WO2014068933A1

WO2014068933A1 - Hot metal refining method

Info

Publication number: WO2014068933A1
Application number: PCT/JP2013/006331
Authority: WO
Inventors: 孝彦前田; 川畑　涼; 田中　高太郎; 山本　和人; 俊朗石毛; 純仁小澤; 満章滝口; 雅之古家
Original assignee: Ｊｆｅスチール株式会社
Priority date: 2012-10-30
Filing date: 2013-10-25
Publication date: 2014-05-08
Also published as: JPWO2014068933A1; TR201504423T1; KR20150076252A; KR101680094B1; JP5807720B2; IN2015KN00602A; CN104769136A; TWI544081B; TW201416456A; BR112015008720B1; CN104769136B; BR112015008720A2

Abstract

When manufacturing molten steel from hot metal using a two base converter-type refining furnace and using one as a hot metal pretreatment refining furnace and the other as a hot metal decarburization refining furnace, the molten slag generated in the decarburization refining furnace is used while still hot as a refining agent in the pretreatment refining furnace without compromising the productivities of the two refining furnaces. A refining method for manufacturing molten steel from hot metal using a converter-type refining furnace with at least two bases and using one as a hot metal pretreatment refining furnace (14) and using the other as a decarburization refining furnace (3) for the hot metal (2) pretreated in the pretreatment refining furnace. After the molten steel (5) obtained by decarburization refining in the decarburization refining furnace has been tapped in a ladle (7), the slag (9) remaining inside the decarburization refining furnace is allowed to flow down, still in the molten state, from above stacked iron scraps to solidify at least a portion of the slag. Then in pretreatment of hot metal in the pretreatment refining furnace, the slag, at least a portion of which has been solidified, is used together with the iron scraps while still hot.

Description

Hot metal refining method

The present invention uses at least two converter-type smelting furnaces, one of which is used as a hot metal pretreatment furnace and the other as a hot metal decarburization furnace pretreated in a pretreatment furnace. The present invention relates to a hot metal refining method for producing molten steel from hot metal. Specifically, the present invention relates to a refining method in which molten slag generated in a decarburizing refining furnace is used as a refining agent in a pretreatment refining furnace while maintaining a high temperature.

Technical development for high quality demands and low price demands on various steel materials is carried out in each steel manufacturing process. In the refining process for melting molten steel from hot metal, refining is completed in order to prevent the impurity components transferred and separated from the molten metal phase to the molten slag phase by refining from returning to the molten metal phase in the subsequent refining process. During the subsequent tapping operation, the molten slag generated in the refining process is controlled so that it does not flow out as much as possible into a hot water receiving container such as a hot metal ladle or a ladle. That is, in the hot water discharge operation from the smelting furnace, the molten metal is discharged from the smelting furnace to the hot water receiving container as much as possible, while the molten metal slag remains in the smelting furnace as much as possible.

The molten slag remaining in the smelting furnace is discharged from the smelting furnace to a slag pan (slag pot), transported to the slag yard by the slag pan, discharged to the slag yard, and allowed to cool in the atmosphere. It was general. However, in recent years, from the viewpoint of reusing slag or effectively utilizing the heat held by the slag, an efficient method for treating the molten slag remaining in the smelting furnace has become a problem. In addition, since it is impossible to completely separate the molten metal and the molten slag in the pouring operation, a small amount of molten metal remains in the smelting furnace after the pouring. Therefore, efficient treatment of the molten metal remaining in the furnace is also desired.

Conventionally, as a method of utilizing converter slag (also referred to as “decarburization slag”) generated in hot metal decarburization refining, hot metal having a low phosphorus concentration (“low” Several methods have been proposed in which molten slag produced by decarburization refining using "phosphorous iron" is reused as a refining agent.

For example, Patent Document 1 discloses that one of two converter-type refining furnaces has a dephosphorizing refining furnace and the other is a decarburizing refining furnace, and degassing of hot metal that has been dephosphorized in the dephosphorizing refining furnace. Once the converter slag generated by decarburization and refining in the smelting furnace is recovered, the recovered converter slag is added to the dephosphorization furnace as a smelting agent, thereby reducing the amount of smelting agent newly added during the dephosphorization process. And a steelmaking method aimed at promoting dephosphorization reaction by promoting hatching of the refining agent.

In Patent Document 2, decarburization slag generated by decarburization refining in a decarburization refining furnace of hot metal subjected to dephosphorization treatment is discharged into a hot metal holding container in which another hot metal is accommodated, and then the hot metal holding is performed. The molten decarburized slag discharged into the vessel and the hot metal previously stored in the hot metal holding vessel are charged into the dephosphorizing furnace, and the dephosphorizing treatment is performed on the hot metal charged in the dephosphorizing furnace. Thus, a refining method for reusing hot decarburized slag in a molten state is disclosed.

Patent Document 3 includes a first step in which hot metal or hot metal and iron scrap are charged as main raw materials in a converter, a second step in which desiliconization and dephosphorization are performed, a third step in which generated slag is discharged, After that, the fourth step of decarburizing and refining, the fifth step of leaving the slag after decarburizing and refining, and then returning to the first step, the slag left in the fifth step in the desiliconization / dephosphorization of the second step In the converter steelmaking method in which the above five steps are repeatedly used, the slag left in the fifth step is cooled to contain a large amount of iron oxide to prevent bumping of the slag left in the fifth step. A converter steelmaking process in which materials are added is disclosed.

Japanese Patent Laid-Open No. 3-115515 JP 2001-172710 A JP 2001-192720 A

However, the above prior art has the following problems.

That is, in Patent Document 1, since the molten slag remaining in the decarburization refining furnace is once recovered and used after being crushed, the heat content of the slag is not recovered. In addition, when the molten slag is discharged from the decarburizing and refining furnace, the molten steel remaining in the decarburizing and refining furnace is discharged out of the refining process system together with the molten slag and processed, so that the molten steel yield deteriorates. It becomes a cause.

In Patent Document 2, it is necessary to arrange a hot metal holding container containing hot metal directly below the decarburization refining furnace, and it may not be possible depending on the height restriction just below the furnace. Also, if possible, place the hot metal holding vessel directly under the decarburization refining furnace, or move the hot metal holding vessel after receiving the slag to the dephosphorizing refining furnace, and transfer it from the hot metal holding vessel to the dephosphorizing refining furnace. Since hot metal is charged or the like, the hot metal holding container is frequently moved and complicated, and time loss is likely to occur, resulting in a decrease in production volume and a decrease in hot metal temperature. Furthermore, when molten slag discharged into the hot metal holding container or undeoxidized molten steel is caught in the hot metal, there is a risk that CO gas is suddenly generated and bumps, and there is a safety problem.

In Patent Document 3, the process from hot metal dephosphorization to decarburization and refining is continuously performed in one converter-type refining furnace, which can prevent heat dissipation associated with tapping, but in the converter-type refining furnace, As a result, the residence time becomes longer and the productivity of the converter-type smelting furnace decreases. The dephosphorization treatment can be performed in a low temperature range where the load on the furnace refractory is low, but since the dephosphorization treatment and the decarburization refining are performed in series, the furnace refractory has a temperature of 1650 ° C. or higher. When it cannot withstand the decarburization refining which will be in a high temperature state, the furnace refractory needs to be repaired, and there is a problem that the refractory cost increases. In addition, a large amount of iron oxide is added to solidify the decarburized slag in the molten state, and an extra heat loss increases due to the amount of heat required for the reduction of this iron oxide, and the furnace body with the added iron oxide There is also the problem of increased wear of refractories. Furthermore, even if it is discharged after the dephosphorization treatment, a part of the slag containing about 2% by mass of phosphorus produced by the dephosphorization treatment remains in the furnace, and in the subsequent decarburization refining, rephosphorization: There is also a problem in that the phosphorus in the hot metal or molten steel shifts to the molten iron or molten steel and the phosphorus concentration of the molten iron or molten steel increases.

The present invention has been made in view of the above circumstances, and the object thereof is to use at least two converter-type smelting furnaces, one of which is pre-treated with hot metal pre-treatment smelting furnace and the other with pre-treatment smelting furnace. When melting molten steel from molten iron using it as a decarburizing and refining furnace, the molten slag generated in the decarburizing and refining furnace is kept at a high temperature without impairing the productivity of the pretreatment refining furnace and decarburizing and refining furnace. It is to provide a hot metal refining method that can be used as a refining agent in a pretreatment refining furnace.

The present inventors obtained the following knowledge as a result of intensive studies and research in order to solve the above problems.

That is, after decarburizing and refining the hot metal in the decarburizing and refining furnace, this molten slag is heated to a high-temperature state as a method for efficiently utilizing the sensible heat of the molten slag that remains in the decarburizing and refining furnace when the molten steel is discharged. A method of using it as a refining agent in the pretreatment performed in the latest pretreatment refining furnace is effective. For this purpose, the molten slag (hereinafter also referred to as “decarburization slag”) and the undeoxidized molten steel remaining in the decarburization refining furnace together with the molten slag are in contact with the hot metal charged in the pretreatment refining furnace. It reacts abruptly at the moment when it is done, preventing hot metal, slag or flames from blowing out and hindering operations, while making the most of their thermal energy to dissolve iron sources such as iron scrap. It will be necessary.

For this purpose, the molten slag is caused to flow down from above the laminated iron scrap in a molten state, and heat exchange with the iron scrap is performed so as to solidify at least a part of the slag, thereby reducing the reactivity of the slag. Let That is, after reducing the reactivity, the slag is brought into contact with the hot metal charged in the pretreatment smelting furnace, and the slag is heated in the pretreatment smelting furnace together with iron scrap preheated by heat exchange with the slag. It has been found that it is effective to use it for the hot metal pretreatment.

The molten slag and the molten steel thus treated do not react rapidly even when they come into contact with the hot metal, and, unlike limestone as a coolant, solidify as a large mass. Since hatching is not hindered, it can be effectively used as a refining agent even in pretreatment of hot metal at a relatively low temperature.

Also, it is necessary that the component composition of the molten slag is suitable for the latest preliminary treatment and can be used effectively. That is, in order to effectively use the decarburized slag, it is necessary to appropriately control both the thermal treatment operation of the decarburized slag and its component composition. Here, the preliminary treatment is desiliconization treatment or dephosphorization treatment. The dephosphorization treatment includes refining for dephosphorizing hot metal that has been desiliconized and refining for removing silicon and dephosphorizing hot metal that has not been desiliconized. Among the dephosphorization processes, a process in which the desiliconization process and the dephosphorization process are continuously performed is also referred to as a desiliconization / dephosphorization process.

In order to satisfy such requirements, the dephosphorization hot metal used for decarburization and refining is dephosphorized to a low phosphorus concentration of about 0.030% by mass or less, preferably 0.020% by mass or less (low phosphorus hot metal). Is preferably used. By decarburizing and refining this low phosphorus hot metal, decarburized slag with low phosphorus concentration is easily generated, so this should be used as part or all of the basicity adjusting agent of slag during desiliconization treatment. And a part or all of the refining agent for dephosphorization treatment can be used. In this case, the decarburized slag remaining in the decarburization refining furnace is discharged into the slag storage and transfer container, and then used for the latest preliminary treatment without performing water cooling treatment, etc. It is important to make the best use of heat. In the present invention, the basicity of slag is a value represented by the ratio ((mass% CaO) / (mass% SiO ₂ )) of CaO concentration and SiO ₂ concentration in slag.

In this way, it was found that the sensible heat of the molten slag after the decarburization refining of hot metal can be efficiently recovered. Also, after decarburization and refining, the molten steel is discharged from the decarburization and refining furnace, but the molten steel remains in the decarburization and refining furnace. It has also been found that heat and iron can be advantageously recovered.

The present invention has been made based on the above findings, and the gist thereof is as follows.
[1] Using at least two converter-type refining furnaces, using one as a hot metal pretreatment refining furnace, and using the other as a hot metal decarburization refining furnace pretreated in the pretreatment refining furnace, A hot metal refining method for producing molten steel from hot metal, in which the molten steel obtained by decarburizing and refining in the decarburizing and refining furnace is poured into a ladle, and the slag remaining in the decarburizing and refining furnace is laminated. The molten iron scrap is allowed to flow down in a molten state to solidify at least a part of the slag, and then the slag is at least partially solidified by the hot metal pretreatment in the pretreatment smelting furnace. A hot metal refining method, characterized by being used at a high temperature.
[2] The slag remaining in the decarburization refining furnace is discharged into a slag containing transport container previously charged with iron scrap, and remains in a molten state from above the iron scrap stacked in the slag containing transport container Flowing down, solidifying at least a part of the slag, and then charging the slag solidified at least partially contained in the slag containing transport container together with the iron scrap into the pretreatment smelting furnace, The hot metal refining method according to [1] above, wherein hot metal is charged into the pretreatment refining furnace and the hot metal is pretreated.
[3] The pretreatment smelting furnace in which the slag remaining in the decarburization smelting furnace is discharged into a slag storage and transfer container, and then the slag stored in the slag storage and transfer container is preliminarily charged with iron scrap. At least a part of the slag is allowed to flow in a molten state from the iron scrap stacked in the pretreatment smelting furnace and solidified at least a part of the slag, and then the pretreatment The hot metal refining method according to [1] above, wherein hot metal is charged into a refining furnace and the hot metal is preliminarily treated.
[4] The hot metal refining method according to the above [3], wherein a refractory layer is constructed on the inner surface side of the slag containing transport container.
[5] The hot metal desiliconization process is performed in the pretreatment smelting furnace, and then the intermediate slag in which a part of the slag after the hot metal and the desiliconization process remains in the pretreatment smelting furnace is performed. The above [1] to the above [1], wherein the CaO-based solvent is added to the hot metal left in the treatment refining furnace and the oxygen gas is supplied to perform the dephosphorization of the hot metal. 4] The hot metal refining method according to any one of [4].
[6] The hot metal dephosphorization treatment is performed in the pretreatment smelting furnace, the hot metal after the dephosphorization treatment is discharged from the pretreatment smelting furnace, and the slag after the dephosphorization treatment is left in the furnace. The hot metal of the next charge is charged into the treatment smelting furnace, and the degassing process is performed on the hot metal, and then the intermediate slag is performed to leave a part of the slag after the hot metal and desiliconization process in the pretreatment smelting furnace. Subsequently, the CaO-based solvent is added to the hot metal after the desiliconization treatment left in the preliminary treatment smelting furnace, and oxygen gas is supplied to perform the dephosphorization of the hot metal. The method for refining hot metal as described in 5].
[7] The above [1] to the above [1], wherein the pretreatment in the pretreatment smelting furnace is dephosphorization, and the phosphorus concentration of the dephosphorized hot metal is 0.030% by mass or less. [6] The hot metal refining method according to any one of [6].
[8] The mass of iron scrap previously charged into the slag containing transport container or the mass of iron scrap charged before pretreatment into the pretreatment smelting furnace, iron ore, sintered ore of iron ore, mill scale, The mass of the iron source charged into the pretreatment smelting furnace from the top of the pretreatment smelting furnace, which is any one or two or more of iron sources consisting of iron dust, magnetic separation scraps, and steel cutting scraps; Any one of the above-mentioned [2] to [7], wherein the total mass of the slag is determined in accordance with a heat recovery amount of the slag charged into the pretreatment refining furnace by the slag containing transport container. The method for refining hot metal as described in 1.

In the present invention, the decarburization slag remaining in the decarburization refining furnace is caused to flow down in a molten state from the laminated iron scrap to solidify at least a part of the slag, and then the hot metal in the pretreatment refining furnace In the preliminary treatment, the slag that is at least partially solidified is used together with the iron scrap at a high temperature. As a result, the sensible heat of the molten slag generated by hot metal decarburization refining can be utilized to the maximum in the pretreatment of hot metal in the pretreatment refining furnace, and the amount of iron sources such as iron scrap is increased. Is realized. In addition, since the slag produced by decarburization refining functions as a slag basicity adjusting agent and a dephosphorizing refining agent in the pretreatment, the basic unit of the slag basicity adjusting agent in the desiliconization treatment in the pretreatment refining furnace. In the dephosphorization treatment, the basic unit of the dephosphorization refining agent is reduced. In addition, the molten steel remaining in the decarburization refining furnace or the solidified solidified iron of this molten steel is charged into the pretreatment refining furnace together with the decarburization slag, so the yield of hot metal discharged from the pretreatment refining furnace is improved. To do.

FIG. 1 is a schematic diagram of a processing flow of a hot metal refining method according to the present invention.

Hereinafter, the present invention will be specifically described with reference to the accompanying drawings. FIG. 1 is a schematic diagram of a processing flow of a hot metal refining method according to the present invention.

A low phosphorous iron 2 that has been dephosphorized in the hot metal pretreatment step 1 to reduce the phosphorus concentration, or a dephosphorized hot metal 2 ′ that has been desiliconized in the hot metal pretreatment step 1 to reduce the silicon concentration, is converted into a converter. A decarburization refining furnace 3 which is a type refining furnace, and further charged with quick lime (CaO) or dolomite (CaO-MgO) as a medium solvent, and low phosphorus hot metal 2 using top blowing oxygen or bottom blowing oxygen or Decarburization refining is performed on the desiliconized hot metal 2 '(decarburization refining process 4). Here, as described above, the dephosphorization treatment refers to both the case of desiliconizing and dephosphorizing hot metal that has not been desiliconized, and the case of dephosphorizing the desiliconized hot metal. Including. Quick lime, dolomite, limestone (CaCO ₃ ) and the like are called CaO-based solvents because they contain CaO as a main component.

By decarburization refining, the low phosphorus hot metal 2 or the desiliconized hot metal 2 ′ is refined into the molten steel 5. Also, by decarburization refining, the basicity ((mass% CaO) / (mass% SiO ₂ )) of quick lime and dolomite and silicon oxide (SiO ₂ ) contained in the molten iron is about 3-5. Of molten slag (decarburized slag) 6 is produced.

After completion of the decarburization refining, the molten steel 5 is discharged from the decarburization refining furnace 3 to the ladle 7 through a tap (not shown) provided on the side wall of the decarburization refining furnace 3. At that time, the molten slag 6 generated during the decarburization refining is controlled so as to remain in the decarburization refining furnace 3 as much as possible. However, a part of the molten slag 6 is mixed into the molten steel 5 and flows out into the ladle 7 at the end of the hot water. Although not shown, the molten steel 5 discharged to the ladle 7 is transported to a continuous casting process through secondary refining in the next process as necessary, and the molten steel 5 is continuously cast into a slab.

After completion of the tapping, the decarburization refining furnace 3 is tilted to the opposite side to the tapping side, and the residual molten slag 9 left in the decarburizing refining furnace is transferred from the furnace port of the decarburizing refining furnace 3 to the slag containing transport container 10. Alternatively, it is discharged directly to the slag containing transport container 11. The slag containing transport container 10 has a wide spout with a refractory layer 10a constructed on the inner surface side and protruding. On the other hand, the slag containing transport container 11 has a protruding wide spout, but does not have a refractory layer, and is made of, for example, a metal made of cast iron, cast steel, or the like, and has an iron scrap 12 in advance. Is charged. At this time, a small amount of residual molten steel 8 remaining in the decarburization refining furnace 3 is also discharged together with the residual molten slag 9 into the slag containing transport container 10 or the slag containing transport container 11.

The residual molten slag 9 is discharged into a slag containing transport container 11 in which iron scrap 12 has been charged in advance, and is allowed to flow down in a molten state from the iron scrap stacked in the slag containing transport container, whereby the residual molten slag 9 At least a part of the solidifies.

In addition, the slag accommodation conveyance container 10 is a container for conveying the residual molten slag 9 to the pretreatment refining furnace 14 in a molten state, and the refractory layer 10a is constructed on the inner surface side, but the refractory layer 10a. Construction is not essential. Even if the slag container 10 is made of metal such as cast iron, the residual molten slag 9 accommodated in the slag container 10 is not immediately solidified, and the pretreatment refining is performed while the residual molten slag 9 is in a molten state. It is possible to charge the furnace 14. When the refractory layer 10a is applied, when the residual molten slag 9 can be charged into the pretreatment refining furnace 14 in a short time after receiving the residual molten slag 9, the effect of reducing heat loss can be enjoyed. When the holding time becomes long and a part of the residual molten slag 9 or the residual molten steel 8 is solidified and adheres to the inner surface of the container, the separation is difficult, and the operation is confused. In such a case, it is preferable not to construct the refractory layer 10a.

Subsequently, the residual molten steel 8 and the residual molten slag 9 discharged from the decarburization refining furnace 3 to the slag containing and transporting container 10 are loaded into a pretreatment refining furnace 14 which is a converter type refining furnace in which iron scrap 12 is previously charged. Enter. When the refractory layer 10a is applied to the slag container transport container 10, the heat retaining property is high, and the residual molten steel 8 and the residual molten slag 9 are almost retained even if held in the slag container transport container 10 for about 5 to 30 minutes. It does not solidify.

Thereafter, the hot metal 15 is charged into the pretreatment smelting furnace 14, and the silicon melt 16 (residual molten steel 8 + hot metal 15 + molten iron scrap 12) in the pretreatment smelting furnace is subjected to desiliconization or dephosphorization. In the desiliconization process, the residual molten slag 9 charged in the pretreatment refining furnace 14 functions as a slag basicity adjuster, and in the dephosphorization process, the residual molten slag 9 charged in the pretreatment refining furnace 14. Functions as a dephosphorizing agent. Here, the dephosphorization refining agent is a refining agent for fixing phosphorous oxide (P ₂ O ₅ ) generated by the dephosphorization reaction in the slag as 3CaO · P ₂ O ₅ .

At least a part of the residual molten slag 9 adheres to the iron scrap 12 by flowing down from above the iron scrap 12 stacked in the pretreatment smelting furnace while at least a part of the residual molten slag 9 remains in a molten state. It solidifies so as to enter the gap between the iron scraps 12. Further, the residual molten steel 8 having a higher melting point and higher thermal conductivity than the residual molten slag 9 is almost solidified by flowing down from the iron scrap 12 simultaneously with the residual molten slag 9.

In this way, the residual molten slag 9 and the residual molten steel 8 after heat exchange with the iron scrap 12 are in a state in which the liquid phase ratio is reduced and the reactivity with the molten iron is reduced, and are charged into the pretreatment smelting furnace. Operation trouble due to a rapid reaction with hot metal 15 is prevented. Contrary to this method, the residual molten steel 8 and the residual molten slag 9 discharged into the slag containing and transporting container 10 are charged into an empty pretreatment smelting furnace 14 after being discharged and discharged, When the iron scrap 12 is charged and then the molten iron 15 is charged, the residual molten steel 8 and the residual molten slag 9 are not sufficiently heat exchanged with the iron scrap 12 and remain highly reactive with the molten iron. In addition, when the hot metal 15 is charged, there may be an operation trouble due to hot metal or a jet of flame, which is not desirable.

Further, since the residual molten slag 9 solidified as described above is solidified in a finely divided state without forming a large mass of solidified slag, hatching is hindered even in a pretreatment of a relatively low temperature hot metal. It functions effectively as a refining agent.

Similarly, the residual molten steel 8 and the residual molten slag 9 discharged from the decarburization refining furnace 3 to the metal slag containing and transporting container 11 in which the iron scrap 12 has been charged in advance are also supplied to the pretreatment refining furnace 14 in the iron scrap 12 Charge with. However, the residual molten steel 8 and the residual molten slag 9 discharged to the metal slag containing transport container 11 are flowed down from the iron scrap 12 previously charged in the slag containing transport container 11, and the residual molten steel 8 and residual The sensible heat of the molten slag 9 is spent on preheating the iron scrap 12. As a result, at least a part of the residual molten steel 8 and the residual molten slag 9 is solidified and solidified to form a metal-containing slag 13 in which the solidified iron and the solidified slag are mixed. That is, since the residual molten steel 8 and the residual molten slag 9 become a bullion bar 13 with reduced reactivity with the hot metal, it is safe even if the hot metal 15 is further charged immediately after being charged into the pretreatment refining furnace 14. Can perform operations. In addition, since the bullion bar 13 is subdivided by the falling energy when charged into the pretreatment smelting furnace 14 together with the iron scrap 12, this method is also advantageous in that the hatching is promoted in the pretreatment smelting. .

The mass of the iron scrap 12 charged in advance into the metal slag containing transport container 11 is 1.5 to 4.5 times the total mass of the residual molten steel 8 and the residual molten slag 9 discharged from the decarburization refining furnace 3. It is preferably some, more preferably 2 to 3 times. When the amount of iron scrap charged in advance is small, solidification and solidification of the residual molten steel 8 and the residual molten slag 9 is insufficient, and when the molten iron 15 is charged into the pretreatment refining furnace 14, the molten iron is rapidly generated by CO gas generation. And the risk of slag ejection increases. In addition, the total amount of iron source used is reduced, and the sensible heat of the residual molten slag 9 cannot be used effectively, or the work time is extended to introduce additional iron scrap, resulting in a decrease in productivity. That is also a problem.

On the other hand, if there is a large amount of iron scrap to be charged in advance, there will be a problem that the refining load for temperature rise etc. will increase, leading to an increase in cost and refining time. The problem that 12 cannot be dissolved also occurs. Moreover, the problem that the capacity | capacitance slag accommodation conveyance container 11 becomes large also arises.

In addition, it is preferable that the amount of iron scrap 12 charged into the slag containing transport container 11 is the total amount of iron scrap charged into the pretreatment refining furnace 14. As a result, iron scrap charging and slag charging can be combined, and the slag of the decarburization smelting furnace 3 is pretreated while preventing the decrease in productivity by increasing the number of times of charging and increasing the work time. The refining furnace 14 can be reused hot.

Thus, the residual molten steel 8 and the residual molten slag 9 are solidified and solidified to form a bullion 13. The sensible heat is recovered in the iron scrap 12 charged into the pretreatment refining furnace 14 and functions as heat for melting the iron scrap 12 in the pretreatment in the pretreatment refining furnace 14 in the next step. Even though it is solidified and solidified, the bullion bar 13 is also at a high temperature of about 300 ° C. or higher, and the sensible heat of the bullion bar 13 is also recovered during the preliminary treatment.

Thereafter, the hot metal 15 is charged into the pretreatment smelting furnace 14 and preliminarily treated for all the molten metal 16 (solid iron in the metal bar 13 + hot metal 15) in the pretreatment smelting furnace. In this pretreatment, the solidified residual molten slag 9 charged as the metal slag 13 is hatched by receiving the heat of the hot metal 15, and as a slag basicity adjusting agent when the pretreatment is a desiliconization process. It functions as a dephosphorizing agent in the case of dephosphorization.

The pretreatment in the pretreatment refining furnace 14 is performed by blowing oxygen gas from the top blowing lance onto the entire molten metal 16 while blowing nitrogen gas or the like from the bottom blowing tuyeres of the furnace bottom as a stirring gas into the molten metal 16. Do it. When the pretreatment is a desiliconization treatment, the silicon in the molten iron is oxidized by the oxygen gas blown up (desiliconization reaction: Si + O ₂ → SiO ₂ ), and becomes silicon oxide (SiO ₂ ). This silicon oxide reacts with the residual molten slag 9 or CaO contained in the metal bar 13 to form slag in the furnace. In the case where the pretreatment is a dephosphorization treatment, the phosphorus in the hot metal is oxidized by the oxygen gas blown up (dephosphorization reaction: 2P + 5 / 2O ₂ → P ₂ O ₅ ) and phosphor oxide (P ₂ O ₅ ). It becomes. This phosphorous oxide is combined with CaO functioning as a dephosphorizing refining agent contained in the residual molten slag 9 or the metal bar 13 charged in the furnace, and is fixed as 3CaO · P ₂ O ₅ .

When dephosphorizing hot metal that has not been desiliconized, the above desiliconization reaction occurs in the initial stage of the dephosphorization process, and the silicon concentration in the hot metal is reduced to less than about 0.10% by mass. The dephosphorization reaction occurs. In this case, the period in which the desiliconization reaction mainly occurs is also referred to as the desiliconization period, and the period in which the latter dephosphorization reaction occurs is also referred to as the dephosphorization period. 3CaO · P ₂ O ₅ is not formed when the basicity of the slag in the furnace is low. Therefore, the basicity of the slag generated in the furnace is not increased with the charged residual molten slag 9 or the metal bar 13 alone. When 2.0 or more cannot be secured, it is preferable to add quick lime (CaO) or the like as a dephosphorizing refining agent in order to lower the phosphorus concentration. .

In the pretreatment step 1 of the hot metal 15, when the pretreatment is dephosphorization, the phosphorus concentration of the low phosphorus hot metal 2 after dephosphorization is set to 0.030 mass% or less, preferably 0.020 mass% or less. It is preferable to make it. When this low phosphorus hot metal 2 is decarburized and refined in the decarburizing and refining furnace 3, the phosphorus concentration of the molten slag 6 to be produced is reduced to a low concentration of about 1.5% by mass or less in terms of P ₂ O ₅ conversion. When such a low phosphorus concentration molten slag 6 is used as a part of a dephosphorization refining agent in the next pretreatment refining furnace 14, an increase in the phosphorus concentration in the slag is suppressed, which is more efficient. Can be easily removed.

In the present invention, the molten molten residual steel 8 and the residual molten slag 9 or the iron scrap 12 and the metal bar 13 preheated with the residual molten steel 8 and the residual molten slag 9 are charged into the pretreatment smelting furnace 14. The amount of heat input in the preliminary process is increased by the amount of the charged portion as compared with the conventional preliminary process. If iron scrap or the like is not added, the hot metal temperature at the end of the pretreatment will increase by an amount corresponding to the increase in heat input. If the temperature is within the temperature range, the lower the hot metal temperature, the more the dephosphorization reaction is promoted. Accordingly, the mass of iron scrap previously charged in the pretreatment smelting furnace 14 or the slag containing transport container 11 is charged in advance corresponding to the increase in heat input due to the molten molten steel 8 and the residual molten slag 9. It is preferable to increase the amount of iron scrap used and the amount of iron source used, such as magnetically separated slag-containing slag-containing slag-containing slag-containing slag-containing slag-containing slag. Also in the case of desiliconization, from the viewpoint of improving productivity, it is preferable to increase the amount of iron scrap used corresponding to the increase in heat input due to the residual molten steel 8 and the residual molten slag 9.

The present inventors increased the iron source such as iron scrap or magnetic separation scrap of about 1.5 tons or less per ton of the total amount of residual molten steel 8 and residual molten slag 9 to be recycled by the above method in the pretreatment refining furnace 14. It is confirmed from the survey results that even if it is charged, it dissolves completely, including the amount added during the pretreatment.

Therefore, according to the heat recovery amount of the residual molten slag 9 (residual molten slag 9 after solidification) recycled to the pretreatment smelting furnace 14 by the slag containing

transport containers

10 and 11, the slag containing transport container 11 is charged in advance. It is preferable to determine the total mass of the mass of the iron scrap 12 or the mass of the iron scrap 12 charged in advance into the pretreatment smelting furnace 14 and the mass of the iron source such as magnetic separation scraps charged from the hopper on the furnace. . As iron sources to be fed from the hopper on the furnace, iron ore, iron ore sintered ore, mill scale, steelmaking dust, steel cutting chips can be used in addition to magnetically selected scraps. .

The amount of heat recovered by charging the residual molten steel 8 and the residual molten slag 9 into the pretreatment refining furnace 14 by the slag containing

transfer containers

10 and 11 is “molten steel (residual molten steel 8) specific heat × molten steel mass × molten steel temperature + slag ( Residual molten slag 9) Specific heat × molten slag mass × slag temperature ”. In actual operation, heat recovery amount = “(average specific heat of residual molten slag 9 and residual molten steel 8) × (total mass of residual molten slag 9 and residual molten steel 8) × (average of residual molten slag 9 and residual molten steel 8) Temperature) ”may be simplified.

In actual operation, the mass of iron scrap charged in advance into the pretreatment smelting furnace 14 or the mass of iron scrap charged into the pretreatment smelting furnace 14 by the slag containing transport container 11 is obtained from experience. With a certain value less than the possible mass, one or more of iron ore, iron ore sintered ore, mill scale, iron making dust, magnetic separation scrap, steel cutting scrap or more The total charged mass of the iron source charged into the pretreatment smelting furnace 14 from the top of the furnace is the residual molten steel 8 (including the solidified residual molten steel 8) charged into the pretreatment smelting furnace 14 by the slag containing transport containers 10 and 11. ) And the residual molten slag 9 (residual molten slag 9 after solidification), the effect of the present invention can be obtained.

In the present invention, the pretreatment in the pretreatment smelting furnace 14 includes (1) desiliconization treatment, preliminary treatment of the process consisting of waste, (2) dephosphorization treatment of the desiliconized hot metal, preliminary treatment of the process consisting of waste, (3) Pretreatment of the process consisting of desiliconization / dephosphorization treatment and waste removal, (4) Pretreatment of the process consisting of desiliconization / dephosphorization treatment, leaving slag in the furnace, and charging the hot metal of the next charge, ( 5) Any of the pretreatment of the process consisting of desiliconization treatment, intermediate waste removal, dephosphorization treatment, slag remaining in the furnace, and hot metal charging of the next charge is possible. Further, the same thermal effect can be obtained in any pretreatment. In addition, the recovered heat from the residual molten slag 9 (residual molten slag 9 after solidification) enables slag hatching to be promoted even during a short desiliconization period. Efficient pretreatment is possible by preventing re-phosphorus from the slag.

As described above, according to the present invention, the sensible heat of the molten slag 6 generated by the decarburization refining in the decarburization refining furnace 3 and the sensible heat of the residual molten steel 8 in the furnace are used as the hot metal in the pretreatment refining furnace 14. In the pretreatment smelting furnace 14, the basic unit of the slag basicity adjusting agent or the dephosphorizing smelting agent is reduced, and further, the tapping yield is improved.

Hereinafter, the present invention will be described in more detail with reference to examples. The following tests were performed along the processing flow of the hot metal refining method according to the present invention shown in FIG. In the following tests, the dephosphorization treatment (desiliconization / dephosphorization treatment) of the hot metal that was not desiliconized as a pretreatment in the pretreatment refining furnace 14 was performed.

Low phosphorus hot metal 2 having a phosphorus concentration of 0.020% by mass is charged into a 300-ton capacity decarburization refining furnace 3 (converter), and further, quick lime and dolomite are charged as solvent, and the bottom of the furnace is blown off. Decarburization and refining were performed by supplying oxygen gas from an upper blowing lance while blowing argon gas (Ar gas) as a stirring gas from the tuyere. After the decarburization refining, the molten steel 5 obtained is poured into the ladle 7 and the molten steel 5 discharged into the ladle 7 is transferred to the casting process through the secondary refining of the next process as necessary. Was cast into a slab. On the other hand, about 7 tons of residual molten slag 9 and about 2 tons of residual molten steel 8 remained in the decarburization refining furnace after completion of the tapping operation.

The operating conditions of the dephosphorization treatment of the hot metal 15 in the converter type pretreatment refining furnace 14 were set within the following normal processing conditions in both the comparative example and the present invention example.

1. Temperature of hot metal 15 before dephosphorization: 1270 to 1320 ° C.
2. Silicon concentration of hot metal 15 before dephosphorization: 0.25 to 0.35 mass%
3. Phosphorus concentration of hot metal 15 before dephosphorization: 0.100 to 0.120% by mass
4). Phosphorus concentration of low phosphorus hot metal at the end of dephosphorization treatment: 0.005 to 0.030 mass%
5. Basicity of furnace slag at the end of dephosphorization: 2.0 to 3.0
6). Total iron concentration in furnace slag at the end of dephosphorization: 5.0 to 15.0 mass%
In the test of Comparative Example 1, the residual molten slag 9 and the residual molten steel 8 in the decarburization refining furnace are not used as hot charging raw materials to the pretreatment refining furnace 14, but from the decarburization refining furnace 3 as usual. After the molten steel 5 was discharged, it was discharged into a slag pan, conveyed to a slag yard with a slag pan, and discharged into the slag yard and allowed to cool.

That is, the residual molten slag 9 and the residual molten steel 8 are discharged out of the refining process system, and slag treatment (cooling in the air) and solidified iron recovery treatment (solidified iron by a magnetic separator from slag crushed after solidification) Recovery). Then, the converter-type pretreatment smelting furnace 14 having a capacity of 300 tons was charged with 30 tons of iron scrap in advance, and then the hot metal 15 accommodated in the hot metal ladle was charged and dephosphorized. During the dephosphorization treatment, the dephosphorization treatment was carried out without using other iron sources such as magnetic separation scrap, iron ore, and iron ore sintered ore.

The temperature of the low phosphorus hot metal at the end of the dephosphorization treatment in Comparative Example 1 was in the temperature range of 1280 to 1320 ° C.

In Example 1 of the present invention, after the molten steel 5 is discharged from the decarburizing and refining furnace 3, the entire amount of the residual molten slag 9 and the residual molten steel 8 in the decarburizing and refining furnace is quickly formed with a refractory layer on the inner surface. It discharged | emitted to the slag accommodation conveyance container 10. FIG. As a result of measuring the temperature of the residual molten slag 9 and the residual molten steel 8 in this slag containing and conveying container, the temperature of the residual molten slag 9 and the residual molten steel 8 is in the range of 1560 to 1610 ° C., that is, the molten state of the molten steel and slag. It was a range. Thereafter, the total amount of the residual molten slag 9 of about 7 tons and the residual molten steel 8 of about 2 tons accommodated in the slag containing transport container 10 is transferred to the pretreatment smelting furnace 14 in which 30 tons of iron scrap is charged in advance. After charging, the hot metal 15 was charged and dephosphorization was performed. In order to confirm the superiority of the post-treatment temperature with respect to the comparative example 1 described above, even in the present invention example 1, the dephosphorization treatment is performed without using other iron sources such as magnetic separation scrap, iron ore, and sintered iron ore. did.

It was confirmed that the temperature of the low phosphorus hot metal at the end of the dephosphorization treatment in Invention Example 1 was in the temperature range of 1325 to 1365 ° C., and the temperature of the low phosphorus hot metal was about 45 ° C. higher than that of Comparative Example 1. This temperature difference is caused by the sensible heat of the residual molten slag 9 and the residual molten steel 8 charged in the pretreatment refining furnace 14.

In Example 2 of the present invention, after the molten steel 5 is discharged from the decarburizing and refining furnace 3, a refractory layer is quickly formed on the inner surface of the remaining molten slag 9 and the remaining molten steel 8 in the decarburizing and refining furnace immediately. It discharged | emitted to the slag accommodation conveyance container 10. FIG. Thereafter, the entire amount of the residual molten slag 9 of about 7 tons and the residual molten steel 8 of about 2 tons accommodated in the slag containing transport container 10 is transferred to the pretreatment smelting furnace 14 in which 30 tons of iron scrap is previously charged. After charging, hot metal 15 is charged, and any one of iron sources consisting of iron ore, iron ore sintered ore, mill scale, iron making dust, magnetic separation scrap, and steel cutting scrap from the furnace. The seed or two or more kinds of iron sources were added according to the amount of heat recovered from the residual molten slag 9 and the residual molten steel 8 to perform the dephosphorization treatment. For example, in the case of magnetic separation waste, 5 to 10 tons were added.

The temperature of the low phosphorus hot metal at the end of the dephosphorization treatment of Invention Example 2 was a temperature range of 1280 to 1320 ° C. equivalent to that of Comparative Example 1. Thus, in Invention Example 2, even if an iron source such as magnetic separation was additionally added, it could be operated without any problem, and the production amount could be increased compared to Comparative Example 1.

In Example 3 of the present invention, after the molten steel 5 is discharged from the decarburizing and refining furnace 3, the entire amount of the residual molten slag 9 and the residual molten steel 8 in the decarburizing and refining furnace is quickly formed with a refractory layer on the inner surface. It discharged | emitted to the slag accommodation conveyance container 10. FIG. Thereafter, a pretreatment smelting furnace in which 35 to 40 tons of iron scrap is preliminarily charged into the total amount of about 7 tons of residual molten slag 9 and about 2 tons of residual molten steel 8 accommodated in the slag containing transport container 10. 14 and then the hot metal 15 was charged to perform a dephosphorization process. Thus, in Example 3 of the present invention, the amount of iron scrap charged in advance into the pretreatment refining furnace 14 was further increased by 5 to 10 tons from 30 tons in Comparative Example 1.

The temperature of the low phosphorus hot metal at the end of the dephosphorization treatment of Invention Example 3 was a temperature range of 1280 to 1320 ° C. equivalent to that of Comparative Example 1. As described above, in Example 3 of the present invention, even if the amount of iron scrap used was increased, it could be operated without any problem, and the production amount could be increased compared to Comparative Example 1.

In Example 4 of the present invention, after the molten steel 5 is discharged from the decarburizing and refining furnace 3, the entire amount of the residual molten slag 9 and the residual molten steel 8 in the decarburizing and refining furnace is rapidly formed on the inner surface of the refractory layer. It discharged | emitted to the slag accommodation conveyance container 10. FIG. In Example 4 of the present invention, it is assumed that iron scrap previously charged in the pretreatment refining furnace 14 and an iron source to be added from the furnace are used together, and iron scrap charged in the pretreatment refining furnace 14 is used. The amount was set to 30 to 40 tons, and the amount of iron source to be added from the furnace was set according to the amount of iron scrap charged. Specifically, the total amount of the iron scrap charged in advance and the iron source charged and added from the furnace was 40 tons.

In other words, the total amount of about 7 tons of residual molten slag 9 and about 2 tons of residual molten steel 8 accommodated in the slag containing transport container 10 in which the refractory layer is formed is previously loaded with 30 to 40 tons of iron scrap. After charging the pretreatment smelting furnace 14, the hot metal 15 was charged. Then, one or more types of iron sources selected from iron ore, iron ore sintered ore, mill scale, iron making dust, magnetic separation scrap, and steel cutting scrap input from the furnace, In the range of 0 to 10 tons depending on the amount of iron scrap charged in the furnace in advance so that the total mass of the mass of iron scrap charged in advance and the mass of the iron source charged from the top of the furnace becomes 40 tons. A dephosphorization treatment was performed after setting and adding.

The temperature of the low phosphorus hot metal at the end of the dephosphorization treatment of Invention Example 4 was a temperature range of 1280 to 1320 ° C. equivalent to that of Comparative Example 1. As described above, in Example 4 of the present invention, even if an iron source such as an increase in the amount of iron scrap to be charged in advance or a magnetic separation scrap is added, the operation can be performed without any problem, and the production amount is increased with respect to Comparative Example 1. I was able to.

In Example 5 of the present invention, after the molten steel 5 is discharged from the decarburizing and refining furnace 3, the entire amount of residual molten slag 9 and residual molten steel 8 in the decarburizing and refining furnace is quickly charged with 20 to 30 tons of iron scrap. The metal slag containing transport container 11 was discharged. The residual molten slag 9 and the residual molten steel 8 that flowed out to the slag containing transport container 11 were cooled in contact with the iron scrap, and a bullion bar 13 of about 9 tons was formed.

In Example 5 of the present invention, the amount of iron scrap used in the dephosphorization treatment including the iron source charged from the furnace was set to 40 tons. In other words, the amount of iron scrap previously charged in the pretreatment smelting furnace 14 is 10 tons, and the total amount of the metal slag 13 of about 9 tons together with 20 to 30 tons of iron scrap accommodated in the metal slag containing transport container 11. Was charged into the pretreatment smelting furnace 14 and then the hot metal 15 was charged. Thereafter, one or two or more types of iron sources of iron ore, iron ore sintered ore, mill scale, iron making dust, magnetic separation scrap, and steel cutting scrap are transferred into the slag containing transport container 11. The amount was set in the range of 0 to 10 tons according to the amount of iron scrap charged from the furnace, and the set amount was added from the furnace to perform the dephosphorization treatment.

The temperature of the low phosphorus hot metal at the end of the dephosphorization treatment of Invention Example 5 was a temperature range of 1280 to 1320 ° C. equivalent to that of Comparative Example 1. As described above, in Example 5 of the present invention, even if an iron source such as magnetic separation was additionally added, it could be operated without any problem and the production amount could be increased.

In Example 6 of the present invention, after the molten steel 5 is discharged from the decarburizing and refining furnace 3, the entire amount of residual molten slag 9 and residual molten steel 8 in the decarburizing and refining furnace is quickly charged with 30 to 40 tons of iron scrap. The metal slag containing transport container 11 was discharged. The residual molten slag 9 and the residual molten steel 8 that flowed out to the slag containing transport container 11 were cooled in contact with the iron scrap, and a bullion bar 13 of about 9 tons was formed.

In Example 6 of the present invention, the amount of iron scrap charged in the pretreatment refining furnace 14 in advance is set to zero, and the amount of iron scrap used in the dephosphorization process including the iron source charged from the furnace is set to 40 tons. did. That is, the entire amount of the metal slag 13 of about 9 tons together with 30 to 40 tons of iron scrap accommodated in the slag containing transport container 11 was charged into the pretreatment smelting furnace 14, and then the hot metal 15 was charged. Thereafter, one or two or more types of iron sources of iron ore, iron ore sintered ore, mill scale, iron making dust, magnetic separation scrap, and steel cutting scrap are transferred into the slag containing transport container 11. The amount was set in the range of 0 to 10 tons according to the amount of iron scrap charged from the furnace, and the set amount was added from the furnace to perform the dephosphorization treatment.

The temperature of the low phosphorus hot metal at the end of the dephosphorization treatment of Invention Example 6 was a temperature range of 1280 to 1320 ° C. equivalent to that of Comparative Example 1. Further, in Example 6 of the present invention, iron scrap is not charged alone into the pretreatment smelting furnace 14, so that the removal time including the charging time of the residual molten slag 9 and the charging time of the iron scrap 12 is removed. The phosphorus treatment time interval could be shortened by about 10%, and the productivity could be improved due to the increase in the production amount due to the introduction of iron sources such as iron scrap and magnetic separation waste.

In Example 7 of the present invention, after the molten steel 5 is discharged from the decarburizing and refining furnace 3, the entire amount of residual molten slag 9 and residual molten steel 8 in the decarburizing and refining furnace is quickly charged with 30 to 40 tons of iron scrap. The metal slag containing transport container 11 was discharged. The residual molten slag 9 and the residual molten steel 8 that flowed out to the slag containing transport container 11 were cooled in contact with the iron scrap, and a bullion bar 13 of about 9 tons was formed.

In Example 7 of the present invention, as a pretreatment in the pretreatment refining furnace 14, the oxygen blowing is temporarily interrupted after the desiliconization period in which the hot metal is mainly desiliconized, and the slag in the furnace is discharged ("intermediate waste"). Then, the method of adding quick lime to the pretreatment smelting furnace 14 and dephosphorizing the hot metal (dephosphorization period) was adopted. The basicity of the furnace slag at the end of the desiliconization period is adjusted to the range of 1.0 to 1.5, and the furnace slag of about 10 kg / molten iron-t remains while the blowing is interrupted for about 4 minutes. Intermediate excretion was carried out. Further, in Example 7 of the present invention, the amount of iron scrap to be charged into the pretreatment refining furnace 14 in advance is set to zero, and the amount of iron scrap used in the dephosphorization process including the iron source charged from the top of the furnace is 40 tons. Set to.

In other words, about 9 tons of metal slag 13 together with 30 to 40 tons of iron scrap accommodated in a metal slag containing transport container 11 was charged into the pretreatment smelting furnace 14, and then hot metal 15 was charged. . Thereafter, one or two or more types of iron sources of iron ore, iron ore sintered ore, mill scale, iron making dust, magnetic separation scrap, and steel cutting scrap are transferred into the slag containing transport container 11. The amount was set in the range of 0 to 10 tons according to the amount of iron scrap charged from the furnace, and the set amount was added from the furnace to perform desiliconization and dephosphorization.

The temperature of the low phosphorus hot metal at the end of the dephosphorization treatment of Invention Example 7 is in the temperature range of 1280 to 1320 ° C., and the phosphorus concentration of the low phosphorus hot metal at the end of the dephosphorization treatment is 0.005 to 0.020 mass. %Met. In Invention Example 7, the phosphorus concentration of the low phosphorus molten iron at the end of the dephosphorization process was lower than that of Invention Examples 1 to 6 and Comparative Example 1 in which intermediate waste was not performed after the desiliconization period.

As described above, in Example 7 of the present invention, by performing intermediate waste after the desiliconization period, recovery from residual molten slag 9 is prevented, and the concentration of low phosphorus molten iron at the end of the dephosphorization process is reduced. I was able to.

In Example 8 of the present invention, after the molten steel 5 is discharged from the decarburizing and refining furnace 3, 35 to 40 tons of iron scrap is quickly charged into the entire amount of the residual molten slag 9 and the remaining molten steel 8 in the decarburizing and refining furnace. The metal slag containing transport container 11 was discharged. The residual molten slag 9 and the residual molten steel 8 that flowed out to the slag containing transport container 11 were cooled in contact with the iron scrap, and a bullion bar 13 of about 9 tons was formed.

In Example 8 of the present invention, as a pretreatment, while the slag after the dephosphorization treatment of the precharge in the pretreatment refining furnace 14 is left in the furnace, the hot metal of the charge is charged and the pretreatment refining is started. After the desiliconization period when the hot metal is mainly desiliconized, the oxygen blowing is temporarily interrupted, the slag in the furnace is intermediately discharged, and then quick lime is added to the pretreatment refining furnace 14 to dephosphorize the hot metal ( (Dephosphorization period) was adopted. The basicity of the furnace slag at the end of the desiliconization period is adjusted to the range of 1.0 to 1.5, and the furnace slag of about 10 kg / molten iron-t remains while the blowing is interrupted for about 4 minutes. Intermediate excretion was carried out. Further, in Example 8 of the present invention, the amount of iron scrap used in the dephosphorization treatment including the iron source charged from the top of the furnace after making the amount of iron scrap charged into the pretreatment refining furnace 14 zero is 42 tons. Set to.

In other words, about 35 tons of iron scrap accommodated in the metal slag containing transport container 11 and the entire amount of about 9 tons of the metal bar 13 were charged into the pretreatment refining furnace 14, and then the hot metal 15 was charged. . Thereafter, one or two or more types of iron sources of iron ore, iron ore sintered ore, mill scale, iron making dust, magnetic separation scrap, and steel cutting scrap are transferred into the slag containing transport container 11. The amount was set in the range of 2 to 7 tons according to the amount of iron scrap charged from the furnace, and the set amount was added from the furnace to perform desiliconization and dephosphorization.

The temperature of the low phosphorus hot metal at the end of the dephosphorization treatment in Invention Example 8 is in the temperature range of 1280 to 1320 ° C., and the phosphorus concentration of the low phosphorus hot metal at the end of the dephosphorization treatment is 0.005 to 0.020 mass. %Met. In Example 8 of the present invention, the phosphorus concentration of the low phosphorus molten iron at the end of the dephosphorization treatment was decreased compared to Examples 1 to 6 of the present invention and Comparative Example 1 in which intermediate waste was not performed after the desiliconization period. It was the same level as Invention Example 7.

As described above, in Example 8 of the present invention, the slag after the dephosphorization treatment is reused, and the intermediate waste is performed after the desiliconization period, so that the reused slag after the dephosphorization treatment and the residual molten slag 9 Rephosphorization was prevented, and the low phosphorus concentration at the end of the dephosphorization process could be reduced. In addition, by utilizing the reused slag after dephosphorization as a refining agent during the desiliconization period, the sensible heat possessed by the slag after dephosphorization could be used more effectively.

Table 1 summarizes the results of Comparative Example 1 and Invention Examples 1 to 8.

DESCRIPTION OF SYMBOLS 1 Pretreatment process 2 Low phosphorus hot metal 2 'Desiliconization hot metal 3 Decarburization refining furnace 4 Decarburization refining process 5 Molten steel 6 Molten slag 7 Ladle 8 Residual molten steel 9 Residual molten slag 10 Slag accommodation conveyance container 10a Refractory material layer 11 Slag accommodation Transport container 12 Iron scrap 13 Metal bar 14 Pretreatment smelting furnace 15 Hot metal 16 Total molten metal

Claims

Using at least two converter-type refining furnaces, one is used as a hot metal pretreatment refining furnace, and the other is used as a decarburization refining furnace for hot metal pretreated in the pretreatment refining furnace. In which the molten steel obtained by decarburization and refining in the decarburization and refining furnace is poured into a ladle, and the slag remaining in the decarburization and refining furnace is laminated to the laminated iron. The molten slag is allowed to flow in a molten state from above the scrap to solidify at least a part of the slag, and then at least a part of the slag solidified in the pretreatment smelting furnace is heated together with the iron scrap at a high temperature. A method for refining hot metal, which is used as it is.
The slag remaining in the decarburization refining furnace is discharged into a slag containing transport container in which iron scrap has been charged in advance and allowed to flow down in a molten state from above the iron scrap stacked in the slag containing transport container. , Solidifying at least a part of the slag, and then charging the slag contained in the slag containing and transporting container into the pretreatment smelting furnace together with the iron scrap, and then performing the pretreatment The hot metal refining method according to claim 1, wherein hot metal is charged into a refining furnace and the hot metal is preliminarily treated.
The slag remaining in the decarburization refining furnace is discharged into a slag storage and transfer container, and then the slag stored in the slag storage and transfer container is charged into the pretreatment refining furnace in which iron scrap has been charged in advance. Then, at least a part of the slag is allowed to flow down in a molten state from above the iron scrap stacked in the pretreatment smelting furnace, and at least a part of the slag is solidified, and then the pretreatment smelting furnace The hot metal refining method according to claim 1, wherein the hot metal is charged and the hot metal is pretreated.
4. The hot metal refining method according to claim 3, wherein a refractory layer is constructed on the inner surface side of the slag containing transport container.
Perform desiliconization of hot metal in the pretreatment smelting furnace, and then perform intermediate waste to leave a part of the slag after the hot metal and desiliconization treatment in the pretreatment smelting furnace, and then continue with the pretreatment smelting furnace 5. The hot metal dephosphorization treatment is performed by adding a CaO-based solvent to the hot metal remaining in the steel after desiliconization treatment and supplying oxygen gas. 6. The method for refining hot metal as described in item 1.
The hot metal dephosphorization treatment is performed in the pretreatment refining furnace, the hot metal after the dephosphorization treatment is discharged from the pretreatment refining furnace, and the pretreatment refining furnace remains with the slag after the dephosphorization treatment remaining in the furnace. Then, the hot metal of the next charge is charged, the hot metal is subjected to desiliconization treatment, and then the intermediate waste for leaving a part of the molten iron and the slag after the desiliconization treatment is left in the pretreatment smelting furnace, 6. The hot metal dephosphorization treatment is performed by adding a CaO-based solvent to the hot metal left in the pretreatment smelting furnace and supplying an oxygen gas to the hot metal after the desiliconization treatment. Refining hot metal.
The pretreatment in the pretreatment smelting furnace is a dephosphorization treatment, and the phosphorus concentration of the dephosphorized hot metal is 0.030% by mass or less. The method for refining hot metal as described in item 1.
The mass of iron scrap previously charged into the slag containing transport container or the mass of iron scrap charged before pretreatment into the pretreatment smelting furnace, iron ore, iron ore sintered ore, mill scale, ironmaking dust, The total mass of the iron source to be charged into the pretreatment smelting furnace from the top of the pretreatment smelting furnace, which is any one or two or more of iron sources composed of magnetic separation scrap and steel cutting scraps The hot metal according to any one of claims 2 to 7, wherein the hot metal is determined in accordance with a heat recovery amount of slag charged into a pretreatment refining furnace by the slag containing transport container. Refining method.