what are the applications of Nodular cast iron?

Answer 1

Cast iron treated in the molten state with a master alloy containing an element such as magnesium which favors formation of spheroidal graphite. Also known as ductile iron; spheroidal graphite cast iron.
Applications:
Much of the annual production of ductile iron is in the form of ductile cast iron pipe, used for water and sewer lines. Ductile iron pipe is stronger, easier to tap, requires less support and provides greater flow area compared to pipe made from other materials. In difficult terrain it can be a better choice than PVC, concrete, polyethylene or steel pipe.

Castings made of ductile iron are widely used. Examples include automobile components, industrial machinery, wind turbine electrical energy generation, valves, air conditioning machinery, lawn and garden equipment, and agricultural products
source: wikipedia and answers.com

Answer 2

As stated in the previous answer, nodular (ductile) iron is gray iron alloyed with magnesium or cerium. By alloying with these metals, you get a product with properties similar to steel. Another interesting feature of nodular cast iron is that it can be heat treated to have three different structures each having a different strength. Ferritic Nodular iron is obtained by heating the as-cast pearlitic cast iron for a long period of time. Ferritic cast iron has a ferrite substructure and has a yield strength of around 40,000psi. As cast (pearlitic, most common) has a yield strength of about 70,000psi. Tempered nodular cast iron has a yield of about 120,000 psi. Just to put some numbers with the ductility - nodular cast has 12-18% elongation depending on the heat treatment. The applications are endless; nodular is usually a cheap alternative to steel in production parts. Engine blocks and other machine cases are commonly made from ductile iron.