HOT STAMPED BODY

Abstract

Provided is a hot-stamped article comprising a steel base material and an Al-Zn-Mg plating layer formed on the surface of the steel base material, wherein: the plating layer has a prescribed chemical composition; the plating layer comprises an interface layer that contains Fe and Al and is positioned at the interface with the steel base material, and a main layer that is positioned on the interface layer; the main layer includes a Mg-Zn-containing phase at an area ratio of 10.0-70.0%, and a Fe-Al-containing phase at an area ratio of 30.0-90.0%; the Mg-Zn-containing phase includes at least one phase selected from the group consisting of a MgZn phase, a Mg2Zn3 phase, and a MgZn2 phase; and the Fe-Al-containing phase includes a Fe-Al phase and a Fe-Al-Zn phase, with the area ratio of the Fe-Al-Zn phase within the main phase being more than 10.0% but not more than 75.0%.

Description

HOT STAMPED BODY Field of invention [1] The present invention relates to a hot-stamped body. ML / í ¿¿34 Background of the invention [2] Hot stamping (hot pressing) is a technique for forming a difficult-to-mold material, such as a high-strength steel sheet, by pressing. Hot stamping is a hot forming technique that shapes a material supplied for shaping after heating it. In this technique, the material is shaped after heating; therefore, at the time of shaping, the steel material is soft and has good formability. Thus, even a high-strength steel material can be precisely shaped into a complex form. Furthermore, the press die simultaneously performs forming and hardening, so the steel material is known to have sufficient strength after forming. [3] PTL 1 describes a hot-pressed plated steel sheet characterized by having an Al-Zn-based alloy plating layer containing Al: 20 to 95% by mass, Ca+Mg: 0.01 to 10% by mass, and Si on the surface of the steel sheet. Furthermore, PTL 1 describes that such a plated steel sheet can prevent the plating from adhering to the die during hot pressing, as Ca or Mg oxides form on the surface of the Al-Zn-based alloy plating layer. [4] With regard to an Al-Zn-based alloy plating, PTL 2 describes an alloy-plated steel material characterized by containing, by mass percent, Al: 2 to 75%, Fe: 2 to 75%, and a remainder of 2% or more of Zn and unavoidable impurities in the plating layer. Furthermore, PTL 2 states that, from the standpoint of improving corrosion resistance, it is effective to also include Mg: 0.02 to 10%, Ca: 0.01 to 2%, Si: 0.02 to 3%, etc., in the plating layer. [5] In addition, with regard to an Al-Zn-based alloy plating, PTL 3 describes a hot-pressed Zn-based plated steel material having in the outermost layer an oxide layer comprising mainly Zn and containing Mn at 1% or more by mass, having beneath it a plating layer comprising a Zn-based alloy, and containing in the Zn-based plating layer one or more of Ni: 0.01 to 20%, Cr: 0.01 to 10%, Mn: 0.01 to 10%, Mo: 0.01 to 5%, Co: 0.01 to 5%, Al: 0.01 to 60%, Si: 0.01 to 5%, Mg: 0.01 to 10%, Ca: 0.01 to 5% and Sn: 0.01 to 10%. [6] In addition, PTL 4 describes a plated steel material ML / í ¿¿34 comprising a steel material and a plating layer disposed on the surface of the steel material and containing a Zn-Al-Mg alloy layer, wherein the Zn-Al-Mg alloy layer has a Zn phase, the Zn phase contains an Mg-Sn intermetallic compound phase, and the plating layer contains, in % by mass, Zn: more than 65.0%, Al: more than 5.0% to less than 25%, Mg: more than 3.0% to less than 12.5%, Ca: 0% to 3.00%, Si: 0% to less than 2.5%, etc. [7] Similarly, PTL 5 describes a clad steel material comprising a steel material and a cladding layer disposed on a surface of the steel material and containing a Zn-Al-Mg alloy layer, wherein, in a cross section of the Zn-Al-Mg alloy layer, the area ratio of an MgZn2 phase is 45 to 75%, the area ratio of the total MgZn2 phase to the Al phase is 70% or more, the area ratio of a Zn-Al-MgZn2 ternary eutectic structure is 0 to 5%, and the cladding layer contains, in mass %, Zn: more than 44.90% to less than 79.90%, Al: more than 15% to less than 35%, Mg: more than 5% to less than 20%, Ca: 0.1% to less than 3.0%, Yes: 0% to 1.0%, etc. ML / í ¿¿34 List of appointments Patent literature [8] PTL 1: Publication of an unexamined Japanese patent No. 2012-112010 PTL 2: Publication of an unexamined Japanese patent No. 2009-120948 ML / t / ZUZZ / U í ¿¿34 PTL WO 2005-113233 PTL WO 2018 / 139619 PTL WO 2018 / 139620 Summary of the invention Technical problem [9] If, for example, a zinc-based steel material is hot-stamped, and the material is worked in a molten state, the molten zinc will sometimes penetrate the steel and cause internal cracking. This phenomenon is called liquid metal embrittlement (LME). LME is known to reduce the fatigue characteristics of steel.

[10] On the other hand, if a plated steel material containing Al is used as a component of the plating layer in hot stamping, it is known that, for example, hydrogen generated at the time of heating in hot stamping will sometimes penetrate the steel material and cause hydrogen embrittlement cracking.

[11] However, in conventional Al-Zn-based plated steel materials used in hot stamping, there has not necessarily been sufficient study from the point of view of suppressing hydrogen embrittlement cracking and LME. As a result, in a hot-stamped body obtained from such a plated steel material, there was still room for improvement with regard to LME resistance and hydrogen penetration resistance.

[12] Therefore, an object of the present invention is to provide a hot-stamped body improved in LME resistance and hydrogen penetration resistance and, furthermore, excellent in corrosion resistance. Solution to the problem

[13] The present invention, to achieve the above object, is as follows: (1) A hot-stamped body comprising a steel base material and a plating layer formed on a surface of the steel base material, wherein the plating layer has a chemical composition comprising, in % by mass, Al: 15.00 to 45.00%, Mg: 5.50 to 12.00%, Yes: 0.05 to 3.00%, MA / í ¿¿34 Ca: 0.05 to 3.00%, Fe: 20.00 to 50.00%, Sb: 0 to 0.50%, Pb: 0 to 0.50%, Cu: 0 to 1.00%, Sn: 0 to 1.00%, Ti: 0 to 1.00%, Mr: 0 to 0.50%, Cr: 0 to 1.00%, Ni: 0 to 1.00%, Mn: 0 to 1.00%, and the remainder: Zn and impurities, the plating layer comprises an interfacial layer placed at an interface with the steel base material and containing Fe and Al and a main layer placed over the interfacial layer, the main layer comprises, by area ratio, 10.0 to 70.0% of a phase containing Mg-Zn and 30.0 to 90.0% of a phase containing Fe-Al, the phase containing Mg-Zn comprises at least one selected from the group consisting of an MgZn phase, an Mg2Zn3 phase and an MgZn2 phase, and the phase containing Fe-Al comprises an FeAl phase and a Fe-Al-Zn phase and an area ratio of the Fe-Al-Zn phase in the main layer is more than 10.0 to 75.0%. (2) The hot-stamped body in accordance with (1) above, wherein the chemical composition of the plating layer comprises, in % by mass, At: 25.00 to 35.00% and Mg: 6.00 to 10.00%. (3) The hot-stamped body in accordance with (1) or (2) above, wherein the Mg-Zn containing phase comprises an MgZn phase, and an area ratio of the MgZn phase in the main layer is 5.0% or more. (4) The hot-stamped body in accordance with any of (1) to (3) above, wherein the Mg-Zn containing phase comprises an MgZn phase and an Mg2Zns phase, and an area ratio of a total MgZn phase and Mg2Zn3 phase in the main layer is 25.0 to 50.0%. (5) The hot-stamped body conforming to any of (1) to (4) above, wherein the area ratio of the FeAl phase in the main layer is from 5.0 to 25.0%. Advantageous effects of the invention

[14] In accordance with the present invention, it is possible to provide a hot-stamped body improved in LME resistance and hydrogen penetration resistance and, in addition, excellent in corrosion resistance. Brief description of the drawings

[15] Figure 1 shows a backscattered electron (BSE) scanning electron microscope (SEM) image of a cross-section of a plating layer on a conventional hot-stamped body that includes an Al-Zn-Mg based plating layer. Figure 2 shows a backscattered electron (BSE) image from a scanning electron microscope (SEM) of a cross-section of a plating layer on a hot-stamped body according to the present invention (Example 13). Figure 3 shows a backscattered electron (BSE) scan electron microscope (SEM) image of a plating layer surface prior to hot stamping on a hot stamped body according to the present invention. Figure 4 is a graph showing a relationship between a cooling rate change point when a plating layer is cooled and the formation of an acicular Al-Zn-Si-Ca phase. Description of the modalities

[16] Hot stamped body The hot-stamped body according to one embodiment of the present invention comprises a material ML / t / ZUZZ / U í ¿¿34 steel base and a plating layer formed on a surface of the steel base material, wherein the plating layer has a chemical composition comprising, in % by mass, Al: 15.00 to 45.00%, Mg: 5.50 to 12.00%, Si: 0.05 to 3.00%, Ca: 0.05 to 3.00%, Fe: 20.00 to 50.00%, Sb: 0 to 0.50%, Pb: 0 to 0.50%, Cu: 0 to 1.00%, Sn: 0 to 1.00%, Ti: 0 to 1.00%, Sr: 0 to 0.50%, Cr: 0 to 1.00%, Ni: 0 to 1.00%, Mn: 0 to 1.00%, and the remainder: Zn and impurities, the plating layer comprises an interfacial layer placed at an interface with the steel base material and containing Fe and Al and a main layer placed over the interfacial layer, the main layer comprising, by area ratio, 10.0 to 70.0% of a phase containing Mg-Zn and 30.0 to 90.0% of ML / t / ZUZZ / U í ¿¿34 a phase containing Fe-Al, the phase containing Mg-Zn comprises at least one selected from the group consisting of an MgZn phase, an MgzZns phase and an MgZn2 phase, and the phase containing Fe-Al comprises an FeAl phase and a Fe-Al-Zn phase and an area ratio of the Fe-Al-Zn phase in the main layer is more than 10.0 to 75.0%.

[17] For example, if a conventional Zn-based plated steel material or an Al-Zn-based plated steel material is used for hot stamping, the plated steel material will generally be heated in hot stamping to about 900°C or higher. Zn has a boiling point of approximately 907°C, which is relatively low; therefore, at such a high temperature, the Zn in the plating layer will evaporate or melt, resulting in the partial formation of a high-concentration liquid Zn phase in the plating layer. The penetration of the liquid Zn into the grain boundaries of the steel can, in some cases, cause liquid metal embrittlement (LME) cracking.

[18] On the other hand, in a conventional aluminum-clad steel material that does not contain zinc, LME cracking due to zinc will not occur. However, during heating in hot stamping, the water vapor in the atmosphere will sometimes be reduced by the aluminum in the plating layer, resulting in hydrogen generation. As a result, the generated hydrogen will sometimes penetrate the steel material and cause hydrogen embrittlement cracking. Furthermore, in an aluminum-zinc-based steel material, since zinc has a relatively low boiling point as explained above, during hot stamping at a temperature of 900°C or higher, some of the zinc will evaporate and sometimes react with water vapor in the atmosphere, causing hydrogen generation.In such a case, hydrogen embrittlement cracking is likely to occur because hydrogen penetrates the steel material due not only to the aluminum but also to the zinc. Furthermore, from the perspective of corrosion resistance enhancement, with respect to magnesium and other elements added to zinc-based or aluminum-zinc-based steel, some of these elements will evaporate during high-temperature hot stamping and, as with zinc, will produce hydrogen, triggering hydrogen embrittlement cracking.

[19] Furthermore, if the Zn and / or Mg elements that enhance corrosion resistance evaporate during high-temperature hot stamping and some of these elements are lost, the problem will naturally arise that it is not possible to maintain sufficient corrosion resistance in the body after hot stamping. Additionally, if the Zn and / or Mg in the plating layer evaporate and are lost, relatively large quantities of Al-Fe and / or Zn-Fe intermetallic compounds will form in the plating layer after hot stamping between the Fe that had diffused from the base iron and the Al and / or Zn in the plating layer. These intermetallic compounds become causes of red rust in corrosive environments.

[20] Therefore, the inventors studied the corrosion resistance, LME resistance, and hydrogen penetration resistance of hot-stamped bodies incorporating AlZn-Mg-based coating layers. As a result, the inventors discovered that in a hot-stamped body comprising an Al-Zn-Mg-based plating layer having a predetermined chemical composition and containing a predetermined amount of a Mg-Zn-containing phase in the plating layer after hot stamping, it is possible to significantly reduce or suppress LME and hydrogen penetration in the steel material due to the heating during hot stamping and achieve sufficient corrosion resistance. This will be explained more specifically below with reference to the drawings.

[21] Figure 1 shows a backscattered electron (BSE) scanning electron microscope (SEM) image of a cross-section of a plating layer on a conventional hot-stamped body containing an Al-Zn-Mg-based plating layer. Referring to Figure 1, it is understood that the plating layer 1 contains a thick oxide layer 2 containing Zn and Mg. The oxide layer 2 is believed to be the result of the evaporation of at least some of the Zn and Mg due to heating to approximately 900°C during hot stamping or a higher temperature, which is then deposited on the surface of the plating layer as oxides. A diffusion layer 3 is placed beneath the plating layer 1. The diffusion layer 3 is part of the steel base material 4.Diffusion layer 3 results from the Al component in the plating layer diffusing into the steel base material 4 and forming a solid solution due to heating in hot stamping.

[22] In a conventional hot-stamped body containing an Al-Zn-Mg plating layer, as shown in Figure 1, the Zn and Mg evaporate during heating in the hot stamping process, resulting in the penetration of LME and hydrogen into the steel material. Furthermore, the corrosion resistance of the hot-stamped body drops considerably due to the loss of at least some of the Zn and Mg through evaporation and the decrease in Zn and Mg in the metallic phase that accompanies oxide formation. Moreover, for example, LME cracking is likely to occur even when the Zn concentration in plating layer 1 increases relatively due to Mg evaporation.

[23] Figure 2 shows a backscattered electron (BSE) scanning electron microscope (SEM) image of a cross-section of a plating layer on a hot-stamped body according to the present invention (Example 13). Referring to Figure 2, the plating layer 1 comprises an interfacial layer 5 positioned at the interface with the steel base material 4, more specifically at the interface with the diffusion layer 3, which is part of the steel base material 4 and contains Fe and Al, and a main layer 6 positioned over the interfacial layer 5.Furthermore, it shall be understood that the principal layer 6, in contrast to the case in Figure 1, contains a phase containing Mg-Zn 7, which contains at least one selected from the group consisting of an MgZn phase, an Mg2Zna phase, and an MgZn2 phase, and a phase containing Fe-Al 8, composed of a Fe-Al-Zn 8a phase (relatively dark-colored phase islands) and a FeAl 8b phase (relatively light-colored phase islands). In particular, it shall be understood that the principal layer 6 shown in Figure 2 has a structure (island-in-the-sea structure) of a matrix phase containing Mg-Zn 7, in which FeAl-containing 8 phase islands (Fe-Al-Zn 8a phase islands and FeAl 8b phase islands) are present, specifically dispersed.In the hot-stamped body according to the present invention, by including a phase containing Mg-Zn 7 as shown in Figure 2 in the main layer 6 of the plating layer 1 in a relatively large amount, it is possible to significantly reduce or suppress the occurrence of LME and hydrogen penetration into the steel material and achieve sufficient corrosion resistance.

[24] Without intending to be limited by any specific theory, in the hot-stamped body according to the present invention, as explained in detail later in relation to the production method, at the beginning of heating in hot stamping, it is believed that the Ca leached from the acicular Al-Zn-Si-Ca phase present in the surface structure of the plating layer is preferably oxidized by atmospheric oxygen and forms a dense Ca-based oxide film on the outermost part of the plating layer.In other words, the acicular Al-Zn-Si-Ca phase present in the surface structure of the plating layer before hot stamping is believed to act as a source of Ca supply to form a Ca-based oxide film at the beginning of heating in hot stamping. The Ca-based oxide film obtained by oxidation of the supplied Ca, more specifically an oxide film containing Ca and Mg, acts as a barrier layer.

[25] Due to the function of this barrier layer, it is believed that the evaporation of Zn and Mg from the plating layer to the outside and the related appearance of LME and hydrogen penetration from the outside can be reduced or suppressed. Consequently, it is believed that in the final body obtained after hot stamping, unlike the case in Figure 1, the formation of a thick oxide layer of Zn and Mg in the plating layer can be prevented. They can be present as a phase containing Mg-Zn 7 in a relatively large amount, i.e., in an amount of 10.0 to 70.0% by area ratio in the main layer 6, and thus the drop in corrosion resistance due to the evaporation of Zn and Mg to the outside can be significantly suppressed.

[26] The hot-stamped body according to one embodiment of the present invention will now be explained in detail. In the following explanation, "containing the constituents" means % by mass unless otherwise stated. MA / í ¿¿34

[27] Steel base material The steel base material according to the embodiment of the present invention may be a material of any thickness and composition. It is not particularly limited, but, for example, it is preferably a material having a thickness and composition suitable for hot stamping. Such steel base material is known and may include, for example, a steel sheet having a thickness of 0.3 to 2.3 mm and comprising, by mass percent, C: 0.05 to 0.40%, Si: 0.50% or less, Mn: 0.50 to 2.50%, P: 0.03% or less, S: 0.010% or less, Al: 0.10% or less, N: 0.010% or less, and a remainder of Fe and impurities (for example, a cold-rolled steel sheet), etc. The constituents contained in the steel base material preferably used in the present invention will be explained in detail below.

[28] C: 0.05 to 0.40% Carbon (C) is an effective element for increasing the strength of a hot-stamped body. However, if the C content is too high, the hot-stamped body sometimes loses hardness. Therefore, the C content is 0.05 to 0.40%. The C content is preferably 0.10% or more, very preferably 0.13% or more. The C content is preferably 0.35% or less.

[29] If: 0 to 0.50% Silicon (Si) is an effective element for deoxidizing steel. However, if the Si content is too high, the Si in the steel diffuses during heating in hot stamping and forms oxides on the surface of the steel material. As a result, the efficiency of the phosphate treatment sometimes decreases. Furthermore, Si raises the AC3 point of steel. For this reason, since the heating temperature for hot stamping must be at or above the AC3 point, if the amount of Si becomes excessive, the heating temperature for hot stamping the steel will inevitably be higher. In other words, steel with a high Si content will be heated to a higher temperature during hot stamping, and as a result, the Zn, etc., in the plating layer will inevitably evaporate. To avoid this situation, the Si content should be 0.50% or less. The Si content should preferably be 0.50%.30% or less, very preferably 0.20% or less. The Si content can also be 0%, but to obtain the deoxidation effect, etc., the lower limit value for the Si content, although it changes depending on the desired level of deoxidation, is generally 0.05%.

[30] Mn: 0.50 to 2.50% Manganese (Mn) increases hardenability and strength of hot-stamped parts. However, even excessive Mn saturates the effect. Therefore, the Mn content is 0.50 to 2.50%. Preferably, the Mn content is 0.60% or more, and very preferably 0.70% or more. A lower Mn content is also preferable, and a lower Mn content is 2.40% or less, and very preferably 2.30% or less.

[31] P: 0.03% or less Phosphorus (P) is an impurity contained in steel. Phosphorus (P) segregates at the grain boundaries, causing a decrease in steel toughness and delayed fracture resistance. Therefore, the P content is 0.03% or less. The P content is preferably as small as possible, ideally 0.02% or less. However, excessively reducing the P content increases costs, so the P content is preferably 0.0001% or more. P inclusion is not mandatory, so the lower limit for P content is 0%.

[32] S: 0.010% or less Sulfur (S) is an impurity contained in steel. Sulfur (S) forms sulfides, which reduces the toughness of steel and decreases its delayed fracture resistance. Therefore, the S content is 0.010% or less. Ideally, the S content should be as low as possible, preferably 0.005% or less. However, excessively reducing the S content increases costs, so the S content is preferably 0.0001% or more. The inclusion of S is not mandatory, so the lower limit for S content is 0%. ML / í ¿¿34

[33] In the sun: 0 to 0.10% Aluminum (Al) is effective for deoxidizing steel. However, excessive Al inclusion raises the melting point (Acj) of the steel material, consequently increasing the heating temperature for hot stamping and causing the Zn, etc., in the plating layer to inevitably evaporate. Therefore, the Al content is 0.10% or less, preferably 0.05% or less. The Al content can also be 0%, but to achieve the desired deoxidation effect, etc., the Al content may be 0.01% or more. In this description, Al content refers to the content of so-called acid-soluble Al (Al sol.).

[34] N: 0.010% or less Nitrogen (N) is an unavoidable impurity in steel. N forms nitrides, which reduces the steel's toughness. If more boron (B) is present, N combines with B, reducing the amount of B in solid solution and decreasing hardenability. Therefore, the N content is 0.010% or less. Ideally, the N content should be as low as possible, preferably 0.005% or less. However, excessively reducing the N content increases costs, so 0.0001% or more is preferable. The inclusion of N is not essential, so the lower limit for N content is 0%.

[35] The basic chemical composition of the steel base material suitable for use in accordance with the present invention is as explained above. In addition, the above steel base material may optionally contain one or more of the following: B: 0 to 0.005%, Ti: 0 to 0.10%, Cr: 0 to 0.50%, Mo: 0 to 0.50%, Nb: 0 to 0.10%, and Ni: 0 to 1.00%. These elements will be explained in detail below. The inclusion of these elements is not mandatory; therefore, the lower limits for the content of these elements are 0%.

[36] B: 0 to 0.005% Boron (B) increases the hardenability of steel and its strength after hot stamping, so it can be included in the steel base material. However, even with excessive B inclusion, the effect is limited to saturation. Therefore, the B content is typically 0 to 0.005%. It can also be 0.0001% or higher.

[37] Ti: 0 to 0.10% Titanium (Ti) can combine with nitrogen (N) to form nitrides, preventing a decrease in hardenability due to nitrogen nitride (BN) formation. Furthermore, due to its fixative effect, Ti can refine the austenite grain size and increase the toughness of steel during hot stamping. However, even with excessive Ti, the effect is limited to saturation. Additionally, if excessive Ti nitride precipitates, the steel's toughness may decrease. Therefore, the Ti content is typically 0 to 0.10%. It can be 0.01% or higher.

[38] Cr: 0 to 0.50% Chromium (Cr) is effective in increasing the hardenability of steel and the strength of hot-stamped parts. However, if the Cr content is excessive and a large amount of chromium carbides form, which are difficult to melt during the hot-stamping heating process, the steel struggles to transform into austenite, and its hardenability decreases. Therefore, the Cr content is typically between 0 and 0.50%. It can also be 0.10% or higher.

[39] Mo: 0 to 0.50% Molybdenum (Mo) increases the hardenability of steel. However, even if Mo is included in excess, the effect is saturated. Therefore, the Mo content is 0 to 0.50%. The Mo content can also be 0.05% or more.

[40] Nb: 0 to 0.10% Niobium (Nb) is an element that forms carbides to refine the crystal grains during hot stamping and increase the toughness of steel. However, if Nb is included in excess, this effect becomes saturated and hardenability decreases even further. Therefore, the Nb content is typically 0 to 0.10%. It can also be 0.02% or higher.

[41] Ni: 0 to 1.00% Nickel (Ni) is an element capable of suppressing the embrittlement caused by molten zinc during heating in hot stamping. However, even with excessive Ni, the effect becomes saturated. Therefore, the Ni content is typically 0 to 1.00%. It can also be 0.10% or higher.

[42] In the steel base material according to the embodiment of the present invention, the remainder, apart from the constituents mentioned above, is composed of Fe and impurities. The impurities in the steel base material mean components that enter due to various factors in the production process, primarily raw materials such as ore and scrap, when the hot-stamped body is industrially produced according to the embodiment of the present invention, and are not intentionally added to the hot-stamped body. MA / í ¿¿34

[43] Veneer layer According to the embodiment of the present invention, a plating layer is formed on the surface of the aforementioned steel base material. For example, if the steel base material is a steel sheet, the plating layer is formed on at least one surface of the steel sheet, i.e., one or both surfaces of the steel sheet. The plating layer comprises an interfacial layer positioned at the interface with the steel base material and containing Fe and Al, and a main layer positioned over the interfacial layer. The plating layer has the following average composition.

[44] Al: 15.00 to 45.00% Aluminum (Al) is essential for suppressing the evaporation of zinc (Zn) and magnesium (Mg) during heating in hot stamping. As explained earlier, it is believed that, due to the presence of the Al-Zn-Si-Ca acicular phase in the surface structure of the plating layer before hot stamping, the calcium leached from this phase at the beginning of heating is preferentially oxidized by atmospheric oxygen. This forms a dense calcium-based oxide film, specifically a calcium- and magnesium-containing oxide film, on the outermost surface of the plating layer. This calcium-based oxide film is believed to act as a barrier layer to suppress the evaporation of zinc and magnesium. To achieve this barrier layer function, the aluminum content in the plating layer after hot stamping should be 15.00% or more, preferably 20.00% or more. 25.00% or more. On the other hand, if the Al content is greater than 45.00%, CaAl and other intermetallic compounds preferentially form in the plating layer before hot stamping, and the formation of a sufficient quantity of the acicular Al-Zn-Si-Ca phase becomes difficult. Therefore, the Al content is 45.00% or less, preferably 40.00% or less, or 35.00% or less.

[45] Mg: 5.50 to 12.00% Magnesium (Mg) is an effective element for improving the corrosion resistance of the plating layer and reducing blistering in the coating. Furthermore, Mg forms Zn-Mg compounds in the liquid phase, suppressing liquid metal oxidation (LME) cracking during hot stamping. A low Mg content increases the likelihood of LME. For enhanced corrosion resistance and LME suppression, the Mg content should be 5.50% or higher, preferably 6.00% or higher. Conversely, excessively high Mg content can lead to excessive sacrificial corrosion, causing blistering in the coating and a rapid increase in flux oxidation. Therefore, the Mg content should be 12.00% or lower, preferably 10.00% or lower.

[46] Yes: 0.05 to 3.00% Silicon (Si) is essential for suppressing the evaporation of zinc (Zn) and magnesium (Mg) during heating in hot stamping. As explained earlier, the presence of the acicular Al-Zn-Si-Ca phase in the surface structure of the plating layer before hot stamping allows for the formation of a barrier layer composed of a calcium-based oxide film. This barrier layer suppresses the evaporation of Zn and Mg during heating in hot stamping. To ensure the barrier layer's effectiveness, the Si content in the plating layer after hot stamping should be 0.05% or higher, preferably 0.10% or higher, and ideally 0.40% or higher. Conversely, if the Si content is excessive, a Mg₂Si phase forms at the interface between the steel base material and the plating layer before hot stamping, significantly reducing corrosion resistance.Furthermore, if the Si content is excessive, the Mg₂Si phase preferentially forms in the plating layer before hot stamping, making it difficult to achieve a sufficient Al-Zn-Si-Ca acicular phase. Therefore, the Si content is 3.00% or less, preferably 1.60% or less, and most preferably 1.00% or less.

[47] Ca: 0.05 to 3.00% Calcium (Ca) is essential for suppressing the evaporation of zinc (Zn) and magnesium (Mg) during heating in hot stamping. As explained earlier, the presence of the acicular Al-Zn-Si-Ca phase in the surface structure of the plating layer before hot stamping allows for the formation of a barrier layer composed of a calcium-based oxide film. This barrier layer suppresses the evaporation of Zn and Mg during heating in hot stamping. To ensure the barrier layer's effectiveness, the Ca content in the plating layer after hot stamping should be 0.05% or higher, preferably 0.40% or higher. However, if the Ca content is excessive, AliCa and other intermetallic compounds will preferentially form in the plating layer before hot stamping, making it difficult to achieve a sufficient Al-Zn-Si-Ca acicular phase. Therefore, the recommended Ca content is 3%.00% or less, preferably 2.00% or less, very preferably 1.50% or less.

[48] ​​Fe: 20.00 to 50.00% If the plated steel material is heated during hot stamping, the iron (Fe) from the base steel material diffuses into the plating layer, so the plating layer inevitably contains Fe. The Fe combines with the aluminum (Al) in the plating layer to form an interfacial layer at the interface with the base steel material. This interfacial layer is primarily composed of an intermetallic compound containing Fe and Al, and it also forms an Fe-Al phase in the main layer above the interfacial layer. Therefore, the Fe content increases with the thickness of the interfacial layer and the amount of Fe-Al phase in the main layer. If the Fe content is low, the amount of Fe-Al phase decreases, and the main layer structure collapses easily.More specifically, if the Fe content is low, the Zn and Mg contents increase relatively. Therefore, during heating in hot stamping, these elements evaporate easily, resulting in readily hydrogen penetration. Therefore, the Fe content should be 20.00% or higher, preferably 25.00% or higher. Conversely, if the Fe content is too high, the amount of Fe-Al containing phase in the main layer increases, while the amount of Mg-Zn containing phase in the main layer decreases, thus reducing corrosion resistance. Therefore, the Fe content should be 50.00% or lower, preferably 45.00% or lower, and ideally 40.00% or lower.

[49] The chemical composition of the plating layer is as explained above. In addition, the plating layer may optionally contain one or more of the following: Sb: 0 to 0.50%, Pb: 0 to 0.50%, Cu: 0 to 1.00%, Sn: 0 to 1.00%, Ti: 0 to 1.00%, Sr: 0 to 0.50%, Cr: 0 to 1.00%, Ni: 0 to 1.00%, and Mn: 0 to 1.00%. Although not strictly limited to this, from the standpoint of ensuring that the actions and functions of the aforementioned basic constituents forming the plating layer are sufficiently manifested, the total content of these elements is preferably 5.00% or less, and very preferably 2.00% or less. These elements will be explained in detail below.

[50] Sb: 0 to 0.50%, Pb: 0 to 0.50%, Cu: 0 to 1.00%, Sn: 0 to 1.00% and Ti: 0 to 1.00% Sb, Pb, Cu, Sn, and Ti may be present in the MgZn2 phase of the main layer, but if they are within predetermined ranges, they do not negatively affect the performance of the hot-stamped body. However, if the content of these elements is excessive, during heating in the hot-stamping process, oxides of these elements may precipitate, leading to deterioration of the surface properties of the hot-stamped body. This results in poor phosphate treatment and impaired corrosion resistance after coating. Furthermore, if the Pb and Sn content becomes excessive, LME resistance will tend to decrease. Therefore, Sb and Pb contents should be 0.50% or less, preferably 0.20% or less, while Cu, Sn, and Ti contents should be 1.00% or less, preferably 0.80% or less, preferably 0.50% or less. Alternatively, the content of these elements may also be 0.01% or more. These elements are not essential. The lower limit for the content of these elements is 0%.

[51] Mr: 0 to 0.50% Sr can be added to the plating bath during the plating process to suppress the formation of the top slag. Additionally, Sr suppresses oxidation by air during heating in hot stamping, thus preventing discoloration of the body after hot stamping. These effects are noticeable even in small amounts, so the Sr content can be 0.01% or higher. However, if the Sr content is excessive, blistering of the coating and flux oxidation increase, and corrosion resistance deteriorates. Therefore, the Sr content is 0.50% or less, preferably 0.30% or less, and most preferably 0.10% or less.

[52] Cr: 0 to 1.00%, Ni: 0 to 1.00% and Mn: 0 to 1.00% Cr, Ni, and Mn concentrate near the interface between the plating layer and the steel base material and have the effect of removing flecks from the surface of the plating layer, etc. To achieve this effect, the Cr, Ni, and Mn contents are preferably respectively 0.01% or more. Alternatively, these elements may be included in the interfacial layer or in the Fe-Al-containing phase present in the main layer. However, if the content of these elements is excessive, blistering of the coating and flux oxidation increase, and corrosion resistance tends to deteriorate. Therefore, the contents of Cr, Ni, and Mn are 1.00% or less, preferably 0.50% or less, and very preferably 0.10% or less.

[53] The remainder: Zn and impurities The remainder of the plating layer, apart from the constituents mentioned above, consists of zinc and impurities. Zinc is an essential component of the plating layer from a corrosion prevention standpoint. It is present primarily as a magnesium-zinc phase in the main plating layer and significantly contributes to improved corrosion resistance. If the zinc content is below 3.00%, sufficient corrosion resistance may not be maintained. Therefore, a zinc content of 3.00% or higher is preferable. The lower limit for zinc content can be 10.00%, 15.00%, or 20.00%. Conversely, if the zinc content is too high, it evaporates easily during the hot stamping process, resulting in readily penetrating LME and hydrogen. Therefore, a zinc content of 50.00% or less is preferable.The upper limit of the Zn content can be 45.00%, 40.00%, or 35.00%. Furthermore, Zn can be substituted with Al, so a small amount of Zn can form a solid solution with Fe in the Fe-Al phase. Additionally, impurities in the plating layer are components introduced due to various factors in the production process, primarily the raw materials, during the production of the plating layer, and are not intentionally added to it. In the plating layer, impurities may contain elements other than those described above in minimal quantities, to a degree that does not detract from the effect of the present invention.

[54] The chemical composition of the plating layer is determined by dissolving the plating layer in an acidic solution to which an inhibitor is added to inhibit corrosion of the steel base material and measuring the resulting solution using ICP (inductively coupled plasma high-frequency) emission spectrometry. In this case, the measured chemical composition is the average composition of the total main layer and the interfacial layer.

[55] The thickness of the plating layer can be, for example, from 3 to 50 pm. Furthermore, if the base steel material is a steel sheet, the plating layer can be provided on both surfaces of the steel sheet or it can be provided MA / only on one surface. The amount of plating layer deposited is not particularly limited, but for example, it can be from 10 to 170 g / m² per surface. The lower limit can be 20 or 30 g / m² and the upper limit can be 150 or 130 g / m². In the present invention, the amount of plating layer deposited is determined from the change in weight before and after acid washing by dissolving the plating layer in an acidic solution to which an inhibitor has been added to inhibit corrosion of the base iron.

[56] Interfacial layer The interfacial layer is a layer containing Fe and Al, more specifically a layer in which, at the time of heating in hot stamping, the Fe from the steel base material diffuses into the plating layer and bonds with the Al in the plating layer and is composed mainly of an intermetallic compound containing Fe and Al (hereafter also referred to simply as an intermetallic compound containing Fe-Al).

[57] An Fe-Al intermetallic compound is an intermetallic compound with a predetermined mass or atomic ratio and generally has a stoichiometric composition (mass %) of Fe: approximately 67% and Al: approximately 33%. According to examination under a transmission electron microscope (TEM), a FeAla phase with a high concentration of Al sometimes forms as non-layering microprecipitates on the surface of the interfacial layer, and a FesAl phase, etc., with a high concentration of Fe, forms as non-layering microprecipitates near the steel base material. If scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDX), etc., is used to quantitatively analyze the interfacial layer at approximately 5000X magnification, the Al content fluctuates in the range of 30.0 to 36.0%. In addition, the interfacial layer sometimes contains small amounts of Zn, Mn, Si, Ni, etc.According to the chemical compositions of the base steel material and the plating layer. Therefore, the interfacial layer generally contains Al: 30.0 to 36.0% and has a remainder of Fe and less than 3.0% of other constituents (e.g., Zn, Mn, Si and Ni).

[58] The interfacial layer also forms a barrier layer from the steel base material and has some corrosion resistance. Therefore, the interfacial layer prevents leaching of the steel base material during corrosion beneath the coating and can suppress the formation of flux rust generated by a cut (specifically, red rust forming streak patterns dripping from the cut). To achieve this effect, the thickness of the interfacial layer is preferably 0.1 pm or more, and very preferably 0.5 pm or more. However, if the interfacial layer is too thick, the fatigue characteristics after hot stamping are sometimes reduced because the Fe-Al-containing intermetallic compound is brittle. For this reason, the thickness of the interfacial layer is preferably 10.0 pm or less, very preferably 7.0 pm or less, and most preferably 5.0 pm or less.

[59] Main layer The main layer comprises an area ratio of 10.0 to 70.0% of a Mg-Zn phase and 30.0 to 90.0% of an Fe-Al phase. This layer inhibits scale formation during hot stamping and contributes to the corrosion resistance of the hot-stamped body. The main layer has a mixed structure of an Mg-Zn phase and an Fe-Al phase, and, as shown in Figure 2, exhibits an island-in-the-sea structure of a matrix phase containing Mg-Zn, within which islands of Fe-Al are present, particularly dispersed. Referring to Figure 2, the islands of the phase containing Fe-Al 8 include not only the islands of the Fe-Al-Zn 8a phase and the islands of the FeAl 8b phase present individually respectively, but also groups of islands of the phase of Fe-Al-Zn 8a adjacent to each other.

[60] Phase containing Mg-Zn In one embodiment according to the present invention, by configuring the plating layer after hot stamping such that Zn and Mg, which have a corrosion-resistant effect, are present as an Mg-Zn-containing phase in the main layer with an area ratio of 10.0 to 70.0%, the occurrence of low-molecular-weight corrosion (LMWC) and hydrogen penetration into the steel material due to heating during hot stamping can be significantly reduced or suppressed, and sufficient corrosion resistance can be achieved even in the body after hot stamping. If the area ratio of the Mg-Zn-containing phase is less than 10.0%, this effect cannot be sufficiently achieved. Therefore, the area ratio of the Mg-Zn-containing phase is 10.0% or more, preferably 15.0% or more, and most preferably 25.0% or more. Alternatively, the area ratio of the Mg-Zn-containing phase can be 70.0%.0% or less, for example, could be 60.0% or less or 50.0% or less.

[61] The Mg-Zn containing phase includes at least one phase selected from the group consisting of an MgZn phase, an Mg2Zn3 phase, and an MgZn2 phase. Here, the MgZn phase, the Mg2Zn3 phase, and the MgZnz phase are intermetallic compounds; therefore, while the atomic ratios of Mg and Zn in the phases can be considered substantially constant, they actually fluctuate a little since sometimes Al, Fe, etc., partially dissolve. Therefore, in the present invention, in phases having a chemical composition in which the total content of Mg and Zn is 90.0% or more, a phase in which the atomic ratio of Mg / Zn is from 0.90 to 1.10 is defined as an MgZn phase, a phase in which an atomic ratio of Mg / Zn is from 0.58 to 0.74 is defined as an MgsZna phase, and a phase in which an atomic ratio of Mg / Zn is from 0.43 to 0.57 is defined as an MgZn2 phase.By incorporating a Mg-Zn-containing phase that includes these phases, the corrosion resistance of the hot-stamped body can be significantly improved. In particular, when the Mg-Zn-containing phase includes an MgZn phase and / or an Mg₂Zn₃ phase, it is possible to suppress the LME (Liquid Metal Effect) during hot stamping. To reliably achieve this effect, the Mg-Zn-containing phase preferably includes an MgZn phase with a high Mg content. The area ratio of the MgZn phase in the main layer is preferably 5.0% or more, and 10.0% or more is even more preferable. Furthermore, the Mg-Zn-containing phase preferably includes an MgZn phase and an Mg₂Zn₃ phase. The area ratio of the total MgZn phase to the Mg₂Zn₃ phase in the main layer is preferably 10.0% or more, or 25.0% or more. On the other hand, it can be 60.0% or less or 50.0% or less.By controlling the Mg-Zn containing phase within this range, it is possible to significantly reduce or suppress the occurrence of LME and hydrogen penetration into the steel material due to heating at the time of hot stamping and possibly even in the body after hot stamping, to achieve sufficient corrosion resistance. ML / t / ZUZZ / U í ¿¿34

[62] Phase containing Fe-Al As explained previously, the main layer comprises an area ratio of 30.0 to 90.0% of an Fe-Al phase. If the area ratio of the Fe-Al phase exceeds 90.0%, the amount of Mg-Zn phase in the main layer decreases, and corrosion resistance is reduced. Furthermore, the area ratio of the Fe-Al phase can be 30.0% or higher, for example, 40.0% or more. The Fe-Al phase acts as a barrier to the progression of corrosion in the Mg-Zn phase; therefore, establishing the presence of the Fe-Al phase can improve corrosion resistance.To explain this in more detail, the Fe-Al-containing phase (Fe-Al-Zn and FeAl phases) is present in the main layer not as a lamellar structure, but as an island structure. Therefore, if corrosion progresses in the Mg-Zn-containing phase, which enhances corrosion resistance, the corrosion will proceed in a localized state, bypassing these Fe-Al-containing phase islands. As a result, it is believed that it is possible to delay the progression of corrosion in the Mg-Zn-containing phase.

[63] The Fe-Al-containing phase includes the Fe-AlZn phase and the FeAl phase. The area ratio of the Fe-AlZn phase in the main layer is greater than 10.0 to 75.0%. In the present invention, the Fe-Al-containing phase means a phase having a chemical composition in which the total Fe, Al, and Zn is 90.0% or more. In the Fe-Al-containing phase having such a chemical composition, a phase where the Zn content is 1.0% or more is defined as an Fe-Al-Zn phase, and a phase where the Zn content is less than 1.0% is defined as an FeAl phase.While not intended to be limited to any specific theory, it is believed that the Fe-Al-Zn phase and the FeAl phase do not grow at the interface of the plating layer and the steel base material from the steel base material to the interior of the plating layer in a layer-like fashion, but rather form spherical cores in the molten plating layer at the time of heating in hot stamping and then grow into island shapes.

[64] As explained in detail below, by properly controlling the production conditions of the plated steel material before hot stamping, it is possible to establish the presence of the acicular Al-Zn-Si-Ca phase dispersed in the surface structure of the plating layer. As a result, it is possible to suppress the evaporation of Zn and Mg during heating in hot stamping. By suppressing the evaporation of Zn and Mg, it is believed that nuclei form within the main layer in the molten state, and the Fe-Al-containing phase grows in an island-like manner. In one embodiment according to the present invention, the area ratio of the Fe-Al-Zn phase in the main layer can be, for example, 20.0% or more or 30.0% or more, and can be 70.0% or less, 65.0% or less, or 60.0% or less. Furthermore, in an embodiment according to the present invention, the area ratio of the FeAl phase in the main layer can be, for example, 3.0% or more or 5.0% or more and can be 25.0% or less, 20.0% or less, or 17.0% or less. As explained earlier, the Fe-Al-containing phase, particularly the Fe-Al-Zn and FeAl phases, has an island shape. While not strictly limited, the aspect ratio is almost never greater than 5.0. In general, the Fe-Al-containing phase has island shapes with an aspect ratio of 5.0 or less, for example, 4.0 or less or 3.0 or less. The lower limit of the aspect ratio is not specifically prescribed but can be, for example, 1.0 or more, 1.2 or more, or 1.5 or more. In the present invention, the aspect ratio means the ratio of the longest axis of the Fe-Al containing phase (Fe-Al-Zn phase and FeAl phase) (long axis) and the longest axis in the axes of the Fe-Al containing phase perpendicular to it (short axis). ML / í ¿¿34

[65] Other intermetallic compounds The main layer may contain other intermetallic compounds besides those contained in the Mg-Zn and Fe-Al phases. These other intermetallic compounds are not particularly restricted, but, for example, they may include Si and Ca or other elements contained in the plating layer, specifically Mg₂Si, Al₁₄Ca, etc. However, if the area ratio of the other intermetallic compounds in the main layer becomes too large, it is sometimes not possible to adequately ensure the presence of the Mg-Zn and / or Fe-Al phases. Therefore, the area ratio of the other intermetallic compounds, for example, the Mg₂Si to Al₁₄Ca ratio, is preferably 10.0% or less. 5.0% or less is even more preferable.

[66] Oxide layer The surface of the form with an oxide layer, due to the oxidation of the coating components, is prone to causing a drop in the coating capacity of the plating layer. This is sometimes due to the oxidation of the components. Such an oxide layer is prone to chemical convertibility and electroplating after hot stamping. Therefore, the thickness of the oxide layer is preferably small. For example, it is preferably 1.0 pm or less. If the Zn and Mg evaporate during hot stamping, a thick Mg-Zn oxide layer of more than 1.0 pm is formed.

[67] Diffusion layer In one embodiment according to the present invention, as shown in Figure 2, a diffusion layer 3 is sometimes formed beneath the plating layer 1. The diffusion layer is part of the steel base material. More specifically, due to heating during hot stamping, the Al component in the plating layer diffuses into the steel base material and forms a solid solution. If a diffusion layer is present, its thickness is generally 0.1 µm or more, for example, 0.5 µm or more, or 1.0 µm or more. However, if the diffusion layer becomes too thick, the Al component in the plating layer, particularly the main layer, becomes too small, which is undesirable. Therefore, the thickness of the diffusion layer is generally 15.0 µm or less, preferably 10.0 µm or less, and most preferably 5.0 µm or less.

[68] The thicknesses of the main layer, interfacial layer, diffusion layer, and oxide layer are determined by cutting a test piece from the hot-stamped body, embedding it in resin, etc., then polishing the cross-section and measuring the image observed by a SEM. Furthermore, if examined in a backscattered electron image from the SEM, the contrast at the time of observation will differ depending on the metallic components, making it possible to identify the layers and confirm their thicknesses. If the interface between the interfacial and main layers is difficult to discern and the thickness of the interfacial layer cannot be specifically determined, it is also possible to perform line analysis and identify the position where the Al content becomes 30.0 to 36.0% as the interface between the interfacial and main layers.The thicknesses of the main layer, interfacial layer, diffusion layer, and oxide layer are determined by making similar observations in three or more different fields and finding the averages of these.

[69] In the present invention, the area ratios of the main layer phases are determined as follows. First, a prepared sample is cut to a size of 25 mm x 15 mm, and any cross-section of the plating layer is photographed at 1500X magnification using a scanning electron microscope (SEM). From the BSE image thereof and a SEM-EDS map image, the area ratios of the phases in the main layer were measured by computer image processing. The averages of the measurement values ​​in any five fields (however, the areas measured in the fields are 400 pm² or more) were determined as the area ratios of the MgZn phase, Mg₂Zn₃ phase, MgZn₂ phase, FeAl phase, Fe-Al-Zn phase, and other intermetallic compounds.Furthermore, the area ratio of the Mg-Zn-containing phase was determined as the area ratio of the total MgZn phase, the Mg2Zn3 phase, and the MgZn2 phase. Similarly, the area ratio of the Fe-Al-containing phase was determined as the area ratio of the total FeAl phase and the Fe-Al-Zn phase. ML / í ¿¿34

[70] Method for producing hot stamped body A preferred method for producing the hot-stamped body according to the embodiment of the present invention will now be explained. The following explanation is intended to illustrate a characteristic method for producing a hot-stamped body according to the embodiment of the present invention and is not intended to limit the hot-stamped body to one produced by a production method as described below.

[71] The above production method comprises forming the steel base material, forming a plating layer onto the steel base material, and hot stamping (hot pressing) the steel base material onto which the plating layer is formed. Each step will be explained in detail below.

[72] Steel base material forming step In the process of forming the steel base material, for example, molten steel is first produced, which has the same chemical composition as that described for the steel base material. The molten steel is then used to produce a plate using a casting method. Alternatively, the molten steel can be used to produce an ingot using an ingot-making method. The plate or ingot is then hot-rolled to produce the steel base material (hot-rolled steel sheet). Depending on the requirements, the hot-rolled steel sheet can be pickled, and then it can be cold-rolled. The resulting cold-rolled steel sheet can then be used as steel base material.

[73] Veneer layer formation step Next, in the step of forming the plating layer, a plating layer having the chemical composition explained above is formed on at least one surface of the base steel material, preferably on both surfaces.

[74] More specifically, first, the material of The steel base material is reduced by heating it in a mixed N2-H2 gas atmosphere to a predetermined temperature and time, for example, 750 to 850°C, then cooled in a nitrogen or other inert atmosphere to near the plating bath temperature. The steel base material is then immersed in a plating bath of a predetermined chemical composition for 0.1 to 60 seconds, then lifted, and the amount of plating layer deposition is adjusted within a predetermined range by immediately injecting N2 gas or air using the gas flushing method.

[75] Furthermore, the amount of plating layer deposition is preferably 10 to 170 g / m² per surface. In this step, as an aid to plating deposition, it is also possible to apply a Ni pre-plating, a Sn pre-plating, or another pre-plating. However, these pre-platings cause changes in the alloying reactions, so the amount of plating deposition is preferably 2.0 g / m² per surface or less.

[76] Finally, the steel base material onto which the plating layer is deposited is cooled, so that the plating layer forms on one or both surfaces of the steel base material. In the present method, it is important to form the acicular Al-Zn phase during this cooling process. The Si-Ca intermetallic compound, composed mainly of Al, Zn, Si, and Ca, is present in the surface structure of the plating layer. Figure 3 shows a backscattered electron (BSE) image from a scanning electron microscope (SEM) of the plating layer surface before hot stamping of the hot-stamped body according to the present invention. Referring to Figure 3, it is understood that, in the surface structure of the plating layer, in addition to phase 11 (dendritic structure in Figure 3) and the eutectic α / τ phase 12, the acicular Al-Zn-Si-Ca phase 13 is present in a relatively large amount. The α phase is a structure composed mainly of Al and Zn, while the τ phase is a structure composed mainly of Mg, Zn, and Al.

[77] Without intending to be linked to any specific theory, it is believed that the acicular phase 13 of Al-Zn-Si-Ca shown in Figure 3 functions as a source of Ca to form a Ca-based oxide film at the beginning of heating in hot stamping. More specifically, it is believed that due to the presence of the Al-Zn-Si-Ca acicular phase 13 in the surface structure of the plating layer before hot stamping, the Ca that leaches from the Al-Zn-Si-Ca acicular phase 13 at the beginning of heating in hot stamping is preferentially oxidized by atmospheric oxygen and forms a dense Ca-based oxide film, more specifically an oxide film containing Ca and Mg, on the surface of the plating layer. This Ca-based oxide film is believed to function as a barrier layer to suppress the evaporation of Zn and Mg.In particular, the presence of the acicular Al-Zn-Si-Ca 13 phase in a predetermined quantity, specifically an area ratio of 2.0% or more, in the surface structure of the plating layer effectively acts as a barrier layer. Therefore, it is possible to reduce or eliminate the evaporation of Zn and Mg from the plating layer to the outside and the penetration of hydrogen from the outside during hot stamping. Furthermore, it is possible to significantly reduce the decrease in corrosion resistance due to the evaporation of Zn and Mg to the outside.

[78] In the present method, proper control of the cooling conditions during the solidification of the liquid plating layer, more specifically the two-stage cooling of the steel base material onto which the plating layer is deposited, is extremely important for the acicular Al-Zn-Si-Ca phase that will form in a predetermined amount in the surface structure of the plating layer. To explain further, the specific cooling rate can vary depending on the chemical composition, etc., of the plating layer. MA / t / ZUZZ / U í ¿¿34 plating, but to make the acicular Al-Zn-Si-Ca phase reliably form in a predetermined amount, it is effective to first cool the steel base material on which the plating layer is deposited at an average cooling rate of 14°C / s plus, preferably 15°C / s plus, from the bath temperature (generally 500 to 700°C) to 450°C, then cooling it at an average cooling rate of 5.5°C / s minus, preferably 5°C / s minus, from 450°C to 350°C.Under such cooling conditions—that is, through two-stage cooling of rapid and slow cooling—a supersaturated state is created during the first rapid cooling stage, producing a state in which Al-Zn-Si-Ca acicular phase nuclei can readily form, resulting in a large number of nuclei. During the subsequent slow cooling stage, the nuclei grow slowly, leading to the formation of an area ratio of 2.0% or more of the Al-Zn-Si-Ca acicular phase in the surface structure of the plating layer, particularly in a dispersed form. As a result, even with a heating temperature of 900°C or higher during hot stamping, it is possible to suppress the evaporation of Zn and Mg and significantly reduce or eliminate LME (Liquid Molecules) and hydrogen penetration into the steel material, achieving sufficient corrosion resistance even after hot stamping.On the other hand, if the two-stage cooling process is not performed beforehand, the acicular Al-Zn-Si-Ca phase cannot form in the surface structure of the plating layer, or cannot form in sufficient quantity. Therefore, during heating in hot stamping, a large portion of the Zn and Mg in the plating layer evaporates. Some of the evaporated Zn and Mg are deposited as oxides onto the steel base material. Generally, a thick oxide layer containing Mg-Zn of more than 1.0 pm forms, for example, 2.0 pm or more, or 3.0 pm or more. As a result, the LME resistance, hydrogen penetration resistance, and corrosion resistance of the resulting hot-stamped body are significantly reduced.

[79] If the cooling rate change point between rapid and slow cooling exceeds approximately 450°C, the Al-Zn-Si-Ca acicular phase nuclei sometimes fail to form sufficiently. Conversely, if the cooling rate change point falls below approximately 450°C, the formed nuclei sometimes fail to grow sufficiently. In either case, it becomes difficult to achieve a predetermined Al-Zn-Si-Ca acicular phase, specifically an area ratio of 2.0% or more in the surface structure of the plating layer. Therefore, the cooling rate change point, as explained above, should be selected within a range of 425 to 475°C. For the formation of the Al-Zn-Si-Ca acicular phase, 450°C is preferable.

[80] Hot stamping step (hot pressing) Finally, in the hot stamping (hot pressing) step, the steel base material with the plating layer is hot-pressed. This step is performed by loading the steel base material with the plating layer into a heating furnace, holding it for a predetermined holding time after reaching 900°C, and then hot-pressing it. The holding time refers to the time the temperature is maintained from 900°C or higher to less than 1000°C after reaching 900°C. The specific holding time may vary depending on the holding temperature and the chemical composition of the plating layer, etc., but it is generally 30 seconds or more and 4 minutes or less.To reliably obtain the hot-stamped body in accordance with the embodiment of the present invention having the plating layer provided with the main layer including the Mg-Zn containing phase and the Fe-Al containing phase explained above, the time is 1 minute or more and 3.5 minutes or less. Examples

[81] The following examples will be used to explain the present invention in more detail, but the present invention is in no way limited to these examples. MA / í ¿¿34

[82] Example A In the present example, several hot-stamped bodies were produced in accordance with embodiments of the present invention under various conditions and their characteristics were investigated.

[83] First, molten steel comprising, by mass, a C content of 0.20%, a Si content of 0.20%, a Mn content of 1.30%, a P content of 0.01%, a S content of 0.005%, an Al content of 0.02%, a N content of 0.002%, a B content of 0.002%, a Ti content of 0.02%, a Cr content of 0.20%, and the remainder being Fe and impurities, was used to produce a plate by continuous casting. The plate was then hot-rolled to produce a hot-rolled steel sheet, the hot-rolled steel sheet was pickled, and then the sheet was cold-rolled to produce a cold-rolled steel sheet (steel base material) with a sheet thickness of 1.4 mm.

[84] The produced steel base material was then cut to 100 mm x 200 mm, and subsequently coated using a discontinuous hot-dip coating apparatus manufactured by Rhesca. More specifically, the produced steel base material was first reduced by heating it in a furnace with an oxygen concentration of 20 ppm or less in a mixed gas atmosphere of N2-5% H2 at 800°C, then cooled in N2 to the plating bath temperature of +20°C. The steel base material was then immersed in a plating bath with a predetermined chemical composition for approximately 3 seconds, then raised at a lifting rate of 20 to 200 mm / s and adjusted by sweeping with N2 gas to a plating layer deposition amount of the value shown in Table 1.The base steel material onto which the plating layer was deposited was then cooled in two stages under the conditions shown in Table 1, resulting in a plated steel material with a plating layer formed on both surfaces. The temperature of the sheet was measured using a thermocouple spot-welded to the center of the base steel material.

[85] The resulting plated steel material was then hot-stamped. Specifically, hot stamping was performed by loading the plated steel material into a heating furnace, heating it to 900°C and holding it there for a predetermined time, and then hot-pressing it using a die equipped with a water-cooling jacket. As heat treatment conditions at the time of hot stamping (HS), any of the following conditions X and Y were selected. The tempering was controlled by the die to provide a cooling rate of 50°C / s or more until approximately the point of onset of martensite transformation (410°C). X: Hold at 900°C for 1 minute And: Hold at 900°C for 4 minutes ΜΛ / t / ZUZZ / U í ¿¿34 ^Tq^i

[98] Production Method Heat Treatment HS XXXXXXXXXXXXXXX Average Cooling Rate at 450 to 350°C “Tn ω os os 50 os os o in os os os os os os OS os o LíS 150 os Average Cooling Rate at Bath Temperature to 450°C 'Tn o in 15.0 150 15.0 0 SI 15.0 15.0 o in 15.0 o iri o iri 15.0 15.0 o in o iri 15.0 os Bath Temperature Oo) 520 530 570 530 570 580 580 580 08S 580 575 570 570 570 620 570 570 Amount of Plating Layer Deposition per Surface (g / m2) CQ CO O oo co 5 3 co OO «O CO CO O in 5 in Ό Chemical composition of the plating layer (% by mass) tn o O Total value 00Ό 0.03 oooooo 0.00 0.20 0.00 0£ 0 0.00 10Ό 0.00 0.00 0.05 0.03 0.00 00Ό OOO Type < p or ±ii N¡:0.20 Mn:0.30 1 Sr:0.01 1 SOOAS Pb:0.03 • i • <11 76.00 78.50 00 oz 20.00 79.60 23.13 24.24 25.45 26.47 27.54 28.57 31.03 31.05 31.05 31.03 31.03 31.03 CD s LOO 0 80 O 00 o 0.00 LL'O 0.76 0.75 0.74 0.72 0.71 69 0 ID O Ó SO 0 3.00 690 0.69 ώ 0.05 in o or 0 40 oo 0.32 0.39 0.38 0.37 0.37 O or 0.43 0.41 0.41 O or 0.41 0.41 0.41 Mg 0.00 !l 12 00 0 00 0.00 5.60 11.36 00 CO 8.82 8.70 8.57 8.28 8.28 8.30 00 ZL 8.28 8.28 < 14.00 oost 20 00 20.00 15.20 23.13 24.24 24.50 26.47 27.54 28.57 31.03 SO 10 31.10 00 10 00 10 31.03 c N 9.94 6.41 46 80 58.80 88.7 46.78 39.02 39.65 37.13 35.09 33.14 28.56 29.10 29.07 22.52 28.56 28.56 Φ (Λ ω CL E o Ld Ej. comp. Example E o lZT Ej. comp. Example Example Example Example Example Example Example Example Example Example Example E o ¡IT Ej. comp. No. - CXI 00 in -or* 00 o O - CSI 2 in o £. ML / £ / ¿U¿¿ / U / 0034 XXXXXXXXXXXXXXXXX o iri o iri o LO O iri o iri o iri p iri o iri o iri o iri o iri o iri p iri o iri o iri o iri OSl o iri o iri o iri o iri o iri O iri o iri o iri o iri o iri o iri o iri o iri o iri o iri o iri o iri o iri φ _Q nte disponible 610 O mo lo o in O IO O ιο o lo O oo co oo en o ID OO LO O in O 5 o 00 o O o nente disponible 5 o- 00 in 5 00 in es co co co en s O es Ό en <SJ LO ente comercialr te comercialme 0 00 O o o o O o o q o o o o o o o d o SO 0 o o o d o o ó O o o 0.05 co o o o o o 0 00 rsión en calii ión en calien i • o o c z in o o Cu:0.70 ΤιΌ.ΟΙ I Sn:0 05 Cr:0.03 1 la por inme por inmers 23.08 eo Le εο LE 33.33 33.38 εο ie 34 21 35.08 36.08 36.71 37.50 38.65 38 29 39.41 42.86 43.82 a-recoc¡( •o recubierta con Al 0.77 O o o o -O O CO en O CO in O CO in o en O en o 0.38 en Ó CO ó cñ O O co O CO CS| O LO O galvanizad 0.46 0.00 3.59 0.40 o ó -O O m o co p s m CSI CO es es es o co CS¡ Ό LO O a de acero ina de acei 13.00 8.28 8.28 00 8 s oo co CS oo 00 o in d in iri d O o -oo iri a iri o iri o in iri es O iri Lámini Lám 23.08 31.03 31.03 33.33 33.38 31.03 34 21 35.00 36.08 36.71 37.50 38.65 38.29 39.41 45.00 46.00 39.61 28.97 25.38 24.40 23.93 25.73 O in csi es 22.34 20.22 19.19 17.33 iri 16 23 14.04 3.56 3.44 Ej. comp. Ex. comp. Ex. comp. Example Example Eg. comp. Example Example Example Example Example Example Example Example Example Eg. comp. Ex. comp. Ex. comp. co OO CS CS CS CS co CS es m CS Ό CS es 00 es oes O co CO es en CO eo eo in eo. φ φ φ φ en en en en E en (Λ OJ

[87] Table Assessment Result Hydrogen Penetration QQ 00 QQ 00 00 00 00 00 00 03 00 03 03 OO Corrosion resistance QQ 00 QO < < < <1 <1 <r < < O o 1X1 Q Q < Q Q < < < < < < < < < < < < < O o Capa de enchapado Capa principal Capa de óxido que contiene Mg-Zn Espesor(um) CM CM CM d in CM O CO CM d CM d CM d CM d CM d CM CM d CM d CM d CM d in co CM Otros compuestos intermetálicos Relación de área O d O d c d o d o d o d o d o d o d o d O d o d o d o d o d o d o d Fase que contiene Fe-AI(%) Fase de FeAl Relación de área 3 3 o d 3 3 o θ' co o in in o <>o CM d 3 3 Fe-Al-Zn phase Area ratio 3 3 od CM 3 3 co co ID 00 Ό for CM md in LO O CO m LO <> co <υ o 1— relación de área 3 o d co md 00 cm m in ό o* lo p fase que contiene mg-zn (%) en σ ó co cd s csl cmi c n π3 capa interfacial espesor (iim) - <n •o difusión (um) <3 clase ej. comp. e llt φ lu φ 0) ixi u? ut uj l¡t iu no. £2 2 όω QQ 03 m O co 03 03 m □3 m 03 03 03 O < QQQO < < ω < < < < < < < < 03 ω Q 00 AA QQ AAA AAA Q AAA AAA < < < < < < < < o Q AAA <0.2 3 <0.2 CSI o CSJ o <0.2 <0.2 CSI O <sj o csi e <0.2 o q iri 13.3 10.8 disponible i ¡sponi ble csi tü ím 13.2 ó 9 01 16.4 14.4 15.0 0 91 18.0 20.0 19.8 ercialment cialmente 0¿z to 64 8 60 3 019 66.7 09 58.6 69.1 6 99 68.4 67.7 ¿69 69 75.0 71.8 aliente comí ente comen 29.0 64.8 74 2 ¿99 71.4 83.5 18 84 4 85.7 877 ¿68 06 sión en c ón cali p 20.1 17.4 por inmer or inmersii 25.0 θ' 00 14.1 co -q 5 csi oq la-recocida rta con al pi 46.0 16.5 17.0 14.5 19.0 13.4 13.5 lo 101 in galvaniza! lámina de acero recubiei olí 25.6 25.8 28.6 18.1 15.6 14.3 12.3 10 lina acere - tu co ό c4 id 10.5 h '<0 _l 14.2 13.1 4.4 0όι ej. comp. ejemplo e a lll o» oj 04 c3 m cn <s| coin ιη in Φ in in ΜΛ / t / ZUZZ / U í ¿¿34

[88] The chemical compositions and structures of the coating layers on the hot-stamped bodies obtained in the Examples and Comparative Examples and the various characteristics when hot-stamping the plated steel materials were investigated by the following methods: The results are shown in Tables 1 and 2. In Tables 1 and 2, Comparative Examples 34 and 35, respectively, refer to hot-dip annealed galvanized steel sheet (Zn-11%Fe) and hot-dip aluminum-coated steel sheets (Al10%Si) conventionally used as plated steel materials for hot stamping and show the results when hot-stamping these steel sheets.The chemical compositions and structures of the plating layers of Comparative Examples 34 and 35 differ significantly from the chemical compositions and surface structures of the plating layers according to the present invention. Therefore, the analysis of the chemical compositions and structures of these plating layers was omitted. Furthermore, Comparative Examples 34 and 35 are simply commercially available products that were evaluated. Consequently, the details of the production methods for these steel sheets are unknown. Additionally, although not shown in Table 2, the Fe-Al-containing phase (Fe-Al-Zn phase and FeAl phase) is island-shaped. In the Fe-Al-containing phase... ML / t / ZUZZ / U í ¿¿34 MA / the aspect ratio was 5.0 or less.

[89] Chemical composition of the veneer layer The chemical composition of the plating layer was determined by dissolving the plating layer in an acidic solution to which an inhibitor was added that inhibited corrosion of the steel base material and measuring the resulting solution using the TCP emission spectrometry method.

[90] Thicknesses of the interfacial layer, the diffusion layer, and the oxide layer The thicknesses of the interfacial layer, diffusion layer, and oxide layer were determined by cutting a test piece from the hot-stamped body, burying it in a resin, etc., then polishing the cross-section, measuring the image observed by a SEM, and averaging the measured values ​​of these in three different fields and considering the averages as the thicknesses of the interfacial layer, diffusion layer, and oxide layer.

[91] Area relations and phase compositions in the main layer The area ratios of the phases in the main layer were determined as follows. First, a prepared sample was cut to a size of 25 mm x 15 mm, then any cross-section of the plating layer was photographed at 1500X magnification using a SEM. From the BSE image of this cross-section and a SEM-EDS map image, the area ratios of the phases in the main layer were measured using computer image processing. The averages of the measurement values ​​in any five fields were determined as the area ratios of the MgZn phase, the Mg₂Zn₃ phase, the MgZn₂ phase, the FeAl phase, the Fe-Al-Zn phase, and other intermetallic compounds. Additionally, the area ratio of the Mg-Zn-containing phase was determined as the area ratio of the total MgZn phase, the Mg₂Zn₃ phase, and the MgZn₂ phase.Similarly, the area ratio of the Fe-Al containing phase is determined as the area ratio of the total FeAl phase and the Fe-Al-Zn phase.

[92] Resistance to LME The resistance to heat transfer moisture (HTM) was evaluated by subjecting a sample of the pre-hot-stamped steel material to a hot V-bend test. Specifically, a 170 mm x 30 mm sample of the pre-hot-stamped steel material was heated in a heating furnace and removed when the sample temperature reached 900°C. A precision press was used to perform the V-bend test. The V-bend die was shaped like a 90° V-bend angle with R = 1, 2, 3, 4, 5, and 10 mm. The HTM resistance was rated as follows: AAA, AA, A, and B ratings were considered acceptable. AAA: No LME cracking occurred even with R of 1 mm. AA: LME cracking occurred with R of 1 mm, but no LME cracking occurred with R of 2 mm A: LME cracking occurred with an R of 2 mm, but no LME cracking occurred with an R of 3 mm B: LME cracking occurred with R of 3 mm, but no LME cracking occurred with R of 4 mm C: LME cracking occurred with R of 4 mm, but no LME cracking occurred with R of 5 mm D: LME cracking occurred with an R of 5 mm, but no LME cracking occurred with an R of 10 mm

[93] Corrosion resistance The corrosion resistance of the hot-stamped body was evaluated as follows. First, a 50 mm x 100 mm sample of the hot-stamped body was treated with zinc phosphate (SD5350 System: standard manufactured by Nippon Paint Industrial Coatings Co., Ltd.), then coated by electrodeposition (PN110 Powernix Gray: standard manufactured by Nippon Paint Industrial Coatings Co., Ltd.). ML / í ¿¿34 Coatings Co., Ltd.) with a thickness of 20 µm and baked at 150°C for 20 minutes. Cross-sections (40 xy / 2 mm, 2) were then made down to the base iron. The coated body was used for a combined cyclic corrosion test in accordance with JASO (M609-91). The maximum blister widths were measured at eight locations around the cross-sections after 150 cycles. The average of the measured values ​​was calculated and classified as follows: Samples rated A and B were considered passed. A: Width of the coating blister from the cross-section of 1 mm or less B: Width of the coating blister from the cross-section of 1 to 2 mm C: Width of the coating blister from the cross-section of 2 to 4 mm D: Red oxidation MA / í ¿¿34

[94] Resistance to hydrogen penetration The hydrogen penetration resistance of the hot-stamped body was determined as follows: First, a sample of the hot-stamped body was stored in liquid nitrogen. Thermal desorption spectroscopy was used to determine the concentration of hydrogen penetrating the hot-stamped body. Specifically, the sample was heated in a heating oven equipped with a gas chromatograph, and the amount of hydrogen released from the sample was measured up to 250°C. The measured amount of hydrogen was divided by the mass of the sample to determine the hydrogen penetration level. This was classified as follows: AAA, AA, A, and B ratings were considered acceptable. AAA: Hydrogen penetration quantity of 0.1 ppm or less AA: Hydrogen penetration amount of more than 0.1 to 0.2 ppm A: Hydrogen penetration amount of more than 0.2 to 0.3 ppm B: Hydrogen penetration amount of more than 0.3 to 0.5 ppm C: Hydrogen penetration amount of more than 0.5 to 0.7 ppm D: Hydrogen penetration amount of 0.7 ppm or more

[95] With reference to Tables 1 and 2, in Comparative Example 1, the Al and Ca contents in the plating layer were small; therefore, the acicular Al-Zn-Si-Ca phase did not form sufficiently in the surface structure of the plating layer before hot stamping. It is believed that a barrier layer composed of a film did not form. ML / í ¿¿34 of Ca-based oxide at the time of heating in hot stamping. As a result, at the time of the above heating, the Zn and Mg in the plating layer evaporated, a thick oxide layer containing Mg-Zn of more than 1.0 pm was formed, a phase containing Mg-Zn did not form in the main layer, and the LME resistance, hydrogen penetration resistance, and corrosion resistance were all evaluated as deficient. In Comparative Example 2, similarly, the Ca content in the plating layer was small; therefore, at the time of heating in hot stamping, a barrier layer did not form, and the LME resistance, hydrogen penetration resistance, and corrosion resistance were all evaluated as poor.In Comparative Example 4, Mg was not contained in the plating layer; therefore, a Mg-Zn phase did not form in the main layer, and the LME resistance, hydrogen penetration resistance, and corrosion resistance were rated as poor. In Comparative Example 5, Ca was not contained in the plating layer; therefore, a barrier layer did not form during hot stamping, and the LME resistance, hydrogen penetration resistance, and corrosion resistance were rated as poor.In comparative examples 16 and 17, the cooling of the plating layer did not meet the predetermined two-stage cooling conditions. Consequently, an AlZn-Si-Ca acicular phase did not form sufficiently in the surface structure of the plating layer before hot stamping. During the hot stamping process, the Zn and Mg in the plating layer evaporated, resulting in poor LME resistance, hydrogen penetration resistance, and corrosion resistance. In comparative example 18, the Mg content in the plating layer was high, and the corrosion resistance decreased due to excessive sacrificial corrosion prevention. Alternatively, because of the high Mg content, hydrogen penetration occurred due to Mg evaporation during hot stamping.In Comparative Example 19, Si was not present in the plating layer; therefore, an Al-Zn-Si-Ca acicular phase did not form in the surface structure of the plating layer before hot stamping. As a result, LME resistance, hydrogen penetration resistance, and corrosion resistance were rated as poor. In Comparative Example 20, the Si content in the plating layer was too high. Consequently, a Mg₂Si phase (another intermetallic compound in Table 2) formed preferentially in the plating layer before hot stamping. The Al-Zn-Si-Ca acicular phase did not form sufficiently, and as a result, LME resistance, hydrogen penetration resistance, and corrosion resistance were rated as poor.In comparative examples 23 and 33, the Ca or Al content in the plating layer was too high. Consequently, in the plating layer prior to hot stamping, Al14Oa and other intermetallic compounds (other intermetallic compounds in Table 2) formed preferentially. An acicular Al-Zn-SiCa phase did not form sufficiently, and as a result, the LME resistance, hydrogen penetration resistance, and corrosion resistance were all rated as poor. In comparative example 34, which used conventional hot-dip galvanized annealed steel sheet, the hydrogen penetration resistance was excellent, but the LME resistance and corrosion resistance were rated as poor.In Comparative Example 35 using conventional steel sheet coated with hot-dip aluminum, the LME resistance and corrosion resistance were excellent, but the hydrogen penetration resistance was rated as poor.

[96] Conversely, in all examples according to the present invention, by properly controlling the chemical composition of the plating layer and the phases contained in the main layer and their area ratios, a hot-stamped body is obtained in which the resistance to LME and hydrogen penetration is improved, and, moreover, excellent corrosion resistance is achieved. In particular, if reference is made to Tables 1 and 2, it is understood that by controlling the Al content in the plating layer to 25.00 to 35.00%, the LME resistance is markedly improved, and similarly, by controlling the Mg content in the plating layer to 6.00 to 10.00%, the corrosion resistance is markedly improved.Based on the BSE SEM image of the plating layer surface before hot stamping (and in accordance with the need for the SEM-EDS mapping image), in all examples, an acicular Al-Zn-Si-Ca phase was present in an area ratio of 2.0% or more in the plating layer surface structure before hot stamping.

[97] Example B In this example, the inventors studied the two-stage cooling conditions in the plating layer formation step, as explained with reference to the hot-stamped body production method. Except for the use of plating baths with predetermined chemical compositions and the further formation of plating layers with the chemical compositions shown in Table 3 under the conditions shown in that table, they followed the same procedure as in Example A to obtain plated steel materials with plating layers formed on both surfaces of the base steel materials. The plating layer structures in the resulting plated steel materials, etc., were investigated using methods similar to those in Example A. The results are shown in Table 4. ML / 1 / ZUZ ¿ / u /

[98] Table σι Evaluation result Hydrogen penetration Q or Q Corrosion resistance Q or Q LME QQQ Plating layer | Main layer | Oxide layer containing Mg-Zn Thickness (µm) 3.5 3.0 00 CN Other intermetallic compounds Area ratio 0.0 0.0 OO Phase containing Fe-Al(%) FeAl phase Area ratio ÜT ÜTJ ÜT Fe-Al-Zn phase Area ratio ÜT ÜTJ ÍLfl Total Area ratio ÍLfl 9 ÍLfl Phase containing Mq-Zn (%) I MgZnz Area ratio 0 o O o O o Mg,Zn3 Area ratio 0.0 0.0 0.0 MgZn Area ratio 0O 0.0 oo Total Area ratio ÍLfl ÍLfl στ» Interfacial layer Thickness (µm) ÜT ÍLfl ÜTJ Diffusion layer Thickness (um) Csj in 13.7 Class Ex. comp. comp. comp. No. CSI ω ω ω ω σι

[100] Referring to Tables 3 and 4, in Comparative Example 41, where the average cooling rate of the first stage of the plating layer was 10°C / s, since that average cooling rate was somewhat low, the acicular phase of Al-Zn-Si-Ca did not form sufficiently in the surface structure of the plating layer before hot stamping. At the time of heating in hot stamping, the Zn and Mg in the plating layer evaporated, and as a result, the desired structure of the plating layer could not be obtained, and the LME resistance, hydrogen penetration resistance, and corrosion resistance were rated as poor.Furthermore, in Comparative Examples 42 and 43, where the average cooling rate of the second plating stage was 7°C / s, the Al-Zn-Si-Ca acicular phase did not form sufficiently in the plating layer's surface structure before hot stamping. During the hot stamping process, the Zn and Mg in the plating layer evaporated, preventing the desired plating structure from being achieved. Consequently, the LME resistance, hydrogen penetration resistance, and corrosion resistance were all rated as poor. The results in Tables 1-4 indicate that to create the Al-Zn acicular phase... To form Si-Ca more reliably at a 2.0% or greater area ratio, it is preferable to first cool at an average cooling rate of 14°C / s plus or 15°C / s plus from the bath temperature to 450°C, then cool at an average cooling rate of 5.5°C / s minus or 5°C / s minus from 450°C to 350°C. MA / í ¿¿34

[101] Example C In this example, the inventors studied the cooling rate change point between rapid and slow cooling in the two-stage cooling of a plating layer. Except for the use of a plating bath to form a plating layer similar to Example 12, etc. (bath temperature 600°C) and the additional change of the cooling rate change point to 375°C, 400°C, 425°C, 450°C, 475°C, and 500°C, and making the average cooling rate of the first stage 15°C / s and the average cooling rate of the second stage 5°C / s, they followed the same procedure as in Example A to obtain plated steel materials with coating layers formed on both surfaces of the base steel materials. They examined the area relationships of the acicular phases of Al-Zn-Si-Ca in the surface structures of the coating layers in the obtained plated steel materials.The results are shown in Figure 4.

[102] Referring to Figure 4, if the cooling rate change point is 400°C, the area ratio of the acicular Al-Zn-Si-Ca phase is 1.9%, and therefore 2.0% or more could not be guaranteed. However, if the cooling rate change point is 425°C, 450°C, and 475°C, 2.0% or more of the acicular Al-Zn-Si-Ca phase could form. In particular, if the cooling rate change point is 450°C, the highest area ratio of the acicular Al-Zn-Si-Ca phase could be achieved. List of reference signs

[103] 1 plating layer oxide layer diffusion layer steel base material 5 interfacial layer 6 main layer 7 Mg-Zn containing phase 8 Fe-Al containing phase 8a Fe-Al-Zn phase 8b FeAl phase 11 a phase< / sj>

Claims

1. A hot-stamped body comprising a steel base material and a plating layer formed on a surface of the steel base material, wherein the plating layer has a chemical composition comprising, in % by mass, Al: 15.00 to 45.00%, Mg: 5.50 to 12.00%, Si: 0.05 to 3.00%, Ca: 0.05 to 3.00%, Fe: 20.00 to 50.00%, Sb: 0 to 0.50%, Pb: 0 to 0.50%, Cu: 0 to 1.00%, Sn: 0 to 1.00%, Ti: 0 to 1.00%, Sr: 0 to 0.50%, Cr: 0 to 1.00%, Ni: 0 to 1.00%, Mn: 0 to 1.00%, and the remainder: Zn and impurities, the plating layer comprises an interfacial layer placed at an interface with the steel base material and containing Fe and Al and a main layer placed over the interfacial layer, the main layer comprising, by area ratio, 10.0 to 70.0% of a phase containing Mg-Zn and 30.0 to 90.0% of a phase containing Fe-Al, the phase containing Mg-Zn comprises at least one selected from the group consisting of an MgZn phase, an Mg2Zn3 phase and an MgZnz phase, and the phase containing Fe-Al comprises an FeAl phase and a Fe-Al-Zn phase and an area ratio of the Fe-Al-Zn phase in the main layer is more than 10.0 to 75.0%.

2. The hot-stamped body according to claim 1, wherein the chemical composition of the plating layer comprises, in % by mass, Al: 25.00 to 35.00% and Mg: 6.00 to 10.00%.

3. The hot-stamped body according to claim 1 or 2, wherein the MgZn-containing phase comprises an MgZn phase, and an area ratio of the MgZn phase in the main layer is 5.0% or more.

4. The hot-stamped body according to any of claims 1 to 3, wherein the Mg-Zn containing phase comprises an MgZn phase and an Mg2Zna phase, and an area ratio of the total MgZn phase and the Mg2Zna phase in the main layer is 25.0 to 50.0%.

5. The hot-stamped body in accordance with any one of claims 1 to 4, wherein the area ratio of the FeAl phase in the main layer is from 5.0 to 25.0%.