Grades of carbon steel. classification, GOST, application. Deciphering steel grades 08 deciphering steel

Steel grade: 08kp (substitute: 08).

Class: quality structural carbon steel.

Industrial use: for gaskets, washers, forks, pipes, as well as parts subjected to chemical and thermal treatment - bushings, eyes, rods.

Hardness: HB 10 -1 = 179 MPa

Weldability of the material: without restrictions, except for chemically - thermally treated parts; welding methods: RDS, ADS submerged arc m gas protection, KTS.

Forging temperature, o С: beginning 1250, end 800. Workpieces with a cross section of up to 300 mm are cooled in air.

Flock sensitivity: not sensitive.

Tendency to temper brittleness: not inclined.

Delivery type:

• Sections, including shaped: GOST 2590-2006, GOST 2879-2006, GOST 8509-93, GOST 10702-78.
• Calibrated rod GOST 7417-75, GOST 8560-78, GOST 10702-78.
• Polished rod and silver thread GOST 10702-78, GOST 14955-77.
• Thin sheet GOST 16523-97, GOST 19903-74, GOST 19904-90, GOST 9045-93.
• Tape GOST 503-81, GOST 10234-77.
• Strip GOST 1577-93, GOST 82-70.
• Pipes GOST 10704-91, GOST 10705-80.
• Thick sheet GOST 4041-71, GOST 19903-74, GOST 1577-93.

We present you the popular material 08kp. It is a structural carbon steel of high quality. "KP" in the name means that the steel is boiling (meaning the degree of steel deoxidation). And "08" indicates a carbon content of about 0.08 percent. Analogue 08kp - brand 08, which is its substitute.

If you are interested in information about various steel grades, then you will find full descriptions of popular materials on the pages of our website. You can also order the products you are interested in in our company. Managers of the company "Atlant Metal" are always ready to advise you on issues of interest. Give us a call anytime, we are available 24/7!

Steel 08kp and its characteristics

The material has unlimited weldability (this does not apply to elements processed by chemical and thermal methods). Products can be welded in various ways: using manual arc welding and resistance spot welding, submerged argon arc welding (addition - gas shielding).

To start forging material 08kp,> it is necessary to heat the equipment to a temperature of 1,250 degrees Celsius. By the end of forging, it should be reduced to 800 degrees.

The material is not sensitive to flocks. Steel 08kp is not prone to temper brittleness.

As for cooling, it must be carried out in the usual way for workpieces with a cross section of more than 300 millimeters. If it is less, then the parts should be air-cooled.

Hardness St08kp: HB 10 -1 = 179 MPa.

Steel 08kp and its application

This material is used everywhere. In the industrial sector, it is used for the manufacture of a number of parts, for example, fasteners, pipes, forks, auxiliary elements. Also, from this brand, elements are created that will be further processed by chemical and thermal methods, for example, parts with a cylindrical shape and an axial hole, rods and lugs.

From steel 08kp in accordance with GOST 2590-2006, GOST 10702-78 and others, long products, as well as shaped steel, are manufactured. You can see various rods created from this material that have been polished and calibrated. Silver is in high demand. For the manufacture of parts, tapes and strips are used. In many areas, pipes from this steel grade are used. For the manufacture of blanks, sheets of different thicknesses are used.

Steel is a product of ferrous metallurgy, the main product of which is building fittings, rolled metal products of various profiles, pipes, parts, mechanisms and tools.

Steel production

Ferrous metallurgy is also engaged in steel. Cast iron is a hard but not durable material. Steel - durable, reliable, ductile, prone to being used in foundry, rolling, forging and stamping.

There are several ways to smelt steel:

1. Converter. Equipment: Charge (raw materials): scrap steel, limestone. Only carbon steels are produced.
2. Martenovsky. Equipment: open-hearth furnace. Charge: liquid pig iron, steel scrap, iron ore. Universal for both carbon and alloy steels.
3. Electric arc. Equipment: electric arc furnace. Charge: steel scrap, cast iron, coke, limestone. Universal method.
4. Induction. Equipment: induction furnace. Charge: steel and cast iron scrap metal, ferroalloys.

The essence of the steel production process is to reduce the amount of negative chemical inclusions in order to obtain a metal that is popularly called "iron", or rather, an iron-carbon alloy with a carbon content of not more than 2.14%.

Deoxidation processes

For steel at the final stage of smelting, a boiling process is characteristic, which is influenced by the nitrogen, hydrogen, and carbon oxides inherent in it. Such an alloy in the solidified state has a porous structure, which is removed by rolling. It is soft and plastic, but not strong enough.

The deoxidation process consists in the deactivation of boiling impurities by introducing ferromanganese, ferrosilicon, and aluminum into the alloy. Depending on the amount of residual gases and deoxidizing elements, steel can be semi-calm or calm.

The finished steel of the required degree of deoxidation is poured into molds for crystallization and use at subsequent technological stages in the manufacture of finished steel products.

Classification of carbon steel

All steel that exists on the world market can be divided into carbon and alloy. All grades of carbon steel are divided into different classifier groups and designation features.

Based on the main classification features, there are:

1. Carbon structural steels. They contain less than 0.8% carbon. They are used for the manufacture of fittings, rolling products and castings.
2. Carbon tool steels containing 0.7% to 1.3% carbon. They are used for tools, instrumentation equipment.

According to the methods of deoxidation:

• boiling - deoxidizing elements (RE) in the composition of less than 0.05%;
• semi-calm - 0.05%≤RE≤0.15%;
• calm - 0.15%≤RE≤0.3%.

By chemical composition:

• low-carbon (0.3% ≤ C);
• medium carbon (0.3≤С≤0.65%);
• high-carbon (0.65≤С≤1.3%).

Depending on the microstructure:

• hypoeutectoid - in such steel, carbon in the composition is less than 0.8%;
• eutectoid - these are steels with a carbon content of 0.8%;
• hypereutectoid - steels with a carbon content of more than 0.8%.

By quality:

1. Regular quality. Sulfur here contains less than 0.06%, phosphorus - no more than 0.07%.
2. Quality steels. They do not contain sulfur and phosphorus more than 0.04%.
3. High quality. The amount of sulfur here does not exceed 0.025%, and phosphorus - no more than 0.018%.

According to the main standard, carbon steel grades are distributed into:

• structural of ordinary quality;
• structural quality;
• instrumental quality;
• instrumental high quality.

Features of marking structural steel of ordinary quality

Steels of ordinary quality contain: C - up to 0.6%, S - up to 0.06%, P - up to 0.07%. Let's look at how this carbon steel is marked. GOST 380 defines the following nuances of designation:

• A, B, C - group; A - not indicated in stamps;
• 0-6 after the letters "St" - a serial number in which the chemical composition and (or) mechanical properties are encrypted;
• G - the presence of Mangan Mn (manganese);
• kp, ps, cn - degree of deoxidation (boiling, semi-calm, calm).

The numbers from 1 to 6 after the degree of deoxidation through a dash are categories. In this case, the first category is not indicated in any way.

The letters M, K at the beginning of the brand can mean a metallurgical method of production: open-hearth or oxygen-converter. By the way, carbon steels of ordinary quality are represented by the quantitative composition of grades, approximately 47 pieces.

Classification of structural steels of ordinary quality

Carbon steels of ordinary quality are divided into groups.

• Group A: steels that must exactly match the specified mechanical properties. They are supplied to the consumer most often in the form of sheet and diversified products (sheets, tees, I-beams, fittings, rivets and cases). Grades: St0, St1 - St6 (kp, ps, sp), categories 1-3, including St3Gps, St5Gps.
• Group B: steels that must be regulated by the necessary chemical composition and properties. Castings and rolled products are produced, which will be subjected to additional machining by pressure in a hot state (forging, stamping). Marks: Bst0, Bst1 (kp-sp), Bst2 (kp, ps), Bst3 (kp-sp, including Bst3Gps), Bst4 (kp, ps), Bst 6 (ps, sp), categories 1 and 2.
• Group B: steels that must meet the required chemical, physical, mechanical and technological properties. This group is characterized by a variety of grades from which plastic sheet products are made, durable fittings for working in areas of significant temperature differences, critical parts (bolts, nuts, axles, piston pins). All products of different composition, properties and grades of this group are united by good technological weldability. Grades: VSt1-VSt6 (kp, ps, sp), VSt5 (ps, sp), including VSt3Gps, categories 1-6.

Structural steels of ordinary quality are alloys that have a wide variety of uses in industry.

Marking of carbon quality steel

Carbon quality steels have in the composition of S and P no more than 0.04%, respectively.

Marking (GOST 1050-88):

• numbers 05-60 - encrypted presence of carbon (minimum - 0.05%, maximum - 0.6%);
• kp, ps, cn - the degree of deoxidation ("cp" is not indicated);
• G, Yu, F - contain manganese, aluminum, vanadium.

Exceptions to labeling

Carbon quality steels in their marking have exceptions:

• 15K, 20K, 22K - high-quality steels, applicable in boiler building;
• 20-PV - carbon - 0.2%, steel is applicable in the manufacture of pipes by hot rolling, in boiler building and installation of heating systems, contains copper and chromium;
• OSV - steel for the manufacture of wagon axles, contains nickel, chromium, copper.

For all grades of quality steels, the possible need to use thermal (for example, normalization) and chemical-thermal treatment (for example, carburizing) is typical.

Classification of carbon quality steels

This type of carbon steels can be divided into 4 groups:

1. Highly plastic material applicable for cold machining (rolling), sheet and pipe rolling. Grades - steel 08ps, steel 08, steel 08kp.
2. A metal used in hot rolling and stamping that will perform under thermally aggressive conditions. Grades - from steel 10 to steel 25.
3. Steel that has found application in the manufacture of critical parts, including springs, springs, couplings, bolts, shafts. Grades - from steel 60 to steel 85.
4. Steels that require reliable operation in aggressive conditions (for example, the chain of a caterpillar tractor). Grades steel 30, steel 50, steel 30G, steel 50G.

It is also possible to divide into 2 groups all known grades of carbon steel from the quality class: conventional structural and manganese-containing structural.

Application of carbon structural steel

Carbon tool steels are characterized by high strength and toughness. They are necessarily subject to multi-stage heat treatment.

Brand designation (GOST 1435-74):

• U - carbon instrumental;
• 7 -13 - the carbon content in it is 0.7-1.3%, respectively;
• G - the presence of manganese in the composition;
• A is high quality.

An exception to the basic principles of marking carbon tool steels is the material for parts of watch movements A75, ASU10E, AU10E.

Requirements for carbon tool steels

In accordance with GOST, tool steels must comply with a number of characteristics.

Required physical, chemical and mechanical properties: quality indicators of hardness, impact strength, strength, resistance to temperature changes during operation (during cutting, drilling, shock loads), corrosion resistance.

Given technological properties:

• resistance to negative processes of cutting technology (chip sticking, hardening);
• good machinability by turning and grinding;
• susceptibility to heat treatment;
• overheat resistance.

To improve the quality of mechanical and technological indicators, tool steels are subjected to multi-stage heat treatment:

• annealing of the starting material before making tools;
• hardening (cooling in salt solutions) and subsequent tempering of finished products (mainly low tempering).

The obtained properties are determined by the chemical composition and the resulting microstructure: martensite with cementite and austenite inclusions.

Use of carbon tool steels

The described steels are used for the manufacture of all kinds of tools: cutting, percussion, auxiliary.

• Steel U7, U7A - hammers, chisels, axes, chisels, sledgehammers, chisels, fish hooks.
• Steel U8, U8A, U8G - saws, screwdrivers, center punches, countersinks, cutters, pliers.
• Steel U9, U9A - metalwork tools, tools for cutting wood.
• U11, U11A - rasps, taps, auxiliary tools for stamping and calibration.
• U 12, U12A - reamers, taps, measuring tools.
• U13, U13A - files, shaving and surgical instruments, stamping punches.

A rational choice of carbon steel grade, its heat treatment technology, understanding of its properties and features is the key to a long service life of manufactured, processed or used structures or tools.

Any specialist dealing with metal is familiar with the concept of "steel grade". Deciphering the marking of steel alloys makes it possible to get an idea of ​​their chemical composition and physical characteristics. Understanding this marking, despite its apparent complexity, is quite simple - it is only important to know on what basis it is compiled.

The alloy is designated with letters and numbers, by which it is possible to accurately determine which chemical elements it contains and in what quantity. Knowing this, as well as how each of these elements can affect the finished alloy, it is possible to determine with a high degree of probability which technical characteristics are characteristic of a particular steel grade.

Types of steels and features of their marking

Steel is an alloy of iron with carbon, while the content of the latter in it is not more than 2.14%. Carbon gives the alloy hardness, but when it is in excess, the metal becomes too brittle.

One of the most important parameters according to which steels are divided into different classes is the chemical composition. Among steels according to this criterion, alloyed and carbon steels are distinguished, the latter are divided into low-carbon (up to 0.25%), medium-(0.25–0.6%) and high-carbon (they contain more than 0.6% carbon).

By including alloying elements in the composition of steel, it can be given the required characteristics. It is in this way, by combining the type and quantitative content of additives, that grades with improved mechanical properties, corrosion resistance, magnetic and electrical characteristics are obtained. Of course, it is possible to improve the characteristics of steels with the help of heat treatment, but alloying additives make it possible to do this more efficiently.

According to the quantitative composition of alloying elements, low-, medium- and high-alloyed alloys are distinguished. In the first alloying elements, no more than 2.5%, in medium-alloyed - 2.5-10%, in high-alloyed - more than 10%.

The classification of steels is also carried out according to their purpose. So, there are instrumental and structural types, brands that differ in special physical properties. Tool types are used for the production of stamping, measuring, and cutting tools, structural - for the production of products used in construction and engineering. From alloys with special physical properties (also called precision alloys), products are made that must have special characteristics (magnetic, strength, etc.).

Steels are opposed to each other by special chemical properties. The alloys of this group include stainless, scale-resistant, heat-resistant, etc. Typically, they can be corrosion-resistant and are different categories.

In addition to useful elements, steel also includes harmful impurities, the main of which are sulfur and phosphorus. It also contains gases in an unbound state (oxygen and nitrogen), which negatively affects its characteristics.

If we consider the main harmful impurities, then phosphorus increases the brittleness of the alloy, which is especially pronounced at low temperatures (the so-called cold brittleness), and sulfur causes the appearance of cracks in the metal heated to a high temperature (red brittleness). Phosphorus, among other things, significantly reduces the ductility of the heated metal. According to the quantitative content of these two elements, steels of ordinary quality (not more than 0.06–0.07% sulfur and phosphorus), high-quality (up to 0.035%), high-quality (up to 0.025%) and especially high-quality (sulfur - up to 0.015%, phosphorus - up to 0.02%).

The marking of steels also indicates the extent to which oxygen has been removed from their composition. According to the level of deoxidation, steels are distinguished:

• calm type, denoted by the letter combination "SP";
• semi-calm - "PS";
• boiling - "KP".

What does steel marking say?

Deciphering the brand of steel is quite simple, you only need to have certain information. Structural steels of ordinary quality and not containing alloying elements are marked with the letter combination "St". By the number after the letters in the brand name, you can determine how much carbon is in such an alloy (calculated in tenths of a percent). The letters “KP” may follow the numbers: it becomes clear from them that this alloy has not completely gone through the process of deoxidation in the furnace, respectively, it belongs to the boiling category. If the brand name does not contain such letters, then the steel corresponds to the calm category.

Structural, belonging to the category of quality, has two digits in its designation, they determine the average carbon content in it (calculated in hundredths of a percent).

Before proceeding to consider the grades of those steels that include alloying additives, you should understand how these additives are designated. Marking of alloy steels may include the following letters:

Designation of steels with alloying elements

As mentioned above, the classification of steels with alloying elements includes several categories. The marking of alloy steels is compiled according to certain rules, the knowledge of which makes it quite easy to determine the category of a particular alloy and its main area of ​​​​application. In the initial part of the names of such brands there are numbers (two or one) indicating the carbon content. Two numbers indicate its average content in the alloy in hundredths of a percent, and one - in tenths. There are also steels that do not have numbers at the beginning of the brand name. This means that carbon in these alloys is contained within 1%.

The letters that can be seen behind the first digits of the brand name indicate what this alloy consists of. Behind the letters, giving information about a particular element in its composition, there may or may not be numbers. If there is a number, then it determines (in whole percent) the average content of the element indicated by the letter in the composition of the alloy, and if there is no number, then this element is contained in the range from 1 to 1.5%.

At the end of the marking of certain types of steels, the letter "A" may be placed. This suggests that we have high-quality steel. Such grades may include carbon steels and alloys with alloying additives in their composition. According to the classification, this category of steels includes those in which sulfur and phosphorus make up no more than 0.03%.

Examples of marking steels of various types

Determining the grade of steel and assigning an alloy to a certain type is a task that should not cause any problems for a specialist. There is not always a table at hand that gives a breakdown of the brand names, but the examples below will help you figure it out.

Structural steels that do not contain alloying elements are designated by the letter combination "St". The numbers following are the carbon content, calculated in hundredths of a percent. Low-alloy structural steels are marked somewhat differently. For example, steel grade 09G2S contains 0.09% carbon, and alloying additives (manganese, silicon, etc.) are contained in it within 2.5%. Very similar in their markings, 10KhSND and 15KhSND differ in different amounts of carbon, and the share of each alloying element in them is no more than 1%. That is why there are no numbers after the letters denoting each alloying element in such an alloy.

20X, 30X, 40X, etc. - this is how structural alloyed steels are marked, the predominant alloying element in them is chromium. The number at the beginning of such a brand is the carbon content in the alloy in question, calculated in hundredths of a percent. Behind the letter designation of each alloying element, a number can be affixed, by which its quantitative content in the alloy is determined. If it is not there, then the specified element in the steel contains no more than 1.5%.

You can consider an example of the designation of chromium-silicon-manganese steel 30KhGSA. It, according to the marking, consists of carbon (0.3%), manganese, silicon, and chromium. Each of these elements is contained in it within the boundaries of 0.8–1.1%.

How to decipher steel markings?

So that deciphering the designation of various types of steel does not cause difficulties, you should know well what they are. Separate categories of steels have a special marking. It is customary to designate them with certain letters, which allows you to immediately understand both the purpose of the metal in question and its approximate composition. Consider some of these brands and understand their designation.

Structural steels specially designed for the manufacture of bearings can be recognized by the letter "Ш", this letter is placed at the very beginning of their marking. After it in the brand name comes the letter designation of the corresponding alloying additives, as well as numbers by which the quantitative content of these additives is recognized. So, in steel grades ШХ4 and ШХ15, in addition to iron with carbon, chromium is contained in an amount of 0.4 and 1.5%, respectively.

The letter "K", which comes after the first digits in the brand name, reporting the quantitative content of carbon, denotes structural unalloyed steels used for the production of vessels and steam boilers operating under high pressure (20K, 22K, etc.).

High-quality alloy steels that have improved casting properties can be recognized by the letter "L" at the very end of the marking (35KhML, 40KhL, etc.).

Some difficulty, if you do not know the features of the marking, can be caused by deciphering the grades of building steel. Alloys of this category are designated by the letter "C", which is placed at the very beginning. The numbers following it indicate the minimum yield strength. These stamps also use additional letter designations:

• letter T - heat-strengthened rolled products;
• the letter K - steel, characterized by increased corrosion resistance;
• letter D - an alloy characterized by a high content of copper (C345T, C390K, etc.).

Unalloyed steels belonging to the category of tool steels are designated by the letter "U", it is affixed at the beginning of their marking. The number following this letter expresses the quantitative content of carbon in the alloy in question. Steels of this category can be high-quality and high-quality (they can be identified by the letter "A", it is affixed at the end of the brand name). Their marking may contain the letter "G", which means an increased content of manganese (U7, U8, U8A, U8GA, etc.).

The marking of those steels that are included in the category of high-speed cutting begins with the letter "P", followed by numbers indicating the quantitative content of tungsten. Otherwise, the grades of such alloys are named according to the standard principle: letters denoting the element, and, accordingly, numbers reflecting its quantitative content. In the designation of such steels, chromium is not indicated, since its standard content in them is about 4%, as well as carbon, the amount of which is proportional to the content of vanadium. If the amount of vanadium exceeds 2.5%, then its letter designation and quantitative content are put down at the very end of the marking (Z9, R18, R6M5F3, etc.).

Unalloyed steels belonging to the category of electrical engineering are marked in a special way (they are also often called pure technical iron). The low electrical resistance of such metals is ensured due to the fact that their composition is characterized by a minimum carbon content - less than 0.04%. There are no letters in the designation of the grades of such steels, only numbers: 10880, 20880, etc. The first digit indicates the classification according to the type of processing: hot-rolled or forged - 1, calibrated - 2. The second digit is associated with the category of the aging coefficient: 0 - non-standardized, 1 - normalized. The third digit indicates the group to which this steel belongs according to the normalized characteristic, taken as the main one. The value of the normalized characteristic is determined by the fourth and fifth digits.

The principles by which the designation of steel alloys is carried out were developed back in the Soviet period, but to this day they are successfully used not only in Russia, but also in the CIS countries. Having information about a particular steel grade, one can not only determine its chemical composition, but also effectively select metals with the required characteristics.

Steel is an alloy of iron and carbon, the content of which does not exceed 2.14%. It has high ductility and rollability, which is the reason for its widespread use in industry, mechanical engineering and other industries.

In metallurgical production, where rolled products differ not only in profile, but also in steel grades, the marking of each piece of rolled products has long become an indispensable rule. The decoding of steels makes it possible to immediately draw a conclusion about the applicability of a given metal for a particular technological operation or for a specific product in general.

The marking is applied to the end of each profile unit by the method of "hot stamping" in the production stream by the so-called stamping machines. The marking contains: steel grade, heat number, manufacturer's mark. In addition, each workpiece is marked with indelible paint in a combination of colors according to steel groups on the cooled workpieces. By agreement of the parties, color marking can be applied to individual profiles in a package in the amount of 1-3 pieces per package. Package - a bundle of profiles with a total weight of 6-10 tons, packed with a bundle of rolled wire with a diameter of 6 mm in 6-8 threads.

Alloy steels

The table for decoding steels by composition is presented below.

If the name contains the letter "Ch", then the alloying elements include rare earth elements - niobium, lanthanum, cerium.

Cerium (Ce) - affects the strength characteristics and ductility.

Lanthanum (La) and neodymium (Ne) - reduce the sulfur content and reduce the porosity of the metal, leading to a decrease in graininess.

Deciphering steels: examples

For an example of decoding, consider a common steel grade 12X18H10T.

The number "12" at the beginning of the brand name is an indicator of the carbon content in this steel, it does not exceed 0.12%. Next comes the designation "X18" - therefore, the steel contains the element chromium in the amount of 18%. The abbreviation "H10" refers to the presence of nickel in the amount of 10%. The letter "T" indicates the presence of titanium, the absence of a digital expression means that it is less than 1.5% there. Obviously, a qualified decoding of steels by composition immediately gives an idea of ​​its qualitative characteristics.

If we compare the designations of alloyed and carbon steels, this becomes a noticeable difference, indicating the special properties of the metal, due to specially introduced alloying additives. The decoding of steels and alloys indicates their chemical composition. The main alloying additives are:

• nickel (Ni) - reduces chemical activity and improves the hardenability of the metal;
• chromium (Cr) - increases the tensile strength and yield strength of alloys;
• niobium (Nb) - increases acid resistance and corrosion resistance of welded joints;
• cobalt (Co) - increases heat resistance and toughness.

Alloying - the mechanism of action of alloying elements

It is difficult to decipher steels. Materials science comprehensively studies this subject.

In any case, the impact of alloying additives is associated with the distortion of the iron crystal lattice, the introduction of foreign atoms of a different size into it.

How is it easier to decipher steels (materials science)? The table provides useful information.

Positive aspects of doping

Features of properties are most clearly manifested after heat treatment, in connection with this, all parts made of such steel are processed before use.

1. Steels and alloys improved by alloying have higher mechanical properties compared to structural ones.
2. Alloy additives contribute to the stabilization of austenite, improving the hardenability index of steels.
3. Due to the reduction in the degree of decomposition of austenite, the formation of hardening cracks and warping of parts is reduced.
4. The impact strength increases, which leads to a decrease in cold brittleness, and alloy steel parts have a higher durability.

Negative sides

Along with the positive aspects, the alloying of steels also has a number of characteristic disadvantages. Among them are the following:

1. In products made of alloyed steels, reversible temper brittleness of the second kind is observed.
2. Alloys of the high-alloy class include residual austenite, which reduces the hardness and resistance to fatigue factors.
3. The tendency to form dendritic segregations, which leads to the appearance of stitched structures after rolling or forging. Diffusion tempering is used to eliminate the effect.
4. Such steels are prone to the formation of flocs.

Steel classification

How is steel decoded by composition? Materials containing less than 2.5% of alloying additives are classified as low-alloyed, with an amount of 2.5 to 10% are considered alloyed, more than 10% - high-alloyed.

• high carbon;
• medium carbon;
• low carbon.

The chemical composition determines the division of steels into:

• carbonaceous;
• doped.

cast iron

Cast iron is an alloy of iron and carbon with a content of the latter above 2.15%. It is divided into unalloyed and alloyed containing manganese, chromium, nickel and other alloying additives.

Differences in structure divide cast iron into two types: white (has a silver-white fracture) and gray (a characteristic gray fracture). The form of carbon in white cast iron is cementite. Gray is graphite.

Gray cast iron is divided into several varieties:

• malleable;
• heat resistant;
• high strength;
• heat resistant;
• antifriction;
• corrosion resistant.

Designation of cast iron grades

Different grades of cast iron are designed to be used for different purposes. The main ones are the following:

1. Pig irons. They are designated as "P1", "P2" and are intended for remelting in the production of steel; cast iron with the designations "PL" are used in the foundry for the manufacture of castings; refining with a high content of phosphorus, denoted by the letters "PF"; conversion of high quality is denoted by the abbreviation "PVK".
2. Cast iron, in which graphite is in lamellar form - "MF".
3. Antifriction cast irons: gray - "ACHS"; high strength - "ACV"; malleable - "ACC".
4. Nodular cast iron used in foundry production - "HF".
5. Cast iron with alloying additives, endowed with special properties - "Ch". Alloying elements are marked with letters in the same way as for steel. The designation with the letter "Ш" at the end of the name of the grade of cast iron speaks of the spherical state of graphite in such a grade.
6. Malleable cast iron - "KCh".

Deciphering steels and cast irons

For cast irons, called gray, the characteristic form of graphite is lamellar. They are marked with the letters SCH, the numbers after the letter indicate the minimum value of the tensile strength.

Example 1: ChS20 - gray cast iron, has a tensile strength of up to 200 MPa. Gray cast irons are characterized by high casting properties. It is well machined, has anti-friction characteristics. Products made of gray cast iron are able to dampen vibrations well.

At the same time, they are not sufficiently resistant to tensile loads and do not have impact resistance.

Example 2: VCh50 - high resistance cast iron with tensile strength up to 500 MPa. Having a structure in the form of nodular graphite, it has higher strength characteristics than gray cast irons. They have some ductility and higher impact strength. Along with gray, high-strength cast irons, good casting characteristics, anti-friction and damping properties are characteristic.

These cast irons are used in the production of heavy parts, such as beds for pressing equipment or rolling rolls, crankshafts for internal combustion engines, and so on.

Example 3: KCh35-10 - malleable cast iron, having a tensile strength of up to 350 MPa and allowing a relative elongation of up to 10%.

Malleable cast irons, in comparison with gray ones, have greater strength and ductility. They are used for the production of thin-walled parts that experience shock and vibration loads: hubs, flanges, crankcases of engines and machine tools, cardan shaft forks, and so on.

Conclusion

The breadth of the use of metals in industry requires the ability to quickly navigate the properties and capabilities of products. Indicators such as elasticity, weldability, wear, occur almost daily in one form or another.

For many decades, the volume of iron and steel production per capita was one of the most important factors in assessing the success of the state. The successful work of mechanical engineering, the automotive industry and many other branches of the national economy depended on metallurgy, and now depends on it. The state of our only true ally - the army and navy - depends on the presence of a large amount of high-quality metal. Metal serves us on water, under water and in the air.

Steel is the main metal material used in the manufacture of machines, tools and appliances. Its widespread use is explained by the presence in this material of a whole complex of valuable technological, mechanical, and physicochemical properties. In addition, steel has a relatively low cost and can be produced in large batches. The production process of this material is constantly being improved, thanks to which the properties and quality of steel can ensure trouble-free operation of modern machines and devices at high operating parameters.

General principles for the classification of steel grades

The main classification features of steels: chemical composition, purpose, quality, degree of deoxidation, structure.

• Become by chemical composition subdivided into carbon and alloyed. According to the mass fraction of carbon, both the first and second groups of steels are divided into: low-carbon (less than 0.3% C), medium-carbon (C concentration is in the range of 0.3-07%), high-carbon - with a carbon concentration of more than 0.7%.

Alloyed steels are called steels containing, in addition to permanent impurities, additives introduced to improve the mechanical properties of this material.

Chromium, manganese, nickel, silicon, molybdenum, tungsten, titanium, vanadium and many others are used as alloying additives, as well as a combination of these elements in various percentages. By the number of additives steels are divided into low-alloyed (alloying elements less than 5%), medium-alloyed (5-10%), high-alloyed (contain more than 10% additives).

• According to its purpose steels are structural, tool and special-purpose materials with special properties.

The most extensive class are structural steels, which are intended for the manufacture of building structures, parts of instruments and machines. In turn, structural steels are subdivided into spring-spring, improved, case-hardened and high-strength steels.

Tool steels are distinguished depending on the purpose of the tool produced from them: measuring, cutting, hot and cold deformation stamps.

Special purpose steels are divided into several groups: corrosion-resistant (or stainless), heat-resistant, heat-resistant, electrical.

• By quality steels are of ordinary quality, high-quality, high-quality and especially high-quality.

The quality of steel is understood as a combination of properties due to the process of its manufacture. These characteristics include: uniformity of structure, chemical composition, mechanical properties, manufacturability. The quality of steel depends on the content of gases in the material - oxygen, nitrogen, hydrogen, as well as harmful impurities - phosphorus and sulfur.

• According to the degree of deoxidation and the nature of the solidification process, steels are calm, semi-calm and boiling.

Deoxidation is the operation of removing oxygen from liquid steel, which provokes brittle fracture of the material during hot deformations. Quiet steels are deoxidized using silicon, manganese and aluminum.

• By structure separate steel in the annealed (equilibrium) state and normalized. Structural forms of steels are ferrite, perlite, cementite, austenite, martensite, ledeburite and others.

Effect of carbon and alloying elements on the properties of steel

Industrial steels are chemically complex alloys of iron and carbon. In addition to these basic elements, as well as alloying components in alloyed steels, the material contains permanent and random impurities. The main characteristics of steel depend on the percentage of these components.

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Carbon has a decisive influence on the properties of steel. After annealing, the structure of this material consists of ferrite and cementite, the content of which increases in proportion to the increase in carbon concentration. Ferrite is a low-strength and ductile structure, while cementite is hard and brittle. Therefore, an increase in carbon content leads to an increase in hardness and strength and a decrease in ductility and toughness. Carbon changes the technological characteristics of steel: workability by pressure and cutting, weldability. Increasing the concentration of carbon leads to a deterioration in machinability due to hardening and a decrease in thermal conductivity. The separation of chips from high-strength steels increases the amount of heat generated, which leads to a decrease in tool life. But low-carbon steels with low toughness are also poorly machined, since chips that are difficult to remove are formed.

Steels with a carbon content of 0.3-0.4% have the best machinability.

An increase in the concentration of carbon leads to a decrease in the ability of steel to deform in hot and cold states. For steel intended for complex cold forming, the amount of carbon is limited to 0.1%.

Low carbon steels have good weldability. For welding medium and high carbon steels, heating, slow cooling and other technological operations are used to prevent the appearance of cold and hot cracks.

To obtain high strength properties, the amount of alloying components must be rational. An excess of alloying, excluding the introduction of nickel, leads to a decrease in the toughness margin and the provocation of brittle fracture.

• Chromium is a non-deficient alloying component that has a positive effect on the mechanical properties of steel when its content is up to 2%.
• Nickel is the most valuable and scarce alloying addition introduced at a concentration of 1-5%. It most effectively reduces the threshold of cold brittleness and contributes to an increase in the temperature reserve of viscosity.
• Manganese, as a cheaper component, is often used as a substitute for nickel. Increases yield strength, but can make steel susceptible to overheating.
• Molybdenum and tungsten are expensive and scarce elements used to improve the heat resistance of high speed steels.

Principles of steel marking according to the Russian system

There is no common steel marking system on the modern metal products market, which greatly complicates trading operations, leading to frequent ordering errors.

In Russia, an alphanumeric designation system has been adopted, in which the names of the elements contained in steel are marked with letters, and their number with numbers. The letters also indicate the method of deoxidation. The marking "KP" denotes boiling steel, "PS" - semi-calm, and "SP" - calm steel.

• Steels of ordinary quality have the index St, after which the conditional number of the brand is indicated from 0 to 6. Then the degree of deoxidation is indicated. The group number is put in front: A - steel with guaranteed mechanical characteristics, B - chemical composition, C - both properties. As a rule, the group A index is not set. Designation example - B Art.2 KP.
• To designate structural quality carbon steels, a two-digit number is indicated in front, indicating the C content in hundredths of a percent. At the end - the degree of deoxidation. For example, steel 08KP. High-quality tool carbon steels have the letter U in front, and then the carbon concentration in a two-digit number in tenths of a percent - for example, U8 steel. High-quality steels have the letter A at the end of the grade.
• In grades of alloyed steels, alloying elements are denoted by letters: “H” - nickel, “X” - chromium, “M” - molybdenum, “T” - titanium, “B” - tungsten, “U” - aluminum. In structural alloy steels, the C content in hundredths of a percent is indicated in front. In tool alloy steels, carbon is marked in tenths of a percent, if the content of this component exceeds 1.5%, its concentration is not indicated.
• High-speed tool steels are designated with the P index and an indication of the tungsten content as a percentage, for example, P18.

Steel marking according to American and European systems

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In the United States, there are several steel marking systems developed by various standards organizations. For stainless steels, most often, the AISI system is used, which is also valid in Europe. According to AISI, steel is denoted by three numbers, in some cases followed by one or more letters. The first digit indicates the class of steel, if it is 2 or 3, then this is an austenitic class, if 4 is ferritic or martensitic. The next two digits indicate the serial number of the material in the group. The letters stand for:

• L - low mass fraction of carbon, less than 0.03%;
• S - normal concentration of C, less than 0.08%;
• N - means that nitrogen is added;
• LN - low carbon content combined with the addition of nitrogen;
• F - increased concentration of phosphorus and sulfur;
• Se - steel contains selenium, B - silicon, Cu - copper.

In Europe, the EN system is used, which differs from the Russian one in that it first lists all alloying elements, and then, in the same order, their mass fraction is indicated in numbers. The first digit is the carbon concentration in hundredths of a percent.

If alloy steels, structural and tool steels, except for high-speed ones, include more than 5% of at least one alloying additive, the letter “X” is put in front of the carbon content.

EU countries use the EN marking, in some cases indicating the national mark in parallel, but marked "obsolete".

International analogues of corrosion-resistant and heat-resistant steels

Corrosion resistant steels

Heat resistant steel grades

Grades of high speed steels

Structural steel

Basic range of stainless steel grades

Bearing steel

Spring steel

heat resistant steel

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