KurzfassungDas Fließspannungsverhalten einer hochlegierten metastabilen Stahlgusslegierung wurde in einem weiten Bereich der Dehnrate (4·10−4 s−1 bis 2200 s−1) unter Zug- und Druckbeanspruchung untersucht. Dabei wurde ein ausgeprägter TRIP(TRansformation Induced Plasticity)-Effekt der austenitischen Legierung auf CrMnNi-Basis beobachtet, welcher zu hohen Festigkeiten und exzellenter Verformbarkeit führt. Bei Temperaturen oberhalb von 60°C bis 100°C zeigte sich zusätzlich eine mechanische Zwillingsbildung (TWIP- Effekt). Ein besonderes Augenmerk lag auf der Untersuchung der durch die mechanische Beanspruchung hervorgerufenen Mikrostrukturentwicklung. Es wurde festgestellt, dass erhöhte Beanspruchungsgeschwindigkeiten wesentlich das Werkstoffverhalten der untersuchten Legierungen beeinflussen. Mit steigender Dehnrate erfolgt eine Erwärmung der Probe, welche der Entstehung von α'-Martensit entgegenwirkt und so maßgeblich das Verfestigungsverhalten des Werkstoffes beeinflusst.

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This study focuses on the characterization of the microstructures of an FeCrMoVC alloy in two states (an as-cast and a heat-treated state) as well as the compressive strain rate-dependent material and fracture toughness behavior. Both microstructures consist of martensite, retained austenite and complex carbides. Tempering results in a transformation of retained austenite into martensite, the precipitation of fine alloy carbides, and diffusion processes. High yield stresses, flow and ultimate compressive strength values at a relatively good deformability were measured. The yield and flow stresses at the onset of deformation are higher for the heat-treated state due to higher martensitic phase fractions and fine precipitations of alloy carbides respectively. Compressive deformation causes a straininduced transformation of retained austenite to a 0 -martensite. Hence, both high-strength alloys are TRIP-assisted steels (TRansformation-Induced Plasticity). However, the martensitic transformation is more pronounced in the as-cast state due to higher phase fractions of retained austenite already in the initial state. Examinations of strained microstructures showed decreased crystallite sizes with increasing deformation. It is assumed that, during plastic deformation, the amount of low angle grain boundaries increases while the incremental formation of a 0 -martensite leads to decreased crystallite size. In general, lower microstrains were determined in the heat-treated state as a consequence of stress relaxation during tempering. In comparison to commercially available tool steels, the determined fracture toughness K Ic of both variants revealed relatively high fracture toughness values. It was found that the lower shelf of K Ic is already reached at room temperature. Higher loading rates _ K resulted in lower dynamic fracture toughness K Id values. Notch fracture toughness K A measurements indicate that the critical notch tip radii of the examined materials are slightly smaller than 0.09 mm.

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