The joining of cemented carbides to steels used in the drilling/excavation industries due to their distinct characteristics has posed a significant challenge. This research systematically investigates the effect of brazing temperature (650, 700, and 750 °C) and time (5, 10, and 15 min) as the most effective brazing parameters on the phase transformations and interfacial microstructure of WC-Co/AISI 4140 steel joints. Low-temperature brazing due to eliminating the destructive η carbides at the cermet interface, makes it a more appropriate procedure, as compared to fusion-welding methods, as per the findings of the current study. It was revealed that the optimal condition for the process is at 650 °C for a duration of 10 min, in which the eutectic structure is refined and the distribution of primary dendrites is uniform. The microstructure of the brazed area presents a multiphase structure, comprised of a copper-rich solid solution (Cu,Zn), a silver-rich solid solution (Ag,Cd), a eutectic structure as well as the β′-CuZn ordered phase. The β embedded in ternary eutectic structure was partially transformed to β′ during the cooling cycle of the brazing process. Diffusion of silver and cadmium in cemented carbide, as well as the formation of Co-Fe-Cu reaction product, were proposed as the bonding mechanisms. The effectiveness of brazing temperature in enlarging the cobalt-depleted zone appearing in WC-Co is comparatively higher than that of brazing time. It is also concluded that by increasing the brazing temperature and duration, the fraction of copper solid-solution dendrites distributed in the joint area decreases, however, the size increases.