JP2998038B2 - Manufacturing method of ultra-low carbon steel - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an RH recirculation type degassing apparatus (hereinafter, referred to as RH), wherein carbon in molten steel (hereinafter, referred to as RH).
[C]) is extremely small, for example, 0.001 w
The present invention relates to an efficient and economical method for removing ultra-low carbon steel up to t%.

[0002]

2. Description of the Related Art In RH, a method of blowing an inert gas into molten steel in a vacuum chamber is often used to increase a degassing rate. The method disclosed in Japanese Patent Application Laid-Open No. 57-110611 is one example. In this method, a gas outlet is provided at the bottom of the vacuum tank, and an inert gas is blown into the molten steel from the gas outlet to promote decarburization. In addition, a method of blowing an inert gas from a gas outlet provided on a side wall of the vacuum chamber may be used.

[0003]

In the method of blowing an inert gas into molten steel from a gas outlet installed on the bottom or side wall of a vacuum chamber, in order to prevent molten steel from entering the gas outlet, While the gas jet is immersed in the molten steel,
The gas must always flow. Therefore, the cost of degassing increases due to an increase in the amount of inert gas used and an increase in the amount of water vapor used to increase the amount of evacuation. Furthermore, large gas injection in the high carbon concentration region
[C] Pick-up which promotes splash generation and re-dissolves the metal adhered to the inner wall of the vacuum chamber makes it difficult to produce ultra-low carbon steel.

On the other hand, according to a method in which a porous plug is provided at the bottom of the vacuum chamber and an inert gas is blown, the inert gas can be blown only when necessary, so that the above-mentioned problems can be prevented. . However, when injecting gas using a porous plug, it is difficult to inject sufficient gas to increase the decarburization rate because the upper limit of the gas injection flow rate is limited.

[0005]

In order to solve the above-mentioned problems, the gist of the present invention is to decarburize RH.
In performing the treatment, a lance that can change the height of the lance is installed on the vacuum tank canopy. In the [C] concentration range from the start of the decarburization treatment to the [C] concentration of 0.005 wt%, the lance is placed in the molten steel. The decarburization treatment is performed without immersion and without flowing gas from the lance, and when the [C] concentration is in the [C] concentration range of 0.005 wt% or less, the lance is viewed from above the vacuum tank.
Of common tangent lines of two dip tubes that do not cross each other and of the dip tubes
A method for producing an ultra-low carbon steel, characterized by immersing the molten steel in a section of the vacuum chamber except for a portion surrounded by the periphery and blowing an inert gas into the molten steel.

[0006]

Hereinafter, the present invention will be described in detail. In RH, when the [C] concentration is higher than 0.005 wt%,
Even if Ar gas is blown into the vacuum chamber, the amount of increase in the decarburization rate is small. That is, in this [C] concentration region, the amount of CO gas generated from inside the molten steel by the decarburization reaction is much larger than the flow rate of the blown gas. The contribution of the increase in the area and the increase in the stirring of the molten steel to the promotion of decarburization is very small. Therefore, in the [C] concentration region, blowing the inert gas not only increases the amount of the inert gas used and the amount of steam used for evacuation, increases the decarburization processing cost, but also increases the splash. An increase in the amount of [C] pick-up due to an increase in the amount of generation causes a reduction in the apparent decarburization rate and an increase in the attained [C] concentration.

On the other hand, in the [C] concentration range where the [C] concentration is 0.005 wt% or less, the amount of generated CO bubbles is reduced, and the area of the gas-liquid reaction interface is reduced and the stirring power of molten steel is reduced. Speed decreases. In this region, blowing an inert gas into the molten steel in the vacuum chamber is effective for increasing the area of the gas-liquid reaction interface and increasing the stirring force of the molten steel, thereby increasing the decarburization rate. In particular, blowing the inert gas into a portion near the inner wall of the vacuum tank where the flow of the molten steel is relatively small to stir the molten steel is effective for promoting decarburization.

Hereinafter, the present invention will be described in detail based on an embodiment shown in the drawings. 1 and 2 are longitudinal sectional views of an RH embodying the present invention. The two immersion tubes 2A and 2B at the lower end of the vacuum chamber 1 are immersed in the molten steel 3, evacuated from the exhaust port 4, and blown with an inert gas from the gas inlet 5 provided in the middle of the immersion tube 2A. In a device for sucking and circulating molten steel 3 into the vacuum chamber 1, a lance 6 for blowing an inert gas is provided on the canopy of the vacuum chamber 1.

In performing decarburization of molten steel using the present apparatus, the concentration of [C] is 0.005 wt% from the start of decarburization.
Up to this point, as shown in FIG.
The decarburization treatment is performed without immersion in the inert gas and without flowing an inert gas. In the [C] concentration range where the [C] concentration is 0.005 wt% or less, as shown in FIG. While immersing it in the molten steel 7 in the vacuum chamber
Degassing treatment is performed by blowing inert gas. Here, FIG. 3 is a view of the cross section of the vacuum tank viewed from above, and a hatched portion in FIG. 3 indicates a portion surrounded by a common tangent line which does not intersect with each other and the inner periphery of the dip tube. It is a vacuum tank cross-section removed.

In the method of the present invention, the flow rate of the inert gas blown from the lance 6 into the molten steel 7 is shown in FIG. 4 in comparison with the conventional method. According to the method of the present invention, the amount of inert gas blown into the vacuum chamber can be significantly reduced. Since the flow rate of the inert gas blown into the vacuum chamber can be reduced, the amount of evacuation can be reduced, and the amount of water vapor used for evacuation can be reduced.

Further, in the method of the present invention, an inert gas is not blown into the molten steel in the vacuum chamber at an early stage of the decarburization treatment, so that the amount of generated splash is small and the amount of metal adhered to the inner wall of the vacuum chamber is small. Therefore, [C] from bullion at the end of decarburization
Pickup is also small. Further, the molten steel can be agitated by blowing an inert gas into a portion of the molten steel in the vacuum chamber where the flow is relatively small. As a result, as shown in FIG. 5, in the [C] concentration range where the [C] concentration is 0.0025 wt% or less, the decarburization rate apparently increases and the attained [C] concentration also decreases.

As described above, in order to reduce the amount of inert gas used and the amount of water vapor to be used to melt ultra-low carbon steel, the inert gas must be constantly evacuated during the decarburization process as in the conventional method. It is not possible to cope with the method of blowing into molten steel in the tank, and it is more advantageous to cope with the method of blowing an inert gas into the molten steel in the vacuum tank as necessary, as in the method of the present invention.

[0013]

EXAMPLES The initial component was [C]; 0.04 wt%, [S
i]: 0.01 wt% or less, [Mn]: 0.05-0.
2 wt%, [P]: 0.005 to 0.02 wt%,
[S]: 0.003 to 0.015 wt%, [Al];
RH of 300 tons of molten steel at 0.001 wt% or less
The decarburization treatment was performed using.

As shown in FIG. 4, the lance 6 installed on the canopy of the vacuum tank 1 is immersed in the molten steel 7 in the vacuum tank for about 8 minutes from the start of the decarburization treatment until the [C] concentration reaches 0.005 wt%. Decarburizing without flowing inert gas,
[C] When the concentration is 0.005 wt% or less,
Was immersed in the molten steel 7 and the Ar gas was blown into the molten steel at 2000 Nl / min. 2 from the start of the decarburization process
Table 1 shows the amount of water vapor used for 0 minute, and FIG. 5 shows the change over time of the [C] concentration.

Comparative Example 1 is a case where Ar gas was blown into molten steel at the flow rate of 2000 Nl / min from the start of the decarburization process from a gas outlet installed at the bottom of the vacuum chamber. The Ar gas flow rate for reflux was set to 2000 Nl / min. Comparative Example 2
The lance 6 installed on the canopy of the vacuum tank 1 is not immersed in the molten steel 7 in the vacuum tank for about 8 minutes from the start of the decarburization treatment until the [C] concentration reaches 0.005 wt%, and inert gas is removed. The decarburization treatment was performed without flowing, and the lance 6 was not melted at the concentration of [C] of 0.005 wt% or less and the lance 6 was not shaded in FIG.
In this case, 2000 Nl / min of Ar gas was blown into the molten steel.

As shown in Table 1, according to the method of the present invention, the amount of use of Ar gas and the amount of water vapor are reduced as compared with Comparative Example 1, and as shown in FIG. 5 as compared with Comparative Examples 1 and 2. Thus, molten steel having a lower [C] concentration could be produced.

[0017]

[Table 1]

[0018]

According to the method of the present invention, the amount of inert gas and water vapor used during decarburization treatment in RH is reduced, and ultra-low carbon steel having a [C] concentration of 0.001 wt% or less can be easily melted. Can now be manufactured.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing an embodiment of the present invention (a step of performing a decarburization treatment without dipping a lance in molten steel in a vacuum chamber and flowing an inert gas).

FIG. 2 is an embodiment of the present invention (a step of immersing the lance in molten steel in a vacuum chamber in a hatched portion in FIG. 3 and blowing an inert gas to perform a decarburization treatment). FIG.

FIG. 3 is a view of a cross section of the vacuum chamber seen from above.

FIG. 4 is a diagram showing a change with time of an inert gas blowing flow rate into molten steel in a vacuum chamber according to the present invention and a comparative example.

FIG. 5 shows [C] in Examples and Comparative Examples of the present invention.
It is a figure which shows a time-dependent change of density | concentration.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Vacuum tank 2A Dip pipe 2B Dip pipe 3 Molten steel 4 Exhaust port 5 Gas inlet for recirculation 6 Lance 7 Molten steel in vacuum tank 8 Molten steel ladle

──────────────────────────────────────────────────の Continued on the front page (72) Inventor Muneyasu Nasu 1 Kimitsu, Kimitsu City, Chiba Prefecture Inside Nippon Steel Corporation Kimitsu Works (72) Inventor Shigeaki Ogibayashi 1 Kimitsu, Kimitsu City, Chiba Prefecture New Japan (56) References JP-A-1-246314 (JP, A) JP-A-2-217412 (JP, A) JP-A-53-92319 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) C21C 7/10 C21C 7/068

Claims (1)

(57) [Claims] In the RH recirculation type degassing apparatus, a lance capable of changing a lance height is installed on a vacuum tank canopy to perform a decarburization process, and the concentration of [C] is 0.005 wt. %, The lance is not immersed in the molten steel, and decarburization is performed without flowing gas from the lance. In the [C] concentration range where the [C] concentration is 0.005 wt% or less, , Looking at the lance from above the vacuum chamber
Of common tangent lines of two dip tubes that do not cross each other and of the dip tubes
A method for producing ultra-low carbon steel, characterized by immersing the molten steel in the cross section of the vacuum chamber excluding the part surrounded by the periphery and blowing an inert gas into the molten steel.