Effect of austenitizing temperature and holding time on austenite grain size of EQ70 steel

Effects of austenitizing temperature and holding time on prior austenitic grain size and its distribution were studied based on optical microscope observation and Image J analysis software. The results show that the prior austenite grain size increases with the increasing of austenitizing temperature,the coarsening temperature of austenitic grain is 950 ℃ and the phenomenon of mixed grain occurs at 1000 ℃. Austenite grain size of EQ70 steel increases with the increasing of holding time as austenitized at 850 ℃,but with the increase of holding time over 2 h,the increasing rate of austenite grain size is reduced.