JPH0448027A - Method and device for reduced pressure and vacuum refining of molten steel - Google Patents

Abstract

PURPOSE:To efficiently and simultaneously progress decarburizing and denitrifying by executing the pressure reduction or vacuum refining by the combination of induction stirring and gas blowing. CONSTITUTION:A reduced pressure or vacuum reaction chamber 7 is installed in the upper part of a molten steel housing ladle 1 and a part of the molten steel 5 to be decarburized is pulled up into the reduced pressure or vacuum reaction chamber 7. While the molten steel 5 in the ladle and the molten steel 6 in the reaction chamber 7 are replaced, the molten steel 6 which is pulled up is heated and stirred by a low-frequency induction coil 2. An inert gas is simultaneously blown via a gas blowing plug or gas blowing nozzle 3 into the molten steel 6 in the reaction chamber 7. The blown gases are finely dispersed into the molten steel 6 in this way and the gas-liquid reaction boundary area is increased, by which finer bubbles 12 are formed. Then the time when the bubbles stagnate in the molten steel 6 increases and the reaction rate increases extremely. The amt. of the molten steel to be splashed is extremely lessened even if the amt. of the gas to be blown is increased.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention is a method for producing ultra-low carbon steel by removing carbon (C) contained in molten steel to an extremely small amount, for example, 0.001 wt% or less. Efficient, simple, and inexpensive decompression/vacuum refining method for molten steel for producing molten steel, producing molten steel with extremely low nitrogen concentration or extremely low hydrogen concentration, or producing highly clean steel, and its method. The present invention relates to a device for realizing this.

(Conventional technology) When steel is used as thin steel sheets for automobiles or beverage cans, carbon and nitrogen contained in steel must be contained in extremely small amounts in order to improve workability and prevent an increase in deep drawing resistance due to aging. something is required. Furthermore, materials such as steel for thick steel plates and bearings, or ultra-fine wire steel, are required to be clean with very few inclusions and to have an extremely low hydrogen concentration in order to improve material strength and workability.

Generally, in the steel industry, degassing refining of molten steel is carried out using various vacuum/decompression decarburization equipment, RH and D
It is implemented using H1 or VOD. Furthermore, in the case of removing non-metallic inclusions, a method using flux injection or Ar bubbling in combination has been implemented.

In other words, decarburization of molten steel is carried out by oxygen [O
] Alternatively, carbon (C) contained in molten steel is removed by the following reaction using various oxidation sources such as iron ore PexOy*oxygen gas 02.

(C) + (0) = CO(1--1-------
----- (1) On the other hand, denitrification and dehydrogenation of molten steel are carried out through the following reactions through the gas-liquid reaction interface via the CO bubbles generated in the above decarburization reaction and the gas-liquid interface in the blown Ar bubbles. proceed.

(N) 10 (N) = Nzte, s+ −−−−−−
−−−−−−(2)(H)+ (H)=Hz, −□,
−・・−・−−−−1. (3) Furthermore, inclusions suspended in molten steel collide with each other and coalesce,
It is removed by flotation and separation based on the difference in specific gravity, or by trapping it in air bubbles.

However, even if vacuum/reducing equipment is used, carbon in molten steel
% (C) is 0.015 wt% or less, the Ninal decarburization rate starts to decrease, and in addition, when wt% (C) is 0.005 wt%
Below this level, the decarburization rate further decreases, making it difficult to produce molten steel with an extremely low carbon concentration. At the same time, as a result, the generation of CO bubbles is extremely reduced, so that the denitrification and dehydrogenation reactions are also inhibited.

In order to overcome this phenomenon and increase the reaction rate, conventional methods use gas bubbling and gas injection in combination to increase the flow rate of gas blown into molten steel in a vacuum/reduced pressure tank. . However, under reduced pressure or vacuum below 50 smHg, increasing the insufflation gas flow rate will cause
Due to the combination of the blown gas and the atrium, it is not possible to secure a sufficient area for the reaction site, which is the gas/liquid area.On the other hand, the amount of molten copper scattering increases, and the amount of base metal adhering to the inner walls of the vacuum/decompression tank increases. This makes stable refining difficult. Furthermore, since the blown gas is not sufficiently dispersed, the removal of inclusions is also insufficient.

Even so, in order to produce high-purity, high-cleanliness molten steel despite these difficulties, the vacuum refining time must be extended, and the molten steel must be reheated to compensate for the drop in molten steel temperature at that time. Alternatively, this problem is dealt with by raising the temperature of the molten steel to be refined in advance. However, when the temperature of the molten steel is raised, the refractories are eroded and damaged, the refractory unit consumption increases, and the cost for refining increases. In this way, even with the use of vacuum and decompression equipment, current refining methods cannot be said to be sufficiently efficient or economical, and it is extremely difficult to reliably produce molten steel of high purity and cleanliness. Have difficulty.

(Problems to be Solved by the Invention) The present invention has extremely low concentrations of gas components (C, H, N), and
The purpose of the present invention is to provide a method and apparatus for efficiently and easily melting highly clean molten steel with few inclusions under reduced pressure or vacuum while compensating for the temperature drop of the molten steel. .

(Means for Solving the Problems) FIGS. 1 and 2 show schematic diagrams of an apparatus for carrying out the method of the present invention.

■ is a storage container (ladle) for molten steel, 2 is an induction stirring/heating coil, 3 is a gas blowing plug or gas blowing nozzle,
4 is a lance for gas spraying and oxide spraying, 5 is a molten steel to be refined, 6 is a molten steel drawn up into a reduced pressure or vacuum reaction tank, 7 is a reduced pressure or vacuum reaction tank, and 8 is an airtight tank made of non-magnetic material. 9 is an airtight jacket, 10 is a refractory, 11 is a shield, 12 is a dispersion bubble, 13 is a molten steel circulation gas, and 14 is a ladle-like molten steel stirring gas.

Based on the above, as a means for achieving the object, the present invention installs a reduced pressure or vacuum reaction tank 7 on the upper part of the molten steel storage ladle 1, and a part of the molten steel 5 to be decarburized is subjected to a reduced pressure/vacuum reaction. Raised to tank 7, bay steel 5 in ladle and reduced pressure/vacuum reaction tank 7
While heating and stirring the pulled molten steel 6 with the low-frequency induction coil 2, an inert gas is passed through the gas blowing plug or the gas blowing nozzle 3 into the depressurized or vacuum reaction tank 7. This is a method for depressurizing/vacuum refining of molten steel, which is characterized by blowing into molten steel 6 in the molten steel, and an apparatus therefor.

That is, the roots of the technical idea of the present invention are the above-mentioned (1) to (3).
In order to purify the molten steel according to the formula and remove inclusions to make it highly clean, the molten steel 6 in the reduced pressure/vacuum reaction tank 7 is made to flow by induction stirring to achieve fine dispersion of the blown gas. The objective is to increase the area for the gas-liquid interface reaction and to lengthen the residence time of the bubbles 12 due to fine dispersion of the blown gas, thereby increasing the utilization efficiency of the blown gas. This makes it possible to improve the efficiency of refining molten steel to achieve high purity and high cleanliness under reduced pressure or vacuum, while at the same time suppressing the occurrence of splash and compensating for the drop in temperature of molten steel.

(for production) The effect of induced stirring in the present invention is important.

That is, in order to increase the reaction rate, it is necessary to strengthen the stirring of the molten steel 6 and increase the reaction interface area. Therefore, in order to increase the reaction rate, gas bubbling or gas injection is performed to increase the flow rate of the blown gas. However, as mentioned above, with conventional methods and equipment, when the flow rate of the blown gas is increased under reduced pressure or vacuum, the blown gas cannot be sufficiently enlarged due to coalescence and blow-out of the blown gas, which is the reaction site. However, there were limits to increasing the reaction rate. Furthermore, if the amount of blown gas is increased, the amount of molten steel splashed will increase, and the base metal will adhere to the inner wall of the reduced pressure/vacuum reaction tank 7, making stable refining difficult.

However, when induction stirring is combined as in the present invention, (1) the injected gas is finely dispersed inside the molten steel 6, the gas-liquid reaction interface area increases, and (2) the bubbles 12 become fine, which leads to ) The residence time inside the molten steel 6 becomes longer and the reaction rate becomes extremely high, and even if the amount of blown gas is increased, the amount of molten steel scattering can be extremely reduced.

At this time, the fine dispersion effect of the blown gas depends on the flow rate caused by electromagnetic induction stirring of the molten steel 6, so the strength of this induction stirring is at least 20 (Cl1l/s) higher than the molten steel flow rate.
It is necessary to input more power into the coil. Molten steel 6
As shown in Figure 8, there are several induction stirring methods such as (a) horizontal stirring, working) vertical one-directional stirring, and (C) vertical two-directional stirring, but none of these methods can be used. The effect is the same.

In carrying out the present invention, gas blowing means in combination with induction stirring is important. That is, unless a gas blowing plug or a gas blowing nozzle 3 is present in the area where induction stirring is being performed, the fine dispersion effect of the blowing gas cannot be utilized to its fullest extent.

Therefore, the gas injection plug or gas injection nozzle 3
The installation position should be as deep as possible in the induction stirring part, and it is necessary to ensure a depth of at least about 10 cm or more from the surface of the molten steel 6 in the reduced pressure/vacuum reaction tank 7. 1
If the depth is less than 0 cm, the time during which the finely dispersed air bubbles 12 can stay inside the molten steel 6 is too short, and as a result, the reaction rate increases only slightly, and a sufficient effect is not achieved.

As a gas blowing plug or gas blowing nozzle 3,
Existing porous plug or refractory pore nozzles, single tube or double tube metal nozzles can be used. In order to increase the amount of gas blown and to increase the reaction rate, it is effective to use a plurality of gas blowing plugs or gas blowing nozzles 3.

The blowing gas used in the present invention is basically an inert gas, but an oxygen-containing gas can also be used at the same time. - For boat fishing, use Ar as an inert gas.

0 as oxygen-containing gas. Gas, COt gas, or a mixed gas of an inert gas and an oxygen-containing gas are preferred. When the purpose is decarburization treatment, use 003 gas at the same time as inert gas! Gas and Nz gas can also be used together.

Furthermore, when decarburizing molten steel by the method of the present invention, in a region where wt% (C) is 0.005 wt% or less, the molten steel contains an oxygen concentration of -1% (0). The sulfur concentration wt% [S] is maintained within a range limited by the following relational expression.

((1÷72・wtχ(S )/160) (1
-0,25)≦wtχ(0)≦((1÷72・yoket%
S])/160) (1+1.50)...(4
) That is, it has been found that the decarburization reaction rate in the extremely low carbon concentration region of 0.005 wt% or less can be increased by controlling the [O] concentration according to the [S] concentration, which is a surface active element. Based on this basic idea, a method for producing ultra-low carbon steel has already been disclosed in JP-A-61-82239.

According to the present invention, the decarburization reaction site is enlarged by fine dispersion of the blown gas, and at the same time, the wt
The decarburization rate can be increased by adjusting %[O] by adding a deoxidizing agent or the like to reduce the inhibitory factor of the decarburization reaction.

[O] concentration control is Aj, T when [O] is high concentration.
It is carried out by adding a deoxidizing agent such as i, or by blowing in hydrogen gas or a mixed gas of inert gas and hydrogen gas.If (0) is at a low concentration, it is carried out by blowing in oxygen gas or by blowing in iron ore. This is done by adding oxides such as stone, manganese ore, chromium ore, etc. to molten steel.

(Example) 1 star ■ A ladle equipped with a gas blowing plug for stirring molten steel at the bottom of the soil.
The composition is 0.015wt% (C) 0.04wt% (0
) 100 tons of molten steel with a concentration of 0.006 wt% [S] was charged, and the molten steel was decarburized and refined using a refining facility as shown in FIG. 1, which was equipped with a vacuum reaction tank above. The (N) concentration of the molten steel before refining was 0.0030 to 0.0035 wt%. The pressure inside the vacuum reactor reached 1 wHg or less after 5 sins. Therefore, after starting this vacuum evacuation, 5 sin
After this time, a total amount of Ar gas of 0 to 200 ml was supplied from three gas blowing plugs installed on the inner wall of the vacuum reaction tank.
Blowing was carried out at a flow rate in the range of 0 (j!/■in), and at the same time induction stirring was carried out. Molten steel flow rate V 5t due to this induction stirring
sst is 30 to 60 (C/s). Installation depth L of the Ar gas injection plug from the surface of the molten steel in the vacuum reaction tank
was changed to 5, 10, 30, 100°130C11.

At this point, the molten steel pulled up into the vacuum reaction tank installed at the top of the ladle is blown by Ar from the blowing plug.
The molten steel is being heated and stirred by a low-frequency induction coil while gas is being blown into it, and therefore the molten steel is moving between the ladle and the vacuum reaction tank at the bottom end of the vacuum reaction tank, and the molten steel as a whole is circulating. are doing.

Decarburization speed ratio V ratt0 and Ar gas flow rate Far (42
/win) is shown in Figure 3. are the decarburization speed VAr-IN obtained when "r induction stirring 1-Ar blowing" and the decarburization speed ■ obtained when only Ar blowing from the plug is carried out without induction stirring. It represents the ratio of When the installation depth L of the gas injection plug is 10 cm or more, V rmLig becomes extremely large. At this time,
V ratt. increases as FAr increases, and the decarburization treatment time can be significantly shortened.

The (N) concentration at the end of the refining process of 25ml1n is FAr
It is also shown in Figure 3 in relation to the above. At the end of the refining process (
N) The fi degree becomes lower as the FAr increases, allowing simultaneous decarburization and denitrification.

Regarding the above, the same results were obtained when the blow plug was used as the blow nozzle.

Futane Base I A ladle equipped with a gas blowing plug for stirring molten steel at the bottom.
Composition is 0.25wt% (C)-0.02~0.04wt
% (0) 0.006 wt% (Sol, (Cr
) 100 tons of molten steel with varying concentration or (Mn) 1 degree in the range of 5 to 30 wt% is charged, and the molten steel is decarburized in the refining equipment shown in Figure 1 with a vacuum reaction tank installed at the top. Refined. The pressure inside the vacuum reactor becomes lmH after 5 sin.
Reached below g. Therefore, after approximately 5 wins had passed after the start of this vacuum evacuation, Ar gas was injected at 1500 (f
/win) and induced stirring was performed. The molten steel flow velocity V5LaaL due to induction stirring is 40 to 50 (cm
/S), however, a lance installed at the top of the vacuum reactor is used to supply oxygen gas or chromite powder alone or in combination for (Cr)-containing molten steel, and oxygen gas for (Mn)-containing molten steel. Alternatively, manganese ore powder was supplied alone or in combination to the molten steel. No matter which method was used, the effect of the difference in the oxygen source supply method on the decarburization rate was extremely small. At this time, the installation depth of the Ar gas injection plug from the surface of the molten steel in the vacuum reaction tank was 30c+a.
Met.

Decarburization speed ratio ■10. . and (Cr) concentration or (Mn
) Decarburization rate ratio V rat whose relationship with concentration is shown in Figure 4
Mu. represents the ratio of the decarburization speed vAr + IN obtained when "induction stirring + Ar injection" to the decarburization speed var obtained when only Ar injection from the plug is performed without induction stirring. . Regardless of the (Cr)i11 degree or (Mn) concentration, the decarburization rate is approximately 4 times faster by performing induction stirring and gas injection compared to only gas injection.
The decarburization process time can be significantly reduced.

The ladle is equipped with a gas blowing plug for stirring molten steel at the bottom of the main body.
The composition is 0.80wt% (C30, 35wt% (Si)
100 tons of molten steel containing 0.95 wt% (Mn) was charged, and the molten steel was refined in a refining facility as shown in FIG. 1, which was equipped with a vacuum reaction tank above. The pressure inside the vacuum reactor is 5
After the win, it reached 1m11g or less. At the same time as the start of evacuation, Ar gas was supplied from the gas blowing plug installed on the inner wall of the vacuum reactor at a rate of 0 to 2000 (j!/5hi
Induction stirring was performed by blowing at a flow rate of n). The flow rate of molten steel by induction stirring■□11111 is 30 to 60 (cIl/s
), and the installation depth of the Ar gas injection plug from the surface of the molten steel in the vacuum reaction tank was 30 cm.

The inclusion removal rate ratio V ``crat=., the dehydrogenation rate ratio V' r a t i. and the Ar gas flow rate F Ar (
1/5h) is shown in Figure 5. vA″Cr
,stomach. are the inclusion removal speed obtained when r induced stirring + Ar injection j ``Ar+IN'' and the inclusion removal rate obtained when only Ar injection from the plug is performed without induction stirring v''' It represents the ratio between cA, , and V'rmL! .

are the dehydrogenation rate V'Ar+IN obtained when fg-induced stirring + Ar injection 1, and the dehydrogenation rate vHAr when only Ar injection from the plug is performed without induction stirring.
It represents the ratio of

V ``Crac!.'' and V ``raLi.'' increase with increasing FAr, and by performing induction stirring and gas injection simultaneously, the inclusion removal rate and dehydrogenation rate are improved compared to the case of gas injection alone. It becomes extremely large, and it becomes easy to melt steel with low hydrogen content and high purity.

The composition of the royal life is 0.025wt% (C) 0.04wt% [O
] -0,007 t% [S] of 10 l of molten steel was charged into a ladle, and the molten steel was refined in a refining facility as shown in Fig. 2, which had a vacuum reaction tank installed above. The (N) concentration at this time was 0.0030 to 0.0035 t%.In this case, a gas blowing plug was installed at the bottom of the vacuum reactor.On the other hand, the immersion tube nozzle was used to circulate the molten steel. The pressure inside the vacuum reactor reached 1m+sHg or less after 5 sins.Therefore, from the point when 5 sins had passed after the start of evacuation, the above-mentioned Ar gas installed at the bottom of the vacuum reactor was injected. Ar gas is 0 from the gas injection plug.
Blowing and induction stirring were carried out at a flow rate in the range of ~2000 (ffi/s+in). Molten steel flow rate by induction stirring■,
5. . 1 is 30 to 60 (1/S), and the installation depth of the Ar gas injection plug from the surface of the molten steel in the vacuum reaction tank was changed to 5.10 cm and 20.30 cm. .

Figure 6 shows the relationship between the decarburization speed ratio and the Ar gas flow rate F□(i!, /win). Coal speed VAr*I
It represents the ratio of N to the decarburization rate VAr when only Ar injection from the plug is performed without induction stirring.* V r a L k o increases as F'ar increases. , the decarburization treatment time can be significantly shortened.

(N) concentration and F^ at the end of the refining process of 25ml1n,
The relationship between the two is also shown in Figure 6. At the end of the refining process (
N) concentration decreases as F□ increases, resulting in simultaneous decarburization and
Can denitrify.

The same results were obtained when the blow plug was used as the blow nozzle.

1 ship 1 Composition is 0.011wt% (C) 0.005-0.0
100 tons of molten steel containing 8 wt% [O] was charged into a ladle, and the molten steel was refined in a refining facility as shown in Figure 2, which had a vacuum reaction tank installed above. In this case, a gas blowing plug was attached to the bottom of the vacuum reactor. On the other hand, Ar gas for circulating molten steel is blown from the immersion pipe. The pressure inside the vacuum reactor reached 1 Hg or less after 5 +wins. At the same time as the start of evacuation, Ar gas was supplied at 1200 (1/
Induction stirring was carried out by blowing at a flow rate in the range of (win).

At this time, the installation depth of the Ar gas blowing plug from the surface of the molten steel in the vacuum reaction tank was 30C1l.

Decarburization rate ratio ■r□ in the concentration range of (C) 0.005 wt% or less. The relationship between and [O] concentration is shown in Figure 7*
vrat=. is the ratio of the decarburization rate obtained when the [O] concentration is 0.010 wt % to the decarburization rate that can be achieved at each [O] concentration based on y(0)-6·''Ar+IN. ■The value of r□1° is wt% (0), wt%
Depending on [S], it becomes the largest when held within the range limited by the following relational expression.

((1+72 HwtX (S))/160)
(1-0,25) ≦wtX (0)≦((1+72・
胛tχ(5) )/160 ) (1+1.50) (Effect of the invention) As explained above, by applying the method according to the present invention or using the apparatus according to the present invention, induction stirring and gas blowing can be performed. If molten steel is depressurized or vacuum refined using a combination of
As the liquid reaction interface area increases, (1) the microbubbles ride the flow of molten steel due to electromagnetic induction, and the time they stay inside the molten steel increases. Due to these two effects, decarburization and denitrification proceed efficiently at the same time by injecting a small amount of gas. By using refining equipment suitable for mass production, high-purity steel or high-cleanliness steel can be melted economically. Can be manufactured.

[Brief explanation of drawings]

1 and 2 are diagrams showing an overview of a refining installation for carrying out the method of the invention; FIG. 3 shows the flow of blown gas from the plug IFA- and the decarburization rate ratio V rac5. Relationship with and after refining treatment (N)
Figure 4 shows the relationship between concentration and decarburization rate ratio V rmLi. Figure 5 shows the relationship between the (Cr) concentration and the (Mn) concentration.
A diagram showing the relationship between Hr□1° and the blown Ar gas flow rate FAr, and FIG. 6 shows the blown gas flow rate FAr from the plug and the decarburization speed ratio V ratm. Relationship with and after refining treatment (N)
Figure 7 shows the relationship between concentration and decarburization rate ratio V rmLi. FIG. 8 is a diagram showing the relationship between O and [O] concentration, and FIG. 8 is a diagram showing the method of induction stirring. 1... Container for molten steel (ladle), 2... Induction stirring/
Heating coil, 3... Gas blowing plug or gas blowing nozzle, 4... Lance for gas blowing and oxide blowing, 5... Molten steel to be refined, 6... Reduced pressure or vacuum reaction tank Molten steel sucked up into the chamber, 7... reduced pressure or vacuum reaction tank, 8... airtight jacket made of non-magnetic material, 9...
・Airtight outer covering, 10... Refractory material, 11... Shielding material,
12... Dispersion bubbles, 13... Molten steel circulation gas, 14
...Ladle-like molten steel stirring gas. Fig. 3 Ar (h'yr) Fig. 5 1r (J!/)R, ri Fig. 4 wr4 (Crl, wrx (1-b)) Fig. 6 5θO /θ00 iso. Ar (L bias i) t) Figure 7 Figure 8 770θ2 θoo, f θ, θ! Wt3 (-0) θO2 θ, θ5 σ, IQ (b) (C) Procedural amendment (voluntary) September 2, 1991

Claims (1)

[Claims] (1) When carrying out depressurization/vacuum refining of molten steel, a depressurization or vacuum reaction tank (hereinafter referred to as a reaction tank) is installed above the molten steel storage ladle, and the molten steel to be decarburized is While circulating the molten steel between the ladle and the reaction tank, the molten steel pulled into the reaction tank is heated and stirred by a low frequency induction coil, and at the same time, an inert gas is introduced into the reaction tank. A method for depressurizing and vacuum refining of molten steel, which is characterized by injecting the molten steel into the molten steel in a reaction tank. (2) Reduced pressure/vacuum refining of molten steel according to claim 1, characterized in that a porous plug or a pore nozzle is embedded in the inner wall of the reaction tank, and an inert gas is blown through the porous plug or pore nozzle. Method. (3) In a region where the carbon concentration of the molten steel to be decarburized is 0.005 wt% or less, the sulfur concentration wt% contained in the molten steel [
3. The reduced pressure/vacuum refining method of molten steel according to claim 1 or 2, characterized in that the oxygen concentration wt% [O] of the molten steel is maintained within a range limited by the following relational expression according to S]. ((1+72・wt% [S])/160}(1-0.2
5)≦wt%[O]≦{(1+72・wt%[S]/1
60} (1+1.50) (4) In a molten steel depressurization/vacuum refining device in which a decompression or vacuum reaction tank (hereinafter referred to as a reaction tank) is installed above the molten steel storage ladle, molten steel is removed from the molten steel storage ladle. The structure is such that a portion of the molten steel is pulled up into the reaction tank and the molten steel is circulated between the ladle and the reaction tank, and the molten steel pulled into the reaction tank is heated and heated around the outer periphery of the reaction tank.
1. A reduced pressure/vacuum refining device for molten steel, characterized in that it is provided with a low frequency induction coil for stirring, and has a component for blowing an inert gas into the reaction tank. (5) The molten steel reduced pressure/vacuum refining apparatus according to claim 1, wherein the component for blowing inert gas into the reaction tank is a porous plug or a pore nozzle embedded in the inner wall of the reaction tank. .