The Research About Surface Quality Improved Of Hot Galvanizing Product

The reasons for hot rolled galvanization plate defects of Tangsteel,such as pits,spots,zinc removal and passivation,has been researched by means of OM,SEM and EDS,and the solving measures have been proposed.The process of hot rolled galvanizing line has been optimized,which obtains the plates of good coating performance,and meets the requirements of high-end users.The main conclusions are as follows:The pits are intermittent on the surface of plate,and they are not periodic.The shape of the pits is extremely regular,which is mainly caused by mechanical scratch,different dendrite crystallization rate and formation time.The diameter of black spot is about400?m.The dendrite at the defect is fricted or compressed.To make it more reductive than the surrounding position,the defect part is higher than the normal.Thus the black spot defect is appeared.The height of the bright spot is slightly higher than the surrounding area,but it is less than the black spots defects.The causes of bright spots may be the formation of aluminum or zinc oxide in zinc liquid.Continuous hot galvanizing technology has been optimized,which included the decrease of temperature when the strip was put into the zinc pot,reducing and controlling the stability of liquid temperature of zinc,lowering Fe content in liquid zinc,as well as increasing the cooling rate after strip galvanizing.Fe diffusion to zinc layer is limited by Al inhibition layer which is closer to the zinc layer,which significantly improves the adhesion of zinc layer and reduce the appearance of all kinds of defectsThe associated parameters,such as gradient temperature of strip and the excess air coefficient in NOF furnace are optimized by the research of improving the atmosphere in the furnace and the effect of oxidation/reduction.The method of piping high hydrogen into the furnace has successfully solved the problem of oxidation/reduction and poor adhesion of zinc layer.