The metallurgical heat treatment known as austempering produces a microstructural result of__________________?
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Answer: A. formation of bainite structure
Explanation
Austempering is an isothermal heat treatment that transforms steel into a tough bainite microstructure. The process involves heating steel into the austenitic phase and quenching it into a molten salt bath maintained at a constant elevated temperature. This isothermal holding prevents the formation of brittle martensite and produces a uniform bainitic structure with superior toughness. Heat treatment processes alter the internal crystalline microstructure of steels to achieve desired mechanical properties like hardness and ductility. Bainite is a needle-like microstructure consisting of ferrite and cementite that offers an excellent combination of strength and toughness. Unlike conventional quenching and tempering, austempering bypasses the martensitic transformation phase entirely.
Option B is incorrect because carburizing involves diffusing carbon into the surface of steel rather than isothermal austempering. Option C is wrong because martensite is formed by rapid cooling to low temperatures, not by isothermal transformation to bainite. Option D is incorrect because lamellar pearlite forms during slow continuous cooling rather than isothermal austempering baths.
- Subject
- Engineering
- Category
- Mechanical Engineering
- Topic
- —
- Difficulty
- medium
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