What is Ductile Iron

What is Ductile Iron?

  Ductile iron is a kind of high-strength cast iron material developed in the 1950s. Ductile iron exhibits high strength, flexibility, durability and elasticity due to their unique micro-structure. Its mechanical properties are similar to steel, and far exceed those of standard cast irons.Its comprehensive performance is close to that of steel.

  It is based on its excellent performance and has been successfully used to cast some casting parts with high stress, high strength, toughness and wear resistance.

Ductile iron has rapidly developed into a widely used cast iron material after gray cast iron. The so-called “iron-based steel” mainly refers to ductile iron. Ductile Iron is also called ductile cast iron, spheroidal graphite cast iron, or nodular cast iron

  The graphite and carbon contained in cast iron occur as flakes; cast iron exhibits positive compressive load capabilities, but tensile loading above its natural tensile strength can cause cracks to form and propagate rapidly out from stress points within the flaked graphite micro structure. As a result, cast iron has virtually no elongation. It is a brittle material, and therefore limited in its use in tensile and shock loading applications.

  The graphite within ductile iron occurs as spheroids, so it is sometimes referred to as spheroidal graphite. Similarly, the term nodular iron stems from the fact that the carbon contained in ductile iron is held in the form of nodules. This unique micro-structure causes ductile iron to withstand bending and shock loading far better than traditional cast iron.

Iron CarbonSiliconManganeseMagnesiumPhosphorusSulfurCopper
~94%2 – 3.60%2.2 – 2.8%0.1 – 0.2%0.03 – 0.04%0.005 – 0.04%0.005 – 0.02%<= 0.40%


  • To improve the strength of ductile iron, additional tin or copper can be added.
  • To improve corrosion resistance, copper, nickel, or chromium can replace anywhere from 15-30% of the iron.

Ductile Iron Advantages

  • Ductile iron can be easily cast and machined.
  • Excellent strength to weight ratio.
  • Ductile iron can be made for a much lower cost than steel.
  • Superior castability and machinability.
  • Ductile iron provides a designer with an exceptional combination of toughness, low cost manufacturing, and reliability.

Ductile Iron Applications

Automotive components  Gears and Gear Boxes pump housings
Idler arms  Housings and manifolds Machine Tooling
Connecting rods (like in engines) Crankshafts Large Machines
Wheel hubs Valves (especially high-pressure valves) Axles
Spindle supports Steering knuckles Suspension system parts

What is the difference between Ductile Iron and Cast Iron?

  Cast iron refers to all iron parts that are cast and have a high carbon content, but in normal usage. Cast iron refers to gray iron, the cast parts with weaker iron structures containing graphite flakes. Ductile iron must specifically have the spherical graphite structure in the metal.

  Regular cast iron can be cast cheaply, machined very easily, and strength can be added through heat treating. Gray iron lacks the strength and durability of ductile cast iron. Ductile iron castings are not much more expensive than gray iron castings. If there is no need for the benefits of ductile iron you should probably stick with the gray iron castings.

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