KR20080089650A - Method of dephosphorization of molten iron - Google Patents

Abstract

A method in which a smelting agent consisting mainly of a CaO source and an oxygen source are added to molten iron to conduct a dephosphorization treatment. In the method, the molten iron is dephosphorized so that the slag after the treatment has a basicity of 2.2-3.5, excluding 2.2, and a total iron concentration of 10-30 mass% and that the final treatment temperature of the molten iron is 1,320°C or higher. Thus, the dephosphorization can be accelerated while ensuring a high manganese yield and the molten iron can be efficiently dephosphorized.

Description

Chartered Tallinn Method {METHOD OF DEPHOSPHORIZATION OF MOLTEN IRON}

The present invention relates to a method for dephosphorization of molten iron which is carried out as hot metal pretreatment.

Instead of the conventional converter method, the molten iron preliminary treatment method of performing the dephosphorization treatment in the molten iron phase has been widely used. This is because the lower the refining temperature is, the easier it is to proceed thermodynamically (although there is a lower limit of the temperature that can be treated), and the lower the refining temperature, the lower the refining agent, the lower the refining agent can be, the lower the refining agent.

In general, in the preliminary treatment of molten iron, first, a solid oxygen source such as iron oxide is added to the molten iron to carry out the desulfurization treatment, the slag generated in the desulfurization treatment is removed, and then, by adding a refining agent (delining agent and fluxing agent), Run the process. Usually, CaO type refiners, such as lime, are used as a refining agent for dechlorination, and a solid oxygen source (iron oxide etc.) and gaseous oxygen are used as an oxygen source. In addition, torpedo car, ladle (load ladle), converter type container, etc. are used as a processing container.

In conventional molten iron, the addition of CaF ₂ (fluorite) has been widely practiced to promote the fluxing of CaO-based refining agents. However, in recent years, in the viewpoint of environmental protection and the tendency for the regulatory requirements of the F elution amount from the slag enhance, reduce the amount of CaF ₂ for this purpose, or operation that does not use CaF ₂ (F No Operation) is required have.

In F-free operation, it is important to promote CaO residue and maintain dephosphorization efficiency, and it is common to perform operation (low C / S operation) with relatively low slag basicity in order to sufficiently leave CaO (e.g., Japanese Patent Laid-Open Publication No. Hei 9-143529). In addition, since the treatment temperature is advantageously lower thermodynamically, the operation of lowering the treatment temperature in order to increase the desalinating efficiency is carried out (for example, Japanese Patent Application Laid-Open No. 2000-8112 and Japanese Patent Laid-Open No. 2002-309312).

However, in the low C / S operation (or low C / S operation at which the treatment temperature is lowered), there is a limit to increasing the dechlorination rate within a limited treatment time. Moreover, even if the dephosphorization rate can be raised to some extent, there exists a problem that MnO concentration in slag increases in low C / S operation, and Mn yield in a dephosphorization process falls. Therefore, in the case of carrying out an operation without F in the prior art anyway,

[a] promoting the debrisization of CaO to obtain high thallinity,

[b] to ensure high Mn yield

Is a difficult task to be compatible. However, the compatibility of these [a] and [b] is not only a problem of molten iron delineation but also very important in securing total Mn yield including the decarburization process. That is, in the case where steel having a relatively high Mn concentration is obtained through the dephosphorization step and the decarburization step, the Mn ore is charged in the decarburization step, and this is reduced to increase the Mn concentration in the molten steel, but the above [a] is realized. This reduces the dephosphorization load in the decarburization step, thereby making it possible to decarburize at a low slag amount, and to easily increase the Mn concentration in molten steel due to the reduction of Mn ore, and further realize [b]. This makes it possible to increase the Mn concentration in the molten steel to a desired level with a small amount of Mn ore in the decarburization step, and as a result, it is possible to effectively increase the total Mn yield in the entire refining.

In addition, in Japanese Patent Publication No. Hei 9-143529, in spite of low C / S operation, relatively good Mn yield is achieved when powder is supplied by bottom blowing. Attempts to quantify the stirring force by powder blowing have not been successful enough, but experience is known to be significantly greater than the stirring force by blowing gas only, for example. Therefore, the said effect in the same publication is considered to be the cause by the strong stirring force by the powder which was taken up. In fact, even in the same publication, when unloading of powder is not performed, Mn yield is extremely low (Table 1 of the same publication).

However, in order to supply powder by deodorization, a dedicated facility is required, and the tuyere wears badly. It is necessary to stop the converter in order to exchange the windball, and if the frequency is high, it becomes extremely uneconomical for operation.

Therefore, an object of the present invention is to promote a delineation reaction while ensuring a high Mn yield, and to perform efficient molten metal delineation, and a method with little facility burden, in particular, it is possible to realize this with an extremely low F-addition or no F-source. It is to provide the molten iron delineation method.

The present inventors examine the optimum dephosphorization treatment conditions that can solve the above problems, and as a result, the slag basicity after the treatment is set to a relatively high specific region and the treatment end temperature of the molten iron is set to a predetermined level or more, and then the treatment is performed. By carrying out the treatment in a condition where the T. Fe concentration in the slag is sufficiently high, it was found that efficient molten iron delineation can be carried out by promoting the delineation reaction while ensuring a high Mn yield. In general, the treatment conditions for molten iron

[Iii] Increasing slag basicity causes problems such as increased cost due to increased input of refining agent (CaO), lack of refining of refining agent,

[Ii] Increasing the treatment temperature causes deterioration of the delinquency efficiency and the problem of wear of the refractory in the furnace.

[Iii] It is considered that raising the T. Fe concentration in slag causes problems such as lowering of iron yield, but the present inventors have boldly combined the above conditions, which have all been considered to be undesirable in operation. The same unpredictable effect was found.

This invention is made | formed based on this knowledge, The summary is as follows.

[1] A slag forming method is performed by adding a refining agent mainly composed of a CaO source and an oxygen source to the molten iron and forming slag, wherein the basicity of the slag (% CaO /% SiO _{2) is maintained} until at least the dephosphorization treatment is completed. ) Is 2.2 to 3.5 or less, T.Fe concentration is 10-30 mass%, and the molten iron delineation method characterized in that the end point temperature of molten iron is 1320 degreeC or more.

[2] The molten iron dephosphorization method according to the above [1], wherein the slag has a basicity (% CaO /% SiO ₂ ) of not less than 2.2 and not more than 3.0 up to the end of the dephosphorization treatment.

[3] The molten iron dephosphorization method according to the above [1] or [2], wherein the treatment end temperature is 1320 ° C to 1400 ° C.

[4] The molten iron delineation method according to any one of [1] to [3], wherein the T.Fe concentration of the slag is 15 to 25 mass%, at least until the completion of the delineation treatment.

[5] The molten iron delineation method according to any one of the above [1] to [4], wherein at least one selected from a titanium oxide source and an Al ₂ O ₃ source is used as part of the refining agent.

[6] In the molten iron dephosphorization method according to the above [5], the titanium oxide source and the total amount of titanium oxide (in terms of TiO ₂ ) and Al ₂ O ₃ of the slag after treatment are ₃ to 15 mass%; At least one selected from the group Al ₂ O ₃ is added.

[7] The molten iron delining method according to any one of [1] to [6], wherein the F concentration of the slag after the treatment is 0.2 mass% or less.

[8] The molten iron dephosphorizing method according to any one of the above [1] to [7], wherein the molten iron is dephosphorized to a P content (component standard value of steel) required for crude steel.

1 is a graph showing the relationship between slag basicity C / S (horizontal axis) and de-P ratio (%) (vertical axis) after dephosphorization.

2 is a graph showing the relationship between slag basicity C / S (horizontal axis) and Mn yield (%) (vertical axis) after dephosphorization.

3 is a graph showing the relationship between the dephosphorization treatment end point temperature (° C.) (horizontal axis) of molten iron and the de-P ratio (%) (vertical axis).

4 is a graph showing the relationship between the dephosphorization treatment end point temperature (° C) (horizontal axis) of molten iron and Mn yield (%) (vertical axis).

Fig. 5 is a graph showing the relationship between T.Fe concentration (mass%) (horizontal axis) and de-P ratio (%) (vertical axis) of slag after dephosphorization.

Fig. 6 is a graph showing the relationship between T.Fe concentration (mass%) (horizontal axis) and Mn yield (%) (vertical axis) of slag after dephosphorization.

The present invention is a method of performing dephosphorization by adding a refining agent mainly composed of CaO and an oxygen source to molten iron, wherein the basicity (=% CaO /% SiO ₂ , mass ratio, below) of slag after treatment is greater than 2.2. The molten iron is dephosphorized so that the T.Fe concentration is 10 to 30 mass% or less and the end point temperature of the molten iron is 1320 ° C or lower. Further, most of the slag is formed during the dephosphorization treatment, but for example, some slag may be turned over from the previous charging.

In the present invention, by optimizing the three conditions of the slag basicity, T.Fe concentration and the end point temperature of the molten iron after treatment as described above, by the action of the following (I) to (III) with high Mn yield and delineation efficiency You can run Charter Tallinn.

[I] Since the higher the slag basicity and the higher the treatment temperature, Mn in the molten iron becomes harder to be oxidized, the higher the slag basicity (greater than 2.2) and the high temperature treatment of 1320 占 폚 or higher to give a high Mn yield. Is obtained.

[II] The high temperature treatment promotes the deoxidation of CaO, so that the effect of improving the delineation reaction by increasing the slag basicity can be sufficiently obtained, and the high temperature, which is detrimental to delineation, is increased by increasing the T.Fe concentration in the slag. The fall of the dephosphorization efficiency by treatment can be compensated for, and as a result, a high dephosphorization efficiency can be obtained. Here, in terms of thermodynamics, the higher the slag basicity and the higher the treatment temperature (melting temperature), the lower the FeO concentration in the slag is, and therefore, the condition becomes difficult to increase the T.Fe concentration. However, the T.Fe concentration can be effectively increased by carrying out a special operation described below under conditions in which both the slag basicity and the treatment temperature are increased, thereby achieving high dephosphorization efficiency.

When the concentration of T.Fe in the [III] slag increases, the oxygen potential of the slag increases, which is an adverse condition for the Mn yield. However, since the action of [I] is superior, a high Mn yield is obtained.

In addition, the reason to be prescribed | regulated by the slag composition and treatment end point temperature after treatment is that in the case of dephosphorization treatment, these termination values are the target values of control, and therefore it is expected that the dephosphorization reaction is progressing at a condition close to the termination at the end of at least the dephosphorization treatment. Because it becomes.

Hereinafter, the processing conditions of the present invention will be described in detail.

<Overview of Tallinn Treatment and Main Supplies>

In the present invention, delineation treatment is performed by adding a refining agent mainly composed of a CaO source and an oxygen source to the molten iron. Here, the CaO source is a _secondary raw material containing CaO or Ca compound capable of forming CaO (CaCO ₃ , Ca (OH) ₂ , CaMgO _2, etc.). Although quicklime is generally used as a CaO source, limestone, slaked lime, dolomite, and used slag (converter residue, playing residue, ingot residue, etc.) can also be mentioned. In addition, "the refiner which mainly uses a CaO source" shall refer to what contains 40 mass% or more of CaO source in CaO source in a refiner.

Other components of the refining agent will be described later in detail.

The refining agent can be supplied to the molten metal by any method such as top charge, injection from the immersion lance into the molten metal, projection through a top injection lance, and the like. Among them, the top loading, projection by the upper lance, and combinations thereof are preferable because of little damage to the equipment, and the effect can be sufficiently obtained by these means.

As the oxygen source, gaseous oxygen (oxygen gas or oxygen-containing gas) and / or solid oxygen source (for example, iron ore, mill scale, sand iron, dust collecting dust (blast furnace, converter, sintering process, etc.) Iron oxide) such as dust) containing iron recovered from the gas. Among these, gaseous oxygen may be injected into the molten iron by an upper injection, an injection into the molten iron or a lower air intake, and a solid oxygen source may be charged into the upper portion, or injected into the molten iron from the immersion lance. Each can be supplied in the molten iron by any method such as projection through a lance. Among them, the fresh air (gas oxygen), the top charge (solid oxygen source), the projection by the fresh lance (solid oxygen source), and any combination of these are preferable because of little damage to the equipment, and the effect can be sufficiently obtained by these means. Can be.

In particular, when the dephosphorization treatment is carried out using a converter type vessel, it is common to carry out the gaseous oxygen uptake from the fresh feed lance and to supply the solid oxygen source in the above-described manner as necessary. It is also preferable to stir the molten iron in order to effectively perform the dephosphorization. In general, the stirring is a gas stirring in which an inert gas or oxygen gas is blown from an immersion lance or a nozzle (furnace) embedded in the bottom of a furnace. Is executed.

<Basicity of Slag>

In the present invention, by performing a high temperature treatment of 1320 ° C. (the end point temperature of molten iron) or higher and setting the slag basicity after the treatment to 2.2, a high Mn yield in the dephosphorization step as described above is obtained, Since CaO descaling is accelerated | stimulated, the effect of improving the dephosphorization efficiency by raising slag basicity can fully be taken out. However, if the slag basicity after the treatment exceeds 3.5, the proportion of solid phase in the slag becomes high, and the reactivity decreases, resulting in poor phosphorus. In view of this, the slag basicity after treatment is preferably 3.5 or less.

For the above reasons, in the present invention, the slag basicity after the treatment is set to 2.2 seconds or more and 3.5 or less, and more preferably 2.5 to 3.0.

This was confirmed by the following experiment, for example.

Experiment 1

The blast furnace molten metal previously desintered was desalinated using a converter vessel (300 tons). In this dephosphorization treatment, quick-loading of the quicklime of the CaO principal which does not contain a fluorine source such as fluorite as a dephosphorization agent was charged. Oxygen gas was supplied from the upper lance and a solid oxygen source mainly loaded with iron ore was charged. The delivery conditions of oxygen gas (oxygen gas) were 15000-400000 Nm <3> / hr. The unit of oxygen source was 12 Nm <3> / molten iron t except oxygen required for desulfurization. The slag basicity C / S was adjusted to 1.7 to 4.1 by adjusting the input amount of quicklime. Moreover, the feed ratio of a gaseous oxygen source and a solid oxygen source was adjusted so that the molten iron temperature after a dephosphorization process might be set to 1350 degreeC.

In this treatment, the target of dephosphorization rate of phosphorus in molten iron | metal was made into 80% or more, and the target of Mn yield in molten iron | metal was made into 30% or more. In addition, the de-P ratio (%) and Mn yield (%) were defined by the following formula.

(P concentration) = {[(P concentration before treatment)-(P concentration after treatment)] / (P concentration before treatment)｝ × 100

(Mn yield) = [(Mn concentration after treatment) / (Mn concentration before treatment)] × 100

In the above formula, the values of the de-P ratio and the Mn yield do not depend on the units of the P concentration and the Mn concentration. In this case, however, the mass concentration with respect to the molten iron is employed as the P concentration and the Mn concentration.

The slag basic degree after the treatment takes C / S on the horizontal axis, and the results of examining the relationship between the de-P ratio and the Mn yield (%) are shown in FIGS. 1 and 2. According to this, when slag basicity C / S is 2.2 or less, the de-P ratio and Mn yield are low. On the other hand, in the range where the slag basicity of C / S is 2.2 seconds and 3.5 or less, both the desorption rate and the Mn yield have reached the target values. However, when C / S exceeds 3.5, the desorption rate decreases again. In addition, it can be seen that the slag base is also stable because the variation in the de-P ratio is particularly small when the C / S is 2.2 seconds or more and 3.0 or less.

In the above example, the same tendency was observed even when the refining agent mainly composed of quicklime was projected from the upper lance instead of the upper charging of the refining agent.

As the control means for slag basicity C / S, in addition to controlling the input amount of the CaO source as described above, control of the input amount of known SiO ₂ sources such as silica or brick pieces, pre-de-silification treatment, or addition of FeSi alloy There is a means of controlling the concentration of Si in the molten iron.

<Tallin Treatment End Temperature>

In the present invention, since the CaO residue is promoted by carrying out the high temperature treatment at which the end point temperature of the molten iron is 1320 占 폚 or higher, the effect of improving the dephosphorization efficiency by increasing the slag basicity can be sufficiently obtained. Also, thermodynamically, the Mn yield is good. Moreover, from this viewpoint, more preferable process end temperature is 1350 degreeC or more. On the other hand, if the treatment end temperature exceeds 1400 ° C, it becomes an unfavorable temperature condition for Tallinn, and in order to compensate for this, a large amount of slag is required, and as a result, the Mn yield in the subsequent decarburization step is greatly reduced. In addition, this tendency becomes particularly remarkable when the treatment end temperature is 1420 DEG C or higher, and a large amount of slag is required. For the above reasons, in the present invention, the end point temperature of molten iron is preferably 1320 ° C or higher, preferably 1350 ° C or higher, and the upper limit thereof is 1400 ° C.

This was confirmed by the following experiment, for example.

In addition, in the case of Tallinn using a converter type container, the end point temperature of molten iron is often measured after tapping on the ladle due to equipment reasons. Therefore, also in the present invention, the temperature measured after tapping on the ladle was employed. This is generally about 20 ° C. lower than the measured value in the converter vessel.

Experiment 2

The blast furnace molten metal previously desintered was desalinated using a converter vessel (300 tons). In this dephosphorization treatment, the quicklime of CaO main body which does not contain a fluorine source such as fluorite as a dephosphorization agent was charged up. The amount of quicklime adjusted was adjusted so that the slag basicity after dephosphorization was 3.0. Oxygen gas was supplied from the upper lance and a solid oxygen source mainly loaded with iron ore was charged. The delivery conditions of oxygen gas (oxygen gas) were 15000-400000 Nm <3> / hr. The unit of oxygen source was 12 Nm <3> / molten iron t except oxygen required for desulfurization. The treatment end temperature of the molten iron was adjusted to about 1310 to 1430 ° C by adjusting the supply ratio of the gaseous oxygen source and the solid oxygen source.

The end point temperature (° C) of the molten iron is taken along the horizontal axis, and the relationship between the de-P ratio (%) and the Mn yield (%) is shown in FIGS. 3 and 4.

According to this, while the treatment end temperature is higher, the Mn yield in the dephosphorization treatment is improved, but the de-P ratio is lowered. It can be seen that the treatment end temperature is in the range of 1320 to 1400 ° C under conditions that the dephosphorization rate of phosphorus in molten iron is 80% or more and the yield of Mn in molten iron is 30% or more. Moreover, when it is 1350 degreeC or more, it turns out that especially the deviation of the minimum of Mn yield becomes small and it is stable.

In the above example, the same tendency was observed even when the refining agent mainly composed of quicklime was projected from the upper lance instead of the upper charging of the refining agent.

As a control means for the end point of the delineation treatment of molten iron, as well as adjusting the supply ratio of the gaseous oxygen source and the solid oxygen source as described above, the means for adjusting the input amount of iron source such as scrap and the input amount of carbonaceous material, etc. have.

<T.Fe concentration of slag>

In the present invention, by reducing the T.Fe concentration of the slag after treatment to 10 mass% or more, it is possible to compensate for the lowering of the dephosphorization efficiency due to the high temperature treatment unfavorable to the dephosphorization, and to optimize the slag basicity as described above, and to achieve a high dephosphorization efficiency. You can get it. In addition, from this viewpoint, the lower limit of the more preferable T.Fe concentration is 15 mass%. On the other hand, when the T.Fe concentration of slag after treatment exceeds 30 mass%, the iron content discharged with slag increases, and the fall of iron yield cannot be ignored. Moreover, from this viewpoint, the upper limit of T.Fe concentration which is more preferable is 25 mass%. For the above reason, in the present invention, the T.Fe concentration of the slag after the treatment is 10 to 30 mass%, preferably 15 to 25 mass%.

As described above, thermodynamically, the higher the slag basicity and the higher the treatment temperature (melting temperature), the lower the FeO concentration in the slag is, and therefore, the condition becomes difficult to increase the T.Fe concentration. At the slag basicity and the treatment end point temperature of the present invention, in order to make the T.Fe concentration in the slag after the treatment 10% by mass or more, an active operation (action) to increase the T.Fe concentration is required. It is not possible to increase the Fe concentration to 10 mass% or more.

As this special operation, for example, a method of carrying out the delivery from the acid lance by soft blow and controlling the input amount of the iron oxide source may be mentioned.

Soft blow from the intake transpiration lance reduces the delivery speed from the same lance and decreases the dynamic pressure of the molten iron bath surface caused by the kinetic energy of the gaseous oxygen taken up (for example, 0.03 MPa or less, preferably 0.02 MPa or less). will be. In addition, the dynamic pressure Pd (MPa) of a molten iron bath surface is a following formula

Pd = Uo × (de / H _L ) × COSθ × (1/2) × (1 / (0.016 + 0.19 / Pi)) / 10

Uo ： Lance nozzle exit flow rate (m / s)

de ： Lance nozzle outlet diameter (m)

H _L : Lance height (m)

θ: Angle formed between the lance nozzle central axis and the lance central axis (rad)

Pi: Lance nozzle inlet pressure (MPa)

It is assumed that the value calculated by.

In this way, when the delivery from the uptake delivery lance is performed by soft blow, the oxygen supply to the slag is sufficiently performed, and the T.Fe in the slag can be maintained at a high concentration. This soft blow may be performed at least in the second half of the dephosphorization treatment.

In addition, in the method of injecting the iron oxide into the slag, a large amount of the iron oxide source is added in the second half or the end of the treatment in order to secure the T.Fe concentration in the slag in the second half of the treatment. In this case, for example, two-thirds or more of the scheduled iron oxide input is introduced after the midpoint of the treatment period (blowing period).

As an iron oxide source, iron ore, mill scale, sand iron, dust collection dust, etc. can be used, and as an input method, arbitrary methods, such as upper charging, projection from a top lance, and an injection, can be taken.

The effect of T.Fe concentration was confirmed by the following experiment, for example.

Experiment 3

The blast furnace molten metal previously desintered was desalinated using a converter vessel (300 tons). In this dephosphorization treatment, the quicklime of CaO main body which does not contain a fluorine source such as fluorite as a dephosphorization agent was charged up. The input amount of quicklime was adjusted so that slag basicity after dephosphorization was 3.0. Oxygen gas was supplied from the upper lance and a solid oxygen source mainly loaded with iron ore was charged. Oxygen gas delivery conditions were 15000-400000 Nm <3> / hr. The unit of oxygen source was 12 Nm <3> / molten iron t except oxygen required for desulfurization. Moreover, the feed ratio of a gaseous oxygen source and a solid oxygen source was adjusted so that the molten iron temperature after a dephosphorization process might be set to 1350 degreeC. At this time, the input pattern of the solid oxygen source was changed in various ways, and the slag T.Fe concentration after the treatment was changed to about 5 to 28%. In particular, in the case of achieving a T.Fe concentration of 15 mass% or more, at least 2/3 of the planned solid oxygen source input is to be introduced after the midpoint of the treatment period (blowing period). The input costs after the point increased.

The T.Fe concentration (mass%) of the slag after the treatment is taken along the horizontal axis, and the relationship between the de-P% (%) and the Mn yield (%) is shown in FIGS. 5 and 6. According to this, when T.Fe concentration is 10 mass% or more, it turns out that both a P removal rate and Mn yield satisfy | fill the target.

As described above, when the FeO concentration in the slag increases, the oxygen potential of the slag increases, which is an unfavorable condition for securing the Mn yield. However, in the present invention, since the action of the optimization of the slag basicity and the treatment end temperature is superior, Mn yield is obtained. Moreover, when T.Fe concentration becomes 15 mass% or more, it turns out that especially the variation of Mn yield becomes small and it is stable.

In the above example, the same tendency was observed even when the refining agent mainly composed of quicklime was projected from the upper lance instead of the upper charging of the refining agent.

<Additives of Refiner>

In the present invention, by using a refining agent substantially free of F source (CaF ₂ etc.) or by using a refining agent having a small amount of F source addition, it is possible to make the F concentration of slag to be 0.2 mass% or less through the treatment period. In the present invention, even when such a refining agent is used, high dephosphorization efficiency can be obtained. In addition, the F concentration of the slag may be managed by the value after the treatment.

Here, the fact that the refining agent does not contain an F source means that it does not substantially contain an F source. Therefore, it does not interfere that a small amount of F sources are inevitably contained, for example, as an impurity.

In addition, in the present invention, by using a titanium oxide source and / or an Al ₂ O ₃ source as a part of the refining agent, degreasing of the CaO-based refining agent is promoted, and the oxygen potential of the slag also increases, so that the slag delinquency ability is also improved. As a result, the delineation reaction is also promoted, so that more efficient molten metal delineation can be carried out. That is, since the titanium oxide source and / or the Al ₂ O ₃ source functions as a degreasing accelerator of the CaO-based refining agent, especially when a refining agent that does not substantially contain the F source or uses a small amount of the F source as described above is used. Valid.

While the form of titanium oxide include _{TiO, TiO 2, Ti 2 O} 3, Ti 3 O 5, or may be of any type. Examples of the titanium oxide-containing material which is a titanium oxide source include iron iron, ilmenite ore (titanium iron ore), rutile ore (rutile ore), titanium oxide-containing iron ore, and the like. Among these, iron iron is generally a fine grain having a particle diameter of 1 mm or less, and is particularly preferable because it is rapidly melted in the reaction vessel. In addition, by adding iron sand to slag, the concentration of T.Fe in the slag can be increased, that is, it also functions as an iron oxide source (the same is true for ilmenite ore and titanium oxide-containing iron ore). The grade of iron sand varies depending on the producing region, but generally contains about ₅ to 8% by mass of TiO _2, and may contain about 13% by mass of high one. On the other hand, Ilmenite ore or rutile ore may contain conventional TiO ₂ more than 30mass%.

As the titanium-containing material causes the titanium oxide is preferable to use a material containing titanium oxide as TiO ₂ or more 3mass% conversion. A substance having a titanium oxide content of less than 3 mass% in terms of TiO ₂ does not have a good effect of promoting the debrisization of CaO-based refining agent, and if it is to be obtained, the amount of addition increases, the slag amount increases, and the Mn yield decreases. Do it. Therefore, in any case, a substance having a small amount of titanium oxide is inadequate as a titanium oxide source (titanium oxide-containing material).

As the Al ₂ O ₃ source, commercially available calcium aluminate solvents, aluminum oxides such as aluminum ash and bauxite, or the like can be used. In addition, by-products of the steelmaking process including aluminum oxide in high concentration such as ingot residue, secondary refining slag, brick residue, and the like can also be used. Al ₂ O ₃ won as it is preferred to contain not less than 20mass% in terms of Al ₂ O _3.

It is preferable that the titanium source and / or Al ₂ O ₃ source of titanium oxide in the slag after the treatment as the addition amount of the oxide, the total content of (where, in terms of TiO ₂₎ and Al ₂ O ₃ to be equal to or less than 15mass%. If the total content exceeds 15% by mass, CaO necessary for the dephosphorization reaction is thinned and the dephosphorylation ability is lowered. In addition, in the normal delineation operation, both of them inevitably contain about 1.0 to 2.5% mass in the slag, but less than 3 mass% does not have sufficient effect of promoting the degreasing of the CaO-based refiner. Therefore, the total content of titanium oxide in the slag after the treatment (where, in terms of TiO ₂₎ and Al ₂ O ₃ is preferably not less than 3mass%.

In the dephosphorization treatment, in addition to the above, an MgO source or the like may be added for the purpose of protecting the furnace body.

<Others>

As the vessel to which molten iron of the present invention is applied, any vessel such as a converter type vessel, a molten iron port, or a topido can be used. However, a free board (top board) is formed on the top surface of the molten metal in the vessel or on the upper surface of the slag. The converter-type container is most preferable at the point which can fully secure the clearance to).

In addition, molten iron delineation of the present invention

Dealing and decarburization are carried out separately using different vessels (e.g. converter vessels).

· The method of carrying out the dephosphorization treatment and the decarburization treatment continuously using the same converter type with the intermediate discharge intervened.

You may apply to either.

The molten iron treatment time depends on the shape and capacity of the vessel, but it is preferably about 5 to 30 minutes.

Moreover, according to this invention, molten iron can be refine | purified easily up to P content (a component standard value of steel) below required for crude steel. In this way, by removing the molten iron below the P content (steel component specification value) required for the crude steel, in the subsequent decarburization step, substantial delining need not be performed, and thus, decarburization and refining can be carried out with a very small amount of slag. As a result, high Mn yield can be realized, particularly in the case where Mn ore is added to increase the Mn concentration in the molten steel. In addition, decarburization and refining can be extremely simplified, and the refining time can be shortened, thereby improving overall steelmaking efficiency.

In addition, examples of the P content required in the crude steel include 0.03 mass% or less (normal steel), 0.015 mass% or less (low-lining steel), and the like.

<Example 1>

The blast furnace molten iron (Mn concentration of 0.3 mass%) previously de-sintered was desalinated using a converter vessel (300 tons). In this dephosphorization treatment, the quicklime of CaO, which does not contain a fluorine source such as fluorite, as a dephosphorization agent was charged up. Oxygen gas was supplied from the upper lance and a solid oxygen source mainly loaded with iron ore was charged. Oxygen gas delivery conditions were 15000-400000 Nm <3> / hr. The unit of oxygen source was 12 Nm <3> / molten iron t except oxygen required for desulfurization. There are two types of solid oxygen sources: the equal input (evenly divided) over the entire blowing time, and the more than two-thirds of the planned input after the midpoint of the refining period (late slope). Was run.

After the Tallinn blowing, the molten iron was charged into a separate converter type container (300 tons) to carry out the decarburization treatment. At the time of decarburization blown, Mn ore was injected into the top as Mn source. The amount of Mn ore was adjusted to 4 kg in net Mn per ton of molten steel.

The de-P ratio and Mn yield after the Tallinn blowing are shown in Table 1 together with the Tallinn treatment conditions. Moreover, Mn yield in a total of delineation and decarburization is also shown in Table 1. The Mn yield in the total of delineation and decarburization was calculated by the following formula.

(Total Mn Yield) = {(Mn Concentration After Decarburization) / (Mn Concentration Before Detalization) + (Mn Concentration During Decarburization)} × 100

TABLE 1

  No.   division Tallinn Decarburization Condition  Total Mn yield (%) Solid Oxygen Source Input Method ^{* 1} Treatment Endpoint Melt Temperature (℃)  Slag basicity  T.Fe concentration in slag (mass%)  De-P Ratio (%)  Mn yield (%)  Mn addition amount (KgMn / molten steel t)  Mn concentration in molten steel (mass%) One Invention Late slope 1320 2.5 10 90 40 4 0.29 44.6 2 Invention Late slope 1370 3.0 15 88 50 4 0.32 49.6 3 Invention Late slope 1400 3.5 25 85 52 4 0.33 50.6 4 Invention Late slope 1370 3.0 15 90 50 4 0.32 49.2 5 Comparative example Evenly split 1300 3.0 10 85 13 4 0.21 32.5 6 Comparative example Evenly split 1350 2.0 20 75 22 4 0.22 33.4 7 Comparative example Evenly split 1430 3.0 15 55 50 4 0.14 21.3 8 Comparative example Evenly split 1350 3.0 5 50 55 4 0.10 15.4

* 1) Late slope: More than two-thirds of the planned dose is added after the midpoint of the drilling period.

    Divided into equal parts: input the planned input over the whole period

In the example of this invention, 85% or more of the P removal rate after a Tallinn blow, and 40% or more of Mn yield were obtained. As a result, in decarburization blowing, the charging Mn concentration was high, the charging P concentration was low, and the blowing at a low slag amount was able to be performed, resulting in a Mn yield of the total delineation and decarburization total exceeding 45%.

On the other hand, in the comparative example, the compatibility of the high thallin rate and the high Mn yield could not be realized. As a result, in the decarburization blow-off, the charged Mn concentration was low, the charged P concentration was high, and the blown at a high slag amount resulted in the blown, and thus the Mn yield of the total delineation and decarburization total was low.

<Example 2>

In the same manner as in Example 1, except that ferrous iron (TiO ₂ content: 7.5 mass%), which is a titanium oxide source, or ingot waste (Al ₂ O ₃ content: 30 mass%), which was a source of aluminum oxide, was partially charged as a part of the refining agent for tallinning, Desalination and decarburization were carried out. The total content of TiO ₂ concentration in the Tallinn slag in blowing using iron sand was 4.0 mass%, and the content of TiO ₂ and Al ₂ O ₃ was 6.3 mass%. In addition, Al ₂ O ₃ concentration in the slag in the Tallinn blown with jogoe debris total content of 4.5mass%, TiO ₂ and Al ₂ O ₃ was 6.1mass%. The de-P ratio and Mn yield after the Tallinn blowing are shown in Table 2 together with the Tallinn treatment conditions. Moreover, Mn yield in a total of delineation and decarburization is also shown in Table 2. Also in any case, the result which compatible 85% or more of P removal rate after a Tallinn blow and 40% or more of Mn yield was obtained. As a result, the Mn yield of the total delineation and decarburization total also resulted in over 45%.

TABLE 2

  No.   division Tallinn Decarburization Condition  Total Mn yield (%)  Raw materials  Treatment end molten iron temperature (℃)  Slag basicity  T. Fe concentration in slag (mass%)   De-P Ratio (%)  Mn yield (%)  Mn addition amount (KgMn / molten steel t)  Mn concentration in molten steel (mass%) 9 Invention Private railway 1370 3.0 15 90 48 4 0.31 48.3  10  Invention Lump waste  1370  3.0  15  86  50  4  0.32  49.7

<Example 3>

The blast furnace molten iron (Mn concentration of 0.3 mass%) previously de-sintered was desalinated using a converter vessel (300 tons). In this dechlorination process, oxygen gas was supplied from the upper lance and a solid oxygen source mainly loaded with iron ore was charged. Then, quicklime or calcium carbonate of CaO principal containing no fluorine source such as fluorite as a dephosphorizer was projected from the upper lance with oxygen gas. Oxygen gas delivery conditions were set to 15000 to 40000 Nm 3 / hr, and the projected amount of the dephosphorizing agent was adjusted within the range of 6000 to 30000 kg / hr. The unit of oxygen source was 12 Nm <3> / molten iron t except oxygen required for desulfurization. The delivery from the upper lance was carried out in two cases, in which the dynamic pressure of the molten iron bath surface by the delivery was 0.01 to 0.02 MPa (soft blow) and more than 0.03 MPa (hard blow) in the second half of the refining period.

In some test materials, iron oxide (TiO ₂ content: 7.5 mass%), which is a titanium oxide source, or brick residue (Al ₂ O ₃ content: 30 mass%), which is an aluminum oxide source, was similarly charged as a part of the refining agent for dephosphorization.

The results are shown in Table 3.

TABLE 3

  No.   division Tallinn Decarburization Condition  Total Mn yield (%)  Wealth raw material Deodorization Song ^{* 1} Treatment Endpoint Melt Temperature (℃)  Slag basicity  T. Fe concentration in slag (mass%)   De-P Ratio (%)  Mn yield (%)  Mn addition amount (KgMn / molten steel t)  Mn concentration in molten steel (mass%)  11  Invention - Soft blow  1320  2.5  20  90  44  4  0.30  46.4  12  Invention - Soft blow  1370  3.0  17  92  50  4  0.32  48.5  13  Invention - Soft blow  1400  3.5  15  90  52  4  0.33  50.1  14  Invention Private railway Soft blow  1370  2.5  18  90  44  4  0.30  46.4  15  Invention Brick debris Soft blow  1370  2.5  20  88  40  4  0.29  45.0  16  Invention Siege + Brick Scrap Soft blow  1370  2.5  25  90  42  4  0.30  45.5  17  Comparative example - Hard blow  1350  2.5  9  77  20  4  0.22  33.6  18  Comparative example - Hard blow  1350  3.5  6  60  45  4  0.18  27.5  19  Comparative example - Soft blow  1430  3.0  14  65  30  4  0.18  27.6  20  Comparative example - Soft blow  1350  2.0  19  66  41  4  0.22  33.9  21  Invention Calcium Carbonate Projection Soft blow  1380  2.5  17  89  41  4  0.29  45.3

* 1) Soft blow: The dynamic pressure of the molten iron bath surface due to delivery from the intake lance is 0.01 to 0.02 Mpa later in the refining period.

         Hard blow: The dynamic pressure of the molten iron bath surface due to delivery from the intake lance exceeds 0.03 Mpa later in the refining period.

In the example of this invention, the result of having the dephosphorization rate 85% or more and Mn yield 40% or more compatible with Tallinn blowing was obtained, and the Mn yield of the total Tallinn detalanization also exceeded 45%.

On the other hand, in the comparative example, compatibility of the high thallin rate and the high Mn yield could not be realized, and as a result, the Mn yield of the total delineation and detantalization total was low.

<Example 4>

The blast furnace molten iron (Mn concentration of 0.3 mass%) previously de-sintered was desalinated using a converter vessel (300 tons). In this dechlorination process, oxygen gas was supplied from the upper lance and the majority of the solid oxygen source mainly composed of the scale was projected together with the inert gas from another projection port provided in the same lance. Then, two cases of the case where the quicklime of the quicklime of the CaO main body which does not contain a fluorine source such as fluorite as a dephosphorizing agent and the case of projecting from the upper lance with oxygen gas were performed.

The delivery conditions of oxygen gas were 15000-40000 Nm <3> / hr, and the projection amount of the dephosphorizing agent was adjusted in the range of 6000-30000 kg / hr. The unit of oxygen source was 12 Nm <3> / molten iron t except oxygen required for desulfurization. The delivery from the upper lance was carried out in two cases, in which the dynamic pressure of the molten iron bath surface by the delivery was 0.01 to 0.02 MPa (soft blow) and more than 0.03 MPa (hard blow) in the second half of the refining period.

In some test materials, ingots (Al ₂ O ₃ content: 30 mass%), which is an aluminum oxide source, were similarly charged as a part of the refining agent for Tallinn.

The results are shown in Table 4.

TABLE 4

  No.   division Tallinn Decarburization Condition  Total Mn yield (%)  Wealth raw material  Deodorization Song * 1 Cao source input method ^{* 2} Treatment Endpoint Melt Temperature (℃)  Slag basicity  T. Fe concentration in slag (mass%)   De-P Ratio (%)  Mn yield (%)  Mn addition amount (KgMn / molten steel t)  Mn concentration in molten steel (mass%)  22  Invention - Soft blow Upper loading  1360  2.5  12  87  48  4  0.32  48.8  23  Invention - Soft blow Upper loading  1370  2.7  15  89  50  4  0.32  49.4  24  Invention - Soft blow Upper loading  1395  3.0  14  90  52  4  0.33  50.1  25  Invention - Soft blow Drunken  1365  2.3  21  92  47  4  0.31  47.2  26  Invention - Soft blow Drunken  1370  2.6  18  93  53  4  0.32  49.5  27  Invention - Soft blow Drunken  1380  3.4  14  92  60  4  0.35  53.2  28  Invention Lump waste Soft blow Drunken  1370  2.5  15  90  54  4  0.33  51.0  29  Comparative example - Hard blow Upper loading  1370  2.0  14  73  20  4  0.20  31.0  30  Comparative example - Hard blow Upper loading  1365  2.5  6  60  50  4  0.19  29.8  31  Comparative example - Soft blow Deodorant Fighter  1430  2.0  17  60  25  4  0.12  18.3

* 1) Soft blow: The dynamic pressure of the molten iron bath surface due to delivery from the intake lance is 0.01 to 0.02 Mpa later in the refining period.

   Hard blow: The dynamic pressure of the molten iron bath surface due to delivery from the intake lance exceeds 0.03 Mpa later in the refining period.

* 2) Top loading: Cao source is introduced from the hearth hopper

    Fragrance Fighter: Project Cao One from the Fragrance Lance.

In the example of this invention, the result of having 85% or more of P removal rate and 40% or more of Mn yields after a Tallinn blow was obtained, and the Mn yield of the total of delineation and decarburization also exceeded 45%.

On the other hand, in the comparative example, compatibility of the high thallin rate and the high Mn yield could not be realized, and as a result, the Mn yield of the total thallin and detantalized total was low.

According to the present invention, by optimizing three conditions of slag basicity, T.Fe concentration and end point temperature of molten iron after treatment, the molten iron reaction can be promoted and efficient molten iron can be carried out while securing a high Mn yield. .

In addition, by delineating molten iron below the P content (steel component standard value) required for the crude steel, the delineation in the decarburization process becomes substantially unnecessary, so that the amount of decarburization slag can be minimized, and even higher in the entire refining process. Mn yield can be realized.

Claims (8)

As a method of adding a refining agent mainly composed of a CaO source and an oxygen source to the molten iron, and performing dephosphorization while forming slag, At least until the end of the dephosphorization treatment, the basicity (% CaO /% SiO ₂ ) of the slag is 2.2 to 3.5 or less, and the T.Fe concentration is 10 to 30 mass%. The molten iron delinquency method characterized by the above-mentioned end point temperature of molten iron being 1320 degreeC or more. The method of claim 1, And at least until the end of the dephosphorization treatment, the slag basicity (% CaO /% SiO ₂ ) is set to 2.2 or more and 3.0 or less. The method according to claim 1 or 2, The molten iron Tallinn method characterized in that the treatment end temperature is 1320 ℃ to 1400 ℃. The method according to claim 1 or 2, And a T.Fe concentration of the slag is 15 to 25 mass%, at least until the end of the dephosphorization treatment. The method according to claim 1 or 2, At least one selected from a titanium oxide source and an Al ₂ O ₃ source is used as part of the refining agent. The method of claim 5, wherein At least 1 selected from the titanium oxide source and the Al ₂ O ₃ member so that the sum of the content of titanium oxide (in terms of TiO ₂ ) and Al ₂ O ₃ of the slag is ₃ to 15 mass%, at least until the end of the dephosphorization treatment. The molten iron delinquency method characterized by the addition of a species. The method according to claim 1 or 2, The molten iron Tallinn method characterized by the F concentration of the slag is 0.2 mass% or less. The method according to claim 1 or 2, A molten iron delineation method characterized by delineating molten iron below P content (steel component specification value) required for crude steel.

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