Influence of carbon content and processing treatment of metallic binder on the outgassing and sintering of NbC based cemented carbide

Abstract In this study, two grades of high speed steel (HSS), having different carbon content and processing treatment (i.e. cryo-milling and atomization), were used as a metallic binder for NbC cemented carbides. Thermoanalytical methods were used to investigate the outgassing and sintering of the two NbC cemented carbides during heat treatment. For this mean, thermogravimetry (TG), differential scanning calorimetry (DSC) and evolved gas (EG) analysis during thermal heat treatment were carried out. The results indicated that the processing treatment has a great impact on the thermal behavior of the steel powders, which later can be traced in the thermal behavior of the compacts. Higher decarburization was traced during the thermal analysis on the powder prepared via cryo-milling compared to the one made by the atomization process. From the TG analysis of the green compacts, it was evident that intensive outgassing occurs at temperatures above 850 °C. This phenomenon is associated with the activation of several mechanism in NbC and steel above this temperature which was realized from the evaluation of the initial powders. To gain a deeper understanding on the basic reactions and the effect of carbon content on phase transformations during the thermal process, thermodynamic studies was performed using commercial software (Thermo-Calc). It was evident that decreasing the carbon content shifts the transformation temperatures (e.g. liquid formation) to higher levels. This is especially important in adjusting the sintering temperature in NbC-high speed steel system as sufficient portion of liquid phase should be presented during the sintering process in order to obtain a satisfactory sintering.