Niobium Carbide

Niobium carbide (NbC and Nb₂C) is an extremely hard refractory ceramic material, commercially used in tool bits for cutting tools. It is usually processed by sintering and is a frequent additive in cemented carbides. It has the appearance of a brown-gray metallic powder with purple lustre. It is highly corrosion resistant.

Niobium carbide is a frequent intentional product in microalloyed steels due to its extremely low solubility product in austenite, the lowest of all the refractory metal carbides. This means that micrometre-sized precipitates of NbC are virtually insoluble in steels at all processing temperatures and their location at grain boundaries helps prevent excessive grain growth in these steels. This is of enormous benefit, and the cornerstone of microalloyed steels, because it is their uniform, very fine grain size that ensures both toughness and strength. The only commonly occurring compound with a lower solubility and hence, greater potential for restricting the grain growth of steels is titanium nitride. Depending on grain size, niobium carbide may burn at 200-800 °C in air.°

A layer of niobium carbide can be created by chemical vapor deposition.

Zirconium carbide and niobium carbide can be used as refractory coatings in nuclear reactors.