Hot-stamped part

Abstract

This hot-stamped part comprises a steel sheet, an Al-Fe alloy plating layer disposed on a surface of the steel sheet, an Al oxide layer disposed on a surface of the Al-Fe alloy plating layer, and a film disposed on a surface of the Al oxide layer. The film contains an amphoteric oxide of a d block element. When the average particle diameter of the amphoteric oxide is noted as Bs in unit of nm and the thickness of the Al oxide layer X is noted as Xt in unit of nm, Bs / Xt is 0.010 to 2.000.

Description

Hot stamped parts

[0001] This application claims priority to Japanese Patent Application No. 2024-077547, filed May 10, 2024, the contents of which are incorporated herein by reference.

[0002] In recent years, there has been an increasing demand to reduce the consumption of chemical fuels in order to protect the environment and prevent global warming, and this demand is having an impact on various manufacturing industries.

[0003] For example, automobiles, which are an essential means of transportation for daily life and activities, are no exception, and there is a demand for improvements in fuel efficiency through measures such as reducing the weight of the vehicle body. However, simply reducing the weight of an automobile body may lead to a decrease in safety. Therefore, when reducing the weight of a vehicle body, it is necessary to ensure greater safety.

[0004] Many automobile structures are made of iron, particularly steel plates. Therefore, reducing the weight of steel plates is extremely effective in reducing the weight of the vehicle body. Furthermore, the demand for weight reduction of such steel plates is increasing not only in the automobile manufacturing industry but also in various other manufacturing industries.

[0005] In order to meet such demands, it is conceivable to simply reduce the weight of steel plates by reducing the thickness of the steel plates. However, reducing the thickness of steel plates leads to a decrease in the strength of structures constructed using the steel plates. Therefore, in recent years, research and development has been conducted on steel plates that can maintain or increase the mechanical strength of structures by increasing the mechanical strength of the steel plates, even when they are thinner than steel plates that have been used previously.

[0006] Generally, materials with high mechanical strength tend to have poor shape fixability during forming processes such as bending, etc. Therefore, when materials with high mechanical strength are processed into complex shapes, the processing itself becomes difficult.

[0007] One method for solving such problems with formability is the so-called "hot stamping method (also known as hot pressing method, hot pressing method, high-temperature pressing method, or die quenching method)." In this hot stamping method, the material to be formed is heated to a high temperature to transform (austenitize) it into a structure called austenite, and the heated, softened steel sheet is pressed to form it, and then cooled after forming. According to this hot stamping method, the material is first heated to a high temperature to soften it, so that the material can be easily press-formed. Furthermore, the quenching effect caused by cooling after forming can increase the mechanical strength of the material. Therefore, this hot stamping method can produce formed products with good shape fixability and high mechanical strength.

[0008] For example, Patent Document 1 discloses a technique for manufacturing a molded product that can be used as an automobile part by processing a galvannealed steel sheet by a hot stamping method, and Patent Document 2 discloses a technique for improving the corrosion resistance of a hot-stamped part after painting.

[0009] Japanese Patent Application Publication No. 2003-126921 International Publication No. 2009 / 131233

[0010] The hot stamping method described in Patent Document 1 requires heating the steel sheet to the Ac3 point or higher. Therefore, time must be ensured to heat the steel sheet to the desired temperature, leaving room for improvement in productivity. Furthermore, the method described in Patent Document 2 has good reactivity with the chemical conversion treatment agent applied to the steel sheet, but the amount of the applied chemical conversion treatment agent is relatively large, leaving room for economic improvement. Furthermore, hot stamped parts capable of improving corrosion resistance after painting have been studied for some time, but in recent years, even higher levels of corrosion resistance after painting have been desired. However, conventional techniques have made it difficult to realize hot stamped parts with high levels of corrosion resistance after painting that can meet such demands.

[0011] The present invention has been made in view of the above problems, and has an object to provide a hot stamped part having excellent corrosion resistance after painting.

[0012] In order to solve the above problems, the present inventors conducted extensive research and found that applying a coating containing an amphoteric oxide of a d-block element onto an Al-Fe alloy plating layer can improve the corrosion resistance of hot-stamped parts after painting. The gist of the present invention, which was completed based on this finding, is as follows.

[0013] [1] A hot-stamped part according to one aspect of the present invention is an aluminum-plated hot-stamped part comprising: a steel sheet, an Al—Fe alloy plating layer disposed on a surface of the steel sheet, an Al oxide layer disposed on the surface of the Al—Fe alloy plating layer, and a coating disposed on the surface of the Al oxide layer, wherein the coating contains an amphoteric oxide of a d-block element, and wherein Bs / Xt is 0.010 or more and 2.000 or less, where Bs is an average particle size (unit: nm) of the amphoteric oxide and Xt is a thickness (unit: nm) of the Al oxide layer. [2] In the hot-stamped part described in [1] above, the amphoteric oxide may have a rutile structure, and Bs may be 10 to 100 nm. [3] In the hot stamped part according to the above [1] or [2], the chemical composition of the steel sheet is, in mass%, C: 0.10 to 0.40%, Si: 0.01 to 0.60%, Mn: 0.50 to 3.00%, P: 0.050% or less, S: 0.020% or less, Al: 0.100% or less, Ti: 0.01 to 0.10%, B: 0.0001 to 0.0100%, N: 0.0100% or less, Cr: 0 to 1.00%, Cu: 0 to 1.000%, Ni: 0 to 2.00%, Nb: 0 to 1.00%, V: 0 to 1.00%, Mo: 0 to 1.00%, W: 0 to 1.00%, Sn: 0 to 1.00%, Ca: 0 to 0.0100%, REM: 0 to 0.3000%, and the balance may be Fe and impurities.

[0014] According to the above-described aspects of the present invention, a hot stamped part having excellent corrosion resistance after painting can be provided.

[0015] 1 is a cross-sectional view of a hot-stamped steel sheet used in a method for producing a hot-stamped part according to an embodiment of the present invention, taken along a thickness direction of the hot-stamped steel sheet;

[0016] Preferred embodiments of the present invention will be described in detail below.

[0017] (Hot-stamped part) Fig. 1 is a cross-sectional schematic view of a hot-stamped part according to this embodiment, taken along the sheet thickness direction. As shown in Fig. 1, the hot-stamped part according to this embodiment has a steel sheet, an Al-Fe alloy plating layer located on the surface of the steel sheet, an Al oxide layer X located on the surface of the Al-Fe alloy plating layer, and a coating Y located on the Al oxide layer X. The hot-stamped part is obtained by hot stamping an aluminum-plated steel sheet for hot stamping as a raw material. The hot-stamped part is also called a "hot-stamped body" or a "hot-stamped product."

[0018] An Al oxide layer X is provided on the surface of the Al—Fe alloy plating layer on the side of the coating Y. The coating Y contains an amphoteric oxide B of a d-block element. A hot stamped part having such a configuration can achieve good corrosion resistance after painting.

[0019] Here, "corrosion resistance after painting" refers to the corrosion resistance after an electrodeposition coating film is formed on a hot stamped part, as will be explained in the examples below.

[0020] <Al—Fe Alloy Plated Layer> The Al—Fe alloy plated layer in the hot stamped component according to this embodiment will be described in detail.

[0021] The hot-stamped part according to this embodiment has an Al—Fe alloy plating layer on the surface of the steel sheet. The Al—Fe alloy plating layer may be provided on the entire surface of the steel sheet, or on one or both surfaces of the steel sheet. By providing the Al—Fe alloy plating layer on the steel sheet, it is possible to further improve the corrosion resistance after painting following hot stamping. Furthermore, the presence of the Al—Fe alloy plating layer on the steel sheet can prevent the formation of iron scale due to heating during hot stamping. Iron scale contaminates heating furnaces and adheres to rolls used for transportation, which is a burden in manufacturing. Therefore, if iron scale is formed, a process such as shot blasting is required to remove the iron scale, which is economically undesirable.

[0022] The thickness of the Al—Fe alloy plating layer is 10 μm or more per side. If the thickness of the Al—Fe alloy plating layer is less than 100 μm, the corrosion resistance after painting will decrease. The thickness of the Al—Fe alloy plating layer is preferably 15 μm or more, more preferably 20 μm or more.

[0023] The upper limit of the thickness of the Al—Fe alloy plating layer is not limited. On the other hand, if the thickness exceeds 45 μm, the shear force that the plating layer receives from the mold during hot stamping and the stress during compressive deformation become large. In this case, there is a concern that the plating layer will be prone to peeling, resulting in a decrease in corrosion resistance after painting. Therefore, the thickness of the Al—Fe alloy plating layer per side is preferably 45 μm or less, and more preferably 40 μm or less.

[0024] The thickness of the Al-Fe alloy plating layer is determined by the following method. A sample embedded in resin is etched with nital so that the cross section of the Al-Fe alloy plating layer is exposed, and then observed with an SEM. The boundary between the base material and the Al-Fe alloy plating layer is determined as the position where the base material structure appears in the secondary electron image on the obtained SEM image. Next, the thickness of the Al-Fe alloy plating layer is measured at five points at 500 nm intervals, and the average value is defined as the "thickness of the Al-Fe alloy plating layer." The cross-sectional image of the Al-Fe alloy plating layer is selected from an area that does not have obvious defects such as scratches or corrosion and has not been processed.

[0025] The Al-Fe alloy plating layer contains Al, Fe, and impurities. The Al-Fe alloy plating layer may be composed of Al, Fe, and impurities. Furthermore, the Al-Fe alloy plating layer may contain, in addition to Al and Fe, one or more elements having the effect of improving corrosion resistance selected from Si, Mn, B, W, Mo, Sb, Sn, Cr, Co, Cu, Ni, Ta, Ca, Mg, Sr, Se, Re, Hf, Mg, Ca, Sr, Li, and Zn.

[0026] The Al content of the Al-Fe alloy plating layer is 30% by mass or more. The sum of the Al content and the Fe content is preferably 80% or more. More preferably, the sum of the Al content and the Fe content is 90% or more. The total content (mass%) of the corrosion resistance improving elements such as Si and Mn is preferably 0.005 to 8.0%.

[0027] The Al—Fe alloy plating layer preferably contains one or more intermetallic compounds, and more preferably consists essentially of one or more intermetallic compounds and unavoidably contained impurities.

[0028] Specific examples of intermetallic compounds constituting the Al-Fe alloy plating layer include Fe, ２ Al ５ , FeAl ２ , FeAl (also called ordered BCC), α-Fe (also called disordered BCC), Al-dissolved α-Fe, and compositions in which Si is dissolved in these compositions. Furthermore, although the detailed stoichiometric composition may not be specified, examples include ternary alloy compositions of Al-Fe-Si (12 types of τ1 to τ12 have been specified, with τ5 being particularly called the α phase and τ6 being called the β phase).

[0029] Impurities contained in the Al-Fe alloy plating layer include, for example, components of stainless steel and ceramics generally used in hot-dip plating equipment, and thermally sprayed coatings on these materials.

[0030] The presence of the intermetallic compound in the Al—Fe alloy plating layer can be confirmed by using the selected area electron diffraction function and EDS function of a field emission-transmission electron microscope (FE-TEM).

[0031] Specifically, a cross section of the Al—Fe alloy plating layer in the cross section of the hot stamped part along the sheet thickness direction is first processed into a thin section with a thickness of about 100 nm, and then the thin section is measured using an FE-TEM. If a diffraction pattern of the above compound is detected as a result of the measurement, it can be determined that the intermetallic compound is present at that point. Even if a diffraction pattern derived from crystals is not measured in the above measurement, the compound can be identified from the ratio of each element by analyzing the same point using an EDS function. Furthermore, if five points are measured randomly in the above manner and an intermetallic compound is present at all of the points, in this embodiment, it is determined that the Al—Fe alloy plating layer is substantially composed of one or more intermetallic compounds.

[0032] [Al oxide layer X] An Al oxide layer X made of Al oxide is further disposed on the surface of the Al—Fe alloy plating layer. By having the Al oxide layer X on the Al—Fe alloy plating layer, the adhesion of the coating Y (hereinafter also referred to as coating adhesion) can be improved. The presence of the Al oxide layer X on the surface of the Al—Fe alloy plating layer promotes the formation of the coating Y on the Al oxide layer X, thereby improving the coating adhesion.

[0033] The Al oxide layer X may contain Mg and / or Ca, and the Mg oxide may be a composite oxide of Mg and Al, and the Ca oxide may be a composite oxide of Ca and Al.

[0034] The thickness of the Al oxide layer X is preferably 0.05 μm or more and 3.00 μm or less. If the thickness of the Al oxide layer is less than 0.05 μm, sufficient coating adhesion may not be obtained. On the other hand, if the thickness of the Al oxide layer X exceeds 3.00 μm, the adhesion of the Al oxide layer X to the plating layer may decrease, which may lead to peeling of the electrodeposition coating formed on the hot-stamped part. The thickness of the Al oxide layer X is preferably 0.02 μm or more on average, more preferably 0.1 μm or more. The thickness of the Al oxide layer X is preferably 0.80 μm or less on average, more preferably 0.50 μm or less.

[0035] <Coating Y> The coating Y of this embodiment is a surface treatment coating provided on the Al oxide layer X. The desired post-painting corrosion resistance can be achieved by adjusting the content of metal oxides, etc., in the coating Y, as well as the film thickness, etc. Specifically, the coating Y contains an amphoteric oxide B of a d-block element, and further, when the average particle size of the amphoteric oxide B is Bs and the thickness of the Al oxide layer X is Xt, the ratio Bs / Xt is 0.010 or more and 2.000 or less.

[0036] [Amphoteric Oxide B of d-Block Elements] The coating Y contains an amphoteric oxide B of a d-block element. This improves corrosion resistance after painting. The mechanism by which the inclusion of an amphoteric oxide B of a d-block element in the coating Y improves corrosion resistance after painting is unclear, but is thought to be as follows. When a painted Al-Fe alloy-plated steel sheet is exposed to a corrosive environment, the plating metal (Al-Fe) dissolves, causing a hydrolysis reaction of ions present in the dissolved area, resulting in a decrease in pH. This shift in pH toward the acidic side creates a situation in which the metal is more likely to dissolve. In contrast, amphoteric oxides of d-block elements act as a base against HCl in an acidic environment, i.e., in the presence of an acid (e.g., HCl), and thus can suppress the shift to the acidic side caused by HCl. As a result, metal dissolution can be prevented, thereby improving corrosion resistance after painting. On the other hand, the presence of oxides generally poses a risk of localized pH increases due to reduction reactions of dissolved oxygen, etc. If the pH rises too high, the plating metal, such as Al, may dissolve as complex ions, or the coating may peel off, exposing the plating metal to a corrosive environment and further dissolution may occur. However, amphoteric oxides also act as acids, so the increase in pH can be suppressed. In other words, the inclusion of amphoteric oxides of d-block elements in the coating Y can prevent dissolution of the plating metal and improve corrosion resistance after painting.

[0037] Specifically, the "d-block elements" include scandium (Sc), titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), zinc (Zn), yttrium (Y), zirconium (Zr), niobium (Nb), molybdenum (Mo), technetium (Tc), ruthenium (Ru), rhodium (Rh), palladium (Pd), silver (Ag), Cadmium (Cd), lanthanum (La), lutetium (Lu), hafnium (Hf), tantalum (Ta), tungsten (W), rhenium (Re), osmium (Os), iridium (Ir), platinum (Pt), gold (Au), mercury (Hg), actinium (Ac), lawrencium (Lr), rutherfordium (Rf), dubnium (Db), seaborgium (Sg), bohrium (Bh), hassium (Hs), meitnerium (Mt), darmstadtium (Ds), roentgenium (Rg), and copernicium (Cn). The term "amphoteric oxide of a d-block element" refers to an oxide of one or more d-block element species with a valence of 2 to 5.

[0038] It is preferable that the amphoteric oxide B has a rutile structure. When the amphoteric oxide B has a rutile structure, even better corrosion resistance after painting can be obtained. The reason for this is unclear, but it is thought to be as follows: In a rutile structure, the anions are in a slightly distorted state. In other words, in the case of an oxide with a rutile structure, the polarity, which is the electrical bias of the oxygen atoms (oxide ions), tends to be large. Therefore, when an electrodeposition coating film with the same polarity is applied, it is thought that if the coating contains an amphoteric oxide B with a rutile structure, the electrodeposition coating film will adhere more firmly and the corrosion resistance after painting will be better.

[0039] The total amount of amphoteric oxide B in the coating Y was 0.05 g / m ２ The coating amount is preferably 0.05 g / m or more. ２ By adjusting the total amount of the amphoteric oxide B to 1.3 g / m or more, good corrosion resistance after painting can be achieved. ２ It is preferable to do the following:

[0040] The total adhesion amount of amphoteric oxide B can be determined by preparing a calibration curve of the detection intensity and adhesion amount of the d-block elements contained in amphoteric oxide B of a sample with a known adhesion amount using a fluorescent X-ray analyzer.

[0041] In the coating Y, where the average particle size of the amphoteric oxide B is Bs (nm) and the thickness of the Al oxide layer X is Xt (nm), the ratio Bs / Xt is 0.010 or more and 2.000 or less. When the ratio Bs / Xt of the average particle size Bs of the amphoteric oxide B to the thickness Xt of the Al oxide layer X is 0.010 or more and 2.000 or less, the desired corrosion resistance after painting can be achieved. In other words, when the average particle size of the amphoteric oxide B relative to the thickness Xt of the Al oxide layer X is within a certain range, the effect of the amphoteric oxide B of the d-block element described above is fully exerted, and the corrosion resistance after painting can be improved.

[0042] If Bs / Xt is less than 0.010, it becomes difficult to sufficiently improve corrosion resistance after painting. Therefore, Bs / Xt is 0.010 or more. Preferably, Bs / Xt is 0.040 or more, more preferably 0.100 or more. On the other hand, if Bs / Xt exceeds 2.000, the amphoteric oxide B becomes too large relative to the thickness of the Al oxide layer X, and the function of suppressing the above-mentioned pH decrease or increase becomes weak. As a result, corrosion resistance after painting may decrease. Therefore, Bs / Xt is 2.000 or less. Preferably, Bs / Xt is 1.500 or less, more preferably 1.000 or less.

[0043] The type and average particle size Bs of the amphoteric oxide B and the thickness Xt of the Al oxide layer X can be measured by cross-sectional analysis of the coating Y using a transmission electron microscope (TEM) as follows.

[0044] An analytical sample was cut from near the center of a 100 mm x 200 mm sample cut from a hot-stamped part, and a 2 μm x 2 μm area in the thickness direction of coating Y and the direction perpendicular to the thickness (horizontal direction of the plate) was analyzed by TEM and EDS analysis. The crystalline structure of the oxide and the presence or absence of d-block elements were determined from the electron beam diffraction image and EDS analysis. If a crystalline structure containing d-block elements was confirmed, the oxide was identified as amphoteric oxide B. Even if a crystalline structure was not confirmed, the oxide could be identified as an amphoteric oxide from the ratio of oxygen in EDS analysis.

[0045] Next, the average particle size Bs of the amphoteric oxide B is determined by calculating the average values ​​of the longest particle size (major axis) and the smallest particle size (minor axis) passing through the center of each of five amphoteric oxides B within the above-mentioned range, and then averaging the average values ​​of any five of these values ​​to obtain the average particle size Bs.

[0046] The thickness Xt of the Al oxide layer X is determined by the following method. First, within the above-mentioned region, it is confirmed that the layer is Al oxide based on an electron beam diffraction image and EDS analysis, and the thickness is measured at three points perpendicular to the thickness direction at intervals of 0.1 μm or more. The average value of the thicknesses measured at the three points is defined as the thickness Xt of the Al oxide layer X.

[0047] The hot stamped part according to this embodiment can obtain excellent corrosion resistance after painting by applying the configuration having the above-described characteristics.

[0048] <Base Steel Sheet> The steel sheet (base steel sheet) that serves as the base material of the hot-stamped component according to this embodiment, i.e., the base steel sheet of the aluminum-plated steel sheet for hot stamping that is the raw material of the hot-stamped component, is not particularly limited as long as it is a steel sheet that can be suitably used in a hot stamping method.

[0049] An example of a steel sheet that can be used as the base steel sheet for the hot stamped part according to this embodiment is a steel sheet whose chemical components, in mass %, are C: 0.10 to 0.40%, Si: 0.01 to 0.60%, Mn: 0.50 to 3.00%, P: 0.050% or less, S: 0.020% or less, Al: 0.100% or less, Ti: 0.01 to 0.10%, B: 0.0001 to 0.0100%, N: 0.0100% or less, and the balance being Fe and impurities.

[0050] Examples of the form of the base steel sheet include hot-rolled steel sheets and cold-rolled steel sheets. The chemical components of the base steel sheet will be described in detail below. In the following description of the chemical components of the base steel sheet, the notation "%" means "mass %" unless otherwise specified.

[0051] [C: 0.10 to 0.40%] C is an element effective in improving mechanical strength. When the C content is 0.10% or more, a sufficient improvement in mechanical strength is obtained. Therefore, the C content is preferably 0.10% or more. The C content is more preferably 0.20% or more. On the other hand, when the C content is 0.40% or less, the strength of the steel sheet can be hardened and improved while suppressing a decrease in elongation and reduction of area. Therefore, the C content is preferably 0.40% or less. The C content is more preferably 0.35% or less.

[0052] [Si: 0.01 to 0.60%] Like C, Si is one of the elements that improve mechanical strength. When the Si content is 0.01% or more, the strength-improving effect is fully exerted, and a sufficient improvement in mechanical strength is obtained. Therefore, the Si content is preferably 0.01% or more. The Si content is more preferably 0.10% or more. On the other hand, since Si is also an easily oxidizable element, when the Si content is 0.60% or less, a decrease in wettability during hot-dip Al plating due to the influence of Si oxides formed on the steel sheet surface layer is suppressed, and the occurrence of bare spots can be suppressed. Therefore, the Si content is preferably 0.60% or less. The Si content is more preferably 0.40% or less.

[0053] [Mn: 0.50 to 3.00%] Mn is one of the strengthening elements that strengthen steel and is also one of the elements that improve hardenability. Furthermore, Mn is an element that is effective in preventing hot embrittlement caused by the impurity S. When the Mn content is 0.50% or more, these effects are sufficiently obtained. Therefore, in order to reliably exhibit the above effects, the Mn content is preferably 0.50% or more. The Mn content is more preferably 0.80% or more. On the other hand, Mn is an austenite-forming element. When the Mn content is 3.00% or less, the amount of retained austenite phase does not become too large, and a decrease in strength can be suppressed. Therefore, the Mn content is preferably 3.00% or less. The Mn content is more preferably 1.50% or less.

[0054] [P: 0.050% or less] P is an impurity contained in steel. When the P content is 0.050% or less, it is possible to prevent the P contained in the steel sheet from segregating at the grain boundaries of the steel sheet, thereby reducing the toughness of the base material of the hot-stamped body, and thus to prevent a decrease in the delayed fracture resistance of the steel sheet. Therefore, the P content is preferably 0.050% or less, and it is preferable to reduce the P content as much as possible. The P content may be 0%. However, reducing the P content to less than 0.001% significantly increases the dephosphorization cost, which is economically undesirable. Therefore, the P content may be 0.001% or more or 0.005% or more.

[0055] [S: 0.020% or less] S is an impurity contained in steel. When the S content is 0.020% or less, the S contained in the steel sheet can be prevented from forming sulfides, which reduces the toughness of the steel sheet, and the deterioration of the delayed fracture resistance of the steel sheet can be suppressed. Therefore, the S content is preferably 0.020% or less, and it is preferable to reduce the S content as much as possible. The S content may be 0%. However, reducing the S content to less than 0.0001% significantly increases the desulfurization cost, which is economically undesirable. Therefore, the S content may be 0.0001% or more or 0.0002% or more.

[0056] [Al: 0.100% or less] Al is generally an element that has the effect of deoxidizing molten steel. Therefore, the Al content may be 0.001% or more. The Al content is preferably 0.010% or more. On the other hand, when the Al content is 0.100% or less, the increase in the Ac3 point of the steel sheet is suppressed, so that the heating temperature required to ensure the hardenability of the steel during hot stamping can be reduced, which is desirable for hot stamping production. Therefore, the Al content of the steel sheet is preferably 0.100% or less, more preferably 0.050% or less, and even more preferably 0.010% or less.

[0057] [Ti: 0.01 to 0.10%] Ti is one of the strength-enhancing elements. When the Ti content is 0.01% or more, the strength-improving effect and the oxidation resistance-improving effect are sufficiently obtained. Therefore, in order to reliably realize the above effects, the Ti content is preferably 0.01% or more. The Ti content is more preferably 0.03% or more. On the other hand, when the Ti content is 0.10% or less, for example, the formation of carbides and nitrides is suppressed, which can suppress softening of the steel and ensure sufficient mechanical strength. Therefore, the Ti content is preferably 0.10% or less. The Ti content is more preferably 0.08% or less.

[0058] [B: 0.0001 to 0.0100%] B acts during quenching to improve strength. When the B content is 0.0001% or more, this strength-improving effect is sufficiently obtained. Therefore, the B content is preferably 0.0001% or more. The B content is more preferably 0.0010% or more. On the other hand, when the B content is 0.0100% or less, the formation of inclusions is reduced, which suppresses embrittlement of the steel sheet and can suppress a decrease in fatigue strength. Therefore, the B content is preferably 0.0100% or less. The B content is more preferably 0.0040% or less.

[0059] [N: 0.0100% or less] N is an impurity contained in steel. When the N content is 0.010% or less, the formation of nitrides due to N contained in the steel sheet is suppressed, thereby suppressing a decrease in the toughness of the steel sheet. Furthermore, when B is contained in the steel sheet, the N contained in the steel sheet is prevented from bonding with B, thereby suppressing a decrease in the amount of solute B, thereby suppressing a decrease in the hardenability-improving effect of B. Therefore, the N content is preferably 0.010% or less, and it is more preferable to reduce the N content as much as possible.

[0060] Furthermore, the base steel sheet of the hot stamped part according to the present embodiment may further contain, as an optional added element, one or more of Cr, Ni, Cu, Mo, V, Nb, Sn, W, Ca, and REM.

[0061] [Cr: 0 to 1.00%] Cr is an element that improves the hardenability of steel sheet. To fully obtain this effect, the Cr content is preferably 0.01% or more. On the other hand, by setting the Cr content to 1.00% or less, the effect can be fully obtained while suppressing an increase in costs. Therefore, when Cr is contained, the Cr content is preferably 1.00% or less.

[0062] [Ni: 0 to 2.00%] Ni is an element that improves the hardenability of steel and enables the strength of hot-stamped parts to be stably ensured after quenching. To fully exert this effect, the Ni content is preferably 0.10% or more. On the other hand, by keeping the Ni content at 2.00% or less, the above effects can be fully obtained while improving economic efficiency. Therefore, when Ni is contained, the Ni content is preferably 2.00% or less.

[0063] [Cu: 0 to 1.000%] Cu is an element that improves the hardenability of steel and enables the strength of hot-stamped parts after quenching to be stably ensured. Cu also improves pitting corrosion resistance in corrosive environments. To fully exert this effect, the Cu content is preferably 0.100% or more. On the other hand, by setting the Cu content to 1.000% or less, the above effects can be fully obtained while improving economic efficiency. Therefore, when Cu is contained, the Cu content is preferably 1.000% or less.

[0064] [Mo: 0 to 1.00%] Mo is an element that improves the hardenability of steel and enables the strength of hot-stamped parts to be stably ensured after quenching. To fully exert this effect, the Mo content is preferably 0.10% or more. On the other hand, by setting the Mo content to 1.00% or less, the above effects can be fully obtained while improving economic efficiency. Therefore, when Mo is contained, the Mo content is preferably 1.00% or less.

[0065] [V: 0 to 1.00%] V is an element that improves the hardenability of steel and enables the strength of hot-stamped parts to be stably ensured after quenching. To fully exert this effect, the V content is preferably 0.10% or more. On the other hand, by setting the V content to 1.00% or less, the above effect can be fully obtained while improving economic efficiency. Therefore, when V is contained, the V content is preferably 1.00% or less.

[0066] [Nb: 0 to 1.00%] Nb is an element that improves the hardenability of steel and enables the strength of hot-stamped parts after quenching to be stably ensured. To fully exert this effect, the Nb content is preferably 0.01% or more. On the other hand, by setting the Nb content to 1.00% or less, the above-mentioned effects can be fully obtained while improving economic efficiency. Therefore, when Nb is contained, the Nb content is preferably 1.00% or less.

[0067] [Sn: 0 to 1.00%] Sn is an element that improves pitting corrosion resistance in a corrosive environment. To fully exert this effect, the Sn content is preferably 0.01% or more. On the other hand, when the Sn content is 1.00% or less, a decrease in grain boundary strength is suppressed, and a decrease in toughness can be suppressed. Therefore, when Sn is contained, the Sn content is preferably 1.00% or less.

[0068] [W: 0 to 1.00%] W is an element that improves the hardenability of steel and enables the strength of hot-stamped parts to be stably ensured after quenching. W also improves pitting corrosion resistance in corrosive environments. To fully exert this effect, the W content is preferably 0.01% or more. On the other hand, by setting the W content to 1.00% or less, the above-mentioned effect can be fully obtained while improving economic efficiency. Therefore, when W is contained, the W content is preferably 1.00% or less.

[0069] [Ca: 0 to 0.0100%] Ca is an element that has the effect of refining inclusions in steel and improving toughness and ductility after quenching. In order to fully exert this effect, the Ca content is preferably 0.0010% or more, and more preferably 0.0020% or more. On the other hand, by setting the Ca content to 0.0100% or less, the effect can be fully obtained while reducing costs. Therefore, when Ca is contained, the Ca content is preferably 0.0100% or less, and more preferably 0.004% or less.

[0070] [REM: 0 to 0.3000%] Like Ca, REM is an element that has the effect of refining inclusions in steel and improving toughness and ductility after quenching. In order to fully exert this effect, the REM content is preferably 0.0010% or more, and more preferably 0.002% or more. On the other hand, by setting the REM content to 0.3000% or less, the effect can be fully obtained while reducing costs. Therefore, when REM is contained, the REM content is preferably 0.3000% or less, and more preferably 0.2000% or less. Here, REM refers to a total of 17 elements, including Sc, Y, and lanthanoids, and the REM content refers to the total content of these elements.

[0071] The remainder other than the above components is Fe and impurities, which are components that are mixed in during the manufacturing process, for example.

[0072] An example of the chemical composition of the base steel sheet of the steel sheet for hot stamping according to this embodiment has been described in detail above.

[0073] The chemical composition of the steel sheet (base steel sheet) constituting the above-mentioned hot-stamped part can be measured by taking a test piece from the steel sheet constituting the hot-stamped part, removing the plating layer, Al oxide layer, and coating from the steel sheet, and then measuring the average element content throughout the sheet thickness using a common analytical method. For example, this can be measured using inductively coupled plasma optical emission spectrometry (ICP-AES) or inductively coupled plasma mass spectrometry. C and S can be measured using a combustion-infrared absorption method, and O and N can be measured using an inert gas fusion-infrared absorption method or an inert gas fusion-thermal conductivity method. Al can be measured by ICP-AES using the filtrate obtained by thermally decomposing a sample with acid.

[0074] (Method for manufacturing hot-stamped part) Next, a preferred method for manufacturing the hot-stamped part of this embodiment will be described. The method for manufacturing the hot-stamped part of this embodiment includes a plating step of forming an Al plating layer on the base steel sheet, a coating step of applying a surface treatment liquid to the Al plating layer to form a film Y1 for the coating Y, and a hot stamping step of hot-stamping the steel sheet for hot stamping on which the Al plating layer and the film Y1 have been formed, to obtain a hot-stamped part including an Al—Fe alloy plating layer and the coating Y.

[0075] <Plating step> Fig. 2 is a cross-sectional schematic view taken along the thickness direction of a steel sheet for hot stamping used in a method for producing a hot-stamped part. The hot-stamped part of this embodiment can be obtained by hot stamping the steel sheet for hot stamping shown in Fig. 2.

[0076] First, as shown in Figure 2, an Al plating layer is formed on a base steel sheet. Methods for forming the Al plating layer include, but are not limited to, hot-dip galvanization, electroplating, physical vapor deposition, and chemical vapor deposition. When the Al plating layer is formed by hot-dip galvanization, the bath composition may be aluminum alone or may be aluminum containing silicon. The Al plating layer is formed by diffusing Fe in the base steel sheet into the hot-dip galvanized layer during plating. Hereinafter, the steel sheet on which the Al plating layer is formed will also be referred to as a plated steel sheet.

[0077] <Coating Process> Next, a surface treatment liquid is applied to the plated steel sheet to form a film Y1 for the coating Y. The coating Y according to this embodiment can be formed by applying a surface treatment liquid containing a specific amphoteric oxide, prepared by an appropriate method, to the surface of the Al plating layer to form the film Y1 for the coating Y, and then optimizing the conditions for the hot stamping process described below. As a result, in the coating Y according to this embodiment, the amphoteric oxide can be dispersed throughout the coating Y. The dispersed presence of the amphoteric oxide throughout the coating Y reduces surface irregularities throughout the coating, and as a result, the coating Y can exhibit uniform post-painting corrosion resistance throughout the coating Y.

[0078] When applying a surface treatment liquid to the entire surface of a plated steel sheet, an organic or inorganic surface treatment liquid containing an amphoteric oxide of the d-block element described above is used. This surface treatment liquid is applied to the entire surface of the steel sheet using a roll coater, curtain coater, or inkjet, and then the volatile components in the surface treatment liquid are dried, thereby forming a film Y1 for the coating Y. Inkjet application is particularly preferred because it allows for continuous change in film thickness.

[0079] However, simply applying a surface treatment solution containing amphoteric oxides B of d-block elements does not result in amphoteric oxides B being dispersed throughout the entire film Y1, and the hot-stamped part does not exhibit the post-painting corrosion resistance required for the hot-stamped part. In other words, applying a surface treatment solution containing amphoteric oxides B of d-block elements and then heating and drying the treatment solution on the steel sheet under appropriate conditions can disperse amphoteric oxides B throughout the entire film Y1, thereby improving the post-painting corrosion resistance of the hot-stamped part. Specifically, the dispersibility of amphoteric oxides B can be evaluated from the results of mapping the d-block elements on the steel sheet surface at 3000x magnification. In other words, the ratio of the average intensity of a 0.3mm square region where the intensity of the d-block elements is lowest to the average intensity of a 0.3mm square region where the intensity of the d-block elements is lowest is calculated within a 2mm square field of view. If this ratio is 50 times or less, the dispersibility of amphoteric oxides B throughout the entire film Y1 is determined to be good.

[0080] When the thickness of the plated steel sheet is F [mm], the ratio of the wet film thickness Zt [μm] of the surface treatment solution to the thickness At [μm] of the Al—Fe alloy plating layer is a, the maximum sheet temperature reached during drying of the surface treatment solution is Tmax [° C.], the time required for the sheet temperature to reach 50° C. from 25° C. is tm [s], and the time required for the sheet temperature to reach Tmax from 50° C. is tn [s], the surface treatment solution is dried so that the PYS represented by formula (1) is 190 or more and 36,000 or less.

[0081] PYS=(Tmax+273.15)×(0.8tm+tn) / (a×F)…Equation (1)

[0082] If the PYS is less than 190, the amphoteric oxides will aggregate due to insufficient heating, and will not be able to be dispersed throughout the film Y1, making it impossible to improve the corrosion resistance of the hot-stamped part after painting. On the other hand, if the PYS is more than 36,000, the amount of heating will be too great, and the film will be formed before the oxides can be dispersed throughout the film Y1, making it impossible to improve the corrosion resistance of the hot-stamped part.

[0083] Here, the wet film thickness Zt is defined as follows: As shown in the following formula (2), the wet film thickness Zt is calculated by dividing the dried film thickness Yt [μm] by the solid content concentration Cq (mass%) in the surface treatment liquid, multiplying this by 100, and then further multiplying this by the specific gravity D [g / cm ３ Although the specific gravity D of the surface treatment solution does not necessarily coincide with the specific gravity of the solid content, the above value can be used as a substitute. If the specific gravity D of the surface treatment solution is unknown, it is assumed that 1 g / cm ３ Let's say.

[0084] Zt=100×Yt / (Cq×D)…Formula (2)

[0085] In addition to the amphoteric oxide, the surface treatment solution may contain various binder components, additives, and silica.

[0086] [Binder Component] The binder component that can be contained in the coating Y according to this embodiment is preferably a water-dispersible or water-soluble resin. The content of the binder component selected from water-dispersible or water-soluble resins is preferably 40% by volume or more relative to the total volume of the coating Y.

[0087] As the binder component selected from water-dispersible or water-soluble resins, various known resins exhibiting water dispersibility or water solubility can be used. Examples of such water-dispersible or water-soluble resins include polyurethane resins, polyester resins, acrylic resins, epoxy resins, fluororesins, polyamide resins, polyolefin resins, and polymer compounds obtained by hydrolysis and condensation polymerization of silane coupling agents. It is more preferable that the binder component is one or more selected from the group consisting of polyester resins, polyurethane resins, polyolefin resins, acrylic resins, epoxy resins, fluororesins, and polyamide resins. When multiple resins are used as the binder component, the total content of the multiple resins used is treated as the content of the binder component.

[0088] When a polyurethane resin is used as the binder component, the polyurethane resin is preferably a polyether-based resin. This is because, compared to polyester-based polyurethane resins, polyether-based polyurethane resins can prevent hydrolysis caused by acids or alkalis. Furthermore, compared to polycarbonate-based polyurethane resins, the formation of a hard and brittle film can be suppressed, ensuring adhesion during processing and corrosion resistance of the processed part.

[0089] Whether or not a polyurethane resin is contained can be determined by detecting a peak at 3330 cm in an infrared absorption spectrum obtained by infrared spectroscopy. －１ (NH telescopic), 1730cm －１ (C=O expansion / contraction), 1530cm －１ (CN), 1250cm －１ This can be determined based on whether the characteristic absorption of (C—O) is observed.

[0090] The polyurethane resin content can be determined by the following method. First, a calibration curve showing the relationship between the polyurethane resin content and the characteristic absorption intensity is created using samples with a known polyurethane resin content. The content can then be determined from the obtained characteristic absorption intensity.

[0091] For resins other than the polyurethane resins described above, it is possible to determine whether or not they are contained and the amount of content thereof, in the same way as for the polyurethane resins described above, by focusing on the characteristic absorption derived from the functional groups specific to each resin.

[0092] [Additives] The coating Y according to this embodiment can contain various additives, such as a leveling agent, a water-soluble solvent, a metal stabilizer, an etching inhibitor, etc., as additives used in preparing the treatment liquid before coating formation, within a range that does not impair the effects of the present invention.

[0093] The leveling agent may be a nonionic or cationic surfactant, such as a polyethylene oxide or polypropylene oxide adduct, or an acetylene glycol compound.

[0094] Examples of the water-soluble solvent include alcohols such as ethanol, isopropyl alcohol, t-butyl alcohol, and propylene glycol; cellosolves such as ethylene glycol monobutyl ether and ethylene glycol monoethyl ether; esters such as ethyl acetate and butyl acetate; and ketones such as acetone, methyl ethyl ketone, and methyl isobutyl ketone.

[0095] Examples of metal stabilizers include chelating compounds such as EDTA (ethylenediaminetetraacetic acid) and DTPA (diethylenetriaminepentaacetic acid).

[0096] Examples of etching inhibitors include amine compounds such as ethylenediamine, triethylenepentamine, guanidine, and pyrimidine.

[0097] The content of the additives can also be measured after preparing a calibration curve using a fluorescent X-ray analyzer, in the same manner as in the case of metal oxides.

[0098] Furthermore, for the purpose of reducing the temperature rise time during heating in hot stamping, carbon-derived pigments such as carbon black, graphite, and soot may be added as additives that enhance absorption of radiant heat.

[0099] [Silica] The coating Y according to this embodiment may contain silica. More specifically, the content of silica in the coating Y according to this embodiment is 0 to 0.3 g / m ２ Silica is 0.3 g / m ２ If the content of silica exceeds 0.3 g / m, the temperature rise effect during hot stamping is not so great and the cost is high, which is not preferable from the economic point of view. Furthermore, silica is a substance with low electrical conductivity. Therefore, if the content of silica exceeds 0.3 g / m, ２ If the content exceeds 100%, it is not preferable in terms of weldability after hot stamping. When silica is contained, the smaller the silica content of the coating Y, the better. The silica content of the coating Y is more preferably 0.10 g / m ２ More preferably, it is 0.05 g / m or less. ２ The following is the result.

[0100] <Hot stamping step> In the hot stamping step, the plated steel sheet having the film Y1 obtained in the above-mentioned film coating step is first subjected to various processes such as cutting and punching by press to obtain a steel sheet for hot stamping. Note that a steel sheet for hot stamping can also be obtained by previously cutting or punching by press the plated steel sheet and then providing the film Y1 thereto.

[0101] Next, the steel sheet for hot stamping is hot stamped. Examples of heating devices that can be used include an electric heating furnace, a gas heating furnace, a far-infrared furnace, and a conventional heating device equipped with an infrared heater. The specific heating conditions during hot stamping are not particularly limited. The heating device and other components may be appropriately controlled, and the heating atmosphere may be air. The Al oxide layer formed on the surface of the Al—Fe alloy plating layer after hot stamping has a dense structure. Therefore, the hot-stamped component according to this embodiment has a slower time for corrosive factors such as saltwater and oxygen to reach the surface of the Al—Fe alloy plating layer than components having an Al oxide layer obtained by other methods, resulting in excellent corrosion resistance after painting. Other methods for forming an Al oxide layer on the surface of an Al—Fe alloy plating layer include, for example, vapor deposition, but it is difficult to form an Al oxide layer on the surface of an Al—Fe alloy plating layer without defects and with excellent adhesion.

[0102] The heated steel sheet for hot stamping is then formed and cooled to obtain a hot-stamped part according to this embodiment. The part heated to or above the Ac3 point temperature at which the metal structure transforms into the austenite phase is quenched to increase its strength. This makes it possible to obtain a hot-stamped part with improved strength due to quenching. Note that the Al oxide layer in this embodiment is formed on the surface of the Al-Fe alloy plating layer by the hot stamping process.

[0103] By setting the hot stamping conditions as follows, the thickness of the Al—Fe alloy plating layer can be controlled to 10.0 to 60.0 μm, and the thickness Xt of the Al oxide layer X can be controlled to 0.05 to 3.00 μm. That is, the average heating rate HR1 from 25° C. to 700° C. at the center of the sample (the center of the hot stamping steel sheet) during hot stamping is set to a range of 3.0° C. / s to 6.0° C. / s, and the average heating rate HR2 from 700° C. to reach the holding temperature HST is set to a range of 0.8° C. / s to 3.1° C. / s. The holding temperature HST is preferably set to a range of 890° C. to 945° C., and may be set to a temperature 5 to 15° C. lower than the target final temperature.

[0104] Furthermore, the time from reaching the holding temperature HST to the start of cooling is set to 720 seconds to 1785 seconds, the average cooling rate CR1 when decreasing the temperature from the holding temperature HST to 500°C during cooling is set to 51 to 91°C / s, and the average cooling rate CR2 when decreasing the temperature from 500°C to 70°C is set to 16 to 61°C / s. If the time from reaching the holding temperature HST to the start of cooling is less than 720 seconds, the thickness of the Al oxide layer may be insufficient, and sufficient corrosion resistance may not be obtained. On the other hand, if this time exceeds 1785 seconds, the thickness of the Al oxide becomes too thick, resulting in reduced spot weldability between hot-stamped parts. Furthermore, if the average cooling rate CR1 when decreasing the temperature from the holding temperature HST to 500°C during cooling is less than 51°C / s, cooling may take a long time, and productivity may decrease. Furthermore, if the average cooling rate CR1 exceeds 91°C / s, the hot-stamped part is cooled rapidly, which may result in a decrease in adhesion between the Al oxide layer and the coating located on the surface of the Al oxide layer. Furthermore, if the average cooling rate CR2 from 500°C to 70°C is less than 16°C / s, cooling takes a long time, which may result in a decrease in productivity. If the average cooling rate CR2 exceeds 61°C / s, the hot-stamped part is cooled rapidly, which may result in a decrease in adhesion between the Al oxide layer and the coating located on the surface of the Al oxide layer.

[0105] The heating method for achieving the above heating rate is not particularly limited, and may be an electric resistance furnace that utilizes radiant heat, an infrared heating furnace, or the like, and the atmosphere may be air or an atmospheric gas with an oxygen concentration of 20% to 50%. In order to achieve the above cooling rate, in addition to cooling using a mold, the cooling rate may be increased by bringing the sample into contact with a liquid such as water.

[0106] Furthermore, in order to set the average particle size Bs of the amphoteric oxide B to 10 to 100 nm, the amphoteric oxide B having a particle size of 10 to 30 nm is used when preparing the surface treatment solution, and the above-mentioned parameter PYS when forming the film Y1 is set to 190 to 36,000, thereby suppressing aggregation of the oxides and achieving this.

[0107] Furthermore, a Bs / Xt ratio of 0.010 to 2.000 can be achieved by controlling the parameter PYS within a predetermined range and setting the total time (sec) from 500°C to the holding temperature HST and the holding time HSt (sec) at the holding temperature HST to 500 to 1400 seconds. In other words, by optimizing the conditions of the hot stamping process, it is possible to obtain a coating Y having an amphoteric oxide that satisfies the Bs / Xt ratio of 0.010 to 2.000.

[0108] Examples of the present invention will be described below, but the conditions in the examples are merely examples adopted to confirm the feasibility and effects of the present invention, and the present invention is not limited to these examples. Various conditions can be adopted in the present invention as long as they do not deviate from the gist of the present invention and the object of the present invention is achieved.

[0109] As the base steel sheet, it is preferable to use a steel sheet that can provide the desired mechanical properties (meaning various properties related to mechanical deformation and fracture, such as tensile strength, yield point, elongation, reduction of area, hardness, impact value, fatigue strength, etc.) after hot stamping. The chemical compositions of the base steel sheets before plating that were used for the steel sheets for hot stamping shown in the following examples are shown in Table 1 below.

[0110]

[0111] Aluminum-plated steel sheets for hot stamping (steel sheet symbols A1 to A13) were produced by applying an aluminum plating and a surface treatment film shown in Table 2 to base steel sheets (steel Nos. S1 to S11) having the chemical compositions shown in Table 1. More specifically, for each base steel sheet, a steel sheet measuring 100 mm in width, 200 mm in length, and 1.4 mm in thickness was prepared, and after being plated with an Al-10% by mass Si plating by a hot-dip galvanizing method, a surface treatment film was applied over the entire surface of one or both sides.

[0112] In addition to the water-based urethane resin binder, Sc ２ O ３ , TiO ２ , V ２ O5, Cr ２ O ３ , MnO ２ , Fe ２ O３ , Co ２ O ３ , NiO, CuO, ZrO ２ , W ２ O ３ A surface treatment solution containing at least one amphoteric oxide B compound such as the above was applied to both surfaces of a base steel sheet using a bar coater and dried to form film Y1. Some of the surface treatment solutions further contained silica and carbon black in addition to the above components. The film thickness Yt of film Y1 was set to a range of 0.4 to 4.6 μm.

[0113]

[0114] A thermocouple was then connected to the center of the steel sheet with the Y1 coating to enable temperature measurement. The steel sheet was then heated in an electric heating furnace, with the furnace temperature set so that the holding temperature HST shown in Table 3 was 890 to 944°C. An average heating rate HR1 from 25 to 700°C and an average heating rate HR2 from 700°C to the HST were controlled. After the Y1 coating steel sheet reached the HST temperature and the holding time HSt elapsed, the steel sheet was removed from the heating furnace. After reaching the HST temperature, the time until the start of cooling, the average cooling rate CR1 from the HST temperature to 500°C, and the average cooling rate CR2 from 500°C to 70°C were controlled, and a hot stamped part was obtained.

[0115]

[0116] The coating corrosion resistance after hot stamping was investigated for samples prepared so that the elements, average particle diameter Bs, and structure of the amphoteric oxide B in the Al—Fe alloy plating layer, Al oxide layer X, and coating Y, and the ratio Bs / Xt of the average particle diameter Bs to the thickness Xt of the Al oxide layer X, were set to predetermined values. The evaluation methods for each evaluation item were as follows.

[0117] [Corrosion Resistance After Hot Stamping (Corrosion Resistance After Painting)] The corrosion resistance after painting was evaluated according to the method specified in JASO M609 established by the Society of Automotive Engineers of Japan. Specifically, the evaluation was performed using the following method. A sample measuring 100 mm in length and 50 mm in width was taken from a position 20 mm away from the end of the hot stamped part. A 10 mm long scratch was made on the surface of the sample, which had a 15 μm thick electrodeposition coating, using a cutter, and the sample was subjected to a corrosion test. After 240 cycles, the sample was removed and the width of the paint blister from the scratch (maximum value on one side) was measured. A rating of A or B or higher was considered a pass.

[0118] (Rating) A: Blister width less than 2 mm B: Blister width 2 mm or more and less than 4 mm C: Blister width 4 mm or more

[0119] Inventive Examples C1 to C11, which satisfied the range of the present invention, exhibited excellent corrosion resistance after painting of the hot stamped parts, while Comparative Examples c1 to c8, which did not satisfy the range of the present invention, exhibited inferior corrosion resistance after painting of the hot stamped parts.

[0120] Furthermore, in Example C2 in which the amphoteric oxide B was of the rutile type, the hot stamped parts had even better corrosion resistance after painting.

[0121] In Comparative Examples c1 and c2, after the surface treatment solution was applied to the surface of the aluminum-plated steel sheet, the parameter PYS when dried exceeded 36,000, and the ratio Bs / Xt of the average particle size Bs of the amphoteric oxide B to the thickness Xt of the Al oxide layer X was less than 0.010 or exceeded 2.000, resulting in poor corrosion resistance after painting (rating C).

[0122] In Comparative Example c3, the time from 500°C to the holding temperature and the time at the holding temperature were short, so the ratio Bs / Xt was less than 0.010, and the corrosion resistance after hot stamping was poor (rating C).

[0123] In Comparative Example c4, the average heating rate from 25°C to 700°C during hot stamp heating exceeded 6.0°C / sec, so the ratio Bs / Xt exceeded 2.000, and in Comparative Example c5, the average heating rate from 25°C to 700°C during hot stamp heating was less than 3.0, so the ratio Bs / Xt was less than 0.010, and both were poor in corrosion resistance after painting (rating C).

[0124] In Comparative Example c6, the average heating rate from 700°C to the holding temperature during hot stamp heating was less than 0.8°C / sec, so the ratio Bs / Xt was less than 0.010, and in Comparative Example c7, the average heating rate from 700°C to the holding temperature during hot stamp heating exceeded 3.1, so the ratio Bs / Xt was less than 0.010, and both were found to have poor corrosion resistance after painting (rating C).

[0125] In Comparative Example c8, the time from 500°C to the holding temperature and the time at the holding temperature were too long, so the ratio Bs / Xt was less than 0.010, and the corrosion resistance after hot stamping was poor (rating C).

[0126] In both Comparative Examples c9 and c10, when the surface treatment solution applied to the surface of the plated steel sheet was dried, the PYS value, which is a parameter for the drying conditions, was less than 190. As a result, aggregation of the amphoteric oxides progressed due to insufficient heating, and the amphoteric oxide B could not be dispersed throughout the entire film Y1, resulting in a ratio Bs / Xt of less than 0.010 and poor corrosion resistance after hot stamping (rating C).

[0127]

[0128] According to the above aspects of the present invention, an aluminum-plated hot-stamped part having excellent corrosion resistance after painting can be provided. Therefore, the obtained hot-stamped part can be suitably used as an automotive part, etc., and therefore has high industrial applicability.

Claims

1. A hot stamped part comprising: a steel sheet; an Al-Fe alloy plating layer located on a surface of the steel sheet; an Al oxide layer located on the surface of the Al-Fe alloy plating layer; and a coating located on the surface of the Al oxide layer, wherein the coating contains an amphoteric oxide of a d-block element, and where Bs is the average particle size of the amphoteric oxide in nm and Xt is the thickness of the Al oxide layer in nm, Bs / Xt is 0.010 or more and 2.000 or less.

2. The hot stamped part according to claim 1, wherein the amphoteric oxide B has a rutile structure, and the Bs is 10 to 100 nm.

3. The chemical composition of the steel plate is, in mass%, C: 0.10 to 0.40%, Si: 0.01 to 0.60%, Mn: 0.50 to 3.00%, P: 0.050% or less, S: 0.020% or less, Al: 0.100% or less, Ti: 0.01 to 0.10%, B: 0.0001 to 0.0100%, N: 0.0100% or less, Cr: 0 to 1.00%, Cu: 0 to 1.000%, Ni: 0 to 2.00%, Nb: 0 to 1.00%, V: 0 to 1.00%, Mo: 0 to 1.00%, W: 0 to 1.00%, Sn: 0 to 1.00%, The hot stamped part according to claim 1 or 2, characterized in that it contains: Ca: 0 to 0.0100%, REM: 0 to 0.3000%, and the balance: Fe and impurities.

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