What Is SG42 Spheroidal Graphite Cast Iron?

SG42 (SG 420/12) Spheroidal Graphite Cast Iron is a ductile cast iron grade defined by BS EN 1563 (and ISO 1083), with 420 MPa minimum tensile strength and 12% minimum elongation. It is also called nodular cast iron or SG iron.

SG42 is cast iron where graphite forms spherical nodules (not flakes as in gray iron). This is achieved by adding magnesium or cerium (nodulizers) to molten iron. The rounded graphite eliminates stress concentration, giving the material high ductility and toughness.

Chemical Composition (Typical)

Carbon (C): 3.2–3.8%Silicon (Si): 2.0–2.8%Manganese (Mn): 0.2–0.6%Phosphorus (P): ≤ 0.05%Sulfur (S): ≤ 0.02%Magnesium (Mg): 0.03–0.06% (residual for nodularization)

Main AdvantagesHigh ductility & toughness (far better than gray iron)Good strength-to-weight ratioExcellent castability (like cast iron)Good wear resistance & vibration dampingLower cost than steel for many applications

SG42 Cast Iron Applications

SG42 is used for medium-strength, high-ductility cast parts that need to resist shock and deformation — typical in valves, pumps, gearboxes, automotive, agricultural, and general machinery.