JPH09157720A - Method for desulfurizing molten iron - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an extra-low sulfur molten iron by efficiently executing desulfurizing treatment of the molten iron in a short time. SOLUTION: In a desulfurizing treatment process of the molten iron by using plural desulfurizing agent filling wires 11, 21, reaction sites in the molten iron 31 are distributed in the vertical direction by changing the charging speed of each of the wires 11, 21 or using the metallic materials having different melting points as sheath materials of the desulfurizing agent filling wires. Therefore, reaction interfacial area of the desulfurizing reaction can be increased and the efficient desulfurizing treatment to the extra-low sulfur range can be obtd.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention is particularly applicable to a target sulfur concentration of 30.
The present invention relates to a hot metal desulfurization method suitable for producing ultra-low sulfur hot metal having a ppm or less.

[0002]

2. Description of the Related Art A general method for producing an extremely low sulfur steel having a sulfur concentration reduced to 20 ppm or less is 30 pp at the hot metal stage.
It is desulfurized to m or less and finish desulfurized in the secondary refining process. In the secondary refining process, the oxygen concentration in the steel is high and the desulfurization efficiency tends to be low, so that rapid desulfurization treatment is difficult. Therefore, it is desirable to desulfurize to the lowest possible sulfur concentration in the hot metal stage. The desulfurizing agent used for desulfurizing hot metal mainly contains lime, calcium carbide, soda ash and the like. However, conventional desulfurizing agents have various drawbacks. For example, a lime-based desulfurizing agent is the cheapest, but the main component, lime, is solid at the hot metal temperature, and the treatment time tends to be long. Calcium carbide produces toxic phosphine, which contains P as an impurity, and is environmentally problematic. Soda ash has a high vapor pressure, produces a large amount of white smoke during processing, and significantly lowers the hot metal temperature. Moreover, the desulfurized slag derived from calcium carbide and soda ash is difficult to recycle, and is also difficult in terms of slag treatment. As an alternative to these desulfurizing agents, magnesium-based desulfurizing agents have been receiving attention in recent years. The magnesium-based desulfurizing agent is generally used as a mixed powder of lime and magnesium, and is supplied into the hot metal by gas injection or a wire feeder. The magnesium-based desulfurizing agent can be expected to have high desulfurization efficiency, and since the main component of the generated slag after treatment is CaO-MgO-based, it has the advantages that it is easy to perform slag treatment and reuse, and there are few environmental problems. is there.

[0003]

Even when a conventional desulfurizing agent is used in addition to the magnesium-based desulfurizing agent, the desulfurization efficiency is not improved in the final stage of the desulfurization treatment, specifically, in the concentration range where the sulfur concentration is less than 30 ppm. It took a long time and a large amount of desulfurizing agent to stably obtain ultra-low sulfur hot metal. Therefore, how to improve the desulfurization efficiency in the extremely low sulfur area is an important issue for producing the extremely low sulfur hot metal with high productivity. The present invention has been devised to meet such a problem, and by distributing the desulfurization reaction sites in the hot metal in the vertical direction, a small amount of desulfurizing agent can be used efficiently and in a short treatment time with a target sulfur concentration of 30 ppm. The purpose is to obtain the following ultra-low sulfur hot metal.

[0004]

In order to achieve the object, the present invention, when desulfurizing hot metal by supplying a plurality of desulfurizing agent-filled wires to the hot metal in a container, sets the wire feeding speed to two or more. It is characterized by setting and distributing the reaction sites in the hot metal in the vertical direction. It is also possible to use two or more kinds of metals having different melting points as the sheath of the desulfurizing agent-filled wire and distribute the reaction sites in the hot metal in the vertical direction based on the difference in the melting points.

[0005]

When the chemical reaction kinetics is examined, it is considered that in the low sulfur concentration range, the movement rate of sulfur atoms in the hot metal limits the reaction, which causes the reduction in the reaction rate. When the movement of the sulfur atom controls the reaction, in order to increase the reaction rate further, it is effective to shorten the distance to the reaction site or increase the number of reaction sites themselves. Therefore, in the present invention, the sites where the desulfurization reaction occurs are diversified in the depth direction in the concentration range where the estimated sulfur concentration in the hot metal is lower than 30 ppm. Specifically, the feeding speed of the desulfurizing agent-filled wire to be fed is set separately for each wire, the depth at which the reaction occurs is controlled individually for each wire, and the reaction is caused in the entire area of the hot metal ladle. In this case, the wire supplied at a high speed causes a desulfurization reaction at a deep position, and the wire supplied at a low speed causes a desulfurization reaction at a shallow position. Further, since the entire hot metal is stirred with the start and progress of the desulfurization reaction, the desulfurization reaction is evenly spread over the entire hot metal by the enhanced stirring. Further, in order to improve the desulfurization efficiency, an inert gas, a stirring gas such as nitrogen, may be blown into the hot metal. Alternatively, it is also effective to select and use two or more kinds of metal materials having different melting points as the sheath material for coating the desulfurizing agent. In this case, even if the feeding speed is the same, the position where the reaction occurs changes due to the different melting points of the sheath materials, and the same effect can be obtained. In this case, it is not necessary to change the supply rate of the desulfurizing agent, unlike the case where the feeding rate of the wire is changed.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION The hot metal desulfurization according to the present invention is carried out, for example, in the form shown in FIG. Wire feeder 1
The desulfurizing agent-filled wires 21 and 22 are put into the hot metal 31 in the processing container 30 using 0 and 20 to desulfurize the hot metal 31. The desulfurizing agent-filled wires 21 and 22 are sent out from the payoff reels 12 and 22, respectively, and the guide 1
It is fed into the hot metal 31 through 3,23. The sheaths of the desulfurizing agent-filled wires 21, 22 are melted in the hot metal 31, and the desulfurizing agents 14, 24 are dispersed in the hot metal 31. The initial number of inserted wires is usually taken into consideration based on the desulfurizing agent supply rate and the amount of magnesium compounded in the desulfurizing agent, which maximizes the reaction efficiency, and is generally 2 or more. Therefore, the following two methods are considered as means for distributing the desulfurization reaction sites in the depth direction of the hot metal.

First, a method of individually setting the feeding speeds of the wires 11 and 21 can be considered. Desulfurizing agent, sheath material,
When the wire outer diameter, the desulfurizing agent filling amount, and the like are the same, the time required from the charging to the start of the reaction is constant, so the depth at which the reaction occurs is uniquely determined by the wire charging speed. As a result, there are a plurality of positions in the depth direction where the reaction occurs, and the desulfurization reaction occurs in the entire region of the hot metal 21. In the second method, the material of the sheath material is changed at the same feeding speed. Low carbon steel is usually used as the sheath material,
By using another material having a different melting point, the time required for melting the sheath material changes. For example, when a sheath material having a low melting point is used, a reaction occurs at a shallow position. As the low melting point sheath material, an aluminum-based alloy is preferable because it can be easily processed into a wire, has sufficient strength, and can control the residual concentration in the steelmaking process after the desulfurization step.

[0008]

【Example】

Example 1: 90 tons of blast furnace hot metal was charged into a processing vessel having a cross-sectional area of 5.4 m ² , and magnesium concentration was 50% by weight and lime was 50.
A desulfurizing agent-filled wire in which a desulfurizing agent having a composition of wt% was coated with a sheath material made of low carbon steel was put in to perform desulfurization treatment. Table 1 shows the processing conditions at this time. The initial number of wires was set to 2, and the wire introduction speed was set so that the pure magnesium content supply rate was 0.11 kg / min · ton. In this case, 80m of one desulfurizing agent filled wire
/ Min, the other desulfurizing agent-filled wire was charged at 40 m / min. [S] concentration in the hot metal was continuously measured during the desulfurization treatment. The [S] concentration in the hot metal decreased almost linearly as shown in FIG. 2, and decreased to 20 ppm about 8 minutes after the start of charging.

Example 2: Basically, the same hot metal as in Example 1 was charged with one wire having a low carbon steel sheath and another wire having an aluminum alloy sheath. The wire feeding speed was set to 60 m / min in all cases, and the pure magnesium supply rate was set to be the same as in Example 1. The [S] concentration in the hot metal decreased almost linearly to 20 ppm as shown in FIG. 3, but the desulfurization rate at the very early stage was higher than that in Example 1. Therefore, the [S] concentration in the hot metal is 20 ppm in about 7 minutes after the start of charging.
Reached.

COMPARATIVE EXAMPLE: Under the same initial conditions as in Example 1, two wires were introduced at a rate of 60 m / min. At this time, the [S] concentration in the hot metal decreased almost linearly up to 50 ppm, as shown in FIG. 4, and thereafter the desulfurization rate decreased. And 1 after the start of charging
It dropped to 30 ppm at 0 minutes. The above operational specifications are shown in Table 1, and the desulfurization treatment results are summarized in Table 2. As shown in Table 2, it was confirmed that extremely efficient desulfurization treatment can be realized under the conditions of Examples 1 and 2.

[0011]

[0012]

[0013]

As described above, in the desulfurization method of the present invention, by changing the feeding speed of the desulfurization agent-filled wire or by using a metal material having a different melting point as a sheath material of the desulfurization agent-filled wire, The desulfurization reaction sites are dispersed in the depth direction. As a result, the desulfurization reaction spreads throughout the hot metal, and the desulfurization reaction proceeds smoothly and quickly even in the region where the [S] concentration in the hot metal is low. As a result, hot metal having a sulfur concentration of 30 ppm or less can be produced in a short time.

[Brief description of the drawings]

FIG. 1 is an example of an embodiment of a desulfurization treatment according to the present invention.

FIG. 2 is a temporal change in [S] concentration in hot metal in Example 1.

FIG. 3 is a change with time of the [S] concentration in the hot metal in Example 2.

FIG. 4 is a temporal change of [S] concentration in hot metal in a comparative example.

[Explanation of symbols]

10,20: Wire feeder 11,21: Desulfurizing agent filled wire 12,22: Payoff reel 13,2
3: Guide 14, 24: Desulfurization agent required for hot metal from desulfurization agent-filled wire 30: Processing container 31: Hot metal

Front page continuation (72) Inventor Jun Hirama 3-4-1, Marunouchi, Chiyoda-ku, Tokyo Nisshin Steel Co., Ltd.

Claims (2)

[Claims] 1. When supplying a plurality of desulfurizing agent-filled wires to the hot metal in the container to desulfurize the hot metal, the feeding speed of the wires is set to two or more, and the reaction sites in the hot metal are vertically distributed. A method for desulfurizing hot metal, which is characterized by: 2. When desulfurizing the hot metal by supplying a plurality of desulfurizing agent-filled wires to the hot metal in the container, two or more kinds of metals having different melting points are used as the sheath of the desulfurizing agent-filling wire, and based on the difference in melting points. A method for desulfurizing hot metal, characterized in that the reaction sites in the hot metal are vertically distributed.