What steel are bolts made from - Metals and their processing

What steel are bolts made from?

1 Strength classes and materials of fasteners and their mechanical characteristics | Vostok-Inter company articles
- 1.1 Bolts, screws, studs
- 1.2 Nuts
- 1.3 Technical documentation
- 1.4 Articles
2 Production of nuts at the factory: how and from what steel they are made, equipment for the production of nuts
3 High-strength bolt: features, scope, basic parameters and characteristics (75 photos)
4 Strength of bolts made of steels, alloys and plastics
5 Bolt strength class and marking according to GOST 7798-70
6 Bolt strength class according to GOST 7798-70, documentation and steel grade
- 6.1 How is the marking deciphered?
- 6.2 GOST No. 7798 of 1970
7 Bolts of strength classes 6.6, 5.6, 4.6 according to GOST

Recommendations for the selection of materials for threaded fasteners depending on strength classes.

In the article Technical requirements for fastening threaded parts, we examined the designation of strength classes for bolts, screws and studs made of carbon unalloyed and alloyed steels, the determination of the strength and yield limits of materials, as well as the test voltage of the material for nuts.

Below we will take a closer look at what materials are used for the production of threaded products and what strength classes correspond to them (read about the mechanical properties of fasteners made of stainless steel grades in our article - A2, A4 - Characteristics of fasteners made of stainless steels).

The tables are given in accordance with GOST 1759.0-87. Bolts, screws, studs and nuts. Technical specifications" for fasteners widely used on the market. For details on strength classes, materials and mechanical properties, see the technical documentation indicated at the end of the article.

Bolts, screws, studs

Strength class Steel grade Strength limit σB, MPa Yield limit σT, MPa Hardness HB

3.6	10, 10kp	300330	180190	90238
4.6	20	400	240	114238
4.8	10, 10kp	400420	320340	124238
5.6	30, 35	500	300	147238
5.8	10, 10kp, 20, 20kp	500520	400420	152238
6.6	35, 45, 40G	600	360	181238
6.8	20, 20kp	600	480	181238
8.8	35, 35Х, 38ХА, 45Г, 40Г2, 40Х, 30ХГСА, 35ХГСА, 16ХСН, 20Г2Р	800*	640*	238304*
8.8	800830**	640660**	242318**
9.8*	900	720	276342
10.9	10001040	900940	304361
12.9	12001220	1080110	366414

Nuts

Strength class Steel grade Stress from test load σF, MPa Hardness HB

4.0	20, St3kp3, St3sp3	510	112288
5.0	10, 10kp, 20	520630	124288
135288
6.0	10, 10kp, 15, 15kp	600720	138288
04	380	162288
8.0	35, 20, 20kp	800920	162288
9.0	10401060	180288
10.0	35Х, 38ХА, 20Г2Р, 16ХСН	900920	260335
12.0	11501200	280335
05	500	260335

Note: recommended combinations of strength classes of nuts and bolts for various thread diameters: a) 4-3.6, 4-3.8, 4-4.

8 (M > 16); b) 5-3.

6, 5-4.6, 5-4.8, 9-9.8 (M≤16); c) 5-5.6, 5-5.8, 6-6.8, 8-8.8, 10-10.9, 12-12.9 (M≤48);

d) 9-8.8 (> M16≤M48).

* For nominal diameters d≤16 mm. ** For nominal diameters d > 16 mm.

*** For bolt strength classes 8.8, 9.8 and 12.9, the conventional yield limit is σ0.2.

Fracture of a steel bolt when its tensile strength is exceeded.

Source: https://steelfactoryrus.com/iz-kakoy-stali-delayut-bolty/

Products – Tekhmashholding – group of companies, official website

Types of nuts

There are many types of this product:

Crown - equipped with additional protrusions at one end.
Body nuts are a square nut with a counterplate that are used in the automotive industry.
Wing - have at least two blades and are designed to be twisted by hand.
Slotted - used for flush screwing using a fork screwdriver.
Push-type - used in the instrument-making industry and tightened by hand.

Cap nut

Cap-shaped ones are decorative, as they are made in the shape of a cap at the top.
Square - designed for screwing in bolts. This type is fixed in the socket until installation begins.
End - made in the form of the letter T and used in the machine tool industry.
Flanged - have notches on one side that replace a washer.
Self-locking - prevents self-unwinding. Used under increased vibration loads.

Eye nut

An eye nut is a ring-shaped connection that is used for rigging work.
Riveted - they have a threaded connection at one end, and at the other they resemble a regular rivet.
Connecting nuts are a regular elongated nut. You can screw two bolts into it.
Welded - additionally have excess metal at the edges for welding.
Blind - closed on the top side.

In addition to the above types, there are various forms: low and high, wide and narrow.

What are nuts made of?

It should be noted that the composition of nuts is very diverse and depends on the strength class and scope of application. Today the most common material is steel. It is suitable for cold stamping using presses. Low-carbon steel is also used, but hardening is used during the production process. Additionally, bronze, titanium and brass can be used. Duralumin and magnesium alloy are not very widely used.

Production process

You can learn how nuts are made in Russia from the patents of various factories. There is a well-proven method according to RF patent No. 2361695. It uses the cold stamping method.

Stamping process according to GOST

The first step is to obtain a workpiece using drawing or calibration. Next, the product is formed on presses in five stages (the method is similar to the production of bolts):

At the first or third stage, upsetting is carried out, a cylinder is formed and a preliminary hole is marked.
On the fourth, a jumper is formed for the final hole and gives an almost finished look.
Fifth, punch a hole in the middle.

After going through the stamping stage, the nut is threaded or rolled. The product is ready, all that remains is to test it. The main parameter is the load that the product can withstand before the thread breaks. Various tests are also carried out for horizontal rupture, artificial aging and deformation under various loads.

https://www.youtube.com/watch?v=xRoixZtkEVc

The hot forging method is very common. The cut pieces are heated to 1200 degrees. Next, a hydraulic hammer stamps hexagons with holes inside. The next step is cooling and threading using oil. Sometimes hardening is used. To do this, the product is placed in an oven at a temperature of 800 degrees, quickly cooled and immersed in oil for 5 minutes. The second heating is carried out for an hour to minimize brittleness and maintain strength.

The detailed production process is shown in the video.

Equipment for the production of nuts

The main equipment for production are machines for upsetting and threading.

Most enterprises purchase equipment from Taiwan. Presses must have a closed design for safe cutting of products. It is advisable to choose forming matrices in a round shape, as it provides excellent balancing characteristics. The connecting rod mechanism must be made of alloy steel. An important feature is the oil filtration system (usually magnetic), which reduces costs.

Nut setting machine from Taiwan

For thread cutting, it is recommended to use pneumatic machines with multiple spindles for high speed operation. Such spindles can be programmed for different types of work, for example, for long and short threads or left and right. It is also worth taking care of overload and jam fuses.

Vote:

kakdelayut.ru

CARBON STEEL

According to the requirements of DSTU ISO 898-1:2003, the following steel grades are used for the manufacture of bolts, screws, and studs:

Strength class	Material and processing	Boundary chemical composition (control analysis), %	Holiday temperature, 0С, min
carbon (C)	phosphorus (P)	sulfur (S)	boron (B)
min	max	max	max	max
3.6	Carbon steel1	—	0,20	0,05	0,06	0,003	—
4.6	—	0,55	0,05	0,06	0,003	—
4.8
5.6	0,13	0,55	0,05	0,06	0,003	—
5.8	—	0,55	0,05	0,06	0,003	—
6.8
8.8	Carbon steel with additives (such as B, Mn or Cr), quenched and tempered	0,15	0,40	0,035	0,035	0,003	425
Carbon steel quenched and tempered	0,25	0,55	0,035	0,035	425
9.8	Carbon steel with additives (such as B, Mn or Cr), quenched and tempered	0,15	0,35	0,035	0,035	0,003	425
Carbon steel quenched and tempered	0,25	0,55	0,035	0,035
10.9	Carbon steel with additives (such as B, Mn or Cr), quenched and tempered	0,15	0,35	0,035	0,035	0,003	340
10.9	Carbon steel quenched and tempered	0,25	0,55	0,035	0,035	0,003	425
Carbon steel with additives (such as B, Mn or Cr), quenched and tempered	0,20	0,55	0,035	0,035
Alloy steel2 quenched and tempered	0,20	0,55	0,035
12.9	Alloy steel quenched and tempered	0,28	0,55	0,035	0,035	0,003	380

1 Carbon steel is an alloy of iron (Fe) with carbon (C). There are low-carbon (C≤0.25%), medium-carbon (0.25%0.55%).

2 Alloy steel - carbon steel, in the chemical composition of which additional elements (alloying additives) are introduced. There are low-alloy steels (content of alloying elements up to 2÷4%), medium-alloy (4÷11%) and high-alloy (over 11%). Alloying elements do not include carbon and inevitable impurities.

According to the requirements of DSTU ISO 898-2:2004, the following steel grades are used for the manufacture of nuts:

Strength class	Limitation on chemical composition (control analysis), %
carbon	manganese	phosphorus	sulfur
max	min	max	max
4; 5; 6	—	0,50	—	0,060	0,150
8; 9	04	0,58	0,25	0,060	0,150
10	05	0,58	0,30	0,048	0,058
12	—	0,58	0,45	0,048	0,058

According to the requirements of GOST 18123-82, the following steel grades are used for the manufacture of washers:

View	Brand	Standard designation	Symbol of the brand (group)
Carbon steels	08, 08kp10, 10kp	GOST 1050-88	01
St3St3 kp	GOST 380-94	02
15	GOST 1050-88	03
20	04
35	05
45	06
Alloy steels	40X	GOST 4543-71	11

CORROSION-RESISTANT STEEL1

According to the requirements of DSTU ISO 3506-1:2006, bolts, screws, studs and nuts are made from the following grades of stainless steel:

Class	Brand	Restriction on chemical composition, %
C

Source: https://pellete.ru/stal/iz-kakoj-stali-delayut-bolty.html

Bolt strength class according to GOST

On sale you can find a variety of fasteners that can be used to connect several products into one structure. The most common proposal is bolts. They have been used for the past several decades.

Different types of bolts are characterized by different geometric parameters and performance characteristics. For example, the strength class of bolts can vary over a fairly wide range.

Let's take a closer look at the characteristics of the bolts, which determine the scope of application of the resulting mechanisms and its service life.

Bolt strength class

Strength class of threaded fasteners

The strength class of nuts is determined by its mechanical properties. To classify the product according to this parameter, GOST 1759 4-67 is used. According to regulatory documentation, the strength class is divided into 11 categories.

Download GOST 1759.4-87 Bolts, screws and studs. Mechanical properties and test methods"

The screw designation used has the following features:

It is quite easy to decipher strength class 10 or 9. The applied marking rules make it possible to simplify the task of selecting suitable fasteners.
The strength class of washers or other fastening materials can be determined by reviewing the regulatory documentation. The first digit of the designation is multiplied by 100, resulting in an indicator of tensile and tear strength. Tensile strength determines how strong the fastener used is.
There is also a second number in the labeling, which can be used when calculating the main indicators. For example, accuracy class 8.8 indicates that the second indicator corresponds to the ratio of yield strength to tensile strength. In this case the figure is 80%.

When making fasteners from stainless steel or other materials, the following points should be considered:

Yield strength is the value of the load at which a material cannot be restored after deformation. When calculating the load that affects the thread, the point that there must be a threefold safety margin is taken into account.
The bolt strength chart is used to select the most suitable fastening material.

Breaking loads for bolts

The bolts used in accordance with GOST with a resistance of 800 MPa and more can withstand significant loads. That is why they have become widespread in the construction of bridges or other critical structures.

Nuances of choosing fasteners

The choice of fasteners should be treated with great responsibility. This is due to the fact that their strength indicator may differ significantly. The selection is made taking into account which grade of steel bolts has more suitable performance properties. The key points include the following information:

Type of material used in manufacturing.
Accuracy class.
Applied methods of thermal and chemical treatment.

High-strength bolts can be made from a variety of metals. Let's call the key points:

In most cases, the following metals are used: 10KP, 20KP, steel 10, steel 20, 20G2R, 40X. These metals meet all established requirements for physical and mechanical properties.
To improve performance, heat treatment can be carried out. To perform this operation, special electric ovens are used. By creating a special protective environment, the required performance qualities are ensured.
Carbon steels are the most widely used. This is due to their relatively low cost, as well as high performance.

Galvanized bolts

The diameter of the bolts is also an important selection criterion.
Diametrical dimensions can vary over a fairly wide range. With an increase in the cross-sectional area, the strength and reliability of the connection increases. The length of the bolts is considered the most important geometric indicator that must be taken into account. The materials used can have very different characteristics. For example, attention is paid to the hardness of the bolts.

Too low a value can cause deformation of the threaded surface when a longitudinal load occurs.

Before choosing the most suitable fastener, you need to take into account the features of connecting parts when using this fastening material:

The conducted studies indicate that with the correct choice of strength class and tightening torque, the highest quality connection can be ensured. In addition, it provides protection against spontaneous unscrewing and long service life of the product.
High-quality fasteners can withstand transverse and axial loads. In the manufacture of fasteners, special metals and alloys are used that effectively withstand loads acting in any direction.
The installation and dismantling process is greatly simplified. It is worth considering that some metals can oxidize, and after some time it will be difficult to dismantle the structure. However, the task can be simplified by using a special substance.
It is possible to obtain detachable connections. Very often you can encounter a situation where in order to perform various works it is necessary to disassemble the structure. To carry out dismantling work, simple tools are required, and the work usually takes little time to complete.
The cost of the resulting product is significantly reduced. Welding a joint is expensive, as it requires the use of a special welding machine.

The quality of connections can be significantly improved by using additional various elements.
For example, washers and locknuts are used, which significantly improve the quality and reliability of the connection. However, threaded connections also have several significant disadvantages:

Stress concentration at the root of the thread profile. It is worth considering that the use of special metal can significantly increase the reliability of the threaded surface.
There is a possibility that the nut will unscrew under strong mechanical stress. Of course, to exclude such a possibility, various fixation methods can be used.

In addition, there are several types of threaded fastening. An example is a bolted and screwed connection. Some connections can be made using studs. The choice of a more suitable fastening element is carried out taking into account what qualities the product should have.

Bolt markings

Marking of bolts can be carried out using developed ISO standards.
The labeling system involves the use of special tables. In addition, all standards used in Russia were developed several decades ago. The strength class is considered the most important indicator, which is taken into account in the production of almost all fasteners. When considering the designation of bolts, you should pay attention to the following points:

Mandatory marking is carried out in the manufacture of screws whose diameter is more than 6 mm. Bolt strength and other indicators are marked on products of smaller diameter only at the request of the manufacturer.
The range of fasteners used with cross-shaped or straight slots does not provide for marking. Products with hexagonal slots must be marked.
Non-stamped versions that are manufactured by turning and cutting are not subject to mandatory marking. Marking is applied only if required by the customer. However, decryption can be carried out in different ways; standards are not applied in all cases.

When considering the parts of the bolt on which markings are applied, attention should be paid to the end and side surfaces. If a side surface is used, then the designations are applied with recessed signs.

Bolt classification

There are many different types of bolts. The choice is made depending on what performance qualities the product being created should have. Bolts can be classified according to several criteria:

Strength class. If we consider the most common tables, the strength class becomes the main criterion. It determines the possibility of using the product in certain cases. Special bolts can have high strength and are used in the construction of bridges or other critical structures. The strength class of fasteners is indicated by almost all manufacturers. This is due to the fact that the strength class determines the possibility of using products in certain conditions.
Size classification is important. This is because as the cross-sectional area increases, the torsional resistance increases. However, larger fasteners require larger diameter holes. As for the length of the rod, it is selected depending on the thickness of the elements to be connected and the required length of the threaded connection.
There are different types of heads. An example is a product with a hexagonal head or in the form of an octagon. It is worth considering that this indicator only determines which tool is most suitable for the job.

Types of bolts

Other indicators may be used to classify fasteners. For example, in some cases, the most attention is paid to surface hardness. However, the choice is often made taking into account the accuracy class. That is why the classification is carried out according to the accuracy class, which is indicated in regulatory documentation and during design.

High Strength Bolts

In most cases, conventional connecting elements are used, in the manufacture of which carbon steel is used.
However, if necessary, you can purchase high-strength bolts that can be used to create high-strength connections. Marking of high-strength bolts is carried out according to general standards. The production of high-strength bolts is carried out taking into account the information below:

In manufacturing, special alloys are used, which are characterized by high strength and hardness. They are more expensive than carbon steel, but still the use of the resulting products is advisable in a wide variety of cases.
Heat treatment is carried out to increase strength and hardness. It involves changing the chemical composition of the metal and the structure of the resulting material.

High Strength Bolts

High-strength bolts may require their own regulatory documentation. In addition, the classification is carried out as follows:

Fasteners with the letter “U” in the marking are used for operation at temperatures below -40 degrees Celsius. However, the letter in question is not indicated in all cases of marking.
Offers with HL design can be operated in more severe operating conditions, for example, at temperatures from -40 to -65 degrees Celsius. When marking in this case, the accuracy class is indicated.

High-strength bolts and nuts are quite common today. This is due to high performance qualities, which allow you to expand the scope of the product.

Bolt accuracy

Another important indicator is the accuracy class of bolts. This is due to the fact that during manufacturing a variety of thread cutting and cylindrical surface processing methods can be used. Considering the accuracy indicator, we note the following points:

With increased precision, the resulting threaded connection lasts much longer.
The proposal has a more precise geometric shape.
There is no space between the fastener and the hole created that could cause the connection to become loose.

As accuracy increases, the cost of fasteners also increases.

That is why fastening materials used in the manufacture of non-critical mechanisms have an average accuracy rating. The use of modern equipment for turning allows us to obtain fasteners with a high level of accuracy.

In conclusion, we note that various companies are engaged in the production of the materials in question. In many ways, the quality of the resulting product depends on the equipment used and production technology.

Some manufacturers may reduce the quality of fasteners in order to reduce their cost.

Source: https://stankiexpert.ru/tehnologii/klass-prochnosti-boltov-po-gost.html

Mechanical properties of bolts, screws, studs, nuts

page » Designs of machine parts online » Connections of machine parts » Threaded connections » Mechanical properties of bolts, screws, studs, nuts.

The grades and mechanical properties of carbon and alloy steels used for the manufacture of screws, bolts and studs are given in Table. 1.

Table 1

Mechanical properties	Strength class
3.6	4.6	4.8	5.6	5.8	6.6	6.8	8.8	9.8	10.9	12.9
≤M16	>M16
Tensile strength σ, N/mm2	Nom.	300	400	500	600	800	800	900	1000	1200
Name	330	400	420	500	520	600	800	830	900	1040	1220
Yield strength σt, N/mm2	Nom.	180	240	320	300	400	360	480	—	—	—	—	—
Name	190	240	340	300	420	360	480	—	—	—	—	—
Conditional yield strength σ0.2, N/mm2	Nom.	—	—	—	—	—	—	640	640	720	900	1088
Name	—	—	—	—	—	—	640	660	720	940	1100

Depending on the mechanical properties, strength classes of materials are established, which are included in the symbols of threaded parts. The strength class is indicated by two numbers.

The first number, multiplied by 100, determines the value of the minimum tensile strength σв in MPa, the second number, multiplied by 10, determines the ratio of the yield strength σт to the tensile strength σв in percent; the product of numbers determines the value of the yield strength in MPa; for strength class 3.6, the mechanical properties are approximate.

For example, strength class 5.8 is deciphered as follows:

σв = 5 100 = 500 MPa,

σт/σв=8·10=80%or

σt=5·8·10=400 MPa.

Materials for bolts, screws and studs with metric threads from 1 to 48 mm according to GOST 1759.4 (ISO 898/1)

In table Table 2 shows the recommended steel grades and technological processes for the manufacture of fasteners.

table 2

Strength class	Material and type of heat treatment	Technological processes	steel grade	Standard designation
3.6	Low carbon steel	Hot stamping Cold stamping followed by softening heat treatment	10, 10kp	GOST 10702
4.6	Low or medium carbon steel	Hot stamping Cold stamping followed by softening heat treatment	20	GOST 1050
4.8	Cold stamping	10, 10kp	GOST 10702
5.6	Hot stamping Cold stamping followed by softening heat treatment	30, 35	GOST 1050, GOST 4543, GOST 10702
5.8	Low or medium carbon steel	Cold stamping	10, 10kp20, 20kp
6.6	Hot stamping followed by quenching and tempering Cold stamping followed by quenching and tempering	35	GOST 1050, GOST 4543, GOST 5663, GOST 10702
Hot stamping	45, 40G
6.8	Cold stamping	20, 20kp	GOST 1050, GOST 5663, GOST 10702
8.8 12.9	Low carbon steel with additives (eg boron, manganese or chromium) quenched and tempered. Medium carbon steel with additives (eg boron, manganese or chromium) quenched and tempered. Alloy steel quenched and tempered.	Hot stamping followed by quenching and tempering Cold stamping followed by quenching and tempering Cutting followed by quenching and tempering Cold stamping from heat-strengthened material	35, 35Х, 35ХА, 40Г2, 40Х, 30ХГСА, 35ХГСА,16ХСН, 20Г2Р	GOST 4543, GOST 10702

Material for nuts according to GOST 1759.5

In table Table 3 shows the recommended steel grades and technological processes for the manufacture of nuts.

Strength classes of nuts and bolts with metric threads from 1 to 48 mm according to GOST 1759.5

In table 4 shows the recommended combinations of strength classes of mating parts for various thread diameters. In special cases, fasteners can be made from corrosion-resistant, heat-resistant, heat-resistant steels, as well as non-ferrous alloys. The strength class of the nuts is indicated by a number which, when multiplied by 100, gives the value of the stress from the test load in MPa.

As a rule, nuts of high strength classes can replace nuts of low strength classes. This replacement is recommended for bolt-nut connections, the stress in which will be higher than the yield strength, or the stress from the test load of the bolt.

Source: https://pro-techinfo.ru/konstruktsii-detalej-mashin-onlajn/soedineniya-detalej-mashin/rezbovye-soedineniya/mehanicheskie-svojstva-boltov-vintov-shpilek-gaek/

Bolt strength class and marking according to GOST 7798-70

Fasteners are available in an assortment. You can find products that are designed for ordinary connection of parts in assembly units. And there are also those that are designed to increase the reliability of the node in which they will be installed. When choosing fasteners, it is necessary to take into account the strength class of the bolts and clearly understand what type and size of load they will face. Accordingly, starting from this, choose its standard size and strength group.

Fastener properties

Hardware produced by various enterprises differ from each other in geometric parameters, shape, material, and purpose. In addition, they can be distinguished by the type of coating and a number of others. In addition to the mentioned properties, bolts of the same type differ in strength parameters.

For example, an M16 bolt can be used to fasten parts of a fence or fence, and the same bolt can be used to assemble a bridge or crane structure.

Accordingly, for the first option, a bolt with lower strength parameters can be used than for the second application option. Bolts used to assemble cranes and similar equipment are called crane bolts.

They are distinguished by higher strength and especially strong steels are used for their manufacture. In the Russian Federation, GOST 7817-70 is in force, which normalizes the requirements for fasteners used in particularly critical structures.

Hardware has several forms - bolts, nuts, screws, etc. Each of these products is used to solve specific problems. Various steels and different technologies are used for their manufacture. The marking that will be applied to the surface of the fastener also depends on this.

Features of the production of high-strength bolts

The class is determined not only by the grade of steel, but also by the method used for their production. Thus, high-class bolts are produced on automatic heading machines (cold or hot). The thread is rolled using special technological equipment. Then they are sent for heat treatment. After applying a coating that protects the bolts from corrosion and aging, they are ready for shipment to consumers.

Fasteners are sent to the consumer in boxes of a certain weight. In some cases, a layer of oil is applied to their surface, which ensures long-term storage of hardware products.

Equipment used for the production of high-class bolts can produce from 100 to 200 products per minute. For manufacturing, rolled wire made from low-carbon or alloy steel is used.

Steels for making bolts

Several grades of steel are used for production. The most common ones are 10KP, 20KP, 10, 20, 35, 20G2R, 65G, 40X. After heat treatment, the bolts receive the specified parameters defined in the relevant regulations. Heat treatment is carried out in electric furnaces using a protective environment. It prevents carbon from leaving the steel.

High strength bolts can be produced from different grades and products will be obtained that will belong to different strength groups. By varying various heat treatment modes, it is possible to obtain products with different strength parameters.

As an example, we can consider the use of steel 35 for the production of bolts belonging to different strength groups:

6 — bolts are made on machines of the turning and milling group;
6 and 6.8 - fastening is carried out on upsetting press equipment;
8 - this class will be obtained after undergoing heat treatment.

High-strength bolts also include specialized hardware that are used strictly in certain areas. Product requirements are determined in industry documents.

Fasteners used in the aircraft industry are produced on the basis of so-called normals (industry standards). These hardware are distinguished by increased strength, light weight and accuracy. The use of these bolts and nuts ensures safe operation of the equipment. For their production, carbon or alloy steels are used. Finished products are coated with a reinforced layer of anti-corrosion coating.

Products used in the construction of bridge structures and their structural elements are standardized by GOST R 52644-2006.

Bolts of special strength are produced in different designs. There are several options. Bolts of category “U” are allowed to operate at – 40 ºC. Products of the “HL” type are operated in the range from – 40 to – 65ºC.

For the manufacture of high-strength hardware, the following grades of alloys are used: 30Kh3MF, 30Kh2AF, 30Kh2NMFA.

Types of tests performed

To confirm the quality of products, manufacturing plants conduct a series of tests. The list and test methods are defined in GOST R 52627-2006. Tests can be carried out in the factory or any other laboratory that has passed the appropriate certification at the Rosstandart center. Below is a short list of tests:

stretching;
torsion;
hardness;

Based on the results of the tests, the properties of the product will be determined, in particular - tensile strength, yield strength and a number of others.

Navy

On sale you can find a variety of fasteners that can be used to connect several products into one structure. The most common proposal is bolts. They have been used for the past several decades.

Different types of bolts are characterized by different geometric parameters and performance characteristics. For example, the strength class of bolts can vary over a fairly wide range.

Let's take a closer look at the characteristics of the bolts, which determine the scope of application of the resulting mechanisms and its service life.

What steel are bolts made of? — Machine tools, welding, metalworking

A nut is a fastener with a thread inside, usually in the shape of a hexagon according to GOST for use with a wrench. It is connected using a bolt, stud or screw.

Strength class of bolts and their markings - Turner Master

Modern trends in mechanical engineering, construction, oil and gas and other industries, in order to increase competitiveness, require a reduction in the metal intensity of products and structures, but without loss of joint strength. This can be achieved by using high-strength fasteners. It is not always needed.

To attach a canopy or fence board, fasteners with a strength class of 3.6 or 4.8 are sufficient. Another thing is the fastening of metal structures of bridges, roofs, and critical parts of transport mechanisms. Without bolts, nuts, studs with strength class 8.8, 10.9, 12.

9 in this case, it is impossible to do and neglecting an accurate calculation and the use of fasteners of the appropriate strength class can lead to disastrous consequences.

What does “high-strength fastener” mean?

Let's look at this issue using bolts as an example. Threaded fasteners made of carbon steels are produced in 11 strength classes, from 3.6 to 12.9. In accordance with GOST R 52644-2006, high-strength (high-strength) fasteners include bolts with a strength class with digital markings 6.8, 8.8, 10.9, 12.9. According to European standards, high-strength fasteners begin with strength class 8.8.

The first digit in the strength class marking is defined as one hundredth of the nominal tensile strength expressed in MPa. The same value is the tensile strength. For example, for a bolt with strength class 8.8 it will be equal to: 8/0.01 = 800 MPa

The second number denotes a tenth of the yield strength (when such a load is reached, irreversible plastic deformations occur in the bolt) in relation to the tensile strength. The same bolt 8.8 will have a minimum yield strength: 800 * (8 * 0.1) = 640 MPa.

The yield strength value is the maximum operating stress. When calculating loads, this value is multiplied by ½ or ⅓.

The strength class of fasteners is determined by the following parameters:

steel grade
type of production
type of processing

From steel of the same grade, fasteners with different strength classes can be obtained. For example, bolts made of St35 steel, manufactured by cold heading (heading) without subsequent processing, will have a strength class of 6.8, and those subjected to heat treatment - 8.8.

Below is a table of correspondence between the strength classes of fasteners and the grades of steel from which they are made:

Strength classes and steel grades for bolts, screws and studs

GOST and DIN for high-strength fasteners

High-strength bolts, screws, and studs can be produced both according to general GOSTs, which do not specify the specific use of fasteners, and according to industry-specific ones. The first include:

international standards for bolts - GOST 7798, GOST 7805, German - DIN 933, DIN 931;
threaded rods (one- and two-meter) DIN 975;
internal hexagon screws (with countersunk or cylindrical head) GOST 11378, GOST R ISO 10642, DIN 7991;
a number of other standards.

The industry-specific ones primarily include GOST R 52644-2006 for high-strength bolts for metal structures with an enlarged hexagonal head.

From 01/07/2015 new standards for bolt kits GOST 32464.1-2013 – GOST 32484.6-2013 came into force, which were supposed to replace GOST R 52644.

But while hardware plants are undergoing the process of adaptation to new standards, GOST R 52644-52646 has been extended.

Strength marking

The following are subject to mandatory marking:

bolts with a diameter of 6 mm
hexagon socket screws with a diameter of 6 mm or more

Marking of screws with a cross-shaped, flat or other slot, or bolts made by cutting or turning (not upsetting) is not required. In this case, marking is carried out according to the technological capabilities of the manufacturer in agreement with the customer.

Hardware is marked with the manufacturer's mark and strength class numbers, which are applied to the end or top of the head in the form of a convexity or indentation (on the end only as an indentation).

If the size or shape of the head does not allow the application of numbers and letters, the standard provides for the application of special hour symbols.

For studs with a diameter of 12 mm or more, the marking is applied to the area without thread.

Alternative marks (symbols) for marking studs (applied on the end) and their correspondence to the strength class:

Articles about products 02/08/2018 12:59:21

Source: https://tokarmaster.ru/osnovy-varki/klass-prochnosti-boltov-i-ih-markirovka.html

Strength class DIN and GOST

The strength class of DIN and GOST is the tensile strength of steel, therefore, when installing on objects and equipment, it is necessary to take into account the environment in which the fastening will be located, as well as what load, vibration and pressure the connection will be subject to.

The main fastening standards that are used in the Russian Federation are DIN (German standard), ISO and GOST.

Each standard has 10 strength classes, which differ for bolts, screws and studs depending on their mechanical characteristics.

The strength class shows an important mechanical characteristic of metal fasteners. This indicates the tensile limit of the metal. For fasteners that are made of carbon steel, it has a designation in the form of two numbers, which are separated by a dot. At the same time, the standard with the requirements of which the fastener is manufactured is indicated.

Bolts, nuts, studs are divided into 10 strength classes

The first number shows a hundred times reduced value of the critical breaking limit. It is expressed by the designation N/mm². That is, the effect of tensile force on the cross-sectional area of the hardware. For example, in the value 8.8, the first digit indicates that the strength limit is 800 N/mm². The second figure eight shows the yield point, after which deformation processes begin. The second number can be written as 800(N/mm²).

Set of products Strength class Tensile strength, N/mm2 Stress from test load, N/mm2 Nominal No less than Nominal Bolt, screw, hexagon socket screw, stud.

3.6	300	330	200
4.6	400	400	225
4.8	400	420	310
5.6	500	500	280
5.8	500	520	380
6.6	600	600	440
8.8	800	800*	580**
9.8	900	900	650
10.9	1000	1040	830
12.9	1200	1220	970

* For bolts with a diameter of more than 16 mm, the value is 830 N/mm2

** For bolts with a diameter of more than 16 mm, the value is 600 N/mm2

For bolts, screws and studs made of carbon unalloyed or alloyed steels, in accordance with GOST ISO 898-1-2014, the following strength classes are established:

3.6;
4.6;
4.8;
5.6;
5.8;
6.8;
8.8;
9.8;
10.9
12.9.

For convenient selection of hardware based on mechanical and other properties, special tables are created that reflect the strength class of DIN and GOST. This allows customers of fastening materials to more quickly fill out applications indicating absolutely accurate parameters, as well as resistance to force effects on tearing, shearing, and so on.

Bolt strength class

The strength of the bolts is marked and checked for tearing and shearing. Bolts are tested if the first number is greater than the second, then the bolts are more tensile strength, but less flexible.

4.85.8	They are made from steel grades 10 and 20. They have relatively low tensile strength. Bolts of strength class 5.8 can withstand loads 20% greater than bolts of strength class 4.8. They are widely used in all sectors of the national economy for lightly loaded connections.
8.8	They are made of steel 35, 20G2R, 40X with subsequent hardening. They withstand twice the destructive impact compared to strength class 4.8. We recommend using them in critical structures and mechanisms.
10.912.9	They are made only from steel 20G2R, 40Х, 30Х3МФ depending on the diameter of the bolt with subsequent hardening. They withstand destructive effects 2.7 times more compared to strength class 4.8. The high strength class allows the use of smaller fasteners under the same loads; reduce the metal consumption of fasteners and reduce the price by 30-40%. Indispensable in mechanisms that require frequent assembly and disassembly, lifting machines and critical structures.

Strength classes according to DIN and GOST

Bolts strength class 5.8 according to GOST GOST 7798, GOST 7805, GOST 15589, GOST 7795, GOST 7796, GOST 7808 GOST 7795, GOST 7796, GOST 7808

Bolts strength class 5.8 according to DIN

DIN 931, DIN 933

Bolts strength class 6.8 according to GOST

GOST 7805,

Bolts strength class 6.8 according to GOST

DIN 931, DIN 933

Bolts strength class 8.8 according to GOST

GOST 7798, GOST 7805, GOST 7808, GOST 22353-77, GOST 7795, GOST 7796,

Bolts strength class 8.8 according to GOST

DIN 931, DIN 933

Bolts strength class 10.9, 11.0 HL, according to GOST

GOST R52644, GOST 22353

Bolts strength class 10.9 according to DIN

DIN 931, DIN 933

Nut strength class

Attention!
The strength class of nuts is marked only starting from strength class 8! Nuts, strength class 5.8 according to GOST Nut GOST 5915, GOST 5927, GOST 15526 (strength class 6.0)

Nuts strength class 5.8 according to DIN

DIN934

Nuts strength class 8.8 according to GOST

GOST 5915, GOST 5927,

Nuts strength class 8.0 according to DIN

DIN 934

Nuts strength class 10.9, 11.0 HL according to GOST

GOST R52645-2006, GOST 22354-77

Washer strength class

There is no strength class for washers. The hardness of washers is measured in HV units. A standard DIN 125 washer has a standard hardness of 140 HV. The high-strength washer EN 14399 has a hardness of 300 HV. Washers strength class 5.8 according to GOST

The materials were prepared by specialists from the Triv-Komplekt company.
When copying texts and other materials from the site, it is mandatory to provide a link to the site www.traiv-komplekt.ru!

Source: https://traiv-komplekt.ru/techinfo/klass-prochnosti-din-i-gost/

Strength classes and materials of fasteners and their mechanical characteristics | Vostok-Inter company articles

Recommendations for the selection of materials for threaded fasteners depending on strength classes.

Below we will take a closer look at what materials are used for the production of threaded products and what strength classes correspond to them (read about the mechanical properties of fasteners made of stainless steel grades in our article - A2, A4 - Characteristics of fasteners made of stainless steels).

The tables are given in accordance with GOST 1759.0-87. Bolts, screws, studs and nuts. Technical specifications" for fasteners widely used on the market. For details on strength classes, materials and mechanical properties, see the technical documentation indicated at the end of the article.

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