Gray Cast Iron is a type of cast iron containing graphite flakes within its microstructure, giving it a characteristic gray fracture appearance. It is widely used due to excellent machinability, high damping capacity, good compressive strength, and cost-effectiveness.
The graphite flakes provide natural lubrication, superior wear resistance, and exceptional vibration damping, making gray cast iron ideal for automotive, machinery, and industrial applications.
Chemical Composition
| Element | Typical Range (%) | Role |
|---|---|---|
| Carbon (C) | 2.5 – 4.0 | Graphite formation, fluidity |
| Silicon (Si) | 1.8 – 3.0 | Promotes graphite, lowers chill |
| Manganese (Mn) | 0.2 – 1.0 | Controls sulfur, pearlite |
| Phosphorus (P) | 0.02 – 0.20 | Improves fluidity |
| Sulfur (S) | 0.02 – 0.12 | Affects machinability |
| Iron (Fe) | Balance | Matrix |
Key Mechanical Properties
| Property | Typical Range |
|---|---|
| Tensile Strength | 140 – 350 MPa |
| Compressive Strength | 600 – 1,400 MPa |
| Hardness | 140 – 260 HB |
| Elongation | ~0–1% |
| Fatigue Strength | Moderate |
| Impact Resistance | Low |
Physical Properties
| Property | Value |
|---|---|
| Density | 7.1 – 7.3 g/cm³ |
| Melting Range | 1,150 – 1,200 °C |
| Thermal Conductivity | 45 – 60 W/m·K |
| Specific Heat | ~460 J/kg·K |
| Thermal Expansion | 10 – 11 µm/m·°C |
| Damping Capacity | Very High |
Key Characteristics
✔ Exceptional vibration damping
✔ Outstanding machinability
✔ High thermal conductivity
✔ Superior castability
Available Forms
Sand cast components
Centrifugal cast pipes
Continuous cast bars and plates
Near-net-shape custom castings
Machined finished parts
Applications
Automotive components (engine blocks, brake discs)
Machine tool beds and housings
Pumps, valves, compressors
Pipes, manhole covers, counterweights
Heat exchangers and radiators
Advantages
✔ Excellent damping and machinability
✔ High compressive strength
✔ Cost-effective material
✔ Dimensional stability
Limitations
❌ Low tensile and impact strength
❌ Brittle fracture behavior
❌ Poor weldability
❌ Not suitable for shock loading
Why Choose Gray Cast Iron?
Gray cast iron is ideal where vibration control, machinability, thermal performance, and economical mass production are more important than tensile strength.