What is the most expensive steel alloy?
Monel is a group of alloys of nickel (52% to 67%) and copper, with small amounts of iron, manganese, carbon, and silicon. Monel is not a cupronickel alloy because it contains less than 60% copper.
Monel is stronger than pure nickel and resistant to corrosion by many corrosive media, including fast-moving seawater. They can be easily manufactured by hot working, cold working, machining and welding
Monel was created in 1905 by Robert Crooks Stanley, who was then working for the International Nickel Company (Inco). Monel was named after company president Ambrose Monell and patented in 1906. An L was removed because surnames were not allowed as trademarks at the time. The trademark was registered in May 1921 and the name is now a trademark of Special Metals Corporation.
As an expensive alloy, its use is limited to applications where it cannot be replaced by cheaper alternatives. For example, in 2015 Monel pipes cost three times more than equivalent pipes made from carbon steel
Monel alloy is a solid solution binary alloy. Since nickel and copper are mutually soluble in any proportion, they are single-phase alloys. Monel is very difficult to machine compared to steel because it work-hardens very quickly. It requires turning and machining at low speeds and feed rates. It is corrosion-resistant, acid-resistant, and some alloys are fire-resistant in pure oxygen. It is typically used in applications with highly corrosive conditions. Adding small amounts of aluminum and titanium results in an alloy (K-500) with the same corrosion resistance, but with greater strength due to the formation of the gamma phase upon aging. Monel is generally much more expensive than stainless steel.
Monel 400 has a specific gravity of 8.80, a melting range of 1300–1350 °C, a conductivity of approximately 34% IACS, and a hardness of 65 Rockwell B. Monel 400 is known for its toughness, which it maintains over a considerable temperature range.
Monel 400 has excellent mechanical properties at sub-zero temperatures. Strength and hardness are increased, but ductility or impact resistance is only slightly compromised. The alloy does not undergo a ductile to brittle transition even when cooled to liquid hydrogen temperatures. This is in contrast to many ferrous materials which, despite their increased strength, are brittle at low temperatures.
