Effect of boundary conditions and workpiece geometry on residual stresses and microstructure in quenching process

In this study, the internal and residual stress states in quenched C60 steel cylinders are analyzed both numerically and experimentally in order to investigate the effects of boundary conditions (such as quench severity and temperature of quench bath) and specimen geometry Specimen geometry has been analyzed by introducing a hole in a cylinder arid varying hole diameter and its' eccentricity. In the numerical analysis, the finite element method is applied and both temperature gradients and Phase transformations are considered. Experiments include microstructural examination and X-ray measurements of residual stresses of the first kind. it has been found that the value of the convective heat transfer coefficient is very critical to obtain simulation results close to real Ones. For instance; when a constant value obtained as the mean of a temperature dependent distribution is used for this parameter, residual stresses are seriously underestimated (up to 40%). The temperature of the quench bath affects directly the convective heat transfer coefficient. The lower the bath temperature, the higher are the resulting residual stresses. Under the same quenching conditions, if the diameter of the hole is greater than a critical value, a transition occurs from the shallow hardening case to the through hardening case, i.e., the residual stress distribution is reversed. On the other hand, for a constant hole diameter, if the eccentricity ratio reaches a critical value, a complex residual stress state results, i.e., compressive/tensile stress transition regions along the circumference are observed