Difference Between Hastelloy and Inconel

Hastelloy and Inconel are both high-performance superalloys known for their excellent resistance to high temperatures and corrosion. Although they share similarities, such as being nickel-based alloys, they are engineered for different purposes and perform optimally in different environments. Let’s explore the differences between Hastelloy and Inconel in terms of composition, properties, and applications.

Composition

1. Hastelloy:  
   Hastelloy is a trademarked name for a group of corrosion-resistant superalloys, primarily composed of nickel along with significant amounts of molybdenum and chromium. These elements provide excellent resistance to pitting, stress corrosion cracking, and other forms of corrosion, especially in highly aggressive environments such as those with high concentrations of chlorine, acids, and other corrosive agents. The composition can vary between different grades like Hastelloy C-276, C-22, B-3, etc.

2. Inconel:  
   Inconel alloys, on the other hand, are primarily composed of nickel and chromium but also contain other elements such as iron, molybdenum, and niobium, depending on the specific alloy (e.g., Inconel 600, 625, 718). The high nickel content in Inconel makes it ideal for applications requiring high temperature resistance, while chromium enhances its resistance to oxidation. Inconel alloys are typically designed for high-temperature applications rather than corrosion resistance in extreme chemical environments.

Key Differences

1. Corrosion Resistance:  
   - Hastelloy: Hastelloy is known for its superior resistance to corrosion, particularly in aggressive environments that contain chlorides, acids, or high temperatures. The combination of nickel, molybdenum, and chromium gives Hastelloy excellent resistance to pitting and stress corrosion cracking. Hastelloy C-276, for example, is particularly resistant to sulfuric and hydrochloric acids, making it ideal for chemical processing industries.
   - Inconel: Inconel alloys are also resistant to oxidation and corrosion, especially at high temperatures. However, they are not as resistant as Hastelloy in extremely aggressive chemical environments. Inconel is better suited for high-temperature applications where oxidation resistance is critical, such as in gas turbines, jet engines, and heat exchangers.

2. Temperature Resistance:  
   - Hastelloy: While Hastelloy is capable of withstanding high temperatures, its main strength lies in its ability to resist corrosion in harsh chemical environments. Hastelloy alloys typically perform well in temperatures up to around 1,800°F (982°C) depending on the grade.
   - Inconel: Inconel is designed to maintain strength and stability at significantly higher temperatures than Hastelloy. Inconel alloys like Inconel 718 can withstand temperatures up to 1,800°F (982°C), while others like Inconel 625 and Inconel 600 can operate at temperatures of up to 2,000°F (1,093°C) or more, making them ideal for high-temperature applications like jet engines and gas turbines.

3. Mechanical Properties:  
   - Hastelloy: Hastelloy alloys are designed to offer excellent strength and toughness in highly corrosive environments. However, they tend to be less strong at elevated temperatures compared to Inconel. They are primarily used in applications where resistance to corrosion is more critical than temperature resistance.
   - Inconel: Inconel alloys are known for their high strength at elevated temperatures. The combination of nickel and chromium in Inconel provides excellent resistance to thermal fatigue, oxidation, and thermal creep. Inconel alloys maintain their mechanical properties even under extreme heat and stress.

4. Applications:  
   - Hastelloy: Hastelloy is commonly used in chemical processing, pharmaceutical manufacturing, pollution control systems, and power plants. It is the material of choice for equipment exposed to strong acids, alkalis, and other corrosive chemicals. Hastelloy’s resistance to pitting and stress corrosion cracking makes it ideal for reactors, heat exchangers, and piping in aggressive environments.
   - Inconel: Inconel is primarily used in high-temperature applications such as jet engines, gas turbines, rocket engines, and power plants. Inconel alloys are commonly used for components that need to withstand high mechanical stress and oxidation at elevated temperatures, including turbine blades, combustion chambers, and exhaust systems.

5. Cost:  
   In general, Hastelloy is more expensive than Inconel due to its higher molybdenum content and superior corrosion resistance in highly aggressive environments. Hastelloy alloys are typically used in niche applications that demand these advanced properties, while Inconel alloys, though expensive, are more widely used in high-temperature industries.

Conclusion

Hastelloy and Inconel are both high-performance alloys that excel in different environments. Hastelloy stands out for its excellent corrosion resistance, particularly in aggressive chemical environments, while Inconel is favored for its high-temperature strength and resistance to oxidation. The choice between these two alloys depends on the specific demands of your application, such as temperature conditions or exposure to corrosive substances.