MELT INSTABILITIES AND THE EFFECT OF SURFACE-TENSION ON PREVENTING EDGE SERRATIONS IN MELT OVERFLOW ALLOY STRIP CASTING

Direct casting of metallic strip onto a single rotating chiller is pos sible by the displacement of liquid metal in a horizontal pouring chan nel against a vertically moving chiller surface. In the case where of a high liquid/vapour surface tension exists, the liquid cannot be drag ged out of the melt pool by momentum transfer. The critical surface te nsion values for making strip in a series of 304 stainless steels as m easured by a modified oscillating droplet technique, values 2.1-1.4 N m(-1). Surface tension values greater than these lead strip breakup. C asting 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 Maran goni, Kelvin-Helmholtz and capillary waves. These waves result in the formation of edge serrations in the solidified strip. If the casting s peed is sufficiently high to overcome these melt instabilities, strips can be produced with a smooth edge and uniform dimensions. In this pa per 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.