High-performance nickel alloys are often the material of choice when strength, corrosion resistance, and superior performance are required. In this in-depth review, we’ll be looking at two popular alloys from the INCONEL range – INCONEL alloy 725 and INCONEL alloy 625.
Overview of INCONEL Alloys
INCONEL alloys are renowned for their exceptional versatility and excellent corrosion resistance. They’ve been solving material challenges for design engineers for over 50 years now, and their popularity hasn’t waned.
INCONEL Alloy 625
The flagship of the INCONEL range, alloy 625 is one of the most versatile materials ever created. It is a nickel-heavy alloy that is known for its outstanding corrosion resistance and high strength. This blend of properties makes it suitable for a wide array of applications across numerous industries.
Composition of INCONEL Alloy 625
The wide range of desirable properties offered by INCONEL alloy 625 stems from its unique composition. The blend consists of a minimum of 58% nickel, along with notable amounts of chromium (20-23%), molybdenum (8-10%), and added niobium (3.15-4.15%).
This unique mix distorts the alloy’s atomic matrix, which results in high strength in the annealed condition without the need for a specific strengthening heat treatment. The nickel and chromium confer outstanding corrosion resistance, enabling the material to withstand highly corrosive elements and environments.
Strength of INCONEL Alloy 625
INCONEL alloy 625 is a strong nickel alloy, with its strength primarily coming from its unique composition and the effect of adding niobium. The blend of niobium with molybdenum produces a stiffening effect, eliminating the need for a precipitation-hardening treatment. It still outperforms many other nickel alloys in terms of strength.
INCONEL Alloy 725
If high strength is the priority, INCONEL alloy 725 might be a better fit. It is similar to INCONEL alloy 625 in terms of corrosion resistance, but there are notable differences between the two that can affect the decision of which to use.
Composition of INCONEL Alloy 725
INCONEL alloy 725 shares many of the compositional elements of alloy 625. It retains a high quantity of both nickel (55-59%) and chromium (19-22.5%), plus molybdenum (7-9.50%). As such, the material has similar corrosion resistance to INCONEL alloy 625.
However, there are subtle differences in the overall composition of the two materials. INCONEL alloy 725 has a higher amount of titanium (1-1.7%) and iron makes up the balance, rather than having a 5% maximum as per INCONEL alloy 625. These additions and differences allow for micro precipitates to form during the heat-treating process, which gives INCONEL alloy 725 its greatly increased strength value.
Strength of INCONEL Alloy 725
The strength of age-hardened INCONEL alloy 725 is roughly twice the strength of annealed INCONEL alloy 625. Since INCONEL alloy 725 is strengthened through heat treatment, and not through cold working, it retains high ductility and toughness. This strength can be imparted to large and non-uniform sections of material that can’t be strengthened by cold work.
Application Differences Between INCONEL 625 and 725
The choice of which material to go for often comes down to the intended final application of the alloy.
Applications of INCONEL Alloy 625
INCONEL alloy 625 is employed in a wide variety of industries, thanks to its versatility. It’s often used in sea-water applications due to its resistance against localized attack, such as pitting and crevice corrosion. Its applications include propeller blades for gunboats, submarine propulsion motors, exhaust ducts for Navy utility boats, and sheathing for undersea communication cables.
It’s also a material of choice in the aerospace industry, where its high strength, fatigue resistance, and excellent weldability are desirable assets. Other industry applications include nuclear reactor components and chemical processing plants.
Applications of INCONEL Alloy 725
INCONEL alloy 725 is used across numerous industries, but it’s chosen over INCONEL alloy 625 when exceptionally high strength is required. It’s used in the collection of sour gas, where exceptional resistance to highly corrosive media is required. INCONEL alloy 725 is also used in the marine industry for high-strength fasteners, where extra strength is required without sacrificing resistance to corrosion, pitting, or crevice attack.
For more information on INCONEL alloy 625 or INCONEL alloy 725, contact an experienced member of our sales team today.
Conclusion: Inconel 725 vs 625
When it comes to the comparison of inconel 725 vs 625, both alloys have excellent performance characteristics that make them suitable for many applications. The choice between the two often comes down to specific application needs and the priority of high strength or corrosion resistance. Through a detailed understanding of the properties of each alloy, an informed decision can be made on which alloy is best suited for your project requirements.
