Aging behavior of a low-carbon ferrite-martensite dual-phase steel

The aging reaction of ferrite and changes in tensile property due to aging were investigated in a 0.08C-1.45 Mn-0.21 Si steel after intercritical quenching from 760 C. The aging temperature ranged from room temperature to 170 C. Aging leads to precipitation of fine carbides in ferrite. The distribution of the fine precipitates is not homogeneous. The density of precipitates is reduced in the ferrite adjacent to the martensite. The transition from continuous to discontinuous yielding occures gradually with aging time at higher temperature. No discontinuous yielding appears in specimens aged at room temperature after 10 months. The strain hardening rate at small strains is reduced with aging time in specimens aged at temperatures higher than 70 C, resulting in an increase in ductility. Due to the effect of aging, the yield strength is increased. The ultimate tensile strength is increased at first, and then reduced.