A Review of the Rhomboidity Problem in Billet Casting Jorge Madias Metallon 432, 9 de Julio street, B2900HGJ San Nicolas, Buenos Aires, Argentina Phone/Fax: 011 54 3461 421318 Key words: continuous casting, billets, quality, rhomboidity, mold INTRODUCTION Despite rhomboidity is known from the first times of billet and bloom casting, during the last decade in the start-up of modern casters this shape defect has frequently occurred, calling for continuous improvement work to overcome it. In this paper, the literature on rhomboidity in billets and blooms is reviewed. Evaluation methods, as well as the consequences regarding billet/bloom quality and rolling operation are analyzed. A discussion is made about the mechanisms proposed for its formation. Recent industrial experiences are summarized. DISCUSSION Rhomboidity assessment A first evaluation can be carried out by observation through the peepholes of the secondary cooling chamber. The obtuse corner should be colder than the acute corner. Then, the billet shape after oxygen cutting may be looked at. As an example, a paper classifies different occurrences of rhomboidity according to the strand features when exiting the mold [1]:  Rhomboidity in all strands, with dark and bright spots in the faces  Rhomboidity in all strands, but uniform at mold exit  Strong rhomboidity in one or two strands, with variable orientation  Strong rhomboidity in one or two strands, with fixed orientation Sometimes twisting of billet with off-squareness has been observed in the cooling bed, revealing changes in the rhomboidity behavior [2]. Rhomboidity is determined by the difference n=between the two diagonals (d 1 e d 2 ), expressed in mm or percentage: Rhomboidity (%) = ((d 2 - d 1 )/((d 2 + d 1 )/2)) x 100 It is measured directly on the billet by means of a compass and rule or on a transverse cut with a caliper. Rhomboidity may vary significantly along the billet [2]. For instance, in figure 1 the variation in difference between diagonals is presented for six 6 m long billets of 0.32% C Boron steel and along one particular billet. AISTech 2012 Proceedings 1241