JP5487959B2 - Hot metal removal Si removal P treatment method - Google Patents

Description

  The present invention relates to a converter type hot metal de-Si removal P treatment method, and more particularly to a hot metal de-Si removal P treatment method in which intermediate waste is performed after de-Si treatment.

  Performing hot metal preliminary treatment such as hot metal de-Si removal P in a converter type furnace has been conventionally performed as shown in Patent Document 1, and the hot metal subjected to de-Si de-P treatment is further converted into a converter. After being de-C treated, it is sent to the casting process. Further, Patent Document 1 discloses that the CaO source required for de-Si de-P can be reduced by performing intermediate waste for discharging de-Si slag to the slag pan between de-Si treatment and de-P treatment. .

  This intermediate waste is performed by tilting the converter-type smelting furnace and letting out only the slag floating on the surface layer of the hot metal, but in order to smoothly carry out the intermediate waste, in the de-Si treatment process It is necessary that the fluidity of the generated slag is sufficiently high. For this purpose, Patent Document 1 discloses that it is necessary to adjust the CaO / SiO2 of the slag at the end of the Si removal treatment to a range of 0.3 to 1.3. For example, when adjusting the CaO content mainly using bulk lime, the bulk lime has a composition of CaO: 94%, others: 6%, its melting point is 2927 ° C., and it takes a long time to dissolve. In combination with fluorite having a melting point of 1350 ° C., the fluidity of the slag was increased to such an extent that it could be eliminated in a short time of about 10 minutes. However, burying slag generated from the treatment process using fluorine-containing fluorite in the ground or using it as roadbed material has been in conflict with soil regulations, so fluorite is currently used. Therefore, it is difficult to carry out an operation mode in which intermediate evacuation is performed after Si removal.

  Moreover, even if the removal of Si is completed in a short time of about 10 minutes by using fluorite together and the intermediate waste is performed, the removal of Si proceeds during that time until the Si concentration in the molten iron becomes 0.1% or less. It was. Thus, when the Si removal progresses, the de-C reaction starts, and CO is generated by the reaction of C + (1/2) O 2 → CO, and the molten iron is vigorously stirred. As a result, granular iron is involved in the de-Si slag and discharged to the outside, which deteriorates the molten steel yield. In the present specification, “%” means “% by mass”.

  Also, when the slag is discharged into the slag pan after the Si removal treatment, there is a problem that the granular iron and slag cause a reaction of C + FeO → Fe + CO in the slag pan and bump into the slag, and the slag flows out due to the generated CO gas. was there. Thus, when trying to save the CaO source by the intermediate waste, the molten steel yield may be deteriorated or the slag may flow out from the slag pan.

Japanese Patent Laid-Open No. 10-152714

  Therefore, the object of the present invention is to solve the above-mentioned conventional problems, improve the fluidity of the slag at the time of intermediate discharge without using fluorite, prevent deterioration of the molten steel yield and slag outflow, It is an object of the present invention to provide a hot metal de-Si de-P treatment method capable of reducing the CaO source by waste.

The present invention, which has been made to solve the above-mentioned problems, is a hot metal process in which, after performing hot metal de-Si treatment in a converter type furnace, intermediate waste is performed and further de-P treatment is performed in the same furnace. In the de-Si de-P treatment method, the intermediate waste is performed in a state where the Si concentration in the hot metal exceeds 0.2%, and the slag generated in the post-process after the de-P treatment is put into the furnace for performing the de-Si treatment The slag basicity (CaO / SiO ₂ ) is adjusted to a range of 0.5 to 1.8, and the Si removal treatment is performed. In addition, it is preferable to use the ingot slag which generate | occur | produces in the converter slag generate | occur | produced in a de-C furnace, or a casting process as slag generate | occur | produced in a post process from P removal processing.

In the hot metal de-Si removal P treatment method of the present invention, after the hot metal de-Si treatment is performed in a converter type furnace , the intermediate waste is performed with the Si concentration in the hot metal exceeding 0.2%. Thus, it is possible to save the CaO source as before, but unlike the conventional case, the slag generated in the subsequent process rather than the de-P process, typically the converter slag is put into the furnace that performs the de-Si process. As a result, the slag basicity (CaO / SiO ₂ ) is adjusted to a range of 0.5 to 1.8, and the Si removal treatment is performed. Converter slag has a melting point of about 1350 ° C. like fluorite, so it is easy to melt. Especially when the slag basicity is adjusted in the range of 0.5 to 1.8, the liquid phase rate of slag is high at 1300 ° C. Since the property is improved, the intermediate waste can be smoothly performed. For this reason, dissolution time can be significantly shortened compared with the case of using only lump lime or fluorite as a CaO source. For example, the de-Si treatment can be completed in about 5 minutes.

At this stage, the Si concentration in the hot metal is at a level exceeding 0.2%, and the de-C reaction of the hot metal has not yet occurred. Therefore, the hot metal is not stirred by the gas generated with the de-C reaction as in the prior art, and the granular iron is not involved in the de-Si slag, so that the molten steel yield is improved. Further, when the slag is intermediately discharged into the slag pan after the Si removal treatment, the granular iron and the slag do not react in the slag pan, and the outflow of the slag by the generated gas can be prevented. Therefore, according to the present invention, it is possible to reduce the CaO source by intermediate waste without using fluorite, and to prevent the deterioration of molten steel yield and the outflow of slag from the slag pan. be able to.

It is process explanatory drawing of this invention. It is a ternary diagram of SiO2-CaO-FeO. It is a graph which shows the molten steel yield change by an intermediate waste.

Embodiments of the present invention will be described below.
FIG. 1 is an explanatory view showing an embodiment of the present invention. Pig iron produced by a blast furnace is injected into a converter type furnace (smelting furnace) 1 and, for example, high pressure oxygen is blown from an upper blowing lance 2 to remove Si. I do. In order to capture the SiO 2 generated in the de-Si process, in the present invention, the slag generated in the post-process after the de-P process is returned to the de-Si process and used. Since the post-process is generally a de-C process and a casting process in the converter 3 than the de-P process, the slag generated in the post-process rather than the de-P process is the converter slag generated from the de-C process or It means ingot slag generated from the casting process (slag remaining in the ladle).

  In the present invention, these converter slag and ingot slag are charged into the furnace 1 and adjusted so that the slag basicity (CaO / SiO2) at the end of the de-Si treatment is in the range of 0.5 to 1.8. However, the Si removal treatment is performed. FIG. 2 is an isothermal cross-sectional view at 1300 ° C. of a ternary diagram of SiO 2 —CaO—FeO. The graph shows a straight line with CaO / SiO 2 of 0.5 and a straight line with CaO / SiO 2 of 1.8. As shown in this graph, slag easily forms a liquid phase within this range, and excellent fluidity can be obtained. However, when the basicity is out of this range, the melting point increases. The range indicated by the ellipse in the graph is the target composition of the slag composition.

If the composition is adjusted in this manner, the melting point of the slag is lowered, and the slag charged into the furnace 1 is also melted in a short time. Therefore, in the present invention, it can be completely melted in about 5 minutes without requiring a long time as in the conventional method in which lump lime having a melting point of about 2930 ° C. is added. Therefore, in the present invention, intermediate waste is performed in which only the de-Si slag is discharged to the slag pan 4 in a state where the Si concentration in the hot metal exceeds 0.2%. On the other hand, when massive quicklime is used, it hardly melts in about 5 minutes, so the slag discharge property at the time of intermediate discharge is extremely bad, and a large amount of unreacted CaO remains in the discharged slag. When reused as a roadbed material, it becomes a cause of problems of strong alkalinization and expansion. In addition, if the desiliconization process is performed for a long time to avoid this, the cycle time of the furnace becomes longer and the productivity is lowered, and the desiliconization reaction proceeds to a silicon concentration of 0.2% or less. Yield deterioration is inevitable. Since the de-C reaction of pig iron does not yet occur when the Si concentration exceeds 0.2% , it is possible to avoid troubles in which the CO generated by the de-C reaction stirs the molten iron vigorously. There is no iron involved. Moreover, the granular iron and slag in the slag pan 4 do not react, and the outflow of slag due to bumping can be prevented.

Therefore, the granular iron is not involved in the de-Si slag as in the prior art and is not discharged to the outside, and the molten steel yield is improved. FIG. 3 is a graph showing the yield of molten steel when no intermediate waste is performed as a reference (0.0%). As shown in FIG. 3, when the Si removal treatment is performed until the Si concentration in the molten iron decreases to 0.2% or less and the intermediate waste is performed, the entrained granular iron is discharged, so the molten steel yield is minus 0. However, when the intermediate waste is performed at the stage where the Si concentration in the hot metal exceeds 0.2% as in the present invention, it becomes 0.28%. The reason why the yield is improved as compared with the case where intermediate waste is not performed is that the amount of slag generated at the time of de-P is reduced, and the iron content lost by de-P slag is reduced.

  The CaO reduction effect by the intermediate waste is known, but a specific average value shows that when the charged Si is 0.6%, the CaO required for the de-Si removal P step without intermediate waste is 17 kg / In contrast, when the intermediate waste is performed, the amount is reduced to 13 kg / ton. When the charged Si is 0.8%, the Si removal PCaO is 22 kg / ton without the intermediate waste. On the other hand, if the intermediate excretion is performed, it is reduced to 15 kg / ton.

  After removing Si-free slag by intermediate waste, high-pressure oxygen is blown again from the top blowing lance 2 to perform the P removal treatment. The de-P treatment itself is the same as the conventional one, and the hot metal from which de-Si and de-P have been performed in this way is transferred to the pan 5 and de-C treatment is performed in the converter 3. The converter slag generated in this step is returned to the Si removal treatment step as described above. Similarly, the ingot slag is returned to the Si removal treatment process.

  As described above, since fluorite is not used as the CaO source in the refining process of the present invention, the generated slag does not conflict with soil regulations and can be reused as roadbed material.

The results of experiments conducted to confirm the effects of the present invention are summarized in Table 1.
No. 1-No. 14 is an embodiment of the present invention, by using a converter slag and ingot casting slag without using fluorite, return the converter slag in de Si process, Si concentration of 0.2 percent to 0.3 This is an example in which intermediate elimination was performed at the stage of%. The Si concentration in the hot metal after the de-Si removal P treatment is reduced below the detection limit, and the P concentration is reduced to 0.012 to 0.053%. The amount of CaO required for the deSi removal P treatment at this time is as shown in the table, and is in the range of 10.0 to 21.0 kg / ton. The converter slag used has a composition of CaO: 46%, SiO ₂ : 14%, FeO: 24%, others: 16%, and its melting point is 1320 ° C. The ingot slag used has a composition of CaO: 34%, SiO ₂ : 13%, FeO: 12%, and others: 41%, and its melting point is 1150 ° C.

  No. 15 and no. The comparative example 1 shown in 16 is a case where the slag basicity after completion | finish of Si removal processing is less than 0.5. When the treatment was started after the intermediate evacuation, the slag violently flowed out of the furnace port, making the treatment difficult. Moreover, the comparative example 2 shown to No17 and No18 is a case where the slag basicity after completion | finish of Si removal process exceeded 1.8. As the basicity increased, the slag discharge performance during intermediate drainage deteriorated.

  No. 19-No. The comparative example 3 shown in 22 is a case where the Si concentration in the hot metal after completion of the Si removal treatment is less than 0.2%. When the Si concentration in the hot metal after the Si removal treatment was lower than 0.1%, slag flowed out of the furnace port during the Si removal. Slag also flowed out from the slag pan after the intermediate evacuation. When the Si concentration in the hot metal after completion of the Si removal treatment was 0.1% to 0.2%, the slag did not flow out from the furnace port during the Si removal, but the slag flowed out from the slag pan after the intermediate waste.

The comparative example 4 shown to No23-No27 of Table 1 is a case where an intermediate waste was not performed. Although there was no hindrance to operability, the basic unit of CaO used for de-Si de-P treatment deteriorated. The comparative example 5 shown to No28-No32 is a case where the slag as an auxiliary material at the time of Si removal processing was not recycled. Since it took time to form slag during the Si removal treatment, fluorite was used as a test. However, even if fluorite was used, the Si concentration in the hot metal after the Si removal treatment was over 0.2% , and the treatment could not be completed, and the slag flowed out from the slag pan after the intermediate waste.

  Table 2 shows the results of investigating operability by changing the slag basicity at the end of Si removal. Slag basicity was adjusted using converter slag and lump lime, and the intermediate waste was carried out when the Si concentration in the hot metal was around 0.25%. The value of slag basicity is a calculated value from the amount of added auxiliary raw material and the hot metal component change.

  Paying attention to the slag discharge performance during intermediate discharge, if the slag basicity is 1.8 or less, the bowl-shaped slag will slowly flow out according to the tilting of the furnace, and after the slag is discharged to the outside to some extent It was confirmed visually that the hot metal began to flow out. This is considered because slag with a high liquid phase rate was able to be formed in a short time. On the other hand, when the basicity was adjusted to 1.8 or more, slag was not easily discharged even when the furnace was tilted, and when the furnace was further tilted, hot metal flowed out prior to the slag. This is thought to be because a large amount of converter slag and bulk lime were required to be added in order to increase the basicity, so that it was not completely dissolved in a short time and the liquid phase rate was low. If the slag cannot be discharged outside the furnace, the effect of removing Si out of the furnace cannot be obtained, and the amount of CaO used during de-P cannot be reduced, so the basicity of de-Si slag should be adjusted to 1.8 or less. Is desirable.

  On the other hand, when attention is paid to the de-P treatment status after the intermediate evacuation, the slag basicity can be operated without any problems if the basicity is 0.5 or more, whereas if the basicity is 0.5 or less, de-P After a while after the oxygen supply was started, slag spilled violently from the furnace port and the treatment could not be continued. This is because the lower the basicity of the de-Si slag, the higher the viscosity of the slag, so if the basicity of the de-Si slag is too low, the CO gas generated by de-C by oxygen supply cannot pass through the slag, This is probably because the slag has been pushed up. For the operability of the de-P treatment, it is desirable to adjust the basicity of the de-Si slag to 0.5 or more.

  From the above two points, it was confirmed that the basicity of the de-Si slag is preferably adjusted in the range of 0.5 to 1.8.

Table 3 shows the test results on how the operability changes depending on the hot metal [Si] after de-Si. When evacuation is attempted after de-Si removal to hot metal [Si] <0.10%, slag outflow from the furnace port during de-Si treatment and slag leakage from the slag pan after intermediate evacuation are severe, and operability is very high It was bad. When evacuation was attempted after desiliconization to a range of hot metal [Si] = 0.10 to 0.20%, slag outflow from the furnace port during desiliconization treatment did not occur. The slag leakage continued and the operability was poor. On the other hand, when intermediate waste was performed in the range of hot metal [Si]> 0.20%, slag leakage from the slag pan after intermediate waste did not occur, and operability was improved. Investigating the relationship between the type of auxiliary material used to adjust the basicity at the time of de-Si and the slag discharging property at the time of intermediate waste, if the hot metal [Si] ≤ 0.20 %, regardless of the type of auxiliary material used Slag discharge was good, but when hot metal [Si]> 0.20%, when using quicklime and fluorite, slag discharge is poor and Si cannot be discharged outside the furnace. The CaO reduction effect can no longer be obtained. On the other hand, when converter slag or ingot slag was used according to the present invention, slag discharge was good even in the hot metal [Si]> 0.20% region, and a CaO reduction effect could be enjoyed.

1 furnace 2 top blowing lance 3 converter 4 slag pan 5 pan

Claims (3)

After the de-Si process in the molten iron in a converter furnace type furnace, subjected to intermediate Haikasu, in the de Si de P processing method hot metal performing de P further processed in the same furnace, hot metal in the intermediate Haikasu In a state where the Si concentration exceeds 0.2%, slag generated in the post-process after the de-P treatment is put into a furnace for performing the de-Si treatment, and the slag basicity (CaO / SiO ₂ ) is set to 0. 0. A hot metal de-Si de-P treatment method, wherein the de-Si treatment is performed within a range of 5 to 1.8. 2. The hot metal de-Si de-P treatment method according to claim 1 , wherein converter slag generated in a de-C furnace is used as slag generated in a post-process after de-P treatment. 2. The hot metal de-Si de-P treatment method according to claim 1, wherein the ingot slag generated in the casting process is used as the slag generated in the post-process after the de-P process.