KR20230018937A - Steel sheet for hot press and Hot stamping component manufactured using the same - Google Patents

Abstract

The present invention is to provide a steel sheet for hot pressing that has sacrificial corrosion protection and at the same time has excellent workability by adding Si, Zn, and Mg at an appropriate ratio when forming an aluminum-based plating layer, and a hot stamping component manufactured using the steel sheet for hot pressing. In one embodiment of the present invention, disclosed is a steel sheet for hot pressing, comprising a base steel sheet and a plating layer located on the base steel sheet and having a diffusion layer and a surface layer sequentially laminated, wherein the diffusion layer includes an Fe-Al alloyed layer and a Fe-Al intermetallic compound layer which are sequentially located on the base steel sheet and each include silicon, and the area fraction of the Fe-Al intermetallic compound layer to the diffusion layer is 84.5 % to 98.0 %.

Description

Steel sheet for hot press and hot stamping component manufactured using the same {Steel sheet for hot press and hot stamping component manufactured using the same}

Embodiments of the present invention relate to a steel sheet for hot pressing and a hot stamping part manufactured using the same.

Recently, as environmental regulations and safety standards in the automobile industry are strengthened, the application of high-strength steel for weight reduction and stability of automobiles is increasing. On the other hand, high-strength steel can secure high-strength characteristics compared to its weight, but it is difficult to form a product having a complex and precise shape due to breakage of the material or spring back phenomenon during processing. Therefore, as a method for solving these problems, the application of hot press molding is expanding.

Hot press forming (hot stamping) facilitates forming of steel materials by heating and press-processing steel sheets at high temperatures, and secures the strength of molded products by performing rapid cooling through a mold. However, since the steel sheet is heated to a high temperature for hot press forming, there is a problem in that the surface of the steel sheet is oxidized. In order to solve this problem, US Patent Registration No. 6,296,805 proposes a method of hot press forming an aluminum-plated steel sheet. According to the invention of US Patent No. 6,296,805, since the aluminum plating layer exists on the surface of the steel sheet, oxidation of the surface of the steel sheet due to heating of the steel sheet can be prevented.

As such an aluminum plating layer, Al-Si-based plating is applied by hot stamping. However, Al-Si-based plating has excellent high-temperature oxidation resistance, but due to the high hardness of the plating layer and the pores present on the plating surface after hot stamping, the plating layer cracks and falls off during processing, reducing the molding workability and corrosion resistance due to the loss of the plating layer. It has the downside of reducing In addition, existing Al-Si-based hot stamping plating materials have a function of corrosion resistance of the plating layer after hot stamping, which simply acts as a protective film, so that the plating layer lost due to friction during molding is easily applied when exposed to a corrosive environment. cries will occur.

In order to improve this problem, a Zn-based hot stamping plating technology in which the metal of the plating layer has sacrificial corrosion resistance has been developed. (LME, liquid metal embrittlement) has many limitations in commercialization.

US 6,296,805

Embodiments of the present invention provide a hot-pressing steel sheet having sacrificial anticorrosiveness and excellent processability by adding Si, Zn, and Mg in an appropriate ratio in forming an aluminum-based plating layer, and hot stamping parts manufactured using the same.

According to one aspect of the present invention, the base steel plate; And disposed on the base steel sheet, zinc (Zn): 20 wt% to 45 wt%, magnesium (Mg): 0.2 wt% to 3 wt%, silicon (Si): 1 wt% to 5 wt%, the remainder There is provided a steel sheet for hot pressing having a; plating layer containing aluminum (Al) and other unavoidable impurities.

According to this embodiment, magnesium (Mg) on the surface of the plating layer is distributed as an Mg-based intermetallic compound, and 80% or more of the Mg-based intermetallic compound is distributed in a zinc rich region located on the surface of the plating layer. can

According to this embodiment, the Mg-based intermetallic compound may include Mg ₂ Si phase.

According to this embodiment, the Mg ₂ Si phase distributed on the surface of the plating layer may have a phase fraction of 2% to 10%.

According to one aspect of the present invention, the base steel plate; and a plating layer disposed on the base steel sheet and containing zinc (Zn), magnesium (Mg), silicon (Si), aluminum (Al), iron (Fe), and other unavoidable impurities. includes an alloying layer, an intermediate alloy layer, and a surface layer sequentially stacked from the base steel sheet, wherein the surface layer includes a first enriched portion in which zinc (Zn) is enriched and a second enriched portion in which magnesium (Mg) is enriched, Hot stamping parts are provided.

According to the present embodiment, the first enrichment unit contains iron (Fe): 2 wt% to 12 wt%, aluminum (Al): 0 wt% to 10 wt%, silicon (Si): 0 wt% to 2 wt%, Magnesium (Mg): 1 wt% to 10 wt% and zinc (Zn): 40 wt% to 80 wt%.

According to the present embodiment, the second enrichment unit contains iron (Fe): 10 wt% to 20 wt%, aluminum (Al): 1 wt% to 20 wt%, silicon (Si): 0 wt% to 2 wt%, Zinc (Zn): 5 wt% to 20 wt% and magnesium (Mg): 10 wt% to 40 wt% may be included.

According to this embodiment, the alloying layer includes iron (Fe): 70 wt% to 90 wt%, aluminum (Al): 5 wt% to 15 wt%, and silicon (Si): 0.5 wt% to 4 wt% can do.

According to this embodiment, the thickness of the alloying layer may be 20 μm or less.

According to this embodiment, the intermediate alloy layer is iron (Fe): 35 wt% to 45 wt%, aluminum (Al): 30 wt% to 45 wt%, silicon (Si): 0.5 wt% to 5 wt%, and Zinc (Zn): 5 wt% to 20 wt% may be included.

According to this embodiment, the surface layer may include iron (Fe): 20 wt% to 45 wt% and aluminum (Al): 10 wt% to 35 wt%.

According to this embodiment, the first thickening part may have an average thickness of 1 μm or more and 10 μm or less.

According to this embodiment, the average thickness of the plating layer may be 15 μm to 40 μm.

According to embodiments of the present invention, in forming an aluminum-based plating layer, Si, Zn, and Mg are added in an appropriate ratio to manufacture a hot-pressing steel sheet having sacrificial anticorrosiveness and excellent workability and a hot stamping part manufactured using the same. can do.

1 is a cross-sectional view showing a cross section of a steel sheet for hot pressing according to an embodiment of the present invention.
2 and 3 are images in which specific elements are mapped on the surface of the plating layer of the steel sheet for hot pressing according to an embodiment of the present invention.
FIG. 4 is a flowchart schematically illustrating a method of manufacturing a steel sheet for hot pressing shown in FIG. 1 .
5 and 6 are TEM (Transmission Electron Microscopy) images of a cross section of a hot stamping part according to an embodiment of the present invention.
7A is a TEM (Transmission Electron Microscopy) image of a cross section of a hot stamping part according to an embodiment of the present invention.
7B and 7C are images obtained by mapping specific elements in the cross section of the hot stamping part of FIG. 7A.

Since the present invention can apply various transformations and have various embodiments, specific embodiments will be illustrated in the drawings and described in detail in the detailed description. Effects and features of the present invention, and methods for achieving them will become clear with reference to the embodiments described later in detail together with the drawings. However, the present invention is not limited to the embodiments disclosed below and may be implemented in various forms.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings, and when describing with reference to the drawings, the same or corresponding components are assigned the same reference numerals, and overlapping descriptions thereof will be omitted. .

In this specification, terms such as first and second are used for the purpose of distinguishing one component from another component without limiting meaning.

In this specification, singular expressions include plural expressions unless the context clearly dictates otherwise.

In this specification, terms such as include or have mean that features or elements described in the specification exist, and do not preclude the possibility that one or more other features or elements may be added.

In this specification, when a part such as a film, region, component, etc. is said to be on or on another part, not only when it is directly above the other part, but also when another film, region, component, etc. is interposed therebetween. include

In this specification, when films, regions, components, etc. are connected, when films, regions, and components are directly connected, or/and other films, regions, and components are interposed between the films, regions, and components. Including cases of indirect connection. For example, when a film, region, component, etc. is electrically connected in this specification, when a film, region, component, etc. is directly electrically connected, and/or another film, region, component, etc. is interposed therebetween. This indicates an indirect electrical connection.

In this specification, "A and/or B" represents the case of A, B, or A and B. And, "at least one of A and B" represents the case of A, B, or A and B.

In this specification, the x-axis, y-axis, and z-axis are not limited to three axes on the Cartesian coordinate system, and may be interpreted in a broad sense including them. For example, the x-axis, y-axis, and z-axis may be orthogonal to each other, but may refer to different directions that are not orthogonal to each other.

In this specification, when an embodiment is otherwise embodied, a specific process sequence may be performed differently from the described sequence. For example, two processes described in succession may be performed substantially simultaneously, or may be performed in an order reverse to the order described.

In the drawings, the size of components may be exaggerated or reduced for convenience of description. For example, since the size and thickness of each component shown in the drawings are arbitrarily shown for convenience of description, the present invention is not necessarily limited to the illustrated bar.

1 is a cross-sectional view showing a cross section of a steel sheet for hot pressing according to an embodiment of the present invention, and FIGS. 2 and 3 are maps of specific elements on the surface of the plating layer of the steel sheet for hot pressing according to an embodiment of the present invention. They are images.

Referring to FIG. 1 , a steel sheet 10 for hot pressing according to an embodiment of the present invention may include a base steel sheet 100 and a plating layer 200 disposed on the base steel sheet 100 .

The base steel sheet 100 may be a steel sheet manufactured by performing a hot rolling process and a cold rolling process on a steel slab cast to include a predetermined amount of a predetermined alloy element. For example, the base steel sheet 100 may include a first alloy composition. The first alloy composition contains 0.01 wt% or more and 0.5 wt% or less of carbon (C), 0.01 wt% or more and 3.0 wt% or less of silicon (Si), 0.3 wt% or more and 5.0 wt% or less of manganese (Mn), and more than 0 phosphorus (P). It may contain 0.1 wt% or less, sulfur (S) greater than 0 and 0.1 wt% or less, the balance of iron (Fe) and other unavoidable impurities.

In addition, the first alloy composition may further include one or more of boron (B), titanium (Ti), niobium (Nb), chromium (Cr), molybdenum (Mo), and nickel (Ni). Specifically, the first alloy composition includes boron (B) 0.0001 wt% or more and 0.005 wt% or less, titanium (Ti) 0.01 wt% or more and 0.1 wt% or less, niobium (Nb) 0.01 wt% or more and 0.1 wt% or less, chromium (Cr) ) 0.01wt% or more and 0.5wt% or less, molybdenum (Mo) 0.01wt% or more and 0.5wt% or less, and nickel (Ni) 0.01wt% or more and 1.0wt% or less may further include one or more components.

Carbon (C) is a major element that determines the strength and hardness of the base steel sheet 100, and is added for the purpose of securing tensile strength and hardenability of the base steel sheet 100 after the hot press process. Such carbon may be included in an amount of 0.01wt% to 0.5wt% based on the total weight of the base steel sheet 100. If the carbon content is less than 0.01wt%, it is difficult to secure the mechanical strength of the base steel sheet 100, whereas if the carbon content exceeds 0.5wt%, the toughness of the base steel sheet 100 or brittleness control problems are caused It can be.

Silicon (Si) acts as a ferrite stabilizing element in the base steel sheet 100. Silicon (Si), as a solid-solution strengthening element, can improve the ductility of the base steel sheet 100 and improve carbon concentration in austenite by suppressing the formation of low-temperature carbides. In addition, silicon (Si) is a key element for hot rolling, cold rolling, hot press structure homogenization (perlite, manganese segregation zone control), and fine dispersion of ferrite. Silicon may be included in an amount of 0.01 wt % to 3.0 wt % based on the total weight of the base steel sheet 100 . When silicon is contained in less than 0.01wt%, it is difficult to obtain the above-described effect, and conversely, when the silicon content exceeds 3.0wt%, the hot rolling and cold rolling loads increase and the hot rolled red scale becomes excessive and the base steel sheet 100 Plating properties may deteriorate.

Manganese (Mn) is added for the purpose of increasing hardenability and strength during heat treatment. Manganese may be included in an amount of 0.3 wt% or more and 5.0 wt% or less based on the total weight of the base steel sheet 100. If the manganese content is less than 0.3 wt%, the crystal grain refinement effect is not sufficient, and the hard phase fraction in the molded article after hot pressing may be insufficient. On the other hand, if the content of manganese exceeds 5.0 wt%, ductility and toughness may be reduced due to segregation of manganese or pearlite band, and a deterioration in bending performance may occur and a heterogeneous microstructure may occur.

Phosphorus (P) may be included in an amount greater than 0 and less than 0.1 wt% with respect to the total weight of the base steel sheet 100 in order to prevent deterioration in toughness of the base steel sheet 100 . When phosphorus exceeds 0.1 wt % in the base steel sheet 100, a phosphide iron compound is formed to decrease toughness, and cracks may be induced in the base steel sheet 100 during the manufacturing process.

Sulfur (S) may be included in an amount greater than 0 and 0.1 wt% or less based on the total weight of the base steel sheet 100. When the sulfur content exceeds 0.1 wt%, hot workability is deteriorated, and surface defects such as cracks may occur due to the formation of large inclusions.

Boron (B) is added for the purpose of securing hardenability and strength of the base steel sheet 100 by securing a martensitic structure, and has an effect of grain refinement by increasing the austenite grain growth temperature. Boron may be included in an amount of 0.0001 wt% to 0.005 wt% based on the total weight of the base steel sheet 100. When boron is included in the above range, it is possible to prevent grain boundary brittleness in the hard phase and to secure high toughness and bendability.

Titanium (Ti) may be added for the purpose of strengthening hardenability and improving the material by forming precipitates after hot press heat treatment. In addition, by forming a precipitate phase such as Ti(C,N) at high temperature, it effectively contributes to the refinement of austenite crystal grains. Titanium may be included in an amount of 0.01wt% to 0.1wt% based on the total weight of the base steel sheet 100. When titanium is included in the content range, it is possible to prevent poor performance and coarsening of precipitates, easily secure physical properties of the steel, and prevent defects such as cracks on the surface of the steel.

Niobium (Nb) is added for the purpose of increasing strength and toughness by reducing martensite packet size. Niobium may be included in an amount of 0.01wt% to 0.1wt based on the total weight of the base steel sheet 100. When niobium is included in the above range, the crystal grain refinement effect of the steel material is excellent in the hot rolling and cold rolling process, cracking of the slab during steelmaking/playing, and brittle fracture of the product are prevented, and the generation of coarse precipitates in steelmaking can be minimized. can

Chromium (Cr) is added for the purpose of improving hardenability and strength of the base steel sheet 100. Chromium may be included in an amount of 0.01wt% to 0.5wt% based on the total weight of the base steel sheet 100. When chromium is included in the above range, it is possible to improve hardenability and strength of the base steel sheet 100, and to prevent an increase in production cost and a decrease in toughness of steel.

Molybdenum (Mo) may contribute to improving the strength of the base steel sheet 100 by suppressing coarsening of precipitates and increasing hardenability during hot rolling and hot pressing. Such molybdenum (Mo) may be included in an amount of 0.01 wt % to 0.5 wt % based on the total weight of the base steel sheet 100 .

The plating layer 200 may be formed to a thickness of 10 μm to 50 μm on at least one surface of the base steel plate 100 . Here, the thickness of the plating layer 200 may mean an average thickness of the plating layer 200 over the entire area of the plating layer 200 . When the thickness of the plating layer 200 is less than 10 μm, corrosion resistance deteriorates, and when the thickness of the plating layer 200 exceeds 50 μm, the productivity of the steel sheet 10 for hot pressing decreases, and the plating layer on the roller or mold during the hot pressing process 200 may be attached and the plating layer 200 may be peeled off from the base steel plate 100 .

The plating layer 200 may include silicon (Si), zinc (Zn), magnesium (Mg), aluminum (Al), and other unavoidable impurities.

Silicon (Si) may be added for the purpose of improving the workability of the plating layer 200 by reducing the growth of the alloy layer during plating. Silicon (Si) may be included in an amount of 1 wt% or more and 5 wt% or less, preferably 1 wt% to 3 wt%, based on the total weight of the plating layer 200 . When the content of silicon (Si) is less than 1 wt%, it is insufficient to control the growth of the alloy layer in the hot stamping heat treatment process of the plating layer 200, and thus the processability of the plating layer 200 may decrease during processing. In addition, when the content of silicon (Si) exceeds 5wt%, silicon (Si) is precipitated in a coarse single-phase form during plating in a cold rolling process, and workability and corrosion resistance may be deteriorated. When silicon (Si) is excessively included as such, the physical properties of the steel sheet 10 for hot pressing may be insufficient to be used for general building materials or home appliances. In addition, when silicon (Si) is excessively included, after hot stamping the steel sheet 10 for hot pressing, a phase having a high silicon (Si) content is increased in the intermediate alloy layer 220 to be described later, and the silicon (Si) content As the fraction of this high phase increases, the corrosion resistance of the plating layer 200 after hot stamping may decrease.

Zinc (Zn) may be added for the purpose of improving sacrificial corrosion protection. Zinc (Zn) may be included in an amount of 20 wt% to 45 wt%, preferably 25 wt% to 40 wt%, based on the total weight of the plating layer 200 . When the content of zinc (Zn) is less than 20 wt%, the content of zinc (Zn) included in the plating layer 200 may be insufficient to express corrosion resistance through sacrificial corrosion protection. If the amount of zinc (Zn) exceeds 45wt%, the zinc (Zn) component is scattered from the plating bath during the cold rolling process and the probability of generating Zn Ash (ZnO) defects increases, so the plating quality may deteriorate. there is. In addition, when the ?t amount of zinc (Zn) exceeds 45 wt%, the probability of liquid metal embrittlement occurring in the processing part during high-temperature processing after hot stamping heat treatment may increase.

Magnesium (Mg) may be added for the purpose of improving corrosion resistance. Magnesium (Mg) may be included in an amount of 0.2 wt% to 3 wt%, preferably 0.2 wt% to 1 wt%, based on the total weight of the plating layer 200 . When the content of magnesium (Mg) is less than 0.2wt%, the effect of improving corrosion resistance may not be sufficiently expressed. When the content of magnesium (Mg) exceeds 3 wt%, surface quality may be deteriorated during plating due to excessive oxidation of magnesium (Mg).

Meanwhile, an aluminum-rich region (Al-rich) and a zinc-rich region (Zn-rich) may exist on the surface of the plating layer 200 . The aluminum-enriched region (Al-rich) may mean a region in which aluminum (Al) is concentrated at a high rate, and the zinc-rich region (Zn-rich) may mean a region in which zinc (Zn) is concentrated at a high rate. In addition, a magnesium (Mg) compound and/or a magnesium (Mg) alloy phase may be included on the surface of the plating layer 200 .

2 and 3 are images in which a specific element is mapped on the surface of the plating layer 200, FIG. 2 is an image in which aluminum (Al) is mapped on the surface of the plating layer 200, and FIG. 3 is magnesium ( Mg) is an image mapped. In FIG. 2 , a colored (eg, green) portion is a region in which aluminum (Al) is concentrated, and magnesium (Mg) may be mainly distributed in a black portion. In addition, a portion represented by a color (eg, red) in FIG. 3 may be a region in which magnesium (Mg) is concentrated.

In one embodiment, magnesium (Mg) present on the surface of the plating layer 200 may be distributed as an Mg-based intermetallic compound containing magnesium (Mg). An area fraction of the Mg-based intermetallic compound present on the surface of the plating layer 200 may be about 2% or more and about 20% or less. More specifically, the Mg-based intermetallic compound present on the surface of the plating layer 200 may be mainly distributed in a zinc-rich region (Zn-rich). For example, 80% or more of the Mg-based intermetallic compound present on the surface of the plating layer 200 may be distributed in a zinc-rich region (Zn-rich). Since the Mg-based intermetallic compound can disintegrate the Al ₂ O ₃ oxide film of the aluminum enriched region (Al-Rich) having solid corrosion resistance, the fraction is preferably 2% to 20%, of which 80% or more is zinc. It is preferable to be distributed in the enriched area (Zn-Rich).

The Mg-based intermetallic compound may include, for example, Mg ₂ Si phase. The Mg ₂ Si phase is formed by reacting silicon (Si) and magnesium (Mg) included in the plating layer 200, and the Mg ₂ Si phase may be a precipitate phase that improves corrosion resistance. The Mg ₂ Si phase may be distributed on both the surface and inside of the plating layer 200 . Therefore, the fact that the Mg ₂ Si phase is distributed on the surface of the plating layer 200 may mean that a part of the Mg ₂ Si phase is exposed through the surface of the plating layer 200 . In one embodiment, a fraction of the Mg ₂ Si phase distributed on the surface of the plating layer 200 may be about 2% to about 10%. This Mg ₂ Si phase quickly penetrates into the zinc-rich region (Zn-rich) in a corrosive environment and can reduce the corrosion rate going down toward the base steel sheet 100, as well as magnesium (Mg) eluted from the Mg ₂ Si phase. Among silver zinc oxides, the corrosion resistance of the plating layer 200 can be further enhanced by playing a role of stabilizing the generation of simoncolite, which improves corrosion resistance.

On the other hand, when the content of magnesium (Mg) and silicon (Si) exceeds the above-described range, a large amount of network-type Mg ₂ Si phase is formed on the surface of the plating layer 200, which is the surface of the plating layer 200 in a corrosive environment. Alkalinity can be raised and galvanic corrosion can be created at the same time. This phenomenon may reduce corrosion resistance by generating pitting as well as disintegrating the aluminum-enriched region (Al-rich) having solid corrosion resistance by the aluminum oxide film (Al ₂ O ₃ ). In order to minimize this phenomenon, the range of the fraction of the Mg ₂ Si phase distributed on the surface of the plating layer 200 as described above may be 2% to 10%. When the fraction of the Mg ₂ Si phase distributed on the surface of the plating layer 200 is less than 2%, corrosion penetration control of the zinc-rich region (Zn-rich) is insufficient, and the Mg ₂ Si phase exposed through the surface of the plating layer 200 is insufficient. If the fraction is generated in excess of 10%, the probability of generating pitting in a corrosive environment may increase rapidly.

Meanwhile, the Mg ₂ Si phase may not remain after hot stamping the steel sheet 10 for hot pressing.

FIG. 4 is a flowchart schematically illustrating a method of manufacturing a steel sheet for hot pressing shown in FIG. 1 . Hereinafter, a method of manufacturing a steel sheet for hot pressing will be described with reference to FIGS. 1 and 4 together.

A method for manufacturing a steel sheet for hot pressing according to an embodiment of the present invention includes hot rolling of a steel slab (S310), cooling/coiling (S320), cold rolling (S330), annealing heat treatment (S340), and melting A plating step (S350) may be included.

First, a steel slab in a semi-finished state to be subjected to a process of forming a coated steel sheet is prepared. The steel slab contains 0.15 wt% to 0.40 wt% of carbon (C), 0.05 wt% to 3.0 wt% of silicon (Si), 0.1 wt% to 5.0 wt% of manganese (Mn), and more than 0.05 wt% of phosphorus (P). , Sulfur (S) greater than 0 and 0.03 wt% or less, aluminum (Al) greater than 0 and 0.1 wt% or less, the balance of iron (Fe) and other unavoidable impurities may be included. In addition, the steel slab may further include one or more components of 0.0005wt% to 0.01wt% of boron (B).

내지 1400

일 수 있다. 슬라브 재가열 온도(SRT)가 1200

보다 낮은 경우에는 주조 시 편석된 성분이 충분히 재고용되지 못해 합금 원소의 균질화 효과를 크게 보기 어렵고, 티타늄(Ti)의 고용 효과를 크게 보기 어렵다는 문제점이 있다. 슬라브 재가열 온도(SRT)는 고온일수록 균질화에 유리하나 1400

를 초과할 경우에는 오스테나이트 결정 입도가 증가하여 강도 확보가 어려울 뿐만 아니라 과도한 가열 공정으로 인하여 강판의 제조 비용만 상승할 수 있다.For hot rolling, the steel slab is reheated. In the steel slab reheating step, components segregated during casting are re-dissolved by reheating the steel slab obtained through the continuous casting process to a predetermined temperature. In one embodiment, the slab reheating temperature (SRT) is 1200

to 1400

can be The slab reheat temperature (SRT) is 1200

If it is lower than this, there is a problem in that the components segregated during casting are not sufficiently re-dissolved, so that it is difficult to see a large homogenization effect of alloy elements and a large solid solution effect of titanium (Ti). The higher the slab reheating temperature (SRT), the better homogenization is, but 1400

If it exceeds, the austenite grain size increases, making it difficult to secure strength, and only the manufacturing cost of the steel sheet may increase due to an excessive heating process.

내지 950

일 수 있다. 이때, 마무리 압연 온도(FDT)가 880

보다 낮으면, 이상영역 압연에 의한 혼립 조직이 발생으로 강판의 가공성 확보가 어렵고, 미세조직 불균일에 따라 가공성이 저하되는 문제가 있을 뿐만 아니라 급격한 상 변화에 의해 열간압연중 통판성의 문제가 발생한다. 마무리 압연 온도(FDT)가 950

를 초과할 경우에는 오스테나이트 결정립이 조대화된다. 또한, TiC 석출물이 조대화되어 최종 부품 성능이 저하될 위험이 있다.In the hot rolling step (S310), the reheated steel slab is hot rolled at a predetermined finish rolling temperature. In one embodiment, the Finishing Delivery Temperature (FDT) is 880

to 950

can be At this time, the finish rolling temperature (FDT) is 880

If it is lower than this, it is difficult to secure the workability of the steel sheet due to the occurrence of a mixed structure due to abnormal region rolling, and there is a problem of deterioration of workability due to non-uniformity of the microstructure, and a problem of sheet passability during hot rolling due to a rapid phase change occurs. Finish rolling temperature (FDT) is 950

If it exceeds, the austenite grains are coarsened. In addition, there is a risk that the TiC precipitate is coarsened and the performance of the final part is deteriorated.

내지 800

일 수 있다. 상기 권취 온도는 탄소(C)의 재분배에 영향을 미치며, 권취 온도가 550

미만일 경우에는 과냉으로 인한 저온상 분율이 높아져 강도 증가 및 냉간압연 시 압연부하가 심화될 우려가 있으며, 연성이 급격히 저하되는 문제점이 있다. 반대로, 권취 온도가 800

를 초과할 경우에는 이상 결정입자 성장이나 과도한 결정입자 성장으로 성형성 및 강도 열화가 발생하는 문제가 있다.In the cooling/coiling step (S320), the hot-rolled steel sheet is cooled to a predetermined coiling temperature (CT) and wound. In one embodiment, the winding temperature is 550

to 800

can be The coiling temperature affects the redistribution of carbon (C), and the coiling temperature is 550

If it is less than, there is a concern that the low-temperature phase fraction increases due to overcooling, and the rolling load during cold rolling increases in strength and intensifies, and there is a problem in that ductility rapidly deteriorates. Conversely, when the winding temperature is 800

If it exceeds, there is a problem in that moldability and strength deterioration occurs due to abnormal crystal grain growth or excessive crystal grain growth.

In the cold rolling step (S330), the rolled steel sheet is uncoiled, pickled, and then cold rolled. At this time, pickling is performed for the purpose of removing the scale of the rolled steel sheet, that is, the hot-rolled coil manufactured through the hot-rolling process.

이상의 온도에서 소둔 열처리하는 단계이다. 일 구체예에서 소둔 열처리 온도는 700

내지 850

일 수 있다. 소둔은 수소 10 ~ 30%, 질소 70 ~ 90%로 구성된 환원 분위기에서 실시할 수 있다. 소둔 열처리는 냉연 판재를 가열하고, 가열된 냉연 판재를 소정의 냉각속도로 냉각하는 단계를 포함할 수 있다.In the annealing heat treatment step (S340), the cold-rolled steel sheet is subjected to 700

It is a step of annealing heat treatment at a temperature higher than or equal to. In one embodiment, the annealing heat treatment temperature is 700

to 850

can be Annealing may be performed in a reducing atmosphere composed of 10 to 30% hydrogen and 70 to 90% nitrogen. The annealing heat treatment may include heating the cold-rolled sheet material and cooling the heated cold-rolled sheet material at a predetermined cooling rate.

The hot-dip plating step (S350) is a step of forming a plating layer on the annealed and heat-treated steel sheet. In the hot-dip plating step (S350), the plating layer 200 may be formed on the steel sheet subjected to the annealing heat treatment, that is, the base steel sheet 100.

내지 660

, 더욱 바람직하게는 550

내지 660

의 온도를 가지는 도금욕에 침지시켜 베이스 강판(100)의 표면에 용융도금층을 형성하는 단계와 상기 용융도금층이 형성된 상기 베이스 강판(100)을 냉각시켜 도금층(200)을 형성하는 냉각 단계를 포함할 수 있다.Specifically, in the hot-dip plating step (S350), the base steel sheet 100 is 520

to 660

, more preferably 550

to 660

Forming a hot-dip plating layer on the surface of the base steel sheet 100 by immersing it in a plating bath having a temperature of can

The plating bath may include 1 wt% to 5 wt% of silicon (Si), 20 wt% to 45 wt% of zinc (Zn), 0.2 wt% to 3 wt% of magnesium (Mg), and the balance of aluminum (Al). there is. More preferably, the plating bath contains 25 wt% to 45 wt% of zinc (Zn), 0.2 wt% to 1 wt% of magnesium (Mg), 1 wt% to 3 wt% of silicon (Si), and the balance of aluminum (Al). can include

In particular, silicon (Si) included in the plating bath may be added for the purpose of improving the workability of the plating layer 200 by reducing the growth of the alloy layer during plating. When the content of silicon (Si) is less than 1 wt%, it is insufficient to control the growth of the alloy layer in the hot stamping heat treatment process of the plating layer 200, and thus the processability of the plating layer 200 may decrease during processing. In addition, when the content of silicon (Si) exceeds 5wt%, silicon (Si) is precipitated in a coarse single-phase form during plating in a cold rolling process, and workability and corrosion resistance may be deteriorated.

Zinc (Zn) included in the plating bath may be added for the purpose of improving sacrificial corrosion protection. When the content of zinc (Zn) is less than 20 wt%, the content of zinc (Zn) included in the plating layer 200 may be insufficient to express corrosion resistance through sacrificial corrosion protection. If the amount of zinc (Zn) exceeds 45wt%, the zinc (Zn) component is scattered from the plating bath during the cold rolling process and the probability of generating Zn Ash (ZnO) defects increases, so the plating quality may deteriorate. there is. In addition, when the ?t amount of zinc (Zn) exceeds 45 wt%, the probability of liquid metal embrittlement occurring in the processing part during high-temperature processing after hot stamping heat treatment may increase.

Magnesium (Mg) included in the plating bath may be added for the purpose of improving corrosion resistance. When the content of magnesium (Mg) is less than 0.2wt%, the effect of improving corrosion resistance may not be sufficiently expressed. When the content of magnesium (Mg) exceeds 3 wt%, surface quality may be deteriorated during plating due to excessive oxidation of magnesium (Mg).

/s 내지 30

/s일 수 있다.The cooling step of cooling the base steel sheet 100 on which the hot-dip plating layer is formed may include a cooling step of cooling the base steel sheet 100 from the temperature of the plating bath to room temperature at an average cooling rate. At this time, the temperature of the plating bath to room temperature The overall average cooling rate of cooling up to 5

/s to 30

can be /s.

The plating layer 200 formed through the above process may be an Al-Si-Zn-Mg-based plating layer, and may be formed on at least one surface of the base steel sheet 100 in an amount of 20 g/m ² to 100 g/m ² . The thickness of the plating layer 200 can be adjusted by spraying air or gas onto the base steel sheet 100 to wipe the hot-dip plating layer before cooling the base steel sheet 100 on which the hot-dip plating layer is formed.

5 and 6 are TEM (Transmission Electron Microscopy) images of hot stamping parts according to an embodiment of the present invention. 5 is an image corresponding to the surface of the hot stamping part, and FIG. 6 is an image corresponding to the cross section of the hot stamping part.

Referring to FIGS. 5 and 6 together, the hot stamping part 20 may include a base steel plate 100' and a plating layer 200' attached on the base steel plate 100'. The hot stamping part 20 according to an embodiment of the present invention may be manufactured by applying a hot stamping process to the steel sheet 10 for hot pressing described with reference to FIGS. 1 to 3 .

The base steel sheet 100 ′ may be a steel sheet manufactured by performing a hot rolling process and/or a cold rolling process on a slab cast to include a predetermined amount of a predetermined alloy element. In one embodiment, the base steel sheet 100 ′ may include a first alloy composition. The first alloy composition contains 0.01 wt% or more and 0.5 wt% or less of carbon (C), 0.01 wt% or more and 3.0 wt% or less of silicon (Si), 0.3 wt% or more and 5.0 wt% or less of manganese (Mn), and more than 0 phosphorus (P). It may contain 0.1 wt% or less, sulfur (S) greater than 0 and 0.1 wt% or less, the balance of iron (Fe) and other unavoidable impurities.

In addition, the first alloy composition may further include one or more of boron (B), titanium (Ti), niobium (Nb), chromium (Cr), molybdenum (Mo), and nickel (Ni). Specifically, the first alloy composition includes boron (B) 0.0001 wt% or more and 0.005 wt% or less, titanium (Ti) 0.01 wt% or more and 0.1 wt% or less, niobium (Nb) 0.01 wt% or more and 0.1 wt% or less, chromium (Cr) ) 0.01wt% or more and 0.5wt% or less, molybdenum (Mo) 0.01wt% or more and 0.5wt% or less, and nickel (Ni) 0.01wt% or more and 1.0wt% or less may further include one or more components.

Carbon (C) acts as an austenite stabilizing element in the base steel sheet 100'. Carbon is a major element that determines the strength and hardness of the base steel sheet 100', and is added for the purpose of securing tensile strength and hardenability of the base steel sheet 100' after the hot stamping process. Carbon may be included in an amount of 0.01 wt% or more and 0.5 wt% or less based on the total weight of the base steel sheet 100'. When the carbon content is less than 0.01wt%, it is difficult to secure a hard phase (martensite, etc.) and thus it is difficult to satisfy the mechanical strength of the base steel sheet 100'. Conversely, if the carbon content exceeds 0.5 wt%, brittleness of the base steel sheet 100' or reduction in bending performance may be caused.

Silicon (Si) acts as a ferrite stabilizing element in the base steel sheet 100'. Silicon (Si), as a solid-solution strengthening element, improves the strength of the base steel sheet 100' and improves the carbon concentration in austenite by suppressing the formation of low-temperature carbides. In addition, silicon is a key element for hot rolling, cold rolling, hot press structure homogenization (perlite, manganese segregation zone control), and fine dispersion of ferrite. Silicon acts as a martensitic strength heterogeneity control element and serves to improve impact performance. Silicon may be included in an amount of 0.01 wt% or more and 3.0 wt% or less based on the total weight of the base steel sheet 100'. If the content of silicon is less than 0.01wt%, it is difficult to obtain the above-mentioned effect, cementite formation and coarsening may occur in the final hot stamping martensite structure, and the uniformity effect of the base steel sheet is insignificant and the V-bending angle cannot be secured. do. On the contrary, when the content of silicon exceeds 0.3wt%, the hot rolling and cold rolling loads increase, the hot rolled red scale becomes excessive, and the plating characteristics of the base steel sheet 100' may deteriorate.

Manganese (Mn) acts as an austenite stabilizing element in the base steel sheet 100'. Manganese is added for the purpose of increasing hardenability and strength during heat treatment. Such manganese may be included in an amount of 0.3 wt% or more and 5.0 wt% or less based on the total weight of the base steel sheet 100'. When the content of manganese is less than 0.3 wt%, the hardenability effect is not sufficient, and the hard phase fraction in the molded article after hot stamping may be insufficient due to insufficient hardenability. On the other hand, when the content of manganese exceeds 5.0 wt%, ductility and toughness may be deteriorated due to segregation of manganese or pearlite band, and a deterioration in bending performance may occur and a heterogeneous microstructure may occur.

Phosphorus (P) may be included in an amount greater than 0 and less than 0.1 wt% based on the total weight of the base steel sheet in order to prevent deterioration in the toughness of the base steel sheet 100'. When the content of phosphorus exceeds 0.1 wt%, iron phosphide compounds are formed to deteriorate toughness and weldability, and cracks may be induced in the base steel sheet during the hot stamping process.

Sulfur (S) may be included in an amount greater than 0 and 0.1 wt% or less based on the total weight of the base steel sheet 100'. If the sulfur content exceeds 0.1 wt%, hot workability, weldability, and impact characteristics after hot stamping may deteriorate, and surface defects such as cracks may occur due to the formation of large inclusions.

Boron (B) is added for the purpose of securing hardenability and strength of the base steel sheet 100' by suppressing ferrite, pearlite, and bainite transformation to secure martensite structure, and grain refinement by increasing austenite grain growth temperature have an effect Boron may be included in an amount of 0.0001 wt% to 0.005 wt% based on the total weight of the base steel sheet 100'. When boron is included in the above range, it is possible to prevent grain boundary brittleness in the hard phase and to secure high toughness and bendability.

Titanium (Ti) may be added for the purpose of strengthening hardenability and improving the material by forming precipitates after the hot stamping process. In addition, by forming a precipitate phase such as Ti(C,N) at high temperature, it effectively contributes to the refinement of austenite crystal grains. Titanium may be included in an amount of 0.01wt% to 0.1wt% based on the total weight of the base steel sheet 100'. When titanium is included in the content range, it is possible to prevent poor performance and coarsening of precipitates, easily secure physical properties of the steel, and prevent defects such as cracks on the surface of the steel.

Niobium (Nb) is added for the purpose of increasing strength and toughness by reducing martensite packet size. Niobium may be included in an amount of 0.01wt% to 0.1wt based on the total weight of the base steel sheet 100'. When niobium is included in the above range, the crystal grain refinement effect of the steel material is excellent in the hot rolling and cold rolling process, cracking of the slab during steelmaking/playing, and brittle fracture of the product are prevented, and the generation of coarse precipitates in steelmaking can be minimized. can

Chromium (Cr) is added for the purpose of improving hardenability and strength of the base steel sheet 100'. Chromium may be included in an amount of 0.01wt% to 0.5wt% based on the total weight of the base steel sheet 100'. When chromium is included in the above range, it is possible to improve hardenability and strength of the base steel sheet 100', and to prevent an increase in production cost and a decrease in toughness of steel.

Molybdenum (Mo) can contribute to improving the strength of the base steel sheet 100' by suppressing coarsening of precipitates and increasing hardenability during hot rolling and hot pressing. Such molybdenum (Mo) may be included in an amount of 0.01wt% to 0.5wt% based on the total weight of the base steel sheet 100'.

The hot stamping part 20 according to an embodiment of the present invention may include a plating layer 200' attached to the base steel sheet 100'. In one embodiment, the plating layer 200' may include silicon (Si), zinc (Zn), magnesium (Mg), aluminum (Al), iron (Fe), and other unavoidable impurities. In one embodiment, after the hot stamping process, the plating layer 200' may have a thickness of 15 μm to 40 μm. In this case, the thickness of the plating layer 200' may mean the average thickness of the plating layer 200'. When the thickness of the plating layer 200' is less than 15 μm, corrosion resistance as the plating layer 200' is not sufficient, and when the thickness of the plating layer 200' exceeds 40 μm, the plating layer 200' peels off during the hot stamping process. There may be a risk of becoming

The plating layer 200' may include an alloying layer 210, an intermediate alloy layer 220, and a surface layer 230 sequentially stacked on the base steel sheet 100'.

The alloying layer 210 is a layer disposed closest to the base steel sheet 100', and may be a layer having an iron (Fe) content as high as possible in the plating layer 200'. The alloying layer 210 is a layer produced by mutual diffusion of an iron (Fe) component in the base steel sheet 100' and an aluminum (Al) component in the plating layer 200', and is Fe-Al and/or Fe-Al- Si compounds may be included. Since the alloying layer 210 has a higher melting point than the surface layer 230, the surface layer 230 is melted during the hot stamping process and aluminum (Al) penetrates into the structure of the base steel sheet 100', a liquid metal embrittlement phenomenon. (Liquid Metal Embrittlement) can be prevented from occurring.

In one embodiment, the alloying layer 210 may have a thickness of 20 μm or less, more preferably 15 μm or less. When the thickness of the alloying layer 210 is formed to exceed 20 μm, a problem in that the plating layer 200 ′ of the processed portion may be removed during the hot stamping process may occur. The thickness of the alloying layer 210 may be controlled by the content of silicon (Si) or heat treatment conditions. In one embodiment, the alloying layer 210 may include 70wt% or more and 90wt% or less of iron (Fe), 5wt% or more and 15wt% or less of aluminum (Al), and 0.5wt% or more and 4wt% or less of silicon (Si).

The intermediate alloy layer 220 is a layer that plays a major role in forming corrosion resistance of the entire plating layer 200', and may contain a relatively large amount of zinc (Zn) compared to the alloying layer 210. Corrosion resistance of the plating layer 200' may be improved through a large amount of zinc (Zn) included in the intermediate alloy layer 220. In one embodiment, the intermediate alloy layer 220 contains iron (Fe) 35wt% or more and 45wt% or less, aluminum (Al) 30wt% or more and 45wt% or less, silicon (Si) 0.5wt% or more and 5wt% or less, and zinc (Zn) ) 5wt% or more and 20wt% or less.

The surface layer 230 is substantially provided on the surface layer portion of the plating layer 200' and preliminarily takes charge of corrosion resistance, and a region in which zinc (Zn) is concentrated (hereinafter, a first enriched portion) and magnesium (Mg) are concentrated. may include an area (hereinafter referred to as a second enrichment unit). In one embodiment, the surface layer 230 may include 20 wt% or more and 45 wt% or less of iron (Fe), 10 wt% or more and 35 wt% or less of aluminum (Al), and zinc (Zn) and magnesium (Mg).

7A to 7C are images of a cross section of a hot stamping part according to an embodiment of the present invention, FIG. 7A is a TEM image of a cross section of the hot stamping part, and FIG. It is an image in which (Zn) components are mapped, and FIG. 7c is an image in which magnesium (Mg) components are mapped based on the cross section of FIG. 7a.

Referring to FIGS. 7A to 7C , the surface layer 230 includes a first enriched portion 231 in which zinc (Zn) is concentrated (see FIG. 7B ) and a second enriched portion 232 in which magnesium (Mg) is concentrated (see FIG. 7C ). reference) may be included. The first enrichment unit 231 and the second enrichment unit 232 may serve to improve corrosion resistance by a corrosion product generated by participating in a chemical reaction in a corrosive environment.

The first enrichment part 231 and the second enrichment part 232 may be formed through a hot stamping process. That is, the first enrichment part 231 and the second enrichment part 232 may not exist in the plating layer 200 of the hot-pressed steel sheet 10 described with reference to FIGS. 1 to 3 before the hot stamping process. Zinc (Zn) and magnesium (Mg) components distributed in the plating layer 200 of the hot-pressed steel sheet 10 move to the surface layer of the plating layer 200 during the hot stamping process, and the hot stamping part 20 It may be distributed as a first enrichment part 231 and a second enrichment part 232 on the surface layer 230 of the .

As shown in FIGS. 7B and 7C , each of the first enrichment unit 231 and the second enrichment unit 232 may be formed as a separate layered structure. Alternatively, in some regions, the first enrichment unit 231 and the second enrichment unit 232 may be mixed and provided. In other words, it may be a structure in which the second enrichment unit 232 is disposed on the first enrichment unit 231 in some areas, and the first enrichment unit 231 is placed on the second enrichment unit 232 in other partial areas. may be arranged, and the first enrichment unit 231 is disposed in a substantially layered structure, and the second enrichment unit 232 penetrates the first enrichment unit 231 to form an upper or lower portion of the first enrichment unit 231. It may also be a structure disposed at the bottom.

In order for the first enriched portion 231 in which zinc (Zn) is concentrated to exhibit sufficient corrosion resistance in the plating layer 200', the average thickness of the first enriched portion 231 is 1 μm or more and 10 μm or less, more preferably, It is preferably formed to be 1 μm or more and 5 μm or less. In one embodiment, the first enrichment unit 231 contains iron (Fe) of 2wt% or more and 12wt% or less, aluminum (Al) of 0wt% or more and 10wt% or less, silicon (Si) of 0wt% or more and 2wt% or less, zinc (Zn) 40wt% or more and 80wt% or less and magnesium (Mg) 1wt% or more and 10wt% or less may be included.

In order for the second enriched portion 232 in which magnesium (Mg) is concentrated to exhibit sufficient corrosion resistance in the plating layer 200', the average thickness of the second enriched portion 232 is preferably formed to be 1 μm or more and 10 μm or less. do. In one embodiment, the second enrichment unit 232 includes iron (Fe) of 10wt% or more and 20wt% or less, aluminum (Al) of 1wt% or more and 20wt% or less, silicon (Si) of 0wt% or more and 2wt% or less, zinc (Zn) 5wt% or more and 20wt% or less and magnesium (Mg) 10wt% or more and 40wt% or less may be included.

Hereinafter, the present invention will be described in more detail through examples. However, the following examples are intended to explain the present invention in more detail, and the scope of the present invention is not limited by the following examples. The following examples may be appropriately modified or changed by those skilled in the art within the scope of the present invention.

<Evaluation method>

The steel sheet used as an example includes carbon (C) 0.01 wt% or more and 0.5 wt% or less, silicon (Si) 0.01 wt% or more and 3.0 wt% or less, manganese (Mn) 0.3 wt% or more and 5.0 wt% or less, phosphorus (P) More than 0 and less than 0.1wt%, sulfur (S) More than 0 and less than 0.1wt%, at least one of boron (B), titanium (Ti), niobium (Nb), chromium (Cr), molybdenum (Mo) and nickel (Ni) components, the balance of which includes iron (Fe) and other unavoidable impurities.

A cold-rolled steel sheet having a thickness of 1.0 mm is immersed in an alkali solution at 50 ° C for 30 minutes, and then washed with water to remove foreign substances and oil on the surface. This specimen is annealed and then plated.

Annealing is performed in a reducing atmosphere composed of about 10% to 30% hydrogen and about 70% to 90% nitrogen, and the annealing heat treatment temperature is 700 ° C to 850 ° C.

For plating, after cooling the annealed specimen to the plating bath temperature, immersing it in the plating bath for 2 seconds, pulling it up, adjusting the plating thickness to around 25㎛ with nitrogen wiping, and cooling at 5℃/sec to 30℃/sec Cool to room temperature at a rate to solidify. At this time, the plating bath temperature is 520 ° C to 660 ° C. After manufacturing the coated steel sheet under the above conditions, it is heated at 850° C. to 960° C. for 3 minutes to 10 minutes for hot stamping, and then hot stamping is performed on the heated coated steel sheet using a press mold. At this time, a specimen (hereinafter referred to as a hot stamping part) was manufactured by cooling at a cooling rate of 25° C./sec simultaneously with hot stamping molding.

<Evaluation of corrosion resistance before electrodeposition coating>

For hot stamping parts, a relative evaluation is conducted on the area where red rust occurs on the surface before electrodeposition coating, but as a comparative example (hereinafter, comparative example 1), a hot-dip galvanized steel sheet that has undergone a hot stamping process (e.g., Al-Si coated steel sheet) Compared to , the case where the red rust generation area was very good was evaluated as ◎ (excellent corrosion resistance), the excellent case was ○ (excellent corrosion resistance), the similar case was evaluated as △ (average corrosion resistance), and the poor case was evaluated as X (poor corrosion resistance).

<Appearance evaluation>

Regarding appearance evaluation, as a comparative example for hot stamping parts (hereinafter referred to as Comparative Example 1), compared to hot stamping hot-dip galvanized steel sheet (e.g., Al-Si coated steel sheet), surface oxidation stains and stains caused by complex precipitates are at the same level. Cases were evaluated as ○ (equal), inferior cases as △ (inferior), and extremely inferior cases as X (very inferior).

division Al (%) Zn(%) Si(%) Mg (%) 1st Department of Agriculture
average thickness alloying layer
average thickness Before electrodeposition coating
Corrosion resistance evaluation Appearance evaluation Comparative Example 1 Al of balance - 9.3 - - 9 - - Comparative Example 2 Al of balance 10 3 0.8 0.3 15 △ ○ Comparative Example 3 Al of balance 50 3 0.8 4 12 ○ △ Comparative Example 4 Al of balance 30 0.5 0.8 One 22 ○ ○ Comparative Example 5 Al of balance 30 7 0.8 1.7 7 △ ○ Comparative Example 6 Al of balance 30 3 0.1 2 14 △ ○ Comparative Example 7 Al of balance 30 3 4 1.5 13 ◎ △ Example 1 Al of balance 25 3 0.8 1.2 13 ○ ○ Example 2 Al of balance 30 2 0.8 2 16 ○ ○ Example 3 Al of balance 35 3 0.8 2.5 14 ◎ ○ Example 4 Al of balance 40 3 One 3 14 ◎ ○

As can be seen from [Table 1], zinc (Zn): 20 wt% to 45 wt%, magnesium (Mg): 0.2 wt% to 3 wt%, silicon (Si): 1 wt% to 5 wt% Compared to Examples 1 to 4 of the present invention, Comparative Example 2, Comparative Example 5, and Comparative Example 6 formed with a plating layer outside the above-described composition range were found to be inferior in corrosion resistance evaluation before electrodeposition coating, and the rest Comparative examples appeared to be on par. In addition, Comparative Example 3 and Comparative Example 7 were found to be inferior in appearance evaluation compared to Examples 1 to 4 of the present invention, and the remaining Comparative Examples were found to be at the same level.

More specifically, Comparative Example 2 includes 10 wt% of zinc (Zn), and Comparative Example 3 includes 50 wt% of zinc (Zn). Compared to Examples 1 to 4 in which the zinc (Zn) content in the plating layer is 20 wt% to 45 wt%, as in Comparative Example 2, when the zinc (Zn) content is added to less than 20 wt%, the zinc (Zn) included in the plating layer ( Zn) content is not enough to express sacrificial corrosion resistance, and it is difficult to expect additional corrosion resistance improvement because the thickness of the first thickened portion generated on the surface layer after hot stamping is formed thin. In addition, as in Comparative Example 3, when the zinc (Zn) content exceeds 45 wt% and is added, the zinc (Zn) component is scattered in the plating bath and the probability of generating Zn Ash (ZnO) defects increases, so through appearance evaluation As can be seen, it can be seen that the plating quality is deteriorated.

Comparative Example 4 includes 0.5 wt% of silicon (Si), and Comparative Example 5 includes 7 wt% of silicon (Si). Compared to Examples 1 to 4 in which the content of silicon (Si) in the plating layer is 1 wt% to 5 wt%, as in Comparative Example 4, when the content of silicon (Si) is added to less than 1 wt%, the hot stamping heat treatment process of the plating layer Insufficient to control the growth of the alloy layer, resulting in reduced workability of the plating layer during processing. In addition, when the content of silicon (Si) is added in excess of 5 wt% as in Comparative Example 5, a phase having a high content of silicon (Si) is formed before and after hot stamping, and it can be seen that corrosion resistance is deteriorated in a corrosive environment.

Comparative Example 6 includes 0.1 wt% of magnesium (Mg), and Comparative Example 7 includes 4 wt% of magnesium (Mg). Compared to Examples 1 to 4 in which the content of magnesium (Mg) in the plating layer is 0.2 wt% to 3 wt%, as in Comparative Example 6, when magnesium (Mg) is added at less than 0.2 wt%, magnesium (Mg) It can be confirmed that the corrosion resistance improvement is weak because the addition amount is small. In addition, when magnesium (Mg) is added in excess of 3wt% as in Comparative Example 7, it can be seen that the surface quality during plating is poor due to excessive magnesium (Mg) oxidation.

<Evaluation of outdoor exposure corrosion resistance of coated steel sheet before hot pressing>

A relative evaluation is conducted on the red rust generation area (pitting) generated on the surface by outdoor exposure for one year. , Al-Si steel sheet), when the red rust generation area was excellent, ○ (excellent corrosion resistance), inferior cases were evaluated as △ (poor corrosion resistance), and more inferior cases were evaluated as X (extremely poor corrosion resistance).

division Al (%) Zn(%) Si(%) Mg (%) plating surface
Mg2Si phase fraction (%) outdoor exposure
Corrosion resistance evaluation Comparative Example 8 Al of balance - 10 - - X Comparative Example 9 Al of balance 30 0.5 0.8 <1 △ Comparative Example 10 Al of balance 30 7 3 12 △ Example 5 Al of balance 30 3 0.8 5 ○ Example 6 Al of balance 30 2 0.8 3 ○

As can be seen from [Table 2], in Examples 5 and 6 in which the content of silicon (Si) in the plating layer was 1 wt% to 5 wt%, the phase fraction of the Mg2Si phase was formed at 2% to 20%, which was exposed outdoors. It can be seen that the corrosion resistance evaluation according to is excellent. On the other hand, in Comparative Example 9 and Comparative Example 10 in which the content of silicon (Si) in the plating layer was 0.5 wt% and 7 wt%, respectively, the phase fraction of the Mg2Si phase was formed outside the scope of the present invention, respectively, so the corrosion resistance evaluation according to outdoor exposure was relatively You can check what's hot with .

As such, the present invention has been described with reference to an embodiment shown in the drawings, but this is only exemplary, and those skilled in the art will understand that various modifications and variations of the embodiment are possible therefrom. Therefore, the true technical scope of protection of the present invention should be determined by the technical spirit of the appended claims.

100, 100': base steel plate
200, 200': plating layer
210: alloying layer
220: intermediate alloy layer
230: surface layer
231: first agriculture department
232: second agriculture department

Claims (13)

base grater; and
Disposed on the base steel sheet, zinc (Zn): 20 wt% to 45 wt%, magnesium (Mg): 0.2 wt% to 3 wt%, silicon (Si): 1 wt% to 5 wt%, the balance aluminum a plating layer containing (Al) and other unavoidable impurities;
A steel sheet for hot pressing comprising a. According to claim 1,
Magnesium (Mg) on the surface of the plating layer is distributed as an Mg-based intermetallic compound,
80% or more of the Mg-based intermetallic compound is distributed in a zinc rich region located on the surface of the plating layer, hot press steel sheet. According to claim 2,
The Mg-based intermetallic compound comprises a Mg ₂ Si phase, a steel sheet for hot pressing. According to claim 3,
The Mg ₂ Si phase distributed on the surface of the plating layer has a phase fraction of 2% to 10%, a steel sheet for hot pressing. base grater; and
A plating layer disposed on the base steel sheet and containing zinc (Zn), magnesium (Mg), silicon (Si), aluminum (Al), the balance of iron (Fe) and other unavoidable impurities;
The plating layer includes an alloying layer, an intermediate alloy layer, and a surface layer sequentially stacked from the base steel sheet,
The surface layer includes a first enriched portion in which zinc (Zn) is concentrated and a second enriched portion in which magnesium (Mg) is concentrated. According to claim 5,
The first enrichment unit contains iron (Fe): 2 wt% to 12 wt%, aluminum (Al): 0 wt% to 10 wt%, silicon (Si): 0 wt% to 2 wt%, magnesium (Mg): 1 wt% to 10 wt% and zinc (Zn): 40 wt% to 80 wt%. According to claim 5,
The second enrichment part iron (Fe): 10 wt% to 20 wt%, aluminum (Al): 1 wt% to 20 wt%, silicon (Si): 0 wt% to 2 wt%, zinc (Zn): 5 wt% to 20 wt% and Magnesium (Mg): 10 wt% to 40 wt%. According to claim 5,
The alloying layer includes iron (Fe): 70 wt% to 90 wt%, aluminum (Al): 5 wt% to 15 wt%, and silicon (Si): 0.5 wt% to 4 wt%. According to claim 5,
The thickness of the alloying layer is 20㎛ or less, hot stamping parts. According to claim 5,
The intermediate alloy layer contains iron (Fe): 35 wt% to 45 wt%, aluminum (Al): 30 wt% to 45 wt%, silicon (Si): 0.5 wt% to 5 wt%, and zinc (Zn): 5 A hot stamped part comprising from wt% to 20 wt%. According to claim 5,
The surface layer includes iron (Fe): 20 wt% to 45 wt% and aluminum (Al): 10 wt% to 35 wt%. According to claim 5,
The first thickened portion has an average thickness of 1 μm or more and 10 μm or less. According to claim 9,
The average thickness of the plating layer is 15㎛ to 40㎛, hot stamping parts.

Images