Effect Of High Temperature Annealing Process On The Formation Of Magnesium Silicate Bottom Layer On HiB Steel Surface

Oriented silicon steel is mainly used to make the cores of transformers in the power industry.With the increasing use of power resources year by year,more and more people pay more and more attention to the research on the properties of oriented silicon steel.Due to the uneven temperature and atmosphere at each position of the silicon steel coil during the high temperature annealing process of oriented silicon steel,the quality of the magnesium silicate bottom layer generated at each position on the surface of the silicon steel varies greatly.This subject studied the effect of annealing atmosphere on the formation of magnesium silicate underlayer on the surface of silicon steel during the first heating stage of high temperature annealing(25-900 ℃),and the effect of the annealing atmosphere and annealing temperature on the formation of magnesium silicate underlayer on silicon steel surface during the secondary heating stage of high temperature annealing(900-1170 ℃).The influence law of annealing atmosphere on the formation of magnesium silicate bottom layer and the process parameters for forming a good magnesium silicate bottom layer are obtained,in order to provide guidance for industrial production.In this paper,High magnetic orientation silicon steel sheets(HiB steel)coated with magnesium oxide coating on the production site are selected for high temperature annealing experiments.The high-temperature annealed silicon steel was tested and studied by SEM,XRD and EPMA.In the scope of the research conditions of this article,the research results shows:(1)In the first heating stage of high temperature annealing,the water vapor content will affect the morphology and phase of the oxide layer,and then affect the morphology of the magnesium silicate bottom layer.When the water vapor content is low,the thickness of the oxide layer is too thin,resulting in poor adhesion of the magnesium silicate bottom layer;when the water vapor content is appropriate,the quality of the bottom layer is better;when the water vapor content is high,there is too much iron oxide in the oxide layer,resulting more iron above the bottom layer;controlling the water vapor content within a proper range is conducive to generating a better quality magnesium silicate bottom layer.The hydrogen content also affects the morphology and phase of the oxide layer,which in turn affects the morphology of the magnesium silicate bottom layer.When the hydrogen content is low,there is too much iron oxide in the oxide layer,resulting in more iron above the bottom layer;when the hydrogen content is appropriate,the bottom layer quality is better;when the hydrogen content is high,the oxide layer thickness is too thin,resulting in poor adhesion of the bottom layer;When the water vapor content in the annealing atmosphere is high,an appropriate amount of hydrogen can be added to improve the quality of the magnesium silicate bottom layer.When PH2O/PH2=0.1 and PH2O/PH2=0.25 during the primary heating stage of high temperature annealing,the water vapor content and hydrogen content increase at the same time,and the influence of water vapor is dominant.The quality of the magnesium silicate bottom layer on the surface of silicon steel increases first and then decreases.When PH2O/PH2=0.1,the quality of the magnesium silicate bottom layer formed on the surface of silicon steel with d.p.≈25 ℃ and H2 %≈31.27 % is the best;when PH2O/PH2=0.25,the quality of the magnesium silicate bottom layer formed on the surface of silicon steel with d.p.≈10 ℃ and H2 %≈4.85 % is the best.In the second heating stage of high temperature annealing,the water vapor remaining in the annealing atmosphere will aggravate the oxidation process on the surface of the silicon steel.After the magnesium silicate bottom layer is formed,there are still unreacted oxides remaining below it,which will reduce the magnesium silicate bottom layer.The higher content of water vapor in the annealing atmosphere,the thinner the thickness of the magnesium silicate bottom layer.In the high-temperature annealing process,when the annealing temperature is 1050 ℃,a continuous magnesium silicate underlayer has been formed on the surface of the silicon steel sample,but the quality is poor;increasing the annealing temperature is conducive to the full reaction of silicon dioxide and magnesium oxide to form magnesium silicate,and finally The annealing temperature in the range of 1100~1170 ℃ is conducive to the formation of good quality magnesium silicate underlayer.