JPH08325629A - Method for smelting ultra-low carbon steel - Google Patents

Abstract

PURPOSE: To make it possible to smelt ultra-low carbon steel with high productiv ity and high reliability. CONSTITUTION: This refining method comprises blowing gas for reflux from a tuyere disposed by penetrating through the side wall of a riser or from a lance immersed into the molten steel in a ladle right under the riser in an RH decarburization refining method at a rate of blowing of the gas for reflux of >=30Nl/min.ton per 1ton reflux rate of the molten steel. This smelting method comprises controlling the displacement H(kg/Hr.ton) per 1ton amt. of the molten steel to be treated to the following range according to the vacuum degree P(Torr) in a degassing chamber: 100>=H>=70 at P>=300, 80>=H>=40 at 30>=P>=200, 60>=H>=25 at 200>P>=100, 30>=H>=13 at 100>P>=50 and 15>=H>=8 at 50>P>=10.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for melting ultra-low carbon steel using an RH degasser.

[0002]

2. Description of the Related Art In recent years, the production ratio of ultra-low carbon steel by continuous annealing has been increasing in order to meet diversified uses of cold-rolled steel sheets and surface-treated steel sheets and demands for material improvement. Development of low carbon steel melting technology is active. At this time, it is important to efficiently promote the decarburization reaction to shorten the treatment time and to reduce the reached [C] concentration after the decarburization treatment.

Usually, in order to accelerate the decarburization reaction, a means for increasing the gas injection amount for reflux to stir the steel bath strongly to increase the gas-liquid interface area is applied. When this strong stirring technology is applied to high carbon molten steel in the early stages of decarburization, CO is suddenly generated.
A large amount of the steel bath is scattered by the gas bubbles and adheres to the side wall of the vacuum degassing tank. Since this melts into the extremely low carbon region at the final stage of decarburization, the concentration of [C] reached does not decrease and the treatment time is prolonged.

As a method for solving the above-mentioned problems, Japanese Patent Application Laid-Open No. H2-122012 (Prior Art 1) controls the degree of vacuum according to the [C] concentration that changes (decreases) with the progress of decarburization. However, a technique for melting ultra low carbon steel is disclosed.

Prior art 1 is a method in which the degree of vacuum is not excessively lowered with respect to the equilibrium [C] concentration. In other words, during refining, by controlling the degree of vacuum to an appropriate range for the [C] concentration particularly in the high carbon region (initial stage of decarburization), the decarburization rate is secured and the CO gas generation amount is suppressed. This is a method of suppressing the amount of splash of molten steel splash. As a result, the processing time is not extended and the splash does not elute, so the concentration [C] reached is reduced, and at the same time, the vapor energy for reducing pressure is also reduced because the vacuum degree is not excessively lowered. I can.

Japanese Patent Laid-Open No. 63-213617 (Prior Art 2) discloses a method for producing an ultra-low carbon steel by changing the molten steel ring flow rate according to the [C] concentration during decarburization. ing.

In the prior art 2, in the high carbon region where the [C] concentration is 100 ppm or more from the start of decarburization, the molten steel ring flow rate is regulated low, and in the subsequent low carbon region, the molten steel ring flow rate is increased to decarburize. This is a method of speeding up. As a result, in the initial stage of decarburization, the injection amount of the circulating gas is regulated, and the stirring force is suppressed, so the amount of splash of molten steel splash is suppressed, and in the latter stage of decarburization, decarburization is promoted and the [C] concentration reached. And reduction of processing time are achieved at the same time.

[0008]

In the current technology, analysis of the [C] concentration during decarburization (from sampling to [C]
It takes about 3 to 5 minutes to determine the concentration). Therefore, about 10 minutes after the start of the treatment, the [C] concentration was 400 pp.
In the decarburization refining of RH in which m is reduced to around 20 ppm, the [C] concentration at the time of sampling and the time of analysis value determination changes greatly.

Therefore, in the method of Prior Art 1, the degree of vacuum is controlled within an appropriate range by using the [C] concentration at the time of determination as a refining index, in other words, it corresponds to a high [C] concentration 3-5 minutes before. Then, the degree of vacuum is controlled. In this method, since the degree of vacuum is not excessively lowered, the splash amount of splash is suppressed, but the decarburization rate is reduced, so that the productivity of RH is reduced.

Similarly, in the prior art 2, since the molten steel ring flow rate is regulated by using the [C] concentration as a refining index, the analysis time becomes a delay time as in the above-mentioned technique, and [C] during decarburization is in progress. It was not possible to set an appropriate molten steel ring flow rate corresponding to the concentration,
A high decarburization rate cannot be obtained even if the amount of metal deposits in the tank can be suppressed.

Further, in Prior Art 2, it is necessary to increase the molten steel ring flow rate in the low carbon region in the latter stage of decarburization, and therefore the amount of gas blown in must be increased. As a result, in the RH degassing equipment having a small exhaust capacity, it is not possible to secure a high vacuum necessary for melting ultra-low carbon steel, and thus a high decarburization rate cannot be obtained.

Further, the prior art 2 is a melting method in which the absolute amount of the molten steel ring flow rate is regulated so as to keep the decarburization rate high and reduce the amount of metal adhered in the tank. Therefore, in the RH degassing equipment that has a large ladle inner diameter and can secure a large immersion pipe diameter, this absolute amount can be secured, so the decarburization rate can be secured,
RH that can only secure a small dip pipe diameter due to ladle inner diameter restriction
In the degassing equipment, there are cases where this absolute amount cannot be secured due to the increase in the amount of gas blown in.

In the prior art 2, the index proposed by the inventors (details will be described later), that is, the gas injection amount per ton of molten steel ring flow rate is 3.21-10.6 Nl.
Since it is as low as / min · ton, according to the research conducted by the inventors, a high decarburization rate cannot be obtained even though the amount of metal in the tank can be reduced.

The present invention has been proposed in order to solve the above-mentioned problems, and an appropriate amount of gas for recirculation is blown in to secure a sufficient amount of stirring in the steel bath while preventing a decrease in the degree of vacuum. (EN) Provided is a method for melting ultra-low carbon steel capable of securing a charcoal speed and suppressing the amount of splash of molten steel splash. In addition, the decarburization reaction is controlled by using a refining index that does not cause a delay time, and a method for melting ultra-low carbon steel with high productivity and reliability is provided.

[0015]

DISCLOSURE OF THE INVENTION The present invention relates to a smelting method of vacuum decarburizing and refining using an RH degasser to melt extra-low carbon steel, and a wing provided through a side wall of a riser pipe. From the mouth, or from the lance soaked in the molten steel in the ladle just below the rising pipe, and the gas ejection port is arranged toward the opening of the rising pipe,
30Nl / mi per 1ton of molten steel ring flow rate with inert gas
It is a method for melting ultra-low carbon steel, which comprises blowing n or more ton to advance a decarburization reaction.

Further, in the melting method in which ultra-low carbon steel is melted by vacuum decarburization refining using an RH degasser, the exhaust gas amount H per 1 ton of treated molten steel is 100 kg / Hr · t.
It is a melting method for ultra-low carbon steel, characterized in that the decarburization reaction is allowed to proceed by controlling the temperature to be on or below.

Further, an inert gas for reflux is used as a molten steel ring flow rate of 1 t.
Injection of 30 Nl / min · ton or more per 1 ton, and exhaust volume H (kg / Hr · t per 1 ton of molten steel to be treated)
on) is controlled within the range defined below according to the degree of vacuum P (torr) in the degassing tank.

(1) When P ≧ 300, 100 ≧ H ≧ 7
0, (2) 300> P ≧ 200, 80 ≧ H ≧ 40,
(3) If 200> P ≧ 100, 60 ≧ H ≧ 25,
(4) If 100> P ≧ 50, 30 ≧ H ≧ 13, (5)
If 50> P ≧ 10, then 15 ≧ H ≧ 8.

[0019]

According to the present invention, when decarburizing and refining using an RH vacuum degassing apparatus to melt ultra-low carbon steel, a tuyere provided through the side wall of the rising pipe serves as a gas blowing means for reflux. A
An inert gas such as r gas is blown in, or an inert gas is blown in from a lance arranged so as to be immersed in molten steel in a ladle directly below the rising pipe with the gas ejection port facing the opening of the rising pipe.

The total amount of the gas blown from the tuyere or the lance arranged in this way floats (rises) in the rising pipe and can give an upward driving force to the molten steel.
Molten steel circulates between the H vacuum degasser and the ladle.

At this time, at the molten steel-gas interface in the tank under reduced pressure, the decarburization reaction according to the following equation (1) proceeds and ultra low carbon steel is melted.

C + O → CO (g) (1) The present inventors diligently carried out a melting test of an ultra-low carbon steel by the above method, and measured the amount of the inert gas blown from the tuyere as described above. Change the amount of gas for recirculation)
The effect on the reached [C] concentration after 15 minutes from the start of decarburization was investigated. The result is shown in FIG.

As shown in FIG. 1, at any injection amount of the circulating gas, the reached [C] concentration is lower at the flow rate of molten steel of 150 ton / min, and the reached [C] concentration is higher as the gas injection amount is larger. It is decreasing. However, even if the injection amount of the reflux gas is flown over a certain amount, it reaches [C].
The concentration does not decrease further.

As the above test conditions, 25
0 ton of undeoxidized molten steel was tapped, and its molten steel composition had a [C] concentration of about 0.04% and a soluble oxygen concentration of about 500.
Adjusted to ppm. The other molten steel components were in the ranges shown in Table 1.

[0025]

[Table 1]

Here, the molten steel ring flow rate Q (ton / min)
Was calculated by the calculation formula (2) in consideration of the degree of vacuum proposed in Reference 1. (Reference 1: Iron and Steel, Vo
l. 63 (1987) p176) Q = 11.4 x D ^3/4 x G ^1/3 x [ln (P ₁ / P ₂ )] ^1/3 (2) where D is the immersion pipe diameter (m), G is the flow rate of gas for recirculation (Nl / min), P ₁ is the pressure at the recirculation gas injection position (torr), and P ₂ is the pressure in the vacuum chamber (tor).
r).

The molten steel ring flow rate is 100, 150 ton /
In order to have two levels of min, as shown in Table 2, the gas injection amount for reflux was changed in the range of 1000 to 8000 Nl / min, and the immersion pipe diameter was changed corresponding to this gas injection amount, and the test was conducted. . The pressure P ₂ in the vacuum chamber was calculated as 1 torr.

[0028]

[Table 2]

Next, the present inventors divide the amount of gas injected for circulation (horizontal axis) in FIG. 1 by each molten steel ring flow rate, and introduce a new amount of gas injected per ton of molten steel ring flow rate as an index. I arranged 1. The result is shown in FIG.

From FIG. 2, regardless of the flow rate of the molten steel ring,
Gas injection amount per ton of molten steel ring flow rate is 30 Nl /
It is saturated at min · ton, and even if it is blown in further, the reached [C] concentration is within a certain range and does not change. In other words, it has been found that efficient decarburization refining can be achieved by ensuring a gas blowing amount of at least 30 Nl / min · ton.

On the other hand, if the gas is blown in excessively, the amount of splash of molten steel splash increases, which leads to the extension of the processing time, the stop of production due to the removal of metal, and the reduction of the concentration [C] reached.

The inventors of the present invention obtained the exhaust amount H per ton of molten steel treated (this is obtained by dividing the exhaust amount by the tonnage of molten steel in the ladle for one heat (the amount of treated molten steel). The amount of splashing can be suppressed by controlling the value of 100) to 100 kg / Hr · ton or less. As a result,
It has been found that the ultimate [C] concentration does not decrease and the productivity does not decrease.

Here, the exhaust amount is the weight of air exhausted from the inside of the tank per unit time, and is a value calculated by converting into a standard state of 1 atm and 25 ° C.

Further, the present inventors set the gas injection amount per 1 ton of molten steel ring flow rate to 30 Nl / min · ton, and the exhaust capacity in each vacuum degree range is shown in Table 3 (left side of the table).
As a result of investigating the relationship between the exhaust gas amount H per ton of treated molten steel and the decarburization rate constant kc after decarburization refining with the exhaust pattern shown in Fig. 3, the relationship shown in Fig. 3 was found.

[0035]

[Table 3]

The decarburization rate constant kc is a value calculated by the following decarburization reaction rate equation (3).

DC / dt = -kc {[C]-[C] eq} (3) where [C] eq in the equation (3) is the equilibrium [C] concentration,
CO partial pressure in the vacuum tank during processing, free oxygen concentration in molten steel,
It is a value determined by the equilibrium constant K.

As shown in FIG. 1 to No. In 5, the degree of vacuum P is 300 torr or more from the start of the decarburization treatment,
In other words, the displacement in the range of P ≧ 300 is 15000.
〜25,000kg / Hr (This exhaust amount is divided by 250 tons of molten steel for one heat treatment, and the exhaust amount H per ton of treated molten steel is 60 to 100kg / Hr · ton.) Charcoal treated.

As a result, the decarburization rate constant kc increases as the exhaust capacity increases, but even if the decarburization rate constant kc is increased to 70 kg / Hr · ton or more, the decarburization rate constant kc becomes saturated and the decarburization rate does not increase. Found.

Heat No. 6-No. In No. 11, the exhaust capacity of vacuum degree P ≧ 300 is 80 kg / Hr · t in the present invention range.
When the degree of vacuum P was 300> P ≧ 200, the exhaust capacity was changed in the range of 30 to 80 kg / Hr · ton.

As a result, the decarburization rate constant kc increases as the exhaust capacity increases, but even if the decarburization rate constant kc is increased to 40 kg / Hr · ton or more, the decarburization rate constant kc becomes saturated and the decarburization rate does not increase. I found that.

Even in the range of vacuum degree P> 200, Table 3
The decarburization process was performed according to the exhaust pattern shown in. That is, the degree of vacuum P is in the range of 200> P ≧ 100 (heat Nos. 12 to N).
o. 16), the exhaust capacity is 25 kg / Hr · ton or more, and the vacuum degree P is 100> P ≧ 50 (heat No.
17-No. In 21), the exhaust capacity is 13 kg / Hr · t
On or higher, and the degree of vacuum P is 50> P ≧ 10 (heat N
o. 22-No. In 26), the exhaust capacity is 8 kg / Hr.
It was found that the decarburization rate constant kc saturates even if the decarburization rate is increased above ton and the decarburization rate does not increase.

Further, in the present invention, the upper limit of the exhaust capacity is 1 in the range of vacuum degree P ≧ 300 (heat No. 1 to No. 5).
The amount is set to 00 kg / Hr · ton or less. As mentioned above, this range is in the high carbon region, and if an exhaust capacity exceeding 100 kg / Hr · ton is applied, a decarburization promoting effect due to a sudden decrease in vacuum degree can be obtained, but at the same time an increase in the splash scattering amount is caused. This is because the ultimate [C] concentration cannot be reduced as a result.

Similarly, in the range where the vacuum degree P is 300> P ≧ 200 (heat Nos. 1 to 5), the upper limit of the exhaust capacity is 80 kg / Hr · ton or less, and the vacuum degree P is 200> P.
In the range of ≧ 100 (Heat No. 12 to No. 16), the exhaust capacity is 60 kg / Hr · ton or less, and the vacuum degree P is 1.
00> P ≧ 50 (heat No. 17 to No. 2)
In 1), the exhaust capacity is 30 kg / Hr · ton or less, and the vacuum degree P is in the range of 50> P ≧ 10 (heat No. 22 to N).
o. In 26), the exhaust capacity is set to 15 kg / Hr · ton or less. The reason is that the decarburization rate does not increase even if the exhaust capacity is further increased in each of the above-mentioned vacuum degree ranges, resulting in a vapor energy loss.

On the other hand, the degree of vacuum is constantly measured during the decarburization process by the vacuum gauge attached to the RH degasser. In the present invention, since the exhaust amount is controlled by using the degree of vacuum measured in real time as a refining index, it is possible to perform control with short delay time and high responsiveness. As a result, the amount of molten steel scattered can be suppressed while achieving a high decarburization rate, and it becomes possible to produce extremely low carbon steel with high productivity and reliability.

Further, when the circulating gas is blown from the lance, the blown gas is dispersed and rises in the entire riser pipe, so that local damage due to the gas is suppressed as compared with the case where the gas is blown from the tuyere. Therefore, the inner surface of the riser refractory is uniformly damaged, and the life of the riser increases.

Further, if the circulating gas is blown from both the tuyere and the lance, the riser pipe refractories are not damaged.
A larger amount of reflux gas can be blown. Therefore, even with a small volume RH in which only a small-diameter riser pipe is provided due to facility restrictions, it is possible to obtain a large molten steel ring flow rate and to produce extremely low carbon steel with high productivity.

[0048]

【Example】

Confirmation test 1: Investigation of the influence of the injection amount of the gas for recirculation Fig. 4 shows the situation in which ultra-low carbon steel is melted by performing vacuum decarburization refining using an RH vacuum decarburization facility with a processing capacity of 250 tons. Show.

Here, 1 is an RH vacuum chamber, 2 is a riser tube, 3
Is a downcomer pipe, 4 is an exhaust pipe, 5 is an alloy inlet, 6 is a gas inlet for recirculation, 7 is a gas bubble, 8 is a ladle, 9 is molten steel,
Reference numeral 10 is a slag, and 11 is a gas blowing pipe for reflux.

The circulating gas blowing tuyere 6 is provided so as to penetrate through the side wall of the rising pipe 2, from which Ar gas is blown, and the floating force of the gas bubbles 7 causes the molten steel to flow back as indicated by the arrow in the figure. Circulates between the tank and the ladle.

The components of 250 tonnes of undeoxidized molten steel, which was primarily refined in the converter, before the start of decarburization were set within the ranges shown in Table 1 as described above.

Exhaust capacity from decarburization to completion is 80k
g / Hr · ton, immersion pipe diameter (upward pipe 2, downward pipe 3
Both have the same diameter) and the injection amount of the reflux gas is shown in Table 4.
The flow rate of molten steel is uniformly set to 150 ton as shown in
/ Min.

[0053]

[Table 4]

Table 4 shows the carbon concentration obtained every 3 minutes during the decarburization treatment, and FIG. 5 is a graph showing the changes in the carbon concentration and the degree of vacuum in the tank.

From the results shown in FIG. 5, in Examples 1 and 2 satisfying the scope of the present invention, the decarburization treatment time was 15 minutes, and [C]
Ultra-low carbon steel having a concentration of 10 ppm or less was obtained, but in Comparative Examples 1 to 3 which do not satisfy the scope of the present invention, ultra-low carbon steel having a [C] concentration of 10 ppm or less cannot be obtained.

Confirmation test 2: Investigation of influence of exhaust pattern: Gas injection amount for circulation is 6000 Nl / min, immersion pipe diameter is 490 mm, molten steel ring flow rate is 150 ton, gas injection amount per 1 ton of molten steel ring flow rate is 40 Nl of the present invention.
/ Min · ton, decarburization treatment was performed by changing the steam flow rate of each booster and each ejector in order to obtain the exhaust capacity at each vacuum degree shown in Table 5, and the influence of the exhaust pattern was investigated. This result is shown in FIG.

[0057]

[Table 5]

As shown in FIG. 6, in Examples 3 and 4, an ultra-low carbon steel having a [C] concentration of 10 ppm or less was obtained after a decarburizing treatment time of 15 minutes, but Comparative Example 4 which does not satisfy the scope of the present invention. ~
In Comparative Example 9, an ultra low carbon steel having a [C] concentration of 10 ppm or less cannot be obtained.

Particularly, in Comparative Example 5, the exhaust capacity in the high carbon region where the degree of vacuum is 300 torr or more from the start of decarburization is 105 k.
In the case of g / Hr · ton, the initial decarburization rate is the highest, and it is reduced to 20 ppm in 9 minutes from the start of decarburization. However, after that, the decrease of the [C] concentration becomes slow, and an ultra-low carbon steel of 10 ppm or less cannot be obtained. The reason for this is that the splash scattering amount of the molten steel increases due to the amount of 100 kg / Hr · ton or more in the high carbon region, this melts out, and the [C] concentration is picked up.

Confirmation Test 3: Effect of Installation of Oxygen Burner FIG. 7 shows the oxygen burner 1 installed on the inner wall of the vacuum chamber during decarburization.
2 shows the situation in which oxygen gas is blown into the vacuum chamber to melt ultra-low carbon steel.

The test conditions were the same as in Example 1. After the vacuum reaches 200 torr, the flow rate of oxygen gas is 20
Blowing 00 Nm ³ / Hr for 5 minutes. As a result, the CO gas and oxygen gas generated by the decarburization reaction were combusted and the vacuum tank was heated and maintained at a high temperature, and the molten steel splash became even harder to adhere than in Example 1. As a result,
An extremely low carbon steel of 10 ppm or less could be melted more stably in 15 minutes.

Confirmation Test 4: Effect of Lance for Injecting Refluxing Gas FIG. 8 shows, as an embodiment of the present invention, a lance 13 for injecting a recirculating gas soaked in molten steel in a ladle just below an ascending pipe. Then, a state in which a circulating gas is blown from the lance 13 to carry out vacuum decarburization refining to produce an extremely low carbon steel is shown.

In the lance 13 used in this embodiment, the surface of a metal pipe is covered with an irregular refractory material, and the gas ejection port is arranged almost at the center of the ascending pipe opening and as close as possible as shown in the figure. . As a result, as in the case of the embodiment of FIG. 5 (when the circulating gas was blown from the tuyere), almost all of the blown inert gas could act as the circulating gas without leaking out of the rising pipe.

Further, if the pipe diameter of the lance 13 is enlarged, it is possible to blow a large amount of recirculation gas exceeding 6000 Nl / min with a single pipe, and a large flow rate can be flowed as compared with the riser tuyere.

[0065]

EFFECTS OF THE INVENTION According to the present invention, the gas injection amount for reflux is regulated according to the molten steel circulation flow rate, and the exhaust capacity during decarburization is regulated by using the vacuum degree measured in real time as a refining index. It is possible to secure the decarburization rate while securing the bath stirring amount, and also to suppress the splash amount of the molten steel splash. As a result, it becomes possible to provide a method for melting ultra-low carbon steel with high productivity and reliability.

[Brief description of drawings]

FIG. 1 is a diagram showing the influence of the amount of blown-in gas for recirculation on the reached [C] concentration.

FIG. 2 is a diagram showing the relationship between the amount of gas blown in per ton of molten steel ring flow rate and the reached [C] concentration.

[Fig. 3] Exhaust capacity and decarburization rate constant kc at each vacuum level
It is a figure which shows the relationship with.

FIG. 4 is a cross-sectional view showing a state in which an extra low carbon steel is melted by blowing a circulating gas from an ascending pipe tuyere.

FIG. 5 is a diagram for investigating the influence of the injection amount of the reflux gas on the [C] concentration transition in order to confirm the effect of the method of the present invention.

FIG. 6 is a diagram in which the influence of the exhaust pattern on the [C] concentration transition is investigated in order to confirm the effect of the method of the present invention.

FIG. 7 shows a situation in which oxygen gas is blown into the vacuum chamber from an oxygen burner provided on the inner wall of the vacuum chamber to melt the ultra-low carbon steel.

FIG. 8 is a view showing a situation in which a gas is blown from a lance immersed in molten steel in a ladle just below an ascending pipe to produce an extremely low carbon steel.

[Explanation of symbols]

 1 RH vacuum tank 2 Rise pipe 3 Downcomer pipe 6 Circulation gas blowing tuyere 8 Ladle 9 Molten steel 10 Slag 11 Circulation gas blowing pipe 12 Oxygen burner 13 Circulation gas blowing lance

Front Page Continuation (72) Inventor Manabu Tano 1-2-2 Marunouchi, Chiyoda-ku, Tokyo Nihon Steel Pipe Co., Ltd. (72) Inventor Junichi Fukumi 1-2-1 Marunouchi, Chiyoda-ku, Tokyo Nippon Steel Pipe Incorporated (72) Inventor Ryuji Yamaguchi 1-2-2 Marunouchi, Chiyoda-ku, Tokyo Nihon Steel Pipe Co., Ltd. (72) Inventor Hidetoshi Matsuno 1-2 1-2 Marunouchi, Chiyoda-ku, Tokyo (72) Inventor Tsuyoshi Murai 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nihon Steel Pipe Co., Ltd.

Claims (3)

[Claims] 1. A melting method of vacuum decarburizing and refining using an RH degassing device to melt ultra-low carbon steel, wherein a tuyere provided through a side wall of the rising pipe or directly below the rising pipe. Immerse in molten steel in a ladle, and inject deionizing gas of 30 Nl / min · ton or more per 1 ton of molten steel ring flow to advance decarburization reaction from a lance with a gas ejection port facing the opening of the rising pipe. A method for melting ultra-low carbon steel, characterized by: 2. A melting method in which ultra low carbon steel is melted by vacuum decarburization refining using an RH degasser, wherein an exhaust gas amount H per ton of treated molten steel is 100 kg / H.
A method for melting ultra-low carbon steel, characterized in that the decarburization reaction is allowed to proceed at a temperature of r · ton or less. 3. Exhaust volume H per ton of molten steel treated
(Kg / Hr · ton) is the vacuum degree P (t
The melting method of the ultra-low carbon steel according to claim 1, wherein the melting temperature is controlled within the following range according to the oror). (1) P ≧ 300, 100 ≧ H ≧ 70, (2) 300> P ≧ 200, 80 ≧ H ≧ 40, (3) 200> P ≧ 100, 60 ≧ H ≧ 25, (4) 100 > P ≧ 50, 30 ≧ H ≧ 13, (5) 50> P ≧ 10, 15 ≧ H ≧ 8.