Corrosion fatigue resistance of powder metallurgy and forged duplex stainless steels

Abstract

The high cycle corrosion fatigue resistance of powder metallurgically (PM) fabricated and hot isostatically pressed (hipped) duplex stainless steels (DSSs) was investigated and compared with that of a conventional forged DSS. Tests were performed in rotating bending fatigue in a chloride and sulphate containing aqueous solution at room temperature. The hipped PM DSSs studied had small grain size and homogeneous microstructure and isotropic properties and thus, their high cycle corrosion fatigue resistance was generally markedly higher than that of the corresponding forged DSS tested in the longitudinal direction. Fatigue cracks were observed to grow preferentially in the ferrite phase and a retarding effect of the austenite phase on corrosion fatigue crack growth was observed both in the hipped PM and wrought DSSs. Slow cooling after solution annealing improved the corrosion fatigue resistance, even though it induced slight second phase precipitation. Localised corrosion attack was observed at inclusion/matrix interfaces, when oxide inclusions were cerium modified (forged DSS). When oxide inclusions were either unmodified or calcium modified (hipped PM DSSs), no localised corrosion attack was observed.MST/3429