Patent ID: 9290845
Filing Date: 2016-03-22
CPC Classification: C22C,C23C,C23G,H01M,Y02E,Y02P

Claim Text:
1. A preparation method of a stainless steel for a polymer fuel cell separator, comprising C: 0.02 wt % or less, N: 0.02 wt % or less, Si: 0.4 wt % or less, Mn: 0.2 wt % or less, P: 0.04 wt % or less, S: 0.02 wt % or less, Cr: 25.0 to 32.0 wt %, Cu: 0 to 2.0 wt %, Ni: 0.8 wt % or less, Ti: 0.5 wt % or less, Nb: 0.5 wt % or less, waste Fe and inevitably contained elements, in which a second passive film is formed on a surface of the stainless steel, the method comprising: forming a first passive film on the surface of the stainless steel by bright-annealing or annealing-pickling the stainless steel; removing the first passive film by pickling the stainless steel in a 10 to 20 wt % sulfuric acid solution at a temperature of 50 to 75° C. for a first processing time controlled based on a surface roughness Ra of the stainless steel, wherein the first processing time is increased as the surface roughness Ra is increased; water-washing the stainless steel; and forming the second passive film by performing a passivation treatment on the stainless steel in the mixture of a 10 to 20 wt % nitric acid and a 1 to 10 wt % fluorine acid at a temperature of 40 to 60° C. for a second processing time controlled based on the surface roughness Ra, wherein, in the forming of the second passive film, the second processing time is controlled according to the following expression: