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Melt instabilities and the effect of surface tension on preventing edge serrations in melt overflow alloy strip casting

Kalkanlı, Ali
WOOD, John
Braithwaite, Nick
Direct casting of metallic strip onto a single rotating chiller is possible by the displacement of liquid metal in a horizontal pouring channel against a vertically moving chiller surface. In the case where of a high liquid/vapour surface tension exists, the liquid cannot be dragged out of the melt pool by momentum transfer. The critical surface tension values for making strip in a series of 304 stainless steels as measured by a modified oscillating droplet technique, values 2.1-1.4 N m(-1). Surface tension values greater than these lead strip breakup. Casting of alloys with a low surface tension such as 1.3-1.1 N m(-1) at a wheel speed of 2.7ms(-1) can result instability waves such as Marangoni, Kelvin-Helmholtz and capillary waves. These waves result in the formation of edge serrations in the solidified strip. If the casting speed is sufficiently high to overcome these melt instabilities, strips can be produced with a smooth edge and uniform dimensions. In this paper the results of melt overflow direct strip casting experiments with different alloy and process conditions for strip dimensions up to 700 mu m and 40 mm wide are presented.