Monel 400 and Inconel 625 are both very commonly used nickel alloys. However, the properties of these two alloys are very different. They also play different roles in practical applications. When you read this article, I believe you must be curious about the similarities and differences between these two alloys.

In this article, we will compare the properties of these two alloys from multiple dimensions. If you don’t know much about these two alloys, this article will definitely answer many of your questions.

Monel 400 is mainly used at room temperature, while Inconel 625 will be used at higher temperatures. Therefore, Inconel 625 has much stricter control of trace elements than Monel 400. The high purity allows Inconel 625 to achieve better creep strength, fatigue strength, lasting performance and transient performance than Monel 400.

Monel 400 and Inconel 625 are both excellent corrosion-resistant alloys. However, their corrosion resistance mechanisms are not the same.

Monel 400's corrosion resistance comes from the copper element. However, copper's corrosion resistance is limited to oxidative corrosion. At the same time, copper loses this corrosion resistance at high temperatures.

Inconel 625 derives its corrosion resistance from chromium and molybdenum. Chromium provides excellent antioxidant properties at any temperature. Molybdenum brings excellent resistance to reduction.

Therefore, compared to Monel 400, Inconel 625 not only has better overall corrosion resistance, but also can resist corrosion at various temperatures. In other words, Inconel 625 can resist a wider variety of corrosion.

Monel 400 and Inconel 625 are both solid solution alloys. Therefore, their strength can only be increased by cold working.

The difference is that Monel 400 does not have very effective solid solution strengthening elements. Its strength is relatively limited. Inconel 625 adds two very effective solid solution strengthening elements to obtain higher strength. They are molybdenum and niobium. Therefore, Inconel 625 has higher strength than Monel 400. At the same time, the strength of Inconel 625 increases more obviously after cold working.

In addition, compared to Monel 400, Inconel 625’s strength at high temperatures is also very impressive. It should be noted that the heat treatment method of Monel 400 is annealing. Inconel 625 has two heat treatment methods. Inconel 625 for use at low temperatures is mainly delivered in the annealed state. Inconel 625 used at high temperatures needs to be delivered as solution treated.

Since Inconel 625 is more comprehensive than Monel 400 in terms of corrosion resistance and mechanical properties, it is also more widely used in applications.

Inconel 625 is more expensive than Monel 400.

First of all, Inconel 625 has a large number of higher-priced metal components (such as molybdenum and niobium, which Monel 400 does not have). This results in a high price for the material itself.

Secondly, Inconel 625 is stronger than Monel 400. Therefore, it is more difficult to process and more expensive to process. For some products with complex processing (such as seamless pipes tubes), the price of Inconel 625 can even be close to twice that of Monel 400.

Monel 400 and Inconel 625 are both nickel alloys. However, the main components of Monel 400 are nickel and copper. The main components of Inconel 625 are nickel, chromium and molybdenum. This difference results in the overall performance of Inconel 625 being better than Monel 400 in terms of corrosion resistance, mechanical properties, etc. Of course, Inconel 625 is also more expensive. Therefore, we recommend choosing less expensive materials if they are available.

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