Investigations on the influence of machining and sulphur content on the fatigue strength of the quenched and tempered steel 42CrMo4+QT

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Quenched and tempered steels are common material for industrial applications, especially for components exposed to high mechanical or cyclic loads. One of the best known examples of this material class is the quenched and tempered steel AISI 4140 (42CrMo4+QT). It is used in the automotive industry, for example in powertrain components such as connecting rods and crankshafts, but also in general mechanical engineering such as high-pressure pumps for hydraulic systems. Technological trends, such as the downsizing of components in combus-tion engines or increased mechanical and dynamic loads within the area of application, are increasing the demands on the load capacity of these components. Within the scope of the joint research project between the Institute of Machining Technology (ISF) and the Depart-ment of Materials Test Engineering (WPT) of the TU Dortmund University, experimental and theoretical investigations on manufacturing technology and mechanical material behaviour are brought together aiming to improve the fatigue behaviour of deep-drilled components through an optimised machining process. Furthermore, a prediction and description of the fatigue behaviour through innovative characterisation methods is possible. This very success-ful cooperation is to be continued in a second project phase with the aim of further improving the understanding of the targeted surface layer influence, which was developed in the first phase. The aim is to further increase the fatigue strength of deep-drilled components and to improve the non-destructive damage assessment. On the one hand, this will be achieved by extending the analysis methods used during deep drilling. In addition to the mechanical ef-fects, which were the focus of the investigations in the first project phase, thermal influences on the integrity of the bore surface layer will be considered in a detailed way. From this, the fundamental understanding of the thermomechanical effects on the bore surface layer and the resulting mechanical and dynamic strength of the components can be extended. On the other hand, the method of Barkhausen noise analysis will be further developed by compre-hensive microstructural investigations, which should allow an improved assessment of the damage condition of the samples.