Influence of processing parameters on the fatigue life time of specimens made from quenched and tempered steel SAE 4140H

Abstract

Abstract The demands placed on highly stressed components are constantly increasing. For this reason, components with a higher degree of efficiency are required for the competitiveness of metallic components. Therefore, a comprehensive understanding of the fatigue behavior of metallic materials and components as well as the development of new methods for the reliable calculation of service life are of increasing importance. The fatigue properties of components are multi-parameter sets and are strongly influenced by surface integrity, as surface and near-surface zones are the most stressed regions of a component. Surface integrity is influenced by each individual manufacturing process, its parameters, the process order and the process combination. Due to their high complexity, the influence-cause-effect relationships of process chains have not yet been sufficiently understood. In order to analyze the interactions between manufacturing process chains, their design, variations in material properties, in particular the microstructure and the resulting component properties, specimens were processed with specifically different machining parameters with and without polished surface. The specimens were characterized by different analyzing methods, such as X-ray for residual stress measurements and phase analysis as well as surface characterizations through confocal microscopy. The results from these analytics are used as an input for a semi-empirical model and finite element analysis providing effective stress amplitudes which include factors such as stress concentration and residual stress in order to predict their influence on fatigue life. This additional material information can be used in currently existing short-time procedures or for conventional determined SN curves to expand them to a multi-parameter dataset. The investigations presented in the scope of this paper were performed on specimens made from quenched and tempered steel SAE 4140H (42CrMoS4) machined with various processing parameters.