Isothermal hydrogen reduction of oxide scale on hot-rolled steel strip in 30 pct H2[sbnd]N2 atmosphere

Abstract

In order to instead of traditional acid picking method, an environmentally friendly gaseous reduction method was performed to obtain the relationship between of reduction process of oxide scale and morphology of porous iron. The isothermal hydrogen reduction of oxide scale on hot-rolled steel strip in 30 pct H2N2 atmosphere at temperature from 500 °C to 800 °C was investigated. Results show that during heating stage before reduction, the phase composition of oxide scale will transform from magnetite and magnetite/Fe eutectoid to wüstite completely. And then, the oxide scale is reduced to porous iron when temperature was below 600 °C while a dense iron layer formed on the oxide scale surface with a “minimum reduction rate” observed at 700 °C. Once the dense iron is formed, the hydrogen enters the interior of the scale along the defects and reduces the wüstite to the dense iron at the interface between the substrate and the scale. The defects (such as cracks and gaps) in oxide scale and temperature will play a vital role in the whole reduction process.