This invention relates to a steel composition comprising, expressed in percentages by weight: 0.25-0.35% C, 24-28% Cr, 10-15% Ni, 3-6% Mn, 1.75-2.50% Nb, 0.50-0.70% N, 0-0.30% Si, provided that C+N.gtoreq.0.8%, the rest consisting mainly of iron and unavoidable impurities. The invention further relates to a method for making said compositions and valves produced from said compositions or using said method and exhibiting excellent mechanical strength and oxidation resistance at temperatures between 800 and 900.degree. C.