Industrial Test Of Smelting Bearing Steel With High Titanium Molten Iron

The quality of bearing determines the machinery's performance and reliability level.Titanium content in high-quality bearing steel should be very low.Because Ti is easy to form TiN/Ti(CN),which causes damage to the fatigue life of bearing steel.At present,domestic steel mills mainly adopt titanium ore smelting.It results in high titanium content in molten iron.This paper expounded the specific control requirements of titanium content in smelting process and explored the evolution of inclusions.A bearing steel produced by a steel mill was systemically investigated.The equilibrium thermodynamic calculation of titanium and oxygen in converter melt showed that various titanium oxides can form with constant oxygen content at 1450-1600?,such as Ti₃O₅,Ti₂O₃,TiO₂ and TiO.The main titanium oxides generated in bearing steel were Ti₃O₅ and Ti₂O₃.The retaining slag and double slag method was closed to sustain the[C]content while reduce the[Ti]content,and the proper slag dumping temperature was 1410-1440?.The[C]content was 3-4%while[Ti]content in semi-steel was only 20-30ppm in which the activity of Ti₂O₃ was 0.05-0.15.Typically,when the melt temperature was1640-1670?,the activity of Ti₂O₃ in molten steel was 0.005-0.05,where the[C]content was 0.5-0.7%as well as 5-15ppm[Ti]content.Inclusion analysis showed that after ladle furnace refining(LF),vacuum degassing(RH)and weak agitation treatment,inclusions in sample were mainly Al₂O₃,Mns,Al-Mg-Ca-O and TiN.The number of small inclusions(1-10?m)decreased from 42 to 8per square millimeter.Thermodynamic calculation of typical inclusions reflected that TiN and MnS precipitated at 1227?and 862?,respectively.They were in solid phase of bearing steel.Yet Al₂O₃ precipitated at 1677?,which is higher than the liquidus temperature.Al₂O₃precipitated in molten steel.