Mechanism analysis and improvement measures of bare spot defects in galvannealed dual-phase steel
In order to solve the problem of the bare spot defect on the edge of the dual-phase steel in a cold rolled plant,the defect morphology and composition of the bare spot area were analyzed.In combination with the selective oxidation principle of dual-phase steel,the relevant influence parameters were analyzed and identified on the site one by one,and the control range of each parameter was determined.Then the optimal control of key parameters combination was obtained through DOE,and targeted control measures were formulated.The results show that the bare spot defects of Zn-Fe alloy dual-phase steel are caused by poor control of the furnace atmosphere,and selective external oxidation of alloying elements such as Mn and Cr diffusing to the sur-face.Reducing the annealing temperature above the Ac1 line while ensuring mechanical properties is beneficial for the formation of internal oxidation.It is necessary to strengthen the atmosphere management of the humidifier in the furnace nose area,avoi-ding the high dew point at the furnace nose resulting in secondary oxidation of the reduced metal.By adopting a hot zone temperature of 770-790 ℃,a heating zone dew point of-10 ℃ to 15 ℃,and a furnace nose oxygen volume fraction of less than 0.001 0％,the bare spot defect rate of Zn-Fe alloy dual-phase steel has significantly decreased from 8％to 1.42％,and the defects are main-ly concentrated at the head of the strip,with obvious optimization effects.
hot dip galvannealed sheetdual-phase steelselective oxidationDOEannealing temperaturedewpointatmos-phere control
万方数据
维普
