KR101938092B1 - Method of manufacturing hot stamping component and hot stamping component manyfactured thereby - Google Patents

Abstract

One aspect of the present invention relates to a method for manufacturing a hot stamping component capable of securing strength against brittleness. According to the present invention, the method for manufacturing a hot stamping component comprises the steps of: (a) reheating, hot-rolling, cooling, and winding a steel slab to form a steel sheet, wherein the steel slab comprises 0.5 to 1.0 weight percent of C, 0.2 to 0.4 weight percent of Si, 0.6 to 1.0 weight percent of Mn, greater than 0 to 0.015 weight percent or less of P, greater than 0 to 0.005 weight percent or less of S, 0.1 to 1.0 weight percent of Cr, 0.0015 to 0.0050 weight percent of B, 0.03 to 0.04 weight percent of Ti, 0.05 to 0.50 weight percent of Mo, 0.02 to 0.10 weight percent of Nb, and the balance of Fe and inevitable impurities; (b) pickling, rolling, and annealing the steel sheet; and (c) hot-stamping the steel sheet to form a hot stamping component.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a method of manufacturing a hot stamping component, and a hot stamping component manufactured by the same. BACKGROUND OF THE INVENTION [0002]

The present invention relates to a method of manufacturing a steel material, and more particularly, to a method of manufacturing an ultra-high strength hot stamping part having excellent elongation and a hot stamping part manufactured thereby.

Recently, the automotive industry has demanded rigorous body crash performance to enhance passenger safety. In addition, as environmental awareness increases, fuel efficiency standards based on exhaust gas regulations are strengthened, and accordingly, there is a continuing need for weight reduction of the vehicle. As a result of efforts to meet these demands for improved collision performance and lighter weight, the application of high strength steel sheets to the vehicle body is continuously increasing. In the manufacture of automobiles, high-strength parts are applied to reinforce side impacts, which is crucial in ensuring the survival space of a driver in a side collision. In case of 150KPa high strength steel which is mainly used as a collision member of a vehicle, there is a need for a method for improving the collision performance because it may threaten the safety of the driver in the side collision. In the lower part where a brittle failure occurs which threatens the safety of a driver in the event of a side collision, another member is connected by the method of Talyor Welded Blank (TWB) to improve the collision absorbing ability by absorbing impact or adding components .

A related art is Korean Patent Laid-Open Publication No. 2016-0061560 (published on June 1, 2016, Taylor Weldblank).

A problem to be solved by the present invention is to provide a method of manufacturing a hot stamping part capable of improving crashworthiness by securing strength and elongation of steel through control of alloy components and control of process conditions.

One aspect of the invention relates to a method of making a hot stamping component. A method for manufacturing a hot stamping component comprising the steps of: (a) providing a steel sheet having a composition comprising 0.5 to 1.0% by weight of carbon (C), 0.2 to 0.4% by weight of silicon (Si), 0.6 to 1.0% by weight of manganese (Mn) (S): more than 0 and not more than 0.005 wt%, chromium (Cr): 0.1 to 1.0 wt%, boron (B): 0.0015 to 0.0050 wt%, titanium (Ti): 0.03 to 0.04 wt% Hot rolling, cooling and winding a steel slab containing 0.05 to 0.5% by weight of molybdenum (Mo), 0.02 to 0.10% by weight of niobium (Nb) and the balance of Fe and unavoidable impurities, ; (b) pickling, rolling and annealing the steel plate; And (c) hot stamping the steel plate to form a hot stamping part.

In the present invention, the step (a) may include reheating the slab sheet at a temperature of 1,220 to 1,250 ° C., hot-rolling the reheated slab sheet at a finishing rolling temperature of 900 to 950 ° C., And winding the rolled steel sheet at a coiling temperature of 680 to 800 캜.

In the step (c) of the present invention, the step (c) may include heating the steel sheet at a molding temperature of 770 to 1,100 ° C, forming the heated steel sheet by hot forming using a metal mold, Quenching the molded article, and tempering the molded article at a temperature of 180 to 220 DEG C for 200 to 350 minutes.

In the present invention, the hot stamping component formed after step (c) has a tempered martensite volume fraction of 30 to 90% and a martensite + tempered martensite volume fraction of 90 to 100% in the total volume of the steel, Of the microstructure.

In the present invention, the hot stamping component formed after the step (c) preferably has a tensile strength (TS) of 2,400 MPa or more, a yield strength (YS) of 1,600 MPa or more, and an elongation (EL) .

Another aspect of the invention relates to hot stamping parts. Wherein the hot stamping part comprises 0.5 to 1.0% by weight of carbon (C), 0.2 to 0.4% by weight of silicon (Si), 0.6 to 1.0% by weight of manganese (Mn) Sulfur (S): more than 0 to 0.005 wt%, chromium (Cr): 0.1 to 1.0 wt%, boron (B): 0.0015 to 0.0050 wt%, titanium: 0.03 to 0.04 wt%, molybdenum (Mo) (YS): 1,600 MPa or more, and an elongation percentage (YS) of 0.05 to 0.50 wt%, niobium (Nb): 0.02 to 0.10 wt%, and balance of iron (Fe) and unavoidable impurities. (EL): 7% or more.

In the present invention, the hot stamping component may have a microstructure having a tempered martensite volume fraction in the total volume of steel of 30 to 90% and a martensite + tempered martensite volume fraction of 90 to 100% have.

According to the present invention, by controlling the content of an alloy component, it is possible to improve the strength and elongation through fine grain refinement during hot stamping heating, to induce formation and uniform distribution of fine carbides by tempering under predetermined conditions after hot stamping heating, Strength can be secured against brittleness

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a process flow diagram illustrating a method of manufacturing an ultra-high strength hot stamping component with improved brittleness according to one embodiment of the present invention.
FIG. 2 is a photograph showing a process of improving impact performance according to the formation of fine carbides by the tempering effect in the production of hot stamping parts according to one embodiment of the present invention.
FIG. 3 is a photograph showing a process of improving impact performance according to grain refinement in manufacturing a hot stamping part according to one embodiment of the present invention.
FIG. 4 is a graph schematically illustrating a process of improving impact performance according to grain refinement in manufacturing a hot stamping part according to an embodiment of the present invention.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art can easily carry out the present invention. The present invention may be embodied in many different forms and is not limited to the embodiments described herein. Throughout this specification, the same or similar components are denoted by the same reference numerals. In the following description, well-known functions or constructions are not described in detail since they would obscure the invention in unnecessary detail.

The B-pillars, which are important parts for the collision member of the vehicle, are constructed by the TWB and hot stamping method using different strength materials for the upper collision support portion and the lower impact absorbing portion. For example, a high-strength steel material of 150 KPa grade is used as the upper collision support member, and a collision-absorbing member is connected to the lower end of the brittle B-pillar by the TWB technique to improve the shock absorption capability in the event of a vehicle collision. The existing 150K class steel was developed to be made of 100% martensite material through hot stamping process after hot rolling and cold rolling process. Generally, a 150K grade steel exhibits a tensile strength of 1470 MPa and an elongation of 5% after hot stamping. The martensitic steel of 150 K or more can be uniformly formed with fine carbides through tempering or annealing, so that yield strength and elongation can be improved.

On the other hand, the 250K super high strength steel has a carbon content of 0.50% by weight or more and is very brittle after hot stamping. In order to achieve the above object, the present invention relates to a hot stamping method for controlling a component of a hot stamped steel to control fineness of a grain and controlling conditions of a tempering process to improve a brittle characteristic of a 250K grade steel, A method of manufacturing a hot stamping component is presented.

hot Stamping  How to make parts

One aspect of the present invention relates to a method of manufacturing an ultrahigh strength hot stamping component having improved brittleness characteristics.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a process flow diagram illustrating a method of manufacturing an ultra-high strength hot stamping component with improved brittleness according to one embodiment of the present invention.

1, the method of manufacturing the hot stamping component includes a slab reheating / finishing rolling / cooling and winding step (S100), a pickling / rolling / annealing step (S200), and a hot stamping / tempering step (S300) .

Slab Reheating / Finishing Rolling / Cooling and Coiling  In step S100,

In order to manufacture the hot stamping part of the present invention, first, a slab reheating / finishing rolling / cooling and winding step (S100) for forming a hot rolled sheet is performed

In the slab reheating step (S110), the steel slab plate obtained through the continuous casting process is reheated at a slab reheating temperature (SRT) of 1,220 to 1,250 ° C to reuse the segregated components during casting. When the slab reheating temperature (SRT) is lower than 1,220 DEG C, the segregated components are not sufficiently reused during casting, and thus the homogenization effect of the alloying elements is hardly seen. The higher the temperature of the slab reheating temperature (SRT), the better the homogenization. However, if the temperature is higher than 1,250 ° C., the austenite crystal grain size increases and the hardening strength and the hardenability and the endurance are decreased. Can be increased.

In the method of manufacturing a hot stamping part according to the present invention, the semi-finished steel slab plate to be subjected to the hot rolling process is composed of 0.5 to 1.0% by weight of carbon (C), 0.2 to 0.4% by weight of silicon (Si) (S): more than 0 to 0.005 wt%, chromium (Cr): 0.1 to 1.0 wt%, boron (B): 0.0015 to 0.1 wt% (Fe) and unavoidable impurities are contained in an amount of 0.01 to 0.0050 wt%, titanium (Ti): 0.03 to 0.04 wt%, molybdenum (Mo): 0.05 to 0.50 wt%, niobium (Nb)

In the method for manufacturing a hot-rolled steel sheet, which is one aspect of the present invention, it is necessary to control the composition of the components contained in the slab, and the reason thereof will be described in detail.

Carbon (C): 0.5 - 1.0 wt%

Carbon (C) is an element added for the purpose of ensuring tensile strength after hot stamping. In one embodiment, the carbon (C) is preferably added in an amount of 0.5 to 1.0 wt% of the total weight of the steel slab. When the addition amount of carbon (C) is less than 0.5% by weight, it is difficult to secure sufficient strength, so that it is difficult to perform the tempering for a long period of time and the possibility of cracks in the slab due to the formation of the superfine ferrite becomes high. On the other hand, when the addition amount of carbon (C) exceeds 1.0% by weight, it is difficult to secure the elongation and the risk of brittleness is increased.

silicon( Si ): 0.2 ~ 0.4 wt%

Silicon (Si) acts as a deoxidizer and is effective in improving the toughness and ductility of steel by inducing ferrite formation as a ferrite stabilizing element. In one embodiment, the silicon (Si) is preferably added in an amount of 0.2 to 0.4 weight percent of the total weight of the steel slab. If the amount of silicon added is less than 0.2 wt%, it is difficult to suppress the formation of cementite during isothermal transformation, and the effect of improving the elongation can not be obtained. If it exceeds 0.4 wt%, the rolling load may increase or segregation may occur.

Manganese (Mn): 0.6 ~ 1.0 wt%

Manganese (Mn), like silicon (Si), is a component that affects deoxidation, tensile strength and impact toughness. In addition, manganese is a substitutional element having an atomic diameter similar to iron, and is an element highly effective for solid solution strengthening. Manganese also plays a role in improving the hardenability of the steel. The manganese is preferably added in an amount of 0.6 to 1.0% by weight based on the total weight of the steel slab. When the content of manganese (Mn) is less than 0.6% by weight, the above effect can not be expected due to the addition. When the content of manganese (Mn) exceeds 1.0% by weight, the hardenability is improved and the possibility of the low-

(P): exceeding 0 - 0.015 wt%  Below

The phosphorus (P) causes the weldability of the steel to deteriorate and causes the final material deviation due to slab center segregation. Therefore, it is preferable to limit the phosphorus content to 0.015% by weight or less of the total weight of the steel slab.

Sulfur (S): greater than 0 - 0.005 wt%  Below

 Sulfur (S) is an impurity element as well as phosphorus (P), which deteriorates the toughness and weldability of steel and forms an MnS nonmetallic inclusion by binding with manganese, thereby generating a crack during processing of steel. Thus, in one embodiment, it is desirable to limit the content of sulfur to 0.005 wt.% Or less of the total weight of the steel slab.

chrome( Cr ): 0.1 to 1.0 weight%

Chromium (Cr) is an element added for the purpose of ensuring the ingot strength and strength of steel. In one embodiment of the present invention, it is preferable that the chromium (Cr) is added in a range of 0.1 to 1.0 wt% of the total weight of the steel slab. When the content of chromium (Cr) is less than 0.1% by weight, the effect of addition is insignificant. When the content of chromium (Cr) exceeds 1.0% by weight, the toughness is deteriorated.

Boron (B): 0.0015 to 0.0050 weight%

Boron (B) is added for ensuring strength after hot stamping. In one embodiment of the present invention, the boron (B) is preferably added in an amount of 0.0015 to 0.005 wt% of the total weight of the steel slab. When the content of boron (B) is less than 0.0015% by weight, it is difficult to ensure the strength because of difficulty in securing the martensite fraction. When the content of boron (B) exceeds 0.005% by weight, the risk of brittleness increases.

titanium( Ti ): 0.03 to 0.04 weight%

Titanium (Ti) bonds with carbon to form carbides that affect the strength of the steel. Particularly, it is added for the purpose of strengthening the entrapment property by the formation of the precipitate after the hot stamping heat treatment and improving the material. In one embodiment of the present invention, the titanium is preferably added in an amount of 0.03 to 0.04% by weight based on the total weight of the steel slab. When the content of titanium is less than 0.03% by weight, a sufficient strengthening effect can not be obtained. When the content of titanium exceeds 0.04% by weight, not only the manufacturing cost is increased but also the ductility is difficult to secure.

molybdenum( Mo ): 0.05 to 0.50 weight%

Molybdenum (Mo) serves to refine the crystal grains by increasing the austenite grain growth temperature. In one embodiment, the molybdenum (Mo) is preferably added in an amount of 0.05-0.50 wt% of the total weight of the steel slab. When molybdenum (Mo) is added in an amount of less than 0.05 wt%, the effect of the incombustibility and the effect of refining the precipitate can not be sufficiently exhibited, and when added in an amount exceeding 0.5 wt%, the cost is disadvantageous.

Niobium ( Nb ): 0.02 to 0.10 weight%

Niobium (Nb) bonds with carbon to form oxides that affect the strength of the steel. In one embodiment, the niobium comprises 0.02-0.1 wt% of the total weight of the steel slab. If the content of niobium is less than 0.02% by weight, the effect of the addition is insignificant. If the niobium content is more than 0.1% by weight, the yield strength may be increased due to the formation of carbides.

The hot rolling step S120 is a step of hot-rolling the reheated steel slab to produce a hot-rolled steel sheet, wherein the reheated steel slab is hot-rolled at a finishing delivery temperature (FDT) of 900 to 950 ° C .

At this time, if the finishing rolling temperature (FDT) is too low to be lower than 900 占 폚, there is a problem that blended structure due to the abnormal region rolling occurs, and also there is a problem of ductility during hot rolling due to abrupt phase change. The finishing rolling temperature (FDT) is also advantageous for homogenization as the slab reheating temperature (SRT) is similar to the slab reheating temperature (SRT), and is determined according to the SRT and the number of passes. When the finishing rolling temperature (FDT) So that the hardening ability and endurance can be reduced.

In the cooling and winding step (S130), the hot rolled plate is cooled to a coiling temperature (CT) of 680 to 800 ° C. and wound. The cooling after the finish rolling can be both air cooling and water cooling, and cooling is preferably performed at an average cooling rate of 10 to 30 DEG C / sec so as to suppress the growth of coarse crystal grains as much as possible. At a cooling rate of 10 ° C / sec or less, sufficient cooling may not be performed and there is a possibility of causing a scale generated at a high temperature. At a cooling rate of 30 ° C / sec or more, low temperature structure may be generated to decrease ductility.

The coiling temperature (CT) affects redistribution of carbon (C), preferably 680 to 800 ° C. If the coiling temperature is less than 680 DEG C, it is advantageous in securing strength, but there is a problem that the low temperature phase fraction due to overcooling is increased and the ductility is rapidly lowered. On the other hand, when the coiling temperature exceeds 800 ° C, there is a problem that abnormal crystallization grain growth and excessive crystal grain growth cause moldability and strength deterioration, and surface oxidation may occur.

Pickled / Rolled / Annealing  In step S200,

Next, in order to manufacture the hot stamping component of the present invention, the step of forming the hot-rolled steel sheet described above is performed to perform the step of rolling / annealing (S200) of forming the cold-rolled steel sheet.

The pickling step S210 is carried out to remove the scales when a hot-rolled coil having a high coiling temperature after hot rolling and an intergrated oxide layer of silicon (Si) or manganese (Mn) are formed on the steel sheet interface. The pickling process is carried out using a conventional pickling method. The rolled sheet can be uncoiled and then subjected to 20 to 300 seconds using, for example, hydrochloric acid heated at 80 to 90 ° C.

The rolling step (S220) is cold rolling after the pickling, whereby the cold rolled steel sheet can be appropriately formed from the viewpoints of dimensional precision and flatness in the lightening of automobiles and the like. At this time, the cold rolling can be carried out at a predetermined cold rolling rate, and the cold rolling rate in the rolling step is controlled within a range of 20 to 70%, for example, in consideration of the productivity in the factory desirable. However, the form is not limited thereto as long as it can realize the object of the present invention.

In the annealing step S230, the cold-rolled sheet is put into a reducing furnace and heat treatment is performed in a reducing atmosphere. It is possible to remove the contamination on the surface of the steel sheet through pretreatment or the like before such annealing treatment. In one embodiment, the annealing step can be carried out at a temperature of 800 to 850 占 폚, for example, 830 占 폚. When heated to the above-mentioned range, the process efficiency, the strength and the moldability of the steel can be simultaneously excellent.

After the annealing step, the plate exiting the reduction furnace is cooled in the cooling. This idea can be made under normal conditions. For example, at a cooling rate of 30 to 35 DEG C / sec, for example, at a cooling rate of 33 DEG C / sec.

hot Stamping  In step S300,

In the hot stamping step (S300), a bonded steel material is formed through a TWB process on the annealed sheet material, and the hot-stamped material is hot-stamped on the hot stamping die to produce a hot stamping component. More specifically, the hot stamping step (S300) includes a step (S310) of cutting the annealed heat-treated plate to a desired shape to form two blanks of different strengths and heating to a forming temperature (S310) Forming a formed body by hot forming (S320), and quenching the formed body (S330).

In the heating step (S310), the cold-rolled coil subjected to the annealing heat treatment is cut to fit the shape of the metal mold, and the blank is subjected to a TWB process using, for example, laser welding to form a bonded steel, Heat to the molding temperature. At this time, the forming temperature may be 770 to 1,100 ° C, for example, about 930 ° C, and it may be heated for about 5 minutes. The hot stamped steel must be heated to the austenite stabilizing temperature to obtain a structure state that can secure the required strength of the part after quenching. However, if the molding temperature is too low, there is a problem that it can not be attained. On the other hand, The coating layer formed on the surface of the hot stamped steel can be evaporated.

The blank heated to the molding temperature is conveyed to a press mold, which takes about 9 to 11 seconds of transfer time. And is formed into a final part shape in a hot stamping mold. The hot stamped parts are rapidly cooled at a cooling rate of about 90 DEG C / sec. Although not shown, the press mold may be provided with a cooling channel through which the refrigerant circulates. It is possible to quickly quench 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 blank and maintain the desired shape, it is possible to perform quenching while pressing the press mold in a closed state. Such a hot forming method may be performed by well-known techniques, and may be used without limitation as long as it is intended to realize the object of the present invention.

The rapidly cooled hot stamping parts are tempered at a temperature of 180 to 220 ° C for about 200 to 350 minutes. During tempering, rearrangement of the dislocations within the hot stamping component occurs and uniform dispersion of the fine carbide can occur, resulting in reduced brittleness of the hot stamping component. If the tempering temperature is less than 180 ° C, the possibility of brittleness is high. If the tempering temperature is more than 220 ° C, the strength of the component may deteriorate.

The hot stamping part according to the present invention manufactured in the above steps S100 to S300 has a tempered martensite volume fraction of 30 to 90% and a martensite + tempered martensite volume fraction: It has 90-100% microstructure. In addition, it exhibits physical properties of tensile strength (TS) of 2,400 MPa or more, yield strength (YS) of 1,600 MPa or more and elongation (EL) of 7% or more, Performance can be improved. This makes it possible to achieve lighter weight and maximize strength, and can be utilized for 250K class collision members such as steel for hot stamping as well as steel pipes for heat treatment.

FIG. 2 is a photograph showing a process of improving collision performance according to the formation of a fine carbide by a tempering effect in the production of a hot stamping part according to an embodiment of the present invention. FIG. 3 is a cross-sectional view of a hot stamping part according to an embodiment of the present invention. FIG. 4 is a graph schematically illustrating a process of improving impact performance according to the formation of fine carbides and grain refinement in the production of a hot stamping component according to an embodiment of the present invention .

2 to 4, the hot stamping component manufactured according to one embodiment of the present invention may be manufactured by adjusting the content of titanium (Ti) in the alloy component and adding molybdenum (Mo) and niobium (Nb) It is possible to improve the strength and elongation through fine grain refinement during hot stamping heating to improve the collision performance of the vehicle (the right arrow in Fig. 4). In addition, by hot stamping, heating, molding and quenching, fine carbides are formed and uniform distribution is induced by tempering under predetermined conditions, whereby the strength against brittleness can be ensured (left arrow in Fig. 4).

Hereinafter, the configuration and operation of the present invention will be described in more detail with reference to preferred embodiments of the present invention. It is to be understood, however, that the same is by way of illustration and example only and is not to be construed in a limiting sense. In addition, contents not described herein can be sufficiently technically derived by those skilled in the art, so that the description thereof will be omitted.

Example 1

The slab sheets of the examples and comparative examples having the component contents shown in the following Table 1 were reheated at a temperature of 1,230 DEG C and the reheated slab sheet was subjected to finish hot rolling at 900 DEG C and the cooled steel sheet was heated at a temperature of 680 DEG C or higher Annealed and cooled at a temperature of 830 캜 through pickling and rolling, hot stamping the steel at a molding temperature of 930 캜 and a quenching rate of -100 캜 / sec, tempering at a temperature of 200 캜, Components were manufactured. The properties of the hot stamping parts were evaluated using the specimens. The results are shown in Table 1.

The alloy components not shown in Table 1 below are commonly applied to the embodiments and the comparative examples and include 0.2% by weight of Cr, 0.002% by weight of B, 0.035% by weight of Ti, 0.2% by weight of Mo, Nb: 0.004% by weight. The target physical properties are YP: 1,600 MPa or more, TS: 2,400 MPa or more, and EL: 4% or more.

division
Component (% by weight) Properties
Remarks C Mn Si YP (MPa) TS (MPa) EL (%) Example 1 0.52 0.90 0.30 1670 2433 6.5

250K class

Example 2 0.65 0.93 0.28 1788 2466 5.8 Example 3 0.71 0.94 0.25 1855 2478 5.2 Example 4 0.83 0.92 0.24 1911 2488 4.8 Example 5 0.94 0.81 0.28 1978 2511 4.2 Comparative Example 1 0.08 1.65 0.25 320 589 21.5 60K class Comparative Example 2 0.21 1.25 0.20 1199 1367 10.1 130K class Comparative Example 3 0.35 1.30 0.25 1489 1766 7.8 170K class Comparative Example 4 0.45 1.25 0.25 1589 2167 4.2 210K class

Referring to Table 1, in the case of the specimens of Examples 1 to 5 in which the contents of carbon (C), manganese (Mn) and silicon (Si) were appropriately controlled, desired physical properties could be secured in a 250K grade steel . However, in the case of the specimens of Comparative Examples 1 to 4 in which the contents of the above components were not appropriately controlled, the target physical properties of the 250K grade steel could not be secured.

Example 2

Next, in order to investigate the difference in physical properties according to the conditions of the tempering process, a steel sheet was prepared by mixing 0.65% of C, 0.93% of Mn, 0.28% of Si, 0.2% of Cr, 0.002% of B, : 0.2% and Nb: 0.004%, and the remaining steel (Fe) and other impurities were used to prepare specimens of hot stamping parts under the tempering temperature and time conditions shown in Tables 2 to 4 below , The properties were measured by the same method as in Example 1, and the physical properties were measured. The target physical properties are YP: 1,600 MPa or more, TS: 2,400 MPa or more, and EL: 4% or more.

division
Tempering conditions Mechanical properties
Remarks Temperature (℃) Time (minutes) YP (MPa) TS (MPa) EL (%) One 180 60 Brittle 2 180 120 Brittle 3 180 180 1721 2166 2.8 Brittle 4 180 200 1742 2488 4.1 5 180 240 1765 2487 5.3 6 180 280 1788 2466 5.8 7 180 320 1791 2459 6.1 8 180 350 1795 2444 6.1 9 180 380 1799 2439 6.2 10 180 420 1809 2409 6.3 11 200 60 Brittle 12 200 120 Brittle 13 200 180 1731 2199 2.9 Brittle 14 200 200 1752 2479 4.1 15 200 240 1768 2475 5.3 16 200 280 1793 2461 5.8 17 200 320 1798 2448 6.1 18 200 350 1799 2440 6.1 19 200 380 1808 2432 6.2 20 200 420 1815 2388 6.3 Under Material

division
Tempering conditions Mechanical properties
Remarks Temperature (℃) Time (minutes) YP (MPa) TS (MPa) EL (%) One 160 60 Abnormal break Brittle 2 160 120 Abnormal break Brittle 3 160 180 Abnormal break Brittle 4 160 200 Abnormal break Brittle 5 160 240 Abnormal break Brittle 6 160 280 Abnormal break Brittle 7 160 320 Abnormal break Brittle 8 160 350 Abnormal break Brittle 9 160 380 1765 2479 5.7 10 160 420 1769 2466 5.8 11 220 60 Abnormal break Brittle 12 220 120 Abnormal break Brittle 13 220 180 1744 2289 5.5 Under Material 14 220 200 1771 2465 5.9 15 220 240 1778 2459 6.2 16 220 280 1789 2438 6.3 17 220 320 1794 2421 6.2 18 220 350 1799 2412 6.1 19 220 380 1808 2394 6.2 20 220 420 1815 2368 6.3 Under Material

division
Tempering conditions Mechanical properties
Remarks Temperature (℃) Time (minutes) YP (MPa) TS (MPa) EL (%) One 240 60 Abnormal break Brittle 2 240 120 1748 2295 5.4 Under Material 3 240 180 1769 2464 6.1 4 240 200 1778 2421 6.2 5 240 240 1791 2397 6.3 Under Material 6 240 280 1794 2381 6.2 Under Material 7 240 320 1799 2378 6.1 Under Material 8 240 350 1803 2364 6.2 Under Material 9 240 380 1808 2353 6.3 Under Material 10 240 420 1815 2309 6.3 Under Material

Referring to Tables 2 to 4, it can be seen that the physical properties of the hot stamping parts vary depending on the tempering conditions to be performed after the hot stamping heating, the molding and the quenching, that is, the tempering temperature and the tempering time. In particular, if tempering is performed at a temperature of 180 to 220 ° C for 200 to 350 minutes, the desired hot stamping component properties can be secured.

While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not limited to the disclosed embodiments. Such changes and modifications are intended to fall within the scope of the present invention unless they depart from the scope of the present invention. Accordingly, the scope of the present invention should be determined by the following claims.

Claims (7)

(a) from 0.5 to 1.0% by weight of carbon (C), from 0.2 to 0.4% by weight of silicon (Si), from 0.6 to 1.0% by weight of manganese (Mn) S: from more than 0 to 0.005% by weight, from 0.1 to 1.0% by weight of chromium (Cr), from 0.0015 to 0.0050% by weight of boron (B), from 0.03 to 0.04% by weight of titanium (Ti) Hot rolling, cooling and winding a steel slab containing 0.50% by weight of niobium (Nb): 0.02 to 0.10% by weight and the balance of Fe and unavoidable impurities to form a steel plate;
(b) pickling, rolling and annealing the steel plate; And
(c) hot stamping the steel plate to form a hot stamping component.
The method according to claim 1,
The step (a)
Reheating the slab plate at a temperature of 1,220 to 1,250 ° C;
Hot-rolling the reheated slab sheet at a finish rolling temperature of 900 to 950 占 폚;
And winding the hot-rolled steel sheet at a coiling temperature of 680 to 800 ° C.
The method according to claim 1,
The step (c)
Heating the steel plate at a molding temperature of 770 to 1,100 ° C;
Hot-forming the heated steel plate using a metal mold to form a molded product;
Quenching the molded article; And
And tempering the molded article at a temperature of 180 to 220 占 폚 for 200 to 350 minutes.
The method according to claim 1,
The hot stamping component formed after the step (c)
Characterized by having a microstructure having a tempered martensite volume fraction in a total volume of steel of 30 to 90% and a martensite + tempered martensite volume fraction of 90 to 100%.
The method according to claim 1,
The hot stamping component formed after the step (c)
A tensile strength (TS) of 2,400 MPa or more, a yield strength (YS) of 1,600 MPa or more, and an elongation (EL) of 7% or more. (P): more than 0 and not more than 0.015% by weight; sulfur (S): not more than 0.1% by weight; (B): 0.03-0.04 wt%, molybdenum (Mo): 0.05-0.50 wt%, and more preferably 0.005 wt% or less of chromium (Cr) 0.02 to 0.10% by weight of niobium (Nb) and the balance of iron (Fe) and unavoidable impurities,
A tensile strength (TS) of 2,400 MPa or more, a yield strength (YS) of 1,600 MPa or more, and an elongation (EL) of 7% or more. The method according to claim 6,
The hot stamping component comprises:
Characterized by having a microstructure having a tempered martensite volume fraction of 30 to 90% and a martensite + tempered martensite volume fraction of 90 to 100% in the total volume of the steel material.

Images