JPH07207315A - Wire for desulfurizing molten iron and its manufacture - Google Patents

Abstract

PURPOSE:To obtain a wire for desulfurizing, increased in Mg content ratio and effectively consumed in the desulfurization. CONSTITUTION:A series process, in which an iron base stripe material 1 is formed as cylindrical shape and desulfurizing agent 5 is packed into the inner part of the cylindrical formed body 4 and both edge parts in the width direction of the cylindrical formed body 4 are joined to make the wire 9 for desulfurizing, is executed in a chamber 12 filled up with dried inert gas atmosphere. At the time of using the inert gas atmosphere having <=0.5% oxygen concn. and <=0 deg.C dew point, the ratios of the oxygen and moisture possessed in the vol. in the wire are made to be <=1vol%. As Mg of metallic state is fed into molten iron without reacting with the oxygen and the moisture by this method, the desulfurizing efficiency is improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a desulfurizing wire used for desulfurizing hot metal.

[0002]

2. Description of the Related Art The hot metal tapped from a blast furnace contains a relatively large amount of impurities. Prior to refining the hot metal in a converter, various processes such as Si removal, S removal, and P removal are performed. In particular, S contained in the hot metal causes the workability and corrosion resistance of the steel material to decrease, so it is necessary to reduce it to a low level at the hot metal stage. For desulfurization of hot metal, ladle,
A method of adding a desulfurizing agent to the hot metal contained in a hot metal truck or the like is adopted. The desulfurizing agent includes CaO, CaC ₂ , Na ₂
CO ₃ , metal Mg, rare earth metal, etc. are used. For example, Japanese Patent Application Laid-Open No. 3-301461 introduces a desulfurization method in which a flux containing a metal Mg powder and a CaC ₂ powder is gas-injected into hot metal. Above all,
Metal Mg or Mg alloy is considered as an efficient desulfurizing agent because of its high reactivity with [S] of hot metal. Since the metal Mg is a low boiling point and active metal, an explosive vaporization reaction occurs when it comes into contact with the hot metal. Further, MgS generated by the desulfurization reaction is unstable, and S is likely to return to the hot metal again due to the reaction with oxygen in the atmosphere.

[0003]

The Mg-based desulfurizing agent used for hot metal desulfurization is usually gas-injected in the form of powder. However, in the gas injection, of the Mg-based desulfurizing agent blown into the hot metal, what has become Mg vapor is diluted with the carrier gas, and the proportion of Mg vapor contributing to desulfurization decreases. As a result, the amount of desulfurizing agent required to desulfurize to the target [S] also increases,
The time required for the desulfurization treatment also becomes long. Therefore, the temperature drop of the hot metal before and after the treatment is large, and the heat load becomes large in the subsequent steps. Even when the Mg-based additive is fed into the hot metal as a wire, the [S] after the actual treatment is Mg
It is only about 30% of the value calculated from the supply amount of. That is, the percentage of Mg consumed for desulfurization is still low. Improving the desulfurization efficiency of Mg is effective for hot metal desulfurization
It is an important factor when using a g-based additive. The present invention, based on the finding that the low desulfurization reaction efficiency of Mg is caused by oxygen, water, etc. contained in the wire, by filling the iron-based sheath with a desulfurizing agent under an inert atmosphere,
An object of the present invention is to provide a wire for desulfurizing hot metal with high efficiency by eliminating the influence of oxygen, water and the like.

[0004]

In order to achieve the object, a hot metal desulfurizing wire of the present invention has a structure in which an iron-based sheath is filled with a desulfurizing agent in the form of powder, cut wire or wire. Oxygen and moisture in the product (steam conversion)
The ratio is set to 1% or less. This desulfurization wire is a series of steps in which an iron-based strip is formed into a cylindrical shape, a desulfurizing agent is filled inside the cylindrical strip, and the widthwise ends of the cylindrical strip are joined to form a sheath. Is carried out in a dry, inert atmosphere. As the desulfurizing / deoxidizing agent, metallic Mg or Mg-Al alloy is used. Mg-
The Al alloy preferably contains 40 to 95% by weight of Al. The inert atmosphere is preferably adjusted to have an oxygen concentration of 0.5% by volume or less and a dew point of 0 ° C. or less.

[0005]

[Operation] Mg added to the hot metal is Mg (g) + [S]
→ MgS (s) and Mg (l) + [S] → MgS (s)
According to the desulfurization reaction of No. 1, the reaction product reacts with [S] in the hot metal and the reaction product MgS is transferred to slag to desulfurize the hot metal. This desulfurization reaction is effective in reducing the [S] of the hot metal to an extremely low level as compared with the case of using other desulfurizing agents. In order to increase the proportion of Mg that contributes to the desulfurization reaction, it is necessary to maintain the reaction product MgS so that it does not dissociate and dissolve again in the hot metal. However, MgS is an extremely unstable compound,
The presence of oxygen or moisture in the atmosphere or in the wire easily dissociates, resulting in vulcanization. The reaction with oxygen and water contained in the atmosphere can be prevented to some extent by coating the Mg-based desulfurizing agent with an iron-based sheath. The iron-based sheath maintains its self-shape for a predetermined time even if the Mg-based wire comes into contact with the hot metal, and the Mg-based sheath is formed in the deep portion corresponding to the thickness of the sheath.
When the system wire reaches, it melts into the hot metal. As a result, the Mg-based desulfurizing agent is added to the hot metal with almost no contact with the atmosphere.

However, even when the wire in which the iron-based sheath is filled with the Mg-based desulfurizing agent is used, the proportion of Mg contributing to desulfurization is only about 40%. The present inventors hypothesized that the cause of the low desulfurization reaction efficiency of Mg was due to oxygen and water taken in the wire. In fact, in a wire filled with powdered metal Mg or Mg alloy, Mg-Al
Compared to the alloy core wire, it contains a large amount of oxygen and water, and the desulfurization reaction efficiency of Mg is low. Oxygen and moisture contained in the wire can be reduced by performing a series of steps of filling the iron-based sheath with the Mg-based desulfurizing agent to form the wire in an inert atmosphere. Desulfurization with the wire obtained under these conditions dramatically improved the desulfurization reaction efficiency of Mg as compared with the wire manufactured by the usual method. In particular, when the oxygen and water content (converted to water vapor) contained in the wire was 1% or less of the inner volume of the wire, desulfurization became possible with a high desulfurization reaction efficiency of Mg exceeding 60%. The high desulfurization reaction efficiency, combined with the rapid desulfurization reaction by Mg, is a desulfurization method that can sufficiently replace the conventional hot metal desulfurization.

A hot metal desulfurization wire in which inclusion of oxygen, moisture and the like is suppressed is manufactured, for example, in the line shown in FIG. As the iron-based strip material 1 serving as the sheath, ordinary steel having a composition that does not adversely affect the hot metal to be treated is used. Since the penetration depth when the wire is fed into the hot metal changes depending on the thickness of the sheath, it is preferable to use the iron-based strip 1 having a plate thickness of about 0.1 to 0.4 mm. Generally, as the plate thickness increases, the straightness improves and the penetration depth into the hot metal increases. However, if the plate thickness is excessively large, wire forming, winding, and the like become difficult. The iron-based strip 1 is fed from the rewind reel 2 and bent in the width direction by the forming roll 3 to form a cylindrical formed body 4 having an open upper portion. The Mg-based desulfurizing agent 5 is
It is sent from the hopper 6 to the cylindrical molded body 4. As the Mg-based desulfurizing agent 5, metallic Mg, Mg—Al alloy, or the like is used in the form of wire, cut wire, powder, or the like. Also,
CaC _2, Na ₂ CO _3, metal Ca, or other desulfurization agent of the rare earth _{metals, CaO, CaO-Al 2 O} 3, CaO-A
A slag material such as l ₂ O ₃ —SiO ₂ flux may be used in combination with the Mg desulfurizing agent 5.

When a Mg-Al alloy wire is used as the Mg-based desulfurizing agent 5, instead of supplying from the hopper 6, Mg-
A method of feeding the Al alloy wire from the reel into the cylindrical molded body 4 is adopted. The Mg-Al alloy preferably contains 40 to 95% by weight of Al. When the Al content is less than 40% by weight, the Mg content relatively increases, an explosive reaction is likely to occur, and the Al deoxidizing efficiency decreases. On the contrary, when the Al content exceeds 95% by weight, the Mg content becomes relatively low and the degree of desulfurization becomes small. The cylindrical molded body 4 filled with the Mg-based desulfurizing agent 5 is further processed by a molding roll and the opening is closed. Then, both ends in the width direction are sewn together by crimping or the like with a suturing machine 8 to obtain a wire 9 filled with the Mg-based desulfurizing agent 5. The wire 9 is straightened by the straightening roll 10 and then wound around the winding reel 11.

In order to prevent the Mg-based desulfurizing agent 5 from contacting the atmosphere during the process from the rewinding reel 2 to the take-up reel 11, at least the hopper 6 to the sewing machine 8 are N
_2. Arranged in a chamber 12 filled with an inert gas such as Ar. When N ₂ is used as the inert gas, N ₂ is included in the obtained desulfurization wire 9. However, the encapsulated N ₂ is not enough to raise [N] during hot metal desulfurization. The inert atmosphere in the chamber 12 is preferably maintained at an oxygen concentration of 0.5 vol% or less and a dew point of 0 ° C. or less in order to eliminate the adverse effects of oxygen and moisture contained in the wire 9. The oxygen concentration and dew point are the internal oxygen,
The effect on the water content has been clarified by experiments by the present inventors. When the Mg-based desulfurizing agent 5 is filled in an atmosphere having an oxygen concentration of 0.5% by volume or less and a dew point of 0 ° C. or less, the wire 9 is used.
Oxygen and water contained in 1% or less are each less than 1% by volume, and the adverse effects of oxygen and water on desulfurization are not observed.

[0010]

【Example】

Example 1: (Influence of atmosphere on contained oxygen and water) A plain steel strip having a plate thickness of 0.2 mm and a plate width of 25 mm was used as an iron-based sheath, and a granular body of 30% Mg-70% Al alloy was used. Was used as the Mg-based desulfurizing agent. The wire obtained is
It had a diameter of 6 mm and was filled with a Mg-based desulfurizing agent at a rate of 10 g / m. Mg-based desulfurizing agent at a temperature of 20 ° C and relative humidity of 80
% Of oxygen and water contained in the wire (converted into water vapor) were 19% and 3%, respectively, as a proportion of the inner volume of the wire when filled in an air atmosphere. On the other hand, when the Mg-based desulfurizing agent was filled in the chamber filled with N ₂ as the inert gas, the oxygen and water contained in the wire changed according to the oxygen concentration and the dew point of the atmosphere as shown in Table 1. . From this, it is understood that a dry inert atmosphere is necessary to obtain a wire containing a small amount of oxygen and water.

[0011]

[Table 1]

Example 2: (Hot metal desulfurization) [S] discharged from the blast furnace = 250 ppm and a temperature of 13
The hot metal at 20 ° C. was placed in a ladle and the Mg produced in Example 1 was used.
System wire is fed at a feeding speed of 80 m / min, and [S] is 1
It was desulfurized to 0 ppm. When [S] reached 10 ppm, the supply of the Mg-based wire was stopped, and the supply amount of the desulfurizing agent fed into the hot metal was calculated in terms of Mg. Since the desulfurization reaction proceeds according to the reaction of Mg + [S] → MgS, the reference value is 1 when the total amount of supplied Mg is consumed for desulfurization.
The ratio of Mg actually consumed for desulfurization was calculated as desulfurization reaction efficiency. The desulfurization results are arranged by oxygen and water contained in the wire and are shown in (a) and (b) of FIG. 2, respectively. As is clear from FIGS. 2A and 2B, the desulfurization reaction efficiency of Mg is sharply improved when the oxygen and water contained in the wire are 1% by volume or less. This suggests that the wire did not contain oxygen and water that act on the MgS + [O] → MgO + [S] re-sulfurization reaction, and Mg was sent into the hot metal with high efficiency. On the other hand, when the amount of oxygen and water contained in the wire exceeds 1% by volume, the desulfurization reaction efficiency of Mg sharply decreases. This indicates that since Mg is an element with high reaction activity, it reacts with a small amount of oxygen, water, etc., and the proportion of Mg sent to the hot metal in a metallic state is reduced.

[0013]

As described above, according to the present invention, by filling the Mg-based desulfurizing agent in a dry and inert atmosphere, oxygen and water contained in the Mg-based desulfurizing wire are suppressed. ing. Therefore, when the Mg-based desulfurizing wire is fed into the hot metal, re-sulfurization due to dissociation of MgS that is a reaction product is suppressed as much as possible, and desulfurization efficiency is improved. The obtained Mg-based desulfurization wire improves the efficiency of hot metal desulfurization in combination with the rapid reaction of Mg + [S] → MgS.
In this way, hot metal having a very low [S] is obtained.

[Brief description of drawings]

FIG. 1 is a line for producing a Mg-based desulfurizing / deoxidizing wire according to the present invention.

FIG. 2 Effect of entrapped oxygen (a) and water (b) on the proportion of Mg effectively consumed for hot metal desulfurization

[Explanation of symbols]

1: Iron-based strip material 2: Rewind reel 3,7:
Forming roll 4: Cylindrical shaped body 5: Mg-based desulfurizing agent 6: Hopper 8: Suture machine 9: Desulfurization wire 10: Straightening roll 11: Take-up reel 12: Chamber maintained in an inert atmosphere

Claims (5)

[Claims] 1. When manufacturing a desulfurizing wire in which an iron-based sheath is filled with a desulfurizing agent in the form of powder, cut wire or wire, the iron-based strip is formed into a cylindrical shape, and the inside of the cylindrical strip is formed. A method for manufacturing a hot metal desulfurizing wire, wherein a series of steps of filling a desulfurizing agent with each other and joining both widthwise end portions of the cylindrical strip to form a sheath is performed in a dry inert atmosphere. 2. The production method according to claim 1, wherein metallic Mg or Mg—Al alloy is used as a desulfurizing agent. 3. A Mg-A having a Mg content of 5 to 60% by weight.
3. The manufacturing method according to claim 2, wherein an L alloy is used. 4. The oxygen concentration is 0.5% by volume so that the proportion of oxygen and water in the inner volume of the wire is 1% by volume or less.
The production method according to claim 1, wherein an inert atmosphere having a dew point of 0 ° C. or less is used. 5. A hot metal desulfurizing wire having a structure in which an iron-based sheath is filled with a desulfurizing agent in the form of powder, cut wire or wire, and the proportion of oxygen and water in the inner volume of the wire is 1% by volume or less.