The Al addition must not float upward during the tap Out or lose its power as a deoxidizer
by becoming "trapped" in the slag.
Theoretical analysis of the processes and material balance of the steel deoxidizers (calcium and aluminium) at all stages of ladle treatment showed that although << excessive >> amount of calcium during casting and crystallization of metal in the mould (weight of the ingot equaled 3.6 t) ensures with residual (dissolved) aluminium a relatively low content of the dissolved (active) oxygen, at the same time it is to a significant degree responsible for formation of increased amounts and dimensions of both globular inclusions in steel on basis of CaO-[Al.sub.2][O.sub.3] and heterogeneous inclusions on basis of CaO-[Al.sub.2][O.sub.3]-MgO-Si[O.sub.2] (Figure 2, Table 1).
Crystal-chemical structure of multiphase oxide inclusions is determined by physical-chemical state of the pool, sequence of introduction of the deoxidizers, and interaction of dissolved in the metal elements.
Since the STS-refining process used aluminum as a deoxidizer
to remove oxygen frommolten steel, SRS had a high content of [Al.sub.2][O.sub.3] (oxygen affinity: K > Ca > Mg > Al > Ti > C > Si > Mn > Cr > Fe > Ni > Cu).
It should be noted that according to valid normative-technical documentation addition of deoxidizers
and modifiers without limitation of their kinds and residual contents is allowed in melting of the 20GL steel for transport machine building.
By establishing necessary thermodynamic conditions in contacting phases one may regulate migration of nitrogen in the triple system gas-slag-metal , whereby the conditions are ensured by deoxidation of slag and the metal by strong deoxidizers
as it was registered in the process of our meltings in graphite crucibles.
Dependences of silicon and manganese melting loss upon content of carbon at the furnace outlet (Figure 2, a) and changes of carbon content in the ladle-furnace (Figure 2, b) showed that the fuller was decarbonization of metal in the ladle-furnace, the lower was melting loss of deoxidizers
Charges consist of 40-60% foundry returns with the balance made up of low carbon iron or 1010 steel, ferroalloys and deoxidizers
. All foundry-generated returns are color coded and segregated, while purchased scrap is not used in recipes.
Two-percent lithium copper also is an ideal deoxidizer
for pure copper, copper-base alloys and precious metals.