Study On Phosphate Insulating Coating For Grain-oriented Silicon Steel

In order to meet the higher requirements of customers in insulation property,an insulating coating is required to coat on steel.Currently,the inorganic coating is widely used,in addition it takes aluminium dihydrogen phosphate,Ludox and chromic anhydride as main ingredients.Because of toxic Cr6+ in chromic anhydride,the formula will cause harm to human body and pollute the environment.The non-chromium coating formula becomes an important development direction.In this paper,the phase composition,microstructure,and corrosion resistance of insulation coating with the different content of chromium anhydride were studied.And the effects of insulation coating with the different content of chromium anhydride on the iron loss and interlamination resistance were analyzed.Based on the above,a chromium-free insulating coating was investigated.The results show that with the increase of chromium anhydride,the wetting angle between the coating solution and the grain-oriented silicon steel substrate gradually decreases,the wetting property is improved.The interlamination resistance,lamination factor and magnetism induction intensity of grain-oriented silicon steel gradually increase,iron loss gradually decreases.In 3.5wt%NaCl solution,the corrosion resistance of samples gradually improves with the increase of chromium anhydride.When the content of chromium anhydride is 2.5wt%,the coating solution shows the best wettability on the grain-oriented silicon steel substrate.The coating is denser and smoother,and a diffusion area about 0.1 ?m thick at the junction between the insulating coating and the magnesium silicate bottom layer.The optimum values of interlamination resistance,lamination factor,magnetism induction intensity and iron loss of grain-oriented silicon steel are obtained,which are 13221?·mm 2,96.5%,1.888T and 1.141W·kg-1 respectively.The corrosion current density reaches the minimum value,which is0.586?A/cm,the optimal corrosion resistance of the coating can be obtained.The effects of the ratio of sodium tungstate and chromium trioxide on the properties ofphosphate insulating coating for grain-oriented silicon steel were investigated.The results show that,with gradually increasing the ratio of sodium tungstate and chromium trioxide,the wetting angle between the coating solution and the grain-oriented silicon steel substrate first decreases and then increases.The interlamination resistance,lamination factor and magnetism induction intensity of grain-oriented silicon steel first increase and then decrease,iron loss first decreases and then increases.In 3.5wt%NaCl solution,the corrosion resistance of samples first improves and then deteriorates with gradually increasing the ratio of sodium tungstate and chromium trioxide.When the ratio of sodium tungstate and chromium trioxide is 4:1,the coating solution shows the best wettability on the grain-oriented silicon steel substrate.At the ratio of 4:1,the coating is denser and smoother,and there is a diffusion area about 0.8?m thick at the junction between the insulating coating and the magnesium silicate bottom layer.The optimum values of interlamination resistance,lamination factor,magnetism induction intensity and iron loss of grain-oriented silicon steel can be obtained,which are 19073?·mm2,97.0%,1.898T and 1.099W·kg-1 respectively.The corrosion current density reaches the minimum value that is 0.177?A/cm2,the coating can effectively impede the invasion of corrosion solution,thus the optimal corrosion resistance can be obtained.The effects of the ratio of boric acid and chromium trioxide on phosphate insulating coating property of grain-oriented silicon steel were investigated.The results show that with gradually increasing the ratio of boric acid and chromic anhydride,the wetting angle between the coating solution and the grain-oriented silicon steel substrate first decreases and then increases.The interlamination resistance,lamination factor and magnetism induction intensity of grain-oriented silicon steel first increase and then decrease,iron loss first decreases and then increases.In 3.5wt%NaCl solution,the corrosion resistance of samples first improves and then deteriorates with gradually increasing the ratio of boric acid and chromic anhydride.When the ratio of boric acid and chromic anhydride is 3:2,the coating solution shows the best wettability on the grain-oriented silicon steel substrate.The optimum values of interlamination resistance,lamination factor,magnetism induction intensity and iron loss of grain-oriented silicon steel can be obtained,which are 19068 ?·mm2,96.8%,1.890T and 1.106 W·kg-1,respectively.The corrosion current density reaches the minimum value that is 0.178?A/cm2,the coating is compact,smooth and has a good retardative effect on corrosive medium diffusion,which leads to the best corrosion resistance.