Plated steel sheets for hot press forming having excellent hydrogen brittleness resistance and impact resistance, hot press formed parts, and manufacturing methods thereof

Abstract

To provide plated steel sheets for hot press forming having excellent hydrogen brittleness resistance and impact resistance, hot press formed parts, and manufacturing methods thereof.SOLUTION: Provided are plated steel sheets for hot press forming, comprising: a base steel sheet containing, in weight%, C: 0.07-0.5%, Si: 0.05-1%, Mn: 0.5-5%, P: 0.001-0.015%, S: 0.0001-0.02%, Al: 0.01-0.1%, Cr: 0.01-1%, N: 0.001-0.02%, Ti: 0.1% or less, B: 0.01% or less, Sn: 0.01-0.1%, and the balance being Fe and inevitable impurities; an aluminum or aluminum alloy plating layer disposed on at least one surface of the base steel sheet; and an Sn-enriched layer provided between the base steel sheet and the plating layer, wherein the Sn-enriched layer satisfies a specific relationship.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a hot-forming plated steel sheet, a hot-forming member, and a method for manufacturing the same, which are excellent in hydrogen embrittlement resistance and impact resistance.

Background Art

[0002] In recent years, hot-forming members have been widely applied to structural members of automobiles for purposes such as improving fuel efficiency and protecting passengers by reducing the weight of automobiles. In particular, they can be used for bumpers, doors, pillar reinforcements, etc. that require ultra-high strength or high energy absorption capacity. As such a hot-forming technology, typically, there is US Patent No. 6296805 (hereinafter, Patent Document 1). Patent Document 1 discloses that by heating an Al-Si-based plated steel sheet at 850°C or higher and then forming the structure of the member into martensite by hot forming with a press and rapid cooling, ultra-high strength with high tensile strength can be ensured. When applying such an ultra-high strength steel for hot forming, since it is formed at a high temperature, complex shapes can be easily formed, and the effect of weight reduction can be expected due to the increase in strength by rapid cooling in the mold. However, it is known that the martensite structure has low resistance to hydrogen embrittlement. In particular, in hot-forming members, residual stress due to rapid cooling after heating exists, and the amount of diffusible hydrogen in the steel increases, raising concerns about delayed fracture due to hydrogen embrittlement, so there is a drawback that the application of the member is limited. Furthermore, since such an amount of diffusible hydrogen moves to crack generation sites such as grain boundaries when stress is generated, it may deteriorate the impact resistance. Therefore, various studies have been conducted to overcome this.

[0003]

[0004] In addition, changes in process parameters during coil manufacturing may cause overall or local changes in mechanical properties within the sheet. Therefore, sensitivity to changes in manufacturing parameters for producing electroplated steel sheets and hot-formed members with good mechanical properties and homogeneity is required.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] The present invention is for solving the above problems, and provides a hot-formed electroplated steel sheet, a hot-formed member, and a manufacturing method thereof,

[0007] which are excellent in hydrogen embrittlement resistance and impact resistance. The problems of the present invention are not limited to the above content. Those having ordinary knowledge in the technical field to which the present invention belongs will have no difficulty in understanding further problems of the present

[0008] One aspect of the present invention is, by weight%, C: 0.07 to 0.5%, Si: 0.05 to 1%, Mn: 0.5 to 5%, P: 0.001 to 0.015%, S: 0.0001 to 0.02%, Al: 0.01 to 0.1%, Cr: 0.01 to 1%, N: 0.001 to 0.02%, Ti: 0.1% or less, B: 0.01% or less, Sn: 0.01 to 0.1%, the balance being Fe and other inevitable impurities, and a base steel sheet containing An aluminum or aluminum alloy plating provided on at least one surface of the base steel sheet layer, and a Sn enrichment layer provided between the base steel sheet and the plating layer, and includes A plated steel sheet for hot forming that satisfies the following relational expressions 1-1 and 1-2 is provided.

[0009] [Relational Expression 1-1] [Number] [In the above relational expression 1-1, the above Sn coat represents the average Sn content in the plating layer, and the unit is wt%. Also, the above Sn max represents the maximum value of the Sn content in the Sn enrichment layer and the unit is wt%.]

[0010] [Relational Expression 1-2] [Number] [In the above relational expression 1-2, the above Sn(x) represents the Sn content along the x-axis direction from any point in the plating layer toward the base steel sheet side , x1 represents the x-axis point at the boundary between the plating layer and the Sn enrichment layer , and the above x2 represents the x-axis point at the maximum value of the Sn content in the Sn enrichment layer.]

[0011] Still another aspect of the present invention is, in wt%, C: 0.07 to 0.5%, Si: 0.05 to 1%, Mn: 0.5 to 5%, P: 0.001 to 0.015%, S: 0.0001 to 0.0 2%, Al: 0.01 to 0.1%, Cr: 0.01 to 1%, N: 0.001 to 0.02% , Ti: 0.1% or less, B: 0.01% or less, Sn: 0.01 to 0.1%, the balance being Fe and other inevitable impurities, reheating the steel slab to 1050 to 1300°C, and Step of finish rolling a heated steel slab at 750 to 950 °C to obtain a hot-rolled steel sheet, Step of coiling the hot-rolled steel sheet at 500 to 700 °C, Step of pickling the coiled hot-rolled steel sheet so that the product of the acid concentration and the pickling time is 800 to 10,000 g / L*s, Step of pickling, Step of annealing the pickled steel sheet at 700 to 900 °C under the dew point temperature condition of -75 to +20 °C in an annealing furnace, Step of annealing, After annealing, passing the steel sheet through a plating bath made of aluminum or an aluminum alloy, Step of plating, Provided is a method for manufacturing a plated steel sheet for hot forming, including.

[0012] In still another aspect of the present invention, by weight%, C: 0.07 to 0.5%, Si: 0.05 to 1%, Mn: 0.5 to 5%, P: 0.001 to 0.015%, S: 0.0001 to 0.0 2%, Al: 0.01 to 0.1%, Cr: 0.01 to 1%, N: 0.001 to 0.02% , Ti: 0.1% or less, B: 0.01% or less, Sn: 0.01 to 0.1%, the balance being Fe and Other inevitable impurities, and a base steel sheet, An aluminum or aluminum alloy plating layer provided on at least one surface of the base steel sheet, Layer, A Sn-enriched layer provided between the base steel sheet and the plating layer, including, Provided is a hot-forming member that satisfies the following relational expressions 2-1 and 2-2.

[0013] [Relational expression 2-1] [Number] [In the above relational expression 2-1, the above Sn coat Indicates the average Sn content in the plating layer, and the unit Is wt%. Also, the above Sn max Indicates the maximum value of the Sn content in the Sn-enriched layer The units are weight percent.

[0014] [Equation 2-2]

number

[0015] Still another aspect of the present invention is a method for manufacturing a hot forming plated steel sheet by subjecting the above-mentioned hot forming plated steel sheet to a temperature of Ac3 to 950°C. A method for manufacturing a hot-formed part, comprising the steps of: heat-treating the part at a temperature in the range of 1 to 1000 degrees for 1 to 1000 seconds; and then hot-press forming the part. to provide. Effect of the Invention

[0016] According to one aspect of the present invention, a Sn-enriched layer is formed between the base steel sheet and the coating layer. This reduces the amount of diffusible hydrogen in the steel, making it a hot forming plating with excellent resistance to hydrogen embrittlement and impact resistance. It is possible to provide a steel plate, a hot-formed part, and a method for manufacturing the same.

[0017] The various and beneficial advantages and effects of the present invention are not limited to those described above, but may be varied in accordance with the specific This can be more easily understood in the course of explaining the embodiments. [Brief description of the drawings]

[0018]

Figure 1

Figure 2

Figure 3

Figure 4

Number

Figure 5

Figure 6

Mode for Carrying Out the Invention

[0019] Hereinafter, preferred embodiments of the present invention will be described. However, the embodiments of the present invention can be modified into various other forms, and the scope of the present invention is not limited to the embodiments described below. Also, the embodiments of the present invention are provided to more fully explain the present invention to those having average knowledge in the technical field. Diffusible hydrogen at the grain boundaries promotes the generation of cracks at the grain boundaries when stress is generated. Therefore, a method capable of reducing the amount of diffusible hydrogen in steel after hot stamping is essential.

[0020] Diffusible hydrogen at the grain boundaries promotes the generation of cracks at the grain boundaries when stress is generated. Therefore, a method capable of reducing the amount of diffusible hydrogen in steel after hot stamping is essential. Therefore, a method capable of reducing the amount of diffusible hydrogen in steel after hot stamping is necessary. Therefore, a method capable of reducing the amount of diffusible hydrogen in steel after hot stamping is necessary.

[0021] Therefore, the present inventors have used an index that clearly shows the hydrogen embrittlement resistance effect in hot-formed steel materials. A method using the analysis of diffusible hydrogen content in steel and the three-point bending test (VDA238-100), which is one of the indicators capable of indicating impact resistance, was used to analyze the effects of various components including the addition of Sn, manufacturing conditions, microstructure, etc. As a result, it was found that the formation of the Sn enrichment layer can reduce the diffusible hydrogen content, and in addition to hydrogen embrittlement resistance, a hot-forming plated steel sheet, a hot-forming member, and a manufacturing method thereof with excellent impact resistance were devised. First, the hot-forming plated steel sheet and the hot-forming member according to an embodiment of the present invention will be described in detail below. The plated steel sheet according to an embodiment of the present invention contains, by weight%, C: 0.07 to 0.5%, Si: 0.05 to 1%, Mn: 0.5 to 5%, P: 0.001 to 0.015%, S: 0.000 1 to 0.02%, Al: 0.01 to 0.1%, Cr: 0.01 to 1%, N: 0.001 to

[0022] 0.02%, Ti: 0.1% or less, B: 0.01% or less, Sn: 0.01 to 0.1%, and the balance is a base steel sheet containing Fe and other inevitable impurities, an aluminum or aluminum alloy plating layer provided on at least one surface of the base steel sheet, and an Sn enrichment layer provided between the base steel sheet and the plating layer.

[0023] First, the alloy composition of the base steel sheet of the present invention will be described in detail. It should be noted that when each element is expressed by content in the present invention, it means weight% unless otherwise specified. 0.05 to 1%, Mn: 0.5 to 5%, P: 0.001 to 0.015%, S: 0.000 1 to 0.02%, Al: 0.01 to 0.1%, Cr: 0.01 to 1%, N: 0.001 to 0.02%, Ti: 0.1% or less, B: 0.01% or less, Sn: 0.01 to 0.1%, and the balance is a base steel sheet containing Fe and other inevitable impurities, an aluminum or aluminum alloy plating layer provided on at least one surface of the base steel sheet, and an Sn enrichment layer provided between the base steel sheet and the plating layer. First, the alloy composition of the base steel sheet of the present invention will be described in detail. It should be noted that when each element is expressed by content in the present invention, it means weight% unless otherwise specified. First, the alloy composition of the base steel sheet of the present invention will be described in detail. It should be noted that when each element is expressed by content in the present invention, it means weight% unless otherwise specified.

[0024] First, the alloy composition of the base steel sheet of the present invention will be described in detail. It should be noted that when each element is expressed by content in the present invention, it means weight% unless otherwise specified. When expressing each element by content in the present invention, it is necessary to note that it means weight% unless otherwise specified.

[0025] Carbon (C): 0.07 to 0.5% The above C is an element that increases the strength of the heat-treated member and improves the hardening ability, and is for strength adjustment. should be appropriately added as an essential element as needed. When the C content is less than 0.07%, it is difficult to ensure sufficient hardening ability, and sufficient martensite cannot be ensured when the cooling rate decreases, and there is a possibility of inferior impact resistance due to excessive ferrite formation. On the other hand, when the C content exceeds 0.5%, the strength may increase excessively, inducing brittleness, and there is a possibility of inferior weldability. Therefore, it is preferable to control the C content in the range of 0.07 to 0.5%. However, from the perspective of further improving the above effects, the lower limit of the C content may be 0.078%, and the upper limit of the C content may be 0.348%.

[0026] Silicon (Si): 0.05 - 1% The above Si should not only be added as a deoxidizer in steelmaking but is also a solid-solution strengthening element and an element that suppresses carbide formation. Therefore, Si is not only an element effective for homogenizing the internal structure but also contributes to increasing the strength of the hot-forming member and is added as an element effective for material homogenization. However, when the Si content is less than 0.05%, the above effects cannot be expected, and moreover, it is not appropriate because the manufacturing cost and process cost for controlling the Si content increase. On the other hand, when the Si content exceeds 1%, the surface of the steel sheet generates excessive SiO₂ during annealing, significantly reducing the adhesiveness, so it is added at 1% or less. However, from the perspective of further improving the above effects, the lower limit of the Si content may be 0.17%, and the upper limit of the Si content may be 0.8 0%.

[0027] Manganese (Mn): 0.5 - 5% The above Mn can not only ensure the desired strength due to the effect of solid-solution strengthening but also hardening ​​It is necessary to add it in order to suppress the formation of ferrite during hot forming by improving the energy. When the Mn content is less than 0.5%, it is difficult to obtain the effect of sufficient hardening ability, and due to the insufficient hardening ability, other expensive alloying elements are required in excess, resulting in a large increase in manufacturing cost. When the Mn content exceeds 5%, the banded ( band) structure arranged in the rolling direction of the microstructure phase deepens, inducing inhomogeneity in the internal structure, which may reduce the impact resistance. Therefore, it is added at 5% or less. However, from the perspective of further improving the above effects, the lower limit of the above Mn content may be 0.55%, and more preferably, the upper limit of the above Mn content may be 4.4%.

[0028] Phosphorus (P): 0.001 - 0.015% The above P exists as an impurity in the steel. In order for its minimum content to be less than 0.001%, a high manufacturing cost is required, which is not preferable. However, when the P content exceeds 0.015%, the weldability of the hot forming member and the material properties due to high-temperature grain boundary segregation decrease. Therefore, its upper limit is set to 0 .015%. On the other hand, from the perspective of further improving the above effects, the lower limit of the above P content may be 0. 005%, and more preferably, the upper limit of the above P content may be 0.012%.

[0029] Sulfur (S): 0.0001 - 0.02% The above S is an impurity and an element that inhibits the ductility, impact characteristics, and weldability of the member. Therefore, the maximum content is limited to 0.02%. Also, if its minimum content is less than 0.0001%, the manufacturing cost will increase significantly, which is not preferable. On the other hand, from the perspective of further improving the above effects, the lower limit of the above S content may be 0.001%, and the upper limit of the above S content is 0.01%.​ It may be.

[0030] Aluminum (Al): 0.01 - 0.1% The above Al, together with Si, is an element that deoxidizes in steelmaking to improve the cleanliness of steel. When the Al content is less than 0.01%, it is difficult to obtain the above effect. When the content exceeds 0.1%, the hot ductility decreases due to excessive AlN precipitates formed during the continuous casting process, and slab cracks may occur, inducing manufacturing problems. Therefore, the upper limit is set to 0.1%. On the other hand, from the perspective of further improving the above effect, the lower limit of the above Al content may be 0.020%, and the upper limit of the above Al content may be 0.081%.

[0031] Cr: 0.01 - 1% The above Cr is added as an element to ensure the hardenability of steel like Mn and suppress the formation of ferrite after hot forming. When the Cr content is less than 0.01%, it is difficult to ensure the above effect. On the other hand, when the Cr content exceeds 1%, not only is the improvement effect of hardenability slight compared to the addition amount, but also coarse iron carbides are excessively formed, which may induce cracks during stress application, degrading the material quality. Therefore, the upper limit is set to 1%. On the other hand, from the perspective of further improving the above effect, the lower limit of the above Cr content may be 0.10%, and the upper limit of the above Cr content may be 0.61%.

[0032] Nitrogen (N): 0.001 - 0.02% The above N is contained as an impurity in the steel. To make the N content less than 0.001%, it will be accompanied by excessive manufacturing costs. When the content exceeds 0.02%, slab cracks are likely to occur due to the formation of AlN like the added Al. Therefore, the upper limit is set to 0.02 Let it be %. On the other hand, from the viewpoint of further improving the above-mentioned effects, the lower limit of the N content is 0.003% may be, and more preferably, the upper limit of the N content may be 0.005%.

[0033] Ti: 0.1% or less (including 0%) The above Ti is an element selectively added in the present invention, and combines with nitrogen remaining as an impurity in steel to form TiN, thereby protecting B for ensuring hardenability from becoming a compound and playing a role of protecting it. Further, precipitation strengthening and grain refinement effects can be expected by the formation of TiC precipitates. However, if the content exceeds 0.1%, rather coarse TiN is formed in a large amount, deteriorating the quality of the steel, so the upper limit is set to 0.1% . On the other hand, the above Ti is a selective element and includes the case where it is not added, so the lower limit of the Ti content may be 0%, and from the viewpoint of further improving the above-mentioned effects, the lower limit of the Ti content may be 0 .01%, and the upper limit of the Ti content may be 0.035%. .01%, and the upper limit of the Ti content may be 0.035%.

[0034] B: 0.01% or less (including 0%) The above B is an element selectively added in the present invention and is an element that can effectively improve hardenability . When the above B is added, it segregates at the prior austenite grain boundaries and can suppress the brittleness of the hot-formed member due to the grain boundary segregation of impurities P or / and S . However, if it exceeds 0.01%, it may cause brittleness in hot rolling due to the formation of Fe CB6 composite compounds, so the upper limit is set to 0.01%. On the other hand, the above B is a selective element and includes the case where it is not added, so the lower limit of the B content 23 may be 0%, and since it includes the case where it is not added, the lower limit of the B content may be 0% , from the perspective of further improving the above effects, the lower limit of the B content may be 0.002%, and the upper limit of the B content may be 0.008%.

[0035] Sn: 0.01 - 0.1% Sn is an element that is crucial in manufacturing this hot-forming member, and it forms a Sn-concentrated layer at the interface between the base steel plate and the plating layer, reducing the hydrogen content absorbed during heat treatment and playing a role in reducing the susceptibility to hydrogen-induced delayed fracture. When the Sn content is less than 0.01%, a sufficient concentrated layer cannot be formed at the interface between the plating layer and the base iron, and the above-mentioned effects cannot be expected. On the other hand, when the Sn content exceeds 0 .1%, Sn precipitates excessively at the grain boundaries, inducing intergranular fracture during stress generation and deteriorating the material. Therefore, its upper limit is preferably 0.1%. However, from the perspective of further improving the above-mentioned effects, the lower limit of the Sn content may be 0.011%, and more preferably

[0036] the upper limit of the Sn content may be 0.097%. The balance other than the above components is iron (Fe), and if there are components that can be included in the steel plate for hot press forming, no particular additional addition is restricted. Also, since unavoidable impurities may be mixed in from raw materials or the surrounding environment during the normal manufacturing process, it is impossible to exclude them. Since these impurities are understandable to any technician in the normal manufacturing process, all of their contents are not particularly mentioned in this specification.

[0037] Further, the above plating layer includes an aluminum or aluminum alloy plating layer provided on at least one surface of the base steel plate. The above plating layer imparts corrosion resistance to the final hot-forming member. In the present invention, the type of the above plating layer is not particularly limited, and it is the same as the conventional plating steel for hot forming used in the prior art. The plating layer applied to the plate can be applied without limitation in the present invention. One example, the plating layer may be an aluminum or aluminum alloy plating layer, preferably, the plating layer can contain Si: 6 to 12%, Fe: 1 to 4%, and the balance Al and other inevitable impurities.

[0038] According to an embodiment of the present invention, the plated steel sheet can include a Sn-enriched layer provided between the base steel sheet and the plating layer. Such a Sn-enriched layer can be formed in the concentration gradient layer in the boundary region between the base steel sheet and the plating layer. The concentration gradient layer is a layer in which the concentration changes in the boundary region where the base steel sheet and the plating layer are in contact, and is a layer in which Fe ranges from 20 to 99% based on the weight method in the thickness direction of the steel sheet and changes by 0.3 wt% / μm or more in the region. On the other hand, the Sn-enriched layer is a region provided between the base steel sheet and the plating layer and in which Sn is concentrated and divided by the Sn content. Such a Sn-enriched layer and the plating layer can be distinguished by analyzing the change in the Sn content in the thickness direction from any point in the plating layer to the base steel sheet side by utilizing glow discharge spectroscopy (GDS). Specifically, as shown in FIG. 2, the x-axis represents the linear distance in the thickness direction from an arbitrary position inside the plating layer 1 to the base steel sheet 3 side, and the y-axis is judged based on the graph showing the Sn content measured by utilizing the above GDS. For example, based on FIG. 2 schematically showing the above-described GDS measurement results, in the rising section 21 of the Sn content in the x-axis (+) direction provided between the plating layer 1 and the base steel sheet 3, the above and the plating layer are separable by analyzing the change in the Sn content in the thickness direction from any point in the plating layer to the base steel sheet side by utilizing glow discharge spectroscopy (GDS).

[0039] side, and the y-axis represents the Sn content measured by utilizing the above GDS. Based on this graph, it is judged.

[0040] For example, based on FIG. 2 schematically showing the above-described GDS measurement results, in the rising section 21 of the Sn content in the x-axis (+) direction provided between the plating layer 1 and the base steel sheet 3, the above and the plating layer are ​​​On the Sn average content line 10 of the plating layer and above the Sn content line 100 measured using the above GDS From the last contact point 11 in the positive x-axis direction (in the thickness direction on the substrate steel plate 3 side), Sn enrichment Layer 2 is formed.

[0041] At this time, the Sn average content line 10 of the plating layer 1 means the extension line of the Sn average content line for the section from a point 8 μm away from the plating layer 1 side to a point 15 μm away from the point where the Sn content is the maximum value 200 (the point of Sn max max max

[0042] Similarly, for the Sn enrichment layer 2 and the substrate steel plate 3 as well, in the rising section 22 of the Sn content in the negative x-axis direction provided between the substrate steel plate 3 and the plating layer 1 measured using the above GDS, from the last contact point 31 in the negative x-axis direction of the Sn content line 100 measured using the above GDS and the Sn average content line 30 of the substrate steel plate (in the thickness direction on the plating layer 1 side), Sn enrichment layer 2 is formed.

[0043] max max

[0044] As a result of intensive studies by the present inventors, it has been found that reducing the amount of diffusible hydrogen occluded during the heat treatment of hot forming can suppress the induction of defects due to hydrogen delayed fracture. Specifically, during hot forming, a blank having a plating layer made of aluminum or an aluminum alloy is heated. During the heat treatment process, water vapor present in the heat treatment furnace is adsorbed onto the surface of the blank. Subsequently, the hydrogen generated by the dissociation of water is occluded in the steel while it has an austenite phase with a high hydrogen solubility at high temperatures. However, when rapid cooling due to hot forming occurs and it changes to the martensite phase, the solubility of hydrogen rapidly decreases, and the alloy plating layer formed by alloying the plating layer acts as an obstacle that makes it difficult to release hydrogen. Therefore, a certain amount of diffusible hydrogen content remains in the steel, thereby increasing the possibility of crack formation due to hydrogen-induced delayed fracture. Thus, reducing the amount of diffusible hydrogen occluded during heat treatment becomes an important factor for defect suppression.

[0045] Furthermore, as a result of several investigations, the inventors confirmed that the impact resistance increases as the hydrogen content in the steel decreases. This is because the diffusible hydrogen occluded in the steel during heat treatment, especially the diffusible hydrogen present at the grain boundaries, acts to receive stress during bending processing and make it easy to induce and propagate cracks at the grain boundaries. Therefore, by reducing the content of diffusible hydrogen in the steel, properties such as bendability and impact resistance can be improved.

[0046] In particular, the inventors have found that by forming a Sn-concentrated layer having an appropriate concentration and thickness between the base steel plate and the plating layer, such an effect can be achieved. This is because the Sn-concentrated layer serves as an effective protective film that relatively reduces the amount of diffusible hydrogen occluded in the steel.

[0047] According to an embodiment of the present invention, the hydrogen content in the steel is effectively reduced to improve hydrogen embrittlement resistance. At the same time, in order to ensure excellent impact resistance, the hot-forming plated steel sheet preferably satisfies the following Relational expression 1-1 and the following relational expression 1-2. At this time, the unit of the following relational expression 1- 2 corresponds to [μm*wt%] (the same applies to relational expressions 2-2 and 2-3 described later ).

[0048] [Relational expression 1-1]

Number

[0049] [Relational expression 1-2]

Number

[0050] That is, in order to exhibit the intended effects of the present invention, the Sn concentration and thickness of the Sn enrichment layer provided between the base steel sheet and the plating layer must be at a certain level or higher and formed so as to satisfy both of the above-mentioned relational expressions 1-1 and 1-2. At this time, the above Sn , coat , Sn max , Sn(x), x1, x2, etc. are obtained by activating the above-described glow discharge spectroscopy (GDS) When used to analyze the change in the Sn content in the thickness direction of the base steel plate at any one point within the plating layer it can be measured from the obtained data. In other words, the above Sn coat corresponds to the Sn average content line 10 of the plating layer 1 described above in the GDS profile of FIG. 2 of the present application and can correspond to the point 200 where the Sn content in the Sn enrichment layer 2 is at its maximum value in the GDS profile of FIG. 2 of the present application. In the above relational expression 1-1, max if the value of is less than 1.5, or in the above relational expression 1-2, if the value of

[0051] is less than 0.015, the Sn concentration in the Sn enrichment layer or the formation thickness of the Sn enrichment layer is not sufficient, so it cannot be expected to function as a protective film that relatively reduces the amount of diffusible hydrogen occluded in the steel.

Number

Number

[0052] This integral value represents the area of the corresponding region obtained by using the piecewise quadrature method (that is, in the present invention, it can mean the area of the corresponding region obtained by utilizing the piecewise quadrature method) per unit length (or unit depth) of 0.01 μm of the x-axis. In other words, in FIG. 1 described above, the area of the hatched portion is the integral value of the function Sn(x) showing the change in the Sn content along the x-axis direction from the base steel plate side at any one point within the plating layer from x1 (the x-axis point at the boundary 11 between the plating layer and the Sn enrichment layer) to x2 (the x-axis point at the maximum value 200 of the Sn content in the Sn enrichment layer). This integral value represents the area of the corresponding region obtained by using the piecewise quadrature method (that is, in the present invention, it can mean the area of the corresponding region obtained by utilizing the piecewise quadrature method) per unit length (or unit depth) of 0.01 μm of the x-axis. This integral value represents the area of the corresponding region obtained by using the piecewise quadrature method (that is, in the present invention, it can mean the area of the corresponding region obtained by utilizing the piecewise quadrature method) per unit length (or unit depth) of 0.01 μm of the x-axis. This integral value represents the area of the corresponding region obtained by using the piecewise quadrature method (that is, in the present invention, it can mean the area of the corresponding region obtained by utilizing the piecewise quadrature method) per unit length (or unit depth) of 0.01 μm of the x-axis. This integral value represents the area of the corresponding region obtained by using the piecewise quadrature method (that is, in the present invention, it can mean the area of the corresponding region obtained by utilizing the piecewise quadrature method) per unit length (or unit depth) of 0.01 μm of the x-axis. This integral value represents the area of the corresponding region obtained by using the piecewise quadrature method (that is, in the present invention, it can mean the area of the corresponding region obtained by utilizing the piecewise quadrature method) per unit length (or unit depth) of 0.01 μm of the x-axis. It can be obtained by calculation.

[0053] Alternatively, according to one embodiment of the present invention, more preferably, defined from the above relational expression 1-1 Sn max / Sn coat The lower limit of the value may be 1.53, and more preferably, Sn defined from the above relational expression 1-1 max / Sn coat The upper limit of the value may be 13.0 as well.

[0054] Also, according to one embodiment of the present invention, more preferably, defined from the above relational expression 1-2 of

Number

Number

[0055] Also, according to one embodiment of the present invention, although not particularly limited, on the above galvanized steel sheet the thickness of the above Sn enrichment layer may be in the range of 1 to 20 μm (that is, 1 μm or more and 20 μm or less). If the thickness of the Sn enrichment layer in the above galvanized steel sheet is less than 1 μm, even if the subsequent heat treatment for hot forming is performed, a sufficient Sn enrichment layer cannot be generated, and it may be difficult to expect the effects for the purposes of improving hydrogen embrittlement resistance and impact resistance. Also, if the thickness of the above Sn enrichment layer exceeds 2

[0056] 0 μm, Sn precipitates excessively at the grain boundaries after hot forming, and cracks occur when stress is generated and it may be difficult to expect the effects for the purposes of improving hydrogen embrittlement resistance and impact resistance. Also, if the thickness of the above Sn enrichment layer exceeds 2 0 μm, Sn precipitates excessively at the grain boundaries after hot forming, and cracks occur when stress is generated 0 μm, Sn precipitates excessively at the grain boundaries after hot forming, and cracks occur when stress is generated It may act as a crack site and be inferior in impact resistance. On the other hand, from the perspective of further improving the above-described effects, in the above electroplated steel sheet, the lower limit of the thickness of the Sn-enriched layer may be 3 μm, and the upper limit of the thickness of the Sn-enriched layer may be 15 μm. From the viewpoint of further improving the above effects, in the electroplated steel sheet, the lower limit of the thickness of the Sn-enriched layer may be 3 μm, and the upper limit of the thickness of the Sn-enriched layer may be 15 μm. From the viewpoint of further improving the above effects, in the electroplated steel sheet, the lower limit of the thickness of the Sn-enriched layer may be 3 μm, and the upper limit of the thickness of the Sn-enriched layer may be 15 μm.

[0057] On the other hand, as a result of intensive studies to further improve the physical properties of the electroplated steel sheet and the member, the inventors found that the performance is improved by enriching an appropriate amount of Sn in the manganese segregation band present in the base steel sheet of the electroplated steel sheet. That is, as a result of examining various conditions, the inventors confirmed that when the Sn enrichment amount in the segregation band satisfies a certain level or more, or in addition to this, when the thickness of the Mn segregation band satisfies a certain level or less, such an effect is more enhanced. As a result of intensive studies to further improve the physical properties of the electroplated steel sheet and the member, the inventors found that the performance is improved by enriching an appropriate amount of Sn in the manganese segregation band present in the base steel sheet of the electroplated steel sheet. As a result of intensive studies to further improve the physical properties of the electroplated steel sheet and the member, the inventors found that the performance is improved by enriching an appropriate amount of Sn in the manganese segregation band present in the base steel sheet of the electroplated steel sheet. That is, as a result of examining various conditions, the inventors confirmed that when the Sn enrichment amount in the segregation band satisfies a certain level or more, or in addition to this, when the thickness of the Mn segregation band satisfies a certain level or less, such an effect is more enhanced. As a result of intensive studies to further improve the physical properties of the electroplated steel sheet and the member, the inventors found that the performance is improved by enriching an appropriate amount of Sn in the manganese segregation band present in the base steel sheet of the electroplated steel sheet. That is, as a result of examining various conditions, the inventors confirmed that when the Sn enrichment amount in the segregation band satisfies a certain level or more, or in addition to this, when the thickness of the Mn segregation band satisfies a certain level or less, such an effect is more enhanced. As a result of intensive studies to further improve the physical properties of the electroplated steel sheet and the member, the inventors found that the performance is improved by enriching an appropriate amount of Sn in the manganese segregation band present in the base steel sheet of the electroplated steel sheet. That is, as a result of examining various conditions, the inventors confirmed that when the Sn enrichment amount in the segregation band satisfies a certain level or more, or in addition to this, when the thickness of the Mn segregation band satisfies a certain level or less, such an effect is more enhanced. As a result of intensive studies to further improve the physical properties of the electroplated steel sheet and the member, the inventors found that the performance is improved by enriching an appropriate amount of Sn in the manganese segregation band present in the base steel sheet of the electroplated steel sheet. That is, as a result of examining various conditions, the inventors confirmed that when the Sn enrichment amount in the segregation band satisfies a certain level or more, or in addition to this, when the thickness of the Mn segregation band satisfies a certain level or less, such an effect is more enhanced.

[0058] Specifically, according to an embodiment of the present invention, in the electroplated steel sheet, the base steel sheet includes a Mn segregation band, and among the Mn segregation bands, the region where the average Sn content is 1.015 times or more the average Sn content in the base steel sheet may be 50% or more (or 60% or more) in terms of area fraction. By satisfying this, the generation of inclusions such as MnS mainly generated in the Mn segregation band can be reduced, and it plays a role in suppressing the generation and propagation sites (sites) of cracks during stress generation, and excellent impact resistance can be ensured. In addition, when MnS is excessively generated, there may be a problem that brittle fracture surfaces are excessively developed. Therefore, by satisfying the above-described configuration during Sn enrichment, MnS can be reduced, and thereby the brittle fracture surface can be reduced and the bendability can be further improved.

[0059] ​​​​​​​​At this time, the upper limit of the average Sn content in the Mn segregation band is not particularly limited, but , as an example, it may be 5 times that of the average Sn content in the region of the base steel plate other than the Mn segregation band or less. Also, although not particularly limited, among the above Mn segregation bands, Sn The upper limit of the area of the portion where the average content is 1.015 times or more the average Sn content in the base steel plate may be 90%.

[0060] The Mn segregation band can be distinguished by utilizing the EPMA component mapping result for Mn as shown in FIG. 5. Specifically, after heat-treating the plated steel sheet at a temperature of 1200 °C or higher for several hours , rapidly cooling to remove the Mn segregation band and then measuring the average value of the Mn intensity by EPMA as Mn0. Thereafter, among the points measured by EPMA, with a specific point as the center draw a square with an area of 0.4 μm 2 vertically and horizontally. When the area of the points located within the above square is 50% or more in the region where the Mn intensity is 1.015 times or more that of Mn0, the specific point is defined as an Mn segregation point, and if it is less than 50%, it is defined as not an Mn segregation point. By collecting such Mn segregation points and connecting the Mn segregation points located on the outermost contour with straight lines, the drawn region is defined as the Mn segregation band.

[0061] Also, the ratio (Sn2 / Sn1) of the average Sn content (Sn2) of the Mn segregation band to the average Sn content (Sn1) of the base steel plate can be measured by utilizing the ratio of the intensity by the Sn component mapping result using EPMA.

[0062] Also, according to one embodiment of the present invention, the thickness of the Mn segregation band may be 20 μm or less. By satisfying this condition, it is possible to further improve the impact resistance and bending property. The thinner the Mn segregation zone is, the better the bendability is. Therefore, the lower limit of the thickness of the Mn segregation zone is However, as an example, the lower limit of the thickness of the Mn segregation zone is 1 μm. In this case, the thickness of the Mn segregation zone may be determined by the index of the Mn segregation zone determined by the above-mentioned method. The average thickness in the thickness direction (perpendicular to the rolling direction of the steel plate) was measured from the image. It can be defined as the thickness of the segregation zone. In this case, from the viewpoint of further improving the above-mentioned effect, In the plated steel sheet, the lower limit of the thickness of the Mn segregation zone may be 3.0 μm. Alternatively, the upper limit of the thickness of the Mn segregation zone may be 13.4 μm.

[0063] On the other hand, the hot forming plated steel sheet having the above-mentioned configuration is subjected to a hot press forming method described later. This makes it possible to manufacture hot-formed parts having excellent hydrogen embrittlement resistance and impact resistance.

[0064] The hot-formed member according to one embodiment of the present invention has the same alloy composition as the base steel sheet of the above-mentioned plated steel sheet. A base steel sheet having a composition and an aluminum or aluminum alloy plate provided on at least one surface of the base steel sheet. An aluminum alloy plating layer and an Sn-enriched layer provided between the sintered steel sheet and the plating layer. and the hot-formed member satisfies the following relational formula 2-1 and the following relational formula 2-2. In this case, the explanations for the base steel sheet, the coating layer and the Sn-enriched layer shall apply in the same manner as above. In this case, since the above-mentioned relations 2-1 and 2-2 are values ​​obtained empirically, Therefore, it is not necessary to specify a specific unit, as long as the unit of each variable is satisfied.

[0065] [Equation 2-1]

number

[0066] [Relational expression 2-2] [Number] [In the above relational expression 2-2, the above Sn(x) represents the Sn content along the x-axis direction from any point in the plating layer toward the base steel plate side , x1 represents the x-axis point at the boundary between the above plating layer and the Sn enrichment layer , and the above x2 represents the x-axis point at the maximum value of the Sn content in the above Sn enrichment layer .]

[0067] In the present invention, when the plated steel sheet is heated for hot forming, the Sn enrichment degree of the Sn enrichment layer becomes deeper. Therefore, in the hot formed member according to the present invention, by satisfying the above relational expressions 2 -1 and 2-2, the hydrogen content in the steel can be effectively reduced, thereby improving the water embrittlement resistance and the collision resistance. At this time, in the hot formed member, the method for distinguishing between the above plating layer and the Sn enrichment layer and the method for distinguishing between the above base steel plate and the Sn enrichment layer can be applied in the same manner as the distinguishing method in the plated steel sheet described above .

[0068] Alternatively, according to an embodiment of the present invention, more preferably, the lower limit of the Sn / Sn max value defined by the above relational expression 2-1 may be 1.83, and more preferably coat , the Sn / Sn max value defined by the above relational expression 2-1 coatThe upper limit of the value may be 13.46. It may be.

[0069] Also, according to one embodiment of the present invention, more preferably, it is defined from the above relational expression 2-2 to be

Number

Number

[0070] Alternatively, according to one embodiment of the present invention, more preferably, it can satisfy the following relational expression 2-3, and thereby the hydrogen embrittlement resistance and the impact resistance can be further improved.

[0071] [Relational Expression 2-3]

Number

[0072] According to one embodiment of the present invention, in the above hot-formed member, the microstructure of the base steel sheet can contain 5% or less (including 0%) of ferrite and the balance martensite. Or, additionally, it can further contain 1% or less of other phases such as upper bainite, retained austenite, cementite, and pearlite.

[0073] According to one embodiment of the present invention, the above base steel sheet can contain 5% or less ( including 0%) of ferrite in terms of area fraction, which ensures the hardening ability by adjusting the steel components in hot forming ​​By ensuring protection and a sufficient cooling rate, the ferrite fraction can be controlled to 5% or less. On the other hand, in the hot-formed member, if the ferrite fraction of the base steel sheet exceeds 5%, not only does the strength decrease, but relatively, local stress concentrates in the soft ferrite, which may promote crack propagation and significantly deteriorate the impact resistance.

[0074] Also, according to one embodiment of the present invention, in the hot-formed member, the thickness of the Sn-enriched layer may be 2 to 30 μm.

[0075] If the thickness of the Sn-enriched layer in the hot-formed member is less than 2 μm, during hot forming, the hydrogen permeating into the steel cannot be effectively suppressed, and the effects of improving hydrogen embrittlement resistance and impact resistance characteristics may not be fully exerted. Also, if the thickness of the Sn-enriched layer in the hot-formed member exceeds 30 μm, Sn not only forms the enriched layer, but may also precipitate excessively at the grain boundaries of the surface layer of the base iron, which may promote the generation and propagation of cracks during bending and reduce the impact resistance characteristics. On the other hand, from the perspective of further improving the aforementioned effects, in the hot-formed member, the lower limit of the thickness of the Sn-enriched layer may be 3.4 μm,

[0076] and the upper limit of the thickness of the Sn-enriched layer may be 25 μm.

[0076] Also, according to one embodiment of the present invention, the diffusible hydrogen content of the hot-formed member may be 0.4 ppm or less, thereby ensuring excellent hydrogen embrittlement resistance. Such a diffusible hydrogen content of 0.4 ppm or less is because even when the test piece is stressed by bending under the same yield stress of the material for 120 hours, no cracks occur in the parts.

[0077] Further, according to an embodiment of the present invention, in the hot-formed member, the base steel sheet contains Mn segregation bands, and among the Mn segregation bands, the area fraction of the region where the average Sn content is 1.015 times or more the average Sn content in the base steel sheet may be 50% or more (alternatively, more preferably 60% or more). By satisfying this, the generation of inclusions such as MnS mainly occurring in the Mn segregation bands can be reduced, and the generation and propagation sites of cracks during stress generation can be suppressed, and excellent impact resistance can be ensured overall . Further, when MnS is excessively generated, there may be a problem that brittle fracture surfaces are excessively developed. Therefore, by satisfying the above-described configuration during Sn enrichment, MnS can be reduced , and thereby the brittle fracture surface can be reduced and the bendability can be further improved . . Also, when MnS is excessively generated, there may be a problem that brittle fracture surfaces are excessively developed. Therefore, by satisfying the above-described configuration during Sn enrichment, MnS can be reduced , and thereby the brittle fracture surface can be reduced and the bendability can be further improved .

[0078] At this time, the upper limit of the average Sn content in the Mn segregation band is not particularly limited, but , as an example, it may be 5 times or less the average Sn content in the region of the base steel sheet other than the Mn segregation band . Note that, although not particularly limited, among the Mn segregation bands, the upper limit of the area of the portion where the average Sn content is 1.015 times or more the average Sn content in the base steel sheet may be 95% . .

[0079] Further, according to an embodiment of the present invention, in the hot-formed member, the thickness of the Mn segregation band may be 15 μm or less, and by satisfying this, the impact resistance and bendability can be further improved . The impact resistance and bendability can be improved as the thickness of the Mn segregation band becomes thinner , so the lower limit of the thickness of the Mn segregation band does not need to be separately limited. However, as an example, the lower limit of the thickness of the Mn segregation band may be 1.5 μm

[0080] On the other hand, from the viewpoint of further improving the above effects, in the hot-formed member, the Mn segregation The lower limit of the thickness of the band may be 4.1 μm, or the upper limit of the thickness of the Mn segregation band may be 15.0 μm.

[0081] At this time, in the hot-formed member, the definition of the Mn segregation band, the average Sn content in the base steel sheet The ratio of the average Sn content in the Mn segregation band to the average Sn content in the base steel sheet, and the measurement of the thickness of the Mn segregation band can be applied in the same manner as the measurement method and measurement criteria in the above-mentioned plated steel sheet.

[0082] Next, a method for manufacturing a hot-formed plated steel sheet, which is still another embodiment of the present invention, will be described.

[0083] The hot-formed plated steel sheet according to an embodiment of the present invention has the above-described alloy composition by weight %, and reheats a steel slab having the above-described alloy composition to 1050 to 1300 °C, and then reheats the heated steel slab at 750 ~950 °C for finish rolling to obtain a hot-rolled steel sheet, winding the hot-rolled steel sheet at 500 to 700 °C ~950 °C for finish rolling to obtain a hot-rolled steel sheet, winding the hot-rolled steel sheet at 500 to 700 °C rolling to obtain a hot-rolled steel sheet, winding the hot-rolled steel sheet at 500 to 700 °C ~10,000 g / L*s for pickling treatment, annealing the pickled hot-rolled steel sheet at 700 to 860 °C under the dew point temperature condition of - 75 to -20 °C in an annealing furnace, and after annealing, passing the hot-rolled steel sheet through a plating bath made of aluminum or an aluminum alloy for plating and can include.

[0084] Slab reheating stage First, the slab having the above-described alloy composition is reheated to 1050 to 1300 °C. The above-mentioned re- When the heating temperature is less than 1050 °C, the slab structure is not sufficiently homogenized, so when precipitating elements are utilized, it is difficult to re-dissolve them. On the other hand, when the reheating temperature exceeds 1300 °C, an excessive oxidation layer is formed, leading to an increase in manufacturing costs for removing the oxidation layer, and surface defects are likely to occur after finish rolling.

[0085] Finish rolling stage Finish rolling should be carried out at 750 - 950 °C. When the finish rolling temperature is less than 750 °C, two-phase region rolling progresses, ferrite is introduced into the surface layer of the steel plate, and it is difficult to control the plate shape. On the other hand, when the finish rolling temperature exceeds 950 °C, coarsening of the hot-rolled crystal grains may occur, excessive hot scale is generated, and the manufacturing cost of the subsequent processes increases, so it is not appropriate.

[0086] Coiling stage After finish rolling, the hot-rolled steel plate is coiled at 500 - 700 °C and then cooled to produce a hot-rolled coil. When the coiling temperature is less than 500 °C, martensite is formed entirely or partially in the steel plate, making it difficult to control the coil shape and there is also a problem that the excessive strength increase of the hot-rolled steel plate reduces the subsequent cold rolling property. On the other hand, when the coiling temperature exceeds 700 °C, excessive coarse carbides are formed, and the generation of cracks is promoted when stress occurs in the hot-formed member, resulting in a problem of reduced impact resistance.

[0087] Pickling treatment stage The coiled hot-rolled steel plate is pickled so that the product of the acid concentration and the pickling time is 800 - 10,000 g / L*s. In the steel plate that has undergone the above-mentioned reheating, finish rolling, and coiling stages, an Sn concentration layer is formed. However, in the pickling treatment process, when the product of the acid concentration and the pickling time is 800 - 1 ​ When applied within the range of 0,000 g / L*s, the Sn enrichment layer, which is the core of the present invention, can be effectively protected and the effect of reducing the amount of diffusible hydrogen in steel can be exerted. Specifically, when the product of the acid concentration and the pickling time is less than 800 g / L*s, the scale generated during finish rolling may not be sufficiently removed, which may induce product quality problems.

[0088] On the contrary, when the product of the acid concentration and the pickling time exceeds 10,000 g / L*s, all or part of the Sn enrichment layer will be lost during pickling, not only failing to achieve the expected effect, but also potentially increasing the manufacturing cost. Therefore, the upper limit is set at 10,000 g / L*s. However, if there is more than one pickling tank and the corresponding acid concentration and pickling time are different, the above value can be represented by adding the products of the acid concentration and pickling time for each tank. On the other hand, from the perspective of further improving the above-mentioned effect, the lower limit of the product of the acid concentration and the pickling time may be 900 g / L*s, or the upper limit of the product of the acid concentration and the pickling time may be 4 ,200 g / L*s.

[0089]

[0090] According to an embodiment of the present invention, as the acid that can be used in the pickling treatment stage, those that can be usually used in the technical field can be applied. Typically, there are hydrochloric acid (HCl ), sulfuric acid (H2SO4), etc. In particular, in the present invention, using hydrochloric acid (HCl) has superior pickling ability compared to using other acids, the process cost is economical, the possibility of generating surface foreign matters after pickling is small, and it is easy to ensure the surface quality. ), sulfuric acid (H2SO4), etc. In particular, in the present invention, using hydrochloric acid (HCl) has superior pickling ability compared to using other acids, the process cost is economical, the possibility of generating surface foreign matters after pickling is small, and it is easy to ensure the surface quality. ), sulfuric acid (H2SO4), etc. In particular, in the present invention, using hydrochloric acid (HCl) has superior pickling ability compared to using other acids, the process cost is economical, the possibility of generating surface foreign matters after pickling is small, and it is easy to ensure the surface quality. ), sulfuric acid (H2SO4), etc. In particular, in the present invention, using hydrochloric acid (HCl) has superior pickling ability compared to using other acids, the process cost is economical, the possibility of generating surface foreign matters after pickling is small, and it is easy to ensure the surface quality.

[0090] On the other hand, although not particularly limited, according to an embodiment of the present invention, the concentration of the above acid is 4 It may also be in the range of 0 to 500 g / L. If the acid concentration is less than 40 g / L, the surface scale generated during hot rolling may not be sufficiently removed during the limited pickling time, and defects may occur in the surface layer of the steel plate. On the other hand, if the acid concentration exceeds 500 g / L, due to the loss of the Sn enriched layer, it is difficult to exert the effects aimed at in the final hot-formed member, and there is a possibility of inducing defects in the surface layer due to over-pickling. On the other hand, from the perspective of further improving the above-mentioned effects, the lower limit of the acid concentration may be 150 g / L, or alternatively, the upper limit of the acid concentration may be 250 g / L.

[0091] Also, although not particularly limited, according to an embodiment of the present invention, the pickling time may be 5 to 60 seconds (s). If the pickling time is less than 5 seconds, the surface scale of the steel plate may not be sufficiently removed, and defects in the surface layer may be induced. If the pickling time exceeds 60 seconds, due to the loss of the Sn enriched layer, there is a possibility of reducing productivity and increasing process costs. On the other hand, from the perspective of further improving the above-mentioned effects, the pickling time may be 5 to 25 seconds.

[0092] Also, although not particularly limited, according to an embodiment of the present invention, the pickling temperature may be 4 0 to 120 °C. If the pickling temperature is less than 40 °C, the pickling power is not sufficient, which may have an adverse effect on the quality of the product. On the other hand, if the pickling temperature exceeds 120 °C, not only does the fixed cost increase to maintain a high temperature, but there is also a problem that the vaporization amount of the pickling solution increases due to the high temperature, and the cost for replenishing the lost pickling solution increases. On the other hand, from the perspective of further improving the above-mentioned effects, the lower limit of the pickling temperature is 50 °C. Alternatively, the upper limit of the pickling temperature may be 100°C.

[0093] Annealing stage The pickled hot-rolled steel sheet described above can be annealed at 700 ~900°C under the dew point temperature condition of -75 to +20°C in an annealing furnace. When the annealing temperature is less than 700°C, the recrystallization of the cold-rolled structure is not sufficiently completed, so the sheet shape may become defective, and the strength may be too high after plating, which may induce die wear during the blanking process. On the other hand, when the annealing temperature exceeds 900°C, the formation of surface oxides is promoted during the annealing process, inducing defects on the Al-S i plating surface. Alternatively, from the perspective of further improving the effect of suppressing die wear and plating surface defects during the blanking process, the annealing temperature may be 750~860°C, or may be 800~860°C.

[0094] Also, the atmosphere during annealing is preferably a non-oxidizing atmosphere, and a hydrogen-nitrogen mixed gas or the like can be used. At this time, the dew point temperature (Dew point t) of the above-described atmosphere gas is carried out at -75°C or higher and +20°C or lower. When the dew point temperature is less than -75°C, there is a problem that additional equipment is required to control the dew point, resulting in an increase in manufacturing cost. On the other hand, when the dew point temperature exceeds +20°C, annealing oxides are formed on the surface of the steel sheet during annealing, which may cause defects in surface quality such as unplated. On the other hand, from the perspective of further improving the above-described effect, the lower limit of the dew point temperature during annealing may be -55°C, or the upper limit of the dew point temperature may be 0°C.

[0095] Plating stage Immediately after the annealing process, Al-Si plating is performed. Specifically, after annealing, the hot-rolled steel sheet is passed through a plating bath made of aluminum or an aluminum alloy to produce a plated steel sheet. At this time, the plating conditions can be applied to the steel sheet for hot press forming without limitation to the present invention as long as they are the plating conditions usually applied to the steel sheet for hot press forming. As an example, the composition of the plating bath may contain Si: 6 to 12%, Fe: 1 to 4%, and the balance Al and other inevitable impurities.

[0096] At this time, although not particularly limited, in the plating step, the plating amount is preferably 15 to 140 g / m on a single-sided basis of the usually produced one. If it is less than 15 g / m 2 on a single-sided basis, it is difficult to ensure the corrosion resistance of the desired hot-formed member. If it exceeds 140 g / m 2 on a single-sided basis, not only does the manufacturing cost increase due to the excessive plating adhesion amount, but it is not easy to uniformly plate the entire width and length of the coil with the plating amount. 2

[0097] Cold rolling stage The method for manufacturing a plated steel sheet for hot forming according to an embodiment of the present invention may further include a step of cold rolling the hot-rolled steel sheet to produce a cold-rolled steel sheet after the pickling treatment step described above.

[0098] Continuous casting stage The method for manufacturing a plated steel sheet for hot forming according to the present invention may further include a step of continuously casting with light reduction before the slab heating step, but is not particularly limited thereto. The present invention can reduce segregation and improve impact resistance by applying light reduction during continuous casting to produce a slab. When slab segregation occurs excessively, it segregates until the final hot-formed member. ​​​​​​​​​​ The bands are thick and concentrated, and a gap is formed between these segregation bands and the base steel sheet area other than the Mn segregation bands. The resulting hardness difference and the formation of inclusions in the segregation zone can reduce impact resistance. It is.

[0099] Therefore, in order to produce this slab, it is necessary to cast the slab before the final solidification position during continuous casting. Soft reduction must be performed, and the total reduction rate during soft reduction by continuous casting is limited to 0.5 to 5%. It is preferable to control the total reduction rate during continuous casting to less than 0.5%, since there is almost no reduction. Since the center segregation is not sufficiently removed, the impact resistance of the hot-formed part may be poor. On the other hand, if the total reduction rate during continuous casting exceeds 5%, the rolling roll equipment will be overloaded. This may lead to accelerated breakdowns and deterioration of equipment.

[0100] The hot forming plated steel sheet manufactured by the above-mentioned manufacturing method is hot press formed to obtain a resistant It is possible to manufacture hot-formed parts having excellent hydrogen embrittlement resistance and impact resistance. The plated steel sheet manufactured by the above method was subjected to hot forming and die quenching to improve resistance to hydrogen embrittlement. The steel composition and manufacturing method for the final component having excellent impact resistance will be described. The plated steel sheet produced by the method is used to produce a blank for hot forming. Blank: Austenite single phase region temperature or higher, more specifically, Ac3 temperature or higher and 975℃ Heat within the following temperature range. If the heating temperature is below the Ac3 temperature, the two-phase region will occur. The presence of untransformed ferrite during welding makes it difficult to ensure strength and crash resistance. However, if the heating temperature exceeds 975°C, excessive oxides will be generated on the surface of the component, causing spot welding failure. It is difficult to ensure the properties, and the manufacturing cost for maintaining a high temperature increases. On the other hand, in the present invention the temperature of the above Ac3 transformation point can be calculated by the following relational expression 3.

[0101] [Relational Expression 3] Ac3 [°C] = 881 - 206 × [C] + 53 × [Si] - 15 × [Mn] - 1 × [Cr + 41 × [Mo] [In the above relational expression 3, [C], [Si], [Mn], [Cr], and [Mo] respectively and independently indicate the content of the average weight % with respect to each element in parentheses contained in the base iron, and for the elements not contained among the above elements, the content is calculated as "0".]

[0102] Thereafter, it is preferable to hold the heated blank for 1 to 1000 seconds within the above temperature range. If the above holding time is less than 1 second, it becomes difficult to obtain a uniform temperature distribution throughout the blank temperature, and there is a possibility of inducing material variations by position. On the other hand, if the above holding time exceeds 100 0 seconds, similar to the case of exceeding the heating temperature, not only is it difficult to ensure spot weldability due to excessive generation of oxides on the member surface, but it also induces an increase in the manufacturing cost of the member.

[0103] The blank thus heated is transferred to a press, and hot forming and die quenching are performed at a cooling rate of -20°C / s or more to manufacture the final member. At this time, at a cooling rate of less than -20°C / s, a ferrite phase is introduced and generated at the grain boundaries during cooling, which may lower the strength and impact resistance. Regarding the above-mentioned transfer, hot forming, and cooling steps of the blank, there is no particular limitation, and the hot forming method usually used can be directly applied as it is.

[0104] The hot-formed member thus manufactured has a concentration existing between the base steel sheet and the plating layer In the gradient layer, an Sn-enriched layer in which Sn is concentrated is formed, whereby a hot-formed member excellent in hydrogen embrittlement resistance and collision resistance due to a decrease in the amount of diffusible hydrogen in steel can be manufactured.

Example

[0105] Hereinafter, the present invention will be described more specifically with reference to examples. However, it should be noted that the following examples are only for exemplifying and embodying the present invention, and are not intended to limit the scope of rights of the present invention. The scope of rights of the present invention is determined by the matters described in the claims and matters reasonably inferred therefrom.

[0106] (Experimental Example 1) The composition of the steel used for the present invention is shown in Table 1 below (the balance being Fe and other impurities), and slabs having respective compositions were produced by vacuum melting at a thickness of 60 mm. After holding such a slab at 1200 °C for 1 hour, hot rolling was performed at a hot rolling finishing temperature of 900 °C, and coiling was performed at a coiling temperature of 580 °C. Thereafter, as a pickling process, pickling was performed at a HCl concentration of 200 g / L and a pickling time of 20 seconds, and after collectively applying the product of the HCl concentration and the pickling time within the range of the present invention at 4,000 g / L·s, annealing was performed under the conditions shown in Table 2 below. In this example, hot forming was performed at various temperatures, the heating time was 6 minutes, the transfer time to the mold was applied for 10 seconds, and then die quenching was applied.

[0107] For the test piece manufactured as described above, a tissue analysis for ferrite observation was performed, and the vicinity of the surface​​​​​​​​​​ To confirm the Sn enrichment layer, GDS850A (model name, manufactured by LECO), DC and F R equipment were used, and by glow discharge spectroscopy (GDS), as shown in Figure 3, the Sn enrichment layer at the interface between the base steel plate and the plating layer was detected. At this time, from the above GDS experimental results, between the base steel plate and the plating layer, in the thickness direction (meaning the direction perpendicular to the rolling direction), a concentration gradient layer that changes by 0.3 wt% / μm or more within a region where Fe is in the range of 20 to 99% based on the gravimetric method was confirmed to exist. Also, it was confirmed that an Sn enrichment layer exists within such a concentration gradient layer was confirmed. Based on this result, as shown in Figure 1, parameters

[0108]

Number

Number

[0109]

[0110] 8; model name) were utilized for measurement. At this time, the temperature was raised to 400 °C at 20 °C / min, and the time was held so that the diffusion hydrogen peak was sufficiently emitted to measure the diffusion hydrogen curve e), and the total amount of diffusible hydrogen in the steel was obtained by integrating such a curve

[0110] On the other hand, VDA238-1, which is one of the indicators that can show the impact resistance of the hot forming member A three-point bending test was conducted using the 00 standard. Also, as shown in the following relational expression 4, P2 was calculated by multiplying the maximum load value by the bending angle at the maximum load value, and the bending property improvement effect was confirmed. At this time, when the P2 value was 35,000 kgf*° or more, it was marked as "good", and when it was less than 35,000 kgf* °, it was marked as "bad". When the maximum load value or the bending angle due to it increases during the above-mentioned bending test, the occurrence of cracks relatively decreases during a collision, and it can be understood that the collision resistance is improved accordingly. Therefore, in order to analyze the improvement effect of the collision resistance for various components including the addition of Sn, this was represented by P2.

[0111] [Relational Expression 4] P2 = Maximum load [kgf] × Maximum bending angle [°]

[0112]

Table 1

[0113]

Table 2

[0114]

Table 3

[0115] As shown in Tables 1 to 3 above, Examples 1 to 6 that satisfy the alloy composition and manufacturing conditions of the present invention have the values of relational expressions 1-1, 1-2, 2-1, and 2-2 satisfying the scope of the present invention, and it was confirmed that the amount of diffusible hydrogen in the steel decreases and the collision resistance is excellent.

[0116] ​​​​On the other hand, in the case of Comparative Examples 1 to 3, since the Sn content in the steel does not reach the range of the present invention, in the plated steel sheet and the hot-formed member [Number] and [Number] the values of cannot satisfy the range of the present invention, and thus the penetration of diffusible hydrogen in the steel cannot be effectively suppressed, resulting in poor impact resistance.

[0117] On the other hand, regarding the above-described Examples and Comparative Examples, the effect of improving the impact resistance by forming the Sn enrichment layer is shown in FIG. 4, and it can be confirmed that the tendency of the impact resistance to increase due to the formation of the Sn enrichment layer in the hot-formed member becomes apparent. Thereby, as the P1 value increases, the Sn enrichment layer serves as an effective protective film for reducing the amount of diffusible hydrogen in the steel, and it can be understood that excellent hydrogen embrittlement resistance can be ensured and excellent impact resistance can also be ensured.

[0118] (Experimental Example 2) Test pieces were manufactured in the same manner as in Experimental Example 1 described above, except that the pickling concentration and pickling time and the hot-forming temperature were changed to the conditions shown in Table 4 below. At this time, the pickling temperature was uniformly applied at 80°C.

[0119] Regarding each Example and Comparative Example shown in Table 4 below, the values of Relational Expressions 1- 1, 1-2, 2-1, and 2-2 were measured in the same manner as in Experimental Example 1 described above and shown in Table 5 below. Also, regarding the plated steel sheet (or the hot-formed member) for each Example and Comparative Example, the change in the Sn content in the thickness direction of the base steel sheet was analyzed by GDS at 10 points on the surface of the plating layer, and the data obtained Based on the data, the method described in the specification was similarly applied to measure the thickness of the Sn enrichment layer ( That is, in FIG. 2 which is a schematic diagram, the Sn content on the Sn enrichment layer 2 in the x-axis (+) direction The straight-line distance in the thickness direction from the last contact point 11 in the x-axis (+) direction of the Sn average content line 10 of the plating layer and the Sn content line 100 by GDS in the rising section 21 To the last contact point 31 in the x-axis (-) direction of the Sn average content line 30 of the base steel plate and the Sn content line 100 by GDS in the rising section 22 of the Sn content in the x-axis (-) direction of the Sn enrichment layer 2 was measured). The average thickness of the Sn enrichment layer for the above 10 points was measured and shown in Table 5 below.

[0120] For the evaluation of each example and comparative example, the diffusible hydrogen amount and impact resistance were evaluated in the same way as in Experimental Example 1 above. Furthermore, to evaluate the surface characteristics (i.e., the presence or absence of surface defects), the presence or absence of the remaining hot-rolled scale after pickling was evaluated. To confirm the presence or absence of the remaining hot-rolled scale after pickling, after pickling, a tape was used to stick to and peel off the surface of the test piece for each steel type, and the oxide attached here was pasted on white paper, and then the whiteness was measured by color difference analysis. At this time, when the whiteness was 95% or more, it was expressed as "good", and when it was less than 95%, it was expressed as "bad".

[0121]

Table 4

[0122]

Table 5

[0123]

Table 6

[0124] As shown in Tables 4 to 6 above, Comparative Example 4, which does not meet the Sn content of the present invention and has a product of acid concentration and pickling time less than 800 g / L*s, was confirmed to have incomplete removal of hot-rolled scale and a high possibility of causing surface defects during subsequent processes.

[0125] In addition, Comparative Examples 5 and 6, in which the product of acid concentration and pickling time exceeds 10,000 g / L*s, do not satisfy any of the relational expressions 1-1, 1-2, 2-1, and 2-2. As a result, the diffusible hydrogen content in the steel increases, resulting in poor hydrogen embrittlement resistance and poor impact resistance.

[0126] On the other hand, in Examples 7 to 10 of the present application, since the steel composition of the present invention and the product of acid concentration and pickling time are in the range of 800 to 10,000 g / L*s, the relational expressions 1-1, 1-2, 2-1, and 2-2 satisfy the scope of the present invention. As a result, not only are the surface characteristics excellent, but the diffusible hydrogen content in the steel decreases, resulting in excellent hydrogen embrittlement resistance and excellent impact resistance.

[0127] (Experimental Example 3) Before reheating the slab, the slab was produced by lightly pressing it with the total pressure reduction amount described in Table 7 below. Test pieces were produced in the same manner as in Experimental Example 1, except that the conditions in Table 7 below were applied. For such test pieces, each characteristic was evaluated in the same manner as in Experimental Example 1 above. Furthermore, the thickness of the Mn segregation band in the steel sheet and the Sn content in the Mn segregation band for the plated steel sheet and the hot-formed member were measured and shown in Table 7 below. In particular, for the thickness of the Mn segregation band and the area of the part of the Mn segregation band where the average Sn content is 1.015 times or more the average Sn content in the base steel sheet, the method described above in the specification was applied.

[0128] EPMA (Electron Probe X-ray Micro Analyzer ) was used for measurement. An example of the results of such elemental mapping for Mn and Sn (for Invention Example 12) is shown in FIGS. 5 and 6 respectively. nt mapping) results (for Invention Example 12) are shown in FIGS. 5 and 6 respectively. respectively.

[0129] At this time, the surface properties, the amount of diffusible hydrogen, and the impact resistance were measured in the same manner as the above-described method.

[0130] Furthermore, in order to evaluate the formability, a bending test was performed on the members produced from each of the examples and comparative examples in Table 7 below. Specifically, when measuring from the surface to 100 μm below with SEM and observing the ratio of the fracture surface, a ductile fracture and a cleavage fracture are generated. At this time, when the area ratio of the ductile fracture surface to the total measurement area satisfies 70% or more, it is represented by "○", and when it is less than that, it is represented by "×" are generated. At this time, when the area ratio of the ductile fracture surface to the total measurement area satisfies 70% or more, it is represented by "○", and when it is less than that, it is represented by "×" Cleavage fracture) are generated. At this time, when the area ratio of the ductile fracture surface to the total measurement area satisfies 70% or more, it is represented by "○", and when it is less than that, it is represented by "×" are generated. At this time, when the area ratio of the ductile fracture surface to the total measurement area satisfies 70% or more, it is represented by "○", and when it is less than that, it is represented by "×" ".

[0131]

Table 7

[0132]

Table 8

[0133]

Table 9

[0134] Ma*: In the plated steel sheet, among the Mn segregation bands, the area [%] of the part where the average Sn content is 1.015 times or more the average Sn content in the base steel sheet n average content in the base steel sheet Mb*: In the hot-formed member, among the Mn segregation bands, the area [%] of the portion where the average Sn content is 1.015 times or more the average Sn content in the base steel sheet of the Mn segregation band where the average Sn content is 1.015 times or more the average Sn content in the base steel sheet

[0135]

Table 10

[0136] As shown in Tables 7 to 10 above, in Comparative Example 7, since the added Sn content was less than the scope of the present invention and Sn did not sufficiently concentrate in the Mn segregation band, poor impact resistance occurred.

[0137] In the case of Comparative Example 8, the total reduction ratio during continuous casting exceeded 5%, and a failure occurred in the continuous casting reduction machine rendering continuous casting impossible, and thus experimental evaluation was impossible.

[0138] On the other hand, Examples 11 to 14 satisfy the relational expressions 1-1, 1-2, 2-1, and 2-2 of the present application and thus have excellent surface characteristics, a small amount of diffusible hydrogen, and excellent hydrogen embrittlement resistance.

[0139] In particular, among the above-described examples, in the case of the plated steel sheet, when the thickness of the Mn segregation band is 20 μm or less ( or in the hot-formed member, when the thickness of the Mn segregation band is 15 μm or less), or in the plated steel sheet and the hot-formed member, when the area of the portion where the average Sn content in the Mn segregation band is 1.015 times or more the average Sn content in the base steel sheet is 60% or more, in the case of Examples 12 to 14, it was confirmed that the formability was more improved compared to Example 11 which does not satisfy one or more of the above-described conditions and Comparative Example 7 which does not satisfy all of the above-described conditions. From the above-described experimental examples, according to the present invention, despite the addition of a small amount of Sn to the steel, the diffusibility

[0140] From the above experimental examples, according to the present invention, despite the addition of a small amount of Sn to the steel, the diffusibility It has not only resistance to hydrogen delayed fracture due to reduction of hydrogen content, but also excellent impact resistance A hot-formed product can be manufactured. Such parts can be applied and utilized in various fields including the automotive manufacturing field as structural materials or reinforcement parts

Explanation of symbols

[0141] 1: Plating layer 2: Sn-enriched layer 21: In the Sn-enriched layer, the rising interval of Sn content in the x-axis (+) direction 22: In the Sn-enriched layer, the rising interval of Sn content in the x-axis (-) direction 3: Base steel plate 10: Sn average content line of the plating layer 11: The last contact point in the x-axis (+) direction between the Sn average content line of the plating layer and the Sn content line by GDS 30: Sn average content line of the base steel plate 31: The last contact point in the x-axis (-) direction between the Sn average content line of the base steel plate and the Sn content line by GDS 100: Sn content line by GDS 200: In the Sn-enriched layer, the point where the Sn content is the maximum value​​​

Claims

1. By weight, C: 0.07 to 0.5%, Si: 0.05 to 1%, Mn: 0.5 to 5%, P : 0.001 to 0.015%, S: 0.0001 to 0.02%, Al: 0.01 to 0.1 %, Cr: 0.01 to 1%, N: 0.001 to 0.02%, Ti: 0.1% or less, B: 0 01% or less, Sn: 0.01 to 0.1%, the balance being Fe and other inevitable impurities, a base steel plate, and an aluminum or aluminum alloy plating layer provided on at least one surface of the base steel plate, and a Sn-enriched layer provided between the base steel plate and the plating layer, comprising a hot-forming plated steel sheet satisfying the following relational expressions 1-1 and 1-2.

2. [Relational Expression 1-1] 【Number 1】 [In the relational expression 1-1, the Sn ｃｏａｔ represents the average Sn content in the plating layer, and the unit is in wt%. Also, the Sn ｍａｘ represents the maximum value of the Sn content in the Sn enrichment layer However, the unit is weight%. [Relational Expression 1-2] 【Number 2】 [In the above Relational Expression 1-2, the Sn(x) indicates the Sn content along the x-axis direction from any point in the plating layer toward the base steel plate side, x1 indicates the x-axis point at the boundary between the plating layer and the Sn-enriched layer, and the x2 indicates the x-axis point at the maximum value of the Sn content in the Sn-enriched layer.]

2. The hot-forming plated steel sheet according to Claim 1, wherein the thickness of the Sn-enriched layer is 1 μm or more and 20 μm or less.

3. The base steel plate includes an Mn segregation band, and in the Mn segregation band, the area of the portion where the average Sn content is 1.0 15 times or more the average Sn content in the base steel plate is 60% or more. The hot-forming plated steel sheet according to Claim 1.

4. The hot-forming plated steel sheet according to Claim 3, wherein the thickness of the Mn segregation band is 20 μm or less.

5. By weight, C: 0.07 to 0.5%, Si: 0.05 to 1%, Mn: 0.5 to 5%, P : 0.001 to 0.015%, S: 0.0001 to 0.02%, Al: 0.01 to 0.1 %, Cr: 0.01 to 1%, N: 0.001 to 0.02%, Ti: 0.1% or less, B: 0 。 01% or less, Sn: 0.01 to 0.1%, reheating a steel slab containing the balance Fe and other inevitable impurities to 1050 to 1300 °C, and finish rolling the heated steel slab at 750 to 950 °C to obtain a hot-rolled steel sheet, and coiling the hot-rolled steel sheet at 500 to 700 °C, and pickling the coiled hot-rolled steel sheet so that the product of the acid concentration and the pickling time is 800 to 10,000 g / L*s, and annealing the pickled steel sheet at 700 to 900 °C under the dew point temperature condition of -75 to +20 °C in an annealing furnace. ​ ​ ​ After annealing, passing the steel sheet through a plating bath made of aluminum or an aluminum alloy for plating, and A method for manufacturing a plated steel sheet for hot forming, including.

6. The concentration of the acid is 40 to 500 g / L, and the plated steel sheet for hot forming according to claim 5 Manufacturing method.

7. The pickling time is 5 to 60 seconds, and the manufacturing method of the plated steel sheet for hot forming according to claim 5 。

8. The pickling temperature is 40 to 120°C, and the manufacturing of the plated steel sheet for hot forming according to claim 5 Method.

9. Before the reheating step, further including a step of continuous casting with a reduction ratio of 0.5 to 5%, The manufacturing method of the plated steel sheet for hot forming according to claim 5.

10. By weight%, C: 0.07 to 0.5%, Si: 0.05 to 1%, Mn: 0.5 to 5%, P : 0.001 to 0.015%, S: 0.0001 to 0.02%, Al: 0.01 to 0.1 %, Cr: 0.01 to 1%, N: 0.001 to 0.02%, Ti: 0.1% or less, B: 0 01% or less, Sn: 0.01 to 0.1%, the balance being Fe and other unavoidable impurities Base steel sheet, and An aluminum or aluminum alloy plating layer provided on at least one surface of the base steel sheet Layer, and An Sn enrichment layer provided between the base steel sheet and the plating layer, including, A hot forming member that satisfies the following relational expressions 2-1 and 2-2. [Relational expression 2-1] 【Mathematics 3】 In the relational expression 2-1, the Sn ｃｏａｔ represents the average Sn content in the plating layer, and the unit is in wt%. Also, the Sn ｍａｘ represents the maximum value of the Sn content in the Sn enrichment layer And the unit is in weight%. ] [Relational expression 2-2] 【Number 4】 [In the relational expression 2-2, the Sn(x) indicates the Sn content along the x-axis direction from any point in the plating layer to the base steel sheet side, x1 indicates the x-axis point at the boundary between the plating layer and the Sn enrichment layer, and the x2 indicates the x-axis Point at the maximum value of the Sn content in the Sn enrichment layer. ]

11. The base steel sheet contains 5% or less ferrite by area fraction, and the hot forming according to claim 10 Forming member.

12. The thickness of the Sn enrichment layer is 2 to 30 μm, and the hot forming member according to claim 10.

13. Satisfying the following relational expression 2-3, the hot forming member according to claim 10. [Relational expression 2-3]

14. 【Number 5】 The diffusible hydrogen content is 0.4 ppm or less, and the hot forming member according to claim 10.

15. The base steel sheet includes an Mn segregation band, Among the Mn segregation bands, the area of the part where the average Sn content is 1.01 5 times or more the average Sn content in the base steel sheet is 60% or more, and the hot forming member according to claim 10. ​

16. The hot-formed member according to claim 15, wherein the thickness of the Mn segregation band is 15 μm or less.

17. A method for manufacturing a hot-formed member, comprising subjecting the hot-formed plated steel sheet according to claim 1 to heat treatment at a temperature in the range of Ac3 to 950 °C for 1 to 1000 seconds and then performing hot press forming.

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