Today, many industries use a wide variety of steel. A variety of quality, mechanical and physical properties is achieved by alloying the metal. The designation of alloying elements in steel helps to determine which components were introduced into the composition, as well as their quantitative content.
General information and general classification
When it comes to alloy steel, this means that special elements were added to the material that changed the mechanical and physical properties of the initial material. In addition, the internal structure of the material is changing. The designation of alloying elements in steel helps not only understand what additives were introduced. Depending on them, there are several classes of the product itself.
The first classification is carried out by the amount of carbon. There are low-carbon steels where the carbon content is up to 0.25%, medium-carbon steels contain from 0.25 to 0.65% additives, high-carbon ones contain more than 0.65% of carbon in the composition.
Other signs of classification
All types of studied material are divided into three categories, depending on the total content of alloying elements in steel. The designation of these groups is low-alloyed, medium-alloyed, and highly alloyed. In the first case, the total mass fraction of additives does not exceed 2.5%, for the second group - no more than 10%, for the third group - from 10 to 50%.
Further, it is worth noting that, depending on the properties that alloying elements give to steel, its internal structure changes. It also requires understanding. In this case, using the designation of alloying elements in steel, you can determine the structure of the product. And on this basis to conduct another classification:
- The hypereutectoid class of steel is too high a ferrite content in the composition.
- The eutectoid class indicates the pearlitic structure of the goods.
- The hypereutectoid product group is characterized by a structure containing secondary carbides.
- The ledeburite class of the material contains primary carbides.
The main components and their influence
Many different components are added to steel. The designation of elements in alloy steels is carried out using letters, most often the first capital letters of the name of the component itself.
You can start with chrome and nickel. They are designated respectively by the letters X and N. If we talk about the effect of chromium, it increases the resistance of steel to corrosion. In addition, strength and hardness are also increased. Chrome is considered the main alloying component in the manufacture of stainless products.
The designation of the elements in the grades of alloy steels helps to quickly determine the properties of the material and its purpose. So, the marking “H” indicates the nickel content, which means that the substance has a high viscosity, greater ductility and good resistance to corrosion.
Additional alloying elements
Next, it should be said about titanium (T) and vanadium (F). An increase in the T content indicates a decrease in the graininess of the structure, due to which strength and density increase. In addition, rust resistance is improved and processing is simplified. As alloying elements in steel grades, vanadium is also indicated by the letter F. In this case, it also contributes to a decrease in grain size, but the result is somewhat different and consists in improving the yield and increasing tensile strength.
Next, talk about molybdenum (M) and tungsten (B).
The introduction of "M" in the composition improves the hardenability of products, increases resistance to corrosion, reduces brittleness. "B" also reduces brittleness during tempering, while heating does not allow the grains to increase, in addition, increasing the overall hardness.
The letter designation of alloying elements in steel sometimes does not coincide with their name in Russian. So, one of the controversial additives - silicon, is indicated by the letter C. If there is only 1-1.5% of this substance in the composition, it can increase strength and at the same time maintain viscosity. If you begin to increase the content of the component in the structure, then the electrical resistance and permeability will increase. In addition, silicon is able to increase elasticity, corrosion resistance and oxidizability. However, with all this, it must be borne in mind that it increases the fragility of steel.
The last two additives are cobalt (K) and aluminum (Yu). The addition of the first element increases the heat resistance and impact resistance. Aluminum increases resistance to scale.
What are impurities?
Speaking of the designation of alloying elements in metal grades, one cannot but mention impurities. Firstly, their presence also affects the properties of the products. Secondly, it is impossible to completely get rid of their presence in the composition of the substance, and therefore their mass fraction is periodically indicated in the labeling.
Various impurities and their influence
The letter A is nitrogen. If available, it is usually indicated approximately in the middle of the marking. In its properties, it is identical to the presence of oxygen. If a certain mass fraction of one of these two elements is exceeded, the material increases brittleness. In addition, characteristics such as viscosity and endurance will decrease.
The controversial impurity is carbon (U). If it contains up to 1.2%, then it can have a positive effect, increasing hardness, strength, yield strength. If even a slight excess of this indicator is observed, then both strength and ductility will rapidly deteriorate.
Manganese (G) and sulfur also belong to impurities. Manganese, like carbon, has a different effect depending on the mass fraction in the structure. If the content of the element "G" does not exceed 0.8%, then it can be called a technological admixture. It increases the degree of deoxidation of steel, reduces the negative impact of sulfur on the product.
If the mass fraction of the second element exceeds 0.65%, then it has a significant detrimental effect. Plasticity, corrosion resistance and impact strength drop significantly. An increase in sulfur in the composition will also worsen the possibility of welding steel.
The last harmful impurity is hydrogen. An increase in the mass fraction of this component leads to a significant increase in fragility.
Labeling Overview
Symbols of alloying elements in steels according to GOST 4543-71 were caused by the fact that there are a lot of materials improved in this way. According to these rules, a letter is first indicated, and after it a number indicating the quantity of this element. You can consider this with an example of a brand such as X5CrNi18-10.
It should be said right away that labeling does not always occur in Russian letters, sometimes in another language, as indicated by an example. In this case, the decoding looks like this: the letter "X" indicates that the alloy belongs to the stainless steel category from a magnetic or chromium group; the number 5 is the carbon content, which in this case is 0.05%; Cr and Ni are chromium and nickel, respectively, and 18 and 10 are their percentage, respectively. That is, the structure of this type of product contains 0.05% carbon, 18% chromium and 10% nickel.
Marking other groups
The designation of the alloying elements that make up the steel can also indicate their belonging to a certain category of products. So, stainless chromium-nickel will have the letter “I” at the beginning of its marking. Ball-bearing and high-speed tool steels at the beginning will have, respectively, the marking "Sh" and "P".
Alloy steels can be high quality or even particularly high quality. In this case, at the end of the marking, “A” or “W” is added to them, respectively. Conventional alloy steels at the end of their marking simply do not have such designations.
It is worth noting here that sometimes a special designation is added to alloy steels if the material was obtained by rolling. In this case, the marking contains either "N" - rolled steel or "TO" - heat-treated steel.
Element Designation Sequence
To determine the most accurate chemical composition of the product, you will have to look at its documentation, however, the ability to understand the labeling can help determine the main alloying additives and impurities.
So, if at the beginning of the marking of steel any number is indicated, then it determines the mass fraction of carbon in the composition in hundredths of a percent. After this, the listing of the additives that make up the alloy steel begins. Immediately after each letter in the designation will be indicated by a figure showing the quantitative content of the chemical element in the composition in percent. However, it also happens that immediately after the letter there is no digit at all. This means that the content of this element in the composition does not exceed 1.5%, which is quite small.
Different alloy steels
In the end, it is worth noting why these types of metal are usually used. There is alloy steel tool type. As the name implies, it is widely used for the production of any tools. It is usually compared to ordinary carbon steel. A chemically improved composition has greater hardness and strength, but all alloyed compositions exhibit greater brittleness than conventional carbon.
Well-proven steel, belonging to the group of high-speed. Such material is characterized by high hardness and red resistance up to 600 degrees Celsius.
A separate large group are structural alloyed steels with special characteristics. That is, it can be stainless products, metal with improved electrical and magnetic characteristics and others.
As can be seen from all of the above, alloyed material is currently used very actively in many industries. For this reason, to know and be able to understand the designation of this kind of steel is worth everyone who is going to deal with it.