The role of elements in large-section ductile iron
Trace elements such as bismuth (Bi), lead (Pb), antimony (Sb), titanium (Ti), and arsenic (As) play an important role in large-section ductile iron. Although these elements were once considered impurities, their influence on the microstructure and properties of the final product should not be overlooked. When magnesium is used for nodularization, these trace elements are typically regarded as harmful impurities, requiring strict control over their concentrations. However, when rare earth elements are added alongside magnesium, the impact of these elements is significantly reduced due to the neutralizing effect of the rare earths. In some cases, the interaction between rare earths and these trace elements can even enhance the spheroidization process, increasing the number of graphite nodules and improving overall quality.
Bismuth and antimony, for example, were traditionally seen as problematic elements. However, recent studies have shown that when added within controlled limits, they can react with rare earths to form high-melting-point compounds. These compounds act as effective nucleation sites during solidification, promoting the formation of more spherical graphite structures. Additionally, Bi and Sb tend to form a protective layer around the graphite nodules, which helps prevent deformation and growth, thus reducing spheroidal distortion and increasing the spheroidization rate.
Understanding the behavior of these trace elements is crucial for optimizing the production of large-section ductile iron. By carefully managing their presence and interactions, manufacturers can achieve better mechanical properties and structural integrity in the final castings.
Nanjing Ningbo Analytical Instrument Co., Ltd. Technology Department
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