Phenomenological Description of the Surface Morphology and Crack Formation of Continuously Cast Peritectic Steel Slabs

The surface quality of continuously cast material is strongly depending on the initial solidification of the steel. Oscillation marks are formed at the very early stages of the strand shell growing process, thus influencing the microstructure and cracking behaviour of the surface and subsurface region. An industrial study of the oscillation mark morphology and the surface structure of peritectic medium carbon steel slabs was performed. The formation of oscillation marks and their effect on the surface quality was examined by metallographic investigations of slab samples. Although constant casting and oscillation conditions were applied, a variation of oscillation mark geometry along the narrow faces of the slabs was measured. A relation between the depth of the oscillation marks and the thickness of a layer of segregated melt situated inside the bottom of the marks was found. Measuring the distribution and length of surface and subsurface segregated cracks in the vicinity of the marks, existing theories of oscillation mark formation could be confirmed. The austenite grain size was found to increase with increasing oscillation mark depth. There was no clear correlation between the austenite and the δ‐ferrite grain size.