---
title: "Types of cast iron"
subject: "Material Science"
chapter: 7
key: "semester_3/material_science:types-of-cast-iron"
source: https://www.bctengineer.com/q/semester_3/material_science/types-of-cast-iron
site: BCT Engineering
---

# Types of cast iron

Material Science · Chapter 7: Types of steels and cast iron

- Asked in: year not given, 8 marks
- Video: [Types Of Cast Iron And Their Differences | An Overview.](https://www.youtube.com/watch?v=GPuX9WncHfE) — James Sword Engineering 
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_3/material_science/types-of-cast-iron
- Whole chapter: https://www.bctengineer.com/md/semester_3/material_science/chapter-7

## Question

Describe the four main types of cast iron (grey, white, malleable and ductile) with their microstructure, properties and applications. Why is cast iron preferred for machine-tool beds?

## Short answer

Grey iron: graphite flakes, good damping, used for machine beds. White iron: cementite, hard and brittle, wear-resistant. Malleable iron: temper carbon rosettes, ductile, from heat-treated white iron. Ductile iron: graphite spheres, high strength and ductility, for crankshafts. Cast iron is preferred for machine beds due to vibration damping, castability, and compressive strength.

## Answer

**Cast iron** is an iron-carbon alloy with 2.14-6.67% C (usually 2.5-4%) and 1-3% Si. Carbon may be present as free graphite or as cementite, depending on composition and cooling rate.

| Type | Carbon form | Matrix | Properties | Uses |
|---|---|---|---|---|
| Grey | Graphite flakes | Ferrite and/or pearlite | Good castability and machinability, excellent damping, high compressive strength, brittle in tension (150-400 MPa) | Machine beds, engine blocks, brake drums |
| White | Cementite (no graphite), ledeburite | Pearlite + cementite | Very hard, brittle, wear resistant, difficult to machine | Wear-resistant liners, grinding balls, base for malleable iron |
| Malleable | Temper carbon (rosettes) | Ferrite or pearlite | Good ductility, toughness and strength; made by heat treating white iron | Pipe fittings, connecting rods, hand tools |
| Ductile (nodular, SG) | Graphite spheres | Ferrite, pearlite or both | Strength like steel (400-800 MPa), good ductility, wear resistance | Crankshafts, gears, pipes, valves |

#### Production notes
- **Grey iron**: slow cooling with high C and Si, which promote graphite.
- **White iron**: rapid cooling (chilling) and low Si keep carbon as cementite.
- **Malleable iron**: white iron annealed at about 900 °C for 2 days, which decomposes cementite into temper carbon.
- **Ductile iron**: Mg (or Ce) added to the melt before casting turns graphite flakes into spheres, which removes the sharp stress-raising edges.

#### Machine-tool beds
Grey cast iron absorbs vibration (graphite flakes damp vibrations), is cheap to cast in complex shapes, machines easily, wears well on slide ways and has high compressive strength.

## Check yourself

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

1. Which pairing of cast iron and carbon form is correct?
   A. Grey - graphite flakes; ductile - graphite spheres
   B. White - graphite flakes; malleable - cementite
   C. Grey - graphite spheres; ductile - flakes
   D. Malleable - graphite flakes; white - temper carbon
   Answer: A. Grey iron has flake graphite and ductile iron has spherical nodules; white iron has cementite; malleable has temper carbon rosettes. (Key point: Form of carbon)

2. How are graphite spheres obtained in ductile iron?
   A. Annealing white iron for 2 days
   B. Rapid chilling of the casting
   C. Adding extra sulphur
   D. Adding Mg (or Ce) to the melt before casting
   Answer: D. Mg or Ce changes graphite flakes into spheres, removing sharp stress-raising edges. (Key point: Making ductile iron)

3. How is malleable cast iron produced?
   A. White iron is annealed at about 900 °C for about 2 days, decomposing cementite to temper carbon
   B. Grey iron is quenched in water
   C. Mg is added to the melt
   D. White iron is cooled very rapidly
   Answer: A. Prolonged annealing of white iron breaks cementite into temper-carbon rosettes, giving ductility. (Key point: Making malleable iron)

4. Why is grey cast iron preferred for machine-tool beds?
   A. It has the highest tensile strength
   B. Graphite flakes damp vibration; it is cheap to cast, machines easily and has high compressive strength
   C. It is fully ductile
   D. It has no carbon
   Answer: B. Excellent vibration damping, castability, machinability and compressive strength suit beds. (Key point: Machine-tool beds)

## Related in Material Science

- [Cooling of 3% C cast iron](https://www.bctengineer.com/question.md?key=semester_3%2Fmaterial_science%3Ahypoeutectic-cast-iron-3-carbon) — Material Science, chapter 6
- [HSLA, stainless and tool steels](https://www.bctengineer.com/question.md?key=semester_3%2Fmaterial_science%3Aalloy-steels-hsla-stainless-tool) — Material Science, chapter 7
- [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

## Related in other subjects

- [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
- [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
- [Cutting tool materials and their properties](https://www.bctengineer.com/question.md?key=semester_4%2Fmanufacturing_and_production_processes%3Acutting-tool-materials-characteristics-economics) — Manufacturing and Production Processes, chapter 7
- [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×