KR20230049472A - Steel sheet for hot press and Hot stamping component manufactured using the same - Google Patents

Abstract

One embodiment 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. Discloses a hot stamping part comprising an alloying layer, an intermediate alloy layer and a surface layer sequentially stacked from the base steel sheet, wherein the intermediate alloy layer contains a Zn rich phase.

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. Due to the liquid metal embrittlement (LME) phenomenon, there are 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 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. The hot stamping part includes an alloying layer, an intermediate alloy layer, and a surface layer sequentially stacked from the base steel sheet, and the intermediate alloy layer includes a zinc rich phase.

According to the present embodiment, the zinc enriched phase includes zinc (Zn): 50 wt% to 99 wt%, iron (Fe): 5 wt% to 20 wt%, aluminum (Al): 0 wt% to 5 wt%, Silicon (Si): 0 wt% to 1 wt% and magnesium (Mg): 0 wt% to 5 wt% may be included.

According to this embodiment, the zinc-enriched phase may be included in 3% to 10% in the intermediate alloy layer.

According to the present embodiment, the surface layer may include a first enriched portion in which zinc (Zn) is enriched.

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 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 this embodiment, the surface layer may further include a second enriched portion in which magnesium (Mg) is concentrated.

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 average thickness of the plating layer may be 15 μm to 40 μm.

According to another aspect of the present invention, the base steel plate; And disposed on the base steel sheet, zinc (Zn): 30 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 embodiments of the present invention, in forming an aluminum-based plating layer, a steel sheet for hot pressing having sacrificial anticorrosiveness and excellent workability and a hot stamping part manufactured using the same can be manufactured by adding Zn in an appropriate ratio.

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.
FIG. 2 is a flowchart schematically illustrating a method of manufacturing a steel sheet for hot pressing shown in FIG. 1 .
3 is a TEM (Transmission Electron Microscopy) image of a cross section of a hot stamping part according to an embodiment of the present invention.
FIG. 4 is a mapped image of zinc (Zn) components based on FIG. 3 .
5 is a flowchart illustrating a method of manufacturing a hot stamping part according to an embodiment of the present invention.

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.

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 the tensile strength of the base steel sheet 100' after the hot press process and securing hardenability characteristics. do. 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 may cause

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 the 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 0.01wt% to 3.0wt% based on the total weight of the base steel sheet 100'. When silicon is included in less than 0.01wt%, it is difficult to obtain the above-mentioned effect, and conversely, when the content of silicon exceeds 3.0wt%, the hot rolling and cold rolling loads increase, and the red scale of hot rolling becomes excessive and the base steel sheet (100') The plating properties of may be deteriorated.

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 the toughness of the base steel sheet 100'. If 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, hardenability and strength of the base steel sheet 100' may be improved, and production cost increase and toughness decrease of the steel material may be prevented.

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 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 roller or mold during the hot pressing process The plating layer 200' is attached to the plated layer 200', and the plating layer 200' may be peeled off from the base steel sheet 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 30wt% to 45wt% based on the total weight of the plating layer 200'. When the content of zinc (Zn) is less than 30wt%, the content of zinc (Zn) included in the plating layer 200' is insufficient, so that a zinc rich phase to be described later is not formed in the plating layer 200'. 200') may not sufficiently express corrosion resistance through the sacrificial corrosion resistance. 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 occurrence of liquid metal embrittlement in the processing part during high-temperature processing after hot stamping heat treatment may increase. That is, when the ?t amount of zinc (Zn) exceeds 45 wt%, the coating layer is easily liquefied during high-temperature heat treatment due to the low melting point of zinc, and tensile stress acts during high-temperature forming such as hot stamping. Fracture of the parent material may occur.

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'.

FIG. 2 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 FIG. 1 together.

A method for manufacturing a steel sheet for hot pressing according to an embodiment of the present invention includes a hot rolling step of a steel slab (S110), a cooling/coiling step (S120), a cold rolling step (S130), an annealing heat treatment step (S140), and melting A plating step (S150) 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).

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) may be 1200 ° C to 1400 ° C. If the slab reheating temperature (SRT) is lower than 1200 ° C., there is a problem that the components segregated during casting are not sufficiently re-dissolved, making it 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 higher the homogenization, but when it exceeds 1400 ° C., the grain size of austenite increases, making it difficult to secure strength, and only the manufacturing cost of the steel sheet may increase due to the excessive heating process.

In the hot rolling step (S110), the reheated steel slab is hot rolled at a predetermined finish rolling temperature. In one embodiment, the finishing delivery temperature (FDT) may be 880 °C to 950 °C. At this time, if the finish rolling temperature (FDT) is lower than 880 ° C, 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 in workability due to non-uniform microstructure, as well as rapid phase change. Due to this, a problem of sheet passability occurs during hot rolling. When the finish rolling temperature (FDT) exceeds 950° C., 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.

In the cooling/coiling step (S120), the hot-rolled steel sheet is cooled to a predetermined coiling temperature (CT) and wound. In one embodiment, the winding temperature may be 550 ℃ to 800 ℃. The coiling temperature affects the redistribution of carbon (C), and if the coiling temperature is less than 550 ° C, the low-temperature phase fraction due to overcooling increases, so there is a risk of increasing strength and intensifying the rolling load during cold rolling, and ductility rapidly decreases There is a problem being Conversely, when the coiling temperature exceeds 800° C., there is a problem in that formability and strength deteriorate due to abnormal crystal grain growth or excessive crystal grain growth.

In the cold rolling step (S130), 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.

The annealing heat treatment step (S140) is a step of annealing the cold-rolled steel sheet at a temperature of 700° C. or higher. In one embodiment, the annealing heat treatment temperature may be 700 °C to 850 °C. 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 (S150) is a step of forming a plating layer on the annealed and heat-treated steel sheet. In the hot-dip plating step (S150), a plating layer 200' may be formed on the steel sheet subjected to the annealing heat treatment, that is, the base steel sheet 100'.

Specifically, in the hot-dip plating step (S150), the base steel sheet 100' is immersed in a plating bath having a temperature of 520°C to 660°C, more preferably 550°C to 660°C, on the surface of the base steel sheet 100'. A step of forming a hot-dip plating layer and a cooling step of forming a plating layer 200' by cooling the base steel sheet 100' on which the hot-dip plating layer is formed may be included.

The plating bath may include 30 wt% to 45 wt% of zinc (Zn), 1 wt% to 5 wt% of silicon (Si), 0.2 wt% to 3 wt% of magnesium (Mg), and the balance of aluminum (Al). there is. More preferably, the plating bath contains 30 wt% to 45 wt% of zinc (Zn), 1 wt% to 3 wt% of silicon (Si), 0.2 wt% to 1 wt% of magnesium (Mg), 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 30 wt%, the content of zinc (Zn) included in the plating layer 200' is insufficient, so that a zinc rich phase to be described later is not formed within an appropriate range in the plating layer 200'. Therefore, corrosion resistance through the sacrificial corrosion resistance of the plating layer 200' may not be sufficiently expressed. 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 occurrence of liquid metal embrittlement 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).

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 The overall average cooling rate for cooling from to room temperature may be 5 ° C / s to 30 ° C / s.

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

FIG. 3 is a TEM (Transmission Electron Microscopy) image of a cross section of a hot stamping part according to an embodiment of the present invention, and FIG. 4 is an image in which zinc (Zn) components are mapped based on FIG. 3 .

Referring to FIG. 3 , 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 hot stamping the steel sheet 10 for hot pressing described with reference to FIGS. 1 and 2 .

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, when 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 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. Such 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%, hot rolling and cold rolling loads increase, hot rolled red scale is excessive, and plating characteristics of the base steel sheet 100 may be deteriorated.

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 0.1 wt% or less based on the total weight of the base steel sheet in order to prevent deterioration in 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 a martensitic structure, and grain refinement effect by increasing austenite grain growth temperature have 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) 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 hot stamping part 20 according to an embodiment of the present invention may include a plating layer 200 attached on 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 an 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 sufficiently exhibited, and when the thickness of the plating layer 200 exceeds 40 μm, there is a concern that the plating layer 200 may be peeled off during the hot stamping process. can

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

The alloying prevention layer 210 is a layer disposed closest to the base steel sheet 100 and may be a layer having an iron (Fe) content in the plating layer 200 as high as possible. The anti-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 prevention layer 210 has a higher melting point than the surface layer 230, the surface layer 230 is melted during the hot stamping process, so that aluminum (Al) penetrates into the structure of the base steel sheet 100. Liquid metal embrittlement ( Liquid Metal Embrittlement (LME) can be prevented from occurring.

In one embodiment, the thickness of the anti-alloying layer 210 may be provided with 20 μm or less, more preferably 15 μm or less. When the thickness of the anti-alloying layer 210 is formed to exceed 20 μm, a problem in that the plated layer 200 in the processing region may be removed during the hot stamping process may occur. The thickness of the anti-alloying layer 210 may be controlled by the content of silicon (Si) or heat treatment conditions. In one embodiment, the anti-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 prevention layer 210. The intermediate alloy layer 220 may include a zinc rich phase 222 in which zinc is intensively precipitated. The zinc enriched phase 222 may be randomly precipitated in the intermediate alloy layer 220 as shown in FIGS. 3 and 4 . In order for the zinc enriched phase 222 to appear in the intermediate alloy layer 220, the zinc content must be 30wt% to 45wt% in the plating layer 200' of the steel sheet 10 for hot pressing before hot stamping described with reference to FIG. 1. do. When the zinc content in the plating layer 200' is less than 30wt%, the zinc enriched image 222 may not be formed.

In one embodiment, the zinc enriched phase 222 in the intermediate alloy layer 220 may be included in an area fraction of about 3% or more and about 10% or less. For example, if the zinc enriched phase 222 is included in less than 3% in the intermediate alloy layer 220, it is insufficient to express corrosion resistance through sacrificial corrosion protection, and if it is included in more than 10%, during processing or welding after hot stamping heat treatment The probability of occurrence of the LME phenomenon may increase. Therefore, when the zinc enriched phase 222 is included in an amount of about 3% or more and 10% or less in the intermediate alloy layer 220, the corrosion resistance of the plating layer 200 is enhanced and the LME phenomenon due to the low melting point of zinc is prevented from occurring. It can be prevented.

In order to form the zinc-enriched phase 222, the temperature during hot stamping should be controlled to about 900° C. or higher and 950° C. or lower. When hot stamping is performed at a temperature of 900° C. or more and 950° C. or less, zinc distributed on aluminum in the plating layer 200 may escape and precipitate in the intermediate alloy layer 220 . For example, when the temperature is less than 900 ° C during hot stamping, diffusion of zinc occurs relatively weakly, so that the zinc enriched phase 222 is not formed in the intermediate alloy layer 220, and when the temperature exceeds 950 ° C during hot stamping, excessive Zn Ash The surface appearance and plating quality of the plating layer 200 may be deteriorated by generating (ZnO) defects.

Corrosion resistance of the plating layer 200 may be improved through the zinc enriched phase 222 included in the intermediate alloy layer 220 . In one embodiment, the zinc enriched phase 222 contains zinc (Zn) of 50 wt% or more and 99 wt% or less, iron (Fe) of 5 wt% or more and 20 wt% or less, aluminum (Al) of 0 wt% or more and 5 wt% or less, and silicon (Si) 0 wt%. % or more and 1 wt% or less, and magnesium (Mg) may include 0 wt% or more and 5 wt% or less.

The surface layer 230 is substantially provided on the surface layer portion of the plating layer 200 and preemptively takes charge of corrosion resistance, and is a region in which zinc (Zn) is concentrated (hereinafter, a first enriched portion) and magnesium (Mg) are concentrated. A region (hereinafter referred to as a second enrichment unit) may be included. 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).

Meanwhile, the surface layer 230 may include a first enriched portion 231 in which zinc (Zn) is concentrated and a second enriched portion 232 in which magnesium (Mg) is concentrated. In FIG. 3 , the first enrichment portion 231 appears in a relatively bright color, and the second enrichment portion 232 appears in a relatively dark color. 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 unit 231 and the second enrichment unit 232 may not exist in the plating layer 200' of the hot-pressed steel sheet 10 described with reference to FIGS. 1 and 2 before the hot stamping process. . That is, the 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 parts It can be distributed as a first enrichment part 231 and a second enrichment part 232 in the surface layer 230 of (20).

In one embodiment, 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 concentrated portion 231 in which zinc (Zn) is concentrated to exhibit sufficient corrosion resistance in the plating layer 200, the average thickness of the first concentrated portion 231 is 1 μm or more and 10 μm or less, more preferably 1 μm. It is preferable that it is formed to be 5 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 to exhibit sufficient corrosion resistance in the plating layer 200 of the second enriched portion 232 in which magnesium (Mg) is concentrated, the average thickness of the second enriched portion 232 is preferably formed to be 1 μm or more and 10 μm or less. . 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.

As described above, the intermediate alloy layer 220 and the surface layer 230 are layers that form corrosion resistance of the plating layer 200, and the zinc enriched phase 222 is included in the intermediate alloy layer 220, and the surface layer 230 ), the first enrichment unit 231 may be included. The zinc enriched image 222 and the first enriched portion 231 may contain a large amount of zinc (Zn), as can be seen from the image in which zinc (Zn) components are mapped as shown in FIG. 4 . Since zinc (Zn) included in the plating layer 200 serves to improve sacrificial corrosion protection, the zinc-enriched phase 222 and the first enriched portion 231 containing a large amount of zinc (Zn) in the plating layer 200 By including them together, the corrosion resistance of the plating layer 200 can be further improved. In particular, since the intermediate alloy layer 220 plays a major role in forming the corrosion resistance of the entire plating layer 200, the corrosion resistance of the entire plating layer 200 is improved through the zinc enriched image 222 included in the intermediate alloy layer 220. and can effectively improve the LME phenomenon.

5 is a flowchart illustrating a method of manufacturing a hot stamping part according to an embodiment of the present invention.

Referring to FIG. 5 , in the method of manufacturing a hot stamping part according to an embodiment, a steel sheet is prepared (S100), a heating step (S200), a transfer step (S300), a forming step (S400), and a cooling step (S500). ) may be included.

The step of preparing the steel sheet (S100) may be a step of manufacturing the steel sheet 10 for hot pressing as described with reference to FIG. 2 . As described with reference to FIG. 1 , the steel sheet 10 for hot pressing may include a base steel sheet 100' and a plating layer 200' provided on the base steel sheet 100'.

Although not shown in FIG. 5, in some cases, the steel sheet 10 for hot pressing manufactured by the manufacturing method of FIG. 2 may further perform a post-processing step. That is, a post-treated steel sheet may be prepared by applying a Si-based inorganic post-treatment agent on the steel sheet on which the plating layer is formed to form a pre-post-treatment layer and drying the pre-treatment layer.

Thereafter, in the heating step (S200), the steel sheet may be put into a heating furnace and heated. In the heating step, the steel sheet may be heated to a target heating temperature in order to secure the material of the steel sheet and prevent evaporation of the plating layer in the heating furnace. The steel sheet may be heated while remaining for about 3 minutes to 10 minutes in the heating step (S200).

In the heating step (S200), the target heating temperature may be about 900 °C to 950 °C. As described with reference to FIGS. 3 and 4 , in order to form a zinc rich phase, the temperature should be controlled to about 900° C. to 950° C. in the heating step (S200). In the process of heating the steel sheet at a temperature of about 900° C. to 950° C., zinc distributed on aluminum in the plating layer may escape and precipitate in the intermediate alloy layer. If the temperature during hot stamping is less than 900℃, diffusion of zinc occurs relatively weakly, and a zinc enriched phase is not formed in the intermediate alloy layer. If the temperature exceeds 950℃ during hot stamping, excessive Zn Ash (ZnO) defects occur. The surface appearance and plating quality of the plating layer may be impaired.

In one embodiment, the precipitated zinc enriched phase may be included in an area fraction of about 3% to 10% in the intermediate alloy layer. When the zinc enriched phase is included in an area fraction of about 3% to 10% in the intermediate alloy layer, the corrosion resistance of the plating layer 200 can be enhanced and the occurrence of the LME phenomenon due to the low melting point of zinc can be prevented. In addition, in one embodiment, the zinc enriched phase includes zinc (Zn) 50wt% or more and 99wt% or less, iron (Fe) 5wt% or more and 20wt% or less, aluminum (Al) 0wt% or more and 5wt% or less, silicon (Si) 0wt% 1 wt% or less, and 0 wt% or more to 5 wt% or less of magnesium (Mg) may be included.

Depending on the embodiment, multi-stage heating or split heating may be performed in the heating step.

The multi-stage heating step may be a step of heating the steel sheet in stages, and the soak heating step may be a step of heating the multi-stage heated steel sheet to a uniform temperature. In the multi-stage heating step, the steel sheet may be gradually heated while passing through a plurality of sections provided in the heating furnace. Among a plurality of sections provided in the heating furnace, there may be a plurality of sections in which the multi-stage heating step is performed, and the temperature is set for each section so as to increase from the inlet of the heating furnace into which the steel plate is introduced to the exit of the heating furnace into which the steel plate is taken out. Thus, the temperature of the steel sheet can be raised step by step. A soak heating step may be performed after the multi-stage heating step. In the soak heating step, the multi-stage heated steel sheet may be heat treated while passing through a section of a heating furnace set at a temperature of about Ac3 to about 910 °C. Also, among a plurality of sections provided in the heating furnace, at least one section in which the soak heating step is performed may be present.

Thereafter, in the transfer step (S300), the heated steel sheet may be transferred from the heating furnace to the press mold. The blank heated in the transfer step (S300) may be air-cooled for 5 to 30 seconds.

The forming step (S400) is a step of hot stamping the transferred steel sheet to form a molded body, that is, a hot stamped part. In the molding step (S400), the molding start temperature may be about 550 °C to about 750 °C. When the molding temperature is about 750 ° C. or higher, cracks of about 10 μm or more occur on the sidewall of the hot stamping part due to liquid metal embrittlement (LME), resulting in a decrease in durability. Conversely, when the forming temperature is about 550° C. or less, there is a problem of insufficient material of the steel sheet.

The cooling step (S500) is a step of cooling the formed molded body. In the cooling step (S500), the average cooling rate may be about 25°C/sec or more.

A final product may be formed by cooling the compact at the same time that it is molded into a final part shape in a press mold. A cooling channel through which a refrigerant circulates may be provided in the press mold. The heated blank can be quenched by circulation of the refrigerant supplied through the cooling channel provided in the press mold. At this time, in order to prevent the spring back phenomenon of the plate material and to maintain the desired shape, rapid cooling may be performed while pressurizing the press mold in a closed state. In forming and cooling the heated blank, it may be cooled at an average cooling rate of at least 10° C./s or more to the end temperature of martensite. The blank may be held in the press mold for 3 to 20 seconds. If the holding time in the press mold is less than 3 seconds, the cooling of the material is not sufficiently performed, and the temperature deviation of each part due to the residual heat may affect the water intake quality. In addition, mechanical properties may not be secured because a sufficient amount of martensite is not generated. On the other hand, when the holding time in the press mold exceeds 20 seconds, the holding time in the press mold becomes long, and productivity may decrease.

The hot stamping part controlled through the manufacturing method according to an embodiment of the present invention includes a zinc rich phase in which zinc is concentrated and precipitated in the plating layer, particularly in the intermediate alloy layer, so that the corrosion resistance of the plating layer is improved. It can be. In this case, the area fraction of the zinc enriched phase may be 3% or more and 10% or less in the intermediate alloy layer.

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, lifting 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 900° C. to 950° 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 referred to as 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).

division Al (%) Zn(%) Si(%) Mg (%) heat treatment temperature
(℃) Zn rich phase area fraction (%) in the intermediate alloy layer Before electrodeposition coating
Corrosion resistance evaluation Comparative Example 1 Al of balance - 9.3 - - - Comparative Example 2 Al of balance 10 3 0.8 930 0 △ Comparative Example 3 Al of balance 20 3 0.8 800 One △ Comparative Example 4 Al of balance 35 3 0.8 800 1.5 △ Example 1 Al of balance 30 2 0.8 900 3 ○ Example 2 Al of balance 30 2 0.8 930 6 ◎ Example 3 Al of balance 40 3 One 930 8 ◎

As described with reference to FIGS. 1 to 5, in order to form a zinc rich phase in the plating layer of a hot stamping part according to an embodiment, the zinc content in the plating layer of the steel sheet for hot pressing before hot stamping is 30wt. % or more and 45 wt% or less, and the heat treatment temperature in the heating step during hot stamping must satisfy 900 ° C. or more and 950 ° C. or less. When the above range is satisfied, a zinc enriched phase may be precipitated in the intermediate alloy layer of the plating layer. At this time, it is preferable that the area fraction of the zinc enriched phase is 3% or more and 10% or less in the intermediate alloy layer.

As can be seen from [Table 1], in the case of Comparative Example 2, 10 wt% of zinc was included in the plating layer, so even if the heat treatment temperature satisfies 930 ° C., it can be seen that no zinc enriched phase was precipitated in the intermediate alloy layer. . In addition, in the case of Comparative Example 3, 20wt% of zinc was included in the plating layer, and the heat treatment temperature was also set to 800° C., so that the area fraction of the zinc enriched phase in the intermediate alloy layer was 1%. In addition, in Comparative Example 4, although the zinc content in the plating layer was 35wt%, it can be seen that the zinc-rich phase was not sufficiently precipitated in the intermediate alloy layer by about 1.5% because the heat treatment temperature was set to 800° C. during hot stamping. It can be seen that the corrosion resistance evaluation before electrodeposition coating of Comparative Examples 2 to 4 was similar to that of Comparative Example 1.

On the other hand, in the case of Examples 1 to 3 of the present invention, the content of zinc in the plating layer satisfies 30 wt% or more and 45 wt% or less, and the heat treatment temperature in the heating step during hot stamping was performed at 900 ° C or more and 950 ° C or less, It can be seen that the area fraction of the zinc enriched phase satisfies a range of 3% or more and 10% or less in the intermediate alloy layer. It can be seen that the corrosion resistance of Examples 1 to 3 before electrodeposition coating is excellent or very excellent when compared to Comparative Example 1.

As such, the present invention has been described with reference to one embodiment shown in the drawings, but this is merely 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 (10)

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 intermediate alloy layer comprises a zinc rich phase, hot stamping parts. According to claim 1,
The zinc enriched phase includes zinc (Zn): 50 wt% to 99 wt%, iron (Fe): 5 wt% to 20 wt%, aluminum (Al): 0 wt% to 5 wt%, silicon (Si): 0 wt% to 1 wt% and Magnesium (Mg): 0 wt% to 5 wt%. According to claim 1,
The zinc enriched phase is contained in 3% to 10% in the intermediate alloy layer, hot stamping parts. According to claim 1,
The surface layer includes a first enriched portion in which zinc (Zn) is enriched. 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 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 4,
The surface layer further includes a second enriched portion in which magnesium (Mg) is concentrated. According to claim 7,
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 1,
The average thickness of the plating layer is 15㎛ to 40㎛, hot stamping parts. base grater; and
Disposed on the base steel sheet, zinc (Zn): 30 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.

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