A sigma particles dissolution model with application to duplex and superduplex stainless steels forged components

Sigma phase in well known as a detrimental precipitate which reduces the mechanical and chemical properties of forged components with particular reference to toughness and corrosion resistance. For this reason, temperatures and times of a sigma phase dissolution heat treatment have to be accurately chosen. The optimum choice has to lead to a complete dissolution of the precipitates in the shortest time without compromising the microstructure of the component. In order to reach this goal, both an accurate prediction of the thermal history in all the points of the component (by numerical simulation) and an accurate knowledge of sigma particles dissolution kinetics are needed. In this paper, the dissolution mechanism of sigma particles is studied with particular reference to duplex and superduplex stainless steels forged components. It was found that sigma phase dissolution kinetics is mainly influenced by Cr and Mo grain boundary diffusion.