Inconel 625 vs Inconel 718: A Comparative Overview

Inconel 625 and Inconel 718 are both high-performance nickel-based superalloys known for their exceptional corrosion resistance, high strength, and versatility. While they share some similarities, they have distinct compositions and applications. Here's a comparative overview of Inconel 625 and Inconel 718:

Chemical Composition:

Inconel 625:

Composition: Inconel 625 is primarily composed of nickel (58%), chromium (20-23%), and molybdenum (8-10%). It also contains smaller amounts of niobium, iron, and other elements.

Key Elements: Nickel provides corrosion resistance, while chromium enhances oxidation resistance. The addition of molybdenum improves resistance to pitting and crevice corrosion.

Inconel 718:

Composition: Inconel 718 consists of nickel (50-55%), chromium (17-21%), niobium (4.75-5.5%), and molybdenum (2.8-3.3%). It also includes smaller amounts of titanium, aluminum, and iron.

Key Elements: The high niobium content contributes to precipitation hardening, providing excellent strength and toughness at elevated temperatures.

Mechanical Properties:

Inconel 625:

Strength: Inconel 625 offers high tensile strength and excellent fatigue strength.

Temperature Resistance: It maintains good mechanical properties at elevated temperatures, making it suitable for various high-temperature applications.

Inconel 718:

Strength: Inconel 718 is renowned for its exceptional strength, especially in high-temperature environments.

Temperature Resistance: It exhibits excellent tensile and impact strength at elevated temperatures, making it suitable for aerospace and high-performance applications.

Corrosion Resistance:

Inconel 625:

General Corrosion: Inconel 625 is highly resistant to corrosion in various environments, including acids and seawater.

Localized Corrosion: Its molybdenum content enhances resistance to pitting and crevice corrosion.

Inconel 718:

General Corrosion: Inconel 718 demonstrates good corrosion resistance in many environments, including acidic and corrosive atmospheres.

Localized Corrosion: It provides resistance to pitting and crevice corrosion, although not as pronounced as Inconel 625.

Applications:

Inconel 625:

Chemical Processing: Widely used in chemical processing industries for its corrosion resistance.

Aerospace: Utilized in aerospace applications, marine engineering, and pollution control equipment.

Oil and Gas: Commonly found in oil and gas processing due to its resistance to sour gas and chloride stress corrosion cracking.

Inconel 718:

Aerospace: Predominantly used in aerospace applications, including aircraft engines and components.

Gas Turbines: Ideal for gas turbine components due to its high-temperature strength and corrosion resistance.

Nuclear Reactors: Applied in nuclear reactors and high-temperature environments.

Weldability and Fabrication:

Inconel 625:

Weldability: Inconel 625 is weldable using various methods, and it is often used in applications requiring welding.

Inconel 718:

Weldability: While weldable, Inconel 718 requires special precautions to maintain its desired properties after welding.

Conclusion: Inconel 625 and Inconel 718 are exceptional alloys with distinct compositions optimized for specific applications. Inconel 625 tubing excels in corrosive environments, making it a go-to choice for chemical processing. In contrast, Inconel 718, with its superior strength at elevated temperatures, finds extensive use in aerospace and high-performance applications. The selection between the two depends on the specific requirements of the intended application, considering factors such as temperature, corrosion resistance, and mechanical properties.