Common Types of Cast Iron

Carbon exists as graphite in most cast irons, and both microstructure and mechanical behavior are affected by composition and heat treatment.

FREMONT, CA: Cast irons come in various shapes and sizes, depending on how the carbon-rich phase forms during solidification. Cast iron microstructure can be adjusted to design products with outstanding ductility, machinability, vibration damping, superior wear resistance, and good thermal conductivity. In addition, cast irons can match the corrosion resistance of stainless steels and nickel-base alloys in many applications with suitable alloying. Carbon exists as graphite in most cast irons, and both microstructure and mechanical behavior are affected by composition and heat treatment. The following are the most common cast iron types:

Gray Cast Iron

Gray cast iron is the most prevalent and oldest variety of cast iron. Gray cast iron is distinguished by its graphitic microstructure, which gives the material a gray appearance in fractures. This is because graphite is present in its makeup. Graphite flakes form in gray cast iron, taking on a three-dimensional structure. Gray cast iron also has a high damping capacity, provided by graphite, which absorbs energy and turns it to heat. Materials used in constructions where undesirable vibrations are created during operation, such as machine tool bases or crankshafts, should have a high damping capability. Materials having low damping capabilities, such as brass and steel, allow vibration energy to pass through them without attenuation.

White Cast Iron

Gray cast irons with softer graphite are relatively strong and machinable, but white cast irons are hard, brittle, and unmachinable. Because the fracture surface of this alloy is white, it is known as white cast iron. In addition, white iron is too brittle for many structural components. Still, because of its hardness and abrasion resistance, as well as its low cost, it finds use in applications where wear resistance is desired, such as excavator teeth, slurry pump impellers and volutes, shell liners, and lifter bars in ball mills.

Malleable Cast Iron

White cast iron that has been annealed is known as malleable cast iron. This is because the brittle structure of the first cast is changed into a pliable form through an annealing heat treatment. As a result, it has a similar composition as white cast iron, with slightly higher carbon and silicon content. It is frequently used in small castings that require high tensile strength and the ability to bend without breaking (ductility). Many critical automotive elements, such as differential carriers, differential cases, bearing caps, and steering-gear housings, are made of malleable cast iron. Hand tools, brackets, machine parts, electrical fittings, pipe fittings, farm equipment, and mining hardware are some of the other applications.