KR101207592B1 - Method for Refining Molten Steel in Converter - Google Patents

Abstract

The present invention relates to a converter refining method for preventing the increase of the nitrogen concentration in the molten steel during the converter refining process, when the nitrogen concentration in the molten steel in the converter refining process, or the nitrogen concentration increases due to re-refining, titanium (Ti By preventing the increase of nitrogen concentration by adding), it is intended to provide a converter refining method that does not overflow slag into the furnace during tapping and improves productivity and quality.
The present invention is an implementation step of carrying out a passion mountain in the converter; Initiation step of starting the refining operation after completing the implementation step; A measuring step of measuring the temperature and carbon amount of the molten steel during the refining operation; Prediction step of predicting the nitrogen concentration at the completion of refining by the measured temperature and carbon amount; An input step of inputting titanium when the estimated nitrogen concentration is measured higher than a target value; A completion step of completing the converter refining after the input step; Measuring step of measuring the temperature and oxygen concentration in the molten steel after the completion step; When the re-refining is carried out by analyzing the temperature and oxygen concentration measured in the measurement step and the temperature abnormality and component abnormalities are expected, the converter refining method including the input step and stirring step of adding titanium to the main point.

Description

Method for Refining Molten Steel in Converter}

The present invention relates to a converter refining method for preventing the increase of the nitrogen concentration in the molten steel during the converter refining process, more specifically, when it is determined that the nitrogen concentration in the molten steel will be increased or increased during the converter refining process, by adding titanium The present invention relates to a converter refining method for preventing an increase in nitrogen concentration.

In the steel manufacturing process for producing steel from raw materials, the raw materials are blown into a furnace and subjected to a steelmaking process to reduce iron ore, and then the necessary alloying elements are added from the iron ore from which the impurities are removed, and the temperature is raised for the subsequent process. Steelmaking process is performed.

The steelmaking process is usually composed of molten iron preliminary treatment, converter refining, secondary refining, in each of these processes to remove sulfur, phosphorus, etc. in the molten iron preliminary treatment, in the converter refining oxidizing and refining the impurities by deodorizing and purifying pure oxygen In the secondary refining, oxygen and oxides caused by oxygen injection during converter refining are removed.

Nitrogen in the steel forms precipitates such as AlN, VCN, NbCN inside the slab during continuous casting, and during rolling, these precipitates increase the local brittleness inside the slab. Since there is a problem of causing surface cracks during rolling, it is necessary to contain as little as possible gas components, especially nitrogen, contained in molten steel from the refining stage in order to produce a product having excellent surface quality satisfactory to the consumer.

In general, in the converter refining method, as shown in FIG. 1, scrap iron and molten iron are charged into the converter 1, oxygen is supplied through the lance 3 from the upper part of the converter, and inert gas such as nitrogen and argon gas is supplied from the lower part of the converter. This is the process of removing impurities from the molten iron and making molten steel with the desired quality, and the molten steel after the converter refining is rolled out.

When the tapping work is completed as described above, as shown in Fig. 2, after placing a certain amount of slag in the slag port, the converter is established by introducing a coating agent, and then subjected to nitrogen spray coating, and when the spray coating is completed, the remaining slag coating is performed. Conduct.

When the remaining slag coating is completed as described above, the converter is charged by charging the scrap iron and molten iron.

In general, the nitrogen concentration present in the molten iron is 60 ~ 80ppm level as shown in Figure 5 is removed by the action by the following reaction formula (1) or (2).

[Reaction Scheme 1]

Ti + N = TiN

Scheme 2

C + O = CO

Reaction formula (1) is a case of forming TiN compound by reacting with titanium in molten iron during the converter refining process, TiN is separated and removed by separation, or CO (carbon dioxide) formed in a strong bath during the decarburization reaction by the reaction of the reaction formula (2). In the process of bubbling, [N] in the bath is diffused into the CO bubble and discharged with the CO bubble. When the converter refining is completed, it is controlled to a level of 10 to 15 ppm, and carbon in molten iron decreases and oxygen increases. As the nitrogen concentration increases, the converter is present at the level of 20 ~ 25ppm when the converter refining is completed.

However, as shown in FIG. 4, as oxygen in molten steel increases, nitrogen is present at 20 ppm or less up to a level of 0.05% carbon, but as the carbon in the molten steel decreases, the oxygen concentration rapidly increases when the oxygen concentration is 700 ppm or more. It can be seen. The reason for the increase in nitrogen concentration as described above is that the oxygen used in the converter refining process is supplied to the converter 1 at supersonic speed through the lance 3, and at the end of the blowdown, the amount of exhaust gas is reduced due to lack of carbon, This is because the inside of the converter is under negative pressure, and the outside air enters the inside of the converter through the furnace, causing the nitrogen concentration to rise as the nitrogen in the air reacts with the molten steel. In particular, in the case of over-blowing (when the end point oxygen concentration is high) or re-refining (a converter refining method in which oxygen is blown again to raise the temperature of the molten steel when the converter refining is completed below the target converter tapping temperature) As the pressure inside is lower than the atmospheric pressure, the outside air is rapidly sucked in and the nitrogen concentration is rapidly increased due to the reaction between the nitrogen in the air and the molten steel.

In order to solve the above problems, conventionally, as shown in FIG. 2, when the decarburization reaction is reduced in the converter refining process, the temperature and the carbon concentration of the molten steel in the converter are measured to predict the carbon concentration of 700 ppm or more. By inputting the system raw materials, the amount of flue gas generated in the converter was increased to keep the inside of the converter at a pressure higher than atmospheric pressure while maximizing the speed of the IDF controlling the flue gas. When the carbon-based raw material is added as described above, nitrogen can be controlled to 25 ppm or less required by the demand.

 However, when the carbonaceous raw material enters the converter, the slag of the converter slag and the carbonaceous raw material continuously react and the slag overflows into the furnace furnace during the tapping. As the P205 is decompensated during the deoxidation process, the quality abnormality occurs due to the component abnormality, or the slag ladle as well as the upper part of the slag or the upper part of the rail which is installed to move the trolley are not pulled out, so the performance is shorted. In order to prevent the slag overflow phenomenon, because the slag is pulled out by slagging the inside of the slag port by tilting the converter to the charging side, a problem that causes a decrease in productivity occurs.

The present invention has been made in view of the above-described problems, and when the oxygen concentration in the molten steel is maintained at 700 ppm or more due to lack of heat source or passionate acid during the converter refining process, the nitrogen concentration is increased or the nitrogen concentration is increased due to re-refining, titanium. By adding (Ti) to prevent an increase in nitrogen concentration, it is intended to provide a converter refining method that does not overflow slag into the furnace during tapping and has an effect of improving productivity and quality.

As a means for realizing this, the converter refining method according to the present invention includes a passion mountain step of carrying out a passion mountain in the converter;

Initiating a converter refining operation after finishing the passion acid step;

Measuring the temperature and carbon amount of the molten steel during the refining operation;

Predicting the nitrogen concentration at the completion of refining by using the temperature and carbon amount of the molten steel measured as described above;

A titanium input step of injecting titanium when the predicted nitrogen concentration is measured to be higher than an appropriate amount as described above;

Completing the converter refining after the titanium input step;

Measuring the temperature and oxygen concentration in the molten steel after the converter refining step as described above;

Analyze the temperature and oxygen concentration measured as described above, if the temperature abnormalities and component abnormalities are expected to be re-refined, the titanium input step of adding titanium, and if the re-refining, after the titanium input step, and re-refining When not carried out, after measuring the temperature and oxygen concentration in the molten steel, characterized in that it comprises a step of stirring for 45 seconds or more.

In the nitrogen concentration prediction step at the completion of the refining, the temperature and carbon amount of the molten steel during the refining operation are measured, and the end point oxygen amount (X) is obtained by the following equation (1) using this measured value. It is preferable to obtain the end point carbon amount by the following formula (2) using (X) and to predict the nitrogen concentration based on the correlation diagram between the end point carbon amount and the end point nitrogen amount as shown in FIG. Do.

[Relationship 1]

X = (actual temperature-target temperature) + {(actual [C] × 57)-(target [C] × 57)}

[Relationship 2]

[C]% = 0.0022 / [O]%

In addition, when the estimated nitrogen concentration is measured to be higher than an appropriate amount, in the titanium input step of injecting titanium, the Ti input amount calculated by the following equation (3) using the end point oxygen amount (X) obtained by the above formula (1). It is preferable to add titanium as much as possible.

[Relationship 3]

Ti injection amount = 0.9797 × X

In addition, in the titanium step of injecting titanium when the re-refining is carried out, it is preferable to inject titanium as much as the Ti input amount calculated by the following formula (4).

[Relationship 4]

Ti injection amount = 0.967 x reblowing flow rate

If the re-refining is carried out after the titanium input step, and if the re-refining is not carried out, after measuring the temperature and oxygen concentration in the molten steel, stirring in the state of sequencing for 45 seconds or more, preferably 120 seconds or more and 300 seconds or less do.

In the stirring step, it is preferable to maintain a low odor flow rate per minute to 15 Nm 3 or more and 30 Nm 3 or less.

In addition, the present invention provides an apparatus capable of preferably implementing the above-described converter refining method of the present invention.

According to the converter refining method of the present invention, even when excessive oxygen is present in the molten steel, even when excessive generation occurs, the nitrogen concentration in the molten steel can be stably controlled, thereby improving productivity by reducing the case of double tapping or steel type change, Quality can be improved by reducing the surface cracks of the final product slab, coil and plate.

1 is a schematic view showing an example of a converter refining apparatus according to the present invention;
2 is a flow chart of the converter refining process according to the conventional method
3 is a flow chart of the converter refining process according to the present invention
4 is a graph showing the relationship between end point carbon and nitrogen
5 is a graph showing the behavior of oxygen and nitrogen during blowing
Description of the Related Art
1: converter
2: skirt
3: lance
4: Lance Motor
5: hopper
6: HMI (Human Machine Interface)
7: controller

Hereinafter, the converter refining method according to the present invention with reference to the accompanying drawings will be described in detail.

Figure 1 shows an example of a device that can preferably implement the converter refining method of the present invention, Figure 3 shows a process flow showing an example of the converter refining process according to the present invention.

As shown in Fig. 1, the converter refining apparatus includes a converter 1 in which refining is performed, a lance 3 for blowing oxygen into the converter, a hearth hopper 5 for accommodating titanium in the converter 1, and a converter refining. HMI (Human Machine Interface) 6 for predicting the nitrogen content in the molten steel at the completion time, and a control unit 7 configured to inject titanium based on the nitrogen content predicted from the HM. In Fig. 1, reference numeral 2 denotes a skirt and 4 denotes a lance motor.

In order to refine the converter according to the present invention, as shown in FIG. 3, after the tapping operation is completed, a predetermined amount of slag is excluded, the converter is established by introducing a coating agent, and then sprayed with nitrogen, and the spray coating is completed. Slag coating is performed.

Next, a passionate acid is carried out in the converter, in which the heat of reaction generated when the element in the molten iron reacts with oxygen, the amount of heat required to melt the scrap metal, and the amount of heat required to melt the subsidiary material injected during refining to meet the target temperature. Calculate the heat input, sensible heat, and heat output on the back.

Next, scrap metal and molten iron are put into the converter 1, the lance 3 is lowered, oxygen is supplied, and converter refinement | purification (blowing) is started.

Next, the temperature and carbon content of the molten steel are measured during the refining operation. In this step, a probe is mounted on the sub lance to measure the temperature and carbon state in the molten steel when the decarburization reaction is slowed down. The measured information is stored in the HMI 6 via the control device 7.

Next, the nitrogen concentration at the completion of refining is predicted by the HMI 6 by using the information on the temperature and carbon amount in the molten steel measured as described above.

The nitrogen concentration at the completion of the refining is measured the temperature of the molten steel and the carbon amount during the refining operation, using this measured value to obtain the end point oxygen amount (X) by the following formula (1), this end point oxygen amount (X) It is preferable to calculate the amount of end point carbon by the following formula (2) using the following formula, and to predict the amount of end point carbon by the correlation diagram between the end point carbon amount and the end point nitrogen amount as shown in FIG.

[Relationship 1]

X = (actual temperature-target temperature) + {(actual [C] × 57)-(target [C] × 57)}

[Relationship 2]

[C]% = 0.0022 / [O]%

Next, when the nitrogen in the molten steel predicted as above is predicted to be higher than an appropriate amount, for example, when the X value becomes -20 or less, the control device 7 issues a command to the feeder of the hearth hopper 5 and the X value. Titanium dose is set accordingly.

Titanium thus added is reacted with nitrogen in the molten steel as in reaction (1) to remove nitrogen.

It is preferable to set the said titanium input amount according to following formula (3).

[Relationship 3]

Ti injection amount = 0.9797 × X

Next, refinement | finishing is completed when the temperature of molten steel is suitable for the temperature required by a post process.

After the completion of the converter refining step to measure the temperature and oxygen concentration in the molten steel, etc. In this step, it is confirmed whether the temperature is possible to tap by measuring the temperature and oxygen concentration of the molten steel. When re-refining is performed in anticipation of abnormal temperature and components, titanium is added. At this time, the amount of titanium added is preferably calculated by the following equation (4).

[Relationship 4]

Ti injection amount = 0.967 x reblowing flow rate

When the re-blowing flow rate is input to the HMI, the control device 7 calculates the titanium input amount according to the above equation (4), for example, sends an electric signal to the feeder of the hearth hopper 5 to input titanium, and Nitrogen is removed by titanium in the same reaction as in Scheme (1).

Next, after the titanium injection step in the case of the re-refining, and after measuring the temperature and oxygen concentration in the molten steel when not re-refining, 45 seconds or more, preferably 120 seconds or more in the converter sizing state Molten steel can be stirred in seconds or less. At this time, more than 45 seconds, preferably more than 120 seconds to ensure a sufficient reaction time for the titanium to fully react with the molten steel in the converter, and stirring below 300 seconds is already reacted before exceeding 300 seconds This is because it takes place sufficiently and no longer needs to be stirred.

At the time of the stirring, the flow rate is preferably performed at 15 Nm 3 or more and 30 Nm 3 or less per minute. This is because when it is carried out at 15N㎥ or less, it is not possible to perform sufficient stirring due to the iron static pressure, and when stirring at 30N㎥ or less, the reaction may occur sufficiently at a flow rate of 30N㎥ or less, so it is not necessary to increase the flow rate beyond that. . Therefore, the flow rate is limited to 15 Nm 3 or more and 30 Nm 3 or less.

Hereinafter, the present invention will be described in more detail with reference to Examples.

[Example]

According to the conventional method shown in Figures 2 and 3 and the converter refining method of the present invention, converter refining was performed and the results are shown in Table 1 below.

End point oxygen (ppm) Input raw material after blown 80% Input amount (Kg) Agitation time (seconds) End point [N] (ppm) Remarks Conventional Example 1 823 Carbon based raw materials 300 30 25 Double tap Conventional Example 2 795 Carbon based raw materials 150 30 28 Double tap Conventional Example 3 912 Carbon based raw materials 500 30 27 Tripod Conventional Example 4 705 Ti 194 30 32 Change of steel grade Conventional Example 5 871 Ti 290 30 34 Change of steel grade Conventional Example 6 777 Ti 285 30 33 Change of steel grade Invention 1 760 Ti 200 120 25 Invention 2 913 Ti 180 150 26 Invention 3 812 Ti 250 180 21

Conventional Examples 1 to 3 follow the conventional method of FIG. 2 and inject a carbonaceous raw material as an input raw material after 80% (dynamic) blowing. In this case, the end point nitrogen concentration was kept low below 30ppm, but the tapping was double or tripled, resulting in a decrease in productivity and component deviation due to the outflow of slag.

Conventional Examples 4 to 5 is a case in which Ti is added as a feedstock after 80% of blowing, and a stirring time of 30 seconds is applied rather than 120 seconds according to the present invention. In this case, the slag overflow phenomenon did not occur because of the addition of Ti, but the steel grade was changed because the end point nitrogen concentration was higher than 30 ppm.

The present invention 1 to 3 corresponding to the present invention is a case in which Ti is added as a feed material after 80% of blowing and a stirring time of 120 seconds or more is applied according to the present invention. Because of the addition of Ti, the target nitrogen concentration of 30ppm or less could be obtained without any outflow of slag.

Claims (6)

Passion mountain step of conducting passion mountain in the converter;
Initiating a converter refining operation after finishing the passion acid step;
Measuring the temperature and carbon amount of the molten steel during the refining operation;
Predicting the nitrogen concentration at the completion of refining by using the temperature and carbon amount of the molten steel measured as described above;
A titanium input step of injecting titanium when the predicted nitrogen concentration is measured to be higher than an appropriate amount as described above;
Completing the converter refining after the titanium input step;
Measuring the temperature and oxygen concentration in the molten steel after the converter refining step as described above;
Titanium input step of injecting titanium when re-treatment is performed by analyzing the measured temperature and oxygen concentration as described above and abnormal temperature and component abnormalities and
When the re-refining is carried out after the titanium input step, and if the re-refining, the converter refining method comprising a stirring step of stirring for 45 seconds or more after measuring the temperature and oxygen concentration in the molten steel.
The method of claim 1, wherein the nitrogen concentration prediction step at the completion of refining
The temperature and carbon content of molten steel during the refining operation were measured and the end point oxygen amount (X) was obtained by the following equation (1) using this measured value, and the end point oxygen amount (X) was obtained by the following equation (2). A converter refining method comprising: obtaining an end point carbon amount and predicting nitrogen concentration based on the degree of correlation between the end point carbon amount and the end point nitrogen amount using the obtained end point carbon amount.
[Relation 1]
X = (actual temperature-target temperature) + {(actual [C] × 57)-(target [C] × 57)}
[Relationship 2]
[C]% = 0.0022 / [O]%
According to claim 1 or 2, when the estimated nitrogen concentration is measured higher than the appropriate amount in the titanium input step of adding titanium using the end point oxygen amount (X) obtained by the formula (1) Converter refining method characterized in that the titanium input as much as the Ti input amount calculated by 3).
[Relationship 3]
Ti injection amount = 0.9797 × X
The converter refining method according to claim 1 or 2, wherein titanium is added as much as Ti input amount calculated by the following equation (4) in the titanium step of adding titanium when re-refining is performed.

[Relationship 4]
Ti injection amount = 0.967 x reblowing flow rate
The converter refining method according to claim 1, wherein the stirring time in the stirring step is 120 seconds or more and 300 seconds or less.
The method of claim 5, wherein in the stirring step, the converter refining method, characterized in that the stirring while maintaining a flow rate of 15N ㎥ or more 30N ㎥ or less per minute.

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