In this study,the matrix structure,state and composition of the mill scales of four typical domestically made 510L hot-rolled strips were observed and analyzed by means of optical microscopy(OM),scanning electron microscopy(SEM) and X-ray diffraction(XRD).The corrosion behavior of the steels with and without mill scales were investigated by means of hot-humid corrosion tests under the condition of relative humidity(RH) of 95% at 50℃ and 70℃,respectively.The results show that the matrix structures,state,composition and thickness of mill scales vary in the strips.The rusting starting time of the specimens with scales is generally a bit longer than that of the specimens without scales,but their corrosion mass-gain is higher.For these two kinds of specimens,their corrosion rate increases significantly with the increase of temperature.The rusting behavior of the 510L strips produced by various plants is different due to the variations of hot-rolling processes and designed chemical compositions.Various relevant aspects should be taken into account in the evaluation of the corrosion behavior of hot-rolled strips. In this study, the matrix structure, state and composition of the mill scales of four typical domestically made 510L hot-rolled strips were observed and analyzed by means of optical microscopy (OM), scanning electron microscopy (SEM) and X-ray diffraction XRD). The corrosion behavior of the steels with and without mill scales were investigated by means of hot-humid corrosion tests under the condition of relative humidity (RH) of 95% at 50 ° C and 70 ° C, respectively. These results show that the matrix structures, state, composition and thickness of mill scales vary in the strips. rusting starting time of the specimens with scales is generally a bit longer than that of the specimens without scales, but their corrosion mass-gain is higher. For these two kinds of specimens, their corrosion rate increased significantly with the increase of temperature.The rusting behavior of the 510L strips produced by various plants is different due to the variations of hot-rolling processes and designed chemical compo sitions.Various relevant aspects should be taken into account in the evaluation of the corrosion behavior of hot-rolled strips.