Comprehensive guide to nickel-based superalloys: Inconel 625 (UNS N06625/W.Nr. 2.4856)
Inconel 625 is a nickel-based high-temperature alloy with a density of 8.4 g/cm3 and a melting point of 1290-1350°C. It has excellent resistance to inorganic acid corrosion and has excellent corrosion resistance to various corrosive media in oxidizing and reducing environments.
Alloy 625 exhibits excellent corrosion resistance in many media. It has excellent resistance to pitting corrosion, crevice corrosion, intergranular corrosion and erosion in chloride media.
Designated UNS N06625 or W.Nr. 2.4856, Inconel 625, also known as Alloy 625, is a nickel-chromium-molybdenum alloy with added niobium that works with the molybdenum to harden the alloy matrix, thereby providing high strength without the need for intensive heat treatment . The alloy is resistant to a variety of severe corrosive environments, especially pitting and crevice corrosion, and has excellent fatigue strength and resistance to chloride ion stress corrosion cracking. Inconel 625 is used in chemical processing, aerospace and marine pipelines, pollution control equipment and nuclear reactors. Typically it can be used at oxidation temperatures up to 980°C [1800°F].
Feature c
1. It has excellent corrosion resistance to various corrosive media in oxidizing and reducing environments.
2. Excellent resistance to pitting corrosion and crevice corrosion, and no stress corrosion cracking caused by chloride.
3. It has excellent corrosion resistance to inorganic acids such as nitric acid, phosphoric acid, sulfuric acid, hydrochloric acid and mixed acids of sulfuric acid and hydrochloric acid.
4. It has excellent corrosion resistance to various inorganic acid mixed solutions.
5. When the temperature is as high as 40°C, it has good corrosion resistance in hydrochloric acid solutions of various concentrations.
6. Good processing performance and welding performance, no post-weld crack sensitivity.
7. Manufacturing certificate for pressure vessels with wall temperature between –196°C and 450°C.
8. Passed the NACE standard (mr-01-75) certification of the American Society of Corrosion Engineers and meets the highest standard for sour gas applications, Level VII.
Metallographic structure of Inconel 625
625 is a face-centered cubic lattice structure. After long-term heat preservation at 650°C, carbon particles and unstable quaternary phase will precipitate and transform into a stable Ni3 (Nb, Ti) rhombic lattice phase. After solid solution strengthening, Mo and Nb in the Ni Cr matrix will improve the mechanical properties, but the plasticity will be reduced.
Corrosion resistance of Inconel 625
Alloy 625 exhibits excellent corrosion resistance in many media. It has excellent resistance to pitting corrosion, crevice corrosion, intergranular corrosion and erosion in chloride media. It has good resistance to inorganic acid corrosion, such as nitric acid, phosphoric acid, sulfuric acid, hydrochloric acid, etc. It also has corrosion resistance to alkali and organic acids in oxidizing and reducing environments. Effectively resists chloride reduction stress corrosion cracking. It has high corrosion resistance to seawater and salt solutions, and also has high temperature resistance. There is no sensitivity when welding. Resistant to carbonization and oxidation in static or cyclic environments, and corrosion resistant to chlorine-containing gases.
