Measurements were made on an operating billet machineBrimacombe was at the Canada Foundation for Innovation, The to determine mould wall temperature profiles for different Centre for Metallurgical Process Engineering, The University of mould flux types, mould cooling water velocity, oscillation

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solidification in the mould. The reasons for these improvepowder lubrication. In the present paper, Part 2, ments have not been clearly established, which was also an billet quality is examined in detail. The difference objective of this research. in turbulence at the meniscus between oil andThere are other defects, prevalent in the continuous casting powder lubrication is established, and the need to of slabs with mould powder, that have not been reported tune mould level sensors when switching to mould for continuous casting of billets with oil as a lubricant. powders is demonstrated. Previous work has Whether these defects will appear as billet producers switch shown that mould level fluctuations have a strong to mould powder lubrication is not clear. A brief survey of influence on defects such as offsquareness and these defects is pertinent to this study. The most widely transverse depressions, both of which are markedly studied surface quality issue is longitudinal midface cracks reduced when casting with mould powders. The in slabs. Steel grades with a carbon content in the range inherent stability of the meniscus is improved 0•08-0•14% are particularly vulnerable to longitudinal when employing mould powder lubrication and cracking.1,2 The carbon effect has been attributed to the a submerged entry nozzle. Furthermore, the relatively large thermal contraction that accompanies the solid significant reduction in mould heat transfer at the state transformation of d ferrite to austenite near the meniscus, meniscus, when mould powders are employed, giving rise to wrinkling of the solidifying shell. Due to the particularly for medium carbon steels has been resulting non-uniformity of the mould-strand gap, local shown to correlate well with the observed hot spots are created, which concentrate the tensile strains, reduction in offsquareness. The paper also and led to longitudinal cracking.3 It is known that mould elucidates the reasons for the reduction, and in powder properties have a decisive influence on longitudinal most cases, elimination of transverse depressions cracking through the following factors: the overall heat flux in B-Ti grades when casting with mould powders. at the meniscus, high friction forces, and variations in heat The mechanism of longitudinal depression flux across the width at the meniscus.4-8 Nakato et al.6 formation and subsurface cracking observed in showed that casting speed and mould flux characteristics many of the powder cast, medium carbon billets are the most important factors influencing the mean heat has also been established. I&S/1430b flux in the mould. Therefore, correct selection of mould flux is critical to controlling longitudinal cracking. Metal level Dr Pinheiro is based in Belo Horizonte, Minas Gerais, Brazil variations have also been identified as critical, since local

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