The Effect of Graphite on the Properties of Cast Iron

White and Gray Cast Iron

• There are two different alloys, or combinations, of metals that create cast iron. The first is known as "white cast iron." It is called "white" because, when it is fractured, it appears white due to the carbon in the cast iron alloy. This form of cast iron does not have a high graphite content. "Gray cast iron," on the other hand, includes silicone, which helps stabilize graphite in the alloy. This alloy is referred to as "gray," also as a result of the color it has when fractured.

Ductile and Gray Cast Iron

• Gray cast iron is the most commonly used cast iron today, largely because of its weight and strength in comparison to steel. Ductile cast iron is another type of cast iron that contains graphite. Although similar to gray cast iron, this type of cast iron has nodules of graphite that give it more flexibility than other, more brittle forms of cast iron. This ductile iron is often used for water and sewage pipes .

Advantages of Gray Cast Iron

• Gray cast iron is more commonly used than other types of cast iron, primarily because of its low production cost. The graphite in gray cast iron alloys also gives it good wear resistance. This is because graphite allows the cast iron to flake rather than fracture as it does in white cast iron. It is also easy to weld, and the silicone helps reduce rusting, a common problem with cast iron.

Disadvantages of Gray Cast Iron

• Because of the graphite content in gray cast iron, it has low strength. Unlike white cast iron, it almost completely lacks shock resistance, which is a major downside to this alloy. However, despite these disadvantages, it is still the most commonly used cast iron for cookware due to its high thermal conductivity.