Material Classification — Is Cast Iron a Ductile Material? Evaluate the statement: “Cast iron is a ductile material.” Choose the most accurate response for general cast irons used in practice.

Introduction / Context:
“Cast iron” covers several families: gray, white, malleable, and spheroidal graphite (SG or ductile iron). Their mechanical behavior varies widely with graphite morphology and matrix structure. In everyday engineering language, “cast iron” is often associated with gray iron, which is not generally considered ductile.

Given Data / Assumptions:

• Room-temperature mechanical behavior is considered.
• Generic, unmodified gray/white cast irons are implied unless specified.
• Understanding that special grades (SG iron) exist but are exceptions.

Concept / Approach:
Gray and white irons are typically brittle at room temperature. Gray iron contains flake graphite that acts as stress concentrators, lowering tensile strength and ductility though providing good damping and machinability. White iron contains cementite networks, giving very high hardness and brittleness. Only specially produced SG (ductile) iron, with graphite in nodular form, offers significant ductility and toughness. Therefore, as a general statement, “cast iron is ductile” is incorrect.

Step-by-Step Solution:
Distinguish cast iron families by graphite form: flake (gray) vs. nodular (SG) vs. carbide (white).Relate morphology to properties: flake/carbide → brittle; nodular → improved ductility.Interpret the blanket statement: for “cast iron” without qualification, the safe generalisation is non-ductile at room temperature.

Verification / Alternative check:
Tensile elongation data: gray/white irons show very low elongation (often near 0–1%), whereas SG irons may show 5–20% depending on grade.

Why Other Options Are Wrong (as general statements):
“Correct”: too broad; typical cast irons are not ductile.“Correct only for SG iron”: while true for that subset, the prompt asks about cast iron generally.“Correct only at elevated temperature”: not the standard way to classify room-temperature ductility.

Common Pitfalls:
Assuming all “cast irons” behave like ductile iron; SG iron is a specialised, nodular graphite product.

Final Answer:
Incorrect