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

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.

Automated summary

Dynamic transformation of austenite to ferrite was observed in a W-containing 9%Cr steel during hot deformation, and it was found to be dependent on the process kinetics, specifically the work-hardening rate and strain rate. The kinetics of the transformation is influenced by competing processes of dislocation immobilisation and remobilisation, which have complex dependencies on the strain rate. The microstructural manifestation of the dynamic transformation differs from that of conventional ferrite due to differences in transformation modes and crystallography. The practical implications of this transformation in thermo-mechanical processing are discussed, including process control and stability.