Due to the increasing relevance of issues such as scarcity of resources or climate change, the requirements for energy efficiency, emissions and resource conservation are increasing. Therefore, components produced by forming processes, such as forward rod extrusion, have a high potential for lightweight construction, high cost-effectiveness and resource efficiency. The resulting defects in the form of micropores and their growth have currently not been taken into account in the design of components. The design has so far been based on the mechanical properties of the material or the use of safety factors. An assessment or control of the occurring damage enables an improved design and the greater use of lightweight construction potential.

In this study, the influence of the varying forming process parameters on the microstructural damage of the case-hardened steel AISI 5115 (16MnCrS5, 1.7139) was examined. The objective was to develop a resistometry-based measurement and sensor system to characterize the forming process-induced damage, to separate application-related fatigue damage mechanisms and to analyze their interaction. The resistometry-based measurement system was used to perform a detailed, non-destructive characterization of the ductile damage while simultaneously recording the temperature. In addition, the degree of ductile damage was confirmed by light and electron microscopic analyses. Furthermore, the changes within the microstructure under fatigue loading were characterized.

With the developed and validated resistometry-based measurement and sensor system, it is possible to characterize and distinguish the different forming-induced damage states of the specimens. Complementary intermittent fatigue tests showed a significant influence of the fatigue loading on the change of the microstructure and the associated resistance behavior. Furthermore, the microstructural differences of the different damage states could be detected and quantified by scanning electron microscopy. The measurement and sensor system developed within the study will offer a time- and resource-efficient non-destructive solution for assessing and characterizing the degree of ductile damage in future.