JP2008063610A - Method for producing molten steel - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an effective refining method which can greatly improve the heat tolerance of molten pig iron while maintaining capacity for dephosphorization and desulfurization processes, which has been achieved in a conventional division refining. <P>SOLUTION: The method for producing molten steel which is supplied to a continuous casting process from the molten pig iron comprises the steps of: charging the molten pig iron which has been tapped out from a blast furnace and is not treated into a converter; and subsequently refining the molten pig iron. The refining process comprises the steps of: desiliconizing and dephosphorizing the molten pig iron; then discharging slag; subsequently decarburizing the molten pig iron in the same converter; tapping the molten steel into a ladle; heating the molten steel with a vacuum arc ladle-refining device. The desiliconization and dephosphorization steps are carried out only in a series of steps after the molten pig iron has been charged into the converter. A desulfurization step is carried out only in the vacuum arc ladle-refining device. Preferably, a turndown carbon concentration (%) in the decarburization treatment is controlled to 0.07% or more, and a turndown temperature is controlled to 1,660°C or lower. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a refining method in which de-Si de-P pretreatment and de-C refining are performed in the same converter using a converter, and thereafter de-S treatment is performed in a ladle refining apparatus equipped with arc heating means. It is.

  Hot metal produced in a blast furnace contains a large amount of impurities such as Si, P, and S, and when manufacturing steel products, it is common to remove impurities and purify them through refining processes such as converters and RH. Established as a steelmaking process. Recently, the introduction of a hot metal pretreatment method for removing impurities in the hot metal stage has progressed, and it has become common to perform Si removal, P removal, and S treatment in torpedo cars and converters before de-C blowing in the converter. Yes.

  In particular, with regard to P, since de-P in the hot metal stage at a low temperature level is efficient, prior de-P is generally performed in the hot metal pretreatment process. In this case, the smelting vessel has a torpedo car method, a ladle method, or a method that uses a converter different from the furnace that performs decarburization, and any of them uses a flux of CaO, iron oxide or the like added upward or by an injection method. It is carried out with gas bubbling stirring or oxygen top blowing.

  For example, in the “method of dephosphorization / desulfurization of hot metal” disclosed in Patent Document 1, a CaO-based flux is blown into the hot metal together with a carrier gas while oxygen is blown up in a hot metal pretreatment furnace, and the slag basicity after treatment is 2. The hot metal dephosphorization is performed so that the iron oxide content is 0 or more and 15% or less, and then the desulfurization treatment is performed by blowing the desulfurizing material without stopping the top blowing oxygen and forcibly removing the slag. A hot metal dephosphorization / desulfurization method is disclosed.

  Furthermore, in the “steel making method” disclosed in Patent Document 2, two upper bottom blow converters are used, one is a dephosphorization furnace, the other is a decarburization furnace, and hot metal is injected into the dephosphorization furnace and obtained after hot metal dephosphorization treatment. A steel making method is disclosed in which dephosphorized hot metal is poured into a decarburization furnace to perform decarburization refining.

  In the “converter refining method” disclosed in Patent Document 3, desiliconization and dephosphorization refining are carried out in the same converter from a refining process in which the conventional desiliconization dephosphorization furnace and decarburization furnace are divided. After that, a steelmaking method is disclosed in which refining is temporarily interrupted to provide an intermediate waste removal step for discharging slag, and decarburization refining is continuously performed after the completion of waste removal.

  Patent Document 4 discloses a technique for removing S at the molten steel stage using a ladle electrode heating device (LF).

  As described above, many techniques for removing and purifying impurities of Si, P, and S contained in the hot metal have been developed and put into practical use. There is a problem that the P removal capacity is insufficient or the de-P removal ability is not sufficiently stable, and it is not optimal in an integrated process for producing molten steel from hot metal.

JP 58-16007 A JP-A-63-195209 Japanese Patent Laid-Open No. 7-18319 Japanese Patent Laid-Open No. 6-145762

  In order to increase the efficiency and productivity of the decarburization process in the converter, Si and P have better de-Si de-P efficiency when the temperature level is lower, so each process of de-Si, de-P and de-S Is generally carried out in the hot metal stage before decarburization treatment in the converter.

  Usually, in hot metal removal S treatment, as described in Patent Document 1, oxygen is not used and heating is not performed, so that the hot metal temperature decreases with the treatment time.

  If the P removal treatment is performed as a refining vessel using the torpedo car method, ladle method, or converter method, a relatively low reached P content level can be achieved by looking at the process capability of low P, but the torpedo car method, In the pan method, the processing time is long and the temperature drop until the molten iron is charged into the converter is large. Even in the converter method disclosed in Patent Document 2, the molten iron is discharged after the treatment, and the temperature is lowered due to recharging in another converter. Is inevitable.

  As described above, de-S in the hot metal pretreatment, de-P in the refining in which the de-P furnace and the de-C furnace are divided results in a decrease in the hot metal temperature, and further, Si, C in the hot metal is accompanied by the de-P process. The concentration decreases, causing a reduction in heat tolerance during de-C refining in the next process. The lack of heat tolerance in the de-C refining process is due to restrictions on the use of cold iron sources, the use of heating materials such as FeSi, blowing down C in molten steel, iron oxidation loss, etc., refining control variations, cost deterioration, slag amount Adverse effects such as an increase in Al and an increase in Al heating in the secondary refining RH process. Especially when it is necessary to limit the use of cold iron sources, the amount of hot metal used will increase, leading to production failures. Therefore, to ensure heat tolerance, it will be necessary to reduce the application ratio of hot metal pretreatment, leading to converter productivity. And P and S component process capability effects also occur.

  On the other hand, in the method of continuously performing de-Si, de-P, waste and de-C in the same converter disclosed in Patent Document 3, although the heat tolerance is improved, slag discharge after de-P Since it is difficult to carry out the process sufficiently stably, there is a problem from the viewpoint of the P removal capability.

  Further, in any process, when the amount of addition of special steel such as special steel is particularly large and the blowing temperature of the converter is high, the P process capability is hindered, and it is difficult to reduce P.

  In addition, although patent document 4 discloses the de-S treatment technique in the molten steel stage after de-C treatment in the converter, it is effective linkage with primary refining (hot metal preliminary treatment and de-C treatment). Does not disclose anything.

  In view of the above circumstances, the present invention maintains a de-P and de-S process capability achieved by the conventional refining process with hot metal, and greatly improves heat tolerance and allows a large amount of cold iron source to be used. An object of the present invention is to provide an optimum refining method in an integrated process for producing molten steel from hot metal.

In order to solve the above-mentioned problems, the present invention effectively removes Si, DeP, and DeS treatments from other treatment steps when refining molten steel supplied from a blast furnace into molten steel for continuous casting. It is a basic feature to be integrated or integrated, and the gist is as follows.
[1] A method for producing molten steel to be subjected to continuous casting from molten iron, in which molten iron discharged from a blast furnace is charged as it is into a converter, and for subsequent refining, after de-Si removal P treatment, After that, the steel was removed from the same converter, and then the molten steel was removed from the ladle and heated by an arc heating ladle refining device. A method for producing molten steel, which is carried out only in a series of entered steps, and the de-S treatment is carried out only by the arc heating ladle refining apparatus.
[2] A method for producing molten steel to be subjected to continuous casting from hot metal, wherein the following steps (1) to (5) are sequentially performed.
(1) The hot metal is charged into the converter, and the molten iron is subjected to de-Si treatment and de-P treatment (2) Only the slag generated in the step (1) is discharged, and the hot metal is converted into the converter (3) The hot metal left in the converter is subjected to de-C treatment, the upper limit of the blowing temperature is limited, and the P concentration in the blowing steel is changed to the hot metal at the end of the step (1). The process of suppressing the P concentration to below the level and putting the steel in the ladle (4) The process of adding Al to the molten steel during or after the steel output and performing the deoxidation process (5) Adding the Al to the deoxidation process Step 3 is a method of producing a molten steel to be subjected to continuous casting from a hot metal while performing a temperature rise and a de-S treatment with an arc heating ladle refining device, and the following (1) to (1) to The series of steps (6) are performed in order, and the method for producing molten steel according to the above [1].
(1) The hot metal is charged into the converter, and the molten iron is subjected to de-Si treatment and de-P treatment (2) Only the slag generated in the step (1) is discharged, and the hot metal is converted into the converter (3) The hot metal remaining in the converter is subjected to de-C treatment, the upper limit of the blowing temperature is limited, and the P concentration in the blowing steel is changed to P in the hot metal at the end of the step (1). The step of suppressing the concentration to below the level and removing the steel in the ladle (4) The step of adding Al to the molten steel during or after the outgoing steel and performing the deoxidation treatment (5) Adding the Al to the deoxidation treatment A step of heating the applied molten steel with an arc heating ladle refining device and performing a de-S treatment (6) A step of subjecting the molten steel subjected to the temperature rise and de-S treatment to vacuum degassing [4] De-C treatment [1] to [1] or Method for producing a molten steel according to any one of the 3].
[5] The molten steel according to any one of [2] to [4], wherein a step of discharging slag on the molten steel is interposed between the steps (4) and (5). Manufacturing method.
[6] The method for producing molten steel according to the above [2], wherein the vacuum degassing treatment does not perform heating by addition of Al.
[7] Instead of charging the molten iron discharged from the blast furnace into the converter as it is, after performing any one or more of de-Si, de-P, and de-S treatments, The method for producing molten steel according to any one of the above [1] to [6], wherein charging is performed.

  According to the present invention, it is possible to rationalize the hot metal pretreatment process with a large heat loss, which has been limited in application, and greatly improve the heat tolerance while maintaining the conventional P and S process capability. The amount of hot metal used can be reduced by expanding the use of cold iron sources such as scrap, and the quality of the molten steel can be reduced by suppressing the C blowdown in the converter and avoiding the increase of Al heat in the RH. It is a very useful invention that can be expected to greatly improve.

  Although the hot metal de-Si, de-P, and de-S treatments have an effect on improving the cleanliness of the steel material, on the other hand, there is a heat loss such as a decrease in the hot metal temperature, so there are restrictions on the amount of cold iron used, When the production amount is necessary, the application of hot metal pretreatment must be reduced, and problems such as low P, low S process capability reduction, and slag volume increase occur.

  As a measure to improve heat tolerance, a method of consolidating the hot metal de-Si and de-P processes into the same converter as the de-C process has also been proposed, but it is always possible to remove slag after de-P stably and sufficiently. It is difficult, and it is difficult to achieve both low P.

  The present inventors have developed to improve the heat tolerance of hot metal, which is a problem, while maintaining the hot metal removal Si and de-P treatment process capability using the same converter as the de-C treatment as well as the split refining process. I got it.

  The present inventors have noted that, based on the metallurgical principle, reduction of the molten metal temperature is effective for promoting the de-P reaction, and the de-S reaction is advantageously performed at the molten steel stage where the molten metal temperature is high. That is, in the de-C process in the primary refining process, it was examined that the blowing temperature was lowered and the de-S treatment was performed at a high temperature while the temperature was raised in the secondary refining process.

  In a method of continuously performing de-Si, de-P, waste, and de-C in the same converter, conventionally, when de-C treatment is completed at a high blowing temperature, it remains in the converter as the temperature rises. A phenomenon was observed in which P moved from the de-P slag thus obtained to the molten steel, and P in the molten steel increased during the de-C treatment. On the other hand, in the present invention, the temperature of the molten steel is raised by an arc heating ladle refining device after the steel is discharged, and the blowing temperature after the de-C treatment is lowered accordingly. By limiting the upper limit of the blow-off temperature after de-C blowing and reducing it by 20 to 40 ° C. than usual, even if the desulfurization after de-P is not enough, the ironmaking added before de-C blowing The efficiency of P reduction to slag by the material is improved, and the amount of molten P before waste can be maintained or reduced. As a result, the present invention can maintain the same de-P process capability as the split refining process using the torpedo car or another converter before de-C blowing. Moreover, the heat tolerance in molten steel manufacture improves by the part which reduced the blow-off temperature.

  Conventionally, C in molten steel was blown down during de-C blowing for the purpose of preventing P increase in the de-C process and securing a heat source. In the present invention, since the increase in P is eliminated in the de-C process by lowering the temperature after de-C treatment, there is no need to blow down C in the molten steel to prevent P increase. Moreover, heat tolerance improves and it becomes unnecessary to blow down C in the molten steel at the time of de-C blowing for securing a heat source. 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. Therefore, it is effective to suppress C blowing down in the converter as much as possible. is there.

  Limiting the upper limit of the molten steel temperature after de-C blowing can be achieved by increasing the amount of cold iron source charged when the molten iron is charged into the converter.

  Next, in the secondary refining process after the converter steel, it is necessary to raise the temperature of the molten steel, but the temperature raising method using the oxidation reaction heat of Al and gaseous oxygen increases the production of alumina inclusions. Since this leads to a reduction in the cleanliness of the molten steel, it is necessary to combine the temperature rise using an arc heating device such as LF. In LF treatment, electric resistance heating of molten slag is carried out, so de-S treatment can be performed very easily in a short time by controlling the slag composition to a high basicity and low oxidation degree. De-S process capability is secured.

  In the present invention, the de-S treatment is performed by the arc heating ladle refining apparatus, and the de-S treatment is not performed in the hot metal before charging the converter. Conventionally, the hot metal temperature was lowered by the hot metal removal S treatment, but since the hot metal removal S treatment was not performed, the hot metal temperature at the time of charging the converter could be increased. The heat tolerance in can be improved. That is, it was possible to improve the heat tolerance in the production of molten steel from both the rise of the molten iron temperature in the converter and the lowering of the blowing temperature after the de-C treatment.

  By the way, prior to the de-S treatment with LF, the dissolved oxygen in the molten steel can be subjected to an effective de-S treatment by adding Al and performing a deoxidation treatment. Alumina inclusions inevitably generated by deoxidation are floated and separated during the LF treatment together with other inclusions to be cleaned.

In order to further improve the refining efficiency in the LF, it is effective to perform the removal before the LF treatment.
Furthermore, when the RH treatment is performed in the next step by controlling the temperature after the LF treatment to be higher, the treatment can be performed without performing the Al heating in RH, and the deterioration of the inclusion quality due to the formation of alumina can be avoided.

  The LF also has a stirring means in addition to the heating means, but ASEA-SKF and VAD having a heating and stirring means in addition to the LF can also be adopted.

  FIG. 1 (a) shows a conceptual diagram of a series of processing flows of the present invention from when the molten iron discharged from the blast furnace is charged into the converter as it is to LF treatment.

  FIG. 1 (b) shows a conceptual diagram of a series of processing flows of the present invention from the charging of the molten iron discharged from the blast furnace to the converter as it is, the LF treatment, and the RH treatment.

  By the way, the hot metal discharged from a normal blast furnace usually has Si ≦ 1.0%, P ≦ 0.150%, and S ≦ 0.030%. It is possible to charge the furnace. When it is necessary to manufacture a higher-purity molten steel, it is possible to further reduce the P and the S by performing the prior de-P de-S treatment at the hot metal stage. In addition, the hot metal component is greatly deteriorated due to variations in blast furnace operation, deterioration of raw material quality, etc., and when Si ≧ 1.50%, P ≧ 0.200%, S ≧ 0.050%, In the next refining, the treatment time is extended and the productivity is assumed to be lowered. In this case as well, it is preferable to perform the pretreatment at the hot metal stage.

  In addition, as shown in FIG. 2, the lower the blowing temperature, the lower the temperature, which is advantageous for lowering the P. However, taking into account the heat removal load in the secondary refining, which is the next process, or ensuring the de-P process capability, It is preferable.

  Next, as the blow-off C of the converter decreases, the oxygen concentration in the molten steel increases, and the T. As shown in FIG. 3, the oxygen concentration rapidly increases in the low C region and generates oxide inclusions and bubble defects as shown in FIG. It is desirable to avoid less than 0.07%. The present invention realizes an improvement in heat tolerance and a reduction in P during de-C treatment due to a decrease in the blow-off temperature, enabling blow-off C 0.07% or more.

  Application of this process makes it possible to significantly increase the hot metal temperature, which has been reduced by the hot metal pretreatment of the conventional split refining process, and to apply arc heating ladle refining (for example, LF) in secondary refining. By doing so, the blow-off temperature of the converter can be greatly reduced, so that the heat tolerance can be greatly improved, and the process capability of de-P, de-S, and further, the quality of alumina inclusions is higher than the conventional level. De-Si is necessary and sufficient for the hot metal treatment before the de-C treatment, and no special treatment after the de-C treatment is necessary.

  Hereinafter, the present invention will be described in more detail with reference to examples.

  Inventive Examples 1 and 2 shown in Tables 1 and 2 are inventive examples in which molten steel was manufactured by a series of processing flows from charging the molten iron discharged from the blast furnace as it was into the converter to RH treatment. The hot metal converter charging temperature is over 1400 ° C, a large amount of cold iron source can be used, and the de-C blowing temperature is limited to 1660 ° C or less, so the blowing P is stabilized at a low level. Yes. Further, S is also sufficiently removed by the LF process.

  Inventive Example 3 shown in Table 3 was subjected to de-Si, de-P, and de-S treatments in a torpedo car (hereinafter referred to as TPC) prior to the charging of the converter for further cleaning. The following is an example of the invention in which the same processing flow as that of Invention Examples 1 and 2 was performed. It was confirmed that the amounts of molten steel P and S after the LF treatment were further reduced from those of Invention Examples 1 and 2, and it was possible to produce a cleaner steel.

  Further, in any of the invention examples, since Al heating can be avoided in the RH process, additional effects such as reduction of alumina inclusions in the molten steel were also obtained.

  In Comparative Example 1 shown in Table 4, after de-S treatment by TPC shown in FIG. 4, two top blowing converters are used, one as a de-Si de-P furnace and the other as a de-C furnace. Thereafter, this is a conventional example in which LF processing is not performed. Although the process capability of de-P and de-S is excellent, the hot metal temperature is low due to the de-S treatment in TPC and the discharge of hot metal after de-Si de-P treatment in the converter, and charging into a separate converter. The source cannot be used in large quantities and is limited.

  Comparative Example 2 shown in Table 5 is a conventional example shown in FIG. 5 in which de-S, de-Si, and de-P treatments are performed by TPC, only de-C treatment is performed in the converter, and then LF treatment is not performed. . The hot metal temperature is lower than in Comparative Example 1, and the amount of cold iron source used is further limited.

  In the hot metal preliminary treatment of Comparative Examples 1 and 2, the amount of cold iron that can be melted in the converter is limited because the furnace charging temperature is lowered and the blowing temperature is high. When a large amount of alloy iron such as special steel is melted, if all the sensible heat required for melting is compensated only by the converter, the blowing temperature will be significantly increased, the use of cold iron source will be reduced, the converter refractory life will be reduced, Since a great adverse effect such as a decrease in yield occurs, the load is usually shared by secondary refining, and heating using reaction heat of Al and oxygen in RH or the like is widely performed. In the comparative example, temperature compensation is required with RH, and Al heating is performed. Therefore, there is a concern that the production of alumina may affect the cleanliness of molten steel.

  Comparative Example 3 shown in Table 6 is a conventional example in which de-S treatment is performed by TPC, de-Si de-P removal is performed in the same converter, followed by de-C treatment, and no LF treatment thereafter. The amount of cold iron source used is constrained by the removal of S in TPC and the high converter blowing temperature. In addition, because P and C are removed in the same converter, the waste after P removal was not sufficient, but P carryover to the C removal stage, such as slag adhesion in the furnace, occurred, maintaining P removal. For this reason, C blowing-down occurs in the de-C period, and accordingly, dissolved oxygen in the molten steel is greatly increased, the amount of alumina produced after deoxidation is increased, and there is a concern about the influence of inclusion quality.

It is a conceptual diagram explaining a series of processing flows of the present invention, (a) is up to LF processing, (b) is up to RH processing. It is a figure which shows the relationship between the blowing temperature and blowing B in the de-C process in a converter. It is a figure which shows the relationship between blow-off C% and oxygen concentration in molten steel in the de-C process in a converter. It is a conceptual diagram explaining a series of conventional processing flows for removing S by TPC, removing Si and removing P by a converter, and then transferring the molten iron to another converter and removing C. It is a conceptual diagram explaining a series of conventional processing flows of performing Si removal, P removal, and S removal treatment with TPC and de-C treatment with a converter.

Claims (7)

  A method for producing molten steel for continuous casting from hot metal, in which the molten iron discharged from the blast furnace is charged into the converter as it is, and after the refining process, after de-Si removal P treatment, After that, in the same converter, the de-C treatment is performed continuously, the molten steel is taken out into a ladle, the temperature is raised with an arc heating ladle refining device, and the de-Si removal P is a series of charged in the converter. The method for producing molten steel is characterized in that it is carried out only in the step, and the de-S treatment is carried out only by the arc heating ladle refining apparatus. The method for producing molten steel to be subjected to continuous casting from hot metal, wherein the following steps (1) to (5) are sequentially performed.
(1) The hot metal is charged into the converter, and the molten iron is subjected to de-Si treatment and de-P treatment (2) Only the slag generated in the step (1) is discharged, and the hot metal is converted into the converter (3) The hot metal left in the converter is subjected to de-C treatment, the upper limit of the blowing temperature is limited, and the P concentration in the blowing steel is changed to the hot metal at the end of the step (1). The process of suppressing the P concentration to below the level of steel in the ladle (4) The process of adding Al to the molten steel during or after the steel output and performing the deoxidation process (5) Adding the Al to the deoxidation process To the molten steel that has been subjected to heat treatment using an arc heating ladle refining device, and to perform a de-S treatment The method for producing molten steel to be subjected to continuous casting from hot metal, wherein the following steps (1) to (6) are sequentially performed.
(1) The hot metal is charged into the converter, and the molten iron is subjected to de-Si treatment and de-P treatment (2) Only the slag generated in the step (1) is discharged, and the hot metal is converted into the converter (3) The hot metal remaining in the converter is subjected to de-C treatment, the upper limit of the blowing temperature is limited, and the P concentration in the blowing steel is changed to P in the hot metal at the end of the step (1). The step of suppressing the concentration to below the level and removing the steel in the ladle (4) The step of adding Al to the molten steel during or after the outgoing steel and performing the deoxidation treatment (5) Adding the Al to the deoxidation treatment A step of subjecting the molten steel to a temperature rise using an arc heating ladle refining device and a step of performing a de-S treatment (6) a step of subjecting the molten steel subjected to the temperature rise and the de-S treatment to a vacuum degassing treatment   The method for producing molten steel according to any one of claims 1 to 3, wherein the blow-off% C for de-C treatment is 0.07% or more and the blow-off temperature is 1660 ° C or less.   The method for producing molten steel according to any one of claims 2 to 4, wherein a step of discharging slag on the molten steel is interposed between the step (4) and the step (5).   The method for producing molten steel according to claim 3, wherein in the vacuum degassing treatment, no heating is performed by addition of Al.   Instead of charging the molten iron discharged from the blast furnace as it is into the converter, it is charged into the converter after performing any one or more of de-Si, de-P, and de-S treatments. The manufacturing method of the molten steel in any one of Claim 1 thru | or 6 characterized by the above-mentioned.

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