Inconel 718

Ⅱ. Chemical Composition (Mass Percentage)

• Nickel (Ni): 50.0 – 55.0%
• Chromium (Cr): 17.0 – 21.0%
• Iron (Fe): Balance
• Niobium (Nb): 4.75 – 5.50%
• Molybdenum (Mo): 2.8 – 3.3%
• Titanium (Ti): 0.65 – 1.15%
• Aluminum (Al): 0.20 – 0.80%
• Carbon (C): ≤0.08%
• Cobalt (Co): ≤1.0%
• Boron (B): ≤0.006%
• Manganese (Mn): ≤0.35%
• Silicon (Si): ≤0.35%
• Phosphorus (P): ≤0.015%
• Sulfur (S): ≤0.015%

Ⅲ. Mechanical Properties (Aged State)

• Tensile Strength: ≥1275 MPa
• Yield Strength (RP₀.₂): ≥1035 MPa
• Elongation (A): ≥12% (bars) to ≥30% (thin plates)
• Brinell Hardness (HB): ≥331
• Density: 8.19 g/cm³
• Melting Point: 1260 – 1336°C
• High – temperature Performance:
  • Tensile strength at 650°C: ≥725 MPa
  • Tensile strength at 700°C: ≥650 MPa
  • Tensile strength at 750°C: ≥580 MPa

Ⅳ. Heat Treatment Requirements

1. Solution Treatment:
   • Temperature: \(980 – 1065^\circ\text{C}\), hold for 1 – 2 hours, then perform rapid water quenching to form a uniform austenitic matrix.
2. Double Aging Treatment:
   • First stage: Hold at \(720^\circ\text{C}\) for 8 hours, then cool to \(620^\circ\text{C}\) at a rate of \(50^\circ\text{C}\) per hour.
   • Second stage: Hold at \(620^\circ\text{C}\) for 8 hours, then air cool to room temperature.
   • Purpose: Precipitate the strengthening phases \(\gamma”\) (\(\text{Ni}_3\text{Nb}\)) and \(\gamma’\) (\(\text{Ni}_3(\text{Al,Ti})\)) to improve strength and creep resistance.
3. Special Treatment:
   • For components with high requirements for notch sensitivity, a lower solution temperature (such as \(950^\circ\text{C}\)) can be used to promote the precipitation of the \(\delta\) phase (\(\text{Ni}_3\text{Nb}\)) and improve fatigue resistance.
   • After welding, aging treatment (\(720^\circ\text{C} \times 8\text{h} + 620^\circ\text{C} \times 8\text{h}\)) is required to restore the properties of the heat – affected zone.

Ⅴ. Main Application Fields

1. Aerospace:
   • Turbine disks, compressor blades, combustion chamber components, high – temperature bolts (such as in CFM56 engines)
   • Airframe structural components (such as landing gear components of Boeing 787)
2. Energy and Nuclear Power:
   • Nuclear reactor fuel rod cladding, pressure vessels, steam generator pipelines
   • High – temperature components of gas turbines (such as GE90 turbine blades)
3. Oil and Natural Gas:
   • Deep – sea Christmas trees, high – temperature and high – pressure valves, downhole tools resistant to H₂S corrosion
   • Acid environment equipment meeting NACE MR0175 standard
4. Chemical and Pharmaceutical:
   • Reactors and heat exchangers resistant to sulfuric acid and chloride corrosion
   • Pipelines of pharmaceutical equipment requiring high purity
5. Precision Instruments:
   • Support structures for superconducting magnets in low – temperature environments (-253°C)
   • Precision sensor components for electron beam welding

Ⅵ. Performance Advantages

• High – temperature strength: Maintains the highest yield strength among wrought superalloys below 650°C.
• Corrosion resistance: The synergistic effect of chromium, molybdenum, and niobium makes it perform excellently in media such as chlorides and sulfuric acid.
• Workability: Can be made into complex shapes (such as turbine disk forgings) through cold/hot working, and its weldability is better than that of other nickel – based alloys.
• Microstructural stability: After double aging treatment, the γ” phase is stable for a long time below 700°C, ensuring the reliability of long – term service.