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.

Understanding Monel

Below, we detail the unique properties of Monel that can make it a great choice for use depending on the specific application.

Mechanical Properties

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.

Thermal Properties

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.

Chemical Properties

Monel often replaces stainless steel as an ideal material for corrosion resistance. 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
Hydrochloric acid	Acceptable
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

Machinability

Monel is very difficult to machine, as it 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 properties 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 alloys are 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
  • Blades
  • 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

Monel alloy 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, Monel 400 is highly used in the chemical, oil, and marine industries.

Monel 401

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

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 405

Monel is a free-machining version of Monel alloy 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.

Monel K-500

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 metal alloys. It’s often a challenge for small machine shops and fabricators to procure Monel 400 in small amounts for specific applications. One of the best ways to mitigate this challenge is to purchase verified Monel 400 remnants available at a low price from a local metal supplier.

Purchase Monel and Other High-Temperature Metals from a Reliable Metal Supplier