JP2002194419A - Method for adding bismuth into molten steel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To uniformly add bismuth which selectively restrains primary recrystallization in a grain oriented electrical steel sheet, into molten steel at good yield. SOLUTION: Into the molten steel flow MF during shifting from coming-out of a ladle 1 to the molten steel surface in a tundish 2, the bismuth grains are added from a hopper 10 by using an electromagnetic feeder 9 with the adding speed Y (kg/t.min)=(12-30)×the target bismuth concentration X (mass%) and the bismuth is uniformly dispersed into the steel and added at the good yield.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a high magnetic flux density,
The present invention relates to a method for adding bismuth to molten steel capable of uniformly dispersing bismuth in the molten steel without excess or deficiency for the purpose of producing a grain-oriented electrical steel sheet having a low iron loss.

[0002]

2. Description of the Related Art Grain-oriented magnetic steel sheets used as iron core materials for transformers, generators, rotating machines, and the like are required to have characteristics of high magnetic flux density and low iron loss. In order to reduce iron loss, it is effective to accumulate the secondary recrystallization orientation in the {110} <001> orientation called the Goss orientation.
In order to increase the degree of accumulation, it is effective to form a precipitation-dispersed phase called an inhibitor uniformly and with an appropriate particle size in the steel and selectively suppress the growth of primary recrystallization.

As inhibitors, substances having low solubility in steel, for example, MnS, MnSe, Cu ₂ S, Cu ₂ Se, AlN, etc., are suitable, and these are left in the steel as a precipitation dispersion phase of an appropriate form. . Also, P, Sn, As, Bi, Sb, B,
The addition of elements such as Mo and Te increases the effect of the inhibitor acting on the selective suppression of primary recrystallization, and these elements are called sub-inhibitors. Among them, bismuth (Bi) is considered to be most promising as a sub-inhibitor because it has a particularly low solubility in iron and a large tendency to segregate at crystal grain boundaries. However, it is very difficult to add bismuth to molten steel because it hardly dissolves in molten steel, has a specific gravity of about 10 which is larger than that of iron, and has a boiling point similar to that of molten steel. Further, in the grain-oriented electrical steel sheet, it is necessary to reduce the fluctuation of the inhibitor component due to the addition of bismuth because the appropriate range of the inhibitor component is narrow.

[0004] The addition of alloying elements for the adjustment of steel components includes addition in a converter, addition in a tapping steel, addition in a vacuum degassing tank such as RH, and addition in a ladle. Top additive (for example,
Japanese Patent Application Laid-Open No. 8-243700), wire addition in a ladle,
There are addition in tundish, addition in mold, etc.
These methods do not work as described below. In the addition in the converter and during the output from the converter, since the boiling point of bismuth is at the same level as the molten steel temperature, most of the added bismuth is vaporized and discharged out of the system. In the addition during the vacuum degassing treatment, evaporation is further promoted due to the treatment under vacuum, and it is difficult to leave bismuth in the steel.

[0005]

In the ladle addition, wire addition, and tundish addition, bismuth is hardly soluble in molten steel and the specific gravity is larger than the molten steel. Retention at the bottom of the dish invalidates the selective suppression enhancement of primary recrystallized grain growth of the inhibitor. In addition, the stagnant remains in the tundish, causing contamination to the next charge. In order to avoid this stagnation, stirring of the molten steel is effective, but the stirring causes the bare metal surface to be exposed, and the reaction between the molten steel and the air causes fluctuations in the molten steel component, so that sufficient primary recrystallized grain growth is selected. Inability to obtain effective restraint.

An object of the present invention is to solve the above-mentioned problems of the prior art and to provide a method of adding bismuth to molten steel capable of uniformly dispersing bismuth particularly useful as a subinhibitor of grain-oriented electrical steel sheets in steel. It is in.

[0007]

The present inventors conducted a basic experiment using a small furnace and obtained the following findings. (1) In the simple top addition method, bismuth evaporates immediately after addition. (2) In the method of forcing bismuth into the bottom of molten steel,
Low evaporation, but settles at the bottom and does not provide uniform dispersion.

As a result of further studies based on these findings, the present inventors have found that the conventional method of combining addition to a molten steel bath in a ladle or tundish with strong stirring is not preferred. It has been found that the method of adding to the molten steel stream being poured from the pot into the tundish is most preferable. In other words, the flow of molten steel from the ladle to the tundish has a large flow velocity, has the same bismuth dispersing effect as strong stirring of the molten steel bath, and the temperature is higher than the temperature of the molten steel bath in the tundish, so that bismuth is more easily dispersed. . The bismuth addition rate at this time is set as follows: bismuth addition rate Y (kg / t · min) = (12 to 30) × target bismuth concentration X (mass%), so that bismuth stays at the bottom of the tundish. And it could be added to the target bismuth concentration without excess or deficiency. Further, it was also found that when bismuth is added to the molten steel stream, it is preferable to add the bismuth from a bismuth inlet provided with a sand seal wall surrounding the molten steel stream, because component fluctuation due to reaction with air can be suppressed.

The gist of the present invention, which has been repeatedly studied based on these findings, is as follows. According to a first aspect of the present invention, in the method for adding bismuth to molten steel, bismuth particles are added to the molten steel flow moving out of the ladle to the molten steel surface in the tundish at a bismuth addition rate Y (kg / t · min). ) = (12 to 30) × target bismuth concentration X (mass%).

According to a second aspect of the present invention, there is provided a method of adding bismuth to molten steel, wherein the molten steel flowing from the ladle to the molten steel surface in the tundish is moved between the ladle and the tundish. Bismuth particles are added from the bismuth inlet provided in the sand seal wall surrounding at a feed rate of bismuth addition rate Y (kg / t min) = (12 to 30) x target bismuth concentration X (mass%) This is a method for adding bismuth to molten steel.

According to a third aspect of the present invention, there is provided a method for adding bismuth to molten steel, wherein the molten steel flowing out of the ladle and into the molten steel bath in the tundish is heated between the ladle and the tundish. Bismuth particles are added from a bismuth inlet provided in a long nozzle wall surrounding the flow at a charging rate of bismuth addition rate Y (kg / t · min) = (12 to 30) × target bismuth concentration X (mass%). This is a method for adding bismuth to molten steel.

[0012]

In the first and second aspects of the present invention, bismuth is added to the molten steel flow from the ladle to the tundish at an appropriate addition rate after the secondary refining of the molten steel, whereby the bismuth is reduced. The flow rate is large and is uniformly added to the high-temperature molten steel flow, and does not stay in the tundish. Further, since the molten steel flow is sealed from the outside air, there is no change in the molten steel component due to the reaction with the air. Bismuth uniformly dispersed in the molten steel stream is supplied from the tundish to the mold on the molten steel stream.

A specific embodiment will be described with reference to FIG. In FIG. 1, a lid placed on a tundish 2
On the upper surface of 2A, a sand seal 3 in which a sand for sealing is inserted in a groove having a U-shaped cross section is provided so as to surround the central opening 3A, and is attached downward to the lower surface of the ladle 1 filled with molten steel. A cylindrical sealing plate 1A is inserted from above into a sand housed in a groove of the sand seal 3. In the tundish 2, two weirs 4 are arranged below the lid 2 </ b> A and in the longitudinal direction of the tundish 2 so as to sandwich the central opening 3 </ b> A. Enclose and form a sealed space that does not allow air to enter. An argon gas supply device 6 is disposed inside the sealing plate 1A, and bismuth is added under a condition that the inside of the sealed space is filled with argon gas supplied from the argon gas supply device 6 to form a non-oxidizing atmosphere (FIG. 4).

For the addition, as shown in FIGS. 2 and 3, a bismuth introduction hole 8 is provided in the sand seal 3, and bismuth particles are introduced into the molten steel flow MF in the seal space from the bismuth introduction hole 8, for example, by a hopper 10 as shown in FIG. It is cut out from the inside and fed using an electromagnetic feeder 9. The bismuth particles are sent in aiming at the molten steel flow MF, and the sent bismuth particles collide with the molten steel flow MF, and are quickly melted and diffused into the molten steel flow MF, thereby forming the two weirs 4 formed in the tundish 2. Injected with molten steel in between. At this time, the bismuth can be more uniformly dispersed by the stirring action generated in the molten steel. Since the inside of the weir 4 is a non-oxidizing atmosphere filled with argon gas, the surface of the molten steel bath MP in the tundish 2 is not oxidized even if it is bare water without flux. The molten steel injected into the weir 4 is supplied to both sides of the tundish 2 through through holes 5 provided at the lower ends of the two weirs 4, respectively.
It is injected into the lower mold through the immersion nozzle 7. Since the molten steel of the tundish 2 existing on the immersion nozzle 7 is in an oxidizing atmosphere, it is coated with the flux F to prevent oxidation of the molten steel.

In the above embodiment, the case where bismuth particles are added from the bismuth inlet provided on the sand seal wall surrounding the molten steel flow between the ladle and the tundish has been described. However, the present invention is not limited to this. Instead, as shown in FIG. 5, a long nozzle 11 is attached to the lower part of the ladle 1 so as to surround the molten steel flow MF downward, and the lower end of the long nozzle 11 is immersed in the molten steel filled in the tundish 2 so as to be exposed to the atmosphere. Bismuth is supplied to the electromagnetic feeder 9 from the bismuth introduction port 8 which forms a closed space and is formed by opening a hole in the long nozzle wall.
Send using.

The feeding of the bismuth to be added aiming at the molten steel flow MF is the same as in FIG. 4, and an inert gas supply device 12 is provided in a space closed with the atmosphere formed by the long nozzle 11.
The argon gas, which is an inert gas, is blown into the long nozzle 11 through the
The inside can be maintained as a non-oxidizing atmosphere.

In place of the method of adding bismuth using the electromagnetic feeder 9, bismuth may be added by a wire method containing bismuth. Table 1 shows the addition method (addition time) in the process of turning molten steel from a converter into a ladle during RH treatment, and then converting it into slabs using a continuous caster. Bismuth was added with various changes, and the yield of bismuth and the fluctuation of other components were investigated.

Here, as an example of the present invention, addition of a sand seal and addition of a long nozzle were carried out, and as comparative examples, addition in a conventionally known converter steel tapping, addition during vacuum degassing, ladle Addition in the inside, addition of wire in a ladle and addition in a tundish were performed. As a result, Examples 1 to 6 in which bismuth is added to the molten steel flow from the ladle 1 to the tundish 2 shown in the present invention have a higher yield than Comparative Examples 1 to 5, and Al and N added as inhibitors. Was small and it was found that this was an excellent addition method.

[0019]

[Table 1]

Next, regarding the bismuth addition rate at the time of adding bismuth to the molten steel flow from the ladle 1 to the tundish 2, the present inventors measured the amount of bismuth flowing out and the amount discharged from the tundish 2 into the tundish. The study was conducted based on the flow inside the tank 2 and the tank row model. The addition method was a sand sealing method shown in FIG. FIG. 6 shows the results of an investigation on the target bismuth concentration and the bismuth addition rate. In the figure, the symbol ○ indicates that the target bismuth concentration range was achieved, the symbol Δ indicates that sedimentation was observed in the tundish 2, and after completion of casting, residual bismuth was confirmed in the tundish 2, and the symbol × indicates the target. It did not reach the bismuth concentration range. From FIG. 6, it can be seen that the optimal addition rate range for adding bismuth to molten steel without excess or deficiency is the bismuth addition rate Y (kg / t · min = (12 to 30) × target bismuth concentration X (mass%)). That is, when the addition rate is lower than the bismuth addition rate of the present invention, the required concentration is not reached, and, for example, in the grain-oriented electrical steel sheet, the target magnetic properties cannot be obtained. If added at a rate, bismuth may be added in excess of the required concentration,
Even if the bismuth concentration in the molten steel is within an appropriate range, there is a danger that bismuth will remain in the tundish 2 and become a contamination source for the next charge, deteriorate the surface properties of the slab, and cause a breakout. is there. There is also a problem in terms of production cost.

[0021]

As described above, according to the present invention, bismuth particles are added to the molten steel flow moving out of the ladle to the molten steel surface in the tundish by the bismuth addition rate Y (kg / t · mi).
n) = (12-30) × Target bismuth concentration X (mass%) is added at a feed rate, so that bismuth useful as a sub-inhibitor of directional magnetic steel can be uniformly dispersed in steel at a high yield. . As a result, there is an excellent effect that the product quality of the grain-oriented electrical steel having a high magnetic flux density and a low iron loss can be stably obtained.

[Brief description of the drawings]

FIG. 1 is a partial side sectional view showing a bismuth addition apparatus for implementing the present invention.

FIG. 2 is a perspective view showing a main part of a bismuth addition apparatus for implementing the present invention.

FIG. 3 is a front partial cross-sectional view showing a bismuth addition apparatus for implementing the present invention.

FIG. 4 is a cross-sectional view taken along line AA of FIG.

FIG. 5 is a front partial cross-sectional view showing a bismuth addition apparatus embodying the present invention.

FIG. 6 is a graph showing a relationship between a target bismuth concentration (%) and a bismuth addition rate (kg / t · min).

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Ladle 1A Seal plate 2 Tundish 2A lid 3 Sand seal 3A Central opening 4 Weir 5 Through hole 6 Argon gas supply device 7 Immersion nozzle 8 Bismuth introduction port 9 Electromagnetic feeder 10 Hopper 11 Long nozzle F Flux MF Molten steel flow MP Tundish Steel bath inside

Continued on the front page (51) Int.Cl. ⁷ Identification FI FI Theme Court II (Reference) C22C 33/04 C22C 33/04 J (72) Inventor Kunihiro Senda 1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Kawasaki Steel Corporation (72) Inventor Hiroki Nishi 1-chome, Kawasaki-dori, Mizushima, Kurashiki-shi, Okayama Pref. FA12

Claims (3)

[Claims] In a method of adding bismuth to molten steel, bismuth particles are added to a molten steel flow moving out of a ladle to a molten steel surface in a tundish, and a bismuth addition speed Y (kg / t · min) = (12 ~ 30) A method for adding bismuth to molten steel, characterized by adding at a feed rate of × target bismuth concentration X (mass%). 2. A method for adding bismuth to molten steel, wherein the molten steel flowing out of the ladle to the molten steel surface in the tundish is provided on a sand seal wall surrounding the molten steel flow between the ladle and the tundish. Bismuth grains are added from the bismuth inlet at a feed rate of bismuth addition rate Y (kg / t · min) = (12 to 30) × target bismuth concentration X (mass%). Bismuth addition method. 3. A method for adding bismuth to molten steel, wherein the molten steel flowing out of the ladle and into the molten steel bath in the tundish has a long nozzle wall surrounding the molten steel flow between the ladle and the tundish. Bismuth grains are added from the provided bismuth inlet to molten steel characterized by adding bismuth at a charging rate of bismuth addition rate Y (kg / t · min) = (12 to 30) × target bismuth concentration X (mass%). Bismuth addition method.