Ductile iron (also called nodular or spheroidal graphite iron) contains magnesium additions that cause graphite to form as spheres rather than flakes, giving it significantly higher tensile strength and impact resistance than gray iron. For trade professionals, the distinction matters because product specifications, applicable ASTM standards, and sometimes HTS subheadings differ between the two grades — and antidumping scope language may be grade-specific.

The casting process itself generally does not change HTS classification, which is driven by metal composition and article form. However, process documentation is relevant for quality certification (e.g., ASTM A536 for ductile iron) and for demonstrating that a casting was produced — not merely finished — in the declared country of origin, which is critical when active antidumping orders cover iron castings from specific countries.