What is the composition of 625?
625 Alloy Grade 1 / UNS N06625 / W.NR. 2.4856
Description
625 alloy is a nickel-chromium-molybdenum alloy that is widely used for its high strength, toughness, and excellent corrosion resistance. The strength of 625 alloy is derived from the hardening effect of molybdenum and niobium on its nickel-chromium matrix. Although the alloy was developed for high-temperature strength, its highly alloyed composition also provides fairly high general corrosion resistance.
Industries and Applications
625 alloy is used in a variety of industries including automotive, marine, aerospace, oil and gas, chemical processing, and nuclear energy. Typical end-use applications include heat exchangers, bellows, expansion joints, exhaust systems, fasteners, quick-connect fittings, and many other applications requiring strength and resistance to corrosive environments.
Corrosion Resistance
625 alloy has good resistance to oxidation and scaling at elevated temperatures. At 1800°F, scaling resistance becomes an important factor in service. It outperforms many other high-temperature alloys under cyclic heating and cooling conditions. The combination of alloying elements in 625 alloy enables it to withstand a wide range of severe corrosive environments. It is virtually unaffected by corrosion in mild environments, such as fresh and seawater, neutral pH environments, and alkaline media. The alloy's chromium content gives it excellent resistance to oxidizing environments. The high molybdenum content makes 625 alloy very resistant to pitting and crevice corrosion.
Fabrication and Heat Treatment
625 alloy can be formed using a variety of cold and hot working processes. 625 alloy resists deformation at hot working temperatures, so higher loads are required to form the material. Hot forming should be performed in the temperature range of 1700° to 2150°F. During cold working, the material work-hardens faster than conventional austenitic stainless steels. Alloy 625 is available in three heat treatments: 1) 2000/2200°F solution anneal and air quench or faster; 2) 1600/1900°F anneal and air quench or faster; 3) 1100/1500°F stress relieve and air quench. Solution annealed (Grade 2) material is typically used above 1500°F where creep resistance is important. Soft annealed material (Grade 1) is typically used at lower temperatures and has the best combination of tensile and fracture properties.
