In life we constantly come across alloys, the most common of which is steel. Therefore, it is not surprising that someone would have a question about how steel is made?

Steel is one of the alloys of iron and carbon, which is widely used in Everyday life. The steel production process is multi-stage and consists of several stages: ore mining and beneficiation, sinter production, iron production and steel smelting.

Ore and sinter

Ore deposits allow the extraction of both rich and poor rocks. High-grade ore can be immediately used as industrial raw materials. In order to be able to smelt low-grade ore, it must be enriched, that is, the content of pure metal in it must be increased. To do this, the ore is crushed and, using various technologies, particles rich in metal compounds are separated. For example, for iron ores, magnetic separation is used - the effect magnetic field on the feedstock in order to separate iron-rich particles.

The result is a low-dispersion concentrate, which is sintered into larger pieces. The result of roasting iron ores is an agglomerate. Types of agglomerates are named after the main raw materials included in their composition. In our case, this is iron ore sinter. Now, in order to understand how steel is made, it is necessary to trace the further technological process.

Iron production.

Pig iron is smelted in blast furnaces, which operate on the countercurrent principle. Loading of sinter, coke and other charge material is carried out from above. From the bottom up, towards these materials, streams of hot gas rise from the combustion of coke. The series begins chemical processes, resulting in the reduction of iron and its saturation with carbon. Temperature at the same time it remains in the region of 400-500 degrees Celsius. In the lower parts of the furnace, where the reduced iron is gradually lowered, the temperature increases to 900-950 degrees. A liquid alloy of iron and carbon is formed - cast iron. The main chemical characteristics of cast iron include: carbon content more than 2.14%, the mandatory presence of sulfur, silicon, phosphorus and manganese. Cast iron is characterized by increased fragility.

Steel smelting.

Now we are getting closer to last stage, allowing you to learn how steel is made. Chemically, steel differs from cast iron in having a lower carbon content; accordingly, the main task production process– reduce the content of carbon and other impurities in the main iron alloy. Open hearth furnaces, oxygen converters or electric furnaces are used to produce steel.

By various technologies The molten cast iron is purged with oxygen at very high temperatures. The reverse process occurs - oxidation of iron at the level of impurities included in the alloy. The resulting slag is subsequently removed. As a result of oxygen purging, the carbon content is reduced and the cast iron is converted into steel.

Alloying elements can be added to steel to change the properties of the material. Therefore, steel is considered an iron-carbon alloy with an iron content of at least 45%.

The above processes explained how steel is made, from what materials and using what technologies.

Iron in its pure form is a ductile metal. gray, easy to process. And yet, for humans, the Fe element is more practical in combination with carbon and other impurities that allow the formation of metal alloys - steel and cast iron. 95% - this is exactly how much of all metal products produced on the planet contains iron as the main element.

Iron: history

The first iron products made by man are dated by scientists in the 4th millennium BC. e., and studies have shown that meteoric iron, which is characterized by a 5-30 percent nickel content, was used for their production. It’s interesting, but until humanity mastered the extraction of Fe by smelting it, iron was valued more than gold. This was explained by the fact that stronger and more reliable steel was much more suitable for the manufacture of tools and weapons than copper and bronze.

The ancient Romans learned how to produce the first cast iron: their furnaces could raise the temperature of the ore to 1400 o C, while 1100-1200 o C was enough for cast iron. Subsequently, they also obtained pure steel, the melting point of which, as is known, is 1535 degrees Celsius. Celsius.

Chemical properties of Fe

What does iron interact with? Iron interacts with oxygen, which is accompanied by the formation of oxides; with water in the presence of oxygen; with sulfuric and hydrochloric acids:

3Fe+2O2 = Fe3O4
4Fe+3O 2 +6H 2 O = 4Fe(OH) 3
Fe+H 2 SO 4 = FeSO 4 +H 2
Fe+2HCl = FeCl 2 +H 2

Also, iron reacts to alkalis only if they are melts of strong oxidizing agents. Iron does not react with oxidizing agents at normal temperatures, but always begins to react when it increases.

Use of iron in construction

The use of iron in the construction industry today cannot be overestimated, because metal structures are the basis of absolutely any modern building. In this area, Fe is used in common steels, cast iron and wrought iron. This element is found everywhere, from critical structures to anchor bolts and nails.

The construction of building structures made of steel is much cheaper, and we can also talk about higher construction rates. This markedly increases the use of iron in construction, while the industry itself is embracing the use of new, more efficient and reliable Fe-based alloys.

Use of iron in industry

The use of iron and its alloys - cast iron and steel - is the basis of modern machine-tool, aircraft, instrument making and the manufacture of other equipment. Thanks to Fe cyanides and oxides, the paint and varnish industry functions; iron sulfates are used in water treatment. Heavy industry is completely unthinkable without the use of Fe+C-based alloys. In a word, Iron is an irreplaceable, but at the same time accessible and relatively inexpensive metal, which, as part of its alloys, has an almost unlimited scope of application.

Use of iron in medicine

It is known that every adult contains up to 4 grams of iron. This element is extremely important for the functioning of the body, in particular for health. circulatory system(hemoglobin in red blood cells). There are many medicines iron-based, which allow you to increase the Fe content to avoid the development of iron deficiency anemia.

Vacuum melting

Industrial grades of technical iron (Armco type), obtained by pyrometallurgical method, correspond to a purity of 99.75-99.85% Fe. Removal of volatile metal and non-metallic impurities (C, O, S, P, N) is possible by melting iron in a high vacuum or annealing in an atmosphere of dry hydrogen. When induction melting of iron in a vacuum, highly volatile impurities are removed from the metal, the evaporation rate of which increases from arsenic to lead in the following sequence:

As→S→Sn→Sb→Cu→Mn→Ag→Pb.

After an hour of melting in a vacuum of 10V-3 mmHg. Art. at 1580°C it was removed from iron most of impurities of antimony, copper, manganese, silver and lead. Impurities of chromium, arsenic, sulfur and phosphorus are removed worse, and impurities of tungsten, nickel and cobalt are practically not removed.
At 1600° C, the vapor pressure of copper is 10 times higher than that of iron; when melting iron in a vacuum (10v-3 mm Hg), the copper content decreases to 1 * 10v-3% and manganese decreases by 80% in an hour. The content of impurities of bismuth, aluminum, tin and other highly volatile impurities is significantly reduced; In this case, an increase in temperature affects the reduction of impurity content more effectively than an increase in the duration of smelting.
In the presence of oxygen inclusions, volatile oxides of tungsten, molybdenum, titanium, phosphorus and carbon can form, which leads to a decrease in the concentration of these impurities. The purification of iron from sulfur increases significantly in the presence of silicon and carbon. So, for example, when the cast iron contains 4.5% C and 0.25% S, after melting the metal in a vacuum, the sulfur content decreases to 7 * 10v-3%.
The content of gas impurities during iron smelting is reduced by approximately 30-80%. The nitrogen and hydrogen content in molten iron is determined by the pressure of the residual gases. If at atmospheric pressure the solubility of nitrogen in iron is ~0.4%, then at 1600° C and a residual pressure of 1*10v-3 mm Hg. Art. it is 4*10v-5%, and for hydrogen 3*10v-6%. The removal of nitrogen and hydrogen from molten iron is completed mainly during the first hour of smelting; in this case, the amount of remaining gases is approximately two orders of magnitude higher than their equilibrium content at a pressure of 10v-3 mm Hg. Art. A decrease in the oxygen content present in the form of oxides can occur as a result of the interaction of oxides with reducing agents - carbon, hydrogen and some metals.

Purification of iron by distillation in vacuum with condensation on a heated surface

In 1952, Amonenko and co-authors used a method of vacuum distillation of iron with its condensation on a heated surface.
All highly volatile impurities condense in the colder zone of the condenser, and iron, which has a low vapor pressure, remains in the zone with a higher temperature.
For melting, crucibles made of aluminum oxide and beryllium with a capacity of up to 3 liters were used. The vapors condensed on thin sheets of armco iron, since when condensing on ceramics, the iron at the condensation temperature sintered with the condenser material and was destroyed when the condensate was removed.
The optimal distillation mode was as follows: evaporation temperature 1580 ° C, condensation temperature from 1300 (at the bottom of the condenser) to 1100 ° C (at the top). The evaporation rate of iron is 1 g/cm2*h; yield of pure metal ~ 80% of total number condensate and more than 60% of the load weight. After double distillation of iron, the content of impurities significantly decreased: manganese, magnesium, copper and lead, nitrogen and oxygen. When iron was melted in an alundum crucible, it became contaminated with aluminum. The carbon content after the first distillation dropped to 3*10v-3% and did not decrease during subsequent distillation.
At a condensation temperature of 1200° C, needle-shaped iron crystals formed. The residual resistance of such crystals, expressed as the ratio Rt/R0°C, at 77° K was 7.34 * 10v-2 and at 4.2° K 4.37 * 10v-3. This value corresponds to an iron purity of 99.996%.

Electrolytic iron refining

Electrolytic refining of iron can be carried out in chloride and sulfate electrolytes.
According to one of the methods, iron was precipitated from an electrolyte of the following composition: 45-60 g/l Fe2+ (in the form of FeCl2), 5-10 g/l BaCl2 and 15 g/l NaHCO3. Armco iron plates served as anodes, and pure aluminum as cathodes. At a cathode current density of 0.1 A/dm2 and room temperature A coarse-crystalline sediment was obtained containing about 1*10-2% carbon, “traces” of phosphorus and free of sulfur impurities. However, the metal contained a significant amount of oxygen (1-2*10v-1%).
When using a sulfate electrolyte, the sulfur content in iron reaches 15*10v-3-5*10v-2%. To remove oxygen, iron was treated with hydrogen or the metal was melted in a vacuum in the presence of carbon. In this case, the oxygen content decreased to 2*10v-3%. Similar results for oxygen content (3*10v-3%) are obtained by annealing iron in a stream of dry hydrogen at 900-1400° C. Metal desulfurization is carried out in high vacuum using additives of tin, antimony and bismuth, which form volatile sulfides.

Electrolytic production of pure iron

One method of electrolytically obtaining highly pure iron (30-60 parts per million of impurities) is to extract ferric chloride with ether from solution (6-N HCl) and then reduce the ferric chloride with very pure iron to ferric chloride.
After additional purification of ferric chloride from copper by treatment with a sulfur reagent and ether, a pure solution of ferric chloride is obtained, which is subjected to electrolysis. The resulting very pure iron deposits are annealed in hydrogen to remove oxygen and carbon. Compact iron is produced by powder metallurgy - pressing into rods and sintering in a hydrogen atmosphere.

Carbonyl method of iron purification

Pure iron is obtained by the decomposition of iron pentacarbonyl Fe (CO)5 at 200-300 ° C. Carbonyl iron does not usually contain impurities accompanying iron (S, P, Cu, Mn, Ni, Co, Cr, Mo, Zn and Si). However, it contains oxygen and carbon. The carbon content reaches 1%, but it can be reduced to 3*10-2% by adding a small amount of ammonia to the iron carbonyl vapor or treating the iron powder with hydrogen. In the latter case, the carbon content is reduced to 1*10v-2%, and the oxygen impurity is reduced to “traces”.
Carbonyl iron has a high magnetic permeability of 20,000 Oe and low hysteresis (6,000). It is used for the manufacture of a number of electrical parts. Sintered carbonyl iron is so ductile that it can be deep drawn. By thermal decomposition of iron carbonyl vapor, iron coatings are obtained on various surfaces heated to a temperature above the decomposition point of pentacarbonyl vapor.

Purification of iron by zone recrystallization

The use of zone melting for iron purification has given good results. During zone refining of iron, the content of the following impurities is reduced: aluminum, copper, cobalt, titanium, calcium, silicon, magnesium, etc.
Iron containing 0.3% C was purified using the floating zone method. Eight passes of the zone at a speed of 0.425 mm/min after vacuum melting resulted in an iron microstructure free of carbide inclusions. During six passes of the zone, the phosphorus content decreased by 30 times.
The ingots after zone melting had high tensile ductility even in the region of helium temperatures. As the purity of iron increased, the oxygen content decreased. During multiple zone refining, the oxygen content was 6 ppm.
According to the work, zone melting of electrolytic iron was carried out in an atmosphere of purified argon. The metal was in a boat made of calcium oxide. The zone moved at a speed of 6 mm/h. After nine passes of the zone, the oxygen content decreased from 4*10v-3% to 3*10v-4% at the beginning of the ingot; sulfur - from 15*10v-4 to 5*10v-4%, and phosphorus - from 1-2*10v-4 to 5*10v-6%. The ability of iron to absorb cathode hydrogen decreased as a result of zone melting from (10-40) * 10v-4% to (3-5) * 10v-4%.
The rods, made from carbonyl iron purified by zone melting, had extremely low coercivity. After one passage of the zone at a speed of 0.3 mm/min, the minimum value of the coercive force in the rods was 19 me and after a five-time pass it was 16 me.
The behavior of carbon, phosphorus, sulfur and oxygen impurities during zone smelting of iron was studied. The experiments were carried out in an argon environment in a horizontal furnace, heated by an inductor, on an ingot 300 mm long. The experimental value of the equilibrium carbon partition coefficient was 0.29; phosphorus 0.18; sulfur 0.05 and oxygen 0.022.
The diffusion coefficient of these impurities was determined to be equal for carbon 6*10v-4 cm21 sec, phosphorus 1*10v4 cm2/sec, sulfur 1*10v-4 cm2/sec and for oxygen 3*10v-4 cm2)sec, the thickness of the diffusion layer is accordingly equaled 0.3; 0.11; 0.12 and 0.12 cm.

Known to mankind was of cosmic origin, or, more precisely, meteorite. It began to be used as an instrumental material approximately 4 thousand years BC. The technology of metal smelting appeared several times and was lost as a result of wars and unrest, but, according to historians, the Hittites were the first to master smelting.

It is worth noting that we are talking about iron alloys with a small amount of impurities. It became possible to obtain chemically pure metal only with the advent of modern technologies. This article will tell you in detail about the features of metal production by direct reduction, flash, sponge, raw material, hot briquetted iron, and we will touch on the production of chlorine and pure substances.

First, it’s worth considering the method of producing iron from iron ore. Iron is a very common element. In terms of content in the earth's crust, the metal ranks 4th among all elements and 2nd among metals. In the lithosphere, iron is usually presented in the form of silicates. Its highest content is observed in basic and ultrabasic rocks.

Almost all mining ores contain some amount of iron. However, only those rocks in which the proportion of the element is of industrial importance are developed. But even in this case, the amount of minerals suitable for development is more than large.

First of all, this iron ore– red (hematite), magnetic (magnetite) and brown (limonite). These are complex iron oxides with an element content of 70–74%. Brown iron ore is more often found in weathering crusts, where it forms so-called “iron hats” up to several hundred meters thick. The rest are mainly of sedimentary origin.
Very common iron sulfide– pyrite or sulfur pyrite, but it is not considered iron ore and is used for the production of sulfuric acid.
Siderite– iron carbonate, includes up to 35%, this ore is medium in element content.
Marcasite– includes up to 46.6%.
Mispickel– a compound with arsenic and sulfur, contains up to 34.3% iron.
Lellingit– contains only 27.2% of the element and is considered a low-grade ore.

Mineral rocks are classified according to their iron content as follows:

rich– with a metal content of more than 57%, with a silica content of less than 8–10%, and an admixture of sulfur and phosphorus of less than 0.15%. Such ores are not enriched and are immediately sent to production;
medium grade ore includes at least 35% of the substance and needs to be enriched;
poor iron ores must contain at least 26%, and are also enriched before being sent to the workshop.

The general technological cycle of iron production in the form of cast iron, steel and rolled products is discussed in this video:

Mining

There are several methods for extracting ore. The one that is found most economically feasible is used.

Open development method- or career. Designed for shallow mineral rock. For mining, a quarry is dug to a depth of up to 500 m and a width depending on the thickness of the deposit. Iron ore is extracted from the quarry and transported by vehicles designed to carry heavy loads. As a rule, this is how high-grade ore is mined, so there is no need to enrich it.
Shakhtny– when the rock occurs at a depth of 600–900 m, mines are drilled. Such development is much more dangerous because it involves underground blasting: the discovered layers are blasted, and then the collected ore is transported upward. Despite its dangers, this method is considered more effective.
Hydro production– in this case, wells are drilled to a certain depth. Pipes are lowered into the mine and water is supplied under very high pressure. The water jet crushes the rock, and then the iron ore is lifted to the surface. Borehole hydraulic production is not widespread, as it requires high costs.

Iron production technologies

All metals and alloys are divided into non-ferrous (like, etc.) and ferrous. The latter include cast iron and steel. 95% of all metallurgical processes occur in ferrous metallurgy.

Despite the incredible variety of steels produced, there are not so many manufacturing technologies. Besides, cast iron and steel are not exactly 2 different products, cast iron is a mandatory preliminary stage in the production of steel.

Product classification

Both cast iron and steel are classified as iron alloys, where the alloying component is carbon. Its share is small, but it gives the metal very high hardness and some brittleness. Cast iron, because it contains more carbon, is more brittle than steel. Less plastic, but has better heat capacity and resistance to internal pressure.

Cast iron is produced by blast furnace smelting. There are 3 types:

gray or cast– obtained by slow cooling method. The alloy contains from 1.7 to 4.2% carbon. Gray cast iron can be easily processed with mechanical tools and fills molds well, which is why it is used for the production of castings;
white– or conversion, obtained by rapid cooling. The share of carbon is up to 4.5%. May include additional impurities, graphite, manganese. White cast iron is hard and brittle and is mainly used for making steel;
malleable– includes from 2 to 2.2% carbon. Produced from white cast iron by long-term heating of castings and slow, long-term cooling.

Steel can contain no more than 2% carbon; it is produced in 3 main ways. But in any case, the essence of steelmaking comes down to annealing unwanted impurities of silicon, manganese, sulfur, and so on. In addition, if alloy steel is produced, additional ingredients are introduced during the manufacturing process.

According to purpose, steel is divided into 4 groups:

construction– used in the form of rental without heat treatment. This is a material for the construction of bridges, frames, the manufacture of carriages, and so on;
mechanical engineering– structural, belongs to the category of carbon steel, contains no more than 0.75% carbon and no more than 1.1% manganese. Used to produce a variety of machine parts;
instrumental– also carbon, but with low content manganese – no more than 0.4%. It is used to produce a variety of tools, in particular metal-cutting ones;
special purpose steel– this group includes all alloys with special properties: heat-resistant steel, stainless steel, acid-resistant and so on.

Preliminary stage

Even rich ore must be prepared before smelting cast iron - freed from waste rock.

Agglomeration method– the ore is crushed, ground and poured along with coke onto the belt of the sintering machine. The tape passes through burners, where the temperature ignites the coke. In this case, the ore is sintered, and sulfur and other impurities burn out. The resulting agglomerate is fed into bunker bowls, where it is cooled with water and blown with an air stream.
Magnetic separation method– the ore is crushed and fed to a magnetic separator, since iron has the ability to be magnetized, minerals, when washed with water, remain in the separator, and waste rock is washed away. Then the resulting concentrate is used to make pellets and hot briquetted iron. The latter can be used to prepare steel, bypassing the stage of producing cast iron.

This video will tell you in detail about the production of iron:

Iron smelting

Pig iron is smelted from ore in a blast furnace:

prepare the charge - sinter, pellets, coke, limestone, dolomite, etc. The composition depends on the type of cast iron;
The charge is loaded into the blast furnace using a skip hoist. The temperature in the oven is 1600 C, hot air is supplied from below;
At this temperature, iron begins to melt and coke begins to burn. In this case, the reduction of iron occurs: first, when burning coal, they obtain carbon monoxide. Carbon monoxide reacts with iron oxide to produce pure metal and carbon dioxide;
flux - limestone, dolomite, is added to the charge to convert unwanted impurities into a form that is easier to eliminate. For example, silicon oxides do not melt at such low temperatures and it is impossible to separate them from iron. But when interacting with calcium oxide obtained by the decomposition of limestone, quartz turns into calcium silicate. The latter melts at this temperature. It is lighter than cast iron and remains floating on the surface. Separating it is quite simple - the slag is periodically released through tap holes;
Liquid iron and slag flow through different channels into ladles.

The resulting cast iron is transported in ladles to a steelmaking shop or to a casting machine, where cast iron ingots are produced.

Steelmaking

Turning cast iron into steel is done in 3 ways. During the smelting process, excess carbon and unwanted impurities are burned off, and necessary components are also added - when welding special steels, for example.

Open hearth is the most popular production method, as it provides high quality steel. Molten or solid cast iron with the addition of ore or scrap is fed into an open-hearth furnace and melted. The temperature is about 2000 C, maintained by the combustion of gaseous fuel. The essence of the process comes down to burning carbon and other impurities from iron. The necessary additives, when it comes to alloy steel, are added at the end of smelting. The finished product is poured into ladles or into ingots into molds.

Oxygen-envelope method - or Bessemer. Features higher performance. The technology involves blowing compressed air through the thickness of cast iron at a pressure of 26 kg/sq. cm. In this case, the carbon burns, and the cast iron becomes steel. The reaction is exothermic, so the temperature rises to 1600 C. To improve product quality, a mixture of air and oxygen or even pure oxygen is blown through the cast iron.
The electric melting method is considered the most effective. Most often it is used to produce multi-alloy steels, since the smelting technology in this case eliminates the ingress of unnecessary impurities from air or gas. The maximum temperature in the iron production furnace is about 2200 C due to the electric arc.

Direct Receipt

Since 1970, the method of direct reduction of iron has also been used. The method allows you to bypass the costly stage of producing cast iron in the presence of coke. The first installations of this kind were not very productive, but today the method has become quite well known: it turned out that natural gas can be used as a reducing agent.

The raw materials for recovery are pellets. They are loaded into a shaft furnace, heated and purged with a gas conversion product - carbon monoxide, ammonia, but mainly hydrogen. The reaction occurs at a temperature of 1000 C, with hydrogen reducing iron from the oxide.

We will talk about manufacturers of traditional (not chlorine, etc.) iron in the world below.

Famous manufacturers

The largest share of iron ore deposits is in Russia and Brazil – 18%, Australia – 14%, and Ukraine – 11%. The largest exporters are Australia, Brazil and India. The peak price of iron was observed in 2011, when a ton of metal was estimated at $180. By 2016 the price had dropped to $35 per ton.

The largest iron producers include the following companies:

Vale S.A. is a Brazilian mining company, the largest producer of iron and;
BHP Billiton is an Australian company. Its main direction is oil and gas production. But at the same time, it is also the largest supplier of copper and iron;
Rio Tinto Group is an Australian-British concern. Rio Tinto Group mines and produces gold, iron, diamonds and uranium;
Fortescue Metals Group is another Australian company specializing in ore mining and iron production;
In Russia, the largest producer is Evrazholding, a metallurgical and mining company. Also known on the world market are Metallinvest and MMK;
Metinvest Holding LLC is a Ukrainian mining and metallurgical company.

The prevalence of iron is great, the extraction method is quite simple, and ultimately smelting is an economically profitable process. Together with physical characteristics production and provides iron with the role of the main structural material.

The production of ferric chloride is shown in this video:

Send your good work in the knowledge base is simple. Use the form below

Students, graduate students, young scientists who use the knowledge base in their studies and work will be very grateful to you.

Posted on http://www.allbest.ru/

Processes for direct extraction of iron from ores

Steel production
Essence of the process
Steel smelting methods
Bibliography

Steel production

Processes for direct extraction of iron from ores

Direct iron production processes 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 tested in various ways, but only a few have been implemented and, moreover, on a small industrial scale.

IN last 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. 1.

steel sponge iron open hearth furnace

Rice. 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 hopper 1 to screen 2 enter box 10 of the charge filling machine and from there into the shaft furnace 9 , operating on the counterflow principle. Spill from the pellets enters hopper 3 with a briquetting press and is again supplied to the screen in the form of pellets. To recover iron from the pellets, a mixture of natural and blast furnace gases, subjected in installation 7, is supplied to the furnace through pipeline 8 conversion, as a result of which the mixture decomposes into hydrogen and carbon monoxide. In the reduction zone of furnace B 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 m3.

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 ground, obtaining iron powder with an iron content of up to 99%, carbon - 0.1...0.2%.

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).

The content of carbon and impurities in steel is significantly lower than in cast iron. Therefore, the essence of any metallurgical conversion of cast iron into steel is to reduce the content of carbon and impurities by selectively oxidizing them and converting them into slag and gases during the smelting process.

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. For this purpose, it is advisable to carry out smelting in the main furnace, which contains slag. 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 interacts 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.

When melting, an increase in the oxygen content in the metal is necessary for the oxidation of impurities, but in finished steel oxygen is 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 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, which have a greater affinity for oxygen than iron (), are 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.) in 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.

Rice. 2. Scheme of an open hearth furnace

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 into 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 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.

Melting duration is 3...6 hours, for large furnaces - up to 12 hours. The finished melt is released through a hole located in back wall on lower level Poda. 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 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. Oxides form slag with high content oxides of iron and manganese (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 mixture must contain excess carbon. At this stage, the metal is brought to the specified level 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 steels, low- and medium-alloy steels (manganese, chromium), are smelted, except for 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.

Steels contain less hydrogen and oxygen and non-metallic inclusions. Consequently, acid steel has higher mechanical properties, especially impact strength and ductility, and is used for particularly critical parts: crankshafts of large engines, rotors of powerful turbines, ball bearings.

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.

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.

The 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. 3.

Rice. 3. 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. (3. a), cast iron is poured at a temperature of 1250...1400 0 C (Fig. 3. b).

After this, the converter is turned to the working position (Fig. 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%). At increased content To remove phosphorus, 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. 3. d), where it is deoxidized using the precipitation method with ferromanganese, ferrosilicon and aluminum, then the slag is drained (Fig. 3. e).

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.

Melting in converters with a capacity of 130...300 tons ends in 25...30 minutes.

Bibliography

1. Materials science and metal technology: Textbook for universities on mechanical engineering specialties / G.P. Fetisov, M.G. Karpman, V.M. Matyunin and others - M.: graduate School, 2000. - 637 pp.: ill.

2. Materials science: Textbook for universities teaching in the field of training and specialization in the field of engineering and technology / B.N. Arzamasov, V.I. Makarova, G.G. Mukhin et al. - 5th ed., stereotype. - M.: Publishing house of MSTU im. N.E. Bauman, 2003. - 646 pp.: ill.

3. Lakhtin Yu.M., Leontyeva V.N. Materials Science. Textbook for technical universities. specialist. - 3rd ed. - M. Mechanical Engineering, 2000. - 528 p.

4. Technology of structural materials: Textbook for students of mechanical engineering universities / A.M. Dalsky, T.M. Barsukova, L.N. Bukharkin and others; Under general ed.A.M. Dalsky. - 5th ed., rev. - M. Mechanical Engineering, 2003. - 511 p.: ill.

5. Technology of structural materials. A textbook for students of mechanical engineering specialties at universities in 4 hours. Edited by D.M. Sokolova, S.A. Vasin, G. G Dubensky. - Tula. Publishing house of Tula State University. - 2007.

6. Materials science and technology of structural materials. Textbook for universities / Yu.P. Solntsev, V.A. Veselov, V.P. Demyantsevich, A.V. Kuzin, D.I. Chashnikov. - 2nd ed., revised, additional. - M. MISIS, 2006. - 576 p.

7. Bogodukhov S.I. Materials science course in questions and answers: Proc. manual for universities, educational. in the direction of preparation. Bachelor's degree in "Technology, equipment and automatic machine building production" and specialization. “Mechanical engineering technology”, “Metal-cutting machines and tools”, etc. / S.I. Bogodukhov, V.F. Grebenyuk, A.V. Sinyukhin. - M.: Mechanical Engineering, 2003. - 255 pp.: ill.

8. Kolesov S.N. Materials science and technology of structural materials: Textbook for students of electrical engineering and electromechanical specialists. Universities / S.N. Kolesov, I.S. Kolesov. - M. Higher School, 2004. - 518 p.: ill.

9. Materials science. Technology of construction materials: tutorial for university students, training. for example "Electrical engineering, electromechanics and electrical technology" / A.V. Shishkin and others; edited by V.S. Cherednichenko. - 3rd ed., erased. - M.: OMEGA-L, 2007. - 751 p.: ill. (Higher technical education). - (Tutorial)

10. Drits M.E., Moskalev M.A. Technology of structural materials and materials science: Proc. for students of non-mechanical engineering specialties. Universities. - M.: Higher School, 2005. - 446 p., ill.

11. Tarasov V.L. Technology of structural materials: Textbook. for universities according to special needs "Woodworking technology" / Moscow. state University of Forests. - M.: Publishing house Mosk. state University of Forests, 2006. - 326 p.: ill.

Posted on Allbest.ru

...