Elemental tin, ytterbium, etc., which promote pearlite generation, are given full attention

Higher carbon equivalents and increased silicon content promote the formation of a ferrite matrix, but excessive silicon can significantly reduce the material's toughness. Manganese encourages the development of pearlite, carbide formation, and segregation tendencies, which negatively impact the material’s ductility. Phosphorus segregation can lead to the formation of phosphorus eutectic at grain boundaries, posing a serious threat to the toughness of ferritic ductile iron. Sulfur depletion in the nodulizer affects the spheroidization process, leading to irregular graphite structures and inclusion formation. Therefore, it is essential to strictly control the levels of manganese, phosphorus, and sulfur.

The residual amounts of rare earth elements and magnesium should be kept within a lower limit range to ensure effective spheroidization. In production, the chemical composition must be carefully controlled within an appropriate range based on actual conditions. Special attention should be given to microelements that influence spheroidization, as well as elements like tin and antimony that promote pearlite formation. Using stable and high-quality raw materials and fuels is crucial for consistent and reliable production of ductile iron pipes. The molten iron should meet specific requirements—high carbon, low silicon, low manganese, phosphorus, and sulfur—to maintain a stable chemical composition. Coke used in the process should have a high calorific value, sufficient strength, and low sulfur content.

The type and quantity of spheroidizing agent play a critical role in the quality and stability of cast ductile iron pipes, especially in reducing the risk of white cast iron formation. In China, rare earth-magnesium spheroidizing agents are commonly used. These agents are added during the spheroidizing process. Rare earths help purify the molten metal by removing sulfur, oxygen, and gas. Their oxides and sulfides form stable compounds that can be easily removed during the melting process. Additionally, rare earths interact with low-melting-point elements such as arsenic, lead, zinc, and tin, forming high-melting-point compounds that do not dissolve in the molten iron. They also counteract the negative effects of anti-graphitizing elements like titanium and arsenic, effectively reducing their harmful impact on graphitization. This makes the addition of rare earths beneficial for achieving better spheroidization and overall material performance.