Computer simulation of the heat treatment process applied to a forged shaft

Process modelling using finite elements analysis is very effective to design an optimized process in order to obtain high quality forging parts. For instance, the application of computational analysis on heavy forgings allows the definition of an adequate forging process in terms of temperature, pressure and ramp speed as well as the heat treatment procedure. Quenching and tempering represent a critical phase in the production of heavy forged steel parts. In fact, improper cooling can cause the obtainment of undesired microstructure (i.e. bainite instead of martensite at the component surface as a consequence of a soft cooling) or unexpected residual stress distribution, related to severe heat treatment steps causing cracks. The aim of the present study was to evaluate the adequacy of an industrial heat treatment procedure applied to a heavy 4140 steel forged shaft by means of finite elements simulation, a technique able to predict the temperature/time distribution along the thickness of the forged part in various heating or cooling conditions. A comparative study of experimental and numerical superficial temperature distribution was also proposed, allowing the validation of the numerical model used and, subsequently, of the internal temperatures and stresses distribution.