Optimization of hot-dip galvanizing process of reactive steels: Minimizing zinc consumption without alloy additions (original) (raw)
Optimizing Hot Dip Galvanizing Operations of Steel Sheets for better Quality
The zinc phosphate or chromate coating layer contains from about 0.5 to 10.0% by weight of magnesium, from about 0.1 to 2.0% by weight of nickel, and from about 0.5 to 8.0% by weight of manganese (US Patent 6322906, 2001). The performance of galvanized coating is known to depend to a large extent upon the nature of the environment to which it is exposed. However, for any specific exposure condition the thickness of galvanized coating is the most important factor determining its life of corrosion protection (Wall, 1989). Galvanized coating comprises an outer 'pure' zinc layer and several inner alloy layers of iron and zinc inter-metallic phases, the layers becoming successively richer in iron with depth. The role each of these layers plays in
Metallurgical and Materials Engineering, 2014
The purpose of this work is to identify the influence of zinc bath temperature on the morphology, texture and corrosion behavior of hot-dip galvanized coatings. Hot-dip galvanized samples were prepared at temperature in the range of 450-480 °C in steps of 10 °C, which is the conventional galvanizing temperature range in the galvanizing industries. The morphology of coatings was examined with optical microscopy and scanning electron microscopy (SEM). The composition of the coating layers was determined using energy dispersive spectroscopy (EDS) analysis. The texture of the coatings was evaluated using X-ray diffraction. Corrosion behavior was performed using salt spray cabinet test and Tafel extrapolation test. From the experimental results, it was found that increasing the zinc bath temperature affects the morphology of the galvanized coatings provoking the appearance of cracks in the coating structure. These cracks prevent formation of a compact structure. In addition, it was concl...
Development of Bath Chemical Composition for Batch Hot-Dip Galvanizing—A Review
Materials
Obtaining zinc coatings by the batch hot-dip galvanizing process currently represents one of the most effective and economical methods of protecting steel products and structures against corrosion. The batch hot-dip galvanizing process has been used for over 150 years, but for several decades, there has been a dynamic development of this technology, the purpose of which is to improve the efficiency of zinc use and reduce its consumption and improve the quality of the coating. The appropriate selection of the chemical composition of the galvanizing bath enables us to control the reactivity of steel, improve the drainage of liquid zinc from the product surface, and reduce the amount of waste, which directly affects the quality of the coating and the technology of the galvanizing process. For this purpose, the effect of many alloying additives to the zinc bath on the structure and thickness of the coating was tested. The article reviews the influence of various elements introduced into...
Nature of Steel Effect on Intermetallic Compounds Obtained by Galvanization
International Journal of Thermal and Environmental Engineering
Zinc and some of its alloys have a number of characteristics that make it well suited for use as a protective coating against the corrosion of steel substrates under severe atmospheric conditions. The metal of zinc, which represents the main galvanization element offer then a cathodic protection to the ferrous materials. Because of these excellent characteristics, galvanization coatings are expected to be used for different protective applications fields. The objective of this work is to study the influence of the nature of steel substrate on the microstructure and the hardness of the intermetallic compounds. The steels used as the substrate are employed in agriculture field as tubes and irrigation elements in pivot. After an optimal preparation of the surface of the substrate by an appropriate roughness process, the steels specimen were immersed in a molten zinc bath maintained at 450°C. The chemical reactions which take place between the steel and the liquid zinc give rise to the ...
Coloring hot-dip galvanization of steel samples in industrial zinc-manganese baths
Journal of Mining and Metallurgy, Section B: Metallurgy, 2017
Colored hot dip galvanization of various steel samples was realized in an industrial bath containing 738 kg of a Zn-Mn liquid alloy at 450?C. Zinc was alloyed in three steps to reach 0.1, 0.15 and 0.2 w% of Mn in liquid zinc, and galvanization of 9 different steel samples was performed in all three baths. The obtained colors change in the sequence blue - yellow - pink - green with increasing the Mn-content of the bath and with increasing the wall thickness of the steel samples. The results are analyzed by Glow-discharge optical emission spectroscopy (GD-OES) and Secondary Neutral Mass Spectrometry (SNMS) techniques. It is shown that depending on the Mn-content and on the wall thickness of the steel the samples are coated by MnO of various thicknesses (in the range between 30 - 230 nm). This layer forms when the samples are removed from the Zn-Mn bath into surrounding air, before the Zn-layer is solidified. Light interference on this thin MnO layer causes the colors of the galvanized...
Microstructure of zinc hot-dip galvanized coatings used for corrosion protection
Materials Letters, 2006
Low carbon steel substrates were galvanized in molten zinc containing 1 wt.% manganese. The as-cast coatings were examined with optical microscopy, scanning electron microscopy and X-ray diffraction. From the above investigation it was deduced that, although Mn concentration in the coating cross-section is very low (below the EDS sensitivity), Mn-rich crystals are deposited at the lateral surface of the hot-dip galvanized coating. These Mn "islands" are very beneficial with regard to the corrosion performance of the coating, because they act as sacrificial anodes that protect Zn.
Study of zinc coatings on steel substrate attained by two different techniques
Surface and Coatings Technology, 1999
The purpose of this work was to identify the influence of different process variables, such as bath temperature, cooling rate, air knives wiping, immersion time and bath alloy additions, on the morphology and coating thickness attained using two different galvanizing processes: Cook Norteman and Sendzimir. The data of these operational variables were reported for each process. Scanning electron microscopy was used to characterize the microstructure of the metallic samples. Also, impact and bending tests were performed, in order to evaluate the adhesion of the coatings. The most influential step found in coating thickness was immersion time. In contrast, aluminum concentration was the most important factor determining coating morphology, since it controls the formation of Fe-Zn intermetallic phases. For Al concentration lower than 0.09 wt.%, the layer formed on the steel consisted of g, f, d and C phases. Higher concentration of Al (more than 0.16 wt.%) produced a thicker layer of g phase, that is richer in Zn than in the former case. Also, lamellae rich in Fe, Al and Zn were formed close to the substrate-coating interphase. Both coatings showed good adhesive strenght, under the same testing conditions.
Pitting Corrosion of Hot-Dip Galvanized Coatings
Materials, 2020
Lead (Pb) addition to hot-dip galvanizing (HDG) baths affects the physical characteristics of zinc coatings and is also useful to protect kettles. The influence of lead additions on both corrosion rate and morphology as well as on structure of zinc coating is less investigated. In this paper, three different additions, (Pb = 0.4–0.8–1.2 w/w) were chosen for three series of steel substrates, plus references without lead. The three steels chosen as substrates contained silicon (Si) = 0.18, 0.028, 0.225 w/w, respectively. The experimental part included both macro- and micro-electrochemical measurements, weight loss vs. time plots, Glow Discharge Optical Emission Spectroscopy (GDOS) and SEM/EDX microanalysis of both surface and cross-section of samples. Lead concentration is responsible for evident bimetallic coupling in the surrounding of lead inclusion with consequent increased dissolution rate, chunk effect, and rougher surface morphology.
Crystal Research and Technology, 2004
The influence of the alloying elements on the interface reactions of zinc coatings during the galvanization process was examined. These reactions affect the crystallization and the structure and properties of the outer layer of the coatings. Depending on the type and concentration of the alloying additions in the galvanizing bath differences were induced in the crystallization process of the Fe-Zn phases. It was found that both the concentration and the distribution of the alloying elements played an important role in the growth of the phases. The formation of the phases and the distribution of the alloying elements in the coatings were determined using X-Ray diffraction (XRD) and Scanning Electron Microscopy (SEM) associated with an Energy Dispersive X-Ray Spectroscopy (EDS) analysis. Finally the behaviour of the galvanized coatings was examined under accelerated salt spray corrosion conditions.