Monel® vs. Inconel®: What Are the Key Differences?

Inconel® and  Monel® are two different nickel-based alloy families. The main alloying element in Inconel grades is chromium, with smaller additions of other alloys that make it suitable for extreme high-temperature service. The major addition to the nickel in alloys of the Monel group is copper, which gives these alloys excellent corrosion resistance in moderately high-temperature environments.

This article explores and compares these two alloy types in terms of their composition, how they are made, types, properties, uses, and advantages and disadvantages. 

What Is Monel?

Monel is a trademarked name for a group of nickel alloys, primarily composed of nickel, copper, and small amounts of other elements such as iron and manganese, among others. However, the exact composition of a certain type of Monel will depend on the desired properties and intended use. Monels are typically known for their corrosion resistance (in both fresh and saltwater environments) and high strength, as well as their good low- and medium-temperature resistance. Monel alloys are often used in environments where corrosion and erosion are significant concerns, such as in the marine and chemical processing industries.

To learn more, see our guide on What is Monel Material.

What Is Monel Made Of?

Alloys in the Monel family consist of 52-67% nickel, approximately 28-34% copper, and small amounts of other elements, such as: iron, manganese, aluminum, silicon, sulfur, titanium, and carbon. 

How Is Monel Made?

Monel is typically manufactured through a multi-step process of melting and casting. The process begins with high-purity nickel and copper — the primary components of Monel. These raw materials are melted in a furnace, often an electric arc or induction furnace. Alloying elements, including small amounts of iron, manganese, silicon, and others, are carefully added to attain specific mechanical and chemical properties. Once the alloy is molten, it is cast into the desired shape, such as ingots or billets. It can also be continuous cast. 

Following casting, the alloy undergoes various forming processes to achieve its final form. These may include:  hot rolling, cold rolling, forging, extrusion, cast-to-shape products, Monel powders, and additive manufacturing (3D printing). Through methods, the alloy is either molded into the intended shapes, such as: sheets, bars, plates, rods, or wires, or shaped into the final product through processes like 3D printing. 

Some Monel alloys may undergo heat treatment to optimize their mechanical properties. This involves controlled heating and cooling to induce specific microstructural changes. Finally, the finished Monel products may undergo additional processes, such as machining and polishing, to meet precise dimensional specifications and surface finish requirements. 

What Are the Different Types of Monel?

There are a lot of different Monel alloy grades available in the market. Each of these grades has a somewhat different alloy composition and mechanical properties and therefore has different applications. Some of the common Monel grades include Monel 400, 401, 404, 405, 450, K-500, and 502. 

Each Monel grade serves specific needs dictated by its composition and mechanical attributes. Alloy 400 exhibits high strength and corrosion resistance, making it suitable for hydrocarbon processing, marine use, and heat exchangers. Alloy 401, with compatible brazing properties (its ability to be joined effectively with other metals using a brazing process), finds application in electrical and electronic contexts, such as: precision electronic components, electronic assemblies, and electronic connectors and contacts. The ability to be effectively brazed is important in electronic and electrical applications because it allows for the creation of strong, reliable joints between different components. The compatibility of Monel 401 with brazing means it can be securely joined to other metals without compromising its integrity or the functionality of the electronic device. Alloy 404, known for its low magnetic permeability, is used in electrical and electronic applications. Alloy 405, is essentially a free-machining version of Monel 400. It shares many of the same properties as Monel 400, including its high strength and corrosion resistance. The primary distinction between Monel 405 and Monel 400 lies in Monel 405's increased sulfur content, which is specifically added to enhance its machinability.

What Are the Advantages of Monel?

Monel offers the following advantages and benefits:

1. Combination of high strength and exceptional corrosion resistance. It has good corrosion resistance properties in different environments. This includes resistance to acids, alkalis, and fresh and saltwater exposure. Its corrosion resistance surpasses that of other common corrosion-resistant metals such as 316 stainless steel. 
2. Monel, particularly Monel 400, has a higher yield and tensile strength compared to 316 stainless steel.
3. Monel has a lower coefficient of thermal expansion compared to austenitic stainless steels. This is a significant advantage in applications where dimensional stability is critical under varying temperature conditions.
4. Can be easily welded, soldered, and brazed.
5. Performs well in both low- and high-temperature applications. It maintains its strength in temperatures ranging from sub-zero to 480 °C. 
6. Monel is non-magnetic and has a very low Curie point.
7. A key benefit of wrought, nickel-based alloys known for their corrosion resistance is their strong ability to withstand chloride-induced stress corrosion cracking (SCC). This type of corrosion is a common issue for stainless steels. Interestingly, it has been observed that the resistance of these nickel alloys to SCC decreases as their iron content increases. This implies that nickel alloys with lower iron content are more effective in resisting this particularly damaging form of corrosion. However, both Monel K-500 and Alloy 400 are vulnerable to stress corrosion cracking, but they are generally still considered better than austenitic stainless in that regard.

What Are the Disadvantages of Monel?

Monels have the following disadvantages relative to other potential materials for corrosive environments :

1. Their rate of work hardening during machining is very high. This makes subsequent cuts more challenging and contributes to accelerated tool wear. To address this, Monel R-405 has been specially developed to enhance machinability.
2. Although Monels exhibit resistance to fast-flowing seawater, they are susceptible to pitting corrosion when exposed to seawater for extended periods at low flow velocities.
3. Galvanic corrosion can occur when certain metals, including aluminum, zinc, and iron, are in direct contact with Monel and simultaneously exposed to harsh weather elements. As a result, using these metals as fasteners or connectors in conjunction with Monel is generally not advisable to prevent corrosion.
4. Are expensive due to their composition. These alloys are more expensive than some alternative materials with similar properties, such as duplex stainless steel, particularly grades like 2205.

What Is Inconel?

The name Inconel refers to a group of nickel-based superalloys that have chromium as their major alloying element (14-31 wt %) and may contain iron, molybdenum, copper, titanium, aluminum, and niobium in smaller amounts to enhance specific mechanical or physical properties. The Inconels are renowned for their outstanding corrosion and oxidation resistance, impressive strength at high temperatures, and excellent mechanical properties. 

Inconel alloys are well-suited for use in extreme environments, including high-temperature and corrosive conditions. They are strong, ductile, and creep- and oxidation-resistant under conditions of elevated temperature, making them valuable in industries such as: aerospace, chemical processing, and marine engineering. Some of their applications include use in nuclear reactors and gas turbines, for example.

What Is Inconel Made Of?

The exact composition of Inconel can vary greatly from grade to grade. The initial Inconel alloy, designated as Inconel 600, has a composition comprising over 72% nickel, 14–17% chromium, 6–10% iron, and approximately 1% manganese. Additionally, traces of other elements such as copper, silicon, carbon, and sulfur are present. The proportions of these constituents can vary, and other alloys within the Inconel family incorporate additional elements to tailor their properties for specific applications. These supplementary elements may include niobium, molybdenum, cobalt, tantalum, titanium, lead, aluminum, and boron, each contributing distinct characteristics to the alloy, such as: enhanced corrosion resistance, high-temperature strength, and other desirable mechanical properties. 

How Is Inconel Made?

The production of Inconel alloys involves melting nickel with chromium and other elements such as iron, molybdenum, and niobium in precise proportions to achieve the desired material properties. This is done using an electric arc or vacuum induction furnace. The molten alloy is then cast into forms such as ingots or billets. After solidification, the alloy undergoes heat treatments, including solution annealing, quenching, and precipitation hardening (age hardening) to enhance its mechanical properties and resistance to corrosion. Solution annealing involves heating the alloy and rapidly cooling it, while precipitation hardening further strengthens the alloy by heating it at lower temperatures for an extended period. Once heat treated, the Inconel is formed into various shapes like sheets, bars, or tubes through methods like forging or extrusion. The process concludes with finishing steps such as machining or surface treatments to achieve the desired dimensions and surface quality. The specific conditions for each step vary depending on the Inconel grade, aiming to optimize strength, ductility, and corrosion resistance.

What Are the Different Types of Inconel?

Just like Monel, Inconel is available in many different grades, each with its own composition and use cases. Some common types of Inconel include: Inconel 600, Inconel 601, Inconel 625, Inconel 690, Inconel 718, Inconel X-750, and Inconel 792. Inconel 600, the original Inconel alloy, is known for its heat and corrosion resistance, making it suitable for chemical plant components. Inconel 601 excels in high-temperature organic-chemical plants — displaying excellent oxidation resistance and resistance to carburization. Inconel 625 surpasses both 601 and 600 in corrosion resistance, creep resistance, and in retaining strength up to 980 °C. 

Inconel 718 is designed for precipitation hardening and provides good strength and toughness up to 650 °C, with corrosion/oxidation resistance. Inconel X-750 has even better corrosion resistance and oxidation resistance than Inconel 718, which is especially beneficial for aerospace and industrial gas turbine components. Inconel 690 offers superior resistance to chloride corrosion and finds application in environments like: nitric acid, steam generators, and nuclear waste treatment plants. Lastly, Inconel 702, is a casting alloy with notably high strength.

What Are the Advantages of Inconel?

Inconel alloys offer several advantages such as:

1. Have exceptional corrosion resistance, especially in harsh environments.
2. Retains their strength and structural integrity at high temperatures. 
3. Exhibit excellent oxidation resistance.
4. Different grades of Inconel are tailored to provide specific combinations of such properties as corrosion resistance, strength, and heat resistance.
5. Inconel alloys, particularly certain grades, such as Inconel 625, demonstrate excellent resistance to creep deformation at high temperatures, ensuring long-term structural stability in demanding conditions.
6. Exhibit good fatigue strength, allowing them to withstand cyclic loading and prolonged use without experiencing failure.
7. Generally weldable.

What Are the Disadvantages of Inconel?

Although Inconel comes with a lot of notable advantages, it also has some disadvantages to consider such as: 

1. Are expensive
2. Are hard to work and are hard to machine.
3. Some grades, like Inconel 718 are also sensitive to hydrogen embrittlement.

How To Choose Between Monel and Inconel

When deciding between Monel and Inconel, several key factors come into play, such as: the specific application requirements, cost considerations, and the environmental conditions the alloys will face. 

Both are nickel-based alloys, with Monel incorporating copper as its secondary alloyant, and Inconel utilizing chromium. In terms of performance, Monel excels at corrosion resistance in very aggressive solutions up to mid-range temperatures, and Inconel excels at high-temperature strength, creep resistance, and oxidation resistance. Price-wise, Inconel is generally considered to be more expensive than Monel, primarily due to its composition, which often includes higher amounts of nickel and chromium. However, it's important to note that the cost difference is not fixed and can vary based on several factors. These include fluctuations in commodity prices, particularly for nickel and chromium, as well as the specific grades and alloy compositions being considered. Market conditions and the demand for specific alloy properties can also impact the relative pricing of Inconel and Monel. Corrosion resistance is excellent in both alloys, with Monel excelling in seawater resistance due to its copper content, but Inconel 625 also does particularly well in seawater conditions. However, Inconel's high-temperature oxidation resistance is a key characteristic that sets it apart, especially in applications where exposure to high temperatures and oxidizing conditions is a primary concern. 

Monel, while excellent in corrosion resistance, also has a respectable high-temperature performance for a range of applications. It can typically operate effectively in temperatures up to approximately 600 °C (1112 °F). Inconel, on the other hand, is known for its exceptional high-temperature capabilities due to its higher nickel and chromium content. It can maintain its strength and resist oxidation at much higher temperatures, often up to around 982 °C (1800 °F) or more, depending on the specific grade. 

The alloys also differ in their melting points, densities, and heat treatment methods. Additionally, Inconel alloys have a higher yield strength and tensile strength than Monel, making them suitable for applications such as structural products or for use in chemical plants.

When looking at common applications, Monel is often used in marine hardware, chemical processing equipment, and hydrocarbon processing systems. Inconel, in contrast, is frequently utilized in turbine blades, nuclear reactor components, and exhaust systems in high-performance automotive and aerospace industries. These applications reflect the alloys' respective strengths in corrosion resistance and high-temperature performance.

What Are the Properties of Monel and Inconel?

The properties of Inconel and Monel are outlined in Table 1 and Table 2, respectively. 

Can You Laser Weld Monel and Inconel?

Yes, both Monel and Inconel can be laser welded, however this is only true for some grades. Grades that can be welded include: Monel 400, Inconel 600, Inconel 718, and Inconel 825.  

To learn more, see our full guide on What is Laser Welding.

Is Monel Harder Than Inconel?

Monel and Inconel can exhibit similar high strength and hardness, but within each alloy family, the hardness depends on the particular alloy composition and heat-treatment condition of a given sample. It is, however, common for Inconel alloys to be stronger and harder than Monels. 

Can You Laser Cut Monel and Inconel?

Yes, both Monel and Inconel alloys can be laser cut. However, they can be challenging to cut because of their high reflectivity and melting temperatures. This can be overcome with the right equipment and cutting parameters. 

Fiber lasers are ideal for cutting reflective materials such as Monel and Inconel. Different grades of Monel and Inconel will, however, perform differently with laser cutters due to their differences in properties. Inconel 718 is one of the materials that performs well with a laser cutter. Monel 400 has also been successfully cut using laser technology. 

Does Inconel Rust?

No, Inconel is a nickel-based alloy with minimal iron content and does not rust like iron-based alloys do. Rust is specific to iron and steel, involving the formation of iron oxides. Instead, Inconel forms a tightly adherent oxide passivating layer that protects the metal from further corrosion. This oxide layer is primarily composed of chromium oxide, which forms on the surface of the Inconel when it is exposed to oxygen. The presence of this protective layer is a key factor in Inconel's high corrosion resistance, particularly in extreme environments. 

While Inconel is highly resistant to various forms of corrosion, including pitting and crevice corrosion, it is not immune to all types of corrosion, particularly in extreme conditions. However, its corrosion resistance exceeds that of stainless steel, but this comes with a higher price point. Inconel alloy 625 is particularly known for its excellent corrosion resistance, including seawater applications, with resistance to both pitting and crevice corrosion. Additionally, it possesses high tensile strength, high corrosion-fatigue strength, and is resistant to chloride-ion stress-corrosion cracking.

What Are the Applications of Monel and Inconel?

Monel and Inconel each have their ideal use cases. Each grade within the Monel and Inconel families has its unique composition and thus specific properties that make it suitable for certain environments and uses. For example, some grades might be more resistant to certain types of corrosion, while others might have better high-temperature strength or resistance to thermal cycling.

Therefore, when selecting a grade of Monel or Inconel for a particular application, it's important to consider the specific environmental conditions, temperature ranges, mechanical stresses, and corrosion types that the alloy will encounter. 

The general applications for both of these alloy groups are listed below. The exact applications of specific types, will, however, be slightly different based on their composition and properties. 

Common applications for Monel alloys are:

1. Monel alloys, particularly Monel 400 and Monel K-500, are used in marine applications due to their excellent resistance to corrosion from saltwater and other harsh marine environments. They are used in: propeller shafts, seawater valves, pump shafts, and other components in shipbuilding.
2. They are used in equipment such as: heat exchangers, reaction vessels, and piping systems. This is especially true for Monel grades 400 and 404. 
3. Monel alloys, including Monel K-500, are used in aerospace applications where moderate high-temperature strength and excellent corrosion resistance are required.  They can be found in components like aircraft frames, exhaust systems, and rocket engines.
4. They are used in oil and gas extraction and processing equipment where resistance to corrosive environments is crucial. Applications include: valves, pumps, and tubing. Monels used for these applications include Monel 400 and Monel 500.
5. Monel 404 is utilized in electronics for its high electrical conductivity and low magnetic permeability. They can be found in electronic components and connectors.

Common applications for Inconel alloys are:

1. They are used in aerospace applications — especially jet engines — due to their ability to withstand high temperatures and extreme conditions. Components fabricated from Inconels include: turbine blades, exhaust systems, fuel nozzles, afterburner rings, and other parts in aircraft engines. Inconel can also be found in rocket engines and space vehicles. Common alloys in the aerospace industry include Inconel 718 and 625. 
2. They are utilized in the nuclear power industry, particularly for nuclear reactor vessels. These reactor vessels demand high strength, good high-temperature performance, and high corrosion resistance. Common alloys found in this industry include Inconel 690 and 600. 
3. Inconel alloys, known for their excellent oxidation resistance at both high and low temperatures, are ideal for manufacturing processes involving rapid temperature changes. This includes equipment used in heat treatments, where Inconel baskets can hold materials like steel or titanium alloys. These baskets withstand extreme temperature variations from near-cryogenic lows to high-temperature heat treatment, maintaining structural integrity and minimizing thermal expansion or contraction. 
4. Inconel alloy 625, renowned for its high-temperature strength, corrosion resistance, and durability, is used extensively in the automotive industry, particularly in high-performance and supercars. Its primary application is in the fabrication of exhaust systems. This is crucial in Formula 1 and other high-performance vehicles where the exhaust must withstand extreme heat and corrosive conditions. Beyond the exhaust systems, Inconel 625 is also employed in other engine components, turbochargers, braking systems, and certain electrical components like connectors and protective casings.
5. Find numerous applications in seawater environments, particularly in offshore platforms and power/processing plants using seawater as a coolant. Inconel alloy 625 is utilized in wire ropes, propulsion motors, propeller blades, and sheathing for undersea communication cables in corrosive seawater conditions. Other marine uses include: down-hole equipment, platform risers, hangers, and high-strength fasteners.

How Much Do Monel and Inconel Cost?

The cost of Monel and Inconel alloys is influenced by their high nickel content and the inclusion of other expensive alloying elements. In Monel, copper is a significant element alongside nickel, contributing to its corrosion resistance and strength. Inconel, however, includes a considerable amount of chromium, enhancing its high-temperature strength and corrosion resistance. Chromium, being more expensive than copper, contributes to Inconel's higher cost. Additionally, Inconel often contains other costly elements like niobium, titanium, and molybdenum, further increasing its price. Both alloys are more expensive than standard stainless steel, with Inconel generally commanding a higher price due to its specialized alloy composition for superior performance in extreme conditions.

Summary

This article presented Monel® and Inconel®, explained each of them, and discussed their various key differences. To learn more about Monel® and Inconel®, contact a Xometry representative.

Xometry provides a wide range of manufacturing capabilities and other value-added services for all of your prototyping and production needs. Visit our website to learn more or to request a free, no-obligation quote.

Copyright and Trademark and Notices

1. Inconel® and Monel® are registered trademarks of Special Metals Corporation. 

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