How steel is made from cast iron

Iron and steel production

Metals and alloys according to their chemical composition are divided into non-ferrous (copper, aluminum, lead, bronze, brass, etc.) and ferrous (iron, steel, cast iron). Metals are rarely used in their pure form, but mostly in the form of alloys.

Cast iron and steel are alloys of iron and carbon , in which the presence of impurities of other chemical elements is inevitable:

 Steel: Fe + C (< 2%) + impurities (relatively few);

Cast iron: Fe + C (> 2%) + impurities (more than steel).

What are the similarities and what are the differences (Table 1.3) between these alloys?

The basis is one - iron. The main difference is that cast iron has a high carbon content (over 2% in cast iron and up to 2% in steel). The boundary between these alloys is based on the carbon content in the alloy. Many cast irons also contain more manganese, sulfur, phosphorus and silicon.

Steel is often harder, stronger and more wear-resistant. Cast iron is more brittle, but has good casting properties. Steel is a derivative of cast iron. Its production is mainly two-stage: first, cast iron is obtained from iron ores, then steel is obtained from cast iron and scrap steel.

Table 1.3 Comparative indicators of cast irons and steels

№	The name of indicators	Cast iron	Steel
1	carbon,%	> 2%	< 2%
2	S, P, Mn, Si	A lot of *	less
3	Structure	ice drill.	austenite, ferrite,
4	Fragility	more fragile *
5	Hardness	harder *
6	Strength	higher *
7	Ductility	higher *
8	Foundry properties	higher
9	Manufactured parts	frames, housings,	shafts, gears,
10	Manufacturing technology	casting and mechanics processing	rolling and fur. arr.

 * - more often.

Iron in ore is in the form of oxides, oxides, carbonates and other chemical compounds. In addition, the ore contains a lot (up to 30–60%) of waste rock: quartzite (sand), clayey substances, etc.

Main iron ores:

1. Magnetic iron ore Fe O - oxide (up to 65% iron). (Sokolovskoye and Sarbaiskoye fields, Kursk magnetic anomaly)

2. Red iron ore Fe O - oxide (up to 60% iron). (Krivoy Rog field, Kursk magnetic anomaly)

3. Brown iron ore n Fe O x mH 2 O - carbonate (up to 55% iron). (Lisakovskoye field)

4. Spar iron ore Fe CO 3 - carbon dioxide salt (up to 40% iron). (Krivoy Rog field)

Almost half of the world's proven iron reserves are located in the CIS countries. The former USSR produced and produced more iron and steel than anyone else in the world.

The reasons for this “achievement” were: imperfect designs and low reliability of machinery and equipment; low quality of smelted cast iron and steel; huge territories; large length of roads and communications; low efficiency of agricultural production, construction and road work.

All this required much more metal than in other countries. And besides, there was more metal buried in the ground at construction sites, abandoned in landfills, in forests, swamps and fields than anyone else in the world.

Historically, the production of ferrous metals developed in the following stages:

1. Cheese-making process (1500 BC). The productivity of the process is very low; only up to 0.5–0.6 kg of iron was obtained in 1 hour. In forges, iron was reduced from ore with coal when blown with air (Fig. 1.19) using blacksmith bellows.

Carbon monoxide was initially produced when charcoal burned.

C + O2 Ù CO,

which restored pure iron from ore

CO + Fe Ù Fe + C O2.

As a result of long-term air blowing from pieces of ore, pieces of pure iron were obtained, practically free of impurities, which were welded together using a forge into strips, which were then used to produce products necessary for humans.

This technically pure iron contained very little carbon and few impurities (pure charcoal and good ore), so it forged and welded well and practically did not corrode. The process took place at a relatively low temperature (up to 1100-1350 ° C), the metal did not melt, i.e., the reduction of the metal took place in the solid phase. The result was malleable iron.

This method existed until the 14th century, and in a slightly improved form until the beginning of the 20th century, but was gradually replaced by critical redistribution.

It follows that historically the very first metal welder was a blacksmith, and the very first welding method was forge welding.

2. With the increase in the size of the cheese furnaces and the intensification of the process, the carbon content in iron increased, the melting point of this alloy (cast iron) turned out to be lower than that of purer iron, and part of the metal was obtained in the form of molten cast iron, which, as a production waste, flowed out of the furnace along with the slag .

In the 14th century, a two-stage method for producing iron was developed in Europe (a small blast furnace, then a furnace process). Productivity increased to 40-50 kg/hour of iron. A water wheel was used to supply air. Critical processing is the process of refining cast iron (reducing the amount of C, Si, Mn) in order to obtain cast iron (welding) iron.

3. At the end of the 18th century in Europe, mineral fuels began to be used in the blast furnace process and in the puddling process. In the puddling process, coal is burned in a furnace, gas passes through the bath, melts and purifies the metal. In China, even earlier, in the 10th century, cast iron was smelted, and then steel was obtained by the process of puddling. Pudding is the cleaning of cast iron in a fiery furnace.

During cleaning, iron grains collect into clumps. The pudliner turns the mass over and over with a crowbar and divides it into 35 parts - krits. In a forge or rolling machine, grains are welded to produce strips and other blanks. Steam engines are already used instead of a water wheel. Productivity increases to 140 kg of wrought iron per hour.

4. At the end of the 19th century, three new processes for producing steel were introduced almost simultaneously: Bessemer, open-hearth and Thomas. Steel melting productivity increases sharply (up to 6 tons/hour).

In the middle of the 20th century: oxygen blasting, process automation and continuous casting of steel were introduced.

During the cheese-blowing, krichny and puddling processes, iron did not melt (the technical level of that time did not make it possible to ensure its melting temperature). Blowing oxygen through the molten metal in a Bessemer converter, due to the sharp increase in the contact surface of the metal with the oxidizing agent (oxygen), accelerates chemical reactions a thousand times compared to a puddling furnace.

In the cheese-blowing and casting processes, malleable, wrought iron (low-carbon steel) was obtained in a single-stage method, which had a small amount of impurities and was therefore very resistant to corrosion. Currently, a single-stage steel production process is under development: ore beneficiation (production of pellets containing 90–95% iron) and steel smelting in an electric furnace.

Modern production of cast iron and steel is carried out according to the following scheme (Fig. 1.20).

Iron production

Cast iron is smelted in blast furnaces. This is a complex engineering structure that operates continuously for 5..10 years.

The oven operates on the counterflow principle. Ore, fluxes and coke are loaded from above, and air is supplied from below. Coke serves to heat and melt the ore, and also participates in the reduction of iron from ore oxides. Coke should contain a minimum of sulfur and phosphorus.

 Fluxes (limestones, silicas) are necessary to obtain slags. When fuel is burned, carbon monoxide is formed, which is the main reducing agent for iron.

The reduction of iron occurs from higher oxides to lower ones and, ultimately, to the metal:

Fe2 O3 ® Fe3 O4 ® Fe O ® Fe

carbon monoxide CO and solid carbon C. The reduction of manganese, silicon and other elements is also carried out with coke.

The products of blast furnace production are:

pig iron containing 44.5% C, 0.60.8% Si, 0.251.0% Mn, up to 0.3% S and up to 0.05% P;

cast iron containing about 3% Si;

ferroalloys: ferrosilicon (9-13% Si) and ferromanganese (70-75% Mn), intended for deoxidation and alloying of steels;

slag used for the production of slag wool, cinder blocks, and cement.

Steel production

To obtain steel from cast iron, it is necessary to reduce the amount of carbon, manganese, sulfur and phosphorus in it. Steel is produced in oxygen converters, open-hearth furnaces and electric furnaces.

The converter (Fig. 1.21) is a pear-shaped vessel, lined inside with refractory bricks and suspended on two brackets.

Liquid cast iron (1250-1400 °C), obtained in a blast furnace, is poured into a converter using a ladle. To obtain slag, iron ore and lime, bauxite and fluorspar are added to the converter. Air is supplied to the converter from below, or oxygen is supplied from above. The process of producing steel occurs quickly, with three periods clearly visible (Fig. 1.22).

In the first 4-5 minutes of the process, iron is oxidized

Fe + O2 ® FeO.

Next, the resulting iron oxide oxidizes silicon and manganese:

Source: http://www.npokz.ru/tekhnicheskaja-informatsija/svarka-metallov/proizvodstvo-chuguna-i-stali/

Steel: steel production, process and methods. Steel production technology

Steel products, even against the backdrop of the active spread of high-strength plastics, retain their position in the market. Carbon alloys with different characteristics are used in instrument and automotive industries, construction and manufacturing.

The unique combination of elasticity and strength makes the material beneficial in terms of long-term use. Accordingly, the products last longer and are cheaper to maintain. But these are not all the advantages that steel has.

The production of steel using modern technologies makes it possible to impart the metal structure and additional properties.

General information about production technologies

The technologist’s task is to ensure a process in which the content of carbon and all kinds of impurities, such as sulfur and phosphorus, is reduced in the workpiece. The basis for the workpiece is cast iron.

It is worth noting that furnaces for the production of cast iron appeared in the Middle Ages, while the first production of steel was realized only in 1885, and to this day methods for producing the alloy are developing and improving.

Differences in approaches to the process are mainly due to the method of carbon oxidation.

Cast iron is used as the starting material. It can be applied in solid or molten form. Iron-containing products obtained by direct reduction can also be used. Almost all methods for producing steel in one form or another also involve a refining process to remove impurities. For example, converter technology ensures that they are blown out with oxygen.

Scope of application

Low-carbon alloys are widely used in various areas of industry and production.

The following groups of products are classified by profile type:

• Flat sheet metal. Corrugated, thick-sheet, thin-sheet, wide-strip, strip products.
• Equal and unequal corner profiles.
• Channels.
• Pipes, round, square, rectangular section.
• Tauris, I-beams. I-beams, wide flange, ordinary.
• Profiled metal sheet of various thicknesses.

The largest product segment is flat rolled sheets and strips. Cold stamping produces high-strength wire, springs, springs for mechanical engineering. Parts and workpieces are easily welded and are widely used in the construction industry and the automotive industry. Low-carbon alloys are used to make body parts, axles, fuel tanks, agricultural machine frames and many other parts that are constantly encountered in everyday life.

Converter method

With this method, molten cast iron can be used as a base, as well as impurities and waste in the form of ore, scrap metal and flux. Compressed air is supplied through technological holes to the prepared base, facilitating chemical reactions.

The process also involves thermal action, which causes the oxidation of oxygen and impurities. The characteristics of the furnace structure in which the steel is processed are also of particular importance. Steel can be produced in units with different linings - the most common methods of protecting structures are fire-resistant bricks and dolomite mass.

Based on the type of lining, the converter method is also divided into two other methods: Thomas and Bessemer.

Types of cast iron

As you can see, the question of how to get cast iron in a blast furnace is relatively simple. Ultimately, however, the furnace may leave a material that is slightly different in chemical composition and physical properties. All cast irons are mainly divided into two varieties: pig iron (white) and foundry cast iron (gray). The first type is used as a raw material in the production of steel. Foundry is used to produce various types of cast iron products, which are in good demand on the market.

Thomas method

A special feature of this method is the thorough processing of cast iron containing up to 2% phosphorus impurities. As for the lining technique, it is implemented using calcium and magnesium oxides. Thanks to this solution, slag-forming elements are endowed with an excess amount of oxides. The phosphorus combustion process is one of the key sources of thermal energy in this case.

By the way, the combustion of 1% phosphorus filling increases the temperature of the furnace by 150 °C. Thomas alloys have a low carbon content and are most often used as technical iron. Later, wire, roofing iron, etc. are made from it.

In addition, the production of steel (cast iron) can be used to produce phosphorous slag for further use as a fertilizer on soils with high acidity.

Half-hearted

An intermediate material between the first two varieties is half-cast iron. The carbon it contains is presented in the form of graphite and carbide in approximately equal proportions. In addition, such an alloy may contain small amounts of lideburite (no more than 3%) and cementite (no more than 1%).

The total carbon content of half cast iron ranges from 3.5 to 4.2%. This variety is used for the production of parts that are operated under conditions of constant friction. These include automobile brake pads, as well as rolls for grinding machines. To further increase wear resistance, all sorts of additives are added to the alloy.

Bessemer method

This method involves processing bases that contain small amounts of sulfur and phosphorus. But at the same time, there is also a high silicon content - about 2%. During the blowing process, silicon oxidation occurs first, which contributes to intense heat release. As a result, the temperature in the furnace rises to 1600 °C.

Iron oxidation also occurs intensively as carbon and silicon burn. With the Bessemer method, the steel production process involves the complete conversion of phosphorus into steel. All reactions in the oven occur quickly - on average 15 minutes.

This is due to the fact that oxygen blown through the cast iron base reacts with the corresponding substances throughout the entire volume. Finished steel may contain a high concentration of iron monoxide in dissolved form. This feature is one of the disadvantages of the process, since the overall quality of the metal decreases.

For this reason, technologists recommend deoxidizing alloys before casting using special components in the form of ferromanganese, ferrosilicon or aluminum.

Agglomeration process

In fact, we’ll look at how cast iron is produced below. Now let's talk about how ore is prepared for smelting directly at metallurgical plants.

If ordinary crushed material is used for smelting, the productivity of the blast furnace will drop sharply. The fact is that such a charge has a low degree of gas permeability. Therefore, before loading into the blast furnace, ore must undergo an agglomeration process.

This procedure is carried out in specialized workshops of metallurgical plants and is a process of sintering rock into pieces of a certain size most suitable for smelting cast iron. Adhesion occurs at a high temperature sufficient to easily melt the surface of the charge particles.

As a result, the latter simply stick together to form pieces. In this case, the ore is first mixed with coal. As a result of the combustion of the latter, the temperature necessary for obtaining pieces is achieved.

The agglomeration process is stimulated by passing air flows through the layer of ore with coal (from top to bottom).

Not only ore can be used to obtain sinter. Sometimes it is also made from small pieces of iron. Its alloy with what substance makes it possible to obtain cast iron will be discussed below. Of course, it is not pig iron that is used to produce this metal. Regular scrap metal is melted down into cast iron.

Production in open hearth furnaces

If in the case of the converter method of metal production, burning with air oxygen is provided, then the open-hearth method requires the inclusion of iron ores and rusty scrap in the technological process. From these materials, iron oxide oxygen is formed, which also contributes to the combustion of carbon.

The furnace itself includes a melting bath at the core of the structure, which is covered with a heat-resistant brick wall. There are also several regenerator chambers that provide preheating of the air mass and gas. Regenerating blocks are equipped with special nozzles made of fire-resistant brick.

Like converters, open-hearth smelters operate periodically. As new batches of charge, that is, the cast iron base, are laid, steel is gradually produced. The production of steel is slow, since the processing of cast iron takes about 7 hours.

But open-hearth furnaces make it possible to regulate the chemical properties of the alloy by introducing iron additives in different proportions - ore and scrap are used for this. At the final stage of metal formation, the furnace operation is stopped, the slag is drained, after which a deoxidizer is added.

By the way, alloy steels can also be produced in such a furnace.

Malleable

This alloy is a type of white cast iron, which is subjected to special firing in order to graphitize free carbon. Compared to steel, such cast iron has improved damping properties. In addition, it is not as sensitive to cuts and performs well in low temperature conditions.

We suggest you read: Why the stove smokes in a house or bathhouse and what to do in this situation » Make a fireplace

In such cast iron, the mass fraction of carbon is no more than 3.5%. In the alloy it is presented in the form of ferrite, granular pearlite containing inclusions of graphite or ferrite-pearlite. Malleable cast iron, like half-cast iron, is used mainly in the production of parts operating under conditions of continuous friction. To improve the performance characteristics of the material, magnesium, tellurium and boron are added to the alloy.

Electrothermal method

Today, electrothermal steel production is considered the most effective. Thus, in comparison with open-hearth furnaces and converters, this technique provides the possibility of more accurate control of steel quality, including through the regulation of the chemical composition.

The interaction of furnace chambers with the air environment also deserves special attention. Electrothermal steel production technology provides for minimal access to air, leading to other advantages.

For example, this allows minimizing the accumulation of iron monoxide and foreign particles in the alloy, as well as ensuring more efficient burnout of phosphorus and sulfur.

The high temperature regime at 1650 °C makes it possible to melt problematic slags that require thermal exposure at increased power. Also in electric furnaces it is possible to alloy steel with refractory metals, including tungsten and molybdenum. However, this method of producing steel also has a serious drawback. The ovens used require large amounts of energy, making this process the most expensive.

Varieties

We have already found out what cast iron is and how it is obtained, now we will understand the classification of this material. Pipe and foundry cast iron is produced using the method described above.

Pig iron is used in steel production via the oxygen converter route. This type is characterized by a low content of silicon and manganese in the alloy. Foundry cast iron is used in the production of all kinds of products. It is divided into five types, each of which will be considered separately.

Dependence of metal properties on the element base

The performance qualities of steel are determined by the set of chemical elements with which the alloy was endowed during manufacturing. One of the key components thanks to which this metal acquires its basic properties in the form of hardness and strength is carbon. The higher it is, the more reliable the steel.

Manganese and silicon do not have a special effect on the quality of the material, but their use is necessary in the manufacture of certain grades of steel to carry out the deoxidation process. Sulfur and phosphorus have a negative effect on the formation of the product. Depending on the technique used to produce it, the composition of the steel may have different concentrations of these elements.

In any case, sulfur increases the fragility of the metal, and also reduces the properties of strength and ductility. Phosphorus, in turn, gives steel cold brittleness, which during operation can be expressed as brittleness.

Source: https://instanko.ru/drugoe/izgotovlenie-stali.html

How to make steel from cast iron?

​Cast iron contains iron, carbon and various impurities that give the alloy certain properties. The mass fraction of carbon in the material must be at least 2.14%, otherwise it will not be cast iron, but steel. This element gives the alloy increased hardness, but reduces its malleability and ductility.

Therefore, cast iron is a fairly brittle material. Other permanent impurities include silicon, manganese, sulfur and phosphorus. Additional additives are introduced into some grades of cast iron, which make it possible to impart additional properties to the alloy.

Chromium, nickel, vanadium and aluminum are used as alloying elements.

The density of cast iron is 7.2 grams per cubic centimeter. This is a fairly high indicator for metals and their alloys. Cast iron is excellent for casting in the production of a variety of products for all industries. According to this indicator, it is slightly inferior to some steel grades, surpassing all other iron alloys.

The melting point of cast iron is 1200 degrees Celsius, which is 250-300 degrees lower than what is needed to melt steel. This is due to the increased carbon content and, as a consequence, its less close connection with iron atoms at the intermolecular level.

During the smelting of cast iron and subsequent crystallization, all the carbon does not have time to penetrate into the structural lattice of the iron, so the cast iron turns out to be brittle. It is not used for the production of products that will be operated under the influence of constant dynamic loads.

But it is ideal for parts that require increased strength.

Cast iron technology

Producing cast iron is a very material-intensive process that requires significant costs. It takes about 550 kilograms of coke and 900 liters of water to produce one ton of the alloy. Ore costs depend on the iron content in it.

Usually, raw materials with a mass fraction of the element of at least 70% are used, since processing poorer ores is not economically justified. Such raw materials first undergo an enrichment procedure, and only then are sent for smelting. Iron production takes place in blast furnaces.

Only about 2% of all material produced in the world is smelted in an electric furnace.

The technological process consists of several interconnected stages. At the first stage, ore is loaded into the blast furnace, which contains the so-called magnetic iron ore (a compound of divalent and trivalent iron oxides).

Ores containing hydrous iron oxide or its salts can also be used as raw materials. Along with the raw materials, coking coals are loaded into the furnace, which are designed to create and maintain high temperatures.

In addition, their combustion products take part in chemical reactions as iron reducers.

Additionally, flux is supplied to the furnace, which acts as a catalyst and helps the rocks melt faster, thereby releasing iron. It is worth noting that before entering the blast furnace, the ore undergoes special pre-treatment.

They are crushed using a crushing plant, since small particles will melt faster. It is then washed to remove all unnecessary elements that do not contain metal.

After this, the dried raw materials are fired in special ovens, which removes sulfur and other foreign elements from the compounds.

When the blast furnace is loaded and ready for operation, the second stage of production begins. After the burners start, the coke begins to heat the raw material, releasing carbon, which, passing through the air, reacts with oxygen and forms an oxide. This oxide is actively involved in the reduction of iron from compounds found in the ore. Moreover, the more gas there is in the furnace, the weaker the chemical reaction proceeds.

After reaching a certain proportion, it stops altogether. Excess gases are used as fuel to maintain the temperature in the furnace. This approach has several positive aspects. Firstly, the cost of fossil fuels is reduced, which somewhat reduces the cost of production.

And, secondly, combustion products are not released into the atmosphere, polluting it with harmful impurities, but continue to participate in the technological process.

Excess carbon mixes with the melt and, absorbed by iron, forms cast iron. All unmelted rock elements float to the surface and are removed from the material. The waste is called slag, which will then be used to produce other materials. After removing all excess particles, various additives are added to the melt if necessary. In this way, two types of alloys are produced: pig iron and cast iron.

Types of cast iron

Conversion material is used to produce steel using the oxygen converter method. This type is characterized by a low content of manganese and silicon in the alloy composition. Foundry cast iron is used to produce a variety of products. It is divided into five varieties, which are worth considering in more detail.

White cast iron is an alloy in which the excess carbon is contained in the form of cementite or carbide. It got its name from the characteristic white color in the fracture area. The mass fraction of carbon in it is more than 3%.

This material is characterized by increased fragility and fragility, so its use is very limited.

This type is used in the production of simple parts that operate under static conditions and do not bear additional load. Adding alloying additives to the alloy can improve the technical characteristics of the material. For these purposes, nickel or chromium is used, less commonly aluminum and vanadium.

This brand of this variety, which is called “sormite,” is used as a heating element in various devices. It has good resistivity and operates without problems at temperatures up to 900 degrees Celsius.

Bathtubs for domestic needs are made from white cast iron.

Gray cast iron is the most common type of material, which is used in many sectors of the national economy. In this alloy, carbon is present in the form of graphite, pearlite or ferrite-pearlite. The mass fraction of carbon is at the level of 2.5%.

The material has high strength for cast iron, therefore it is used for the production of parts that have a cyclic load of a certain level. Bushings, housings of various industrial equipment, brackets, and gears are made from it.

Graphite significantly improves the effect of lubrication and reduces the influence of friction, so that the parts have increased resistance to this type of wear. If it is necessary to operate in aggressive environments, additional elements are introduced into the gray cast iron that will allow it to withstand the negative impact.

These include nickel, chromium, molybdenum, boron, antimony, and copper. These elements help protect cast iron from the effects of corrosion.

Also, some of them increase the level of graphitization of free carbon in the alloy, which makes it possible to create a protective barrier through which no destructive elements can break through.

Half cast iron is an intermediate material between the first two varieties. It contains part of the carbon in the form of graphite, and part in the form of carbide. The alloy may also contain cementite (up to 1%) and lideburite (up to 3%) in small proportions. The mass fraction of carbon in the material is 3.5-4.2%.

This variety is used for the production of parts that will be used under conditions of constant friction. These include brake pads for the automotive industry and a variety of grinding rolls for machine tools. To increase wear resistance, alloying additives are traditionally introduced into the alloy.

Ductile iron is a type of white alloy that has been specially annealed to graphitize the free carbon in the material. This type has improved damping properties compared to steel. In addition, it is less sensitive to cuts and performs well at low temperatures.

Carbon, the mass fraction of which is up to 3.5%, is found in the alloy in the form of ferrite, ferrite-pearlite or granular pearlite interspersed with graphite. This material is used in the automotive industry for the manufacture of parts operating under constant friction.

To improve its performance characteristics, magnesium, boron and tellurium are added to the alloy.

High-strength cast iron is obtained as a result of the formation of a spherical graphite inclusion in the alloy in a metal lattice. This weakens the metal backbone of the crystal lattice and results in improved mechanical properties.

The process of formation of spherical graphite is carried out by introducing magnesium, cerium, yttrium and calcium into the alloy. According to its technical characteristics, the material is very close to high-carbon steel. It lends itself well to casting and is capable of replacing cast steel elements in mechanisms.

The high level of thermal conductivity allows this type to be used in the manufacture of heating devices and pipelines.

What difficulties is the iron industry experiencing?

The prospects for the development of the cast iron industry do not look particularly rosy. The high cost of producing one ton of material and the large amount of waste force industrialists to look for cheaper substitutes.

The rapid development of science is already making it possible to obtain better alloys at lower costs. And in conditions of global environmental danger, it is unacceptable to ignore the polluting factor in production.

Therefore, metallurgists around the world are abandoning blast furnaces in favor of electrical equipment.

But it is physically impossible to transfer iron smelting to these rails in the shortest possible time. This will require colossal financial costs that no state can bear.

So we can only wait to see how soon industrialists will be able to organize mass production of new alloys. Of course, it will not be possible to completely abandon cast iron in the coming decades, but its global production will steadily decline.

This trend has been observed over the past 5-7 years.

Source: https://varimtutru.com/kak-iz-chuguna-sdelat-stal/

Composition and structure, as well as features of cast iron production

Cast iron is an important product of ferrous metallurgy, on which the efficiency of many industries depends. We will consider the main features and methods of its production in this article.

The production of iron and steel is an important industry in the life of the country. And first, we’ll talk about the composition of the first metal.

Cast iron is made from iron ore. After production, cast iron has the following composition:

• Iron, which contains carbon.
• Manganese impurity.
• Sulfur impurity.
• Phosphorus impurity.
• Silicon impurity.

The percentage of carbon in cast iron is approximately 2.14%.

There are several types of cast iron: white and gray. Each type has an individual composition and structure.

This video will tell you about the composition of cast iron and steel, as well as the nuances of their production:

Due to the characteristics of its composition, white cast iron has a light shade. Consider the composition of white cast iron:

• Cementite (carbon is found here in this state).
• Perlite.
• Ledeburite.
• Silicon.
• Phosphorus.
• Manganese.
• Sulfur.

Gray view

Gray cast iron is missing one component (ledeburite). Gray cast iron consists of:

• Graphite (some of the carbon is present here in this form).
• Perlite.
• Silicon.
• Phosphorus.
• Manganese.
• Sulfur.

Carbon and other components

• The most important element in cast iron is, of course, carbon. Depending on its quantitative content, different types of material are obtained.
• After carbon, silicon comes in second place. Its percentage affects the softness, fluidity and casting properties of the material.
• Thanks to an element such as manganese, cast iron gains strength.
• The presence of phosphorus in the material makes it capable of quickly forming cracks in cold castings. In addition, this impurity significantly reduces the mechanical properties of cast iron. Phosphorus makes cast iron hard and very durable. But such cast iron is not used for the production of parts that require increased strength.
• The most harmful impurity is sulfur. Its presence negatively affects the refractoriness and fluidity of the material.

If you break white and gray cast iron, you can see completely different structures.

Visually, the structure of gray cast iron can be represented as a metal matrix with graphite crystals. The matrix can have a completely different appearance. There are:

• Ferritic type (there is no bound carbon in the structure).
• Ferrite-pearlite type (there is bound carbon in an amount of up to 0.8%).
• Pearlite type (carbon amount 0.8%).

Structures are affected by temperature. In the case of rapid cooling, a pearlite structure is obtained, and in the case of slow cooling, a ferritic structure is obtained.

Graphite

Depending on the form of graphite, they are distinguished:

• Malleable cast iron (graphite crystals are flaky).
• Ductile iron (graphite crystals are spherical).
• Ordinary gray cast iron (graphite has a lamellar shape).

Graphite can be incorporated into the structure of gray cast iron in various ways. Depending on this, cast iron is:

• With a nest-like structure.
• With a needle-like structure.
• With a plate-like rectilinear structure.
• With a lamellar swirl structure.

If we compare white and gray cast iron, then gray is the most used. White cast iron is difficult to cut and is difficult to cast. In addition, it is characterized by hardness and fragility.

Chemical composition

Cast irons can be manufactured according to their intended purpose. Depending on the purpose and specific chemical composition, cast irons are:

1. High strength . High-strength cast iron is produced by introducing special additives into gray cast iron (liquid state). It is used for very important parts. Ductile iron is often used to replace steel.
2. Malleable . Malleable cast iron is obtained from white cast iron. Heat treatment is used for production. Malleable cast iron has good toughness, high ductility, increased resistance to impact and stretching.
3. Alloyed . Alloy cast iron contains almost all elements. That is, it contains titanium, chromium, nickel, and sulfur. The material is wear-resistant, hard and durable. This type of cast iron is mainly used for the production of machine parts with high mechanical properties. Depending on the predominant element, cast irons are nickel, chromium and titanium.
4. Special (ferroalloys). Special cast iron contains a high content of several elements: silicon and manganese. Such cast irons are mainly used for melting steel and make it possible to remove harmful impurities (oxygen) from steel.

Next, foundry, blast furnace and other processes in the production of cast iron are considered, and the source materials for this are also indicated.

This video will tell you about the production of iron and steel:

To produce cast iron, a huge blast furnace is required. The overall dimensions of this furnace are impressive: height 30 meters, internal diameter 12 meters.

• The widest part of the blast furnace is called steam.
• The lower part is called the forge (hot air enters the oven through it).
• The uppermost part of a blast furnace is called the shaft. It has an upper hole, which is called a Kalashnik. The Kalashnik is closed with a special bolt.

The operation of a blast furnace is based on counterflow. Air is supplied from below, and materials (coke, fluxes and ore) are charged from above. Coke is needed to heat, melt and reduce ore. Without flux, slag cannot form. And ore is the main raw material for the production of cast iron.

In addition to the blast furnace, for the production of cast iron you will definitely need:

• trolleys,
• special crane,
• bunkers,
• conveyors
• and more, in the conditions of a metallurgical plant.

Set of substances

The composition of iron ore includes ore substance and waste rock, which consists of: sandstone with an admixture of clay substances, quartzite, limestone and dolomite. Ore matter refers to iron carbonates, oxides and silicates.

The ore may contain varying amounts of ore matter. Depending on this, she can be rich or poor. Low-grade ore is sent for beneficiation, and rich ore is immediately used in production.

Iron ores come in several types:

1. Brown iron ore . The composition includes iron in the form of aqueous oxides. The total percentage of iron is 25-50%. The waste rock of such iron ore can be siliceous-alumina and differ in clay content.
2. Red iron ore . The material has a second name - hematite. Iron in the structure of this iron ore is presented in the form of anhydrous oxide. Such iron ore contains very few harmful impurities, and the iron itself contains 45-55%. The color of the ore ranges from dark red to dark gray.
3. Magnetic iron ore . Iron is presented in the form of iron oxide and makes up 30-37% of the total amount. This ore is black or dark gray in color. Gang rock is a siliceous mass with other oxides.
4. Spar iron ore . The second name is siderite. The color of this substance is dirty gray or yellowish-white. This material is easy to restore. Ironstone oxidizes quite easily and turns into brown limestone. Iron in spar iron ore is presented in the form of carbon dioxide salt.

Manganese ores are used in the iron production process. They are added to the charge to increase the amount of manganese in the cast iron.

Read below about what substances are raw materials for the production of cast iron.

Calculation

To produce one ton of cast iron you will need:

• Three tons of iron ore.
• One ton of fuel coke.
• Flux (amount depends on the type of ore).
• Twenty tons of water.

Next, the technology of cast iron production is considered.

Technologies

Cast iron production technology consists of the following stages:

1. Ore preparation . Its essence is to re-sort the ore according to the size of the pieces and chemical composition. Large-sized ore is crushed into smaller pieces, and fractions in the form of dust or small particles, on the contrary, are agglomerated. The agglomeration process is based on agglomeration, during which the charge is sintered and a porous product is formed. Also at this stage, the procedure for enriching low-grade ores is carried out. During processing, most of the waste rock is removed and the iron content increases.
2. Fuel preparation . The coke is screened. This process removes unnecessary fines that could cause heat loss during the smelting process.
3. Preparation of fluxes . The flux is also crushed and fines are sifted out. After this, all materials are loaded into the oven.
4. Blast furnace production process . The blast furnace is filled with coke, then with an agglomerator (ore sintered with flux) and again with coke. The temperature for smelting is maintained by injecting heated air. In the forge, coke burns and carbon dioxide is formed. The CO2 passes through the coke and forms CO. Carbon monoxide reduces the bulk of the ore. When reduced, the iron becomes hard. It gradually moves into the hotter part of the blast furnace, where it dissolves carbon within itself. The result is cast iron. Liquid cast iron flows into special ladles, from where it is poured into molds or mixing containers intended for it.

The blast furnace operates in continuous mode. Simultaneously with the production of cast iron, manganese, silicon and other impurities are restored.

The final section of the article will briefly talk about the production and producers (manufacturers) of cast iron in Russia and countries around the world.

Blast furnace production of cast iron

The world's producers of cast iron account for about 900 million tons of products per year. If we compare production volumes, the leaders are: China (550 million tons of pig iron per year), then Japan (already 69 million tons), after Russia (45 million tons), India (29 million tons per year) and South Korea (27 million tons).

• In China, cast iron and steel are produced at five plants: Baotous, Baoshan, Shungan, Anshan and Wuhan.
• The largest enterprises in Russia in the field of iron processing are considered to be Magnitogorsk, Chelyabinsk Combine, Ural Steel LLC, Cherepovets Iron and Steel Works, Novokuznetsk Iron and Steel Works and others.

Blast furnace production of cast iron is discussed in detail in this video:

Source: http://stroyres.net/metallicheskie/vidyi/chyornyie/chugun/proizvodstvo-i-syire.html

What is cast iron? Properties, composition, preparation and use:

Many people know about such a material as cast iron and its strength characteristics. Today we will deepen this knowledge and find out what cast iron is, what it consists of, what types it comes in and how it is produced.

Compound

What is cast iron? It is an alloy of iron, carbon and various impurities, thanks to which it acquires the necessary properties. The material must contain at least 2.14% carbon. Otherwise, it will be steel, not cast iron. It is thanks to carbon that cast iron has increased hardness. At the same time, this element reduces the ductility and malleability of the material, making it brittle.

In addition to carbon, cast iron necessarily includes: manganese, silicon, phosphorus and sulfur. Some brands also contain additional additives to give the material specific properties. Commonly used alloying elements include chromium, vanadium, nickel and aluminum.

Properties of cast iron

The material has a density of 7.2 g/cm3. For metals and their alloys this is a fairly high figure. Cast iron is well suited for the production of all kinds of products by casting. In this regard, it is superior to all iron alloys except some grades of steel.

The melting point of cast iron is 1200 degrees. For steel, this figure is 250-300 degrees higher. The reason for this lies in the increased carbon content in cast iron, which causes less close bonds between iron atoms.

During the smelting of cast iron and its subsequent crystallization, carbon does not have time to fully penetrate into the structure of the iron. Therefore, the material turns out to be brittle. The structure of cast iron does not allow it to be used for the production of products that are constantly subject to dynamic loads.

But what cast iron is ideal for is for parts that must have increased strength.

Receipt

Producing cast iron is a very costly and material-intensive process. To obtain one ton of alloy, 550 kg of coke and 900 liters of water are needed. As for ore, its quantity depends on the iron content in it. As a rule, ore with a mass fraction of iron of at least 70% is used. Processing less rich ores is not economically feasible.

Before being melted down, the material is enriched. Pig iron production in 98% of cases occurs in blast furnaces.

The technological process includes several stages. First, ore is loaded into the blast furnace, which includes magnetic iron ore (a compound of di- and trivalent iron oxide). Ores that contain hydrous oxide of iron or its salts can also be used. In addition to raw materials, coking coals are placed in the furnace, which are necessary to create and maintain high temperatures. Coal combustion products, as iron reducers, also participate in chemical reactions.

Additionally, flux is supplied to the furnace, which plays the role of a catalyst. It accelerates the process of melting rocks and releasing iron. It is important to note that before entering the furnace, the ore must undergo special processing.

Since small parts melt better, it is pre-crushed in a crushing plant. The ore is then washed to remove non-metal impurities. Then the raw materials are dried and fired in ovens.

Thanks to firing, sulfur and other foreign elements are removed from it.

After the furnace is fully loaded, the second stage of production begins. When the burners are started, the coke gradually heats the raw material. This releases carbon, which reacts with oxygen to form an oxide. The latter takes an active part in the reduction of iron from compounds in the ore. The more gas accumulates in the furnace, the slower the reaction proceeds.

When the required proportion is reached, the reaction stops altogether. The excess gases subsequently serve as fuel to maintain the required temperature in the furnace. This method has several strengths. Firstly, it allows you to reduce fuel costs, which reduces the cost of the production process.

And, secondly, combustion products do not enter the atmosphere, polluting it, but continue to participate in production.

Excess carbon is mixed with the melt and absorbed by iron. This is how cast iron is made. Impurities that have not melted float to the surface of the mixture and are removed. They are called slag. Slag is used in the production of certain materials. When all excess particles are removed from the melt, special additives are added to it.

White

This alloy is characterized by the content of excess carbon in the form of carbide or cementite. The name of this species was given for the white color at the fracture site. carbon in such cast iron usually exceeds 3%. White cast iron is highly brittle and brittle, so its use is limited. This type is used for the production of parts of a simple configuration that perform static functions and do not bear heavy loads.

By adding alloying additives to white cast iron, it is possible to increase the technical parameters of the material. For this purpose, chromium or nickel is most often used, less often vanadium or aluminum. A brand with this kind of additives is called “sormite”.

It is used in various devices as a heating element. “Sormite” has a high resistivity and works well at temperatures no higher than 900 degrees. The most common use of white cast iron is in the production of household bathtubs.

Grey

This is the most common type of cast iron. It has found application in various areas of the national economy. In gray cast iron, carbon is present in the form of pearlite, graphite or ferrite-perlite.

In such an alloy the carbon content is about 2.5%. Like cast iron, this material has high strength, so it is used in the production of parts that receive cyclic loads.

Gray cast iron is used to make bushings, brackets, gears and housings for industrial equipment.

Thanks to graphite, gray cast iron reduces friction and improves the effect of lubricants. Therefore, parts made of gray cast iron are highly resistant to this type of wear. When operating in particularly aggressive environments, additional additives are introduced into the material to neutralize the negative impact.

These include: molybdenum, nickel, chromium, boron, copper and antimony. These elements protect gray cast iron from corrosion. In addition, some of them increase the graphitization of free carbon in the alloy.

Thanks to this, a protective barrier is created that prevents destructive elements from reaching the surface of the cast iron.

High strength

This type of cast iron is obtained due to the formation of spherical graphite inclusions in the metal lattice. Because of this, the metal base of the crystal lattice weakens, and the alloy acquires improved mechanical properties.

The formation of spherical graphite occurs due to the introduction of magnesium, yttrium, calcium and cerium into the material. High-strength cast iron is close in its parameters to high-carbon steel. It lends itself well to casting and can completely replace steel parts of mechanisms.

Due to its high thermal conductivity, this material can be used for the manufacture of pipelines and heating devices.

Industry challenges

Today, cast iron casting has dubious prospects. The fact is that due to high costs and large amounts of waste, industrialists are increasingly abandoning cast iron in favor of cheap substitutes. Thanks to the rapid development of science, it has long been possible to obtain higher quality materials at lower costs. Environmental protection plays a major role in this issue and does not accept the use of blast furnaces.

It will take years, if not decades, to completely convert iron smelting to electric furnaces. Why so long? Because it is very expensive, and not every state can afford it. Therefore, all that remains is to wait until mass production of new alloys is established. Of course, it will not be possible to completely stop the industrial use of cast iron in the near future. But it is obvious that the scale of its production will fall every year.

This trend began 5-7 years ago.

Conclusion

Having dealt with the question: “What is cast iron?”, we can draw several conclusions. First, cast iron is an alloy of iron, carbon and additives. Secondly, it has six types. Thirdly, cast iron is a very useful and versatile material, so for a long time its expensive production was feasible. Fourthly, today cast iron is already considered a relic of the past, and is systematically losing its position to more reliable and cheaper materials.

Source: https://www.syl.ru/article/304510/chto-takoe-chugun-svoystva-sostav-poluchenie-i-primenenie

Iron and steel production (page 1 of 4)

TOLYATTI POLYTECHNIC INSTITUTE

Faculty of Mechanical Engineering

Department of Cutting, Machines and Tools

ABSTRACT

"Technology for the production of cast iron and steel"

Student: Sergeev Andrey

Group: M – 104

Teacher: Malyshev V.I.

Tolyatti - 1999

1.Production of iron and steel.

Iron had industrial uses already before our era. In ancient times it was obtained in a plastic state in forges. The slag was separated by squeezing it out of sponge iron with hammer blows.

As iron production technology developed, the temperature at which the process was carried out gradually increased. The metal and slag began to melt; it became possible to separate them much more completely. But at the same time, the content of carbon and other impurities in the metal increased - the metal became brittle and inflexible. This is how cast iron appeared.

Later they learned to process cast iron; a two-stage method of producing iron from ore was born. In principle, it continues to this day: the modern scheme for producing steel consists of a blast furnace process, during which cast iron is obtained from ore, and steelmaking, which leads to a decrease in the amount of carbon and other impurities in the metal.

The modern high level of metallurgical production is based on theoretical research and discoveries made in various countries, and on rich practical experience. A significant share in this process belongs to Russian scientists. For example, Russian scientists were the first to widely use natural gas for blast furnace smelting.

2. Iron production.

2.1. Source materials.

Iron ores. The main source material for the production of pig iron in blast furnaces is iron ore. These include rocks containing iron in such quantities that smelting becomes economically profitable.

Iron ore consists of ore material and gangue. Ore substances are most often iron oxides, silicates and carbonates. And waste rock usually consists of quartzite or sandstone with an admixture of clay substances and, less commonly, dolomite or limestone.

Depending on the ore substance, iron ores are rich, which are used directly, and poor, which are subjected to enrichment.

Various iron ores are used in blast furnace production.

Red iron ore (hematite) contains iron in the form of anhydrous ferric oxide. It has different colors (from dark red to dark gray). The ore contains a lot of iron (45-65%) and few harmful impurities. We will recover good iron from ore.

Brown iron ore contains iron in the form of hydrous oxides. It contains 25-50% iron. The color changes from yellow to brownish-yellow. Waste rock of iron ore is clayey, sometimes siliceous-alumina.

Magnetic iron ore contains 40-70% iron in the form of ferrous oxide.

The ore has well-defined magnetic properties and is dark gray or black with various shades of color. Waste ore is siliceous with admixtures of other oxides. Iron from magnetic iron ore is more difficult to recover than from other ores.

Spar iron ore (siderite) contains iron in the form of carbon dioxide salt. This iron ore contains 30-37% iron. Siderite has a yellowish-white and dirty gray color. It oxidizes easily and turns into brown iron ore. Of all iron ores, it has the highest reducibility.

Manganese ores contain 25-45% manganese in the form of various manganese oxides. They are added to the charge to increase the amount of manganese in the cast iron.

2.2. Production of cast iron in a blast furnace.

Pig iron is smelted in huge blast furnaces, lined with refractory bricks reaching 30 m in height with an internal diameter of about 12 m.

A section of a blast furnace is shown schematically in the figure.

Its upper half is called the shaft and ends at the top with a hole - a kalashnik, which is closed by a movable column - a kalashnikov bolt. The widest part of the oven is called the steam room, and the lower part is called the hearth. through special holes in the furnace ( tuyere) .

The blast furnace is loaded first with coke, and then layer by layer with sinter and coke. Agglomerate is ore prepared in a certain way, sintered with flux. Combustion and the temperature necessary for smelting cast iron are maintained by injecting heated air or oxygen into the forge.

The latter enters a ring pipe located around the bottom of the furnace, and from it through curved tubes through tuyeres into the hearth. In the forge, coke burns, forming CO2, which, rising up and passing through layers of heated coke, interacts with it and forms CO.

The resulting carbon monoxide reduces most of the ore, turning back into CO2.

The process of ore recovery occurs mainly in the upper part of the mine. It can be expressed by the summary equation:

Fe2O3 + 3CO = 2Fe + 3CO2

The gangue in the ore is formed mainly by silicon dioxide, SiO2.

This is a refractory substance. To convert refractory impurities into more fusible compounds, flux is added to the ore. Usually CaCo3 is used as a flux. When it interacts with SiO2, CaSiO2 is formed, which is easily separated in the form of slag.

When the ore is reduced, the iron is obtained in a solid state. Gradually it descends into the hotter part of the furnace - steam - and dissolves carbon in itself; cast iron is formed. The latter melts and flows into the lower part of the hearth, and liquid slag collects on the surface of the cast iron, protecting it from oxidation. Cast iron and slag are released as they accumulate through special holes that are otherwise clogged with clay.

The gases leaving the furnace opening contain up to 25% CO. They are burned in special apparatuses - cowpers, designed to preheat the air blown into the furnace. The blast furnace operates continuously.

As the top layers of ore and coke sink, new portions are added to the furnace. The mixture of ore and coke is delivered by elevators to the upper platform of the furnace and loaded into a cast-iron funnel, closed at the bottom with a flue gate. When the shutter is lowered, the mixture enters the oven.

The operation of the furnace continues for several years until the furnace requires major repairs.

The smelting process can be accelerated by using oxygen in blast furnaces. When oxygen-enriched air is blown into a blast furnace, preheating it becomes unnecessary, which means that there is no need for bulky and complex cowpers and the whole process is simplified. At the same time, the furnace productivity increases and fuel consumption decreases. Such a blast furnace produces 1.5 times more iron and requires ¼ less coke than a conventional one.

3 Steel production.

Compared to cast iron, steel contains less carbon, silicon, sulfur and phosphorus. To produce steel from cast iron, it is necessary to reduce the concentration of substances by oxidative smelting.

In the modern metallurgical industry, steel is smelted mainly in three units: convectors, open-hearth furnaces and electric furnaces.

3.1. Steel production in converters.

The converter is a pear-shaped vessel. The upper part is called a visor or helmet. It has a neck through which liquid cast iron and steel and slag are drained. The middle part has a cylindrical shape. In the lower part there is an attached bottom, which is replaced with a new one as it wears out. An air box is attached to the bottom, into which compressed air enters.

The capacity of modern convectors is 60 - 100 tons or more, and the air blast pressure is 0.3-1.35 Mn/m. The amount of air required to process 1 ton of cast iron is 350 cubic meters.

Before pouring cast iron, the convector is turned to a horizontal position, at which the tuyere holes are above the level of the poured cast iron. Then it is slowly returned to a vertical position and at the same time a blast is applied, which prevents the metal from penetrating through the holes of the tuyeres into the air box. In the process of blowing air through liquid cast iron, silicon, manganese, carbon and partially iron burn out.

When the required carbon concentration is reached, the convector is returned to a horizontal position and the air supply is stopped. The finished metal is deoxidized and poured into a ladle.

Bessemer process. Liquid cast iron with a fairly high content of silicon (up to 2.25% and higher), manganese (0.6-0.9%), and a minimum amount of sulfur and phosphorus is poured into the converter.

Based on the nature of the reaction occurring, the Bessemer process can be divided into three periods. The first period begins after the blast is started in the converter and lasts 3-6 minutes. Small drops of liquid cast iron fly out of the converter neck along with the gases, forming sparks. During this period, silicon, manganese and partially iron are oxidized according to the reactions:

Source: https://mirznanii.com/a/170882/proizvodstvo-chuguna-i-stali