JPWO2020110392A1 - Steel manufacturing method and slag basicity reduction method - Google Patents

Abstract

Provided are a method for producing steel and a method for reducing the basicity of slag, which can reduce the basicity of slag and suppress a decrease in production efficiency. A method for producing molten steel by subjecting hot metal to oxidative refining treatment in a converter (1). In a converter (1), an oxygen source containing at least oxygen gas is added to the hot metal for oxidation. By performing the refining treatment, after the refining treatment step of turning the hot metal into molten steel and the refining treatment step, a silica-containing substance containing at least SiO2 is added to the furnace body (2) of the converter (1) in which the molten steel is housed. It is provided with an addition step of adding from the above, and a steel ejection step of tilting the furnace body (2) and discharging molten steel from the furnace body (2) after the addition step.

Description

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

In the steelmaking process of a steel mill, an oxidative refining process (decarburization process) for producing molten steel is performed by adding an oxygen source such as oxygen gas to hot metal in a converter. In this oxidative refining treatment, slag is generated by an oxidation reaction of added auxiliary materials and impurity components in the hot metal. After being recovered, this slag is reused as a raw material for various purposes.

One of the uses of slag generated in converters is roadbed material. When slag is used as a roadbed material, the coefficient of thermal expansion in water must meet the quality standards defined by standards such as JIS, and for example, it must be 1.5% or less according to JIS standards. In order to reduce the water immersion expansion rate of slag, it is necessary to reduce the amount of free lime in the slag, and the basicity of the slag (the ratio of the SiO ₂ content to the CaO content of the slag ((% CaO) / (%). It is important to reduce SiO ₂ ))).

However, in the oxidative refining treatment in a converter, when the basicity of the slag is low, the slag is likely to expand due to CO gas or the like generated during the treatment, and the dephosphorization efficiency is also low. Therefore, a decrease in the basicity of slag in the oxidative refining treatment causes operational troubles and reduces the production efficiency. In addition, in the oxidative refining treatment in a converter, generally, only the amount corresponding to the target slag composition determined according to the blowing conditions such as the target component and temperature of the molten iron after the oxidative refining treatment and the efficiency of the refining reaction. At the beginning of the oxidative refining process, auxiliary materials such as silica stone and lime are added. However, it has been difficult to reduce the basicity of slag during the oxidative refining treatment from the viewpoint of promoting the dephosphorization reaction.

To deal with such a problem, for example, Patent Document 1 describes a substance in which one or more of SiO ₂ , Al ₂ O ₃ , FeO, Fe ₂ O ₃ , and P ₂ O ₅ are contained in the steelmaking slag (hereinafter, “modified”). A method for modifying slag is disclosed by adding a substance to which "pawnbroker" is added and then heat-treating at a temperature equal to or higher than the melting temperature for 10 minutes or less.

Japanese Patent No. 4571818

By the way, in the method described in Patent Document 1, when reforming slag in a converter, a modifier is added in a state where only slag is contained in the converter, or a modifier is added to an empty converter. Slag will be added after placing. For this reason, the method described in Patent Document 1 has a problem that the production efficiency is lowered because it is necessary to provide a treatment associated with the reforming in addition to the series of operation processes for performing the oxidative refining treatment.

Therefore, the present invention has been made by paying attention to the above problems, and is a method for producing steel and a basicity of slag, which can reduce the basicity of slag and suppress a decrease in production efficiency. It is intended to provide a reduction method.

According to one aspect of the present invention, it is a method for producing molten steel by subjecting hot metal to oxidative refining treatment in a converter, and in the converter, oxygen containing at least oxygen gas in the hot metal. The molten steel contained in the furnace body of the converter contains at least SiO ₂ after the refining treatment step of converting the hot metal into the molten steel by adding a source and performing the oxidation refining treatment, and the refining treatment step. Provided is a method for producing steel, comprising an addition step of adding a silica-containing substance, and a steel ejection step of tilting the furnace body and discharging the molten steel from the furnace body after the addition step.

According to one aspect of the present invention, it is a method for reducing the basicity of slag, which reduces the basicity of slag generated when molten steel is produced by subjecting hot metal to oxidative refining treatment in a converter. In the converter, an oxygen source containing at least oxygen gas is added to the hot metal and subjected to oxidative refining treatment to make the hot metal into the molten steel. After the refining treatment step, the furnace of the converter An addition step of adding a silica-containing substance containing at least SiO ₂ to the molten steel contained in the body, and a steel ejection step of tilting the furnace body to discharge the molten steel from the furnace body after the addition step. , A method for reducing the basicity of slag is provided.

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

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

It is a schematic diagram which shows the equipment composition of a converter. It is a graph which shows the relationship between the calculated basicity and the actual basicity in an Example and a comparative example.

In the following detailed description, many specific details will be described by exemplifying embodiments of the invention to provide a complete understanding of the invention. However, it is clear that one or more embodiments can be implemented without such particular detail description. Also, for the sake of brevity, the drawings are schematic representations of well-known structures and devices.

<Steel manufacturing method>
A method for producing steel according to an embodiment of the present invention will be described with reference to FIG. In the present embodiment, molten steel is produced from hot metal by oxidative refining treatment of molten iron 6 using an upper bottom blowing type converter 1. 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 having a refractory inside. The furnace body 2 has an opening called a furnace port 21 at the upper part in the state shown in FIG. Further, the furnace body 2 is configured to be tiltable around a pair of trunnion shafts 22 provided on the side surfaces.

The plurality of bottom blowing tuyere 3 is a tuyere of a double pipe provided at the bottom of the furnace body 2. The plurality of bottom blowing tuyere 3s are configured to blow at least oxygen gas from the inner pipe and hydrocarbon gas from the outer pipe into the inside of the furnace body 2, respectively.
The top-blown lance 4 is a lance that can be inserted into the inside of the furnace body 2 from above the furnace body 2 through the furnace opening 21. The top blown lance 4 is configured to be able to inject at least oxygen gas from a lance hole formed at the lower tip.
The chute 5 is a device provided above the furnace body 2. The tip of the chute 5 is arranged toward the furnace opening 21. The chute 5 conveys auxiliary raw materials such as a refining agent and a slag-making agent cut out from a hopper (not shown) and puts them into the furnace body 2.

In the method for producing steel according to the present embodiment, molten steel is produced by accommodating the hot metal from the blast furnace in the furnace body 2 and performing an oxidative refining treatment. In the following, hot metal and molten steel are also collectively referred to as molten iron 6. The hot metal to be oxidatively refined may be subjected to a hot metal pretreatment such as a desiliconization treatment, a dephosphorization treatment, and a desulfurization treatment in advance at another refining facility.

In the present embodiment, first, molten iron 6 which is hot metal is charged into the furnace body 2, oxygen gas and hydrocarbon gas are blown into the molten iron 6 from a plurality of bottom blowing tuyere 3, and oxygen gas is blown from the top blowing lance 4. By injecting into the molten iron 6, a refining treatment step of performing an oxidation refining treatment is performed. The oxidative refining treatment is a treatment in which an oxygen source is added to the hot metal to oxidize and remove impurity components such as carbon and phosphorus in the hot metal. In the present embodiment, the oxidative refining treatment proceeds with a decarburization reaction in which at least carbon in the molten iron 6 is removed and a dephosphorization reaction in which phosphorus in the molten iron 6 is removed. In the following, the addition of oxygen gas (oxygen source) to the molten iron 6 by blowing oxygen gas from the plurality of bottom blowing tuyere 3s and injecting oxygen gas from the top blowing lance 4 is also referred to as blowing.

In the refining treatment step, as the decarburization reaction proceeds, the carbon in the molten iron 6 is oxidized and removed, and molten steel having a low carbon concentration is produced. Further, in the refining treatment step, in order to promote the dephosphorization reaction, auxiliary raw materials such as a slag-making agent are charged into the furnace body 2. At this time, a plurality of types of slag-forming agents having different component compositions are added in an amount corresponding to the target slag composition. Auxiliary raw materials such as slag smelting agent are determined in advance according to various blowing conditions such as the component and temperature of molten iron 6 before the oxidative refining treatment, the target component and temperature of the molten iron 6 after the oxidative refining treatment, and the efficiency of the refining reaction. The determined input amount is input at the initial stage of the oxidative refining process. In the composition of the slag, the ratio of the CaO concentration (mass%) to the SiO ₂ concentration (mass%) ((% CaO) / (% SiO ₂ )) is referred to as basicity. In addition, the estimated basicity of slag after the oxidative refining treatment, which is calculated in advance before the oxidative refining treatment, is also referred to as the calculated basicity, depending on the mass balance of the auxiliary raw materials to be added, the components of the molten iron 6, and the planned amount of the oxygen source to be added. Say. When a general steel type is melted, the calculated basicity is usually 4.0 or more in the top-bottom blown converter 1. In the smelting treatment step, the auxiliary raw material is added and the smelting treatment is performed, and the oxidative refining treatment is completed when the components and the temperature of the molten iron 6 are targeted.

After the refining treatment step, a silica-containing substance containing at least SiO ₂ is added to the molten iron 6 which is the molten steel contained in the furnace body 2 via the chute 5.
The operating procedure of the addition step is not particularly specified, but it is desirable to take the following operating procedure because the melting of the silica-containing substance is promoted.

In the case of a top-blown or top-bottom-blown converter in which the converter 1 is a converter having a top-blown lance, after the refining process, the top-blown lance is placed in a standby position while injecting oxygen gas to prevent nozzle clogging. The addition of the silica-containing substance to the molten steel may be started during the period of raising to. In this case, when the necessary refining operation is completed, the operator (operator) operates the operation panel to send a refining end command. Immediately after sending this command, the required amount of silica-containing substance is cut out from the bunker to the hopper, and the gate of the hopper is opened. When this operation is performed, the silica-containing substance is added onto the molten steel bath surface in the furnace via the chute after the top-blown lance starts to rise to the standby position. In order to avoid nozzle clogging, the top-blown lance has a lower flow rate than during the oxidative refining process, but oxygen injection continues even during the rise. At this time, the molten steel is agitated by the blown oxygen gas (stirring effect). In addition, the molten steel is oxidized by the blown oxygen gas, and FeO is generated to promote the slag formation (slagging effect). Therefore, the melting of the silica-containing substance is promoted by the stirring effect and the slagging effect of the oxygen gas. In addition, in order to accelerate the timing of addition and the start of furnace tilting (steel ejection), the silica-containing substance to be added is cut out from the bunker at the end of the refining process and stored in the hopper in a state where it can be added. The operation of opening the hopper gate may be performed immediately after the refining end command is sent.

Further, in the case of an upper bottom blowing type or bottom blowing type converter in which the converter has a bottom blowing tuyere, the conditions for blowing the bottom blowing gas blown from the bottom blowing tuyere after the refining treatment step are set. A silica-containing substance may be added to the molten steel during the period from the switching to the conditions for tilting the furnace body to the start of tilting of the furnace body. In this case, immediately after the operator operates the operation panel to send the refining end command, the required amount of the silica-containing substance is cut out from the bunker to the hopper, and the gate of the hopper is opened. When the refining end command is sent, it is blown from the bottom blowing tuyere in the bottom blowing type or bottom blowing type converter that can bottom blow oxygen gas, inert gas, mixed gas of oxygen gas and inert gas, etc. The conditions for blowing the bottom-blown gas are switched from the conditions in the refining process to the conditions for tilting the furnace body in the steel ejection process described later. Specifically, under the blowing conditions when the furnace body is tilted to eject steel, the type of bottom blowing gas is switched to the inert gas, and the flow rate of the bottom blowing gas causes the bottom blowing tuyere to be blocked during steel ejection. The flow rate is set to a low level. The silica-containing substance is a molten steel bath in the furnace from the hopper via the chute 5 during the period from immediately after the bottom blowing gas blowing condition is switched to that for tilting the furnace body until the tilting of the furnace body is started. It will be added on the surface. It is preferable that the furnace body is in an upright state while the silica-containing substance is added. According to such an operation procedure, the melting of the silica-containing substance is promoted by the stirring effect of the molten steel by the bottom blowing gas. In addition, in order to accelerate the timing of addition and the timing of starting tilting (steel ejection) of the furnace body, the silica-containing substance to be added is cut out from the bunker at the end of the refining process and put into the hopper in a state where it can be added. It may be stored and only the operation of opening the gate of the hopper may be performed immediately after sending the refining end command.

Silica-containing material, but may be any those containing SiO _2, preferably the majority of the components are SiO _2, it is preferably SiO ₂ content higher. For example, as the silica-containing substance, silica stone containing mainly SiO ₂ can be used. Further, as the silica-containing substance, it is preferable to use a slag-forming agent mainly containing SiO ₂ from the viewpoint of restrictions on storage equipment such as a hopper. Since silica stone is generally used as a slag-making agent, it is preferable to use silica stone from this viewpoint as well. Further, in the present embodiment, as an example, when silica stone is used as the silica-containing substance, the particle size of the 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, if the particle size of the silica-containing substance is too small, the input yield may decrease due to scattering. In addition, when the finely powdered silica-containing substance is sent by air and used, there is a possibility that a sufficient input amount cannot be secured for continuous processing due to restrictions of storage equipment and transportation equipment. On the other hand, when the particle size of the silica-containing substance is large, the above problem does not occur when the particle size is small, but the added silica-containing substance may not be sufficiently melted. Therefore, the particle size of the silica-containing substance is preferably 5 mm or more and 40 mm or less.

In the addition step, the amount of the silica-containing substance to be added is determined according to the calculated basicity of the slag 7 after the refining treatment step and the target basicity set from the water immersion expansion rate of the slag. Specifically, the slag amount is estimated to calculate basicity after refining process slag 7, SiO ₂ amount required for slag 7 becomes the target basicity is determined, the SiO ₂ amount min The amount of silica-containing substance is the input amount. The coefficient of water immersion expansion of the slag is determined by the F. It is a value determined by the content of CaO (Free-CaO), and increases as the basicity of the slag increases. In the case of slag used for roadbed materials, JIS stipulates that the water immersion expansion rate should be 1.5% or less, and in this embodiment, the water immersion expansion rate of slag is set to 0 as a stricter standard. The goal is to keep it below 5%. In order to satisfy the water immersion expansion coefficient of 0.5%, in the case of a top-bottom blown converter as in this embodiment, the target basicity is preferably less than 3.8 and 3.6 or less. Is more preferable. By setting the target basicity, that is, the calculated basicity of the slag after adding the silica-containing substance to less than 3.8, preferably 3.6 or less, the F. slag in the slag. The CaO content can be sufficiently reduced, and the standard of water immersion expansion rate ≤ 0.5% can be satisfied. Further, in the addition step, the target basicity is preferably 3.0 or more. When the target basicity, that is, the calculated basicity of the slag 7 after adding the silica-containing substance is less than 3.0, the phosphorus distribution ratio of the slag decreases and the phosphorus in the slag returns to the molten steel, so that the molten steel Rephosphorus may occur, which increases the phosphorus concentration. For this reason, it may be a problem for steel grades with a strict upper limit of phosphorus concentration.

Further, in the addition step, it is determined whether or not the calculated basicity of the slag 7 after the refining step is 3.8 or more, and silica is used only when the calculated basicity of the slag 7 after the refining step is 3.8 or more. The contained substance may be added. In this case, if the calculated basicity of the slag 7 after the refining step is less than 3.8, the silica-containing substance is not added and the steel ejection step described later is carried out.
The silica-containing substance added in the addition step is charged into the inside of the high-temperature furnace body 2 from the chute 5 and is added to the slag 7 floating above the molten iron 6. Then, the added silica-containing substance is melted by the high-temperature molten iron 6 and slag 7, and becomes a part of the melted slag 7.

After the addition step, a steel ejection step is performed in which the furnace body 2 is tilted to discharge the molten iron 6 from the furnace body 2. In the steel ejection process, the furnace body 2 is tilted around the pair of trunnion shafts 22, and the molten iron 6 is discharged from a hot water discharge hole (not shown) provided on 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 process. In the steel ejection process, the molten iron 6 and the slag 7 flow inside the furnace body 2 due to the tilting of the furnace body 2, so that the melting of the silica-containing substance charged in the addition step is further promoted.

After the steel removal process, the slag 7 remains in the furnace body 2. Then, the slag 7 remaining in the furnace body 2 is discharged downward from the furnace opening 21 by tilting the furnace body 2 to the side opposite to the steel ejection process. The discharged slag 7 is collected in a slag pot arranged below the furnace body 2, and then reused through appropriate treatments such as aging treatment and magnetic separation treatment.
The molten iron 6 stored in the ladle (not shown) after the steel ejection process is appropriately subjected to secondary refining according to the target component composition of the steel type to be manufactured, and then cast in a casting facility such as a continuous casting machine. It becomes a slab. The obtained slab is rolled or heat-treated so that its dimensions, shape, characteristics, etc. satisfy the specifications of the shipped product to become steel of the product.

<Modification example>
Although the present invention has been described above with reference to specific embodiments, it is not intended to limit the invention by these descriptions. By reference to the description of the invention, one of ordinary skill in the art will appreciate other embodiments of the invention that include various modifications as well as the disclosed embodiments. Therefore, it should be understood that the embodiments of the invention described in the claims also include embodiments including these modifications described in the present specification alone or in combination.

For example, in the above embodiment, the converter 1 is a top-bottom blown converter, but the present invention is not limited to this example. For example, the converter 1 may be a top-blown converter that injects oxygen gas only from the top-blown lance 4, or a bottom-blown converter that injects oxygen gas only from the bottom-blown tuyere 3. Further, when the converter 1 is an upper bottom blowing type converter, it is a converter capable of bottom blowing oxygen gas as in the above embodiment and a converter capable of bottom blowing only an inert gas. May be good. Further, in the converter 1, the top-blown lance 4 is provided with a lance hole different from the oxygen gas, and an auxiliary material such as lime can be injected (projected) onto the molten iron 6 together with the transport gas from the lance hole. May be good.

Further, in the above embodiment, it is preferable that the target basicity is less than 3.8, more preferably 3.6 or less, but the present invention is not limited to such an example. Further, in the addition step, it may be determined whether or not the silica-containing substance is added in the addition step from the judgment result of whether or not the calculated basicity of the slag 7 after the refining step is 3.8 or more. However, the present invention is not limited to such an example. The above target basicity and threshold value are 0.5% or less in a top-bottom-blown or bottom-blown converter, which is a converter-type refining in which oxygen gas is blown from at least a plurality of bottom-blown tuyere. It is suitable for achieving a water immersion expansion rate. That is, the above-mentioned target basicity and threshold value can be changed according to the target water immersion expansion rate and the difference in the blowing form of the converter.
Further, in the above embodiment, the oxidative refining treatment is performed by adding oxygen gas as an oxygen source, but the present invention is not limited to such an example. For example, as the oxygen source, a solid oxygen source such as iron oxide may be further used in addition to oxygen gas.

<Effect of embodiment>
(1) The method for producing steel according to one aspect of the present invention is a method for producing molten steel by subjecting hot metal to oxidative refining treatment in converter 1, and in converter 1, hot metal is produced. By adding an oxygen source containing at least oxygen gas to the steel and performing an oxidative refining treatment, at least a refining treatment step of making hot metal into molten steel and a furnace body 2 of a converter 1 containing molten steel after the refining treatment step are performed. It includes an addition step of adding a silica-containing substance containing SiO ₂ from above, and a steel ejection step of tilting the furnace body 2 and discharging molten steel from the furnace body 2 after the addition step.

According to the configuration of (1) above, since the silica-containing substance is added in a state where the high-temperature molten steel which is molten iron 6 is housed inside the furnace body 2, the silica-containing substance is easily melted. Further, in the steel ejection process, the tilting of the furnace body 2 causes the molten iron 6 and the slag 7 to flow inside the furnace body 2, so that the melting of the silica-containing substance is further promoted. Therefore, the added silica-containing substance can be sufficiently melted, and the basicity of the slag 7 can be reduced accurately. Further, in the configuration of the above (1), since the silica-containing substance is easily dissolved, a silica-containing substance having a larger particle size can be used. As a result, the production efficiency can be improved and the manufacturing cost can be reduced.

Further, in the configuration of the above (1), it is not necessary to lower the basicity of the slag 7 in the refining treatment step. If the basicity of the slag 7 becomes low in the refining process, the forming of the slag 7 may occur. When the slag 7 is ejected from the furnace body 2 due to forming, the yield is lowered and the Noro pot line under the furnace is depressed, so that stable operation cannot be performed. On the other hand, in the configuration of the above (1), the frequency of occurrence of forming of the slag 7 is suppressed, and stable operation can be performed. Further, when the basicity of slag 7 is lowered in the refining treatment step, the phosphorus distribution ratio of slag 7 is lowered, so that dephosphorization cannot be sufficiently performed, or a slag-containing agent containing CaO is used to increase the amount of slag 7. The input amount of slag may increase. On the other hand, in the configuration of (1) above, the period during which the basicity of slag 7 decreases is a short period from the addition process to the steel removal process, and the amount of rephosphorus due to the decrease in the phosphorus distribution ratio is extremely small. It will be something like that. From this, the influence of the decrease in the phosphorus distribution ratio can be minimized, and the manufacturing cost can be further reduced. Further, since the influence on the composition of the molten iron 6 is negligible, such as the amount of rephosphorus being extremely small, the product characteristics and the like are the same as those of the conventional steel.

(2) In the configuration of (1) above, the converter 1 has a bottom blowing tuyere 3 provided at the bottom of the furnace body 2, and in the refining process, at least the bottom is used as the oxygen gas contained in the oxygen source. Oxidation refining treatment is performed by blowing oxygen gas into the hot metal from the blowing tuyere 3.
According to the configuration of (2) above, even in a bottom-blown or top-bottom-blown converter in which it is difficult to lower the basicity of slag as compared with a top-blown converter due to the difference in blowing form. Since the basicity of the slag can be reduced, the reuse of the slag can be promoted.

(3) In the configuration of (1) or (2) above, the converter 1 has a top-blown lance 4, and in the addition step, after the refining treatment step, while injecting oxygen gas to prevent nozzle clogging. During the period for raising the top blown lance 4 to the standby position, the addition of the silica-containing substance to the molten steel is started.
According to the configuration of (3) above, melting of the silica-containing substance is promoted by the stirring effect and the slagging effect of the blown oxygen gas.

(4) In any one of the above configurations (1) to (3), the converter 1 has a bottom blowing tuyere 3 provided at the bottom of the furnace body 2, and the addition step is a refining treatment step. After that, the molten steel contains silica during the period from when the conditions for blowing the bottom blown gas blown from the bottom blown tuyere 3 are changed to the conditions for tilting the furnace body 2 until the tilting of the furnace body 2 is started. Add the substance.
According to the configuration of (4) above, the molten steel is agitated by the bottom-blown gas blown from the bottom-blown gas even in the addition step, and the melting of the silica-containing substance is promoted.

(5) In any one of the above 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 The input amount of the silica-containing substance is determined so that the calculated basicity of 7 is 3.6 or less.
According to the configuration of (5) above, the coefficient of thermal expansion of the slag 7 can be set to 0.5% or less in the converter 1 having the configuration of (2) above.

(6) In any one of the above configurations (1) to (5), in the addition step, the amount of the silica-containing substance added so that the calculated basicity of the slag 7 in the furnace body 2 is 3.0 or more. To determine.
According to the configuration of (6) above, the amount of rephosphorus can be sufficiently suppressed, and the manufacturing cost can be further reduced.

(7) The method for reducing the basicity of slag according to one aspect of the present invention is to reduce the basicity of slag 7 generated when molten steel is produced by subjecting hot metal to an oxidative refining treatment in converter 1. In the basic oxygen steelmaking method of No. 7, in the converter 1, an oxygen source containing at least oxygen gas is added to the hot metal, and the hot metal is subjected to an oxidation refining treatment to make the hot metal into molten steel. After that, an addition step of adding a silica-containing substance containing at least SiO ₂ to the molten steel contained in the furnace body 2 of the converter 1 and after the addition step, the furnace body 2 is tilted to discharge the molten steel from the furnace body. It is equipped with a steelmaking process.
According to the configuration of the above (7), the same effect as the above (1) can be obtained.

(8) In the configuration of (7) above, the converter 1 has a top-blown lance 4, and in the addition step, after the refining process, the top-blown lance 4 is injected with oxygen gas to prevent nozzle clogging. The addition of the silica-containing substance to the molten steel is started during the period of raising the gas to the standby position.
According to the configuration of the above (8), the same effect as the configuration of the above (3) can be obtained.

(9) In the configuration of (7) or (8) above, the converter 1 has a bottom blowing tuyere 3 provided at the bottom of the furnace body 2, and in the addition step, the bottom blowing is performed after the refining treatment step. A silica-containing substance is added to the molten steel during the period from when the conditions for blowing the bottom blown gas blown from the tuyere 3 are changed to the conditions for tilting the furnace body 2 until the tilting of the furnace body 2 is started. ..
According to the configuration of (9) above, the same effect as the configuration of (4) above can be obtained.

Examples carried out by the present inventors will be described. In the embodiment, the molten iron 6 was refined in the converter 1 using the same steel manufacturing method as in the above embodiment to reduce the basicity of the slag. Specifically, in the example, molten steel was produced by subjecting the hot metal to an oxidative refining treatment in the top-bottom blowing type converter 1 in the refining treatment step. In the refining treatment step, the oxidation refining treatment of molten iron 6 was carried out under the condition that the calculated basicity was 4 or more. Next, in the addition step, silica stone was added as a silica-containing substance with the target basicity of 3.6 (Example 1) or 3.2 (Example 2). Further, in the steel ejection process, when the molten iron 6 is discharged from the furnace body 2, the slag 7 in the furnace body 2 is collected and the CaO concentration and the SiO ₂ concentration are measured to obtain the basicity (also referred to as “actual basicity”). ) Was measured.

Further, in the example, as a comparison, steel was produced by a conventional method in which the steel ejection step was performed without performing the addition step after the refining step (comparative example). In the comparative example as well, the slag 7 was collected in the steel ejection process and the actual basicity was measured in the same manner as in the examples. Further, in the comparative example, the actual basicity was measured under a plurality of conditions (Comparative Examples 1 to 4) having different calculated basicity, and the relationship between the calculated basicity and the actual basicity was investigated.

FIG. 2 shows the relationship between the calculated basicity and the actual basicity in Examples and Comparative Examples. In the plot of the comparative example shown in FIG. 2, the calculated basicity of Comparative Example 1 is 3.49 or less (N (number of samples) = 42), and that of Comparative Example 2 is 3.50 or more and 3.99 or less (N). = 182), Comparative Example 3 shows the condition that the calculated basicity is 4.00 or more and 4.49 or less (N = 467), and Comparative Example 4 shows the condition that the calculated basicity is 4.50 or more (N = 722). In FIG. 2, the plot shows the average value of a plurality of data, and the bars extending vertically and horizontally show the standard deviation (σ). As shown in FIG. 2, it was confirmed that the basicity of the conventional slags shown in Comparative Examples 1 to 4 showed a correlation between the calculated basicity and the actual basicity. Here, the calculated basicity is calculated from the mass balance under the expected blowing conditions such as the amount of hot metal components and various auxiliary raw materials input and the amount of oxygen source including oxygen gas in the oxidative refining treatment. It is a thing. Therefore, the actual basicity tends to be lower than the calculated basicity by a certain amount due to factors such as the actual reaction efficiency.

Further, as shown in FIG. 2, in Example 1 (N = 423) having a target basicity of 3.6 and Example 2 (N = 36) having a target basicity of 3.2, the target basicity However, it was confirmed that the actual basicity was sufficiently low, and it was confirmed that the added silica-containing substance was dissolved in the slag.

Further, in the example, the slag 7 treated in the same manner as in the above-mentioned Example 1 was discharged from the furnace body 2 and recovered, and then the basicity was analyzed and the water immersion expansion rate was measured. The basicity was determined by performing fluorescent X-ray analysis on a sample for analysis of slag 7, quantifying the CaO concentration (mass%) and the SiO ₂ concentration (mass%), and determining from these ratios. The measurement of the coefficient of expansion in water was carried out in accordance with Japanese Industrial Standard JIS A5015 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, for slag having a calculated basicity of 4.0 or more, which was treated in the same manner as in the comparative example, the basicity was analyzed and the water immersion expansion rate was measured after recovery. At this time, the analysis and measurement were carried out in the same manner as in the above-mentioned Examples. As a result, it was confirmed that the basicity of the slag was 3.5 and the coefficient of expansion in water was 1.5% or more, and the target quality could not be satisfied.

1 converter 2 furnace body 21 furnace opening 22 trunnion shaft 3 bottom blowing tuyere 4 top blowing lance 5 chute 6 molten iron 7 slag

Claims (9)

It is a steel manufacturing method that manufactures molten steel by subjecting hot metal to oxidative refining treatment in a converter.
In the converter, an oxygen source containing at least oxygen gas is added to the hot metal and oxidative refining treatment is performed to make the hot metal into the molten steel.
After the refining treatment step, an addition step of adding a silica-containing substance containing at least SiO ₂ to the molten steel housed in the furnace body of the converter.
After the addition step, a steel ejection step of tilting the furnace body to discharge the molten steel from the furnace body, and
A method of manufacturing steel. The converter has a bottom blowing tuyere provided at the bottom of the furnace body.
The production of the steel according to claim 1, wherein in the refining treatment step, the oxidation refining treatment is performed by blowing oxygen gas into the hot metal from at least the bottom blowing tuyere as the oxygen gas contained in the oxygen source. Method. The converter has a top-blown lance and
In the addition step, after the refining treatment step, the silica-containing substance is added to the molten steel during a period in which the top blowing lance is raised to a standby position while injecting the oxygen gas to prevent nozzle clogging. The method for producing steel according to claim 1 or 2, which is started. The converter has a bottom blowing tuyere provided at the bottom of the furnace body.
In the addition step, after the refining treatment step, the conditions for blowing the bottom blown gas blown from the bottom blown tuyere are switched to the conditions for tilting the furnace body, and then the tilting of the furnace body is started. The method for producing steel according to any one of claims 1 to 3, wherein the silica-containing substance is added to the molten steel during the period up to. In the addition step, when the calculated basicity of the slag in the furnace body after the refining treatment step is 3.8 or more, the silica-containing substance is such that the calculated basicity of the slag is 3.6 or less. The method for producing steel according to any one of claims 1 to 4, wherein the amount of the steel to be charged is determined. The steel according to any one of claims 1 to 5, wherein in the addition step, the input amount of the silica-containing substance is determined so that the calculated basicity of the slag in the furnace is 3.0 or more. Production method. A method for reducing the basicity of slag, which reduces the basicity of slag generated when molten steel is manufactured by subjecting hot metal to oxidative refining treatment in a converter.
In the converter, an oxygen source containing at least oxygen gas is added to the hot metal and oxidative refining treatment is performed to make the hot metal into the molten steel.
After the refining treatment step, an addition step of adding a silica-containing substance containing at least SiO ₂ to the molten steel housed in the furnace body of the converter.
After the addition step, a steel ejection step of tilting the furnace body to discharge the molten steel from the furnace body, and
A method for reducing the basicity of slag. The converter has a top-blown lance and
In the addition step, after the refining treatment step, the silica-containing substance is added to the molten steel during a period in which the top blowing lance is raised to a standby position while injecting the oxygen gas to prevent nozzle clogging. The method for reducing the basicity of slag according to claim 7, which is started. The converter has a bottom blowing tuyere provided at the bottom of the furnace body.
In the addition step, after the refining treatment step, the blowing condition of the bottom blowing gas blown from the bottom blowing tuyere is switched to the condition for tilting the furnace body, and then the tilting of the furnace body is started. The method for reducing the basicity of slag according to claim 7 or 8, wherein the silica-containing substance is added to the molten steel during the period up to.

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