2020 年 106 巻 12 号 p. 953-960
The deformation-induced martensitic transformation is a very effective phenomenon that improves mechanical properties of steels, and well known to be beneficial also in rolling contact fatigue (RCF) of bearings. In the present study, the characteristics of the deformation-induced martensitic transformation in the case of RCF of carburized, quenched and tempered SAE4320 steel were investigated in detail using a scanning electron microscopy – electron backscattering diffraction and an automated crystal orientation mapping - transmission electron microscopy. These analyses clarified that the extremely fine deformation-induced martensites as small as several tens of nm were formed with different variants within an austenite grain in the case of RCF, and the martensites were speculated to have the Kurdumov-Sachs or the Nishiyama-Wasserman relationship with retained austenite. Furthermore, the deformation-induced martensites were formed preferentially within the retained austenite grains, not from the interface between tempered martensite and retained austenite. Therefore, it was suggested that the deformation-induced martensites in RCF were formed from some localized regions that were plastically introduced within the retained austenite grains.
