EBSD based studies on various modes of cyclic deformation at 923 K in a type 316LN stainless steel

The study presents an EBSD based investigation on the nature of deformation occurring under different modes of cyclic loading viz. low cycle fatigue (LCF), creep-fatigue interaction (CF) and LCF-creep-HCF. Compared to LCF, cyclic life was found to decrease for CF or LCF-creep-HCF loading conditions. This was attributed to the additional damage contributions from creep in CF cycling and a combination of creep and HCF in LCF-creep-HCF loading conditions, as substantiated through a highly intergranular fracture observed in those cases. Local misorientation map derived from EBSD showed that the misorientation spread is highest for the LCF condition compared to CF and LCF-creep-HCF. This was attributed to the enhanced thermal recovery taking place during CF and LCF-creep-HCF conditions in comparison to LCF. The dislocations generated during cycling rearrange themselves into a stabilized substructure in the form of cells in the above loading conditions leading to a lower value of local misorientation in those cases. This was also accompanied by a significant decrease in number of twins in CF and LCF-creep-HCF conditions compared to LCF. The dislocation-twin interaction responsible for the process of de-twinning was found to be expedited in the former cases owing to a higher thermal recovery.