Whether you are a supplier or a end user of Inconel alloys, you may face challenges when deciding between Inconel 625 and Inconel 718 alloy or advising customers on material selection.
Both Inconel 625 and Inconel 718 are superalloys known for their exceptional properties.
The primary difference between them is that Inconel 625 is optimized for corrosion resistance, whereas Inconel 718 is designed for high strength.
This article will compare alloy 625 and alloy 718 across various aspects, providing you with a clearer understanding of these two alloys.
INCONEL® nickel-chromium alloy 625 (UNS N06625 / W.Nr. 2.4856) is used for its high strength, excellent fabricability (including joining), and outstanding corrosion resistance. Service temperatures range from cryogenic to 1800°F (982°C).
What is Inconel Alloy 718?
INCONEL® alloy 718 (UNS N07718 / W.Nr. 2.4668) is a high-strength, corrosion-resistant nickel chromium material used at -423° to 1300°F. The age-hardenable alloy can be readily fabricated, even into complex parts. Its welding characteristics, especially its resistance to postweld cracking, are outstanding.
Inconel Alloy 625 vs Inconel Alloy 718 Chemical Composition
Here’s a comparison table for the chemical composition of Inconel 625 and Inconel 718:
Inconel Alloy 625 vs Inconel Alloy 718 Corrosion Resistance
Inconel 625 contains significantly less iron than Inconel 718, resulting in higher levels of nickel, chromium, and molybdenum.
Nickel inherently provides good corrosion resistance, and chromium is a crucial element for corrosion resistance in superalloys. Consequently, Inconel 625 offers superior corrosion resistance compared to Inconel 718.
The presence of molybdenum in Inconel 625 enhances its ability to resist reducing environments and improves its overall corrosion resistance. This further increases the disparity in corrosion resistance between Inconel 625 and Inconel 718.
Inconel Alloy 625 vs Inconel Alloy 718 Mechanical Behavior
A key difference between Inconel 625 and Inconel 718 lies in their strengthening mechanisms.
Inconel 625 is primarily a solid solution strengthened alloy. Most of the aluminum and titanium dissolve into the alloy matrix (γ-austenite), which provides a limited strengthening effect.
In contrast, Inconel 718 is a precipitation-hardened alloy. During production, aluminum and titanium precipitate from the matrix to form the γ’ phase, significantly enhancing the alloy’s strength.
This fundamental difference makes Inconel 718 much stronger than Inconel 625.
In Inconel 625, niobium and tantalum contribute to solid solution strengthening. Due to their large atomic radii, they have a greater strengthening effect than aluminum and titanium.
In Inconel 718, niobium and tantalum also play a role in precipitation strengthening. Unlike aluminum and titanium, some niobium and tantalum enter the γ matrix for solid solution strengthening, while others form the γ’ phase to enhance precipitation strengthening. Additionally, a significant portion of niobium and tantalum forms the γ” precipitation strengthening phase, which has a pronounced strengthening effect at medium and low temperatures. However, at high temperatures, the effectiveness of the γ” phase diminishes significantly.
Inconel Alloy 625 vs Inconel Alloy 718 Physical Properties
| Inconel 625 | Inconel 718 | |
|---|---|---|
| Density, g/cm³ | 8.44 | 8.19 |
| Density, lb/in.³ | 0.305 | 0.296 |
| Melting Range, °F | 2350-2460 | 2300-2437 |
| Melting Range, °C | 1290-1350 | 1260-1336 |
| Permeability at 200 oersted (15.9 kA/m) | 1.0006 | 1.0006 |
| Curie Temperature, °F | <-320 | -170 |
| Curie Temperature, °C | -196 | -112 |
Inconel Alloy 625 vs Inconel Alloy 718 Application
Due to its excellent corrosion resistance, a typical application of Inconel 625 is marine. Its resistance to localized corrosion (pitting and crevice corrosion), chloride ion stress corrosion, and its excellent fatigue strength make it widely used in marine parts such as propeller blades, exhaust pipes, and fasteners. For ambient temperature applications, Inconel 625 is recommended to be delivered annealed.
In addition, Inconel 625 is also widely used in the aerospace field, thanks to its excellent high-temperature tensile properties and creep strength. Through processing and welding, Inconel 625 can be used in components such as aircraft piping systems, engine exhaust systems, fuel and hydraulic lines, and heat exchanger tubes. The high temperature properties of Inconel 625 alloy also make it used in heat treatment equipment and chemical industry.
The ease and economy with which INCONEL alloy 718 can be fabricated, combined with good tensile, fatigue, creep, and rupture strength, have resulted in its use in a wide range of applications. Examples of these are components for liquid fueled rockets, rings, casings and various formed sheet metal parts for aircraft and land-based gas turbine engines, and cryogenic tankage. It is also used for fasteners and instrumentation parts.
Inconel Alloy 625 vs Inconel Alloy 718 Main Standards
Here’s a comparison table for the standards of Inconel alloy 625 and Inconel alloy 718:
Inconel Alloy 625 vs Inconel Alloy 718 Cost
Alloy 718 features a more intricate alloying composition, challenging processing requirements, and superior performance, resulting in a significantly higher price compared to Inconel 625.
If Inconel 625 meets all the requirements for your project, we recommend opting for this alloy initially to achieve cost savings.
Conclusion
Inconel 625 is known for its excellent corrosion resistance due to its solid solution strengthening.
Inconel 718, a precipitation-hardened alloy, is characterized by its exceptionally high strength.
Each alloy serves its specific purposes and cannot substitute for the other.
HZW supplies both Inconel 625 and Inconel 718 products, adhering to standard solution treatment or aging treatment processes. For material purchase inquiries, please feel free to contact us.
