LAUSR

Abstract The objective of this research was to investigate the bainitic formation in austempered SAE 52100 steel. The original microstructure of SAE 52100 steel consisted of spheroidized pearlite. In the formation of bainite, SAE 52100 steel samples were austenitized at a temperature of 849 °C for 20 min, and then quickly quenched to the isothermal temperatures between 232 °C and 427 °C for various holding times from 20 s to 120 min. The hardness and microstructure of austempered SAE 52100 samples were analyzed using a Rockwell C hardness tester and metallurgical optical microscope. In addition, the bainitic formation in SAE 52100 steel was characterized using the theory of kinetic phase transformation. The activation energies of lower bainite and upper bainite microstructure were found to be 4.72 × 104 J/mol and 6.07 × 104 J/mol with frequency factors of 23.03 (1/s) and 273.65 (1/s), respectively.