JPH02267213A - Method for vacuum-decarbonizing molten steel - Google Patents

Abstract

PURPOSE:To accelerate decarbonizing velocity at the extremely low carbon range (C<80ppm) and to lower decarbonizing lower limit by blowing inert gas of Ar, N2, etc., into molten steel during decarbonization of the molten steel from side blow tuyeres arranged to submerged part into molten steel in an RH vacuum vessel. CONSTITUTION:The side blow tuyeres 4 are set at side wall in the vacuum vessel 1 so as to position these below the molten steel 5 surface in the vessel. The tuyeres 4 are set at e.g. four pieces or three pieces at suitable interval in circumferential wall of the vacuum vessel 1. Then, in this vessel 1, the inert gas of Ar, N2, etc., is blown from the tuyeres 4 during decarbonization of the molten steel. By this method, the molten steel 5 in the vacuum vessel 1 is stirred and the decarbonizing velocity is risen because of increase of reaction area.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application This invention relates to a method for decarburizing molten steel using an R1-1 vacuum degassing device, particularly for increasing the decarburization rate in the extremely low carbon range (C<80pan). The present invention relates to a vacuum decarburization method for lowering the decarburization limit value.

Conventional Technology Generally, DH equipment and RH equipment are used for vacuum processing of molten steel.

In DH equipment, a vacuum tank with one immersion tube is immersed in a ladle of solid solution steel, the pressure inside the tank is reduced to suck up the molten steel, and the vacuum tank itself is roughly moved up and down to create a flow of molten steel and degas it. Vacuum treatment is performed in a manner that promotes.

On the other hand, in the R1-1 equipment, a vacuum tank with two immersion tubes is immersed in molten steel, the pressure inside the tank is reduced and the molten steel is sucked up, and the one of the two immersion tubes that sucks up the molten steel is connected to the riser tube. , the other is made to function as a molten steel downcomer pipe, and molten steel is circulated between the ladle and the vacuum tank to perform vacuum degassing treatment.

In this RH vacuum degassing process, it is common and necessary to blow inert gas from the riser pipe and use the buoyancy of the gas to assist the circulation of the molten steel (Japanese Patent Laid-Open No. 55-161023
Publication No. Minoru).

By the way, recently, steel sheets for deep drawing, electric! There is an increasing demand for ultra-low carbon steels such as i-steel plates to improve deep drawing value and elongation.

However, the RH decarburization limit in the current CV-RH-CC process is about 15 ppm on average, and the decarburization rate rapidly decreases from about 0.5 ppm, so an extension of the processing time is unavoidable.

The main cause of the decrease in the decarburization rate in this extremely low carbon region is the decrease in the reaction interface area.If the reaction interface area is secured sufficiently, a C value close to the parallel value can be obtained, and the decarburization rate can be improved. It can be measured.

However, with the method of injecting inert gas from the riser pipe implemented in RH equipment, although the molten steel circulation effect can be obtained,
Since the molten steel stirring effect in the vacuum chamber is low, a sufficient reaction interface area cannot be secured. Furthermore, since this method blows gas into a narrow immersion tube, there is also the problem that blow-by occurs when gas is blown in an amount exceeding a critical gas amount, and the molten steel circulation speed is restricted.

Note that Japanese Patent Application Laid-open No. 56-44711 discloses a method of blowing CO2 gas through tuyeres or bricks provided below the bath surface of a vacuum tank; The purpose is to cause an endothermic reaction and extend the life of the refractories in the vacuum chamber, and it is not intended to stir molten steel in the vacuum chamber, so it has little effect on improving decarburization efficiency. do not have.

Problems to be Solved by the Invention The present invention solves the problem of a decrease in the reaction interface area, which is the cause of the decrease in the decarburization rate in the extremely low carbon range, in a method for decarburizing molten steel using RH vacuum degassing equipment, and This paper attempts to propose a vacuum decarburization method for molten steel that can increase the decarburization rate in the low carbon region and lower the decarburization limit value.

Means for Solving the Problems In the vacuum decarburization method of molten steel according to the present invention, a horizontal blowing tuyere is provided in the molten steel immersion part of the RH vacuum tank, and an inert gas such as Ar or N2 is injected from the tuyere during decarburization of the molten steel. The purpose is to lower the decarburization limit value in the ultra-low carbon range (C<aoppm) by injecting C into molten steel.

Effect R)-f Ar
By injecting an inert gas such as , N2, etc. into molten steel decarburization, the molten steel in the vacuum chamber is agitated, and as a result, a sufficient reaction interface area is ensured and the IIR coal velocity is increased.

Embodiment FIGS. 1 and 2 show R for carrying out the method of this invention.
FIG. 1 is a schematic diagram showing a vacuum chamber; FIG. 1 is a front view, and FIG. 2 is a plan view, in which (1) is a vacuum chamber, (2) is an ascending pipe, (3) is a downcomer pipe, and (4) is a free pipe. This is a side blowing tuyere for active gas injection.

That is, when carrying out the method of this invention, a vacuum chamber (1
) A horizontal blowing tuyere (4) is installed on the side wall of the tank so that it is below the bath surface of the molten steel (5) in the tank. For example, four or three horizontal blowing tuyeres may be installed at appropriate intervals on the peripheral wall of the vacuum chamber. Of course, the number of tuyeres is not limited, but in order to enhance the effect of stirring the molten steel in the vacuum chamber, it is preferable to install a plurality of tuyere at equal intervals.

In the vacuum chamber (1), the side blowing tuyere (
When an inert gas such as Ar or N2 is blown from step 4), the solution 1i11(5) in the vacuum chamber is stirred, the reaction interfacial area increases, and the decarburization rate increases.

Next, RH vacuum ll? :L Four horizontal blowing tuyeres were installed in the vacuum chamber of the gas equipment as shown in Figure 1, and a total of 533 kg/dish of A was blown from these four tuyeres during decarburization. As shown in the figure.

For comparison, FIG. 3 shows the results of decarburization (conventional example) without blowing Ar gas through the side blowing tuyere.

As is clear from Figures 2 and 3, 1. By injecting K from the side wall of the vacuum chamber, the decarburization rate decreases only slightly in the extremely low carbon range, and the achieved C is less than 10 pplT1, which is lower than in the conventional case where Ar is not injected.

In addition, IPco was previously required to be 0.03 atm, but
Due to Ar agitation in the tank, the temperature has decreased to O, Olatm.

Although it is still higher than PCQ O,004atm calculated from the vacuum degree in the tank, by increasing the number of tuyeres and performing strong stirring in the tank, Pco can be lowered, reducing the amount of C reached and eliminating The charcoal speed will be improved.

As described in detail of the invention, according to the method of this invention, the solid solution in the vacuum tank is stirred by blowing inert gas through the side blowing tuyere provided on the side wall of the vacuum tank of the RH vacuum degassing equipment. As a result, it is possible to secure a sufficient reaction interface area, increase the decarburization rate in the ultra-low carbon range, and lower the decarburization limit value, making it suitable for the production of ultra-low carbon steel. It has great effects.

[Brief explanation of drawings]

Figure 1 shows the method of this invention in practice/Jf! R for i]-
1 is a schematic plan view showing a vacuum chamber, FIG. 2 is a schematic plan view of the same vacuum chamber, FIG. 3 is a view showing a decarburization situation in an embodiment of the present invention, and FIG. 4 is a diagram showing the same (conventional decarburization situation) FIG. 1...Vacuum chamber 2...Rising pipe 3...
・Downcomer pipe 4...Side blowing tuyere 5...
Molten Steel Agent Patent Attorney Yoshihisa Oshida Figure 3 Time (min) Figure 1 Figure 2 Figure 4 Time (min)

Claims (1)

[Claims] A horizontal blowing tuyere is provided in the molten steel immersion part of the RH vacuum tank, and inert gases such as Ar and N_2 are blown into the molten steel through the tuyere during decarburization of the molten steel. A vacuum decarburization method for molten steel characterized by lowering the decarburization limit value.