Monel 400 alloy is mainly composed of 30% Cu and 65% Ni plus a small amount of Fe (1%-2%), and the structure is a typical single-phase austenite structure. Since nickel and copper are mutually soluble in any ratio, there is generally no intermetallic phase precipitation.

Monel 400 is a solid solution alloy that can be hardened only by cold working. It exhibits great strength over a wide temperature range and shows excellent corrosion resistance.

This alloy resists stress corrosion cracking because of its high nickel content. The presence of copper also gives it resistance to sulfuric acid and other reducing agents in both extreme and mild temperature conditions. It also shows high resistance to alkalis.