Hot stamped component and method for manufacturing the same

Abstract

The present invention provides a hot-stamped member including a base material, a decarburized layer disposed on a surface of the base material, and an inner oxide layer disposed on a surface of the decarburized layer, in which the hot-stamped member has a tensile strength (TS) of 1680 MPa to 2000 MPa, and a tensile strength (TS) of 2,000 MPa to 2,000 MPa. And the hardness of the hot-stamped member within a depth of 50 [mu] m from the surface in the plate thickness direction of the hot-stamped member and the average hardness of the hot-stamped member satisfy relational expression 1. Lt; the relational expression is 1gt; (A / B) < = 0.7 (In relational expression 1, A is the hardness (Hv (< = 50 [mu] m) in a depth of 50 [mu] m in the plate thickness direction of the hot-stamped member, and B is the average hardness (Hv (average)) of the hot-stamped member).

Description

Technical Field

[0001] The present application relates to a hot stamping component and a method for manufacturing the same. Background Art

[0002] As environmental regulations and fuel economy-related regulations are strengthened around the world, the demand for lighter vehicle materials is increasing. Therefore, ultra-high strength steel and hot stamping steel have been actively researched and developed.

[0003] The hot stamping process generally includes heating / forming / cooling / trimming, and the phase transformation and microstructural changes of the material can be used during the process. In order to improve the toughness of hot stamping steel, methods of improving the toughness of the base material by using alloy components have been actively studied.

[0004] However, when alloy compositions are changed or increased, costs may increase and economic feasibility may decrease.

[0005] Related technologies include Korean Patent Publication No. 10-2021-0129902 (titled “Hot stamping product and method of manufacturing the same”). Summary of the invention

[0006] Technical issues

[0007] The embodiments of the present application can improve the toughness of the manufactured hot stamping parts by appropriately forming a decarburized layer and an inner oxide layer on the surface of the base material, and can also prevent cracks from occurring during the hot stamping forming process.

[0008] Solution to the problem

[0009] An embodiment of the present application provides a hot stamping component, comprising: a base material, a decarburized layer located on the base material, and an inner oxide layer located on the decarburized layer, wherein the hot stamping component has a tensile strength (TS) of 1680 MPa to 2000 MPa, and the hardness of the hot stamping component within a depth of 50 μm from the surface of the hot stamping component in the plate thickness direction of the hot stamping component and the average hardness of the hot stamping component satisfy Relationship 1.

[0010] <Relation 1>

[0011] (A / B)≤0.7

[0012] (In Relational Formula 1, A represents the hardness within a depth of 50 μm in the plate thickness direction of the hot stamped part (Hv (≤ 50 μm)), and B represents the average hardness of the hot stamped part (Hv (average)).)

[0013] In this embodiment, the depth of the inner oxide layer may satisfy Relationship 2.

[0014] <Relation 2>

[0015] C≤5μm

[0016] (In Relational Formula 2, C represents the depth of the inner oxide layer in the sheet thickness direction of the hot stamped part.)

[0017] In this embodiment, the hot stamped part may have a VDA bend angle of 60° or more.

[0018] In the present embodiment, the hot stamped part may have a yield strength (YP) of 1150 MPa to 1500 MPa and an elongation (EL) of 4% to 10%.

[0019] In the present embodiment, the hot stamped part may have a microstructure having a martensite fraction of 90% or more.

[0020] In this embodiment, the hot stamped part may further include a plating layer, the plating layer being located on the surface of the inner oxide layer.

[0021] In this embodiment, the thickness of the plating layer may be 10 μm to 30 μm.

[0022] Another embodiment of the present application provides a method for manufacturing a hot stamping part, the method comprising: forming a blank by cutting a coated steel plate having a coating formed on at least one surface of a base material, and heating the blank in a heating furnace having a plurality of intervals with different temperature ranges, wherein the heating of the blank comprises: a multi-stage heating step of heating the blank in stages, and a uniform heating step of heating the staged heated blank to a temperature of Ac3 to 910°C, wherein the hardness of the hot stamping part within a depth of 50 μm from the surface of the hot stamping part in the plate thickness direction of the hot stamping part and the average hardness of the hot stamping part satisfy Relationship 3.

[0023] <Relation 3>

[0024] (A / B)≤0.7

[0025] (In Relational Expression 3, A represents the hardness within a depth of 50 μm in the plate thickness direction of the hot stamped part (Hv(≤50 μm)), and B represents the average hardness of the hot stamped part (Hv(average)).)

[0026] In this embodiment, the dew point of the annealing furnace of the base material may be -15°C to +15°C.

[0027] In this embodiment, the annealing temperature of the base material may be 750°C to 900°C.

[0028] In the present embodiment, the method of manufacturing a hot stamped part may further include: after heating the blank, transferring the heated blank; forming a molded body by pressing the transferred blank using a mold; and cooling the formed molded body.

[0029] In the present embodiment, the hot stamped part may further include: a decarburized layer formed on the surface of the base material; and an inner oxide layer formed on the surface of the decarburized layer.

[0030] In this embodiment, the depth of the inner oxide layer may satisfy Relationship 4.

[0031] <Relation 4>

[0032] C≤5μm

[0033] (In Relational Formula 4, C represents the depth of the inner oxide layer in the sheet thickness direction of the hot stamped part.)

[0034] Other aspects, features, and advantages of the present application will become more apparent from the detailed description, claims, and accompanying drawings that are intended to implement the present application.

[0035] Advantageous Effects of the Invention

[0036] According to the embodiment of the present application as described above, since the decarburized layer is formed on the surface of the base material, the toughness of the manufactured hot stamping part can be improved.

[0037] In addition, according to the embodiment of the present application, since the inner oxide layer formed on the surface of the decarburized layer is arranged below a preset depth, cracks may be prevented from occurring during the hot stamping process. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 Schematically shows a cross-sectional view of a hot stamping component according to an embodiment of the present application.

[0039] Figure 2 The flowchart schematically shows a method for manufacturing a hot stamping component according to an embodiment of the present application.

[0040] Figures 3 to 5 It is a cross-sectional view schematically showing a method of manufacturing a hot stamping part according to an embodiment of the present application.

[0041] Figure 6 The flowchart schematically shows the hot stamping steps according to the embodiment of the present application.

[0042] Figure 7 The flowchart schematically shows the heating step according to the embodiment of the present application.

[0043] Figure 8is a schematic diagram for describing a heating furnace having a plurality of zones in a heating step of a method for manufacturing a hot stamping part according to an embodiment of the present application. DETAILED DESCRIPTION

[0044] Since the present application allows various changes and multiple embodiments, certain embodiments will be shown in the drawings and described in the detailed description. The effects and features of the present application and the methods for realizing them will be explained with reference to the embodiments described in detail below with reference to the drawings. However, the present application is not limited to the following embodiments and can be implemented in various forms.

[0045] Although the terms “first”, “second”, etc. may be used to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another.

[0046] As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise.

[0047] It will also be understood that the terms “comprises” or “comprising” used herein indicate the presence of stated features or components, but do not preclude the presence or addition of one or more other features or components.

[0048] It will also be understood that when a layer, region or component is referred to as being “on” another layer, region or component, it can be directly on the other layer, region or component or be indirectly on the other layer, region or component with intervening layers, regions or components therebetween.

[0049] For the convenience of explanation, the size of the components in the drawings may be enlarged or reduced. For example, since the size and thickness of the elements in the drawings are arbitrarily shown for the convenience of explanation, the present application is not limited thereto.

[0050] “A and / or B” is used herein to select only A, only B, or both A and B. In addition, “at least one of A and B” is used herein to select only A, only B, or both A and B.

[0051] In the following embodiments, a “plan view of an object” means a “view of an object seen from above”, and a “cross-sectional view of an object” means a “view of an object cut vertically and seen from the inside”. In the following embodiments, when elements “overlap”, it may mean that the elements overlap in both the “plan view” and the “cross-sectional view”.

[0052] Hereinafter, embodiments of the present application will be described in detail with reference to the accompanying drawings, wherein the same or corresponding elements are denoted by the same reference numerals throughout.

[0053] Figure 1Schematically shows a cross-sectional view of a hot stamping component according to an embodiment of the present application.

[0054] refer to Figure 1 The hot stamping part 1 according to the embodiment may include a base material 100, a decarburized layer 200, an inner oxide layer 300 and a plating layer 400. The base material 100, the decarburized layer 200, the inner oxide layer 300 and the plating layer 400 may be sequentially stacked in the plate thickness direction of the hot stamping part 1.

[0055] In an embodiment, the base material 100 may include carbon (C), silicon (Si), manganese (Mn), phosphorus (P), sulfur (S), boron (B), the balance of iron (Fe) and other inevitable impurities. For example, the base material 100 may include about 0.25 wt% to about 0.5 wt% of carbon (C), about 0.1 wt% to about 0.8 wt% of silicon (Si), about 0.3 wt% to about 3.0 wt% of manganese (Mn), more than 0 wt% but not more than about 0.05 wt% of phosphorus (P), more than 0 wt% but not more than about 0.01 wt% of sulfur (S), about 0.0005 wt% to about 0.005 wt% of boron (B), the balance of iron (Fe) and other inevitable impurities.

[0056] In addition, the base material 100 may further include at least one component of titanium (Ti), niobium (Nb), and vanadium (V). In addition, the base material 100 may further include chromium (Cr), molybdenum (Mo), and nickel (Ni).

[0057] The base material 100 may further include at least one component of titanium (Ti), niobium (Nb), and vanadium (V), and the sum of at least one component of titanium (Ti), niobium (Nb), and vanadium (V) may be about 0.01 wt % to about 0.1 wt %. For example, the base material 100 may include titanium (Ti) and niobium (Nb), and the sum of titanium (Ti) and niobium (Nb) contained in the base material 100 may be about 0.01 wt % to about 0.1 wt %.

[0058] In addition, the base material 100 may further include about 0.01 wt % to about 1.0 wt % of chromium (Cr), about 0.01 wt % to about 1.0 wt % of molybdenum (Mo), and about 0.001 wt % to about 1.0 wt % of nickel (Ni).

[0059] Carbon (C) is the main element that determines the strength and hardness of steel, and carbon can be added to ensure the tensile strength of steel material after hot stamping (or hot pressing) process. In addition, carbon (C) can be added to ensure the hardenability characteristics of steel material. In an embodiment, based on the gross weight of base material 100, carbon (C) can be included in an amount of about 0.25 wt % to about 0.5 wt %. When carbon (C) is included in an amount less than about 0.25 wt % based on the gross weight of base material 100, it may be difficult to achieve desired mechanical strength. On the other hand, when carbon (C) is included in an amount greater than about 0.5 wt % based on the gross weight of base material 100, the toughness of steel material may be reduced, or the problem of controlling the embrittlement of steel may occur.

[0060] Silicon (Si) can be used as a ferrite stabilizing element in the matrix material 100. Silicon (Si) can improve ductility by purifying ferrite, and can improve the carbon concentration in austenite by suppressing the formation of low-temperature carbides. In addition, silicon (Si) can be a key element for hot rolling, cold rolling, hot stamping structural homogenization (pearlite and manganese segregation control) and ferrite micro-dispersion. In an embodiment, based on the gross weight of the matrix material 100, silicon (Si) can be included in an amount of about 0.1 wt % to about 0.8 wt %. When silicon (Si) is included in an amount less than about 0.1 wt % based on the gross weight of the matrix material 100, the above-mentioned effect may not be fully obtained. On the other hand, when silicon (Si) is included in an amount greater than about 0.8 wt % based on the gross weight of the matrix material 100, hot rolling load and cold rolling load may increase, hot rolling red oxide scale may be too much, and adhesion may deteriorate.

[0061] Manganese (Mn) can be added to improve hardenability and strength during heat treatment. In an embodiment, based on the gross weight of the base material 100, manganese (Mn) can be included in an amount of about 0.3 wt % to about 3.0 wt %. When manganese (Mn) is included in an amount less than about 0.3 wt % based on the gross weight of the base material 100, due to insufficient hardenability, the material after hot stamping is likely to be insufficient (e.g., insufficient hard phase fraction). On the other hand, when manganese (Mn) is included in an amount greater than about 3.0 wt % based on the gross weight of the base material 100, due to manganese (Mn) segregation or pearlite bands, ductility and toughness may be reduced, bending properties may be reduced, and an uneven microstructure may be produced.

[0062] Phosphorus (P) may be an element that is prone to segregation and reduces the toughness of steel. In an embodiment, phosphorus (P) may be included in an amount greater than 0 wt % and less than or equal to about 0.05 wt % based on the total weight of the base material 100. When phosphorus (P) is included in the above range based on the total weight of the base material 100, the toughness of the steel can be prevented from being reduced. On the other hand, when phosphorus (P) is included in an amount greater than about 0.05 wt % based on the total weight of the base material 100, cracks may occur during the process, and iron phosphide compounds may be formed, thereby reducing the toughness of the steel.

[0063] Sulfur (S) may be an element that reduces workability and physical properties. In an embodiment, sulfur (S) may be included in an amount greater than 0 wt % and less than or equal to about 0.01 wt % based on the total weight of the base material 100. When sulfur (S) is included in an amount greater than about 0.01 wt % based on the total weight of the base material 100, hot workability may be reduced, and surface defects (e.g., cracks) may occur due to the formation of larger inclusions.

[0064] Boron (B) is added to ensure the hardenability and strength of the steel by ensuring a martensitic structure, and can have a grain refining effect by increasing the austenite grain growth temperature. In an embodiment, boron (B) may be included in an amount of about 0.0005 wt % to about 0.005 wt % based on the total weight of the base material 100. When boron (B) is included in the above range based on the total weight of the base material 100, hard grain boundary embrittlement can be prevented, and high toughness and bendability can be ensured.

[0065] Titanium (Ti) can be added to improve hardenability and improve the material by forming a precipitation phase after hot stamping heat treatment. In addition, titanium (Ti) can effectively contribute to the refinement of austenite grains by forming a precipitation phase (such as Ti (C, N)) at high temperature.

[0066] Niobium (Nb) may be added to improve strength and toughness according to the reduction in martensite lath bundle size.

[0067] Vanadium (V) may be added to improve the strength of steel by a precipitation strengthening effect of forming a precipitation phase.

[0068] In an embodiment, titanium (Ti), niobium (Nb), and vanadium (V) may be selectively included in the base material 100. In this case, when at least one of titanium (Ti), niobium (Nb), and vanadium (V) is included in the base material, the total of at least one of titanium (Ti), niobium (Nb), and vanadium (V) may be about 0.01 wt % to about 0.1 wt %.

[0069] Chromium (Cr) may be added to improve the hardenability and strength of the steel. In an embodiment, chromium (Cr) may be included in an amount of about 0.01 wt % to about 1.0 wt % based on the total weight of the base material 100. When chromium (Cr) is included in the above range based on the total weight of the base material 100, the hardenability and strength of the steel may be improved, an increase in production costs may be prevented, and a decrease in toughness of the steel material may be prevented.

[0070] Molybdenum (Mo) can contribute to improving strength by suppressing the coarsening of the precipitated phase and improving the hardenability during hot rolling and hot stamping. Molybdenum (Mo) may be included in an amount of about 0.01 wt % to about 1.0 wt % based on the total weight of the base material 100. When molybdenum (Mo) is included in the above range based on the total weight of the base material 100, the effect of suppressing the coarsening of the precipitated phase and improving the hardenability during hot rolling and hot stamping can be excellent.

[0071] Nickel (Ni) can be added to ensure hardenability and strength. In addition, nickel (Ni) is a kind of austenite stabilizing element, and can contribute to improving elongation by controlling austenite transformation. In an embodiment, based on the gross weight of base material 100, nickel (Ni) can be included in an amount of about 0.001 wt % to about 1.0 wt %. When nickel (Ni) is included in an amount less than about 0.001 wt % based on the gross weight of base material 100, it may be difficult to appropriately achieve the above effect. When nickel (Ni) is included in an amount greater than about 1.0 wt % based on the gross weight of base material 100, toughness may be reduced, cold workability may be reduced, and product manufacturing cost may increase.

[0072] In an embodiment, the base material 100 may have a microstructure having a martensite fraction of about 90% or more. In detail, the microstructure of the base material 100 may include about 90% or more of martensite, and less than 10% of the remaining other inevitable structures and other precipitation phases.

[0073] In an embodiment, the decarburized layer 200 may be located on the base material 100. In detail, the decarburized layer 200 may be located on the surface of the base material 100. When the decarburized layer 200 is located on the base material 100, since the decarburized layer 200 is softer than the base material 100, the toughness of the hot stamping part 1 may be improved.

[0074] A layer having a hardness of about 70% or less compared to the average hardness at a point about 1 / 4 away from the surface of the base material 100 in the plate thickness direction of the hot stamping part 1 may be defined as the decarburized layer 200. Alternatively, a layer having a hardness of about 70% or less compared to the average hardness at a point about 1 / 4 away from the surface of the hot stamping part 1 in the plate thickness direction of the hot stamping part 1 may be defined as the decarburized layer 200. That is, the average hardness of the decarburized layer 200 may be about 70% or less of the average hardness at a point about 1 / 4 away from the surface of the base material 100 or the surface of the hot stamping part 1 in the plate thickness direction of the hot stamping part 1. In other words, the average hardness of the decarburized layer 200 may be about 70% or less of the average hardness at a point about 1 / 4 away from the surface of the base material 100 or the surface of the hot stamping part 1 in the plate thickness direction of the hot stamping part 1.

[0075] In an embodiment, the inner oxide layer 300 may be located on the decarburized layer 200. In detail, the inner oxide layer 300 may be located on the surface of the decarburized layer 200. The inner oxide layer 300 may include silicon (Si), manganese (Mn), chromium (Cr), and the like.

[0076] In an embodiment, the depth (or thickness t1 ) of the inner oxide layer 300 in the sheet thickness direction of the hot stamped part 1 may be about 5 μm, which will be described in detail below.

[0077] In an embodiment, the plating layer 400 may be located on the inner oxide layer 300. In detail, the plating layer 400 may be located on the surface of the inner oxide layer 300. The plating layer 400 may be a zinc (Zn)-based plating layer or an aluminum (Al)-based plating layer. For example, the plating layer 400 may contain zinc (Zn) and / or aluminum (Al).

[0078] In an embodiment, when the plating layer 400 is a zinc (Zn)-based plating layer, the plating layer 400 may contain iron (Fe), aluminum (Al), manganese (Mn), silicon (Si), the balance of zinc (Zn) and other inevitable impurities. For example, the plating layer 400 may contain about 10 wt% to about 70 wt% of iron (Fe), greater than 0 wt% but not greater than about 5 wt% of aluminum (Al), greater than 0 wt% but not greater than about 1 wt% of manganese (Mn), greater than 0 wt% but not greater than about 1 wt% of silicon (Si), the balance of zinc (Zn) and other inevitable impurities.

[0079] The depth (or thickness t2) of the plating layer 400 in the plate thickness direction of the hot stamping part 1 may be about 10 μm to about 30 μm. When the thickness t2 of the plating layer 400 is less than about 10 μm, the sacrificial effect of zinc may be reduced, and when the thickness t2 of the plating layer 400 is greater than about 30 μm, the thickness t2 of the plating layer 400 is too large, and thus, the toughness of the hot stamping part 1 including the plating layer 400 may be reduced. Therefore, when the thickness t2 of the plating layer 400 is about 10 μm to about 30 μm, the surface of the base material (or steel material) may be protected, and at the same time, the reduction in toughness of the hot stamping part 1 may be prevented or minimized.

[0080] The decarburized layer 200 is softer than the base material 100 , and when the hot stamped component 1 includes the decarburized layer 200 , the toughness of the hot stamped component 1 including the decarburized layer 200 may be improved.

[0081] However, as described above, when the depth (or thickness t1) of the inner oxide layer 300 is too large, liquid zinc may more easily penetrate into the base material 100 through the inner oxide layer 300, and the risk of cracking during hot stamping may increase, and thus, the bendability of the manufactured hot stamping part 1 may decrease. In detail, when the depth (or thickness t1) of the inner oxide layer 300 is greater than about 5 μm, liquid zinc may more easily penetrate into the base material 100 due to the inner oxide layer 300, and the risk of cracking during hot stamping may increase, and thus, the bendability of the manufactured hot stamping part 1 may decrease.

[0082] As described below, in the method of manufacturing a hot stamping part, a decarburized layer 200 may be formed on a base material 100 in an annealing step. In this case, an inner oxide layer 300 may be simultaneously formed on the decarburized layer 200. In detail, in the annealing step, the decarburized layer 200 may be formed on the surface of the base material 100, and at the same time, the inner oxide layer 300 may be formed on the surface of the decarburized layer 200.

[0083] When the dew point of the annealing furnace performing the annealing step increases, the depth (or thickness) of the decarburized layer 200 may increase. However, when the depth (or thickness) of the decarburized layer 200 increases, the depth (or thickness) of the inner oxide layer 300 may also increase. That is, in order to improve the toughness of the hot stamping part 1, the depth (or thickness) of the decarburized layer 200 should be increased. However, when the depth (or thickness) of the decarburized layer 200 increases, the depth (or thickness) of the inner oxide layer 300 may also increase, thereby increasing the risk of cracking during hot stamping and reducing the bendability of the manufactured hot stamping part 1. Therefore, it is necessary to appropriately adjust the depth (or thickness) of the decarburized layer 200 and the depth (or thickness) of the inner oxide layer 300.

[0084] Therefore, the inventors of the present application derived Relationships 1 and 2 through a large number of repeated experiments so that the hot stamping part 1 has a VDA bending angle of about 60° or more. In the embodiment, the hot stamping part 1 can satisfy Relationships 1 and 2. In detail, the hardness within a depth of about 50 μm from the surface of the hot stamping part 1 in the plate thickness direction of the hot stamping part 1 and the average hardness of the hot stamping part 1 can satisfy Relationship 1, and the depth (or thickness) of the inner oxide layer 300 can satisfy Relationship 2. For example, the hot stamping part 1 can satisfy Relationships 1 and 2 at the same time.

[0085] <Relation 1>

[0086] (A / B)≤0.7

[0087] In Relational Expression 1, A represents the hardness within a depth (or thickness) of about 50 μm in the plate thickness direction of the hot stamped part 1 (Hv (≤50 μm)), and B represents the average hardness (Hv (average)) of the hot stamped part 1 .

[0088] In this case, the hardness within a depth of about 50 μm from the surface of the hot stamping part 1 in the plate thickness direction of the hot stamping part 1 may be a hardness value measured at a depth of about 50 μm or less from the surface of the hot stamping part 1 in the plate thickness direction of the hot stamping part 1 using a Vickers hardness tester, and the average hardness (Hv(average)) of the hot stamping part 1 may be a hardness value measured at about a 1 / 4 point in the plate thickness direction of the hot stamping part 1 using a Vickers hardness tester.

[0089] <Relation 2>

[0090] C≤5μm

[0091] In Relational Expression 2, C represents the depth (or thickness) of the inner oxide layer 300 in the sheet thickness direction of the hot stamped part 1 .

[0092] Since the decarburized layer 200 is located on the surface of the base material 100, the decarburized layer 200 may be located on a portion adjacent to the surface of the hot stamping part 1. Since the decarburized layer 200 is softer than the base material 100, the hardness of the portion of the hot stamping part 1 adjacent to the surface of the hot stamping part 1 may be less than the average hardness of the hot stamping part 1. In this case, when the depth (or thickness) of the decarburized layer 200 increases, the difference between the hardness of the portion of the hot stamping part 1 adjacent to the surface of the hot stamping part 1 and the average hardness of the hot stamping part 1 may increase. On the other hand, when the depth (or thickness) of the decarburized layer 200 decreases, the difference between the hardness of the portion of the hot stamping part 1 adjacent to the surface of the hot stamping part 1 and the average hardness of the hot stamping part 1 may decrease.

[0093] When the ratio between the hardness (Hv(≤50μm)) within a depth (or thickness) of about 50μm in the plate thickness direction of the hot stamping part 1 and the average hardness (Hv(average)) of the hot stamping part 1 is greater than 0.7, the decarburized layer 200 cannot be formed (or arranged) to a sufficient depth (or thickness), and thus, the toughness of the hot stamping part 1 including the decarburized layer 200 may be low. In particular, the VDA bending angle of the hot stamping part 1 may be less than about 60°.

[0094] When the ratio between the hardness (Hv (≤50 μm)) within a depth (or thickness) of about 50 μm in the plate thickness direction of the hot stamping part 1 and the average hardness (Hv (average)) of the hot stamping part 1 is equal to or less than 0.7, this may mean that the decarburized layer 200 is formed (or arranged) to a sufficient depth (or thickness). Therefore, when the ratio between the hardness (Hv (≤50 μm)) within a depth (or thickness) of about 50 μm in the plate thickness direction of the hot stamping part 1 and the average hardness (Hv (average)) of the hot stamping part 1 satisfies 0.7 or less, the decarburized layer 200 is formed (or arranged) to a sufficient depth (or thickness), and thus, the toughness of the hot stamping part 1 including the decarburized layer 200 may be improved. In particular, the VDA bending angle of the hot stamping part 1 may be about 60° or more.

[0095] In addition, as described above, the depth (or thickness) of the inner oxide layer 300 included in the hot stamped part 1 may be about 5 μm or less.

[0096] When the coating 400 is a zinc (Zn)-based coating, liquid metal embrittlement (LME) may occur due to the low melting point of zinc, which may cause cracks inside and may reduce the bendability of the hot stamping part 1. In this case, when the depth (or thickness) of the inner oxide layer 300 is large, liquid zinc may more easily penetrate into the inside due to the inner oxide layer 300, and the risk of cracking during hot stamping may increase, and therefore, the bendability of the manufactured hot stamping part 1 may be reduced.

[0097] When the depth (or thickness) of the inner oxide layer 300 is greater than about 5 μm, liquid zinc may more easily penetrate into the interior due to the inner oxide layer 300 , the risk of cracking during hot stamping may increase, and thus, the bendability of the manufactured hot stamped part 1 may decrease.

[0098] Therefore, when the depth (or thickness) of the inner oxide layer 300 in the plate thickness direction of the hot stamping part 1 is about 5 μm or less, cracks can be prevented from occurring during hot stamping, and thus, the high temperature formability of the hot stamping part (or blank) can be improved.

[0099] In the embodiment, the hot stamping part 1 may satisfy both Relationship 1 and Relationship 2. When the hot stamping part 1 satisfies both Relationship 1 and Relationship 2, the hot stamping part 1 may have high toughness, and the high temperature formability of the hot stamping part 1 may be excellent. In detail, when the hardness within a depth of about 50 μm from the surface of the hot stamping part 1 in the plate thickness direction of the hot stamping part 1 and the average hardness of the hot stamping part 1 satisfy Relationship 1, and the depth (or thickness) of the inner oxide layer 300 satisfies Relationship 2, the hot stamping part 1 may have high toughness, and the high temperature formability of the hot stamping part 1 may be excellent.

[0100] In an embodiment, when the hot stamping part 1 satisfies both Relationship 1 and Relationship 2, the hot stamping part 1 may have a tensile strength (TS) of about 1680 MPa to about 2000 MPa, a yield strength (YP) of about 1150 MPa to about 1500 MPa, and an elongation (EL) of about 4% to about 10%. In addition, the VDA bending angle of the hot stamping part 1 may be about 60° or more. In this case, the VDA bending angle may be measured according to the VDA standard (VDA238-100).

[0101] Figure 2 The flowchart schematically shows a method for manufacturing a hot stamping component according to an embodiment of the present application. Figures 3 to 5 It is a cross-sectional view schematically showing a method of manufacturing a hot stamping part according to an embodiment of the present application.

[0102] refer to Figures 2 to 5 , according to the embodiment of the hot stamping part 1 (see Figure 1 ) may include a hot rolling step S100, a cooling / coiling step S200, a cold rolling step S300, an annealing step S400, a plating step S500 and a hot stamping step S600.

[0103] First, we can refer to Figure 1The base material 100 (e.g., a steel billet) prepared by the described composition is subjected to a reheating step. In the steel billet reheating step, the steel billet obtained by the continuous casting process can be reheated to a certain temperature so that the components segregated during the casting process are dissolved. In an embodiment, the slab reheating temperature (SRT) can be about 1200°C to about 1400°C. When the slab reheating temperature (SRT) is lower than about 1200°C, the components segregated during the casting process may not be fully dissolved, and therefore, it may be difficult to have a significant alloying element homogenization effect, and it may be difficult to have a significant titanium (Ti) dissolution effect. When the slab reheating temperature (SRT) is high, the slab reheating temperature (SRT) is conducive to homogenization. However, when the slab reheating temperature (SRT) is higher than about 1400°C, the austenite grain size may increase, so it may be difficult to ensure strength, and due to excessive heating processes, the manufacturing cost of the steel plate may increase.

[0104] In the hot rolling step S100, the reheated base material 100 may be hot rolled at a certain finishing temperature. The hot rolled steel sheet may be manufactured by the hot rolling step S100. In an embodiment, the finishing exit temperature (FDT) may be from about 880°C to about 950°C. In this case, when the finishing exit temperature (FDT) is lower than about 880°C, the processability of the steel sheet may not be ensured due to the appearance of a mixed grain structure caused by rolling in irregular regions, the processability may be reduced due to the inhomogeneity of the microstructure, and flowability problems may occur during the hot rolling process due to rapid phase transformation. When the finishing exit temperature (FDT) is higher than about 950°C, the austenite grains may coarsen, the TiC precipitation phase may coarsen, and therefore, the performance of the hot stamping parts may deteriorate.

[0105] In the cooling / coiling step S200, the hot-rolled base material 100 may be cooled to a certain coiling temperature (CT) and coiled at a certain coiling temperature (CT). In an embodiment, the coiling temperature (CT) of the cooling / coiling step S300 may be about 550°C to about 800°C. The coiling temperature (CT) may affect the redistribution of carbon (C), and when the coiling temperature (CT) is lower than about 550°C, the low-temperature phase fraction may increase due to overcooling, the strength may increase, the rolling load during cold rolling may increase, and the ductility may decrease rapidly. On the contrary, when the coiling temperature (CT) is higher than about 800°C, irregular grain growth or excessive grain growth may cause poor formability and strength.

[0106] In the cold rolling step S300, the coiled base material 100 may be unwound, pickled, and then cold rolled. In this case, pickling may be performed to remove scale from the coiled steel sheet (or base material) (i.e., the hot rolled coil produced by the above hot rolling process). A cold rolled steel sheet may be produced by the cold rolling step S300.

[0107] In the annealing step S400, the cold rolled base material 100 may be annealed at a temperature of about 700°C or higher. For example, the annealing step S400 may include heating the cold rolled base material 100 and cooling the heated base material 100 at a certain cooling rate.

[0108] In an embodiment, the base material may be annealed in an annealing step S400. The annealing step S400 may be performed in an annealing furnace.

[0109] The annealing of the base material 100 can be carried out under an atmosphere containing about 0.5 volume % to about 25 volume % of hydrogen and the remainder of nitrogen. In this case, water can be sprayed into the annealing furnace together with the hydrogen and nitrogen. When water is sprayed into the annealing furnace, the dew point of the annealing furnace may increase. Therefore, the dew point of the annealing furnace can be controlled by controlling the amount of water sprayed into the annealing furnace.

[0110] In an embodiment, when the dew point of the annealing furnace increases, the decarburized layer 200 may be formed on the base material 100. For example, carbon may be lost from the surface of the base material 100 to form the decarburized layer 200. In addition, at the same time, the inner oxide layer 300 may be formed on the decarburized layer 200. That is, the decarburized layer 200 may be formed on the surface of the base material 100, and the inner oxide layer 300 may be formed on the surface of the decarburized layer 200. In this case, the decarburized layer 200 and the inner oxide layer 300 may be layers obtained by changing a portion of the base material 100.

[0111] In this case, a layer having a hardness of about 80% or less compared to the average hardness at about 1 / 4 point from the surface of the base material 100 may be defined as the decarburized layer 200. That is, the average hardness of the decarburized layer 200 may be about 80% or less of the average hardness at about 1 / 4 point from the surface of the base material 100.

[0112] In an embodiment, the dew point of the annealing furnace for annealing the base material 100 may be about -15°C to about +15°C. A decarburized layer 200 is formed on the base material 100, thereby improving the toughness of the manufactured hot stamping part 1. However, when the dew point of the annealing furnace is about -15°C or lower, the depth (or thickness) of the decarburized layer 200 may be too small, and therefore, the effect of improving the toughness of the manufactured hot stamping part may not be significant. On the other hand, when the dew point of the annealing furnace is about +15°C or higher, the depth (or thickness t3) of the inner oxide layer 300 may be too large, and therefore, LME cracks may occur, and operability may be reduced due to oxidation of the equipment. For example, a large amount of water should be supplied to the annealing furnace to increase the dew point of the annealing furnace. When a large amount of water is supplied to the annealing furnace, the equipment of the annealing furnace may be oxidized, and it takes a long time to clean the equipment, thereby reducing operability. In addition, when the dew point of the annealing furnace is high, the depth (or thickness t3) of the inner oxide layer 300 and the decarburized layer 200 may increase, and therefore, during high temperature forming, cracks may occur inside due to the inner oxide layer 300. Therefore, when the dew point of the annealing furnace for annealing the base material 100 satisfies about -15°C to about +15°C, the toughness of the manufactured hot stamping part 1 can be improved, and the efficiency of the manufacturing process can be improved.

[0113] In an embodiment, the linear speed of the annealing furnace for annealing the base material 100 may be about 30 meters per minute (mpm) to about 200 mpm. When the linear speed of the annealing furnace is 30 mpm or less, the moving speed of the base material 100 may be too low, which may lead to a sharp drop in productivity. When the linear speed of the annealing furnace is 200 mpm or more, the residence time of the annealing furnace may be too short, and the depth (or thickness) of the decarburized layer 200 may be reduced, and therefore, the effect of improving the toughness of the manufactured hot stamping parts may not be significant. Therefore, when the linear speed of the annealing furnace for annealing the base material 100 meets about 30 mpm to about 200 mpm, the productivity of the hot stamping parts can be improved, and at the same time, the toughness of the manufactured hot stamping parts can be improved.

[0114] In an embodiment, the annealing temperature of the base material 100 may be about 750°C to about 900°C. When the annealing temperature of the base material 100 is lower than about 750°C, the desired structure may not be obtained, and recrystallization may not be sufficiently completed. On the other hand, when the annealing temperature of the base material 100 is higher than about 900°C, the annealing temperature may be too high, and thus, the efficiency of the manufacturing process may be reduced. Therefore, when the annealing temperature of the base material 100 satisfies about 750°C to about 900°C, the desired structure may be obtained, recrystallization may be sufficiently completed, and the efficiency of the manufacturing process may be improved.

[0115] The plating step S500 may be a step of forming the plating layer 400 on the annealed base material 100. In an embodiment, the plating layer 400 may be formed on the annealed base material 100 by the plating step S500. In detail, the plating layer 400 may be formed on the surface of the inner oxide layer 300 by the plating step S500. In this case, the plating layer 400 may include a zinc (Zn)-based plating layer or an aluminum (Al)-based plating layer.

[0116] In detail, in the plating step S500, the annealed base material 100 may be immersed in a plating bath. In this case, the plating bath may be maintained at a temperature of about 400° C. to about 700° C. The amount of the plating layer attached to both surfaces of the base material 100 (or the inner oxide layer 300) may be about 40 g / m 2 About 200g / m 2 .

[0117] In an embodiment, the depth (or thickness t4) of the coating 400 formed on the base material 100 or the decarburized layer 200 in the plate thickness direction of the base material can be about 5 μm to about 20 μm. When the depth (or thickness t4) of the coating 400 is about 5 μm or less, the sacrificial method of the coating 400 may not be significant. When the depth (or thickness) of the coating 400 is about 20 μm or more, the cost of forming the coating 400 may increase, thereby reducing economic feasibility. Therefore, when the depth (or thickness t4) of the coating 400 meets about 5 μm to about 20 μm, the corrosion of the base material 100 of the hot stamping part 1 can be prevented or minimized.

[0118] In an embodiment, annealing step S400 and plating step S500 can be performed on the same line. Therefore, the line speed for plating step S500 can be about 30mpm to about 200mpm. When the line speed is about 30mpm or less, the line speed may be too low, and therefore, productivity may decrease. The plating amount is controlled by using an air knife. When the line speed is about 200mpm or greater, the line speed may be too fast, and therefore, it may be difficult to control the plating amount by using an air knife. Therefore, when the line speed for plating step S500 satisfies about 30mpm to about 200mpm, productivity can be improved, and at the same time, the plating amount can be easily controlled.

[0119] In an embodiment, a plated steel sheet having a plating layer 400 formed on at least one surface of a base material 100 may be manufactured by a plating step S500. In this case, the plated steel sheet may include a base material 100, a decarburized layer 200 formed on the base material 100, an inner oxide layer 300 formed on the decarburized layer 200, and a plating layer 400 formed on the inner oxide layer 300. In detail, the plated steel sheet may include a base material 100, a decarburized layer 200 formed on a surface of the base material 100, an inner oxide layer 300 formed on a surface of the decarburized layer 200, and a plating layer 400 formed on a surface of the inner oxide layer 300.

[0120] Figure 6 The flowchart schematically shows the hot stamping steps according to the embodiment of the present application. Figure 7 The flowchart schematically shows the heating step according to the embodiment of the present application.

[0121] refer to Figure 6 and Figure 7 , the hot stamping step S600 may be performed after the plating step S500 (see Figure 2 ). The hot stamping step S600 may include a heating step S610, a transferring step S620, a molding step S630, and a cooling step S640.

[0122] First, the substrate 100 (see Figure 5 ) is formed on at least one surface of the plated layer 400 (see Figure 5 ) is used to form the blank. In this case, the decarburized layer 200 (see Figure 5 ) and inner oxide layer 300 (see Figure 5 ) may be located between the base material 100 and the plating layer 400 .

[0123] In the heating step S610, the blank may be heated in a heating furnace having a plurality of zones with different temperature ranges. Figure 7 As shown, the heating step S610 may include a multi-stage heating step S611 and a soaking heating step S612. The multi-stage heating step S611 and the soaking heating step S612 may be steps of heating the blank while passing through a plurality of zones arranged in the heating furnace.

[0124] In an embodiment, the overall temperature of the heating furnace may be about 680° C. to about 910° C. In detail, the overall temperature of the heating furnace performing the multi-stage heating step S611 and the soaking heating step S612 may be about 680° C. to about 910° C. In this case, the temperature of the heating furnace performing the multi-stage heating step S611 may be about 680° C. to about Ac3, and the temperature of the heating furnace performing the soaking heating step S612 may be about Ac3 to about 910° C.

[0125] In the multi-stage heating step S611, the billet may be heated in stages while passing through a plurality of sections arranged in the heating furnace. Among the plurality of sections arranged in the heating furnace, there may be a plurality of sections for performing the multi-stage heating step S611, and the temperature may be set for each section so as to increase in a direction from an inlet of the heating furnace where the billet is inserted to an outlet of the heating furnace where the billet is taken out, and thus the temperature of the billet may be increased in stages.

[0126] The soaking heating step S612 may be performed after the multi-stage heating step S611. In the soaking heating step S612, the ingot heated in stages is heated (or soaking heated) while passing through a heating furnace set to a temperature interval of about Ac3 to about 910° C. Among the multiple intervals arranged in the heating furnace, there may be at least one interval in which the soaking heating step S612 is performed.

[0127] Figure 8 is a schematic diagram for describing a heating furnace having a plurality of zones in a heating step of a method for manufacturing a hot stamping part according to an embodiment of the present application.

[0128] refer to Figure 8 , the heating furnace according to the embodiment may include a plurality of zones with different temperature ranges. In detail, the heating furnace may include a first zone P1 with a first temperature range T1, a second zone P2 with a second temperature range T2, a third zone P3 with a third temperature range T3, a fourth zone P4 with a fourth temperature range T4, a fifth zone P5 with a fifth temperature range T5, a sixth zone P6 with a sixth temperature range T6, and a seventh zone P7 with a seventh temperature range T7.

[0129] In the embodiment, in the multi-stage heating step S611, the blank is heated in stages while passing through the first section P1 to the fourth section P4 defined in the heating furnace. In addition, in the uniform heating step S612, the blank heated in stages in the first section P1 to the fourth section P4 may be uniformly heated while passing through the fifth section P5 to the seventh section P7.

[0130] The first section P1 to the seventh section P7 may be arranged in sequence in the heating furnace. The first section P1 having the first temperature range T1 may be adjacent to the inlet of the heating furnace for inserting the blank, and the seventh section P7 having the seventh temperature range T7 may be adjacent to the outlet of the heating furnace for taking out the blank. Therefore, the first section P1 having the first temperature range T1 may be the first section of the heating furnace, and the seventh section P7 having the seventh temperature range T7 may be the last section of the heating furnace.

[0131] The temperatures of the multiple sections arranged in the heating furnace (e.g., the temperatures of the first section P1 to the seventh section P7) may be increased in the direction from the inlet of the heating furnace for inserting the blank to the outlet of the heating furnace for taking out the blank. However, the temperatures of the fifth section P5, the sixth section P6, and the seventh section P7 may be the same. In addition, the temperature difference between two adjacent sections of the multiple sections arranged in the heating furnace may be greater than about 0°C and less than or equal to about 100°C. For example, the temperature difference between the first section P1 and the second section P2 may be greater than about 0°C and less than or equal to about 100°C.

[0132] The heating furnace temperature of the soaking heating step S612 may be about Ac3 to about 910°C. When the heating furnace temperature of the soaking heating step S612 is about Ac3 or lower, the manufactured hot stamping part may not have the desired material. On the other hand, when the heating furnace temperature of the soaking heating step S612 is about 910°C or higher, zinc (Zn) contained in the plating layer 400 may evaporate, resulting in the loss of the plating layer 400. Therefore, when the heating furnace temperature of the soaking heating step S612 satisfies about Ac3 to about 910°C, the manufactured hot stamping part can be formed into the desired material, and the loss of the plating layer 400 can be prevented.

[0133] Although the heating furnace according to the embodiment includes Figure 8 The heating furnace may include seven zones with different temperature ranges, but the present application is not limited thereto. The heating furnace may include five, six or eight zones with different temperature ranges.

[0134] In the embodiment, since the heating step S610 includes the multi-stage heating step S611 and the soaking heating step S612, the temperature of the heating furnace can be set in stages, and thus the energy efficiency of the heating furnace can be improved.

[0135] In an embodiment, the heating furnace may have a length of about 20m to about 40m along the transport path of the blank. The heating furnace may include a plurality of intervals with different temperature ranges, and the ratio between the length of the interval for heating the blank in stages and the length of the interval for uniform heating of the blank in the plurality of intervals may satisfy about 1:1 to about 4:1. When the length of the interval for uniform heating of the blank in the heating furnace increases and the ratio between the length of the interval for heating the blank in stages and the length of the interval for uniform heating of the blank is greater than about 1:1, the amount of hydrogen that penetrates into the blank in the uniform heating interval may increase, thereby increasing delayed fracture. On the other hand, when the length of the interval for uniform heating of the blank decreases and the ratio between the length of the interval for heating the blank in stages and the length of the interval for uniform heating of the blank is less than about 4:1, the uniform heating interval (or time) cannot be fully ensured, so the strength of the hot stamping part manufactured by the method for manufacturing a hot stamping part may be uneven. For example, the length of the uniform heating interval in the plurality of intervals arranged in the heating furnace may be about 20% to about 50% of the total length of the heating furnace.

[0136] In an embodiment, the total heating time for performing the heating step S610 can be from about 2 min to about 20 min. That is, the total time that the blank is kept in the heating furnace can be from about 2 min to about 20 min. When the total heating time for performing the heating step S610 is about 2 min or less, the heating time may be insufficient, and therefore, the manufactured hot stamping component 1 may not have the desired material. On the other hand, when the total heating time for performing the heating step S610 is about 20 min or longer, the heating time may be too long, so the production speed may be reduced, and the economic feasibility may be reduced. Therefore, when the total heating time for performing the heating step S610 satisfies about 2 min to about 20 min, the manufactured hot stamping component 1 can have the desired material, and at the same time, the reduction in the economic feasibility of the manufacturing process can be prevented or minimized.

[0137] After the heating step S610 , a transfer step S620 , a molding step S630 , and a cooling step S640 may be performed.

[0138] In an embodiment, the transfer step S620 may be a step of transferring the heated blank from the heating furnace to the mold. In this case, in the transfer step S620, the heated blank may be cooled to atmospheric temperature (or room temperature). That is, during the transfer, the heated blank may be air cooled. When the heated blank is not air cooled, the mold entry temperature (e.g., the forming start temperature) may increase, and therefore, wrinkles (or bends) may appear on the surface of the manufactured hot stamping part 1. In addition, since the use of a refrigerant may affect post-processing (hot stamping), it may be preferred to air cool the heated blank during the transfer.

[0139] In an embodiment, the forming step S630 may be a step of hot stamping the transferred blank to form a formed body. In detail, in the forming step S630, the blank may be pressed using a mold to form a formed body.

[0140] In an embodiment, the forming start temperature may be from about 500°C to about 700°C. When the forming start temperature is lower than about 500°C, the forming start temperature may be too low, and therefore, the formability of the blank may be reduced, and the manufactured hot stamping part 1 may not have the desired structure and properties. On the other hand, when the forming start temperature is higher than about 700°C, wrinkles (or bends) may appear on the surface of the manufactured hot stamping part 1. In addition, the coating 400 may adhere to the mold. Therefore, when the forming start temperature is from about 500°C to about 700°C, the formability of the blank can be improved, the manufactured hot stamping part 1 can have the desired structure and properties, and wrinkles (or bends) on the surface of the manufactured hot stamping part 1 can be prevented or minimized.

[0141] In an embodiment, the cooling step S640 may be a step of cooling the formed body. The cooling step S640 may be performed in a mold for pressing the blank.

[0142] In detail, the final product can be formed by cooling the molded body while forming the molded body into the final part shape. A cooling channel through which a refrigerant circulates can be arranged in the mold. The molded body can be quickly cooled by the circulation of the refrigerant provided by the cooling channel arranged in the mold. In this case, in order to prevent the springback phenomenon of the plate material and maintain the desired shape, the blank can be pressed and quickly cooled when the mold is closed. When the molded body is formed and cooled, the molded body can be cooled to the martensite finish temperature at an average cooling rate of at least about 10°C / s.

[0143] In an embodiment, the cooling end temperature at which the cooling step S640 ends may be from about room temperature to about 200°C. When the cooling end temperature is lower than room temperature, the productivity of the manufacturing process may decrease. On the other hand, when the cooling end temperature is higher than about 200°C, the manufactured hot stamping part 1 is air-cooled at room temperature, and in this case, the hot stamping part 1 may be deformed, and it may be difficult to ensure the target material. Therefore, when the cooling end temperature at which the cooling step S640 ends satisfies room temperature to about 200°C, the productivity of the manufacturing process can be improved, and the deformation of the manufactured hot stamping part 1 can be prevented or minimized.

[0144] Therefore, the inventors of the present application derived equations 3 and 4 through a large number of repeated experiments so that the manufactured hot stamping part 1 has a VDA bending angle of about 60° or more. In the embodiment, the manufactured hot stamping part 1 can satisfy equations 3 and 4. In detail, the hardness within a depth of about 50 μm from the surface of the hot stamping part 1 in the plate thickness direction of the hot stamping part 1 and the average hardness of the hot stamping part 1 can satisfy equation 3, and the depth (or thickness) of the inner oxide layer 300 can satisfy equation 4. For example, the hot stamping part 1 can satisfy equations 3 and 4 at the same time.

[0145] <Relation 3>

[0146] (A / B)≤0.7

[0147] In Relational Expression 3, A represents the hardness within a depth (or thickness) of about 50 μm in the plate thickness direction of the hot stamped part 1 (Hv (≤50 μm)), and B represents the average hardness (Hv (average)) of the hot stamped part 1 .

[0148] In this case, the hardness within a depth of about 50 μm from the surface of the hot stamping part 1 in the plate thickness direction of the hot stamping part 1 may be a hardness value measured at a depth of about 50 μm or less from the surface of the hot stamping part 1 in the plate thickness direction of the hot stamping part 1 using a Vickers hardness tester, and the average hardness (Hv(average)) of the hot stamping part 1 may be a hardness value measured at about a 1 / 4 point in the plate thickness direction of the hot stamping part 1 using a Vickers hardness tester.

[0149] <Equation 4>

[0150] C≤5μm

[0151] In Relational Expression 4, C represents the depth (or thickness) of the inner oxide layer 300 in the sheet thickness direction of the hot stamped part 1 .

[0152] In the embodiment, when the manufactured hot stamping part 1 satisfies both Relationship 3 and Relationship 4, the toughness of the hot stamping part 1 manufactured by the method for manufacturing a hot stamping part can be improved. For example, the hot stamping part 1 manufactured by the method for manufacturing a hot stamping part can have a VDA bending angle of about 60° or more. In addition, the hot stamping part 1 manufactured by the method for manufacturing a hot stamping part can have a tensile strength (TS) of about 1680 MPa to about 2000 MPa, a yield strength (YP) of about 1150 MPa to about 1500 MPa, and an elongation (EL) of about 4% to about 10%.

[0153] <Experimental Example>

[0154] Hereinafter, the application will be described by experimental examples. However, the following experimental examples are intended to explain the application in more detail, and the scope of the application is not limited by the following experimental examples. Those skilled in the art can appropriately modify and change the following experimental examples within the scope of the application.

[0155]

Table 1

[0156]

[0157]

[0158]

Table 2

[0159]

[0160] Example 1, Example 2, Comparative Example 1 and Comparative Example 2 are hot stamped parts (samples) manufactured under the process conditions shown in Table 2 using slabs having the composition shown in Table 1.

[0161]

Table 3

[0162]

[0163] In Table 3, A represents the hardness within a depth (or thickness) of about 50 μm in the plate thickness direction of the hot stamping part (Hv (≤50 μm)), B represents the average hardness (Hv (average)) of the hot stamping part, and C represents the depth (or thickness) of the inner oxide layer 300 in the plate thickness direction of the hot stamping part. In this case, the hardness within a depth of about 50 μm from the surface of the hot stamping part 1 in the plate thickness direction of the hot stamping part 1 may be a hardness value measured at a depth of about 50 μm or less from the surface of the hot stamping part 1 in the plate thickness direction of the hot stamping part 1 using a Vickers hardness tester, and the average hardness (Hv (average)) of the hot stamping part 1 may be a hardness value measured at a point about 1 / 4 in the plate thickness direction of the hot stamping part 1 using a Vickers hardness tester.

[0164] In Table 3, the VDA bending angle was evaluated using the VDA standard (VDA238-100), and the crack depth was measured by using a scanning electron microscope. In this case, the crack depth corresponds to the deepest crack depth measured by the scanning electron microscope.

[0165] The VDA bending angle of the hot stamping part required by the present application is about 60° or more. In addition, when the crack depth in the hot stamping part is large, the VDA bending angle of the hot stamping part may decrease, and the toughness of the hot stamping part may decrease. Therefore, the crack depth of the hot stamping part required by the present invention is about 10 μm or less. When the crack depth is outside the range, it corresponds to a case where the required conditions are not met.

[0166] Examples 1 and 2 correspond to the case where both Relational Formula 1 ((A / B) ≤ 0.7) and Relational Formula 2 (C ≤ 5) are satisfied, Comparative Example 1 corresponds to the case where Relational Formula 2 (C ≤ 5) is not satisfied, and Comparative Example 2 corresponds to the case where Relational Formula 1 ((A / B) ≤ 0.7) is not satisfied. Example 1, Example 2, Comparative Example 1, and Comparative Example 2 correspond to the case where Relational Formula 1 ((A / B) ≤ 0.7) is not satisfied according to the method for manufacturing a hot stamping part. Figure 1 However, due to the difference in process control conditions, Comparative Example 1 and Comparative Example 2 are samples that do not satisfy Relationship 1 ((A / B)≤0.7) and / or Relationship 2 (C≤5).

[0167] When both Relationship 1 ((A / B) ≤ 0.7) and Relationship 2 (C ≤ 5) are satisfied, it can be found that the VDA bending angle and the crack depth meet the required conditions. In detail, when both Relationship 1 ((A / B) ≤ 0.7) and Relationship 2 (C ≤ 5) are satisfied, it can be found that the VDA bending angle is 60° or more, and the crack depth is 10 μm or less.

[0168] However, when relational expression 2 (C≤5) is not satisfied, it can be found that the VDA bending angle and the crack depth do not satisfy the required conditions. In detail, when relational expression 2 (C≤5) is not satisfied, it can be found that the VDA bending angle is less than 60° and the crack depth is greater than 10 μm.

[0169] Furthermore, when the relational expression 1 ((A / B) ≤ 0.7) is not satisfied, it can be found that the VDA bending angle does not satisfy the required conditions. In detail, when the relational expression 1 ((A / B) ≤ 0.7) is not satisfied, it can be found that the VDA bending angle is less than 60°.

[0170] Therefore, when the hot stamping part 1 satisfies both the relational expression 1 ((A / B)≤0.7) and the relational expression 2 (C≤5), the hot stamping part 1 can have a desired VDA bending angle, and the crack depth of the hot stamping part 1 can be formed to be less than a preset value. That is, when the hot stamping part 1 satisfies both the relational expression 1 ((A / B)≤0.7) and the relational expression 2 (C≤5), the hot stamping part 1 can have excellent toughness and high temperature formability.

[0171] Although the present application has been specifically shown and described with reference to the embodiments, the embodiments are provided for the purpose of illustration, and it will be appreciated by those skilled in the art that various modifications and other equivalent embodiments may be made from the present application. Therefore, the true technical scope of the present application is limited by the technical spirit of the appended claims.

Claims

1. A hot stamping component, comprising: Base material; a decarburized layer, the decarburized layer being located on the base material; as well as an inner oxide layer, the inner oxide layer being located on the decarburized layer, wherein the hot stamping part has a tensile strength (TS) of 1680 MPa to 2000 MPa, and The hardness of the hot stamping part within a depth of 50 μm from the surface of the hot stamping part in the plate thickness direction of the hot stamping part and the average hardness of the hot stamping part satisfy the relationship 1, <Relation 1> (A / B)≤0.7 (In Relational Formula 1, A represents the hardness within a depth of 50 μm in the plate thickness direction of the hot stamped part (Hv(≤50 μm)), and B represents the average hardness of the hot stamped part (Hv(average))).

2. The hot stamped component according to claim 1, wherein: The depth of the inner oxide layer satisfies the relation 2, <Relation 2> C≤5μm (In Relationship 2, C represents the depth of the inner oxide layer in the sheet thickness direction of the hot stamped part).

3. The hot stamped component according to claim 1, wherein: The hot stamped part has a VDA bending angle of 60° or more.

4. The hot stamped component according to claim 1, wherein: The hot stamped part has a yield strength (YP) of 1150 MPa to 1500 MPa and an elongation (EL) of 4% to 10%.

5. The hot stamped component according to claim 1, wherein: The hot stamped part has a microstructure having a martensite fraction of 90% or more. 6 . The hot stamping component according to claim 1 , further comprising a plating layer, wherein the plating layer is located on the inner oxide layer.

7. The hot stamped component according to claim 6, wherein: The thickness of the coating is 10 μm to 30 μm.

8. A method of manufacturing a hot stamping component, the method comprising: forming a blank by cutting a plated steel sheet having a plated layer formed on at least one surface of a base material; and heating the blank in a heating furnace having a plurality of zones with different temperature ranges, Among them, the heating of the blank includes: A multi-stage heating step of heating the blank in stages; and A soaking heating step of heating the stepwise heated blank to a temperature of Ac3 to 910° C., The hardness of the hot stamping part within a depth of 50 μm from the surface of the hot stamping part in the plate thickness direction of the hot stamping part and the average hardness of the hot stamping part satisfy the relational expression 3. <Relation 3> (A / B)≤0.7 (In Relational Expression 3, A represents the hardness within a depth of 50 μm in the plate thickness direction of the hot stamped part (Hv(≤50 μm)), and B represents the average hardness of the hot stamped part (Hv(average))).

9. The method for manufacturing a hot stamped component according to claim 8, wherein: The dew point of the annealing furnace for the base material is -15°C to +15°C.

10. The method for manufacturing a hot stamped component according to claim 8, wherein: The annealing temperature of the base material is 750°C to 900°C.

11. The method for manufacturing a hot stamping component according to claim 8, further comprising: After heating the blank, transferring the heated blank; forming a formed body by pressing the transferred blank using a die; as well as The formed shaped body is cooled.

12. The method for manufacturing a hot stamped component according to claim 11, wherein: The hot stamping component also includes: a decarburized layer formed on the base material; and An inner oxide layer is formed on the decarburized layer.

13. The method for manufacturing a hot stamped component according to claim 12, wherein: The depth of the inner oxide layer satisfies the relation 4, <Equation 4> C≤5μm (In Relationship 4, C represents the depth of the inner oxide layer in the sheet thickness direction of the hot stamped part).

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