Difference Between Inconel 625 and 825

The key difference between Inconel 625 and 825 is that the Inconel 625 contains a high amount of nickel compared to the Inconel 825.

Inconel is a nickel-based superalloy. We can grade this alloy differently, according to the amount of nickel present in the alloy and considering many other parameters. Inconel 625 and Inconel 825 are two such grades. More importantly, we should not confuse with the two terms Inconel and Incoloy; although both of these are nickel-based alloys, they are different commercial brands with different chemical and physical properties.

1. Overview and Key Difference
2. What is Inconel 625
3. What is Inconel 825
4. Side by Side Comparison – Inconel 625 vs 825 in Tabular Form
5. Summary

What is Inconel 625?

Inconel 625 is a nickel-based superalloy containing a high amount of nickel than other grades of Inconel. It has high strength and great resistivity to higher temperatures. Moreover, it shows great protection against corrosion and oxidation. These specific properties make it very useful in nuclear and marine applications.

Figure 01: A Refractory lined joint fabricated with Inconel 625

The service temperatures of this superalloy range from cryogenic to 982°C. The high strength of this alloy is due to the stiffening effect of molybdenum and niobium, which locates in the nickel-chromium matrix. Therefore, this alloy does not require precipitation hardening treatments. The high corrosion-fatigue strength, high tensile strength and the resistance to chloride-ion stress-corrosion cracking make this alloy an excellent choice for seawater applications.

Apart from that, Inconel 625 shows an excellent ductility and toughness at low temperatures. When considering the microstructure of this alloy, it is a solid-solution matrix-stiffened face-centred-cubic alloy. Moreover, this alloy contains carbides rich with nickel, chromium, molybdenum, etc.

What is Inconel 825?

Inconel 825 is a nickel-based superalloy containing a moderate amount of nickel when compared to other grades of Inconel. It has a higher melting point but has a low tensile strength and a low yield strength. This alloy contains nickel and chromium along with molybdenum, copper and titanium. It has an exceptional corrosion resistance specifically, to aqueous corrosion. Moreover, it shows resistance to oxidizing and reducing acids, such as sulfuric acid, phosphoric acid, etc.

What is the Difference Between Inconel 625 and 825?

Inconel 625 is a nickel-based superalloy containing a high amount of nickel than other grades of Inconel whereas Inconel 825 is a nickel-based superalloy containing a moderate amount of nickel when compared to other grades of Inconel. The major difference between Inconel 625 and 825 is the nickel content; Inconel 625 contains about 58% of nickel while Inconel 825 contains about 36-48% of nickel. Moreover, they have different melting points as well. The melting point of Inconel 625 is 1350◦C, but it is 1400◦C for Inconel 825. Apart from that, another important difference between Inconel 625 and 825 is their strength; Inconel 625 has a very high tensile strength and a yield strength when compared to Inconel 825.

Summary – Inconel 625 vs 825

Both Inconel 625 and 825 are two commercial brands of nickel-based superalloys. They contain nickel and chromium as the main components. The key difference between Inconel 625 and 825 is that the Inconel 625 contains a high amount of nickel compared to the Inconel 825.

Reference:

1. “Inconel 625.” Wikipedia, Wikimedia Foundation, 9 July 2018. Available here
2. Steel, Hitesh. Difference Between Inconel 625 and 825. Available here