In situ monitoring of isothermal phase transformation in two Nb stabilized austenitic stainless steels (316Nb) by neutron diffraction

In this study, neutron diffraction measurements have been performed to study the phase transformations taking place during isothermal treatments of two 316Nb type austenitic stainless steels with different δ ferrite content. Kinetics of phase transformations during heating, isothermal hold at 900 °C and cooling have been monitored and the phase fractions quantified using Rietveld refinements. Two main transformation mechanisms are evidenced and quantified: the δ ferrite transformation into σ phase and austenite and the σ phase precipitation inside the austenitic matrix.