the effect of carbon content of the mechanical properties - McMaster ...

ABSTRACT
The development of new materials with a combination of high strength and
ductility is required for the automotive industry, due to the demand for increased fuel
efficiency while maintaining vehicle safety and performance. High-Mn steels combine
exceptional strength and ductility to achieve the sustained rates of high work hardening
required to achieve these objectives. Fe-22Mn-C alloys containing strain-induced
deformation products (twins and ε-martensite) contribute to the high work hardening
rates, by acting as boundaries for dislocation motion. Three Fe-22Mn-C alloys are
investigated with varying carbon contents of 0.6, 0.4 and 0.2 wt% and stacking fault
energies (SFEs) of 37.2, 33.4 and 29.6 mJ/m 2 , respectively. Their microstructural
evolution and mechanical properties are evaluated.
The Fe-22Mn-0.6C alloy comprised of a single phase austenitic microstructure,
produced twins during deformation and had the highest sustained work hardening rate of
the three alloys. The kinematic hardening contribution was due to the production of twins
during deformation, adding to the overall flow stress. The flow stress was successfully
modeled with contributions from the yield strength, isotropic hardening and kinematic
hardening. The main damage mechanism was the separation of grain boundaries and the
production of twins during deformation classified the 0.6C alloy as a TWIP steel.
The Fe-22Mn-0.4C alloy displayed an austenitic matrix in the as-annealed
microstructure with twins and ε-martensite produced during deformation. The work
hardening rate was sustained from the continuous production of deformation products.
iii