Types of Recarburizers

There are many materials that can be used as a recarburizer for cast iron. Commonly used are artificial graphite, calcined petroleum coke, natural graphite, coke, anthracite and mixtures made of such materials.

artificial graphite

Among the various recarburizers mentioned above, the best quality is artificial graphite.

The main raw material for the manufacture of 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 together, they are pressed and formed, and then treated in a non-oxidizing atmosphere at 2500-3000 ° C to make them graphitized. After high temperature treatment, the ash, sulfur and gas content are greatly reduced.

Due to the high price of artificial graphite products, most of the artificial graphite recarburizers commonly used in foundries are recycled materials such as chips, waste electrodes and graphite blocks when manufacturing graphite electrodes to reduce production costs.

When smelting ductile iron, in order to make the metallurgical quality of the cast iron high, artificial graphite should be the first choice for the recarburizer.

Petroleum coke

Petroleum coke is a widely used recarburizer.

Petroleum coke is a by-product obtained by refining crude oil. Residues and petroleum pitches obtained by distillation under normal pressure or under reduced pressure of crude oil can be used as raw materials for the manufacture of petroleum coke, and then green petroleum coke can be obtained after coking. The production of green petroleum coke is approximately less than 5% of the amount of crude oil used. The annual production of raw petroleum coke in the United States is about 30 million tons. The impurity content in green petroleum coke is high, so it cannot be directly used as a recarburizer, and must be calcined first.

Raw petroleum coke is available in sponge-like, needle-like, granular and fluid forms.

Sponge petroleum coke is prepared by delayed coking method. Due to its high sulfur and metal content, it is usually used as a fuel during calcination, and can also be used as a raw material for calcined petroleum coke. The calcined sponge coke is mainly used in the aluminum industry and as a recarburizer.

Needle petroleum coke is prepared by delayed coking method with raw materials with high content of aromatic hydrocarbons and low content of impurities. This coke has an easily fractured needle-like structure, sometimes called graphite coke, and is mainly used to make graphite electrodes after calcination.

Granular petroleum coke is in the form of hard granules and is made from raw materials with high content of sulfur and asphaltene by delayed coking method, and is mainly used as fuel.

Fluidized petroleum coke is obtained by continuous coking in a fluidized bed.

The calcination of petroleum coke is to remove sulfur, moisture, and volatiles. Calcination of green petroleum coke at 1200-1350°C can make it substantially pure carbon.

The largest user of calcined petroleum coke is the aluminum industry, 70% of which is used to make anodes that reduce bauxite. About 6% of the calcined petroleum coke produced in the United States is used for cast iron recarburizers.

natural graphite

Natural graphite can be divided into two types: flake graphite and microcrystalline graphite.

Microcrystalline graphite has a high ash content and is generally not used as a recarburizer for cast iron.

There are many varieties of flake graphite: high carbon flake graphite needs to be extracted by chemical methods, or heated to high temperature to decompose and volatilize the oxides in it. The ash content in graphite is high, so it is not suitable to be used as a recarburizer; medium carbon graphite is mainly used as a recarburizer, but the amount is not much.

Coke and Anthracite

In the process of electric arc furnace steelmaking, coke or anthracite can be added as a recarburizer when charging. Due to its high ash and volatile content, induction furnace smelting cast iron is rarely used as a recarburizer.