S.G

Ease of Machining 
Free graphite in the structure also lends itself to machining (chip formation).

 

Cost per Unit Strength 
Significantly cheaper than most materials.

 

The composition of S.G Iron varies little to that of Grey Iron, yet this material offers ductility and increased strength.The reason lies as one of its many names suggests in its microstructure (Nodular Iron), which refers to the formation of graphite spheres (nodules) rather than flakes. The flakes whilst giving grey iron its unique properties are detrimental to its mechanical strength, breaking up the continuity of the metallic matrix preventing ductility. On top of this the sharp edges of the flakes act as stress raisers further reducing strength.S.G Iron does not have this problem as the graphite is in discrete spheres, giving continuity of the matrix therefore allowing ductility. As the graphite has no sharp edges there are no stress raisers that would otherwise reduce the strength of the metal matrix.