After introducing the Leibniz IWT, the presentation summarizes a series of findings from research projects that investigated the effect of retained austenite on the material and component properties of low-alloy steels. The main motivation for the projects summarized was to increase the service life and defect tolerance of machine elements through targeted control of the residual austenite morphology and an increased residual austenite content. The corresponding influences are evaluated on the basis of tests on standard samples and components.
After an introduction to the fundamental aspects of the formation and transformation of austenite in low-alloy steels and the resulting mechanical properties, particular attention is paid to the influence of heat treatment according to the "quenching and partitioning" (Q&P) concept on the microstructure, including residual austenite. Here, a steel with a suitable composition is quenched after austenitization to a temperature at which only incomplete martensite formation is achieved. Subsequently, holding or reheating causes a redistribution of carbon (partitioning) from martensite to residual austenite. The kinetics of carbon partitioning can be tracked by in-situ X-ray diffraction. The fundamental influence of the carbon content is determined by dilatometry on samples with varying degrees of carburization. In addition to the two-phase microstructure of martensite and residual austenite, which is common for Q&P steels, resulting microstructures with bainitic components are also examined.