Fatigue damage evolution and lifetime prediction of ferrite-cementite steel with combined plasticity

Abstract

Rolling contact fatigue of rail steel caused by repeated contact stresses with the wheel needs to be clarified to ensure the safety of wheel-rail operation. The fatigue damage of rail steel studied from an experimental perspective provides a good phenomenon of its surface spalling in rail transportation, whereas the damage activity below the contact surface that triggers this failure phenomenon is difficult to observe. In this work, a combined plasticity model for ferrite with crystal plasticity and cementite with isotropic plasticity is proposed, which has been used to study the fatigue damage behavior of pearlitic rail steel. The results indicate that the subsurface crack propagation approximately parallel to the contact surface is the final link in the formation of the surface micropit. The downward expanding crack from the surface will meet up with the deeper internal cracks to produce macropit. As the sphericity of the grains increases from 0.145 to 0.2, the surface crack in the ferrite-cementite steel with the grain size of 50 μm extends all the way to the bottom of the upcoming macropit and lacks the micropit formation stage. In addition, the surface spalling associated with micropit connections can be delayed by increasing the cementite fraction. The presence of macropits destroys the surface integrity of rail steel, so it needs to be detected and addressed in a timely manner.