Characteristics of steels using regulatory documents. Regulatory documentation for individual groups of plants. Terms and explanations

1. General characteristics of steels

2. Marking, decoding, properties, heat treatment and scope of application

2.1 Carbon structural steels

2.2 Free-cut steels

2.3 Structural low-alloy steels

2.4 Structural case-hardening steels

2.5 Structural upgradeable steels

2.6 Spring steels

2.7 Ball bearing steels

2.8 Wear-resistant steels

2.9 Corrosion-resistant steels

2.10 Heat-resistant steels and alloys

1. General characteristics of steels

Ferrous alloys with a carbon content of up to 2.14% are called steels. In addition to iron and carbon, steels contain useful and harmful impurities.

Steel is the main metal material widely used for the manufacture of machine parts, aircraft, instruments, various tools and building structures. The widespread use of steels is due to a complex of mechanical, physicochemical and technological properties. Methods for widespread steel production were discovered in the mid-19th century.IXV. At the same time, the first metallographic studies of iron and its alloys were already carried out.

Steels combine high rigidity with sufficient static and cyclic strength. These parameters can be changed over a wide range by changing the concentration of carbon, alloying elements and thermal and chemical-thermal treatment technologies. By changing the chemical composition, it is possible to obtain steel with different properties, and use them in many branches of technology and the national economy.

Carbon steels are classified according to carbon content, purpose, quality, degree of deoxidation and structure in an equilibrium state.

According to their purpose, steels are classified into structural and instrumental. Structural steels represent the most extensive group intended for the manufacture of building structures, machine parts and instruments. These steels include case-hardened, tempered, high-strength and spring-spring steels. Tool steels are divided into steels for cutting, measuring tools, cold and hot dies (up to 200 0 C) deformation.

According to the quality of steel, they are classified into ordinary quality, high-quality, high-quality. The quality of steel is understood as a set of properties determined by the metallurgical process of its production. Ordinary quality steels are only carbon (up to 0.5% C), high-quality and high-quality steels are carbon and alloyed.

According to the degree of deoxidation and the nature of solidification, steels are classified into calm, semi-calm and boiling. Deoxidation is a process of removing oxygen from liquid metal, carried out to prevent brittle fracture of steel during hot deformation.

Semi-quiet steels, in terms of the degree of deoxidation, occupy an intermediate position between calm and boiling steels.

According to the structure in the equilibrium state, steels are divided into: 1) hypoeutectoid, having ferrite and pearlite in the structure; 2) eutectoid, the structure of which consists of pearlite; 3) hypereutectoid, having pearlite and secondary cementite in the structure.

2. Marking, decoding, properties, heat treatment and scope of application.

2.1 Carbon structural steels

Ordinary quality steels are produced in the form of rolled products (rods, beams, sheets, angles, pipes, channels, etc.) in a normalized state and, depending on the purpose and set of properties, are divided into groups: A, B, C.

Steels are marked with a combination of the letters St and a number (from 0 to 6), indicating the grade number, and not the average carbon content in it, although as the number increases, the carbon content in the steel increases. Steels of groups B and C have the letters B and C in front of the grade, indicating their belonging to these groups. Group A is not indicated in the steel grade designation. The degree of deoxidation is indicated by adding indices: in calm steels – “sp”, semi-quiet steels – “ps”, boiling steels – “kp”, and the category of standardized properties (except for category 1) is indicated by a subsequent number. Calm and semi-calm steels are produced from St1 – St6, boiling – St1 – St4 of all three groups. St0 steel is not divided according to the degree of deoxidation.

Group A steels are used in the as-delivered state for products the manufacture of which is not accompanied by hot working. In this case, they retain the normalization structure and mechanical properties guaranteed by the standard.

Steel grade St3 is used in the delivered state without pressure treatment or welding. It is widely used in construction for the manufacture of metal structures.

Group B steels are used for products manufactured using hot processing (forging, welding and, in some cases, heat treatment), in which the original structure and mechanical properties are not preserved. For such parts, information about the chemical composition is important to determine the hot working mode.

Steels of group B are more expensive than steels of groups A and B; they are used for critical parts (for the production of welded structures).

Carbon steels of ordinary quality (all three groups) are intended for the manufacture of various metal structures, as well as lightly loaded machine and instrument parts. These steels are used when the performance of parts and structures is ensured by rigidity. Carbon steels of ordinary quality are widely used in construction in the manufacture of reinforced concrete structures. Steels of groups B and C, numbers 1-4, are capable of welding and cold working, therefore welded trusses, various frames and building metal structures are made from them, in addition, fasteners, some of which are subjected to carburization.

Medium carbon steels numbers 5 and 6, which have great strength, are intended for rails, railway wheels, as well as shafts, pulleys, gears and other parts of lifting and agricultural machines. Some parts from these steels of groups B and C are subjected to heat treatment - hardening followed by high tempering.

In mechanical engineering, high-quality carbon steels are used for the manufacture of parts for various, most often non-critical purposes, and are a fairly cheap material. These steels are supplied to industry in the form of rolled products, forgings, and profiles for various purposes with guaranteed chemical composition and mechanical properties.

In mechanical engineering, high-quality carbon steels supplied in accordance with GOST 1050-74 are used. These steels are marked with two-digit numbers 05, 08, 10, 15, 20, ..., 75, 80, 85, indicating the average carbon content in hundredths of a percent.

Carbon steels also include steels with a high manganese content (0.7-1.0%) grades 15G, 20G, 25G, ..., 70G, which have increased hardenability.

Quiet steels are marked without an index, semi-quiet and boiling steels are marked with the index “ps” and “kp”, respectively. Boiling steels are produced in grades 05kp, 08kp, 10kp, 15kp, 20kp, semi-quiet steels - 08ps, 10ps, 15ps, 20ps.

High-quality steels are widely used in mechanical engineering and instrument making, since due to the different carbon content in them and, accordingly, heat treatment, a wide range of mechanical and technological properties can be obtained.

Low-carbon steels 05kp, 08kp, 10kp, 15kp, 20kp are characterized by low strength and high ductility in the cold state. These steels are mainly produced in thin sheet form and are used after annealing or normalization for deep drawing cold forming. They are easy to stamp due to their low carbon content and small amount of silicon, which makes them very soft. They can be used in the automotive industry to produce parts with complex shapes. Deep drawing from sheets of these steels is used in the manufacture of cans, enamelware and other industrial products.

Mild steels 08, 10 are used in the annealed state for structures of low strength - containers, pipes, etc.

Steels 10, 15, 20 and 25 are also low-carbon steels; they are ductile, easy to weld and stamp. In a normalized state, they are mainly used for fasteners - rollers, axles, etc.

To increase the surface strength of these steels, they are cemented (saturate the surface with carbon) and used for small parts, such as lightly loaded gears, cams, etc.

Medium carbon steels 30, 35, 40, 45, 50 and similar steels with a high manganese content 30G, 40G and 50G in a normalized state are characterized by increased strength, but correspondingly lower toughness and ductility. Depending on the operating conditions of parts made of these steels, various types of heat treatment are applied to them: normalization, improvement, hardening with low tempering, high-frequency hardening, etc.

Medium carbon steels are used for the manufacture of small shafts, connecting rods, gears and parts subject to cyclic loads. In large-sized parts with large cross-sections, due to poor hardenability, the mechanical properties are significantly reduced.

High-carbon steels 60, 65, 70, 75, 80 and 85, as well as with a high manganese content 60G, 65G and 70G, are mainly used for the manufacture of springs, springs, high-strength wire and other products with high elasticity and wear resistance. They are subjected to quenching and medium tempering to a troostite structure combined with satisfactory toughness and good endurance limit.

Along with standards, ND on standardization legally includes international and interstate standards, rules, norms and recommendations applied in the prescribed manner. Let's briefly look at the features of standards and other regulatory documents.

1. Standards as applied to a specific area of activity.

State standard(GOST, GOST R). The objects of state standards include:

1) organizational, methodological and general technical objects of intersectoral application;

2) products, processes and services of cross-industry significance.

For state standards, a certain designation structure has been established. For standards included in a certain system, for example, the system of standards of ergonomics and technical aesthetics (SSETE), the system of reliability standards, the designation consists of the standard category index (GOST R or GOST), the standard system index (XX), the classification group code (X ), the number of the standard in the group (XX) and the last two digits – the year of registration of the standard. Example: for SSETE we have GOST 30.001-83. Basic provisions. Here 30 is the system index (XX), 0 is the classification group code. 01 is the number of the standard in the group, 83 is the year of registration of the standard.

Features of the development of OST, STO, STP are set out in GOST R 1.4 - 93. It should be noted that the use of enterprise standards (STP) and technical specifications (TS) is limited by the framework of the organization (enterprise).

Industry standard(OST ). Industry standards, like government standards, are intended for the same types of objects. The designation of an industry standard consists of an index (OST), a symbol of the ministry (department), registration number, and year of approval of the standard. Example: OST56–98–93.

Society standards(ONE HUNDRED). The objects of the service station are: 1) fundamentally new (pioneer) types of products and services; 2) new test methods, examination methodology; 3) non-traditional technologies for development, manufacturing, storage and new principles of organization and production management (research results); 4) other types of activities. This type of standards is intellectual property and subject to copyright. The STO designation consists of an index (STO), an abbreviation of the company, a registration number and numbers that determine the year of approval of the standard. Example: STO ROO 10.01–95, where ROO is the Russian Society of Appraisers.

Enterprise standards(STP ). This type of standards is developed by business entities in the following cases: 1) to ensure the application of state standards, industry standards and standards of other categories at the enterprise; 2) on products, processes and services created and used at this enterprise. The STP is approved by the head of the enterprise, it is mandatory for employees of this enterprise and is a local regulatory act.

Example: enterprise standard – STP-SK-02.05-99, where STP is the index of the standard, SK is the index of the standardization object, i.e. SK – quality system, 02.05 – registration number and 99 – year of approval of the standard.

2. Standards applied to objects.

Fundamental Standards– a normative document that has a wide scope or contains general provisions for a certain area of activity.

Standards for products (services) establish requirements for groups of homogeneous products (services) or for specific products (services). Homogeneous products– a set of products characterized by a common purpose, scope of application, design and technological solution, and a range of quality indicators.

The following types of standards are being developed for products: a standard of general technical conditions and a standard of technical conditions. In the first case, the standard contains general requirements for groups of homogeneous products; in the second - to establish quality characteristics based on control and testing. In general, product standards include the following sections: terms and definitions, basic parameters or dimensions, general technical requirements for products, rules for acceptance, labeling, packaging, transportation and storage. To assess the quality of each product, a package of standards is compiled.

Standards for processes (works) establish requirements for the performance of various types of work at individual stages of the product (service) life cycle - development, manufacturing, storage, transportation, operation, disposal to ensure their technical unity and optimality. A typical subject of industry standards is standard technological processes. Example: OST 36–71–82 “Thermal insulating mineral wool slabs. Typical technological process."

At the present stage, standards for management processes within the system of ensuring the quality of products (services) - documentation management, product purchases, personnel training - are becoming of great importance. There are standards for computer-aided design (CAD) systems

Standards for control methods(testing, measurement, analysis) must first of all provide a comprehensive verification of all mandatory requirements for the quality of products (services). Control methods must be objective, accurate and provide reproducible results.

3. Other normative documents on standardization. These legally include: rules (PR), recommendations (R), norms (N) and technical conditions (TU).

Rules(PR) – a document establishing mandatory organizational, technical and (or) general technical provisions, procedures, methods of performing work. Example: Rules for certification in the Russian Federation (approved by Decree of the State Standard of Russia on May 10, 2000, No. 26); PR 50.2.002–94 State system for ensuring the uniformity of measurements.

Recommendations(P) – a document containing voluntary organizational, technical and (or) general technical provisions, procedures, methods of performing work. Example: R 50.1.006–95. State supervision of compliance with mandatory requirements of state standards and certified industrial products. Gosstandart of Russia.

Norm (N) – a provision establishing quantitative and qualitative criteria that must be satisfied. Example: “Radiation safety standard”. State Sanitary and Epidemiological Supervision of the Russian Federation. M.: 1996.

Specifications(TU) were included in the ND in order to create legitimate opportunities for their use for state regulation of product safety and quality. ND includes only those specifications in respect of which, firstly, the legislation has already introduced or will introduce provisions for their registration, or approval at the federal level; second, to which references are made in contracts for supplied products. In accordance with GOST 2.114, specifications are developed for one product or for several specific products. The TU fund contains about 150 thousand units. TU designations are formed from the code - “TU”, the product group code according to the product classifier (OKP), the three-digit registration number of the enterprise code according to the classifier of enterprises and organizations (OKPO), the last two digits are the year of approval of the document. Example: TU 1115–017–38576343-93, where 1115 is the product group code according to OKP; 017 – registration number; 38576343 – enterprise code according to OKPO; 93 – year of registration.

2. Marking, decoding, properties, heat treatment and scope of application

2.1 Carbon structural steels

2.2 Free-cut steels

2.3 Structural low-alloy steels

2.4 Structural case-hardening steels

2.5 Structural upgradeable steels

2.6 Spring steels

2.7 Ball bearing steels

2.8 Wear-resistant steels

2.9 Corrosion-resistant steels

2.10 Heat-resistant steels and alloys

1. General characteristics of steels

Ferrous alloys with a carbon content of up to 2.14% are called steels. In addition to iron and carbon, steels contain useful and harmful impurities.

Steel is the main metal material widely used for the manufacture of machine parts, aircraft, instruments, various tools and building structures. The widespread use of steels is due to a complex of mechanical, physicochemical and technological properties. Methods for widespread steel production were discovered in the mid-19th century.
At the same time, the first metallographic studies of iron and its alloys were already carried out.

Carbon steels are classified according to carbon content, purpose, quality, degree of deoxidation and structure in an equilibrium state.

According to the quality of steel, they are classified into ordinary quality, high-quality, high-quality. The quality of steel is understood as a set of properties determined by the metallurgical process of its production. Ordinary quality steels are only carbon (up to
0.5% C), high-quality and high-quality - carbon and alloy.

Semi-quiet steels, in terms of the degree of deoxidation, occupy an intermediate position between calm and boiling steels.

2. Marking, decoding, properties, heat treatment and scope of application.

2.1 Carbon structural steels

Steels are marked with a combination of the letters St and a number (from 0 to 6), indicating the grade number, and not the average carbon content in it, although as the number increases, the carbon content in the steel increases. Steels of groups B and C have the letters B and C in front of the grade, indicating their belonging to these groups. Group A is not indicated in the steel grade designation. The degree of deoxidation is indicated by adding indices: in calm steels – “sp”, semi-quiet steels – “ps”, boiling steels – “kp”, and the category of standardized properties
(except category 1) is indicated by a subsequent digit. Calm and semi-calm steels are produced from St1 – St6, boiling – St1 – St4 of all three groups. St0 steel is not divided according to the degree of deoxidation.

Steel grade St3 is used in the delivered state without pressure treatment or welding. It is widely used in construction for the manufacture of metal structures.

Steels of group B are more expensive than steels of groups A and B; they are used for critical parts (for the production of welded structures).

Carbon steels of ordinary quality (all three groups) are intended for the manufacture of various metal structures, as well as lightly loaded machine and instrument parts. These steels are used when the performance of parts and structures is ensured by rigidity.
Carbon steels of ordinary quality are widely used in construction in the manufacture of reinforced concrete structures. Steels of groups B and C, numbers 1-4, are capable of welding and cold working, therefore welded trusses, various frames and building metal structures are made from them, in addition, fasteners, some of which are subjected to carburization.

Medium carbon steels numbers 5 and 6, which have great strength, are intended for rails, railway wheels, as well as shafts, pulleys, gears and other parts of lifting and agricultural machines.
Some parts from these steels of groups B and C are subjected to heat treatment - hardening followed by high tempering.

In mechanical engineering, high-quality carbon steels supplied in accordance with GOST 1050-74 are used. These steels are marked with two-digit numbers 05,
08, 10, 15, 20, …, 75, 80, 85, indicating the average carbon content in hundredths of a percent.

Carbon steels also include steels with a high manganese content (0.7-1.0%) grades 15G, 20G, 25G, ..., 70G, which have increased hardenability.

Quiet steels are marked without an index, semi-quiet and boiling steels are marked with the index “ps” and “kp”, respectively. Boiling steels produce grades 05kp,
08kp, 10kp, 15kp, 20kp, semi-quiet - 08ps, 10ps, 15ps, 20ps.

Mild steels 08, 10 are used in the annealed state for structures of low strength - containers, pipes, etc.

Steels 10, 15, 20 and 25 are also low-carbon steels; they are ductile, easy to weld and stamp. In a normalized state, they are mainly used for fasteners - rollers, axles, etc.

To increase the surface strength of these steels, they are cemented
(saturate the surface with carbon) and are used for small parts, such as lightly loaded gears, cams, etc.

2.2 Automatic steels

These steels are marked with the letter A (automatic) and numbers showing the average carbon content in hundredths of a percent. If automatic steel is alloyed with lead, then the brand designation begins with the combination of letters “AC”.
To prevent red brittleness, the amount of manganese in steels is increased. Adding lead, selenium and tellurium to cutting steels allows cutting tool consumption to be reduced by 2-3 times.

Improved machinability is achieved by modification with calcium
(introduced into liquid steel in the form of silicocalcium), which globulizes sulfide inclusions, which has a positive effect on machinability, but not as actively as sulfur and phosphorus.

Sulfur forms a large number of manganese sulfides, elongated in the rolling direction. Sulfides have a lubricating effect, thereby disrupting the continuity of the metal. Phosphorus increases the brittleness of ferrite, making it easier to separate metal chips during the cutting process. Both of these elements help reduce sticking on the cutting tool and produce a smooth, shiny work surface.

However, it must be remembered that increasing the sulfur and phosphorus content reduces the quality of steel. Steels containing sulfur have a pronounced anisotropy of mechanical properties and reduced corrosion resistance.

Steels A11, A12, A20 are used for fasteners and products of complex shapes that do not experience heavy loads, but they are subject to high demands on dimensional accuracy and surface cleanliness.

Steels A30 and A40G are intended for parts experiencing higher stresses.

In automatic selenium-containing steels, machinability is increased due to the formation of selenides and sulfoselenides, which envelop solid oxide inclusions and thereby eliminate their abrasive effect. In addition, selenides retain their globular shape after pressure treatment, therefore they practically do not cause anisotropy of properties and do not impair the corrosion resistance of steel, like sulfur. The use of these steels reduces tool consumption by half and increases productivity by up to 30%.

2.3 Structural low-alloy steels

Low alloy steels contain up to 2.5% alloying elements.
The brand designation includes numbers and letters indicating the approximate composition of the steel. At the beginning of the stamp there are two-digit numbers indicating the average carbon content in hundredths of a percent. The letters to the right of the number indicate alloying elements: A - nitrogen, B - niobium, B - tungsten, G - manganese, D - copper, E - selenium, K - cobalt, N - nickel, M - molybdenum, P - phosphorus, P - boron, C – silicon, T – titanium, F – vanadium, X – chromium, C – zirconium, Ch – rare earth elements, Yu – aluminum. The numbers following the letter indicate the approximate content (in whole percentages) of the corresponding alloying element (for a content of 1-1.5% or less, the number is missing).

This group includes steels with a carbon content of 0.1-0.3%, which, after chemical-thermal treatment, hardening and low tempering, provide high surface hardness with a viscous but sufficiently strong core. These steels are used for the manufacture of machine parts and devices.
(cams, gears, etc.) experiencing variable and shock loads and at the same time subject to wear.

2.4 Structural case-hardening steels

Carbide- and nitride-forming elements (such as Cr, Mn, Mo, etc.) help increase hardenability, surface hardness, wear resistance and contact endurance. Nickel increases the viscosity of the core and diffusion layer and reduces the cold brittleness threshold. Cementable
(nitrocarburized) alloy steels are divided into two groups according to their mechanical properties: medium-strength steels with a yield strength of less than 700 MPa (15Х, 15ХФ) and increased strength with a yield strength of 700-
1100 MPa (12Х2Н4А, 18Х2Н4МА, etc.).

Chromium (15Х, 20Х) and chrome vanadium (15ХФ) steels are cemented to a depth of 1.5 mm. After quenching (880 0С, water, oil) and subsequent tempering (180 0С, air, oil) the steels have the following properties: ?в = 690-
800 MPa, ? = 11-12%, KCU = 0.62 MJ/m2.

Chromium-manganese steels (18ХГТ, 25ХГТ), widely used in the automotive industry, contain 1% chromium and manganese each (a cheap substitute for nickel in steel), as well as 0.06% titanium. Their disadvantage is the tendency to internal oxidation during gas carburization, which leads to a decrease in the hardness of the layer and the endurance limit. This drawback is eliminated by alloying steel with molybdenum (25 hgm). For work under wear conditions, 20KhGR steel alloyed with boron is used. Boron increases the hardenability and strength of steel, but reduces its toughness and ductility.

Chromium-nickel-molybdenum (tungsten) steel 18Х2Н4МА (18Х2Н4ВА) belongs to the martensitic class and is hardened in air, which helps reduce warping. Alloying of chromium-nickel steels W or
Mo further increases their hardenability. Moreover, Mo significantly increases the hardenability of the cemented layer, while chromium and manganese primarily increase the hardenability of the core. In the cemented state, this steel is used for the manufacture of gears for aircraft engines, ship gearboxes and other large parts for critical purposes. This steel is also used as an improvement in the manufacture of parts subject to large static and impact loads.

2.5 Structural upgradeable steels

Improved steels are those that are used after hardening with high tempering (improvement). These steels (40Kh, 40KhFA, 30KhGSA, 38KhN3MFA, etc.) contain 0.3-0.5% carbon and 1-6% alloying elements. Steels are hardened from 820-880 0C in oil (large parts - in water); high tempering is carried out at 500-650 0C followed by cooling in water, oil or air (depending on the composition of the steel). The steel structure after improvement is sorbitol. These steels are used for the manufacture of shafts, connecting rods, rods and other parts subject to cyclic or shock loads.
In this regard, the steels being improved must have a high yield strength, ductility, toughness, and low sensitivity to notch.

The steels belong to the martensitic class and slightly soften when heated to 300-400 0C. They are used to make turbine shafts and rotors, and heavily loaded parts of gearboxes and compressors.

2.6 Spring steels

Springs, leaf springs and other elastic elements work in the area of elastic deformation of the material. At the same time, many of them are subject to cyclic loads. Therefore, the main requirements for spring steels are to ensure high values of elasticity, yield, endurance, as well as the necessary ductility and resistance to brittle fracture.

Steels for springs and springs contain 0.5-0.75% C; they are also additionally alloyed with silicon (up to 2.8%), manganese (up to 1.2%), chromium
(up to 1.2%), vanadium (up to 0.25%), tungsten (up to 1.2%) and nickel (up to 1.7
%). In this case, grain refinement occurs, which contributes to an increase in the steel’s resistance to small plastic deformations, and, consequently, its relaxation resistance.

Silicon steels 55S2, 60S2A,
70С3А. However, they can be subject to decarburization and graphitization, which sharply reduces the elasticity and endurance characteristics of the material. Elimination of these defects, as well as an increase in hardenability and inhibition of grain growth during heating, is achieved by additionally introducing chromium, vanadium, tungsten and nickel into silicon steels.

50HFA steel, which is widely used for the manufacture of automobile springs, has better technological properties than silicon steels.
Valve springs are made of 50HFA steel, which is not prone to decarburization and overheating, but has low hardenability.

Heat treatment of alloyed spring steels (hardening 850-880
0С, tempering 380-550 0С) provide high strength and fluidity limits. Isothermal hardening is also used.

The maximum endurance limit is obtained by heat treatment to a hardness of HRC 42-48.

For the manufacture of springs, cold-drawn wire (or tape) from high-carbon steels 65, 65G, 70, U8, U10, etc. is also used.

Springs and other special-purpose elements are made from high-chromium martensitic (30Х13), maraging-aging (03Х12Н10Д2Т), austenitic stainless steel (12Х18Н10Т), austenitic-martensitic (09Х15Н8У) and other steels and alloys.

2.7 Ball bearing steels

To ensure the performance of products, ball bearing steel must have high hardness, strength and contact endurance.
This is achieved by improving the quality of the metal: by cleaning it from non-metallic inclusions and reducing porosity through the use of electroslag or vacuum-arc remelting.

In the manufacture of bearing parts, ball bearing (W) chromium (X) steels ШХ15СГ are widely used (the subsequent number 15 indicates the chromium content in tenths of a percent - 1.5%). ShKh15SG is additionally alloyed with silicon and manganese to increase hardenability. Annealing steel to a hardness of about 190 HB ensures the machinability of semi-finished products by cutting and the stampability of parts in a cold state. Hardening of bearing parts (balls, rollers and rings) is carried out in oil at temperatures of 840-860 0C. Before tempering, the parts are cooled to 20-25 0C to ensure stability of their operation (by reducing the amount of retained austenite). Steel tempering is carried out at 150-
170 0C for 1-2 hours.

Parts of rolling bearings that experience large dynamic loads are made from steels 20Х2Н4А and 18ХГТ with their subsequent carburization and heat treatment. For bearing parts operating in nitric acid and other aggressive environments, 95X18 steel is used, containing 0.95% C and 18% Cr.

2.8 Wear-resistant steels

The wear resistance of parts is usually primarily ensured by increased surface hardness. However, high-manganese austenitic steel 110G13L (1.25% C, 13% Mn, 1% Cr, 1% Ni) with a low initial hardness (180-220 HB) successfully wears out under conditions of abrasive friction, accompanied by exposure to high pressure and high dynamic forces. (shock) loads (such operating conditions are typical for tracks of tracked vehicles, jaws of crushers, etc.). This is explained by the increased ability of steel to harden during cold plastic deformation, equal to 70%, the hardness of steel increases from 210 HB to 530 HB. High wear resistance of steel is achieved not only by strain hardening of austenite, but also by the formation of martensite with a hexagonal or rhombohedral lattice. With a phosphorus content of more than 0.025%, steel becomes cold-brittle. The structure of cast steel is austenite with excess manganese carbides precipitated along the grain boundaries, reducing the strength and toughness of the material. To obtain a single-phase austenitic structure, castings are quenched in water from a temperature of 1050-1100 0C. In this state, steel has high ductility, low hardness and low strength.

Products operating under conditions of cavitation wear are made from steels 30Х10Г10, 0Х14Г12М.

2.9 Corrosion-resistant steels

Steels that are resistant to electrochemical corrosion are called corrosion-resistant (stainless). The resistance of steel against corrosion is achieved by introducing into it elements that form dense protective films on the surface, firmly connected to the base, preventing direct contact of the steel with an aggressive environment, and also increasing its electrochemical potential in this environment.

Stainless steels are divided into two main groups: chromium and chromium-nickel.

Chromium corrosion-resistant steels are used in three types: 13, 17 and
27% Cr, while in steels with 13% Cr the carbon content can vary depending on requirements in the range from 0.08 to 0.40%. The structure and properties of chromium steels depend on the amount of chromium and carbon. In accordance with the structure obtained during normalization, chromium steels are divided into the following classes: ferritic (steels 08Х13, 12Х17, 15Х25Т,
15Х28), martensitic-ferritic (12Х13) and martensitic (20Х13, 30Х13,
40X13).

Steels with low carbon content (08Х13, 12Х13) are ductile, easy to weld and stamp. They are subjected to quenching in oil (1000-1050 0C) with high tempering at 600-800 0C and are used for the manufacture of parts experiencing shock loads (valves of hydraulic presses) or operating in slightly aggressive environments (blades of hydraulic and steam turbines and compressors). These steels can be used at temperatures up to 450
0C (long-term operation) and up to 550 0C (short-term operation). Steels 30Х13 and 40Х13 have high hardness and increased strength. These steels are hardened with
1000-1050 0С in oil and released at 200-300 0С. These steels are used to make carburetor needles, springs, surgical instruments, etc.
High-chromium steels of the ferritic class (12Х17, 15Х25Т and 15Х28) have higher corrosion resistance compared to steels containing
13% Cr. These steels are not hardened by heat treatment. They are prone to strong grain growth when heated above 850 0C. High-chromium steels of the ferritic class are often used as scale-resistant steels.

Chromium-nickel stainless steels, depending on their structure, are divided into austenitic, austenitic-martensitic and austenitic-ferritic. The structure of chromium-nickel steels depends on the content of carbon, chromium, nickel and other elements.

Austenitic steels with 18% Cr and 9-10% Ni (12Х18Н9, 17Х18Н9, etc.) as a result of hardening acquire an austenitic structure and are characterized by high ductility, moderate strength, and good corrosion resistance in oxidizing environments. These have become technologically advanced
(well welded, stamped, cold rolled, etc.).

Steels 12Х18Н9, 17Х18Н9 after slow cooling from the austenitic region have a structure consisting of austenite, ferrite and carbides. In order to dissolve carbides, as well as prevent their precipitation during slow cooling, austenitic steels are heated to 1050-1120 0C and quenched in water, oil or air. Austenitic steels are not prone to brittle fracture at low temperatures, therefore chromium-nickel corrosion-resistant steels are widely used in cryogenic technology for storing liquefied gases, making shells for fuel tanks and rockets, etc.

Steels of the austenitic-martensitic class (09Х15Н8У, 09Х17Н7У) are widely used mainly as high-strength steels. They weld well and are resistant to atmospheric corrosion. In order to ensure sufficient strength and at the same time increased corrosion resistance, steel 09Х15Н8У is subjected to the following heat treatment: hardening to austenite (925-975
0C) followed by cold treatment (-70 0C) and aging (350-3800C).

These steels are used for the manufacture of skins, nozzle structures and power elements of aircraft components.

Austenitic-ferritic steels (08Х22Н6Т, 03Х23Н6, 08Х21Н6М2Т,
10Х25Н5М2, etc.) contain 18-30% Cr, 5-8% Ni, up to 3% Mo, 0.03-0.10% C, as well as additives Ti, Nb, Cu, Si and Ni. These steels after quenching in water with 1000-
1100 0C have a structure consisting of grains of austenite and ferrite uniformly distributed among themselves with a content of the latter of the order of 40-60%. These steels are used in chemical and food engineering, shipbuilding, aviation, and medicine.

2.10 Heat-resistant steels and alloys

These steels are used when working under load and have sufficient heat resistance at temperatures above 500 0C.

Heat-resistant pearlitic steels are low-alloy steels
(12Х1МФ, 25Х1М1Ф, 20Х1М1Ф1Бр, etc.), containing 0.08-0.25% C and alloying elements – Cr, V, Mo, Nb. The best complex of mechanical properties is ensured by quenching in oil (or normalization) from 880-1080 0C followed by high tempering at 640-750 0C. Pearlitic steels are used for the manufacture of parts that operate for a long time in creep mode at temperatures up to 500-580 0C and low loads: these are superheater pipes, steam boiler fittings, and fasteners.

Steels of martensitic and martensitic-ferritic classes (15Х11МФ,
11Х11Н2В2МФ, 15Х12ВНМФ, 18Х12ВМБФР, etc.) are used at temperatures up to
580-600 0С. Steels with a lower chromium content (up to 11%) belong to the martensitic class, and those with a higher chromium content (11-13%) belong to the martensitic-ferritic class.
Steels are hardened to martensite at temperatures of 1000-1100 0C in oil or in air. After tempering at 600-750 0C, the steel acquires a sorbitol structure.
Steels are used for the manufacture of parts for gas turbines and steam power plants.

Austenitic steels have greater heat resistance than martensitic steels,
- their operating temperatures reach 700-750 0C. Austenitic steels are ductile and weld well. According to the method of hardening, austenitic steels are divided into three groups:

1) solid solutions that are not strengthened by aging;

2) solid solutions with carbide strengthening;

3) solid solutions with intermetallic strengthening.

Steels of the first group (08Kh15N24V4TR, 09Kh14N19V2BR) are used in a hardened state (quenching 1100-1600 0C, water or air). These steels are used for the manufacture of pipelines for high-pressure power plants operating at 600-700 0C.

Austenitic heat-resistant steels with carbide and intermetallic hardening are usually subjected to hardening from 1050-1200 0C in water, oil or air and subsequent aging at 600-850 0C.

Steels with intermetallic hardening are used for the manufacture of combustion chambers, turbine disks and blades, as well as welded structures operating at temperatures up to 700 0C.

Heat-resistant alloys based on iron-nickel (for example, KhN35VT,
KhN35VTYu, etc.) are additionally alloyed with chromium, titanium, tungsten, aluminum, and boron. They are strengthened, like austenitic steels, by hardening and aging. Alloy KhN35VTYu is used for the manufacture of turbine blades and disks, nozzle rings and other parts operating at temperatures up to 750 0C.

7. The essence, advantages and disadvantages of the open-hearth method of steel production.

8. The essence, advantages and disadvantages of the Bessemer (converter) method of steel production.

9. What is deoxidation of steel with manganese and silicon. Explain the phenomenon of "boiling" of steel.

10. The essence, advantages and disadvantages of steel production in electric furnaces. What kind of steel is smelted in electric furnaces?

11. Name the methods for casting steel.

Independent work No. 6.

Heat treatment defects, methods for their prevention and elimination.

Promising types of diffusion saturation of alloys. Their application in the automotive industry.

Form of work: compiling notes on educational literature and working using Internet resources and periodicals.

4 hours

Work completion time: when studying the topic “Heat treatment”, “Types of heat treatment”.

1. " Maintenance defects." After studying this topic, fill out the table describing 6 types of defects:

2. " Promising types of diffusion saturation of alloys". After studying this topic, provide a brief summary of it in any form (summary, diagram, drawings with explanations, etc.). Pay attention to the following questions:

1. What is diffusion saturation of a metal, its purpose.

2. Traditional and promising types of saturation.

3. Which automotive products can be subjected to the specified treatment.

4. Your personal thoughts about the prospects of such processing.

Independent work No. 7.

Characteristics of steels using regulatory documents and Internet resources.

The use of alloy steels in the automotive industry.

Form of work: characteristics of materials using Internet resources and regulatory documentation.

Number of hours to complete the work: 5 o'clock

Work completion time: when studying the topics “Carbon and alloy steels”, performing laboratory work “Analysis of the microstructure of steels”.

Instructions for completing the task: enter sites for the sale and characteristics of materials. Open a window on the website “Steel” or “Alloy brand”. Using the brand, find and characterize the steels that correspond to your option.

Please indicate: area of application of steel (with examples of manufactured products),

possible substitutes and foreign analogues of the brand;

complete chemical composition;

mechanical properties (strength, ductility, hardness, etc.);

technological properties.

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ONE HUNDRED 22-04-02

STANDARD
Research and Production Consortium
RESOURCE

Complex:

RESOURCE
CONSTRUCTIONS
INDUSTRIAL
BUILDINGS AND STRUCTURES

Moscow

2003 G.

Goritsky V.M. - metallurgical engineer, doctor of technical sciences, professor;

Goritsky O.V. - metallurgical engineer;

INTRODUCTION

Institute TsNIIPSK im. Melnikov for 10 years in the metal examination department studied various methods for determining the characteristics of the metal of operating structures without their destruction.

The mechanical properties of steel are assessed with a selected degree of confidence from 75% to 99%.

1. GENERAL PROVISIONS

1.2. The load-bearing capacity of the metal structures under study as a result of sampling and microsampling provided for in this manual is practically not reduced, which eliminates the need for restoration repairs performed when selecting fragments (cuttings or other macrosamples) using standard methods.

1.3. Sampling and microsampling from steel welded or riveted structures can be used for:

Preparation of an examination of the technical condition of structures of buildings and structures of a hazardous facility;

For research and other purposes.

1.4. This manual aims to determine the steel grade and its category, which is achieved by determining the chemical composition, yield strength, tensile strength and critical brittleness temperature of the steel.

1.5. The scope of application of this manual is low-carbon and low-alloy steels with a nominal yield strength of 150 ... 440 MPa (16 ... 45 kg/mm 2).

1.6. The manual is intended for laboratories equipped with light metallographic microscopes, mechanical testing equipment, verified by the State Metrological Service, and staffed with qualified personnel in the field of metallurgy.

2. TERMS, DEFINITIONS, TECHNICAL CONCEPTS

2.1. Critical brittleness temperature- temperature at which the value of impact strength reaches a certain standardized value a cr, indicated by an index, for example, T 29 - temperature above which the value of impact strength, determined on samples with a U-shaped notch, is not less than 29 J/cm 2 (3 kgf · m/cm 2).

2.2. Metallography- the science of the structure and physical properties of metals and alloys, exploring the relationship between their properties and structure at various temperatures.

2.3. Metal microsample- this is a volume of metal of reduced size, from which it is impossible to make at least one standard sample for tensile or impact bending and, the dimensions of which are mostly 5 - 10 times smaller than standard samples intended for mechanical tests.

2.4. Metal sample- the volume of metal from which no more than one sample of a standard size can be made, intended for tensile or impact bending tests.

2.5. Menage sample- a sample with a U-shaped notch for testing materials for impact strength during impact bending on pendulum impact drivers (type 1 - 3 according to GOST 9454).

2.6. Charpy sample- a sample with a V-shaped notch for testing materials for impact strength during impact bending on pendulum impact drivers (type 11 - 13 according to GOST 9454).

3. SAMPLING AND MICRO-SAMPLES OF METAL

3.1. Sampling and microsampling sites should be established based on the condition of obtaining representative information about the quality of the steel of the metal structure element under study.

3.2. The possibility and location of sampling depend on the design features of the metal structure and are established by the Specialized Organization.

3.3. Samples and microsamples of metal should be taken from the edge of the metal structure element under study. In the case of edges formed by gas cutting - outside the heat-affected zone.

3.4. The sampling and microsampling technology should ensure minimal deformation and heating of the metal not higher than 150 °C.

3.4.1. Microsamples from the edges of metal structure elements should be taken by cutting or sawing using a hacksaw or cutting wheel in accordance with Fig. 1, and for elements up to 10 mm thick inclusive and Fig. 1b for elements with a thickness of more than 10 mm.

The shape of the microsample (prismatic or pyramidal) is determined by the convenience of cutting (cutting) the microsample.

The dimensions of the microsample must be no less than а?b?t(h), where t is the thickness of the element, mm;

b? 5 mm - in the case of a rolled or machined edge;

b? 0.5t + 5 mm at t? 10 mm and b ? max (10 mm; 0.25t) at t > 10 mm in the case of an edge obtained using gas cutting or another similar method;

3.4.2. Microsamples from the central parts of structural elements must be at least 1.2 x 2.5 x 15 mm. The minimum cross-sectional area of the microsample in the central part must be at least 3 mm 2.

3.5. Sampling, as a rule, is carried out from unloaded or lightly loaded elements of building structures.

3.6. The minimum sample size is determined by the requirements of GOST 9454 for the size of standard impact samples, taking into account the allowance for mechanical processing of the surface of the samples. When sampling, it is necessary to take into account the regulatory requirements for the orientation of impact samples (along or perpendicular to the rolling direction) to determine impact toughness.

3.7. The location of samples and microsamples, their location and orientation must be indicated in the accompanying note.

3.8. After sampling and microsampling, the cutting areas must be subjected to mechanical cleaning (using a grinding machine or other methods to eliminate stress concentrators), and, if necessary, strengthened. 1

1 The need for reinforcement is established by the organization diagnosing the technical condition of the structure.

4. DETERMINATION OF CHEMICAL COMPOSITION

4.1. The determination of the chemical composition of steel is carried out in accordance with the requirements of GOST 22536 by titrimetric, spectral or other methods that ensure the necessary accuracy of the analysis.

4.2. Chemical analysis of steel is carried out after cleaning the metal surface (micro-sample) to a metallic shine, which eliminates distortion of the results of the analysis of the metal composition.

4.3. When determining the chemical composition by spectral methods, the surface prepared for analysis should not deviate from the normal to the surface of the rolled product by an angle of more than 30°.

4.4. When interpreting the results of chemical analysis, allowable deviations in the content of alloying elements in finished rolled products are taken into account in accordance with the technical requirements for low-carbon and low-alloy steels (GOST 27772, GOST 380, GOST 19281, etc.).

5. METALLOGRAPHIC ANALYSIS

5.1. To determine the yield strength (according to clause 6.6.2) and impact strength, metallographic sections must be prepared and examined.

5.2. Microsamples cut out in accordance with paragraph 3 of these instructions must be embedded in Wood's alloy, epoxy resin or other similar substances to prepare thin sections.

5.3. The sections are made in a plane perpendicular to the rolled surface. It is allowed to produce polished sections in planes with a deviation from the normal to the surface by an angle of no more than 30°. Quantitative metallographic analysis is carried out in sections of sections located at a distance of at least 0.25 mm from the surface of the rolled product.

5.4. The composition of etchants and the technology for preparing thin sections for research are established in accordance with GOST 5639, GOST 5640.

5.5. When performing metallographic analysis, it is necessary to evaluate:

The actual grain size d is the average nominal diameter (average chord) and number (score) of ferrite grain for ferritic-pearlite steels in accordance with GOST 5639;

For thermally strengthened steels and steels in the structure of which shear transformation products are present, it is possible to determine the value of the average conventional grain of ferrite d y using the formula d y = d fts /0.6, where d fts is the average nominal diameter (average chord) of the transgranular cleavage facets, determined from fractograms using the methods outlined in Section. 3 GOST 5639;

Size (diameter) D of dispersed strengthening particles when alloying steel with strong carbonitride-forming elements (for example, vanadium, niobium, titanium) - using extraction replicas, and the interparticle distance? - on thin foils using transmission electron microscopy methods;

Dislocation density? (if necessary) on thin foils using transmission electron microscopy.

5.6. In what follows, the effective grain size deff (in millimeters) is understood as the ferrite grain size for ferritic-pearlitic steels or the average ferrite grain size for thermally hardened steels noted in paragraph 5.5.

5.7. The grain size is determined in at least three sections of the thin section (negatives), in each of which the number of points of intersection of secants with the boundaries of structural components must be at least 100.

In the case of structural heterogeneity of the metal along the thickness of the rolled product revealed by light microscopy methods, the number and location of the analyzed fields of view during metallographic analysis are selected in such a way as to ensure an adequate assessment of the cross-sectional average values of the determined characteristics.

6. DETERMINATION OF TEMPORARY RESISTANCE ? c AND YIELD STRENGTH? T

6.1. Temporary resistance? in the steels under study should be determined by calculation method based on the results of measuring the hardness of steel using the Vickers (HV) or Brinell (NB) methods on stationary hardness testers in accordance with GOST 2999 and GOST 9012.

6.2. If hardening of the metal is unavoidable when taking microsamples according to clause 3.3.2, hardness measurements should be carried out directly on the object using portable static hardness testers in accordance with GOST 22761 or dynamic impact in accordance with GOST 18661. The use of other types of hardness testers is allowed if the required measurement accuracy is ensured.

Requirements for the size, curvature of the prepared site and the quality of surface cleaning must comply with the data in the technical passport of the hardness tester used. The prepared site must be located at a distance of at least 100 mm from the weld and no further than 300 mm from the place where the microsample was taken.

6.3. In the range from 90 to 270 HV (90 to 270 HV), which is the scope of this instruction, the hardness values determined by the Brinell and Vickers methods are the same. Further in the text, in all calculation formulas, HB values can be replaced by HV values.

6.4. The number of hardness measurements must be at least:

9 measurements using stationary hardness testers for all steels (except boiling steel);

18 measurements when using portable hardness testers and when assessing the hardness of boiling steels using hardness testers of any type.

Based on the measurements obtained, the average NV values are determined. When determining the average hardness value, the minimum and maximum measurement results are discarded.

6.5. Temporary resistance should be determined by the formula:

B = 112 + 2.4НВ, MPa

6.6. Determination of the yield strength must be carried out using one of the following methods:

The method of measuring hardness at the yield point;

Based on chemical, durometric and metallographic analysis.

6.6.1. Determination of the yield strength by measuring hardness at the yield point is carried out in accordance with GOST 22762.

6.6.2. The yield strength based on the results of chemical, durometric and metallographic analysis is determined by the formula:

T = 1.5 + 0.6?? t * + 0.74?НВ, MPa,

where HB is the hardness value, and the magnitude? t* is determined according to the expression:

T * = (? 0 2 + ? p 2) 1/2 + (?? 2 t.r. + ?? 2 d.u. + ?? 2 d.) 1/2 + K y d eff -1/2,

Where: ? 0 - friction stress of the iron lattice, for this calculation is taken equal to 30 MPa;

P - stress due to strengthening of steel with pearlite, ? n = 2.4P, MPa,

where: P is the percentage of pearlite component;

T.r. - stress due to hardening of the solid solution with alloying elements; is determined by the concentration of C i (in % by mass of alloying elements in α-iron (ferrite));

T.r. = 4670C C+N + 33C Mn + 86C Si + 31C Cr + 30C Ni + 11C Mo + 60C Al + 39C Cu + 690C P + 3C V + 82C Ti, MPa;

D.u. - stress due to strengthening of steel by dispersed particles, determined taking into account the data in clause 5.5:

where: G = 8.4?10 4 MPa - shear modulus, b = 2.5?10 -7 mm - Burgers vector;

D = stress due to dislocation strengthening, estimated from dislocation density?,

D = 5G?b?? 1/2 (for hot-rolled steels it is allowed to take ?? d = 30 MPa), K y = 20 MPa? mm 1/2.

6.7. If it is impossible to measure hardness, it is allowed to calculate the tensile strength and yield strength of unhardened steel using the formulas:

B = 251 + 1.44?? t**, MPa,

Where? t** = (? 0 2 + ? p 2) 1/2 + (?? 2 t.r. + ?? 2 d.u. + ?? 2 d.) 1/2;

6.8. Accuracy of determining the values of tensile strength and yield strength.

6.8.1. The accuracy of determining the yield strength according to clause 6.6.1 is ±7%.

6.8.2. The values of tensile strength and yield strength calculated in accordance with clause 6.5, clauses 6.6.2 and 6.7 are the mathematical expectation of the indicated values.

6.8.3. The lower limit of the confidence interval for strength characteristics (? in (min), ? t (min)) is calculated based on the actual values of hardness, yield strength and the required degree of confidence? according to the expressions:

V(min) = ? c - K 1 (?)? K 2 (HB), MPa (when calculated according to clause 6.5);

T(min) = ? t - K 3 (?)? K 4 (NV, ? t *), MPa (when calculated according to clause 6.6.2);

V(min) = ? c - K 5 (?)? K 6 (? t**), MPa (when calculated according to clause 6.7);

T(min) = ? t - K 7 (?)?K 8 (? t *), MPa (when calculated according to clause 6.7),

where the values of K 1 (?), K 2 (HB), K 3 (?), K 4 (HB, ? t *), K 5 (?), K 6 (? t **), K 7 (?) and K 8 (? t *) are determined in accordance with table. 1 - 5 of the mandatory Appendix A.

7. ASSESSMENT OF METAL COLD RESISTANCE

7.1. The cold resistance of the metal under study is assessed based on the value of the critical brittleness temperature

7.2. The value of acr is selected in accordance with the requirements of standards or technical specifications for the impact strength of the steel under study (impact strength value, test temperature).

7.3. The critical brittleness temperature (°C) is determined from microsamples cut in accordance with Section 3 of this RD and is calculated using the following formula:

where coefficients a 0 , a 1 and a 2 are selected for samples with a U-shaped notch (Menage) depending on the value of a cr established by regulatory documents (Table 1).

As experimental data accumulates, the coefficients a 0 , a 1 and a 2 will also be determined for samples with a V-shaped notch (Charpy), which will allow a more reliable assessment of the steel’s fracture resistance.

Table 1.

Formula coefficients for determining

For rolled products with a thickness from 7.5 mm to 9 mm (determination of impact strength on type 2 samples according to GOST 9454-78), the value is taken to be 10 °C lower, and for rolled products with a thickness from 4 mm to 7.4 mm (determination of impact strength on samples of type 3 according to GOST 9454-78) - 20 °C lower compared to the values calculated by the formula.

If necessary, the value for the values a cr = 39 J/cm 2 and a cr = 44 J/cm 2 can be determined by linear interpolation using the corresponding values of T 34 and T 49.

7.4. For cold-worked steel, the value determined in accordance with clause 7.3 increases by 0.6??HB, where?HB is the increase in hardness due to cold-hardening of the metal.

7.5. The values of the critical brittleness temperature calculated in accordance with clause 7.3 and clause 7.4 are the mathematical expectation of the specified value.

7.6. Is the upper limit of the confidence interval for the critical brittleness temperature calculated based on the actual values of hardness, yield strength and the required degree of confidence? according to the expression:

where the values of K 9 (?) and K 10 (d eff, HB) are determined in accordance with table. 1 and 6 of the mandatory Appendix A.

If, according to the current regulatory documentation (GOST, TU) for the steel grade under study, when performing impact bending tests on one of three samples, a decrease in impact strength relative to the standardized value is allowed, the value is reduced by 5 °C.

7.7. In accordance with the requirements of GOST (TU), steel has the appropriate quality category if the condition is met

where a nf Ti is the actual value of impact strength at the test temperature T and, and nn Ti is the value of impact toughness normalized by GOST (TU) at the same temperature.

7.8. The inequality in paragraph 7.5 is equivalent to the condition

7.9. The steel under study is considered to satisfy the requirements of the corresponding GOST (TU) for steels of a given quality category if the inequality according to clause 7.6 is satisfied. In accordance with clause 7.5, the specific value of T is determined by the established category of steel quality.

7.10. The choice of test temperature for an impact specimen made from a sample is determined by the research task: determining a given quality category or establishing a critical brittleness temperature.

7.10.1. When determining a given quality category, the test temperature of a sample is assigned based on the condition that the level of impact strength corresponds to the value regulated by GOST (TU) in accordance with clause 7.5. For example, when checking the compliance of St3ps steel with the 5th quality category, the sample test temperature is assigned to -20 °C.

7.10.2. When establishing the critical brittleness temperature, the test temperature of the sample is assigned in accordance with clause 7.3 from the condition of selecting the standard value of impact strength according to GOST (TU) and determining the level of hardness and the size of the actual ferrite grain.

7.10.3. Determination of hardness and measurement of ferrite grain diameter is carried out on the sample face, perpendicular to the rolled surface and parallel to the rolling direction.

7.11. When obtaining values of a cr that do not coincide with the standard values according to GOST (TU), it is allowed to determine the value according to clause 7.3 by the method of linear interpolation using the corresponding standard values of a cr.

8. DETERMINATION OF MECHANICAL PROPERTIES OF BOILING STEEL

8.1. A feature of determining the mechanical properties of rolled products from boiling steels is the need to take into account its heterogeneity along the length and cross-section.

8.2. The heterogeneity of rolled products can be taken into account using a system of coefficients (clause 8.3) or by increasing the number of microsamples taken (clause 8.4).

8.3. The critical temperature calculated in accordance with section 7 of these instructions for boiling steels shifts by 10 °C to the positive temperature region.

8.4. When determining the mechanical properties of rolled products, at least two microsamples are taken from boiling steel. It is recommended to take microsamples from similar structural elements. It is allowed to take microsamples from the same structural element; in this case, the microsampling sites must be separated from each other by a distance of at least 2 m.

Mechanical properties are determined for each microsample in accordance with sections 6 and 7 of this instruction, and the worst values for the studied microsamples are taken as the actual properties of rolled products from boiling steels .

9. PRESENTATION OF RESULTS

9.1. Based on the data obtained in accordance with sections 4 ... 8, a Conclusion on the quality of steel is drawn up, which includes the results of determining:

chemical composition;

tensile strength and yield strength;

9.2. The conclusion is signed by the head of the laboratory and approved by the head of the organization that includes the laboratory.

10. LIST OF REGULATIVE DOCUMENTATION USED

GOST 380-94 “Ordinary quality carbon steel.”

GOST 2999-75* “Metals and alloys. Vickers hardness measurement method."

GOST 5639-82* “Steels and alloys. Methods for identifying and determining grain size.”

GOST 5640-68 “Steel. Metallographic method for assessing the microstructure of sheets and tape."

GOST 9012-59* “Metals and alloys. Brinell hardness measurement method."

GOST 9454-78* “Metals. Test method for impact bending at low, room and elevated temperatures."

GOST 18661-73 “Steel. Hardness measurement using the impact imprint method."

GOST 19281-89*“Rolled products made of high-strength steel. General technical conditions".

GOST 22536.0-87*“Carbon steel and unalloyed cast iron. General requirements for methods of analysis."

GOST 22536.1-88 “Carbon steel and unalloyed cast iron. Methods for determining total carbon and graphite."

GOST 22536.2-87* “Carbon steel and unalloyed cast iron. Methods for determining sulfur".

GOST 22536.3-88 “Carbon steel and unalloyed cast iron. Methods for determining phosphorus".

GOST 22536.4-88 “Carbon steel and unalloyed cast iron. Methods for determining silicon."

GOST 22536.5-87* “Carbon steel and unalloyed cast iron. Methods for determining manganese".

GOST 22536.6-88 “Carbon steel and unalloyed cast iron. Methods for determining arsenic."

GOST 22536.7-88 “Carbon steel and unalloyed cast iron. Methods for determining chromium".

GOST 22536.8-87*“Carbon steel and unalloyed cast iron. Methods for determining copper".

GOST 22536.9-88 “Carbon steel and unalloyed cast iron. Methods for determining nickel."

GOST 22536.10-88 “Carbon steel and unalloyed cast iron. Methods for determining aluminum."

GOST 22536.11-87* “Carbon steel and unalloyed cast iron. Methods for determining titanium".

GOST 22536.12-88 “Carbon steel and unalloyed cast iron. Methods for determining vanadium".

GOST 22761-77 “Metals and alloys. Method for measuring Brinell hardness with portable static hardness testers.”

GOST 22762-77 “Metals and alloys. Method for measuring hardness at the yield point by indenting a ball."

GOST 27772-88*“Rolled products for building steel structures. General technical conditions".

APPENDIX (A)

(required)

Table 1

The values of the coefficients K 1 (?), K 3 (?), K 5 (?), K 7 (?) and K 9 (?)

Degree of confidence?, %	K 1(?), MPa	K 3(?), MPa	K 5 (?), MPa	K 7(?), MPa	K 9(?), MPa

table 2

Values of coefficient K 2 (NV)

Hardness HB

Hardness HB

Table 3

Values of coefficient K4 (NV, ? t *)

Hardness HB	Yield limit? t*, MPa
Hardness HB