The effect of casting conditions on the formation of longitudinal surface crack in the beam blank caster

Abstract

To understand the effects of casting conditions on the formation of longitudinal surface crack, the crack morphology of over 2000 charges at scarfed beam blanks were investigated. The results whow that the most sensitive crack susceptibility range of carbon contents lie in the 0.12–0.13 wt.% range. This was due to the effect of shell irregularity between mold surface and solidified shell withdrawn by δ-γ transformation and the embrittlement phenomena by liquid film of soluble elements such as phosphorous and sulfur at the dendrite interface. It was found that the increase of crack formation is attributed to the increase of phosphorous and sulfur contents segregated at the dendrite interface. The increase of crack formation with increasing Phosphorous and Sulfur contents is due to the enlargement of the ΔT range, which is defined as the temperature difference between LIT (liquid impenetrable temperature) and ZDT (zero ductility temperature). The effect of casting speed on crack formation shows a linear relationship. As casting speed is increased, the solidified shell had little time to grow and the width of shell became smaller. As, the heat flux from the thinner shell increased, the thermal strain was increased, increasing crack formation.