What is the Classification of Hastelloy?

In industries such as chemical processing, aerospace, marine engineering, and pollution control, choosing the right material is critical to ensure resistance against corrosion, oxidation, and high-temperature stress. One family of alloys that has gained global recognition for its reliability is Hastelloy. But many engineers and procurement specialists often ask: What is the classification of Hastelloy?

This article provides a comprehensive overview of the classification of Hastelloy, its different grades, their chemical compositions, unique properties, and industrial applications.

What is Hastelloy?

Hastelloy is a registered trademark of Haynes International and refers to a group of corrosion-resistant metal alloys. These alloys are mainly based on nickel, with varying amounts of molybdenum, iron, cobalt, and chromium added to enhance performance.

Key Characteristics:

• Exceptional resistance to oxidizing and reducing agents

• High strength at elevated temperatures

• Excellent resistance to localized corrosion, including pitting and stress corrosion cracking

• Suitable for harsh chemical environments

Because of these properties, Hastelloy is often referred to as a “superalloy” and is widely used in chemical and industrial plants.

The Classification of Hastelloy

Hastelloy alloys can be classified based on their chemical composition and corrosion resistance behavior. Broadly, they are divided into nickel-molybdenum alloys and nickel-chromium-molybdenum alloys.

1. Nickel-Molybdenum Alloys (B-Series)

The B-series alloys focus on resistance to reducing agents such as hydrochloric acid, sulfuric acid, and phosphoric acid.

• Hastelloy B and B-2

  • High molybdenum content (~28–30%)

  • Excellent resistance to hydrochloric acid at all concentrations and temperatures

  • Not suitable for oxidizing environments unless specially treated

Applications: Chemical processing involving strong reducing acids.

2. Nickel-Chromium-Molybdenum Alloys (C-Series)

The C-series alloys are the most versatile and widely used Hastelloy grades. By adding chromium, these alloys gain resistance to oxidizing agents while maintaining molybdenum’s protection against reducing agents.

• Hastelloy C, C-22, and C-276

  • C-22: Excellent resistance to oxidizing chemicals such as chlorine and nitric acid

  • C-276: One of the most widely used, with outstanding resistance to strong oxidizers and reducing agents

  • C-4: Exceptional stability at high temperatures

Applications: Flue gas scrubbers, pulp and paper bleaching, pharmaceutical reactors, and waste treatment.

3. Nickel-Iron-Chromium Alloys (G-Series)

The G-series Hastelloys are designed for resistance to both oxidizing and reducing conditions, but with an added emphasis on resistance to phosphoric acid and wet-process phosphoric acid.

• Hastelloy G, G-30, and G-35

  • Excellent resistance to “mixed acid” environments

  • Often used in fertilizer production

Applications: Agriculture, fertilizer plants, and phosphoric acid manufacturing.

4. Other Specialized Hastelloy Grades

• Hastelloy X

  • Designed for high-temperature strength and oxidation resistance

  • Used in gas turbines and aerospace engines

• Hastelloy N

  • Specifically developed for molten salt reactors in nuclear energy applications

Comparison of Major Hastelloy Grades