Which material typically contains more carbon content and is categorized into Grey cast iron, White cast iron, Malleable cast iron, and Ductile/Nodular cast iron?

• A. Steel
• B. Cast iron
• C. Bronze
• D. Aluminum

Answer: (B)

The idea being tested is that carbon content distinguishes cast iron from other ferrous materials, and the subtypes listed—grey, white, malleable, and ductile—are all forms of cast iron. Cast iron contains significantly more carbon than steel and other common metals, typically around 2.5–4% carbon by weight. That higher carbon content drives the formation of different microstructures during solidification, which leads to the distinct categories you see.

Grey cast iron forms graphite flakes that give good machinability and damping. White cast iron has a hard, brittle cementite network that makes it very wear-resistant but not tough. Malleable cast iron starts as white iron and is heat-treated to convert some cementite into clusters of graphite, increasing ductility. Ductile (nodular) cast iron adds elements that promote spherical graphite, boosting toughness and impact resistance. Because these variations all stem from the high carbon content and how it exists in the microstructure, this group is specifically cast iron.

Other materials listed—steel, bronze, and aluminum—have different carbon contents and belong to different families, not the cast iron categories.