JPH02122013A - Method for degassing and dephosphorizing molten steel - Google Patents

Abstract

PURPOSE:To avoid mutual interference of decarbonizing reaction and dephosphorizing reaction and to efficiently execute the dephosphorization with a little quantity of the dephosphorizing agent by controlling vacuum degree in a vessel in accordance with [C] at the time of executing the dephosphorization in molten steel by injecting the dephosphorizing agent. CONSTITUTION:The powdery dephosphorizing agent is sent from a dephosphorizing agent supplying device 7 through a powder supplying pipe 6 during vacuum degassing treatment, and injected into molten steel, which is not yet deoxidized (free oxygen >100ppm) 3, from a tuyere 5 to execute the dephosphorization in the molten steel 3. Then, by setting an evacuating equipment 10 in accordance with [C] level in the molten steel 3 at 'on' or 'off' to adjust suction gas quantity, the vacuum degree in the vessel 1 measured with a vacuum degree measuring instrument 9 is controlled in the prescribed optimum control range to execute the degassing and dephosphorizing treatment. By this method, the dephosphorization can be efficiently executed with a little quantity of the dephosphorizing agent.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention is directed to ultra-low phosphor steel (for example, (P) <50 ppm).
) is produced by dephosphorizing it at the molten steel stage, or when the (P) level of molten steel is
) When the level is high and it is necessary to dephosphorize molten steel to the quality required level, it is possible to efficiently dephosphorize molten steel by controlling the degree of vacuum in the degassing tank according to the [C] level in vacuum degassing equipment. It's about how to do it.

(Prior Art) As a conventional method for dephosphorizing molten steel using a vacuum degassing tank, there is a method described in JP-A-62-205221 (Method for degassing and dephosphorizing molten steel). Free oxygen 100%
~800ppm? It is characterized by injecting a powder film phosphor into No. 6 steel. However, according to this method, the decarburization reaction occurs simultaneously with the dephosphorization reaction due to the characteristics of the vacuum degassing equipment.

In other words, as shown below, since both decarburization and dephosphorization reactions are oxidation reactions, they compete with each other for free oxygen in the molten steel in the degassing tank, and as a result, the dephosphorization reaction rate decreases. .

Decarburization reaction Cto0-CO Dephosphorization reaction dCaO+2P + 50 = 4CaO・PzOs(
Problems to be Solved by the Invention) The present invention solves the disadvantage of the prior art in that the decarburization reaction and the dephosphorization reaction occur simultaneously and compete for oxygen with each other, reducing the dephosphorization rate. This problem is overcome by controlling the degree of vacuum in the tank according to the [C] level to preferentially perform dephosphorization under conditions where decarburization and dephosphorization reactions do not compete with each other.

(Means for Solving the Problems) The gist of the present invention is to dephosphorize molten steel by blowing a dephosphorizing agent into undeoxidized molten steel (free oxygen > 10,100 pp) in a vacuum degassing tank, depending on the [C] level. This is a method for degassing and dephosphorizing molten steel, which is characterized in that the degree of vacuum in the degassing tank is controlled to perform degassing and dephosphorizing treatment.

That is, the present invention solves the above-mentioned problems of the prior art when dephosphorizing molten steel by blowing a dephosphorizing agent into it.
C) Control the degree of vacuum in the degassing tank during dephosphorization agent injection according to the level to avoid competition between decarburization and dephosphorization reactions,
This problem can be solved by improving the dephosphorization rate.

Next, an example of the present invention will be described in detail based on FIG.

Figure 1 shows an example of RH vacuum degassing equipment, where l is a vacuum degassing tank, 2 is an exhaust hole, 3 is molten steel, 4 is a ladle, 5 is a body dephosphorizing agent injection panel, and 6 is a A powder supply pipe, 7 a dephosphorizing agent supply device, 8 a carrier gas body, 9 a vacuum degree measuring device in a degassing tank, and 10 a vacuum evacuation facility.

In the present invention, a dephosphorizing agent is blown into the molten steel 3 from the powder blowing tuyere 5 through the powder supply pipe 6 from the dephosphorizing agent feeding device 7 during the vacuum degassing process, and the molten steel 7j! When performing dephosphorization, depending on the [C] level of the container, the vacuum evacuation equipment 10 (ejector, etc.) is turned on and off, and the amount of suction gas is adjusted to maintain the vacuum level in the tank 11. This is to control the degree of vacuum measured at. At this time, the free oxygen level should be 100 to 800 ppm for the sake of reaction efficiency, and
Refractories) desirable from the perspective of preventing damage.

Figure 2 shows the optimal control range for the [C] level and the degree of vacuum in the chamber.
, 5] torr [C] ≧ 40 ppm, the degree of vacuum > (100, Oxzog [C] ppm-1
20,0) torr. That is, [
C] At extremely low carbon levels <40 ppm, the decarburization reaction stagnates even under high vacuum conditions, so the dephosphorization reaction occurs efficiently even under high vacuum conditions. However, 40ppm≦[C]
In the range of , the decarburization reaction occurs even in a low vacuum state, so it is necessary to control the degree of vacuum to a low level in order to efficiently perform the dephosphorization reaction. Here, high [C] material (for example, [C] = 0.15
%), it is impossible to completely eliminate the decarburization reaction even if the degree of vacuum is controlled, and carburization with a carburizing agent must be carried out after the dephosphorizing agent has been injected. At this time, if a recarburizing agent is added during the dephosphorizing agent injection, the free oxygen level in the tonne steel will be lowered, and therefore the dephosphorizing rate will be lowered.

Therefore, for high (C) materials, the lower the degree of vacuum during dephosphorization, the better.On the other hand, if the powder blowing surface is not immersed in the molten steel, the blown powder may float on the surface of the molten steel, or the vacuum exhaust equipment The dephosphorization efficiency deteriorates because the tuyere is sucked in and does not contribute to the dephosphorization reaction.Therefore, the degree of vacuum in which the tuyere is immersed is the lowest degree of vacuum, and there are slight differences depending on the installation position of the tuyere.

(Example) FIG. 3 shows an example in which the dephosphorization rates of the conventional technique and the method of the present invention are compared under the following conditions. This example is based on quality requirements [C
] Level 5 oppm 25OL molten steel (free oxygen-4
50ppm), dephosphorizing agent (65%Cab-35%
CEIF2) at 1 OONm3/h with r gas.
The dephosphorization behavior when 4 kg/min was blown at a rate of 0.00 kg/min was compared twice with the vacuum degree controlled to 1 torr and the case where it was controlled to 8 Q torr based on the present invention. It is.

As shown in FIG. 3, by applying the present invention and controlling the degree of vacuum, a significant effect of improving the dephosphorization rate can be obtained. This makes it possible to escape stably even when the initial stage (P) is higher than before.
The number of dephosphorizing agent layer units required to obtain the phosphorizing effect is reduced, the temperature drop of molten steel due to the dephosphorizing agent is also reduced, and the dephosphorizing agent injection time is also shortened.
The H treatment time can also be shortened, making it possible to significantly reduce molten steel dephosphorization costs.

(Effects of the Invention) According to the present invention, when dephosphorizing molten steel in a vacuum degassing device, dephosphorization can be performed efficiently with less dephosphorizing agent compared to conventional methods. It becomes possible to reduce the amount of molten steel and the associated drop in molten steel temperature, and to shorten the RH treatment time, making it possible to significantly reduce dephosphorization treatment costs.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an example of an apparatus to which the present invention is applied, FIG. 2 is a diagram specifically showing the limited range of the present invention, and FIG. 3 is a diagram comparing the effects of the present invention with conventional methods. ! 030 gu00 [C] (pp)71)

Claims (1)

[Claims] Undeoxidized molten steel in a vacuum degassing tank (free oxygen > 100 pp
When dephosphorizing molten steel by blowing a dephosphorizing agent into m),
C] A method for degassing and dephosphorizing molten steel, characterized by performing degassing and dephosphorization by controlling the degree of vacuum in the degassing tank according to the level.