Microstructure and rolling contact fatigue behavior of martensitic nodular cast irons with different graphite sizes and densities

Martensitic nodular cast irons (MNCIs) with different graphite sizes and number densities are produced through continuous casting and cyclic heat treatments to refine their microstructures and to obtain a hardness of 60 HRC, and their rolling contact fatigue (RCF) properties, fractography, and subsurface microstructures have been investigated in the present study. RCF tests show that the RCF life is mainly determined by the applied Hertzian stress. Based on the calculation of characteristic parameter size and the analysis of stress concentration factor, it is found that the lower nodularity rate of graphite brings about the larger stress concentration at matrix‐graphite interfaces. This stress concentration induces a debonding of the matrix and graphite, cracks, deformation, and carbon redistribution in a local volume, which results in the formation of a white etching area. The present study indicates that MNCIs are a potential material for lubricant‐free bearings after chemical homogenization, microstructure refinement, and hardness enhancement. Highlights The experimental material is nodular cast iron with a martensitic matrix. The influence of graphite on fatigue life is analogous to that of inclusions. The lower nodularity rate of graphite, the larger stress concentration factor. The martensitic nodular cast irons are a potential material for bearings.