Evolution of Microstructure and Mechanical Properties of the Gears on Coal-Cutting Machines in the Processes of Rapid Carburization and Heat Treatments: Numerical Modeling and Experiments

Abstract

To modify the rapid carburization and heat treatments of 18Cr2Ni4WA heavy-duty gears on coal-cutting machines, numerical modeling and experimental investigations are carried out for understanding the evolution of microstructure and properties. Through numerical modeling, the fractions of austenite, bainite, and martensite are evaluated. The Vickers hardness distribution across the hardening layer, calculated by the Maynier equation, compares well with the experimental measurement. The microstructure of the hardening layer is mainly composed of fine martensite and carbides, while that of the interior area is the martensite. The gradient of the microstructure from the hardening layer to the interior area leads to the variation of the hardness distribution. The experimental results show that the high-temperature tempering and quenching are beneficial for the refinements of the grains in the hardening layer and the interior area. The present study indicates that the combination of numerical modeling and experimental observation provides a powerful tool for the modification and improvement of the carburization and heat treatment processes.