MONEL 400

UNS N04400

Other common names: Alloy 400

Monel 400 is a nickel-copper alloy (about 67% Ni--23% Cu) that is resistant to sea water and steam at high temperatures as well as to salt and caustic solutions. Alloy 400 is a solid solution alloy that can only be hardened by cold working. This nickel alloy exhibits characteristics like good corrosion resistance, good weldability and high strength. A low corrosion rate in rapidly flowing brackish or seawater combined with excellent resistance to stress-corrosion cracking in most freshwaters, and its resistance to a variety of corrosive conditions led to its wide use in marine applications and other non-oxidizing chloride solutions. This nickel alloy is particularly resistant to hydrochloric and hydrofluoric acids when they are de-aerated. As would be expected from its high copper content, alloy 400 is rapidly attacked by nitric acid and ammonia systems.

General Properties

Alloy 400 (UNS N04400) is a ductile nickel-copper alloy with resistance to a variety of corrosive conditions. The alloy is most frequently specified in environments ranging from mildly oxidizing through neutral and in moderately reducing conditions. An additional application area of the material is in marine environments and other nonoxidizing chloride solutions.

The alloy has a long history of use as a corrosion resistant material, dating back to the early 20th century when it was developed as an attempt to use a high copper content nickel ore. The nickel and copper contents of the ore were in the approximate ratio which is now formally specified for the alloy.

As with commercially pure nickel, Alloy 400 is low in strength in the annealed condition. For this reason, a variety of tempers are used which have the effect of increasing the strength level of the material.