WO2023074088A1 - めっき鋼板 - Google Patents
めっき鋼板 Download PDFInfo
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- WO2023074088A1 WO2023074088A1 PCT/JP2022/030932 JP2022030932W WO2023074088A1 WO 2023074088 A1 WO2023074088 A1 WO 2023074088A1 JP 2022030932 W JP2022030932 W JP 2022030932W WO 2023074088 A1 WO2023074088 A1 WO 2023074088A1
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- WIPO (PCT)
- Prior art keywords
- plating layer
- ray diffraction
- phase
- corrosion resistance
- steel sheet
- Prior art date
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- 229910000831 Steel Inorganic materials 0.000 title claims abstract description 117
- 239000010959 steel Substances 0.000 title claims abstract description 117
- 238000007747 plating Methods 0.000 claims abstract description 245
- 238000002441 X-ray diffraction Methods 0.000 claims abstract description 106
- 229910052718 tin Inorganic materials 0.000 claims abstract description 15
- 229910052746 lanthanum Inorganic materials 0.000 claims abstract description 14
- 229910052759 nickel Inorganic materials 0.000 claims abstract description 14
- 229910052727 yttrium Inorganic materials 0.000 claims abstract description 14
- 229910052684 Cerium Inorganic materials 0.000 claims abstract description 13
- 229910052797 bismuth Inorganic materials 0.000 claims abstract description 13
- 229910052804 chromium Inorganic materials 0.000 claims abstract description 13
- 229910052738 indium Inorganic materials 0.000 claims abstract description 13
- 229910052791 calcium Inorganic materials 0.000 claims abstract description 11
- 229910052802 copper Inorganic materials 0.000 claims abstract description 11
- 229910052748 manganese Inorganic materials 0.000 claims abstract description 10
- 229910052758 niobium Inorganic materials 0.000 claims abstract description 10
- 229910052719 titanium Inorganic materials 0.000 claims abstract description 10
- 229910052720 vanadium Inorganic materials 0.000 claims abstract description 10
- 229910017706 MgZn Inorganic materials 0.000 claims description 42
- 239000000126 substance Substances 0.000 claims description 39
- 239000000203 mixture Substances 0.000 claims description 38
- 229910018137 Al-Zn Inorganic materials 0.000 claims description 21
- 229910018573 Al—Zn Inorganic materials 0.000 claims description 21
- 229910004860 CaZn Inorganic materials 0.000 claims description 12
- 239000012535 impurity Substances 0.000 claims description 6
- 229910044991 metal oxide Inorganic materials 0.000 claims description 6
- 150000004706 metal oxides Chemical class 0.000 claims description 6
- NAWXUBYGYWOOIX-SFHVURJKSA-N (2s)-2-[[4-[2-(2,4-diaminoquinazolin-6-yl)ethyl]benzoyl]amino]-4-methylidenepentanedioic acid Chemical compound C1=CC2=NC(N)=NC(N)=C2C=C1CCC1=CC=C(C(=O)N[C@@H](CC(=C)C(O)=O)C(O)=O)C=C1 NAWXUBYGYWOOIX-SFHVURJKSA-N 0.000 claims description 4
- 229910017708 MgZn2 Inorganic materials 0.000 abstract description 10
- 229910004858 CaZn2 Inorganic materials 0.000 abstract description 3
- 239000010410 layer Substances 0.000 description 246
- 238000005260 corrosion Methods 0.000 description 211
- 230000007797 corrosion Effects 0.000 description 209
- 239000012071 phase Substances 0.000 description 139
- 239000011701 zinc Substances 0.000 description 90
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- 229910052725 zinc Inorganic materials 0.000 description 13
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- 229910000861 Mg alloy Inorganic materials 0.000 description 11
- 150000001875 compounds Chemical class 0.000 description 11
- 229910052749 magnesium Inorganic materials 0.000 description 11
- 238000006243 chemical reaction Methods 0.000 description 10
- 229910052742 iron Inorganic materials 0.000 description 10
- 239000011572 manganese Substances 0.000 description 10
- 239000012298 atmosphere Substances 0.000 description 9
- ZCDOYSPFYFSLEW-UHFFFAOYSA-N chromate(2-) Chemical compound [O-][Cr]([O-])(=O)=O ZCDOYSPFYFSLEW-UHFFFAOYSA-N 0.000 description 9
- AWJWCTOOIBYHON-UHFFFAOYSA-N furo[3,4-b]pyrazine-5,7-dione Chemical compound C1=CN=C2C(=O)OC(=O)C2=N1 AWJWCTOOIBYHON-UHFFFAOYSA-N 0.000 description 9
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- 239000010955 niobium Substances 0.000 description 7
- 238000011002 quantification Methods 0.000 description 7
- 239000000243 solution Substances 0.000 description 7
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 6
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- 229910000676 Si alloy Inorganic materials 0.000 description 4
- QAOWNCQODCNURD-UHFFFAOYSA-N Sulfuric acid Chemical compound OS(O)(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-N 0.000 description 4
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- 229910052712 strontium Inorganic materials 0.000 description 4
- 229910052721 tungsten Inorganic materials 0.000 description 4
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- 229910019142 PO4 Inorganic materials 0.000 description 3
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- NBIIXXVUZAFLBC-UHFFFAOYSA-K phosphate Chemical compound [O-]P([O-])([O-])=O NBIIXXVUZAFLBC-UHFFFAOYSA-K 0.000 description 3
- 239000010452 phosphate Substances 0.000 description 3
- 229920000178 Acrylic resin Polymers 0.000 description 2
- 239000004925 Acrylic resin Substances 0.000 description 2
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- XKRFYHLGVUSROY-UHFFFAOYSA-N Argon Chemical compound [Ar] XKRFYHLGVUSROY-UHFFFAOYSA-N 0.000 description 2
- 229910001335 Galvanized steel Inorganic materials 0.000 description 2
- 229910019021 Mg 2 Sn Inorganic materials 0.000 description 2
- NBIIXXVUZAFLBC-UHFFFAOYSA-N Phosphoric acid Chemical compound OP(O)(O)=O NBIIXXVUZAFLBC-UHFFFAOYSA-N 0.000 description 2
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 2
- 238000000441 X-ray spectroscopy Methods 0.000 description 2
- 238000005275 alloying Methods 0.000 description 2
- 235000011114 ammonium hydroxide Nutrition 0.000 description 2
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 2
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- 230000008859 change Effects 0.000 description 2
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- 238000005868 electrolysis reaction Methods 0.000 description 2
- 239000003822 epoxy resin Substances 0.000 description 2
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- 229910052739 hydrogen Inorganic materials 0.000 description 2
- JEIPFZHSYJVQDO-UHFFFAOYSA-N iron(III) oxide Inorganic materials O=[Fe]O[Fe]=O JEIPFZHSYJVQDO-UHFFFAOYSA-N 0.000 description 2
- 230000008018 melting Effects 0.000 description 2
- 238000002844 melting Methods 0.000 description 2
- PXHVJJICTQNCMI-UHFFFAOYSA-N nickel Substances [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 description 2
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- QGZKDVFQNNGYKY-UHFFFAOYSA-N Ammonia Chemical compound N QGZKDVFQNNGYKY-UHFFFAOYSA-N 0.000 description 1
- 229910014458 Ca-Si Inorganic materials 0.000 description 1
- -1 CaAlSi Chemical class 0.000 description 1
- 229910004706 CaSi2 Inorganic materials 0.000 description 1
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 description 1
- 229910000677 High-carbon steel Inorganic materials 0.000 description 1
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 description 1
- 229910000655 Killed steel Inorganic materials 0.000 description 1
- 229910001209 Low-carbon steel Inorganic materials 0.000 description 1
- 229910019018 Mg 2 Si Inorganic materials 0.000 description 1
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- IQBJFLXHQFMQRP-UHFFFAOYSA-K calcium;zinc;phosphate Chemical compound [Ca+2].[Zn+2].[O-]P([O-])([O-])=O IQBJFLXHQFMQRP-UHFFFAOYSA-K 0.000 description 1
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- LRXTYHSAJDENHV-UHFFFAOYSA-H zinc phosphate Chemical compound [Zn+2].[Zn+2].[Zn+2].[O-]P([O-])([O-])=O.[O-]P([O-])([O-])=O LRXTYHSAJDENHV-UHFFFAOYSA-H 0.000 description 1
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Images
Classifications
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C18/00—Alloys based on zinc
- C22C18/04—Alloys based on zinc with aluminium as the next major constituent
-
- 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
- C23C2/06—Zinc or cadmium 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
Definitions
- the present invention relates to plated steel sheets. This application claims priority based on Japanese Patent Application No. 2021-174676 filed in Japan on October 26, 2021, the content of which is incorporated herein.
- Plated steel sheets are used in various fields of building materials. Since the service life of a building depends on the wear rate of the plating layer, it is preferable to use a highly corrosion-resistant plated steel sheet as a building material.
- a highly corrosion-resistant plated steel sheet as a building material.
- the plated steel sheets described in Patent Documents 1 to 3 are known as steel sheets exhibiting high corrosion resistance.
- Al-based plated steel sheets generally known as Galvalume Steel Sheets (registered trademark)
- Galvalume Steel Sheets registered trademark
- the Al-plated steel sheet has low corrosion resistance and sacrificial corrosion resistance in an alkaline environment such as an ammonia gas atmosphere generated from compost barns such as cow barns and pig barns, so the scope of its use is limited.
- the Zn-based plated steel sheet as shown in Patent Documents 1 to 3 has a wider application range, but the Zn-based plated steel sheet tends to have lower corrosion resistance in an acidic environment than the Al-based plated steel sheet. Corrosion resistance improvement is demanded. That is, plated steel sheets are required to exhibit high corrosion resistance in all regions from the acid side to the alkali side.
- the present invention has been made in view of the above circumstances, and an object of the present invention is to provide a plated steel sheet that exhibits high corrosion resistance in an acid-alkali environment.
- a plated steel sheet having a plated layer on the surface of the steel sheet The average chemical composition of the plating layer is mass%, Al: more than 15.0%, 30.0% or less, Mg: more than 5.0%, 15.0% or less, Sn: 0-0.70%, Bi: 0 to 0.35%, In: 0-0.35%, Ca: 0.03-0.60%, Y: 0 to 0.30%, La: 0 to 0.30%, Ce: 0 to 0.30%, Si: 0.01 to 0.75%, Cr: 0-0.25%, Ti: 0-0.25%, Ni: 0 to 1.00%, Co: 0-0.25%, V: 0 to 0.25%, Nb: 0 to 0.25%, Cu: 0-0.25%, Mn: 0-0.25%, Fe: 0 to 5.0%, Sr: 0-0.5%, Sb: 0-0.5%, Pb: 0 to 0.5%, B: 0 to 0.5%, Li: 0 to 0.5%, Zr: 0 to 0.5%, Mo:
- I 1 to I 3 , I 4 obtained from the X-ray diffraction peak of CaZn 2 , and I 5 and I 6 obtained from the X-ray diffraction peak of ⁇ '-MgZn 2 are represented by the following formulas (1) to (6 ), a plated steel sheet that satisfies the following formulas (A) and (B).
- Imax (k ⁇ m °) is the maximum value of the X-ray diffraction intensity between k ⁇ m ° at the diffraction angle 2 ⁇
- I (n °) is the diffraction angle. It is the X-ray diffraction intensity at n° in 2 ⁇ , and k, m, and n are the diffraction angles 2 ⁇ shown in the above formulas (1) to (6), respectively.
- Imax (k ⁇ m °) is the maximum value of the X-ray diffraction intensity between k ⁇ m ° at the diffraction angle 2 ⁇
- I (n °) is the diffraction angle. It is the X-ray diffraction intensity at n° in 2 ⁇
- k, m, and n are the diffraction angles 2 ⁇ shown in the above formulas (1) to (6), respectively.
- the plating layer contains Zn phase, Al phase, Al-Zn phase, ⁇ '-MgZn 2 phase and MgZn 2 phase. Galvanized steel sheet.
- the Zn phase and the Al--Zn phase are phases with low corrosion resistance, and the corrosion resistance is extremely low, especially in acidic and alkaline environments, so it is necessary to reduce the content of these phases.
- Mg-containing phases generally have high corrosion resistance in alkaline environments, but not very high corrosion resistance in acidic environments.
- a Ca--Al--Zn compound is a compound with a nobler natural potential than Al, and has a lower corrosion rate than the Al phase, so that corrosion resistance can be improved.
- the corrosion resistance in an acidic environment is improved by reducing the amount of Zn phase in the plating layer
- the corrosion resistance in an alkaline environment will decrease.
- MgZn2 phase has good corrosion resistance under alkaline environment. Further, in order to further improve the corrosion resistance in an alkaline environment, it is preferable to introduce into the plating layer a compound that is more excellent in alkali corrosion resistance than the MgZn2 phase.
- Such compounds include the ⁇ '-MgZn 2 phase, which has a different crystal structure from the MgZn 2 phase.
- the ⁇ '-MgZn 2 phase has high corrosion resistance, especially in an alkaline environment, and even if the MgZn 2 phase is transformed into the ⁇ '-MgZn 2 phase, the amount of elements does not increase or decrease, so it can be used in an acidic environment. Corrosion resistance in an alkaline environment can be improved without impairing corrosion resistance.
- a plated steel sheet according to an embodiment of the present invention will be described below.
- a plated steel sheet according to an embodiment of the present invention (hereinafter referred to as a plated steel sheet according to the present embodiment) is a plated steel sheet having a plating layer on the surface of the steel sheet, and the average chemical composition of the plating layer is, in mass%, Al: More than 15.0%, 30.0% or less, Mg: more than 5.0%, 15.0% or less, Sn: 0-0.70%, Bi: 0-0.35%, In: 0-0.
- Imax (k ⁇ m °) is the maximum value of the X-ray diffraction intensity between k ⁇ m ° at the diffraction angle 2 ⁇
- I (n °) is the diffraction angle. It is the X-ray diffraction intensity at n° in 2 ⁇
- k, m, and n are the diffraction angles 2 ⁇ shown in the above formulas (1) to (6), respectively.
- the "%" display of the content of each element in the chemical composition means “% by mass”.
- a numerical range represented using “to” means a range including the numerical values described before and after “to” as lower and upper limits.
- a numerical range to which "more than” or “less than” is attached means a range that does not include these numerical values as lower or upper limits.
- corrosion resistance refers to the property of a plated steel sheet that is resistant to corrosion.
- the Zn-based plating layer has a sacrificial anti-corrosion effect on steel materials. In the corrosion process of a plated steel sheet having a Zn-based plating layer, the plating layer corrodes and turns into white rust before the steel sheet corrodes, and after the white rusted plating layer disappears, the steel sheet corrodes and produces red rust.
- a steel sheet to be plated will be described.
- the shape of the steel plate is mainly a plate material, but the size is not particularly limited.
- a plated steel sheet in which a coating layer is formed on a sheet material is a plated steel sheet manufactured by a normal hot-dip galvanizing process, and is immersed in molten metal such as a continuous hot-dip galvanizing line (CGL) or a batch-type dipping galvanizing process.
- CGL continuous hot-dip galvanizing line
- processing including welding
- combining the plated steel sheets manufactured by such a method it is possible to process them into various products and to manufacture steel structural members with excellent corrosion resistance.
- hot-rolled steel sheets according to JIS G 3193:2019 and cold-rolled steel sheets according to JIS G 3141:2021 are the most common base sheets for plating.
- the steel sheet is not particularly limited in terms of conditions such as the steel manufacturing method (blast furnace material, electric furnace material), the steel sheet manufacturing method (hot rolling method, pickling method, cold rolling method, etc.). .
- a plating layer of Zn, Ni, Sn, Fe, or an alloy system of a combination of these elements having a thickness of 30 ⁇ m or less is pre-plated on the surface of the steel sheet. pre-plated steel sheet may be used.
- the plating layer according to this embodiment includes a Zn--Al--Mg alloy layer. Addition of alloying elements such as Al and Mg to Zn improves the corrosion resistance, so that a thin film, for example, about half the corrosion resistance of a normal Zn plating layer, has the same corrosion resistance. Therefore, even in this embodiment, the thin plating layer ensures corrosion resistance equal to or higher than that of the normal Zn plating layer. Also, the plating layer may include an Al—Fe alloy layer.
- the Zn-Al-Mg alloy layer is made of a Zn-Al-Mg alloy.
- a Zn-Al-Mg alloy means a ternary alloy containing Zn, Al and Mg.
- the Al-Fe alloy layer is an interfacial alloy layer between the steel plate and the Zn-Al-Mg alloy layer.
- the plated layer according to the present embodiment may have a single layer structure of a Zn-Al-Mg alloy layer, or may have a laminated structure including a Zn-Al-Mg alloy layer and an Al-Fe alloy layer. good.
- a pre-plated material coated with a metal having a high melting point over 600 ° C.
- the layer containing the metal layer may be traced in some way on the Fe surface or as a substitute for the Al—Fe intermetallic compound. Almost no trace remains of metals that dissolve in the vicinity of the plating bath temperature.
- the Zn--Al--Mg alloy layer is preferably a layer forming the surface of the plating layer.
- an oxide film of less than 1 ⁇ m of the elements constituting the plating layer is formed on the outermost surface of the plating layer.
- the elements contained in the plating layer combine with oxygen on the surface of the plating layer, so surface analysis such as XPS (X-ray spectroscopy) reveals There is a thin oxide film in which bonds such as —O are confirmed. Elements that are relatively easily oxidized tend to exist on the plating surface.
- the Al--Fe alloy layer joins the steel material and the Zn--Al--Mg alloy layer.
- the thickness of the interfacial alloy layer can be controlled by the plating bath temperature during production of the plated steel sheet and the immersion time in the plating bath.
- the Zn-Al-Mg alloy layer is the main coating layer, and the thickness of the Al-Fe alloy layer is sufficiently small. Since it is small and formed near the interface, it hardly affects the corrosion resistance at the initial stage of corrosion or the appearance of the plating layer.
- the elements contained in the pre-plating layer may be contained in the Al—Fe alloy layer depending on the thickness of the pre-plating layer. Even after plating on the Fe surface, it remains as a pre-plating layer, and an interfacial alloy layer may be formed thereon.
- plating elements are actively diffused, and when the plating elements diffuse to the Fe side, an Al--Fe alloy layer may be formed under the pre-plating layer.
- the performance change due to these layers is not large due to their thin thickness.
- the thickness of the entire plating layer is not particularly limited because it depends on the plating conditions. Also, the thickness of the entire plating layer depends on the viscosity and specific gravity of the plating bath, for example, in a normal hot dip plating method. Furthermore, the coating weight is adjusted by the drawing speed of the steel sheet (coating base sheet) and the strength of wiping.
- the maximum thickness of a plating layer formed by a normal hot-dip plating method is often 100 ⁇ m or less for continuous hot-dip plating and 200 ⁇ m or less for batch-type plating.
- the Al--Fe alloy layer is formed on the surface of the steel sheet (specifically, between the steel sheet and the Zn--Al--Mg alloy layer), and is a layer whose main phase is Al 5 Fe 2 phase as a structure.
- the Al—Fe alloy layer is formed by mutual atomic diffusion of the base steel (steel plate) and the plating bath.
- hot-dip plating is used as the method for forming the plating layer, an Al--Fe alloy layer is likely to be formed in the plating layer containing the Al element.
- the Al 5 Fe 2 phase is formed most frequently because the plating bath contains Al at a certain concentration or higher.
- a solid phase is generated in the plating bath.
- the Al-Fe alloy layer may partially contain an AlFe phase, an Al 3 Fe phase, etc. in addition to the Al 5 Fe 2 phase in small amounts.
- the plating bath contains Zn at a certain concentration
- the Al—Fe alloy layer also contains a small amount of Zn.
- the Al--Fe alloy layer also contains a small amount of Si, which tends to accumulate at the interface.
- the plating layer contains Si
- Si is particularly likely to be incorporated into the Al--Fe alloy layer, so that the Al--Fe alloy layer may become an Al--Fe--Si intermetallic compound phase.
- the intermetallic compound phases identified in the Al--Fe--Si intermetallic compound phase is the AlFeSi phase. Therefore, these AlFeSi phases and the like may be detected in the Al--Fe alloy layer.
- a layer containing these AlFeSi phases is called an Al--Fe--Si alloy layer.
- the plating layer according to the present embodiment may consist of a Zn-Al-Mg alloy layer, may consist of a Zn-Al-Mg alloy layer and an Al-Fe alloy layer, or may consist of a Zn-Al- It may consist of a Mg alloy layer and an Al--Fe--Si alloy layer.
- the Al—Fe alloy layer it is inevitable that a part of Zn, which has an atomic radius close to that of Al, is incorporated as a substitute, and the transition metals Ni, Cr, Co, etc., which have an atomic radius close to that of Fe, are also incorporated into these materials. Incorporation into the intermetallic compound as a substitute is unavoidable, but the main structure can be treated as an Al--Fe alloy layer.
- the average chemical composition of the entire plating layer is the average chemical composition of the Zn--Al--Mg alloy layer when the plating layer has a single-layer structure of the Zn--Al--Mg alloy layer.
- the plated layer has a laminated structure of an Al--Fe alloy layer and a Zn--Al--Mg alloy layer, it is the average chemical composition of the total of the Al--Fe alloy layer and the Zn--Al--Mg alloy layer.
- the plating layer has a laminated structure of an Al-Fe-Si alloy layer and a Zn-Al-Mg alloy layer, it is the average chemical composition of the total of the Al-Fe-Si alloy layer and the Zn-Al-Mg alloy layer. .
- the chemical composition of the Zn-Al-Mg alloy layer is almost the same as that of the plating bath because the reaction for forming the plating layer is almost completed in the plating bath.
- the Al—Fe alloy layer is instantly formed and grown immediately after immersion in the plating bath. Then, the Al--Fe alloy layer completes the formation/growth reaction until it reaches around 550.degree. It is often sufficiently small with respect to the Al--Mg alloy layer.
- the average chemical composition of the entire plating layer is substantially the same as that of the Zn-Al-Mg alloy layer, and that of the Al-Fe alloy layer. component can be ignored.
- the components of the Al--Fe--Si alloy layer can be ignored.
- Al More than 15.0% and 30.0% or less Al is an element that constitutes the main component of the plating layer, like Zn. Zn--Al--Mg-based plating mainly forms an Al phase in the plating layer. If the Al content is 15.0% or less, the corrosion resistance in an acidic environment is insufficient. Therefore, the Al content should be more than 15.0%. Preferably, it is 18.0% or more. More preferably, it is 20% or more. On the other hand, when the Al content exceeds 30.0%, the corrosion resistance in an alkaline environment is insufficient. Therefore, the Al content is set to 30.0% or less. Preferably, it is 25.0% or less.
- the Al content in the coating layer increases, the Zn content relatively decreases and the sacrificial corrosion resistance deteriorates. % and 30.0% or less.
- an Al—Zn phase (a phase containing about 20 mass % of Al) with low corrosion resistance is formed. Therefore, in this embodiment, the Al--Zn phase is reduced by adopting the manufacturing method described later. This improves corrosion resistance and makes it easier to ensure corrosion resistance in acidic and alkaline environments.
- Mg more than 5.0% and 15.0% or less Mg is an element that constitutes the main constituent of the plating layer, like Zn. If the Mg is insufficient, the corrosion resistance in an alkaline environment tends to be lowered, so the Mg content is made more than 5.0%. Preferably, it is 7.0% or more. On the other hand, if the Mg content exceeds 15.0%, the corrosion resistance in an acidic environment deteriorates. Therefore, the Mg content is set to 15.0% or less. It is preferably 13.0% or less, more preferably 10.0% or less.
- Element group A Sn: 0-0.70% Bi: 0-0.35% In: 0-0.35% Total amount of Sn, Bi, and In ⁇ A: 0% or more and less than 0.75%
- Each element of the element group A (Sn, Bi, In) is an element that can be contained arbitrarily, so the content of each is set to 0%. That's it.
- Sn is an element necessary for forming Mg 9 Sn 5 that greatly improves the corrosion resistance of the plating layer in acidic and alkaline environments. Since the minimum Sn content required to form Mg 9 Sn 5 is 0.01%, the Sn content may be 0.01% or more.
- Bi and In which form intermetallic compounds that improve corrosion resistance in alkaline environments.
- intermetallic compounds include Bi 2 Mg 3 and InMg 3 . Since Sn, Bi, and In form mutual substitutions with each other, Sn may be contained in an amount of 0.70% or less, and each of Bi and In may be contained in an amount of 0.35% or less.
- the elements of element group A are effective in improving corrosion resistance in an alkaline environment, but when the content exceeds the upper limit, the corrosion resistance in an acidic environment is extremely deteriorated.
- the total amount ⁇ A of Sn, Bi and In is set to 0% or more and less than 0.75%.
- the total amount ⁇ A is preferably 0.01% or less, more preferably 0.05% or less, and still more preferably 0.10% or more.
- the total amount ⁇ A is preferably 0.60% or less, more preferably 0.50% or less.
- the total amount ⁇ A of Sn, Bi and In is the total content of Sn, Bi and In.
- element group B Ca: 0.03-0.60% Y: 0 to 0.30% La: 0-0.30% Ce: 0-0.30% Total amount of Ca, Y, La and Ce ⁇ B: 0.03 to 0.60% Ca is not the main element in the plating layer, but is an element necessary for forming Al2.15Zn1.85Ca . Ca is also an element necessary for forming CaZn2 . Therefore, since the minimum Ca content required to form these intermetallic compounds is 0.03% or more, the Ca content is made 0.03% or more. The inclusion of these intermetallic compounds improves corrosion resistance in acidic and alkaline environments.
- the Ca content is preferably 0.05% or more, more preferably 0.10% or more, and even more preferably 0.20% or more.
- the Ca content is set to 0.60% or less. It is preferably 0.50% or less, more preferably 0.40% or less.
- Elements that play the same role as Ca include Y, La, and Ce. Since these elements are optional additional elements, the content of each is set to 0% or more. These elements tend to substitute for Ca. However, when Ca is not contained, even if Y, La, and Ce are contained, sufficient performance cannot be exhibited. When Ca is contained in the above content and Y, La, and Ce are each contained in a range of 0.30% or less, mutual substitutions are formed with each other to improve corrosion resistance in an alkaline environment. However, if each of Y, La and Ce exceeds 0.30%, the corrosion resistance in an alkaline environment is extremely deteriorated. Therefore, the contents of Y, La, and Ce are each set to 0.30% or less.
- the total amount ⁇ B of Ca, Y, La and Ce is set to 0.03 to 0.60%.
- the total amount ⁇ B is preferably 0.05% or more, more preferably 0.10% or more, and still more preferably 0.20% or more.
- the total amount ⁇ B is preferably 0.50% or less, more preferably 0.40% or less.
- the total amount ⁇ B of Ca, Y, La and Ce is the total content of Ca, Y, La and Ce.
- Si 0.01-0.75%
- Si is an element necessary for forming an intermetallic compound in the plating layer. Since the plating composition in this embodiment has a high melting point, the operating temperature is around 500° C. when hot-dip plating is performed. At this operating temperature, when the steel sheet is immersed in the plating bath, Al and Zn actively interdiffusion with Fe to form an intermetallic compound, but Si suppresses this excessive reaction. When the Si content is 0.01% or more, the diffusion reaction of Fe is greatly suppressed, and the formation of intermetallic compounds contained in the plating layer is easily controlled.
- the Si content is set to 0.01% or more. It is preferably 0.10% or more, more preferably 0.20% or more. Even if the Si content is excessive, the Si content is reduced to 0.75% or less because the corrosion resistance in acidic and alkaline environments deteriorates due to the bonding of Si to the constituent elements of the plating layer. It is preferably 0.50% or less, more preferably 0.40% or less.
- Si is an element that is extremely easily combined with Ca, and easily forms various Al--Ca--Si compounds such as CaAlSi, Al 2 CaSi 2 , Ca 2 Al 4 Si 3 and Ca 2 Al 3 Si 4 . .
- Al--Ca--Si compounds such as CaAlSi, Al 2 CaSi 2 , Ca 2 Al 4 Si 3 and Ca 2 Al 3 Si 4 .
- it is better to create free Ca, but if the Si content is high, these intermetallic compounds are likely to form.
- element group C Cr: 0-0.25% Ti: 0-0.25% Ni: 0-1.00% Co: 0-0.25% V: 0-0.25% Nb: 0-0.25% Cu: 0-0.25% Mn: 0-0.25% Total amount of Cr, Ti, Ni, Co, V, Nb, Cu and Mn ⁇ C: 0 to 1.00% Since the elements of the element group C are optional additive elements in the plating layer, the content of each element is set to 0% or more. These metals tend to substitute with Al, Zn, etc. in the plating layer, and the potential tends to move nobler, and the content within the above range tends to improve the corrosion resistance in an acidic environment.
- the contents of Cr, Ti, Co, V, Nb, Cu, and Mn should each be 0.25% or less.
- the Ni content is set to 1.00% or less.
- the total amount ⁇ C of Cr, Ti, Ni, Co, V, Nb, Cu and Mn is 1.00. % or less.
- the total amount ⁇ C is preferably 0.80% or less, more preferably 0.50% or less.
- the total amount ⁇ C of Cr, Ti, Ni, Co, V, Nb, Cu and Mn is the total content of Cr, Ti, Ni, Co, V, Nb, Cu and Mn.
- Fe 0-5.0% Since the plated steel sheet according to the present embodiment is a hot dip plated steel sheet, Fe may diffuse from the steel sheet (plating base sheet) into the plating layer during production. A maximum of 5.0% Fe may be contained in the plating layer, but no change in corrosion resistance due to the inclusion of this element has been confirmed. Therefore, the Fe content is set to 0 to 5.0%.
- Element group D Sr: 0-0.5% Sb: 0-0.5% Pb: 0-0.5% B: 0-0.5% Li: 0-0.5% Zr: 0-0.5% Mo: 0-0.5% W: 0-0.5% Ag: 0-0.5% P: 0-0.5% Since the elements of the element group D are arbitrary additive elements that may be contained in the plating layer, the content of each element is set to 0% or more. These elements have the same effect as the elements of the element group C described above, and are relatively easier to contain than the elements of the element group C. Therefore, the content of each element of element group D is set to 0 to 0.5%.
- the total amount ⁇ D of Sr, Sb, Pb, B, Li, Zr, Mo, W, Ag and P may be 0 to 0.5%.
- the total amount ⁇ D of Sr, Sb, Pb, B, Li, Zr, Mo, W, Ag and P is the content of Sr, Sb, Pb, B, Li, Zr, Mo, W, Ag and P is the sum of
- the plated steel sheet according to the present embodiment is a highly versatile Zn-based plated steel sheet, and by containing a certain amount or more of Zn for the purpose of ensuring sacrificial corrosion resistance, the steel sheet is imparted with appropriate sacrificial corrosion resistance. For example, even in an environment where a cut end face of 1.6 mm or more is open, if the amount of Zn exceeds 50.0%, a sufficient sacrificial anti-corrosion effect appears on the cut end face portion, and high corrosion resistance can be maintained.
- the Zn content when the Zn content is 50.00% or less, the corrosion resistance in an alkaline environment is extremely deteriorated, so the Zn content is preferably more than 50.00%.
- the Zn content is preferably 55.00% or more, more preferably 60.00% or more, and still more preferably 65.00% or more.
- Impurities are components contained in raw materials, or components that are mixed in the manufacturing process and are not intentionally included, and / or to the extent that they do not adversely affect the plated steel sheet according to the present embodiment.
- the plating layer may contain a small amount of components other than Fe as impurities due to mutual atomic diffusion between the steel sheet (base iron) and the plating bath.
- Si content should be greater than or equal to the Sn content. If the Si content is less than the Sn content, excess Fe diffuses from the steel sheet into the coating layer, making it difficult to form the desired intermetallic compounds. As a result, corrosion resistance in acidic and alkaline environments deteriorates. Note that Sn and Si in "Sn ⁇ Si" represent the contents of Sn and Si in the plating layer in terms of mass %, respectively.
- the Si content must satisfy 20.0 ⁇ Mg/Si.
- the Si content is high relative to the Mg content, a large amount of Mg 2 Si is formed in the plating layer, and the corrosion resistance in an acidic environment cannot be sufficiently exhibited.
- the Si content is high relative to the Mg content, the formation of Al--Ca--Si compounds is promoted and intermetallic compounds (Al 2.15 Zn 1.85 Ca) are not formed.
- Mg/Si exceeds 38.0, MgAlSi is no longer formed in the plating layer, as will be described later. Therefore, when MgAlSi is formed in the plating layer, it is preferable to set Mg/Si to 38.0 or less.
- Mg and Si in "Mg/Si" represent the content of Mg and Si in the plating layer in mass %, respectively.
- Al content and the Mg content may satisfy 3.00 ⁇ Al/Mg ⁇ 4.00.
- MgAlSi can be formed in the plating layer.
- Al and Mg in "Al/Mg" represent contents in mass % of Al and Mg in the plating layer, respectively.
- an acid solution is obtained by stripping and dissolving a plating layer with an acid containing an inhibitor that suppresses the corrosion of the base iron (steel plate).
- the average chemical composition of the plating layer can be obtained by measuring the resulting acid solution by ICP emission spectrometry or ICP-MS.
- the acid species is not particularly limited as long as it is an acid capable of dissolving the plating layer. If the area and weight before and after peeling are measured, the coating weight (g/m 2 ) can also be obtained at the same time.
- the intermetallic compound contained in the plating layer Since the plating layer according to the present embodiment is formed by Zn-Al-Mg alloy plating, the main phases in the plating layer are Zn phase, Al phase, Al-Zn phase, ⁇ '-MgZn 2 phase and MgZn. It contains two phases. Corrosion resistance varies depending on the content of each phase, but by controlling the plating structure such as the content of intermetallic compounds, it is possible to achieve corrosion resistance in acidic environments below pH 3.5 and corrosion resistance in alkaline environments above pH 11.5. The difference becomes smaller, and corrosion resistance can be secured. Phases other than the main phase include the above-described intermetallic compounds made of elements added other than Zn, Al, and Mg, such as Al--Ca--Si compounds and Mg--Sn compounds.
- Zn phase ( ⁇ phase: in the Zn-Al phase diagram)
- the Zn phase is present in the plating layer and mainly present in the ternary eutectic structure (Zn/Al/ MgZn2 ternary eutectic structure).
- Zn phases include Zn phases containing less than about 20 mass% Al.
- the Zn phase in the plating layer can ensure corrosion resistance in an environment of pH 5.0 to 11.5, and the amount of corrosion in this range is small, but the corrosion rate is high in other ranges. .
- Al phase ( ⁇ phase: in the Zn-Al phase diagram)
- the Al phase is present in the plated layer as Al primary crystals in a lump, and is also contained in a certain amount in the ternary eutectic structure.
- the Al phase in the plating layer can ensure corrosion resistance in an environment of pH 3.5 to 10.5, and the amount of corrosion in this range is small, but the range outside the pH 3.5 to 10.5 Corrosion rate is high at
- the Al phase contains approximately 90 mass % of Al and the remainder contains Zn. For this reason, the properties of Al appear strongly, and the Al content differs from that of the Al—Zn phase, which will be described later.
- Al-Zn phase (a phase other than ⁇ phase and ⁇ phase in the Zn-Al phase diagram consisting of Al and Zn) and ⁇ '-MgZn two- phase Al-Zn phase contains about 20 mass% or more of Al. It is a Zn phase containing, and the properties of both the Al phase and the Zn phase appear.
- the Al—Zn phase is naturally generated when the plating layer according to this embodiment is produced.
- the Al—Zn phase referred to here is a phase composed of two elements, Al and Zn, although it is different from both the Al phase and the Zn phase.
- the Al-Zn phase is a phase generated by the separation of the Zn phase from the Al phase during the solidification of the coating layer, and is mainly due to the decrease in the solid solubility limit of the Al phase during the process up to room temperature. Form. When confirmed by the crystal size, it is a structure in which fine crystal grains of several nanometers to about 3 ⁇ m are aggregated.
- the Al—Zn phase exhibits both performance as a Zn phase and an Al phase because it has aggregates of the Zn phase and the Al phase in fine grain units inside it, and does not have any special properties. It doesn't mean there is.
- the fine phase promotes coupling reactions at grain boundaries and adjacent phases with different potentials, so the corrosion resistance of this phase is higher than that of the Al phase ( ⁇ ) and Zn phase ( ⁇ ) in the coating layer. Corrosion resistance tends to be inferior.
- the Al—Zn phase significantly deteriorates corrosion resistance in acidic/alkaline environments.
- an appropriate heat treatment heat treatment for forming the ⁇ '-MgZn 2 phase
- the heat treatment reduces the Al--Zn phase and forms ⁇ '-MgZn 2 , thereby improving the corrosion resistance in the pH range of 3.5 to 10.5.
- MgZn 2- phase exists in the coating layer, and in addition to being present in the form of massive MgZn 2- phase, it forms a dendrite-like structure when solidified along the Al-MgZn 2 eutectic line together with the Al phase, and a ternary eutectic. A certain amount is also contained in the structure (Zn/Al/MgZn 2 ).
- the MgZn 2 phase in the plating layer can improve corrosion resistance in the range of pH 5.0 to pH 11.5, and can reduce the amount of corrosion in this range. However, the corrosion rate in other pH ranges can hardly be changed. Since the most abundant phase among the phases contained in the plating layer is the MgZn 2 phase, the pH range in which corrosion resistance can be secured by changing the ratio of the phase composition is 3.5 to 11.5. It is difficult to ensure corrosion resistance outside.
- the present inventors improved the plating layer with the aim of ensuring corrosion resistance outside the pH range of 3.5 to 11.5. It was found that the corrosion resistance outside the range can be secured.
- X-ray diffraction is preferably used to determine the inclusion of specific intermetallic compounds in the plating layer. Compared with SEM observation, TEM observation, etc., this detection method obtains average information of the plating layer, has less selectivity of the measurement point (field of view), and is excellent in quantification.
- the measurement conditions are specified, the diffraction peak intensity at the same angle (2 ⁇ ) can be obtained at a fixed ratio when a specific intermetallic compound is present, so it is possible to easily estimate the internal structure of the plating layer. be.
- the conditions for obtaining an X-ray diffraction image are as follows.
- the X-ray diffraction method with Cu as the target is the most convenient because it can obtain average information on the constituent phases in the plating layer.
- a Cu-K ⁇ ray is used, and the X-ray output voltage is 40 kV and the current is 150 mA.
- the X-ray diffractometer is not particularly limited, but for example, a sample horizontal strong X-ray diffractometer RINT-TTR III manufactured by Rigaku Corporation can be used.
- Intermetallic compound Al2.15Zn1.85Ca Al 2.15 Zn 1.85 Ca is a substance indicated by database number (ICDD-JCPDS powder diffraction database) 01-078-9051.
- a Ca-Al-Zn-based intermetallic compound for example, is widely introduced in (Z, Kristallogr.224 (2009) 397-406), but forms a structure (partially substituted with Zn) analogous to Al 4 Ca. do.
- Examples of substances having the same structure include Al 4 Ca, Ca 0.5 Zn 3.5 , Al 3 CaZn, Al 2.5 CaZn 1.5 , Al 2.06 CaZn 1.62 , Al 2 CaZn 2 , Al Substances such as 1.75 CaZn 2.25 , in which Al positions are partially substituted with Zn (0 to 2.25), also exhibit similar structures, and thus are expected to have similar properties. However, since these substances are substituents with different atomic radii, diffraction peaks are not necessarily obtained at the same position. On the other hand, in the present embodiment, since a diffraction peak is obtained as Al 2.15 Zn 1.85 Ca at a specific angle, this substance is treated as contained.
- the diffraction angle 2 ⁇ is 22.89° (101 plane), 31.67° (103 plane), and 43.94° (200 plane). Diffraction peaks appearing at these diffraction angles are convenient for quantification and determination of content because the diffraction peaks do not overlap with the main crystal structure of the plating layer. That is, if a diffraction peak with a diffraction intensity exceeding a certain amount is obtained at these diffraction angles, it can be said that the target intermetallic compound is surely contained.
- the production situation of the intermetallic compound in the JCPDS data is not necessarily the same but different, so a slight shift in the diffraction peak is observed, 22.89 ° (101 plane) 22.90°, 31.62° corresponding to 31.67° (103 planes), and 44.04° corresponding to 43.94° (200 planes).
- Intermetallic compound CaZn2 This intermetallic compound is a substance indicated by (ICDD-JCPDS powder diffraction database) 01-072-5741. As a substitute, Ca(Al 1.7 Zn 0.3 ) (JCPDS card 01-077-6005) is assumed, but this substitute is a different substance mainly having a CaAl 2 structure, are different from each other in diffraction peak position, they are not considered in this embodiment.
- the diffraction angle 2 ⁇ is 33.35° (121 plane) (strongest line).
- the diffraction peak at this diffraction angle is convenient for quantification and determining the content because the diffraction peak does not overlap with the main crystal structure in the plating layer. That is, if a diffraction peak with a diffraction intensity exceeding a certain amount is obtained at this diffraction angle, it can be said that the target intermetallic compound is surely contained.
- the plated layer studied by the present inventors is not necessarily the same as the manufacturing situation of the intermetallic compound in the JCPDS data, but is different. 35° is fine.
- intermetallic compounds of Al 2.15 Zn 1.85 Ca and CaZn 2 are intermetallic compounds formed by forming a plating layer having the plating composition in this embodiment and performing a special heat treatment.
- Zn that originally precipitates as a Zn phase is substituted with a part of Al 4 Ca, and Ca, which is easily incorporated into another intermetallic compound as Al—Ca—Si, is combined with Al and Zn. Formed by
- the content of these intermetallic compounds reduces the amount of Zn phase in the plating layer, so the corrosion resistance in an alkaline environment tends to slightly decrease at pH 10.0 or higher.
- Imax (k ⁇ m °) is the maximum value of the X-ray diffraction intensity between k ⁇ m ° at the diffraction angle 2 ⁇
- I (n °) is the diffraction angle. It is the X-ray diffraction intensity at n° in 2 ⁇
- k, m, and n are diffraction angles 2 ⁇ shown in the above formulas (1) to (4), respectively.
- Imax (22.54 to 23.30°) in the above formula (1) is the maximum value of the X-ray diffraction intensity at the diffraction angle 2 ⁇ between 22.54° and 23.30°
- I (22. 54°) and I (23.30°) are the X-ray diffraction intensities at diffraction angles 2 ⁇ of 22.54° and 23.30°, respectively.
- Imax (31.00 to 32.00°) in the above formula (2) is the maximum value of the X-ray diffraction intensity at the diffraction angle 2 ⁇ between 31.00° and 32.00°
- I (31.00° ) and I(32.00°) are X-ray diffraction intensities at diffraction angles 2 ⁇ of 31.00° and 32.00°, respectively.
- Imax (43.80 to 44.30°) in formula (3) is the maximum value of the X-ray diffraction intensity between 43.80 and 44.30° at the diffraction angle 2 ⁇ , I (43.80°), I(44.30°) is the X-ray diffraction intensity at diffraction angles 2 ⁇ of 43.80° and 44.30°, respectively.
- Imax (33.00 to 33.80°) in formula (4) is the maximum value of the X-ray diffraction intensity between 33.00 to 33.80° at the diffraction angle 2 ⁇ , I (33.00°), I(33.80°) is the X-ray diffraction intensity at diffraction angles 2 ⁇ of 33.00° and 33.80°, respectively.
- the denominator and numerator of formula (1) are described below.
- the numerator of formula (1) is obtained by calculating the background intensity at a diffraction angle 2 ⁇ of 22.90° from the diffraction intensity at 22.54° and 23.30°. That is, as shown in FIG. 1, a straight line connecting the diffraction line at 22.54° and the diffraction line at 23.30° is drawn. This straight line becomes the baseline of the diffraction peaks. Next, I(23.30°)-I(22.54°) is obtained.
- Intermetallic compound ⁇ '- MgZn2 ⁇ ′-MgZn 2 is a substance indicated by (ICDD-JCPDS powder diffraction database) 01-073-2566.
- This intermetallic compound is widely introduced, for example, in (ACTA, METALLURGICA VOL, 18 AUGUST 1970 881-890), but is a substance that has a different crystal structure from MgZn2 , which is the main phase.
- the diffraction peaks at these diffraction angles do not overlap with the diffraction peaks of the main crystal structure of the plating layer, they are convenient for quantification and determining the content. That is, if a diffraction peak with a diffraction intensity exceeding a certain amount is obtained at these diffraction angles, it can be said that the target intermetallic compound is surely contained.
- the manufacturing conditions of the intermetallic compounds in the JCPDS data are not necessarily the same, but different, so a slight shift in the diffraction peak can be seen, corresponding to 26.20 ° (100 planes) 26.15°, and 49.22° ( ⁇ 221 plane) can be 49.22° as it is.
- Imax (k° to m°) is the maximum value of the X-ray diffraction intensity between k° to m° at the diffraction angle 2 ⁇
- I (n°) is It is the X-ray diffraction intensity at the diffraction angle 2 ⁇ and n°, where k, m, and n are the diffraction angles 2 ⁇ shown in the above formulas (5) and (6), respectively.
- Imax (26.00 ° to 26.40 °) in the above formula (5) is the maximum value of the X-ray diffraction intensity at the diffraction angle 2 ⁇ between 26.00 ° and 26.40 °
- I (26 .00°) and I(26.40°) are the X-ray diffraction intensities at diffraction angles 2 ⁇ of 26.00° and 26.40°, respectively.
- Imax (49.00° to 49.60°) in the above formula (6) is the maximum value of the X-ray diffraction intensity at the diffraction angle 2 ⁇ between 49.00° and 46.60°
- I (49 .00°) and I (49.60°) are X-ray diffraction intensities at diffraction angles 2 ⁇ of 49.00° and 49.60°, respectively.
- ⁇ '- MgZn2 has higher corrosion resistance than normal MgZn2 .
- the sum of I5 and I6 is also preferably large, but preferably 2.30 or less.
- the Ca content when the Ca content is higher than the Si content of the plating layer, ⁇ '-MgZn 2 is easily formed, and the Ca/Si ratio is preferably 0.40 to 0.70.
- the chemical composition of the plating layer in order to satisfy the formula (B), must satisfy the range of the present invention, and an appropriate heat treatment must be performed in the manufacturing method.
- ⁇ '- MgZn2 tends to form simultaneously with Al2.15Zn1.85Ca and Al4Ca , and the complex and special crystal structure of ⁇ '- MgZn2 influences the formation of surrounding intermetallic compounds . is considered to give The simultaneous formation of these intermetallic compounds improves both corrosion resistance in acidic and alkaline environments.
- Intermetallic compound MgAlSi Furthermore, when the plating layer has a specific component composition and satisfies specific manufacturing conditions, an intermetallic compound MgAlSi is formed in the plating layer. That is, the average chemical composition of the plating layer satisfies 20.0 ⁇ Mg / Si ⁇ 38.0 and 3.00 ⁇ Al / Mg ⁇ 4.00, and the temperature range where ⁇ '-MgZn 2 is easy to form and if held for a sufficient time, MgAlSi is formed.
- This intermetallic compound MgAlSi is a substance indicated by (ICDD-JCPDS powder diffraction database) 01-074-9054.
- ICDD-JCPDS powder diffraction database 01-074-9054.
- the diffraction peaks at these diffraction angles are convenient for quantification and determining the content because the diffraction peaks do not overlap with the main crystal structure of the plating layer. That is, if a diffraction peak with a diffraction intensity exceeding a certain amount is obtained at these diffraction angles, it can be said that the target intermetallic compound is surely contained.
- the plated layer studied by the present inventors is not necessarily the same as the manufacturing situation of the intermetallic compound in the JCPDS data, but it is different, so a slight shift in the diffraction peak is observed, and 24.66 ° (011 plane) is 24 .66° may remain, the corresponding to 46.35° (302 plane) is 46.28°, and 49.15° (213 plane) may remain 49.15°.
- I 7 to I 9 obtained from the X-ray diffraction peaks of MgAlSi are calculated by the following formula ( When defined in 7) to (8), it is preferable to satisfy the following formula (C).
- Imax (k° to m°) is the maximum value of the X-ray diffraction intensity between k° to m° at the diffraction angle 2 ⁇
- I (n°) is It is an X-ray diffraction intensity at a diffraction angle 2 ⁇ of n°, where k, m, and n are the diffraction angles 2 ⁇ shown in the above formulas (7) to (9), respectively.
- Imax (24.30° to 24.90°) in formula (7) is the maximum value of the X-ray diffraction intensity at the diffraction angle 2 ⁇ between 24.30° and 24.90°
- I (24. 30°) and I (24.90°) are the X-ray diffraction intensities at diffraction angles 2 ⁇ of 24.30° and 24.90°, respectively.
- Imax (46.10 ° to 46.40 °) in the above formula (8) is the maximum value of the X-ray diffraction intensity between 46.10 ° and 46.40 ° at the diffraction angle 2 ⁇
- I (46.10 °) and I(46.40°) are the X-ray diffraction intensities at diffraction angles 2 ⁇ of 46.10° and 46.40°, respectively.
- Imax (49.00 ° to 49.60 °) in the above formula (9) is the maximum value of the X-ray diffraction intensity between 49.00 ° and 49.60 ° at the diffraction angle 2 ⁇
- I (49.00 °) and I(49.60°) are X-ray diffraction intensities at diffraction angles 2 ⁇ of 49.00° and 49.60°, respectively.
- Intermetallic compound Mg 9 Sn 5 Furthermore, when the average chemical composition of the plating layer satisfies 0.01 ⁇ Sn and the temperature is maintained for a sufficient time in the temperature range where ⁇ ′-MgZn 2 is easily formed, Mg 9 Sn 5 is generated in the plating layer. .
- This intermetallic compound Mg 9 Sn 5 is a substance indicated by (ICDD-JCPDS powder diffraction database) 01-072-8010.
- Mg 2 Sn (00-031-0812 or 01-080-4461) is formed, but Mg 9 Sn 5 is The crystal structure is completely different from that of the intermetallic compound of
- the diffraction angle 2 ⁇ is 23.29° (300 planes).
- the diffraction peak at this diffraction angle does not overlap with the main crystal structure of the plating layer, so it is convenient for quantification and determining the content. That is, if a diffraction peak with a diffraction intensity exceeding a certain amount is obtained at these diffraction angles, it can be said that the target intermetallic compound is surely contained.
- the plating layer studied by the present inventors is not necessarily the same as the manufacturing situation of the intermetallic compound in the JCPDS data, but is different, so a slight shift in the diffraction peak is observed, corresponding to 23.29 ° (300 planes). What does is 23.40°.
- I 10 obtained from the X-ray diffraction peak of Mg 9 Sn 5 is expressed by the following formula (When defined in 10), it is preferable to satisfy the following formula (D).
- Imax (23.10 ° to 23.30 °) is the maximum value of the X-ray diffraction intensity at the diffraction angle 2 ⁇ between 23.10 ° and 23.30 °
- I ( 23.10°) is the X-ray diffraction intensity at a diffraction angle 2 ⁇ of 23.10°
- I(23.30°) is the X-ray diffraction intensity at a diffraction angle 2 ⁇ of 23.30°.
- I10 when I10 is 1.04 or more, corrosion resistance in an alkaline environment exceeding pH 11.5 is improved. Since Mg 9 Sn 5 has a smaller number of bonds between Sn and Mg than Mg 2 Sn, it has a slightly nobler natural potential than Mg 9 Sn 5 and stable corrosion resistance in an alkaline environment. I10 may be 1.10 or less.
- an oxide film may be formed on the surface of the plating layer if it is held in a high temperature range for a long time in order to form ⁇ ′-MgZn 2 in an atmospheric environment. The presence or absence of formation of these substances is changed by heating in a nitrogen atmosphere.
- the compound in this oxide film has not been fully identified, it is assumed that it is an oxide film caused by a metal oxide because some diffraction peaks appear in the diffraction angle 2 ⁇ in the range of 0 to 20 ° in X-ray diffraction. be.
- the diffraction peaks at the diffraction angles 2 ⁇ of 10.45°, 12.83°, and 17.36° do not overlap with the main crystal structure of the plating layer, so they are convenient for quantification and content determination. . That is, if a diffraction peak with a diffraction intensity exceeding a certain amount is obtained at these diffraction angles, it can be said that the target metal oxide is surely contained.
- Imax (k° to m°) is the maximum value of the X-ray diffraction intensity between k° to m° at the diffraction angle 2 ⁇
- I (n°) is It is the X-ray diffraction intensity at the diffraction angle 2 ⁇ and n°, where k, m, and n are the diffraction angles 2 ⁇ shown in the above formulas (11) to (13), respectively.
- Imax (10.30 ° to 10.70 °) in the above formula (11) is the maximum value of the X-ray diffraction intensity at the diffraction angle 2 ⁇ between 10.30 ° and 10.70 °
- I (10 .30°) and I(10.70°) are the X-ray diffraction intensities at diffraction angles 2 ⁇ of 10.30° and 10.70°, respectively.
- Imax (12.30 ° to 13.30 °) in the above formula (12) is the maximum value of the X-ray diffraction intensity between 12.30 ° and 13.30 ° at the diffraction angle 2 ⁇
- I (12.30 °) and I(13.30°) are the X-ray diffraction intensities at diffraction angles 2 ⁇ of 12.30° and 13.30°, respectively.
- Imax (17.10 ° to 17.50 °) in the above formula (13) is the maximum value of the X-ray diffraction intensity at the diffraction angle 2 ⁇ between 17.10 ° and 17.50 °
- I (17.10 °) and I(17.50°) are the X-ray diffraction intensities at diffraction angles 2 ⁇ of 17.10° and 17.50°, respectively.
- the plated steel sheet according to this embodiment includes a steel sheet and a plating layer formed on the surface of the steel sheet.
- Zn--Al--Mg-based plating usually forms a plating layer through metal deposition and solidification reaction.
- the easiest means for forming a coating layer is to form a coating layer on the surface of the steel sheet by a hot-dip plating method, which can be formed by the Zenzimer method, the flux method, or the like.
- the plated steel sheet according to the present embodiment can be manufactured by either an immersion plating method (batch type) or a continuous plating method.
- the size, shape, surface morphology, etc. of the steel sheet to be plated there are no particular restrictions on the size, shape, surface morphology, etc. of the steel sheet to be plated. Ordinary steel plates, stainless steel, etc. are applicable as long as they are steel plates. Strips of general structural steel are most preferred.
- the surface may be finished by shot blasting or the like, and there is no problem even if plating is performed after attaching a metal film or alloy film of 3 g/m 2 or less such as Ni, Fe, Zn plating to the surface. do not have.
- a plated base sheet and a galvanized sheet (hot-dip Zn-plated steel sheet or electroplated steel sheet) of 150 g/m 2 or less.
- the steel sheet After sufficiently heating and reducing the surface of the steel sheet with a reducing gas such as H 2 , the steel sheet is immersed in a plating bath containing predetermined components.
- a reducing gas such as H 2
- the components of the plating layer can be controlled by the components of the plating bath to be prepared.
- the plating bath is prepared by mixing a predetermined amount of pure metals, for example, by a dissolution method under an inert atmosphere.
- a plating layer with almost the same composition as the plating bath is formed. If the immersion time is prolonged or it takes a long time to complete the solidification, the formation of the interfacial alloy layer is activated, so the Fe content in the plating layer may increase. If the bath temperature of the plating bath is less than 500°C, the reaction between the steel sheet and the coating layer is rapidly slowed down, so the Fe content in the coating layer is usually less than 5.0%.
- the reduced steel sheet For the formation of the plating layer, it is preferable to immerse the reduced steel sheet in a plating bath at 500-650°C for several seconds. On the surface of the reduced steel sheet, Fe diffuses into the plating bath and reacts with the components in the plating bath to form an interfacial alloy layer (mainly an Al—Fe alloy layer) at the interface between the plating layer and the steel sheet. .
- the interfacial alloy layer provides metal-chemical bonding between the steel plate below the interfacial alloy layer and the coating layer above.
- the steel sheet After the steel sheet is immersed in the plating bath for a predetermined time, the steel sheet is pulled out of the plating bath, and N2 wiping is performed while the metal adhering to the surface is in a molten state to adjust the coating layer to a predetermined thickness. It is preferable to adjust the thickness of the plating layer to 3 to 80 ⁇ m. When converted to the coating amount of the plating layer, it is 10 to 500 g/m 2 (one side). Also, the thickness of the plating layer may be adjusted to 5 to 70 ⁇ m. Converting to the adhesion amount, it is 20 to 400 g/m 2 (one side).
- Cooling means during solidification of the plating may be carried out by spraying nitrogen, air, or a mixed gas of hydrogen and helium, mist cooling, or immersion in water. Cooling means for solidifying the plating is preferably mist cooling, more preferably mist cooling in which water is contained in nitrogen. The cooling rate should be adjusted according to the content of water. If an oxide film or the like is to be formed on the plated surface, the production may be carried out by cooling in an atmospheric environment. On the other hand, in order to avoid the formation of an oxide film, it is preferable to perform cooling with N 2 gas, for example, in a N 2 replacement furnace in which the oxygen concentration is lowered to less than 20 ppm.
- the average cooling rate at 500 to 480° C. in cooling during plating solidification is preferably 30° C./second or more.
- Intermetallic compounds such as Al--Ca--Si and Mg.sub.2Si tend to form at 500 to 480.degree.
- cooling by means of a very high cooling rate such as immersion in a coolant (e.g., water) at a temperature of about 30°C (about room temperature), tends to increase corrosion resistance in acidic and alkaline environments. .
- intermetallic compounds of Al 2.15 Zn 1.85 Ca, CaZn 2 , ⁇ '-MgZn 2 , MgAlSi and Mg 9 Sn 5 which are important in the present embodiment, are formed by aging treatment by holding at low temperature for a long time. conduct. The temperature in the aging process must be strictly limited on the lower and upper limits.
- the temperature range for aging treatment is 80 to 140°C, preferably 90 to 110°C. If the temperature is less than 80° C., the temperature is too low to form the desired intermetallic compound, and the Al—Zn phase (approximately 20 mass % Al) remains to deteriorate the corrosion resistance. If the temperature exceeds 140° C., the formation of phases other than the desired intermetallic compound becomes active, and especially the Al—Zn phase (approximately 20 mass % Al) is stabilized, further deteriorating the corrosion resistance. In addition, the MgZn 2 phase is stabilized more than the ⁇ '-MgZn 2 phase, and the ⁇ '-MgZn 2 phase is not formed.
- the retention time for the aging process is 72 to 750 hours. Aging for 72 hours or more can cause intermetallic compounds to form. In addition, aging for 750 hours or less can prevent excessive oxidation of the plating layer and deterioration of corrosion resistance. More preferably, the holding time is 250 hours or more and 500 hours or less.
- the atmosphere of the aging treatment is not particularly limited.
- the atmosphere may be used, or an inert atmosphere such as nitrogen or argon may be used.
- Mg 2 Zn 11 phase may be formed in the plating layer by aging treatment, but deterioration of corrosion resistance due to Mg 2 Zn 11 phase formation has not been confirmed.
- the Mg 2 Zn 11 phase is assumed to form by-product due to the crystal structure to ⁇ ′-MgZn 2 .
- MgAlSi is further formed if the contents of Mg, Al, and Si satisfy the desired relationship. Moreover, when the plating layer contains a desired amount of Sn or the like, Mg 9 Sn 5 is likely to be formed. Furthermore, when aging treatment is performed in an atmospheric environment, metal oxides are formed on the surface. With the above, the plating layer of the plated steel sheet defined in the present embodiment is completed.
- a film may be formed on the plating layer of the plated steel sheet according to the present embodiment.
- the coating can form one layer or two or more layers. Examples of the type of coating directly on the plating layer include a chromate coating, a phosphate coating, and a chromate-free coating. Chromate treatment, phosphate treatment, and chromate-free treatment for forming these coatings can be performed by known methods.
- Chromate treatment includes electrolytic chromate treatment, in which a chromate film is formed by electrolysis, reactive chromate treatment, in which a film is formed by using a reaction with the material, and then excess treatment liquid is washed away, and treatment liquid is applied to the object to be coated.
- phosphate treatment examples include zinc phosphate treatment, zinc calcium phosphate treatment, and manganese phosphate treatment.
- Chromate-free treatment is particularly suitable because it does not burden the environment.
- Chromate-free treatment includes electrolytic-type chromate-free treatment that forms a chromate-free film by electrolysis, reaction-type chromate-free treatment that forms a film using reaction with the material, and then rinses off the excess treatment solution, and
- organic resin coating may be provided on the coating directly on the plating layer.
- the organic resin is not limited to a specific type, and examples thereof include polyester resins, polyurethane resins, epoxy resins, acrylic resins, polyolefin resins, modified products of these resins, and the like.
- the modified product is a reaction of the reactive functional group contained in the structure of these resins with another compound (monomer, cross-linking agent, etc.) containing a functional group capable of reacting with the functional group in the structure. It refers to resin.
- organic resin one or two or more organic resins (unmodified) may be mixed and used, or in the presence of at least one organic resin, at least one other One or a mixture of two or more organic resins obtained by modifying the organic resin may be used.
- the organic resin coating may contain any color pigment or rust preventive pigment.
- a water-based product obtained by dissolving or dispersing in water can also be used.
- the corrosion resistance in an acidic environment and an alkaline environment is measured and evaluated as follows.
- Corrosion resistance of less than 5g/ m2 after 60 cycles is acid environment side corrosion resistance "S+" Corrosion resistance in an acidic environment "S” for corrosion weight loss after 60 cycles of 5 g/m 2 or more and less than 10 g/m 2 Corrosion resistance in an acidic environment "A+” when corrosion weight loss after 60 cycles is 10 g/m 2 or more and less than 15 g/m 2 Corrosion resistance in an acidic environment is "A” when the corrosion weight loss after 60 cycles is 15 g/m 2 or more and less than 20 g/m 2 Corrosion resistance in an acidic environment "B” when corrosion weight loss after 60 cycles is 20 g/m 2 or more and less than 30 g/m 2 Corrosion resistance in an acidic environment "C” when corrosion weight loss after 60 cycles is 30 g/m 2 or more and less than 40 g/m 2 Corrosion resistance in an acidic environment "D” when corrosion weight loss after 60 cycles is 40 g/m 2 or more and less than 50
- Corrosion resistance in an alkaline environment "S+” means that the corrosion weight loss after 60 cycles is less than 5 g/m 2 .
- Corrosion resistance in an alkaline environment is "S" when the corrosion weight loss after 60 cycles is 5 g/m 2 or more and less than 10 g/m 2
- Corrosion resistance in an alkaline environment is "A+” if the corrosion weight loss after 60 cycles is 10 g/m 2 or more and less than 15 g/m 2
- Corrosion resistance in an alkaline environment is "A” when the corrosion weight loss after 60 cycles is 15 g/m 2 or more and less than 20 g/m 2
- Corrosion resistance in an alkaline environment is "B+” if the corrosion weight loss after 60 cycles is 20 g/m 2 or more and less than 30 g/m 2 Corrosion resistance in an alkaline environment is "B” if the corrosion weight loss after 60 cycles is 30 g/m 2 or more and less than 35 g/m 2 Cor
- the present invention is not limited to this one conditional example. Various conditions can be adopted in the present invention as long as the objects of the present invention are achieved without departing from the gist of the present invention.
- Plated steel sheets shown in Tables 2A-1 to 6B-2 were produced and their performance was evaluated.
- Various plating baths were prepared by mixing pure metals.
- Fe powder was added after the bath was prepared so that the Fe concentration did not increase during the test.
- the value described as "0" in the table indicates that the ICP was less than the 0.005% detection limit.
- a 180 ⁇ 100 size steel plate (1.6 mm) was used as the plated steel plate.
- a batch-type hot-dip plating simulator (manufactured by our company) was used to form the plating layer.
- a K thermocouple was attached to a part of the plated steel sheet, and annealing was performed by heating and holding at 800° C. in a mixed gas atmosphere of 95 vol % N 2 -5 vol % H 2 to sufficiently reduce the surface of the steel sheet. After that, it was immersed in a plating bath with a bath temperature of 500 to 650° C. for 3 seconds, then pulled out and adjusted to a plating layer thickness of 25 to 30 ⁇ m by N 2 gas wiping.
- A After wiping with N2 gas, immerse in water from 500°C (cooling rate of 100°C/sec or more: the water temperature (about 30°C) is reached within 2 seconds) and cool B: After wiping with N2 gas, 500 to 480°C After blowing N 2 gas so that the average cooling rate of 40 ° C./sec. After gas wiping, cool by blowing N2 gas so that the average cooling rate at 500-50°C is 10-20°C/sec.
- each sample was subjected to heat treatment (aging treatment) as shown in Tables 1A-1 to 1B-2.
- aging treatment heat treatment
- Tables 1A-1 to 1B-2 “atmosphere” indicates the atmosphere during the aging treatment
- reheating temperature” indicates the heating temperature during the aging treatment
- time indicates the holding time during the aging treatment.
- the resulting plated steel sheet was cut into 20 mm squares, and the X-ray diffraction pattern of the surface of the plating layer was analyzed using a sample horizontal strong X-ray diffractometer (model number RINT-TTR III) manufactured by Rigaku Corporation. Specifically, Cu-K ⁇ rays are used, the X-ray output is 40 kV and 150 mA, a copper target, a goniometer TTR (horizontal goniometer), a K ⁇ filter slit width of 0.05 mm, a longitudinal limiting slit width of 2 mm, and a light receiving The slit width is 8 mm, the light receiving slit 2 is open, and the scanning speed is 5 deg. /min, a step width of 0.01 deg, and a scan axis 2 ⁇ (5 to 90°) to obtain the X-ray diffraction intensity at each angle.
- a sample horizontal strong X-ray diffractometer model number RINT-TTR III
- the superiority or inferiority of corrosion resistance in was determined (six-grade evaluation). When the evaluation was from D to S+, it was determined to be acceptable as having excellent corrosion resistance in an acidic environment. On the other hand, when the evaluation was E, it was determined to be unacceptable due to poor corrosion resistance in an acidic environment.
- Corrosion resistance of less than 5g/ m2 after 60 cycles is acid environment side corrosion resistance "S+" If the corrosion weight loss after 60 cycles is 5 g/m 2 or more and less than 10 g/m 2 , the acid environment side corrosion resistance is "S".
- Corrosion resistance in an acidic environment "A+” when corrosion weight loss after 60 cycles is 10 g/m 2 or more and less than 15 g/m 2 Corrosion resistance in an acidic environment is "A” when the corrosion weight loss after 60 cycles is 15 g/m 2 or more and less than 20 g/m 2 Corrosion resistance in an acidic environment "B” when corrosion weight loss after 60 cycles is 20 g/m 2 or more and less than 30 g/m 2 Corrosion resistance in an acidic environment "C” when corrosion weight loss after 60 cycles is 30 g/m 2 or more and less than 40 g/m 2 Corrosion resistance in an acidic environment "D” when corrosion weight loss after 60 cycles is 40 g/m 2 or more and less than 50 g/m 2 Corrosion resistance in an acidic environment "E” if the corrosion weight loss after 60 cycles is 50 g / m 2 or more
- Corrosion resistance in an alkaline environment is "A+” if the corrosion weight loss after 60 cycles is 10 g/m 2 or more and less than 15 g/m 2 Corrosion resistance in an alkaline environment is "A” when the corrosion weight loss after 60 cycles is 15 g/m 2 or more and less than 20 g/m 2 Corrosion resistance in an alkaline environment is "B+” if the corrosion weight loss after 60 cycles is 20 g/m 2 or more and less than 30 g/m 2 Corrosion resistance in an alkaline environment is "B” if the corrosion weight loss after 60 cycles is 30 g/m 2 or more and less than 35 g/m 2 Corrosion resistance in an alkaline environment is "C” if the corrosion weight loss after 60 cycles is 35 g/m 2 or more and less than 40 g/m 2 Corrosion resistance in an alkaline environment "D” for corrosion weight loss after 60 cycles of 40 g/m 2 or more and less than 50 g/m 2 Corrosion
- the chemical composition of the plating layer was within the range of the present invention, and the manufacturing conditions were within the preferable range, so corrosion resistance was excellent in both acidic and alkaline environments.
- the plating layers of these test examples contained Zn phase, Al phase, Al--Zn phase, ⁇ '-MgZn 2 phase and MgZn 2 phase as main phases.
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Abstract
Description
本願は、2021年10月26日に、日本に出願された特願2021-174676号に基づき優先権を主張し、その内容をここに援用する。
前記めっき層の平均化学組成が、質量%で、
Al:15.0%超、30.0%以下、
Mg:5.0%超、15.0%以下、
Sn:0~0.70%、
Bi:0~0.35%、
In:0~0.35%、
Ca:0.03~0.60%、
Y :0~0.30%、
La:0~0.30%、
Ce:0~0.30%、
Si:0.01~0.75%、
Cr:0~0.25%、
Ti:0~0.25%、
Ni:0~1.00%、
Co:0~0.25%、
V :0~0.25%、
Nb:0~0.25%、
Cu:0~0.25%、
Mn:0~0.25%、
Fe:0~5.0%、
Sr:0~0.5%、
Sb:0~0.5%、
Pb:0~0.5%、
B :0~0.5%、
Li:0~0.5%、
Zr:0~0.5%、
Mo:0~0.5%、
W :0~0.5%、
Ag:0~0.5%、
P :0~0.5%、
残部がZnおよび不純物からなり、
Sn、BiおよびInの合計量ΣAが0%以上、0.75%未満であり、
Ca、Y、LaおよびCeの合計量ΣBが0.03~0.60%であり、
Cr、Ti、Ni、Co、V、Nb、CuおよびMnの合計量ΣCが0~1.00%であり、
Sn≦Siおよび20.0≦Mg/Siを満たし、
Cu-Kα線を使用し、X線出力が40kV及び150mAである条件で測定した、前記めっき層表面のX線回折パターンにおいて、Al2.15Zn1.85CaのX線回折ピークから求められるI1~I3と、CaZn2のX線回折ピークから求められるI4と、η’-MgZn2のX線回折ピークから求められるI5およびI6と、を下記式(1)~(6)で定義した場合に、下記式(A)および(B)を満足する、めっき鋼板。
Cu-Kα線を使用し、X線出力が40kV及び150mAである条件で測定した、前記めっき層表面のX線回折パターンにおいて、MgAlSiのX線回折ピークから求められるI7~I9を下記式(7)~(8)で定義した場合に、下記式(C)を満足する、[1]に記載のめっき鋼板。
Cu-Kα線を使用し、X線出力が40kV及び150mAである条件で測定した、前記めっき層表面のX線回折パターンにおいて、Mg9Sn5のX線回折ピークから求められるI10を下記式(10)で定義した場合に、下記式(D)を満足する、[1]または[2]に記載のめっき鋼板。
鋼板の形状は、主に板材であるがそのサイズに特に制限は無い。板材にめっき層を形成しためっき鋼板としては、通常の溶融亜鉛めっき工程で製造されるめっき鋼板であって、連続溶融亜鉛めっきライン(CGL)やバッチ式どぶ漬け亜鉛めっき工程など、溶融金属に浸漬して凝固させる工程で製造されるめっき鋼板がこれに当てはまる。このような方法により製造されためっき鋼板を加工(溶接を含む)、組み合わせをすれば、様々な製品に加工でき、耐食性に優れた鋼構造部材を製造することが可能である。
2段めっきやプレめっきなどの置換めっきを形成した際には、プレめっき層の厚みによって、プレめっき層中に含まれていた元素がAl-Fe合金層に含有される場合がある。Fe面上にめっき後にも、プレめっき層として残存し、その上に、界面合金層ができる場合もある。また、めっき元素の拡散が活発に行われ、Fe側へめっき成分が拡散するとプレめっき層下でAl-Fe合金層が形成する場合もある、反応性によって部分的に発生する場合もあり、厳密にはその位置は定義できないがこれらの層による性能変化は厚みが薄いため大きくない。
すなわち、本実施形態に係るめっき層は、Zn-Al-Mg合金層からなっていてもよく、Zn-Al-Mg合金層とAl-Fe合金層とからなっていてもよく、Zn-Al-Mg合金層とAl-Fe-Si合金層とからなっていてもよい。なお、Al-Fe合金層には、Alと原子半径の近いZnなどが置換体として一部取り込まれることが必然的に起こり、Feと原子半径の近い遷移金属Ni、Cr、Coなどもこれらの金属間化合物に置換体として取り込まれることは避けられないが、主たる構造はAl-Fe合金層として扱うことができる。
Alは、Znと同様に、めっき層の主体を構成する元素である。Zn-Al-Mg系めっきでは、めっき層中で主にAl相を形成する。Al含有量が15.0%以下であると、酸性環境での耐食性が十分でない。そのため、Al含有量は15.0%超とする。好ましくは、18.0%以上である。さらに好ましくは20%以上である。一方、Al含有量が30.0%を超えると、アルカリ性環境での耐食性が十分でない。そのため、Al含有量は30.0%以下とする。好ましくは、25.0%以下である。なお、めっき層中のAl含有量が高くなると相対的にZn含有量が減少して犠牲防食性が低下するため、めっき鋼板として犠牲防食性を確保するためには、Al含有量は15.0%超、30.0%以下とするべきである。ただし、この組成範囲では、耐食性が低いAl-Zn相(約20mass%のAlを含む相)が形成する。そのため、本実施形態では、後述する製造方法を採用することでAl-Zn相を少なくする。これにより、耐食性が向上し、酸性環境、アルカリ性環境での耐食性が確保しやすくなる。
Mgは、Znと同様に、めっき層の主体を構成する元素である。Mgが不足するとアルカリ性環境での耐食性が低くなる傾向にあることから、Mg含有量を5.0%超とする。好ましくは、7.0%以上である。一方、Mg含有量が15.0%超では酸性環境での耐食性が悪化する。そのため、Mg含有量は15.0%以下とする。好ましくは13.0%以下であり、より好ましくは10.0%以下である。
Sn:0~0.70%
Bi:0~0.35%
In:0~0.35%
Sn、BiおよびInの合計量ΣA:0%以上、0.75%未満
元素群A(Sn、Bi、In)の各元素は、任意に含有できる元素であるので、それぞれの含有量を0%以上とする。また、Snは、酸性環境およびアルカリ性環境でのめっき層の耐食性を大幅に向上させるMg9Sn5の形成に必要な元素である。Mg9Sn5の形成に最低限必要なSn含有量は0.01%であるから、Sn含有量は0.01%以上としてもよい。
なお、Sn、BiおよびInの合計量ΣAとは、Sn、BiおよびInの含有量の合計のことである。
Ca:0.03~0.60%
Y :0~0.30%
La:0~0.30%
Ce:0~0.30%
Ca、Y、LaおよびCeの合計量ΣB:0.03~0.60%
Caは、めっき層中の主要元素ではないが、Al2.15Zn1.85Caを形成するために必要な元素である。また、Caは、CaZn2を形成するためにも必要な元素である。このため、これらの金属間化合物を形成するのに最低限必要なCa含有量は0.03%以上であるため、Ca含有量は0.03%以上とする。これらの金属間化合物の含有によって酸性環境およびアルカリ性環境での耐食性が改善する。Ca含有量は、好ましくは0.05%以上であり、より好ましくは0.10%以上であり、より一層好ましくは0.20%以上である。一方、Ca含有量が0.60%超であると、酸性環境およびアルカリ性環境での耐食性が劣化する。そのため、Ca含有量は0.60%以下とする。好ましくは0.50%以下であり、より好ましくは0.40%以下である。
なお、Ca、Y、LaおよびCeの合計量ΣBとは、Ca、Y、LaおよびCeの含有量の合計のことである。
Siは、めっき層中で、金属間化合物を形成させるために必要な元素である。本実施形態におけるめっき組成は、融点が高いため、溶融めっきをする際には500℃近傍の操業温度となる。この操業温度では、鋼板をめっき浴に浸漬した際に、AlおよびZnがFeと活発な相互拡散現象を起こして金属間化合物を形成するが、Siがこの過剰な反応を抑制する。Si含有量が0.01%以上であれば、Feの拡散反応が大幅に抑制されて、めっき層に含有される金属間化合物の形成が制御されやすい。しかし、Si含有量が0.01%未満では、めっき層内にFeが過剰に拡散することでめっき層の成分が不均一になって、酸性環境およびアルカリ性環境での耐食性が極端に悪化する。そのため、Si含有量は0.01%以上とする。好ましくは0.10%以上であり、より好ましくは0.20%以上である。Si含有量が過剰になっても、Siがめっき層の構成元素と結合することで酸性環境およびアルカリ性環境での耐食性が悪化することから、Si含有量は0.75%以下とする。好ましくは0.50%以下であり、より好ましくは0.40%以下である。
Cr:0~0.25%
Ti:0~0.25%
Ni:0~1.00%
Co:0~0.25%
V :0~0.25%
Nb:0~0.25%
Cu:0~0.25%
Mn:0~0.25%
Cr、Ti、Ni、Co、V、Nb、CuおよびMnの合計量ΣC:0~1.00%
元素群Cの元素は、めっき層における任意添加元素であるため、それぞれの含有量は0%以上とする。これらの金属はめっき層中でAl、Znなどと置換し、電位が貴に移動する傾向があり、上記含有量範囲の含有で酸性環境での耐食性が改善する傾向にある。これらの元素の過剰な含有は、これらの元素を含む金属間化合物を形成するため、酸性環境およびアルカリ性環境での耐食性を悪化させる。従って、Cr、Ti、Co、V、Nb、Cu、Mnの含有量はそれぞれ0.25%以下とする。また、Niの含有量は1.00%以下とする。更に、元素群Cの合計量が過剰であると、酸性環境およびアルカリ性環境での耐食性を悪化させるため、Cr、Ti、Ni、Co、V、Nb、CuおよびMnの合計量ΣCは1.00%以下とする。合計量ΣCは、好ましくは0.80%以下であり、より好ましくは0.50%以下である。
なお、Cr、Ti、Ni、Co、V、Nb、CuおよびMnの合計量ΣCとは、Cr、Ti、Ni、Co、V、Nb、CuおよびMnの含有量の合計のことである。
本実施形態に係るめっき鋼板は溶融めっき鋼板であるため、製造時に鋼板(めっき原板)よりFeがめっき層に拡散する場合がある。めっき層中にFeが最大5.0%まで含有することがあるが、この元素の含有による耐食性変化は確認されていない。よって、Fe含有量は0~5.0%とする。
Sr:0~0.5%
Sb:0~0.5%
Pb:0~0.5%
B :0~0.5%
Li:0~0.5%
Zr:0~0.5%
Mo:0~0.5%
W :0~0.5%
Ag:0~0.5%
P :0~0.5%
元素群Dの元素は、めっき層に含有させてもよい任意添加元素であるため、それぞれの含有量は0%以上とする。これらの元素は、先に説明した元素群Cの元素と同様の効果があり、元素群Cよりも比較的含有させやすい元素である。よって、元素群Dの各元素の含有量はそれぞれ、0~0.5%とする。Sr、Sb、Pb、B、Li、Zr、Mo、W、AgおよびPの合計量ΣDは0~0.5%としてもよい。
なお、Sr、Sb、Pb、B、Li、Zr、Mo、W、AgおよびPの合計量ΣDとは、Sr、Sb、Pb、B、Li、Zr、Mo、W、AgおよびPの含有量の合計のことである。
Znは、50.00%超の割合で含有することが好ましい。本実施形態に係るめっき鋼板は、汎用性の高いZn系めっき鋼板であり、犠牲防食性を確保する目的で一定量以上のZnを含有させることで、鋼板に適切な犠牲防食性を付与する。例えば、1.6mm以上の切断端面が開放されるような環境でも、Zn量が50.0%を超えていれば、切断端面部に十分な犠牲防食性作用が現れ、高い耐食性を維持できる。特に、Zn含有量が50.00%以下の場合は、アルカリ性環境における耐食性が極端に悪化することから、Zn含有量は50.00%超とすることが好ましい。Zn含有量は、好ましくは55.00%以上であり、より好ましくは60.00%以上であり、より一層好ましくは65.00%以上である。
Si含有量は、Sn含有量以上にする必要がある。Si含有量がSn含有量未満になると、鋼板からめっき層中に過剰なFeが拡散し、目的とする金属間化合物形成が困難になる。その結果、酸性環境およびアルカリ性環境での耐食性が悪化する。
なお、「Sn≦Si」におけるSn、Siは、それぞれめっき層中のSn、Siの質量%での含有量を表す。
さらにSi含有量については、20.0≦Mg/Siを満たす必要がある。Mg含有量に対してSi含有量が高い場合、めっき層中にMg2Siが多量に形成するようになり、酸性環境での耐食性を十分に発揮することができなくなる。また、Mg含有量に対してSi含有量が高いと、Al-Ca-Si化合物の形成が促進されて、金属間化合物(Al2.15Zn1.85Ca)が形成されなくなる。ただし、Mg/Siが38.0を超えると、後述するように、めっき層中にMgAlSiが形成されなくなる。そのため、めっき層中にMgAlSiを形成させる場合は、Mg/Siを38.0以下とすることが好ましい。
なお、「Mg/Si」におけるMg、Siは、それぞれめっき層中のMg、Siの質量%での含有量を表す。
Al含有量およびMg含有量については、3.00≦Al/Mg≦4.00を満たすようにしてもよい。3.00≦Al/Mg≦4.00を満たすことで、めっき層中にMgAlSiを形成できるようになる。なお、「Al/Mg」におけるAl、Mgは、それぞれめっき層中のAl、Mgの質量%での含有量を表す。
本実施形態に係るめっき層は、Zn-Al-Mg系合金めっきにより形成されることから、主たる相としてめっき層中にZn相、Al相、Al-Zn相、η’-MgZn2相およびMgZn2相が含有される。各相の含有量によって耐食性は変化するが、金属間化合物の含有などめっき組織を制御することで、pH3.5未満の酸性環境での耐食性と、pH11.5超のアルカリ性環境での耐食性との差が小さくなり、耐食性を確保することができる。なお、主たる相を除く相としてはZn、Al、Mg元素以外に添加された元素による上記記載の金属間化合物でAl-Ca-Si化合物やMg-Sn化合物などである。
Zn相は、めっき層中に存在し、三元共晶組織(Zn/Al/MgZn2三元共晶組織)中に主に存在している。Zn相は、約20mass%未満のAlを含むZn相が含まれる。めっき層中のZn相は、pH5.0~11.5の環境下での耐食性を確保することが可能であり、この範囲での腐食量は少ないが、それ以外の範囲での腐食速度は大きい。
Al相は、めっき層中にAl初晶として塊状に存在するほか、三元共晶組織中にも一定量含有される。めっき層中のAl相は、pH3.5~10.5の環境下での耐食性を確保することが可能であり、この範囲での腐食量は少ないが、pH3.5~10.5から外れる範囲での腐食速度が大きい。
Al相中には、約90mass%のAlを含み残部にZnが含まれる。このためAlとしての性質が強く表れ、後述するAl-Zn相とはAl含有量が異なる。
Al-Zn相は、約20mass%の以上のAlを含むZn相であって、Al相、Zn相両方の性質が表れる。Al-Zn相は、本実施形態に係るめっき層を作製した場合、自ずと生成する。ここでいうAl-Zn相とは、前記の、Al相、Zn相の両方とも異なるが、AlおよびZnの2元素によって構成される相である。
Al-Zn相は、めっき層の凝固中に、Al相からZn相が分離したことによって生成した相であり、主に、室温に至るまでの過程でAl相の固溶限の低下が要因で形成する。結晶サイズで確認すると数nm~約3μmの細かい結晶粒が集合した組織である。Al-Zn相は、Zn相、Al相としての両方の性能を示すのは、その内部に細かい結晶粒単位でZn相、Al相の集合体を有するためで、何ら特別な性質を有しているわけではない。一方で、微細相は結晶粒界や、電位の異なる相の隣接はカップリング反応が促進されるため、この相の耐食性は、めっき層中のAl相(α)、Zn相(η)よりも耐食性が劣る傾向にある。
Al-Zn相は、酸性環境・アルカリ性環境での耐食性を極めて悪化させる。ただし、適切な熱処理(η’-MgZn2相の形成のための熱処理)によって、Al-Zn相を減少させることができ、酸性環境・アルカリ性環境での耐食性の悪化の懸念がなくなる。熱処理によって、Al-Zn相が減少してη’-MgZn2が生成することで、pH3.5~10.5の範囲における耐食性が向上する。
MgZn2相はめっき層中に存在し、MgZn2相として塊状に存在するほか、Al相と共にAl-MgZn2共晶線上で凝固した際に形成したデンドライト状組織や、三元共晶組織(Zn/Al/MgZn2)中にも一定量含有される。めっき層中のMgZn2相はpH5.0~pH11.5の範囲における耐食性を向上させることが可能であり、この範囲での腐食量を少なくすることができる。しかし、それ以外のpH範囲での腐食速度はほとんど変化させることができない。めっき層に含まれる相の中で最も多く存在する相がMgZn2相であるため、相構成の割合を変化させることによって耐食性を確保できるpH範囲は3.5~11.5であり、この範囲外での耐食性確保は困難である。
Al2.15Zn1.85Caは、データベース番号(ICDD-JCPDS粉末回折データベース)01-078-9051で示される物質である。Ca-Al-Zn系の金属間化合物は、例えば、(Z,Kristallogr.224(2009)397-406)で広く紹介されるが、Al4Caと相似する構造(一部Zn置換体)を形成する。これらの同構造の物質として例えば、Al4Ca、Ca0.5Zn3.5、Al3CaZn、Al2.5CaZn1.5、Al2.06CaZn1.62、Al2CaZn2、Al1.75CaZn2.25など、Al位置に一部がZn(0~2.25)に置換した物質も相似構造を示すことになるため、同種の性質をもつことが予測される。ただし、これらの物質は、原子半径が異なる置換体であるため、必ずしも回折ピークが同じ位置で得られるとは限らない。一方で、本実施形態では、特定の角度でAl2.15Zn1.85Caとして回折ピークが得られるものであるので、この物質が含有されるものとして扱う。
ただし、本発明者らが検討しためっき層においては、必ずしもJCPDSデータの金属間化合物の製造状況と同じではなく異なるために、僅かに回折ピークのシフトが見られ、22.89°(101面)に対応するものは22.90°、31.67°(103面)に対応するものは31.62°、43.94°(200面)に対応するものは44.04°になる。
この金属間化合物は、(ICDD-JCPDS粉末回折データベース)01-072-5741で示される物質である。置換体としてはCa(Al1.7Zn0.3)(JCPDSカード01-077-6005)が想定されるが、この置換体は、CaAl2構造を主とした異なる物質であり、CaZn2とは回折ピーク位置が異なるので、本実施形態では対象としない。
η’-MgZn2は、(ICDD-JCPDS粉末回折データベース)01-073-2566で示される物質である。この金属間化合物は、例えば、(ACTA,METALLURGICA VOL,18 AUGUST 1970 881-890)で広く紹介されるが、主相であるMgZn2とは結晶構造が異なる物質である。本実施形態に係るめっき層の組成範囲で、この金属間化合物に検出するのに都合の良い回折角度2θは2つあり、回折角度2θで26.20°(100面)および49.22°(-221面)である。これらの回折角度における回折ピークは、めっき層の主要の結晶構造の回折ピークが重ならないことから、定量化と含有量の見極めに都合が良い。すなわち、これらの回折角度において回折強度が一定量を超える回折ピークが得られれば、目的とする金属間化合物が確実に含有されているといえる。ただし、本発明者らが検討しためっき層においては必ずしもJCPDSデータの金属間化合物の製造状況が同じではなく異なるから、僅かに回折ピークのシフトが見られ、26.20°(100面)に対応するものは26.15°であり、49.22°(-221面)はそのまま49.22°でよい。
更に、めっき層が特定の成分組成となり、特定の製造条件を満たす場合は、めっき層中に金属間化合物MgAlSiが形成される。すなわち、めっき層の平均化学組成が、20.0≦Mg/Si≦38.0、及び、3.00≦Al/Mg≦4.00を満たすとともに、η’-MgZn2が形成しやすい温度領域で、十分な時間保持がなされた場合に、MgAlSiが形成される。
I7、I8およびI9の合計は3.10以下としてもよい。
更に、めっき層の平均化学組成が0.01≦Snを満たし、η’-MgZn2の形成しやすい温度領域で、十分な時間保持がなされたときには、Mg9Sn5がめっき層中に生成する。
I10は1.10以下としてもよい。
また、大気環境中でη’-MgZn2を形成させるべく、高温領域で長時間保持すると、めっき層の表面に酸化被膜が形成する場合がある。これらは窒素雰囲気中の加熱で形成の有無が変わる。
I11、I12およびI13の合計は3.10以下としてもよい。
本実施形態に係るめっき鋼板は、鋼板と、鋼板の表面に形成されためっき層とを備える。通常、Zn-Al-Mg系めっきは、金属の堆積と凝固反応によってめっき層を形成させる。最もめっき層を形成するのに容易な手段は、溶融めっき法により鋼板表面にめっき層を形成させることであり、ゼンジマー法やフラックス法などによって形成することが可能である。
以上をもって、本実施形態にて定義されるめっき鋼板のめっき層は完成する。
なお、めっき層の表面に被膜を有する場合には、湿式研磨などで、機械的除去によってめっき層に入熱が加わらないように完全に除去した後、上述のX線回折を実行する。
純水を希硫酸(0.4体積%)の滴下によってpH3.0に調整して、1リットルの酸溶液(常温23℃)を作製する。
試験片を酸溶液に1秒間浸漬し、引き上げ後、水平置きで温度:50℃、湿度:10%未満の大気開放型の乾燥炉に24時間放置する。
これを1サイクルとして60サイクル繰り返す。
60サイクル後、30重量%クロム酸(VI)(常温23℃)に試験片を浸漬して、めっき層表面に形成した腐食生成物を除去して、試験前後の腐食減量を測定し、酸性環境における耐食性の優劣を判定(6段階評価)する。評価がD~S+であれば、酸性環境における耐食性に優れると判断することができる。
60サイクル後の腐食減量が5g/m2以上、10g/m2未満のものを酸性環境の耐食性「S」
60サイクル後の腐食減量が10g/m2以上、15g/m2未満のものを酸性環境の耐食性「A+」
60サイクル後の腐食減量が15g/m2以上、20g/m2未満のものを酸性環境の耐食性「A」
60サイクル後の腐食減量が20g/m2以上、30g/m2未満のものを酸性環境の耐食性「B」
60サイクル後の腐食減量が30g/m2以上、40g/m2未満のものを酸性環境の耐食性「C」
60サイクル後の腐食減量が40g/m2以上、50g/m2未満のものを酸性環境の耐食性「D」
60サイクル後の腐食減量が50g/m2以上のものを酸性環境の耐食性「E」
純水をアンモニア水(3体積%)の滴下によってpH11.8に調整して1リットルのアルカリ溶液(常温23℃)を作製する。
試験片をアルカリ溶液に1秒間浸漬し、引き上げ後、水平置きで温度:50℃、湿度:10%未満の大気開放型の乾燥炉に24時間放置する。
これを1サイクルとして60サイクル繰り返す。
60サイクル後、30重量%クロム酸(VI)(常温23℃)に試験片を浸漬して、めっき層表面に形成した腐食生成物を除去して、試験前後の腐食減量を測定し、アルカリ性環境における耐食性の優劣を判定する。評価がD~S+であれば、アルカリ性環境における耐食性に優れると判断することができる。
60サイクル後の腐食減量が5g/m2以上、10g/m2未満のものをアルカリ性環境の耐食性「S」
60サイクル後の腐食減量が10g/m2以上、15g/m2未満のものをアルカリ性環境の耐食性「A+」
60サイクル後の腐食減量が15g/m2以上、20g/m2未満のものをアルカリ性環境の耐食性「A」
60サイクル後の腐食減量が20g/m2以上、30g/m2未満のものをアルカリ性環境の耐食性「B+」
60サイクル後の腐食減量が30g/m2以上、35g/m2未満のものをアルカリ性環境の耐食性「B」
60サイクル後の腐食減量が35g/m2以上、40g/m2未満のものをアルカリ性環境の耐食性「C」
60サイクル後の腐食減量が40g/m2以上、50g/m2未満のものをアルカリ性環境の耐食性「D」
60サイクル後の腐食減量が50g/m2以上のものをアルカリ性環境の耐食性「E」
表2A-1~表6B-2に示すめっき鋼板を製造し、性能を評価した。
各種めっき浴は、純金属を調合することで建浴した。めっき合金の成分は建浴後、Fe粉を添加して、試験中にFe濃度が上昇しないようにした。
なお、表中において「0」と記載した値については、ICPにおいて0.005%検出限界値未満であったことを示す。
B:N2ガスワイピング後、500~480℃の平均冷却速度が40℃/秒となるようにN2ガスを吹き付けた後、480~50℃の平均冷却速度が10~20℃/秒となるようN2ガスを吹き付けて冷却
C:N2ガスワイピング後、500~50℃の平均冷却速度が10~20℃/秒となるようN2ガスを吹き付けて冷却
純水を希硫酸(0.4体積%)の滴下によってpH3.0に調整して、1リットルの酸溶液(常温23℃)を作製した。次いで、試験片を酸溶液に1秒間浸漬し、引き上げ後、水平置きで温度:50℃、湿度:10%未満の大気開放型の乾燥炉に24時間放置した。これを1サイクルとして60サイクル繰り返した。60サイクル後、30重量%クロム酸(VI)(常温23℃)に試験片を浸漬して、めっき層表面に形成した腐食生成物を除去して、試験前後の腐食減量を測定し、酸性環境における耐食性の優劣を判定(6段階評価)した。
評価がD~S+であった場合、酸性環境における耐食性に優れるとして合格と判定した。一方、評価がEであった場合、酸性環境における耐食性に劣るとして不合格と判定した。
60サイクル後の腐食減量が5g/m2以上、10g/m2未満のものを酸性環境側の耐食性「S」
60サイクル後の腐食減量が10g/m2以上、15g/m2未満のものを酸性環境の耐食性「A+」
60サイクル後の腐食減量が15g/m2以上、20g/m2未満のものを酸性環境の耐食性「A」
60サイクル後の腐食減量が20g/m2以上、30g/m2未満のものを酸性環境の耐食性「B」
60サイクル後の腐食減量が30g/m2以上、40g/m2未満のものを酸性環境の耐食性「C」
60サイクル後の腐食減量が40g/m2以上、50g/m2未満のものを酸性環境の耐食性「D」
60サイクル後の腐食減量が50g/m2以上のものを酸性環境の耐食性「E」
純水をアンモニア水(3体積%)の滴下によってpH11.8に調整して1リットルのアルカリ溶液(常温23℃)を作製した。次いで、試験片をアルカリ溶液に1秒間浸漬し、引き上げ後、水平置きで温度:50℃、湿度:10%未満の大気開放型の乾燥炉に24時間放置した。これを1サイクルとして60サイクル繰り返した。60サイクル後、30重量%クロム酸(VI)(常温23℃)に試験片を浸漬して、めっき層表面に形成した腐食生成物を除去して、試験前後の腐食減量を測定し、耐食性の優劣を判定した。
60サイクル後の腐食減量が5g/m2以上、10g/m2未満のものをアルカリ性環境側の耐食性「S」
60サイクル後の腐食減量が10g/m2以上、15g/m2未満のものをアルカリ性環境の耐食性「A+」
60サイクル後の腐食減量が15g/m2以上、20g/m2未満のものをアルカリ性環境の耐食性「A」
60サイクル後の腐食減量が20g/m2以上、30g/m2未満のものをアルカリ性環境の耐食性「B+」
60サイクル後の腐食減量が30g/m2以上、35g/m2未満のものをアルカリ性環境の耐食性「B」
60サイクル後の腐食減量が35g/m2以上、40g/m2未満のものをアルカリ性環境の耐食性「C」
60サイクル後の腐食減量が40g/m2以上、50g/m2未満のものをアルカリ性環境の耐食性「D」
60サイクル後の腐食減量が50g/m2以上のものをアルカリ性環境の耐食性「E」
Claims (7)
- 鋼板表面に、めっき層を有するめっき鋼板であって、
前記めっき層の平均化学組成が、質量%で、
Al:15.0%超、30.0%以下、
Mg:5.0%超、15.0%以下、
Sn:0~0.70%、
Bi:0~0.35%、
In:0~0.35%、
Ca:0.03~0.60%、
Y :0~0.30%、
La:0~0.30%、
Ce:0~0.30%、
Si:0.01~0.75%、
Cr:0~0.25%、
Ti:0~0.25%、
Ni:0~1.00%、
Co:0~0.25%、
V :0~0.25%、
Nb:0~0.25%、
Cu:0~0.25%、
Mn:0~0.25%、
Fe:0~5.0%、
Sr:0~0.5%、
Sb:0~0.5%、
Pb:0~0.5%、
B :0~0.5%、
Li:0~0.5%、
Zr:0~0.5%、
Mo:0~0.5%、
W :0~0.5%、
Ag:0~0.5%、
P :0~0.5%、
残部がZnおよび不純物からなり、
Sn、BiおよびInの合計量ΣAが0%以上、0.75%未満であり、
Ca、Y、LaおよびCeの合計量ΣBが0.03~0.60%であり、
Cr、Ti、Ni、Co、V、Nb、CuおよびMnの合計量ΣCが0~1.00%であり、
Sn≦Siおよび20.0≦Mg/Siを満たし、
Cu-Kα線を使用し、X線出力が40kV及び150mAである条件で測定した、前記めっき層表面のX線回折パターンにおいて、Al2.15Zn1.85CaのX線回折ピークから求められるI1~I3と、CaZn2のX線回折ピークから求められるI4と、η’-MgZn2のX線回折ピークから求められるI5およびI6と、を下記式(1)~(6)で定義した場合に、下記式(A)および(B)を満足する、めっき鋼板。
- 前記めっき層の平均化学組成が、20.0≦Mg/Si≦38.0および3.00≦Al/Mg≦4.00を満足し、
Cu-Kα線を使用し、X線出力が40kV及び150mAである条件で測定した、前記めっき層表面のX線回折パターンにおいて、MgAlSiのX線回折ピークから求められるI7~I9を下記式(7)~(8)で定義した場合に、下記式(C)を満足する、請求項1に記載のめっき鋼板。
- 前記めっき層の平均化学組成が、0.01≦Snを満たし、
Cu-Kα線を使用し、X線出力が40kV及び150mAである条件で測定した、前記めっき層表面のX線回折パターンにおいて、Mg9Sn5のX線回折ピークから求められるI10を下記式(10)で定義した場合に、下記式(D)を満足する、請求項1に記載のめっき鋼板。
- 前記めっき層の平均化学組成が、0.01≦Snを満たし、
Cu-Kα線を使用し、X線出力が40kV及び150mAである条件で測定した、前記めっき層表面のX線回折パターンにおいて、Mg9Sn5のX線回折ピークから求められるI10を下記式(10)で定義した場合に、下記式(D)を満足する、請求項2に記載のめっき鋼板。
- 前記めっき層中に、Zn相、Al相、Al-Zn相、η’-MgZn2相およびMgZn2相が含有される、請求項1乃至請求項4のいずれか一項に記載のめっき鋼板。
- 前記めっき層中に、Zn相、Al相、Al-Zn相、η’-MgZn2相およびMgZn2相が含有される、請求項5に記載のめっき鋼板。
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