TECHNICAL INFORMATIONAnasayfa / Technical Information / Steel Alloys
Mn, Si gibi elementlerinin bir veya ikisinin çeliğin içindeki değerleri, (en az Mn %1,65 – Si %0,60) geçmiyor ve kimyasal bileşiminde başka herhangi bir alaşım elementinin belirli bir miktarda (en az) bulunması istenmiyorsa bu çelikler, karbonlu çelikler sınıfına girer.
If the values of one or two of the elements such as Mn and Si in the steel do not exceed (at least Mn 1.65% – Si 0.60%) and if it is not desired to have any other alloying element in a certain amount (at least) in its chemical composition, these steels are carbon steels. enters the group.
Steels made by adding one or more alloying elements in order to gain unique properties that cannot normally be obtained from carbon steels are alloy steels. One or more of the alloying elements such as Mn, Si are more than Mn 1.65% Si 0.60% in the steel and other elements added to them (Al, B, Cr, Co, Mo, N, Ti, W, V) , Zr) one or more of the steels that are desired to be found are classified as alloyed steels. The difference between the lower and upper limit values of the alloying elements of the alloy steel is very small, and as the number of alloying elements increases, the number of unsuitable castings also increases. Alloyed steel ingots and billets are slowly cooled in special well pits so that they do not cause possible cracks both on the face and inside. Also, before rolling and forging, errors are finally removed. For these reasons, alloy steel making is more difficult than carbon steels.
It is the most important of the alloying elements in the steel and the element that affects the mechanical properties the most. As the carbon ratio increases, the hardness, strength, water absorption and hot rolling properties of the steel increase. On the other hand, flexibility, forging, hot forming, elongation, welding, cutting properties weaken the machining ability. The material can be given rare properties by adding special alloy elements without spoiling the structural characteristics of carbon steel. Thus, normal carbon steels have a prototype feature in the evaluation of microscopic structure and alloy effects by comparison. It does not affect the corrosive resistance of the steel against humidity, acids and hot gases.
It is an alloying element that improves the strength of steel. Slightly reduces its flexibility. It has a positive effect on forging and welding. The feature of manganese, which increases its hardness and strength, depends on the amount of carbon. The effect of manganese in high carbon steels is greater than in low carbon steels. Manganese increases the quenching depth. It improves its resistance to rust and corrosion.
It increases the physical strength and specific gravity in steel castings. Silicon is an element found in all steels, such as manganese. In steelmaking, some silica from iron ore or bricks with a furnace lining enters the steel itself. Silicon steels statement; It is used for steels with more than 0.40% silicon in their composition. Although the presence of silicon in steel negatively affects flexibility, it increases the tensile strength by 10 kg/mm² and the yield strength similarly for each 1% increase. Since steels with 14% silicon are resistant to chemical reactions, steels in this state cannot be forged.
Phosphorus; it is generally known as harmful to steel, the percentage of phosphorus in high quality steels is kept between 0.030-0.050 at most. Only in free cutting steels, the sulfur content is increased much higher than in normal steels, as it makes the chips brittle. In addition, it increases the resistance to corrosion and abrasion, it also reduces the notch toughness and increases the possibility of cracking during welding.
Sulfur; makes the steel brittle and difficult to roll. It is an element that is considered as undesirable foreign matter such as phosphorus, unless it is possible to increase the machinability of the steel. Normally the allowable amount is limited to a maximum of 0.025-0.050%. Only in free cutting steels, the sulfur content is increased to a much higher level (4%) than in normal steels, as it makes the chips brittle.
Chromium; It is an alloying element that increases the strength property of steel but, on the other hand, negatively affects its flexibility to a very small extent. Chromium increases the heat resistance of steel. The crust prevents scale-making. The high content of chromium in it; It increases the corrosion resistance of steel. In chromium stainless steels, as the chromium content increases, its weldability decreases. Chromium forms carbide, which is unstable. For each 1% increase in the chromium percentage in steel, an increase of approximately 8-10 kg/mm² is observed in the tensile strength. Although not within the same ratio, the notch strength decreases as the yield strength increases.
Nickel; It increases the strength of steel less than silicon and manganese. Nickel in steel, especially when combined with chromium, makes the hardness go deep. Chromium-nickel steels are stainless, resistant to incrustation and heat. It increases the notch strength of machine building steels especially at low temperatures. Nickel increases the strength of tempered and cemented steels, and is a suitable alloying element for steels with the desired structure and steels that are resistant to corrosion and incrustation.
Molybdenum increases the tensile strength of steel, especially its heat resistance, and its ability to be welded. The high amount of molybdenum makes it difficult to forge steels. Molybdenum is used more often with chromium. The effect of molybdenum is similar to wolfram. In alloy steels, when molybdenum is used together with chromium-nickel, it increases the yield and tensile strength. Since molybdenum forms strong carbide, it is used in air and hot work steels, austenitic rust resistant steels, cementation, machine building steels and heat resistant steels.
Vanadium increases the heat resistance of steel when used in very low amounts. Vanadium ensures that the grain structures of alloyed machine structural steels are fine and their physical properties are improved. It also keeps steel inserts sharp for longer. The amount of vanadium generally found in alloyed machine building steels varies between 0.03 and 0.25%. It has a strong tendency to make carbide. It increases the tensile and yield strength of steel. It is used with tungsten in machine building and hot work steels, especially vanadium chromium, air hardening steels and machine building steels.
Tungsten is an alloying element that increases the strength of steel. In tool steels, it increases the hardness of the cutting edges, extends the service life and provides high temperature resistance. In this respect, it is widely used as an alloying element in air steels, tool steels and reclamation steels. The presence of tungsten in steel improves weldability up to certain percentages. Each tungsten percentage added to the steel increases the yield and tensile strength up to 4 kg/mm². Tungsten has a strong tendency to form carbide and is preferred in the production of heat resistant steels, as it ensures that the steel does not become tempered and lose its hardness at high operating temperature.
Even if it is added at very low rates (such as 0.001), heat treatment causes the hardness to reach deep in quenching steels and increase the strength of the center parts of the cementation steels. Boron can be used instead of a large percentage of other alloying elements without deteriorating the mechanical properties of hardened and tempered steels. In addition, due to its high neutron absorption, it is the main alloying element in the steels used in the construction of nuclear power plants.
It is a very strong oxidizer (deoxidant) and nitrogen absorber. If it is used in small amounts, it reduces the tendency of steels to age and causes the thinning of their crystals. In addition, it takes the gases melted in the liquid metal and prevents pitting and decomposition in the steel. It is used as an alloying element in iron, nickel, cobalt and aluminum magnet steels, since aluminum forms very hard nitrides with nitrogen, reduces corrosion in nitride steels, heat-resistant steels in ferritic oil, and increases the coercive strength.
Calcium does not mix with iron. Although it is known that small amounts of calcium are found in steel from time to time, these amounts are thought to consist of non-metallic masses. Calcium has a lower melting point than iron. Therefore, it causes great difficulties in adding calcium to steel. It can easily combine with other alloying elements. It is used for the purification of sulfur and phosphorus and for deoxidation (deoxidation) in the form of silicon-calcium together with silicon. Calcium reduces hot scale formation in high temperature resistant steels.
It does not cause carbide formation in steel, thus increasing hardness. On the other hand, it prevents crystal growth and strength reduction at high temperatures. Therefore, it is an important alloying element in air steels, hot work steels and steels operating at very high temperatures. It increases corrosion and wear resistance, provides a slow increase in tensile and yield strengths, but reduces its tensile strength. In addition, it is the main alloying element of high value magnet steels as it increases the remanence, coercive power and thermal conductivity properties of steels.
Copper increases the tensile strength and yield limit in steels, and reduces elongation. It does not affect the weldability of the steel. It is added to steel to improve atmospheric corrosion resistance. The amount of copper in the steel is between 0.2% and 0.5%. It makes it difficult to shape in the heat. Its most characteristic feature is that it reduces the tendency of steels to rust under the influence of atmosphere.