MECHANISM OF RED SCALE DEFECT FORMATION IN SI-ADDED HOT-ROLLED STEEL SHEETS

The red scale, which is one of the major defects on hot-rolled Si added steel sheets, is reproduced experimentally. On the basis of detailed observation of the scale properties, we propose the mechanism of formation of the red scale. Imcomplete descaling of FeO prior to hot rolling causes red scale formation even in Si-free steels, since the reaction from FeO to Fe3O4 and red Fe2O3 is largely accelerated by the breakage of the FeO scale. In Si-added steels, descaling is quite difficult to perform, because the eutectic compound of FeO/Fe2SiO4 is formed at the scale/steel interface and penetrates irregularly into both upper FeO and lower steel sides. Quite high strength of the eutectic compound, even just below the solidus temperature of 1173 degrees C, can also make it difficult to descale.