STAINLESS STEEL HAVING EXCELLENT CONTACT RESISTANCE FOR PEMFC SEPARATOR AND METHOD OF MANUFACTURING THE SAME
Stainless steel having excellent contact resistance for a PEMFC separator and a method for manufacturing the stainless steel are disclosed. The stainless steel for the Polymer Electrolyte Membrane Fuel Cell (PEMFC) separator according to an embodiment of the present disclosure may include: by weight percent, 0 to 0.02% of C (excluding 0%), 0 to 0.02% of N (excluding 0%), 0 to 0.25% of Si (excluding 0%), 0% to 0.2% of Mn (excluding 0%), 0 to 0.04% of P (excluding 0%), 0 to 0.02% of S (excluding 0%), 25 to 34% of Cr, 0 to 0.5% of Ti (excluding 0%), 0 to 0.5% of Nb (excluding 0%), 0 to 0.6% of Sn (excluding 0%) and the remainder comprising iron (Fe) and other unavoidable impurities, wherein the value of the following formula (1) with respect to the atomic ratio of X and Sn in the region within 3 nm in thickness from a surface of a passive film is 0.001 or more. X/Sn formula (1) Where X is Cl or F.
1 . Stainless steel with improved contact resistance for a Polymer Electrolyte Membrane Fuel Cell (PEMFC) separator, the stainless steel comprising: by weight percent, 0 to 0.02% of C (excluding 0%), 0 to 0.02% of N (excluding 0%), 0 to 0.25% of Si (excluding 0%), 0% to 0.2% of Mn (excluding 0%), 0 to 0.04% of P (excluding 0%), 0 to 0.02% of S (excluding 0%), 25 to 34% of Cr, 0 to 0.5% of Ti (excluding 0%), 0 to 0.5% of Nb (excluding 0%), 0 to 0.6% of Sn (excluding 0%) and the remainder comprising iron (Fe) and other unavoidable impurities, wherein the value of the following formula (1) with respect to the atomic ratio of X and Sn in the region within 3 nm in thickness of a surface of a passive film is 0.001 or more.
X/Sn formula (1)
Where X is Cl or F.
2 . The stainless steel of claim 1 , wherein the contact resistance index defined by the following formula (2) relating to the content of Cr and Sn is 25 or more and the value of the following formula (3) with respect to the atomic ratio of Sn and Cr in a region within 3 nm in thickness from the surface of the passive film is 0.001 or more.
Cr+10Sn formula (2))
(10*Sn)/Cr formula (3)
3 . The stainless steel of claim 2 , wherein the value of formula (3) is 0.004 or more.
4 . The stainless steel of claim 1 , wherein the contact resistance of the stainless steel may be 20 mΩ·cm2 or less.
5 . The stainless steel of claim 1 , wherein the stainless steel further includes at least one selected from a group consisting of 0 to 0.6% of Cu (excluding 0%), 0 to 0.6% of V (excluding 0%), and 0.05 to 2.5% of Mo.
6 . A method of manufacturing stainless steel with improved contact resistance for a Polymer Electrolyte Membrane Fuel Cell (PEMFC) separator, the method comprising: hot-rolling and cold-rolling stainless steel comprising by weight percent, 0 to 0.02% of C (excluding 0%), 0 to 0.02% of N (excluding 0%), 0 to 0.25% of Si (excluding 0%), 0% to 0.2% of Mn (excluding 0%), 0 to 0.04% of P (excluding 0%), 0 to 0.02% of S (excluding 0%), 25 to 34% of Cr, 0 to 0.5% of Ti (excluding 0%), 0 to 0.5% of Nb (excluding 0%), 0 to 0.6% of Sn (excluding 0%), and the remainder comprising iron (Fe) and other unavoidable impurities, to manufacture a cold-rolled thin steel sheet; and soaking the cold-rolled thin steel sheet in an acid solution containing at least one of Cl or F.
7 . The method of claim 6 , wherein the acid solution includes hydrochloric acid or hydrofluoric acid.