The properties of ductile iron, also known as nodular iron or SG iron (Spheroid Graphite), follow the same basic rules as those governing Gray iron regarding the importance of the metallurgical structure. The spheroid form of the graphite in ductile iron results in the almost complete annihilation of its effects, leaving as an active matrix a mere combination of the pearlite and ferrite phases, exactly like what takes place in steel. This explains why the properties of ductile iron are similar to those encountered in steel, especially in terms of elongation.