CN115135798A - Hot-stamped component and method for producing same - Google Patents
Hot-stamped component and method for producing same Download PDFInfo
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- CN115135798A CN115135798A CN202180014842.0A CN202180014842A CN115135798A CN 115135798 A CN115135798 A CN 115135798A CN 202180014842 A CN202180014842 A CN 202180014842A CN 115135798 A CN115135798 A CN 115135798A
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- 238000007747 plating Methods 0.000 claims abstract description 238
- 229910000831 Steel Inorganic materials 0.000 claims abstract description 164
- 239000010959 steel Substances 0.000 claims abstract description 164
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- 239000006104 solid solution Substances 0.000 claims abstract description 51
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Images
Classifications
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C21/00—Alloys based on aluminium
- C22C21/02—Alloys based on aluminium with silicon as the next major constituent
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/60—Ferrous alloys, e.g. steel alloys containing lead, selenium, tellurium, or antimony, or more than 0.04% by weight of sulfur
-
- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
- C23C2/04—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor characterised by the coating material
- C23C2/12—Aluminium or alloys based thereon
-
- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
- C23C2/26—After-treatment
- C23C2/28—Thermal after-treatment, e.g. treatment in oil bath
-
- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
- C23C2/26—After-treatment
- C23C2/28—Thermal after-treatment, e.g. treatment in oil bath
- C23C2/29—Cooling or quenching
-
- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
- C23C2/34—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor characterised by the shape of the material to be treated
- C23C2/36—Elongated material
- C23C2/40—Plates; Strips
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- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Materials Engineering (AREA)
- Mechanical Engineering (AREA)
- Metallurgy (AREA)
- Organic Chemistry (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Physics & Mathematics (AREA)
- Oil, Petroleum & Natural Gas (AREA)
- Thermal Sciences (AREA)
- Coating With Molten Metal (AREA)
- Heat Treatment Of Sheet Steel (AREA)
Abstract
The hot stamping member has: a base steel plate; and an Fe-Al based plating layer formed on one surface or both surfaces of the base steel sheet, the Fe-Al based plating layer containing, in mass%, Fe: 64.0-99.4%, Al: 0.5% -30.0%, Si: 0.1% -60% of Si in mass% of the Fe-Al based plating layer is W Si Setting the Al content to W Al When the above W is present Si And the above W Al Satisfy 5 xW Si ≤W Al The Fe-Al based plating layer comprises 2 layers of a FeAl layer and an Al solid solution ferrite layer in this order from the surface side, and the thickness of the Fe-Al based plating layer is 5 μm to 80 μm.
Description
Technical Field
The invention relates to a hot stamped component and a method of manufacturing the same.
This application claims priority based on Japanese application No. 2020-120494, filed on 14/07/2020, and the contents of which are incorporated herein by reference.
Background
In recent years, it has been demanded to suppress consumption of chemical fuel for environmental protection and global warming prevention. Such a demand is not exceptional for automobiles which are indispensable as moving mechanisms in daily life and activities, for example. In response to such a demand, for automobiles, improvement of fuel efficiency due to weight reduction of a vehicle body and the like have been studied. Since the structure of an automobile is often formed of iron, particularly steel plate, reducing the weight by thinning the steel plate is effective for reducing the weight of the automobile body. However, if the thickness of the steel sheet is simply reduced to reduce the weight of the steel sheet, the strength of the structure may be reduced, and safety may be reduced. Therefore, in order to reduce the thickness of the steel sheet, it is required to improve the mechanical strength of the steel sheet used so as not to reduce the strength of the structure.
Therefore, research and development have been conducted on steel sheets that can maintain or improve the mechanical strength even when the steel sheets are thinner than those used in the past by improving the mechanical strength of the steel sheets. Such a demand for steel sheets is not only in the automobile manufacturing industry but also in various manufacturing industries.
In general, a material having high mechanical strength tends to have low shape freezing property in a forming process such as bending, and when the material is processed into a complicated shape, the processing itself becomes difficult. One of means for solving the problem of the moldability is a so-called "hot press method (hot press method, high temperature press method, die quenching method)". In this hot press method, a material to be molded is once heated to a high temperature (austenite region temperature if steel) and the material softened by heating is rapidly cooled by heat removal by contact with a press die after or simultaneously with molding by press working to cause martensitic transformation, thereby obtaining high mechanical strength.
According to this hot press method, the material is heated once to a high temperature to be softened, and press processing is performed in a state where the material is softened, so that the press processing can be easily performed on the material. Therefore, by this hot press working, a press-molded product having both good shape freezing properties and high mechanical strength can be obtained. In particular, when the material is steel, the mechanical strength of the molded product can be increased by a quenching effect due to cooling performed simultaneously with or after molding.
Such hot press method is expected as a method for forming a high-strength member, but generally has a step of heating a steel sheet in the atmosphere to form oxides (scale) on the surface of the steel sheet. Therefore, it is necessary to remove the metal oxide by a subsequent step such as shot blasting or acid washing. However, in the shot blasting, it is difficult to completely remove the scale, and there is a possibility that the shot causes deformation of the steel sheet. In addition, in the case of pickling, it is necessary to perform waste water treatment or the like, and there are cases where countermeasures are taken from the viewpoint of environmental load. Therefore, there is a problem that the production cost is increased when shot blasting or acid pickling is performed.
In order to solve such a problem, a technique has been proposed in which a so-called Al-plated steel sheet obtained by Al-plating a steel sheet is used to suppress oxidation during heating. For example, patent document 1 discloses a coated steel sheet having an aluminum coating layer on the surface of the steel sheet and having high corrosion resistance by preventing oxidation of a base metal during heat treatment. Furthermore, it is shown that the coating upon heat treatment changes to a ferro-alloy and thus has a high hardness which may exceed 600 HV. Further, patent document 2 discloses a coated steel product in which a base steel is coated with an aluminum precoat or an aluminum alloy precoat, and the coating layer includes an interdiffusion layer, an intermediate layer, an intermetallic compound layer, and a surface layer in this order from the base steel toward the outside. In addition, the hardness of the intermediate layer and the surface layer is 900-1000 HV. Patent document 3 discloses a method for producing an automobile member by hot pressing using a plated steel sheet mainly composed of Al, the steel containing, in mass%, C: 0.05 to 0.7%, Si: 0.1-1%, Mn: 0.7-2%, P: 0.003-0.1%, S: 0.003-0.1% of a steel component, wherein the high-strength automobile part has a surface containing FeAl 2 、Fe 2 Al 5 、FeAl 3 And an alloy layer of 2 or more kinds of solid solution of FeAl and Al in alpha-Fe, wherein the alloy layer has a structure of 3 layers, and the outermost layer is made of FeAl 2 A layer as a main component.
However, the techniques disclosed in patent documents 1 to 2 have a problem that the plating layer has a hard layer, and if a strong impact is applied during hot pressing, the plating layer may peel off, and the corrosion resistance of the molded article may be reduced. In addition, in the component described in patent document 3, FeAl is used 2 、FeAl 3 、Fe 2 Al 5 Since the alloy layer is hard, there is a problem that the plating layer may be peeled off and the corrosion resistance of the molded article may be lowered in any of the cases where the alloy layer has any structure.
Patent document 4 discloses a hot press-formed member characterized in that a hot-dip aluminum plated layer is formed on the surface of a base steel sheet, and the plated layer is composed of only a single soft diffusion layer made of α -Fe in which Al is dissolved in solid solution.
However, in the technique disclosed in patent document 4, when the steel sheet is rolled at the time of forming and subjected to very severe forming such as reduction in sheet thickness, the steel sheet cannot withstand the impact at the time of forming only by a single soft diffusion layer, and there is a problem that flaws or plating peeling occur, and the corrosion resistance of the formed product is lowered.
Documents of the prior art
Patent document
Patent document 1: japanese patent laid-open publication No. 2000-38640
Patent document 2: international publication No. 2008/053273
Patent document 3: japanese laid-open patent publication No. 2007-314874
Patent document 4: international publication No. 2016/190538
Disclosure of Invention
Problems to be solved by the invention
The present invention has been made in view of the above problems. The invention provides a hot-stamped member having excellent corrosion resistance of a formed part even after severe forming such as reduction of the thickness of a steel sheet during forming, and a method for manufacturing the same.
Means for solving the problems
The inventors of the present invention have studied a method for further improving the corrosion resistance of a formed portion of a hot-stamped member obtained after hot stamping on the premise that a plated steel sheet containing Al is hot-stamped to obtain the hot-stamped member in order to suppress oxidation during heating. In particular, a method has been studied in which excellent corrosion resistance of a formed portion can be obtained even after severe forming such as reduction in the thickness of a steel sheet is performed at the time of forming.
As a result of the study, it was found that: the decrease in corrosion resistance of the formed portion of the hot-stamped member is caused by the following 2 points with respect to the Fe — Al plating layer formed on the surface of the base steel sheet: 1) peeling of the plating layer at the time of hot forming, 2) ratio of Si content to Al content in the plating layer. The present inventors have further studied and found that: 1) and 2), the corrosion resistance of the molded part is improved by carrying out the following measures.
Specifically, as a countermeasure for the plating layer peeling in 1), FeAl, which is a hard compound in the Fe-Al-based phase, is suppressed 2 、FeAl 3 、Fe 2 Al 5 (Al: 40-65 mass%) and the Al content (W) is determined for the plating composition (chemical composition of plating layer) after hot press heating Al Mass%) 0.5 to 30.0% and Si content (W) Si And mass%) of 0.1 to 6.0% and an Fe content (mass%) of 64.0 to 99.4% are effective. In particular, Fe 2 Al 5 Also has a Vickers hardness HV900 to 1000. The Fe-Al based phase includes a 2-membered phase containing Fe-Al, a 3-membered phase containing Fe-Al-Si containing Si, and a phase in which elements other than Fe, Al, and Si are dissolved in the 2-membered phase and the 3-membered phase.
Furthermore, it is also known that: structure of Fe-Al based coating layer formation of 2-layer structure containing FeAl as a specific amount of 2-layer structure improves resistance to mold damage during press forming and suppresses coating peeling 2 、FeAl 3 、Fe 2 Al 5 (Al: 40-65 mass%) two layers of a soft FeAl layer and an Al solid solution ferrite layer (the Vickers hardness of the FeAl layer and the Al solid solution ferrite layer is, for example, HV 300-700), and a FeAl layer harder than the Al solid solution ferrite layer is present on the surface side.
In general, Si is an element which is more stable in activity (has a lower ionization tendency) than Fe, and is an element which inhibits the substitution corrosion prevention of the base material by the plating layer and lowers the corrosion resistance. On the other hand, Si is also the following element: the excessive growth of a hard alloy layer formed at the interface between a plating layer and a base metal when the base metal is immersed in a hot dip aluminizing bath is suppressed, and the plating layer peeling phenomenon during temper rolling and processing is suppressed. Therefore, Si is generally contained in the aluminum plating bath in the production process of the hot-dip aluminum-plated steel sheet. The present inventors have found that: even if the Al-based plating contains Si, for exampleIf the Si content in the plating layer (W content) is set to a ratio of the Si content to the Al content in the plating layer, the Si content in the plating layer (W content) can be reduced by alloying the plating layer in the hot stamping heating step, so that the Si content in the plating layer can be reduced after hot stamping of the component, and further, if Al is an element more active (having a higher ionization tendency) than Fe Si Mass%) relative to the Al content (W) Al Mass%) can be suppressed to the range shown in formula (1), the corrosion resistance of the molded portion can be improved.
5×W Si ≤W Al Formula (1)
The present invention has been made based on the above findings, and the gist thereof is as follows.
[1]A hot stamped member according to one aspect of the present invention includes: a base steel plate; and an Fe-Al based plating layer formed on one surface or both surfaces of the base steel sheet, the Fe-Al based plating layer containing, in mass%, Fe: 64.0-99.4%, Al: 0.5% -30.0%, Si: 0.1 to 6.0%, wherein the content of Si in mass% of the Fe-Al based plating layer is W Si And the Al content is set to W Al When W is above Si And the above W Al The Fe-Al based plating layer comprises 2 layers of a FeAl layer and an Al solid solution ferrite layer in this order from the surface side, and the thickness of the Fe-Al based plating layer is 5 to 80 μm.
5×W Si ≤W Al Formula (1)
[2] The hot-stamped member according to item [1], wherein a ratio D2/D1 between a thickness D1 of the FeAl layer and a thickness D2 of the Al solid solution ferrite layer may be 0.8 to 2.5.
[3] The hot-stamped member according to the item [1] or [2], wherein the Fe-Al plating layer may contain voids, and the voids have a diameter of 5 to 15 μm.
[4] The hot-stamped member according to any one of the above [1] to [3], wherein the maximum value of the Al content of the Fe-Al based plating layer may be 30.0% by mass or less.
[5] The hot-stamped member according to any one of [1] to [4], wherein the base steel sheet may have a chemical composition containing, in mass%, C: 0.10% -0.50%, Si: 0.01% -2.00%, Mn: 0.30% -5.00%, B: 0.0002 to 0.0100%, Al: 1.00% or less, P: 0.100% or less, S: 0.100% or less, N: 0.0100% or less, Cr: 0% -2.00%, W: 0% -3.0%, Mo: 0% -3.0%, Co: 0% -3.0%, V: 0% -2.0%, Ti: 0% -0.50%, Nb: 0% -1.00%, Ni: 0% -5.0%, Cu: 0% -3.0%, Sn: 0% -0.10%, Sb: 0% -0.10%, Mg: 0% -0.0100%, Ca: 0% -0.0100%, Zr: 0% -0.0100%, REM: 0% -0.0100%, O: 0 to 0.0070 percent, and the balance of Fe and impurities.
[6]A method for producing a hot-stamped member according to another aspect of the present invention is the method for producing [1] above]The method for hot stamping a member includes the steps of: a blanking step of blanking (blanking) an Al-based plated steel sheet having a base steel sheet and an Al-based plating layer formed on the base steel sheet; a heating step of heating the Al-based plated steel sheet after the blanking step; and a forming step of forming and cooling the Al-based plated steel sheet after the heating step, wherein an adhesion amount of the Al-based plating layer per one surface is 5g/m 2 ～100g/m 2 The Al-based plating layer contains, in mass%, Al: 83.0% -95.0%, Si: 5.0% -12.0%, Fe: 0% to 5.0%, and the maximum heating temperature in the heating step is set to T in units of DEG C Max And the heating step is performed from the above-mentioned T Max To (T) Max T is T in minutes and W is the amount of deposit between-10 ℃ and the Al-based plated steel sheet Max T and W satisfy the following formula (2), T Max The temperature is 850 ℃ or higher, and 15 seconds or less from the end of the heating step to the start of the cooling in the molding step.
700≤(T Max -850) 2 X (t/W) is less than or equal to 4000 formula (2)
[7]According to [6] above]In the method of manufacturing a hot-stamped member, the amount of W attached to one surface of the Al plating layer may be 10g/m 2 ～80g/m 2 。
[8]According to [6] above]Or [7 ]]The method for producing a hot-stamped member, wherein T is Max T and W may satisfy the following formula (3).
1000≤(T Max -850) 2 X (t/W) is less than or equal to 3000 formula (3)
[9] The method for producing a hot-stamped component according to any one of the above [6] to [8], wherein the chemical composition of the base steel sheet may include, in mass%, C: 0.10% -0.50%, Si: 0.01% -2.00%, Mn: 0.30% -5.00%, B: 0.0002 to 0.0100%, Al: 1.00% or less, P: 0.100% or less, S: 0.100% or less, N: 0.0100% or less, Cr: 0% -2.00%, W: 0% -3.0%, Mo: 0% -3.0%, Co: 0% -3.0%, V: 0% -2.0%, Ti: 0% -0.50%, Nb: 0% -1.00%, Ni: 0% to 5.0%, Cu: 0% -3.0%, Sn: 0% -0.10%, Sb: 0% -0.10%, Mg: 0% -0.0100%, Ca: 0% -0.0100%, Zr: 0% -0.0100%, REM: 0% -0.0100%, O: 0 to 0.0070 percent, and the balance of Fe and impurities.
[10] The method for manufacturing a hot-stamped member according to any one of the items [6] to [9], wherein an interface alloy layer may be present between the base steel sheet and the Al-based plating layer in the Al-based plated steel sheet.
Effects of the invention
According to the aspect of the present invention, a hot stamped member (a molded member obtained by hot stamping) having a molded portion with excellent corrosion resistance and a method for manufacturing the same can be provided.
When such a hot-stamped member is applied to a part of an automobile, the impact safety of the automobile is improved, the fuel efficiency is improved by the weight reduction of the automobile, and CO is generated 2 And the like, reduction of exhaust gas.
Drawings
Fig. 1 is a schematic view of a hot-stamped member 1 according to the present embodiment, and is a schematic view showing the structure of Fe — Al plating layers formed on both surfaces of a base steel sheet 2, the Fe — Al plating layers including 2 layers of FeAl layers 4A and 4B and Al solid solution ferrite layers 3A and 3B in this order from the surface.
FIG. 2 is a view obtained by observing an Fe-Al-based plating layer (having an amount of adhesion of 80g/m per surface) obtained by quenching an Al-based plated steel sheet (having no change in sheet thickness) by removing heat from a flat die, the Fe-Al-based plating layer including 2 FeAl layers (the surface side) and an Al solid solution ferrite layer (the surface side) with an optical microscope 2 ) Held at 1050 ℃ for 2 minutes to form on the surface of the base steel sheet.
FIG. 3 shows an example of measuring the diameters (. mu.m) of the voids (a) and (b) contained in the Fe-Al based plating layer of FIG. 2 by an optical microscope.
FIG. 4 is a view showing an Fe-Al based plating layer (a plating layer having a general structure in the prior art) formed by removing heat from a flat die and rapidly cooling the plating layer (without processing to change the plate thickness) by an optical microscope, the Fe-Al based plating layer being obtained by coating an Al based plated steel sheet (the coating amount per one surface is 80 g/m) 2 ) Formed on the surface of the base steel sheet by holding at 950 ℃ for 0.5 minute. The 1 st and 3 rd layers from the surface being Fe 2 Al 5 。
Fig. 5A is a view showing an example of the state of peeling of the plating layer of the Fe — Al plating layer of the hot stamped member after press forming by hot stamping, and the cross section of the plating layer of the present embodiment in which the plating layer has a 2-layer structure is observed with an optical microscope. The press forming in this case was performed by rolling, and was performed so that the plate thickness ratio before and after rolling (1- (plate thickness after rolling/plate thickness before rolling)) × 100) became 15%.
Fig. 5B is a view showing an example of the state of peeling of the plating layer of the Fe — Al plating layer of the hot stamped member after press forming by hot stamping, and the cross section of the plating layer of the prior art having a 5-layer structure is observed with an optical microscope. The press forming in this case was performed by rolling, and was performed so that the plate thickness ratio before and after rolling (1- (plate thickness after rolling/plate thickness before rolling)) × 100) became 15%.
FIG. 6 is a W showing the composition of the plating layer of the hot-stamped member according to the present embodiment obtained based on the EDS analysis result from the cross section of the plating layer Al 、W Si (●: analysis points in the figure are 10 points marked by X in FIG. 2), the range of the invention example of the present application (mesh point part in the figure), and the composition W of the Fe-Al based plating layer in the conventional technique Al 、W Si Graph of (1) measurement example (Δ in the graph).
Detailed Description
As shown in fig. 1, a hot stamped member (a hot stamped member of the present embodiment) 1 of one embodiment of the present invention has: a base steel plate 2; and an Fe-Al based plating layer formed on the surface of the base steel sheet 2, wherein the Fe-Al based plating layer contains, by mass%, 64.0% to 99.4% of Fe, 0.1% to 6.0% of Si, and 0.5% to 30.0% of Al, and the Si content by mass% of the Fe-Al based plating layer is W Si Setting the Al content to W Al When it is in contact with the substrate, it satisfies 5 XW Si ≤W Al . The Fe — Al plating layer of the hot stamped member of the present embodiment includes 2 layers of FeAl layers 4A and 4B and Al solid solution ferrite layers 3A and 3B in this order from the front surface side, and the thickness of the Fe — Al plating layer is 5 μm to 80 μm.
In fig. 1, the Fe — Al plating layers are formed on both surfaces of the base steel sheet, but may be formed only on one surface.
The hot stamped member of the present embodiment will be described in detail below. Hereinafter, "%" of the content means "% by mass" unless otherwise specified.
< Fe-Al based coating layer >
The hot-stamped member of the present embodiment has an Fe — Al plating layer formed on one surface or both surfaces of the base steel sheet 2. In the present embodiment, the Fe — Al plating layer refers to a 2-component phase of Fe — Al, a 3-component phase of Fe — Al — Si containing Si, and a phase in which elements other than Fe, Al, and Si are dissolved in the 2-component phase and the 3-component phase, and is a layer containing 30% or more of Fe and 50% or more of Fe and Al in total. Examples of the elements that may be contained in addition to Fe, Al, and Si include elements mixed from the base steel sheet and hot-dip Al plating facilities, and impurities in the ingot of the Al plating bath. For example, C, Mn, B, Al, P, S, N, Cr, W, Mo, V, Ti, Nb, Ni, Cu, Sn, Sb, Mg, Ca, O, Zn may be contained in the Fe-Al based plating layer in a proportion of 0% to 5.0%.
(containing, in mass%, 64.0 to 99.4% of Fe, 0.1 to 6.0% of Si, and 0.5 to 30.0% of Al)
As described above, it is considered that: the reason why the corrosion resistance of the formed portion of the hot stamped member is lowered is peeling of the plating layer at the time of hot forming and existence of a plating structure containing Si which is an element stable in reactivity (compared with the base material) and Al which is an element active in reactivity (compared with the base material) in the plating layer.
By controlling the Al content (W) of the Fe-Al based plating layer after hot stamping Al Mass%) of 30.0% or less, and can suppress FeAl 2 、FeAl 3 And/or Fe 2 Al 5 And the like, formation of hard intermetallic compounds. If the Al content of the Fe-Al based plating layer exceeds 30.0%, a hard intermetallic compound is generated, and the plating layer is easily peeled off by forming. Therefore, the Al content is set to 30.0% or less. The Al content is preferably 28.0% or less.
On the other hand, Al is a ferrite-forming element and has an action of promoting formation of an Al solid-solution ferrite layer. Further, Al is an element having an active property, and therefore has a substitution corrosion prevention effect of the base material by the plating layer, and improves the corrosion resistance of the molded portion. When the Al content is less than 0.5%, the effect of improving the Al content cannot be obtained. Therefore, the Al content is set to 0.5% or more. The Al content is preferably 1.0% or more.
Further, Si is an element having stable element activity, and the Si content (W) of the Fe-Al plating layer after hot stamping Si And mass%) exceeding 6.0% not only inhibits the substitution corrosion prevention effect of the plating layer but also promotes Al which is a relatively hard 3-membered alloy phase 2 Fe 3 Si 3 (τ 1, possibly not having a stoichiometric composition). In this case, there is a possibility that the plating layer may be peeled off. Therefore, the Si content is set to 6.0% or less. The Si content is preferably 5.5% or less, more preferably 5.0% or less, and further preferably 4.5%, 4.0% or 3.8% or less.
On the other hand, if the Si content is less than 0.1%, Si becomes too small in the Al-based plated steel sheet before hot stamping, resulting in temper rolling and plating peeling during processing, and also in a decrease in corrosion resistance of the formed portion of the hot stamped member. Further, since Si is a ferrite-forming element as in Al, and promotes formation of an Al solid solution ferrite layer to soften the alloy layer, if the Si content is excessively reduced, the plating layer becomes brittle and the corrosion resistance of the formed portion is reduced. Therefore, the Si content is 0.1% or more. The Si content is preferably 0.2% or more.
The remainder of the Fe-Al based plating layer other than Al and Si is Fe and impurities. The Fe content is 64.0-99.4%.
Examples of the impurity elements include C, Mn, B, Al, P, S, N, Cr, W, Mo, V, Ti, Nb, Ni, Cu, Sn, Sb, Mg, Ca, O, and Zn contained in the plating layer from a base steel sheet, a hot-dip Al plating facility, an ingot of an Al plating bath, and the like. These impurities do not substantially affect the properties of the composition if the total content of the impurities is 5.0% or less.
The chemical composition of the Fe-Al based plating layer is an average composition obtained by analyzing 10 points of the Fe-Al based plating layer at regular intervals from the surface toward the base material as described later. However, in order not to generate hard intermetallic compounds, the maximum value (maximum Al content) of the Al contents at the respective measurement points is preferably 30.0% by mass or less.
(the Si content in mass% is set as W Si Setting the Al content to W Al When it is in contact with the substrate, it satisfies 5 XW Si ≤W Al )
In the hot-stamped member of the present embodiment, the Si content of the Fe — Al plating layer is further set to W Si Setting the Al content to W Al When it is in contact with the substrate, it satisfies 5 XW Si ≤W Al . The effect of improving the corrosion resistance of the formed portion of the Fe — Al plating layer can be achieved by suppressing the content of Si, which is an element having stable elemental activity, to 1/5 or less, which is the content of Al, which is an element having active elemental activity. More preferably, it satisfies 6 XW Si ≤W Al The relationship (c) in (c).
That is, in the Fe — Al plating layer of the hot stamped member of the present embodiment, the Al content and the Si content are in the ranges shown in the dot portions of fig. 6.
The Fe — Al based plating layer is formed, for example, by: on the base steel plateAn Al-based plated steel sheet having an Al-based plating layer on the surface is heated at the time of hot stamping, and Fe diffuses into the plating layer. An intermetallic compound which can be formed as an Fe-Al based plating layer is, for example, Fe 3 Al, FeAl, epsilon phase (phase produced by peritectic reaction between FeAl phase and liquid phase), FeAl 2 Zeta phase, Fe 2 Al 5 (eta phase), FeAl 3 (theta phase), or Al solid solution ferrite. When Si is contained in the plating layer, an Fe-Al-Si intermetallic compound is generated instead of a part of the Fe-Al intermetallic compound. Fe-Al-Si based intermetallic compound such as Al 2 Fe 3 Si 3 (τ1)、Al 3 FeSi(τ2)、Al 2 FeSi(τ3)、Al 3 FeSi 2 (τ4)、Al 8 Fe 2 Si(τ5)、Al 9 Fe 2 Si 2 (τ6)、Al 3 Fe 2 Si 3 (τ7)、Al 2 Fe 3 Si 4 (τ8)、Al 4 Fe 1.7 Si(τ10)、τ11-Al 5 Fe 2 Si (. tau.11), or Al, Si solid solution ferrite.
When an Al-based plated steel sheet (Al-plating bath composition: Al-9.5% Si) is hot-stamped under the conditions of the prior art, the structure of the plating layer becomes a 5-layer structure as shown in FIG. 4 (1 st layer: Fe in order from the surface side) 2 Al 5 Layer, layer 2: τ 1 or FeAl layer, layer 3: fe 2 Al 5 Layer, layer 4: FeAl or τ 1 layer, 5 th layer: al solid solution ferrite), or Fe in order from the surface side 2 Al 5 A layer (. tau.1 or FeAl dispersion), a FeAl layer (. tau.1) or a layer of FeAl, and an Al solid solution ferrite layer. In either case, hard Fe is formed 2 Al 5 And (3) a layer.
In the Fe — Al plating layer of the hot stamped member according to the present embodiment, the Al content and the Si content are controlled as described above, and the production conditions of the hot stamping are appropriately controlled as described below, so that FeAl, which is a hard intermetallic compound causing peeling, among the formable intermetallic compounds described above is not generated 2 、FeAl 3 、Fe 2 Al 5 (40-60% of Al and 900-1000% of HV, respectively).
The Fe-Al based plating layer of the hot stamped member of the present embodiment is a 2-layer plating layer (both Al: 30.0 mass% or less) including a soft Al solid solution ferrite layer and a FeAl layer of HV300 to 700. The Fe — Al plating layer has a 2-layer structure in which a FeAl layer harder than the Al solid solution ferrite layer is formed on the front surface side (the FeAl layer and the Al solid solution ferrite layer are formed in this order from the front surface side). By forming the Fe — Al plating layer into such a 2-layer structure, a hot stamped member can be obtained which is excellent in corrosion resistance of a formed part, excellent in damage resistance to a die in press forming, and capable of suppressing plating peeling.
Fig. 2 shows an example of a hot-stamped member having a layer structure in which the Fe — Al plating layer includes 2 layers of a FeAl layer and an Al solid solution ferrite layer in this order from the surface. Further, FIG. 4 shows that the Fe-Al based plating layer is formed of Fe 2 Al 5 An example of a case where the layer (1 st layer, 3 rd layer) has a 5-layer structure.
FIG. 2 shows an Al-based plated steel sheet (the amount of adhesion per one side is 80 g/m) 2 ) A cross-sectional view of the plated layer obtained by holding at 1050 ℃ for 2 minutes (after holding, observation was carried out after cooling using a flat mold). The symbol "x" in the figure is an analysis point of the composition of the Fe-Al based plating layer, and shows 10 points analyzed at equal intervals from the surface toward the base material.
FIG. 4 shows an Al-based plated steel sheet (the amount of adhesion per one side is 80 g/m) 2 ) A cross-sectional view of the plated layer obtained by holding at 950 ℃ for 0.5 minute (after holding, observation was performed after cooling using a flat mold).
Fig. 5A and 5B show photographs of cross sections of the plated layers after hot forming the plated layers of fig. 2 and 4, respectively. Knowing: do not contain Fe 2 Al 5 In the case of the 2-layer plating layer (fig. 5A) consisting of the FeAl layer and the Al solid solution ferrite layer, the frequency of cracks occurring is reduced as compared with the 5-layer plating layer (fig. 5B), and the frequency of cracks occurring is further reduced in the case of the Al solid solution ferrite layer which is softer than the FeAl layer.
The composition and layer structure of the Fe — Al based plating layer can be determined by the following method.
The composition of the Fe-Al based plating layer can be determined as follows: will heat upThe press member was cut out and polished in cross section, then, nital-etching was performed, and elemental analysis was performed on the Fe — Al plating layer by observing the cross section using an electron beam microanalyzer (EPMA) at a magnification of 1000 times as a composition image. In the elemental analysis, for example, as shown by the X-marks in FIG. 2 (which is a drawing of an optical microscope), 10 point analyses were performed with the positions of the points set at equal intervals from the surface of the plating layer toward the base material, and the mass% of Fe, Al, and Si at the 1 st point (1 st point: W) was obtained Fe1 、W Al1 、W Si2 ) And the mass% of Fe, Al, and Si at point 2 (point 2: w Fe2 、W Al2 、W Si2 ) … …, and 10 th site (10 th site: w Fe10 、W Al10 、W Si10 ) W is to be Fe1 、W Fe2 、……、W Fe10 Is set as W Fe W is to be Al1 、W Al2 、……、W Al10 Is set as W Al W is to be Si1 、W Si2 、……、W Si10 Is set as W Si 。
In addition, similarly, as a method of confirming whether or not the formula (1) is satisfied, the obtained W is used Si 、W Al Whether or not the measured value is 5 XW is confirmed Si ≤W Al . When mass% is determined by the so-called elemental analysis using EPMA, C, O elements were removed from the detected elements to calculate the mass% so as to exclude the influence of contamination (element: C, O) during the analysis.
Further, with respect to the layer structure of the Fe-Al based plating layer, the analysis result (W) of the Al content measured at equal intervals from the surface toward the base material direction Al1 、W Al2 、……、W Al10 A value of (d) exceeding 20.0% and not more than 30.0% in mass% each is defined as a FeAl layer, and a range of 0.5% to 20.0% is defined as an Al solid solution ferrite layer.
As a method for determining the FeAl layer other than the composition, there is a method based on structural analysis by Transmission Electron Microscopy (TEM), but in the present embodiment, as a simple method, the analysis result of the Al concentration obtained by EPMA is used.
In the case of the example shown in FIG. 2, the boundary between the Fe-Al layer and the Al solid solution ferrite layer exists in the vicinity of the gap in the plating layer, and the FeAl layer is on the front surface side (upper side in the figure) and the Al solid solution ferrite layer is on the base material side (lower side in the figure).
The EPMA analysis also enables the determination of the Fe, Al, and Si contents of the Fe-Al based plating layer.
(the ratio of the thickness D1(μm) of the FeAl layer to the thickness D2(μm) of the Al solid solution ferrite layer D2/D1 is 0.8 to 2.5)
FeAl layer and Al solid solution ferrite layer are both larger than Fe 2 Al 5 Since the material is softer, it is an important layer in terms of corrosion resistance of the molded part during very severe molding such as reduction in sheet thickness, and a ratio of D2/D1 of 0.8 to 2.5 is preferable from the viewpoint of improvement in corrosion resistance of the molded part. Here, the forming means that the steel sheet is subjected to rolling such that, for example, the sheet thickness ratio (1- (sheet thickness after rolling/sheet thickness before rolling)) × 100) becomes 10% or more.
If D2/D1 is less than 0.8, the proportion of the softer Al solid solution ferrite layer in the Fe-Al based plating layer is small, and therefore, there is a possibility that plating peeling increases during hot forming and the corrosion resistance of the formed part decreases. Therefore, D2/D1 are preferably 0.8 or more. D2/D1 are more preferably 1.0 or more. On the other hand, if D2/D1 exceeds 2.5, the proportion of the FeAl layer in the Fe-Al based plating layer is small, and therefore, the damage from the die during press molding increases, and the corrosion resistance of the molded part may decrease. Therefore, D2/D1 are preferably 2.5 or less. More preferably 2.1 or less.
The thickness D1 of the FeAl layer and the thickness of the Al solid solution ferrite D2 were controlled by the hot stamping heating conditions and the plating adhesion amount of the heated Al-based plated steel sheet, and the longer the holding time, the higher the heating temperature, or the more the plating adhesion amount at the time of hot stamping, the more the D1 and the D2 were increased, respectively.
(thickness of Fe-Al plating layer: 5 to 80 μm)
The thickness of the Fe-Al plating layer of the hot stamped member of the present embodiment is 5 to 80 μm. When the thickness of the Fe-Al based plating layer is less than 5 μm, the corrosion resistance of the molded part is lowered. The thickness of the Fe-Al based plating layer is preferably 7 μm or more, and more preferably 10 μm or more. On the other hand, if the thickness of the Fe — Al plating layer exceeds 80 μm, the plating layer is strongly subjected to shear stress and compressive stress during press molding, and is easily damaged (also referred to as a powdering phenomenon), and the corrosion resistance of the molded portion is lowered. The thickness of the Fe-Al based plating layer is preferably 70 μm or less, and more preferably 60 μm or less.
The thickness D1 of the FeAl layer, the thickness D2 of the Al solid solution ferrite layer, and the thickness (D1+ D2) of the Fe — Al plating layer were measured, for example, by observing a sample having a polished cross section with EPMA in which the size of 1 field is set to 100 μm × 100 μm. In the measurement of the thickness, the midpoint in the thickness direction between the measurement point having an adjacent Al content of 0.5% to 20.0% and the measurement point having an Al content of more than 20.0% and not more than 30.0% is regarded as the boundary between the FeAl layer and the Al solid solution ferrite layer.
(containing voids having a diameter of 5 to 15 μm)
Preferably, the Fe — Al plating layer of the hot stamped member of the present embodiment contains voids, and the size of the voids is 5 μm to 15 μm in diameter. It is believed that: the voids are Kirkendall voids (Kirkendall voids) generated by a difference in diffusion rate between the inward diffusion of Al of the Al plating layer toward the base steel sheet and the outward diffusion of Fe of the base steel sheet toward the Al plating layer. By including the kirkendall voids in the Fe — Al plating layer, stress concentration applied to the plating layer during forming by hot stamping is relaxed, and peeling of the plating layer is suppressed, resulting in improvement in corrosion resistance of the formed portion. This improvement effect cannot be obtained when the size of the voids is less than 5 μm in terms of diameter defined by the method described later. Therefore, the size of the voids is 5 μm or more in diameter. Preferably 6 μm or more, more preferably 7 μm or more or 8 μm or more.
The size of the voids is preferably 15 μm or less in diameter. If the diameter exceeds 15 μm, the voids become starting points of cracks formed during hot press forming, and the plating peeling increases. The diameter of the voids is preferably 14 μm or less, more preferably 13 μm or less or 12 μm or less.
The voids are voids contained in the Fe — Al based plating layer exemplified in fig. 3. As shown in fig. 3, voids are formed in the vicinity of the interface between the FeAl layer and the Al solid solution ferrite layer in many cases, but the effect can be obtained at any position.
As a method for determining the size of the void, a hot stamped member was cut out, a cross section was polished, nital etching was performed, and the cross section was observed at a magnification of 1000 times using an optical microscope. The voids were observed as depressions in the optical microscope because they were voids in the plating layer. The minimum circumscribed circle of the voids observed in the inner package was drawn, and the diameter of this circumscribed circle was measured as the diameter of the voids. For example, in FIG. 3, (a) the diameter of the voids is 5.0. mu.m, and in (b) the diameter of the voids is 6.1. mu.m. In the present embodiment, the diameters of the voids in 10 locations are measured in order from the large void, and the average value is set as the diameter of the void. The voids are generally circular or elliptical, and are affected by the heating temperature and holding time of hot stamping or diffusion of Al and Fe, and in some cases, a plurality of voids may come into contact with each other in the process of expansion to be indefinite.
< base Steel sheet >
The base steel sheet included in the hot-stamped member of the present embodiment will be described in detail.
(chemical composition)
The Fe — Al plating layer is important for the hot-stamped member of the present embodiment, and the base steel sheet is not necessarily limited. However, since the hot stamping method is a method of performing press working and quenching with a die substantially simultaneously, the chemical composition of the base steel sheet is preferably in the following range as a component system having good hardenability. In the following description, "%" with respect to a component means "% by mass" unless otherwise specified.
The base steel sheet of the hot-stamped member according to the present embodiment preferably has a chemical composition containing, in mass%, C: 0.10% -0.50%, Si: 0.01% -2.00%, Mn: 0.30% -5.00%, B: 0.0002 to 0.0100%, Al: 1.00% or less, P: 0.100% or less, S: 0.100% or less, N: 0.0100% or less, optionally containing Cr selected from: 2.00% or less, W: 3.0% or less, Mo: 3.0% or less, Co: 3.0% or less, V: 2.0% or less, Ti: 0.50% or less, Nb: 1.00% or less, Ni: 5.0% or less, Cu: 3.0% or less, Sn: 0.10% or less, Sb: 0.10% or less, Mg: 0.0100% or less, Ca: 0.0100% or less, Zr: 0.0100% or less, REM: 0.0100% or less and O: 0.0070% or less, and the balance of Fe and impurities.
(C：0.10％～0.50％)
Carbon (C) is an element that improves hardenability. When the C content is less than 0.10%, hardenability is reduced and the strength of the hot stamped member is insufficient. Therefore, the C content is preferably set to 0.10% or more. The C content is more preferably 0.15% or more, and still more preferably 0.20% or more, 0.25% or more, or 0.28% or more.
On the other hand, if the C content exceeds 0.50%, the toughness of the steel sheet is significantly reduced, and the workability is reduced. Therefore, the C content is preferably set to 0.50% or less. The C content is more preferably 0.45% or less, and still more preferably 0.43% or less or 0.40% or less.
(Si：0.01％～2.00％)
When the content of silicon (Si) is less than 0.01%, hardenability decreases, and the strength of the hot stamped member decreases. In addition, fatigue characteristics are also reduced. Therefore, the Si content is preferably set to 0.01% or more. The Si content is more preferably 0.02% or more, and still more preferably 0.03% or more.
On the other hand, Si is an element (easily oxidizable element) that is more easily oxidized than Fe, and if the Si content exceeds 2.00% in the continuous annealing plating line, a stable Si-based oxide film is formed on the steel sheet surface during annealing treatment, which hinders the adhesion (adhesiveness) of hot-dip Al plating, resulting in generation of non-plating. Therefore, the Si content is preferably set to 2.00% or less. The Si content is more preferably 1.50% or less, and still more preferably 1.00% or less, 0.50% or less, or 0.10% or less.
(Mn：0.30％～5.00％)
Manganese (Mn) is an element that can improve hardenability of steel and further suppress hot shortness due to S. In the case where the Mn content is less than 0.30%, hardenability is lowered and strength is insufficient. Therefore, the Mn content is preferably set to 0.30% or more. The Mn content is more preferably 0.40% or more, and still more preferably 0.50% or more or 0.60% or more.
On the other hand, when the Mn content exceeds 5.00%, the collision resistance of the hot stamped member after quenching is lowered. Therefore, the Mn content is preferably set to 5.00% or less. The Mn content is more preferably 4.50% or less, and still more preferably 4.00% or less or 3.50% or less.
(B：0.0002％～0.0100％)
Boron (B) is a useful element from the viewpoint of hardenability. In order to obtain this effect, the B content is preferably set to 0.0002% or more. The B content is more preferably 0.0005% or more, and still more preferably 0.0010%, 0.0015% or more, or 0.0020% or more.
On the other hand, if the B content exceeds 0.0100%, the hardenability-improving effect described above is saturated, and casting defects, cracks at the time of hot rolling, and the like are generated, thereby deteriorating the manufacturability. Therefore, the B content is preferably set to 0.0100% or less. The B content is more preferably 0.0080% or less, and still more preferably 0.0070% or less, or 0.0060% or less.
(P: 0.100% or less)
Phosphorus (P) is an element contained as an impurity. If the P content exceeds 0.100%, adverse effects such as a decrease in toughness become significant. Therefore, the P content is preferably set to 0.100% or less. The P content is more preferably 0.080% or less, and still more preferably 0.060% or less or 0.050% or less.
On the other hand, the lower limit of the P content is not particularly limited, and may be set to 0%. However, setting the P content to less than 0.001% is uneconomical from the viewpoint of the refining limit. P is also a solid-solution strengthening element, and the strength of the steel sheet can be increased at relatively low cost. Therefore, the P content may be set to 0.001% or more.
(S: 0.100% or less)
Sulfur (S) is an element contained as an impurity, and is an element which becomes an inclusion in steel as MnS. When the S content exceeds 0.100%, MnS becomes a starting point of fracture, ductility and toughness are reduced, and workability is reduced. Therefore, the S content is preferably set to 0.100% or less. The S content is more preferably 0.080% or less, and still more preferably 0.050% or less or 0.030% or less.
On the other hand, the lower limit of the S content is not particularly limited, and may be set to 0%. However, setting the S content to less than 0.001% is uneconomical from the viewpoint of the refining limit. Therefore, the S content may be set to 0.001% or more.
(Al: 1.00% or less)
Aluminum (Al) is contained in steel as a deoxidizer. Since Al is an oxidizable element compared to Fe, if the Al content exceeds 1.00%, a stable Al-based oxide film is formed on the steel sheet surface during the annealing treatment, which impairs the adhesion of hot-dip Al and causes unplating. Therefore, the Al content is preferably set to 1.00% or less. The Al content is more preferably 0.50% or less, and still more preferably 0.30% or less, 0.20% or less, or 0.10% or less.
On the other hand, the lower limit of the Al content is not particularly limited, and may be set to 0%, but when the Al content is set to less than 0.01%, it is uneconomical from the viewpoint of the refining limit. Therefore, the Al content may be set to 0.01% or more.
(N: 0.0100% or less)
Nitrogen (N) is an element contained as an impurity. Since solid-solution N adversely affects the characteristics, N is preferably in an inclusion state from the viewpoint of stabilization of the characteristics, and is preferably bonded to Ti, Nb, Al, or the like. If the N content is increased, the content of the element to be contained for fixing N as an inclusion becomes large, resulting in an increase in cost. Therefore, the N content is preferably set to 0.0100% or less. The N content is more preferably 0.0080% or less, and still more preferably 0.0060% or less.
On the other hand, the lower limit of the N content is not particularly limited and may be set to 0%, but if the N content is set to less than 0.0010%, it is uneconomical from the viewpoint of the refining limit. Therefore, the N content may be set to 0.0010% or more.
The base steel sheet of the hot-stamped component according to the present embodiment may further contain the following elements (components) in addition to the above elements. Since a preferable base steel sheet can be obtained without including the elements described below, the lower limit values of the following elements are all 0%.
(Cr：0％～2.00％)
Chromium (Cr) is an element having an effect of improving the hardenability of steel similarly to Mn, but generally is more expensive than Mn, and therefore may not be contained (may be 0%). However, Cr is preferably contained when hardenability is insufficient due to Mn alone, and in this case, the Cr content is preferably set to 0.01% or more. The Cr content is more preferably 0.10% or more.
On the other hand, since Cr is an element (easily oxidizable element) that is more easily oxidized than Fe, if the Cr content exceeds 2.00%, a stable Cr-based oxide film is formed on the steel sheet surface during the CGL annealing treatment, which inhibits the adhesion of hot-dip Al plating and causes unplating. Therefore, the Cr content is preferably set to 2.00% or less. The Cr content is more preferably 1.60% or less, and still more preferably 1.40% or less.
(W, Mo, Co: 0% to 3.0% respectively)
Tungsten (W), molybdenum (Mo), and cobalt (Co) are elements that improve the hardenability of steel, respectively. In order to obtain this effect, W, Mo, and Co are preferably contained in an amount of 0.01% or more, and more preferably 0.1% or more, respectively.
On the other hand, when the contents of W, Mo, and Co exceed 3.0%, the above effects are saturated, and the cost is also increased. Therefore, the contents of W, Mo, and Co are preferably set to 3.0% or less, respectively. More preferably, the contents of W, Mo and Co are 1.0% or less, respectively.
(V：0％～2.0％)
Vanadium (V) is an element that improves the hardenability of steel. In order to obtain this effect, the V content is preferably set to 0.01% or more. The V content is more preferably 0.05% or more, and still more preferably 0.1% or more.
On the other hand, if the V content exceeds 2.0%, the above effect is saturated and the cost is also increased. Therefore, the V content is preferably set to 2.0% or less. The V content is more preferably 1.0% or less.
(Ti：0％～0.50％)
Titanium (Ti) is an effective element for fixing N. Therefore, Ti is preferably contained. In particular, when the effect of fixing N is to be obtained, it is more preferable that the content of N is about 3.4 times or more in mass%. Even if the N content is reduced, it is often about 10ppm (0.001%), and therefore, as the actual Ti content, it is more preferably 0.005% or more.
On the other hand, if the Ti content becomes excessive, hardenability decreases and strength decreases. If the Ti content exceeds 0.50%, such a decrease in hardenability and strength becomes significant. Therefore, the Ti content is preferably set to 0.50% or less. The Ti content is more preferably 0.10% or less.
(Nb：0％～1.00％)
Niobium (Nb) is an effective element for fixing N. Therefore, Nb is preferably contained. In particular, when the effect of fixing N is to be obtained, it is more preferable that the content of N is about 6.6 times or more in mass%. Even if the N content is reduced, the N content is often about 10ppm (0.001%), and therefore, the actual Nb content is more preferably 0.01% or more.
On the other hand, if the Nb content becomes excessive, hardenability decreases and strength decreases. If the Nb content exceeds 1.00%, such a decrease in hardenability and strength becomes significant, and therefore the Nb content is preferably set to 1.00% or less.
Further, even if Ni, Cu, Sn, Sb, or the like is contained as the chemical composition of the base steel sheet, the intended effect of the hot-stamped member of the present embodiment is not inhibited.
(Ni：0％～5.0％)
Nickel (Ni) is an element useful from the viewpoint of improvement in hardenability and low-temperature toughness associated with improvement in impact resistance. Therefore, Ni is preferably contained. In order to obtain these effects, the Ni content is preferably set to 0.01% or more. The Ni content is more preferably 0.1% or more.
On the other hand, if the Ni content exceeds 5.0%, the above-described effects are saturated and the cost is increased. Therefore, the Ni content is preferably set to 5.0% or less.
(Cu：0％～3.0％)
Copper (Cu) is an element useful from the viewpoint of hardenability and toughness, and therefore, it is preferable to contain Cu. In order to obtain this effect, the Cu content is preferably set to 0.01% or more. The Cu content is more preferably 0.1% or more.
On the other hand, if the Cu content exceeds 3.0%, the above-described effects are saturated and the cost is increased. In addition, excessive Cu causes deterioration of the properties of the cast slab, cracking during hot rolling, and generation of flaws. Therefore, the Cu content is preferably set to 3.0% or less.
(0% to 0.10% of each of Sn and Sb)
Tin (Sn) and antimony (Sb) are effective elements for improving wettability and adhesion of plating. Therefore, Sn and Sb are preferably contained. In order to obtain the above-described effects, at least one of Sn and Sb is preferably contained in an amount of 0.005% or more. More preferably, the content of at least one of Sn and Sb is 0.01% or more.
On the other hand, when at least one of Sn and Sb is contained in an amount exceeding 0.10%, defects are likely to occur during production, and the toughness is lowered. Accordingly, the Sn content and the Sb content are preferably 0.10% or less, respectively.
(Mg, Ca, Zr and REM are 0 to 0.0100% respectively)
When the contents of calcium (Ca), magnesium (Mg), zirconium (Zr) and rare earth element (REM; RareEarth Metal) are 0.0001% or more, respectively, it is effective for refining inclusions. Therefore, the contents of Ca, Mg, Zr, and REM are preferably 0.0001% or more, respectively.
On the other hand, when the content of each element exceeds 0.0100%, the above-described effect is saturated. Therefore, the contents of Ca, Mg, Zr, and REM are preferably 0.0100% or less, respectively. REM means 17 elements in total of Sc, Y and lanthanoid, and is at least 1 of them. The content of REM is a total content of at least 1 of these elements.
(O：0％～0.0070％)
Oxygen (O) is not an essential element and is contained as an impurity in steel, for example. O is an element that forms an oxide and may deteriorate the characteristics of the hot stamped member. For example, oxides present in the vicinity of the surface of the steel sheet cause surface defects. If an oxide is present in the cut surface, a notch-like flaw is formed at the end surface, resulting in deterioration of the characteristics of the hot stamped member. Therefore, the lower the O content, the better. In particular, since the deterioration of the characteristics becomes remarkable when the O content exceeds 0.0070%, the O content is set to 0.0070% or less. The O content is preferably 0.0060% or less, more preferably 0.0050% or less. The O content may be 0%, but from the viewpoint of economic cost at the limit of refining, the O content is preferably 0.0001% or more.
(with respect to other ingredients)
Other components are not particularly limited, but elements such As may be mixed in from scrap. However, if the mixing amount is in the normal range, the properties of the hot-stamped member of the present embodiment are not affected.
The remainder of the chemical composition of the base steel sheet is Fe and impurities. The impurities are components mixed from raw materials such as ores and scraps or various factors in a manufacturing process in the industrial production of steel materials, and are components that are allowed within a range that does not adversely affect the hot stamped member of the present embodiment.
The chemical composition of the base steel sheet of the hot-stamped member of the present embodiment is set to the chemical composition of the portion other than the Fe — Al plating layer on the surface, and can be measured by the following method.
First, an analysis sample was cut out of the hot stamped member, and the Fe — Al plating layer on the surface was removed by surface grinding. Thereafter, the chemical composition is analyzed by elemental analysis such as ICP (inductively coupled plasma) luminescence analysis.
Since the chemical composition of the base material does not change before and after hot stamping, when the above-described chemical composition is to be obtained in the base steel sheet of the hot stamped member according to the present embodiment, the chemical composition of the base steel sheet of the plated steel sheet to be subjected to hot stamping may be set to the above-described range.
(Metal structure)
The base steel sheet included in the hot-stamped component of the present embodiment is preferably formed of martensite in the metal structure in order to improve the collision resistance of the automobile. The martensite is preferably 50% or more in terms of area ratio.
The hardness of the base steel sheet is not limited, but is preferably 300HV or more in terms of vickers hardness (load of 1kgf) as a member having excellent collision resistance.
In the case of measuring the hardness of the base steel sheet, a sample was collected so that the cross section of the base steel sheet in the thickness direction thereof became a measurement surface, and the distance from the measurement surface of the sample to a position where the surface was 1/4 of the thickness thereof was measured in accordance with JIS Z2244: 2009, the load was set to 1kgf, and the hardness was measured.
< method for producing Hot-stamped Member >
The hot stamped member according to the present embodiment can be obtained by a manufacturing method including the following steps.
(i) A cutting step of cutting an Al-based plated steel sheet having a base steel sheet and an Al-based plating layer formed on the base steel sheet;
(ii) a heating step of heating the Al-based plated steel sheet after the blanking step;
(iii) and a forming step of forming and cooling the Al-based plated steel sheet after the heating step.
Preferred conditions for each step will be described below.
(cutting step)
In the cutting step, an Al-based plated steel sheet having a base steel sheet and an Al-based plating layer formed on the base steel sheet is cut. The blanking method is not particularly limited, but may be a method such as blanking, shearing, or laser cutting using a die.
The Al-based plated steel sheet for blanking can be obtained by hot-dip Al-plating the base steel sheet having the above chemical composition. The method for producing the base steel sheet is not limited, and the base steel sheet may be produced under known conditions. For example, after the chemical composition is adjusted in the steel making process, a slab (base material) is produced by continuous casting, then the obtained slab (base material) is hot-rolled, pickled, and cold-rolled to produce a cold-rolled steel sheet, and the obtained cold-rolled steel sheet is continuously subjected to recrystallization annealing and hot-dip aluminum plating treatment (adjustment of the adhesion amount of hot-dip aluminum plating by dipping in a hot-dip aluminum plating bath and by gas wiping) in a hot-dip plating line, thereby obtaining an Al-based plated steel sheet.
The amount of Al-based plating deposited on one surface was set to 5g/m 2 ～100g/m 2 . The adhesion amount is less than 5g/m 2 In this case, the corrosion resistance of the molded part is lowered. Therefore, the amount of adhesion was set to 5g/m 2 The above. The amount of Al-based plating is also important in view of increasing the FeAl layer of the hot-stamped member, and is preferably 10g/m 2 The above. The amount of adhesion is more preferably 12g/m 2 Above, more preferably 15g/m 2 As described above.
On the other hand, the amount of Al-based plating layer deposited exceeds 100g/m 2 In this case, hard Fe is formed on the hot stamped member 2 Al 5 The corrosion resistance of the molded part is lowered. Therefore, the amount of adhesion was set to 100g/m 2 The following. Further, the thickness of the Al-based plating layer having a large adhesion amount (the thickness in μm is roughly adjusted to the adhesion amount/3) also becomes large, and the Al-based plating layer is strongly subjected to shear stress and compressive stress during press molding. Therefore, the amount of adhesion is preferably 80g/m 2 Hereinafter, more preferably 75g/m 2 Hereinafter, more preferably 70g/m 2 The following.
The Al-based plating layer contains, in mass%, Al: 83.0% -95.0%, Si: 5.0% -12.0%, Fe: 0 to 5.0 percent.
Al is an element necessary for improving oxidation resistance during heating of hot stamping and corrosion resistance of a formed part, and when the Al content is less than 83.0%, the corrosion resistance of a plating layer when a hot stamped member is produced is inferior. On the other hand, when the Al content exceeds 95.0%, the plating layer is likely to be peeled off during the molding by hot stamping, and the corrosion resistance of the molded portion is poor.
Si is an element necessary for improving the corrosion resistance of the formed portion of the hot stamped member. Since the alloying reaction between Al and Fe can be suppressed by containing Si, the formation of a hard Al — Fe alloy layer can be suppressed, and the corrosion resistance of the molded portion is excellent. When the Si content is less than 5.0%, the corrosion resistance of the formed portion is poor, and when the Si content exceeds 12.0%, the amount of the element having stable activity contained in the plating layer becomes excessive, and the corrosion resistance of the formed portion is lowered. Therefore, the Si content is 5.0% or more, preferably 7.0% or more. Further, the Si content is 12.0% or less, preferably 11.0% or less.
Fe is inevitably contained by elution of Fe when the base steel sheet is immersed in the hot dip aluminizing bath. The lower limit is not particularly limited, but is 0%, and it is preferable to set the lower limit to 0.01% because it costs the industry. In the case where the Fe content exceeds 5.0%, precipitates (dross) of the alloy are formed in the plating bath because the dissolution limit of Fe in the Al plating bath is exceeded, resulting in the adherence of the dross to the plating layer. In this case, the molded article becomes crushed during press molding, and the appearance quality is impaired. Therefore, the Fe content is set to 5.0% or less.
Examples of the elements that can be contained in the Al-based plating layer in addition to Al, Si, and Fe include elements mixed from the base steel sheet, hot-dip aluminum plating facilities, and elements such as impurities in an ingot of an aluminum plating bath. Examples of such elements include C, Mn, B, Al, P, S, N, Cr, W, Mo, V, Ti, Nb, Ni, Cu, Sn, Sb, Mg, Ca, O, and Zn, and the total content of these elements in the Al-based plating layer may be 0% to 5.0%.
In the case where the Al-based plating layer is produced by hot dip aluminum plating, an interface alloy layer (generally made of Al) may be formed between the base steel sheet and the Al-based plating layer during immersion in a hot dip aluminum plating bath 8 Fe 2 Si(τ5)、FeAl 3 (theta) a layer of 1 to 5 [ mu ] m). The deposition amount and composition of the Al-based plating layer in the present embodiment are values not including the interfacial alloy layer.
Examples of the method for determining the amount of Al deposited include a sodium hydroxide-hexamethylenetetramine-hydrochloric acid stripping gravimetric method. Specifically, as defined in JIS G3314: 2011, a predetermined area S (m) is prepared 2 ) (e.g., 50 mm. times.50 mm) and the weight w is measured 1 (g) In that respect Then, the mixture was immersed in an aqueous sodium hydroxide solution and an aqueous hydrochloric acid solution containing hexamethylenetetramine in this order until the foam disappeared, and then immediatelyNamely, washing with water, and measuring the weight w again 2 (g) In that respect At this time, the amount of Al plating deposited on both surfaces of the test piece (g/m) 2 ) Can be prepared from (w) 1 -w 2 ) Is calculated as,/S. The method utilizes the following properties: al, Si, and solid-dissolved Fe and the like are dissolved by the aqueous sodium hydroxide solution, but the interface alloy layer containing Fe and the base material do not dissolve.
Further, as a method for determining the composition (contents of Al, Si, and Fe) of the Al-based plating layer, there is a method in which the plating layer is dissolved and the solution is quantitatively analyzed by an Inductively Coupled Plasma (ICP) emission spectroscopy. As a method of dissolving the Al-based plating layer, for example, a method of immersing in an aqueous sodium hydroxide solution is cited. Specifically, as defined in JIS G3314: 2011, an aqueous solution prepared by dissolving 2g of sodium hydroxide (JIS K8576) in 8mL of water is heated to 85 ℃ or higher, and the sample is immersed in the solution until the foaming caused by the dissolution of the plating layer disappears, whereby the Al plating layer can be dissolved. The method utilizes the following properties: al, Si, and solid-dissolved Fe are dissolved by the aqueous sodium hydroxide solution, but the interface alloy layer containing Fe and the base material do not dissolve.
(heating step)
In the heating step, the Al-based plated steel sheet after the blanking step is heated. In the heating step, heating is performed as follows: to a maximum heating temperature T MAX (. degree. C.) and from T MAX To (T) MAX A time (holding time) t (minute) for holding the Al-based plated steel sheet at-10 ℃ and an adhesion amount W (g/m) per one surface of the Al-based plating layer of the Al-based plated steel sheet 2 ) Satisfies the formula (2). Wherein, T MAX The temperature is set to 850 ℃ or higher.
700≤(T MAX -850) 2 X (t/W) is less than or equal to 4000 formula (2)
(T MAX -850) 2 When x (t/W) is less than 700, the holding time may be short, the maximum heating temperature may be low, and Fe may be formed 2 Al 5 、FeAl 2 、FeAl 3 Remains in the Fe-Al based plating layerFe 2 Al 5 、FeAl 2 、FeAl 3 The case (2) is a case where the Fe-Al based plating layer has a 3-layer structure or a 5-layer structure, or the case where the Si content is large. In this case, the corrosion resistance of the molded part is lowered. Thus, (T) MAX -850) 2 X (t/W) is 700 or more, preferably 800 or more, and more preferably 900 or more.
Furthermore, the maximum heating temperature T MAX If the temperature is less than 850 ℃, the austenite region temperature of the base steel sheet may not be reached, and the desired mechanical strength may not be obtained. Further, the alloying reaction between the base steel sheet and the Al-based plating layer becomes insufficient, and pure Al may remain in the plating layer to deteriorate the corrosion resistance.
On the other hand, (T) MAX -850) 2 When x (t/W) exceeds 4000, excessive heating may reduce the FeAl layer in the Fe-Al based plating layer and deteriorate the scratch resistance. Further, the thickness of the Fe — Al plating layer may become excessively thick, and the Al content may become small due to the single-layer structure of only Al solid-solution ferrite. In this case, the corrosion resistance of the molded part is poor. Thus, (T) MAX -850) 2 X (t/W) is 4000 or less, preferably 3800 or less and 3600 or less.
With respect to the maximum heating temperature T MAX The upper limit of (3) is preferably 1050 ℃ and more preferably 980 ℃. The lower limit is preferably 880 ℃ and more preferably 900 ℃. In addition, with respect to slave T MAX To (T) MAX The upper limit of the holding time t between-10 ℃ is preferably 18.0 minutes, more preferably 12.0 minutes. The lower limit is preferably 1.0 minute, and more preferably 2.0 minutes.
Further, by heating so as to satisfy the formula (3), the size of the voids contained in the FeAl layer and the Al solid solution ferrite layer can be controlled, and the corrosion resistance of the formed portion can be improved. Therefore, in the heating step, heating is preferably performed so as to satisfy formula (3).
1000≤(T MAX -850) 2 X (t/W) is less than or equal to 3000 formula (3)
(Molding Process)
In the forming step, the Al-based plated steel sheet after the heating step is cooled simultaneously with or after forming.
The cooling is started within 15 seconds from the end of the heating step (from the completion of the extraction in the heating furnace), and is performed by heat removal by contact with the mold, for example, simultaneously with the molding.
If the time after the heating step until the start of cooling (in the case of simultaneous cooling and forming, the start of cooling and forming) exceeds 15 seconds, not only a martensite structure is not obtained and the collision resistance of the part is reduced, but also the Fe — Al plating layer is hardened due to the temperature reduction at the time of forming the steel sheet, so that an impact is strongly applied at the time of forming by the die, the plating layer is promoted to be peeled off, and the corrosion resistance of the formed portion of the hot stamped member is reduced.
In the cooling in the molding step, the cooling is preferably performed at an average cooling rate of 50 ℃/sec or more to 200 ℃ or less. If the average cooling rate is less than 50 ℃/sec, the hardenability of the base steel sheet is lowered, and the collision resistance is lowered even when the steel sheet is formed into a part. On the other hand, the upper limit of the average cooling rate is not necessarily limited, but is preferably set to 1000 ℃/sec or less as a limit for cooling by heat removal in a mold, cooling with water, or the like.
Further, when the cooling stop temperature exceeds 200 ℃, the hardenability of the base steel sheet is lowered, and the collision resistance is lowered even when the steel sheet is formed into a part.
Examples of the method of measuring the temperature of the steel sheet include a method of indirectly measuring the temperature by imaging with a thermal imaging camera, and a method of directly measuring the temperature by spot-welding a thermocouple (a position where a die is not damaged during press molding) to an end portion of the steel sheet.
According to the above-described manufacturing method, the hot stamped member of the present embodiment can be obtained.
Examples
Hereinafter, the hot-stamped member and the method for manufacturing the same according to the present invention will be described in more detail with reference to examples. The following embodiments are merely examples of the hot-stamped member and the method of manufacturing the same according to the present invention, and the hot-stamped member and the method of manufacturing the same according to the present invention are not limited to the following examples.
First, base steel sheets (1.4 mm in thickness) having chemical compositions shown in a1 to a20 in table 1 were produced through a usual steel-making process, hot rolling process, pickling process, and cold rolling process, and used as test materials. Then, this base steel sheet is continuously annealed and hot-dip aluminized by a sendzimir type hot-dip plating line to produce an Al-based plated steel sheet. The amount of Al deposited is 3 to 110g/m by gas wiping 2 And with respect to the composition of the hot dip aluminizing bath, also in the Si: 1-20%, Fe: 1 to 8% and the balance of Al composition. The composition of the Al plating layer of the obtained Al-based plated steel sheet was quantitatively measured by the ICP described above. The results are shown in table 2.
[ Table 1]
The obtained Al-based plated steel sheet (table 2) was cut by shearing (blanking step), to prepare a blank of Al-based plated steel sheet having a size of 200 × 300 mm. The produced blanks of Al-based plated steel sheets were heated in an electric furnace under various conditions such that the maximum reaching temperature was 750 to 1150 ℃ as shown in table 2 (heating step). The holding time is set so that the time from the maximum reaching temperature to (maximum reaching temperature-10 ℃) is 1.0 to 18 minutes. After the billet is taken out of the electric furnace, rolling is started in such a manner that the plate thickness ratio (1- (plate thickness after rolling/plate thickness before rolling)) × 100) becomes 15% between 6 and 30 seconds, and immediately after the rolling, the billet is rapidly cooled to 200 ℃ or less by a flat die (forming step). Thereafter, the test piece cut into a size of 70mm × 150mm was used as a test piece of the hot-stamped member.
The Fe-Al-based plating layer was examined for the test piece in the following manner. Further, the corrosion resistance of the molded portion was evaluated.
The thicknesses of the FeAl layer and the Al solid solution ferrite layer, the Al content in the Fe-Al based plating layer, the Si content, the Fe content, and the layer structure of the Fe-Al based plating layer were evaluated by the following methods. Further, the structure of the base steel sheet was also observed.
(thickness of Fe-Al based plating layer)
A sample having a size of 15 mm. times.20 mm was cut out from the test piece, subjected to insert polishing and nital etching, and then measured by observing the cross section of the Fe-Al based plating layer with SEM.
(Al content (W) in Fe-Al based coating layer Al ) Si content (W) Si ) Fe content (W) Fe ))
EPMA analysis was performed from the above cross section, and the Al content and Si content at 10 points were measured at equal intervals in the direction from the surface toward the base material, and the average value of each was W Al 、W Si . The remainder of the coating was Fe, so (100-W) was Al -W Si ) Is set to W Fe . The results are shown in table 3. The maximum Al content in 10 points is also shown in table 3.
(layer Structure of Fe-Al based plating layer and thicknesses of FeAl layer and Al solid solution ferrite layer)
Among the measurement points obtained by EPMA analysis of 10 sites at equal intervals in the thickness direction of the Fe-Al based plating layer, the Al content is set to a range of 0.5% to 20.0% as the Al solid solution ferrite layer, and a range of more than 20.0% and not more than 30.0% as the FeAl layer. In addition, the range of Al content of 40.0% to 65.0% is set as Fe 2 Al 5 The layer (4) has an Al content of more than 30.0% and less than 40.0% and an Si content of 2% to 15% as τ 1. Layers other than those described above are not confirmed in this embodiment.
In the table, "2 layers" represent a 2-layer structure including a FeAl layer and an Al solid solution ferrite layer in this order from the front surface side. Further, the respective thicknesses were determined by setting the size of 1 field to a range of 100 μm × 100 μm using EPMA and observing 3 fields, and were determined as the average value of the thicknesses measured in the 3 fields, after the FeAl layer and the Al solid solution ferrite layer were determined).
In the measurement of the thickness, when adjacent measurement points are determined to be different layers based on the analysis result, it is considered that a layer boundary exists at a midpoint in the thickness direction of the measurement points.
In the table, "5 layers" means Fe in order from the surface 2 Al 5 Layer of τ 1, Fe 2 Al 5 A FeAl layer, and an Al solid solution ferrite layer. "1 layer" means a single layer of an Al solid solution ferrite layer.
(diameter of gap)
A10 mm × 20mm sample was cut out from the test piece, and the cross section in the plate thickness direction was polished as an observation surface, followed by nital etching, and the observation surface was observed with an optical microscope in the range of 100 μm × 100 μm, and the diameter of the void was determined from the diameter of the smallest circumscribed circle of the included void. The average value obtained by measuring the voids at 10 sites was defined as the diameter of the voids in the test piece.
(Structure of base Steel plate)
A sample having a size of 15 × 20mm was cut out from the test piece, subjected to insert polishing and nital etching, and then observed with an optical microscope at a position 1/4 where the thickness of the surface of the base steel sheet is equal to the thickness of the base steel sheet in the thickness cross section of the base steel sheet.
(Corrosion resistance of molded portion)
After the test piece was subjected to chemical conversion treatment and corrosion resistant coating, the coating film was scratched with a cutter to expose the metal surface, and the test piece thus obtained was used to perform a corrosion test. Specifically, the coating solution was chemically converted by PB-SX35, a chemical conversion treatment solution prepared by Nihon Parkerizing (Kabushiki Co., Ltd.), and then coated with POWERNIX110, a cationic electrodeposition coating material prepared by NIPPON PAINT (Kabushiki Co., Ltd.) in a thickness of about 15 μm. Then, the electrodeposited coating film was scratched with a cutter to form a cross-cut flaw, and a 180-cycle (60-day) composite corrosion test (JASO M610-92) defined by the automotive society was performed to measure the amount of reduction in the thickness of the cross-cut portion.
At this time, if the amount exceeds that of the galvannealed steel sheet GA (the amount of adhesion is 45g/m on one side) 2 ) If the amount of reduction in sheet thickness is less than the amount of reduction in sheet thickness, the corrosion resistance is set to NG (poor), if the amount is less than the amount of reduction in sheet thickness, the corrosion resistance is set to G (good), and if the amount is further suppressed to 3/4 or less, the corrosion resistance is set toVG (excellent) is preferable, and if it is suppressed to 1/2 or less, the corrosion resistance is set to VG2 (more preferable).
The evaluation results are shown in table 3.
[ Table 2]
[ Table 3]
With respect to the invention examples of the present application shown in table 3, i.e., levels B1 to B20, hot stamped members having excellent corrosion resistance of the molded portion were obtained. In particular, the evaluation results of the corrosion resistance of the molded parts of B1 and B5 were G, whereas the evaluation results of the corrosion resistance of the molded parts were VG and were good when D2/D1 of the Fe — Al plating layers of the hot stamped members of B2 to B4 satisfied 0.8 to 2.5. Further, when the sizes of the voids in the hot stamped members of B9 to B20 were 5 μm to 15 μm in diameter, the evaluation result of the corrosion resistance of the molded part was VG2, which was more preferable. The structure of the base steel sheet is martensite.
The results of evaluating the corrosion resistance of the molded part were NG and inferior to those of B21 to B35 which are comparative examples of the present application shown in table 3. This is due to: thickness of Fe-Al based coating layer, Al content W Al Si content W Si At least 1 of the Fe content, the formula (1) and the layer structure does not satisfy the specified conditions.
B21 shows a small amount of Al plating on the Al-plated steel sheet, and shows a low (T) value during hot stamping Max -850) 2 The value of X (t/W) is small. Therefore, in the hot stamped member, the thickness of the Fe — Al based plating layer is insufficient, and further, in the Fe — Al based plating layer, the Al content and the Si content do not satisfy formula (1). As a result, sufficient corrosion resistance of the molded part cannot be obtained.
B22 shows a small amount of Al plating on the Al-plated steel sheet, and shows a low (T) value during hot stamping Max -850) 2 The value of x (t/W) is small. Thus, inIn the hot stamped member, the thickness of the Fe-Al based plating layer is insufficient, and further, the Al content and the Si content in the Fe-Al based plating layer do not satisfy formula (1). The plating layer is formed of 1 layer of the Al solid solution ferrite layer. As a result, sufficient corrosion resistance of the molded part cannot be obtained.
B23 shows a small amount of Al plating on the Al-plated steel sheet, and shows a low (T) value during hot stamping Max -850) 2 The value of x (t/W) is large. Therefore, in the hot stamped member, the Al content of the Fe — Al plating layer is small, and the Al content and the Si content do not satisfy formula (1). Further, excessive diffusion of Fe causes a large amount of Fe-Al based plating. The plating layer is formed of 1 layer of the Al solid solution ferrite layer. As a result, sufficient corrosion resistance of the molded part cannot be obtained.
B24 shows a large amount of Al plating on the Al-based plated steel sheet. Therefore, in the hot stamped member, the thickness of the Fe — Al based plating layer is excessive. Further, the plating layer was formed of 5 layers. As a result, sufficient corrosion resistance of the molded part cannot be obtained.
B25 indicates that the Al plating layer of the Al-based plated steel sheet adheres in a large amount and (T) during hot stamping Max -850) 2 The value of x (t/W) is large. Therefore, in the hot stamped member, the thickness of the Fe — Al based plating layer is excessive. As a result, sufficient corrosion resistance of the molded part cannot be obtained.
B26, B27 and B29 in hot stamping (T) Max -850) 2 The value of x (t/W) is small. Therefore, the composition of the Fe — Al based plating layer in the hot stamped member deviates from the scope of the present invention. Further, the plating layer was formed of 5 layers. As a result, sufficient corrosion resistance of the molded part cannot be obtained.
(T) in the case of B28 in hot stamping Max -850) 2 The value of x (t/W) is large. The plating layer is formed of 1 layer of the Al solid solution ferrite layer. As a result, sufficient corrosion resistance of the molded part cannot be obtained.
In the case of B30, (T) in hot stamping Max -850) 2 The value of x (t/W) is small. Therefore, the plating layer becomes a plating layer formed of 5 layers. As a result, sufficient corrosion resistance of the molded part cannot be obtained.
In the case of B31, (T) in hot stamping Max -850) 2 The value of X (t/W) is large. Therefore, in the hot stamped member, the thickness of the Fe — Al based plating layer is excessive. As a result, sufficient corrosion resistance of the molded part cannot be obtained.
B32 indicates that the Al plating layer of the Al-based plated steel sheet has a low Al content and a high Si content. Therefore, in the Fe — Al based plating layer of the hot stamped member, the Si content deviates from the scope of the present invention and does not satisfy formula (1). Further, the plating layer was a plating layer formed of 5 layers. As a result, sufficient corrosion resistance of the molded part cannot be obtained.
In B33, the Al plating layer of the Al-based plated steel sheet has a high Al content and a low Si content. Therefore, the Si content in the Fe — Al based plating layer of the hot stamped member deviates from the scope of the present invention. As a result, sufficient corrosion resistance of the molded part cannot be obtained.
B34 is long in time after heating until molding is started. Therefore, in the hot stamped member, the Al content and the Si content of the Fe — Al plating layer do not satisfy formula (1). As a result, sufficient corrosion resistance of the molded part cannot be obtained.
In B35, the maximum heating temperature in the heating step was low. Therefore, the alloying reaction between the base steel sheet and the Al-based plating layer is insufficient, and the FeAl layer and the Al solid solution ferrite layer are not formed, so that pure Al remains in the plating layer and the Al content becomes excessive. As a result, sufficient corrosion resistance of the molded part cannot be obtained.
The base steel sheets of B21 to B33 all had martensite, B34 had bainite, and B35 had a composite structure of ferrite and pearlite.
Industrial applicability
According to the present invention, a hot-stamped member having a molded portion with excellent corrosion resistance and a method for manufacturing the same can be provided. Application of such a hot-stamped member to an automobile member leads to improvement in collision safety of an automobile, improvement in fuel efficiency by weight reduction of an automobile, and CO 2 And the like, reduction of exhaust gas.
Description of the symbols
1 Hot stamping component
2 base metal steel plate
3A, 3B Al solid solution ferrite layer
4A, 4B FeAl layer.
Claims (10)
1. A hot stamped component, comprising:
a base steel plate; and
an Fe-Al plating layer formed on one surface or both surfaces of the base steel sheet,
the Fe-Al based coating contains, in mass%:
Fe：64.0％～99.4％、
Al：0.5％～30.0％、
Si：0.1％～6.0％，
the content of Si in mass% of the Fe-Al based plating layer is W Si Setting the Al content to W Al When said W is Si And said W Al Satisfies the following formula (1),
the Fe-Al based plating layer comprises 2 layers of a FeAl layer and an Al solid solution ferrite layer in this order from the surface side,
the thickness of the Fe-Al plating layer is 5-80 μm,
5×W Si ≤W Al formula (1).
2. The hot-stamped member according to claim 1, wherein a ratio D2/D1 of a thickness D1 of the FeAl layer to a thickness D2 of the Al solid solution ferrite layer is 0.8 to 2.5.
3. The hot-stamped member as claimed in claim 1 or 2, wherein the Fe — Al-based plating layer contains voids, and the voids have a diameter of 5 μm to 15 μm.
4. The hot-stamped member as claimed in any one of claims 1 to 3, wherein the maximum Al content of the Fe-Al based plating layer is 30.0% by mass or less.
5. The hot-stamped component according to any one of claims 1 to 4, wherein the base steel sheet has a chemical composition containing, in mass%:
C：0.10％～0.50％、
Si：0.01％～2.00％、
Mn：0.30％～5.00％、
B：0.0002％～0.0100％、
al: less than 1.00 percent,
P: less than 0.100 percent,
S: less than 0.100 percent,
N: less than 0.0100%,
Cr：0％～2.00％、
W：0％～3.0％、
Mo：0％～3.0％、
Co：0％～3.0％、
V：0％～2.0％、
Ti：0％～0.50％、
Nb：0％～1.00％、
Ni：0％～5.0％、
Cu：0％～3.0％、
Sn：0％～0.10％、
Sb：0％～0.10％、
Mg：0％～0.0100％、
Ca：0％～0.0100％、
Zr：0％～0.0100％、
REM：0％～0.0100％、
O：0％～0.0070％，
The balance being Fe and impurities.
6. A method for manufacturing a hot-stamped member according to claim 1, comprising the steps of:
a cutting step of cutting an Al-based plated steel sheet having a base steel sheet and an Al-based plating layer formed on the base steel sheet;
a heating step of heating the Al-based plated steel sheet after the blanking step; and
a forming step of forming and cooling the Al-based plated steel sheet after the heating step,
wherein the Al-based plating layer has an adhesion amount of 5g/m per one surface 2 ～100g/m 2 ，
The Al-based plating layer contains, in mass%:
Al：83.0％～95.0％、
Si：5.0％～12.0％、
Fe：0％～5.0％，
the maximum heating temperature in the heating step is set to T Max And the heating step is performed from the temperature T Max To (T) Max T is a time in minutes and W is a time in minutes for holding the Al-based plated steel sheet at-10 DEG C Max T and W satisfy the following formula (2), T Max The temperature of the mixture is above 850 ℃ and,
15 seconds or less from the end of the heating step to the start of the cooling in the molding step,
700≤(T Max -850) 2 x (t/W) is not more than 4000 formula (2).
7. The method of manufacturing a hot-stamped member according to claim 6, wherein the amount of the Al-based plating layer deposited per one surface, i.e., W, is 10g/m 2 ～80g/m 2 。
8. Method for manufacturing a hot-stamped component according to claim 6 or 7, wherein T is Max Wherein t and W satisfy the following formula (3),
1000≤(T Max -850) 2 x (t/W) is less than or equal to 3000 formula (3).
9. The method of manufacturing a hot-stamped member according to any one of claims 6 to 8, wherein the base steel sheet has a chemical composition containing, in mass%:
C：0.10％～0.50％、
Si：0.01％～2.00％、
Mn：0.30％～5.00％、
B：0.0002％～0.0100％、
al: less than 1.00 percent,
P: less than 0.100 percent,
S: less than 0.100 percent,
N: less than 0.0100%,
Cr：0％～2.00％、
W：0％～3.0％、
Mo：0％～3.0％、
Co：0％～3.0％、
V：0％～2.0％、
Ti：0％～0.50％、
Nb：0％～1.00％、
Ni：0％～5.0％、
Cu：0％～3.0％、
Sn：0％～0.10％、
Sb：0％～0.10％、
Mg：0％～0.0100％、
Ca：0％～0.0100％、
Zr：0％～0.0100％、
REM：0％～0.0100％、
O：0％～0.0070％，
The balance being Fe and impurities.
10. The method of manufacturing a hot-stamped member according to any one of claims 6 to 9, wherein an interface alloy layer is present between the base steel sheet and the Al-based plated layer in the Al-based plated steel sheet.
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| CN110914464A (en) * | 2017-07-31 | 2020-03-24 | 日本制铁株式会社 | Hot-dip galvanized steel sheet |
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| CN1145645A (en) * | 1995-02-24 | 1997-03-19 | 日新制钢株式会社 | Hot-dip aluminized sheet, process for producing the sheet, and alloy layer control device |
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