Steelmaking with calcium metal is a common practice for improving steel quality. It is mainly used for deoxidation and desulfurization of the steel in liquid steel refining treating processes.
It is injected into a ladle through cored wire injection technology and guarantees that the contact time between Ca and molten steel is short, makes the oxidation of line material and efflorescence impossible.
Unlike other alloying elements, calcium is relatively inexpensive. It is found in a variety of minerals including dolomite, limestone and gypsum, the latter two being common in China. It also serves as a key raw material for making battery electrodes and is used in chemical processes to refine thorium, uranium and zirconium.
In steelmaking, the primary application of calcium metal is to control the shape and composition of oxide and sulphide inclusions. The treatment modifies the globular shapes of these inclusions, preventing them from breaking down during hot rolling and reducing directional anisotropy in through-thickness ductility.
In addition, it also reduces sulphur content to a desirable level. This is important as sulphur is a detrimental impurity in most commercial grades of steel and can cause serious problems in forming and welding. It also enables the use of lower quality iron ore, a significant cost saving. This is especially important in developing countries where the demand for steel is rising due to infrastructure construction.
The demand for metallic calcium is mainly in the steelmaking, alloying and refining industries. The raw material for the production of metallic calcium is limestone which is widely distributed and occurs naturally. It is also used as a dehydrating agent for organic solvents, and as a getter in the production of vacuum tubes.
The primary use of calcium metal in steelmaking is as a deoxidizer and desulphurizer. It decreases the volume fraction of oxide and sulphide inclusions in liquid steel, changes their composition and shape and modifies their distribution. The result of Ca treatment is a much cleaner molten steel with improved fluidity which reduces nozzle blockage in continuous casting operations.
The unique structure of the core wire enables calcium to enter into the steelmaking ladle through diathermic furnace heating back with real core metal calcium material and continuously extrude one-tenth solid wire material, guarantee that the contact time between calcium and air is short, make sure the oxidation and efflorescence does not occur in the process. This makes the low-nitrogen ferrotitanium steel-making with calcium highly efficient.
The calcium treatment is used in steelmaking to produce high quality and special type of steel. The Ca addition prevents the clogging of the caster nozzle during casting by modifying the composition and shape of the oxides, sulfides and silicates present in the liquid steel. In addition the calcium globularises the alumina inclusions and improves transverse mechanical properties of the steel.
The addition of Ca also modifies the directional anisotropy of the molten steel as it has a positive influence on the hole expansion behaviour. It is important that the reoxidation of the steel after the Ca addition is prevented as this may promote the formation of high melting point calcium aluminates rather than the desired alumina(Al2O3)/silica (SiO2) precipitates. This is achieved by the use of protective slag blankets, inert gas or refractory shrouded caster nozzles.
Some steelmakers have experimented with the use of magnesium oxide from magnesia (commonly referred to as magnesite) in place of dolomitic lime during the calcium treatment, on the claim that it goes into solution more quickly. However, it has been shown that the performance of this substitute is no better than that of dolomitic lime.
The demand for metallic calcium is dominated by the steel industry. It is used as a deoxidizing, desulfurizing and decarburizing agent for special steels and alloy steels. It also serves as a reducing agent in the smelting of nonferrous metal and rare earth metals.
Limestone is the main raw material for the production of calcium metal. It is calcined to produce calcium oxide and then reduced through vacuum and electric current to form a molten Ca-aluminate. This is then cast into ingots.
In addition to its role in steelmaking, calcium can be used for the treatment of liquid steels and irons. This can reduce the oxygen content of the molten steel, prevent clogging of the caster nozzles and globularise the alumina inclusions. It can also improve the cleanliness of molten steels by lowering the sulphur content and improving the machinability of finished products. This is known as the calcium treatment. It is also used to modify the morphology of oxide and sulphide inclusions in aluminium killed steels.
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