Question

The effect of grain growth on the mechanical properties of a metal is

• A. Increases hardness
• B. Decreases electrical resistance
• C. Reduces strength
• D. Enhances corrosion resistance

Hint:

Grain Growth Effects. Larger grains = Fewer grain boundaries = Easier dislocation motion = Lower strength and hardness. Grain growth typically occurs after recrystallization during high-temperature annealing.

Answer 1

The Correct Option is C

Grain growth occurs during annealing at temperatures above the recrystallization temperature, where larger strain-free grains grow by consuming smaller ones.
This process leads to an increase in the average grain size and a decrease in the total grain boundary area.
Grain boundaries act as obstacles to dislocation motion, thus contributing to the strength and hardness of polycrystalline materials (as described by the Hall-Petch relationship).
By reducing the density of grain boundaries, grain growth makes dislocation movement easier, resulting in a decrease in yield strength and hardness (softening) of the metal.
Effects on electrical resistance and corrosion resistance are generally secondary or more complex compared to the primary effect on mechanical strength.