UNS N07718, Alloy 718, W.Nr. 2.4668, Inconel® 718
Note that the designation “ Inconel®” is registered trademarks of the Special Metals Corporation group of companies. 

UNS N07718 is a high-strength and corrosion-resistant age-hardenable alloy, the age hardening is achieved by specific additions of niobium, titanium and aluminum. The alloy suitable for temperatures from -423° to 1300°F. Its welding characteristics, especially its resistance to post weld cracking, are outstanding. In addition, Inconel 718 can be fabricated with ease and economy, combined with good tensile, fatigue, creep, and rupture strength, have resulted in its use in a wide range of applications.

Inconel 718 has excellent corrosion resistance to many media, making it highly suitable for applications where corrosion resistance is critical.The high nickel contents of the alloy contributes to corrosion resistance in many inorganic and organic, and combating chloride-ion stress-corrosion cracking. In addition, chromium imparts an ability to withstand attack by oxidizing media and sulfur compounds, molybdenum is contribute to resistance to pitting in many media. Please note that the specific corrosion resistance of Alloy 718 can vary depending on the concentration and temperature of the corrosive media, as well as other environmental factors.  

There are two main heat treatment methods commonly used for Inconel 718. The first one is solution anneal at 1700-1850°F followed by rapid cooling, usually in water, plus precipitation hardening at 1325°F for 8 hours, furnace cool to 1150°F, hold at 1150°F for a total aging time of 18 hours, followed by air cooling. The second is Solution anneal at 1900-1950°F followed by rapid cooling, usually in water, plus precipitation hardening at 1400°F for 10 hours, furnace cool to 1200°F, hold at 1200°F for a total aging time of 20 hours, followed by air cooling. If the material is to be machined, formed, or welded, it typically is purchased in the mill annealed or stress relieved condition. The material is then fabricated in its most malleable condition. After fabrication, it can be heat treated as required per the applicable specification.

When heating Inconel 718, it is crucial to ensure that both the furnace and the material being heated at correct temperatures, and fuels used for heating must be extremely low in sulfur. In addition, The alloy must be absolutely clean and free from all oil, paint, grease, and shop soil when charged into the furnace. To prevent air infiltration, a slight positive pressure should be maintained in the furnace. Please note that a thin, adherent green-black film of oxide will be left on the surface of the material when Alloy 718 is heated in a reducing atmosphere. When Alloy 718 is heated in a oxidizing atmospheres, a heavy black scale is produced that is very difficult to remove. Every precaution should be taken in heating so that only the green-black film is formed. 

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