Stainless steel for fuel cell separator

1 . A stainless steel for a fuel cell separator, wherein the stainless steel is a ferritic stainless steel comprising, in percent by weight (wt %), at most 0.02% of C, at most 0.02% of N, 15 to 35% of Cr, at most 0.03% of C+N, and the balance of Fe and other inevitable impurities, and

wherein an arithmetic mean summit curvature (Ssc) of a surface defined according to the ISO 25178 standard is at least 6.0 μm −1 , a root mean square surface slope (Sdq) is at least 23, and a contact resistance is at most 10 mΩ·cm 2 .

2 . The stainless steel according to claim 1 , wherein the ferritic stainless steel further comprises at least one of, in percent by weight (wt %), at most 0.4% of Si, at most 0.2% of Mn, at most 2% of Cu, and at most 1.0% of a sum of Ti, Nb, and V.

3 . The stainless steel according to claim 1 , wherein a thickness of a passivated layer is at most 3 nm.

4 . A stainless steel for a fuel cell separator, wherein the stainless steel is an austenitic stainless steel comprising, in percent by weight (wt %), at most 0.09% of C, 15 to 30% of Cr, 7 to 15% of Ni, and the balance of Fe and other inevitable impurities, and

wherein an arithmetic mean summit curvature (Ssc) of a surface defined according to the ISO 25178 standard is at least 6.0 μm −1 , a root mean square surface slope (Sdq) is at least 23, and a contact resistance is at most 10 mΩ·cm 2 .

5 . The stainless steel according to claim 4 , wherein the austenitic stainless steel further comprises at least one of, in percent by weight (wt %), at most 2.5% of Si, at most 3% of Mn, at most 3% of Mo, at most 0.3% of N, and at most 1.0% of a sum of Ti, Nb, and V.

6 . The stainless steel according to claim 4 , wherein a thickness of a passivated layer is at most 3 nm.