In environments where temperatures are high, many metals lose their strength, corrosion resistance, and other unique selling properties. However, superalloys of nickel and other specialty metals can be extremely useful for high-temperature applications. In this regard, Monel is one of the best nickel alloys for moderately high-temperature applications up to 900°F and is ideal for harsh conditions like refinery components.
What is Monel? Monel is a nickel-based superalloy containing nearly two-thirds nickel and one-third copper. Monel and its alloys are highly sought-after for highly corrosive marine and chemical applications.
This article offers essential knowledge to help you better understand Monel and its alloys as well as the applications it’s generally used for.
Below, we detail the unique properties of Monel that can make it a great choice for use depending on the specific application.
Some essential mechanical properties of Monel are as follows:
- Density: 8400
- Specific gravity: 8.80 at 2,372-2,462°F (Monel 400)
- Young’s Modulus: 1.8
- Poisson’s ratio: 0.31
- Hardness: 65 Rockwell B (Monel 400)
Monel is a very tough material. Unlike stainless steel, it does not dent when subjected to high force. Post-cold-working, its strength can be increased up to 125,000 psi. However, the parts made out of Monel are heavier as compared to stainless steel due to Monel’s high density.
Some essential thermal properties of Monel include:
- Thermal expansion: 14
- Thermal conductivity: 20
- Specific heat: 427
Monel retains its strength at very high temperatures; however, it also displays excellent mechanical properties at subzero temperatures as well. This is highly unlikely in other ferrous materials. In general, ferrous materials become too brittle at low temperatures despite their increased strength. However, for Monel, the mechanical strength increases with only a slight impairment of ductility at low temperatures.
Monel often replaces steel as an ideal corrosion-resistant material. Monel 400, in particular, is used for handling sulfuric acid solutions under reducing conditions. Monel 400, R-405, and K-500 alloys are resistant to chloride cracking. The table below shows the corrosion resistance behavior of these three alloys in different acidic environments.
|Acidic Environment||Monel 400, R-405, K-500|
|Sulfuric acid||Good to excellent|
|Hydrofluoric acid||Good to excellent|
|Phosphoric acid||Good to excellent|
|Nitric acid||Not suitable|
|Organic acids||Good to excellent|
|Alkalines & salts||Good to excellent|
|Seawater||Good to excellent|
Monel is very difficult to machine, as it work hardens rapidly. Cutting Monel generates a lot of heat that can affect the blade life and wear out the saw teeth. The localization of heat at the surface can even affect the structure and property of materials, so Monel must be machined at a slow speed and with low feed rates. Most importantly, the right industrial saw must be used to cut high-temperature metals to the dimensions and tolerances required without heat distortion and work hardening.
What is Monel Used for in Industrial Applications?
Monel is highly used for highly corrosive applications. Additions of aluminum and titanium can further increase its strength. Some common applications of Monel are as follows:
- Oil and refinery
- Feedwater heaters
- Pump shafts
- Oil well tools
- Propeller shafts
- Musical instruments
- Marine applications
- Pumping shafts
- Seawater valves
- Aerospace applications
- Frame structures
- Holding parts
- Exhaust assemblies
- Safety wires
Though Monel is a great option for moderately high-temperature applications, for extremely high service temperatures (above 2,000°F), true high-temperature specialty metals like Inconel, molybdenum, Hastelloy, and tungsten could be a better choice.
Grades of Monel
Monel is available in five different grades, listed below:
Monel 400 is one of the most widely used Monel alloys, as it is particularly resistant to hydrochloric and hydrofluoric acids under de-aerated conditions. Therefore, this alloy is highly used in the chemical, oil, and marine industries.
Because of its low coefficient of electrical resistivity under corrosive conditions, Monel 401 is used in electrical and electronics applications as strips and wires.
Monel 404 is an ideal choice for applications that require retaining strength over a wide range of temperature differences under harsh environments. It also displays excellent brazing and low permeability, ideal for specialized electronics applications.
Monel is a free-machining version of Monel 400 with comparatively higher sulfur content. Due to its high sulfur content, it offers excellent machinability and is recommended for use with automatic screw machines.
It exhibits the excellent corrosion resistance of Monel 400 alloy but with improved strength and hardness. This non-magnetic alloy is highly used in extreme marine and chemical environments.
Monel is Useful but Can Be Expensive
Monel is a nickel-based alloy. Unlike steel, nickels are very hard to mine. That’s why Monel 400 costs six to eight times more than 304 stainless steel alloys. It’s often a challenge for small machine shops and fabricators to procure Monel in small amounts for specific applications. One of the best ways to mitigate this challenge is to purchase verified Monel remnants available at a low price from a local metal supplier.
Purchase Monel and Other High-Temperature Metals from a Reliable Metal Supplier
Specialty metals are always in demand yet can be hard to procure in small amounts for small-scale manufacturing requirements. Industrial Metal Service has been providing high-temperature specialty alloys to machinists and small shop owners in the San Francisco Bay Area and beyond for more than two decades. We supply a wide inventory of specialty metals, such as Monel, Invar, tungsten, and molybdenum, at a fair market price, and we stock new metals sourced straight from U.S. mills as well as verified metal remnants to meet your budget requirements.