JPS6037847B2 - Molten steel refining method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for refining molten steel for obtaining copper (low P steel) with an extremely low phosphorus (P) content in a short time and at low cost.

Conventionally, a converter blowing method has been known as a means for obtaining low P steel.

As the converter blowing mirror method, the ordinary blowing sickle method, soft blowing method, double slug method, and double tapping method are known, but in these methods, the P content in the molten steel is 1
It can only be lowered to about 50, 10Q80 and 70 (ppm). The reason why the P content of molten steel cannot be lowered in this way is as follows. In other words, converter blowing iron is
It is mainly controlled by the decarburization treatment time, and since the treatment time is short, sufficient dephosphorization treatment time cannot be taken to obtain low P steel. In addition, slag volume (amount) for dephosphorization
If the amount is increased, there is a risk of slag blowing out, etc., and there are problems with workability, so there is a limit to the amount of slag polymer for removing P. Therefore, in the converter blow sickle, the P of molten steel is
It was not possible to lower the content. Therefore, this invention was made to provide a method for refining molten steel that can obtain copper with an extremely low P content, which could not be obtained by the converter blowing sickle method. molten steel,
The molten steel is poured into a ladle that has a sealing lid and into which gas can be blown, and then a refining flux is added to the molten steel in the ladle, and then the molten steel is poured into the twill steel in the ladle above it. The molten steel in the ladle and the molten steel and the molten steel are injected into the molten steel from a lance for injecting the molten steel into the molten steel in an oxidizing gas atmosphere. Then, the tip of a heating electrode is immersed in the slag above the molten steel in the ladle, and the molten steel in the ladle is subjected to post-treatment such as casting temperature and RH treatment temperature. It is characterized by heating at a suitable predetermined temperature.

Heating by heating electrodes includes electric arc heating and resistance heating, and the advantage of heating in this way is that the tapping temperature of the steelmaking furnace can be lowered.

That is, Fig. 1 shows the relationship between the refractory corrosion coefficient of a steelmaking furnace (converter) and its tapping temperature, and Fig.
As can be seen from the diagrams showing the relationship between [P] (P concentration) of raw steel obtained in a converter and its tapping temperature (in both figures, curve a is for the normal blowing method, curve b is The lower the tapping temperature (Incidentally, the tapping temperature in this invention is 1,590 to 1,640C, and the conventional value is about 1,650 to 17,200C), the higher the refractory quality. The erosion coefficient is lower, and [
P] is lower (therefore, it is advantageous for refining in a ladle), and furthermore, the yield is improved. Further, an advantage of performing the refining before heating is that the refining can be performed at a relatively low temperature, and therefore the dephosphorization efficiency can be increased.

For example, FIG. 3 shows the relationship between the dephosphorization rate and the molten steel temperature when 20 k9 of sodium metasilicate is used per ton of molten steel as a refining flux. Furthermore, the advantage of only heating being performed (that is, the refining process and heat treatment are separated) is that there is less variation in the surface of the molten steel in the ladle. Since the heating is not carried out in the same manner as above), heating can be carried out stably and the life of the electrode combs can be extended. As is well known, when heating with a heating electrode, impurities such as gas (sulfur, sulfur, etc.) to promote heating enter the steel from the lance submerged into the steel in the ladle from above. No gas, e.g. 02
, fugas, etc.) is injected into the molten steel to clear the port steel and improve the heating efficiency by the heating electrode (the amount of injection is 0.4N per ton of steel or less than 4N min). The reason for this is that if the heating rate is less than 0.4 NZ/min, it will take a long time to heat, making it impractical from the point of view of heating efficiency.On the other hand, if the heating rate is 4 N NZ/min or more, the base metal will become attached to the electrode due to molten steel scattering. (This is because it will adhere and shorten the life of the electrode.) Further, after heating is completed in late winter, the heating electrode is raised to separate its tip from the slag in the ladle. From the point of view of not reducing refining efficiency, the flow rate of waste gas (a gas that does not allow impurities such as S, S, etc. to enter the steel, such as 02 gas, etc.) from the lance is 4N per Iton of steel. It is preferable that the molten steel surface rises too much due to gas injection, making it impractical to make the so-called free board in the ladle large. (note that such a large amount of gas blown can only be obtained with a lance structure in which the molten steel is immersed into the lacquered steel from above).

). The manner in which the gas is ejected from the lance into the molten steel is preferably within a range of 1y in the vertical direction with respect to the horizontal direction. This is because the gas ejected from the lance first spreads horizontally and then rises vertically, so the gas blown into the molten steel is utilized extremely effectively and high efficiency is achieved. In addition, the shape of the gas flow passage of the lance for this purpose is a fourth shape that shows a condensation mode when viewed from the longitudinal section.
There are two spout holes la at the tip of the lance 1 as shown in Figure A.
It is preferable to use a T-shaped two-hole type in which a hole is located, and an L-shaped one-hole type in which an ejection hole 1'a is located at one point at the tip of a lance 1' as shown in the opening of FIG. By using such a lasso, as shown in the figure, the molten steel can be made to flow from the side walls of the steel toward the center, so that the slag and steel bath are mixed uniformly on the steel surface and The refining flux, which is carried out deep in the bath and added after electrode heating, is easily mixed with the molten steel by contact with the molten steel, according to the gas imitation from the lance, and electrode heating for the purpose of melting is therefore not necessary. In addition, the flux (slag) that has been turned into a lotus in a short time continues to come into contact with the molten steel and mix vigorously, so that the slag-metal reaction progresses quickly and high refining performance is achieved. Fifth
Figure 5A is a sectional view showing an example of the steel taken to carry out the present invention, Figure 5B shows a heating mode using a heating electrode, and Figure 5B shows a refining mode using a lance. .

As shown in the figure, 2 is the ladle body, 2a is the ladle lid, 3 is the molten steel, 4 is the slag when the heating electrode is immersed, 4' is the slag after adding the refining flux, and the ladle lid is In 2a,
A gas supply pipe 5 for adjusting the atmosphere inside the ladle and a hopper 6 for additives into the ladle are attached, and a heating electrode 7 that can be raised and lowered and a lance for blowing gas are attached to the ladle lid 2a. 8 is passing through. Reference numeral 9 denotes a sealing material (for example, Kaoru) having excellent heat resistance, airtightness, and plasticity, and is interposed between the upper end of the ladle main body 2 and the lower end of the ladle lid 2a.

Note that the arrow in the figure indicates molten steel 3 due to gas injection from lance 8.
It shows the flow. Next, embodiments of this invention will be described. The lacquered steel from the 25-town converter, which had undergone oxidation refining at a lacquered steel temperature of 1640 do, was tapped (transferred) into a 250-ton ladle having the structure shown in Fig. 5 (a) and (b). Next, a ladle lid was attached to the ladle body, 5 tons of sodium metasilicate was added, a T-shaped two-hole lance was immersed in the molten steel, and Ar gas of 2.0 N and 1 min was started to be blown into the molten steel. At the same time, 0.4 liters of air was introduced into the ladle from the gas supply pipe for adjusting the atmosphere inside the ladle.
Refining (gas injection) was performed for 8 minutes while supplying N at a rate of 1/min to create an oxidizing atmosphere inside the steel plate. Next, the heating electrode is immersed in the ladle slag, and at the same time as electricity is started, the amount of gas blown into the lance is reduced to 0. Down to 18
The molten steel was heated while stirring for a minute. As a result, as shown in Table 1, it was 0/010% [P] when steel was tapped in a steelmaking furnace.
However, a steel was obtained in which the content was reduced to 0.003%. As explained above in Table 1, in this invention, extremely
It is possible to provide a refining method that yields steel with a low P content.

[Brief explanation of the drawing]

Figure 1 shows the relationship between the refractory melting coefficient of a steelmaking furnace (converter) and its tapping temperature, and Figure 2 shows the [P] of raw steel obtained in a steelmaking furnace (converter) and its Figure 3 shows the relationship between the tapping temperature and the molten steel temperature.
Figure A: The mouth is a cross-sectional view of the lance immersed in the molten steel in the ladle.
FIG. 5A is a sectional view showing an example of a ladle for carrying out the present invention. 1, 1', 8... Lance, 2... Ladle body, 2a... Ladle lid, 3... Molten steel,
4,4'...Slag, 5...Gas supply pipe for adjusting the atmosphere inside molten steel, 6...Hopper, 7......
Heating electrode, 9...Sealing material. Diagram 3 Figure 2 *4 Figure 5

Claims (1)

[Claims] 1. Transfer the molten steel refined in the steelmaking furnace to a ladle that has a sealing lid and into which gas can be blown, then add refining flux to the molten steel in the ladle, and then In an oxidizing gas atmosphere by blowing stirring gas into the molten steel from a lance for blowing stirring gas immersed into the molten steel in the ladle from above,
Stir the molten steel in the ladle, the molten steel, and the slag on the molten steel, and then immerse the tip of a heating electrode in the slag on the molten steel in the ladle to heat the molten steel in the ladle to a predetermined temperature. A method for refining molten steel characterized by: