Steel is one of the most sought after materials in the world today. Without it, it’s difficult to imagine any existing construction site, machine-building enterprises, and many other places and things that surround us in everyday life. However, this alloy of iron with carbon can be quite different, therefore, in this article we will consider the influence of alloying elements on the properties of steel, as well as its types, grades and purpose.
general information
Today, many brands have become widely used in almost any area of human activity. This is largely due to the fact that this alloy optimally combines a whole range of mechanical, physico-chemical and technological properties that do not have any other materials. The process of steelmaking is constantly being improved and therefore its properties and quality make it possible to obtain the required performance indicators of the resulting mechanisms, parts and machines.
Intended classification
Each steel, depending on what it is created for, can be included in one of the following categories without fail:
- Constructional.
- Instrumental.
- Special purpose with special properties.
The most numerous class is structural steels designed to create a variety of building structures, devices, machines. Structural grades are divided into improved, cemented, spring-spring, high-strength.
Tool steels are differentiated depending on what tool they are produced for: cutting, measuring, etc. It goes without saying that the influence of alloying elements on the properties of steel of this group is also great.
Special steels have their own division, which provides for the following groups:
- Corrosion-proof (they are also corrosion resistant).
- Heat resistant.
- Heat resistant.
- Electrical Engineering.
Chemical steel groups
The classification of voiced steel, depending on the chemical elements that form them:
- Carbon steel grades.
- Alloyed.
At the same time, both of these groups are additionally separated by the amount of carbon contained in them by:
- Low carbon (carbon fiber less than 0.3%).
- Medium carbon (carbon concentration is 0.3 - 0.7%).
- High carbon (carbon fiber more than 0.7%).
What is alloy steel?
This definition should be understood as steels, which contain, in parallel with constant impurities, also additives introduced into the alloy structure, in order to increase the mechanical properties of the ultimately obtained material.
A few words about the quality of steel
This parameter of this alloy implies a set of properties, which, in turn, are directly determined by the process of its production. Similar characteristics to which alloyed tool steels obey include:
- Chemical composition.
- The homogeneity of the structure.
- Manufacturability.
- Mechanical properties.
The quality of any steel directly depends on how much oxygen, hydrogen, nitrogen, sulfur and phosphorus it contains. The method of obtaining steel also plays a significant role. The most accurate from the point of view of getting into the required range of impurities is the method of steelmaking in electric furnaces.
Alloy steel and changing its properties
Alloy steel, the grades of which contain lettering of forced elements in their markings, changes its properties not only from these third-party substances, but also from their mutual action between themselves.
If we consider specifically carbon, then by interaction with it alloying elements can be divided into two large groups:
- Elements that form a chemical compound (carbide) with carbon - molybdenum, chromium, vanadium, tungsten, manganese.
- Carbide-free elements - silicon, aluminum, nickel.
It is worth noting that steels that are alloyed with carbide-forming substances have a very high hardness and increased wear resistance.
Low alloy steel (grades: 20HGS2, 09G2, 12G2SMF, 12KHGN2MFBAY and others). A special place is occupied by alloy 13X, which is hard enough for the manufacture of surgical, engraving, jewelry equipment, razors.
Decryption
The content of alloying elements in steel can be determined by its marking. Each of these components introduced into the alloy has its own letter designation. For instance:
- Chrome - Cr.
- Vanadium –V.
- Manganese –Mn.
- Niobium - Nb.
- Tungsten –W.
- Titanium - Ti.
Sometimes at the beginning of the steel index are letters. Each of them has a special meaning. In particular, the letter "P" means that the steel is high-speed, "" indicates that the ball bearing steel, "A" is automatic, "E" is electrical, etc. High-quality steels have in their alphanumeric designation at the end letter "A", and especially high-quality letters contain the letter "" at the very end of the marking.
Impact of alloying elements
First of all, it should be said that carbon has a fundamental effect on the properties of steel. It is this element that provides, with an increase in its concentration, an increase in strength and hardness with a decrease in viscosity and ductility. In addition, an increased carbon concentration guarantees a deterioration in machinability.
The chromium content in steel directly affects its corrosion resistance. This chemical element forms a thin protective oxide film on the surface of the alloy in an aggressive oxidizing environment. However, to achieve such an effect in chromium steel should be at least 11.7%.
Of particular note is aluminum. It is used in the process of alloying steel to remove oxygen and nitrogen after it has been purged in order to help reduce the aging of the alloy. In addition, aluminum significantly increases toughness and fluidity, and neutralizes the extremely harmful effect of phosphorus.
Vanadium is a special alloying element, due to which alloyed tool steels get high hardness and strength. At the same time, grain decreases in the alloy and density increases.
Alloy steel, grades of which contain tungsten, is endowed with high hardness and red resistance. Tungsten is also good because it completely eliminates brittleness during the planned vacation of the alloy.
To increase the heat resistance, magnetic properties and resistance to significant impact loads, steel is alloyed with cobalt. But one of those elements that does not have any significant effect on steel is silicon. However, in those steel grades that are intended for welded metal structures, the silicon concentration must be necessarily in the range of 0.12-0.25%.
Significantly improves the mechanical properties of magnesium steel. It is also used as a desulfurizer in the case of using implanted desulfurization of cast iron.
Low alloy steel (its grades contain alloying elements of less than 2.5%) very often contains manganese, which provides it with an indispensable increase in hardness and wear resistance while maintaining optimal ductility. But at the same time, the concentration of this element should be more than 1%, otherwise it will not be possible to achieve these properties.
Carbon steel grades, smelted for various large-scale building structures, contain copper, which provides maximum anti-corrosion properties.
To increase the redness, elasticity, tensile strength and corrosion resistance, molybdenum is necessarily introduced into the steel, which also increases the oxidation resistance of the metal when heated to high temperature values. In turn, cerium and neodymium are used to reduce the porosity of the alloy.
Considering the influence of alloying elements on the properties of steel, nickel cannot be ignored. This metal allows steel to obtain excellent hardenability and strength, increase ductility and impact resistance and lower the cold brittleness limit.
It is very widely used as an alloying additive and niobium. Its concentration, which is 6-10 times higher than the amount of necessarily present carbon in the alloy, eliminates intergranular corrosion of stainless steel and protects welds from extremely undesirable destruction.
Titanium allows you to get the most optimal indicators of strength and ductility, as well as improve corrosion resistance. Those steels that contain this additive are very well processed by various special-purpose tools on modern metal-cutting machines.
The introduction of zirconium into the steel alloy makes it possible to obtain the required grain size and, if necessary, influence precisely the grain growth.
Random impurities
Arsenic, tin, antimony are extremely undesirable elements that have a very negative effect on the quality of steel. Their appearance in the alloy always leads to the fact that steel becomes very brittle along the boundaries of its grains, which is especially noticeable when winding steel strips and during the annealing of low-carbon steel grades.
Conclusion
Nowadays, the influence of alloying elements on the properties of steel is fairly well understood. Experts carefully conducted an analysis of the effects of each additive in the alloy. The obtained theoretical knowledge allows metallurgists already at the stage of placing an order to formulate a schematic diagram of steelmaking, determine the technology and the amount of consumables required (ore, concentrate, pellets, additives, etc.). Most often, steelmakers use chromium, vanadium, cobalt and other alloying elements, which are quite expensive.