Alloying and aging effects on the fatigue crack growth of duplex stainless steels

The effect of the addition of W instead of Mo on fatigue crack growth (FCG) behavior has been studied for duplex (ferritic–austenitic) stainless steels. The microstructure and the FCG properties of the homogenized alloys are basically insensitive to the variation of W content. For the alloys aged at 900°C for 30 min after homogenization, however, the apparent FCG resistance is significantly increased and is attributed principally to the roughness-induced crack closure due to the existence of brittle secondary phases precipitated during aging. With an increase in W content, the quantity and size of the brittle σ and χ precipitates decrease and the ductility of the aged alloys increases. In accordance, the intrinsic FCG resistance of the aged alloys is improved with increasing W content.