Working Principle of Ductile Iron Casting

Working Principle of Ductile Iron Casting

1. Nodularization

• Mechanism: Add magnesium/rare-earth agents to molten iron during solidification, converting graphite from flakes to spheres.
• Effect: Reduces stress concentration, enhancing tensile strength (~400–1,200 MPa) and ductility (2–18% elongation).
• Process: Temperature 1,380–1,450°C, reaction time 3–5 mins.

2. Inoculation

• Mechanism: Add ferrosilicon inoculants to refine graphite, increasing nucleation sites for uniform, fine spheres.
• Effect: Improves toughness, reduces chill, and optimizes machinability.

3. Melting & Alloying

• Raw Materials: Pig iron (C 3.5–4.0%), scrap steel, return scrap.
• Melting: 1,450–1,550°C in electric/cupola furnaces; adjust Si (1.8–2.5%), Mn (0.3–0.6%).

4. Molding & Core Making

• Methods:

1. Sand Casting: Patterns (wood/metal) + green/resin sand.
2. Lost Foam: Polystyrene patterns vaporize upon pouring.

• Cores: Hot-box (thermoset resin) or cold-box (gaseous catalyst) processes.

5. Pouring

• Temperature: 1,300–1,380°C for fluidity.
• Control: Slow pouring to avoid turbulence; optimized gating system.

6. Solidification & Cooling

• Directional Solidification: Riser placement + chill blocks to feed shrinkage zones.
• Cooling Rate: Controlled to prevent cracks.

7. Finishing & Heat Treatment

• Cleaning: Shot blasting (sand removal) + grinding (gates/flash).

• Heat Treatment:

1. Annealing (relieves stress).
2. Normalizing (refines pearlite).
3. Quenching/tempering (for wear resistance).

8. Microstructure & Properties

• Structure: Spherical graphite + ferrite/pearlite matrix.

• Advantages:

1. Higher strength/toughness than gray iron.
2. Fatigue-resistant (ideal for dynamic loads).

9. Applications

• Automotive: Engine blocks, crankshafts.
• Industrial: Wind turbine hubs, gearbox casings.
• Railway: Wheelsets, brake disks.