Alloy 625 (UNS N06625) is a low-carbon nickel-chromiummolybdenum-niobium alloy which shows excellent resistance to a variety of corrosive media.
Due to its low carbon content and stabilising heat treatment, Alloy 625 shows little tendency to sensitisation even after 50 hours at temperatures in the range 650–900°C (1200–1650°F).
The alloy is supplied in the soft-annealed condition for applications involving wet corrosion, and is approved by TUV for pressure vessels in the temperature range –196 to 450°C (–321 to 840°F). For high-temperature applications a modified version of Alloy 625 is available on request.
The mechanical properties of Alloy 625 can be increased by age-hardening.
This alloy is characterised by:
• outstanding resistance to pitting, crevice corrosion, impingement corrosion and intergranular attack
• almost complete freedom from chloride-induced stress-corrosion cracking
• good resistance to mineral acids, such as nitric, phosphoric, sulphuric and hydrochloric acids
• good resistance to alkalis and organic acids
• good mechanical properties
In special high-temperature applications where very high strength and creep values are required, the high-carbon, solution treated version (Alloy 625, grade 2) should be used.