Hot pressed assemblies and the method of manufacturing them, and coated steel sheets for hot press forming.

Abstract

DEPCT66 What was revealed was a hot-molded assembly with excellent paint adhesion and resistance. Post-painting corrosion when subjected to electrostatic deposition painting. The zirconium-based chemically conjugated hot-molded components revealed herein include: Steel base plate; a Fe-Zn-Al-Mg based alloy coating containing an alpha-Fe phase. The gamma phase is formed on at least one surface of the base steel plate at a weight of coating material. The surface area is 40-400 g / m²; and an oxide layer containing Zn, Al, and Mg forms on the coating. Fe-Zn-Al-Mg based alloys, where the gamma-I / alpha I ratio is 0.5 or less when measured. By X-ray diffraction using a Co-K alpha radiation source (wavelength: 1.79021 angstroms). At an angle of incidence of 25 degrees, where I gamma is the intensity of the diffraction peak of the plane (411) of the phase. The gamma appearing in the angular range of 41.5 degrees is less than or equal to 2 theta less than or equal to 43.0 degrees, and alpha is the peak intensity. The plane diffraction (110) of the alpha-Fe phase appearing in the angular range of 51.0 degrees is less than or equal to 2 theta, less than or equal to 52.0. The degree, and the sum of the concentrations of Al and Mg in the oxide layer, is 28 percent by atom. Or more -----------------------------------------------------------

Description

Hot press member and method for manufacturing the same, and plated steel sheet for hot pressing This invention relates to a hot-pressed member, a method for manufacturing the same, and a plated steel sheet for hot pressing. Traditionally, many components of automobiles, such as suspension and body structural parts, have been manufactured by press-forming steel sheets with a specified strength. In recent years, from the perspective of protecting the global environment, there has been a strong desire to reduce the weight of automobile bodies, and efforts have been made to increase the strength of the steel sheets used and reduce their thickness. However, as the strength of the steel sheets increases, their press-formability decreases, making it increasingly difficult to process the steel sheets into the desired component shapes. To address these problems, a processing technique called hot pressing has been proposed, which enables both ease of processing and high strength by rapidly cooling a heated steel sheet while processing it using a die and punch. Zn alloy plated steel sheets are attracting attention as hot pressing steel sheets with high corrosion resistance because an electrochemically less noble plating layer remains after heating compared to the base steel sheet, and hot pressing components and manufacturing methods using this Zn alloy plated steel sheet have been proposed. Patent Document 1 states that the Al concentration {Al} in the plating layer is 0.2 to 1.0 g / m². 2 The invention describes a plated steel sheet for hot pressing, which is within the range and satisfies the relationship between the Mg concentration {Mg} (mass%) in the plating layer and the Al concentration of 0.10 ≤ {Mg} / {Al} ≤ 5, and a hot-pressed member obtained by heating and then hot-pressing this plated steel sheet for hot pressing. Japanese Patent Publication No. 2006-265706 Patent Document 1 describes that the hot-pressed member described in Patent Document 1 exhibits excellent post-coating corrosion resistance when electrodeposited after zinc phosphate-based chemical conversion treatment. However, in recent years, zirconium-based chemical conversion treatment has begun to become widespread as an alternative to conventional zinc phosphate-based chemical conversion treatment. Therefore, hot-pressed members are now also required to have good coating adhesion and post-coating corrosion resistance when electrodeposited after zirconium-based chemical conversion treatment. However, as a result of the inventors' investigations, it was found that while the hot-pressed member disclosed in Patent Document 1 exhibits excellent post-coating corrosion resistance when electrodeposited after zinc phosphate-based chemical conversion treatment, it has insufficient coating adhesion and post-coating corrosion resistance when electrodeposited after zirconium-based chemical conversion treatment. Therefore, in view of the above problems, the present invention aims to provide a hot-pressed member that exhibits excellent coating adhesion and corrosion resistance after coating when electroplating is performed after zirconium-based chemical treatment, and a suitable method for manufacturing the same. Furthermore, the present invention aims to provide a plated steel sheet for hot pressing that is suitable as a material for obtaining such hot-pressed members. In order to solve the above problems, the inventors of this invention have diligently conducted research and obtained the following findings. In the Fe-Zn-Al-Mg alloy plating layer of a hot-pressed member, the deposition of the Γ phase, which consists of electrochemically noble intermetallic compounds such as the Fe3Zn10 phase, is limited, and the combined concentration of Al and Mg in the Zn-Al-Mg-containing oxide layer formed on the plating layer is increased, thereby improving the adhesion of the coating and the corrosion resistance after coating when electrodeposition coating is performed after zirconium-based chemical conversion treatment. In order to manufacture a hot-pressed member having an Fe-Zn-Al-Mg alloy plating layer with a low amount of Γ phase deposition and an oxide layer with a high sum of Al and Mg concentrations, it is necessary to heat a hot-pressed plated steel sheet having a Zn-Al-Mg alloy plating layer with predetermined amounts of Al and Mg and a liquidus temperature of 400°C or lower to a relatively low temperature before hot-pressing. Based on the above findings, the gist of the present invention is as follows. [1] Base steel plate and At least one side of the aforementioned base steel plate has an adhesion amount of 40 to 400 g / m² per side. 2 A Fe-Zn-Al-Mg alloy plating layer formed with α-Fe phase and Γ phase, An oxide layer containing Zn, Al, and Mg is formed on the Fe-Zn-Al-Mg alloy plating layer, It has, X-ray diffraction using a Co-Kα source (wavelength 1.79021 Å) at an incident angle of 25°, intensity I of the diffraction peak of the (411) plane of the Γ phase located at 41.5° ≤ 2θ ≤ 43.0°. Γ And the intensity of the diffraction peak I of the (110) plane of the α-Fe phase located at 51.0° ≤ 2θ ≤ 52.0° α Ratio I Γ / I α It is 0.5 or less, The sum of the Al concentration and Mg concentration in the oxide layer is 28 atomic percent or more. A hot-pressed member characterized by the following features. [2] Substrate steel plate and At least one side of the aforementioned base steel plate has an adhesion amount of 30 to 180 g / m² per side. 2 A Zn-Al-Mg alloy plating layer formed by having a component composition of mass%, containing Al: 3-10% and Mg: 0.2-0.8%, with the remainder being Zn and unavoidable impurities, and having a liquidus temperature of 400°C or less in an atmospheric environment, A method for manufacturing a hot-pressed member, characterized by heating a plated steel sheet for hot pressing to a temperature range of Ac3 transformation point to 1000°C, and then hot-pressing it. [3] The method for manufacturing a hot-pressed member according to [2] above, wherein the component composition of the Zn-Al-Mg alloy plating layer further includes, in mass%, at least one selected from Ca, Sr, Mn, V, Cr, Mo, Ti, Ni, Co, Sb, Zr, and B, in a total amount of 1% or less. [4] Base steel plate and At least one side of the aforementioned base steel plate has an adhesion amount of 30 to 180 g / m² per side. 2An Fe-Zn-Mg alloy plating layer formed to have a component composition in mass% including Al: 3 to 10% and Mg: 0.2 to 0.8%, with the balance being Zn and inevitable impurities, and having a liquidus temperature of 400°C or lower in an air atmosphere, and A plated steel sheet for hot pressing, characterized by having the same. [5] The plated steel sheet for hot pressing according to [4] above, wherein the component composition of the Fe-Zn-Mg alloy plating layer further contains at least one selected from Ca, Sr, Mn, V, Cr, Mo, Ti, Ni, Co, Sb, Zr, and B in a total range of 1% or less by mass%. The hot press member of the present invention is excellent in coating adhesion and corrosion resistance after electrodeposition coating when subjected to a zirconium-based chemical conversion treatment. Further, according to the method for manufacturing a hot press member of the present invention, a hot press member excellent in coating adhesion and corrosion resistance after electrodeposition coating when subjected to a zirconium-based chemical conversion treatment can be manufactured. The plated steel sheet for hot pressing of the present invention is suitable as a material for manufacturing a hot press member excellent in coating adhesion and corrosion resistance after electrodeposition coating when subjected to a zirconium-based chemical conversion treatment. Representing an invention example, it is a cross-sectional SEM image of the Fe-Zn-Mg alloy plating layer of the hot press member according to No. 2. Representing a comparative example, it is a cross-sectional SEM image of the Fe-Zn-Mg alloy plating layer of the hot press member according to No. 8. (Hot press member) A hot press member according to an embodiment of the present invention includes a base steel sheet, an Fe-Zn-Mg alloy plating layer formed on at least one side of the base steel sheet, and an oxide layer formed on the Fe-Zn-Mg alloy plating layer. [Base steel sheet] The base steel sheet in the hot press member of the present embodiment is not particularly limited, but in order to make the tensile strength TS of the hot press member 1470 MPa or more, it is preferable to use a steel sheet having the component composition described in the section of the plated steel sheet for hot pressing described later. [Fe-Zn-Mg alloy plating layer] The Fe-Zn-Al-Mg alloy plating layer in the hot-pressed member of this embodiment contains an α-Fe phase and a Γ phase, and preferably consists of an α-Fe phase and a Γ phase. The α-Fe phase is a solid solution phase mainly composed of Fe and containing Zn, Al, and Mg. When a hot-pressed plated steel sheet having a Zn-Al-Mg alloy plating layer is subjected to hot pressing, Zn, Al, and Mg in the plating layer diffuse into the underlying steel sheet, forming a solid solution phase (α-Fe phase) mainly composed of Fe and containing Zn, Al, and Mg in this diffusion region. The α-Fe phase is formed by eroding the surface layer of the underlying steel sheet in the plated steel sheet, but in hot-pressed members, it is generally considered to constitute a part of the Fe-Zn-Al-Mg alloy plating layer located on the underlying steel sheet. The Γ phase is a phase consisting of intermetallic compounds mainly composed of Zn, containing Al, Mg, and Fe, and mainly consists of the Fe3Zn10 phase. Furthermore, the Γ1 phase has a crystal structure similar to the Γ phase and is difficult to distinguish by X-ray diffraction, so in this specification, "Γ phase" also includes the Γ1 phase. Examples of other intermetallic compounds that constitute the Γ phase include Fe4Zn9, FeZn4, and Fe5Zn21. During hot pressing, the Zn-Al-Mg alloy plating layer that remains without contributing to diffusion into the base steel sheet incorporates Fe diffused from the base steel sheet, thereby forming the Γ phase consisting of intermetallic compounds, which constitutes a part of the Fe-Zn-Al-Mg alloy plating layer in the hot-pressed member. Here, the α-Fe phase and the Γ phase can be distinguished from each other by their distinctly different contrasts in the cross-sectional SEM image of the Fe-Zn-Al-Mg alloy plating layer of the hot-pressed member. Referring to Figures 1 and 2, the relatively bright areas on the surface of the hot-pressed member are the Γ phase, and the relatively dark areas are the α-Fe phase. Furthermore, the α-Fe phase and the Γ phase can be identified by X-ray diffraction using a Co-Kα (wavelength 1.79021 Å) source at an incident angle of 25°. The Γ phase in the Fe-Zn-Al-Mg alloy plating layer has a significantly lower potential than the underlying steel plate and the α-Fe phase, and therefore is preferentially corroded when exposed to a corrosive environment. In other words, the Γ phase exhibits sacrificial corrosion protection against the underlying steel plate and the α-Fe phase. Here, the zinc phosphate-based chemical conversion coating has a function as an excellent corrosion inhibitor for Zn-based alloys. Therefore, even when a member obtained by electrocoating after subjecting a hot-pressed member obtained by hot-pressing a Zn—Al—Mg-based alloy plated steel sheet to a zinc phosphate-based chemical conversion treatment receives a flaw that penetrates the coating film, the chemical conversion coating film, and the plating layer and reaches the base steel sheet and enters a sacrificial corrosion state, the corrosion rate of the Γ phase is small, the corrosion rate under the coating film is sufficiently small, and the corrosion resistance after painting does not pose a problem in the actual use environment. On the other hand, the zirconium oxide-based chemical conversion coating does not have a corrosion inhibitor function for Zn-based alloys. Therefore, after entering a sacrificial corrosion state, the corrosion rate of the Γ phase is high, and as a result, the corrosion rate under the coating film becomes high. When the amount of the Γ phase is large and the Γ phase continuously exists in the Fe—Zn—Al—Mg-based alloy plating layer without being segmented, when entering a sacrificial corrosion state, the corrosion of the Γ phase propagates in-plane in the environment under the coating film and is visually recognized as an appearance defect such as coating film swelling. Therefore, when applying a zirconium-based chemical conversion treatment, it is important to limit the amount of the Γ phase in order to ensure the corrosion resistance after painting. Therefore, in the present embodiment, as one of the necessary conditions for improving the corrosion resistance after painting when electrocoating is performed after subjecting a hot-pressed member to a zirconium-based chemical conversion treatment, it is important to limit the precipitation of the Γ phase composed of an electrochemically base intermetallic compound such as the Fe3Zn10 phase. Specifically, the intensity I of the diffraction peak of the (411) plane of the Γ phase existing at 41.5° ≤ 2θ ≤ 43.0° by X-ray diffraction using Co—Kα (wavelength 1.79021 Å) with an incident angle of 25° as a radiation source Γ and the intensity I of the diffraction peak of the (110) plane of the α-Fe phase existing at 51.0° ≤ 2θ ≤ 52.0° α and the ratio I Γ / I α is required to be 0.5 or less. When I Γ / I α exceeds 0.5, the corrosion resistance after painting when electrocoating is performed after subjecting a hot-pressed member to a zirconium-based chemical conversion treatment becomes insufficient. I Γ / I αIf the ratio is 0.5 or less, the Γ phase in the Fe-Zn-Al-Mg alloy plating layer is sufficiently fragmented by the α-Fe phase, and excellent post-coating corrosion resistance can be obtained when electrodeposition coating is performed after zirconium-based chemical conversion treatment is applied to a hot-pressed member. I Γ / I α Since a smaller value is preferable, the lower limit is not particularly limited, but the I detected when measured by X-ray diffraction as described above... Γ / I α The value is usually 0.01 or higher. Note that the measurement conditions for X-ray diffraction other than the incident angle and radiation source mentioned above are as follows: Ratio I Γ / I α Although this does not affect the outcome, the conditions described in the examples below can be adopted. Adhesion amount per side: 40-400 g / m 2 The amount of Fe-Zn-Al-Mg alloy plating layer adhering to hot-pressed members is 40 to 400 g / m². 2 By doing so, a hot-pressed member with excellent corrosion resistance can be obtained. Adhesion amount: 40 g / m 2 If the amount is less than 400 g / m², it is not possible to obtain a hot-pressed member with the desired corrosion resistance. 2 If this value is exceeded, the number of cracks traversing the plating layer increases significantly due to the solidification shrinkage of the plating layer after hot pressing, and the adhesion within the plating layer deteriorates significantly. The amount of plating layer adhering to the hot-pressed member is preferably 50 g / m². 2 The above is preferable, with a more preferable 60 g / m² 2 The above is required. Furthermore, the amount of plating layer adhering to the hot-pressed member is preferably 350 g / m². 2 The following, more preferably 300 g / m² 2 The following applies: In this specification, the "amount of Fe-Zn-Al-Mg alloy plating layer per side" of a hot-pressed member shall be determined by the following method. Three 48 mmφ samples are taken by punching out the hot-pressed member to be evaluated. Then, the non-evaluation side opposite the side on which the amount of plating is to be evaluated is masked for each sample. First, the oxide layer is dissolved by immersing each sample in a 20% chromium(VI) oxide aqueous solution at room temperature for 10 minutes, and each sample is weighed. Next, the Fe-Zn-Al-Mg alloy plating layer is dissolved by immersing each sample in a solution prepared by diluting 500 mL of 35% hydrochloric acid aqueous solution with 3.5 g of hexamethylenetetramine to 1 L for 120 minutes, and each sample is weighed again. The amount of plating per unit area for each sample is calculated from the mass difference before and after the dissolution of the Fe-Zn-Al-Mg alloy plating layer. Then, the average value of the three samples is taken as the amount of adhesion per side. [Oxide layer] The oxide layer in the hot-press member of this embodiment is formed on an Fe-Zn-Al-Mg alloy plating layer and contains Zn, Al, and Mg. When a hot-pressed plated steel sheet having a Zn-Al-Mg alloy plating layer is subjected to hot pressing, the Zn, Al, and Mg in the plating layer combine with oxygen present in the heating atmosphere to form an oxide layer containing Zn, Al, and Mg. The oxide layer mainly consists of Al oxide, but may also contain Zn and Mg contained in the plating layer, and may further contain elements that make up the base steel sheet, such as Fe, Mn, Cr, etc. In this embodiment, another necessary condition for improving the post-coating corrosion resistance when a hot-pressed member is subjected to zirconium-based chemical conversion treatment followed by electrodeposition coating is that the sum of the Al and Mg concentrations in the oxide layer is 28 atomic percent or more. If the sum of the Al and Mg concentrations in the oxide layer is less than 28 atomic percent, the above I Γ / I αEven if the value is 0.5 or less, the post-coating corrosion resistance will be insufficient when electrodeposition coating is performed after zirconium-based chemical conversion treatment on a hot-pressed member. This is presumed to be because, when the Zn concentration constituting the oxide layer is high, the reaction between the chemical conversion treatment solution and the oxide layer becomes non-uniform, resulting in greater unevenness in the thickness of the zirconium-based chemical conversion treatment film formed on the surface of the oxide layer. In other words, areas where the chemical conversion treatment film is thin are more likely to form, reducing the adhesion between the oxide layer and the chemical conversion treatment film, or between the chemical conversion treatment film and the coating film, or resulting in incomplete coverage of the chemical conversion treatment film. On the other hand, if the sum of the Al concentration and Mg concentration of the oxide layer is 28 atomic percent or more, the zirconium-based chemical conversion treatment film is formed properly, and excellent post-coating corrosion resistance can be obtained when electrodeposition coating is performed after zirconium-based chemical conversion treatment on a hot-pressed member. Furthermore, if the sum of the Al and Mg concentrations in the oxide layer is less than 28 atomic percent, the oxide layer becomes brittle, resulting in insufficient adhesion of the coating when electrodeposition coating is applied to a hot-pressed member after zirconium-based chemical conversion treatment. In contrast, if the sum of the Al and Mg concentrations in the oxide layer is 28 atomic percent or more, the oxide layer has sufficient strength, resulting in good adhesion of the coating when electrodeposition coating is applied to a hot-pressed member after zirconium-based chemical conversion treatment. There is no particular upper limit to the sum of the Al and Mg concentrations in the oxide layer. However, an oxide layer containing excessively high concentrations of Al and Mg is chemically stable in acidic environments such as chemical conversion treatment solutions used for paint primers, and may hinder the formation of a chemical conversion treatment film. Therefore, it is preferable that the sum of the Al and Mg concentrations in the oxide layer be 50 atomic percent or less. In this embodiment, the oxide layer is formed very thinly on the Fe-Zn-Al-Mg alloy plating layer, and as shown in Figure 1, it may not be visible in the cross-sectional SEM image. However, the oxide layer can be identified as a region where oxygen is detected by measuring the cross-section of the surface layer of the hot-pressed member by energy-dispersive X-ray analysis (EDX) combined with SEM and performing elemental mapping. Furthermore, in this specification, the "Al concentration and Mg concentration of the oxide layer" shall be the values ​​measured by the following method. That is, a test piece for cross-sectional observation is taken from the flat part of the hot-pressed member. The cross-section of the test piece, including the Fe-Zn-Al-Mg alloy plating layer and the oxide layer, is observed at 10,000x magnification using a scanning electron microscope (SEM) with an acceleration voltage of 15 kV, and the composition of the oxide layer is measured at three arbitrary locations by energy-dispersive X-ray analysis (EDX). The average of the Al concentration and Mg concentration at the three locations is defined as the "Al concentration of the oxide layer" and the "Mg concentration of the oxide layer," respectively. (Method for manufacturing hot-pressed members) A method for manufacturing a hot-pressed member according to one embodiment of the present invention is characterized by heating a hot-pressed plated steel sheet according to one embodiment of the present invention, as described later, to a temperature range of Ac3 transformation point to 1000°C, and then hot-pressing it. By heating the steel sheet for hot pressing to an Ac3 transformation point to 1000°C before hot pressing, an Fe-Zn-Al-Mg alloy plating layer having α-Fe phase and Γ phase, as well as an oxide layer having predetermined Al and Mg concentrations, can be obtained as described above. If the heating temperature is lower than the Ac3 transformation point, after hot pressing, the I of the Fe-Zn-Al-Mg alloy plating layer will be affected. Γ / I αThe value exceeds 0.5. As a result, the corrosion resistance after coating is insufficient when electrodeposition coating is performed on a hot-pressed member after zirconium-based chemical conversion treatment. If the heating temperature exceeds 1000°C, the desired oxide layer cannot be obtained, and the adhesion of the coating and the corrosion resistance after coating are insufficient when electrodeposition coating is performed on a hot-pressed member after zirconium-based chemical conversion treatment. Here, "heating temperature" refers to the highest temperature reached by the steel sheet. In this specification, the "Ac3 transformation point" is a value calculated from the following formula based on the component composition of the steel sheet. Ac3 transformation point (°C) = 910 - 203°C 1 / 2 +44.7Si-4Mn+11Cr Note that the element symbols on the right-hand side of the equation indicate the amount of each element present; if Cr is not present, Cr = 0. While there are no limitations on the heating temperature or the holding time after heating, it is desirable to set the holding time to 30 seconds or more from the viewpoint of eliminating the Γ phase and avoiding liquid metal embrittlement cracking during hot pressing. From the viewpoint of avoiding hydrogen infiltration due to the intake of water vapor in the furnace during the holding time, it is preferable to set the holding time to 5 minutes or less, more preferably 3 minutes or less, and even more preferably 2 minutes or less. There are no limitations on the method of heating steel sheets for hot pressing; examples include furnace heating using electric or gas furnaces, electrostatic heating, induction heating, high-frequency heating, and flame heating. In hot pressing, a hot-pressed plated steel sheet, heated as described above, is simultaneously press-formed and hardened using a forming die to obtain a hot-pressed member of a predetermined shape. The conditions for hot pressing are not particularly limited, and a standard method can be adopted. (Plated steel sheet for hot pressing) A plated steel sheet for hot pressing according to one embodiment of the present invention comprises a base steel sheet and a plated steel sheet with a coating amount of 30 to 180 g / m² per side on at least one side of the base steel sheet. 2 The present invention is characterized by having a Zn-Al-Mg alloy plating layer formed by mass%, having a component composition in which Al: 3-10% and Mg: 0.2-0.8%, with the remainder being Zn and unavoidable impurities, and having a liquidus temperature of 400°C or less in an atmospheric environment. [Substrate steel plate] To obtain a hot-pressed member having a tensile strength TS of 1470 MPa or higher, it is preferable to use a steel sheet as the base steel sheet having a composition in which, by mass%, C: 0.20 to 0.35%, Si: 0.1 to 0.5%, Mn: 1.0 to 3.0%, P: 0.1% or less, S: 0.05% or less, Al: 0.1% or less, and N: 0.01% or less, with the remainder being Fe and unavoidable impurities. The base steel sheet may be either a cold-rolled steel sheet or a hot-rolled steel sheet. The reasons for limiting each component element are explained below. C: 0.20-0.35% Carbon (C) improves strength by forming martensite and other structures within the steel microstructure. To obtain a total strength (TS) of 1470 MPa or higher, the carbon content must be 0.20% or more. On the other hand, if the carbon content exceeds 0.35%, the toughness of the spot weld deteriorates. Therefore, it is preferable to have a carbon content of 0.20 to 0.35%. Si: 0.1-0.5% Si (silicon) is an effective element for strengthening steel and obtaining good material properties. Therefore, the Si content needs to be 0.1% or more. On the other hand, if the Si content exceeds 0.5%, ferrite is stabilized, reducing hardenability. For this reason, the Si content is preferably between 0.1% and 0.5%. Mn: 1.0-3.0% Mn is an effective element for increasing the strength of steel. To ensure mechanical properties and strength, the Mn content must be 1.0% or higher. On the other hand, if the Mn content exceeds 3.0%, surface enrichment during annealing increases, making it difficult to ensure plating adhesion. Therefore, the Mn content is preferably between 1.0% and 3.0%. P: 0.1% or less If the phosphorus content exceeds 0.1%, grain boundary embrittlement due to phosphorus segregation at austenite grain boundaries during casting leads to a deterioration of local ductility, resulting in a decrease in the balance between strength and ductility. Therefore, it is preferable to keep the phosphorus content below 0.1%. Furthermore, from the viewpoint of steelmaking costs, it is preferable to keep the phosphorus content above 0.01%. S: 0.05% or less S (sulfur) acts as an inclusion such as MnS, causing deterioration of impact resistance and cracking along the metal flow of the weld. Therefore, it is desirable to reduce the amount of S as much as possible, preferably to 0.05% or less. Furthermore, in order to ensure good elongation flange properties, the amount of S should more preferably be 0.01% or less. Also, from the viewpoint of steelmaking costs, it is preferable that the amount of S be 0.002% or more. Al: 0.1% or less If the Al content exceeds 0.1%, the blanking processability and hardenability of the base steel plate will decrease. Therefore, it is preferable to keep the Al content at 0.1% or less. Furthermore, from the viewpoint of ensuring the effectiveness as a deoxidizing agent, it is preferable to keep the Al content at 0.01% or more. N: 0.01% or less If the nitrogen content exceeds 0.01%, AlN is generated during hot rolling and heating before hot pressing, which reduces the blanking processability and hardenability of the base steel sheet. Therefore, it is preferable to keep the nitrogen content at 0.01% or less. Furthermore, from the viewpoint of steelmaking costs, it is preferable to keep the nitrogen content at 0.001% or more. The remainder of the elements other than those listed above consists of Fe and unavoidable impurities. However, for the following reasons, at least one element selected from Nb: 0.05% or less, Ti: 0.05% or less, B: 0.0002 to 0.005%, Cr: 0.1 to 0.3%, and Sb: 0.003 to 0.03% by mass may be appropriately included as needed. Nb: 0.05% or less While Nb is an effective component for strengthening steel, excessive amounts reduce its shape-freezing properties. Therefore, when Nb is included, its content should be 0.05% or less. Ti: 0.05% or less Like Nb, Ti is effective in strengthening steel, but excessive amounts reduce its shape-freezing properties. Therefore, when Ti is included, the Ti content should be 0.05% or less. B: 0.0002-0.005% B has the effect of suppressing ferrite formation and growth from austenite grain boundaries. Therefore, it is preferable that the amount of B be 0.0002% or more. On the other hand, the addition of excessive B greatly impairs moldability. Therefore, when B is included, the amount of B should be 0.005% or less. Cr: 0.1-0.3% Cr is useful for strengthening steel and improving its hardenability. To achieve these effects, it is preferable that the Cr content be 0.1% or more. On the other hand, from the viewpoint of alloy cost, if Cr is included, the Cr content should be 0.3% or less. Sb: 0.003-0.03% Sb has the effect of suppressing decarburization of the steel sheet surface during hot pressing. To achieve this effect, it is preferable to have an Sb content of 0.003% or more. On the other hand, if the Sb content exceeds 0.03%, it leads to an increase in rolling load and a decrease in productivity. Therefore, when including Sb, the Sb content should be 0.03% or less. [Zn-Al-Mg alloy plating layer] In this embodiment, the Zn-Al-Mg alloy plating layer of the hot-press plated steel sheet contains, by mass%, Al: 3 to 10% and Mg: 0.2 to 0.8%, with the remainder being Zn and unavoidable impurities, and has a component composition such that the liquidus temperature in an atmospheric environment is 400°C or less. Al: 3-10% If the Al content is less than 3%, after hot pressing, the I of the Fe-Zn-Al-Mg alloy plating layer Γ / I α The ratio exceeds 0.5, and the sum of the Al and Mg concentrations in the oxide layer becomes less than 28 atomic percent. As a result, when electrodeposition coating is performed after zirconium-based chemical conversion treatment on a hot-pressed member, the adhesion of the coating film and corrosion resistance after coating become insufficient. Also, if the Al content is less than 3%, depending on the Mg content, it may not be possible to keep the liquidus temperature below 400°C as described later. On the other hand, if the Al content exceeds 10%, it may not be possible to keep the liquidus temperature below 400°C as described later, and after hot pressing, the I of the Fe-Zn-Al-Mg alloy plating layer Γ / I αThe value exceeds 0.5. As a result, the corrosion resistance after electrodeposition coating is insufficient when a zirconium-based chemical treatment is applied to a hot-pressed member. Therefore, the Al content should be 3 to 10%. Mg: 0.2-0.8% If the Mg content is less than 0.2%, after hot pressing, the I of the Fe-Zn-Al-Mg alloy plating layer Γ / I α If the Mg content exceeds 0.5, the corrosion resistance after electrodeposition coating is insufficient when the hot-pressed member is subjected to zirconium-based chemical conversion treatment. Therefore, the Mg content should be 0.2% or more, preferably 0.3% or more, and more preferably 0.4% or more. On the other hand, if the Mg content exceeds 0.8%, the sum of the Al concentration and Mg concentration in the oxide layer after hot pressing will be less than 28 atomic percent. As a result, the adhesion of the coating and the corrosion resistance after electrodeposition coating are insufficient when the hot-pressed member is subjected to zirconium-based chemical conversion treatment. Therefore, the Mg content should be 0.8% or less, preferably 0.7% or less, and more preferably 0.6% or less. Liquidus temperature under atmospheric conditions: 400°C or less In this embodiment, it is essential to control the Al content and Mg content appropriately to keep the liquidus temperature of the Zn-Al-Mg alloy plating layer below 400°C in an atmospheric environment. If the liquidus temperature exceeds 400°C, the I of the Fe-Zn-Al-Mg alloy plating layer after hot pressing Γ / I α The value exceeds 0.5. As a result, the corrosion resistance after electrodeposition coating is insufficient when a hot-pressed member is subjected to zirconium-based chemical conversion treatment. The lower limit of the liquidus temperature is not particularly limited, but within the above range of Al and Mg content, the liquidus temperature is generally 380°C or higher. The liquidus temperature of the Zn-Al-Mg alloy layer in an atmospheric environment can be determined by calculating it using a database with the thermodynamic calculation software Thermo Calc. Inevitable impurities in the Zn-Al-Mg alloy plating layer include components of the substrate steel sheet incorporated into the plating layer through the reaction between the plating bath and the substrate steel sheet during the plating process, as well as unavoidable impurities in the plating bath. The substrate steel sheet components incorporated into the plating layer include approximately 0.01% to several percent Fe. Examples of unavoidable impurities in the plating bath include Fe, Cr, Cu, Mo, Ni, and Zr. Regarding Fe in the plating layer, it is not possible to distinguish between Fe incorporated from the substrate steel sheet and Fe incorporated from the plating bath. While there are no particular limitations on the total content of unavoidable impurities, from the viewpoint of uniformly melting the plating layer during the hot pressing process, it is preferable that the total amount of unavoidable impurities excluding Fe be 1% by mass or less. The component composition of the Zn-Al-Mg alloy plating layer may further include, in mass%, at least one selected from Ca, Sr, Mn, V, Cr, Mo, Ti, Ni, Co, Sb, Zr, and B, in a total amount of 1% or less. Adhesion amount per side: 30-180 g / m 2 The amount of Zn-Al-Mg alloy plating layer deposited is 30 to 180 g / m². 2 By doing so, a hot-pressed member with excellent corrosion resistance and resistance to liquid metal embrittlement cracking during hot pressing can be obtained. Adhesion amount: 30 g / m 2 If the amount is less than 180 g / m², it is not possible to obtain a hot-pressed member with the desired corrosion resistance. 2 If the amount exceeds this, alloying may not be completed during the heating process before hot pressing, and a liquid phase may remain, potentially leading to liquid metal embrittlement cracking. The amount of Zn-Al-Mg alloy plating layer is preferably 45 g / m². 2 The above is preferable, and more preferably 55 g / m² 2 The above is complete. Furthermore, the amount of Zn-Al-Mg alloy plating layer is preferably 120 g / m². 2 The following, more preferably 100 g / m² 2 The following applies: In this specification, the "amount of Zn-Al-Mg alloy plating layer per side" shall be determined by the following method. Three 48 mmφ samples are obtained by punching out a Zn-Al-Mg alloy plated steel sheet to be evaluated, and each sample is weighed. Then, the non-evaluation side opposite to the side on which the amount of coating is to be evaluated is masked for each sample. Next, each sample is immersed for 10 minutes in a solution prepared by diluting 500 mL of 35% hydrochloric acid aqueous solution containing 3.5 g of hexamethylenetetramine to 1 L to dissolve the Zn-Al-Mg alloy plating layer, and each sample is weighed again. The amount of coating per unit area for each sample is calculated from the mass difference before and after dissolution of the Zn-Al-Mg alloy plating layer. The average value of the three samples is then taken as the amount of coating per side. In this embodiment, a separate coating may be provided below or above the Zn-Al-Mg alloy plating layer, depending on the purpose, as long as it does not affect the effects of the present invention. Examples of the lower coating include nickel pre-plating. Examples of the upper coating include a chemical conversion coating containing zirconium oxide or zirconium-titanium oxide. As the base steel sheet, a 1.4 mm thick cold-rolled steel sheet was used, having a composition by mass% of C: 0.23%, Si: 0.25%, Mn: 1.2%, P: 0.005%, S: 0.001%, Al: 0.03%, N: 0.004%, Nb: 0.02%, Ti: 0.02%, B: 0.002%, Cr: 0.2%, and Sb: 0.008%, with the remainder being Fe and unavoidable impurities (Ac3 = 814°C). This cold-rolled steel sheet was immersed in a molten Zn-Al-Mg plating bath having a predetermined composition and bath temperature using a hot-dip plating facility, and then N2 gas wiping was performed to produce hot-press plated steel sheets of levels No. 1 to 14 shown in Table 1. Table 1 shows the Al content, Mg content, and other elemental content in the Zn-Al-Mg alloy plating layer, as well as the liquidus temperature under atmospheric conditions. The content of each element and the liquidus temperature were controlled by adjusting the composition of the plating bath. The content of each element in the plating layer was determined by quantitative analysis of each component contained in the hydrochloric acid stripping solution of the plating layer using ICP-AES. The liquidus temperature of the plating layer was determined by the method described above. Table 1 also shows the amount of Zn-Al-Mg alloy plating layer deposited on one side, determined by the method described above. The amount of plating deposited was controlled by adjusting the flow rate of the wiping gas and the line speed. Next, the hot-press steel sheet described above was subjected to hot pressing. Specifically, a 150 mm x 300 mm test piece was taken from the obtained hot-press steel sheet and heat-treated in an electric furnace. The heat treatment conditions (heating temperature, holding time) are shown in Table 1. After heat treatment, the test piece was removed from the electric furnace and immediately hot-pressed using a hat-shaped die at a forming start temperature of 700°C to obtain a hot-pressed member. The shape of the obtained hot-pressed member is such that the length of the flat section on the top surface is 100 mm, the length of the flat section on the side surface is 50 mm, and the length of the flat section on the bottom surface is 50 mm. The bending radius of the die is 7R on both shoulders of the top surface and both shoulders of the bottom surface. (Evaluation of Fe-Zn-Al-Mg alloy plating layer / oxide layer of hot-pressed components) A test piece for cross-sectional observation was taken from the flat upper surface of the obtained hot-pressed member, and the cross-section of the Fe-Zn-Al-Mg alloy plating layer was observed using SEM. At each level, the α-Fe phase and the Γ phase were distinguishable from each other, as they had clearly different contrasts in the cross-sectional SEM image. Figure 1 shows a cross-sectional SEM image of the Fe-Zn-Al-Mg alloy plating layer of the hot-pressed member according to No. 2, representing the example of the invention, and Figure 2 shows a cross-sectional SEM image of the Fe-Zn-Al-Mg alloy plating layer of the hot-pressed member according to No. 8, representing the comparative example. In Figure 1, the precipitation of the Γ phase is suppressed, and the Γ phase is discontinuously scattered within the α-Fe phase. In contrast, in Figure 2, a large amount of the Γ phase is precipitated, and the Γ phase exists in a continuous planar manner. Furthermore, the intensity I of the diffraction peak of the (411) plane of the Γ phase located at 41.5° ≤ 2θ ≤ 43.0° was obtained by X-ray diffraction using a Co-Kα (wavelength 1.79021 Å) source at an incident angle of 25°. Γ And the intensity of the diffraction peak I of the (110) plane of the α-Fe phase located at 51.0° ≤ 2θ ≤ 52.0° α Measure and respectively, and their ratio I Γ / I α The results are shown in Table 1. X-ray diffraction measurements were performed using a curved IPX-ray diffractometer (Rigaku Corporation, RINT-RAPID II-R) under the following conditions: tube voltage: 45 kV, tube current: 160 mA, integration time: 600 seconds, and collimator diameter: 3 mm. Furthermore, the Al and Mg concentrations of the oxide layer were measured at each level using the method described above and are shown in Table 1. In addition, the amount of deposit per side of the Fe-Zn-Al-Mg alloy plating layer was measured at each level using the method described above and is shown in Table 1. (Evaluation 1: Coating adhesion) A 70 mm x 150 mm test piece was cut from the flat upper surface of the obtained hot-pressed member, and this test piece was subjected to a zirconium-based chemical conversion treatment. Specifically, a commercially available chemical conversion solution (zirconium-based chemical conversion treatment: Palmina 2100, manufactured by Nippon Parkerizing Co., Ltd.) was used, and the chemical conversion treatment was carried out under the conditions of a bath temperature of 35°C and a treatment time of 120 seconds. After that, a commercially available cationic electrodeposition paint was applied to each test piece, and the voltage was increased for 30 seconds and held at a constant voltage for 150 seconds, and then energized at a voltage condition that resulted in a coating film thickness of 15 μm after baking, and baked in an electric furnace at an ambient temperature of 170°C for 20 minutes. The cationic electrodeposition paint used was Electron GT-100V-1 Gray, manufactured by Kansai Paint. After electrodeposition coating, 11 cuts were made on the test piece using a utility knife, each 1 mm apart in the vertical and horizontal directions, reaching the underlying steel plate, creating 100 grid squares. Cellophane tape (registered trademark) was firmly pressed onto the grid squares, and the end of the tape was peeled off in one swift motion at a 45° angle. The number of squares of paint film peeled off from the surface of the test piece was measured, and the results were judged according to the following criteria, with ◎ or ○ indicating a pass. The evaluation results are shown in Table 1. ◎: Number of detached cells = 0 ○: Number of peeled-off squares = 1 △: Number of peeled-off squares = 2-5 ×: Number of peeled-off squares > 5 (Evaluation 2: Corrosion resistance after painting) A test specimen was prepared using the same method as in Evaluation 1, including electrodeposition coating. The edges of the evaluation surface (7.5 mm) and the non-evaluation surface (back) were sealed with tape. Then, a cross-cut scratch, 60 mm long and with a central angle of 60°, was made in the center of the evaluation surface using a utility knife, to a depth that reached the underlying steel plate. This test specimen was subjected to a corrosion test (VDA 233-102), and the corrosion status after 4 weeks was evaluated. The maximum bulge on one side from the crosscut was measured and judged according to the following criteria, with ◎ or ○ being considered a pass. The evaluation results are shown in Table 1. ◎: Maximum swelling width on one side < 1.5 mm ○: 1.5 mm ≤ Maximum bulge width on one side < 3.0 mm △: 3.0 mm ≤ Maximum bulge width on one side < 4.0 mm ×: 4.0 mm ≤ maximum bulge width on one side The results shown in Table 1 indicate that the hot-pressed member of the present invention exhibits excellent coating adhesion and corrosion resistance after electrodeposition coating following zirconium-based chemical conversion treatment. The hot-pressed member of the present invention is suitable for use as a suspension member or body structure member of an automobile.

Claims

DEPCT661. Hot-formed composite consisting of: a base steel plate; a Fe-Zn-Al-Mg based alloy coating containing alpha-Fe and gamma phases, formed on at least one surface of the base steel plate at a coating weight per surface of 40 g / m² to 400 g / m²; and an oxide layer containing Zn, Al, and Mg, formed on the Fe-Zn-Al-Mg based alloy coating, where the ratio of I-gamma / I-alpha is 0.5 or less when measured by X-ray diffraction using a microscope. Co-K alpha radiation source (wavelength: 1.79021 angstroms) at an angle of incidence of 25 degrees, where I gamma is the intensity of the plane diffraction peak (411) of the gamma phase appearing in the angular range of 41.5 degrees less than or equal to 2 theta less than or equal to 43.0 degrees, and l alpha is the intensity of the plane diffraction peak (110) of the alpha-Fe phase appearing in the angular range of 51.0 degrees less than or equal to 2 theta less than or equal to 52.0 degrees, and the sum of the Al and Mg concentrations in the oxide layer is 28 percent by atom or greater than 2.The method of producing hot-pressed components involves heating the coated steel sheet for hot-pressing to a temperature range of AC3 to 1000°C. The coated steel sheet for hot-pressing consists of: a base steel sheet; and a Zn-Al-Mg based alloy coating formed on at least one surface of the base steel sheet at a coating weight of 30 g / m² to 180 g / m². The chemical composition, in percentage by mass, is Al: 3% to 10% and Mg: 0.2% to 0.8%, with unavoidable Zn and impurities present. The coating reaches a liquid temperature in an atmospheric air of 400°C or lower, and the coated steel sheet is then subjected to hot-pressing.Method of manufacturing hot pressed components according to claim 2, whereby the chemical composition of the Zn-Al-Mg-based alloy coating is supplemented with at least one selected element from the group of Ca, Sr, Mn, V, Cr, Mo, Ti, Ni, Co, Sb, Zr, and B in total amounts of 1 percent by mass or less.

4. Coated steel sheets for hot press forming consisting of: base steel sheet; and a Zn-Al-Mg-based alloy coating formed on at least one surface of the base steel sheet at a coating weight per surface of 30 g / m² to 180 g / m², whose chemical composition in percentages by mass is Al: 3% to 10% and Mg: 0.2% to 0.8%, with a balance of Zn and unavoidable impurities, and a melting temperature in an atmospheric atmosphere of 400 °C or less. 5.Coated steel sheets for hot pressing forming according to claim 4, whereby the chemical composition of the Zn-Al-Mg-based alloy coating is further supplemented with at least one selected element from the group of Ca, Sr, Mn, V, Cr, Mo, Ti, Ni, Co, Sb, Zr, and B in a total amount of 1 percent by mass or less.