Effect of substrate grain size on iron-zinc reaction kinetics during hot-dip galvanizing

In the galvanizing process, it has been proposed that the grain size of the substrate steel influences the Fe-Zn alloy phase reaction kinetics and growth rate during immersion in the liquid Zn bath. Two grain sizes (nominally 15 and 85 μm) were developed in a decarburized low-carbon (0.005) steel and hot-dipped galvanized in 0.00 wt pct Al-Zn and 0.20 wt pct Al-Zn baths to study the effect of substrate grain size on Fe-Zn phase formation. Uniform attack of the substrate steel occurred in the 0.00 wt pct Al-Zn bath, since an Fe₂Al₅ inhibition layer did not form. No barrier to nucleation of the Fe-Zn phases exists in this Zn bath, and therefore, the substrate steel grain size had no significant effect on the kinetics of phase growth for the gamma, delta, and zeta phase layers. In the 0.20 wt pct Al-Zn bath, discontinuous Fe-Zn phase growth (outburst formation) occurred due to the initial formation of the Fe-Al inhibition layer. The nucleation of the Fe-Zn phases was significantly retarded in this bath for the large (85 μm) substrate grain size. Whereas outbursts were found in the 15-μm grain size substrate after 10 seconds of immersion time, it required 1200 seconds to nucleate just a few outbursts in the 85-μm substrate. These results support the mechanism that Fe-Al inhibition layer breakdown occurs along fast diffusion paths for Zn in the inhibition layer that correspond to the location of substrate steel grain boundaries where reaction with Fe can occur.     

Reactivity of silicon steels hot-dip galvanizing

Abstract

Excessive reactivity of silicon-bearing steels in hot-dip galvanizing is well known. No adequate explanation exists as to why silicon should be so effective in destabilizing the layers of Fe-Zn intermetallies allowing free access of zinc to the reaction interface and causing linear kinetics to persist throughout the galvanizing reactions. Another important aspect of the silicon effect is the formation of grey coatings.

Special galvanizing experiments combined with electron microprobe and scanning electron microscope analyses and a critical reconsideration of existing knowledge allow us to present a consistent mechanistic picture of the silicon-induced reactivity and grey-coating phenomena.

Résumé

La réactivité excessive des aciers con tenant du silicium, lors de la galvanisation par immersion, est bien connue. Il n'existe aucune explication satisfaisante de la grande efficacité du silicium pour provoquer l'instabilité des couches d'intermétalliques Fe-Zn. Cette instabilité permet au zinc d'atteindre librement l'interface de réaction, ce qui fait que la cinétique demeure linéaire tout au cours des réactions de galvanisation. De plus, le silicium a une influence importante sur la formation de revêtements gris

Des expériences spéciales de galvanization combinées avec des analyses à la microsonde et au microscope électronique à balayage et un examen critique des connaissances actuelles, nous permettent de suggérer une image logique des phénomènes de la réactivité engendrée par le silicium et du revêtement gris.     

The effect of iron oxide as an inhibition layer on iron-zinc reactions during Hot-Dip galvanizing

A study was conducted on the effect of a uniform oxide layer on the galvanizing reaction in 0.20 wt pct Al-Zn and pure Zn baths at 450 °C. In the 0.20 wt pct Al-Zn bath, poor wettability of the oxide layer was observed. No significant liquid Zn penetration of the oxide occurred and, therefore, attack of the steel substrate to form localized Fe-Zn growth did not occur. It was found that the iron oxide acted as a physical barrier or inhibition layer in the pure Zn bath, similar to the Fe₂Al₅ inhibition layer that forms at the steel interface in Al-Zn baths. The inhibition effect of the oxide in the pure Zn bath was temporary, since cracks and other macrodefects in the oxide acted as fast diffusion paths for Zn. Localized Fe-Zn growth (outbursts) formed at the steel/coating interface, and the number of outbursts was generally inversely proportional to the oxide layer thickness at constant immersion times. Increased immersion time for a constant oxide layer thickness led to an increase in the number of outbursts. These results simulate the diffusion short circuit mechanisms for Fe₂Al₅ inhibition layer breakdown in Al-containing Zn baths.     

Application of thermal spray and surface treatment techniques in hot-dip galvanizing line pot hardware

The failure of zinc pot hardware in continuous hot-dip galvanizing lines( CGLs) is due to zinc corrosion,abrasion,and dross build-up. Enhancing the life of pot hardware will not only upgrade the quality of the sheet products but also will increase the efficiency of CGLs,with decreasing cost and increasing energy savings. This paper introduces the current research and development for thermal spray coatings for pot rolls,sleeves,and bushings,and analyses the thermal spray and surface treatment technique details of dross adhesion prevention. It provides the potential applications and developing trends in thermal spray coatings and surface treatment techniques for pot hardware.     

连续热镀锌楔形气刀对镀层均匀性的影响

利用流体力学计算方法,对连续热镀锌气刀射流拭锌过程中带钢表面气流压力和温度分布进行了仿真研究。模拟结果表明:气刀喷吹时,带钢边部5mm范围内出现压力衰减,且边部散热较中心处快,易使带钢出现边部过镀锌缺陷;为避免该缺陷发生,设计了增大边部开口度的楔形刀唇结构气刀,有效阻碍了带钢边部压力衰减,且边部镀层减薄率随楔形开口度的增加而线性增加;对于平行段开口度为1.10mm的气刀,边部开口度选定为1.18~1.22mm,有利于改善镀层均匀性。     

热镀锌无铬钝化膜脱落的分析与控制

针对采用某无Cr钝化剂后,某钢厂热镀Zn无Cr钝化钢板在脱脂清洗过程中钝化膜脱落及喷粉附着力不足的问题,通过膜厚检测、盐雾试验、红外光谱分析、能谱分析、辉光（GDS）分析、扫描电镜等手段,研究了该问题的机理。结果表明,钝化膜脱落是由于钝化板生产过程中水分没有充分挥发,阻断钝化膜老化,在遇到高湿度条件时发生过度溶胀所致;通过生产工艺调整和优化,使皮膜充分固化,以提高无Cr钝化剂与生产设备的适应性,解决了该钝化膜脱落问题,从而满足某钢厂的使用需求。     

连续热镀锌锌锅内物理场的数值模拟

在带钢连续热镀锌生产中,锌锅中的铝含量及其波动对产品质量有着极其重要的影响,而铝的质量浓度场的分布与锌液在锌锅内的流动、温度分布和锌铝锭的添加位置紧密相关。以某连续热镀锌锌锅为研究对象,采用流体力学方法研究锌铝锭添加对锌锅内流场、温度场和成分场的综合影响。模拟结果表明,自然对流效应改变了锌锅后侧锌液流动形式,冷锌液流向锌锅底部,锌锅后侧形成大范围涡流;锌锅整体温度波动较小,补锭口温度为锌锅最低,锌锅进出口温度较高;B锭(Zn-0.2%Al)融化补充的铝主要进入锌锅底部,高铝锌锭F锭(Zn-10%Al)的添加可调整V形区内的铝溶度分布。此研究为减少锌锅内铝浓度的波动和优化补锭工艺奠定了基础。     

热浸镀锌锌锅中锌液流动的数值模拟

根据包钢薄板厂热镀锌锅的结构和操作工艺参数,采用Fluent软件,建立了热镀锌锅的三维模型,在不考虑锌锅锅壁与锅底的厚度和炉鼻以及气刀对锌液流动影响的情况下,对热镀锌锅内锌液的流动进行了计算。模拟结果表明：钢带拉速是锌液运动的主动力,宏观上锌液的速度正比于钢带拉速;钢带宽度影响着锌锅内漩涡的大小和位置,进而影响着锌液的整体流动状态;感应加热器的功率变化只对其附近区域锌液的流动有影响。     

Recent development of UHSS and its hot-dip galvanizing processes in Baosteel

Baosteel has excelled in automotive steel sheets in the past three decades.It has made a significant contribution to the development of China’s automotive industry by producing a wide range of high-quality steel products.Some milestones achieved by Baosteel automotive steel sheet were briefly reviewed.The current challenges in producing ultra-high strength steel(UHSS),especially hot-dip galvanized UHSS,were summarized.The most current advancements in UHSS and the corresponding hot-dip galvanizin...     

Application of WC cermet sprayed composite coating in hot-dip galvanizing lines

With the rapid development of the automobile industry,the use of galvannealed and galvanized steel sheets in automobiles is on the rise. These sheets must meet very high surface quality requirements. The surface treatment of line rolls is known to have a great impact on strip quality. To prevent dusts such as zinc ash from pressing into the strip surface,we used a composite thermal spray surface treatment technique to treat rolls. The successfully developed tungsten carbide( WC) + Ni-P composite plating technology improved the quality of the tungsten carbide thermally sprayed WC roll surface. This technique is also helpful to control defects such as adhered foreign materials in hot-dip galvanized automobile outer panel surfaces.     

基于偏最小二乘回归模型的带钢热镀锌质量监控方法

提出了基于偏最小二乘回归模型的带钢热镀锌质量监控方法.以带钢热镀锌生产中带钢力学性能和锌层质量的质量监控为研究对象,用偏最小二乘方法建立了生产过程参数与质量结果之间的回归模型,对生产过程控制能力进行了分析,并给出了产品质量的预测方法.用鞍钢股份有限公司带钢热镀锌的实际生产数据进行验证.结果表明,偏最小二乘法比传统的多元线性回归方法具有更好的预测精度,基于偏最小二乘回归的锌层质量预测模型,其相对预测误差可达到5.93%.     

利用热镀锌渣制备超细锌粉的试验研究

利用冷轧厂热镀锌渣为原料,采用蒸发-冷凝法直接制备出超细锌粉。采用新型蒸发装置、冷却装置,考察了最大蒸发温度、恒温时间、保护气体通入量、蒸发物料量、冷却强度等对锌粉收得率及粒度分布的影响。对所得超细锌粉的化学成分、粒度分布、XRD和微观结构进行测试,并讨论了锌粉团聚的原因及对策。     

Zn-Al-Mg系热浸镀层钢板的研究进展

介绍了Zn-Al-Mg系合金镀层的发展及日本2家企业开发的2种高耐蚀性合金镀层钢板的性能,分析了添加合金元素对镀层组织的影响以及微观结构对镀层性能的影响,总结出合金镀层具有高耐蚀性的机理,指出了Zn-Al-Mg系高耐蚀热浸镀合金镀层的研究方向。     

气刀对热镀锌锅流场影响的数值模拟

气刀喷吹是带钢连续热镀锌生产的重要工序,理解气刀喷吹过程对锌锅内部流场和表面流场规律的影响对提高带钢质量具有重要意义.建立了带钢连续热镀锌过程中气刀喷吹三维流场数学模型及锌锅流场三维数学模型,将气刀喷吹在锌锅表面的压力作为动量源项加载到锌锅流场数学模型的动量方程中,分析气刀喷吹压力及带钢速度对锌锅内部及表面流场的影响,...     

电脉冲处理对热镀锌镀层生长动力学影响

采用正交试验的方法,研究了电脉冲处理对热镀锌镀层生长动力学的影响.以合金层生长速率时间指数为评价指标对电脉冲处理效果进行了优化.正交试验结果表明,电脉冲处理参数中电容量是主要影响因素,处理时间影响不明显,在电容量200μF,电压700 V,频率2 Hz,处理时间30 s的条件下作用效果较好.在此参数条件下的热镀锌实验结果表明:合金层的生长受到抑制,厚度减薄,组织变得均匀致密;合金层生长速率时间指数由0.717下降到0.428,合金层的生长方式由界面反应和扩散联合控制转变为仅受扩散控制.     

改良森吉米尔生产工艺在越南Galvalume生产线上的应用

介绍了中国出口越南的1条薄规格改良森吉米尔法热镀Galvalume产品的生产工艺和调试工作,阐明了改良森吉米尔工艺生产热镀Galvalume产品的核心工艺制度,包括钢板前处理工艺、NOF炉设计、浸镀工艺等,优化了产品质量。     

Effect of particle size on surface segregation

Translated from Poroshkovaya Metallurgiya, No. 10(310), pp. 14–16, October, 1988.     

连续热镀锌机组锌液温度的精确控制

锌液温度的控制直接影响到连续热镀锌机组锌锅内锌渣的产生量和锌层中抑制层的成分及结构,进而影响热镀锌产品的表面质量。系统分析影响连续热镀锌机组锌液温度精确控制的因素,改进带钢入锌锅温度的控制、锌液温度的检控精度,精确控制锌锅加锌速度,优化锌锅辊预热温度控制,实现锌液温度的精确控制。     

热镀锌机组圆盘剪工艺参数优化技术的开发

热镀锌机组圆盘剪工作时,由于剪切工艺参数设定不当等原因造成圆盘剪设备的故障以及带钢边部出现有扣边、毛刺和切断比失衡等主要切边质量问题,以某钢厂热镀锌机组圆盘剪设备为研究对象,对其设备本身和工艺参数展开研究.通过对影响带钢边部质量缺陷因素的分析,以及BP神经网络输入变量相关性要求选择前张力、间隙量、重叠量、切边量4个因素...