Enhancing oxidation protection and stability of Al2O3-glass coating for 06Ni9DR alloy steel via double-layer design

The development of highly oxidation-protective and stable coatings is crucial for significantly reducing the oxidation of 06Ni9DR alloy steels during heating before hot rolling, thereby enabling the products with superior surface quality. In this study, three types of coatings—Al 2 O 3 -glass coating, a 10 wt% NiO-90 wt% Al 2 O 3 ceramic coating, and a double-layer coating Al 2 O 3 -glass top layer and NiO-Al 2 O 3 ceramic bottom layer)—were prepared, and their oxidation protection and underlying mechanisms were systematically investigated. The results revealed that the oxidation protection ratio of the glass coating sharply decreased from 96.6 % for 10 min to 44.9 % for 180 min at 1200 °C. In contrast, the oxidation protection of the ceramic coating increased slightly with the oxidation time. Notably, the excellent oxidation protection ratio of the double-layer coating was obtained as 86.2 % for 180 min. The rapid densification of the Al 2 O 3 -glass layer in the double-layer design provided good oxidation protection and significantly reduced the formation of iron oxides in the initial oxidation stage; NiO-Al 2 O 3 ceramic layer reacted with Fe 2+ to form a relatively dense composite spinel barrier layer, which further improved the thermal stability of the Al 2 O 3 -glass layer, and greatly enhanced the oxidation protection and stability of the double-layer coating.