Monel 400 Alloy (UNS N04400)

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.

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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.

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Applications
Marine and chemical processing equipment
Valves, pumps, propeller shafts
Marine fixtures and fasteners
Gasoline and fresh water tanks
Process vessels and piping
Heat exchangers

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Standards
ASTM......................... B 127
ASME......................... SB 127
AMS ........................... 4544
Federal or Military...... QQ-N-281

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Corrosion Resistance
Alloy 400 is more corrosion resistant than commercially pure nickel (UNS N02200) under reducing conditions, and more resistant than refined copper alloys under oxidizing conditions.

In moderately reducing acids, neutral or alkaline solutions, Alloy 400 may be considered for use. The alloy is resistant to most alkalies, salts, organic substances, and atmospheric conditions. Alloy 400 is a consideration for cooler alkaline caustic conditions, although high temperature, high stress, and high concentrations of caustic have produced caustic stress corrosion cracking in the material. The alloy is used in reducing acids like sulfuric and hydrochloric, especially in the absence of aeration and oxidizing species.

Alloy 400 is exceptionally resistant to chloride stress corrosion cracking.

Application in waters, including sea and brackish water, is a major use of the material.

Alloy 400 is attacked in sulfur-bearing gases above approximately 700F (371C), and molten sulfur attacks the alloy at temperatures over approximately 500F (260C).

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Chemical Analysis
Typical Analysis (Weight %)

C Mn P S Si Al Ni + Co Cu Fe
0.10 0.50 0.005 0.005 0.25 0.02 Balance* 32.0 1.0

*By difference - For material furnished to QQ-N-281, lead, tin, and zinc are each typically <0.003.

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Mechanical Properties
The following are typical room temperature mechanical properties of Alloy 400. The lowest strength and most ductile condition is the annealed condition with typical properties as shown below.

Magnetic Permeability:
In the annealed condition the alloy is often moderately to faintly magnetic at room temperature. The Curie temperature of the material is close to room temperature. Above the Curie temperature, the material is nonmagnetic. The Curie temperature is influenced by minor composition variations, so some heats of material will be magnetic at room temperature and others will not.

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Heat Treatment
The anneal cycle conducted on Alloy 400 is typically in the 1400 to 1800F (760 to 980C) range for short times at temperature. The purpose is to soften the material after forming operations while maintaining a relatively fine grain size.

Annealing should be done in an atmosphere as free of sulfur compounds as possible since sulfur will embrittle the material in extended exposure time at the anneal temperature range.

A low temperature stress relief may be conducted on cold deformed material by heating to approximately 575F (300C) for 1 to 3 hours.

A large percentage of Alloy 400 is put into service without final heat treatment. This is done to increase the strength of the material.

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Processing
Cold Forming
Alloy 400 exhibits excellent cold forming characteristics normally associated with chromium nickel stainless steels. The alloy has a lower work hardening rate than Alloys 301 or 304 stainless steel and can be used in multiple draw forming operations where relatively large amounts of deformation occur between anneals.

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Welding
Alloy 400 may be joined by a variety of processes including gas tungsten-arc, gas metal-arc and shielded metal-arc processes. In all of these processes, thorough cleaning of the joint area is necessary to avoid embrittlement from such sources as lubricants and paints. The material must be free of scale for best welding.

Welding procedures for Alloy 400 are similar to those used for austenitic stainless steels. Neither preheating nor post-weld heat treatment are generally required.

Joint design is similar to that used for austenitic stainless steels with two exceptions. The first is the need to accommodate the sluggish nature of the molten weld metal, necessitating a joint design sufficiently open to allow full filler wire access to fill the joint. The second is the high thermal conductivity and purity of the material which makes weld penetration lower than in austenitic stainless steels.