Steel transformations — hyper-eutectoid equilibrium product: Under equilibrium (slow) cooling from the austenitic state, a hyper-eutectoid plain carbon steel will consist of:

Introduction / Context:
Interpreting the iron–carbon diagram is essential for predicting microstructures after equilibrium cooling. The products differ depending on whether the composition lies below, at, or above the eutectoid point (0.8% C).

Given Data / Assumptions:

• Composition is hyper-eutectoid (carbon > 0.8%).
• Cooling is slow enough to approximate equilibrium (no martensite).
• Plain carbon steel with no alloying complications.

Concept / Approach:
For hyper-eutectoid steels, as the alloy cools from austenite, proeutectoid cementite forms first along grain boundaries. At the eutectoid temperature, the remaining austenite transforms into pearlite. Therefore, the final microstructure contains pearlite plus proeutectoid cementite. Ferrite is the proeutectoid phase only for hypo-eutectoid steels; martensite requires rapid quenching; bainite forms under specific non-equilibrium isothermal or continuous-cooling conditions.

Step-by-Step Solution:
Start above the eutectoid: fully austenitic.On cooling, form proeutectoid cementite at grain edges.At eutectoid temperature, remaining austenite → pearlite.Result: pearlite + proeutectoid cementite.

Verification / Alternative check:
Textbook micrographs show pearlite colonies bounded by continuous cementite networks in hyper-eutectoid steels.

Why Other Options Are Wrong:
Ferrite + pearlite corresponds to hypo-eutectoid compositions.

Ferrite + bainite and cementite + martensite involve non-equilibrium transformations.

Only cementite is impossible for practical carbon ranges and would be extremely brittle.

Common Pitfalls:
Mixing up proeutectoid phases; assuming similar behaviour on both sides of the eutectoid composition.

Final Answer:
Cementite and pearlite