PURPOSE: To enhance the resistance of a steel product to corrosion due to chloride and the stripping resistance of a diffused layer, by depositing Ni on the surface of the steel product from a vapor phase Ni compound at a prescribed temp. and by diffusing the Ni in the steel up to a prescribed depth.

CONSTITUTION: Vapor of a volatile Ni compound is brought into contact with a steel product to be treated at 1,000W1,300°C in a nonoxidizing atmosphere. Ni is deposited on the surface of the steel product from the vapor by reduction, and simultaneously the Ni is diffused in the steel to form a diffused Ni layer having ≥5μm thickness. Thus, a steel product having superior resistance to corrosion due to chloride and causing no stripping of Ni is obtd.