Monel 400 Nickel Based Alloy

Monel alloy is a Ni-based alloy, its main chemical composition is nickel (Ni), the highest content is up to 67%, the other main chemical composition is copper (Cu), and also contains a small amount of iron (Fe), manganese (Mn) and carbon ( C), silicon (Si) and other elements.

The strength of Monel alloy is higher than that of pure nickel, and it can withstand the corrosion of various media, including fast-flowing seawater. The processing methods of Monel alloy include hot working, cold working, machining and welding.

In 1901, Robert Crooks Stanley, a metallurgist at the International Nickel Company (INCO), created the Monel alloy.

The source of the Monel alloy name is based on information to pay tribute to the then chairman of the company Ambrose Monell (Ambrose Monell). Later, Mr. Stanley also served as the chairman of International Nickel Corporation. Monel alloy was granted a patent in 1906.

Monel alloy is an expensive alloy whose price is 5-10 times that of pure copper and pure nickel. Therefore, it is only used in applications where it cannot be replaced by cheap alternatives.

 

Chemical Compostion and Mechanicl Properties of Monel 400 Alloy (N0440):

 

Chemical Composition of Monel 400 Alloy (%)
C ≤	Si ≤	Mn ≤	P ≤	S ≤	Cr ≥	Ni ≥	Mo ≥	Cu ≤
0.3	0.5	2	-	0.024	-	63	-	28.0-34.0
Others	N ≤	A l≤	Ti ≤	F e≤	Co ≤	V ≤	W ≤	Nb ≤
	-	-	-	2.5	-	-	-	-

1. Monel 400 (N04400) alloy tensile strength: σb ≥ 450 Mpa.
2. Monel 400 (N04400) alloy yield strength: σb ≥ 170 Mpa.
3. Monel 400 (N04400) alloy elongation: δ ≥ 30%.

 

Properties of Monel Alloy

Monel alloy is a solid solution binary alloy. Since Ni and Cu are dissolved in each other, it is also a single-phase alloy. Compared with steel, machining of Monel alloy is difficult, mainly due to its rapid work hardening characteristics. It requires turning at low speeds and low feed rates.

The density of Monel alloy 400 is 8.80 g/cm3, the melting temperature range is 1300~1350 °C, the conductivity is about 34% IACS (IACS refers to the International Standard Conductivity of Annealed Copper), and the annealed hardness value is 65 HRB. Monel alloy 400 is well-known for its toughness and can maintain this toughness in a considerable temperature range.

It can withstand the corrosion of various acids and alkalis, and some Monel alloys can even withstand pure oxygen burning. It is usually used in highly corrosive environments. Monel alloy K-500 formed after adding a small amount of aluminum (Al) and titanium (Ti) has the same corrosion resistance as Monel alloy 400 but higher strength, which is mainly due to the formation of γ'phase during aging treatment. Under normal circumstances, Monel alloy is much more expensive than stainless steel.

Monel alloy 400 can also maintain excellent mechanical properties below zero. Although the strength and hardness will increase, the plasticity or toughness will only slightly decrease. Even if it is cooled in liquid hydrogen, the alloy will not undergo ductile-brittle transition. This is the most significant difference between Monel alloy and ferrous metal materials (steel and iron) with low temperature brittleness.

Monel alloy has good corrosion resistance in many environments, but it is prone to rust when exposed to salt water; it cannot withstand the corrosion of media containing nitric oxide, nitric acid, sulfur dioxide and hypochlorite. The use of Monel alloy will also cause electrochemical corrosion. In other words, when fasteners made of aluminum, zinc or iron come into contact with Monel alloy, under certain conditions (such as use in fast-flowing seawater), metal fastening The parts will be corroded quickly.

 

Uses of Monel alloy

Aerospace
In the 1960s. Monel alloy has won a large number of orders in the field of space and aircraft construction. Especially used to build the fuselage and skin of experimental jet aircraft. For example, the North American X-15 can be used to withstand the large amount of heat generated by aerodynamic friction during extremely fast flight. Monel alloy can still maintain its strength at extremely high temperatures, allowing it to maintain its shape stability at high atmospheric flight speeds. During aircraft maintenance, Monel alloy is used as a lock wire in high temperature areas to ensure that the fasteners are locked; for economic reasons, stainless steel lock wires are usually used in other areas.

Oil Extraction and Refining
Monel is used to make parts that directly contact concentrated hydrofluoric acid in an alkylation unit. Monel alloy's extraordinary resistance to hydrofluoric acid corrosion is amazing. It can withstand all concentrations of hydrofluoric acid, and the temperature can reach the boiling point of hydrofluoric acid. This may be the material with the best corrosion resistance among commonly used engineering alloy materials. Monel alloy can also withstand the corrosion of various sulfides and hydrochloric acid in a reducing environment.

Marine Engineering
The corrosion resistance of Monel alloy makes it an ideal material for marine applications, such as piping systems, pump shafts, sea valves, trolling fishing lines, and basket filters. Some Monel alloys are completely non-magnetic, and are used to make anchor cables for minesweepers and housings for magnetic field measurement equipment. On yachts, Monel alloy wire is used to lock anchor cable shackles. Monel alloy is also used to make water tanks and fuel tanks and other underwater devices, such as propeller shafts and keel bolts.

It should be noted that due to the problem of electrochemical corrosion (bimetallic corrosion) in seawater, the Monel alloy must be isolated from other metals (such as steel) during shipbuilding. The New York Times published on August 25, 1915. An article in ”reported on the accident of a 215-foot-long yacht: “The first yacht whose hull was constructed entirely of Monel alloy was turned into fragments in just six weeks and was forced to scrap”. Thanks to electrochemical corrosion, the steel structure keel of the yacht was quickly eroded and thinned after contact with Monel alloy, which eventually led to the collapse of the yacht's bottom. In terms of seabird research, especially the selection of materials for the bird's foot identification ring, the bird's foot identification ring made of Monel alloy has been used in many kinds of seabirds, such as albatross living in corrosive seawater environments.

Musical Instrument
Monel alloy is used to make certain high-quality musical instrument valve pistons or rotors, such as small, large and French horns. RotoSound used Monel alloy to make electric guitar strings in 1962. These strings are used by many artists. In 2017, the D'Addario string company (D'Addario string company) released a set of violin string products, which are also round-wound strings with Monel alloy wound on D and G strings.

 

Other Uses
Identity tags made of Monel alloy (Dog tags for American soldiers during World War II)

Excellent corrosion resistance to various acids and oxygen makes Monel alloy a high-quality material in the chemical industry. Other usage scenarios such as:
1. Uranium enrichment, most of the large-diameter pipelines used for uranium hexafluoride are made of Monel alloy;
2. Regulating valve for high pressure and strong reactive bottled gas (such as HCl);
3. In the early twentieth century, Monel alloy was widely used in the superheated steam system of steam generator sets;
4. Monel alloy is also often used to make kitchen sinks and spectacle frames;
5. The combustion chamber used to make the boiler ignition tube;
6. The design life of the Clock of Long Now is 10,000 years. On the premise that no precious metals are used, some parts of the clock are made of Monel alloy material based on concerns about corrosion resistance.