KR102275914B1 - Method of manufacturing hot stamping parts and hot stamping parts manufactured thereby - Google Patents

Abstract

A method of manufacturing a hot stamping part according to an aspect is, by weight, carbon (C): 0.29 to 0.40%, silicon (Si): 0.20 to 0.40%, manganese (Mn): 1.00 to 1.50%, phosphorus (P) : More than 0 0.012% or less, Sulfur (S): More than 0 0.002% or less, Chromium (Cr): 0.10 to 0.30%, Boron (B): 0.0015 to 0.003%, Titanium (Ti): 0.027 to 0.037%, Molybdenum ( Mo): 0.01 to 0.30%, niobium (Nb): 0.001 to 0.05%, and the remainder of the steel slab containing iron (Fe) and unavoidable impurities to a temperature of 1,200 to 1,250 ° C. Reheating the reheated steel slab Finish rolling at a temperature of 900 to 950 ° C. Cooling the hot rolled steel sheet and winding it at 680 to 800 ° C. to form a hot rolled decarburization layer on the surface of the steel sheet. Cold rolling after pickling the wound steel sheet, cold rolling Annealing the annealed plate in a reducing atmosphere, plating the annealed plate to form a plated layer of 40 to 100 g/m 2 , and hot stamping the plated plate.

Description

Method of manufacturing hot stamping parts and hot stamping parts manufactured thereby {METHOD OF MANUFACTURING HOT STAMPING PARTS AND HOT STAMPING PARTS MANUFACTURED THEREBY}

The present invention relates to a steel material and a method for manufacturing the same, and more particularly, to a method for manufacturing a hot stamping part and a hot stamping part manufactured thereby.

The automobile industry is demanding strict car 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. High-strength parts are applied to reinforce the side impact when manufacturing the vehicle body, because it plays a very important role in securing the driver's survival space in the event of a side collision.

The B-pillar, an important component for collision members of automobiles, is constructed through TWB and hot stamping methods using steels of different strengths for the upper collision support part and the lower shock absorber part. For the upper collision support part, for example, 150KPa class ultra-high strength steel is used, and a member with good collision absorption performance is connected to the lower part of the B-pillar, which is brittle, using the TWB method to improve the shock absorption ability in the event of a vehicle collision. Since 150K-class parts used as collision members can threaten the safety of the driver in a side collision when applying lightweight (thickness reduction, etc.) for future responses such as electric vehicles, a method to improve performance such as collision and bending is required.

As a technology related thereto, there is Korean Patent Publication No. 2016-0061560 (published on June 1, 2016, Taylor welded blank manufacturing method).

An object of the present invention is to provide a hot stamping steel material with improved performance and a method for manufacturing the same by controlling the alloy composition and the thickness of the plating layer.

The method of manufacturing a hot stamping part according to an aspect of the present invention, by weight, carbon (C): 0.29 to 0.40%, silicon (Si): 0.20 to 0.40%, manganese (Mn): 1.00 to 1.50%, phosphorus (P): more than 0 and less than 0.012%, sulfur (S): more than 0 and less than or equal to 0.002%, chromium (Cr): 0.10 to 0.30%, boron (B): 0.0015 to 0.003%, titanium (Ti): 0.027 to 0.037% , molybdenum (Mo): 0.01 to 0.30%, niobium (Nb): 0.001 to 0.05% and the remainder iron (Fe) and reheating the steel slab containing unavoidable impurities to a temperature of 1,200 to 1,250 ℃; finishing rolling the reheated steel slab at a temperature of 900 to 950°C; Cooling the hot-rolled steel sheet and winding at 680 ~ 800 ℃ to generate a hot-rolled decarburization layer on the surface of the steel sheet; cold rolling the wound steel sheet after pickling; annealing the cold-rolled sheet material in a reducing atmosphere; forming a plating layer of 40-100 g/m 2 by plating the annealed plate material; and hot stamping the plated plate.

In one embodiment, after hot stamping, the hot-rolled decarburized layer may be formed to a thickness of 10 ~ 35㎛ from the surface.

In an embodiment, the cold rolling may be performed at a reduction ratio of 30 to 50%.

In one embodiment, the microstructure of the hot-rolled decarburized layer after hot stamping may have a composite structure made of ferrite and pearlite.

In one embodiment, after hot stamping, tensile strength (TS): 1,800 MPa or more, yield strength (YS): 1,200 MPa or more, and elongation (EL): 5% or more may have physical properties.

Hot stamping parts according to another aspect of the present invention, by weight, carbon (C): 0.29 to 0.40%, silicon (Si): 0.20 to 0.40%, manganese (Mn): 1.00 to 1.50%, phosphorus (P) : More than 0 0.012% or less, Sulfur (S): More than 0 0.002% or less, Chromium (Cr): 0.10 to 0.30%, Boron (B): 0.0015 to 0.003%, Titanium (Ti): 0.027 to 0.037%, Molybdenum ( Mo): 0.01 to 0.30%, niobium (Nb): 0.001 to 0.05%, and a steel material composed of iron (Fe) and unavoidable impurities in the remainder, and an aluminum-silicon (Al-Si) plating layer formed on the surface of the steel material. and a decarburized layer having a thickness of 1.3 to 9.5 μm formed at the interface between the aluminum-silicon (Al-Si) plating layer and the steel, tensile strength (TS): 1,800 MPa or more, yield strength (YS): 1,200 MPa or more, Elongation (EL): It has a physical property of 5% or more.

In one embodiment, the microstructure of the surface decarburized layer may have an α-BCC structure.
In one embodiment, the thickness of the aluminum-silicon (Al-Si) plating layer may be 13.6 ~ 29.9㎛.

According to the present invention, by controlling the alloy composition and the thickness of the plating layer, it is possible to obtain a hot stamping part having excellent physical performance, such as collision performance, bending property, high strength toughness.

1A to 1C are electron microscope (SEM) photos showing the formation of a decarburized layer after hot stamping for each thickness of an Al-Si plating layer.
2 is a graph showing the performance improvement according to the presence of the decarburized layer for each thickness of the plating layer of hot stamping steel.
3 is a process flow chart showing a method of manufacturing a hot stamping part according to an embodiment of the present invention.
4 is an electron microscope (SEM) photograph observing a change in the microstructure before and after hot stamping according to the Al-Si plating amount.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings so that those of ordinary skill in the art to which the present invention pertains can easily practice it. The present invention may be embodied in several different forms, and is not limited to the embodiments described herein. The same reference numerals are assigned to the same or similar components throughout this specification. In addition, detailed descriptions of well-known functions and configurations that may unnecessarily obscure the gist of the present invention will be omitted.

As used herein, the hot-rolled decarburized layer refers to a decarburized layer produced in steel through a hot rolling process including hot rolling, cooling, and winding steps. The hot-rolled decarburized layer may remain in the steel even after the cold-rolling process is completed. As an example, the hot-rolled decarburized layer may remain on the surface of the steel after cold rolling, annealing, plating, and hot stamping processes, and bainite and ferrite layers are generated in the hot-rolled decarburized layer, thereby improving bending performance. The improved bending performance may improve the impact performance of hot stamped products.

After repeated experiments, the inventors of the present invention found that when the thickness of the aluminum (Al)-silicon (Si) plating layer is 100 g/m 2 or less, α-BCC with a thickness of several μm after hot stamping, that is, a hot-rolled decarburized layer structure is formed, and the toughness of the steel is improved. It was derived that there is less risk of increasing the surface brittleness of automobile rough parts, and the improvement of plasticity/elongation increases bendability and improves the impact performance of the final product.

1A to 1C are electron microscope (SEM) photos showing the formation of a decarburized layer after hot stamping according to the Al-Si plating amount, and FIG. 2 is a graph showing the performance improvement according to the presence of the decarburized layer according to the plating amount of the hot stamping steel.

Specifically, FIG. 1A is a photograph of a sample having an Al-Si plating weight of 150 g/m2, FIG. 1B is a photograph of a sample having an Al-Si plating weight of 100 g/m2, and FIG. 1C is a sample having an Al-Si plating weight of 40 g/m2. is a picture of

Referring to FIGS. 1A to 1C , it can be seen that the thickness of the decarburized layer increases as the Al-Si plating amount decreases from 150 g/m 2 to 100 g/m 2 and 40 g/m 2 . In addition, referring to FIG. 2, as the Al-Si plating amount decreased from 150 g/m (A) to 100 g/m (B) and 40 g/m (C), it was found that the bendability of the steel improved at the tensile strength of 150 MPa to 180 MPa. can

As such, in the present invention, in order to improve the strength of the martensitic hot stamping part to be reduced in weight, the content of high carbon (C), titanium (Ti), etc. is optimized to complete the 180K class component system, while aluminum (Al)-silicon ( Si) By controlling the thickness of the plating layer, after hot stamping, a ㎛-thick decarburization layer (α-BCC) is formed at the lower part of the interface between the plating layer and the base material, thereby reducing the risk that the brittleness of 180K class hot stamping steel may increase compared to 150K class hot stamping steel. We present technologies that can reduce and improve performance.

Manufacturing method of hot stamping parts

One aspect of the present invention relates to a method of manufacturing a hot stamped part.

3 is a process flow chart showing a method of manufacturing a hot stamping part according to an embodiment of the present invention.

3, the method of manufacturing a hot stamping part according to an embodiment of the present invention includes a slab reheating step (S10), a hot rolling step (S20), a winding step (S30), a cold rolling step (S40), an annealing step (S50), a plating step (S60) and a hot stamping step (S70).

More specifically, the manufacturing method of the hot stamping part is by weight, carbon (C): 0.29 to 0.40%, silicon (Si): 0.20 to 0.40%, manganese (Mn): 1.00 to 1.50%, phosphorus (P) : More than 0 0.012% or less, Sulfur (S): More than 0 0.002% or less, Chromium (Cr): 0.10 to 0.30%, Boron (B): 0.0015 to 0.003%, Titanium (Ti): 0.027 to 0.037%, Molybdenum ( Mo): 0.01 to 0.30%, niobium (Nb): 0.001 to 0.05% and the remainder iron (Fe) and reheating the steel slab containing unavoidable impurities to a temperature of 1,200 to 1,250 ° C (S10); finishing rolling the reheated steel slab at a temperature of 900 to 950° C. (S20); forming a hot-rolled decarburization layer on the surface of the steel sheet by water-free cooling the hot-rolled steel sheet and winding it at 680 to 800° C. (S30); Cold rolling after pickling the wound steel sheet (S40); annealing the cold-rolled sheet material in a reducing atmosphere (S50), and plating the annealed sheet material (S60); and hot stamping the plated plate (S70).

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

(S10) slab reheating step

This step is by weight %, carbon (C): 0.29 to 0.40%, silicon (Si): 0.20 to 0.40%, manganese (Mn): 1.00 to 1.50%, phosphorus (P): more than 0 and 0.012% or less, sulfur ( S): greater than 0 and less than or equal to 0.002%, chromium (Cr): 0.10 to 0.30%, boron (B): 0.0015 to 0.003%, titanium (Ti): 0.027 to 0.037%, molybdenum (Mo): 0.01 to 0.30%, niobium (Nb): This is a step of reheating a steel slab containing 0.001 to 0.05% and the remainder of iron (Fe) and unavoidable impurities to a temperature of 1,200 to 1,250 ° C.

Hereinafter, the role and content of the components included in the steel slab will be described in detail.

carbon (C)

Carbon (C) is a major element that determines the strength and hardness of steel, and is added for the purpose of securing the tensile strength of the steel after the hot stamping (or hot pressing) process. In one embodiment, the carbon (C) is included in 0.29 to 0.49 wt% based on the total weight of the steel slab. When the carbon (C) is included in less than 0.29 wt%, it is difficult to achieve the mechanical strength of the present invention, and when it exceeds 0.49 wt%, a problem of lowering the toughness of the steel or a problem of controlling the brittleness of the steel may be caused.

Silicon (Si)

Silicon (Si) acts as a ferrite stabilizing element in the steel sheet. By cleaning ferrite, ductility is improved, and carbon concentration in austenite can be improved by suppressing the formation of carbides in the low-temperature region. In one embodiment, the silicon (Si) is included in an amount of 0.20 to 0.40 wt% based on the total weight of the steel slab. When the silicon (Si) is included in an amount of less than 0.20 wt %, the above-described function cannot be sufficiently exhibited, and when it exceeds 0.40 wt %, weldability may be deteriorated.

Manganese (Mn)

Manganese (Mn) is added to increase hardenability and strength during heat treatment. In one embodiment, the manganese (Mn) is included in 1.00 to 1.50 wt% based on the total weight of the steel slab. When the manganese (Mn) is included in an amount of less than 1.00 wt%, hardenability and strength may be reduced, and when the manganese (Mn) is included in an amount exceeding 1.50 wt%, ductility and toughness may be reduced due to manganese (Mn) segregation.

Phosphorus (P)

Phosphorus (P) is an element that segregates easily and is an element that inhibits the toughness of steel. In one embodiment, the phosphorus (P) is included in an amount of greater than 0 wt% and 0.012 wt% or less based on the total weight of the steel slab. When included in the above range, it is possible to prevent deterioration of toughness. When the phosphorus (P) is included in an amount exceeding 0.012 wt %, 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. In one embodiment, the sulfur (S) may be included in an amount of more than 0% by weight and 0.002% by weight or less based on the total weight of the steel slab. When the sulfur is included in an amount exceeding 0.002% by weight, the hot workability is deteriorated, and surface defects such as cracks may occur due to the generation of large inclusions.

Chromium (Cr)

Chromium (Cr) is added for the purpose of improving the hardenability and strength of steel. In one embodiment, the chromium (Cr) is included in an amount of 0.10 to 0.30 wt% based on the total weight of the steel slab. When the chromium (Cr) is included in an amount of less than 0.10 wt%, the effect of adding chromium (Cr) cannot be properly exhibited, and when the chromium (Cr) is included in an amount exceeding 1.30 wt%, it may cause a decrease in toughness of the steel and an increase in cost.

Boron (Β)

Boron (B) is added for the purpose of securing the hardenability and strength of steel by securing the martensite structure, and has a grain refinement effect by increasing the austenite grain growth temperature. In one embodiment, the boron (B) is included in an amount of 0.0015 to 0.0030 wt% based on the total weight of the steel slab. When the boron (B) is included in an amount of less than 0.0015% by weight, the hardenability effect is insufficient, and when it includes more than 0.0030% by weight, the risk of inferior elongation may increase.

Titanium (Ti)

Titanium (Ti) is added for the purpose of strengthening hardenability by forming precipitates and upgrading the material after hot stamping heat treatment. In addition, it effectively contributes to austenite grain refinement by forming a precipitated phase such as Ti(C,N) at high temperature. In one embodiment, the titanium (Ti) is included in an amount of 0.027 to 0.037 wt% based on the total weight of the steel slab. When the titanium (Ti) is included in an amount of less than 0.027 wt%, the effect of addition is insignificant, and when it is included in an amount exceeding 0.037 wt%, poor performance occurs, it is difficult to secure the physical properties of the steel, the elongation is lowered, and cracks on the surface of the steel material can occur

Molybdenum (Mo)

Molybdenum (Mo) may contribute to strength improvement by suppressing coarsening of precipitates during hot rolling and hot stamping and increasing hardenability. In one embodiment, molybdenum (Mo) may be added in an amount of 0.01 wt% to 0.30 wt% of the total weight of the steel sheet. When the content of molybdenum (Mo) is less than 0.01% by weight, the effect of the addition cannot be properly exhibited, and when it exceeds 0.30% by weight, it may cause a problem of lowering economic efficiency due to an increase in alloy cost.

Niobium (Nb)

Niobium (Nb) is added for the purpose of increasing strength and toughness according to a decrease in martensite packet size. In one embodiment, the niobium (Nb) is included in an amount of 0.001 wt% to 0.05 wt% based on the total weight of the steel slab. When the niobium (Nb) is included in an amount of less than 0.001% 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 included in more than 0.05% by weight, coarse precipitates in steelmaking may be generated, and the elongation of the steel This decreases, which is disadvantageous in terms of cost.

In one embodiment, the steel slab may be heated at a slab reheating temperature (SRT): 1,200 °C to 1,250 °C. At the reheating temperature of the steel slab, it is advantageous for solid solution homogenization of alloying elements such as titanium (Ti), niobium (Nb), and molybdenum (Mo). When the steel slab is reheated at less than 1,200° C., the homogenization effect of the alloying element components is reduced, and the process cost may increase when reheating above 1,250° C.

(S20) hot rolling step

This step is a step of hot rolling the reheated steel slab. In one embodiment, the hot rolling may be performed at a finish rolling temperature (FDT) of the reheated steel slab: 900 ℃ ~ 950 ℃ condition. It is advantageous for homogenization of alloy element components during hot rolling at the finish rolling temperature, and the rigidity and formability of the steel may be excellent.

(S30) winding step

This step is a step of manufacturing a hot-rolled coil by winding the hot-rolled steel sheet. In one embodiment, the hot-rolled steel sheet may be cooled and wound under the condition of a coiling temperature (CT): 680 to 800°C. The redistribution of carbon is easily made under the conditions of the coiling temperature, and it is possible to secure a sufficient hot-rolled decarburized layer and prevent the hot-rolled coil from being crushed.

In one embodiment, the cooling may be applied to a water-free cooling method that does not use water. When the water-free cooling method is applied, it may be advantageous for the formation of a decarburized layer by increasing the contact time between the surface of the hot-rolled steel sheet and oxygen by lowering the cooling rate of the hot-rolled coil. When the coiling temperature is carried out at less than 680° C., it is difficult to secure a sufficient hot-rolled decarburized layer, and distortion of the hot-rolled coil may occur. When the coiling temperature exceeds 800°C, moldability or strength deterioration may occur due to abnormal crystal grain growth or excessive crystal grain growth. In one embodiment, the hot-rolled decarburized layer of the wound hot-rolled coil may be formed to a thickness of 10-35 μm from the surface.

(S40) cold rolling step

This step is a step of manufacturing a cold rolled sheet material by uncoiling and cold rolling the hot rolled coil. In one embodiment, the hot-rolled coil may be uncoiled and then cold-rolled after pickling treatment. The pickling may be performed for the purpose of removing scale formed on the surface of the hot-rolled coil. In one embodiment, the cold rolling may be performed at a cold rolling reduction of 30-50% of the pickling-treated hot-rolled sheet material. When the cold rolling reduction is less than 30%, the deformation effect of the hot-rolled structure is small.

Conversely, when the cold rolling reduction ratio exceeds 50%, the cost required for cold rolling may increase, as well as impair drawability and cause a problem in that the steel sheet is fractured due to the occurrence of cracks at the edge of the steel sheet. In addition, due to the reduction in the thickness of the hot-rolled decarburized layer, the remaining thickness of the decarburized layer of the final product or part may be insignificant.

(S50) annealing step

This step is a step of annealing and plating the cold-rolled sheet material. The annealing process may be performed at a temperature of 730 to 830 °C. In one embodiment, the annealing treatment is performed at a dew point of -15° C. or less in a gas atmosphere consisting of hydrogen and the remainder nitrogen, thereby preventing the occurrence of decarburization during the annealing process.

Then, the annealing process may be completed to cool the plate material. The cooling may be performed, for example, at a cooling rate of 20 to 50° C./sec.

(S60) Plating step

After the annealing process is finished, the plating process may be continuously performed. The plating process may be performed by stopping the cooling of the plate and immersing the plate in a plating bath of 610 to 710° C. As an example, the plating process may be an aluminum-silicon (Al-Si) plating layer forming process, and the plating bath may include molten aluminum and molten silicon. In addition, when the combined plating amount of the front and back surfaces is 40 to 100 g/m2, a decarburized layer of several μm is formed under the interface between the plating layer and the base material after hot stamping, so that the bendability of hot stamping parts is improved and hydrogen embrittlement is reduced. have. If the plating amount is less than 40 g/m2, there is a risk of oxidation of the base material and deterioration of the plating layer during the hot stamping process, and when it exceeds 100 g/m2, the decarburized layer of the final product or part may not exist.

(S70) hot stamping step

In the hot stamping step, the plated plate is heated and hot stamped in a mold of a predetermined shape. The hot stamping process may include cutting the cold-rolled sheet material to form a blank, and then heating the blank to 880 to 930° C. and then hot forming using a press mold. After the hot stamping, it is cooled at a rate of 30° C./s.

In one embodiment, after the hot stamping process, the hot-rolled decarburized layer may have a thickness of 5 to 15㎛ from the surface. The hot-rolled decarburized layer may have a microstructure made of ferrite and pearlite. The surface brittleness of the hot stamping part can be alleviated by the ferrite structure of the hot-rolled decarburized layer, and the plasticity, bending performance and collision performance can be improved.

Hot stamping parts manufactured by the manufacturing method of hot stamping parts

Another aspect of the present invention relates to a hot stamped part manufactured by the method for manufacturing the hot stamped part. In one embodiment, the hot stamping part is, by weight %, carbon (C): 0.29-0.40%, silicon (Si): 0.20-0.40%, manganese (Mn): 1.00-1.50%, phosphorus (P): greater than 0 0.012% or less, sulfur (S): more than 0 and 0.002% or less, chromium (Cr): 0.10 to 0.30%, boron (B): 0.0015 to 0.003%, titanium (Ti): 0.027 to 0.037%, molybdenum (Mo): 0.01 to 0.30%, niobium (Nb): 0.001 to 0.05%, and a steel material composed of iron (Fe) and unavoidable impurities of the remainder, and an aluminum-silicon (Al-Si) plating layer formed on the surface of the steel material, and the It has an aluminum-silicon (Al-Si) plating layer and a decarburized layer with a thickness of 1.3 to 9.5 μm formed at the interface between the steel material, tensile strength (TS): 1,800 MPa or more, yield strength (YS): 1,200 MPa or more, and elongation ( EL): 5% or more. Since the components and contents of the hot stamping parts are the same as those included in the steel slab, a detailed description thereof will be omitted. The surface decarburized layer may be due to the hot rolled decarburized layer generated after the hot rolling process.

In one embodiment, the microstructure of the surface decarburized layer present in the hot stamping part may be made of ferrite, bainite and martensite. At this time, the surface brittleness of the hot stamping part can be alleviated by the ferrite structure of the surface decarburization layer, and the plasticity, bending performance, and collision performance can be improved.

Example

Hereinafter, the configuration and operation of the present invention will be described in more detail through preferred embodiments of the present invention. However, this is presented as a preferred example of the present invention and cannot be construed as limiting the present invention in any sense.

After reheating the steel slab containing the components of Table 1 below, which satisfies the composition range of Examples of the present invention, and the remaining amount of iron (Fe) and other unavoidable impurities to 1,200° C., a hot rolling process according to the process conditions of Table 2 below to prepare the specimens of Comparative Examples 1 to 2, and Examples 1 to 6 by proceeding.

In addition, the hot-rolled specimens of Comparative Examples 1 to 2 and Examples 1 to 6 were subjected to cold rolling, followed by annealing heat treatment, followed by cooling. During the cooling, an aluminum-silicon (Al-Si) plating layer forming process was performed by immersing in a plating bath containing molten aluminum and molten silicon. The annealing treatment was performed in a gas atmosphere consisting of hydrogen and the remainder nitrogen.

In addition, after heating the specimens of Comparative Examples 1 to 2 and Examples 1 to 6 in which the plating layer was formed under the process conditions shown in Table 2, the heated bonding steel material was transferred to a mold for hot pressing, and hot press molding was performed to obtain a molded body. and cooling the molded body to prepare hot stamping parts, respectively.

In addition, for the specimens of Comparative Examples 1 to 2 and Examples 1 to 6, the thickness of the grain size was measured for the steel sheet after the cold rolling process and after cooling the mold. In addition, for the specimens of Comparative Examples 1 and 2 and Examples 1 to 6, the plating amount and thus the thickness of the plating layer before hot stamping were measured, respectively.

ingredient C Si Mn P S Cr B Ti Mo Nb Comparative Example 1 0.23 0.25 1.18 0.014 0.004 0.21 0.0026 0.028 Comparative Example 2 0.38 0.21 1.30 0.014 0.003 0.20 0.0029 0.030 0.03 0.002 Example 1 0.36 0.20 1.40 0.013 0.004 0.19 0.0030 0.029 0.08 0.008 Example 2 0.33 0.25 1.30 0.012 0.003 0.25 0.0030 0.032 0.10 0.011 Example 3 0.32 0.24 1.29 0.011 0.003 0.23 0.0030 0.032 0.15 0.021 Example 4 0.31 0.23 1.32 0.015 0.002 0.21 0.0031 0.033 0.21 0.031 Example 5 0.29 0.20 1.48 0.011 0.002 0.20 0.0030 0.033 0.25 0.038 Example 6 0.29 0.28 1.45 0.012 0.002 0.20 0.0025 0.036 0.028 0.0043

division FDT(℃) CT(℃) Cold-rolled product grain size (㎛) After cooling the mold, the grain size (㎛) Al-Si coating weight (g/m ² ) Plating layer thickness before hot stamping (㎛) Comparative Example 1 911 745 12 24 150 28.0 Comparative Example 2 913 720 13 22 149 28.5 Example 1 885 720 13 25 100 21.0 Example 2 927 797 13 25 72 16.3 Example 3 913 720 13 22 65 14.5 Example 4 915 750 13 26 55 12.6 Example 5 911 732 13 24 48 10.3 Example 6 916 755 12 23 42 9.3

In addition, for the specimens of Comparative Examples 1 and 2 and Examples 1 to 6 after hot stamping, the thickness of the plating layer and the thickness of the decarburized layer were respectively measured and shown in Table 3 below. In addition, a collision performance simulation test was performed on the specimens of Comparative Examples 1 and 2 and Examples 1 to 6, and the results are shown in Table 3.

division After hot stamping plating layer thickness
(μm) α-BCC thickness
(μm) YP
(MPa) ts
(MPa) EL
(%) weight
(kN) displacement
(mm) bend angle
( ^o ) energy
(J) Comparative Example 1 45.7 0.0 1100 1504 4.4 6.1 7.5 55.3 47.3 Comparative Example 2 46.4 0.0 1257 1804 4.7 8.1 6.7 43.5 51.5 Example 1 29.9 1.3 1250 1800 5.3 8.1 7.5 55.1 58.5 Example 2 23.5 3.3 1240 1810 5.4 8.1 7.6 60.5 61.8 Example 3 21.4 5.4 1257 1804 5.6 8.1 7.7 64.5 63.5 Example 4 18.1 7.5 1267 1800 5.8 8.1 7.7 68.3 65.8 Example 5 15.5 8.3 1260 1803 5.9 8.1 7.8 70.1 66.3 Example 6 13.6 9.5 1264 1805 6.0 8.1 7.8 72.6 67.9

Referring to Tables 2 and 3, it can be seen that the thickness of the plating layer was increased after hot stamping in the specimens of Comparative Examples and Examples. In addition, the decarburized layer after hot stamping was not measured in the specimens of Comparative Examples 1 and 2, but was measured in the specimens of Examples 1 to 6, and as the plating amount before hot stamping was smaller, the thickness of the decarburized layer after hot stamping was measured to be thicker. The yield strength (YP) and tensile strength (TS) were not significantly different in Comparative Examples and Examples, but in the case of elongation and shock absorption energy, the specimens of Examples showed greater than those of Comparative Examples. That is, when comparing the specimens of Comparative Examples 1 and 2 and Examples 1 to 6, in the case of Examples 1 to 6 having a relatively thick surface decarburization layer, the load, displacement, bending angle, and bending compared to Comparative Examples 1 and 2 It can be seen that the numerical value of energy shows a relatively excellent value.

4 is an electron microscope (SEM) photograph observing a change in the microstructure before and after hot stamping according to the Al-Si plating amount.

Referring to FIG. 4 , SEM photographs before and after the hot stamping process when the plating amount is 150 g/m 2 , 65 g/m 2 , and 40 g/m 2 are respectively shown. As shown in the SEM photo, when the plating amount was 150g/m2, the decarburized layer was hardly observed after hot stamping, and when the plating amount was 65g/m2 and 40g/m2, the decarburized layer could be observed, and the plating amount was small 40g/m2. In the case of m2, a thicker decarburized layer can be observed.

Although the above description has been focused on the embodiments of the present invention, various changes or modifications may be made at the level of those skilled in the art. Such changes and modifications can be said to belong to the present invention without departing from the scope of the present invention. Accordingly, the scope of the present invention should be judged by the claims described below.

Claims (8)

delete delete delete delete delete By weight%, carbon (C): 0.29 to 0.40%, silicon (Si): 0.20 to 0.40%, manganese (Mn): 1.00 to 1.50%, phosphorus (P): more than 0 and 0.012% or less, sulfur (S): More than 0 0.002% or less, Chromium (Cr): 0.10 to 0.30%, Boron (B): 0.0015 to 0.003%, Titanium (Ti): 0.027 to 0.037%, Molybdenum (Mo): 0.01 to 0.30%, Niobium (Nb) : Steel composed of 0.001 to 0.05% and the remainder iron (Fe) and unavoidable impurities,
An aluminum-silicon (Al-Si) plating layer formed on the surface of the steel material,
It has a decarburized layer of 1.3 ~ 9.5㎛ thickness formed at the interface between the aluminum-silicon (Al-Si) plating layer and the steel,
Tensile strength (TS): 1,800 MPa or more, yield strength (YS): 1,200 MPa or more, elongation (EL): having physical properties of 5% or more,
hot stamping parts.
7. The method of claim 6,
The microstructure of the surface decarburized layer has a composite structure made of ferrite and pearlite,
hot stamping parts.
7. The method of claim 6,
The thickness of the aluminum-silicon (Al-Si) plating layer is characterized in that 13.6 ~ 29.9㎛,
hot stamping parts.

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