Microstructure analysis of an induction hardened gear studied by neutron Bragg-edge transmission imaging

Su, Y. H.  ; Oikawa, Kenichi   ; Shinohara, Takenao   ; Kai, Tetsuya   ; Hiroi, Kosuke  ; Hayashida, Hirotoshi*; Zhang, S.*; Parker, J. D.*; Matsumoto, Yoshihiro*; Sato, Hirotaka*; Tomota, Yo*

Induction hardening is an important heat-treatment technique that can be used to harden only selected portions of an object, providing excellent mechanical properties such as high wear resistance and fatigue strength. We have applied the time-of-flight neutron transmission imaging technique to investigate the residual strain and the microstructure distribution in a typical induction-hardened gear. The experiment was performed at RADEN, BL22, at the J-PARC/MLF. The measured Bragg-edge transmission (BET) spectra of the ferrite (110) edges were fitted using the RITS code. The crystal lattice plane spacing in the tooth is larger than that in the gear body due to the harder fine-grained martensitic structure. A comparison of 2D maps of the residual strain and microstructure obtained by BET to the hardening case depth (Vickers hardness distribution) of the gear will be presented.