The characteristics of the use of 15 steel, as well as the process of its production, led to the fact that it began to be assigned to the group of structural steels.
Steel structure
The most important requirement for this type of steel is high hardness. In order to achieve this indicator, a large amount of carbon is used as an alloying element, and a certain amount of chromium is also added.
At the time of delivery of this steel, its structure is a ferrite-carbide mixture. Most often, upon delivery of this type they write that it is annealed to granular perlite. It is also important to note that high ductility also belongs to the characteristics of the application of 15 steel, which must be observed, since the raw materials of this brand are often used for the production of various ductile structures.
The temperature of hardening of steel at which it undergoes heat treatment is 830-840 degrees Celsius. The release of raw materials is carried out at a temperature of from 150 to 160 degrees, and the time required to complete the operation is 1-2 hours.
Carbide phase
Further characteristics of the use of 15 steel largely depend on the carbide phase and on its successful completion. If we consider its flow under a microscope, we can observe that upon successful completion, the force required to break the matrix is โโ140 kN.
In order to achieve such an indicator, the ball, which is the main element of the structure, must have a uniform matrix, as well as sufficiently uniform carbides. They should be identical both in size and in their distribution in the matrix. If something went wrong during the processing, the force required to break the structure can drop to 68 kN. If this happens, then the structure of the ball turned out to be heterogeneous. Carbides in this case may be unevenly located and / or have a different size. This figure is very significant for steel.
Carbide phase defects
Since the characteristics of the application of 15 steel largely depend on the occurrence of the carbide phase, it is important to know what defects of this process may be:
- One of the first defects is carbide banding. It arises due to the fact that there is a heterogeneity of the steel structure after its hardening. In those areas where a large amount of carbides is present, a martensitic-troostite structure appears, and in those places where the amount of this substance is small, needle-like martensite appears.
- Another defect that may occur is carbide segregation. In the bearing type of steel, a large inclusion of carbides is often found, which are located along the rolling direction - this is called carbide segregation. The defect of this phenomenon is that these elements are characterized by high strength, but also high brittleness. Most often, such elements are destroyed when steel comes to the working surface, because of which a center of destruction is formed. A pronounced defect of this type greatly increases the wear of ball-bearing steel.
Steel bearings
Due to the characteristics of the application of steel 15, it has often been used for the production of balls, rollers and bearing rings.
It is worth noting that during the operation of these parts they are constantly subjected to high alternating voltages. It is also important to understand that a roller or ball, as well as a track made of rings, experience a high load at a single point in time, which is distributed over a very small portion of the plane. Because of this, such alternating stresses of the order of 3-5 MN / m 2 (300-500 kgf / cm 2 ) alternately arise in such areas.
It is precisely because of such loads that the temperature of steel quenching is very high in order to impart high strength to the material. It is also important to note that such high loads do not pass without a trace, they leave a slight deformation of the bearing elements. Because of this, fatigue cracks form on the bearing. The appearance of these defects leads to the fact that during the passage of this section, an impact occurs, due to which the deformation only intensifies, and ultimately the bearing completely fails.
Bearing steel: specifications
This steel grade is used for the production of balls with a diameter of up to 150 mm, rollers with a diameter of up to 23 mm, as well as for the production of bearing rings, the wall thickness of which is 14 mm. Also, this steel can be used for the manufacture of plug bushings, pressure valves, as well as other parts for which the main requirement is high hardness, high wear resistance, and contact strength.
Bearing steel of this brand also has a number of certain characteristics, such as: a tendency to temper brittleness or flock sensitivity. The limits of short-term strength of this material are in the region from 590 to 750 MPa. The proportionality limit for this material is 370-410 MPa. The elongation of the material at break is 20%. Steel grade 15 has a relative narrowing of 45%. In addition, there is also a characteristic of impact strength, an indicator of which is 440 kJ / m 2 .
Properties of ShH15 steel
If we talk about the properties of this brand, then you need to pay attention to its chemical composition, which largely affects the formation of these properties. Steel 15 contains the following chemical elements:
- C - 0.95 -1.0;
- Si 0.17-0.37;
- Mn 0.2-0.4;
- Cr - 1.35-1.65.
Also, this brand is characterized by another parameter - a critical temperature point. For steel 15, this indicator is in the region from 735 to 765 degrees Celsius.
In order to achieve the desired strength, this type of alloy is subjected to strong heating, the temperature of which exceeds the eutectoid transformation. It provides the desired concentration of an element such as C and Cr in the solid composition of steel , and also makes the structure of a fine uniform grain.
The decoding of 15 steel, which is obtained as a result of all these operations, is as follows: the letter means that the material belongs to the group of bearing steels, and the letter X indicates that the material contains chromium, which is one of the alloyed elements.
Carbon steel
Steel 15 - carbon and low alloy steel, which in the manufacture of knives acquired the name "carbon". This material has been used for approximately 100 years. The main field of application of this material is bearing, wear-resistant and cutting parts or elements.
It is also worth noting that this group of steel is a classic for the manufacture of knives and abroad. A knife from 15 will have tremendous strength, as well as significant sharpness. Such products are most often used for any cutting tools, however, ordinary kitchen knives can also be made from it.
Features of use
The decoding of 15 steel speaks for itself, but it is worth adding that 15 is an indicator of the amount of chromium in the material, which is contained in the amount of 1.5%.
When operating products from this steel in a metastable environment with high loads, geometric changes in the dimensions of the part are quite possible. After observing hardened samples and their size changes, as well as after radiographic studies, people found that in order to stabilize a substance such as martensite, it is necessary to harden the raw material for 2-4 hours at a temperature of 150 degrees Celsius. If it is necessary to stabilize martensite for further use of the substance in elevated temperature conditions, then the tempering process should take place at a temperature threshold that will exceed the operating temperature by 50-100 degrees Celsius.
It can be noted that the main reason why steel changes its geometric parameters after quenching and tempering is the effect of residual austenite. In order to give a vivid example, one can present the following statement: 1% of the autensite, when converted to martensite, will change the size of the part by 1 โข 10 -4 . For a clearer definition, this means that resizing will occur by 10 microns for every 100 mm of size.