Abstract
“Quenching and Partitioning” (Q&P) steels have a microstructure consisting of a tempered martensitic matrix with austenite islands, which can be stabilized to room temperature due to the C partitioning from martensite to the remaining austenite. This heat-treatment is a novel approach for producing ultra-high strength and good formable steels. In the present work the impact of the Q&P processing parameters on the phase transformation behavior and mechanical properties of a 4.5 wt.% Mn steel was investigated. Using dilatometry the influence of the quenching temperature (TQ) on the amount of martensite and the kinetics of the bainitic transformation was thoroughly studied. The microstructure was characterized by means of light optical and scanning electron microscopy. The amount of retained austenite was determined using the saturation magnetization measurement. In order to obtain the mechanical properties hardness measurements according to Vickers were performed. Furthermore, using tensile tests the Q&P concept was compared to the Quenching and Tempering (Q&T) process in terms of strength-ductility performance.
Kurzfassung
„Quenching and Partitioning“ (Q&P)-Stähle weisen ein Gefüge aus einer angelassenen martensitischen Matrix mit feinverteiltem Austenit auf, welcher durch die Umverteilung von Kohlenstoff aus dem Martensit in den Austenit bis auf Raumtemperatur (RT) stabilisiert wird. Derart wärmebehandelte Stähle verfügen über eine hohe Festigkeit bei gleichzeitig guter Umformbarkeit. In der vorliegenden Arbeit wurde die Abhängigkeit des Umwandlungsverhaltens und folglich der mechanischen Eigenschaften von den Q&P-Prozessparametern für einen Stahl mit 4,5 % Mn untersucht. Mittels Dilatometrie wurde der Einfluss der Quenching-Temperatur (TQ) auf die Martensitmenge und die Kinetik der anschließenden Bainitumwandlung analysiert. Die Gefügecharakterisierung erfolgte durch den Einsatz von Licht- und Rasterelektronenmikroskopie. Die Restaustenitmenge wurde mittels magnetischer Methode bestimmt. Neben der Härteprüfung nach Vickers wurden die mechanischen Eigenschaften durch Zugversuche ermittelt und hier ein Vergleich zwischen dem Q&P-Prozess und dem Vergüten gezogen.
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