Carbon distribution in WC based cemented carbides

•Free carbon is found at the carbide–binder interface of WC based cemented carbides.•Mechanism of free carbon formation at the carbide–binder interface is proposed.•Degradation of solid solution in the binder phase during cooling is discussed.•Four ranges of cooling rates are identified for cemented carbides.•Reverse dependence of carbon amount in the binder on the cooling rate is found.

Is there carbon in the binder phase of conventional cemented carbides? The effect of formation of the layer of free carbon at the carbide–binder interface is employed to explain the reduction of carbon concentration in the binder phase on alloys with larger binder phase size after intermediate and faster cooling from high temperature. Dependence of the carbon concentration in the binder phase versus the cooling rate and the binder size is modeled by computer simulation. It is shown that the carbon concentration goes through a local maximum at the moderate values of the cooling rate. The maximal carbon concentration in the binder phase corresponds to the slowest cooling rate for the selected binder size at which the layer of free carbon is formed at the carbide–binder interface. Increase of the cooling rate after the formation of the free carbon at the carbide–binder interface reduces the carbon concentration. Further increase of the cooling rate and the relative slowing down of the interface reaction at the carbide–binder interface and the diffusion of carbon can freeze up the carbon content at higher levels in the binder phase. Possible decarburization during the liquid phase sintering reduces the initial amount of carbon in the binder phase and can also cause the full decarburization of the binder during cooling due to the deposition of all the carbon from the binder phase onto WC crystals.