JPH1030108A - Decarburizing method in top-bottom combination-blown converter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an oxygen-blowing method which can satisfy both of the restraint of lowering of the yield caused by a top-blown lance and the restraint of lowering of the yield caused by oxidation of iron, in a decarburizing method of molten steel with a top-bottom combination-blown converter. SOLUTION: This decarburizing method in the top-bottom combination-blown converter is so executed that as for the ratio P/PO of a designed secondary pressure PO of the top-blown lance nozzle and an operational secondary pressure P, at the time of making the P/PO to 1.2-1.7 in the high carbon concn. range, the P/PO is regulated to >=1.8 in the low carbon concn. range, or at the time of making the P/Po to 0.5-0.8 in the high carbon concn. range, the P/Po is regulated to 0.9-1.1 in the low carbon concn. range.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for decarburizing molten steel using a top-bottom blow converter. In particular, the present invention relates to a method for decarburizing molten steel by using an upper-bottom blow converter that can reduce the generation of dust and the oxidation of iron.

[0002]

2. Description of the Related Art In a method of decarburizing molten steel by a top-bottom blowing converter, a region where the carbon concentration in the molten steel is higher than 0.6 to 0.2% is defined as a high-carbon region, and a region where the carbon concentration is 0.6 to 0.2%. The following areas are called low-carbon areas. The high-carbon region is a period when almost all of the supplied oxygen is subjected to the decarburization reaction, and the low-carbon region is a period when a part of the oxygen is also used for the oxidation of iron. The carbon concentration transitioning from the high-carbon region to the low-carbon region is affected by the oxygen supply rate and the bottom-blowing stirring power.
It is well known that it is 2%.

[0003] In converter refining, a blowing acid method for suppressing a reduction in yield due to generation of dust is desired in a high-carbon region, and a blowing acid method for suppressing a reduction in yield due to oxidation of iron is desired in a low-carbon region. .

Various blowing acid methods have been proposed in response to such demands. For example, Japanese Patent Application Laid-Open No. S60-165313 discloses a method of reducing dust using a multi-hole nozzle, in which the overlapping of hot spots on the surface of molten steel is considered. The technique is disclosed using a smelting lance that minimizes

Japanese Patent Application Laid-Open No. 2-294420 discloses a technique of a blowing acid method in which an inert gas is mixed with top-blown oxygen during a low-carbon period as a measure for reducing oxidation of iron in a low-carbon region. .

However, in any of these methods, if an attempt is made to suppress the yield reduction due to the generation of dust in the high-carbon region, the reduction of the yield due to oxidation of iron in the low-carbon region cannot be realized. If it is attempted to suppress the yield reduction due to the oxidation of iron in the low-carbon region, it is not possible to realize the suppression of the reduction in yield due to the generation of dust in the high-carbon region. Thus, the suppression of dust generation and the suppression of iron oxidation are inextricably linked, and the conventional method has not been able to solve both problems.

On the other hand, as for the lance used in the decarburization method using the top-blowing converter, the nozzle 1 of the top-blowing lance generally has a widening shape (Laval nozzle) as shown in FIG. Narrowest portion is referred to as the throat 2, designed secondary pressure ^{_{P o (kgf / cm 2)}} , the following relationship between the throat diameter d (mm), outlet diameter D (mm).

D = [(4 / π) × S · {(1 + 0.2 · Mp ² ) /1.2} ³ / Mp] ^1/2 S = (π (d / 2) ² ) Mp = [5 × [ {(P _o +1.033) /1.033} ^2/7 -1]] ^1/2 Also, the design acid supply rate F _E (Nm ³ / Hr) has the following function when the number of nozzles is n.

F _E = S × {0.581 · n · (P _o +1.033)} On the other hand, the operating gas supply speed F (Nm ³ / H
r) and the secondary pressure at that time (operating secondary pressure: P) have the following relationship.

F = S × {0.581 ・ n ・ (P +1.033)}

[0011]

SUMMARY OF THE INVENTION The present invention provides a method for decarburizing molten steel using a top and bottom blown converter, which satisfies both suppression of reduction in yield due to dust generation and suppression of reduction in yield due to oxidation of iron. It is an object of the present invention to provide a method for blowing acid which can be used.

[0012]

In order to reduce dust in a high-carbon region, it is effective to lower the flash point temperature.
For that purpose, it is most important to reduce the jet flow velocity at the molten steel surface position, that is, to perform soft blow. On the other hand, in order to suppress iron oxidation in the low-carbon region, it is effective to raise the flash point temperature, which means increasing the jet flow velocity at the molten steel surface position, that is, hard blowing. Is the most important. The present inventors have realized that this is controlled by the relationship between the design secondary pressure of the nozzle and the operation secondary pressure, and have completed the present invention.

The specific solution of the present invention is as follows.

(1) Design of upper blowing lance nozzle Secondary pressure P
The ratio P / P _o of _o and operation secondary pressure P, than high carbon concentration high coal region, decarburization method upper base blown converter, characterized in that to increase the area of low-carbon low carbon concentration .

[0015] In (2) above (1), that the high carbon concentration high coal area and 1.2 to 1.7 for P / P _o, to 1.8 or more in the low carbon concentration low carbon region Characteristic decarburization method for top and bottom blown converters.

[0016] (3) In the above (1), in the high carbon concentration high coal region and 0.5-0.8 the P / P _o, and 0.9 to 1.1 in the low carbon concentration low carbon region A method for decarburizing an upper and lower blown converter.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION High and low coal regions during oxygen blowing
The boundaries of the carbon concentration with the shape of the converter, stirring power,
Fluctuates depending on the operating conditions of the converter.
Concentration at the boundary between the area and the low-carbon area is 0.6-0.2
%. Therefore, charcoal higher than 0.6%
P / P outside the conditions of the present invention at elemental concentration_OWhere operations were carried out at
In such a case, the generation of dust cannot be sufficiently reduced.
P / P outside the conditions of the invention at carbon concentrations below 2%_Oso
In operation, iron oxidation cannot be reduced sufficiently.
However, in the range of 0.6 to 0.2%,
Determines whether it is a high coal area or a low coal area according to the operating conditions,
P / P that matches it_OCondition may be selected. First
First, the design secondary pressure P of the top blowing lance nozzle _oAnd operation 2
Ratio P / P of secondary pressure P_oIs larger in the low coal area than in the high coal area.
It is necessary to work. This is our detailed
According to the experiment, the jet flow velocity U at the molten steel surface position and the nozzle outlet
Jet velocity U_OAnd the ratio (U / U_o) Is P / P_oIncrease
Increase the amount of hard blow
You.

The optimum conditions are the following two conditions.

FIG. 1 is a graph showing the relationship between the value of P / P _{O and} the amount of dust generated (kg / t) in a high-carbon region where the carbon concentration is high. As shown in FIG. 1, the dust in the range with 1.2 to 1.7 of P / P _o in the high carbon region is high carbon concentration is related to the change and the dust generation amount of the value of P / P _O The amount of generation is reduced.

FIG. 2 shows the value of P / P _O in the low-carbon region where the carbon concentration is low and the generation ratio of the iron concentration in the slag (T · Fe
%). As shown in FIG. 2, when the value of P / P _O is 1.8 or more in the low-carbon region, the effect of reducing iron oxide occurs.

Therefore, according to the present invention, when decarbonizing and refining molten steel by the upper blowing lance, the P / P _O of the low-carbon region where the carbon concentration is lower than the value of P / PO in the high-carbon region where the carbon concentration is high.
By increasing the value of P _O , reduction of dust generation and reduction of iron oxide generation can be achieved.

The specific value of P / P _O in each region is
It is preferable that P / P _O be 1.2 to 1.7 in the high-carbon region and P / _PO be 1.8 or more in the low-carbon region. The reason for the 1.2 to 1.7 of P / P _o in the high coal region, since the gas which is oxygen-flow in the state of gas Underexpanded reaches the nozzle outlet, rapidly inflated immediately after leaving the nozzle, This is due to a large attenuation and soft blow, and as a result, dust is reduced as shown in FIG. If it is smaller than 1.2, the above damping effect is small, and if it is larger than 1.7, the effect that the kinetic energy itself of the gas due to the increase of the back pressure becomes larger than the above damping effect. Is predominant, so that a soft blow effect cannot be obtained.
The reason why the ratio is set to 1.8 or more in the low-carbon region is that the kinetic energy of the gas increases due to the increase in the back pressure, so that the hard blow effect is obtained. As a result, as shown in FIG. The iron concentration (T · Fe) in is reduced. If it is smaller than 1.8, a sufficient hard blow effect cannot be obtained because the above-described damping effect appears.

FIG. 3 is a graph showing the relationship between the low P / P _O value and the amount of dust generation (kg / t) in the high carbon region where the carbon concentration is high.

[0024] In the present invention, lowering the value of the further P / P _O than the value of P / P _O in FIG. 1, has been found that there is a range dust generation amount is small as shown in FIG. 3 .

That is, as shown in FIG. 3, when the value of P / P _O is 0.8 or less, the amount of generated dust is reduced.

[0026] Therefore, in the present invention, in the high carbon concentration high coal region and 0.5-0.8 the P / P _o, in the low carbon region and P / P _O as shown in Figure 2 0. 9 to 1.1. 0.5 to 0 and P / P _o in the high coal region.
The reason for setting to 8 is that the gas reaches the nozzle outlet in an over-expanded state and the potential core is shortened due to the damping in the nozzle, resulting in a soft blow. As a result, dust is reduced as shown in FIG. You. If it is less than 0.5, the energy in projecting the nozzle becomes too small, so that the splash in the blowing acid may enter the nozzle,
If it is larger than 0.8, the softening effect cannot be obtained because the above damping effect becomes small. The reason for setting P / P _O to 0.9 to 1.1 in the low-carbon region is that the gas pressure is efficiently converted to kinetic energy by setting the appropriate expansion conditions, so that a hard blow effect is obtained. Yes, as a result, iron concentration in slag (T • Fe)
Is reduced. If the value is smaller than 0.9, the above-described damping effect appears, so that a sufficient hard blow effect cannot be obtained. If the value is larger than 1.1, damping due to insufficient expansion appears as described above, so that sufficient This is because a hard blow effect cannot be obtained.

[0027]

【Example】

 (Example 1) A decarburization test was performed in a 350-ton converter. for
The upper blowing lance was a 4-hole Laval nozzle with a throat diameter
d is 55.5 mm, outlet diameter D is 72 mm, design 2
Next pressure P _OIs 7 (kgf / cm^Two), Design acid feed rate F_EIs 4
5000 (Nm^Three/ Hr). This lance
In the range where the carbon concentration is higher than 0.45%,
Industry secondary pressure P is 11.5 (kgf / cm^Two), Ie P / P_O
Was set to 1.6 and the operating gas supply rate F was 7 using pure oxygen gas.
0000 (Nm^Three/ Hr) and decarbonize at 0.45% or less
Is Ar or CO in pure oxygen gas._TwoMix gas and operate 2
Next pressure P is 14 (kgf / cm^Two), Ie P / P_O2.0
And the operating gas supply speed F is set to 84500 (Nm^Three/ H
Decarburized in r). As a result, the dust amount was 15 kg / t,
In slag when carbon is blown at 0.04% (TF
e) was 14.5%.

(Example 2) A decarburization test was performed using a 350-ton converter.
Carried out. The upper blowing lance used is a 4-hole Laval nozzle
And the throat diameter d is 71.5 mm and the outlet diameter D is 101 m
m and the design secondary pressure P _OIs 10 (kgf / cm^Two), Setting
Total acid feed rate F_EIs 103000 (Nm^Three/ Hr)
is there. Using this lance, the carbon concentration becomes 0.45%
In the high range, the operation secondary pressure P is increased to 6.5 (kgf / cm
^Two), Ie P / P_OAnd operation using pure oxygen gas
Gas supply speed F is set to 70,000 (Nm^Three/ Hr)
However, at 0.45% or less, Ar or CO is added to pure oxygen gas._Two
The gas is mixed and the secondary pressure P for operation is set to 10 (kgf / c
m^Two), Ie P / P_OIs set to 1 and the operating gas supply speed F is set to 1
03000 (Nm^Three/ Hr). As a result,
The strike amount was 14 kg / t and carbon was blown off at 0.04%.
(T.Fe) in the slag at that time was 16%.

(Example 3) A decarburization test was performed using a 350-ton converter.
Carried out. The upper blowing lance used is a 4-hole Laval nozzle
And the throat diameter d is 71.5 mm and the outlet diameter D is 101 m
m and the design secondary pressure P _OIs 10 (kgf / cm^Two), Setting
Total acid feed rate F_EIs 103000 (Nm^Three/ Hr)
is there. Using this lance, the carbon concentration becomes 0.45%
In the high range, the operation secondary pressure P is increased to 6.5 (kgf / cm
^Two), Ie P / P_OAnd operation using pure oxygen gas
Gas supply speed F is set to 70,000 (Nm^Three/ Hr)
Was. When the carbon reaches 0.45%, the top blowing lance is
With a 4-hole Laval nozzle, the throat diameter d is 55.5 mm,
The outlet diameter D is 72 mm and the design secondary pressure P _OIs 10 (k
gf / cm^Two), Design acid feed rate F_EIs 45000 (Nm^Three
/ Hr) and use this lance to remove pure oxygen
With gas, the operation secondary pressure P is set to 10 (kgf / cm^Two), Ie
P / P_OAnd the operating gas supply speed F is 45000.
(Nm^Three/ Hr). As a result, the dust amount is 1
4.5 kg / t, carbon when 0.04% blow off
The lag (T.Fe) was 15%.

(Comparative Example) The upper blowing lance used in the comparative example
4 hole Laval nozzle, throat diameter d is 59mm, outlet
The diameter D is 83.5 mm and the design secondary pressure P _OIs 10 (k
gf / cm^Two), Design acid feed rate F_EIs 70000 (Nm^Three
/ Hr). Using this lance, the carbon concentration
Irrespective of the secondary pressure P (10 kgf / c
m^Two), Ie P / P_OOperating gas using pure oxygen gas
Supply speed F is set to 70,000 (Nm^Three/ Hr).
As a result, the dust amount was 23 kg / t and carbon was 0.04%.
(T.Fe) in the slag when blown with 18.5%
became.

As is clear from the above Examples 1 to 3 and Comparative Example, according to the present invention, the amount of generated dust can be reduced and the iron concentration in the slag is also reduced. However, as shown in the comparative example, when the decarburization operation is performed under a constant condition with P / _Po being 1,
Although the iron concentration in the slag was reduced, the reduction of dust generation was not achieved.

[0032]

According to the method for decarburizing an upper-blowing converter according to the present invention, it is possible to effectively achieve both reduction of dust generation and reduction of iron oxidation, which were difficult in the conventional converter operation. Therefore, the harm associated with the reduction in decarburization efficiency can be effectively eliminated.

[Brief description of the drawings]

FIG. 1 is a diagram showing the relationship between the value of P / P _O and the amount of generated dust (kg / t) in a high-carbon region where the carbon concentration is high.

FIG. 2 is a diagram showing a value of P / P _O in a low-carbon region having a low carbon concentration and a generation ratio (T · Fe%) of an iron concentration in slag.

FIG. 3 Low P / P _O in high carbon region with high carbon concentration
FIG. 4 is a diagram showing a relationship between the value of the and the amount of dust generation (kg / t).

FIG. 4 is a cross-sectional view of the tip of the Laval lance nozzle.

[Explanation of symbols]

 1 Nozzle 2 Throat 3 Oxygen gas jet

Claims (3)

[Claims] The method according to claim 1] top lance nozzles ratio P / P _o of design secondary pressure P _o and operating secondary pressure P of, than high carbon concentration high coal regions, largely in the area of low-carbon low carbon concentration A method for decarburizing an upper and lower blown converter. 2. The method of claim 1, and characterized in that the high carbon concentration high coal area and 1.2 to 1.7 for P / P _o, to 1.8 or more in the low carbon concentration low carbon region To decarburize the top and bottom blown converter. 3. The method of claim 1, in a high carbon concentration high coal region and 0.5-0.8 the P / P _o, to 0.9 to 1.1 in the low carbon concentration low carbon region A method for decarburizing an upper and lower blown converter.