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Have you got the classifications of cast iron?

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Have you got the classifications of cast iron? 
By megan2008 on Nov 04, 2013 09:06 AM
'Cast iron' is a term covering many metals with different properties,which is widely used in mining machnery castings,construction machinery castings,motor casting,iron casting tractor parts,automotive castings etc.They are made by melting iron in a furnace and hardening it in a mold. All types of cast iron contain more than 2 percent carbon. Cast iron must also contain silicon, typically 1-3 percent. The percentage and form of alloying elements determines the property of the metal. All cast irons are brittle and most cannot be worked either cold or hot.

Gray Cast Irons

Gray irons are produced by slow cooling. They take their name from the gray color they show along fractured surfaces. The carbon in gray irons takes the form of graphite flakes which make them more brittle than other forms. Tensile strength (the pulling stress a substance can withstand) is low for cast iron and especially so for gray irons. Gray irons are used for flywheels and other parts where their superior vibration absorbance is valuable.

White Cast Iron

This class of cast irons show white along fractured surfaces. The carbon in white cast iron is not separate as in gray cast iron, but combined chemically to some of the iron atoms in the form of carbide of iron. This makes white cast iron less brittle than gray and gives it a higher tensile strength, although it is still brittle. White irons are abrasion resistant and are used for parts like brake shoes and crushers.

Malleable Cast Irons

Malleable cast irons are made by heat treating white irons. This makes the metal more malleable (better able to tolerate bending stresses) and more ductile (able to tolerate pulling stress). The iron in malleable cast iron takes the form of ferrite and the free carbon is in the form of graphite particles. Unlike most cast irons, malleable cast irons can be machined. Among other applications, malleable cast irons are used to make railroad and agricultural equipment.

Nodular Cast Irons

Nodular cast irons are also known as ductile cast irons, reflecting their superior ability to tolerate pulling stresses. Nodular cast irons are a form of gray cast iron. They are made by adding a small percentage of manganese (typically around 0.1 to 1.0 per cent) to the melted iron before casting. The manganese modifies the carbon so that it forms nodular graphite particles. Nodular cast iron has good resistance to wear and fatigue.

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