Relationship between repeatedly quenching and fisheye cracks around TiN and Al2O3 inclusions in high carbon bearing steel

Martensitic high carbon high strength SAE 52100 bearing steel is one of the main alloys used for rolling contact applications where high wear resistance is required. Refining the prior austenite grain size through repeated heating is a process commonly used to enhance the material's strength. In this work, the microstructure of repeatedly quenched Ti, N rich ultraclean SAE 52100 steel was investigated. The crack origin on the fracture surface was investigated. It was found repeated furnace quenching effectively refined the martensitic structure and increased the retained austenite content. Furthermore, most of the cracks originated from Al2O3 inclusions in the material quenched once, and most of the cracks grew from TiN inclusions in the specimens quenched thrice.