Incoloy 825 and Incoloy 925 are two alloys whose corrosion resistance is almost identical. The difference is entirely in strength — 925 is the precipitation hardening version of 825.
When aluminium is added
According to our datasheets, nickel is 38.0–46.0% in 825 and 42.0–46.0% in 925. The chromium, molybdenum and copper contents are very close: Mo 2.50–3.50% and Cu 1.50–3.00% in 825; the same ranges in 925.
The decisive difference is in two elements: titanium rises from 0.60–1.20% in 825 to 1.90–2.40% in 925, and aluminium, present only at impurity level in 825, is deliberately included in 925 in the 0.10–0.50% range.
Together, titanium and aluminium form gamma prime precipitates with nickel during the ageing treatment. While 825 can only be used in the annealed condition, 925 can be aged to a far higher yield and tensile strength — without giving up corrosion resistance.
Carbon is lowered as well: max 0.05% in 825 against max 0.03% in 925.
Comparison in numbers
| PROPERTY | Incoloy 825 | Incoloy 925 |
|---|---|---|
| Nickel (Ni) | 38.0 – 46.0% | 42.0 – 46.0% |
| Chromium (Cr) | 19.5 – 23.5% | 19.5 – 22.5% |
| Iron (Fe) | min 22.0% | min 22.0% |
| Molybdenum (Mo) | 2.50 – 3.50% | 2.50 – 3.50% |
| Copper (Cu) | 1.50 – 3.00% | 1.50 – 3.00% |
| Titanium (Ti) | 0.60 – 1.20% | 1.90 – 2.40% |
| Aluminium (Al) | max 0.20% | 0.10 – 0.50% |
| Carbon (C) | max 0.05% | max 0.03% |
| Niobium (Nb) | — | max 0.50% |
| Manganese (Mn) | max 1.00% | max 1.00% |
| Hardening | Annealed (not hardenable) | Precipitation (ageing) |
| UNS | N08825 | N09925 |
| W.Nr (DIN/EN) | 2.4858 | — |
Values are taken from our product datasheets; section thickness and the applied heat treatment regime change the result.
Which one, and when?
Incoloy 825 is sufficient — acid process tanks and piping, heat exchanger tubes, chemical process equipment, seawater lines. Where strength is secondary and the part does not carry very high stress under pressure.
Incoloy 925 is required — oil and gas wellhead equipment, downhole components, subsea valves and fasteners, highly stressed parts in “sour” service containing H₂S. API specifications call out the 925 class directly for these applications.
A practical rule: the environment is the same, the stress is not. In corrosion terms both do the same job; if the part has to carry load, the move is to 925.
Neighbouring alloys
For its high-temperature sibling, see our Incoloy 800H – 825 comparison; for higher corrosion resistance, Inconel 625 and Hastelloy C-276.
Technical datasheets
Incoloy 825 — chemical composition, mechanical values, standard equivalents
Incoloy 925 — chemical composition, mechanical values, standard equivalents
Both grades are supplied to order in round bar, flat bar, plate, sheet, pipe and forged forms. Contact us for a quotation.