JP2018127671A - Refining method for molten steel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To control slag foaming and prevent slopping which induces operation troubles and deteriorates yield in a desiliconizing process of molten steel of high Si concentration.SOLUTION: There is provided a refining method for molten steel which is subjected to desiliconization treatment by charging a desiliconizing agent into molten steel of high Si concentration in a refining vessel. (i) A desiliconizing agent having a gaseous oxygen ratio Rof 0.70 or more is charged into molten steel having a forming index S of 0.06 or more so that the foaming index S decreases to less than 0.06, where Rindicates a ratio of gaseous oxygen to oxygen in the desiliconizing agent. (ii) Subsequently, a required amount of the desiliconizing agent is charged at a time. S=ΔSi×Cwhere ΔSi=([%Si]-0.20), C=5-(0.0026*T-0.32×[%Si]+1.25), [%Si]is Si concentration (mass%) of molten steel, Tis temperature (°C) of molten steel. R=F/(F+F) where Fis gaseous oxygen blowing speed (Nm/min)×1.429 (kg/Nm), Fis solid oxygen source blowing speed (kg/min)×α where α is an adjustment factor by the solid oxygen source.SELECTED DRAWING: None

Description

  The present invention relates to a refining method that suppresses slag forming and prevents slopping in refining hot metal, particularly refining hot metal contained in a kneading vehicle.

  Conventionally, in order to produce high-quality steel that meets various applications, in preparation for refining in the converter, it is a spare that removes impurities (S, P, etc.) and adjusts the amount of Si in the hot metal contained in the kneading car Refining is done.

  In the preliminary refining, a solid oxygen source (usually iron oxide) is introduced into the hot metal contained in the kneading vehicle from the receiving port, or a solid oxygen source (usually iron oxide) and / or from a lance inserted into the hot metal. Although a gaseous oxygen source is blown in, oxygen reacts with C in the molten iron to generate CO gas, and a phenomenon in which the volume of slag is increased by this CO gas, that is, slag foaming occurs.

  The kneading vehicle has a narrow free board (the space from the molten metal surface to the receiving port). Therefore, if excessive slag forming occurs, a phenomenon in which the slag overflows from the receiving port, that is, slopping occurs.

  Since slopping leads to operational troubles and reduced yields, many technologies have been proposed to prevent slugging and prevent slopping in the preliminary refining of hot metal contained in a kneading vehicle ( For example, see Patent Documents 1 to 6.)

  For example, in Patent Document 5, a pretreatment agent such as desiliconization or dephosphorization of hot metal is introduced by introducing a pretreatment agent such as a solid oxide, a lime compound, or gaseous oxygen into the hot metal in the reaction vessel while suppressing slag forming. In the hot metal preliminary refining method for refining, a region where slopping is likely to occur based on the slump generation conditions of slag obtained by using the solid oxide and gaseous oxygen input to the hot metal and the slag basicity as an index, and There has been proposed a hot metal preliminary refining method characterized by determining the criticality of occurrence with a region that is difficult to generate and controlling the amount of oxygen input per hour to be within the determined criticality of generation.

  Further, Patent Document 6 discloses an injection having a gas injection port (x) on the side in a hot metal preliminary treatment method in which a solid oxygen source is blown into an hot metal held in a topped car through an injection lance to perform desiliconization and dephosphorization. Using a lance, blowing a solid oxygen source into the hot metal from the injection port at the tip of the lance, and (i) oxygen gas from the gas injection port (x) of the injection lance to the adhering metal inside the topped car at the initial stage of the treatment And (ii) after the middle stage of the treatment, the gas injection port (x) of the injection lance is positioned in the slag, and from the gas injection port (x) There has been proposed a hot metal preliminary treatment method in which nitrogen gas is injected into the slag to stir the slag.

JP-A-02-290911 Japanese Patent Laid-Open No. 05-125424 JP-A-10-176210 JP-A-10-183217 Japanese Patent Laid-Open No. 10-195515 JP 2008-297590 A

  Slag forming is usually caused by the reaction between C and oxygen in the hot metal (decarburization reaction) and hardly occurs in the composition region where this decarburization reaction is difficult to occur. The prior art is for slag forming by the above decarburization reaction. According to the experience of the present inventors, slag forming occurs frequently even in the refining of hot metal having a high Si concentration where the above decarburization reaction hardly occurs. .

  Therefore, in view of the frequent occurrence of this slag forming, the present invention has an object to suppress slug forming in the desiliconization treatment of hot metal having a high Si concentration, and to prevent slopping that causes operational trouble and yield reduction. It aims at providing the refining method of the hot metal which solves this subject.

  The present inventors diligently studied a method for solving the above problems. As a result, in the desiliconization treatment of hot metal having a high Si concentration, before the solid oxygen source (iron oxide) is introduced, a desiliconizing agent mainly composed of a gaseous oxygen source is introduced, while the hot metal temperature is increased. It has been found that when the concentration is lowered and the C saturation solubility is increased, slag foaming is less likely to occur, and then full-scale desiliconization treatment can be performed. This point will be described later.

  The present invention has been made based on the above findings, and the gist thereof is as follows.

(1) In a hot metal refining method in which a silicon removal agent is added to a high Si concentration hot metal contained in a refining vessel and subjected to a desiliconization treatment.
(I) Gas oxygen ratio R indicating the ratio of gaseous oxygen to oxygen in the desiliconizing agent, defined by the following formula (2), in the hot metal having a forming index S defined by the following formula (1) of 0.06 or more A desiliconizing agent having _O2 of 0.70 or more is added until the forming index S is less than 0.06, and then
(Ii) A hot metal refining method characterized in that a necessary amount of a desiliconizing agent is charged in a lump.
S = ΔSi × C _index ^1.3 (1)
ΔSi = ([% Si] _HM −0.20)
C _index = 5- (0.0026 * T _HM −0.32 * [% Si] _HM +1.25)
[% Si] _HM : Si concentration of molten iron (mass%)
T _HM : Hot metal temperature (° C)
^{_{R O2 = F O _ O2 /}} (F O _ O2 + F O _ FetO) ··· (2)
F _O ^_ _O2: gaseous oxygen source blowing rate (Nm ³ / ^{min) × 1.429 (kg / Nm 3} )
F _O ^_ _FetO: solid oxygen source blowing rate (kg / min) × alpha
α: Adjustment factor for solid oxygen source

  (2) The hot metal refining method according to (1), wherein the high Si concentration hot metal has a Si concentration of 0.60% by mass or more.

  (3) The hot metal refining method according to (1) or (2), wherein Si in the hot metal is reduced to 0.20% by mass or less by the desiliconization treatment.

  (4) The hot metal refining method according to any one of (1) to (3), wherein the desiliconizing agent comprises iron oxide, gaseous oxygen, and lime-based flux.

  (5) The hot metal refining method according to any one of (1) to (4), wherein the refining vessel is a chaotic vehicle.

  According to the present invention, in the refining of hot metal having a high Si concentration, slag forming can be suppressed, and slopping that can cause operational troubles and a decrease in yield can be prevented, thereby performing desiliconization treatment.

  The hot metal refining method of the present invention (hereinafter also referred to as “the present invention refining method”) is a function of the hot metal Si concentration and the hot metal temperature in order to suppress slag forming in the refining of hot metal with a high Si concentration. An index is defined, and until the index falls below a threshold value, a preliminary desiliconization treatment is performed by introducing a desiliconization agent having a gas oxygen ratio of a certain value or more indicating a ratio of gaseous oxygen to oxygen in the desiliconization agent, and thereafter The basic idea is to perform full-scale siliconization.

Specifically, the refining method of the present invention is a refining method for hot metal in which a silicon removal agent is added to a high Si concentration hot metal contained in a refining vessel and subjected to desiliconization treatment.
(I) Gas oxygen ratio R indicating the ratio of gaseous oxygen to oxygen in the desiliconizing agent, defined by the following formula (2), in the hot metal having a forming index S defined by the following formula (1) of 0.06 or more A desiliconizing agent having _O2 of 0.70 or more is added until the forming index S is less than 0.06, and then
(Ii) It is characterized in that a necessary amount of desiliconizing agent is added all at once.

S = ΔSi × C _index ^1.3 (1)
ΔSi = ([% Si] _HM −0.20)
C _index = 5- (0.0026 * T _HM −0.32 * [% Si] _HM +1.25)
[% Si] _HM : Si concentration of molten iron (mass%)
T _HM : Hot metal temperature (° C)
^{_{R O2 = F O _ O2 /}} (F O _ O2 + F O _ FetO) ··· (2)
F _O ^_ _O2: gaseous oxygen blowing rate (Nm ³ / ^{min) × 1.429 (kg / Nm 3} )
F _O ^_ _FetO: solid oxygen source blowing rate (kg / min) × alpha
α: Adjustment factor for solid oxygen source

  Hereinafter, the refining method of the present invention will be described.

  As described above, slag forming frequently occurs even in the desiliconization treatment of hot metal having a high Si concentration in which decarburization reaction hardly occurs. Regarding the frequent occurrence of this slag forming, the present inventors have stated that “the higher the concentration of Si, the lower the saturation C concentration. Therefore, when the hot metal temperature is lowered by the introduction of a solid oxygen source (iron oxide), C precipitates and precipitates C The solid oxygen source (iron oxide) in the slag reacts to generate CO gas, resulting in slag forming. "

  In the desiliconization treatment of hot metal having a high Si concentration, before the solid oxygen source (iron oxide) is introduced, a desiliconizing agent mainly composed of a gaseous oxygen source is introduced to increase the Si concentration while increasing the hot metal temperature. If the C saturation solubility is lowered and the generation of slag foaming due to the precipitation of C can be suppressed, the solid oxygen source (iron oxide) is charged all at once in the next stage. It has been found that even if the temperature is lowered, C does not precipitate and CO is not generated, so that slag forming hardly occurs and a full-scale silicon removal treatment can be performed.

  Hereinafter, refining conditions for suppressing slag forming will be described.

Forming index S: ΔSi × C _index ^1.3 (formula (1) above)
The characteristics of the hot metal that affects the occurrence of slag forming vary depending on the composition of C and Si and the hot metal temperature. In the refining of hot metal having a high Si concentration, the present inventors define the characteristics of hot metal by the above formula (1) as an index for uniquely evaluating the composition of C and Si and the hot metal temperature. A forming index S (hereinafter also referred to as “index S”) was introduced.

Index S is the product of C _index of C _index ^1.3 to define the ΔSi be defined by the following formula, also by the following equation.
ΔSi = ([% Si] _HM −0.20)
C _index = 5- (0.0026 * T _HM −0.32 * [% Si] _HM +1.25)
[% Si] _HM : Si concentration of molten iron (mass%)
T _HM : Hot metal temperature (° C)

ΔSi is the difference between the Si concentration (mass%) of molten iron: [% Si] _HM and the Si concentration (mass%) aimed at reaching by desiliconization treatment: 0.20 (mass%), that is, reduced by desiliconization treatment. It is a parameter | index which shows the amount of Si to do. When ΔSi is large, a large amount of gaseous oxygen source and / or solid oxygen source is required, and forming is likely to occur during the desiliconization process. Therefore, ΔSi is also an index indicating the possibility of forming.

C _index is a precipitation index of C defined by [% Si] _HM and hot metal temperature (° C.): T _HM . [% Si] When the _HM is high, the saturated C concentration (mass%) of the hot metal is low, and when T _HM is high, the saturated C concentration (mass%) of the hot metal is high, so the C _index is the saturated C concentration (mass%). ) Is an index that comprehensively considers the influence of [% Si] _HM and T _HM , and a large C _index indicates that C is likely to precipitate due to a decrease in hot metal temperature due to the introduction of a desiliconizing agent.

Since the precipitation amount of C greatly affects the occurrence of slag forming, C _index is multiplied by ΔSi as C _index ^1.3 . That is, the index S is an index indicating the probability that slag forming will occur in the desiliconization process in which the Si concentration of the hot Si molten iron is reduced to 0.20 mass% or less.

  In the refining method of the present invention, as described above, in refining hot metal having a high Si concentration, a threshold is set for the index S in order to suppress slag forming during the desiliconization process, Until the S falls below the threshold value, preliminary desiliconization is performed by introducing a desiliconization agent in which the ratio of gaseous oxygen to oxygen in the desiliconization agent is a certain value or more.

In the refining method of the present invention, the threshold value of the index S is set to 0.06 on the basis of the refining conditions in which slapping has occurred in actual operation, and the following formula (2) A desiliconizing agent having a gas oxygen ratio R _O2 of 0.70 or more, which indicates the ratio of gaseous oxygen to oxygen in the desiliconizing agent, is defined until the index S reaches less than 0.06. In the desiliconization process including the process, the occurrence of slag forming is suppressed. This is a finding found by the present inventors and is a feature of the refining method of the present invention.

^{_{R O2 = F O _ O2 /}} (F O _ O2 + F O _ FetO) ··· (2)
F _O ^_ _O2: gaseous oxygen blowing rate (Nm ³ / ^{min) × 1.429 (kg / Nm 3} )
F _O ^_ _FetO: solid oxygen source blowing rate (kg / min) × alpha
α: Adjustment factor for solid oxygen source

Gaseous oxygen ratio ^{_{R O2: F O _ O2 /}} (F O _ O2 + F O _ FetO) ( the formula (2))
In the desiliconization agent mainly composed of solid oxygen source (iron oxide), gaseous oxygen source, and lime-based flux, the ratio of gaseous oxygen to the total oxygen content (gas oxygen content + solid oxygen content) R _O2 is defined by the above formula (2).

The amount of solid oxygen solid oxygen source in is different depending on the type of solid oxygen source, multiplying the α adjustment coefficient corresponding to the type of solid oxygen source to F _O ^_ _FetO. For example, when the solid oxygen source is mill scale, α = 0.22. When the solid oxygen source is iron ore, α = 0.30, which is usually 1.0 or less.

The gas oxygen ratio R _O2 of the silicon removal agent is important together with the index S in that it suppresses the occurrence of slag foaming. In the preliminary desiliconization treatment, it is necessary to set a threshold value for the gas oxygen ratio R _O2 in order to suppress the decrease in the hot metal temperature, avoid the precipitation of C, and reduce the Si concentration. The inventors set the gas oxygen ratio R _O2 to be 0.70 or more based on the refining conditions in which slapping occurred in actual operation.

That is, when the gas oxygen ratio R _O2 is less than 0.70, the proportion of solid oxygen increases, the hot metal temperature (T _HM ) decreases, C precipitates, and CO gas that causes slag foaming is generated. Therefore, the gas oxygen ratio R _O2 is set to 0.70 or more. Preferably it is 0.75 or more.

In the preliminary desiliconization treatment of hot metal having a high Si concentration, by introducing a desiliconizing agent having a gas oxygen ratio R _O2 of 0.70 or more into the hot metal, the hot metal temperature (T _HM ) is not lowered, that is, the hot metal temperature is reduced. C precipitation due to the decrease can be avoided, slag forming can be suppressed, and hot metal having an index S of less than 0.06 can be obtained.

In the next stage, a necessary amount of desiliconizing agent is added all at once to the hot metal having an index S of less than 0.06 by introducing a desiliconizing agent having a gas oxygen ratio R _O2 of 0.70 or more. The concentration is reduced to a required level, for example, 0.20% by mass or less. The R _O2 of the desiliconized material to be charged all at once in this desiliconization treatment is not particularly limited. Even in this desiliconization process, slag forming does not occur.

  In the refining method of the present invention, the refining vessel that accommodates the hot metal having a high Si concentration is not particularly limited to a specific refining vessel. A container that transports the hot metal discharged from the blast furnace to the next process, and a container that can be refined during transportation (for example, a kneading car, a hot metal ladle, etc.) can be used as a refining container. In particular, it is suitable for the desiliconization treatment of hot metal contained in a kneading wheel with a narrow free board.

  Next, examples of the present invention will be described. The conditions in the examples are one example of conditions used for confirming the feasibility and effects of the present invention, and the present invention is based on this one example of conditions. It is not limited. The present invention can adopt various conditions as long as the object of the present invention is achieved without departing from the gist of the present invention.

Example 1
Preliminary desiliconization treatment is performed on hot metal contained in a kneading vehicle with an index S of 0.06 or more under the conditions shown in Table 1, and then desiliconization treatment is performed under the conditions shown in Table 1 to determine whether slag foaming occurs. The treatment was evaluated.

  Evaluation 1 evaluated whether or not slag foaming occurred during the preliminary desiliconization treatment. Evaluation 2 evaluated whether or not slag foaming occurred during the desiliconization treatment after the desiliconization treatment, and in the same manner as in Evaluation 1, the case where the slag was formed was evaluated as x, and the case where the slag was not formed was evaluated as ◯.

In Comparative Example 1 in which the pre-silicon removal treatment was performed using a silicon removal material having an R _O2 of less than 0.70, the index S did not reach less than 0.06 after the treatment, and the pre-silicon removal treatment was in progress. Slag forming occurred (see “Evaluation 1”), and the process was interrupted (see “Evaluation 2”).

In Comparative Example 2 where the pre-silicon removal treatment was performed using a silicon removal agent having an R _O2 of 0.70 or more, no slag forming occurred during the treatment (see “Evaluation 1”). Since the index S exceeds 0.06, slag foaming occurred during the subsequent desiliconization process (see “Evaluation 2”).

Therefore, if preliminary desiliconization treatment is performed with a desiliconization agent having an R _O2 of less than 0.70, slag forming occurs during the preliminary desiliconization treatment, and a desiliconization agent having an R _O2 of 0.70 or more. When the preliminary desiliconization process is performed, the occurrence of forming during the process can be suppressed, but the index S does not reach less than 0.06, and it can be confirmed that slag forming occurs during the subsequent desiliconization process.

In Examples 1 to 3 where R _O2 is pre-silicon removal treatment with a desiliconization agent of 0.70 or more and the index S after the pre-silicon removal treatment is less than 0.06, in the silicon removal treatment following the preliminary silicon removal treatment , Even if a desiliconized material having a small R _O2 (a large amount of solid oxygen) is added, slag forming is suppressed, and no slopping occurs, and finally the Si concentration is reduced to 0.20% by mass or less. (See “Evaluation 1”, “Evaluation 2”).

From the above, in the refining of hot metal with a high Si concentration, first, the Si concentration is reduced until the index S is less than 0.06 by using a desiliconizing agent having a gas oxygen ratio R _O2 of 0.70 or more. It is understood that it is necessary to carry out (preliminary desiliconization treatment) and then carry out the desiliconization treatment by supplying a necessary amount of desiliconization agent (gas oxygen ratio R _O2 may be less than 0.70) all at once.

  As described above, according to the present invention, in the refining of hot metal having a high Si concentration, slag forming can be suppressed, and operation troubles and slopping that can lead to a decrease in yield can be prevented, and desiliconization can be performed. . Therefore, the present invention has high applicability in the steel industry.

Claims (5)

In a hot metal refining method in which a silicon removal agent is added to a high Si concentration hot metal contained in a refining vessel and subjected to a desiliconization treatment.
(I) Gas oxygen ratio R indicating the ratio of gaseous oxygen to oxygen in the desiliconizing agent, defined by the following formula (2), in the hot metal having a forming index S defined by the following formula (1) of 0.06 or more A desiliconizing agent having _O2 of 0.70 or more is added until the forming index S is less than 0.06, and then
(Ii) A hot metal refining method characterized in that a necessary amount of a desiliconizing agent is charged in a lump.
S = ΔSi × C _index ^1.3 (1)
ΔSi = ([% Si] _HM −0.20)
C _index = 5- (0.0026 * T _HM −0.32 * [% Si] _HM +1.25)
[% Si] _HM : Si concentration of molten iron (mass%)
T _HM : Hot metal temperature (° C)
^{_{R O2 = F O _ O2 /}} (F O _ O2 + F O _ FetO) ··· (2)
F _O ^_ _O2: gaseous oxygen blowing rate (Nm ³ / ^{min) × 1.429 (kg / Nm 3} )
F _O ^_ _FetO: solid oxygen source blowing rate (kg / min) × alpha
α: Adjustment factor for solid oxygen source   The hot metal refining method according to claim 1, wherein the high Si concentration hot metal has a Si concentration of 0.60 mass% or more.   The hot metal refining method according to claim 1 or 2, wherein Si in the hot metal is reduced to 0.20 mass% or less by the desiliconization treatment.   The hot metal refining method according to any one of claims 1 to 3, wherein the desiliconizing agent comprises a solid oxygen source, a gaseous oxygen source, and a lime-based flux.   The hot metal refining method according to claim 1, wherein the refining vessel is a chaotic vehicle.