Effect of Mn on the Formation of Pickups on Thermal Spray Coatings

Thermal spray coatings have been applied on furnace rolls in continuous annealing lines to improve product quality and prolong roll service life. The most common defects formed on working furnace rolls are oxide pickups. In this study, HVOF sprayed cermet coatings are used to duplicate pickups by reacting with iron and manganese oxides. The reactions are performed in a furnace at 900 °C with inert gas flow. After testing for eight days, large Mn-rich pickups were formed on the coatings while pickups without Mn were very small. Mn was shown to enhance the reaction between the coating and the iron oxide. Pickups from a furnace roll were also investigated and compared with the laboratory samples.