Influence of cold rolling deformation mechanisms on the grain refinement of Fe-15Mn-10Cr-8Ni-4Si austenitic alloy

The efficiency of rolling deformation mechanisms on grain refinement during recrystallization annealing was studied in Fe-15Mn-10Cr-8Ni-4Si austenitic alloy samples rolled to different strains at 0, 25, 100 and 200 degrees C. Two deformation routes were examined: rolling to a fixed strain (r) of 48% and rolling to strains of 55, 67, 88 and 93%, which were identified as the maximum allowable strains achieved in the alloy at 0, 25, 100 and 200 degrees C, respectively. The increase in rolling temperature changed the major deformation mechanism from deformationinduced epsilon-martensitic transformation (epsilon-MT) at 0 < T <= 25 degrees C, which provided the formation of multi-phase austenite/epsilon-martensite microstructure, to mechanical twinning of austenite at 100 < T < 200 degrees C; both of these deformation mechanisms were accompanied by dislocation slip. Moderate rolling strains of 48-67% were sufficient to produce multi-phase microstructures with a sufficiently high driving force for the formation of truly recrystallized grains (approximately 2 mu m in size) during annealing at 700 degrees C for 30 min. The change in the deformation mechanism from deformation-induced epsilon-MT to mechanical twinning reduced the recrystallization driving force due to a decrease in stored dislocation density and an increase in microstructure homogeneity. In a single-phase microstructure, rolling strains above 88% were required to provide a sufficiently large driving force for the formation of fully recrystallized fine-grained microstructures during annealing.