Cast Iron

Iron is found in the composition of many different metal alloys. Without it, carbon steel, stainless steel, superalloys, and several other metal alloy groups could not be manufactured. However, cast iron, ironically the metal alloy group with “iron” in its name, is often misunderstood as to what it is, how it is made, and what it can be used for. This article takes an in-depth look at cast iron.

What is cast iron?

Cast iron is a term used to describe a family of metal alloys who primary alloying element is iron. Because of its name, some people tend to think that cast iron is basically 100% iron. This is simply not true. In fact, carbon steels have higher amounts of iron element in them than do cast irons.

To be considered a cast iron, a predominantly iron alloy must have over 2% carbon to for the final alloy to be considered cast iron. Cast irons also have smaller amounts of other alloys, with manganese and silicon being two of the most popular. These additional alloying elements are used to further modify the properties of cast iron and result in specific cast iron alloy designations.

There also is not just one group of cast irons. In fact, there are four major subtypes of cast iron alloys. These are:

  • Ductile cast iron: Contains nodules of graphite making it more ductile than other cast irons while still having excellent strength properties
  • Gray cast iron: Has flakes of graphite in it which improves its machinability relative to other cast irons
  • White cast iron: Has high amounts of iron carbides, making it very brittle but with a high degree of wear resistance
  • Malleable cast iron: Essentially white cast iron that has been specially heat treated to transform the iron carbides into graphite nodules; it has similar properties to ductile cast iron

How is cast iron made?

The manufacturing process of cast iron is how the metal gets its name. To make cast iron, iron ore is heated in a furnace until it becomes molten. Then the molten metal is cast (poured out and allowed to harden, in the shape of an ingot). The cast iron ingots are melted again into a final mold. During this subsequent remelting, the cast iron may have several metallurgical modifications made to it through the introduction of alloying elements or heat-treating processes. Oftentimes, this is where a cast iron falls into the specifications of one of the four groups mentioned above.

Cast iron, when molten, has better fluidity than steel. Cast iron also has a low melting temperature. These two attributes make cast iron an ideal candidate for the casting process. This is partially why it is so popular. However, with improved technology for manufacturing and forming steel, use of cast iron has diminished over the past several centuries.

Where is cast iron used?

Cast iron is used abundantly in applications that require high hardness and abrasion resistance and are less concerned about structural properties. This is because steel can generally be modified to have more desirable structural characteristics than cast iron for many projects. Although, before steel became more common, cast iron was somewhat popular for structural purposes. Cast iron is also quite affordable because of its basic alloying element requirements and low-cost method to produce. Therefore, it is still quite common to see cast iron used around the world today. Here are some examples, although it is important to know that these will vary depending on what one of the four types of cast iron mentioned above is selected:

  • Brake discs
  • Gears and gear plates
  • Sprockets
  • Chains
  • Machinery
  • Cookware
  • Decorative architectural pieces
  • Engine blocks
  • Shafts and rods of various types
  • Housings
  • Mining equipment

 

Reference URL’s:

https://www.britannica.com/
https://monroeengineering.com/
https://www.machinedesign.com/
https://www.engineeringtoolbox.com/

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