Abstract

A continuous galvanizing line (CGL) has a zinc pot, which is filled with molten zinc for zinc coating. In a zinc pot there are pot rolls to guide steel strip. Usually WC-Co thermal sprayed coatings are used for protection of the pot rolls from severe corrosion by molten zinc. Authors analyzed WC-Co coatings used in a zinc pot of a CGL for 33 and 56 days. On the surface of a WC-Co coated roll, many kinds of deposits were observed including top dross, Fe2Al5 inter-metallic compound, which might induce dross defect on the surface of galvanized steel. Diffusion depth of zinc into the WC-Co coating used for 33 days was only within 10µm but some areas were severely attacked along cracks within the coating layer. Usually molten zinc contains small amount of aluminum about 0.12 - 0.2%. Through SEM study, we observed that not only zinc but also aluminum diffused into the WC-Co coating after service in the zinc pot for 56 days. Al-Fe rich layers were observed on the surface of the spray coating for some cases. The phase of those layers might be Fe2Al5 since their chemical compositions are similar to Fe2Al5 top dross.

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