Spring steel grades - properties and scope of application. Spring steel
When choosing knife It is very important to consider the material from which it is made. After all, to perform various functions, the blade must not only be sharp, but also durable. In addition, you need to pay attention so that the blades do not become dull or bend under light load. These properties depend on the material from which they are made knives. Depending on the tasks that the knife must perform, be it a cutting knife, a hunting knife or a tourist knife, the characteristics of the material also differ.
Knives from springs, undoubtedly, were the most popular among people who had anything to do with cars. They were actually made from springs of old cars, since it was one of the most affordable materials. In this case, knives were used as in the kitchen For cutting products and for household needs.
Nowadays, spring steel is not losing its position and is quite common in the production of knives.
Why a car spring?
Firstly, thanks to the “ideality” of our roads, this element of the chassis often fell into disrepair, which is why it was famous for its availability, and it could often be found on the roads and in the garages of ordinary citizens.
Secondly, in design springs Multiple sheets of carbon steel are used. Many knives could be made from these sheets at home.
Third, spring steel has high elasticity, so its processing is possible for anyone with a minimum set of tools and equipment.
What is special about a knife made from a spring?
Here, first of all, it is necessary to mention the features of the steel from which the blade is made. In production it is called structural spring steel 65G, and, as the name implies, it is used in the manufacture of springs, spring springs, washers and other parts that operate without shock loads. It is considered one of the cheapest brands of carbon become, however, it has good flexibility and toughness, which makes it easier to process. In addition, this type of material has good hardness, which plays an important role when choosing knife.
The presence of silicon, manganese, chromium and nickel in steel ensures high elasticity and hardening. Galvanization is used as anti-corrosion protection. However, in practice this is not enough, and the biggest disadvantage of this material remains its high susceptibility to corrosion. Yet steel 65G has great advantages, and has been widely used in the production of various tools for which important feature is wear resistance.
Application of spring steel
Due to its versatility due to the characteristics of steel, knife It is made from springs both at home and in series. These can be kitchen knives that perfectly cut food and cut meat, army, tourist and survival knives that can open a can of canned food or sharpen a stake.
All-metal machetes and axes are also produced from 65G steel, since their blades are excellent For cuttings A sword can be forged inexpensively and quickly from leaf springs, and many reenactors use this steel in their hobby. Unfortunately, spring steel is prone to rust, so it is not suitable for scuba diving.
Kitchen knife
The spring knife is widely used in the kitchen. Back then, many had access to this material and tried to use it as much as possible. Nice knives serial production sometimes they were unaffordable ordinary family, but expensive equipment was not required for cutting food. Therefore, universal knives were made from springs and with a variety of homemade handles made of epoxy resin, wood or ordinary electrical tape. Such knives are not famous for their outstanding characteristics, but they do their job perfectly.
Tourist knife
A spring knife is perfect for use in wild conditions. Usually the load on it is small. But, it is worth considering that if the steel was not hardened enough, the blade will become dull at the very first tin can. Sharpening a stake is not a problem for such a knife, but you should be careful of moisture - spring steel is susceptible to corrosion.
Army knife
The excellent properties of spring steel make it possible to create good tactical knives. Due to the strength of this metal, they cut ropes and fabric without any problems, and can be used for household purposes, as well as for rescue work. But still, in military conditions, preference is given to stainless steel knives.
Axe, machete, sword
As for more impressive tools, their manufacture requires both sheet steel and specially purchased steel. 65G steel has such strength that it is used in buckets of bulldozers, scrapers and other equipment. It is clear that the thickness of the material also affects the strength, so for the manufacture of larger tools you will need a spring from a truck or specially ordered at the factory.
With proper processing and proper care, spring steel makes excellent axes, which are useful on the farm for chopping small objects. A long sheet will also make such an exotic weapon as a machete, which can easily handle branches or bushes. Thanks to the good toughness of 65G steel, even the most advanced machete can be made at home, straight, curved or serrated. The making of a sword occurs in the same way.
Making a knife from a spring at home
As already noted, due to the availability and ease of processing, spring steel knives can be made at home. At first glance, there is nothing complicated about this, but you still need to know some features that affect the quality of the output product. On the Internet you can find many videos describing the process of forging, hardening the blade and making the handle.
In general, spring steel can be used to make both professional edged weapons with remarkable characteristics and elegant shape, as well as ordinary knives for household needs, which are not inferior in durability and strength.
First you need to decide for what purposes and what exactly will be done. If this kitchen knife, then any sheet will do. And if you want to make a machete, sword or ax, then it is better to choose a spring from a truck. Of course, to make knives with the best characteristics, it is better to purchase steel from a manufacturer. For household purposes, old used material is useful. The leaf spring can be from 5 to 8 mm thick, depending on the car. Truck steel is traditionally stronger, so it should be used for long, strong blades.
The next step may be the usual sharpening of one or both edges of the spring. If you need to make the product thinner, coarse sandpaper or a sharpening stone will be suitable for this task. Of course, this procedure will take a lot of time, but the result is worth it.
Forging creates the shape of the knife and changes its width. Hardening steel improves the quality of the material, heating it in oil gives it a black color (blued), which also provides additional protection against corrosion. In addition, blued steel knives look very impressive.
Spring steel for knife allows you to easily engrave or create grooves on the blade. If desired, you can make the blade with one-sided or double-sided sharpening. Also very important detail The knife has a handle. It should be comfortable for the hand and can be made of epoxy resin, wood, metal and bone.
Even with the shortcomings spring steel 65G, it has not lost its popularity and allows you to make knives for various needs, which are famous for their strength and durability.
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Springs and springs are elastic elements of various machines, mechanisms and devices designed to create, perceive or absorb shocks, vibrations, shocks, as well as to drive moving parts or to measure forces.
The variety of types of springs used in modern technology is very large. According to the nature of the work, they are distinguished:
According to their shape, springs are divided into screw, spiral, disc, etc.
Various types of springs can be used under static load application (for example, constantly compressed), under dynamic loads (buffer springs) in repeated dynamic loads with a large number load cycles of different frequencies (engine valve springs).
The main operating characteristic of springs is their stiffness, i.e. the ability to deform to a certain size under given loads. The magnitude and constancy of performance characteristics, as well as the absence of breakages and dimensional changes (sagging, stretching) characterize the quality of the springs.
Rice. 1. Types of springs:
a – cylindrical compression spring; b – conical compression spring made of round wire;
c – telescopic compression spring made from a rectangular section; d – cylindrical extension spring;
d – torsion spring; e – flat spiral spring; g – package of disc springs;
h – plate bending spring; and – leaf spring.
Helical springs are the most widely used in technology. Large coil springs are made from rods with a diameter of more than 12 mm, medium ones are made from wire or rods with a diameter of 1.5–12 mm. Small springs are made from wire with a diameter of 0.2–1.5 mm.
In most springs, the material is subject to torsion, so the shear modulus of the material is used to calculate springs. Tensile tests are used to assess the quality of spring materials.
At making the right choice the standard size of springs and springs in accordance with the magnitude and nature of operational loads, their durability and reliability are influenced by the following factors:
Steels for springs and springs are a special group of structural steels with a characteristic set of properties, the most important of which is resistance to small plastic deformations. It is characterized by a conditional elastic limit corresponding to the appearance of a residual deformation of 10-3–10-4%. The value of the elastic limit determines the maximum stresses that should not be exceeded in elastic elements during operation. Also, the following requirements apply to the materials of springs and springs:
According to their purpose, spring steels are classified into:
The main methods of strengthening spring steels are:
Heat treatment of springs made of general purpose steels, hardened by cold plastic deformation followed by tempering
The advantage of such springs is the simplicity and economy of the technological process of their manufacture, along with a high set of properties that ensure long-term reliable operation. The absence of hardening makes it possible to obtain high accuracy of the configuration and dimensions of the springs with an almost complete absence of surface decarburization and oxidation, which sharply reduce fatigue strength.
For the manufacture of springs, heat treated to a given level of strength or cold-deformed, pre-heat-treated (usually patented) wire or tape is used. Due to the low ductility of steels processed to high strength, springs of simple configurations are made from them.
Hardened and tempered spring wire or tape is made from carbon (68A, U7A–U12A) and alloy steels (65GA, 68GA, 50KhFA, 60S2A, 70S2XA). The strength level of the tape is supplied in three groups: 1P, 2P and 3P. As the group number increases, the level of strength increases, but the viscosity of the tape, determined by the number of variable bends, decreases.
Springs made from heat-treated tape are tempered at 240–250 °C for 1 hour to reduce internal stresses and additional decay of retained austenite. Heating is carried out in electric furnaces in an air environment so that a thin oxide film (colorization) is formed along the cut planes during cutting, which somewhat improves the corrosion resistance of the springs.
In most cases, the material for the manufacture of springs is wire or tape obtained by cold plastic deformation (drawing, rolling) of workpieces with a previously prepared initial structure. The main pre-heat treatment is patenting. The resulting thin-plate pearlite structure allows cold deformation with high reduction rates. The steel is significantly strengthened, maintaining ductility and toughness sufficient for winding springs in a cold state.
Strengthening during strain hardening depends both on the composition of the steel and its structure, and on the degree of deformation. High spring properties are achieved after deformation with large degrees of compression and therefore can be obtained on wire and tape of small sections (diameter or thickness up to 6–8 mm).
The most high-strength wire is made from steels U7A, U8A, U9A; wire with increased strength - made of steel 65G. The higher the carbon content of the steel, the higher the strength after patenting and subsequent cold deformation.
The technological process for manufacturing small and medium-sized springs includes the following operations: cold coiling, straightening, cutting off excess turns, sharpening and grinding the ends, heat treatment, compression until the turns touch, testing springs and checking dimensions, applying anti-corrosion coatings and checking their quality, as well as final control.
Heat treatment of springs involves releasing them. As a result of tempering, the elastic limit, relaxation resistance, and fatigue strength increase, residual stresses and residual deformation of springs under loading are reduced, and the shape of the springs and their power characteristics are stabilized.
The release modes of springs after coiling vary widely. Due to the fact that tempering processes are thermally activated, a lower temperature must correspond to a longer holding time. Tempering is most often performed at temperatures of 175–250 °C.
For tempering, bath furnaces with hot oil or molten salts are used. The disadvantage of molten salts is the formation of a salt jacket around the coils, the removal of which requires thorough washing, for example, in a hot soda solution. Tempering can also be carried out in electric furnaces with built-in fans for intensive atmospheric circulation, ensuring uniform low-temperature heating of the charge.
IN last years To prepare the initial structure, along with patenting, normalization, isothermal hardening to lower bainite, and hardening with high-speed electrical tempering are increasingly used.
Heat treatment of springs made of general purpose steels, strengthened by quenching and tempering
To produce springs that are strengthened by subsequent quenching and tempering, cold-deformed annealed wire or strip, hot-rolled or cold-rolled bars or wire rod are used. In the initial state, these semi-finished products are not characterized by high strength, but have increased ductility, which makes it possible to produce springs of complex configurations. Large springs are made using hot deformation.
The technological process for producing springs by hot deformation generally includes the following operations: cutting off blanks, drawing or rolling the ends of blanks in a hot state (950–1150 °C), winding or stamping in a hot state (800–1000 °C), trimming ends, sharpening and grinding the ends of the springs (if necessary), heat treatment, hydro-sandblasting (sometimes shot peening), spring testing and dimensional checking.
The main type of heat treatment of springs is hardening and tempering. Quenching should ensure the formation of martensite in the structure without troostite areas and with a minimum amount of retained austenite. Residual austenite has a reduced elastic limit, and its possible transformation into martensite causes a decrease in relaxation resistance and a tendency to delayed fracture. In this regard, it is advisable to carry out cold treatment after hardening.
To reduce the tendency to brittle fracture and the temperature of the ductile-brittle transition, it is necessary to strive to obtain fine-grained austenite during heating for quenching and to reduce the level of internal stresses during quenching.
To prevent surface oxidation and decarburization, heating of springs, especially small thicknesses, should be carried out in a protective atmosphere or vacuum. Heating in salt baths provides a clean surface, but can cause surface damage that reduces fatigue strength, which is unacceptable for critical springs.
The final properties are determined by the holiday conditions. Release modes should be selected taking into account the purpose and loading conditions of the elastic elements in operation. For most springs, tempering is carried out at temperatures that provide high elastic limit values: carbon steels - 200–250 °C; alloyed – 300–350 °C.
In order to avoid undesirable changes in the structure (coagulation of carbides, etc.), the tempering regime must be strictly regulated in terms of temperature and duration.
For springs operating under dynamic loading conditions, for which the occurrence of sudden or delayed brittle fractures is especially dangerous, the level of ductility and resistance to brittle fracture also become decisive for the choice of tempering mode. In this regard, the tempering temperature rises above that which corresponds to the highest elastic limit.
Higher limits of elasticity, toughness and fatigue strength are achieved by isothermal hardening of spring steels to obtain a lower bainite structure, which is explained by a different substructure in which twinned martensite is absent. And additional tempering of these steels at temperatures close to the temperature of formation of lower bainite further increases the spring properties of the steels. This process is called double isothermal hardening. It should be noted that the presence of upper bainite is unacceptable, as it worsens the entire complex of properties.
When hardening and tempering springs, it is necessary to take measures to reduce their deformation. Subsequent straightening of elastic elements is undesirable, as it causes the appearance of residual stresses and deterioration of properties.
Measures to reduce deformation are developed in relation to specific types and sizes of springs. You can use techniques such as uniformly laying springs in the oven; devices that fix the shape and size of springs during heating and cooling (Fig. 2); vacation on mandrels. An effective remedy Reducing deformation is isothermal hardening.
Rice. 2. Device for hardening compression springs:
1 – spring; 2 - mandrel
Heat treatment modes and mechanical properties (minimum) of spring steels for general purposes.
| steel grade | Critical points, °C | Quenching and tempering mode | Mechanical properties | ||||||
| Ac1 | Ac3 | Tzak, °С | quenching medium | Tmp, °С | σ in, MPa | σ 0.2, MPa | δ, % | ψ, % | |
| 65 | 727 | 782 | 840 | oil | 470 | 800 | 1000 | 10 | 35 |
| 85 | 730 | - | 820 | oil | 470 | 1000 | 1150 | 8 | 30 |
| U10A | 730 | - | 770-810 | oil | 300-420 | - | - | - | - |
| 65G | - | - | 830 | oil | 470 | 800 | 1000 | 8 | 30 |
| 55С2 | 775 | 840 | 870 | oil | 470 | 1200 | 1300 | 6 | 30 |
| 60С2 | 750 | 820 | 870 | oil | 470 | 1200 | 1300 | 6 | 25 |
| 50ХГ | 750 | 775 | 850 | oil | 470 | 1200 | 1300 | 7 | 35 |
| 50HGR | 750 | 790 | 850 | oil | 470 | 1200 | 1300 | 7 | 35 |
| 50HFA | - | - | 850 | oil | 470 | 1100 | 1300 | 8 | 35 |
| 60С2Н2А | - | - | 870 | oil | 470 | 1350 | 1500 | 8 | 30 |
| 70С3А | - | - | 850 | oil | 470 | 1500 | 1700 | 6 | 25 |
Spring heat treatment technology
In terms of design and operating conditions, springs of transport devices represent a separate group of elastic elements. Spring leaves must have high resistance to static and cyclic loads, fretting fatigue, subsidence and abrasion. The predominant type of loading is cyclic bending.
Experimental data show that the chemical composition of spring steels (except for carbon content) has a minor (within 10–15%) effect on the cyclic strength characteristics. The main purpose of alloying spring steels is to ensure complete hardenability of the spring sheets. In this case, cheap and abundant alloying elements are used, which increase the hardenability of steel.
For the manufacture of springs, GOST 14959–79 provides for 25 grades of steel. In the production of automobile springs, mainly steels 60С2 (55С2), 60ХГС, 50ХГ (50ХГА) and to a lesser extent (for passenger car springs) steels 50ХГФА and 50ХФА are used. A number of works have shown the prospects of 55KhGR steel containing 0.001–0.003% B.
The main technological characteristics of spring steels are their tendency to overheat and decarbonize.
The technological process currently in place at most factories for the production of leaf automobile springs includes cutting hot-rolled strips into measured blanks, finishing operations (extruding fixing buttons, punching holes for tightening bolts, bending ends, bending ears), heat treatment, during which the strips are bent , shot peening (double-sided or, according to at least, from the side of the concave surface), settlement and control. Finishing (preparing) operations are carried out by local heating of individual sections of spring sheets in slotted gas heating devices or by induction.
A schematic flow diagram of the line for complete heat treatment of spring sheets is shown in Fig. 3.
Rice. 3. Technological diagram of the line for heat treatment of spring sheets:
1 – conveyor furnace for heating for hardening; 2 – hardening furnace conveyor;
3 – bending hardening drum; 4 – conveyor of the quenching tank;
5 – tempering furnace; 6 – tempering furnace conveyor; 7 – water tank; 8 – oil tank
For heating for hardening, gas or oil furnaces, as well as electric furnaces, are used. To increase the productivity of the lines, forced heating is used, which involves a significant temperature difference between the furnace and the heated metal.
Taking into account the permissible limits of heating temperatures, with the practically possible accuracy of maintaining the temperature in the furnace and the speed of passage of the conveyor through the furnace, the furnace temperature is maintained within the range of 980–1000 °C for sheets of steel 60С2 and within the range of 880–900 °С for sheets of steel 50ХГ. In this case, the duration of heating of sheets with a thickness of 6–10 mm for hardening is selected in the range of 10–25 minutes.
The heated sheets are placed in a bending die installed on a multi-position (8–12 positions) drum. The stamp is closed and this ensures bending of the sheet; the drum rotates, immersing the sheet in the quenching oil. To prevent deformation of the sheets, the duration of their cooling in the stamp should be 40–60 s. From the hardening die, the sheets fall onto a conveyor, which moves them from the oil tank to the tempering furnace.
The sheets are released in an electric conveyor furnace with the sheets laid on an edge perpendicular to the direction of movement of the conveyor. The tempering temperature for steels 60С2 and 60ХГ corresponds to 450–480 °С. Taking into account the high density of sheets on the conveyor and the temperature difference between the area where the thermocouples are located and the metal, the temperature in the furnace is maintained above the set metal temperature by 100–150 °C; vacation duration 45–50 minutes. After tempering, the sheets are cooled in water (in a shower device), which speeds up the technological cycle and also helps eliminate the tendency to temper brittleness of the second type.
The sheets are subjected to double hardening and tempering. The first (preliminary through) hardening is performed to strengthen the core of the sheet and prepare the initial structure so that during the second (surface) hardening using high-speed induction heating, a surface hardened word is obtained to a depth of 0.15–0.2 of the thickness of the sheet with very fine grain austenite (14–15 points according to GOST 5639–82). During surface heating for the second hardening, the core of the sheet is tempered to a hardness of HRC 38–40.
The presence of such fine grains in combination with high residual compressive stresses in the surface hardened layer with a hardness of HRC 58–59 and hardening of the core to a hardness of HRC 38–40 provides high resistance of the sheets to static and cyclic loads.
In an automatic heat treatment line using a new method, 18 mm thick spring sheets made of 60C2 steel are moved through a series of inductors and sprayers located in series. The line also carries out extrusion of centering buttons and bending of sheets.
The use of a new method made it possible to increase the durability of springs, reduce their metal consumption, and fully automate the heat treatment process.
Thermo-mechanical treatment of springs and leaf springs
During high-temperature mechanical processing(HTMT) of spring steels, the austenitization temperature is taken to be 100–150 °C above AC3, the degree of deformation is 25–60% with simultaneous compression and up to 70% with fractional deformation. Optimal HTMT modes are selected empirically for each product. As a result of HTMT, an increase in static and fatigue (including low-cycle) strength, fracture resistance, ductility and impact toughness is achieved; lowering the cold brittleness threshold temperature, eliminating reversible temper embrittlement and reducing hydrogen embrittlement when applying galvanic anti-corrosion coatings.
An increase in the complex of properties during HTMT has been established for a wide range of spring steels with varying degrees of alloying: silicon (55S2, 60S2), chromium-manganese (50KhGA), steel grades 50KhFA, 45KhN2MFA, etc. The greatest efficiency from HTMT has been achieved on steels containing carbide-forming elements - chromium, vanadium, molybdenum, zirconium, niobium, etc. (steel grades 50ХМФ, 50Х5СМЗФ, etc.).
During HTMT, it is possible to use various deformation schemes (rolling, drawing, extrusion, stamping), but due to the anisotropy of hardening, it is necessary that the direction in which maximum hardening is achieved coincides with the direction of the maximum stresses during operation, i.e., the principal stress schemes during HTMT and in operation should be close.
An important advantage of HTMT, which expands its scope of application, is the inheritance of the substructure created by this treatment, even after re-hardening.
A promising method for processing spring steels is additional hardening by cold plastic deformation, carried out after HTMT.
As a result of final tempering at 250 °C, the strength characteristics of the steel are preserved and its ductility increases.
Low temperature thermomechanical treatment(NTMO) makes it possible to obtain a high complex of spring properties on carbon (U7A) and alloy steels (70S2KhA, etc.), which is associated both with the inheritance of the dislocation structure of deformed austenite by martensite and with the development of bainite transformation in the process of plastic deformation. The elastic limit increases most strongly after LTMT. The hardening effect during LTMT is usually higher than during HTMT. From the point of view of practical implementation, HTMO is a more complex processing.
The properties of steel after HTMT, especially the elastic limit and relaxation resistance, can be increased to an even greater extent by cold plastic deformation with a reduction of 10% and aging.
The stability of the substructure and the stability of hardening during heating of steel after LTMT are significantly less than after HTMT. Repeated hardening almost completely removes the LTMO effect.
The disadvantage of LTMT is that an increase in hardening is often accompanied by a decrease in ductility and an increase in sensitivity to stress concentrators.
Art. , Art. , Art. , Art. , Art. ,
Art. , Art. , Art.65GA, Art.65S2VA, Art.68A, Art.68GA,
Art. , Art.70G, Art.70C3A, Art.75, Art.80, Art.85
Application of spring-spring steel GOST 14959-79
:
Steel 50ХГ
* Used for the production of automobile and tractor springs, springs for railway rolling stock.
Steel 50HGA
* Used for the production of springs for automobile vehicles and tractors, springs for rolling stock of railway transport.
Steel 50HGFA
Steel 50ХСА
* Used for the production of watch mechanism springs, large springs for critical purposes
Steel 50HFA
* Used for the manufacture of heavily loaded critical parts that are subject to high fatigue strength requirements; springs operating at temperatures up to +300 °C; measuring tapes.
Steel 51HFA
* Used for the production of wire rod and strip used for the manufacture of heavily loaded critical parts that are subject to high fatigue strength requirements; for the production of heat-treated wire with a diameter of 1.2-5.5 mm, intended for the manufacture of springs.
Steel 55S2
* Used for the manufacture of springs and leaf springs used in automobile and tractor construction, railway transport and other branches of mechanical engineering.
Steel 55S2A
* Used for the production of motor vehicle springs, railway rolling stock springs, other springs and springs in various branches of mechanical engineering.
Steel 55S2GF
* Used for the manufacture of springs for special purposes, vehicle springs.
Steel 55KhGR
* Used for the production of spring strip steel with a thickness of 3.0-24.0 mm.
Steel 60G
* Used for the manufacture of flat and round springs, springs, spring rings and other spring-type parts that require high elastic properties and wear resistance; tires, brake drums and bands, brackets, bushings and other parts of general and heavy engineering; knives of earth-moving machines (bulldozers, scrapers, graders and motor graders, as well as for knives of bulldozer and grader equipment of excavators, rollers and other earth-moving machines); measuring tapes.
Steel 60S2
* Used for the manufacture of heavily loaded springs, torsion shafts, spring rings and washers, collets, friction discs.
Steel 60S2A
* Used for the manufacture of heavily loaded springs, torsion shafts, spring rings and washers, collets, friction discs, Grover washers; spring thrust flat internal eccentric rings used for fixing parts in housings up to +200 °C; cold-rolled heat-treated tape with a thickness of 0.05-1.30 mm and flattened heat-treated tape with a thickness of 0.15-2.00 mm for the manufacture of spring parts and springs, with the exception of winding ones; measuring tapes.
Steel 60S2G
* Used for the manufacture of automobile and tractor springs, springs of railway rolling stock.
Steel 60S2N2A
* Used for the production of critical and heavily loaded springs and leaf springs.
Steel 60S2ХА
* Used for the manufacture of large, highly loaded springs and springs for critical purposes.
Steel 60S2HFA
* Used for the manufacture of critical and highly loaded springs and leaf springs.
Steel 65
* Used for the production of springs, springs and other parts that require increased strength and elastic properties, wear resistance; parts operating under friction conditions in the presence of high static and vibration loads; hot-rolled strip profile with slope for agricultural machines; knives of earth-moving machines (bulldozers, scrapers, graders and motor graders, as well as for knives of bulldozer and grader equipment of excavators, rollers and other earth-moving machines).
Steel 65G
* Used for the production of 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 operating without shock loads; wire of square, rectangular and trapezoidal sections, intended for the manufacture of spring washers; knives of earth-moving machines (bulldozers, scrapers, graders and motor graders, as well as for knives of bulldozer and grader equipment of excavators, rollers and other earth-moving machines); flattened heat-treated tape with a thickness of 0.15-2.00 mm for the manufacture of spring parts and springs, with the exception of winding ones; measuring tapes.
Steel 65GA
Steel 65S2VA
* Used for the manufacture of especially critical and highly loaded springs and leaf springs; thin springs and measuring tapes.
Steel 68A
* Used for the production of heat-treated wire with a diameter of 1.2-5.5 mm, intended for the manufacture of springs.
Steel 68GA
* Used for the production of heat-treated wire with a diameter of 1.2-5.5 mm, intended for the manufacture of springs.
Steel 70
* Used for the production of springs, springs and other parts that require increased strength and elastic properties, as well as wear resistance; wire of square, rectangular and trapezoidal sections, intended for the manufacture of spring washers; knives of earth-moving machines (bulldozers, scrapers, graders and motor graders, as well as for knives of bulldozer and grader equipment of excavators, rollers and other earth-moving machines); cold-rolled heat-treated tape with a thickness of 0.05-1.30 mm and rolled heat-treated tape with a thickness of 0.15-2.00 mm for the manufacture of spring parts and springs, with the exception of winding ones.
Steel 70G
* Used for the manufacture of springs for various machines and mechanisms in various industries; knives of earth-moving machines (bulldozers, scrapers, graders and motor graders, as well as for knives of bulldozer and grader equipment of excavators, rollers and other earth-moving machines); measuring tapes.
Steel 70G2
* Used for the manufacture of springs for various machines and mechanisms in various industries; knives of earth-moving machines (bulldozers, scrapers, graders and motor graders, as well as for knives of bulldozer and grader equipment of excavators, rollers and other earth-moving machines).
Steel 70S2ХА (EI142)
* Used for the manufacture of watch mechanism springs; large springs for critical purposes; cold-rolled heat-treated tape with a thickness of 0.05-1.30 mm and flattened heat-treated tape with a thickness of 0.15-2.00 mm for the manufacture of spring parts and springs, with the exception of winding ones; measuring tapes.
Steel 70S3A
* Used for the production of heavily loaded springs for critical and special purposes.
Steel 75
* Used for the manufacture of round and flat springs of various sizes, car engine valve springs, shock absorber springs, springs, lock washers, clutch discs, eccentrics, spindles, shims and other parts operating under friction conditions and under the influence of static and vibration loads; knives of earth-moving machines (bulldozers, scrapers, graders and motor graders, as well as for knives of bulldozer and grader equipment of excavators, rollers and other earth-moving machines).
Steel 80
* Used for the production of round and flat springs and parts operating under friction and vibration loads; knives of earth-moving machines (bulldozers, scrapers, graders and motor graders, as well as for knives of bulldozer and grader equipment of excavators, rollers and other earth-moving machines).
Steel 85
* Used for the manufacture of springs, friction discs and other parts that require high strength and elastic properties and wear resistance; knives of earth-moving machines (bulldozers, scrapers, graders and motor graders, as well as for knives of bulldozer and grader equipment of excavators, rollers and other earth-moving machines); springs and measuring tapes.
Steel with a high elastic (yield) limit.
To get high elastic characteristics spring steels are subjected to hardening followed by medium-temperature tempering to obtain troostite in the structure. To achieve higher performance characteristics, steels alloyed with silicon, chromium and vanadium are used.
A characteristic feature of spring steels is the presence of carbon in them in an amount of 0.5...0.8%. The composition of these steels can be either carbon or alloy. Spring steels, first of all, must have a high yield strength, which ensures high elastic properties. This is achieved by hardening followed by medium tempering. The tempering temperature should be selected within the range of 350–500 °C (sometimes, depending on the composition and purpose, it can reach up to 600 °C). In addition, they must have a high endurance limit and a sufficiently high tensile strength. But the ductility of these steels should be reduced (5–10% in relative elongation and 20–35% in relative contraction). This is due to the fact that plastic deformation is not allowed in leaf springs.
Carbon steels are used for the manufacture of small-section springs operating at low voltages. These steels are hardened in oil. Table 1 shows the heat treatment modes, mechanical properties (minimum) and endurance limit (calculated) for carbon steels.
More often, silicon steels with a silicon concentration of 2% (50С2, 55С2 and 60С2) are used for the manufacture of springs and springs. Silicon in such steels retards the decomposition of martensite during tempering, which leads to an increase in the yield strength and, therefore, to an increase in elastic characteristics. The proof strength (σ 0.2) of these steels is 1100–1200 MPa, the ultimate strength is 1200…1300 MPa, the relative elongation is 6%, the relative contraction is 30–25% and the endurance limit calculated from the proof strength is 42–44 MPa.
The disadvantages of these steels include their tendency to decarburization and the formation of surface defects during hot working, leading to a decrease in the endurance limit. In order to prevent the formation of these defects, silicon steels are additionally alloyed with chromium, manganese, vanadium, nickel and tungsten.
Heat treatment modes for silicon spring steels are given in Table 2.
Steel grades 50С2, 55С2, 60С2 and 70С3А can be used for the manufacture of springs and springs with a diameter or thickness of up to 18 mm. They are resistant to grain growth when heated for quenching, but are prone to decarburization, leading to a decrease in the endurance limit.
Steel 60S2ХА is used for the manufacture of large springs for critical purposes. When quenching in oil, it is calcined to a depth of up to 50 mm. The disadvantage of this steel is its tendency to break during drawing.
Steel grades 60S2N2A and 60S2KhFA have higher hardenability (up to 80 mm) and are used for the manufacture of springs for especially critical purposes. At the same time, steel 60S2N2A has the best combination of technological and operational properties. A general disadvantage of silicon spring steels is their increased sensitivity to external surface defects (scratches, scratches, nicks), which play the role of internal stress concentrators, as a result of which the endurance limit is reduced. Therefore, silicon-free spring steels are currently widely used in practice.
At the same carbon concentration as in silicon steels, silicon in them is replaced by the following possible combinations of alloying elements: chromium + manganese, chromium + vanadium, chromium + manganese + vanadium, chromium + manganese + boron. For example, 50ХГ, 50ХФ, 50ХГФ, 55ХГР. These steels have increased toughness and are less sensitive to cuts. To improve performance characteristics, especially for springs operating under long-term alternating loads, it is prescribed to blow the surface of the springs with shot. The compressive stresses arising in the surface layer lead to an increase in the endurance limit.
The highest mechanical and performance characteristics can be obtained by cold drawing of pre-patented wire with a diameter of up to 2 mm made of carbon steel, subjected to high degrees of reduction (70–90%).
The patenting process is carried out between broaches. It consists of heating the wire by 50–100 °C above the Ac 3 point, followed by cooling in a bath of molten lead. The melt temperature should be 450–550 °C. As a result of this heat treatment, isothermal decomposition of austenite occurs with the formation of thin-plate sorbitol.
