Steel member for use under hot or warm conditions and method for producing same

摘要

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≦S/N≦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° C. to carry out a gas sulfonitriding treatment on the member; and slowly cooling the sulfonitrided member at 30-25° C. /hr.