What is the Difference Between INCONEL 617 and 625

In industries where components must endure extreme heat, pressure, and corrosion, nickel-based superalloys like INCONEL 617 and INCONEL 625 have become indispensable. Both alloys belong to the same INCONEL family and share a nickel-chromium base, yet they are designed for different operational environments and performance requirements.

In this article, SASAALLOY explains in detail the difference between INCONEL 617 and 625, comparing their composition, properties, applications, and advantages. This comprehensive guide will help engineers, buyers, and industrial professionals choose the right alloy for their specific needs.

1. Overview of INCONEL Alloys

INCONEL alloys are high-performance nickel-chromium materials known for their outstanding strength, oxidation resistance, and corrosion resistance under extreme conditions.

Both INCONEL 617 and INCONEL 625 belong to this family but are optimized for different working conditions:

  • INCONEL 617: Designed for high-temperature applications exceeding 1000°C.

  • INCONEL 625: Designed for corrosive environments at moderate to high temperatures (up to 980°C).

Understanding their distinctions begins with examining their chemical composition and alloy design philosophy.

2. Chemical Composition Comparison

Element INCONEL 617 (%) INCONEL 625 (%) Function in Alloy
Nickel (Ni) Balance (≥ 44.5) Balance (58.0 min) Base metal, corrosion and heat resistance
Chromium (Cr) 20.0 – 24.0 20.0 – 23.0 Improves oxidation and scaling resistance
Molybdenum (Mo) 8.0 – 10.0 8.0 – 10.0 Provides strength and pitting resistance
Cobalt (Co) 10.0 – 15.0 — Enhances strength at very high temperatures
Iron (Fe) ≤ 3.0 5.0 max Minor strengthening element
Niobium (Nb + Ta) — 3.15 – 4.15 Adds solid-solution and precipitation hardening
Aluminum (Al) 0.8 – 1.5 0.40 max Improves oxidation resistance
Titanium (Ti) ≤ 0.6 0.40 max Contributes to stabilization and strength
Carbon (C) 0.05 – 0.15 0.10 max Increases creep rupture strength

Key Difference

  • INCONEL 617 contains cobalt and higher aluminum, enhancing its oxidation resistance and thermal strength at extremely high temperatures.

  • INCONEL 625, however, uses niobium and molybdenum for superior corrosion and seawater resistance, making it more suitable for marine and chemical environments.

3. Mechanical Properties Comparison

Property INCONEL 617 INCONEL 625
Density 8.36 g/cm³ 8.44 g/cm³
Tensile Strength (Room Temp) 890 MPa 930 MPa
Yield Strength (0.2% offset) 440 MPa 450 MPa
Elongation 45% 45%
Hardness (Brinell) ~170 HB ~200 HB
Operating Temperature Limit Up to 1100°C Up to 980°C
Melting Range 1330–1380°C 1290–1350°C

INCONEL 617 maintains strength and stability above 1000°C, while INCONEL 625 offers superior strength and corrosion protection below 980°C.

4. High-Temperature Performance

INCONEL 617

  • Specifically developed for extreme high-temperature applications.

  • Retains mechanical strength beyond 1000°C, thanks to its cobalt and aluminum content.

  • Excellent oxidation and creep resistance in air or combustion gas environments.

  • Commonly used in gas turbines, reformers, and heat exchangers.

INCONEL 625

  • Performs best at temperatures up to 980°C.

  • Beyond this limit, its strength decreases faster than INCONEL 617.

  • Ideal for medium-temperature and corrosive conditions, such as chemical plants, offshore equipment, and marine components.

5. Oxidation and Corrosion Resistance

Oxidation Resistance

  • INCONEL 617: Superior due to high chromium and aluminum; forms a strong oxide film that protects against scaling up to 1100°C.

  • INCONEL 625: Excellent oxidation resistance but slightly less effective above 1000°C.

Corrosion Resistance

  • INCONEL 625: Excels in aqueous, chloride, and acidic environments (especially seawater and chemical plants).

  • INCONEL 617: Performs best in oxidizing and carburizing atmospheres but less corrosion-resistant in acidic conditions compared to 625.

Summary:
Choose INCONEL 617 for heat; choose INCONEL 625 for corrosion.

6. Creep and Fatigue Strength

Both alloys have good creep and fatigue resistance, but INCONEL 617 outperforms 625 in extremely hot conditions.

  • INCONEL 617:
    Exceptional creep rupture strength (100 MPa at 1000°C for 100 hours).
    Maintains microstructural stability under long-term stress.

  • INCONEL 625:
    Excellent fatigue strength under cyclic loads at moderate temperatures.
    Commonly used in environments requiring flexibility, like bellows and expansion joints.

7. Weldability and Fabrication

Both alloys are easily fabricated using conventional nickel-alloy techniques, but there are subtle differences.

INCONEL 617

  • Can be welded using GTAW or GMAW processes.

  • No post-weld heat treatment required.

  • Suitable filler metals: INCONEL 617 or 625.

  • Excellent formability and hot workability (900–1200°C).

INCONEL 625

  • Highly weldable, even for complex assemblies.

  • Filler metal: INCONEL 625.

  • Superior performance in repair welding due to lower cracking risk.

  • Widely used for overlay cladding on steel components to enhance corrosion resistance.

8. Applications of INCONEL 617

INCONEL 617 is preferred for high-temperature and oxidation environments, including:

  1. Power Generation

    • Gas turbine combustor liners and transition ducts

    • Heat recovery systems and superheater tubes

  2. Chemical Processing

    • Steam reformer tubes, catalyst grids, and furnace manifolds

  3. Aerospace and Aviation

    • Jet engine exhaust components

    • Turbine shrouds and afterburner ducts

  4. Nuclear Industry

    • High-temperature heat exchangers and advanced reactor systems

Its combination of strength, oxidation resistance, and thermal stability makes it one of the most reliable materials for long-term high-heat exposure.

9. Applications of INCONEL 625

INCONEL 625 dominates in corrosive and moderate-temperature environments, including:

  1. Marine and Offshore Engineering

    • Seawater piping systems

    • Subsea equipment and fasteners

  2. Chemical Processing

    • Acid production, pollution control, and heat exchangers

  3. Aerospace

    • Engine exhaust systems and flexible joints

  4. Oil and Gas Industry

    • Piping, tubing, and downhole tools exposed to corrosive gases

  5. Environmental Systems

    • Scrubbers and chimney liners

Its ability to resist pitting, crevice corrosion, and chloride attack makes INCONEL 625 indispensable in chemical and marine environments.

10. Standards and Specifications

Alloy Standard Specifications
INCONEL 617 ASTM B166, B167, B168, B564; ASME SB166/SB167
INCONEL 625 ASTM B443, B444, B446, B564; ASME SB443/SB444

Both are certified for use in high-pressure and high-temperature components under ASME Boiler and Pressure Vessel Code (Section II, Part D).

11. Comparative Summary Table

Feature INCONEL 617 INCONEL 625
Base Composition Ni-Cr-Co-Mo-Al Ni-Cr-Mo-Nb
Main Strengthening Mechanism Solid-solution strengthening Solid-solution + precipitation hardening
Maximum Service Temperature Up to 1100°C Up to 980°C
Oxidation Resistance Excellent Excellent (below 1000°C)
Corrosion Resistance Good Outstanding
Creep Resistance Excellent Good
Fatigue Strength High High
Fabricability Good Excellent
Primary Application Turbines, heat exchangers Chemical, marine, and offshore systems
Cost Slightly higher Moderate

Conclusion:
Choose INCONEL 617 when your design involves extreme heat and oxidation; choose INCONEL 625 when facing corrosion and aggressive chemical conditions.

12. Cost and Availability

Both alloys are considered premium materials due to their nickel and molybdenum content.

  • INCONEL 617 is generally more expensive, owing to its cobalt content and use in advanced turbine and reactor applications.

  • INCONEL 625 offers a more cost-effective solution for corrosion resistance where ultra-high-temperature performance is not required.

SASAALLOY maintains extensive inventories of both alloys in plates, bars, tubes, and forgings to ensure fast delivery and consistent quality worldwide.

13. Quality and Supply by SASAALLOY

As a global supplier of high-performance nickel-based alloys, SASAALLOY offers comprehensive supply solutions for INCONEL 617 and INCONEL 625.

SASAALLOY Product Range

  • Round bars, plates, and sheets

  • Seamless and welded pipes

  • Forged blocks and flanges

  • Customized machined components

Advantages of Choosing SASAALLOY

  1. Guaranteed Quality – All materials conform to ASTM, ASME, and EN standards with EN 10204 3.1 certification.

  2. Technical Expertise – Support from metallurgists and engineers specializing in high-temperature alloys.

  3. Global Reach – Reliable export service to over 40 countries.

  4. Competitive Pricing – Factory-direct supply with strong inventory control.

  5. Custom Solutions – Tailored dimensions, heat treatments, and machining on request.

With decades of industry experience, SASAALLOY ensures that every batch of INCONEL 617 and 625 meets strict quality and performance standards for demanding industrial applications.

14. Choosing Between INCONEL 617 and 625

Operating Condition Recommended Alloy
High-temperature service above 1000°C INCONEL 617
Strong oxidation and carburization resistance INCONEL 617
Marine and offshore environments INCONEL 625
Acidic and chemical exposure INCONEL 625
High creep strength at elevated temperatures INCONEL 617
General corrosion protection INCONEL 625

15. Conclusion

While INCONEL 617 and INCONEL 625 share a common nickel-chromium foundation, they excel in different fields of application.

  • INCONEL 617 is the better choice for extreme heat and oxidation environments, such as turbines and reactors.

  • INCONEL 625 is ideal for corrosive and seawater conditions, such as chemical processing and offshore operations.

Both alloys demonstrate the strength, stability, and reliability expected from premium nickel-based materials.

With strict quality assurance and global delivery capability, SASAALLOY continues to be a trusted supplier for high-performance alloys—helping industries achieve longer service life, higher efficiency, and better operational safety.

Post time: Oct-28-2025