Method for manufacturing stainless steel for polymer fuel cell separator having excellent contact resistance
Disclosed is a method of manufacturing a stainless steel with excellent contact resistance for a polymer fuel cell separator. The method of manufacturing a stainless steel with excellent contact resistance for a polymer fuel cell separator according to an embodiment of the present disclosure includes: electrolyzing to remove a first passivation film formed on a cold-rolled thin sheet of a stainless steel comprising, in percent (%) by weight of the entire composition, C: greater than 0 to 0.1%, N: greater than 0 to 0.02%, Si: greater than 0 to 0.25%, Mn: greater than 0 to 0.2%, P: greater than 0 to 0.04%, S: greater than 0 to 0.02%, Cr: 22 to 34%, Ti: greater than 0 to 0.5%, Nb: greater than 0 to 0.5%, the remainder of iron (Fe) and other inevitable impurities; and immersing in a mixed acid solution of nitric acid and hydrofluoric acid to form a second passivation film on the stainless cold-rolled thin sheet.
1. A method of manufacturing a stainless steel for a polymer fuel cell separator, the method comprising:
electrolyzing to remove a first passivation film formed on a cold-rolled sheet of a stainless steel comprising, in percent (%) by weight of the entire composition, C: greater than 0 to 0.1%, N: greater than 0 to 0.02%, Si: greater than 0 to 0.25%, Mn: greater than 0 to 0.2%, P: greater than 0 to 0.04%, S: greater than 0 to 0.02%, Cr: 29.7 to 30.1%, Ti: greater than 0 to 0.5%, Nb: greater than 0 to 0.5%, the remainder of iron (Fe) and inevitable impurities; and
immersing in an acid solution to form a second passivation film on the stainless cold-rolled sheet,
wherein the electrolyzing is performed in 5 to 30% by weight of sulfuric acid solution at 40 to 80° C. and a cathode applied current density (Ic) is 4 to 15 A/dm 2 ,
the immersing in the acid solution is performed in 10 to 15% by weight of nitric acid at 40 to 60° C.,
the acid solution does not comprise hydrofluoric acid,
a contact resistance of the second passivation film is 18.2 mΩcm 2 or less, and
no surface rust is found on a surface of the polymer fuel cell separator after performing a static potential endurance test at 0.6V for 300 hours.
2. The method of claim 1 , wherein the cold-rolled sheet of the stainless steel further comprises any one or more selected from the group consisting of Cu: greater than 0 to 0.6%, V: greater than 0 to 0.6%, and Mo: 0.05 to 2.5%.