Development of ultrafine bainite + martensite duplex microstructure in SAE 52100 bearing steel by prior cold deformation

We explore microstructural refinement through complete/partial recrystallization of prior cold-deformed ferrite during austenitizing or austempering of SAE 52100 steel to obtain ultrafine bainite and martensite. Optical and scanning/transmission electron microscopy coupled with compositional microanalysis were employed to determine the volume fraction and dimension (thickness/length) of ferritic sheaves and carbides. Characterization of mechanical properties indicates that 5–15% cold deformation significantly enhances the impact strength (∼72 J) with marginal improvement in hardness and tensile strength over that in the undeformed condition.