In malleable cast iron, what happens to carbon during the annealing process?

• A. It forms rounded particles
• B. It forms graphite flakes
• C. It forms cementite
• D. It forms martensite

Answer: (B)

Carbon in malleable cast iron rearranges into graphite during annealing. The heat treatment allows carbon to diffuse out of the initial iron carbide and precipitate as graphite within the metal matrix. In this material, that graphite typically appears as flakes, which is why graphite flakes is the best description of what carbon becomes during annealing. Cementite would not persist as the dominant phase after proper annealing, martensite forms from rapid cooling rather than slow annealing, and while graphite can be present as spherical particles in some graphite-containing irons, the common description for this annealing process in malleable iron is graphite in flake form.