Different types of recarburizers

Types of recarburizers
There are many materials that can be used as recarburizers for cast iron, and the commonly used ones are artificial graphite, calcined petroleum coke, natural graphite, coke, anthracite, and mixtures made of these materials.

1. Artificial graphite
Among the various recarburizers mentioned above, artificial graphite is of good quality.
The main raw material for making artificial graphite is powdered high-quality calcined petroleum coke, in which asphalt is added as a binder, and a small amount of other auxiliary materials are added. After the various raw materials are mixed, they are pressed into shape and then treated in a non-oxidizing atmosphere at 2500-3000℃ to graphitize them. After high-temperature treatment, the ash, sulfur, and gas content are greatly reduced.
Due to the high price of artificial graphite products, the artificial graphite recarburizers commonly used in foundries are mostly recycled materials such as chips, waste electrodes, and graphite blocks when making graphite electrodes to reduce production costs.
When smelting ductile iron, in order to achieve the best metallurgical quality of cast iron, artificial graphite should be selected as the recarburizer.

2. Petroleum coke Petroleum coke is a widely used recarburizer. Petroleum coke is a byproduct of crude oil refining. Residue oil and petroleum asphalt obtained by normal pressure distillation or vacuum distillation of crude oil can be used as raw materials for making petroleum coke, and then raw petroleum coke is obtained after coking. The output of raw petroleum coke is less than 5% of the amount of crude oil used. The annual output of raw petroleum coke in the United States is about 30 million tons. The impurity content in raw petroleum coke is high and cannot be used directly as a recarburizer. It must be calcined first. Raw petroleum coke has sponge, needle, granular and fluid varieties. Sponge petroleum coke is made by delayed coking. Due to its high sulfur and metal content, it is usually used as a fuel for calcination and can also be used as a raw material for calcining petroleum coke. Calcined sponge coke is mainly used in the aluminum industry and as a recarburizer. Needle petroleum coke is made by delayed coking using raw materials with high aromatic hydrocarbon content and low impurity content. This type of coke has a needle-like structure that is easy to break, and is sometimes called graphite coke. After calcination, it is mainly used to make graphite electrodes.

Pelletized petroleum coke is in the form of hard particles. It is made by delayed coking with raw materials with high sulfur and asphaltene content and is mainly used as fuel.

Fluidized petroleum coke is made by continuous coking in a fluidized bed. It is in the form of fine particles, has a non-directional structure, high sulfur content and low volatile matter.

The calcination of petroleum coke is to remove sulfur, moisture, and volatile matter. Calcining raw petroleum coke at 1200-1350°C can make it basically pure carbon.