TW202020166A - Steel production method and method for reducing slag basicity - Google Patents

Abstract

Provided are a steel production method and a method for reducing slag basicity that are capable of reducing slag basicity and preventing reductions in production efficiency. The present invention pertains to a steel production method in which molten steel is produced by oxidatively refining molten iron in a converter (1), the method comprising: a refining process step of adding an oxygen source that includes at least oxygen gas to the molten iron in the converter (1) and performing an oxidative refining process to convert the molten iron to molten steel; an addition step, following the refining process step, of adding a silica-containing material containing at least SiO2 from above into a vessel (2) of the converter (1) accommodating the molten steel; and a tapping step, following the addition step, of tilting the vessel (2) to discharge the molten steel from the vessel (2).

Description

Steel manufacturing method and slag salt base reduction method

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

In the steelmaking step of the ironworks, oxidation refining treatment (decarburization treatment) is performed, that is, molten steel (molten steel) is manufactured by adding oxygen sources such as oxygen to the molten metal (hot metal) using a converter. In this oxidation refining process, slag is generated by the oxidation reaction of the added by-products or impurity components in the molten metal. After being recovered, the slag is reused as a raw material for various purposes.

One of the uses of slag produced in converters is roadbed materials. When slag is used as a roadbed material, the immersion swelling rate must meet the quality standards prescribed by standards such as Japanese Industrial Standards (JIS). For example, JIS standards must be 1.5% or less. In order to reduce the slag water swelling rate, it is necessary to reduce the amount of free lime in the slag, and it is important to reduce the basicity of the slag (SiO ₂ content relative to the slag CaO content ratio ((%CaO)/(%SiO ₂ ) )).

However, in the oxidation refining treatment in the converter, if the basicity of the slag is reduced, foaming of the slag is likely to occur due to CO gas generated during the treatment, and the dephosphorization efficiency is also reduced. Therefore, a decrease in the basicity of the slag from the oxidation refining process becomes a cause of work failure, which lowers the production efficiency. In addition, in the oxidation refining process in the converter, usually at the beginning of the oxidation refining process, each of the auxiliary materials such as silica and lime is added, and the auxiliary raw materials are only in accordance with the target composition or target temperature of the molten iron after the oxidation refining process, Refining reaction efficiency and other blowing conditions determine the corresponding amount of target slag composition. However, from the viewpoint of promoting the dephosphorization reaction and the like, it is difficult to reduce the basicity of the slag in the oxidation refining process.

In response to the above-mentioned problems, for example, Patent Document 1 discloses a method of adding the following substances to steel-making slag, the substance added to SiO ₂ , Al ₂ O ₃ , FeO, Fe ₂ O ₃ , and P ₂ O ₅ One or more substances (hereinafter also referred to as "improvers"), and then heat treatment at a temperature above the melting temperature for 10 minutes or less, thereby improving the slag. [Prior Art Literature] [Patent Literature]

Patent Document 1: Japanese Patent No. 4571818

[Problems to be solved by the invention]

In addition, in the method described in Patent Document 1, when the converter is used to improve the slag, the modifier is added in a state where the converter contains only the slag, or the slag is added after the modifier is put in the empty converter. Therefore, in the method described in Patent Document 1, unlike the series of work processes for performing the oxidation refining process, it is necessary to provide a process accompanying the improvement, so that the reduction in production efficiency becomes a problem.

Therefore, the present invention has been developed focusing on the above-mentioned problems, and an object thereof is to provide a method for manufacturing steel and a method for reducing the basicity of slag that can reduce the basicity of slag and can suppress a reduction in production efficiency. [Means to solve the problem]

According to one aspect of the present invention, there is provided a method of manufacturing steel, which uses a converter to perform an oxidative refining process on molten metal to produce molten steel. The method of manufacturing the steel includes a refining process step by using the Converter, adding an oxygen source containing at least oxygen to the molten metal to perform an oxidation refining process, thereby forming the molten metal into the molten steel; an adding step, after the refining process step, the The molten steel of the furnace body is added with a material containing silicon dioxide containing at least SiO ₂ ; and a tapping step, after the addition step, the furnace body is tilted to discharge the molten steel from the furnace body steel.

According to one aspect of the present invention, there is provided a method for reducing the basicity of slag, which reduces the basicity of slag generated when molten steel is manufactured by performing an oxidation refining process on molten metal by using a converter The method of reducing the salinity includes: a refining treatment step, by using the converter, adding an oxygen source containing at least oxygen to the molten metal to perform an oxidation refining treatment, thereby forming the molten metal into the molten steel; adding Step, after the refining treatment step, to the molten steel contained in the furnace body of the converter, add a material containing silicon dioxide containing at least SiO ₂ ; and a tapping step, after the adding step, The furnace body is tilted to discharge the molten steel from the furnace body.

According to one aspect of the present invention, there is provided a method for manufacturing steel and a method for reducing the basicity of slag that can reduce the basicity of slag and can suppress a decrease in production efficiency. [Effect of invention]

According to one aspect of the present invention, there is provided a method for manufacturing steel and a method for reducing the basicity of slag that can reduce the basicity of slag and can suppress a decrease in production efficiency.

In the following detailed description, in order to provide a complete understanding of the present invention, the embodiment of the present invention is exemplified to describe a plurality of specific details. However, it is clear that more than one implementation aspect can be implemented even without the description of the specific details. In addition, the drawings are simplified diagrams showing well-known structures and devices.

<Manufacturing method of steel> 1, a method of manufacturing steel according to an embodiment of the present invention will be described. In the present embodiment, the molten iron 6 is subjected to an oxidation refining process by using the bottom-blowing converter 1 to produce molten steel from molten metal. As shown in FIG. 1, the converter 1 includes a furnace body 2, a plurality of bottom blowing tuyere 3, a top blowing lance 4, and a chute 5. The furnace body 2 is a refining container to which a refractory material is applied. In the state shown in FIG. 1, the furnace body 2 has an opening called the furnace port 21 at the upper part. In addition, the furnace body 2 is configured to be tiltable about a pair of trunnions 22 provided on the side surfaces.

The plurality of bottom air outlets 3 are air outlets of double pipes provided at the bottom of the furnace body 2. The plurality of bottom air outlets 3 are configured to blow the inside of the furnace body 2 into at least oxygen from the inner tube and hydrocarbon gas from the outer tube. The top blowing nozzle 4 is a nozzle configured to be inserted into the furnace body 2 through the furnace opening 21 from above the furnace body 2. The top blowing nozzle 4 is configured so that at least oxygen can be ejected from the nozzle hole formed at the lower front end. The chute 5 is a device provided above the furnace body 2. The front end of the chute 5 is arranged toward the furnace port 21. The chute 5 conveys auxiliary raw materials such as refining agent and slag-forming agent cut from a hopper not shown, and puts them into the furnace body 2.

In the method of manufacturing steel according to the present embodiment, molten steel sent from the blast furnace is stored in the furnace body 2 and subjected to oxidation refining treatment to produce molten steel. In addition, hereinafter, the molten metal and molten steel are also collectively referred to as molten iron 6. The molten metal subjected to the oxidation refining treatment may also be subjected to pre-treatment of molten metal such as desiliconization treatment, dephosphorization treatment, and desulfurization treatment by other refining equipment.

In this embodiment, the following refining process step is first performed: after the molten iron 6 as molten metal is charged into the furnace body 2, oxygen and hydrocarbon gas are blown into the molten iron 6 from the plurality of bottom blow-off ports 3, and are blown from the top The nozzle 4 injects oxygen to the molten iron 6 to perform oxidation refining treatment. The oxidation refining process is a process of adding an oxygen source to the molten metal to oxidize and remove impurities such as carbon or phosphorus in the molten metal. In this embodiment, at least the decarburization reaction for removing carbon in molten iron 6 and the dephosphorization reaction for removing phosphorus in molten iron 6 are performed by oxidation refining treatment. In addition, hereinafter, the addition of oxygen (oxygen source) to the molten iron 6 by blowing oxygen from the plurality of bottom blow ports 3 and spraying oxygen from the top blowing nozzle 4 is also referred to as blowing.

In the refining treatment step, by performing a decarburization reaction, the carbon in the molten iron 6 is oxidized and removed, thereby producing molten steel having a low carbon concentration. In addition, in the refining treatment step, in order to promote the dephosphorization reaction, auxiliary raw materials such as slag-forming agent are introduced into the furnace body 2. At this time, only the amount corresponding to the target slag composition is added to the various slag-forming agents with different composition. The auxiliary raw materials such as slagging agent are determined in advance according to various blowing conditions such as the composition or temperature of the molten iron 6 before the oxidation refining process, the target composition or target temperature of the molten iron 6 after the oxidation refining process, and the efficiency of the refining reaction. The decided input amount is the initial input in the oxidation refining process. In addition, in the composition of the slag, the ratio ((%CaO)/(%SiO ₂ )) of the CaO concentration (mass%) to the SiO ₂ concentration (mass%) is called the basicity. In addition, the estimated basicity of the slag after the oxidation refining treatment calculated in advance before the oxidation refining treatment is based on the mass balance of the input auxiliary raw materials, the composition of the molten iron 6, the predetermined amount of oxygen source input, etc. Calculate the salinity. In the case of melting a general steel grade, in the converter 1 of the top-bottom blowing type, the calculated basicity is usually 4.0 or more. In the refining process step, the auxiliary raw materials are added, and then the blowing process is performed. The composition and temperature of the molten iron 6 become the target composition and temperature, whereby the oxidation refining process ends.

After the refining treatment step, the following addition step is performed: to the molten iron 6 that is molten steel housed in the furnace body 2, a material containing silicon dioxide containing at least SiO ₂ is added through the chute 5. The operation sequence of the addition step is not particularly specified, but if the following operation sequence is adopted, the melting of the silicon dioxide-containing substance is promoted, which is preferable.

In the case where the converter 1 is a converter with a top-blowing nozzle, that is, a top-blowing or top-bottom-blowing converter, after the refining step, the top-blowing nozzle may be raised while spraying oxygen to prevent nozzle clogging During the period up to the standby position, silicon dioxide-containing substances were added to the molten steel. In this case, when the necessary refining operation ends, the operator (operator) operates the operation panel and sends a refining end instruction. Then, immediately after sending this instruction, proceed as follows: Cut the necessary amount of silica-containing substance from the silo to the hopper, and open the door of the hopper. When this operation is performed, after the top blowing nozzle starts to rise to the standby position, the silicon dioxide-containing substance is added to the molten steel bath surface in the furnace through the chute. Although the top-blowing nozzle has a lower flow rate than the oxidation refining process in order to avoid nozzle clogging, it continues to inject oxygen during ascent. At this time, the molten steel is stirred by the blown oxygen (stirring effect). In addition, the molten oxygen is oxidized to generate FeO using the supplied oxygen, thereby promoting slag formation (slag formation effect). Therefore, by using the oxygen stirring effect and the slagging effect, the melting of the silica-containing material is promoted. In addition, in order to advance the timing of addition and the start of furnace tilting (tapping), the following operations can also be carried out: the addition of a predetermined amount of silicon dioxide-containing material is cut out of the silo at the end of the refining process step, so that The added state is stored in the hopper, and the door of the hopper is opened immediately after sending the refining instruction.

In addition, in the case where the converter is a converter having a bottom blowing port, that is, an upper bottom blowing type or a bottom blowing type converter, after the refining process step, the bottom blowing gas blown in from the bottom blowing port may also be blown in After the condition is switched to the condition when the furnace body is tilted, a substance containing silicon dioxide is added to the molten steel during the period until the furnace body starts to tilt. In this case, after the operator operates the operation panel and sends the refining end command, he immediately performs the following operations: cutting out the necessary amount of the silica-containing substance from the silo to the hopper, and opening the hopper door. If the refining end command is sent, in the bottom-blowing type or bottom-blowing type converter that can carry out bottom blowing of oxygen or inert gas, mixed gas of oxygen and inert gas, the bottom blowing gas is blown in from the bottom blowing port The blowing conditions are the conditions in the refining process step, and are switched to the conditions when the furnace body is tilted in the steel step described later. Specifically, under the blowing conditions when the furnace body is tilted and tapped out, the type of bottom blown gas is switched to inert gas, and the flow rate of the bottom blown gas is set so low that no blockage of the bottom blowing opening occurs during tapping Degree of flow. The material containing silicon dioxide is added into the furnace from the hopper through the chute 5 during the period immediately after the blowing conditions of the bottom blowing gas are switched to the blowing conditions when the furnace body is tilted until the furnace body starts to tilt Molten steel bath surface. In addition, during the addition of the silicon dioxide-containing substance, the furnace body is preferably in an upright state. If this kind of operation sequence is adopted, the melting of the material containing silicon dioxide is promoted by the stirring effect of the molten steel using the bottom blowing gas. In addition, in order to make the timing of the addition and the timing of the start of tilting (tapping) of the furnace body, only the following operation may be performed: the predetermined amount of the silicon dioxide-containing substance is cut from the silo at the end of the refining process step It is stored in the hopper in a state where it can be added, and the door of the hopper is opened immediately after sending the refining end command.

The silicon dioxide-containing substance may be any one that contains SiO ₂ , and it is preferable that most of the components are SiO ₂ , and it is more preferable that the SiO ₂ content is greater. For example, for the silica-containing substance, silica mainly containing SiO ₂ can be used. In addition, as the silica-containing substance, from the viewpoint of restrictions on storage equipment such as a hopper, it is preferable to use a substance mainly containing SiO ₂ in the slag-forming agent used in the refining process step. In addition, since silica is generally used as a slag-forming agent, from this viewpoint, it is also preferable to use silica. Furthermore, in this embodiment, as an example, when silica is used as the silica-containing substance, the particle diameter of silica is set to 5 mm or more and 40 mm or less. Substances containing silicon dioxide have a smaller particle size and are easier to melt. However, if the particle size of the silicon dioxide-containing substance is too small, there is a possibility that the input yield will decrease due to scattering. In addition, when a fine powdered silicon dioxide-containing substance is used for air delivery, there is a possibility that a sufficient input amount cannot be ensured in the case of continuous processing due to restrictions of storage facilities or conveyance facilities. On the other hand, when the particle size of the silicon dioxide-containing substance is large, although the above-mentioned problem does not occur when the particle size is small, there is a case that the input silicon dioxide-containing substance does not sufficiently melt possibility. Therefore, the particle size of the silicon dioxide-containing substance is preferably 5 mm or more and 40 mm or less.

In the addition step, the input amount of the silicon dioxide-containing substance is determined based on the calculated salinity after the refining treatment step of the slag 7 and the target salinity set according to the slag water swelling rate. Specifically, the amount of SiO ₂ necessary for the slag 7 to reach the target degree of basic slag is obtained from the calculated basicity and the estimated amount of slag after the slag 7 refining process step, and the amount corresponding to the SiO ₂ amount The amount of silicon dioxide-containing substance becomes the input amount. The slag water swell rate is a value determined by the content of F.CaO (Free-CaO, free calcium oxide) in the slag. The higher the slag basicity, the greater the water swell rate. In the case of slag used for roadbed materials, it is determined in accordance with JIS such that the swell rate of water immersion becomes 1.5% or less. In this embodiment, as a stricter standard than this, the goal is to set the slag water swell rate as Below 0.5%. In order to satisfy the immersion swelling rate of 0.5%, in the case of a top-blown converter as in the present embodiment, the target salinity 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 content of F.CaO in the slag can be sufficiently reduced, which can be satisfied The standard of immersion swelling rate≦0.5%. In addition, in the addition step, the target basicity is preferably 3.0 or more. At the target basicity, that is, when the calculated basicity of the slag 7 after adding the silica-containing material becomes less than 3.0, the phosphorus distribution ratio of the slag decreases, and there is a phenomenon in which the phosphorus in the slag returns to the molten steel. Possibility of double phosphorus with increased phosphorus concentration in molten steel. Therefore, it may be a problem in steel grades where the upper limit of the phosphorus concentration is strict.

In addition, in the addition step, it can also be determined whether the calculated basicity of the slag 7 after the refining step is 3.8 or more, and only when the calculated basicity of the slag 7 after the refining step is 3.8 or more Substance. In this case, when the calculated basicity of the slag 7 after the refining step is less than 3.8, the steel-drawing step described later is performed without adding a substance containing silicon dioxide. The silicon dioxide-containing substance added in the addition step is added to the slag 7 floating above the molten iron 6 by being thrown into the high-temperature furnace body 2 from the chute 5. Then, the introduced silicon dioxide-containing substance 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, the tapping step of tilting the furnace body 2 and discharging the molten iron 6 from the furnace body 2 is performed. In the tapping step, the furnace body 2 is tilted with the pair of trunnions 22 as the center, and the molten iron 6 is discharged from the tap hole (not shown) provided in the side wall portion of the furnace body 2. The discharged molten iron 6 is housed in a ladle (not shown) arranged below the furnace body 2 and sent to the next step. In the tapping step, the molten iron 6 or slag 7 flows inside the furnace body 2 by tilting the furnace body 2, thereby further promoting the melting of the silicon dioxide-containing substance introduced in the addition step.

After the tapping step, slag 7 remains in the furnace body 2. Then, the slag 7 remaining in the furnace body 2 is tilted to the side opposite to the tapping step by the furnace body 2 and discharged downward from the furnace port 21. The discharged slag 7 is recovered to a slag ladle disposed under the furnace body 2 and then reused after appropriate treatment such as aging treatment or magnetic separation treatment. After the tapping step, the molten iron 6 stored in the ladle (not shown) is appropriately refined twice according to the target composition of the steel type to be manufactured, and then cast using casting equipment such as a continuous casting machine to become a slab. The obtained cast piece is rolled or heat-treated in order to satisfy the specifications of the product to be shipped, such as dimensions, shapes, and characteristics, to become the steel of the product.

<Modification> Although the present invention has been described above with reference to specific embodiments, it is not intended that these descriptions limit the invention. By referring to the description of the present invention, those skilled in the art will understand other embodiments of the present invention including various modifications together with the disclosed embodiments. Therefore, it should be understood that the embodiments of the invention described in the scope of the patent application also include embodiments in which these modified examples described in this specification are included alone or in combination.

For example, in the above-mentioned embodiment, the converter 1 is a top-bottom type converter, but the present invention is not limited to the examples. For example, the converter 1 may be a top-blowing converter that injects oxygen only from the top-blowing nozzle 4 or a bottom-blowing converter that injects oxygen only from the bottom blowing port 3. Furthermore, in the case where the converter 1 is a bottom-blowing type converter, in addition to the bottom-blown converter as in the above-described embodiment, the bottom-blown converter may be a bottom-blown converter. In addition, the converter 1 may be provided with another nozzle hole different from oxygen in the top blowing nozzle 4, and from this nozzle hole, auxiliary materials such as lime and the transport gas are sprayed (projected) on the molten iron 6 together.

In addition, in the above-mentioned embodiment, although the target salinity is preferably less than 3.8, and more preferably 3.6 or less, the present invention is not limited to the example. Furthermore, in the addition step, it is possible to determine whether to add a substance containing silicon dioxide in the addition step based on the judgment result of whether the calculated basicity of the slag 7 after the refining step is 3.8 or more, but the invention is not limited To the example. The target salinity and threshold value are suitable to achieve a reduction of 0.5% or less in a converter type refining in which the oxygen is blown from at least a plurality of bottom blowers, that is, a top-bottom type or bottom-blowing type converter. Water swelling rate. That is, the target salinity or threshold value can be changed according to the target water swell expansion rate or the difference in the blowing form of the converter. Furthermore, in the above embodiment, the oxidation refining treatment is performed by adding oxygen as an oxygen source, but the present invention is not limited to the above examples. For example, as the oxygen source, in addition to oxygen, a solid oxygen source such as iron oxide may be further used.

<Effects of the embodiment> (1) The method for manufacturing steel according to one aspect of the present invention manufactures molten steel by performing an oxidative refining process on molten metal using the converter 1, and the steel manufacturing method includes a refining process step by By using the converter 1, an oxygen source containing at least oxygen is added to the molten metal to perform an oxidative refining process to form the molten metal into molten steel; the addition step is to the furnace body 2 of the converter 1 containing the molten steel after the refining process step , Adding a silicon dioxide-containing substance containing at least SiO ₂ from above; and a tapping step, after the addition step, the furnace body 2 is tilted to discharge molten steel from the furnace body 2.

According to the configuration of (1), in the state where the high-temperature molten steel as the molten iron 6 is housed in the furnace body 2, the silicon dioxide-containing substance is added, so the silicon dioxide-containing substance is easily melted. In addition, in the tapping step, the molten iron 6 or slag 7 flows inside the furnace body 2 due to the tilting of the furnace body 2, thereby further promoting the melting of the material containing silicon dioxide. Therefore, the added silicon dioxide-containing substance can be sufficiently melted, and the basicity of the slag 7 can be reduced with high accuracy. In addition, in the configuration of (1) above, since the silica-containing substance is easily melted, a silica-containing substance with a larger particle size can be used. Thereby, production efficiency can be improved, and manufacturing costs can also be reduced.

In addition, in the configuration of the above (1), in the refining treatment step, it is not necessary to reduce the basicity of the slag 7. If the basicity of the slag 7 decreases in the refining process step, there is a possibility that the slag 7 foams. If the slag 7 is ejected from the furnace body 2 by foaming, the yield will drop or the slag barrel line under the furnace will sink, etc., and stable operation cannot be performed. In contrast, in the configuration of (1) above, the frequency of occurrence of foaming of the slag 7 is suppressed, and stable operation can be performed. Furthermore, if the basicity of the slag 7 decreases in the refining process, the phosphorus distribution ratio of the slag 7 decreases, so there is insufficient dephosphorization, or the input amount of the slag-forming agent containing CaO increases in order to increase the amount of the slag 7 Case. In contrast, in the configuration of (1) above, the period during which the basicity of the slag 7 decreases becomes a short period from the addition step to the tapping step, and as the phosphorus distribution ratio decreases, the amount of compound phosphorus also becomes Very little. Therefore, the influence caused by the decrease in the phosphorus distribution ratio can be minimized, and the manufacturing cost can be further reduced. In addition, since the amount of the compound phosphorus is extremely small, the influence on the composition of the molten iron 6 is negligibly small, so that it becomes a steel with normal product characteristics and the like.

(2) In the configuration of (1) above, the converter 1 has a bottom blow port 3 provided at the bottom of the furnace body 2, and in the refining process step, as the oxygen contained in the oxygen source, at least from the bottom blow port 3 Oxygen is blown into the molten metal to perform oxidation refining treatment. According to the configuration of (2) above, in the case of bottom blowing type or top bottom blowing type converters, which are difficult to reduce the slag basicity compared to top blowing type converters in terms of the blowing form, it can also be reduced The basicity of slag can therefore promote the reuse of slag.

(3) In the configuration of (1) or (2) above, the converter 1 has a top-blowing nozzle 4, and in the addition step, after the refining treatment step, the top-blowing is performed while spraying oxygen to prevent nozzle clogging During the period until the tube 4 rises to the standby position, the silicon dioxide-containing substance is added to the molten steel. According to the configuration of the above (3), the stirring effect and the slagging effect by the blown oxygen are used to promote the melting of the silica-containing substance.

(4) In any of the above-mentioned configurations (1) to (3), the converter 1 has a bottom air outlet 3 provided at the bottom of the furnace body 2. In the addition step, after the refining treatment step, the bottom After switching the blowing conditions of the bottom blowing gas blown into the blow port 3 to the conditions when the furnace body 2 is tilted, a material containing silicon dioxide is added to the molten steel during the period until the furnace body 2 starts to tilt. According to the configuration of the above (4), in the addition step, the molten steel is stirred by the bottom blowing gas blown in from the bottom blowing gas to promote the melting of the material containing silicon dioxide.

(5) In any of the above-mentioned configurations (1) to (4), in the addition step, when the calculated basicity of the slag 7 in the furnace body 2 after the refining treatment step becomes 3.8 or more, the slag 7 Determine the input amount of silicon dioxide-containing substances in such a way that the calculated basicity becomes 3.6 or less. According to the configuration of the above (5), in the converter 1 of the configuration of the above (2), the water swell expansion ratio of the slag 7 can be set to 0.5% or less.

(6) In any of the above-mentioned configurations (1) to (5), in the adding step, the silica-containing silica is determined so that the calculated basicity of the slag 7 in the furnace body 2 becomes 3.0 or more The amount of input of the substance. According to the configuration of (6), the amount of compound phosphorus can be sufficiently suppressed, and the manufacturing cost can be further reduced.

(7) The method for reducing the basicity of the slag according to one aspect of the present invention is to use the converter 1 to perform an oxidative refining process on molten metal to produce slag 7 that has a reduced basicity when molten steel is produced. The method for reducing the salinity includes: a refining process step, which uses an oxygen source containing at least oxygen to the molten metal to perform an oxidative refining process using the converter 1, thereby forming the molten metal into molten steel; After that, a silicon dioxide-containing substance containing at least SiO ₂ is added to the molten steel stored in the furnace body 2 of the converter 1; and a tapping step, after the addition step, the furnace body 2 is tilted to discharge the molten steel from the furnace body . According to the configuration of (7), the same effect as (1) can be obtained.

(8) In the configuration of (7) above, the converter 1 has a top blowing nozzle 4, and in the addition step, after the refining treatment step, the top blowing nozzle 4 is raised to the top while blowing oxygen to prevent nozzle clogging During the period up to the standby position, the addition of silicon dioxide-containing substances to the molten steel was started. According to the configuration of (8), the same effect as the configuration of (3) is obtained.

(9) In the configuration of (7) or (8) above, the converter 1 has a bottom air outlet 3 provided at the bottom of the furnace body 2, and in the addition step, after the refining treatment step, the bottom air outlet 3 After the blowing conditions of the bottom blowing gas to be blown are switched to the conditions when the furnace body 2 is tilted, a material containing silicon dioxide is added to the molten steel during the period until the furnace body 2 starts to tilt. According to the configuration of (9), the same effect as the configuration of (4) is obtained. [Example]

The embodiments performed by the inventors and others will be described. In the examples, the same steel manufacturing method as the above-described embodiment was used, and the converter 1 was used to perform the refining process of the molten iron 6 to lower the slag saltiness. Specifically, in the embodiment, in the refining treatment step, the molten steel is produced by subjecting the molten metal to an oxidative refining treatment by using the bottom-blown converter 1. In the refining treatment step, the oxidation refining treatment of the molten iron 6 is performed under the condition that the calculated basicity is 4 or more. Then, in the addition step, the target basicity is set to 3.6 (Example 1) or 3.2 (Example 2), and silica is added as the silica-containing substance. Further, in the tapping step, when the molten iron 6 is discharged from the furnace body 2, the slag 7 in the furnace body 2 is collected to measure the CaO concentration and the SiO ₂ concentration, thereby measuring the degree of salinity (also called "actual Basicity").

In addition, in the Examples, for comparison, after the refining step, the steel was produced according to a conventional method of performing the tapping step without performing the addition step (Comparative Example). In the comparative example, in the same way as the example, the slag 7 was collected in the tapping step to measure the actual salinity. In addition, in the comparative example, under a plurality of conditions (Comparative Example 1 to Comparative Example 4) in which the calculated basicity is different, the actual basicity is measured to investigate the relationship between the calculated basicity and the actual basicity.

FIG. 2 shows the relationship between the calculated salinity and the actual salinity in Examples and Comparative Examples. The graph of the comparative example shown in FIG. 2 shows that the calculated basicity of Comparative Example 1 becomes 3.49 or less (N (number of samples)=42), and the calculated basicity of Comparative Example 2 becomes 3.50 or more and 3.99 or less ( N=182), the calculated salinity of Comparative Example 3 becomes 4.00 or more and 4.49 or less (N=467), and the calculated salinity of Comparative Example 4 becomes a condition of 4.50 or more (N=722). In addition, in FIG. 2, the average value of a plurality of data is shown in the graph, and the horizontally and vertically extending bar indicates the standard deviation (σ). As shown in FIG. 2, it can be confirmed that the basicity of the conventional slag shown in Comparative Examples 1 to 4 is a basicity that shows a correlation between the actual basicity and the calculated basicity. Here, the calculated basicity is calculated based on the mass balance under the pre-conceived blowing conditions such as the composition of the molten metal in the oxidation refining process, the input amount of various auxiliary materials, the amount of the oxygen source containing oxygen, and the like. Therefore, according to factors such as actual reaction efficiency, there is a tendency that the actual basicity will only decrease to a certain degree relative to the calculated basicity.

Furthermore, as shown in FIG. 2, in Example 1 (N=423) where the target basicity is set to 3.6 and Example 2 (N=36) where the target basicity is set to 3.2, it can be confirmed that The target salinity is actually reduced sufficiently, and it can be confirmed that the added silica-containing material melts in the slag.

In addition, in the Examples, the slag 7 treated in the same manner as in the above Example 1 was discharged from the furnace body 2 and recovered, and then the analysis of the salinity and the immersion swelling rate were measured. The salinity is determined by performing fluorescent X-ray analysis on the sample for analysis of the slag 7, quantifying the CaO concentration (mass%) and SiO ₂ concentration (mass%), and determining the ratio of these concentrations. The measurement of the immersion swelling rate is carried out in accordance with Japanese Industrial Standard JISA5015 Appendix B. As a result, it was confirmed that the basicity of the slag was 2.7, and the water swell rate was 0.5% or less. On the other hand, for the slag having a calculated basicity of 4.0 or more processed by the same method as the comparative example, after the recovery, the basicity is analyzed and the immersion swelling rate is measured. At this time, the analysis and measurement were carried out by the same method as in the above examples. As a result, it was confirmed that the basicity of the slag was 3.5, and the water swell rate was 1.5% or more, and the target quality could not be satisfied.

1: converter 2: furnace body 3: bottom air outlet 4: Top blowing nozzle 5: Chute 6: molten iron 7: Slag 21: Furnace 22: trunnion

FIG. 1 is a schematic diagram showing the equipment configuration of a converter. FIG. 2 is a graph showing the relationship between the calculated salinity and the actual salinity in Examples and Comparative Examples.

1: converter

2: furnace body

3: bottom air outlet

4: Top blowing nozzle

5: Chute

6: molten iron

7: Slag

21: Furnace

22: trunnion

Claims (9)

A method of manufacturing steel, which uses a converter to perform an oxidative refining process on molten metal to produce molten steel. The method of manufacturing the steel includes: a refining process step, by using the converter, adding at least to the molten metal Oxygen refining treatment is performed by an oxygen source of oxygen to form the molten metal into the molten steel; an adding step, after the refining treatment step, add at least the molten steel stored in the furnace body of the converter A silicon dioxide-containing substance containing SiO ₂ ; and a tapping step, after the adding step, the furnace body is tilted to discharge the molten steel from the furnace body. The method for manufacturing steel as described in item 1 of the patent application scope, wherein The converter has a bottom air outlet provided at the bottom of the furnace body, and In the refining treatment step, as the oxygen gas contained in the oxygen source, oxygen gas is blown into the molten metal from at least the bottom blowing port, thereby performing the oxidation refining treatment. The method for manufacturing steel according to item 1 or item 2 of the patent application scope, wherein The converter has a top blowing nozzle, and In the addition step, after the refining treatment step, while the oxygen is sprayed to prevent the nozzle from clogging while the top blowing nozzle is raised to the standby position, the addition to the molten steel starts The substance containing silicon dioxide. The method for manufacturing steel according to any one of the first to third patent application scopes, wherein The converter has a bottom air outlet provided at the bottom of the furnace body, and In the addition step, after the refining treatment step, the blowing conditions of the bottom blowing gas blown from the bottom blowing port are switched to the conditions when the furnace body is tilted, until the furnace body During the period until tilting is started, the silicon dioxide-containing substance is added to the molten steel. The method for manufacturing steel as described in any one of the first to fourth patent applications, wherein In the addition step, when the calculated basicity of the slag in the furnace body after the refining treatment step becomes 3.8 or more, the determination is made so that the calculated basicity of the slag becomes 3.6 or less Describe the amount of input of silicon dioxide-containing substances. The method for manufacturing steel according to any one of the first to fifth patent applications, wherein In the addition step, the input amount of the silicon dioxide-containing substance is determined so that the calculated basicity of the slag in the furnace body becomes 3.0 or more. A method for reducing the basicity of slag, which reduces the basicity of slag generated when molten steel is produced by oxidizing and refining molten metal by using a converter. The method for reducing the basicity of slag includes: refining treatment Step, by using the converter, adding an oxygen source containing at least oxygen to the molten metal to perform an oxidation refining process, thereby forming the molten metal into the molten steel; an adding step, after the refining process step, To the molten steel stored in the furnace body of the converter, a silicon dioxide-containing substance containing at least SiO ₂ is added; and a tapping step, after the addition step, the furnace body is tilted to remove The molten steel is discharged from the furnace body. The method for reducing the salinity of slag as described in item 7 of the patent application scope, in which The converter has a top blowing nozzle, and In the addition step, after the refining treatment step, while the oxygen is sprayed to prevent the nozzle from clogging while the top blowing nozzle is raised to the standby position, the addition to the molten steel starts The substance containing silicon dioxide. The method for reducing the salinity of the slag as described in item 7 or 8 of the patent application scope, in which The converter has a bottom air outlet provided at the bottom of the furnace body, and In the addition step, after the refining treatment step, the blowing conditions of the bottom blowing gas blown from the bottom blowing port are switched to the conditions when the furnace body is tilted, until the furnace body During the period until tilting is started, the silicon dioxide-containing substance is added to the molten steel.

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