Analysis on central cracks in a continuous casting bloom of non-quenched and tempered steel 49MnVS3

Macro- and micro-characteristics at the center of a continuous casting bloom of non-quenched and tempered steel 49MnVS3 were investigated by optical microscopy, scanning electron microscopy and energy dispersive spectrometry. It is found that serious segregation induces a central crack. The crack occurs at the end of columnar grains and the zone of coarse equiaxed grains, and propagates along the boundaries of primary dendrites. The clacking mode is intergranular cracking, which happens in the liquid phase. There are two kinds of grain boundary segregations, one is the precipitation of MnS inclusions, and the other is the concentration of liquid steel. The precipitated inclusions at the central position do not meet the requirements of the non-quenched and tempered steel.