Knives made of spring steel. Elastic properties and main characteristics of springs and leaf springs

The elastic properties of spring suspension are assessed using force characteristics and a stiffness coefficient or a flexibility coefficient (flexibility). In addition, springs and springs are characterized by geometric dimensions. The main dimensions (Fig. 1) include: the height of the spring or spring in a free state without a load H st and the height under a load H gr, the length of the spring, the diameter of the spring, the diameter of the rod, the number of working turns of the spring. The difference between Hst and Hgr is called spring deflectionf. The deflection obtained from a load lying quietly on the spring is called static. For leaf springs, for more convenient measurement, the deflection is determined by the dimensions H St and H Gr near the clamp. Flexible properties of springs are determined by one of two quantities:

• flexibility factor(or just flexibility);
• hardness coefficient(or just toughness).

Rice. 1 - Main dimensions of springs and springs

The deflection of a spring (spring) under the influence of a force equal to unity is called flexibility f 0:

where P is the external force acting on the spring, N;

f - spring deflection, m.

An important characteristic of a spring is its stiffness and, which is numerically equal to the force causing a deflection equal to one. Thus,

and= P/f.

For springs in which the deflection is proportional to the load, the equality is true

P= and f.

Rigidity- the reciprocal of flexibility. Flexibility and rigidity of springs (springs) depend on their main dimensions. As the length of the spring increases or the number and cross-section of sheets decreases, its flexibility increases and its rigidity decreases. For springs, with an increase in the average diameter of the coils and their number and with a decrease in the cross-section of the rod, the flexibility increases and the rigidity decreases.

Based on the stiffness and deflection of a spring or spring, a linear relationship is determined between its deflection and the elastic force P = and f, presented graphically in (Fig. 2). The operation diagram of a frictionless cylindrical spring (Fig. 2, a) is depicted by one straight line 0A, corresponding to both the loading of the spring (an increase in P) and its unloading (a decrease in P). The rigidity in this case is constant:

and= P/f∙tg α.

Springs of variable stiffness (aperiodic) without friction have a diagram in the form of line 0AB (Fig. 2, b).

Rice. 2 - Diagrams of operation of springs (a, b) and springs (c)

At leaf spring operation friction arises between its sheets, which contributes to the attenuation of vibrations of the sprung vehicle and creates a calmer movement. At the same time, too much friction, increasing the stiffness of the spring, worsens the quality of the suspension. The nature of the change in the elastic force of the spring under static loading is shown in (Fig. 2, c). This dependence represents a closed curved line, the upper branch of which 0A 1 shows the relationship between the load and the deflection of the spring when it is loaded, and the lower branch A 1 A 2 0 - when unloaded. The difference between the branches characterizing the change in the elastic forces of the spring during its loading and unloading is determined by friction forces. The area limited by the branches is equal to the work spent on overcoming the frictional forces between the spring leaves. When loaded, friction forces seem to resist an increase in deflection, and when unloaded, they prevent the spring from straightening. In carriage springs, the friction force increases in proportion to the deflection, since the forces pressing the sheets against each other increase accordingly. The amount of friction in a spring is usually estimated by the so-called relative friction coefficient φ, equal to the ratio of the friction force R tr to the force P creating elastic deformation of the spring:

The magnitude of the friction force is related to the deflection f and spring stiffness and, due to its elastic properties, dependence

Spring steel is used for the production of elastic products, which are characterized by the ability to restore their original shape after twisting and significant bending.

1. Why do we need stainless and regular spring steel?
2. Spring steels according to GOST 14959–79
3. Other requirements for spring steels according to GOST
4. Features of spring steels

1 Why do we need stainless and regular spring steel?

In many modern mechanisms, units and machines, springs and springs, as well as other elastic parts, perform very important functions. Such elements are subject to variable, repeated loads, which leads to their deformation. It is clear that for normal operation of the mechanism it is required that after such influences the part returns to its original state (that is, it must restore its original geometric dimensions and shape).

For the manufacture of parts that do not experience residual deformation under significant shock and static loads, spring steels are used.

A number of requirements are put forward to them. Firstly, they must resist stress relaxation and have high rates of fluidity, elasticity and endurance. Secondly, such alloys must qualitatively resist the phenomenon of brittle fracture and be characterized by a sufficient level of ductility.

The required yield strength of various grades of spring steels is obtained by hardening them, which is supplemented by tempering (this is usually performed at temperatures from 300 to 480 degrees). The choice of this particular temperature range is not accidental. It has been proven that in this case the elastic limit of steel becomes as high as possible. And this is exactly what is required for spring alloys.

The steel grades we describe are used for the manufacture of elastic products with high wear resistance:

• feeding and clamping collets;
• flanges;
• brake bands;
• the already mentioned springs and springs;
• bearing housings;
• friction discs;
• thrust washers;
• flanges;
• various gears.

2 Spring steels according to GOST 14959–79

By such alloys we mean medium and high carbon steels. as well as steels with low alloy levels. State standard 14959 includes the following grades as alloyed compounds: 70С2ХА, 65С2ВА, 60С2ХА, 50ХГФА, 50 ХФА, 50 ХГА, 60С2Г, 60С2А, 55С2А, 70Г, 60Г, 60С2Н2А, 60С2ХФА, 55С2ГФ, 55ХГР, 50ХГ, 70С3А, 60С2, 55С2, 65Г. Carbon steels are listed below: 65, 80, 70, 85, 75.

The first two digits in the marking indicate, in fractions of a percent, the mass fraction (average) of carbon in a particular alloy. The letters after the numbers indicate what alloying additives are present in the composition, and the numbers after them indicate the content of elements. Moreover, if its amount is less than 1.5%, the number is not given; if the content of the alloying component is more than 2.5%, the number 3 is given; from 1.5 to 2.5% - number 2.

Rolled steel of spring class (sheets, stainless strip, hexagon, square, etc.) are divided into different groups according to the following characteristics:

• by chemical composition: high-quality, high-quality stainless steel sheets. and also standardized according to indicators (in the latter case, rental is further divided into 14 categories - from 1 to 4B);
• by processing option: hot-rolled strip with a ground or turned surface, rolled stock with special finishing, calibrated, hot-rolled and forged.

Spring steels contain from 0.25 (carbon and medium alloy alloys) to 1.2 (60S2KhFA, 50KhGA and others) percent chromium, from 0.5 to 1.25 percent manganese, from 0.17 to 2.8 percent (70S3A) silicon, from 0.46 (50ХГ) to 0.9 (85) percent carbon. Residual nickel in rolled springs (sheet steel) should be no more than 0.25%, copper - up to 0.20%.

Let us note that any ordinary and stainless steel from which elastic elements are made is checked and standardized according to their chemical composition. But other characteristics for some categories are not standardized. For example, a band of categories 1, 1A and 1B is not standardized for the indicator of the decarbonized layer, hardenability, mechanical values ​​​​on samples that have undergone heat treatment (quenching and tempering).

3 Other requirements for spring steels according to GOST

Relative contraction of rolled products varies from 20 (65S2VA, 60 S2A) to 35% (stainless steel 50 HGFA), relative elongation - from 5 to 10%, tensile strength - from 980 (steel 65) to 1860 (65S2VA) MPa, limit fluidity - from 785 (60G) to 1665 (65S2VA) MPa.

Forged and hot-rolled wire, strip and rods must be cut. In this case, bending of the rolled product and burrs are not allowed. In cases where cutting is performed under hammers or on presses, the strip and rods may have minor crumples at their ends. However, the consumer has the right to demand that this defect be eliminated.

General decarbonization in depth can be as follows:

• for silicon-alloyed alloys – 2.5% (for thickness or cross-section of rolled products less than 8 mm), 2% (more than 8 mm);
• for the rest – 2 and 1.5%.

Without a decarburized layer, hot-rolled round bars are produced.

Spring steels 55S2 and 55S2A, 50KhGA, 50KhG and 50KhGFA, 60S2A and 60S2 are examined for austenitic grain index. According to Gosstandart 5639, it should be no higher than the fifth number (for 50HGFA - no higher than the sixth).

The consumer may require that the steel we describe (grades may be different) be produced:

• with regulation of martensitic areas;
• with controlled microstructure;
• with reduced minimum and maximum carbon content;
• with fatigue testing;
• with the establishment of the elastic limit;
• with limited indicators of contamination of alloys with non-metals.

4 Features of spring steels

High- and medium-carbon grades of such steels are strengthened through plastic cold deformation, which involves the use of water-abrasive and shot-blasting technologies. With this type of processing, compressive stress (residual stress) is applied to the surface of the product.

Almost any spring steel (stainless, without special anti-corrosion properties) must undergo a hardenability procedure using a through method. Due to this, the finished product will have a troostite structure throughout its entire cross-section.

Quenching in oil at a temperature of 820–870 degrees, combined with tempering at 400–480 degrees, ensures an increase in the elastic limit - the most important performance characteristic of the steels described. Isothermal hardening is often used, which guarantees not only high elasticity, but also increased ductility, strength and toughness of the material.

Stainless steel strip and wire made from 70 and 65 steels are most often used to produce automotive springs. In the transport sector, silicon spring rolled grades are also actively used - 60С2А, 70С3А and 55С2. In principle, they are prone to decarbonization, which reduces their elasticity and endurance. But due to the addition of chromium, vanadium and some other elements, all these potential threats are neutralized.

• springs for various mechanisms and installations in the machine, tractor and automotive industries - 55S2, 50HFA, 50HG, 50HGA;
• heavily loaded springs - 60 S2G, 60S2A, 60S2, 60S2N2A, 65S2VA;
• wear-resistant flat and round springs (a strip is used), operating at high vibrations - 80, 85, 75.

Let us finally add that the steel grades we described have two disadvantages:

• poor weldability (in fact, any type of welding does not give the expected results when it comes to spring steels);
• complexity of cutting (the operation can be performed, but the machinability of springs and other elements in this way is minimal).

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Non-ferrous metals and alloys

Structural steels and alloys

Spring steel, grades of which are applicable in the manufacture of tight products, characterized by restoration of the original shape, with strong bending and significant twisting.

The most important parts in the production of mechanisms that experience variable, repeated loads, under the influence of which severe deformation occurs. As soon as the load stops, these elements return to their original shape. There is a feature in the operation of these parts that does not allow residual destruction; it must only be elastic. Excessive production requirements are placed on spring steels. Let's figure out what kind of steel springs are made of?

Why is spring alloy produced?

Both alloy steel and carbon steel can be used to produce parts; they have increased elasticity, toughness, endurance and ductility. Due to the properties of these types of steel, elastic destruction is limited.

Spring steels are affordable, technologically advanced, and have a high limit of relaxation resistance.

Interesting: to obtain high-quality products from carbon and alloy steel, it is hardened at a temperature of 420-520 degrees, which produces the effect of a troostite structure.

Spring steels resist fragile fracture and are characterized by increased ductility. They are used to produce products with high wear resistance, for example:

• clamping collets;
• brake rolling;
• edges;
• springs and leaf springs;
• thrust washers;
• bearing torsos;
• friction discs;
• gears.

Steel grades according to GOST 14959–79

These are steels with a high carbon content, but with low alloying. Gosstandart 14959 means alloyed alloy of the following grades:

• 3K-7 - used in the production of cold-drawn wire, from which non-hardening springs are made;
• 50ХГ – produce springs for cars and springs for railways. compositions;
• 50HGA - purpose in production as in the previous brand of spring steel;
• 50HGFA – produce special springs and spring parts for cars;
• 50ХСА – special-purpose springs and small parts for watch mechanisms;
• 50HFA - they produce parts with increased load, with the requirements of the highest stability and strength, which operate at high temperatures - up to 300 degrees.
• 51HFA – for spring wire;
• 55С2 - for the production of spring mechanisms and springs used in tractor construction, mechanical engineering, for railway rolling stock;
• 55С2А – produces auto springs, springs for trains;
• 55S2GF - for the production of very strong springs of a special type, autosprings;

• 55KhGR – produce spring strip steel, the thickness of which varies from 3 to 24 mm;
• 60G - for the production of round and smooth springs, rings and other spring-type products with high wear resistance and elasticity, for example, staples, bushings, tambourines for braking systems used in heavy engineering;

Interesting: torsion steel, grade 60C2 - high-load springs, friction discs, spring washers;

• 60С2А - produce the same products as from the previous type of steel;
• 60S2G – type of spring steel from which tractor and auto springs are produced;
• 60С2Н2А – produce responsible springs with a high load on the alloy;
• 60С2ХА – for the production of highly loaded spring products subject to constant load;
• 60S2HFA is a round steel with calibration elements, from which springs and spring plates are produced with high responsibility;
• 65 – produce parts with increased strength and elasticity, which are operated under high pressure, high static loads and strong vibration;
• 65G - produce parts that will work without shock loads;
• 65GA – hardened wire for springs;
• spring steel grade - 65S2VA, highly loaded leaf springs and springs;
• 68A – hardened wire for the production of spring devices with a caliber of 1.2-5.5 mm;
• 70 – parts for mechanical engineering that require increased wear resistance;
• 70G – for spring elements;
• 70G2 - produce digging knives and springs for various industries;
• 70С2ХА – spring elements for watch devices and large springs for special purposes;
• 70С3А – springs with high load;
• spring steel grade 70HGFA – wire for the production of spring elements with heat treatment;
• 75 – any spring and other parts used in mechanical engineering that are subject to heavy vibration loads;
• 80 – for producing flat parts;
• 85 – wear-resistant parts;
• SH, SL, SM, DN, DM – machine springs operating under static loads;
• KT-2 – for the production of cold-drawn wire, which is wound without heat treatment.

The first numbers indicate the average carbon content in a particular steel and indicate it in percentage terms. After the numbers there is a letter indicating the specific alloying additives added to the alloy, and the last number is the content of the additives. It is worth noting that if the alloying binder is less than 1.5%, then the number is not written, a content of more than 2.5% is indicated by a three, an intermediate value between the first two values ​​is written by the number 2.

Spring rolled products, whether non-corrosive strip, sheets, hexagons or squares, are divided into groups with certain characteristics:

• chemical composition – first-class stainless steel sheet, which is standardized according to values ​​from 1 to 4B;
• processing method - hot-rolled strip, the surface of which is turned or ground, calibrated rolled products, forged, specially finished rolled products.

Steel 60s2a spring

Stainless spring steel is cheap, has great elasticity, wear resistance, and does not have temper brittleness. This alloy does not deform under mechanical loads. It is used effectively at high humidity, as it has a stainless steel coating. It is used at a temperature of no more than 250 degrees, and is used for the production of rolled metal products.

Stainless steel is used to produce equipment in the marine industry, medicine, and food production. Its use in these industries is due to the corrosion-resistant alloy.

Interesting: stability is associated with a high content of molybdenum and chromium. The alloy has good resistance to cracking under heavy loads.

This grade of stainless, heat-resistant steel is used in the production of rolled thin sheets, seamless pipes and various tools for the food and chemical industries.

Specifications of spring alloys

High- and medium-carbon types of these alloys are strengthened by fine cold destruction, allowing the introduction of shot blasting and water-abrasive methods. With this type of impact, residual compression forces are applied to the plane of the products.

In fact, any spring steel (non-corrosive, without special anti-corrosion properties) must undergo a high-heat operation using the through-hole method. Therefore, the finished metal product will have a troostite structure in its cut.

Oil hardening at a temperature of 830–880 degrees, combined with tempering at 410–480 degrees, guarantees an increase in the elasticity limit - the most important working property of the above steels. Isothermal hardening is often used, which provides not only high elasticity, but also increased plasticity, stability and viscosity of the substance.

Non-corrosive tape and wire made from alloys 70 and 65 are most often used to create machine springs. In the automotive industry, silicon spring steels of the spring rolling grade – 60С2А, 70С3А and 55С2 – are also dynamically used. They are prone to decarbonization, which reduces their elasticity and endurance characteristics. But due to the additives of chromium, vanadium and certain components, all these possible dangers are neutralized.

Areas of application for spring rolling of the most popular steel grades:

• springs for any devices and assemblies of the machine and automobile construction areas - 55S2, 50ХГ, 50ХГА;
• heavily loaded springs - 60 S2G, 60S2, 65S2VA, 60S2N2A;
• wear-resistant springs are round and flat (a strip is used), operating at high vibrations - 80, 75.85.

In conclusion, a little about the disadvantages

• poor weldability;
• difficulty cutting.

Kazan State Technical University named after. A. N. Tupolev

Institute of Aviation, Land Transport and Energy

Department: “Materials science and structure of formative technologies”

Discipline: “Materials Science Part 2”

Course work

Topic: “Spring steels”

Completed:

Checked:

Yelabuga, 2009

Plan:

1. Description

2. Application

3. Marking and main characteristics

4. Feature of spring steel rolling

5. Basic requirements for spring steel

6. Characteristics of material 68A

7. Literature

Description:

Spring steel - steel intended for the manufacture of elastic elements (springs, leaf springs, etc.)

The operation of springs, springs and similar parts is characterized by the fact that they use only the elastic properties of steel. The large total amount of elastic deformation of a spring (spring, etc.) is determined by its design - the number and diameter of turns, the length of the spring. Since the occurrence of plastic deformation in springs is not allowed, the material of such products is not required to have high impact strength and high ductility. The main requirement is that the steel has a high elastic (yield) limit. This is achieved by hardening followed by tempering at a temperature in the region of 300-400 ° C. At this tempering temperature, the elastic (yield) limit receives the highest value, and the fact that this temperature lies in the range of development of type I temper brittleness, due to the above-mentioned circumstance doesn't matter much.

Springs, springs and similar parts are made from structural steels with a high carbon content (but, as a rule, still lower than that of tool steels) - approximately in the range of 0.5-0.7% C, often with the addition of manganese and silicon For especially critical springs, 50HF steel is used, which contains chromium and vanadium and has the highest elastic properties. Heat treatment of springs and springs made of alloy steels consists of hardening from 800-850 ° C (depending on the steel grade) in oil or water, followed by tempering in the region of 400-500 ° C to a hardness of HRC 35-45. This corresponds to st = 1304-1600 kgf/mm 2.

Sometimes such heat treatment is applied to structural parts of long length and with thin walls, which must have high springing properties. In this case, ZOHGS steel is used; after quenching and tempering at 250° C, it will have a strength (a c) 160 kgf/mm 2, but viscosity (a d) only 5 kgf-m/cm 2, and ductility (b) 7% and (f.) 40%. Springs are often made from polished cold-drawn wire (so-called silver wire). Hardening (hardening) from cold drawing creates high hardness and elasticity. After winding (or another manufacturing method), the spring should be released at 250-350°C to relieve internal stress, which will increase the elastic limit. For the manufacture of silver steel, ordinary carbon tool steels U7, U8, U9, U10 are used.

The quality and performance of the spring is greatly influenced by the condition of the surface. In the presence of cracks, caps and other surface defects, the springs become unstable in operation and are destroyed due to the development of fatigue phenomena in places where stress is concentrated around these defects. In addition to ordinary spring materials, there are also special ones that work in specific conditions (elevated temperatures, aggressive environments, etc.).

General characteristics: spring steel, insensitive to flocking, prone to temper brittleness with Mn content ≥1%, not used for welded structures. Density at 20°C - 7.81x10³kg/m³. The normal elastic modulus at 20°C is 215 GPa. Specific heat capacity at 20-100°C - 490 J/(kg °C)

They work in the area of ​​elastic deformation of metal under the influence of cyclic loads. Therefore, they must have a high elastic limit, yield strength, endurance, if necessary, ductility and high resistance to brittle fracture.

Spring steels contain C = 0.5 - 0.75%, Si up to 2.8%, Mn up to 1.2%, Cr up to 1.2%, V up to 0.25%, Be up to 1.2%, Ni 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, 70S3A are widely used in transport. 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. For the manufacture of springs, cold-drawn wire (or tape) from high-carbon steels 65, 65G, 70, U8, U10, etc. is also used. Special purpose springs are also used from martensitic steels 30Х13А, maraging-aging 03Х12Н10Д2Т, austenitic-martensitic 09Х15Н8У and other steels and alloys Steels are hardened at temperatures of 830 - 880°C and tempered to trostite (380 - 550°C).

They have a high yield strength. The ratio of yield strength to tensile strength is 0.8−0.9. For leaf springs and suspension springs, silicon and manganese steels 50KhG, 50G2, 05G, 55S2, etc. are used. For torsion shafts, steels 45KhNMFA, G0C2A, 70SZA are used.

To increase the fatigue strength of parts operating under high oscillatory loads, it is necessary to ensure the creation of residual compressive stresses in the surface layer. For this purpose, bonding of springs, bonding and chasing of torsion shafts, rolling in rollers, plastic upsetting and shot blasting of leaf springs are used. Alloy spring steel, heat treated to a hardness of HRC 45-50, has a torsional fatigue limit of 190 MPa. After shot blasting, the fatigue limit increases to 350 MPa (3500 kgf/cm2).

Application:

Springs, springs, thrust washers, brake bands, friction discs, gears, flanges, bearing housings, clamping and feed collets and other parts that require increased wear resistance, and parts that operate without shock loads.

Types of products supplied: in a hot-rolled state (without heat treatment) with a hardness of no more than HB285; in a highly tempered state - no more than HB241

Markings and main characteristics:

Spring steel grades:

Basic mechanical properties of spring steel after special heat treatment.

Feature of spring steel rolling:

The peculiarity lies in the sequence of heat treatment of such steels. Thus, when winding springs, the rod is in an annealed state, which ensures ease of operation. The spring is then hardened. The last stage is low release (130...150 degrees), it is also called spring.

Basic requirements for spring steel:

The general requirement for spring steels is to ensure high resistance to small plastic deformations (elastic limit) and relaxation resistance (stress relaxation resistance). These characteristics ensure the accuracy and reliability of the springs and the constancy over time of such operational properties as torque and power parameters. Spring steels in the form of wire and tape are strengthened by cold plastic deformation and martensite hardening followed by tempering. Finished springs are subjected to stabilizing tempering.

Structural carbon or high-carbon steel includes spring steel. To give it highly targeted properties, it is doped in small quantities with 2-3 elements, for a total of up to 2.5%. But the use of these steel grades is not limited to the manufacture of springs. This group is called that because the name most strongly reflects their main feature - elasticity.

Characteristics of spring steels

Spring steels are characterized by increased yield strength (δ B) and elasticity. This is the most important characteristic of metal - to withstand mechanical loads without changing its original shape. Those. a metal subjected to tension or, conversely, compression (elastic deformation), after removing the acting forces from it, must remain in its original shape (without residual deformation).

Types and scope of spring steel

Based on the presence of additional properties, spring steel is divided into alloy (stainless) and carbon. Alloy steel is based on carbon steel with a C content of 65-85% and is alloyed with 4 main elements, all or selectively, each of which brings its own characteristics:

1. chromium;
2. manganese;
3. silicon;
4. tungsten.

Chromium - at a concentration of more than 13%, works to ensure the corrosion resistance of the metal. With a chromium concentration of about 30%, the product can work in aggressive environments: acidic (except sulfuric acid), alkaline, aqueous. Corrosion spring steel is always alloyed with a second accompanying element - tungsten and/or manganese. Operating temperature up to 250 °C.

Tungsten is a refractory substance. When its powder gets into the melt, it forms numerous crystallization centers, crushing the grain, which leads to increased plasticity without loss of strength. This brings its advantages: the quality of such a structure remains very high during heating and intense abrasion of the surface. During heat treatment, this element retains its fine-grained structure and eliminates softening of steel during heating (during operation) and dislocation. During hardening, it increases hardenability, as a result of which the structure becomes homogeneous to a greater depth, which in turn increases the service life of the product.

Manganese and silicon usually participate in mutual doping, and the ratio always increases in favor of manganese, up to about 1.5 times. That is, if the silicon content is 1%, then manganese is added in an amount of 1.1-1.5%.

Refractory silicon is a non-carbide-forming element. When it enters the melt, it is one of the first to take part in crystallization, pushing carbon carbides to the grain boundaries, which accordingly leads to strengthening of the metal.

Manganese can be called a structure stabilizer. By simultaneously distorting the metal lattice and strengthening it, manganese eliminates the excessive strength of silicon.

In some steel grades (when the product is operating in high-temperature conditions, at temperatures above 300 ºC), nickel is added to the steel. It eliminates the formation of chromium carbides along grain boundaries, which lead to matrix destruction.

Vanadium can also be an alloying element, its function is similar to that of tungsten.

Spring brands specify the element copper; its content should not exceed 0.15%. Since copper, being a low-melting substance, concentrates at the grain boundaries, reducing strength.

Spring brands include: 50HG, 3K-7, 65G, 65GA, 50HGFA, 50HFA, 51HFA, 50HSA, 55S2, 55S2A, 55S2GF, 55HGR, 60G, 60S2, 60S2A, 605, 70, 70G,75, 80, 85, 60С2ХА , 60S2HFA, 65S2VA, 68A, 68GA, 70G2, 70S2XA, 70S3A, 70HGFA, SH, SL, SM, DM, DN, KT-2.

Grades of such steel are used for the manufacture of not only springs and leaf springs, although this is their main purpose, which characterizes the main property. They are used wherever there is a need to provide the product with elasticity, ductility and strength at the same time. All parts made from these grades are subject to tension and compression. Many of them experience loads that periodically replace each other, and with a huge cyclic frequency. This:

• bearing housings that experience compression and tension at each point with high frequency;
• friction discs experiencing dynamic loads and compression;
• thrust washers, most of the time they experience compression loads, but a sharp change in tension can also be added to them;
• brake belts, for which one of the main tasks is elasticity under repeated stretching. With this dynamic of increased aging and wear, stronger steel (with less elasticity) is susceptible to rapid aging and sudden failure.

The same applies to gears, flanges, washers, collets, etc.

Marking

Spring-spring steels can be grouped by position:

• unalloyed with a carbon content of 65-85% - inexpensive general purpose steel;
• manganese-silicon - the cheapest with high physical and chemical properties;
• chrome-manganese - stainless steel, works in aggressive environments at t -250 +250 C;
• additionally alloyed and/or tungsten, vanadium, boron - they are steels with an increased service life due to their homogeneous structure, an excellent strength-to-ductility ratio due to fine grains and can withstand high mechanical loads. They are used on such objects as railway transport.

Marking of spring steels is carried out as follows. Let's look at the example of 60S2HFA:

• 60 - percentage of carbon in tenths (carbon is not indicated in a letter value);
• C2 - letter designation of silicon with index 2, indicates a 2-fold increase in the standard content (1-1.5%);
• X - presence of chromium up to 0.9-1%;
• F - tungsten content up to 1%;
• A - the added letter index A at the end of the marking indicates the minimum content of harmful impurities of phosphorus and sulfur, no more than 0.015%.

Production

Depending on further processing and the final type of part, steel is supplied in sheets, wire, hexagons, and squares. High performance qualities of the product are ensured by 2 components:

1. the structure of the metal, which is determined by the chemical composition and subsequent processing;
2. the presence of non-metallic inclusions in the structure, or rather the minimum quantity and size, which is eliminated at the stage of smelting and casting;
3. the shape of the part (spiral, arc) and its dimensions, which is determined by the calculation method.

When a spring is stretched, the inner and outer sides of the coils experience different degrees of stress: the outer ones are less susceptible to stretching, while the inner ones experience the greatest degree of deformation. The same applies to the ends of the spring: they serve as attachment points, which increases the load in these and adjacent places. Therefore, steel grades have been developed that are preferably used for compression or tension.

Thermo-mechanical treatment

Without exception, all spring steels are subjected to thermomechanical treatment. After it, strength and wear resistance can increase 2 times. The product is shaped in an annealed state, when the steel has the maximum possible softness, after which it is heated to 830-870 C and cooled in an oil or water environment (only for grade 60 CA). The resulting martensite is tempered at a temperature of 480 ºC.