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Phases in 0.33% carbon steel

Short answer

Via lever rule: cementite = 0.33/6.67 ≈ 4.95%; total ferrite = 100 − 4.95 = 95.05%; pearlite = 0.33/0.80 = 41.25%; free proeutectoid ferrite = 58.75%. Answer: cementite 4.95%, ferrite 95.05% (58.75% free), pearlite 41.25%.

In steel, the percentage of carbon is found to be 0.33% in the form of iron carbide. What will be the percentage of cementite, ferrite and pearlite?

The carbon is present as iron carbide (Fe3CFe_3C, cementite). Pearlite is the eutectoid mixture of ferrite and cementite containing 0.80% C, and the steel is hypo-eutectoid (C<0.80%C < 0.80\%), so it has free ferrite plus pearlite.

Data: C=0.33%C = 0.33\%; cementite has 6.67% C; pearlite has 0.80% C.

Cementite

Cementite=0.336.67×100=4.95%\text{Cementite} = \frac{0.33}{6.67} \times 100 = 4.95\%

Ferrite (total, free + in pearlite)

Ferrite=100−4.95=95.05%\text{Ferrite} = 100 - 4.95 = 95.05\%

Pearlite

Pearlite=0.330.80×100=41.25%\text{Pearlite} = \frac{0.33}{0.80} \times 100 = 41.25\%

The rest, 100−41.25=58.75%100 - 41.25 = 58.75\%, is free (proeutectoid) ferrite. The ferrite and cementite inside the pearlite are in the ratio 88.01 : 11.99.

Answer: Cementite = 4.95%; total ferrite = 95.05% (of which free ferrite = 58.75%); pearlite = 41.25%.

✓ Answer checked by Claude Opus 5.5 (high effort)

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