Microstructural manifestation and kinetics of dynamic transformation in a W-modified 9%Cr steel

Abstract

Dynamic transformation (DT) of austenite to ferrite is shown to occur in a W-containing 9%Cr steel during hot deformation across a wide range of strain rates. A new facet of DT, namely its dependency on process kinetics, is revealed by examining work-hardening rate and strain rate. The kinetics of DT is associated with competing processes of dislocation immobilisation and remobilisation, both of which have a complex dependence on strain rate. The microstructural manifestation of DT-ferrite is examined and contrasted with that of conventional ferrite on the basis on morphology. This contrast arises from different modes of transformation and resultant differences in crystallography. DT is placed in the practical context of thermo-mechanical processing by addressing issues of process control and stability.