Alloy 718

The Alloy 718 is a precipitation hardening nickel-chromium alloy with an exceptional combination of corrosion resistance and high strength together with an ease of fabrication and an exceptional weldability. The alloy’s improved properties are obtained through additions of niobium, molybdenum, aluminum, iron and titanium. The unique blend of properties on offer allows its usage for components in the aerospace, chemical, marine, nuclear, petrochemical and offshore industries.

Columbia Metals stocks the Alloy 718 in the solution treated condition as per AMS 5662 and to the API 6A specification. AMS5662 is ideal for heavy machining, welding or forming as it is in its most malleable state, whereas API 6A offers high strength while meeting the maximum hardness necessities of the MR0103, NACE MR0175 and ISO 15156-3 specifications for use in oil tools in corrosive environments.

The Alloy 718 can be age hardened and solution treated at a number of varied temperatures in order to fulfill the requirements of individual specifications. Each heat treatment can offer the user with a different set of physical and mechanical properties ideal for varied applications.

The AMS 5662 specification specifies that it is necessary for the material to be supplied in the solution treated condition (i.e. heat treated within the range 941-1010 °C). The subsequent age hardening process provides the Alloy 718 the best combination of rupture life, rupture ductility and notch rupture. The increased properties are attained due to the development of a fine grain structure that also offers its highest tensile and yield strengths via an extensive range of temperatures from –253 ºC to 705 ºC.

The Alloy 718 also offers exceptional corrosion resistance in a wide range of media. It excels in a number of different environments including organic acids, inorganic acids (not strongly oxidizing), sour gasses and hydrogen sulfide. It is also particularly resistant to chloride stress-corrosion cracking. The chromium content existing in the material results in an exceptional resistance to oxidation and sulfur compounds up to temperatures of around 980 ºC. The molybdenum content helps in the overall pitting resistance of the material.

This alloy can be readily machined in the solution treated condition but the material’s work-hardening characteristics and high strength should be taken into account. The material can be hot worked between 985-1150 °C or cold worked whilst in the solution treated condition because of its high elongation. However, inter stage annealing (between 925 to 1010 °C) may be required for more complex forming operations. Any cold or hot working should be followed by annealing and quenching in order to restore the best balance of properties. It is also possible to readily weld this material by the gas tungsten arc (TIG) process and it is particularly resistant to post weld cracking.

This mixture of properties leads to a material that truly can be described as a “Superalloy”. Particular applications include valves, choke stems, fasteners, down-hole tooling, cryogenic storage tanks, jet engines, pump bodies, gas turbines and nuclear reactor parts. It is also ideal for shear blades and extrusion dies where standard tool steels do not offer the needed high temperature strength.

  • Easily joined/welded
  • High resistance to stress rupture
  • Resistance to stress corrosion
  • Exceptional strength levels
  • Outstanding corrosion resistance
  • Excellent pitting resistance
  • Superb high temperature strength
  • Oxidation resistance up to 982 oC
  • Good forming/fabrication properties
  • Extremely high resistance to creep

Technical Data

Nominal Composition (%)

Ni Cr Fe Nb Mo Ti Al
53 19 18 5 3 0.9 0.5

 

Typical Mechanical Properties

  As Delivered
Solution Treated
Age Hardened
Room Temperature
(Longitudinal)
<127 mm dia
Hardness (HB) 277 -
Ultimate Tensile Strength (N/mm2) - 1276
0.2% Proof Strength (N/mm2) - 1034
Elongation (%) - 12
Reduction of Area (%) - 15

 

Typical Physical Properties

 

  Age Hardened
Density (g/cm3) 8.22
Melting Range (°C) 1260 - 1335
Young’s Modulus (GPa) 204
Thermal conductivity (0-200 °C; W/m°K) 14.2
Coeff. Thermal Exp. (m/m °K x 10-6) 13.5
Magnetic Permeability 1.0011

 

Round Bar Weight and Stock Sizes

Diameter Weight Diameter Weight Diameter Weight
ins kg/ft kg/m ins kg/ft kg/m ins kg/ft kg/m
10 mm 0.19 0.63 1” 1.27 4.15 3” 11.39 37.36
1/2” 0.32 1.04 1.1/4” 1.98 6.49 4” 20.31 66.64
5/8” 0.49 1.62 1.1/2” 2.85 9.34 5” 31.74 104.13
3/4” 0.71 2.34 2” 5.06 16.61 6” 45.70 145.94

 

NB Weight data for guidance only

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