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 METHOD FOR STEEL MANUFACTURE INVOLVING HOT METAL PRE-TREATMENT FOR DESILICONIZING OF THE HOT METAL.


2 APPLICANT (S)
Name : Nationality : Address :
JSW Steel Limited.
An Indian Company.
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.


FILED OF THE INVENTION
The present invention relates to a method for steel making and ,in particular, to a method of de-siliconisation of hot metal in steel making process directed to meeting increasingly cleanliness requirements and high production rates inspite of the deteriorating raw material quality. More particularly, the present invention relates to a method for de-siliconisation of hot metal involving a hot metal pre-treatment step to maintain desired low silicon input in LD converter. The method of the invention is directed to on one hand favor reduced slag generation in LD converter due to better controlled and low Si containing input of hot pr-treated hot metal and on the other hand enable simple and reliable process control during final steel making, eliminate extra refining operation, reduce processing time and resulting in a slag character suitable for reutilization. The method of the present invention is thus having prospect of wide industrial application to achieve improved quality and productivity of steel production in LD converters.
BACKGROUND ART
The existing steel making process involve steps starting with de-sulphurisation followed by primary steel making in LD converters, secondary steel making in steel ladles and casting into slabs at continuous casting plant. The hot metal impurities in the form of sulphur is removed at de-sulphurization station, whereas silicon, carbon and phosphorous are removed in LD converter in the stated order. Silicon (Si) is removed as Si02 and phosphorous as P2O5 into the slag and carbon is removed in the form of CO and C02, all of which are the products of reaction with blown oxygen. Higher the Si and P in hot metal, higher is SiO2 and P2O5 transferred to slag and hence higher is the slag generated. Slag is dumped into pits after the process. Thus the existing method of steel making includes unavoidable longer process time, need for excess blowing for the reactions to be completed and more over lower yields of process due to higher slag volume, needing subsequent refining with incidence of extra cost of processing.
The known steel-making route also has limited refining capabilities. Stringent quality requirements, high production rates and deteriorating raw material quality have made it increasingly difficult to meet the customer requirements in terms of chemical composition

and physical characteristics. Conventionally, total silicon removal is carried out in converter steel making by using lime and oxygen. It generates huge amount slag and is carried during the complete blowing process of converter steel making. Any increase in hot metal silicon results in increased slag generation and affects process control, other is unsuitable for re-utilization. This necessitated the requirement of additional pre-refining units in the present route to provide de-siliconisation functions,
There has thus been a persistent need in the art to develop a method for pre-treatment of the hot metal at transfer ladle in order to reduce the input Si in LD converter and thus reducing the requirement of carrying out elaborate oxidizing reactions for voluminous slag formation with increased duration of oxygen blowing requirements. Desiliconisation carried out prior to processing of steel in the LD converter substantially reduce total processing time and thus increase productivity, saving on blowing/oxygen lancing requirement ensuring consistent steel quality and favorable slag characteristics suitable for reutilization.
OBJECTS OF THE INVENTION
It is thus the basic object of the present invention to provide for a method for de¬siliconisation of hot metal using sinter fines in transfer ladle for steel production directed to reduce oxygen blowing, improve slag character, reduce slag reaction and volume at the converter stage and thus reducing the total processing time and improving quality and productivity of steel.
Another object of the present invention is directed to providing for a method for de¬siliconisation of hot metal in transfer ladle in steel making process by selective addition of sinter fines as iron oxide and gaseous oxygen as de-siliconisation agent.
A further object of the present invention is directed to providing a method for de-siliconization of hot metal in transfer ladles in steel production process involving selective sinter fines and gaseous oxygen blowing at desired rate to initiate and complete reactions and slag formation.

A further object of the present invention is directed to developing a method for de-siliconization of hot metal in transfer ladles applied in steel making whereby the silicon level could be brought down from 1.2 wt% to 0.4 wt %.
A still further object of the present invention is directed to developing a method for de-siliconization of hot metal in transfer ladles in production process of steel wherein average silicon levels in converter hot metals can be brought down by 0.3 wt %.
A still further object of the present invention is directed to developing a method for de-siliconization of hot metal in transfer ladles wherein the number of re-blows in converter could be reduced significantly.
A still further object of the present invention is directed to developing a method for de-siliconisation of hot metal in transfer ladles wherein the lime consumption and slag generation could be reduced in the LD converter.
A still further object of the present invention is directed to developing a method for de-siliconisation of hot metal involving sinter fines and oxygen blowing and addition patterns such as to achieve desired de-siliconisation and ensure much required quantity control of Si in converter input.
SUMMARY OF THE INVENTION
Thus according to the basic aspect of the present invention there is provided for in a
method for steel manufacture the step of desiliconizing of the hot metal comprising :
hot metal pre-treatment involving selectively de-siliconizing the hot metal in transfer ladle such as to maintain low silicon input in the molten metal in the LD converter and onward processing of the molten metal.
A further aspect of the present invention is directed to said method comprising removal of silicon by injection of reagents and fluxes in the transfer ladle.

A still further aspect of the present invention is directed to said method wherein said de-siliconisation comprises oxidizing the hot metal along with added lime and sinter fines (iron oxide) to form a CaO-FeO-SiO2 slag, sinter fines and gaseous oxygen used as de-siliconizing agents.
A still further aspect of the present invention is directed to said method wherein the sinter fines used as iron oxide flux comprise sinter fines of less than 5 mm size.
According to yet another aspect of the present invention is directed to said method wherein the sinter fines are added onto the surface of the hot metal from the bunkers though the addition chute.
A still further aspect of the present invention is directed to said method wherein after 60% of the blowing time, sinter fines addition is stopped and replaced by gaseous oxygen to maintain the kinetics of the reaction such that the gaseous oxygen first reacts with the molten metal to form FeO which in turn reacts with the silicon to form SiO2.
A still further aspect of the present invention is directed to said method wherein the exothermic reaction of silicon to silica raises the temperature of the bath which gets compensated for the temperature drop due to said additions.
A still further aspect of the present invention is directed to said method comprising providing lance heights adapted to keep the FeO content in the slag after the treatment very small.
A still further aspect of the present invention is directed to said method wherein the ladles are de-slagged after every treatment.

A still further aspect of the present invention is directed to said method comprising selective blowing and addition pattern to selectively desiliconize the hot metal involving said sinter fines and oxygen in transfer ladle and maintaining desired sinter fines :oxygen ratio index for process control.
A still further aspect of the present invention is directed to said method wherein
said selective blowing and addition pattern comprises optimized sequential addition; and
said desired sinter fines :oxygen ratio index comprises in range of 8-10.
The present invention and its objects and advantages are described in greater details with reference to the accompanying non- limiting illustrative figure.
BRIEF DESCRIPTION OF THE ACCOMPANYING FIGURE
Figure 1: is the schematic illustration of the selective pattern defining the sinter fine addition and oxygen blowing in liquid metal transfer ladle for desired de-siliconisation according to the method of the present invention.
DEATAILED DESCRIPTION OF THE INVENTION WITH REFERENCE TO THE ACOMPANYING FIGURE
The present invention is directed to selectively de-siliconize the hot metal in transfer ladle and maintain low silicon input in LD converter in order to reduce slag formation in converter, improved yield and reduced total processing time in steel making.

This necessitated the requirement of additional pre-refining units in the present route to provide de-siliconisation functions. To meet the requirements of stringent quality and high productivity, the applicants introduced for the first time Hot Metal Pre-Treatment (HMPT) facility in one of their steel plant- HMPT enabled the removal of silicon by injection of reagents and fluxes in the transfer ladle. De-siliconisation was attempted by oxidizing the hot metal along with added lime and sinter fines (iron oxide) to form a CaO-FeO-SiO2 slag. Sinter fines and gaseous oxygen act as de-siliconizing agents. Sinter fines, used as, iron oxide flux are less than 5 mm size. Sinter fines are added onto the surface of the hot metal from the bunkers though the addition chute.
Reference is now invited to the accompanying Figure 1 that schematically illustrates the selective blowing and addition pattern developed to selectively de-siliconize the hot metal using sinter fines and oxygen in transfer ladle, according to the method of the present invention.
It is apparent from the addition pattern proposed as in accompanying Figure 1 that after about 60% of the blowing time, sinter fines addition is stopped and gaseous oxygen is blown at desired rate through the molten pool to maintain the kinetics of the reaction, Gaseous oxygen first reacts with the molten metal to form FeO which in turn reacts with the silicon to form Si02 similar to the cxygen reaction in basic oxygen furnace. The exothermic reaction of silicon to silica raises the temperature of the bath and gets compensated for the temperature drop due to additions.
Advantageously, in the addition cum oxygen blowing process, the optimum lance heights resulted in keeping the FeO content in the slag after the treatment very small. The ladles are de-slagged after every treatment. Importantly also, Sinter fines/Oxygen ratio index in the preferred range of 8 to 10 is used with advantage for process control is steel refining.
It is apparent from the accompanying Figure 1, that the ladle refining process that continues for 25 to 30 minutes, lime fine is added at the rate of 40Kg/min for the entire duration of the transfer ladle pre-treatment operation.
Sinter fine addition starts after initial 5 minutes time and continues at the rate of 160kg/min for up to 20 minute duration or about 60% of the addition time. Blowing of gaseous oxygen starts before the sinter fine addition ends and is continued at the rate of 40 l\lm3/min with

some incremental flow rates of 10 Nm3/min towards the end of the addition cum blowing pattern for molten metal in transfer ladle. The pattern so followed ensure obtaining the pretreated steel quality for LD converter input comprising average silicon levels in converter hot metal brought down by 0.3% and also ensure requirement of number of re-blows has been reduced from 10% to 6 % in LD converter and also reduced lime consumption and slag generation in converter.
It is thus possible by way of the present invention to developing a method for desiliconisation of hot metal using sinter fines in transfer ladles such that the pre-treated metal used as input to LD converter for steel making with reduced silicon content and thus needing less processing time and slag formation in terms of reaction time and volume. The method thus ensure production of superior quality steel with improved productivity at less time and cost. The resulting slag produced with pre-treatment of molten metal is also suitable for reutilization. A typical addition and blowing pattern is selectively deployed to meet the end objective of controlled Si (<0.4wt%) in molten metal in transfer ladle while the ratio of sinter fines to oxygen is used as an index for process control. The method according to the present invention is thus adapted to provide means for pre-treatment of molten metal in transfer ladle such that the processing of steel in LD converter in the next stage is faster, cleaner and less energy consuming with optimized lancing directed to improving the productivity of steel at less cost and thus having prospects of wide industrial application.

WE CLAIM:
1. In a method for steel manufacture the step of de-siliconizing of the hot metal comprising:
hot metal pre-treatment involving selectively de-siliconizing the hot metal in transfer ladle such as to maintain low silicon input in the molten metal in the LD converter and onward processing of the molten metal.
2. A method as claimed in claim 1 comprising removal of silicon by injection of reagents and fluxes in the transfer ladle.
3. A method as claimed in anyone of claims 1 or 2 wherein said de-siliconisation comprises oxidizing the hot metal along with added lime and sinter fines (iron oxide) to form a CaO-FeO-SiO2 slag, sinter fines and gaseous oxygen used as de-siliconizing agents.
4. A method as claimed in claim 4 wherein the sinter fines used as iron oxide flux comprise sinter fines of less than 5 mm size.
5. A method as claimed in anyone of claims 3 or 4 wherein the sinter fines are added onto the surface of the hot metal from the bunkers though the addition chute.
6. A method as claimed in anyone of claims 1 to 5 wherein after 60% of the blowing time, sinter fines addition is stopped and replaced by gaseous oxygen to maintain the kinetics of the reaction such that the gaseous oxygen first reacts with the molten metal to form FeO which in turn reacts with the silicon to form SiO2.

7. A method as claimed in claim 7 wherein the exothermic reaction of silicon to silica raises the temperature of the bath which gets compensated for the temperature drop due to said additions.
8. A method as claimed in anyone of claims 1 to 7 comprising providing lance heights adapted to keep the FeO content in the slag after the treatment very small.
9. A method as claimed in anyone of claims 1 to 8 wherein the ladles are de-slagged after every treatment.
10. A method as claimed in anyone of claims 1 to 9 comprising selective blowing and
addition pattern to selectively desiliconize the hot metal involving said sinter fines and
oxygen in transfer ladle and maintaining desired sinter fines: oxygen ratio index for process
control.
11. A method as claimed in claim 10 wherein
said selective blowing and addition pattern comprises optimized sequential addition; and said desired sinter fines :oxygen ratio index comprises range of 8-10.
12. In a method for steel manufacture the step of desiliconizing of the hot metal
substantially as here in described and illustrated with reference to the accompanying
figures.