Surely many have come across in everyday life or in production with cast iron products. This material has good strength and excellent casting properties.

Cast iron is a steel, or rather, an iron-carbon alloy, consisting of iron and carbon, which has a volume of 2.14% to a maximum of 6.67% and can be included as cementite or graphite. Cast iron, by definition, is an engineering material that is cheap and easy to manufacture and serves as the basis for steelmaking. Its production refers to complex chemical processes occurring at certain stages of production.

Main characteristics and composition

This alloy, in addition to iron with carbon, includes additional impurities that affect its properties. The diverse composition of cast iron provides it with high hardness, fluidity, and increases brittleness. It includes: sulfur, silicon, manganese, phosphorus. Cast iron alloy due to incoming carbon has high performance in hardness, but this reduces malleability, as well as the ductility of the substance. To give the metal special characteristics, some additives are added. As alloying components are used: nickel, vanadium, as well as chromium, aluminum. The cast iron formula consists of an iron-carbon base with additional inclusions. It has a density of about 7.2 g/cm3, which is a rather high value for metal compounds.

Cast iron consists of several components, due to which the properties of its variations can differ significantly. In addition to carbon and iron, the composition includes up to 2% manganese, 1.2% phosphorus, 4.3% silicon and up to 0.07% sulfur. Silicon is responsible for the state of fluidity, significantly improves casting qualities, and also makes it softer. Manganese is used to enhance strength. The addition of sulfur reduces the refractoriness and lowers its fluidity. In addition, she provides harmful effect, manifested in the appearance of cracks on hot castings (red brittleness). The presence of phosphorus reduces the mechanical properties, but allows casting objects of complex shape.

The structure of cast iron looks like a metal base with graphite inclusions. Depending on the type, it includes perlite, lamellar graphite, and also ledeburite. These elements determine its characteristics and are present in various quantities or completely absent.

The melting temperature ranges from the minimum +1160 °C to the maximum +1250 °C. It has high anti-corrosion performance, actively counteracts both dry (chemical) and wet corrosion. Thanks to him, stainless steel was born - a steel alloy that has a high content of chromium component.

Application area

Cast iron is widely used in mechanical engineering for casting various parts. It is used for the manufacture of crankshafts, as well as motor blocks. In addition, high-quality pads with high friction resistance are produced. They are used at low temperatures, where only cast iron is used due to its high performance properties. These qualities are used in the production of various machine elements, where cast iron alloy is used to work in harsh climates. This material is widely used by metallurgists due to its excellent casting characteristics and low price. Cast products have high wear resistance, increased strength.

Many plumbing parts are also made from a cast iron base. These are batteries, heating radiators, pipes, bathtubs, various sinks with sinks. Many products still serve to this day, although they were installed several decades ago. These items retain their original appearance. long years and do not require restoration work. In addition, cast iron cookware is considered one of the most convenient for cooking many dishes.

Varieties

Cast iron alloy according to its characteristics is divided into conversion, as well as foundry. The first is used in steelmaking using the oxygen-converter method. This type characterized by a reduced amount of manganese and silicon. Cast iron material is used for the production of numerous parts. Samples of products from this base can be seen in the corresponding photos.

Nickel-chromium alloys (nihards) belong to a special variety. These include low carbon as well as high carbon cast iron. The first is characterized by increased strength, and the second - by increased wear resistance. The main varieties are white and gray alloys. These materials differ in carbon content as well as properties. In addition, malleable, alloyed and high-strength types are actively used.

Grey

Gray cast irons have low ductility, toughness, and are easy to cut during processing. They are used in the manufacture of non-critical parts, as well as elements that work for wear. Gray cast iron contains carbon in the form of graphite, pearlite or ferrite pearlite. Its amount is about 2.5%, which provides high strength products. Cases of various industrial equipment, gears, brackets, bushings are made from gray alloy. A material containing a high amount of phosphorus (about 0.3 - 1.2%) has good fluidity and is used in art casting.

White

Contains a large amount of carbon (over 3%), presented in the form of cementite or carbide. The white color at the fracture site of this material gave the name to the compound. An alloy of this type has increased brittleness, as well as brittleness, which significantly narrows the scope of use. Based on it, parts of a simple form are produced to perform static functions without the impact of significant loads. Specifications white material can be improved by adding alloying components. For this, nickel, chromium, and much less often aluminum or vanadium are used. A brand with such additives is called "sormite". It is used as a heating element in various devices. Sormite is characterized by stable characteristics at temperatures not exceeding +900 °C. This material serves as the basis for the manufacture of conventional household bathtubs.

Malleable

This type is obtained from white by casting with further heat treatment. In this case, long-term exposure annealing is used, in which the cementite disintegrates, forming graphite. This process is called graphitization with the formation of carbon flakes in the structure. Graphite acquires this shape due to prolonged annealing. This has a positive effect on the metal base, which becomes more solid, plastic and viscous.

Malleable cast iron performs well at low temperatures and is not very sensitive to notching. It is used in the manufacture of elements operating under continuous friction. In addition, the malleable alloy serves as the basis for products of a very complex configuration: squares, brake pads, tees, car crankcases for rear axles and other structures. Improvement of properties is achieved by adding boron, tellurium, magnesium.

high strength

It has increased strength and is used to obtain products for critical purposes, and in some cases even replaces steel. This high-strength cast iron is obtained by adding special impurities (cerium, calcium, yttrium, magnesium) to the gray look. Gears, pistons, crankshafts and other parts are produced from it. High thermal conductivity allows you to cast elements for heating units, as well as pipelines.

Alloy

Cast iron alloy of an alloyed type contains additional impurities. The composition includes a high content of titanium, nickel, chromium, as well as zirconium, vanadium, molybdenum, aluminum and other elements. They give high strength, hardness, wear resistance. Alloyed materials are used in the production of parts of mechanisms that interact with gas, aggressive media, and also work under the influence of aqueous solutions.

Advantages of metal

This alloy belongs to the materials produced by ferrous metallurgy. It is often compared with steel in determining certain characteristics. An item made of cast iron has a low cost compared to a steel counterpart. In addition, cast iron elements have less weight and strength. These properties of cast iron are greatly expanded through the use of various additives in alloys. Its parameters have the following positive qualities:

• environmentally friendly material that is used in the production of household items, including dishes;
• resistant to acid-base environment;
• hygienic;
• the ability to maintain temperature for a long time;
• some types have strength comparable to steel;
• duration of operation, in which its quality indicators are only improving;
• complete harmlessness to the body.

Production

The production of cast iron alloy is a material-intensive and costly process. The smelting of one ton of material will require about 900 liters of ordinary water and about 550 kg of coke. The melting temperature is about +1200 °C, which requires specific melting equipment. To obtain the mass, ore is needed, where the mass fraction of iron contained is over 70%. Depleted ore rocks are not used due to economic inefficiency.

The material is smelted in special blast furnaces. There, iron ore goes through a full technological cycle, starting with the reduction of ore oxides and ending with the production of an iron alloy at the output. Casting material requires the presence of fuel: coke, thermoanthracite, as well as natural gas. At the end of the reduction process, iron in solid form is placed in a special part of the furnace to dissolve carbon in it. After interaction, a cast-iron mass is obtained, which, in liquid form, falls down. Unmelted impurities are pushed to the surface and subsequently removed. This slag is used to produce numerous materials. After removing unnecessary particles from the melt, additives are added to obtain certain grades of cast iron alloys.

Cast iron is an alloy of iron and carbon (the amount of which is more than 2.14%), characterized by eutectic formations. Carbon in cast iron is in the form of graphite and cementite. Depending on the forms of graphite, and the amount of cementite, cast iron is divided into: white and gray, malleable and ductile cast iron. Chem. the composition of cast iron contains permanent impurities (Si, Mn, PS, P), and in rare cases there are also alloying elements such as (> Cr, Ni, V, Al, etc.). Cast iron is usually brittle. The great spread of cast iron in mechanical engineering was facilitated by the presence of good foundries, as well as strength and hardness. World production of pig iron before the crisis of 2008 amounted to more than 953 million tons (in particular, China smelted 477 million tons).

The chemical composition of cast iron and its types

White and gray types of cast iron are distinguished by the color of the fracture, which is determined by the structure of carbon in the cast iron as iron carbide or free graphite, ductile iron with nodular graphite, compact graphite cast iron are called malleable. The carbon in white iron is in the form of cementite, and in gray iron it is in the form of graphite.

Composition of white cast iron

In white cast iron, all carbon present arrives in the cementite state. The structure of white cast iron includes perlite, ledeburite, and also cementite. Due to the light shade, cast iron was called white.

The composition of gray cast iron and its structure

Gray cast iron is a type of cast iron that, while not containing ledeburite, contains all or part of the carbon in the form of graphite. The name was given due to the gray color of the fracture surface.

Along with white cast iron, it belongs to the main types of cast iron. The composition of gray cast iron, in addition to iron and carbon (2.5 ... 4.5%), includes silicon about (0.8 ... 4.5%), as well as manganese (0.1 ... 1, 2%), and phosphorus (0.02 ... 0.3%) with sulfur (0.02 ... 0.15%). Tensile strength of gray cast irons in tension - 100 ... 350 MPa, compression - 450 ... 1400 MPa, Brinell hardness - 143 ... 289 HB.

The main characteristic of gray cast iron is low tear resistance, rather low impact strength. Therefore, the smaller the graphite plates are and the stronger the plates are isolated from one another, the higher the strength properties of cast iron with the same metal base. This structure is obtained by modification, the process of introducing small amounts of substances into the liquid metal alloy, which are called modifiers (ferrosilicon and silicocalcium)

Malleable iron, production process

Ductile iron is obtained by long-term annealing of white cast iron, after this process flake-shaped graphite is formed. The metal base of ductile iron contains: ferrite and less often pearlite.

Ductile iron structure

In its structure, ductile iron has nodular graphite, it is obtained in the process of crystallization of the material. Nodular graphite greatly weakens the metal base as much as tabular, not a stress concentrator.

Structural characteristics of cast iron

Part of the carbon in cast iron (more than 0.8%) is in the form of cementite. The main structural components of this cast iron are perlite, ledeburite and flat graphite.

Cast iron classification

From the chemical composition of cast iron and carbon content gray cast iron called hypoeutectic has (2.14-4.3% carbon), and eutectic has (4.3%) hypereutectic has (4.3-6.67%). The composition of the alloy strongly influences the structure of the final material.

In industry, different types of cast iron have the following markings:

• cast iron-P1, P2;
• cast iron for castings is used - PL1, PL2,
• processing phosphorous type of cast iron-PF1, PF2, PF3,
• processing high-quality type of cast iron-PVK1, PVK2, PVK3;
• cast iron having lamellar graphite-MF (the numbers after the letters "> SC" indicate the value of the tensile strength (vkgf / mm);

Anti-friction cast iron types:

• anti-friction gray-ASF,
• anti-friction high-strength type-ACV,
• anti-friction malleable type-ACC;

Cast iron having nodular graphite for castings - HF (the numbers after the letters "HF" mean the tensile strength Vkgf / mm;

At the beginning of the 16th century, cast iron began to be smelted in the Russian Empire. Cast iron smelting grew at a very high pace, and during the reign of Peter the Great, Russia was the leader in metal smelting in Europe. Over time, the foundries began to separate from the blast furnaces, which gave impetus to the development of independent iron foundries. At the beginning of the 19th century, factories began to produce ductile iron, and at the end of the 20th century they mastered the production of alloyed cast iron.

1. Features of unalloyed cast irons

Characteristics of gray cast iron

The production of gray cast iron is carried out in a blast furnace. The source material is . The formation of the gray alloy structure is carried out only under conditions of low cooling rates. In its form, the carbon, which is in cast iron, resembles lamellar graphite. That is why the fracture is characterized by gray color.

Marking features

For marking gray cast iron, the letters SCH and numbers are used. The last of them indicate what tensile strength the material has during the stretching period. This material is characterized by universal casting properties - low shrinkage and high fluidity.

Application

The material is characterized by the presence of a high ability to dissipate vibrational vibrations under conditions of variable loads. The metal is characterized by high cyclic toughness. That is why rolling machines, machine beds are made from this material. Also, flywheels, pulleys, housings, piston rings, etc. are made from a gray alloy.

Characteristics of ductile iron

Ductile iron is characterized by the presence of spherical graphite inclusions. These inclusions are obtained by modifying gray cast iron. Due to the spherical shape of graphite, the creation of a sharp concentration of stresses does not occur. That is why this material is characterized by a high level of strength during stretching and bending.

Ductile iron is characterized by the presence of HF markings and numbers that indicate the strength of this material. This metal is characterized by high fluidity and low shrinkage.

2. Features of alloy cast irons

Alloyed cast iron is obtained by introducing alloyed components, such as, and others, into the composition of ordinary cast iron. With the help of alloying, cast iron acquires special properties. Alloyed cast irons according to their features can be:

wear resistant;
heat resistant;
antifriction;
Heat resistant.

Marking of alloyed cast irons is carried out in accordance with the type of steel: Ch is heat-resistant cast iron, ICh is wear-resistant cast iron, ACh is anti-friction cast iron, ZhCh is heat-resistant cast iron. This may be followed by letters that indicate alloying elements. The letters are followed by numbers that tell about the approximate content of alloying elements in percentage. In the absence of a number, one can judge the presence of approximately one percent of the alloying element.

Characteristics of wear-resistant cast iron

Wear resistance is a property of a material that allows it to resist wear during friction. In order to provide cast iron with this property, chromium, tungsten and molybdenum are added to white cast iron.

To mark a wear-resistant alloy, the letters ICH and numbers indicating the percentage of alloying elements in them are used.

Wear-resistant cast iron is characterized by a high level of resistance to abrasive wear, which allows it to be used for the production of clutch discs, brakes, parts for pumps that pump abrasive media, and parts for sand throwers.

Characteristics of refractory cast irons

Heat resistance is a characteristic at which a material is able to resist oxidation in a gaseous environment at high temperatures.

Heat resistance is ensured by alloying gray or white cast iron using materials such as silicon, chromium, and aluminum. On the surface of the material there are dense protective oxide films, with the help of which the alloy is protected from oxidation at high temperatures.

Marking of heat-resistant cast iron is carried out using the letters ZhCh. After that, there are numbers by which the designation of alloying elements is carried out.

With the help of ZhCH, parts are made that operate in an alkaline, gas, air environment, and are able to withstand temperatures up to 1100 degrees Celsius. They are used in the manufacture of structures for such furnaces as thermal, blast furnace and open-hearth furnaces.

Characteristics of refractory cast iron

Heat resistance is the ability of a metal to maintain its properties at high temperatures.
Heat resistance is carried out if gray or white cast iron is alloyed using materials such as chromium, nickel, or molybdenum. All refractory materials are also refractory at the same time, but not all refractory materials are refractory. The marking of the heat-resistant alloy is carried out by the letter H.

This material is widely used for the production of gas furnaces. With its help, parts are made, the installation of which is carried out in diesel engines of compressor equipment. Also, parts made of this material are installed in saunas and baths. Heat resistant cast iron is a material that has spheroidal graphite.

Characteristics of anti-friction cast irons

Antifriction refers to the ability of a material to work under friction conditions. Anti-friction cast iron can be gray, ductile or malleable cast iron, which is characterized by a pearlitic or pearlitic-ferritic structure (pearlite< 85 %). Для легирования антифрикционных чугунов в большинстве случаев используется хром, медь или титан.

This results in a finely dispersed pearlite-ferrite structure. Anti-friction cast iron has the following properties: a high level of wear resistance and a fairly low cost. If we compare this material with, then it has a lower level of friction.

The basis for the production of this material are gray (AShS), ductile (AChK) and high-strength (AHV) cast irons. This material is very often used as a substitute for non-ferrous alloys. In order for the material to work efficiently and correctly, it must be provided with regular and high-quality lubrication. If there is a high impact load, then this leads to a decrease in the quality of the anti-friction cast iron.

Cast iron is an alloy of iron with carbon and other elements.

Characteristics of cast iron

An important factor in the production of cast iron is that the minimum amount of carbon in the composition of the alloy is 2.14% or more. If the carbon content in the alloy is below the specified amount, then this alloy is not cast iron, but is called steel. The production process for steel and cast iron is about the same. The main difference between these two alloys is the quantitative content of carbon in their composition. Since cast iron contains more carbon than steel, cast iron is a very strong but brittle material. Whereas steel is very flexible. It is the high carbon content in the composition of cast iron that gives this material exceptional hardness, which on the Mohs scale is as much as 7.5 points. This indicator is significantly higher than that of quartz, however, less than that of diamond, but only by 2.5 points.

The carbon in cast iron can be cementite and graphite. It is the form of graphite and the quantitative content of cementite in the alloy that determines the type of cast iron. Thus, cast iron is divided into white, gray, malleable and high-strength. The chemical composition of cast iron, which contains impurities such as silicon, manganese, sulfur and phosphorus, is almost always constant. However, in some cases, cast iron may also contain the following alloying elements: chromium, nickel, aluminum, vanadium and others. These components are introduced into the composition of the alloy in order to give it greater strength, wear resistance, heat resistance, corrosion resistance, and non-magnetism. Cast iron, in which these impurities are present, is called alloyed cast iron. The quantitative content of these impurities in the alloy determines the degree of alloying. Depending on this, there are:

• low alloy cast iron. It contains less than 2.5% of all alloying impurities;
• medium alloy cast iron. Here the impurities are of the order of 2.5 - 10%;
• highly alloyed, containing more than 10% of alloying elements.

The chemical characteristics of alloy cast irons are the main factor for their classification. Thus, among alloyed cast irons, there are:

• aluminum cast iron. It contains aluminum in an amount from 0.6 to 31%. Such cast iron is more durable, more heat-resistant, resistant to corrosion, and also has high wear resistance. The use of this alloy is appropriate where work is carried out in an aggressive environment and at high temperatures - thermal furnaces, chemical equipment, gas engines.
• nickel iron. Nickel is present in its composition in an amount from 0.3-0.7% to 19-21%. The nickel content directly affects the shape of graphite precipitates in the structure of nickel cast iron. This alloy has properties such as high corrosion resistance, high resistance to both high and fairly low temperatures (heat resistance and cold resistance), and is also able to withstand the impact of such an aggressive environment as sea ​​water. The last property of nickel cast iron determines the high demand for this material in shipbuilding, as it is used for the manufacture of parts operating in sea water.
• chrome cast iron. This alloy contains about 32% chromium. This type of alloyed cast iron has the following properties: heat resistance, corrosion resistance, wear resistance.

It should be noted that, in general, the cost of alloyed cast irons is significantly lower than the cost of stainless steels. In addition, they have good casting properties. In this regard, products from this alloy are very durable, high-quality, and at the same time economical.

The extraction of pig iron is carried out in the process of smelting iron ore in blast furnaces at a temperature in the range of 1150 - 1200 0 C.

Cast iron has been known to mankind since ancient times, which go back to the era BC. This is evidenced by numerous archaeological finds, among which there are both cast-iron objects and the raw furnaces themselves, in which, in fact, people received this material. However, iron is far from the first historical metal that mankind has met. Initially, people used native copper, which was mined in shallow mines. However, despite the appearance of metal in people's lives, stone remained very popular for quite a long time. Later, people learned how to make bronze, and only in VI-V BC, iron appeared in people's lives, and with it steel and cast iron.

China is the birthplace of cast iron products. It was there that the technology of casting iron was first mastered and this term was born, which later came to Russia through the Tatar-Mongol mediation. Thus, the first cast iron products also appeared in China. It was a wide variety of everyday items, kitchen utensils, as well as coins. The wok pan, which is quite popular today, was one of the first made in China from cast iron. In those distant times, it was a vessel, the diameter of which reached one meter. This pan also had very thin walls. Its cost was quite high, however, despite this, this kitchen utensil was extremely popular and in demand in large Chinese families.

In addition, archaeologists find unique things cast from cast iron, among which a cast-iron lion, 6 meters high and 5 meters long, should be noted. According to scientists, this statue was cast in one go. This indicates that in those distant prehistoric times, in the absence of modern high-class technologies, Chinese metallurgists achieved great skill in working with metals, in particular with cast iron.

Quite interesting and to some extent unusual fact is that it is believed that malleable iron was only produced in the 19th century AD, despite the fact that archaeologists find cast iron swords dating back to the pre-Christian era.

Russia and Europe got acquainted with cast iron more than one century later, namely only in the 14th - 16th centuries. At this time, cast iron was the main material for the production of artillery shells and weapons. And only in the XVII century, the use of cast iron significantly expanded. This was facilitated by the development metallurgical industry. The era of artillery use of cast iron gradually ended and the era of artistic casting began - the new capital Russian Empire cast fences, benches, and other elements of thin iron casting were decorated everywhere. Cast iron also caused changes in the stove business, as cast-iron valves and stove doors came to replace them, which have a significant advantage - resistance to high temperatures, as well as tightness, which did not allow stove smoke to leave the stove and smoke the room.

Russian master metallurgists were considered the best in those days. They owned many technologies for processing cast iron, which were constantly adopted by English, French and German craftsmen.

Today, in the era of nano-technologies and technological progress, when every year new materials appear, the development of metallurgy does not stop and continues to move forward. And after more than two thousand years, humanity has not been able to find a material that could replace cast iron. It continues to be used for the manufacture of various objects surrounding people.

The properties of cast iron are so unique that no more suitable material has yet been found to replace this alloy. In addition, cast iron is a fairly cheap material. In this regard, the use of cast iron remains wide and varied. Especially the use of cast iron is appropriate where it is necessary to manufacture parts that have a complex shape, as well as having high strength. In this regard, cast iron has found its wide application in the following areas of human activity:

• Automotive industry. In this case, vermicular graphite cast iron is used. It is he who is the main material for the manufacture of crankshafts of diesel engines, as well as engine blocks internal combustion. Due to the content of graphite, the strength of the alloy increases several times, which is the main reason for the popularity of cast iron in this industry.
• plumbing equipment. As in the case of the automotive industry, graphite cast iron is also used. It is this material that is excellent for the production of pipes used for both drainage and water supply. It is also actively used in the manufacture of bathtubs, sinks, washstands, fittings and much more. In this case, the products are highly reliable, do not require any specific maintenance, and retain their original appearance for a long period.
• Oil and gas industry. Not only water pipes are made of cast iron, but also pipes for transporting, pumping and pumping oil and gas. The main reason for the use of cast iron in this industry lies in the fact that cast iron products have a fairly high performance.
• heating. Pipes and heating radiators are made from cast iron. The use of the material in this case is due to its high heat transfer, as well as good heat storage properties, which is very important and beneficial. After turning off the heating, after an hour of time, cast-iron pipes are able to continue to radiate heat by a third of their original power. And here cast iron completely prevails over steel, which cannot boast of such qualities, because steel pipes cool down twice as fast.
• kitchen tools. The material has large pores, due to which it has the ability to absorb fats during cooking. In this regard, pots, cauldrons and pans are made from cast iron, the non-stick properties of which are getting better over the years. In addition, scientists have proven that while cooking in cast iron cookware, food is enriched with useful nutritional properties. In addition, cast iron cookware is able to prevent carcinogens during further storage of food.

Fences and gratings, spiral staircases, balconies, gazebos, fireplaces, lamps, poles, lanterns, sculptures, etc. are made of cast iron.

How to identify cast iron

Knowing the material from which certain objects are made is very important. For example, it is necessary in order to produce repair work certain automotive components, individual parts or other items. This is primarily due to the fact that different material lends itself different types and processing methods (for example, welding, drilling, etc.).

So, cast iron can in some cases be determined visually. However, this method is suitable if there are any cracks, chips or breaks in the material. If any such defects are present, it should be carefully inspected. A broken or cracked cast iron part will be painted dark gray and have a matte finish. While the steel will have a light grey, closer to white, color and glossy sheen. If you look closely at the surface defects, then the cast iron will have characteristic hemispherical fine grains. Unfortunately, this method is not an accurate determination of the material, since it is possible to determine “by eye” whether cast iron is or not only if the alloy (in this case, cast iron) was poured into the mold at a low temperature, was not processed further and was not covered no paints. It is the characteristic small hemispherical grains that indicate the pouring of the alloy at high temperature.

More information in determining cast iron can be given by a mechanical method. To do this, you need to get an alloy chip. This can be done by drilling to a shallow depth of some section of the non-working part. For high-strength cast iron, the chips will be characteristic - they will crumble, rubbing into dust in the hands and leaving a mark on the fingers that looks like a stylus from a simple pencil. Cast iron shavings are not able to wrap themselves in a twisted loach. This is due to one of the properties of cast iron - brittleness.

If you try to cut the cast-iron product with a grinder, then short sparks will fly from it, having a reddish tint on the asterisk at the end of the track.

All of these options have a place to be for determining cast iron at home. However, they cannot give a 100% definition. For more exact definition alloys use spectral analysis, microscopic analysis, as well as weighing and volume determination.

(Polish stal, from German Stahl) - a deformable (ductile) alloy of iron with carbon (and other elements), characterized by a eutectoid transformation. The carbon content in steel is not more than 2.14%, but not less than 0.022%. Carbon gives iron alloys strength and hardness, reducing ductility and toughness.

Given that alloying elements can be added to steel, steel is an alloy of iron containing at least 45% iron with carbon and alloying elements (alloyed, high-alloyed steel).

In ancient Russian written sources, steel was referred to by special terms: "Otsel", "Kharolug" and "Uklad". In some Slavic languages ​​today steel is called "Ocel", for example in Czech.

Steel is the most important structural material for mechanical engineering, transport, construction and other industries National economy.

Steels with high elastic properties are widely used in machine and instrument making. In mechanical engineering, they are used for the manufacture of springs, shock absorbers, power springs for various purposes, in instrumentation - for numerous elastic elements: membranes, springs, relay plates, bellows, stretch marks, suspensions.

Springs, springs of machines and elastic elements of devices are characterized by a variety [source not specified 122 days] of shapes, sizes, various working conditions. The peculiarity of their work is that under large static, cyclic or shock loads, residual deformation is not allowed in them. In this regard, all spring alloys, in addition to the mechanical properties characteristic of all structural materials (strength, ductility, toughness, endurance), must have a high resistance to small plastic deformations. Under conditions of short-term static loading, resistance to small plastic deformations is characterized by the elastic limit, under long-term static or cyclic loading - by relaxation resistance

Classification

Steels are divided into structural and tool steels. A variety of tool is high-speed steel.

By chemical composition steels are divided into carbon and alloyed; including by carbon content - into low-carbon (up to 0.25% C), medium-carbon (0.3-0.55% C) and high-carbon (0.6-0.85% C); Alloy steels according to the content of alloying elements are divided into low-alloyed, medium-alloyed and high-alloyed.

Steels, depending on the method of their production, contain different amounts of non-metallic inclusions. The content of impurities underlies the classification of steels by quality: ordinary quality, high-quality, high-quality and especially high-quality.

According to the structure, steel differs in austenitic, ferritic, martensitic, bainitic or pearlitic. If the structure is dominated by two or more phases, then the steel is divided into two-phase and multi-phase.

Steel characteristics

Density - 7700-7900 kg/m³.

Specific gravity- 75537-77499 n/m³ (7700-7900 kgf/m³ in the MKGSS system).

Specific heat capacity at 20 °C - 462 J/(kg °C) (110 cal/(kg °C)).

Melting point - 1450-1520 °C.

The specific heat of fusion is 84 kJ/kg (20 kcal/kg).

Thermal conductivity coefficient - 39 kcal / (m h ° C) (45.5 W / (m K)). [source not specified 136 days]

Coefficient of linear thermal expansion at approx. 20 °C:

steel St3 (grade 20) - (1/deg);

stainless steel - (1/deg).

Tensile strength of steel:

steel for structures - 38-42 (kg / mm²);

silicon-chromium-manganese steel - 155 (kg / mm²);

engineering steel (carbon) - 32-80 (kg / mm²);

rail steel - 70-80 (kg / mm²);

An alloy of iron with carbon (usually more than 2.14%), characterized by a eutectic transformation. Carbon in cast iron can be contained in the form of cementite and graphite. Depending on the shape of graphite and the amount of cementite, there are: white, gray, malleable and high-strength cast irons. Cast irons contain permanent impurities (Si, Mn, S, P), and in some cases also alloying elements (Cr, Ni, V, Al, etc.). As a rule, cast iron is brittle. World production of pig iron in 2007 amounted to 953 million tons (including in China - 477 million tons).

Types of cast iron

white cast iron

In white cast iron, all carbon is in the form of cementite. The structure of such cast iron is perlite, ledeburite and cementite. This cast iron got its name because of the light color of the fracture.

Gray cast iron

Gray cast iron is an alloy of iron, silicon (from 1.2-3.5%) and carbon, also containing constant impurities of Mn, P, S. In the structure of such cast irons, most or all of the carbon is in the form of lamellar graphite. The fracture of such cast iron due to the presence of graphite has a gray color.

malleable iron

Ductile iron is obtained by long-term annealing of white iron, which results in the formation of flaky graphite. The metal base of such cast iron: ferrite and less often perlite.

Ductile iron

Ductile iron has nodular graphite in its structure, which is formed during the crystallization process. Spheroidal graphite does not weaken the metal base as much as lamellar graphite, and is not a stress concentrator.

half cast iron

In cast iron, part of the carbon (more than 0.8%) is contained in the form of cementite. The structural components of such cast iron are pearlite, ledeburite and lamellar graphite.

Classification

Depending on the carbon content, gray cast iron is called hypoeutectic (2.14-4.3% carbon), eutectic (4.3%) or hypereutectic (4.3-6.67%). The composition of the alloy affects the structure of the material.

Depending on the state and content of carbon in cast iron, they are distinguished: white and gray (according to the color of the fracture, which is determined by the structure of carbon in cast iron in the form of iron carbide or free graphite), high-strength with nodular graphite, ductile irons, cast iron with vermicular graphite. In white cast iron, carbon is present in the form of cementite, in gray cast iron - mainly in the form of graphite.

In industry, varieties of cast iron are marked as follows:

pig iron- P1, P2;

pig iron for castings - PL1, PL2,

conversion phosphorous cast iron - PF1, PF2, PF3,

conversion high-quality cast iron - PVK1, PVK2, PVK3;

cast iron with lamellar graphite - SCH (the numbers after the letters "SCH" indicate the value of the tensile strength in kgf / mm);

anti-friction cast iron

anti-friction gray - ASF,

antifriction high-strength - AChV,

antifriction malleable - AChK;

nodular cast iron for castings - HF (numbers after the letters "HF" mean tensile strength in kgf / mm and relative elongation (%);

cast iron alloyed with special properties - Ch.

3. Blast furnace,

blast furnace - a large metallurgical, vertically located shaft-type furnace for smelting cast iron, ferroalloys from iron ore raw materials. The first blast furnaces appeared in Europe in the middle of the 14th century, in Russia around 1630.

Description

The blast furnace is a structure with a height of up to 35 m, the height is limited by the strength of the coke, which holds the entire column of charge materials. The charge is loaded from above, through a typical loading device, which is also the gas seal of the blast furnace. In the blast furnace, rich iron ore is restored (at present stage reserves of rich iron ore are preserved only in Australia and Brazil), sinter or pellets. Sometimes briquettes are used as ore raw materials.

The blast furnace consists of five structural elements: the upper cylindrical part - the top, which is necessary for loading and efficient distribution of the charge in the furnace; the largest in height expanding conical part - the mine, in which the processes of heating materials and the reduction of iron from oxides take place; the widest cylindrical part - steam, in which the processes of softening and melting of reduced iron take place; tapering conical part - shoulders, where a reducing gas is formed - carbon monoxide; the cylindrical part - the hearth, which serves to accumulate liquid products of the blast-furnace process - cast iron and slag.

In the upper part of the hearth there are lances - holes for supplying blast heated to a high temperature - compressed air enriched with oxygen and hydrocarbon fuel.

At the level of the lances, a temperature of about 2000 °C develops. As you move up, the temperature decreases, and at the tops it reaches about 270 ° C. Thus, different temperatures are set in the furnace at different heights, due to which various chemical processes of the transition of ore into metal take place.

Processes taking place in the furnace

At the top of the hearth, where the oxygen supply is high enough, the coke burns to form carbon dioxide and release a large number heat.

C + O 2 \u003d CO 2 + Q

Carbon dioxide, leaving the zone enriched with oxygen, reacts with coke and forms carbon monoxide - the main reducing agent of the blast-furnace process.

Rising up, carbon monoxide interacts with iron oxides, taking away oxygen from them and reducing them to metal:

Fe 2 O 3 + 3CO \u003d 2Fe + 3CO 2

The iron obtained as a result of the reaction flows down in drops over the hot coke, being saturated with carbon, resulting in an alloy containing 2.14 - 6.67% carbon. This alloy is called cast iron. In addition to carbon, it includes a small proportion of silicon and manganese. In the amount of tenths of a percent, the composition of cast iron also includes harmful impurities - sulfur and phosphorus. In addition to cast iron, slag is formed and accumulated in the furnace, in which all harmful impurities are collected.

Previously, slag was tapped through a separate slag taphole. At present, both pig iron and slag are tapped through the Pig-iron tap-hole at the same time. The separation of pig iron and slag takes place already outside the blast furnace - in the chute, using a separating plate. The pig iron separated from the slag is poured into pig iron ladles and transported to the steelmaking shop.