Cast iron has higher carbon and silicon contents than steel. Because of the higher carbon content, the structure of cast iron, as opposed to that of steel, exhibits a rich carbon phase. Depending primarily on composition, cooling rate and melt treatment, cast iron can solidify according to the thermodynamically metastable Fe-Fe3C system or the stable Fe-Gr system.


Various types of cast irons are widely used in industry, especially for valves, pumps, pipes, filters and certain mechanical parts. Cast iron can be considered an alloy of Fe, Si and C. The carbon concentration is between 1.7 and 4.5 %, most of which is present in insoluble form (e.g. graphite flakes or nodules). Such material is, however, normally called unalloyed cast iron and exists in four main types:

White iron, which is brittle and glass hard. Unalloyed gray iron, which is soft but still brittle, and which is the most common form of unalloyed cast iron. More ductile malleable iron. Nodular or ductile cast iron, the best modern form of cast iron, which has superior mechanical properties and equivalent corrosion resistance.

In addition there are a number of alloy cast irons, many of which have improved (corrosion) resistance and substantially modified mechanical and physical properties. Some of the most wellknown classes include the high-silicon and nickel cast irons.

• Available in a wide range of mechanical/physical properties, i.e. tensile strength from 20 KSI to over 200 KSI, hardness from 120 to about 300 Brinell in standard grades and up to about 600 Brinell in special abrasion resistant grades
• Good strength to weight ratio
• Typically lower cost than competing materials and relatively low cost per unit of strength than other materials
• Lower density and higher thermal conductivity than steels at comparable tensile strength levels
• Excellent machinability, allowing for high speeds and feeds and reduced (minimal) energy due to the presence of free graphite
• Many iron castings can be used without heat treatment (as-cast) but, when needed, can be heat treated to enhance overall properties or localized properties such as surface hardness
• Excellent damping capacity, especially in Gray Irons
• Chemical analysis can be modified to provide improved special properties such as corrosion resistance, oxidation resistance, wear or abrasion resistance, etc.
• Rapid transition from design to finished product
• Capability of producing highly complex geometries and section sizes in a wide range of sizes, from ounces to over 100 tons
• Flexibility in design and ability to optimize appearance for sales appeal
• Possibility of casting intricate shapes as well as very thin to very thick section sizes
• Capability of redesigning and combining two or more components from other materials into a single casting, thus reducing assembly cost and time
• Capability of casting with inserts of other materials
• Variety of casting processes for low, medium or high production
• Reduced tendency toward residual stresses and warpage than some competitive materials