A class of alloys known as Monel® is primarily composed of nickel (52–67%) and copper (28–33%) with trace amounts of silicon, iron, manganese, carbon, and other elements. Special Metals Corporation owns a trademark called Monel®, which is used to categorize multiple kinds of nickel-copper alloys.
It was first created by engineers employed by the International Nickel Company. All related alloys, including those produced by other businesses, are likewise referred to as Monel. It is very strong and resilient across a broad temperature range and exhibits good resistance to numerous corrosive conditions.
History and Discovery of Monel Alloys
- Robert Crooks Stanley, an International Nickel Company (INCO) employee, created Monel in 1901. Acknowledging the significance of the finding, Stanley dubbed his new invention after INCO President Ambrose Monell, omitting the one L out of the name because names of families weren’t allowed as trademarks at the time.
- The alloy carries Ambrose Monell’s name, who owned the business at the time, and was granted a patent in 1905.
- Roofing of the Pennsylvania Station in New York was done with Monel in 1908.
- Monel was utilized for appliances, countertops, sinks, and roof flashing starting in the 1920s and continuing into the 1930s.
- In 1921, the brand name Monel was submitted for trademark registration.
- Although Monel was one of the most widely used metals in the market until the 1940s, the more adaptable stainless steels took its place starting in the 1950s.
- Special Metals Corporation, a business that specializes in nickel and cobalt alloys, is the current owner of the trademark.
Fabrication of Monel Alloys
- In this class of nickel alloys, silicon, carbon, manganese, and iron are present in trace proportions together with nickel (usually 52–67%) and copper as the main constituents.
- Hot and cold working, machining, and welding are used to create Monel alloys.
- They can endure a fire in pure oxygen as well as are resistant to corrosion from a variety of substances, including quickly running seawater.
- Monel alloy is expensive to produce so it is not applicable in every industry for daily use. It is only used in the adverse environment or the high-risk industries such as aerospace industry, petroleum industries, etc.
Physical Properties of Monel
| Properties | Monel K-500 | Monel R-400 | Monel 400 |
| Density | 8.44 gm/cm3 | 8.8 gm/cm3 | 8.8 gm/cm3 |
| Curie Temperature | – | 28 – 34 TC | 21 – 49 TC |
| Electrical Resistivity @ 100 °C (Annealed) | 0.618 µΩ.m | 0.537 µΩ.m | 0.537 µΩ.m |
| Specific Heat @ 100 °C (Annealed) | 448 J/kg °C | 445 J/kg °C | 445 J/kg °C |
| Thermal Conductivity @ 100 °C (Annealed) (W/m °C) | 19.4 | 24 | 24 |
| Thermal Linear Expansion @ 100 °C (Annealed) | 13.7 µm/m °C | 14.2 µm/m °C | 14.2 µm/m °C |
Types of Monel Alloys
There are six types of Monel alloys but we are going to look into three important Monel here.
Monel 400
- Monel 400 alloy has at least 63% nickel and 28-34% copper, with quite a bit of iron.
- This alloy is a solid-solution alloy that needs to be hardened via cold working. This material exhibits exceptional strength and toughness across a wide temperature range, as well as remarkable corrosion resistance.
- It provides great strength and toughness over a wide temperature range.
- Many industries, particularly the marine and chemical processing industries, employ alloy 400 widely.
- Common uses include valves and pumps, pump and propeller shafts, marine fixtures and fasteners, electrical and electronic components, springs, chemical processing equipment, gasoline and freshwater tanks, crude petroleum stills, process vessels, and piping.
Monel R405
- Alloy R405, a variation of nickel-copper alloy 400, provides high corrosion resistance in a wide range of applications. Alloy R405 is distinguished by its excellent resistance to corrosion with medium to high strength.
- Except for a little increase in sulfur concentration (from 0.024 to 0.06%), this alloy is identical to Monel 400’s composition. The addition of sulfur improves machining over alloy 400.
- The alloy has been employed in a wide range of applications
- It is highly resistant to fast-flowing and warm seawater, brackish water, and steam.
- It is exceptionally resistant to de-aerated hydrochloric and hydrofluoric acids.
- This alloy can exhibit slight magnetic properties at the normal room temperature.
- Alloy R405 is extensively utilized in the chemical, oil, and marine engineering industries.
Monel K-500
- Monel® K-500, is an age-harden nickel-copper alloy. Combining the corrosion resistance of alloy 400 with high strength, corrosion fatigue, and erosion resistance, we get Monel K-500.
- This alloy is a high-strength version of Monel 400 with tiny additions of aluminum and titanium to the base composition,
- Alloy 400’s exceptional resistance to corrosion is maintained in alloy K-500’s chemical composition.
- Alloy K-500 provides approximately three times the yield strength and quadruple the tensile strength of alloy 400. Cold working with K-500 before precipitation hardening gives it significant strength.
- At temperatures below freezing, even at cryogenic levels, the alloy demonstrates exceptional qualities, such as nearly unaltered toughness and ductility.
- It is non-magnetic at temperatures as low as minus 101°C and has limited permeability.
Composition of Monel Alloys
| Elements (in wt.%) | Monel K-500 | Monel R-400 | Monel 400 |
| Nickel | 63 min. | 63 min. | 63 min. |
| Copper | 27-33 | 28-34 | 28-34 |
| Iron | 2 max. | 2.5 max. | 2.5 max. |
| Manganese | 1.5 max. | 2 max. | 2 max. |
| Almunium | 2.3 – 3.15 | 0 | 0 |
| Silicon | 0.5 max. | 0.5 max. | 0.5 max. |
| Sulfur | 0.01 max. | 0.025 – 0.060 | 0.24 max. |
| Titanium | 0.35 – 0.85 | 0 | 0 |
Advantages of Monel Alloys
There are a lot of advantages for using the Monel alloys. Some of the major advantages are:
Corrosion Resistance
Monel alloys are significantly more resistant to the corrosion then steel materials, and they can function steadily in a variety of challenging conditions, including acids, alkalis, salts, and oxides, for extended periods of time.
Stability
In comparison to steel materials, Monel alloys exhibit superior stability at high temperatures, are resistant to deformation and cracking, and are capable of functioning firmly in conditions that are oxidizing at high temperatures for extended periods of time.
Strength
Monel alloys are stronger and can function at higher temperatures than steel materials. Strength and hardness increase with minimal loss of ductility or impact resistance. At temperatures higher than 1300 °C, they can still function effectively and maintain stability. The tensile strength of these alloys can be in the range of 600-1300 MPa at the temperature ranging between 600-1300 °C.
Ductility
Despite being cooled to liquid hydrogen temperatures, the alloy remains ductile and not brittle.
In contrast, many ferrous materials become brittle at low temperatures, despite their increased strength.
Resistant to Oxidation
Monel alloys can perform under severe oxidizing condition for a longer period of time. These alloys are less prone to oxidation and erosion as compared to those of steel materials.
Easy to Work
Monel alloys are easy to work with. They can be processed easily as compared to steel. Various techniques such as forging, rolling, and stretching can be performed with these alloys. This property can be helpful to make parts and components with different shapes. These alloy can be turned into tubes, pipes, rods, bars and plates.
Electrical Conductivity
Monel alloy has good electrical conductivity, which makes it a popular material in electronic components. Its electrical conductivity, while not as high as pure copper, is adequate for most applications.
Mechanical Properties of Monel Alloys
| Properties | Monel K-500 | Monel R-400 | Monel 400 |
| Hardening Procedure | Hot finished and Aged | Cold drawn | Cold drawn and stress relieved |
| Tensile Strength | 695 MPa – 1310 MPa | 586 MPa – 793 MPa | 579 MPa – 827 MPa |
| Elongation | 20 % – 30 % | 15 % – 35 % | 22 % – 40 % |
| Yield Strength (0.2 % Offset) | 690 MPa – 1034 MPa | 345 MPa – 724 MPa | 379 MPa – 690 MPa |
| Hardness (Rockwell) | 27 – 38 C | 23 – 85 B | 20 – 85 B |
Drawbacks of Monel Alloys
Even though Monel alloys has a lots of advantages associated with it; it also has some drawbacks which are discussed here:
Poor Machinability
These alloys have poor machining mainly because of their tendency to immediately work-harden. During machining, Monel metal hardens, making successive cuts more difficult and causing faster tool wear. Monel R-405 was specifically designed to increase machinability.
Pitting
Alloy 400 and nickel-base alloys comprising chromium and iron are extremely resistant with flowing saltwater. However, in stagnant or lower velocity seawater, pitting (a cavity, hole, or pit that forms in a small area or point) or crevice corrosion can occur, especially when exposed to fouling organisms or other types of deposits.
Stress Corrosion Cracking
It has long been recognized that Monel is sensitive to intergranular stress corrosion cracking in fluosilicic acid. It was startling, however, to discover “K” Monel bolts shattering transgranular in hydrofluoric acid vapor.
Galvanic Corrosion
Aluminum, zinc, or iron-based metal fasteners that are used to secure Monel Under some circumstances, will corrode rapidly. A galvanic cell is readily formed when Monel is attached to steel, hastening the corrosion process.
Corrosive to Certain Acids
Although it is corrosion resistant in most situations, it will corrode if subjected to certain contaminants. Nitric oxide, nitrous acid, sulfur dioxide, and hypochlorite are all damaging to Monel.
Expensive Alloy to Produce
Monel alloy is expensive to produce so it is not applicable in every industries for daily use. It is only used in the adverse environment or the high risk industries such as aerospace industry, petroleum industries, etc.
Applications of Monel Alloys
There are some great applications of Monel alloys which are discussed here:
Aerospace Industries
- Monel alloys are appropriate for usage in the aviation industry because of several significant benefits.
- They are very resistant to various types of corrosion and oxidation (since they contain more than 30% copper).
- These alloys also resist reducing media and stress corrosion cracking.
- Monel alloys’ anti-corrosive qualities make them suitable for exhaust manifolds and carburetors in aeronautical projects.
- Monel alloys are commonly used in the aerospace sector to manufacture landing gear parts like as gears and chains, as well as various tubes and pipes.
- Monel alloys can also be employed in combustion chambers since they have their ability to withstand high temperatures and pressure.
Marine Engineering
- Monel’s strong corrosion resistance makes it popular in marine engineering.
- Monel’s corrosion resistance makes it perfect for pipe systems, pump shafts, seawater valves, trolling wire, and strainer baskets.
- Some alloys are fully nonmagnetic and are employed as anchor cables on minesweepers or in housings for magnetic-field measuring equipment.
- It can be found in a variety of applications, including pipes, pump shafts, basket strainers, anchor cables, magnetic field measurement equipment, water and fuel tanks, propellers, bolts, valves, and fishing line.
Petroleum Industry
- Monel is used for alkylation units that come into direct contact with concentrated hydrofluoric acid.
- Monel is commonly used for crude oil towers, extraction wells, and valves, among other applications.
- It is widely employed in slurries involving hydrofluoric acid, sulfides, and extremely high temperatures.
Music Industry
- It is mostly utilized in high-end instruments and their components, where the utmost quality is needed.
- Monel is used for valve pistons or rotors in high-end musical instruments such as trumpets, tubas, and French horns.
- Monel is used in the rotor or piston valves on wind instruments, as well as in the strings of electric guitars and violins.
Chemical Industries
- Monel alloys are used in different chemical industries. They can function steadily in a variety of challenging conditions, including acids, alkalis, salts, and oxide.
- Monel’s strong resistance to oxygen and acid corrosion makes it a valuable material for the chemical industry.
- Monel equipment is capable of handling even corrosive fluorides; this has been demonstrated extensively during the uranium enrichment process at the Oak Ridge Gaseous Diffusion Plant.
Everyday Products
- Among many other things, it is also used production of water tanks and heaters, kitchen sinks, gas boiler parts, and eyeglass frames.
Frequently Asked Questions (FAQs)
What is Monel?
A class of nickel alloys with copper serving as the primary alloying element are referred to as monel. Monel alloys may contain trace amounts of iron, manganese, carbon, silicon, sulfur, aluminum, and titanium, in addition to the two basic metals
What are the advantages of Monel alloy?
The major advantages of monel alloy are: corrosion resistance, formability, and weldability.
What is Monel metal used for in everyday life?
Monel is utilized in marine engineering, chemical and hydrocarbon processing machinery, valves, pumps, shafts, fittings, fasteners, and heat exchangers. It is also utilized in the manufacture of metal instruments and eyeglass frames.
Video Reference
References
- https://meridian.allenpress.com/corrosion/article-abstract/12/12/71/157033/Stress-Corrosion-Cracking-Of-Monel-in-Hydrofluoric?redirectedFrom=fulltext
- https://www.linkedin.com/pulse/what-advantages-nickel-based-alloys
- https://www.ulmaforge.com/en/new/what-is-monel-and-what-is-it-used-for/
- https://www.alloywire.com/alloys/monel-400/
- https://nickelinstitute.org/blog/2021/march/historic-monel-the-alloy-that-time-forgot/
- https://www.langleyalloys.com/knowledge-advice/what-does-monel-mean/
- https://www.neonickel.com/monel-alloys/
- https://www.specialmetals.com/documents/technical-bulletins/monel-alloy-r-405.pdf
- https://www.specialmetals.com/documents/technical-bulletins/monel-alloy-400.pdf
- https://www.xometry.com/resources/materials/what-is-monel/
- https://www.thoughtco.com/monel-alloys-composition-properties-and-uses-2340255
