Reinforcing steel: brand, GOST, strength class. Steel reinforcement

2024 Author: Howard Calhoun | [email protected]. Last modified: 2023-12-17 10:16

Reinforcing steel is not officially called that: if you study GOST 5781-82, you can find out that the correct name sounds like "hot-rolled reinforced concrete reinforced concrete". However, the name turned out to be too long, so in a professional environment it was quickly reduced to a simple "fitting". It's clearer, easier, and faster.

General information

It is customary to distinguish several classes of reinforcement. The division is based on the following features:

• periodic profile;
• mechanical parameters.

Reinforcing steel comes in the following grades:

• AII.
• AIII.
• AIV.
• AV.

For several years now, the demand for A500C reinforcing steel has been quite high on the market. If you study GOST 5781-82, you will not be able to find descriptions similar to it in terms of its parameters. This product is manufactured to the following standards:

• STO ASChM 7-93;
• technical specifications.

Such a standardization system, according to which hot-rolled reinforcing steel of a periodic profile is grouped into categories, was introduced by enterprises operating in the field of ferrous metallurgy. They are united in a single association, which has taken over, among other things,development of rules for the production of goods.

Special occasion

The described A500C reinforcing steel is not the only exception in the world of hot-rolled products. Also, the AI class deserves special attention, which in GOST is commonly referred to as A240. The key feature is the smooth profile. Steel 3 SP (PS) is used as a raw material for the production process. The diameter and deviations from it for any products with a smooth profile are regulated by GOST 2590-88. This normative document also specifies the rolling accuracy for general cases.

Smooth reinforcing steel is produced in the following formats:

• bars;
• bays.

In coils you can find sizes from 6 to 14 mm (step - 2 mm). The choice of reinforcement in bars is somewhat wider. The minimum possible diameter is 16 mm, and the largest available is 40 mm. From 16 to 22 mm, the pitch is 2 mm, from 25 to 40 mm it increases to three.

How and why?

The A240 reinforcing steel grade is necessary in construction and other areas where reinforced concrete structures are used, as it is used to reinforce them. Some experts call this category of materials "loop", since it is customary to use reinforcement to form loop-shaped elements that reinforce reinforced concrete products. This is most relevant when the element stands out from the main plane of the structure. Hot rolled A1 reinforcing steel is suitable for creating elements that simplify the loading of finished blocks, transportation and unloading. In addition, directly on the construction site soit is easier to connect different elements together.

The AI rebar grade, like the round one, is necessary for a wide range of designs. When using it, they make:

• fencing;
• furniture;
• railings.

Circle and metal fittings A1, if they are made in accordance with specialized standards, are used as raw materials: wire can be drawn from them. Profiles allowed:

• periodic;
• smooth.

If the valve factory has the appropriate equipment, then A1 steel can be used for the manufacture of various products on lathes or milling machines. The material is processed mechanically.

Keeping the regulations in mind

Tells about what reinforcing steel should be, GOST 5781.82. According to the regulations, carbon in the composition of the metal can be no more than 0.3%, only then the product is applicable to reinforced concrete. Reinforcement is used for both previously stressed raw materials and for conventional ones.

If pre-treated and stressed reinforced concrete is used, then the reinforcement is chosen to be able to cope with quite serious loads inherent in this environment. As a rule, the voltage is quite large, which requires that the metal reinforcement be of increased strength and be made strictly from reliable steel. If wire is used, then high requirements are also placed on its strength.

If hot rolled reinforcing steel is to be used in structures, nosubject to stress, then the use of ordinary raw materials is allowed. The following steel grades are relevant here:

• ST3.
• ST5.

For prestressing, it is customary to take steel with a carbon content:

• medium;
• high.

Also can be used steel rebar, thermally treated to increase the strength parameters.

Steel: which one shall we take?

In order to make high-quality reinforcing steel, GOST 5781.82 recommends taking reliable steel:

• carbon;
• low-alloyed.

There are several grades applicable for different types of material mentioned. As a rule, the customer, when sending an order to a valve plant, indicates from which raw materials he wants to see the finished product. If the manufacturer does not receive such recommendations, then the manufacturing company independently decides in favor of the best option for a particular type of product. In particular, for the A800 it is customary to use the following brands:

• 22X2G2AYU.
• 22X2Y2R.
• 20X2Y2SR.

What else matters?

When creating non-stressed reinforced concrete structures, you should choose classes from the first to the third, and higher ones will be useful if the structure has been prestressed.

If you have to work at low temperatures, and the object will continue to be operated in extreme conditions, then such a brand of fittings is more suitable, which is distinguished by a reducedpercentage of carbon. Alternatively, you can choose options for raw materials that have undergone additional high-temperature processing.

But if it was decided to use wire as a reinforcing material, then it is better to give preference to the one in which carbon is either completely absent, or its content does not exceed 0.8%. This material is characterized by increased strength - up to 180 kgf/mm2 inclusive. These options are provided:

• high temperature treatment;
• hardened.

Carbon and material quality

Regulates what raw materials construction fittings should be made of, GOST 5781-82. In particular, the percentage of carbon has a rather strong influence on the final parameters of a reinforced concrete product, on its durability and reliability. The more carbon is contained in the metal, the higher will be the hardness inherent in the reinforcement, but at the same time, the brittleness increases. In addition, welding high-carbon steel is very difficult, often the result is of insufficient quality, which affects the reliability of the entire structure as a whole.

The percentage of carbon allows you to enter the following classification:

• low-carbon steel fittings, where this compound is contained in an amount of not more than a quarter of a percent;
• with an average level of content - from a quarter of a percent to 0.6;
• high content ranging from 0.6 to 2%.

How to improve?

In order for reinforcing steel to have the best quality, it is possible to addadditional components. It is customary to use as alloying components:

• tungsten;
• vanadium;
• chrome;
• nickel.

In some alloys, only one or two additional components are added, in others - a mixture of 5-6 metals. This makes it possible to obtain high quality alloy steel with high performance:

• strength;
• hardness;
• corrosion resistance.

To obtain alloyed steel, silicon, manganese can be included in the raw materials. Depending on how many additives are contained in the substance, it is customary to talk about the belonging of the material to one of the following classes:

• low alloy reinforcing steel containing no more than five percent inclusions;
• medium alloyed, in which the amount of additives varies between 5-10%;
• highly alloyed, one tenth or more of additional components.

What's in my name to you?

Reinforcing steel is not just steel, but also a large number of other chemical components. About what inclusions are in the material, you can find out from the name. Standards have been developed for the designation of certain additives in the name of the material. Examples:

• X is chrome.
• Z – zirconium.
• T is titanium.

After the stamp numbers are written. They reflect how much carbon is contained in the material. Hundredths are indicated. Next write the letters. They represent the chemical elementwhich indicates how much of it is contained in the reinforcement. If no figure is given, it can be concluded that the substance is included in less than one percent.

less than a percent of the total amount of material).

What to demand and wait for?

According to current standards, reinforcing steel should be:

• easy to weld;
• plastic;
• durable.

Strength is commonly understood as the ability of reinforcement to withstand destructive loads of the environment. External influences can stretch the metal and bend, twist and compress, cut. For each type of load, separate strength indicators are distinguished. Reinforcement is more often used in conditions where tensile loads are high, so it is this value that you should pay attention to in the first place. To assess how the reinforcement is able to resist stretching, you need to evaluate:

• current limit;
• breaking resistance.

Plasticity is a parameter that reflects the adaptability of a material to external loads that try to change the shape of the product, its cross section. If the reinforcement in such conditions retains its initial parameters, then after the load is removed, it can return to its original state orsave your changes. Ductility is expressed in elongation at break, angle of bend, number of kinks remaining after the metal has cooled.

Weldability is an indicator that reflects the ability to qualitatively connect with other materials when using a particular welding method. This setting is determined by:

• metal composition;
• by smelting method;
• size of rods in section;
• connective features;
• plasticity.

Mechanics and reliability

The above parameters allow us to talk about how good the mechanical parameters of the steel are. It is on their basis that technical characteristics and indicators are distinguished.

An important feature of reinforcement is its tensile strength. To determine it, as well as to identify how large the fluid limit is, how large the elongation of steel can be relative to the initial value, special tests are carried out in production: tensile machines designed for this task are used.

The work is done as follows: when the machine is started, the load gradually increases on the placed sample. At the same time, the armature is in a rigid fastening system that does not allow the “escape” of the instance. The mechanisms try to lengthen the rod longitudinally by deforming it. The indicators taken from the reinforcement allow you to form a tension diagram (the scale is set arbitrarily).

Specifications

Straight sections of the diagram reflect such loads under which the sample is not deformed. With an increaseloads, one can see a proportional increase in length, which makes it possible to draw conclusions about the reliability of steel and the ability to resist external influences. The limit value of the load applied to the test specimen is predetermined. Upon reaching this value, the influence of the mechanical force is also gradually reduced.

In the best case, the rod, stretched under the influence of a large external force, returns to its original state when the load is removed. This ability is due to the elasticity of steel. It should be understood that the elastic zone for a metal has certain limitations. When indicators exceeding these limits are reached, a return to the original values will become impossible. When such a boundary indicator is revealed, they say that the elastic limit has been reached.

If you test the reinforcement made in accordance with the current GOST of steel ST3, then you will be able to get parameters close to the following:

• yield strength - 2460 kgf/cm2;
• elongation - 25;
• tensile strength in a given time interval - 4,000 kgf/cm2.

Parameters and scope

Reinforcement with high strength values usually costs more than low-quality material. At the same time, practice shows that the use of such a material makes it possible to achieve significant savings, since the reinforcement of reinforced concrete structures requires more economical metal consumption.

Pay attention to the plasticity of reinforcement: yescertain boundaries, beyond which it is extremely undesirable. If this parameter drops below a certain level, it is impossible to use rolled products for full strength. A structure made using such consumable raw materials becomes brittle and can unpredictably collapse under the influence of external factors. There is another risk associated with a decrease in metal plasticity: the probability of brittle fracture increases already at the stage of reinforcing reinforced concrete structures.

Impact on steel samples

To improve the performance of reinforcement, they resort to various technologies of external influence. In particular, the practice of thermal hardening is widespread. In this case, the strength of the material doubles, and sometimes more. This is most applicable to low-alloy, carbonaceous compounds. But the cost of the material grows by only 10-12%. Thermal hardening shows the best performance compared to mechanical hardening, but for its implementation it is necessary to have serious modern equipment and a team of highly qualified specialists. The quality of the final product (and the reputation of its manufacturer) is greatly affected by even small errors in the process.

Work hardening is achieved using:

• winches;
• hydraulic jacks;
• profiled rolls.

The latter are needed to flatten steel. When hardening, it is possible to achieve plastic deformations, due to which the strength increases by 50%relative to the original value.

The most popular - what is it?

Traditionally, the most demanded in the market of rolled metal fittings are 8 mm in diameter. It belongs to the third class and is produced in bays, coils, rods. 8 mm - the parameter of the average diameter of the building material. The production of such fittings must comply with GOST 30136-95. Rebar produced in coils is called “rolled wire” by specialists.

The 8mm rebar is made from low carbon steel. The grades CT0, CT3 are used. There are two (sometimes one) cooling stages in the manufacturing process, which makes it possible to achieve high material reliability indicators. Rolled wire in coils is a wire.

A3 rebar - steel with a circle in cross section. It is necessary for the subsequent production of wire, springs. Raw materials are also indispensable in the production process of building cold-drawn reinforcement.

Production and sale

8 mm rebar is usually made on wire-section machines from raw materials that comply with GOST 380. This is a standard technology, assuming the presence of bar steel processed by a shaft system. On machines, the material is rolled and stretched, heated and cooled. Depending on the characteristics of a particular product, it will be cooled naturally or by force.

On sale such a product is present both in linear meters and in large skeins (for wholesale buyers).

Why is this needed?

Reinforcement 8 mm is indispensable in the constructionreinforced concrete and metal structures. Wire rod is quite thin, therefore it is used in the manufacture of nets, frames, ropes. Reinforcement is effective as a basis for staples. It is used to strengthen building structures. A specific option is chosen by analyzing the operating conditions of the building, on the basis of which a decision is made in favor of a particular brand.

Reinforcement is more often used as a raw material for the manufacture of other building products, and not as an independent material. If wire rod is needed to produce nails, cables, then you need to control the evenness of the products: rough surfaces are unacceptable, this will significantly reduce the strength of the finished product. In the manufacture of thick reinforcement, staples, the requirements for surface smoothness are not so significant. The fittings used for the arrangement of load-bearing walls cannot contain cavities or cracks filled with air. If 8 mm diameter rebar is purchased in bars, quality control involves tracking the identity of the products.

Some Features

It should also be noted that rebar having a round periodic profile is usually equipped with longitudinal ribs. Helical protrusions run across the rods, laid along a line with three runs. If the bar diameter is up to 6 mm, then the protrusions can run along the helix in one go. Two leads are allowed for 8 mm.

Reinforcing, ranked as the third class, happens:

• regular;
• special.

It is designated as A300 and Ac300, respectively. For such raw materialsprotrusions are characteristic, in which the entry on both sides of the profile is uniform. Here the lines also go with a screw. But for the A400-A1000, a prerequisite is that the entrances are right on one side and left on the other.

Screw lugs may be misaligned. This parameter is not standardized according to current GOSTs.

Another distinctive moment characterizes the production of A800 steel. The following brands can be used for it:

• 22X2G2AYU.
• 22X2Y2R.
• 20X2Y2SR.

At the same time, the features of the final product are usually regulated by customer requirements.

According to the recommendations of Gosstroy, it is recommended to use the following grades on the territory of the Russian Federation:

• A400C.
• A500C.

Both of them are suitable for strengthening reinforced concrete structures and replace the previously widely used A-III. These are made taking into account the requirements specified in GOST 5781-82.