Question

Strain hardening in metals leads to:

• A. A decrease in dislocation density
• B. An increase in porosity
• C. An increase in hardness and strength
• D. A reduction in grain size

Hint:

Strain hardening increases dislocation density, which strengthens the material by making it harder for dislocations to move — leading to increased hardness and tensile strength.

Answer 1

The Correct Option is C

Strain hardening, also known as work hardening, is a phenomenon where a metal becomes harder and stronger as it is plastically deformed.
This occurs because plastic deformation increases the dislocation density within the material. As dislocations multiply and interact, their movement becomes more difficult due to entanglement and obstruction, making further deformation more challenging.
As a result:
- Strength and hardness increase,
- Ductility decreases,
- No significant change in grain size occurs during strain hardening (unless followed by heat treatment).
Therefore, the correct answer is the increase in hardness and strength due to higher resistance to dislocation motion.