Reduction Behavior of Oxide Scales Containing Different Structures on the Surface of Hot-Rolled Steel Strip in Gas Mixture H2/Ar at 400-625 °C

The reduction behavior of the oxide scales with two different microstructures in the gas of H-2:Ar = 1:2 at 400-625 degrees C is investigated in detail. The mass change in the scale is measured by thermogravimetric analysis, and a function between reduction degree, reduction temperature, and reaction time is established. The experiment results show that the increase in temperature has an accelerating influence on the reduction reaction of the scale with eutectoid (Fe3O4/alpha-Fe) until reaching 550 degrees C, and then the further increase in temperature decelerates the reduction. For the scale without eutectoid, the reduction rate at 450 degrees C is extremely high, and then the rate decreases with the increase in temperatures. Additionally, the reduction rate in the scale with eutectoid is faster than that without eutectoid at the temperature range of this study. At 400-550 degrees C, a large number of phase interfaces appear within the scale with eutectoid, which can provide diffusion channels for hydrogen atoms and water molecules within the Fe oxides. When the temperature reaches 575-625 degrees C, the phase transformation in the scale (Fe3O4 + alpha-Fe -> FeO) is accompanied by the reduction reaction, which is believed to be responsible for the lower reaction rate.