JPH10296405A - Method for setting steel tapping temperature of converter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the energy loss and the wearing of a refractory by lowering steel tapping temp. of a converter in the first operation of a continuous casting to the min. limit in the necessary temp. SOLUTION: High temp. inert gas is continuously supplied into a tundish while alternately using plural heat-storage type preheaters. Then, the temp. lowering of the tundish under waiting and heat-holding is stabilized by adopting the non-oxidizing heat-holding method for holding the heat of the tundish under non-oxidizing. This tundish temp. at the time of tapping the molten steel is accurately estimated with an approximate expression containing a function of the heat-holding time while using the last casting molten steel temp. at the previous heat as an initial value, and the steel tapping temp. at this heat is set under consideration of the temp. lowering degree, etc., at the time of pouring the molten steel into this tundish. Further, in the case of starting heat-holding of the tundish after some interval since starting of the waiting, the tundish temp. lowered during no heat-holding is estimated with a different approximate expression and while using this estimated value as an initial value, the tundish temp. during heat-holding is estimated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for setting a tapping temperature of a converter, and more particularly to a method for repeatedly using a tundish for continuous casting (hereinafter, also simply referred to as continuous casting).
When a method of keeping the tundish in a non-oxidized state by using a plurality of regenerative preheaters is used, one of the following castings is performed.
This is suitable for setting the tapping temperature of the charge.

[0002]

2. Description of the Related Art A tundish for receiving molten steel from a ladle and distributing it to a mold does not have a heating element itself. Therefore, when used, it is separately heated by a heating means to secure a temperature at which casting is possible. There is a need. In addition, when casting is performed continuously while exchanging a plurality of tundishes (hereinafter, also referred to as continuous / continuous casting), for example, when the steel type is changed, the tundish is exchanged with a standby tundish. ,
There is a use of a tundish such that the one that had been used until then is waited until the next reuse. And for the waiting tundish,
Heating to a temperature at which casting is also possible is required at least before use.

[0003] When the tundish is heated in this way, it is desired that the remaining steel inside the tundish is not oxidized. Therefore, the present applicant has previously described Japanese Patent Application Laid-Open
A non-oxidizing heating method for tundish described in Japanese Patent No. 59664 was proposed. In this non-oxidizing heating method of the tundish, two or more regenerative preheaters are connected to the tundish, and one of them is heated by passing through a heat storage body provided in the regenerative preheater. The inert gas charged into the tundish is drawn into the tundish, and the inert gas charged into the tundish is sucked from the remaining regenerative preheater, and is burned only by the regenerative preheater that sucks the inert gas. The heat storage body is heated by burning the gas, and the combustion exhaust gas and the sucked inert gas are exhausted. By doing so, the tundish can be kept at an extremely high temperature without flowing oxygen contained in the combustion exhaust gas into the tundish. In addition,
In this non-oxidizing heating method, it is necessary to keep the inside of the tundish at a positive pressure and to carefully control the flow rates of the inert gas, combustion gas and combustion air to be injected and sucked so that air does not flow in from the outside. Becomes

[0004]

Incidentally, it is desired that the tapping temperature from the converter be as low as possible from the viewpoint of energy. Generally, the tapping temperature of the converter is the temperature drop during casting, the drop during moving the pot, and the drop due to the secondary refining process, with respect to the molten steel temperature required by the continuous caster set first. , And the sum of the drop during tapping. Among these, the temperature required in the continuous caster is a temperature at which the molten steel does not solidify when the pot of the charge ends. Further, the temperature decrease during casting is the sum of the decrease during the casting time of the charge and the decrease due to the low temperature of the tundish when the molten steel is poured. Then, actually, it is a measured value of the pot temperature or disclosed in JP-A-5-5121.
Of the ladle temperature described in Japanese Unexamined Patent Publication (Kokai) No. H11-15083, and the drop due to the input of ferro-alloy, for example,
In the tundish heated by the plasma heating device described in JP 78353, a control value of molten steel temperature,
The temperature drop after the converter estimated from the secondary refining processing time and the like is added to the required molten steel temperature at the end of the casting of the charge in the continuous casting machine to obtain the steel tapping temperature of the converter. The tapping temperature of the converter calculated and set in this way is sufficiently accurate at least when continuous casting is performed by a continuous casting machine in a steady state.

[0005] However, the temperature of the tundish is not constant in the casting of the first charge in the continuous caster, so that it is not possible to quantitatively grasp the temperature drop when molten steel is poured into the tundish. Therefore, it is necessary to set the tapping temperature of the first charge to a safe side, that is, a high temperature so that the tapping does not harden, which hinders a drop in tapping temperature from the converter.

The present invention has been developed in view of these problems, and has a non-oxidizing heat retention of a tundish using the regenerative preheater, in which the temperature is stable even if the heat retention time is long. Focusing on the method, when using the non-oxidizing heat preservation method of the tundish, for example, the molten steel temperature of the last charge at the time of the last casting is set as the initial value, and the temperature of the tundish that changes with the elapse of the heat preservation time is maintained. By accurately expressing the temperature of this tundish by expressing it as a function of the heat time, it is possible to reduce the energy loss by lowering the tapping temperature from the converter to the minimum required even during the first charge casting. It is an object of the present invention to provide a method for setting a converter tapping temperature that can reduce wear of refractories.

[0007]

Means for Solving the Problems To solve the above problems, a method for setting a converter tapping temperature according to claim 1 of the present invention provides a method for maintaining the temperature of a tundish used in continuous casting. From any of the plurality of regenerative preheaters connected to the tundish, an inert gas that has been heated by passing through the regenerator provided in the regenerative preheater is injected into the tundish, and the remaining The regenerative preheater sucks the inert gas charged into the tundish, and also burns the combustion gas only with the regenerative preheater that sucks the inert gas to heat the regenerator, thereby producing the flue gas. When the non-oxidizing heat retention method of exhausting the sucked inert gas is used, the molten steel temperature in the last charge of the previous casting using the tundish and the heat retention of the tundish are used. Estimating the temperature of the tundish from the usage time of the regenerative preheater to be used, and setting the tapping temperature of the converter at the first charge of the next casting using the estimated temperature of the tundish. It is characterized by the following.

In the converter tapping temperature setting method according to a second aspect of the present invention, when estimating the temperature of the tundish, the temperature of the tundish in the time until the heat storage by the regenerative preheater is started. It is characterized by taking into account the drop in dish temperature.

In the method for setting a tapping temperature of a converter according to a third aspect of the present invention, when the tapping temperature of the converter is set, the molten steel temperature is reduced in accordance with the estimated temperature of the tundish. It is characterized by adding an amount.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, an embodiment of a method for setting a converter tapping temperature according to the present invention will be described with reference to the drawings.

First, an outline of a facility to which the method for setting a converter tapping temperature according to the present embodiment shown in FIG. 1 will be described. In the figure, reference numeral 1 denotes a ladle. Molten steel is poured from the ladle 1 into one of the two tundishes 2, and the molten steel is cast from the tundish 2 into the mold 3 of the continuous casting machine. Usually, casting is performed using one of the tundishes 2 and the other is on standby. Then, for example, the casting is temporarily terminated in accordance with a change in the steel type of the molten steel, and the casting is restarted using the other tundish 2 which has been waiting until then. At this time, in order to enable smooth and prompt resumption of casting, the waiting tundish is kept at a temperature at which at least molten steel to be poured is cooled and hardened, and the nozzle at the bottom of the tundish is not clogged. Need to be. It is also necessary to maintain the inside of the tundish as free of oxidation as possible in order to prevent the occurrence of iron oxide which causes swelling and blistering in the next casting. Also, if the residual steel in the tundish has already been oxidized, it is desirable to have a reducing atmosphere as well as no oxidation if possible so that it can be reduced.

In order to realize this non-oxidative heat retention, a non-oxidative heat retention device as shown in FIG. 2 is connected to the tundish in a standby state. The tundish 2 has a regenerative preheater 4 in each of two openings provided in its lid.
A and 4B are linked in two groups. These regenerative preheaters 4A and 4B have, for example, a large heat transfer area,
Thermal storage chambers 5A and 5B filled with spherical or pipe-shaped thermal storage bodies made of ceramic, metal, or the like;
Combustion chambers 6A and 6B for heating the regenerator 5B are provided adjacent to each other in series, and insertion tubes (connection tubes) 7A and 7B are provided.
The combustion chambers 6A and 6B are respectively connected to the openings of the tundish 2 via a, and a main burner and a pilot burner (not shown) are provided in the combustion chambers 6A and 6B. A sealing device (not shown) is provided between the insertion tubes 7A and 7B and the respective openings of the tundish 1 in order to shut off external air and maintain the inside of the tundish 2 in a non-oxidized state. Is equipped. The nozzles at the bottom of the tundish are not shown in FIG.

Next, each of the regenerative preheaters 4 similar to each other
The state of the piping to A and 4B will be described. Each heat storage type preheater 4
Main burners and pilot burners (not shown) of the combustion chambers 6A and 6B of A and 4B are commonly connected to a combustion gas supply source and a combustion air supply source (from the atmosphere). Also,
The heat storage chambers 5A and 5B are commonly connected to a nitrogen supply source used as an inert gas and an exhaust destination. An on-off valve 8A capable of controlling a flow rate is provided between each connection destination.
To 11B are interposed. Among these, the on-off valve interposed between the combustion gas supply source and the combustion gas on-off valve 8A,
8B, the on-off valves interposed between the combustion air supply source are combustion air on-off valves 9A and 9B, and the on-off valves interposed between the nitrogen supply source are nitrogen on-off valves 10A and 10B. And the on-off valve interposed between the exhaust on-off valves 11A and 11A.
B.

Now, in the state shown in the figure, only the nitrogen on-off valve 10B is opened with respect to the regenerative preheater 4B on the right side in the figure, and the other combustion gas on-off valves 8B are also connected to the combustion air on-off valve 9B. Since the exhaust opening / closing valve 11B is also closed, the nitrogen that has passed through the heat storage chamber 5B that has been heated to a high temperature is heated to a high temperature and is injected into the tundish 2. on the other hand,
In the regenerative preheater 4A on the left side of the figure, the combustion gas on-off valve 8A
Since both the combustion air opening / closing valve 9A and the combustion air opening / closing valve 9A are open, combustion is performed by the main burner in the combustion chamber 6A. On the other hand, the nitrogen on-off valve 10A is closed and the exhaust on-off valve 1
Since 1A is open, the combustion exhaust gas generated in the combustion chamber 6A and the excess nitrogen in the tundish 2 are sucked and exhausted. The sensible heat of the high-temperature nitrogen injected as described above is, of course, used to keep the tundish, but if the tundish is kept at a sufficiently high temperature, the nitrogen temperature drops significantly. Not something. Therefore, the sensible heat of the combustion exhaust gas is recovered to the heat storage body in the heat storage chamber 5A of the regenerative preheater 4A on the left side in accordance with the sensible heat of nitrogen still at a sufficiently high temperature, and is heated to a high temperature. As described above, the combustion exhaust gas containing a large amount of the O component must not flow into the tundish, and the outside air must not flow into the tundish. In other words, it is necessary to sufficiently exhaust the combustion exhaust gas while the tundish is always maintained at a positive pressure. For this purpose, the supply amount and the exhaust amount of each gas must be carefully controlled.

In this state, for example, if the temperature of the heat storage body in the heat storage chamber 5A of the regenerative preheater 4A on the left side of the drawing rises to a predetermined temperature, or if the above-mentioned state continues for a predetermined time, combustion is started. Each open / close valve is opened / closed in the reverse order in which the exhaust gas and the atmosphere do not flow into the tundish. Only, the high-temperature nitrogen is introduced into the tundish, and conversely, in the regenerative preheater 4B on the right side of the figure, the combustion gas on-off valve 8B and the combustion air on-off valve 9
B is opened to perform combustion, and the exhaust opening / closing valve 11B is opened to heat and exhaust the combustion exhaust gas and excess nitrogen in the tundish while heating the heat storage body in the heat storage chamber 6B.

By alternately repeating this, high-temperature nitrogen (inert gas) is continuously supplied into the tundish, and the entire area of the tundish can be stably kept at a high temperature. In addition, since the nitrogen sensible heat in a high temperature state is once recovered in the heat storage body and converted into the next nitrogen sensible heat to be supplied, energy loss can be reduced. Further, if the inside of the tundish can be maintained at a positive pressure while exhausting the combustion exhaust gas completely, the inflow of air from the outside can be avoided, and the inside of the tundish can be maintained in an unoxidized state.
Although not shown in this embodiment, if a small amount of a reducing gas such as hydrogen is mixed into the supplied inert gas, the inside of the tundish becomes a non-oxidizing and reducing atmosphere as described above. be able to. By the way, when reducing iron oxide at such a high temperature, it has been found that the amount of the reducing gas to be added may be extremely small.

Next, the converter tapping temperature setting method of the present embodiment will be specifically described. FIG. 3 is an explanatory diagram of the timing of setting the converter tapping temperature. As is clear from FIG. 3, the tapping temperature has already been set before the start of the converter blowing. This is made possible by accurately estimating the temperature of the tundish to be used from the elapsed time from tapping necessary for secondary refining and the like, as described later.

First, the method of setting the converter tapping temperature of this embodiment became possible because the establishment of the non-oxidizing heat retaining method for the tundish using the regenerative preheater described above reduces the temperature of the tundish. This is due to the stability. FIG.
Shows the relationship between the temperature of the tundish during heat retention (T / D temperature in the figure) and the elapsed time. As mentioned above, the tundish has to be kept at a temperature that prevents the molten steel to be poured next from cooling and hardening, or the nozzle at the bottom from being clogged, until it is reused. There is no need to heat to or above the temperature. Therefore, when the heat retention state is entered, the temperature of the tundish gradually decreases. However, as described above, in the heat retention method using the regenerative preheater to which the high-temperature inert gas can be continuously supplied, the manner of lowering the temperature of the tundish is stable. For example, in the present embodiment, the temperature T _{(T / D)} of the tundish can be approximated by the following equation.

T _{(T / D)} = at · t + bt · ² + T _{(T / D−1)} (1) where, t: Tundish heat retention time (equivalent to the use time of the regenerative preheater) T _{(T / D-1)} : the temperature of molten steel in the last charge of the previous casting using this tundish a, b: coefficient By the way, in the conventional method of heating the tundish by gas combustion or plasma torch, the tundish In this case, the temperature of the tundish is not uniform, and the temperature of the tundish during the heat retention cannot be accurately estimated. Further, as the temperature T _{(T / D)} of the tundish, an approximate expression other than the above expression 1 can be applied.

On the other hand, after the use of the tundish is completed,
In other words, immediately after the tundish starts to wait, the non-oxidizing heat retention by the regenerative preheater may not be performed immediately. FIG. 5 shows the relationship between the temperature of the tundish (T / D temperature in the figure) and the elapsed time at this time. As is clear from the figure, the temperature of the tundish is stable even when the heat is not kept, but the temperature gradient is larger than when the heat is kept. Then, the temperature of the tundish until the heat retention is performed is also approximated by the quadratic equation substantially equal to the above-described equation (1). Therefore, if heat retention is not performed immediately after the tundish starts to stand by, the amount of temperature decrease corresponding to the time is determined according to FIG. 5, and the final tundish temperature is calculated by the above equation (1). T
_{(T / D-1)} , that is, the term of the molten steel temperature in the last charge of the previous casting using the tundish may be substituted. Alternatively, the same applies if the approximate expression of the tundish temperature in a state where heat is not retained is directly substituted into the term of T _{(T / D-1)} .

After accurately estimating the temperature of the tundish in this way, as shown in FIG. 6, for example, the amount of decrease in the temperature of the molten steel corresponding to the temperature of the tundish is determined. The final converter tapping temperature may be set by adding the required molten steel temperature. In addition to this, the final setting of the converter tapping temperature includes the temperature reduction during the operation of the pan, the temperature reduction during casting, the reduction during the movement of the pan, the secondary refining, This is carried out taking into account the reduction due to the treatment and the reduction during tapping.

It is also possible to set the final temperature of the secondary refining by the same method, thereby reducing the casting speed due to the molten steel temperature being too high and leaving the pot hot water due to the molten steel temperature being too low. Can be prevented.

With these methods, in this embodiment, the amount of temperature drop in the continuous casting machine can be accurately estimated, and the tapping temperature of the first charge of the continuous casting in the converter is reduced to 0.1.
As a result, the temperature can be reduced by 2 ° C. As a result, for example, it is possible to reduce the wear of refractories and the like and to reduce the energy loss.

[0024]

As described above, according to the method for setting the tapping temperature of the converter according to the first aspect of the present invention, the non-oxidizing protection of the tundish using the regenerative preheater having stable temperature characteristics. Using the thermal method, accurately estimate the temperature of the tundish from the molten steel temperature in the last charge of the previous casting using the tundish and the time of use of the regenerative preheater used to maintain the heat of the tundish Therefore, the tapping temperature of the converter at the first charge of the next casting can be set to the minimum necessary, and the energy loss can be reduced by that much, and for example, the wear of refractories etc. can be reduced. Can be achieved.

Further, according to the converter tapping temperature setting method according to the second aspect of the present invention, in estimating the temperature of the tundish, the time required until the heat retention by the regenerative preheater is started. By taking into account the temperature drop of the tundish, the accuracy of estimating the temperature of the tundish can be further improved, and the effect of the converter tapping temperature setting method according to claim 1 can be further assured. it can.

Further, according to the converter tapping temperature setting method of the present invention, in setting the tapping temperature of the converter, the molten steel temperature corresponding to the estimated temperature of the tundish is set. By taking into account the amount of decrease, the tapping temperature of the converter can be set more accurately, and the effect of the converter tapping temperature setting method according to claim 1 can be further ensured.

[Brief description of the drawings]

FIG. 1 is a schematic explanatory diagram of a converter-continuous casting facility that implements a converter tapping temperature setting method of the present invention.

FIG. 2 is a schematic explanatory view of a non-oxidative heat retention method using a regenerative preheater used in the tundish of FIG.

FIG. 3 is an explanatory diagram of the timing of setting the tapping temperature from the converter by the converter tapping temperature setting method of the present invention.

FIG. 4 is an explanatory diagram of temperature characteristics of a tundish when a non-oxidizing heat retention method using a regenerative preheater is used.

FIG. 5 is an explanatory diagram of a temperature characteristic of a tundish when a non-oxidation heat retention method using a regenerative preheater is not used.

FIG. 6 is an explanatory diagram of a temperature drop characteristic of molten steel according to a temperature of a tundish.

[Explanation of symbols]

 1 is a ladle 2 is a tundish 3 is a mold 4A, 4B is a regenerative preheater 5A, 5B is a regenerator 6A, 6B is a combustion chamber 7A, 7B is an insertion pipe 8A, 8B is a combustion gas on / off valve 9A, 9B is a combustion Air on-off valves 10A and 10B are nitrogen on-off valves 11A and 11B are exhaust on-off valves

Claims (3)

[Claims] In order to keep heat in a tundish used for continuous casting, a heat storage body to be installed in the heat storage preheater is selected from one of a plurality of heat storage preheaters connected to the tundish. A heat storage type in which the inert gas that has passed and heated is charged into the tundish, and the inert gas charged into the tundish is sucked from the remaining heat storage type preheater, and the inert gas is sucked. When using the non-oxidizing heat retention method of burning the combustion gas by burning the combustion gas only in the preheater and exhausting the combustion exhaust gas and the sucked inert gas, the previous time using the tundish The temperature of the tundish is estimated from the temperature of the molten steel at the final charge of the casting and the operating time of the regenerative preheater used to maintain the heat of the tundish. A method for setting a tapping temperature of a converter at a first charge of the next casting, using a temperature of the converter. 2. The method according to claim 1, wherein in estimating the temperature of the tundish, a decrease in the temperature of the tundish in a time period until the heat retention by the regenerative preheater is started is taken into account. Converter tapping temperature setting method. 3. The converter according to claim 1, wherein, when setting the tapping temperature of the converter, a decrease in molten steel temperature in accordance with the estimated temperature of the tundish is taken into account. Furnace tapping temperature setting method.