Research On Effect Of Calcium Treatment On Oxysulfides Of Hundred Nanometer Scale Inclusions In High-Grade Non-Oriented Silicon Steel

The hundred nanometer scale inclusions,which are similar to the domain wall size of electrical steel,affect the rotation and movement of the domain and deteriorate the magnetic properties of non-oriented electrical steel.It is of great theoretical and application value to improve the magnetic properties and stability of electrical steel,especially high-grade non-oriented silicon steel,to study the removal and modification of hundred nanometer scale inclusions.The production process elements of the typical grade（W350）,the control status of large inclusions,the control status of microscopic inclusions,and the types,sizes and morphological characteristics of microscopic inclusions were analyzed by industrial tests,laboratory analysis and detection methods.Experiments and inclusion detection and analysis have clarified the calcium concentration of hundred nanometer scale oxide inclusions in the steel;the mechanism of calcium treatment of denatured inclusions（Al₂O₃,m Si O₂·n Al₂O₃,m Mg O·n Al₂O₃）has been analyzed;through the thermodynamic analysis of sulfide precipitation,the effect of calcium treatment on steel has been compared and analyzed.The effect of sulfide precipitation;through industrial experiments,the effect of calcium treatment on hundred nanometer scale inclusions and properties in the production process of high-grade silicon steel（W350）was verified.The research conclusions are as follows:（1）The production process of W350 grade non-oriented silicon steel,the total amount of large inclusions（>50μm）in continuous casting billets are 6.49,6.20,6.30mg/10kg.The number density of inclusions（1～50μm）are 19.70,21.34,16.67/mm2,and the area fractions of inclusions are 189,180,223×10^-6.In the whole production process,the average temperature before and after KR treatment were 1369°C and1306°C,respectively,and the standard deviations were 38.7 and 30,respectively,and the KR process temperature was unstable.（2）Through thermodynamic analysis,it is concluded that the ideal RH refining top slag composition range is Ca O:50～60%,Si O₂:0～15%,Ca O/Al₂O₃=1～1.5;The composition of refining top slag in ideal zone and non-ideal zone was compared by experiment.The results showed that T.[O]in ideal zone decreased by 7ppm and aluminum loss decreased by 64ppm.（3）Thermodynamic calculation and experimental verification show that the reasonable concentration of oxide-modified calcium in W350 non-oriented silicon steel is 11～39ppm.Compared with the silicon steel sheet without calcium treatment,the proportion of Al₂O₃ in the hundred nanometer scale inclusions in the tundish,billet and hot-rolled plate after calcium treatment decreases from 78.2%,72.4%and75.6%to 49.8%,52.4%and 51.7%.（4）Calcium treatment coarsens the hundred nanometer scale inclusions.The average size of tundish,billet and hot rolled plate increased from（229～231nm）and（231～237nm）to（371～381nm）,（426～428nm）and（371～381nm）,（389～394nm）.The density of the hundred nanometer scale inclusions decreased from（51023～56427nm）,（49782～53264nm）and（50326～53465nm）inclusions/mm² without calcium treatment to（46109～48267nm）,（44328～46213nm）and（45912～47385nm）inclusions/mm².The pinning forces of 100-300nm with equivalent diameters of199nm of the hundred nanometer scale inclusions before and after calcium treatment were reduced from 2.35×10⁴Pa to 2.16×10⁴Pa,respectively.The critical grain size was increased from 8.76μm to 9.53μm,respectively.The average grain size of the finished board increases from 92.5μm to 99.8μm.（5）The factors that improve the magnetic properties of W350 non-oriented silicon steel by calcium treatment（11-39ppm）process include:the total amount of the hundred nanometer scale inclusions in the steel is reduced,the pinning forces is reduced,and the finished product structure is coarsened;inclusions spheroidization,inclusions coarsening.