Nodularguss

Nodularguss, also known as nodular cast iron or ductile iron, is a class of cast iron in which the graphite forms as discrete nodules (spheroidal shapes) rather than flakes. This microstructure, produced by introducing nodulizing elements into the molten metal, gives the material significantly different mechanical properties from traditional gray cast iron.

In nodular cast iron, graphite nodules are embedded in a metallic matrix that can be ferritic, pearlitic, or tempered. The nodules interrupt crack propagation and impart high ductility and toughness while maintaining relatively good strength. Depending on the matrix, ductile iron can exhibit a range of properties, from high elongation and impact resistance to higher hardness and strength.

Production and treatment typically involve melting pig iron with steel scrap and alloying additions, then adding nodulizing agents such as magnesium or rare earth elements (and sometimes inoculants) in the ladle before casting. Post-casting heat treatments, such as tempering or austempering, can further modify the balance of strength and toughness. Ductile iron can also be alloyed to improve corrosion resistance or wear properties.

Applications for nodular cast iron are broad and include automotive components (crankshafts, gears, connecting rods, pump housings), machinery parts, valve bodies, and large piping systems. It is valued for its combination of strength, ductility, machinability, and castability. Standards for ductile iron parts are provided by organizations such as ASTM (for example, ASTM A536), which cover chemical composition, mechanical properties, and testing methods.