Room temperature low cycle fatigue behaviour of two high strength lamellar duplex ferrite-martensite (DFM) steels

Room temperarure low cycle fatigue (LCF) behaviour of two high strength Duplex ferrite-martnsite (DFM) steels with lamellar morphology developed from a commercial V-bearing low carbon microalloyed steel has been studied. Cyclic hardening and better LCF performance were observed in case of the steel containing ∼45% martensite as compared to the steel with 60% martensite exhibiting cyclic softening behaviour. Cyclic hardening/softening behaviour of the steels has been qualitatively explained in terms of dislocation phenomena involved in the cyclic plastic deformation process. Both the steels followed Coffin-Manson (C-M) and Basquin behavior. The reason for poor fatigue performance with higher amount of martensite has been attributed to the plastic strain magnification at ferrite-martensite interfaces.