Difference Between Ductile Iron And Cast Iron

Knowledgebase

Ductile iron and cast iron are materials used in manufacturing a variety of products, such as pipes, valves, and other components. Both are iron-based alloys, but the major difference is that ductile iron contains more graphite, making it stronger and more malleable than cast iron.

Ductile iron is often the preferred choice for applications that require a combination of strength and ductility. It can be made into complex shapes with ease, making it suitable for parts that require intricate designs or tight tolerances. It’s also highly resistant to corrosion, making it a great option for products used in wet environments.

Ductile Iron Vs Cast Iron

What Is Ductile Iron?

Ductile iron is an alloy of iron, carbon, and other elements that is formed by casting into a mold. It can be cast in almost any shape and contains more graphite than traditional cast iron, which makes it stronger and more malleable. The extra graphite particles also give ductile iron greater shock resistance and make it better suited for use in applications that require high levels of stress.

What Is Cast Iron?

Cast iron is an alloy of iron and carbon that is formed by melting and pouring into a mold. It is typically stronger than steel but lacks ductility, making it more susceptible to breaking when subjected to high levels of stress.

How Is Ductile Iron Made?

Ductile iron is made by introducing magnesium, cerium, and other elements into molten iron and then pouring it into a mold. The additional elements help form graphite particles in the iron, which give ductile iron its unique properties. The molten metal is then cast into various shapes to create the desired product.

How Is Cast Iron Made?

Cast iron is made by heating and melting pig iron, scrap steel, and other materials in a furnace. The molten metal is then poured into molds, where it cools and hardens to form the desired shape. Cast iron is usually heavier than ductile iron but provides more strength which makes it well-suited for applications that don’t require a high degree of flexibility.

What Is Ductile Iron Used For?

  • Pipes
  • Valves
  • Manhole covers
  • Machine components
  • High pressure vessels

What Is Cast Iron Used For?

  • Cookware
  • Railroad tracks
  • Automotive components
  • Bridges and buildings
  • Sculptures and decorative items.

What Are The Differences Between Ductile Iron And Cast Iron?

Property ductile iron Cast iron
origin: Ductile iron is a type of cast iron with a higher tensile strength than traditional grey cast iron. It was first developed in the 1940s when scientists discovered that adding small amounts of magnesium to molten iron created graphite nodules instead of flakes, resulting in higher strength and ductility. Cast iron has been used for centuries for a variety of applications due to its low cost and high strength. It is made by melting iron ore with coke or charcoal, which then solidifies into a brittle material that can be formed as desired. However, traditional cast iron has limited ductility and tensile strength.
texture: smooth, metallic-like texture. It is strong and malleable but still rigid enough to hold shapes. hard, brittle surface with a slightly rough texture. It is much less malleable and cannot be formed into shapes as easily as ductile iron.
strength: can withstand higher levels of stress due to its strength and ductility, making it ideal for applications in critical components such as automotive parts or machine frames. has lower tensile strength, meaning it is not suitable for high-stress applications.
corrosion resistance: higher corrosion resistance than cast iron and is less prone to rusting or staining. It can also be coated with enamel or galvanized for added protection against corrosion. more susceptible to corrosion due to a lack of malleability. If not properly treated, it may corrode quickly which can lead to structural damage over time.
cost: more expensive cheaper
Machinability:  Very easy to machine and can be cut, drilled, and shaped with relative ease. Difficult to the machine. It requires specialized tools and a skilled machinist to work with it successfully.
Heat resistance:  Higher melting point than cast iron and is more resistant to heat-related damage. Melts at lower temperatures than ductile iron, making it more susceptible to heat damage.
Elongation: Capable of elongating up to 20% before breaking, making it highly resistant to stress. Lower elongation rate of 1–2%, meaning it is not suitable for high-stress applications.
Weldability: can be welded with special welding rods cannot be welded
Composition: Composed of graphite particles in a matrix of ferrite or pearlite, making it more ductile than cast iron.  Composed mainly of carbon and iron,. It also contains trace amounts of silicon and manganese.
Durability: more durable relatively weak
Ease of Installation: can be installed quickly difficult to install
Carbon content:  a higher percentage of carbon a lower percentage of carbon
Silicon content:  a higher percentage of silicon a lower percentage of silicon
Tensile and Yield Strength: Higher tensile and yield strengths than cast iron, making it stronger and more resistant to damage. lower tensile and yield strengths than ductile iron, making it weaker and more vulnerable to damage.
Thermal Conductivity: Higher thermal conductivity than cast iron, meaning it can transfer heat more efficiently. Lower thermal conductivity than ductile iron, meaning it cannot transfer heat as efficiently.
Vibration Damping: much better at dampening vibrations much less effective at dampening vibrations
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Which Alloy Is Better?

If high pressures and impacts are involved, ductile iron is likely a better choice due to its higher tensile strength and impact resistance. However if the application requires high temperatures or machinability, then cast iron might be a better option. Ultimately the decision should be based on which alloy is best-suited to the specific application.

FAQs

Does Ductile Iron Cost More Than Cast Iron?

Yes, ductile iron typically costs more than cast iron due to its higher tensile strength and impact resistance. However, it also offers better corrosion resistance and can be used in applications where high pressures are involved or where the material needs to be machined.

Is Cast Iron Ductile Or Not?

Cast iron is not ductile because it has lower tensile strength and impact resistance compared to ductile iron. It is also not typically used in applications where high pressures are involved or where the material needs to be machined.

Do Both Ductile Iron And Cast Iron Rust?

Both ductile iron and cast iron can rust, however, ductile iron typically has better corrosion resistance than cast iron. This is because it contains a higher amount of alloying elements, such as chromium or nickel, which help protect the material from corrosion.

Does Cast Iron Or Ductile Iron Have A Higher Melting Point?

Cast iron typically has a higher melting point than ductile iron because it contains more carbon. The higher the amount of carbon, the higher the material’s melting point. Ductile iron can also be alloyed with elements such as chromium or nickel to increase its melting point.

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Is Cast Iron Ductile Or Brittle?

Cast iron is generally considered to be brittle because it has a lower tensile strength and impact resistance compared to ductile iron. It also tends to be more prone to cracking or shattering under high load or shock.

Is Ductile Iron Stronger Than Cast Iron?

Yes, ductile iron is typically stronger than cast iron due to its higher tensile strength and impact resistance. This makes it a better choice for applications that require high pressures or impacts. It is also more resistant to corrosion than cast iron.

Why Is It Called A Cast Iron?

Cast iron is called cast iron because it is made by pouring molten metal into a mold or casting. This casting process helps to give the material its unique properties, such as a higher melting point and increased strength.

What Is Cast Iron Called?

Cast iron is usually referred to as cast iron or wrought iron. The latter refers to the fact that it is made by hammering the material into shape rather than pouring it into a mold. Wrought iron is often used in decorative applications due to its aesthetic qualities.

Why Is Cast Iron Called Pig Iron?

Cast iron is sometimes referred to as pig iron because it was originally produced from the smelting of ore in a blast furnace. This process created large amounts of molten metal, which were then poured into molds and allowed to cool. The resulting material was then called “pig iron.”

Which One Is Heavier, Ductile Iron Or Cast Iron?

Ductile iron is typically heavier than cast iron due to its higher density. This makes it a better choice for applications that require a material that is durable and heavy-duty. Cast iron, on the other hand, is usually lighter in weight, making it more suitable for decorative purposes.

What Is The Purest Form Of Iron?

The purest form of iron is cast iron. Cast iron has a high carbon content and is made by pouring molten metal into molds. The resulting material has a low sulfur and phosphorus content, which makes it strong and resistant to corrosion.

Why Can’t You Weld Ductile Iron Parts?

Ductile iron parts cannot be welded because it has a higher melting point than regular cast iron. Welding also tends to weaken the material due to the high temperatures involved.

Conclusion

ductile iron and cast iron are both iron-based alloys that have unique properties. Ductile iron is stronger and more malleable than cast iron and is better suited for applications that require a combination of strength and flexibility. Cast iron is typically used in applications that require greater strength but less flexibility. Ultimately, it’s important to consider the requirements of your application before deciding which material is best for you.

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