What is the difference between ductile iron and grey iron?

One of the fundamental determinations that must be made regarding the production of your parts relies on the difference between ductile iron and grey iron.  The characteristic differences between the two make them ideal for some purposes and specifically excluded for other purposes.  The differences are directly related to the fact that ductile iron is actually an alloy containing primarily iron and a variety of other metals in much smaller amounts.  Magnesium is the most often used component, with cerium and tellurium used less often.  Varying amounts of nickel, copper, or chromium have also been used to replace up to 30% of the iron to improve corrosion resistance.  Copper and tin have also been used to improve tensile strength.
The primary differences between the two can be broken down into five key areas.  The first two are related in that they are measurements of how the material can be manipulated.  The ductility of a metal is a measurement of the ability of a metal to deform or elongate while under tension.  Tensile strength is similar but is a measurement of the ability of a metal to withstand compression.  Ductile iron performs better in these two categories, primarily because it is designed with that purpose in mind.  Due to the composition of this alloy, it resists the flaking characteristic to grey iron.  Ductile iron also has a minimum tensile strength that is at the maximum standard tensile range for grey iron.
The third area of difference is in impact resistance.  Ductile iron performs better in this area, as well.  As a general rule, ductile iron can withstand 10-15 foot-pounds of impact while grey iron can only resist up to two foot-pounds of impact.
The fourth comparison is the thermal conductivity of the two materials.  According to Ductile.org, “Material properties which contribute to good thermal fatigue resistance are: high thermal conductivity, low modulus of elasticity and high strength and ductility.”  They conclude that grey iron is superior to ductile iron due to this thermal fatigue resistance.
The fifth and final characteristic comparison is the ability of the material to dampen vibration.  In this area, grey iron again performs better than its cousin.  The flaking characteristic that works against grey iron in ductility allows it to absorb and distribute vibrations across its entire surface.
Pouring Metal at the Willman Industries Iron Foundry
We hope that this article has helped you to understand the differences between ductile iron and grey cast iron.  Willman Industries employs the best and most experienced people in the industry to ensure the highest quality of the materials we provide.  Our experts are available to help you to determine your needs and help you with your next project!  Call us now to see how Willman Industries can help you achieve success with your next project!
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