Reaction between molten steel and CaO–SiO2–MgO–Al2O3-FetO slag under varying amounts of converter carryover slag

Abstract

Converter carryover slag during tapping has been a trouble for improvement of steel quality. In order to give an insight into the action mechanism of carryover slag on steel during tapping, a serious of molten steel-slag reaction experiments was conducted to elucidate the reaction mechanism between 3% Al steel and CaO–SiO2–MgO–Al2O3-FetO type slag at 1600 °C as well as its resulting effect on cleanliness under varying amount of converter carryover slag was investigated in laboratory. Composition evolutions in molten steel and slag during the reaction and microstructure on the steel-slag interface were investigated by employing different experimental techniques. 2[Al] + (Fe2O3) = 2[Fe] + (Al2O3) and 4[Al] + 3(SiO2) = 3[Si] + 2(Al2O3) were confirmed as a major reaction in the system. The initial (Fe2O3) content in experiments increased from 3% to 15%. The results indicated the metal-slag reaction tended to stable after about 10 min, the mass transfer of [Al] in molten steel was the rate-controlling step [Als] was more prone to react with (SiO2) for slags with initial (Fe2O3) less than 4.07%, but it reacted with both (Fe2O3) and (SiO2) when (Fe2O3) content was more. It was therefore suitable addition of Al alloy should take (SiO2) into consideration in addition to (Fe2O3) and dissolved [O]. Increase of carryover slag amount represented by increase of initial (Fe2O3) decreased the sulfur distribution but promoted the formation of MgO·Al2O3 inclusion. The sulfur distribution ratio decreased from roughly 5000 to 2000 but the number density of inclusion increased from 22.125/mm2 to 45.875/mm2 with increase of initial (Fe2O3) from 3% to 15%.

Keywords

• Carryover slag
• Converter tapping
• Aluminum deoxidation
• Reaction mechanism
• Desulfurization
• Inclusion