Optimization and industrial testing of LF refining slag system for Q690 steel
In order to control T[O]content and inclusions of Q690 steel,improve cleanliness and seek suitable refi-ning slag system,the control status of refining slag system and inclusions in the original process was investigated firstly.The morphology,size and composition of inclusions larger than 2 μm in steel were detected and analyzed by Aspex automatic scanning electron microscope,and the time of calcium treatment was determined.Secondly,the thermodynamic calculation of refining slag-liquid steel-inclusions equilibrium was carried out by FactSage software,and the influence of refining slag composition on the composition of inclusions in steel was analyzed.At the same time,laboratory experiments were carried out.Based on the experimental results and theoretical models,the disso-lution rate cloud diagram of A12O3 in CaO-Al2O3-SiO2 slag at 1 550 ℃ and 1 600 ℃ was calculated.Finally,the suitable refining slag system of Q690 steel was determined,and the calcium-aluminum ratio of the original process slag system was reduced.The optimized w(CaO)/w(Al2O3)of slag system was controlled between 1.8 and 2.0,and the basicity was controlled between 5.0 and 7.0.The industrial test results show that the T[O]mass fraction of Q690 steel after RH can be reduced to less than 7×10-6,and the maximum diameter of inclusions is reduced from 40-60 μm to 10-20 μm.The area fraction,number density and maximum diameter of inclusions detected in the steel are significantly reduced.The number density of inclusions in the slab steel samples can be reduced to less than 1 piece/mm2,the area fraction of inclusions can be reduced to less than 16 × 10-6,and the maximum diameter can be reduced to less than 18 μm.The D-type and DS-type inclusions in the rolled plate are all less than 1.0,which meets the requirements of high-quality steel.The research results provide a certain reference for the stable produc-tion of clean steel.
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