Abstract: Research was conducted on the kinetics of bainite transformation of a medium carbon under a wide range of iso-thermal temperatures. The 4140 steel studied is commonly used in structural components or tooling purposes. To convert a steel into a bainitic steel will make it more ductile yet with sufficient strength, toughness and fatigue limit as compared to martensitic steel. The bainite transformation kinetic characterization is studied. The bainite transformation and hardness functions are determined using the Johnson-Mehl- Kolmogorov-Avrami (JMKA) equation, and bainite volume fraction progressing curves are calculated. Phase transformation activation energy is calculated using the Arrhenius equation. The iso-thermal conditions studied covers a wide range of temperatures, in which four major material phases or mixed phase are produced. The four phases are upper bainite, upper and lower bainite mixed phase, lower bainite phases and martensite and lower bainite mixed phase (lower bainite transformed under Ms temperature). The calculated results do show the differences in terms of kinetics characteristics for the various phases or mixed phases of the microstructures.
Authors: Jian Zhu, Xichen Sun, Gary Barber, Xue Han, and Hao Qin
Keywords: Iso-thermal, Upper and lower bainite, Transformation Kinetics, Activation energy