JPH0431003B2 - - Google Patents

Description

[Detailed description of the invention]

<Industrial Application Field> This invention is used in a steelmaking process in which two converter-type furnaces are used to dephosphorize hot metal in one furnace and decarburize it in the other. The present invention relates to a method for preventing smoke generation when tapping hot water to ensure good workability and environmental protection. <Prior art and its problems> In recent years, quality requirements for various steel materials have become more sophisticated day by day, and with this, various innovations have been attempted in steel manufacturing methods and various new methods have been introduced. Under these circumstances, there have recently been great expectations for the development of a means to stably melt low-phosphorus steel at even lower costs, and much research is being carried out toward its realization. By the way, regarding the minimization of the total cost of steel manufacturing and the stable production of low phosphorous steel, the following preliminary dephosphorization method of hot metal has been proposed, and some of it has been put into practical use. In other words, preliminary dephosphorization is carried out by injecting quicklime-based dephosphorizing agent or soda ash into the hot metal in the torpedo car, and by injecting or blasting (spraying) quicklime-based flux into the hot metal in the ladle. A method of performing preliminary dephosphorization, a method of performing preliminary dephosphorization by blasting hot metal with quicklime-based flux in a blast furnace casthouse trough. However, although it is possible to achieve a relatively low P content level using the methods described in () and () above, dephosphorization is limited to "reactions that proceed during the floating process of the dephosphorizing agent (transitary reactor reaction)". However, the method described above has the problem that the utilization efficiency of dephosphorization flux is not necessarily good, and the longer the treatment time, the more heat is removed during treatment, which lowers the hot metal temperature. The hot metal temperature can be kept higher than the previous two methods, but since the dephosphorization treatment is performed on the hot metal immediately after being tapped from the blast furnace, the dephosphorization treatment temperature is too high and the P content level reached is the same. (mentioned above)
Both methods were unsatisfactory because they were worse than the methods (and). Furthermore, when using quicklime etc. as flux for hot metal dephosphorization, considering the amount of quicklime etc. used in the subsequent converter blowing, neither of the methods described above It was also pointed out that the required amount of slag-forming agent (the amount of quicklime, etc.) was not significantly reduced compared to the method of dephosphorizing using only a converter, omitting the process. Therefore, we have developed a method that can minimize the amount of slag-forming agent used, which greatly affects steelmaking costs, and that can efficiently produce high-quality steel without requiring any new equipment. The applicant strongly recognized the need for ``slag-metal countercurrent refining,'' in which slag and metal come into contact with each other in a countercurrent manner, and the amount of slag forming agent required throughout the entire steelmaking process is minimal. However, in reality, it is almost impossible to fully realize countercurrent refining, and the only steelmaking method that has the potential to reduce the amount of slag-forming agent with the least effort is currently A method in which the phosphorization process is divided into two stages and the slag generated in the lower stage is used as a dephosphorizing agent in the upper stage (i.e., a method in which converter slag is used as the main component of the flux for hot metal dephosphorization, for example, This is the basic idea of ``method of reusing converter slag as hot metal dephosphorization flux in outside-furnace refining,'' which the present applicant previously proposed in Japanese Patent Publication No. 55-30042. Based on the research results, he added, ``The steelmaking methods that have been proposed so far by reusing converter slag also involve out-of-furnace refining, making it extremely difficult to stably secure efficient working conditions.'' Moreover, the dephosphorization efficiency is not as high as expected, and mass production requires a special exhaust gas dust collector and dephosphorization slag removal equipment, making it a step forward as a means of mass production of high-quality steel. After paying attention to the problem in actual work, such as "It's something people hesitate to do," they proposed the following new steel manufacturing method (Patent application 1986-
No. 132517). That is, as shown in Figure 2, ``Two converter-type furnaces with both upper and lower blowing functions are used, and one of them is used as the dephosphorization furnace 1.
The other side is a decarburization furnace 2, and a refining agent mainly composed of converter slag 4 generated in the decarburization furnace 2 is added to the hot metal 3 injected into the dephosphorization furnace 1.
The temperature of the hot metal 3 in the dephosphorization furnace 1 is controlled by blowing oxygen gas upward from the lance 6 while stirring the bottom-blown gas.
This is a method in which hot metal is dephosphorized while being kept at 1400°C or lower, and then the obtained dephosphorized hot metal is decarburized in a decarburization furnace 2. According to this method, it has become possible to manufacture steel with a normal phosphorus level or low phosphorus steel with good workability and at low cost even with an extremely small amount of slag forming agent. The main advantages of the above method are specifically listed below. Because it is a "two-stage countercurrent refining" method that uses converter slag as the hot metal dephosphorization flux, the amount of quicklime used in the entire steelmaking process is significantly reduced compared to conventional methods.
It is possible to blow low phosphorus steel with an extremely small amount of quicklime. FeO in the converter slag is effectively used, improving the recovery rate of granulated iron and metal. Generally, when manganese ore or ferromanganese ore is used in a decarburization furnace, about half of these ores are Mn.
However, in the method of this invention, the slag is reused as hot metal dephosphorization flux, so the residual ore is effectively used, and the "[Mn] loss" in the hot metal is reduced. It is useful for “reducing ” or “increasing [Mn]”. Since the furnace used is a converter-type furnace, for example, even in the case of a dephosphorization furnace, only the dephosphorized pig iron can be tapped from the tapping port into the ladle, and then the slag in the furnace can be discharged into the slag ladle. Removal of slag is easier than in other dephosphorization methods. Since the furnace used is a converter-type furnace with both upper and lower blowing functions, the hot metal can be stirred strongly and the treatment can be carried out in a short time.Therefore, the amount of heat removed is small, compared to other dephosphorization treatment methods. It is extremely advantageous in terms of thermoeconomics. In particular, when melting converter slag is used, it becomes more thermoeconomically advantageous due to its sensible heat. Since the slag generated in the dephosphorization furnace has little free lime (free CaO is less than 1%), it can be effectively used as a roadbed material. Since two furnaces are used, there is no concern about poor dephosphorization due to P ₂ O ₅ adhering to the furnace body.
In other words, since high P ₂ O ₅ slag adheres to the dephosphorization furnace and only low P ₂ O ₅ slag adheres to the decarburization furnace, dephosphorization defects do not occur in the decarburization furnace. Moreover, when molten converter slag is used, the molten converter slag is charged into the dephosphorization furnace after the hot metal is charged, so there is no fear that a sudden explosive reaction will occur. Since dephosphorization is performed while stirring the bottom-blown gas,
Unlike the conventional hot metal dephosphorization method, there is no need to finely grind the dephosphorizing agent to near powder form, making it possible to reduce costs accordingly. If there is an idle converter, it can be used immediately as a dephosphorization furnace, and there is no need to prepare special equipment. In addition, for example, in the case of a factory operating 1/2 converter furnaces, one furnace can be used as a dephosphorization furnace, and this invention can be implemented without capital investment by operating 2/2 converters. It is possible. If it became necessary to build one of the bricks to extend the lifespan of the bricks, measures were taken to carry out conventional converter blowing using only one converter during this period to avoid leaving idle furnaces. Flexible refining is possible. As mentioned above, the "steel manufacturing method using two converter-type furnaces" proposed earlier by the applicant has many advantages, especially as a means of producing low phosphorus steel. However, as a result of further examination through many actual operations, the following new problems that needed improvement were recognized. That is, when steelmaking is carried out using a converter-type dephosphorization furnace and a decarburization furnace, the process of pouring dephosphorized pig iron into the decarburization furnace is, of course, essential.
For this purpose, when the furnace is tilted and the dephosphorized pig iron is tapped into the ladle, the slag layer floating on the hot metal as the furnace tilts first passes through the tap hole of the furnace, and then the hot metal layer. The iron reaches the tapping hole and tapping is performed. Therefore, it is impossible to prevent the slag from flowing out into the ladle from the tapping hole, although it is a small amount. However, when hot metal dephosphorization is carried out in a converter-type dephosphorization furnace, the oxygen in the slag, that is, (FeO), is about 3 to 10% (slag basicity is (about 2)
is highly controlled. Moreover, the tapped molten metal is dephosphorized hot metal with a high C content of around 4%. Therefore, when dephosphorizing pig iron is tapped, the slag that flows into the ladle is stirred by the hot metal flow and comes into contact with it, so oxygen in the slag (in the form of FeO) and carbon in the hot metal react violently, causing CO The problem is that the gas is blown up, and fine particles of slag, iron oxide, etc. are stirred up by this violent CO gas flow, creating a "smoking phenomenon" that has an extremely serious adverse effect on the working environment. Of course, it would be possible to avoid the negative effects of smoke generation by strengthening dust collection equipment as a countermeasure against smoke generation, but such measures would increase equipment costs and would require the use of two converters to reduce steelmaking costs. The advantages of the steelmaking method used cannot be fully utilized. <Means for Solving the Problems> Therefore, the present inventors have developed a method to ensure stable steelmaking workability by fundamentally suppressing the above-mentioned "smoke phenomenon," which must be avoided from the viewpoint of work efficiency and environmental protection. After conducting research from various viewpoints, we found that (a) The phenomenon of smoke emitted from the ladle during dephosphorization tapping is due to the oxidizing slag that leaked into the ladle at the early stage of tapping, as mentioned earlier. Although it is caused by the reaction between oxygen and carbon in hot metal, this reaction alone only generates CO gas, and the phenomenon that can be detected as "smoke" occurs only when the basicity is around 2. (b) However, as shown in Figure 1, the dry slag properties peculiar to slag are involved, and this slag is stirred up by the generated CO gas flow and scattered. At the early stage of tapping after the completion of dephosphorization and refining in the furnace) 7 (within 50% of the total tapping time from the start of tapping), silica sand, quicklime and a small amount of aluminum (in bulk) are poured into the ladle 9 using a chute 8, etc. Al)
When a low-melting point slag 10 with a predetermined basicity is formed by introducing slag, the violent reaction between the carbon in the hot metal and the oxygen in the slag is somewhat suppressed, and the slag properties change by adjusting the basicity. As a result, the slag particles do not scatter or the iron oxide in the slag is not caught up in the generated CO gas flow, and the above-mentioned smoke phenomenon is almost no longer observed. It is. In FIG. 1, reference numeral 11 indicates oxidizing slag, and reference numeral 12 indicates hot metal. This invention was made based on the above knowledge, and uses a converter-type dephosphorization furnace and a decarburization furnace, respectively, and transfers dephosphorized hot metal obtained by refining in the dephosphorization furnace to the decarburization furnace. During pouring and decarburizing refining, when hot metal is tapped from the dephosphorization furnace into a ladle, silica sand, quicklime, and aluminum are poured into the ladle to reduce the basicity to 0.5 or more.
By forming a slag with a low melting point of 1.5, it is possible to stably prevent smoke generation during hot metal tapping and ensure a good working environment during hot metal tapping. The term “converter type furnace” used here refers to a general hot metal processing furnace that taps hot metal by tilting.
In order to efficiently produce low-phosphorous steel using a small amount of quicklime, as in the method proposed earlier in Japanese Patent Application No. 61-132517, it is preferable to use a ``currently used upper and lower double blowing combined blowing converter''. Among the auxiliary materials put into the ladle, silica sand and quicklime are used to lower the melting point of the molten slag as much as possible to form a slag with a basicity of 0.5 to 1.5 that exhibits good fluidity. On the other hand, aluminum has the role of removing oxygen from the slag and mitigating the CO gas generation reaction, and if any of these is missing, it will not be possible to stabilize the smoke generation phenomenon. The mixing ratio of the above-mentioned auxiliary raw materials may be aimed at a slag basicity of 0.5 to 1.5, but the mixing ratio as shown in Table 1 can be recommended, for example.

[Table] Also, the reason why the basicity of the slag in the ladle is adjusted to 0.5 to 1.5 is that if the basicity is less than 0.5 and
In any case where the value exceeds 1.5, the slag becomes dry and has a high melting point, and slag occurs in areas other than the extremely thin layer that is in direct contact with the hot metal.
This is because the scattering caused by the CO gas flow becomes more intense, resulting in an unacceptable smoke phenomenon. Next, the present invention will be specifically explained using examples and comparing with comparative examples. <Example> First, the second
250 tons of hot metal with the composition shown in the upper row of the table was poured into a double blowing combined blowing converter used as a dephosphorization furnace, and the converter slag generated in a similar type of decarburization furnace was cooled.・25Kg/T of solidified and crushed to a particle size of 30mm or less, 10Kg/T of iron ore with a similar particle size
T, and fluorite 4Kg/T are added in a mixed state.
Dephosphorization treatment was performed for 10 minutes. The dephosphorization furnace and decarburization furnace used are both capable of stirring by blowing gas from the bottom of the furnace, as mentioned above.
It is a 250-ton upper and lower double blowing combined blowing converter, and the operating conditions shown in Table 3 were adopted. The dephosphorized pig iron thus obtained (the composition is shown in the middle row of Table 2) is tapped into a ladle and then poured into a decarburizing furnace to produce quicklime used in normal converter operation. Main blowing was carried out using 10Kg/T and 1Kg/T of fluorite as slag forming agents, but when tapping into the ladle, the first
figure

【table】

【table】

【table】

[Table] As shown in Table 4, during the initial stage of tapping (from the start of tapping to 50% of the total tapping time), the auxiliary materials in the proportions shown in Table 4 are introduced from the chute, and the slum in the ladle is Tapping was carried out while adjusting the basicity of the iron as shown in Table 4. As a result, as shown in Table 4, when tapping was carried out according to the conditions stipulated in the present invention (test numbers 3 to 5), there was almost no smoke emission from the ladle and good results were obtained. The work could be carried out, but the auxiliary raw material was not added (test number 1), the slag basicity adjustment by adding the auxiliary material did not satisfy the conditions specified in the present invention (test numbers 2 and 6), or If aluminum was not added as a raw material (Test No. 7), the continuation of the work would have to be stopped due to severe smoke generation, or the workability would deteriorate significantly due to the deterioration of the working environment. It has been confirmed that this occurs. During the main blowing in the decarburization furnace, iron ore was added as a coolant at appropriate times so that the end point temperature (blowing end temperature) was 1675°C. The converter slag generated at this time weighed 25 kg/T, and was added to the dephosphorization furnace together with iron ore and fluorite as a dephosphorizing agent raw material for the next charge, and a series of dephosphorization operations were repeated. As a result, the amount of quicklime used in the entire steelmaking process is extremely small, about 1/4 of that in normal converter single blowing, and the amount of P in the steel is as shown in the lower part of Table 2:
It was possible to obtain 0.013% by weight molten steel. <Summary of Effects> As explained above, according to the present invention, two furnaces, a converter-type dephosphorization furnace and a decarburization furnace, are extremely advantageous when producing high-quality steel at low cost. It is possible to stably and reliably suppress the "smoking phenomenon in the ladle when hot metal is tapped from the converter", which is a problem when implementing the "steelmaking method used", without requiring special equipment, and is suitable for industrial use. This brings about extremely useful effects industrially, such as making it possible to fully ensure the efficiency of tapping without any problems.

[Brief explanation of drawings]

FIG. 1 is a schematic explanatory diagram showing an example of the tapping method after dephosphorization and refining according to the present invention, and FIG. 2 is a schematic explanatory diagram showing an outline of the steel manufacturing method using two converters. In the drawings, 1, 7...Dephosphorization furnace, 2...Decarburization furnace, 3, 12...Hot metal, 4...Converter slag, 4', 1
1... Dephosphorization slag (oxidizing slag) mainly composed of converter slag, 5... Stirring gas blowing nozzle, 6...
... Lance, 8... Shoot, 9... Ladle, 10...
...Low melting point slag.

Claims (1)

[Claims] 1. When dephosphorizing hot metal obtained by refining in the dephosphorizing furnace is poured into the decarburizing furnace and decarburizing by using a converter-type dephosphorizing furnace and a decarburizing furnace, When pouring hot metal into a ladle, silica sand, quicklime, and aluminum are added into the ladle and the basicity is 0.5~
A method for preventing smoke generation during tapping of hot metal, characterized by forming a low melting point slag of 1.5.