Carbon migration in a bearing steel with spheroidal cementite subjected to ultrasonic nanocrystalline surface modification

This paper deals with bearing steel with spheroidal cementite dispersed in a ferrite matrix subjected to ultrasonic nanocrystalline surface modification (UNSM) treatment. Carbon migration microstructure development, including grain size refinement and dissolution of cementite, was studied utilizing electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM). Accumulated multiple gliding progressively refines cementite into nano-sized cementite particles mixed within ferrite nano-grains in the top surface layer. A decreasing volume fraction of cementite is observed with increasing depth in the top deformed layer, indicative of dissolution of cementite induced by plastic deformation.