CA1075012A - Process for dephosphorizing molten pig iron - Google Patents
Process for dephosphorizing molten pig ironInfo
- Publication number
- CA1075012A CA1075012A CA262,213A CA262213A CA1075012A CA 1075012 A CA1075012 A CA 1075012A CA 262213 A CA262213 A CA 262213A CA 1075012 A CA1075012 A CA 1075012A
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- pig iron
- molten pig
- process according
- added
- iron
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- Refinement Of Pig-Iron, Manufacture Of Cast Iron, And Steel Manufacture Other Than In Revolving Furnaces (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
A process for dephosphorizing molten pig iron by adding (a) line C???? slag and/or iron oxide (b) iron oxide and/or oxidizing gas, and if necessary (c) fluor???? and/or soda ash to the molten pig iron stored in a treating vessel in order to adjust the amount of CaO to correspond to at least 0.3 times the sum of the amounts of SiO and P2O5 and to adjust the amount of T.Fe to 15 to 50% in the slag com-position after trestment, thereby obtaining a hig dephos-phorisation.
A process for dephosphorizing molten pig iron by adding (a) line C???? slag and/or iron oxide (b) iron oxide and/or oxidizing gas, and if necessary (c) fluor???? and/or soda ash to the molten pig iron stored in a treating vessel in order to adjust the amount of CaO to correspond to at least 0.3 times the sum of the amounts of SiO and P2O5 and to adjust the amount of T.Fe to 15 to 50% in the slag com-position after trestment, thereby obtaining a hig dephos-phorisation.
Description
~o750~Z
BACKGROUND OF THE INVENTION
FIELD OF THE INVENTION
The present invention relates to a process for dephosphorizing molten pig iron. More specifically, it relates to a process for lowering the phosphorous content with a small decarburization amount of 1.5 wt.% or less, by treating molten pig iron at less than 1,450C prior to charging it into a steel-making furnace.
'', -DESCRIPTION OF THE PRIOR ART --It has been known for a long time that phos-phorus in steel is a harmful impurity since it causes - -temper brittleness and it lowers the product toughness.
For this reason, dephosphorization of steel has been an important problem in steel production. It is no exag- -geration to say that the progress of the steel-making ~ -process has been directly related to the progress of the dephosphorization process. However, the steel-making ~ -process has changed little since the invention of the LD
converter after World War II which provides for a high dephosphorization rate. It is now the main technique in the steel-making process.
- . . .:
~0750~2 However, in recent years the kinds of steel requiring high touqhness such as steel sheet for low temperature use and high tension steel have become more important, and these steels cannot contain phosphorus in amounts of more than 0.01 to 0.015 wt.%.
It is difficult to produce such low phos-phorus steel by the normal single slag converter oxida-tion smelting technique, and thus a double slag converter oxidation smelting technique has been employed.
According to the condition of the raw ma-terials, there are instances where pig iron containing phosphorus in amounts of far more than only 0.1 to 0.2 wt.%
is used, and in such cases the double slag technique has to be employed if steel conforming to the severe phos-phorus standard as mentioned above is to be produced, or even if ordinary steel containing not more than 0.035 wt.%
of phosphorus is to be produced.
However, the double slag technique involves grave problems due to d~sadvantages such as the drop of converter productivity caused by long smelting time, the drop of the iron yield caused by intermediate slagging off, etc.
7 . : " `
., . ~
10750~Z
SU~ARY OF THE INVENTION
The primary object of the present invention is to provide a process for preliminarily dephosphorizing mol-ten pig iron before charging it into a steel-making furnace.
It is a further object of the present invention to provide for the production of steel with a low phosphorus content - -even by the single slag converter oxidation smelting technique. Thus, the present invention overcomes the above-mentioned disadvantages of the double slag technique. -According to the process of the present inven-tion, (a) dephosphorizing agents are added to the molten pig iron to adjust the amount of CaO to correspond to -at least 0.3 times the sum of the amounts of Si02 and P205 -and to adjust the amount of T.Fe to 15 to 50~ in terms of ~ -the dephosphorized slag composition after treatment, and, in addition, (b) iron oxide and/or oxidizing gas corres-ponding to not more than the amount of oxygen required to oxidize all the amounts of silicon, manganese, and phos-phorus and 1.5 wt.% of the carbon contained in the molten pig iron before treatment are added to the molten pig iron before it is charged into the steel-making furnace. The .. ' .
.: . . . , - :. . .-.
---, , i~75012 ;-,:
,~
dephosphorizing agents and oxidizing agents are made to come into contact with the molten pig iron with stirring to lower the phosphorus content with a small decarburi- -zation amount of 1~5 wt.% or less.
5 . - DETAIIi!~D DESCRIPTIO~ OF THE INVE~TION
.
~ In the dephosphorization of molten pig iron, phosphorus is surmised ~o be absorbed and re ved by slag as oxide. However, since phosphorus has less af-finity for oxygen than silicon and manganese in molten pig iron, sufficient oxidizing power to almost com-pletely oxidize silicon and mangançse must be provided - ~ for effective dephosphorization. Such strong oxidizing power, however, causes concurrent decarburization.
~ ~ In the pretreatment of lten pig iron be-15 ; fore charging it into the steel-making furnace, it is ; - - desirable to keep the decarburization amount as small as ' possible. In fact the amvunt must be suppressed to 1.5 wt.X or less in light of equipment conditions as well as the safety of ~he heat source in the following step in the converterO
: ' .
~ ~ - 5 -~075012 This can be achieved by treating the molten pig iron at less than 1,450C. The treatment at a temper-ature of more than 1,450C causes active decarburization;
however it does not allow for the attainment of a high de-phosphorization with a decarburization amount of 1.5 wt.%
or less. A lower treatment temperature of below 1,450C
allows for a more effective dephosphorization with a smaller decarburization. For example, treatment at 1,300C allows for the attainment of a high dephosphori- ;
zation with a small decarburization of 0.4 to 0.7 wt.%.
As mentioned above, in dephosphorization the phosphorus is absorbed and removed by the slag as oxide.
In this case, the slag basicity represented by CaO/(SiO2 +
P205) and the oxidizing power of the slag represented by T.Fe are important factors. That is, the higher the slag -basicity and T.Fe, the higher the dephosphorization which can be attained. ----However, if the oxidizing power is provided mainly by an oxidizing gas as in the conventional steel- - -20 making process, the temperature rises greatly, thus not ~-allowing for the treatment at less than 1,450C, and ' ' ' ' ' ' ' ' ' . . : ' : . '-' -' -~0~ Z
decarburization is cauaed. This does not provide for a high T.Fe of 15X or re (due to a high carbon content).
In the case of the present invention, if the oxidizing power is provided mainly by iron oxide, the treatment te_perature can be held at less than 1,450C, -- keeping the decarburization amount small, and the T.Fe of the slag can be obtained at 15% to 50%.
Further re, the low temperature treatment is - -advantageous for dephosphorization also because the ther-~ _~dynamics allows for dephosphorization at a low basicity which would be inconceivable in the steel-ma~ing process.
If the treatment temperature is as low as 1~300C, the slag T.Fe of 40 to 50% allows the dephosphorization of 40 ~ ~ to 60X even with a basicity of 0.3~ However, if the lS ~ basicity becomes smaller than 0.3, effective dephosphori- `--~ zation cannot be made, however high the T.Fe may be. Of course, the higher the basicity of the slag, the re --effective the dephosphorization is. If the T.Fe is 15X
, -~ ~ or more in this treatment process at less than 1,450C, a~ a~ 3 -20 n~ a basicity of ~ allows for sufficient dephosphorization, and a baPicity higher than it is not required. From the . .
10750~Z
- above, it can be said that the dephosphorized slag in the range from 0.3 to 3 in basicity and in the range from 15 to 50a in T.Fe is the most suitable for this `process.
For dephosphorization of molten pig iron with such dephosphorizing slag, it is necessary, as mentioned above, to provide sufficient oxygen to oxidize all the amounts of silicon and manganese with stronger affinity for oxygen than phosphorus so as to oxidize silicon, manganese and phosphorus and less than about 1.5 wt.~ of the carbon. If oxygen or any other oxidizing gas is used as the only oxygen source, the temperature rise by the - ~-treatment is great. Therefore, unless the temperature of the molten pig iron before treatment is as low as about 1,200C, it is difficult to keep the tempertaure of the molten pig iron at less than 1,450C during treat-ment. On the contrary, if the oxygen is provided by iron oxide such as iron ores or scale, the temperature drop ;; by the treatment is great. Therefore, unlesss the temper-ature of the molten pig iron is more than about 1,450C, it is difficult to keep the temperature of the molten pig `~ iron at more~than 1,250C after treatment. For dephos-~ - phorization of molten pig iron which does not meet the ' ' -:
:, . .:
~075012 above temperature conditions, iron oxide, such as iron ores or scale, and an oxidizing gas, such as oxygen, must be used together as the oxygen source.
The dephosphorizing agents for producing de-phosphorizing slag must comprise CaO and iron oxide as mentioned above.
When sufficient dephosphorization can be obtained at the relatively low basicity as in the process of the present invention, LD converter slag can in part --be used as the CaO and iron oxide source. In addition, if limestone is used as the CaO source, it is changed into CaO at the treatment temperature, and quick lime itself can of course be used. From the above, the de-phosphorizing agents can be (1) LD converter slag and iron oxide such as iron ores or scale, (2) limestone and iron oxide such as iron ores or scale, and (3) quick lime and iron oxide such as iron ores or scale. When these de-phosphorizing agents and oxidizing agents are used for dephosphorization, the slagging of these additions is very important. If the mixture poses difficulty in slagging, the addition of Fluorspar and/or soda ash promotes slagging.
When these are used for dephosphorization, the stirring of the ~olten pig iron and dephosphorizing agents or dephosphorizing slag is important for sufficient re-action and for shortening of the treatment time. As a means of stirring, an impeller is the most effective, but bubbling by using an inert gas such as nitrogen, argon, etc., or air can be used, too, for stirring.
When oxidizing gas is supplied to the molten pig iron, if the dephosphorizing slag layer is thick, it 10 can be supplied through an immersion pipe, but if the de- --phosphorized slag layer is relatively thin, it may be blown into molten pig iron through the slag by using a water-cooled lance.
This dephosphorizing treatment of molten pig -iron can be performed in a ladle used for charging molten - pig iron into a converter, and this method is advantageous . . -,...
.
.' ~ ' ' .
~ `~ ~
for skimming of slag after treatment and for charging into the converter. The treatment of molten pig iron in a tor-pedo car can be performed effectively, too.
Embodiments of the present invention will be given below.
Embodiment I
With 45 tons (t) of molten pig iron stored in a ladle, 30kg/t of converter slag and 40kg/t of scale were added to the molten pig iron as dephosphorizing agents, and further 35kg/t of scale was added as an oxidizing agent.
While 7.2Nm3/t of oxidizing gas was blown into the molten pig iron by using an immersion pipe, the mixture was stirred by an impeller at 100 rpm. The results as shown in Table 1 were obtained.
Table 1 __ Temperature of molten pig iron 1,320C
before treatment Temp~rature of molten pig iron 1,275C
after treatment _ Components of molten pig iron before treatment (% by wt.) C Si Mn P S
4.06 0.82 0.50 0.112 0.027 ... _ . .
Components of molten pig iron after treatment (~ by wt.) C Si Mn P S
3.53 trace trace 0.023 0.027 . .
Components of dephos- CaO/(SiO2+P205) = 0.37 phorized slag T.Fe = 41.1 Treatment time 35 min.
~07501Z
As shown above, the treatment in the ranqe from 1,275 to 1,320 allowed for a high dephosphorization amount of 79% with a small decarburization amount of 0.53 wt.%.
Embodiment II
With 45t of molten pig iron stored in a ladle, 30kg/t of quick lime and-25kg/t of iron ore as dephosphorizing agents and lOkg/t of Fluorspar as a slagging promoter were added to the molten pig iron and --further 20kg/t of iron ore was added as an oxidizing agent. While 10.2Nm3/t of oxygen was blown through an immersion pipe, N2 bubbling was performed for stirring by using another immersion pipe. The results as shown - -in Table 2 were obtained.
- Table 2 , .
Temperature of molten pig iron 1,350C
before treatment _ .
Temperature of molten pig iron 1,370C
after~treatment Components of molten pig iron ~- before treatment (% by wt.) C Si Mn P S
4.07 0.64 0.59 0.113 0.012 ~ :, Components of molten pig iron after treatment (% by wt.) C Si Mn P S
3.54 trace 0.13 0.015 0.013 ~Components of dephos- CaO/(SiO2+P205) = 1.79 - -phorized slag T.Fe = 15.8 Treatment time 40 min.
: .
. .
10750~Z
; . .
-,~
As shown above, the treatment in the range ~
from 1,350 to 1,370C allowed for a high dephosphori~ r zation amount of 87X with a s~all decarburization amount --of 0.53 wt.~
S Embodiment III
With 41.5t of molten pig iron stored in a lad~e, 30kg/t of limestone and 32kg/t of iron ore were added to the molten pig iron as dephosphorizing agents, ~- and further 20kg/t of iron ore was added as an oxidizing agent. And ll.5Nm3/t of oxygen gas was blown into the - molten pig iron by using a water-cooled lance, the ~ix-ture was stirred by an impeller at 100rpm. The results as shown in Table 3 were obtained : . , Table 3 ~ Temperature of molten pig iron1,370C -before treatment Temp~rature of molten pig iron1,345C
. after treatment A' ~ CDmponents of molten pig iron 5~ `
before treat~ent (% by wt.) C ~ Mn P S F
4.18 0.~2 0.48 0.121 0.032 f oomponents of molten pig iron S~' . after treatment (X by wt.) C S Mn P S
~ 3.56 trace 0.07 0.021 0.030 Components of dephos- CaO/(SiO2+P2Os) ~ 0.92 : ~ phorized slaq _ T.Fe = 36.2X
Treatment time 37 min.
,- ~
.
As shown above, the treatment in the range from 1,370 to 1,345C allowed for a high dephosphorization amount ~- ~ of 82.6X with a small decarburization rate of 0.62 wt.%~ ~
t
BACKGROUND OF THE INVENTION
FIELD OF THE INVENTION
The present invention relates to a process for dephosphorizing molten pig iron. More specifically, it relates to a process for lowering the phosphorous content with a small decarburization amount of 1.5 wt.% or less, by treating molten pig iron at less than 1,450C prior to charging it into a steel-making furnace.
'', -DESCRIPTION OF THE PRIOR ART --It has been known for a long time that phos-phorus in steel is a harmful impurity since it causes - -temper brittleness and it lowers the product toughness.
For this reason, dephosphorization of steel has been an important problem in steel production. It is no exag- -geration to say that the progress of the steel-making ~ -process has been directly related to the progress of the dephosphorization process. However, the steel-making ~ -process has changed little since the invention of the LD
converter after World War II which provides for a high dephosphorization rate. It is now the main technique in the steel-making process.
- . . .:
~0750~2 However, in recent years the kinds of steel requiring high touqhness such as steel sheet for low temperature use and high tension steel have become more important, and these steels cannot contain phosphorus in amounts of more than 0.01 to 0.015 wt.%.
It is difficult to produce such low phos-phorus steel by the normal single slag converter oxida-tion smelting technique, and thus a double slag converter oxidation smelting technique has been employed.
According to the condition of the raw ma-terials, there are instances where pig iron containing phosphorus in amounts of far more than only 0.1 to 0.2 wt.%
is used, and in such cases the double slag technique has to be employed if steel conforming to the severe phos-phorus standard as mentioned above is to be produced, or even if ordinary steel containing not more than 0.035 wt.%
of phosphorus is to be produced.
However, the double slag technique involves grave problems due to d~sadvantages such as the drop of converter productivity caused by long smelting time, the drop of the iron yield caused by intermediate slagging off, etc.
7 . : " `
., . ~
10750~Z
SU~ARY OF THE INVENTION
The primary object of the present invention is to provide a process for preliminarily dephosphorizing mol-ten pig iron before charging it into a steel-making furnace.
It is a further object of the present invention to provide for the production of steel with a low phosphorus content - -even by the single slag converter oxidation smelting technique. Thus, the present invention overcomes the above-mentioned disadvantages of the double slag technique. -According to the process of the present inven-tion, (a) dephosphorizing agents are added to the molten pig iron to adjust the amount of CaO to correspond to -at least 0.3 times the sum of the amounts of Si02 and P205 -and to adjust the amount of T.Fe to 15 to 50~ in terms of ~ -the dephosphorized slag composition after treatment, and, in addition, (b) iron oxide and/or oxidizing gas corres-ponding to not more than the amount of oxygen required to oxidize all the amounts of silicon, manganese, and phos-phorus and 1.5 wt.% of the carbon contained in the molten pig iron before treatment are added to the molten pig iron before it is charged into the steel-making furnace. The .. ' .
.: . . . , - :. . .-.
---, , i~75012 ;-,:
,~
dephosphorizing agents and oxidizing agents are made to come into contact with the molten pig iron with stirring to lower the phosphorus content with a small decarburi- -zation amount of 1~5 wt.% or less.
5 . - DETAIIi!~D DESCRIPTIO~ OF THE INVE~TION
.
~ In the dephosphorization of molten pig iron, phosphorus is surmised ~o be absorbed and re ved by slag as oxide. However, since phosphorus has less af-finity for oxygen than silicon and manganese in molten pig iron, sufficient oxidizing power to almost com-pletely oxidize silicon and mangançse must be provided - ~ for effective dephosphorization. Such strong oxidizing power, however, causes concurrent decarburization.
~ ~ In the pretreatment of lten pig iron be-15 ; fore charging it into the steel-making furnace, it is ; - - desirable to keep the decarburization amount as small as ' possible. In fact the amvunt must be suppressed to 1.5 wt.X or less in light of equipment conditions as well as the safety of ~he heat source in the following step in the converterO
: ' .
~ ~ - 5 -~075012 This can be achieved by treating the molten pig iron at less than 1,450C. The treatment at a temper-ature of more than 1,450C causes active decarburization;
however it does not allow for the attainment of a high de-phosphorization with a decarburization amount of 1.5 wt.%
or less. A lower treatment temperature of below 1,450C
allows for a more effective dephosphorization with a smaller decarburization. For example, treatment at 1,300C allows for the attainment of a high dephosphori- ;
zation with a small decarburization of 0.4 to 0.7 wt.%.
As mentioned above, in dephosphorization the phosphorus is absorbed and removed by the slag as oxide.
In this case, the slag basicity represented by CaO/(SiO2 +
P205) and the oxidizing power of the slag represented by T.Fe are important factors. That is, the higher the slag -basicity and T.Fe, the higher the dephosphorization which can be attained. ----However, if the oxidizing power is provided mainly by an oxidizing gas as in the conventional steel- - -20 making process, the temperature rises greatly, thus not ~-allowing for the treatment at less than 1,450C, and ' ' ' ' ' ' ' ' ' . . : ' : . '-' -' -~0~ Z
decarburization is cauaed. This does not provide for a high T.Fe of 15X or re (due to a high carbon content).
In the case of the present invention, if the oxidizing power is provided mainly by iron oxide, the treatment te_perature can be held at less than 1,450C, -- keeping the decarburization amount small, and the T.Fe of the slag can be obtained at 15% to 50%.
Further re, the low temperature treatment is - -advantageous for dephosphorization also because the ther-~ _~dynamics allows for dephosphorization at a low basicity which would be inconceivable in the steel-ma~ing process.
If the treatment temperature is as low as 1~300C, the slag T.Fe of 40 to 50% allows the dephosphorization of 40 ~ ~ to 60X even with a basicity of 0.3~ However, if the lS ~ basicity becomes smaller than 0.3, effective dephosphori- `--~ zation cannot be made, however high the T.Fe may be. Of course, the higher the basicity of the slag, the re --effective the dephosphorization is. If the T.Fe is 15X
, -~ ~ or more in this treatment process at less than 1,450C, a~ a~ 3 -20 n~ a basicity of ~ allows for sufficient dephosphorization, and a baPicity higher than it is not required. From the . .
10750~Z
- above, it can be said that the dephosphorized slag in the range from 0.3 to 3 in basicity and in the range from 15 to 50a in T.Fe is the most suitable for this `process.
For dephosphorization of molten pig iron with such dephosphorizing slag, it is necessary, as mentioned above, to provide sufficient oxygen to oxidize all the amounts of silicon and manganese with stronger affinity for oxygen than phosphorus so as to oxidize silicon, manganese and phosphorus and less than about 1.5 wt.~ of the carbon. If oxygen or any other oxidizing gas is used as the only oxygen source, the temperature rise by the - ~-treatment is great. Therefore, unless the temperature of the molten pig iron before treatment is as low as about 1,200C, it is difficult to keep the tempertaure of the molten pig iron at less than 1,450C during treat-ment. On the contrary, if the oxygen is provided by iron oxide such as iron ores or scale, the temperature drop ;; by the treatment is great. Therefore, unlesss the temper-ature of the molten pig iron is more than about 1,450C, it is difficult to keep the temperature of the molten pig `~ iron at more~than 1,250C after treatment. For dephos-~ - phorization of molten pig iron which does not meet the ' ' -:
:, . .:
~075012 above temperature conditions, iron oxide, such as iron ores or scale, and an oxidizing gas, such as oxygen, must be used together as the oxygen source.
The dephosphorizing agents for producing de-phosphorizing slag must comprise CaO and iron oxide as mentioned above.
When sufficient dephosphorization can be obtained at the relatively low basicity as in the process of the present invention, LD converter slag can in part --be used as the CaO and iron oxide source. In addition, if limestone is used as the CaO source, it is changed into CaO at the treatment temperature, and quick lime itself can of course be used. From the above, the de-phosphorizing agents can be (1) LD converter slag and iron oxide such as iron ores or scale, (2) limestone and iron oxide such as iron ores or scale, and (3) quick lime and iron oxide such as iron ores or scale. When these de-phosphorizing agents and oxidizing agents are used for dephosphorization, the slagging of these additions is very important. If the mixture poses difficulty in slagging, the addition of Fluorspar and/or soda ash promotes slagging.
When these are used for dephosphorization, the stirring of the ~olten pig iron and dephosphorizing agents or dephosphorizing slag is important for sufficient re-action and for shortening of the treatment time. As a means of stirring, an impeller is the most effective, but bubbling by using an inert gas such as nitrogen, argon, etc., or air can be used, too, for stirring.
When oxidizing gas is supplied to the molten pig iron, if the dephosphorizing slag layer is thick, it 10 can be supplied through an immersion pipe, but if the de- --phosphorized slag layer is relatively thin, it may be blown into molten pig iron through the slag by using a water-cooled lance.
This dephosphorizing treatment of molten pig -iron can be performed in a ladle used for charging molten - pig iron into a converter, and this method is advantageous . . -,...
.
.' ~ ' ' .
~ `~ ~
for skimming of slag after treatment and for charging into the converter. The treatment of molten pig iron in a tor-pedo car can be performed effectively, too.
Embodiments of the present invention will be given below.
Embodiment I
With 45 tons (t) of molten pig iron stored in a ladle, 30kg/t of converter slag and 40kg/t of scale were added to the molten pig iron as dephosphorizing agents, and further 35kg/t of scale was added as an oxidizing agent.
While 7.2Nm3/t of oxidizing gas was blown into the molten pig iron by using an immersion pipe, the mixture was stirred by an impeller at 100 rpm. The results as shown in Table 1 were obtained.
Table 1 __ Temperature of molten pig iron 1,320C
before treatment Temp~rature of molten pig iron 1,275C
after treatment _ Components of molten pig iron before treatment (% by wt.) C Si Mn P S
4.06 0.82 0.50 0.112 0.027 ... _ . .
Components of molten pig iron after treatment (~ by wt.) C Si Mn P S
3.53 trace trace 0.023 0.027 . .
Components of dephos- CaO/(SiO2+P205) = 0.37 phorized slag T.Fe = 41.1 Treatment time 35 min.
~07501Z
As shown above, the treatment in the ranqe from 1,275 to 1,320 allowed for a high dephosphorization amount of 79% with a small decarburization amount of 0.53 wt.%.
Embodiment II
With 45t of molten pig iron stored in a ladle, 30kg/t of quick lime and-25kg/t of iron ore as dephosphorizing agents and lOkg/t of Fluorspar as a slagging promoter were added to the molten pig iron and --further 20kg/t of iron ore was added as an oxidizing agent. While 10.2Nm3/t of oxygen was blown through an immersion pipe, N2 bubbling was performed for stirring by using another immersion pipe. The results as shown - -in Table 2 were obtained.
- Table 2 , .
Temperature of molten pig iron 1,350C
before treatment _ .
Temperature of molten pig iron 1,370C
after~treatment Components of molten pig iron ~- before treatment (% by wt.) C Si Mn P S
4.07 0.64 0.59 0.113 0.012 ~ :, Components of molten pig iron after treatment (% by wt.) C Si Mn P S
3.54 trace 0.13 0.015 0.013 ~Components of dephos- CaO/(SiO2+P205) = 1.79 - -phorized slag T.Fe = 15.8 Treatment time 40 min.
: .
. .
10750~Z
; . .
-,~
As shown above, the treatment in the range ~
from 1,350 to 1,370C allowed for a high dephosphori~ r zation amount of 87X with a s~all decarburization amount --of 0.53 wt.~
S Embodiment III
With 41.5t of molten pig iron stored in a lad~e, 30kg/t of limestone and 32kg/t of iron ore were added to the molten pig iron as dephosphorizing agents, ~- and further 20kg/t of iron ore was added as an oxidizing agent. And ll.5Nm3/t of oxygen gas was blown into the - molten pig iron by using a water-cooled lance, the ~ix-ture was stirred by an impeller at 100rpm. The results as shown in Table 3 were obtained : . , Table 3 ~ Temperature of molten pig iron1,370C -before treatment Temp~rature of molten pig iron1,345C
. after treatment A' ~ CDmponents of molten pig iron 5~ `
before treat~ent (% by wt.) C ~ Mn P S F
4.18 0.~2 0.48 0.121 0.032 f oomponents of molten pig iron S~' . after treatment (X by wt.) C S Mn P S
~ 3.56 trace 0.07 0.021 0.030 Components of dephos- CaO/(SiO2+P2Os) ~ 0.92 : ~ phorized slaq _ T.Fe = 36.2X
Treatment time 37 min.
,- ~
.
As shown above, the treatment in the range from 1,370 to 1,345C allowed for a high dephosphorization amount ~- ~ of 82.6X with a small decarburization rate of 0.62 wt.%~ ~
t
Claims (13)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A process for dephosphorizing molten pig iron comprising the step of adding to the molten pig iron (a) a dephosphorizing agent containing CaO, and (b) an oxidizing agent, such that a slag is formed which contains CaO in an amount which corresponds to at least 0.3 times the sum of the amounts of SiO2 and P2O5, and which has a T.Fe of 15 to 50%.
2. A process according to claim 1, wherein said dephosphorizing agent is selected from the group consisting of iron oxide, converter slag, limestone and lime.
3. The process according to claim 1, wherein said oxidizing agent is selected from the group consisting of iron oxide, oxygen gas and mixtures thereof.
4. The process according to claim 1, wherein the components (a) and (b) are added to said molten pig iron when said molten pig iron is at a temperature of less than 1450°C.
5. The process according to claim 1, wherein in addition to components (a) and (b), at least one slagging promoter (c) is added to said molten pig iron.
6. The process according to claim 5, wherein said slagging promoters are selected from the group consisting of fluorspar and soda ash.
7. The process according to claim 5, wherein said slagging promoter is added to said molten pig iron in an amount of up to 15 kg per ton of pig iron.
8. The process according to claim 1, wherein said component (b) is added to said pig iron in an amount which oxidizes all the Si and Mn contained in said pig iron but no more than 1.5 wt.% of the carbon.
9. The process according to claim 1, wherein said component (b) is an oxidizing gas which is added to said molten pig iron by passage through an immersed inlet.
10. The process according to claim 1, wherein said component (b) is an oxidizing gas which is added to said molten pig iron in the form of a gaseous stream blown onto the surface of the molten pig iron.
11. The process according to claim 1, wherein said components (a) and (b) are added to said molten pig iron while said molten pig iron is stirred by bubbling an inert gas therethrough.
12. The process according to claim 1, wherein said components (a) and (b) are added to said molten pig iron while said molten pig iron is stirred by an impeller.
13. The process according to claim 1, 2 or 3 wherein CaO is added in an amount such that the slag contains CaO
in an amount corresponding to 0.3 to 3 times the sum of the amounts of SiO2 and P205.
in an amount corresponding to 0.3 to 3 times the sum of the amounts of SiO2 and P205.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA262,213A CA1075012A (en) | 1976-09-28 | 1976-09-28 | Process for dephosphorizing molten pig iron |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA262,213A CA1075012A (en) | 1976-09-28 | 1976-09-28 | Process for dephosphorizing molten pig iron |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1075012A true CA1075012A (en) | 1980-04-08 |
Family
ID=4106950
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA262,213A Expired CA1075012A (en) | 1976-09-28 | 1976-09-28 | Process for dephosphorizing molten pig iron |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1075012A (en) |
-
1976
- 1976-09-28 CA CA262,213A patent/CA1075012A/en not_active Expired
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