Title of Invention	"AN IMPROVED PROCESS FOR PRODUCING CLEAN STEEL BY MODIFICATION OF ALUMINA INCLUSIONS INTO GLOBULAR CALCIUM ALUMINATE"
Abstract	The invention provides an improved process for producing clean steel by modification of alumina inclusions into globular calcium aluminate at a reduced cost. The process comprises the steps of : a) preparing a low cost non-metallic synthetic powder as substitute for the conventionally used expensive Ca bearing alloys, such as CaSi, by synthesising flux ingredients (lime & flourspar) commonly used in steel making process; b) blowing argon carrier gas into a dispenser containing the synthetic powder of lime based flux at a flow rate 1.5-2.0 Nm3/hr and pressure 1.5-6kg/cm2 ; c) applying an inert slag cover on the top of aluminium deoxidised/killed molten steel to prevent oxygen pickup due to entrainment from atmosphere; and d) injecting the flux into liquid steel (Al killed steel) in an induction furnace (by way of an example only) through a refractory coated top lance at a rate of 15-100 gm/min for a duration 2.5-7.0 min and at an injection depth of 100-120 mm.

Title of Invention

"AN IMPROVED PROCESS FOR PRODUCING CLEAN STEEL BY MODIFICATION OF ALUMINA INCLUSIONS INTO GLOBULAR CALCIUM ALUMINATE"

Abstract

The invention provides an improved process for producing clean steel by modification of alumina inclusions into globular calcium aluminate at a reduced cost. The process comprises the steps of : a) preparing a low cost non-metallic synthetic powder as substitute for the conventionally used expensive Ca bearing alloys, such as CaSi, by synthesising flux ingredients (lime & flourspar) commonly used in steel making process; b) blowing argon carrier gas into a dispenser containing the synthetic powder of lime based flux at a flow rate 1.5-2.0 Nm3/hr and pressure 1.5-6kg/cm2 ; c) applying an inert slag cover on the top of aluminium deoxidised/killed molten steel to prevent oxygen pickup due to entrainment from atmosphere; and d) injecting the flux into liquid steel (Al killed steel) in an induction furnace (by way of an example only) through a refractory coated top lance at a rate of 15-100 gm/min for a duration 2.5-7.0 min and at an injection depth of 100-120 mm.

Full Text	The present invention relates to an improved process for producing clean steel by modification of alumina inclusions into globular calcium aluminate. Aluminium is commonly used as one of deoxidisers in steel making. The deoxidation product, alumina (Al2O3) is formed. Alumina is high melting and remains solid at steel making temperature. Some of the alumina inclusions float up during argon rinsing of molten steel. However a substantial amount of the alumina inclusions remain in the steel. These inclusions are harmful and affect the cleanliness as well as the quality of the steel. Cleanliness of steel is improved by Ca-treatment. By Ca - treatment the high melting solid Al2O3 inclusions are modified into low melting complex inclusions i.e. globular calcium aluminate. Globular calcium aluminate liquid inclusions thus formed easily separate out and the steel becomes cleaner. Calcium has a high vapour pressure at steel making temperature. So it is used in the form of calcium tearing alloys such as CaSi, for the modification of alumina inclusions into calcium aluminate. But the disadvantage of using the calcium bearing alloys is that these are very i costly and their use raises the cost of the process. The object of the present invention is to provide a relatively low cost process for producing clean steel of improved quality. In the present invention a synthetic nonmetallic powder is used for modification of alumina inclusions into globular calcium aluminate. The flux is cheaper than the calcium bearing alloys and is synthesiaed from known flux ingrediants commonly used in steel making processes. The flux is injected into molten steel using argon as the carrier gas at an appropriate injection rate. The invented process is described fully and by way of example only with reference in the accompanying drawings in which - Figure 1 is a sectional sketch of the dispenser for holding and injecting synthetic powder with argon carrier gas; Figure 2 is a sectional sketch of the top lance used for injecting the synthetic powder using argon as carrier gas into the molten steel in a furnace; and Figure 3 is a flow chart showing the steps followed in sequence in the invented process. Referring to Fig. 1, the dispenser (1) comprises a cylindrical part (2) enclosing inlet pipe (4) and outlet pipe (5) and a conical part (3) at the bottom aid is mounted firmly on a stand. The synthetic powder is blown from the dispenser using argon gas as carrier through the inlet pipe and is allowed to eject out through the outlet pipe alongwith the carrier gas. Referring to Fig. 2, the top lance comprises a single injection pipe (7) of preferred diameter 10 mm, the part (8) of which is coated with a refractory material (9). The flux from dispenser along with argon as carrier is injected into molten steel in a furnace (an induction furnace) through the injection pipe of the lance at a given range of depth, rate and duration. The extent of modification depends on sulphur, oxygen and Al content of steel. The steel should be Al killed steel and an inert top slag cover should oe provided on molten liquid steel. The typical operating conditions followed in the invented process are outlined in Table I. Referring to Fig. 3, the invented process comprises the following steps in sequence :- a) Preparing a low cost non-metallic synthetic flux powder by synthesising flux ingredients such as lime and fluorspar, commonly used in steel making process, as substitute for the conventionally used expensive Ca bearing alloys such as CaSi; b) Applying an inert slag cover on the top of aluminium deoxidized/killed molten steel to prevent oxygen pick-up due to entrainment from atmosphere; c) Blowing argon carrier gas into a dispenser containing the non-metallic synthetic flux powder at and a flow rate 1.5-2.0Nm3/hr/pressure 1.5-6.0 kg/cm2 and d) Injecting the non-metallic synthetic flux powder into liquid Al killed steel in an induction furnace through a refractory coated top lance, such as herein described, at a rate of 15-100 gm/min for a duration 2.5-7.0 min and at an injection depth of 100-120 mm TABLE I Typical operating conditions followed in the process 1. Injection rate of synthetic powder: l5-100gm/min 2. Argon gas flow rate: 1.5-2 Nm3/hr 3. Argon gas pressure : 2-6 kg/cm 4. Injection duration: 2.5 - 7.0 min. 5. Top lance injection depth : 100-120 mm. The invented process is described further by way of an example only as follows : In an induction furnace of 100 kg capacity, Al- deoxidised/killed molten steel of 40-50 kg weight is made. The synthetic powder is injected into the molten steel using argon as carrier at the rate of 15-100 gm/min. , preferably 30-70 gm/min, and more preferably 45-55 gm/min; at a flow rate of 1.5-2.0 Nnr/hr, preferably 1.6-1.9 Nnr/hr and more preferably 2 1.7-1.8 Nm3/hr; at a pressure of 1.5-6 kg/cm , 2 preferably 3-5 kg/cm2 , more preferably 3.5-4.5 kg/cm and still more preferably 1.5-2.5 kg/cm2 , for a duration 2.5-7.0 min, preferably 3.5-6.0 min and more preferably 4.0-5.0 min and at an injection depth of the lance in the molten steel of 100-120 mm, preverably 105-115 mm and more preferably 108-112 mm. The commonly followed metallographic examination of the steel produced reveals that both the volume fraction and mean size of the inclusions in the steel produced in the invented process are reduced in comparison with the plainly argon purged steel sample. The study of the impact strength of the steel produced in the invented process by means of charpy V-notch test reveals that the toughness of the steel has improved. We Claim :- 1. An improved process for producing clean steel by modification of alumina inclusions into globular calcium aluminate at a reduced cost, comprising the following steps in sequence :- a) Preparing a low cost non-metallic synthetic flux powder by synthesising flux ingredients such as lime and fluorspar, commonly used in steel making process, as substitute for the conventionally used expensive Ca bearing alloys such as CaSi b) Applying an inert slag cover on the top of aluminium deoxidized/killed molten steel to prevent oxygen pick-up due to entrainment from atmosphere; c) Blowing argon carrier gas into a dispenser containing the non-metallic synthetic flux powder at a flow rate 1.5-2.0 Nn3/hr and pressure 1.5-6.0 kg/cm ; and d) Injecting the non-metallic synthetic flux powder into liquid Al killed steel in an induction furnace through a refractory coated top lance, such as herein described, at a rate of 15-100 gm/min for a duration 2.5-7.0 min and at an injection depth of 100-120 mm. 2. The process as claimed in claim 1, wherein 45-50 kg of aluminium deoxidized/killed steel is melted in an induction furnace of 100 kg capacity. 3. The process as claimed in claim 1 or 2, wherein the flux powder along with the argon carrier gas is injected into the molten steel at a rate of 30-70 gm/min, preferably 45-55 gm/min. 4. The process as claimed in any preceding claim, wherein the argon gas is blown into the dispenser at a flow rate of 1.6-1.9 Nnr/hr, more preferably 1.7-1.8 Nnr/hr. 5. The process as claimed in any preceding claim, wherein the argon gas is blown into the dispenser at a pressure of 2 3-5 kg/cm more preferably 3.5-4.5 kg/cm2 , still more preferably 1.5-2.5 kg/cm2. 6. The process as claimed in any preceding claim, wherein the argon carriwr gas alongwith the flux is injected into the molten steel for duration of 3.5-6.0 min., more preferably 4 .0-5.0 min. 7. The process as claimed in any preceding claim, wherein the argon carrier gas along with the flux is injected into molten steel at a depth of 105-115 mm,more preferably 108-112 mm.

Full Text

The present invention relates to an improved process for producing clean steel by modification of alumina inclusions into globular calcium aluminate.
Aluminium is commonly used as one of deoxidisers in steel making. The deoxidation product, alumina (Al2O3) is formed. Alumina is high melting and remains solid at steel making temperature. Some of the alumina inclusions float up during argon rinsing of molten steel. However a substantial amount of the alumina inclusions remain in the steel. These inclusions are harmful and affect the cleanliness as well as the quality of the steel.
Cleanliness of steel is improved by Ca-treatment.
By Ca - treatment the high melting solid Al2O3 inclusions are
modified into low melting complex inclusions i.e. globular
calcium aluminate. Globular calcium aluminate liquid
inclusions thus formed easily separate out and the steel becomes cleaner. Calcium has a high vapour pressure at steel making temperature. So it is used in the form of calcium
tearing alloys such as CaSi, for the modification of alumina
inclusions into calcium aluminate. But the disadvantage of

using the calcium bearing alloys is that these are very
i
costly and their use raises the cost of the process.

The object of the present invention is to provide a
relatively low cost process for producing clean steel of improved quality.

In the present invention a synthetic
nonmetallic powder is used for modification of alumina inclusions into globular calcium aluminate. The flux is cheaper than the calcium bearing alloys and is synthesiaed from known flux ingrediants commonly used in steel making processes. The flux is injected into molten steel using argon as the carrier gas at an appropriate injection rate. The invented process is described fully and by way of example only with reference in the accompanying drawings in which -
Figure 1 is a sectional sketch of the dispenser for holding and injecting synthetic powder with argon carrier gas;
Figure 2 is a sectional sketch of the top lance used for injecting the synthetic powder using argon as carrier gas into the molten steel in a furnace; and
Figure 3 is a flow chart showing the steps followed in sequence in the invented process.
Referring to Fig. 1, the dispenser (1) comprises a cylindrical part (2) enclosing inlet pipe (4) and outlet pipe (5) and a conical part (3) at the bottom aid is mounted firmly on a stand. The synthetic powder is blown from the dispenser using argon gas as carrier through the inlet pipe and is allowed to eject out through the outlet pipe alongwith the carrier gas.
Referring to Fig. 2, the top lance comprises a single injection pipe (7) of preferred diameter 10 mm, the part (8) of which is coated with a refractory material (9). The flux from dispenser along with argon

as carrier is injected into molten steel in a furnace (an induction furnace) through the injection pipe of the lance at a given range of depth, rate and duration. The extent of modification depends on sulphur, oxygen and Al content of steel. The steel should be Al killed steel and an inert top slag cover should oe provided on molten liquid steel. The typical operating conditions followed in the invented process are outlined in Table I.
Referring to Fig. 3, the invented process comprises the following steps in sequence :-
a) Preparing a low cost non-metallic synthetic
flux powder by synthesising flux ingredients such as
lime and fluorspar, commonly used in steel making
process, as substitute for the conventionally used
expensive Ca bearing alloys such as CaSi;
b) Applying an inert slag cover on the top of
aluminium deoxidized/killed molten steel to prevent
oxygen pick-up due to entrainment from atmosphere;
c) Blowing argon carrier gas into a dispenser
containing the non-metallic synthetic flux powder at
and
a flow rate 1.5-2.0Nm3/hr/pressure 1.5-6.0 kg/cm2 and
d) Injecting the non-metallic synthetic flux
powder into liquid Al killed steel in an induction
furnace through a refractory coated top lance, such as
herein described, at a rate of 15-100 gm/min for a
duration 2.5-7.0 min and at an injection depth of
100-120 mm
TABLE I Typical operating conditions followed in the process
1. Injection rate of synthetic powder: l5-100gm/min
2. Argon gas flow rate: 1.5-2 Nm3/hr

3. Argon gas pressure : 2-6 kg/cm
4. Injection duration: 2.5 - 7.0 min.
5. Top lance injection depth : 100-120 mm.
The invented process is described further by way of an example only as follows :
In an induction furnace of 100 kg capacity, Al- deoxidised/killed molten steel of 40-50 kg weight is made. The synthetic powder is injected into the molten steel using argon as carrier at the rate of 15-100 gm/min. , preferably 30-70 gm/min, and more preferably 45-55 gm/min; at a flow rate of 1.5-2.0 Nnr/hr, preferably 1.6-1.9 Nnr/hr and more preferably
2
1.7-1.8 Nm3/hr; at a pressure of 1.5-6 kg/cm ,
2
preferably 3-5 kg/cm2 , more preferably 3.5-4.5 kg/cm
and still more preferably 1.5-2.5 kg/cm2 , for a
duration 2.5-7.0 min, preferably 3.5-6.0 min and more preferably 4.0-5.0 min and at an injection depth of the lance in the molten steel of 100-120 mm, preverably 105-115 mm and more preferably 108-112 mm.
The commonly followed metallographic examination of the steel produced reveals that both the volume fraction and mean size of the inclusions in the steel produced in the invented process are reduced in comparison with the plainly argon purged steel sample.
The study of the impact strength of the steel produced in the invented process by means of charpy V-notch test reveals that the toughness of the steel has improved.

We Claim :-
1. An improved process for producing clean steel
by modification of alumina inclusions into globular
calcium aluminate at a reduced cost, comprising the
following steps in sequence :-
a) Preparing a low cost non-metallic synthetic
flux powder by synthesising flux ingredients such as
lime and fluorspar, commonly used in steel making
process, as substitute for the conventionally used
expensive Ca bearing alloys such as CaSi
b) Applying an inert slag cover on the top of
aluminium deoxidized/killed molten steel to prevent
oxygen pick-up due to entrainment from atmosphere;
c) Blowing argon carrier gas into a dispenser
containing the non-metallic synthetic flux powder at
a flow rate 1.5-2.0 Nn3/hr and pressure 1.5-6.0
kg/cm ; and
d) Injecting the non-metallic synthetic flux
powder into liquid Al killed steel in an induction
furnace through a refractory coated top lance,
such as herein described, at a rate of 15-100 gm/min for a duration 2.5-7.0 min and at an injection depth of 100-120 mm.
2. The process as claimed in claim 1, wherein
45-50 kg of aluminium deoxidized/killed steel is
melted in an induction furnace of 100 kg capacity.
3. The process as claimed in claim 1 or 2,
wherein the flux powder along with the argon carrier
gas is injected into the molten steel at a rate of
30-70 gm/min, preferably 45-55 gm/min.

4. The process as claimed in any preceding claim, wherein
the argon gas is blown into the dispenser at a flow rate of
1.6-1.9 Nnr/hr, more preferably 1.7-1.8 Nnr/hr.
5. The process as claimed in any preceding claim, wherein
the argon gas is blown into the dispenser at a pressure of
2
3-5 kg/cm more preferably 3.5-4.5 kg/cm2 , still more preferably
1.5-2.5 kg/cm2.
6. The process as claimed in any preceding claim, wherein
the argon carriwr gas alongwith the flux is injected into the
molten steel for duration of 3.5-6.0 min., more preferably
4 .0-5.0 min.
7. The process as claimed in any preceding claim, wherein
the argon carrier gas along with the flux is injected into
molten steel at a depth of 105-115 mm,more preferably
108-112 mm.

Documents:

1-del-1997-abstract.pdf

1-del-1997-claims.pdf

1-del-1997-correspondence-others.pdf

1-del-1997-correspondence-po.pdf

1-del-1997-description (complete).pdf

1-del-1997-drawings.pdf

1-del-1997-form-1.pdf

1-del-1997-form-19.pdf

1-del-1997-form-2.pdf

1-del-1997-gpa.pdf

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Patent Number

232033

Indian Patent Application Number

1/DEL/1997

PG Journal Number

13/2009

Publication Date

27-Mar-2009

Grant Date

15-Mar-2009

Date of Filing

01-Jan-1997

Name of Patentee

STEEL AUTHORITY OF INDIA LTD., RESEARCH & DEVELOPMENT CENTRE FOR IRON & STEEL

Applicant Address

ISPAT BHAWAN, LODI ROAD, NEW DELHI-110003.

Inventors:

#	Inventor's Name	Inventor's Address
1	SAROJ KISHORE SAHAY	PRE, RDCIS, SAIL, RANCHI.
2	DR.SHIBNATH MAZUMDAR	AGM, RDCIS, SAIL, RANCHI

PCT International Classification Number

C22C 36/00

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA