Nodulizing Treatment: Turning Iron into "Gold"
Ductile iron is called "steel made of iron" — tensile strength 400~800MPa, far above ordinary cast iron. The starting point: nodulizer added before pouring.
What Is Nodulizer?
Core component is magnesium (Mg): pure Mg, Mg-FeSi, RE-Mg-FeSi, Ba-Mg alloys. Mg changes graphite crystallization from flakes to spheres. Rare earths assist, resisting anti-nodulizing elements (Ti, S) and smoothing the reaction.
Nodulizing Temperature
Highly temperature-sensitive:
- Too low (<1450°C): incomplete melting, low nodularity
- Too high (>1520°C): severe Mg burn-off, wasted nodulizer
- Ideal: 1480~1520°C — smooth reaction, high absorption
Measure temperature first — adjust, then treat.
Treatment Methods
Plunge (most common): nodulizer in a ladle-bottom pocket covered with steel shot; poured iron dissolves it. Simple, reliable, small batches.
Wire feeding: cored wire fed to the ladle bottom — uniform, fume-free, high absorption. Mass production.
In-mold: nodulizer in the gating system; reaction during pouring — minimal fade, demanding control.
Common Failures
- High sulfur (anti-nodulizing, consumes Mg) — desulfurize or raise dosage
- Wrong temperature — burn-off or incomplete reaction
- Damp nodulizer — violent reaction, splash hazard
- Long hold after treatment — fade, graphite reverts to flakes
Quick Assessment
Sample after treatment: silvery fine-grained fracture, ringing sound (gray iron is dull), surface shrink depression — usually good nodularity. Thermal analysis gives a nodularity reference in minutes.
Summary
Nodulizing turns ordinary iron into near-steel performance. Right nodulizer, right temperature, standard practice — front-line temperature measurement is the first safeguard.