---
title: "Phases in 0.35% carbon steel"
subject: "Civil Engineering Materials"
chapter: 8
key: "semester_3/civil_engineering_materials:carbon-percent-0-35-phases"
source: https://www.bctengineer.com/q/semester_3/civil_engineering_materials/carbon-percent-0-35-phases
site: BCT Engineering
---

# Phases in 0.35% carbon steel

Civil Engineering Materials · Chapter 8: Metals and Alloys

- Asked in: 2057 Chaitra (old course), 4 marks
- Video: [Steel phase diagram cooling and Lever Rule example problem](https://www.youtube.com/watch?v=fjqeEYhaXcI) — Taylor Sparks
- 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-0-35-phases
- Whole chapter: https://www.bctengineer.com/md/semester_3/civil_engineering_materials/chapter-8

## Question

If a steel contains 0.35% of carbon in the form of iron carbide, what are the percentages of ferrite, cementite and pearlite present in the steel?

## Short answer

By lever rule: cementite = 0.35/6.67 ≈ 5.25%; total ferrite = 100 − 5.25 = 94.75%; pearlite = 0.35/0.80 = 43.75%; free proeutectoid ferrite = 56.25%. Therefore: cementite 5.25%, ferrite 94.75% (56.25% free), pearlite 43.75%.

## 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:** $C = 0.35\%$; cementite has 6.67% C; pearlite has 0.80% C.

#### Cementite

$$
\text{Cementite} = \frac{0.35}{6.67} \times 100 = 5.25\%
$$

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

$$
\text{Ferrite} = 100 - 5.25 = 94.75\%
$$

#### Pearlite

$$
\text{Pearlite} = \frac{0.35}{0.80} \times 100 = 43.75\%
$$

The rest, $100 - 43.75 = 56.25\%$, is free (proeutectoid) ferrite. The ferrite and cementite inside the pearlite are in the ratio 88.01 : 11.99.

**Answer: Cementite = 5.25%; total ferrite = 94.75% (of which free ferrite = 56.25%); pearlite = 43.75%.**

## Check yourself

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

1. Cementite percentage with 0.35% C is:
   A. 0.35/6.67 x 100 = 5.25%
   B. 0.35/0.80 x 100
   C. 94.75%
   D. 56.25%
   Answer: A. Cementite = 0.35/6.67 x 100 = 5.25%. (Key point: Cementite)

2. Pearlite percentage is:
   A. 5.25%
   B. 56.25%
   C. 94.75%
   D. 43.75%
   Answer: D. Pearlite = 0.35/0.80 x 100 = 43.75%. (Key point: Pearlite)

3. Total ferrite is:
   A. 100 - 5.25 = 94.75%
   B. 43.75%
   C. 56.25%
   D. 5.25%
   Answer: A. Ferrite = 100 minus cementite. (Key point: Total ferrite)

4. Free ferrite (outside pearlite) is:
   A. 43.75%
   B. 94.75%
   C. 56.25%
   D. 5.25%
   Answer: C. 100 - 43.75 = 56.25%. (Key point: Free ferrite)

## Related in Civil Engineering Materials

- [Phases in 0.33% carbon steel](https://www.bctengineer.com/question.md?key=semester_3%2Fcivil_engineering_materials%3Acarbon-percent-0-33-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
- [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×
- [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
- [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 1.2% C steel](https://www.bctengineer.com/question.md?key=semester_3%2Fmaterial_science%3Ahypereutectoid-steel-12-carbon) — 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