Why does grey cast iron appear grey?

Why does grey cast iron appear grey?

• A. Because carbon precipitates as graphite
• B. Because of iron carbide coloring
• C. Due to chromium content
• D. Due to oxidation layer

Answer: (A)

Grey cast iron looks grey because its carbon forms graphite in flakes within the metal. The graphite flakes are the form of carbon that light interacts with differently than the iron carbide or the metal matrix, so the fracture surface appears a dull grey instead of bright. This is why white cast iron, where carbon is present as cementite, shows a white fracture surface, and factors like chromium content or surface oxidation don’t determine the grey appearance. The key idea is that carbon precipitates as graphite in grey cast iron.

Grey cast iron looks grey because its carbon forms graphite in flakes within the metal. The graphite flakes are the form of carbon that light interacts with differently than the iron carbide or the metal matrix, so the fracture surface appears a dull grey instead of bright. This is why white cast iron, where carbon is present as cementite, shows a white fracture surface, and factors like chromium content or surface oxidation don’t determine the grey appearance. The key idea is that carbon precipitates as graphite in grey cast iron.