Analysis of inclusions in whole smelting process of non-oriented silicon steel 23W1700 by rare earth treatment
In non-oriented silicon steel,fine inclusions and precipitates can seriously deteriorate the iron loss and magnetic induction strength of material.The inclusions in the whole production process of a high-grade,non-oriented silicon steel 23W1700 which was produced by a steelmaking plant was studied.The morphology,size and type of inclusions were analyzed by scanning electron microscope and energy dispersive spectrometer analysis and the precipitates in the casting process was calculated.The results show that in the production process of non-oriented silicon steel,after adding aluminum in Ruhrstahl Heraeus(RH)Vacuum refining treatment,the primary inclusions are AlN,with a small amount of Al2O3 and its composite inclusions.After adding rare earth alloy to RH,the inclu-sions will transform into ReS inclusions and some of them are wrapped by AlN inclusion.After adding desulfurizer,the primary inclusions are small-sized Re2O2S wrapped by AlN composite inclusions.In tundish,the inclusions are Re2O2S or ReAlO3 as the core and wrapped by AlN composite inclusions.In slab,spherical MgS was found and Re2O2S or ReAlO3 cored inclusions with the same composition as in the tundish were also found.And the composi-tion of two types of inclusions is slight different in tundish and slab.Throughout the entire smelting process,as the content of rare earth in liquid steel decreases,the trend of changes in rare earth inclusions is ReS→Re2O2S→ReAlO3.The average size of inclusions mainly ranges from 2 μm to 4 μm,the inclusion size is the smallest before adding rare earth to RH,and the inclusion size increases slightly after adding rare earth to RH.After the completion of RH treatment,the inclusion size tends to stabilize,and ultimately the inclusion average size in the slab is 2.9 μm.Using the calculation software Thermo-calc,the precipitation of inclusions in molten steel was calculated.The ther-modynamic calculation results showed that when the molten steel was not solidified,the primary inclusions were Al2O3.After all the molten steel solidified,Ce2O2S,Ce2S3,AlN,and MnS would precipitate in sequence,which is also consistent with the types of inclusions obtained in the experiment.
non-oriented silicon steelwhole smelting processrare-earth inclusioninclusion analysiscalculation of precipitates
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