Oxide shape control

It consists of modifying   inclusions.  is solid at steelmaking temperature and is brittle in nature. On rolling, alumina inclusions break up which is a serious surface defect. The alumina may accumulate in the continuous casting nozzle causing clogging of the nozzle.

For a normal aluminum killed steel calcium will first modify the oxide inclusions. Thermodynamically it is easier to form   type of inclusions which will be converted to   and finally liquid calcium aluminate rich is . The calcium will then desulphurize steel to very low levels.

Thus it is possible that calcium will react with sulphur to form CaS before there is oxide shape modification. The sulphur level where CaS is more stable will depend on Al content. It must also be noted that  is liquid product at steelmaking temperature. Thus it is important to control the concentration of Al, S and Ca in molten steel for engineering of oxide inclusions.