THE TERM "CAST IRON," like the term "steel," identifies a large family of ferrous alloys. Cast irons primarily are alloys of iron that contain more than 2% carbon and from 1 to 3% silicon. Wide variations in properties can be achieved by varying the balance between carbon and silicon, by alloying with various metallic or nonmetallic elements, and by varying melting, casting, and heat-treating practices.

Cast iron is produced by adding excess amounts of carbon to an austenite structure. During solidification, a portion of this carbon separates from the melt as either iron carbide or graphite. The form that the excess carbon takes is determined by the rate of cooling. If the cooling is rapid, the carbon will solidify as iron carbide. If the cooling is slow, the carbon will solidify as graphite. The type of carbon present and its shape will determine the type and, in particular, the properties of the cast iron.

Following a brief review of the classification and characteristics of cast irons, this article will review the processes used to clean iron castings as well as surface treatments used to extend casting life when resistance to corrosion, wear, and erosion is required. Additional information on the cleaning and coating processes described herein can be found in the cited articles appearing elsewhere in this Volume.

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