Claims:1. A process for continuous casting of Low Carbon Aluminium Killed (LCAK) steel having high sulfur content (i.e. upto 0.03-0.04 %S) without nozzle clogging in the ladle / tundish and reducing the flow of liquid steel into casting mould comprising the following steps:
- adding (2) the alloying element like Ferro alloys, Coke and Aluminium during tapping of the liquid steel (3) into ladle(4) to reduce the amount of oxygen dissolved in liquid steel.
- reacting the Ferro-alloys with the dissolved oxygen to form corresponding oxide inclusions.
- adding the calcium in the treated liquid steel to reduce the clogging of the ladle / tundish nozzle by transforming the inclusion morphology as well as reducing its melting point, and
- adding the Aluminium after calcium injection for meeting the grade requirement of the steel as produced.

2. A process as claimed in claim 1, wherein the alloying elements like Ferro alloys (Fe-Mn,Si-Mn, Fe-Si), coke and aluminium.

3. A process as claimed in claim 1, wherein the oxide inclusions formed due to reaction of alloying element with oxygen are Al2O3, SiO2, MnO and the like.

4. A process as claimed in claim 1 and 3, wherein the oxides formed are having high melting point of >1700°C.

5. A process as claimed in claimed in claim 1 and 2, wherein the added aluminium in steel is maintained between 0.01 to 0.015% to start Ca-Si treatment.
6. A process as claimed in claim 1, wherein % ‘Sulfur’ in steel is more than 0.01 (i.e upto 0.03-0.04 %S) for billet and bloom casting, where in Calcium is injected prior to Aluminium addition.
7. A process as claimed in claim 1, wherein calcium added in the form of Ca-Si cored wire of 10-13 mm in diameter.

8. A process as claimed in claim 1, wherein calcium added is in 0.1-0.2kg/ton of steel.

9. A process as claimed in claim 1, wherein Aluminium addition after Calcium injection is for meeting the grade requirement i.e > 0.020 % Al at a wire speed of 100-150 meters/min before dispatching the heat for continuous casting.
, Description:FIELD OF THE INVENTION:
The present invention relates to a process for effective modification of oxide inclusions which are formed by ferro alloys addition during tapping of the liquid steel from the converter. After that steel is transported to the Ladle heating Furnace, after all the necessary corrections in temperature and chemical composition to meet the grade requirement followed by calcium treatment. Steel cleanliness is mainly associated with inclusion engineering which emphasizes on the reduction of inclusion density either by changing the morphology/chemical composition of the inclusions or forcing it to float to the top and join the slag phase. Calcium treatment is the part of inclusion engineering in which the detrimental effect of high sulfur is neutralized by developing an innovative approach to deal with inclusions.
BACK GROUND OF THE INVENTION:
The steel is produced through Basic Oxygen furnace (BOF). In BOF hot metal from Blast Furnace is poured into the BOF vessel and oxygen is blown at high pressure to oxidize impurities present in hot metal. These impurities are converted to respective oxides and these oxides are removed later as slag. The solubility of Oxygen in steel is very high at steel making temperatures. During solidification of steel the solubility of oxygen in steel is decreased. If this oxygen is not removed properly before casting of the steel, the produced steel quality is very poor after solidification. To remove this excess oxygen ferro alloys and Aluminium are added (2) into steel during taping of liquid steel into ladles (1). These additives are also required to meet the specification of the steel grade to be produced. Some times to meet the grade requirement, additions are also made into steel ladle at Ladle heating Furnace (LHF). These additives cause formation of non metallic inclusions. These Non-metallic inclusions like Al2O3, SiO2 and MnO, which have high melting point at steel making / casting temperature, may clog the ladle / tundish nozzle as well as the slide gate resulting in reduced flow of liquid steel into continuous casting mould and in turn cause loss in productivity. To ensure smooth casting, Calcium treatment is required. Added calcium will modify the oxide inclusions in to low melting point liquid calcium aluminates such as C3A (M.P:1535°C), C12A7 (M.P:1455°C) and CA (M.P:1605°C). Where C: CaO and A: Al2O3.
For successful calcium treatment, in current / conventional practice it is necessary to reduce the sulfur level to the allowable limit i.e below (0.01%) before calcium addition. But in the Present invention, it follows a different approach for complete modification of alumina inclusions in to liquid ones without reducing the sulfur level (0.03-0.04%). This actually involves two steps.
Completely modifying the solid alumina with calcium at low dissolved aluminium content to avoid the CaS formation.
After 4 minutes of modification interval, addition of required aluminium to meet the grade requirement (min 0.02% Al) and retain the modified alumina inclusions from step 1.
Existing practices for Calcium treatment:
Generally, the percentage of Sulphur in Liquid steel at VSP is in the range of 0.03-0.04%, which is much higher than the allowable range for calcium treatment. So, prior to calcium treatment, liquid steel should be de-sulphurized to less than 0.01% S. So, deep de-sulphurization is required.
Conditions required for desulphurization are,
Slag should be highly basic, for which additions like Lime are required.
Slag should be fluid and to achieve this condition alumina in slag should be higher for which either aluminium or slag fluidizers are to be added.
Slag should be completely de-oxidized
Temperature should be high which requires additional heat / arcing
Dissolved oxygen in steel should be very low
Vigorous rinsing / purging for better slag metal reaction
In the existing practice, to achieve the allowable Sulfur limit, in Al-killed steels, %Al is maintained on the higher side (0.025-0.03%Al) in the liquid steel at the tapping stage (by addition in the form of Al-bars), for effective desulfurization ( to make the slag fluid)
After desulphurization, required Al is maintained (min. 0.02%), by adding Al in the form of wire at LHF.
As a final step, calcium treatment will be done for effective modification of solid alumina inclusions to liquid ones.
OBJECT OF THE INVENTION:
The object of the present invention is to minimize the inclusion content for achieving clean steel production and to eliminate the clogging problem due to solid inclusions so that smooth casting can be ensured even at higher sulphur content in steel than the allowable limit for Ca-Si treatment.

SUMMARY OF THE INVENTION:
Present invention eliminates the requirement of desulphurization before calcium treatment. Thus calcium treatment can be done at high sulfur level i.e. 0.03-0.04 %S. In the Present invention, there is no need to maintain high %Al in steel at LHF (so Al addition at converter during tapping can be reduced by 80-100kg). It is based on the fact that for low % Al dissolved in steel; the allowable Sulfur limit is more for efficient calcium treatment that can be understood by Al-S diagram (shown in Figure 2). Hence maintaining low %Al in steel i.e. 0.008-0.012% is sufficient to start calcium treatment having 0.03-0.04% S. As a final step, Aluminum as per grade requirement can then be added. The detailed process flow charts for existing and Present invention are shown below:


(a) Existing practice (b) Practice discussed in present
Invention
BRIEF DESCRIPTION OF THE DRAWINGS:
Fig. 1 shows the Steel tapping from converter and Ferro alloy additions
Fig. 2 shows the Invariant equilibrium for CaS and C12A7 as a function of percentage Al and S at 1550°C and 1600°C
Fig. 3 shows SEM image of Inclusion of sample no H1 in Billet (with EDS)
Fig.4 shows SEM image of Inclusion of sample no H2 in Billet (with EDS)
Fig.5 shows SEM image of Inclusion of sample no H4 in Billet (with EDS)
Fig:6 shows the Composition of inclusions plotted on (a) CaO-Al2O3-MgO diagram and (b) Ca-Al-S diagram from billet sample H1
Fig:7 shows the Composition of inclusions plotted on (a) CaO-Al2O3-MgO diagram and (b) Ca-Al-S diagram from billet sample H2
Fig:8 shows the Composition of inclusions plotted on (a) CaO-Al2O3-MgO diagram and (b) Ca-Al-S diagram from billet sample H3
Fig:9 shows the Composition of inclusions plotted on (a) CaO-Al2O3-MgO diagram and (b) Ca-Al-S diagram from billet sample H4
DETAILED DESCRIPTION OF THE INVENTION:
After the Hot metal is blown in the converter(1), it is tapped in to ladle(4). During tapping, Ferro-alloys(2), Coke and Aluminium are added as alloying elements as well as to reduce the amount of oxygen dissolved in liquid steel. Ferro-alloys (like Al, Si-Mn and Fe-Si) reacts with the dissolved oxygen in steel and form corresponding oxides like Al2O3, SiO2, and MnO. These oxides have high melting point i.e. >1700°C which is much higher than the steel making/casting temperature i.e. 1600°C. So, at steel making/casting temperature, these inclusions or oxides will remain in solid form and cause clogging of ladle / tundish nozzle /slide gate.
To avoid this clogging, liquid steel (3) is treated with calcium mainly in the form of Ca-Si cored wire (13 mm in diameter contains minimum of 30% Calcium) to reduce the melting point of these inclusions. In the present invention practice, calcium (0.10-0.20 Kg per ton) was injected into bath at low level of Aluminium present in the liquid steel. But for successful calcium treatment, it is necessary to have Sulfur in the allowable limit otherwise added calcium will react with Sulfur and forms CaS. The sulfides are solid at steelmaking temperatures can agglomerate and sinter, forming accretions that are as problematic as alumina. In other words, desulphurization is needed before calcium treatment.
But in the present invention, the need for desulfurization is eliminated i.e. is based on the concept of Al-S diagram shown in Figure 2. Elimination of desulphurization will result in lot of saving in terms of
LF treatment time will be reduced as further heating for desulfurization is not required
Aluminium consumption can be reduced by 80-100 Kg per heat.
Refractory erosion will be decreased as excess arcing is not required for desulphurization
Lime addition can be reduced as high basicity need not be maintained which is a must for desulfurization.
Slag fluidizers like synthetic slag, Aluminium shots, Calcined bauxite etc. consumption can be minimized
Table 1.Different practices employed in the Current and Present invention
Sl. No. Parameter Current Practice Present invention
1. % S in Liquid Steel In current practice, liquid steel is de-sulfurized from initial % S level of 0.03-0.04% to <0.01%. De-sulfurization is not required in the Present invention. Calcium treatment can be done in steel having 0.03-0.04% S (high sulfur).
2. % Al in liquid steel at LHF In current practice, 200-260 Kg of Al is added at converter, resulting 0.025-0.03% Al in liquid steel at LHF which is required for deep desulfurization. In Present invention, there is no need to maintain such high %Al in steel at LHF (so Al addition at converter during tapping can be reduced to 150 Kg introduces saving of 80-100 Kg of Al). Maintaining %Al at LHF 0.01% is enough to start calcium treatment.
3. Loss of Al Maintain high % Al i.e. 0.025-0.03 in steel at LHF results in fading of Al. During de-sulphurization %Al in steel drops to 0.01%.
So, again 60-80Kg of Al to be added at LHF in the form of Al wire. Initial low %Al in steel at LHF i.e. 0.01% results in less or no fading of Al. So, Al loss is negligible in the Present invention method.
4. Addition sequence of Al wire and Calcium Wire As soon as ladle is placed in LHF, composition of steel is checked if it is >= 0.025% Al, no need to add Al wire otherwise 60-80 Kg of Al is added (as per the %Al in the 1st LHF sample) in wire form to get 0.025% Al in liquid steel.
After de-sulphurization Calcium wire is injected in the liquid steel by maintaining %Al in steel as per grade.
Calcium addition is the last treatment in the current practice. As soon as ladle is placed in LHF, composition of steel is checked if it is >= 0.01% Al, no need to add Al wire otherwise 15-25Kg Al is added (as per the %Al in the 1st LHF sample) in wire form to get 0.01% Al in liquid steel.
After that the Calcium wire is injected in liquid steel.
After 5 mins of mild purging after calcium addition, 40-50 Kg of Al wire is again added to meet grade requirement.
Al wire addition is the last treatment in the Present invention.
5. Basis of this invention Since %Al in steel is more i.e. 0.025-0.03%, thus the operating window for handling sulfur is low. So, deep de-sulphurization is required. It is based on the fact that for low % Al dissolved in steel; the operating window of %S is more for efficient calcium treatment that can be understood by Al-S diagram.
So, maintaining low %Al in steel i.e. 0.01% is sufficient to start calcium treatment having 0.03-0.04% S.

OPERATING FACTORS AFFECTING CALCIUM TREATMENT:
TEMPERATURE-: Since the boiling point of Calcium is very low as compared to steel making temperature, hence high operating temperature will lead to low recovery of Calcium.
SPEED OF Ca-Si INJECTION-: Calcium injection speed should be high enough to avoid the vaporization of calcium (boiling point of Calcium is low).
AMOUNT OF CALCIUM ADDITION-: Amount of calcium injection is also critical in the sense that, low calcium addition results in only a partial transformation of Alumina inclusions. On the other hand in high sulphur containing steels excessive Calcium results in solid CaS formation, which is more detrimental than Al2O3 for nozzle clogging.
ARGON FLOWRATE-: Argon flow rate should also be very low otherwise it will affect the Calcium recovery.
PROBLEM ASSOCIATED WITH CALCIUM TREATMENT:
Most important factor in the Calcium treatment is the percentage sulfur, which should be as low as possible i.e. 0.01% maximum as per Al-S diagram in aluminium killed steel (>0.03% Al). Otherwise added Calcium will react with the Sulfur in the steel and forms CaS. This CaS may also cause nozzle clogging as other non-metallic inclusions do. To reduce %S in the steel to desired amount, desulphurization is required. In the Present invention, without de-sulphurization Calcium is added to steel on the basis of Al-S diagram.
COLLECTION OF DATA:
On the basis of above said concept, some industrial trials were taken and data were analyzed.
ACTIVITIES REGARDING CALCIUM TREATMENT FROM CONVERTER TO LHF (EXISTING):
In Al killed steels, de-oxidation is mainly done through Aluminium. While heat is being tapped, initially de-oxidation is done by the addition of small quantity of coke i.e. about 40kg. Then Ferro-alloy addition is done as per the grade requirement. After completing 2/3rd tapping, 220 to 260 kg of Aluminium is added in the form of bars.
Oxygen ppm of steel is measured at LHF immediately after receiving the heat at Ladle Furnace. After a four minute purging operation, a sample is taken for chemical analysis. During the period, Argon purging is continued and after obtaining the analysis, necessary corrections to temperature and composition are carried out, consistent with regular practice.
Slag condition is monitored before Ca treatment for necessary slag conditioning. Slag and steel samples are obtained before commencing Ca addition.
The addition is carried out in the form of Ca Si wire injection in different heats at wire speed of 200 meters per minute and varying quantities of Calcium addition (0.10-0.20 kg per ton) depending on the alumina content (added Aluminium during the process). After the desired calcium addition, the liquid steel in ladle (heat) was purged mildly for 4-6 minutes and then sent for casting.
Generally Ca-Si treatment will be the last activity before sending the heat for casting.

ANALYSIS OF DATA
The main objective of inclusion modification is to transform solid inclusions to liquid inclusions. Calcium treatment is employed to modify solid Al2O3 to liquid ones by changing the chemical and phase composition in aluminium killed steel. The amount of calcium added should be appropriate in order to transform the solid alumina inclusions to liquid ones. Liquid inclusions agglomerate more easily to form larger inclusions. Researchers have pointed out that castability problems due to clogging can be resolved even with a portion of the inclusion contain more than 50% liquid. If calcium addition is low partially transformed alumina inclusions will be formed, more calcium addition will generate CaO rich inclusions. if dissolved sulphur is more it react with calcium to form CaS inclusions. These inclusions not only alter the quality of steel, more detrimental than Al2O3.
To prove the above existing literature, several industrial trials were carried out in Al-Killed steel during closed casting in a continuous caster machine (bloom / billet). Industrial trials also confirmed that inclusions containing more than 50% liquid will enhance castability. The de-oxidation practice was followed as per the existing practice with reduced quantity of Aluminium (Addition of 120-150 kg). Oxygen ppm of steel was measured at LHF immediately after receiving the heat at Ladle Furnace. After a four minute purging operation, a sample was taken for chemical analysis. During the period, Argon purging was continued and after obtaining the analysis, necessary corrections to temperature and composition were carried out, consistent with regular practice. Then calcium addition was carried out in the form of Ca-Si wire injection in different heats at wire speed of 150-250 meters per minute and varying quantities of Calcium addition (0.10-0.20 kg per ton). These variations were necessary in order to optimize Calcium treatment. After the desired calcium addition, the liquid steel heat was purged mildly for 4-6 minutes, then Aluminium wire (40-50 Kg) was added at wire speed of 100-150 meters per minute to meet the grade requirement (min 0.02%Al). After addition of aluminium mild purging for about 4-5 minutes, the heat was sent for casting.
Chemical compositions of four steel samples before calcium addition and after calcium & Aluminium addition are presented in Table 2 and Table 3 respectively, along with details of amount calcium per ton added during treatment. Samples of calcium treated Al-killed steel were collected from the solidified Billet. Characteristics (composition and morphology) of inclusions in steel samples were examined using a CARL ZEISS SUPRA 55 make scanning electron microscope (SEM) fitted with energy dispersive spectroscopy (EDS). Most of the inclusions in steel samples obtained were found to be quite small in size (<5 µm).
Table 2. Steel composition (wt.%) before the Calcium treatment
Sample ID Amount of
Calcium addition
(kg) Overall chemical composition
C Mn P S Si Al
H1 0.10 0.16 0.88 0.017 0.023 0.21 0.006
H2 0.13 0.11 0.66 0.014 0.037 0.14 0.009
H3 0.16 0.15 0.90 0.015 0.036 0.17 0.011
H4 0.20 0.16 0.89 0.021 0.035 0.19 0.013
Table 3. Final steel composition (wt.%) after Calcium and Aluminium addition
Sample ID Overall chemical composition
C Mn P S Si Al
H1 0.16 0.86 0.016 0.013 0.20 0.030
H2 0.15 0.91 0.019 0.036 0.17 0.029
H3 0.16 0.95 0.014 0.029 0.20 0.027
H4 0.17 0.97 0.023 0.033 0.22 0.037

According to an embodiment of the present invention, a process for continuous casting of steel having high sulfur content (0.03-0.04 % S) without clogging the ladle / tundish nozzle and reducing the flow of liquid steel into casting mould comprises of the following steps:
Adding the alloying elements (2) like Fe-Mn, Si-Mn, Coke and Aluminium (120-150 Kg) during tapping of the liquid steel (3) into ladle (4) to reduce the amount of oxygen dissolved in liquid steel.
Reacting the Ferro-alloys with the dissolved oxygen to form corresponding oxide inclusions.
Adding less aluminium (150 Kg) during tapping leads to low opening of % Al in the 1st LHF sample. As per Al-S diagram, high sulfur (0.03-0.04 % S) with low % Al in steel, operating window for Calcium treatment is more. Thus successful calcium treatment may be done with high sulfur without desulphurization.
Treating the liquid steel with the calcium @ 200 meters/min to minimize the clogging of the ladle / tundish nozzle by transforming the inclusion morphology as well as reducing its melting point.
Adding the final Aluminium @ 100-150 meters/min after calcium injection for meeting the grade requirement (min %Al 0.02)
According to another embodiment of the invention, the alloying elements are Ferro alloys (Fe-Mn, Si-Mn, Fe-Si), coke and aluminium and Aluminium addition is made after Ca injection for meeting the grade requirement i.e > 0.020 % Al at a wire speed of 100-150 meters/min wherein % ‘S’ in steel is more than 0.01 for billet and bloom casting where in Calcium is injected prior to Aluminium addition.
The invention is further illustrated hereinafter by means of example without limiting the scope of the invention.
In most of the samples different types of inclusions were found. Generally Al2O3 inclusions containing a trace of MgO, SiO2 are the main inclusions after tapping at BOF. With the slag/steel interface reaction, the MgO content increases with MgO-Al2O3-SiO2 system inclusions formed in the LHF refining process. In the later stage of LHF refining, after calcium addition most of the MgO-Al2O3-SiO2 system inclusions change into CaO-Al2O3-SiO2 system inclusions, part of them are already in the liquid composition region. Finally, the inclusions are very close to calcium aluminate with low melting point.
The typical morphologies and EDS spectra of inclusions in the calcium treated samples are shown in Figure 3, 4 and 5. In the calcium treatment process, there are mainly CaO-Al2O3-SiO2 system inclusions, these calcium aluminate inclusions mainly observed after calcium treatment in LHF and solidified Billet samples. Al2O3 inclusions have begun to react with dissolved calcium; typically these inclusions are blocky or spherical/globular and mainly observed in the Billet. Since sulfur will be precipitated during the solidification process of the steel, there is a small amount of CaS precipitated at the inclusion surface as shown in Figure 5.
Table 4.Composition of some of the representative inclusions observed in steel samples
S.No. SEM-EDS Elemental
analysis ( at%) Calculated Oxide and
Sulfides ( Mole%) CaO/(?Al?_2 O_3 ) Inclusion type
1 O=64.99, Mg=1.07, Al=17.32,
S =2.3 ,Ca =10.41 ,Mn =0.52, Si = 3.39 MgO =1.07 Al2O3 =8.66, CaO =8.63, CaS =1.78, MnS = 0.52, SiO2 = 3.39 1.00 C12A7+SiO2+CaS
2 O=67.27, Mg=1.81, Al=15.68,
S =1.21 ,Ca =11.11 ,Mn =0.37, Si = 2.56 MgO =1.81 Al2O3 =7.84, CaO =10.27, CaS =0.84, MnS = 0.37, SiO2 = 2.56 1.31 C12A7+SiO2+CaS
3 O=63.8, Mg=1.83, Al=18.81,
S =1.42 ,Ca =13.37 ,Mn =0.16, Si =0.59 MgO =1.83, Al2O3 =9.41, CaO =12.11, CaS =1.26, MnS = 0.16, SiO2 = 0.59 1.29 C12A7+SiO2+CaS
4 O=55.08, Mg=2.01, Al=18.47,
S =6.39 ,Ca =12.65 ,Mn =0.41, Si = 1.01 MgO =2.01, Al2O3 =9.24, CaO =6.67, CaS =5.98, MnS = 0.41, SiO2 = 1.01 0.72 CA+SiO2+CaS
5 O=64.93, Mg=2.29, Al=18.47,
S =1.31 ,Ca =11.70 ,Mn =0.0, Si = 1.29 MgO =2.29, Al2O3 =9.24, CaO =10.39, CaS =1.31, MnS = 0.0, SiO2 = 1.29 1.13 C12A7+SiO2+CaS
6 O=65.57, Mg=0.0, Al=14.16,
S =5.22 ,Ca =13.54 ,Mn =0.39, Si = 1.12 MgO =0.0, Al2O3 =7.08, CaO =8.71, CaS =4.83, MnS = 0.39, SiO2 = 1.12 1.23 C12A7+SiO2+CaS
7 O=61.98, Mg=0.78, Al=18.97,
S =4.25,Ca =13.67 ,Mn =0.0, Si = 0.35 MgO =0.78, Al2O3 =9.49, CaO =9.42, CaS =4.25, MnS = 0.0, SiO2 = 0.35 0.99 C12A7+SiO2+CaS

The figures 6,7,8 and 9 show the inclusion composition distributions of four samples on ternary CaO-Al2O3-MgO and Ca-S-Al plots to know inclusions transformation as well as the castability behavior respectively. The inclusions are typically mixtures of CaO, Al2O3, MgO and CaS. For Ca-S-Al plots, oxygen was deleted from the EDS data collected and Ca+S+Al total normalized to 100%. To draw the CaO-Al2O3-MgO plots, CaS was subtracted to show the oxide part of the inclusions. Inclusion compositions which are 50% liquid boundaries at 1550°C are indicated by a dashed line in the Ca-S-Al and CaO-Al2O3-MgO plots.
The inclusions plotted on the ternary diagrams of sample IDs H1 and H2 are shown in Figure 6 and Figure 7. Where, most of the inclusions are with in or near the 50% liquid inclusions region. The treatment was aimed at achieving more than 50% liquid inclusions, as liquid inclusions of more than 50% does not cause nozzle clogging. This is in agreement with already existing literature. From Figure 6(a) and Figure 7(a) of the CaO-Al2O3-MgO ternary diagrams, most of the inclusions are in the complete liquid (C3A+ C12A7) or semi liquid range (C12A7+CA). Although the MgO content of the inclusions decreases after calcium treatment, in most of the inclusions small percentage of MgO is present. This greatly helps in increasing the proportion of liquid in the inclusions. The significant contribution of Magnesium in the liquefaction of inclusions by calcium has been well addressed by various authors.
From the inclusions plotted on a Ca-Al-S ternary diagrams as shown in Figure 6(b) and Figure 7(b), it is evident that the inclusions were duplex, consisting of a calcium aluminate phase and calcium sulfide phase as a ring over the inclusion. The Inclusion compositions fall in a suitable region (50% liquid region) to maintain good castability. The CaS content in calcium aluminate inclusions was low, which is indicative of adequate modification due to sufficient amount of Ca addition in these heats.
The inclusions plotted on the ternary diagrams of sample IDs H3 and H4 are shown in Figure 8 and Figure 9. In all these cases, most of the calcium aluminate inclusions follow the same trend like in sample–H1 and H2, where inclusions are within the 50% liquid inclusions region. From Figure 8(a) and Figure 9(a) of the CaO-Al2O3-MgO ternary diagrams, most of the inclusions are in the complete liquid (C3A+ C12A7) or semi liquid (CaO+C3A).
From the inclusions plotted on a Ca-Al-S ternary diagrams, it is evident that the inclusions were duplex type and same as results obtained for samples H1 and H2, consisting of a calcium aluminate phase and calcium sulfide phase. The CaS content in calcium aluminate inclusions was high but not high enough to cause adverse effect of nozzles clogging. This is indication of over-modification due to higher Ca addition than required. The same is evident from Figure 8(b) and Figure 9(b). Excessive calcium usage leads to the formation of inclusions too rich in CaO or CaS along with Ca-rich calcium aluminate. Ca-rich Calcium Aluminates cause erosion of nozzles and CaS along with rich Calcium aluminates cause clogging of nozzles.
It is understood that various omissions and substitutions of equivalents are contemplated as circumstances may suggest or render expedient, but these are intended to cover the application or implementation without departing from the spirit or scope of the present invention. Further, it will nevertheless be understood that no limitation in the scope of the invention is thereby intended, such alterations and further modifications in the figures and such further applications of the principles of the invention as illustrated herein being contemplated as would normally occur to one skilled in the art to which the invention relates.