How does carbon content affect the corrosion resistance of steel?

Higher carbon content typically decreases corrosion resistance in steel due to several factors associated with its microstructure and the formation of corrosion products. Carbon, when added to steel, creates a solid solution that can enhance certain mechanical properties like strength and hardness. However, this increase in carbon also leads to a more brittle microstructure which can make the material more susceptible to localized corrosion forms such as pitting.

As carbon content rises, the formation of iron carbides (cementite) occurs, which can disrupt the protective oxide layer that forms on the steel surface. This layered barrier is vital for preventing corrosion. High carbon steels can also have a reduced capability to form passivating oxide films compared to lower carbon steels, leading to greater vulnerability to environmental factors that promote corrosion.

In addition, elevated carbon levels can impact the steel's overall composition and lead to more challenging welding conditions, further compromising the integrity of protective coatings. Because of these reasons, materials with higher carbon content are typically less resistant to corrosion, making this response the best choice.