Carbon in iron — terminology for free carbon State whether the statement is correct: “In iron, the presence of carbon in free (uncombined) form is called graphite.”

Introduction / Context:
In iron–carbon alloys, carbon may exist as free carbon (graphite) or as combined carbon in iron carbide (cementite, Fe3C). The form present governs properties such as hardness, machinability, and fracture behavior. Correct terminology is essential to avoid confusion between cast irons and steels.

Given Data / Assumptions:

• “Free carbon” means not chemically combined with iron.
• Microstructural context: cast irons often show free carbon as graphite; steels mostly retain carbon in combined form.

Concept / Approach:
When carbon precipitates out of solution in iron as elemental carbon, it appears as graphite. In grey cast iron, graphite takes a flake morphology; in ductile (spheroidal) iron, graphite appears as nodules. By contrast, “combined carbon” refers to cementite, an intermetallic compound Fe3C. Therefore, “free carbon in iron is called graphite” is the correct, concise statement.

Step-by-Step Solution:
Define terms: free carbon → graphite; combined carbon → cementite.Relate to alloys: cast irons often favor graphitization (free carbon) depending on composition and cooling rate.Hence, the statement is correct.

Verification / Alternative check:
Metallography of grey and ductile irons clearly shows graphite; white cast iron (rapidly cooled) contains cementite with little or no free carbon.

Why Other Options Are Wrong:

• “Disagree” or variants contradict standard definitions.
• “Free carbon is cementite” is wrong; cementite is a compound, not free carbon.

Common Pitfalls:
Assuming steels contain graphite; typical steels retain carbon mainly in carbides and pearlite unless subjected to special graphitizing treatments.

Final Answer:
Agree