Modelling of Deformation and Residual Stresses in large component gears after carburisation and heat treatment

A new Finite Element model has been developed to predict the deformations, stresses, phase compositions, and carbon concentration gradient that arise as a consequence of the physical processes involved in the carburisation and quenching process of a large steel gear. Firstly, the diffusion of carbon at elevated temperatures in the austenitic range is studied in a diffusion model. Secondly, the calculated carbon concentration distribution has been used as an input in a model that couples the thermal, metallographic and mechanical effects during the quenching process and calculates the evolution of the temperature, phase composition, and deformation history at any point in the gear. Some specific effects typical for oil quenching of large gears, like for example the influence of the gear’s own weight while hanging on chains before, during, and after entering the quench bath are also modelled. It is shown that these effects  should be incorporated in the model.