Ductile iron is not a single material but is part of a group of materials which can be produced to have a wide range of properties through control of the microstructure. The common defining characteristic of this group of materials is the shape of the graphite. In ductile irons, the graphite is in the form of nodules rather than flakes as it is in grey iron. The sharp shape of the flakes of graphite create stress concentration points within the metal matrix and the rounded shape of the nodules less so, thus inhibiting the creation of cracks and providing the enhanced ductility that gives the alloy its name. The formation of nodules is achieved by the addition of 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. Yttrium, often a component of Misch metal, has also been studied as a possible nodulizer.
Ductile (Nodular) Cast Iron Mechanical Properties
Item according to DIN EN 1563
2% Yield Strength
ferritic + pearlite
ferritic + pearlite
Modules of elasticity
Ductile cast iron castings are the casting components made of ductile cast iron. At RMC Foundry, the ductile iron could be cast and poured by many casting processes including sand casting, shell casting, investment casting, lost foam casting and vacuum casting, depending the exact usage or if special requirements of the desired castings.
In the design stage of castings, a special project team should be set up to conduct "Design Failure Mode and Effects Analysis" (DFMEA). The project team generally consists of product designers, casting process designers, and environmental protection professionals. The main content of the DFMEA analysis should include whether the requirements of the casting quality for the part structure, the casting process for the casting structure, and the casting process for environmental protection requirements are all met.
Performance Characteristics of Ductile Iron Castings
• Fluidity and line shrinkage of ductile iron are very close to those of gray cast iron
• The tendency of volume shrinkage and internal stress formation is greater than that of gray cast iron, which is prone to shrinkage and cracks
• The strength, plasticity, and elastic modulus of ductile iron are larger than those of gray cast iron, with good abrasion resistance
• Shock absorption is worse than gray cast iron
Structural Characteristics of Ductile Iron Castings
• Generally designed to be uniform wall thickness, and try thick section should be avoid if possible
• For certain thick and large section castings, hollow structure or structure with reinforced ribs should be adopted
Ductile (Nodular) Cast Iron
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