Cast iron is a metal widely used in various industries, characterized by remarkable performance characteristics. The process of obtaining it is relatively simple and does not include too many steps. This material is smelted in blast furnaces - special furnaces, which are something like an enlarged copy of a test tube. About how to get cast iron, and we will talk further in all details.
Mining and processing plants
The main raw material used in the production of pig iron is iron ore. They get it in quarries in different places of our country. As you know, mined ore contains a large number of various impurities. Of course, it is impossible to use it for smelting cast iron in such a "raw" form. Therefore, at the first stage, it goes to special enterprises - mining and processing plants. Here, waste rock is removed from it and crushed. Then, pure ore is loaded into train cars and sent to metallurgical plants.
Sintering process
Actually, how to get cast iron, consider a little lower. Now let's talk about how ore is prepared for smelting directly at metallurgical plants.
If conventional crushed material is used for remelting, the productivity of the blast furnace will drop sharply. The fact is that such a mixture has a low degree of gas permeability. Therefore, before loading into the blast furnace, the sintering process is mandatory.
This procedure is carried out in specialized workshops of metallurgical plants and is a process of sintering the rock into pieces of a certain size that is most suitable for smelting cast iron. Adhesion occurs at a high temperature sufficient to easily melt the surface of the charge particles. As a result, the latter simply stick together with each other, forming pieces. In this case, the ore is preliminarily mixed with coal. As a result of the combustion of the latter, the temperature necessary to obtain the pieces is achieved. The agglomeration process is stimulated by passing air flows (from top to bottom) through an ore layer with coal.
To obtain sinter, not only ore can be used. Sometimes it is also made from small pieces of iron. Its alloy with which substance makes it possible to obtain cast iron will be discussed below. Of course, it is not iron in the ingots that is used to produce this metal. Smelted into cast iron ordinary scrap metal.
What happens in the oven
So, let's see how they get cast iron in a blast furnace. Inside the furnace of this design is faced with brick. The principle of its operation is relatively simple. In the production of pig iron, in addition to sinter, coke, lime and flux are used. A mixture of these materials is prepared in a certain proportion. It is called a blast furnace charge. It is poured into special lifts and lifted to the very top of the furnace.
In order for the coke to catch fire, a large amount of oxygen-enriched air is needed. It is fed into the blast furnace from below, through special openings called tuyeres. He is blown into the furnace under very high pressure. This is necessary so that air penetrates through the reservoir fed from above the charge. In this case, the flow is preheated to 600-800 degrees, otherwise the temperature inside the furnace will decrease.
The pig iron obtained by straightening the mixture flows down and is released approximately every 40 minutes at a time through a special opening called a tap hole. Then it is poured into bowls of large capacity and transported to steelmaking workshops.
Reduction and carburization of iron in a furnace
All blast furnaces work on a counterflow principle. Moreover, the following chemical processes take place in them in turn:
- Iron recovery. This process occurs sequentially and looks like this: Fe 2 O 3 - Fe 3 O 4 - FeO - Fe. In this case, carbon monoxide (CO) formed during the interaction of CO 2 with red-hot coke, as well as solid carbon of the latter, acts as a reducing agent.
- Carburization of iron. The reaction in this case looks like this: 3Fe + 2CO = Fe 3 C + CO 2 + Q. Fe 3 C carbide is easily mixed with solid iron, as a result of which the alloy of the latter with carbon is formed. Flowing down, it washes pieces of coke and is even more carbonized. In addition, substances such as manganese, sulfur, silicon, etc. are dissolved in it.
Thus, it becomes clear that a domain metal is an alloy of iron with which substance. Cast iron can be obtained simply by carburizing the melt of the mixture.
Restore other items
Mn, silicon, sulfur and phosphorus enter the blast furnace together with the charge in the form of various chemical compounds. Higher manganese oxides are reduced to MnO by approximately the same principle as iron: MnO 2 - Mn 2 O 3 - Mn 3 O 4 - MnO. Pure manganese is released as follows: MnO + C = Mn + CO - Q. Silicon enters the furnace in the form of silica SiO 2 . Its reduction occurs by the reaction SiO 2 + 2C = Si + 2CO - Q.
Phosphorus is reduced by hydrogen, solid carbon, and CO and, unfortunately, goes almost completely to cast iron. This element degrades the blast alloy of iron. Allows you to get good quality cast iron present in the mixture of silica, as well as higher manganese oxides. Mn in some cases is added to the blast furnace specifically. This produces a special type of cast iron - manganese.
Sulfur removal
The question of how to get cast iron of good quality comes down to including cleaning it from this undesirable element. Sulfur is the main harmful impurity, significantly worsening the properties of the final smelting product. Its main amount is contained in coke. Sulfur is removed by increasing the content of lime (CaO) in the mixture and increasing the temperature in the furnace. The reaction in this case looks like this: FeS + CaO = FeO + CaO + Q. Other methods can be used to reduce the percentage of sulfur in pig iron. For example, sometimes already melted material is processed in an outlet trough or bowl with soda. In this case, sulfur removal occurs as a result of the reaction FeS + NaCO 3 = FeO + Na 2 S + CO 2 .
Slag formation
Thus, we have figured out how to get cast iron. However, in the smelting of this material, one more product is widely used in the national economy. When melting 1 ton of pig iron, 0.6 ton of slag comes out. The fact is that even in refined iron ore quite a large amount of clay is contained. Coke also contains ash. To remove these unnecessary elements, fluxes (calcium and magnesium carbonates) are added to the charge, among other things. During the smelting process, they enter into a chemical reaction with various impurities, as a result of which slag is formed. It is an aluminosilicate or silicate melt.
Slag density is lower than molten iron. Therefore, in the process of melting, it is located under it. It is removed periodically through a separate tap hole, called slag. This by-product of iron production is used mainly for the manufacture of cement and building blocks as a filler.
Types of cast iron
As you can see, the question of how to get cast iron in the blast furnace is relatively simple. Ultimately, however, material may be released from the furnace that differs slightly in chemical composition and physical properties. All cast irons are mainly divided into two varieties: conversion (white) and foundry (gray). The first type is used as raw material in the production of steel. Foundry is used to produce various kinds of cast iron products that are in good demand on the market.
White cast iron
The proportion of this type of metal smelted in blast furnaces is 75-80%. The main properties of such cast iron are: high hardness, brittleness and wear resistance. It usually contains more manganese and sulfur than in foundry. White cast iron is difficult to process. It is impossible to use ordinary cutting tools of modern machines for the manufacture of any products from it. But steel is obtained from cast iron of this variety is quite simple. Converted blast furnace metal is divided according to the method of further remelting into three classes: open-hearth (M), Bessemer (B) and Thomas (T).
Foundry iron
The carbon in this material is mainly contained in the form of free graphite, which contains silicon. It is supplied for the manufacture of cast iron products in the form of ingots. This material is marked with the letter "L" and the numbers from "1" to "6", depending on the purpose. There is also magnesium-refined cast iron, marked with the letters "LR".
Well, hopefully, we have fully answered the question of what alloy of iron with which substance allows to obtain cast iron. This is ordinary carbon, replacing oxygen in a blast furnace. The main properties of cast iron depend on the amount of impurities included in its composition: manganese, phosphorus, silicon and sulfur.