Cast Iron

Overview

Engineering reference data for Cast Iron in material science and properties.

Key Formulas

Stress

$\sigma = \frac{F}{A}$

Force per unit area.

Strain

$\varepsilon = \frac{\Delta L}{L_0}$

Change in length per original length.

Hooke's Law

$\sigma = E \varepsilon$

Stress proportional to strain in elastic region.

Thermal Expansion

$\Delta L = \alpha L_0 \Delta T$

Length change due to temperature.

Variables

Types of Cast Iron

Four primary types of cast iron exist, each with distinct microstructures and properties:

White Cast Iron
Characterized by the prevalence of carbides in its microstructure. Key properties include high compressive strength, hardness, and good resistance to wear.

Gray Cast Iron
Contains graphite flakes in its microstructure. This provides good machinability and good resistance to wear and galling.

Ductile Cast Iron
Also known as nodular cast iron, it is produced by adding small amounts of magnesium and/or cerium to gray iron. This treatment causes the graphite to form spherical nodules, resulting in high strength and high ductility.

Malleable Cast Iron
Is produced by heat-treating white cast iron. This process improves its ductility, making it less brittle than white iron while maintaining good strength.

Microstructure and Properties

The fundamental properties of each cast iron type are dictated by its graphite morphology and matrix structure:

• White Cast Iron: The prevalence of iron carbide (cementite) in the microstructure results in high compressive strength, hardness, and excellent wear resistance. It is brittle and difficult to machine.
• Gray Cast Iron: Graphite forms as interconnected flakes, providing good machinability, excellent damping capacity, and resistance to wear and galling. The flakes also act as stress concentrators, reducing tensile strength.
• Ductile (Nodular) Cast Iron: Small additions of magnesium and cerium (typically 0.03–0.06% Mg) during melting cause the graphite to form spheroids instead of flakes. This nodulization significantly increases strength and ductility while retaining good machinability.
• Malleable Cast Iron: Produced by a prolonged annealing heat treatment of white cast iron. This process decomposes the brittle cementite into temper carbon (irregularly shaped graphite nodules) in a ferritic or pearlitic matrix, substantially improving ductility and toughness.

Composition and Processing

The properties of cast iron are fundamentally determined by its composition and subsequent processing:

• Gray Iron: Graphite forms as flakes during solidification. Its machinability and wear resistance stem from the lubricating effect of these graphite flakes.
• Ductile Iron: Small, controlled additions of magnesium (Mg) or cerium (Ce) during production cause the graphite to form as spheres (nodules) instead of flakes. This "nodularization" is the critical process that imparts high strength and ductility.
• Malleable Iron: Produced by first creating white iron (with carbon as iron carbide, Fe₃C) and then heat-treating it (annealing) for an extended period. This process decomposes the brittle carbide into temper carbon nodules, significantly improving ductility.

Performance Characteristics Summary

References

• Original Source