Prediction and measurement of residual stresses in quenched stainless-steel spheres

Abstract

A finite element (FE) technique has been used to predict the residual and thermal stresses which occur during water quenching of solid stainless-steel (SS) spherical balls. The variations of residual stresses at different positions and cross-sections, e.g. the radial, axial and tangential directions, have been examined. Also, the influence of heat transfer coefficient, the initial temperature and the hardening assumption on residual stress results has been investigated. The results show that high compressive residual stresses occur along the cooling surface. Moving away from the surface, these residual stresses begin to decrease and reverse their sign, and near the centre are tensile. Preliminary quenching experiments have been carried out using spheres of type 316L stainless steel. The temperature during quenching was recorded and compared with finite element simulations. The surface residual stresses were determined using the incremental centre-hole measurement technique. Neutron diffraction (ND) was used to determine the residual stresses in the centre of the sphere. The paper compares these measurements with the finite element results as well as comparing the measured cooling temperature history with simulation. Overall there is good agreement between the predicted and measured stresses.