July 02, 2024

Inconel 625 and Inconel 718 are nickel-based superalloys with great strength, exceptional corrosion resistance, and the ability to tolerate extreme temperatures. However, there are significant variances in composition, mechanical qualities, and common applications. This is a full comparison:

Chemical Composition

Inconel 625:

  • Nickel (Ni): 58% minimum
  • Chromium (Cr): 20-23%
  • Molybdenum (Mo): 8-10%
  • Niobium (Nb): 3.15-4.15%
  • Iron (Fe): 5% maximum
  • Other elements: Carbon (C), Manganese (Mn), Silicon (Si), Phosphorus (P), Sulfur (S), Aluminum (Al), Titanium (Ti), Cobalt (Co)

Inconel 718:

  • Nickel (Ni): 50-55%
  • Chromium (Cr): 17-21%
  • Iron (Fe): 17% maximum
  • Niobium (Nb): 4.75-5.50%
  • Molybdenum (Mo): 2.80-3.30%
  • Titanium (Ti): 0.65-1.15%
  • Aluminum (Al): 0.20-0.80%
  • Other elements: Carbon (C), Manganese (Mn), Silicon (Si), Phosphorus (P), Sulfur (S), Cobalt (Co), Boron (B), Copper (Cu)

Mechanical Properties

Inconel 625:

  • Excellent fatigue and thermal-fatigue strength
  • Good oxidation and corrosion resistance
  • High tensile, creep, and rupture strength
  • Service temperature range: -238°F to 1800°F (-150°C to 982°C)

Inconel 718:

  • Superior mechanical properties at high temperatures
  • High yield, tensile, and creep-rupture properties
  • Excellent weldability, especially compared to other nickel-based alloys
  • Service temperature range: -423°F to 1300°F (-253°C to 704°C)
  • Precipitation hardenable, which allows for enhanced mechanical properties through heat treatment

Applications Industries

Inconel 625:

  • Aerospace: jet engine exhaust systems, engine thrust-reverser systems
  • Marine: sea-water components, submarine propulsion systems
  • Chemical processing: heat exchangers, reactor cores, pressure vessels
  • Power generation: furnace hardware, gas turbine engine ducting

Inconel 718:

  • Aerospace: gas turbine engines, rocket motors and engine components, spacecraft
  • Power generation: gas turbine components
  • Oil and gas: wellhead components, downhole shafting
  • Nuclear: reactor cores, nuclear fuel element spacers

 

Inconel 625 is well-known for its high resistance to oxidation and corrosion, particularly in severe settings. It has excellent mechanical qualities and thermal stability, making it ideal for a variety of applications, particularly those requiring resistance to corrosive environments.

Because of its precipitation hardening capability, Inconel 718 has excellent mechanical strength and high-temperature performance. Its weldability and resistance to post-weld cracking make it suitable for high-stress, high-temperature applications, particularly in the aerospace industry.

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