HIGHLY CORROSION RESISTANCE SURFACE TREATED STEEL PLATE

PURPOSE:To provide a highly corrosion resistant surface treated steel plate which is improved in paintability, corrosion resistance after painting and weldability by providing two layers of plating films of an Ni-Fe alloy and a Zn-Ni alloy on the surface of the steel plate. CONSTITUTION:A highly corrosion resistant surface treated steel plate wherein the double films consisting of an Ni-Fe alloy plating layer as the 1st layer and a Zn-Ni alloy plating layer as the 2nd layer are provided on at least one surface of a steel plate for outside plate of automotive bodies, etc. In this stage, the coated weight of the Zn-Ni alloy plating is made preferably 5-50g/m and the coated weight of the Ni-Fe alloy 1/50-1/2 of the coated weight of the Zn-Ni alloy plating. The film compsn. of Zn-Ni is made about 10-20wt% in terms of content of Ni and the film compsn. of the Ni-Fe about 5-90% in terms of content of Fe. If the double layered films are provided on one surface of the steel plate and the Ni-Fe plating layer is provided on the other surface, the performance suited for use environment is provided.