Annealing hearths used in continuous galvanizing lines (CGL) producing sheet steels commonly use stainless steel hearth rolls to guide the sheet through the heat treatment process. The surfaces of these rolls need to maintain a speci
c roughness to add sucient friction force to move the sheet forward. In addition the surface has to be able to combat against the formation and growth of oxide build-ups and metallic pick-ups which can form due to the contact with the surface of the steel strip in the hearth. When such anomalies have been successfully prevented, the surface of the sheet will not be damaged. Thermally sprayed metallic, ceramic and cermet coatings have been utilized in this application. The coating material and the coating method used to produce the coating determine the performance of the coating in the application. As an additional challenge, the coating material is required to have high thermal shock resistance to be able to endure maintenance shutdowns. Eight different coating types were produced for the experimental part of this thesis. These coatings were subjected to wear resistance, thermal shock and build-up formation tests. The results received from the tests were used to draw conclusions on the effects of different variables between the coatings. Very high quality 5@565_545Y5L coatings were successfully sprayed with the high velocity air fuel (HVAF) method. The chromium carbide coatings provided the highest wear resistances
t for use in lower temperatures. The metallic 5@565_545Y5L coatings did not provide adequate wear resistance even though they had excellent thermal shock resistances. The atmosphere plasma spray (APS) method increased the wear resistance of the 5@565_545Y5L coatings, but made them vulnerable to thermal shock. The addition of alumina increased the wear resistances of the high velocity oxygen fuel (HVOF) and HVAF sprayed 5@565_545Y5L coatings without noticeable drawbacks. The metallic and cermet 5@565_545Y5L coatings sprayed with HVOF and HVAF methods formed large build-ups in the iron oxide build-up test. This was so because pure iron was developed onto the coating by the reduction of the iron oxide powder. The 5@565_545Y5L coatings sprayed with the APS method absorbed more manganese in the manganese oxide build-up test probably due to the greater surface area. Furthermore, the increasing thickness of the formed oxide layers on top of the coatings did not have an increasing effect on the amount of formed manganese oxide compounds.