Pearlite composition check — weight fractions of constituents Evaluate the statement: “Pearlite is a combination of 87% ferrite and 13% cementite (by weight).” Is this statement correct for eutectoid pearlite?

Introduction / Context:
Pearlite is the lamellar microconstituent formed at the eutectoid temperature in plain carbon steels. It is composed of alternating plates of ferrite and cementite. Knowing its approximate constituent proportions is useful for quick property estimates and for validating microstructural descriptions in exams and practice.

Given Data / Assumptions:

• Plain carbon steel at eutectoid composition (~0.8% C).
• Slow cooling to form well-developed pearlite.
• Composition percentages interpreted as weight fractions.

Concept / Approach:
At the eutectoid point, the lever rule applied on the Fe–Fe3C diagram gives approximately 88% ferrite and 12% cementite by weight in pearlite. Many texts round this to 87% ferrite and 13% cementite for simplicity. While exact values can vary slightly with temperature rounding and data sources, the commonly accepted approximation 87/13 captures the essence of eutectoid pearlite composition by weight.

Step-by-Step Solution:

Verification / Alternative check:
Microstructure atlases and many metallurgy textbooks quote pearlite as roughly 7/8 ferrite and 1/8 cementite by weight, aligning with the 87/13 statement.

Why Other Options Are Wrong:

• “No”: contradicts established approximations for eutectoid pearlite.
• “Only for hypo/hypereutectoid”: pearlite itself at eutectoid has fixed fraction; hypo-/hyper-eutectoid steels contain proeutectoid phases in addition to pearlite.
• “True only by volume”: the classic 87/13 figure is a weight fraction approximation, not strictly a volume fraction.

Common Pitfalls:
Mixing up weight and volume fractions; misquoting the figures as 13% ferrite and 87% cementite (reversed).

Final Answer: