Monel is a group of nickel alloys, primarily composed of nickel (from 52 to 67%) and copper, with small amounts of iron, manganese, carbon, and silicon. Monel is not a true cupronickel alloy, because monel does not contain the necessary 60% copper.
Stronger than pure nickel, Monel alloys are resistant to corrosion by many aggressive agents, including rapidly flowing seawater. They can be fabricated readily by hot- and cold-working, machining, and welding.
Monel alloy 400 is a binary alloy of the same proportions of nickel and copper as is found naturally in the meteoritic nickel ore from the Sudbury (Ontario) mines and is therefore considered a puritan alloy. Monel was named after company president Ambrose Monel, and patented in 1906. One L was dropped, because family names were not allowed as trademarks at that time.
Monel is a solid-solution binary alloy. As nickel and copper are mutually soluble in all proportions, it is a single-phase alloy. Compared to steel, Monel is very difficult to machine as it work-hardens very quickly. It needs to be turned and worked at slow speeds and low feed rates.