Ductile iron is one type of cast iron. It was invented in 1942 by Keith Millis[1].

A typical chemical analysis of this material is:

• Carbon 3.3 to 3.8%
• Silicon 2.2 to 2.8%
• Manganese 0.1 to 0.5%
• Sulfur 0.005 to 0.02%
• Phosphorus 0.005 to 0.04%
• Magnesium 0.03 to 0.05%

Other elements such as copper may be added intentionally to increase tensile and yield strength while simulaneously reducing elongation.

The unique characteristic of ductile iron is that the graphite forms into a spherical shape. Sometimes this is referred to as a "nodular" shape. Ductile iron may also be called "nodular iron".