JP6135449B2 - How to use generated slag - Google Patents

Description

  The present invention relates to a method for making it possible to effectively use slag generated during hot metal pretreatment in steel refining in the converter process and to further reduce the cost in the converter process.

When the [Si] concentration of the hot metal coming out of the blast furnace is high, there are problems in operation in the converter process due to slopping and an increase in the amount of refining agent used. Therefore, desiliconization is performed as a hot metal pretreatment before dephosphorization or decarburization of hot metal in the converter process. On the other hand, slag is generated even in the desiliconization process.
Patent Document 1 discloses a method of reusing desiliconized slag in a dephosphorization process. However, there is no disclosure about the reuse of desiliconized slag in the decarburization process.

Moreover, when performing desiliconization processing, it is important to control basicity. Obviously, in order to reduce the amount of desiliconized slag produced and the cost of the desiliconization treatment, it is desirable to perform the treatment with a low basicity that requires less CaO to be added. Here, the basicity is a value obtained by dividing the mass concentration of CaO in the slag by the mass concentration of SiO ₂ .
However, desiliconization at extremely low basicity reduces the desiliconization oxygen efficiency. Non-Patent Document 1 reports the relationship between the basicity of slag and the desiliconization oxygen efficiency (η _O ). However, when the basicity is 0.5 or less, the desiliconization oxygen efficiency is remarkably lowered and iron oxide is generated. When the silicon removal treatment is performed at such an extremely low basicity, the iron yield decreases.

Therefore, if desiliconized slag can be reused in the refining process, it is considered that iron oxide produced by the desiliconization process can be recovered as an iron source. From the viewpoint of heat compensation and stirring strength, the converter has the highest degree of freedom in use, but when it is reused in the decarburization process, P contained in the slag becomes a problem. Usually, the slag generated by the desiliconization process contains a slight amount of P. If this P cannot be controlled below a certain concentration, an unexpected increase in the concentration of P in steel will occur when it is reused in the decarburization process.
Conventionally, there is no guideline that enables control of the P concentration of slag as obtained by desiliconization treatment, and the relationship between the treatment conditions and P concentration is not disclosed. There was a problem that reuse was difficult.

Furthermore, there is another problem with the slag generated in the preliminary processing. When manufacturing a high Mn steel, it is common to adjust the concentration of Mn components by adding a manganese alloy. The hot metal from the blast furnace often contains around 0.2% of Mn, but most of it is removed by the slag before the dephosphorization or decarburization process, so an expensive manganese alloy is used. You have to adjust the ingredients.
On the other hand, as disclosed in Patent Document 2, there is a method of reducing alloy costs by introducing manganese ore into a converter and reducing it in the furnace. However, most manganese ores are mainly composed of MnO ₂ and require a lot of energy for the reduction. Also, depending on the reduction efficiency, it is often higher than when it is added as an alloy after the converter process. As described above, there is a problem in that it is difficult to reduce the manganese oxide in the converter because the heat compensation and the unit cost are the bottleneck.

JP 2004-307943 A JP-A-3-153811

Japan Iron and Steel Institute, Production Engineering Division, Steelmaking Subcommittee, Steelmaking Slag Minimization Study Group: “Development Trends and Challenges for Minimizing Steelmaking Slag”-Final Report on Steelmaking Slag Minimization Study Group, (1999), p. 10

The present invention has a problem that when pretreatment such as desiliconization treatment is performed on hot metal, iron loss and problems of reuse of generated slag mainly due to contained P, and further, the cost of adding manganese is high. The purpose is to solve.
That is, by controlling the P contained in the slag, the pretreated slag can be reused in the decarburization process so that iron lost to the slag during the hot metal desiliconization process can be recovered in the converter process, and further, It is an object of the present invention to make it possible to recover Mn contained in hot metal during dredging in a decarburization process.

As described above, the preliminary treatment at low basicity has been practically performed by desiliconization, and problems of desiliconization oxygen efficiency have been reported. However, there was no knowledge about phosphorus moving to slag. In particular, since phosphorus is a problem for reuse in the decarburization process, knowledge about phosphorus is important.
The inventors of the present invention have found basicity conditions that can substantially solve the problem of phosphorus recovery by investigating the behavior of phosphorus at a low basicity in the hot metal pretreatment. On the other hand, it has also been found that the loss of valuable metal to slag, which is a problem with low basicity, can be solved by using it in the decarburization process.
The gist of the present invention thus made is as follows.

(1) A hot metal pretreatment for reacting hot metal with a gas containing oxygen or a refining agent containing iron oxide is performed so that the basicity of the slag after the pretreatment is 0.5 or less. A method of using generated slag characterized by reusing slag in a decarburization process in a converter.

(2) The method for using generated slag as described in (1) above, wherein a mass ratio P / Mn of P content and Mn content in the slag after the treatment is 0.1 or less.
(3) The method for using generated slag according to (1) or (2) above, wherein a mass ratio Si / Mn of Si content and Mn content in the slag after the treatment is 2 or less. .

(4) The method for using the generated slag according to any one of (1) to (3) above, wherein an oxygen supply rate in the hot metal preliminary treatment is 0.2 Nm ³ / min / t or less.
(5) The method for using the generated slag according to any one of (1) to (4), wherein 30% or more of the supplied oxygen in the hot metal preliminary treatment is supplied as iron oxide.
(6) A gas supply device including a tank storing oxygen-containing gas and / or a container storing iron oxide and a continuous supply device of iron oxide are attached to the transfer container, and oxygen is continuously supplied during transfer. Then, the hot metal preliminary treatment is performed, and the method for using the generated slag according to any one of the above (1) to (5).

(7) The method for using the generated slag according to any one of (1) to (6), wherein the hot metal temperature at the end of the hot metal pretreatment is 1300 ° C. or higher and 1450 ° C. or lower.

(8) The hot metal component before hot metal pretreatment is C ≧ 3.5 mass%, Si ≦ 0.6 mass%, Mn ≧ 0.1 mass%, P ≦ 0.15 mass%, (1) to (7 ) Use of generated slag as described in any of the above.
(9) The method for using generated slag according to any one of (1) to (8) above, wherein the concentration of Si in the hot metal before decarburization is less than 0.15% by mass.

(10) The method for using the generated slag according to any one of (1) to (9), wherein a decarburized soot is used as the iron oxide content.
(11) The method for using the generated slag according to any one of (1) to (10), wherein slag obtained by the preliminary treatment is used as the iron oxide content.

(12) The refractory in at least a portion in contact with the slag of the container for performing the pretreatment is mainly composed of at least one of alumina or silica, according to the above (1) to (11) Use method of generated slag in any one.

  According to the present invention, it is possible to reduce iron loss during hot metal desiliconization processing, reduce processing costs, and facilitate reuse of the generated slag in the decarburization process. By reducing the manganese oxide obtained from the above, manganese yield can be improved in the whole system, and as a result, refining costs can be reduced.

It is a figure which shows the relationship between the mass concentration ratio P / Mn in a slag, and the basicity of a post-process slag in the hot metal pretreatment.

In the pretreatment of hot metal in which an oxygen source is supplied to the hot metal and the hot metal reacts with the oxygen source, when the hot metal pretreatment is performed at a low basicity, P in the slag after the treatment has a constant concentration. The conditions to be controlled are examined below. As a result, it was found that there is a region of basicity in which dephosphorization hardly occurs. Furthermore, since the components of the obtained slag are mainly composed of oxides of Fe, Mn, and Si, it is possible to recover iron and manganese by reusing this slag in the converter decarburization process. I also found out.
First, the basic form of the present invention will be described.

(Basic form of the invention)
The present inventors use a mass ratio P / Mn of P content and Mn content in slag expressed as mass% as an index of phosphorus concentration in slag, and the base of the slag after treatment with respect to the value of this ratio We investigated the effect of degree (weight ratio of CaO content and SiO ₂ content expressed in mass%).
In FIG. 1, the mass concentration ratio P in the slag obtained as a result of adding iron oxide as an oxygen source to the hot metal and changing the addition amount of CaO to adjust the basicity of the slag after treatment and pre-treatment. The relationship between / Mn and the basicity of slag after a process is shown.
From FIG. 1, it has been found that the value of the ratio P / Mn is greatly influenced by the basicity of the slag after the treatment, and in particular, in the region where the basicity is 0.5 or less, the P / Mn is remarkably reduced.

Since the pretreatment slag in which P / Mn is remarkably reduced has a low phosphorus concentration in the slag, when used in the decarburization process, there is no strict restriction on the amount of use due to fear of recovery.
Furthermore, this pretreatment slag contains Fe, Si, and Mn oxides as main components. When slag is discharged outside the system, Fe, Mn, etc. are lost without being recovered, but iron and Mn can be recovered by reusing in the decarburization process. This is a recycling method that can be achieved only with slag with low P in hot metal pretreatment slag.

  Conventionally, desiliconization treatment has been known as a hot metal pretreatment performed at a low basicity. However, for the purpose of avoiding iron oxide loss and the like, a treatment at a high basicity is generally used compared to the present invention. It was. In this case, since not a little P enters the slag, it was difficult to reuse in the decarburization process due to recovery. On the other hand, in the present invention, by performing the preliminary treatment at a low basicity as described above, the P concentration in the slag can be lowered, and the reverse phosphorus in the decarburization process does not become a problem, while the low It is possible to recover Fe and Mn once lost to slag due to basicity.

  The basic aspect of the present invention has been described above. Further, individual conditions of the basic form, more preferable conditions, or means for achieving each condition will be described.

(Oxygen source)
When this hot metal pretreatment is performed, an oxygen source is required to utilize the oxidation reaction.
One method for supplying an oxygen source to the hot metal is to supply a gas containing oxygen to the hot metal. As the gas containing oxygen at this time, oxygen gas, air, or air enriched with oxygen can be used. The oxygen concentration is not particularly limited, and a gas in which oxygen is mixed with an arbitrary gas at an arbitrary ratio may be used. A gas containing oxygen is blown or blown to react with hot metal.

As another oxygen source supply method, there is a method of adding iron oxide. As the iron oxide, iron ore, sintered ore, converter dust, or scale can be used, but it is desirable to use the pretreated slag obtained in the present invention. By repeatedly using the pretreatment slag obtained in the present invention in the pretreatment step, the effect of further concentration of SiO ₂ and MnO can be obtained. Moreover, a decarburized soot can also be used. In this case, there is an advantage that MnO and iron oxide can be effectively used.
The solid containing these oxygen sources can be added in a lump or granular form from above, but it is desirable to blow nitrogen or air or the aforementioned oxygen mixed gas as a carrier gas as a powder.

(Adjustment of basicity, addition of smelting agent)
When adjusting the basicity so that the basicity of the treated slag is 0.5 or less, the amount of CaO added as a refining agent is adjusted. Calculate the silicon removal width (difference between the initial silicon concentration and the final silicon concentration in the hot metal), the CaO content and SiO ₂ content in the pre-treatment slag that are inevitably mixed, and the added CaO content. _By dividing by the total of ₂ minutes, the basicity after the treatment can be estimated. The basicity can be reduced to 0.5 or less by adjusting the amount of added CaO with respect to the desired desiliconization width. At this time, CaO may not be added at all as a refining agent.

The refining agent other than the oxygen source is not particularly defined, but can include Al ₂ O ₃ , MgO, SiO ₂ , and MnO. However, CaO content such as quicklime, limestone, and dolomite needs to be in an amount that meets the condition that the basicity of the slag after treatment is 0.5 or less, and is desirably not contained as much as possible.
If blast furnace slag is present before treatment, it is necessary to remove the slag so that the basicity of the slag after treatment is 0.5 or less when this slag is mixed with the refining agent and oxidation products. It becomes.

(Management of slag for reuse in the decarburization process)
It may be necessary to manage the slag when the slag after the pretreatment by the above method is reused in the decarburization process. If the basicity of the slag after the treatment is 0.5 or less, the P concentration is so low that it does not cause a problem in the reuse with a general steel type, but in the following cases, depending on the input amount of slag, Management of slag composition is required.

When used as a substitute for manganese ore For example, when used as a substitute for manganese ore when reusing, the ratio between the P concentration in the slag and the Mn concentration is important as the input concept. The lower this value, the smaller the P input increment to the decarburization process and the greater the Mn recovery width.
In order to obtain a merit (increment of Mn amount) exceeding the processing cost of the P input increment, it is desirable that P / Mn is 0.1 or less. This will be briefly described below.

For example, if the input increment of P brought into the decarburization process by the slag reused in this method is 0.1 kg · t ⁻¹ , consider several cases where the input increment of Mn is different. Here, kg · t ⁻¹ is a unit indicating the increment (kg) of P per 1 t of molten steel, and the same applies hereinafter. The target end point P is the same in each case.
Considering the refining cost increment necessary to eliminate the P increment, in order to reliably enjoy the benefits of Mn recovery, the Mn input increment is preferably ¹ kg · t ⁻¹ or more in consideration of yield, etc. . Also, P / Mn of slag to be reused is equal to P input increment / Mn input increment at that time. Therefore, the P / Mn of the slag in this desirable case is 0.1 (0.1 kg · t ⁻¹ / 1 kg · t ⁻¹ ) or less. From the above, it is desirable that P / Mn is 0.1 or less.

As utilized Likewise the SiO ₂ minutes for basicity adjustment, if utilized as a SiO ₂ minutes for basicity adjustment is considered. In this case, it is desirable that Si / Mn is 2 or less. Since the reusable amount is determined by the amount of Si in the slag, the lower this value, the greater the amount of Mn input to the decarburization process per Si amount. Generally, the amount of SiO ₂ input is designed based on the required amount of slag and the desired basicity, but in many cases, the amount of input is 2 kg / t or more in terms of Si. A desirable Mn input increment when expecting Mn recovery merit is 1 kg · t ⁻¹ or more as described above. Therefore, a desirable Si / Mn ratio is 2 (2 kg · t ⁻¹ / 1 kg · t ⁻¹ ) or less.

Slag management method As a slag management method, it is desirable to separately manage slag having P / Mn of 0.1 or less and slag having Si / Mn of 2 or less. If there is enough space to manage, three types of slag that meet each of these two conditions and slag that satisfies the two conditions can be managed separately and reused according to the purpose. If there is not enough space, only slag that satisfies the two conditions at the same time is managed separately.

About the ratio of P / Mn, it is desirable to analyze and manage P concentration and Mn concentration in slag. If this is not possible, an empirical formula for the relationship between hot metal components, slag components, processing temperature, etc. and P / Mn can be prepared in advance and managed according to the calculated value obtained using this formula. It is.
As for the ratio of Si / Mn, it is desirable to manage with an analytical value as in the case of the ratio of P / Mn, but a calculated value can be used after providing an empirical formula.

  Since these empirical formulas are greatly affected by the shape of the container and the stirring state, those who carry out the present invention can formulate them as appropriate within the scope of common knowledge of those skilled in the art. The method to obtain empirically from ingredients is shown.

The following formula is shown as an example of a method for obtaining from the hot metal component change.
P / Mn = αΔ [P] / Δ [Mn] (1)
Si / Mn = βΔ [Si] / Δ [Mn] (2)
However, (DELTA) shows the difference (mass%) of an initial stage density | concentration and an end point density | concentration, (alpha) and (beta) are values calculated | required empirically.

As an example of a method for empirically obtaining from a target slag component, the following equation is shown.
P / Mn = {a (CaO / SiO ₂ ) ² + b (CaO / SiO ₂ ) + c (Al ₂ O ₃ )
+ D (1 / T)} [P] _S / “Mn” _S (3)
Si / Mn = {e (CaO / SiO ₂ ) ² + f (CaO / SiO ₂ ) + g (Al ₂ O ₃ )
+ H (1 / T)} [Si] _S / “Mn” _S (4)
However, a, b, c, d, e, f, g, and h are values obtained empirically as arbitrary real numbers, CaO / SiO ₂ is obtained by mass balance, and Al ₂ O ₃ (mass%) is Empirically obtained values can be used. T is the hot metal temperature (K), [P] _S , [Mn] _S , and [Si] _S are the concentration (mass%) of each component in the hot metal before treatment.

(Other pretreatment conditions)
Next, the influence of the oxygen supply rate during the hot metal preliminary treatment was investigated.
When the hot metal pretreatment is performed at a low basicity, the viscosity of the slag becomes high, and the foaming of the slag due to the generated CO bubbles becomes intense. As a result, a so-called slopping phenomenon occurs that slag overflows from the container. It is desirable to avoid slapping as much as possible because it causes an operation failure such as equipment failure.

The present inventors investigated the relationship between the oxygen supply rate and slag bubbling in the low basicity region, and the oxygen supply rate was 0.2 Nm ³ / min / t or less even in the region where the basicity was 0.5 or less. Then, it was clarified that the risk of slipping can be reduced to an acceptable level.
In this case, the oxygen supply rate refers to the oxygen content in the gas entering the furnace and the oxygen content supplied as iron oxide. The lower limit of the oxygen supply rate is not particularly defined, but may be determined based on allowable productivity.

Further, as a result of investigating the oxygen supply mode, the present inventors have supplied 30% or more of the supplied oxygen content as iron oxide (that is, oxygen supplied as a gas). It was found that it is desirable to make it 70% or less. If this ratio exceeds 30%, the ratio of oxygen used for iron oxide generation and decarburization will decrease, leaving C as a heat source for the next process, and the generation of CO bubbles can be moderated. The risk of slipping is further reduced. There is no particular upper limit to the ratio of oxygen supplied by iron oxide. Although it is possible to supply all the amount of iron oxide, it is necessary to make a selection that matches the heat balance.

  In addition, the present inventors also examined a method for supplying oxygen. Considering the oxygen supply rate and the loss of iron oxidation as described above, a sufficient treatment time is required. With such a low oxygen supply rate, it was considered that almost no exhaust dust collection equipment was required, so that it could be processed even during transportation. Therefore, the present inventors maintained high production efficiency by treating the transport container as a processing container and attaching the apparatus capable of continuously supplying oxygen and / or iron oxide to the transport container itself. It was confirmed that the treatment can be performed as it is.

Hot metal temperature As for the conditions during the pretreatment, it was found that the influence of the hot metal temperature is large. When the hot metal temperature is 1300 ° C. or less, P / Mn is deteriorated (increased) because P transferred into the slag increases. Further, when the hot metal temperature is 1450 ° C. or higher, Si / Mn is deteriorated (increased). For this reason, it is desirable that the hot metal temperature after the pretreatment is 1300 ° C. or higher and 1450 ° C. or lower.

Hot metal component The desirable composition of the hot metal component before hot metal pretreatment was also investigated.
As a result, when C is less than 3.5% by mass, the heat source in the decarburization process is insufficient when decarburization during the pretreatment is taken into consideration, so that it may be 3.5% by mass or more. desirable.
For Si, if the amount exceeds 0.6% by mass, the amount of pre-treated slag generated becomes excessive and there is a risk of slopping, and Si / Mn in the pre-treated slag becomes high, resulting in a Mn content. Since collection becomes difficult, it is desirable that it is 0.6 mass% or less.
Regarding Mn, in order to keep the Si / Mn ratio and P / Mn ratio of the pretreated slag low, the higher the initial concentration, the better. When the Mn concentration is less than 0.1% by mass, these ratios are extremely high and are not suitable for recovering Mn. For this reason, it is desirable that it is 0.1 mass% or more.
When P exceeds 0.15% by mass, P / Mn deteriorates because P transferred to slag increases. For this reason, it is desirable that it is less than 0.15 mass%.

Pretreatment with decarburization step the hot metal (e.g., molten iron after pretreatment) when Si concentration is 0.15% or more, because the SiO ₂ minutes to produce during the decarburization, with SiO ₂ alternative The amount of the pretreatment slag of the present invention to be input is limited. Therefore, it is desirable that the Si concentration in the hot metal before decarburization is less than 0.15% by mass.

Pretreatment container In a container for pretreatment, it is desirable that the refractory in contact with the slag is mainly composed of alumina or silica. Compared to the case where MgO, which is a typical refractory material, is used as a main component, MgO, which is a basic component, is less likely to be mixed in the slag, and thus the effect of improving the P / Mn ratio can be obtained. .

  Although the embodiment of the present invention has been described above, an example of a method for using the generated slag according to the present invention will be described with a more specific example. In Table 1, the conditions of the comparative examples and the examples and the obtained results are shown in a list.

(Comparative example)
A treatment for supplying a refining agent mainly composed of lime with oxygen gas from an immersed refractory blowing lance was performed for about 300 t of hot metal in the kneading vehicle for 30 minutes.
The oxygen supply rate was 0.28 Nm ³ / min / t, and the lime supply rate was 0.33 kg / t / min. Further, the hot metal component before treatment was 4.5% [C] -0.7% [Si] -0.2% [Mn] -0.16% [P] in terms of mass concentration, and the hot metal temperature was 1200 ° C.
In addition to the blast furnace slag that inevitably entered the chaotic car, lime was blown, so the basicity of the slag after treatment was 0.88. As for the ratio of the components in the pretreated slag obtained at this time, the P / Mn ratio was 0.25, and the Si / Mn ratio was 2.96.
The obtained slag was recycled 14 kg / t into a converter decarburization process of hot metal having a composition of 4.5% [C] -0.3% [Si] -0.2% [Mn] -0.11% [P]. The recovery width of Mn in the converter decarburization process was 0.04% for the change in the Mn concentration in the metal, and the pickup width of P was 0.020% for the change in the P concentration in the metal.
In addition, although this example was implemented limiting the steel type as a comparative example this time, such a P pickup is generally an unacceptable amount, and it is difficult to establish an actual process.

Example 1
In the same operation as in the comparative example, no lime was blown during the preliminary treatment, and the treatment was performed such that the basicity of the slag after treatment was 0.29. As a result, P / Mn in the slag after treatment was 0.14, and Si / Mn was 2.6.
When this slag was recycled at a rate of 10 kg / t with respect to the decarburization step, the amount of P pickup was reduced to half by 0.010% despite the Mn recovery being 0.04%, which was equivalent to the comparative example.
The reason why Mn recovery was secured with a small amount of recycle is because the Mn concentration in the slag is high, and this is because the amount of generated slag determined by the generated SiO ₂ is small because the basicity is low. . With this level of P pickup amount, it is possible to have a wide range of target steel types and treatments, and this is an actual process.

(Example 2)
The pretreatment slag obtained by the hot metal treatment similar to that in Example 1 was separately managed with a P / Mn of 0.1 or less determined based on the dephosphorization width, and only the P / Mn of 0.1 or less was obtained. Recycled to decarburization process. In addition, as a result of performing the pretreatment under the same conditions as in Example 1, the P / Mn predicted based on the dephosphorization width exceeded 0.1 at a ratio of about 2 ch after 10 ch treatment, and particularly the hot metal temperature was A tendency to occur at low ch was observed.
The recycled slag had a P / Mn of 0.09. When this slag was recycled to the 13 kg / t decarburization process, the Mn recovery width increased to 0.05%, and the P pickup amount decreased to 0.008%.

(Example 3)
In the pretreatment slag obtained by performing the hot metal treatment under the same conditions as in Example 1, the Si / Mn obtained based on the desiliconization width is separated and managed, and this Si / Mn is 2 or less. Only the ones were recycled to the decarburization process. In order to set the Si / Mn ratio to 2 or less, hot metal having an initial Si content of about 0.3% was processed, and the end point Si of the hot metal was adjusted to control the desiliconization width.
When the treatment is terminated with the hot metal end point Si high, the slag amount decreases, so the P concentration of the pretreatment slag tends to increase, but if the addition amount is determined by the Si concentration of the pretreatment slag, Si It is important to keep the / Mn ratio low.
The basicity of the recycled slag was 0.41, P / Mn was 0.11, and Si / Mn was 1.83. As a result, the amount of recovered Mn increased to 0.07% and the P pickup amounted to 0.015%. It is applicable to steel types that have a relatively wide P pick-up tolerance and Mn recovery merit.

Example 4
In the same treatment as in Example 1, the acid feed rate was reduced to 0.17 Nm ³ / min / t and the treatment time was extended from 30 minutes to 40 minutes. As a result, P / Mn was 0.09 and Si / Mn was 1.83. . The obtained slag 13 kg / t was reused in the decarburization process. As a result, it was possible to suppress Mn recovery to 0.07% and P pickup to 0.011%.

(Example 5)
Similar to Example 4, except that all the oxygen was supplied with iron oxide (until Example 4 was supplied with oxygen gas). As a result, P / Mn decreased to 0.07 because the P removal width further decreased, and when the obtained slag 13 kg / t was recycled to the decarburization process, the P pickup width was 0.009%, which is compared with Example 4. But it was even lower.

(Example 6)
A process similar to that of Example 4 is performed by supplying oxygen as oxygen gas, but attaching a small gas tank pressurized inside with oxygen to a kneading vehicle, and blowing oxygen from the tank into the hot metal with a refractory lance. Went. As a result, the treatment time could be extended to 60 minutes without changing the oxygen intensity, and the acid feed rate could be reduced to 0.11 Nm ³ / min / t. Furthermore, since the processing can be performed during conveyance, it is not necessary to occupy the processing position, and the processing time can be extended without impairing productivity. As a result, the P pickup width was 0.007%, which was even lower than that of Example 5.

(Example 7)
In the hot metal up to Example 6, the temperature at the end of the treatment was 1200 ° C, but in this example, the treatment was started at 1350 ° C. Other conditions are the same as in Example 6. As a result, the P pickup width was 0.006%, which was even lower than Example 6.

(Example 8)
The same treatment as in Example 7 was performed with the composition of the hot metal before the treatment being 4.5% [C] -0.3% [Si] -0.3% [Mn] -0.11% [P]. As a result, the Mn recovery amount was 0.1, and the P pickup amount was 0.003%, which was even lower than Example 7.

Example 9
The pretreated slag of Example 8 was reused in the decarburization process. It was reused when the initial hot metal composition before treatment was 4.5% [C] -0.01% [Si] -0.04% [Mn] -0.03% [P].
As a result, since there is almost no Si supply from hot metal due to the basicity constraint, a large amount of recycled slag can be used. For example, in Example 8, it was about 13 kg / t, but in this example, 18 kg / t. More slag could be reused. As a result, the amount of recovered Mn was 0.13%, and the P pickup was also suppressed to 0.004%.

(Example 10)
In the same manner as in Example 5, the hot metal pretreatment was performed using the same hot metal composition in the pretreatment as in Example 9, and the obtained slag was reused in the decarburization furnace. In the hot metal preliminary treatment, slag (C / S = 3.5, T.Fe = 16%, P ₂ O ₅ = 2%) generated in the decarburization treatment was used as a part of the oxygen source. The initial hot metal Si concentration in the treatment of the decarburization furnace was 0.01%.
As a result, the cost of the iron oxide raw material can be reduced, and the iron oxide in the slag lost in the converter process can be recovered. The amount of recovered Mn was the same as in Example 9, and the P pickup slightly increased due to the effect of P in the decarburized soot, but could be suppressed to 0.006%.

(Example 11)
The same treatment as in Example 10 was performed. However, the slag used in the pretreatment was not decarburized slag but the pretreatment slag of the present invention (pretreatment slag of Example 8). The pretreatment slag obtained in the present invention contains a large amount of iron oxide and is more efficient as an oxygen source than decarburized slag. The obtained slag had a lower iron oxide concentration than when it was added. Whether it can be used more than once can be judged from the iron oxide concentration.
A higher amount of recovered Mn than Example 8 could be obtained.

(Example 12)
Up to Example 11, the inside of the kneading vehicle was protected with a refractory containing MgO, but in this example, the same treatment as in Example 9 was changed to a refractory in the pretreatment container containing alumina as a main component. I went there. The MgO concentration, which is a basic component in slag, decreased, and the P pickup decreased.

Claims (12)

  The hot metal pretreatment for reacting the hot metal with a gas containing oxygen or a refining agent containing iron oxide is performed so that the basicity of the slag after the pretreatment is 0.5 or less, and the obtained slag is converted into a converter. Of using generated slag, characterized in that it is reused in the decarburization process in Japan.   The method for using generated slag according to claim 1, wherein a mass ratio P / Mn of P content and Mn content in the slag after the treatment is 0.1 or less.   The method for using generated slag according to claim 1 or 2, wherein a mass ratio Si / Mn of Si content and Mn content in the slag after the treatment is 2 or less. The method for using the generated slag according to any one of claims 1 to ³ , wherein a supply rate of oxygen in the hot metal pretreatment is 0.2 Nm ³ / min / t or less.   The method for using the generated slag according to any one of claims 1 to 4, wherein 30% or more of the supplied oxygen in the hot metal pretreatment is supplied as iron oxide.   A gas supply device including a tank storing oxygen-containing gas and / or a container storing iron oxide content and a continuous supply device of iron oxide are attached to the transfer container, and oxygen is continuously supplied during transfer to hot metal. The method for using the generated slag according to any one of claims 1 to 5, wherein preliminary processing is performed.   The method for using the generated slag according to any one of claims 1 to 6, wherein the hot metal temperature at the end of the hot metal pretreatment is 1300 ° C or higher and 1450 ° C or lower.   The hot metal component before hot metal pretreatment is C ≧ 3.5 mass%, Si ≦ 0.6 mass%, Mn ≧ 0.1 mass%, P ≦ 0.15 mass%, any one of claims 1 to 7, How to use the generated slag as described in 1.   The method for using the generated slag according to any one of claims 1 to 8, wherein the Si concentration in the hot metal before decarburization is less than 0.15 mass%.   The method for using the generated slag according to any one of claims 1 to 9, wherein decarburized soot is used as the iron oxide component.   The method for using the generated slag according to any one of claims 1 to 10, wherein the slag obtained by the preliminary treatment is used as the iron oxide content.   The refractory in at least a portion in contact with the slag of the container for performing the pretreatment is mainly composed of at least one of alumina and silica. How to use slag.

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