ANALYSIS OF SURFACE AND INTERNAL CRACKS IN CONTINUOUSLY CAST BEAM BLANK

A two-dimensional transient coupled thermoelastoplastic finite element model has been developed, The model incorporates the effect of micros egregation of solute elements on hot tears using a thermomechanical pr operty model of the mushy zone and the two phase zone of delta and gam ma. The model successfully analyses the thermomechanical behaviour of the solidifying shell of a beam blank during solidification in the mou ld. Air gaps form at the flange tip corners in the initial stage of so lidification which reduce the heat flow and give rise to hot spots at the flange tip corners. Large tensile stresses develop in the surface layers of the web and the fillet which can cause surface cracks in the initial stage of beam blank casting. The flange tip region is in a br ittle temperature range during casting because the air gap reduces the heat transfer from the beam blank to the mould. A large tensile stres s develops in the internal region of the flange tip from the intermedi ate stage of casting, which in turn can cause internal cracking in the flange tip region. These analysis results are in good agreement with reported observations.