Critical isothermal temperature and optimum mechanical behaviour of high Si-containing bainitic steels

The redistribution of carbon during partitioning between retained austenite and bainitic ferrite decides the stability of the retained austenite. The martensitic start temperature (MS) based on the carbon enriched retained austenite is observed to be the deciding factor for the volume fraction of the constituent phases obtained on isothermal bainitic transformation. The volume fraction of the phases is also calculated on the basis of metastable equi-free energy (T0) curve. A good agreement is found between experimentally and theoretically calculated fractions of the phases. The isothermal holding temperature and time, the fraction of phases based on initial carbon content of the steel and MS temperatures have a close relation with the optimum mechanical properties of bainitic steels.