Monel is a registered trademark that encompasses a series of nickel-copper alloys. With a range of alloys including Monel 400, 401, 404, K-500 and R-405, Monel is often used in applications requiring a high degree of corrosion-resistance as well as moderate heat-resistance. In addition to nickel and copper, Monel alloys often include trace amounts of iron, manganese, carbon and sulphur.

Characteristics of Monel alloys include high strength, high malleability, low coefficient of thermal expansion and excellent sanitation. As a result, Monel alloys are often used in industries including: marine, for seawater valves, strainer baskets, trolling wire and various fixtures and fasteners; petroleum, for gasoline tanks, off-shore oil rigs, petroleum stills and varied processing equipment; music, for instruments including trumpets, French horns and tubas and accessories such as bass guitar strings; residential, for use in household fixtures such as kitchen sinks and interior d├ęcor such as doorknobs and decorative screens; and industrial manufacturing, for use in boilers, chemical tanks and various stock such as tubes, wire, sheet and plate used in manufacturing equipment and parts.

Monel is often manufactured to standards set by the American Society for Testing and Materials (ASTM) or the American Society of Mechanical Engineers (ASME).

The basic composition of Monel is 65-70% nickel, 20-29% copper, 5% manganese and small percentages of iron and other elements. The various Monel alloys differ slightly in terms of composition: for instance, Monel 400 is composed of 63% nickel, 28-34% copper, 2.5% iron, 2% manganese and small amounts of sulphur, carbon and silicone; Monel 404 is composed of 52-57% nickel, 2% iron, 45% copper and small amounts of aluminum, manganese, silicone, carbon and sulfur; and Monel K-500 is composed of 64% nickel, 30% copper, 1% iron, 2.8% aluminum and small amounts of carbon, titanium and manganese.

The varied chemical compositions make the Monel alloys well-suited for specific tasks. For example, Monel 404 is often used in the electronics industry because of its low permeability, while MonelK500 is ideal for marine equipment applications because of its high-resistance to corrosive seawater elements.

Although Monel alloys are malleable, they can be difficult to machine because they tend to work harden instantly in response to heat. As a result, Monel alloys must be turned while machining at slow speeds and with low feed rates. Thus, when being machined, Monel alloys are typically forged using an open die forging technique.