Iron ore. How they get it. How iron ore is mined and steel is smelted Iron smelting

Iron and steel based on it are used everywhere in industry and everyday human life. However, few people know what iron is made of, or rather, how it is mined and converted into a steel alloy.

Popular Misconception

First, let's define the concepts, since people are often confused and do not quite understand in general. This is a chemical element and a simple substance that is not found or used in its pure form. But steel is an alloy based on iron. It is rich in various chemical elements, and also contains carbon in its composition, which is necessary to impart strength and hardness.

Therefore, it is not entirely correct to talk about what iron is made of, since it is a chemical element that exists in nature. A person makes steel from it, which can later be used to make anything: bearings, car bodies, doors, etc. It is impossible to list all the items that are made from it. So, below we will not discuss what iron is made of. Instead, let's talk about converting this element into steel.

Production

There are many quarries in Russia and the world where iron ore is mined. These are huge and heavy stones that are quite difficult to get out of the quarry, since they are part of one large rock. Directly at the quarries, explosives are placed in the rock and detonated, after which huge pieces of stones fly in different directions. Then they are collected, loaded onto large dump trucks (such as BelAZ) and transported to a processing plant. Iron will be extracted from this rock.

Sometimes, if the ore is on the surface, it is not necessary to mine it. It is enough to split it into pieces in any other way, load it onto a dump truck and take it away.

Production

So now we understand what iron is made of. The rock is the raw material for its extraction. It is taken to a processing plant, loaded into a blast furnace and heated to a temperature of 1400-1500 degrees. This temperature must be maintained for a certain time. The iron contained in the rock melts and takes on a liquid form. Then it remains to be poured into special forms. The resulting slags are separated, and the iron itself is clean. The agglomerate is then fed into bunker bowls, where it is blown through with air flow and cooled with water.

There is another way to obtain iron: the rock is crushed and fed to a special magnetic separator. Since iron has the ability to be magnetized, the minerals remain on the separator, and everything is washed out. Of course, in order to turn iron into a metal and give it a solid form, it must be alloyed with another component - carbon. Its share in the composition is very small, but it is thanks to it that the metal becomes highly durable.

It is worth noting that depending on the volume of carbon added to the composition, the steel may be different. In particular, it can be more or less soft. There is, for example, special engineering steel, in the production of which only 0.75% carbon and manganese are added to iron.

Now you know what iron is made from and how it is converted into steel. Of course, the methods are described very superficially, but they convey the essence. You need to remember that iron is made from rock, which can then be used to make steel.

Manufacturers

Today, there are large deposits of iron ore in different countries, which are the basis for the production of the world's steel reserves. In particular, Russia and Brazil account for 18% of the world, Australia - 14%, Ukraine - 11%. The largest exporters are India, Brazil, and Australia. Please note that metal prices are constantly changing. Thus, in 2011, the cost of one ton of metal was 180 US dollars, and by 2016 the price was fixed at 35 US dollars per ton.

Conclusion

Now you know what iron consists of (available in and how it is produced. The use of this material is widespread throughout the world, and its importance is almost impossible to overestimate, since it is used in industrial and household industries. In addition, the economies of some countries are built on the basis metal production and its subsequent export.

We looked at what the alloy consists of. Iron in its composition is mixed with carbon, and such a mixture is the basis for the manufacture of most known metals.

Iron ore is obtained in the usual way: open-pit or underground mining and subsequent transportation to initial preparation, where the material is crushed, washed and processed.

The ore is poured into a blast furnace and blasted with hot air and heat, which turns it into molten iron. It is then removed from the bottom of the furnace into molds known as pigs, where it cools to produce cast iron. It is turned into wrought iron or processed into steel in several ways.

What is steel?

In the beginning there was iron. It is one of the It can be found almost everywhere, combined with many other elements, in the form of ore. In Europe, the beginning of working with iron dates back to 1700 BC.

In 1786, French scientists Berthollet, Monge and Vandermonde accurately determined that the difference between iron, cast iron and steel was due to different carbon content. However, steel, made from iron, quickly became the most important metal of the Industrial Revolution. At the beginning of the 20th century, global steel production was 28 million tons, six times more than in 1880. By the beginning of the First World War, its production was 85 million tons. Within a few decades, it practically replaced iron.

There are currently more than 3,000 cataloged brands (chemical compounds), not counting those created to meet individual needs. All of them contribute to making steel the most suitable material for solving the challenges of the future.

Raw materials for steelmaking: primary and secondary

Smelting this metal using many components is the most common mining method. Charge materials can be either primary or secondary. The main composition of the charge is usually 55% pig iron and 45% remaining scrap metal. Ferroalloys, converted cast iron and technically pure metals are used as the main element of the alloy; secondary elements, as a rule, include all types of ferrous metal.

Iron ore is the most important and basic raw material in iron and steel industry. To produce a ton of cast iron, about 1.5 tons of this material are required. About 450 tons of coke are used to produce one ton of pig iron. Many metallurgical plants even use

Water is an important raw material for the iron and steel industry. It is mainly used for coke hardening, blast furnace cooling, steam generation for hydraulic equipment operation and waste water disposal. It takes about 4 tons of air to produce a ton of steel. Flux is used in a blast furnace to remove impurities from smelting ore. Limestone and dolomite combine with the extracted impurities to form slag.

Both blast and steel furnaces are lined with refractories. They are used for liner furnaces designed for smelting iron ore. Silica or sand is used for molding. Aluminum, chromium, cobalt, copper, lead, manganese, molybdenum, nickel, tin, tungsten, zinc, vanadium, etc. are used to produce various grades of steel. Among all these ferroalloys, manganese is widely used in steel smelting.

Iron waste obtained from dismantled plant structures, machinery, old vehicles, etc. is recycled and widely used in this industry.

Cast iron for steel

Steel smelting using cast iron is carried out much more often than with other materials. Cast iron is a term that usually refers to gray iron, however it is also identified with a large group of ferroalloys. Carbon makes up about 2.1 to 4 wt.%, while silicon typically makes up 1 to 3 wt.% in the alloy.

Iron and steel are smelted at a melting point between 1150 and 1200 degrees, which is about 300 degrees lower than the melting point of pure iron. Cast iron also exhibits good fluidity, excellent machinability, and resistance to deformation, oxidation, and casting.

Steel is also an alloy of iron with variable carbon content. The carbon content of steel ranges from 0.2 to 2.1 mass%, and it is the most economical alloying material for iron. Smelting steel from cast iron is useful for a variety of engineering and structural purposes.

Iron Ore for Steel

The process of steel smelting begins with the processing of iron ore. The rock containing the iron ore is crushed. Ore is mined using magnetic rollers. Fine-grained iron ore is processed into coarse-grained lumps for use in the blast furnace. Coal is purified from impurities resulting in an almost pure form of carbon. The mixture of iron ore and coal is then heated to produce molten iron or pig iron, which is used to make steel.

In the main oxygen furnace, molten iron ore is the main raw material and is mixed with varying amounts of scrap steel and alloys to produce different grades of steel. An electric arc furnace melts recycled steel scrap directly into new steel. About 12% of steel is made from recycled material.

Smelting technology

Melting is the process by which a metal is obtained either as an element or as a simple compound from its ore by heating above its melting point, usually in the presence of oxidizing agents such as air or reducing agents such as coke.

In steelmaking technology, a metal that combines with oxygen, such as iron oxide, is heated to a high temperature, and the oxide is formed in combination with the carbon in the fuel, which comes out as carbon monoxide or carbon dioxide.
Other impurities, collectively called veins, are removed by the addition of a stream with which they combine to form slag.

Modern steel melting uses a reverberatory furnace. Concentrated ore and stream (usually limestone) are loaded into the top, and molten matte (a compound of copper, iron, sulfur and slag) is pulled from the bottom. A second heat treatment in a converter oven is necessary to remove iron from the matte surface.

Oxygen-convector method

The BOF process is the leading steelmaking process in the world. World production of converter steel in 2003 amounted to 964.8 million tons or 63.3% of total production. Converter production is a source of environmental pollution. The main challenges of this are the reduction of emissions, discharges and waste reduction. Their essence lies in the use of secondary energy and material resources.

Exothermic heat is generated by oxidation reactions during blowdown.

The main process of steelmaking using our own reserves:

• Molten pig iron (sometimes called hot metal) from a blast furnace is poured into a large fireproof lined container called a ladle.
• The metal in the ladle is sent directly to the main steel production or pre-processing stage.
• High-purity oxygen at a pressure of 700-1000 kilopascals is injected at supersonic speeds onto the surface of the iron bath through a water-cooled lance that is suspended in a vessel and held several feet above the bath.

The decision to pretreat depends on the quality of the hot metal and the desired final steel quality. The very first converters with removable bottoms, which could be detached and repaired, are still in use. The spears used for blowing have been changed. To prevent jamming of the tuyere during purging, slotted cuffs with a long tapering copper tip were used. The tip tips, after combustion, burn off the CO produced by blowing into CO 2 and provide additional heat. Darts, refractory balls and slag detectors are used to remove slag.

Oxygen-convection method: advantages and disadvantages

Does not require costs for gas purification equipment, since dust formation, i.e. evaporation of iron, is reduced by 3 times. Due to a decrease in the yield of iron, an increase in the yield of liquid steel is observed by 1.5 - 2.5%. Another advantage is that the intensity of purging in this method increases, which makes it possible to increase the productivity of the converter by 18%. The quality of steel is higher because the temperature in the blowing zone is reduced, which leads to a decrease in the formation of nitrogen.

The disadvantages of this method of steel smelting have led to a decrease in demand for consumption, since the level of oxygen consumption increases by 7% due to the high consumption of fuel combustion. There is an increased hydrogen content in the processed metal, which is why it is necessary to carry out purging with oxygen for some time after the end of the process. Among all the methods, the oxygen-converter method has the highest slag formation; the reason is the inability to monitor the oxidation process inside the equipment.

Open hearth method

The open hearth process comprised the bulk of the processing of all steel produced in the world for most of the 20th century. William Siemens in the 1860s sought a means of increasing the temperature in a metallurgical furnace, resurrecting an old proposal to use the waste heat generated by the furnace. He heated the brick to a high temperature, then used the same path to introduce air into the kiln. Preheated air significantly increased the flame temperature.

Natural gas or atomized heavy oils are used as fuel; air and fuel are heated before combustion. The furnace is loaded with liquid blast iron and steel scrap along with iron ore, limestone, dolomite and fluxes.

The stove itself is made of highly refractory materials, such as magnesite bricks for the hearths. Open hearth furnaces weigh up to 600 tons and are typically installed in groups so that the massive auxiliary equipment required to charge the furnaces and process the liquid steel can be efficiently utilized.

Although the open hearth process has been almost completely replaced in most industrialized countries by the basic oxygen process and electric arc furnace, it produces about 1/6 of all steel produced worldwide.

Advantages and disadvantages of this method

The advantages include ease of use and ease of production of alloy steel with various additives that give the material various specialized properties. The necessary additives and alloys are added immediately before the end of smelting.

The disadvantages include reduced efficiency compared to the oxygen-converter method. Also, the quality of steel is lower compared to other methods of metal smelting.

Electric steelmaking method

The modern method of smelting steel using its own reserves is a furnace that heats charged material using an electric arc. Industrial arc furnaces range in size from small units with a load capacity of about one ton (used in foundries to produce cast iron products) to 400 ton units used in secondary metallurgy.

Arc furnaces used in research laboratories may have a capacity of only a few tens of grams. Industrial electric arc furnace temperatures can be up to 1800 °C (3.272 °F), while laboratory installations can exceed 3000 °C (5432 °F).

Arc furnaces differ from induction furnaces in that the charging material is directly exposed to the electric arc, and the current in the terminals passes through the charged material. The electric arc furnace is used for steel production, consists of a refractory lining, usually water-cooled, is large in size, and covered with a retractable roof.

The oven is mainly divided into three sections:

• Shell consisting of side walls and a lower steel bowl.
• The hearth consists of a refractory that extends the lower bowl.
• The fire-lined or water-cooled roof can be designed as a ball section or as a truncated cone (conical section).

Advantages and disadvantages of the method

This method occupies a leading position in the field of steel production. The steel smelting method is used to create a high-quality metal that is either completely devoid of or contains small amounts of unwanted impurities such as sulfur, phosphorus and oxygen.

The main advantage of the method is for heating, thanks to which you can easily control the melting temperature and achieve incredible heating rates for the metal. Automated work will be a pleasant addition to the excellent opportunity for high-quality processing of various scrap metal.

The disadvantages include high energy consumption.

Part 1. Why is all this necessary?

If we are talking about creating a replica of a historical artifact (for example, a knife or ax of the 10th century), then the master faces at least 3 tasks:

1. Repeat the appearance. In other words, create a mass-dimensional model. An example of a replica of an ax from the Jakštaicai burial ground, Lithuania. The ax is made in compliance with the dimensions of the original.

The appearance of medieval weapons was studied by such famous authors as Edward Oakeshott, Jan Petersen, Anatoly Kirpichnikov.

2. Structure of the forged product. Most medieval artifacts were made, in modern terms, from at least two different grades of steel. Here we are talking about the technology of forge welding, the technology of manufacturing Damascus steel. Due to the high cost of carbon steel in the Middle Ages, technology was widely used when only the working part of the product (for example, in a knife, this blade) was steel, and everything else was made of iron or low-quality steel.

This topic is discussed in more detail in practice using an example . The structure of medieval forged products can be judged from books such as “Damascus steel in the countries of the Baltic Sea basin” by Antein A.K. and “Blacksmith's craft of the Polotsk land. IX–XIII centuries.” Gurin, M.F.

3. Actually metal. Steel of the 10th century and steel of the 21st century are two fundamentally different methods of obtaining the material. And as a result, the properties of these materials differ. Probably because of these differences, such a direction in blacksmithing as Damascus steel has become widespread. Ax made of raw iron.

The main method of obtaining iron in the Middle Ages was the smelting of bog ore in cheese furnaces. The essence of the cheese-blowing process is that the air for fuel combustion is supplied unheated, at atmospheric parameters.

The design of medieval furnaces is described in Boris Kolchin’s book “Ferrous metallurgy and metalworking in Ancient Rus'”.

Part 2. Raw materials and preparation for smelting.

Swamp ore is brown iron ore, or limonite. The main thing it consists of is Fe2O3. This is what it looks like in nature.

The ore is reduced to pure metal using charcoal. Before smelting, the ore is enriched by washing to remove excess rock.

I did the first smelting of ore in a graphite-chamotte crucible in a gas furnace chamber. From 400 grams of ore, 160 grams of iron were obtained. The ingot is porous, the pores are clean without non-metallic inclusions.

A spectral analysis of this ingot was made for alloying elements and impurities.

The analysis showed a carbon content of 0.14%. Carbon probably entered the iron from charcoal as a result of the process of surface cementation. Probably, the long-term exposure of the iron ingot to high temperatures ensured good diffusion of carbon, and as a result, its uniform distribution throughout the entire volume of the sample. Thus we can talk about obtaining low-carbon steel. The high content of phosphorus and sulfur (1.49% and 0.075%, respectively) significantly reduces the quality of the metal both from the point of view of forging processing and from the point of view of the operation of future products. To reduce the content of sulfur and phosphorus in the composition of the charge (Batch is a mixture of materials loaded into a smelting furnace to obtain a metal of a certain composition), calcium oxide CaO (quicklime) should be added. For example, add chalk CaCO3. At high temperatures (1000-1100 °C), chalk inside the forge will become quicklime.

Part 3. Ore smelting in authentic cheese furnaces.

On July 22-23, 2017, at the Dudutki museum complex, ore smelting in cheese furnaces took place at the festival of the glory of Belarusian weapons “Our Grunwald-2017”. The purpose of this experiment is to obtain practical answers to the following questions:

1. Materials and design of cheese furnaces.

2. Method of supplying air for fuel combustion. Blowing modes.

3. Composition of the charge.

4. Slag formation and its effect on the smelting process.

5. Obtaining pure metal.

6. Obtaining metal of better quality than during the first melting in a crucible.

Looking ahead, I can say that all the assigned tasks were solved. 2 cheese furnaces were made from different materials, different designs and sizes. One of the two forges was made from local raw materials, the air was supplied by two-chamber bellows.

Building forges, drying them, heating them and then melting them is a very labor-intensive task. The whole process took 2 days, the work was carried out from early morning until late at night, taking into account the fact that a whole team of assistants helped me. The experiment was successful - the resulting metal is approximately 7 times cleaner in terms of harmful impurities compared to crucible melting. However, there was not much metal left. The main volume is small metal balls in pieces of slag.

Probably, if you create a higher temperature in the forge and increase the melting time, then these balls will be welded together and form a kritsa suitable for forging. Spectral analysis did not determine the carbon content, probably due to its uneven distribution in the ingot. This probably also indirectly indicates the need to increase the melting time. The experiment showed that the main parameters were generally chosen correctly, which means their optimization will lead to an improvement in the result. I will write about this later, as events develop.

Iron makes up more than 5% of the earth's crust. The main ores used to extract iron are hematite and magnetite. These ores contain from 20 to 70% iron. The most important iron impurities in these ores are sand and alumina (aluminum oxide).

Earth's core

Based on indirect evidence, we can conclude that the Earth's core is mainly an iron alloy. Its radius is approximately 3470 km, while the radius of the Earth is 6370 km. The Earth's inner core appears to be solid and has a radius of about 1,200 km. It is surrounded by a liquid outer core. The turbulent flow of fluid in this part of the core creates the Earth's magnetic field. The pressure inside the core ranges from 1.3 to 3.5 million atmospheres, and the temperature ranges from

Although it is established that the Earth's core is composed mostly of iron, its exact composition is unknown. It is estimated that 8 to 10% of the mass of the earth's core is made up of elements such as nickel, sulfur (in the form of iron sulfide), oxygen (in the form of iron oxide) and silicon (in the form of iron silicide).

At least 12 countries in the world have proven iron ore reserves that exceed a billion tons. These countries include Australia, Canada, USA, South Africa, India, USSR and France. The global level of steel production currently reaches 700 million tons. The main producers of steel are the USSR, the USA, and Japan; each of these countries produces more than 100 million tons of steel per year. In Great Britain, the level of steel production is 20 million tons per year.

Iron production

The extraction of iron from iron ore is carried out in two stages. It begins with preparing the ore—grinding and heating. The ore is crushed into pieces with a diameter of no more than 10 cm. The crushed ore is then calcined to remove water and volatile impurities.

In the second stage, iron ore is reduced to iron using carbon monoxide in a blast furnace (Fig. 14.12). Reduction is carried out at temperatures of about 700°C:

To increase the yield of iron, this process is carried out under conditions of excess carbon dioxide

Carbon monoxide CO is formed in a blast furnace from coke and air. The air is first heated to approximately 600 °C and forced into the furnace through a special pipe - a tuyere. The coke burns in hot compressed air to form carbon dioxide. This reaction is exothermic and causes a temperature increase above 1700 °C:

Carbon dioxide rises up in the furnace and reacts with more coke to form carbon monoxide. This reaction is endothermic:

Rice. 14.12. Blast furnace, 1 - iron ore, limestone, coke, 2 loading cone (top), 3 - top gas, 4 - furnace masonry, 5 - iron oxide reduction zone, 6 - slag formation zone, 7 - coke combustion zone, 8 - injection of heated air through tuyeres, 9 - molten iron, 10 - molten slag.

The iron formed during the reduction of ore is contaminated with impurities of sand and alumina (see above). To remove them, limestone is added to the kiln. At the temperatures existing in the kiln, limestone undergoes thermal decomposition with the formation of calcium oxide and carbon dioxide:

Calcium oxide combines with impurities to form slag. The slag contains calcium silicate and calcium aluminate:

Iron melts at 1540°C (see Table 14.2). The molten iron along with the molten slag flows into the lower part of the furnace. Molten slag floats on the surface of molten iron. Each of these layers is periodically released from the oven at the appropriate level.

The blast furnace operates around the clock, in continuous mode. The raw materials for the blast furnace process are iron ore, coke and limestone. They are constantly fed into the oven through the top. Iron is released from the furnace four times a day, at regular intervals. It pours out of the furnace in a fiery stream at a temperature of about 1500 °C. Blast furnaces come in different sizes and productivity (1000-3000 tons per day). In the USA there are some new oven designs with

four outlets and continuous release of molten iron. Such furnaces have a capacity of up to 10,000 tons per day.

Iron smelted in a blast furnace is poured into sand molds. This kind of iron is called cast iron. The iron content in cast iron is about 95%. Cast iron is a hard but brittle substance with a melting point of about 1200 °C.

Cast iron is made by fusing a mixture of pig iron, scrap metal and steel with coke. Molten iron is poured into molds and cooled.

Wrought iron is the purest form of industrial iron. It is produced by heating crude iron with hematite and limestone in a smelting furnace. This increases the purity of iron to approximately 99.5%. Its melting point rises to 1400 °C. Wrought iron has great strength, malleability and ductility. However, for many applications it is replaced by mild steel (see below).

Steel production

Steels are divided into two types. Carbon steels contain up to 1.5% carbon. Alloy steels contain not only small amounts of carbon, but also specially introduced impurities (additives) of other metals. The different types of steels, their properties and applications are discussed in detail below.

Oxygen converter process. In recent decades, steel production has been revolutionized by the development of the basic oxygen process (also known as the Linz-Donawitz process). This process began to be used in 1953 in steelworks in two Austrian metallurgical centers - Linz and Donawitz.

The oxygen converter process uses an oxygen converter with a main lining (lining) (Fig. 14.13). The converter is loaded in an inclined position

Rice. 14.13. Converter for steel smelting, 1 - oxygen and 2 - water-cooled tube for oxygen blast, 3 - slag. 4-axis, 5-molten steel, 6-steel body.

molten pig iron from the smelting furnace and scrap metal, then returned to a vertical position. After this, a water-cooled copper tube is inserted into the converter from above and through it a stream of oxygen mixed with powdered lime is directed onto the surface of the molten iron. This “oxygen purge”, which lasts 20 minutes, leads to intense oxidation of iron impurities, and the contents of the converter remain liquid due to the release of energy during the oxidation reaction. The resulting oxides combine with lime and turn into slag. The copper tube is then pulled out and the converter is tilted to drain the slag. After repeated blowing, the molten steel is poured from the converter (in an inclined position) into a ladle.

The oxygen-converter process is used primarily to produce carbon steels. It is characterized by high productivity. In 40-45 minutes, 300-350 tons of steel can be produced in one converter.

Currently, all steel in the UK and most steel worldwide is produced using this process.

Electric steelmaking process. Electric furnaces are used primarily for converting scrap steel and cast iron into high-quality alloy steels such as stainless steel. The electric furnace is a round deep tank lined with refractory bricks. The furnace is loaded with scrap metal through the open lid, then the lid is closed and electrodes are lowered into the furnace through the holes in it until they come into contact with the scrap metal. After this, the current is turned on. An arc occurs between the electrodes, in which a temperature above 3000 °C develops. At this temperature, the metal melts and new steel is formed. Each furnace load allows you to produce 25-50 tons of steel.

Processes for direct extraction of iron from ores

By direct iron production processes we mean such chemical, electrochemical or chemical-thermal processes that make it possible to obtain metallic iron in the form of a sponge, crust or liquid metal directly from ore, bypassing a blast furnace.

Such processes are carried out without consuming metallurgical coke, fluxes, or electricity (for the preparation of compressed air), and also make it possible to obtain very pure metal.

Methods for direct production of iron have been known for a long time. More than 70 different methods have been tested, but only a few have been implemented and, moreover, on a small industrial scale.

In recent years, interest in this problem has grown, which is associated, in addition to the replacement of coke with other fuels, with the development of methods for deep enrichment of ores, ensuring not only a high iron content in concentrates (70...72%), but also its almost complete release from sulfur and phosphorus .

Production of sponge iron in shaft furnaces.

The process diagram is shown in Fig. 2.1.

Rice. 2.1. Installation diagram for direct reduction of iron from ores and production of metallized pellets

When sponge iron is obtained, the mined ore is enriched and pellets are obtained. Pellets from bunker 1 through screen 2 enter box 10 of the charge filling machine and from there into the shaft furnace 9 , operating on the counterflow principle. The spillage from the pellets enters the hopper 3 with the briquetting press and in the form of pellets again enters the screen 2 . To restore iron from pellets, a mixture of natural and blast furnace gases is supplied to the furnace through pipeline 8, subjected to conversion in installation 7, as a result of which the mixture decomposes into hydrogen and carbon monoxide. In the reduction zone of the furnace, a temperature of 1000...1100 0 C is created, at which iron ore in pellets is reduced to solid sponge iron. The iron content in the pellets reaches 90...95%. To cool iron pellets through pipeline 6 to the cooling zone 0 ovens supply air. Cooled pellets 5 are delivered to conveyor 4 and are sent to steel smelting in electric furnaces.

Reduction of iron in a fluidized bed.

Fine-grained ore or concentrate is placed on a grid through which hydrogen or other reducing gas is supplied at a pressure of 1.5 MPa. Under hydrogen pressure, ore particles are suspended, undergoing continuous movement and forming a “boiling”, “fluidized” layer. In the fluidized bed, good contact of the reducing gas with the iron oxide particles is ensured. For one ton of recovered powder, hydrogen consumption is 600...650 m 3 .

Preparation of sponge iron in crucible capsules.

Silicon carbide capsules with a diameter of 500 mm and a height of 1500 mm are used. The charge is loaded in concentric layers. The inside of the capsule is filled with a reducing agent - crushed solid fuel and limestone (10...15%) to remove sulfur. The second layer is reduced crushed ore or concentrate, scale, then another concentric layer of reducing agent and limestone. The capsules installed on trolleys move slowly in a tunnel oven up to 140 m long, where they are heated, held at 1200 0 C and cooled for 100 hours.

Reduced iron is obtained in the form of thick-walled pipes, they are cleaned, crushed and crushed, obtaining iron powder with an iron content of up to 99%, carbon - 0.1...0.2%.

Steel production

Essence of the process

Become– iron-carbon alloys containing almost 1.5% carbon; with a higher content, the hardness and brittleness of steels significantly increase and they are not widely used.

The main source materials for steel production are pig iron and steel scrap (scrap).

Iron is oxidized primarily when cast iron reacts with oxygen in steelmaking furnaces:

Simultaneously with iron, silicon, phosphorus, manganese and carbon are oxidized. The resulting iron oxide at high temperatures gives up its oxygen to more active impurities in the cast iron, oxidizing them.

Steel smelting processes are carried out in three stages.

The first stage is melting the charge and heating the liquid metal bath.

The temperature of the metal is relatively low, the oxidation of iron occurs intensively, the formation of iron oxide and the oxidation of impurities: silicon, manganese and phosphorus.

The most important task of the stage is phosphorus removal. To do this, it is desirable to carry out smelting in the main furnace, where the slag contains. Phosphoric anhydride forms an unstable compound with iron oxide. Calcium oxide is a stronger base than iron oxide, therefore at low temperatures it binds and turns it into slag:

To remove phosphorus, low temperatures of the metal and slag bath and sufficient content in the slag are required. To increase the content in the slag and accelerate the oxidation of impurities, iron ore and scale are added to the furnace, introducing ferruginous slag. As phosphorus is removed from the metal into the slag, the phosphorus content in the slag increases. Therefore, it is necessary to remove this slag from the metal surface and replace it with a new one with fresh additives.

The second stage - boiling of the metal bath - begins as it warms up to higher temperatures.

As the temperature rises, the carbon oxidation reaction occurs more intensely, occurring with the absorption of heat:

To oxidize carbon, a small amount of ore, scale, or oxygen is injected into the metal.

When iron oxide reacts with carbon, bubbles of carbon monoxide are released from the liquid metal, causing a “bath boil.” During “boiling,” the carbon content in the metal is reduced to the required level, the temperature is equalized throughout the bath volume, and non-metallic inclusions adhering to the floating bubbles, as well as gases penetrating into the bubbles, are partially removed. All this helps to improve the quality of the metal. Consequently, this stage is the main one in the steel smelting process.

Conditions are also created for the removal of sulfur. Sulfur in steel is in the form of sulfide (), which also dissolves in the main slag. The higher the temperature, the greater the amount of iron sulfide dissolves in the slag and reacts with calcium oxide:

The resulting compound dissolves in the slag, but does not dissolve in the iron, so the sulfur is removed into the slag.

The third stage, steel deoxidation, involves the reduction of iron oxide dissolved in the liquid metal.

During melting, an increase in the oxygen content in the metal is necessary for the oxidation of impurities, but in finished steel oxygen is a harmful impurity, as it reduces the mechanical properties of steel, especially at high temperatures.

Steel is deoxidized in two ways: precipitation and diffusion.

Precipitation deoxidation is carried out by introducing into liquid steel soluble deoxidizers (ferromanganese, ferrosilicon, aluminum) containing elements that have a greater affinity for oxygen than iron.

As a result of deoxidation, iron is reduced and oxides are formed: , which have a lower density than steel and are removed into slag.

Diffusion deoxidation is carried out by deoxidation of the slag. Ferromanganese, ferrosilicon and aluminum in crushed form are loaded onto the surface of the slag. Deoxidizers, by reducing iron oxide, reduce its content in the slag. Consequently, iron oxide dissolved in steel turns into slag. The oxides formed during this process remain in the slag, and the reduced iron passes into steel, while the content of non-metallic inclusions in the steel decreases and its quality increases.

Depending on the degree of deoxidation, steels are smelted:

a) calm

b) boiling,

c) semi-calm.

Calm steel is obtained by complete deoxidation in the furnace and ladle.

Boiling steel is not completely deoxidized in the furnace. Its deoxidation continues in the mold during solidification of the ingot, due to the interaction of iron oxide and carbon:

The resulting carbon monoxide is released from the steel, helping to remove nitrogen and hydrogen from the steel, the gases are released in the form of bubbles, causing it to boil. Boiling steel does not contain non-metallic inclusions, therefore it has good ductility.

Semi-quiet steel has an intermediate deoxidation between calm and boiling. It is partially deoxidized in the furnace and in the ladle, and partially in the mold, due to the interaction of iron oxide and carbon contained in the steel.

Alloying of steel is carried out by introducing ferroalloys or pure metals in the required quantity into the melt. Alloying elements, which have a lower affinity for oxygen than iron (), do not oxidize during melting and casting, so they are introduced at any time during melting. Alloying elements that have a greater affinity for oxygen than iron ( ), is introduced into the metal after deoxidation or simultaneously with it at the end of the melt, and sometimes into the ladle.

Steel smelting methods

Cast iron is converted into steel in metallurgical units of various operating principles: open-hearth furnaces, oxygen converters, electric furnaces.

Steel production in open hearth furnaces

Martin process (1864-1865, France). Until the seventies it was the main method of steel production. The method is characterized by relatively low productivity and the possibility of using secondary metal – steel scrap. The capacity of the furnace is 200…900 tons. The method makes it possible to produce high-quality steel.

The open hearth furnace (Fig. 2.2.) according to its design and principle of operation is a flame reverberatory regenerative furnace. Gaseous gas is burned in the smelting space

fuel or fuel oil. The high temperature for obtaining steel in a molten state is provided by heat recovery from furnace gases.

A modern open-hearth furnace is a horizontally elongated chamber made of refractory brick. The working melting space is limited from below by the hearth 12, from above by the arch 11 , and on the sides there are 5 front and 10 rear walls. The hearth has the shape of a bathtub with slopes towards the walls of the furnace. In the front wall there are loading windows 4 for supplying charge and flux, and in the rear wall there is a hole 9 for releasing finished steel.

Fig.2.2. Open hearth furnace diagram

A characteristic of the working space is the area of ​​the furnace bottom, which is calculated at the level of the thresholds of the loading windows. At both ends of the melting space there are furnace heads 2, which serve to mix fuel with air and supply this mixture to the melting space. Natural gas and fuel oil are used as fuel.

To heat air and gas when operating on low-calorie gas, the furnace has two regenerators 1.

Regenerator - a chamber in which a nozzle is placed - a refractory brick laid out in a cage, designed to heat air and gases.

The gases leaving the furnace have a temperature of 1500...1600 0 C. Entering the regenerator, the gases heat the nozzle to a temperature of 1250 0 C. Air is supplied through one of the regenerators, which, passing through the nozzle, heats up to 1200 0 C and enters the furnace head, where it mixes with fuel, a torch 7 is formed at the exit from the head, directed towards the charge 6.

The exhaust gases pass through the opposite head (left), cleaning devices (slag tanks), which serve to separate slag and dust particles from the gas and are sent to the second regenerator.

Cooled gases leave the furnace through chimney 8.

After cooling, the nozzles of the right regenerator switch the valves, and the flow of gases in the furnace changes direction.

The temperature of the flame reaches 1800 0 C. The torch heats the working space of the furnace and the charge. The torch promotes the oxidation of charge impurities during smelting.

The duration of melting is 3...6 hours, for large furnaces - up to 12 hours. The finished melt is released through a hole located in the rear wall at the lower level of the hearth. The hole is tightly plugged with low-caking refractory materials, which are knocked out when the melt is released. The furnaces operate continuously until they are stopped for major repairs - 400...600 heats.

Depending on the composition of the charge used in smelting, there are different types of open-hearth process:

– scrap process, in which the charge consists of steel scrap (scrap) and 25...45% pig iron, the process is used in factories where there are no blast furnaces, but a lot of scrap metal.

– scrap-ore process, in which the charge consists of liquid cast iron (55...75%), scrap and iron ore, the process is used in metallurgical plants with blast furnaces.

The furnace lining can be basic or acidic. If, during the steel melting process, basic oxides predominate in the slag, then the process is called main open-hearth process, and if acidic – sour.

The largest amount of steel is produced by the scrap ore process in open hearth furnaces with a main lining.

Iron ore and limestone are loaded into the furnace, and after heating, scrap is fed. After heating the scrap, liquid cast iron is poured into the furnace. During the melting period, due to ore oxides and scrap, cast iron impurities are intensively oxidized: silicon, phosphorus, manganese and, partially, carbon. The oxides form a slag with a high content of iron and manganese oxides (iron slag). After this, a period of “boiling” of the bath is carried out: iron ore is loaded into the furnace and the bath is purged with oxygen supplied through pipes 3. At this time, the supply of fuel and air to the furnace is turned off and the slag is removed.

To remove sulfur, new slag is created by applying lime with the addition of bauxite to the metal surface to reduce the viscosity of the slag. The content in the slag increases and decreases.

During the “boiling” period, carbon is intensively oxidized, so the charge must contain excess carbon. At this stage, the metal is brought to a given chemical composition, gases and non-metallic inclusions are removed from it.

Then the metal is deoxidized in two stages. First, deoxidation occurs by oxidizing the carbon of the metal, with the simultaneous supply of deoxidizing agents - ferromanganese, ferrosilicon, aluminum - to the bath. The final deoxidation with aluminum and ferrosilicon is carried out in a ladle when the steel is released from the furnace. After taking control samples, the steel is released into the ladle.

In the main open-hearth furnaces, carbon structural, low- and medium-alloy steels (manganese, chromium) are smelted, in addition to high-alloy steels and alloys, which are produced in electric melting furnaces.

High-quality steels are smelted in acidic open-hearth furnaces. A mixture with low sulfur and phosphorus content is used.

The main technical and economic indicators of steel production in open hearth furnaces are:

· furnace productivity – steel removal from 1m2 of hearth area per day (t/m2 per day), on average 10 t/m2; R

· fuel consumption per 1 ton of steel produced is on average 80 kg/t.

As furnaces become larger, their economic efficiency increases.

Steel production in oxygen converters.

The oxygen-converter process is the smelting of steel from liquid cast iron in a converter with a main lining and blowing oxygen through a water-cooled lance.

The first experiments in 1933-1934 - Mozgovoy.

On an industrial scale - in 1952-1953 at factories in Linz and Donawitz (Austria) - it was called the LD process. Currently, the method is the main one in the mass production of steel.

An oxygen converter is a pear-shaped vessel made of steel sheet, lined with base brick.

Converter capacity is 130...350 tons of liquid cast iron. During operation, the converter can be rotated 360° to load scrap, pour cast iron, drain steel and slag.

The charge materials of the oxygen-converter process are liquid pig iron, steel scrap (no more than 30%), lime for slag removal, iron ore, as well as bauxite and fluorspar for slag liquefaction.

The sequence of technological operations when melting steel in oxygen converters is presented in Fig. 2.3.

Fig.2.3. The sequence of technological operations when melting steel in oxygen converters

After the next steel melting, the outlet hole is sealed with a refractory mass and the lining is inspected and repaired.

Before melting, the converter is tilted and scrap rice is loaded using charging machines. (2.3.a), cast iron is poured at a temperature of 1250...1400 0 C (Fig. 2.3.b).

After this, the converter is turned to the working position (Fig. 2.3.c), a cooled lance is inserted inside and oxygen is supplied through it at a pressure of 0.9...1.4 MPa. Simultaneously with the start of blowing, lime, bauxite, and iron ore are loaded. Oxygen penetrates the metal, causing it to circulate in the converter and mix with the slag. A temperature of 2400 0 C develops under the tuyere. Iron is oxidized in the zone of contact of the oxygen jet with the metal. Iron oxide dissolves in the slag and metal, enriching the metal with oxygen. Dissolved oxygen oxidizes silicon, manganese, and carbon in the metal, and their content decreases. The metal is heated by the heat released during oxidation.

Phosphorus is removed at the beginning of purging the bath with oxygen, when its temperature is low (the phosphorus content in cast iron should not exceed 0.15%). If the phosphorus content is high, to remove it, it is necessary to drain the slag and introduce a new one, which reduces the productivity of the converter.

Sulfur is removed throughout the entire melting process (the sulfur content in cast iron should be up to 0.07%).

The oxygen supply is stopped when the carbon content in the metal corresponds to the specified value. After this, the converter is turned and the steel is released into a ladle (Fig. 2.3.d), where it is deoxidized using the precipitation method with ferromanganese, ferrosilicon and aluminum, then the slag is drained (Fig. 2.3.d).

In oxygen converters, steels with different carbon contents, boiling and calm, as well as low-alloy steels are smelted. Alloying elements in molten form are introduced into the ladle before steel is released into it.