Difficulty: Easy
Correct Answer: Magnesium
Explanation:
ConceptNodular (spheroidal graphite) cast iron is produced by magnesium treatment (sometimes rare earths like cerium are also used). Mg modifies graphite morphology from flakes to spheroids, improving ductility and toughness.
Why not othersNi, Cr, and Cu are alloying elements for strength/corrosion/wear but do not cause graphite nodularisation.
Final AnswerMagnesium
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