Ductile Cast Iron—also known as Nodular Cast Iron or Spheroidal Graphite (SG) Iron— contains spherical graphite nodules instead of flake graphite. This structure provides high strength, excellent toughness, superior ductility, and good impact resistance.
It delivers steel-like mechanical performance while retaining the castability and cost advantages of traditional cast iron, making it ideal for high-load and fatigue-critical applications.
Chemical Composition
| Element | Typical Range (%) | Function |
|---|---|---|
| Carbon (C) | 3.2 – 4.0 | Graphite formation, fluidity |
| Silicon (Si) | 2.2 – 2.8 | Promotes graphite nodules |
| Manganese (Mn) | 0.1 – 0.5 | Pearlite control |
| Magnesium (Mg) | 0.03 – 0.06 | Graphite nodulizer |
| Phosphorus (P) | ≤ 0.05 | Avoids brittleness |
| Sulfur (S) | ≤ 0.02 | Maintains nodularity |
| Iron (Fe) | Balance | Matrix |
Common Standards & Grades
ASTM A536 (60-40-18, 65-45-12, 80-55-06, 100-70-03)
EN 1563 (EN-GJS-400-15, 500-7, 700-2)
IS 1865 (SG 400/15, 500/7, 700/2)
Key Mechanical Properties
| Property | Typical Range |
|---|---|
| Tensile Strength | 400 – 900 MPa |
| Yield Strength | 250 – 600 MPa |
| Elongation | 2 – 25% |
| Hardness | 130 – 300 HB |
| Impact Strength | Moderate to High |
| Fatigue Strength | Excellent |
Physical Properties
| Property | Value |
|---|---|
| Density | 7.1 – 7.3 g/cm³ |
| Melting Range | 1,150 – 1,200 °C |
| Thermal Conductivity | 30 – 40 W/m·K |
| Specific Heat | ~460 J/kg·K |
| Thermal Expansion | 11 – 12 µm/m·°C |
| Damping Capacity | Moderate |
Key Characteristics
✔ High strength with ductility
✔ Excellent fatigue resistance
✔ Good impact toughness
✔ Castability with steel-like performance
Available Forms
Sand cast components
Centrifugally cast pipes
Continuous cast bars & blocks
Machined precision parts
Austempered (ADI) components
Applications
Water & sewage pipes, valves, fittings
Automotive crankshafts, suspension parts
Gears, wind turbine hubs
Hydraulic & construction equipment parts
Pump housings and compressor bodies
Advantages
✔ High tensile & yield strength
✔ Excellent ductility and toughness
✔ Superior fatigue performance
✔ Cost-effective steel alternative
Limitations
❌ Lower damping than gray iron
❌ Requires strict process control
❌ Slightly higher cost than gray iron
❌ Weldability requires care
Why Choose Ductile Cast Iron?
Ductile cast iron is chosen when steel-like strength, impact resistance, and fatigue performance are required while retaining economical casting and design flexibility.