N. P. Singh, B. J. Yang, W. Li, M. L. Johnson, Caterpillar Inc, Mossville, IL
One of the major goals in several of the induction hardened steel components is to achieve compressive stress at the surface to enhance component’s fatigue life. At the same time, this induction process should not impose high enough tensile stress under the surface to crack the component. Because of too many process parameters involved in a typical induction hardening process, it is of great advantage to us to be able to numerically predict the residual stresses. Several authors have used elastic-plastic continuum models in the past for residual stress prediction due to quenching. The purpose of this paper is to incorporate several microstructural features, which are derived from the micro-scale kinetic model, in a component level finite element model. One particular such feature is the existence of transition zone above austenitic temperature, with a mix of original microstructure and austenite. The thickness of this ‘mushy’ zone depends on depth of heating among other intuitive factors. It also depends on not so intuitive factors like the heating rate. The constants of Johnson-Mehl-Avrami type equation are derived from kinetic model for the austenite transformation during heating and used to predict such a zone on a component level. Microstructure and hardness profile as a result of induction heating is also predicted.
Summary: One of the major goals in several of the induction hardened steel components is to achieve compressive residual stress at the surface to enhance component fatigue life. At the same time, this induction process should not impose tensile stresses high enough to crack the component. Because of the many process parameters involved in a typical induction heat-treatment process, it is of great advantage to numerically predict the residual stresses. The numerical approach in the present work involves solving coupled electromagnetic and thermal equations to get the thermal history of the heat-treatment process. This thermal history is then used to solve stress field using elastic-plastic continuum models. The predicted maximum temperature and case depth are in good agreement with the experiments.
