Correlation between evolution of surface roughness parameters and micropitting of carburized steel under boundary lubrication condition

This paper investigates the evolution of amplitude and spatial roughness parameters during rolling contact fatigue experiments on carburized samples with around 0%, 15% and 70% retained austenite (RA) under boundary lubrication condition. The 0% RA samples failed due to early crack initiation and rapid crack propagation. The 15% and 70% RA samples showed initiation and propagation of micropitting. Four amplitude surface parameters (R-a, R-RMS, R-sk, and R-ku) and one spatial parameter (2D auto-correlation length) were analyzed for correlations between micropitting initiation and propagation during RCF cycles. It was observed that during run-in, a significant decrease in Ra and Rams were observed, while the correlation length increased and stabilized for all samples. The evolution of the 2D autocorrelation length correlated well with the evolution of crack propagation. It was observed that, while R-a and R-RMS values follow the same trend as propagation of micropitting, skewness and kurtosis can be used to better predict initiation and propagation of micropitting on the surface. Significant propagation of micropitting was accompanied by a decreasing trend of skewness and increasing trend of kurtosis. Transverse directional correlation length also showed good correlation with propagation of micropitting, with the correlation length decreasing during increase of micropitting on sample surfaces.