Like the precious metals,
niobium is very ductile and extremely slow to work harden. It cuts easily with a jeweler’s saw and can be hand formed, dapped, chased, and forged with ease. It has moderate density-about a third that of gold, twice that of titanium, and 10 percent greater than that of iron. In cold working, such as rolling, drawing, forging, and swedging, niobium can be reduced as much as 90 percent in cross-sectional area before annealing. In some processes, annealing is not necessary and reduction is unlimited.
At room temperatures, a thin adherent oxide film forms on the metal’s surface. This film is transparent and self-healing. It protects the metal from corrosion and protects the wearer from the metal. Niobium reacts with atmospheric oxygen and other gases at temperatures as low as 230°C/446°F. The metal should not be exposed to an atmosphere above 370°C/700°F for longer than a few minutes to prevent further oxidation.
Niobium’s tendency to oxidize also means that annealing requires a high vacuum (10-4 Torr min.) or an inert atmosphere, vacuum being preferred. Heat treatment at 1,200°C/2,218°F for one hour provides for complete recrystalization of material cold worked over 50 percent.
