NOVELTY - A stainless steel contains (in %mass) carbon (0.01 or less), silicon (1 or less), manganese (1 or less), sulfur (0.01 or less), phosphorus (0.05 or less), aluminum (0.2 or less), nitrogen (0.02 or less), chromium (20-40), molybdenum (4 or less), niobium, titanium and zirconium, and remainder of iron and unavoidable impurities. Precipitate having equivalent diameter of 0.1 mu m or more exists per 100 mu m2 of steel surface. The total content of niobium, titanium and zirconium is 0.05-0.6 %mass. The thickness of stainless steel is 200 mu m or less.    USE - Stainless steel is used for separator of fuel cell for power supply of motor vehicles, domestic appliances, portable and compact power systems, and stationary-type compact electric generators. Uses include but are not limited to molten carbonate fuel cell, phosphoric acid fuel cell, solid-oxide fuel cell, alkaline fuel cell, polymer electrolyte fuel cell and proton-exchange membrane fuel cell.    ADVANTAGE - The stainless steel has excellent electroconductivity and ductility.    DETAILED DESCRIPTION - A stainless steel contains (in %mass) carbon (0.01 or less), silicon (1 or less), manganese (1 or less), sulfur (0.01 or less), phosphorus (0.05 or less), aluminum (0.2 or less), nitrogen (0.02 or less), chromium (20-40), molybdenum (4 or less), niobium, titanium and zirconium, and remainder of iron and unavoidable impurities. Precipitate having equivalent diameter of 0.1 mu m or more exists per 100 mu m2 of steel surface. The total content of niobium, titanium and zirconium is 0.05-0.6 %mass. The ratio of maximum diameter (D) of precipitate to thickness (t) of stainless steel satisfies the formula: 20 less than or equal to t/D. The thickness of stainless steel is 200 mu m or less. An INDEPENDENT CLAIM is included for manufacture of stainless steel.    DESCRIPTION OF DRAWING(S) - The drawing shows the schematic structure of fuel cell.    Membrane electrode assembly (1)    Gas-diffusion layers (2,3)    Separators (4,5)    Air-flow path (6)    Hydrogen-flow path (7)