Laboratory Study on the Formation of Endogenous CaO‐Containing Inclusion in Gear Steel SCr420H during the Simulated LF Refining Process without Ca Treatment

The individual effect of Ca‐containing ferrosilicon, MgO crucible, and slag–steel refining on the formation of endogenous CaO‐containing inclusion in steel is investigated by contrast experiments. Experiments using Ca‐containing ferrosilicon are compared with the effect of high basicity slag and MgO crucible on inclusions compared to experiments with high purity Si. It is found that the influence of Ca‐containing ferrosilicon has a noticeable impact on endogenous CaO‐containing, while slag–steel reaction and MgO refractory mainly increase the (MgO) in inclusion. When Ca‐containing ferrosilicon is added after Al deoxidation, Al2O3 and MgO–xAl2O3 inclusions with low MgO content are modified into CaO‐containing inclusions preferentially, and [Mg] supplied by MgO refractory reacts mainly with (Al2O3) in inclusions in the subsequent refining process. Ca‐containing ferrosilicon addition before Al deoxidation is helpful in reducing Ca content in the steel. The dissolution of refractory in slag has a significant effect on slag–steel reaction by changing slag composition. Under the effect of slag and MgO refractory, MgO‐saturated spinel and MgO form in steel during the whole process. Herein, Ca‐containing ferrosilicon is a significant contributor to endogenous CaO‐containing inclusions during the simulated ladle furnace refining process without Ca treatment. Experiments using Ca‐containing ferrosilicon are compared with the effect of high basicity slag and MgO crucible on inclusions in contrast to experiments with high purity Si. It is found that the influence of Ca‐containing ferrosilicon has a noticeable impact on endogenous CaO‐containing, while slag–steel reaction and MgO refractory mainly increase the (MgO) in inclusion.