Development of New Mold Flux for Continuous Casting Based on Non-Newtonian Fluid Properties

Abstract

Due to the importance of the physical and chemical properties of the mold flux used in the production of high-quality steel, in particular the suppression of surface defects on steel sheets, steelmaking engineers have attempted to develop new types of mold flux. This paper presents the results of research on entrapment of mold flux and on heat transfer between the mold and the solidified shell. The authors have been developing a mold flux with non-Newtonian fluid properties using nitrogen. That is, the viscosity of the molten mold flux is low at a high shear rate to reduce the friction between the mold and the solidified shell, but is high at a low shear rate to prevent mold flux entrapment. In order to approximate the properties of mold flux as a non-Newtonian fluid, nitride is added to the conventional flux to adjust the silicate network structure through the reaction between nitrogen and calcium. The contact angle of the nonNewtonian mold flux, which represents the wettability between the mold and the solidified shell, is low in comparison with that of the normal mold flux without nitrogen. It is suggested that the non-Newtonian mold flux increases the heat transfer between the mold and the solidified shell. A casting test was carried out using this non-Newtonian mold flux, and the results showed that entrapment of mold flux decreased and heat transfer increased, as assumed.

Structure and Properties of Slags Used in the Continuous Casting of Steel: Part 2 Specialist Mould Powders

“…As mentioned in Section 2.6, the principal problems associated with high-speed-and thin slab casting (with V c up to 8 m min − 1 ) are: (i) poor powder consumption (ii) problems Mini-caster Vc=1.6 m min 20,21) steel grades, and was attributed to the lower contact angle providing better contact.…”

“…This weak bond shears when the stress rate exceeds a critical value and results in a decrease in the viscosity of the slag. 20,21) …”

“…shell lubrication). An alternative action is to use non-Newtonian slags; 20,21) most molten slags are Newtonian (i.e. viscosity values are unaffected by shear rate) but slags containing N are considered to be nonNewtonian since they form weak bonds which break at high shear rates.…”

“…Consequently, in a non-Newtonian slag the viscosity is high in the meniscus region (thereby reducing slag entrapment) and low in the mouth of the infiltration channel (leading to good lubrication). 20,21) A non-Newtonian slag (containing 0.2%N) was prepared by adding Si 3 N 4 to a conventional slag (with C/S = 0.9) at 1 723 K and holding the slag at this temperature for 1 hour. 20,21) 2.4.…”

“…20,21) A non-Newtonian slag (containing 0.2%N) was prepared by adding Si 3 N 4 to a conventional slag (with C/S = 0.9) at 1 723 K and holding the slag at this temperature for 1 hour. 20,21) 2.4. Mould Slags for Casting Steels with High Al Contents High Al steels have excellent properties since Al enhances austenite stability.…”