Malleable cast iron is produced by annealing white cast iron to transform carbon into rounded particles.

• A. Grey cast iron
• B. White cast iron
• C. Malleable cast iron
• D. Ductile cast iron

Answer: (C)

The test is about how malleable cast iron gets its ductile, bendable nature. White cast iron is very hard and brittle because carbon is locked up as cementite (iron carbide). When white iron is annealed, carbon diffuses and forms rounded particles, or temper carbon, within a ferritic/pearlitic matrix. This graphite in rounded form disrupts brittle cementite and allows the material to deform rather than crack, producing malleable cast iron. This is different from grey cast iron, which already contains graphite in flakes, and from ductile cast iron, which achieves spheroidal graphite by alloying the melt (not by annealing white iron). Therefore, the described heat-treatment path correctly identifies malleable cast iron.