How is cast iron produced?

Cast iron

Cast iron began to be used many decades ago. This material has special performance characteristics that differ from those characteristic of steel. The production of cast iron, despite the emergence of a large number of different alloys, is established in many countries. In order to determine the properties of cast iron, one should consider the features of its chemical composition, on which certain physical qualities depend.

Cast iron

The chemical composition of cast iron is an important factor that largely determines the mechanical properties of the resulting castings. In addition, many properties are influenced by the mechanisms of primary and secondary crystallization.

carbon in cast iron can vary from 2.14 to 6.67 percent. Modern production technologies make it possible to control the concentration of all elements in the composition with high precision, thereby reducing the fragility index and increasing other performance characteristics.

Considering the chemical composition of cast iron, it should be noted that, in addition to iron and carbon, it necessarily includes the following elements:

1. Silicon (concentration no more than 4.3%). This element has a beneficial effect on cast iron, making it softer and improving its casting properties. However, too high a concentration may make the material more susceptible to plastic deformation.
2. Manganese (no more than 2%). By adding this element to the composition, the strength of the material increases significantly. However, too high a concentration can cause the structure to become brittle.
3. Sulfur is a harmful impurity that can significantly impair the performance of the material. As a rule, the concentration of sulfur in cast iron does not exceed 0.07%. Sulfur causes cracks to appear when the composition is heated.
4. Phosphorus is contained in the composition in a concentration of less than 1.2%. An increase in the concentration of phosphorus in the composition causes cracks to appear when the composition cools. In addition, this element causes deterioration of other mechanical properties.

As with many other compounds, the most important chemical element in cast iron is carbon. The type of material depends on its concentration and type. The structure of cast iron can vary significantly depending on the production technology used.

Physical properties

Cast iron has become widespread due to its attractive physical properties:

1. The cost of the material is significantly lower than the cost of other alloys. That is why it is used to create a wide variety of products.
2. Considering the density of cast iron, we note that this indicator is significantly lower than that of steel, due to which the material becomes much lighter.
3. The melting point of cast iron can vary slightly depending on its structure, but in most cases it is 1,200 degrees Celsius. Due to the inclusion of various additives in the composition, the melting point of cast iron can significantly increase or decrease.
4. When choosing a material, many pay attention to the fact that the color of cast iron may differ slightly depending on the structure and chemical composition.

The boiling point of cast iron also largely depends on the chemical composition. In order to consider the physical properties of a material, attention should be paid to each of its varieties. A different structure and chemical composition cause different physical and mechanical properties to be imparted.

Production technology

Cast iron has been smelted for several decades, which is due to its unique performance qualities. The large number of varieties of alloys determines the application of special marking rules. Marking of cast iron is carried out as follows:

1. Foundries are designated by the letter L.
2. Gray has become widespread; the combination of letters “SCH” is used to designate it.
3. Malleable is designated KCH.
4. Extreme or white is designated by the letter P.
5. Anti-friction or gray indicate ASF.
6. Alloy cast irons can have a wide variety of chemical compositions and are designated by the letter “C”.

The technology of cast iron production involves several stages that make it possible to obtain the required structure. Considering the process of producing cast iron, we note the following points:

1. Production is carried out in special blast furnaces.
2. Alloyed and heat-resistant cast iron can be obtained by using iron ore as a raw material.
3. The technology is presented in the reduction of iron oxides ore. As a result of the restructuring of the crystal lattice and changes in the structure, the output is a material called cast iron.
4. Considering production methods, we note that the features of the technology also lie in the materials used - cokes. Coke refers to natural gas or thermoanthracite, which acts as fuel.
5. The production of cast iron involves tempering iron in solid form using a special furnace. At this stage, liquid cast iron is obtained.

Equipment for the production of cast iron can vary significantly. In addition, the production technology used largely determines what kind of material will be obtained. An example is the production of ductile iron, which involves giving the structure an unusual shape.

There are quite a large number of varieties of the material in question. The classification of cast iron largely depends on the structure and chemical composition. The following types of cast iron are distinguished:

1. Grey. This type of material is characterized by low ductility and high viscosity, as well as good machinability. Carbon is contained in the form of graphite. Area of ​​application – mechanical engineering; production of wear parts. As practice shows, phosphorus concentration can vary over a fairly wide range: from 0.3 to 1.2%. Due to its special chemical composition, the material has high fluidity and is often used in artistic casting. Anti-friction cast iron is relatively inexpensive, which also determines its widespread use.
2. White. Due to the fact that in this composition carbon is presented as cementite, the structure is characterized by extreme fragility and increased hardness, as well as low casting properties and poor machinability. It is worth considering that white cast iron is used for conversion into steel or for the manufacture of malleable iron. Very often it is called the limit.
3. Half-type is characterized by increased wear resistance, which is associated with the distribution of carbon into a cementite and free base. Often this type of material is used in mechanical engineering and machine tool building.
4. Alloy. In order to give special properties to cast iron, alloying is also carried out. Alloy cast iron has increased wear resistance and corrosion resistance due to the inclusion of nickel and chromium, as well as copper. Such versions of cast iron get their name depending on how the alloying element was used in their manufacture.
5. Ductile iron is produced by introducing various elements, such as magnesium and calcium, into liquid gray cast iron. As a result of alloying, the shape of graphite changes - it resembles a sphere and does not change the crystal lattice. It is worth considering that in its properties this metal resembles carbon steel and is used mainly in the manufacture of various wear-resistant parts.
6. Malleable. It is obtained by melting white cast iron, which should be heated to a high temperature and maintained in this state. In some cases, alloying elements are added to impart special qualities to the composition. The main properties include high viscosity and an increased degree of plasticity. Widespread in the engineering industry.
7. Special. It is an alloy that contains a large amount of manganese and silicon. It is often used to remove oxygen from steel during its production or remelting, thereby lowering the melting point.

Iron casting

Each type of cast iron has its own special structure and chemical composition, which determine the scope of application.

Due to its special physical and mechanical qualities, the use of cast iron has become possible in a wide variety of areas:

1. For the production of various parts in the mechanical engineering industry. For many years, this alloy has been used in the manufacture of a wide variety of parts for internal combustion engines. At the same time, automakers change the basic properties of the material by alloying it, which is necessary to achieve unique qualities. In addition, brake pads made of this alloy have become widespread.
2. Cast iron products can withstand low temperatures. Therefore, the material is used in the production of equipment and tools that are used in harsh climatic conditions.
3. Cast iron is valued in the metallurgical field. This is due to the low cost, which largely depends on the carbon concentration and the characteristics of the resulting structure. High castability also makes the material more attractive. The resulting products are characterized by high strength and wear resistance.
4. Over the past few decades, the alloy in question has been widely used in the manufacture of sanitary equipment. This is due to high anti-corrosion abilities, as well as the possibility of obtaining products of a wide variety of shapes. Examples include cast iron bathtubs and radiators, various pipes, radiators and sinks. Despite the emergence of materials that could replace cast iron, such products are very popular. This is due to the fact that they retain their original appearance over a long period of use.
5. The alloy is also used for the manufacture of various decorative elements, which is associated with high casting qualities. An example is a railing grid, various figurines and much more.

Cast iron frying pansCast iron radiators

In addition, the scope of application depends on the following properties of the material in question:

1. Some brands have high strength, which is characteristic of steel. That is why the material is used even after the advent of modern alloys.
2. Cast iron products can retain heat for a long period. In this case, thermal energy can be distributed evenly throughout the material. These qualities began to be used in the manufacture of heating radiators or other similar products.
3. It is generally accepted that cast iron is an environmentally friendly material. That is why it is often used in the manufacture of various dishes, for example, cauldrons.
4. High resistance to acid-base environments.
5. High hygiene, since all contaminants can be easily removed from the surface.
6. The material in question is characterized by a fairly long service life, provided that the operating recommendations are followed.
7. The chemicals included in the composition cannot cause harm to health.

In conclusion, we note that the long-discovered production technology of the material in question has remained virtually unchanged for many years. This is due to the fact that a large volume of molten alloy could be obtained at relatively low cost. Today, material is often produced from scrap, which makes it possible to further reduce the cost of the resulting product.

Source: https://stankiexpert.ru/spravochnik/materialovedenie/chugun.html

The concept of cast iron, its features and nuances of use

Cast iron firmly entered our lives many years ago. It is relatively easy to produce and widely used in various fields. To have a clear understanding of this material, you need to know its features, disadvantages, advantages, chemical composition, properties, structure of cast iron and its alloys, their production and scope of application.

So, let's find out which iron-carbon alloys are called cast irons.

Concept

Cast iron is an iron-carbon alloy containing carbon, that is, it means a material that consists of an alloy of iron and carbon. The percentage of carbon in cast iron is more than 2.14%. The latter element can be included in cast iron in the form of graphite or cementite.

This video talks about the features of cast iron:

There are white and gray cast iron.

• The carbon in white cast iron is in the form of iron carbide. If you break it, you can see a white tint. White cast iron is not used in its pure form. It is added to the process of producing malleable iron.
• At a fracture, gray cast iron has a silvery tint. This type of cast iron has a wide range of uses. It lends itself well to processing with cutters.

In addition, cast irons are high-strength, malleable and with special properties.

• High-strength cast iron is used to increase the strength of the product. The mechanical properties of such cast iron allow this to be done perfectly. High-strength cast iron is obtained from gray cast iron by adding magnesium to the mass.
• Ductile iron is a type of gray iron. The name does not mean that this cast iron is easily forged. It has increased plasticity properties. It is obtained by annealing white cast iron.
• There is also a distinction between half cast iron. Some of the carbon in it is in the form of graphite, and the remaining part is in the form of cementite.

Special Features

The peculiarity of cast iron lies in the process of its production. The average melting point of different types of cast iron is 1200ºC. This value is 300 degrees less than that of steel. This is due to the very high carbon content. Carbon and iron atoms do not have a very close connection with each other.

When the smelting process takes place, carbon cannot be completely incorporated into the iron lattice. As a result, cast iron takes on the property of brittleness. It cannot be used for the manufacture of parts that will be subject to constant load.

Cast iron is a ferrous metallurgy material. Its characteristics are often compared to steel. Products made of steel or cast iron are widely used in our lives. Their use is justified. After comparing the characteristics, we can say the following about these two materials:

• The cost of cast iron products is lower than the cost of steel ones.
• Materials vary in color. Cast iron is a dark matte material, while steel is light and shiny.
• Cast iron is easier to cast than steel. But steel is easier to weld and forge.
• Cast iron is less durable than steel.
• Cast iron is lighter in weight than steel.
• Steel has a higher carbon content than steel.

Advantages and disadvantages

Cast iron, like any material, has positive and negative sides.

The advantages of cast iron include:

• Carbon in cast iron can be in different states. Therefore, this material can be of two types (gray and white).
• Certain types of cast iron have increased strength, so cast iron is sometimes placed on the same line as steel.
• Cast iron can maintain temperature for quite a long time. That is, when heated, the heat is evenly distributed throughout the material and remains in it for a long time.
• In terms of environmental friendliness, cast iron is a clean material. Therefore, it is often used to make dishes in which food is subsequently prepared.
• Cast iron is resistant to acid-base conditions.
• Cast iron has good hygiene.
• The material has a fairly long service life. It has been noticed that the longer cast iron is used, the better its quality.
• Cast iron is a durable material.
• Cast iron is a harmless material. It is not capable of causing even slight harm to the body.

The disadvantages of cast iron include:

• Cast iron will rust if it is exposed to water for a short time.
• Cast iron is an expensive material. However, this minus is justified. Cast iron is very high quality, practical and reliable. Items made from it are also high quality and durable.
• Gray cast iron is characterized by low ductility.
• White cast iron is characterized by brittleness. It is mainly used for smelting.

Properties and characteristics

Cast iron has the following properties:

1. Physical . These characteristics include: specific gravity, coefficient of linear expansion, actual shrinkage. Specific gravity varies depending on the carbon content of the material.
2. Thermal . The thermal conductivity of a material is usually calculated using the displacement rule. For solid cast iron, the volumetric heat capacity is 1 cal/cm3*oC. If cast iron is liquid, then it is approximately 1.5 cal/cm3*oC.
3. Mechanical . These properties depend on the base itself, as well as on the size and shape of the graphite. Gray cast iron with a pearlite base is considered the most durable, and the most ductile is with a ferritic base. The maximum reduction in strength is observed with the “plate” shape of graphite, and the minimum – with the “ball” shape.
4. Hydrodynamic . Viscosity in cast iron varies depending on the presence of manganese and sulfur. It also increases sharply when the temperature of cast iron passes the point where solidification begins.
5. Technological. Cast iron has excellent casting properties, resistance to wear and vibration.
6. Chemical . According to the electrode potential (in decreasing order), the structural components of cast iron are arranged in the following form: cementite - phosphide eutectic - ferrite.

Differences between cast iron and steel in chemical composition and properties

The properties of cast iron are affected by special impurities.

• Thus, the addition of sulfur can significantly reduce fluidity and reduce refractoriness.
• The addition of phosphorus simultaneously makes it possible to create a product of complex shape, but does not give it increased strength.
• The silicon impurity makes the melting point not so high and significantly improves the casting properties. Different percentages of silicon create different types of cast iron, from pure white to ferritic.
• Manganese worsens casting and technological properties, but increases strength and hardness.

In addition to the mentioned impurities, cast iron may also contain other components. Then such materials will be called alloyed. The most common materials added to cast iron are titanium, chromium, aluminum, nickel and copper.

Next, you will find out what elements are included in the chemical composition of cast iron.

The video below will show you how to weld cast iron using electric welding:

If we consider cast iron as a structural material, then it is a metal cavity with graphite inclusions. The structure of cast iron is mainly pearlite, ledeburite and ductile graphite. Moreover, for each type of cast iron these elements predominate in different proportions or are absent altogether.

According to the structure of cast iron there are:

• perlite,
• ferritic and
• ferritic-pearlitic.

Graphite is present in this material in one of the forms:

• Globular. Graphite takes on this shape when magnesium is added. The spherical shape of graphite is characteristic of high-strength cast irons.
• Plastic. Graphite is similar to the shape of petals. In this form, graphite is present in ordinary cast iron. This cast iron has increased ductility properties.
• Flaky. Graphite acquires this shape by annealing white cast iron. Graphite is found in flake form in malleable cast iron.
• Vermicular. The named form of graphite is found in gray cast iron. It was developed specifically to improve ductility and other properties.

Metal production

Cast iron is produced in special blast furnaces. The main raw material for producing cast iron is iron ore. The technological process consists of reducing the iron oxides of the ore and obtaining another material as a result - cast iron. The following fuels are used to make cast iron: coke, natural gas and thermal anthracite.

Once the ore is reduced, the iron is in a solid form. Next, it is lowered into a special part of the furnace (steam), where carbon is dissolved in the iron. The output is liquid cast iron, which falls into the lower part of the furnace.

The price of cast iron (per 1 kg) depends on the amount of carbon in it, the presence of additional impurities and alloying components. Approximately the price of a ton of cast iron will be 8,000 rubles.

Cast iron is common in many areas.

• It is used for the production of parts in mechanical engineering. Engine blocks and crankshafts are mainly made from cast iron. The latter require advanced cast iron, to which special graphite additives are added. Due to the resistance of cast iron to friction, it is used to make excellent quality brake pads.
• Cast iron can operate smoothly even at extremely low temperatures. Therefore, it is often used in the production of machine parts that will have to work in harsh climatic conditions.
• Cast iron has proven itself well in the metallurgical field. It is valued for its relatively low price and excellent casting properties. Products made from cast iron are characterized by excellent strength and wear resistance.
• A large variety of plumbing products are made from cast iron. These include sinks, radiators, sinks and various pipes. Cast iron bathtubs and heating radiators are especially famous. Some of them still serve in apartments today, although they were purchased many years ago. Cast iron products retain their original appearance and do not require restoration.
• Thanks to its good casting properties, cast iron produces real works of art. It is often used in the manufacture of artistic products. For example, such as beautiful openwork gates or architectural monuments.

Are you choosing a bath? Don't know which is better, cast iron or steel? Then this video will help you:

Source: http://stroyres.net/metallicheskie/vidyi/chyornyie/chugun/ponyatie-osobennosti.html

How is cast iron obtained? An alloy of iron with which substance produces cast iron?

Cast iron is a metal widely used in various industries, characterized by remarkable performance characteristics. The process of obtaining it is relatively simple and does not include too many steps. This material is smelted in blast furnaces - special furnaces that are something like an enlarged copy of a test tube. We’ll talk about how cast iron is made further in detail.

Mining and processing plants

The main raw material used in the production of cast iron is iron ore. It is mined in quarries in different places in our country. As you know, mined ore contains a large amount of various types of impurities.

Of course, it cannot be used for melting cast iron in such a “raw” form. Therefore, at the first stage, it goes to special enterprises - mining and processing plants. Here waste rocks are removed from it and crushed.

Then the clean ore is loaded into train cars and sent to metallurgical plants.

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.

So, let's look at how pig iron is produced in a blast furnace. The inside of a stove of this design is lined with brick. The principle of its operation is relatively simple. In the production of cast iron, in addition to sinter, coke, lime and flux are used. A mixture of these materials is prepared in a certain proportion. This is what is called a blast furnace charge. It is poured into special lifts and raised to the very top of the furnace.

In order for coke to ignite, a large amount of air enriched with oxygen is necessary. It is fed into the blast furnace from below, through special openings called tuyeres. It is blown into the furnace under very high pressure. This is necessary so that air penetrates through the layer of charge supplied from above. In this case, the flow is preheated to 600-800 degrees, otherwise the temperature inside the furnace will drop.

The cast iron obtained by straightening the charge flows down and is released out through a special hole called a taphole at intervals of approximately once every 40 minutes. Next, it is poured into large-capacity bowls and transported to steelmaking shops.

Reduction and carburization of iron in a furnace

All blast furnaces operate on the counterflow principle. At the same time, the following chemical processes alternately occur in them:

1. Iron recovery. This process occurs sequentially and looks like this: Fe2O3 - Fe3O4 - FeO - Fe. The reducing agent in this case is carbon monoxide (CO), formed by the interaction of CO2 with hot coke, as well as solid carbon of the latter.
2. Carbonization of iron. The reaction in this case looks like this: 3Fe + 2CO = Fe3C + CO2 + Q. Fe3C carbide easily mixes with solid iron, resulting in the formation of an alloy of the latter with carbon. Flowing down, it washes the pieces of coke and carbonizes even more. In addition, substances such as manganese, sulfur, silicon, etc. dissolve in it.

Thus, it becomes clear that blast furnace metal is an alloy of iron with what substance. Cast iron can be obtained simply by carburizing the charge melt.

Restoring other items

Mn, silicon, sulfur and phosphorus enter the blast furnace along with the charge in the form of various chemical compounds. Higher manganese oxides are reduced to MnO according to approximately the same principle as iron: MnO2 - Mn2O3 - Mn3O4 - MnO. Pure manganese is released as follows: MnO + C = Mn + CO - Q. Silicon enters the furnace in the form of silica SiO2. Its reduction occurs by the reaction SiO2 + 2C = Si + 2CO - Q.

Phosphorus is reduced by hydrogen, solid carbon and CO and, unfortunately, goes into cast iron almost completely. This element deteriorates the blast furnace iron alloy. Allows you to obtain good quality cast iron with silica present in the charge, as well as higher manganese oxides. In some cases, Mn is added to the blast furnace on purpose. This produces a special type of cast iron - manganese.

Wax removal

The question of how to obtain cast iron of good quality also comes down to cleaning it from this undesirable element. Sulfur is the main harmful impurity that significantly worsens the properties of the final smelting product. Its main quantity is contained in coke.

Sulfur is removed by increasing the lime (CaO) content in the charge and increasing the temperature in the furnace. The reaction in this case looks like this: FeS + CaO = FeO + CaO + Q. Other methods can be used to reduce the percentage of sulfur content in cast iron. For example, sometimes the already smelted material is processed in a discharge chute or a bowl of soda.

In this case, the removal of sulfur occurs as a result of the reaction FeS + NaCO3 = FeO + Na2S + CO2.

Slag formation

Thus, we have found out how cast iron is produced. However, when this material is smelted, another product is obtained that is widely used in the national economy. When melting 1 ton of cast iron, 0.6 tons of slag comes out. The fact is that even refined iron ore contains a fairly large amount of clay.

Coke also contains ash. To remove these unnecessary elements, among other things, fluxes (calcium and magnesium carbonates) are added to the charge. During the smelting process, they enter into a chemical reaction with various types of impurities, resulting in the formation of slag.

It is an aluminosilicate or silicate melt.

The density of slag is less than that of liquid cast iron. Therefore, during the melting process it is located underneath. It is removed periodically through a separate taphole, called a slag taphole. This by-product of iron foundries is used mainly for the production of cement and building blocks as a filler.

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.

White cast iron

The share of this type of metal smelted in blast furnaces is 75-80%. The main properties of such cast iron are: high hardness, brittleness and wear resistance. It usually contains more manganese and sulfur than foundry. White cast iron is difficult to process.

It is impossible to use conventional cutting tools of modern machines to make any products from it. But steel is obtained from cast iron of this type quite simply.

Depending on the method of further smelting, pig furnace metal is divided into three classes: open-hearth (M), Bessemer (B) and Thomas (T).

Cast iron

Carbon in this material is mainly contained in the form of free graphite, which contains silicon. It is supplied for the manufacture of cast iron products in the form of pigs. This material is marked with the letter “L” and numbers from “1” to “6”, depending on its purpose. There is also cast iron refined by magnesium, marked with the letters “LR”.

Well, we hope that we have sufficiently answered the question of what alloy of iron with what substance makes it possible to obtain cast iron. This is ordinary carbon that replaces the oxygen contained in the ore in the blast furnace. The main properties of cast iron depend on the amount of impurities included in its composition: manganese, phosphorus, silicon and sulfur.

Source: https://FB.ru/article/222584/kak-poluchayut-chugun-splav-jeleza-s-kakim-veschestvom-pozvolyaet-poluchit-chugun

Cast iron: production process, classification and marking

In the age of rapid development of the metallurgical industry and production, cast iron plays a key role. Let's figure out what kind of material this is, how it appeared, how it is produced, what properties it has, what types of classification of cast iron exist, and how it is used in various fields of industry.

Definition

Cast iron is a mixture of 2.14% carbon with iron, obtained by thermal heating in blast furnaces to 1200 degrees Celsius. With the help of the sixth element of the periodic table, iron in the form of an alloy acquires increased hardness, losing ductility and malleability, making the material brittle.

In addition to carbon, to obtain special parameters, elements such as Si, Mg, P, S are added to the metal matrix. Alloying agents are also widely used - Cr, V, Ni, Al.

Story

The technology for making cast iron came to us from China, where cast iron money circulated back in the 10th century AD. The descendants of the Mongols already prepared boilers from this alloy in the 13th century.

On the battlefields of the Hundred Years' War, artillery pieces and ammunition cast from this solid solution were used for the first time. In Russia, its widespread use in the manufacture of weapons was established in the 16th century after the appearance of the blast furnace.

In this regard, the Ural Iron Foundry was built in 1701, which became the beginning of a folk craft called “Kasli casting”.

Since the 18th century, Great Britain has been the world's leading iron producer. Thanks to Wilkinson's new technology, by the mid-19th century this country produced half the world's total.

Manufacturing technology did not stand still, which allowed the United States to take the lead at the end of the 19th century.

At that time, rails, water and sewer pipes, fireplaces, and such complex engineering structures as bridges began to be made from this alloy.

Iron production process

The production of cast iron is carried out in blast furnaces. This process is quite energy-intensive and costly production. 4 main groups of ores are used as raw materials:

• Hematite iron ore, consisting of iron anhydrite oxide, holds 70% (Fe) and 30% (O);
• Magnetite iron ore contains 72.4% (Fe), and 27.6% (O);
• Brown iron ore contains 59.8% elemental iron;
• Siderite iron ore, contains 48.3% (Fe).

The technological process takes place in several stages

First, during the preparation process, iron ore containing iron oxides (FeO and Fe2O3) of at least 40% of the total mass is crushed. Then, by crushing, screening, averaging, washing, enrichment and roasting, they get rid of non-metallic impurities - S, P, As, and increase the mass fraction of the base metal in the ore.

At the end of the preparatory stage, all components are loaded into the oven.

A blast furnace is a continuously operating metallurgical equipment in the form of a shaft, weighing 30 thousand tons. The blast furnace consists of 5 elements: the upper part in the shape of a cylinder - the furnace, the wide conical part - the shaft, the wide part - the steam chamber, the narrowed part - the shoulders and the lower part - the hearth. All components are produced from above through the furnace, and the finished product and slag come out separately from below from the furnace.

Simultaneously with the ore, coking coals are placed into the blast furnace to act as fuel. During the thermal decomposition of coals, carbon compounds are formed that act as a reducing agent. Fluxes are added to speed up the process of releasing metal from the ore. Typically these are rocks containing oxides of calcium and magnesium.

After the loading stage is completed, the smelting process begins, where the loaded components are converted into an alloy, slag and gas. The physicochemical reactions occurring in this case can be characterized as reduction-oxidation, since the reduction of iron oxides and the oxidation of the reducing agent occurs.

Processes occurring in the furnace

The processes occurring in a blast furnace can be described by the following chemical equations:

When coke is heated, elemental carbon is released, which forms carbon dioxide with oxygen.

C + O2 = CO2 + energy release

CO2, when heated, is further oxidized to carbon monoxide, and reduces elemental iron from its oxides in the ore.

CO2 + C = 2CO

Fe2O3 + 3 CO = 2Fe + 3 CO2

After the reduction reaction, the metal is saturated with carbon, and when it reaches 1150-1200°C, it flows in the form of a metal compound into the furnace. From the remains of empty ore and fluxes, waste is formed - slag, which is continuously removed.

Cast iron parameters

Density - 7.2 g/cm3. The melting point is 1200 °C. The fragility and low ductility of the alloy is due to the following factors:

1. Increased bond length between Fe atoms due to increased carbon content;
2. Incomplete introduction of carbon atoms into the structure of the iron matrix due to the low melting point compared to steel.

It is for these reasons that this solid metal solution has found wide application in the production of parts with high strength. However, it is not suitable for products subject to loads that change rapidly over time.

Classification of cast irons

There are several types of classification of cast iron.

1. Based on elemental carbon content they are divided into:
   • hypoeutectic (2.14-4.3%);
   • eutectic (4.3%);
   • hypereutectic (4.3-6.67%).
2. By type of carbon and fracture color:
   • White (C > 3%, in carbide form). Its use is limited to the production of products that are not subject to heavy loads due to its significant fragility. But when adding alloying additives containing chromium, nickel, vanadium, aluminum, its performance parameters increase;
   • Gray (C -2.5%, in the form of perlite) has good wear resistance and reduces friction. Used in the manufacture of industrial equipment parts subject to cyclic loads. When adding special additives containing Mo, Ni, Cr, B, Cb, Sb, resistance improves when used in aggressive environments;
   • Half (C – 3.5-4.2%, in the form of graphite and carbide and the presence of trace amounts of cementite and ledeburite). This type has found its application in the production of products subject to constant friction.
3. According to physical parameters, according to GOST 1412-54 and 1215-59, cast iron grades are distinguished:
   • Malleable (CC), is its white variety after special firing. At the same time, the proportion of carbon is at the level of 3.5%, and it is presented in the form of Fe2O3 or granular pearlite, with graphite inclusions. Mg, Te, B are usually added as additives to increase friction resistance. It should be noted that this brand is never forged, in the literal sense of the word;
   • High-strength (HF), is formed by interspersing spherical carbon inclusions into a metal lattice and introducing magnesium, calcium, selenium, and yttrium into the composition. Characterized by improved mechanical, thermally conductive plastic parameters.
4. By specific properties:
   • Wear-resistant;
   • Antifriction;
   • Corrosion resistant;
   • Heat resistant;
   • Non-magnetic.
5. According to the Brinell hardness scale:
   • Soft (HB less than 149);
   • Moderate hardness (HB 149-197);
   • Improved hardness (HB 197-269);
   • Hard (HB more than 269).
6. According to the value of temporary tensile strength:
   • Ordinary strength (less than 20 kgf/mm2);
   • Improved strength (20-38 kgf/mm2);
   • Maximum strength (more than 38 kgf/mm2).
7. According to magnetic characteristics:
   • Ferromagnetic - having magnetic properties, due to the high content of ferrite and cementite in the metal matrix;
   • Vapor-magnetic – having low magnetic permeability, containing additives of chromium, copper and aluminum.

Marking

According to GOST, all existing brands are designated by 2 letters and 2 numbers, with the numbers reflecting the values ​​of tensile strength (kgf/mm2) and elongation (%). For example, the numbers in the KCh-30-6 brand show a temporary resistance of 30 kgf/mm2 and a relative elongation of 6%.

By introducing special additives into the composition, the composition of the alloy is modified. Then the letter M is added to the brand name.

Areas of use

The use of different grades of cast iron depends on the metallurgical compound and its performance characteristics.

The white type is used in the production of heating elements and household sanitary ware (baths, sinks), and is also a raw material for the production of malleable varieties of solid solutions.

Gray - is part of various engine components for the engineering industry.

Malleable – in the manufacture of brake pads and parts for industrial grinding equipment. In addition, it has wide application in the textile industry in casting complex shaped spare parts for machinery. KCh is used in the manufacture of kitchen utensils, interior elements, street lamps, and railings for stairs.

The high-strength grade is used in the production of pipes, fittings for water supply, sewerage, and oil production. In addition, sectional radiators are made from it, used in central heating systems of residential buildings and administrative buildings.

Electrical panels and other components of electrical equipment are made from the ferromagnetic type, while its non-magnetic type, on the contrary, is used as an electrical insulating material.

Pig iron is used in huge quantities as a raw material in steel foundries.

Interesting Facts

According to Professor Marienbach, cast iron got its name from the Chinese word “zhugun”, which means “foundry worker”.

Cast iron cookware has long been used around the world and is very convenient for preparing various types of food.

An integral attribute of Russian folk tales is the oven, in which, in a cast iron pot - a vessel of a certain shape and cast from a given alloy, the heroes cooked the main dish - jacket potatoes.

The best pancakes are made in a cast iron skillet.

Before the advent of electric irons, housewives used heavy cast iron irons with perfectly smooth soles, heating them until red hot over a fire source.

The next stage was coal cast-iron irons, whose design resembled small stoves. To heat them, birch charcoal was placed inside. This iron even had a pipe to obtain the necessary traction.

The sewer manholes for inspection wells known to us from childhood were round in shape, cast from cast iron and were first made one hundred and fifty years ago.

Pig iron production worldwide in 2015 amounted to more than 898 million tons, which is 3% less than in 2008.

Conclusion

Having examined in detail the questions posed above, we can conclude:

1. Cast iron is an alloy of iron and carbon with the addition of special modifiers;
2. For its production, various types of ores are mined, subjected to preliminary preparation and enrichment;
3. Smelting takes place in a blast furnace, which operates continuously and represents a whole metallurgical complex of equipment;
4. Depending on the amount and forms of dissolved carbon in the metal matrix, all alloys are divided into different types and have different properties;
5. The use of various grades of cast iron directly depends on its physical and chemical parameters of the resulting alloy;
6. Despite the availability of new types of materials, cast iron cookware is still in demand among many housewives and cooks;
7. Ancient coal cast iron irons were a small stove and heated with coal, which made the ironing process very tedious and a fire hazard;
8. The production of cast iron is quite an energy-intensive and financially expensive business, so at present its volume is invariably declining throughout the world, as other modern, wear-resistant and cheap-to-manufacture composite materials are replacing it.

Source: https://SoproMats.ru/materialyi/metallyi/chugun/

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.

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.

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.

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.

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.

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.

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.

Production of iron and steel. Blast furnace. Notes – TeacherPRO

Key words of the summary: iron production, steel production, iron ore, cast iron, steel, ore, coke, calcium silicate, pyrite, blast furnace.

Iron production. blast furnace

In terms of production and consumption, iron is the most important metal. Iron is usually used in the form of alloys. The industry that produces iron and its alloys is ferrous metallurgy.

The source of iron is iron ore . The main components of the ore are iron compounds:

• Fe3O4 – magnetite (magnetic iron ore),
• Fe2O3 – hematite (red iron ore),
• Fe2O3 nH2O – limonite (brown iron ore),
• FeS2 – pyrite (iron pyrite, sulfur pyrite).

Pyrite is first burned (in the production of sulfuric acid) and the cinder (Fe2O3) is used in the production of cast iron.

The products produced are cast iron and steel.

Cast iron is an alloy of iron and carbon, in which the mass fraction of carbon is more than 2%, and also contains impurities of silicon, phosphorus, sulfur and manganese.

The production of cast iron is carried out in blast furnaces (see figure). The raw materials for production are iron ore, coke, limestone and hot air.

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, in this case with limestone.) Through special holes (tuyeres) hot air enriched with oxygen is supplied to the lower part of the blast furnace. At the bottom of the blast furnace, coke burns, forming CO2, which, rising up and passing through layers of heated coke, interacts with it and forms CO:

The ore consistently undergoes transformations:

The ore also contains waste rock, which is formed mainly by silica - SiO2. This is a refractory substance. To convert it into fusible compounds, flux is added to the ore. This is usually limestone. When it interacts with silica (SiO2), calcium silicate is formed:

CaC O3 + SiO2 = CaSiO3 + CO2 (800 ° C )

The resulting silicate is easily separated as slag.

When the ore is reduced, 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 blast furnace, and liquid slag collects on the surface of the cast iron, protecting it from oxidation. Cast iron and slag are periodically released through special openings.

When metallic iron is released in a liquid state, carbon dissolves in it relatively well. When such a solution crystallizes, cast iron is formed - an alloy of iron and carbon. It is highly brittle due to the high content of iron carbide Fe3C (cementite), which is formed as a result of side reactions:

3Fe + C = Fe3C
3Fe + 2СО = Fe3C + CO2

Cast iron contains impurities of phosphorus and sulfur. Sulfur impairs the fluidity of cast iron and causes steel to become red-brittle - brittle when heated to a red-hot temperature. Phosphorus causes cold brittleness in steel - brittleness at ordinary temperatures.

Steel production

Steel is an alloy of iron and carbon, in which the mass fraction of carbon is less than 2%.

The essence of producing steel from cast iron is to reduce the carbon content in the metal and remove impurities as completely as possible - sulfur and phosphorus, as well as to bring the content of silicon, manganese and other elements to the required limits.

There are several ways to process cast iron into steel: open hearth, Bessemer and Thomas . They differ in oxidation methods.

In the Bessemer and Thomas methods, oxidation is carried out by oxygen from air blown through the molten metal. In all processes, the carbon contained in the metal is oxidized to CO and CO2, which are removed from the reaction zone. Silicon Si, manganese Mn, chromium Cr and other metals, when oxidized, pass into slag in the form of SiO2, MnO, etc.

The mechanism of the oxidation process can be presented as follows. First of all, part of the iron is oxidized. Some of the resulting oxides dissolve in the metal and interact with impurities:

C + FeO ⇆ Fe + CO
Si + 2FeO ⇆ 2 Fe + SiO2
2 P + 5 FeO ⇆ 5 Fe + P2 O5

To maximize the removal of sulfur and phosphorus impurities, it is necessary that the main slags be obtained during the processing of cast iron; this is achieved by adding limestone or lime. Sulfur contained in cast iron in the form of FeS reacts with calcium oxide CaO:

FeS + CaO = CaS + FeO

The resulting calcium sulfide turns into slag. The resulting P2O5 also interacts with lime, forming calcium phosphate, which turns into slag:

3CaO + P2 O5 = Ca3(P O4)2

The Bessemer and Thomas methods are carried out in converters. Converters are pear-shaped devices made of special boiler steel (casing) and lined from the inside with refractory materials.

Chemistry lesson summary “Production of iron and steel. Blast furnace". Select next action:

Source: https://uchitel.pro/%D0%BF%D1%80%D0%BE%D0%B8%D0%B7%D0%B2%D0%BE%D0%B4%D1%81%D1%82 %D0%B2%D0%BE-%D1%87%D1%83%D0%B3%D1%83%D0%BD%D0%B0-%D0%B8-%D1%81%D1%82%D0% B0%D0%BB%D0%B8-%D0%B4%D0%BE%D0%BC%D0%B5%D0%BD%D0%BD%D0%B0%D1%8F/

Forging iron

Malleable cast iron is a type of cast iron obtained by heat treating white cast iron. A distinctive feature of malleable cast iron is the presence of graphite in flake form.

Which cast iron is called malleable

It must be understood that malleable cast iron is not cast iron obtained by forging. Products made of malleable cast iron can become deformed at high humidity even at room temperature. This property of malleable cast iron predetermined its name. Malleable cast iron is produced by casting. An interesting and important feature of malleable cast iron is the absence of internal stresses.

Types of cast iron

Let us recall that all cast irons are divided into the following groups:

• white;
• gray (GOST 1412);
• malleable (GOST 1215);
• high-strength (GOST 7293).

In white cast iron, carbon is present in the form of cementite. White cast irons have high hardness and wear resistance. Due to its high hardness, white cast iron is very difficult to process with metal-cutting equipment.

In gray cast iron, carbon is present in lamellar form. Gray cast irons are not as hard as white ones. Their main area of ​​application is in structures that do not experience shock loads.

In malleable cast iron, graphite is present in flake form. Ductile iron is used to make products that operate under high shock and vibration loads.

In ductile iron, graphite is present in spherical form. High-strength cast iron is produced by modifying it with magnesium, which ensures the formation of carbon in the form of balls. High-strength cast irons are similar in properties to carbon steels. Pistons, crankshafts, and various components of braking systems are made from high-strength cast iron.

Preparation of malleable cast iron

As mentioned above, malleable cast iron is obtained by heat treatment of white cast iron followed by simmering (holding at a certain temperature).

Since white cast irons have poor casting properties, during the production of malleable cast irons it is necessary to take measures aimed at reducing casting defects. For this purpose, white cast iron is overheated, and during casting, its shrinkage is taken into account, as well as changes in the dimensions of the workpieces during simmering, which is carried out at a temperature of 1350-1450 ° C.

The process of simmering malleable cast iron is carried out in special workshops, where blanks made of cast iron alloys are placed in pots that can hold up to 300 castings.

Malleable cast iron obtains maximum strength if it undergoes an annealing process in pots made of white cast iron alloyed with chromium.

Malleable cast iron is produced in electric muffle furnaces, which can flexibly regulate the temperature in the simmering mode, while the products of fuel combustion do not come into contact with the pots and the stacked workpieces.

Ductile iron grades

Malleable cast iron is marked with CN 45 - 6. The first number is the tensile strength, the second is the elongation as a percentage.

The main physical and technical parameters of a malleable cast iron alloy are standardized in GOST 1215-79.

The specific brand of CP directly depends on the conditions under which the simmering was carried out. After this operation, three classes of cast iron are obtained:

• Ferritic class contains ferrite and flake graphite:
  • CC 30-6
  • CC 33-8
  • CC 35-10
  • CC 37-12
  • The pearlite class contains pearlite and flake graphite:
    • CC 45-7
    • CC 50-5
    • CC 56-4
    • CC 60-3
    • CC 65-3
    • CC 70-2
    • CC 80-1.5
    • The ferrite-pearlite class contains ferrite, pearlite and flake graphite.

Structure of Ductile Iron

Compact graphite inclusions, which are the main feature of the microstructure of ductile cast iron, determine its high strength and ductility. Low carbon ductile iron is the only type of cast iron that can be welded. It is well pressed, hammered, easily filling gaps and voids.

Composition of malleable cast iron:

• C – 2.4-3.0%
• Si – 0.8-1.4%
• Mn – 0.3-1.0%
• P – up to 0.2%
• S – up to 0.1%

After going through the simmering process, malleable cast iron contains austenite and graphite.

With slow cooling, the cementite that is part of pearlite decomposes, and the structure takes on the appearance of ferrite and graphite (ferritic malleable cast iron).

Rapid cooling produces pearlitic ductile iron because there is no second stage of decomposition.

Application of Ductile Iron

The use of ductile iron products is due to its mechanical properties, which are between steel and gray cast iron. On the one hand, malleable cast iron has high fluidity, wear resistance, and good anti-corrosion properties. On the other hand, ductile cast irons are high-strength, which allows them to be used in the production of pipeline fittings for gas and water.

At low temperatures, malleable cast iron becomes quite brittle and is susceptible to shock loads.

Products made of malleable cast iron are widely used in mechanical engineering, automotive industry, and railway transport.

The most widely used are ferrite castings, which are cheaper to produce. Gearbox housings, hubs, hooks, brackets, clamps, couplings, and flanges are made from ferritic malleable cast iron.

Pearlitic malleable cast iron is used for the manufacture of parts operating in units under high loads. Perlite cast iron is used to make driveshaft forks, links and rollers of conveyor chains, and brake pads.

Malleable cast iron is used to produce castings with a thin wall, the size of which can range from 3 to 40 mm.

Source: http://mining-prom.ru/rud/zhelez/kovka-chuguna/

Cast iron - composition, properties and characteristics

The term “cast iron” can mean both a structural material based on iron and a metal vessel, a round pot for cooking. The latter is rare. Modern dishes are crowding.

The word “cast iron” is completely outdated. This is what the railway was called in the 19th and early 20th centuries.

What is cast iron

This is an alloy of iron and carbon with a carbon content of 2.14%. Ideally. In fact, in addition to those indicated, there are always impurities and alloying elements. So the distinction “floats”.

Depending on the carbon content relative to the eutectic, metal varieties are distinguished. Eutectic is the composition of an alloy with a minimum melting point.  

For cast iron, the carbon content is approximately 4.3%. Why “approximately” has already been said. Therefore, it is customary to divide cast iron into:

• hypoeutectic - 2.14 - 4.3% carbon;

• eutectic - 4.3% carbon;

• hypereutectic - from 4.3 to 6.67% carbon. 

Types of cast iron

In the generally accepted classification, they are divided according to the form of carbon they contain.

Peredelny

Used as a raw material for steel smelting. Often it does not even leave the enterprise where it was made.

Special

The production of such brands is small, up to 2% of the total volume. May contain significant amounts of alloying elements. Designed for limited purposes and specific conditions. Corrosion and chemically resistant ferroalloys are common.

One of the varieties is anti-friction cast iron. Used for the manufacture of rubbing parts. Alloyed primarily with chromium. Nickel, titanium, copper and others are also added.

It is characterized by high hardness (up to HB 300) and low coefficient of friction (up to 0.8 in the absence of lubricating emulsions).

Base materials: gray, ductile and high-strength cast iron. The markings are respectively AChS, AChK, AChV. The digital components are described above.

Advantages and disadvantages of the material

It is worth discussing in comparison with steel, although low-quality carbon steel is essentially the same as cast iron.

In some parameters (density, magnetic properties, typical chemical reactions) ferroalloys are almost identical. There are significant differences in the technology of use.

Advantages:

1. Moderate cost. Carbonation is part of the smelting process from ore. A decrease in its content will inevitably increase the price of the metal.

2. Excellent casting qualities. The melt is fluid. With low crystallization shrinkage, which minimizes defects. Relatively low melting point.

3. The products are durable, have a hard surface, and are wear-resistant.

4. The compositions used in mechanical engineering can be processed by cutting.

5. Durable. Including plumbing and sewer parts.

6. Items that have become unnecessary are easy to recycle. Any reception point with hands will be torn off.

Flaws:

1. Due to the high carbon content it is fragile. Not very suitable for pressure treatment. Certain brands produce forged products of excellent quality. But this is rather piece work and unprofitable on an industrial scale.

2. Welding is allowed only in extreme cases. The technology is quite complex, and the risk of defects is high.

3. The products are always massive. A thin-walled structure will not work, since it will not support its own weight and will not be able to be manufactured.

4. Easily oxidizes in a humid environment. It will not rust through due to its inevitable monumentality, but it will take on an unkempt appearance. Parts located outdoors require a corrosion-resistant coating.

Iron production

People mastered the rudiments of ferrous metallurgy already in the 2nd millennium BC. e. To obtain steel. But blast furnaces appeared in Europe only in the 14th and 15th centuries. Pig iron was obtained as a waste by-product.

They appreciated it when they noticed its outstanding casting qualities. It is convenient for making cannonballs, and it is also more convenient to obtain steel from it.

Technology reached Russia in a meaningful way in the 17th century. This happened under Peter I, when they were looking for material for weapons.

Iron ore is usually used as a raw material. The highest yield is obtained from magnetic and red, abundantly containing Fe.

Coke is used to maintain temperature. Combustion air is supplied forcibly. Flux (limestone) is designed to supply carbon dioxide. Main reaction:

.

The reduced Fe is lowered into the furnace, where it is saturated with carbon. The furnace operating cycle is continuous.

Getting steel

About 85% of cast iron is used for further steel production. An open hearth furnace is used for smelting.

During the melting process of the loaded raw material, a significant mass of FeO oxide is formed. As it heats up, the following reaction occurs:

.

Excess carbon is removed.

Electric arc and induction furnaces are also used. 

Areas of use

Due to the modern tendency to make equipment as light as possible, cast iron is used less and less. 

But there are areas where it is still indispensable and cost-effective:

1. In mechanical engineering it is used for large body parts with low tensile loads. Beds for machine tools, cylinder blocks for internal combustion engines. Flywheels, pulleys, gears, hydraulic cylinders, gear housings, electric motors, pistons.

2. Plumbing fittings, sewer pipes.

3. Decorative elements: fences, grilles, gates.

4. Stoves for houses, baths.

Source: https://nauka.club/materialovedenie/chugun.html