Selected Carbon Black types act as a lubricant in metal casting processes. For example, in foundry moulds they help to release to final good, else it would be sticking.
In the metal casting process the surface of the melted metal at such high temperatures would be oxidized. Under air, Carbon Black will burn at high temperatures. Depending on the Carbon Black type the starting temperature variates. Also Carbon Black is a good thermal conductivity depending on particle size and Carbon Black form (powder or beads).
In steel casting mold fluxes are used to cover the surface against oxidation processes and to protect it. Carbon Black is one of a dozen additives in the mould flux. The high temperature of this process needs a complex mixture to withstand this process for the needed time. Carbon Black helps to regulate it. In continuous copper casting some special Carbon Black grades can be used without any additives to cover and protect the liquid copper. The temperature of this process is way lower.