Alloy 925 (UNS N09925)

Alloy 925, also known as Incoloy 925 (trademark of Special Metals Corporation), is a nickel-iron-chromium alloy strengthened by additions of molybdenum, copper, titanium and aluminium. It is supplied in both solution annealed and aged conditions.

Age Hardening
The titanium and aluminium content enables precipitation strengthening during ageing. Ni₃(Al,Ti) gamma prime (γ′) precipitates form throughout the alloy matrix, significantly increasing hardness and strength. This mechanism is comparable to Alloy K500, Alloy 718 and Alloy 725.

Corrosion Resistance
Alloy 925 combines the resistance of Alloy 825 with enhanced localised corrosion performance.
• High nickel content provides resistance to stress corrosion cracking.
• Molybdenum and copper improve performance in reducing environments.
• Chromium offers protection in oxidising environments.
• PREN exceeds 26, ensuring resistance to pitting and crevice corrosion in chloride-bearing conditions.

Mechanical Properties
In the aged condition, Alloy 925 provides high yield and tensile strengths while retaining ductility and toughness. Its strength allows for thinner wall sections without loss of integrity, important for high-pressure equipment.

Applications
Alloy 925 is widely used in demanding service environments, including:
• Downhole and subsea oil and gas equipment such as tubulars, hangers, packers and safety valves.
• Sour service conditions involving hydrogen sulphide and chlorides.
• Marine applications where resistance to seawater-induced corrosion is critical.
• Chemical processing and pollution control equipment handling aggressive aqueous media.

Standards
Alloy 925 is covered by key industry specifications including:
• ASTM B805 for wrought products.
• NACE MR0175 / ISO 15156 for sour service applications.

Summary
Alloy 925 provides a unique balance of high strength from precipitation hardening and corrosion resistance comparable to leading nickel alloys. This combination underpins its adoption across industries where both structural performance and durability in aggressive environments are essential.