Influence of Silicon on Oxidation and Adhesion of Oxide Scale on Hot-Rolled Steel Strips

Abstract

This research focuses on the influence of silicon alloys in hot-rolled steel strips. The steel used in the study was obtained from a hot rolling process with different silicon contents of 0.01, 0.1, 0.2, and 0.3 wt.%. The as-received oxide scale on the hot-rolled steel surface was completely removed by SiC paper and re-oxidized in a horizontal furnace with an atmosphere of 17% H2O-N2 at temperatures of 600°C, 650°C, and 700°C for 10 seconds. An investigation of scale adhesion can be done using a tensile testing machine with a CCD camera. The adhesion of the oxide scale to the steel surface was recorded on video. The oxide phase was examined by means of X-ray diffraction (XRD). The microstructure and thickness of the oxide scale were examined by a scanning electron microscope (SEM) with energy-dispersive X-ray spectroscopy (EDS). The results indicated that all steels studied produced oxide scales that consisted of hematite (Fe2O3) and magnetite (Fe3O4), which contained iron (Fe). The scale thickness tends to increase with increasing temperature, while thickness decreases with increasing Si content in steel. The oxide scale adhesion was indicated by the strain initiating the first spallation during tensile load. The results showed that the strain initiating the first scale spallation tends to decrease with increasing temperature, while scale adhesion increases with increasing Si content in steel. The mechanical adhesion of the oxide scale to the steel substrate was considered in terms of energy. The results indicate that the scale adhesion of steel with 0.3 wt.% Si was higher than that in another sample. It was possible that the presence of an oxide that contains Si at the scale-steel interface, which encourages scale adhesion. The mechanical adhesion energy of the oxide scale was shown in the range of 2-20 J/m2. The qualitative assessment of scale adhesion in terms of strain initiating the first spallation and mechanical adhesion energy suggested the good adhesion behavior of scale grown in the hot-rolled steel with 0.3 wt.% Si. This result indicates that scale formed on steel with a high silicon content tends to be difficult to remove. There was a need to control the Si content in the hot-rolled steel in a satisfactory way to save energy during the de-scale process.