Topic: Material Science
What is the primary mechanism responsible for the increase in strength and hardness during cold working of metals?
- A. Formation of new grains through recrystallization
- B. Increase in dislocation density and entanglement, hindering dislocation movement
- C. Reduction of dislocations in the crystal structure
- D. Melting of metal surface layers due to deformation
Answer: B. Increase in dislocation density and entanglement, hindering dislocation movement
Explanation: Cold working (strain hardening) plastically deforms a metal below its recrystallization temperature. This deformation drastically increases the dislocation density in the crystal lattice. These dislocations entangle and form obstacles to one another, requiring higher stress to cause further plastic flow, hence increasing strength and hardness.