Hot stamp component

Abstract

The present invention provides a hot stamp component comprising a body and a flange. The body includes: at least one hole; a hole-softened region surrounding the hole; and a quenched region. The flange includes a flange cut surface and a flange-softened region adjacent to the flange cut surface. The hole-softened region and the flange-softened region have a mixed microstructure of tempered martensite and bainite, and the quenched region has a microstructure of martensite.

Description

Hot stamped parts

[0001] The present invention relates to a hot stamped part having high hydrogen embrittlement resistance.

[0002] As environmental and fuel efficiency regulations tighten globally, the need for lighter vehicle materials is increasing. Consequently, research and development on ultra-high-strength steel and hot-stamping steel is actively underway.

[0003] The hot stamping process is a process of manufacturing a high-strength molded body by heating a material such as steel plate to a predetermined temperature, press-forming the material while it is heated, and cooling the material inside the mold.

[0004] These high-strength molded parts, i.e. hot stamped parts, are manufactured into parts of car bodies, etc. by cutting or trimming the edge portions into the desired shape.

[0005] Traditionally, when trimming high-strength hot stamped parts, a laser trimming process was used to ensure good quality shear sections.

[0006] However, the laser trimming process had the problem of low productivity, high energy consumption, and high carbon emissions.

[0007] Meanwhile, when trimming high-strength hot stamped parts through cold trimming or mechanical shearing processes, there was a disadvantage in that the problem of hydrogen delay fracture was aggravated due to poor shearing quality.

[0008] The present invention is intended to solve various problems including the above-described problems, and according to one embodiment of the present invention, a hot stamped part having high hydrogen embrittlement resistance is provided, which can reduce hot stamping process costs, reduce carbon emissions, and improve productivity.

[0009] However, these tasks are exemplary and the scope of the present invention is not limited thereby.

[0010] According to one aspect of the present invention, a hot stamped part including a body and a flange is provided, wherein the body includes at least one hole, a hole softening portion surrounding the hole, and a quenching portion, the flange includes a flange cut surface and a flange softening portion adjacent to the flange cut surface, the hole softening portion and the flange softening portion have a mixed microstructure of tempered martensite and bainite, and the quenching portion has a martensite microstructure.

[0011] According to one aspect of the present invention, a method for manufacturing a hot stamped part is provided, comprising: a step of heating a blank; a step of controlling molding and cooling the heated blank; and a step of cold press cutting the molded blank; wherein, in the step of controlling molding and cooling the heated blank, the blank includes a pre-quenching section and a pre-softening section, a cooling rate of the pre-softening section is lower than a cooling rate of the pre-quenching section, and a temperature difference between the pre-softening section and the pre-quenching section is 200° C. or more after the step of controlling molding and cooling the heated blank is completed.

[0012] According to one embodiment of the present invention, as described above, a hot stamped part with high hydrogen embrittlement resistance can be provided, which can reduce hot stamping process costs, reduce carbon emissions, and improve productivity. Of course, the scope of the present invention is not limited by these effects.

[0013] FIG. 1 is a perspective view schematically illustrating a hot stamp part according to one embodiment of the present invention.

[0014] Figure 2 is an enlarged plan view of area A of the hot stamp part according to Figure 1.

[0015] Figure 3 is an enlarged plan view of area B of the hot stamp part according to Figure 1.

[0016] Figure 4 is a flowchart showing a method for manufacturing a hot stamp part according to one embodiment of the present invention.

[0017] Figure 5 is a cross-sectional view schematically illustrating a softening process method according to one embodiment of the present invention.

[0018] Figure 6 is a cross-sectional view schematically illustrating a softening process method according to one embodiment of the present invention.

[0019] Figure 7 is a cross-sectional view schematically illustrating a softening process method according to one embodiment of the present invention.

[0020] FIG. 8 is a graph showing the hardness of a hot stamped part according to the distance from the cross-section according to one embodiment of the present invention.

[0021] Figure 9 is a graph showing the hardness of a hot stamped part according to the distance from the cross-section according to a comparative example of the present invention.

[0022] Fig. 10 is a drawing showing a softening unit according to one embodiment of the present invention.

[0023] Fig. 11 is a drawing showing a rapid cooling unit according to one embodiment and a comparative example of the present invention.

[0024] Fig. 12 is a drawing showing a cross-section according to one embodiment of the present invention.

[0025] Fig. 13 is a drawing showing a cross-section according to a comparative example of the present invention.

[0026] Figure 14 is a graph showing the results of a diffusible hydrogen measurement test according to one embodiment and a comparative example of the present invention.

[0027] In one embodiment of the present invention, the flange softening section includes a first section that is spaced apart from the flange cut surface by 250 ㎛ or more and 500 ㎛ or less, and a second section that is spaced apart from the flange cut surface by 600 ㎛ or more, and a ratio of the hardness value of the first section to the hardness value of the quenching section may be 0.75 or more and less than 1.0.

[0028] The ratio of the hardness value of the second region to the hardness value of the above-mentioned rapid cooling section may be 0.7 or more and 0.9 or less.

[0029] The above hole softening section includes a third section that is a section spaced apart from the hole cutting surface by 250 ㎛ or more and 500 ㎛ or less, and a fourth section that is a section spaced apart from the hole cutting surface by 600 ㎛ or more, and a ratio of the hardness value of the third section to the hardness value of the quenching section may be 0.75 or more and less than 1.0.

[0030] The ratio of the hardness value of the fourth region to the hardness value of the above-mentioned rapid cooling section may be 0.7 or more and 0.9 or less.

[0031] In one embodiment of the present invention, in the step of controlling the forming and cooling of the heated blank, the upper die and the lower die may include a groove, and the position where the groove is formed may be adjacent to the preliminary softening section.

[0032] In the step of forming and cooling the heated blank, a low heat conductive material may be placed between the upper die and the preliminary softening section, and a low heat conductive material may be placed between the lower die and the preliminary softening section.

[0033] In the step of forming and cooling the heated blank, a heat generating unit may be arranged adjacent to a pre-softening unit of the upper die, and a heat generating unit may be arranged adjacent to a pre-softening unit of the lower die.

[0034] After the step of controlling the forming and cooling of the heated blank is completed, the pre-softening section may have a mixed microstructure of tempered martensite and bainite, and the pre-quenching section may have a martensite microstructure.

[0035] Other aspects, features and advantages other than those described above will become apparent from the following detailed description, claims and drawings for carrying out the invention.

[0036] Hereinafter, the present invention will be described in detail. When describing the present invention, if it is determined that a detailed description of a related known technology or configuration may unnecessarily obscure the gist of the present invention, such detailed description will be omitted.

[0037] In the examples below, the terms first, second, etc. are not used in a limiting sense, but are used for the purpose of distinguishing one component from another.

[0038] In the examples below, singular expressions include plural expressions unless the context clearly indicates otherwise.

[0039] In the following examples, when various components such as layers, films, regions, and plates are said to be “on” other components, this includes not only cases where they are “directly on” other components, but also cases where other components are interposed between them.

[0040] For convenience of explanation, the sizes of components in the drawings may be exaggerated or reduced. For example, the sizes and thicknesses of each component shown in the drawings are arbitrarily shown for convenience of explanation, and the present invention is not necessarily limited to what is shown.

[0041] In the following examples, terms such as “include” or “have” mean that a feature or component described in the specification is present, and do not preclude the possibility that one or more other features or components may be added.

[0042] In this specification, “A and / or B” refers to the case where it is A, or B, or both A and B. In addition, in this specification, “at least one of A and B” refers to the case where it is A, or B, or both A and B.

[0043] Although not defined otherwise, all terms, including technical and scientific terms, used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present invention pertains. Terms defined in commonly used dictionaries are further interpreted to have meanings consistent with the relevant technical literature and the present disclosure, and are not to be construed as ideal or overly formal unless otherwise defined.

[0044] Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art can easily implement them. However, the present invention may be implemented in various different forms and is not limited to the embodiments described herein.

[0045] FIG. 1 is a perspective view schematically illustrating a hot stamp part according to one embodiment of the present invention.

[0046] As described below, hot stamped parts can be manufactured into the shape of a final product by press forming a heated blank to create a desired shape, cutting a flange to the required shape, and punching holes.

[0047] Referring to FIG. 1, a hot stamp part according to one embodiment of the present invention includes a body portion (20) and a flange (10), the body portion (20) includes at least one hole (200), a hole softening portion (250) formed around the hole (200) and surrounding the hole (200), and a quenching portion (300), and the flange (10) may include a flange softening portion (150).

[0048] Hot stamped parts include a rapid cooling section because the blank is rapidly cooled during press forming of the heated blank. However, as described below, a hot stamped part according to one embodiment of the present invention may include a softening section because it undergoes a softening process that reduces the cooling rate in some areas.

[0049] When cutting a hot stamped part into a desired shape, press cutting is performed at the softening section, so in the final product, the hot stamped part, the softening section may be a predetermined area from the cut surface.

[0050] Referring back to FIG. 1, the flange (10) may include a flange cut surface (110), which is a surface where a portion of the flange (10) is cut off and removed. In addition, the flange softening portion (150) may be formed on the flange (10) and may occupy a certain area from the flange cut surface (110). That is, the flange softening portion (150) may be adjacent to the flange cut surface (110). Accordingly, the flange softening portion (150) may be formed along the longitudinal direction of the flange (10).

[0051] Additionally, the hole softening portion (250) may be formed to occupy a certain area from the hole cutting surface (210). That is, the hole softening portion (250) may be adjacent to the hole cutting surface (210). Accordingly, the hole softening portion (250) may surround the hole (200).

[0052] The softened portion (150, 250) may have a mixed microstructure of tempered martensite and bainite.

[0053] The rapid cooling section (300) may be a section that has not undergone a softening process that reduces the cooling rate during press forming of a heated blank. In other words, the rapid cooling section (300) may be a section other than the softening section (150, 250).

[0054] The rapid cooling section (300) may have a martensite microstructure.

[0055] FIG. 2 is an enlarged plan view of area A of the hot stamp part according to FIG. 1, and FIG. 3 is an enlarged plan view of area B of the hot stamp part according to FIG. 1.

[0056] Referring to FIG. 2, the flange softening portion (150) is formed adjacent to the flange cutting surface (110) and can be formed in a predetermined section extending from the flange cutting surface (110).

[0057] At this time, the flange softening section (150) may include a first region (160) and a second region (170).

[0058] The first region (160) may be an area from a portion spaced apart from the flange cut surface (110) by a first distance (d1) to a portion spaced apart from the flange cut surface (110) by a second distance (d2).

[0059] The first distance (d1) may be about 250 μm, and the second distance (d2) may be about 500 μm. That is, the first region (160) may be an area from a portion spaced apart by 250 μm from the flange cut surface (110) to a portion spaced apart by 500 μm. In other words, the first region (160) may be an area spaced apart by 250 μm or more and 500 μm or less from the flange cut surface (110).

[0060] When a blank is press-cut, the portion being cut and the portion adjacent to it undergo work hardening, increasing the hardness.

[0061] The first region (160) may be a region less affected by this work hardening.

[0062] The second region (170) may be a region spaced apart from the flange cut surface (110) by a third distance (d3).

[0063] The above third distance (d3) may be about 600 μm. That is, the second region (170) may be a region spaced apart from the flange cut surface (110) by 600 μm or more.

[0064] The second region (170) may be a region that is not affected by the aforementioned processing hardening.

[0065] In one embodiment, the ratio of the hardness value of the first region (160) to the hardness value of the quenching section (300) may be greater than or equal to 0.75 and less than or equal to 1.0. In one embodiment, the ratio of the hardness value of the first region (160) to the hardness value of the quenching section (300) may be greater than or equal to about 0.90 and less than or equal to about 0.95.

[0066] When the hardness value satisfies this numerical range, microcracks on the cut surface are reduced and hydrogen embrittlement resistance can be improved.

[0067] In one embodiment, the ratio of the hardness value of the second region (170) to the hardness value of the quenching section (300) may be greater than or equal to 0.7 and less than or equal to 0.9. In one embodiment, the ratio of the hardness value of the second region (170) to the hardness value of the quenching section (300) may be greater than or equal to about 0.85 and less than or equal to about 0.90.

[0068] When the hardness value satisfies this numerical range, the toughness of the hot stamped part is improved, which can improve the crash performance and fracture resistance.

[0069] Referring to FIG. 3, the hole softening portion (250) is formed adjacent to the hole cutting surface (210) and can be formed in a predetermined section extending from the hole cutting surface (210).

[0070] At this time, the hole softening section (250) may include a third region (260) and a fourth region (270).

[0071] The third region (260) may be an area from a portion spaced apart from the hole cut surface (210) by a fourth distance (d4) to a portion spaced apart from the hole cut surface (210) by a fifth distance (d5).

[0072] The fourth distance (d4) may be about 250 μm, and the fifth distance (d5) may be about 500 μm. That is, the third region (260) may be an area from a portion spaced apart by 250 μm from the hole cutting surface (210) to a portion spaced apart by 500 μm. In other words, the third region (260) may be an area spaced apart by 250 μm or more and 500 μm or less from the hole cutting surface (210).

[0073] The third region (260) may be a region less affected by the aforementioned work hardening.

[0074] The fourth region (270) may be a region spaced apart from the hole cut surface (210) by a sixth distance (d6).

[0075] The above sixth distance (d6) may be about 600 μm. That is, the fourth region (270) may be a region spaced apart from the hole cut surface (210) by 600 μm or more.

[0076] The fourth region (270) may be a region that is not affected by the aforementioned work hardening.

[0077] In one embodiment, the ratio of the hardness value of the third region (260) to the hardness value of the quenching section (300) may be greater than or equal to 0.75 and less than or equal to 1.0. In one embodiment, the ratio of the hardness value of the first region (160) to the hardness value of the quenching section (300) may be greater than or equal to about 0.90 and less than or equal to about 0.95.

[0078] When the hardness value satisfies this numerical range, microcracks on the cut surface are reduced and hydrogen embrittlement resistance can be improved.

[0079] In one embodiment, the ratio of the hardness value of the fourth region (270) to the hardness value of the quenching section (300) may be greater than or equal to 0.7 and less than or equal to 0.9. In one embodiment, the ratio of the hardness value of the second region (170) to the hardness value of the quenching section (300) may be greater than or equal to about 0.85 and less than or equal to about 0.90.

[0080] When the hardness value satisfies this numerical range, the toughness of the hot stamped part is improved, which can improve the crash performance and fracture resistance.

[0081] Hereinafter, a method for manufacturing a hot stamp part according to one embodiment of the present invention as described above will be described.

[0082] Referring to FIG. 4, a method for manufacturing a hot stamp part according to one embodiment of the present invention may include a blank heating step (S100), a blank forming and cooling control step (S200), and a cold press cutting step (S300).

[0083] In the blank heating step (S100), the blank can be heated so that the blank can be formed well in a press later.

[0084] Afterwards, a blank forming and cooling control step (S200) may be performed. In the blank forming and cooling control step (S200), a heated blank may be loaded into a press and then formed and cooled.

[0085] At this time, a softening process can be performed to control or reduce the cooling rate for a predetermined area including a location where a hole is to be formed and a predetermined area from a portion to be cut. That is, the softening process can be performed on a preliminary softening section that will become a softening section.

[0086] Specifically, the blank heated in the blank heating step (S100) may include a preliminary quenching section that will become a quenching section in a later process, and a preliminary softening section that will become a softening section. In the blank forming and cooling control step (S200), the cooling rate of the preliminary softening section may be set to be lower than the cooling rate of the preliminary quenching section.

[0087] Figures 5 to 7 are cross-sectional views schematically illustrating a softening process method according to one embodiment of the present invention. Specifically, Figures 5 to 7 illustrate a method for controlling the cooling rate in the pre-softening section to be lower than the cooling rate in the pre-quenching section when pressing a heated blank. A heated blank (500) can be loaded into a press. That is, the heated blank (500) can be loaded between the upper die (410) and the lower die (420) of the press.

[0088] When loading the blank into the press and forming it, the press has a low temperature, so the blank can be rapidly cooled. Meanwhile, to form a softened section, a portion of the upper die and a portion of the lower die corresponding to the preliminary softened section can be configured as shown in FIGS. 5 to 7.

[0089] Referring to FIG. 5, a groove (450) may be formed in the upper die (410) and the lower die (420). In the groove (450), the die and the blank (500) may not be in direct contact. Therefore, the cooling rate of the blank (500) located in the groove (450) may be relatively reduced.

[0090] In this way, the upper die (410) and the lower die (420) may include a groove (450), and since the cooling rate of the blank is low at the portion where the groove (450) is formed, the position where the groove (450) is formed may be adjacent to the pre-softening section. That is, in the blank forming and cooling control step (S200), the pre-softening section of the blank (500) may be controlled to have a cooling rate lower than that of the pre-quenching section that will become the quenching section.

[0091] Referring to FIG. 6, a low thermal conductivity material (460) may be placed between the pre-softening section and the upper die (410), and between the pre-softening section and the lower die (420). In this case as well, since the blank (500) and the die do not come into direct contact in the pre-softening section, the cooling rate of the pre-softening section may be reduced.

[0092] Referring to FIG. 7, a heat generating unit (470) may be placed adjacent to a preliminary softening unit of an upper die (410), and a heat generating unit (470) may be placed adjacent to a preliminary softening unit of a lower die (420).

[0093] In this case, the blank (500) and the die are in direct contact in the pre-softening section, but the temperature of the die adjacent to the pre-softening section is higher than the temperature of the die adjacent to the quenching section, so the cooling speed of the pre-softening section may decrease.

[0094] After the blank forming and cooling control step (S200) is completed, the temperature difference between the pre-softening section and the pre-quenching section may be 200°C or more. When the temperature difference is 200°C or more, the amount of diffusible hydrogen in the final product may be reduced, thereby increasing hydrogen embrittlement resistance.

[0095] When the blank forming and cooling control step (S200) is completed, the pre-softening section may have a mixed microstructure of tempered martensite and bainite, and the pre-quenching section may have a martensite microstructure.

[0096] After the blank forming and cooling control step (S200) is completed, the cold press cutting step (S300) can be performed.

[0097] In the cold press cutting step (S300), a hole can be formed in the pre-softening section or the blank formed along the pre-softening section can be cut to manufacture the final hot stamped part.

[0098] When manufacturing hot stamped parts as described above, a highly productive cold press cutting process can be used, which can reduce process costs and carbon emissions and promote productivity improvements.

[0099] Hereinafter, the structure and operation of the present invention will be described in more detail through preferred embodiments of the present invention. However, these are presented as preferred examples of the present invention and should not be construed as limiting the present invention in any way.

[0100] Experimental example

[0101] Below, the present invention will be described in more detail through experimental examples. However, the following experimental examples are intended to further illustrate the present invention, and the scope of the present invention is not limited by these examples. Those skilled in the art may appropriately modify or alter the following experimental examples within the scope of the present invention.

[0102] Cross-section microcrack observation test

[0103] Example

[0104] As described above, a hot stamped part was manufactured by performing a softening process. That is, after forming a softened portion, the blank was cut along the softened portion.

[0105] Comparative example

[0106] Hot stamped parts were manufactured without performing a softening process. That is, test pieces were manufactured in the same shape as the examples without forming a softened portion.

[0107] Fig. 8 is a graph showing the Vickers hardness of a hot stamped part according to the distance from the cross-section (Distance from the edge, μm) according to one embodiment of the present invention, and Fig. 9 is a graph showing the Vickers hardness of a hot stamped part according to the distance from the cross-section (Distance from the edge, μm) according to one comparative example of the present invention. In this case, the Vickers hardness means the hardness (HV0.05) when a test load of 0.05 kgf is applied.

[0108] In the comparative example, since the softening process was not performed, the softened portion is not included. Therefore, the hardness in the region located at least 600 μm away from the shear surface, which is an area not affected by work hardening in Fig. 9, may be almost the same as the hardness in the quenched portion of the example. That is, the hardness of the quenched portion in the example was 512 HV0.05.

[0109] Referring to FIGS. 8 and 9, the ratio of the hardness value of the first region to the hardness value of the quenched portion of the embodiment is 0.90 or more and 0.95 or less, satisfying a numerical range of 0.75 or more and less than 1.0, and the ratio of the hardness value of the second region to the hardness value of the quenched portion of the embodiment is 0.89, satisfying a range of 0.7 or more and 0.9 or less.

[0110] Meanwhile, in the case of the comparative example, the ratio of the hardness value of the region corresponding to the first region of the embodiment (the region spaced apart by 250 ㎛ or more and 500 ㎛ or less from the cross-section) to the hardness value of the rapid cooling section is 1.02 or more.

[0111] FIG. 10 is a drawing showing a softening unit according to one embodiment of the present invention, and FIG. 11 is a drawing showing a rapid cooling unit according to one embodiment of the present invention and a comparative example.

[0112] Referring to Figures 10 and 11, the softened zone has a microstructure that includes tempered martensite as the main structure and the remainder bainite. The quenched zone has only martensite as the microstructure.

[0113] Accordingly, referring to FIGS. 12 and 13, in the case of the example in which a softened portion having relatively high ductility was formed, no microcracks were observed on the cut surface, whereas in the comparative example, since it has a martensite microstructure with high strength and low ductility, microcracks were observed on the cut surface.

[0114] Diffusible hydrogen measurement test

[0115] To verify hydrogen embrittlement resistance, diffusible hydrogen measurements were performed on the cross-sections of examples and comparative examples. This was performed using a TDS (Thermal Desorption Spectroscopy) test.

[0116] Fig. 14 is a graph showing the results of a diffusible hydrogen measurement test according to an embodiment and a comparative example of the present invention. That is, Fig. 14 is a graph showing the diffusible hydrogen desorption rate of the embodiment and the comparative example according to temperature.

[0117] For the examples, the test was performed three times, and for the comparative examples, the test was performed twice.

[0118] In the examples, all three experiments showed a desorption rate of 0.002 ppm / s, indicating that the amount of diffusible hydrogen was measured to be less than the results of the comparative example experiments. In other words, the examples showed excellent hydrogen embrittlement resistance.

[0119] The embodiments of the present invention are merely illustrative, and those skilled in the art will understand that various modifications and equivalent alternative embodiments are possible. Therefore, the true scope of technical protection of the present invention should be determined by the technical spirit of the appended claims.

Claims

1. For hot stamped parts including a body and a flange, The body includes at least one hole, a hole softening portion surrounding the hole, and a quenching portion, The flange includes a flange cut surface and a flange softening portion adjacent to the flange cut surface, A hot stamped part, wherein the above-mentioned hole softening section and the above-mentioned flange softening section have a mixed microstructure of tempered martensite and bainite, and the above-mentioned quenching section has a martensite microstructure.

2. In paragraph 1, The above flange softening part, A first region is a region spaced apart from the flange cut surface by 250 ㎛ or more and 500 ㎛ or less, and a second region is a region spaced apart from the flange cut surface by 600 ㎛ or more, A hot stamped part, wherein a ratio of the hardness value of the first region to the hardness value of the quenched portion is 0.75 or more and less than 1.

0.

3. In paragraph 2, A hot stamped part, wherein the ratio of the hardness value of the second region to the hardness value of the above-mentioned rapid cooling section is 0.7 or more and 0.9 or less.

4. In paragraph 1, The above hole softening part is, A third region is a region spaced apart from the hole cut surface by 250 ㎛ or more and 500 ㎛ or less, and a fourth region is a region spaced apart from the hole cut surface by 600 ㎛ or more, A hot stamped part, wherein the ratio of the hardness value of the third region to the hardness value of the above-mentioned quenched section is 0.75 or more and less than 1.

0.

5. In paragraph 4, A hot stamped part, wherein the ratio of the hardness value of the fourth region to the hardness value of the above-mentioned rapid cooling section is 0.7 or more and 0.9 or less.

6. Step of heating the blank; A step of forming and cooling the heated blank; and A step of cold press cutting the formed blank; Including, In the step of forming and cooling the heated blank, the blank includes a pre-quenching section and a pre-softening section, and the cooling rate of the pre-softening section is lower than the cooling rate of the pre-quenching section. A method for manufacturing a hot stamped part, wherein the temperature difference between the pre-softening section and the pre-quenching section is 200°C or more after the step of forming and cooling the heated blank is completed.

7. In paragraph 6, In the step of forming and cooling the heated blank, A method for manufacturing a hot stamped part, wherein the upper die and the lower die may include a groove, and the position where the groove is formed is adjacent to the preliminary softening section.

8. In paragraph 6, In the step of forming and cooling the heated blank, A method for manufacturing a hot stamped part, wherein a low heat-conducting material is placed between an upper die and the above-mentioned preliminary softening section, and a low heat-conducting material is placed between a lower die and the above-mentioned preliminary softening section.

9. In paragraph 6, In the step of forming and cooling the heated blank, A method for manufacturing a hot stamped part, wherein a heat generating unit is arranged in a portion adjacent to a preliminary softening unit of an upper die, and a heat generating unit is arranged in a portion adjacent to a preliminary softening unit of a lower die.

10. In paragraph 6, A method for manufacturing a hot stamped part, wherein after the step of controlling the forming and cooling of the heated blank is completed, the pre-softening section has a mixed microstructure of tempered martensite and bainite, and the pre-quenching section has a martensite microstructure.

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