INFLUENCE OF HEAT-TRANSFER ON THE DEVELOPMENT OF RESIDUAL-STRESSES INQUENCHED STEEL CYLINDERS

In this paper results of systematic FE-calculations about the influenc e of characteristic points of the temperature dependent heat transfer coefficient, especially the Leidenfrost point and the point of maximum heat transfer coefficient on the development of residual stresses are discussed. The numerical investigations were carried out for SAE 1045 and 4140 steel cylinders with 10 and 20 mm empty set quenched in wate r and oil, respectively. In this work experimentally determined h, T-c urves are linearly approximated in the successive stages of heat trans fer. Changes of the Leidenfrost-temperature do not influence the middl e plane residual stresses of the cylinders investigated. Increasing ma ximum heat transfer coefficients and low temperatures of maximum heat transfer coefficient, respectively, cause higher magnitudes of residua l stress. The development of residual stresses is determined by the te mperature dependent gradient of the heat flux density deltaq/deltaT in the temperature range of martensitic transformation. Increasing Leide nfrost-temperatures cause more homogeneous stress and residual stress states at the surface of quenched cylinders due to the symmetrical coo ling of the sample in axial as well as in radial direction. In particu lar, it was shown that during immersion cooling of cylindrical parts t he heat transfer is locally dependent. Simulating immersion cooling th is dependence has to be considered using effective local heat transfer coefficients.