Alloy 725 and 625 differ only slightly in composition, but 725 is more than double the tensile strength of 625.
Inconel 725 is a nickel-based grade, alloyed primarily with chromium. Its composition is very similar to Inconel 625, except for an addition of titanium that, with an additional heat treatment, gives significantly higher strength.
Composition
The table below sets out the two compositions side by side: Inconel 625 and Inconel 725 are near-identical across nickel, chromium, molybdenum and niobium, giving them near-identical physical properties. The one difference is Inconel 725’s addition of 1.00-1.75% titanium.
Why the strength differs
The titanium forms very fine precipitates throughout the metal during an additional heat treatment. These precipitates help to ‘pin’ the microstructure under load, increasing strength and toughness. This precipitation strengthening makes Inconel 725 more than double the strength of Inconel 625, suiting it to load-bearing oil and gas applications where resistance to H2S ‘sour corrosion’ is also demanded. Beyond high-strength fasteners, it is used in hangers, landing nipples, mandrels and polished bore receptacles.
Langley Alloys stocks Alloy 725 as round bars from 1”-4” diameter (25.4-101.6mm).
| Element | Inconel 625 | Inconel 725 |
|---|---|---|
| Nickel | >58% | 55-59% |
| Chromium | 20-23% | 19-22.5% |
| Molybdenum | 8-10% | 7-9.5% |
| Niobium | 3.15-4.15% | 2.75-4% |
| Titanium | - | 1.00-1.75% |