Inconel 600 and Inconel 625 are the two most widely used members of the nickel-based alloys. Although their names are close, they were designed for different problems: 600 focuses on oxidation at high temperature, 625 on corrosion and strength.
Molybdenum and niobium
According to our datasheets, Inconel 600 is a simple nickel–chromium–iron alloy: nickel min 72.0%, chromium 14.0–17.0%, iron 6.00–10.0%. There is no molybdenum or niobium in its composition.
In Inconel 625, nickel falls to min 58.0% but in its place come 8.00–10.0% molybdenum and 3.15–4.15% niobium + tantalum. Chromium also rises to 20.0–23.0% and iron is held below 5.00%.
Those additions have two separate consequences. Molybdenum and chromium together provide superior resistance to pitting and crevice corrosion in chloride and acidic environments. Niobium strengthens the alloy by solid solution hardening without any heat treatment — 625 has high strength even in the annealed condition.
The strength of Inconel 600 lies elsewhere: thanks to its very high nickel content it is nearly immune to chloride-induced stress corrosion cracking and it resists oxidation at temperatures reaching 1000 °C.
Comparison in numbers
| PROPERTY | Inconel 600 | Inconel 625 |
|---|---|---|
| Nickel (Ni) | min 72.0% | min 58.0% |
| Chromium (Cr) | 14.0 – 17.0% | 20.0 – 23.0% |
| Iron (Fe) | 6.00 – 10.0% | max 5.00% |
| Molybdenum (Mo) | — | 8.00 – 10.0% |
| Niobium + Tantalum | — | 3.15 – 4.15% |
| Carbon (C) | max 0.15% | max 0.10% |
| Copper (Cu) | max 0.50% | — |
| Cobalt (Co) | — | max 1.00% |
| UNS | N06600 | N06625 |
| W.Nr (DIN/EN) | 2.4816 | 2.4856 |
| EN chemical symbol | NiCr15Fe | NiCr22Mo9Nb |
| AMS | 5540 · 5665 | 5599 · 5666 · 5837 |
Values are taken from our product datasheets; section thickness and the applied heat treatment regime change the result.
Which one, and when?
Inconel 600 is sufficient — furnace muffles and retorts, heat treatment equipment, thermocouple protection tubes, nuclear steam generator tubing, caustic environments. Oxidation resistance at high temperature and immunity to stress cracking are what stand out. If the specification calls out AMS 5540 or AMS 5665, this is the grade being asked for.
Inconel 625 is required — seawater equipment, offshore pipelines, flue gas desulphurisation systems, chemical process equipment, aircraft exhaust components and fuel lines. It is chosen where both corrosion resistance and strength are needed; if the specification calls out AMS 5599 or AMS 5666, 600 is not an acceptable substitute.
The other members of the family
Where high strength at high temperature is wanted, the precipitation hardening Inconel 718 comes into play; we covered its difference from 625 in this article. For an alternative with even higher oxidation resistance there is Inconel 601.
Technical datasheets
Inconel 600 — chemical composition, mechanical values, standard equivalents
Inconel 625 — 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.