Bainite kinetic energy, activation energy, and tribological behavior of austempered AISI4340 steel

Abstract A study has been made of the effect of heat-treatment on the microstructures of commercial quality AISI4340 steel after austenitizing at 1128 K and austempering at temperatures ranging from 561 K to 644 K. The morphologies of the bainite structure were observed after etching using optical microscopy. The “Avrami” equation was used to determine the relationship between the transformed fraction and different austempering temperature. The activation energy was determined by using the “Arrhenius” equation. The results show the bainite sheaves and bainite width grow as the austempering temperature increases. High temperature results in fast bainite transformation and the bainite activation energy is 5.302 × 103 J/mol. The bainite microstructures highly enhanced tribological performance as compared to tempered martensite microstructures at the same hardness.