【作者】 刘仁彬；

【导师】 孔纲；

【作者基本信息】 华南理工大学 ， 材料物理与化学， 2011， 硕士

【摘要】 一定含硅量的钢（通常在0.1%Si附近和0.25%Si以上）在440 460℃采用常规方法热浸镀锌时,铁锌反应剧烈,相过快生长,生成超厚、表面灰暗且粘附力差的镀层。这种现象在热镀锌行业称为Sandelin效应。高温热浸镀锌（520-600℃）可以消除相,是一种解决包括含硅量高于0.25%在内的所有含硅活性钢镀锌问题的可能途径之一。本文选取了四种典型含硅量的钢（0.02%Si, 0.11%Si, 0.20%Si和0.49%Si）,利用光学金相显微镜、扫描电镜和电子探针等分析测试方法系统地研究了在不同锌液温度（440-600℃）下的镀层组织变化规律,探讨了高温热浸镀锌的可行性;利用自然对流条件下质量传输准数方程与溶解速率模型建立了固相Fe在520-600℃液相Zn中的溶解速率方程,并推算出了520-600℃下固相Fe在液相Zn中的扩散系数D。主要得出以下结论:亚Sandelin（0.02%Si）钢和Sebisty（0.20%Si）钢在440℃和480℃热浸镀锌时,镀层组织均致密而连续,从钢基体向外依次为Γ、δ、ζ,以及最外层的自由锌η相组成,镀层生长遵循抛物线规律,主要由扩散机制控制;Sandelin（0.11%Si）钢在440℃和480℃时,从钢基体向外依次为Γ、锯齿层状、块状,以及最外层的自由锌相组成,440℃时镀层生长呈抛物线规律,主要由扩散机制控制;但在480℃时,镀层生长呈直线规律,主要为界面反应机制控制。过Sandelin（0.49%Si）钢在440℃和480℃热浸镀锌时,镀层为薄而连续层和破碎的块状相组成,均未发现Γ相。镀层生长呈直线规律,主要由界面反应机制控制。在520℃热浸镀锌时,亚Sandelin钢、Sebisty钢、Sandelin钢和过Sandelin钢镀层组织均为极薄的Γ层,致密层k和疏松的p层组成,镀层生长均呈抛物线规律,主要由扩散机制控制。在560℃和600℃热浸镀锌时,镀层组织为Γ层和致密的相层,部分粒子弥散分布在层中,镀层生长伴随有显著的相的溶解过程。与常规温度（440-460℃）镀锌相比, 520-600℃热浸镀锌时,亚Sandelin钢、Sebisty钢、Sandelin钢和过Sandelin钢镀层组织均为较连续致密的层状组织,没有出现相,镀层厚度易于控制。特别是对过Sandelin钢镀锌层效果尤为明显。借助固相Fe在（520-600℃）液相Zn中的溶解速率方程分析了镀层生长控制步骤。固相Fe在520℃热浸镀锌时,镀层生长主要是由界面反应和Fe原子在合金相中的扩散控制的;而在560℃和600℃时,镀层的生长主要由Fe原子通过Fe/Zn界面处液相Zn中浓度边界层的扩散所决定。研究表明,固相Fe浸入520℃-600℃液相Zn中,随温度的升高Fe的扩散系数D变大,由520℃的7.79×10-10m²·s^-1增加到560℃时的1.76×10-9m²·s^-1和600℃时的2.01×10-9m²·s^-1。锌液温度超过560℃后,镀层溶解速度加快,镀层过薄,镀层厚度难以达到标准要求,故推荐高温热浸镀锌温度为520-560℃。更多还原

【Abstract】 The presence of silicon at certain levels （in the vicinity of 0.1% and above 0.25%） in steels, can result in the rapid growth of layer, producing a coating of excessive thickness, having gray appearance and poor adherence. This is known as Sandelin effect in galvanizing industy. High temperature hot-dip galvanizing （HT-HDG） is one of the potential approachs to solve Sandelin effects of the silicon containing reactive steel. In this paper, four typical types of silicon containing steels （0.02%, 0.11%, 0.20% and 0.49%Si） were selected and obtained hot dip galvanized coatings of those steels under different liquid zinc temperature （440-600℃）. The law of coating structure changing and the feasibility of HT-HDG were studied by various testing methods such as optical metallographic microscope, SEM and EDS and so on. Based on the current theory of solidification and mass transfer, the dissolution rate equation of solid iron in liquid zinc at 520-560℃was established by using the natural convection condition mass transport equations and the dissolution rate model, and deduced the diffusion coefficient D of Fe in liquid Zn. The following main results were obtained.When hypo-Sandelin（0.02%Si） and Sebisty（0.20%Si） steel hot dip galvanized at 440℃and 480℃, the compact and continuous coating outward from the steel substrate areΓ, , and the outmost layer of freedom phase. The coating grow follow the parabolic law, mainly controlled by diffusion mechanism. At 440℃and 480℃, the Sandelin（0.11%Si） steel’s coating outward from the steel substrate areΓ, jagged , massive thick growth of and the outmost layer of . The coating grow follow the parabolic law and controlled by diffusion mechanism. But when Sandelin steel galvanized at 480℃, the growth of phase allow a linear law, this time the coating growth mechanism controlled by interface reaction. When hyper-Sandelin（0.49%Si） steel hot dip galvanized at 440℃and 480℃, the coating is composed of thin and continuous layer of and the broken block , no foundΓphase. phase grow too fast. The coating grow follow the linear rule and controlled by the interface reaction mechanism.When the hypo-sandelin, sandelin, sebisty and hyper-sandelin steel galvanized at 520℃, the coating consist of very thinΓlayer, dense layer k and loose p. The coating growth followed parabola regularity and controlled by diffusion mechanism. At 520℃and 560℃, the coating containΓlayer and the compact . Part of the particle dispersion distribute in layer and significantly associated with dissolution process.Compared with conventional temperature （440-460℃）, when galvanized at 520-600℃, the coatings of hypo-sandelin, sandelin, sebisty and hyper-sandelin steel are compact and continuous, not appeared and the coating growth is easy to control. It is especially effective for hyper-sandelin steel.The control step of coating growth was analyzed using the dissolution rate equation of solid iron in liquid zinc at 520-560℃. When galvanized temperature is at 520℃, the coating growth process was governed by Fe diffuse in liquid and chemical reaction of the intermetallic compound layers. But at 560℃and 600℃, the coating growth was controlled by Fe across Fe/Zn interface diffuse in a concentration boundary layer in liquid zinc. Research shows that solid Fe immersed in 520-560℃liquid zinc, the diffusion coefficient D become large with the temperature increased, from 7.79×10-10m²·s^-1 at 520℃added to 2.01×10-9m²·s^-1 at 600℃. The temperature of liquid Zn higher than 560℃, the dissolution rate of Fe increase greatly, the coating is over thin and difficult to meet the standards. Therefore, it recommended the temperature of high temperature hot dip galvanizing is 520-560℃.更多还原