Alloy 718 (UNS N07718)
Alloy 718 is a precipitation-hardening nickel-chromium alloy containing significant amounts of iron, columbium, and molybdenum, along with lesser amounts of aluminum and titanium. Alloy 718 maintains high strength and good ductility up to 1300°F (704°C). This alloy has relatively good weldability, formability, and excellent cryogenic properties compared to other precipitation hardening nickel alloys. The sluggish precipitation hardening response of this alloy allows it to be readily welded without hardening or cracking.
Alloy 718 has good corrosion resistance and oxidation resistance in jet engine and gas turbine applications. This alloy is used for parts requiring high resistance to creep and stress rupture up to 1300°F (704°C) and oxidation resistance up to 1800°F (982°C). Alloy 718 exhibits excellent tensile and impact properties even at cryogenic temperatures. AMS 5662 requires minimum yield strength of 150,000 psi at room temperature.
Classified as a precipitation-hardening alloy that can be age hardened by heat treatment. Grain structure remains austenitic at all temperatures. Various solution and aging treatments are used during heat treatment of this grade to optimize either short or long time elevated temperature mechanical properties.
Chemical Composition (wt%) limits as specified in ASTM B637*
*Maximum, unless range is indicated
Physical properties for 718
|Modulus of Elasticity, psi||29 x 106|
|Coefficient of Thermal Expansion, 68-212˚F, /˚F||7.1 x 10-6|
|Thermal Conductivity, Btu/ft hr ˚F||6.5|
|Specific Heat, Btu/lb ˚F||0.10|
|Electrical Resistivity, Microhm-in||47.6|
Mechanical property requirements for heat treated product (solution+precipitation harden) as specified in ASTM B637
|Yield Strength, min. (ksi)||150|
|Tensile Strength, min. (ksi)||185|
|Elongation, min. (%)||12|
|Brinell Hardness, min||331|
Typical standards for 718