Effect of pre-deformation of austenite on shape memory properties in Fe-Mn-Si-based alloys containing Nb and C

The shape memory properties of Fe-Mn-Si-based alloys containing Nb and C are further improved by pre-rolling of the solution-treated austenite and the subsequent ageing treatment. For an Fe-28Mn-6Si-5Cr-0.53Nb-0.06C (mass%) alloy, 9017, of an initial 4% strain is recovered on heating without any previous training treatment, if the alloy in austenitic state is rolled by 6-14% at 870 K and aged at 1070 K for 10 min to produce NbC precipitates. In the same condition, the alloy develops shape recovery stresses of 255 MPa and 295 MPa for 6% and 14% pre-rolling, respectively, when initially deformed by 4.5%. TEM observations indicate that these improved shape memory characteristics are related to a fine distribution of NbC precipitates in the fcc matrix and their interaction with stacking faults.