HIGH TEMPERATURE HOT-DIP GALVANIZING OF FASTENERS
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DOI:
https://doi.org/10.25712/ASTU.2072-8921.2025.02.031Keywords:
hot-dip galvanizing, high temperature hot-dip galvanizing, zinc coating, temperature galvanizing, gal-vanizing of fasteners, structural coatings, coating coatingsAbstract
High-temperature hot-dip galvanizing involves immersing steel products in molten zinc at temperatures above 500°C. There is data on the peculiarities of the phase structure of zinc coating obtained at such temperatures that provide a lower coating thickness. Threaded fasteners require a minimum coating thickness to ensure satisfactory product make-up. However, it is also necessary to ensure a high level of performance properties of the coating on the fastener, such as the hardness of the steel base, coating hardness, coefficient of friction, and corrosion resistance. In this regard, the goal of the work was to study the structure and properties of zinc coatings formed in the melt at a temperature of 450-560°C on threaded fasteners. It has been established that exposure to high melt temperatures leads to a decrease in the hardness of steel bolts, but the hardness remains within normal limits. It has been shown that the minimum coating thickness on all steels under study is formed in the galvanizing temperature range of 530-560°C. A joint analysis of X-ray phase analysis and energy-dispersive microanalysis data showed that the coating formed in the melt at a temperature of 530°C practically does not contain the ζ-phase, which is responsible for the intensive growth of the coating. The properties of zinc coatings formed in the melt in the high temperature range meet the operational requirements for fasteners. The coatings have 1.5-2 times greater hardness, greater surface roughness, and a lower coefficient of friction compared to standard zinc coatings formed in the melt at 450°C. The coating formed in the melt at 530°C is more chemically resistant compared to standard zinc coating.
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