Question

In cold working of metals, the working temperature is

• A. Less than the room temperature
• B. Room temperature
• C. Below the recrystallization temperature
• D. Above the recrystallization temperature

Hint:

Cold working occurs below the recrystallization temperature to retain strain hardening, typically at or near room temperature for most metals.

Answer 1

The Correct Option is C

Step 1: Understand cold working of metals.
Cold working is a metal forming process where the metal is deformed plastically at a temperature below its recrystallization temperature. This process increases the strength and hardness of the metal through strain hardening (work hardening) but reduces ductility. Step 2: Define the recrystallization temperature.
The recrystallization temperature is the temperature at which new, strain-free grains form in the metal, relieving internal stresses and softening the material. For most metals, this temperature is approximately 0.3 to 0.5 times the melting point (in Kelvin). For example:
For steel, the recrystallization temperature is typically around 400–700°C, depending on the alloy.
Room temperature (around 20–25°C) is well below this value for most metals.
Step 3: Analyze the working temperature in cold working.
In cold working, the deformation occurs below the recrystallization temperature to retain the strain hardening effects. If the temperature were above the recrystallization temperature, the metal would undergo recrystallization, leading to softening (as in hot working or annealing).
Cold working is often performed at or near room temperature, but the defining criterion is that the temperature must be below the recrystallization temperature, not necessarily below room temperature. Step 4: Evaluate the options.
(1) Less than the room temperature: Cold working can occur at room temperature, so it’s not necessarily below room temperature (e.g., refrigeration is not required). Incorrect.
(2) Room temperature: While cold working is often done at room temperature, the key criterion is being below the recrystallization temperature, not specifically at room temperature. Incorrect.
(3) Below the recrystallization temperature: This is the precise definition of cold working, as it ensures strain hardening without recrystallization. Correct.
(4) Above the recrystallization temperature: This describes hot working, not cold working. Incorrect. Step 5: Select the correct answer.
In cold working of metals, the working temperature is below the recrystallization temperature, matching option (3).