Abstract: The steel member for use under hot or warm conditions has a surface layer including (a) an oxygen-containing mixture layer comprising iron sulfide particles and iron nitride particles and substantially satisfying 0.5.ltoreq.S/N.ltoreq.10; (b) an intermediate layer of iron sulfide, iron nitride and iron oxide; (c) and a nitride layer comprising a nitrogen-diffused layer on this order from the member surface. The member is produced by supplying a colorless ammonium sulfide solution and a yellow ammonium sulfide solution at a weight ratio of 6/1-1/1 to a gas generator to form a solution mixture from which a head gas is generated; disposing a steel member in a reactor; introducing the head gas and nitrogen into the reactor at 100-600 ppm of H.sub.2 S and 0.1-1.0% of NH.sub.3 ; supplying nitrogen and NH.sub.3 to the reactor to adjust the concentration of NH.sub.3 to 10-70% in the reactor; heating the reactor to 460-600.degree. C.

Abstract: Solid-solution strengthened austenitic alloys consisting of, in weight percent, no more than 0.1 % carbon, from 4 (%C) to 1 % titanium and/or niobium (alone or in combination), no more than 75 % cobalt, no more than 26 % chromium, from 8 % to 40 % tungsten, wherein the amount of 1/5 (%Co) + (%Cr) + (%W) is in the range from 38 % to 46 %, with or without at least one element from the group consisting of no more than 0.1 % boron, no more than 0.5 % zirconium, no more than 0.5 % yttrium and no more than 1 % hafnium, and the balance essentially nickel except for impurities.These alloys possess excellent high-temperature strength as well as good workability.