Ripple Marks on Cast Steel Surfaces

摘要

Surface features developing on steel in static ingot casting were investigated using iron melts of 25 kg with 0.09% carbon. The main type of feature was the normal ripple marks which form directly at the meniscus line by the overflow of the melt over the tip of the solid shell. Their spacing and depth (groove depth) was measured, and both were found to decrease with increasing superheat and increasing casting speed (rate of meniscus rise). From the comparison with other spacing data published in the literature, it seems that ripple formation is influenced at least by two main factors. One is heat flow and the other is wave motion. The latter can be understood quantitatively. A different type of surface marks forms at strong cooling of the meniscus when freezing occurs already at the flat surface of the meniscus. This happened in casting in a helium gas phase. Their spacing and depth also decreases with increasing superheat. But they are wider and deeper, respectively, than those of the normal ripple marks developing in an argon gas phase. A third feature are transverse depressions which develop at a later stage, after solidification. Ripple mark formation may play a role also in continuous casting. According to a recent investigation by Tacke horizontal surface marks on thick slabs have non-normally wide spacings, compared to regular oscillation marks, at low casting speed. Tacke's data were discussed with respect to their possible relationship to ripple marks.