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 these materials. High temperature asphalt

1. Artificial graphite

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

The main raw material for manufacturing artificial graphite is powdered high-quality calcined petroleum coke, in which pitch is added as a binder, and a small amount of other auxiliary materials are added. After the various raw materials are matched, they are pressed into shape, and then processed in a non-oxidizing atmosphere at 2500~3000℃ 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, the artificial graphite recarburizers commonly used in foundries are mostly 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 superior, the recarburizer should be artificial graphite.

2. Petroleum coke

Petroleum coke is currently a widely used recarburizer.

Petroleum coke is a by-product obtained from refining crude oil. Residues and petroleum pitch obtained by crude oil distillation under pressure or vacuum can be used as raw materials for making petroleum coke. After coking, raw petroleum coke can be obtained. The production of raw petroleum coke is less than 5% of the crude oil used. The annual output of raw petroleum coke in the United States is about 30 million tons. Raw petroleum coke has a high impurity content and cannot be used directly as a recarburizer. It must be calcined first.

Raw petroleum coke comes in spongy, needle, granular and fluid forms.

Sponge petroleum coke is produced by delayed coking. Because of its high content of sulfur and metals, it is usually used as a fuel during calcination, and it can also be used as a raw material for calcining petroleum coke. The calcined sponge coke is mainly used in the aluminum industry and as a recarburizer.

Needle-shaped petroleum coke is produced by the delayed coking method using raw materials with high aromatic hydrocarbon content and low impurity content. This kind of coke has a needle-like structure that is easy to crack, sometimes called graphite coke, and is mainly used to make graphite electrodes after calcination.

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

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

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

The user of calcined petroleum coke is the aluminum industry, and 70% is used to make anodes for reducing bauxite. Calcined petroleum coke produced in the United States accounts for about 6% of cast iron recarburizers.

3. Natural graphite

Natural graphite can be divided into 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 types of flake graphite: high-carbon flake graphite needs to be extracted by chemical methods, or heated to a high temperature to decompose and volatilize the oxides in it. This kind of flake graphite has a small output and high price, and it is generally not used as a recarburizer; low carbon flakes 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 large.

4. Coke and anthracite

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