| The high strength and ultra deep drawing steel containing phosphorus has achieved the lightweight of the automobile with better strength and deep drawing capability.The samples of typical IF steel types with high strength were sampled in the whole process and the technological parameters were investigated and analyzed.Measures such as controlling end-point oxygen in BOF,optimizing modifier composition,controlling inlet steel temperature of RH,adjusting Al deoxidation and alloying time interval were adopted,and the thermodynamic calculation of top slag modification of high strength IF steel containing phosphorus was carried out by FactSage.The industrial experiment was carried out by optimizing the composition of slag and so on.The following conclusions are drawn:?1?Before optimization,the average converter end-point tapping temperature of phosphorus-containing IF steel is 1703.9oC,the transfer time is long,the average RH inlet temperature is 1630.4oC,and the process temperature drop is 71.7oC.The average oxygen content of the molten steel at the end of the converter is 743×10-6,which is116×10-6 higher than that of ordinary IF steel.The Al2O3 and TiN inclusion produced by deoxidation of molten steel and secondary oxidation are the main factors causing inclusion defects in cold rolled sheet.?2?The time interval between Al and Ti addition in RH at a time is more than 3minutes.The pure degassing time after alloying is more than 8 minutes.The standing time of 30-40 minutes is favorable for inclusion removal.The Mn alloying process in the vacuum process resulted in enhanced oxidation of the top slag of the ladle.Adding intermediate carbon in converter tapping process is beneficial to reduce the oxidation of top slag.?3?With the increase of SiO2 content,it is necessary to increase the ratio of calcium to aluminum?C/A?in the slag to ensure that the top slag of ladle is in the region with lower melting point.When the content of FeO in slag is less than 10%,and the content of SiO2 is 2wt%,6wt%and 8wt%,the value of C/A should be controlled at 1.2,1.4-1.5and 1.6-1.8 respectively to ensure that the top slag is in the low melting zone.?4?After optimization of top slag modification,the content of FeO in top slag can be controlled below 10%,and the content of T.O in molten steel can be controlled below20×10-6 after RH treatment.Compared with that before optimization,the average diameter of inclusions in the steel after top slag modification and optimization is obviously reduced.The size of inclusions is mostly between 2 and 5?m,and a small amount of inclusions is about 5 to 10?m.The inclusion does not exceed 20?m.?5?The defective ratio of billet by inclusions decreased from 0.45%before optimization to 0.26%,and the effect was good. |
PDF Full Text Request