What is the difference between Alloy 725 and 625?

The difference between Alloy 725 and 625 is small in terms of their composition, but far more significant in terms of their tensile strength.

Inconel 725 is a nickel-based grade, primarily alloyed with chromium. It is very similar to the composition of Inconel 625, except that an addition of titanium is made that, when subject to an additional heat treatment process, result in significantly higher strength.

Inconel 625 is composed of at least 58% nickel, 20-23% nickel, 8-10% molybdenum, 3.15-4.15% niobium and trace amounts of other elements. Inconel 725 is composed of 55-59% nickel, 19-22.5% chromium, 7-9.5% molybdenum, and 2.75-4% niobium, so very similar to that of Inconel 625 and resulting in near-identical physical properties. However, 1.00-1.75% titanium is added. This contributes to the formation of very fine precipitates throughout the metal when it is subject to an additional heat treatment process. These precipitates help to ‘pin’ the microstructure of the metal when it is subject to an external load, increasing its strength and toughness. The so-called precipitation-strengthening means that Inconel 725 is more than double the strength of Inconel 625. This makes it suitable for a range of load-bearing applications in the Oil and Gas industry, where resistance to H2S ‘sour corrosion’ is also demanded. Apart from high-strength fasteners, it will be used in other components such as hangers, landing nipples, mandrels and polished bore receptacles.

Langley Alloys stocks Alloy 725 as round bars from 1”-4” diameter (25.4-101.6mm).

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