difference in thermal contraction coefficients of the ferrite (d) and austenite (c) phases, which produces stresses in the The break temperatures of mould fluxes are shell that can only be relieved by cracking. To minimise these important since they help to control the horizontal stresses it is necessary to create a thin and uniform shell heat transfer and lubrication between the steel by controlling the horizontal heat transfer. This is usually shell and the mould, and consequently affect achieved by producing a thick slag layer which, in turn, is occurrences of longitudinal cracking and sticker obtained by tailoring the slag chemistry to create a slag breakout in continuous casting. Break temperatures with a high solidification temperature. T br have been determined for both steady state Sticker breakouts are caused by (i) lack of lubrication and dynamic measurement of the viscosity, and and (ii) creation of a shell with a low mechanical strength, equations relating T br to chemical composition such as those formed with high (more than 0•4%C and have been obtained for both cases. It has been sometimes as low as 0•18%C) carbon steels. Thus, to avoid found that T br can be affected by (i) cooling rates the problem, it is customary to create a thick metal shell and and (ii) fluorine losses during the measurements.provide constant liquid slag lubrication. This is achieved I&S/1436 by using a slag with a low solidification temperature to (i) minimise the thickness of the slag layer and (ii) maximiseAt the time the work was carried out Dr Sridhar and Professor Mills the liquid slag lubrication.

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