Ductile Iron Castings
Ductile iron, also known as ductile cast iron, nodular cast iron, spheroidal graphite iron, spheroidal graphite cast iron, and SG iron, is a type of cast iron invented in 1943 by Keith Millis. While most varieties of cast iron are brittle, DI has much more impact and fatigue resistance due to its nodular graphite inclusions.
Applications of Ductile Iron Castings
Ductile iron is used across a wide range of industries due to its superior strength and versatility.
- Water and Sewer Lines: Commonly used in ductile iron pipes.
- Automotive Components: Ideal for parts requiring higher strength than aluminum.
- Agricultural Machinery: Used in tractors and other farm equipment.
- Oil and Gas: Essential for oil well pumps and related equipment.
- Wind Power: Used in hubs and structural parts like machine frames.
Much of the annual production of DI is in the form of ductile iron pipe, used for water and sewer lines, but there are many ductile iron castings applications in multiple market segments. It competes with polymeric materials such as PVC, HDPE, LDPE, and polypropylene, which are all much lighter than steel or ductile iron; being more flexible, these require protection from physical damage.
Ductile Iron Casting Uses
Ductile iron is specifically useful in many automotive components, where strength needs surpass that of aluminum but do not necessarily require steel. Other major industrial applications include off-highway diesel trucks, Class 8 trucks, agricultural tractors, and oil well pumps. In the wind power industry, nodular cast iron is used for hubs and structural parts like machine frames. Nodular cast iron is suitable for large and complex shapes, commonly castings, and high fatigue loads. Ductile iron castings are thus used in a wide variety of industries.
Benefits of Ductile Iron Castings
The unique properties of ductile iron make it an ideal material for various demanding applications.
- Impact Resistance: Higher impact resistance compared to other cast irons.
- Fatigue Resistance: Excellent performance under cyclic loads.
- Versatility: Suitable for both large and complex shapes.
Ductile Iron Chemical Make-Up
DI is not a single material but part of a group of materials which can be produced with a wide range of properties through control of their microstructure. The common defining characteristic of this group of materials is the shape of the graphite. In ductile irons, graphite is in the form of nodules rather than flakes as in grey iron. Whereas sharp graphite flakes create stress concentration points within the metal matrix, the rounded nodules in ductile iron inhibit the creation of cracks, thus providing the enhanced ductility that gives the alloy its name. Nodule formation is achieved by adding nodulizing elements, most commonly magnesium (note magnesium boils at 1100°C and iron melts at 1500°C) and, less often now, cerium (usually in the form of Mischmetal). Tellurium has also been used.
Key Characteristics of Ductile Iron
The chemical composition and microstructure of ductile iron give it unique properties.
- Nodular Graphite: Provides increased ductility and resistance to cracking.
- Magnesium Additives: Essential for forming nodular graphite structures.
- Versatile Microstructure: Can be adjusted to achieve a wide range of properties.
One of the occurrences that must be monitored when producing nodular iron castings is “magnesium fade.” Nodularity is lost with time, and so the timing of when the inoculant is added to the molten metal to when the metal is cast is critical to maintaining the necessary material properties.
Austempered Ductile Iron (ADI)
ADI is a special type of ductile iron that undergoes a sophisticated heat treatment process to enhance its properties further.
- Austenite Formation: The “aus” in ADI refers to the austenitic structure achieved through heat treatment.
- Enhanced Properties: ADI offers superior strength, toughness, and wear resistance.
Work With Us
If you’re looking for a reliable partner for your ductile iron casting needs, Quaker City Castings is here to help. Visit our contact us page directly to discuss how we can assist you. We are dedicated to providing solutions that enhance the efficiency and productivity of your operations.