What are the Properties of Ductile Iron?

What are the qualities that are unique to ductile iron? How can we distinguish ductile iron properties from ordinary grey iron?  Ductile iron properties offer extraordinary mechanical properties due to the uniqueness of the graphite particles that are created in the process of creating this type of iron. These graphite particles spheroidal in nature and because of that fact, this type of iron can offer greater elasticity, impact strength, and elongation

Ductile Iron Properties – Defining Different Irons

When defining irons, we need to consider the ferrous product classification which can be looked at in terms of the carbon content of the basic metal.

Here is a breakdown of that:

  • iron : 0 to 0.1% C
  • steel : 0.1 to 1.7% C
  • cast iron or ductile iron: 1.7 to 5% C

If the carbon content is below 1.7 %, the solidification will produce an austenitic single-phase material, with the carbon present in the structure in solid solution. If the carbon content is above 1.7%, the carbon won’t be able to fully dissolve in the iron structure. In that case, the carbon solidifies in the form of a secondary phase, creating either graphite (pure C) or iron carbide (Fe3C).

What elements that make up the multi-phase material that is Iron?

Iron is a complex structure made up of three basic things. The primary elements are ferrite (Feα) and pearlite (Feα + Fe3C). Of course, carbon as we have said above, and in lower proportions, Iron is made up of silicon. This makes iron a ternary alloy meaning it has 3 basic components, Iron, carbon, and silicon. Other elements present in iron in very low proportions have an effect on the structure, mechanical properties, and casting of the metal.

What are the different types of cast iron?

The cast iron designation includes a wide variety of Fe-C-Si alloys. They are generally grouped according to the condition and shape of the graphite condition and the structure of the metal matrix.

When referring to grey irons, the graphite forms flakes and are therefore called, flake graphite iron or sometimes lamellar graphite irons. The flakes can cause cracking when put through concentrated abnormal stress.
Metallurgists work to diminish, or eliminate, this issue by changing the size or distribution of the flakes. By using a centrifugal process, it’s possible to cast flake graphite iron pipes also known as grey iron pipes which improve this by producing very fine graphite flakes.

In 1948 a British research team discovered the process that would allow for casting spheroidal graphite iron, more commonly known as ductile iron.
The graphite doesn’t form flakes but rather presents itself in spherical form, therefore, eliminating the high probability of crack propagation lines forming to create cracks. This graphite spheroidal form is created by the controlled addition of a small amount of magnesium to the previously desulfurized base iron.

Ductile Iron Properties – What makes it unique?

Due to the spheroidal shape of its graphite, ductile iron has remarkable mechanical properties:

  • tensile strength
  • good elongation
  • impact resistance
  • high elastic limit

By controlling the chemical analysis and the heat treatment of the metal matrix, ductile iron’s properties are even more greatly enhanced.
The high carbon content in ductile iron allows it to maintain the traditional qualities of other cast irons such as:

  • compression strength
  • machinability
  • fatigue strength
  • castability
  • abrasion resistance

When seeking a foundry that is capable of assisting you with your ductile iron casting needs, please consider Faircast Inc. We have been in the business of casting ductile and grey iron for decades and our engineers will work with you to help discover the best ways to fulfill your project needs.