IMPROVED METHOD OF FLU1DIZING STEELMAKING LADLE TOP SLAG
FIELD OF INVENTION
The present invention relates to an improved method of fluidizing steelmaking ladle
top slag in any steel melting shop. More particularly the present invention discloses
modifications in steelmaking ladle top slag chemistry by addition of a modified
synthetic flux for good fluidity.
BACKGROUND ART
Ladle top slag is a combination of carryover slag from steelmaking primary vessel,
added fluxes and deoxidation products. The various functions of steelmaking ladle
top slag are:
• Prevents heat loss & protects the steel from atmosphere
• Helps in steel desulphurization.
• Absorption of non-metallic inclusions.
• Noise control during arcing.
Most of the above mentioned functions require good fluidity of ladle top slag.
The most common slag fluidizer in steelmaking is fluorspar, a mineral primarily
composed CaF2. Due to increasing consumption, decreasing availability of
expensive fluorspar and its negative effect on the environment, steelmakers are
seeking alternative combinations to achieve optimal slag fluidity.
In metallurgical practice, the CaF2 beneficial effect in molten slag set for
desulphurization is broadly known. For the slags with a low content of silica, the
affirmative beneficial effect of CaF2 could be explained by slag dilution, in which the
slag melting temperature is reduced due to formation of easily meltable CaO-CaF2
phases with lower viscosity. CaF2 has been also promoting a reduction of the
sulphur activity in the slag, leading to an increased capacity of the slag to bind
sulphur.

Disadvantages of using the fluorspar technologies:-
Fluorspar in contact with liquid metal and/or liquid slag releases environmentally
unfriendly fluorides (e.g. SiF4), which worsen the working and surrounding
environment.
Fluorspar in the ladle slag, increases lining wear, especially in the area of the ladle
slag line, and thus significantly reduces the overall life of the ladle lining.
That is why both many foreign and domestic steelworks have abandoned the use of
fluorspar for a slag forming additive. The current trend includes a quality, industrially
produced synthetic slag, which is provided in different proportions between
AI2O3/CaO. The slag is typically designed for use with a lime additive in the ladle,
while creating the final slag system with the desired flow properties and basicity.
Steel Melting Shop-I (SMS-I) of Bhilai steel plant (BSP) is producing wide range of
rimming, semi killed and Si/AI killed steel through Twin Hearth Furnace (THF) - Ingot
Casting top pouring route. Sometimes bottom pouring is also being practice in case
of sophisticated grades. Around 2.5 million tonnes of steel is being made at SMS-I,
BSP every year.
A mechanical mixture of lime (CaO), bauxite and fluorspar is being produced at
RMP-I of BSP, which is being used as a synthetic flux in SMS-I. The purpose of
addition of this type of mixture is:-
a) Maintaining slag basicity for effective De-sulphurisation.
b) Maintain slag basicity > 2.0 for lower slag zone erosion
c) Fluid ladle top slag for inclusion absorption and effective slag-metal
interaction
d) Fluid ladle top slag for easy removal of entrapped gases in steel and gaseous
product of carbon & oxygen reaction
e) to get a fluid ladle top slag for easy dumping and to prevent the left over slag
not to settle at ladle bottom.
f) To reduce the reactivity of ladle top slag.

In view of adverse effects of fluorspar as discussed before, the present invention
proposes a modification in the chemistry of the existing synthetic flux without
fluorspar addition in the mixture.
One possible alternative to CaF2 is bauxite. This material is widely available and
considered non-toxic, meaning that its use in steelmaking would helps to reduce
negative environmental impacts. In this work, the employment of bauxite as a
replacement for fluorspar in synthetic slags was analyzed. Based on chemical
composition analysis of different slag mixtures, the experimental result indicated that
the addition of bauxite has a positive effect on slag fluidity.
Effect of Fluorspar on Health & Environment
In oxide slags, H2O is both chemically-bonded to the slag and adsorbed on the slag.
However, the effects of moisture are more severe in the case of slags containing
fluorides because of the reaction:
CaF2 (slag) + H2O (g) = CaO (slag) + 2HF (g)
The HF emitted can cause plant corrosion and pose a threat to the health of the
plant personnel. Synthetic slags are basically unstable at high temperatures (1500-
1600 °C) since two or more components react such as:
3CaF2 (slag) + Al2O3 (slag) = AIF3 (g) + 3CaO (slag)
AIF3 would react with Si02, forming volatile SiF4, as follows:
4AIF3 (g) + 3SiO2 = 3SiF4 (g) + 2AI2O3
Hydrofluoric acid is a highly corrosive acid, capable of dissolving many materials,
especially oxides, it can also dissolve glass. Hydrogen fluoride gas is an acute
poison that may immediately and permanently damage lungs and the corneas of the
eyes. SiF4 can cause burns. It may be fatal if inhaled. Silicon tetra fluoride is a
colourless gas with a pungent odour. It fumes to form a dense white cloud in moist
air. Silicon tetra fluoride's immediate health hazard is that it is a poison gas. It reacts
with water vapour in the air to form other corrosive, toxic substances. Therefore
addition of calcium fluoride should be minimized in any kind of slag system. Fig 1
shows the dependence of fluorides emission on the CaF2 content in the slag mixture.

Effect of Fluorspar on Ladle Refractories
If fluorspar-containing slags are in contact with magnesia refractories, then
significant refractory wear can occur if the slag is not MgO or CaO saturated. If the
slag is CaO-saturated but MgO-unsaturated, then the extent of refractory wear could
be minimized even though the slag is not fully chemically compatible with the
refractories.
However, if the slag is also CaO unsaturated then severe refractory wear can occur
in just one heat. The above is true for any slag, CaF2-containing or not, but the
presence of CaF2 accelerates the wear because of its depression of the solidus
temperature of the slag, which causes deeper penetration into the refractory matrix.
SUMMARY OF INVENTION
The present invention relates to a modified process of fluidizing steelmaking ladle
top slag in any steel melting shop with modifications in steelmaking ladle top slag
chemistry by addition of a modified synthetic flux. Adoption of this modified process
results in good fluidity of ladle top slag even though there is no addition of any
fluorspar (CaF2) in synthetic flux. The modified synthetic flux helped in achieving
good fluidity of ladle top slag which is necessary prerequisite for many secondary
metallurgical operations. Also, good fluidity of slag helps in easy dumping of left over
slag after casting resulting in clean ladle and decreases the chances of ladle skull
formation due to viscous slag.
Therefore such as herein described there is provided method of fluidizing
steelmaking ladle top slag comprising the steps of: preparing a mixture of synthetic
flux having composition of AI2O3 ~ 38 %, SiO2 ~ 12 % & CaO - 45 % and adding
the flux in the ratio of 2kg per ton of steel; pouring 50% quantity of the said mixture of
flux after filling 1/3rd of the ladle with molten steel; pouring remaining 50% quantity of
the said mixture of flux after filling 2/3rd of the ladle with molten steel; and filling the
rest 1/3rd of the ladle with molten steel for slag formation.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Fig 1 illustrates a graph showing the dependence of fluorides emission on the CaF2
content in the slag mixture;
Fig 2: illustrates a graph showing the effect of alumina on slag viscosity;
Fig 3: illustrates identified fluid slag zone for aluminium killed and silicon killed steel
in a ladle in accordance with the present invention;
Fig 4 : illustrates pictorial representation of the condition of ladle top slag after
synthetic flux addition in modified practice after 2 min. of tapping finish in accordance
with the present invention;
Fig 5: illustrates pictorial representation of the condition of ladle top slag after
synthetic flux addition in conventional practice after 2 min. of tapping finish in
accordance with the present invention;
Fig 6: illustrates pictorial representation of the condition of ladle bottom after
dumping of left slag during trials in accordance with the present invention;
Figure 7 & 8: illustrates pictorial representation of the easy disposal of perfectly fluid
slag even after completion of teeming was observed in the modified practice in
accordance with the present invention.
DETAILED DESCRIPTION
Adoption of this modified process results in good fluidity of ladle top slag even
though there is no addition of any fluorspar (CaF2) in synthetic flux. The modified
synthetic flux helped in achieving good fluidity of ladle top slag which is necessary
prerequisite for many secondary metallurgical operations. Also, good fluidity of slag
helps in easy dumping of left over slag after casting resulting in clean ladle and
decreases the chances of ladle skull formation due to viscous slag.
A standard practice has been developed for fluidizing steelmaking ladle top slag with
a modified synthetic flux mixture made from lime and bauxite. The improved mixture
does not have any fluorspar in it. Thus, eliminating health, environment as well as
refractory erosion problem due to fluorspar. The improved mixture having

composition of Al2O3 ~ 38 %, SiO2 ~ 12 % & CaO ~ 45 % -2.5% TiO2, & -2.5%
MgO was found very effective in obtaining good fluidity as well as viscosity of slag
during trials in SMS-I of BSP.
A two stage addition pattern is designed to get the best result while using this type of
fluxes. The three stage addition includes:
Half of the material when the ladle is 1/3rd filled.
Remaining 50% of the synthetic flux after 2/3rd filing of ladle.
This addition pattern is helpful in faster dissolution of synthetic flux and early slag
formation.
1. LOW COST METHOD OF PRODUCING SYNTHETIC SLAG MIXTURE FOR
OBTAINING LOW VISCOSITY FLUID SLAG.
Fluorspar is a costly mineral. It costs around Rs 25000/ton. The traditional mixture at
SMS-I BSP was made through addition of 60% lime, 30% bauxite and 10% fluorspar.
The modified mixture does not contain any fluorspar. The mixture can be made by
addition of 50% lime and 50% calcined bauxite (70% AI2O3 Min.) for silicon/semi
killed steel and 65% lime and 35% bauxite (70% Al2O3 Min.) for aluminium killed
steel. During the investigation a particular slag chemistry zone was identified for fluid
slag for Al-killed as well as Si killed steel. The zones are shown in Fig 3. The
identified fluid slag zone for aluminium killed and silicon killed steel is shown
separately.
2. ADDITION PATTERN OF SYNTHETIC SLAG MIXTURE
The modified practice for fluidizing steel making ladle top slag is experimentally
utilized in any steel melting shop with minor modifications in mixture chemistry after
considering the deoxidation practice followed in the shop. Adoption of modified
practice results in better fluidity and viscosity of ladle top slag, thus making it easier
for dumping after completion of teeming or casting. Good fluid ladle slag also
contributes in desulphurization and inclusion absorption

The refining of steel using the flux according to the invention can be practiced both in
converters and electric furnaces including ladle furnaces (LF). The refining can be
combined with VOD-process for production of stainless steel. Also, the refining can
be applied to top-blowing converter operation. The flux for refining according to the
invention may be conveniently used if it is prepared in certain compositions and
processed into pellets or briquettes. At refining of steel using the flux according to
the invention aluminum is used as the deoxidizing agent and Al2O3 resulting from the
aluminum goes into the flux, and therefore, it is inevitable that the flux composition
may change during the refining. Though the amount of the occurring alumina is not
so large, and therefore it may often be neglected, it is preferable that the refining is
carried out with consideration of such initial formulation of the flux materials may give
desired composition of the flux at the later period of refining taking into account
anticipated increase of AI2O3 resulting from oxidation of Al in the refining flux.
Specifically in regard to the denitrification of steel, it is preferable to combine the
refining using the flux of the invention with conventional degassing technologies.
Known degassing technologies are, in addition to DH-process and RH-process
mentioned above, LVD-process and REDA-process may be combined with the
present refining. These degassing processes need treatment for a long period of
time, and therefore, temperature of the molted steel may decrease during the
refining. To cope with this problem ASEA-SKF process, VAD-process or refining in
LF under vacuum or Ar-bubbling are recommended.
The refining of steel using the present flux makes it possible to produce steel
containing impurities in the amounts remarkably smaller than the limits achieved in
the conventional steelmaking technologies. Thus, using a flux containing no
fluorides, pure steel containing impurities of the amount less than conventional steel
can be.produced. The present flux, due to MgO component therein, contributes to
prevention of damage of MgO-based refractory. Since no fluoride such as CaF2 is
contained, at disposal or reuse of the used flux, different from the conventional flux
containing a fluoride, it is not necessary to take a measure to leaching out of fluorine
compound and the used flux can be directly used as a roadbed material or a soil-
improving agent.

Example :- First Phase Trial
During first phase of trial 50% bauxite and 50% lime mixture was used. Visual
monitoring of ladle top slag as well as ladle bottom after slag dumping was also done
for visual examination of slag fluidity. Fig 4, 5 & 6 shows the slag condition and ladle
condition during the trial.
During visual monitoring of ladle slag it was found that the slag was sufficiently fluid
and no problem at all was observed during slag dumping after teeming operation (fig
7 & 8). Slag samples of heats made with modified synthetic flux was collected to for
determining the viscosity and melting point.
To validate the visual finding about good fluid ladle top slag, the viscosity and
melting point of the collected slag samples of heats made with modified flux and
conventional flux was determined using FACT sage software.
Table 1: Chemistry, Melting Point & Viscosity of Slag during 1st Phase of Trial
The viscosity and melting point of slag of trial heats in case of modified practice


showed excellent resemblance with the conventional slag made with CaF2 bearing
synthetic slag. The chemistry, melting point and viscosity of slags in case of modified
practice and conventional practice is represented in table 1 & 2.

Table 2: Chemistry, Melting Point & Viscosity of Slag of Conventional Heats
(Slag Analysis of BSP, RCL)
Comparison of modified practice vis-a-vis conventional practice revealed that quite a
low viscosity of 0.307 poise average and average melting point of 1180°C was
achieved in slags in which modified synthetic flux was used. Whereas, average
viscosity of 0.346 poise and average melting point of 1217°C was achieved in slags
in which conventional synthetic flux (CaF2 bearing) was used.
The comparison validates that good slag fluidity can be achieved in ladle top slag
without any addition of CaF2 in synthetic flux. Bauxite is a good slag modifier and an
optimum composition of synthetic flux with lime and bauxite can only be used for
making a completely fluid ladle top slag.
Second Phase Trial
A modified slag with 65% lime and 35% bauxite in mixture was used in second
phase of trials. After successful demonstration of completely fluid slag even in
absence of CaF2 in synthetic slag mixture
The melting point and viscosity of ladle top slags were determined using Facts age
software. Very low average viscosity of 0.29 poise at 1600°C and an average melting

point of 1147°C were achieved which showed completely fluid slag at steel making
temperature. The calculated melting point and viscosity of slags during second
phase of trial are shown in table 3.
Table 3: Chemistry, Melting Point & Viscosity of Slag during 2nd Phase Trials
(Slag Analysis of BSP, RCL)

Techno-Economic Evaluations
Techno-Economics Calculation for Usage of Low Cost Bauxite
Cost Data
Cost Data (Source. RMP-I, BSP)
• Calcined bauxite = Rs 7600/t ( Source. RDCIS Purchase Order)
• Cost of Lime = Rs 8753/t
• Fluorspar = Rs 21740/t
• Operating cost = Rs 2900/t
Chemistry of Raw Materials
• CaO in BSP Lime = 88% (Source: RMP-I, BSP)
• Alumina in Calcined Bauxite = 73% (Source: Test Certificate of supplier)

Case-I (Conventional Practice)
Existing practice of making synthetic flux
Composition of conventional mixture is
67% Lime + 23% Bauxite + 10% Fluorspar
Cost of 1 ton of Mixture = Raw material cost + Operating Cost
= (670x8.753) + (230x23.25) + (100x21.74) + 2900
= Rs16286/ton(A1)
Case-ll (Modified Practice)
Assuming 50% Lime & 50% Calcined Bauxite is used in making 1 ton of
modified mixture
Expected Resultant Composition of 1 ton of mixture
CaO = (0.88x500) x100/1000 = 44%
Al2O3= (0.73x500) xl00/1000 = 36.5%
Cost of 1 ton of modified mixture = (8753x0.5) + (7600x0.5) +2900 = Rs 11076/t
(A2) •
Therefore, there is a saving of Rs 5210/ton (A1-A2) with modified flux.
Although the foregoing description of the present invention has been shown and
described with reference to particular embodiments and applications thereof, it has
been presented for purposes of illustration and description and is not intended to be
exhaustive or to limit the invention to the particular embodiments and applications
disclosed. It will be apparent to those having ordinary skill in the art that a number of
changes, modifications, variations, or alterations to the invention as described herein
may be made, none of which depart from the spirit or scope of the present invention.
The particular embodiments and applications were chosen and described to provide
the best illustration of the principles of the invention and its practical application to
thereby enable one of ordinary skill in the art to utilize the invention in various
embodiments and with various modifications as are suited to the particular use
contemplated. All such changes, modifications, variations, and alterations should
therefore be seen as being within the scope of the present invention as determined
by the appended claims when interpreted in accordance with the breadth to which
they are fairly, legally, and equitably entitled.

WE CLAIM
1. A method of fluidizing steelmaking ladle top slag comprising the steps of :-
preparing a mixture of synthetic flux having composition of AI2O3 ~ 38 %, SiO2 ~ 12
% & CaO ~ 45 % in the ratio of 2kg flux per ton of crude steel;
pouring 50% quantity of the said mixture of flux after filling 1/3rd of the ladle with
molten steel;
pouring remaining 50% quantity of the said mixture of flux after filling 2/3rd of the
ladle with molten steel; and
filling the rest 1/3rd of the ladle with molten steel for slag formation.
2. A method of fluidizing steelmaking ladle top slag as claimed in claim 1,
wherein the mixture of flux having composition of 50% lime and 50% calcined
bauxite (70% AI2O3 Min.) for silicon killed steel.
3. A method of fluidizing steelmaking ladle top slag as claimed in claim 1,
wherein the mixture of flux having composition of 65% lime and 35% calcined
bauxite (70% AI203 Min.) for aluminium killed steel.
4. A method of fluidizing steelmaking ladle top slag as claimed in claim 1, 2 or 3,
wherein the components of synthetic flux are granulated into pellets or briquettes.
5. A method of fluidizing steelmaking ladle top slag as claimed in claim 1, 2 or 3,
wherein the Aluminium is used as a deoxidizing agent.
6. A method of fluidizing steelmaking ladle top slag as claimed in claim 1, 2 or 3,
wherein the flux is used in combination with vacuum degassing.

ABSTRACT

The present invention relates to a method of fluidizing steelmaking ladle top slag
comprising the steps of preparing a mixture of synthetic flux having composition of
Al2O3 ~ 38 %, SiO2 ~ 12 % & CaO ~ 45 % in the ratio of 2kg flux per ton of crude
steel, pouring 50% quantity of the said mixture of flux after filling 1/3rd of the ladle
with molten steel, pouring remaining 50% quantity of the said mixture of flux after
filling 2/3rd of the ladle with molten steel, and filling the rest 1/3rd of the ladle with
molten steel for slag formation.