METHOD FOR HARDENING STEEL ARTICLE SURFACES Russian patent published in 1998 - IPC

FIELD: metallurgy, in particular, hardening the surfaces of machine parts, cutting and stamping tools. SUBSTANCE: after heat treatment, articles are loaded into furnace preliminarily heated up to 500-520 C. Articles are heated in furnace air atmosphere up to 500-520 C. Articles are heated in furnace air atmosphere up to 400 C for 5-10 min to produce oxide surface layer. Then, ammonia is supplied in process of heating in ammonia medium for cleaning article surface with hydrogen in ammonia dissociation in heating process in ammonia medium up to 520 C. So, clean metal surface is obtained and thin oxide layer of iron oxides is removed with hydrogen in ammonia dissociation. Carbonitriding is carried out at temperature from 520 to 580 C and decomposition of carbide or simultaneously with supply of ammonia with its dissociation degree of less than 20%. Then articles are cooled together with furnace. EFFECT: intensified process of hardening and increased wear resistance of steel articles. 1 tbl