---
title: "Compare cast iron, steel, aluminium"
subject: "Civil Engineering Materials"
chapter: 8
key: "semester_3/civil_engineering_materials:compare-cast-iron-steel-aluminium"
source: https://www.bctengineer.com/q/semester_3/civil_engineering_materials/compare-cast-iron-steel-aluminium
site: BCT Engineering
---

# Compare cast iron, steel, aluminium

Civil Engineering Materials · Chapter 8: Metals and Alloys

- Asked in: 2059 Poush (old course), 6 marks
- Video: [Engine Block Materials Explained | Strength vs Weight](https://www.youtube.com/watch?v=ZlWI-JVa61Y) — The Engineers Post
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_3/civil_engineering_materials/compare-cast-iron-steel-aluminium
- Whole chapter: https://www.bctengineer.com/md/semester_3/civil_engineering_materials/chapter-8

## Question

Compare the properties and uses of cast iron, steel and aluminium.

## Short answer

Cast iron (high carbon) is brittle with high compressive strength, used for pipes and manholes. Steel (0.05-1.5% C) is strong, ductile but rusts, for structures. Aluminium (density 2700 kg/m³) is light, corrosion-resistant, conductive, for windows and cladding.

## Answer

| Property | Cast iron | Steel | Aluminium |
|---|---|---|---|
| Composition | Fe with 2-4.5% C | Fe with 0.05-1.5% C | Pure Al or alloys |
| Density | About 7200 kg/m³ | About 7850 kg/m³ | About 2700 kg/m³ |
| Strength | Low tensile, high compressive | High tensile and compressive | Low to moderate (alloys are good) |
| Ductility | Brittle | Ductile | Ductile |
| Weldability | Poor | Good | Fair, needs special methods |
| Corrosion | Fair | Rusts, needs protection | Very good (oxide film) |
| Conductivity | Low | Low | High (thermal and electrical) |
| Melting point | 1150-1300 °C | 1400-1500 °C | 660 °C |
| Cost | Low | Moderate | High |
| Fire resistance | Good | Loses strength at about 550 °C | Weak at high temperature |

#### Uses
- **Cast iron:** pipes, columns, manhole covers, brackets, drainage fittings.
- **Steel:** reinforcement, structural frames, bridges, trusses, roofs, tanks.
- **Aluminium:** windows, doors, roof sheets, cladding, curtain walls, conductors.

## Check yourself

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

1. Which has the lowest density?
   A. Cast iron (7200)
   B. Steel (7850)
   C. Aluminium (about 2700 kg/m3)
   D. All the same
   Answer: C. Aluminium is about one third as dense as steel. (Key point: Density)

2. Which is brittle with low tensile but high compressive strength?
   A. Steel
   B. Aluminium
   C. Cast iron
   D. None
   Answer: C. Cast iron is brittle. (Key point: Strength and ductility)

3. Which pairing is correct?
   A. Aluminium: very good corrosion resistance by oxide film, melts about 660 C
   B. Aluminium rusts, melts 1500 C
   C. Steel resists corrosion best
   D. Cast iron melts at 660 C
   Answer: A. Aluminium forms a protective oxide film and melts at 660 C. (Key point: Corrosion and melting)

4. Which use matches?
   A. Steel: manhole covers; cast iron: reinforcement
   B. Aluminium: reinforcement; steel: windows
   C. Cast iron: pipes, columns, manhole covers; steel: reinforcement and frames; aluminium: windows, cladding
   D. All used for same purpose
   Answer: C. Each metal's properties suit different uses. (Key point: Uses)

## Related in Civil Engineering Materials

- [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 manufacture and properties](https://www.bctengineer.com/question.md?key=semester_3%2Fcivil_engineering_materials%3Acast-iron-manufacture-properties) — Civil Engineering Materials, chapter 8
- [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
- [Asphalt properties and uses](https://www.bctengineer.com/question.md?key=semester_3%2Fcivil_engineering_materials%3Aasphalt-properties-uses) — Civil Engineering Materials, chapter 10, asked 4×
- [Types of lime, properties and uses](https://www.bctengineer.com/question.md?key=semester_3%2Fcivil_engineering_materials%3Atypes-of-lime-uses) — Civil Engineering Materials, chapter 4, asked 3×
- [Properties and uses of glass](https://www.bctengineer.com/question.md?key=semester_3%2Fcivil_engineering_materials%3Aproperties-uses-of-glass) — Civil Engineering Materials, chapter 10, asked 3×

## 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
- [Aluminium alloys compared with steel](https://www.bctengineer.com/question.md?key=semester_3%2Fmaterial_science%3Aaluminium-versus-steel-applications) — Material Science, chapter 9
- [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