(Chemical symbol: Nb) A ductile metallic element used in alloys, tools and dies and superconductor magnets. Also known as columbium (Cb). It is used as a major alloying element in nickel-base, high-temperature alloys and as an important additive to high-strength structural steel. Atomic number, 41; atomic weight, 92.906; melting point, 2468°C (4474°F); specific gravity, 8.57 at 20°C (68°F).