Cast Irons

Cast irons are a large group of ferrous alloys which solidify with a eutectic. They contain high amounts of iron, significant amounts of silicon (about 1-3%), and are considered to be ternary alloys (Fe-C-Si). Cast irons tend to be brittle depending on the particular alloy. They generally have low melting points, good fluidity, castability, wear resistance, and excellent mechanicability. Because of these benefits, cast irons are being included in an increasing number of engineering applications, including pipes, machines, and car parts. Cast irons are available in two colors: gray and white.

Gray cast irons contain a significant amount of silicon. When this silicon is alloyed with ferrite and carbon (approximately 2% of each), the iron carbide becomes unstable. The silicon causes the carbon to quickly pull out of the solution, resulting in graphite. Once the carbon is extracted, the solution becomes a matrix of relatively pure, soft iron. Weak bonding occurs between the plates of graphite and leads to high-energy growth in that direction. As a result of that growth, thin flakes are formed. The benefit of working with graphite is that it can improve wear resistance due to its high thermal conductivity. When compared to steel, however, gray cast irons have less strength and shock resistance. 

White cast irons have a lower silicone content and faster cooling times. Unlike gray cast irons, the carbon in white cast irons expedites out of the melt as the metastable phase cementite. The eutectic mixture that emerges from the initial participation is large and cannot undergo participation hardening. Instead, this mixture increases the bulk hardness. White cast irons are too brittle to be used in more structural components but their hardness and abrasion resistance allow them to be used in wear surfaces such as slurry pumps, lifter bars, shell liners, grinding mills, and the balls and rings of coal pulverizers.

Another form of cast irons is known as “malleable iron”. Malleable iron starts outs as white cast iron and is then heated to approximately 900° C. At this temperature the graphite separates out slowly, allowing surface tension to form into spheroidal particles rather than flakes. The end result is more like mild steel but there is a size limit because the material is made from white cast irons. Malleable irons are ideal for castings, especially ducts. The castings that use these irons most often are electrical fittings, hand tools, pipe fittings, washers, brackets, fence fittings, power line hardware, machine parts, farm equipment, and mining hardware. 

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Part Numbers for Cast Irons