KR102412350B1 - How to dephosphorize a chartered boat - Google Patents

Abstract

The method of dephosphorizing molten iron of the present invention is a method of dephosphorizing molten iron in a converter equipped with a top blow lance, wherein the carbon concentration in the molten iron in the converter is 3.0 mass % or more, using the top blow lance to the molten iron, It has a process of starting injection of the mixed gas of oxygen gas and an inert gas.

Description

How to dephosphorize a chartered boat

The present invention relates to a method of dephosphorization of molten iron using a converter.

This application claims priority on the basis of Japanese Patent Application No. 2018-082767, filed in Japan on April 24, 2018, and Japanese Patent Application No. 2019-004338, filed in Japan on January 15, 2019, , their contents are cited here.

In recent years, the demand for steel materials is increasing, and the demand for low tensile steel having high strength, high toughness, and the like is increasing. Therefore, improvement of production efficiency and reduction of manufacturing cost are important, and shortening of the operating time is desired not only for general steel having a phosphorus concentration of less than 0.02 mass%, but also for low phosphorus steel having a phosphorus concentration of less than 0.015 mass%, Reduction of manufacturing cost is calculated|required.

Currently, the method of processing dephosphorization blow temper of molten iron|metal on the low-temperature conditions favorable to advancing of such a dephosphorization reaction based on the dephosphorization reaction shown by following (A) formula is performed widely. (A) In the formula, elements described in [ ] represent components in molten iron, and compounds described in ( ) represent components in slag.

2[P]+5(FeO)+3(CaO)=(3CaO·P ₂ O ₅ )+5Fe···(A)

Since dephosphorization reaction advances so that it is low temperature, dephosphorization blow temper is performed at the stage of relatively low-temperature molten iron|metal about 1300-1400 degreeC. As an apparatus used for such molten iron|metal dephosphorization, a converter is used in many cases, and a top-bottom odor converter is especially suitable. In the top-bottom odor converter, steel is refined by blowing in low-odor gas from the bottom of the converter while blowing in oxygen from the top blowing lance of the upper part of the converter. Oxygen blown into the molten iron from the top blow Lance acts as an oxidizing agent necessary for dephosphorization, and has little heat loss compared to a solid oxidation source. Moreover, it is possible to improve the oxidation reaction rate of phosphorus by performing odor with a large stirring force simultaneously with upper odor.

In addition, after dephosphorization, the slag with increased phosphorus concentration is separated from the molten iron, and for the purpose of removing the remaining phosphorus and decarburizing, a new refining material is added to the copper molten iron, and oxygen is sprayed from the top blow lance of the converter at high speed, and the bottom of the converter Decarburization blow tempering is performed by blowing low odor gas from The decarburization reaction in this decarburization blow temper advances, so that an oxygen supply rate is high. Therefore, in order to improve production efficiency, it is preferable to increase the rate of the decarburization reaction by increasing the oxygen supply rate. On the other hand, in the dephosphorization reaction in dephosphorization blow tempering, the reaction rate is governed by the substance transfer rate of phosphorus in either or both of the metal side or the slag side. Therefore, it is preferable to lengthen blow temper time as much as possible by reducing an oxygen supply rate and suppressing the slag forming mentioned later.

As a method of performing dephosphorization blow temper and decarburization blow temper as described above in one converter, a MURC (Multi-Refining Converter) method is known. In this MURC method, after dephosphorization blow tempering, a part of the slag with a high phosphorus concentration is discharged to the outside of the furnace by tilting the converter, and a new refining material is added to the converter which has left the dephosphorized molten iron, and the remaining phosphorus is removed and decarburized. do Compared with the case of performing dephosphorization blow tempering and decarburization blow tempering using two converters, the MURC method does not require discharge of molten iron from the converter and charging into the next converter, so the cycle time is short and the heat loss is small. , excellent productivity and economy. In addition, in recent years, the desiliconization blow temper is separated from the dephosphorization blow temper, and the desiliconization blow temper, dephosphorization blow temper, and decarburization blow temper are performed in one converter (for example, refer to the following Patent Documents 1 and 2) is also disclosed.

As for the top blow lance of a converter, the nozzle of the predetermined number of nozzle holes is provided at the front-end|tip, and injects oxygen toward the molten iron surface in a converter from a nozzle. As for the upper blow lance, the upper limit and the lower limit of the sending speed are determined by the tuyere shape (nozzle diameter and the number of nozzle holes).

In the MURC method, it is necessary to control the transmission speed in one upper air lance accompanying the converter. In the decarburization blow tempering performed after dephosphorization blow tempering, in order to burn and decarburize the carbon contained abundantly in molten iron|metal in a short time, the blow temper in a high output speed is calculated|required. In the upper blow Lance designed for realizing such a high-speed feed, the upper limit of the feed rate is set to a level that enables high-speed feed in the decarburization blow temper, so the lower limit of the feed rate inevitably becomes a high value.

On the other hand, in dephosphorization blow temper, even if it is going to reduce a feed rate, it is necessary to transmit at a feed rate higher than the lower limit of the said determined feed rate. When it operates at the feed rate below the lower limit of the feed rate, oxygen gas is not sufficiently supplied to the molten iron, and there is a problem in safety due to dephosphorization failure, backfire, or the like.

Therefore, when it intends to perform MURC method refinement|refining using the lance suitable for high-speed feeding in decarburization blow tempering in this way, it cannot but blow at the sending speed higher than the optimal sending speed in dephosphorization blow tempering. As a result, at the interface between the molten iron and the slag, CO bubbles generated by the reaction between C in the molten iron and FeO (iron oxide) in the slag, and in the slag itself, FeO in the slag and C in the iron particles contained in the slag react Foaming may occur due to the generated CO bubbles (foaming). When the FeO concentration in the slag is high, CO bubbles are generated in a large amount, so that the slag having a high FeO concentration has strong foaming properties (characteristics that expand rapidly and easily overflow from the converter).

If the foaming of the slag is severe, the sloping occurs in which the high-temperature slag overflows from the converter furnace. When sloping occurs and the refining equipment around the converter or the conveying vessel waiting under the converter is damaged, much time and effort are required for restoration. Therefore, if sloping generate|occur|produces during dephosphorization blow tempering, blow tempering should be stopped at that stage. As a result, the time for dephosphorization blow tempering cannot fully be ensured and the phosphorus concentration in steel cannot fully be reduced.

In order to prevent the foaming slag from overflowing, there is a method in which the slag is contracted by destroying the layer (hereinafter, sometimes referred to as "foam layer") in which the CO bubbles are retained. A method is generally known in which a lump that is specifically gasified inside the slag is put into the slag, and the foam layer is destroyed using the volume expansion energy when the lump is gasified by thermal decomposition. Usually, the bulky substance having such a destructive action is called a sedative (refer to Patent Documents 3 to 5).

Japanese Patent Publication No. 5671801 Japanese Patent Laid-Open No. 2018-188730 Japanese Patent Laid-Open No. 54-032116 Japanese Patent Laid-Open No. 11-050124 Japanese Patent Laid-Open No. 2008-255446

However, with the above method of destroying the foam layer, it is difficult to stably and rapidly calm the forming slag. In order to quickly calm the foaming slag, for example, a large amount of a sedative is one method, but this large amount of injection causes an increase in refining cost, and there is a problem in terms of economical efficiency.

Therefore, when performing both dephosphorization blow temper and decarburization blow temper using one converter and one top blow lance like the MURC method, it originates in the sending speed|rate is excessive in dephosphorization blow temper, and foaming occurs frequently. Therefore, conventionally, it is difficult to suppress slag forming stably and economically, the blow tempering time must be interrupted, and the phosphorus concentration in steel was not able to fully reduce.

The present invention was made in view of the above circumstances, and in the method of dephosphorizing molten iron using a converter, slag forming can be stably and economically suppressed, and an object of the present invention is to provide a method of dephosphorizing molten iron.

MEANS TO SOLVE THE PROBLEM The present inventors studied earnestly the method of solving the said subject, and by supplying the mixed gas of oxygen gas and an inert gas to molten iron|metal from a top blow lance, suppressing slag forming, The present inventors discovered that oxygen supply rate could be reduced. The gist of the method of dephosphorizing such molten iron is as follows.

[1] It is a method of dephosphorizing molten iron in a converter equipped with a top blow lance, wherein the carbon concentration in the molten iron in the converter is 3.0 mass % or more, using the top blow lance to the molten iron with oxygen gas and an inert gas The dephosphorization method of molten iron|metal which has the process of starting injection of mixed gas.

[2] The dephosphorization method of molten iron|metal of [1] which injects only the said mixed gas toward the said molten iron from the said top blow lance.

[3] The method of dephosphorization of molten iron according to [1] or [2], in which the carbon concentration in the molten iron is 3.0 mass% or more and 3.8 mass% or less, and the injection of the mixed gas is started.

[4] The molten iron dephosphorization method according to any one of [1] to [3], wherein the stirring power density E _TOP of the mixed gas supplied from the upper blow Lance, defined by the following (1) formula, is 140 W/t or less.

E _TOP =0.137·cosθ·(Q _I ·M _I +Q _O2 ·M _O2 )·(Q _I +Q _O2 ) ² /(Wm·Λ ² ·D ³ ·H) ···(1)

here,

θ is the nozzle inclination angle (°) of the upper blow Lance,

Q _I is the flow rate (Nm 3 /s) of the inert gas contained in the mixed gas,

M _I is the molecular weight of the inert gas contained in the mixed gas,

Q _O2 is the flow rate of the oxygen gas contained in the mixed gas (Nm 3 /s),

M _O2 is the molecular weight of the oxygen gas contained in the mixed gas,

Wm is the weight (t) of the molten iron,

Λ is the number of nozzle holes of the upper blow Lance (-),

D is the outlet diameter of the nozzle of the upper blow Lance (m),

H is the distance between the nozzle of the upper blow Lance and the stationary liquid level of the molten iron (m),

to be.

[5] The molten iron dephosphorization method according to any one of [1] to [4], wherein a ratio of the flow rate N _I of the inert gas to the flow rate N _O2 of the oxygen gas is N _I /N _O2 =0.03 to 0.20.

[6] The method of dephosphorization of molten iron according to [5], wherein a ratio of the flow rate N _I of the inert gas to the flow rate N _O2 of the oxygen gas is N _I /N _O2 =0.05 to 0.20.

According to said each aspect of this invention, when dephosphorizing molten iron|metal in a converter, slag forming in dephosphorization blow tempering is suppressed, and phosphorus concentration is fully reduced, molten iron|metal dephosphorization can be performed, without causing a raise of cost.

BRIEF DESCRIPTION OF THE DRAWINGS It is a longitudinal sectional view which shows the schematic structure of the converter which concerns on one Embodiment of this invention.

EMBODIMENT OF THE INVENTION Hereinafter, one Embodiment of this invention is described.

As mentioned above, as for the upper blow lance of a converter, the upper limit and lower limit of the gas supply rate are determined by the air outlet shape (nozzle diameter or the number of nozzle holes). In the case of controlling the delivery speed of dephosphorization blow temper and decarburization blow temper in one top blow lance accompanying the converter, the lance tuyere shape is designed so that the upper limit of the gas supply speed can realize high-speed delivery in the decarburization blow temper, so as a result, gas is supplied The lower limit of the speed also becomes a high value. When the supply rate of oxygen sprayed to molten iron|metal from a top blow lance is operated below the supply rate lower limit determined from a tuyere shape, oxygen gas will not fully be supplied to molten iron|metal. As a result, there are safety problems due to poor phosphorus removal or backfire. Therefore, if the oxygen supply rate in decarburization blow temper is speeded up for the improvement of production efficiency, the oxygen supply rate of dephosphorization blow tempering cannot but be speeded up inevitably.

As mentioned above, the lower limit is set as for the supply rate of the gas injected to molten iron|metal from a top blow lance. When only oxygen is supplied from the upper blow Lance, the minimum value of the oxygen supply rate possible on equipment becomes the lower limit of the gas supply rate. When this oxygen supply rate is higher than the upper limit of the suitable oxygen supply rate in dephosphorization blow tempering, supplied oxygen reacts with Fe in molten iron|metal, and FeO is produced|generated excessively. Since CO bubble will generate|occur|produce abundantly by reaction with C in molten iron|metal when FeO density|concentration in slag is high as mentioned above, slag forming will occur at the early timing of blow tempering. In addition, as shown in the formula (A) above, the FeO concentration in the slag also contributes to the progress of the dephosphorization reaction, but if the FeO concentration is excessive, sloping occurs and blow tempering is stopped. have.

1 is a longitudinal sectional view showing a schematic configuration of a converter 1 according to the present embodiment. In this embodiment, toward the liquid level of the molten iron|metal 2 in the converter 1, the mixed gas after mixing oxygen gas and an inert gas using the upper blow lance 3 is injected. By mixing oxygen gas and an inert gas, it is possible to inject oxygen to the molten iron|metal 2 at a low supply rate, without being less than the lower limit set value of the gas supply rate of the upper blow lance 3 . That is, by injecting the gas which mixed oxygen gas and an inert gas from the upper blow lance 3, it is possible to reduce an oxygen supply rate, to suppress the production|generation of FeO, and to suppress slag forming. In addition, the slag forming is accelerated at a higher temperature, and the dephosphorization reaction is accelerated at a lower temperature. When paying attention to the temperature of molten iron|metal or slag at the time of blowing only oxygen gas into the molten iron|metal 2, in order to generate heat by the oxidation reaction of oxygen and each molten iron|metal component, slag forming will be accelerated|stimulated and dephosphorization reaction will be suppressed. On the other hand, since an inert gas does not react with molten iron|metal, it acts as cooling gas of the molten iron|metal 2 and slag. Therefore, spraying after mixing oxygen gas and an inert gas beforehand is effective in both suppression of slag forming and promotion of a dephosphorization reaction compared with the case where only oxygen gas is blown.

The inert gas is, for example, N ₂ gas. The N ₂ gas is inexpensive compared to other inert gases, and the above-described effects can be achieved at low cost. In addition, the same effect can be expressed with Ar gas, CO ₂ gas, or H ₂ O gas instead of N ₂ gas.

In dephosphorization blow tempering, at the beginning of a blow tempering start, oxygen gas is injected from the upper blow lance 3, and then, at a predetermined timing, it switches to injection of the mixed gas of oxygen gas and an inert gas. Decarburization advances also during dephosphorization blow tempering, and the carbon concentration in the molten iron|metal 2 falls gradually. As a timing to start injection of the mixed gas from the top blow lance 3 (timing to start mixing an inert gas in top blow gas), the carbon concentration in molten iron|metal needs to be 3.0 mass % or more. When oxygen gas is continuously supplied at a high supply rate until the carbon concentration in the molten iron|metal 2 becomes 3.0 mass % or less, sloping will generate|occur|produce. Therefore, when the carbon concentration at the time of starting mixing of the inert gas is lower than 3.0 mass %, suppression of sloping is difficult.

Moreover, the present inventors earnestly studied about the timing which starts injection of the mixed gas of oxygen and an inert gas from the upper blow lance 3 . As a result, when the carbon concentration in the molten iron|metal 2 was higher than 3.8 mass %, even if it changed the timing to start spraying with respect to the effect for suppressing sloping and extending blow temper time, it revealed that there is not a big difference.

As mentioned above, as a timing to start injection of mixed gas, the time of carbon concentration in the molten iron|metal 2 being 3.0 mass % or more and 3.8 mass % or less is preferable. In other words, as a lower limit of the said carbon concentration, it is more preferable that it is 3.1 mass %.

Generally, dephosphorization blow temper is performed by adding a refining material to molten iron|metal from the furnace opening of a converter, and supplying oxygen from a top blow lance. In this embodiment, in the case of dephosphorization blow tempering, the refining agent 4 is added to the molten iron|metal 2 from the furnace port of the converter 1, When only the mixed gas of oxygen gas and an inert gas is supplied from the top blow lance 3 Also, of course, the above-described effect is exhibited.

The scouring agent 4 is basically supplied from only the furnace port of the converter 1, and is not supplied from other locations, such as the top blow lance 3. That is, from the upper blowing lance 3, only mixed gas is injected toward the molten iron|metal 2. However, you may add the refining agent 4 also from the top blowing lance 3 in addition to the said furnace mouth as needed.

In addition, the present inventors, when the carbon concentration in molten iron is 3.0 mass % or more and 3.8 mass % or less, when switching from oxygen gas to the said mixed gas and starting injection, calculated by the formula (1) mentioned later, It was found that dephosphorization reaction can be promoted while further suppressing sloping by setting the stirring power density E _TOP by the overhead gas to 140 (W/t) or less. First, the following (1)' formula will be described.

E _TOP =0.137·cosθ·Q ³ ·M/(Wm·Λ ² ·D ³ ·H) ···(1)'

where θ is the nozzle inclination angle (°) of the top blowing lance, Q is the top blowing gas flow rate (Nm3/s), M is the gas molecular weight, Wm is the molten iron weight (t), Λ is the nozzle hole number of the top blowing lance (-), D is the outlet diameter (m) of the nozzle of the top blowing lance, and H is the lance gap (distance between the nozzle of the top blowing lance and the still liquid level) (m).

In addition, the formula (1)' above is reported by Kai et al. (Document: Tsuyoshi Kai, Kazuo Okobirashi, Shozo Murakami, Nobuo Sato: Iron and Steel, 68 (1982), 82), in which the upper odor gas is the sole gas species. is the case. As in the present embodiment, when a mixed gas of oxygen gas and inert gas is used, the following formula (1) obtained by modifying (Q ³ ·N) in the formula (1)' is used.

E _TOP =0.137·cosθ·(Q _I ·M _I +Q _O2 ·M _O2 )·(Q _I +Q _O2 ) ² /(Wm·Λ ² ·D ³ ·H) ···(1)

here,

θ is the nozzle inclination angle (°) of the upper blow lance (3),

Q _I is the flow rate of the inert gas contained in the mixed gas (Nm 3 /s),

M _I is the molecular weight of the inert gas contained in the mixed gas,

Q _O2 is the flow rate of oxygen gas contained in the mixed gas (Nm 3 /s),

M _O2 is the molecular weight of the oxygen gas contained in the mixed gas,

Wm is the weight of the molten iron (t),

Λ is the number of nozzle holes (-) of the upper blow lance (3),

D is the nozzle outlet diameter (m) of the upper blow lance (3),

H is the distance (m) between the nozzle of the upper blowing lance (3) and the stationary liquid level of the molten iron (2),

to be.

As the reason for suppressing the sloping, by setting it to 140 (W/t) or less, the generation of gas accompanying the progress of the decarburization reaction was suppressed by suppressing the scattering of grain iron into the slag and suppressing agitation at the slag-metal interface. it is estimated that

In addition, the present inventors investigated an appropriate ratio of the flow rate N _O2 of the oxygen gas supplied from the upper blow lance 3 and the flow rate N _I of the inert gas, and controlled to N _I /N _O2 = 0.03 to 0.20, thereby sloping It was found that dephosphorization reaction can be promoted while suppressing. Here, the flow rate of each gas is the flow rate value per ton of molten iron|metal which measured the gas supplied to the upper blow lance 3 individually with an orifice gas flow meter, respectively. When N _I /N _{O 2} is smaller than 0.03, the amount of the inert gas is small and the oxygen supply rate cannot be sufficiently reduced, so that slag forming cannot be suppressed. On the other hand, when N _I /N _{O 2} is larger than 0.20, the rate of oxygen supply is low, so the rate of formation of FeO in the slag becomes slow, and the dephosphorization reaction shown in the formula (A) slows down.

In addition, it is good also considering the lower limit of N _I /N _O2 as 0.05 instead of 0.03. That is, it is good also as N _I /N _O2 =0.05 - 0.20.

Moreover, it is preferable to adapt this invention to the case where the charging basicity of slag is 3.0 or less. Here, the charging basicity refers to "the sum of the mass of CaO contained in the auxiliary material supplied into the converter" as a numerator, and "the sum of the mass of SiO ₂ contained in the auxiliary material supplied into the converter" and "Si contained in the molten iron and scrap" It is a numerical value of ratio calculated by making the sum total _of SiO2 mass in _the case where it is assumed that all is oxidized to SiO2" as a denominator.

This is because, when the charged basicity is larger than 3.0, the proportion of the solid phase in the slag increases, and sloping tends to be suppressed by the effect. Moreover, the case of 2.0 or less is preferable.

Example

The molten iron that was tapped from the furnace and desulfurized in the KR (Kanbara Reactor) method was used. The KR method is a method in which the desulfurization agent is dispersed in the molten iron by rotating an impeller in a molten iron ladle to generate a desulfurization reaction at the interface between the dispersed particles and the molten iron and at the interface between the dispersed particles and the molten iron and the surface of the molten iron bath and the floating desulfurization agent. This molten iron was charged into the top blow converter (converter 1 shown in FIG. 1). The carbon concentration in the molten iron|metal 2 in the converter 1 was 4.3 mass %. The shapes (nozzle diameter, nozzle inclination angle, number of nozzle holes) of the nozzles provided at the tip of the upper blow lance 3 are all the same, and the lower limit of the gas supply rate is 98 Nm 3 /hr·t. In addition, all of the low odor conditions are the same. Specifically, the nozzle inclination angle θ(°) of the top blowing lance 3 is 18°, the number of nozzle holes Λ(-) of the top blowing lance 3 is 5, and the nozzle outlet diameter D( m) is 0.079 m, the weight Wm(t) of the molten iron is 340t, and the distance H(m) between the nozzle of the upper blow lance 3 and the stationary liquid level of the molten iron 2 is 3.0 m or more.

Next, quicklime was added as a refining agent 4 to this molten iron|metal 2 from the furnace port of the converter 1, and dephosphorization blow tempering was started. At this time, the charging basicity was made into 1.0-2.0. In this charge basicity, "the sum of the mass of CaO contained in the auxiliary material supplied into the converter" is the numerator, "the sum of the mass of SiO ₂ contained in the auxiliary material supplied into the converter" and "Si contained in the molten iron and scrap is It is a numerical value of ratio calculated by making the sum total _of SiO2 mass at the time _of assuming that all were oxidized to SiO2 as a denominator.

Oxygen gas is sprayed from the top blow lance 3 to the molten iron 2 at a flow rate of 99 Nm 3 /hr t while blowing a predetermined flow rate of a gas containing nitrogen as a main component as a low odor gas from a tuyere (not shown) at the bottom of the converter. and dephosphorization blow tempering was started. At the timing when the dephosphorization blow tempering progresses and the carbon concentration in the molten iron reaches the “carbon concentration at the start of the mixed gas injection” in Table 1, the mixture is switched to a mixed gas of oxygen gas and nitrogen gas under each condition shown in Table 1, and mixed gas The dephosphorization was continued by spraying the molten iron. Then, the dephosphorization blow tempering was made into completion|finish at the timing which sloping generate|occur|produced, and the molten iron|metal sample was collect|collected. The molten iron|metal sample performed quantitative analysis of each component using the emission spectroscopy apparatus.

The unit [Nm 3 /hr·t] of the flow rate N _{O 2} of the oxygen gas and the flow rate N _I of the inert gas represents the gas flow rate in the standard state per 1 t of molten iron. In addition, E _TOP is the stirring power density by the upper part of the said (1) formula. The Lance gap H (the distance between the nozzle of the upper blow Lance and the still liquid level) is appropriately changed for each Example so that the stirring power density becomes the value shown in Table 1. In addition, No. 7 is the comparative example which sprayed only oxygen gas to molten iron|metal without mixing nitrogen gas from a top blow lance.

The blow tempering time shown in Table 1 is dephosphorization blow temper time, and the phosphorus concentration in steel after dephosphorization blow temper is the phosphorus concentration in steel which analyzed the metal sample collect|collected after dephosphorization blow temper with the emission spectroscopy apparatus.

In addition, "the carbon concentration at the time of mixed gas injection start" in Table 1 is the carbon concentration in the molten iron|metal 2, and was calculated|required by the combustion method using the infrared absorbing device made by LECO Japan.

In invention examples Nos. 1 to 6 and 9 to 13 in Table 1, compared with Comparative Examples No. 7 and 8, phosphorus concentration in steel after dephosphorization blow tempering (hereinafter, after dephosphorization blow tempering [%P]) lowered When gas is supplied to the molten iron 2 in the converter 1 using the upper blow lance 3, the carbon concentration in the molten iron is 3.0 mass % or more, and the gas to be supplied is supplied from oxygen gas to oxygen gas and inert gas. By switching to mixed gas and performing injection, the supply flow rate of oxygen gas is reduced, the sloping from the furnace opening of the converter 1 by slag forming is suppressed, and the dephosphorization blow time is comparative example No. 7 and 8. It is presumed to be due to the length

Moreover, compared with No. 1, No. 2 had almost no difference in [%P] after blow temper time and dephosphorization blow temper. Moreover, as for No. 3, compared with No. 2, blow temper time was short, and [%P] after dephosphorization blow temper was high. From this result, even if the timing of switching injection gas from oxygen gas to mixed gas is so quick that the carbon concentration in molten iron|metal exceeds 3.8 mass %, the dephosphorization effect is considered to be equivalent to the case of 3.8 mass %.

Compared with No. 3, No. 4 had a long blow tempering time, and [%P] after dephosphorization blow tempering was low. It is estimated that this is because the generation|occurrence|production timing of sloping became slow by suppressing the gas generation accompanying advancing of a decarburization reaction by making E _TOP into 140 (W/t) or less.

No. 5 had a long blow tempering time with respect to No. 1, No. 2, No. 3, No. 4, and No. 6, and [%P] after dephosphorization blow tempering was low. For this reason, E _TOP is made 140 (W/t) or less, and the value is set to the smallest value in Examples, N _I /N _O2 = 0.03 to 0.20, while suppressing slag forming, dephosphorization It is estimated that it was because FeO in slag which is important for this was able to be controlled more appropriately.

The present invention is applicable as a method of dephosphorizing molten iron in a converter.

1: converter
2: Charter
3: Sangchwi Lance
4: Refining agent

Claims (9)

It is a method of dephosphorizing molten iron in a converter equipped with a top breath lance,
In a state where the carbon concentration in the molten iron in the converter is 3.0 mass % or more and 3.8 mass % or less, using a top blow lance, starting injection of a mixed gas of oxygen gas and an inert gas to the molten iron using a lance,
The stirring power density E _TOP of the mixed gas supplied from a top blow Lance prescribed by following (1) Formula shall be 140 W/t or less, The dephosphorization method of molten iron|metal characterized by the above-mentioned.
E _TOP =0.137·cosθ·(Q _I ·M _I +Q _O2 ·M _O2 )·(Q _I +Q _O2 ) ² /(Wm·Λ ² ·D ³ ·H) ···(1)
here,
θ is the nozzle inclination angle (°) of the upper blow Lance,
Q _I is the flow rate (Nm 3 /s) of the inert gas contained in the mixed gas,
M _I is the molecular weight of the inert gas contained in the mixed gas,
Q _O2 is the flow rate of the oxygen gas contained in the mixed gas (Nm 3 /s),
M _O2 is the molecular weight of the oxygen gas contained in the mixed gas,
Wm is the weight (t) of the molten iron,
Λ is the number of nozzle holes of the upper blow Lance (-),
D is the outlet diameter of the nozzle of the upper blow Lance (m),
H is the distance between the nozzle of the upper blow Lance and the stationary liquid level of the molten iron (m),
to be. The method for dephosphorizing molten iron according to claim 1, wherein only the mixed gas is sprayed toward the molten iron from the top blowing lance. The method according to claim 1 or 2, wherein a ratio of a flow rate N _I of the inert gas to a flow rate N _O2 of the oxygen gas is N _I /N _O2 =0.03 to 0.20. The method according to claim 3, wherein the ratio of the flow rate N _I of the inert gas to the flow rate N _O2 of the oxygen gas is N _I /N _O2 =0.05 to 0.20. delete delete delete delete delete

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