Instability of the Delta-ferrite/austenite Interface in Low Carbon Steels: The Influence of Delta-ferrite Recovery Sub-structures

Abstract

An in-situ study of the delta-ferrite/austenite phase transformation in low carbon steels utilising laser scanning confocal microscopy has found that the presence of a recovery sub-structure in the delta-ferrite phase plays an active role in the apparent instability of delta-ferrite/austenite interfaces. Phase field modelling conducted in an attempt to quantify the influence of sub-boundaries on the transformation rate of delta-ferrite to austenite in Fe-C and Fe-C-Mn alloys, confirmed the in-situ observations that austenite grows preferentially along delta-ferrite sub-boundaries. The modelling studies also predicted that the transformation kinetics of the delta-ferrite to austenite would be enhanced if a sub-boundary network were present in the delta-ferrite grains.