Basic iron alloys. iron alloys

As already mentioned, alloys of iron with carbon are divided into steels and cast irons. Steels, in turn, are divided into groups according to their chemical composition and purpose, and cast irons - according to the state of carbon in them.

According to the chemical composition, steels are divided into carbon and alloy steels.

carbon steels- these are alloys of iron with carbon, and the content of the latter does not exceed 2.14%. However, in carbon steel industrial production there are always impurities of many elements. The presence of some impurities is due to the peculiarities of steel production; for example, during deoxidation (see § 239), small amounts of manganese or silicon are introduced into steel, which partially pass into the slag in the form of oxides, and partially remain in the steel. The presence of other impurities is due to the fact that they are contained in the original ore and in small quantities pass into cast iron, and then into steel. It is difficult to get rid of them completely. As a consequence, for example, carbon steels typically contain 0.05-0.1% phosphorus and sulfur.

The mechanical properties of slowly cooled carbon steel are highly dependent on its carbon content. Slowly cooled steel is composed of ferrite and cementite, the amount of cementite being proportional to the carbon content. The hardness of cementite is much higher than the hardness of ferrite. Therefore, with an increase in the carbon content in steel, its hardness increases. In addition, cementite particles impede the movement of dislocations in the main phase - in ferrite. For this reason, increasing the amount of carbon reduces the ductility of the steel.

Carbon steel has a very wide range of uses. Depending on the purpose, steel with a low or higher carbon content is used, without heat treatment (in a "raw" form - after rolling) or with quenching and tempering.

Alloy steels. Elements specially introduced into steel in certain concentrations to change its properties are called alloying elements, and steel containing such elements is called alloyed steel. The most important alloying elements include chromium, nickel, manganese, silicon, vanadium, molybdenum.

Various alloying elements change the structure and properties of steel in different ways. Thus, some elements form solid solutions in y-iron, which are stable over a wide range of temperatures. For example, solid solutions of manganese or nickel in y-iron with a significant content of these elements are stable from room temperature to the melting point. Alloys of iron with similar metals are called therefore austenitic steels or austenitic alloys.

The influence of alloying elements on the properties of steel is also due to the fact that some of them form carbides with carbon, which can be simple, for example Mn 3 C, Cr 7 C 3, and also complex (double), for example (Fe, Cr) 3 C. The presence of carbides, especially in the form of dispersed inclusions in the structure of steel, in some cases has a strong effect on its mechanical and physicochemical properties.

According to their purpose, steels are divided into structural, tool and steels with special properties. Structural steels are used for the manufacture of machine parts, structures and structures. Both carbon and alloy steels can be used as structural steels. Structural steels have high strength and ductility. At the same time, they must lend themselves well to pressure treatment, cutting, and good welding. The main alloying elements of structural steels are chromium (about 1%), nickel (1-4%) and manganese (1-1.5%).

Tool steels- These are carbon and alloy steels with high hardness, strength and wear resistance. They are used for the manufacture of cutting and measuring tools, stamps. The required hardness is provided by the carbon contained in these steels (in an amount of 0.8 to 1.3%). The main alloying element of tool steels is chromium; sometimes they also introduce tungsten and vanadium. A special group of tool steels is high-speed steel, which retains cutting properties at high cutting speeds, when the temperature of the working part of the cutter rises to 600-700 ° C. The main alloying elements of this steel are chromium and tungsten.

Steel with special properties. This group includes stainless, heat-resistant, heat-resistant, magnetic and some other steels. Stainless steels are resistant to corrosion in the atmosphere, moisture and acid solutions, heat-resistant - in corrosive environments at high temperatures. Heat-resistant steels keep high mechanical properties when heated to significant temperatures, which is important in the manufacture of gas turbine blades, parts of jet engines and rocket launchers. The most important alloying elements of heat-resistant steels are chromium (15-20%), nickel (8-15%), tungsten. Heat-resistant steels belong to austenitic alloys.

Magnetic steels are used for the manufacture of permanent magnets and cores of magnetic devices operating in alternating fields. For permanent magnets, high-carbon steels alloyed with chromium or tungsten are used. They are well magnetized and retain residual induction for a long time. The cores of magnetic devices are made from low-carbon (less than 0.005% C) iron-silicon alloys. These steels are easily remagnetized and are characterized by low electrical losses.

To designate alloy steel grades, an alphanumeric system is used. Each alloying element is indicated by a letter: H - nickel, X - chromium, G - manganese, etc. The first digits in the designation show the carbon content in steel (in hundredths of a percent). The number following the letter indicates the content of this element (if its content is about 1% or less, the number is not put). For example, steel with a composition of 0.10-0.15% carbon and 1.3-1.7% manganese is designated 12G2. The X18H9 grade denotes steel containing 18% chromium and 9% nickel. In addition to this system, non-standard designations are sometimes used.

Cast iron differs from steel in its properties. It is capable of plastic deformation to a very small extent (it cannot be forged under normal conditions), but it has good casting properties. Cast iron became cheaper.

As already mentioned, during the crystallization of liquid iron, as well as during the decomposition of austenite, the carbon contained in these phases is usually released in the form of cementite. However, under the conditions under consideration, cementite is thermodynamically unstable. Its formation is due only to the fact that the nuclei of its crystallization are formed much more easily and require less diffusion changes than graphite nuclei. Therefore, under conditions of very slow cooling of liquid iron, carbon can crystallize not in the form of cementite, but in the form of graphite. The formation of graphite is greatly facilitated also in the presence of small particles of impurities (especially graphite impurities) in the molten iron.

Thus, depending on the crystallization conditions, cast iron may contain carbon in the form of cementite, graphite, or a mixture of both. The shape of the resulting graphite can also be different.

white cast iron contains all carbon in the form of cementite. It has high hardness, brittleness and therefore has limited application. Basically, it is smelted for redistribution into steel.

AT gray cast iron carbon is contained mainly in the form of graphite plates. Gray cast iron is characterized by high casting properties (low crystallization temperature, fluidity in the liquid state, low shrinkage) and serves as the main casting material. It is widely used in mechanical engineering for casting machine and mechanism frames, pistons, and cylinders. In addition to carbon, gray cast iron always contains other elements. The most important of them are silicon and manganese. In most grades of gray cast iron, the carbon content lies in the range of 2.4-3.8%, silicon 1-4% and manganese up to 1.4%.

Ductile iron obtained by adding certain elements to liquid iron, in particular magnesium, under the influence of which graphite crystallizes into a spherical shape. Spherical graphite improves the mechanical properties of cast iron. Ductile iron is used to manufacture crankshafts, cylinder heads, parts of rolling mills, rolling rolls, pumps, and valves.

malleable iron obtained by prolonged heating of castings made of white cast iron. It is used for the manufacture of parts operating under shock and vibration loads (for example, crankcases, rear axle of a car). The ductility and strength of ductile iron is due to the fact that carbon is in it in the form of flaky graphite.

Element of group VIII of the Periodic system of D. I. Mendeleev. It is similar to nickel and cobalt, the outer orbitals of the atoms of these elements differ only in the addition of one d-electron - 3d 6 s 2 (Fe), 3d 7 s 2 (Ni), 3d 8 s 2 (Co).

It was known to mankind at least six millennia BC. e., first in the form of meteorites, usually containing 90% Fe; 8.5% Ni and 0.5% Co. In the earth's crust, the reserves of these metals approximately correspond to the ratio 2 10 3 ; 2 10 2:1

They learned to smelt from ores no later than 15 centuriesBC e., in 1500 its world production reached 50 thousand tons, inat present it is close to 500 million tons.

Pure iron is a silvery-white ductile and malleable metal; when melted, it increases in volume by 4.4%.

In 1868 D. K. Chernov discovered the allotropy of iron, determined the temperatures of transformations, called them critical points ( rice., a) and found that the mode of hot working and the conditions of subsequent cooling determine the structure and properties of iron alloys. The significance of the work of D.K. Chernov is difficult to overestimate. In 1900, at the opening of the World Industrial Exhibition in Paris, Paul Montgolfier declared: “I consider it my duty to openly and publicly declare in the presence of so many connoisseurs and specialists that our factories and the entire steelmaking business owe their present development and success to a large extent to the work and research of Russian engineer Chernov.

Rice. Iron-carbon system:

a- critical points of iron; b - state diagram

Modification of solid iron α, β and δ differ in temperature intervals of stable existence, α- and β-iron have a spatial lattice of a centered cube, and γ-iron - a cube lattice with centered faces. Below a temperature of 768 ° C, iron has ferromagnetic properties. Above this temperature, it loses them. Therefore, modifications а and.р differ only in magneticness.

With carbon, iron forms carbide (cementite) Fe3C. From Chernov's coverage of critical points formed the basis of the diagram

iron states - ( rice.,b), which characterizes phase and structural transformations in iron-carbon alloys with a change in temperature. An alloy with a content of 6.66% C is iron carbide Fe 3 C. Point E on the diagram corresponds to the limiting solubility of carbon in solid iron. iron with a carbon content of up to 2% is called steel, more than 2% - cast iron. The carbon content largely determines the properties of steel. With led away The increase in carbon increases the hardness and strength of steel with a simultaneous decrease in ductility.

The properties of steel are also significantly affected by other elements often included in its composition: silicon, etc. So, contained in any steel from 0.2 to 1.0% and over 1% in manganese steels, increases the ability of steel to be hardened , increases its hardness, strength, yield strength, lowers plastic properties- relative compression, elongation and viscosity. is contained in common steel grades in an amount of not more than 0.4%, and in silicon steels - over 0.5%. increases the ability of steel to harden and increases its tensile strength.

Some others are special additivemi. They are introduced into steel to give it special properties. Steel containing additives is called alloy steel.

Harmful impurities in steel are dissolved gases. causes brittleness of steel in a hot state (red brittleness), heterogeneity of the ingot in composition, worsens mechanical and plastic properties. Therefore, the sulfur content should be no more than 0.02-0.05%.

Increases the brittleness of steel in a cold state (cold brittleness) and reduces impact strength. The maximum phosphorus content should not exceed 0.02-0.03%.

By purpose, steel is divided into three main classes: structural (spring, boiler, ball-bearing, etc.), used in mechanical engineering; instrumental, used for the manufacture of tools; steel with special properties - stainless, acid-resistant, heat-resistant, heat-resistant, steel with special magnetic properties, etc.

Iron content in the earth's crust ranks fourth (4.7%). The prevalence of iron, high concentration in large deposits, various high physical and technical properties of iron alloys made it the most widely used metal. Cast iron is hard, brittle and difficult to machine. Therefore, it cannot always be used directly, but serves as a rough metal for obtaining steel of various grades and for the production of cast iron. Thus, modern steel production is carried out in two stages: obtaining a rough metal - cast iron and refining it to turn it into steel.

Article on the topic of iron

Strictly speaking, the only representative of ferrous metals proper is iron, but this class of metals also includes the so-called iron alloys: cast iron, steel, ferroalloys.

Iron is a ductile, shiny gray-white metal capable of dissolving carbon and other elements, which creates conditions for obtaining alloys based on it. Iron is easily forged in a cold and heated state, lends itself to various methods of mechanical processing (rolling, stamping, cutting, etc.). This is the most accessible and cheap metal.

In the solid state, it has several crystalline modifications that can change from one to another when heated or cooled. The changed structure of the crystal lattice, acquired by the metal at a lower temperature, is usually denoted by the letter α (α-iron), at a higher temperature - by the letter β (β-iron), with a further increase in temperature - by the letter γ (γ-iron). So, when heated above 723 ° C, α-iron passes into γ-iron. This most important transformation is widely used in heat treatment. It is accompanied by a rearrangement of the lattice with the decay of existing crystals and the formation of new ones. At the same time, the ability of iron to dissolve carbon sharply increases and the mechanical properties of its alloys improve.

Iron forms alloys with many metals and non-metals. Iron-carbon alloys have the most diverse properties, which is associated with their structure. The structural components of iron-carbon alloys include: ferrite, austenite, cementite, pearlite, ledeburite.

Ferrite

Ferrite is a solid solution of carbon (up to 0.02%) in a-iron. Since α-iron dissolves carbon at room temperature only in thousandths of a percent, the properties of ferrite are close to those of pure iron. It has little strength and hardness, but is very ductile. This structure predominates in thin sheet and low carbon steel.

austenite

Austenite is a solid solution of carbon (up to 2%) and alloying elements in α-iron. Its hardness is 2-2.5 times greater than that of ferrite, with high ductility. This structure is obtained by thermal and chemical-thermal treatment.

Cementite

Cementite is a chemical compound of iron and carbon (6.67%), very brittle, approaching diamond in hardness.

Perlite

Perlite is a mechanical mixture of ferrite with cementite, formed during the decomposition of austenite, with a content of 0.8% carbon. The most common structural component of steels and cast irons.

ledeburite

Ledeburite is one of the main structural constituents of iron-carbon alloys. At the time of formation, it consists of cementite and austenite, and after cooling, it consists of cementite and perlite. Contains 4.3% carbon, is characterized by high hardness and brittleness.

Cast iron

Cast iron is an alloy of iron with carbon (2 - 4.3%), containing permanent impurities of silicon (up to 4.5%), manganese (1.5%), phosphorus (up to 1.5%) and sulfur (0.08% ), and in some cases, alloying elements (usually metals, such as nickel, chromium, copper, aluminum), included in alloys to give the latter the required properties.

Distinguish between pig iron (usually white), used for processing into steel, and foundry (gray), which is used to produce castings. The share of pig iron in the total volume of smelted iron is about 80%.

To improve the properties, gray cast iron is modified or alloyed. A variety of alloyed cast irons are special cast irons, which include anti-friction, heat-resistant, wear-resistant, etc. Malleable cast iron, which occupies an intermediate position between cast iron and steel, has higher mechanical properties and less brittleness than gray cast iron.

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

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

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

Introduction

3. Structural steels

4. Tool steels

Conclusion

Bibliography

steel alloy cast iron metal

Introduction

Since technically pure metals are relatively rarely used in mechanical engineering due to insufficient strength properties, alloys are mainly used as structural materials. An alloy is a substance consisting of two or more components obtained by mixing these components in liquid form. Components can be metals and non-metals. In addition to the main components, the alloy may contain impurities that can be useful, improving the performance properties of the alloy, or harmful, worsening these properties. Also, impurities are divided into those accidentally falling into the alloy during its preparation and specially added in order to give the alloy the desired properties.

After the alloy hardens, the components form a solid solution, a chemical compound, or a mechanical mixture. In a solid solution, one of the components (the base) usually retains its crystal lattice, while the other, in the form of individual atoms, is distributed inside this lattice. In a chemical compound, the components enter into chemical interaction with the formation of a new crystal lattice. In a mechanical mixture, the components are completely insoluble and each retain their own crystal lattice, and the alloy consists of a mixture of crystals of these components.

Alloys always have a specific basis on which they are divided into groups, for example, iron-based alloys are called black, these include steels and cast irons, and alloys based on aluminum, magnesium, titanium and beryllium have a low density and are called light non-ferrous alloys , alloys based on copper, lead, tin and a number of others - heavy non-ferrous alloys, alloys based on zinc, cadmium, tin, lead, bismuth - low-melting non-ferrous alloys, alloys based on molybdenum, niobium, zirconium, tungsten, vanadium and a number of other metals - refractory non-ferrous alloys.

1. Alloys based on iron. General information

The most common in industry alloys based on iron with the addition of carbon, which are called iron-carbon alloys and divide steels and cast irons. When the carbon content is less than 2.14%, the alloys are steels, more - cast irons. Steels and cast irons are the most important metal alloys of modern technology. Their production in volume exceeds the production of all other metals combined by more than 10 times.

According to the purpose, steel is divided into the following groups:

1) Structural steels (machine-building steels are intended for the manufacture of various parts of machines and mechanisms, and construction steels are for structures and structures).

2) Tool steels (have high hardness, strength and wear resistance and are used for the manufacture of various tools).

3) Steels and alloys with special physical properties(steels and alloys for which the main requirement for them is to provide a certain level of physical properties. The mechanical properties of these steels and alloys are often not of primary importance. Many of these alloys are precision in terms of high accuracy of the chemical composition and production technology).

In the processes of obtaining ferrous metals, cast iron occupies a particularly important place, since it is the primary product of smelting from ores in blast furnaces. According to their purpose, blast-furnace irons are divided into:

1) Pig iron, that is, going into processing for steel.

2) Cast iron - for the production of shaped castings.

3) Special cast irons, or blast-furnace ferroalloys.

Cast iron differs from steel: in composition - a higher content of carbon and impurities; in terms of technological properties - higher casting properties, low ability to plastic deformation, almost never used in welded structures.

Depending on the state of carbon in cast iron, there are:

White cast iron (carbon in a bound state in the form of cementite, in a fracture it has a white color and a metallic luster);

Gray cast iron (all or most of the carbon is in the free state in the form of graphite, and in the bound state there is no more than 0.8% of carbon, due to the large amount of graphite, its fracture is gray);

Half (part of the carbon is in the free state in the form of graphite, but no more than 2% of carbon is in the form of cementite, little used in technology).

2. Steel. General information

One of the most important classification features of steels is their chemical composition, since additional alloying components are introduced into them to obtain the desired properties.

So, according to the chemical composition, steel is divided into:

1) Carbon steels:

low carbon with 0.09 - 0.2% carbon content,

medium carbon with 0.2 - 0.45% carbon,

high carbon with more than 0.5% carbon;

2) Alloy steels:

low-alloyed, containing alloying elements up to 2.5%,

medium-alloyed, containing alloying elements 2.5 - 10%,

highly alloyed, containing more than 10% alloying elements.

Alloying is understood as the addition of other metals to the base metal to improve its properties.

The properties of steels are determined by the amount of carbon and impurities that interact with iron and carbon.

With an increase in the carbon content in the steel structure, ductility decreases and strength and hardness increase. The strength increases to about 1% carbon content, then it starts to decrease. With an increase in the carbon content, the cold brittleness threshold also increases (in this case, impact strength decreases), electrical resistance, coercive force, magnetic permeability and magnetic induction density decrease. Carbon also affects the technological properties. An increase in the carbon content worsens the casting properties of steel (steels with a carbon content of up to 0.4% are used), workability by pressure and cutting, and weldability. It should be taken into account that steels with a low carbon content are also poorly machined.

There are always impurities in steels, which are divided into 4 groups:

1) Permanent impurities: silicon, manganese, sulfur, phosphorus. Manganese and silicon are introduced in the process of steel smelting for deoxidation, they are technological impurities. Manganese increases strength without reducing ductility, and sharply reduces the red brittleness of steel caused by the influence of sulfur. Silicon, degassing the metal, increases the density of the ingot. Silicon increases the strength of steel, especially the yield strength, but there is a slight decrease in ductility, which reduces the ability of the steel to draw. Phosphorus distorts the plastic lattice, increases the tensile strength and yield strength, but reduces plasticity and viscosity, and causes cold brittleness. Sulfur is a harmful impurity that enters steel from cast iron, causes red brittleness (increased brittleness at high temperatures), reduces mechanical properties, especially impact strength and ductility, as well as endurance limit, worsens weldability and corrosion resistance. The content of phosphorus and sulfur in steel is undesirably higher than 0.03% each.

2) Hidden impurities - gases (nitrogen, oxygen, hydrogen) - enter the steel during smelting. Interstitial impurities (nitrogen and oxygen) increase the cold brittleness threshold and reduce the resistance to brittle fracture. Non-metallic inclusions (oxides, nitrides), being stress concentrators, can significantly reduce the endurance limit and viscosity. Hydrogen dissolved in steel is very harmful, which significantly embrittles the steel. It leads to the formation of flocs in rolled blanks and forgings. Flocks - thin cracks of oval or rounded shape, having the appearance of spots in a break - silver flakes. Metal with flocks cannot be used in industry; during welding, cold cracks form in the deposited and base metal. Vacuum is used to remove hidden impurities.

3) Special impurities are specially introduced into the steel to obtain the desired properties. The impurities are called alloying elements, and the steels are called alloy steels. Manganese and silicon can also be considered alloying elements if their content is more than 1.0 and 0.8%, respectively. Phosphorus and sulfur are extremely rare but still used as alloying elements in some specialty steels.

4) Random impurities.

Chromium is the main alloying element. It increases the hardenability, contributes to obtaining high and uniform hardness of steel.

Boron and manganese increase the hardenability and also increase the cold brittleness threshold.

Titanium is introduced to grind grain in chromium-manganese steel.

The introduction of molybdenum increases the hardenability, lowers the cold brittleness threshold, increases the static, dynamic and fatigue strength of the steel, eliminates the tendency to internal oxidation. In addition, it reduces the tendency to temper brittleness of steels containing nickel.

Vanadium refines the grain and increases strength and toughness.

Nickel increases strength and hardenability, lowers the cold brittleness threshold, but at the same time increases the tendency to temper brittleness (this disadvantage is compensated by molybdenum). Chrome-nickel steels have the best set of properties. However, nickel is a scarce metal and the use of such steels is limited. A significant amount of nickel can be replaced by copper, this does not lead to a decrease in viscosity.

When alloying chromium-manganese steels with silicon, steels are obtained - chromansil (20KhGS, 30KhGSA). Steels have a good combination of strength and toughness, are well welded, stamped and machined. Silicon increases impact strength and thermal toughness. The addition of lead, calcium improves machinability.

All structural materials are marked, that is, they have a brand (a kind of label), often reflecting the presence of the most important chemical elements in their composition.

An alphanumeric designation of steels has been adopted. And according to the type of designation, steel is also divided into several groups:

1) Carbon steels ordinary quality(GOST 380)

St is the index of this group of steels.

Digits from 0 to 6 - the conditional number of the steel grade. As the grade number increases, strength increases and ductility decreases.

Under delivery guarantees, there are 3 groups of steels: A, B and C. A - mechanical properties are guaranteed, the group A index is not indicated in the designation. B - guaranteed chemical composition. B - both mechanical properties and chemical composition are guaranteed.

The indexes kp, ps and cn indicate the degree of deoxidation of steel: kp - boiling, ps - semi-calm, cn - calm.

2) Quality carbon steels are supplied with guaranteed mechanical properties and chemical composition (group B). The degree of deoxidation is mostly calm.

Structural high-quality carbon steels are marked with a 2-digit number indicating the average carbon content in hundredths of a percent. The degree of deacidification is indicated if it differs from calm.

Steel 08kp, steel 10ps, steel 45.

Tool high-quality carbon steels are marked with the letter U (carbon tool steel) and a number indicating the carbon content in tenths of a percent.

U8 steel, U13 steel.

Tool high-quality carbon steels are marked similarly to high-quality tool carbon steels, only at the end of the brand they put the letter A, to indicate high quality steel.

Steel U10A.

3) Quality and high quality alloy steels.

Alloying elements are symbolized by the letters of the Russian alphabet: X - chromium, H - nickel, M - molybdenum, B - tungsten, K - cobalt, T - titanium, A - nitrogen (indicated in the middle of the brand), G - manganese, D - copper , F - vanadium, C - silicon, P - phosphorus, P - boron, B - niobium, C - zirconium, Yu - aluminum.

Alloy structural steels (steel 15Kh25N19VS2). At the beginning of the stamp, a 2-digit number is indicated, indicating the carbon content in hundredths of a percent. The alloying elements are listed below. The number following symbol element, shows its content as a percentage. If the number does not stand, then the content of the element does not exceed 1.5%. The specified steel grade contains 0.15% carbon, 35% chromium, 19% nickel, up to 1.5% tungsten, up to 2% silicon. To designate high-quality alloy steels, the symbol A is indicated at the end of the grade.

Alloyed tool steels (steel 9XC, steel HVG). At the beginning of the brand, a single-digit number is indicated, showing the carbon content in tenths of a percent. When the carbon content is more than 1%, the number is not indicated. The alloying elements are listed below with their contents. Some steels have non-standard designations.

4) High-speed tool steels (P18 steel).

P is the index of this group of steels. The carbon content is more than 1%. The number shows the content of the main alloying element - tungsten. Here - 18%. If steels contain an alloying element, then their content is indicated after the designation of the corresponding element.

5) Ball bearing steels (ShKh6 steel, ShKh15GS steel).

W - index of this group of steels, X - indicates the presence of chromium in the steel. The next number shows the chromium content in tenths of a percent, in the indicated steels, respectively, 0.6% and 1.5%. The alloying elements included in the steel are also indicated. The carbon content is more than 1%.

3. Structural steels

The following requirements are imposed on structural steels used for the manufacture of various machine parts:

Combination of high strength and sufficient viscosity;

Good technological properties;

Profitability;

Non-deficiency.

Details of modern machines and structures operate under conditions of high dynamic loads, high stress concentrations and low temperatures. All this contributes to brittle fracture and reduces the reliability of machines. Structural steels must have a high yield strength, which is the main characteristic in the calculation of machine parts and structures, in combination with high ductility, resistance to brittle fracture and low cold brittleness threshold. The durability of a product depends on its resistance to fatigue, wear and corrosion. All this determines the structural strength of steel. High structural strength of steel is achieved by rational choice of chemical composition, heat treatment modes, surface hardening methods, and improvement of metallurgical quality. Carbon plays a decisive role in the composition of structural steels. It increases the strength of steel, but reduces ductility and toughness, and increases the cold brittleness threshold. Therefore, its content is regulated and rarely exceeds 0.6%.

Alloying elements influence the structural strength. An increase in structural strength during alloying is associated with high hardenability, a decrease in the critical hardening rate, and grain refinement. The use of hardening heat treatment improves the complex of mechanical properties. Metallurgical quality also affects structural strength. Pure steel with the same strength properties has increased reliability characteristics. Machine-building structural steels are intended for the manufacture of various parts of machines and mechanisms. They are classified:

By chemical composition (carbon and alloyed);

By processing (cemented, improved);

By appointment (spring, ball-bearing).

Carbon steels differ in quality (ordinary quality steels and high-quality carbon steels), carbon content.

Steels of ordinary quality are used for the manufacture of hot-rolled ordinary products: beams, channels, angles, bars, as well as sheets, pipes and forgings. Steels as delivered are widely used in construction for welded, riveted and bolted structures. Ordinary quality steels often have a specialized purpose (bridge and shipbuilding, agricultural engineering, and others) and come in special specifications. The mechanical properties of steel of ordinary quality can be significantly increased, and the cold brittleness threshold is lowered by quenching in water from rolling heating.

High-quality carbon steels are smelted under more stringent conditions regarding the composition of the charge and the conduct of melting and casting. They are subject to higher requirements in terms of chemical composition and structure.

Low-carbon steels (carbon content less than 0.25%) have low strength and high ductility. These steels without heat treatment are used for lightly loaded parts - washers, gaskets, etc. Thin-sheet cold-rolled low-carbon steel is used for cold stamping of products. Low-carbon high-quality steels are also used for critical welded structures, as well as for machine parts hardened by carburizing.

Medium carbon steels (0.3 - 0.5% carbon) are used after normalization, thermal improvement and surface hardening for a wide variety of parts in all branches of engineering. These steels in the normalized state, compared with low-carbon steels, have higher strength at lower ductility. After thermal improvement, the best combination of mechanical properties is observed. In the annealed state, steels are well machined by cutting. The hardenability is low, and therefore they should be used for the manufacture of small parts or larger ones that do not require through hardenability. After surface hardening, they have high surface hardness and wear resistance.

High-carbon steels (0.6 - 0.8% carbon) have increased strength, wear resistance and elastic properties; they are used after heat treatment for parts operating under friction conditions in the presence of high static vibration loads. Springs and springs, spindles, lock washers, rolling rolls, etc. are made from these parts. The advantages of high-quality carbon steels are low cost and manufacturability. But due to the low hardenability, these steels do not provide the required set of mechanical properties in parts with a cross section of more than 20 mm.

Alloy steels are widely used in tractor and agricultural engineering, in the automotive industry, in heavy and transport engineering, and to a lesser extent in machine tool building, tool and other industries. These steels are widely used for heavy-duty metal structures. The higher the alloying of the steel and the smaller the dimensions of the semi-finished product, the higher the cost of the steel. The price of calibrated and ground steel is higher. The most widespread in construction are low-alloy steels (due to their good weldability, that is, the properties of the welded joint and the areas adjacent to it - heat-affected zones, are close to the properties of the base metal), and alloyed in mechanical engineering. High-alloy steels, as a rule, have a special purpose (corrosion-resistant, heat-resistant, non-magnetic).

Case-hardened steels are used for the manufacture of parts subject to wear and subject to variable and shock loads. Parts must combine high surface strength and hardness with sufficient core toughness. Carburizing is carried out on low-carbon steels with a carbon content of up to 0.25%. For parts that work with heavy loads, steels with a high carbon content (up to 0.35%) are used. As the carbon content increases, the strength of the core increases and the toughness decreases. Details are subjected to cyanidation and carbonitriding. Case-hardened carbon steels are used for the manufacture of small-sized parts operating under wear conditions at low loads (bushings, rollers, axles, studs). The hardness on the surface is 60-64 HRC, the core remains soft. Case-hardened alloy steels are used for the manufacture of parts in which, in addition to high surface hardness, it is necessary to have a sufficiently strong core (cam couplings, pistons, pins, bushings). The heat treatment modes and properties of steels approved by GOST 4543-71 are characteristic only for samples (when steel is accepted) and cannot be used in relation to products. The properties of steel (parts) are determined by the final thermal and chemical-thermal treatment adopted at a particular plant.

Many machine parts operating in difficult stressful conditions (under the action of various loads, including variable and dynamic), such as crankshafts, axles, rods, connecting rods, critical parts of turbines and compressor machines, are made of medium carbon steels and subjected to thermal improvement. Such steels take shock loads well. The resistance to brittle fracture is important. Improved carbon steels are cheap, they are used to make parts that experience low stresses and parts that require increased strength. But the thermal improvement of these steels provides a high complex of mechanical properties only in small-section parts, since the steels have low hardenability. The steels of this group can also be used in the normalized state. Improved alloy steels are used for larger and more heavily loaded critical parts. Steels have a better set of mechanical properties: higher strength while maintaining sufficient toughness and ductility, lower cold brittleness threshold.

High-strength steels are those with a tensile strength of more than 1500 MPa, which is achieved by selecting the chemical composition and optimal heat treatment. This level of strength can be achieved in medium carbon alloy steels by appropriate heat treatment, maraging steels and trip or tnp steels. High structural strength of the product is achieved only when it is made of a material with high strength and high resistance to brittle fracture. These requirements are largely met by carbon-free (less than 0.03%) maraging steels, hardened by quenching followed by aging. Maraging steels are used in aviation industry, rocket technology, shipbuilding, instrumentation for elastic elements, in cryogenic technology. Maraging steels are superior in structural strength and manufacturability to medium-carbon alloy steels. They have low notch sensitivity, high resistance to brittle fracture and low cold brittleness threshold with a strength of about 2000 MPa. However, these have become quite expensive. Metastable high-strength austenitic steels are called TRIP steels (TRIP from the initial letters - Transformation Induced Plasticity) or TNP steels (transformation induced plasticity). Characteristic of this group of steels is a high value of fracture toughness and endurance limit. With the same or close strength, PNP steels are more ductile, and with equal ductility, they have a higher yield strength than maraging or alloyed high-strength steels. The wide use of PNP steels is hindered by their high alloying, the need to use powerful equipment for deformation at relatively low temperatures, the difficulty of welding, the anisotropy of the properties of the deformed metal, etc. These steels are used for the manufacture of highly loaded parts, wire, cables, fasteners, etc.

Springs, springs and other elastic elements in operation experience multiple variable loads. A feature of the work is that under significant static and shock loads, the parts should experience only elastic deformation, residual deformation is not allowed. The main requirements for spring steels are to ensure high values of elastic limits, endurance, as well as the necessary ductility and resistance to brittle fracture, resistance to stress relaxation. The elastic and strength properties of spring steels are achieved by isothermal hardening. Spring steels are alloyed with elements that increase the elastic limit - silicon, manganese, chromium, tungsten, vanadium, boron. In order to increase the fatigue strength, decarburization during heating for quenching is not allowed and it is required high quality surfaces. In addition to general-purpose spring steels, spring steels and special-purpose alloys are widely used in mechanical engineering. In addition to high mechanical properties and stress relaxation resistance, they must have high corrosion resistance, non-magneticness, heat resistance and other special properties. These steels include high-alloyed martensitic (high-chromium corrosion-resistant steels), maraging, austenitic (corrosion-resistant, non-magnetic, heat-resistant) steels, etc.

Ball bearing steels are subjected to high, variable loads. The main requirements are high strength and wear resistance, high endurance limit, absence of stress concentrators, non-metallic inclusions, cavities, segregations. Ball bearing steels are characterized by a high carbon content (about 1%) and the presence of chromium, subjected to strict metallurgical control for the presence of porosity, non-metallic inclusions, carbide mesh, carbide segregation.

Machinability is one of the important technological characteristics become. Good machinability increases labor productivity and reduces tool consumption, which is especially important for mass production (auto and tractor building, agricultural engineering, machine tool building, etc.).

Therefore, so-called free-cutting steels are widely used in industry, which make it possible to carry out cutting at high speed, increase tool life and obtain a high quality of the surface to be machined. Significant anisotropy of impact strength in high machinability steels does not allow us to recommend them for parts operating in a complexly stressed state, as well as with significant stress concentrations.

Corrosion is the destruction of metals under the influence of environment. In this case, metals are often covered with corrosion products (rust). As a result of environmental influences, the mechanical properties of metals deteriorate sharply, sometimes even in the absence of a visible change. appearance surfaces. There are chemical corrosion occurring when the metal is exposed to gases (gas corrosion) and non-electrolytes (oil and its derivatives), and electrochemical corrosion caused by the action of electrolytes: acids, alkalis and salts. Electrochemical corrosion also includes atmospheric and soil corrosion. Steel that is resistant to gas corrosion at high temperatures (above 550ºC) is called scale-resistant (heat-resistant). Steels resistant to electrochemical, chemical (atmospheric, soil, alkaline, acid, salt), intercrystalline and other types of corrosion are called corrosion-resistant (stainless). An increase in the resistance of steel to corrosion is achieved by introducing elements into it that form protective films on the surface that are firmly bonded to the base metal and prevent contact between the steel and the external aggressive environment, as well as increasing the electrochemical potential of steel in various aggressive environments. Scale resistance depends on the composition of the steel, and not on its structure. The compositions of steels resistant to electrochemical corrosion are set depending on the environment for which they are intended. For parts of chemical equipment (housings of apparatuses, bottoms, flanges, nozzles, etc.) operating in a corrosive environment, two-layer steels have been used, consisting of a base layer - low-alloy or carbon steel and a corrosion-resistant cladding layer 1-6 mm thick of corrosion-resistant - resistant steels or nickel alloys.

Low temperatures (artificial cold) are widely used in industry, rocket and space technology, and in everyday life. Temperatures below the boiling point of oxygen (-183ºC) are called cryogenic. To work at these temperatures, special cryogenic steels and alloys with a low cold brittleness threshold are required. Cryogenic steels must have sufficient strength at normal temperature, combined with high resistance to brittle fracture at low temperatures. These steels are often required to have high corrosion resistance. As cryogenic, low-carbon nickel steels and austenitic steels are used, which are not prone to cold brittleness.

Heat-resistant steels and alloys are those that can work under stress at high temperatures for a certain time and at the same time have sufficient heat resistance. Heat-resistant steels and alloys are used to manufacture many parts of boilers, gas turbines, jet engines, rockets, etc., operating at high temperatures. Heat-resistant steels due to their relatively low cost (compared to the cost of other heat-resistant alloys) are widely used in high-temperature technology. Operating temperatures of heat-resistant steels are 500-750ºС. The more complex the composition of the steel, the higher the alloying of the solid solution and the more strengthening phases, the higher their heat resistance. Nickel-based heat-resistant steels are often called nimonics. These alloys are widely used in various fields of technology (aircraft engines, stationary gas turbines, chemical apparatus building, etc.). The alloys are intended for the manufacture of rotor blades, turbine disks, rings, fasteners with a long service life, nozzle blades and other parts of gas turbines operating at temperatures up to 850ºC.

4. Tool steels

Tool steels are called carbon and alloy steels, which have high hardness, strength and wear resistance and are used for the manufacture of various tools. One of the main characteristics of tool steels is heat resistance (or red hardness), that is, the ability to maintain high hardness when heated.

All tool steels are divided into 3 groups: non-heat-resistant (carbon and alloy steels containing up to 3-4% alloying elements), semi-heat-resistant up to 400-500ºС (containing over 0.6-0.7% carbon and 4-18% chromium ), and heat-resistant up to 550-650ºС (high-alloy steels containing chromium, tungsten, vanadium, molybdenum, cobalt, ledeburite class), the latter are called high-speed. Another important characteristic tool steels is hardenability. High-alloy heat-resistant and semi-heat-resistant steels have high hardenability. Tool steels that do not have heat resistance are divided into steels of low hardenability (carbon) and high hardenability (alloyed).

Steels for cutting tools after appropriate heat treatment should have a high hardness in the cutting edge, significantly exceeding the hardness of the material being processed; high wear resistance necessary to maintain the size and shape of the cutting edge during cutting; sufficient strength at some toughness to prevent tool breakage during operation and heat resistance when cutting is performed at an increased speed, since cutting edges can be heated to a temperature of 500-900ºC.

Carbon tool steels contain 0.65-1.35% carbon. Due to the low stability of supercooled austenite, they have low hardenability, and therefore these steels are used for small tools.

Alloyed tool steels contain 0.9-1.4% carbon and, like carbon steels, do not have heat resistance and are only suitable for cutting low-strength materials at low speeds. They are used for tools that are not subjected to heat in excess of 200-250ºC. Alloy steels have higher hardenability. High hardenability steels have high heat resistance, good cutting properties and relatively little deformation during hardening. High hardness and wear resistance are mainly determined by the high carbon content. The total content of alloying elements is up to 5%. These steels are used to make impact and cutting tools.

High speed steels get their name from their properties. Due to their high heat resistance, tools made from them can work with enough high speeds cutting. Steels contain 0.7-1.5% carbon, up to 18% of the main alloying element - tungsten, up to 5% chromium and molybdenum, up to 10% cobalt, which increases heat resistance. The main forks of cutting tools made of high-speed steel are cutters, drills, cutters, broaches, machine taps, and paper cutting knives. Often, only the working part of the tool is made of high-speed steel.

Steels for measuring tools (tiles, gauges, templates) must have high hardness and wear resistance, maintain dimensional stability for a long time and be well ground. Constancy of dimensions is ensured by the minimum temperature coefficient of linear expansion and minimization of structural transformations over time. For the manufacture of measuring instruments, the following are used: high-carbon tool steels, alloyed and carbon after appropriate heat treatment; low-carbon steels after carburizing; nitraloy after nitriding for high hardness.

The tool used for metal forming (dies, punches, matrices) is made of die steels. Distinguish steel for stamps of cold and hot deformation.

Cold forming dies operate under high variable loads, fail due to brittle fracture, low-cycle fatigue, and changes in shape and size due to crushing (plastic deformation) and wear. Therefore, steels used for the manufacture of dies that plastically deform metal at normal temperatures must have high hardness, wear resistance and strength, combined with sufficient toughness. In the process of deformation at a high speed, the dies are heated up to 200-350ºC, so steels of this class must also be heat-resistant. For small dies (up to 25 mm), carbon tool steels are used; for larger products, alloy steels are used, which have better hardenability. If the die tool experiences shock loads, then steels with higher toughness are used. This is achieved by reducing the carbon content, introducing alloying elements and appropriate heat treatment. Quite often, high-speed steels are used to make cold forming dies.

Dies for hot deformation work under severe loading conditions and fail (break) due to plastic deformation (collapse), brittle fracture, formation of a crack network (cracks) and wear of the working surface. Therefore, steels used for dies that deform metal in a hot state must have high mechanical properties (strength and toughness) at elevated temperatures and have wear resistance, scale resistance and heat resistance, that is, the ability to withstand repeated heating and cooling without the formation of fire cracks. In addition, steels must have high hardenability to ensure high strength over the entire cross section of the tool and thermal conductivity for better heat removal from the working surfaces of the stamp. For the manufacture of hammer dies, chromium-nickel medium carbon steels are used.

Hot pressing dies work in more difficult conditions, where the surface heating during deformation is up to 600-700ºС. Steels of increased heat resistance are used for their manufacture. The materials used for tools are hard alloys, which consist of hard carbides and a binder phase. They are manufactured by powder metallurgy.

5. Steels and alloys with special physical properties

Steels and alloys with special physical properties are divided into the following groups:

v Magnetic steels and alloys:

Ш Magnetically hard steels and alloys are used for the manufacture of permanent magnets. For this, high-carbon steels with a carbon content of 1%, alloyed with chromium or chromium and cobalt, are used.

Ш Magnetically soft steels (electrical steel) are used for the manufacture of DC and AC magnetic circuits. They are intended for the manufacture of armatures and poles of DC machines, rotors and stators of asynchronous motors, for magnetic circuits of large electrical machines, power transformers, devices, devices, etc. As a magnetically soft material, low-carbon iron-silicon alloys (0.05-0.005% carbon, 0.8-4.8% silicon) are widely used.

Ш Paramagnetic steels (non-magnetic) are used in electrical engineering, instrument making, shipbuilding and special areas of technology. The disadvantage of these steels is the low yield strength, which makes it difficult to use them for highly loaded machine parts.

v Metallic glasses (amorphous alloys) - the scope is approximately the same as that of soft magnetic steels.

v Steels and alloys with high electrical resistance for heating elements.

v Alloys with a given temperature coefficient of linear expansion - are widely used in mechanical engineering and instrument making. The most common iron-nickel alloys (Invars).

v Alloys with shape memory effect. At a stress above the elastic limit, after the load is removed, the metal does not reproduce its original dimensions and shape. Relatively recently discovered alloys with the effect of "shape memory". These alloys, after plastic deformation, restore their original geometric shape either as a result of heating (the "shape memory" effect), or immediately after removing the load (superelasticity). The most common iron-containing alloys are iron-nickel alloys.

Gray cast iron is widely used in mechanical engineering, as it is easy to process and has good properties. Depending on the strength, gray cast iron is divided into 10 grades. Given the low resistance of gray iron castings to tensile and shock loads, this material should be used for parts that are subjected to compressive and bending loads. In machine tool building, these are basic, body parts, brackets, gears, guides; in the automotive industry - cylinder blocks, piston rings, camshafts, clutch discs.

Ductile irons are obtained from gray irons by inoculation with magnesium or cerium. Compared to gray cast irons, the mechanical properties are improved. From high-strength cast iron, thin-walled castings (piston rings), forging hammers, beds and frames of presses and rolling machines, molds, tool holders, and faceplates are made.

Ductile iron is obtained by annealing white cast iron. In terms of mechanical and technological properties, malleable cast iron occupies an intermediate position between gray cast iron and steel. The disadvantage of ductile iron compared to ductile iron is the limitation of the wall thickness for casting and the need for annealing. Ductile iron castings are used for parts operating under shock and vibration loads.

Ferritic cast irons are used to make gearbox housings, hubs, hooks, brackets, clamps, couplings, flanges.

Perlitic cast irons, characterized by high strength and sufficient ductility, are used to make forks of cardan shafts, links and rollers of conveyor chains, and brake shoes.

Chilled cast irons are castings whose surface consists of white cast iron, and the inside is gray or ductile cast iron. They have high surface hardness and very high wear resistance. Used for the manufacture of rolling shafts, wagon wheels with bleached rims, balls for ball mills.

For the manufacture of parts operating under abrasive wear conditions, white cast irons alloyed with chromium, chromium and manganese, chromium and nickel are used. Cast iron castings are characterized by high hardness and wear resistance.

Conclusion

We examined the main features and characteristics of perhaps the most widely used material in the industry at the moment. Since ancient times, people have used iron and its alloys to create tools, jewelry, weapons, and household items. Today, more than 10,000 iron-based alloys are used in industry. Not a single metal is capable of such transformations as iron, and only iron widely uses its properties in alloying and heat treatment. The range of properties of its alloys is unusually wide: from pure iron as soft as lead to tool steel as hard as diamond, from dynamo and transformer sheet with special magnetic properties to non-magnetic iron alloys, from wear-resistant special steels to corrosion-resistant and stainless steels. Alloying and heat treatment using pressure and radiation can produce iron materials with incredible properties. And this is by no means the end, but only the beginning of a grandiose path of development of iron metallurgy. Scientists are constantly busy obtaining new data that contribute to the improvement and creation of new methods for the production and processing of iron-based materials.

Bibliography

1. Beckert M. Iron. Facts and legends. Translated from German by G.G.Kefer. Moscow: Metallurgy, 1984. 232 p.

2. Lakhtin Yu.M., Leontieva V.P. Materials Science: Textbook. 6th ed., LLC Publishing House Alliance, 2011. 528 p.

3. Checheta I.A. Technological processes in mechanical engineering. Initial parameters and definitions: tutorial/ I.A. Checheta. - Voronezh: VPO "Voronezh State Technical University", 2012. 200 p.

Hosted on Allbest.ru

...

COMPONENTS AND PHASES IN THE IRON-CARBON SYSTEM

Iron is a grayish metal. Atomic number 26, atomic mass 55.85, atomic radius 0.127 nm. The pure iron currently available contains 99.999% Fe, technical grades 99.8-99.9 % Fe. The melting point of iron is 1539 °C. Iron has two polymorphic modifications a and u. Modification of a-iron exists at temperatures below 910 ° C and above 1392 ° C (Fig. 82). In the temperature range 1392-1539 ° C, a-iron is often referred to as b-iron.

The crystal lattice of a-iron is a body-centered cube with a lattice period of 0.28606 nm. Up to a temperature of 768 °C, a-iron is magnetic (ferromagnetic). The temperature of 768 ° C, corresponding to the magnetic transformation, i.e., the transition from the ferromagnetic state to the paramagnetic state, is called the Curie point and denoted A. g.

The density of a-iron is 7.68 g/cm 3 .

Rice. 82. Pure iron cooling curve (a) and microstructure diagram of a-Fe ferrite (b) and austenite y-Fe (c), X 150

y-iron exists at a temperature of 910-

1392 °С; it is paramagnetic.

The crystal lattice of y-iron is face-centered cubic (a =

0.3645 nm at 910°C).

The critical point of transformation a^=ty(pnc. 821 at 910 C C is denoted, respectively, Ac 3(on heating) and Ag b(on cooling). Critical transition point y ^ a at 1392 °C denote Ac x(on heating) and Ag 4(on cooling).

Carbon is a non-metallic element of period II of group IV periodic system, atomic number 6, density 2.5 g/cm 8 , melting point 3500 C, atomic radius 0.077 nm. Carbon is polymorphic. Under normal conditions, it exists as a modification of graphite, but it can also exist as a metastable modification of diamond.

Carbon is soluble in iron in liquid and solid states, and can also be in the form of a chemical compound - cementite, and in high-carbon alloys and in the form of graphite.

In the Fe-C system, the following phases are distinguished: liquid alloy, solid solutions - ferrite and austenite, as well as cementite and graphite.

Ferrite(F) - solid solution of carbon and other impurities in a-iron. Distinguish low-temperature a-ferrite with carbon solubility up to 0.02 % and high-temperature 6-ferrite with a limiting carbon solubility of 0.1%. The carbon atom is located in the ferrite lattice in the center of the cube face, where a sphere with a radius of 0.29 of the atomic radius of iron is placed, as well as in vacancies, on dislocations, etc. Under a microscope, ferrite is detected in the form of homogeneous polyhedral grains (see Fig. 82, b).

Ferrite (at 0.06 % C) has approximately the following mechanical properties: a n = 250 MPa, a oa = 120 MPa, b 50 %, f ^ 80%, 80-90 HB.

austenite(A) - solid solution of carbon and other impurities in y-iron. The limiting solubility of carbon in y-iron is 2.14%. The carbon atom in the lattice of y-iron is located in the center of the unit cell (see Fig. 29b), in which a sphere with a radius of 0.41# can fit (# is the atomic radius of iron) and in the defective regions of the crystal.

The different volumes of elementary spheres in the bcc and fcc lattices predetermined the much higher solubility of carbon in y-iron compared to the solubility in a-iron. Austenite has high ductility, low yield strength and strength. The microstructure of austenite is polyhedral grains (Fig. 82, in).

Cementite(C) is a chemical compound of iron with carbon - iron carbide Fe 3 G. Cementite contains 6.67% C. Cementite has a complex rhombic lattice with a dense packing of atoms. The melting point of cementite has not been accurately determined due to the possibility of its decomposition. Up to a temperature of 210 b C, denoted A 0 , cementite is ferromagnetic. The characteristic features of cementite are high hardness of 1000 HV and very low ductility. Cementite is a metastable phase. Under equilibrium conditions, graphite is formed in alloys with a high carbon content.

Graphite has a hexagonal layered (see Fig. 88, a) crystal lattice. The interatomic distances in the lattice are small and amount to 0.142 nm, the distance between the planes is 0.340 nm. Graphite is soft, has low strength and electrical conductivity.

In Fe-G alloys, there are two high-carbon phases: metastable - cementite and stable - graphite. Therefore, two state diagrams are distinguished - metastable Fe-Fe 3 G and stable Fe-G (graphite).

The designations Ac and Ag come from the initial letters of the French words: A - arreter - stop (platform on the cooling curve), c - choffage-heating ig - refroidissnwnt - cooling.

Basic iron alloys. iron alloys

Ferrite

austenite

Cementite

Perlite

ledeburite

Cast iron

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

Similar Documents

COMPONENTS AND PHASES IN THE IRON-CARBON SYSTEM

Read also

Scenario of the holiday "meeting of spring"

Registration of the reception group "Stars

Scenario "cool stories" for the competition "class of the year" The two-story school stands

THE BELL