Influence of coating and dew point on hearth roll pickup

Thermal spray coatings have been widely used on hearth rolls in a continuous annealing line to improve steel sheet quality and prolong the roll service life. One of the common defects formed on a working hearth roll is the oxide pickup. The most common cause of the pickup formation is that the active Mn oxide reacts with coating. The potentials of two different coatings, CoCrAlYTa–Al2O3 (No. 1) and CoCrYNi–Y2O3 (No. 2), to duplicate pickups by reacting with Fe and Mn oxides were studied. There are three stages during pickup producing and growing. No. 2 coating effectively reduced the corrosion of Mn oxide. The characterization and modification of the surface oxide formed can be changed with different dew points. The results indicate that the dew point from − 53 to − 10 °C can change the depth of Mn oxide, such that an alteration can prevent the first stage and second stage and is good for preventing the pickup growing.