JP2022185789A - Converter blowing method and converter facility - Google Patents

Abstract

To provide a converter blowing method capable of suppressing nitrogen absorption and phosphorus condensation of hot metal or molten steel.SOLUTION: A converter blowing method satisfies the following requirements 1-1 and 1-2. Requirement 1-1: A top-blown gas with a nitrogen concentration of 0.3 mol% or less is blown from a top-blown lance to hot metal or molten steel from the start point of blowing TS to TA1. Here, the total amount of oxygen sprayed from the top blowing lance from the start point of blowing TS to TA1 is more than 60% of the total amount of oxygen sprayed from the top blowing lance from the start point of blowing TS to the end point of blowing TE. Requirement 1-2: A dephosphorizing agent comprising Ca is sprayed from the top blowing lance to hot metal or molten steel from at least time point TA1 to the end of blowing, with low nitrogen concentration gas as the top blowing gas. The low nitrogen concentration gas contains oxygen and carrier gas and has a nitrogen concentration of 0.3 mol% or less.SELECTED DRAWING: Figure 1

Description

The present application discloses a converter blowing method and converter equipment.

As a method for producing low-phosphorus steel from blast furnace molten iron, as disclosed in Patent Document 1, molten iron is dephosphorized in a low temperature and high carbon concentration range that is thermodynamically advantageous for dephosphorization, and then , methods for decarburization blowing of hot metal are known. Since the dephosphorization-treated hot metal has a lower phosphorus concentration than untreated hot metal, the dephosphorization load in the next step of decarburization blowing is reduced. On the other hand, hot metal that has been dephosphorized inevitably contains dephosphorization slag generated by the dephosphorization treatment. That is, part of the dephosphorization slag produced in the dephosphorization treatment is brought into the decarburization blowing in the next step. Here, in the decarburization blowing, since the temperature and carbon concentration range is thermodynamically disadvantageous for dephosphorization, rephosphorization from the dephosphorization slag to molten pig iron or molten steel is likely to occur. In this regard, it is necessary to add a dephosphorization agent during decarburization blowing in order to suppress the rephosphorization of molten steel from dephosphorization slag during decarburization blowing.

The dephosphorization agent added in decarburization blowing includes a dephosphorization agent containing Ca. For example, dephosphorization agents may include CaO and _CaCO3 . These dephosphorizing agents form slag at a high temperature fire point and efficiently undergo a dephosphorizing reaction through a transitory reaction. As a method of adding a dephosphorization agent in decarburization blowing, it is common to add a block of dephosphorization agent to the hot metal or molten steel by placing it on top of the hot metal or molten steel. There is also a method of spraying phosphorus. In this case, the dephosphorization agent carried by the carrier gas and the oxygen gas are combined and then top-blown. In other words, the top-blown gas contains the oxygen gas and the carrier gas.

Nitrogen gas is usually used as the carrier gas for the dephosphorization agent from the viewpoints of cost and safety. However, when nitrogen gas is used as the carrier gas, a top blowing gas having a high nitrogen concentration is blown from the top blowing lance to the molten steel during decarburization blowing, which increases the nitrogen concentration of the molten steel. Since nitrogen in steel lowers the toughness of steel, it is desirable to keep the nitrogen concentration in the final molten steel as low as possible.

To address the above problem, Patent Document 2 discloses a method of blowing a dephosphorizing agent together with a top-blown gas when the blown oxygen amount is 10% or more and 50% or less of the total oxygen amount in decarburization blowing. It is That is, by spraying the dephosphorizing agent in the first half of blowing, it is possible to suppress the absorption of nitrogen into the molten iron or molten steel in the latter half of blowing, and to keep the nitrogen concentration in the final molten steel low. can.

JP 2011-144415 A JP 2020-105562 A

According to the findings of the present inventors, as disclosed in Patent Document 2, by spraying a dephosphorizing agent in the first half of blowing, the dephosphorization of the molten pig iron or molten steel is promoted while suppressing the absorption of nitrogen into the molten pig iron or molten steel. However, rephosphorization occurs in the latter half of blowing where the temperature is higher, and the effect of promoting dephosphorization in the first half of blowing is reduced. In this regard, a new technology capable of suppressing nitrogen absorption and rephosphorization of molten pig iron or molten steel is required in converter blowing.

As one means for solving the above problems, the present application provides
A converter blowing method,
Blowing a top-blowing gas containing oxygen from a top-blowing lance onto the molten pig iron or molten steel in the converter,
meet the following requirements 1-1 and 1-2,
A converter blowing method is disclosed.

Requirement 1-1: From blowing start time T _S to time T _A1 , top blowing gas having a nitrogen concentration of 0.3 mol % or less is blown from the top blowing lance to the molten iron or molten steel. Here, the total amount of oxygen blown from the top blowing lance from the blow start time T _S to the time T _A1 is the amount of oxygen blown from the top blow lance from the blow start time T _S to the blow end time T _E 60% or more of the total oxygen available.

Requirement 1-2: At least from the time T _A1 to the end of blowing, a dephosphorizing agent containing Ca is blown from the top blowing lance to the molten iron or molten steel together with a low nitrogen concentration gas as a top blowing gas. Here, the low nitrogen concentration gas contains oxygen and a carrier gas and has a nitrogen concentration of 0.3 mol % or less.

The converter blowing method of the present disclosure may satisfy the following requirements 1-1a and 1-1b.

Requirement 1-1a: Nitrogen concentration from the top blowing lance to the molten iron or molten steel from the blowing start time T _S to any time T _B1 after the blowing start has a nitrogen concentration of 0.3 mol% or less The dephosphorization agent is not sprayed while the top-blown gas is blown.

Requirement 1-1b: From the time T _B1 to the time T _A1 , the dephosphorizing agent is blown from the top blowing lance onto the molten iron or molten steel together with the low nitrogen concentration gas as the top blowing gas.

As one of the means for solving the above problems, the present application provides
A converter blowing method,
Blowing a top blowing gas containing oxygen from a top blowing lance onto molten iron or molten steel in a converter,
meet the following requirement 2-1,
A converter blowing method is disclosed.

Requirement 2-1: From the time T _A2 after the start of blowing to the end of blowing, from the top blowing lance to the molten pig iron or molten steel, together with a low nitrogen concentration gas as the top blowing gas, a dephosphorizing agent containing Ca spray. Here, the total amount of oxygen blown from the top blowing _lance from the blowing start time _{T S} to the time T _A2 is The low nitrogen concentration gas comprises oxygen and a carrier gas and has a nitrogen concentration of 0.3 mol % or less.

The converter blowing method of the present disclosure may satisfy the following requirement 2-2.

Requirement 2-2: From the blowing start time T _S to the time T _A2 , or from any time T _B2 after the start of blowing to the time T _A2 , from the top blowing lance to the molten iron or molten steel Then, a top-blown gas having a nitrogen concentration of more than 0.3 mol % is blown, and at the time _TA2 , the top-blown gas is switched to the low nitrogen concentration gas.

The converter blowing method of the present disclosure may satisfy the following requirements 2-2a and 2-2b.

Requirement 2-2a: From the blowing start time T _S to the time T _B2 , from the top blowing lance to the molten iron or molten steel, top blowing gas having a nitrogen concentration of more than 0.3 mol% or 0.3 While blowing a top-blown gas having a nitrogen concentration of mol % or less, the dephosphorization agent is not blown.

Requirement 2-2b: From the time point T _B2 to the time point T _A2 , the dephosphorizing agent is sprayed from the top blowing lance to the molten iron or molten steel together with a high nitrogen concentration gas as the top blowing gas, and the above time point At _TA2 , the type of top-blown gas is switched. Here, the high nitrogen concentration gas contains oxygen and a carrier gas and has a nitrogen concentration of more than 0.3 mol %.

As one means for solving the above problems, the present application provides
A converter facility comprising a converter, a top-blowing lance, a first supply line, a second supply line, a first supply source, a second supply source, a third supply source, and a fourth supply source and
The first supply line is connected to the top blowing lance or the second supply line,
The second supply line is connected to the top blowing lance or the first supply line,
The first supply source is connected to the first supply line and is configured to be capable of supplying oxygen gas to the first supply line,
the second supply source is connected to the second supply line and is configured to be capable of supplying a first carrier gas to the second supply line;
the third supply source is connected to the second supply line and configured to supply a second carrier gas to the second supply line;
The fourth supply source is connected to the second supply line and configured to be capable of supplying a dephosphorization agent containing Ca to the second supply line,
The dephosphorization agent supplied to the second supply line is sent to the top blowing lance or the first supply line together with the first carrier gas or the second carrier gas via the second supply line. configured to be able to supply
The first carrier gas or the second carrier gas supplied to the top blowing lance or the first supply line and the dephosphorizing agent together with the oxygen rise from the top blowing lance into the converter. configured to be blowable,
The carrier gas supplied to the second supply line is configured to be switchable between the first carrier gas and the second carrier gas,
By switching the carrier gas, the top-blown gas blown from the top-blowing lance into the converter is a low nitrogen concentration gas having a nitrogen concentration of 0.3 mol% or less and a nitrogen concentration of more than 0.3 mol%. is configured to be switchable between a high nitrogen concentration gas having a nitrogen concentration of
A converter installation is disclosed.

According to the technique of the present disclosure, it is possible to suppress nitrogen absorption and rephosphorization of molten pig iron or molten steel in converter blowing.

An example of the flow in the converter blowing method according to the first embodiment is shown. An example of the flow in the converter blowing method according to the first embodiment is shown. An example of the flow in the converter blowing method according to the second embodiment is shown. An example of the flow in the converter blowing method according to the second embodiment is shown. 1 schematically shows an example of the configuration of a converter installation;

1. Converter blowing method The converter blowing method of the present disclosure does not contain nitrogen or has a nitrogen gas concentration when blowing top blowing gas containing oxygen from the top blowing lance to the molten iron or molten steel in the converter. By top-blowing the dephosphorizing agent together with the above-mentioned oxygen using a low carrier gas, low-phosphorus steel is produced while suppressing absorption and rephosphorization of molten pig iron or molten steel. Two forms of the converter blowing method of the present disclosure are exemplified below.

1.1 First Mode A converter blowing method according to the first mode includes blowing top-blowing gas containing oxygen from a top-blowing lance to molten pig iron or molten steel in a converter, as shown in FIG. As such, it satisfies the following requirements 1-1 and 1-2.

Requirement 1-1: From blowing start time T _S to time T _A1 , top blowing gas having a nitrogen concentration of 0.3 mol % or less is blown from the top blowing lance to the molten iron or molten steel. Here, the total amount of oxygen blown from the top blowing lance from the blow start time T _S to the time T _A1 is the amount of oxygen blown from the top blow lance from the blow start time T _S to the blow end time T _E 60% or more of the total oxygen available.

Requirement 1-2: At least from the time T _A1 to the end of blowing, a dephosphorizing agent containing Ca is blown from the top blowing lance to the molten iron or molten steel together with a low nitrogen concentration gas as a top blowing gas. Here, the low nitrogen concentration gas contains oxygen and a carrier gas and has a nitrogen concentration of 0.3 mol % or less.

1.1.1 Requirement 1-1
As shown in FIG. 1, in the converter blowing method according to the first embodiment, _{0.3 mol} % or less of A top blown gas having a nitrogen concentration is blown. Here, the total amount of oxygen blown from the top blowing lance from the blowing start time T _S to the time T _A1 is the total amount of oxygen blown from the top blowing lance from the blow start time T _S to the blow end time T _E 60% or more of the volume.

The “blow start time T _S ” refers to the time when the top blowing of oxygen from the top blowing lance is started in the converter blowing (when the top blowing oxygen amount is 0%). For example, it may be the time when top blowing of oxygen is started in decarburization blowing.

"Blowing end point _TE " means the point in time when the top blowing of oxygen from the top blowing lance is finished in the converter blowing (when the amount of top blowing oxygen reaches 100%). For example, in decarburization blowing, it may be the time when the top blowing of oxygen is finished and the molten steel is melted.

“Time point T _A1 ” is the time point at which 60% or more of the total amount of oxygen blown from the top-blowing lance is blown from the blow start time T _S to the blow end time T _E . Time point _TA1 is the time point at which 65% or more, 70% or more, 75% or more, or 80% or more of the total amount of oxygen blown from the top blowing _lance is blown from the blowing start time _TS to the blowing end time TE. may be

The "top-blown gas having a nitrogen concentration of 0.3 mol% or less" may be oxygen only, or a mixed gas of oxygen and a gas other than oxygen, as shown in FIG. . Gases other than oxygen in this case include, for example, argon, carbon dioxide, and air. In particular, when argon or carbon dioxide is used, the nitrogen concentration of the top-blown gas can be further reduced. The mixing ratio of oxygen and gases other than oxygen in the mixed gas is not particularly limited, and may be appropriately adjusted according to the target blowing conditions. The gas other than oxygen may be a carrier gas for carrying a dephosphorizing agent, which will be described later. That is, as shown in FIG. 1, in the converter blowing method according to the first embodiment, the top blowing of the dephosphorization agent is performed together with the top blowing gas from the blowing start time T _S to the time T _A1 . may or may not.

As _shown in FIG. 1, in the converter _blowing method according to the first embodiment, more than 0.3 mol% of A top-blown gas having a nitrogen concentration of 0.3 mol % or less is blown instead of blowing a top-blown gas having a nitrogen concentration. According to the findings of the present inventor, when top-blown gas having a nitrogen concentration of more than 0.3 mol% is blown from the blowing start time T _S to the time T _A1 , molten pig iron or molten steel Nitrogen absorption occurs, and the nitrogen taken into the molten pig iron or molten steel is not sufficiently removed by the end of the blowing, resulting in a high nitrogen concentration in the finally melted steel. On the other hand, as in the converter blowing method according to the first embodiment, a nitrogen concentration of 0.3 mol% or less is supplied from the top blowing lance to the molten iron or molten steel from the blowing start time T _S to the time T _A1 . By blowing the top-blown gas, it is possible to suppress the absorption of nitrogen into the molten iron or molten steel in the first half of the blowing, and the nitrogen concentration of the finally melted steel is likely to be reduced.

1.1.2 Requirement 1-2
As shown in FIG. 1, in the converter blowing method according to the first embodiment, from at least time point _TA1 to the end of blowing, from the top blowing lance to molten iron or molten steel, low nitrogen concentration gas as top blowing gas At the same time, a dephosphorizing agent containing Ca is sprayed. Here, the low nitrogen concentration gas contains oxygen and a carrier gas and has a nitrogen concentration of 0.3 mol % or less.

“Last stage of blowing” means the period from just before the end of blowing to the end of blowing, specifically, the total amount of oxygen blown from the top-blowing _lance from the start of blowing _TS to the end of blowing TE. The period when more than 95% of is blown can be considered as the end of blowing.

The "low nitrogen concentration gas" is blown from a top-blowing lance to molten iron or molten steel as a top-blowing gas. The low nitrogen concentration gas contains oxygen and carrier gas. The nitrogen concentration in the low nitrogen concentration gas is 0.3 mol % or less, and may be 0.2 mol % or less. The lower limit of the nitrogen concentration in the low nitrogen concentration gas is not particularly limited, and may be substantially zero. The mixing ratio of oxygen and carrier gas in the low nitrogen concentration gas is not particularly limited, and may be appropriately adjusted according to the target blowing conditions so as to satisfy the above nitrogen concentration.

A "carrier gas" is utilized to carry the dephosphorizing agent and may form part of the top-blown gas. In order to form a low-concentration nitrogen gas with a nitrogen concentration of 0.3 mol % or less, a carrier gas that does not contain nitrogen or has a low nitrogen concentration is used. Such carrier gases include, for example, argon, carbon dioxide and air. In particular, when argon or carbon dioxide is used, the nitrogen concentration can be further reduced. Also, when air is used as the carrier gas, it should be combined with argon or carbon dioxide to dilute the nitrogen in the air. From the viewpoint of safety, it is better to avoid using oxygen as a carrier gas. In this regard, the carrier gas contains 50 mol% or less, 40 mol% or less, 30 mol% or less, 20 mol% or less, 10 mol% or less, 5 mol% or less, 1 mol% or less, or 0.1 mol% or less of oxygen. It may have a concentration.

Any "dephosphorizing agent" can be used as long as it contains Ca and exhibits a dephosphorizing function. For example, a dephosphorization agent containing CaO, a dephosphorization agent containing _CaCO3 , or the like can be employed. The dephosphorization agent may include a _SiO2 source. _SiO2 sources include silica stone, olivine, and the like. As shown in FIG. 1, the dephosphorization agent is sprayed onto molten pig iron or molten steel together with the low nitrogen concentration gas as the top blowing gas. That is, in the converter blowing method of the present disclosure, the powdery dephosphorization agent is blown onto the molten iron or molten steel together with the top-blown gas, instead of adding the lumpy dephosphorization agent to the hot metal or molten steel. The shape and size (particle size) of the dephosphorizing agent are not particularly limited as long as it can be sprayed from a top-blowing lance.

In the converter blowing method according to the first embodiment, for example, the dephosphorizing agent carried by the carrier gas and the top-blown oxygen are combined, so that the top-blowing gas is blown from the top-blowing lance to the molten pig iron or molten steel. The dephosphorizing agent is sprayed together with a low nitrogen concentration gas (mixed gas of oxygen and carrier gas) as the . The nitrogen concentration in the low nitrogen concentration gas is 0.3 mol % or less, thereby suppressing absorption of nitrogen into molten pig iron or molten steel.

As shown in FIG. 1, in the converter blowing method according to the first embodiment, the dephosphorization agent may be top-blown together with the low nitrogen concentration gas at least from time _TA1 to the end of blowing. That is, the top blowing of the dephosphorization agent is not limited to the point of time _TA1 , and as shown in FIG. 1, the dephosphorization agent may be sprayed before the point of time _TA1 . Further, the time point at which the blowing of the dephosphorizing agent ends is not limited to the time point at which the blowing ends, and as shown in FIG. 1, the blowing of the dephosphorizing agent may end before the blowing ends. From the viewpoint of further enhancing the dephosphorization effect, the dephosphorization agent may be sprayed before time _TA1 , and from the viewpoint of cost reduction, the dephosphorization agent should not be sprayed before time _TA1 . good too.

1.1.3 Requirements 1-1a and 1-1b
As shown in FIG. 2, the converter blowing method according to the first embodiment may satisfy the following requirements 1-1a and 1-1b.

Requirement 1-1a: Nitrogen concentration from the top blowing lance to the molten iron or molten steel from the blowing start time T _S to any time T _B1 after the blowing start has a nitrogen concentration of 0.3 mol% or less The dephosphorization agent is not sprayed while the top-blown gas is blown.

Requirement 1-1b: From the time T _B1 to the time T _A1 , the dephosphorizing agent is blown from the top blowing lance onto the molten iron or molten steel together with the low nitrogen concentration gas as the top blowing gas.

As shown in FIGS. 1 and 2, requirements 1-1a and 1-1b correspond to examples of requirement 1-1 above. That is, in the converter blowing method according to the first embodiment, from the start of blowing to a certain point T _B1 , only top blowing gas with a low nitrogen concentration is blown, and top blowing of the dephosphorization agent is not performed. Top blowing of the dephosphorizing agent may be started together with the low nitrogen concentration gas from time _TB1 . In this way, the top blowing of the dephosphorization agent is not performed from the blowing start time point _TS to the time point _TB1 , and the top blowing of the dephosphorization agent is started from the time point _TB1 , whereby the dephosphorization agent is stably top blown. can do.

As shown in FIG. 2, point T _B1 is the point at which less than 60% of the total amount of oxygen blown from the top blowing lance from blow start time T _S to blow end time T _E has been blown. For example, the time point TB1 is 1% or more, 5% or more, or 10% or more, 50% or less, or 40% of the total amount of oxygen _blown from the top blowing _lance from the blowing start time _TS to the blowing end time TE. After that, it may be the time when 30% or less or 20% or less is blown.

As described above, in the converter blowing method according to the first embodiment, nitrogen absorption in molten pig iron or molten steel can be suppressed by not blowing top blowing gas having a high nitrogen concentration in the first half to the middle stage of blowing. Further, in the converter blowing method according to the first embodiment, the dephosphorization agent is blown together with the low nitrogen concentration top blowing gas from the latter half to the final stage of the blowing when the molten iron or molten steel becomes hot and has a low carbon concentration. Therefore, it is possible to suppress rephosphorization of molten iron or molten steel (promote dephosphorization) while suppressing absorption of nitrogen into molten iron or molten steel. As a result, the nitrogen concentration and phosphorus concentration of the finally melted steel are likely to be reduced.

1.2 Second Mode A converter blowing method according to the second mode includes blowing top-blowing gas containing oxygen from a top-blowing lance to molten pig iron or molten steel in a converter, as shown in FIG. As such, it satisfies the following requirements 2-1.

Requirement 2-1: From the time T _A2 after the start of blowing to the end of blowing, from the top blowing lance to the molten pig iron or molten steel, together with a low nitrogen concentration gas as the top blowing gas, a dephosphorizing agent containing Ca spray. Here, the total amount of oxygen blown from the top blowing _lance from the blowing start time _{T S} to the time T _A2 is The low nitrogen concentration gas comprises oxygen and a carrier gas and has a nitrogen concentration of 0.3 mol % or less.

1.2.1 Requirement 2-1
As shown in FIG. 3, in the converter blowing method according to the second embodiment, the total amount of oxygen blown from the top blowing lance from the blow start time T _S to the time T _A2 is equal to the blow start time T _S is less than 60% of the total amount of oxygen blown from the top-blowing _lance from to the blow end time TE. In other words, "point T _A2 " is the point at which less than 60% of the total amount of oxygen blown from the top blowing lance is blown from the blow start time T _S to the blow end time T _E . The time point TA2 is 1% or more, 5% or more, 10% or more, 20% or more, 30% or more of the total amount of oxygen _blown from the top blowing _lance from the blowing start time _TS to the blowing end time TE, or It may be at a point when 40% or more, 59% or less, 58% or less, 57% or less, 55% or less, 50% or less, 40% or less, 30% or less, or 20% or less is blown. Alternatively, as will be described later, when the high nitrogen concentration gas is blown until time _TA2 and the top blown gas is switched from the high nitrogen concentration gas to the low nitrogen concentration at time _TA2 , time _TA2 is the start of blowing. When 40% or more, 45% or more, or 50% or more, 59% or less, 58% or less, or 57% or less of the total amount of oxygen blown from the top blowing lance is blown from the time point T _S to the blow end time T _E may be By setting the time _TA2 as late as possible, the amount of low nitrogen concentration carrier gas (such as argon), which is generally expensive, can be reduced.

According to the findings of the present inventor, from time _TA2 to the end of blowing, a dephosphorizing agent containing Ca was blown from a top blowing lance to molten pig iron or molten steel together with a low nitrogen concentration gas as a top blowing gas. In this case, even if the absorption of nitrogen into the molten iron or molten steel occurs before time _TA2 , the nitrogen in the molten iron or molten steel is removed from time _TA2 to the end of blowing, and finally melts. Nitrogen concentration in the steel to be manufactured tends to be reduced. In addition, by spraying the dephosphorizing agent from time _TA2 to the end of blowing, the rephosphorization of molten iron or molten steel is suppressed (dephosphorization promote phosphorus). As a result, the nitrogen concentration and phosphorus concentration of the finally melted steel are likely to be reduced.

1.2.2 Requirement 2-2
As described above, in the converter blowing method according to the second embodiment, absorption and nitriding of the molten iron or molten steel occurs from the blowing start time _TS to the time _TA2 , and the nitrogen concentration in the molten iron or molten steel is high. It may be. That is, as shown in FIG. 3, from the blowing start time T _S to the time T _A2 , as the top blowing gas, only oxygen may be used, or a low nitrogen concentration gas may be used. , a nitrogen-rich gas may be used. In particular, before time _TA2 , a high nitrogen concentration gas is blown as a top blowing gas from a top blowing lance to molten pig iron or molten steel, and at time _TA2 , by switching the top blowing gas to a low nitrogen concentration gas, general The amount of low nitrogen concentration carrier gas, which is relatively expensive, can be reduced. That is, as shown in FIG. 4, the converter blowing method according to the second embodiment may satisfy the following requirements 2-2.

Requirement 2-2: From the blowing start time T _S to the time T _A2 , or from any time T _B2 after the start of blowing to the time T _A2 , from the top blowing lance to the molten iron or molten steel Then, a top-blown gas having a nitrogen concentration of more than 0.3 mol % is blown, and at the time _TA2 , the top-blown gas is switched to the low nitrogen concentration gas.

The "top blown gas having a nitrogen concentration of more than 0.3 mol%" may be, for example, a mixed gas of oxygen and a gas with a high nitrogen concentration, or may be a "high nitrogen concentration gas" described later. .

The method for switching the top-blown gas from a gas with a high nitrogen concentration to a gas with a low nitrogen concentration is not particularly limited. For example, as described later, in a converter facility having an oxygen supply line (first supply line) and a carrier gas supply line (second supply line), switching the type of carrier gas supplied to the carrier gas supply line As a result, the top-blown gas can be switched from gas with a high nitrogen concentration to gas with a low nitrogen concentration. In addition, when the carrier gas is switched from a gas with a high nitrogen concentration to a gas with a low nitrogen concentration during blowing, the carrier gas with a high nitrogen concentration remaining in the supply line or the fourth supply source (powder supply device) described later is mixed with a gas with a low nitrogen concentration, and the gas with a low nitrogen concentration cannot always be blown upward immediately after switching. Taking this into consideration, it is preferable to control the timing of switching the carrier gas and the nitrogen concentration in the top-blown gas.

1.2.3 Requirements 2-2a and 2-2b
As shown in FIG. 3, in the converter blowing method according to the second embodiment, the top blowing of the dephosphorizing agent may be performed from the blowing start time _TS , or at any time after the blowing start. The top blowing of the dephosphorization agent may be performed from time _TB2 . In particular, the top blowing of the dephosphorizing agent is not performed from the blowing start point _TS to the point _TB2 , and the top blowing of the dephosphorizing agent is started from the point _TB2 , thereby stably top blowing the dephosphorizing agent. can be done. That is, the converter blowing method according to the second embodiment may satisfy the following requirements 2-2a and 2-2b as shown in FIG.

Requirement 2-2a: From the blowing start time T _S to the time T _B2 , from the top blowing lance to the molten iron or molten steel, top blowing gas having a nitrogen concentration of more than 0.3 mol% or 0.3 While blowing a top-blown gas having a nitrogen concentration of mol % or less, the dephosphorization agent is not blown.

Requirement 2-2b: From the time point T _B2 to the time point T _A2 , the dephosphorizing agent is sprayed from the top blowing lance to the molten iron or molten steel together with a high nitrogen concentration gas as the top blowing gas, and the above time point At _TA2 , the type of top-blown gas is switched. Here, the high nitrogen concentration gas contains oxygen and a carrier gas and has a nitrogen concentration of more than 0.3 mol %.

The "time point _TB2 " may be between the blow temper start time point _TS and the time point _TA2 . For example, the time point TB2 is more than 0%, 1% or more, 3% or more, or 5% or more, 40% of the total amount of oxygen _blown from the top blowing _lance from the blowing start time _TS to the blowing end time TE. It may be when less than, 30% or less, 20% or less or 15% or less is blown.

A "nitrogen-rich gas" includes oxygen and a carrier gas and has a nitrogen concentration greater than 0.3 mol %. That is, the carrier gas used for the high nitrogen concentration gas has a high nitrogen concentration. Examples of such carrier gas include nitrogen, air, and the like. The nitrogen concentration in the high nitrogen concentration gas is more than 0.3 mol%, and may be 0.5 mol% or more, 1.0 mol% or more, 1.5 mol% or more, or 2.0 mol% or more.

1.3 Supplement In the converter blowing method according to the first and second forms, following requirements 1-2 and 2-1, even from the end of blowing to the end of blowing, hot metal or iron from the top blowing lance A top-blown gas having a nitrogen concentration of 0.3 mol % or less is preferably blown onto the molten steel. In other words, as shown in FIGS. 2 and 4, it is better not to blow top-blowing gas with a nitrogen concentration greater than 0.3 mol % from the top-blowing lance into the hot metal or molten steel at the end of blowing. In the final stage of blowing, by blowing a top-blown gas having a nitrogen concentration of 0.3 mol% or less into the molten iron or molten steel from the top-blowing lance, absorption of nitrogen into the molten iron or molten steel in the final stage of blowing can be suppressed. It becomes easier to further reduce the nitrogen concentration of the steel that is typically melted. As described above, at the end of blowing, the top blowing of the dephosphorizing agent may be performed together with the low nitrogen concentration gas until the end of blowing, or the top blowing of the dephosphorizing agent may be stopped just before the end of blowing. Only top blowing with a top blowing gas having a nitrogen concentration of 0.3 mol % or less may be performed.

In the converter blowing method according to the first form and the second form, it is sufficient that the above requirements are satisfied, and other blowing conditions (flow rate and flow velocity of top blowing gas from top blowing lance, molten iron and molten steel (composition, temperature, etc.) may be the same as conventional ones.

1.4 Effect As described above, according to the converter blowing method of the present disclosure, a dephosphorization rate higher than the rephosphorization rate can be obtained at the hot point by spraying the dephosphorization agent onto the molten pig iron or molten steel in the latter half of the blowing. Therefore, it is possible to eliminate the rephosphorization of molten iron or molten steel, which is a concern in the latter half to the final stage of blowing, which becomes high temperature. absorption of nitrogen can also be suppressed. As a result, steel with low nitrogen and phosphorus concentrations is likely to be melted.

2. Converter equipment The converter blowing method of the present disclosure may be implemented, for example, in a converter equipment capable of switching the type of top-blown gas. The technology of the present disclosure also has an aspect as converter equipment.

As shown in FIG. 5, the converter facility 100 according to one embodiment includes a converter 10, a top blowing lance 20, a first supply line 31, a second supply line 32, a first supply source 41, , a second source 42 , a third source 43 and a fourth source 44 . The first supply line 31 is connected to the top blowing lance 20 or the second supply line 32 . The second supply line 32 is connected to the top blowing lance 20 or the first supply line 31 . The first supply source 41 is connected to the first supply line 31 and configured to be able to supply oxygen gas to the first supply line 31 . The second supply source 42 is connected to the second supply line 32 and configured to be able to supply the second supply line 32 with the first carrier gas. The third supply source 43 is connected to the second supply line 32 and configured to be able to supply the second carrier gas to the second supply line 32 . The fourth supply source 44 is connected to the second supply line 32 and configured to be able to supply the dephosphorization agent containing Ca to the second supply line 32 . As shown in FIG. 5 , the converter facility 100 allows the dephosphorization agent supplied to the second supply line 32 to pass through the second supply line 32 to the first carrier gas or the second It is configured to be able to be supplied to the top blowing lance 20 or the first supply line 31 together with the carrier gas, and the first carrier supplied to the top blowing lance 20 or the first supply line 31 The gas or the second carrier gas and the dephosphorization agent are configured to be top-blown together with the oxygen from the top-blowing lance 20 into the converter 10, and the second supply line 32 The carrier gas supplied to the converter 10 can be switched between the first carrier gas and the second carrier gas, and by switching the carrier gas, the top blowing lance 20 into the converter 10 It seems that the top-blown gas blown to the top is switchable between a low nitrogen concentration gas having a nitrogen concentration of 0.3 mol% or less and a high nitrogen concentration gas having a nitrogen concentration of more than 0.3 mol% is configured to

As the converter 10, a conventional one may be used. In the converter installation of the present disclosure, the converter 10 may be either a top-blown converter or a top-bottom blown converter. The top-bottom blown converter may have a plurality of flow paths at its bottom for supplying the bottom-blown gas into the furnace. Further, the converter may be provided with a tapping port or the like for tapping the molten steel after smelting on its side.

As the molten iron 1 charged into the converter 10, for example, any general blast furnace molten iron can be used. The hot metal 1 contains P and C as impurities, and may contain Si. When the hot metal 1 contains Si, desiliconization reaction of Si in the hot metal proceeds by oxidation refining with oxygen gas, followed by dephosphorization reaction. After desiliconization, the desiliconization slag in the converter 10 may be discharged, or the dephosphorization by the method of the present disclosure may be performed with the desiliconization slag remaining in the converter 10 . The molten iron 1 may be a mixture of molten iron (for example, blast furnace molten iron) and additive materials such as scrap. The method of charging the hot metal 1 into the converter 10 is also not particularly limited, and for example, a method of pouring the hot metal 1 into the converter 10 using a known container such as a hot metal ladle can be mentioned. As described above, the converter blowing method of the present disclosure may be applied during decarburization blowing, in which case the hot metal 1 in the converter 10 may be dephosphorization hot metal after dephosphorization treatment.

As for the top-blowing lance 20, a lance similar to the conventional one can be used. For example, the upper end side (upstream side) of the top blowing lance 20 may be directly or indirectly connected to the first supply line 31 or the second supply line 32, so that during refining in the converter, the second Oxygen, or oxygen and a carrier gas, or oxygen, a carrier gas and a dephosphorizing agent are supplied from the first supply line 31 or the second supply line 32 to the top blowing lance 20, and the oxygen supplied to the top blowing lance 20, The carrier gas and the dephosphorizing agent are blown out from the outlet on the lower end side of the top blowing lance 20 to the molten iron 1 or molten steel. By blowing a top-blown gas containing oxygen into the hot metal 1 from the top-blowing lance 20, the hot metal 1 can be stirred while oxidative refining can proceed. In addition, when the converter 10 is a top-bottom blowing converter, continuous or intermittent blowing of bottom-blowing gas from the bottom of the converter 10 can also enhance agitation of the molten iron 1 during refining.

The 1st supply line 31 and the 2nd supply line 32 can be constituted by publicly known piping, for example. In particular, since at least a part of the first supply line 31 and the second supply line 32 is configured by a flexible tube, the first supply line 31 and the second supply line 32 can be used to move the upward blowing lance 20 up and down. becomes easier to follow. The first supply line 31 is connected to the top blowing lance 20 or the second supply line 32 , and the second supply line 32 is connected to the top blowing lance 20 or the first supply line 31 . That is, the first supply line 31 and the second supply line 32 may join each other on the upstream side of the top blowing lance 20, or the first supply line 31 and the second supply line 32 may be the top blowing line. They may be separately connected to the lance 20 and merged within the lance.

The first supply source 41 is an oxygen gas supply source, the second supply source 42 is a first carrier gas supply source, the third supply source 43 is a second carrier gas supply source, and the fourth supply source 44 is the source of the dephosphorizing agent. The first supply source 41 is connected to the first supply line 31 via a pipe or the like, and is configured to be able to supply oxygen gas to the first supply line 31 . The second supply source 42 is connected to the second supply line 32 via a pipe or the like, and is configured to be able to supply the first carrier gas to the second supply line 32 . The third supply source 43 is connected to the second supply line 32 via a pipe or the like, and is configured to be able to supply the second carrier gas to the second supply line 32 . The fourth supply source 44 is connected to the second supply line 32 via a pipe or the like, and is configured to be able to supply the dephosphorization agent containing Ca to the second supply line 32 .

The first supply source 41, the second supply source 42, and the third supply source 43, which are gas supply sources, may be containers containing high-pressure gas, for example. Alternatively, if air is used as the carrier gas, the air source 42 or 43 may be the atmosphere, ie the air may be supplied from the atmosphere via a pump or the like. Examples of the first carrier gas include gases with a high nitrogen concentration, and specific examples include nitrogen and air. Examples of the second carrier gas include gases with a low nitrogen concentration, and specific examples include argon and carbon dioxide. The supply source 44 of the dephosphorization agent may be any device capable of supplying the dephosphorization agent in the form of powder to the second supply line 32, and a general powder supply device may be employed.

The converter facility 100 can supply the dephosphorizing agent supplied to the second supply line 32 to the top blowing lance 20 or the first supply line 31 through the second supply line 32 together with the carrier gas. The carrier gas and the dephosphorizing agent supplied to the top blowing lance 20 or the first supply line 31 enter the converter 10 from the top blowing lance 20 together with oxygen from the first supply line. and can be blown upward. Further, the carrier gas supplied to the second supply line 32 is configured to be switchable between the first carrier gas and the second carrier gas, so that the upper blowing lance 20 into the converter 10 The blown top-blown gas is configured to be switchable between a low nitrogen concentration gas having a nitrogen concentration of 0.3 mol% or less and a high nitrogen concentration gas having a nitrogen concentration of more than 0.3 mol%. ing. For example, by configuring a part of the supply source or supply line to be openable/closable by a valve or the like, it is possible to switch between supplying the carrier gas and the dephosphorizing agent from the second supply line 32 to the lance and stopping the supply. Further, the carrier gas supplied to the second supply line 32 can be switched between the first carrier gas and the second carrier gas. Thus, according to the converter equipment 100, the first supply line 31, which is the oxygen supply line, and the second supply line 32, which is the supply line for the carrier gas and the dephosphorizing agent, are connected to the top blowing lance 20 respectively. , and whether or not the carrier gas and the dephosphorizing agent are supplied from the second supply line 32 to the top blowing lance 20, and the type of carrier gas supplied to the top blowing lance 20 can be switched. By being configured, both of the converter blowing methods according to the first and second embodiments can be implemented.

EXAMPLES The present invention will be further described below with reference to examples, but the present invention is not limited to the following examples. The present invention can adopt various conditions as long as it achieves its purpose without departing from the gist thereof.

1. Experiment 1
A test converter was used to investigate the upper limit of the nitrogen concentration contained in the top-blown gas in the case of blowing while blowing CaO powder into the hot metal to obtain molten steel with a sufficiently low nitrogen concentration. Specifically, in a decarburization blowing experiment of hot metal using a test converter as shown in FIG. Phosphorus concentration and nitrogen concentration in molten steel were measured. The experimental conditions are as follows.

First, 2.0 tons of hot metal at a temperature of 1300° C. to 1400° C. was charged into a test converter of top and bottom blowing. The hot metal has a carbon concentration equivalent to desiliconization and dephosphorization of 3.2 to 3.5% by mass, a silicon concentration of 0.05% by mass or less, a manganese concentration of 0.1% by mass or less, and a phosphorus concentration of 0.03 to 3.5% by mass. Hot metal with a composition of 0.05% by mass and a sulfur concentration of 0.005 to 0.01% by mass was used. A 5-hole lance was used as the top blowing lance. As the CaO-containing powder, quicklime powder having a pure CaO content of 97% was used. The quicklime powder was transported from the powder feeder to the upper end of the lance through a pipe and a flexible hose by a carrier gas, connected to the oxygen supply pipe at the upper end of the lance, and merged with the top-blown oxygen gas. After that, oxygen gas, carrier gas, and CaO-containing powder were mixed and passed through the lance, and were sprayed toward the molten iron from five nozzles provided at the tip of the lance. A total of 20 kg of quicklime powder was blown at a constant supply rate from the beginning to the end of blowing by the above method. The oxygen gas for top blowing is 6.5 Nm ³ /min, the carrier gas flow rate is 0.1 to 0.3 Nm ³ /min, the total gas flow rate is 6.6 to 6.8 Nm ³ /min, and the lance height is Blowing was performed at 450 mm. Various gases as shown in Table 1 below were used as the carrier gas, and the experiment was carried out by adjusting the nitrogen concentration to 0 to 4.4 mol % when mixed with oxygen gas. In addition to the above dephosphorization agent, 5.0 kg of silica stone and 3.0 kg of MgO grains were added as fluxes by placing them on the hot metal before blowing. Further, bottom blowing was performed by blowing argon gas at a flow rate of 0.1 Nm ³ /min from each of the four tuyeres.

Molten steel in the furnace was sampled after blow tempering, and the phosphorus concentration and nitrogen concentration in the molten steel were analyzed. The phosphorus concentration in the molten steel was 0.005% or less under any conditions. On the other hand, the nitrogen concentration was a different value for each condition. Table 1 below shows experimental conditions and experimental results.

As is clear from the results shown in Table 1, the higher the nitrogen concentration in the top-blown gas, the higher the nitrogen concentration in the molten steel. As shown in Table 1, in order to make the nitrogen concentration in the molten steel 0.0015% by mass or less, which is equivalent to the case of top-blowing only oxygen gas, the nitrogen concentration in the top-blowing gas must be 0.3 mol. % or less.

2. Experiment 2
In the above examination, it was assumed that the carrier gas was also kept flowing because the quicklime powder was continuously blown upward during the blowing. On the other hand, in order to keep the nitrogen concentration in the top-blown gas at 0.3 mol % or less, a large amount of expensive carrier gas with a low nitrogen concentration is consumed, which may lead to a significant cost increase. Therefore, from the viewpoint of reducing the consumption of expensive carrier gas, conditions for top blowing quick lime powder after the second half of blowing when rephosphorization is remarkable without continuing top blowing quick lime powder from the beginning to the end of blowing, The condition of using an inexpensive carrier gas with high nitrogen concentration in the first half of blowing and using an expensive carrier gas with low nitrogen concentration in the latter half of blowing was investigated. The experimental conditions are as follows.

In the converter equipment as shown in FIG. 5, 290 to 310 tons of hot metal is charged into the top and bottom blown converter, and after adding auxiliary materials, oxygen gas is blown onto the hot metal from a top blowing lance to decarburize. did A five-hole lance was used as the top blowing lance. An oxygen gas supply pipe (first supply line) is connected to the upper end of the lance, and a powder supply pipe (second supply line) is connected to the oxygen gas supply pipe near the upper end of the lance. A valve is provided in the powder supply pipe in the vicinity of the connection with the supply pipe, and the valve can be opened when the powder is to be supplied and closed when the powder is not to be supplied, and when the powder supply is not required. Waste of carrier gas can be suppressed. Further, an oxygen supply source (first supply source) is connected to the oxygen gas supply pipe so that oxygen can flow, while a first carrier gas supply source (second supply source) and a second 2 A carrier gas supply source (third supply source) and a powder supply device as a powder supply source (fourth supply source) are connected, and the vicinity of the first carrier gas supply source and the second carrier gas supply source are connected. , respectively, so that the carrier gas supplied to the powder supply pipe can be switched between the first carrier gas and the second carrier gas. Molten iron is molten iron that has undergone desiliconization and dephosphorization treatment in advance in a dephosphorization converter and is once discharged from the dephosphorization converter into a hot metal ladle. A silicon concentration of 0.05% by mass or less, a manganese concentration of 0.1% by mass or less, a phosphorus concentration of 0.02 to 0.04% by mass, and a sulfur concentration of 0.005 to 0.01% by mass was used. . As auxiliary raw materials, 2.4 to 3.4 t of lump quicklime, 0.5 to 0.8 t of silica stone, 0.6 to 1.0 t of peridotite, and up to 3.0 t of iron ore were added.

For Comparative Examples 1 to 12 and Examples 1 to 6, decarburization blowing was performed under the experimental conditions shown in Table 2 below, and after blowing, the phosphorus concentration and nitrogen concentration in the molten steel were analyzed. When the phosphorus concentration in molten steel was 0.005% by mass or less, it was evaluated as acceptable (⊚, ◯), and when it exceeded 0.005% by mass, it was evaluated as unacceptable (×). In particular, when the phosphorus concentration in the molten steel was 0.003% by mass or less, it was evaluated as good (⊚). In addition, when the nitrogen concentration in the molten steel is 0.0015% by mass or less in the molten steel obtained by decarburization blowing without powder top blowing, it is evaluated as passing (○), and 0.00% by mass. A case of exceeding 0015% by mass was evaluated as disqualified (x). The results are shown in Table 2 below.

The results shown in Table 2 reveal the following.

Comparative Example 1 is an example in which CaO powder is top-blown with oxygen at 0.8 kg/min/t from 10% of blowing (top-blown oxygen amount ratio) to 100% of blowing. N ₂ gas was used as the carrier gas, and the CaO powder was supplied to the oxygen line at a carrier gas flow rate of 2000 Nm ³ /min. The oxygen gas flow rate was 48,000 to 65,000 Nm ³ /h, the total flow rate of the top-blown gas was 50,000 to 67,000 Nm ³ /h, and the N ₂ concentration of the top-blown gas was 3.0 to 4.0 mol %. When the phosphorus concentration and nitrogen concentration in the molten steel were analyzed after the end of blowing, the phosphorus concentration in the molten steel was 0.003% by mass, indicating sufficient dephosphorization. It is considered that the rephosphorization was suppressed by the top blowing of the powder until the end of blowing. On the other hand, the nitrogen concentration in molten steel was 0.0042% by mass, which was significantly higher than the 0.0015% by mass nitrogen concentration in molten steel obtained by decarburization blowing without powder top blowing. Since the nitrogen concentration in the top-blown gas at the time of powder top-blowing was too high, nitrogen absorption occurred in the molten steel during blowing, and it is thought that this remained even after the end of blowing.

Comparative Examples 2 to 5 are examples in which air is used as the carrier gas, and decarburization blowing is performed with the powder top blowing end timing set at 70% to 100% of the blowing. When the phosphorus concentration and nitrogen concentration in the molten steel were analyzed after the end of blowing, the phosphorus concentration in the molten steel was 0.005% or less as in Comparative Example 1, and there was no problem with dephosphorization. The nitrogen concentration significantly increased from the nitrogen concentration of 0.0015% by mass in molten steel obtained by decarburization blowing without powder top blowing. As in Comparative Example 1, the nitrogen concentration in the top-blown gas at the time of powder top-blowing was too high.

Example 1 is an example in which CaO powder was top-blown together with oxygen from 10% of blowing (top-blown oxygen amount ratio) to 100% of blowing. However, argon containing no nitrogen was used as a carrier gas for the CaO powder. When the phosphorus concentration and nitrogen concentration in the molten steel were analyzed after blowing, the phosphorus concentration in the molten steel was good at 0.002% by mass, and the nitrogen concentration in the molten steel was 0.0012% by mass. It was possible to achieve a low concentration equivalent to the case where the body blowing is not performed.

However, in Example 1, powder top blowing was performed using argon as the carrier gas over a period of 60% or more of the blowing, so the manufacturing cost was lower than when nitrogen or air was used as the carrier gas. There is concern about an increase in In order to solve this problem, the following comparative examples and examples were examined.

Comparative Examples 6 to 8 are examples in which air was used as a carrier gas and CaO powder was top-blown only in the final stage of blowing. Specifically, top blowing of CaO powder was started at the time of 80% to 95% of blowing, and CaO powder was top blown with oxygen at 0.8 to 0.9 kg/min/t until the end of blowing. When the phosphorus concentration and nitrogen concentration in the molten steel were analyzed after blowing, the phosphorus concentration in the molten steel was as low as 0.004 to 0.005% by mass, but the nitrogen concentration in the molten steel was similar to that of powder. The nitrogen concentration in molten steel obtained by decarburization blowing without top blowing was greatly increased from 0.0015% by mass. As in Comparative Examples 1 to 5, the nitrogen concentration in the top-blown gas at the time of powder top-blowing was too high.

Examples 2 to 4 are examples in which a nitrogen-free carrier gas was used and CaO powder was top-blown only in the final stage of blowing. Specifically, top blowing of CaO powder was started at the time of 80% to 95% of blowing, and CaO powder was top blown with oxygen at 0.8 to 1.2 kg/min/t until the end of blowing. When the phosphorus concentration and nitrogen concentration in the molten steel were analyzed after blowing, the phosphorus concentration in the molten steel was as low as 0.005% by mass, and the nitrogen concentration was also 0.0010 to 0.001%. 0013% by mass, which is equivalent to the case where the powder top blowing is not carried out, could be made as low as possible. In this way, by performing top blowing with a top blowing gas with a low nitrogen concentration from the start of blowing to the end of blowing, and top blowing CaO powder at the end of blowing, in addition to the powder cost, the carrier gas cost was also able to be suppressed as compared with Example 1.

As described above, good dephosphorization results were obtained in Examples 2 to 4 in which CaO powder was top-blown only in the final stage of blowing. Phosphorus concentration inside is slightly high. In this respect, from the viewpoint of dephosphorization, it can be said that it is preferable to top blow CaO powder from the first half of blowing to the final stage of blowing. In this respect, although the CaO powder is top-blown from the first half of the blowing process, switching the carrier gas species during the blowing process has been considered.

Examples 5 and 6, and Comparative Examples 9 and 10 are examples in which CaO powder is top-blown from the first half of blowing, and the carrier gas type is switched from a high nitrogen concentration gas to a low nitrogen concentration gas in the middle of blowing. . As is clear from the results of Examples 5 and 6, air was used as the carrier gas in the first half of the blowing period, and by switching the carrier gas to Ar gas before reaching 60% of the blowing period, The phosphorus concentration in the molten steel could be lowered to 0.003% by mass or less, and the nitrogen concentration in the molten steel could be similarly suppressed to a low level. However, as is clear from the results of Comparative Examples 9 and 10, if the timing of switching the carrier gas is too late, the concentration of nitrogen in the finally obtained molten steel increases. It is thought that the absorption of nitrogen in the molten pig iron or molten steel occurred in the first half of the blowing and remained after the end of the blowing. From the results of Examples 5 and 6 and Comparative Examples 9 and 10, it can be seen that the nitrogen concentration in the finally obtained molten steel can be reduced by switching the carrier gas at a stage of less than 60% of blowing. .

Comparative Examples 11 and 12 correspond to the prior art. That is, this is an example in which CaO powder is top-blown in the first half of blowing, and only top-blowing gas (oxygen) is top-blown without top-blowing CaO powder in the second half of blowing. In this case, although the nitrogen concentration in the finally obtained molten steel can be reduced, the phosphorus concentration will increase significantly. It is considered that rephosphorization occurred in the latter half of blowing, when the temperature was higher, and the effect of promoting dephosphorization in the first half of blowing was reduced.

3. Summary From the above experiments, in the converter blowing method in which the top blowing gas containing oxygen is blown from the top blowing lance to the molten pig iron or molten steel in the converter, when the following requirements 1-1 and 1-2 are satisfied Alternatively, when the following requirement 2-1 is satisfied, it can be said that nitrogen absorption and rephosphorization of molten iron or molten steel can be suppressed, and the phosphorus concentration and nitrogen concentration of the finally obtained molten steel can be sufficiently reduced.

Requirement 1-1: From the blowing start time T _S to time T _A1 , a top blowing gas having a nitrogen concentration of 0.3 mol % or less is blown from a top blowing lance to molten iron or molten steel. Here, the total amount of oxygen blown from the top blowing lance from the blowing start time _TS to the time _TA1 is the total amount of oxygen blown from the top blowing _lance from the blowing start time _TS to the blowing end time TE. 60% or more of the oxygen content.

Requirement 1-2: A dephosphorizing agent containing Ca is blown together with a low nitrogen concentration gas as a top blowing gas from a top blowing lance to the molten pig iron or molten steel at least from time T _A1 to the end of blowing. Here, the low nitrogen concentration gas contains oxygen and a carrier gas and has a nitrogen concentration of 0.3 mol % or less.

Requirement 2-1: From time _TA2 after the start of blowing to the end of blowing, a dephosphorizing agent containing Ca is blown together with a low nitrogen concentration gas as a top blowing gas from a top blowing lance to molten iron or molten steel. Here, the total amount of oxygen blown from the top blowing lance from the blowing start time T _S to the time T _A2 is the total amount of oxygen blown from the top blowing lance from the blow start time T _S to the blow end time T _E less than 60% of the volume, the low nitrogen concentration gas includes oxygen and a carrier gas and has a nitrogen concentration of 0.3 mol% or less.

100 converter equipment 1 molten iron (or molten steel)
10 converter 20 top blowing lance 31 first supply line 32 second supply line 41 first supply source 42 second supply source 43 third supply source 44 fourth supply source

Claims (6)

A converter blowing method,
Blowing a top-blowing gas containing oxygen from a top-blowing lance onto the molten pig iron or molten steel in the converter,
meet the following requirements 1-1 and 1-2,
Converter blowing method.
Requirement 1-1: From blowing start time T _S to time T _A1 , top blowing gas having a nitrogen concentration of 0.3 mol % or less is blown from the top blowing lance to the molten iron or molten steel. Here, the total amount of oxygen blown from the top blowing lance from the blow start time T _S to the time T _A1 is the amount of oxygen blown from the top blow lance from the blow start time T _S to the blow end time T _E 60% or more of the total oxygen available.
Requirement 1-2: At least from the time T _A1 to the end of blowing, a dephosphorizing agent containing Ca is blown from the top blowing lance to the molten iron or molten steel together with a low nitrogen concentration gas as a top blowing gas. Here, the low nitrogen concentration gas contains oxygen and a carrier gas and has a nitrogen concentration of 0.3 mol % or less. meet the following requirements 1-1a and 1-1b,
The converter blowing method according to claim 1.
Requirement 1-1a: Nitrogen concentration from the top blowing lance to the molten iron or molten steel from the blowing start time T _S to any time T _B1 after the blowing start has a nitrogen concentration of 0.3 mol% or less The dephosphorization agent is not sprayed while the top-blown gas is blown.
Requirement 1-1b: From the time T _B1 to the time T _A1 , the dephosphorizing agent is blown from the top blowing lance onto the molten iron or molten steel together with the low nitrogen concentration gas as the top blowing gas. A converter blowing method,
Blowing a top-blowing gas containing oxygen from a top-blowing lance onto the molten pig iron or molten steel in the converter,
meet the following requirement 2-1,
Converter blowing method.
Requirement 2-1: From the time T _A2 after the start of blowing to the end of blowing, from the top blowing lance to the molten pig iron or molten steel, together with a low nitrogen concentration gas as the top blowing gas, a dephosphorizing agent containing Ca spray. Here, the total amount of oxygen blown from the top blowing _lance from the blowing start time _{T S} to the time T _A2 is The low nitrogen concentration gas comprises oxygen and a carrier gas and has a nitrogen concentration of 0.3 mol % or less. meet the following requirement 2-2,
The converter blowing method according to claim 3.
Requirement 2-2: From the blowing start time T _S to the time T _A2 , or from any time T _B2 after the start of blowing to the time T _A2 , from the top blowing lance to the molten iron or molten steel Then, a top-blown gas having a nitrogen concentration of more than 0.3 mol % is blown, and at the time _TA2 , the top-blown gas is switched to the low nitrogen concentration gas. meet the following requirements 2-2a and 2-2b,
The converter blowing method according to claim 4.
Requirement 2-2a: From the blowing start time T _S to the time T _B2 , from the top blowing lance to the molten iron or molten steel, top blowing gas having a nitrogen concentration of more than 0.3 mol% or 0.3 While blowing a top-blown gas having a nitrogen concentration of mol % or less, the dephosphorization agent is not blown.
Requirement 2-2b: From the time point T _B2 to the time point T _A2 , the dephosphorizing agent is sprayed from the top blowing lance to the molten iron or molten steel together with a high nitrogen concentration gas as the top blowing gas, and the above time point At _TA2 , the type of top-blown gas is switched. Here, the high nitrogen concentration gas contains oxygen and a carrier gas and has a nitrogen concentration of more than 0.3 mol %. A converter facility comprising a converter, a top-blowing lance, a first supply line, a second supply line, a first supply source, a second supply source, a third supply source, and a fourth supply source and
The first supply line is connected to the top blowing lance or the second supply line,
The second supply line is connected to the top blowing lance or the first supply line,
The first supply source is connected to the first supply line and is configured to be capable of supplying oxygen gas to the first supply line,
the second supply source is connected to the second supply line and is configured to be capable of supplying a first carrier gas to the second supply line;
the third supply source is connected to the second supply line and configured to supply a second carrier gas to the second supply line;
The fourth supply source is connected to the second supply line and configured to be capable of supplying a dephosphorization agent containing Ca to the second supply line,
The dephosphorization agent supplied to the second supply line is sent to the top blowing lance or the first supply line together with the first carrier gas or the second carrier gas via the second supply line. configured to be able to supply
The first carrier gas or the second carrier gas supplied to the top blowing lance or the first supply line and the dephosphorizing agent together with the oxygen rise from the top blowing lance into the converter. configured to be blowable,
The carrier gas supplied to the second supply line is configured to be switchable between the first carrier gas and the second carrier gas,
By switching the carrier gas, the top-blown gas blown from the top-blowing lance into the converter is a low nitrogen concentration gas having a nitrogen concentration of 0.3 mol% or less and a nitrogen concentration of more than 0.3 mol%. is configured to be switchable between a high nitrogen concentration gas having a nitrogen concentration of
Converter equipment.

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