Method of surface treatment for stainless steel product for fuel cell

A method of surface treatment for stainless steel products for fuel cells, being a method of surface treatment for austenitic stainless steel products for fuel cells comprising, by weight, C:

• 0.15% or less, Si:
• 0.01 to 1.5%, Mn:
• 0.01 to 2.5%, P:
• 0.035% or less, S:
• 0.01% or less, Al:
• 0.001 to 0.2%, N:
• 0.3% or less, Cu:
• 0 to 3%, Ni:
• 7 to 50%, Cr:
• 17 to 30%, Mo:
• 0 to 7%, B:
• 0.005 to 3.5%, and balance:
• Fe and inevitable impurities, with the contents of Cr, Mo, and B satisfying the following formula, comprising a first step of forming a passive film preliminarily on the surface of the austenitic stainless steel product of the specified composition by an oxidizing acid, a second step of protruding one or more types of conductive inclusions M23C6 type carbide, M23(C, B)6 type boron carbide, and M2B type boride on the surface by etching the passive film 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:
• Cr(%)+3×Mo(%)−2.5×B(%)≧17
• wherein element symbols denote contents (wt. %).

A method of surface treatment for stainless steel products for fuel cells, being a method of surface treatment for ferritic stainless steel products for fuel cells comprising, by weight, C:

• 0.15% or less, Si:
• 0.01 to 1.5%, Mn:
• 0.01 to 1.5%, P:
• 0.035% or less, S:
• 0.01% or less, Al:
• 0.001 to 0.2%, N:
• 0.35% or less, Cu:
• 0 to 1%, Ni:
• 0 to 5%, Cr:
• 17 to 36%, Mo:
• 0 to 7%, B:
• 0.005 to 3.5%, and balance:
• Fe and inevitable impurities, with the contents of Cr, Mo, and B satisfying the following formula, comprising a first step of forming a passive film preliminarily on the surface of the ferritic stainless steel product of the specified composition by an oxidizing acid, a second step of protruding one or more types of conductive inclusions M23C6 type carbide, M23(C, B)6 type boron carbide, and M2B type boride on the surface by etching the passive film 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:
• Cr(%)+3×Mo(%)−2.5×B(%)≧17
• wherein element symbols denote contents (wt. %).

A method of surface treatment for stainless steel products for fuel cells, being a surface treatment method of bright annealed austenitic stainless steel products for fuel cells comprising, by weight, C:

• 0.15% or less, Si:
• 0.01 to 1.5%, Mn:
• 0.01 to 2.5%, P:
• 0.035% or less, S:
• 0.01% or less, Al:
• 0.001 to 0.2%, N:
• 0.3% or less, Cu:
• 0 to 3%, Ni:
• 7 to 50%, Cr:
• 17 to 30%, Mo:
• 0 to 7%, B:
• 0.005 to 3.5%, and balance:
• Fe and inevitable impurities, with the contents of Cr, Mo and B satisfying the following formula, comprising a first step of forming a passive film preliminarily on the surface of the austenitic stainless steel product of the specified composition by an oxidizing acid, a second step of protruding one or more types of conductive inclusions M23C6 type carbide, M23(C, B)6 type boron carbide, and M2B type boride on the surface by etching the passive film 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:
• Cr(%)+3×Mo(%)−2.5×B(%)≧17
• wherein element symbols denote contents (wt. %).

A method of surface treatment for stainless steel products for fuel cells, being a surface treatment method of bright annealed ferritic stainless steel products for fuel cells comprising, by weight, C:

• 0.15% or less, Si:
• 0.01 to 1.5%, Mn:
• 0.01 to 1.5%, P:
• 0.035% or less, S:
• 0.01% or less, Al:
• 0.001 to 0.2%, N:
• 0.35% or less, Cu:
• 0 to 1%, Ni:
• 0 to 5%, Cr:
• 17 to 36%, Mo:
• 0 to 7%, B:
• 0.005 to 3.5%, and balance:
• Fe and inevitable impurities, with the contents of Cr, Mo, and B satisfying the following formula, comprising a first step of forming a passive film preliminarily on the surface of the ferritic stainless steel product of the specified composition by an oxidizing acid, a second step of protruding one or more types of conductive inclusions M23C6 type carbide, M23(C, B)6 type boron carbide, and M2B type boride on the surface by etching the passive film 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:
• Cr(%)+3×Mo(%)−2.5×B(%)−17
• wherein element symbols denote contents (wt. %).