JP7363731B2 - Method for dephosphorizing hot metal and manufacturing method for molten steel - Google Patents

Description

The present invention relates to a method for dephosphorizing hot metal and a method for producing molten steel, which reuses slag produced during a refining process.

By consolidating the multi-step refining process into a converter, it is possible to significantly reduce the energy loss of hot metal, and to significantly reduce the fixed costs (equipment costs and labor costs) of processes before and after the converter. The method is disclosed in, for example, Patent Documents 1 and 2.

Patent Document 1 discloses that after decarburization refining is completed, the decarburized and refined molten steel is tapped from within the refining container, and all or part of the decarburized slag generated in the decarburization refining is left in the refining container to be cooled and solidified. When charging the next charge of hot metal and iron scrap into the smelting vessel and performing desiliconization and dephosphorization treatment, the slag from the smelting vessel or A technique is disclosed that uses decarburized slag that has been discharged from another smelting vessel, cooled and solidified.

In addition, Patent Document 2 describes that when melting one charge of molten steel using the same converter or two converters in succession for the purpose of reforming the converter slag so that it does not expand. In a method of discharging slag twice or more, a technique is disclosed in which the second and subsequent slag is discharged on top of the slag discharged the first time to mix the two slags.

Japanese Patent Application Publication No. 2014-169492 Japanese Patent Application Publication No. 2005-194574

However, the above conventional technology has the following problems that still need to be solved. The technology disclosed in Patent Document 1 uses decarburized slag that has been solidified in advance as a cooling agent for the decarburized slag, so the basicity is high, and the initial basicity during the desiliconization and dephosphorization treatment increases. There was a risk of poor slag formation. Furthermore, in operations where intermediate slag is carried out after desiliconization and dephosphorization treatment, two types of slag are generated, creating problems that require complicated management such as separate operation of slag storage sites and management of slag characteristics for roadbeds.

In addition, the technology disclosed in Patent Document 2 is to mix the two types of slag and reform the converter slag into raw materials for other materials such as roadbed materials, but the technology is based on decomposition that can be used as a refining agent. There was a problem that the coal slag was discharged and could not be used effectively.

The present invention has been made in view of the above circumstances, and its objectives are to promote early slag formation of a refining agent during desiliconization and dephosphorization treatment of hot metal, reduce CaO sources, and further improve iron The purpose of this invention is to propose a method for dephosphorizing hot metal and a method for manufacturing molten steel that contribute to improving yield.

The present invention, which was developed to solve the above problems and achieve the above objects, is as shown in the following summary structure. That is, in the method for dephosphorizing hot metal according to the present invention, at least hot metal is charged into a molten metal container, a refining agent containing CaO is added, and the molten metal is dephosphorized by oxygen blowing. A part or all of the decarburized slag generated during oxygen blowing to produce molten steel from the hot metal of the previous charge is left in the molten metal container, and as a cooling material for the decarburized slag left in the molten metal container, It is characterized by using solidified slag that has been generated in the dephosphorization process of hot metal and then cooled and solidified.

Further, the method for producing molten steel according to the present invention includes a first step of charging hot metal or hot metal and a cold iron source into a converter-type refining vessel and performing desiliconization and dephosphorization treatment; a second step of discharging a portion of the generated dephosphorizing slag from the refining container while retaining the molten pig iron that has been desiliconized and dephosphorized in the first step; A third step of obtaining molten steel by decarburizing and final dephosphorization by adding a refining agent containing CaO to the held hot metal and oxygen blowing the same, wherein the charge is heated in the refining vessel. The molten pig iron of the charge is charged while some or all of the decarburization slag generated during oxygen blowing to produce molten steel from the hot metal of the previous charge remains in the refining vessel, and the decarburization slag that remains in the refining vessel is charged. It is characterized by using solidified slag, which is generated in the dephosphorization process of hot metal, cooled and solidified, as the slag coolant.

Further, the method for producing molten steel according to the present invention includes, secondly, a first step of charging hot metal or hot metal and a cold iron source into a converter-type refining vessel and performing desiliconization and dephosphorization treatment; a second step of discharging a portion of the generated dephosphorizing slag from the refining container while retaining the molten pig iron that has been desiliconized and dephosphorized in the first step; A third step of obtaining molten steel by decarburizing and final dephosphorization by adding a refining agent containing CaO to the retained molten pig iron and oxygen blowing, and releasing the molten steel obtained in the third step. a fourth step of cooling and solidifying at least a portion of the decarburized slag in the refining container, leaving part or all of the decarburized slag in the refining container in the refining container for use in refining the next charge of hot metal; The decarburization slag left in the refining vessel in the fourth step was discharged, cooled, and solidified in the second step of the previous charge as a coolant after repeated implementation. It is characterized by using solidified slag.

Regarding the method for manufacturing molten steel according to the present invention,
a. The solidified slag added into the refining container in the fourth step is the dephosphorization slag generated in the first step and the decarburization slag generated in the third step in a waste container or a slag treatment plant. be mixed at least partially in a molten state;
b. In the second step, the dephosphorized slag discharged from the refining container is stored in a slag container, and in the fourth step, the decarburized slag in the smelting container is stored in the slag container containing the dephosphorized slag. discharging a part of the mixed slag containing the dephosphorization slag and the decarburization slag from the slag container, cooling and solidifying the mixed slag,
c. The solidified slag is a mixture of 80% by mass or less of the decarburized slag generated in the third step with respect to the total of the dephosphorized slag generated in the first step and the decarburized slag generated in the third step. There is something
d. The solidified slag has a particle size of 50 mm or less;
It is thought that this could be a more preferable solution.

As explained above, according to the method for dephosphorizing hot metal and the method for producing molten steel according to the present invention, low basicity slag containing dephosphorization slag is used as a coolant for so-called decarburization slag left in the refining vessel. Therefore, the formation of slag slag during desiliconization and dephosphorization processing is promoted, making it possible to reduce CaO sources and shorten processing time.At the same time, the amount of decarburized slag remaining after decarburization and refining increases, reducing new CaO sources and improving iron yield. It is possible to improve the

FIG. 2 is an explanatory diagram of a method for manufacturing molten steel according to an embodiment of the present invention.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a diagram illustrating a method for producing molten steel according to an embodiment of the present invention. The hot metal 10 produced in the blast furnace becomes molten steel 11 through the steps (a) to (g) in order, and then goes through the step (h) to each step (a) to (h) after the next charge. ) in order.

(First step)
Hot metal 10 or hot metal 10 and iron scrap 12 as a cold iron source are charged into a converter-type refining vessel 1, and desiliconization and dephosphorization treatments are performed. FIG. 1A shows a state in which iron scrap 12 as a source of cold iron is charged into a converter 1 (an example of a molten metal container or a refining container). FIG. 1(b) shows how hot metal 10 is then poured into the converter 1 from the hot metal ladle 2. FIG. 1(c) shows a situation where the converter 1 is tilted and the limit tilt angle is confirmed after the injection of the hot metal 10 is completed. Then, the converter 1 is kept in an upright state, and a heating source and a refining agent are added as necessary. Next, the top blowing lance 3 is lowered into the converter 1 from above, and an oxygen source is supplied from the top blowing lance 3 to reduce the Si (silicon) and P (phosphorus) in the hot metal 10 to a preset concentration. A desiliconization and dephosphorization treatment is performed to remove the silicon (FIG. 1(d)). Although hot metal and iron scrap are used as the main raw materials here, iron scrap may not be used if necessary. Note that the hot metal 10 may be treated in a hot metal pretreatment step to reduce the Si, P, and S (sulfur) in the hot metal 10 to a preset concentration. Furthermore, instead of or in addition to the supply of oxygen from the top blowing lance 3, oxidizing gas may be supplied from the bottom blowing tuyere 4. A non-oxidizing gas may be supplied from the bottom blowing tuyeres 4 for stirring the hot metal 10.

(Second process)
The upright converter 1 is tilted toward the tailings side, and the slag (dephosphorization slag) 13 generated in the first step is discharged from the converter 1 to the tailings container 5 (FIG. 1(e)). The slag container 5 is transported to a slag treatment plant by a transport truck (not shown) or the like.

(Third step)
With the converter 1 standing upright, a refining agent containing CaO is added, the top blowing lance 3 is lowered into the converter 1, and oxygen is supplied from the top blowing lance 3 (oxygen blowing). The C (carbon) and P in the hot metal 10 that has been subjected to the desiliconization and dephosphorization treatment in the first step is reduced to a preset concentration to form the molten steel 11 through decarburization refining and final dephosphorization treatment (Fig. 1(f) )). Here, instead of or in addition to the supply of oxygen from the top blowing lance 3, oxidizing gas may be supplied from the bottom blowing tuyere 4. A non-oxidizing gas may be supplied from the bottom blowing tuyere 4 for stirring the hot metal. The refining agent may be supplied simultaneously with the oxidizing gas and the non-oxidizing gas from the top blowing lance 3 or the bottom blowing tuyere.

(Steel tapping process)
The upright converter 1 is tilted toward the tapping side, and the molten steel 11 obtained in the third step is tapped into a molten steel ladle (not shown) through the outlet 6 provided on the side wall of the converter 1. (Figure 1(g)).

(Fourth step)
The slag (decarburized slag) 14 generated in the third step is left in the converter 1 to be cooled and solidified (FIG. 1(h)). Here, the upright converter 1 is tilted toward the tailings side, and the remainder of the decarburized slag 14 is discharged into the tailings container 5 so that a portion of the decarburized slag 14 remains inside the converter 1. However, all of the decarburized slag 14 may be left in the converter 1.

With the decarburized slag 14 solidified as described above remaining in the converter 1, return to the first step described above and charge the next charge of hot metal 10 and cold iron source 12 into the converter 1 again. Then, repeat the steps up to the fourth step.

In the above example, one converter 1 is used to perform the first step of desiliconization and dephosphorization treatment (FIG. 1(d)) and the third step of oxygen blowing (FIG. 1(f)). ing. Alternatively, only the hot metal 10 may be discharged from the discharge port 6 after the first step, and then the slag 13 may be discharged in the second step (FIG. 1(e)). Furthermore, the hot metal 11 subjected to desiliconization and dephosphorization treatment in the first step may be charged into another converter 1 and oxygen blowing (FIG. 1(f)) in the third step may be performed.

In the production of molten steel described above, the following conditions are necessary to effectively reuse the slag 14 produced in the third step.
・The coolant 15 added to the slag 14 left in the converter 1 in the fourth step is to ensure that the slag is quickly remelted during the desiliconization and dephosphorization treatment in the first step. The basicity of the slag left in the furnace should not become too high.
- As a raw material for roadbed materials, it is possible to use slag with the strength required for the product, the expansion rate during hydration reactions reduced, and basicity appropriately controlled.
- Provided that the above two conditions are met, productivity should not be hindered.

Here, in order to satisfy the above conditions, first, as shown in FIG. 1, the dephosphorization slag 13 that has been discharged from the converter 1 (or another converter) and cooled and solidified is used. was found to be effective. Compared to the case where only the decarburization slag 14 is solidified and used as a coolant, by using the dephosphorization slag 13 as a coolant to solidify the decarburization slag 14, the basicity of the solidified slag is lowered, and the decarburization in the first step is reduced. Slag formation is promoted at the start of silica and phosphorization treatment. As a result, the processing time can be shortened, and by solidifying the decarburized slag, the amount of decarburized slag remaining from the previous charge is increased, and since the decarburized slag contains granular iron, it can be used as a new source of CaO. It has become possible to reduce the amount of iron and improve the iron yield.

Also for the purpose of adjusting the characteristics of the slag, it is preferable to mix the dephosphorization slag 13 and the decarburization slag 14. Due to its characteristics, dephosphorization slag has a low basicity (CaO/SiO ₂ ) and a relatively low free lime content, so its expansion rate in a water immersion expansion test is relatively low, but it does contain foamed bubbles. This slag has a low density, and the strength of the slag particles produced by crushing after solidification is relatively low, so there is a problem that it is not suitable for use in some civil engineering applications. On the other hand, decarburized slag has a high basicity and contains a large amount of free lime (F.CaO), so in order to use it for applications such as roadbed materials, it is necessary to sufficiently suppress hydration expansion by steam aging, etc. However, since the slag has low viscosity and relatively high fluidity, it has a low porosity and tends to be dense and strong slag particles. By mixing both of these slags in a state where at least a portion is molten, it is possible to obtain intermediate characteristics between the respective slags, and for example, to develop the strength required for roadbed material products, such as modified CBR. , and it becomes possible to obtain a raw material slag suitable for reducing the slag expansion rate during the hydration reaction. As a method of mixing both slags, it is preferable to mix the slags in a state in which at least a portion of the slags are melted in the waste container 5 or in the slag processing plant. Specifically, these slags can contain a large amount of low melting point liquid phase such as CaO-SiO ₂ -Fe ₂ O ₃ system or CaO-SiO ₂ -Al ₂ O ₃ system even at a temperature of about 1250 ° C. It is preferable to mix both slags while at least a part of the slag is at 1250°C or higher, and if the converter slag is mixed at 1400°C or higher with relatively good fluidity, the discharged slag It is more preferable that a sufficient mixed state can be achieved simply by utilizing the kinetic energy due to free fall. When mixing in the slag container 5, the slag container 5 that has received the dephosphorized slag 13 in the second step can be kept on standby, and the decarburized slag can be received in the fourth step. More preferred. By doing this, the low melting point dephosphorization slag 13 is melted by the sensible heat of the decarburization slag treated at about 1600°C, and is thoroughly mixed in the slag container, resulting in physically more uniform properties. It can be a mixed slag. Therefore, more appropriate quality can be ensured both as a coolant in the fourth step and as a raw material for roadbed material.

As the coolant in the fourth step, the amount of decarburized slag in the mixed slag is preferably 80% by mass or less. This is because if the decarburized slag exceeds 80% by mass, the basicity and melting point of the slag after cooling and solidification will become too high, and the time required to melt the slag in the first step will increase unnecessarily.

Further, as a raw material for roadbed material, it is preferable that the decarburized slag in the mixed slag is 30 to 70% by mass. If the decarburized slag in the mixed slag is 30% by mass or more, it is effective in reducing the amount of pores in the mixed slag and improving the strength of slag particles suitable for uses such as roadbed materials. If the decarburized slag in the mixture is 70% by mass or less, the free lime content in the mixed slag will be relatively low, and by appropriate steam aging treatment, the slag material will have a low water immersion expansion coefficient and is suitable for uses such as roadbed materials. can be obtained more reliably.

The mixed slag used as the coolant 15 in the fourth step is preferably a cooled and solidified slag that is pulverized and adjusted to a particle size of 50 mm or less. Here, the particle size of 50 mm or less means that the undersieve in which the short axis or short side of the mesh is 50 mm is used. By adjusting the slag particle size, the reaction with the decarburized slag 14 can be promoted and the decarburized slag 14 can be solidified quickly.

Next, examples performed to confirm the effects of the present invention will be described.
The test was conducted using the following procedure.
First, dephosphorization slag and decarburization slag are mixed in advance with approximately 3 to 13 kg of decarburization slag remaining in a converter-type refining vessel 1 that can be charged with a capacity of 380 tons and capable of top-bottom blowing. The mixed slag that had been mixed was used as a coolant and 1 to 20 kg/ton of hot metal was added to solidify the decarburized slag.

Subsequently, the cold iron source 12 is charged into the above-mentioned refining vessel 1 in a ratio of about 10 to 20% by mass based on the total charge, and then hot metal is charged, and silicon is added depending on the Si concentration in the hot metal. After adding a lime source and a lime source for basicity adjustment, blowing for desiliconization and dephosphorization treatment was carried out (first step). As a silicon source which is a heat source during this blowing, SiC briquette, FeSi alloy, or silica stone was used. After the first step was completed, intermediate slag removal work (second step) was immediately performed, followed by decarburization blowing (third step) and steel tapping (steel tapping step).

The mixed slag used here is obtained by collecting a portion of the slag 14 remaining after tapping in the fourth step in the slag container 5 that has received the dephosphorization slag 13 in the above-mentioned intermediate slag, and then discharging it. The slag was melted and mixed in the slag container 5, cooled and solidified, and then pulverized to adjust the particle size to 50 mm or less.

The evaluation was performed by changing the slag mixing ratio and brand of coolant and comparing the slag slag formation before desiliconization and dephosphorization treatment, initial basicity, and treatment time. If there was no bumping during charging of hot metal and the unslag disappeared within 12 minutes, it was marked with a circle. In addition, cases in which unslaged slag remained for more than 12 minutes were marked as x. The slag formation status of the slag was determined by taking a slag sample, cooling it, and observing the cross section as an area ratio.
Table 1 shows the test conditions and test results.

From the results in Table 1, it can be seen that treatment No. 1 using dephosphorization slag and mixed slag as a coolant for decarburization slag left in the converter. Nos. 1 to 5 were excellent in initial slag formation during desiliconization and dephosphorization treatments, and shortening of treatment time was observed. Process No. 1 using 100% decarburized slag as a coolant. In No. 6, the initial slag formation during desiliconization and dephosphorization treatment was poor, and the treatment time increased. In addition, processing No. 1 using iron ore as a coolant. In No. 7, bumping occurred during the desiliconization and dephosphorization treatment, and the treatment was forced to be interrupted.

Next, in order to evaluate the characteristics of mixed slag as a raw material for roadbed material, slag with various compositions were prepared. The properties of the mixture were determined by measuring the water immersion expansion coefficient and general bulk strength in accordance with JIS A5015:2013.
Table 2 shows the test conditions and test results.

From the evaluation results in Table 2, No. 1, in which appropriate amounts of dephosphorization slag and decarburization slag were mixed. It can be seen that slags Nos. 2 to 4 have excellent bulk strength and water immersion expandability, and are suitable for applications such as roadbed materials. Those containing too much dephosphorization slag (No. 1) are inferior in bulk strength, and those containing too much decarburization slag (Nos. 5 and 6) are inferior in water immersion expansion. Note that Table 2 also lists the suitability of the residual decarburized slag shown in Table 1 as a coolant. No. Slags 1 to 5 have suitability as coolants.

Although the present invention has been described above with reference to the embodiments, the present invention is not limited to the configuration described in the above embodiments, and the present invention is not limited to the configurations described in the above embodiments. This also includes a case where a part or all of them are combined to constitute the method for producing molten steel of the present invention. Furthermore, the present invention is suitable for application to the effective use of a plurality of slags having different properties.

1 Converter type refining vessel 2 Hot metal pot 3 Top blowing lance 4 Bottom blowing tuyere 5 Slag container 6 Discharge port 10 Hot metal 11 Molten steel 12 Cold iron source (iron scrap)
13 Dephosphorization slag 14 Decarburization slag 15 Coolant (solidified slag)

Claims (6)

In dephosphorizing the hot metal by charging at least hot metal into a molten metal container, adding a refining agent containing CaO and oxygen blowing,
Leaving some or all of the decarburization slag generated during oxygen blowing in which molten steel is produced from molten metal in the previous charge in the molten metal container in the molten metal container;
As a coolant for the decarburized slag left in the molten metal container, solidified slag generated in the dephosphorization process of hot metal, cooled and solidified, is used ,
A method for dephosphorizing hot metal, characterized in that the solidified slag is a mixture of decarburization slag in a range of 30 to 80% by mass based on the total of dephosphorization slag and decarburization slag. A first step of charging hot metal or hot metal and a cold iron source into a converter-type refining vessel and performing desiliconization and dephosphorization treatment;
a second step of discharging a portion of the generated dephosphorization slag from the refining container while retaining the molten metal that has been desiliconized and dephosphorized in the first step;
A third step of obtaining molten steel by decarburizing and final dephosphorization by adding a refining agent containing CaO to the hot metal held in the refining container and oxygen blowing,
Charge the molten pig iron of the charge while leaving some or all of the decarburized slag generated during oxygen blowing in the refining container to produce molten steel from the molten metal of the charge before the charge,
As a coolant for the decarburized slag left in the refining vessel, solidified slag generated in the dephosphorization process of hot metal, cooled and solidified, is used ,
The solidified slag contains 30 to 80% by mass of the decarburized slag generated in the third step based on the total of the dephosphorized slag generated in the first step and the decarburized slag generated in the third step. A method for producing molten steel, characterized in that it is a mixture of molten steel within the range of . A first step of charging hot metal or hot metal and a cold iron source into a converter-type refining vessel and performing desiliconization and dephosphorization treatment;
a second step of discharging a portion of the generated dephosphorization slag from the refining container while retaining the molten metal that has been desiliconized and dephosphorized in the first step;
A third step of obtaining molten steel by decarburizing and final dephosphorization by adding a refining agent containing CaO to the molten metal held in the refining container and oxygen blowing;
The molten steel obtained in the third step is tapped, some or all of the decarburized slag in the refining vessel is left in the refining vessel for use in refining the next charge of hot metal, and at least The fourth step of solidifying a portion is repeated,
As a coolant for the decarburized slag left in the refining container in the fourth step, use solidified slag that has been discharged, cooled, and solidified in the second step of the charge that is earlier than the charge ,
The solidified slag contains 30 to 80% by mass of the decarburized slag generated in the third step based on the total of the dephosphorized slag generated in the first step and the decarburized slag generated in the third step. A method for producing molten steel, characterized in that it is a mixture of molten steel within the range of . The solidified slag added into the refining container in the fourth step is the dephosphorization slag generated in the first step and the decarburization slag generated in the third step in a waste container or a slag treatment plant. 4. The method for producing molten steel according to claim 3, wherein the molten steel is mixed in a state where at least a portion of the molten steel is molten. In the second step, the dephosphorization slag discharged from the refining container is stored in a slag container,
In the fourth step, a portion of the decarburized slag in the refining container is discharged into the slag container containing the dephosphorized slag and mixed in a state where at least a portion of the decarburized slag is molten,
5. The method for producing molten steel according to claim 3, further comprising discharging the mixed slag containing dephosphorization slag and decarburization slag from the slag container, cooling it, and solidifying it. The method for producing molten steel according to any one of claims 2 to 5 , wherein the solidified slag has a particle size of 50 mm or less.

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