TWI315745B

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. The characteristic is in that: (1) 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) the region to a depth of 500 mu m 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 mu m. (3) the average ferrite crystal grain size in the specified region of the surface layer part in the steel sheet is