Shape Control of Alumina Inclusions by Double Calcium Addition Treatment

Experimental and theoretical studies were carried out to clarify shape control of alumina inclusions during calcium double treatment in a line pipe steel for sour service. Calcium (Ca) double addition method were experimented by 280 t-scale commercial plant. In this method, Ca powder was firstly injected for shape control of alumina inclusions by flux injection process (FI), and was secondly added for shape control of MnS to CaS in tundish of continuous casting machine after eliminating the first step Ca by RH degasser. The degree of shape control of alumina inclusions of this method was increased compared with that of the conventional Ca treatment by FI or tundish addition, and approaches to the equilibrium condition among Ca-CaO-Al2O3 system. To explain the shape control rate of alumina inclusions, the non-reacted core model fitted by the laboratory scale experimental results was applied for this experimental data. The calculated values from this model in the Ca double addition method agreed well with the observed ones.