Residual stress and microstructure evolution in steel tubes for different cooling conditions – Simulation and verification

Abstract

A finite element modelling approach is applied to investigate the evolution of residual stresses, temperature and phase fraction during quenching of low-alloyed seamless steel tubes. Under real-process quenching conditions, non-continuous cooling occurs that results in a stopping and restarting transformation front throughout the tube's radial direction. It is shown that the simulated temperature history, transformation kinetics and the residual stresses from the thermo-mechanical model can be correlated with experimentally observed residual stresses and micro-hardness investigations of produced tubes. The effect of the discontinuous cooling was found to be negligible with respect to residual stresses for comparable conditions, but it can cause local self-annealing and micro-hardness drops. The combination of outer and inner cooling of the tube influences residual stress and micro-hardness distribution significantly.