Inconel 625 and Inconel 718 are two commonly used nickel-based superalloys that are very important in many industrial applications, especially in high-temperature, high-pressure, and corrosive environments. Here are some main differences between these two alloys:
1.Chemical Composition
- Inconel 625 is a high-performance alloy with main chemical components including nickel (Ni) about 61.0%, chromium (Cr) about 21.5%, molybdenum (Mo) about 9.0%, and niobium (Nb) + tantalum (Ta) about 3.6%. These components provide it with excellent corrosion resistance, especially in environments containing chlorides.
- Inconel 718 is also a nickel-based alloy but has precipitation hardening characteristics, containing a higher proportion of iron, as well as alloying elements such as niobium (Nb) and molybdenum (Mo), which give it higher strength after aging treatment.
2. Mechanical Properties
- Inconel 625 demonstrates excellent mechanical properties at both very low and very high temperatures, has high oxidation resistance, and is highly resistant to a variety of organic and mineral acids.
- Inconel 718 is known for its high strength at temperatures below 650°C, good toughness, and corrosion resistance in both high and low-temperature environments, with a yield strength twice as strong as that of 625.
3. Application Fields
- Inconel 625 is widely used in oil and gas production, chemical equipment, marine engineering, and components that are exposed to seawater and subject to high mechanical stress.
- Inconel 718 is widely used in aerospace, nuclear engineering, oil and gas industries, especially in manufacturing turbine blades, discs, shafts, and other components that require high strength and high-temperature resistance.
4. Processing and Welding
- The processing difficulty of Inconel 625 is medium to difficult, but it has good weldability and is suitable for various welding techniques.
- Inconel 718 also has good processing and welding performance, suitable for arc welding, plasma welding, etc., and has high weldability, maintaining its mechanical properties and corrosion resistance even after welding.
5. Corrosion Resistance
- Inconel 625 has the characteristic of being almost completely unaffected by stress corrosion cracking caused by chlorides, and has high oxidation resistance at temperatures up to 1050°C.
- Inconel 718 has good corrosion resistance to acidic gases, HCl, H2SO4, and shows strong resistance to uniform corrosion in the oil and gas field environment, with a very low corrosion rate even at high temperatures.
In summary, the choice between Inconel 625 and Inconel 718 depends on the specific application requirements. If the application environment involves high temperatures and chlorides, Inconel 625 may be a better choice; whereas if high strength is required at extreme temperatures, Inconel 718 may be more suitable.