Inconel 718 is a nickel-chromium-molybdenum alloy designed to resist a wide range of severely corrosive environments, pitting and crevice corrosion. This nickel steel alloy also displays exceptionally high yield, tensile, and creep-rupture properties at high temperatures. This nickel alloy is used from cryogenic temperatures up to long term service at 1200° F. One of the distinguishing features of Inconel 718's composition is the addition of niobium to permit age hardening which allows annealing and welding without spontaneous hardening during heating and cooling.
The addition of niobium acts with the molybdenum to stiffen the alloy's matrix and provide high strength without a strengthening heat treatment. Other popular nickel-chromium alloys are age hardened through the addition of aluminum and titanium. This nickel steel alloy is readily fabricated and may be welded in either the annealed or precipitation (age) hardened condition. This nickel alloy is used in a variety of industries such as aerospace, chemical processing, marine engineering, pollution-control equipment, and nuclear reactors.
Chemical Composition
| Ni | Fe | Cr | Cu | Mo | Nb | C | Mn | P | S | Si | Ti | Al | Co | B |
| 50.00-55.00 | Remainder | 17.00-21.00 | .30 max | 2.80-3.30 | 4.75-5.50 | .08 max | .35 max | .015 max | .015 max | .35 max | .65-1.15 | .20-.80 | 1.00 max | .006 max |
Mechanical Properties
| Ultimate Tensile Strength, psi | .2% Yield Strength psi | Elongation % | Hardness Rockwell B |
| 135,000 | 70,000 | 45 | 100 |
Advantage of Inconel 718
1. Good mechanical properties – tensile, fatigue and creep-rupture.
2. Yield tensile strength, creep, and rupture strength properties are exceedingly high.
3. Highly resistant to chloride and sulfide stress corrosion cracking.
4. Resistant to aqueous corrosion and chloride ion stress corrosion cracking.
5. High temperature resistant.
6. Age-hardenable with a unique property of slow aging response that permits heating and cooling during annealing without the danger of cracking.
7. Excellent welding characteristics, resistant to postweld age cracking.
Application of Inconel 718
INCONEL alloy 718 is often used within the aviation and aerospace industries. Engineers are constantly looking to improve the reliability and efficiency of engines, not to mention their longevity. Superalloys, and in particular alloy 718, are selected for their balance between cost and performance.
It’s imperative to use materials that can retain their strength and resistance to corrosion in the hottest sections of these engines. The materials used are under challenging conditions, with both mechanical and atmospheric stresses to consider.
INCONEL alloy 718 is ideal for use in these circumstances. For example, it has been used in jet engine and high-speed airframe parts, including wheels, fasteners, instrumentation parts, bolts, spacers and buckets. It is also used to engineer components for liquid-fuelled rockets, rings and casings, as well as various formed sheet metal parts for turbine engines, both aircraft and land-based.
At the other end of the temperature scale, INCONEL alloy 718 is also used in cryogenic tankage.
If you’re considering using INCONEL alloy 718 in your next project, welcome any inquiry!
