Precipitation of σ-phase and creep-fatigue behavior of 308L steel weldment

The creep-fatigue properties of a 308L steel weldment after different post-weld heat treatments (PWHT) are investigated. The microstructure and phase transformation of the as-welded and PWHT weldments are examined using scanning and transmission electron microscopy. Special attention is paid to the decomposition of δ-ferrite and the precipitation of σ-phase. Energy dispersive spectroscopy is also used for detecting the elements distribution. The results show that PWHT promotes the creep-fatigue resistance of the weldment. δ-Ferrite mainly transforms into secondary austenite and σ-phase. The decomposition ratio of δ-ferrite shows a tendency to decrease after high temperature PWHT. This can be attributed to the reduction of silicon segregation near the δ/γ interface.