JP7712533B2 - Converter blowing method and converter equipment - Google Patents

Description

This application discloses a converter blowing method and converter equipment.

As disclosed in Patent Document 1, a method for producing low-phosphorus steel from blast furnace hot metal is known in which the hot metal is dephosphorized at a low temperature and high carbon concentration range that are thermodynamically favorable for dephosphorization, and then the hot metal is decarburized and blown. Since the dephosphorized hot metal has a lower phosphorus concentration than untreated hot metal, the dephosphorization load in the next decarburization blowing process is reduced. On the other hand, the dephosphorized hot metal inevitably contains dephosphorization slag generated in the dephosphorization process. In other words, a portion of the dephosphorization slag generated in the dephosphorization process is carried over to the next decarburization blowing process. Here, in the decarburization blowing, the high temperature and low carbon concentration range are thermodynamically unfavorable for dephosphorization, and therefore rephosphorization of the dephosphorization slag into the hot metal or molten steel is likely to occur. In this regard, in order to prevent rephosphorization from the dephosphorization slag into molten steel during decarburization blowing, it is necessary to add a dephosphorization agent during decarburization blowing.

Examples of dephosphorization agents added in decarburization blowing include Ca-containing dephosphorization agents. For example, the dephosphorization agent may contain CaO or CaCO _3. These dephosphorization agents turn into slag at a high-temperature hot point and efficiently cause a dephosphorization reaction by a transitory reaction. A method of adding a dephosphorization agent in decarburization blowing is generally a method of adding a lump of dephosphorization agent to the molten pig iron or molten steel from above, but there is also a method of blowing the dephosphorization agent from a top-blowing lance onto the molten pig iron or molten steel together with top-blowing gas. In this case, the dephosphorization agent and oxygen gas carried by the carrier gas are merged and then top-blowing is performed, in other words, the top-blowing gas contains oxygen gas and carrier gas.

Nitrogen gas is usually used as the carrier gas for the dephosphorization agent from the standpoint of cost and safety. However, when nitrogen gas is used as the carrier gas, top-blowing gas with a high nitrogen concentration is blown from the top lance onto the molten steel during decarburization blowing, which increases the nitrogen concentration in the molten steel. Since nitrogen in steel reduces the toughness of the 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 dephosphorization agent together with the top-blowing gas during decarburization blowing when the amount of blown oxygen is 10% to 50% of the total amount of oxygen. In other words, by blowing a dephosphorization agent in the first half of blowing, it is possible to suppress nitrogen absorption into the molten pig iron or molten steel in the second half of blowing, and it is possible to keep the nitrogen concentration in the final molten steel low.

JP 2011-144415 A JP 2020-105562 A

According to the findings of the present inventors, by spraying a dephosphorization agent in the first half of blowing as disclosed in Patent Document 2, it is possible to promote dephosphorization of molten pig iron or molten steel while suppressing nitrogen absorption into the molten pig iron or molten steel, but rephosphorization occurs in the second half of blowing where the temperature is higher, reducing the dephosphorization promotion effect in the first half of blowing. In this regard, a new technology capable of suppressing nitrogen absorption and rephosphorization of molten pig iron or molten steel in converter blowing is needed.

As one of the means for solving the above problems, the present application provides:
A converter blowing method, comprising the steps of:
The method includes blowing a top-blowing gas containing oxygen from a top-blowing lance onto the molten iron or steel in the converter,
The following requirements 1-1 and 1-2 are met:
A converter blowing method is disclosed.

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

Requirement 1-2: From at least the time T _A1 to the end of blowing, a dephosphorizing agent containing Ca is blown from the top blowing lance onto the molten pig iron or molten steel together with a low-nitrogen concentration gas as a top blown gas, wherein 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 disclosed herein may satisfy the following requirements 1-1a and 1-1b.

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

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

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

Requirement 2-1: From time T _A2 after the start of blowing to the end of blowing, a dephosphorizing agent containing Ca is sprayed from the top lance onto the molten pig iron or molten steel together with a low-nitrogen concentration gas as the top-blowing gas, wherein the total amount of oxygen blown from the top lance from the start of blowing T _S to the time T _A2 is less than 60% of the total amount of oxygen blown from the top lance from the start of blowing T _S to the end of blowing T _E , and 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 disclosed herein 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 , a top-blowing gas having a nitrogen concentration of more than 0.3 mol% is blown from the top-blowing lance to the molten iron or molten steel, and at the time T _A2 , the top-blowing gas is switched to the low-nitrogen concentration gas.

The converter blowing method disclosed herein 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 , a top-blowing gas having a nitrogen concentration of more than 0.3 mol % or a top-blowing gas having a nitrogen concentration of 0.3 mol % or less is blown from the top blowing lance onto the molten pig iron or the molten steel, while the dephosphorization agent is not blown.

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

As one of the 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;
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 able to supply oxygen gas to the first supply line;
the second supply source is connected to the second supply line and is configured to be able to supply a first carrier gas to the second supply line;
the third supply source is connected to the second supply line and is configured to be able to supply a second carrier gas to the second supply line;
the fourth supply source is connected to the second supply line and is configured to be able to supply a dephosphorization agent containing Ca to the second supply line;
The dephosphorization agent supplied to the second supply line can be supplied to the top blowing lance or the first supply line via the second supply line together with the first carrier gas or the second carrier gas,
the first carrier gas or the second carrier gas and the dephosphorization agent supplied to the top-blowing lance or the first supply line can be blown from the top into the converter together with the oxygen,
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-blowing gas blown from the top-blowing lance into the converter can be switched 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%.
A converter furnace system is disclosed.

The technology disclosed herein makes it possible to suppress nitrogen absorption and rephosphorization of molten iron or steel during converter blowing.

2 shows an example of a flow in a converter blowing method according to the first embodiment. 2 shows an example of a flow in a converter blowing method according to the first embodiment. 2 shows an example of a flow in a converter blowing method according to a second embodiment. 2 shows an example of a flow in a converter blowing method according to a second embodiment. 1 shows a schematic diagram of an example of the configuration of a converter facility.

1. Converter Blowing Method The converter blowing method of the present disclosure is a method for producing low-phosphorus steel while suppressing absorption and rephosphorization of the molten pig iron or molten steel by blowing a top-blowing gas containing oxygen from a top-blowing lance onto the molten pig iron or molten steel in a converter, using a carrier gas that does not contain nitrogen or has a low nitrogen gas concentration, and top-blowing a dephosphorizing agent together with the oxygen. Two embodiments of the converter blowing method of the present disclosure are described below.

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

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

Requirement 1-2: From at least the time T _A1 to the end of blowing, a dephosphorizing agent containing Ca is blown from the top blowing lance onto the molten pig iron or molten steel together with a low-nitrogen concentration gas as a top blown gas, wherein 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
1 , in the converter blowing method according to the first embodiment, top blown gas having a nitrogen concentration of 0.3 mol% or less is blown from a top lance onto molten pig iron or molten steel from a blowing start time T _S to a blowing end time T _A1 , where the total amount of oxygen blown from the top lance from the blowing start time T _S to _the blowing end time T A1 is 60% or more of the total amount of oxygen blown from the top lance from the blowing start time T _S to the blowing end time T _E.

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

The "end of blowing time T _E " refers to the time when the top blowing of oxygen from the top lance is ended in converter blowing (the time when the top-blown oxygen amount is 100%). For example, in decarburization blowing, it may be the time when the top blowing of oxygen is ended and molten steel is produced.

"Time _TA1 " refers to the time when 60% or more of the total amount of oxygen blown from the top lance from the blowing start time _TS to the blowing end time _TE has been blown. Time _TA1 may be the time when 65% or more, 70% or more, 75% or more, or 80% or more of the total amount of oxygen blown from the top lance from the blowing start time _TS to the blowing end time _TE has been blown.

As shown in FIG. 1, the "top blown gas having a nitrogen concentration of 0.3 mol % or less" may be oxygen alone or a mixed gas of oxygen and a gas other than oxygen. In this case, examples of the gas other than oxygen include 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 to a gas other than oxygen in the mixed gas is not particularly limited, and may be appropriately adjusted according to the intended blowing conditions. The gas other than oxygen may be a carrier gas for carrying a dephosphorization agent, which will be described later. That is, as shown in FIG. 1, in the converter blowing method according to the first embodiment, a dephosphorization agent may or may not be top-blown together with the top blown gas during the period from the blowing start time T _S to the time T _A1 .

1, in the converter blowing method according to the first embodiment, from the blowing start time T _S to time T _A1 , top blown gas having a nitrogen concentration of 0.3 mol% or less is blown from the top blowing lance onto the molten pig iron or molten steel, without blowing a top blown gas having a nitrogen concentration of more than 0.3 mol%. According to the findings of the present inventors, if top blown gas having a nitrogen concentration of more than 0.3 mol% is blown from the blowing start time T _S to time T _A1 , nitrogen absorption into the molten pig iron or molten steel occurs, and the nitrogen taken into the molten pig iron or molten steel is not sufficiently removed by the time the blowing is completed, resulting in a high nitrogen concentration in the finally produced steel. In contrast, by blowing top blown gas having a nitrogen concentration of 0.3 mol% or less from the top lance onto the molten pig iron or molten steel from the start time _Ts of blowing to the time _TAl , as in the converter blowing method according to the first embodiment, it is possible to suppress nitrogen absorption into the molten pig iron or molten steel in the first half of the blowing, and the nitrogen concentration of the steel that is finally produced 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, a dephosphorizing agent containing _Ca is blown from a top lance to molten pig iron or molten steel together with a low-nitrogen gas as a top-blowing gas from at least a time point T A1 to the end of blowing. Here, the low-nitrogen gas contains oxygen and a carrier gas and has a nitrogen concentration of 0.3 mol% or less.

The "end of blowing" refers to the period from just before the end of blowing to the end of blowing. Specifically, the period when more than 95% of the total amount of oxygen blown from the top lance between the start time T _S and the end time T _E of blowing is blown can be regarded as the end of blowing.

The "low nitrogen gas" is blown from a top blowing lance onto the molten iron or steel as a top blown gas. The low nitrogen gas contains oxygen and a carrier gas. The nitrogen concentration in the low nitrogen 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 gas is not particularly limited, and may be substantially 0. The mixture ratio of oxygen and carrier gas in the low nitrogen gas is not particularly limited, and may be appropriately adjusted to satisfy the above nitrogen concentration depending on the intended blowing conditions.

The "carrier gas" is used to transport the dephosphorization agent and may constitute a 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 gas that does not contain nitrogen or has a low nitrogen concentration is used as the carrier gas. Examples of such carrier gases include argon, carbon dioxide, and air. In particular, when argon or carbon dioxide is used, it is easier to reduce the nitrogen concentration. In addition, even when air is used as the carrier gas, it is better to combine it with argon or carbon dioxide in order to dilute the nitrogen in the air. From the viewpoint of safety, it is better to avoid using oxygen as the carrier gas. In this regard, the carrier gas may have an oxygen concentration of 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.

The "dephosphorization agent" may be any agent that contains Ca and exhibits a dephosphorization function. For example, a dephosphorization agent containing CaO or a dephosphorization agent containing CaCO ₃ may be used. The dephosphorization agent may contain a SiO ₂ source. Examples of the SiO ₂ source include silica stone and olivine. As shown in FIG. 1, the dephosphorization agent is blown onto the molten pig iron or molten steel together with the low nitrogen concentration gas as the top blown gas. That is, in the converter blowing method of the present disclosure, a lump dephosphorization agent is not added to the molten pig iron or molten steel from above, but a powder dephosphorization agent is blown onto the molten pig iron or molten steel together with the top blown gas. As long as the dephosphorization agent can be blown from the top blowing lance, the shape and size (particle diameter) of the dephosphorization agent are not particularly limited.

In the converter blowing method according to the first embodiment, for example, the dephosphorization agent carried by the above-mentioned carrier gas and the top-blown oxygen are joined together, and the dephosphorization agent is blown from the top-blowing lance onto the molten pig iron or molten steel together with a low-nitrogen concentration gas (a mixture of oxygen and carrier gas) as a top-blown gas. The nitrogen concentration in the low-nitrogen concentration gas is 0.3 mol% or less, which suppresses nitrogen absorption into the molten pig iron or molten steel.

As shown in Fig. 1, in the converter blowing method according to the first embodiment, it is sufficient that the dephosphorization agent is top-blown together with the low-nitrogen concentration gas at least from time T _A1 to the end of blowing. That is, the start time of top blowing of the dephosphorization agent is not limited to time T _A1 , and the dephosphorization agent may be blown before time T _A1 as shown in Fig. 1. The end time of blowing of the dephosphorization agent is not limited to the end of blowing, and the dephosphorization agent may be blown before the end of blowing as shown in Fig. 1. From the viewpoint of further enhancing the dephosphorization effect, the dephosphorization agent may be blown before time T _A1 , and from the viewpoint of reducing costs, the dephosphorization agent does not need to be blown before time T _A1 .

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: From the blowing start time T _S to any time T _B1 after the start of blowing, a top blown gas having a nitrogen concentration of 0.3 mol % or less is blown from the top blowing lance onto the molten pig iron or the molten steel, while the dephosphorization agent is not blown.

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

1 and 2, requirements 1-1a and 1-1b correspond to an example of requirement 1-1. That is, in the converter blowing method according to the first embodiment, only the blowing of a top-blown gas having a low nitrogen concentration may be performed from the start of blowing to a certain time T _B1 , without top blowing of a dephosphorization agent, and top blowing of the dephosphorization agent together with the low-nitrogen concentration gas may be started from the certain time T _B1 . In this way, by not performing top blowing of the dephosphorization agent from the start of blowing time T _S to time T _B1 , and starting top blowing of the dephosphorization agent from time T _B1 , the dephosphorization agent can be stably blown from the top.

2, time T _B1 is the time when less than 60% of the total amount of oxygen blown from the top lance from the blowing start time T _S to the blowing end time T _E has been blown. For example, time T _B1 may be the time when 1% or more, 5% or more, or 10% or more, 50% or less, 40% or less, 30% or less, or 20% or less of the total amount of oxygen blown from the _{top lance} from the blowing start time T S to the blowing end time T E has been blown.

As described above, in the converter blowing method according to the first embodiment, by not injecting top blown gas with a high nitrogen concentration in the first to middle stages of blowing, it is possible to suppress nitrogen absorption in the molten pig iron or molten steel. In addition, in the converter blowing method according to the first embodiment, by injecting a dephosphorizing agent together with top blown gas with a low nitrogen concentration in the second to final stages of blowing when the molten pig iron or molten steel has a high temperature and a low carbon concentration, it is possible to suppress rephosphorization of the molten pig iron or molten steel while suppressing nitrogen absorption in the molten pig iron or molten steel (promoting dephosphorization). As a result, the nitrogen and phosphorus concentrations of the final steel are likely to be reduced.

1.2 Second embodiment A converter blowing method according to a second embodiment includes blowing a top-blowing gas containing oxygen from a top-blowing lance onto molten pig iron or molten steel in a converter, and as shown in FIG. 3, satisfies the following requirement 2-1.

Requirement 2-1: From time T _A2 after the start of blowing to the end of blowing, a dephosphorizing agent containing Ca is sprayed from the top lance onto the molten pig iron or molten steel together with a low-nitrogen concentration gas as the top-blowing gas, wherein the total amount of oxygen blown from the top lance from the start of blowing T _S to the time T _A2 is less than 60% of the total amount of oxygen blown from the top lance from the start of blowing T _S to the end of blowing T _E , and the low-nitrogen concentration gas contains 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 lance from the blowing start time T _S to the blowing end time T _E is less than 60% of the total amount of oxygen blown from the top lance from the blowing start time T _S to the blowing end time T _E. In other words, "time T _A2 " is the time when less than 60% of the total amount of oxygen blown from the top lance from the blowing start time T _S to the blowing end time T _E has been blown. Time T _A2 may be the time when 1% or _more , 5% or more, 10% or more, 20% or more, 30% or more, or 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 of the total amount of oxygen blown from the top lance from the blowing start time T S to the blowing end time T E has been blown. Alternatively, as described below, when a high nitrogen concentration gas is injected until time T _A2 and the top blown gas is switched from a high nitrogen concentration gas to a low nitrogen concentration gas at time T _A2 , time T _A2 may be the time 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 from the blowing start time T _S to the blowing end time T E is blown. By setting time T _A2 to as late as possible, the amount of low nitrogen concentration carrier gas (argon, etc.) used, which is generally expensive, can be reduced.

According to the findings of the present inventors, when a dephosphorizing agent containing Ca is sprayed from the top blowing lance to the molten pig iron or molten steel together with a low-nitrogen gas as a top blown gas from time T _A2 to the end of blowing, even if nitrogen absorption into the molten pig iron or molten steel occurs before time T _A2 , the nitrogen in the molten pig iron or molten steel is removed from time T _A2 to the end of blowing, and the nitrogen concentration of the finally produced steel is likely to be reduced. Moreover, by spraying a dephosphorizing agent from time T _A2 to the end of blowing, rephosphorization of the molten pig iron or molten steel can be suppressed (dephosphorization can be promoted) from the latter half to the end of blowing when the molten pig iron or molten steel has a high temperature and a low carbon concentration. As a result, the nitrogen and phosphorus concentrations of the finally produced 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, nitrogen absorption may occur in the molten pig iron or molten steel between the blowing start time T _S and the time T _A2 , and the nitrogen concentration in the molten pig _iron or molten steel may be high. That is, as shown in Fig. 3, only oxygen may be used as the top blown gas, or a low-nitrogen concentration gas or a high-nitrogen concentration gas may be used between _the blowing start time T S and the time T _A2 . In particular, by blowing a high-nitrogen concentration gas as the top blown gas from the top blowing lance to the molten pig iron or molten steel before the time T _A2 and switching the top blown gas to a low-nitrogen concentration gas at the time T A2, the amount of low-nitrogen concentration carrier gas, which is generally expensive, can be reduced. That is, as shown in Fig. 4, the converter blowing method according to the second embodiment 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 , a top-blowing gas having a nitrogen concentration of more than 0.3 mol% is blown from the top-blowing lance to the molten iron or molten steel, and at the time T _A2 , the top-blowing gas is switched to the low-nitrogen concentration gas.

"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 below.

The method of 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 below, in a converter furnace having an oxygen supply line (first supply line) and a carrier gas supply line (second supply line), by switching the type of carrier gas supplied to the carrier gas supply line, the top-blown gas can be switched from a gas with a high nitrogen concentration to a gas with a low nitrogen concentration. Note that 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 below will mix with the gas with a low nitrogen concentration, and the gas with a low nitrogen concentration will not necessarily be able to be blown up immediately after the switch. Taking this into consideration, it is preferable to manage the timing of the carrier gas switch 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 dephosphorization agent may be performed from the blowing start time T _S , or from any time T _B2 after the start of blowing. In particular, by not performing top blowing of the dephosphorization agent from the blowing start time T _S to time T _B2 and starting top blowing of the dephosphorization agent from time T _B2 , the dephosphorization agent can be stably top blown. 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. 4.

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

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

"Time T _B2 " may be any time between the blowing start time T _S and the above-mentioned time T _A2 . For example, time T _B2 may be the time when more than 0%, 1 _% or more, 3 _% or more, or 5% or more, less than 40%, 30% or less, 20% or less, or 15% or less of the total amount of oxygen blown from the top lance from the blowing start time T S to the blowing end time T E has been blown.

"High nitrogen concentration gas" contains oxygen and a carrier gas, and has a nitrogen concentration of more than 0.3 mol%. That is, the carrier gas used in high nitrogen concentration gas has a high nitrogen concentration. Examples of such carrier gas include nitrogen and air. The nitrogen concentration in 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 Supplementary Note In the converter blowing method according to the first and second embodiments, following the requirements 1-2 and 2-1, it is preferable to blow top-blowing gas having a nitrogen concentration of 0.3 mol% or less from the top lance to the molten pig iron or molten steel even from the final stage of blowing to the end of blowing. In other words, as shown in Figures 2 and 4, it is preferable not to blow top-blowing gas having a nitrogen concentration of more than 0.3 mol% from the top lance to the molten pig iron or molten steel at the final stage of blowing. By blowing top-blowing gas having a nitrogen concentration of 0.3 mol% or less from the top lance to the molten pig iron or molten steel at the final stage of blowing, it is possible to suppress nitrogen absorption into the molten pig iron or molten steel at the final stage of blowing, and it becomes easier to further reduce the nitrogen concentration of the finally produced steel. As described above, in the final stage of blowing, the dephosphorization agent may be top-blown together with the low-nitrogen concentration gas until the end of blowing, or the top blowing of the dephosphorization agent may be stopped immediately before the end of blowing, and only top blowing with the top-blown gas having a nitrogen concentration of 0.3 mol% or less may be performed.

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

1.4 Effects As described above, according to the converter blowing method disclosed herein, by spraying a dephosphorization agent onto the molten pig iron or molten steel in the latter half of blowing, a dephosphorization rate equal to or higher than the rephosphorization rate can be obtained at the hot point, so that it is possible to eliminate the rephosphorization of the molten pig iron or molten steel, which is a concern from the latter half to the end of blowing when the temperature becomes high, and also, by using a carrier gas with a low nitrogen concentration, it is possible to suppress nitrogen absorption into the molten pig iron or molten steel. As a result, steel with low nitrogen and phosphorus concentrations is easily produced.

The converter blowing method of the present disclosure can be implemented in, for example, a converter facility capable of switching the type of top-blown gas.

As shown in FIG. 5, the converter equipment 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 supply source 42, a third supply source 43, and a fourth supply 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 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 and is configured to be able to supply a first carrier gas to the second supply line 32. The third supply source 43 is connected to the second supply line 32 and is configured to be able to supply a second carrier gas to the second supply line 32. The fourth supply source 44 is connected to the second supply line 32 and is configured to be able to supply a dephosphorization agent containing Ca to the second supply line 32 . As shown in FIG. 5, the converter equipment 100 is configured so that the dephosphorization agent supplied to the second supply line 32 can be supplied to the top-blowing lance 20 or the first supply line 31 together with the first carrier gas or the second carrier gas via the second supply line 32, and the first carrier gas or the second carrier gas and the dephosphorization agent supplied to the top-blowing lance 20 or the first supply line 31 can be blown upward from the top-blowing lance 20 into the converter 10 together with the oxygen. 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, and the top-blowing gas blown upward from the top-blowing lance 20 into the converter 10 by switching the carrier 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%.

The converter 10 may be the same as that used in the past. In the converter equipment disclosed herein, 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 bottom-blown gas into the furnace. The converter may also have a tapping port or the like at its side for tapping the molten steel after melting.

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

A lance similar to that used in the past can also be used for the top-blowing lance 20. For example, the top end (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 oxygen, or oxygen and carrier gas, or oxygen, carrier gas and dephosphorizing agent are supplied from the first supply line 31 or the second supply line 32 to the top-blowing lance 20 during converter refining, and the oxygen, carrier gas and dephosphorizing agent supplied to the top-blowing lance 20 are blown out from the outlet on the lower end side of the top-blowing lance 20 into the molten pig iron 1 or molten steel. By blowing top-blowing gas containing oxygen from the top-blowing lance 20 into the molten pig iron 1, oxidation refining can be carried out while stirring the molten pig iron 1. In addition, if the converter 10 is a top-bottom blown converter, the stirring of the molten iron 1 during refining can be enhanced by continuously or intermittently blowing bottom-blown gas from the bottom of the converter 10.

The first supply line 31 and the second supply line 32 may be formed, for example, by known piping. In particular, by forming at least a part of the first supply line 31 and the second supply line 32 by a flexible pipe, the first supply line 31 and the second supply line 32 can easily follow the up-down movement of the top-blowing lance 20. 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 merge with each other upstream of the top-blowing lance 20, or the first supply line 31 and the second supply line 32 may be connected separately to the top-blowing lance 20 and merge within the lance.

The first supply source 41 is a supply source of oxygen gas, the second supply source 42 is a supply source of the first carrier gas, the third supply source 43 is a supply source of the second carrier gas, and the fourth supply source 44 is a supply source of the dephosphorization 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, for example, containers containing high-pressure gas. Alternatively, when air is used as the carrier gas, the air supply source 42 or 43 may be the atmosphere, that is, 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, specifically nitrogen and air. Examples of the second carrier gas include gases with a low nitrogen concentration, specifically argon and carbon dioxide. The dephosphorizing agent supply source 44 may be any one capable of supplying the dephosphorizing agent, which is a powder, to the second supply line 32, and a general powder supply device may be used.

The converter equipment 100 is configured so that the dephosphorization agent supplied to the second supply line 32 can be supplied to the top-blowing lance 20 or the first supply line 31 together with the carrier gas via the second supply line 32, and the carrier gas and the dephosphorization agent supplied to the top-blowing lance 20 or the first supply line 31 can be blown upward from the top-blowing lance 20 into the converter 10 together with oxygen from the first supply line. In addition, 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 top-blowing gas blown upward from the top-blowing lance 20 into the converter 10 can be switched 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%. For example, by configuring a part of the supply source or the supply line to be openable and closable by a valve or the like, it is possible to switch between supplying the carrier gas and the dephosphorization agent from the second supply line 32 to the lance and stopping the supply, and also to switch the carrier gas supplied to the second supply line 32 between the first carrier gas and the second carrier gas. In this way, according to the converter equipment 100, the first supply line 31, which is an oxygen supply line, and the second supply line 32, which is a supply line for the carrier gas and the dephosphorization agent, are each connected to the top blowing lance 20, and are configured to be able to switch between supplying the carrier gas and the dephosphorization agent 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, so that both the converter blowing method according to the first embodiment and the converter blowing method according to the second embodiment can be implemented.

The present invention will be further explained below with reference to examples, but the present invention is not limited to the following examples. The present invention allows various conditions to be adopted as long as the purpose is achieved without departing from the gist of the invention.

1. Experiment 1
The upper limit of the nitrogen concentration contained in the top-blown gas when molten steel with a sufficiently low nitrogen concentration is obtained by performing blowing while top-blowing CaO powder into molten pig iron was investigated using a test converter. Specifically, in a decarburization blowing experiment of molten pig iron using a test converter as shown in Fig. 5, CaO-containing powder as a dephosphorization agent was top-blown together with an oxygen-containing gas, and the phosphorus and nitrogen concentrations in the molten steel obtained after blowing were measured. The experimental conditions were as follows:

First, 2.0 t of molten pig iron at a temperature of 1300°C to 1400°C was charged into a top-bottom blowing test converter. The molten pig iron used had a composition equivalent to desiliconized and dephosphorized pig iron, with a carbon concentration of 3.2 to 3.5 mass%, a silicon concentration of 0.05 mass% or less, a manganese concentration of 0.1 mass% or less, a phosphorus concentration of 0.03 to 0.05 mass%, and a sulfur concentration of 0.005 to 0.01 mass%. A five-hole lance was used as the top-blowing lance. As the CaO-containing powder, quicklime powder with a CaO purity of 97% was used. The quicklime powder was transported from the powder supply device to the top end of the lance by a carrier gas through a pipe and a flexible hose, and was connected to an oxygen supply pipe at the top end of the lance and merged with the top-blowing oxygen gas. Then, the oxygen gas, carrier gas and CaO-containing powder were mixed and passed through the lance, and were sprayed toward the molten pig iron from five nozzles at the tip of the lance. A total of 20 kg of quicklime powder was sprayed at a constant supply rate from the beginning to the end of the blowing process using the above method. The top-blowing oxygen gas was 6.5 Nm ³ /min, the carrier gas flow rate was 0.1-0.3 Nm ³ /min, the total gas flow rate was 6.6-6.8 Nm ³ /min, and the lance height was 450 mm. Various gases shown in Table 1 below were used as the carrier gas, and the experiments were performed so that the nitrogen concentration when mixed with the oxygen gas was 0-4.4 mol%. 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 top of the molten pig iron before blowing. For bottom blowing, argon gas was blown from each of the four tuyere ports at a flow rate of 0.1 Nm ³ /min.

After blowing, molten steel was sampled from the furnace and the phosphorus and nitrogen concentrations in the molten steel were analyzed. The phosphorus concentration in the molten steel was found to be 0.005% or less under all conditions. However, the nitrogen concentration varied depending on the conditions. The experimental conditions and results are shown in Table 1 below.

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 reduce the nitrogen concentration in the molten steel to 0.0015 mass% or less, which is the same as when only oxygen gas is top-blown, the nitrogen concentration in the top-blown gas needs to be reduced to 0.3 mol% or less.

2. Experiment 2
In the above study, the quicklime powder was continuously blown from the top during blowing, so the carrier gas was also continuously flowing. 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 would be consumed, which could lead to a significant increase in costs. Therefore, from the viewpoint of reducing the consumption of expensive carrier gas, the conditions for top-blowing quicklime powder from the early to the end of blowing, when rephosphorization becomes noticeable, and the conditions for using an inexpensive carrier gas with a high nitrogen concentration in the early stage of blowing and an expensive carrier gas with a low nitrogen concentration in the latter stage of blowing were studied. The experimental conditions are as follows.

In a converter facility as shown in Figure 5, 290-310 t of molten iron was charged into a top-and-bottom blown converter, auxiliary materials were added, and then oxygen gas was blown onto the molten iron from a top-blowing lance to perform decarburization blowing. A five-hole lance was used for the top-blowing lance. An oxygen gas supply pipe (first supply line) was connected to the upper end of the lance, and a powder supply pipe (second supply line) was connected to the oxygen gas supply pipe near the upper end of the lance. A valve was provided on the powder supply pipe near the connection between the oxygen gas supply pipe and the powder gas supply pipe, and the valve could be opened when powder was being supplied and closed when powder was not being supplied, making it possible to reduce waste of carrier gas when powder supply was not required. The oxygen gas supply pipe is connected to an oxygen supply source (first supply source) to allow oxygen to flow, while the powder supply pipe is connected to a first carrier gas supply source (second supply source), a second carrier gas supply source (third supply source), and a powder supply device serving as a powder supply source (fourth supply source), and valves are provided near the first carrier gas supply source and near the second carrier gas supply source, 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. The molten pig iron used was molten pig iron that had been previously desiliconized and dephosphorized in a dephosphorization converter and then tapped from the dephosphorization converter into a molten pig iron ladle, and had a carbon concentration of 3.2 to 3.5 mass%, a silicon concentration of 0.05 mass% or less, a manganese concentration of 0.1 mass% or less, a phosphorus concentration of 0.02 to 0.04 mass%, and a sulfur concentration of 0.005 to 0.01 mass%. As auxiliary raw materials, 2.4 to 3.4 t of lump lime, 0.5 to 0.8 t of silica, 0.6 to 1.0 t of peridotite, and up to 3.0 t of iron ore were added.

For each of Comparative Examples 1 to 12 and Examples 1 to 6, decarburization blowing was performed under the experimental conditions shown in Table 2 below, and the phosphorus and nitrogen concentrations in the molten steel were analyzed after blowing. A phosphorus concentration of 0.005 mass% or less in the molten steel was evaluated as pass (◎, ○), and a concentration exceeding 0.005 mass% was evaluated as fail (×). In particular, a phosphorus concentration of 0.003 mass% or less in the molten steel was evaluated as good (◎). In addition, a nitrogen concentration of 0.0015 mass% or less in the molten steel obtained by decarburization blowing without powder top blowing was evaluated as pass (○), and a concentration exceeding 0.0015 mass% was evaluated as fail (×). 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 was top-blown together with oxygen at 0.8 kg/min/t from 10% (top-blown oxygen ratio) of the blowing to the end of 100% blowing. _N2 gas was used as the carrier gas, and CaO powder was supplied to the oxygen line at a carrier gas flow rate of 2000 ^Nm3 /min. The oxygen gas flow rate was 48000-65000 ^Nm3 /h, the total flow rate of the top-blown gas was 50000-67000 ^Nm3 /h, and the _N2 concentration of the top-blown gas was 3.0-4.0 mol%. After the end of blowing, the phosphorus concentration and nitrogen concentration in the molten steel were analyzed, and the phosphorus concentration in the molten steel was 0.003 mass%, indicating sufficient dephosphorization. It is believed that rephosphorization was suppressed by the powder top blowing performed until the end of blowing. On the other hand, the nitrogen concentration in the molten steel was 0.0042 mass%, which was significantly higher than the nitrogen concentration of 0.0015 mass% in the molten steel obtained in decarburization blowing without top powder blowing. It is considered that the nitrogen concentration in the top blown gas during top powder blowing was too high, causing nitrogen absorption in the molten steel during blowing, and this remained even after the end of blowing.

Comparative Examples 2 to 5 are examples of decarburization blowing in which air was used as the carrier gas and the timing for ending top powder blowing was set to 70% to 100% of the blowing. After the blowing was completed, the phosphorus and nitrogen concentrations in the molten steel were analyzed. As in Comparative Example 1, the phosphorus concentration in the molten steel was 0.005% or less, and there was no problem with dephosphorization, but the nitrogen concentration in the molten steel was significantly higher than the nitrogen concentration of 0.0015 mass% obtained in decarburization blowing without top powder blowing. As in Comparative Example 1, the nitrogen concentration in the top blown gas during top powder blowing was too high, causing nitrogen absorption in the molten steel during blowing, which is thought to have remained even after the blowing was completed.

Example 1 is an example in which CaO powder was top-blown together with oxygen from 10% (top-blown oxygen ratio) of the blowing to the end of 100% of the blowing. However, argon, which does not contain nitrogen, was used as the carrier gas for the CaO powder. After the end of the blowing, the phosphorus concentration and nitrogen concentration in the molten steel were analyzed, and it was found that the phosphorus concentration in the molten steel was a good 0.002% by mass, and the nitrogen concentration in the molten steel was also low at 0.0012% by mass, which is as low as when powder top blowing is not performed.

However, in Example 1, because argon was used as the carrier gas for more than 60% of the blowing period, there is a concern that the production costs will increase compared to when nitrogen or air is used as the carrier gas. 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 the carrier gas and CaO powder was top-blown only at the end of blowing. Specifically, top blowing of CaO powder was started at 80% to 95% of the blowing stage, and CaO powder was top-blown together with oxygen at 0.8 to 0.9 kg/min/t until the end of blowing. When the phosphorus and nitrogen concentrations in the molten steel were analyzed after the end of blowing, the phosphorus concentration in the molten steel was found to be low at 0.004 to 0.005 mass%, but the nitrogen concentration in the molten steel was significantly higher than the nitrogen concentration in the molten steel of 0.0015 mass% obtained in decarburization blowing without top powder blowing. As in Comparative Examples 1 to 5, it is believed that the nitrogen concentration in the top-blown gas during top powder blowing was too high, causing nitrogen absorption in the molten steel during blowing, which remained even after the end of blowing.

In Examples 2 to 4, CaO powder was top-blown only at the end of blowing using a nitrogen-free carrier gas. Specifically, top blowing of CaO powder was started at 80% to 95% of the blowing stage, and CaO powder was top-blown with oxygen at 0.8 to 1.2 kg/min/t until the end of blowing. After the end of blowing, the phosphorus and nitrogen concentrations in the molten steel were analyzed, and the phosphorus concentration in the molten steel was found to be very low at 0.005 mass%, and the nitrogen concentration was also found to be low at 0.0010 to 0.0013 mass%, which is equivalent to the concentration when powder top blowing is not performed. In this way, by performing top blowing with a top-blown gas with a low nitrogen concentration from the start of blowing to the end of blowing, and by top blowing CaO powder at the end of blowing, it was possible to reduce not only the powder cost but also the carrier gas cost compared to Example 1.

As mentioned above, good dephosphorization results were obtained in Examples 2 to 4, in which CaO powder was top-blown only at the end of blowing. However, the phosphorus concentration in the molten steel was slightly higher than in Example 1, in which CaO powder was top-blown from the first half of blowing. From the viewpoint of dephosphorization, it can be said that it is preferable to top-blown CaO powder from the first half of blowing to the end of blowing. In this regard, we investigated the possibility of top-blown CaO powder from the first half of blowing, but switching the carrier gas type midway through blowing.

In Examples 5 and 6 and Comparative Examples 9 and 10, CaO powder was blown from the top from the first half of the blowing, and the carrier gas type was switched from a high nitrogen concentration gas to a low nitrogen concentration gas during the blowing. As is clear from the results of Examples 5 and 6, the phosphorus concentration in the molten steel can be reduced to 0.003 mass% or less by using air as the carrier gas in the first half of the blowing and switching the carrier gas to Ar gas before reaching 60% of the blowing period, and the nitrogen concentration in the molten steel can also be 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 nitrogen concentration in the molten steel finally obtained will be high. It is believed that nitrogen absorption occurred in the molten pig iron or molten steel in the first half of the blowing, and this remained even 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 molten steel finally obtained can be reduced by switching the carrier gas at a stage less than 60% of the blowing period.

Comparative examples 11 and 12 correspond to the conventional technology. In other words, they are examples in which CaO powder was top-blown in the first half of the blowing, and in the second half of the blowing, CaO powder was not top-blown, and only top-blown gas (oxygen) was top-blown. In this case, the nitrogen concentration of the final molten steel can be reduced, but the phosphorus concentration increases significantly. It is believed that rephosphorization occurs in the second half of the blowing, where the temperature is higher, and the dephosphorization promotion effect in the first half of the blowing is reduced.

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

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

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

Requirement 2-1: From time T _A2 after the start of blowing to the end of blowing, a dephosphorizing agent containing Ca is sprayed from the top lance onto the molten pig iron or molten steel together with a low-nitrogen gas as a top-blowing gas, where the total amount of oxygen blown from the top lance from the start of blowing T _S to time T _A2 is less than 60% of the total amount of oxygen blown from the top lance from the start of blowing T _S to the end of blowing T _E , and the low-nitrogen gas contains 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 (5)

A converter blowing method, comprising the steps of:
The method includes blowing a top-blowing gas containing oxygen from a top-blowing lance onto the molten iron or steel in the converter,
Meet the following requirements 1-1 and 1-2,
The phosphorus concentration in the molten steel after completion of blowing is set to 0.005% by mass or less, and the nitrogen concentration is set to 0.0015% by mass or less.
Converter blowing method.
Requirement 1-1: From a blowing start time T _S to a time T _A1 , top blown gas having a nitrogen concentration of 0.3 mol% or less is blown from the top lance onto the molten pig iron or molten steel, where the total amount of oxygen blown from the top lance from the blowing start time T _S to the time T _A1 is 60% or more of the total amount of oxygen blown from the top lance from the blowing start time T _S to the blowing end time T _E.
Requirement 1-2: From at least the time T _A1 to the end of blowing, a dephosphorizing agent containing Ca is blown from the top blowing lance onto the molten pig iron or molten steel together with a low-nitrogen concentration gas as a top blown gas, wherein the low-nitrogen concentration gas contains oxygen and a carrier gas and has a nitrogen concentration of 0.3 mol% or less. The following requirements 1-1a and 1-1b are met:
The converter blowing method according to claim 1.
Requirement 1-1a: From the blowing start time T _S to any time T _B1 after the start of blowing, a top blown gas having a nitrogen concentration of 0.3 mol% or less is blown from the top blowing lance onto the molten pig iron or molten steel, while the dephosphorization agent is not blown, _and the total amount of oxygen blown from the top blowing lance from the blowing start time T _S to the time T _B1 is less than 60% of the total amount of oxygen blown from the top blowing lance from the blowing start time T S to the blowing end time T _E.
Requirement 1-1b: From the time T _B1 to the time T _A1 , the dephosphorization agent is blown from the top blowing lance onto the molten iron or molten steel together with the low-nitrogen concentration gas as a top blown gas. A converter blowing method, comprising the steps of:
The method includes blowing a top-blowing gas containing oxygen from a top-blowing lance onto the molten iron or steel in the converter,
Meet the following requirement 2-1,
The phosphorus concentration in the molten steel after completion of blowing is set to 0.005% by mass or less, and the nitrogen concentration is set to 0.0015% by mass or less.
Converter blowing method.
Requirement 2-1: From time T _A2 after the start of blowing to the end of blowing, a dephosphorizing agent containing Ca is sprayed from the top lance onto the molten pig iron or molten steel together with a low-nitrogen concentration gas as the top-blowing gas, wherein the total amount of oxygen blown from the top lance from the start of blowing T _S to the time T _A2 is less than 60% of the total amount of oxygen blown from the top lance from the start of blowing T _S to the end of blowing T _E , and the low-nitrogen concentration gas contains oxygen and a carrier gas and has a nitrogen concentration of 0.3 mol% or less. Satisfy 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 , a top-blowing gas having a nitrogen concentration of more than 0.3 mol% is blown from the top-blowing lance to the molten iron or molten steel, and at the time T _A2 , the top-blowing gas is switched to the low-nitrogen concentration gas. The following requirements 2-2a and 2-2b are met:
The converter blowing method according to claim 4.
Requirement 2-2a: From the blowing start time T _S to the time T _B2 , a top-blowing gas having a nitrogen concentration of more than 0.3 mol % or a top-blowing gas having a nitrogen concentration of 0.3 mol % or less is blown from the top blowing lance onto the molten pig iron or the molten steel, while the dephosphorization agent is not blown.
Requirement 2-2b: From the time T _B2 to the time T _A2 , the dephosphorization agent is blown from the top blowing lance to the molten pig iron or the molten steel together with a high nitrogen concentration gas as the top blown gas, and the type of the top blown gas is switched at the time T _A2 , where the high nitrogen concentration gas contains oxygen and a carrier gas and has a nitrogen concentration of more than 0.3 mol%.