Abstract: Combined tests of hot deformation and heat treatment for austenite grain growth of a 800 MPa quenched and tempered bainite high strength steel for hydropower were carried out on Gleeble-3500. The steel specimens were deformed by various hot compression and cooled to ambient temperature, and then reheated at 900-1200 ℃ for different holding time to study the influence of the difference of hot deformation microstructure on the austenite grain growth behavior in reheating. The results show that under different strain rates (0.01-10 s^-1), deformation temperatures (900-1150 ℃) and 60% engineering strain, the hot deformed microstructure can be roughly divided into three types: the microstructure with obvious deformation characteristics, the fully recrystallized uniform fine microstructure, and the coarsened recrystallized microstructure. The grain growth trend of the three types of microstructure is basically the same during reheating. The larger the initial grain size, the larger the final austenite grain size is, and when reheated at 950 ℃, the austenite grains of deformed specimens with the first type of deformation microstructure grow slowly at first and then coarsen rapidly. After evaluation and verification, the Sellars model, Beck model andHillert model grain growth kinetics equation have a relatively satisfactory prediction effect on the austenite grain growth behavior of the test steel. The activation energy of austenite growth in Hillert model and Sellars model corresponding to the three types of deformed microstructure is basically the same, indicating that the difference of initial structure of the same composition steel does not have an essential influence on the grain growth mechanism.

Key words: high strength bainitic steel for hydropower, hot deformation, reheating for quenching, austenite, grain growth model