Download

Alloy 718

Alloy718, UNS N07718, W. Nr. 2.4668, GH4169

Alloy 718 is a high strength, corrosion resistant nickel-chrome-iron-molybdenum alloy used at -423° to 1300°F. The age hardening is achieved by specific additions of niobium, titanium and aluminum. It can be delivered in solution-annealed or hardened condition.

The age hardenable alloy can be readily fabricated, even into complex parts. Its welding characteristics, especially its resistance to postweld cracking, are outstanding.While limited to applications below 1200°F (650°C), it is significantly stronger at these lower temperatures than materials such as Waspaloy alloy, R-41 alloy, or X-750 alloy.  It is also much easier to weld than these alloys, and is less susceptible to the strain age cracking problems common for gamma prime strengthened materials. At temperatures greater than 1200°F (650°C), 718 alloy is being replaced by HAYNES® 282® alloy due to the superior strength of 282® alloy at those temperatures as well as its excellent fabricability.

Alloy 718 is characterized by:

◇ Good processing properties in the solution-annealed condition

◇ Good mechanical short and long-term properties, and great fatigue strength in the age hardened condition

◇ Good creep resistance up to 700 °C (1300 °F)

◇ Good oxidation resistance up to approx. 1,000°C (1830 °F)

◇ Excellent ability to resist stress corrosion cracking and pitting corrosion at both high and low temperatures

◇ Excellent mechanical properties in low temperatures

Alloy 718 is normally only used for component applications up to 1200°F (650°C); however, its oxidation resistance is comparable to that for other gamma-prime- strengthened superalloys.

The ease and economy with which alloy 718 can be fabricated, combined with good tensile, fatigue, creep, and rupture strength, have resulted in its use in a wide range of applications. Examples of these are components for liquid fueled rockets, rings, casings and various formed sheet metal parts for aircraft and land-based gas turbine engines, and cryogenic tankage. It is also used for fasteners and instrumentation parts.

Based on its high-temperature resistance up to 700°C (1300°F), its excellent oxidation and corrosion resistance, and its good workability, Alloy 718 is used in many demanding applications. Originally, it was developed and used for static and rotating components in aircraft turbines such as housings, mounting elements and turbine disks, where tough requirements apply for creep resistance and fatigue behavior, in particular for the rotating applications.

Due to its properties, its good workability and efficiency, the material is additionally widely used for static and rotating components in stationary gas turbines, rocket drives and spacecraft, motor vehicle turbo chargers, high-strength screws, springs and mounting elements, and for heat-resistant tools in forgeries, extruders and separating shearers.

Unless otherwise specified, thetubes shall be supplied in the cold worked (cw), or cold worked and precipitation hardened (prec hard), or solution annealed plus precipitation hardened condition.

Alloy 718 has excellent corrosion resistance to many media. This resistance, which is similar to that of other nickel-chromium alloys, is a function of its composition. Nickel contributes to corrosion resistance in many inorganic and organic, other than strongly oxidizing, compounds throughout wide ranges of acidity and alkalinity. It also is useful in combating chloride-ion stress-corrosion cracking. Chromium imparts an ability to withstand attack by oxidizing media and sulfur compounds. Molybdenum is known to contribute to resistance to pitting in many media.

(1) Hot formed, solution annealed, descaled

(2) Cold worked and bright annealed

(3) Cold worked, annealed and descaled

(4) Cold worked, polished (MP, EP etc.)

(5) Cold worked, bright annealed, polished (MP, EP etc.)

Chemical composition

Tension

Hardness

Flaring

Flange

Flattening

Micro structure

Hydrostatic

NDT

Intergranular Corrosion

Surface condition

Shape and dimension

Positive Material Identification