SHAPE-MEMORY EFFECT AND RELATED PHENOMENA IN A MICROALLOYED FE-MN-SI ALLOY

An Fe-32Mn-6Si-0.05Nb-0.04C alloy aged at different temperatures was e mployed to study the epsilon (hcp) martensite transformation, the mech anism of the shape memory effect (SME) associated with the epsilon mar tensite transformation, the effect of precipitation strengthening, and the effect of thermomechanical treatment and deformation temperature on the SME. The results of transformation temperature studies show tha t the M(s) temperature for various heat-treated specimens is in the ra nge of 75-100-degrees-C, the A(s) temperature is 112-125-degrees-C, an d the Neel temperature of this material, T(N), is 8-degrees-C. The SME decreases with increasing plastic deformation and increases with decr easing deformation temperature and increasing thermomechanical trainin g. The critical strength of aged specimens is higher than that of quen ched ones due to the precipitation strengthening of NbC, which improve s the SME for plastic deformation amounts less than 2% at room tempera ture. The microstructure observation by transmission electron microsco py shows that stacking faults play an important role in the formation of the epsilon martensite. Surface relief examination at different tem peratures and the electrical resistance versus temperature relationshi p reveal that the epsilon martensite transformation takes place contin uously at temperatures below the T(N) temperature. An SME mechanism fo r Fe-Mn-Si based alloys is proposed.