Colin Scott

Precipitation strengthening in high manganese austenitic TWIP steels

Abstract At low strains (∊ 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.% (+1 380 MPa/wt.% Ti) but the effect quickly saturated after an increase of ∼+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.

The influence of plastic instabilities on the mechanical properties of a high-manganese austenitic FeMnC steel

Abstract The serrations observed on the stress–strain curves of a Fe-22Mn-0.6C wt.% steel present all the phenomenological features associated with dynamic strain ageing, including negative strain rate sensitivity and thermal activation. We show that the activation energy is, however, inexplicably low and that the dynamic strain ageing contribution to work-hardening is limited, i. e. mechanical twinning is the dominant strain hardening mechanism. Finally, novel in-situ experiments are used to study the dynamic behaviour of intense strain localisation bands which form on tensile samples. In spite of the localisation behaviour seen in tensile tests, stamped parts do not present any surface defects.