The migration of spheroidal cementite towards the surface in nanostructured AISI 52100 steel

• The migration of cementite particles towards the surface was discovered.
• Nanostructured surface was produced by UNSM technique.
• High hardness was obtained by UNSM treatment.

The migration of spheroidal cementite (Fe3C) particles towards the surface by ultrasonic nanocrystalline surface modification (UNSM) technique in AISI 52100 bearing steel was discovered. The migration of Fe3C particles towards the surface, and their density and grain size at the top surface were assessed using an electron backscattered diffraction (EBSD) and a transmission electron microscopy (TEM), respectively. A mechanically continuous cyclic loading of UNSM treatment process refined the Fe3C particles into nano-sized particles along with ferrite (Fe3O4) nano-grains resulted in the migration of Fe3C particles towards the surface. The gradient nano-grained specimen with an increased Fe3C density exhibited a nearly 3 times higher hardness comparable to that of the coarse-grain one.