Superalloys — temperature classification of Incoloy, Hastelloy, and Vitallium Incoloy, Hastelloy, and Vitallium are engineering alloys primarily designed for service at which temperature class?

Introduction / Context:
High-temperature materials are essential in gas turbines, chemical plants, and power generation where creep resistance, oxidation/corrosion resistance, and microstructural stability govern life. Certain trademarked alloy families are synonymous with this service environment.

Given Data / Assumptions:

• Incoloy: iron-nickel-chromium based alloys for high-temperature corrosion environments.
• Hastelloy: nickel-molybdenum or nickel-chromium-molybdenum alloys with excellent corrosion and elevated-temperature strength.
• Vitallium: cobalt-chromium-molybdenum alloy noted for hot strength and corrosion resistance (also used in biomedical implants).

Concept / Approach:
These alloys possess stable precipitate or solid-solution strengthened matrices that retain strength and resist oxidation and sulfidation at elevated temperatures. While individual grades have specific niches, they are broadly classified as high-temperature or superalloy materials compared with ordinary steels or low-temperature alloys.

Step-by-Step Solution:

Verification / Alternative check:
Data sheets specify service temperatures often exceeding 600°C for many grades, confirming their high-temperature classification.

Why Other Options Are Wrong:

• Low/cryogenic/sub-zero only: contradicts typical applications; cryogenic alloys are more commonly austenitic stainless or special Ni alloys optimized for toughness at low temperatures.
• None of these: incorrect because these families are textbook examples of high-temperature alloys.

Common Pitfalls:
Confusing corrosion-resistant nickel alloys for room-temperature service only; ignoring creep and oxidation design data at elevated temperatures.

Final Answer: