A material for electric heater element sheathing, which has good weldability, is oxidation- and corrosion-resistant, and forms an eye-pleasing dark gray or black surface oxide, consists essentially of, by weight, from about 8.75-15.5% nickel, about 19.5-21.0% chromium, about 0.30-0.50 manganese, about...http://www.google.es/patents/US5217545?utm_source=gb-gplus-sharePatente US5217545 - Heater sheath alloy
