The effect of carbon content on fatigue strength of dual-phase steels

Steels which contain 0.085 C, 0.36 C, and 0.38 C were intercritically annealed at 745, 760, 775, and 790 °C for 30 min followed by water quenching to obtain dual-phase (martensite-plus-ferrite) structure. It was found that the volume fraction of martensite increased with increasing annealing temperature. Rotating bending tests (10 million cycles) were conducted on the as-received materials and the dual-phase steels specimens selecting completely reversed cycle of stress. It was seen that the fatigue strength of dual-phase steels increased when compared with as-received materials. The highest fatigue strength was observed in the intercritically annealed steels at 760 °C. The fatigue strength of these steels increased at the annealing temperature up to 760 °C and decreased at the annealing temperatures higher than 760 °C.