JP5605339B2 - Recycling method of steelmaking slag - Google Patents

Description

  The present invention relates to a method for recycling steelmaking slag generated in a steelmaking process.

  The hot metal produced in the blast furnace is used as the main raw material and refined in a steelmaking process centered on the converter. The molten steel that has been refined is cast into a slab mainly by a continuous casting method. In the steelmaking process, hot metal preliminary de-Si / de-P and hot metal pre-desulfurization may be performed before the refining of the converter, and also in the converter process, de-Si / de-P / de-C is performed by one blowing. In addition to the method of combining the above, a method of first removing Si and removing P and then draining the hot water once or after intermediate draining in the same furnace and then performing de-C refining is adopted. Further, after converter refining, RH vacuum degassing, LF treatment, ASEA-SKF treatment, powder blowing treatment, and the like are performed as secondary refining in which molten steel is refined in a ladle.

  Among varieties that are refined in a converter, there are varieties that require RH vacuum degassing. Varieties that have the purpose of controlling the component content within a narrow range, the purpose of controlling molten steel degassing (especially dehydrogenation) and nitrogen level, and the purpose of reducing inclusions in molten steel and achieving the total oxygen concentration stably below 20 ppm. In RH vacuum degassing treatment is essential. The present invention is directed to a method for recycling steelmaking slag in a steelmaking process that requires RH vacuum degassing.

  In the steelmaking process, steelmaking slag is generated as a result of refining. There are pretreatment slag generated as a result of hot metal preliminary de-Si / P removal, hot metal preliminary desulfurization, converter slag generated as a result of converter refining, and secondary refining slag as a result of secondary refining. The secondary refining slag is sometimes called ingot slag or continuous cast slag (continuous cast slag). In addition, when de-P and de-C are separately performed for converter refining, the slag generated may be referred to as converter de-P slag and converter de-C slag.

  Steelmaking slag that is generated in the steelmaking process and discharged out of the system has different properties for each slag that is generated, so the slag is separately managed for each generation process, and further the presence or absence of elution of components such as fluorine is determined, The slag that satisfies the soil environmental standards and the characteristics of roadbed materials is used for roadbed materials, and others are used for marine applications with different environmental standards. Roadbed materials are the most promising resource for steady and stable use of resources. Increase the ratio of slag that can be used as roadbed materials, including the use of fluorine-free materials, and reduce the total amount of steelmaking slag discharged outside the system. is important. In order to control the amount of slag discharged from the steelmaking process to the outside of the system, various methods have been used to recycle slag, and efforts have been made to reduce the amount of slag that needs to be recycled outside the steelmaking process. .

  Patent Documents 1 and 2 refer to converter de-C slag or secondary refining (ingoting, continuous casting) slag, and Patent Documents 3 and 4 refer to secondary refining (ingoting, continuous casting) slag. An invention for recycling to the de-P process is disclosed. However, no countermeasures have been shown for the concern that the converter molten steel is subject to S contamination by secondary refining slag. Further, since the de-P and de-C processes are performed in separate containers, heat loss in the manufacturing process is large.

  As a method of recycling slag in the same furnace while avoiding heat loss, Patent Documents 5 and 6 disclose that de-P slag is discharged by the intermediate evacuation method, and the slag after de-C blowing is hot recycled into the converter. An invention is disclosed in which the amount of CaO used for de-P refining of the next charge is reduced while remaining. However, there is no technical policy regarding the recycling of secondary refining slag.

  Desulfurization refining in the steelmaking process is often performed by hot metal preliminary desulfurization. A desulfurizing agent is added to the hot metal in a torpedo car or hot metal ladle, and the hot metal is stirred to proceed the desulfurization reaction. CaO powder and Al dross are used as desulfurization agents, and hot metal desulfurization slag is difficult to apply to roadbed materials because it is pulverized easily after cooling and has insufficient strength.

  In the converter refining method in which the hot metal charged in the converter is de-Si, de-P refining, intermediate waste is performed, and subsequently de-C refining is performed in the same converter. Part of the de-P slag containing P at a high concentration remains in the converter and enters the de-C blown slag. And since the molten steel temperature (blow-off temperature) at the end of de-C refining is high, the slag generated by de-C refining needs to have sufficient de-P capability, and the slag is in the slag during converter de-C refining. Add fluorite and let the slag sufficiently hatch and have de-P ability. Therefore, in the production of low P steel, the converter de-C slag contains fluorine. Moreover, when recycling the de-C slag containing fluorine to the de-P process, the de-P slag also contains fluorine.

  After the converter refining, the molten steel delivered to the ladle is then subjected to secondary refining such as RH vacuum degassing, LF, ASEA-SKF, and powder blowing. The present invention is directed to varieties that require RH vacuum degassing. When only the RH vacuum degassing treatment is performed, the slag formed on the surface of the molten steel is not sufficiently stirred in the ladle. Therefore, in order to sufficiently reform and homogenize the slag on the ladle surface, Addition is required. Therefore, the secondary refining slag that has undergone the RH treatment contains fluorine.

  Of the secondary refining apparatuses, a secondary refining apparatus having means for arc heating a molten metal containing slag is referred to herein as an “arc heating secondary refining apparatus”. Any of the LF method, the VAD method, and the ASEA-SKF method can melt the flux added to the ladle by arc heating and heat the heated steel in the ladle. As the stirring means, the LF method and the VAD method are performed by blowing an inert gas from the bottom of the pan, and the ASEA-SKF method is performed with a stirrer using electromagnetic force. In these processes, refining using strong reducing slag is possible, and molten steel desulfurization can be performed (Non-Patent Document 1).

  Patent Document 7 discloses a method for producing molten steel for continuous casting from molten iron, in which molten iron discharged from a blast furnace is charged into a converter as it is, and for subsequent refining, de-Si removal P treatment is performed. After that, the waste was drained, and then de-C treatment was performed in the same converter, and the molten steel was taken out into a ladle and heated with an arc heating ladle refining device. A method for producing molten steel is described in which it is performed only in a series of processes, and the de-S treatment is performed only with an arc heating ladle refining device. By reducing the temperature after de-C treatment of the converter, it is not necessary to blow down C in the molten steel in order to prevent P increase during the de-C process of the converter.

Patent Document 8 discloses a desulfurization method in which molten steel held in a ladle is stirred to perform a desulfurization process, and a method in which CaF ₂ is not added to the ladle is disclosed.

Japanese Patent No. 3321536 Japanese Patent No. 3097474 Japanese Patent No. 3218629 Japanese Patent No. 3711835 Japanese Patent No. 2607328 Japanese Patent No. 2958846 JP 2008-63610 A JP 2003-155516 A

Third Edition Steel Handbook II Steelmaking and Steelmaking, pages 679-680

  For hot metal desulfurization slag, the S content in the slag is very high and it is difficult to recycle in the steelmaking process because it is difficult to handle and difficult to handle. High effective use is difficult. Since steelmaking slag containing fluorine may not satisfy the soil environmental standards, its use as a roadbed material is limited. Moreover, if the converter de-C slag containing fluorine is recycled to de-P refining, the converter de-P slag also contains fluorine, and therefore, recycling of de-C slag to de-P refining is restricted. Secondary refining slag that has been subjected to RH treatment is difficult to recycle because it contains fluorine, and when secondary refining is only RH treatment, secondary refining slag does not have desulfurization capability. It is difficult to cope with S contamination when the next refining slag is recycled to the converter.

  The present invention eliminates the generation of hot metal desulfurization slag by not performing the hot metal desulfurization treatment, eliminates the need for fluorite addition to the converter desulfurized C slag, makes the converter slag fluorine-free, and accompanies it. The task is to promote recycling of P-removal process, and to eliminate the addition of fluorite to the secondary refining slag, to make the secondary refining slag fluorine-free and to accompany it with the recycling of the secondary refining slag in the steelmaking process. To do. Thereby, while reducing the amount of slag discharged | emitted out of a system from a steelmaking process, it aims at the promotion of effective utilization of steelmaking slag by implement | achieving fluorine-less of the slag discharged | emitted out of the system.

  The present invention is intended for varieties that require RH vacuum degassing in secondary refining. In addition to refining using an RH vacuum degassing apparatus, refining is performed using an arc heating secondary refining apparatus. It is a way to promote resource recycling.

  In the arc heating secondary refining device, for example, the LF method, the molten steel in the ladle can be heated and heated, so that the blowing temperature in the converter is lowered in response to the heated temperature of the molten steel in the ladle. be able to. Since the slag removal P ability in the converter is improved as the temperature is lower, the P concentration in the molten steel can be reduced without adding fluorite in the removal C slag in the converter removal C refining by lowering the blowing temperature. It can be reduced. Defluorinated C slag does not contain fluorine, so when recycled C slag is recycled for de P refining, it is possible to effectively use the de-P slag as the roadbed material, and effectively use the de-C slag itself as the roadbed material. You can also.

  In the secondary refining using both the arc heating secondary refining apparatus and the RH vacuum degassing apparatus, a method for refining without adding fluorite was found. Thereby, it can be set as the secondary refining slag which does not contain a fluorine, and it becomes possible to discharge | emit secondary refining slag itself out of a system, and to use it effectively as a roadbed material.

  Since desulfurization refining can be performed by secondary refining using an arc heating secondary refining device, the S concentration in the molten steel can be lowered to a target level without performing hot metal preliminary desulfurization. Since hot metal preliminary desulfurization is not performed, hot metal preliminary desulfurization slag is not generated, and therefore, it is not discharged out of the steelmaking process. Further, S contamination when the secondary refining slag is recycled to the converter can be dealt with by performing desulfurization refining in the secondary refining. Therefore, coupled with the fact that the secondary refining slag does not contain fluorine, the secondary refining slag can be recycled to the converter.

This invention is made | formed based on the said knowledge, The place made into the summary is as follows.
(1) Hot metal produced in the blast furnace is refined in a converter, and then secondary refining is performed using a secondary refining device having an arc heating means (hereinafter also referred to as “arc heating secondary refining device”). in a later step, performed secondary refining by using a RH vacuum degassing apparatus, wherein the converter without the addition of auxiliary material containing fluorine, said, it occurs through two types of secondary refining two Part or all of the secondary refining slag is added, and in the refining by the arc heating secondary refining device, desulfurization refining is performed while the molten metal is heated without adding the fluorine-containing secondary material, and the fluorine discharged from the converter is removed. A method for recycling steelmaking slag, wherein the converter slag not containing, or part of the converter slag and secondary refining slag not containing fluorine is discharged out of the system.
(2) The hot metal charged in the converter is de-Si, P-refined, intermediate waste is removed, C-refining is subsequently performed in the same converter, and the secondary refining slag is converted to the converter during de-C refining. The method for recycling steelmaking slag as described in (1) above, which comprises adding.
(3) Resource conversion of steelmaking slag as described in (2) above, wherein the converter slag generated in the de-C process is left in the converter and used for de-Si and de-P refining in the next refining heat. Method.
(4) For the hot metal to be charged into the converter, the hot metal preliminary de-Si and hot metal preliminary desulfurization are not performed before the converter is charged, and the steelmaking according to any one of the above (1) to (3) Recycling method of slag.

  The present invention is intended for varieties in which hot metal is smelted in a converter and subsequently smelted using a RH vacuum degasser, and arc heating secondary smelting is performed before RH vacuum degassing. Add some or all of the secondary refining slag generated by refining with the arc heating secondary refining equipment and RH vacuum degassing equipment without adding the secondary material contained, and fluorine with the refining with the arc heating secondary refining equipment Desulfurization and refining while heating the molten metal without adding the secondary material it contains, converting the converter slag that does not contain fluorine discharged from the converter, or part of the converter slag and secondary refining slag that does not contain fluorine Since it discharges out of the system, the amount of steelmaking slag discharged out of the system from the steelmaking process can be reduced, and slag not containing fluorine can be discharged out of the system.

It is a figure which shows the refining flow outline in the steelmaking process of the example of this invention. It is a figure which shows the refining flow outline in the steelmaking process of a comparative example. It is a figure which shows the relationship between the blowing stop C of a converter, the blowing stop temperature, the presence or absence of fluorite use, and the blowing stop P. It is a figure which shows the basic unit according to the presence or absence of fluorine of the out-of-system discharge slag.

  After the molten iron is charged into the converter, it is treated as the same lot until the converter refining, the steel is taken out to the ladle and the secondary refining of the molten steel is performed. In the present invention, this series of processing units handled as a single lot is called “heat”.

After the converter refining, the molten steel delivered to the ladle is then subjected to secondary refining such as RH vacuum degassing, LF, ASEA-SKF, and powder blowing. The present invention is directed to varieties that require RH vacuum degassing as a secondary refining process. In order to reduce the inclusions of molten steel during RH vacuum degassing treatment, quick lime is introduced into the ladle at the time of leaving the converter to ensure the basicity of the slag formed on the surface of the molten steel in the ladle. Aim to reduce the degree of oxidation (content of T.Fe + MnO in slag). On the other hand, in the RH vacuum degassing process, the molten steel in the ladle is sucked up from the immersion riser pipe of the RH vacuum tank, returned to the ladle from the immersion downpipe, and the molten steel circulates between the ladle and the vacuum tank. Stir refining is mainly performed in a vacuum tank, and the slag formed on the surface of the molten steel is not sufficiently stirred in the ladle, so the ladle slag solidifies during the RH treatment, and the slag -Insufficient metal refining. In particular, since the basicity of the slag is increased by adding quick lime to the ladle at the time of steel leaving the converter, the slag becomes even harder. Therefore, since the slag composition is not uniform, the degree of oxidation cannot be sufficiently lowered, and the dip tube does not penetrate the slag layer at the start of the RH treatment, and the molten steel treatment cannot be performed. In order to avoid such a situation and to sufficiently reform and homogenize the slag in the ladle only by stirring in the ladle at the time of steel leaving the converter, it was necessary to add fluorite, which was subjected to RH treatment. The secondary refining slag contains fluorine.

  The LF method, the VAD method, and the ASEA-SKF method are also collectively referred to as “the ladle refining method”. In any case, it is possible to melt the flux added in the ladle and to raise the temperature of the molten steel in the ladle by arc heating. As the stirring means, the LF method and the VAD method are performed by blowing an inert gas from the bottom of the pan, and the ASEA-SKF method is performed with a stirrer using electromagnetic force. In these processes, refining using strong reducing slag is possible, and molten steel desulfurization can be performed. In the present invention, these secondary refining methods are referred to as “arc heating secondary refining apparatuses” because they have means for arc heating.

  In the P balance between the slag and the metal in the converter, the lower the temperature of the slag and the metal, the more the P moves to the slag side. That is, the slag removal P ability is improved as the temperature is lower. Conventionally, when only the RH vacuum degassing process is performed as the secondary refining, it is necessary to set the blow-off temperature high in order to compensate for the temperature drop in the secondary refining. Of course, when adopting refining that simultaneously performs de-P and de-C in the converter, fluorite is added to the converter slag to promote hatching of slag in order to perform sufficient de-P refining even at high blowing temperatures. It is indispensable to plan. In addition, even in converter refining where the hot metal charged in the converter is de-Si and P refining, intermediate waste is performed, and then de-C refining is performed in the same converter, the de-P slag is partly de-C blown. In order to prevent recovery P from slag at the end of de-C refining, fluorite is added to the slag during converter de-C refining, and the slag is sufficiently hatched to remove P. It is necessary to have Even if secondary smelting is a combination of LF treatment and RH vacuum degassing treatment, it is necessary to keep the blowing temperature at the converter high because conventional heating only involves the purpose of hatching slag. Yes, it was necessary to add fluorite to the slag at the time of converter de-C refining so that the slag was sufficiently hatched to have P removal ability.

  In the present invention, an arc heating secondary refining device is added to the secondary refining after converter refining, and the temperature of the molten steel is increased by heating to lower the blow-off temperature. Without adding fluorite, it becomes possible to reduce the P concentration in the molten steel to the target level. FIG. 2 is a diagram showing the relationship between the blow-stop C of the converter, the blow-stop temperature, whether or not fluorite is used, and the blow-stop arrival P. As can be seen from FIG. 2, by reducing the blowing temperature of the converter by 25 to 50 ° C., it is possible to realize the necessary blowing stop P value without using fluorite in the refining of the converter. .

  In Patent Document 7 as well, the temperature is increased by an arc heating ladle refining device, and the temperature after de-C treatment of the converter is reduced. However, in Patent Document 7, by lowering the temperature after de-C treatment of the converter, the blow-down of C in the molten steel, which has been performed to prevent P rise during the converter de-C treatment, is prevented, and the de-C treatment The purpose is to make the blown-off% C of 0.07% or more. This is because blowing down C in the molten steel increases the oxygen concentration in the molten steel and leads to problems such as an increase in alumina inclusions due to deoxidation treatment. That is, the thing of patent document 7 was made | formed for the purpose of the blow-down prevention of C in molten steel, using the fluorite as it is by refining of a converter.

  In a refining method in which de-P refining-intermediate waste-de-C refining is performed in a converter, de-P refining was originally possible without refining fluorite. This is because the molten metal temperature at the end of de-P refining is kept low. However, conventionally, since the de-C slag contains fluorine, the de-P slag is supposed to contain fluorine by recycling the de-C slag to de-P refining. In the present invention, since the de-C slag does not contain fluorine, when the de-C slag is recycled to de-P refining, the de-P slag does not contain fluorine, and the de-P slag is discharged out of the system from the steelmaking process. It can be effectively used as a roadbed material. Of course, since the de-C slag does not contain fluorine, the de-C slag itself can be discharged out of the system from the steelmaking process and effectively used as a roadbed material.

In the secondary refining using the arc heating secondary refining apparatus in addition to the RH vacuum degassing apparatus, refining can be performed without adding fluorite by adjusting the slag composition of the ladle refining. Preferably, the CaO / Al ₂ O ₃ mass ratio of the slag composition is controlled to a low melting point range of 1.2 to 2.5. Thereby, even if it does not contain fluorine in the slag, it becomes possible to perform a predetermined ladle refining in the arc heating secondary refining apparatus as a low melting point slag. As a result, a secondary refining slag containing no fluorine can be obtained, and the secondary refining slag itself can be discharged out of the system and effectively used as a roadbed material.

  In secondary refining using an arc heating secondary refining apparatus, molten steel desulfurization refining can be performed by forming reduced slag that has been satisfactorily hatched by slag heating and stirring the slag and molten steel. Therefore, the S concentration in the molten steel can be lowered to a target level without performing hot metal preliminary desulfurization. Since hot metal preliminary desulfurization is not performed, hot metal preliminary desulfurization slag is not discharged out of the steelmaking process. Further, S contamination when the secondary refining slag is recycled to the converter can be dealt with by performing desulfurization refining in the secondary refining. Furthermore, in the secondary refining using the arc heating secondary refining apparatus as described above, refining can be performed without adding fluorite, in which case the secondary refining slag does not contain fluorine. Therefore, since the problem of S contamination and the problem of fluorine contamination, which were problems when recycling the secondary smelting slag to the converter, are solved, the secondary smelting slag can be recycled to the converter. As a result, the amount of secondary refining slag discharged out of the system from the steelmaking process can be reduced. Furthermore, since the secondary refining slag does not contain fluorine, the secondary refining slag discharged from the steelmaking process to the outside of the system can be effectively used as a roadbed material.

  When the hot metal discharged in the blast furnace is refined in the converter, and then the secondary refining of the present invention is performed, the hot metal charged in the converter is de-Si, de-P refined, subjected to intermediate waste, and then the same. It is preferable to perform de-C refining in one converter and add secondary refining slag to the converter during de-C refining. Since de-P refining and de-C refining are performed separately, the total amount of secondary materials used can be reduced, and the resulting converter slag can be reduced as a whole. Further, by adding the secondary refining slag to the converter during de-C refining, the secondary material added for de-C refining can be reduced, and the secondary refining slag discharged out of the system can be reduced. Since secondary refining slag does not contain fluorine, de-C slag is not contaminated with fluorine.

In the present invention, it is preferable that part or all of the converter slag generated in the de-C process is left in the converter and used for de-Si and de-P refining in the next refining heat. By using de-C slag for de-P refining, the secondary material added for de-P refining can be reduced, and de-C slag discharged out of the system can be reduced. Since de C slag does not contain fluorine, never contaminate de P slag with fluorine.

  In the present invention, since desulfurization is performed by secondary refining, it is not necessary to perform hot metal preliminary desulfurization. Moreover, since hot metal de-Si is also possible to be performed in conjunction with de-P refining in the converter, it is not necessary to perform hot metal preliminary de-Si removal before charging the converter. Therefore, in the present invention, preferably, the hot metal charged into the converter is not subjected to hot metal preliminary desiliconization or hot metal preliminary desulfurization before charging the converter. As a result, hot metal preliminary desulfurization Si slag and hot metal preliminary desulfurization slag are not generated. When hot metal preliminary desulfurization slag is discharged out of the system, there is a problem that it cannot be recycled as roadbed material because it is pulverized and has insufficient strength. In the refining heat to which the present invention is applied, the hot metal preliminary desiliconization slag and the hot metal preliminary desulfurization slag are not discharged out of the system, so that the above problem can be solved.

The present invention was applied to a steelmaking process of a variety using only hot metal extracted from a blast furnace as a main raw material and performing refining in a 280-ton pure oxygen top-bottom blowing converter and using only RH vacuum degassing as secondary refining. . In the example of the present invention, both LF and RH vacuum degassing are performed. In the present invention example, three types of processes shown in FIGS. 1A to 1C were applied as the refining process. 1 (a) and 1 (b), de-Si de-P refining is first performed in the converter, intermediate waste is performed, and then de-C refining is performed in the same converter. Further, in FIG. 1 (a), the de-C slag generated by de-C refining is left in the converter as it is and used as de-Si de-P refining slag for the next heat in the same converter. In the comparative example, two types of processes shown in FIGS. 1D and 1E were applied as the refining process. The production conditions and production results are shown in Table 1. In Table 1, invention examples a to c correspond to (a) to (c) of FIG. Comparative examples d and e correspond to (d) and (e) in FIG. FIG. 3 shows the basic units for the presence or absence of fluorine in the out-of-system discharge slag for each example.

  The present invention example a and comparative example d in which 18 kg / t of the de-C slag is recycled for de-Si de-P refining will be described. 35 kg / t out of 69 kg / t of slag generated by de-Si de-P refining was discharged as de-P slag by intermediate waste, and the rest remained in the converter. The basic unit of slag generation in de-C refining is 40 kg / t, of which 22 kg / t is discharged out of the system, and the remaining 18 kg / t is left in the converter and de-Si de-P refining for the next heat. Used as slag. Regarding the secondary smelting slag, the generated basic unit is 15 kg / t in the comparative example d in which the molten steel desulfurization is not performed, and the entire amount is discharged out of the system. / T, half of which is recycled for de-C refining.

In any of the inventive examples a to c, in the LF treatment of the secondary refining, by sufficiently heating and heating, the converter blowing-off temperature is lowered to 1630 ° C., and the fluorite in the converter de-C refining is reduced. I was able to stop using it. In both cases, LF treatment is performed in secondary refining, fluorite is not added to the ladle, CaO and Al dross are added to the ladle, and CaO / Al ₂ O ₃ mass in the secondary refining slag The ratio was adjusted to about 1.8. On the other hand, Comparative Examples d and e are only subjected to RH treatment in secondary refining, the converter blowing-off temperature is about 1690 ° C., and the use of fluorite cannot be stopped in converter de-C refining, In the secondary refining, fluorite is added to the ladle.

In any of the inventive examples a to c, hot metal preliminary desulfurization slag is not generated, and no hot metal preliminary desulfurization slag is generated. Since fluorite is not used in the secondary refining process, fluorine is not contained in the secondary refining slag, and Secondary refining slag that does not use fluorite and does not contain fluorine in the furnace refining process is recycled, so the converter slag does not contain fluorine. As a result, the slag discharged out of the system was a part of the converter slag and secondary refining slag, and neither contained fluorine and could be effectively used as a roadbed material. In addition, in all of the inventive examples a to c, about half of the secondary smelting slag is recycled to the converter, and the inventive example a is recycled from the de-C slag to the de-Si de-P process. The slag to be discharged was reduced.

  On the other hand, Comparative Examples d and e used fluorite in the converter de-C process, so that fluorine was contained in the de-C slag, and fluorine was contained in the secondary refining slag, Since it cannot be used as a roadbed material, slag inventory increased. Slag stock containing fluorine needs to be reclaimed for marine applications with different environmental standards or treated as industrial waste.

  The present invention example a in which 18 kg / t of the de-C slag is recycled for de-Si de-P refining is compared with the comparative example d. In Comparative Example d, hot metal pre-desulfurization is performed and 15 kg / t of pretreatment slag is generated, whereas in Example a of the present invention, no pretreatment slag is generated because no hot metal pretreatment is performed. On the other hand, as for the secondary refining slag, half of the secondary refining slag is recycled to de-C refining in the present invention example a. Therefore, the amount of secondary refining slag out of the present invention example a (10 kg / t) Is lower than Comparative Example d (15 kg / t). As a result, the total waste slag-based emission basic unit was reduced to 67 kg / t in Invention Example a against 87 kg / t in Comparative Example d. In Comparative Example d, all of the de-Si de-P slag, de-C slag, and secondary refining slag contain fluorine, and the total amount of out-of-system discharge slag (87 kg / t) including pre-desulfurization slag is the roadbed Cannot be used. On the other hand, in Example a of the present invention, the total amount (67 kg / t) of out-of-system discharged slag was slag not containing fluorine and did not contain pre-desulfurized slag, so that it could be used as a roadbed material.

  The comparison between the present invention example b and the comparative example e is also the same as described above, and the present invention can reduce the total amount of out-of-system discharge slag and can use the entire amount of out-of-system discharge slag as a roadbed material. became.

Claims (4)

The hot metal produced in the blast furnace is refined in a converter, and then secondary refining is performed using a secondary refining device having an arc heating means (hereinafter also referred to as “arc heating secondary refining device”). in step performs secondary refining by using a RH vacuum degassing apparatus, without the addition of auxiliary material wherein the converter containing fluorine, the two types of secondary refining through the generated secondary refining slag In the refining using the arc heating secondary refining equipment, desulfurization refining is performed while heating the molten metal without adding fluorine-containing secondary materials, and the fluorine discharged from the converter is not contained. A method for recycling steelmaking slag, wherein a portion of the furnace slag, or the converter slag and the secondary refining slag not containing fluorine is discharged out of the system.   The molten iron charged in the converter is de-Si, P-refined, intermediate waste is removed, C-refining is subsequently performed in the same converter, and the secondary refining slag is added to the converter during de-C refining. The method for recycling steelmaking slag according to claim 1.   The method for recycling steelmaking slag according to claim 2, wherein the converter slag generated in the de-C process is left in the converter and used for de-Si and de-P refining in the next refining heat.   4. The method for recycling steelmaking slag according to any one of claims 1 to 3, wherein the hot metal charged in the converter is not subjected to hot metal preliminary de-Si and hot metal pre-desulfurization before charging the converter. .

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