Cast Iron (Fe+C)
Cast iron is an iron-carbon alloy with carbon content exceeding 2%, typically 2.5–4%. Known for excellent castability, vibration damping, and compressive strength, it remains essential for engine blocks, machine bases, pipes, and heavy industrial components. Modern ductile iron grades rival steel in many applications.
Properties
- Density
- 6,800–7,800 kg/m³
- Melting Point
- 1,150–1,300 °C
- Boiling Point
- 2,862 °C
- Thermal Conductivity
- 27–46 W/(m·K)
- Electrical Resistivity
- 5.6 × 10⁻⁷ Ω·m
- Tensile Strength
- 150–900 MPa
- Yield Strength
- 100–600 MPa
- Hardness
- 130–500 HB
- Elongation
- 0–18%
- Crystal Structure
- Various (graphite morphology dependent)
Common Grades
- EN-GJL-250: Grey iron with lamellar graphite, min tensile 250 MPa. Machine beds, cylinder blocks.
- EN-GJS-400-18: Ductile iron (spheroidal graphite), 400 MPa tensile, 18% elongation. General engineering.
- EN-GJS-600-3: High-strength ductile iron, 600 MPa tensile. Crankshafts, gears, heavy-duty parts.
- EN-GJL-300: Higher-strength grey iron. Brake discs, hydraulic components.
- EN-GJMW-400-5: Whiteheart malleable iron. Pipe fittings, railings, agricultural parts. Good impact resistance.
- EN-GJS-800-2: ADI (Austempered Ductile Iron), 800 MPa tensile. Gears, crankshafts, mine equipment — rivals steel.
Applications
- Automotive: Engine blocks, brake discs/drums, crankshafts, exhaust manifolds, flywheels
- Infrastructure: Water/sewer pipes, manhole covers, bollards, street furniture
- Machine Building: Machine bases, beds, frames, gearbox housings, pump bodies
- Energy: Wind turbine hubs, valve bodies, turbine housings
FAQ
What is the difference between grey iron and ductile iron?
Grey iron has lamellar (flake) graphite, giving excellent damping and machinability but low ductility (0–1%). Ductile iron has spheroidal (nodular) graphite created by adding magnesium, providing 5–18% elongation and significantly higher tensile strength, approaching that of steel.
Why is cast iron used for machine bases?
Cast iron's superior vibration damping (10× that of steel), excellent compressive strength, and precision castability make it ideal for machine tool bases. The damping properties reduce chatter and improve surface finish quality during machining operations.
What is ADI (Austempered Ductile Iron)?
ADI is ductile iron that has been austempered (heated to 850–950°C then rapidly cooled to 250–400°C and held). This produces a unique ausferrite microstructure with tensile strengths of 800–1,400 MPa — rivaling heat-treated steel at lower cost and 10% lower weight due to graphite nodules.
Can cast iron be repaired by welding?
Yes, but it is challenging. Grey iron requires nickel-based filler metals (ENi-CI or ENiFe-CI), extensive preheating (300–600°C), slow cooling, and often peening between passes. Ductile iron is slightly easier to weld. Cold welding techniques using nickel electrodes with short bead runs are common for repair work.