EFFECT OF INDIVIDUAL FACTORS ON OCCURRENCE OF SURFACE DEFECTS IN CONTINUOUSLY CAST SLABS.

Network cracks and subcutaneous blowholes arising in the shell zone of killed steel slabs are located along the perimeter and within the interior of the strands according to the shrinkage, thermal amechanical stresses during the solidification process, and the movement of the cast strand. Network cracks occur when the total stresses exceed the tensile properties of the solid steel. An additional source of stresses is the high hydrogen content of the metal. Experiments carried out by adding hydrogen by means of water vapour to the metal in the tundish showed that, in the case of killed and low alloy grades of steel, there was an increase in hydrogen content of the molten metal of some 2-3 cm**3/100 g and a simultaneous increase in the number of defects in the shell zone of the slabs.