Strain induced transformation in C–Mn steel during single pass rolling

Abstract

Transformation from austenite to ferrite in a low carbon, low manganese steel was induced to occur during deformation in the roll gap of a laboratory rolling mill. The amount of strain preceding the start of transformation ɛ_pre and that following the start of transformation ɛ_post were varied systematically. Both pre- and post-transformation strains increased the amount of ferrite present on exit from the roll gap, and progressively refined the final ferrite grain size on completion of transformation during subsequent cooling. Transformation started at ɛ_pre with a rapid initial ‘burst’ of ferrite formation, the magnitude of the burst increasing linearly with ɛ_pre. Transformation continued during ɛ_post, the amount of ferrite formed being proportional to ɛ_post. Post-transformation strain refined the final ferrite grain size more effectively than pretransformation strain. Comparison with previous work indicated that strain in the austenite refined the ferrite grain size more effectively when transformation occurred simultaneously with deformation than when deformation ceased before transformation started. It is suggested that heterogeneity of deformation within austenite grains led to initial ferrite formation at grain boundaries and subsequent formation within grains. Finally, the results suggest that there is a limit to the ferrite grain refinement that can be achieved by straining austenite.

MST/1683