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Inconel 625

UNS N06625, Alloy 625, W.Nr. 2.4856, Inconel® 625
Note that the designation “ Inconel®” is registered trademarks of the Special Metals Corporation group of companies. 


UNS N06625 is a widely utilized nickel-chromium alloy renowned for its high strength, excellent fabricability, and exceptional corrosion resistance. Strength of Inconel 625 is derived from the stiffening effect of molybdenum and niobium on its nickel-chromium matrix, thus precipitation hardening treatments are not required, this combination of elements also is responsible for superior resistance to a wide range of corrosive environments of unusual severity as well as to high-temperature effects such as oxidation and carburization. Service temperatures range from cryogenic to 1800°F (982°C). 

  • Sea-water Applications: wire rope for mooring cables, propeller blades for motor patrol gunboats, submarine auxiliary propulsion motors, submarine quick disconnect fittings, exhaust ducts for Navy utility boats, sheathing for undersea communication cables, submarine transducer controls, and steam-line bellows.
  • Aerospace Field: Aircraft ducting systems, engine exhaust systems, thrust-reverser systems, resistance welded honeycomb structures for housing engine controls, fuel and hydraulic line tubing, spray bars, bellows, turbine shroud rings, and heat-exchanger tubing in environmental control systems.
  • Chemical-processing Field: Bubble caps, tubing, reaction vessels, distillation columns, heat exchangers, transfer piping, and valves.
  • Nuclear Field: Reactor-core and control-rod components in nuclear water reactors.
Chemical Composition (%)


Material Ni Cr Fe Mo Nb C Mn Si
N06625 58.0 min 20.0-23.0 5.0 max 8.0-10.0 3.15-4.15 0.10 max 0.50 max 0.50 max
Mechanical Property
Material Tensile strength Yield strength 0,2 Elongation Hardness HB30
N06625 760 N/mm² 345 N/mm² 30% 220HB
Corrosion Resistance

The high alloy content of Inconel 625 enables it to withstand a wide variety of severe corrosive environments. In mild environments such as the atmosphere, fresh water, sea water, neutral salt, and alkaline media, there is almost no attack. In more severe corrosive environments, the presence of nickel and chromium provides the alloy with resistance to oxidizing chemicals, while the combination of nickel and molybdenum provides the alloy with resistance to nonoxidizing environments. In addition, the high molybdenum content also makes this alloy very resistant to pitting and crevice corrosion, and the high nickel content provides freedom from chloride ion stress corrosion cracking. This combination of properties allows Alloy 625 to be used under a wide range of corrosive conditions. 

Heat Treatment

Inconel 625 has excellent strength, toughness, and resistance to high temperatures and corrosion, but the alloy an become susceptible to cracks, distortions, and other issues impacting its performance during the manufacturing process. Heat treatment helps to alleviate these issues by improving the material’s mechanical properties, ensuring its durability and reliability.

Heating and Pickling

Like other nickel-chromium and nickel-chromium-iron alloys, Inconel 625 tends to form a tightly adherent oxide or scale when heated unless it has been bright-annealed in very dry hydrogen or in a vacuum. To remove the oxide which results from heating, treatment in a fused-salt bath prior to pickling is usually recommended. 


After the fused-salt bath treatment, Inconel 625 can undergo pickling, which involves immersing it in an acid solution to further remove any remaining oxides or impurities. Pickling is commonly done using hydrochloric acid or a mixture of nitric and hydrofluoric acids. It's worth noting that the specific pickling processes may vary depending on the application and specific requirements. 

Hot and Cold Forming

Inconel 625 was especially developed to retain high strength at elevated temperature, it resists deformation at hot-working temperatures. If hot forming of this alloy is required, powerful equipment is necessary. When Alloy 625 is hot-formed, it should be heated in a furnace whose temperature is held at (but not above) 2150°F. To guard against duplex grain structure, the work should be given uniform reductions. Final minimum reductions of 15 to 20% for open-die work are recommended.


Inconel 625 can be cold-formed by standard processes. Increased tensile properties can be achieved by cold work for moderate temperature applications. Tensile strengths of more than 300,000 psi accompanied by good ductility have been developed in 0.010-0.020-in-diameter wire after 75-90% cold reduction.


All standard machining operations are readily performed on Inconel 625. For the best machinability, the alloy should be in the solution-treated condition. 


Inconel 625 is best machined in the annealed condition. Low cutting speeds should be used and the cutting tool should be engaged at all times to minimize work-hardening. Adequate cut depth is necessary to assure avoiding contact with the previously formed work-hardened zone. 

Product Forms
  • Bar & Rod
  • Plate & Sheet
  • Coil & Strip
  • Pipe & Tube
  • Fitting: Flange, Tee, Elbow, Reducer etc.
  • Forging: Ring, Shaft, Circle, Block etc.

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