What causes work hardening in metals?

• A. Dislocations multiply and entangle, increasing strength.
• B. Diffusion of atoms to form precipitates.
• C. Grain growth reduces strength.
• D. Recrystallization reduces strength.

Answer: (A)

Work hardening happens because plastic deformation generates dislocations that multiply and become entangled, creating a dense obstacle network that blocks further dislocation motion. As you deform the metal, more dislocations appear and interact, so it becomes progressively harder for additional dislocations to move. This increased resistance raises the stress needed to continue deforming, making the material stronger and harder. Other processes like diffusion to form precipitates, grain growth, or recrystallization involve different microstructural changes and are not the immediate cause of the strengthening seen during deformation. Temperature can influence this by allowing dislocations to bypass obstacles, which can reduce the rate of work hardening.