Graphite in Ductile Iron

• The introduction of magnesium and other metals into the molten iron results in the formation of spherical graphite; during solidification, this graphite causes an expansion of the iron. As a result of this graphite expansion, the cast is free of defects related to shrinking, both with or without the use of feeders. In short, this means that ductile iron requires less material and energy in its manufacture, resulting in substantial savings.
  
  

Alloying

• Alloying is the most common production technique which is used to make ductile iron; pearlite, carbide, martensite, austenite and ferrite are the most common additives into the molten iron besides magnesium, and are used to increase machinability, toughness, lower production cost, reduce the need for annealing heat treatments, and assure maximum ductility.
  
  

Heat Treatments

• Various heat treatments are sometimes applied to many types of ductile iron after casting, particularly to increase hardness and toughness. Martensitic ductile iron is usually treated with a quench-and-temper heat treatment. According to Ductile Iron Data for Design Engineers, austempered ductile iron (ADI) is a type of ductile iron that is given "a special austempering heat treatment. Nearly twice as strong as pearlitic Ductile Iron, ADI still retains high elongation and toughness. This combination provides a material with superior wear resistance and fatigue strength."
  
  

Casting Ductile Iron

• Much of the value of ductile iron is related to the fact that it can simply be cast and cooled without an annealing or heat treatment, and still have superior performance at lower cost than other types of iron or steel. Pearlitic, ferritic, and ferritic pearlitic ductile iron objects are usually sold as-cast.