Effect of carbon content on mechanical properties of steel With an increase in the percentage of carbon in steel (keeping other factors constant), which property decreases most notably for structural applications?

Introduction / Context:
Carbon is the primary alloying element that controls the balance between strength, hardness, and ductility in plain carbon steels. As the carbon percentage rises, microstructural changes shift steel from more ductile ferrite-pearlite to harder, stronger phases, affecting formability and toughness.

Given Data / Assumptions:

• Comparative, qualitative property change with carbon percentage.
• No heat treatment variations considered.
• Room-temperature behavior for structural use.

Concept / Approach:
Higher carbon content increases strength and hardness but reduces ductility and toughness. For structural members that must deform plastically to redistribute stresses, ductility is valuable; hence, structural steels typically keep carbon content modest (e.g., < 0.25%).

Step-by-Step Solution:

Verification / Alternative check:
Stress-strain curves for steels with increasing carbon show lower elongation at fracture and reduced uniform elongation, confirming reduced ductility.

Why Other Options Are Wrong:
Strength and hardness generally increase with carbon; brittleness increases (so it does not decrease); elastic modulus is largely insensitive to composition changes in steels.

Common Pitfalls:
Confusing toughness with hardness; assuming all properties improve together with alloying.

Final Answer:
Ductility