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 H-2-N-2 atmosphere at temperature from 500 degrees C to 800 degrees 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 wustite completely. And then, the oxide scale is reduced to porous iron when temperature was below 600 degrees C while a dense iron layer formed on the oxide scale surface with a "minimum reduction rate" observed at 700 degrees C. Once the dense iron is formed, the hydrogen enters the interior of the scale along the defects and reduces the wustite 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. (C) 2017 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.