Stability of forming induced residual stresses in stainless steel parts at elevated temperature

Abstract

The performance characteristics of technical components are influenced by residual stresses. Depending on their sign and magnitude, they may decrease or enhance the products’ fatigue strength, corrosion resistance and its achievable lifetime. While compressive stresses in the part surface usually increase the fatigue strength, tensile stresses promote crack initiation and growth. In many cases, the forming induced residual stress state is either unknown or tensile, which is why stress-relief annealing is performed to avoid unexpected effects. This time- and energy-intense process step may be avoided with an enhanced understanding of residual stresses.For the prediction of their influences, not only the sign and magnitude, but also the stability during operation is to be taken into account. The aim followed in this paper is to qualify the stability of forming induced residual stresses under typical thermal operation loads. For this purpose, stainless steel specimens are forward rod extruded with different dies, in order to generate varying residual stress states. The formed parts are heat-treated at temperatures between 100 °C and 550 °C to reproduce typical operating conditions. Residual stress measurements based on X-ray diffraction are performed after specific time intervals. From the results, a time and temperature dependent residual stress behavior is derived.