Inclusions in low carbon aluminum killed steel slabs at high casting speed

Abstract

Inclusions in the surface of low carbon aluminum killed steel slabs cast at high casting speed were analyzed by Aspex automated scanning electron microscopy in a large area. The changes in number and size of inclusions were tested at different casting speeds,and the influence of flow fields and sulfur content on the distribution of inclusions was explained in detail. It is found that when the casting speed increases,the depth and length of hooks decrease. Hooks in the slab subsurface is not obvious when the casting speed larger than 2 m·min-1,so inclusions larger than 200 μm cannot be found in the slab surface. Inclusions with the size of 50-200 μm in the slab surface are mainly entrapped by the solidified shell,and the entrapment of inclusions is influenced by forces acting on inclusions at the solidifying front. The flow velocity of molten steel increases due to increasing casting speed,then the washing force becomes large and the entrapping force becomes small,and therefore the number of entrapped inclusions decreases. If the sulfur content in the steel is high at high casting speed,inclusions will be easily entrapped by the solidified shell due to the thermal Marangoni force acting on inclusions obviously.

Keywords

• low carbon steel
• continuous casting
• slabs
• inclusions