Investigation of the Effect of Secondary Oxidation on the Descaling Performance of AISI 5140 Low-Alloy Steel

The oxidation behavior of AISI 5140 low-alloy steel was investigated under air at oxidation temperatures ranging from 800 to 1100 °C and oxidation times ranging from 5 to 120 min. The microstructure and chemical composition of the oxide layer were characterized, and an oxidation kinetic model was constructed. The oxide layer exhibited a multi-layered structure, with the outer layer consisting primarily of Fe₂O₃, the intermediate layer of Fe₃O₄, and the inner layer comprising FeO and pre-eutectic Fe₃O₄. At the scale-substrate interface, a Si and Cr enriched layer was present. This study employed vertical rolling to descale the surface of oxidized samples; the effect of secondary oxidation on descaling performance was investigated. The results indicated that after the specimens were oxidized at 1200 °C in air, they were subjected to descaling and rolling processes, with a large amount of residual oxides remaining on their surfaces and poor flatness. When the specimens were oxidized at 1200 °C in air and descaled, followed by secondary oxidation at 1000 °C in air, and then subjected to descaling and rolling processes, their surfaces exhibited reduced residual oxides and improved flatness.