Effect of initial grain size on evolved ferrite grain size during high Z large strain deformation

AbstractThe effect of initial grain size on the evolved ferrite grain size during high Z large strain deformation was studied in ultralow carbon steel with two widely varying initial microstructures: a coarse grained (200 μm) and an ultrafine grained (0·7 μm) microstructures. Plane strain compression was used for imposing large strain in the test specimen and a thermomechanical simulator was used for varying the strain rate and temperature precisely. Electron backscattered diffraction was used for the analysis of deformed microstructure and for grain size measurements. Deformation conditions were varied to cover wide range of Zener–Hollomon parameters. It was noted that the evolved ferrite grain size solely depends on the Zener–Hollomon parameter and does not depend on the initial grain size. The relation d=10Z–0·12 (Q gb=155 kJ mol–1) was obtained for two initial microstructures with grain sizes varying by three orders of magnitude.