MELTING OF SLAG-FORMING MIXES FOR CBCM MOLDS
S. A. Suvorov
and E. A. Vikhrov
Translated from Novye Ogneupory, No. 6, pp. 29 – 34, June 2010.
Original article submitted December 10, 2009.
The effect is studied of the chemical composition of slag-forming mixes (SFM) on their temperature for the
start of melting and total fusion. The method of multiple correlation established an equation for the depend
ence of the temperature for the start of SFM melting on its chemical composition. A comparison is provided of
melting characteristics of newly developed and commercial SFM. It is shown that the SFM developed exhibits
a lower melting temperature range than commercial mixes.
Keywords: slag-forming mixes, temperature for start of melting, temperature for total fusion, melting temper
One of the mandatory production methods in steel con-
tinuous casting is addition to the molten metal surface in a
mold of a slag-forming mix. Normally an SFM is used with
approximately the following composition, wt.%: CaO 25 – 45,
30 – 50, Al
2 – 10, Fe
1–6, MgO 0–8,
O) 2 – 15, F 0 – 10 with basicity CaO/SiO
Due to the heat of the metal in contact with the liquid
steel an SFM melt forms, that is distributed over the surface
of a billet and forms a molten bath (Fig. 1). From the molten
bath formed as a result of rocking of the mold molten slag
penetrates into the gap between the mold and the continu
ously-cast billet and partly solidifies in a layer 1–3mm
thick in contact with the copper wall of the water-cooled
mold. The thin film of molten SFM with a thickness of
0.1 – 0.6 mm moves together with the shell of the ingot, pro
viding lubrication. The solidifying layer of the SFM melt,
that is in a glassy and (or) crystalline state controls heat re
lease from the ingot to the mold [1 – 4].
Generally an SFM for CBCM molds fulfils the following
functions: a reduction in friction between the solidifying
steel and the mold due to lubrication by a slag film, provision
of uniform heat transfer from the steel to the mold, preven
tion of secondary steel oxidation, absorption of non-metallic
inclusions from the steel, thermal insulation of the metal sur
face in order to prevent partial solidification of the melt from
the surface . Additionally there is a minimum corrosive
effect of the slag coating on the refractory of the slag belt of
the submersed nozzle.
All of these functions are important, but in practice one
of the most significant functions is lubrication of the ingot
with molten SFM. Insufficient lubrication leads to occur-
rence of various defects and problems: longitudinal cracks,
breaks of molten steel as a result of sticking of the ingot skin
to the mold, deep traces of mold rocking, transverses cracks
at corners and depressions .
In order to provide the optimum lubrication of the ingot
shell the depth of the molten SFM should exceed that of the
total travel of the mold and be more than 10 mm. The depth
Refractories and Industrial Ceramics Vol. 51, No. 3, 2010
1083-4877/10/5103-0187 © 2010 Springer Science+Business Media, Inc.
GOUVPO St Petersburg State Technological Institute (Technical
University), St. Petersburg, Russia.
Fig. 1. Diagrammatic representation of different SFM layers in a