INCONEL alloy 625 & INCONEL alloy 725 – a comparison
We'll take an in-depth look at these two popular high-performance nickel alloys and compare their specifications and applications.
If you're looking for a quality material for your next project, a high-performance nickel alloy may be just what you need. However, with a wide range of grades available in the INCONEL family, there's always one that will suit your needs.
INCONEL's flagship alloy is INCONEL 625 alloy, which is one of the most versatile materials ever. It's used in a wide range of industries due to its excellent corrosion resistance and high strength. It's a popular material that helps design engineers solve many material challenges. The fact that it's been popular for over 50 years and is still widely used today is a testament to its superior quality.
However, if high strength is more important to you, INCONEL 725 alloy may be a better fit for you. It's similar to INCONEL 625 alloy, especially when it comes to corrosion resistance. However, there are significant differences between the two that may affect which one you choose.
To help you understand the similarities and differences between these two outstanding materials, we've compared their key properties and performance.
Compositional Differences
The reason INCONEL 625 alloy offers such a wide range of desirable properties is its unique composition. It is a high-nickel alloy, with a minimum nickel content of 58%. It also contains chromium (20-23%) and molybdenum (8-10%), as well as niobium (3.15-4.15%).
Niobium, combined with molybdenum, alters the atomic matrix of the alloy, giving it extremely high strength in the annealed state without requiring special strengthening heat treatments. The high levels of nickel and chromium together give the material excellent corrosion resistance, allowing it to withstand highly corrosive elements and environments.
INCONEL 725 alloy shares many of the same constituent elements as above-in fact, superficially, they are almost identical. It retains higher nickel (55-59%) and chromium (19-22.5%) contents, as well as molybdenum (7-9.50%). As a result, the material has similar corrosion resistance to INCONEL 625 alloy and is suitable for a wide range of highly corrosive environments.
However, there are subtle differences in the overall composition of the two materials. INCONEL Alloy 625 contains small amounts of Cobalt and Silver, which are not present in INCONEL Alloy 725. INCONEL Alloy 725 has a higher titanium content (1-1.7% compared to a maximum of 0.4% for INCONEL Alloy 625), with the remainder made up of Iron, compared to a maximum of 5% for INCONEL Alloy 625. These minor additions and differences allow for the formation of micro-precipitates during heat treatment, which results in significantly higher strength values for INCONEL Alloy 725.
Strength Comparison
INCONEL alloy 625 is a high-strength nickel alloy. As mentioned previously, this is due to its composition and the addition of niobium. The combination of niobium and molybdenum creates a strengthening effect that eliminates the need for precipitation hardening. For many applications, the inherent high strength of this material is more than sufficient. It still outperforms many other nickel alloys in this area.
However, sometimes higher strength is required, but not at the expense of excellent corrosion resistance. INCONEL alloy 625 was originally introduced and sold as a solid solution strengthened alloy. It was discovered that it has age hardening properties and various tests were conducted to study the effects of this over time. It was found that the addition of titanium significantly improved the age hardening reaction. This led to the creation of a new alloy - we call it INCONEL alloy 725 (see this detailed report).
Age hardened INCONEL alloy 725 is about twice as strong as annealed INCONEL alloy 625. Because INCONEL alloy 725 is strengthened by heat treatment rather than cold working, it retains high ductility and toughness. This strength can be imparted to large and non-uniform sections of material that cannot be strengthened by cold working.
Different Applications
The choice of material is often determined by the end use of the alloy.
Because of its versatility, INCONEL 625 alloy is used in a wide range of industries. For example, it is often used in seawater applications due to its resistance to localized corrosion, such as pitting and crevice corrosion. It is also resistant to chloride stress corrosion cracking. As a result, its applications include propeller blades for gunboats, submarine propulsion motors, exhaust pipes for naval multi-purpose boats, and jacketing for submarine communication cables.
It is also the material of choice in the aerospace industry, where its high strength, high fatigue strength, and excellent weldability are valuable advantages. This includes use in aircraft ductwork, engine exhaust systems, and fuel lines. Other industry applications include nuclear reactor components and extensive use in chemical processing plants.
INCONEL 725 alloy also has a wide range of applications in many industries, but when its extreme strength is required, it is preferred over INCONEL 625 alloy. For example, in sour gas collection, where excellent resistance to highly corrosive media is required, INCONEL 725 alloy is used to manufacture hangers, landing nipples, side pocket mandrels and polished bore sockets.
Like INCONEL 625 alloy, INCONEL 725 alloy is also used in the marine industry. It is ideal for areas such as high-strength fasteners where extra strength is required without sacrificing resistance to corrosion, pitting or crevice erosion.
If you are interested in learning more about INCONEL Alloy 625 or INCONEL Alloy 725 and our other product lines, please contact an experienced member of our sales team today.
