JP2015092018A - Method for refining hot pig iron in converter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently remove phosphorous in hot pig iron when a CaO based flux is blown to the ignition point of the hot pig iron bath face in a converter via a top-blow lance, and the hot pig iron is subjected to dephosphorization refining or decarbonization refining.SOLUTION: Regarding the method for refining hot pig iron, when an oxygen gas is blown to hot pig iron in a converter from a top-blown lance, also, a CaO based flux is blown to the impact face in the bath face of the hot pig iron of the oxygen gas from the top-blown lance, and the hot pig iron in the converter is subjected to dephosphorization refining or decarburization refining, the blowing of the CaO based flux from the top-blown lance is performed over the whole period or a part of period from the start of the blowing of an oxygen gas to the point of time at which the 40 vol% oxygen gas of the estimated acid feed amount is fed, and is further performed over the whole period or a part of period from the point of time at which 70 vol% oxygen gas of the estimated acid feed amount is fed to the completion of refining, and in a period at which an oxygen gas below 70 vol% of the estimated acid feed amount is fed after the point of time at which an oxygen gas of 40 vol% of the estimated acid feed amount is fed, the blowing of the CaO based flux from the top-blown lance is stopped.

Description

  The present invention relates to a hot metal refining method in a converter in which oxygen gas and a CaO-based solvent are sprayed onto the same hot metal in a furnace through an upper blowing lance.

  In order to improve the functionality and quality of steel materials, it is necessary to reduce the impurities in the steel to the utmost limit, and a technology to efficiently remove the impurity elements and oxide-based nonmetallic inclusions in the molten steel is required. It has been. Phosphorus (P), which is one of the impurity elements in steel, degrades the ductility and strength of steel materials, so that it is required to reduce the phosphorus content in steel.

In the decarburization and dephosphorization of hot metal to reduce the phosphorus content in steel, phosphorus in the hot metal is oxidized by an oxygen source such as oxygen gas, and the resulting phosphorus oxide (P ₂ O ₅ ) is converted into CaO. Phosphorus in the hot metal is removed by absorbing it in the slag generated by the hatching of the system solvent. Therefore, in order to reduce the phosphorus content in the steel, it is necessary to increase the usage amount of the CaO-based solvent or extend the treatment time, increase the refining cost, and increase the amount of slag generated. There has been a problem that the slag processing cost increases due to the increase.

By the way, in decarburization refining and dephosphorization of hot metal in a converter, a dephosphorization reaction shown in the following formula (1) proceeds between hot metal and slag. That is, phosphorus (P) in the hot metal is oxidized by FeO, and P ₂ O ₅ produced by this oxidation reaction reacts with CaO and is absorbed by the slag. However, in the formula (1), [P] and [Fe] indicate components in the hot metal, and (FeO), (CaO) and (3CaO · P ₂ O ₅ ) indicate components in the slag. Here, the dephosphorization of hot metal is a refining process in which phosphorus in hot metal is removed in advance before decarburization and refining of hot metal in a converter, and is also called preliminary dephosphorization.

2 [P] +5 (FeO) +3 (CaO) = (3CaO · P ₂ O ₅ ) +5 [Fe] (1)
As apparent from the equation (1), it is important to effectively use the action of FeO in the slag in order to promote the dephosphorization reaction rate.

  As a dephosphorization method for hot metal using the formation of FeO, a CaO-based solvent is passed through an upper blowing lance at a location where the oxygen gas injected from the upper blowing lance collides with the hot metal (referred to as “fire point”). (For example, refer to Patent Document 1). In this technology, the CaO-based solvent is directly supplied to the hot spot, the hot spot is high temperature, the hot spot is the place where FeO is generated, and the hot spot contains high concentration of FeO. Therefore, the hatching of the CaO-based solvent is promoted and the reaction of the formula (1) is promoted.

  Further, in Patent Document 2, oxygen gas is supplied to the hot metal from the upper blowing lance, and at the same time, a part of the added CaO-based solvent is blown from the upper blowing lance together with the carrier gas to remove the hot metal in the converter. When refining charcoal, the amount of FeO generated in the furnace is calculated based on the unknown oxygen amount obtained by sequentially calculating the oxygen balance from the oxygen gas flow rate from the top blowing lance, the composition of the exhaust gas during refining, the flow rate of the exhaust gas, etc. Estimate and control the amount of FeO produced in the furnace within the range of 3-30 kg / molten iron-t from the start of refining to the point of supplying 40% by volume of oxygen from the total amount of oxygen. A refining method has been proposed in which the supply of the CaO-based solvent from the top blowing lance is stopped after the time point when the oxygen amount of 40% by volume of the total oxygen amount has been supplied.

JP 58-61211 A JP 2012-67378 A

  In decarburization refining and dephosphorization refining by blowing oxygen gas to the hot metal in the converter through the top blowing lance, the FeO concentration in the slag during refining increases with the start of refining, but then decreases once. And rises rapidly at the end of refining. As is clear from the equation (1), in order to efficiently perform the dephosphorization reaction of the hot metal, it is important to add a CaO-based solvent according to the FeO concentration in the slag. That is, since FeO is generated at the hot spot, adding a CaO-based solvent to the hot spot at the time when the FeO concentration in the slag increases leads to the promotion of the dephosphorization reaction.

  If the above prior art is verified from this point of view, Patent Document 1 shows that by adding a CaO-based solvent to the fire point, the hatching of the CaO-based solvent is promoted and the reaction with FeO is promoted. It is only described that the dephosphorization reaction proceeds even for high carbon steels which are disadvantageous to the phosphorus reaction, and it is described that the CaO-based solvent is added in relation to the time when the FeO concentration in the slag increases. Absent. In the Examples, it is described that a CaO-based medium solvent is added at the initial stage of refining for the purpose of suppressing slag slopping.

  Patent Document 2 proposes a refining method for stopping the supply of the CaO-based medium solvent from the top blowing lance after the time when the oxygen amount of 40% by volume of the total oxygen amount is supplied from the start of refining, No consideration is given to adding a CaO-based solvent in relation to the time when the FeO concentration in the slag is high. Moreover, even if patent document 2 continues the supply of the CaO type | system | group solvent from an upper blowing lance until after exceeding the time of supplying the oxygen amount of 40 volume% of the total oxygen amount, it is superior to a dephosphorization reaction. It states that there is no difference.

  That is, in Patent Document 1 and Patent Document 2, it is difficult to say that phosphorus in hot metal is efficiently removed when decarburization or dephosphorization is performed on the hot metal in the converter. The decarburization and refining of hot metal in the present invention is a refining that requires a dephosphorization reaction as well as a decarburization reaction, and does not include the case of decarburizing and refining the hot metal previously dephosphorized and refined to a steel product level. This is because a dephosphorization reaction is not required in the case of decarburizing and refining hot metal previously dephosphorized and refined to a steel product level.

  The present invention has been made in view of such circumstances. The object of the present invention is to dephosphorize the hot metal by spraying a CaO-based solvent to the hot spot of the hot metal bath surface in the converter through an upper blowing lance. An object of the present invention is to provide a method for refining hot metal in a converter that can efficiently remove phosphorus in hot metal in refining or decarburizing refining.

  In order to solve the above-mentioned problems, the present inventors have conducted intensive studies. As a result, the FeO concentration in the furnace slag begins to increase when oxygen gas starts to be blown from the top blowing lance (referred to as “refining start”), shows a maximum value in the middle of refining, and then decreases. A rapid increase was observed at the end.

In the hot metal dephosphorization reaction, as described above, the phosphorus in the hot metal is oxidized by an oxygen source such as oxygen gas to become phosphor oxide (P ₂ O ₅ ), and this phosphor oxide is generated by the incubation of the CaO-based solvent. It progresses by being absorbed by the slag. Therefore, it is necessary to supply the CaO-based solvent from the start of refining, but the dephosphorization reaction can be achieved by adding the CaO-based solvent to the hot point during the period when the FeO concentration in the slag at the end of refining increases. Was found to be promoted.

The present invention has been made based on the above findings, and the gist thereof is as follows.
[1] Oxygen gas is blown from the upper blowing lance to the hot metal in the converter, and CaO-based solvent is blown from the upper blowing lance to the collision surface of the oxygen gas on the hot metal bath surface to form hot metal in the converter. In the method of refining hot metal in a converter, dephosphorizing or decarburizing refining, spraying of the CaO-based solvent from the top blowing lance is performed at a predetermined amount of acid sent from the start of oxygen gas blowing from the top blowing lance. The entire period or a part of the period up to the point of supplying 40% by volume of oxygen gas, and the entire period or part of the period from the point of supplying 70% by volume of oxygen gas to the end of refining. The period of supplying oxygen gas of less than 70% by volume of the planned amount of oxygen after the point of time when the oxygen gas of 40% by volume of the planned amount of oxygen was supplied is a period of time during which CaO from the top blowing lance is supplied. Spraying solvent Wherein the stopping, refining method of molten iron in the converter.
[2] The addition amount of the CaO-based solvent supplied from the top blowing lance after the time when 70% by volume of oxygen gas is supplied is 10 to 40% by mass of the planned addition amount of the CaO-based solvent. The method for refining hot metal in a converter as described in [1] above, wherein

  According to the present invention, in the dephosphorization or decarburization of hot metal in a converter, not only the initial stage of refining but also the final stage of refining when the FeO concentration in the slag increases, that is, the refining in which FeO is abundant at the fire point. Since the CaO-based solvent is added to the fire point at the end, the dephosphorization reaction is promoted, and the phosphorus concentration in the hot metal or the molten steel at the end of refining can be lowered. In addition, the amount of CaO-based solvent used can be reduced by improving the dephosphorization efficiency, thereby reducing the amount of slag generated and reducing the refining cost.

It is a schematic sectional drawing of the converter equipment used when implementing this invention. It is a figure which compares and shows the phosphorus distribution ratio in decarburization refining with the example of this invention, and a comparative example.

  Hereinafter, the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 is a schematic cross-sectional view of a converter facility used when performing hot metal dephosphorization or hot metal decarburization according to the present invention.

  As shown in FIG. 1, a converter facility 1 has an outer shell composed of an iron shell 4, and a converter 2 in which a refractory 5 is constructed inside the iron shell 4, and is inserted into the converter 2. And an upper blowing lance 3 that is movable in the vertical direction. An upper portion of the converter 2 is provided with a tap 6 for discharging hot metal after refining (in the case of dephosphorization refining) or molten steel after refining (in the case of decarburization refining). A bottom blowing tuyere 7 for blowing the stirring gas 18 into the molten iron 15 in the furnace is provided at the bottom. The bottom blowing tuyere 7 is connected to a gas introduction pipe 8. An oxygen gas pipe 9 is connected to the top blowing lance 3, and oxygen gas for refining is supplied from the tip of the top blowing lance 3 to the inside of the converter 2 at an arbitrary flow rate through the oxygen gas pipe 9. It is like that.

  The top blowing lance 3 is connected to a dispenser 11 containing a CaO-based medium solvent 17 via a transfer pipe 19. On the other hand, the dispenser 11 has an oxygen gas pipe 9 A branched from the oxygen gas pipe 9. In addition, a nitrogen gas pipe 10 is connected. That is, the oxygen gas or nitrogen gas supplied to the dispenser 11 functions as a transport gas for the CaO-based solvent 17 contained in the dispenser 11, and from the tip of the upper blowing lance 3 via the transfer pipe 19. The CaO-based medium solvent 17 can be sprayed and supplied (also referred to as “projection”) toward the bath surface of the hot metal 15 accommodated in the converter 2. The oxygen gas pipe 9 is provided with a flow rate control valve 12, the oxygen gas pipe 9A is provided with a flow rate control valve 13, and the nitrogen gas pipe 10 is provided with a flow rate control valve 14 to raise the oxygen gas. While blowing from the blowing lance 3 at an arbitrary flow rate, oxygen gas or nitrogen gas can be blown as a transfer gas at an arbitrary flow rate via the dispenser 11.

  The oxygen gas pipe 9A and the nitrogen gas pipe 10 are connected to a bypass pipe 20 connected to the transfer pipe 19, and a shutoff valve 21 and a bypass pipe installed in the nitrogen gas pipe 10 after joining the oxygen gas pipe 9A. The shut-off valve 22 installed at 20 can also supply only oxygen gas or nitrogen gas to the top blowing lance 3 without going through the dispenser 11. In this case, instead of nitrogen gas, various gases such as Ar gas and carbon dioxide can be used as the carrier gas. Whether oxygen gas is used as the carrier gas or a gas other than oxygen gas such as nitrogen gas may be appropriately determined from the state of refining.

  In the top blowing lance 3, the refining oxygen gas supply channel and the CaO-based solvent 17 supply channel are independent, but the refining oxygen gas and the CaO system ejected from the tip of the top blowing lance 3. The medium solvent 17 is joined and the CaO-based medium solvent 17 is projected onto the collision surface (fire point) of the refining oxygen gas to the hot metal 15.

  Above the converter 2 is a cold iron source such as iron scrap or magnetic separation scrap, and a hopper containing auxiliary raw materials such as quick lime, dolomite, iron ore and coke, and these cold iron sources contained in the hopper. In addition, a cutting device, a weighing device, and a chute for cutting out and adding the auxiliary material to the converter 2 and adding them to the converter 2 are installed, but are omitted in FIG.

  Using the converter equipment 1 having such a configuration, the dephosphorization refining as a pretreatment for the hot metal, or the steel product that has been subjected to the hot metal or dephosphorization not subjected to the dephosphorization refining Decarburization and refining of hot metal that has not been dephosphorized to the phosphorus level of. The hot metal decarburization refining and dephosphorization refining in the converter 2 have substantially the same refining method. Therefore, hereinafter, a case where the present invention is applied to hot metal decarburization refining will be described as an example.

First, the hot metal 15 is charged into the converter 2. After the hot metal 15 is charged, a cold iron source such as iron scrap is charged as necessary. Thereafter, refining oxygen gas is blown from the top blowing lance 3 onto the bath surface of the hot metal 15 while Ar gas is blown as the stirring gas 18 from the bottom blowing tuyere 7. Simultaneously with or after the spraying of the refining oxygen gas to the hot metal 15, the CaO-based solvent 17 is sprayed from the upper spray lance 3 onto the hot metal bath surface. As the CaO-based medium solvent 17, quick lime (CaO), limestone (CaCO ₃ ), slaked lime (Ca (OH) ₂ ), or the like can be used. In addition, a mixture of fluorite (CaF ₂ ) and alumina (Al ₂ O ₃ ) may be used as the CaO-based solvent 17 under the condition that the content of CaO is 50% by mass or more.

The supplied oxygen gas reacts with the carbon in the hot metal to proceed the decarburization reaction (C + O → CO). Further, when the hot metal 15 contains silicon, a desiliconization reaction (Si + 2O → SiO ₂ ) also occurs simultaneously. In addition, an iron oxidation reaction (Fe + O → FeO) occurs at the fire point.

The CaO-based solvent 17 supplied from the top blowing lance 3 to the hot spot is heated and reacts with FeO to hatch because the hot spot is at a high temperature and a place where FeO is generated. In addition, when the desiliconization reaction occurs, it reacts with the SiO ₂ generated by the desiliconization reaction and hatches. The hatched CaO-based solvent 17 forms slag 16 in the furnace.

When a decarburization reaction or a desiliconization reaction occurs, and the carbon concentration and silicon concentration of the hot metal 15 begin to decrease, the phosphorus in the hot metal is oxidized by the supplied oxygen gas and the generated FeO to form a phosphorus oxide (P ₂ O ₅ ), And the phosphorus oxide (P ₂ O ₅ ) is absorbed by the slag 16 mainly composed of the CaO-based medium solvent 17 which has been hatched, and the dephosphorization reaction represented by the following formula (1) proceeds.
2 [P] +5 (FeO) +3 (CaO) = (3CaO · P ₂ O ₅ ) +5 [Fe] (1)
However, in the formula (1), [P] and [Fe] indicate components in the hot metal, and (FeO), (CaO) and (3CaO · P ₂ O ₅ ) indicate components in the slag.

The higher the basicity of the slag 16 in the furnace ((mass% CaO) / (mass% SiO ₂ )), the more the dephosphorization reaction of the formula (1) proceeds, so the basicity of the slag 16 becomes 3.0 or more. Control. In the present invention, it is essential that the CaO-based solvent 17 is sprayed from the top blowing lance 3 to the fire point. In some cases, a part of the planned addition amount of the CaO-based medium solvent 17 is added over the chute from the hopper arranged above the converter 2 at the initial stage of refining. Also good. At that time, auxiliary materials such as dolomite and iron ore may be added together. Since increasing the basicity of the slag 16 excessively increases the basic unit of the CaO-based solvent 17 and increases the cost, the upper limit of the basicity of the slag 16 is preferably 5.0 or less.

  In the middle stage of decarburization refining, the decarburization reaction is active, and in addition to the stirring of the hot metal 15 and the slag 16 by the stirring gas 18 blown from the bottom blowing tuyere 7, the hot metal 15 by the CO gas generated by the decarburization reaction 15 And the slag 16 are vigorously stirred, and the generated FeO is consumed in the decarburization reaction, and the dephosphorization reaction according to the formula (1) is stagnant. Therefore, at this time, specifically, after the point in time when the oxygen gas of 40% by volume of the planned acid supply amount has been supplied, the supply of the CaO-based solvent 17 from the top blowing lance 3 is stopped.

  In this case, the supply of the CaO-based medium solvent 17 from the top blowing lance 3 may be stopped before the supply of 40% by volume of oxygen gas of the planned amount of acid is completed. Further, it is not necessary to continuously supply the CaO-based solvent 17, and it is intermittently divided into several times in the period from the start of the oxygen gas spraying to the point of supplying 40 vol% oxygen gas of the planned amount of acid. Then, the CaO-based medium solvent 17 may be supplied.

  Here, the planned amount of acid sent is the amount of oxygen gas calculated based on the carbon concentration of the molten iron 15 before decarburization refining, the silicon concentration, and the carbon concentration of the molten steel after decarburization refining. In addition, when iron oxide such as iron ore is used as the oxygen source, the total oxygen source including iron oxide is supplied. A solid oxygen source such as iron oxide is converted into a gas and the supply amount of the total oxygen source is obtained.

  On the other hand, at the end of decarburization refining, the carbon concentration of the hot metal 15 decreases and the decarburization reaction decreases. When the decarburization reaction is lowered, stirring of the hot metal 15 and the slag 16 by the CO gas generated by the decarburization reaction becomes weak, and the generated FeO is not consumed in the decarburization reaction and gradually accumulates in the furnace. That is, it shifts to conditions suitable for the dephosphorization reaction. At this time, specifically, after supplying 70% by volume of oxygen gas of the planned amount of acid, the supply of the CaO-based solvent 17 from the top blowing lance 3 is resumed. In other words, the period of supplying oxygen gas of less than 70% by volume of the planned amount of oxygen after the time when the oxygen gas of 40% by volume of the planned amount of oxygen has been supplied is the CaO-based medium solvent from the top blowing lance 3 Stop spraying 17.

  In this case, the supply of the CaO-based solvent 17 may be resumed immediately after supplying 70% by volume of oxygen gas of the planned amount of acid, or 70% by volume of oxygen gas of the planned amount of acid is supplied. After a certain amount of time has elapsed, for example, the supply of the CaO-based solvent 17 may be resumed from the time when 80% by volume of oxygen gas is supplied. Furthermore, the supply of the CaO-based medium solvent 17 from the top blowing lance 3 may be continued until the end of the decarburization refining, and the supply of the CaO-based medium solvent 17 from the top blowing lance 3 may be continued before the end of the decarburization refining. You may stop.

  The addition amount of the CaO-based medium solvent 17 supplied from the top blowing lance 3 after the time point of supplying 70% by volume of oxygen gas of the planned amount of acid delivery is 10-40% by mass of the planned addition amount of the CaO-based medium solvent 17 It is preferable to be within the range. If the amount of CaO-based solvent 17 supplied after 70% by volume of oxygen gas to be supplied is less than 10% by mass of the planned addition amount, the addition amount is too small to promote the dephosphorization reaction. It is not possible to obtain a sufficient effect. On the other hand, if the addition amount exceeds 40% by mass of the planned addition amount, the addition amount at the initial stage of refining is reduced, and dephosphorization at the initial stage of refining may be stagnant.

  When the carbon concentration of the molten steel produced from the molten iron 15 by the decarburization reaction reaches a predetermined value, the supply of oxygen gas from the top blowing lance 3 is stopped and the decarburization refining is finished.

  The dephosphorization refining of the hot metal 15 may be performed in accordance with the above decarburization refining.

  As described above, according to the present invention, the CaO-based medium solvent 17 is sprayed from the top blowing lance 3 from the start of the oxygen gas spraying to the point of supplying 40% by volume of oxygen gas of the planned amount of acid. It is performed during the entire period or a part of the period, and is performed during the entire period or a part of the period from the supply of 70% by volume of oxygen gas of the planned amount of acid to the end of refining. Since the dephosphorization reaction is promoted in the latter half, the dephosphorization reaction is promoted, and in the case of dephosphorization refining, the phosphorus concentration in the hot metal at the end of refining, and in the case of decarburization refining, the phosphorus concentration of the molten steel at the end of refining The concentration can be lowered.

  Using a converter with a capacity of 370 tons, the present invention was applied to carry out decarburization refining of hot metal. As the CaO-based solvent, quick lime is used, and the addition of this quick lime is performed during the whole or part of the period from the start of the oxygen gas spraying until the point of supplying 40% by volume of oxygen gas to the planned amount of acid, and the planned delivery. The process was divided into all or part of the period from the point of supplying 70% by volume of oxygen gas to the end of refining (Example of the present invention). In the example of the present invention, the addition amount of the CaO-based medium solvent after the time when 70% by volume of oxygen gas is supplied is within the range of 10 to 40% by mass of the planned addition amount of the CaO-based medium solvent. Changed.

  In addition, the operating conditions such as the acid feed rate, lance height, quick lime supply amount, iron ore addition amount, bottom blowing stirring gas flow rate and the like are the same as those in the present invention example, and the quick lime addition is scheduled from the start of oxygen gas blowing. Decarburization refining (comparative example) was carried out only for a part or all of the period up to the point of supplying 40% by volume of oxygen gas.

  After refining, samples for analysis are taken from molten steel and slag in the furnace and analyzed for phosphorus concentration in molten steel and slag. Phosphorus distribution ratio (phosphorus concentration in slag (mass%) / phosphorus in molten steel) The concentration (mass%) was investigated. The higher the phosphorus distribution ratio, the more efficiently the dephosphorization reaction was performed.

  FIG. 2 shows the results of investigation of the phosphorus distribution ratio. As shown in FIG. 2, the phosphorus distribution ratio in the present invention example was higher than that in the comparative example, and it was confirmed that the hot metal could be efficiently dephosphorized.

DESCRIPTION OF SYMBOLS 1 Converter equipment 2 Converter 3 Top blowing lance 4 Iron skin 5 Refractory 6 Outlet 7 Bottom blowing tuyere 8 Gas introduction pipe 9 Oxygen gas piping 10 Nitrogen gas piping 11 Dispenser 12 Flow control valve 13 Flow control valve 14 Flow control Valve 15 Hot metal 16 Slag 17 CaO-based solvent 18 Stirring gas 19 Transfer pipe 20 Bypass pipe 21 Shut-off valve 22 Shut-off valve

Claims (2)

Oxygen gas is blown from the upper blowing lance to the hot metal in the converter, and CaO-based solvent is blown from the upper blowing lance to the collision surface of the oxygen gas on the hot metal bath surface to dephosphorize the hot metal in the converter. Or in the method of refining hot metal in the converter, decarburizing and refining,
The CaO-based solvent is sprayed from the upper blowing lance for the entire period or a part of the period from the start of the oxygen gas blowing from the upper blowing lance to the point of supplying oxygen gas of 40% by volume of the planned acid delivery amount. It was carried out over a period of time, and was performed during the whole period or a part of the period from the time when 70% by volume of oxygen gas was supplied to the end of refining, and 40% by volume of oxygen gas was supplied. After the time has elapsed, the period of supplying oxygen gas of less than 70% by volume of the planned amount of acid sent is that the spraying of the CaO-based solvent from the top blowing lance is stopped, the hot metal in the converter Refining method.   The addition amount of the CaO-based solvent supplied from the top blowing lance after the point of supplying 70% by volume oxygen gas of the planned acid delivery amount is 10 to 40% by mass of the planned addition amount of the CaO-based solvent. The method for refining hot metal in a converter according to claim 1, characterized in that:

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