The Difference between Ductile Iron and Gray Iron

Continuous casting of ductile and gray iron dominates the industry due to its low material cost, high machinability, and high performance. Both metals are utilized for a variety of applications including construction equipment, pipe fittings, oil field machinery, and transportation services.

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Each metal has unique advantages due to differences in carbon content and is employed in distinct applications based on these strengths.

Gray Iron/Ductile Iron Comparison

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1. Gray iron’s tensile strength ranges from 20,000 psi to 60,000 psi, whereas ductile iron ranges from 65,000 psi to 80,000 psi and can be heat-treated to reach 100,000 psi.
2. Ductile iron has lower thermal conductivity, making it a better insulator than gray iron.
3. Ductile iron is more suitable for engineering applications.
4. Graphite in ductile iron is nodular and flaked in gray iron—rendering ductile iron stronger and more ductile.
5. Gray iron dampens vibrations better than ductile iron.

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More details about Versa-Bar gray and ductile iron

Gray and ductile iron are superior alternatives to steel, each with a different composition and suitability for CNC machining.

Gray Iron

American Iron offers a superior replacement for steel through V-2 Class 40 Versa-Bar continuous cast gray iron. During solidification, rod-like graphite flakes form within the composition, differentiating gray iron from ductile iron. Grey continuous cast iron is preferred for its density and strength, as well as its affordability. Continuous cast gray iron combines low costs with high-quality lightweight metal, making it ideal for applications such as vibration damping and manufacturing equipment frames. Gray iron is also used in:

• Construction equipment
• Valves and fittings
• Compressors and pumps
• Diesel engine parts
• Transportation system components

Gray iron's reputation for high machinability, excellent damping properties, durability, and unique metallurgy makes it a popular choice, especially in contexts where strength is not critical, like maintenance hole covers and counterweights. Despite its strength surpassing that of steel, it remains cost-effective. Thus, gray iron is an immediate steel replacement. Ductile iron serves as the next advancement.

Ductile Iron

Ductile iron offers numerous machining advantages over gray iron.

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Ductile continuous cast iron is known for its high tensile strength and flexibility, making it suitable for shaping into wires and other applications requiring elasticity. Unlike the rod-like flakes in gray iron, ductile iron contains graphite nodules, lending it flexibility during solidification. This type of iron is mainly used in areas requiring elongation under tension, such as:

• Couplings
• Machine frames
• Hydraulic valves
• Pumps
• Gearboxes

Continuous cast ductile iron’s high tensile strength and flexibility make it an excellent alternative to steel. American Iron offers two high-quality ductile iron grades, V-3 and V-4. The V-3 65-45-12 grade is the easiest to machine among the three grades of continuously cast metal. V-4 80-55-06 ductile iron, stronger than V-3, is favored for automobile parts and hydraulic cylinders. Ductile iron is not only more versatile but also significantly less expensive than steel. Purchasing Versa-Bar continuous cast ductile iron from American Iron ensures savings on every project.

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American Iron delivers raw stock and custom iron components

Ductile iron stock is available either as raw material for self-processing or as custom finished components based on your specifications at our state-of-the-art CNC facility in Waukesha. The choice is yours. We deliver high-quality ductile iron in any form you need.

Contact American Iron for continuous cast iron supply, custom metal components, and raw gray and ductile iron stock.

Gray or Ductile iron?

A common experience in machining castings is that gray iron is easy to machine, whereas ductile iron can be challenging. Having worked at Moline Iron Foundry, where we cast ductile, malleable, and gray irons, we had to turn test bars from each melt to test the tensile strength. While gray bars posed no issue, ductile bars often had hard spots that could ruin a carbide insert faster than you could react, even causing a lathe to jump. Milling faced similar issues, with hard spots wearing out carbide end mills quickly. Gray iron filled cavities better and provided more detail than ductile iron, which also emitted a sulfur smell when spat on. Additionally, venting and gating ductile castings required trial and error due to gas holes.

The primary difference between gray, malleable, and ductile iron lies in the graphite. Graphite is a nearly pure form of free carbon within the iron. Gray iron contains graphite in thin flakes distributed in a pearlite and ferrite matrix, which gives it excellent machinability and vibration damping but also limits its mechanical properties, such as tensile strength (class 40 has 40,000 psi, class 80 has 80,000 psi). Malleable iron has nodular graphite within a ferritic matrix, with nodules being aggregates of fine flakes, lessening their impact on mechanical properties. Ductile iron features spheroidal graphite achieved by adding magnesium just before pouring, reaching tensile strengths above 150,000 psi.

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