A536 Grade 2
The ASTM A536 ductile iron casting specification is based on demonstrated mechanical properties which depend on the proper cast iron microstructure. 

The difference between the various grades of ductile iron is in the microstructure of the metal around the graphite.  

This microstructure varies with the composition (relative amounts of carbon, silicon, nickel, manganese, etc) and the cooling rates in the casting. 

• High ductility grades have a ferrite microstructure.

• Intermediate grades have a mixed ferrite and pearlite microstructure.

• High strength grades have a primary pearlite microstructure. 

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