HIGHLY CORROSION RESISTANT STEEL

PROBLEM TO BE SOLVED: To provide a highly corrosion resistant steel having excellent corrosion resistance without reducing its mechanical properties and weldability caused by the surplus addition of corrosion resistance improving elements. SOLUTION: (1) The highly corrosion resistant steel has a composition comprising, by mass, 0.01 to 3.0% Zn, 0.05 to 3.0% Cu and 0.05 to 6.0% Ni, and further comprising one or more kinds selected from 0.0005 to 0.0050% Ca, 0.0005 to 0.010% Mg and 0.0005 to 0.010% rare earth metals. (2) Regarding the highly corrosion resistant steel, the region to a depth of 500 μm from the outermost surface of the steel is provided with a Cu+Ni concentrated layer in which the content of Cu+the content of Ni are ≥1.2 times the content of Cu+the content of Ni in the steel and are also ≥1.0 mass%, and the thickness of the concentrated layer is ≥1 μm. (3) In the highly corrosion resistant steel, the average ferrite crystal grain size in the specified region of the surface layer part in the steel sheet is ≤5 μm. COPYRIGHT: (C)2006,JPO&NCIPI