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.

Monel 400 has great mechanical properties at subzero temperatures, can be  used in temperatures up to 1000° F, and its melting point is 2370-2460° F.  However, alloy 400 is low in strength in the annealed condition so, a variety of  tempers may be used to increase the strength.

What are the characteristics of Monel 400?

· Resistant to seawater and steam at high temperatures

· Excellent resistance to rapidly flowing brackish water or seawater

· Excellent resistance to stress corrosion cracking in most freshwaters

· Particularly resistant to hydrochloric and hydrofluoric acids when they are  de-aerated

· Offers some resistance to hydrochloric and sulfuric acids at modest  temperatures and concentrations, but is seldom the material of choice for these  acids

· Excellent resistance to neutral and alkaline salt

· Resistance to chloride induced stress corrosion cracking

· Good mechanical properties from sub-zero temperatures up to 1020° F

· High resistance to alkalis

Chemical Composition, %

Corrosion Resistant Monel 400

Alloy 400 is virtually immune to chloride ion stress corrosion cracking in  typical environments. Generally, its corrosion resistance is very good in  reducing environments, but poor in oxidizing conditions. It is not useful in  oxidizing acids, such as nitric acid and nitrous. Nevertheless, it is resistant  to most alkalis, salts, waters, food products, organic substances and  atmospheric conditions at normal and elevated temperatures.

This nickel alloy is attacked in sulfur-bearing gases above approximately  700° F and molten sulfur attacks the alloy at temperatures over approximately  500° F.

Monel 400 offers about the same corrosion resistance as nickel but with  higher maximum working pressures and temperatures and at a lower cost due to its  superior ability to be machined.

In what applications is Monel 400 used?

· Marine engineering

· Chemical and hydrocarbon processing equipment

· Gasoline and freshwater tanks

· Crude petroleum stills

· De-aerating heaters

· Boiler feed water heaters and other heat exchangers

· Valves, pumps, shafts, fittings, and fasteners

· Industrial heat exchangers

· Chlorinated solvents

· Crude oil distillation towers

Fabrication with Monel 400

Alloy 400 can easily be welded by gas-tungsten arc, gas metal arc or shielded  metal arc processes using appropriate filler metals. There is no need for post  weld heat treatment, however, thorough cleaning after welding is critical for  optimum corrosion resistance, otherwise there is the risk of contamination and  embrittlement.

Finished fabrications can be produced to a wide range of mechanical  properties when proper control of the amount of hot or cold working and the  selection of appropriate thermal treatments is done.

Like most other nickel alloys, Monel 400 is typically tough to machine and  will work harden. However, excellent results can e obtained if you make the  correct choices for tooling and machining.

Click here for more information on fabrication and machining nickel  alloys.

ASTM Specifications

Mechanical Properties

Typical room temperature Tensile Properties of Annealed Material

*The ranges shown are composites for various product sizes and therefore are  not suitable for specification purposes. Hardness values are suitable for  specification purposes provided tensile properties are not also specified.

Alloy 400 Trivia

*Alloy 400 is slightly magnetic at room temperature.

*This 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.