Calcium (Ca) is added to the liquid steel in a professional cored wire injection system. Ca reacts with oxygen and sulfur to remove them from the steel. It also purifies the molten steel by changing the nature and shape of inclusions (e.g. inter dendritic Al2O3 galaxies can be transformed into fine Type III inclusions which do not clog continuous casting nozzles).
It is an ideal composite deoxidizer and desulfurizer.
Alloys containing calcium like silicon manganese steel (CaMnSi), calcium silicide (CaSi) and calcium silicon barium (CaSiBa) are used as deoxidizers for most carbon and some stainless steel grades in submerged arc furnaces. Ca is an effective oxygen scavenger in liquid steel and provides a number of important benefits.
Firstly, it reduces the volume fraction of oxide and sulphide inclusions in the steel (the S content can be brought down to 0.001 % - 0.003 %). It also modifies the shape of the remaining inclusions so that they are less detrimental to mechanical properties in the final product. This effect is known as inclusion morphology control. For example, in Al killed steels the hard inter dendritic Al2O3 galaxies are converted to softer, more brittle, spherical inclusions called calcium aluminates or calcioaluminosilicates. This improves machinability of the finished steel as well as eliminating nozzle blockage in continuous casting.
Unlike most other deoxidizers which are added as solids, the calcium in these alloys is in vapour form at liquid steel temperatures and can therefore only react with the oxygen (O) and sulfur (S) it is intended to remove at the Ca vapour/liquid steel interface. This makes it necessary to inject these additives into the molten steel via cored wire at high rates of injection, 80-300 m/min. It is also important that the Ca/liquid steel interface be as intimate as possible so that reoxidation is minimised.
Calcium silicon alloy is an ideal composite deoxidizer and desulfurization agent. The high affinity of silicon for oxygen and calcium for sulfur make the alloy a perfect deoxidizer for purifying steel liquid. It can replace aluminum for final deoxidation in submerged arc electric furnaces (SAEZ). It also plays an important role in continuous casting to control the shape of inclusions.
The calcium in the alloy has the effect of breaking up inter dendritic inclusions and changing their shape from globular to spheroidal. This makes them less abrasive and causes fewer cracks during continuous casting. It also modifies the shape of sulfide inclusions, reducing their tendency to clog continuous caster nozzles.
In addition, the calcium in the alloy has a very low melting point, so it can be added to liquid steel without disturbing the slag-like chemistry of the iron oxides. This can help achieve the desired sulphur content and improve the quality of the steel produced by the smelter.
The composition of the alloy is based on the specific conditions of the process being used, in particular the oxygen content of the molten steel and the desired ultimate aluminum content. The deoxidizing alloy should contain up to 30 percent barium and strontium, between 20 and 40 percent calcium, and less than 50 percent iron, silicon, and aluminum. The manganese is an unavoidable contaminant and does not adversely affect the results when it is held within the normal limits for impurities in steel.
The warmer is used to make the steelmaking process more effective and improve the quality of finished products. This is achieved by reducing the amount of oxides and sulphide inclusions in the melt. It also helps to control the shape of these inclusions and improves fluidity, machinability and ductility. Compared to calcium addition through the slag, this method is much more efficient and environmentally friendly.
Since Ca exists only in vapor form at the temperatures at which it is added to the liquid steel, the addition is carried out through cored wire injection, which makes contact between the slag and the metal as intimate as possible. This reduces the formation of slag, which would otherwise clog continuous caster nozzles. It also allows Ca to react with oxygen (O) and sulfur (S) at the slag/liquid steel interface for as long as practicable, without the formation of the harmful sulphide compounds.
In addition, the presence of Ca breaks up interdendritic Al2O3 galaxies into fine Type III inclusions. This not only makes it easier for them to dissolve in the slag and improves their morphology, but also allows them to break apart during hot deformation. This is one of the key factors in achieving low inclusion levels and good fatigue resistance. It also enables the steel to be cast at higher speeds, thus improving efficiency and reducing costs.
The calcium addition is usually made after the trim additions and argon rinsing in most of the steel grades. Due to its low density and high reactivity in the ladle, Ca has to be added under special conditions to ensure it can be introduced and retained in the liquid steel. The most commonly used method is the use of cored wires, wherein a sheath of CaSi is inserted into the molten steel. This technique has the advantage of a higher recovery of Ca in steel than the virgin Ca / CaSi lumps addition into the ladle.
Silicon calcium alloy is widely used as a compound deoxidizer and desulfurization agent in the converter steel workshop, especially for rail and low carbon steel, stainless steel, nickel base alloy and other special steel and alloy production. The inoculant made of this compound alloy has strong deoxidation and desulfurization effect and can effectively control the free sulphur, oxygen, magnesium and calcium contents and reduce the non-metallic inclusions.
Adding the silicon calcium alloy powder to the head of the ingot can be an effective warming agent, and improve the quality of ductile iron, especially the mechanical properties. However, its damage control ability is still room for improvement in the actual application process through steel chemical analysis adjustments and electromagnetic swirl stirring. Using the CaSi cored wire, which is a kind of inoculant that has excellent performance in the actual application process, will be more advantageous for steelmakers.
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