Effect of carbon content and cooling rate on the microstructure and hardness of TiC-Fe-Cr-Mo cermets

Abstract

TiC-FeCrMo cermets have been obtained in fully dense form by Sinter HIP at 1400 °C. Significant microstructural changes have been observed in these materials for relatively small variations in their carbon content after sintering. In the cermets with higher carbon content Cr-rich likely M7C3 carbides are observed to precipitate at the (Ti1-x,Mox)yCz - metal interface. In addition, these cermets present a significant amount of retained austenite as part of the metal matrix. No retained austenite and many fewer M7C3 carbides are found in alloys with a reduction of 0.2 wt% in the total C content. Continuous cooling diagrams have been obtained from an austenitizing temperature of 950 °C. Hardness increases by 30% with respect to that of as sintered specimens after cooling at 1 °C/s confirming that these TiC-FeCrMo cermets are suitable for hardening by air-quenching. At this cooling rate, it is observed that the relatively small carbon changes mentioned before have a significant effect on the bainitic transformation, displacing its onset to higher temperatures as the C content is reduced. Slower cooling rates result in complex microstructures, in which, in addition to martensite, ferritic bainite, M7C3 and M23C6 carbides are also found. Microstructure and hardness of TiC-FeCrMo materials can be modified by the use of standard heat treatments to obtain a wide variety of mechanical properties suitable for certain hot rolling applications.