Hot stamping components

Abstract

The present application relates to a hot stamping part and manufacturing method therefor According to the hot press part and manufacturing method therefor of the present application, a hot press part with suppressed hydrogen embrittlement and ultra-high strength can be obtained.

Description

Hot stamping parts

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

[0002] In the automotive industry, environmental and fuel efficiency regulations, as well as safety standards, are being strengthened. Consequently, the application of ultra-high-strength steel and hot-stamped steel is steadily increasing. In particular, research and development is being conducted on hot-stamped steel, including existing 1.5G hot-stamped steel, to enhance toughness and strength.

[0003] The hot stamping process is a technology that applies ultra-high strength by utilizing the microstructure based on the phase transformation of the material during the process, and is generally composed of a heating step, a forming step, a cooling step, and a trim step.

[0004] Unlike conventional cold press forming, the hot stamping process is mostly carried out at high temperatures of over 900℃. Therefore, to ensure the high-temperature stability of body components and to treat their surfaces, plated steel sheets coated with aluminum (Al) alloys are generally used. Among Al alloys, Al-Si, Al-Cu, and Al-Zn alloys have excellent mechanical properties such as fluidity, shrinkage upon solidification, and corrosion resistance. These are widely used as structural castings and coating materials for aircraft and automobiles, and are also widely used as materials for hot stamping.

[0005] Meanwhile, when high-temperature heat treatment is performed in the heating step using a furnace during the hot stamping process, a reaction occurs in which moisture in the air decomposes and forms hydrogen. At this time, as in Patent Document 1 (Korean Patent Publication No. 2012-0134709), a plated steel sheet coated with aluminum-silicon (Al-Si) on hot stamping steel transforms into a liquid state due to its low melting point during high-temperature heat treatment, causing a large amount of hydrogen to flow in from the surface. Afterwards, when it cools through the cooling step, the plated layer transforms into an Al-Fe intermetallic compound layer, trapping the hydrogen that has flowed in the material. At this time, the hydrogen that has flowed in gathers in one place over time, causing hydrogen embrittlement. Therefore, to solve this problem, a hot stamping part that suppresses hydrogen embrittlement and has ultra-high strength is required.

[0006] The object of the present application is to provide a hot stamping part with suppressed hydrogen embrittlement and ultra-high strength, and a method for manufacturing the same.

[0007] To solve the above problem, the hot stamping part of the present application comprises a steel plate; and a plating layer formed on at least one surface of the steel plate, satisfying the following general formula 1, and including zinc.

[0008] [General Formula 1]

[0009]

[0010] (In the above general formula 1, when the plating layer is composed of n layers with distinct structures, L k is the average thickness (㎛) measured along the short axis direction at 10 random locations in the kth layer of the plating layer observed by SEM image, and D k is the value derived through the electrochemical hydrogen permeation experiment method below (m 2 / s), t is the total heating time (sec) during hot stamping molding, and n is an integer greater than or equal to 2.

[0011] Electrochemical hydrogen permeation experiment method

[0012] - A sample formed as the kth layer is placed in the center of two cells, and hydrogen is electrically formed in one cell so that the hydrogen can permeate to the other cell.

[0013] - Measure the time it takes for hydrogen to permeate to the other cell.

[0014] - The value calculated using the general formula 2 below using the measured time and the thickness of the specimen is D k It is said.

[0015] [General Formula 2]

[0016]

[0017] (In the above general formula 2, L sample is the thickness of the specimen (m), and t sample is the time (sec) that the light penetrated the sample.

[0018] In addition, the plating layer can satisfy the following general formula 3.

[0019] [General Formula 3]

[0020]

[0021] (In the above general formula 3, when the plating layer is composed of n layers with distinct structures, L k is the average thickness (㎛) measured along the short axis direction at 10 random locations in the kth layer of the plating layer observed by SEM image, and D k is the value derived through the electrochemical hydrogen permeation experiment method below (m 2 / s), t is the total heating time (sec) during hot stamping molding, and n is an integer greater than or equal to 2.

[0022] Electrochemical hydrogen permeation experiment method

[0023] - A sample formed as the kth layer is placed in the center of two cells, and hydrogen is electrically formed in one cell so that the hydrogen can permeate to the other cell.

[0024] - Measure the time it takes for hydrogen to permeate to the other cell.

[0025] - The value calculated using the general formula 2 below using the measured time and the thickness of the specimen is D k It is said.

[0026] [General Formula 2]

[0027]

[0028] (In the above general formula 2, L sample is the thickness of the specimen (m), and t sample is the time (sec) that the light penetrated the sample.

[0029] In addition, the plating layer can satisfy the following general formula 4.

[0030] [General Formula 4]

[0031]

[0032] (In the above general formula 4, when the plating layer is composed of n layers with distinct structures, L k is the average thickness (㎛) measured along the short axis direction at 10 random locations in the kth layer of the plating layer observed by SEM image, and D k is the value derived through the electrochemical hydrogen permeation experiment method below (m 2 / s), t is the total heating time (sec) during hot stamping molding, and n is an integer greater than or equal to 2.

[0033] Electrochemical hydrogen permeation experiment method

[0034] - A sample formed as the kth layer is placed in the center of two cells, and hydrogen is electrically formed in one cell so that the hydrogen can permeate to the other cell.

[0035] - Measure the time it takes for hydrogen to permeate to the other cell.

[0036] - The value calculated using the general formula 2 below using the measured time and the thickness of the specimen is D k It is said.

[0037] [General Formula 2]

[0038]

[0039] (In the above general formula 2, L sample is the thickness of the specimen (m), and t sample is the time (sec) that the light penetrated the sample.

[0040] In addition, the hot stamping part may be a part manufactured by hot stamping a plated steel sheet having a plated layer including zinc formed on at least one surface of the steel sheet.

[0041] In addition, the hot stamping forming may include a heating step of preparing a plated steel sheet having a plated layer including zinc formed on at least one surface of the steel sheet; a forming step of forming a molded body by stamping the heated plated steel sheet with a press mold; and a cooling step of cooling the molded body.

[0042] In addition, when heating the plated steel sheet prepared in the above heating step, the plated steel sheet can be heated at an average heating rate of 3 ℃ / s to 8 ℃ / s in a temperature range of 600 ℃ to 700 ℃.

[0043] In addition, when heating the plated steel sheet prepared in the heating step, the plated steel sheet can be heated at an average heating rate of 0.5 ℃ / s to 3 ℃ / s in a temperature range of 800 ℃ to X ℃. At this time, X ℃ is the highest temperature at which the plated steel sheet is heated in the heating step - 10 ℃.

[0044] Additionally, the total heating time during the hot stamping forming may be 150 to 450 seconds.

[0045] Additionally, the plating layer may have a thickness of 10 ㎛ to 30 ㎛.

[0046] In addition, the method for manufacturing a hot stamping part of the present application relates to a method for manufacturing a hot stamping part including a steel plate, and a plating layer formed on at least one surface of the steel plate, satisfying the following general formula 1, and containing zinc, the method comprising: preparing a plated steel plate having a plating layer containing zinc formed on at least one surface of the steel plate; heating the prepared plated steel plate; forming a molded body by stamping the heated plated steel plate with a press mold; and cooling the molded body.

[0047] [General Formula 1]

[0048]

[0049] (In the above general formula 1, when the plating layer is composed of n layers with distinct structures, L k is the average thickness (㎛) measured along the short axis direction at 10 random locations in the kth layer of the plating layer observed by SEM image, and D k is the value derived through the electrochemical hydrogen permeation experiment method below (m 2 / s), t is the total heating time (sec) during hot stamping molding, and n is an integer greater than or equal to 2.

[0050] Electrochemical hydrogen permeation experiment method

[0051] - A sample formed as the kth layer is placed in the center of two cells, and hydrogen is electrically formed in one cell so that the hydrogen can permeate to the other cell.

[0052] - Measure the time it takes for hydrogen to permeate to the other cell.

[0053] - The value calculated using the general formula 2 below using the measured time and the thickness of the specimen is D k It is said.

[0054] [General Formula 2]

[0055]

[0056] (In the above general formula 2, Lsample is the thickness of the specimen (m), and t sample is the time (sec) that the light penetrated the sample.

[0057] In addition, when heating the plated steel sheet prepared in the above heating step, the plated steel sheet can be heated at an average heating rate of 3 ℃ / s to 8 ℃ / s in a temperature range of 600 ℃ to 700 ℃.

[0058] In addition, when heating the plated steel sheet prepared in the heating step, the plated steel sheet can be heated at an average heating rate of 0.5 ℃ / s to 3 ℃ / s in a temperature range of 800 ℃ to X ℃. At this time, X ℃ is the highest temperature at which the plated steel sheet is heated in the heating step - 10 ℃.

[0059] Additionally, the plating layer formed on the plated steel sheet prepared in the heating step may include a zeta layer, a delta layer, and a gamma layer.

[0060] According to the hot press part of the present application and the manufacturing method thereof, a hot press part with suppressed hydrogen embrittlement and ultra-high strength can be obtained.

[0061] FIG. 1 is a drawing illustrating an example of a hot stamping part according to one embodiment of the present application.

[0062] Figure 2 is an image taken with a scanning electron microscope at the highest heating temperature of a hot stamping part manufactured in Example 2.

[0063] Figures 3 to 5 are images taken by a camera of the fracture test evaluation results of hot stamping parts manufactured in Example 2, Comparative Example 1, and Comparative Example 2, respectively.

[0064] Hereinafter, the hot stamping part of the present application will be described with reference to the attached drawings. The attached drawings are exemplary, and the hot stamping part of the present application is not limited to the attached drawings.

[0065] FIG. 1 is a drawing exemplifying a hot stamping part according to one embodiment of the present application. As shown in FIG. 1, the hot stamping part (10) of the present application includes a steel plate (11) and a plating layer (12). According to the hot stamping part (10) of the present application, hydrogen embrittlement is suppressed and ultra-high strength can be achieved.

[0066] The above steel plate (11) refers to a plate made of steel used for an automobile body. For example, the steel plate (11) may contain carbon (C), silicon (Si), manganese (Mn), phosphorus (P), sulfur (S), boron (B), a remainder of iron (Fe), and other unavoidable impurities. Specifically, the steel plate (11) may contain carbon (C) 0.1 wt% to 0.5 wt%, silicon (Si) 0.1 wt% to 0.8 wt%, manganese (Mn) 0.3 wt% to 3.0 wt%, phosphorus (P) more than 0 wt% to 0.05 wt%, sulfur (S) more than 0 wt% to 0.03 wt%, boron (B) 0.0005 wt% to 0.005 wt%, a remainder of iron (Fe), and other unavoidable impurities.

[0067] In addition, the steel plate (11) may further include one or more selected from titanium (Ti) and / or niobium (Nb), chromium (Cr), molybdenum (Mo), and nickel (Ni). Specifically, the steel plate (11) may further include 0.01 wt% to 0.1 wt% of titanium (Ti) and / or niobium (Nb), 0.01 wt% to 1.0 wt% of chromium (Cr), 0.01 wt% to 1.0 wt% of molybdenum (Mo), and 0.001 wt% to 1.0 wt% of nickel (Ni).

[0068] The above carbon (C) is a major element that determines the strength and hardness of steel, and can be added for the purpose of securing the tensile strength of steel after hot stamping or hot pressing process. In addition, carbon (C) can be added for the purpose of securing the hardenability characteristics of steel. If the carbon (C) is included in the steel plate (11) in an amount less than the aforementioned content, it may be difficult to achieve the desired mechanical strength. On the other hand, if the carbon (C) is included in the steel plate (11) in an amount exceeding the aforementioned content, a problem of deterioration in the toughness of the steel plate or a problem of controlling brittleness may occur.

[0069] The above silicon (Si) can act as a ferrite stabilizing element in the steel plate (11). The silicon (Si) can improve ductility by purifying ferrite, and can improve the carbon concentration in austenite by suppressing the formation of low-temperature carbides. Furthermore, silicon (Si) can be a key element for hot-rolled, cold-rolled, and hot-stamping tissue homogenization (control of pearlite and manganese segregation zones) and ferrite microdispersion. When the silicon (Si) is included in the steel plate (11) in an amount less than the aforementioned content, the above-mentioned function may not be sufficiently exhibited. On the other hand, when the silicon (Si) is included in the steel plate (11) in an amount exceeding the aforementioned content, hot-rolled and cold-rolled loads may increase, hot-rolled red scale may become excessive, and bondability may deteriorate.

[0070] The manganese (Mn) may be added during heat treatment for the purpose of increasing hardenability and strength. If the manganese (Mn) is contained in the steel plate (11) in an amount less than the aforementioned content, the material after hot stamping may be less than the desired hardenability, for example, there is a high possibility that the hardness fraction may be less than the desired hardenability. On the other hand, if the manganese (Mn) is contained in the steel plate (11) in an amount exceeding the aforementioned content, ductility and toughness may be reduced due to manganese segregation or pearlite bands, which may cause a decrease in bending performance and may result in the occurrence of a heterogeneous microstructure.

[0071] The above phosphorus (P) is an element that is easily segregated and may be an element that lowers the toughness of steel. When the above phosphorus (P) is included in the above steel plate (11) in the above content, the deterioration of the toughness of steel can be prevented. On the other hand, when the above phosphorus (P) is included in the above steel plate (11) in an amount exceeding the above content, cracks may occur during the process and iron phosphide compounds may be formed, which may lower the toughness of steel.

[0072] The above sulfur (S) may be an element that impairs processability and physical properties. If the above sulfur (S) is included in the steel plate (11) in an amount exceeding the aforementioned content, hot processability may be reduced, and surface defects such as cracks may occur due to the formation of large inclusions.

[0073] The above boron (B) is added for the purpose of securing the hardenability and strength of the steel by securing a martensite structure, and can have the effect of refining the crystal grains by increasing the austenite crystal grain growth temperature. When the above boron (B) is included in the above steel plate (11) in the above-mentioned content, the occurrence of hard phase grain boundary embrittlement can be prevented, and high toughness and bendability can be secured.

[0074] The above titanium (Ti) can be added for the purpose of strengthening hardenability and improving material quality by forming precipitates after hot stamping heat treatment. In addition, the titanium (Ti) can effectively contribute to the refinement of austenite grains by forming precipitate phases such as Ti (C, N) at high temperatures.

[0075] The above niobium (Nb) can be added for the purpose of increasing strength and toughness by reducing the martensite packet size.

[0076] The above chromium (Cr) can be added for the purpose of improving the hardenability and strength of the steel. When the above chromium (Cr) is included in the above steel plate (11) in the above-mentioned amount, the hardenability and strength of the steel can be improved, an increase in production costs can be prevented, and the toughness of the steel can be prevented from being reduced.

[0077] The above molybdenum (Mo) can contribute to the improvement of strength by suppressing the coarsening of precipitates during hot rolling and hot stamping and by increasing the hardenability. By including the above molybdenum (Mo) in the above-mentioned content in the steel plate (11), the effect of suppressing the coarsening of precipitates during hot rolling and hot stamping and increasing the hardenability can be excellent.

[0078] The nickel (Ni) may be added for the purpose of securing hardenability and strength. In addition, the nickel (Ni) is an austenite stabilizing element and can contribute to improving elongation by controlling austenite transformation. If the nickel (Ni) is included in the steel plate (11) in an amount less than the aforementioned content, it may be difficult to properly implement the aforementioned effects. In addition, if the nickel (Ni) is included in the steel plate (11) in an amount exceeding the aforementioned content, toughness may be lowered, cold workability may be lowered, and the manufacturing cost of the product may increase.

[0079] In one example, the steel plate (11) may have a microstructure including a martensite fraction of 90% or more. Specifically, the steel plate (11) may have a microstructure including 90% or more of martensite, the remainder being other unavoidable structures and other precipitates, and less than 10%. Preferably, the steel plate (11) may be full martensite. By having the aforementioned microstructure, the steel plate (11) may be capable of securing ultra-high strength.

[0080] In addition, the steel plate (11) may have a tensile strength (TS) of 1,350 MPa or more, for example, 1,680 MPa to 2,300 MPa, a yield stress (YP) of 900 MPa to 1,300 MPa, for example, 1,150 MPa to 1,300 MPa, and an elongation (EL) of 4% to 15%.

[0081] The above-mentioned plating layer (12) is a layer plated on the surface of the steel plate (11), is formed on at least one surface of the steel plate (11), satisfies the following general formula 1, and includes zinc. In this specification, the term "surface" means an outer surface located on one side, both sides, or all sides of the steel plate. For example, one surface of the steel plate (11) may be the upper surface of the steel plate (11).

[0082] [General Formula 1]

[0083]

[0084] (In the above general formula 1, when the plating layer is composed of n layers with distinct structures, L k is the average thickness (㎛) measured along the short axis direction at 10 random locations in the kth layer of the plating layer observed by SEM image, and D k is the value derived through the electrochemical hydrogen permeation experiment method below (m 2 / s), t is the total heating time (sec) during hot stamping molding, and n is an integer greater than or equal to 2.

[0085] Electrochemical hydrogen permeation experiment method

[0086] - A sample formed as the kth layer is placed in the center of two cells, and hydrogen is electrically formed in one cell so that the hydrogen can permeate to the other cell.

[0087] - Measure the time it takes for hydrogen to permeate to the other cell.

[0088] - The value calculated using the general formula 2 below using the measured time and the thickness of the specimen is D kIt is said.

[0089] [General Formula 2]

[0090]

[0091] (In the above general formula 2, L sample is the thickness of the specimen (m), and t sample is the time (sec) that the light penetrated the sample.

[0092] The plating layer (12) above can suppress the amount of diffusible hydrogen to less than 0.5 ppm by satisfying the general formula 1 above, thereby suppressing hydrogen embrittlement of the hot stamping part and enabling it to have ultra-high strength. In contrast, if the plating layer (12) does not satisfy the general formula 1 above, the amount of hydrogen flowing into the steel plate of the hot stamping part, i.e., the amount of diffusible hydrogen, may increase, thereby increasing hydrogen embrittlement.

[0093] In this specification, the term "k-th layer in the plating layer" means the k-th layer in the thickness direction from the surface of the plating layer toward the steel sheet. For example, when n = 3, the k-th layer in the plating layer may be the 1st layer, the 2nd layer, and the 3rd layer. In addition, the term "short-axis direction" in this specification means the stacking direction in which the steel sheet and the plating layer are stacked based on the hot stamping part.

[0094] In another example, the plating layer (12) can satisfy the following general formula 3.

[0095] [General Formula 3]

[0096]

[0097] (In the above general formula 3, when the plating layer is composed of n layers with distinct structures, L k is the average thickness (㎛) measured along the short axis direction at 10 random locations in the kth layer of the plating layer observed by SEM image, and D k is the value derived through the electrochemical hydrogen permeation experiment method below (m 2 / s), t is the total heating time (sec) during hot stamping molding, and n is an integer greater than or equal to 2.

[0098] Electrochemical hydrogen permeation experiment method

[0099] - A sample formed as the kth layer is placed in the center of two cells, and hydrogen is electrically formed in one cell so that the hydrogen can permeate to the other cell.

[0100] - Measure the time it takes for hydrogen to permeate to the other cell.

[0101] - The value calculated using the general formula 2 below using the measured time and the thickness of the specimen is D k It is said.

[0102] [General Formula 2]

[0103]

[0104] (In the above general formula 2, L sample is the thickness of the specimen (m), and t sample is the time (sec) that the light penetrated the sample.

[0105] The plating layer (12) above can suppress the amount of diffusible hydrogen to less than 0.1 ppm by satisfying the general formula 3, thereby further suppressing hydrogen embrittlement of the hot stamping part and enabling it to have ultra-high strength. On the other hand, if the plating layer (12) exceeds the upper limit of the general formula 3, the amount of hydrogen flowing into the steel plate of the hot stamping part increases, which can increase hydrogen embrittlement.

[0106] In another example, the plating layer (12) can satisfy the following general formula 4.

[0107] [General Formula 4]

[0108]

[0109] (In the above general formula 4, when the plating layer is composed of n layers with distinct structures, L kis the average thickness (㎛) measured along the short axis direction at 10 random locations in the kth layer of the plating layer observed by SEM image, and D k is the value derived through the electrochemical hydrogen permeation experiment method below (m 2 / s), t is the total heating time (sec) during hot stamping molding, and n is an integer greater than or equal to 2.

[0110] Electrochemical hydrogen permeation experiment method

[0111] - A sample formed as the kth layer is placed in the center of two cells, and hydrogen is electrically formed in one cell so that the hydrogen can permeate to the other cell.

[0112] - Measure the time it takes for hydrogen to permeate to the other cell.

[0113] - The value calculated using the general formula 2 below using the measured time and the thickness of the specimen is D k It is said.

[0114] [General Formula 2]

[0115]

[0116] (In the above general formula 2, L sample is the thickness of the specimen (m), and t sample is the time (sec) that the light penetrated the sample.

[0117] The plating layer (12) satisfies the general formula 4, thereby further suppressing hydrogen embrittlement of the hot stamping part and enabling ultra-high strength. On the other hand, if the plating layer (12) exceeds the upper limit of the general formula 4, the amount of hydrogen flowing into the steel plate of the hot stamping part may increase, thereby increasing hydrogen embrittlement. In addition, if the plating layer (12) is less than the lower limit of the general formula 4, the total heating time may become extremely short or the thickness of the plating layer (12) may become extremely thin, making it impossible to secure the target material or reducing corrosion resistance.

[0118] As described above, the plating layer (12) may be a zinc-based plating layer containing zinc. For example, the galvanized steel sheet on which the zinc-based plating layer is formed may be at least one of a galvanized iron (GI), an electrogalvanized iron (EGI), and a galvannealed iron (GA). Specifically, the plating layer (12) may include iron (Fe), aluminum (Al), manganese (Mn), a remainder of zinc (Zn), and other unavoidable impurities. More specifically, the plating layer (12) may include 10 wt% to 70 wt% of iron (Fe), 0 wt% to 5 wt% of aluminum (Al), 0 wt% to 1 wt% of manganese (Mn), a remainder of zinc (Zn), and other unavoidable impurities. The above plating layer (12) is formed of a zinc-based plating layer containing the above-described composition, so that the hot stamping part can have ultra-high strength.

[0119] The above-mentioned plating layer (12) may have a thickness of 10 ㎛ to 30 ㎛. By having the above-mentioned thickness, the above-mentioned plating layer (12) can protect the surface of the steel plate (11), and at the same time, can prevent or minimize the deterioration of the toughness of the hot stamping part (10), and can satisfy the above-mentioned general formula 1, general formula 3, or general formula 4, and thereby, the hydrogen embrittlement of the hot stamping part (10) is suppressed, and the hot stamping part (10) can have ultra-high strength. When the thickness of the above-mentioned plating layer (12) is less than the above-mentioned lower limit, the sacrificial method effect unique to zinc may be reduced, and the above-mentioned hot stamping part (10) may not satisfy the above-mentioned general formula 1, general formula 3, or general formula 4. In addition, when the thickness of the plating layer (12) exceeds the upper limit described above, the toughness of the hot stamping part (10) including the plating layer (12) may be reduced.

[0120] In one example, the hot stamping part (10) may be a part manufactured by hot stamping a plated steel sheet (not shown) having a plated layer including zinc formed on at least one surface.

[0121] Specifically, the hot stamping forming may include a heating step, a forming step, and a cooling step.

[0122] The heating step is a step of preparing a plated steel sheet having a plated layer including the zinc formed on at least one surface of the steel sheet (11), and heating the prepared plated steel sheet, which may be performed through a heating furnace having a specific temperature range. For example, the temperature range of the heating furnace may be Ac1 to 950°C, and specifically, Ac3 to 950°C or 860°C to 920°C.

[0123] In one example, when heating the plated steel sheet prepared in the above heating step, the plated steel sheet can be heated at an average heating rate of 3 ℃ / s to 8 ℃ / s in a temperature range of 600 ℃ to 700 ℃. Specifically, the plated steel sheet can be heated at an average heating rate of 4 ℃ / s to 7 ℃ / s or 5 ℃ / s to 6 ℃ / s in the above-described temperature range. By heating the plated steel sheet at the above-described average heating rate in the above-described temperature range, the plated steel sheet can satisfy the above-described general formula 1, general formula 3, or general formula 4, thereby suppressing hydrogen embrittlement and obtaining a hot stamping part having ultra-high strength.

[0124] In another example, when heating the plated steel sheet prepared in the heating step, the plated steel sheet may be heated at an average heating rate of 0.5 ℃ / s to 3 ℃ / s in a temperature range of 800 ℃ to X ℃. At this time, X ℃ is the highest temperature at which the plated steel sheet is heated in the heating step -10 ℃. For example, when the highest temperature at which the plated steel sheet is heated is 860 ℃ to 920 ℃, X ℃ may be 850 ℃ to 910 ℃. The plated steel sheet may satisfy the above-described general formula 1, general formula 3 or general formula 4 by being heated in the above-described temperature range at the above-described average heating rate, thereby suppressing hydrogen embrittlement and obtaining a hot stamping part having ultra-high strength.

[0125] The total heating time during the hot stamping forming, i.e., the total heating time in the heating step, may be 150 seconds to 450 seconds. Specifically, the total heating time during the hot stamping forming may be 165 seconds to 410 seconds, 180 seconds to 370 seconds, 195 seconds to 330 seconds, 210 seconds to 290 seconds, or 225 seconds to 240 seconds. By heating the plated steel sheet for the aforementioned heating time during the hot stamping forming, the above-described general formula 1, general formula 3, or general formula 4 may be satisfied, thereby suppressing hydrogen embrittlement and obtaining a hot stamping part having ultra-high strength.

[0126] The above forming step is a step of forming a formed body from the plated steel sheet heated in the above heating step, and may be performed by stamping with a press mold. For example, in the forming step, the forming start temperature may be 500°C to 700°C. When the forming start temperature in the forming step satisfies the above-mentioned range, the formability of the plated steel sheet may be improved, the manufactured hot stamping part (10) may have the target structure and physical properties, and the occurrence of wrinkles or waviness on the surface of the manufactured hot stamping part (10) may be prevented or minimized. On the other hand, when the forming start temperature in the forming step is below the above-mentioned range, the formability of the plated steel sheet may be reduced, and the manufactured hot stamping part (10) may not have the target structure and physical properties. In addition, when the forming start temperature in the forming step exceeds the above-mentioned range, wrinkles or waviness may occur on the surface of the manufactured hot stamping part (10), and the plating layer (12) may stick to the mold.

[0127] The above cooling step is a step of cooling the molded body formed in the above forming step. The cooling step may be performed in a press mold that pressurizes the plated steel sheet.

[0128] Specifically, the final product can be formed by simultaneously forming the final part shape in the press mold and cooling the molded body. The mold may be provided with a cooling channel through which a coolant circulates inside. The molded body can be rapidly cooled by the circulation of the coolant supplied through the cooling channel provided in the mold. At this time, in order to prevent the spring back phenomenon of the plate material and to maintain the desired shape, the rapid cooling can be performed while applying pressure in a closed state. When forming and cooling the molded body, the average cooling rate can be maintained at 10°C or higher until the martensitic transformation completion temperature (Mf). When the cooling completion temperature in the cooling step satisfies the above-mentioned range, the productivity of the manufacturing process can be improved, and distortion of the manufactured hot stamping part (10) can be prevented or minimized. On the other hand, the cooling completion temperature at which the cooling step is completed can be 25°C to 200°C. If the cooling end temperature in the cooling step falls below the aforementioned range, the productivity of the manufacturing process may deteriorate. Furthermore, if the cooling end temperature in the cooling step exceeds the aforementioned range, distortion may occur in the hot stamping part (10), and securing the target material may be difficult.

[0129] The present application also relates to a method for manufacturing a hot stamped part. The method for manufacturing the hot stamped part relates to a method for manufacturing the hot stamped part described above. Since the specific details of the hot stamped part described below are equally applicable to the hot stamped part described above, they will be omitted.

[0130] The method for manufacturing a hot stamping part of the present application relates to a method for manufacturing a hot stamping part including a steel plate and a plating layer formed on at least one surface of the steel plate, satisfying the following general formula 1, and containing zinc, and includes a heating step, a forming step, and a cooling step.

[0131] [General Formula 1]

[0132]

[0133] (In the above general formula 1, when the plating layer is composed of n layers with distinct structures, L k is the average thickness (㎛) measured along the short axis direction at 10 random locations in the kth layer of the plating layer observed by SEM image, and D k is the value derived through the electrochemical hydrogen permeation experiment method below (m 2 / s), t is the total heating time (sec) during hot stamping molding, and n is an integer greater than or equal to 2.

[0134] Electrochemical hydrogen permeation experiment method

[0135] - A sample formed as the kth layer is placed in the center of two cells, and hydrogen is electrically formed in one cell so that the hydrogen can permeate to the other cell.

[0136] - Measure the time it takes for hydrogen to permeate to the other cell.

[0137] - The value calculated using the general formula 2 below using the measured time and the thickness of the specimen is D k It is said.

[0138] [General Formula 2]

[0139]

[0140] (In the above general formula 2, L sample is the thickness of the specimen (m), and t sample is the time (sec) that the light penetrated the sample.

[0141] A detailed description of the composition and manufacturing method of the above hot stamping part is identical to that described in the above hot stamping, and thus will be omitted. The hot stamping part manufactured by the above hot stamping part manufacturing method can suppress hydrogen embrittlement and have ultra-high strength by satisfying the above-described general formula 1.

[0142] The entire plating layer formed on the plated steel sheet prepared in the above heating step may contain 10 wt% to 70 wt% of iron (Fe), the remainder of zinc (Zn), and other unavoidable impurities.

[0143] The thickness of the plating layer formed on the plated steel sheet prepared in the above heating step may be 5 ㎛ to 20 ㎛, specifically, 8 ㎛ to 18 ㎛ or 10 ㎛ to 15 ㎛. The plating layer formed on the plated steel sheet prepared in the heating step has the above-mentioned thickness, thereby protecting the surface of the steel sheet, and at the same time, preventing or minimizing the deterioration of the toughness of the hot stamping part manufactured according to the above-mentioned manufacturing method. If the thickness of the plating layer formed on the plated steel sheet prepared in the heating step is less than the above-mentioned range, the sacrificial corrosion protection effect unique to zinc may be deteriorated. In addition, if the thickness of the plating layer formed on the plated steel sheet prepared in the heating step exceeds the above-mentioned range, the toughness of the hot stamping part manufactured according to the above-mentioned manufacturing method and including the plating layer may be deteriorated.

[0144] In one example, the plating layer formed on the plated steel sheet prepared in the heating step may include the aforementioned composition, and thus, after alloying, may include a zeta layer, a delta layer, and a gamma layer.

[0145] Since the plated steel sheet prepared in the above heating step includes the above-described layer, the hot stamping part manufactured through the method for manufacturing the hot stamping part can satisfy the general formula 1, general formula 3 or general formula 4, thereby suppressing hydrogen embrittlement and having ultra-high strength. The stacking order of the zeta layer, the delta layer and the gamma layer in the plating layer formed on the plated steel sheet prepared in the above heating step is not particularly limited. For example, the plating layer formed on the plated steel sheet prepared in the above heating step can sequentially include the zeta layer, the delta layer and the gamma layer along the thickness direction from the surface toward the steel sheet.

[0146] The above zeta layer is a layer exhibiting a zeta phase and may contain 3 wt% to 8 wt% of iron (Fe) and the remainder of zinc (Zn) and other unavoidable impurities.

[0147] The thickness of the above zeta layer may be greater than 0 to 4 μm, and specifically, greater than 0 to 3 μm or greater than 0 to 2 μm. By having the above-mentioned thickness of the zeta layer, it may be more advantageous for the hot stamping part to satisfy the general formula 1, the general formula 3 or the general formula 4.

[0148] The above delta layer is a layer representing a delta phase, and may contain 8 to 12 wt% of iron (Fe) and the remainder of zinc (Zn) and other unavoidable impurities.

[0149] The thickness of the above delta layer may be greater than 3 ㎛ to 10 ㎛, and specifically, greater than 6 ㎛ to 10 ㎛ or greater than 8 ㎛ to 9 ㎛. By having the above-mentioned thickness of the delta layer, it may be more advantageous for the hot stamping part to satisfy the general formula 1, the general formula 3 or the general formula 4.

[0150] The above gamma layer is a layer exhibiting a gamma phase, and may contain 19 to 32 wt% of iron (Fe) and the remainder of zinc (Zn) and other unavoidable impurities.

[0151] The thickness of the above gamma layer may be 1 ㎛ to 6 ㎛, and specifically, 1 ㎛ to 5 ㎛ or 1 ㎛ to 4 ㎛. By having the above-mentioned thickness of the gamma layer, it may be more advantageous for the hot stamping part to satisfy the general formula 1, the general formula 3 or the general formula 4.

[0152] In one example, a method for manufacturing a plated steel sheet having a plating layer comprising a layer composed of the above-described structure on the steel sheet includes: immersing the steel sheet in a plating bath to manufacture a hot-dip galvanized steel sheet having a plating layer comprising the above-described structure formed on the steel sheet; and alloying the hot-dip galvanized steel sheet to manufacture an alloyed hot-dip galvanized steel sheet. At this time, the plating bath may include components of less than 0.3 wt% of aluminum, less than 0.1 wt% of iron, a remainder of zinc, and other unavoidable impurities. The plating layer may be attached to each of both surfaces of the steel sheet to a thickness of 10 µm to 15 µm. In addition, a difference between the temperature of the steel sheet immediately before the alloying and the alloying temperature may be 80°C or more. By ensuring that the difference between the steel plate temperature immediately before the alloying and the alloying temperature satisfies the above-mentioned range, a zeta layer, a delta layer, and a gamma layer can be secured in the plating layer formed on the steel plate, and the thickness of the plating layer can be satisfied, thereby satisfying general formula 1, general formula 3, or general formula 4, and thereby suppressing hydrogen embrittlement and obtaining a hot stamping part having ultra-high strength.

[0153] In one example, when heating the plated steel sheet prepared in the above heating step, the steel sheet can be heated at an average heating rate of 3°C / s to 8°C / s in a temperature range of 600°C to 700°C. When heating the plated steel sheet prepared in the above heating step, a specific description of the average heating rate that the steel sheet has in the above-described temperature range is the same as that described in the hot stamping, and therefore will be omitted.

[0154] In addition, when heating the plated steel sheet prepared in the above heating step, the plated steel sheet can be heated at an average heating rate of 0.5 ℃ / s to 3 ℃ / s in a temperature range of 800 ℃ to 900 ℃. When heating the plated steel sheet prepared in the above heating step, a specific description of the average heating rate that the plated steel sheet has in the above-described temperature range is the same as that described in the hot stamping, and therefore, will be omitted.

[0155] Hereinafter, the present application will be described in more detail through examples according to the present application and comparative examples not according to the present application, but the scope of the present application is not limited by the examples presented below.

[0156]

[0157] Example 1

[0158] Manufacturing of hot stamping parts

[0159] A steel sheet having a thickness of 1.2 mm, consisting of 0.29 wt% carbon, 0.2 wt% silicon, 1.5 wt% manganese, 0.02 wt% or less phosphorus, 0.015 wt% or less sulfur, 0.2 wt% chromium, 0.0025 wt% boron, 0.035 wt% titanium, the remainder iron, and other unavoidable impurities was immersed in a plating bath to prepare an alloyed hot-dip galvanized steel sheet in which a plating layer consisting of a zeta layer, a delta layer, and a gamma layer was formed on both upper and lower surfaces of the steel sheet in the thickness direction from the surface toward the steel sheet. At this time, the alloyed hot-dip galvanizing was performed by immersing the steel sheet in the plating bath, adjusting the plating adhesion amount with an air knife, and then alloying so that the average thickness of the plating layer became 12 ㎛. Specifically, the composition of the plating bath was set to include 0.13 wt% of aluminum, 0.06 wt% of iron, the remainder zinc, and other unavoidable impurities, and the temperature of the plating bath was set to 450°C. In addition, the steel sheet was passed through the plating bath at a speed of 120 mpm so that molten zinc was attached to both the upper and lower surfaces of the steel sheet, and then charged into an alloying heating furnace at 530°C so that the iron atoms constituting the steel sheet were diffused into the plating layer, thereby alloying the steel sheet and the molten zinc, thereby manufacturing an alloyed hot-dip galvanized steel sheet. At this time, the position of the alloying heating furnace was adjusted so that the temperature of the steel sheet immediately before being charged into the alloying heating furnace was 420°C, so that the temperature difference between the steel sheet and the alloying heating furnace was 80°C or more. The time maintained at the alloying temperature, i.e., the alloying time, was set to 30 seconds.

[0160] Thereafter, the manufactured galvanized steel sheet was prepared, and the prepared galvanized steel sheet was heated in a heating furnace having a maximum temperature of 900°C for 450 seconds. At this time, the heating furnace was configured to include a plurality of heating zones in which the temperature gradually increases from the inlet side where the galvanized steel sheet is loaded toward the outlet side where the heated galvanized steel sheet is taken out, and the furnace temperature of each heating zone was controlled so that the galvanized steel sheet was heated at an average heating rate of 7.20°C / s in the temperature section where it was heated from 600°C to 700°C, and at an average heating rate of 2.22°C / s in the temperature section where it was heated from 800°C to 890°C.

[0161] Thereafter, the heated galvanized steel plate was stamped with a press to form a molded body, and at the same time, it was rapidly cooled at an average cooling rate of 10°C / s to below 300°C to manufacture a hot stamping part. The physical properties of the manufactured hot stamping part are shown in Table 1 below.

[0162]

[0163] Example 2

[0164] Manufacturing of hot stamping parts

[0165] A hot stamping part was manufactured in the same manner as in Example 1, except that the average heating rate in the temperature range from 600°C to 700°C was 5.20°C / s, and the average heating rate in the temperature range from 800°C to 890°C was 1.21°C / s. The physical properties of the manufactured hot stamping part are shown in Table 1 below.

[0166]

[0167] Example 3

[0168] Manufacturing of hot stamping parts

[0169] A hot stamping part was manufactured in the same manner as in Example 1, except that the average heating rate in the temperature range from 600°C to 700°C was 4.10°C / s, and the average heating rate in the temperature range from 800°C to 890°C was 0.86°C / s. The physical properties of the manufactured hot stamping part are shown in Table 1 below.

[0170]

[0171] Example 4

[0172] Manufacturing of hot stamping parts

[0173] A hot stamping part was manufactured in the same manner as in Example 1, except that the average heating rate in the temperature range from 600°C to 700°C was 3.00°C / s, and the average heating rate in the temperature range from 800°C to 890°C was 0.53°C / s. The physical properties of the manufactured hot stamping part are shown in Table 1 below.

[0174]

[0175] Comparative Example 1

[0176] Manufacturing of hot stamping parts

[0177] A hot stamping part was manufactured in the same manner as in Example 1, except that the average heating rate in the temperature range from 600°C to 700°C was 3.50°C / s, and the average heating rate in the temperature range from 800°C to 890°C was 0.30°C / s. The physical properties of the manufactured hot stamping part are shown in Table 1 below.

[0178]

[0179] Comparative Example 2

[0180] Manufacturing of hot stamping parts

[0181] A hot stamping part was manufactured in the same manner as in Example 1, except that the average heating rate in the temperature range from 600°C to 700°C was 2.91°C / s, and the average heating rate in the temperature range from 800°C to 890°C was 0.52°C / s. The physical properties of the manufactured hot stamping part are shown in Table 1 below.

[0182]

[0183] Comparative Example 3

[0184] Manufacturing of hot stamping parts

[0185] A hot stamping part was manufactured in the same manner as in Example 1, except that the average heating rate in the temperature range from 600°C to 700°C was 2.98°C / s, and the average heating rate in the temperature range from 800°C to 890°C was 0.45°C / s. The physical properties of the manufactured hot stamping part are shown in Table 1 below.

[0186]

[0187] Evaluation Example 1. Evaluation of shape analysis of plating layer

[0188] The plating layers of the hot stamping parts manufactured in the examples and comparative examples were photographed using a scanning electron microscope (SEM), and the results are shown in Table 1, respectively. In particular, the images of the plating layers of the hot stamping parts manufactured in Example 2, photographed using a scanning electron microscope, are shown in Fig. 2. At this time, the structures formed in the plating layers were described in the order of thickness from the surface toward the steel sheet.

[0189]

[0190] Evaluation Example 2. Electrochemical hydrogen permeation experiment evaluation

[0191] In the hot stamping parts manufactured in the examples and comparative examples, the structure of each layer (n layers) formed on the plating layer is confirmed, and each specimen made of each structure is manufactured, and each manufactured specimen is placed in the center of each of two cells, and hydrogen is electrically formed in one cell so that the hydrogen permeates to the other cell. Thereafter, the time for the hydrogen to permeate to the other cell is measured. Using the measured time and the thickness of the specimen, D is calculated by the following general formula 2. k The value was found.

[0192] The specimens of the examples and comparative examples are calculated by the following general formula 2. k The values ​​are 8 X 10 each -14 m 2 / s to 8 X 10 -11 m 2 / s was.

[0193] [General Formula 2]

[0194]

[0195] (In the above general formula 2, L sample is the thickness of the specimen (m), and t sample is the time (sec) that the light penetrated the sample.

[0196]

[0197] Evaluation Example 3. Evaluation of Satisfaction with General Formula 3

[0198] Using the results of the above evaluation examples 1 and 2, the satisfaction of the general formula 3 below of the hot stamping parts manufactured in the examples and comparative examples was evaluated, and the results are shown in Table 1 below.

[0199] [General Formula 3]

[0200]

[0201] (In the above general formula 3, when the plating layer is composed of n layers with distinct structures, L kis the average thickness (㎛) measured along the short axis direction at 10 random locations in the kth layer of the plating layer observed by SEM image, and D k is the value derived through the electrochemical hydrogen permeation experiment method below (m 2 / s), t is the total heating time (sec) during hot stamping molding, and n is an integer greater than or equal to 2.

[0202] Tissue L included in the plating layer k (㎛) Left side value of general formula 3 Example 1 Gamma layer 11.43 Alpha iron layer 29 Example 2 Gamma layer (2) 21.46 Alpha iron layer (1) 23 Example 3 Gamma layer 91.67 Alpha iron layer 19 Example 4 Gamma layer 101.68 Alpha iron layer 20 Comparative example 1 Gamma layer 141.78 Alpha iron layer 19 Comparative example 2 Gamma layer 111.71 Alpha iron layer 20 Comparative example 3 Gamma layer 121.72 Alpha iron layer 21

[0203] As shown in Table 1 above, it was confirmed that the hot stamping parts manufactured in Examples 1 to 4 satisfied General Formula 3. In contrast, it was confirmed that the hot stamping parts manufactured in Comparative Examples 1 to 3 did not satisfy General Formula 3.

[0204]

[0205] Evaluation Example 4. Hydrogen embrittlement evaluation

[0206] The amount of diffusible hydrogen for the hot stamping parts manufactured in each of the examples and comparative examples was measured using the thermal desorption spectroscopy method. Specifically, the amount of hydrogen released from the hot stamping parts manufactured in each of the examples and comparative examples was measured at 350°C or lower while the temperature was increased from room temperature (±20°C) to 500°C at a heating rate of 20°C, and the results are shown in Table 2 below.

[0207] Diffusible hydrogen content (ppm) Example 10.025 Example 20.034 Example 30.059 Example 40.058 Comparative Example 10.423 Comparative Example 20.412 Comparative Example 30.497

[0208] As shown in Table 2 above, the hot stamping parts manufactured in Examples 1 to 4 had a diffusible hydrogen content of less than 0.1 ppm, which was confirmed to be significantly lower than the hot stamping parts manufactured in Comparative Examples 1 to 5, and thus, it was confirmed that hydrogen embrittlement could be suppressed.

[0209]

[0210] Evaluation Example 5. Fracture Test Evaluation

[0211] The hot stamping parts manufactured in Example 2 and Comparative Examples 1 and 2 were evaluated for fracture using a 4-point bending test. Specifically, the 4-point bending test was performed by exposing the hot stamping parts manufactured in each of the Examples and Comparative Examples to a corrosive environment, and applying a stress below the elastic limit, specifically 1,000 MPa in air, to a specific point of each specimen for 100 hours to check whether stress corrosion cracking occurred, i.e., whether fracture occurred, and the results are shown in FIGS. 3 to 5, respectively. Here, stress corrosion cracking refers to cracking that occurs when corrosion and continuous tensile stress are applied simultaneously.

[0212] As shown in Fig. 3, it was confirmed that the hot stamping parts manufactured in Example 2 were not broken. In contrast, the hot stamping parts manufactured in Comparative Examples 1 and 2, shown in Figs. 4 and 5, respectively, were confirmed to be broken. That is, it was confirmed that the hot stamping parts manufactured in Example 2 satisfied the general formula 3, and thus, hydrogen embrittlement was suppressed compared to the hot stamping parts manufactured in Comparative Examples 1 and 2, which did not satisfy the general formula 3.

[0213] <Explanation of symbols>

[0214] 1: Alpha iron layer

[0215] 2: Gamma layer

[0216] 10: Hot stamping parts

[0217] 11: Steel plate

[0218] 12: Plating layer

Claims

DEPCT681. Hot stamping components consisting of: steel plate; and a plating layer formed on at least one surface of the steel plate, conforming to the general formula 1 below, and containing zinc: [General Formula 1] (Formula), (In General Formula 1, when the plating layer consists of n layers with different structures, Lk is the average thickness (µm) measured along the short-axis direction at ten random positions in the k-layer of the plating layer observed in the SEM image, Dk is the value (m² / s) obtained through the electrochemical hydrogen permeation experimental method below, t is the heating time. Total (seconds) during hot stamping, and n is an integer greater than or equal to 2), <Electrochemical Hydrogen Permeation Experimental Method> - A sample formed from layer k is placed in the center of two cells, and hydrogen is electrically generated in one cell and permeated to the other cell, - the time it takes for hydrogen to permeate to the other cell is measured, and - the value is calculated by general formula 2 below using the measured time and the thickness of the sample is defined as Dk: [General Formula 2](formula), (in general formula 2, L sample is the thickness (m) of the sample,And t is the time (seconds) it takes to penetrate the sample.

2. The hot stamping component of claim 1, where the plating layer conforms to the general formula 3 below: [General Formula 3] (Formula), (In General Formula 3, when the plating layer consists of n layers with different structures, Lk is the average thickness (µm) measured along the short-axis direction at ten random positions in the k-th layer of the plating layer observed in the SEM image, Dk is the value (m² / s) obtained through the electrochemical hydrogen permeation experimental method below, t is the total heating time (seconds). )During hot stamping, and n is an integer greater than or equal to 2), <Electrochemical hydrogen permeation experimental method> - A sample formed from layer k is placed in the center of two cells, and hydrogen is electrically generated in one cell and permeated to the other cell, - the time it takes for hydrogen to permeate to the other cell is measured, and - the value is calculated by general formula 2 below by using the measured time and the thickness of the sample is defined as Dk: [General Formula 2](formula), (in General Formula 2, L sample is the thickness (m) of the sample,And t is the time (seconds) it takes to penetrate the sample.

3. The hot stamping component of claim 1, where the plating layer conforms to the general formula 4 below: [General Formula 4] (Formula), (In General Formula 4, when the plating layer consists of n layers with different structures, the average thickness (micrometers) is measured along the short-axis direction at ten random positions in the k-layer of the plating layer observed in the SEM image, Dk is the value (m² / s) obtained through the electrochemical hydrogen permeation experimental method below, t is the total heating time (seconds). During hot stamping, and n is an integer greater than or equal to 2), <Electrochemical hydrogen permeation experimental method> - A sample formed from layer k is placed in the center of two cells, and hydrogen is electrically generated in one cell and permeated to the other cell, - the time it takes for hydrogen to permeate to the other cell is measured, and - the value is calculated by general formula 2 below by using the measured time and the thickness of the sample is defined as Dk: [General Formula 2](formula), (in General Formula 2, L sample is the thickness (m) of the sample,And t is the time (seconds) it takes to penetrate the sample layer.

4. The hot stamping component of claim 1, where the hot stamping component is the component produced by stamping a plated steel sheet with a zinc-formed coating layer on at least one surface of the hot stamped steel sheet.

5. The hot stamping component of claim 4, where the hot stamping consists of: the heating step of preparing the plated steel sheet with the zinc-formed coating layer on at least one surface of the hot stamped steel sheet, and heating the prepared plated steel sheet; the forming step of stamping the hot stamped steel sheet with a die and forming the formed body; and the cooling step of cooling the formed body.

6. The hot stamping component of claim 5, where when the plated steel sheet prepared in the heating step is heated,The quenched steel plate is heated at an average temperature increase rate of 3°C / s to 8°C / s in a temperature gap of 600°C to 700°C.

7. The hot stamping component of claim 5, where, when the quenched steel plate prepared in the heating process is heated, the quenched steel plate is heated at an average temperature increase rate of 0.5°C / s to 3°C / s in a temperature gap of 800°C to X°C, and where X°C equals 8. The maximum temperature at which the quenched steel sheet is heated during the heating process is minus 10 degrees Celsius.

9. The hot stamping component of claim 4, where the heating time during hot stamping is 150 seconds to 450 seconds.

10. The hot stamping component of claim 1, where the quenching layer has a thickness of 10 micrometers to 30 micrometers.

11. The method of manufacturing the hot stamping component, which includes the steel sheet and the quenching layer formed on at least one surface of the steel sheet, in accordance with the general formula 1 below, and containing zinc,The method comprises: the heating step of preparing the quenched steel plate with a zinc-coated layer formed on at least one surface of the steel plate, and heating the prepared quenched steel plate; the forming step of stamping the heated quenched steel plate with a die and forming the formed body; and the cooling step of cooling the formed body [General Formula 1] (Formula), (in General Formula 1, when the quenching layer consists of n layers with different structures, Lk is the average thickness (µm) measured along the short-axis direction at ten random positions in the k-layer of the quenching layer observed in the SEM image, Dk is the value (sq m / s) obtained through the electrochemical hydrogen permeation experimental method below, t is the total heating time (seconds) during hot stamping, and n is an integer greater than or equal to 2), <Electrochemical Hydrogen Permeation Experimental Method> - A specimen formed from the k-layer is placed in the center of two cells, and hydrogen is electrochemically generated in one cell and permeated to the other cell.-The time it takes for hydrogen to permeate into another cell is measured, and the value is calculated by general formula 2 below by using the measured time and the thickness of the sample is defined as Dk:[general formula 2](formula),(in general formula 2, L sample is the thickness (m) of the sample, and t sample is the time (seconds) it takes for hydrogen to permeate the sample).

11. Method of claim 10, in which when a quenched steel plate prepared in the heating process is heated, the quenched steel plate is heated at an average temperature increase rate of 3 degrees Celsius / second to 11. The method of claim 10, in which, when a quenched steel plate prepared in the heating step is heated, the quenched steel plate is heated at an average temperature increase rate of 0.5 °C / s to 3 °C / s in a temperature difference of 800 °C to X °C, and in which X °C is equal to the maximum temperature at which the quenched steel plate is heated in the heating step minus 10 °C.

12. The method of claim 10,Where the quenching layers formed on the heat-treated steel plate consist of zeta, delta, and gamma layers;

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