Cast-iron solidification terminology — composition at the eutectic State whether the statement is correct: “Iron–carbon alloys containing 4.3% carbon are known as hypo-eutectic cast irons.”

Introduction / Context:In the cast-iron range, the eutectic composition of the iron–carbon system is about 4.3% carbon. Understanding the terms hypo-eutectic, eutectic, and hyper-eutectic is critical for predicting primary phases and casting behavior.

Given Data / Assumptions:

• Eutectic composition is approximately 4.3% carbon under idealized conditions.
• Hypo-eutectic means below the eutectic composition; hyper-eutectic means above.
• Terminology is independent of whether graphite or cementite forms subsequently.

Concept / Approach:An alloy exactly at 4.3% carbon is eutectic, not hypo-eutectic. Hypo-eutectic cast irons have carbon less than 4.3% and will form primary austenite before the eutectic reaction during solidification. Hyper-eutectic cast irons have carbon greater than 4.3% and may form primary graphite in grey irons or primary cementite in white irons depending on conditions.

Step-by-Step Solution:Identify reference composition: 4.3% C corresponds to eutectic.Compare statement: calls 4.3% C hypo-eutectic, which contradicts definition.Therefore, the statement is incorrect.Correct classification: 4.3% C is eutectic.

Verification / Alternative check:Textbook Fe–C diagrams label the eutectic point near 4.3% C and 1147°C, confirming the terminology.

Why Other Options Are Wrong:

• Correct or conditional options misapply the definitions of hypo and hyper relative to the eutectic composition.
• Cannot be determined is not applicable because the definition is precise.

Common Pitfalls:Confusing eutectic (liquid to two solids) with eutectoid (solid to two solids at about 0.8% C in steels). The 4.3% value relates to the cast-iron eutectic.

Final Answer:Incorrect