Ductile iron, also known sometimes as nodular iron or spheroidical graphite (SG) iron, has now been universally accepted as an engineering material as it combines high strength to weight ratio, toughness and good machinability. Usually, people consider cast iron as weak and brittle, but ductile is a completely different material. Ductile iron contains nodular graphite due to which it is extremely tough. As its usage is increasing, the production tonnage of ductile iron is second only to grey cast iron. It far exceeds that of malleable iron and cast steel. Currently, 80% of automobile crankshafts are ductile iron castings and this is only the beginning as this portion represents a fraction of its numerous applications.

Prior to the metal casting process, liquid iron is treated with magnesium to produce ductile iron. The addition of magnesium at the molten stage transforms the microstructure of conventional grey iron of thin flakes to spheroidical form providing tensile strength that is at least twice that of grey iron.

It is this higher tensile strength and many other excellent properties of ductile iron over other materials that has resulted in its remarkable progress and increased use. Due to its high strength to weight ratio, engineers have started replacing other materials by ductile iron with significance reductions in weight while maintaining or even improving performance.

The excellent machinability, good vibration damping and superb wear characteristics of ductile iron have often been decisive factors in an engineer's choice for a suitable material. With proper heat treatment, the strength, the toughness and machinability of ductile iron can be improved further. What is more, there are special grades of ductile iron providing good heat corrosion and wear resistant properties.

The advantages can be summarized as follows:

• Equivalent or superior performance with better design
  
  
• Essential strength at less cost
  
  
• Easier machining
  
  
• Extended tool life
  
  
• Reduced machining allowances
  
  
• Improved strength to weight ratio
  
  
• Better casting definition
  
  
• Improved vibration damping
  
  
• Improved thermal properties
  
  
• Superior low temperature performance
  
  
• Good surface finish