Inconel 625 is a solid solution strengthened alloy, the biggest feature is excellent corrosion resistance.
Inconel 718 is a precipitation strengthened alloy, the biggest feature is very high strength.
Inconel 625 (UNS N06625/WNr2.4856) is used for its high strength, excellent manufacturability (including joining) and excellent corrosion resistance. The service temperature range is from cryogenic to 1800°F (982°C).
INCONEL® alloy 718 (UNS NO7718/WNr2.4668) is a high-strength, corrosion-resistant nickel-chromium material used in -423° to 1300°F. This age-hardened alloy can be easily fabricated and even made into complex parts. Its welding characteristics, especially resistance to post-weld cracking, are excellent.
Nickel itself has good corrosion resistance, and chromium is the most important corrosion-resistant element in high-temperature alloys. Therefore, the corrosion resistance of alloy 625 is better than that of alloy 718.
Inconel 718 is heat treated in two ways:
• Solution annealed at 1700-1850°F, followed by rapid cooling (usually in water) and precipitation hardening at 1325°F for 8 hours, furnace cooling to 1150°F, holding at 1150°F for a total aging time of 18 hours, then air cooling.
• Solution annealed at 1900-1950°F, followed by rapid cooling (usually in water), and precipitation hardening at 1400°F for 10 hours, furnace cooling to 1200°F, holding at 1200°F for a total aging time of 20 hours, then air cooling.
