What is alloyed steel - composition, properties, brands, GOST, purpose, processing
Perhaps, there is no such person in the world who would not hear about the most common alloy of iron on earth - steel. Besides the fact that the material has many varieties, it is used in the production of virtually any iron structures and objects. Moreover, special attention deserves alloyed alloys, which have special properties. In modern industry it is difficult to find any industry where no alloyed steel is used. What is and how does this species differ from all the others?
What is this stuff?
Ordinary steel is a compound of iron carbon and a number of impurities. Under the definition of "alloy steel" (LS) means a special alloy, which is obtained by introducing a certain number of chemical elements.This is done in order to obtain the necessary physical and chemical properties of the metal.
As a rule, such elements of the periodic table are added, without which it is difficult to manage, depending on the specific situation:
- Nickel - N (Ni).
- Copper - M (Cu).
- Niobium - B (Nb).
- Chrome - X (Cr).
- Manganese - T (Mn).
- Silicon - C (Si).
- Vanadium - F (V).
- Tungsten - In (W).
- Molybdenum - M (Mo).
- Titanium - T (Ti).
- Aluminum - A (Al).
- Zirconium - C (Zr).
- Cobalt - K (Co).
But besides them, molybdenum with aluminum is used. In addition, each of these elements is added for a specific purpose. And their number directly affects the obtaining of the necessary qualities. Now it is becoming a little clear what alloy steel is.
Some of them, improving some specific properties of the material, underestimate other qualities. For example, with the help of manganese, it is possible to significantly increase the strength and hardness of the metal along with the improvement of the cutting qualities. At the same time, this leads to an increase in grain, which reduces the resistance to shock loads.
Adding chromium, on the contrary, can increase these qualities and at the same time increase the heat resistance. Thanks to nickel, the alloy becomes more elastic, and if its amount prevails, the metal acquires high rates of corrosion resistance and heat resistance.Stainless steel, which everyone knows about, is just an alloy of the last two metals or a material with a chromium content of 27%.
Everyone who knows what a alloy steel is, what doping is, is not fully understood. So, the essence of it is to add these elements. But back to our "impurities" - molybdenum on the one hand increases the hardness, but on the other - leads to a decrease in brittleness. At the expense of tungsten, it is possible to increase not only hardness, but also strength, and with it the cutting qualities of the metal. Moreover, when heated to a high temperature (600-650 ° C), these properties are not lost (red hardness).
Silicon allows you to increase the elasticity of the material, as well as resistance to acids. Adding vanadium increases the plastic properties by reducing the grain. Titanium allows you to get a more durable material.
Now it is clear what alloy steel is. But at the same time you should be aware of the presence of some impurities, which, regardless of the grade of steel, are always present in it. In most cases, these are non-metals:
- Oxygen and Nitrogen.
Carbonmost influences the properties of steel. If it contains no more than 1.2%, then the material is characterized by high hardness and strength. Also increases the yield strength. The excess of this norm leads to a decrease in strength and ductility.
Great contentsulfuralso not good. More than 0,65% - impact strength, corrosion resistance, ductility is reduced. But, in addition to this, the weldability of steel is significantly reduced.
FROMphosphorusone has to be extremely attentive, since its excess, even slightly, adversely affects the metal. Viscosity and plasticity decrease, at the same time brittleness and fluidity increase. All this may affect the processing of alloyed steels.
Excessoxygenandnitrogenleads to excessive brittleness of the material, as well as lower its viscosity.
High contenthydrogenalso gives the metal brittleness, which is undesirable.
Varieties of drugs
Depending on the amount of alloying additives, steel can be divided into three types:
- Low alloy steel - contains no more than 2.5% of additives.
- Medium alloyed steel - the number of alloying elements varies from 2.5 to 10%.
- High alloy steel - here we are talking about a higher content of 10% and higher.
It takes into account the total amount of alloying additives.
To obtain certain qualities, alloyed steels undergo a process of normalization. This is when the material is heated to a temperature of 900 ° C, and then it is cooled in air.
Based on this, the “marking” of alloyed steels may look like this:
- Pearlite - the content of alloying additives for such steels ranges from 5% to 7%. The following structures are obtained: perlite, sorbitol, reed.
- Martensitic - here alloying elements are more than 7-15%, carbon is not more than 0.55%.
- Austenitic - in addition to the content of alloying elements (more than 15%), nickel (8%) and manganese (13%) are present here. The carbon content is not more than 0.2%.
- Ferritic - such a carbon structure also contains no more than 0.2%. While chromium is 17-30% here, silicon is 2.5% (not less). Such steels can be attributed to low-carbon.
- Carbide (ledeburitnaya) - this is high carbon brands (0.7% C). Mainly contain tungsten, vanadium, molybdenum and chromium.
The production of a different grade of alloyed steel, or rather its structure, depends not only on the rate of cooling of the metal in air, but also on the amount of alloying additives and carbon.
Features labeling drugs
At the beginning of the article in the list of alloying elements there are letters near each of them, which is not accidental. It is they who label these metals, but in addition to them there are still numbers. An example is given below.
All this is done according to GOST 4543-71. The alphanumeric designation is not accidental, because all alloy steels have a wide range. And in such a variety is easy to get confused, and therefore the need to systematize.
In addition, each letter of the Cyrillic alphabet (followed by the first) in the designation indicates the presence of one or another element, and the number (usually after the letter) - the content in percent. In this case, if we are talking about the amount of less than 0.99%, then the number is usually not put.
Sometimes rare-earth metals such as yttrium, lanthanum and a number of others can be added to the alloy. In this case, in the designation of steel alloyed according to GOST, only one letter is indicated - Ch. There are other features in the steel marking:
- The first two digits always indicate the percentage of carbon that is never literally denoted.
- If it is high-speed steel, then the content of tungsten is indicated in whole fractions of a percent.Chromium in such alloys is usually 4%.
- For ball-bearing steel, after letters ШХ follows the designation chromium content in tenths of a percent.
- The presence of two letters “A” indicates highly pure alloy steel.
Take for example two markings:
- 03H13AG19-LS contains 0.03% carbon, 13% chromium, 1% nitrogen and 19% manganese.
- 18HGT - this steel has carbon 0.18%, and chromium, titanium and manganese 1% each.
In addition, at the very beginning of any marking of alloyed steels there may be a letter that indicates special-purpose material:
- Electrotechnical - E.
- High-speed - R.
- Ball bearing - W.
- Avtomatnaya - A.
Alloy steels can still belong to the category of high-quality or especially high-quality metals.
In this case, at the end of the marking there will be the letter “A” or “III”, respectively.
All alloy steels have a number of valuable advantages, among which it is worth highlighting:
- the increased resistance to deformations of lamellar character;
- high hardness;
- resistance to cold breaking and viscosity;
- technological quality at a high level.
In addition, this steel is not prone to warping or other defects during the hardening process.
With all the obvious advantages that alloyed tool steel has, or others, there are also disadvantages:
- They are characterized by dendritic segregation, but, fortunately, this can be avoided by conducting diffusion annealing.
- High alloyed grades may contain residual austenite, which reduces the resistance to fatigue and hardness of the material.
- The appearance of flocs, the so-called cracks in the structure of steel, is not excluded. This defect can be avoided by slowing down the cooling of the metal, as well as reducing the hydrogen content during smelting.
Depending on the type of heat treatment, most defects are avoided. As a result, steel acquires the necessary, sometimes unique qualities.
The production process of alloyed tool steels or others takes place in several stages using electric arc furnaces:
Duringcleaningiron ore gets rid of undesirable impurities, such as sulfur and phosphorus. All this happens in an open-type melting furnace. The technology of secondary treatment of steel is also used.Another technological process needed is vacuum melting, which results in the removal of arsenic and a number of non-ferrous metal impurities.
Forswimming trunksThe electric arc furnace is already used for metal, for which the raw material is heated to a high temperature of 400-600 ° C. Here, iron begins to turn into iron, which is characterized by an unstable crystal lattice. But by stabilizing it produces some kind of alloy steel.
This is done as follows. Oxygen enters the working chamber, during combustion of which the atmosphere of the chamber is supplied with carbon. It begins to mix with iron, which leads to the formation of steel.
Then they start to add various raw materials.supplementsdepending on the required properties of the metal. The crystal lattice becomes more dense, and as a result, alloy products are obtained.
In the smelting manufacture of drugs does not end. After that, you need to harden it. Smelted specimens undergo a tempering procedure at a temperature of 1100 ° C. After it, the release of carbon and alloyed steels is needed, and this is done gradually, in order to avoid the appearance of cracks.
This process is required for all hardened parts.His main task is to relieve internal stresses. This reduces the hardness and ductility increases. For vacation can be used different means:
- with molten alkali.
- Oven with forced air circulation.
As for the tempering temperature, it depends on the brand of drug and the required hardness of the material. For example, for HRC 59-60 it is 150-200 ° C. For high-speed drugs, a temperature mode is needed a little more - 540-580 ° C. This is also referred to as secondary hardening, since the hardness of the part increases.
As a rule, after the tempering process, the steel is cooled in the open air. But chromium-nickel products are an exception - they need a bath with water or oil. If cooling is delayed, it will lead to excessive brittleness of the metal.
As for the purpose of alloyed steel, this is practically any sphere of human activity. The tool metal is used to produce cutters, cutters, dies, measuring devices, gears, springs, suspensions, stretch marks, and more. Stainless LS is ideal for the manufacture of dishes, cases of household appliances.
The process of welding drugs is fully dependent on the chemical composition of the metal. Moreover, unlike alloying elements, carbon has the most effect. At the same time, the additives themselves have a different effect on welding. For example, the presence of chromium and manganese to a greater extent leads to the formation of cracks, rather than nickel. But titanium in this process acts quite favorably.
Due to the large amount of sulfur, phosphorus and dissolved gases, the weldability of steel deteriorates significantly. Therefore, their content should not be more than 0.020-0.055%, which will in no way affect the welding of alloyed steels.