Efficient calcium treatment is a major challenge in secondary metallurgy. Many factors influence it including the chemical composition of slag, oxygen and sulfur content in the liquid steel, etc.
The low density and high reactivity of pure Ca make it difficult to introduce it into the steel melt. Cored wire is an efficient way to inject calcium into the steel melt. It eliminates alumina nozzle clogging and spheroids inclusion shape while improving steel purity.
In Al-killed and –killed steels, efficient calcium treatment is a must. It eliminates alumina nozzle clogging in continuous caster, spheroidizes oxide and sulphide inclusions and increases the transverse toughness of the steel. Besides this, it improves the steel purity. Due to its strong affinity for oxygen and sulfur, calcium has a secondary effect in deoxydation and desulfurization by forming CaO first followed by oxysulfides and finally sulfides.
Adding pure calcium to liquid steel is quite difficult, mainly due to its low boiling point and violent reaction with molten steel. Cored wire is the best technology to introduce it into the liquid metal. This new alloy addition method enables a high performance/recovery while ensuring a complete calcium addition in the steel melt with minimal consumptions and without affecting the casting process. The new PapCal and HDx wires represent the State of the art in terms of calcium treatment. They guarantee a perfect calcium addition to the liquid metal thanks to a specific formulation and to the use of thermal insulation layer.
Calcium silicon alloy is an ideal compound deoxidizer and desulfurization agent. It is widely used in steel industry, especially for continuous casting machine as temperature gaining agent and inoculant for cast iron production.
It can be used as a deoxidizer in the furnace to avoid nozzle clogging, and it can also spheroidize oxide and sulphide inclusions. Besides, it can increase the transverse strength of steel and improve its cast ability.
Core wire is a new treatment in secondary steel refining developed on the basis of jet metallurgy technology. It can purify molten steel, change the shape of inclusions, and reduce its cost.
Moreover, it can also help to eliminate air and liquid inclusions in the molten steel by using different ratios of silicon and calcium. It can be used to replace bulk alloy feeding method or powder spraying method. It can greatly reduce the splashing and inhalation of gas, and thereby significantly improve the safety and environmental protection of the ladle.
The atomic structure of calcium sulfide reveals that it is an ionic solid. It forms in a similar fashion to sodium chloride with an octahedron of six Ca2+ ions surrounding an octahedron of S2- ions. In the presence of air it decomposes, forming the oxides CaO and CaS. The formation of these two compounds is the reason for the high melting point of calcium sulfide, which is around 1450 degC.
Pure calcium is a useful addition agent for the treatment of silicon killed steels, e.g. for the desulfurization, globularisation of alumina inclusions and for improving transverse strength. Due to its low density and reactivity with oxygen, it has to be introduced into the liquid steel by special addition methods.
Core wire is a proven refining technology which allows the addition of calcium to molten steel by injection. This method avoids the reaction of calcium with slag and aeration, increases absorption of alloying elements and allows for the control of the shape of included impurities.
Steel fabricators must introduce the necessary amount of calcium to their molten metal at just the right moment, without allowing it to interact with oxygen and become oxidized. This interaction would create sulfides and oxides, which could adhere to the internal walls of flow regulation nozzles in continuous casting installations and block them.
Cored wires are designed to solve this problem by enabling the addition of calcium in the steelmaking process without reacting with oxygen, slag or refractories. They are comprised of a calcium core encased in a ferroalloy sheath that protects it from reactions with these substances.
The new HDx calcium cored wire developed by TITAN is based on this technology. It allows the metallurgical results obtained with conventional calcium treatment to be achieved by a lower consumption of calcium, resulting in a significant reduction in the costs of the calcium treatment. Its use is a valuable contribution to increasing the productivity of the steelmaking process and its efficiency, while ensuring the highest quality of the steel produced.
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