Defect Growth Characterization in Modern Rail Steel

This report discusses a comprehensive fatigue and fracture characterization of modern head-hardened rails in reference to legacy rails. The focus is in on detail (i.e., transverse) fracture, the effects of the microstructural gradient in the railhead, and residual stresses caused by head-hardening and roller straightening. A key objective of this study is to develop the information necessary to determine if an existing rail inspection interval, established for legacy rails is valid for modern, head-hardened rails. Five rails (two head-hardened and one modern control rail and two legacy rails) were investigated. As expected, the head-hardened rails show significantly improved hardness and strength in the railhead, comparing to the legacy rails, which contributes to improved wear resistance. While in many cases, increasing material hardness and strength results in reduction of toughness and fatigue life, results of the current study indicate that this is not the case. Both toughness and fatigue crack growth rates are similar across all investigated rails, which indicates that the rail inspection interval, previously established for legacy rails may not require revisions for modern rails.