KR20210084563A - Steel manufacturing method and slag basicity reduction method - Google Patents

Abstract

The basicity of slag can be reduced, and the manufacturing method of steel which can suppress the fall of production efficiency, and the basicity reduction method of slag are provided. A method for manufacturing molten steel by subjecting molten iron to oxidation refining treatment in a converter 1, wherein in the converter 1, an oxygen source containing at least oxygen gas is added to the molten iron and subjected to oxidation refining treatment, a refining treatment process using molten steel, an addition step of adding a silica-containing material containing _{at least SiO 2} from above to the furnace body 2 of the converter 1 in which the molten steel is accommodated, after the refining treatment step; Then, the steel tapping process which inclines the furnace body 2 and discharges molten steel from the furnace body 2 is provided.

Description

Steel manufacturing method and slag basicity reduction method

The present invention relates to a method for manufacturing steel and a method for reducing the basicity of slag.

In the steelmaking process of an ironworks, the oxidation refining process (decarburization process) which manufactures molten steel by adding oxygen sources, such as oxygen gas, to molten iron|metal with a converter is performed. In this oxidative refining process, slag is generated by an oxidation reaction of an additive component or an impurity component in the molten iron to be added. After this slag is collect|recovered, it is reused as a raw material for various uses.

As one of the uses of the slag generated in the converter, there is a road bed material. When using slag as a roadbed material, it is necessary for the water immersion expansion rate to satisfy the quality standard set by standards, such as JIS, and it is necessary to make it 1.5 % or less by the standard of JIS, for example. In order to reduce the water immersion expansion rate of the slag, it is necessary to reduce the amount of free lime in the slag, and the basicity of the slag _{(ratio of the SiO 2} content to the CaO content of the slag ((%CaO)/(%SiO ₂ )) ) is important to reduce.

However, in the oxidation refining process in a converter, when the basicity of slag becomes low, foaming in which slag expands by CO gas etc. which generate|occur|produced during processing will occur easily, and dephosphorization efficiency will also become low. For this reason, the fall of the basicity of the slag in an oxidation refining process becomes a cause of an operation trouble, and production efficiency is reduced. In addition, in the oxidation refining treatment in a converter, in general, an amount corresponding to the target slag composition determined according to the blow tempering conditions such as the target component or target temperature of molten iron after the oxidation refining treatment, and the efficiency of the refining reaction, at the initial stage of the oxidation refining treatment Additives such as silica stone or lime are added respectively. However, it was difficult to lower the basicity of the slag during the oxidation refining process from the viewpoint of promoting the dephosphorization reaction.

With respect to such a problem, for example, in Patent Document 1, _{a substance containing at least one of SiO 2} , Al ₂ O ₃ , FeO, Fe ₂ O ₃ , and P ₂ O ₅ in steelmaking slag (hereinafter also referred to as “modifier”). A method of reforming slag by heat-treating for 10 minutes or less at a temperature equal to or higher than the melting temperature after the addition of ) added thereto.

Japanese Patent No. 4571818

By the way, in the method described in Patent Document 1, when reforming slag in a converter, the modifier is added in a state in which only the slag is accommodated in the converter, or the slag is added after the modifier is put in an empty converter. For this reason, in the method described in patent document 1, since it was necessary to provide the process accompanying reforming separately from a series of operation processes which perform an oxidative refining process, it was a problem that production efficiency fell.

Therefore, the present invention has been made in view of the above problems, and aims to provide a method for manufacturing steel and a method for reducing the basicity of slag, which can reduce the basicity of slag and suppress a decrease in production efficiency, have.

According to one embodiment of the present invention, there is provided a method for manufacturing molten steel by subjecting molten iron to oxidation refining treatment in a converter, wherein, in the converter, an oxygen source containing at least oxygen gas is added to the molten iron to undergo oxidation refining treatment. By carrying out the refining treatment step of turning the molten iron into the molten steel, and after the refining treatment step, the molten steel accommodated in the furnace of the converter is added with a silica-containing substance containing _{at least SiO 2 added.} The manufacturing method of steel provided with a process and the steel tapping process of discharging the said molten steel from the said furnace by tilting the said furnace body after the said addition process is provided.

According to one embodiment of the present invention, there is provided a method for reducing the basicity of slag, wherein the basicity of the slag generated when manufacturing molten steel is reduced by subjecting the molten iron to oxidation refining in a converter, wherein in the converter, at least oxygen is present in the molten iron. _{At least SiO 2} is contained in the molten steel accommodated in the furnace of the converter after the refining treatment step of turning the molten iron into the molten steel by adding an oxygen source containing a gas and performing an oxidation refining treatment, and after the refining treatment step A method for reducing the basicity of slag is provided, comprising: an addition step of adding a silica-containing material to be added; and a steel taping step of discharging the molten steel from the furnace body by tilting the furnace body after the addition step.

ADVANTAGE OF THE INVENTION According to one Embodiment of this invention, the basicity of slag can be reduced, and the manufacturing method of steel which can suppress the fall of productive efficiency, and the basicity reduction method of slag are provided.

ADVANTAGE OF THE INVENTION According to one Embodiment of this invention, the basicity of slag can be reduced, and the manufacturing method of steel which can suppress the fall of productive efficiency, and the basicity reduction method of slag are provided.

BRIEF DESCRIPTION OF THE DRAWINGS It is a schematic diagram which shows the facility structure of a converter.
It is a graph which shows the relationship between the calculated basicity and actual basicity in an Example and a comparative example.

(Form for implementing the invention)

DETAILED DESCRIPTION In the following detailed description, numerous specific details are set forth by way of illustration of an embodiment of the present invention, in order to provide a thorough understanding of the present invention. However, it is clear that one or more embodiments can be implemented without such specific detailed description. In addition, in the drawings, well-known structures and devices are schematically shown for the sake of brevity.

<Method for manufacturing steel>

With reference to FIG. 1, the manufacturing method of the steel which concerns on one Embodiment of this invention is demonstrated. In this embodiment, molten steel is manufactured from molten iron|metal by carrying out an oxidation refining process of the molten iron 6 using the converter 1 of a top-bottom blow type. As shown in FIG. 1, the converter 1 is equipped with the furnace body 2, the some low odor tuyeres 3, the top blowing lance 4, and the chute 5.

The furnace body 2 is a refining container in which the refractory material was constructed inside. The furnace body 2 has the opening part called the furnace tool 21 in the upper part in the state shown in FIG. Moreover, the furnace body 2 is comprised centering on a pair of trunnion shafts 22 formed in the side surface so that it can tilt.

The some low odor tuyere 3 is a tuyere of a double pipe formed in the bottom of the furnace body 2 . The plurality of low odor vents 3 are configured to blow at least oxygen gas from the inner tube and hydrocarbon gas from the outer tube to the inside of the furnace 2 , respectively.

The upper blowing lance 4 is a lance comprised so that insertion into the inside of the furnace body 2 is possible through the furnace tool 21 from above the furnace body 2 . The upper blowing lance 4 is comprised so that oxygen gas can be injected at least from the lance hole formed in the front-end|tip of the lower side.

The chute 5 is an apparatus formed above the furnace body 2 . As for the chute 5, the front-end|tip is arrange|positioned toward the tool 21. The chute 5 conveys auxiliary materials, such as a scouring agent and a raw material, cut out from a hopper (not shown), and injects|throws-in to the inside of the furnace body 2 .

In the manufacturing method of steel which concerns on this embodiment, molten steel is manufactured by accommodating the molten iron|metal tapped from a blast furnace in the furnace body 2, and carrying out an oxidation refining process. Hereinafter, molten iron and molten steel are collectively referred to as molten iron 6 . As for the molten iron|metal by which an oxidation refining process is carried out, a desiliconization process, a dephosphorization process, and molten iron|metal preliminary|backup process like a desulfurization process may be previously performed by another refinery facility.

In this embodiment, first, after charging the molten iron 6 which is molten iron into the furnace body 2, oxygen gas and hydrocarbon gas are blown into the molten iron 6 from the some low odor tuyeres 3, and the upper blow lance 4 By injecting oxygen gas to the molten iron 6 from the molten iron 6, a refining treatment step of performing an oxidation refining treatment is performed. Oxidation refining process is a process which adds an oxygen source to molten iron|metal, and oxidizes and removes impurity components, such as carbon and phosphorus, in molten iron|metal. In this embodiment, the decarburization reaction in which carbon in the molten iron 6 is removed at least and the dephosphorization reaction in which the phosphorus in the molten iron 6 is removed by oxidation refining process advances. In addition, below, the addition to the molten iron 6 of the oxygen gas (oxygen source) by the blowing of the oxygen gas from the some low odor tuyeres 3 and the injection of the oxygen gas from the upper blow lance 4 is also called blow tempering. do.

In the refining treatment step, as the decarburization reaction proceeds, carbon in the molten iron 6 is oxidized and removed, and molten steel with a low carbon concentration is manufactured. In addition, in the refining process, in order to accelerate|stimulate a dephosphorization reaction, auxiliary materials, such as a raw material, are injected|thrown-in to the inside of the furnace 2 . At this time, a plurality of types of auxiliary agents having different component compositions are each added in an amount corresponding to the target slag composition. Supplementary materials such as crude materials are determined in advance according to various blow tempering conditions such as the component and temperature of the molten iron 6 before oxidation refining treatment, the target component and target temperature of the molten iron 6 after the oxidation refining treatment, and the efficiency of the refining reaction. As a result, the determined input amount is inputted at the beginning of the oxidation refining treatment. Further, as a in the composition of the slag, non ((% CaO) / (% SiO 2)) of the CaO concentration (mass%) of the SiO ₂ concentration (mass%) Basicity. In addition, the estimated basicity of the slag after the oxidation refining treatment, which is calculated in advance before the oxidation refining treatment, depending on the mass balance of the charged auxiliary materials, the components of the molten iron 6, and the predetermined amount of the oxygen source, is also called the calculated basicity. When smelting a general steel type, in the converter 1 of a top-bottom blow type, calculated basicity becomes 4.0 or more normally. In a refining treatment process, the oxidation refining process is complete|finished by throwing-in of an auxiliary material, and a blow tempering process being performed, and the component and temperature of the molten iron 6 becoming a target thing.

After the refining treatment step, an addition step of adding a silica-containing substance containing _{at least SiO 2} through the chute 5 to the molten iron 6 which is the molten steel accommodated in the furnace 2 is performed.

Although the operation order of the addition process is not specifically prescribed|regulated, since melting|fusing of a silica-containing substance is accelerated|stimulated when the following operation procedure is taken, it is preferable.

In the case of a top blow or top blow type converter in which the converter 1 is a converter with a top blow lance, after the refining process, during the period of raising the top blow lance to the standby position while spraying oxygen gas to prevent nozzle clogging, Addition of the silica-containing material may be initiated. In this case, when a necessary refining operation is complete|finished, an operator (operator) operates an operation panel and sends a refining end instruction|command. And immediately after sending this command, the required amount of a silica containing material is cut out from a bunker into a hopper, and operation which opens the gate of a hopper is performed. When this operation is performed, after the top blowing lance starts rising to the standby position, the silica-containing material is added on the molten steel bath surface in the furnace through the chute. Although the flow rate of the upper blow lance is low compared to the time of oxidation refining in order to avoid nozzle clogging, the injection of oxygen continues during ascent. At this time, the molten steel is stirred by the injected oxygen gas (stirring effect). In addition, the molten steel is oxidized by the injected oxygen gas, and FeO is generated, thereby promoting the reification of the slag (refining effect). For this reason, the melting of the silica-containing material is accelerated by the stirring effect and the material effect by the oxygen gas. In addition, in order to advance the timing of addition and the start of furnace hardening (steeling), the silica-containing material of the scheduled addition amount is cut out from the bunker at the end of the refining process, stored in a hopper in a state where it can be added, and the refining end instruction is issued. You may perform the operation which opens the gate of a hopper immediately after sending.

In addition, in the case of a converter of a top-bottom odor type or a low-odor type converter, wherein the converter is a converter having a low odor tuyere, after the refining treatment process, the blowing condition of the low odor gas blown from the low odor tuyere is switched to the condition when the furnace body is tilted A silica-containing substance may be added to the molten steel during the period until the furnace starts to tilt. In this case, immediately after the operator operates the operation panel and sends a refining end command, the required amount of the silica-containing material is cut out from the bunker into the hopper, and the gate of the hopper is opened. When a refining end command is sent, in a top-bottom or low-odor converter capable of reducing odors such as oxygen gas, inert gas, mixed gas of oxygen gas and inert gas, etc., the blowing condition of the low-odor gas blown from the low odor tuyere is the refining treatment process. It switches from the conditions at the time of making a furnace body incline in the steel tapping process mentioned later. Specifically, under the blowing conditions when the furnace body is tilted and tapped, the type of low odor gas is switched to an inert gas, and the flow rate of the low odor gas is set at a flow rate low enough to prevent clogging of the low odor tuyeres during tapping. The silica-containing material is added on the molten steel bath surface in the furnace through the chute 5 from the hopper during the period from immediately after the blowing condition of the low odor gas is switched to that when the furnace body is tilted until the furnace body starts tilting. do. In addition, it is preferable that the furnace body be in an upright state while the silica-containing material is being added. According to such an operation procedure, the melting of the silica-containing substance is accelerated by the stirring effect of the molten steel by the low odor gas. In addition, in order to advance the timing of addition and the timing of starting tilting (steeling) of the furnace body, the silica-containing material of the scheduled addition amount is cut from the bunker at the end of the refining process and stored in a hopper in a state where it can be added. You may perform only the operation which opens the gate of a hopper immediately after sending an end instruction|command.

The silica-containing substance may be any as long as it contains _{SiO 2} , but it is preferable that _{most of the components are SiO 2} , and it is preferable that the content of _{SiO 2 is more.} For example, as the silica-containing material, silica _{stone mainly containing SiO 2} can be used. Further, as a silica-containing material, to use in that it contains the first of jojae, mainly SiO ₂ to be used in the polishing process step, it is preferable in view of limitations in storage facilities of the hopper or the like. In addition, it is preferable to use silica stone also from this viewpoint at the point which is generally used as a forming agent. Moreover, in this embodiment, as an example, when using a silica stone as a silica-containing material, the particle diameter of a silica stone is 5 mm or more and 40 mm or less. The smaller the particle size of the silica-containing substance, the easier it is to melt. However, when the particle size of the silica-containing material is too small, there is a possibility of causing a drop in the input yield due to scattering. In addition, in the case of using a fine-powdered silica-containing substance by air transport, there is a possibility that a sufficient input amount cannot be ensured in the case of continuous processing due to restrictions of storage facilities and conveyance facilities. On the other hand, when the particle diameter of the silica-containing material is large, the above problem in the case of a small particle diameter does not occur, but there is a possibility that the injected silica-containing material is not sufficiently melted. For this reason, it is preferable that the particle diameter of a silica-containing substance shall be 5 mm or more and 40 mm or less.

In the addition process, the input amount of the silica-containing substance is determined according to the calculated basicity after the refining treatment process of the slag 7 and the target basicity set from the water immersion expansion rate of the slag. Specifically, from the calculated basicity after the refining treatment process of the slag 7 and the estimated slag amount, the amount of SiO ₂ required for the slag 7 to reach the target basicity is obtained, and the amount of the silica-containing material for _{this SiO 2 amount is} becomes the input. The water immersion expansion rate of slag is a value determined by the content of F.CaO (Free-CaO) in the slag, and increases as the basicity of the slag increases. In the case of slag used for a road bed material, the JIS determines that the water immersion expansion rate is 1.5% or less, and in this embodiment, as a stricter standard, the slag water immersion expansion rate is set to 0.5% or less. In order to satisfy the water immersion expansion rate of 0.5%, in the case of a top-bottom blower type converter as in the present embodiment, the target basicity is preferably less than 3.8, and more preferably 3.6 or less. By setting the target basicity, that is, the calculated basicity of the slag after adding the silica-containing material to less than 3.8, preferably 3.6 or less, the F.CaO content in the slag can be sufficiently reduced, and the water immersion expansion rate ≤0.5%. can In addition, in an addition process, it is preferable that target basicity shall be 3.0 or more. When the target basicity, that is, the calculated basicity of the slag 7 after addition of the silica-containing material is less than 3.0, the phosphorus distribution ratio of the slag decreases and the phosphorus concentration of the molten steel increases by returning phosphorus in the slag to the molten steel. This is likely to occur. For this reason, in a steel grade with strict upper limit of phosphorus concentration, it may become a problem.

In addition, in the addition step, it is determined whether the calculated basicity of the slag 7 after the refining step is 3.8 or more, and the silica-containing substance may be added only when the calculated basicity of the slag 7 after the refining step is 3.8 or more. In this case, when the calculated basicity of the slag 7 after the refining process is less than 3.8, the addition of the silica-containing substance is not performed, but the steel tapping process mentioned later is performed.

The silica-containing substance added in the addition step is added to the slag 7 floating above the molten iron 6 by being fed from the chute 5 into the high-temperature furnace 2 . Then, the injected silica-containing material is melted by the high-temperature molten iron 6 or slag 7 and becomes a part of the molten slag 7 .

After the addition step, a steel tapping step of inclining the furnace body 2 to discharge the molten iron 6 from the furnace body 2 is performed. In the steel tapping step, the furnace body 2 is tilted centering on the pair of trunnion shafts 22 , and the molten iron 6 is discharged from a tapping hole (not shown) formed in the side wall portion of the furnace body 2 . The discharged molten iron 6 is accommodated in a ladle (not shown) disposed below the furnace body 2 and sent to the next step. In the steel tapping step, the molten iron 6 and the slag 7 flow inside the furnace 2 due to the inclining of the furnace body 2, so that the melting of the silica-containing material introduced in the addition step is further accelerated.

After the steel tapping step, the slag 7 remains in the furnace 2 . And the slag 7 remaining in the furnace 2 is discharged|emitted downward from the furnace 21 when the furnace 2 is inclining to the opposite side to a steel tapping process. The discharged slag 7 is recovered with a slag ladle disposed below the furnace body 2, and thereafter, it is reused through appropriate treatment such as aging treatment and self-bearing treatment.

The molten iron 6 accommodated in a ladle (not shown) through a steel tapping process is subjected to secondary refining appropriately according to the target component composition of the steel type to be manufactured, and then cast with a casting equipment such as a continuous casting machine, be on the side The obtained slab is rolled or heat-treated so that the dimensional shape, characteristics, etc. may satisfy the specifications of the shipped product, and it becomes the steel of the product.

<Modified example>

As mentioned above, although this invention was demonstrated with reference to specific embodiment, it is not intended that it limits invention by these description. Other embodiments of the present invention including various modifications along with the disclosed embodiments are also apparent to those skilled in the art by referring to the description of the present invention. Therefore, it should be understood that the embodiments of the invention described in the claims also encompass the embodiments including these modifications described in this specification alone or in combination.

For example, in the said embodiment, although the converter 1 was a top-bottom blow-type converter, this invention is not limited to this example. For example, the converter 1 may be the converter of the top blow type which injects oxygen gas only from the top blowing lance 4, and the converter of the low odor type which injects oxygen gas only from the bottom blowing tuyere 3 may be sufficient as it. In addition, when the converter 1 is a top-bottom odor converter, a converter capable of odor-saving only of an inert gas may be used in addition to the converter capable of storing oxygen gas as in the above embodiment. In the converter 1, a lance hole different from the oxygen gas is formed in the upper blowing lance 4, and auxiliary materials such as lime along with the carrier gas from this lance hole can be sprayed (projected) onto the molten iron 6 (projection). good.

In addition, in the said embodiment, although it was said that it is good to make target basicity into less than 3.8, More preferably, it is 3.6 or less, this invention is not limited to this example. In addition, in the addition step, it is said that it may be judged whether or not the addition of the silica-containing material is performed in the addition step from the judgment result of whether the calculated basicity of the slag 7 after the refining step is 3.8 or more, but the present invention is in this example not limited The above target basicity and threshold values are suitable for achieving a water immersion expansion rate of 0.5% or less in a top-bottom blowing type or low blowing type converter, which is a blow blowing type converter type refining type in which oxygen gas is blown from at least a plurality of low odor tufts. . That is, the target basicity or the threshold value can be changed according to the target water immersion expansion rate or the difference in the blow temper form of the converter.

In addition, in the said embodiment, although the oxidation refining process is performed by adding oxygen gas as an oxygen source, this invention is not limited to this example. For example, as the oxygen source, a solid oxygen source such as iron oxide other than oxygen gas may be further used.

<Effect of embodiment>

(1) A method for manufacturing steel according to an embodiment of the present invention is a method for manufacturing molten steel by subjecting molten iron to oxidation refining in a converter 1, wherein, in the converter 1, at least oxygen gas is supplied to the molten iron. _{At least SiO 2} is contained in the furnace body 2 of the converter 1 in which the molten steel is accommodated after the refining treatment step of turning the molten iron into molten steel and the refining treatment step by adding an oxygen source containing An addition step of adding the silica-containing substance to be used from above, and a steel taping step of inclining the furnace body 2 and discharging molten steel from the furnace body 2 after the addition step.

According to the structure of said (1), since the silica-containing substance is added in the state that the high temperature molten steel which is molten iron 6 is accommodated in the inside of the furnace 2, a silica-containing substance becomes easy to melt|dissolve. Further, in the steel tapping step, molten iron 6 and slag 7 flow inside the furnace 2 due to the inclination of the furnace body 2 , so that the silica-containing material is more accelerated. For this reason, the added silica-containing substance can fully be melt|dissolved, and the basicity of the slag 7 can be reduced precisely. Moreover, in the structure of said (1), since a silica-containing substance becomes easy to melt|dissolve, a silica-containing substance of a larger particle diameter can be used. Thereby, production efficiency can be improved and manufacturing cost can also be reduced.

Moreover, in the structure of said (1), in a refining process process, it is not necessary to make basicity of the slag 7 low. When the basicity of the slag 7 becomes low in a refining process process, foaming of the slag 7 may generate|occur|produce. When the slag 7 is ejected from the furnace body 2 by foaming, a decrease in yield or a dent of a slag pot railway line below the furnace is caused, and stable operation cannot be performed. On the other hand, in the structure of said (1), the generation frequency of the foaming of the slag 7 is suppressed, and stable operation can be performed. In addition, when the basicity of the slag 7 becomes low in the refining treatment process, since the phosphorus distribution ratio of the slag 7 decreases, dephosphorization cannot be sufficiently performed, or a raw material containing CaO to increase the amount of the slag 7 In some cases, the input amount of the agent increases. In contrast, in the configuration of (1), the period during which the basicity of the slag 7 decreases is short between the addition step and the steel taping step, and the amount of phosphorus associated with the decrease in the phosphorus distribution ratio is very small. In this respect, the influence by the fall of the phosphorus distribution ratio can be suppressed to a minimum, and manufacturing cost can be reduced more. Moreover, since the influence on the component composition of the molten iron 6 on the component composition of the molten iron 6 is so small that the quantity of a blessing is very small, product characteristics, etc. become conventional steel.

(2) In the structure of said (1), the converter 1 has the low odor tuyeres 3 formed in the bottom of the furnace 2, and in a refining process process, as oxygen gas contained in an oxygen source, at least low odor Oxidation refining is performed by blowing oxygen gas into molten iron|metal from the tuyeres 3 .

According to the configuration of the above (2), even in the low odor type or top odor type converter, in which it is difficult to lower the basicity of the slag compared to the top blow type converter from the difference in the blow blow type, the basicity of the slag can be reduced, It can promote the reuse of slag.

(3) In the configuration of (1) or (2) above, the converter 1 has the upper blowing lance 4, and in the addition step, after the refining treatment step, while spraying oxygen gas to prevent clogging of the nozzle. During the period of raising the upper blow lance 4 to the standby position, the addition of the silica-containing material to the molten steel is started.

According to the configuration of (3) above, the melting of the silica-containing material is accelerated by the stirring effect and the material effect by the oxygen gas being injected.

(4) The structure in any one of said (1)-(3) WHEREIN: The converter 1 has the low odor tuyere 3 formed in the bottom of the furnace 2, and, in an addition process, after a refining process process. , Silica-containing in molten steel during the period from when the blowing condition of the low odor gas blown in from the low odor tuyere 3 is switched to the condition at the time of tilting the furnace body 2 and until starting the tilting of the furnace body 2 Add substances.

According to the structure of said (4), also in an addition process, molten steel is stirred by the low-odor gas blown in from the low-odor gas, and melting|dissolution of a silica-containing substance is accelerated|stimulated.

(5) The structure of any one of said (1)-(4) WHEREIN: In an addition process, when the calculated basicity of the slag 7 in the furnace 2 after a refining process process becomes 3.8 or more, slag 7 ), determine the amount of the silica-containing material so that the calculated basicity is 3.6 or less.

According to the structure of said (5), in the converter 1 of the structure of said (2), the water immersion expansion rate of the slag 7 can be made into 0.5 % or less.

(6) In the configuration according to any one of (1) to (5) above, in the addition step, the amount of the silica-containing substance is determined so that the calculated basicity of the slag 7 in the furnace 2 is 3.0 or more.

According to the structure of said (6), the quantity of a blessing can fully be suppressed and manufacturing cost can be reduced more.

(7) The method for reducing the basicity of slag according to an embodiment of the present invention is to reduce the basicity of slag 7 generated when manufacturing molten steel by subjecting molten iron to oxidation refining treatment in a converter 1, slag As the basicity reduction method of (7), in the converter 1, by adding an oxygen source containing at least oxygen gas to the molten iron and performing oxidation refining treatment, the refining treatment step of turning the molten iron into molten steel, and after the refining treatment step _{, An addition step of adding a silica-containing material containing at least SiO 2} to the molten steel accommodated in the furnace 2 of the converter 1, and after the addition step, the furnace 2 is tilted to discharge the molten steel from the furnace body process is provided.

According to the structure of said (7), the same effect as said (1) can be acquired.

(8) In the configuration of the above (7), the converter 1 has the top blowing lance 4, and in the addition step, after the refining treatment step, while spraying oxygen gas to prevent clogging of the nozzle, the top blowing lance 4 ) to the standby position, the addition of the silica-containing material to the molten steel is started.

According to the structure of said (8), the effect similar to the structure of said (3) is acquired.

(9) The structure of said (7) or (8) WHEREIN: The converter 1 has the low odor tuyeres 3 formed in the bottom part of the furnace 2, and in an addition process, after a refining process process, a low odor tuyeres. A silica-containing substance is added to the molten steel during the period from when the blowing condition of the low odor gas blown in from (3) is switched to the condition when the furnace body 2 is tilted and until the furnace body 2 starts tilting. do.

According to the structure of said (9), the effect similar to the structure of said (4) is acquired.

Example

Examples of the present inventors will be described. In the Example, the molten iron 6 was refined in the converter 1 using the manufacturing method of steel similar to the said embodiment, and the basicity of slag was reduced. Specifically, in an Example, molten steel was manufactured by performing an oxidation refining process to molten iron|metal with the converter 1 of a top-bottom blow type in a refining process process. In the refining treatment step, the oxidation refining treatment of the molten iron 6 was performed on the condition that the calculated basicity was set to 4 or more. Next, in the addition step, the target basicity was set to 3.6 (Example 1) or 3.2 (Example 2), and silica was added as a silica-containing substance. In addition, in the steel tapping step, when discharging the molten iron 6 from the furnace 2 , the slag 7 in the furnace 2 is collected and the CaO concentration and the SiO ₂ concentration are measured to measure the basicity (also referred to as “actual basicity”). ) was measured.

In addition, in the Example, as a comparison, steel was manufactured by the conventional method of performing a steel tapping process without performing an addition process after a refining process (comparative example). Also in the comparative example, similarly to the Example, the slag 7 was extract|collected in the steel tapping process, and the actual basicity was measured. In the comparative example, the actual basicity was measured under a plurality of conditions (Comparative Examples 1-4) from which the calculated basicity differs, and the relationship between the calculated basicity and the actual basicity was investigated.

In FIG. 2, the relationship between calculated basicity and actual basicity in an Example and a comparative example is shown. In the plot of the comparative example shown in FIG. 2 , Comparative Example 1 had a calculated basicity of 3.49 or less (N (number of samples) = 42), Comparative Example 2 had a calculated basicity of 3.50 or more and 3.99 or less (N = 182), and Comparative Example 3 had The calculated basicity is 4.00 or more and 4.49 or less (N=467), and Comparative Example 4 shows the conditions under which the calculated basicity is 4.50 or more (N=722), respectively. In addition, in FIG. 2 , a plot represents an average value of a plurality of data, and a bar extending vertically and horizontally represents a standard deviation (σ). As shown in FIG. 2, the basicity of the conventional slag shown in Comparative Examples 1-4 has confirmed that the actual basicity shows a correlation with respect to the calculated basicity. Here, calculation basicity is calculated from the mass balance in blow tempering conditions anticipated in advance, such as the quantity of the input amount of the component of molten iron|metal, various auxiliary materials, and oxygen gas in an oxidation refining process, and oxygen gas. For this reason, from factors such as actual reaction efficiency, the actual basicity tends to decrease by a certain amount with respect to the calculated basicity.

In addition, as shown in Fig. 2, in Example 1 (N=423) in which the target basicity was 3.6 and Example 2 (N=36) in which the target basicity was 3.2, the actual basicity was sufficiently low with respect to the target basicity. It could be confirmed that the slag was lost, and it was confirmed that the added silica-containing material was dissolved in the slag.

In addition, in the Example, about the slag 7 processed similarly to the said Example 1, after being discharged|emitted from the furnace 2 and collect|recovering, the basicity analysis and water immersion expansion rate were measured. Basicity is subjected to the fluorescent X-ray analysis of the sample for analysis of the slag (7), the amount of CaO concentration (mass%) and SiO ₂ concentration (mass%), and was determined from their ratio. The measurement of the water immersion expansion rate was performed based on Japanese Industrial Standards JISA5015 Annex B. As a result, it was confirmed that the basicity of the slag was 2.7 and the water immersion expansion rate was 0.5% or less. On the other hand, basicity analysis and water immersion expansion rate were measured after recovery for slag having a calculated basicity of 4.0 or more, treated in the same manner as in Comparative Example. At this time, analysis and measurement were performed in the same way as in the above-mentioned Example. As a result, the basicity of the slag was 3.5, the water immersion expansion rate was 1.5% or more, and it was confirmed that the target quality could not be satisfied.

1: converter
2: Roche
21 : Rogu
22: trunnion shaft
3: low odor vent
4: Sangche Lance
5: suit
6: molten iron
7: slag

Claims (9)

A method for manufacturing molten steel by subjecting molten iron to oxidation refining in a converter, comprising:
a refining treatment step of turning the molten iron into the molten steel by adding an oxygen source containing at least oxygen gas to the molten iron in the converter and performing an oxidation refining treatment;
an addition step of adding a silica-containing material containing _{at least SiO 2} to the molten steel accommodated in a furnace of the converter after the refining step;
The manufacturing method of steel provided with the steel taping process of inclining the said furnace body and discharging the said molten steel from the said furnace body after the said addition process. According to claim 1,
The converter has a low odor tuyere formed at the bottom of the furnace body,
At the said refining process process, the said oxidation refining process is performed by blowing in oxygen gas into the said molten iron|metal from the said low odor tuyeres at least as said oxygen gas contained in the said oxygen source, The manufacturing method of steel. 3. The method of claim 1 or 2,
The converter has a top blowing lance,
In the addition step, after the refining treatment step, the addition of the silica-containing material to the molten steel is started during a period in which the top blowing lance is raised to a standby position while spraying the oxygen gas to prevent nozzle clogging. manufacturing method. 4. The method according to any one of claims 1 to 3,
The converter has a low odor tuyere formed at the bottom of the furnace body,
In the said addition process, after the said refining process process, after switching the blowing conditions of the low odor gas blown in from the said low odor tuyere to the conditions at the time of making the said furnace incline, during the period until starting the tilting of the said furnace body , adding the silica-containing material to the molten steel. 5. The method according to any one of claims 1 to 4,
In the addition step, when the calculated basicity of the slag in the furnace after the refining treatment step is 3.8 or more, the amount of the silica-containing material is determined so that the calculated basicity of the slag is 3.6 or less. 6. The method according to any one of claims 1 to 5,
In the addition step, the amount of the silica-containing substance is determined so that the calculated basicity of the slag in the furnace is 3.0 or more. As a method for reducing the basicity of slag, which reduces the basicity of slag generated when manufacturing molten steel by subjecting molten iron to oxidation refining in a converter,
a refining treatment step of turning the molten iron into the molten steel by adding an oxygen source containing at least oxygen gas to the molten iron in the converter and performing an oxidation refining treatment;
an addition step of adding a silica-containing material containing _{at least SiO 2} to the molten steel accommodated in the furnace body of the converter after the refining treatment step;
A method for reducing basicity of slag, comprising: a steel tapping step of inclining the furnace body and discharging the molten steel from the furnace body after the addition step. 8. The method of claim 7,
The converter has a top blowing lance,
In the addition step, after the refining treatment step, the addition of the silica-containing material to the molten steel is started during a period during which the top blowing lance is raised to a standby position while spraying the oxygen gas to prevent nozzle clogging. method for reducing the basicity of 9. The method of claim 7 or 8,
The converter has a low odor tuyere formed at the bottom of the furnace body,
In the said addition process, after the said refining process process, after switching the blowing conditions of the low odor gas blown in from the said low odor tuyere to the conditions at the time of making the said furnace incline, during the period until starting the tilting of the said furnace body , A method for reducing the basicity of slag by adding the silica-containing material to the molten steel.

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