Hot stamping component and method of manufacturing the same

Abstract

The present invention relates to a hot stamping part comprising a base steel plate and a zinc-based plating layer on the base steel plate, wherein the base steel plate comprises carbon (C) 0.25 wt% or more and 0.50 wt% or less, silicon (Si) 0.10 wt% or more and 0.80 wt% or less, manganese (Mn) 0.30 wt% or more and 3.0 wt% or less, phosphorus (P) 0 or more and 0.05 wt% or less, sulfur (S) 0 or more and 0.01 wt% or less, boron (B) 0.0005 wt% or more and 0.005 wt% or less, chromium (Cr) 0.01 wt% or more and 1.0 wt% or less, molybdenum (Mo) 0.01 wt% or more and 1.0 wt% or less, nickel (Ni) 0.001 wt% or more and 1.0 wt% or less, and at least one of titanium (Ti), niobium (Nb), and vanadium (V). A hot stamping part is provided that comprises a total of 0.01 weight% or more and 0.1 weight% or less, with the remainder being iron (Fe) and other unavoidable impurities, wherein the plating layer comprises a zinc-rich phase (Zn-rich) and an iron-zinc alloy phase, and the zinc-rich phase has a fraction of 20% to 40% of the entire plating layer.

Description

Technology Field

[0001] The present invention relates to a hot stamping part having excellent formability during hot stamping and a method for manufacturing the same. Background Technology

[0002] With the recent tightening of environmental regulations and safety standards in the automotive industry, the application of high-strength steel for vehicle lightweighting and stability is increasing. While high-strength steel can secure high strength-to-weight ratio characteristics, it can be difficult to form products with complex and precise shapes due to material fracture or springback phenomena occurring during processing.

[0003] Hot stamping is a method to address these issues, and as interest in it grows, research on materials for hot stamping is also actively being conducted. For example, as disclosed in Korean Published Patent Application No. 10-2017-0076009, hot stamping is a forming technology that manufactures high-strength parts by heating a steel plate for hot stamping to a high temperature and then forming and rapidly cooling it simultaneously within a press mold.

[0004] While the hot stamping process offers the advantage of easily forming parts while suppressing springback after forming, it involves high process costs and requires methods to inhibit surface oxidation at high temperatures. Accordingly, active research is being conducted on methods to suppress surface oxidation and enhance corrosion resistance in hot stamping steel sheets by applying a plating layer.

[0005] For example, while Al-Si plating layers exhibit excellent high-temperature oxidation resistance, they have the disadvantage of causing cracking and detachment of the plating layer during processing due to the high hardness of the layer and pores present on the plating surface after hot stamping, thereby reducing formability and decreasing corrosion resistance due to plating loss. Furthermore, since Al-Si plated steel sheets do not possess sacrificial protection capabilities within the plating layer itself, they have the disadvantage of immediately developing red rust in corrosive environments if scratches or cracks occur in the coating layer due to external impact. To overcome these drawbacks, hot stamping technology utilizing zinc-plated steel sheets with sacrificial protection is being developed. Prior art literature

[0006] (Patent Document 0001) KR 2018-0095757 A The problem to be solved

[0007] The present invention aims to solve various problems, including the problems mentioned above, and can provide a hot stamping part with excellent sacrificial properties and a method for manufacturing the same.

[0008] However, these tasks are exemplary and do not limit the scope of the invention. means of solving the problem

[0009] According to one aspect of the present invention, the invention relates to a hot stamping part comprising a base steel plate and a zinc-based plating layer on the base steel plate, wherein the base steel plate comprises carbon (C) 0.25 wt% or more and 0.50 wt% or less, silicon (Si) 0.10 wt% or more and 0.80 wt% or less, manganese (Mn) 0.30 wt% or more and 3.0 wt% or less, phosphorus (P) 0 or more and 0.05 wt% or less, sulfur (S) 0 or more and 0.01 wt% or less, boron (B) 0.0005 wt% or more and 0.005 wt% or less, chromium (Cr) 0.01 wt% or more and 1.0 wt% or less, molybdenum (Mo) 0.01 wt% or more and 1.0 wt% or less, nickel (Ni) 0.001 wt% or more and 1.0 wt% or less, and at least one of titanium (Ti), niobium (Nb), and vanadium (V). A hot stamping part is provided that comprises one or more types totaling 0.01 weight% or more and 0.1 weight% or less, with the remainder being iron (Fe) and other unavoidable impurities, wherein the plating layer comprises a zinc-rich phase (Zn-rich) and an iron-zinc alloy phase, and the zinc-rich phase has a fraction of 20% to 40% of the entire plating layer.

[0010] In one embodiment, the corrosion potential value of the plating layer may be -650 mV to -800 mV.

[0011] In one embodiment, the thickness of the plating layer may be 10㎛ to 40㎛.

[0012] In one embodiment, the plating layer adhesion amount is 40 g / m² per piece. 2 Up to 120 g / m² 2 It could be.

[0013] In one embodiment, the plating layer may contain 10 wt% or more of iron (Fe) and 70 wt% or less of aluminum (Al), 0 wt% or more of aluminum (Al) and 5 wt% or less of manganese (Mn), 0 wt% or more of silicon (Si) and 1 wt% or less of silicon (Si), 33 wt% or more of zinc (Zn) and 99 wt% or less of other impurities.

[0014] In one embodiment, the iron-zinc alloy phase may be located in a portion of the plating layer adjacent to the substrate steel plate.

[0015] In one embodiment, the hot stamping part may contain 90% or more martensite.

[0016] In one embodiment, the tensile strength (TS) of the hot stamping part may be 1680 MPa to 2000 MPa.

[0017] In one embodiment, the yield strength (YP) of the hot stamping part can be found to be 1150 MPa to 1500 MPa.

[0018] In one embodiment, the elongation of the hot stamping part may be 4% or more and 10% or less.

[0019] According to one aspect of the present invention, a method for manufacturing a hot stamping part is provided, comprising: a plating layer forming step of forming a zinc-based plating layer on a base steel plate; a heating step of introducing the base steel plate on which the plating layer is formed into a heating furnace and heating it; a transfer step of transferring the heated base steel plate from the heating furnace to a press mold; a forming step of hot stamping the transferred base steel plate to form a molded body; and a step of cooling the molded body; wherein the heating step is a step of heating the steel plate at a heating temperature of 850°C to 910°C for 240 seconds to 360 seconds.

[0020] In one embodiment, the heating step may be a step of controlling the average heating rate from 700°C to the heating temperature to 1.5°C / s to 7°C / s.

[0021] In one embodiment, in the molding step, the molding start temperature is 550°C to 750°C, and the average cooling rate may be 25°C / s or higher.

[0022] In one embodiment, the thickness of the base steel plate may be 1 mm to 2.5 mm.

[0023] In one embodiment, in the step of forming the plating layer, the amount of plating deposited is 40 g / m² per piece. 2 Up to 120g / m² 2 It could be.

[0024] In one embodiment, the base steel sheet comprises carbon (C) 0.25 wt% or more and 0.50 wt% or less, silicon (Si) 0.10 wt% or more and 0.80 wt% or less, manganese (Mn) 0.30 wt% or more and 3.0 wt% or less, phosphorus (P) 0 or more and 0.05 wt% or less, sulfur (S) 0 or more and 0.01 wt% or less, boron (B) 0.0005 wt% or more and 0.005 wt% or less, chromium (Cr) 0.01 wt% or more and 1.0 wt% or less, molybdenum (Mo) 0.01 wt% or more and 1.0 wt% or less, nickel (Ni) 0.001 wt% or more and 1.0 wt% or less, at least one of titanium (Ti), niobium (Nb), and vanadium (V) in a total of 0.01 wt% or more and 0.1 wt% or less, and the remainder being iron (Fe) and It may contain other unavoidable impurities.

[0025] In one embodiment, in the plating layer forming step, the plating bath may contain iron (Fe) 10 wt% or more and 70 wt% or less, aluminum (Al) 0 wt% or more and 5 wt% or less, manganese (Mn) 0 wt% or more and 1 wt% or less, silicon (Si) 0 wt% or more and 1 wt% or less, zinc (Zn) 33 wt% or more and 99 wt% or less, and other impurities.

[0026] Other aspects, features, and advantages other than those described above will become clear from the following specific details, claims, and drawings for implementing the invention. Effects of the invention

[0027] According to one embodiment of the present invention as described above, a hot stamping steel sheet having excellent surface quality and excellent bake hardening amount, and a method for manufacturing the same can be provided. Of course, the scope of the present invention is not limited by these effects. Brief explanation of the drawing

[0028] FIG. 1 is an SEM image showing a partial cross-section of a hot stamping part according to one embodiment of the present invention. FIG. 2 is a flowchart schematically illustrating a method for manufacturing a steel plate for hot stamping according to one embodiment of the present invention. FIG. 3 is a flowchart schematically illustrating a method for manufacturing a hot stamping part using a hot stamping steel plate according to one embodiment of the present invention. FIG. 4 is SEM images showing a partial cross-section of a hot stamping part according to an embodiment and a comparative example of the present invention. Specific details for implementing the invention

[0029] The present invention will be described in detail below. However, in describing the present invention, if it is determined that a detailed description of related known technologies or configurations may unnecessarily obscure the essence of the present invention, such detailed description will be omitted.

[0030] In the following embodiments, terms such as first, second, etc. are used not in a limiting sense, but for the purpose of distinguishing one component from another component.

[0031] In the following examples, singular expressions include plural expressions unless the context clearly indicates otherwise.

[0032] In the following embodiments, when various components such as layers, films, regions, and plates are described as being "on" another component, this includes not only cases where they are "directly on" another component, but also cases where another component is interposed between them.

[0033] In the drawings, the size of components may be exaggerated or reduced for convenience of explanation. For example, the size and thickness of each component shown in the drawings are depicted arbitrarily for convenience of explanation, and therefore the present invention is not necessarily limited to what is illustrated.

[0034] In the following embodiments, terms such as "include" or "have" mean that the features or components described in the specification are present, and do not preclude the possibility that one or more other features or components may be added.

[0035] In this specification, "A and / or B" indicates the case where it is A, B, or both A and B. Additionally, in this specification, "at least one of A and B" indicates the case where it is A, B, or both A and B.

[0036] Unless otherwise defined, all terms used herein, including technical and scientific terms, have the same meaning as generally understood by those skilled in the art to which this invention pertains. Terms defined in commonly used dictionaries are further interpreted to have meanings consistent with relevant technical literature and the present disclosure, and are not interpreted in an ideal or highly formal sense unless otherwise defined.

[0037] Hereinafter, embodiments of the present invention are described in detail so that those skilled in the art can easily implement the invention. However, the present invention may be embodied in various different forms and is not limited to the embodiments described herein.

[0039] FIG. 1 is an SEM image showing a partial cross-section of a hot stamping part according to one embodiment of the present invention.

[0040] Referring to FIG. 1, a hot stamping part (1) according to one embodiment of the present invention comprises a base steel plate (10) and a plating layer (20) disposed on the base steel plate (10). The plating layer (20) may include a zinc-rich phase (Zn-rich) (22) and an iron-zinc alloy phase (24).

[0041] In one embodiment, the base steel plate (10) of the hot stamping part (1) comprises carbon (C) 0.25 wt% or more and 0.50 wt% or less, silicon (Si) 0.10 wt% or more and 0.80 wt% or less, manganese (Mn) 0.30 wt% or more and 3.0 wt% or less, phosphorus (P) 0 or more and 0.05 wt% or less, sulfur (S) 0 or more and 0.01 wt% or less, boron (B) 0.0005 wt% or more and 0.005 wt% or less, chromium (Cr) 0.01 wt% or more and 1.0 wt% or less, molybdenum (Mo) 0.01 wt% or more and 1.0 wt% or less, nickel (Ni) 0.001 wt% or more and 1.0 wt% or less, and at least one of titanium (Ti), niobium (Nb), and vanadium (V) in total 0.01 wt% or more. It may contain 0.1% by weight or less, and the remainder being iron (Fe) and other unavoidable impurities.

[0042] The reason why the numerical range of the components included in the steel plate (10) is limited is explained below.

[0043] Carbon (C)

[0044] Carbon is an element that increases the strength of steel and stabilizes austenite. In one embodiment, the carbon content in the base steel plate (10) may be 0.25 weight% or more and 0.50 weight% or less. If the carbon content in the base steel plate (10) is less than 0.25 weight%, the strength is reduced, and if the carbon content in the base steel plate (10) is more than 0.50 weight%, weldability may be reduced.

[0045] Silicon (Si)

[0046] Silicon has an excellent effect on increasing strength, homogenizes the hot stamping structure, and finely disperses ferrite. In one embodiment, the silicon content in the base steel plate (10) may be 0.10 weight% or more and 0.80 weight% or less. If the silicon content in the base steel plate (10) is less than 0.10 weight%, the effect on increasing strength is negligible, and if the silicon content in the base steel plate (10) exceeds 0.80 weight%, the plating quality may be degraded.

[0047] Manganese (Mn)

[0048] Manganese is an element that increases the strength of steel and stabilizes austenite. In one embodiment, the manganese content in the base steel plate (10) may be 0.30 wt% or more and 3.0 wt% or less. If the manganese content in the base steel plate (10) is less than 0.30 wt%, the strength is reduced, and if the manganese content in the base steel plate (10) is more than 3.0 wt%, the formability and bendability may be reduced.

[0049] Ph(P)

[0050] Phosphorus can reduce weldability and increase the brittleness of the steel plate. In one embodiment, the phosphorus content in the base steel plate (10) may be 0 or more and 0.05 weight% or less. If the phosphorus content in the base steel plate (10) exceeds 0.05 weight%, the brittleness may increase, making processing difficult.

[0051] Yellow (S)

[0052] Sulfur can reduce weldability and increase the brittleness of the steel plate. In one embodiment, the sulfur content in the base steel plate (10) may be 0 or more and 0.01 weight% or less. If the sulfur content in the base steel plate (10) exceeds 0.01 weight%, the brittleness may increase, making processing difficult.

[0053] Boron (B)

[0054] Boron has the effect of improving hardenability and increasing the strength of the steel plate. In one embodiment, the boron content in the base steel plate (10) may be 0.0005 weight% or more and 0.005 weight% or less. If the boron content in the base steel plate (10) is less than 0.0005 weight%, the hardenability may not be sufficient, and if the boron content in the base steel plate (10) exceeds 0.005 weight%, grain boundary brittleness may occur.

[0055] Chrome (Cr)

[0056] Chromium has the effect of refining grain size and improving hardenability and increasing the strength of the steel plate. In one embodiment, the chromium content in the base steel plate (10) may be 0.01 weight% or more and 1.0 weight% or less. If the chromium content in the base steel plate (10) is less than 0.01 weight%, sufficient strength cannot be secured, and if the chromium content in the base steel plate (10) exceeds 1.0 weight%, the toughness of the steel plate is reduced and the manufacturing cost of the steel plate may increase.

[0057] Molybdenum (Mo)

[0058] Molybdenum is a substitutional element that improves the strength of steel through solid solution strengthening effects. Molybdenum is added for the purpose of suppressing precipitate coarsening and improving hardenability. In addition, molybdenum can play a role in improving the hardenability of steel. In one embodiment, the molybdenum content in the base steel plate (10) may be 0.01 weight% or more and 1.0 weight% or less. If the molybdenum content is less than 0.01 weight%, the above effects cannot be properly exerted. On the other hand, if the molybdenum content exceeds 1.0 weight%, there is a risk of a decrease in rolling productivity and elongation, and there is a problem of increasing manufacturing costs without additional effects.

[0059] Nickel (Ni)

[0060] Nickel is an element effective for improving toughness while improving hardenability. In one embodiment, the nickel content in the base steel sheet (10) may be 0.001 weight% or more and 1.0 weight% or less. If the nickel content is less than 0.001 weight%, the effect of the addition is negligible. On the other hand, if the nickel content exceeds 1.0 weight%, there is a problem of lowering the workability of the steel sheet and increasing manufacturing costs.

[0061] Titanium (Ti)

[0062] Titanium can effectively contribute to grain refinement by forming precipitates at high temperatures. In one embodiment, the titanium content in the base steel plate (10) may be 0.01 weight% or more and 0.1 weight% or less. When titanium is included within the above content range, continuous casting defects and precipitate coarsening can be prevented, the physical properties of the steel can be easily secured, and defects such as cracks on the surface of the steel can be prevented. If the titanium content is less than 0.01 weight%, it is difficult to sufficiently achieve the grain refinement effect, whereas if the titanium content exceeds 0.1 weight%, precipitates coarsen, which may result in a decrease in elongation and bendability.

[0063] Niobium (Nb) and vanadium (V)

[0064] Niobium and vanadium are powerful carbide-forming elements that have a grain refinement effect, such as a reduction in martensite packet size, and have the effect of improving hardenability and increasing the strength of the steel sheet. In one embodiment, the niobium and vanadium content in the base steel sheet (10) may each be 0 or more and 0.1 weight% or less. When niobium and vanadium are included in the above range, the grain refinement effect of the steel material is excellent during the hot rolling and cold rolling processes, preventing cracks in the slab and brittle fracture of the product during steelmaking / continuous casting, and minimizing the formation of coarse precipitates during steelmaking.

[0065] In one embodiment, at least one of titanium (Ti), niobium (Nb), and vanadium (V) included in the base steel plate (10) may have a total of 0.01 weight% or more and 0.1 weight% or less. As described above, titanium (Ti), niobium (Nb), and vanadium (V) are elements involved in the formation of precipitates and grain refinement, and when included within the above range, precipitate coarsening is prevented, thereby ensuring optimal steel properties.

[0066] It will be understood by anyone with ordinary knowledge in the technical field to which this invention pertains that, in addition to the components described above, various components (including impurities) included in steel sheets for hot stamping may be included as components of the steel sheets for hot stamping according to the present invention. Combinations of commonly known components and their applications naturally fall within the scope of the rights of this invention.

[0067] The plating layer (20) can be provided on one side or both sides of the base steel plate (10).

[0068] In one embodiment, the plating layer (20) may be a zinc-based plating layer. A hot stamping steel sheet having a zinc-based plating layer as the plating layer (20) may be, for example, a hot-dip galvanized steel sheet or an alloyed hot-dip galvanized steel sheet. The plating layer (20) may contain iron (Fe) 10 wt% or more and 70 wt% or less, aluminum (Al) 0 wt% or more and 5 wt% or less, manganese (Mn) 0 wt% or more and 1 wt% or less, silicon (Si) 0 wt% or more and 1 wt% or less, zinc (Zn) 33 wt% or more and 99 wt% or less, and other impurities.

[0069] The plating layer (20) may include a zinc-rich phase (22) and an iron-zinc alloy phase (24). In other words, the plating layer (20) may mean a layer in which the zinc-rich phase (22) and the iron-zinc alloy phase (24) exist.

[0070] In one embodiment, the zinc-rich phase (22) is, for example, a gamma phase (Γ phase, Fe3Zn 10It may be. The zinc-rich phase (22) is a portion of the plating layer (20) with a high proportion of zinc, and may be a phase formed by alloying the zinc contained in the plating bath with the iron contained in the base steel plate (10). Accordingly, the zinc-rich phase (22) may have a lower iron concentration and a higher zinc concentration compared to the iron-zinc alloy phase (24). In one embodiment, the zinc-rich phase (22) may contain a zinc concentration of 70 weight% or more and 90 weight% or less, and an iron concentration of 10 weight% or more and 30 weight% or less.

[0071] During the hot stamping process, the plating layer (20) placed on the substrate steel plate (10) contains a zinc-rich phase (22) and an iron-zinc alloy phase (24) due to Fe-Zn diffusion caused by heat. Among these, the zinc-rich phase (22) has a face-centered cubic (FCC) structure and thus has a higher density compared to other phases contained within the plating layer (20). By including the zinc-rich phase (22) within the plating layer (20), the sacrificial corrosion resistance of the hot stamping part (1) can be improved. If the zinc-rich phase (22) is not included within the plating layer (20), the corrosion resistance of the plating layer (20) may deteriorate. On the other hand, if the zinc-rich phase (22) is excessively included within the plating layer (20), there is a problem of cracking being induced during hot stamping. Therefore, in the hot stamping part (1) according to one embodiment of the present invention, it is important to control the zinc-rich phase (22) so that it is included within the plating layer (20) within an appropriate range.

[0072] In one embodiment, the fraction of the zinc-rich phase (22) within the plating layer (20) may be 20% to 40%. Optimal sacrificial corrosion resistance can be achieved when the fraction of the zinc-rich phase (22) within the plating layer (20) satisfies the above range. Specifically, if the fraction of the zinc-rich phase (22) is less than 20% of the total plating layer (20), it is difficult for the plating layer (20) to secure sufficient sacrificial corrosion resistance, and if the fraction of the zinc-rich phase (22) exceeds 40% of the total plating layer (20), it is unsuitable because liquid metal embrittlement (LME) may occur during hot stamping part forming.

[0073] In this way, the electrochemical corrosion potential value of the plating layer (20) containing the zinc-rich phase (22) within the range described above may be -650 mV or higher and -800 mV or lower. The corrosion potential value of the plating layer (20) may be controlled within the range described above so that the plating layer (20) has sacrificial corrosion resistance. In this specification, the corrosion potential value may refer to the average value obtained by measuring the open circuit potential (OPC) for about one hour using electrochemical analysis equipment, or the corrosion potential value obtained through a potentiodynamic experiment. The corrosion potential value may be controlled by the fraction of the zinc-rich phase (22) described above. In other words, if the fraction of the zinc-rich phase (22) within the plating layer (20) is less than 20%, it may be difficult for the corrosion potential value to satisfy the range described above.

[0074] In one embodiment, the fraction of the zinc-rich phase (22) can be controlled through the thickness of the plating layer (20). In one embodiment, the thickness of the plating layer (20) may be 10 μm or more and 40 μm or less. The thickness of the plating layer (20) may refer to the thickness of the plating layer (20) after the hot stamping process. If the thickness of the plating layer (20) is less than 10 μm, the thickness of the plating layer (20) is too thin, which limits the process conditions for forming the zinc-rich phase (22), and if it exceeds 40 μm, the thickness of the plating layer (20) becomes too thick, which increases the amount of zinc scattering during the hot stamping process and may cause liquid metal embrittlement (LME) during molding.

[0075] In addition, the fraction of the zinc-rich phase (22) can be controlled by the heat treatment temperature and heat treatment time during the heating step (S220) in the hot stamping process during the manufacturing process. This will be explained in detail in the method for manufacturing a hot stamping part described with reference to FIGS. 2 and FIGS. 3.

[0076] In one embodiment, the iron-zinc alloy phase (24) may include, for example, alpha-Fe(Zn) (α-Fe(Zn)) as an iron-zinc intermetallic compound phase. The iron-zinc alloy phase (24) may be formed by alloying the zinc of the plating layer with the iron of the base steel plate during the plating layer formation step (or, plating layer alloying step). The iron-zinc alloy phase (24) may be provided near the boundary between the base steel plate (10) and the plating layer (20) to improve the adhesion between the base steel plate (10) and the plating layer (20). The iron-zinc alloy phase (24) may be located, for example, below the zinc-rich phase (22), that is, between the zinc-rich phase (22) and the base steel plate (10).

[0077] Meanwhile, as an optional embodiment, in addition to the zinc-rich phase (22) and the iron-zinc alloy phase (24), the plating layer (20) may further include a delta phase (δ phase) and a zeta phase (ξ phase). In this case, the fraction of the delta phase (δ phase) and the zeta phase (ξ phase) may be less than 10 weight percent.

[0078] The tensile strength of a hot stamping part (1) according to one embodiment of the present invention having the organizational structure as described above may be 1680 MPa or more and 2000 MPa or less, and more preferably, the tensile strength of the hot stamping part (1) may be 1750 MPa or more and 1900 MPa or more.

[0079] Additionally, the yield strength of the hot stamping part (1) may be 1150 MPa or more and 1500 MPa or less, and more preferably, the yield strength of the hot stamping part (1) may be 1250 MPa or more and 1400 MPa or more.

[0080] In addition, the elongation of the hot stamping part (1) may be 4% or more and 10% or less.

[0081] FIG. 2 is a flowchart schematically illustrating a method for manufacturing a steel plate for hot stamping according to one embodiment of the present invention, and FIG. 3 is a flowchart schematically illustrating a method for manufacturing a hot stamping part using a steel plate for hot stamping according to one embodiment of the present invention.

[0082] Referring to FIG. 1, a method for manufacturing a steel sheet for hot stamping according to one embodiment of the present invention may include a hot rolling step (S110), a cold rolling step (S120), an annealing heat treatment step (S130), a plating layer forming step (S140), and a post-treatment step (S150).

[0083] In a method for manufacturing a steel plate for hot stamping according to one embodiment of the present invention, the semi-finished product subject to hot rolling may be a slab. The slab in the semi-finished product state can be obtained through a continuous casting process after obtaining molten steel of a predetermined composition through a steelmaking process.

[0084] In one embodiment, the slab comprises carbon (C) 0.25 wt% or more and 0.50 wt% or less, silicon (Si) 0.10 wt% or more and 0.80 wt% or less, manganese (Mn) 0.30 wt% or more and 3.0 wt% or less, phosphorus (P) 0 or more and 0.05 wt% or less, sulfur (S) 0 or more and 0.01 wt% or less, boron (B) 0.0005 wt% or more and 0.005 wt% or less, chromium (Cr) 0.01 wt% or more and 1.0 wt% or less, molybdenum (Mo) 0.01 wt% or more and 1.0 wt% or less, nickel (Ni) 0.001 wt% or more and 1.0 wt% or less, at least one of titanium (Ti), niobium (Nb), and vanadium (V) in a total of 0.01 wt% or more and 0.1 wt% or less, and the remainder being iron (Fe) and other It may contain unavoidable impurities.

[0085] The melting method for manufacturing the slab described above is not limited, and known methods such as blast furnaces, converters, and electric furnaces may be adopted. For example, the slab can be manufactured for continuous casting by extracting iron from raw materials such as iron ore, steel scrap (hereinafter referred to as scrap), and direct reduced iron.

[0086] Hot rolling step (S110)

[0087] The slab may be reheated for hot rolling prior to the hot rolling step (S110). By reheating the slab, components segregated during casting can be redissolved. The slab reheating temperature (SRT) may be 1200°C to 1400°C. If the slab reheating temperature (SRT) is lower than 1200°C, components segregated during casting may not be sufficiently redissolved, making it difficult to achieve a significant homogenization effect of alloying elements. On the other hand, if the slab reheating temperature (SRT) is higher than 1400°C, the austenite crystal grain size increases, making it difficult to secure strength, and the manufacturing cost of the steel sheet may increase due to the excessive heating process.

[0088] In the hot rolling step (S110), the reheated slab may be hot rolled at a predetermined finishing delivery temperature (FDT). In one embodiment, the finishing delivery temperature (FDT) may be 880°C to 950°C. If the finishing delivery temperature (FDT) is lower than 880°C, it is difficult to ensure workability of the steel sheet due to the occurrence of a mixed grain structure caused by rolling in an abnormal region, workability may be reduced due to microstructural non-uniformity, and problems with sheet throughput may occur during hot rolling due to rapid phase changes. On the other hand, if the finishing delivery temperature (FDT) is higher than 950°C, the austenite grains may coarsen. In addition, there is a risk that the performance of the final part may deteriorate due to the coarsening of TiC precipitates.

[0089] Hot-rolled steel sheets can be coiled after cooling to a predetermined coiling temperature (CT). In one embodiment, the coiling temperature (CT) may be 550°C to 800°C. The coiling temperature (CT) affects the redistribution of carbon (C). If the coiling temperature (CT) is below 550°C, the low-temperature phase fraction increases due to overcooling, which increases strength and may lead to increased rolling load during cold rolling, and may cause a rapid decrease in ductility. On the other hand, if the coiling temperature (CT) exceeds 800°C, deterioration in formability and strength may occur due to abnormal or excessive grain growth.

[0090] Cold rolling step (S120)

[0091] A cold rolling step (S120) may be performed after the hot rolling step (S110). In the cold rolling step (S120), the coiled steel sheet may be uncoiled, pickled, and then cold rolled. At this time, the pickling may be performed for the purpose of removing scale from the coiled steel sheet, that is, the hot-rolled coil produced through the hot rolling process.

[0092] In the cold rolling step (S120), the hot-rolled plate can be cold-rolled to a thickness of 1.0 mm to 2.5 mm. In one embodiment, to impart rollability, the plate temperature (e.g., the temperature of the pre-annealed plate or the hot-rolled plate) may be raised to proceed with warm rolling.

[0093] The reduction rate in the cold rolling step (S120) may be 75% to 85%. If the reduction rate satisfies the above conditions, it is advantageous to induce a texture, and the development of the {111} / / ND texture may be facilitated during subsequent recrystallization heat treatment. If the reduction rate in the cold rolling step (S120) is less than 75%, the {111} / / ND texture may not develop sufficiently, resulting in inferior formability, and if the reduction rate exceeds 85%, the cold rolling load may increase and productivity may decrease.

[0094] After cold rolling, the cold-rolled grain size can be 80㎛ to 160㎛.

[0095] Annealing heat treatment step (S130)

[0096] An annealing heat treatment step (S130) may be performed after the cold rolling step (S120). At this time, the annealing heat treatment step (S130) may be referred to as the final annealing step. In the annealing heat treatment step (S130), a cold-rolled annealed sheet may be manufactured by cold-rolling annealing the cold-rolled sheet. The annealing heat treatment step (S130) may be omitted depending on the characteristic requirements of the final product and the step conditions.

[0097] The annealing heat treatment step (S130) can be performed at a temperature that derives the optimal grain size considering mechanical properties.

[0098] In one embodiment, the annealing heat treatment step (S130) may include the step of heating the cold rolled plate to an annealing temperature of 820°C to 850°C at a heating rate of 3°C / s or more and 8°C / s or less, the step of maintaining it for 5 seconds to 70 seconds, and the step of cooling the annealed cold rolled plate.

[0099] If the annealing temperature is below 820°C, recrystallization may not occur sufficiently, and if the annealing temperature exceeds 850°C, abnormal grain growth may occur, such as a rapid increase in the amount of bainite due to the formation of excessive austenite, and an uneven microstructure according to thickness may develop, which may degrade the material properties of the steel sheet.

[0100] In addition, if the holding time is less than 5 seconds, grain growth may not occur sufficiently, and the elongation may decrease. On the other hand, if the holding time exceeds 70 seconds, productivity may decrease, and the manufacturing cost may increase.

[0101] The annealing heat treatment step (S130) may be performed in an atmosphere containing a mixed gas to prevent excessive oxidation and nitriding of the surface. By performing the annealing heat treatment step (S130) in an atmosphere containing a mixed gas, a cold-rolled annealed plate with excellent surface condition can be obtained. As an example, the annealing heat treatment step (S130) may be performed in a reducing atmosphere composed of 5% to 30% hydrogen and 70% to 90% nitrogen.

[0102] The steel sheet heated through annealing heat treatment may undergo a cooling step at a predetermined cooling rate. For example, the cooling rate may be 5℃ / s to 30℃ / s.

[0103] plating layer formation step (S140)

[0104] In the plating layer formation step (S140), a plating layer is formed on a cold-rolled annealed plate (i.e., a base steel plate) to manufacture a plated steel plate for hot stamping.

[0105] The thickness of the cold-rolled annealed sheet (i.e., base steel sheet) on which the plating layer is formed can satisfy a thickness of 1.0 mm to 2.5 mm. As explained with reference to FIG. 1, the fraction of the zinc-rich phase within the plating layer of the hot-stamping part may be 20% or more and 40% or less. In order to control the fraction of the zinc-rich phase within the plating layer to be within the aforementioned range, the thickness of the base steel sheet must satisfy a thickness of 1.0 mm to 2.5 mm. The thickness of the base steel sheet is related to the heat treatment time during the heating step (S210, FIG. 3) of the hot-stamping process described later. If the thickness of the base steel sheet is less than 1.0 mm, it is difficult to secure the heat treatment time during the hot-stamping process, and if the thickness of the base steel sheet exceeds 2.5 mm, forming may not be easy during the hot-stamping process.

[0106] In the plating layer formation step (S140), a cold-rolled annealed plate can be immersed in a plating bath containing a plating solution to form a plating layer on the surface.

[0107] In one embodiment, the plating layer may be a zinc-based plating layer.

[0108] Specifically, the plating layer formation step (S140) may include a step of forming a molten plating layer on the surface of a steel plate by immersing the steel plate in a plating bath having a temperature of 630°C to 700°C, and a cooling step of forming a plating layer by cooling the steel plate on which the molten plating layer is formed. At this time, the plating bath may include Si, Fe, Al, Mn, Cr, Mg, Ti, Zn, Sb, Sn, Cu, Ni, Co, In, and / or Bi as additive elements, but is not limited thereto. For example, the plating bath may include iron (Fe) 10 wt% or more and 70 wt% or less, aluminum (Al) 0 wt% or more and 5 wt% or less, manganese (Mn) 0 wt% or more and 1 wt% or less, silicon (Si) 0 wt% or more and 1 wt% or less, zinc (Zn) 33 wt% or more and 90 wt% or less, and other impurities.

[0109] In addition, the plating thickness is 40 g / m² per piece. 2 Up to 120 g / m² 2 It can be controlled to satisfy [the condition]. As explained with reference to FIG. 1, the fraction of the zinc-rich phase within the plating layer may be between 20% and 40%; however, in order to control the fraction of the zinc-rich phase within the plating layer in this way, the thickness of the plating layer, i.e., the plating deposition amount, must satisfy within the aforementioned range. The plating deposition amount is 40 g / m² 2 If the deposition is less than 120 g / m², a sufficient zinc-rich phase is not formed, and the plating deposition amount is 120 g / m² 2 If it exceeds [amount], the increase in zinc scattering during the hot stamping process leads to increased contamination during the heating process, the plating layer may be formed unevenly, and liquid metal embrittlement (LME) may occur during the hot stamping forming stage, which may degrade the toughness and / or ductility of the hot stamped part.

[0110] Through the above processes, the steel sheet for hot stamping according to one embodiment of the present invention may be a hot-dip galvanized steel sheet (GI).

[0111] In some cases, the plating layer formation step (S140) may include a plating layer alloying step. In this case, the steel plate with the plating layer formed thereon can be alloyed to produce an alloyed hot-dip galvanized steel plate (GA). In one embodiment, in the plating layer alloying step, an alloying heat treatment may be performed by maintaining the temperature at 450°C or higher and 520°C or lower for a time of 10 seconds or more and 60 seconds or less.

[0112] In one embodiment, the plating layer alloying step can be performed continuously after the plating layer formation step (S140). That is, a separate cooling step may not be performed between the plating layer alloying step and the plating layer formation step (S140).

[0113] Under the above conditions, when alloying heat treatment is performed, the plating layer grows stably, and the adhesion of the plating layer can be excellent.

[0114] The hot stamping steel sheet with the plating layer formed in this way may optionally undergo a shot spinning process to remove zinc oxide formed on the surface of the plating layer.

[0115] A steel plate for hot stamping according to one embodiment of the present invention can be manufactured through the manufacturing steps described above.

[0116] Post-processing step (S150)

[0117] After the plating layer formation step (S140), a post-treatment step (S150) may be performed. In the post-treatment step (S150), a post-treatment agent is applied to the steel plate on which the plating layer has been formed to form a pre-post-treatment layer, and the steel plate is dried to produce a post-treated steel plate.

[0118] In some embodiments, the post-processing step (S150) may be omitted.

[0119] When performing the post-treatment step (S150), the post-treatment agent may be an inorganic or organic post-treatment agent. Specifically, the post-treatment agent may be a Si-based inorganic post-treatment agent, an Al-based inorganic post-treatment agent, or a Ca-based inorganic post-treatment agent. The inorganic post-treatment agent may contain 15 wt% or more and 50 wt% of silicon (Si), aluminum (Al), or carbon (Ca), 5 wt% or more and 50 wt% of zinc (Zn), 0 wt% or more and 15 wt% of iron (Fe), 0 wt% or more and 15 wt% of manganese (Mn), and 10 wt% or more and 80 wt% of oxygen (O). The application amount of the inorganic post-treatment agent is approximately 0.5 g / m² 2 Up to about 3 g / m² 2 The thickness of the post-treatment layer may be about 0.5 μm or more. Thus, a post-treatment layer having the component ratio and thickness within the aforementioned range can prevent oxidation of the plating layer by forming a film on the surface of the steel plate during the hot stamping heat treatment process.

[0120] After that, a hot stamping part can be manufactured by using the above-mentioned hot stamping steel plate and undergoing a hot stamping process.

[0121] Referring to FIG. 2, a method for manufacturing a hot stamping part according to one embodiment may include a heating step (S210), a transfer step (S220), and a forming and cooling step (S230).

[0122] Heating step (S210)

[0123] In the heating step (S210), a steel plate (or blank) for hot stamping can be heated.

[0124] In some embodiments, the heating step (S210) may include a multi-stage heating step and / or a crack heating step.

[0125] In the heating step (S210), a zinc-rich phase (22, FIG. 1) can be formed within the plating layer (20, FIG. 1) as described with reference to FIG. 1 by heating the steel plate for hot stamping. The zinc-rich phase may be included in the plating layer at a fraction of 20% or more and 40% or less, and such a fraction of the zinc-rich phase can be controlled by the heat treatment temperature and heat treatment time during the heating step (S220) in the hot stamping process.

[0126] Specifically, in the heating step (S210), the steel plate for hot stamping is heated in a temperature range of Ac3 or higher and 910°C or lower, and can be performed in a temperature range of Ac3 or higher and 910°C or lower. For example, the heating temperature of the steel plate for hot stamping may satisfy 850°C or higher and 910°C or lower to ensure the material of the hot stamping part and prevent vaporization of the plating layer. If the heating temperature exceeds 910°C, the zinc contained in the plating layer may oxidize or scatter, making it difficult to secure an appropriate zinc-rich phase. In addition, if the heating temperature is below Ac3, it may be difficult to secure strength because a martensite structure cannot be formed after hot stamping.

[0127] The heat treatment time in the heating step (S210) can be performed for 240 seconds to 360 seconds. If the heat treatment time is less than 240 seconds, the fraction of the zinc-rich phase is formed to be more than 40%, which causes the problem of liquid metal embrittlement (LME) to occur during hot stamping part forming. In addition, if the heat treatment time exceeds 360 seconds, the zinc-rich phase disappears due to iron-zinc overalloying, and as the fraction of the zinc-rich phase is less than 20%, the electrochemical corrosion potential value of the plating layer does not satisfy the range of the present invention, and thus sacrificial corrosion resistance may be reduced.

[0128] The thickness of the base steel plate (10) is related to the heat treatment time in the heating step (S210). If the thickness of the base steel plate (10) is excessively thin, the heat treatment time is shortened, making it difficult to secure the heat treatment time within the range described above. Therefore, it is preferable that the thickness of the base steel plate (10) be 1.0 mm or more.

[0129] In one embodiment, a steel sheet for hot stamping can be heat-treated in a heating furnace having a dew point of -20°C or higher and 20°C or lower during the heating step (S210). Since additional equipment is required to set the dew point to less than -20°C, a problem may arise where process costs increase. If the dew point exceeds 20°C, hydrogen embrittlement of the material may occur due to the influx of hydrogen during hot stamping.

[0130] Transfer step (S220)

[0131] A transfer step (S220) may be performed after the heating step (S210). The transfer step (S220) may be a step of transferring the heated hot stamping steel plate from the heating furnace to the press mold. At this time, during the transfer step (S220), the heated hot stamping steel plate may be cooled at ambient temperature (or room temperature). That is, the heated hot stamping steel plate may be air-cooled during transfer. In one embodiment, the time taken to remove the heated hot stamping steel plate from the heating furnace and transfer it to the press mold, i.e., the air-cooling time, may be about 5 seconds or more and 20 seconds or less.

[0132] Molding and cooling step (S230)

[0133] A forming and cooling step (S230) may be performed after the transfer step (S220). The forming and cooling step (S230) may be a step of forming a molded body by pressing the transferred hot stamping steel plate with a press mold and simultaneously cooling the transferred hot stamping steel plate. Specifically, in the forming and cooling step (S230), the hot stamping steel plate may be formed into the shape of a hot stamping part by pressing it with a press mold, and simultaneously, cooling of the hot stamping steel plate may be achieved as the press mold and the hot stamping steel plate come into contact.

[0134] In one embodiment, the forming start temperature may be 550°C or higher and 750°C or lower. If the forming start temperature is less than 550°C, the forming start temperature is too low, which may reduce the formability of the steel sheet for hot stamping and may result in the manufactured hot stamping part failing to possess the desired structure and physical properties. On the other hand, if the forming start temperature exceeds 750°C, wrinkles (or bends) may occur on the surface of the manufactured hot stamping part, and cracks may occur on the surface of the hot stamping part due to the liquid metal embrittlement (LME) phenomenon. Additionally, the plating layer may adhere to the mold. Therefore, when the forming start temperature satisfies 550°C or higher and 750°C or lower, the formability of the steel sheet for hot stamping may be improved, the manufactured hot stamping part may possess the desired structure and physical properties, and the occurrence of wrinkles and cracks on the surface of the manufactured hot stamping part may be minimized.

[0135] Cooling of the hot stamping steel plate can be achieved as the press mold presses the hot stamping steel plate and the press mold comes into contact with the hot stamping steel plate. Specifically, the hot stamping steel plate can be cooled simultaneously with forming the hot stamping steel plate into the shape of a hot stamping part in the press mold. The press mold may be equipped with a cooling channel through which a refrigerant circulates. The formed body (e.g., hot stamping steel plate) can be rapidly cooled by the circulation of the refrigerant 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 maintain the desired shape, rapid cooling can be performed while applying pressure with the mold closed.

[0136] In one embodiment, the cooling rate may be 25°C / s or higher. Additionally, the cooling time for the hot stamping steel sheet in the press may be 3 seconds or more and 20 seconds or less. If the cooling rate is too low (less than 25°C / s) or the cooling time is too short (less than 3 seconds), the martensite structure may not be properly formed, and the desired material property standards may not be satisfied. On the other hand, if the cooling time exceeds 20 seconds, productivity may decrease.

[0137] FIG. 4 is SEM images showing a partial cross-section of a hot stamping part according to an embodiment and a comparative example of the present invention.

[0138] Referring to FIG. 4, the embodiment (A) and comparative example (B) of the present invention show the cross-section of the plating layer of a hot-stamped part after the hot stamping process. The embodiment (A) shows the result of performing the heat treatment for 240 seconds in the heating step (S210), and the comparative example (B) shows the result of performing the heat treatment for 420 seconds in the heating step (S210). In the case of the embodiment (A), as shown in the SEM image, it can be confirmed that the zinc-rich phase (22) is formed in the plating layer (20) in an appropriate proportion. As a result of evaluation, in the case of the embodiment (A), since the heat treatment time satisfies the range of the present invention, the fraction of the zinc-rich phase (22) formed in the plating layer (20) was measured to be about 26%. On the other hand, in the case of the comparative example (B), since the heat treatment time was performed for a long time outside the range of the present invention, the fraction of the zinc-rich phase (22') formed in the plating layer (20') was measured to be about 8%.

[0139] As measured by the above evaluation, in the case of Example (A), the fraction of the zinc-rich phase (22) formed within the plating layer (20) satisfies the scope of the present invention, so Example (A) can have sufficient sacrificial corrosion resistance. On the other hand, in the case of Comparative Example (B), the fraction of the zinc-rich phase (22') formed within the plating layer (20') falls outside the scope of the present invention, so Comparative Example (B) may have reduced corrosion resistance.

[0141] Hereinafter, the structure and operation of the present invention will be explained 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 interpreted in any way as limiting the present invention.

[0143] Experimental Example

[0144] The present invention will be explained in more detail below through experimental examples. However, the following experimental examples are intended to explain the present invention more specifically, and the scope of the present invention is not limited by the following experimental examples. The following experimental examples may be appropriately modified or changed by those skilled in the art within the scope of the present invention.

[0146] Evaluation Method

[0147] To prepare specimens for the examples, a cold-rolled steel sheet having a thickness of 1 mm to 2 mm and containing 0.30 wt% carbon (C), 0.20 wt% silicon (Si), 1.4 wt% manganese (Mn), 0.012 wt% phosphorus (P), 0.002 wt% sulfur (S), 0.002 wt% boron (B), 0.2 wt% chromium (Cr), 0.01 wt% molybdenum (Mo), 0.001 wt% nickel (Ni), and the remainder being iron (Fe) and other unavoidable impurities is immersed in an alkaline solution at 50°C for 30 minutes, and then washed with water to remove foreign substances and oil from the surface to prepare the specimen. After annealing the specimen, a plating layer is formed on the surface. The annealing treatment is carried out in a reducing atmosphere composed of 10% to 30% hydrogen and 70% to 90% nitrogen, and the annealing heat treatment temperature is 700℃ to 850℃.

[0148] For plating, the annealed specimen is cooled to the plating bath temperature, immersed in the bath for 2 seconds, and then lifted out. After nitrogen wiping, the plating adhesion is 40 g / m² per side. 2 Up to 120g / m² 2The internal and external conditions are controlled, and the mixture is cooled to room temperature at a cooling rate of 5°C / sec to 30°C / sec to solidify. At this time, the plating bath temperature is set to 630°C to 700°C. The composition of the plating layer may include iron (Fe) 10 wt% or more and 70 wt% or less, aluminum (Al) 0 wt% or more and 5 wt% or less, manganese (Mn) 0 wt% or more and 1 wt% or less, silicon (Si) 0 wt% or more and 1 wt% or less, zinc (Zn) 33 wt% or more and 90 wt% or less, and other impurities, and a zinc-based plating layer is formed by the above process.

[0149] After manufacturing a plated steel sheet under the above conditions, the heated plated steel sheet was heated for 240 to 420 seconds at a heat treatment temperature of Ac3 or higher and 910℃ or lower for a hot stamping process, and then the heated plated steel sheet was hot stamped using a press die to produce a specimen. The forming start temperature was set to 550℃ to 750℃, and the average cooling rate was set to 25℃ / s or higher.

[0150] In the case of comparative examples, all other conditions were kept the same, except that at least one condition among the plating thickness, heat treatment temperature, heat treatment time, and steel plate thickness fell outside the scope of the present invention.

[0151] <Electrochemical Dynamic Resistance Corrosion Assessment: Tafel>

[0152] The electrochemical kinetic resistance corrosion evaluation was performed by measuring the natural potential value of the specimen while it was immersed in a 3.5% brine solution for 1 hour. An AgCl electrode was used as the reference electrode, and a Pt-coated electrode was used as the counter electrode. The evaluation exposure area was 0.785 cm². 2 (Diameter: 1cm)

[0153] Corrosion Resistance Evaluation

[0154] The corrosion resistance was evaluated by applying a 5% NaCl solution to the specimen at 35°C using a salt spray test. The specimen was evaluated based on the time it took for 5% red rust to appear on the plated surface after hot stamping. If the time it took for 5% red rust to appear on the plated surface was 6 hours or more, the corrosion resistance was evaluated as satisfactory, and if the time it took for 5% red rust to appear on the plated surface was less than 6 hours, the corrosion resistance was evaluated as unsatisfactory.

[0155] <Evaluation of Liquid Metal Embrittlement (LME)>

[0156] After hot stamping the above specimen, if there is a crack of 10㎛ or more in the formed processing part, it is evaluated as unsatisfactory in the LME evaluation, and if there is no crack of 10㎛ or more in the formed processing part, it is evaluated as satisfied in the LME evaluation.

[0158] division Steel plate thickness (mm) Single-sided plating amount (g / m²) 2 ) Heat treatment time(s) Heat treatment temperature (°C) Zinc-rich phase fraction (%) Corrosion potential value (mV) Corrosion resistance evaluation LME evaluation of forming processing divisions Comparative Example 1 1.0 80 390 890 14.1 -570 X ○ Comparative Example 2 1.0 30 240 890 3 -620 X ○ Comparative Example 3 1.0 140 240 890 46.2 -760 ○ X Comparative Example 4 2.0 80 180 870 44.9 -765 ○ X Comparative Example 5 2.0 80 370 870 18.3 -610 X ○ Comparative Example 6 2.0 80 420 870 10.4 -580 X ○ Comparative Example 7 2.0 50 330 910 15.1 -600 X ○ Comparative Example 8 0.6 80 150 850 45.2 -767 ○ X Comparative Example 9 2.0 80 300 830 42.5 -723 ○ X Comparative Example 10 2.0 80 330 940 16.3 -582 X ○ Example 1 1.0 80 260 850 23.5 -705 ○ ○ Example 2 1.0 80 240 850 20.6 -700 ○ ○ Example 3 1.0 120 240 850 38 -750 ○ ○ Example 4 2.0 80 240 870 39.8 -724 ○ ○ Example 5 2.0 80 300 870 33.5 -700 ○ ○ Example 6 2.0 40 240 910 26.8 -705 ○ ○ Example 7 2.0 80 330 910 24.1 -680 ○ ○

[0159] Referring to Table 1 above, Comparative Example 1 was performed with an excessive heat treatment time of 390 seconds during the heating step (S210) in the hot stamping process. As a result, Comparative Example 1 had a zinc-rich phase fraction of 14.1% in the plating layer and a corrosion potential value of -570mV in the plating layer, which is below the range of the present invention. Therefore, it can be confirmed that Comparative Example 1 also showed an inferior level in the corrosion resistance evaluation.

[0160] The single-sided plating amount in Comparative Examples 2 and 3 fell outside the scope of the present invention. In Comparative Example 2, the single-sided plating amount was 30 g / m² 2 As such, it fell short of the scope of the present invention, and Comparative Example 3 had a single-sided plating amount of 140 g / m² 2Thus, the scope of the present invention was exceeded. Accordingly, Comparative Example 2 was unsatisfactory of the scope of the present invention, with a zinc-rich phase fraction of 3% and a corrosion potential value of -620mv in the plating layer, and Comparative Example 3 was unsatisfactory of the scope of the present invention, with a zinc-rich phase fraction of 46.2% and a corrosion potential value of -760mv in the plating layer. Therefore, Comparative Example 2 was found to be inferior in the corrosion resistance evaluation as well. Comparative Example 3 was found to have an excessive zinc-rich phase fraction within the plating layer compared to the scope of the present invention, and was evaluated as satisfactory in the corrosion resistance evaluation; however, it was confirmed in the LME evaluation that cracks occurred in the formed processed part due to liquid metal embrittlement during hot stamping.

[0161] In Comparative Example 4, the heat treatment time during the heating step (S210) in the hot stamping process was 180 seconds, which is shorter than the range of the present invention. As a result, in Comparative Example 4, the fraction of the zinc-rich phase in the plating layer was 44.9%, and the corrosion potential value of the plating layer was -765mV, which is outside the range of the present invention. Since the fraction of the zinc-rich phase in the plating layer in Comparative Example 4 was found to be excessive compared to the range of the present invention, it was evaluated as satisfactory in the corrosion resistance evaluation, but it was confirmed in the LME evaluation that cracks occurred in the formed processed part due to liquid metal embrittlement during hot stamping.

[0162] In Comparative Examples 5 and 6, the heat treatment time in the heating step (S210) during the hot stamping process was 180 seconds, which is longer than the range of the present invention. As a result, in Comparative Examples 5 and 6, the fraction of the zinc-rich phase within the plating layer was 18.3% and 10.4%, respectively, and the corrosion potential values ​​of the plating layer were -610mV and -580mV, respectively, which are outside the range of the present invention. Therefore, it can be confirmed that Comparative Examples 5 and 6 also showed an inferior level in the corrosion resistance evaluation.

[0163] Comparative Example 7 has a single-sided plating amount of 50 g / m² 2As such, it fell outside the scope of the present invention. Accordingly, Comparative Example 7 did not satisfy the scope of the present invention, as the fraction of the zinc-rich phase in the plating layer was 15.1% and the corrosion potential value was -600mv. Therefore, it can be confirmed that Comparative Example 7 also showed an inferior level in the corrosion resistance evaluation.

[0164] In Comparative Example 8, the thickness of the base steel plate fell outside the scope of the present invention. The thickness of the base steel plate is related to the heat treatment time, and if the thickness of the base steel plate is excessively thin, it is difficult to secure sufficient heat treatment time. Since Comparative Example 8 was formed with a thin base steel plate thickness of 0.6 mm, the heat treatment time was shortened to 150 seconds. Consequently, in Comparative Example 8, the fraction of the zinc-rich phase within the plating layer was 45.2%, which fell outside the scope of the present invention. Although Comparative Example 8 was evaluated as satisfactory in the corrosion resistance evaluation because the fraction of the zinc-rich phase within the plating layer was found to be excessive compared to the scope of the present invention, it was confirmed in the LME evaluation that cracks occurred in the formed processed part due to liquid metal embrittlement during hot stamping.

[0165] Comparative Examples 9 and 10 had heat treatment temperatures in the heating step (S210) during the hot stamping process that fell outside the scope of the present invention. Comparative Example 9 had a heat treatment temperature of 830°C, which was below the scope of the present invention, while Comparative Example 10 had a heat treatment temperature of 940°C, which exceeded the scope of the present invention. Consequently, Comparative Example 9 had a zinc-rich phase fraction of 42.5% in the plating layer and a corrosion potential value of -620 mv, which did not satisfy the scope of the present invention, and Comparative Example 10 had a zinc-rich phase fraction of 16.3% in the plating layer and a corrosion potential value of -590 mv, which did not satisfy the scope of the present invention. Therefore, Comparative Example 9 also showed an inferior level in the corrosion resistance evaluation. Comparative Example 10 showed an excessive zinc-rich phase fraction in the plating layer compared to the scope of the present invention, and although it was evaluated as satisfactory in the corrosion resistance evaluation, it was confirmed in the LME evaluation that cracks occurred in the formed processed part due to liquid metal embrittlement during hot stamping.

[0166] On the other hand, Examples 1 to 7 satisfied the range of the present invention described above for steel plate thickness, single-sided plating amount, heat treatment time, and heat treatment temperature. Accordingly, in Examples 1 to 7, the fraction of the zinc-rich phase within the plating layer was measured to be 20% to 40%, and the corrosion potential value of the plating layer satisfied 650mv to 800mv. Therefore, Examples 1 to 7 were evaluated as excellent in both corrosion resistance evaluation and LME evaluation.

[0167] 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 therefrom. Accordingly, the true scope of technical protection of the present invention should be determined by the technical spirit of the appended claims. Explanation of the symbols

[0169] 1: Hot stamping parts 10: Base steel plate 20: Plating layer 22: Zinc-rich layer 24: Iron-zinc alloy phase

Claims

Claim 1 The invention relates to a hot stamping part comprising a base steel plate and a zinc-based plating layer on the base steel plate, wherein the base steel plate comprises carbon (C) 0.25 wt% or more and 0.50 wt% or less, silicon (Si) 0.10 wt% or more and 0.80 wt% or less, manganese (Mn) 0.30 wt% or more and 3.0 wt% or less, phosphorus (P) 0 or more and 0.05 wt% or less, sulfur (S) 0 or more and 0.01 wt% or less, boron (B) 0.0005 wt% or more and 0.005 wt% or less, chromium (Cr) 0.01 wt% or more and 1.0 wt% or less, molybdenum (Mo) 0.01 wt% or more and 1.0 wt% or less, nickel (Ni) 0.001 wt% or more and 1.0 wt% or less, and at least one of titanium (Ti), niobium (Nb), and vanadium (V) in total A hot stamping part comprising 0.01 wt% or more and 0.1 wt% or less, with the remainder being iron (Fe) and other unavoidable impurities, wherein the plating layer comprises a zinc-rich phase (Zn-rich) and an iron-zinc alloy phase, and the zinc-rich phase has a fraction of 20% to 40% of the total plating layer. Claim 2 A hot stamping part according to claim 1, wherein the corrosion potential value of the plating layer is -650 mV to -800 mV. Claim 3 A hot stamping part according to claim 1, wherein the thickness of the plating layer is 10㎛ to 40㎛. Claim 4 In claim 1, the plating layer adhesion amount is 40 g / m² per piece. 2 Up to 120 g / m² 2 Phosphor, hot stamping part. Claim 5 A hot stamping part according to claim 1, wherein the plating layer comprises iron (Fe) 10 wt% or more and 70 wt% or less, aluminum (Al) 0 wt% or more and 5 wt% or less, manganese (Mn) 0 wt% or more and 1 wt% or less, silicon (Si) 0 wt% or more and 1 wt% or less, zinc (Zn) 33 wt% or more and 99 wt% or less, and other impurities. Claim 6 A hot stamping part according to claim 1, wherein the iron-zinc alloy phase is located in a portion of the plating layer adjacent to the base steel plate. Claim 7 In claim 1, the hot stamping part comprises 90% or more martensite. Claim 8 A hot stamping part according to claim 1, wherein the tensile strength (TS) of the hot stamping part is 1680 MPa to 2000 MPa. Claim 9 A hot stamping part according to claim 1, wherein the yield strength (YP) of the hot stamping part is 1150 MPa to 1500 MPa. Claim 10 A hot stamping part according to claim 1, wherein the elongation of the hot stamping part is 4% or more and 10% or less. Claim 11 A method for manufacturing a hot stamping part, comprising: a plating layer forming step of forming a zinc-based plating layer on a base steel plate; a heating step of introducing the base steel plate on which the plating layer is formed into a heating furnace and heating it; a transfer step of transferring the heated base steel plate from the heating furnace to a press mold; a forming step of hot stamping the transferred base steel plate to form a molded body; and a step of cooling the molded body; wherein the heating step is a step of heating the steel plate at a heating temperature of 850°C to 910°C for 240 seconds to 360 seconds. Claim 12 A method for manufacturing a hot stamping part according to claim 11, wherein the heating step is a step of controlling the average heating rate from 700℃ to the heating temperature to 1.5℃ / s to 7℃ / s. Claim 13 A method for manufacturing a hot stamping part according to claim 11, wherein, in the molding step, the molding start temperature is 550℃ to 750℃ and the average cooling rate is 25℃ / s or higher. Claim 14 A method for manufacturing a hot stamping part according to claim 11, wherein the thickness of the base steel plate is 1 mm to 2.5 mm. Claim 15 In claim 11, in the step of forming the plating layer, the plating adhesion amount is 40 g / m² per piece. 2 Up to 120g / m² 2 Method for manufacturing a hot stamping part. Claim 16 In claim 11, the above-mentioned base steel sheet comprises carbon (C) 0.25 wt% or more and 0.50 wt% or less, silicon (Si) 0.10 wt% or more and 0.80 wt% or less, manganese (Mn) 0.30 wt% or more and 3.0 wt% or less, phosphorus (P) 0 or more and 0.05 wt% or less, sulfur (S) 0 or more and 0.01 wt% or less, boron (B) 0.0005 wt% or more and 0.005 wt% or less, chromium (Cr) 0.01 wt% or more and 1.0 wt% or less, molybdenum (Mo) 0.01 wt% or more and 1.0 wt% or less, nickel (Ni) 0.001 wt% or more and 1.0 wt% or less, at least one of titanium (Ti), niobium (Nb), and vanadium (V) in a total of 0.01 wt% or more and 0.1 wt% or less, and the remainder A method for manufacturing a hot stamping part containing iron (Fe) and other unavoidable impurities. Claim 17 A method for manufacturing a hot stamping part according to claim 11, wherein, in the plating layer forming step, the plating bath comprises iron (Fe) 10 wt% or more and 70 wt% or less, aluminum (Al) 0 wt% or more and 5 wt% or less, manganese (Mn) 0 wt% or more and 1 wt% or less, silicon (Si) 0 wt% or more and 1 wt% or less, zinc (Zn) 33 wt% or more and 99 wt% or less, and other impurities.

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