What is Ductile Iron and Why Is It So Important?

In 1943, Keith Millis, along with Alber Gagnebin, and Norman Pilling received a US patent for the making of Ductile Iron using magnesium to strengthen cast iron. The popularity of use of this type of iron increased in the 1950’s and 1960’s as a material for many commercial applications due to many of its useful qualities. 

While ductile iron is a type of cast iron, it is more fatigue and wear-resistant than cast iron because of the round graphite structures that are cast into the metal.  These spherical bits of graphite add to ductile irons ability to withstand greater impact while also allowing for elongation. Ductile iron is often referred to as spheroidal graphite cast iron, or nodular cast iron as well.

Regular cast iron, also known as gray iron, also contains bits of graphite but they appear as squiggly lines which are called flakes as opposed to the spheres of graphite you will see in ductile cast iron. Of course, the only way to see the graphite is with a microscope, not the naked eye.

Ductile iron is typically formed by using primarily iron (about 94%) with a combination of carbon, silicon, manganese, magnesium, phosphorus, sulfur and copper. At times more copper is added to improve strength, as well as nickel or chromium to add resistance to corrosion. In those cases, anywhere from 15 – 30% of the iron is replaced with those other elements.  

When making ductile iron, a foundry, like Faircast Inc. will, of course, start with the iron itself continuing to add carbon until they reach the point where they have added more carbon than the iron would normally be able to absorb. This is what makes Ductile Iron different than steel as steel only has as much carbon in the compound as the iron can absorb.

One of the big benefits of using Ductile Iron castings is that they much stronger than regular cast iron also known as gray iron.  Cast iron offers a tensile strength of about 20,000 – 60,000 psi, however the tensile strength of ductile iron starts in the range of 60,000 psi all the way up to 120,000 psi.  

If you were to drop something made of (gray) cast iron from a height of as little as 10 feet off the ground, it is very probable that you will see the cast iron object break apart. This is not the case with something cast in ductile iron. An object made of ductile iron can be hammered on continuously without cracking. This can be a very important thing to consider when deciding what material will suit the application you need it for. 

The graphite flakes in gray cast iron makes fractures more likely while the spherical nodules in ductile iron actually help to keep the iron together. Gray iron is more brittle and prone to cracking where ductile iron will tent to bend instead. 

Ductile iron is more resistant to wear therefore has more lasting power. So, it’s great for applications where there might be more need for resistance due to rubbing. The graphite structures can act like a dry lubricant in these cases.

This type of iron has the ability to dissipate heat very well and it’s not difficult to machine in general but can be harder to work with than ordinary gray cast iron. It’s a great match for use on large machines because it tends to dampen sound and vibration much better than when using steel.

Some of the best uses of iron using ductile is for applications where you need strong, more wear-resistant metals. Almost half of the iron sold in America is for the use of pipe and pipe fittings.

Other things that are commonly made include:

Auto Parts

  • Car and Truck Axles
  • Connecting Rods for Engines
  • Cylinders
  • Disc Brake Calipers
  • Crankshafts
  • Gears 
  • Gear Boxes
  • Housings
  • Manifolds
  • Hydrostatic Barrels
  • Idler Arms
  • Large Machines
  • Machine Tooling
  • Steering knuckles
  • Suspension system parts
  • Truck axles
  • Valves (especially high-pressure valves)
  • Wheel hubs
  • Yokes for power transmission
  • Water and Sewer Lines
  • Agricultural Tractors
  • Oil well pumps

It is even used for things like piano harps which are the parts that holds the strings of a piano. 

If you would like to learn more about Faircast Inc., please contact us at Call (641) 209-4100.

We would love to talk with you about your project or needs. 

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