Which microstructural feature increases brittleness?

Which microstructural feature increases brittleness?

• A. High yield strength
• B. Small grain size
• C. Large grain size
• D. Precipitates

Answer: (C)

Grain size controls how easily cracks can grow through a metal. Grain boundaries act as barriers that deflect and blunt cracks, absorbing energy as they hinder propagation. When grains are large, there are fewer boundaries to stop a crack, so the crack can propagate more readily along cleavage paths, increasing brittleness. This tendency is particularly relevant for piping materials at lower temperatures, where toughness matters most. Smaller grain size provides more boundaries, making it harder for cracks to advance and thus reducing brittleness. Precipitates and very high strength can influence toughness in different ways, but the clearest microstructural feature that raises brittleness here is large grain size.

Grain size controls how easily cracks can grow through a metal. Grain boundaries act as barriers that deflect and blunt cracks, absorbing energy as they hinder propagation. When grains are large, there are fewer boundaries to stop a crack, so the crack can propagate more readily along cleavage paths, increasing brittleness. This tendency is particularly relevant for piping materials at lower temperatures, where toughness matters most. Smaller grain size provides more boundaries, making it harder for cracks to advance and thus reducing brittleness. Precipitates and very high strength can influence toughness in different ways, but the clearest microstructural feature that raises brittleness here is large grain size.