WHY IS DUCTILE IRON COST LOWER THAN STEEL?
Two factors determine this significant difference in cost:
1- Temperature required
First, steel must be poured at a much higher temperature than ductile iron, which demands greater energy expenditure for an equivalent part.
Another reason of this substantial cost difference is caused by what is called shrinkage. When a metal cools, it shrinks. To avoid creating porosity due to shrinkage, smelters use risers containing metal that will remain in fusion longer than the actual part, providing it with the metal necessary to avoid creating porosity. Using these risers necessitate melting more metal thus using more energy.
With ductile iron, the needed risers are much smaller thanks to the graphite precipitation phenomenon. This brings the cost of ductile iron cast lower than one made of steel.
Ductile iron and steel have similar mechanical properties. The difference in properties shouldn’t therefore influence the choice of one material over the other. Steel has better shock resistance than ductile iron. However, ductile iron has better vibration damping properties rendering ductile iron mechanical components noticeably quieter.
Ductile iron also provides better resistance to corrosion. Cast iron will oxidize faster, but rust will remain superficial. The structural integrity of a ductile iron component will therefore be less impaired.
Finally, it should be noted that ductile iron has low weldability, which necessitate different assembling methods, such as bolting.