2015 年 33 巻 2 号 p. 71s-74s
Whether dislocation network could be introduced into austenite (γ) even during austenitization or not was analyzed by optical microscopy. Austenitization at 1450°C for 300s dissolves MnS completely into γ. It is clarified that isothermal holding at 900°C for 1200s after austenitization forms MnS along small-angle boundary within γ grain. It suggests that dislocation network forming the small-angle boundary is introduced and stable even in the high temperature region of γ. Serial sectioning observations of bainite laths with optical microscope reveals that BWING (bainite lath within γ grain) could nucleate from the dislocation network. Dislocation network forms by reaction of dislocations on each slip system. Each dislocation in a network would have different Burgers vector. Therefore, climbing rate of each dislocation in a network due to absorbing or generating vacancies might be different, resulting in bowing-out of dislocation belonging to a network and in increase in self-energy of a dislocation network. It could be concluded that dislocation network is stable even in γ and the network acts as nucleation site for BWING. Based on the conclusion, nucleation of BWING is enhanced through introduction of dense dislocation networks into γ.
