σ phase dissolution in duplex stainless steel at elevated temperature studied by thermal analysis

The redissolution of σ phase to ferrite in duplex stainless steel (DSS) in high temperature range was studied by differential thermal analysis (DTA) and scanning electron microscopy. DSS samples were aged at different temperatures for various durations. The conditions were chosen such that all the ferrite transformed to σ phase. Subsequent DTA measurements revealed that the onset temperature Ts and the peak temperature Tp for sigma dissolution strongly depend on the initial distribution and the morphology of σ phase. This correlation between the DTA characteristic temperatures and prior ageing temperatures may be used for temperature indication purposes in applications involving hostile environments.