---
title: "Phases in 0.33% carbon steel"
subject: "Civil Engineering Materials"
chapter: 8
key: "semester_3/civil_engineering_materials:carbon-percent-0-33-phases"
source: https://www.bctengineer.com/q/semester_3/civil_engineering_materials/carbon-percent-0-33-phases
site: BCT Engineering
---

# Phases in 0.33% carbon steel

Civil Engineering Materials · Chapter 8: Metals and Alloys

- Asked in: 2066 Shrawan (old course), 4 marks
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_3/civil_engineering_materials/carbon-percent-0-33-phases
- Whole chapter: https://www.bctengineer.com/md/semester_3/civil_engineering_materials/chapter-8

## Question

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?

## 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%.

## Answer

The carbon is present as iron carbide ($Fe_3C$, cementite). Pearlite is the eutectoid mixture of ferrite and cementite containing 0.80% C, and the steel is hypo-eutectoid ($C < 0.80\%$), so it has free ferrite plus pearlite.

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

#### Cementite

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

#### Ferrite (total, free + in pearlite)

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

#### Pearlite

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

The rest, $100 - 41.25 = 58.75\%$, 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%.**

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. Steel with 0.33% C is:
   A. Eutectoid
   B. Hypo-eutectoid, with free ferrite plus pearlite
   C. Hyper-eutectoid
   D. Pure pearlite
   Answer: B. C below 0.80% gives free ferrite plus pearlite. (Key point: Steel type)

2. Cementite percentage is:
   A. 0.33/0.80 x 100 = 41.25%
   B. 0.33/6.67 x 100 = 4.95%
   C. 6.67/0.33
   D. 95.05%
   Answer: B. Cementite = 0.33/6.67 x 100 = 4.95%. (Key point: Cementite)

3. Pearlite percentage is:
   A. 4.95%
   B. 95.05%
   C. 58.75%
   D. 41.25%
   Answer: D. Pearlite = 0.33/0.80 x 100 = 41.25%. (Key point: Pearlite)

4. Free ferrite is:
   A. 41.25%
   B. 95.05%
   C. 58.75% (100 - 41.25)
   D. 4.95%
   Answer: C. Rest of structure after pearlite is free ferrite. (Key point: Free ferrite)

## Related in Civil Engineering Materials

- [Phases in 0.35% carbon steel](https://www.bctengineer.com/question.md?key=semester_3%2Fcivil_engineering_materials%3Acarbon-percent-0-35-phases) — Civil Engineering Materials, chapter 8
- [Ferrite and pearlite in high strength steel](https://www.bctengineer.com/question.md?key=semester_3%2Fcivil_engineering_materials%3Aferrite-pearlite-high-strength-steel) — Civil Engineering Materials, chapter 8
- [Phases in 0.80% carbon steel](https://www.bctengineer.com/question.md?key=semester_3%2Fcivil_engineering_materials%3Acarbon-percent-0-80-phases) — Civil Engineering Materials, chapter 8
- [Modulus of toughness of medium carbon steel](https://www.bctengineer.com/question.md?key=semester_3%2Fcivil_engineering_materials%3Anumerical-modulus-toughness-415) — Civil Engineering Materials, chapter 1
- [Function of carbon in steel](https://www.bctengineer.com/question.md?key=semester_3%2Fcivil_engineering_materials%3Acarbon-function-in-steel) — Civil Engineering Materials, chapter 8, asked 2×
- [Plain carbon steel versus alloy steel](https://www.bctengineer.com/question.md?key=semester_3%2Fcivil_engineering_materials%3Aplain-carbon-vs-alloy-steel) — Civil Engineering Materials, chapter 8

## Related in other subjects

- [Iron-iron carbide phase diagram](https://www.bctengineer.com/question.md?key=semester_3%2Fmaterial_science%3Airon-iron-carbide-phase-diagram) — Material Science, chapter 6
- [Phases and constituents of steel](https://www.bctengineer.com/question.md?key=semester_3%2Fmaterial_science%3Aferrite-austenite-pearlite-martensite) — Material Science, chapter 6
- [Slow cooling of 0.4% C steel](https://www.bctengineer.com/question.md?key=semester_3%2Fmaterial_science%3Aslow-cooling-04-carbon-steel) — Material Science, chapter 6
- [Slow cooling of 1.2% C steel](https://www.bctengineer.com/question.md?key=semester_3%2Fmaterial_science%3Ahypereutectoid-steel-12-carbon) — Material Science, chapter 6