Fatigue properties of ultra-fine grained dual phase ferrite/martensite low carbon steel

An examination has been made of the fatigue properties of ultra-fine grained two phase ferrite/martensite low carbon steel, produced by equal channel angular pressing (ECAP). The fatigue strength and fracture mechanism of the ECAP steel were compared with those of the as-received sample. The fatigue strength of the ECAP steel was twice as high as that of the as-received steel. The fatigue strength was linearly related to the tensile strength for both the ECAP and as-received steels although their slopes were different; the slope for the ECAP steel was greater. In addition, different fracture characteristics were observed; intergranular fractures were dominant in the ECAP steel whereas transgranular fractures occurred in the as-received steel. Such differences in fatigue strength and fracture characteristic are attributed to their material properties.