Inconel 725 is composed of 55-59% nickel, 19-22.5% chromium, 7-9.5% molybdenum and 2.75-4% niobium, plus 1-1.75% titanium. It is a nickel-based grade, alloyed primarily with chromium, and is very similar to Inconel 625 apart from the titanium addition that, with an additional heat treatment, gives significantly higher strength.
How it compares with Inconel 625
Inconel 625 provides the baseline for comparison: at least 58% nickel, 20-23% chromium, 8-10% molybdenum and 3.15-4.15% niobium, without any titanium addition. Its high alloy content lets Inconel 625 withstand severe corrosive environments: nickel and chromium provide resistance to oxidising chemicals, while nickel and molybdenum resist non-oxidising environments, and the high molybdenum content gives strong resistance to pitting and crevice corrosion.
Against that baseline, Inconel 725’s composition is near-identical except for its 1-1.75% titanium content, which is the one addition responsible for its higher strength.
Why the titanium matters
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 - the mechanism behind Inconel 725’s significant strength advantage over the otherwise near-identical Inconel 625.
Langley Alloys stocks Alloy 725 as round bars from 1”-4” diameter (25.4-101.6mm).