In the realm of superalloys, Inconel 725 and 718 stand out due to their exceptional properties. These alloys, developed by Special Metal Corporation and marketed under the Inconel family, are primarily composed of nickel. However, they exhibit distinct differences in their compositions and physical properties. This article delves into a detailed comparison between Inconel 725 and Inconel 718.
Table of Contents
Overview of Inconel
Inconel is a trademark of Special Metals Corporation, denoting a family of nickel-chromium-based superalloys. Notable for their resistance to corrosion and extreme temperatures, these alloys are used in various high-stress environments.
What is Inconel 725?
Inconel 725 is a nickel-chromium alloy with substantial additions of molybdenum, niobium, and titanium. The largest constituent element is nickel, making up 58% of the total composition.
Composition
Inconel 725 consists of the following elements:
- Nickel (58%)
- Chromium (20-23%)
- Molybdenum (8-10%)
- Niobium (4.7-5.5%)
- Titanium (~2.75%)
Properties
Inconel 725 is renowned for its high tensile strength, achieved through a unique heat treatment process. The alloy is resistant to corrosion and exhibits excellent mechanical properties, even under extreme temperature conditions.
What is Inconel 718?
Inconel 718, on the other hand, is a nickel-chromium-molybdenum alloy with a slightly different composition.
Composition
Inconel 718 is composed of:
- Nickel (50-55%)
- Chromium (17-21%)
- Niobium (4.7-5.5%)
- Molybdenum (2.8-3.3%)
Properties
Despite similar nickel content, Inconel 718’s properties are distinct due to its unique composition. This alloy also has excellent strength and corrosion resistance, but its tensile strength is lower compared to Inconel 725.
Key Differences between Inconel 725 and 718
Though both alloys are part of the Inconel family, they exhibit different properties due to variations in their compositions.
- Composition: Inconel 725 contains a higher percentage of nickel compared to Inconel 718. The difference in titanium and molybdenum content also results in varied properties.
- Tensile Strength: Inconel 725 has a higher tensile strength, making it a more suitable choice for applications requiring superior strength.
Applications of Inconel 725 and 718
Inconel 725 and 718 find use in various high-stress applications due to their outstanding properties.
- Inconel 725 is primarily used in the oil and gas industry for downhole components, measurement equipment, drill string parts, valves, seal assemblies, and hangers.
- Inconel 718, on the other hand, is used in aerospace applications, including high-speed airframe parts and rocket engines due to its high-temperature strength.
Machinability of Inconel 725 and 718
Both Inconel 725 and 718 can be machined, but the process requires careful planning to minimize work hardening and tool wear. The use of sharp tools, slow speeds, and ample coolant is recommended.
Cost Comparison
The cost of Inconel alloys is influenced by the price of nickel and other alloying elements. As a result, Inconel 725, with its higher nickel content, is generally more expensive than Inconel 718.
Inconel 725 and 718 in the Oil and Gas Industry
Due to their superior strength and corrosion resistance, both Inconel grades are increasingly being used in the oil and gas industry. However, Inconel 925 is often preferred over Inconel 718 as a cost-effective alternative.
Other Inconel Grades
Apart from Inconel 725 and 718, there are several other Inconel grades, including Incoloy 825 and 925, each having its unique properties and applications.
Conclusion
In summary, both Inconel 725 and 718 are exceptional materials with unique properties that make them suitable for various applications. Although they share a family, their differences in composition result in distinct properties, making each more suited to specific applications. Understanding these differences is crucial when selecting the right material for your specific needs.
