Question

Cold working of metal is carried out at

• A. below recrystallization temperature
• B. above recrystallization temperature
• C. below room temperature
• D. just above the grain growth temperature

Hint:

The distinction between "hot" and "cold" working is not based on room temperature, but rather on the metal's recrystallization temperature.
For example, lead has a recrystallization temperature below room temperature, so working lead at room temperature is actually a "hot working" process.

Answer 1

The Correct Option is A

Step 1: Understanding the Question:
The question asks for the temperature regime in which "cold working" of metals is defined and conducted.

Step 2: Detailed Explanation:

• Definition of Metal Working Regimes:
Plastic deformation processes for metals are classified into cold working, warm working, and hot working based on the recrystallization temperature ($T_{rec}$) of the metal.
The recrystallization temperature is the temperature at which a highly strained grain structure is replaced by a new set of strain-free grains. It is typically in the range of $0.3 \ T_m$ to $0.5 \ T_m$ (where $T_m$ is the absolute melting point).

• Cold Working:
Cold working is plastic deformation carried out at temperatures below the recrystallization temperature.
Often, this is done at room temperature. Because the temperature is too low for recrystallization to occur, the deformed grains remain strained.
This leads to strain hardening (work hardening), which increases the strength and hardness of the metal while decreasing its ductility.

• Hot Working:
Deformation carried out above the recrystallization temperature, where the metal continuously recrystallizes and dynamic recovery occurs, preventing work hardening.

Step 3: Final Answer:
Cold working of metal is carried out at temperatures below the recrystallization temperature.