Is Cast Iron Brittle Or Ductile?

What Are the Symptoms Of Brittle Cast Iron?

We have discovered that cast iron is brittle and can crack or break in certain circumstances. But why is cast iron brittle? And how do we know if our cast iron is damaged?

Cast iron is brittle because of its high carbon content. The more carbon present in a material, the more brittle it is.

Grey cast iron is further impacted by its graphical microstructure. It has tiny cracks and graphite flakes inherent within the material and these also contribute to its brittleness.

Brittle cast iron will usually show signs that it is becoming damaged or impaired.

Cracking — these cracks may be visible, or sometimes a deterioration in performance may suggest damage. If you think your cast iron item is damaged, you should seek expert advice.

Corrosion—again, this will often be visible, but cast iron components are often hidden. Regular checks should be part of your planned maintenance schedule.

Performance – a decline in performance or unusual noises or vibrations will often indicate that a deterioration in the material is present.

Can Cast Iron Be Repaired?

It certainly can. But cast iron is a challenging material to work with, mainly due to its high carbon content. If the repair is not carried out professionally, it can be prone to cracking around the weld area, often due to temperature changes during the weld process.

Nevertheless, by using the correct techniques and skill set, cast iron can be repaired successfully.

Cast Iron Welding Services has developed its own gas fusion welding process to repair and restore damaged cast iron. The technique has been developed successfully over many years and uses cast iron fusion rods to repair damaged items. The fusion rods are made from the same grade of cast iron that the parent material is made from. Using cast iron to repair cast iron retains the integrity of the material and produces a uniform, stress-free weld. The resulting material has improved metallurgical and machining properties compared to the original.

What About Malleable Cast Iron?

Cast iron is made from pig iron. There are different types of cast iron, each produced slightly differently and resulting in a metal with slightly different properties.

Grey cast iron, or gray iron, is composed of a graphical flake-shaped microstructure that produces its grey appearance. This type of cast iron is more brittle, but it is easier to machine and has better wear resistance, making it the most widely used of the cast materials.

White iron is produced by combining the correct carbon content and cooling rate to form iron carbide and results in a hard, brittle material with extremely high compressive strength and wear resistance.

Ductile iron, or nodular iron is formed by adding magnesium into the alloy and produces a spheroidal microstructure, as opposed to flakes. This type of cast iron deforms upon impact, rather than shattering making it a safer choice in certain applications.

Malleable cast iron is made from white iron using a long heat treatment process called annealing. The process converts the carbon into graphic nodules, which creates a pearlitic microstructure. It has a lower silicon content giving it a higher tensile strength than other cast irons.

Malleable cast iron is less brittle than the other cast irons and it is a popular choice for smaller fittings such as piping, plumbing and machine parts. However, it is more expensive than its counterparts and difficult to produce in large quantities.

What is Cast Iron Used For?

Cast iron is best used in applications where compressive strength rather than tensile strength is needed. Or for decorative items requiring good castability.

Cast iron has been used for structural, engineering, defence, utility and decorative purposes since the late 1770s. The material offers huge benefits due to its durability, strength and longevity and has been applied to multiple historic structures worldwide. With correct maintenance, these cast iron structures will remain for years to come.