JPH08232008A - Steelmaking method in converter - Google Patents

Abstract

PURPOSE: To enable dephosphorization at high temp. and to improve desulfurizing efficiency by blowing powdery flux together with oxygen from an oxygen top-blowing lance during blow-refining and promoting the slag-making. CONSTITUTION: Molten iron 2 of a blast furnace is charged into a converter 3 with a molten iron ladle 1 together with scrap 4 and a molded pig iron 5. The flux 6 mainly containing lime is added on the molten iron 2 and the oxygen is top-blown from the oxygen top-blowing lance 7, and N2 and O2 +LPG is bottom-blown from a bottom-blowing device 9, and while controlling the slag 9, P and S in the molten iron are reduced by dephosphorization(de-P) and desulfurization(de-S). After removing the slag 9, the decarburization is executed by adding the flux and blowing the oxygen. The produced slag 9 is remained in the converter 3 to tap the steel. This process is repeated and the steelmaking in a conveter is executed. The powdery flux is blown together with the oxygen from the oxygen top-blowing lance 7 during blow-refining in the de-P and de-S processes and de-P and de-S are facilitated by promoting the slag-making. By this method, the frequency of the occurrence of slopping can drastically be reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a converter steelmaking method in which blast furnace hot metal is charged into a converter for refining, and more specifically, hot metal de-P, de-S, and decarburization are performed in the converter. The present invention relates to a converter steelmaking method in which decarburized slag is hot reused to promote slag slag formation.

[0002]

_2. Description of the Related Art Conventionally, in a converter steelmaking method using molten pig iron from a blast furnace, the molten pig iron is charged into a converter and a steel is produced by introducing a flux mainly containing quick lime and O ₂ blowing. Was the common method. After that, in order to improve the reaction efficiency of de-P and de-S, de-P and de-S removal of the hot metal before charging the converter.
A method of performing a treatment and mainly performing a decarburization reaction in a converter has been adopted.

Further, in recent years, along with the increase in demand for ultra-low carbon steel, decarburization is carried out in the converter in the range of 500 to 200 ppm (C), and after the steel is tapped, the secondary refining process by RH type and DH type vacuum degassing equipment is carried out. In Japan, a method of decarburizing up to the range of 50 ppm (C) or less has also been adopted.

However, in carrying out these conventional examples, a large amount of capital investment and operating personnel were required for each refining process, and an increase in the fixed cost load was unavoidable. Further, it is necessary to sequentially pass through the different steps of the reaction container, and the various materials (refractory, etc.) in each step increase. Further, since it takes a long time to obtain the final molten steel from the tapped blast furnace, there is a problem that energy loss is large and refining cost is increased.

In order to solve these problems, the applicant of the present invention has proposed a molten steel manufacturing method disclosed in Japanese Patent Application Laid-Open No. 4-72007. This molten steel manufacturing method is characterized in that, in order to solve the above-mentioned conventional problems, one of the hot metal pretreatment step, the converter step, and the secondary refining step is integrated into the converter step. It is a thing.

That is, when refining the blast furnace hot metal to produce molten steel, the first step is to load the hot metal into the converter, and the second step is one of charging, spraying and blowing, or two. Flux addition by a combination of two or more methods and oxygen top blowing to perform de-P and de-S refining to reduce to a predetermined P content and S content. As a third step, the converter is used. Roll over and remove the slag generated in the second step, as the fourth step, decarburize to a predetermined C content by flux addition O ₂ and blowing, and generate as the fifth step in the fourth step. The molten steel is produced while leaving the slag left in the converter, returned to another step, and repeatedly performs the above-mentioned 5 steps.

However, in this molten steel manufacturing method, (1) the flux addition in the second step is, as shown in the embodiment, the introduction of the lump flux from above, or the addition of the lump flux from above and the powder. This is done by using the bottom blowing of a flat flux. As described above, when the massive flux is introduced from above, the slag is not sufficiently slagged. That is, actual basicity CaO / SiO in slag
₂ rises only to about 1.5 to 1.7, P removal at high temperature becomes insufficient, and S removal efficiency is low. Furthermore, there is a problem that slag with low basicity is easy to form and sloping occurs frequently.

(2) The addition of the flux in the fourth step is
As shown in the examples, the lumpy flux is introduced from above. As described above, when the massive flux is fed from above, the blow stop [C]> 0.2 to
When refining 0.3% medium-high carbon steel grade in a top-bottom blow converter with strong bottom-blown stirring power, (T.Fe) in the slag does not rise, the slag is not sufficiently solidified, and molten steel is removed. There is a problem that P and S removal are significantly inhibited.

[0009]

The present invention is disclosed in Japanese Unexamined Patent Publication No.
By improving the addition form of the flux, especially CaO, added in the second and fourth steps of the invention of 72007,
The present invention provides a converter steelmaking method that advantageously solves the problems (1) and (2).

[0010]

The first invention of the present invention is as follows:
Blast furnace hot metal is charged into a converter, flux is added, and P and S refining are performed by oxygen top blowing or oxygen top and bottom blowing to reduce P and S in the hot metal to a predetermined level, and to generate slag. After the slag was removed, decarburization was carried out by adding flux and blowing oxygen, and the produced slag was tapped while it was left in the converter and returned to the process again with this slag remaining in the converter. In the converter steel making method, which repeats the steps 1 to 3, the flux of the powder is blown together with oxygen from the oxygen top blowing lance during the blowing in the de-P and de-S steps to promote the slag slag formation, and It is a converter steelmaking method characterized by facilitating the removal of P and the removal of S.

The second invention is the same as the first invention.
In the decarburization process of step 1, the flux of powder is blown together with oxygen from the oxygen top blowing lance to promote slag slag formation, thereby facilitating the removal of P and S of the molten metal in the process of Is characterized by.

[0012]

In the present invention, since at least CaO in the flux added in the hot metal pretreatment step and the decarburization step is blown as a powder together with oxygen from the oxygen top blowing lance, (1) in the hot metal pretreatment step, slag Since the slag formation is promoted, the basicity of the slag is increased, the P removal at high temperature is possible, and the S removal efficiency can be improved. In addition, the frequency of occurrence of sloping can be significantly reduced. (2) In the decarburization process, (T.Fe) in the slag in the medium-high carbon region is increased while the stirring force by bottom blowing is strongly maintained, and de-Ping and S-depletion of the molten steel are promoted. Can be melted. Therefore, by these, a remarkable economic effect can be enjoyed in the converter steelmaking process, and productivity can be improved.

The inventors of the present invention described the above-mentioned Japanese Patent Application Laid-Open No. 4-72007.
In the practical process of the invention of the publication, the following facts were discovered. a. In the hot metal pretreatment step, when the flux is made into a lump and added from above, the actual basicity CaO / SiO _{2 in} the slag rises only up to about 1.5 to 1.7, and P removal at high temperature occurs. Is insufficient, and the S removal efficiency is also low. Furthermore, slag with low basicity is easy to form and sloping occurs frequently. b. In the decarburization step, when the flux is lumped and added from above, blowing stop [C]> 0.2-
When refining 0.3% medium-high carbon steel grade in a top-bottom converter with strong bottom-blown stirring power, (T.Fe%) in the slag does not rise and slag slag formation is not sufficient, De-P and de-S are significantly inhibited. These phenomena are caused by insufficient slag slag formation.

Therefore, the inventors of the present invention conducted various experiments on the conditions for making the slag slag sufficiently. As a result, it was concluded that it is effective to optimize the flux addition form, and further experiments were conducted to complete the present invention.

In the present invention, it is preferable that at least CaO in the flux added in the hot metal pretreatment step and the decarburization step is made into powder, and the particle size of CaO is 2000 μm or less. It is characterized in that this is blown together with oxygen from the oxygen top blowing lance during oxygen blowing. As a matter of course, it is also effective to mix powder of fluorite or alumina with CaO powder and blow it in as a slag formation accelerator.

When the particle size of the flux is 2000 μm or more, the transportability by oxygen is lowered, and the solubility in the molten metal in the converter is lowered to lower the reaction efficiency with P and S in the molten metal. In addition, the effect of suppressing sloping is reduced. If many powders having a particle size of 50 μm or less have a high scattering rate and the addition efficiency decreases, it is preferable to keep the mixing ratio of the particles in this region to 20% or less.

As a method of adding this flux, it is effective to blow this oxygen together with oxygen as a carrier gas from an oxygen top blowing lance during oxygen blowing. The oxygen jet from the top blowing lance forms a fire point with a temperature of 2,000 to several hundred degrees Celsius on the surface of the molten metal. Therefore, blowing CaO powder together with top-blowing oxygen can be added without impairing the oxygen-blowing effect, and the flux is instantly melted in the fire point region due to top-blowing oxygen to promote slag slag formation. The reaction efficiency can be improved. It is also advantageous in terms of equipment layout.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below based on embodiments.
First, FIG. 1 shows a basic process of the present invention in which a hot metal pretreatment process and a decarburization process are integrated. In this example, oxygen is blown upward from the top blowing lance, N ₂ or O ₂ + LPG is fed from the bottom during hot metal pretreatment, and Ar is fed from the bottom during decarburization.
Alternatively, it shows the case of the upper bottom blowing converter steelmaking method in which O ₂ + LPG is bottom blown.

As a first step, molten iron 2 from a blast furnace carried in a molten iron ladle 1 (or a torpedo car) is loaded into a converter 3 together with scrap 4, mold pig 5, and the like.

In the second step, a flux 6 centered on quick lime (CaO) (with dolomite and iron ore if necessary) is added to the hot metal 2 in the converter 3, and oxygen is blown from the oxygen top blowing lance 7. While top blowing, bottom blowing N ₂ or O ₂ + LPG from the bottom blowing device 8 controls the (T.Fe%) of the produced slag 9 in the range of 3 to 10%, while removing P and S. (Preliminary hot metal treatment) is performed to reduce the P and S to predetermined values.

As the third step, the fluidized slag is discharged by tilting the slag 9 generated in the second step in the converter 3 toward the side opposite to the steel strip (slag side).

As a fourth step, after the slag is completed, the converter 3 is erected and some auxiliary materials (quick lime, dolomite, Mn) are added.
(Ore, iron ore, etc.) 10 is added, oxygen is top-blown from the oxygen top-blowing lance 7, and Ar or O ₂ + LPG is bottom-blown from the bottom-blown device 8 at the bottom to remove oxygen. Perform charcoal refining.

In the fifth step, the molten steel 11 is tapped out and received in the molten steel ladle 12 after the blowing is stopped, but the slag 9 produced in the fourth step is left as it is in the converter and the hot metal pretreatment for the next heat is carried out. Use it as a slag for business.

The present invention is characterized by the addition form when the fluxes 6 and 10 centered on quick lime (CaO) are added to the hot metal 2 in the converter in the second step or the fourth step.

FIG. 2 conceptually shows an equipment flow for adding flux in the present invention. Flux 6 (10) with particle size adjusted and compounded in advance
Are loaded by the transport vehicle 13, and from here, the stock tank 1
The gas is conveyed in the air stream 4 and is supplied to the blow tank 16 through the pressure feed tank 15 at appropriate times. Then, a proper amount is cut out to the oxygen supply pipe 18 of the oxygen blowing lance 7 through the rotary feeder 17 and blown into the molten pig iron in the converter 3 together with oxygen from the oxygen blowing lance 7 through the flexible tube 19. Further, N ₂ or Ar or O ₂ + LPG is blown from the bottom blowing device 8 at the bottom.

The equipment for flux addition in the present invention shown in FIG. 2 was connected to the basic process of the present invention for integrating the hot metal pretreatment process and the decarburization process, and the converter operation was carried out. The operating conditions are shown in Table 1. The flux (C
The particle size distribution of aO) is shown in Table 2.

[0027]

[Table 1]

[0028]

[Table 2]

First, in the hot metal pretreatment step (second step), powdered quick lime having a particle size adjusted to 1000 μm or less as shown in Table 2 is blown together with oxygen from the oxygen top blowing lance during oxygen blowing. It was blown into the molten metal. The results are shown in FIGS. 3, 4, 5 and Table 3 in comparison with the case of the conventional example. The conventional example is a case where a massive flux (CaO) having a particle size of 20 to 40 mm is charged from a furnace bunker using a sub material charging chute.

[0030]

[Table 3]

FIG. 3 shows the relationship between the calculated charging basicity and the actual basicity of the slag after the hot metal pretreatment. The actual basicity of slag when lumped quick lime (CaO) was added as in the past was only increased to 1.7, and the slag-forming property was insufficient, but powdery quick lime ( C
According to the present invention in which aO) was blown together with oxygen from the oxygen top blowing lance, the slagging property was remarkably improved, and the actual basicity could be increased to 2.0 to 2.5.

FIG. 4 shows the relationship between the molten metal temperature after the hot metal pretreatment and the [P] in the molten metal after the hot metal pretreatment. When lumpy quick lime is added as in the conventional method, the hot metal [P] after the hot metal pretreatment rises sharply as the temperature rises after the hot metal pretreatment. In the case of the present invention in which oxygen is blown in from the above, even if the temperature after the hot metal pretreatment rises due to the above-mentioned improvement of the slagging property, [P] after the hot metal pretreatment is stable at a low value, which is favorable. The P-free property was exhibited.

FIG. 5 shows the relationship between the actual basicity of the slag after the hot metal pretreatment and the S removal efficiency after the hot metal pretreatment. In the case of the present invention in which powdered quick lime (CaO) is blown together with oxygen from the oxygen top blowing lance, as compared with the case where lumped quick lime is added as in the conventional case, the slagging property is improved and the actual basicity is improved. As a result, the efficiency of removing S agent was remarkably improved.

Table 3 shows the occurrence frequency of sloping at the time of blowing with oxygen and flux. In the case of the present invention in which powdered quick lime is blown together with oxygen from the oxygen top blowing lance, the sloping occurrence frequency is reduced to 1/20 or less as compared with the case where lumped quick lime is charged as in the conventional case.

Next, in the decarburization refining step (fourth step), a powdery flux (CaO) whose particle size is adjusted to 1000 μm or less as shown in Table 2 is supplied from the oxygen top blowing lance during oxygen blowing. It was blown into the molten metal in the converter together with oxygen to produce a medium-high carbon steel grade. The results are shown in FIGS. 6, 7, 8 and 9 in comparison with the case of the conventional example. The conventional example is a case where a massive flux (CaO) having a particle size of 20 to 40 mm is thrown in from a furnace bunker using an auxiliary material chute.

FIG. 6 shows the relationship between the bottom blowing gas flow rate, the slag (T.Fe) and the blow stop [P] when a lumpy flux (CaO) was introduced as in the conventional case during the melting of medium-high carbon steel grades. It is shown. As the amount of bottom blowing gas increases, that is, as the stirring force in the steel bath increases, the (TF
e), that is, the oxygen potential of the slag is reduced, and the deP capacity of the slag is reduced, so that the blow stop [P] is increased.

FIG. 7 shows a bottom blowing gas amount of 0.15 Nm ³ / min-ton.
Shows the relationship between blow stop [C] and slag (T.Fe) when a medium-high carbon steel grade is melted. In the case of the present invention in which powdered quick lime (CaO) is blown together with oxygen from the oxygen top blowing lance, (T.Fe) in the slag is increased, as compared with the case where lumped quick lime is charged as in the conventional case. Therefore, slag with good slag formation and high oxygen potential was obtained.

FIG. 8 shows a bottom blowing gas flow rate of 0.15 Nm ³ / min.
-ton shows the relationship between the slag (T.Fe) and the blow stop [P] when the medium-high carbon steel grade is melted.
In the case of the present invention in which powdered quick lime (CaO) is blown together with oxygen from the oxygen top blowing lance, as compared with the case where lumped quick lime is charged as in the conventional case, (TF
Since e) can be increased, the blow stop [P] can be controlled to a low level, and good P removal characteristics were exhibited.

FIG. 9 shows a bottom blowing gas flow rate of 0.15 Nm ³ / min.
-ton as blow-stop when melting medium-high carbon steel grade [C]
It shows the relationship between and the blow stop [S]. Compared to the case where lumped quick lime is added as in the conventional case, in the case of the present invention in which powdered quick lime (CaO) is blown together with oxygen from the oxygen top blowing lance, the slag slagification property is improved,
Blowing stop [S] could be controlled to a low level and showed good S-removing characteristics.

[0040]

EFFECTS OF THE INVENTION According to the present invention, (1) the slag slag is promoted in the hot metal pretreatment process of de-Ping and de-S, so that the basicity of the slag increases and the de-Ping at high temperature is possible. In addition, the S removal efficiency can be improved. Moreover, the frequency of occurrence of sloping can be significantly reduced. (2) In the decarburization process, (T · Fe) in the slag in the middle and high carbon regions rises while strongly maintaining the stirring force by bottom blowing,
The removal of P and S from molten steel was promoted, making it possible to produce medium-high carbon steel grades. Therefore, by these, a remarkable economic effect can be enjoyed in the converter steelmaking process, and productivity can be improved.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional conceptual explanatory view showing a basic process of a converter steelmaking method to which the present invention is applied.

FIG. 2 is a conceptual explanatory view of a vertical cross section showing a flux addition mode in the present invention.

FIG. 3 is an explanatory diagram of the relationship between the calculated basicity and the actual basicity in the embodiment of the present invention.

FIG. 4 is an explanatory view of a relationship between a temperature after dePing and a [P] after dePing by hot metal pretreatment refining in an example of the present invention.

FIG. 5 is an explanatory view of the relationship between the actual basicity after P removal by the hot metal pretreatment refining and the desulfurizing agent efficiency in the example of the present invention.

6 is an explanatory view of a relationship between a bottom blown gas flow rate during decarburization refining, slag (T.Fe), and blow stop [P] in an example of the present invention.

7 is an explanatory diagram of the relationship between blow stop [C] and (T.Fe) in slag during decarburization refining in an example of the present invention.

8 is an explanatory diagram of a relationship between (T.Fe) in slag and blow stop [P] during decarburization refining in the example of the present invention.

FIG. 9 is an explanatory view of the relationship between blow stop [C] and blow stop [S] during decarburization refining in the embodiment of the present invention.

[Explanation of symbols]

 1 Hot metal ladle 2 Hot metal 3 Converter 4 Scrap 5 Type pig iron 6 Flux (at the time of hot metal pretreatment refining) 7 Oxygen top blowing lance 8 Bottom blowing device 9 Slag 10 Flux (at the time of decarburizing refining) 11 Molten steel 12 Molten steel pot 13 Carrier truck 14 Stock tank 15 Pressure feed tank 16 Blow tank 17 Rotary feeder 18 Oxygen supply pipe 19 Flexible tube

Claims (2)

[Claims] 1. A blast furnace hot metal is charged into a converter, and P and S in the hot metal are reduced to a predetermined level by performing flux removal and oxygen top blowing or oxygen top bottom blowing to perform P and S refining. After the generated slag is discharged, it is decarburized by adding flux and oxygen blowing, and the produced slag is tapped while it remains in the converter. Return to the process and repeat ~
In the converter steelmaking method that carries out the process
In the process, a converter steel making method characterized in that powder flux is blown together with oxygen from an oxygen top blowing lance during blowing to facilitate slag slag formation, thereby facilitating de-P and de-S in hot metal. . 2. In the decarburizing step, the flux of the powder is blown together with oxygen from the oxygen top blowing lance during the blowing so as to promote the slag slag formation, so that the molten metal is removed P and S in the step. 2. The converter steelmaking method according to claim 1, further comprising: