JP2000054020A - Method for refining molten high carbon steel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the obstruction in operation caused by CO gas, to reduce the wear of a refractory, to restrain the generation of oxide of valuable metal, etc., and to obtain molten steel having high cleanliness by adding an exothermic agent in an immersion tube dipped into the molten steel under reducing the pressure after receiving the molten steel having high carbon concn. melted at a temp. lower than a target temp. in a refining furnace, executing oxygen blowing and raising the molten steel temp. to the target temp. SOLUTION: The carbon concn. in molten steel decarburize-refined in a refining furnace is made to 0.20-1.2 wt.% and the molten steel 12 is tapped off into a ladle 11 at a lower temp. by 10-90 deg.C than a target temp. (ordinary molten steel tapping temp.). The pressure in an immersion tube 13 and a vacuum vessel 15 is reduced to 500-750 Torr and continuous stirring is executed in the direction shown with an arrow mark while blowing gaseous argon from a porous plug 21. The prescribed quantity of Al or an Al alloy in a storing hopper 18 is continuously added into the immersion tube 13 as an exothermic agent and also, the Al is burned by blowing the stoichiometrically necessary oxygen from a lance 20 on the molten steel surface 19 and the temp. of the molten steel 12 is easily and efficiently raised with this exothermic heat to become the target temp.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for reducing the load on refractories in a refining furnace and stably raising the temperature of molten steel when performing decarburization refining using a refining furnace and a vacuum refining device. It relates to a method for refining high carbon molten steel that can be produced.

[0002]

2. Description of the Related Art Refining furnaces, such as converters and electric furnaces, have been widely used because they can quickly decarburize a large amount of molten iron under atmospheric pressure and easily produce molten steel. In particular, when smelting molten steel having a high carbon concentration, impurities such as phosphorus (P) and sulfur (S) are removed while performing decarburization, and a reduction in temperature due to tapping and a casting process is taken into consideration. It is necessary to raise the temperature to a predetermined temperature.
The temperature is as high as 0 ° C. However, if decarburization to achieve the target carbon concentration and temperature rise of molten steel are performed at the same time, it is necessary to actively burn carbon and iron to form a high-temperature atmosphere in the furnace. There is a problem that the wear is large and the life of the smelting furnace and the operating rate of the smelting furnace are reduced. As a countermeasure, as described in JP-A-61-91313, the temperature of molten steel discharged from a refining furnace is set to a relatively low temperature and is in a non-deoxidized state. A method has been proposed in which molten steel having a low P content is obtained by refining by adding a deoxidizing agent, alloyed iron, or the like. Further, as described in JP-A-1-79316, the temperature of molten steel to be tapped is lowered and transferred to a ladle, and Al is added to a dipping tube immersed in the molten steel to remove oxygen from a lance. It has been proposed that after passing through a step of raising the temperature of molten steel by blowing acid, a flux is added to the inside of the immersion tube to remove S, thereby melting molten steel having a small amount of P and S. These methods of refining molten steel use a combination of a smelting furnace and a ladle smelting furnace, and perform decarburization smelting in the smelting furnace at a slightly lower temperature, thereby lowering the P or simultaneously reducing the P. This is a refining method mainly aimed at reducing the S.

[0003]

However, in the method described in Japanese Patent Application Laid-Open No. 61-91313, the temperature is lowered in order to promote the removal of P from molten steel. Therefore, it is not possible to reduce the load on the refractory of the smelting furnace for decarburization and the like. Further, when the temperature of the molten steel is significantly reduced, the molten steel is solidified in a casting process or the like, and the adhesion of the metal occurs, thereby lowering the yield and increasing the load of operations such as the metal processing. In addition, in order to transfer the undeoxidized molten steel from the refining furnace to the ladle refining furnace and then add the deoxidizer and ferroalloys, the molten steel treated in the ladle refining furnace contains Oxidation results in turbidity of the generated oxide, which causes inclusions and the like. In particular, in the case of molten steel having a high carbon concentration, when undeoxidized molten steel is treated by a ladle refining furnace, carbon (C) in the molten steel reacts with free oxygen to generate CO gas, and the molten steel is removed. There is a problem such as abnormal combustion (explosion) caused by stagnation in a part of the exhaust system of the pot refining furnace, which hinders stable operation. On the other hand, in the method described in Japanese Patent Application Laid-Open No. 1-79316, when Al is burned to raise the temperature, as described above, one of carbon (C) in the molten steel and free oxygen and oxygen in the The part reacts to generate considerable CO gas, which stays in a part of the exhaust system of the ladle refining furnace, causing abnormal combustion (explosion) and impeding stable operation. This CO
The generation of gas becomes remarkable as the high carbon concentration of the molten steel increases, and abnormal combustion frequently occurs, making it difficult to perform a stable operation. In addition, there is a problem in that the blowing acid for raising the temperature generates Al ₂ O ₃ generated by combustion, oxides of valuable metals in the molten steel, and the like, thereby impairing the quality of the molten steel.

[0004] The present invention has been made in view of the above circumstances, while reducing the wear of refractories in refining furnaces and vacuum refining equipment, avoiding the operation hindrance caused by CO gas generated in the refining process, and reducing It is an object of the present invention to provide a method for refining high carbon molten steel having excellent cleanliness of molten steel by suppressing generation of oxides such as valuable metals.

[0005]

According to the present invention, there is provided a semiconductor device comprising:
The refining method of the high-carbon molten steel according to the description is to perform decarburization refining by a refining furnace, to produce molten steel having a high carbon concentration lower than a target temperature, to receive the molten steel in a ladle, and then into the molten steel. The pressure in the immersed immersion tube is reduced, and an exothermic agent is added to the molten steel in the immersion tube to perform blowing acid to raise the temperature of the molten steel to the target temperature.

[0006] The method for refining high carbon molten steel according to claim 2 comprises:
2. The refining method for high carbon molten steel according to claim 1, wherein the temperature of the molten steel received in the ladle is 10 to 9 lower than the target temperature.
0 ° C lower. Here, the target temperature of the molten steel is the temperature of the molten steel immediately before the end of tapping by adding the amount of temperature decrease over time after tapping, the amount of temperature drop when pouring into a tundish, etc. It is. Further, if the temperature of the molten steel is lower than the target temperature by less than 10 ° C., it takes time to separate and remove oxides generated when a blowing agent is added by adding a heating agent to the molten steel in the dip tube, As a result, the temperature of the molten steel is reduced, and the effect of increasing the temperature is reduced. On the other hand, if the temperature of the molten steel is lower than the target temperature by more than 90 ° C., the amount of the exothermic agent added to the molten steel increases, the turbidity of oxides in the molten steel due to the blowing acid increases, and the fire resistance of the immersion pipe increases. The wear of objects increases.

[0007] The method for refining high carbon molten steel according to claim 3 comprises:
The method for refining high carbon molten steel according to claim 1 or 2,
The carbon concentration of the molten steel decarburized and refined by the refining furnace is 0.20 to 1.2% by weight.

[0008] A method for refining high carbon molten steel according to claim 4 is as follows.
In the method for refining high carbon molten steel according to any one of claims 1 to 3, Al or an Al alloy is continuously added as the exothermic agent.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, embodiments of the present invention will be described with reference to the accompanying drawings to provide an understanding of the present invention. FIG. 1 is an overall view of a vacuum refining apparatus 10 to which a method for refining high carbon molten steel according to an embodiment of the present invention is applied. First, the vacuum refining apparatus 10 includes an immersion pipe 13 immersed in molten steel 12 in a ladle 11,
Vacuum chamber 15 fixed by a fastening means such as a flange 14
And an exhaust duct 16 connected to an ejector for sucking and depressurizing the inside of the immersion tube 13 and the vacuum tank 15,
A chute 17 for adding Al, which is an example of a heat generating agent, and a storage hopper 18 for Al are provided therein. A lance 20 for blowing oxygen to the molten steel surface 19 in the immersion pipe 13 is provided at the upper part of the vacuum chamber 15 so as to be able to freely move up and down. Further, a porous plug 21 connected to a supply source of an inert gas is provided at the bottom 11 a of the ladle 11, and the inert gas is blown into the molten steel 12 from the porous plug 21. In addition, 19a
Is a molten metal surface of the molten steel 12 formed in the ladle 11.

Next, a method for refining high carbon molten steel using the vacuum refining apparatus 10 will be described. Decarburization refining is performed using a converter, which is an example of a refining furnace, to obtain a carbon concentration of 0.20-1.
2 wt%, and the molten steel 12 at that time is set to a temperature 10 to 90 ° C. lower than a normal tapping temperature (that is, a target temperature) to obtain a capacity 35
Steel was tapped on a ladle 11 of 0 tons. When the carbon concentration of the molten steel 12 is lower than 0.20% by weight, the load of the decarburization refining of the converter increases, and the total refractory wear of the converter and the decompression refining apparatus 10 increases. Furthermore, the carbon concentration is 1.2% by weight.
Above, the wear of refractories decreases as the carbon concentration increases during decarburization refining using a converter, but the load of the subsequent blowing acid (heating refining) under reduced pressure increases significantly. It is not possible to reduce the total refractory.

On the other hand, if the tapping temperature is lower than the target temperature by less than 10 ° C., the temperature drop occurring during the time of raising the temperature and the amount of Al used are small, so that the heat transfer efficiency deteriorates. As a result, the amount of Al added increases. On the other hand, when the tapping temperature is lower than the target temperature by more than 90 ° C., the temperature of the molten steel 12 becomes too low when tapping from the converter to the ladle, so that the deposited metal or the nozzle is clogged. And hinder operation,
Further, a part of the Al ₂ O _{3 and the} like generated by the increase in the amount of Al added and the amount of oxygen used for the blowing acid increases in the molten steel 1.
2 may cause turbidity and cause inclusions. For this reason, a more preferable result is obtained when the tapping temperature is set to a temperature 20 to 75 ° C. lower than the target temperature. This ladle 11
The immersion pipe 13 having a diameter of 2.0 m is immersed in the molten steel 12 in the inside,
500-750 torr in the immersion tube 13 and the vacuum chamber 15
The molten steel 12 was continuously formed by forming a flow indicated by an arrow in FIG. 1 while blowing 0.6 to 15 NL / (min./ton of molten steel) of an inert gas as an example of an inert gas from the porous plug 21. Stirring was performed. Next, 50-180 kg of Al in the storage hopper 18 is cut out,
Al is burned by adding oxygen from the lance 20 to the molten steel surface 19 formed in the immersion tube 13 while adding the slag to the immersion tube 13 from the chute 17. For the addition of Al, a part of the total addition amount determined in consideration of the heat transfer efficiency when burning Al from the temperature of the molten steel 12 is added first, and then the lance 20 is used to blow acid (ascending). (Smelting).
One minute after the start of the blowing acid, the immersion tube 13
Al is added in several portions. The combustion of Al generates the heat of 7407 kcal / kg by the reaction represented by the equation (1), and the heat generated causes the temperature of the molten steel 12 to rise to a predetermined temperature. 2Al + 3O → Al ₂ O ₃ (1) Accordingly, the amount of oxygen to be blown is stoichiometrically set to the amount required for the reaction of the formula (1), and the supply of excess oxygen is eliminated. Oxidation loss of the 12 valuable metals can be prevented.
Further, by adding Al into the immersion tube 13 before the blowing acid, the concentration of Al in the molten steel 12 in the immersion tube 13 is extremely increased, and oxygen is sprayed on the molten steel surface 19.
Since Al can be burned preferentially, the temperature of the molten steel 12 can be increased with less oxidation of valuable metals in the molten steel 12. For this reason, more preferable results can be obtained by adding Al continuously according to the amount of oxygen to be blown. Also, the degree of vacuum at the start of the addition of Al and the blowing acid is
At a high vacuum of less than 500 torr, the added Al causes a sudden abnormal reaction (thermite reaction) with the oxides and oxygen in the molten steel 12 to cause bumping, and the metal scattered by the bumping is immersed in the immersion tube 13 and the vacuum tank 15. Remains in the inside and causes carbon pickup when refining the next low carbon material.

On the other hand, in the case of a low vacuum exceeding 750 torr (on the side closer to the atmospheric pressure), the immersion tube 13 and the vacuum tank 1
The outside air intrudes into 5 and oxidation of the valuable metal in the molten steel 12 or a decrease in the amount of water drawn into the immersion tube 13 weakens the stirring of the molten steel 12 and lowers the heat transfer efficiency to the molten steel 12. For this reason, when starting the addition of Al and the blowing acid, a more preferable result is obtained by reducing the pressure to 550 to 700 torr.

The heat generated by the burning of Al in the immersion tube 13 is transferred to the molten steel 1 by circulation of the molten steel 12 by stirring argon gas.
2 and the temperature is raised. In addition, by blowing acid, Al
Is burned, the free oxygen in the molten steel 12 and the oxygen from the blowing acid react with the carbon to generate CO gas. However, since the inside of the immersion pipe 13 and the vacuum chamber 15 is exhausted by an ejector, The gas is quickly discharged without staying in the exhaust system, and operation troubles such as an explosion caused by the CO gas can be avoided. Further, since the temperature is raised in a reduced pressure state with a low vacuum, it is possible to shut off the outside air that enters the immersion pipe 13 and the vacuum tank 15, so that oxidation of valuable metals and the like of the molten steel 12 in the immersion pipe 13 can be prevented, Since oxides that are turbid in the molten steel 12 can be reduced, inclusions are reduced and the cleanliness (quality) of the molten steel 12 can be greatly improved.

In the process of raising the temperature, the decarburization reaction is caused by the stirring of the molten steel 12 and the reaction of free oxygen in the molten steel 12 and oxygen by the blowing acid with carbon. Not so much as to lower the target carbon concentration of the molten steel 12. In this refining, unlike the conventional case where the carbon concentration and the temperature are each set to a predetermined value using a converter,
Since only the temperature of the molten steel 12 is actively lowered, and it is not necessary to raise the temperature by supplying a large amount of oxygen, the oxidation of iron and valuable metals is small, and the oxides in the generated slag can be reduced. Also, the wear of the refractory of the converter can be greatly reduced. As described above, the temperature of the molten steel 12 is raised in a limited area in the immersion tube 13 under reduced pressure, so that the temperature can be guaranteed with a small amount of blowing acid, the generation of oxides to be generated is reduced, and the refractory material is reduced. Can be reduced. After the temperature is raised, the molten steel 12 stops blowing acid, and the inside of the immersion pipe 13 and the vacuum chamber 15 is double-pressurized to the atmospheric pressure to raise the immersion pipe 13 and finish the refining. The molten steel 12 thus heated in a reduced pressure atmosphere is cast into a slab by continuous casting or the like, and then subjected to rolling or the like.

[0015]

Next, an embodiment of the method for refining high carbon molten steel of the present invention will be described. As shown in Table 1, in Example 1, the acid was blown in a converter, the carbon concentration was 0.25% by weight, and the molten steel temperature was 1550 ° C. lower than the normal target temperature after tapping.
C. was poured into a ladle having a capacity of 350 tons. While injecting 1 NL / (min / ton of molten steel) of argon gas from a porous plug into this ladle, a 2.0 m diameter immersion tube is immersed in the molten steel, and the inside of the immersion tube and the vacuum chamber is 500 torr.
The pressure was reduced to a low vacuum of r, and the molten steel was continuously stirred. Then, 45 kg of Al was added to the immersion tube to start blowing acid, and after 1 minute from the start of the first blowing acid, 135 kg of Al was further added to the immersion tube in three portions, and the total was added. The amount of Al added was 180 kg, and a total of 5
Acid (heating and refining) for 15 minutes to reach the target temperature of 15
The temperature was raised to 65 ° C. Thereafter, the inside of the immersion tube was double-pressurized to atmospheric pressure, and the immersion tube was raised from the molten steel to finish the treatment. As a result, the total refractory wear index including the converter and the vacuum refining equipment can be significantly reduced to 0.7 (when the conventional example is set to 1.0). The cleanliness evaluation is also in a good (o) state without inclusions and the like, and the operation trouble occurrence index of the decompression smelting apparatus is 0.1 (when the conventional example is set to 1.0), which is excellent as an overall evaluation. (◎)
The result was obtained.

[0016]

[Table 1]

In Example 2, 35% of molten steel having a carbon concentration of 0.80% by weight and a molten steel temperature of 1530 ° C., which is 10 ° C. lower than the target temperature after tapping, was subjected to blowing acid in a converter.
The steel was tapped in a ladle with a capacity of 0 tons. While blowing 2 NL / (min./ton of molten steel) of argon gas from a porous plug into the ladle, a 2.0 m diameter immersion tube is immersed in the molten steel, and the inside of the immersion tube and the vacuum chamber is reduced to a low vacuum of 600 torr. The pressure was reduced and the molten steel was continuously stirred. Then, 60 kg of Al was added to the immersion tube to start the blowing acid, and after 1 minute from the start of the first blowing acid, another 60 kg of Al was added to the immersion tube to reduce the total amount of Al added. 120
kg, followed by blowing acid (heating and refining) for a total of 4 minutes to raise the temperature to 1540 ° C., which is the target temperature. as a result,
The total refractory wear index including the converter and the vacuum refining equipment can be greatly reduced to 0.7 (when the conventional example is set to 1.0). It is in a good (o) state without inclusions and the like, and the operation trouble occurrence index of the decompression refining apparatus is 0.1 (when the conventional example is set to 1.0), which is excellent as a comprehensive evaluation (◎). The result was obtained.

On the other hand, in the conventional example, molten steel having a carbon concentration of 0.25% by weight and a molten steel temperature of a normal tapping temperature of 1570.degree. Steel tapping. Without raising the temperature of the molten steel in the ladle, a dipping tube having a diameter of 2.0 m was immersed, and argon gas was supplied from the porous plug at a rate of 3 NL / g in a state where the pressure in the dipping tube and the vacuum chamber was not reduced (atmospheric pressure). While supplying (minute / ton of molten steel), 50 kg of Al was added into the immersion tube, and blowing acid was added to the blowing acid (heating refining) for 4 minutes to raise the temperature to the target temperature of 1575 ° C. As a result, the total refractory wear index including the converter and the decompression smelter becomes 1.0, the repair and the operation time of the converter are shortened, the life of the converter is shortened, and CO gas is exhausted to the exhaust system of the decompression smelter. A small explosion caused by blasting caused the operation trouble occurrence index of the vacuum refining equipment to be as high as 1.0, and there was no difference in the cleanliness evaluation of the molten steel, but the overall evaluation was bad (×)
The result was.

Although the embodiment of the present invention has been described above, the present invention is not limited to the above-described embodiment.
All changes in conditions that do not depart from the gist are within the scope of the present invention. For example, although the case where Al is used as the heat generating agent has been described, an Al alloy, a ferrosilicon alloy, another Si alloy, or the like can be used. In addition, the shape of the dip tube may be an elliptical cross-sectional shape in addition to the cylindrical shape, and the shape of the vacuum tank may be the same diameter as the dip tube, a part of the vacuum tank, or Alternatively, a vacuum chamber whose entire diameter is larger than the diameter of the dip tube can be used.

[0020]

According to the method for refining high carbon molten steel according to claims 1 to 4, decarburization refining is performed in a refining furnace to melt molten steel having a high carbon concentration below a target temperature and receive it in a ladle. After steel, the pressure in the immersion pipe immersed in the molten steel is reduced, and a heating agent is added to the molten steel in the immersion pipe to perform blowing acid to raise the temperature of the molten steel to a target temperature. , The temperature of the molten steel can be raised easily and efficiently, the adhesion of ingots on refining furnaces and vacuum refining equipment and the wear of refractories are reduced, and the production of highly clean molten steel becomes possible. .

In particular, in the method for refining high carbon molten steel according to the second aspect, the temperature of the molten steel received in the ladle is set at 10 to 90 ° C. lower than the target temperature, so that the temperature of the molten steel can be raised efficiently. In addition, oxides mixed in the molten steel can be suppressed, and wear of refractories in the smelting furnace can be reduced, so that consumption of total refractories including the vacuum refining device can be reduced.

In the method for refining high carbon molten steel according to the third aspect, since the carbon concentration of the molten steel decarburized and refined by the refining furnace is set to 0.20 to 1.2% by weight, the load on the refining furnace can be reduced. It becomes possible, and wear of the refractory can be suppressed.

In the refining method of high carbon molten steel according to the present invention, since Al or an Al alloy is continuously added as a heat generating agent, the temperature of the molten steel can be raised with a small amount of addition, and the generated oxidation Deterioration of the quality of molten steel by the material can be prevented.

[Brief description of the drawings]

FIG. 1 is an overall view of a vacuum refining apparatus to which a method for refining high carbon molten steel according to an embodiment of the present invention is applied.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 10 Decompression refining apparatus 11 Ladle 11a Bottom part 12 Molten steel 13 Immersion pipe 14 Flange 15 Vacuum tank 16 Exhaust duct 17 Chute 18 Storage hopper 19 Molten steel surface 19a Metal surface 20 Lance 21 Porous plug

Claims (4)

[Claims] 1. A decarburization refining is performed by a refining furnace to melt molten steel having a high carbon concentration lower than a target temperature, and the molten steel is received in a ladle. A method for refining high carbon molten steel, comprising reducing the pressure, adding an exothermic agent to the molten steel in the immersion tube and performing blowing acid to raise the temperature of the molten steel to the target temperature. 2. The method for refining high carbon molten steel according to claim 1, wherein the temperature of the molten steel received in the ladle is lower by 10 to 90 ° C. than the target temperature. 3. The method for refining high carbon molten steel according to claim 1, wherein the carbon concentration of the molten steel decarburized and refined by the refining furnace is 0.20 to 1.2% by weight. 4. The method for refining high carbon molten steel according to claim 1, wherein Al or an Al alloy is continuously added as the exothermic agent.