When adding carbon to ductile iron, should one choose graphitized petroleum coke or calcined coal?

[] It is recommended to choose graphitized petroleum coke as the carburizer for ductile iron for the following reasons:

1. Superior chemical composition:
   • Graphitized petroleum coke: It typically contains more than 99.5% carbon and less than 0.05% sulfur. The high carbon and low sulfur characteristics help increase the carbon content of ductile iron while reducing the adverse effects of sulfur on nodularization and graphitization, thereby preventing defects in the castings.
   • Calcined anthracite carburizer: It generally has a carbon content of 90-93% and a sulfur content of 0.3-0.5%. The relatively low carbon content and high sulfur content may increase the sulfur content in the castings, affecting the nodularization effect and casting properties.
2. Higher absorption efficiency:
   • Graphitized petroleum coke: Subject to high-temperature graphitization treatment, the carbon atoms are arranged in an orderly manner, forming a flake graphite structure. This facilitates rapid dissolution and absorption in molten iron, resulting in high carburization efficiency and effectively increasing the carbon content of the molten iron.
   • Calcined anthracite carburizer: With a lower carbon content, it melts more slowly and has relatively lower absorption efficiency, which may prolong the melting time and increase energy consumption.
3. Impact on nodularization and graphitization:
   • Graphitized petroleum coke: The low sulfur content reduces interference with the nodularizing agent, helping to achieve good nodularization effects and graphite morphology, thereby improving the mechanical properties of ductile iron.
   • Calcined anthracite carburizer: The higher sulfur content may interfere with the nodularization process, affecting the nucleation and growth of graphite, leading to degraded casting properties.
4. Casting quality:
   • Graphitized petroleum coke: Using it results in superior metallurgical quality of the castings, effectively enhancing the strength and toughness of ductile iron and reducing defects such as porosity and shrinkage, thereby improving the product qualification rate.
   • Calcined anthracite carburizer: Due to its higher sulfur content, it may cause porosity in the castings and reduce mechanical properties, affecting casting quality.
5. Usage cost:
   • Graphitized petroleum coke: Although its price may be slightly higher than that of calcined anthracite carburizer, its high carburization efficiency reduces the amount of carburizer required, lowering melting costs. Additionally, it improves product quality and reduces the scrap rate, resulting in lower overall usage costs.
   • Calcined anthracite carburizer: While its price is relatively lower, its low absorption efficiency may necessitate increased usage, and it may affect casting quality, leading to higher subsequent processing costs.