Industry News

Working Principle of Ductile Iron Casting

2025-05-15

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.


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