Plated steel material and method for manufacturing plated steel material
Provided are a coated steel product in which a coating layer has a predetermined chemical composition, and in a backscattered electron image of a Zn—Al—Mg alloy layer, obtained by polishing a surface of the coating layer to ½ of a layer thickness, and observing the surface at a magnification of 100× with a scanning electron microscope, Zn/Al/MgZn 2 ternary eutectics are present, and an average value of a cumulative circumferential length of the Zn/Al/MgZn 2 ternary eutectics is from 100 to 300 mm/mm 2 and a method of manufacturing the coated steel product.
1 . A coated steel product comprising a base steel and a coating layer including a Zn—Al—Mg alloy layer provided on a surface of the base steel, wherein the coating layer has a chemical composition composed of, in terms of % by mass:
Zn at more than 65.00%,
Al at more than 5.00% and less than 25.00%,
Mg at more than 3.00% and less than 12.50%,
Sn at from 0% to 3.00%,
Bi at from 0% to less than 5.00%,
In at from 0% to less than 2.00%,
Ca at from 0% to 3.00%,
Y at from 0% to 0.50%,
La at from 0% to less than 0.50%,
Ce at from 0% to less than 0.50%,
Si at from 0% to less than 2.50%,
Cr at from 0% to less than 0.25%,
Ti at from 0% to less than 0.25%,
Zr at from 0% to less than 0.25%,
Mo at from 0% to less than 0.25%,
W at from 0% to less than 0.25%,
Ag at from 0% to less than 0.25%,
P at from 0% to less than 0.25%,
Ni at from 0% to less than 0.25%,
Co at from 0% to less than 0.25%,
V at from 0% to less than 0.25%,
Nb at from 0% to less than 0.25%,
Cu at from 0% to less than 0.25%,
Mn at from 0% to less than 0.25%,
Li at from 0% to less than 0.25%,
Na at from 0% to less than 0.25%,
K at from 0% to less than 0.25%,
Fe at from 0% to 5.00%,
Sr at from 0% to less than 0.50%,
Sb at from 0% to less than 0.50%,
Pb at from 0% to less than 0.50%,
B at from 0% to less than 0.50%, and
impurities,
wherein, in a backscattered electron image of the Zn—Al—Mg alloy layer, obtained by polishing a surface of the coating layer to ½ of a layer thickness, and observing the surface at a magnification of 100× with a scanning electron microscope, Zn/Al/MgZn 2 ternary eutectics are present, and an average value of a cumulative circumferential length of the Zn/Al/MgZn 2 ternary eutectics is from 100 to 300 mm/mm 2 .
2 . The coated steel product according to claim 1 , wherein the coating layer has an Al—Fe alloy layer between the base steel and the Zn—Al—Mg alloy layer.
3 . The coated steel product according to claim 1 , wherein an interface roughness Ra between the base steel and the coating layer is from 0.3 to 2.0 μm.
4 . A method of manufacturing the coated steel product according to claim 1 ,
wherein a base steel having a surface roughness Ra of a surface to be coated of from 0.3 to 2.0 μm is immersed in a coating bath and pulled up from the coating bath, and then cooled down in a temperature range of from 450° C. to 395° C. at an average cooling rate of from 5 to 20° C./s, cooled down in a temperature range of from 395° C. to 340° C. at an average cooling rate of 3° C./s or less, and cooled down in a temperature range of from 340° C. to 280° C. at an average cooling rate of from 10 to 20° C./s.