CA1092828A - Basic oxygen furnace argon refining blow - Google Patents
Basic oxygen furnace argon refining blowInfo
- Publication number
- CA1092828A CA1092828A CA337,600A CA337600A CA1092828A CA 1092828 A CA1092828 A CA 1092828A CA 337600 A CA337600 A CA 337600A CA 1092828 A CA1092828 A CA 1092828A
- Authority
- CA
- Canada
- Prior art keywords
- oxygen
- bath
- carbon content
- argon
- steel
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Abstract
ABSTRACT
An improvement is disclosed in the manufacture of steel in a basic oxygen furnace wherein oxygen is introduced through a lance onto the melt until the carbon content of the bath is about 0-10% above the desired finished carbon content.
The introduction of oxygen is stopped and argon is introduced through the lance to complete the refining to the desired carbon content.
An improvement is disclosed in the manufacture of steel in a basic oxygen furnace wherein oxygen is introduced through a lance onto the melt until the carbon content of the bath is about 0-10% above the desired finished carbon content.
The introduction of oxygen is stopped and argon is introduced through the lance to complete the refining to the desired carbon content.
Description
lO9Z828 BASIC OXYGEN FURNACE ARGON REFINING BLOW
The present invention relates to the manufacture of steel and more particularly to an improvement in pneumatic steel making processes wherein oxygen is introduced through a lance and blown downwardly onto the surface of a bath to effect refinement of the melt.
In the`basic oxygen process, substantially pure oxygen is introduced from above the surface of the bath in a basic-lined vessel. After the furnace is charged with controlled amounts of scrap and molten iron, the furnace is brought into an upright position and the oxygen lance is lowered to a predetermined position above the surface of the bath. Oxygen gas issues from the jet nozzle at high velocity with the action of the oxygen jet being partially chemical and partially physical. On striking the surface of the liquid bath, the oxygen immediately starts reacting leading to the formation of iron oxides with carbon monoxide being evolved which gives rise to a vigorous boiling action and accelerates refining metallurgical reactions.
The slag forming fluxes,which are chiefly bu~ned lime, flu~rspar and millscale, are added in controlled amounts after the oxygen introduction begins. These materials serve to produce a slag of the desired basicity and fluidity.
There are several advantages of the basic oxygen process in its flexibility in handling raw materials of many types and compositions. The scraP, which is employed, mav be either heavy or li`ght an~ the oxide charae, if used, mav ~e drv~eres, sinter, p~llets or millscale. The process may be operated on any kind of hot metal that can be used in the basic open hearth furnace.
3 ~n the manufacture of steel in the basic oxygen furnace, a very large percentage of the heats are required to ~ ' , . ' ~
lO9Z8Z~
be finished at YerX low carbon values. The final car~ons are frequently as low as 0.03% in order to meet the Q.Q5% ~aximum car-bon aim in low alloy high strength steel, enamelling s-teels, deep drawing steels and electrïcal steels~ In many grades of steel it is advantageous to have a res-i`dual carbon content as low as 0.02%
to obtain certaïn desïred strength and other metallurgical pro-perties.
A standard basic oxygen furnace charge is approx-imately 7Q% hot metal and 30~ steel scrap and has an average carbon content in the range of 2.5 to 3.0%. It is customary to remove the excess carbon from the melt by oxidation employing high purity oxygen introduced through a lance as the oxidizing agent. ~nfortunately, as the carbon is oxidized there is a simultaneous oxidation of iron. The lower the carbonis in the melt, the higher is the percentage of iron oxidized to FeO. This oxidized iron is permanently lost to the formed slag. In melts of very low carbon i.e. 0.03%, the FeO in the slag may be as high as 35.0%. As it is normal practice to carry between 250 and 300 lbs of slag per ton of metal, the iron losses are thus consider-able. In addition, high FeO slags are very fluid and chemically active and may result in severe attack on the furnace refractory lining.
Melts which are at low carbon levels and contain high slaglevels may have as high as 1000 ppm oxygen dissolved in the steel. This oxygen is c~nx~ly removed from the steel by addition of aluminum. Apart fram the high cost of this deoxidation practice, not all of the alumina is rem~ved from the steel and may be a source of defects in the fmal product.
The above mentioned problems which are an in-herent feature of the basic oxygen furnace steel making process have to date been philosophically accepted by the steel industry and it is~ an object of the present invention to reduce these problems to a ~inimu~.
It is a further object of the present invention to reduce the iron loss to the slag during the refining process.
It is a further object of the present inven~ion to increase the viscosity of the slag.
It is yet a further object of the present invention to provide an improved process for the refining of steel.
Thus, in accordance with the present teachings, an improvement is provided in the process for the manufacture of steel in a basic oxygen furnace wherein a bath of metal is refined by the introduction of oxygen through a lance onto the surface of the bath. The improvement which is provided comprises blowing the bath with oxygen until the carbon content of the bath is about 0.10% above the desired finished carbon content and discontinuing the oxygen introduction and introducing argon through the lance until the desired carbon content of the bath is achieved.
At the completion of the argon blow, the amount of oxygen remaining dissolved in the molten steel is considerably below the level encountered when the melt is blown in the usual normal manner with 100% oxygen only. The use of the argon blow results in a lower level of non metallic deoxidation products and thus a cleaner steel product is obtained. Ladle deoxidant recoveries, when argon is employed following the oxygen blow, have also been found to be much higher, as for example, the aluminum deoxidation efficiences are in the range of 60 to 75%. This compares very favorable with 25 to 50% efficiences which is experienced with heats which have been blown with oxygen only in melts containing similar carbon, manganese and temperature levels.
The use of argon in completing the refining of the melt has also been found to result in a significant increase in the viscosity of the slag.
During tapping of the melt, the much stiffer obtained slag is more readily retained in the furnace and the exclusion of large volumes of iron oxide bearing slag from the ladle is a contribut-.~-lO~Z828 ing factor in improyed deoxidant effici.encx. It should als,o be noted that increased s:lag vi.~cosity also acts to reduce the attack on the furnace and ladle lini`ngs whi:ch results: in a significant increase i`n the life of the refractory employed for such li.nings.
Although applicant does not wish to be confined to any theoretical discuss:ion it is belîeved that the intimate mixing of the slag containing FeO which.is produced during the oxygen blow and the ~etal containing carbon would provide the chemical reac~ion FeO + C ~ Fe + CO.
The carbon monoxide escapes to atmosphere and the reduced metallic iron reverts back to the metai bath. During the argon blow, the free volume of the vessel is filled with argon gas and the partial pressure of CO in contact with the bath would be very low. This further accelerates the FeO + C reaction. In view of the turbul-ence of the bath with ~he introduction of the argon through the lance, the dissolved oxygen in the metal also reacts with the carbon C + 1/2 2 ~ CO.
In accordance with the present process, it is desired to produce a steel having a finished carbon content of 0.04%. The steel is blown with oxygen in the basic oxygen furnace in the normal manner until the carbon content of the bath is approximately 0.14% or about 0.10% above the required finishing carbon content. In place of oxygen the blow is now continued employing 100% argon gas. To create the emulsion between the slag and the metal, the flow rate of the argon gas is substantially the same as that which is employed for oxygen in conventional basic oxygen furnace processes and typically a 120 ton capacity vessel would employ a flow rate in the order of about 7,3Q0 cu.
ft/min.
The following Example and data is being provided to illustrate the present invention and is not intended to limit the scope of the concept.
EXAMPLEI
Oxygen was; b.lown downwardly onto the 12Q ton heats.unti.l th.e resi.dual carbon co~tent of the melt reacfied approximately Q.2 to 0.25% (or as indicated in ~able 1~. The oxygen flow was stopped and a sample of each. melt was taken (Sample I~. Following this, pure argon was substi.tuted for oxygen and blown onto the melt for two periods of 2 mins. each at a flow rate of between 3000 and 6000 cu.ft./min. Samples were taken after each period of treat-ment with.the argon (Samples II and III). The resulting reduction in the amounts- of carbon and dissolved oxygen remaining in the melt is shown in Table 1.
~0~282~
~ ~ `T~ . _ ~
., ~ ,.. ,.. .. .
~ .~
¢jo~ 0 ~ ~3 j3 ¢ 4~ o o o o o o c) I O . o o o o o O
~ ~ ~ o o o o o o 1~ 0 C~u~ ~D c~ `D ~ ~ ~:
o l * e C ~ I~ ~ l ~ ~ I , .a ., o ~ ~ ~ ~ ~, l ¢& ~ , ~ ~ o l o ~ ~ Z ~ ~ X
. e ~ O ~ ~ ~ __ ~ O O
O~ O~ l ~
l o - ~ ~ ~ ~ ~. _ o o . l ~, Z ~, ~ s~
. _ _ ' ~ ~ ~ ~ ~ ~ ~ ~ U~ l .~ ¢ O ~ : O ~ _ Z ~ C~ ~ . . .
O _ . R
O ¢ e ~ c O ~ ~ ~ ~ ~
~ o ~ Z Z: ~ Z Z ~ O
_~ ' _ _ .
~3 r~ ~D 1~ O O ~1 ¢ ~00 : N O~ ~U) :, N a O~ ~o P
C~ ', _ _ _ _ ~ _ H E-l P. O G O 1~ o :, O 1~
F~ ~ :e ~ ~ o a~:~D o o cq ~i ~ ,E-l O C~l ~) N N ~') ~ V ~) i~i I : d ~D ___ _ . ~ ~
O ~ al ~ ~ ~D ~') C`l r~ c) ~ ~ H ~ !~1 Z ~1 ~1 r~ ~1 ~ ia3 C~
, _ ~__ O
U~ 11~ : `$ : N ~1 O ~
q~ to ~ ~ ~ ~ ' `D ~ b~
~¢ I ~ /~0~ 00 r-l '~) ~ 'O ¢ o _ __ , ~ ~
, I ¢ e ~ ~ ~ ~ ~ ,, o z o _ æ z ~ h O j ~ u~ O u~ O o o ~ ::
m ~ ~ ~ ~ ~ ~ ~ o :
E-~ O N N N N N ~ Cl ~
_. ~`I O _ _ __ O ~ . . l:~ ~ ~: J-H ~ ~Z : __ z: Z _ :~? ? ,~
~j ~ ~ ~ ~ U~ Z ~ ¢ ¢
__ _ _ _ __ _ _ a~
~.) ~ N N N N N : O
_ tYi _ _ __ . ~ _ _ o oX Z
~ ~ o ~ cr o ~
E~ ~ ~ : u-, ~--1 N N
NN ) '1 ~5LZ ,_ _~_ _ IY_ _~_,___ _ ~_ _g_ ¢ o ~: z lO~Z828 As may readily be observed from the above data the carbon content is effectively reduced to the desired levels with no significant reduction in manganese. In addition, through the use of the present teachings, some of the oxidized iron which has been permanently lost to the slag is through the use of the argon blow reduced to metallic iron and reverts back to the metal bath--~urthermDre, the finishing blow employing argon also acts to remove dissolved oxygen thereby reducing the oxidation practice normally effected.
It will be obvious to those skilled in the art that various modifications may be resorted to without departing from the spirit of the invention.
.:
The present invention relates to the manufacture of steel and more particularly to an improvement in pneumatic steel making processes wherein oxygen is introduced through a lance and blown downwardly onto the surface of a bath to effect refinement of the melt.
In the`basic oxygen process, substantially pure oxygen is introduced from above the surface of the bath in a basic-lined vessel. After the furnace is charged with controlled amounts of scrap and molten iron, the furnace is brought into an upright position and the oxygen lance is lowered to a predetermined position above the surface of the bath. Oxygen gas issues from the jet nozzle at high velocity with the action of the oxygen jet being partially chemical and partially physical. On striking the surface of the liquid bath, the oxygen immediately starts reacting leading to the formation of iron oxides with carbon monoxide being evolved which gives rise to a vigorous boiling action and accelerates refining metallurgical reactions.
The slag forming fluxes,which are chiefly bu~ned lime, flu~rspar and millscale, are added in controlled amounts after the oxygen introduction begins. These materials serve to produce a slag of the desired basicity and fluidity.
There are several advantages of the basic oxygen process in its flexibility in handling raw materials of many types and compositions. The scraP, which is employed, mav be either heavy or li`ght an~ the oxide charae, if used, mav ~e drv~eres, sinter, p~llets or millscale. The process may be operated on any kind of hot metal that can be used in the basic open hearth furnace.
3 ~n the manufacture of steel in the basic oxygen furnace, a very large percentage of the heats are required to ~ ' , . ' ~
lO9Z8Z~
be finished at YerX low carbon values. The final car~ons are frequently as low as 0.03% in order to meet the Q.Q5% ~aximum car-bon aim in low alloy high strength steel, enamelling s-teels, deep drawing steels and electrïcal steels~ In many grades of steel it is advantageous to have a res-i`dual carbon content as low as 0.02%
to obtain certaïn desïred strength and other metallurgical pro-perties.
A standard basic oxygen furnace charge is approx-imately 7Q% hot metal and 30~ steel scrap and has an average carbon content in the range of 2.5 to 3.0%. It is customary to remove the excess carbon from the melt by oxidation employing high purity oxygen introduced through a lance as the oxidizing agent. ~nfortunately, as the carbon is oxidized there is a simultaneous oxidation of iron. The lower the carbonis in the melt, the higher is the percentage of iron oxidized to FeO. This oxidized iron is permanently lost to the formed slag. In melts of very low carbon i.e. 0.03%, the FeO in the slag may be as high as 35.0%. As it is normal practice to carry between 250 and 300 lbs of slag per ton of metal, the iron losses are thus consider-able. In addition, high FeO slags are very fluid and chemically active and may result in severe attack on the furnace refractory lining.
Melts which are at low carbon levels and contain high slaglevels may have as high as 1000 ppm oxygen dissolved in the steel. This oxygen is c~nx~ly removed from the steel by addition of aluminum. Apart fram the high cost of this deoxidation practice, not all of the alumina is rem~ved from the steel and may be a source of defects in the fmal product.
The above mentioned problems which are an in-herent feature of the basic oxygen furnace steel making process have to date been philosophically accepted by the steel industry and it is~ an object of the present invention to reduce these problems to a ~inimu~.
It is a further object of the present invention to reduce the iron loss to the slag during the refining process.
It is a further object of the present inven~ion to increase the viscosity of the slag.
It is yet a further object of the present invention to provide an improved process for the refining of steel.
Thus, in accordance with the present teachings, an improvement is provided in the process for the manufacture of steel in a basic oxygen furnace wherein a bath of metal is refined by the introduction of oxygen through a lance onto the surface of the bath. The improvement which is provided comprises blowing the bath with oxygen until the carbon content of the bath is about 0.10% above the desired finished carbon content and discontinuing the oxygen introduction and introducing argon through the lance until the desired carbon content of the bath is achieved.
At the completion of the argon blow, the amount of oxygen remaining dissolved in the molten steel is considerably below the level encountered when the melt is blown in the usual normal manner with 100% oxygen only. The use of the argon blow results in a lower level of non metallic deoxidation products and thus a cleaner steel product is obtained. Ladle deoxidant recoveries, when argon is employed following the oxygen blow, have also been found to be much higher, as for example, the aluminum deoxidation efficiences are in the range of 60 to 75%. This compares very favorable with 25 to 50% efficiences which is experienced with heats which have been blown with oxygen only in melts containing similar carbon, manganese and temperature levels.
The use of argon in completing the refining of the melt has also been found to result in a significant increase in the viscosity of the slag.
During tapping of the melt, the much stiffer obtained slag is more readily retained in the furnace and the exclusion of large volumes of iron oxide bearing slag from the ladle is a contribut-.~-lO~Z828 ing factor in improyed deoxidant effici.encx. It should als,o be noted that increased s:lag vi.~cosity also acts to reduce the attack on the furnace and ladle lini`ngs whi:ch results: in a significant increase i`n the life of the refractory employed for such li.nings.
Although applicant does not wish to be confined to any theoretical discuss:ion it is belîeved that the intimate mixing of the slag containing FeO which.is produced during the oxygen blow and the ~etal containing carbon would provide the chemical reac~ion FeO + C ~ Fe + CO.
The carbon monoxide escapes to atmosphere and the reduced metallic iron reverts back to the metai bath. During the argon blow, the free volume of the vessel is filled with argon gas and the partial pressure of CO in contact with the bath would be very low. This further accelerates the FeO + C reaction. In view of the turbul-ence of the bath with ~he introduction of the argon through the lance, the dissolved oxygen in the metal also reacts with the carbon C + 1/2 2 ~ CO.
In accordance with the present process, it is desired to produce a steel having a finished carbon content of 0.04%. The steel is blown with oxygen in the basic oxygen furnace in the normal manner until the carbon content of the bath is approximately 0.14% or about 0.10% above the required finishing carbon content. In place of oxygen the blow is now continued employing 100% argon gas. To create the emulsion between the slag and the metal, the flow rate of the argon gas is substantially the same as that which is employed for oxygen in conventional basic oxygen furnace processes and typically a 120 ton capacity vessel would employ a flow rate in the order of about 7,3Q0 cu.
ft/min.
The following Example and data is being provided to illustrate the present invention and is not intended to limit the scope of the concept.
EXAMPLEI
Oxygen was; b.lown downwardly onto the 12Q ton heats.unti.l th.e resi.dual carbon co~tent of the melt reacfied approximately Q.2 to 0.25% (or as indicated in ~able 1~. The oxygen flow was stopped and a sample of each. melt was taken (Sample I~. Following this, pure argon was substi.tuted for oxygen and blown onto the melt for two periods of 2 mins. each at a flow rate of between 3000 and 6000 cu.ft./min. Samples were taken after each period of treat-ment with.the argon (Samples II and III). The resulting reduction in the amounts- of carbon and dissolved oxygen remaining in the melt is shown in Table 1.
~0~282~
~ ~ `T~ . _ ~
., ~ ,.. ,.. .. .
~ .~
¢jo~ 0 ~ ~3 j3 ¢ 4~ o o o o o o c) I O . o o o o o O
~ ~ ~ o o o o o o 1~ 0 C~u~ ~D c~ `D ~ ~ ~:
o l * e C ~ I~ ~ l ~ ~ I , .a ., o ~ ~ ~ ~ ~, l ¢& ~ , ~ ~ o l o ~ ~ Z ~ ~ X
. e ~ O ~ ~ ~ __ ~ O O
O~ O~ l ~
l o - ~ ~ ~ ~ ~. _ o o . l ~, Z ~, ~ s~
. _ _ ' ~ ~ ~ ~ ~ ~ ~ ~ U~ l .~ ¢ O ~ : O ~ _ Z ~ C~ ~ . . .
O _ . R
O ¢ e ~ c O ~ ~ ~ ~ ~
~ o ~ Z Z: ~ Z Z ~ O
_~ ' _ _ .
~3 r~ ~D 1~ O O ~1 ¢ ~00 : N O~ ~U) :, N a O~ ~o P
C~ ', _ _ _ _ ~ _ H E-l P. O G O 1~ o :, O 1~
F~ ~ :e ~ ~ o a~:~D o o cq ~i ~ ,E-l O C~l ~) N N ~') ~ V ~) i~i I : d ~D ___ _ . ~ ~
O ~ al ~ ~ ~D ~') C`l r~ c) ~ ~ H ~ !~1 Z ~1 ~1 r~ ~1 ~ ia3 C~
, _ ~__ O
U~ 11~ : `$ : N ~1 O ~
q~ to ~ ~ ~ ~ ' `D ~ b~
~¢ I ~ /~0~ 00 r-l '~) ~ 'O ¢ o _ __ , ~ ~
, I ¢ e ~ ~ ~ ~ ~ ,, o z o _ æ z ~ h O j ~ u~ O u~ O o o ~ ::
m ~ ~ ~ ~ ~ ~ ~ o :
E-~ O N N N N N ~ Cl ~
_. ~`I O _ _ __ O ~ . . l:~ ~ ~: J-H ~ ~Z : __ z: Z _ :~? ? ,~
~j ~ ~ ~ ~ U~ Z ~ ¢ ¢
__ _ _ _ __ _ _ a~
~.) ~ N N N N N : O
_ tYi _ _ __ . ~ _ _ o oX Z
~ ~ o ~ cr o ~
E~ ~ ~ : u-, ~--1 N N
NN ) '1 ~5LZ ,_ _~_ _ IY_ _~_,___ _ ~_ _g_ ¢ o ~: z lO~Z828 As may readily be observed from the above data the carbon content is effectively reduced to the desired levels with no significant reduction in manganese. In addition, through the use of the present teachings, some of the oxidized iron which has been permanently lost to the slag is through the use of the argon blow reduced to metallic iron and reverts back to the metal bath--~urthermDre, the finishing blow employing argon also acts to remove dissolved oxygen thereby reducing the oxidation practice normally effected.
It will be obvious to those skilled in the art that various modifications may be resorted to without departing from the spirit of the invention.
.:
Claims (4)
1. In the process for the manufacture of steel in a basic oxygen furnace wherein a bath of metal is refined by introducing oxygen through a lance onto the surface of the bath, the improvement comprising blowing the bath with oxygen until the carbon content of the bath is about 0.10% above the desired finished carbon content, discontinuing the oxygen introduction and introducing argon through the lance until the desired carbon content of the bath is achieved.
2. The process of claim 1 wherein the flow rate of argon is approximately 3,000 cu.ft./minute.
3. The process of claim 1 wherein the flow rate of argon is approximately 7,OOO cu.ft/minute.
4. The process of claims 1, 2 or 3 wherein the finished carbon content of the bath is 0.04% and the oxygen blow is discontinued at a carbon content of 0.14%.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US95251578A | 1978-10-18 | 1978-10-18 | |
| US952,515 | 1978-10-18 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1092828A true CA1092828A (en) | 1981-01-06 |
Family
ID=25492980
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA337,600A Expired CA1092828A (en) | 1978-10-18 | 1979-10-15 | Basic oxygen furnace argon refining blow |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1092828A (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN100507014C (en) * | 2004-01-23 | 2009-07-01 | 普莱克斯技术有限公司 | Method for producing low carbon steel |
-
1979
- 1979-10-15 CA CA337,600A patent/CA1092828A/en not_active Expired
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN100507014C (en) * | 2004-01-23 | 2009-07-01 | 普莱克斯技术有限公司 | Method for producing low carbon steel |
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| Date | Code | Title | Description |
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| MKEX | Expiry |