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, and hot press formed parts.SOLUTION: A plated steel sheet for hot press forming comprising: a base steel sheet; an aluminum or aluminum alloy plated layer provided on at least one surface of the base steel sheet; and a Sb-rich layer provided between the base steel sheet and the plated layer, wherein relational expressions 1-1 and 1-2 below are satisfied. [Relational Expression 1-1] 1.2≤Sbmax / Sbcoat≤5.11. [Relational Expression 1-2] 0.008≤(Sbmax-Sbcoat) / 2×Δt≤0.1438. [In the relational expressions, Sbcoat represents the average Sb content in the plated layer, the unit thereof being weight percent. Sbmax represents the maximum Sb content in the Sb-rich layer, the unit thereof being weight percent. Δt represents the linear distance from the boundary between the plated layer and the Sb-rich layer to the point where Sbmax was measured, the unit thereof being μm.]SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a hot-forming plated steel sheet having excellent hydrogen embrittlement resistance and collision resistance, a hot-forming member, and and methods for producing them. [Background technology]

[0002] In recent years, hot-formed components have been used in automobiles for the purposes of improving fuel efficiency by reducing the weight of automobiles and protecting passengers. It is widely used in the structural components of automobiles. In particular, it has ultra-high strength and high energy absorption capacity. It can be used for bumpers, doors, pillar reinforcements, etc., which require high temperature forming. A representative example of such technology is US Patent Publication No. 6296805 (hereinafter referred to as Patent Document 1).

[0003] Patent Document 1 discloses a method for heating an Al-Si plated steel sheet to 850°C or higher and then hot pressing the sheet. By forming and quenching the structure of the part as martensite, the tensile strength When such ultra-high strength steel for hot forming is applied, In this case, molding is performed at high temperatures, so complex shapes can be easily formed, and strength is improved by rapid cooling inside the mold. However, the martensite structure has a low resistance to hydrogen embrittlement. It is known to have low resistance, and in particular, hot-formed parts are prone to residual heat caused by rapid cooling after heating. Therefore, if the amount of diffusible hydrogen in steel increases, the delayed fracture due to hydrogen embrittlement will occur. There is a drawback in that the application of the member is limited due to concerns about breakage.

[0004] Also, variations in process parameters can lead to changes in global or local mechanical properties within the sheet. Therefore, it is possible to obtain a plated steel sheet and a hot forming steel sheet having good mechanical properties and homogeneity. A steel composition that is less sensitive to changes in manufacturing parameters for manufacturing components is required. Although it is necessary to prevent delayed fracture due to hydrogen embrittlement, there is still a need to meet all of this demand. No technology has been developed that can meet this requirement. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] U.S. Register Publication No. 6296805 Summary of the Invention [Problem to be solved by the invention]

[0006] The present invention is intended to solve the above problems, and is directed to improving hydrogen embrittlement resistance and collision resistance. The present invention provides a plated steel sheet for hot forming, a hot-formed member, and methods for producing the same, which have excellent heat resistance.

[0007] The object of the present invention is not limited to the above. Anyone skilled in the art can easily understand the further object of the present invention from the entire contents of the present specification. There is no difficulty in understanding the subject. [Means for solving the problem]

[0008] One aspect of the present invention is In weight percent, C: 0.14 to 0.5%, Si: 0.001 to 1%, Mn: 0.3 to 4%, P:0.001~0.015%, S:0.0001~0.02%, Al:0.001~0 .1%, Cr: 0.001~1%, N: 0.001~0.02%, Ti: 0.1% or less, B: 0.01% or less, Sb: 0.005 to 0.1%, balance Fe and other unavoidable impurities a base steel sheet comprising: Aluminum or aluminum alloy plating provided on at least one surface of the base steel sheet Layers and an Sb-enriched layer provided between the base steel sheet and the coating layer, Provided is a plated steel sheet for hot forming that satisfies the following relational expressions 1-1 and 1-2.

[0009]

number

[0010] Yet another aspect of the present invention is In weight percent, C: 0.14 to 0.5%, Si: 0.001 to 1%, Mn: 0.3 to 4%, P:0.001~0.015%, S:0.0001~0.02%, Al:0.001~0 .1%, Cr: 0.001~1%, N: 0.001~0.02%, Ti: 0.1% or less, B: 0.01% or less, Sb: 0.005 to 0.1%, balance Fe and other unavoidable impurities Reheating the steel slab to 1050-1300°C; A step of finish rolling the heated steel slab at 800 to 950 ° C to obtain a hot-rolled steel sheet; a step of coiling the hot-rolled steel sheet at 500 to 700 ° C; The coiled hot-rolled steel sheet is pickled at an acid concentration of 800 to 10,000 g / L*s. and pickling the surface of the substrate so that the surface is smooth. The pickled steel sheet is annealed in an annealing furnace at a dew point temperature of -75 to +20°C and at a temperature of 700 to 900°C. and annealing the After annealing, the steel sheet is passed through a plating bath made of aluminum or an aluminum alloy. plating; The present invention provides a method for producing a plated steel sheet for hot forming, comprising:

[0011] Yet another aspect of the present invention is In weight percent, C: 0.14 to 0.5%, Si: 0.001 to 1%, Mn: 0.3 to 4%, P:0.001~0.015%, S:0.0001~0.02%, Al:0.001~0 .1%, Cr: 0.001~1%, N: 0.001~0.02%, Ti: 0.1% or less, B: 0.01% or less, Sb: 0.005 to 0.1%, balance Fe and other unavoidable impurities a base steel sheet comprising: Aluminum or aluminum alloy plating provided on at least one surface of the base steel sheet Layers and an Sb-enriched layer provided between the base steel sheet and the coating layer, A hot-formed member is provided that satisfies the following relations 2-1 and 2-2.

[0012]

number

[0013] Yet another aspect of the present invention is The hot-forming plated steel sheet manufactured by the above-mentioned manufacturing method of the hot-forming plated steel sheet is referred to as A. c) Heat treatment in the temperature range of 3 to 950°C for 1 to 1000 seconds, then hot press forming. A method for manufacturing a molded part is provided. [Effects of the Invention]

[0014] According to one aspect of the present invention, a coating layer having an Sb-enriched layer between the base steel sheet and the coating layer is provided. By manufacturing steel plates, the amount of diffusible hydrogen in the steel is reduced, improving resistance to hydrogen embrittlement and collision resistance. It is possible to provide an excellent plated steel sheet for hot forming, a hot formed member, and a manufacturing method thereof. do.

[0015] The various beneficial advantages and effects of the present invention are not limited to those described above, but may be realized by the specific embodiments of the present invention. This can be more easily understood in the course of explaining the embodiments. [Brief explanation of the drawings]

[0016] [Figure 1] 1 is a schematic diagram showing a gradient concentration graph of the Sb-enriched layer at the interface between the base steel sheet and the coating layer. [Figure 2] This is a schematic diagram of the load-displacement curve during a three-point bending test and the CIE used to indicate crashworthiness. [Figure 3] 1 is a graph showing a concentration gradient of Sb content in a thickness direction from a coating layer to a base steel sheet side, measured by glow discharge optical emission spectrometry (GDS) for Examples and Comparative Examples of the present application. [Figure 4] 1 is a graph showing the change in diffusible hydrogen content with the (Sbmax-Sbcoat) / 2*Δt parameter for an exemplary hot-formed member of the present invention. [Figure 5] 1 is a CIE distribution graph of the (Sbmax-Sbcoat) / 2*Δt parameter for a hot-formed member of the present invention. [Figure 6] 6 shows the results of EPMA element mapping for confirming the Mn segregation zone (FIG. 6a) and the amount of Sb enrichment in the Mn segregation zone (FIG. 6b) for the hot-formed part of Example 14 of the present application. [Figure 7] 1 is a schematic diagram showing an Sb concentration gradient graph obtained by an exemplary GDS of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0017] The following describes preferred embodiments of the present invention. However, the present invention may be embodied in various ways. The present invention can be modified into various other forms, and the scope of the present invention is limited to the embodiments described below. Furthermore, the embodiments of the present invention are not intended to be limiting to the scope of the present invention. These and other aspects of the present invention are provided to more fully describe the present invention.

[0018] Diffusible hydrogen at grain boundaries is believed to be the cause of grain boundary cracking when stress is applied. Therefore, a method is needed to reduce the amount of diffusible hydrogen in steel after hot stamping. is.

[0019] Therefore, the inventors have developed an index that clearly shows the hydrogen embrittlement resistance effect in hot forming steel materials. The analysis of the amount of diffusible hydrogen in steel and the three-point bending test, which is one of the indicators that can show the crash resistance, During the bending test (VDA238-100), the area (CIE: Crac) until the maximum load is reached k initiation energy) calculations revealed that various components, including Sb addition, The effects of the manufacturing conditions, structure, etc. were analyzed. As a result, it was found that the amount of diffusible hydrogen is increased by the formation of an Sb-enriched layer. We have found that this can reduce the impact of hydrogen embrittlement and have developed a hot-formed alloy that is excellent in both resistance to hydrogen embrittlement and impact resistance. This led to the development of a plated steel sheet for automotive applications, a hot-formed member, and a manufacturing method thereof.

[0020] First, the following describes a plated steel sheet for hot forming and a hot-formed member according to one embodiment of the present invention. This will be explained in detail.

[0021] The plated steel sheet according to one embodiment of the present invention contains, by weight, C: 0.14 to 0.5%, Si: 0. 001~1%, Mn:0.3~4%, P:0.001~0.015%, S:0.0001 ~0.02%, Al:0.001~0.1%, Cr:0.001~1%, N:0.001 ~0.02%, Ti: 0.1% or less, B: 0.01% or less, Sb: 0.005~0.1% a base steel sheet containing Fe and other inevitable impurities, and at least one surface of the base steel sheet and the aluminum or aluminum alloy plating layer provided on the base steel sheet and the plating layer. and an Sb-enriched layer provided between the layers.

[0022] First, the alloy composition of the base steel sheet of the present invention will be described in detail. It should be noted that when content is expressed, it means % by weight unless otherwise specified.

[0023] Carbon (C): 0.14~0.5% The above-mentioned C is an element that increases the strength of the heat-treated member and improves the hardening ability, and is used to adjust the strength. If the C content is less than 0.14%, If the hardening ability is low and the cooling rate is reduced, sufficient martensite cannot be secured and ferrite The formation of , which results in poor impact resistance, should be added at 0.14% or more. If it exceeds 0.5%, the strength increases excessively, which may induce brittleness and result in poor weldability. Therefore, the upper limit of the C content is preferably 0.5% or less. The upper limit of the C content may be 0.147%, more preferably 0.335%. That's fine.

[0024] Silicon (Si): 0.001 to 1% The above-mentioned Si should be added not only as a deoxidizer in steelmaking, but also as a solid solution strengthening element. Therefore, Si is an element that contributes to the uniformity of the internal structure. It is not only an effective element for the production of hot-formed parts, but also contributes to increasing the strength of the parts and is effective in homogenizing the material. However, if the Si content is less than 0.001%, the above effects cannot be expected. Furthermore, the manufacturing and process costs for controlling the Si content increase, which is not appropriate. On the other hand, if the Si content exceeds 1%, excessive Si oxide is generated on the surface of the steel sheet during annealing. Since the plating property is significantly reduced by the presence of oxides, 1% or less is added. The lower limit of the Si content may be 0.11%, and more preferably, the upper limit of the Si content is 0.11%. The limit may be 0.81%.

[0025] Manganese (Mn): 0.3-4% The above Mn not only ensures the desired strength through the effect of solid solution strengthening, but also It must be added to suppress the formation of ferrite during hot forming by improving the hardening ability. If the Mn content is less than 0.3%, it is difficult to obtain sufficient hardening effect, and the insufficient hardening effect This requires excessive amounts of other expensive alloying elements, which significantly increases manufacturing costs. Problems arise when the Mn content exceeds 4%. (Band) The deeper the structure, the more uneven the internal structure becomes, which reduces impact resistance. Therefore, 4% or less of Mn is added. The lower limit may be 0.5%, more preferably, the upper limit of the Mn content is 3.7%. Good too.

[0026] Phosphorus (P): 0.001 to 0.015% The above P exists as an impurity in steel, and in order for its minimum content to be less than 0.001%, However, if the P content exceeds 0.015%, it is not preferable because it requires high production costs. However, the weldability of hot-formed components and the material properties due to high-temperature grain boundary segregation are reduced. More preferably, the lower limit of the P content is 0.003%. More preferably, the upper limit of the P content may be 0.013%.

[0027] Sulfur (S): 0.0001 to 0.02% The above S is an impurity and is an element that inhibits the ductility, impact properties and weldability of components. The maximum content is limited to 0.02%. If the minimum content is less than 0.0001%, the product This is not preferable because it significantly increases the manufacturing cost. It may be 1%, more preferably, the upper limit of the S content may be 0.007%.

[0028] Aluminum (Al): 0.001 to 0.1% The above-mentioned Al, together with Si, is an element that acts as a deoxidizer in steelmaking and increases the cleanliness of steel. If the Al content is less than 0.001%, it is difficult to obtain the above effects, and if the Al content exceeds 0.1%, However, excessive AlN precipitates formed during the continuous casting process reduce the high-temperature ductility and cause slab cracking. Since this may cause cracks and lead to manufacturing problems, the upper limit is set at 0.1%. Or, more preferably, the lower limit of the Al content may be 0.011%. The upper limit of the Al content may be 0.071%.

[0029] Cr: 0.001 to 1% The above-mentioned Cr, like Mn, ensures the hardening ability of steel and suppresses the formation of ferrite after hot forming. If the Cr content is less than 0.001%, it is not possible to ensure the above effect. On the other hand, if the Cr content exceeds 1%, the effect of improving hardening ability is not as good as the amount of addition. Not only is it slight, but excessive coarse iron carbides are formed, which induces cracks when stress is applied. The upper limit of the content of Cr is set at 1%. The lower limit of the Cr content may be 0.011%, and more preferably, The upper limit may be 0.50%.

[0030] Nitrogen (N): 0.001-0.02% The above-mentioned N is contained in steel as an impurity. In order for the N content to be less than 0.001%, The excessive manufacturing costs for Al are involved, and when its content exceeds 0.02%, the added Al As shown above, slab cracks are likely to occur due to the formation of AlN, so the upper limit is set to 0.0 2%. Alternatively, more preferably, the lower limit of the N content may be 0.0026%. More preferably, the upper limit of the N content may be 0.0077%.

[0031] Ti: 0.1% or less (including 0) The above Ti is an element that is selectively added in the present invention and does not remain as an impurity in the steel. By combining with the nitrogen present in the alloy to form TiN, B, which ensures hardening ability, is added to the compound. In addition, the formation of TiC precipitates The effects of precipitation strengthening and grain refinement can be expected. However, if the content exceeds 0.1%, Rather, a large amount of coarse TiN is formed, which deteriorates the quality of the steel, so the upper limit is set at 0.1%. On the other hand, the above Ti is a selective element and may not be added in some cases. The lower limit may be 0%.

[0032] B: 0.01% or less (including 0) The above-mentioned B is an element that is selectively added in the present invention, and effectively improves hardenability. When B is added, it segregates at the prior austenite grain boundaries. This can suppress the embrittlement of hot-formed parts caused by the grain boundary segregation of impurities such as P and / or S. However, if it exceeds 0.01%, Fe 23 CB6 complex compound formed by hot pressing The upper limit of B is set at 0.01%. Since B is an optional element and may not be added in some cases, the lower limit of the B content may be 0%. stomach.

[0033] Sb: 0.005 to 0.1% Sb is a key element in manufacturing this hot-formed part, and it is An Sb-enriched layer is formed at the interface, reducing the amount of hydrogen absorbed during heat treatment and improving the hydrogen delayed fracture susceptibility. If the Sb content is less than 0.005%, the plating layer and the substrate A sufficient enriched layer is not formed at the interface with the iron, and the above-mentioned effect cannot be expected. If it exceeds 0.1%, Sb will precipitate excessively at the grain boundaries, causing grain boundary fracture when stress occurs, resulting in material deterioration. Therefore, the upper limit is preferably set to 0.1%. The lower limit of the Sb content may be 0.006%, more preferably 0.006%. may be 0.095%.

[0034] The balance other than the above components is iron (Fe), which is a component that can be contained in steel sheets for hot press forming. If there are any, there are no particular restrictions on the addition of additional additives. Unintended impurities can inevitably be introduced from the product, and this cannot be excluded. These impurities are obvious to any engineer working in the normal manufacturing process. This specification does not specifically refer to all of the contents thereof.

[0035] The plating layer is made of aluminum or aluminum alloy provided on at least one surface of the base steel sheet. The aluminum alloy plating layer provides corrosion resistance in the final hot-formed part. do.

[0036] In the present invention, the type of the plating layer is not particularly limited, and may be any of conventional plated steel sheets for hot forming. Any plating layer that can be applied to the above can be applied to the present invention without any restrictions. Alternatively, the plating layer may be an aluminum or aluminum alloy plating layer. Preferably, the plating layer contains 6 to 12% Si, 1 to 4% Fe, and the balance being Al and other impurities. It may contain unavoidable impurities.

[0037] According to one aspect of the present invention, the plated steel sheet further comprises a base steel sheet and a coating layer. The Sb-enriched layer may include an Sb-enriched layer. In this case, the Sb-enriched layer may be formed by This is the area where Sb is concentrated and classified as Sb content.

[0038] Although not particularly limited, according to one embodiment of the present invention, such an Sb-enriched layer and The coating layer is measured by Glow Discharge Spectroscopy (GDS) from any point in the coating layer to the base steel. This can be distinguished by analyzing the change in Sb content across the thickness of the plate.

[0039] Specifically, according to one embodiment of the present invention, as shown in FIG. The x-axis represents the linear distance from an arbitrary position inside the coating layer 1 to the thickness direction of the base steel sheet 3. The y-axis is determined based on the graph showing the Sb content measured using the GDS. .

[0040] For example, based on Figure 7, which shows the GDS measurement results, In the section 21 in which the Sb content increases in the x-axis (+) direction provided between the base steel sheet 3 and the base steel sheet 3, The average Sb content of the plating layer is shown as 10 and the Sb content measured using the GDS is shown as 100. From the last contact point 11 in the x-axis (+) direction (in the thickness direction of the base steel sheet 3), the Sb-enriched layer Considered as 2.

[0041] At this time, the Sb average content line 10 of the plating layer 1 is The maximum value is at point 200 (Sb max A point 15 μm away from the point (point 1) on the plating layer 1 side This means the extension of the average Sb content line for the section from the point to a point 20 μm away. Cut.

[0042] Similarly, the Sb-enriched layer 2 and the base steel sheet 3 were measured using the GDS in the same manner as described above. The Sb content in the x-axis (-) direction provided between the base steel sheet 3 and the coating layer 1 is In the rising section 22, the average Sb content line 30 of the base steel sheet and the Sb content measured using the GDS The Sb content line 100 is measured from the last contact point 31 in the x-axis (-) direction (thickness of the plating layer 1 side). It is considered as Sb-enriched layer 2 (in the vertical direction).

[0043] At this time, the Sb average content line 30 of the base steel sheet 3 is The maximum value is at point 200 (Sb max A point 15 μm away from the point (point ) on the base steel sheet 3 side This means the extension of the average Sb content line for the section from the point to a point 20 μm away. Cut.

[0044] As a result of extensive research, the inventors of the present invention have found that the amount of diffusible hydrogen absorbed during the heat treatment of hot forming is It was found that reducing the amount of heat can suppress the induction of defects due to delayed hydrogen fracture. A blank having a plating layer made of aluminum or aluminum alloy is heated during cold forming. During this step, the water vapor present in the heat treatment furnace is adsorbed on the surface of the blank. The hydrogen generated by dissociation of SiO2 is absorbed into the steel while it is in the austenite phase, which has high hydrogen solubility at high temperatures. However, rapid cooling caused by hot forming causes the alloy to change to the martensite phase. Then, the solubility of hydrogen drops sharply, and the alloy plating layer formed by alloying the plating layer becomes It acts as a barrier that makes it difficult to release hydrogen. A certain amount of diffusible hydrogen remains in the steel, which prevents crack formation due to hydrogen delayed fracture. Therefore, reducing the amount of diffusible hydrogen absorbed during heat treatment is effective in suppressing defects. This is an important element for the control.

[0045] Furthermore, as a result of several investigations, the inventors have found that as the hydrogen content in steel decreases, It was confirmed that the impact resistance tends to increase with increasing the amount of hydrogen absorbed in the steel during heat treatment. Diffusible hydrogen, especially diffusible hydrogen present at grain boundaries, is subjected to stress during bending and disperses into the grains. Therefore, the amount of diffusible hydrogen in the steel is By reducing the content, properties such as bendability and impact resistance can be improved.

[0046] In particular, the inventors have found that an Sb-rich layer having an appropriate concentration and thickness can be formed between the base steel sheet and the coating layer. It has been found that such an effect can be achieved by forming a crystalline layer. The Sb-enriched layer acts as an effective barrier film that relatively reduces the amount of diffusible hydrogen absorbed in the steel. This is to fulfill our role.

[0047] Specifically, it effectively reduces the hydrogen content in the steel to improve hydrogen embrittlement resistance and provides excellent In order to ensure the above-mentioned crash resistance, the above-mentioned plated steel sheet for hot forming satisfies the following relations 1-1 and 1-2. In this case, the above-mentioned relations 1-1 and 1-2 are empirically obtained. Since the value is a variable, there is no need to specify a specific unit. As long as the unit of each variable defined below is satisfied, That's fine.

[0048]

number

[0049] That is, in order to achieve the intended effect of the present invention, a thin film is required between the base steel sheet and the coating layer. The Sb concentration and thickness of the Sb-enriched layer to be provided must be above a certain level, and the above-mentioned relational expression 1-1 and It must be formed so as to satisfy both 1-2.coat , Sb max and Δt are determined by utilizing the glow discharge spectroscopy (GDS) mentioned above. When analyzing the change in Sb content in the thickness direction of the base steel sheet at one point, the data obtained In other words, the above Sb coat is measured by the method shown in Figure 7 of the present application. In the GDS profile graph, the area with the maximum Sb content in Sb-enriched layer 2 is Point 200(Sb max From the point 15 μm away to the plating layer 1 side, This can be interpreted as an extension of the average Sb content line for the section up to the point where the Sb content is measured.

[0050] In the above relational formula 1-1, Sb max / Sb coat If the value of is less than 1.2 or In the above relational expression 1-2, (Sb max -Sb coat ) / 2×Δt is less than 0.008 If the Sb concentration is less than 100%, the Sb concentration or thickness of the Sb-enriched layer is insufficient, and the Sb is not absorbed in the steel. It is not possible to expect the film to function as a barrier to relatively reduce the amount of diffusible hydrogen that is released. 1 shows the area corresponding to the above relational expression 1-2 in the comb tooth part, and The area is Sb coat The measurement points and Sb max Δ indicates the distance between the measured point and The Sb concentration gradient with t is shown.

[0051] Alternatively, according to one embodiment of the present invention, it is more preferable to use the formula defined by the above-mentioned relation 1-1. RuSb max / Sb coat The lower limit of the value may be 1.20, and more preferably, Sb defined by Coefficient 1-1 max / Sb coatThe upper limit of the value may be 5.11 .

[0052] Furthermore, according to one embodiment of the present invention, it is more preferable that the above-mentioned relational expression 1-2 be defined as follows: Sb max / Sb coat The lower limit of the ) / 2×Δt value may be 0.0080, and more preferably Preferably, (Sb max / Sb coat ) / 2×Δt value The upper limit may be 0.1438.

[0053] On the other hand, although not particularly limited, according to one embodiment of the present invention, However, in the above-mentioned plated steel sheets, the thickness of the above-mentioned Sb-enriched layer is in the range of 1 μm to 20 μm. If the thickness of the Sb-enriched layer in the plated steel sheet is less than 1 μm, the Sb-enriched layer may be easily removed by subsequent hot rolling. Even if heat treatment is performed for forming, a sufficient Sb-enriched layer is not formed, and hydrogen embrittlement resistance and impact resistance characteristics are poor. In addition, the Sb-enriched layer may be difficult to achieve the intended effect of improving the corrosion resistance. If the thickness exceeds 15 μm, Sb will precipitate excessively at the grain boundaries after hot forming, and when stress occurs, It may act as a crack site and result in poor impact resistance.

[0054] In order to maximize the above-mentioned effects, it is more preferable that the above-mentioned plated steel sheet contains S The lower limit of the thickness of the Sb-enriched layer may be 3 μm, and the upper limit of the thickness of the Sb-enriched layer may be in the range of 15 μm. Alternatively, in the above-mentioned plated steel sheet, the thickness of the Sb-enriched layer may be in the range of 3 to 15 μm. The range may be m.

[0055] Meanwhile, the present inventors have been conducting extensive research to further improve the physical properties of plated steel sheets and components. As a result of this investigation, it was found that Sb was present in the manganese segregation bands present in the base steel sheet of the coated steel sheet. It was found that the performance can be improved by concentrating the appropriate amount. As a result of examining the above conditions, it was found that the amount of Sb enrichment in the segregation zone must be above a certain level, or In addition, when the thickness of the Mn segregation zone is below a certain level, this effect becomes more pronounced. It was confirmed that there was an improvement.

[0056] Specifically, according to one embodiment of the present invention, the above-mentioned plated steel sheet is, but not limited to, wherein the base steel sheet contains a Mn segregation zone, and the Mn segregation zone has an average Sb content of 0.01% or less. The area where the Sb content is 1.015 times or more of the average Sb content in the base steel sheet is 60% or more in terms of area fraction. It may be above (or, more preferably, 70% or more). This reduces the generation of inclusions such as MnS that mainly occur in the Mn segregation zone, and reduces stress generation. It also plays a role in suppressing crack occurrence and propagation sites, providing excellent impact resistance. Moreover, if MnS is generated excessively, the brittle fracture surface will be excessively Therefore, by satisfying the above-mentioned composition when Sb is enriched, This reduces MnS, which reduces brittle fractures and improves bendability. It is possible.

[0057] In this case, the upper limit of the average Sb content in the Mn segregation zone is not particularly limited. For example, the Sb content is 5 times the average Sb content in the region of the base steel sheet other than the Mn segregation zone. Furthermore, although not particularly limited, among the Mn segregation zones, Sb The area of the part where the average content is 1.015 times or more the average Sb content in the base steel sheet The upper limit may be 90%.

[0058] The Mn segregation zone was identified using the EPMA element mapping results for Mn, as shown in Figure 6a. Specifically, plated steel sheets are heat treated at temperatures above 1200°C for several hours. After that, the specimen was rapidly cooled to remove the Mn segregation zone, and the Mn intensity (intensity The average value of Mn0 is taken as Mn0. Hereafter, a specific point among the points measured by EPMA is used as the center. The area of the center is 0.4 μm 2 When a square is drawn, the Among the points, if the area where the Mn intensity is 1.015 times or more than Mn0 is 50% or more, The specific point is defined as the Mn segregation point, and if it is less than 50%, it is defined as not being the Mn segregation point. These Mn segregation points are collected and drawn by connecting the outermost Mn segregation points with straight lines. The region where this occurs is the Mn segregation zone.

[0059] In addition, the average Sb content of the Mn segregation zone relative to the average Sb content of the base steel sheet (Sb1) The ratio of Sb2 to Sb1 (Sb2 / Sb1) was calculated based on the Sb component mapping results using EPMA. It can be measured by utilizing the ratio of the intensities of the two.

[0060] According to one embodiment of the present invention, the hot forming plating is preferably, but not limited to, In the steel sheet, the thickness of the Mn segregation zone may be 20 μm or less. The impact resistance and bendability can be further improved by Mn segregation. The thinner the band, the greater the improvement, so there is no need to separately set a lower limit for the thickness of the Mn segregation band. However, as an example, the lower limit of the thickness of the Mn segregation zone is set to more than 0 μm or 1 μm or more. At this time, the thickness of the Mn segregation zone can be determined by the Mn segregation zone determined by the above-mentioned method. The average thickness measured in the thickness direction (direction perpendicular to the rolling direction of the steel plate) from the image of the band can be defined as the thickness of the Mn segregation zone. From the viewpoint of maximizing the above-mentioned effect, it is more preferable that the upper limit of the thickness of the Mn segregation zone is 1 Alternatively, the lower limit of the thickness of the Mn segregation zone may be 6.9 μm. Good too.

[0061] On the other hand, the plated steel sheet for hot forming having the above-mentioned configuration is formed by a hot press forming method described later. As a result, it is possible to produce a hot-formed part having excellent resistance to hydrogen embrittlement and collision resistance.

[0062] The hot-formed member according to one aspect of the present invention has the same alloy composition as the base steel sheet of the above-mentioned plated steel sheet. and aluminum or aluminum alloy provided on at least one surface of the base steel sheet. an Sb-enriched layer provided between the sintered steel sheet and the plating layer; The hot-formed member satisfies the following relations 2-1 and 2-2. The above explanations for the plate, plating layer, and Sb-enriched layer can be applied in the same way. In this case, the above relational expressions 2-1 and 2-2 are values obtained empirically, so the units are It is not necessary to define it, as long as the units of each variable are satisfied.

[0063]

number

[0064] In the present invention, when the plated steel sheet is heated for hot forming, the Sb concentration in the Sb-enriched layer increases. Therefore, in the hot-formed member according to the present invention, the above-mentioned relational expression 2 By satisfying the conditions of -1 and 2-2, the hydrogen content in the steel can be effectively reduced, thereby achieving hydrogen resistance. In this case, the hot-formed member can be improved in brittleness and impact resistance. The method of classifying the boundary between the Sb-rich layer and the Sb-rich layer and the boundary between the base steel sheet and the Sb-rich layer is as follows: The classification method for plated steel sheets described above can be applied in the same manner.

[0065] Alternatively, according to one embodiment of the present invention, it is more preferable to use the formula defined by the above-mentioned relation 2-1. RuSb max / Sb coat The lower limit of the value may be 1.57, and more preferably, Sb defined by Equation 2-1 max / Sb coat The upper limit of the value may be 7.39 .

[0066] Furthermore, according to one embodiment of the present invention, it is more preferable that the above-mentioned relational expression 2-2 ( Sb max / Sb coat The lower limit of the ) / 2×Δt value may be 0.0148, and more preferably Preferably, (Sb max / Sb coat ) / 2×Δt value The upper limit may be 0.1940.

[0067] Alternatively, although not particularly limited, according to one embodiment of the present invention, more preferably The following relational expression 2-3 can be satisfied, thereby further improving hydrogen embrittlement resistance and collision resistance. It is possible.

[0068]

number

[0069] Although not particularly limited, according to one embodiment of the present invention, in the hot-formed member The microstructure of the base steel sheet may contain 5% or less ferrite and the remainder martensite. Furthermore, the upper bainite, retained austenite, cementite and porphyrins may be less than 1%. It may further contain other phases such as arsenite.

[0070] According to one embodiment of the present invention, the base steel sheet contains ferrite in an area fraction of 5% or less. This is because the hardening ability can be ensured by adjusting the steel composition during hot forming and sufficient cooling can be achieved. By ensuring the required speed, the ferrite fraction can be controlled to 5% or less. In the case of shaped components, if the ferrite fraction of the base steel sheet exceeds 5%, a decrease in strength occurs. Not only that, but local stress is concentrated in the relatively soft ferrite, which accelerates crack propagation. This may promote scattering and significantly reduce crashworthiness.

[0071] Furthermore, according to one embodiment of the present invention, the hot-formed member may be, but is not limited to, In the hot-formed member, the thickness of the Sb-enriched layer may be 2 to 30 μm. When the thickness of the enriched layer is less than 2 μm, it effectively suppresses hydrogen penetration into the steel during hot forming. As a result, the intended effect of improving hydrogen embrittlement resistance and crash resistance cannot be fully achieved. In addition, if the thickness of the Sb-enriched layer in the hot-formed part exceeds 30 μm, Not only does Sb form a concentrated layer, but it can also precipitate excessively at the grain boundaries in the surface layer of the base steel. This may accelerate the generation and propagation of cracks during bending, resulting in a decrease in crashworthiness. be.

[0072] From the viewpoint of further maximizing the above-mentioned effects, it is more preferable that in the hot-formed member, The lower limit of the thickness of the Sb-enriched layer may be 3 μm, or Alternatively, in the hot-formed part, the upper limit of the Sb-enriched layer may be 25 μm. The thickness may be in the range of 3 to 25 μm.

[0073] Furthermore, although not particularly limited, according to one embodiment of the present invention, the hot-formed member The amount of diffusible hydrogen may be 0.2 ppm or less, thereby ensuring excellent resistance to hydrogen embrittlement. Such a diffusible hydrogen content of 0.2 ppm or less can be maintained for 120 hours. Even if the test specimen is subjected to stress by bending under the same yield stress of the material, the part will not crack. This is because.

[0074] Furthermore, although not particularly limited, according to one embodiment of the present invention, the hot-formed member In the present invention, the base steel sheet includes a Mn segregation zone, and the Mn segregation zone has an average Sb content of 1000 ppm or less. The area fraction of the steel sheet containing 1.015 times or more of the average Sb content is 60% or more. (or, more preferably, 70% or more). This reduces the generation of inclusions such as MnS that mainly occur in the Mn segregation zone, and It plays a role in suppressing the occurrence and propagation of cracks, providing excellent impact resistance. Furthermore, if MnS is generated excessively, brittle fractures will occur excessively. Therefore, by satisfying the above-mentioned structure during Sb enrichment, It is possible to reduce MnS, which reduces brittle fractures and improves bendability. It is possible.

[0075] In this case, the upper limit of the average Sb content in the Mn segregation zone is not particularly limited. For example, the Sb content is 5 times the average Sb content in the region of the base steel sheet other than the Mn segregation zone. Although not particularly limited, among the Mn segregation zones, Sb The area of the part where the average content is 1.015 times or more the average Sb content in the base steel sheet The upper limit may be 95%.

[0076] Furthermore, although not particularly limited, according to one embodiment of the present invention, the hot-formed member In this case, the thickness of the Mn segregation zone may be 15 μm (or 15.0 μm) or less. By satisfying this requirement, the crash resistance and bending properties can be further improved. The thinner the Mn segregation zone, the better the bending strength and bending property. However, as an example, the lower limit of the thickness of the Mn segregation zone may be 0 μm. On the other hand, from the viewpoint of maximizing the above-mentioned effect, More preferably, the upper limit of the thickness of the Mn segregation zone may be 12.0 μm, or The lower limit of the thickness of the Mn segregation zone may be 6.0 μm.

[0077] At this time, in the hot-formed parts, the definition of the Mn segregation zone, the average Sb content in the base steel sheet, The ratio of the average Sb content in the Mn segregation zone to the Sb content and the thickness of the Mn segregation zone were measured as described above. The measurement methods and standards for plated steel sheets can be similarly applied.

[0078] Next, a method for producing a plated steel sheet for hot forming, which is yet another embodiment of the present invention, will be described. do.

[0079] The plated steel sheet for hot forming according to one aspect of the present invention has the alloy composition described above in weight percent. A step of reheating the steel slab to 1050-1300°C and a step of heating the heated steel slab to 800-9 A step of obtaining a hot-rolled steel sheet by finish rolling at 50°C, and winding the hot-rolled steel sheet at 500 to 700°C. The product of the acid concentration and pickling time of the coiled hot-rolled steel sheet is 800 to 10,000 g. The pickled hot-rolled steel sheet is then placed in an annealing furnace at -75 Annealing at 700-860°C under a dew point temperature condition of -20°C. After annealing, a step of passing the aluminum or aluminum alloy through a plating bath to plate the aluminum or aluminum alloy; may include:

[0080] Slab reheating stage First, a slab having the above-mentioned alloy composition is reheated to 1050 to 1300°C. If the heating temperature is less than 1050°C, the slab structure will not be homogenized sufficiently, and the precipitated elements will On the other hand, if the reheating temperature exceeds 1300°C, excessive An oxide layer is formed, which increases the production cost for removing the oxide layer. This increases the possibility of surface defects occurring.

[0081] Finishing rolling stage Finish rolling should be performed at 800 to 950°C. If the finish rolling temperature is less than 800°C, As the rolling progresses through the two-phase region, ferrite is introduced into the surface layer of the steel sheet, making it difficult to control the sheet shape. On the other hand, if the finish rolling temperature exceeds 950°C, coarsening of the hot-rolled grains may occur. .

[0082] Winding stage After the finish rolling is completed, the hot rolled steel sheet is coiled at 500 to 700°C, cooled, and then hot rolled. If the coiling temperature is less than 500°C, the steel sheet may be partially or entirely martensite-coated. This not only makes it difficult to control the coil shape, but also causes excessive strength increase in the hot-rolled steel sheet. On the other hand, if the coiling temperature exceeds 700°C, the subsequent cold rolling properties will be deteriorated. If the temperature is too high, excessive coarse carbides will be formed, which will cause cracks to occur when stress is generated in the hot-formed parts. This leads to a problem of reduced crashworthiness.

[0083] Pickling treatment stage The coiled hot-rolled steel sheet is pickled at an acid concentration of 800 to 10,000 g / L*s. The steel sheet that has undergone the above-mentioned reheating, finish rolling and coiling steps is subjected to pickling treatment so that the b) A thickened layer is formed, but in the pickling process, the product of the acid concentration and the pickling time is 800-1 When applied within the range of 0,000g / L*s, the Sb-enriched layer, which is the core of this invention, is effective. This effectively protects the steel and can reduce the amount of diffusible hydrogen in the steel.

[0084] Specifically, when the product of the acid concentration and the pickling time is less than 800g / L*s, the finish rolling If the scale generated during the process is not removed sufficiently, it may cause quality problems in the product. On the other hand, if the product of the acid concentration and pickling time exceeds 10,000g / L*s, the Sb-enriched layer Not only will all or part of the above be washed away during pickling, preventing the expected effect from being achieved, but it will also increase production costs. Therefore, the upper limit is set at 10,000g / L*s. However, If there is more than one pickling tank and the acid concentration and pickling time are different, The above values can be expressed by adding the products of the concentrations of the other acids and the pickling times.

[0085] On the other hand, from the viewpoint of further maximizing the above-mentioned effect, it is more preferable to set the above-mentioned acid concentration and pickling time to The lower limit of the product between the acid concentration and the pickling time may be 3,000 g / L*s, or The upper limit of the product may be 5,000 g / L*s.

[0086] Although not particularly limited, according to one embodiment of the present invention, the pickling treatment step can be performed using As the acid to be used, any acid that can be commonly used in the art can be used. Typical examples include hydrochloric acid (HCl) and sulfuric acid (H2SO4). In particular, in the present invention, hydrochloric acid (HCl l) has better pickling ability and is more economical than using other acids. This is effective, and there is little possibility of foreign matter being generated on the surface after pickling, making it easy to ensure surface quality.

[0087] On the other hand, although not particularly limited, according to one embodiment of the present invention, the concentration of the acid is 40 If the acid concentration is less than 40 g / L, the acid concentration may be in the range of 100 to 500 g / L. During the washing time, the surface scale generated during hot rolling is not sufficiently removed, and the surface of the steel sheet is damaged. On the other hand, when the acid concentration exceeds 500 g / L, Sb The thickened layer is washed away, making it difficult to achieve the intended effect of the invention in the final hot-formed part. This may lead to defects in the surface layer due to over-pickling. From the viewpoint of further maximizing the above, the lower limit of the acid concentration is more preferably 180 g / L. Alternatively, the upper limit of the acid concentration may be 230 g / L.

[0088] Although not particularly limited, according to one embodiment of the present invention, the pickling time is 5 to 10 minutes. If the pickling time is less than 5 seconds, the surface scale of the steel sheet may be If the pickling time exceeds 60 seconds, the surface may be damaged due to insufficient removal of the metal. If this occurs, the Sb-enriched layer will be washed away, which may reduce productivity and increase process costs. In order to maximize the above-mentioned effect, the lower limit of the pickling time is more preferably 1 Alternatively, the upper limit of the pickling time may be 50 seconds. .

[0089] Although not particularly limited, according to one embodiment of the present invention, the pickling temperature is 40 If the pickling temperature is less than 40°C, the pickling power may be insufficient, This may have a negative effect on the quality of the product. This not only increases the fixed cost of maintaining the high temperature, but also increases the This may increase the amount of evaporation of the pickling solution, which may result in increased costs for replenishing the lost pickling solution. From the viewpoint of maximizing the effect, the lower limit of the pickling temperature may more preferably be 50°C. Alternatively, the upper limit of the pickling temperature may be 100°C. The temperature may be in the range of 50 to 100°C.

[0090] Annealing stage The above-mentioned pickled hot-rolled steel sheet was heated at 700°C in an annealing furnace at a dew point temperature of -75 to +20°C. If the annealing temperature is less than 700°C, the cold-rolled steel sheet can be annealed to a temperature of 100°C or higher. The recrystallization of the structure is not completed sufficiently, which may result in a poor sheet shape. The strength is too high and may cause die wear during the blanking process. When the annealing temperature exceeds 900°C, the formation of surface oxides is promoted during the annealing process, resulting in Al-S This can cause defects on the plating surface. Alternatively, the die wear during the blanking process and the plating surface can be damaged. From the viewpoint of suppressing planar defects, the lower limit of the annealing temperature is more preferably 750°C. The upper limit of the annealing temperature may be 800° C., and most preferably 800° C. Similarly, the upper limit of the annealing temperature may be Preferably, it may be 860°C.

[0091] The atmosphere during annealing is preferably a non-oxidizing atmosphere, such as a hydrogen-nitrogen mixed gas. In this case, the dew point temperature of the atmospheric gas can be used. t) is performed between -75°C and +20°C. If the dew point temperature is below -75°C, the dew point control This poses a problem of increased manufacturing costs because additional equipment is required for this purpose. On the other hand, if the dew point temperature exceeds +20°C, annealing oxides are formed on the surface of the steel sheet during annealing, This may result in poor surface quality such as unplated areas. On the other hand, in order to maximize the above-mentioned effects, From this viewpoint, the lower limit of the dew point temperature during the annealing may more preferably be -70°C, and most preferably be 100°C. Preferably, the upper limit of the dew point temperature during the annealing may be -40°C. Preferably, it may be +15°C, and most preferably, it may be -20°C.

[0092] Plating stage Immediately after the annealing process, the hot-rolled steel sheet is plated with Al-Si. A plated steel sheet is produced by passing the steel sheet through a plating bath made of aluminum or an aluminum alloy. In this case, the plating conditions are the same as those normally applied to steel sheets for hot press forming. The present invention can be applied without limitation as long as the plating conditions are met. The bath composition is Si: 6-12%, Fe: 1-4%, the rest is Al and other unavoidable impurities. It can include.

[0093] At this time, although there is no particular limitation, in the plating stage, the plating amount is usually Standard single-sided printing: 20-140 g / m 2 It is preferable to use a standard weight of 20 g / m on one side. 2 less than It is difficult to ensure the desired corrosion resistance of the hot-formed parts. 2 In excess, excessive licking Not only does the amount of coating increase the manufacturing cost, but it is also difficult to uniformly coat the entire coil width and length. It is not easy to plate in the right direction.

[0094] Cold rolling stage According to one aspect of the present invention, a method for manufacturing a plated steel sheet for hot forming includes the steps of: After the step (a), the method may further include a step of cold rolling the hot-rolled steel sheet to manufacture a cold-rolled steel sheet.

[0095] Continuous casting stage The method for producing a hot-forming plated steel sheet according to the present invention comprises the steps of: The method may further include, but is not limited to, a continuous casting step. The invention reduces segregation and improves collision resistance by applying a soft reduction during continuous casting to produce slabs. If excessive slab segregation occurs, the segregation will continue until the final hot-formed part. The bands are thick and concentrated, and the area between these segregation bands and the base steel sheet area other than the Mn segregation bands is The resulting hardness difference and the formation of inclusions in the segregation zone can reduce impact resistance. be.

[0096] 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%. If the total reduction rate during continuous casting is less than 0.5%, there is almost no reduction. As a result, center segregation is not sufficiently removed, which may result in poor impact resistance within the hot-formed part. On the other hand, if the total reduction rate during continuous casting exceeds 5%, the reduction roll equipment will be overloaded. This may accelerate the breakdown and deterioration of facilities. From the viewpoint of increasing the size, it is more preferable that the lower limit of the total reduction rate during soft reduction by continuous casting is 0. 0.52%, or the upper limit of the total reduction rate during soft reduction by the above continuous casting is 4. It could be 10%.

[0097] The hot-formed plated steel sheet manufactured by the above-mentioned manufacturing method is hot-press-formed to obtain a durable It is possible to manufacture hot-formed parts that are excellent in hydrogen embrittlement resistance and collision resistance. The plated steel sheet manufactured by this method is subjected to hot forming and die quenching to improve resistance to hydrogen embrittlement and The steel composition and manufacturing method for the final component with excellent crashworthiness will be described. The plated steel sheet produced by this method is used to produce a blank for hot forming. In terms of rank, the austenite single phase region temperature or higher, more specifically, the Ac3 temperature or higher and 975°C or higher If the heating temperature is below the Ac3 temperature, the two-phase region The presence of untransformed ferrite during heating makes it difficult to ensure strength and crash resistance. If the temperature exceeds 975°C, excessive oxides will be generated on the surface of the component, which will affect the spot weldability. This makes it difficult to maintain a high temperature, and increases the manufacturing cost.

[0098] Thereafter, the heated blank is preferably maintained at the above temperature range for 1 to 1000 seconds. If the holding time is less than 1 second, it is difficult to obtain a uniform temperature distribution over the entire blank. On the other hand, if the above holding time is 100 If the heating time exceeds 0 seconds, excessive oxides will be generated on the surface of the component, causing damage, just as if the heating temperature were exceeded. Not only does this make it difficult to ensure good weldability, but it also increases the manufacturing costs of the components.

[0099] The heated blank is transferred to the press and cooled at a rate of -20°C / s or faster. The final part is manufactured by forming and die hardening. At this time, the cooling rate is less than -20°C / s. At high temperatures, ferrite phases are introduced during cooling and formed at the grain boundaries, reducing strength and crashworthiness. The blank transport, hot forming and cooling steps described above may be particularly There is no limitation, and a commonly used hot forming method can be applied as is.

[0100] In the hot-formed parts manufactured in this way, Sb is concentrated between the base steel sheet and the coating layer. This results in a reduction in the amount of diffusible hydrogen in the steel, improving resistance to hydrogen embrittlement and It is possible to manufacture hot-formed parts with excellent impact resistance. [Example]

[0101] The present invention will be described in more detail below with reference to examples. The following is a summary of the present invention and should not be construed as limiting the scope of the present invention. It should be noted that the scope of the present invention is not limited to the scope of the claims. The determination shall be based on the matters set forth and matters that can be reasonably inferred from them.

[0102] (Experimental Example 1) The composition of the steel used for the present invention is shown in Table 1 below (balance Fe and other impurities). Slabs with each composition were produced by vacuum melting at a thickness of 40 mm. After holding the slab at 1200°C for 1 hour, the slab was cooled to 900°C to finish hot rolling. The steel is hot rolled at a temperature of 600°C and coiled at a coiling temperature of 600°C. After that, it is pickled and cold rolled. After that, annealing was carried out under the conditions in Table 2 below, and the composition was Al-9%Si-2%Fe and the balance was a trace of impurities. The plating was carried out by immersing the steel in a plating bath containing 200 g / L of H The pickling was carried out at a Cl concentration of 20 seconds for a pickling time of 20 seconds, and the product of the HCl concentration and the pickling time was within the range of the present invention. It was applied in bulk at a dose of 4,000 g / L·s.

[0103] In this example, hot forming was performed at various temperatures, the heating time was 6 minutes, and the transfer time to the mold was 10 minutes. was applied for 10 seconds, followed by die quenching.

[0104] The test specimens manufactured as described above were subjected to structural analysis to observe ferrite. To confirm the Sb-enriched layer, GDS850A (model name, manufactured by LECO), DC and F Using the R equipment, glow discharge spectroscopy (GDS) As shown in Figure 3, the chromatic aberration of the substrate was measured by ical emission spectroscopy (Emission Spectrometry). The Sb-enriched layer at the interface between the iron and the plating layer was detected. Based on this result, as shown in Figure 1, , the parameter Sb max , Sb coat , Δt were measured and used to calculate the values shown in the table below. The enrichment layer parameter P1 was calculated, and the resulting diffusible hydrogen amount was confirmed by TDA (T Thermal Desorption Analysis) equipment (Bruker G8; The measurement was carried out using a model (model name). At this time, the temperature was raised to 400°C at a rate of 20°C / min. Hold the time until the peak appears sufficiently and measure the hydrogen diffusion curve. The total amount of diffusible hydrogen in the steel was determined by integrating this curve.

[0105] In addition, to confirm the crashworthiness, the bending property was evaluated one week after the hot forming heat treatment. The load-displacement curve obtained from the three-point bending test shown in Figure 2 shows the maximum load. Evaluated using the area (CIE: Crack initiation Energy) index To determine whether or not a car has excellent crashworthiness, the CIE value measured is 35,000 N·m or more. The above cases were rated as "good" and cases below 35,000N·m were rated as "poor". Shown in 2 and 3.

[0106] [Table 1]

[0107] [Table 2]

[0108] [Table 3]

[0109] As shown in Tables 1 to 3 above, in Comparative Examples 1 to 5, the Sb content in the steel did not reach the range of the present invention. Without, Sb max / Sb coat The ratio and P1 value do not meet the range of the present invention. Therefore, the penetration of diffusible hydrogen into the steel could not be effectively suppressed, resulting in poor crash resistance.

[0110] In contrast, in Examples 1 to 8, the values of the relational expressions 1-1, 1-2, 2-1 and 2-2 are By satisfying the scope of the invention, the amount of diffusible hydrogen in the steel is reduced and the impact resistance index is increased. It was confirmed that the CIE value increased and the film had excellent impact resistance.

[0111] On the other hand, excluding some results where the ferrite structure was outside the range of the present invention, as shown in Figure 4, It was found that the amount of diffusible hydrogen gradually decreased as the P1 value increased, and the Sb-enriched layer It can be seen that this plays the role of an effective barrier film to reduce the amount of diffusible hydrogen in the steel. Due to this effect, as shown in Figure 5, when an Sb-enriched layer appears, the CIE value increases significantly. It can be seen that excellent crash resistance can be ensured at the same time.

[0112] (Experimental Example 2) The pickling concentration and pickling time were changed as shown in Table 4 below, and the hot forming temperature was applied under the conditions in Table 4. The test pieces were manufactured in the same manner as in Experimental Example 1, except that the pickling temperature was It was applied in bulk at 80°C.

[0113] For each of the Examples and Comparative Examples in Table 4 below, the relational expression 1 was calculated using the same method as in Experimental Example 1. The values of 1-1, 1-2, 2-1 and 2-2 were measured and are shown in Table 5 below. For the comparative example, the plated steel sheet (or hot formed member) was The change in Sb content in the thickness direction of the base steel sheet is analyzed using GDS for 0 points. Based on the data, the thickness of the Sb-enriched layer was measured using the same method described in the specification. (That is, the Sb content line of the plating layer in the schematic diagram of Figure 7 and the Sb content line by GDS From the last contact point 11 in the x-axis (+) direction, the average Sb content line of the base steel sheet and the S content line by GDS The linear distance in the thickness direction to the last contact point 31 of the b content line in the x-axis (-) direction was measured. The average thickness of the Sb-enriched layer was measured at the above 10 points and is shown in Table 5 below. .

[0114] In order to evaluate each of the examples and comparative examples, the collision resistance was measured in the same manner as in Experimental Example 1. To evaluate the surface characteristics (i.e., the presence or absence of surface defects), the specimens were heat treated after pickling. The presence or absence of hot scale remaining after pickling was evaluated. To confirm this, after pickling, tape was attached to the surface of the test piece for each steel type and then peeled off. The oxide thus formed was then attached to a piece of white paper, and the whiteness was measured by color difference analysis. In this case, if the whiteness is 95% or more, it is expressed as "good," and if it is less than 95%, it is expressed as "poor." did.

[0115] [Table 4]

[0116] [Table 5]

[0117] [Table 6]

[0118] As shown in Tables 4 to 6 above, the Sb content of the present invention is not satisfied, and the product of the acid concentration and the pickling time is Comparative Example 6, which has a viscosity of less than 800 g / L*s, satisfies the relations 1-1, 1-2, 2-1 and 2-2. Not only is this not sufficient, but hot scale is not completely removed, causing surface defects during subsequent processing. confirmed that this was a high possibility.

[0119] In addition, in Comparative Examples 7 and 8, where the product of the acid concentration and the pickling time exceeds 10,000 g / L*s, None of the relations 1-1, 1-2, 2-1 and 2-2 is satisfied, and as a result, the diffusion The amount of reactive hydrogen increases, resulting in poor hydrogen embrittlement resistance, and the CIE value, which is an index of impact resistance, is also low. It also had poor crashworthiness.

[0120] On the other hand, in Examples 9 to 12 of the present application, the steel composition of the present invention and the product of the acid concentration and the pickling time are 800 Since the range is 10,000g / L*s, relations 1-1, 1-2, 2-1 and 2-2 This not only provides excellent surface properties but also improves the diffusion resistance in the steel. The amount of hydrogen is reduced, resulting in excellent resistance to hydrogen embrittlement. The value increases, and the crashworthiness is excellent.

[0121] (Experimental Example 3) Before reheating the slab, the slab was lightly pressed to the total reduction amount shown in Table 7 below to produce the slab. Test pieces were produced in the same manner as in Experimental Example 1, except that the conditions in Table 7 were applied. The properties of the test pieces were evaluated in the same manner as in Experimental Example 1. The thickness of the Mn segregation zone in the steel plate for the formed part and the Sb content in the Mn segregation zone were measured, and the following Shown in Table 7.

[0122] In particular, the thickness of the Mn segregation zone and the average Sb content of the Mn segregation zone are The area of the part where the content is 1.015 times or more of the average content is calculated by applying the method described above in the specification. EPMA(Electron Probe X-ray Micro Analyzer ) method, and element mapping (Element Mn and Sb) for each of these elements was performed. The results of the ent mapping are shown in Figures 6a and 6b.

[0123] At this time, the surface characteristics, the amount of diffusible hydrogen, and the collision resistance were measured in the same manner as described above.

[0124] In addition, in order to further evaluate the bending property, the samples manufactured from each of the Examples and Comparative Examples in Table 7 below were A bending test was carried out on the component. Specifically, measurements were taken from the surface to 100 μm below using an SEM. When observing the ratio of fracture surfaces, it is clear that there are two types of fracture surfaces: ductile fracture and brittle fracture. Cleavage fractures are generated. If the area ratio of the fractured surface is 70% or more, it is indicated by "○", and if it is less than that, it is indicated by "×". Ta.

[0125] [Table 7]

[0126] [Table 8]

[0127] [Table 9]

[0128] [Table 10]

[0129] As shown in Tables 7 to 10, in Comparative Example 9, the added Sb content was below the range of the present invention. Furthermore, Sb was not sufficiently concentrated in the Mn segregation zone, resulting in poor impact resistance.

[0130] In the case of Comparative Example 10, the total reduction rate during continuous casting exceeded 5%, and problems occurred during continuous casting reduction. Continuous casting was not possible, and experimental evaluation was therefore impossible.

[0131] On the other hand, Examples 13 to 16 are those in which the ranges of the relational expressions 1-1, 1-2, 2-1 and 2-2 of the present application are satisfied. By satisfying these conditions, the steel has excellent surface properties, a small amount of diffusible hydrogen, and excellent resistance to hydrogen embrittlement.

[0132] In particular, in the above-mentioned examples, in the plated steel sheet, the thickness of the Mn segregation band is 20 μm or less ( Or, in the case of hot-formed parts, the thickness of the Mn segregation zone is 15 μm or less, or In the plated steel sheet and hot-formed parts, the Sb content in the Mn segregation zone relative to the average Sb content in the base steel sheet In Examples 14 to 16, where the average content ratio is 60% or more, one or more of the above conditions is satisfied. Compared with Example 13 which does not satisfy the above conditions and Comparative Example 9 which does not satisfy all of the above conditions, It was confirmed that there would be further improvement.

[0133] From the above experimental examples, it can be seen that, according to the present invention, the diffusibility of Sb is improved despite the addition of a small amount of Sb to the steel. Not only is it resistant to delayed hydrogen fracture due to the reduced amount of hydrogen, but it also has excellent crash resistance. Such parts can be used as structural or reinforcing parts. This technology can be applied and utilized in various fields, including the automobile manufacturing field. [Explanation of symbols]

[0134] 1: Plating layer 2: Sb concentrated layer 21: In the Sb-enriched layer, the Sb content increases in the x-axis (+) direction. 22: In the Sb-enriched layer, the Sb content increases in the x-axis (-) direction. 3: Base steel sheet 10: Average Sb content of the plating layer 11: The average Sb content line of the coating layer and the maximum Sb content line by GDS in the x-axis (+) direction Post-contact point 30: Average Sb content of base steel sheet 31: The Sb average content line of the base steel sheet and the Sb content line by GDS are plotted in the x-axis (-) direction. Post-contact point 100: Sb content line by GDS 200: The point in the Sb-enriched layer where the Sb content is at its maximum

Claims

1. In weight percent, C: 0.14 to 0.5%, Si: 0.001 to 1%, Mn: 0.3 to 4%, P: 0.001-0.015%, S: 0.0001-0.02%, Al: 0.001-0 .. 1%, Cr: 0.001-1%, N: 0.001-0.02%, Ti: 0.1% or less, B: 0.01% or less, Sb: 0.005 to 0.1%, balance Fe and other unavoidable impurities a base steel sheet comprising: Aluminum or aluminum alloy plating provided on at least one surface of the base steel sheet Layers and an Sb-enriched layer provided between the base steel sheet and the coating layer, A plated steel sheet for hot forming, which satisfies the following relations 1-1 and 1-2. [Equation 1] [In the above-mentioned Relational Formulas 1-1 and 1-2, the Sb ｃｏａｔ is the average S The unit is weight percent. ｍａｘ is the Sb content in the Sb-enriched layer The unit is weight percent. The Δt is the maximum value of the time between the plating layer and the Sb-enriched layer. From the boundary to the Sb ｍａｘ The unit is μm.

2. 2. The hot forming method according to claim 1, wherein the thickness of the Sb-enriched layer is 1 μm or more and 20 μm or less. Plated steel sheet.

3. The base steel sheet includes an Mn segregation zone, In the Mn segregation zone, the average Sb content is 1.0 times the average Sb content in the base steel sheet.

2. The plated steel for hot forming according to claim 1, wherein the area of the portion where the thickness is 15 times or more is 60% or more. Board.

4. The plated steel sheet for hot forming according to claim 3, wherein the thickness of the Mn segregation zone is 20 μm or less. 。

5. In weight percent, C: 0.14 to 0.5%, Si: 0.001 to 1%, Mn: 0.3 to 4%, P: 0.001-0.015%, S: 0.0001-0.02%, Al: 0.001-0 .. 1%, Cr: 0.001-1%, N: 0.001-0.02%, Ti: 0.1% or less, B: 0.01% or less, Sb: 0.005 to 0.1%, balance Fe and other unavoidable impurities Reheating the steel slab to 1050-1300°C; A step of finish rolling the heated steel slab at 800 to 950°C to obtain a hot-rolled steel sheet; coiling the hot-rolled steel sheet at 500 to 700°C; The coiled hot-rolled steel sheet is pickled so that the product of the acid concentration and the pickling time is 800 to 10,000 g / L*s. and pickling the surface of the substrate so that the surface is smooth. The pickled steel sheet is annealed in an annealing furnace at a dew point temperature of -75 to +20°C and at a temperature of 700 to 900°C. and annealing the After annealing, the steel sheet is passed through a plating bath made of aluminum or an aluminum alloy. plating; A method for producing a plated steel sheet for hot forming, comprising:

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

7. The method for producing a plated steel sheet for hot forming according to claim 5, wherein the pickling time is 5 to 60 seconds. 。

8. The method for producing a plated steel sheet for hot forming according to claim 5, wherein the pickling temperature is 40 to 120°C. method.

9. Before the reheating step, a step of soft reduction at a reduction rate of 0.5 to 5% and continuous casting is further performed. The method for producing a plated steel sheet for hot forming according to claim 5, further comprising:

10. In weight percent, C: 0.14 to 0.5%, Si: 0.001 to 1%, Mn: 0.3 to 4%, P: 0.001-0.015%, S: 0.0001-0.02%, Al: 0.001-0 .. 1%, Cr: 0.001-1%, N: 0.001-0.02%, Ti: 0.1% or less, B: 0.01% or less, Sb: 0.005 to 0.1%, balance Fe and other unavoidable impurities a base steel sheet comprising: Aluminum or aluminum alloy plating provided on at least one surface of the base steel sheet Layers and an Sb-enriched layer provided between the base steel sheet and the coating layer, A hot-formed member that satisfies the following relations 2-1 and 2-2. [Equation 2] [In the above-mentioned Relational Formulas 2-1 and 2-2, the Sb ｃｏａｔ is the average S The unit is weight percent. ｍａｘ is the Sb content in the Sb-enriched layer The unit is weight percent. The Δt is the maximum value of the difference between the plating layer and the Sb-enriched layer. From the boundary between ｍａｘ The unit is μm. ］

11. The hot-rolled steel sheet according to claim 10, wherein the base steel sheet contains ferrite in an area fraction of 5% or less. Shape member.

12. The hot-formed member according to claim 10, wherein the thickness of the Sb-enriched layer is 2 to 30 μm.

13. The hot-formed member according to claim 10, which satisfies the following relational expression 2-3. [Equation 3]

14. 11. The hot-formed part according to claim 10, wherein the amount of diffusible hydrogen is 0.2 ppm or less.

15. The base steel sheet includes an Mn segregation zone, In the Mn segregation zone, the average Sb content is 1.0 times the average Sb content in the base steel sheet. The hot-formed member according to claim 10, wherein the area of the portion where the deformation is 15 times or more is 60% or more.

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

17. The plated steel sheet for hot forming manufactured according to claim 5 is heated at a temperature range of Ac3 to 950°C for 1 to 120°C. A method for producing a hot-formed member, comprising heat treating for 1000 seconds and then hot press-forming.

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