FORM 2
THE PATENT ACT 1970
(39 OF 1970)
&
The Patent Rules, 2003
COMPLETE SPECIFICATION
(See Section 10 and Rule 13)
1 TITLE OF THE INVENTION :
A PROCESS FOR TREATING HIGH Mn(>0.5 %) HOT METAL IN LD CONVERTER.
2 APPLICANT (S)
Name : JSW STEEL LIMITED.
Nationality : An Indian Company.
Address : Jindal Mansion, 5-A, Dr. G. Deshmukh Marg, Mumbai - 400 026,
State of Maharastra, India.
3 PREAMBLE TO THE DESCRIPTION
COMPLETE
The following specification particularly describes the invention and the manner in which it is to be performed.

FIELD OF THE INVENTION
The present invention relates to a process for treating high manganese (>0.5%) containing hot metal in LD converter. More particularly, the present invention is directed to providing a process to remove high amount of Mn from the hot metal in the LD converters without affecting the refractories and other elements. Importantly, the process according to the present invention adopted steps to oxidize the Mn as early as possible and remove the high MnO slag from the converter through intermediate de-slagging so as to reduce the refractory erosion and to avoid difficulty of end point prediction and increased reblows. As Mn is best oxidized under the conditions of low temperature, high FeO and low basicity in the slag, lime and dolomite additions have been suitably reduced to decrease the slag basicity and iron ore addition is introduced from 2-3 min of blow start to increase the FeO in the initial slag. The addition and blowing pattern as well as intermediate de-slagging just after complete de-siliconization (20-30% of the blow time, exact point can be identified by the observing the change in the slope of CO-C02 curve of the off gas analysis) according to the process of the invention, ensure least impact on the converter refractories which is exposed to high Mn slag for a very short duration and thereby minimizing its erosion.
BACKGROUND OF THE INVENTION
It is well known in the field of iron and steel making that the hot metal from iron making units such as blast furnace contains silicon phosphorous, manganese, carbon and sulphur as impurities and varies significantly from unit to unit and ladle to ladle. These impurities need to be removed during the steel making process. In modern steel making process, hot metal from blast furnace is pre-treated for removal of sulphur before charging into the converter for the final steel making process. Silicon, manganese, carbon and phosphorous are removed in the LD process, where the hot metal is charged into the converter and oxygen is blown through a top lance for about 17 mins with the addition of fluxes and iron ore at intermediate stages. Normal composition of hot metal charged to converter is Si - 0.8 %, P - 0.1 %, S - 0.01 %, Mn - 0.2%, C - 4.5 % and rest Fe. Silicon, Manganese and phosphorous are oxidized to Si02, MnO and P205 and transferred into slag, which is removed from the converter after the blow is finished. Carbon is oxidized to CO and C02 and is continuously

removed through gas cleaning system from the top opening of the converter by ID fan. With increased amount of certain impurities beyond the normal levels (as mention above), the blowing duration extends. This also increases the amount of slag resulting in heavy slopping and blowing interruptions. The applicants experience in their iron making process in recent past encountered high manganese (Mn) in the hot metal ( > 1 %) due to usage of iron ore with high MnO content. BOF operation with such high levels of Mn has never been reported in any steel making operations. Mn in Hot metal can only be removed in steelmaking by oxidizing it to form MnO during blowing, which is captured in the slag. Existing practice is the same blowing with extended duration.
Normal blowing practice with high Mn hot metal resulted in high MnO in the slag. With increased Mn oxidation (exothermic reactions), temperature control at the end of the blow becomes difficult. This resulted in difficulty in the end point prediction and necessitated increased re-blows. High MnO slags causes high refractory wear due to reduced melting point of slag (high fluidity) and increased oxidizing potential. Handling high MnO slag also resulted in high tapping temperatures, high FeO in final slag and lower yields. During the blowing, slopping tendency also increased resulting in unwanted blow stops. Such operations are thus unsustainable.
There has been therefore a persistent need for selective treatment of hot metal with high Mn(>0.50%) content in LD converters involving a new addition as well as blowing strategy so that the above stated problems and limitations of the existing high Mn based molten metal treatment is avoided and higher refractory life and desired steel consistent steel quality can be ensured at the subsequent steel making stage.
OBJECTS OF THE INVENTION
The basic object of the present invention is thus directed to a process for treatment of hot metal with high Mn(>0.5%) content in LD converters with reduced refractory erosion and enhanced refractory lining life, controlled tap temperature, reduced blowing and ensure desired quality of steel produced.

A further object of the present invention is directed to a process for treatment of hot metal with high Mn(>0.5%) content in LD converters wherein the Mn is oxidized as early as possible, Point of MnO peak identification and the high MnO slag is removed from the converter through intermediate de-slagging whereby the problem of iack of temperature control at the end of the blow is avoided and end point prediction is ensured.
A still further object of the present invention is directed to a process for treatment of hot metal with high Mn(>0.5%) content in LD converters wherein high refractory wear caused due to high MnO slag with reduced melting point of slag resulting in high fluidity and increased oxidizing potential is avoided.
A still further object of the present invention is directed to a process for treatment of hot metal with high Mn(>0.5%) content in LD converters wherein Mn oxidation during the initial part of the blow before intermediate-deslagging is implemented by modified flux additions.
A still further object of the present invention is directed to a process for treatment of hot metal with high Mn(>0.5%) content in LD converters wherein the point where the slag must be de-slagged is selected based on the change in the slope of CO-C02 curve of the off gas analysis to have the least impact on the refractories.
A still further object of the present invention is directed to a process for treatment of hot metal with high Mn(>0.5%) content in LD converters wherein converter refractories would be exposed to high MnO slag for a very short duration by modifying flux addition with selective blowing and intermediate de-slagging process, and thereby its erosion can be minimized.
A still further object of the present invention is directed to a process for treatment of hot metal with high Mn(>0.5%) content in LD converters wherein slopping during blowing and reduced equipment damage is minimized.
A still further object of the present invention is directed to a process for treatment of hot metal with high Mn(>0.5%) content in LD converters wherein reduced tapping temperature, reduced FeO in final slag and thereby higher yield in LD converter is

achieved by implementing selected right point for forming and deslagging of high MnO slag.
SUMMARY OF THE INVENTION
The basic aspect of the present invention is thus directed to a process for treating high Mn(>0.5 %) hot metal in LD converter for reducing refractory erosion and increasing converter lining life comprising
during initial part of blowing of hot metal with flux addition containing Lime calcined dolomite and Iron ore to suit Mn oxidation of hot metal containing high level of Mn(>0.5 %) to thereby generate High MnO slag ;
intermediate de-slagging of the High MnO slag ; and
continued further blowing involving further addition of flux to thereby control the MnO in the final slag to < 5%.
A further aspect of the present invention is directed to a process for treating high Mn(>0.5 %) hot metal in LD converter wherein said step of said intermediate de-slagging is carried out just after completion of de-siliconization preferably within about 20-30% of the blow time where exact point can be identified by the observing the change in the slope of CO-C02 curve of the off gas analysis.
A still further aspect of the present invention is directed to a process for treating high Mn(>0.5 %) hot metal in LD converter wherein said flux addition comprising lime, calcined dolomite and Iron ore during initial part of blowing was done to suit Mn oxidation before said step of intermediate deslagging.
A still further aspect of the present invention is directed to a process for treating high Mn(>0.5 %) hot metal in LD converter wherein said flux addition comprise reduced lime and dolomite addition preferably in amounts of 2.5 to 3.0 T/heat by wt and 1.5 to 2 T/heat by wt. respectively and Introduction of iron ore addition in amounts of 700 to 800 kgs/heat.

A still further aspect of the present invention is directed to a process for treating high Mn(>0.5 %) hot metal in LD converter which is carried out in the process of steel making for both high Si and low Si hot metals.
A still further aspect of the present invention is directed to a process for treating high Mn(>0.5 %) hot metal in LD converter wherein the intermediate slag comprises of CaO upto 35 %, Si02 upto 18%, MnO upto 18% and FeO upto 18%.
A still further aspect of the present invention is directed to a process for treating high Mn(>0.5 %) hot metal in LD converter wherein the final slag comprises of CaO upto 42 %, Si02 upto 10%, MnO upto 5.0% and FeO upto 23%.
Yet another aspect of the present invention is directed to a process for treating high Mn(>0.5 %) hot metal in LD converter favoring maintaining reduced tapping temperature in the range of 1650 to 1660 °C.
A further aspect of the present invention is directed to a process for treating high Mn(>0.5 %) hot metal in LD converter wherein said intermediate de-slagging step was selected based on the end of the de-Siliconisation reaction where exact point is identified by the observing the change in the slope of CO-C02 curve of the off gas analysis to carry out the said step of said intermediate de-slagging.
A still further aspect of the present invention is directed to a process for treating high Mn(>0.5 %) hot metal in LD converter comprising reduced amount of lime and dolomite addition preferably lime 2.5 T to 3.0 t per heat by wt and dolomite 1.5 T to 2.0 T per heat by wt. to thereby decrease the slag basicity and iron ore addition preferably 700 Kgs to 800 Kgs per heat was carried out such as to increase the FeO in the intermediate slag.
A still further aspect of the present invention is directed to a process for treating high Mn(>0.5 %) hot metal in LD converter wherein said step of intermediate de-slagging is carried out in about 3-6 minutes of the initiation of the blowing operation.
The various other objects and advantages are described in greater details with reference to the following accompanying non limiting illustrative drawings.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1: is the graphical presentation of the blow time versus bath Mn wt% indicating the Mn dip in bath with corresponding MnO peak in slag, just after complete de-siliconization which is the point where the slag must be de-slagged to have the least impact on the refractories.
Figure 2: is the schematic illustration of a composite chart showing the Blowing, addition and deslagging pattern according to the process for treatment of High Mn hot metal as of the present invention.
DETAILED DESCRIPTION OF THE INVENTION WITH REFERENCE TO THE ACCOMPANYING DRAWINGS
The present invention relates to a process for treatment of hot metal with high Mn(>0.05%) content in LD converters with reduced refractory erosion and enhanced refractory lining life, controlled tap temperature, reduced blowing and ensure desired quality of steel produced by oxidizing the Mn as early as possible through selective flux addition and oxygen blowing and remove the high MnO slag from the converter through intermediate de-slagging so as to reduce the refractory erosion and ensure end point prediction with reduced re-blows.
In order to ascertain the addition and blowing as well as deslagging process for early formation of Mn saturated slag and its intermediate deslagging at right point of time to eliminate the adverse effects on refractory lining as well as to attain the desired steel composition with reduced blow, series of experiments were conducted to develop a most appropriate bowing strategy. As previously described, formation of large amount of MnO during the blowing and getting high MnO in the final slag is not desired for normal steel making operation for the reasons mentioned above. However, Mn Oxidation is inevitable during blowing. It has been observed that the best way to reduce the refractory erosion and the problem of end point prediction is to oxidize the Mn as early as possible and remove the high MnO slag from the converter through intermediate de-slagging. It has also been found through repeated trials that Mn is best oxidized under the conditions of low temperature, high FeO and

low basicity in the slag. Based on the experiments it is further observed that time of de-slagging is the most critical parameter for best handling of high Mn hot metal and reduce its ill effects. During blowing, there is a Mn dip in hot metal or MnO peak in slag, just after complete de-siliconization (20-30% of the blow time). This is the point where the slag must be de-slagged to have the least impact on the refractories. Accompanying Figure 1 is the graphical presentation of the blowtime versus bath Mn wt% experimental verification of Mn dip in bath indicating the MnO peak in slag, just after complete de-siliconization after about 20-30% of the blow start which is the point where the slag must be de-slagged to have the least impact on the refractories.
Based on the above studies, a new blowing process has been developed with compulsorily having intermediate de-slagging for hot metals with high Mn (> 0.5 %). Flux additions have been modified to suit Mn oxidation during the initial part of the blow before intermediate-deslagging. Lime and dolomite additions are suitably reduced to decrease the slag basicity and iron ore addition is introduced from 2-3 min of blow start to increase the FeO in the initial slag. As observed the Mn saturated slag started forming just after completion of de-siliconisation reactions. Ideal de-slagging time has been set based on the initial silicon levels, which governs the end of de-Siliconisation reaction where exact point is identified by the observing the change in the slope of CO-C02 curve of the off gas analysis. With the implementation of new addition and intermediate de-slagging process, converter refractories are exposed to high Mn slag for a very short duration and thereby its erosion has been minimized. For most part of the blow, the slag and the converter conditions are maintained as good as the normal blowing. Accompanying Figure 2 illustrates a chart showing the blowing, addition and deslagging pattern according to the process of the present invention for treatment of High Mn hot metal. It is apparent from the figure that the total oxygen blowing lasts for about 17 minutes. The addition of lime, dolomite as flux and iron ore as coolant once done at 2-3 min after start of blowing which helps formation of high MnO initial slag and also de-siliconisation time decided based on initial Si content in molten metal so that the intermediate deslagging is selectively performed immediately after de-siliconisation and at 3-6 min after start of oxygen blowing. Further flux and coolant addition comprising lime, dolomite and iron ore is repeated just after intermediate deslagging to produce low MnO, FeO in final slag which helps preventing erosion of refractory lining of converter and attaining control on tap temperature vis-a-vis end point prediction.

The modified addition and blowing pattern as well as the selective intermediate deslagging of high Mn slag according to the present invention enabled achieving the following advantages:
-Reduction in Refractory erosion or increase in converter lining life.
-Minimizing of slopping during blowing and reduced equipment damage.
-MnO in final slag reduced from 15% to < 5 %
-Better end point control.
-FeO in final slag reduced from 27% to 23%.
-Reduction in tapping temperatures.
It is thus possible by way of the present invention to developing a blowing, addition pattern to quickly de-manganese the hot metal and identification of most appropriate intermediate de-slagging time (formation of Mn saturated slag) during converter blowing so as to enhance life of converter refractory lining and ensure obtaining desired composition of steel with optimized flux and coolant addition in converter as well as reduced re-blow and reduced tap temperature in a faster and cost effective manner.

We Claim:
1. A process for treating high Mn(>0.5 %) hot metal in LD converter for reducing
refractory erosion and increasing converter lining life comprising
during initial part of blowing of hot metal with flux addition to suit Mn oxidation of hot metal containing high level of Mn(>0.5 %) to thereby generate High MnO slag ;
intermediate de-slagging of the High MnO slag ; and
continued further blowing involving further addition of flux to thereby control the MnO in the final slag to < 5%.
2. A process for treating high Mn(>0.5 %) hot metal in LD converter as claimed in claim 1 wherein said step of said intermediate de-slagging is carried out just after completion of de-siliconization preferably within about 20-30% of the blow time.
3. A process for treating high Mn(>0.5 %) hot metal in LD converter as claimed in anyone of claims 1 or 2 wherein said flux addition during initial part of blowing was done to suit Mn oxidation before said step of intermediate deslagging.
4. A process for treating high Mn(>0.5 %) hot metal in LD converter as claimed in claim 3 wherein said flux addition comprise reduced lime and dolomite addition preferably in amounts of 2.5 T to 3.0 T per heat by and 1.5 to 2T per heat by wt respectively and increased Iron Ore addition in amounts of 700 kgs to 800 kgs per heat by wt.
5. A process for treating high Mn(>0.5 %) hot metal in LD converter as claimed in anyone of claims 1 to 4 which is carried out in the process of steel making both high Si and low Si hot metals.
6. A process for treating high Mn(>0.5 %) hot metal in LD converter as claimed in anyone of claims 1 to 5 wherein the MnO in the Intermediate slag is controlled to upto 18% and FeO in the intermediate slag upto 18 %.

7. A process for treating high Mn(>0.5 %) hot metal in LD converter as claimed in anyone of claims 1 to 5 wherein the MnO in the final slag is controlled to upto <5% and FeO in the final slag upto 23 %.
8. A process for treating high Mn(>0.5 %) hot metal in LD converter as claimed in anyone of claims 1 to 7 favouring maintaining reduced tapping temperature in the range of 1650 to 1660 °C.
9. A process for treating high Mn(>0.5 %) hot metal in LD converter as claimed in anyone of claims 1 to 8 wherein said intermediate de- slagging step was selected based on the initial silicon level which in turn govern the end of the-de-Siliconisation reaction to carry out the said step of said intermediate de-slagging where exact point is identified by the observing the change in the slope of CO-C02 curve of the off gas analysis.

10. A process for treating high Mn(>0.5 %) hot metal in LD converter as claimed in anyone of claims 1 to 9 comprising reduced amount of lime and dolomite addition preferably lime 2.5 T to 3.0 T per heat by wt and dolomite 1.5 to 2.0 T per heat by wt. to thereby decrease the slag basicity and iron ore addition was carried out such as to increase the FeO in the initial slag.
11. A process for treating high Mn(>0.5 %) hot metal in LD converter as claimed in anyone of claims 1 to 11 wherein said step of intermediate de-slagging is carried out in about 3-6 minutes of the initiation of the blowing operation.