JPH03281720A - Production of dead-soft carbon steel - Google Patents

Abstract

PURPOSE:To stably produce a molten dead-soft carbon steel in a short time by evacuating the inside of a vacuum degassing tank and changing the blowing depth of an inert gas according to the [C] concentration in a molten gas at the time of carrying out vacuum refining by blowing the inert gas into the molten steel in a ladle combined with the vacuum degassing tank. CONSTITUTION:Vacuum refining is carried out by blowing an inert gas via a blowing lance 5 into an undeoxidized molten steel 2 in a ladle 1 combined with a vacuum degassing tank. At this time, the inside of the vacuum degassing tank is evacuated and the blowing depth of the inert gas into the undeoxidized molten steel 2 is changed according to the [C] concentration in the molten steel 2, and further, the inert gas is blown at a flow rate of blowing gas of 5-16Nl/min.ts so that h/H is regulated to 0.5-0.8 in a high carbon concentration region of >=30ppm [C] and also h/H is regulated to 0.05-0.15 in a region of <30ppm [C] when H represents the distance between a vacuum interface 3 and a ladle bottom 4 and (h) represents the distance between the vacuum interface 3 and a gas blowing hole 6 of the inert gas blowing lance 4. By this method, the molten dead-soft carbon steel can be stably produced in a short time.

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Industrial Application" The present invention relates to a method for producing ultra-low carbon steel using a micro-pressure refining apparatus.

"Conventional technology" Conventionally, as a manufacturing method for ultra-low carbon steel, an RH circulation type vacuum degassing treatment device is used to blow inert gas into undeoxidized molten steel and circulate the molten steel in a vacuum chamber. This has led to decarburization in molten steel. In order to improve the decarburization reaction efficiency when processing molten steel, the diameter of the immersion pipe is increased.
Emphasis has been placed on increasing the flow rate of molten steel by increasing the flow rate of circulating Ar gas, as well as increasing the stirring power of the molten steel. As an example, a vacuum degassing treatment device described in JP-A-57-110611 has been developed. Are known.

As shown in FIG. 4, this device has a gas jet port 11 located at the bottom of a vacuum tank 8 and between the open ends of the tank 9A and 9B.
The amount of molten steel (height) in the vacuum chamber is 50
The gas outlet 11 under the condition of increasing from 0 to 1000 mm.
By injecting 500 to 2000 Np/sin of an inert gas such as Ar and a neutral or oxidizing flux into the molten steel, the molten steel 2 is promoted to form droplets and the exposed area in the vacuum chamber is increased. This is intended to effectively promote decarburization.

[Problems to be Solved by the Invention] In the conventional ultra-low carbon steel production equipment described above, in order to increase the decarburization efficiency (specifically, to shorten the decarburization treatment time and to reduce the concentration achieved in ultra-low carbon steel) (reduction), the amount of molten steel in the vacuum chamber is increased, and the flow rate of gas blown from the gas outlet 11 is increased to expand the reaction area of molten steel. However, in this method, there is an upper limit to the flow rate of the blown gas for promoting the decarburization reaction, and when the upper limit is exceeded, gas blow-through occurs, and the reaction area with molten steel is conversely reduced. This method of blowing inert gas into the bottom of the molten steel (recirculation) and from the open end has an upper limit on the gas flow rate so that gas blow-through does not occur, so there is a limit to the decarburization efficiency -F, and the vacuum Tank bottom.

Gas or gas+ from upwards (towards the exhaust port)
Because Franks is injected, metal is scattered not only inside the vacuum chamber but also into the gas cooler of the vacuum evacuation equipment, making it virtually impossible to operate.

As a means of overcoming the drawbacks of the prior art, the present inventors have developed an undeoxidized solution in the ladle in combination with a vacuum degassing tank, as shown in FIGS. 2 and 3. We invented a method for vacuum refining by blowing inert gas or other gas into a TJ net under limited operating conditions, but as a result of further research, we decided to change the immersion depth of the lance depending on the [C] concentration in the molten steel. We have discovered that it is possible to produce ultra-low carbon steel more efficiently by doing this.

"Means for Solving the Problems" The present invention advantageously solves the drawbacks of the prior art as described above, and the gist thereof is as follows.

(1) In a method of blowing gas such as an inert gas into the molten steel in a ladle combined with a vacuum degassing tank to reduce the pressure, the pressure inside the vacuum degassing tank is reduced and the deoxidization of the undeoxidized steel is A method for producing ultra-low carbon steel, characterized in that the depth of active gas injection is changed depending on the [C] concentration in molten steel.

(2) At a blowing gas flow rate of 5 to 16 N e /5 in-ts, in the high carbon concentration region of [C] ≧ 30 ppm, in the range of h/H = 0.5 to 0.8, (C] < 3
The method for producing ultra-low carbon steel according to the above item I, characterized in that in the 0 ppm region, inert gas is blown in a range of h/H = 0.05 to 0.15.

However, H - Distance between the vacuum interface and the bottom of the ladle h = Distance between the vacuum interface and the gas outlet of the inert gas blowing lance, that is, in the present invention, the ladle-shaped molten steel installed in the vacuum chamber is exposed to the upper part under a reduced pressure atmosphere. The decarburization reaction is promoted by injecting more inert gas and reducing the gas injection depth at the final stage of decarburization to promote the formation of molten steel droplets and increase the air-liquid interface area within the vacuum chamber.

The present inventors investigated and examined the influence of various factors on the decarburization rate under reduced pressure. As a result, as shown in Fig. 1, the decarburization rate changes under reduced pressure in one region where the decarburization rate is high at [C]≧30ppn+, and at [C]〈30ppm, the decarburization rate is low and decarburization stagnates. II iJf region, and in one region, the decarburization promotion means is to deepen the gas injection depth and increase the gas injection amount to increase the uniform mixing time τ.
In the II jJf region, it was found that it is effective to reduce the gas injection depth, increase the amount of gas injection, increase the amount of splash generation, and increase the gas-liquid interface area in the vacuum chamber. . Furthermore, even if the gas flow rate is the same, the larger the gas injection depth h, the smaller the value, and if b is small and the gas is blown near the vacuum interface, τ
It was found that the amount of splash generated increases as the amount of water increases.

The details of the present invention will be described below.

In the present invention, so-called ordinary non-deoxidized steel is used as the molten steel.

First, a ladle containing molten steel is combined with a vacuum degassing tank. In this case, the premise is that it is possible to blow inert gas into the molten steel on the device in parallel with the vacuum degassing treatment.

The inside of the vacuum degassing tank first begins to be depressurized and reaches a normal vacuum state. Inert gas is blown into the molten steel approximately in parallel with these pressure reduction processes.

That is, at a blowing gas flow rate of 5 to 16 N 127 IIlin-ts, h/H = 0.5 to 0.8 in the high carbon concentration region of [C] ≧ 30 ppm, and h / H = 0.5 to 0.8 in the region of [C] < 30 ppm. h/H=0.05
This is a method for producing ultra-low carbon steel in a short time and stably by blowing inert gas in the range of 0.15 to 0.15.

Although the decarburization rate increases by increasing the blowing gas flow rate, the amount of metal flowing out becomes noticeable due to the shaking of the molten steel and the increase in the amount of splash generated due to the increase in stirring force.
In practice, the blowing gas flow rate is 5 to 16 Nj2/m1n=t
It is regulated within the range of s.

Note that if the Ar gas blowing depth becomes extremely deep, the erosion of the paving bricks on the ladle bottom 4 will be severe, so it is necessary to set h/H≦0.8 to avoid having a negative effect on the paving bricks. be.

Note that the present invention has an improvement effect not only on decarburization but also on degassing such as dehydrogenation.

"Operation and Examples" Next, an example and a comparative example according to the method of the present invention are shown in FIG. FIG. 1 shows the progress of decarburization in an example of molten steel of 300 t/ch, and is compared with the conventional technology.

"Effects of the Invention" As described above, according to the present invention, it is possible to stably produce ultra-low carbon molten steel.

[Brief explanation of drawings]

Fig. 1 is a diagram showing an embodiment of the present invention in comparison with the prior art, Figs. 2 and 3 are explanatory diagrams showing embodiments of the processing method according to the present invention, and Fig. 4 is a diagram showing the processing method according to the prior art. It is an explanatory diagram showing an embodiment. 1... Ladle, 2... Undeoxidized molten steel, 3... Vacuum interface, 4... Ladle bottom, 5... Inert gas blowing lance, 6... Inert gas blowing lance. Gas outlet, 7... Splash prevention lid, 8... RH vacuum chamber,
9A...Suction pipe, 9B...Down pipe, 10...
Inert gas outlet, 11...Inert gas outlet. Time 0 minutes) Figure Figure 3

Claims (2)

[Claims] (1) In a method of vacuum refining by blowing a gas such as an inert gas into the molten steel in a ladle combined with a vacuum degassing tank, the pressure inside the vacuum degassing tank is reduced and the inert gas is injected into the undeoxidized molten steel. A method for producing ultra-low carbon steel, the method comprising changing the blowing depth according to the [C] concentration in molten steel. (2) At a blowing gas flow rate of 5 to 16 Nl/min・ts, in the high carbon concentration region of [C]≧30 ppm, h
Claim 1, characterized in that inert gas is blown in the range of /H = 0.5 to 0.8, and in the range of h/H = 0.05 to 0.15 in the region of [C] < 30 ppm. The method for manufacturing the ultra-low carbon steel described. However, H = distance between the vacuum interface and the bottom of the ladle h = distance between the vacuum interface and the gas outlet of the inert gas blowing lance