Abstract
This research investigated the effects of various cobalt and nickel/cobalt additions to P/M 304L stainless steel on oxidation behavior at 900 °C, hardness and bending strength. A single action press at 498 MPa was used for compacting powder mixture specimens. They were then sintered at 1300 °C for 30 minutes in hydrogen atmosphere and heat treated at 900 °C for 2, 5, 10, 20, 25, 40, 60, 80 and 100 hours in air for oxidation tests. It is clearly shown in the results that cobalt addition could improve density, hardness and bending strength. However, only 1 wt.-% Co addition was the best condition for oxidation resistance. The detrimental effect of Ni addition dominated the beneficial effect of Co addition, because its bigger powder size led to more pore formation. The resulting mechanical properties and oxidation behaviour depend on microstructures, porosity and powder size.
Kurzfassung
Die diesem Beitrag zugrundeliegenden Forschungsarbeiten dienten der Untersuchung der Auswirkungen von verschiedenen Kobalt- sowie Nickel-/Kobaltzusätzen auf das Oxidationsverhalten bei 900 °C, die Härte und die Biegefestigkeit eines rostfreien Stahles P/M 304L. Eine Einfachpresse wurde bei 498 MPa eingesetzt, um Proben aus Pulvermischungen zu kompaktieren. Die Proben wurden danach bei 1300 °C für 30 Minuten in einer Wasserstoffatmosphäre gesintert und bei 900 °C für 2, 5, 10, 20, 25, 40, 60, 80 und 100 Stunden an Luft wärmebehandelt. Es zeigt sich in den Ergebnissen klar, dass die Kobaltzugabe die Dichte, Härte und Biegefestigkeit verbessern kann. Die Zugabe von nur 1 Gew.-% Kobalt stellte die beste Bedingung für Oxidationsbeständigkeit dar. Der nachteilige Effekt einer Nickelzugabe dominierte gegenüber der vorteilhaften Auswirkung einer Kobaltzugabe, da die größere Pulverpartikelgröße zu einer vermehrten Porenbildung führte. Die resultierenden mechanischen Eigenschaften und das Oxidationsverhalten hängen von den Mikrostrukturen, der Porosität und der Pulvergröße ab.
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