Casting Process

• During the iron casting process, carbon is added to molten iron in amounts that surpass solubility confines to create graphite particles. Silicon is then added to the mixture to form graphite. This enhances the properties already existing in the iron. Additional alloys may be used to further shape the graphite as well.
  
  

Gray

• Gray iron is cast by pouring the molten iron into patterned sand molds. Its graphite content is flaked, which gives it excellent machinability as well as hardness, wear-resistance and vibration-inhibiting properties. Gray iron is cast for use as machinery supports as well as in automotive cylinder blocks and brake components.
  
  

Ductile

• The graphite in ductile iron is shaped as spheroids rather than flakes. This difference is created by adding alloys to the metal. Because of its high flexibility, this type of iron may be cast in a range of sizes and thicknesses. In heavy pieces, alloys may be added to increase strength as well.
  
  

Compacted Graphite

• The graphite present in compacted graphite iron is formed as connected rounded flakes. This structure gives it the strength and hardness of ductile iron as well as the thermal conductivity and machinability of gray iron. It is useful in applications where the metal is subjected to heavy loads. To be considered CGI, the metal produced must contain at least eighty-percent compacted, worm-shaped graphite particles and less than twenty-percent spheroidal graphite particles.
  
  

White

• White iron is hardened with a cementite compound and contains almost no graphite. The carbides in white iron create a medium that may be worked to form a ferritic or pearlitic metal, or metal that contains alternating layers of ferrite and carbide. It may also be cast to an austenitic metal, containing lower amounts of carbon and silicon with alloys like nickel added, or it may be martensitic, where the metal is cooled rapidly to prevent the formation of austenite or pearlite. White irons with high chromium content are typically used in applications involving high temperatures. Those with high nickel content are used where abrasion resistance is required.
  
  

Malleable

• Malleable iron contains graphite that is present in unevenly shaped lumps formed during extensive heat treatment. Malleable cast iron is used for thin sections or components where flexibility is needed. Although it has excellent machining properties, malleable iron is not as strong as other types of iron and ductile iron is often used in place of malleable as it shares many of the same properties, but ductile doesn’t require extensive heat treatment to produce graphite.
  
  

Alloyed

• Gray, ductile and white irons containing more than three-percent alloys such as nickel, silicon, copper or chromium, are called alloyed irons. Malleable irons are not included in this group because they cannot be alloyed heavily enough. Corrosion-resistant alloyed irons are used in engineering applications which operate in moist environments where the metal is exposed to sea water or acids and alkalis. Elevated-temperature service alloyed irons are used in the manufacturing of components used in chemical and petroleum processing and refining, food production and marine applications.