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Precautions for ductile cast iron
Release date:
2021-02-22
The characteristic of spheroidal graphite cast iron undergoing paste-like solidification determines the properties of the resulting castings; however, poor feeding often leads to defects such as shrinkage cavities and looseness. To predict these defects before casting production begins, numerical simulation techniques for casting processes have been developed both domestically and internationally for many years. In fact, the production of spheroidal graphite cast iron comes with highly stringent requirements. Here are a few key considerations for working with this material—let’s take a look together!
The characteristic of nodular cast iron's paste-like solidification determines the properties of the cast iron produced; however, poor feeding often leads to defects such as shrinkage cavities and looseness. To predict these defects before casting, numerical simulations of the casting process have been developed both domestically and internationally for many years. In fact, the production of nodular cast iron comes with highly stringent requirements. Here are a few key considerations for working with nodular cast iron—let’s take a look together!
1. Ductile iron has stringent requirements for its chemical composition—for instance, the carbon and silicon content of the original molten iron must be higher than that of gray cast iron, while the levels of manganese, phosphorus, and sulfur in ductile iron need to be reduced.
2. The molten iron needs to be tapped at a higher temperature than gray cast iron, to compensate for the temperature loss during spheroidizing treatment. Spheroidizing involves adding a spheroidizing agent to the molten iron and then treating it with appropriate fluxes.
4. Ductile iron has poor fluidity but significant shrinkage, so it requires higher pouring temperatures and larger gating system dimensions. Additionally, risers and chills should be used appropriately, following the principle of sequential solidification.
5. When heat treating ductile cast iron, annealing can enhance ductility and toughness, relieve internal stresses, and improve machinability. Normalizing, on the other hand, is highly effective in boosting strength and wear resistance. Quenching and tempering produces a microstructure dominated by tempered sorbite, delivering excellent overall mechanical properties. Meanwhile, isothermal quenching enables complex-shaped parts with stringent performance requirements to achieve a lower bainitic matrix, resulting in superior combinations of high strength, high hardness, and outstanding toughness—while also preventing cracking during heat treatment. Examples include spindles, crankshafts, gears, and other critical components.
Because with the continuous advancement of industry, ductile iron has developed distinct characteristics, making it a common material in the production of parts that endure complex stresses and require high strength, toughness, and wear resistance—such as crankshafts and camshafts used in automobiles, tractors, and internal combustion engines, as well as medium-pressure valves for general-purpose machinery.
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