Effects of Spheroidized Microstructure on Bainite Nucleation in SAE 52100 Steel

Abstract

Annealed SAE 52100 steel samples with different spheroidized microstructures were austempered to produce a bainitic+martensitic duplex microstructure. The effects of the spheroidized microstructure on bainite ferrite (BF) nucleation during austempering were discussed. Results show that the proportion of lower bainite increased, and the BF plates initially widened and subsequently narrowed in the duplex microstructure with an increase in the unit volume density of the cementite particles (ρ v ) in the spheroidized microstructure. An improved model was suggested to predict the bainite transformation including consummated α b by considering the effects of ρ v on BF nucleation. The model was validated with the experimental data of SAE 52100 steel.