What is the difference between Incoloy 825 and 925?

Incoloy 825 and 925 are very similar in terms of composition and so have near identical physical properties but have very different tensile properties.

Incoloy is a registered trademark of Special Metals Incorporated and is applied to a family of nickel-based alloys primarily alloyed with chromium. There are more than ten different grades currently named within the Incoloy family, but the two most widely used Incoloy grades are Incoloy 825 and Incoloy 925.

Both Incoloy 825 and Incoloy 925 have similar compositions:

Nickel: up to 46%, ensuring resistance to stress corrosion cracking and a wider temperature operating range than many stainless steels.

Chromium: up to 23.5% chromium, which improves their general corrosion resistance, as well as corrosion resistance against a wide range of acids such as nitric acid and sulphuric acid.

Molybdenum: up to 3.5% molybdenum provides a general uplift in overall pitting and corrosion resistance.

Copper: up to 3% copper, which has been widely shown to improve resistance to acids, particularly sulphuric acid. This effect is also exploited in Ferralium 255 super duplex stainless steel (containing 2% copper addition) and the much more highly alloyed Alloy 20 (3-4% copper).

Titanium: up to 2.4% titanium protects these Incoloy grades from intergranular corrosion.

The mechanical properties of Incoloy 925 are achieved through precipitation-strengthening. Small additions of titanium and aluminium combine to form fine precipitates throughout the metal when it is subjected to a secondary heat treatment process. These precipitates help to ‘pin’ the microstructure of the metal when it is subject to an external load, increasing its strength and toughness. Incoloy 925 can therefore provide 3-4 times the tensile strength of the equivalent component supplied from Incoloy 825.

Langley Alloys stocks Alloy 825 as round bars from 5/8”-10” diameter (15.87-254mm). Pipes and hollow bars are also available. Alloy 925 is less readily available in the smallest diameters, so our stock typically starts at 4”-10” (101.6-254mm) diameter.

For More Information  

For more information about our range of alloys, please contact Langley Alloys today.