Inclusions in Calcium‐Treated and Resulfurized Al‐Killed Steels

Abstract

Industrial trials and theoretical analysis are performed to study the effect of addition sequences of calcium and sulfur on inclusions in a calcium‐treated and resulfurized Al‐killed steel. The evolution path of inclusions at each production step is Al2O3 → Al2O3–CaO–MgO → Al2O3–MgO and Al2O3–CaS–CaO → Al2O3–MgO–CaS with the calcium treatment before sulfur addition. Calcium treatment after the sulfur addition promotes the formation of (Mn, Ca)S complex sulfide inclusions and is beneficial to modify the shape of sulfide inclusions to spherical ones in the rolled steel, where the size of sulfide inclusions is smaller than that of the heat of calcium treatment before sulfur addition. The relative plasticity of (Mn, Ca)S complex inclusions has a linear relationship with the content of CaS. Thermodynamic calculation results show that the critical solute sulfur content corresponding to the formation of CaS in the molten steel decreases sharply with the increase of the calcium content. With the same amount of calcium in the steel, the calcium treatment after sulfur addition promotes the formation of small (Mn, Ca)S complex sulfide inclusions with lower deformability during the hot rolling process, which is helpful for the mechanical property of the calcium‐treated and resulfurized Al‐killed steel.