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Alloy 718

  • Material

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

  • Overview

    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.

  • Characteristics

    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

  • Application

    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.

  • Chemical Composition (wt%)

    Material

    Fe

    Ni+Co

    Co

    Cr

    Mo

    Ti

    B

    Cu

    Pb

    Se

    Alloy 718

    Bal.

    50.0-55.0

    ≤1.00

    17.0-21.0

    2.80-3.30

    0.65-1.15

    ≤0.006

    ≤0.30

    ≤5ppm

    ≤3ppm

    Material

    C

    Al

    Mn

    Si

    P

    S

    Nb+Ta

    Ta

    Bi

     

    Alloy 718

    ≤0.08

    0.20-0.80

    ≤0.35

    ≤0.35

    ≤0.015

    ≤0.015

    4.75-5.50

    ≤0.05

    ≤0.3ppm


  • Mechanical Property (in solution ann + precipication hardended)

    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.

    Tensile strength

    ksi (MPa)

    Yield strength at

    0.2 offset ksi (MPa)

    Elongation in 2” 

    % min.

    Hardness

    HRC max.

    150 (1034)

    125 (862)

    20

    40

  • Corrosion Resistance

    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.

  • Available Process

    (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.)

  • Common Tests

    Chemical composition

    Tension

    Hardness

    Flaring

    Flange

    Flattening

    Micro structure

    Hydrostatic

    NDT

    Intergranular Corrosion

    Surface condition

    Shape and dimension

    Positive Material Identification

  • Product Forms

    Form

    Size range

    Capillary tube

    OD 0.08 ~ 6.0 mm

    WT 0.015 ~ 1.5 mm

    Thin wall & Ultra thin wall seamless tube

    OD6.0 ~80.0 mm

    WT 0.05 ~4.5 mm

    Micro ID and heavy thick wall seamless tube

    OD3.0 ~50.0 mm

    ID 0.30 ~5.0 mm

    Precision conic seamless tube

    Bigger end: OD3.0 - 426.0mm

    Smaller end: OD2.5 - 346.0mm

    WT: 0.15 - 40.0mm

    HP /UHP BA+ tube

    EP tube

    OD 1.0 ~ 76 mm

    WT 0.10 ~ 10.0 mm

    Small caliber precision seamless tube

    OD6.0 ~89 mm

    WT 0.50 ~9.0 mm

    Profiled seamless tube

    Build to drawing

    Build to specification

    Bourdon tube

    Y40, Y50, Y60, Y70, Y100, Y150

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