Study On Solid Solution And Precipitation Behavior Of Second Phase Particles In Thin Continuous Casting Strip Of Fe-3.0%Si Non-oriented Silicon Steel

In motor and generator rotor, non-oriented silicon steel is the mian material of iron core used in rotating magnetic field, the usage of non-oriented silicon steel requires excellent magnetic properties and performance. Impurities and inclusions existed in silicon steel matrix have a powerful influence on iron loss. In this paper, thin casting strip of3.0Si%non-oriented silicon steel is taken as experimental materials, and a series of experiments including isothermal heat treatment and cooling, normalizing, cold rolling, annealing process are carried out. Through these experiments, solutionizing and precipitation mechanism of AIN and MnS are identified, and the effects of normalizing, cold rolling and annealing process on magnetic properties of non-oriented silicon steel are deeply discussed. The main contents are summarized as follows.(1) Continuous casting process of thin steel strip is introduced in this paper, combined with the effects of flow distribution nozzle on temperature of molten steel and the cooling capacity of the casting rolls, the forming process of casting strip are analyzed. Changes of metallographic structure along the width of continuous casting strip are discussed and the factors that affect the distribution of the precipitates are reasoned in this page.(2) Isothermal heat treatment is carried out on MMS-300thermal simulation testing machine, the temperature range of isothermal process is from1100℃to1380℃. Combined with solid solubility of AIN and MnS, variation of precipitates with isothermal temperature is obtained through the analysis on the size and composition of precipitates.(3) According to the results of isothermal heat treatment, after AIN and MnS reach equilibrium solid solubility in1380℃, a series of cooling process with various cooling speed and temperature range is carried out. In this experiment, variation of composition, size, shape and amount of precipitates is analyzed, at the same time, the proper cooling speed and temperature range are obtained.(4) By the observation on cold-rolled microstructure of thin continuous casting strip which is firstly dealt with normalizing, the change of precipitates’shape during cold rolling process is analyzed. By rapid annealing process with high temperature, the effects of high temperature-annealing after cold rolling on precipitates are discussed.(5) According to variation of precipitates’size during isothermal and cooling process, a series of manufacturing processes of non-oriented silicon steel are designed.These processes involve normalizing, cold rolling and annealing treatment. The main factors that affect the size of precipitates are gained through the analysis on magnetic precipitates, grain size and texture of non-oriented silicon steel.