Question

A material undergoes recrystallization at 250\(^\circ\)C. If the material is heated to 300\(^\circ\)C, what process is most likely occurring?

• A. Melting
• B. Grain growth
• C. Recovery
• D. Further recrystallization

Hint:

Annealing Stages. Recovery (Stress relief) \(\rightarrow\) Recrystallization (New grain formation, restores ductility) \(\rightarrow\) Grain Growth (Existing grains enlarge, can reduce strength). Occur with increasing temperature/time.

Answer 1

The Correct Option is B

Annealing of a cold-worked metal typically involves three stages occurring at increasing temperatures:
(1) Recovery: Relief of internal stresses at lower temperatures, primarily through dislocation movement and annihilation, with little change in microstructure or mechanical properties like strength.

(2) Recrystallization: Formation of new, strain-free grains within the deformed structure.
This occurs above the recrystallization temperature (given as 250°C here) and leads to a significant drop in strength and increase in ductility.

(3) Grain Growth: If heating continues or occurs at temperatures significantly above the recrystallization temperature, the newly formed strain-free grains tend to grow larger by consuming smaller grains, driven by the reduction of grain boundary area/energy.
Since the material has already undergone recrystallization at 250°C, heating it further to 300°C (which is above the recrystallization temperature) will primarily promote the growth of the existing recrystallized grains.
Melting would occur at a much higher temperature.
Recovery precedes recrystallization.
Further recrystallization implies more cold work followed by heating, which isn't stated.
Thus, grain growth is the most likely process occurring at 300°C after recrystallization at 250°C.