Which statement is true about carbon content and ductility?

• A. Ductility decreases as carbon content increases
• B. Ductility increases as carbon content increases
• C. Ductility is unaffected by carbon content
• D. Ductility depends only on alloy content

Answer: (A)

Higher carbon content in steel generally reduces ductility. Ductility is the material’s ability to deform plastically before breaking; as carbon rises, the microstructure shifts from ductile ferrite toward harder phases like pearlite and cementite. These harder phases impede dislocation movement, making the steel harder but less able to deform without fracturing under stress. That’s why low-carbon steels are typically very ductile, while high-carbon steels are stronger but more brittle. Other factors, such as additional alloying elements and heat treatment, also influence ductility, but carbon content is a primary driver of this trend.