Formation Mechanism And Precipitation Behavior Of Inclusions In High Aluminium Content Non-oriented Silicon Steel

At present,high grade non-oriented silicon steel becomes the focus products of industry for its high properties and excellent market prospects.Reasonable control of chemical composition of steel,optimization of refining process,reduction of large inclusions in steel,inhibitting precipitation of the precipitates in steel by heat treatment process,and promoting the growth of grain and precipitates are the basic requirements for obtaining excellent magnetic properties of non-oriented silicon steel.In this paper,the desulphurization effect of high aluminum content non-oriented silicon steel during RH refining was evaluated,and the effect of hot charging temperature on precipitation behavior of inclusions and precipitates in non-oriented silicon steel was investigated.The thermodynamic forming conditions of inclusions in steel were calculated,and the precipitation process of precipitates and its formation mechanism in non-oriented silicon steel were analyzed,which will provide reference data for control the conditions for the formation of the inclusions and precipitates,and casting heat treatment process.The conclusions are as follows:?1?Desulphirization proceeded in some degree in the tested steel during RH refining process.Sulfur content in the tested steel can be reduced from 0.0027%at the initial refining process to 0.0018%at the refining end.?2?The results show that oxide inclusions in the non-oriented silicon steel mainly included3Al₂O₃·2SiO₂,2MgO·SiO₂andmagnesiumaluminumsilicate.Thermodynamic calculation results indicate magnesium content and characteristics of oxides decide the composition of inclusions in the steel.MgS is easy to precipitate with2MgO·SiO₂,MgO-Al₂O₃-SiO₂ complex with high MgO-bearing and sulphur capacity,or AlN.There is a small number of CaS in steel which are precipitated on the oxide cores.?3?The precipitates in the tested steel are mainly MgS and AlN,which formed during solidification of molten steel,and any type of MnS isn't found in the steel.The existence of MgS in the steel will inhibit MnS from precipitating.Properly increasing the content of MgO in the refining slag is conducive to the precipitation of MgS on the oxide surface ahead of time,and then which will inhibite the precipitation of MnS in steel and promote the growth of precipitates in steel.?4?It is helpful to reduce the number of inclusions below 0.5?m in the non-oriented silicon steel by reducing the hot charging temperature before hot rolling.Under the experimental conditions,the appropriate hot charging temperature is 700?.The precipitation rate of AlN in as-cast non-oriented silicon steel is higher than that of MgS,when the test steel is heated over 1000?.?5?The size of inclusions forming by MgS orienteering precipitating on oxides matrix or with AlN is much bigger,and their precipitation and growth method relates with the crystal structure of MgS and inclusions matrix.The mean size of MgS-bearing compound oxide inclusions is 1²?m.MgS-bearing inclusions exist in the steel with three forms.MgS wraps with spherical oxide core,uniformly distributes on the surface of spherical oxides,and orienteering precipitates on oxides matrix or with AlN.MgS can be compound with oxide,combined with CaS or AlN to compound with oxides,or to precipitate with AlN.With the decrease of hot charging temperature,MgS content in the compound inclusions and also the average size of the MgS-bearing inclusions will increase.However,the precipitation of CaS will inhibit the precipitation of MgS in the complex inclusions.