热镀锌铁合金双相钢漏镀缺陷机理分析及改进措施

Mechanism analysis and improvement measures of bare spot defects in galvannealed dual-phase steel

针对某冷轧厂生产的双相钢边部存在漏镀缺陷的问题,对漏镀部位的缺陷形貌和成分进行了分析,结合高强双相钢选择性氧化原理对现场的相关影响参数逐个进行剖析、识别,确定出各个参数的控制范围,随后通过试验设计得出了关键控制参数的最佳组合,并针对性制定了控制措施。结果表明:锌铁合金双相钢的漏镀缺陷是由于炉内气氛控制不好,锰、铬等合金元素扩散到表面出现选择性外氧化导致的;在保证性能的前提下,在Ac_1线以上适当降低退火温度,有利于内氧化的形成;炉鼻子气氛控制要加强对加湿器的管理,一旦加湿过大就会引起炉鼻子处露点过高,导致冷区氧含量过高,造成已还原的金属出现二次氧化;通过采取热区温度770~790℃,加热区露点-10~15℃,炉鼻子氧体积分数小于0.001 0%,锌铁合金双相钢的漏镀缺陷率由改善前的8%大幅下降到1.42%,且缺陷主要集中在带钢头部位置,优化效果明显。

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 surface.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,avoiding 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 0.0010%,the bare spot defect rate of Zn-Fe alloy dual-phase steel has significantly decreased from 8%to 1.42%,and the defects are mainly concentrated at the head of the strip,with obvious optimization effects.