Question:
In hot rolling of metal
In hot rolling of metal
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When thinking about hot working, always remember two things: 1) High temperature makes the metal soft (low forces) and allows recrystallization (grain refinement). 2) High temperature also causes oxidation (bad surface finish/scale).
Updated On: Jul 2, 2026
- grain refinement is not possible
- surface finish is not very good
- annealing operation is a must
- electrical power requirement is very high
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The Correct Option is B
Solution and Explanation
Step 1: Understanding the Concept:
Hot rolling is a metal forming process performed at temperatures above the material's recrystallization temperature. This high temperature imparts specific characteristics, advantages, and disadvantages to the process and the final product. The question asks to identify a true statement about hot rolling.
Step 2: Detailed Explanation:
Let's evaluate each option:
• (A) grain refinement is not possible: This is false. Grain refinement is one of the primary advantages of hot rolling. The large, coarse grains of a cast ingot are deformed and broken down, and the high temperature allows for repeated cycles of dynamic recrystallization, which creates new, fine, equiaxed grains, improving the mechanical properties.
• (B) surface finish is not very good: This is true. The high temperatures used in hot rolling cause the metal surface to react with oxygen in the air, forming a brittle, rough layer of oxide called "scale." This scale results in a poor surface finish and some loss of dimensional accuracy. The scale typically needs to be removed in a subsequent step like pickling.
• (C) annealing operation is a must: This is false. Because hot rolling is performed above the recrystallization temperature, the material does not strain harden significantly. It continuously softens through recovery and recrystallization. Therefore, a post-rolling annealing operation to restore ductility is generally not necessary.
• (D) electrical power requirement is very high: While any large industrial process requires significant power, the force and power requirements for hot rolling are substantially lower than for cold rolling the same material. This is because the high temperature makes the metal soft and easy to deform. So, compared to the alternative (cold rolling), this statement is misleading.
Step 3: Final Answer:
A key characteristic and disadvantage of hot rolling is that the resulting surface finish is not very good due to the formation of oxide scale.
Hot rolling is a metal forming process performed at temperatures above the material's recrystallization temperature. This high temperature imparts specific characteristics, advantages, and disadvantages to the process and the final product. The question asks to identify a true statement about hot rolling.
Step 2: Detailed Explanation:
Let's evaluate each option:
• (A) grain refinement is not possible: This is false. Grain refinement is one of the primary advantages of hot rolling. The large, coarse grains of a cast ingot are deformed and broken down, and the high temperature allows for repeated cycles of dynamic recrystallization, which creates new, fine, equiaxed grains, improving the mechanical properties.
• (B) surface finish is not very good: This is true. The high temperatures used in hot rolling cause the metal surface to react with oxygen in the air, forming a brittle, rough layer of oxide called "scale." This scale results in a poor surface finish and some loss of dimensional accuracy. The scale typically needs to be removed in a subsequent step like pickling.
• (C) annealing operation is a must: This is false. Because hot rolling is performed above the recrystallization temperature, the material does not strain harden significantly. It continuously softens through recovery and recrystallization. Therefore, a post-rolling annealing operation to restore ductility is generally not necessary.
• (D) electrical power requirement is very high: While any large industrial process requires significant power, the force and power requirements for hot rolling are substantially lower than for cold rolling the same material. This is because the high temperature makes the metal soft and easy to deform. So, compared to the alternative (cold rolling), this statement is misleading.
Step 3: Final Answer:
A key characteristic and disadvantage of hot rolling is that the resulting surface finish is not very good due to the formation of oxide scale.
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