Tailor welded blanks, hot formed components and their manufacturing methods

Abstract

Provided are a tailor welded blank and a hot-formed member having a welded portion that can effectively prevent deterioration of physical properties after hot forming, and methods for manufacturing the same. [Solution] The present invention includes a first base steel sheet, a first plated steel sheet including a first Al-based plating layer on at least one surface of the first base steel sheet, a second base steel sheet, a second plated steel sheet including a second Al-based plating layer on at least one surface of the second base steel sheet, and a welded joint located between the first plated steel sheet and the second plated steel sheet, connecting the first plated steel sheet and the second plated steel sheet, and satisfying the following [Relational Formula 1] and [Relational Formula 2], wherein the welded joint is: When the Ni content in the welded joint is 2.2% by weight or more, the following [Relationship 3] is satisfied, and when the Ni content in the welded joint is less than 2.2% by weight, the following [Relationship 4] is satisfied.

Description

[Technical field]

[0001] The present invention relates to a tailor welded blank, a hot-formed component, and a manufacturing method thereof, and more particularly to a tailor welded blank, a hot-formed component, and a manufacturing method thereof, each having a weld that can effectively prevent deterioration of physical properties after hot forming. [Background technology]

[0002] In recent years, there have been attempts to utilize ultra-high strength hot-formed components as structural components of automobiles in order to improve fuel efficiency and ensure passenger safety by reducing the weight of automobiles, and various research projects are being conducted in related fields.

[0003] Patent Document 1 discloses such a hot forming technique, in which an Al-Si plated steel sheet is heated to a temperature range of Ac1 or higher, and then the sheet is hot formed by pressing and rapidly cooled to make the structure of the base material consist of martensite, thereby ensuring a tensile strength of 1500 MPa or higher.

[0004] On the other hand, when a tailor welded blank is manufactured using an Al-Si plated steel sheet, there is a possibility that the components of the plated layer melted during laser welding may be mixed into the molten region. In particular, Al is a component that promotes the formation of ferrite, and the Al mixed into the molten region may prevent the welded joint after hot forming from becoming martensite to the desired level, and when an external force is transmitted to the final part, this may cause a fracture at the welded joint or the heat-affected zone adjacent to the welded joint. Patent Document 2 discloses a technique for performing laser welding after alloying the plated layer in order to prevent the phenomenon of the plated layer components flowing into the welded joint, but there is a limit to which the phenomenon of the Al components of the plated layer flowing into the welded joint cannot be completely prevented even by alloying the plated layer.

[0005] Patent Document 3 discloses a technique for partially removing the plating layer near the weld before laser welding in order to prevent the intrusion of Al components into the weld joint. When the plating layer near the weld is partially removed in this way, it is possible to partially alleviate the phenomenon in which the Al components of the plating layer flow into the weld joint, but it is necessary to introduce additional equipment for removing the plating layer, and the partial removal of the plating layer near the weld may result in a decrease in corrosion resistance in the area near the weld.

[0006] Therefore, there is a need for development of a technology that can effectively prevent the phenomenon in which the physical properties of the welded joint or the heat-affected zone adjacent to the welded joint are deteriorated due to the inflow of Al components into the welded joint even when welding is performed without ablation of part or all of the coating layer. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] European Patent Application Publication No. 0971044 [Patent Document 2] European Patent Application Publication No. 3805421 [Patent Document 3] Korean Patent Publication No. 10-2009-0005004 Summary of the Invention [Problem to be solved by the invention]

[0008] An object of the present invention is to provide a tailor welded blank and a hot-formed part having a welded part that can effectively prevent deterioration of physical properties after hot forming, and a method for manufacturing the same.

[0009] The subject of the present invention is not limited to the above-mentioned contents. A person skilled in the art will have no difficulty in understanding further subjects of the present invention from the overall content of this specification. [Means for solving the problem]

[0010] The tailor welded blank of the present invention includes a first base steel sheet, a first plated steel sheet including a first Al-based plating layer on at least one surface of the first base steel sheet, a second base steel sheet, a second plated steel sheet including a second Al-based plating layer on at least one surface of the second base steel sheet, and a welded joint located between the first plated steel sheet and the second plated steel sheet, connecting the first plated steel sheet and the second plated steel sheet, and satisfying the following [Relational formula 1] and [Relational formula 2], wherein the welded joint satisfies the following [Relational formula 3] when the Ni content contained in the welded joint is 2.2 wt% or more, and satisfies the following [Relational formula 4] when the Ni content contained in the welded joint is less than 2.2 wt%. [Equation 1] 4.44*[C]+0.355*[Mn]+0.505*[Ni]+0.148*[Cr]-[Al]-1.388>0 [Equation 2] 1.0<[Cr]<8.0 [Equation 3] 0.8≦[Ni] / [Cr]≦1.2 [Equation 4] 0.3≦[Mn] / [Cr]≦1.1 In the above [Relational Formula 1] to [Relational Formula 4], [C], [Mn], [Ni], [Cr] and [Al] respectively mean the contents (wt%) of C, Mn, Ni, Cr and Al contained in the welded joint.

[0011] The above welded joint can satisfy one or more of the following [Relationship 5] and [Relationship 6]. [Equation 5] [Mn]≦4.5 [Equation 6] [Ni]≦9.0 In the above [Relational formula 5] and [Relational formula 6], [Mn] and [Ni] mean the contents (wt %) of Mn and Ni contained in the welded joint.

[0012] The first Al-based plating layer may be any one selected from an Al-Si-based plating layer or an Al-Fe-based alloy plating layer, and the second Al-based plating layer may be any one selected from an Al-Si-based plating layer or an Al-Fe-based alloy plating layer.

[0013] The first base steel sheet or the second base steel sheet contains, by weight, C: 0.01 to 0.15%, Si: 0.1 to 0.5%, Mn: 0.5 to 2.5%, P: 0.05% or less, S: 0.01% or less, Al: 0.5% or less, Ti: 0.1% or less, Cr: 0.5% or less, Mo: 0.5% or less, B: 0.01% or less, with the remainder being Fe and other unavoidable impurities, or contains, by weight, C: more than 0.15% and 0.25% or less, Si: 0.1 to 0.5%, Mn: 0.5 to 2.5%, P: 0.05% or less, S: 0.01% or less, It may contain Al: 0.5% or less, Ti: 0.1% or less, Cr: 0.5% or less, Mo: 0.5% or less, B: 0.01% or less, with the remainder being Fe and other unavoidable impurities, or it may contain, by weight percentage, C: more than 0.25% and 0.45% or less, Si: 0.3 to 1.0%, Mn: 0.3 to 1.2%, P: 0.05% or less, S: 0.01% or less, Al: 0.5% or less, Ti: 0.1% or less, Cr: 0.5% or less, Mo: 0.5% or less, B: 0.01% or less, with the remainder being Fe and other unavoidable impurities.

[0014] A manufacturing method of a tailor welded blank of the present invention includes the steps of providing a first plated steel sheet and a second plated steel sheet having a first Al-based plating layer and a second Al-based plating layer formed on at least one surface of a first base steel sheet and a second base steel sheet, respectively, and a butt welding step of positioning the first plated steel sheet and the second plated steel sheet adjacent to each other and supplying a filler wire and irradiating a laser beam to form a weld joint so as to satisfy the following [Relational Formula 1] and [Relational Formula 2]. When the filler wire is a NiCr-based filler wire, butt welding can be performed so that the weld joint satisfies the following [Relational Formula 3], and when the filler wire is a CrMn-based filler wire, butt welding can be performed so that the weld joint satisfies the following [Relational Formula 4]. [Equation 1] 4.44*[C]+0.355*[Mn]+0.505*[Ni]+0.148*[Cr]-[Al]-1.388>0 [Equation 2] 1.0<[Cr]<8.0 [Equation 3] 0.8≦[Ni] / [Cr]≦1.2 [Equation 4] 0.3≦[Mn] / [Cr]≦1.1 In the above [Relational Formula 1] to [Relational Formula 4], [C], [Mn], [Ni], [Cr] and [Al] respectively mean the contents (wt%) of C, Mn, Ni, Cr and Al contained in the welded joint.

[0015] In the butt welding step, butt welding may be performed so that the welded joint satisfies at least one of the following [Relationship 5] and [Relationship 6]. [Equation 5] [Mn]≦4.5 [Equation 6] [Ni]≦9.0 In the above [Relational formula 5] and [Relational formula 6], [Mn] and [Ni] mean the contents (wt %) of Mn and Ni contained in the welded joint.

[0016] The NiCr-based filler wire is a filler wire containing, by weight, 0.15 to 0.40% C, 40.0 to 50.0% Ni, 30.0 to 40.0% Cr, 4.5% or less (including 0%) Mn, 8% or less (including 0%) Mo, 0.4% or less (including 0%) Si, and other unavoidable impurities, and the CrMn-based filler wire can be a filler wire containing, by weight, 0.1 to 0.25% C, 30.0 to 40.0% Cr, 8.0 to 20.0% Mn, 5.0 to 15.0% Ni, 0.4% or less (including 0%) Si, and other unavoidable impurities.

[0017] The dilution ratio of the filler wire provided to the molten pool formed by the laser beam is 5 to 2 0% It can be.

[0018] The output of the laser beam may be 2 to 10 kW, and the welding speed of the laser beam may be 1 to 6 m / min.

[0019] The first Al-based plating layer or the second Al-based plating layer may be an Al-Si-based plating layer formed by immersing the first base steel sheet or the second base steel sheet in an Al-Si-based plating bath, or an Al-Fe-based alloyed plating layer formed by alloying the Al-Si-based plating layer.

[0020] The butt welding can be performed without partial or total ablation of the first or second plating layer adjacent to the weld joint.

[0021] The first base steel sheet or the second base steel sheet contains, by weight, C: 0.01 to 0.15%, Si: 0.1 to 0.5%, Mn: 0.5 to 2.5%, P: 0.05% or less, S: 0.01% or less, Al: 0.5% or less, Ti: 0.1% or less, Cr: 0.5% or less, Mo: 0.5% or less, B: 0.01% or less, with the remainder being Fe and other unavoidable impurities, or contains, by weight, C: more than 0.15% and 0.25% or less, Si: 0.1 to 0.5%, Mn: 0.5 to 2.5%, P: 0.05% or less, S: 0.01% or less, It may contain Al: 0.5% or less, Ti: 0.1% or less, Cr: 0.5% or less, Mo: 0.5% or less, B: 0.01% or less, with the remainder being Fe and other unavoidable impurities, or it may contain, by weight percentage, C: more than 0.25% and 0.45% or less, Si: 0.3 to 1.0%, Mn: 0.3 to 1.2%, P: 0.05% or less, S: 0.01% or less, Al: 0.5% or less, Ti: 0.1% or less, Cr: 0.5% or less, Mo: 0.5% or less, B: 0.01% or less, with the remainder being Fe and other unavoidable impurities.

[0022] The hot-formed member of the present invention includes a first base steel sheet, a first plated steel sheet including a first Al-based plating layer on at least one surface of the first base steel sheet, a second base steel sheet, a second plated steel sheet including a second Al-based plating layer on at least one surface of the second base steel sheet, and a welded joint located between the first plated steel sheet and the second plated steel sheet and satisfying the following [Relational formula 1] and [Relational formula 2], wherein the first base steel sheet and the second base steel sheet each include 90% or more by area of ​​martensite as a microstructure, and the welded joint satisfies the following [Relational formula 3] when the Ni content contained in the welded joint is 2.2% by weight or more, and satisfies the following [Relational formula 4] when the Ni content contained in the welded joint is less than 2.2% by weight. [Equation 1] 4.44*[C]+0.355*[Mn]+0.505*[Ni]+0.148*[Cr]-[Al]-1.388>0 [Equation 2] 1.0<[Cr]<8.0 [Equation 3] 0.8≦[Ni] / [Cr]≦1.2 [Equation 4] 0.3≦[Mn] / [Cr]≦1.1 In the above [Relational Formula 1] to [Relational Formula 4], [C], [Mn], [Ni], [Cr] and [Al] respectively mean the contents (wt%) of C, Mn, Ni, Cr and Al contained in the welded joint.

[0023] The above welded joint can satisfy one or more of the following [Relationship 5] and [Relationship 6]. [Equation 5] [Mn]≦4.5 [Equation 6] [Ni]≦9.0 In the above [Relational formula 5] and [Relational formula 6], [Mn] and [Ni] mean the contents (wt %) of Mn and Ni contained in the welded joint.

[0024] The first Al-based plating layer and the second Al-based plating layer may be Al-Fe-based alloy plating layers.

[0025] The first base steel sheet or the second base steel sheet contains, by weight, C: 0.01 to 0.15%, Si: 0.1 to 0.5%, Mn: 0.5 to 2.5%, P: 0.05% or less, S: 0.01% or less, Al: 0.5% or less, Ti: 0.1% or less, Cr: 0.5% or less, Mo: 0.5% or less, B: 0.01% or less, with the remainder being Fe and other unavoidable impurities, or contains, by weight, C: more than 0.15% and 0.25% or less, Si: 0.1 to 0.5%, Mn: 0.5 to 2.5%, P: 0.05% or less, S: 0.01% or less, It may contain Al: 0.5% or less, Ti: 0.1% or less, Cr: 0.5% or less, Mo: 0.5% or less, B: 0.01% or less, with the remainder being Fe and other unavoidable impurities, or it may contain, by weight percentage, C: more than 0.25% and 0.45% or less, Si: 0.3 to 1.0%, Mn: 0.3 to 1.2%, P: 0.05% or less, S: 0.01% or less, Al: 0.5% or less, Ti: 0.1% or less, Cr: 0.5% or less, Mo: 0.5% or less, B: 0.01% or less, with the remainder being Fe and other unavoidable impurities.

[0026] When the first base steel sheet and the second base steel sheet are the same type of steel sheet, when the hardness value (Hv) is measured at the center of the thickness of the welded joint at an interval of 0.3 mm under a load of 500 gf, the maximum hardness value (Hv max ) and the average hardness value of the above base steel sheet (Hv mean ) and the difference (ΔH max ) and the absolute value of the minimum hardness value (Hv min ) and the average hardness value of the above base steel sheet (Hv mean ) and the difference (ΔH min ) may be 70Hv or less.

[0027] When the first base steel sheet and the second base steel sheet are dissimilar steel sheets, when the hardness value (Hv) is measured at the center of the thickness of the welded joint at an interval of 0.3 mm under a load of 500 gf, the maximum hardness value (Hv max ) is the average hardness value (Hv) of the center of the relatively hard base steel sheet of the first and second base steel sheets. mean 1) +50Hv or less, and the minimum hardness value of the above welded joint (Hvmin ) is the average hardness value (Hv) of the center of the relatively soft base steel sheet of the first and second base steel sheets. mean 2) It may have a hardness value of -50Hv or more.

[0028] The fracture rate at the welded joint may be less than 3% (including 0%).

[0029] The method for producing a hot-formed part of the present invention can include a heating step of heating the tailor-welded blank provided by the above-mentioned method for producing a tailor-welded blank to a temperature range equal to or higher than the austenitizing temperature, and a hot forming step of hot-forming the heated tailor-welded blank with a water-coolable die, and then immediately cooling it to a temperature range equal to or lower than the start of martensitic transformation.

[0030] The above solutions to the problems are not intended to be exhaustive, and the various features of the present invention and their associated advantages and benefits can be more fully understood with reference to the following specific examples. Effect of the Invention

[0031] According to the present invention, it is possible to provide a tailor welded blank that does not cause fracture at the welded joint or the heat-affected zone adjacent to the welded joint in a tensile test after hot forming, even if welding is performed without ablation of a part or all of the plating layer.

[0032] According to the present invention, it is possible to provide a hot-formed part that has high strength characteristics and excellent collision safety, and is suitable for use as an anti-intrusion part, an energy absorbing part, etc. of an automobile.

[0033] The effects of the present invention are not limited to the above-mentioned matters, but can be interpreted as including matters that a person of ordinary skill in the art can reasonably infer from the matters described in this specification. [Brief description of the drawings]

[0034] [Figure 1] 1 is a graph showing the results of measuring Vickers hardness of test piece 6. [Diagram 2] 2 is a graph showing the results of measuring the Vickers hardness of the test piece 10. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0035] The present invention relates to tailor welded blanks, hot formed parts and their manufacturing methods, and the following describes preferred embodiments of the present invention. The embodiments of the present invention can be modified in various ways, and the scope of the present invention should not be construed as being limited to the embodiments described below. The embodiments are provided to further explain the present invention to those skilled in the art to which the present invention pertains.

[0036] The tailor welded blank of the present invention will now be described in more detail.

[0037] The tailor welded blank of the present invention may include a weld joint provided between the first and second plated steel sheets and the first and second plated steel sheets to connect the first and second plated steel sheets. Although a tailor welded blank having a structure in which two plated steel sheets are connected via a weld joint will be described below as an example, the present invention may be interpreted as a concept including a tailor welded blank having a structure in which three or more plated steel sheets are connected via weld joints.

[0038] The first plated steel sheet may include a first base steel sheet and a first plating layer formed on at least one surface of the first base steel sheet, and the second plated steel sheet may include a second base steel sheet and a second plating layer formed on at least one surface of the second base steel sheet.

[0039] The first and second plating layers may be Al-based plating layers, and may be any one of an Al-Si-based plating layer and an Al-Fe-based plating layer. The first and second plating layers may be provided as the same or different plating layers.

[0040] As a non-limiting example, the Al-based plating layer may contain, by weight percent, 3 to 15% Si, the remainder Al, and other impurities that inevitably flow in. The impurities that inevitably flow into the Al-based plating layer can be interpreted as including components that flow in from the base steel.

[0041] The thickness of the first plating layer and the second plating layer is not particularly limited, and the first plating layer and the second plating layer may be provided with a thickness corresponding to that of a plated steel sheet used in the manufacture of a conventional tailor welded blank.

[0042] The first and second base steel sheets provided in the present invention are not particularly limited as long as they are steel sheets that can be hardened by hot forming.

[0043] As a non-limiting example, the first base steel sheet and the second base steel sheet may be steel sheets having any one component selected from the following steel sheets 1 to 3, and the first base steel sheet and the second base steel sheet may be prepared as the same or different components.

[0044] Steel plate 1: By weight, it contains C: 0.01-0.15%, Si: 0.1-0.5%, Mn: 0.5-2.5%, P: 0.05% or less, S: 0.01% or less, Al: 0.5% or less, Ti: 0.1% or less, Cr: 0.5% or less, Mo: 0.5% or less, B: 0.01% or less, and the remainder is Fe and other unavoidable impurities.

[0045] Steel plate 2: By weight, it contains C: more than 0.15% and not more than 0.25%, Si: 0.1 to 0.5%, Mn: 0.5 to 2.5%, P: not more than 0.05%, S: not more than 0.01%, Al: not more than 0.5%, Ti: not more than 0.1%, Cr: not more than 0.5%, Mo: not more than 0.5%, B: not more than 0.01%, and the remainder being Fe and other unavoidable impurities.

[0046] Steel plate 3: By weight, it contains C: more than 0.25% and not more than 0.45%, Si: 0.3 to 1.0%, Mn: 0.3 to 1.2%, P: not more than 0.05%, S: not more than 0.01%, Al: not more than 0.5%, Ti: not more than 0.1%, Cr: not more than 0.5%, Mo: not more than 0.5%, B: not more than 0.01%, and the remainder being Fe and other unavoidable impurities.

[0047] For example, steel plate 1 may have a tensile strength of about 500 to 1000 MPa after hot forming, steel plate 2 may have a tensile strength of about 1500 MPa after hot forming, and steel plate 3 may have a tensile strength of about 1800 MPa to 2000 MPa after hot forming.

[0048] The first and second base steel sheets may be provided with the same or different thicknesses, and the first and second base steel sheets may have a base steel sheet thickness corresponding to that of a plated steel sheet used in the manufacture of a typical tailor welded blank. Exemplarily, the first and second plated steel sheets may have a thickness of 0.8 to 2.8 mm.

[0049] The inventors of the present invention conducted in-depth research into the conditions under which no fracture occurs in the welded joint or the heat-affected zone adjacent to the welded joint in a tensile test after hot forming even if some of the Al component of the plating layer flows into the welded joint. They recognized that the collision safety of hot-formed components can be ensured by controlling the content of specific alloy components contained in the welded joint within a certain range, and thus derive the present invention.

[0050] The weld joints contained in the tailor welded blank of the present invention will be described in more detail below.

[0051] The tailor welded blank of the present invention can satisfy both of the following [Relational formula 1] and [Relational formula 2]. [Equation 1] 4.44*[C]+0.355*[Mn]+0.505*[Ni]+0.148*[Cr]-[Al]-1.388>0 [Equation 2] 1.0<[Cr]<8.0 In the above [Relational Formula 1] and [Relational Formula 2], [C], [Mn], [Ni], [Cr] and [Al] respectively mean the contents (weight %) of C, Mn, Ni, Cr and Al contained in the welded joint.

[0052] The inventors of the present invention recognized that stable austenitization of a welded joint during heating for hot forming is a major factor in suppressing the fracture rate of the welded joint, and derived [Relationship 1]. Even if Al, a ferrite-forming element, flows into the welded joint, the welded joint can be stably austenitized during the hot forming process by controlling the relative content range of C, Mn, Ni, Cr, and Al contained in the welded joint according to [Relationship 1], and homogeneous martensite can be formed in the welded joint. That is, since the alloy components of the welded joint are controlled according to [Relationship 1] in the present invention, the fracture rate of the welded joint can be limited to a level of less than 3% during a tensile test after hot forming. The fracture rate of the welded joint can be preferably 1% or less, and more preferably 0%. Meanwhile, the present invention does not particularly limit the upper limit of [Relationship 1], but the upper limit of [Relationship 1] can be limited to 5.0 from the viewpoint of ensuring economic efficiency.

[0053] The inventors of the present invention have confirmed that not only the relative contents of C, Mn, Ni, Cr, and Al contained in a welded joint, but also the individual content range of Cr contained in the welded joint are factors that have a major effect on the fracture rate of the welded joint, and have derived [Relationship 2]. Since Cr is an advantageous component for ensuring the strength of a welded joint, it can be contained in the welded joint at a level of 1.0 wt% or more as shown in [Relationship 2]. A preferred Cr content can be 2.0 wt% or more, and a more preferred Cr content can be 2.5 wt%. Meanwhile, since Cr is also a component that promotes the formation of ferrite, the Cr content contained in the welded joint can be limited to 8.0 wt% or less. A preferred Cr content can be 7 wt% or less, and a more preferred Cr content can be 5 wt% or less.

[0054] The tailor welded blank of the present invention can further satisfy either the following [Relationship 3] or [Relationship 4] depending on the Ni content in the welded joint. When the Ni content in the welded joint is 2.2 wt% or more, the following [Relationship 3] can be satisfied, and when the Ni content in the welded joint is less than 2.2 wt%, the following [Relationship 4] can be satisfied. [Equation 3] 0.8≦[Ni] / [Cr]≦1.2 [Equation 4] 0.3≦[Mn] / [Cr]≦1.1 In the above [Relational formula 3] and [Relational formula 4], [Mn], [Ni] and [Cr] respectively mean the contents (wt%) of Mn, Ni and Cr contained in the welded joint.

[0055] The inventors of the present invention confirmed that when the Ni content in the welded joint is 2.2 wt% or more, the relative contents of Ni and Cr in the welded joint are the main factors in ensuring the physical properties of the welded joint, and derived [Relationship 3].

[0056] When the Ni content of the welded joint is 2.2% by weight or more, if the ratio of the Ni content to the Cr content of the welded joint is too low, the austenite forming ability of the welded joint is reduced, and soft ferrite remains at room temperature, which may result in deterioration of the physical properties of the welded joint. Therefore, when the Ni content of the welded joint is 2.2% by weight or more, in order to ensure the physical properties of the welded joint, the ratio of the Ni content to the Cr content ([Ni] / [Cr]) can be limited to a level of 0.8 or more as shown in [Relationship 3], and more preferably, can be a level of 0.85 or more. On the other hand, when the Ni content of the welded joint is 2.2% by weight or more, if the ratio of the Ni content to the Cr content of the welded joint is too high, the austenite stability of the welded joint may be too high and austenite may remain even at room temperature, which may result in deterioration of the physical properties of the welded joint. Therefore, when the Ni content in the welded joint is 2.2 wt.% or more, in order to ensure the physical properties of the welded joint, the ratio of the Ni content to the Cr content ([Ni] / [Cr]) can be limited to a level of 1.2 or less, more preferably 1.1 or less, as shown in [Relationship 3].

[0057] When the Ni content of the welded joint is less than 2.2% by weight, if the ratio of the Mn content to the Cr content of the welded joint is too low, the austenite forming ability of the welded joint is reduced, and soft ferrite remains at room temperature, which may result in deterioration of the physical properties of the welded joint. Therefore, when the Ni content of the welded joint is less than 2.2% by weight, in order to ensure the physical properties of the welded joint, the ratio of the Mn content to the Cr content ([Mn] / [Cr]) can be limited to a level of 0.3 or more, as shown in [Relationship 4], and more preferably, can be a level of 0.4 or more. On the other hand, when the Ni content of the welded joint is less than 2.2% by weight, if the ratio of the Mn content to the Cr content of the welded joint is too high, the austenite stability of the welded joint may be too high, and austenite may remain even at room temperature, which may result in deterioration of the physical properties of the welded joint. Therefore, when the Ni content in the welded joint is less than 2.2% by weight, in order to ensure the physical properties of the welded joint, the ratio of the Mn content to the Cr content ([Mn] / [Cr]) can be limited to a level of 1.1 or less, more preferably 1.0 or less, as shown in [Relationship 4].

[0058] The tailor welded blank of the present invention can satisfy one or more of the following [Relationship 5] and [Relationship 6]. [Equation 5] [Mn]≦4.5 [Equation 6] [Ni]≦9.0 In the above [Relational formula 5] and [Relational formula 6], [Mn] and [Ni] mean the Mn and Ni contents (wt %) contained in the welded joint.

[0059] Ni and Mn are representative austenite stabilizing elements, and are elements that effectively contribute to uniform austenitization of welded joints during heating for hot forming. However, if the Ni and Mn contents exceed a certain range, austenite may exist in the welded joint even at room temperature due to excessive austenite stability, which may cause a deterioration in the physical properties of the welded joint. Therefore, as shown in [Relationship 5] and [Relationship 6], the Mn and Ni contents in the welded joint can be limited to 4.5 wt% or less and 9.0 wt% or less, respectively.

[0060] Because the tailor welded blank of the present invention controls the alloy composition of the weld joint as described above, even if plated steel sheets are welded without ablation of part or all of the plating layer, it is possible to effectively suppress the deterioration of physical properties that occurs when the Al component of the plating layer flows into the weld joint, and it is possible to effectively prevent fracture at the weld joint or the heat-affected zone adjacent to the weld joint in a tensile test after hot forming.

[0061] The method for producing a tailor welded blank of the present invention will now be described in more detail.

[0062] A method of making a tailor welded blank of the present invention may include providing a plated steel sheet and performing a butt weld.

[0063] In the step of providing the plated steel sheet, a first plated steel sheet having a first Al-based plating layer formed on at least one surface of a first base steel sheet and a second plated steel sheet having a second Al-based plating layer formed on at least one surface of a second base steel sheet can be provided.

[0064] The first Al-based plating layer and the second Al-based plating layer may be an Al-Si-based plating layer formed by immersing a base steel sheet in an Al-Si-based plating bath, or may be an Al-Fe-based alloyed plating layer provided by performing an alloying treatment after the formation of the Al-Si-based plating layer. The Al-Si-based plating bath may contain 3 to 15 wt % Si, the remainder Al, and other inevitable impurities.

[0065] Specific details regarding the first and second base steel sheets, the first plating layer and the second plating layer correspond to those of the above-mentioned plated steel sheets, and therefore the description of the plated steel sheets provided for the manufacture of the tailor welded blanks replaces the description of the above-mentioned plated steel sheets.

[0066] In the butt welding step, an end of the first plated steel sheet and an end of the second plated steel sheet are positioned adjacent to each other, and a laser beam is applied while a filler wire is supplied to form a welded joint. In this case, the butt welding can be performed after ablation is performed on a part or the whole of the first plated layer or the second plated layer in the adjacent regions, but the butt welding may be performed without ablation in part or in whole.

[0067] The filler wire used in the butt welding of the present invention may be a NiCr-based filler wire or a CrMn-based filler wire. The NiCr-based filler wire may mean a filler wire containing Ni and Cr as main components. As a non-limiting example, the NiCr-based filler wire may contain, by weight percent, C: 0.15 to 0.40%, Ni: 40.0 to 50.0%, Cr: 30.0 to 40.0%, Mn: 4.5% or less (including 0%), Mo: 8% or less (including 0%), Si: 0.4% or less (including 0%), and other inevitable impurities. The CrMn-based filler wire may mean a filler wire containing Cr and Mn as main components. As a non-limiting example, a CrMn-based filler wire may contain, by weight percent, C: 0.1-0.25%, Cr: 30.0-40.0%, Mn: 8.0-20.0%, Ni: 5.0-15.0%, Si: 0.4% or less (including 0%), and other unavoidable impurities.

[0068] In the butt welding stage, laser welding can be performed so that the weld joint formed by butt welding satisfies the following [Relationship 1] and [Relationship 2]. When butt welding is performed using a NiCr-based filler wire, laser welding can be performed so that the following [Relationship 3] is satisfied, and when butt welding is performed using a CrMn-based filler wire, laser welding can be performed so that the following [Relationship 4] is satisfied. [Equation 1] 4.44*[C]+0.355*[Mn]+0.505*[Ni]+0.148*[Cr]-[Al]-1.388>0 [Equation 2] 1.0<[Cr]<8.0 [Equation 3] 0.8≦[Ni] / [Cr]≦1.2 [Equation 4] 0.3≦[Mn] / [Cr]≦1.1 In the above [Relational Formula 1] to [Relational Formula 4], [C], [Mn], [Ni], [Cr] and [Al] respectively mean the contents (wt%) of C, Mn, Ni, Cr and Al contained in the welded joint.

[0069] The reasons for the limitations of [Relational formula 1] to [Relational formula 4] correspond to the reasons for the limitations of the relational formulas of the tailor welded blank described above, so the specific explanation of [Relational formula 1] to [Relational formula 4] replaces the explanation described above.

[0070] In the butt welding step, laser welding can be performed so that the welded joint satisfies one or more of the following [Relationship 5] and [Relationship 6]. [Equation 5] [Mn]≦4.5 [Equation 6] [Ni]≦9.0 In the above [Relational formula 5] and [Relational formula 6], [Mn] and [Ni] mean the Mn and Ni contents (wt %) contained in the welded joint.

[0071] The reasons for the limitations of [Relationship 5] and [Relationship 6] correspond to the reasons for the limitations of the relations of the tailor welded blank described above, so the specific explanation of [Relationship 5] and [Relationship 6] replaces the explanation described above.

[0072] The alloy composition of the weld joint is influenced in part by the alloy composition of the base steel sheet and the alloy composition of the coating layer, but can be influenced more significantly by the laser welding conditions. That is, the alloy composition of the weld joint can be controlled by the alloy composition of the filler wire used in laser welding, the rate at which the filler wire is diluted in the molten pool, the power of the laser beam, the welding speed of the laser beam, etc.

[0073] The method for producing a tailor welded blank of the present invention limits the filler wire used in laser welding to a NiCr-based filler wire or a CrMn-based filler wire so that the weld joint formed by butt welding satisfies the above-mentioned [Relational Formula 1] to [Relational Formula 6], and limits the dilution rate of the filler wire in the molten pool formed by the laser beam to 5 to 2 0% In this case, the laser beam output can be in the range of 2 to 10 kW, and the welding speed of the laser beam can be in the range of 1 to 6 m / min. In order to prevent oxidation of the molten metal during butt welding and to remove fumes, inert gases such as He and Ar can be used as protective gases, but are not necessarily limited thereto.

[0074] The hot-formed part and the method for producing the same of the present invention will be described in more detail below.

[0075] The hot-formed member of the present invention can be provided by hot forming the above-mentioned tailor-welded blank. That is, the hot-formed member of the present invention can be manufactured through a heating step of heating the above-mentioned tailor-welded blank to a temperature range equal to or higher than the austenitizing temperature, and a hot forming step of hot forming the tailor-welded blank heated in a water-coolable die and then immediately cooling it to a temperature range equal to or lower than the start of martensitic transformation.

[0076] The hot-formed member of the present invention may include a first plated steel sheet, a second plated steel sheet, and a welded joint connecting the first plated steel sheet and the second plated steel sheet. Since the hot-formed member of the present invention is provided by hot forming the above-mentioned tailor welded blank, there may be differences in the shape of the above-mentioned tailor welded blank, the composition of the plated layer, and the microstructure of the base steel sheet. During the hot forming process, alloying of the plated layer may occur, and some components of the base steel sheet may flow into the plated layer. Martensite may be formed in the base steel sheet through heating and quenching processes in the hot forming process, and the base steel sheet provided in the formed member may include about 90 area % or more (including 100%) of martensite.

[0077] Although the welded joint is transformed into martensite through the hot forming process, the alloy composition of the welded joint does not change significantly before and after the hot forming process. Therefore, the welded joint provided in the formed member of the present invention can also satisfy the above-mentioned [Relational formula 1] to [Relational formula 6].

[0078] The formed part of the present invention reduces local deviations in physical properties between the base steel plate and the welded joint, so that the fracture rate at the welded joint during a tensile test of the formed part can be controlled to less than 3% (including 0%).

[0079] When the first and second base steel sheets of the formed member are the same type of steel sheet, the maximum hardness value (Hv) of the welded joint is measured at the center of the thickness of the welded joint at an interval of 0.3 mm under a load of 500 gf. max ) and the average hardness value of the base steel sheet (Hvmean ) and the difference (ΔH max ) and the absolute value of the minimum hardness value of the welded joint (Hv min ) and the average hardness value of the base steel sheet (Hv mean ) and the difference (ΔH min ) may each have an absolute value of 70 Hv or less.

[0080] On the other hand, when the first and second base steel sheets provided in the formed member are different steel sheets, when the hardness value (Hv) is measured at the center of the thickness of the welded joint at an interval of 0.3 mm under a load of 500 gf, the maximum hardness value (Hv max ) is the average hardness value (Hv mean 1) +50Hv or less, and the minimum hardness value of the welded joint (Hv min ) is the average hardness value (Hv mean 2) It may have a hardness value of -50Hv or more.

[0081] Therefore, the molded member of the present invention not only has high strength characteristics, but also has excellent collision safety and physical properties suitable for use in anti-intrusion parts, energy absorbing parts, etc. of automobiles.

[0082] The tailor welded blank, hot formed member and manufacturing method thereof of the present invention will be described in more detail below with reference to specific examples. It should be noted that the following examples are merely for the purpose of understanding the present invention and are not intended to specify the scope of the present invention. The scope of the present invention can be determined by the matters described in the claims and matters that can be reasonably inferred therefrom. EXAMPLES

[0083] Tailor-welded blank test pieces were fabricated using the welding conditions shown in Table 1.

[0084] Base steel sheet A in Table 1 is a base steel sheet containing, by weight, C: 0.01-0.15%, Si: 0.1-0.5%, Mn: 0.5-2.5%, P: 0.05% or less, S: 0.01% or less, Al: 0.5% or less, Ti: 0.1% or less, Cr: 0.5% or less, Mo: 0.5% or less, B: 0.01% or less, with the remainder being Fe and other unavoidable impurities, and means a steel sheet that is capable of ensuring a tensile strength of approximately 1000 MPa after hot forming. Base steel sheet B is a base steel sheet containing, by weight, C: more than 0.15% and not more than 0.25%, Si: 0.1 to 0.5%, Mn: 0.5 to 2.5%, P: 0.05% or less, S: 0.01% or less, Al: 0.5% or less, Ti: 0.1% or less, Cr: 0.5% or less, Mo: 0.5% or less, B: 0.01% or less, with the remainder being Fe and other unavoidable impurities, and means a steel sheet that is capable of ensuring a tensile strength of approximately 1500 MPa after hot forming. Base steel sheet C is a base steel sheet containing, by weight, C: more than 0.25% and not more than 0.45%, Si: 0.3 to 1.0%, Mn: 0.3 to 1.2%, P: 0.05% or less, S: 0.01% or less, Al: 0.5% or less, Ti: 0.1% or less, Cr: 0.5% or less, Mo: 0.5% or less, B: 0.01% or less, with the remainder being Fe and other unavoidable impurities, and means a steel sheet that can ensure a tensile strength of approximately 1800 MPa after hot forming. Base steel sheets A to C were each manufactured to satisfy the thicknesses listed in Table 1.

[0085] Each base steel sheet was immersed in an aluminum plating bath containing 4 to 15% by weight of Si, and the aluminum was plated on one side at 10 to 40 g / m 2 With regard to pre-alloying, the mark "○" indicates that the plating layer was subjected to alloying treatment before laser welding, and the mark "×" indicates that the plating layer was not subjected to alloying treatment before laser welding.

[0086] For some of the test pieces before laser welding, an ablation treatment was performed to remove the plating layer on the edge side of the plated steel sheet. Regarding the ablation treatment, a mark "◯" indicates that the ablation treatment was performed, and a mark "×" indicates that the ablation treatment was not performed.

[0087] Butt welding was performed at a welding speed of 1 to 3 m / min using a laser beam whose power was adjusted in the range of 3 to 5 kW, and a filler wire was fed into the molten pool formed by the laser beam with the dilution ratio listed in Table 1. Of the filler wires listed in Table 1, NiCr-based filler wire refers to a filler wire containing, by weight, 0.15-0.40% C, 40.0-50.0% Ni, 30.0-40.0% Cr, 4.5% or less (including 0%) Mn, 8% or less (including 0%) Mo, 0.4% or less (including 0%) Si, and other unavoidable impurities, and CrMn-based filler wire refers to a filler wire containing, by weight, 0.1-0.25% C, 30.0-40.0% Cr, 8.0-20.0% Mn, 5.0-15.0% Ni, 0.4% or less (including 0%) Si, and other unavoidable impurities.

[0088] [Table 1]

[0089] For each test piece in Table 1, each test piece was heated to a temperature range of 870 to 950 ° C. and maintained for 5 minutes, and hot forming was simulated by press quenching using a mold capable of internal water cooling. Each test piece was cut to form a cross section perpendicular to the welding direction, and the alloy composition of the welded joint in the cross section of each test piece was analyzed using EPMA and EDS quantitative analysis of SEM. The welded part in the cross section of each test piece, excluding the welded heat affected zone, was divided into 8 to 12 regions, and area analysis was performed for each region, and the average values ​​of the component contents measured in each region are listed in Table 2. In addition, the substitution results of these component contents in Relation 1, Relation 3, and Relation 4 are also listed in Table 2. Tensile tests were conducted on multiple tensile test specimens (ISO 6892-1 Type 1, the weld was located in the direction perpendicular to the tensile load from the center of the parallel part) taken from each test piece, and the ratio of the number of tensile test specimens in which fracture occurred at the weld with respect to the number of tensile tests (number of tensile test specimens with weld fracture / total number of tensile test specimens) was calculated to measure the fracture rate of the weld of each test piece as shown in Table 2. Using a Vickers hardness tester, the hardness value (Hv) was measured at intervals of 0.3 mm at the center of the thickness of the weld joint under a load of 500 gf, and the maximum hardness value (Hv max ) and the average hardness value of the base steel sheet (Hv mean ) and the difference (ΔH max ) and the minimum hardness value of the welded joint (Hv min ) and the average hardness value of the base steel sheet (Hv mean ) and the difference (ΔH min ) were calculated and are shown in Table 2. Meanwhile, Figs. 1 and 2 are graphs showing the results of Vickers hardness measurements of test piece 6 and test piece 10, respectively. As shown in Fig. 1, it can be confirmed that in test piece 6, the base material portion of the first plated steel sheet exhibits an average hardness of about 490 Hv, the base material portion of the second plated steel sheet exhibits an average hardness of about 390 Hv, and the welded joint exhibits a hardness of 446 to 474 Hv. Also, as shown in Fig. 2, it can be confirmed that in test piece 10, the base material portion of the first plated steel sheet exhibits an average hardness of about 488 Hv, the base material portion of the second plated steel sheet exhibits an average hardness of about 563 Hv, and the welded joint exhibits a hardness of 525 to 551 Hv. That is, in test piece 6 and test piece 10, the maximum hardness value (Hv max) is the average hardness value (Hv mean 1) +50Hv" and the minimum hardness value of the welded joint (Hv min ) is the average hardness value (Hv mean 2) -50Hv" or higher, so it can be confirmed that the level is 3% or less.

[0090] [Table 1]

[0091] As shown in Tables 1 and 2, the test pieces satisfying the conditions of the present invention had a fracture rate of the welded joint. 3% The fracture rate of the welded part of the test piece not satisfying the conditions of the present invention is less than 100%. 3% It can be seen that it significantly exceeds

[0092] Therefore, the tailor welded blank of the present invention can provide a hot-formed component that does not suffer fracture at the welded joint or the heat-affected zone adjacent to the welded joint in a tensile test after hot forming, even if welding is performed without ablation of part or all of the plating layer.

[0093] Although the present invention has been described in detail with reference to the embodiments, other embodiments are possible, and therefore the technical spirit and scope of the claims set forth below are not limited to the embodiments.

Claims

1. a first base steel sheet; and a first plated steel sheet including a first Al-based plating layer on at least one surface of the first base steel sheet; a second base steel sheet, and a second plated steel sheet including a second Al-based plating layer on at least one surface of the second base steel sheet; The present invention includes a weld joint located between the first plated steel sheet and the second plated steel sheet, connecting the first plated steel sheet and the second plated steel sheet, and satisfying the following [Relational Formula 1] and [Relational Formula 2], The weld joint is A tailor welded blank, characterized in that when the Ni content in the welded joint is 2.2 wt% or more, the following [Relationship 3] is satisfied, and when the Ni content in the welded joint is less than 2.2 wt%, the following [Relationship 4] is satisfied. [Relationship 1] 4.44*[C]+0.355*[Mn]+0.505*[Ni]+0.148*[Cr]-[Al]-1.388>0 [Relationship 2] 1.0<[Cr]<8.0 [Relationship 3] 0.8≦[Ni] / [Cr]≦1.2 [Relationship 4] 0.3≦[Mn] / [Cr]≦1.1 In the above [Relational Formula 1] to [Relational Formula 4], [C], [Mn], [Ni], [Cr] and [Al] respectively mean the contents (wt%) of C, Mn, Ni, Cr and Al contained in the weld joint.

2. The first Al-based plating layer is any one selected from an Al-Si-based plating layer or an Al-Fe-based alloy plating layer, 2. The tailor welded blank according to claim 1, wherein the second Al-based plating layer is any one selected from an Al-Si-based plating layer and an Al-Fe-based alloy plating layer.

3. The first base steel sheet or the second base steel sheet has The alloy contains, by weight, C: 0.01-0.15%, Si: 0.1-0.5%, Mn: 0.5-2.5%, P: 0.05% or less, S: 0.01% or less, Al: 0.5% or less, Ti: 0.1% or less, Cr: 0.5% or less, Mo: 0.5% or less, B: 0.01% or less, with the remainder being Fe and other unavoidable impurities, The alloy contains, by weight, C: more than 0.15% and not more than 0.25%, Si: 0.1 to 0.5%, Mn: 0.5 to 2.5%, P: not more than 0.05%, S: not more than 0.01%, Al: not more than 0.5%, Ti: not more than 0.1%, Cr: not more than 0.5%, Mo: not more than 0.5%, B: not more than 0.01%, and the remainder being Fe and other unavoidable impurities, 2. The tailor welded blank according to claim 1, characterized in that it contains, by weight, C: more than 0.25% and not more than 0.45%, Si: 0.3 to 1.0%, Mn: 0.3 to 1.2%, P: not more than 0.05%, S: not more than 0.01%, Al: not more than 0.5%, Ti: not more than 0.1%, Cr: not more than 0.5%, Mo: not more than 0.5%, B: not more than 0.01%, and the remainder consisting of Fe and other unavoidable impurities.

4. providing a first plated steel sheet and a second plated steel sheet, in which a first Al-based plating layer and a second Al-based plating layer are formed on at least one surface of the first base steel sheet and the second base steel sheet, respectively; and The method includes a butt welding step of positioning the first plated steel sheet and the second plated steel sheet adjacent to each other, supplying a filler wire and irradiating a laser beam to form a weld joint so as to satisfy the following [Relationship 1] and [Relationship 2], A method for manufacturing a tailor welded blank, characterized in that, when the filler wire is a NiCr-based filler wire, butt welding is performed so that the weld joint satisfies the following [Relationship 3], and, when the filler wire is a CrMn-based filler wire, butt welding is performed so that the weld joint satisfies the following [Relationship 4]. [Relationship 1] 4.44*[C]+0.355*[Mn]+0.505*[Ni]+0.148*[Cr]-[Al]-1.388>0 [Relationship 2] 1.0<[Cr]<8.0 [Relationship 3] 0.8≦[Ni] / [Cr]≦1.2 [Relationship 4] 0.3≦[Mn] / [Cr]≦1.1 In the above [Relational Formula 1] to [Relational Formula 4], [C], [Mn], [Ni], [Cr] and [Al] respectively mean the contents (wt%) of C, Mn, Ni, Cr and Al contained in the weld joint.

5. The NiCr-based filler wire is a filler wire containing, by weight percent, C: 0.15 to 0.40%, Ni: 40.0 to 50.0%, Cr: 30.0 to 40.0%, Mn: 4.5% or less (including 0%), Mo: 8% or less (including 0%), Si: 0.4% or less (including 0%), and other unavoidable impurities; The method for manufacturing a tailor welded blank according to claim 4, characterized in that the CrMn-based filler wire is a filler wire containing, by weight, C: 0.1 to 0.25%, Cr: 30.0 to 40.0%, Mn: 8.0 to 20.0%, Ni: 5.0 to 15.0%, Si: 0.4% or less (including 0%), and other unavoidable impurities.

6. The method for manufacturing a tailor welded blank according to claim 4, characterized in that the dilution ratio of the filler wire provided to the molten pool formed by the laser beam is 5-20%.

7. The power of the laser beam is 2 to 10 kW, The method for manufacturing a tailor welded blank according to claim 4, characterized in that the welding speed of the laser beam is 1 to 6 m / min.

8. The first Al-based plating layer or the second Al-based plating layer is an Al-Si-based plating layer formed by immersing the first base steel sheet or the second base steel sheet in an Al-Si-based plating bath; The method for manufacturing a tailor welded blank according to claim 4, characterized in that the Al-Si based plating layer is an Al-Fe based alloyed plating layer formed by alloying the Al-Si based plating layer.

9. A method for manufacturing a tailor welded blank as claimed in claim 4, characterized in that butt welding is performed while omitting partial or total ablation of the first plating layer or the second plating layer adjacent to the weld joint.

10. The first base steel sheet or the second base steel sheet has The alloy contains, by weight, C: 0.01-0.15%, Si: 0.1-0.5%, Mn: 0.5-2.5%, P: 0.05% or less, S: 0.01% or less, Al: 0.5% or less, Ti: 0.1% or less, Cr: 0.5% or less, Mo: 0.5% or less, B: 0.01% or less, with the remainder being Fe and other unavoidable impurities, The alloy contains, by weight, C: more than 0.15% and not more than 0.25%, Si: 0.1 to 0.5%, Mn: 0.5 to 2.5%, P: not more than 0.05%, S: not more than 0.01%, Al: not more than 0.5%, Ti: not more than 0.1%, Cr: not more than 0.5%, Mo: not more than 0.5%, B: not more than 0.01%, and the remainder being Fe and other unavoidable impurities, 5. A method for producing a tailor welded blank as described in claim 4, characterized in that the material contains, by weight, C: more than 0.25% and not more than 0.45%, Si: 0.3 to 1.0%, Mn: 0.3 to 1.2%, P: not more than 0.05%, S: not more than 0.01%, Al: not more than 0.5%, Ti: not more than 0.1%, Cr: not more than 0.5%, Mo: not more than 0.5%, B: not more than 0.01%, and the remainder consisting of Fe and other unavoidable impurities.

11. a first base steel sheet; and a first plated steel sheet including a first Al-based plating layer on at least one surface of the first base steel sheet; A second base steel sheet, and a second plated steel sheet including a second Al-based plating layer on at least one surface of the second base steel sheet, and The weld joint is located between the first plated steel sheet and the second plated steel sheet and satisfies the following [Relational Formula 1] and [Relational Formula 2], The first base steel sheet and the second base steel sheet each contain 90% or more by area of ​​martensite as a microstructure, The weld joint is When the Ni content in the welded joint is 2.2 wt% or more, the following [Relationship 3] is satisfied, and when the Ni content in the welded joint is less than 2.2 wt%, the following [Relationship 4] is satisfied. [Relationship 1] 4.44*[C]+0.355*[Mn]+0.505*[Ni]+0.148*[Cr]-[Al]-1.388>0 [Relationship 2] 1.0<[Cr]<8.0 [Relationship 3] 0.8≦[Ni] / [Cr]≦1.2 [Relationship 4] 0.3≦[Mn] / [Cr]≦1.1 In the above [Relational Formula 1] to [Relational Formula 4], [C], [Mn], [Ni], [Cr] and [Al] respectively mean the contents (wt%) of C, Mn, Ni, Cr and Al contained in the weld joint.

12. The hot-formed member according to claim 11, wherein the first Al-based plating layer and the second Al-based plating layer are Al-Fe-based alloy plating layers.

13. The first base steel sheet or the second base steel sheet has The alloy contains, by weight, C: 0.01-0.15%, Si: 0.1-0.5%, Mn: 0.5-2.5%, P: 0.05% or less, S: 0.01% or less, Al: 0.5% or less, Ti: 0.1% or less, Cr: 0.5% or less, Mo: 0.5% or less, B: 0.01% or less, with the remainder being Fe and other unavoidable impurities, The alloy contains, by weight, C: more than 0.15% and not more than 0.25%, Si: 0.1 to 0.5%, Mn: 0.5 to 2.5%, P: not more than 0.05%, S: not more than 0.01%, Al: not more than 0.5%, Ti: not more than 0.1%, Cr: not more than 0.5%, Mo: not more than 0.5%, B: not more than 0.01%, and the remainder being Fe and other unavoidable impurities, The hot-formed member according to claim 11, characterized in that it contains, in weight percent, C: more than 0.25% and not more than 0.45%, Si: 0.3 to 1.0%, Mn: 0.3 to 1.2%, P: not more than 0.05%, S: not more than 0.01%, Al: not more than 0.5%, Ti: not more than 0.1%, Cr: not more than 0.5%, Mo: not more than 0.5%, B: not more than 0.01%, and the remainder consisting of Fe and other unavoidable impurities.

14. When the first base steel sheet and the second base steel sheet are the same type of steel sheet, when the hardness value (Hv) is measured at an interval of 0.3 mm at the thickness center of the welded joint under a load of 500 gf, the maximum hardness value (Hv ｍａｘ ) and the average hardness value (Hv ｍｅａｎ ) and the difference (ΔH ｍａｘ ) and the absolute value of the minimum hardness value (Hv ｍｉｎ ) and the average hardness value (Hv ｍｅａｎ ) and the difference (ΔH ｍｉｎ 14. The hot formed part according to claim 13, characterized in that the absolute value of Hv is 70 Hv or less.

15. When the first base steel sheet and the second base steel sheet are different types of steel sheets, when the hardness value (Hv) is measured at an interval of 0.3 mm at the thickness center of the welded joint under a load of 500 gf, the maximum hardness value (Hv ｍａｘ ) is the average hardness value (Hv) of the center part of the first and second base steel sheets, which is relatively hard. ｍｅａｎ 1) +50Hv or less, and the minimum hardness value of the welded joint (Hv ｍｉｎ ) is the average hardness value (Hv) of the central portion of the relatively soft base steel sheet of the first and second base steel sheets. ｍｅａｎ 2) A hardness value of -50 Hv or more.

16. The hot-formed component according to claim 11, characterized in that the fracture rate at the welded joint is less than 3% (including 0%).

17. A heating step of heating the tailor welded blank provided by the manufacturing method according to any one of claims 4 to 10 to a temperature range equal to or greater than the austenitizing temperature; The method for producing a hot-formed part includes a hot forming step of hot forming the heated tailor welded blank with a water-coolable die, and then immediately cooling the hot-formed blank to a temperature range below the onset of martensitic transformation.

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