FERRITIC-AUSTENITIC STAINLESS STEEL AND A HEAT TREATMENT PROCESS FOR PRECIPITATION HARDENING OF THE STEEL

摘要

Stainless ferritic-austenitic steel with very high strength, good ductility and impact strength as well as good resistance to general and intercrystalline corrosion. The steel has the following composition expressed as weight percent: C max 0.04; Si 1.5-2.5; Mn max 2.0; Cr 18.0-22.0; Ni 4.0-8.0; Mo 1.5-3.0; Nb max 1.0; Ti max 0.5; balance iron and impurities and accessory components normal for this type of steel and wherein (atom % Nb + atom % Ti) >/= atom % C, preferably >/= (atom % C + atom % N). The steel is precipitation hardened through solution heat treatment at 1000-1200 DEG C and ageing at 500-700 DEG C, preferably subsequent to pre-ageing at 400-500 DEG C prior to final ageing at 500-700 DEG C.