Precipitation strengthening in high manganese austenitic TWIP steels

At low strains (epsilon < 0.25), the precipitation of Ti, Nb, V carbides in austenitic Fe-Mn-C steels which exhibit twinning induced plasticity has no significant effect on work hardening. Strengthening follows the Orowan mechanism and can be described by a simple yield stress offset. However, at higher strains (epsilon > 0.3) the work hardening rate decreased slightly. Synchrotron X-ray diffraction analysis suggested that this was due to a reduction in the kinetics of twin formation. The highest strengthening coefficient in cold strips was obtained with Ti additions <= 0.1 wt.% (+1380 MPa/wt.% Ti) but the effect quickly saturated after an increase of similar to+150 MPa. With Nb additions only modest hardening (+187 MPa/wt.%) could be achieved. The strengthening due to V was >530 MPa/wt.% for V additions <= 0.4 wt.% Saturation effects are less critical with V additions and yield stress increases of +375 MPa were demonstrated.