Inconel 718 vs 625 – What’s the Difference

Inconel 718 vs 625

Inconel is a family of high-performance nickel-chromium-based alloys used in extreme environments such as aerospace, chemical processing, and nuclear power generation. Inconel 718 and Inconel 625 are two of the most popular alloys in this family and are known for their excellent strength, corrosion resistance, and high-temperature properties. However, some key differences between these alloys make them suitable for different applications. This blog post will closely examine Inconel 718 vs 625 to help you understand their similarities and differences.

What is Inconel 718?

Inconel 718 is a nickel-based superalloy known for its high strength, corrosion resistance, and superior heat resistance. It is an age-hardenable alloy composed of nickel (54%), chromium (17-21%), iron (19-23%) plus smaller amounts of molybdenum (2.8 – 3.3%), titanium (.65 – 1.15%), aluminium (.2 – .8%), and other elements making it an ideal material for use in extreme environments like space or the deep sea where there are extreme temperatures and pressures.

What is Inconel 625?

Inconel 625 is a nickel-based superalloy with excellent corrosion, oxidation, and heat resistance. It contains niobium for added strength and corrosion resistance in hot acid environments such as sulfuric acid. Inconel 625 is used for chemical plants, marine components, aerospace components, food processing equipment and water treatment systems due to its exceptional mechanical properties at high temperatures. Furthermore, it can be easily machined into complex shapes without suffering from cracking or other pathological issues associated with alloys made of harder metals.

Difference Between Inconel 718 and 625

Inconel 718 and 625 are nickel-based alloys with high strength and corrosion resistance. The main difference is that 718 has better hot workability, creep resistance, and fatigue strength than 625. Both have low thermal expansion coefficients and offer excellent weldability.

Chemical Composition

One of the main differences between Inconel 718 and Inconel 625 lies in their chemical composition. Inconel 718 is a nickel-chromium alloy containing molybdenum, niobium, iron, and small amounts of titanium and aluminium. On the other hand, Inconel 625 is a nickel-chromium-molybdenum alloy that also contains niobium and small amounts of iron, titanium, and aluminium. These different elements give each alloy different physical and mechanical properties.

Strength and Hardness

Inconel 718 has a higher tensile strength and yield strength than Inconel 625 due to its higher nickel and molybdenum content. It is also harder and more resistant to deformation at high temperatures. Inconel 718 is often used in applications where high strength and resistance to fatigue are required, such as gas turbine engines and rocket motors. In contrast, Inconel 625 is preferred for applications that require good corrosion resistance and high toughness, such as chemical processing equipment and marine engineering.

Corrosion Resistance

Inconel 718 and Inconel 625 are known for their excellent corrosion resistance in many environments, including high-temperature and corrosive gases. However, Inconel 625 has better pitting and crevice corrosion resistance than Inconel 718. It is also more resistant to low sulfuric and hydrochloric acid concentrations. For this reason, Inconel 625 is often used in chemical processing plants and offshore structures where corrosion resistance is critical.

Weldability

Inconel 625 has better weldability than Inconel 718 due to its low carbon content and high nickel content. It can be easily welded using standard welding techniques such as gas tungsten arc welding (GTAW), gas metal arc welding (GMAW), and shielded metal arc welding (SMAW). In contrast, Inconel 718 is more difficult to weld due to its high carbon and nitrogen content, which can cause cracking and other defects during welding.

Cost

Inconel 718 is generally more expensive than Inconel 625 due to its higher nickel and molybdenum content. However, the cost difference may vary depending on the quantity and specifications of the alloy required. In general, Inconel 718 is used in applications with high strength and resistance to fatigue, while Inconel 625 is preferred for applications that require good corrosion resistance and high toughness.

Conclusion

Inconel 718 and Inconel 625 are two high-performance alloys widely used in extreme environments. While both alloys share some similarities, such as their excellent corrosion resistance and high-temperature properties, they also have some key differences. Inconel 718 is preferred for applications that require high strength and resistance to fatigue, while Inconel 625 is preferred for applications that require good corrosion resistance and high toughness. As always, consult an expert in the field before deciding which alloy is right for your specific application.