An Introduction to Inconel 625

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Inconel 625 is a nickel-chromium-molybdenum alloy with excellent corrosion and oxidation resistance at high temperatures. This guide provides a comprehensive look at Inconel 625’s properties, applications, specifications, grades, suppliers, and pros/cons.

Overview of Inconel 625

Inconel 625 is a solid-solution strengthened nickel-based superalloy. Key features:

  • Excellent corrosion resistance, oxidation resistance, and strength at high temperatures
  • Maintains high tensile strength and creep rupture properties up to 1300°F (700°C)
  • Withstands a wide range of severely corrosive environments and high stress -Used for applications like chemical processing, aerospace, marine, and heat treating

Its unique composition enables exceptional performance in demanding conditions.

Inconel 625 Composition and Properties

The major alloy elements in Inconel 625 provide its distinctive properties:

Inconel 625 Composition

ElementWeight %
Nickel58.0 min
Chromium20.0-23.0
Molybdenum8.0-10.0
Niobium3.15-4.15
Iron5.0 max
Cobalt1.0 max

Inconel 625 Properties

  • Excellent tensile, fatigue, creep, and rupture strength at high temperatures up to 1300°F
  • Resists a wide range of corrosive environments and acids
  • Good oxidation resistance up to 2150°F
  • Highly weldable for easy fabrication
  • Good machinability compared to other nickel alloys
  • Non-magnetic

The balance of nickel, chromium, and molybdenum imparts Inconel 625’s unique combination of strength, corrosion resistance, and ease of fabrication.

Applications of Inconel 625

Key industries using Inconel 625 include:

Inconel 625 Applications

IndustryUses
AerospaceExhaust systems, thrust reverser systems, ducting, combustion cans, hangar clips
Chemical ProcessingHeat exchangers, valves, piping, condensers, reaction vessels
MarinePropeller shafts, marine fasteners, sonar equipment
Oil & GasWellhead equipment, downhole tubing, valves, subsea components
Pollution ControlScrubbers, precipitators, stacks, chimneys, ducting
Food/PharmaceuticalTubing, transfer piping, valves, processing equipment

Inconel 625’s strength, corrosion resistance and high temperature performance make it ideal for demanding environments across industries.

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Specifications and Grades

Inconel 625 is available in various product forms and meets international specifications:

Inconel 625 Specifications

SpecificationGradeDescription
AMS 5599AnnealedAnnealed sheet, strip, and plate
AMS 5666Solution annealedSolution annealed superalloy bar, wire, and forging stock
AMS 5837Annealed and agedTubing seamless and welded annealed
AMS 5879Solution treatedSheet and strip solution treated
AMS 5891Precipitation hardenedBar, forging stock and wire solution and precipitation treated

Inconel 625 Product Forms

  • Sheet – From 0.406 mm to 6.35 mm thickness
  • Plate – Up to 152 mm thickness
  • Bar – Rounds, squares, rectangles and hexagons
  • Tube – Seamless and welded
  • Pipe – Seamless and welded
  • Forging Stock – Rounds, blocks, shafts
  • Wire – Annealed, aged or cold worked

Inconel 625 is produced in all common wrought product forms for extensive applications.

Suppliers and Pricing

Inconel 625 is available from major alloy suppliers:

Inconel 625 Suppliers

SupplierDescription
Haynes InternationalGlobal nickel alloy manufacturer. Full range of Inconel 625 products.
Special Metals CorporationProduces Inconel 625 in wrought forms. Distribution worldwide.
Aalco MetalsStocks Inconel 625 plate, sheet, bar, pipe, fittings and flanges.
GoodfellowResearch and specialist alloys. Small quantity supplier of Inconel 625.
Eagle AlloysWide inventory of Inconel 625 plate, sheet, bar and tube.

Inconel 625 Pricing

As a premium alloy, Inconel 625 has a higher cost than carbon steel or stainless steel:

  • Inconel 625 Plate: $55 – $65 per kg
  • Inconel 625 Sheet: $50 – $60 per kg
  • Inconel 625 Bar: $45 – $55 per kg
  • Inconel 625 Tube: $65 – $75 per kg

Pricing can vary based on quantity, product form, gauge/thickness, supplier and geographical region.

Comparison to Stainless Steel

While more expensive, Inconel 625 provides major advantages over stainless steel:

ParameterInconel 625Stainless Steel
Strength at high temperatureExcellent – retains strength up to 1300°FFair – strength declines above 600°F
Corrosion resistanceSuperior – resists wide range of acids, alloys, saltsModerate – prone to pitting and crevice corrosion
Cost2x to 5x more expensiveLower material cost
FabricationGood weldability and machiningEasier to weld and machine
Work hardeningLow work hardening ratesSevere work hardening if overworked
Magnetic permeabilityNon-magneticMartensitic and ferritic grades are magnetic

For critical applications, Inconel 625 provides superior performance despite higher cost. Stainless is more economical for less demanding uses.

Applications Pros and Cons

ApplicationPros of Inconel 625Potential Cons
High temperature heat exchangersWithstands corrosion and oxidation at extreme tempsCost is much higher than stainless
Chemical processing equipmentResists almost all wet and dry chlorine compoundsDifficult to cut or machine thick sections
Aerospace exhaust componentsMaintains strength in hot exhaust gas environmentRequires age hardening for optimal properties
Subsea oil and gas componentsExceptional resistance to seawater corrosion and erosionSusceptible to stress corrosion cracking above 500°F
Food/pharma tubingPrevents metallic contamination of productsLow thermal conductivity compared to copper alloys

Inconel 625 provides unmatched performance in harsh environments despite higher cost and fabrication challenges.

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FAQ

What is Inconel 625 used for?

Inconel 625’s key uses are in heat exchangers, chemical and food processing equipment, exhaust and emission systems, subsea oil and gas components, aerospace ducting and engine parts. It withstands extreme temperatures and corrosion.

Is Inconel 625 weldable?

Yes, Inconel 625 can be readily welded using GTAW and GMAW methods. Proper techniques should be followed to avoid weld cracking. Post-weld annealing improves ductility and strength.

What is the difference between Inconel 600 and 625?

Inconel 625 has higher molybdenum content for increased corrosion resistance and strength at high temperatures compared to Inconel 600. Inconel 600 is more oxidation resistant above 1000°C.

What is the melting point of Inconel 625?

The melting range of Inconel 625 is 2290-2460°F (1260-1350°C). It retains significant strength up to 1300°F.

Is Inconel 625 suitable for marine applications?

Yes, Inconel 625’s resistance to seawater corrosion makes it well-suited for marine components like propeller shafts, fasteners, sonar equipment. It also has good cavitation erosion resistance.

What is the density of Inconel 625?

Inconel 625 has a density of 8.44 g/cm3, which is slightly higher than stainless steel. The nickel and molybdenum content increases its density.

Inconel 625’s impressive properties make it the top choice for demanding applications, despite higher cost. Proper selection ensures it provides maximum performance and value.

Conclusion

With its carefully balanced nickel-chromium-molybdenum alloying, Inconel 625 offers an unmatched combination of high strength, outstanding corrosion resistance, and ease of fabrication. It performs well from cryogenic temperatures up to 1300°F in even the most aggressive environments. Key applications across aerospace, chemical processing, oil and gas, and other industries rely on Inconel 625’s capabilities. While costlier than stainless steels, its superior performance makes it an excellent investment for critical components and systems. Inconel 625 has become a trusted and widely-used superalloy thanks to its exceptional characteristics.

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