Residual Stress Field Analysis and Prediction in Nitrided Tool Steel

Abstract

Residual stresses are present in engineering components as an unintended consequence of manufacturing processes, but they are also deliberately introduced to beneficial effect during surface engineering procedures. Plasma nitriding is a process of particular importance for forming tools and dies, giving significant advantages in wear, and fatigue resistance through the generation of near-surface compressive residual stresses. A precise knowledge of the level and distribution of residual stresses that exist in engineering components is necessary for an accurate design and prediction of a component's fatigue resistance. However, measurement of residual stresses is not always possible, which is especially true for forming tools. Therefore, other methods for residual stress evaluation and prediction are required. Results of this investigation show that residual stress level and depth in plasma nitrided tool steel increase with nitriding time and temperature. On the other hand, experimental data indicates that the residual stress distribution in plasma nitrided tool steels can be determined on the basis of microhardness depth distribution. A minimum in the microhardness depth profile derived over depth corresponds to the location of the compressive residual stress maximum. Furthermore, the residual stress level can be extrapolated by using reference residual stress data and genetic programming. In this way the residual stress level and distribution can be obtained even for components where measurement is not possible.