JP2009228102A - Method for treating residue in converter after tapping - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for treating residue in a converter after tapping, with which the residual molten steel at the last refining time is not shifted to a slag ladle side as far as possible while removing the slag at the last refining time, and thus, a steel-making yield in the converter, that is, [1-(the charged iron source-tapping quantity)/(the charged iron source)], is improved. <P>SOLUTION: After cooling the residue in the furnace by charging a solid iron source as the cooling material to the residue in the furnace remaining in the converter after tapping, the remaining molten steel in the above residue in the furnace, is stuck and solidified to the furnace bottom and the furnace wall of the converter by swinging the furnace body of the converter while maintaining the remaining slag in the molten state and thereafter, the molten slag is discharged by tilting the converter. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for treating in-furnace residue mainly composed of residual molten steel and molten slag remaining in a converter after steelmaking. The present invention also relates to a converter steelmaking method in which residual molten steel remaining in a converter furnace after steel is output is directly reused as an iron source for the next converter operation.

  After the converter steel is discharged, molten steel remains in the converter together with the converter slag. These in-furnace residues after steel are usually transferred to a so-called Noro pot and further cooled in a Noro treatment plant. At this time, the molten steel remaining in the converter becomes a so-called bare metal despite the fact that it has a target component composition, which causes a reduction in steelmaking yield. Therefore, minimizing the amount of molten steel that moves to the side of such a ladle is to make the steelmaking yield in the converter, that is, (1- (input iron source-outgoing steel amount) / (input iron source)). It leads to improvement.

  As a method for treating the residue in the converter after the steel is discharged, Patent Document 1 discloses that when the molten steel is discharged, the decarburized slag generated by the decarburization process is left in the refining vessel, and the steel is left. After charging the solid iron source into the smelting vessel, this smelting vessel is tilted back and forth several times to solidify the slag so as to be entangled with the surface of the solid iron source and used for the next decarburization and refining. It is disclosed.

  Moreover, although it does not relate to the processing method of the residue in the converter, Patent Document 2 discloses that every time the solidified slag adhered to the inner surface of the receiving vessel that receives and transports the molten slag discharged from the iron refining vessel is peeled off. Disclosed is a method for treating molten slag in a receiving container that is received a plurality of times without being performed.

JP 2004-256839 A JP 2003-294376 A

  However, when the means disclosed by Patent Document 1 is used, all of the residual slag and residual molten steel of the previous charge after refining will be reused at the next refining, but without the discharge of residual slag, Depending on the steel type of the next refining, this means may not be available. Considering the next refining, it is required to discharge the slag from the previous refining as much as possible. Further, using the means disclosed in Patent Document 2, it may be possible to leave the slag and molten steel from the previous refining as they are in the converter and accept the hot metal for the next refining. There is a similar problem.

  The present invention eliminates the slag from the previous refining and prevents the residual molten steel from the previous refining from moving to the side of the pan as much as possible, so that the steelmaking yield in the converter, that is, (1- (charged iron source-outlet steel). It is an object of the present invention to propose a method for treating residues in a post-steel converter that improves (quantity) / (charged iron source)).

  In the method for treating a residue in a post-steel converter according to the present invention, a solid iron source is added as a coolant to the in-furnace residue remaining in the post-steel converter to cool the in-furnace residue. After that, while maintaining the residual slag in a molten state, the converter furnace body is swung to adhere and solidify at least the residual molten steel on the bottom of the converter furnace, and then tilt the converter. The molten slag is discharged.

  In the said invention, it is preferable to introduce | transduce raw dolomite with a solid iron source as a coolant.

  Moreover, it is preferable to use the steelmaking process generation | occurence | production metal | metal | money by which the solid iron source was crushed by the delivery dimension: 1-150mm. In addition, it is preferable that the average value is 20-80 mm.

  It is preferable that cooling gas is blown from the bottom of the converter furnace when the converter furnace body in each of the inventions is swung.

It is preferable to maintain the viscosity of the molten slag at 10 P until the molten slag is discharged after the coolant is charged in each of the inventions.
Decarburization and refining can be performed by charging molten iron into the converter in which the residue in the furnace has been treated by the treatment method of each invention.

  According to the present invention, while the slag from the previous smelting is removed, the residual molten steel from the previous smelting is prevented from moving to the side of the pan as much as possible, so that the steelmaking yield in the converter, that is, (1- (charged iron source-outgoing steel) Quantity) / (charged iron source)). In addition, the wear amount of the converter furnace bottom brick can be reduced.

  In applying the present invention, first, the converter operation is performed according to a normal method, and the steel output operation is performed as usual, for example, while suppressing the transition of the slag into the steel output ladle by introducing a dart. . The residual amount of molten slag and molten steel in the converter after steel is about 5 to 10% for molten slag and 0.5 to 2% for residual molten steel (both mass ratio) with respect to the amount of charged iron. do it. Moreover, the temperature is the residual slag: 1600-1700 degreeC and the residual molten steel: 1550-1600 degreeC at the time of completion | finish of steel production.

  A solid iron source is put into the converter in which the molten slag and the residual molten steel remain as furnace residues in the converter after steel output. As solid iron sources, steel scrap such as steel plate end plates, bullion with a ladle for a steel ladle, continuous cast tundish glass bullion, steel slag collection bullion, etc. can be used. However, since this solid metal is introduced for the purpose of lowering the temperature of the residual molten steel and solidifying the residual molten steel in the converter, its C content should be low, for example, desulfurization slag of pig iron The recovered metal is not suitable as the solid iron source of the present invention.

  The solid iron source is preferably crushed to a passing dimension of 1 to 150 mm. When the size is less than 1 mm, the molten steel stays in the molten slag when it is put into the converter, cannot reach the residual molten steel below it, and cannot effectively cool the residual molten steel. . On the other hand, if the size is over 150 mm, the occurrence of splash from the molten slag layer becomes large at the time of charging, and the cooling effect in the residual molten steel becomes localized later. This makes it difficult to uniformly solidify and adhere the residual molten steel to the bottom of the converter furnace due to the oscillation of the converter. The solid iron source should preferably have a dimension of 20 to 80 mm as an average of the dimension of the delivery, if possible, and if it can achieve the above-mentioned purpose, it is allowed to have a dimension of less than 10 mm in the dimension of the delivery. .

In charging the solid iron source, raw dolomite is preferably charged together with the solid iron source. When using a solid iron source as a coolant, especially recovered metal from crushed steelmaking slag, the so-called rim reaction C + O → CO is caused by the temperature drop of the residual oxygen-rich molten steel.
Although the reaction occurs and the generation of the gas, the dust generated by the dust adhering to the recovered metal is blown up by the active gas generation, the generation of the dust is suppressed when the raw dolomite is introduced together with the solid iron source. Although the cause is not clear, the temperature of the molten slag decreases with the addition of raw dolomite and the viscosity increases with the increase in basicity, and the dust generated as a result of gas generation is trapped in the molten slag. Presumed to be.

The input amount of raw dolomite may be 3 to 8% (mass ratio) with respect to the residual slag amount (estimated value), and the particle size is preferably 5 to 10 mm on the average of the passing diameter. The temperature of the molten slag at the completion of charging of these coolants is estimated to be 1530 to 1560 ° C. Moreover, it is desirable to maintain the viscosity of the residual slag at this time to 10 P (poise) or less. The residual amount of residual slag can be measured by visual observation.

FIG. 1 is a graph showing the relationship between the viscosity of residual slag after charging the coolant and the discharge rate from the furnace port. The emission rate here is
((Residual slag amount (kg)-(melted slag discharge from the furnace port (kg)) / (residual slag amount (kg)
Is calculated by As apparent from FIG. 1, when the residual slag viscosity is 10 P or less, the discharge rate of the slag from the furnace port is 60% or more, but when it exceeds the discharge rate, the discharge rate is lowered, which hinders the next refining. The viscosity of the residual slag is an estimated value obtained by comparing the result of the flow test of the sample slag before the furnace with the standard material, and the molten slag discharge amount is determined by inspection or visual observation. .

  On the other hand, the temperature of the molten molten steel at the completion of the charging of the coolant is estimated to be about 1450 to 1500 ° C. This temperature corresponds to a temperature immediately above the solidification temperature of the residual molten steel, and the residual molten steel can be adhered to and solidified on the converter furnace bottom and the furnace wall by swinging the converter furnace body described later. In other words, it is important to select the amount of the coolant to be charged so that the state of the residual slag and the residual molten steel after the injection satisfies the above state.

  After the coolant is added as described above to adjust the state of residual slag and residual molten steel, an operation of swinging the converter furnace body is performed. The swinging operation of the converter furnace body may be performed so that the molten steel in the furnace residue adheres to and solidifies at least on the converter furnace bottom and further on the converter furnace wall. It is sufficient to repeat the operation of tilting 50 to 65 ° toward the front of the furnace and 35 to 45 ° toward the back of the furnace and performing 3 to 5 times.

  The above swinging operation is particularly effective when the converter type has a single-tube bottom blowing gas tuyere 3 at the furnace bottom 2 of the converter body 1 as shown in FIG. It is preferable to carry out while blowing an inert gas, for example, nitrogen gas, from the blowing gas blowing tuyere. As a result, the molten molten steel can be smoothly cooled and adhered to the furnace bottom and solidified, and a gas blowdown tuyere can be prevented from being blocked by the molten molten steel. It should be noted that the solidification / adhesion of the molten steel is required to be performed at least over the bottom of the converter furnace, particularly the region where the blown tuyere exists, in order to contribute to the protection of the gas blown brick described later. It may extend to the furnace wall.

  After the converter is rocked as described above, the converter is tilted to discharge the molten slag. This operation may be performed in the same manner as a normal evacuation operation.

  FIG. 3 is a schematic view of the bottom of the furnace showing the state of adhesion and solidification of the residual molten steel to the furnace bottom and the furnace wall after the slag is discharged by using the gas blowing from the furnace bottom together. As shown here, solidification and deposits 4 of residual molten steel are observed uniformly on the furnace bottom. By achieving solidification and adhesion of residual molten steel to the converter furnace bottom and furnace wall, the protection of the gas blowing bricks at the furnace bottom is strengthened, and the amount of wear of tuyere bricks at the converter furnace bottom is reduced. The effect of drastically decreasing is obtained. In fact, the remaining thickness of tuyere bricks when the converter was used 5000 times was 450 mm before the present invention was implemented, but became 700 mm by the implementation of the present invention (combined with furnace bottom gas blowing).

As described above, the furnace residue after the steel from the converter is treated, and at least the residual molten steel solidifies and adheres to the bottom of the furnace and slag is discharged. Can be used for the next refining operation. As a result, the molten steel remaining in the furnace during the previous rotary furnace operation can be used again as an iron source, and the amount of steel output increases accordingly, and the steel output yield at the establishment of the converter is improved. That is, in the conventional operation, the yield of converter steel is 1- (input iron source-output amount) / (input iron source) (1)
However, in the present invention, the amount of residual molten steel reused by solidification / adhesion is assumed to be K (kg), and is corrected as shown in the following equation (2), thereby improving the yield. .
(1- (charge iron source + K) − (steel output + K)) / (charge iron source + K)
= (1- (Feed iron source-Steel output) / (Feed iron source + K) (2)

  Using a nominal 300 converter, low-carbon steel was melted and blown at a blowing temperature of 1650 ° C., and then steel was produced using a slag dart. 24t of slag and 3t of molten steel remained in the converter after steel output. Moreover, the temperature was residual slag: 1620 degreeC and residual molten steel: 1580 degreeC. For the residue in the post-steeling furnace in the above state, the converter slag recovered to an average of 80 mm as a coolant: 1500 kg (5.6% of the post-steeling furnace residue), raw dolomite: 1500 kg ( 5.6%) of the residue in the furnace after steeling. The state of the solidified molten steel and slag after charging was as follows. In addition, dust generation at the time of charging was slight.

Solidified molten steel temperature: 1090 ° C (estimated value)
Slag temperature: 1470 ° C, slag viscosity: 7P
However, the slag viscosity is a value measured by reheating a slag sample collected from the furnace to 1470 ° C., which is the same as the slag temperature in the converter, using a rotational viscometer.

  After confirming the above state, the operation of tilting the converter 60 ° toward the front of the furnace and 40 ° toward the back of the furnace was repeated three times, and then the converter was tilted to discharge the molten slag. The amount of slag discharged was 25t, and no bullion was discharged at the same time. Observation of the solidification and adhesion of the residual molten steel to the furnace bottom after slag discharge confirmed that the residual molten steel was almost uniformly solidified and adhered to the entire furnace bottom.

  Thus, decarburization refining was carried out by newly charging an iron source such as hot metal and auxiliary materials to the converter in which the residue in the converter was treated after steel output. As a result, the steel output obtained was 300 t. This amount is increased by 3t compared to the case where the present invention is not applied, and the yield is improved by 1%.

It is a related figure of the viscosity of the molten slag after cooling material injection | throwing-in, and the discharge rate from a furnace port. It is a schematic diagram which shows the tuyere arrangement | sequence of the bottom blowing gas tuyere to which this invention is applied. It is the schematic diagram of the furnace bottom which showed the adhesion and solidification state of the residual molten steel to the furnace bottom when performing this invention together with gas blowing.

Explanation of symbols

1: Converter body 2: Furnace bottom 3: Gas blowing tuyere 4: Solidified / adhered molten steel

Claims (6)

  The solid iron source is added as a coolant to the in-furnace residue remaining in the converter after steelmaking, and after cooling the in-furnace residue, the converter furnace body is maintained while maintaining the residual slag in a molten state. The inside of the post-steel converter is characterized by swinging to adhere and solidify at least the residual molten steel to the bottom of the converter furnace, and then tilting the converter to discharge molten slag. Residue treatment method.   Raw dolomite is put together with a solid iron source as a coolant, and the processing method of the residue in the post-steering converter of Claim 1 characterized by the above-mentioned.   3. The method for treating residues in a post-steeling converter according to claim 1 or 2, wherein the solid iron source is a steelmaking process generated metal crushed to a passing dimension of 1 to 150 mm.   4. The method for treating residues in a post-steeling converter according to any one of claims 1 to 3, wherein cooling gas is blown from the bottom of the converter furnace when the converter body is swung.   The method for treating a residue in a post-steeling converter according to any one of claims 1 to 4, wherein the viscosity of the molten slag is maintained at 10 P or less after the coolant is charged until the molten slag is discharged. .   A converter steelmaking method, wherein the converter treated with the residue in the furnace is charged with hot metal and decarburized and refined by the processing method according to claim 1.

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