Question

Cast iron is

• A. Eutectic alloy
• B. Isomorphous alloy
• C. Peritectic alloy
• D. Peritectoid alloy

Hint:

Remember: The eutectic composition of iron–carbon system occurs at 4.3% carbon.

Answer 1

The Correct Option is A

Step 1: Understanding cast iron composition.
Cast iron contains more than 2% carbon, typically around 4.3% carbon, which corresponds to the eutectic composition in the iron–carbon phase diagram.
Step 2: Eutectic reaction in cast iron.
At 4.3% carbon, liquid iron transforms directly into a mixture of austenite and cementite at a constant temperature, which is known as a eutectic reaction.
Step 3: Analysis of other options.
(B) Isomorphous alloy: These alloys show complete solubility, which is not the case for iron–carbon systems.
(C) Peritectic alloy: Involves a different type of phase transformation.
(D) Peritectoid alloy: Occurs in solid-state reactions only.
Step 4: Conclusion.
Cast iron is correctly classified as a eutectic alloy.