Development of an assessment method for pickup formation on furnace rolls

Introduction. During the recrystallization annealing of cold-rolled electrical and automotive steels, the formation of pickups on the surface of furnace rolls presents a significant issue, as they lead to surface damage of the steel strip in the form of indentations. The focus of the present study is the evaluation of this defect. Methods. To this end, a laboratory-based methodology was developed to assess the tendency of furnace rolls to form pickups. The method replicates the contact interaction between the furnace roll and the steel strip under real annealing conditions, taking into account the applied contact pressure, a temperature range of 700–900 °C, the (H2–N2) furnace atmosphere, and a humidity level arising from the presence of oxygen adsorbed on the steel strip. To validate the method’s reliability, a comparative analysis was conducted between pickups formed on the roll surface after industrial operation and those generated under laboratory conditions in the contact zone between steel samples made of roll and strip materials. The analysis employed optical microscopy, X-ray diffraction, and scanning electron microscopy. Results and discussion. The study confirmed that the developed methodology produces pickups on the specimen surfaces with morphology, chemical composition, and phase structure closely resembling those observed on the furnace rolls. A comparative assessment of the pickup formation rate between a typical furnace roll material (EI 283 steel) and a NiCrAlY coating applied by plasma spraying revealed that the pickup formation rate for the EI 283 steel was an order of magnitude higher. The validated methodology can thus be used to evaluate the effectiveness of strategies aimed at mitigating pickup formation on furnace rolls under long-term high-temperature contact conditions.