Specification
Title of invention: Aluminum-based plated steel sheet, method for manufacturing aluminum-based plated steel sheet, and method for manufacturing automobile parts
Technical field
[0001]
　The present invention relates to an aluminum-based plated steel sheet, a method for manufacturing an aluminum-based plated steel sheet, and a method for manufacturing an automobile part.
　The present application claims priority based on Japanese Patent Application No. 2017-233620 filed in Japan on December 5, 2017, the contents of which are incorporated herein by reference.
Background technology
[0002]
　In recent years, in applications of automobile steel sheets (for example, automobile pillars, door impact beams, bumper beams, etc.), a steel sheet that has both high strength and high formability has been desired. TRIP (Transformation Induced Plasticity) steel utilizing the martensitic transformation of retained austenite is one of the steel sheets that have both high strength and high formability. With such TRIP steel, it is possible to manufacture a high-strength steel plate having excellent formability and strength of about 1000 MPa class. However, even when TRIP steel is used, it is difficult to secure formability while achieving even higher strength (for example, ultrahigh strength of 1500 MPa or more), and the shape fixability after forming is poor. There is a problem that the dimensional accuracy of the molded product is poor.
[0003]
　While forming using TRIP steel as described above is a method of forming at around room temperature (so-called cold press method), hot stamping (hot press, hot press, die quench, Also called press quench etc.) There is a construction method. This hot stamping method secures formability by hot pressing immediately after heating a steel sheet to an austenite region of 800° C. or higher, and quenches the material by quenching with a mold while holding the bottom dead center. This is a method of manufacturing a component that realizes a desired high-strength material after pressing. According to this method, it is possible to obtain an automobile part that is also excellent in shape fixability after molding.
[0004]
　The hot stamping method is promising as a method for molding an ultrahigh-strength member, but it is generally said to have two major problems. The first problem is a problem regarding the scale during heating. Hot stamping usually has a step of heating a steel sheet in the atmosphere, and an oxide (scale) is generated on the surface of the steel sheet during such heating. Therefore, a step of removing the scale is required, and the productivity is reduced. The second problem is a problem related to a decrease in productivity with heating time. In the case of furnace heating in an electric furnace or a gas furnace, it usually takes 180 to 290 seconds before heating because the average temperature rising rate when heating from room temperature to about 900 °C is 3 to 5 °C/second. However, the number of parts that can be molded by the hot stamping method was about 1 to 3 parts/minute, which was extremely low in productivity.
[0005]
　As a technique for improving the above-mentioned problem relating to the scale, which is the first problem, and enhancing the corrosion resistance of a hot stamped product, for example, in Patent Documents 1 to 3 below, aluminum-based plating is used as a steel plate for hot stamping. A technique for suppressing the generation of scale during heating by using a steel plate has been proposed.
[0006]
　Further, as a technique for improving the heating efficiency of the aluminum plating in order to improve the problem of the productivity reduction due to the heating time, which is the second problem described above, for example, in Patent Document 4 and Patent Document 5 below, A technique has been proposed that focuses on the fact that the rate of temperature increase increases when the alloying reaction of Al and Fe that occurs during heating reaches the surface.
[0007]
　More specifically, in Patent Document 4 below, the problem of heating efficiency is solved by reducing the thickness of the plating layer of aluminum plating.
[0008]
　Further, in the following Patent Document 5, before hot stamping, a coil of an aluminum-plated steel sheet is preliminarily held at a temperature equal to or lower than the melting point of the aluminum plating for a certain period of time in a box-type annealing furnace to promote an alloying reaction of Al and Fe. This solves the problem of heating efficiency.
Prior art documents
Patent literature
[0009]
Patent Document 1: Japanese Unexamined Patent Publication No. Hei 9-202953
Patent Document 2: Japanese Unexamined
Patent Publication No. 2003-181549 Japanese Patent Unexamined Publication No. 2003-49256 Japanese Patent Publication
No. 2010-70800 JP
Patent Document 5: Japanese Patent Application 2010-519842 Patent Publication
Summary of the invention
Problems to be Solved by the Invention
[0010]
　As described above, an aluminum-based plated steel sheet is considered promising as a material that solves the problem of scale during hot stamping and also has corrosion resistance.
[0011]
　However, in the techniques disclosed in Patent Documents 1 to 3, the scale removing step is omitted by suppressing the generation of scale during heating, which is the first problem, and the productivity is improved. Although it is possible to solve the problem, the problem of the decrease in productivity with heating time, which is the second problem, cannot be solved.
[0012]
　Further, although the technique disclosed in Patent Document 4 can solve the problem of productivity decrease due to heating time, which is the second problem, the suppression of scale, which is the first problem, becomes insufficient. As a result, it becomes necessary to provide a scale removing step, which reduces productivity. In addition, since the thickness of the plating layer is thin, there is a problem that the corrosion resistance decreases.
[0013]
　Further, in the technique disclosed in Patent Document 5, although the heating time in hot stamping can be shortened, a process of preheating a coil of an aluminum-plated steel sheet in a box-type annealing furnace is added. Will increase. The Al—Fe intermetallic compound formed by the alloying reaction of Al and Fe generally has high hardness. Therefore, there is a problem that the plating is peeled off and the corrosion resistance is deteriorated in the case of being subjected to extension/bending processing at the time of skin pass rolling or coil winding, or at a portion subjected to processing such as an end surface at the time of blank cutting before hot stamping.
[0014]
　Thus, there is a need for an aluminum-based plated steel sheet capable of further improving the productivity due to the heating time of the hot stamping method without increasing the number of manufacturing steps while achieving excellent corrosion resistance. It is in.
[0015]
　Therefore, the present invention has been made in view of such a problem, and the object thereof is to achieve excellent corrosion resistance while improving productivity due to the heating time of the hot stamping method without increasing the number of manufacturing steps. An object of the present invention is to provide an aluminum-based plated steel sheet, a method for manufacturing an aluminum-based plated steel sheet, and a method for manufacturing an automobile part that can be further improved.
Means for solving the problem
[0016]
　The gist of the present invention is as follows.
(1) An aluminum-based plated steel sheet according to one aspect of the present invention is located between a base material, an aluminum-based plating layer located above the base material, and the base material and the aluminum-based plating layer, 1. An intermetallic compound layer containing an intermetallic compound of Al and Fe, wherein the base material is C: 0.15% or more and 0.50% or less, Si: 0.010% or more and 2. 000% or less, Mn: 0.3% or more and 5.0% or less, Cr: 0.010% or more and 2.000% or less, P: 0.1% or less, S: 0.1% or less, Al: 0. 5% or less, B: 0.0002% or more and 0.0100% or less, N: 0% or more and 0.01% or less, W: 0% or more and 3% or less, Mo: 0% or more and 3% or less, V:0% 2% or less, Ti: 0% or more and 0.5% or less, Nb: 0% or more and 1% or less, Ni: 0% or more and 5% or less, Cu: 0% or more and 3% or less, Sn: 0% or more and 0. 1% or less and Sb: 0% or more and 0.1% or less, the balance consisting of Fe and impurities, and the aluminum-based plating layer has an average of 80% by weight or more and 97% by weight or less Al and 3 Mass% or more and 15 mass% or less Si, 0 mass% or more and 5 mass% or less Zn, 0 mass% or more and 5 mass% or less Fe, and 0 mass% or more and 3 mass% or less of Mg and Ca in total. One or more selected from the group consisting of and impurities such that the total amount is 100% by mass, and the average value of the thickness of the intermetallic compound layer is 2 μm or more and 10 μm or less. The maximum value of the layer thickness is 10 μm or more and 25 μm or less, and the standard deviation of the thickness of the intermetallic compound layer is 2 μm or more and 10 μm or less.
(2) The aluminum-plated steel sheet according to (1) above has Si oxide, Mn within a range of 5 μm from the interface between the base metal and the intermetallic compound layer toward the center of the base metal. You may have the oxide containing area|region which contains 1 mass% or more and 10 mass% or less in total of 1 or more types selected from the group which consists of an oxide, Cr oxide, and B oxide.
(3) In the aluminum-plated steel sheet according to (1) or (2), the aluminum-plated layer has a total of 0.01% by mass or more of at least one selected from the group consisting of Mg and Ca. You may contain less than mass %.
(4) A method for manufacturing an aluminum-plated steel sheet according to another aspect of the present invention is the method for manufacturing an aluminum-plated steel sheet according to any one of (1) to (3) above, wherein a steel slab is used. Hot rolling to obtain a hot rolled steel sheet, winding the hot rolled steel sheet, pickling the hot rolled steel sheet, cold rolling the hot rolled steel sheet to obtain a cold rolled steel sheet And a step of continuously performing annealing treatment and hot dip aluminum plating treatment on the cold-rolled steel sheet, wherein the components of the steel slab are C: 0.15% or more and 0.50% or less by mass %, Si: 0.010% to 2.000%, Mn: 0.3% to 5.0%, Cr: 0.010% to 2.000%, P: 0.1% or less, S:0 1% or less, Al: 0.5% or less, B: 0.0002% or more and 0.0100% or less, N: 0% or more and 0.01% or less, W: 0% or more and 3% or less, Mo: 0% Above 3% or less, V: 0% to 2%, Ti: 0% to 0.5%, Nb: 0% to 1%, Ni: 0% to 5%, Cu: 0% to 3% Hereinafter, Sn: 0% or more and 0.1% or less, and Sb: 0% or more and 0.1% or less, the balance consisting of Fe and impurities, and the steel sheet winding temperature CT in the winding is 700° C. 850 °C or less, the arithmetic mean roughness Ra of the surface of the cold rolled steel sheet after the cold rolling is 0.5 µm or more and 5 µm or less, and the plating bath in the hot dip aluminum plating treatment is 80% by mass or more. 97 mass% or less Al, 3 mass% or more and 15 mass% or less Si, impurities, 0 mass% or more and 5 mass% or less Zn, and 0 mass% or more and 5 mass% or less Fe in total 0 It is contained in an amount of 100% by mass or more and 1% or more selected from the group consisting of Mg and Ca in an amount of 3% by mass or more and 3% by mass or less.
(5) In the method for producing an aluminum-plated steel sheet according to (4) above, in the annealing treatment, the steam partial pressure P H2O and the hydrogen partial pressure P H in an annealing atmosphere in the range of a plate temperature of 650° C. to 900° C. H2 relation log (P with H2 O / P H2 value of) the -3 -0.5, the annealing time in the plate temperature may be 500 seconds or less than 60 seconds.
(6) In the method for producing an aluminum-based plated steel sheet according to (4) or (5), the plating bath contains 0.01% by mass in total of one or more kinds selected from the group consisting of Mg and Ca. The content may be 3% by mass or less.
(7) A method of manufacturing an automobile part according to another aspect of the present invention includes a step of heating the aluminum-plated steel sheet according to any one of (1) to (3) above to 850° C. or higher, The method includes the steps of press-molding the aluminum-based plated steel sheet with a mold and quenching the aluminum-based plated steel sheet with the mold at a cooling rate of 30° C./s or more.
Effect of the invention
[0017]
　According to the present invention, while achieving excellent corrosion resistance, it is possible to further improve the productivity due to the heating time of the hot stamping method without increasing the number of manufacturing steps, an aluminum-based plated steel sheet, an aluminum-based plating A method for manufacturing a steel plate and a method for manufacturing automobile parts can be provided.
Brief description of the drawings
[0018]
FIG. 1 is a schematic diagram showing an example of a configuration of an aluminum-based plated steel sheet according to an embodiment of the present invention.
FIG. 2 is a schematic view showing another configuration example of the aluminum-plated steel sheet according to the same embodiment.
FIG. 3 is an example of a secondary electron image obtained by observing a cross section near the surface of the aluminum-plated steel sheet according to the embodiment with a scanning electron microscope (SEM).
FIG. 4 is an example of a secondary electron image obtained by observing a cross section near the surface of a conventional aluminum-plated steel sheet with an SEM.
[FIG. 5] Regarding the intermetallic compound layer of the aluminum-plated steel sheet according to the embodiment, based on the secondary electron image of the cross section near the surface, the average value of the thickness at each location, the maximum value of the thickness, and the standard deviation of the thickness This is an actual measurement example.
MODE FOR CARRYING OUT THE INVENTION
[0019]
　The present inventors have conducted extensive studies to solve the above problems. Then, the present inventors have focused on the rate of temperature rise during heating as a factor that impedes the heating efficiency of aluminum-based plating. As a result, it was found that the rate of temperature rise was particularly slow from room temperature to about 750°C, while the rate of temperature rise was higher at 750°C or higher. Although the cause of this phenomenon is not clear, the temperature at which the temperature rising rate changes is a value close to 660° C., which is the melting point of metallic Al, and is therefore estimated as follows. That is, it is considered that, in addition to originally having a low emissivity, Al melts in the temperature range from the melting point of the plating to 750° C., whereby the plating surface is smoothed and the emissivity is further lowered. On the other hand, in the temperature range of 750° C. or higher, the alloying reaction between Al and Fe is promoted, whereby an intermetallic compound of Al and Fe is formed up to the surface of the aluminum-based plating, and as a result, the emissivity is improved. However, it is considered that the absorption of heat is improved. As will be described later, the “intermetallic compound of Al and Fe” includes not only Fe—Al based intermetallic compounds but also elements other than Fe and Al, such as Fe—Al—Si based intermetallic compounds. The concept also includes the intermetallic compound contained.
[0020]
　The fact that the emissivity is improved when the intermetallic compound of Al and Fe is formed includes the following phenomena. Regarding the surface appearance of the aluminum-based plating, the appearance is silver-white with metallic luster before heating, whereas when an intermetallic compound of Al and Fe is formed up to the surface of the aluminum-based plating, the appearance becomes dark. It changes to a tinged color and loses metallic luster.
[0021]
　Based on the above findings, the present inventors have formed a large amount of an intermetallic compound of Al and Fe before hot stamping during aluminum-based plating so that Al and Fe can reach the surface of the aluminum-based plated in a short time. It was considered effective to improve the heating rate of the steel sheet during hot stamping and increase the heating efficiency by advancing the alloying reaction with. Here, the Zenzimer type hot-dip aluminum plating method, which is one of the hot-dip aluminum plating methods, can form an intermetallic compound layer of Al and Fe at the interface between the aluminum-based plating layer and the base material. Therefore, it was considered that the use of the Sendzimer type hot dip aluminum plating method enables a large amount of the intermetallic compound layer containing the intermetallic compound of Al and Fe as described above to be formed before the hot stamping. ..
[0022]
　On the other hand, since the intermetallic compound of Al and Fe is hard, if a large amount of the intermetallic compound of Al and Fe is formed, the intermetallic compound layer is likely to be broken, causing a problem in plating adhesion. .. Therefore, the present inventors have further studied the solution to this problem. As a result, with respect to the thickness of the intermetallic compound layer containing the intermetallic compound of Al and Fe, it is possible to suppress the overall thickness from becoming excessively thick, and locally form a thick portion at a constant ratio. It was found that the alloying reaction between Al and Fe can be advanced to the surface of the aluminum-based plating in a short time while ensuring the plating adhesion of the aluminum-based plated steel sheet before hot stamping. Thereby, the problem of plating adhesion can be solved and the heating efficiency can be further promoted.
[0023]
　In general, the thinner the steel plate, the faster the heating rate in the heating process during hot stamping, and the higher the heating efficiency. Similarly, the thinner the aluminum-based plating layer, the shorter the alloying time of plating (the time until the surface becomes black with no metallic luster and the heat absorption efficiency improves), so the heating efficiency during hot stamping is improves. Here, the “excellent heating efficiency” referred to in the present embodiment means that a steel sheet having an aluminum-based plating layer of the same temperature condition, the same plate thickness and the same thickness has a higher heating efficiency than the conventional technique.
[0024]
　Hereinafter, preferred embodiments of the present invention completed based on the above findings will be described in detail with reference to the accompanying drawings. In this specification and the drawings, constituent elements having substantially the same functional configuration are designated by the same reference numerals, and duplicate description is omitted.
[0025]
　As briefly mentioned above, aluminum-plated steel sheets are regarded as promising as a material that solves the problem of scale during hot stamping and also has corrosion resistance. To reduce productivity due to low heating efficiency during hot stamping, an aluminum-based plated steel sheet that secures the thickness of the aluminum-based plating layer, does not increase the number of steel plate manufacturing processes, and has improved heating efficiency during hot stamping The situation is sought after.
[0026]
　In view of this point, the embodiment of the present invention described in detail below relates to a hot-dip hot-dip aluminum-plated steel sheet and a method for producing the same, and a method for producing an automobile part, and particularly, the heating efficiency of the hot stamp. The invention relates to an excellent aluminum-based plated steel sheet and a method for manufacturing the same.
[0027]
[Regarding Aluminum-Plated Steel Sheet]

　Hereinafter, the overall structure of the aluminum-plated steel sheet according to the present embodiment will be described with reference to FIGS. 1 and 2. FIG. 1 is a schematic view showing an example of an aluminum-based plated steel sheet according to an embodiment of the present invention, and shows a cross section obtained by cutting the aluminum-based plated steel sheet in the thickness direction. FIG. 2 is a schematic diagram showing another configuration example of the aluminum-plated steel sheet of this embodiment.
[0028]
　As shown in FIG. 1, the aluminum-based plated steel sheet according to the present embodiment includes a base material 1, an aluminum-based plating layer 2 located above one surface of the base material 1, a base material 1 and an aluminum-based plating layer. 2 and an intermetallic compound layer 3 located between the two. Further, as shown in FIG. 2, the aluminum-based plated steel sheet according to the present embodiment includes an aluminum-based plating layer 2 located above one surface of the base material 1, a base material 1 and an aluminum-based plating layer 2. An intermetallic compound layer 3 located between them, and an oxide-containing region 4 inside the base material 1 near the interface between the base material 1 and the intermetallic compound layer 3. Is preferred.
[0029]
　1 and 2, the aluminum-based plating layer 2, the intermetallic compound layer 3, and the oxide-containing region 4 described above are present on one surface of the base material. The aluminum-based plating layer 2, the intermetallic compound layer 3, and the oxide-containing region 4 as described above may be present on both surfaces.
[0030]

　First, the base material 1 included in the aluminum-based plated steel sheet according to the present embodiment will be described in detail below.
　Since the hot stamping method is a method of simultaneously performing press working with a die and quenching, the chemical composition of the base material 1 of the aluminum-plated steel sheet according to the present embodiment is a composition system having good hardenability. preferable. The chemical components of the base material according to this embodiment will be described in detail below. In the following description, "%" of a component means "mass%" unless otherwise specified.
[0031]
　From the above viewpoint, the chemical composition of the base material 1 according to the present embodiment is, in mass %, C: 0.15% or more and 0.5% or less, Si: 0.01% or more and 2.0% or less, Mn: 0.3% or more and 5.0% or less, Cr: 0.01% or more and 2.0% or less, P: 0.1% or less, S: 0.1% or less, Al: 0.5% or less, B: 0.0002% or more and 0.01% or less, and the balance contains Fe and impurities. In addition, the chemical composition of the base material 1 according to the present embodiment is optionally, in mass%, N: 0% or more and 0.01% or less, W: 0% or more and 3% or less, Mo: 0% or more and 3% or less. , V: 0% to 2%, Ti: 0% to 0.5%, Nb: 0% to 1%, Ni: 0% to 5%, Cu: 0% to 3%, Sn: One or more selected from the group consisting of 0% or more and 0.1% or less and Sb: 0% or more and 0.1% or less may be included.
[0032]
(C: 0.15% or more and 0.50% or less)
　The molded product obtained by the hot stamping method according to the present embodiment has a high strength of, for example, 1000 MPa or more, and the structure of the molded product is It is required to transform into a structure mainly composed of martensite by rapid cooling after hot stamping. If the content of carbon (C) is less than 0.15%, the hardenability deteriorates and the strength becomes insufficient. On the other hand, when the content of C exceeds 0.50%, the toughness of the steel sheet is remarkably deteriorated and the workability is deteriorated. Therefore, the content of C is set to 0.15% or more and 0.50% or less. The content of C is preferably 0.20% or more, 0.25% or more, or 0.28% or more. The content of C is preferably 0.40% or less, 0.35% or less, or 0.30% or less.
[0033]
(Si: 0.010% or more and 2.000% or less) When
　the content of silicon (Si) is less than 0.010%, hardenability and fatigue properties are poor. On the other hand, since Si is an element that is more easily oxidized than Fe (oxidizable element), if the Si content exceeds 2.000% in the continuous annealing plating line, a stable Si-based oxide film is formed during the annealing treatment. It is formed on the surface of the steel sheet and inhibits the adhesion of the molten Al plating, resulting in non-plating. Therefore, the Si content is set to 0.010% or more and 2.000% or less. The Si content is preferably 0.050% or more, 0.100% or more, or 0.300% or more. The Si content is preferably 1.000% or less, 0.800% or less, or 0.600% or less.
[0034]
(Mn: 0.3% or more and 5.0% or less)
　Manganese (Mn) is an element that enhances the hardenability of the steel sheet and further suppresses the hot brittleness due to S that can be mixed in the steel sheet. If the Mn content is less than 0.3%, the hardenability is reduced and the strength is insufficient. On the other hand, if the Mn content exceeds 5.0%, the impact properties after quenching deteriorate. Therefore, the Mn content is 0.3% or more and 5.0% or less. The Mn content is preferably 0.5% or more, 0.8% or more, or 1.0% or more. The Mn content is preferably 4.0% or less, 3.0% or more, or 2.0% or less.
[0035]
(Cr: 0.010% or more and 2.000% or less)
　Chromium (Cr) is an element that has an effect of enhancing the hardenability of the steel sheet, but when the content of Cr is less than 0.010%, The effect of improving the hardenability as described above cannot be obtained and the strength becomes insufficient. On the other hand, since Cr is an element that is more easily oxidized than Fe (oxidizable element), when the content of Cr exceeds 2.000%, a stable Cr-based oxide film during the annealing treatment is applied to the steel plate surface. Are formed on the surface of the molten Al, which hinders the adhesion of the molten Al plating and causes non-plating. Therefore, the content of Cr is set to 0.010% or more and 2.000% or less. The Cr content is preferably 0.100% or more, 0.400% or more, or 0.800% or more. The content of Cr is preferably 1.600% or less, 1.400% or less, or 1.000% or less.
[0036]
(P: 0.1% or less)
　Phosphorus (P) is also a solid solution strengthening element and can increase the strength of the steel sheet at a relatively low cost. Here, if the P content exceeds 0.1%, adverse effects such as lowering the toughness may occur, so the P content is set to 0.1% or less. On the other hand, since P is not required in the aluminum-plated steel sheet according to this embodiment, the lower limit of the P content is not particularly limited and may be 0%. When the P content is less than 0.001%, it is not economical from the refining limit, so the P content may be 0.001% or more. The content of P is preferably 0.05% or less, more preferably 0.01% or less or 0.005% or less.
[0037]
(S: 0.1% or less)
　Sulfur (S) becomes inclusions in the steel as MnS. Here, when the content of S exceeds 0.1%, MnS becomes a starting point of fracture, ductility and toughness deteriorate, and workability deteriorates. Therefore, the content of S is 0.1%. Below. On the other hand, since S is not required in the aluminum-plated steel sheet according to this embodiment, the lower limit of the S content is not particularly limited and may be 0%. When the S content is less than 0.001%, it is not economical from the refining limit, so the S content may be 0.001% or more. The S content is preferably 0.05% or less, more preferably 0.01% or less, or 0.005% or less.
[0038]
(Al: 0.5% or less)
　Aluminum (Al) is contained in steel as a deoxidizing agent. Since Al is an element that is more easily oxidizable than Fe, if the Al content exceeds 0.5%, a stable Al-based oxide film is formed on the surface of the steel sheet during the annealing treatment, and molten Al The adhesion of plating is obstructed and non-plating occurs. Therefore, the Al content is 0.5% or less. On the other hand, the lower limit of the Al content is not particularly limited and may be 0%. When the Al content is less than 0.01%, it is not economical from the refining limit, so the Al content may be 0.01% or more. The Al content is preferably 0.2% or less, more preferably 0.1% or less, or 0.08% or less.
[0039]
(B: 0.0002% or more and 0.0100% or less)
　Boron (B) is a useful element from the viewpoint of hardenability, and by containing 0.0002% or more, hardenability is improved. However, when B is contained in an amount of more than 0.0100%, the effect of improving the hardenability is saturated. In addition, when B is contained excessively, manufacturability deteriorates such as causing casting defects and cracks during hot rolling. Therefore, the content of B is set to 0.0002% or more and 0.0100% or less. The content of B is preferably 0.0010% or more, 0.0020% or more, or 0.0030% or more. The content of B is preferably 0.0080% or less, 0.0070% or less, or 0.0060% or less.
[0040]
　Next, the components that can be selectively contained in the base material 1 will be described in detail below. However, the aluminum-based plated steel sheet according to the present embodiment can solve the problem without using the optional components of the base material 1 described below. Therefore, the lower limit values ​​of the contents of the optional components of the base material 1 are all 0%.
[0041]
(N: 0% or more and 0.01% or less)
　Nitrogen (N) is preferably fixed from the viewpoint of stabilizing characteristics, and can be fixed using Ti, Nb, Al or the like. When the content of N increases, the content of the element to be contained for fixing N becomes large, resulting in an increase in cost. Therefore, the N content is preferably 0.01% or less. The N content is more preferably 0.008% or less.
[0042]
(W, Mo: 0% or more and 3% or less
　, respectively ) Tungsten (W) and molybdenum (Mo) are useful elements from the viewpoint of hardenability, and by containing 0.01% or more, hardenability is improved. Exert the effect of causing. On the other hand, when the contents of W and Mo exceed 3%, respectively, the above effect is saturated and the cost is increased. Therefore, the W and Mo contents are preferably 0.01% or more and 3% or less, respectively. The content of W and Mo is more preferably 0.05% or more. The content of W and Mo is more preferably 1% or less.
[0043]
(V: 0% or more and 2% or less)
　Vanadium (V) is a useful element from the viewpoint of hardenability, and by containing 0.01% or more, it exhibits the effect of improving hardenability. However, when V is contained in excess of 2%, the effect is saturated and the cost is increased. Therefore, the V content is preferably 0.01% or more and 2% or less. The V content is more preferably 0.05% or more. The V content is more preferably 1% or less.
[0044]
(Ti: 0% or more and 0.5% or less)
　Titanium (Ti) can be contained from the viewpoint of fixing N, and it is preferable to contain titanium in an amount of about 3.4 times the content of N in mass %. Since the N content is often about 10 ppm (0.001%) even if it is reduced, the Ti content is preferably 0.005% or more. On the other hand, when Ti is contained excessively, hardenability is deteriorated and strength is also deteriorated. Such a decrease in hardenability and strength becomes remarkable when the Ti content exceeds 0.5%, so the upper limit of the Ti content is preferably 0.5%. The content of Ti is more preferably 0.01% or more. The content of Ti is more preferably 0.1% or less.
[0045]
(Nb: 0% or more and 1% or less)
　Niobium (Nb) can be contained from the viewpoint of N fixation, and it is preferable to contain about 6.6 times the N content in mass %. Since the N content is often about 10 ppm (0.001%) even if it is reduced, the Nb content is preferably 0.01% or more. On the other hand, when Nb is excessively contained, the hardenability is deteriorated and the strength is deteriorated. Such a decrease in hardenability and strength becomes remarkable when the Nb content exceeds 1%, so the upper limit of the Nb content is preferably set to 1%. The Nb content is more preferably 0.02% or more. The Nb content is more preferably 0.1% or less.
[0046]
　Further, even if Ni, Cu, Sn, Sb, etc. are contained as the chemical components in the base material 1, the effect of the present invention is not impaired.
[0047]
(Ni: 0% or more and 5% or less)
　Nickel (Ni) is a useful element from the viewpoint of low-temperature toughness that leads to improvement of impact resistance characteristics in addition to hardenability. Is demonstrated. However, even if the content exceeds 5%, the above effects are saturated and the cost is increased. Therefore, Ni may be contained in the range of 0.01% or more and 5% or less.
[0048]
(Cu: 0% to 3%)
　Copper (Cu) is a useful element from the viewpoint of toughness in addition to hardenability, and by containing 0.01% or more, such an effect is exhibited. However, even if the content exceeds 3%, the above effects are saturated and the cost is increased. In addition, excessive Cu causes deterioration of slab properties and generation of cracks and flaws during hot rolling. Therefore, Cu may be contained in the range of 0.01% or more and 3% or less.
[0049]
(Sn, Sb: 0% or more and 0.1% or less, respectively)
　Tin (Sn) and antimony (Sb) are both effective elements for improving the wettability and adhesion of plating. By containing at least one of 0.005% or more, the above effects are exhibited. On the other hand, when at least one of Sn and Sb is contained in an amount of more than 0.1%, defects are likely to occur during production, and toughness is reduced. Therefore, the content of at least one of Sn and Sb is preferably 0.1% or less.
[0050]
(Regarding Other Components)
　Other components are not particularly specified, but elements such as Zr and As may be mixed from scrap. However, if the mixing amount is within the normal range, the characteristics of the base material 1 according to the present embodiment are not affected.
　The balance of the chemical composition of the base material 1 is iron and impurities. Impurities, when industrially manufacturing steel materials, raw materials such as ores or scraps, or components mixed by various factors of the manufacturing process, adversely affect the aluminum-based plated steel sheet according to the present embodiment. It means what is allowed in the range not given.
[0051]
　The base material 1 included in the aluminum-plated steel sheet according to the present embodiment has been described above in detail.
[0052]

　Aluminum plating means aluminum plating and alloy plating containing aluminum as a main component. The aluminum-based plating layer 2 is a plating layer that is made of aluminum-based plating and does not contain an intermetallic compound of Al and Fe. In the aluminum-based plated steel sheet according to the present embodiment, the aluminum-based plated layer 2 includes at least 80% or more and 97% or less of Al on average, 3% or more and 15% or less of Si, and impurities in total of 100%. It is a layer contained so that. The aluminum-based plating layer 2 contains, in addition to the above Al and Fe, 0% by mass or more and 5% by mass or less Zn on average, and 0% by mass or more and 5% by mass or less Fe under the condition that the total is 100%. You may contain 0 mass% or more and 3 mass% or less in total and 1 or more types selected from the group which consists of Mg and Ca. Hereinafter, the aluminum-based plating layer 2 will be described in detail. The concentration distribution of the chemical components of the aluminum-based plating layer 2 according to this embodiment is usually inclined in the thickness direction, but in this embodiment, the chemical components are defined by the average value. Hereinafter, unless otherwise specified, the value indicating the chemical composition of the aluminum-based plating layer 2 is an average value in the entire aluminum-based plating layer 2.
[0053]
(Regarding Method of Forming
　Aluminum Plating Layer 2 ) The aluminum plating layer 2 is intended to suppress the generation of oxide scale on the base material in the heating step of the hot stamp and to suppress corrosion after press molding. Is formed. Examples of the method for forming the aluminum-based plating layer 2 include various methods such as a hot dipping method, an electroplating method, a vacuum vapor deposition method, and a clad method. Currently, the most popular plating method is the hot-dip plating method because it is industrially low in cost, and the hot-dip plating method is preferably used for forming the aluminum-based plating layer 2. The aluminum-based plating layer 2 according to the present embodiment will be described in detail below by taking the hot dip plating method as an example.
[0054]
(Al: 80% or More and 97% or Less)
　The aluminum-based plating layer 2 according to this embodiment contains 80% or more of Al. Al has a melting point of 660° C. and a boiling point of 2470° C., and the melting point, the boiling point, and the Sn (melting point 231.9° C.) of zinc (Zn: melting point 419.5° C., boiling point 907° C.) that is typical as another plating species. , The boiling point of 2603° C.) is higher than the melting point. Therefore, it is required for the plating of steel materials used for hot stamping that has a heating step before pressing, suppression of oxide scale generation on the base material, and suppression of contamination due to adhesion of plating components to equipment in the heating step. From a viewpoint, aluminum-based plating is superior to Zn and Sn. Further, since hot stamping is performed at a high temperature immediately after the heating step, the liquid metal embrittlement (LME) that occurs in the Zn plating treatment is suppressed, and Al-based plating is also hot stamping. Excellent for plating steel materials. The Al content in the aluminum-based plating layer 3 is set to 80% or more from the viewpoints of suppressing the generation of oxide scale on the base material, suppressing the equipment contamination, and suppressing the LME. Further, as will be described later, since the Si content in the aluminum plating layer 2 according to the present embodiment is 3% or more, the upper limit of the Al content in the aluminum plating layer 3 is 97%. Therefore, in the aluminum-based plating layer 2 according to this embodiment, the Al content is 80% or more and 97% or less. The Al content is preferably 82% or more, 84% or more, or 86% or more. The Al content is preferably 95% or less, 93% or less, or 90% or less.
[0055]
(Si: 3% to 15%)
　The aluminum-based plating layer 2 according to the present embodiment further contains Si as a component other than Al in an amount of 3% to 15%. By including molten Si in the plating solution in the hot dip plating method, the thickness of the intermetallic compound layer 3 containing the intermetallic compound of Al and Fe generated during the aluminum plating treatment can be controlled. When the Si content is less than 3% by mass, the intermetallic compound layer 3 grows thick at the stage of applying Al plating, which promotes cracking of the plating layer during processing and may adversely affect corrosion resistance. There is a nature. On the other hand, when the Si content exceeds 15% by mass, the thickness of the Al—Fe intermetallic compound layer may be excessively suppressed, and the heating efficiency during hot stamping may decrease. Therefore, the Si content is 3% by mass or more and 15% by mass or less. The Si content is preferably 5% by mass or more, 7% by mass or more, or 8% by mass or more. The Si content is preferably 13% by mass or less, 11% by mass or less, or 10% by mass or less.
[0056]
(Zn: 5% or less) When
　Zn is contained in the aluminum-based plating layer 2, LME may be generated as described above. Therefore, from the viewpoint of suppressing LME, the Zn content is preferably 5% by mass or less, 4% by mass or less, or 3% by mass or less. Since Zn is not required in the aluminum-based plated layer 2 of the aluminum-based plated steel sheet according to this embodiment, Zn may not be contained in the aluminum-based plated layer 2. That is, the Zn content of the aluminum-based plating layer 2 may be 0% by mass.
[0057]
(Fe: 5% or less) When
　the aluminum plating layer 2 is formed by the hot dipping method, 2 to 4 mass% of Fe eluted from the equipment or steel strip in the bath is contained in the aluminum plating layer 2. Sometimes. In the aluminum-based plating layer 2, 2 to 4% by mass of Fe is allowed. On the other hand, when the Fe content exceeds 5%, cracks are generated in the aluminum-based plating layer 2 during coil winding, so that the generation of Fe oxide scale during hot stamping may not be sufficiently suppressed. Therefore, the content of Fe in the aluminum plating layer 2 is preferably 5% or less. On the other hand, since Fe is not required in the aluminum-based plating layer 2 of the aluminum-based plated steel sheet according to this embodiment, Fe may not be contained in the aluminum-based plating layer 2. That is, the Fe content of the aluminum-based plating layer 2 may be 0% by mass.
　In addition to Fe, Cr, Mo, V, W, Mn and the like can be cited as elements that may be eluted from the equipment or steel strip in the bath. These elements may also be contained as impurities in the aluminum plating layer 2 within a range that does not adversely affect the characteristics of the aluminum plating steel sheet according to the present embodiment.
[0058]
　The aluminum-based plating layer 2 according to the present embodiment can further contain at least one of magnesium (Mg), calcium (Ca), strontium (Sr), and lithium (Li). Since these elements are not essential in the aluminum-based plating layer 2, the content may be 0%. On the other hand, in particular, Mg and Ca can increase the emissivity of the surface of the aluminum-based plating layer 2 and improve the efficiency of heat absorption. Also, according to the Ellingham diagram, Mg and Ca are more easily oxidizable elements than Al. Therefore, by containing at least one of Mg and Ca in a total amount of 0.01% or more, the oxidation resistance of the plating in the hot stamp heating step can be improved, and the corrosion resistance after hot stamping can be further improved. it can. Furthermore, the Mg- and Ca-based oxides formed during hot stamping improve the emissivity of the surface of the aluminum-based plating layer 2 to increase the heat absorption efficiency and improve the heating efficiency during hot stamping. On the other hand, if at least one of Mg and Ca is contained in a total amount of more than 3%, an oxide film is formed in the plating bath during hot dip plating to increase the oxidizing property excessively, and the plating appearance after the process deteriorates. And lead to non-plating. Therefore, the aluminum-based plating layer 2 according to the present embodiment preferably contains at least one of Mg and Ca in a total amount of 0.01% or more and 3% or less. The total content of at least one of Mg and Ca is more preferably 0.05% or more. The total content of at least one of Mg and Ca is more preferably 1% or less.
　The chemical composition of the aluminum-based plating layer 2 according to the present embodiment contains Al, Si, Zn, Fe, Mg, Ca, Sr, Li and impurities in a total amount of 100% by mass. Impurities are, for example, components eluted from the equipment in the bath, alloy components eluted from the base steel plate, components mixed in the raw material of the plating bath, and the like, and the characteristics of the aluminum-based plated steel sheet according to the present embodiment. It is an acceptable component within the range that does not adversely affect the.
[0059]
(Regarding composition analysis method)
　As a method for identifying the components of the aluminum-based plating layer 2, the plating layer is dissolved, and the solution is quantitatively analyzed using a high frequency inductively coupled plasma (ICP) emission spectroscopy. There is a method. As a method for dissolving the aluminum-based plating layer 2, for example, a method of dipping in an aqueous solution of sodium hydroxide can be mentioned. Specifically, as described in JIS G 3314:2011, an aqueous solution prepared by dissolving 8 g of water in 2 g of sodium hydroxide (JIS K8576) is heated to 85° C. or higher, and the test material (for example, size The aluminum-based plating layer 2 can be dissolved by immersing the surface of the surface opposite to the surface to be measured with a tape of 30×30 mm in advance) until the foaming caused by the dissolution of the plating is settled. In this method, aluminum is dissolved in an aqueous sodium hydroxide solution, but the Al-Fe intermetallic compound layer containing Fe and the base material are not dissolved.
[0060]
(Regarding Total Thickness of Aluminum Plating Layer 2 and Intermetallic Compound Layer 3) The thickness of the
　aluminum plating layer 2 is not particularly limited. For example, the total thickness of the aluminum plating layer 2 and the intermetallic compound layer 3 is preferably 10 μm or more and 40 μm or less. When the total thickness of the aluminum-based plating layer 2 and the intermetallic compound layer 3 is 10 μm or more, suppression of generation of oxide scale in the base material 1 in the hot stamp heating step and corrosion after press molding in hot stamping Can be sufficiently suppressed. On the other hand, when the total thickness of the aluminum-based plating layer 2 and the intermetallic compound layer 3 is 40 μm or less, by suppressing the peeling of the plating at the site where shear stress or compressive stress is applied during press molding in hot stamping, It is possible to further inhibit the corrosion generated from the peeled portion and further suppress the corrosion after the press molding.
[0061]
　As a method for specifying the total thickness of the aluminum-based plating layer 2 and the intermetallic compound layer 3, for example, a cross section of the aluminum-based plating layer 2 and the intermetallic compound layer 3 is analyzed by an optical microscope or a scanning electron microscope (SEM). There is a method of measuring by observing with.
[0062]
　The aluminum-based plating layer 2 included in the aluminum-based plated steel sheet according to this embodiment has been described above in detail.
[0063]
In the
　present embodiment, the intermetallic compound layer 3 plays the most important role in order to improve the heating efficiency in the heating step during hot stamping. Hereinafter, the intermetallic compound layer 3 will be described in detail.
[0064]
(Regarding Components of
　Intermetallic Compound Layer 3 ) As described above, the intermetallic compound layer 3 is a layer that is located between the base material 1 and the aluminum-based plating layer 2 and that includes an intermetallic compound of Al and Fe. .. The chemical composition of the intermetallic compound layer 3 is not particularly limited. If the chemical composition of the base material 1 and the chemical composition of the aluminum-based plating layer 2 are within the above range and the alloying treatment is performed so that the thickness of the intermetallic compound layer 3 is within the range described below, the metal This is because good characteristics can be obtained regardless of the chemical composition of the intermetallic compound layer 3. The chemical components of the intermetallic compound layer 3 usually contain, on average, 35 to 65% by mass of Al, 5 to 15% by mass of Si, and the balance is Fe and impurities (components other than Al and Si. Is also included in the intermetallic compound layer 3), but is not limited thereto.
　The intermetallic compound of Al and Fe includes not only an Fe-Al-based intermetallic compound but also an intermetallic compound containing an element other than Fe and Al, such as an Fe-Al-Si-based intermetallic compound. It is a concept. The Fe-Al-based intermetallic compound is, for example, Fe 3 Al, FeAl, ε phase (phase generated by peritectic reaction from FeAl phase and liquid phase), FeAl 2 (ζ), Fe 2 Al 5 (η), FeAl 3 (θ), FeAl 5 , and FeAl 4 and the like. The Fe—Al—Si intermetallic compound is, for example, Al 3Fe 3 Si 2 (τ 1 ), Al 12 Fe 5 Si 5 (τ 2 ), Al 9 Fe 5 Si 5 (τ 3 ), Al 3 FeSi 2 (τ 4 ), Al 15 Fe 5 Si 5 (τ 5 ). , And Al 4 FeSi(τ 5) Etc. These intermetallic compounds are generally very hard and have common properties in that they have brittleness. Also, regarding the thermal characteristics during hot stamping, it is considered that there is no particular difference between these phases. Therefore, in the aluminum-plated steel sheet according to this embodiment, the type of intermetallic compound of Al and Fe is not particularly limited. The composition of the intermetallic compound layer 3 is known.
　As described above, since the intermetallic compound layer 3 is generally extremely hard and brittle, when it is processed, a crack is generated and becomes a starting point of fracture, and from this starting point, the aluminum-based plating layer 2 is formed. Is caused to crack. In a severe case, the intermetallic compound layer 3 may be cracked during skin pass rolling or leveling after plating or during the blanking process, and the aluminum-based plating layer 2 may peel off.
[0065]
　Further, the intermetallic compound layer 3 plays an extremely important role with respect to the temperature rising rate in the heating step of the hot stamp. In the heating process of hot stamping, current heating, near infrared heating, far infrared heating, radiant heating, etc. are used as heating methods, but in particular, near-red heating is advantageous because of high industrial productivity and less blank size restrictions. External heating, far infrared heating, and radiant heating are often used. In any of these heating methods, the emissivity of the surface of the steel sheet greatly affects the heating rate of heating. Then, as a result of intensive studies, the present inventors have found that the intermetallic compound layer 3 is extremely important for increasing the emissivity of the steel sheet surface.
[0066]
　In the heating step during hot stamping, in the intermetallic compound layer 3, since Fe in the base material 1 (for example, near the surface of the base material 1) diffuses into the aluminum-based plating layer 2 as the temperature rises, While the thickness of the aluminum-based plating layer 2 having a high Al concentration decreases, the intermetallic compound layer 3 grows and the thickness increases. In the heating step during hot stamping, the intermetallic compound layer 3 is finally formed up to the outermost surface of the aluminum-based plating layer 2. Further, it was found that the heating rate during the heating process during hot stamping was slow from room temperature to about 750°C, and was faster at 750°C or higher. It was also found that the rate of temperature rise was the slowest particularly in the temperature range of 650 to 750°C. Although the cause of such a phenomenon is not clear, the temperature range of 650 to 750° C. at which the rate of temperature rise is particularly slow is close to the melting point of metal Al of 660° C., and is therefore estimated as follows. That is, although Al originally has a low emissivity, it is considered that when the temperature reaches 650 to 750° C., the surface of the aluminum is smoothed by melting Al and the emissivity is further lowered. Further, in the temperature range of 750° C. or higher, the intermetallic compound layer 3 made of an intermetallic compound of Al and Fe is formed up to the surface, so that the emissivity is improved. As the emissivity changes in this way, the heat absorption efficiency also changes, so it is considered that the temperature rising rate varies depending on the temperature region.
[0067]
　As a fact suggesting that the emissivity is improved when an intermetallic compound of Al and Fe is formed, regarding the surface appearance of the aluminum-based plating layer 2, before heating, the surface appearance is silver-white with metallic luster. On the other hand, when an intermetallic compound of Al and Fe is formed up to the surface of the aluminum-based plating layer 2, the surface appearance changes to a blackish color and the metallic luster disappears. As described above, it was found that it is important for improving heating efficiency that the intermetallic compound of Al and Fe is formed up to the surface of the aluminum-based plating layer 2 in the heating process during hot stamping.
[0068]
　On the other hand, since the intermetallic compound layer is hard as described above, if it is formed in a large amount, it is easily broken, and a problem of plating adhesion arises during hot stamping. Therefore, the present inventors have conceived to locally form thick portions at a constant rate while suppressing the average thickness of the intermetallic compound layer 3 from being excessively increased. Thereby, the problem of plating adhesion can be solved, and further, in the heating step at the time of hot stamping, an intermetallic compound of Al and Fe can be formed even on the surface of the aluminum-based plating, and heating efficiency can be promoted.
[0069]
(Average value of thickness of intermetallic compound layer 3: 2 μm or more and 10 μm or less)
　Based on the above consideration, the average thickness of the intermetallic compound layer 3 is 2 μm or more and 10 μm or less. If the average value of the thickness is less than 2 μm, it takes time for the intermetallic compound to grow to the surface in the heating step of the hot stamp, and the temperature rising rate cannot be sufficiently improved. On the other hand, when the average value of the thickness exceeds 10 μm, the problem of plating adhesion occurs during skin pass rolling, leveler straightening, blanking process and the like. The average value of the thickness of the intermetallic compound layer 3 is preferably 3 μm or more, 4 μm or more, or 5 μm or more. The average value of the thickness of the intermetallic compound layer 3 is preferably 10 μm or less, 9 μm or less, or 8 μm or less.
[0070]
(The maximum value of the thickness of the intermetallic compound layer 3 is 10 μm or more and 25 μm or less)
　The maximum value of the thickness of the intermetallic compound layer 3 is 10 μm or more and 25 μm or less. When the maximum value of the thickness is less than 10 μm, it takes time for the intermetallic compound to grow to the surface in the heating step of the hot stamp, and the temperature rising rate cannot be sufficiently improved. On the other hand, when the maximum value of the thickness exceeds 25 μm, a problem of plating adhesion occurs during skin pass rolling, leveler straightening, blanking process and the like. The maximum value of the thickness of the intermetallic compound layer 3 is preferably 10 μm or more, 12 μm or more, or 15 μm or more. The maximum value of the thickness of the intermetallic compound layer 3 is preferably 23 μm, 21 μm or less, or 18 μm or less.
[0071]
(Standard deviation of thickness of intermetallic compound layer 3: 2 μm or more and 10 μm or less)
　The standard deviation of thickness of the intermetallic compound layer 3 is 2 μm or more and 10 μm or less. If the standard deviation of the thickness is less than 2 μm, it takes time for the intermetallic compound to grow to the surface in the heating step of the hot stamp, and the temperature rising rate cannot be sufficiently improved. On the other hand, when the standard deviation of the thickness exceeds 10 μm, the problem of plating adhesion occurs during skin pass rolling, leveler straightening, blanking process and the like. The standard deviation of the thickness of the intermetallic compound layer 3 is preferably 2 μm or more, 3 μm or more, or 4 μm or more. The standard deviation of the thickness of the intermetallic compound layer 3 is preferably 9 μm or less, 8 μm or less, or 7 μm or less.
[0072]
(About the measuring method and the calculating method of the average value, the maximum value, and the standard deviation of the thickness of the intermetallic compound layer 3) The average value, the maximum value, and the standard deviation of the
　above-mentioned thickness are obtained by making the aluminum-based plated steel sheet parallel to the thickness direction. It is measured in a cross section that is cut and appropriately prepared such as polishing. Specifically, the range in which the intermetallic compound layer 3 is imaged in the cross section is observed with a SEM at 300 times. The image obtained by SEM observation may be either a secondary electron image or a backscattered electron image. The base material, the intermetallic compound layer, and the aluminum-based plating layer of the aluminum-based plated steel sheet according to the present embodiment can usually be clearly distinguished by SEM observation as illustrated in FIG. When the interface between the base material, the intermetallic compound layer, and the aluminum-based plating layer cannot be clearly confirmed by SEM observation, surface analysis of the plating components by EPMA is performed to identify the intermetallic compound of Fe and Al. To do. Then, the region containing the intermetallic compound of Fe and Al is regarded as the intermetallic compound layer 3, the region mainly containing Al not containing the intermetallic compound of Fe and Al is regarded as the aluminum plating layer 2, and the Fe and Al The Fe-based region containing no intermetallic compound is regarded as the base material 1.
　The thickness of the intermetallic compound layer 3 in the obtained observation photograph is measured at 20 points, as illustrated in FIG. The measurement is performed at regular intervals in the observation photograph, and the distance between the measurement points is 6.5 μm. In the aluminum-based plated steel sheet according to this embodiment, the interface between the base material 1 and the intermetallic compound layer 3 and the interface between the intermetallic compound layer 3 and the aluminum-based plated layer 2 may have irregular shapes. Normally, such an irregular shape needs to be reflected in the thickness measurement value at each measurement location.
　Thickness values ​​d 1 to d 20 of the intermetallic compound layer 3 at each measurement location measured in the observation photograph Using, the average value, maximum value, and standard deviation of the thickness of the intermetallic compound layer 3 in the observation photograph can be obtained as follows. That is, the arithmetic average value d AVE of d 1 to d 20 is set as the average value of the thickness of the intermetallic compound layer 3 in the observation photograph. The largest value of d 1 to d 20 is the maximum value of the thickness of the intermetallic compound layer 3 in the observation photograph. The standard deviation of the thickness of the intermetallic compound layer 3 in the observation photograph is calculated according to the following formula.
[0073]
[Number 1]

[0074]
　Here, s is the standard deviation of the thickness of the intermetallic compound layer 3, i is the measurement number (1 to 20), and d AVE is the arithmetic mean value of d 1 to d 20 as described above . FIG. 5 is an example of actually measuring the intermetallic compound layer 3 according to the present embodiment for the average value, the maximum value, and the standard deviation of these thicknesses.
　The intermetallic compound layer 3 included in the aluminum-plated steel sheet according to this embodiment has been described above in detail.
[0075]
As
　schematically shown in FIG. 2, in the aluminum-plated steel sheet according to the present embodiment, in the vicinity of the interface between the base material 1 and the intermetallic compound layer 3 inside the base material 1. It is preferable that the oxide-containing region 4 is present. As a result of intensive studies by the present inventors, it has been clarified that the intermetallic compound of Al and Fe is more effectively formed by providing the oxide-containing region 4. The cause of this is not clear, but the presence of oxides near the surface of the base material 1 reduces the amount of solid solution of elements other than Fe near the surface of the base material 1 and causes diffusion of Fe into the aluminum-based plating layer 2. Is believed to be promoted. By promoting the diffusion of Fe into the aluminum-based plating layer 2, the time until the intermetallic compound of Al and Fe is formed on the surface of the aluminum-based plating layer 2 is shortened, and as a result, the heating efficiency of the steel sheet is improved. It is further improved (that is, the temperature rising rate is further improved).
[0076]
(Regarding Existence Range of
　Oxide-Containing Region 4 ) The oxide-containing region 4 exists within a range of 5 μm from the interface between the base material 1 and the intermetallic compound layer 3 in the thickness center direction of the base material 1. Preferably.
[0077]
(Regarding Oxide Content)
　The oxide-containing region 4 may contain at least one oxide of Si, Mn, Cr, and B in a total content of 1% by mass or more and 10% by mass or less. preferable. By setting the total content of such oxides to 1% or more, the above effects can be reliably obtained. On the other hand, when the total content of oxides is 10% by mass or less, diffusion of iron into the plating can be ensured and heating efficiency can be kept higher. Furthermore, if the total content of oxides is 10% by mass or less, the plating adhesion can be kept even higher. The total content of oxides is preferably 10% by mass or less.
[0078]
(Regarding Method for Specifying Oxide Content)
　The total content of the above oxides can be specified as follows.
　That is, in a cross section cut along the thickness direction of the steel sheet, arbitrary 100 points within 5 μm from the interface between the base material 1 and the intermetallic compound layer 3 into the base material are analyzed by EPMA. The distance between the measurement points should be 0.2 μm or more, and the measurement points must be evenly distributed in the region within 5 μm from the interface between the base material 1 and the intermetallic compound layer 3 into the base material. In this specification, the total content of oxides is defined as follows. By EPMA analysis, the strengths of Si, Mn, Cr, and B are more than three times higher than the strength at the position of 30 μm deep from the interface between the base material 1 and the intermetallic compound layer 3 into the base material. The number of the spots where the peak of concentration of oxygen (O) is recognized is counted. Then, the ratio obtained by dividing the obtained number of places by 100 is shown as a percentage, which is taken as the total content of oxides (expressed as mass% here).
　The oxide-containing region 4 that can be provided in the aluminum-plated steel sheet according to this embodiment has been described above.
[0079]
[Production Method of Aluminum-Plated Steel Sheet]
　Next, a production method of an aluminum-plated steel sheet having excellent heating efficiency for hot stamping according to the embodiment of the present invention will be described in detail.
[0080]
　The method for manufacturing an aluminum-plated steel sheet according to the present embodiment includes a step of hot rolling a steel slab to obtain a hot rolled steel sheet, a step of winding the hot rolled steel sheet, a step of pickling the hot rolled steel sheet, and a heat treatment. The method includes a step of cold rolling a rolled steel sheet to obtain a cold rolled steel sheet, and a step of continuously performing annealing treatment and hot dip aluminum plating treatment on the cold rolled steel sheet. The components of the steel slab are% by mass, C: 0.15% or more and 0.5% or less, Si: 0.01% or more and 2.0% or less, Mn: 0.3% or more and 5.0% or less, Cr. : 0.01% or more and 2.0% or less, P: 0.1% or less, S: 0.1% or less, Al: 0.5% or less, B: 0.0002% or more and 0.01% or less, N : 0% to 0.01%, W: 0% to 3%, Mo: 0% to 3%, V: 0% to 2%, Ti: 0% to 0.5%, Nb: 0% or more and 1% or less, Ni: 0% or more and 5% or less, Cu: 0% or more and 3% or less, Sn: 0% or more and 0.1% or less, and Sb: 0% or more and 0.1% or less The balance contains Fe and impurities. That is, the composition of the steel slab is equal to that of the base material 1. The preferable composition of the steel slab is in accordance with the preferable chemical composition of the base material 1 described above. Further, in the method for manufacturing an aluminum-plated steel sheet according to the present embodiment, the steel sheet winding temperature CT during winding is set to 700° C. or more and 850° C. or less, and the arithmetic mean roughness of the surface of the cold rolled steel sheet after cold rolling is set. Ra is 0.5 μm or more and 5 μm or less, and the plating bath in the molten aluminum-based plating treatment is 80 mass% or more and 97 mass% or less Al, 3 mass% or more and 15 mass% or less Si, and impurities. Mass% or more and 5 mass% or less Zn, 0 mass% or more and 5 mass% or less Fe, and 0 mass% or more and 3 mass% or less in total, one or more selected from the group consisting of Mg and Ca, The content is 100% by mass in total. In the method for manufacturing an aluminum-based plated steel sheet according to the present embodiment, in the annealing treatment, the steam partial pressure P H2O and the hydrogen partial pressure P H of the annealing atmosphere in the range of the plate temperature of 650° C. or higher and 900° C. or lower are used. H2 relation log (P with H2 O / P H2 value of) the -3 -0.5, the annealing time in the plate temperature may be 500 seconds or less than 60 seconds. In the method for manufacturing an aluminum-plated steel sheet according to the present embodiment, the plating bath may contain one or more kinds selected from the group consisting of Mg and Ca in a total amount of 0.01% by mass or more and 3% by mass or less. ..
　Hereinafter, more specific manufacturing conditions will be described in detail. According to the manufacturing method that satisfies the manufacturing conditions described below, the aluminum-plated steel sheet according to the present embodiment can be preferably manufactured. However, as a matter of course, the method for manufacturing the aluminum-plated steel sheet according to this embodiment is not particularly limited. The aluminum-plated steel sheet having the above-mentioned configuration is regarded as the aluminum-plated steel sheet according to this embodiment regardless of the manufacturing conditions.
[0081]

　After adjusting the chemical composition of the steel in the steel making process so as to satisfy the chemical composition of the base material 1 described above, this steel is continuously cast into a slab. To do. For the obtained slab (steel), for example, hot rolling is started at a heating temperature of 1300°C or lower (for example, 1000 to 1300°C), and hot rolling is performed at around 900°C (for example, 850 to 950°C). Is completed, and thereby a hot rolled steel sheet is obtained. The hot rolling rate may be, for example, 60 to 90%.
[0082]
(About coiling temperature CT of hot rolled steel sheet after hot rolling)
　The coiling temperature CT of the hot rolled steel sheet after hot rolling is one of the important conditions for an aluminum-based plated steel sheet for hot stamping, which has excellent heating efficiency. Generally, the coiling temperature CT is preferably a low temperature of about 500 to 600° C. for the purpose of suppressing carbides (deteriorating the ductility of the material) that occur in the hot rolled steel sheet during cooling after coiling. However, the inventors of the present invention set the steel plate winding temperature CT to 700° C. or higher to determine the average value, the maximum value, and the standard deviation of the thickness of the intermetallic compound layer 3 after hot-dip aluminum plating by heating the hot stamp. It was found that the heating efficiency in the process can be controlled so as to be excellent. Although the reason for this is not clear, the present inventors presume as follows. That is, since the intermetallic compound 3 is formed by the reaction of Al, which is a plating component, with Fe in the base material 1 during the molten aluminum plating treatment, the reactivity of Fe in the base material 1 is different from that of the intermetallic compound. It is important for generation. Here, by setting the steel plate winding temperature CT to 700° C. or higher, diffusion of elements other than Fe contained in the base material 1 to the base material surface can be promoted. Since the atmosphere of hot rolling is the atmosphere, Fe scale is formed on the surface of the base material (hot rolled steel sheet) during the period between the hot rolling and the winding, and other than Fe that has reached the surface of the base material. The elements are also easily oxidized, and a complex oxide scale of Fe and an element other than Fe is formed, or a subscale is formed at the interface between the Fe scale and the base material. Both of these scales are removed by pickling in the subsequent step, but the concentration of elements other than Fe decreases and the Fe concentration relatively increases on the surface of the base material. It is considered that this promotes the diffusion of Fe into the aluminum-based plating during the molten aluminum-based plating treatment. Furthermore, the decrease in the concentration of elements other than Fe near the surface of the base material is particularly promoted at the Fe crystal grain boundaries, so the maximum value of the intermetallic compound layer 3 and the standard deviation can be increased. .. Further, the effect of facilitating the diffusion of Fe in the base material 1 into the aluminum-based plating is recognized, and the heating efficiency of the steel sheet in the heating step during hot stamping is also excellent. As mentioned above
[0083]
　In order to obtain the above effects, the steel plate winding temperature CT is set to 700° C. or higher. If the steel sheet winding temperature CT exceeds 850° C., the average value, the maximum value, and the standard deviation of the thickness of the intermetallic compound layer 3 become excessively large, and it becomes difficult to secure the temperature for hot rolling. Therefore, the steel plate winding temperature CT has an upper limit of 850°C. The steel sheet winding temperature CT after hot rolling is preferably 710° C. or higher, or 720° C. or higher. The steel sheet winding temperature CT after hot rolling is preferably 830°C or lower, or 810°C or lower.
[0084]

　The condition of the pickling treatment of the hot rolled steel sheet after winding is not particularly limited, and any method such as hydrochloric acid pickling or sulfuric acid pickling may be used, but hydrochloric acid pickling is more preferable than sulfuric acid pickling. It is preferable to use hydrochloric acid pickling because washing can more easily maintain a decrease in the element concentration other than Fe on the surface of the steel sheet. In addition, by leaving a part of the composite oxide scale of Fe and an element other than Fe and the subscale generated at the interface between the Fe scale and the base material 1, the mother after the molten aluminum-based plating treatment in the subsequent step is performed. It is also possible to form an oxide-containing region inside the material. Therefore, the pickling time is preferably 600 seconds or less. However, if the pickling time is less than 10 seconds, Fe scale remains and unplated is formed during the hot dip treatment, which is not practical. Therefore, the pickling time is preferably 10 seconds or more and 600 seconds or less. The pickling time is more preferably 20 seconds or more and 400 seconds or less.
[0085]

(Cold Rolling Ratio and Surface Roughness
　of Cold Rolled Steel Sheet ) After pickling, the hot rolled steel sheet is cold rolled. The cold rolling rate in such cold rolling can be, for example, 30 to 90%, and preferably 40% or more and 70% or less.
　Further, it is considered that by applying the above-described winding conditions, it is necessary to form unevenness by cold rolling on the surface of the base material from which a part of the alloy components has been removed and the Fe concentration has been increased. By increasing the surface roughness of the steel sheet after cold rolling (that is, cold rolled steel sheet), the contact surface area between the aluminum-based plating layer 2 and the base material 1 can be increased, and the diffusion efficiency of Fe can be further improved. it can. Further, by making the interface between the aluminum-based plating layer 2 and the base material 1 non-uniform, the diffusion of Fe can be made more non-uniform, and the standard deviation of the thickness of the intermetallic compound layer can be increased. Actually, the unevenness of the thickness of the intermetallic compound layer does not simply follow the expected unevenness of the base material surface, and as shown in FIG. 3, the recessed base material surface causes the thicker intermetallic compound layer. I found out.
　In order to obtain this effect, it is important that the surface roughness of the base material after cold rolling is 0.5 μm or more and 5 μm or less in terms of arithmetic average roughness Ra. By setting the arithmetic average roughness Ra of the surface to 0.5 μm or more, the diffusion of Fe into the aluminum plating during the molten aluminum plating treatment is particularly locally promoted, and the average value of the thickness of the intermetallic compound layer 3 is increased. , The maximum value and standard deviation are large. Further, when the arithmetic average roughness Ra is 0.5 μm or more, Fe easily diffuses into the aluminum-based plating layer 2 in the heating step during hot stamping. As a result, the surface of the aluminum-based plating layer 2 can be alloyed in a short time, so that the heating efficiency in the heating process during hot stamping is improved. On the other hand, when the arithmetic average roughness Ra exceeds 5 μm, the thickness of the intermetallic compound layer 3 becomes excessively non-uniform, and the formability at the time of hot stamping decreases, and in addition, the hearth in the annealing furnace of the hot dip coating line Damage the roll. Therefore, the arithmetic average roughness Ra is set to 5 μm or less. The surface roughness (arithmetic mean roughness Ra) of the steel sheet after cold rolling is preferably 0.7 μm or more, or 0.9 μm or more. The surface roughness (arithmetic mean roughness Ra) of the base material after cold rolling is preferably 4 μm or less, or 3 μm or less.
　The arithmetic mean roughness of the surface of the base material can be controlled via the surface roughness of the roll for cold rolling. Further, since the pressure applied to the roll and the speed at which the base material passes through the roll also affect the arithmetic average roughness of the surface of the base material, it can be used as a control factor for the arithmetic average roughness of the surface of the base material. ..
　In addition, by setting the surface roughness within the above range and increasing the Fe concentration on the base material surface by setting the winding temperature within the above range, the intermetallic compound layer finally obtained can be obtained. Mean, maximum, and standard deviation of thickness are all preferably controlled. It is difficult to preferably produce the intermetallic compound layer only through optimization of either the winding temperature or the surface roughness. For example, it is possible to increase the standard deviation of the thickness of the intermetallic compound layer by setting the winding temperature to exceed the above range or to set the surface roughness to exceed the above range. In this case, either or both of the average value and the maximum value of the thickness of the intermetallic compound layer become excessive. The reason why such a winding temperature synergistically affects the surface roughness of the base material is that the surface of the base material is softened by decarburizing by increasing the winding temperature. It is possible that the influence of the surface roughness of the roll on the surface roughness of the base material was promoted.
[0086]
(Regarding Method of Measuring Arithmetic Average Roughness Ra)
　The arithmetic average roughness Ra of the steel sheet after cold rolling is in accordance with JIS B0601 (2013) (a standard corresponding to ISO4287), and is a contact-type surface roughness. It can be determined by measuring the surface of the cold-rolled steel sheet using a meter. In the present embodiment, the average value of the values ​​obtained by performing the above method 5 times is taken as the arithmetic average roughness Ra of the steel sheet after cold rolling.
[0087]

　The cold-rolled steel sheet obtained by the above treatment is continuously subjected to recrystallization annealing and hot dip aluminum plating treatment in a hot dip coating line. Annealing in the hot dip galvanizing line uses a total reduction furnace that uses radiant tube heating, or an oxidation furnace that is commonly called a Sendzimir type annealing furnace that is heated by combustion gas and a reduction furnace that is heated by radiant tube heating. Although a reduction furnace or the like is used, this embodiment can be achieved by any type of heating furnace. The maximum ultimate plate temperature in the annealing step is preferably 700°C or higher and 900°C or lower. Further, in the annealing step, in the range where the plate temperature is 650° C. or higher and 900° C. or lower, the annealing atmosphere has a common logarithm log(P H2O /P H2 ) of a value obtained by dividing the steam partial pressure P H2O by the hydrogen partial pressure P H2. It is preferable that the atmosphere having an oxygen potential value of −3 or more and −0.5 or less is used, and the annealing time within this range is 60 seconds or more and 500 seconds or less. For example, when the maximum temperature reached is 750° C., the temperature range for controlling the oxygen potential is preferably a plate temperature range of 650° C. or higher and 750° C. or lower. It is preferably set to be less than or equal to seconds.
[0088]
(Regarding oxygen potential) In
　order to maintain a constant product quality, it is required to control the atmosphere in the furnace. The oxygen potential may be used as an index of the atmosphere in the furnace, and the oxygen potential is expressed by a relational expression log(P H2O /P H2 ) between the partial pressure of steam P H2O and the partial pressure of hydrogen P H2 using common logarithm. .. At this time, PH2O is the partial pressure of water vapor in the furnace, and PH2 is the partial pressure of hydrogen in the furnace. The oxidation state of the steel sheet can be controlled by the oxygen potential related to the steel sheet temperature.
[0089]
　In the present embodiment, it is preferable that the value of the oxygen potential is −3 or more and −0.5 or less when the plate temperature during annealing is in the range of 650° C. or more and 900° C. or less. It is generally known that elements such as Si and Mn contained in a steel sheet form an oxide film on the steel sheet surface. Due to such an oxide film, diffusion of Fe is hindered in a heating process by a hot stamp which is a post process. However, when the oxygen potential is -3 or more, elements such as Si or Mn, Cr, and B are oxidized inside the steel sheet, so-called internal oxidation occurs, so that formation of an oxide film on the steel sheet surface can be suppressed. it can. Therefore, the oxygen potential is preferably −3 or more. On the other hand, when the oxygen potential exceeds -0.5, a large amount of Fe oxide is generated, and the aluminum-based plating may repel pinholes during the hot dipping treatment after annealing, resulting in non-plating. The value of the oxygen potential is more preferably -3 or more and -1 or less.
[0090]
(Maximum Ultimate Plate Temperature and Annealing Time)
　The maximum ultimate plate temperature in the annealing step can be 700° C. or more and 900° C. or less, as mentioned earlier. When the maximum ultimate plate temperature in the annealing step is less than 700° C., the plate temperature may be lower than the melting point of the molten aluminum-based plating bath, so that the adhesiveness of the molten aluminum-based plating may decrease. If it is not preferable and the maximum ultimate temperature in the annealing step exceeds 900° C., an oxide film of easily oxidizable elements such as Si or Mn is formed on the surface, and the adhesion of the molten aluminum-based plating is hindered to form a pinhole. It is not preferable because non-plating may be formed. Further, in order to sufficiently promote the internal oxidation of elements such as Si and Mn, the annealing time when the oxygen potential is −3 to −0.5 in the range of the plate temperature of 650° C. to 900° C. is 60. It is preferably at least 2 seconds. Further, when the internal oxide is excessively generated, it is highly possible that peeling occurs from a portion where the internal oxide is generated during press molding with a hot stamp. Therefore, the annealing time is preferably 500 seconds or less when the oxygen potential is -3 or more and -0.5 or less in the range of the plate temperature of 650°C or more and 900°C or less. The annealing time is more preferably 80 seconds or more and 400 seconds or less.
[0091]
(Regarding Measuring Method)
　The steel sheet temperature during annealing can be measured using a radiation thermometer arranged in advance in the annealing equipment or a thermocouple attached to the steel sheet itself. Further, the water vapor partial pressure P H2O can be measured by a dew point meter previously arranged in the annealing equipment, and the hydrogen partial pressure P H2 is a flow rate of hydrogen to be introduced occupying in a flow rate of all gases introduced into the annealing furnace. It can be calculated from the ratio. In general, the atmosphere introduced into the annealing furnace of the hot dip coating line is hydrogen and nitrogen, and the ratio of hydrogen is 1% or more and 20% or less.
[0092]

(Aluminum plating layer adhesion amount)
　After annealing as described above, the steel plate is continuously immersed in a molten aluminum bath during cooling, and the adhesion amount of the aluminum plating solution is controlled by wiping treatment. Then, the aluminum-based plating layer 2 is formed. The adhesion amount of the aluminum-based plating layer 2 is not particularly limited, but is preferably 30 g/m 2 or more and 120 g/m 2 or less , for example . When the adhesion amount is less than 30 g/m 2 , the corrosion resistance after hot stamping may be insufficient. On the other hand, when the adhesion amount exceeds 120 g/m 2 , in the heating step of the hot stamp, it takes a long time for Fe to sufficiently diffuse, resulting in a decrease in productivity, and plating during hot stamping. The problem of peeling may occur. The adhesion amount of the aluminum-based plating layer 2 is more preferably 40 g/m 2 or more. The adhesion amount of the aluminum-based plating layer 2 is more preferably 100 g/m 2 or less.
[0093]
(Regarding Method for Measuring Amount of Adhesion of
　Aluminum Plating Layer ) As a method for specifying the amount of adhesion of the aluminum plating layer 2, for example, a sodium hydroxide-hexamethylenetetramine/hydrochloric acid stripping weight method can be mentioned. Specifically, as described in JIS G 3314:2011, a test piece having a predetermined area S (m 2 ) (for example, 50×50 mm) is prepared and the weight w1 (g) is measured. Then, it is immersed in an aqueous solution of sodium hydroxide and an aqueous solution of hydrochloric acid added with hexamethylenetetramine in order until the foaming caused by the dissolution of the plating subsides, and then immediately washed with water and the weight w2 (g) is measured again. At this time, the adhesion amount (g/m 2 ) of the aluminum-based plating can be calculated from (w1-w2)/S.
[0094]

(Al: 80% to 97%)
　Regarding the components of the molten aluminum bath, the Al content is 80% by mass or more. If the Al content is less than 80%, the oxidation resistance is poor and scale is generated during hot stamp heating. Further, as will be described later, since the content of Si in the molten aluminum bath is 3% or more, the Al content is 97% or less. The Al content in the molten aluminum bath is preferably 82% or more, or 84% or more. The Al content in the molten aluminum bath is preferably 95% or less, or 93% or less.
[0095]
(Si: 3% or more and 15% or less)
　Si contained in the aluminum-based plating layer 2 affects the reaction between Al and Fe generated during hot stamping heating. If Al and Fe react excessively in the heating step during hot stamping, the press formability of the aluminum-based plating layer 2 itself may be impaired. On the other hand, if such a reaction is excessively suppressed in the heating step during hot stamping, Al may be attached to the press die. In order to avoid such a problem, the Si content in the molten aluminum bath is set to 3% or more and 15% or less. The Si content in the molten aluminum bath is preferably 5% or more, or 7% or more. The Si content in the molten aluminum bath is preferably 13% or less, or 11% or less.
[0096]
(Mg, Ca: 0% or more and 3% or less in total) In
　order to improve the oxidation resistance of the aluminum-based plating layer 2, at least magnesium (Mg), calcium (Ca), strontium (Sr) and lithium (Li) are used. It is also possible to contain any of them, and it is particularly preferable to contain at least one of Mg and Ca in a total amount of 0.01% or more and 3% or less in the molten aluminum bath. When the total content of Mg and Ca is 0.01% or more, the effect of improving the oxidation resistance can be obtained. However, even if a plating bath containing no Mg and Ca is used, it is possible to produce an aluminum-based plated steel sheet having excellent corrosion resistance and thermal characteristics, so the total content of Mg and Ca in the plating bath is 0%. It may be. On the other hand, if the total content of Mg and Ca exceeds 3%, the problem of non-plating may occur during the hot dip plating process due to the formation of excess oxide. The total content of Mg and Ca is more preferably 0.05% or more. The total content of Mg and Ca is more preferably 1% or less.
[0097]
　Such a hot dip bath contains the above-mentioned components and impurities in a total amount of 100% by mass. Examples of impurities include Fe, Cr, Mo, V, W, and Zn, and it is particularly preferable that Fe and Zn are each 5% or less.
[0098]
　The method for manufacturing the aluminum-plated steel sheet according to this embodiment has been described above in detail.
[0099]
[Production method for automobile parts]
　A hot stamping method in which an aluminum-based plated steel sheet produced by the method described above is heated at 850°C or higher and then rapidly cooled by a mold at a cooling rate of 30°C/s or more. By molding with, it is possible to manufacture automobile parts. Hereinafter, a method for manufacturing an automobile part will be briefly described.
[0100]
(Regarding Hot Stamping Method)
　The aluminum-plated steel sheet obtained as described above has excellent heating efficiency in the hot stamping step and can achieve a large heating rate. Further, the aluminum-based plating layer 2 of the aluminum-plated steel sheet as described above becomes an alloy layer containing an intermetallic compound of Al and Fe after the heating in the hot stamping process up to the plating surface. Such an alloy layer contains 30% or more of Fe and 65% or less of Al.
[0101]
(Regarding hot stamping temperature) As for
　the heating method during hot stamping, as described above, the present application is a technology that improves the production rate by utilizing the increase in surface emissivity, so it is used for furnace heating by ordinary electric heaters and far infrared rays. It is possible to use a heating method using radiant heat such as a mid-infrared ray or a near infrared ray. Note that the present application is not used in a heating method using Joule heat generation, such as an electric heating method. In addition, in the heating step, the maximum reached plate temperature is 850°C or higher. There are two reasons why the maximum ultimate plate temperature is set to 850° C. or higher. The first reason is that the steel sheet is heated to the austenite region and then rapidly cooled to cause martensitic transformation, thereby increasing the strength of the base material. The second reason is that Fe is sufficiently diffused to the surface of the aluminum-plated steel sheet to promote alloying of the aluminum-plated layer 2. Although the upper limit of the maximum plate temperature of the aluminum-plated steel sheet during hot stamping is not particularly limited, it is preferably 1050° C. or lower from the viewpoint of durability of the heating heater and heating furnace body. The maximum ultimate plate temperature during heating by hot stamping is more preferably 870°C or higher and 1000°C or lower.
[0102]
(Hot stamping and cooling rate)
　Next, the aluminum-plated steel sheet in a heated state is placed between, for example, a pair of upper and lower forming dies, press-formed, and rapidly cooled during the press to obtain a desired shape. To mold. By holding the aluminum-based plated steel sheet still at the bottom dead center of the press for a few seconds, it is possible to perform quenching by contact cooling with a molding die and obtain a hot stamped high-strength component. The cooling rate during such cooling is set to 30° C./s or more because the base material mainly contains the martensite phase. This cooling rate is the start temperature (that is, the plate temperature of the material when the mold and material are first contacted) and the end temperature (that is, when the mold and material are separated) of forced cooling using the mold. Is a value obtained by dividing the difference between the material temperature and the plate temperature of the material) by the time during which forced cooling is performed, which is the so-called average cooling rate. The upper limit of the cooling rate is not particularly limited, but can be set to 1000° C./s or less, for example. The cooling rate is more preferably 50° C./s or more. The cooling rate is more preferably 500° C./s or less.
[0103]
(Hardness of base material after hot stamping) In
　order to be used as an automobile part, a steel sheet after hot stamping needs to have high strength. In steel materials, hardness and tensile strength are in a substantially proportional relationship up to a Vickers hardness of about 600 Hv. Therefore, in the present invention, the hardness is increased by the quenching by the contact cooling with the molding die in the hot stamping step after including the elements related to the hardenability as the steel sheet components. As a specific hardness, the Vickers hardness of the base material of the member after hot stamping in a cross section corresponding to a plate thickness of 1/4 needs to be 300 Hv or more when measured with a load of 1 kg.
　In addition, the cross section corresponding to the plate thickness 1/4 of the base metal was sampled using the plate thickness cross section parallel to the rolling direction of the base metal steel plate as the observation surface, and the observation surface was polished and nital-etched. It means a cross section of a region having a depth of about ¼ of the thickness t of the steel sheet from the rolled surface of the steel sheet. The 1/4t portion of the steel sheet may be defined as a region between the surface having a depth of 1/8t and the surface having a depth of 3/8t from the rolled surface of the steel sheet.
[0104]
(Regarding Finishing Process)
　The molded part after hot stamping becomes a final part (that is, an automobile part) through a finishing process such as welding, chemical conversion treatment, and electrodeposition coating. As the chemical conversion treatment, a zinc phosphate chemical conversion treatment or a zirconium chemical conversion treatment is usually used. Usually, cationic electrodeposition coating is often used as the electrodeposition coating, and the film thickness thereof is about 5 to 50 μm. After the electrodeposition coating, a coating such as an intermediate coating or a top coating may be further applied in order to improve the appearance quality and the corrosion resistance.
Example
[0105]
　Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples. The embodiments described below are merely examples, and the present invention is not limited to the following examples.
[0106]

　A cold-rolled steel sheet having a base metal component as shown in Table 1 was processed into a predetermined sheet thickness and used as a test material. The size of the test material is 240 mm×300 mm. These test materials were manufactured through a normal hot rolling step, a pickling step, and a cold rolling step in which the arithmetic mean roughness Ra of the surface of the cold rolled steel sheet was 0.5 μm or more and 5 μm or less. First, a cold-rolled steel sheet (sheet thickness 1.4 mm) having a steel component as shown in Table 1 below was used as a test material, and wettability during plating treatment, hot stamp formability, and hot stamp after hot stamping depending on the base material component. The effect on the hardness of was verified. Regarding the test material, the steel plate winding temperature after hot rolling is adjusted to 700°C or more and 800°C or less, annealed in a Sendzimir type heating furnace, and continuously subjected to hot dip aluminum plating treatment, and aluminum plating is performed. A steel plate was produced.
[0107]
　Regarding the annealing process, the annealing temperature of the reduction furnace (that is, the maximum reached plate temperature) is 750° C., and the atmosphere of the reduction furnace has an oxygen potential of −5 or more and −0.5 or less at a plate temperature of 700° C. or more, and the oxygen potential range. The holding time was 30 seconds or more and 500 seconds or less.
　Regarding the plating bath components, the Al content was 70% or more and 96% or less, the Si content was 3% or more and 15% or less, and the Fe content was 1 to 4%. The deposition amount of the plating solution was adjusted by the gas wiping method so that the deposition amount of the aluminum-based plating layer 2 was about 60 g/m 2 per side .
[0108]
　In the hot stamping step, the aluminum-plated steel sheet obtained as described above was heated to 900° C. in a radiant heating furnace, and immediately, the mold was cooled at a cooling rate of 50° C./s or more, and the following table was used. The high-strength parts B1 to B48 shown in No. 2 were obtained. The die used is a hat die, and the radius of curvature R of all R parts is 5 mm.
[0109]
[table 1]

[0110]
　Table 2 shows the evaluation results of the wettability during the plating treatment, the hot stamping formability, and the hardness after hot stamping.
　The plating wettability was determined to be G (GOOD) if no pinhole-like non-plating was visually observed during hot dip treatment, and B (BAD) if observed. The formability after hot stamping was determined by observing the cross section of the hat-shaped R portion and determining G (GOOD) when there was no crack in the base material, and determining B (BAD) when there was. The cross-section hardness corresponding to the plate thickness 1/4 of the base material after hot stamping is measured by a Vickers hardness tester, and 300 Hv (load 1 kg) or more is determined as G (GOOD), and less than 300 Hv is determined as B (BAD). did.
[0111]
[Table 2]

[0112]
　As shown in Table 2, Examples B1 to B39 of the present invention using A1 to A39 shown in Table 1 as the base steel sheet are all G (GOOD) in terms of plating wettability, formability and hardness after hot stamping. there were. On the other hand, Comparative Examples B40 to B52 using A40 to A52 shown in Table 1 as the base material steel sheet are B(BAD) in any of plating wettability, hot stamp formability and hardness after hot stamp Was not suitable as a high-strength component of
[0113]

　Next, the components of the aluminum-based plating layer 2, the average value, the maximum value, and the standard deviation of the thickness of the Al-Fe intermetallic compound layer 3 are the heating efficiency during hot stamping and the Fe scale during hot stamping. The presence or absence and the effect on the corrosion resistance after hot stamping were verified. Furthermore, the oxide content in the range of 5 μm from the interface between the base material 1 and the intermetallic compound 2 toward the center of the base material 1, and Mg and Ca in the aluminum-based plating layer, heating efficiency during hot stamping, The presence or absence of Fe scale during hot stamping and the effect on corrosion resistance after hot stamping were verified.
[0114]
　Under the same conditions as in Example 1, an aluminum-based plated steel sheet was prepared using a cold-rolled steel sheet (sheet thickness 1.4 mm) having the steel components shown in Table 1 as a test material, and hot under the same conditions as in Example 1. Stamping was performed to obtain a molded product. However, in Comparative Examples C23 and C24 in Table 3 below, the hot coiling temperature CT was set to 600°C to 650°C. Further, as shown in Table 5 below, in some of the invention examples (E1 to E9), 0.01% or more and 3% or less of Mg or Ca was further added to the plating bath component. The balance of the components of the aluminum-based plating layer shown in Tables 3 to 5 was Fe and impurities.
[0115]
　Tables 3 and 4 show the results of analyzing the proportions of Al, Si, Mg, and Ca of the aluminum-based plating layer, the intermetallic compound layer of Al and Fe, and the content of oxides on the surface of the base steel sheet in the invention example of the present application. , Shown in Table 5. The proportions of Al, Si, Mg, and Ca in the aluminum-based plating layer 2 were obtained by dissolving the plating layer and quantitatively analyzing the solution using ICP emission spectroscopy as described above. Regarding the intermetallic compound layer 3 made of an intermetallic compound of Al and Fe, a cross section obtained by cutting the aluminum-based plated steel sheet along the thickness direction is observed by SEM as described above, and the average value of the thickness and the maximum thickness. Values ​​and standard deviations of thickness were calculated. An example of the measurement is as shown in FIG. 5, for example. The total content of oxides within a range of 5 μm from the interface between the base material 1 and the intermetallic compound layer 3 toward the center of the base material 1 was obtained by the EPMA analysis as described above.
[0116]
　The produced sample was evaluated for heating efficiency during hot stamping, Fe scale during hot stamping, and corrosion resistance after hot stamping.
[0117]
(Evaluation of heating efficiency during hot stamping) A
　K-type thermocouple was attached to the center of a 240 mm×300 mm sample of the aluminum-plated steel sheet obtained by the above method, and the temperature was measured during hot stamping. The heating efficiency was evaluated by calculating the average value of changes in temperature from 100° C. to 880° C., which was measured by charging the radiant heating type heating furnace. In Tables 3 to 5 below, among comparative examples having the same plate thickness and basis weight as those of the invention examples, the case where the temperature rising rate is improved by 1.3 times or more with reference to the level C23 is VG (VERY GOOD). The case where the increase was 1.2 times or more and less than 1.3 times was defined as G (GOOD), and the case where there was almost no change at the temperature increase rate of less than 1.1 times was defined as B (BAD).
　If the heating rate is increased by 1.2 times or more, the heating time or the length of the heating furnace in the heating section is reduced by about 0.8 times or less. This improvement in heating efficiency, that is, a value of 1.2 times, is equivalent to equipment cost, operating energy, operating cost, space saving of equipment , productivity such as environment (CO 2 ), and running cost in actual production . From a viewpoint, it is a very meaningful value.
[0118]
(Presence or absence of Fe scale during hot stamping)
　The surface of the R portion of the hat-molded portion obtained by hot stamping was analyzed by EPMA. In Tables 3 to 5, when the oxygen intensity is detected at 10 mass% or more, it is expressed as B (BAD) with the Fe scale, and when the oxygen detection amount is less than 10 mass% without the Fe scale, G (GOOD). ).
[0119]
(Corrosion resistance of molded product after hot stamping)
　A hat molded product obtained by hot stamping was used as a test piece, and the test piece was subjected to chemical conversion treatment and corrosion resistant coating. A corrosion test was performed using a test piece in which the coating film on the flange portion of the test piece was scratched to expose the metal surface. Specifically, a chemical conversion treatment liquid PB-SX35 manufactured by Nippon Parkerizing Co., Ltd. was applied, and then a cationic electrodeposition paint Powernics 110 manufactured by Nippon Paint Co., Ltd. was applied to a thickness of about 20 μm. After that, a cross cut was put into the coating film of the flange portion with a cutter, and a composite corrosion test (JASO M610-92) defined by the Society of Automotive Engineers of Japan was conducted for 180 cycles (60 days) to measure the amount of reduction in the thickness of the cross cut portion. .. At this time, the corrosion resistance is B (BAD) if it exceeds the sheet thickness reduction depth of the alloyed hot-dip galvanized steel sheet GA (adhesion amount one side 45 g/m 2 ), and if it is less than G (GOOD), further 2/3. If suppressed below, the corrosion resistance was defined as VG (VERY GOOD).
[0120]
　Table 3 below shows the results of the above evaluation items when the components of the aluminum-based plating layer 2 and the average value, maximum value and standard deviation of the thickness of the Al—Fe intermetallic compound layer 3 were changed. As is clear from Table 3, Comparative Examples C21 to C24 are for any one or more of the composition of the aluminum-based plating layer 2, the average value of the thickness of the intermetallic compound layer 3, the maximum value of the thickness, and the standard deviation of the thickness. This embodiment is not satisfied. Comparative Examples C21 to C24 were inferior in any one of heating efficiency during hot stamping, generation of Fe scale during hot stamping, and corrosion resistance of high-strength parts after hot stamping. On the other hand, in the invention examples C1 to C20 of the present application, all the above evaluation items were good.
[0121]
[Table 3]

[0122]
　Table 4 below shows the results of the above evaluation items when the total content of oxides in the range of 5 μm from the interface between the base material 1 and the intermetallic compound 2 toward the center of the base material 1 was changed. Indicates. As shown in Table 4, the heating efficiency at the time of hot stamping of Invention Examples D1 to D4 of the present invention in which the total amount of oxides contained in the surface of the base steel sheet was 1 to 10% was more excellent.
[0123]
[Table 4]

[0124]
　As shown in Table 5 below, the heating efficiency at the time of hot stamping and invention after hot stamping of invention examples E1 to E9 of the present invention in which the aluminum-based plating layer 2 contains 0.01 to 3% in total of at least one of Mg and Ca Corrosion resistance of both was better. Since E11 and E12, which are comparative examples, contained Mg and Ca in excess, there was no plating during hot dipping, and evaluation was not possible.
[0125]
[Table 5]

[0126]

　Next, the steel sheet winding temperature CT in the hot rolling step, the surface roughness Ra of the steel sheet after the cold rolling step, and the molten aluminum-based plating bath composition are heating efficiency during hot stamping and hot stamping. The presence or absence of Fe scale and the effect on the corrosion resistance of hot stamped products were verified. Furthermore, when the annealing atmosphere and at least one of Mg and Ca are contained in the aluminum-based plating layer, the heating efficiency during hot stamping, the presence or absence of Fe scale during hot stamping, and the effect on the corrosion resistance of hot stamped products are verified. did.
[0127]
　Steel slabs having the steel components shown in Table 1 were subjected to normal hot rolling treatment, pickling treatment, and cold rolling treatment under the conditions shown in Tables 6 to 8 to obtain a cold rolled steel sheet (sheet thickness: 1.5 mm). ) Was produced. Using this cold-rolled steel sheet as the test material, annealing and hot dip aluminum plating treatment were continuously performed in a Sendzimir type heating furnace to produce an aluminum-plated steel sheet. In the annealing step, the annealing temperature (i.e. peak metal temperature) was 800 ° C., water vapor partial pressure P in the annealing atmosphere is the plate temperature is 700 ° C. H2O hydrogen partial pressure P H2 common logarithm log (P value divided by H2O /P H2 ) (that is, oxygen potential) was changed.
[0128]
　In the aluminum-based plating treatment step, the amount of deposited plating was adjusted by a gas wiping method after plating to be about 80 g/m 2 per surface . The temperature of the aluminum-based plated steel sheet at the time of hot stamping was set to 900° C., and the mold was immediately cooled at a cooling rate of 50° C./s or more to obtain a sample of a molded product.
[0129]
　With respect to the produced sample, the heating efficiency during hot stamping, the presence or absence of Fe scale during hot stamping, and the corrosion resistance of the molded product after hot stamping were evaluated in the same manner as in Example 2.
[0130]
　Regarding the evaluation of the heating efficiency at the time of hot stamping, in Tables 6 to 8, VG (VERY GOOD) when the level was improved to 1.3 times or more based on the level F21, and the heating rate was 1.2 times or more. G (GOOD) when it was improved to B, and B (BAD) when there was almost no change at a temperature rising rate of less than 1.1 times.
[0131]
[Table 6]

[0132]
　In Comparative Examples F21 to F28 shown in Table 6, any one or more of the hot rolling coiling temperature CT, the surface roughness Ra after cold rolling, and the bath composition of the molten aluminum-based plating do not satisfy the scope of the present invention. Here is an example. All of Comparative Examples F21 to F28 are inferior in any one of the heating efficiency during hot stamping, the generation of Fe scale during hot stamping, and the corrosion resistance after hot stamping. On the other hand, invention examples F1 to F20 satisfying the invention range of the present application were good in all of the above evaluation items.
[0133]
[Table 7]

[0134]
　As shown in Table 7, the common logarithm log(P H2O /P H2 ) (that is, oxygen potential) of the value obtained by dividing the water vapor partial pressure P H2O in the annealing atmosphere by the hydrogen partial pressure P H2 is −3 or more and −0.5 or less. In addition, the invention examples G1 to G9 of the present invention in which the annealing time within the above range was 30 seconds or more and 500 seconds or less were more excellent in heating efficiency during hot stamping.
[0135]
[Table 8]

[0136]
　As shown in Table 8, in the case of Invention Examples H1 to H7 of the present application in which at least one kind of Mg and Ca is contained in a total of 0.01% or more and 3% or less in the bath of the molten aluminum-based plating, the heating efficiency at the time of hot stamping, The corrosion resistance after hot stamping was better. However, Comparative Examples H9 and H10 could not be evaluated because unplating occurred because Mg and Ca were excessively contained.
[0137]
　FIG. 3 shows an example in which the aluminum-based plating layer 2 of F3 in Table 6 which is an example of the present invention is observed by SEM. Further, FIG. 4 shows an example of observing the F21 aluminum-based plating layer 2 of Table 6 by SEM as a comparative example. It can be seen that the maximum value and the standard deviation of the thickness of the intermetallic compound layer 3 of FIG. 3, which is an example of the present invention, are clearly different and larger than those of FIG. FIG. 5 is an example of actually measuring the average value, the maximum value, and the standard deviation of the thickness of the intermetallic compound layer 3 of FIG. As described above, the present invention having FIG. 3 as an example of the invention is excellent in heating efficiency during hot stamping, ability to suppress Fe scale during hot stamping, and corrosion resistance after hot stamping.
[0138]
　The preferred embodiments of the present invention have been described above with reference to the accompanying drawings, but it goes without saying that the present invention is not limited to such examples. It is obvious to those skilled in the art that various changes or modifications can be conceived within the scope of the claims, and naturally, these also belong to the technical scope of the present invention. Understood.
Explanation of symbols
[0139]
1 Base Material
2 Aluminum Plating Layer
3 Intermetallic Compound Layer
4 Oxide Containing Region
The scope of the claims
[Claim 1]
　A base material,
　an aluminum-based plating layer located above the base material,
　and an intermetallic compound layer located between the base material and the aluminum-based plating layer and containing an intermetallic compound of Al and Fe,
the provided,
　in the base material, the
　mass%, C: 0.15% to 0.50% or
　less, Si: 2.000% 0.010% or more or
　less, Mn: 0.3% to 5.0% or less ,
　Cr: 0.010% or more and 2.000% or less,
　P: 0.1% or less,
　S: 0.1% or less,
　Al: 0.5% or less,
　B: 0.0002% or more and 0.0100% or less. ,
　N: 0% or more and 0.01% or less,
　W: 0% or more and 3% or less,
　Mo: 0% or more and 3% or less,
　V: 0% or more and 2% or less,
　Ti: 0% or more and 0.5% or less,
　Nb: 0% or more and 1% or less,
　Ni: 0% or more and 5% or less,
　Cu: 0% or more and 3% or less,
　Sn: 0% or more and 0.1% or less, and
　Sb: 0% or more and 0.1% or less.
And the balance
　consists of Fe and impurities, and the aluminum-based plating layer has an average of
　80% by mass to 97% by mass of Al,
　3% by mass to 15% by mass of Si, and
　0% by mass or more. 5 mass% or less of Zn,
　0 mass% to 5 mass% of Fe,
　3% by mass or less 0 mass% or more in total, and at least one member selected from the group consisting of Mg and Ca,
　and impurities,
the It is contained so as to be 100% by mass in total,
　the average value of the thickness of the intermetallic compound layer is 2 μm or more and 10 μm or less, and
　the maximum value of the thickness of the intermetallic compound layer is 10 μm or more and 25 μm or less,
　The standard deviation of the thickness of the intermetallic compound layer is 2 μm or more and 10 μm or less,
an aluminum-based plated steel sheet.
[Claim 2]
　Within the range of 5 μm from the interface between the base material and the intermetallic compound layer toward the center of the base material, selected from the group consisting of Si oxide, Mn oxide, Cr oxide and B oxide. The aluminum-based plated steel sheet according to claim 1, wherein the aluminum-based plated steel sheet has an oxide-containing region containing at least 1% by mass and 10% by mass or less in total.
[Claim 3]
　The aluminum-based plating layer contains one or more selected from the group consisting of Mg and Ca in a total amount of 0.01% by mass or more and 3% by mass or less. Plated steel sheet.
[Claim 4]
　The method for manufacturing an aluminum-plated steel sheet according to any one of claims 1 to 3
　,
　comprising a step of hot rolling a steel slab to obtain a hot rolled steel sheet, and a step of winding the hot rolled steel sheet.
　A step of pickling the hot-rolled steel sheet, a step
　of cold-rolling the hot-rolled steel sheet to obtain a cold-rolled steel sheet, and a step
　of continuously performing annealing treatment and hot dip aluminum plating treatment on the cold-rolled steel sheet,
the provided,
　components of the steel slab containing, by
　mass%, C: 0.15% to 0.50% or
　less, Si: 2.000% 0.010% or more or less,
　Mn: 0.3% to 5.0 %
　Or less, Cr: 0.010% or more and 2.000% or less,
　P: 0.1% or less,
　S: 0.1% or less,
　Al: 0.5% or less,
　B: 0.0002% or more 0.0100. % Or less,
　N: 0% or more and 0.01% or less,
　W: 0% or more and 3% or less,
　Mo: 0% or more and 3% or less,
　V: 0% or more and 2% or less,
　Ti: 0% or more and 0.5% Below,
　Nb: 0% to 1%,
　Ni: 0% or more and 5% or less,
　Cu: 0% or more and 3% or less,
　Sn: 0% or more and 0.1% or less, and
　Sb: 0% or more and 0.1% or less
, with the balance being Fe and impurities And
　the steel sheet winding temperature CT in the winding is 700° C. or more and 850° C. or less, and
　the arithmetic average roughness Ra of the surface of the cold rolled steel sheet after the cold rolling is 0.5 μm or more and 5 μm or less. ,
　the plating bath in the molten aluminum-based plating
　process, and 80 wt% or more 97 wt% or less of Al,
　3 mass% to 15 mass% of Si,
　and impurities,
　and 0 mass% to 5 mass% of Zn , 0
　mass% to 5 mass% of Fe,
　3% by mass or less 0 mass% or more in total, and at least one member selected from the group consisting of Mg and Ca,
containing such that 100 wt% in total A
method for manufacturing an aluminum-based plated steel sheet, comprising:
[Claim 5]
　In the annealing treatment, the value of the relational expression log(P H2O /P H2 ) between the steam partial pressure P H2O and the hydrogen partial pressure P H2 in the annealing atmosphere in the range of the plate temperature of 650°C to 900°C is -3 or more- The 　method for manufacturing an aluminum-plated steel sheet according to claim 4 , wherein the annealing time at the plate temperature is set to 0.5 or less and the annealing time is set to 60 seconds or more and 500 seconds or less.
[Claim 6]
　The said plating bath contains 0.01 mass% or more and 3 mass% or less in total of 1 or more types selected from the group which consists of Mg and Ca, The aluminum-type plating of Claim 4 or 5 characterized by the above-mentioned. Steel plate manufacturing method.
[Claim 7]
　A step of heating the aluminum-based plated steel sheet according to any one of claims 1 to 3 to 850°C or higher, a step
　of press-molding the
　aluminum-based plated steel sheet with a mold, and the aluminum-based plated steel sheet as described above. And a step of rapidly cooling with a mold at a cooling rate of 30° C./s or more
.