Cast iron is an alloy of iron, silicon and carbon. Typically, the concentration of carbon is between 3-4 % by weight, most of which is present in insoluble forms (e.g. graphite flakes or nodules). The two main types are grey cast iron and nodular (ductile) cast iron.
The corrosion resistance of cast iron is comparable to that of steel – and sometimes even better. To improve corrosion resistance, cast iron can be alloyed with 13-16 % by weight silicon or 15-35 % by weight nickel (Ni-resist), respectively.
Various types of cast iron are widely used in industry, especially for valves, pumps, pipes and automotive parts. Cast iron has good corrosion resistance to neutral and alkaline liquids (high pH). But its resistance to acids (low pH) is poor.
Grundfos cast iron pumps, for example from the CR multistage and the NK/NKE/NKG/NKGE end-suction long-coupled single-stage ranges, are built to resist corrosion by using the cast iron types and the alloys that best match the application.