Mechanical behavior and martensitic transformation of an Fe-Mn-Si-Al-Nb alloy

The microstructure features of an austenitic Fe-23Mn-2Si-2Al (mass%) alloy with addition of niobium (0.017 mass%) were investigated as a function of deformation temperature (20 to -75 degrees C). The observation of optical microscopy and transmission electron microscopy (TEM) indicated that a large number of twins induced by deformation above -60 degrees C result in relatively high total elongations of about 80% and the increase of the ultimate tensile strength from 660 to 750 MPa, which is called twinning-induced plasticity (TWIP). At temperatures below -60 degrees C, the stability of the austenite decreases and multiple martensitic transformations among gamma(fcc)(austenite), epsilon(hep)(hcp-martensite) and alpha(bcc)(bcc-martensite) occur after TWIP effect, which were determined by both TEM and X-ray diffraction. With transformation-induced plasticity, total elongations reached 87% and ultimate tensile strength reached 8 10 MPa. The effect of Nb on TWIP/TRIP in the steel is discussed. (c) 2006 Elsevier B.V. All rights reserved.