Product Focus – INCONEL alloy 718 | View of a aeroplane engine being serviced

If you need high strength alongside good corrosion resistance for demanding environments, one material worth your consideration is INCONEL alloy 718. We take a look at its specifications in more detail.

When your project demands an alloy that offers superior high strength, why not take a look at INCONEL alloy 718? This nickel/cobalt and chromium material is a potential option for use in a range of fields, including liquid-fuelled rockets, rings, casings and formed sheet metal parts for aircraft and land-based gas turbine engines, and cryogenic tankage – all applications where metals need to perform at the highest levels. Its excellent mechanical properties are consistent over a wide temperature range, from -423°F up to 1300°F.

As well as high strength, INCONEL alloy 718 has good levels of corrosion resistance in many environments, and it is useful in combating chloride-ion stress-corrosion cracking. The addition of chromium into the nickel-based alloy gives it resistance to oxidising elements and sulphur compounds. Molybdenum, as a supporting element, contributes resistance to pitting in a range of circumstances.

It is often selected because it is a versatile metal that can be readily fabricated into complex parts. It is known for its outstanding resistance to post-weld cracking. It can also be easily machined, though its strength must be considered when looking at how it will be processed.

Heat treatments

The alloy exhibits good tensile, fatigue, creep and rupture strength under a wide range of conditions. In most cases, INCONEL alloy 718 is specified as solution annealed and precipitation hardened (otherwise called age hardened). In order to maintain the full strength of the alloy, it must be heat treated under very specific conditions. It is hardened by the precipitation of secondary phases, such as gamma prime and gamma double-prime, into the metal matrix. There are two common heat treatments that are generally used for this alloy.

First, a 1700-1850°F anneal with its corresponding aging treatment is the optimum heat treatment for INCONEL alloy 718 to give the best combination of rupture life, notch rupture life and rupture ductility. It also gives the highest room-temperature tensile and yield strengths, as well as the highest fatigue strength.

If, however, your project requires the best transverse ductility in heavy sections, impact strength and low-temperature notch tensile strength, a 1900-1950°F anneal with corresponding aging treatment is required. This process can produce notch brittleness in stress rupture.

For detailed technical specifications of this alloy, see the Grades section on our website. If you have a project that you think would benefit from INCONEL alloy 718, please contact a member of our sales team.

Topics: Corrotherm News

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