The paper investigates the limits of nickel-chromium/chromium-carbide coatings on hearth rolls in industrial scale hot dip galvanizing and annealing lines for high quality steel strip. While complex coatings with various binders and ceramics have been invented and publicized, in voestalpine plants a Ni20Cr-Cr₃C₂ coating has been sufficient for decades. However, the current change in the annealing conditions of some plants led to a beginning unravelling of coatings on some rolls.

Previously, the highest priority was given to the constant buildup of manganese on top of the coating and the isolated formation of so-called pick-ups. The first concern was a smoothing of the surface and therefore less traction for the steel strip and the second was indentation of the steel strip via pick-ups, the paper investigates the conditions under which the coating itself breaks down. This degradation seemingly alleviates the previous problems by removing the top layer, even though it suggests a rather limited lifetime for the coating itself. The investigation was started after an increase in dew point led to an abrupt change in the chemical composition and the visual appearance of the top layer of the coating.

The dew point, hydrogen content, temperature and resulting oxygen pressure are considered and a relation is proposed which moves away from a limitation purely based on temperature. The investigation is conducted on industrial plants and examines coatings, which have occasionally been in use for decades without failure. Depending on economic feasibility, samples are taken for XRD, REM and EDX analysis or analyzed inside the plant using a mobile XRF device and a microscopic camera. A relation between the production process of the coating powder, the ratio of carbide to alloy and the resistance to degradation is proposed. Solutions by utilizing various NiCoCrAlY alloys, Al₂O₃, Y₂O₃, other carbides or purely ceramic coatings will be discussed on a theoretical level.