Competition mechanism between microstructure type and inclusion level in determining VHCF behavior of bainite/martensite dual phase steels

The very high cycle fatigue (VHCF) behaviors of bainite/martensite (B/M) dual phase high-strength low-alloy (HSLA) steels were investigated using ultrasonic fatigue technology. Both non-inclusion and inclusion induced crack initiations occurred in the designed steels under VHCF test. It is shown that the VHCF behaviors are determined by the competition between the inclusion level of steels and the microstructure type consisted of different kinds of phases, microstructure homogeneity and refinement degree. The physical and chemical metallurgy methods could be coordinated to achieve excellent VHCF properties of high strength steels through microstructure optimization and inclusion size reduction.