Research On The Technology To Improving The Cleanliness Of Interstitial-free Steel

IF steel is the new kind of stamping steel after rimmed steel and Al killed steel developed.As it has good deep drawing and no aging,IF steel developed has become an significant symbol of country's automotive producing level.In this paper,through a combination of process characteristics of 240t steel making and continuous casing line in Baogang Rare Earth Steel Plate Plant,system research the transformation rules of Ti-IF steel component and inclusion during the process of KR desulphurization,converter smelting,RH vacuum treatment and continuous casting,to further analysis and evaluate the component such as C,N,P,S,O and the process control of quantity,size,profile of inclusion,propose corresponding process action.In this paper,the hot metal sulfur in converter could be controlled in below 0.002%,and the final sulfur could be controlled in below 0.010%stably by optimizing KR desulfurization process and using slagging and drossing two times.For improving converter's end operation hit ratio,the tapping temperature needs to be increased on the premise of ensuring to hit composition and controlled final carbon content between0.03%⁰.04%at the same time.Absorbing deoxidized product in maximum with adjusting main composition of RH vacuum slag system to CaO-SiO₂-Al₂O₃-MgO.FeO+MnO was also required to be less than 12%to avoid secondary oxidation between RH slag and liquid steel.Via developing key technology for converter smelting process and RH process,the interstitial atoms in steel carbon was stable controlled in below 0.0030%and nitrogen was stable controlled in below 0.0030%.Based on adjusting rising up tendency of stopper rod location and backpressure variation condition of blowing pipeline in time,argon blowing tundish and controlling tension speed above 1.4m/min on continuous casting,the backpressure of stopper rod and nozzle still contained below 2.0 bar when IF steel was cast 15 heats continuously in Baogang Rare-earth Steel Plate Plant,it stayed on the advanced level in domestic.The continuous casting realized metallurgy effect of tundish,increased liquid steel standing time in tundish with using 75t tundish in high capacity for inclusion could be floated into powder and covering agent before liquid steel coming into mould.The study has shown that the IF inclusion content control is run through converter smelting,RH vacuum treatment and every procedure of continuous casting.Via analyzing inclusion origin and researching liquid steel cleanliness control process,the steel making and continuous casting process control has been strengthened,the total volume of a variety inclusions of IF series product in Rare-Earth Steel Plate was less than grade 2.0.