El): 8% or more after hot stamping, and dual phase structure of bainite and martensite Have

The hot stamping part of the present invention is a steel material for TWB, and after being hot-stamped in a state of being bonded to a 150k class steel material, a tensile strength of 80 to 100K class can be reliably implemented. Therefore, the TWB steel material has a higher strength than the conventional 70K class steel material in a state of being joined with a 150K class steel material, and at the same time, it is possible to increase the impact absorption rate.

The role and content of each component included in the TWB steel according to the present invention will be described as follows.

Carbon (C)

Carbon (C) is a major element that determines the strength and hardness of the steel material, and is added for the purpose of securing the tensile strength of the steel material after the hot stamping (or hot pressing) process. In one embodiment, carbon (C) is preferably added in an amount of 0.04 to 0.06% by weight relative to the entire steel for TWB. When carbon (C) is added in an amount of less than 0.04% by weight, it is difficult to achieve mechanical strength of the present invention, and when it is added in an amount exceeding 0.06% by weight, toughness of the steel may be deteriorated.

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 to 0.6% by weight of the steel for TWB according to the present invention. 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. Conversely, when the content of silicon (Si) exceeds 0.6% by weight, there is a problem that the plating properties are deteriorated.

Manganese (Mn)

Manganese (Mn) is added for the purpose of increasing quenchability and strength during heat treatment. Manganese (Mn) is preferably added in a content ratio of 1.7 to 1.9% by weight of the steel for TWB according to the present invention. When the content of manganese (Mn) is less than 1.7% by weight, the grain refinement effect is insufficient. Conversely, when the content of manganese (Mn) exceeds 1.9 wt%, there is a problem that toughness deteriorates due to occurrence of central segregation and disadvantages 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 more than 0 and 0.018% by weight or less of the steel for TWB according to the present invention. When included in the above range, the toughness can be prevented. When the phosphorus is included in an amount exceeding 0.018% by weight, cracks may occur during the process, and iron phosphide compounds may be formed to deteriorate toughness.

Sulfur (S)

Sulfur (S) is an element that inhibits processability and properties. Sulfur (S) is preferably added in a content ratio of more than 0 to 0.003% by weight or less of the steel for TWB according to the present invention. When the sulfur is included in an amount exceeding 0.003% by weight, hot workability is deteriorated, and surface defects such as cracks may occur due to generation of large inclusions.

Chrome (Cr)

Chromium (Cr) is added for the purpose of improving the quenching and strength of the steel. Chromium (Cr) is preferably added in a content ratio of 0.1 to 0.3% by weight of the steel for TWB according to the present invention. When the content of chromium (Cr) is less than 0.1% by weight, the effect of improving the quenching properties and strength is insufficient. Conversely, when the content of chromium (Cr) exceeds 0.3% by weight, there is a problem that the toughness is lowered.

Boron (B)

Boron (B) is added for the purpose of securing soft martensite quenchability and miniaturizing crystal grains. Boron (B) is preferably added in a content ratio of 0.0015 to 0.0025% by weight of the steel for TWB according to the present invention. When the content of boron (B) is less than 0.0015% by weight, the effect of improving quenching is insufficient. Conversely, when the content of boron (B) exceeds 0.0025% by weight, there is a problem in that the risk of elongation deterioration increases.

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 to 0.07% by weight of the steel for TWB according to the present invention. When the content of titanium (Ti) is less than 0.05% by weight, the effect of grain refinement is insufficient. Conversely, when the content of titanium (Ti) exceeds 0.07% by weight, toughness may be reduced.

Niobium (Nb)

Niobium (Nb) is added for the purpose of increasing strength and toughness with decreasing martensite packet size. In addition, niobium (Nb) contributes to the improvement of the elongation of the steel material through stable securing of the ferrite region. In one embodiment, niobium (Nb) is added in an amount of 0.04 to 0.06% by weight of the steel for TWB according to the present invention. When niobium (Nb) is added in an amount of less than 0.04% by weight, the grain refining effect of the steel is minimal in the hot rolling and cold rolling processes, and when it exceeds 0.06% by weight, steelmaking coarse precipitates may be generated, and the steel elongation rate This decreases and is disadvantageous in terms of cost.

Next, a method for manufacturing a hot stamping part using the steel for TWB of the present invention described above will be described in detail.

Manufacturing method of hot stamping parts

Another aspect of the present invention relates to a method of manufacturing a hot stamping part using a steel for TWB that undergoes a TWB process.

1 is a process flow chart illustrating a method of manufacturing a hot stamping part according to the present invention, and FIG. 2 is a flow chart specifically showing a step of preparing a blank for hot stamping of FIG. 1.

Referring to Figure 1, the method of manufacturing a hot stamping part according to an embodiment of the present invention, preparing the hot stamping blanks made of different types of steel (S110), bonding the hot stamping blanks to join the steel Forming step (S120), performing hot stamping using the bonding steel to form a molded body (S130), and cooling the molded body to form a hot stamping part (S140).

Preparing a blank for hot stamping (S110)

In the preparing of the blank for hot stamping (S110), a different sheet material for forming a hot stamping part is cut into a desired shape according to a purpose, for example, a first to be a shock absorber for forming a B-pillar of a vehicle. It is a step of forming a blank and a second blank to be collision supports, respectively.

The first blank is a portion that becomes an impact absorbing part of the B-pillar after hot stamping, and has an appropriate strength to protect the driver in the event of a vehicle collision, but preferably has an elongation to protect the driver by absorbing the impact in the event of a collision. According to a preferred embodiment of the present invention, the first blank after hot stamping is tensile strength (TS): 1000 MPa or more, yield strength (YS): 880 MPa or more, and elongation (El): 8% or more, and bainite. It consists of a steel material having a dual phase structure of martensite.

The second blank is a part that becomes a collision support part of the B-pillar after hot stamping, and has a tensile strength of 1,200 to 1,500 MPa after hot stamping to protect the driver by securing the driver's survival space during a vehicle collision It is made of ultra-high strength steel.

The process of forming the first blank may include a hot rolling step (S210), a cooling / winding step (S220), a cold rolling step (S230), and an annealing heat treatment step (S240), as shown in FIG. 2. .

In the method of manufacturing a hot stamping part according to the present invention, the slab plate material in a semi-finished product which is the subject of the process of forming the first blank is carbon (C): 0.04 to 0.06 wt%, silicon (Si): 0.4 to 0.6 wt. %, Manganese (Mn): 1.7 to 1.9 wt%, phosphorus (P): more than 0 to 0.018 wt%, sulfur (S): more than 0 to 0.003 wt%, chromium (Cr): 0.1 to 0.3 wt%, boron ( B): 0.0015 to 0.0025 wt%, titanium (Ti): 0.05 to 0.07 wt%, niobium (Nb): 0.04 to 0.06 wt%, and the balance of iron (Fe) and unavoidable impurities.

For hot rolling, a reheating step of the slab plate material is performed. In the slab reheating step, the slab plate obtained through the continuous casting process is reheated to SRT (Slab Reheating Temperature): 1200 to 1250 ° C, so that segregated components are re-used during casting. When the slab reheating temperature (SRT) is less than 1200 ° C, the segregated components during casting are not sufficiently re-used, making it difficult to see the homogenizing effect of the alloying elements, and the difficulty of seeing the solid solution effect of titanium (Ti) or niobium (Nb). have. The slab reheating temperature (SRT) is more favorable for homogenization at higher temperatures, but when it exceeds 1250 ° C, the grain size of austenite increases, making it difficult to secure strength as well as reducing hardenability and aging resistance. Only manufacturing costs can rise.

In the hot rolling step (S210), the reheated slab sheet is finished hot rolled under the conditions of Finishing Delivery Temperature (FDT): 860 to 920 ° C. At this time, if the finish rolling temperature (FDT) is too low, less than 860 ° C, it is difficult to secure the workability of the steel sheet due to the occurrence of a mixed structure due to abnormal region rolling, and there is a problem that the workability deteriorates due to non-uniformity of the microstructure as well as a rapid phase. Due to the change, there is a problem of mailability during hot rolling. Like the SRT, the finish rolling temperature (FDT) is more favorable for homogenization and is determined by the number of SRTs and passes, but when the finish rolling temperature (FDT) exceeds 920 ° C, the austenite grains become coarse and burnt. Curing ability and aging resistance decrease.

In the cooling / winding step (S220), the hot rolled sheet material is cooled to a coiling temperature (CT): 620 to 660 ° C. and wound. The coiling temperature affects the redistribution of carbon (C), and when the coiling temperature is less than 620 ° C, the low-temperature phase fraction due to supercooling increases, which increases the strength due to the addition of niobium (Nb) and increases the rolling load during cold rolling. There is a problem that the ductility is rapidly reduced. Conversely, when the coiling temperature exceeds 660 ° C, there is a problem in that moldability and strength deterioration occur due to abnormal grain growth or excessive grain growth.

In the cold rolling step (S230), the wound sheet material is uncoiled and pickled, followed by cold rolling. At this time, pickling is performed for the purpose of removing the scale of the coiled sheet material, that is, the hot rolled coil manufactured through the hot rolling process.

In the cold rolling, it is preferable to cold roll the pickled sheet at a cold rolling reduction ratio of 60 to 80%. When the cold rolling reduction is less than 60%, the deformation effect of the hot-rolled structure is small. Conversely, when the cold rolling reduction rate exceeds 80%, not only does the cost required for cold rolling rise, but also hinders the drawability and may cause a problem that the steel sheet breaks due to the occurrence of cracks at the edge of the steel sheet.

The annealing heat treatment step (S240) is an annealing heat treatment of the cold rolled sheet. In one embodiment, the annealing heat treatment includes heating the cold rolled sheet material and cooling the heated cold rolled sheet material at a cooling rate of 20 to 50 ° C./s. In one embodiment, the cold-rolled sheet during annealing heat treatment may be heated at 700 to 900 ° C. When heated to the above range, the process efficiency and the strength and formability of the steel material may be simultaneously excellent.

When the cold rolled sheet material is cooled at a cooling rate of less than 20 ° C / s, the productivity of the steel material decreases, and when cooling at a cooling rate exceeding 50 ° C / s, it may be difficult to secure a uniform microstructure of the steel material. For example, it can be cooled at a cooling rate of 30 to 40 ° C / s.

On the other hand, in the hot stamping step (S130) of FIG. 1 to be described later, the bonded steel material to be molded is heated to a high temperature, softened, pressed, and then cooled. Therefore, since the bonded steel material is softened by heating to a high temperature, it can be easily pressed, and the mechanical strength of the steel material is increased by quenching by cooling after molding. However, since the steel material is heated to a high temperature of 800 ° C. or higher, iron (Fe) on the surface of the steel material is oxidized to generate oxides (scales). Accordingly, in one embodiment of the present invention, after the annealing heat treatment, a predetermined coating may be applied to the cold rolled steel sheet, but an aluminum (Al) -based metal having a higher melting point than that of an organic-based coating or a zinc (Zn) -based coating. Coating may be performed, for example, aluminum (Al) -silicon (Si) -based plating treatment. The aluminum (Al) -silicon (Si) plated cold-rolled steel sheet can prevent corrosion and prevent the formation of scale on the surface of the hot steel sheet when moving to a press.

Meanwhile, the second blank may be formed by performing a hot rolling step, a cooling / winding step, a cold rolling step, and an annealing heat treatment step.

In the method for manufacturing a hot stamping part according to the present invention, the steel slab in the semi-finished product state, which is the subject of the process of forming the second blank, is carbon (C): 0.20 to 0.50%, silicon (Si): 0.05 by weight. ~ 1.00%, manganese (Mn): 0.10 ~ 2.50%, phosphorus (P): more than 0 and less than 0.015%, sulfur (S): more than 0 and less than 0.005%, chromium (Cr): 0.05-1.00%, boron (B) : 0.001 to 0.009%, titanium (Ti): 0.01 to 0.09% and the balance may be made of iron (Fe) and inevitable impurities. In one embodiment, the hot rolling step includes: reheating the steel slab to a temperature of 1200 to 1250 ° C, and finishing rolling the reheated slab at a temperature of 900 to 950 ° C; The hot-rolled steel sheet may be cooled to 680 ° C to 800 ° C and then wound up. Subsequently, the cold rolling step may include a step of pickling the wound steel sheet and then cold rolling. Subsequently, the annealing heat treatment step may include annealing the cold-rolled sheet material at 740 ° C to 820 ° C. The annealing heat-treated plate material may be cooled to room temperature at a cooling rate of 5 to 50 ° C / sec as an example.

Forming a bonding steel (S120)

The first and second blanks of the different types are joined through a TWB process to form a bonded steel material. In one embodiment, the first blank may be a shock absorber at the bottom of the B-pillar, the second blank may be arranged to be a collision support at the top, and then welded in a butt manner using, for example, a laser.

Hot stamping step (S130)

The bonding steel is heated to a temperature of about 850 to 950 ° C in a heating furnace. As an example, the heating may be performed at a temperature of 930 ° C for about 5 minutes. Subsequently, the heated bonded steel is transferred to a press mold. At this time, a transfer time of about 9 to 11 seconds may be required. After forming into the final part shape in the hot stamping press mold, the final product is formed by rapidly cooling the molded body at a cooling rate of about 30 to 120 ° C / sec.

Although not shown in the drawings, the press mold may be provided with a cooling channel through which the refrigerant circulates. It is possible to rapidly cool the heated blank by circulation by the refrigerant supplied through the provided cooling channel. At this time, in order to prevent the spring back phenomenon of the bonded steel and to maintain a desired shape, rapid cooling may be performed while pressing while the press mold is closed.

The hot stamping part manufactured by the above-described process (S110 to S140) limits the content of carbon (C) contained in the steel part corresponding to the first blank used in the shock absorber to 0.04 to 0.06% by weight, , By expanding the content of boron (B) to 0.0015 to 0.0025% by weight, it will be described below that a minimum component deviation of material deviation can be realized in a hot stamping process variable range.

3 is a view illustrating a concept of microstructure phase transformation according to a temperature change during a hot stamping process in a method of manufacturing a hot stamping part according to an embodiment of the present invention and a comparative example. The blank / mold cooling curve may pass a ferrite phase transformation line, a bainite phase transformation line, and / or a martensite phase transformation line in the process of quenching as in the curves ① or ② of FIG. 3. The phase transformation line indicated by a dotted line relates to a steel for 70K class TWB (comparative example), and the phase transformation line indicated by a solid red line relates to a steel for 80 to 100K class TWB (example). Specifically, 80 to 100K grade TWB steel (example) is carbon (C): 0.04 to 0.06 wt%, silicon (Si): 0.4 to 0.6 wt%, manganese (Mn): 1.7 to 1.9 wt%, phosphorus ( P): more than 0 0.018 wt% or less, sulfur (S): more than 0 0.003 wt% or less, chromium (Cr): 0.1 to 0.3 wt%, boron (B): 0.0015 to 0.0025 wt%, titanium (Ti): 0.05 ~ 0.07% by weight, niobium (Nb): 0.04 ~ 0.06% by weight and the balance is made of iron (Fe) and inevitable impurities, while 70K class TWB steel (comparative example) is carbon (C): 0.06 ~ 0.09 Weight percent, silicon (Si): more than 0 and 0.06 weight percent or less, manganese (Mn): 1.7 to 1.9 weight percent, phosphorus (P): more than 0 0.018 weight percent, sulfur (S): more than 0 and 0.003 weight percent or less, Chromium (Cr): more than 0 to 0.1% by weight, boron (B): more than 0 to 0.001% by weight, titanium (Ti): 0.05 to 0.07% by weight, molybdenum (Mo): 0.15 to 0.20% by weight, niobium (Nb) : 0.04 ~ 0.06% by weight and the balance is composed of iron (Fe) and inevitable impurities.

Referring to FIG. 3, during the hot stamping process, 70K grade TWB steel (comparative example) due to the variables (transfer time after heating, mold cooling rate) has a fast or slow transfer time after heating or blank / mold cooling rate during hot stamping Depending on the proportion of martensite and ferrite changes rapidly, material deviation may occur. The resulting material deviation may be unsuitable for automobile crash member properties. In order to overcome this problem, since the hot stamping process variable is not easy to control, the embodiment of the present invention was intended to overcome the material design concept change. That is, in the embodiment of the present invention, the content of carbon (C) is limited to 0.04 to 0.06% by weight, and the content of boron (B) is expanded to 0.0015 to 0.0025% by weight, so that the final structure is a dual phase of bainite and martensite. The minimum component of material deviation was implemented in the hot stamping process variable range by having the texture.

Experimental example

Hereinafter, the configuration and operation of the present invention will be described in more detail through experimental examples of the present invention. However, this is provided as a preferred example of the present invention and cannot be interpreted as limiting the present invention by any means. In addition, the contents that are not described herein will be sufficiently technically inferred by those skilled in the art, and thus the description thereof will be omitted.

Tables 1 to 3 show the properties and properties of hot stamping parts according to the composition range of niobium (Nb), titanium (Ti), and boron (B), respectively. The basic components of the steel material include carbon (C): 0.05% by weight, silicon (Si): 0.5% by weight, manganese (Mn): 1.8% by weight, and chromium (Cr): 0.2% by weight. In addition, the hot stamping process was performed at a temperature of 930 ° C. for 5 minutes, and then an average cooling rate was performed at about 70 ° C./s.

Nb amount (wt%) YP_MPa TS_MPa El_% Grain size Comparative Example 1-1 0.02 850 950 6 20um Comparative Example 1-2 0.03 870 970 6 17um Example 1-1 0.04 885 1010 8 11um Example 1-2 0.05 900 1015 8 9um Example 1-3 0.06 920 1018 8 7um Comparative Example 1-3 0.07 950 1040 5 5um

Referring to Table 1, the hot stamping part according to the experimental example of the present invention, carbon (C): 0.05 wt%, silicon (Si): 0.5 wt%, manganese (Mn): 1.8 wt%, chromium (Cr): 0.2 Weight%, boron (B): 0.002% by weight, titanium (Ti): 0.06% by weight, but containing the content of niobium (Nb) 0.02% by weight, 0.03% by weight, 0.04% by weight, 0.05% by weight, 0.06% by weight , 0.07% by weight. According to this, when the content of niobium (Nb) is less than 0.04% by weight (Comparative Example 1-1, Comparative Example 1-2), the yield strength (YS) is less than 880 MPa and the elongation (El) is less than 8%. can confirm. In addition, when the content of niobium (Nb) is greater than 0.06% by weight (Comparative Example 1-3), it can be confirmed that the elongation (El) is less than 8%. That is, in order to implement a hot stamping component that satisfies the properties of tensile strength (TS): 1000 MPa or more, yield strength (YS): 880 MPa or more, and elongation (El): 8% or more, carbon (C): 0.05% by weight , Silicon (Si): 0.5% by weight, manganese (Mn): 1.8% by weight, chromium (Cr): 0.2% by weight, boron (B): 0.002% by weight, titanium (Ti): 0.06% by weight, but containing niobium It can be seen that the content of (Nb) is preferably 0.04 to 0.06% by weight (Example 1-1, Example 1-2, Example 1-3).

Ti amount (wt%) YP_MPa TS_MPa El_% Grain size Comparative Example 2-1 0.03 860 930 8 10um Comparative Example 2-2 0.04 870 966 8 9um Example 2-1 0.05 881 1003 8 9um Example 2-2 0.06 900 1015 8 9um Example 2-3 0.07 910 1019 8 8um Comparative Example 2-3 0.08 920 1029 5 7um

Referring to Table 2, the hot stamping part according to the experimental example of the present invention, carbon (C): 0.05 wt%, silicon (Si): 0.5 wt%, manganese (Mn): 1.8 wt%, chromium (Cr): 0.2 Weight%, boron (B): 0.002% by weight, niobium (Nb): containing 0.05% by weight, but the content of titanium (Ti) 0.02% by weight, 0.03% by weight, 0.04% by weight, 0.05% by weight, 0.06% by weight , 0.07% by weight. According to this, when the titanium (Ti) content is less than 0.05% by weight (Comparative Example 2-1, Comparative Example 2-2), the yield strength (YS) is less than 880 MPa, tensile strength (TS) is less than 1000MPa can confirm. In addition, when the content of titanium (Ti) is greater than 0.07% by weight (Comparative Example 2-3), it can be confirmed that the elongation (El) is less than 8%. That is, in order to implement a hot stamping component that satisfies the properties of tensile strength (TS): 1000 MPa or more, yield strength (YS): 880 MPa or more, and elongation (El): 8% or more, carbon (C): 0.05% by weight , Silicon (Si): 0.5% by weight, manganese (Mn): 1.8% by weight, chromium (Cr): 0.2% by weight, boron (B): 0.002% by weight, niobium (Nb): 0.05% by weight, but containing titanium It can be seen that the content of (Ti) is preferably 0.05 to 0.07% by weight (Example 2-1, Example 2-2, Example 2-3).

B amount (wt%) YP_MPa TS_MPa El_% Bending angle Comparative Example 3-1 0.0005 611 766 17 110 ㅀ Comparative Example 3-2 0.0010 690 850 13 110 ㅀ Example 3-1 0.0015 895 1000 9 100 ㅀ Example 3-2 0.0020 900 1015 8 100 ㅀ Example 3-3 0.0025 935 1045 8 100 ㅀ Comparative Example 3-3 0.0030 950 1070 6 90 ㅀ

Referring to Table 3, the hot stamping part according to the experimental example of the present invention is carbon (C): 0.05 wt%, silicon (Si): 0.5 wt%, manganese (Mn): 1.8 wt%, chromium (Cr): 0.2 Wt%, titanium (Ti): 0.06 wt%, niobium (Nb): containing 0.05 wt%, but the content of boron (B) 0.0005 wt%, 0.0010 wt%, 0.0015 wt%, 0.0020 wt%, 0.0025 wt% , 0.0030% by weight. According to this, when the content of boron (B) is less than 0.0015% by weight (Comparative Example 3-1, Comparative Example 3-2), the yield strength (YS) is less than 880 MPa, and the tensile strength (TS) is less than 1000 MPa. can confirm. In addition, when the content of boron (B) is greater than 0.0025% by weight (Comparative Example 3-3), it can be confirmed that the elongation (El) is less than 8%. That is, in order to implement a hot stamping component that satisfies the properties of tensile strength (TS): 1000 MPa or more, yield strength (YS): 880 MPa or more, and elongation (El): 8% or more, carbon (C): 0.05% by weight , Silicon (Si): 0.5% by weight, manganese (Mn): 1.8% by weight, chromium (Cr): 0.2% by weight, titanium (Ti): 0.06% by weight, niobium (Nb): 0.05% by weight, but containing boron It can be confirmed that the content of (B) is preferably 0.0015 to 0.0025% by weight (Example 3-1, Example 3-2, Example 3-3).

In the above, the description has been mainly focused on the embodiment of the present invention, but various changes or modifications can be made at the level of those skilled in the art. It can be said that such modifications and variations belong to the present invention without departing from the scope of the present invention. Therefore, the scope of the present invention will be determined by the claims described below.

Claims (7)

Carbon (C): 0.04 to 0.06 wt%, silicon (Si): 0.4 to 0.6 wt%, manganese (Mn): 1.7 to 1.9 wt%, phosphorus (P): more than 0 and 0.018 wt% or less, sulfur (S): More than 0 and less than 0.003% by weight, chromium (Cr): 0.1 to 0.3% by weight, boron (B): 0.0015 to 0.0025% by weight, titanium (Ti): 0.05 to 0.07% by weight, niobium (Nb): 0.04 to 0.06% by weight And a steel material composed of the remainder of iron (Fe) and inevitable impurities,
The steel material is characterized in that the tensile strength (TS): 1000MPa or more, the yield strength (YS): 880 MPa or more, and the elongation (El): 8% or more,
The steel material is the first blank steel material among the first and second blanks according to the Taylor Welded Blank (TWB) process, and the final microstructure is adjusted by adjusting the content of the carbon (C) and boron (B). It is a dual phase organization of knight and martensite,
The microstructure is characterized in that the grain size is 7㎛ to 11㎛,
Hot stamping parts. delete delete (a) Carbon (C): 0.04 to 0.06 wt%, silicon (Si): 0.4 to 0.6 wt%, manganese (Mn): 1.7 to 1.9 wt%, phosphorus (P): more than 0 and 0.018 wt% or less, sulfur ( S): 0 to 0.003 wt% or less, Chromium (Cr): 0.1 to 0.3 wt%, Boron (B): 0.0015 to 0.0025 wt%, Titanium (Ti): 0.05 to 0.07 wt%, Niobium (Nb): 0.04 to Preparing a second blank by cutting a first blank using a steel slab containing 0.06% by weight and the balance of iron (Fe) and inevitable impurities, and a steel plate provided separately from the first blank;
(b) welding the first blank and the second blank in a Taylor welded blank method to form a joined steel;
(c) forming a molded body by hot stamping the bonded steel material with a press mold; And
(d) cooling the molded body to form a hot stamping part; Including,
The steel material corresponding to the first blank among the molded bodies is characterized in that the tensile strength is 1000 MPa or more, the yield strength is 880 MPa or more, and the elongation is 8% or more,
Through the control of the carbon (C) and boron (B) content, the final microstructure forms bainite and martensite dual phase structures,
The microstructure is characterized in that the grain size is 7㎛ to 11㎛,
Method of manufacturing hot stamping parts. The method of claim 4, wherein
Step (a) is,
(a-1) heating the steel slab under reheating temperature (SRT): 1200 to 1250 ° C;
(a-2) finishing hot rolling the reheated steel slab under a finishing rolling temperature (FDT) of 860 to 920 ° C;
(a-3) winding the finished hot-rolled sheet to a winding temperature (CT): 620 to 660 ° C;
(a-4) uncoiling and cold rolling the wound plate; And
(a-5) heat-treating the cold-rolled sheet material; Containing
Method of manufacturing hot stamping parts. The method of claim 4, wherein
Step (c) is
(c-1) heating the bonded steel material to a temperature of 850 to 950 ° C; And
(c-2) comprising the step of transferring the heated bonded steel to the press mold with a transfer time of 9 to 11 seconds,
Method of manufacturing hot stamping parts. The method of claim 6,
In step (d),
The cooling of the molded body is characterized in that carried out at a rate of 30 ~ 120 ℃ / s,
Method of manufacturing hot stamping parts.

Images