Inconel 625

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Inconel Alloy 625 (UNS designation N06625) is a nickel-based superalloy that possesses high strength properties and resistance to elevated temperatures. It also demonstrates remarkable protection against corrosion and oxidation. Its ability to withstand high stress and a wide range of temperatures, both in and out of water, as well as being able to resist corrosion while being exposed to highly acidic environments makes it a fitting choice for nuclear and marine applications.[1][2][3]

Inconel 625 was developed in the 1960s with the purpose of creating a material that could be used for steam-line piping. Some modifications were made to its original composition that have enabled it to be even more creep-resistant and weldable. Because of this, the uses of Inconel 625 have expanded into a wide range of industries such as the chemical processing industry, and for marine and nuclear applications to make pumps and valves and other high pressure equipment.[4][5]

Because of the metal's high Niobium (Nb) levels as well as its exposure to harsh environments and high temperatures, there was concern about the weldability of Inconel 625. Studies were therefore conducted to test the metal's weldability, tensile strength and creep resistance, and Inconel 625 was found to be an ideal choice for welding.[6][7] Other well known names for Inconel 625 are Haynes 625, Nickelvac 625, Nicrofer 6020, Altemp 625 and Chronic 625


Some chemical properties of Inconel 625 include:[8]

Cr Mo Co Nb+Ta Al Ti C Fe Mn Si P S Ni
Min 20 8 -- 3.15 -- -- -- -- -- -- -- -- Balance
Max 23 10 1 4.15 .4 .4 .1 5 .5 .5 .015 .015 Balance

Inconel 625 was designed as a solid solution strengthened material with no significant microstructure. This holds true at low and high temperatures, but there is a region (923 to 1148 K) where precipitates form that are detrimental to the creep properties, and thus the strength, of the alloy. Under any creep conditions (high temperature with an applied stress), M23C6-type carbides form at the grain boundaries. When tested at 973 K, γ” precipitates begin forming. These γ” phase precipitates are ordered A3 B type with a composition of Ni3(Nb, Al, Ti) and a tetragonal crystal structure. They form a disk-shaped morphology and are coherent with respect to the matrix. When tested at 998 K, a δ-phase precipitate begins forming which consist of Ni3(Nb, Mo) in an orthorhombic crystal structure. They form in a needle-like morphology and are incoherent with the matrix. Both of these precipitates can be completely dissolved back into the matrix when the sample is heated 1148 K. This leads to the ability to recover creep properties of the alloy to prolong the materials lifetime.[9]

ASTM Specifications[edit]

ASTM (American Society for Testing and Materials) for various products made out of Inconel 625 are as follow:[10]

Pipe Seamless Pipe Welded Tube Seamless Tube Welded Sheet/Plate Bar Forging Fitting Wire
B444 B705 B444 B704 B443 B446


Markets for Inconel 625 include:

  • Marine
  • Nuclear
  • Chemical Processing
  • Aerospace


Product and technology applications of Inconel 625 include:[11]

  • Seawater components
  • Flare stacks
  • Aircraft ducting systems
  • Fabrication with Inconel 625
  • Specialized seawater equipment
  • Chemical process equipment
  • Turbine shroud rings
  • Engine thrust-reverser systems
  • Jet engine exhausts systems


Specifications and certifications include:[12][clarification needed]

  • AMS: 5599, 5666
  • MS: 5837
  • ASME: SB 443 Gr 1, SB 446 Gr 1
  • ASTM: B 443 Gr 1, B 446 Gr 1
  • EN: 2.4856
  • ISO: 15156-3
  • NACE: MR0175-3
  • UNS: N06625
  • Werkstoff: 2.4856

See also[edit]


  1. ^ "Special Metals INCONEL® Alloy 625". ASM Aerospace Specification Metals Inc.
  2. ^ "High Temp Super Alloys". ASM Aerospace Specification Metals Inc.
  3. ^ "The Invention and Definition of Alloy 625" (PDF). TMS The Minerals, Metals and Materials Society.
  4. ^ "Alloy 625 - Impressive Past, Significant Presence, Awesome Future" (PDF). TMS The Minerals, Metals and Materials Society.
  5. ^ "Special Metals INCONEL® Alloy 625". ASM Aerospace Specification Metals Inc.
  6. ^ "The Invention and Definition of Alloy 625" (PDF). TMS The Minerals, Metals and Materials Society.
  7. ^ [Research & Reviews: International Journals "Study of Weld Quality Characteristics of Inconel 625 Sheets at Different Modes of Current in Micro Plasma Arc Welding Process"] Check |url= value (help).
  8. ^ "Inconel 625". Rickard.
  9. ^ Mathew, M. D. (2008). "Microstructural changes in alloy 625 during high temperature creep". Materials Characterization. 59.5: 508–513.
  10. ^ "ASTM Specifications".
  11. ^ "Applications of Inconel 625".
  12. ^ "Alloy 625". Rickard.