Optimization of hot-dip galvanizing process of reactive steels: Minimizing zinc consumption without alloy additions (original) (raw)
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Optimisation of a hot-dip galvanising process: minimising zinc consumption with silver additions
International Journal of Surface Science and Engineering, 2012
The addition of silver to the bath of molten zinc in the hot-dip galvanisation process, affects the morphology and the microstructure of the resulted coatings on the surface of the given steel. The effectiveness of the obtained coatings was controlled by physical and chemical parameters of technical procedure: 1 bath temperature 2 immersion time 3 withdrawal speed 4 addition of silver.
Characterization of hot-dip galvanized coating on dual phase steels
Surface & Coatings Technology, 2011
This work explored the microstructure of continuous hot-dip galvanized zinc coating on two dual phase steels, focusing on the sample preparation methods for cross-sectional microstructure and Fe-Al intermetallic compound observation. Based on the microstructure revealed by proper method, we established a relationship between the annealing atmosphere and coating microstructure. The experimental results showed that the coating thickness and Fe-Al intermetallic compound's size are relevant to the annealing atmosphere. And the coexistence of Fe-Al intermetallic compound and Fe-Zn phase has proved indirectly that the aluminothermic reduction is working during hot-dip galvanizing.
Hot-Dip Galvanized and Alternative Zinc Coatings
In the present work an attempt is made to review the most important information regarding zinc deposition methods. Initially hot-dip galvanizing is examined. First, the deposition technology is briefly discussed and afterwards the structure of the galvanized coatings is described. The analysis of the growth mechanism of the coating follows, along with the examination of the Sandelin effect. In the next part the coating optimization is studied, as it is achieved through the dissolution of different alloying elements in liquid zinc (such as aluminum, nickel, bismuth, chromium, titanium etc). Afterwards an analysis of the corrosion performance of the galvanized coatings is presented. Finally, an environmental assessment of galvanizing is made. This part is used for the introduction of the alternative deposition methods (chemical vapor deposition and thermal spraying) which are compared to hot-dip galvanizing. Although their application is much more limited, an effort is made to present their benefits and their potential, after having described the deposition technology and the structure of these coatings. Spraying of molten zinc Thermal spraying Chemical Vapor Deposition Pack cementation/Fluidized bed reactor 2. Hot-dip galvanizing 2.1. Introduction The term hot-dip galvanizing refers to the zinc deposition method where the zinc coating is cast on the ferrous substrate with its immersion in a bath of liquid zinc (or zinc alloy) after the suitable pretreatment of the steel surface. Although some zinc ores and zinc alloys have been known since antiquity [5], hot-dip galvanizing was invented in 1742 when the French chemist P. J. Melouin, in a presentation to the French Royal Academy, described a method of coating iron by dipping it in molten zinc [6, 7]. However, Melouin did not realize the importance of his invention, as he was not interested in corrosion protection. Only in 1829, when M. Faraday studied the electrochemistry of the zinc-iron system, the Melouin method was reexamined from this point of view. Finally in 1836, S. T. M. Sorel, another French chemist, obtained the first patent for a method of coating iron with zinc. Sorel is also the "godfather" of galvanizing because in his application he used this name for the method he described. The first British patent for a similar process was granted in 1837. The success of hot-dipping was enormous. In less than fifteen years, by 1850, the British galvanizing industry had been consuming 10,000 tons of zinc per year. 2.2. The technology of hot-dip galvanizing Hot-dip galvanizing could be divided in batch and continuous [8]. In the case of batch galvanizing objects to be coated are ready for use, as for example lighting poles, crash barriers, water and natural gas pipes, car parts etc. By contrast in continuous galvanizing coiled materials are processed (steel sheets and wires), which will suffer further mechanical processing after coating. The two methods are characterized by small differences, which will be analysed later. In general galvanizing is accomplished in three stages: the pretreatment of the substrate surface, the immersion in liquid zinc and the post-treatment [9, 10]. The surface pre-treatment has three targets: 1. The cleaning of the ferrous substrate from remnants of the manufacturing process, such as mineral oils, emulsified oils, greases etc. 2. The removal of iron oxides that form during thermal treatment, welding and storage of the uncoated material. 3. The growth of a protective layer that inhibits re-oxidation of the substrate after the oxide removal and prior to the immersion in the liquid metal, because the deoxidised steel is extremely active and reacts with the atmospheric oxygen within a few minutes [9]. The first target is achieved with a process called degreasing. In this case the substrate is immersed in an aqueous solution containing about 50% NaOH at about 90 o C [9, 14]. This process is quite effective. However, due to the occupational risk involved from the presence of the hot NaOH solution, several alternative methods have been developed which use mild acidic or alkaline solutions containing special detergents. These solutions, apart from being less dangerous, are effective at lower temperature, increase the speed of the process and have lower consumption. Furthermore, the oil precipitates in the degreasing tank and its evacuation is easier. The removal of the iron oxides (pickling) is accomplished with the immersion in baths of an aqueous solution containing about 16% HCl or 10% H2SO4 [9-11]. It is obvious that an intermediate rinse of the substrate with clean water is necessary when
Steel painting hot-dip galvanized as efficient alternative for corrosion protection
Anais do(a) 2nd (ICAIC) International Conference for Academia and Industry Co-operation & 2nd (IMMSEM) International Meeting in Materials Science and Engineering of Maranhão, 2021
Corrosion of steel is a recurring problem, especially in environments with a high chloride content. Hot dip galvanizing is an efficient alternative to protect steels against corrosion and depending on the aggressiveness of the medium, there is still the possibility of ensuring extra protection of the galvanized with the paint on its surface, a process known as duplex. In the process of hot dip galvanizing the steel is coated with zinc after immersion in a molten liquid zinc bath between 450 and 490ºC and the surface of the immersed material is coated and protected by zinc. The deposited zinc layer has a usual thickness of 75 to 125µm and with abrasive blasting before galvanizing it is possible to reach a layer up to 250μm thick. The duplex coating consisting of hot dip galvanizing followed by painting of structural steel, provides additional corrosion resistance as galvanizing protects the base steel, providing cathodic and barrier protection while the paint in turn provides barrier and anodic inhibition protection to the galvanizing layer, isolating it from the corrosive attack of chlorides and sulfides in the atmosphere. The painting of galvanized steel is indicated between 24 and 48 hours after galvanizing, in order to avoid the formation of zinc oxide in the substrate. The increase in the useful life of structural steel is important for the industry in general, be it for economic or safety aspects to users. In this paper, the benefits of the duplex system were evaluated concluding that this process increases the useful life of the steel and currently this process is the most economical and efficient alternative to protect the steel against corrosion.
A REVIEW OF STUDY ON CORROSION BEHAVIOUR OF ZINC COATED MILD STEEL
IRJET, 2022
Steel is one in all the biggest and oldest materials utilized in all engineering application. Steel is employed in construction, industries, in plant etc. The aim of providing steel in appropriate form is to strength the actual member. Researchers within the area of zinc coatings on steel are rather unending due to the unique properties and therefore the very low cost that it offers. Coatings, either soft or hard, are commonly accustomed protect steel against corrosion for extended service life. With coatings, assessing the corrosion behaviour and standing of the substrate is challenging without destructive analysis. Zinc, a crucial nonferrous metal, is that the fourth most used metal within the world. It's the fourth most used metal within the world. Its innumerable uses in industrial also as in other segments. The first utility of zinc is in galvanization and as an anode within the battery. Steel coated with zinc, which is understood as galvanized steel, is widely utilized in industries. While zinc protects many metals from undergoing corrosion, by itself, it undergoes corrosion in several acids, alkaline, and neutral environments.
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...
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.