Many options exist when selecting the right alloy for your industrial or engineering needs. Among those options are two popular choices – Monel 400 and Inconel 625. Although they are nickel-based alloys and share a lot of similarities, they differ in certain key aspects. Before deciding which alloy to use for your next project, it’s important to understand the differences between Monel 400 and Inconel 625 and where they are best suited. Here, we’ll explore these differences in-depth so you can make an informed decision.
What is Monel 400?
Monel 400 is an alloy composed primarily of nickel and copper, along with some iron and trace amounts of other elements. It is known for its strength, durability, corrosion resistance, and ability to withstand high temperatures. Its toughness makes it excellent for use in environments exposed to various external factors like chemical attacks or extreme temperature changes. Monel 400 can be found in marine components, gas turbine engines, pumps & valves, and pharmaceutical and food processing equipment.
What is Inconel 625?
Inconel 625 is a nickel-based alloy with superior strength and resistance to corrosion, oxidation, and extreme temperatures. It is highly malleable and weldable, making it ideal for applications in aerospace engineering, petrochemical processing, power generation systems, and chemical process equipment. The alloy features excellent fatigue strength and high creep-rupture properties when exposed to temperatures up to 1300°F (704°C).
Difference Between Monel 400 and Inconel 625
Monel 400 is composed of nickel-copper alloy, while Inconel 625 is an alloy of nickel, chromium and molybdenum. Monel 400 has good corrosion resistance to various corrosive conditions, whereas Inconel 625 has increased strength and excellent corrosion resistance in oxidizing and reducing environments. Additionally, Monel 400 can be used in temperatures up to 1000°F (538°C), while Inconel 625 can withstand temperatures up to 2000°F (1094°C).
Composition
One of the most significant differences between Monel 400 and Inconel 625 is their composition. Monel 400 is a nickel-copper alloy that contains a minimum of 63% nickel, while Inconel 625 contains a minimum of 58% nickel and chromium and molybdenum. Monel 400 also has a higher copper content (up to 34%), while Inconel 625 contains only negligible copper. Therefore, Monel 400 is more expensive than Inconel 625. On the other hand, Inconel 625 is more resistant to corrosion and chemical attack due to the presence of high levels of nickel and chromium.
Use Cases
Monel 400 is ideal for high-temperature and acidic environments, such as sulfuric acid processing plants, hydrofluoric acid alkylation units, and marine environments for seawater applications. It is also preferred for applications involving strong oxidizing agents like nitric acid. In contrast, Inconel 625 is ideal for high-stress and high-temperature applications, particularly in offshore and marine environments, due to its high tensile strength, toughness, and excellent corrosion resistance. Inconel 625 is also highly resistant to pitting and crevice corrosion, making it well-suited for aggressive environments.
Physical Properties
Regarding physical properties, Monel 400 has a density of 8.8 g/cm³, a melting point of 1300°C, tensile strength of 480 MPa, and yield strength of 205 MPa. It is highly resistant to corrosion and can withstand high-temperature and acidic environments. On the other hand, Inconel 625 has a density of 8.44 g/cm³, a melting point of 1290°C, tensile strength of 930 MPa, and yield strength of 415 MPa. It also exhibits excellent corrosion resistance and is highly resistant to oxidation and stress corrosion cracking.
Cost
The cost is an important consideration when selecting an alloy for your project. The precise cost will depend on various factors, such as the alloy’s quantity, size, shape, and grade. Monel 400 is more expensive than Inconel 625 due to its higher nickel and copper content. However, Monel 400 is still a widely used alloy due to its excellent corrosion resistance and ability to withstand high-temperature and acidic environments.
Conclusion
When it comes to choosing between Monel 400 and Inconel 625, there is no clear winner. Both alloys are excellent choices but differ in composition, use cases, physical properties, and cost. Therefore, the ultimate choice depends on the specific needs of your project. If you require an alloy that can withstand high-temperature and acidic environments, Monel 400 is an excellent choice. However, if you need an alloy that offers superior corrosion resistance and is resistant to pitting and crevice corrosion, Inconel 625 is a better option. Talk to your supplier to understand the specifics and get their recommendation based on your needs.
