NOVELTY - A stainless steel has a surface portion containing (in mass%) carbon (0.03 or less), silicon (0.01-1.5), manganese (0.01-2.5), phosphorus (0.035 or less), sulfur (0.01 or less), chromium (16.0-30.0), nickel (12.0-50.0), boron (0.4-3.5), aluminum (0.001-0.2), nitrogen (0.01-0.1), molybdenum (7.0 or less), copper (5.0 or less) and iron, and a thickness-direction center portion containing same components with different composition for nickel, boron and nitrogen. The steel has 0.2% yield strength (YS) of 300 N/mm2 or more and elongation (EI) of 40% or more.    USE - Stainless steel is used for separator of fuel cells (claimed) e.g. polymer electrolyte fuel cell used as power supply for small-scale office, motor vehicle and non-portable domestic appliances.    ADVANTAGE - The stainless steel has low contact electrical resistance, excellent moldability, corrosion resistance and high strength. Highly efficient and lightweight separator having low contact electrical resistance, reduced energy loss and high strength is provided economically using the separator.    DETAILED DESCRIPTION - A stainless steel has a surface portion containing (in mass%) carbon (0.03 or less), silicon (0.01-1.5), manganese (0.01-2.5), phosphorus (0.035 or less), sulfur (0.01 or less), chromium (16.0-30.0), nickel (12.0-50.0), boron (0.4-3.5), aluminum (0.001-0.2), nitrogen (0.01-0.1), molybdenum (7.0 or less), copper (5.0 or less), and remainder of iron and impurities, and a thickness-direction center portion containing carbon (0.03 or less), silicon (0.01-1.5), manganese (0.01-2.5), phosphorus (0.035 or less), sulfur (0.01 or less), chromium (16.0-30.0), nickel (6.0-30.0), boron (0.01 or less), aluminum (0.001-0.2), nitrogen (0.06-0.3), molybdenum (7.0 or less), copper (5.0 or less), and remainder of iron and impurities. The content of chromium (Cr), molybdenum (Mo) and boron (B) in the surface portion of stainless steel satisfies a formula: Cr+3Mo-2.5B greater than or equal to 17. The steel has 0.2% yield strength (YS) of 300 N/mm2 or more and elongation (EI) of 40% or more. Boride is dispersed in the surface portion of steel. An INDEPENDENT CLAIM is included for manufacture of stainless steel.    DESCRIPTION OF DRAWING(S) - The drawings show the schematic view of polymer electrolyte fuel cell.    Polymer electrolyte membrane (2)    Anode (3)    Cathode (4)    Separators (5a,5b)    Flow paths (6a,6b)