Deoxidizing of metal

Dipping the contents of oxygen in metal or its linkage in strong bridgings is called deoxidizing effect. The most widespread method of deoxidizing is deep (sedimentary) deoxidizing. It is applied for metal smelting in all units of steel-smelting manufacture and impliment by elements' introduction in metal that bundle oxygen in strong oxide. More or less full disposal of the formed oxide inclusions (products of a deoxidizing effect) occurs as a result of their settling-down or emerging or carrying out by a stream of metal and transition in scoria or moving on firm phase-to-phase surfaces.

In modern metallurgy the aluminium in various forms (as a wire or a bar) is applied for deoxidizing of steels' majority. Application of aluminium allows to receive steel with a fine grain and parameters of plasticity and viscosity, that lay in breaking points of allowable values.

At the same time, application of aluminium can lead to occurrence of some negative factors in future even if the steel is clean:

1) A running quality of steel reduces to some extent and, as a consequence, channels nozzles' tightening isincreases;

2) There is also an opportunity of crystalline pluggings of oxide aluminium's formation, that have an acute-angled form and serve as being a sourse of destroyed voltage (concentrators of voltage). During the treatment of steel, deoxidated by aluminium with the help of a powder wire with calcium weighing material, these negative phenomena substantially becomes less expressed or excludes absolutely.

Treatment of steel by calcium, preliminary deoxidated by aluminium, allows to achieve such values of oxygen's contents, which size is comparable to aluminium. Decrease of oxygen's concentrating during the treatment in the unit «ladle pot — furnace» is a source of reduction of nonmetallics plugging's quantity while steel is refrigerating and solidifying.

It's a well-known fact, that it is possible to achieve a decrease in the contents of oxygen up to thousand fractions of percent during the treatment a wire with the weighing calciferous material at the charge of the last no more than 0, 2 kg / t, that is precisely visible on the submitted diagram.

Thus, efficiency of Ca's activity during deoxidizing depends on the form its existence in a wire: the metal calcium has a melting temperature 851 ⁿ С and temperature of transpiration — 1492 ⁿ С, the melting temperature of the most widespread ferroalloy SK30 (30% Ca and 60 Si in accordance with GOST 4762-71) is 1100 ⁿС, the given material has smaller steam's elasticity, that results to greater efficiency of Ca's activity. At fixed introduction's speed of a powder wire an assimilation of calcium over 20% is provided.

One of the most important goals during steel making, preliminary deoxidated by aluminium, is to exclude the probability of the chanelles' nozzeles tightening in continuous casting pouring of metal. It is provided with regulated input of a powder wire with the calciferous weighing material in a ladle pot in the unit «ladle pot — furnace» in the quantities that depend on the contents of Al, Si, O, S in fluidic metal.

The advantages expressed in reduction of the oxygen's contents in metal during a deoxidizing effect by a powder wire (figure 1) in comparison with the treatment by lumpy materials (figure 2) are clearly visible on the diagram presented below, that shows the dependence of the oxygen contents in steel from the time of treatment.