New constitutive analysis of microstructural evolution: hot compression of gamma iron

Abstract

Work hardening evolution during deformation is typically examined quasi-statically by quenching-in the deformed structure. However quenching of gamma-Fe results in a complex martensitic structure and hence the presumed typical deformation of a face-centred cubic metal can not be easily validated. A recent derivation of constitutive relation can replicate the dynamic stress-strain curve from which the microstructure parameters can be determined (Saimoto and Van Houtte, Acta Mater., 2010 in press). In this determination the mean slip distance is quantitatively derived from the measured curve and correlated to the resolved stress and strain at that point. The plot of shear stress versus inverse mean slip distance reveals that initially the mean slip distance decreases and then increases with strain. At some point a change of slope is observed and this point has been attributed to the matching of the increasing slip distance to that of the decreasing cell size. This analysis have been applied to two low carbon steels, one with 0.002 wt %C and the other with 0.052%C as reported by M. Huang et al. (Scripta Mater, 61, 2009). The results from the compression tests over three-decades of strain rates and temperatures ranging from 920 to 1050°C for these two cases will be compared and discussed.