On rolling contact fatigue of gear steels with differentinclusion content

This work analyses the evolution of rolling contact fatigue damage in ringspecimens made of quenched and tempered SAE 5135 steel for gears, obtained withthree different steel-production processes.The investigation was carried out through a test campaign on a bi-disk machine underpure rolling condition and water lubrication. Early formation of micro-pits, increasingin number with the test progression and joining forming larger pits was observed on therolling surface, while the final failure was always caused by macro-spallingphenomena. The analysis of the specimens section allowed observing the complexpattern of surface and subsurface cracks and the role of inclusions in favouring cracknucleation and propagation. An analysis of inclusion content by means of extreme valuestatistics was also carried out referring to the three different steel-production processesand a relationship between RCF life and maximum expected inclusion size washighlighted.