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.
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.
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.
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.
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.
Monel offers the following advantages and benefits:
Monels have the following disadvantages relative to other potential materials for corrosive environments :
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.
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.
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.
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.
Inconel alloys offer several advantages such as:
Although Inconel comes with a lot of notable advantages, it also has some disadvantages to consider such as:
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.
The properties of Inconel and Monel are outlined in Table 1 and Table 2, respectively.
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