---
title: "Cast iron manufacture and properties"
subject: "Civil Engineering Materials"
chapter: 8
key: "semester_3/civil_engineering_materials:cast-iron-manufacture-properties"
source: https://www.bctengineer.com/q/semester_3/civil_engineering_materials/cast-iron-manufacture-properties
site: BCT Engineering
---

# Cast iron manufacture and properties

Civil Engineering Materials · Chapter 8: Metals and Alloys

- Asked in: 2065 Shrawan (old course), 8 marks
- Video: [Why Is Cast Iron STILL Used Today?](https://www.youtube.com/watch?v=uRYwVk_xhmE) — History of Simple Things
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_3/civil_engineering_materials/cast-iron-manufacture-properties
- Whole chapter: https://www.bctengineer.com/md/semester_3/civil_engineering_materials/chapter-8

## Question

Describe briefly the manufacturing process and properties of cast iron.

## Short answer

Pig iron from a blast furnace is remelted in a cupola furnace with coke and limestone, then cast into moulds. Cast iron has high compressive strength (600–1000 N/mm²), low tensile strength (150–250 N/mm²), is hard, brittle, good castability, wear‑resistant and damps vibration.

## Answer

Cast iron is an iron-carbon alloy containing 2–4.5% carbon (plus Si, Mn, S, P), made by remelting pig iron. It is hard and brittle, and it is cast into shape because it cannot be forged or rolled.

#### Manufacture

Pig iron is first produced in a **blast furnace** from iron ore, coke (fuel and reducing agent) and limestone (flux). The pig iron is then remelted and refined into cast iron in a **cupola furnace**.

1. **Blast furnace:** A charge of ore, coke and limestone is fed from the top, and a hot air blast enters near the bottom. Coke burns to give CO, which reduces the ore ($Fe_2O_3 + 3CO \rightarrow 2Fe + 3CO_2$). Limestone combines with silica impurities to form slag. Molten iron collects at the bottom and is tapped as pig iron.
2. **Cupola furnace:** A vertical cylindrical furnace lined with fire bricks. Pig iron, scrap iron, coke and limestone are charged in layers. An air blast through tuyeres burns the coke and melts the iron. The molten metal is tapped from the bottom, poured into moulds, and cooled to get castings.

```text
   Charge (pig iron+scrap+coke+flux)
            |
        +---v---+
        |       |  <- Cupola
  Air ->|=======|  <- tuyeres
        |       |
        +---+---+
            |  Molten iron -> Mould
            v  Slag tapped separately
```

#### Types

Grey cast iron (flake graphite), white cast iron (carbon as cementite), malleable cast iron (annealed white iron), and nodular (SG) cast iron.

#### Properties

- Carbon content 2–4.5%; melting point about 1200 °C (lower than steel).
- Very high compressive strength (about 600–1000 N/mm²), but low tensile strength (about 150–250 N/mm²).
- Hard and brittle; fails suddenly with little elongation.
- Good fluidity when molten, so complex shapes can be cast.
- Cannot be forged or rolled and is difficult to weld; grey iron can be machined.
- Good wear resistance and vibration damping.
- Resists corrosion better than mild steel; specific gravity about 7.2–7.5.

**Uses:** pipes, manhole covers, columns, brackets, drain fittings, machine beds and railings.

## Check yourself

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

1. In the blast furnace the iron ore is reduced mainly by:
   A. Limestone
   B. CO from burning coke
   C. Slag
   D. Air alone
   Answer: B. Coke burns to CO, which reduces Fe2O3 to Fe; limestone is the flux forming slag. (Key point: Blast furnace)

2. Cast iron is produced from pig iron in a:
   A. Cupola furnace, charged with pig iron, scrap, coke and limestone, with an air blast through tuyeres
   B. Puddling furnace
   C. Open hearth only
   D. Electric arc with no coke
   Answer: A. The cupola remelts pig iron; molten metal is tapped and poured into moulds. (Key point: Cupola furnace)

3. Which property set of cast iron is correct?
   A. Ductile, easily forged
   B. High compressive and low tensile strength, hard and brittle, good fluidity when molten
   C. High tensile strength, weldable
   D. Melts above steel
   Answer: B. Cast iron is strong in compression, weak in tension and brittle, but casts into complex shapes. (Key point: Properties)

4. Which is a type of cast iron?
   A. Grey (flake graphite)
   B. Stainless
   C. Duralumin
   D. Bronze
   Answer: A. Types: grey, white, malleable and nodular (SG) cast iron. (Key point: Types)

## Related in Civil Engineering Materials

- [Compare cast iron, steel, aluminium](https://www.bctengineer.com/question.md?key=semester_3%2Fcivil_engineering_materials%3Acompare-cast-iron-steel-aluminium) — Civil Engineering Materials, chapter 8
- [Wet process of cement manufacture](https://www.bctengineer.com/question.md?key=semester_3%2Fcivil_engineering_materials%3Acement-wet-process-flow-diagram) — Civil Engineering Materials, chapter 5, asked 4×
- [Cast iron versus steel](https://www.bctengineer.com/question.md?key=semester_3%2Fcivil_engineering_materials%3Acast-iron-vs-steel) — Civil Engineering Materials, chapter 8, asked 2×
- [Cast iron versus wrought iron](https://www.bctengineer.com/question.md?key=semester_3%2Fcivil_engineering_materials%3Acast-iron-vs-wrought-iron) — Civil Engineering Materials, chapter 8
- [Dry process of cement manufacture](https://www.bctengineer.com/question.md?key=semester_3%2Fcivil_engineering_materials%3Acement-dry-process-flow-chart) — Civil Engineering Materials, chapter 5
- [Manufacturing process of bricks](https://www.bctengineer.com/question.md?key=semester_3%2Fcivil_engineering_materials%3Amanufacturing-process-of-bricks) — Civil Engineering Materials, chapter 3, asked 4×

## Related in other subjects

- [Types of cast iron](https://www.bctengineer.com/question.md?key=semester_3%2Fmaterial_science%3Atypes-of-cast-iron) — Material Science, chapter 7
- [Cast iron pipe with 85% magnesia insulation](https://www.bctengineer.com/question.md?key=semester_2%2Ffundamental_of_thermodynamics_and_heat_transfer%3Acast-iron-pipe-magnesia-insulation-thickness) — Fundamental of Thermodynamics & Heat Transfer, chapter 7
- [Water hammer in elastic cast-iron pipe](https://www.bctengineer.com/question.md?key=semester_6%2Fhydro_power%3Awater-hammer-cast-iron-pipe) — Hydro Power, chapter 1
- [Cast iron pipe size for given head loss](https://www.bctengineer.com/question.md?key=semester_4%2Fhydraulics%3Acast-iron-pipe-size-for-head-loss) — Hydraulics, chapter 2