Gray Iron VS Ductile Iron

Here at Bell City Foundry we produce multiple grades of gray and ductile iron. The difference in these types of iron are as follows:

Gray Iron

Gray Iron got its name from its dull gray surface appearance when it fractures. Gray Iron is the most widely used cast material based on weight. Benefits of Gray Iron are the following:

• Excellent castability
• Good machinability
• Good wear resistance
• High damping capacity (limits vibration in a finishing casting)
• High thermal conductivity and is able to wick away heat
• Excellent compressive strength
• Good tensile strength

Gray Iron is used for housings where tensile strength is non-critical, such as internal combustion engine, cylinder blocks, pump housings, valve bodies, electrical boxes, and decorative castings. Gray Iron’s high thermal conductivity allows for such uses as cast iron cookware and disc brake rotors.

Ductile Iron

Ductile Iron is when the graphite is like a pillow and acts as “crack-arresters” to give ductility and toughness superior to all other cast irons. Benefits of Ductile Iron are the following:

• Excellent tensile strength
• Increased ductility which ensures finished materials will bend before breaking
• Excellent impact properties
• Good machinability
• High modulus of elasticity which measures the degree of “stiffness” in the metal

Ductile iron is much more flexible and elastic, due to its nodular graphite inclusions. Ductile iron is specifically useful in automotive components, agricultural tractors, and oil well pumps, where strength needs surpass that of aluminum but does not necessarily require steel.