“…Transmission electron microscopic (TEM) analyses have enabled researchers to attribute lath/subgrain coarsening in the martensitic/ferritic microstructure as the primary reason for cyclic softening in this class of steels (Chilukuru et al, 2009;Dubey et al, 2005;Fournier et al, 2006). The degree of microstructural coarsening has been shown to correlate with the applied inelastic strain per cycle (Fournier et al, 2009a) and is enabled by annihilation of dislocations introduced during martensitic transformation (Armas et al, 2004), coarsening of precipitates (Jones, 1983;Kim and Weertman, 1988) and changes in effective applied stress due to surface oxide film formation (Ebi and McEvily, 1984). Analysis of the stress-strain hysteresis loops has revealed that this cyclic softening effect is primarily due to a gradual decrease in the long-range internal stresses or backstresses (Fournier et al, 2006).…”