Effect Of Alloying Scheme And Annealing Temperature On Properties Of Non-oriented Silicon Steel

The drive motor is the heart of new energy vehicles,and non-oriented silicon steel is the key iron core material used in traction motor.The energy conversion capability and efficiency of the drive motor are largely affected by the magnetic properties of the non-oriented silicon steel.Non-oriented silicon steel used for drive motors with low iron loss,high magnetic induction intensity and high strength at high frequency is the premise for realizing the high-quality development of new energy vehicles industry.Different alloying schemes and different annealing temperature are designed in this thesis according to the requirements of new energy vehicle motors for the properties of non-oriented silicon steel.After smelting,rolling,annealing and other processing,the finished steels were obtained,and the effects of different alloy contents and heat treatment temperature on the properties of non-oriented silicon steel were systematically studied.The specific research results are as follows:（1）Compared with the samples with high Al,Mn and low Ca content,less Mg O·Al₂O₃ inclusions are in the experimental steels with low Al,Mn and high Ca content samples,and the size is smaller.Due to the high content of S and N in the samples with high Ca content,more individual Ca S,Al N and Ca S-Al N,Mg O-Al₂O₃-Ca S composite inclusions are formed,resulting in an increase in the total amount of inclusions in the steel.The morphology of inclusions in low Al,Mn and high Ca content samples is more regular.（2）Under the condition that the oxygen content of steel samples with different alloy contents is equal,reducing Al content in the steel narrows the generating dominant area of Mg O·Al₂O₃ inclusions.After the modification of Al₂O₃ and Mg O·Al₂O₃ by Ca treatment,the number of oxide inclusions decreases.Adjusting Al content of alloying elements and the amount of Ca treatment are the key to reducing oxide inclusions in Ca-treated non-oriented silicon steel.The precipitation behavior of Al N,sulfide and their composites is mainly affected by the N and S content in the steel.（3）Before and after stress relief annealing,the number densities of precipitates in high Al and low Ca samples are 1.6×10⁴/mm² and 1.4×10⁴/mm²,respectively.The average size of the precipitates is 0.15μm and 0.18μm,respectively.The number densities of precipitates in the samples with low Al,Mn and high Ca are 2.0×10⁴/mm²and 1.2×10⁴/mm²,respectively.The average size of the precipitates is 0.19μm and0.24μm,respectively.The pinning force to grain boundary is reduced.（4）Before and after stress relief annealing,the average grain size of samples with high Al,Mn and low Ca are 102.48μm and 105.04μm,respectively.The texture factors{100}/{111}are 1.07 and 0.88,respectively.The average grain sizes of the samples with low Al,Mn and high Ca are 90.93μm and 111.91μm,respectively.The texture factors{100}/{111}are 0.97 and 1.17,respectively,which indicates more excellent propeties will be achieved in low Al,Mn and high Ca samples.（5）Before and after stress relief annealing,the iron loss P_1.5/50 value of high Al,Mn and low Ca samples are 2.21 and 2.01 W/kg（0.35 mm）,respectively,and the magnetic induction B₅₀ values are 1.67 T and 1.66 T,respectively.The iron loss P_1.5/50values of low Al and high Ca samples are 2.03 and 1.80 W/kg（0.35 mm）,respectively,and the magnetic induction B₅₀ values are 1.66 T and 1.67 T,respectively,which has better magnetic properties.（6）Before and after stress relief annealing,the Vickers hardness value of high Al,Mn and low Ca samples is 237.8 HV_0.5 and 236.9 HV_0.5,respectively.The Vickers hardness value of the samples with low Al,Mn and high Ca are 211.2 HV_0.5 and 208.1HV_0.5,respectively.The high Al,Mn and low Ca samples contain more alloying elements to improve hardness and more high-hardness oxide inclusions,resulting in relatively high hardness of the samples after continuous annealing,which is not conducive to subsequent stamping.（7）Before and after stress relief annealing,for high Al,Mn and low Ca samples continuous annealing at 830℃,the number densities and average size of the precipitates,the average grain size,magnetic induction,Vickers hardness and strength changes only a little.Because the average size of the samples is only 17.67μm and18.38μm,respectively,the iron loss before and after stress relief annealing increases by 1.84 W/kg and 1.67 W/kg.However,the yield strength,tensile strength and elongation of the samples continuous annealing at 830℃are higher than that at 970℃.High temperature continuous annealing deteriorates the mechanical properties of the present samples.