JPH05311226A - Reduced pressure-vacuum degassing refining method for molten metal - Google Patents

Abstract

PURPOSE:To efficiently and economically execute degassing refining to an ultra low concn. in a short time by applying reduced pressure-vacuum degassing treatment. CONSTITUTION:At the time of executing the degassing refining to the molten metal by setting a circulating type vacuum vessel or a cylindrical type vacuum vessel to the upper part of a ladle incorporating molten metal and introducing a part of the molten metal in a ladle into this vacuum vessel, the difference between the atmospheric pressure and the pressure just above the molten metal surface in the ladle is adjusted in the range of 0.2-2.0atm and the pressure in the vacuum vessel is exhausted to <=200mmHg. Further, in order to improve the degassing effect, Ar is blown into the molten metal in the vacuum vessel. Particularly, at the time of removing the carbon in the molten metal, oxygen concn. contained in this molten metal is adjusted in the range of 0.03-0.10mass%.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention is for removing carbon [C], nitrogen [N] and hydrogen [H] contained in molten metal such as molten steel or molten alloy under reduced pressure and vacuum of 200 mmHg or less. The present invention relates to an efficient degassing and refining method of.

[0002]

2. Description of the Related Art Carbon and nitrogen contained in metals such as steel and alloys are used in steel sheets for automobiles and beverage cans to improve workability and prevent aging, and to use ultrafine steel. In the case of steel for wire steel cord, a very small amount is required to improve ductility. Further, structural steel plates and pipeline steel pipes have a very low hydrogen content to prevent cracking.

Generally, in the steel industry, degassing treatment of molten metal such as molten steel or molten alloy (hereinafter simply referred to as molten steel) is carried out, for example, in the 3rd edition Iron and Steel Handbook II, Ironmaking Steelmaking 671-6.
It is carried out using various decompression / vacuum refining equipment as shown on page 85. Regarding the degassing method (RH degassing method) using a molten steel circulation type depressurization / vacuum tank, a method of blowing gas into the molten steel in the depressurization / vacuum tank (hereinafter, simply referred to as a vacuum tank) is disclosed in, for example, Japanese Patent Laid-Open No. Hei 2 It is known from JP-A-217412 or JP-A-3-61316, and a certain effect can be expected in improving the degassing rate. However,
In such a method, the amount of molten steel in the vacuum tank is small, and therefore the molten steel depth is extremely shallow, and the injected gas is released from the molten steel without sufficiently participating in the reaction. Even if the blowing gas amount is increased to improve the degassing rate, the blowing gas blows out from the molten steel and scatters the molten steel, unnecessarily increasing splash and making stable degassing impossible. ..

The degassing reaction proceeds at the interface (gas / liquid interface) between the liquid phase which is molten steel and the gas phase which is gas. At this time,
The rate of each degassing reaction is shown by the equations (1 ') to (3'). To increase the degassing rate, the reaction rate constant kx
Needs to be increased. Since kx is proportional to the reaction area, therefore, the degassing reaction rate should be increased, and in order to rapidly produce molten steel with extremely low carbon, extremely low nitrogen, and extremely low oxygen, the gas / liquid interface area should be increased. A method and its specific means are needed. [Decarburization treatment] [C] + [O] = CO …………………… (1) d mass% [C] / dt = -kc · mass% [C] …………… (1 ') [Dehydrogenation treatment] [H] + [H] = H ₂ ……………… (2) d mass% [H] / dt = -kc · mass% [H] ………… (2 ' ) [Denitrification treatment] [N] + [N] = H ₂ ……………… (2) d mass% [N] / dt = −kc · mass% [N] ² ………… (2 ')

[0005]

DISCLOSURE OF THE INVENTION The present invention performs decompression / vacuum treatment on molten steel to remove molten steel for producing extremely low carbon, extremely low nitrogen, and extremely low hydrogen molten steel efficiently and economically. It is intended to provide a gas refining method.

[0006]

Means and Actions for Solving the Problems The gist of the present invention is as follows. (1) A circulation type or straight body type decompression / vacuum tank is installed above the ladle containing the molten metal, and a portion of the molten metal in the ladle is introduced into the decompression / vacuum tank to decompress the molten metal.・ When performing vacuum degassing refining, adjust the difference between the atmospheric pressure and the pressure directly above the molten metal surface in the ladle within the range of 0.2 to 2.0 (atm), and reduce the pressure and the pressure in the vacuum tank. 200 mmHg
A depressurized / vacuum degassing refining method for molten metal, comprising:

(2) In the method described in the preceding paragraph 1, the molten metal sucked and pushed up in the vacuum chamber is depressurized.
Decompression and vacuum degassing refining of molten metal, characterized in that Ar or Ar and oxygen gas are blown through a plurality of gas blowing nozzles and / or gas blowing plugs installed at the bottom or deep layer of a vacuum tank. Method. (3) In the method described in 1 or 2 above, when removing carbon ([C]) in the molten metal, the concentration of oxygen ([O]) contained in the molten metal is 0.03 to 0.10 ma.
A depressurizing / vacuum degassing refining method for molten metal, characterized by adjusting to a ss% range.

(4) In the method described in the above item 2 or 3, when carbon ([C]) in the molten metal is removed, the carbon ([C]) concentration of the molten metal is 0.005 mass%.
In the following areas, per unit weight of molten metal in the depressurization / vacuum tank, Ar is supplied through a plurality of gas injection nozzles and / or gas injection plugs installed at the bottom or deep layer of the depressurization / vacuum tank. A decompression / vacuum degassing refining method for molten metal, which comprises blowing 1.5 (Nl / min / ton) or more.

[0009]

The root of the technical idea of the present invention is to constantly supply a larger amount of molten steel 2 into the vacuum tank 5 which is the main reaction section, as shown in FIGS. 3 The space 10 of the internal molten steel is separated from the ladle sealing edge 4 and the vacuum tank collar 6 via the sealing mechanism 15, and the pressurizing gas introduction pipe 11 is introduced into the space 10.
By introducing gas from the above to pressurize the space, the molten steel is sucked and pushed up to the height proportional to the pressure difference ΔP represented by the following relational expression in the vacuum chamber, whereby the residence time of the blown gas is increased. There is a point to increase. That is, the amount of molten steel in the vacuum tank and the depth H of molten steel in the vacuum tank can be significantly increased as compared with the conventional method, and the above-mentioned (1)-
CO, H ₂ , and N ₂ generated by the formula (3) can be absorbed in a sufficiently large amount, and the degassing rate can be extremely increased.

[0010]

[Equation 1]

[0011]

[Equation 2]

H: height of molten steel in the vacuum tank (mm) L: height from the molten steel surface of the ladle to the bottom of the vacuum tank
(Mm) P_total : Vacuum chamber pressure (mmHg) ρ_metal : Density of molten steel (g / cm³) ΔP: Pressure difference (atm) between the atmosphere and the space 10, which makes it possible to obtain a molten steel ring when a circulation type vacuum tank is used.
CO, H to diverted Ar ₂, N₂The absorption amount of
The speed increases. On the other hand, when using a straight body type vacuum chamber
From the molten steel circulating stirring plug 16 installed at the bottom of the ladle
CO, H to Ar bubbles blown₂, N₂Increased absorption of
However, the degassing rate increases.

However, if the value of ΔP is set too large,
The amount of molten steel in the vacuum tank becomes too large, the circulation of molten steel is obstructed, and the reaction rate apparently decreases. Therefore, the value of ΔP is controlled within the range of 0.2 to 2.0 (atm). In order to fully utilize the effect of increasing the bubble / liquid interface area due to the expansion of the blown-in Ar, the pressure in the vacuum chamber / vacuum chamber is more advantageous as the vacuum is higher. Therefore, the substantial degree of vacuum should be 200 mmHg or less.

Further, by using a plurality of gas injection nozzles 8 installed in the deep portion of the vacuum chamber and / or a gas injection plug 9 installed in the bottom of the vacuum chamber, the gas is dispersed in the molten steel in the vacuum chamber. By blowing, the gas-liquid reaction interface area can be further increased, and by blowing bubbles in molten steel to prevent coalescence, a large degassing rate can be obtained.

When carbon ([C]) contained in molten steel is removed by the method of the present invention, especially when the [O] concentration of the molten steel is 0.005 mass% or less, decarburization due to generation of CO bubbles from inside the molten steel. The reaction amount becomes extremely small, and the reaction mainly via the gas-liquid interface by the blown air bubbles becomes the main component. Therefore, in order to promote this reaction, the amount of gas blown into the vacuum tank should be 1.5 (Nl / min / ton) per unit weight of molten steel present in the vacuum tank.
It is effective to secure the bubble / molten steel boundary area by the blown gas. At this time, it is important to maintain the [O] concentration of the molten steel at a high concentration. However, on the other hand, [O] is
Adsorbs on the liquid interface and reduces the decarburization reaction rate. Therefore,
The [O] concentration is in the range of 0.03 to 0.1 mass%.

Further, in practicing the present invention, known gas blowers for dispersing bubbles inside the molten steel, refining the bubbles, preventing coalescence of blown bubbles as much as possible, and increasing the gas-liquid interface area. Including means can be applied. In carrying out the decarburization treatment of molten steel by applying the method of the present invention, in order to maintain or increase the oxygen concentration of the molten steel, oxygen gas or oxygen-containing gas may be blown directly into the molten steel through the blowing nozzle 14. Of course, the spray lance 12 may be used to spray the molten steel surface.

Furthermore, in order to stir the molten steel in the ladle,
It is also possible to use the plug 13 for gas injection installed at the bottom of the ladle.

[0018]

Embodiments of the present invention will be described below with reference to the drawings. Example 1 As shown in FIG. 8, 250 tons of molten steel 1 was charged into a ladle 3 with a sealing edge 4, and a molten steel circulation type decompression / vacuum tank 5 with a collar 6 was immersed in the molten steel from the upper part to leave a space 10 The sealing mechanism 1
The molten steel was decarburized by isolating the molten steel from the atmosphere via No. 5 and evacuating the inside of the vacuum tank to suck the molten steel into the vacuum / vacuum tank.

[O] concentration is 0.04 to 0.05 mass
% Range. Nozzle 7 for injecting Ar gas for molten steel circulation
Was supplied to the molten steel at a rate of 1800 (Nl / min). After 5 minutes from the start of processing, the pressure in the vacuum chamber P
_{The total} becomes 10 mmHg or less, Ar is introduced through the gas supply pipe 11, and the difference ΔP between the pressure in the space 10 and the atmospheric pressure is ΔP.
Was set to 0.6 (atm). At the same time, Ar gas was supplied from the gas injection nozzles 8 or the plugs 8 installed at three deep places in the vacuum chamber to 3.5 per unit weight of molten steel in the vacuum chamber.
(Nl / min / ton)

[C] Changes in concentration over time are shown in FIG. According to the present invention, it is found that ultra low carbon molten steel can be rapidly melted. As a comparative example, ΔP is zero (atm) under the same conditions.
The change over time in the [C] concentration during decarburization is shown by the broken line. According to the present invention, the decarburization rate becomes extremely high as compared with the conventional method. Example 2 As shown in FIG. 9, 250 tons of molten steel 1 was charged into a ladle 3 with a sealing edge 4, and a straight-body type decompression / vacuum tank 5 with a collar 6 was immersed in the molten steel from the upper part to leave a space 10 Was isolated from the atmosphere via the seal mechanism 15, the vacuum tank was evacuated, the molten steel was depressurized and sucked into the vacuum tank, and the molten steel was decarburized.

[O] concentration is 0.04 to 0.05 mass
% Range. Ar gas for circulating and agitating the molten steel was supplied to the molten steel at a rate of 1600 (Nl / min) through a blowing plug 16. After 5 minutes from the start of the treatment, the pressure in the vacuum chamber P _total becomes 10 mmHg or less, and the gas supply pipe 11
Ar was introduced through the chamber and the value of the difference ΔP between the pressure in the space 10 and the atmospheric pressure was set to 0.5 (atm). At the same time, Ar gas was blown at 3.5 (Nl / min / ton) per unit weight of molten steel in the vacuum tank from the gas injection nozzle 8 installed in the deep layer in the vacuum tank.

[C] Changes in concentration with time are shown in FIG. According to the present invention, it is found that ultra low carbon molten steel can be rapidly melted. As a comparative example, ΔP is zero (atm) under the same conditions.
The change over time in the [C] concentration during decarburization is shown by the broken line. According to the present invention, it is apparent that the decarburization rate is extremely high and the ultra low carbon steel can be rapidly melted as compared with the conventional method.

Example 3 Using the apparatus shown in FIGS. 8 and 9, 250 tons of molten steel was decarburized by changing the value of ΔP in the range of 0 to 2.0 (atm). [O] concentration is 0.04 to 0.05 ma
It is in the range of ss%. The circulating Ar flow rate when using the molten steel circulation type vacuum tank was 1800 (Nl / min), and the molten steel circulation stirring gas flow rate when using the straight body type vacuum tank was 1200.
(Nl / min). After 5 minutes from the start of the treatment, the pressure in the vacuum chamber P _total becomes 10 mmHg or less.

In each case, decarburization was also carried out when Ar was blown at a rate of 3.5 (Nl / min / ton) per unit weight of molten steel in the vacuum tank. Fig. 3 shows the decarburization rate constant ratio with and without Ar injection into the vacuum chamber.
The relationship between kc ^Px / kc ^O and ΔP is shown. Where kc ^Px / kc ^O
The value of is the decarburization rate constant ratio in the concentration region where [O] is 0.003 mass% or less.

The value of kc ^O is the decarburization rate constant when ΔP = zero, and the value of kc ^Px is the decarburization rate constant when ΔP = x. The value of kc ^Px / kc ^O begins to increase when the value of ΔP becomes 0.2 (atm) or more, and when Ar is blown in the vacuum chamber, the effect is more remarkable, and the melting of ultra-low carbon molten steel is efficient. Can be implemented Example 4 Using a device as shown in FIG. 8, 250 tons of molten steel was decarburized. At this time, the [O] concentration is set to 0.010 to
It was changed in the range of 0.110 mass%.

Circulating Ar flow rate is 1800 (Nl / min)
After 5 minutes from the start of the treatment, the pressure in the vacuum chamber P
_total becomes 10 mmHg or less, and the value of ΔP is 0.6
(Atm). 3.5 per unit weight of molten steel in the vacuum tank
A decarburization process was also performed when Ar was blown at a rate of (Nl / min / ton).

FIG. 4 shows the relationship between the decarburization rate constant ratio kc ^{[O] x} / kc ^O and the [O] concentration. Here, the value of kc ^O is the decarburization rate constant when [O] = 0.01 mass%, and the value of kc ^{[O] x} is the decarburization rate constant when [O] = x mass%. .. The value of kc ^{[O] x} / kc ^O increases with increasing [O]. When Ar is blown into the vacuum chamber, the effect is more remarkable, and the extremely low carbon molten steel can be efficiently produced. However, when [O] exceeds 0.10 mass%,
The value of kc ^{[O] x} / kc ^O decreases.

Therefore, in order to actually carry out decarburization efficiently, the [O] concentration should be 0.030 mass% or more.
It should be 0.10 mass% or less. Example 5 Using a device as shown in FIGS. 8 and 9, 250 tons of molten steel was degassed. [O] concentration of molten steel is 0.0
It is a killed steel in the range of 01 to 0.005 mass%.

The circulating Ar flow rate when using the molten steel circulation type vacuum tank was 1800 (Nl / min), and the molten steel circulation stirring gas flow rate when using the straight body type vacuum tank was 1200 (Nl / min).
min). After 5 minutes from the start of the treatment, the pressure in the vacuum chamber P _total became 10 mmHg or less, and the value of ΔP was changed in the range of 0 to 1.65 (atm). In both the straight body type and the circulation type, degassing treatment was also performed by blowing Ar at a rate of 3.0 (Nl / min / ton) per unit weight of molten steel in the vacuum tank.

FIG. 5 shows that Ar was blown into the vacuum chamber.
Denitrification rate constant ratio k without_N ^Px/ k_N ^O, Dehydrogenation rate constant
Ratio k_H ^Px/ k_H ^OAnd the relationship between ΔP and ΔP. k_N ^O, K_H ^O
Are the denitrification and dehydrogenation rate constants when ΔP = zero.
, K_N ^Px, K_H ^PxValues are denitrification and dehydration when ΔP = x
It is the elementary rate constant. Rate constant ratio k_N ^Px/ k_N ^OAnd k_H ^Px/ k
_H ^OIncreases when the value of ΔP exceeds 0.2 (atm)
Then, when Ar is blown in the vacuum chamber, the effect is
A more remarkable and efficient degassing process can be performed.

Example 6 Using a device as shown in FIGS. 8 and 9, 250 tons of molten steel was decarburized. At this time, the [O] concentration is 0.0
It is in the range of 5 to 0.06 mass%. When a circulation type vacuum tank is used, the circulating Ar flow rate is 1800 (Nl / min)
Thus, the flow rate of the molten steel circulating stirring gas when using the straight body type vacuum tank is 1200 (Nl / min). After 5 minutes from the start of the treatment, the vacuum chamber internal pressure P _total was maintained at a predetermined pressure. However, the value of ΔP was set to 0.6 (atm).

In each case, the unit weight of molten steel in the vacuum chamber
Blows Ar at a rate of 4.0 (Nl / min / ton)
Intensive decarburization treatment was also carried out. Fig. 6 shows the decarburization rate constant ratio kc
^Tx/ kc^TAnd P_totalHas shown a relationship with. Where kc ^T 
Value of P_total= Decarburization rate constant at 760 mmHg
Yes, kc^TxValue of P _total= Decarburization speed when x mmHg
It is a constant.

Although the value of kc ^Tx / kc ^T increases as the value of P _total becomes higher in vacuum, the value of P _total should be 200 mmHg or less in order to actually perform decarburization efficiently. Example 7 Using a device as shown in FIG. 8, 250 tons of molten steel was decarburized. At this time, the [O] concentration is 0.05 to
It is in the range of 0.06 mass%.

Circulating Ar flow rate is 1800 (Nl / min)
After 5 minutes from the start of the treatment, the pressure in the vacuum chamber P
_{The total} was kept below 10 mmHg. However, the value of ΔP was set to 0.6 (atm). Flow rate F _{Ar of} Ar gas blown into the vacuum chamber is 0 to 25 (Nl / min / ton)
Changed within the range.

In FIG. 7, the [O] concentration is 0.005 mass.
^{Decarburization} rate constant ratio kc ^Arx / kc ^O and F
The relationship with _Ar is shown. The value of kc ^O here is the decarburization rate constant when F _Ar = zero, and the value of kc ^Arx is the decarburization rate constant when F _Ar = x. The value of kc ^Arx / kc ^O increases with increasing F _Ar . Substantially, in order to carry out the decarburization treatment efficiently, it is necessary to secure the value of F _Ar at 1.5 (Nl / min / ton) or more.

[0036]

INDUSTRIAL APPLICABILITY According to the present invention, the degassing rate of molten steel is increased, and molten steel with ultra-low carbon, ultra-low nitrogen and ultra-low hydrogen concentration can be produced efficiently and economically. ..

[Brief description of drawings]

FIG. 1 is a diagram showing a change with time of [C] concentration.

FIG. 2 is a diagram showing a change with time of [C] concentration.

FIG. 3 is a diagram showing a relationship between a decarburization rate constant ratio kc ^Px / kc ^O and ΔP.

FIG. 4 is a diagram showing the relationship between the decarburization rate constant ratio kc ^{[O] x} / kc ^O and the [O] concentration.

[Figure 5] Degassing rate constant ratio k _N ^Px / k _N ^O , k _H ^Px / k _H ^O
It is a figure which shows the relationship between ΔP and.

FIG. 6 is a diagram showing a relationship between a decarburization rate constant ratio kc ^Tx / kc ^T and P _total .

FIG. 7 is a diagram showing a relationship between a decarburization rate constant ratio Kc ^Arx / kc ^O and F _Ar .

FIG. 8 is a diagram showing an example of molten steel circulation type degassing equipment for carrying out the present invention.

FIG. 9 is a diagram showing an example of a straight-body type degassing equipment for carrying out the present invention.

[Explanation of symbols]

 1: Molten steel in ladle 2: Molten steel sucked and pushed up inside vacuum tank 3: Ladle 4: Ladle sealing edge 5: Vacuum tank 6: Vacuum tank collar 7: Gas injection nozzle 8: Gas injection nozzle 9: Gas injection plug 10: Space 11: Pressurization gas introduction pipe 12: Oxygen gas injection lance 13: Gas injection plug 14: Oxygen injection nozzle 15: Seal mechanism 16: Molten steel circulation stirring plug

Claims (4)

[Claims] 1. A circulation type or straight body type decompression / vacuum tank,
It is installed on the top of the ladle containing the molten metal, and a part of the molten metal in the ladle is introduced into the decompression / vacuum tank to decompress the molten metal.
In carrying out the vacuum degassing refining, the difference between the atmospheric pressure and the pressure directly above the molten metal surface in the ladle is 0.2 to 2.0 (at
m) and adjust the decompression / vacuum chamber pressure to 200
Decompression of molten metal characterized by being less than mmHg
Vacuum degassing refining method. 2. The method according to claim 1, wherein the molten metal sucked and pushed up inside the decompression / vacuum chamber has a plurality of gas injection nozzles installed at the bottom or deep layer of the decompression / vacuum chamber. Or Ar via a gas injection plug
Alternatively, a decompression / vacuum degassing refining method for molten metal, which comprises blowing Ar and oxygen gas. 3. The method according to claim 1 or 2, wherein
When removing carbon ([C]) in the molten metal, the concentration of oxygen ([O]) contained in the molten metal is 0.03 to 0.
A depressurizing / vacuum degassing refining method for molten metal, which comprises adjusting the content of the molten metal within a range of 10 mass%. 4. The method according to claim 2 or 3,
When removing carbon ([C]) in the molten metal, in the region where the carbon ([C]) concentration of the molten metal is 0.005 mass% or less, relative to the unit weight of the molten metal in the decompression / vacuum chamber, Melting characterized by blowing Ar of 1.5 (Nl / min / ton) or more through a plurality of gas injection nozzles and / or gas injection plugs installed at the bottom or deep layer of the decompression / vacuum tank. Metal decompression / vacuum degassing refining method.