Alloy 825 (Incoloy® 825, UNS N08825, 2.4858) and Alloy 925 (Incoloy 925, UNS N09925) are nearly identical in composition, so they offer very similar corrosion resistance and physical properties. The difference is strength: Alloy 925 is significantly stronger because it is precipitation strengthened.
Small additions to the composition of Alloy 925 allow microscopic precipitates to form when the alloy undergoes an extended heat treatment. These fine precipitates increase the yield strength by up to 4x.
The Incoloy family
Incoloy is a family of nickel-based alloys primarily alloyed with chromium, produced under a trademark held by Special Metals Incorporated. More than ten grades sit within the family; the two most widely used are Incoloy 825 and Incoloy 925.
Compositions of Alloy 825 and 925
Both grades share a similar composition:
- Nickel: up to 46%, ensuring resistance to stress corrosion cracking and a wider operating temperature range than many stainless steels.
- Chromium: up to 23.5%, improving general corrosion resistance and resistance to a range of acids such as nitric and sulphuric acid.
- Molybdenum: up to 3.5%, giving a general uplift in pitting and corrosion resistance.
- Copper: up to 3%, which improves resistance to acids, particularly sulphuric acid - an effect also exploited in Ferralium® 255 super duplex stainless steel (2% copper) and the more highly alloyed Alloy 20 (3-4% copper).
- Titanium: up to 2.4%, protecting these grades from intergranular corrosion.
Our stock
We stock Alloy 825 as round bar from 5/8"-10" diameter (15.87-254mm), with pipe and hollow bar also available. Alloy 925 is less readily available in the smallest diameters, so our stock typically starts at 4"-10" (101.6-254mm) diameter.