Which material property does not typically improve with carbon addition in steel?

The addition of carbon to steel is primarily aimed at enhancing various mechanical properties, most notably tensile strength, hardness, and wear resistance. When carbon is added, it forms carbides and interacts with the iron matrix, leading to increased strength and hardness due to the solid solution strengthening and the formation of microstructures such as pearlite or martensite.

Tensile strength improves because the presence of carbon hinders the movement of dislocations in the steel, making it more resistant to deformation under stress. Hardness is also enhanced for similar reasons, as the carbon in the steel contributes to the formation of harder phases during heat treatment processes. Wear resistance is improved because harder materials tend to withstand abrasion and wear more effectively.

In contrast, ductility is a measure of a material's ability to deform without breaking. As the carbon content increases in steel, it typically results in a decrease in ductility. This is because higher carbon levels lead to a more brittle structure, particularly if it transitions into harder microstructures that do not allow for significant plastic deformation. Therefore, ductility does not improve with the addition of carbon to steel, making it the correct response to the question.