At low temperatures (e.g., 75°C), steel notched-bar impact values____________________?
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Answer: B. decreases markedly
Explanation
Ferritic steels experience a well documented ductile to brittle transition temperature range. Lowering the temperature causes notched bar impact strength values to drop dramatically and rapidly. Impact energy absorption decreases because atomic lattice mobility becomes severely restricted. Charpy and Izod tests measure the energy absorbed by materials during sudden impact loading. Body centered cubic crystal structures in ferritic steels exhibit pronounced low temperature brittleness. The transition temperature marks the boundary between ductile tearing and brittle cleavage fracture.
Engineers must avoid using carbon steels in cryogenic structures to prevent catastrophic brittle failures. Bridges and pipelines operating in freezing winter environments require specialized high toughness steel grades. Liberty ships suffered historic structural failures due to brittle steel behavior in cold oceans. Impact values never increase markedly when cooling ferritic steel below its transition threshold. Remaining completely constant contradicts the fundamental metallurgical behavior of carbon steel alloys. While heat treatment shifts the transition curve, temperature reduction universally induces embrittlement.
- Subject
- Engineering
- Category
- Mechanical Engineering
- Topic
- —
- Difficulty
- medium
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