What is the alternative to Inconel 625?
We take an in-depth look at these two popular high-performance nickel alloys and compare their specifications and applications.
When you're looking for a quality material for your next project, a high-performance nickel alloy may be just what you need. However, there are several grades to choose from within the INCONEL family, any of which may meet your requirements and needs.
The INCONEL alloy is INCONEL alloy 625, which is one of the most versatile materials ever created. With its excellent corrosion resistance and high strength, it is suitable for a wide range of applications across a wide range of industries. It is a very popular first-choice material that can solve many material problems for design engineers. The fact that it has been doing so for over 50 years and is still commonly used is a testament to its quality.
However, if high strength is a primary consideration, INCONEL alloy 725 may be a better fit. It is similar to INCONEL alloy 625, especially in terms of corrosion resistance. However, there are significant differences between the two, which may affect the decision of which material to use.
To help you understand the differences and similarities between these two special materials, we have compared their key features and properties.
Composition Differences
The reason INCONEL 625 alloy has such a wide range of desirable properties is due to its unique composition. It is a high nickel alloy, with at least 58% nickel in the mix. It also contains chromium (20-23%) and molybdenum (8-10%), as well as added niobium (3.15-4.15%).
Niobium combines with molybdenum and distorts the atomic matrix of the alloy, imparting exceptionally high strength in the annealed condition without the need for specific strengthening heat treatments. The large amounts of nickel and chromium together give the material incredible corrosion resistance, allowing it to withstand highly corrosive elements and environments.
INCONEL 725 alloy shares many of the same constituent elements - in fact, superficially, they are almost identical. It retains large amounts of nickel (55-59%) and chromium (19-22.5%), as well as molybdenum (7-9.50%). As a result, the material has similar corrosion resistance to INCONEL 625 alloy, making it suitable for a wide range of highly corrosive environments.
However, there are subtle differences in the overall composition of the two materials. INCONEL 625 alloy contains small amounts of cobalt and silver, which are not present in INCONEL 725 alloy. INCONEL 725 alloy has a higher titanium content (1-1.7% compared to 0.4% maximum in INCONEL 625 alloy) and the remainder is made up of iron instead of the 5% maximum in INCONEL 625 alloy. These minor additions and differences allow for the formation of micro-precipitates during heat treatment, which results in significantly higher strength values for INCONEL 725 alloy.
Comparative Strength
INCONEL 625 alloy is a strong nickel alloy. As mentioned previously, this is due to the effects of its composition and the addition of niobium. The mixing of niobium with molybdenum creates a hardening effect that eliminates the need for precipitation hardening treatment. 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 introduced and marketed as a solid solution strengthened alloy. It was discovered that it has age-hardening properties, and various tests were conducted over time to study its effects. It was discovered 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 (learn more about it in this detailed report).
Age-hardened INCONEL Alloy 725 is approximately twice as strong as annealed INCONEL Alloy 625. Because INCONEL Alloy 725 is strengthened by heat treatment rather than cold working, it retains its high ductility and toughness. This strength can be imparted to large, non-uniform sections of material that cannot be strengthened by cold working.
Different Applications
Which material is chosen usually depends on the final intended application of the alloy.
INCONEL 625 alloy is very versatile and 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 ion stress corrosion cracking. Therefore, its applications include gunboat propeller blades, submarine propulsion motors, naval multi-purpose vessel exhaust pipes, and submarine communication cable jacketing.
It is also the material of choice in the aerospace industry, where its high strength, high fatigue and excellent weldability are its ideal assets. This includes use in aircraft ductwork, engine exhaust systems, and fuel lines. Other industry applications include nuclear reactor components and is widely used in chemical processing plants.
INCONEL 725 alloy is also quite widely used in multiple industries, but when its extremely high strength is required, people will choose it instead of INCONEL 625 alloy. For example, in sour gas gathering, where excellent resistance to highly corrosive media is required, INCONEL 725 alloy is used in hangers, landing joints, side pocket mandrels, and polished bore sockets, among others.
Like INCONEL 625 alloy, INCONEL 725 alloy is also used in the marine industry. Here, it is a good choice for products such as high-strength fasteners, where its extra strength is needed without sacrificing resistance to corrosion, pitting, or crevice attack.
If you are interested in learning more about INCONEL 625 alloy or INCONEL 725 alloy and our other product lines, contact an experienced member of our sales team today.
