Calcium silicon aluminum manganese alloy is widely used as deoxidizer, desulfurizer and to change the form of steel impurities, improves the quality of molten steel and casting. It is a composite material with a metallic calcium core and an aluminum jacket.
It can be inserted into molten steel or iron through professional wire feeding equipment vertically and the aluminum jacket melts in ideal position. It reduces splashing and gives more consistent results than powdered calcium and aluminum.
A calcium cored wire is a steel strip that has been rolled and stuffed with alloy powders. It consists of a reactive metal, typically calcium, surrounded by a sheath of a non-reactive metal such as aluminum. This type of cored wire is typically characterized by its use in the treatment of molten ferrous metals.
The metallurgical properties of calcium silicon aluminum manganese alloy make it an excellent composite deoxidizer, desulfurizer and inclusion modifier. It is widely used in secondary steel refining, particularly in converters and ladles. This type of cored wire allows a higher percentage of refractory metal and alloy additions to be injected into the iron and steel melt while maintaining the desired chemistry in the resulting molten metal.
In addition to its metallurgical properties, the use of cored wire improves the efficiency of the injection process by reducing wire feed times. This is accomplished by enabling the cored wire to be inserted into the molten metal bath at an ideal depth through professional wire feeding equipment.
Since Ca exists in vapour form at molten steelmaking temperatures, its reaction with oxygen (O) and sulfur (S) is limited to the surface of the slag, unless slag particles are added. Consequently, the injection of cored wires into a molten steel bath must be carried out as intimately as possible to achieve satisfactory metallurgical results.
In addition to calcium, silicon is often added to the iron or steel melt to improve the overall quality of the metal. However, metallic calcium has several inherent problems such as its reactivity and splashing when it is introduced into the molten metal ladle, poor recovery due to evaporation with air or slag, short shelf life of powdered calcium, and high treatment costs. These problems can be overcome by using a cored wire which contains both a metallic calcium core and a silicon coating.
The cored wire comprises a solid inner metallic core of calcium metal encased within a metallic sheath of, for example, steel which is continuously roll formed over the core and protected with a continuous sheath seam or lock seam. The sheath can contain between 15 and 85% of the total wire weight with the remainder being made of the composite calcium/aluminum core. Steel contents higher than 85% result in a wire that is stiff and difficult to handle while lower levels of steel content give insufficient protection of the reactive core material.
The cored wire is vertically and stably inserted into the molten metal bath, such as a steel ladle at an ideal depth by the wire feeder. This allows the chemically active silicon-calcium alloy to play a significant role in improving the overall quality of the iron or steel metallurgy through deoxidation, desulfurization and inclusion modification.
Cored wire is used in a variety of applications in the steel industry, most notably as a deoxidizer or desulfurizer. The calcium in the core acts to prevent oxidation and re-nitriding of the molten metal bath as well as reducing slag formation. The aluminum in the core also reduces reactivity, which can lead to a re-nitriding of the metal or splashing. The calcium/aluminum core also increases the overall yield of a process that would otherwise require multiple steps to accomplish.
Using a cored wire eliminates many of the problems that arise when trying to introduce calcium additives in the form of particulate material. This includes surface oxidation and hydration, dangerous handling due to the hygroscopic nature of metallic calcium, non-uniform fill rates caused by mixing powders with different diameters and morphologies, and the potential for burning or combustion of the paper encasing the cored wire.
U.S. patent 4,481,032 describes a shaped cored wire with a solid calcium core, a steel liner, and a paper wrapper. This cored wire is then inserted into a molten metal bath, e.g., a liquid aluminum steel bath, to introduce calcium and/or alumina to that metal bath. Numerical simulations of the thermal path of this cored wire show that the combustion of the paper encasing the steel lining is prevented by radiation, or by absorbing and reflecting the heat exchange between this paper and the liquid metal bath.
The calcium silicon aluminum manganese alloy has a high affinity for oxygen and sulfur, so it is used as a deoxidizer and desulfurizer in the steel industry. It is easy to float and improves the room-temperature properties of the molten steel, such as impact toughness and plasticity. Zinc is a tolerated impurity in the alloy and can be up to 2.5%.
The use of a cored wire allows the calcium or calcium silicon to be introduced into the steel bath in a much more controlled way. The cored wire is inserted smoothly into the steel strip and can be directed into the molten metal at an ideal depth so that the alloy powder is fully dissolved and the chemical reaction is produced. This minimizes splashing of the metallurgical additives and reduces the risk of long-term longitudinal crack formation in the steel.
The use of the cored wire also eliminates problems associated with the injection of powdered calcium into the molten steel, such as reactivity, surface oxidation and hydration. Moreover, by selecting the right mixture of calcium metal and aluminum strip diameters, widths and gages, the proper ratio of the desired composition can be achieved without blending powders with different densities or morphologies. This also makes the cored wire easier to handle and safer to use. The insulating effect of the steel-clad solid calcium core also contributes to a more reproducible calcium recovery from the ladle.
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