Effect of Small Amount of Ni on Hydranlic-descaling-ability in Si-added Hot-rolled Steel Sheets

摘要

Poor descaling ability in Si-added hot-rolled steel sheets can be explained in term of anchor effect of FeO/Fe_2SiO_4 eutectic-compound cutting into both steel and upper FeO sides, which is formed during slab soaking. Although the uneven interface of eutectic-compound/steel can result from penetrating of liquid FeO/Fe_2SiO_4 eutectic-compound into #gamma# grain boundaries, the details have not been clear so far. Thus, in this work, we have studied the behavior with particular emphasis on the small amount of Ni, which is unavoidably included in the steel making process. Reproduction tests of red scale by a laboratory 3-stand tandem-mill with descaling apparatus suggests that the uneven interface is closely related to the small amount of Ni. That is, in 1.5 wt percent Si-added steel which includes only 0.0034 wt percent Ni, eutectic compound/steel interface in primary scale is flat and no red-scale forms. Whereas, in 0.02 wt percent Ni steel, the interface of eutectic-compound/steel in the primary scale was quite uneven even in the case of lower Si content of 0.5 percent, and typical red scale was observed, resulting in poor descaling ability. Increase of Si, Mn accelerates unevenness of eutectic-compound/steel interface through the growth of internal oxides.