Incoloy 800H and Incoloy 825 are two members of the same brand, but they solve different problems. 800H is a temperature alloy, 825 a corrosion alloy.
Molybdenum and copper, nickel and titanium
According to our datasheets, 800H has nickel at 30.0–35.0%, chromium at 19.0–23.0% and iron at min 39.5%. There is no molybdenum or copper. In exchange, carbon is held deliberately high in the 0.05–0.10% range and aluminium and titanium are added at 0.15–0.60%.
The high carbon forms carbides at the grain boundaries and raises creep strength — that is the point where 800H departs from standard 800. Aluminium and titanium form a stable oxide layer on the surface and provide resistance to carburisation and oxidation.
In Incoloy 825 the picture is different: nickel rises to 38.0–46.0%, 2.50–3.50% molybdenum and 1.50–3.00% copper are added, and carbon is reduced to max 0.05%. Titanium at 0.60–1.20% provides stabilisation.
The high nickel gives resistance to stress corrosion cracking, the molybdenum to pitting corrosion, and the copper to sulphuric acid. The low carbon prevents intergranular corrosion after welding. In short, 825 is an acid and chloride alloy from end to end.
Comparison in numbers
| PROPERTY | Incoloy 800H | Incoloy 825 |
|---|---|---|
| Nickel (Ni) | 30.0 – 35.0% | 38.0 – 46.0% |
| Chromium (Cr) | 19.0 – 23.0% | 19.5 – 23.5% |
| Iron (Fe) | min 39.5% | min 22.0% |
| Molybdenum (Mo) | — | 2.50 – 3.50% |
| Copper (Cu) | max 0.75% | 1.50 – 3.00% |
| Carbon (C) | 0.05 – 0.10% | max 0.05% |
| Aluminium (Al) | 0.15 – 0.60% | max 0.20% |
| Titanium (Ti) | 0.15 – 0.60% | 0.60 – 1.20% |
| Ti + Al | 0.30 – 1.2% | — |
| Manganese (Mn) | max 1.50% | max 1.00% |
| Silicon (Si) | max 1.00% | max 0.50% |
| Sulphur (S) | max 0.015% | max 0.03% |
| UNS | N08810 | N08825 |
| W.Nr (DIN/EN) | 1.4958 | 2.4858 |
| EN chemical symbol | X10NiCrAlTi32-20 | NiCr21Mo |
Values are taken from our product datasheets; section thickness and the applied heat treatment regime change the result.
Which one, and when?
Incoloy 800H is required — ethylene and hydrogen production furnace tubes, heat treatment furnace internals, petrochemical reformer tubes, steam superheaters, nuclear steam generator components. Any structure working continuously above 600 °C.
Incoloy 825 is required — sulphuric and phosphoric acid equipment, seawater heat exchangers, oil and gas well equipment (especially “sour” service containing H₂S), nuclear fuel reprocessing, chemical process tanks. An aggressive chemical environment at room to moderate temperature.
Using one in place of the other does not work: 800H corrodes rapidly in an acid environment, and 825 cannot deliver creep strength at high temperature.
Neighbouring alloys
For the precipitation hardening, higher-strength derivative of 825, see our Incoloy 825 – 925 comparison. For superior oxidation resistance at high temperature, Inconel 601 and Hastelloy X are used.
Technical datasheets
Incoloy 800H — chemical composition, mechanical values, standard equivalents
Incoloy 825 — 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.