In the process of smelting iron and steel products, the smelting loss of carbon element in molten iron is often increased due to factors such as longer smelting time, holding time and overheating time, resulting in a decrease in the carbon content in molten iron, resulting in the carbon content in molten iron not reaching the theoretical value expected for refining.
Carbon-containing substances added in order to make up for the carbon content burned in the steel smelting process are called carburants
1. The function of carburant
For casting, cast iron, cast steel and castings, there will be a requirement for carbon. As the name implies, the carburant is used to increase the carbon content in molten iron. For example, in smelting, the commonly used charge materials are pig iron, scrap steel and return charge materials, and the carbon content of pig iron is high, but the purchase price is higher than that of scrap steel. Therefore, increasing the amount of scrap steel, reducing the amount of cast iron and adding the carburant can play a role in reducing the cost of castings to a certain extent.
The use of carburant can not only make up for the burning loss of carbon in the process of iron and steel smelting and ensure the carbon content requirements of specific steel grades, but also can be used for post-furnace adjustment.
As an important raw material for melting molten iron in induction furnace, the quality and usage of carburant directly affect the state of molten iron.
The carbon content in the ladle can be adjusted by adding a specific grade of carburant to the ladle after slag removal and degassing.
2. Types of carburants
Carburant can be used as cast iron carburizing agents in many materials, commonly used are artificial graphite, calcined petroleum coke, natural graphite, coke, anthracite and mixtures made of such materials.
1 ) Artificial graphite
Among the various carburants mentioned above, the one with best quality is artificial graphite, and its main raw material 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 all kinds of raw materials are mixed, they are pressed and formed and then treated at 2,500 ~ 3,000 ℃ in a non-oxidizing atmosphere to graphitize them.After high temperature treatment, the ash content, sulfur content and gas content are greatly reduced.
Due to the high price of artificial graphite products, the commonly used artificial graphite carburants in foundry factories are mostly recycled materials such as chips, waste electrodes and graphite blocks used in the manufacture of graphite electrodes in order to reduce the production cost.
When smelting nodular cast iron, artificial graphite should be the preferred carburant in order to ensure the metallurgical quality of cast iron.
2 ) Petroleum coke
Calcined petroleum coke is a widely used carburant at present, among which calcined petroleum coke particles with low sulfur quality are used as carburant with high cost performance and are used as cast iron carburant.
3 ) Natural graphite
Natural graphite can be divided into flake graphite and microcrystalline graphite.
Microcrystalline graphite has high ash content and is generally not used as a carburant for cast iron.
There are many kinds of flake graphite: high-carbon flake graphite needs to be extracted by chemical methods or heated to high temperature to decompose and volatilize oxides in it. This kind of flake graphite has low output and high price and is generally not used as a carburant. Low carbon flake graphite has a high ash content and is not suitable for use as a carburant. The main carbon graphite used as the carburant is medium-carbon graphite, but it is not used much.
4 ) Coke and anthracite
In the process of steelmaking in electric arc furnace, coke or anthracite can be added as carburant during charging.Because of its high ash content and volatile matter content, smelting cast iron in induction furnace is rarely used as a carburant.