Abstract
The high demands on wear resistant tools have led to the development of wear resistant claddings on a substrate, which can be a low alloyed steel with higher ductility than the cladding to improve the resistance of the tool against fracture. In this study, the post heat treatment of sinter-cladded X245VCrMo9-4 steel coating on X120Mn12 steel substrate was investigated, as it is expected that the substrate remained austenitic while the coating possessed a tough martensitic matrix with uniform dispersion of carbide precipitates. Samples were prepared by sintering at 1250 °C in a vacuum furnace under a nitrogen atmosphere at 80 kPa and a heating rate of 10 K/min, and was allowed to cool in the furnace after a dwell of 30 min at sintering temperature. These samples were subjected to heat treatment by austenitisation, oil quenching and tempering. The effect of heat treatment procedures deployed on the samples was examined using optical microscopy, scanning electron microscopy, X-ray diffraction and hardness. Experimental results were supported by computational thermodynamic calculations. The results indicated that the optimised heat treatment, through which the hardness of the steel coating is significantly enhanced while the substrate microstructure remained austenitic, is by austenitising at 950 °C, quenching and low temperature tempering at 150 °C. Quenching temperature was significant to the hardness of the steel coating, as quenching from higher temperature led to a lower hardness of the matrix when compared to quenching at lower austenitisation temperature owing to a high fraction of retained austenite.
Kurzfassung
Die hohen Anforderungen an verschleißfeste Werkzeuge haben zur Entwicklung von verschleißbeständigen Beschichtungen auf einem duktilen Substrat geführt. Bei diesem Substrat kann es sich um einen niedrig legierten Stahl handeln, der eine höhere Duktilität als die Beschichtung aufweist, um die Bruchfestigkeit des Werkzeugs zu verbessern. In dieser Studie wurde die Wärmebehandlung eines Sinterverbundes mit einer Beschichtung aus X245VCrMo9-4 auf einem X120Mn12-Stahlsubstrat untersucht. Es ist beabsichtigt, dass nach der Wärmebehandlung das Substrat austenitisch bleibt, während die Beschichtung eine zähe martensitische Matrix mit gleichmäßiger Dispersion von Karbidausscheidungen aufweist. Die Proben wurden durch Sintern bei 1250 °C in einem Vakuumofen unter einer Stickstoffatmosphäre bei 80 kPa und einer Heizrate von 10 K/min hergestellt und nach einer Verweilzeit von 30 min bei Sintertemperatur im Ofen abgekühlt. Diese Proben wurden einer Wärmebehandlung durch Austenitisierung, Ölabschreckung und Anlassen unterzogen. Die Auswirkungen der Wärmebehandlungen, die auf die Proben angewendet wurden, wurden unter Verwendung von Lichtmikroskopie, Rasterelektronenmikroskopie, Röntgenbeugung und Härte untersucht. Die experimentellen Ergebnisse wurden durch rechnergestützte thermodynamische Berechnungen unterstützt. Die Ergebnisse zeigten, dass die optimierte Wärmebehandlung durch Austenitisieren bei 950 °C, Abschrecken und Anlassen bei einer niedrigen Temperatur von 150 °C erfolgt. Hierdurch konnte die Härte der Stahlbeschichtung signifikant gesteigert werden, während das Gefüge des Substrats austenitisch bleibt. Die Wahl der Abschrecktemperatur war ausschlaggebend für die resultierende Härte der Stahlbeschichtung, da das Abschrecken bei höherer Temperatur aufgrund eines hohen Anteils an Restaustenit zu einer geringeren Härte der Matrix im Vergleich zum Abschrecken bei niedrigerer Austenitisierungstemperatur führte.
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