Research On The Deep Desulphurization Process Of Non-oriented Electrical Steel In RH

Sulfur can not only increase core loss of no oriented electrical steel significantly,but also reduce its magnetic sense. So the requirement of sulfur content is lower than30×10-6, even under10×10-6in the high-grade non-oriented electrical steel. Because ofthe hot metal pretreatment and control of converter resulfurization quantity can’tsatisfy the high grade non-oriented electrical steel production, so other processes ofdeep desulfurization outside of furnace need to be developed. The production ofDW800non-oriented electrical steel of takes RH deep desulfurization as the researchbackground in a company. Then RH industrial tests of desulfurization were carried outwith sulfur content in non-oriented electrical steel strip below to20×10-6on the basisof lab study. The following results were obtained.The experimental data show that desulfurization rate increases with the alkalinity,Al2O3and CaF2content first and then decreased when the desulfurizer alkalinityshould be controlled within range of8～12,25%～30%Al2O3,4%～6%CaF2,6%MgO, at the same time the slag system melting point should be below1400℃and the initial steel sulfur content is range0.00933%from0.01073%. It was reachedthe highest point86.8%and the content of sulfur was reduced to0.00133%when thealkalinity was12and it was consist of25%Al2O3,6%CaF2and6%MgO and itsmelting point was1349℃. And the desulfurization time of RH vacuum should becontrolled in8～10min was appropriate.Mathematical model for predicting desulfurization was established in the labstudy according the condition of15kg induction furnace desulfurization test and itwas validated by the experimental data. The calculating results showed that theprediction hitting ratio was82.9%when the error was allowed within2×10-6and themass transfer of sulfur was the restrictive aspect in the molten steel in laboratorydesulfurization test. It was also indicated that the desulfurization effect can beimproved by increasing the blowing argon flow and vacuum degree, increasing thereaction area and the mass transfer rate of the sulfur, increasing the partition ratio ofsulfur and the amount of slag (5%～8%) in RH.The industrial experimental results showed that the content of sulfur was able tomeet the high-grade non-oriented electrical steel deep desulfurization requirements when the6～8kg/t desulphurizer was added and the composition of RH refining endslag was w(CaO)/w(SiO2)：5～7、w(Al2O3)：25%～30%、w（FeO+MnO）：<5%、MI：0.2～0.4. The mean content of sulfur was reduced from32×10-6to18×10-6, thelowest value was13×10-6and the average and highest desulfurization efficiency were43.3%and47.1%respectively. Those factors including, top slag oxidation, alkalinity,MI, sulfur distribution ratio and [Als] can affect the desulfurization rate, but the topslag oxidation played a major role. Meanwhile, the sulfur distribution ratio of decisionhigh-low was affected mainly by the（FeO+MnO）content of top slag. The measuredsulfur distribution ratio was only5when (FeO+MnO) content was up to22.89%andit was reached89when the content of (FeO+MnO) was0.71%.