What is the Difference Between Inconel 625 and X750?

Inconel alloys are known worldwide for their exceptional performance in extreme environments, combining excellent strength, corrosion resistance, and thermal stability. Two of the most well-known grades are Inconel 625 and Inconel X750. While both belong to the nickel-chromium alloy family and share many common characteristics, they are designed for different applications and have distinct mechanical, thermal, and chemical properties.

This article provides a comprehensive comparison of Inconel 625 and Inconel X750, covering their chemical composition, mechanical properties, heat resistance, corrosion performance, and common uses across industries.

Introduction to Inconel Alloys

Inconel is a registered trademark for a family of nickel-chromium-based superalloys designed to provide high strength and resistance to oxidation and corrosion, especially at high temperatures. These alloys are widely used in aerospace, chemical processing, marine, and power generation industries.

While Inconel 625 and Inconel X750 share similar base elements, their alloying additions and strengthening mechanisms differ, resulting in unique performance characteristics.

Chemical Composition

Inconel 625

Inconel 625 is a solid-solution strengthened alloy, meaning its strength comes primarily from the solid-solution hardening effect of its alloying elements. Its typical composition includes:

  • Nickel (Ni) – 58% minimum

  • Chromium (Cr) – 20% to 23%

  • Molybdenum (Mo) – 8% to 10%

  • Niobium + Tantalum (Nb + Ta) – 3.15% to 4.15%

  • Iron (Fe) – 5% maximum

  • Carbon (C) – 0.1% maximum

  • Small amounts of manganese, silicon, and cobalt

The high molybdenum and niobium content give Inconel 625 superior resistance to pitting, crevice corrosion, and chloride-induced stress corrosion cracking.

Inconel X750

Inconel X750 is a precipitation-hardenable nickel-chromium alloy, strengthened by aluminum and titanium additions. Its typical composition includes:

  • Nickel (Ni) – 70% minimum

  • Chromium (Cr) – 14% to 17%

  • Iron (Fe) – 5% to 9%

  • Titanium (Ti) – 2.25% to 2.75%

  • Aluminum (Al) – 0.4% to 1.0%

  • Niobium + Tantalum (Nb + Ta) – 0.7% to 1.2%

  • Carbon (C) – 0.08% maximum

The aluminum and titanium content allows X750 to undergo age hardening for significant increases in high-temperature strength.

Strengthening Mechanism

  • Inconel 625 – Strengthened by solid-solution hardening, which relies on the uniform distribution of alloying elements in the crystal lattice. This method gives excellent toughness and ductility.

  • Inconel X750 – Strengthened by precipitation hardening, where fine particles form during heat treatment, blocking dislocation movement and greatly improving high-temperature strength.

Mechanical Properties

At Room Temperature

Inconel 625 (annealed condition):

  • Tensile Strength: ~120 ksi (827 MPa)

  • Yield Strength: ~60 ksi (414 MPa)

  • Elongation: ~30%

Inconel X750 (precipitation-hardened):

  • Tensile Strength: ~130 ksi (896 MPa)

  • Yield Strength: ~85 ksi (586 MPa)

  • Elongation: ~18%

Key Difference – X750 generally offers higher tensile and yield strength but lower ductility compared to 625.

High-Temperature Performance

  • Inconel 625 – Performs exceptionally up to around 982°C (1800°F), maintaining corrosion resistance and moderate strength.

  • Inconel X750 – Designed for long-term service at temperatures up to 704°C (1300°F), with superior creep and stress rupture resistance due to its precipitation-hardened microstructure.

Summary – Inconel 625 excels in corrosion resistance across a wider temperature range, while X750 offers better high-stress performance in specific elevated temperature environments.

Corrosion Resistance

  • Inconel 625 – Outstanding resistance to a broad range of corrosive environments, including seawater, acidic solutions, and oxidizing or reducing media. It is particularly effective against pitting and crevice corrosion.

  • Inconel X750 – Good oxidation and corrosion resistance, but less resistant to certain aggressive chemicals compared to 625. Performs well in oxidizing atmospheres and high-temperature gas turbine environments.

Conclusion – For severe chemical environments, 625 is the better choice. For high-temperature mechanical loads in less aggressive environments, X750 is more suitable.

Fabrication and Machinability

  • Inconel 625 – More easily fabricated due to its solid-solution strengthening. It can be welded without post-weld heat treatment and maintains corrosion resistance after welding.

  • Inconel X750 – More challenging to machine and form due to higher strength. Requires careful welding procedures and often post-weld heat treatment to restore properties.

Heat Treatment

  • Inconel 625 – Supplied in annealed condition; no precipitation-hardening treatment is required.

  • Inconel X750 – Requires specific heat treatments (solution annealing, aging) to achieve full strength and creep resistance.

Common Applications

Inconel 625 Applications

  • Marine equipment (propeller blades, seawater piping)

  • Chemical processing equipment

  • Heat exchanger tubing

  • Aerospace exhaust systems

  • Flare stacks and superheaters

  • Oil and gas riser systems

Inconel X750 Applications

  • Gas turbine rotor blades and discs

  • Springs and fasteners in high-temperature environments

  • Nuclear reactor control rod components

  • Heat-treating fixtures

  • Aerospace engine thrust reversers

Industry Selection Guide

  • Choose Inconel 625 if:

    • You need superior corrosion resistance in seawater or chemical processing

    • Weldability and post-fabrication resistance are priorities

    • The application involves both high strength and aggressive corrosion conditions

  • Choose Inconel X750 if:

    • High-temperature mechanical performance is the top priority

    • The environment is oxidizing but not highly corrosive

    • The component will undergo precipitation hardening for maximum strength

Standards and Specifications

Inconel 625

  • ASTM B444 (Seamless pipe and tube)

  • ASTM B443 (Plate, sheet, strip)

  • UNS N06625

Inconel X750

  • ASTM B637 (Precipitation-hardened bars, forgings)

  • AMS 5667 (Bars, rings, forgings)

  • UNS N07750

Sustainability and Lifecycle

Both alloys are recyclable and have long service lives, reducing the need for frequent replacements. The durability of Inconel alloys makes them a sustainable choice for industries seeking long-term performance with minimal environmental impact.

Future Outlook

With the growing demand for high-performance materials in aerospace, renewable energy, and offshore oil and gas projects, both Inconel 625 and X750 are expected to see continued use. Advancements in manufacturing, such as additive manufacturing for superalloys, may further enhance their performance and cost-effectiveness.

Conclusion

While Inconel 625 and Inconel X750 share the nickel-chromium base that gives them corrosion and oxidation resistance, they are designed for different operational priorities. Inconel 625 excels in corrosion resistance and fabricability, making it ideal for harsh chemical and marine environments. Inconel X750 stands out for its precipitation-hardened strength and high-temperature creep resistance, making it perfect for aerospace, power generation, and high-stress hot applications.

For industries seeking the right alloy for their specific needs, working with a trusted supplier like sasaalloy ensures access to certified, high-quality materials and expert technical support. Whether you require Inconel 625 for marine corrosion resistance or Inconel X750 for turbine components, sasaalloy provides the right solution for optimal performance and reliability.

Post time: Aug-08-2025