Types of recarburizers

There are many materials that can be used as recarburizers 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 better quality is artificial graphite.

The main raw material for making artificial graphite is powdered 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, the carburizer should be artificial graphite.

Petroleum coke

Petroleum coke is a widely used recarburizer.

Petroleum coke is a by-product obtained by refining crude oil. The residual oil and petroleum pitch obtained from crude oil distillation under normal pressure or under reduced pressure can be used as raw materials for the manufacture of petroleum coke, and after coking, raw petroleum coke can be obtained. 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 has sponge, needle, granular and fluid varieties.

Sponge petroleum coke is prepared by delayed coking method. 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 calcined petroleum coke. The calcined sponge coke is mainly used in the aluminum industry and as a recarburizer.

Carburizer

Carburizer

Needle petroleum coke is produced by delayed coking method using 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. It 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 volatile matter. Calcination of green petroleum coke at 1200-1350°C can make it substantially pure carbon.

The 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 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.

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