Tensile strength (MPa). Great Encyclopedia of Oil and Gas
Steel is smelted from cast iron in Martynov furnaces, converters and electric furnaces. Steel is an alloy of iron with carbon and some impurities (sulfur, phosphorus and other additives). Steel differs from cast iron in that the alloy contains no more than 1.7% carbon.
Depending on the carbon content, steel is divided into low-carbon steel, containing less than 0.25% carbon; medium-carbon with carbon from 0.25 to 0.6%, high-carbon, which contains from 0.6 to 1.7% carbon. Medium-carbon steels are mainly used for reinforcement of reinforced concrete structures.
In order to improve the properties of steel, alloying additives are additionally introduced into the alloy: nickel, chromium, tungsten, vanadium, molybdenum, copper, aluminum, boron, titanium, manganese, silicon, etc., which makes it acquire greater strength and other positive qualities. Steels with such additives are called alloyed. The most widely used in construction are low and medium alloy steels (St.Z, St.5, 18G2S, 35GS, 25G2S, 30HG2S), which contain a small percentage of alloying additives.
Steel has the ability to resist tensile, compressive, bending, and impact forces. Let's consider just one of them - the ability of steel to resist tensile forces, which is most typical for the operating conditions of reinforcing steels.
Tensile strength of steel
The tensile strength of steel is the ability to resist destruction under the influence of external tensile forces (loads). The amount of tensile force on a steel sample being tested divided by its area at any time before failure is called stress and is measured in kg/cm2.Example: the stress in a reinforcing bar with a diameter d = 20 mm, which is stretched by a force P = 5000 kg, will be 1600 kg/cm2. The tensile strength of steel is the highest stress that a rod (specimen) can withstand. Tensile strength is measured in kg/cm2. The main method for determining the strength of a metal is a tensile test. The test results are presented graphically in the form of a diagram (see figure). The values of the tensile forces divided by the area of the sample, i.e., stresses, are plotted along the vertical axis, and the values of the elongations of the rod that occur during tension are plotted along the horizontal axis as a percentage of its original length.
From the considered diagram about deformation (elongation), it is possible to establish the relationship between elongation, called deformation, and tensile stresses of the metal sample.
At the beginning of the test, the deformation increases in proportion to the stresses, i.e., it increases as many times as the tensile stresses increase. The straight line OA at the beginning of the diagram indicates a direct proportional relationship between strains and stresses.
If at this initial stage the stretching process is stopped, that is, the tensile force is removed, then the rod will return to its original length; the deformation at this stage is said to be elastic. Section OA of the diagram is called the zone of elastic deformation, and the stress at point A is called the limit of proportionality.
Thus, the limit of proportionality is the highest stress at which deformation disappears after the stress is removed. Beyond point A, the elongation begins to increase faster than the stress increases, and the straight line turns into the AB curve, which indicates a violation of the proportional relationship between force and elongation.
Beyond point B, the curve turns into a horizontal straight line BV, which corresponds to the state of the sample when the deformation (elongation) of the sample increases without increasing stress. Usually in this case it is customary to say that the steel flows. The part of the diagram corresponding to the horizontal segment BV is called the yield plateau.
The magnitude of the stress at which the yield process began (point B on the diagram) is called the yield strength (at). At the end of the yield process (point B in the diagram), the increase in deformation slows down somewhat and the sample can absorb a greater tensile force than in the yield state. This stretching process beyond the yield point occurs until the sample breaks (point D in the diagram).
The magnitude of the stress at which the failure of the sample occurred is the tensile strength of the steel.
Some types of steel, such as cold-drawn wire, when stretched do not have a clearly defined yield state, in which elongations increase without increasing stress. For such steels, only the tensile strength is determined.
Yield strength and tensile strength of steel
About steel used as reinforcement in reinforced concrete structures, the most important thing to know is the yield strength and tensile strength. If the process of yielding has begun, that is, the reinforcement has received significant elongation, then unacceptably large cracks will appear in the concrete and the process of elongation of the reinforcement will end in the destruction of the reinforced concrete structure. If the reinforcement reaches its ultimate strength, it will rupture and the reinforced concrete structure will collapse instantly (brittle collapse). The table shows the mechanical properties of some reinforcing steels. Determination of tensile strength and other mechanical properties of steel is carried out in the factory laboratory using special tensile testing machines.In addition to tensile testing, steel is tested for cold bending. To do this, the sample is bent in a cold state at an angle, depending on the steel grade, from 45 to 180° around a mandrel with a diameter of 1 to 5 diameters of the sample. After bending, there should be no cracks, delamination or fracture on the outer stretched side of the specimen.
Brittleness of steel
Impact resistance is the ability of steel to resist dynamic impacts arising during operation. Impact testing of steel makes it possible to find out the degree of brittleness, the quality of processing and the value of impact strength, i.e. the ratio of the work (in kgm) spent on destroying the sample to its cross-sectional area (in mm2) at the fracture site. The impact strength of steel is a very important indicator that affects the strength of structures operating under dynamic loads at significant negative air temperatures. In construction practice, there are known cases of reinforced concrete beams collapsing from dynamic loads at a temperature of -20-30° C due to the cold brittleness of reinforcing steel, i.e., the loss of steel’s ability to undergo plastic deformation. Steel grade St. is mainly prone to cold brittleness. 5, especially with high carbon content.I recommend -
When a material is pulled in different directions, tensile stress occurs and the material ruptures as a result. The limiting force at which rupture occurs is called tensile strength (tensile strength).
Tensile strength is measured for materials such as alloys, composites, ceramics and plastics. It is measured in MPa, this is the force applied to the area, i.e. kg/cm2. The higher this value, the more resistant the material is to tensile forces.
During testing, the material goes through a “bell stage” before failure (see Fig. 2).
This test helps to understand the strength of the material.
3. Modulus of elasticity (GPa) / Modulus E / Young’s modulus / Modulus of flexibility.
The hardness and elasticity properties of materials are measured in GPa.
The modulus of elasticity reflects the resistance of a material to external load, in this case bending. The material does not undergo irreversible deformation; after removing the external load, it returns to its original state. That is, in this case, unlike other tests, the material is not destroyed.
Three-point bend test. A block of material is installed on 2 supports and a force F is applied to it (Fig. 7 and 8).
The load increases only until the moment when the material begins to bend (see Fig. 9). The higher this value, the stiffer the material.
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Stiffness is important when selecting a restorative material because you do not want the material to deflect significantly under load. A typical example is intrapulpal pins. Its rigidity should correspond to the rigidity of dentin.
For elastic impression materials, on the contrary, low values are desirable, since in this case the impression will be easily removed from the patient's mouth.
Flexural strength (MPa)
The three-point test is also used to measure it. In this case, the load is applied until the material fails (see Fig. 11).
Flexural strength is the ability of a material to resist fracture under load. It is measured in MPa, megapascals.
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This test resembles a bridge load. A high flexural strength value means that the bridge is highly resistant to fracture.
5. Fatigue limit - cyclic loads
First, a flexural strength test is carried out to determine the ultimate strength of the material (MPa). Then a load lower than the above tensile strength is taken. In the same three-point load configuration, the material is sequentially cyclically loaded. Then they note how many cycles the material can withstand before breaking.
This test simulates chewing loads on the bridge. The more cycles the material can withstand, the better.
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Fatigue of materials. When exposed to a large number of cyclic loads on the prosthesis, destruction of the material may occur. The breaking stress (fatigue limit) turns out to be significantly lower than the tensile strength.
The causes of fatigue are still not entirely clear. Microscopic examination of samples subjected to multiple variable loads showed that after a certain number of loadings a number of lines appear in the grains of the material, indicating the presence of shifts of parts of the grains. Under further load, the lines turn into tiny cracks, which merge into a crack. Further destruction is concentrated around it.
The crack grows with each load, and when the cross-section decreases sufficiently, destruction occurs. The resulting crack acts like a groove, i.e. it causes stress concentration and reduces resistance. The moment of destruction is approaching unnoticed. A structure that is in danger of collapsing works flawlessly, but finally collapses suddenly, and under only a small load.
Very often, the causes of fatigue fractures are sudden changes in the shape of parts (sharp transitions in thickness, cuts, cracks on the surface, pores, etc.), causing stress concentration. Since fatigue cracks appear around these areas, the fight against fatigue, in addition to selecting stronger materials, consists of hardening its surface. So, for metals this is achieved by chemical-thermal treatment, mechanical processing (grinding, polishing), hardening with high-frequency currents. These measures make it possible to increase the fatigue limit by several tens of percent. With regard to plastics, the correct polymerization mode, which does not cause the formation of pores in the dentures, is also of great importance.
Tensile strength of some dental materials:
Elasticity. The ability of a material to change shape under the influence of an external load and restore its shape after removing this load is called elasticity. A typical example of the elastic properties of a material is the bending of a steel wire, the stretching of a metal spring, the compression of a prosthesis made of polyamide plastic, or a piece of hydrocoloid mass. After the force is removed, all these bodies regain their shape. But a return to the previous shape can only occur if the applied force does not exceed a certain value called the elastic limit. The elastic limit is the maximum load at which the material, after deformation and removal of the load, completely restores its shape and dimensions. If the load exceeds the elastic limit, then after removing it the material will not be completely restored to its original state and residual deformation will appear.
The materials used for the manufacture of dentures and appliances have different elasticity. Some structures must necessarily have elastic properties, since they are constantly under force, and the appearance of residual deformation makes them unsuitable (clasps, arches, denture bases, etc.).
In other cases, the manifestation of elastic properties interferes with certain technological stages. For example, stamping crowns is possible if the metal is in a state of least elasticity.
Metals can exhibit elasticity differently depending on their mechanical and thermal treatment. Steel increases its elasticity when it is hammered or drawn, as well as when hardened.
All materials have elastic properties in certain temperature ranges. For metals these intervals reach hundreds of degrees; for plastics they are much smaller. For base plastics they are measured in tens of degrees.
The elasticity of the material is determined on samples that are strengthened in devices such as hydraulic
press and subjected to loading. The change in length of the sample is measured under a maximum load that does not cause residual deformation, after removal of which the sample returns to its original length. The calculation is carried out per 1 mm 2.
It is clear that when determining the loads allowed on various parts of the prosthesis, knowledge of the elastic limit of the material from which it is made is absolutely necessary, since a load above the elastic limit leads to a change in the shape of the prosthesis, and, consequently, to the impossibility of using it.
If you continue to load the sample, it gradually begins to elongate, and its cross-section becomes smaller, and when the load is removed, the sample does not return to its previous dimensions. The more the sample is able to elongate and its cross-section to narrow, the more plastic the material is.
In contrast to ductile materials, brittle materials fracture under load without changing shape. Fragility, as a rule, is a negative property, therefore in orthopedic dentistry most often they use not only strong and elastic materials, but also, to a certain extent, plastic ones.
Plastic. The ability of a material, without collapsing, to change shape under the influence of loads and maintain this shape after the load ceases to act. Many impression materials, wax, plaster, and metals have this property.
All plastic materials thus have a pronounced residual deformation. Plasticity is necessary for impression materials, metals used to produce products by stamping, plastics from which denture bases are formed, and filling materials.
Sometimes a material is chosen only because of its ability to acquire a plastic state. This applies primarily to impression materials and plastics. To obtain maximum ductility of the metal, it is subjected to special heat treatment - annealing, wax and impression masses are heated, gypsum is mixed with water, etc. Typically, treatment that increases ductility reduces resistance to deformation and vice versa.
Viscosity. The ability of a material to stretch under tensile loads. This type of deformation is characterized by the fact that the sample under study increases in size in the direction of the applied force (usually along its length) and narrows in cross section.
Some materials have high viscosity (gold, silver, iron, etc.). Others do not have this ability (cast iron, porcelain, etc.). They belong to the group of fragile materials.
Thus, fragility is the opposite property of viscosity.
When testing various materials, in particular plastics, the method of determining impact strength is widely used. Specific impact strength is the work expended on breaking a sample divided by its cross-sectional area. Impact strength is determined using a pendulum impact tester MK-0.5-1. The device consists of a massive base on which a pendulum-type device is mounted. A pendulum with a replaceable load (10-15-30 kg), mounted on the axis of the frame, is secured at a certain height using a pinch. When the clamp is released, the pendulum falls freely and strikes the sample. The stronger the sample, the lower the height the pendulum rises after impact, i.e., the more work was spent on impact destruction of the sample. The lower the impact strength, the more brittle the material is.
The given mechanical properties of materials make it possible to determine the rigidity of the materials. The ability of structural elements to resist deformation under the influence of external forces is called rigidity.
It should be remembered that when calculating the required dimensions of structural parts under the expected load, they always adhere to the rule that the material should not only not be destroyed, but also deformed. Therefore, when making calculations, they always proceed from a fourfold safety factor, i.e. if the tensile strength of carbon steel is 90 kg/mm2, then the permissible load should be 22-23 kg/mm2. If the workload exceeds these figures, then the dimensions of this part should be increased. So, for example, if we know that the force applied to the prosthesis at the moment of chewing is 60 kg, and the tensile strength of the plastic is 1000 kg/cm2, then the plate should have a width of 2.5 cm in its smallest part, with a thickness 1 mm.
Literature:
1. Popkov V.A. Dental materials science: Textbook / V.A. Popkov. O.V.Nesterova, V.Yu.Reshetnyak, I.N.Avertseva.//M. – MEDpress-inform. – 2009. – 400 p.
2. Craig R. Dental materials: properties and application / R. Craig, J. Powers, J. Vataga // - 2005. – 304 p.
3. http://article-factory.ru/medicina/zubotehnicheskoe-materialovedenie/139-mehanicheskie-svojstva.html
4. www.infodent.ru
Related information.
- compression - determines the ability of a material to resist pressure from an external force;
- bending - affects the flexibility of parts;
- torsion - shows how suitable the material is for loaded drive shafts that transmit torque;
- stretching
- chemical composition of the alloy;
- thermal procedures that help strengthen materials: hardening, tempering, annealing, etc.
- Chromium. Used to increase hardenability and hardness. Share – 0.8-0.2%.
- Bor. Improves cold brittleness and radiation resistance. Share – 0.003%.
- Titanium. Added to improve the structure of Cr-Mn alloys. Share – 0.1%.
- Molybdenum. Increases strength characteristics and corrosion resistance, reduces fragility. Share – 0.15-0.45%.
- Vanadium. Improves strength parameters and elasticity. Share – 0.1-0.3%.
- Nickel. Promotes an increase in strength characteristics and hardenability, but at the same time leads to an increase in fragility. This effect is compensated by the simultaneous addition of molybdenum.
- when compressed;
- when bending;
- in torsion;
- when stretched.
- steel of ordinary quality (GOST 380-50)
- high-quality steel (GOST 1050-52).
wire,
beams, etc.
etc. up to steels M St. 7, B St. 0, B St. 3, B St. 4, B Art. 5, B St. 6.
Great Encyclopedia of Oil and Gas. Strength steel
Ultimate strength of steel in compression and tension
The strength of metal structures is one of the most important parameters that determine their reliability and safety. Since ancient times, issues of strength were solved experimentally - if any product broke, then the next one was made thicker and more massive. Since the 17th century, scientists began a systematic study of the problem; the strength parameters of materials and structures made from them can be calculated in advance, at the design stage. Metallurgists have developed additives that affect the strength of steel alloys.
Tensile strength
Ultimate strength is the maximum stress a material can experience before it begins to fail. Its physical meaning determines the tensile force that must be applied to a rod-like sample of a certain cross-section in order to break it.
How is strength testing performed?
Strength tests for tensile strength are carried out on special test benches. One end of the test sample is fixedly fixed in them, and a drive mount, electromechanical or hydraulic, is attached to the other. This drive creates a smoothly increasing force that acts to break the sample, or to bend or twist it.
The electronic control system records the tensile force and relative elongation, and other types of deformation of the sample.
Types of tensile strength
Tensile strength is one of the main mechanical parameters of steel, as well as any other structural material.
This value is used in strength calculations of parts and structures; based on it, it is decided whether a given material is applicable in a particular area or whether a more durable one needs to be selected.
The following types of tensile strength are distinguished:
The scientific name of the parameter used in standards and other official documents is tensile strength.
Today, steel is still the most used structural material, gradually losing its position to various plastics and composite materials. Its durability, reliability and safety in operation depend on the correct calculation of the strength limits of a metal.
The tensile strength of steel depends on its grade and varies from 300 MPa for ordinary low-carbon structural steel to 900 MPa for special high-alloy grades.
The parameter value is affected by:
Some impurities reduce strength, and they try to get rid of them at the casting and rolling stage, while others, on the contrary, increase it. They are specially added to the alloy composition.
Proof of Yield
In addition to the tensile strength, the related concept of yield strength, denoted σt, is widely used in engineering calculations. It is equal to the amount of tensile strength that must be created in the material in order for the deformation to continue to increase without increasing the load. This state of the material immediately precedes its destruction.
At the microlevel, at such stresses, interatomic bonds in the crystal lattice begin to break, and the specific load on the remaining bonds increases.
General information and characteristics of steels
From the designer’s point of view, the physical and mechanical parameters of steel are of greatest importance for alloys operating under normal conditions. In some cases, when the product is to operate under conditions of extremely high or low temperatures, high pressure, high humidity, or under the influence of aggressive environments, the chemical properties of steel become equally important. Both the physical-mechanical and chemical properties of alloys are largely determined by their chemical composition.
Influence of carbon content on the properties of steels
As the percentage of carbon increases, the plasticity of the substance decreases with a simultaneous increase in strength and hardness. This effect is observed up to approximately 1% share, then a decrease in strength characteristics begins.
Increasing the proportion of carbon also increases the threshold of cold capacity; this is used to create frost-resistant and cryogenic grades.
Manganese and silicon additives
Mn is contained in most grades of steel. It is used to displace oxygen and sulfur from the melt. Increasing the Mn content to a certain limit (2%) improves machinability parameters such as ductility and weldability. After this limit, further increases in content lead to the formation of cracks during heat treatment.
The influence of silicon on the properties of steels
Si is used as a deoxidizer used in the smelting of steel alloys and determines the type of steel. Quiet high-carbon grades should contain no more than 0.6% silicon. For semi-quiet brands, this limit is even lower - 0.1%.
When producing ferrites, silicon increases their strength parameters without reducing their ductility. This effect persists up to the 0.4% threshold.
In combination with Mn or Mo, silicon promotes an increase in hardenability, and together with Cr and Ni increases the corrosion resistance of alloys.
Nitrogen and oxygen in the alloy
These gases, the most common in the earth's atmosphere, have a harmful effect on strength properties. The compounds they form in the form of inclusions in the crystalline structure significantly reduce strength parameters and ductility.
Alloying additives in alloys
These are substances deliberately added to the melt to improve the properties of the alloy and bring its parameters to the required ones. Some of them are added in large quantities (more than a percent), others in very small quantities. I most often use the following alloying additives:
Metallurgists also use more complex combinations of alloying additives, achieving unique combinations of physical and mechanical properties of steel. The cost of such grades is several times (or even tens of times) higher than the cost of conventional low-carbon steels. They are used for particularly critical structures and assemblies.
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Strength of metals:: SYL.ru
Tensile strength is the maximum stress to which a material can be subjected before it fails. If we talk about this indicator in relation to metals, then here it is equal to the ratio of the critical load to its cross-sectional area when conducting a tensile test. In general, strength shows how much force is required to overcome and break internal bonds between the molecules of a material.
How is strength testing performed?
Strength testing of metals is carried out using specialized mechanisms that allow you to set the required power during tensile testing. Such machines consist of a special loading element, with the help of which the necessary force is created.
Equipment for testing metals for strength makes it possible to stretch the materials being tested and set certain values of force that are applied to the sample. Today, there are hydraulic and mechanical types of mechanisms for testing materials.
Types of tensile strength
Tensile strength is one of the main properties of materials. Information about the ultimate strength of certain materials is extremely important when it is necessary to determine the possibilities of their use in certain industrial areas.
There are several separate strength limits of materials:
Formation of the concept of the ultimate strength of metals
Galileo once spoke about the ultimate strength, who determined that the maximum permissible limit of compression and tension of materials depends on their cross-section. Thanks to the scientist's research, a previously unknown quantity arose - fracture stress.
The modern doctrine of the strength of metals was formed in the middle of the 20th century, which was necessary based on the need to develop a scientific approach to prevent possible destruction of industrial structures and machines during their operation. Until this point, when determining the strength of a material, only the degree of its plasticity and elasticity was taken into account and the internal structure was not taken into account at all.
Steel is the main raw material in most industrial applications. It is widely used in construction. That is why it is very important to select in advance a high-quality, truly suitable type of steel to perform specific tasks. The result and quality of the work performed directly depends on the correct calculation of the tensile strength of a certain steel grade.
As an example, we can cite several values of the ultimate strength indicators of steels. These values are based on government standards and are recommended parameters. Thus, for products cast from structural non-alloy steel, the GOST 977-88 standard is provided, according to which the limiting strength value during tensile testing is about 50-60 kg/mm2, which is approximately 400-550 MPa. A similar grade of steel, after undergoing the hardening procedure, acquires a tensile strength value of more than 700 MPa.
The objective tensile strength of steel 45 (or any other grade of material, just like iron or cast iron, as well as other metal alloys) depends on a number of factors that must be determined based on the tasks assigned to the material during its use.
Copper strength
Under normal conditions at room temperature, annealed commercial copper has a tensile strength of about 23 kg/mm2. With significant temperature loads on the material, its ultimate strength is significantly reduced. The indicators of the ultimate strength of copper are reflected by the presence of various impurities in the metal, which can both increase this indicator and lead to its decrease.
Aluminum strength
The annealed fraction of technical aluminum at room temperature has a tensile strength of up to 8 kg/mm2. Increasing the purity of the material increases its ductility, but is reflected in a decrease in strength. An example is aluminum, which has a purity of 99.99%. In this case, the ultimate strength of the material reaches about 5 kg/mm2.
A decrease in the tensile strength of an aluminum dough piece is observed when it is heated during tensile testing. In turn, lowering the metal temperature in the range from +27 to -260°C temporarily increases the test indicator by 4 times, and when testing the highest purity aluminum fraction - by as much as 7 times. At the same time, the strength of aluminum can be slightly increased by alloying it.
Strength of iron
To date, by industrial and chemical processing it has been possible to obtain whisker-like iron crystals with a tensile strength of up to 13,000 MPa. Along with this, the strength of technical iron, which is widely used in a wide variety of fields, is close to 300 MPa.
Naturally, each material sample, when examined for strength level, has its own defects. In practice, it has been proven that the real objective ultimate strength of any metal, regardless of its fraction, is less than the data obtained during theoretical calculations. This information must be taken into account when choosing a specific type and grade of metal to perform specific tasks.
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Carbon steels
Carbon structural steel. In accordance with existing standards, carbon structural steel is divided into:
Standard quality steel
Ordinary quality steel according to GOST 380-50 is divided into two groups (A and B).
Steel group A
Group A unites brands according to mechanical properties guaranteed by the supplier plant; The chemical composition of steel in this group is not specified by GOST, and the supplier plant is not responsible for it.
Group A steel is marked as follows:
etc. to St. 7.
Tensile strength of steel:
Art. 0-32-47 kg/mm2,
at St. 1- 32-40 kg/mm2,
at St. 2-34-42 kg/mm2.
For steels Art. 3, Art. 4, Art. 5, Art. 6 and Art. 7 approximately corresponds to the figure defining the steel grade (in tens of kg/mm2).
For example, at St. 6 the minimum value of the tensile strength will be about 60 kg/mm2.
Group A steels are usually used for the manufacture of products used without heat treatment:
Steel group B
For group B steel, the chemical composition is regulated and the manufacturing method is indicated:
M - open hearth;
B - Bessemer,
T - Thomasovskaya)
The following steel grades are installed in this group:
Group B steels are used for the manufacture of parts of ordinary quality:
The grades and composition of open hearth steel are given in table. 3.
Read the continuation of the classification of carbon steel in the next article.
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Strength - steel - Great Encyclopedia of Oil and Gas, article, page 1
Strength - steel
Page 1
The strength of steels should be in the range of 50 - 90 kg/mm2, in addition, they must be heat-resistant so that at 290 the indicated strength does not decrease significantly. The tolerances in the manufacture of pumps are very small, on the order of 0.003 mm.
The strength of steel can be increased by alloying with copper due to hardening of the solid solution, additional grain refinement, and at higher concentrations up to 0-8% due to dispersion strengthening. At the same time, the critical brittleness temperature can be reduced.
The strength of steels (with some exceptions) increases with low tempering. At the same time, however, fragility also increases. The higher the pressure that the device is designed for, the stricter the heat treatment requirements.
The strength of steels changes significantly when moving to high temperatures. For example, the tensile strength of chromium-nickel steel type 18 - 8 drops from 70 to 40 kg/mm.
The strength of steel can change significantly during prolonged use at elevated and high temperatures. The change in strength is caused by instability of the structure, which manifests itself in the development of spheroidization and graphitization processes.
The strength of steels (with some exceptions) increases with low tempering. At the same time, however, fragility also increases.
The strength of steels at high temperatures changes quite significantly.
Strength of steel / Gray, Advances in pre-modern metal technology.
The strength of 7KhG2VM steel is approximately 20% higher than the strength of steels with 6 - 12% Cr in small sections (stm 315-325 kg/mm at HRC 57 - 56) and significantly higher in large sections.
The strength of steels under an asymmetric loading cycle depends both on the mechanical properties of the material and on stress concentrators. Therefore, when calculating the fatigue strength of machine parts, it is necessary to take into account the influence of cycle asymmetry on its limiting amplitude, depending on the mechanical properties of the material, stress concentrators and the environment in which they are operated.
The strength of steel can reach 1600 MPa if it is subjected to cold plastic deformation before aging.
The strength of steels gradually increases with decreasing temperature, and the presence of individual components has a different effect.
The strength of steel can reach - - 1600 MPa if it is subjected to cold plastic deformation before aging.
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Steel - group - strength
Steel - group - strength
Page 1
Steel of strength group D is used for the manufacture of drill string elements: leading pipes and their subs, drill pipes and couplings for them, drill collars, subs for drill strings, butt-welded drill pipe blanks.
We accept steel of strength group C, pipe wall thickness 9 mm.
Pipes made from steel of strength group E are mainly used for fastening production wells with temperatures at the wellhead of 120 - 220 C. Compared to pipes made from grade D steel, pipes made from alloy steels have greater corrosion resistance and strength, and are made seamless with the same wall thickness along the entire length of the pipes.
Pipes made of steel of strength group D are supplied normalized; pipes made from steel grade 36G2S are normalized or hardened with high tempering, and pipes made from steel grades 40X and ZOKHGS are hardened with high tempering.
MPa for steel of strength group D, 3430 MPa for strength groups K and E and 2450 MPa for strength groups L and M; L - working height of the thread profile, equal to 0 12 cm; [i.
The chemical composition of steel of strength group D is not regulated, only the content of sulfur and phosphorus should be no more than 0.045% of each element.
The chemical composition of steels of strength groups H-40, J-55, N-80 (analogue of steel strength group E) and P-105 (strength group Vl) is not specified in the standards.
The chemical composition of steels of strength groups H-40, J-55, N-80 and P-105 is not specified in the standards.
Testing samples made of steel of strength group D for repeated alternating bending with the simultaneous application of constant tangential stresses showed that the latter do not affect the endurance limit.
Trlbs are made from steel of strength group from inclusive.
Casing pipes are made of steel of strength group 11 - 40 but are subject to heat treatment. In the production of pipes in steel of strength group N-80, quenching and tempering are used more widely than normalization.
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Increase - strength - steel
Page 1
The increase in steel strength at low temperatures was used in the design of an apparatus to obtain a pressure of 100,000 atm, operating at liquid air temperature.
As the strength of steel increases, its sensitivity to stress concentrations caused by the shape of welded joints usually increases. Therefore, to increase the performance of heavily loaded welded structures made of low-alloy steels with a tensile strength of over 600 MPa, they resort to mechanical treatment of the surface of the weld metal. In practice, this operation is widespread and is usually performed with abrasive wheels or cutters. The greatest effect is achieved when cleaning easily accessible butt welds flush with the base metal.
As the strength of steel increases, the manifestation of the adsorption effect increases (Loboiko V.I. et al. [35, p. A feature of shear processes during adsorption fatigue of iron is the almost instantaneous entry into action of a much larger number of sliding planes than when tested in air, as well as an increase in their width and density.The adsorption decrease in surface energy makes it possible to develop those crystal lattice defects that, when the metal is deformed in air, are not able to overcome the energy barrier.
With increasing steel strength (curves / / and / / /), a noticeable decrease in the yield area is observed, and for some steels its complete absence. This property reduces the reliability of steel, increasing its susceptibility to brittle fracture.
Chromium helps to increase the strength of steel, its hardness and wear resistance.
Chromium helps to increase the strength of steel, increases wear resistance, and with increasing carbon content it imparts high hardness to steel. Low- and medium-alloy chromium steels form a group of ball bearing steels and are also widely used for the manufacture of axles, shafts, gears, and tools. High-alloy chromium steel is stainless, has high corrosion resistance, retains strength at elevated temperatures, and can withstand prolonged and high heat without scaling.
The sensitivity of steel to notch increases as the strength of the steel increases. The greatest increase in the notch sensitivity coefficient in absolute value is obtained in the presence of soft notches and a small stress concentration coefficient, while the greatest increase in relative value occurs in the presence of sharp notches and a large stress concentration coefficient. As the radius of the notch bottom increases, the sensitivity to the notch increases, and in the region of small radii this increase occurs especially intensively.
For the weld metal and transition zone, an overestimation of the experimental data is observed in comparison with the calculated ones, however, with an increase in the strength of the steel, this difference decreases. For an entire welded joint, there is a sharp difference between the obtained fracture data and the calculated fatigue curve.
The presence of ferrite, which does not contain carbon from the hardened solution, and the presence of alloying elements Cr, Mo, Ti help to increase the strength of steel at increased loads.
The effect of sodium on fatigue is more complex, since during carburization it, on the one hand, improves resistance to fatigue loads with an increase in steel strength, but at the same time worsens it with a decrease in ductility. With decarbonization, the opposite picture is observed.
Low-carbon, low-alloy mild steels are subject to corrosion cracking in heated solutions of alkalis, nitrates, hydrocyanic acid solutions, hydrogen sulfide-containing environments, etc. Usually, as the strength of steels increases, their resistance to corrosion cracking decreases. Low-alloy, high-strength structural steels with a low-tempered martensite structure have particularly low resistance to stress-corrosion cracking.
An increase in steel strength is observed only at a carbon content of up to 1%; at a carbon content above 1%, secondary cementite appears in the structure.
As the strength of the steels used as the base metal increases, it becomes increasingly difficult to satisfy this requirement. In this regard, it is advisable to make the circumferential seams of vessels less strong than the base metal. The relatively small width of the circumferential welds and the favorable stress state pattern in the cylindrical shell shows that a decrease in the strength of the weld metal relative to the base metal does not affect the strength of the structure as a whole.
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Limit - strength - steel
Limit - strength - steel
Page 1
The tensile strength of steel with increasing temperature, as a rule, first increases and at a temperature of 250 - 300 reaches its highest value, approximately 20 - 25/0 higher than the tensile strength at room temperature. With a further increase in temperature, the tensile strength value sharply decreases. So, for example, for low-carbon steel at 600, the tensile strength is only about 40/0 of the tensile strength of the same steel at room temperature.
The tensile strength of steel with increasing temperature, as a rule, first increases and at a temperature of 250 - 300 reaches its highest value, approximately 20 - 25% higher than the tensile strength at room temperature. With a further increase in temperature, the tensile strength value sharply decreases. So, for example, for low-carbon steel at 600, the tensile strength is only about 40% of the tensile strength of the same steel at room temperature.
The tensile strength of steel with increasing temperature, as a rule, first increases and at a temperature of 250 - 300 C reaches its greatest value, approximately 20 - 25/6 higher than the tensile strength at room temperature. With a further increase in temperature, the tensile strength decreases sharply. For example, for low-carbon steels at 600 C, the tensile strength is only about 40% of the tensile strength of the same steel at room temperature.
The tensile strength of steel varies depending on temperature. As the temperature changes, the internal pressure of the liquefied gas increases.
The tensile strength of steel, as well as its hardness in the low- and medium-tempered state, is determined mainly by the carbon content and practically does not depend on alloying elements. The hardening coefficient after low tempering is also practically independent of alloying and is determined by the carbon content in the solid solution.
The tensile strength of steel with increasing temperature, as a rule, first increases and at a temperature of 250 - 350 reaches its highest value, approximately 20 - 25% higher than the tensile strength at room temperature. With a further increase in temperature, the tensile strength value sharply decreases. So, for example, for low-carbon steel at 600, the tensile strength is only about 40% of its tensile strength at room temperature.
The tensile strength of high-carbon steels treated to high hardness at cryogenic temperatures remains practically unchanged. This is in full accordance with the well-known scheme of cold brittleness by A.F. Ioffe, which provides for the invariance of resistance to separation from the test temperature. Considering that at room temperatures the destruction of hard high-carbon steels occurs from separation, there is every reason to believe that their performance at low, including cryogenic temperatures, does not change.
The tensile strength of steel types 18 - 8, tested for two years in industrial atmospheres and for one year in a marine atmosphere (250 m from the ocean coast), did not change.
If the tensile strength of steel is unknown, but its Brinell hardness is known or can be quickly determined, then with a sufficient degree of accuracy the tensile strength can be determined using the equation ab 0 31 HB.
If the tensile strength of steel is unknown, but its Brinell hardness is known or can be quickly determined, then with a sufficient degree of accuracy the tensile strength can be determined using the HB equation.
The influence of the tensile strength of steel on its endurance in corrosive environments, as can be seen from Fig.
When tempering, the tensile strength of steel increases very slightly, the hardness increases slightly, and the relative elongation decreases. As for the conditional yield strength, its change during training is complex. Thus, for low-carbon steels, the yield strength at a degree of deformation from 0 5 to 1 2% decreases, and with a further increase in the degree of deformation it begins to increase.
However, it is not yet possible to increase the tensile strength of steels to values of 280 - 300 kg/mm2 using this method of thermomechanical treatment.
Hardness characterizes the tensile strength of steels (except for austenitic and martensitic structures) and many non-ferrous alloys. This quantitative dependence is usually not observed in brittle materials, which during tensile tests (compression, bending, torsion) are destroyed without noticeable plastic deformation, and when measuring hardness they receive plastic deformation. Some plastic properties of metals are determined by hardness values.
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Tensile yield strength indicates at what stress value the tensile strength remains constant or decreases despite increasing elongation. In other words, the yield point occurs when a transition occurs from the region of elastic to the region of plastic deformation of the material. The yield strength can also only be determined by testing the bolt shank.
The tensile yield strength is measured in N/mm² and is designated:
- σ t orReL for fasteners manufactured in accordance with the GOST standard;
- ReL for fasteners manufactured in accordance with the DIN standard.
The strength characteristics of the bolt are encoded in the strength class of the product. For bolts, these are two numbers separated by a dot.
The strength class designation consists of two numbers:
a) The first digit of the designation, multiplied by 100 (×100) corresponds to the value of tensile strength (temporary strength) σ (Rm) in N/mm².
b) The second digit of the designation corresponds to 1/10 of the ratio of the nominal value of the yield strength to the tensile strength in percent. The product of the indicated two figures corresponds to 1/10 of the nominal value of the yield strength σ t(R eL) in N/mm²
Example 1: Bolt M10x50 class. pr. 8.8
Tensile strength σ B.(Rm)= 8x100= 800 N/mm² (MPa) ,
Yield strength σ T (R eL) = 8x8x10 = 640 N/mm² (MPa).
Ratio σ t(R eL) / σ .(Rm) = 80%
= σ B.(Rm) ×A s = 800×58.0= 46400 N. = σ t (ReL) × A s = 640 × 58.0 = 37120 N.Where A s— nominal cross-sectional area.
Note:
The tensile strength of some bolts may be coded in a three-digit number. Multiplying a three-digit number by 10 allows you to determine the tensile strength (tensile strength) σ B (Rm) in N/mm².
Example 2: Bolt M24x100.110 GOST 22353-77
σ B(Rm) = 110x10 = 1100 N/mm 2 (MPa).
For reference:
Conversion of units of measurement: 1 Pa = 1N/m²; 1 MPa = 1 N/mm² = 10 kgf/cm²
Steel classification
Steel- a deformable (malleable) alloy of iron with carbon (up to 2%) and other elements. It is an essential material used in most industries. There are a large number of steel grades, differing in structure, chemical composition, mechanical and physical properties. You can view the main types of rolled metal products and get acquainted with prices.Main characteristics of steel:
- density
- elastic modulus and shear modulus
- linear expansion coefficient
- and others
Carbon steel grades
Carbon steel of ordinary quality, depending on its purpose, is divided into three groups:
- group A - supplied according to mechanical properties;
- group B - supplied according to chemical composition;
- group B - supplied according to mechanical properties and chemical composition.
Approximate chemical composition of stainless steel (in%) Damascus and damask steel.Damascus steel- originally the same as damask steel; later - steel obtained by forge welding of steel strips or wires with different carbon contents woven into a bundle. It got its name from the city of Damascus (Syria), where the production of this steel was developed in the Middle Ages and, partly, in modern times. Bulat steel (damask steel)- cast carbon steel with a unique structure and patterned surface, possessing high hardness and elasticity. Edged weapons of exceptional durability and sharpness were made from damask steel. Damask steel was mentioned by Aristotle. The secret of making damask steel, lost in the Middle Ages, was revealed in the 19th century by P.P. Anosov. Based on science, he identified the role of carbon as an element influencing the quality of steel, and also studied the importance of a number of other elements. Having found out the most important conditions for the formation of the best grade of carbon steel - damask steel, Anosov developed a technology for its smelting and processing (Anosov P.P. About damask steel. Mining Journal, 1841, No. 2, p. 157-318). Steel density, specific gravity of steel and other characteristics of steelDensity of steel - (7,7-7,9)*10 3 kg/m 3 ; Specific gravity of steel - (7,7-7,9) G/cm 3 ; Specific heat capacity of steel at 20°C- 0.11 cal/deg; Melting point of steel- 1300-1400°C; Specific heat capacity of steel melting- 49 cal/deg; Thermal conductivity coefficient of steel- 39kcal/m*hour*grad; Linear expansion coefficient of steel(at about 20°C): steel 3 (grade 20) - 11.9 (1/deg); stainless steel - 11.0 (1/deg). Tensile strength of steel: steel for structures - 38-42 (kg/mm 2); silicon-chromium-manganese steel - 155 (kg/mm 2); machine steel (carbon) - 32-80 (kg/mm 2); rail steel - 70-80 (kg/mm 2); Steel density, specific gravity of steel Steel density - (7.7-7.9) * 10 3 kg/m 3 (approximately 7.8 * 10 3 kg/m 3); The density of a substance (in our case steel) is the ratio of the mass of a body to its volume (in other words, the density is equal to the mass of a unit volume of a given substance): d = m/V, where m and V are the mass and volume of the body. Per unit densities take the density of a substance whose unit volume has a mass equal to one:
in the SI system it is 1 kg/m 3, in the SGS system - 1 G/cm 3, in the MKSS system - 1 those/m 3. These units are related to each other by the ratio:1 kg/m 3 =0.001 G/cm 3 =0.102 those/m 3. Specific gravity of steel - (7.7-7.9) G/cm 3 (approximately 7.8 G/cm 3); The specific gravity of a substance (in our case, steel) is the ratio of the force of gravity P of a homogeneous body of a given substance (in our case, steel) to the volume of the body. If we denote specific gravity by the letter γ, then: γ = P/V. On the other hand, specific gravity can be considered as the force of gravity per unit volume of a given substance (in our case, steel). Specific gravity and density are related by the same ratio as the weight and mass of a body: γ/d=P/m=g. The unit of specific gravity is taken to be: in the SI system - 1 n/m 3, in the SGS system - 1 days/cm 3, in the MKSS system - 1 kg/m 3. These units are related to each other by the ratio:1 n/m 3 =0.0001 days/cm 3 =0.102 kg/m 3.Sometimes an off-system unit of 1 G/cm 3 is used. Since the mass of a substance, expressed in G, is equal to its weight, expressed in G, then the specific gravity of a substance (in our case, steel), expressed in these units, is numerically equal to the density of this substance, expressed in the CGS system. A similar numerical equality exists between the density in the SI system and the specific gravity in MKSS system.
Density of steel Elastic modulus of steel and Poisson's ratio
Values of permissible steel stresses (kg/mm 2) Properties of some electrical steels Standardized chemical composition of carbon steels of ordinary quality according to GOST 380-71
| steel grade | Element content, % | ||||
| C | Mn | Si | P | S | |
| no more | |||||
| St0 | No more than 0.23 | - | - | 0,07 | 0,06 |
| St2ps St2sp |
0,09...0,15 | 0,25...0,50 | 0,05...0,07 0,12...0,30 |
0,04 | 0,05 |
| St3kp St3ps St3sp St3Gps |
0,14...0,22 | 0,30...0,60 0,40...0,65 0,40...0,65 0,80...1,10 |
no more than 0.07 0,05...0,17 0,12...0,30 no more than 0.15 |
0,04 | 0,05 |
| St4kp St4ps St4sp |
0,18...0,27 | 0,40...0,70 | no more than 0.07 0,05...0,17 0,12...0,30 |
0,04 | 0,05 |
| St5ps St5sp |
0,28...0,37 | 0,50...0,80 | 0,05...0,17 0,12...0,35 |
0,04 | 0,05 |
| St5Gps | 0,22...0,30 | 0,80...1,20 | no more than 0.15 | 0,04 | 0,05 |
| steel grade | Tensile strength (temporary resistance) σ in, MPa |
Yield strength σ t, MPa | Relative elongation of short samples δ5,% | 180° bending with mandrel diameter d | ||||
| sample thickness s, mm | ||||||||
| up to 20 | 20...40 | 40...100 | up to 20 | 20...40 | 40...100 | up to 20 | ||
| St0 | 310 | - | - | - | 23 | 22 | 20 | d=2s |
| VSt2ps VSt2sp |
340...440 | 230 | 220 | 210 | 32 | 31 | 29 | d=0 (without mandrel) |
| VSt3kp VSt3ps VSt3sp VSt3Gps |
370...470 380...490 380...500 |
240 250 250 |
230 240 240 |
220 230 230 |
27 26 26 |
26 25 25 |
24 23 23 |
d=0.5s |
| VSt4kp VSt4ps VSt4Gsp |
410...520 420...540 |
260 270 |
250 260 |
240 250 |
25 24 |
24 23 |
22 21 |
d=2s | VSt5ps VSt5sp VSt5Gps |
500...640 460...600 |
290 290 |
280 280 |
270 270 |
20 20 |
19 19 |
17 17 |
d=3s |
