Alloy 718 (UNS N07718)

Description:

Alloy 718 is a high-strength, corrosion-resistant nickel chromium alloy supplied in the hot worked, solution annealed and age hardened condition. The addition of Nb, Ti, Al and Ni form a series of precipitates during the controlled solution annealing and ageing process steps, resulting in a significant increase in strength and hardness compared with alternative nickel alloys. These tensile and creep rupture properties are maintained from cryogenic to elevated temperatures, making it suitable for applications between -250oC – 750oC.

As a nickel chromium alloy it possesses acceptable corrosion resistance in a range of environments including sea water, hydrogen sulphide, CO2, elemental sulphur and chloride ions over various temperatures. It is resistant to sulphide stress cracking and is capable of passing the sulphide stress corrosion test in accordance with NACE TM 0177 Method C solution A.  Alloy 718 is supplied to meet both NACE and API 6A standards, meeting the requirements for application in the oil industry where resistance to stress corrosion cracking is needed together with high strength, high creep resistance and weldability. Ideal applications are in oil tools, such as gate valves and choke stems, and high strength applications such as fasteners and turbines.

Key Features:

  • Good strength/ductility properties from sub-zero temperatures to over 750°C
  • Acceptable corrosion resistance and fatigue resistance in a wide variety of corrosive chemicals such as seawater and industrial acids
  • Non-magnetic and spark resistant
  • Excellent resistance to stress corrosion cracking, chloride stress corrosion & sulphide stress cracking
  • High fatigue strength in seawater

Applications:

  • Oil & Gas industry wellhead components, gate valves, choke stems, fasteners, packers, clamps, tubing hangers, downhole equipment
  • Power generation applications such as fasteners, turbines
  • Aerospace components
  • Nuclear power plant containment vessels, valves
  • Engineering applications between 750°C and cryogenic temperatures

Chemical Composition:

Cr Ni Mo Co Nb (+Ta) Ti V W Cu C Mn N Si P S Fe Al
Min 17.00 50.00 2.80 4.70 0.65 0.20
Max 21.00 55.00 3.30 1.00 5.50 1.15 0.30 0.08 0.35 0.35 0.015 0.015 Bal 0.80

Mechanical Properties:

Age hardened 120 ksi Age hardened 140 ksi
Bars up to and including 10” (254) diameter or section Bars greater than 10” (254mm) diameter or section Bars up to and including 10” (254) diameter or section Bars greater than 10” (254mm) diameter or section
0.2% Proof Stress, min 827 N/mm2 125 ksi 827 N/mm2 125 ksi 965 N/mm2 140 ksi 965 N/mm2 140 ksi
0.2% Proof Stress, max 1000 N/mm2 145 ksi 1000 N/mm2 145 ksi 1034 N/mm2 150 ksi 1034 N/mm2 150 ksi
Tensile strength, min 1034 N/mm2 150 ksi 1034 N/mm2 150 ksi 1138 N/mm2 165 ksi 1103 N/mm2 160 ksi
Elongation, 5.65√S0 and 4D 20% 20% 20% 20%
Reduction of Area 35% 25% 35% 25%
Hardness (Rockwell C) 32-40HRC 32-40HRC 34-40 HRC 34-40HRC
Impact Strength (-60oC) Longitudinal <3” <3” <3” <3”
68J av (61J min) 50 ft.lb av (45 ft.lb min) 68J av (61J min) 50 ft.lb av (45 ft.lb min)
Impact Strength (-60oC) Transverse ≥3” – 10” ≥3” – 10” 41J av (37J min) 30 ft.lb av (27 ft.lb min) ≥3” – 10” ≥3” – 10” 41J av (37J min) 30 ft.lb av (27 ft.lb min)
47J av (41J min) 35 ft.lb av (30 ft.lb min) 47J av (41J min) 35 ft.lb av (30 ft.lb min

Notes:

  1. Testing shall be carried out in accordance with ASTM A370 (tensile), ASTM E18 (hardness)
  2. Minimum properties quoted (tested at room temperature in a longitudinal direction)
  3. Testing performed on each melt of material per heat treatment batch
  4. Minimum lateral hole expansion of 0.015” (0.38mm)
  5. Macro-etching
  6. Microstructure certified free from acicular, secondary and laves phases
  7. Grain size determined to be equiaxed and predominantly ASTM3 or finer (ASTM E112 x100 magnification)

Physical Properties:

Density (Kg/m3) 8230
Magnetic Permeability (20°C) <1.002
Young’s Modulus (kN/mm2) 200
Specific Electrical Resistance, 20°C (µΩ-m) 1.25
Mean coefficient of thermal expansion, 20-100°C (m/m/degC) 12.1 x 10-6
Specific Heat, 20°C (J/kg.K) 435
Thermal Conductivity, 20°C (W/m.K) 11.1
Curie Temperature (degC) -112 (aged)

Downloads

Datasheet - NA-Alloy 718

Datasheet - NA-Alloy 718