Microstructure Evolution During Hot Rolling And Normalizing Of Non-oriented Silicon Steel For High Nb-Ti New Energy Automobile

Non-oriented silicon steel for new energy vehicles has the properties of high strength,high fatigue strength,high magnetic induction,low high frequency iron loss and so on.It is an important material for manufacturing new energy vehicle driving motor iron core.In the manufacturing process of its products,the alloy content is high,the purity of steel is high,the metallurgical process is long,the process equipment and the control technology requirements are high,and at present,most of them exist in the form of protected patents.The key to the development of such steels is to significantly improve the strength without degrading the magnetic properties of unoriented silicon steels with high Al+Si content.The strengthening methods mainly include the following: solid solution strengthening of silicon,aluminum,phosphorus,nickel and other elements.The copper component system can delay the recrystallization and strengthen the precipitation by controlling the solid solution copper and copper precipitates.Solution-soluble carbonitides containing niobium and niobium titanium in Nb and Ti component systems can delay recrystallization and improve their strength.Hot rolling and normalization process is an important link in the structure and second phase control of non-oriented silicon steel for new energy vehicles.It is of great significance to formulate reasonable hot rolling and normalization process for the research and development of non-oriented silicon steel for new energy vehicles.In this paper,the non-oriented silicon steel used for new energy vehicles is a high-niobium titanium component system.The microstructure of hot rolling and normalization process and the evolution of the second phase are studied by using ICP-MS,scanning electron microscope,transmission electron microscope,X-ray diffractive meter and Zeisi metallographic microscope.The results show that when the holding time is the same,the heating temperature increases from 1120 ℃ to 1230 ℃,the solid solution of niobium and titanium increases gradually,the second phase decreases gradually,the effect of retarding grain growth decreases,and the average grain size increases gradually,the average size of the second phase increases with the increase of heating temperature in the steel and the remelting of the second phase at M and small size.In the high temperature stage of the rolling process,the precipitation percentage of Nb and Ti increases with the increase of pass number and the increase of the second phase of strain induced precipitation,the dragging effect of solid solution niobium and the pinning effect of precipitating elliptical or agglomerated elliptical(Nb,Ti)C along the large size subgrain boundary hindered the merging of the subgrains,and solid solution niobium played the main role in the high temperature stage,which made the sample difficult to recrystallize,compared with the high temperature stage,the solid solution percentage of Nb and Ti decreases and the dragging effect is weaker,but the pinning effect of the second phase(Nb,Ti)C particles precipitated at the subgrain boundary is stronger,as the rolling temperature decreases,the average particle size of the second phase decreases with the increase of pass times in both high and low temperature phases,a small amount of the second phase tends to the dispersion distribution in the later stage of low temperature rolling.The second phase is coarsened,the pinning effect on the grain boundary is weakened,the sample is completely recrystallized,and the grain size increases with the time of normalization.The texture strength and linear texture of the normalized sample are higher than that of the hot-rolled sample,the copper texture and the strength of brass texture are increased.