What is the relationship between carbon content and ductility in steel?

The relationship between carbon content and ductility in steel is quite significant. Higher carbon content in steel tends to increase hardness and strength due to the formation of harder phases like cementite. However, this increase in carbon also leads to a reduction in ductility. This reduction occurs because the microstructural changes associated with higher carbon concentrations create a more brittle material.

As carbon content increases, the formation of pearlite and cementite—hard phases—predominates over softer phases which contribute to ductility. Materials with a lower carbon content exhibit more austenite and ferrite, which provide greater malleability and the ability to deform under stress. Thus, while carbon is critical for achieving desired strength in steel, excessive amounts can lead to a trade-off where ductility is compromised.

In contrast, other options present relationships that do not accurately reflect the effects of carbon on steel. For instance, stating that lower carbon content consistently decreases steel hardness ignores the balance and transition points between various microstructures. Additionally, asserting that carbon content has no impact on ductility overlooks the established principles of materials science that link carbon levels to both strength and ductility characteristics.