Patent ID: 6884363

Claim:
A method of surface treatment for a stainless steel sheet product for fuel cells, the stainless steel sheet product being formed by a process comprising forming an ingot, hot rolling, cold rolling and annealing to yield the stainless steel sheet product, whereafter the stainless steel sheet product is subjected to a four step process, the stainless steel sheet product comprising, by weight, C: 0.15% or less, Cr: 17 to 36%, and B: 0.005 to 3.5%, the four step process comprising a first step of forming a passive film preliminarily on the surface of the stainless steel sheet product by an oxidizing acid, a second step of protruding one or more types of conductive inclusions M 23 C 6 type carbide, M 23 (C, B) 6 type boron carbide, and M 2 B type boride on the surface by etching the passive filming in an acidic aqueous solution, a third step of forming a passive film on the surface other than the inclusions protruding on the etched surface by an oxidizing acid, and a fourth step of washing in water and drying.