STAINLESS STEEL FOR POLYMER FUEL CELL SEPARATOR AND METHOD FOR PREPARING SAME

The present invention relates to a ferrite stainless steel for a polymer fuel cell separator that has superior corrosion resistance and interface contact resistance in a polymer fuel cell operating environment, and a method for preparing the same. The stainless steel according to the invention consists of, in wt%, C: 0.02 % or less, N: 0.02 % or less, Si: 0.4 % or less, Mn: 0.2 % or less, P: 0.04 % or less, S: 0.02 % or less, Cr: 25.0-32.0 %, Cu: 0-2.0 %, Ni: 0.8 % or less, Ti: 0.01-0.5 % or less, Nb: 0.01-0.5 % or less, residual Fe and unavoidable elements to be included, and the method for preparing the stainless steel that has a secondary passivation coating formed on its surface comprises a step wherein the stainless steel is subjected to bright annealing or annealing and acid washing to form a primary passivation coating; a step wherein the stainless steel is subjected to acid washing in a 10-20 wt% aqueous sulfuric acid solution at a temperature of 50-75°C for a certain period to remove the primary passivation coating; a step wherein the stainless steel is washed; and a step wherein the stainless steel is subjected to passivation treatment in a mixed acid of 10-20 wt% nitric acid with 1-10 wt% hydrofluoric acid at a temperature of 40-60°C for a certain period to form the secondary passivation coating. Based on such configuration, not only can stainless steel with reduced exudation resistance and superior corrosion resistance be prepared but also stainless steel for a polymer fuel cell separator can be produced that has low interfacial contact resistance and superior long-term performance even under fuel cell operation conditions of 60-150°C and various surface roughness conditions. La présente invention concerne un acier inoxydable à base de ferrite pour un séparateur de pile à combustible à polymère qui présente une résistance à la corrosion et une résistance de contact à l'interface supérieures dans l'environnement de fonctionnement d'une pile à combustible à polymère, et qui comprend, en pourcentage pondéral, les éléments suivants : C 0,02 % ou moins, N 0,02 % ou moins, Si 0,4 % ou moins, Mn 0,2 % ou moins, P 0,04 % ou moins, S 0,02 % ou moins, Cr 25,0-32,0 %, Cu 0-2,0 %, Ni 0,8 % ou moins, Ti 0,01-0,5 % ou moins, Nb 0,01-0,5 % ou moins, le reste étant du fer et les inévitables impuretés. L'invention concerne également un procédé de fabrication d'un acier inoxydable dont la surface est recouverte d'un revêtement de passivation secondaire, lequel p