The niobium-carbon system has been investigated by melting point measurements, X-ray analyses and microscopic examinations. An equilibrium diagram up to 63.5 atomic percent carbon was constructed as shown in Fig. 2. The limit of carbon solubility in niobium (α) phase lies at about 2 atomic percent at 2000°C and it decreases abruptly as the temperature decreases. The Nb₂C (β) phase has a very narrow range of homogeneity and the NbC (γ) phase exists in a wide composition range from 41 to 50 atomic percent arbon below 1400°C. Three non-variant reactions in this system were determined as follows.
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