Characteristic Transformation of Manganese-containing Inclusions during Al-killed Process in Ultra-low Carbon Interstitial-free Steel

摘要

Ferromanganese alloys are usually used for the manganese adjustment to meet the requirement of IF steel grade; and the formation and transformation of manganese-containing inclusions were closely relevant with the recovery yield of manganese in the melt and the morphologies of final deoxidation products. Characteristic transformation of manganese-containing inclusions during Al-killed process in ultra-low carbon interstitial-free steel were studied through the factory trial and hot crucible experiment. Factory trial showed that the manganese recovery yield fluctuated between 14% and 92% mainly due to the formation of manganese-containing inclusions. Hot crucible experiment revealed that three different groups of inclusions, including FeO·x MnO (FM), FeO–Al_(2)O_(3) (FA) and Al_(2)O_(3) (AO) inclusions, appeared after semi Al-killed; and five typical Al_(2)O_(3) inclusions, including spherical Al_(2)O_(3), polygonal Al_(2)O_(3), cluster Al_(2)O_(3), dendritic Al_(2)O_(3) and aggregated Al_(2)O_(3), appeared successively based on different formation mechanisms. Under homogenous nucleation condition, the spherical Al_(2)O_(3) appeared firstly, and changed to be cluster Al_(2)O_(3) by collision growth or transformed to be large dendrite Al_(2)O_(3) by single-direction diffusion growth. Under heterogenous nucleation condition, the manganese-containing inclusions were transformed to Al_(2)O_(3) inclusions in the following order: spherical FeO·x MnO → spherical FeO·x MnO with coarse surface → polygonal FeO·Al_(2)O_(3) → polygonal Al_(2)O_(3) → aggregated Al_(2)O_(3).