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There are many types of carbonizers. Based on the raw materials and the composition of their various components, they can be roughly divided into four categories: petroleum coke carbonizers, graphite carbonizers, coal-based carbonizers, and petrocoke carbonizers for desertification control. These various types of carbonizing agents have different raw materials, which means that the values regarding fixed carbon, sulfur, ash, and volatiles in the resulting carbonizing agents also vary. Moreover, the ultimate absorption rates achieved after their use differ as well. Therefore, it is essential to pay close attention to many factors when choosing to purchase carbonizing agents. In particular, the role of carbonizers in gray cast iron and ductile iron is different, and they have a significant impact on the production of castings. It is essential not to purchase carbonizers casually; it is best to get those that are suitable for the purpose. For general gray cast iron production, the carbonizer used is required to have a low sulfur content; sulfur levels of 0.5 or less are generally acceptable, as the requirements are not that strict. Fixed carbon levels of 98.5/98/90/95/92, etc., can all be used. In order to save costs, some manufacturers even use carbonizers with a fixed carbon level of 85, as long as the resulting absorption rate meets the requirements. However, for ductile iron, the requirements are quite strict: not only is the content of fixed carbon important, but low levels of sulfur and nitrogen are also required. In particular, the sulfur content must be very low – only levels below 0.0% are acceptable, as otherwise the castings produced will be brittle and prone to cracks, which significantly affects their quality. There are also certain requirements regarding nitrogen; its level must be low, ideally 600 ppm or less, with some manufacturers even requiring levels below 100 ppm. The lower the nitrogen content, the better, because this results in castings that are smoother and more uniform, without any pores. High nitrogen levels can cause the castings to be uneven, and in some cases, they may even have pores and cracks. Therefore, it is essential to be careful when choosing a carbonizer – it is most important to select a product that suits one’s specific needs based on actual conditions.