the carburization of pig iron

The formation process of pig iron is mainly the process of gradually melting other alloying elements and carburizing into the reduced metallic iron. In the upper part of the blast furnace, part of the iron ore is reduced to metallic iron when it is solid, and gradually reduced from more iron as the temperature rises. The iron that has just been reduced is in the form of a hollow sponge, so it is called sponge iron. This early sponge iron composition is relatively pure and almost contains no carbon. If you want to increase its carbon content, you need to add Recarburizer or Silicon Carbide in the later stage. Sponge iron continuously absorbs carbon and melts during the descending process, and finally obtains liquid pig iron with higher carbon content. The carbon content of this liquid iron is about 4%.



The main characteristic of pig iron formation in the blast furnace is that it must undergo a carburizing process. It can be divided into three stages. The first stage is the carburization of solid metallic iron. This process occurs in the region below 800°C, in the middle and upper layers of the blast furnace, in the solid phase region where a small amount of metallic iron appears. The carburizing amount accounts for about 1.5% of the total carburizing amount. The second stage is the carburization of liquid iron. The molten iron is in direct contact with the coke. Under the action of high temperature, the molten iron flows down quickly and passes through the gaps of the coke. This process can quickly make the molten iron contain carbon. The amount increased to about 4%. The third stage is the carburizing process in the furnace. The amount is relatively small, generally accounting for less than 0.5% of the total carbon content. By comparing the three stages, we can know that the amount of carburizing is related to height and temperature. The higher the temperature and height, the greater the amount of carburizing. There are two forms of carbon in solidified pig iron, which are compound state or graphitic carbon state. The compound is mainly carbide, such as Siliocn Carbide. In this case, the section of pig iron appears silvery white. Graphite carbon is also called free carbon, which makes the fracture of pig iron appear dark gray. This kind of pig iron is called gray iron.

The final content of pig iron is also related to the content of other elements, especially manganes and Silicon. Mn, Cr, V, Ti and other elements can combine with C to form carbides and dissolve in iron, thus increasing the carbon content of pig iron. For example, silicon-manganese with a Mn content of 15%-20% usually has a carbon content of about 5%, and a SiMn Alloy with 80% Manganese has a carbon content of about 7%. On the other hand, several elements such as Si, P, and S can form compounds with iron and promote the decomposition of carbides. These elements can prevent carburization and reduce the carbon content of pig iron (unless you also add Silicon Carbide to it). Due to the high silicon content of cast iron, the carbon content is only 3.5%-4.0%. Ferrosilicon has a lower carbon content, generally less than 0.5%. Generally, the carbon content of steel-making pig iron is about 4%.