Properties Of Nano-CaCO₃ Containing MgO-CaO Refractories And Its Influence On Steel Qualities

Free CaO is expected to exist in working lining of tundish for clean steelmaking,which can purify the steel liquid.Limestone,particle size of which is commonly bellow 0.5mm,was used as the CaO resource during refractories manufacturing process that used for tundish.However,due to the effects of thickness and structure of working lining of tundish on heat transfer and decomposition kinetics of limestone,limestone in refractories do not thoroughly decompose in preheating.CO₂ gas from decomposition of the residual limestone would enter in molten steel,and then have effects on steel quality in continuous casting via the reactions between CO₂ and elements in steel.Larger pores are produced from decomposition of limestone,which would reduce strength of materials also.Nano-CaCO₃ was used instead of limestone as CaO resource in MgO-CaO refractories fabrication in this study,MgO-CaO dry vibration material and MgO-CaO castable were fabricated and effects of nano-CaCO₃ content on properties of materials were studied.Mixes was also made in crucible shape.Effect of MgO-CaO crucible containing nano-CaCO₃ reacting with molten steel on Mn,C content and total oxygen content in steel were investigated via induction furnace.The conclusion are shown as followed:1)Nano-CaCO₃ could fill pores when it is introduced in dry vibration material.The pore size distribution of specimens heated at 1500? transfer to unidomal distribution from the bimodal distribution,and average pore diameter is decreased,apparent porosity is increased.Apparent density and strength of dry vibration material were better when addition content of nano-CaCO₃ is 2.5wt%.The strength of dry vibration material is increased with the increment of phenolic resin content,but pores from decomposition of phenolic resin have a little restriction on sintering.The suitable content of phenolic resin is 1.5bwt% in this experiment.2)When nano-CaCO₃ was used in castable,pore size distribution of specimens heated at 1500? transfer from the bimodal distribution to unimodal distribution,andaverage pore diameter increase a little.Strength and bulk density of specimens is decreased,apparent porosity is increased,the recommend content of nano-CaCO₃ in castable is 5wt% in this experimental condition.3)CO₂ gas from decomposition of nano-CaCO₃ in MgO-CaO refractories would react with elements in molten steel,which resulted in the decrease of [Mn],[C]content.Total oxygen content of steel increase quickly first,then increase slightly with the increment of soaking time.