High cycle fatigue behavior and microstructure of a high-speed rail material

We describe here the high cycle fatigue (HCF) behavior of a rail steel comprised of multiphase structure of bainite, martensite and film-like retained austenite, which was processed by the quenching and tempering (Q&T) heat treatment process. Conventional mechanical properties of experimental materials were determined, and the high cycle fatigue S-N curve of rail steel was obtained through ultrasonic fatigue test. The fatigue fracture details under cyclic stress were observed and analyzed in detail by scanning electron microscope (SEM). It was observed that the bainite/martensite (B/M) composite structure exhibited good performance, and its fatigue limit was as high as -790 MPa, meanwhile the ratio of the fatigue limit to the tensile strength of rail steel was up to -0.53. Finally, a comparison of the mechanical properties with other high-strength steels was made, which suggested that the rail steel with multiphase structure has both good strength and high fatigue limit. Thus, multiphase structure of steel has broad prospects in engineering applications.