Refractory elements:

The term refractory metals denotes metals with a very high melting point, but it is used somewhat arbitrarily in the metals industry. For example, the Refractory Metals Committee, organized under the Metallurgical Society of the American Institute of Mining, Metallurgical and Petroleum Engineers, uses the term refractory to cover only metals with melting points above about 1,900 C (3,500 F). However, according to the Metals Handbook published by the American Society for Metals, the refractory metals are those "metals having melting points above the range of iron, cobalt and nickel." This broader definition would include tungsten, molybdenum, tantalum, niobium, chromium, vanadium, and some less common metals. This section discusses niobium, vanadium, tungsten, and molybdenum. Chromium is discussed above with manganese. Tantalum is omitted from discussion owing to its limited commercial use.

Excerpt from the Encyclopedia Britannica without permission.