Today, there is a huge variety of manufactured steels. Any specialist who deals with them should be able to distinguish between them and do it quickly enough. To determine the chemical composition and physical properties, steel designations have been developed that you should know.
General steel classification
First of all, you should understand that steel itself is an alloy that consists of metal and carbon. The second important point is that carbon contains no more than 2.14% of the composition. It gives steel hardness, but with its increase, the fragility of raw materials will increase. Further, it is worth noting that the basic classification of steel is based on the chemical composition of the alloy. On this basis, two large groups are distinguished - carbon and doped. Carbon steels, in turn, are divided into low carbon, medium carbon and high carbon. The content of the main element in them is: up to 0.25%, from 0.25% to 0.6%, more than 0.6%, respectively. For alloy steels there is also a similar classification into smaller groups. Low-alloyed contain up to 2.5% of alloying elements, medium-alloyed - from 2.5% to 10%, high-alloyed - more than 10%.
Steel, depending on its physical properties, can be further divided into structural and tool. The first category of material is intended for further operation in industry and construction; most of the cutting tools and die measuring devices are smelted from the raw materials of the second category.
Decoding of structural steels
We can begin our consideration of steel notation with simple examples. Suppose structural steel, which does not have alloying elements, and is also characterized by normal quality, is marked with the letters "St". Usually after these letters come any numbers. They indicate the carbon content in a particular type of alloy, and the calculation is in tenths of a percent. If after these numbers there is a combination of letters such as "KP", then this indicates an incomplete passage of the process of deoxidation of steel in the furnace. Thus, a boiling type alloy is obtained, which is indicated by the designation of steel "KP". If they are not there, then the raw material belongs to the calm type.
By a slightly different principle, low alloy structural steel will be marked. Let's say the designation of steel is 09G2S. This product will contain 0.9% carbon, and silicon and manganese are used as alloying elements. Their content in this product is within 2.5%. For example, material 10HSND and 15 HSND have a similar marking. As you can see, the main difference is only in the quantitative carbon content. Also, it became clear from the designation of the brand that none of the letters has a numerical value. This suggests that each of the listed alloying elements is contained in the composition of not more than 1% of the total mass.
There is a marking of another type - 20X, 30X, etc. This is also structural alloyed steel, but chrome will be the main component in its composition. In this case, the first digit indicates the carbon content in hundredths of a percent, not tenths. An example of such steel is 30HGSA. The amount of carbon will be 0.3%, and of the additives - silicon, manganese and chromium. There are no digital coefficients, which means that the content of each of them does not exceed 1-1.5%.
Variety of notation
The designation of steel grades does not always indicate the content of a substance. In some cases, the letter designation will determine the affiliation of raw materials to any class, group of goods. For example, there is a certain group of structural steels, which is intended for the production of bearings. All alloys belonging to this category have in their designation the letter "", which is at the very beginning of the marking. After it, the designation of steel elements continues, indicating their quantitative content. For example, product brands 4 and 15. In addition to iron and carbon, the composition includes chromium in the amount of 0.4% and 1.5%, respectively.
Another marking feature is the introduction of the letter "K". It is placed immediately after the first digits that show the amount of carbon. The presence of this letter in the designation of steel of a structural type indicates that it belongs to an unalloyed class. In addition, the raw materials marked "K" are intended for the creation of steam boilers and vessels, which in the future will be operated under high pressure. Marking looks quite simple, for example, 20K, 22K, etc.
At the end of the marking of structural steel may be the letter "L". Its presence indicates that the products are alloyed and have improved casting properties (40KHL).
Construction, tool alloy
The letters in the designation of steel plays a decisive role, as already noted. So, for example, without knowledge of their decoding, it will be difficult to deal with the construction type of steel. Firstly, such raw materials will be marked with the letter "C" at the very beginning. The numbers immediately following it do not indicate the carbon content, but the yield point of the material. In addition to the main letter, some auxiliary notation is also used. The letter "T" indicates that the steel has passed heat-strengthened steel, "K" is the designation of increased corrosion resistance, "D" is the increased quantitative copper content in the alloy.
As for the decoding of the designation of steel of instrumental type, it begins with the letter "U", standing at the very beginning. It is she who indicates the belonging of raw materials to the instrumental type. In this case, as with the structural one, the following numbers will indicate the carbon content in the composition. Further, it should be noted that tool steel can be of high quality and high quality. The letter "A" at the end of the marking of such an alloy will help to separate them from ordinary grades. Also, the composition can sometimes be increased manganese, if necessary for future use. Such formulations will have an additional letter “G” in the marking. The marking of tool steel looks like this: U8, U8A or U8GA.
It is worth mentioning that the designation of alloying steels of tool type is carried out according to the same rules as the designation of structural steels.
High speed, electrical steel
If we talk about the category of high-speed alloys, then their marking begins with the letter "P". Immediately after it are numbers indicating the quantitative content of tungsten in the alloy. Further, everything goes according to the same principle that was described above. A letter is entered that designates a certain element, after which a number is indicated that indicates the number of elements in the composition.
A feature of such alloys is that the letter and number designation of chromium is never indicated in their marking, since its content in this type of material is always 4%. The same applies to carbon, but its content will be proportional to the content of vanadium in the composition. Typically, the amount of vanadium is less than 2.5%, and therefore neither the letter nor the number are indicated. If, for some reason, the content of the element increases, then its designation is entered in the marking at the very end. The designation of high-speed carbon steel usually includes letters such as H, X, Yu, T, indicating the contents of nickel, chromium, aluminum and titanium, respectively.
Of particular note is the designation of unalloyed electrical alloys. They are often called technical iron. Their main feature is the minimum electrical resistance, which is achieved by an extremely low carbon content of about 0.04%. If we talk about the features of marking this type of technical iron, then it consists in the complete absence of letters, there are only numbers. For example, steel 10880 or 20880. The first digit will indicate the type of processing of the alloy, which can be hot rolled or forged - 1, calibrated - 2. The second digit indicates the aging coefficient of the metal. In this case, 0 indicates that the coefficient is not normalized, 1 - normalized. The third figure will indicate that the material belongs to a certain group according to the characteristic that will be selected as the main one. The last two digits, that is, the fourth and fifth will indicate the coefficient of the selected characteristic.
The designation principles themselves were developed back in the Soviet Union. The GOST designation for steels, which is used today, is also based on Soviet documents. Accordingly, with GOST, steel is marked not only in Russia but also in the CIS countries.
Designation of alloying elements
As it has already become clear, alloying elements are special additives that are introduced into the composition in order to change any physical properties and characteristics. In order to successfully decipher these types of alloys, it is necessary to know the designation of alloying elements in alloy steel.
For designation, letters such as: X, C, T, D, B, G, F, P, A, H, K, M, B, E, C, Y are used. These chemical elements correspond to such chemical elements as: Cr, Si, Ti, Cu, Wo, Mn, W, B, N, Ni, Co, Mo, Nb, Se, Zr, Al. For decoding, it is necessary to know exactly which elements are designated in this way: chromium, silicon, titanium, copper, tungsten, manganese, vanadium, boron, nitrogen, nickel, cobalt, molybdenum, niobium, selenium, zirconium, aluminum, respectively.
Alloy steels
Their designation is carried out according to the same principles that were described above. Where the first digits are the carbon content, and then the additives are listed, indicating their content in the numbers entered immediately after the element is designated.
However, there is another classification of alloy steels - by quality. The quality of such alloys depends on the amount of sulfur and phosphorus, which are harmful impurities that cannot be completely eliminated.
Basically, all steels belong to high-quality alloys. The content of both sulfur and phosphorus in such materials is about 0.035%, and their labeling is standard, which was described above. Next up are high-quality alloy grades. In them, the content of sulfur and phosphorus was reduced to 0.025%. At the end of any grade of high-quality alloy steel, the letter "A" is installed. And the last, third group, especially high-quality steel. The amount of sulfur in the composition is up to 0.015%, phosphorus up to 0.025%. Raw materials of this type are marked with the letter "W", which is installed at the end and is written with a hyphen.
An example is X5CrNi18-10 steel. The number 5 indicates the carbon content in hundredths of a percent, which means it is 0.05% here. Next are the designations Cr and Ni, showing that the composition contains chromium and nickel. Next are the numbers to quantify these two elements 18% and 10%, respectively. A feature of the marking of alloy steels is that after the letter there may not be a numerical coefficient at all. This means that it is in the alloy from 1 to 1.5%. With an increase in the mass fraction of any element, its quantity will be indicated.
Stainless steel
Stainless steel is marked like any other raw material. The designation of this type of alloy is intended to indicate its chemical composition and disclose its basic properties, which is very important.
Since the alloy is manufactured in many countries of the world, the designation of stainless steel could pass according to some international rules. However, to date, such rules do not exist, and therefore different countries are guided by their regulatory documents when marking products. For example, European steel producers label their goods in accordance with the rules of EN 100 27. The Russian Federation relies on GOST guidelines, which were developed on the basis of Soviet marking standards.
For example, P265BR stainless steel is an alloy produced in Europe. The first letter indicates that steel is intended for the manufacture of pressure vessels. The numbers are the yield strength of the alloy, which is 265 N / mm 2 . The last two letters are an additional designation. “B” indicates that steel will be used for the compressed gas cylinder, “R” indicates room temperature.
Components for creating stainless steel and their designation
As for the designation of stainless steel in Russia, then, according to GOST, all the letter designations of chemical elements are unified, and then knowing their decoding, you can easily determine the composition and properties of the material.
The composition includes:
- C is silicon. It is introduced into the composition to avoid the formation of scale on the surface of the metal after heat treatment.
- Yu - aluminum. This component is added to achieve a stable structure of the stainless metal, as well as to reduce the risk of foreign impurities that may occur during contact of the alloy or alloy product with boiling liquid.
- X is chrome. This element is the main part of the stainless steel, since the degree of resistance to corrosion depends on it.
- P is boron. This element is also responsible for increasing corrosion resistance, provided that the metal is exposed to high temperatures or aggressive chemicals.
- K is cobalt. It is used to stabilize the effect of carbon in the composition.
- M is molybdenum. It is introduced into the composition if it is necessary to increase the resistance of steel to an aggressive gas environment.
- F - vanadium. It is introduced into the composition of steel in order to increase its ductility if necessary.
Labeling Explanation
The principle of decoding the marking of stainless steel can be considered on the example of alloy 38XH3MF, where the numbers 38 indicate the carbon content in the amount of 0.33% -0.4%. Next is the letter "X" indicating the presence of chromium. Since there is no coefficient after the letter, it means its mass fraction is about 1% or slightly less. In this alloy, usually 1.2 to 1.5% chromium. After that comes the nickel designation and the number 3, which means its content is about 3-3.5%. The last notation is M and F - molybdenum and vanadium. Since there are no numbers, the mass fraction is less than 1%. For this type of raw material, the amount of molybdenum is 0.35-0.45%, and vanadium is 0.1-0.18%.
These alloys are initially characterized by high resistance to corrosion, however, their degree of protection can be increased even more if you add more copper. Such products will be characterized by the presence of an additional letter "D" in the labeling. Also, manganese "G" and titanium "T" can be added to the composition.
As can be seen from the foregoing, it was not so difficult to understand the marking. For people associated with industry, this knowledge is required. The ability to decipher markings can greatly help an ordinary person when choosing material for any of their individual goals. This is quite important, since you can accurately learn about the chemical composition and physical properties of the product by reading the designation left by the manufacturer. On the territory of the Russian Federation, marking is carried out in accordance with a single GOST, and therefore it will be the same in any region.