JPS62109911A - Desiliconizing and dephosphorizing method for molten iron - Google Patents

Abstract

PURPOSE:To decrease the total amt. of the flux to be used and to attain the reduction of the entire treatment time, the suppression of decarburization, etc. by adjusting the conditions for blowing an injection gas in the period for accelerating desiliconization reaction and specifying the driving power value for stirring. CONSTITUTION:The surface of the molten iron which is substantially not subjected to a desiliconization treatment in a preliminary treatment furnace is coated with a dephosphorizing flux and is subjected to the top blowing of oxygen and injection of a desiliconizing flux. The conditions for blowing the injection gas are so adjusted that the driving power value epsilon for stirring (watt/1 ton of molten steel) determined by the equation attains 650-1,100 in the period for accelerating the desiliconization reaction in the above-mentioned treatment. The rate of blowing the injection gas is so adjusted that the driving power value epsilon for stirring attains >=300 - <650 in the decarburization reaction period. The adjustment is executed by changing the flow rate of the injection gas, the immersion depth of an injection lance, etc. according to the temp. of the molten iron, the amt. of the molten iron to be charged, etc.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is directed to the production of hot metal that has not been substantially pretreated (
Regarding the desiliconization/dephosphorization treatment method used for non-desiliconized hot metal and lightly desiliconized hot metal (the same shall apply hereinafter), it is particularly capable of efficiently carrying out the desiliconization/dephosphorization reaction within a short time. It is about the method.

[Prior art] Pre-treatment of hot metal is carried out with the main purposes of desiliconization, dephosphorization and desulfurization, and by performing such pre-treatment, major impurities such as Si, P and S are removed before charging into a converter. A system is being completed in which decarburization is carried out exclusively in the converter and the temperature of the molten steel is raised accordingly.

By the way, in recent years, research has progressed to improve the desiliconization method in blast furnace casthouses, and a method in which desiliconization is performed during the tapping process from the tap hole and then dephosphorization and desulfurization in the pretreatment furnace has become widely used. When desiliconization of blast furnace cast bed gutter is carried out, the wear and tear of the cast bed gutter becomes quite significant, requiring considerable effort and cost to maintain and manage it, and the loss of valuable elements (Fe and Mn) and drop in hot metal temperature are ignored. It becomes an impossible amount.

Under these circumstances, the present invention targets hot metal that has not been substantially subjected to pretreatment (including cases where it has been desiliconized at once, the same shall apply hereinafter), and does not require desiliconization in the blast furnace cast bed gutter. In the method of desiliconization, dephosphorization, and desulfurization in a pretreatment furnace,
The present invention aims to provide a method that can increase the processing efficiency in a pretreatment furnace.

As a method for desiliconization and dephosphorization in a pretreatment furnace, for example, as disclosed in JP-A-58-16006, Ca
A method in which a flux powder consisting of O1 iron oxide and a solvent (reaction accelerator if necessary) is blown into the deep part of the hot metal using a carrier gas (hereinafter simply referred to as injection), and oxygen top blowing is also used to promote desiliconization and dephosphorization. It is also possible to further perform a desulfurization treatment subsequently.

[Problems to be Solved by the Invention] However, all the flux used in the above method is in powder form, and all of this is supplied by injection method, which not only increases the manufacturing cost of the flux itself, but also increases the production cost of the flux itself. In particular, when applying to hot metal with a high silicon content that has not been subjected to preliminary desiliconization treatment, it is necessary to adjust the slag basicity, so a considerably large amount of flux must be input, which leads to the problem of increasing costs. Contained. Furthermore, if a large amount of flux is to be injected, it is theoretically unavoidable that the total treatment time will become longer, and as a result, decarburization in the hot metal will proceed faster than planned, resulting in a heating effect during converter operation. As a result, a new problem arises: heat compensation in the converter must be taken care of.

On the other hand, there is a considerable difference in the reaction mechanism between the desiliconization reaction and the dephosphorization reaction in hot metal, and it has been confirmed that the desiliconization reaction in particular progresses rapidly at the initial stage, determined by the rate of oxygen supply. Regarding the phosphorus reaction, after the 5ift in the hot metal decreases to a certain level (approximately 0.10%), the phosphorus in the hot metal is trapped by the dephosphorization flux on the surface of the hot metal or the dephosphorization flux floating in the vortex, and the reaction occurs. It has also been confirmed that the speed increases. However, in conventional desiliconization and dephosphorization methods that use pretreatment furnaces, including the method described above, it cannot be said that treatment methods that fully take into account the differences in desiliconization and dephosphorization mechanisms described above are adopted. Therefore, it takes a long time for desiliconization and dephosphorization (which in turn causes a decrease in hot metal temperature or a decrease in C, Mn, etc.),
This poses the problem of consuming a large amount of flux. The present invention has been made in view of these circumstances, and even when applied to hot metal with a high Si content that has not been substantially subjected to desiliconization treatment, the above-mentioned disadvantages occur, and the total amount of flux used is reduced. The purpose is to establish a new desiliconization and dephosphorization method that can reduce the amount of carbon and contribute to cost reduction, shorten the total processing time required for desiliconization and dephosphorization, and suppress decarburization. It is.

[Means for Solving the Problems] The present invention that achieves the above object has the following gist. That is, hot metal that has not been substantially subjected to desiliconization treatment is charged into a pretreatment furnace, the surface of the hot metal in the pretreatment furnace is covered with dephosphorization flux, and top-blowing of oxygen and injection of desiliconization flux are added. In desiliconization and dephosphorization of hot metal, the stirring power value [& (unit: 2 watts/1 ton of hot metal)] determined by the following formula during the desiliconization reaction acceleration period should be 6,650 or more and 1,100 or more. Adjust the injection gas blowing conditions, and then adjust the injection gas blowing conditions so that the power value (&) is 300 or more and less than 650, and perform the injection gas alone or flux injection. Performs silica/dephosphorization.

(ln (1+0.000968/) u ・Z ) However, Q: Carrier gas flow rate (1/min) T Jl: Hot metal temperature (°K) ML: Hot metal density (gr/cm3) Z: Injection lance immersion depth (cm ) To = carrier gas temperature (°K) As is clear from the above technical means, in the present invention, flux injection is not carried out alone, but dephosphorization flux is added at the top (flux is applied to the surface of hot metal). The first point is that it is used in conjunction with the technique of placing a coating (the same applies hereinafter).
In addition, during the desiliconization reaction promotion period at the beginning of the process, the stirring power value (ru) in the previous equation given by the blowing gas for desiliconization flux injection is set to a high value to rapidly accelerate the desiliconization reaction. After that, the power value (a
) is set at a low value to efficiently advance the dephosphorization reaction while minimizing decarburization, etc., and by adopting this configuration, the above-mentioned problems can be solved at once. It turned out that it could be resolved.

The most preferable flux for top addition used in the present invention is one containing CaO as a main component, and the CaO may be of high purity (such as lump lime, which has a concentration of about 98%) or of low purity (transformation). (e.g. around 50% like furnace slag)
can be used. The latter converter slag is i/3 to 1/4 5i0
Although it has the disadvantage that the amount used is slightly larger because it contains 2, it is advantageous in terms of cost reduction and improvement in dephosphorization efficiency due to the increase in slag T-Fe.

CaO selected as the main component is a useful component as a dephosphorizing agent, and the present invention aims at strengthening the dephosphorizing effect by the flux added at the top. Incidentally, since the desiliconization effect by CaO is also exhibited in parallel, the hot metal pretreatment effect according to the present invention has a remarkable effect not only in dephosphorization but also in desiliconization.

However, CaO has a drawback of having a high melting point and lacking in slag forming properties, so low melting point components such as Mn ore and calcium fluoride are used in combination as a slag slag forming property improving material. That is, the top-added flux (dephosphorization flux) used in the present invention is mainly composed of CaO and a slag slag-improving material, and the synergistic action of these forms a slag with good fluidity, and the top-blown oxygen Coupled with the effect of increasing oxygen potential, various reactions such as dephosphorization at the slag-metal interface are promoted. Judging from the viewpoint of promoting the dephosphorization reaction, the lower the interfacial temperature mentioned above, the better the results, so it is also effective to mix mill scale or iron ore into the above flux as a coolant, which lowers the melting point of the slag. It can also be expected to contribute to dephosphorization by promoting the slag-metal reaction and improving the oxygen potential in the slag. Further, since CaO has the function of promoting not only the dephosphorization reaction but also the desiliconization reaction, it can effectively proceed with the desiliconization and dephosphorization of hot metal in combination with the injection of the desiliconization flux described below.

Next is the desiliconization flux.As mentioned above, the desiliconization reaction progresses rapidly depending on the rate of oxygen supply, so iron oxides with high oxygen supplying ability (including mill scale and iron ore, the same applies hereinafter)
The best one is one containing as the main component. When the desiliconization flux is mixed with iron oxide only, there is no need to mix a slag-improving agent such as CaF2, but if the flux for injection is expected to have a dephosphorizing effect, it is necessary to add CaO to the flux. It can also be blended, and in such a case, it is recommended to blend some sludge accelerator.

By the way, if we examine in detail the process of reduction of Si and P during the desiliconization and dephosphorization of hot metal, we can see that the desiliconization reaction progresses rapidly and most of the Si is The process is such that the dephosphorization reaction progresses after the carbon is removed, and in order to complete the dephosphorization in a short time, the desiliconization reaction must proceed quickly.

To this end, taking into account that the desiliconization reaction initially progresses at a rate limited by oxygen supply, a large amount of desiliconization flux is injected from the initial stage of pretreatment, and the agitation effect of the injection gas is also increased to increase top-blown oxygen and hot metal. It is thought that it would be better to increase the frequency of contact, and in fact, desiliconization progresses quickly through such treatment. However, if these processing conditions are continued as they are, not only will the metal loss due to scattering (adhesion to the upper wall of the pretreatment furnace) increase and the yield will decrease, but also the decarburization and deMn reactions will become significant. Furthermore, the slag on the bath surface causes a reduction reaction with hot metal carbon, lowering the oxygen potential, which is disadvantageous for the dephosphorization reaction. Therefore, the present inventors have solved these problems by developing a system that can not only complete desiliconization in the shortest possible time, but also quickly proceed with the subsequent dephosphorization reaction, and improve the oxygen potential of the top slag for decarburization, deMn reaction, and top slag. In order to minimize the decrease in Further research was carried out by introducing the concept of value (ko). As a result, injection was performed so that (2) above fell within the range of 650 to 1100 during the desiliconization reaction promotion period, and so that (d) above fell within the range of 300 to less than 650 during the dephosphorization reaction period. We discovered that the above problems could be solved by adjusting the gas flow rate and injection depth.

However, if (5) is less than 650 during the desiliconization reaction promotion stage, the injected desiliconization flux will not be sufficiently dispersed in the hot metal and will float to the surface as slag because the hot metal is not sufficiently stirred. Moreover, the frequency of contact between the top-blown oxygen and the hot metal cannot be sufficiently increased, and as a result, the oxygen supply to the hot metal becomes insufficient and the desiliconization reaction slows down. However, 6)
If the value is set to 50 or more, the desiliconization flux will be uniformly dispersed into the hot metal and will become slag and float, and the top-blown oxygen will come into contact with the hot metal efficiently at the hot metal surface, resulting in a rapid desiliconization reaction. You can proceed. However, the effect of promoting the desiliconization reaction due to strong stirring reaches a saturation state when (d) is around 1100, and no further effect can be expected; in addition, the scattering of hot metal becomes more intense and the amount of hot metal adhering to the upper wall of the furnace increases. However, problems such as hot water spillage and lower yields, significant decarburization and deMn reactions, and shortened lifespans of furnace wall refractories and injection lance refractories may occur. must be kept below. In the present invention, the desiliconization reaction acceleration period refers to the period when the amount of Si decreases rapidly at the beginning of the preliminary treatment, and the first 3 minutes can be considered as a rough guide.

Next, regarding the dephosphorization reaction period, the dephosphorization reaction takes place mainly at the interface between the upper flux, which has turned into slag, and the hot metal. The most important point in proceeding with the dephosphorization reaction is whether or not the dephosphorization reaction is allowed to proceed. In other words, during the dephosphorization reaction period, the stirring power value (gate) should be as high as possible within a range that does not inhibit the above-mentioned interfacial reaction, and in order to meet these requirements, the present invention sets a range of 300 or more and less than 650. ing. However, if (d) is less than 300, the phosphorus in the deep part of the hot metal will not move sufficiently to the slag-metal interface due to insufficient stirring, and the reaction rate will decrease. As a result, dephosphorization becomes insufficient.

On the other hand, if it exceeds 650, the stirring force is too strong and the slag on the bath surface causes a reduction reaction with hot metal carbon, reducing the oxygen potential and causing the dephosphorization efficiency to tend to decrease.

The time required for dephosphorization varies slightly depending on the amount of hot metal processed, the shape of the pretreatment furnace, the nozzle structure of the injection lance, the composition and charging amount of the upper dephosphorization flux, the target P concentration, etc., but in general Under such conditions, approximately 7 to 10 minutes after the expiration of the desiliconization reaction promotion period can be considered as a tentative guideline.

As can be easily understood from the above equation, the above stirring power value (d) can be adjusted by changing the flow rate of injection gas and the immersion depth of the injection lance according to the hot metal temperature, the amount of hot metal charged, etc. good. In addition, during the dephosphorization reaction period, it is sufficient to simply inject the injection gas alone to ensure the specified (&) value, but if a method is adopted in which the injection gas is injected together with an appropriate amount of desiliconization flux or dephosphorization flux, dephosphorization can be achieved. It becomes possible to further advance silica/dephosphorization.

In the present invention, under the above-mentioned conditions, top blowing of oxygen is used in combination, and this is because improving the oxygen potential by top blowing oxygen is an essential requirement for the progress of desiliconization and dephosphorization reactions. It is from.

[Example] The flux conditions and top-blown oxygen conditions shown below were set, and the stirring power value (3
) was changed in various ways as shown in Table 1, and undesiliconized molten pig iron was subjected to desiliconization and dephosphorization treatments, and changes in each component over time were investigated. The stirring power value (λ) was adjusted by changing the immersion depth of the injection lance.

Dephosphorization flux (top addition) Mass quicklime: 7. OKg/t (1 ton of hot metal: same below) Mn ore: 6.5 g/l scale - 8.4 g/l desiliconization flux (injection) CaO: 44% Scale: 44% CaF2: 12% Injection Amount: 22.5 g/min Cutting speed: 1.9 Kg/t・min Injection gas: Top-blown oxygen total injection fi: 6.2 Nm3/Oxygen feeding rate: 0.52N m3/t・min No.
Table 1 Table 1 De-Si phase: De-silicification reaction promotion phase De-P phase: De-phosphorization reaction phase The results are shown in Table 2 and can be considered as follows.

■In the conventional method, a relatively small stirring power value (k) is used throughout the desiliconization reaction promotion period and the dephosphorization reaction period, so the desiliconization rate during the desiliconization reaction promotion period is slow, and as a result, the dephosphorization The dephosphorization reaction during the reaction period is also delayed, and it takes a long time to advance the dephosphorization to the target level.

■On the other hand, according to the embodiment of the present invention, as a result of the desiliconization reaction proceeding efficiently during the desiliconization reaction acceleration period of 3 minutes, the subsequent
The phosphorus content can be reduced to approximately the target level during the dephosphorization reaction period of minutes.

■On the other hand, the comparative example is an example in which a high stirring power value was applied throughout the desiliconization reaction acceleration period and the dephosphorization reaction period, and although both desiliconization and dephosphorization achieved their objectives, the metal adhesion to the soil part of the furnace wall Not only is the yield considerably lower, but decarburization has also progressed considerably, which is expected to cause problems with heat security in the future.

9. , ζ ・ Table 2 [Effects of the Invention] The present invention is configured as described above, and conditions are set so that each stirring power value falls within an appropriate range, especially during the desiliconization reaction promotion period and the dephosphorization reaction period. By doing so, the desiliconizing and dephosphorizing effects of the injection desiliconizing flux, the upper dephosphorizing flux, and the top-blown oxygen are maximized, and high desiliconizing and dephosphorizing effects can be obtained in a short time. Furthermore, with the reduction in treatment time, decarburization and deMn reactions are suppressed, and a drop in hot metal temperature can also be suppressed to a minimum, and many other secondary effects can be enjoyed.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a graph showing how Si and P decrease during desiliconization and dephosphorization.

Claims (1)

[Claims] Hot metal that has not been substantially subjected to desiliconization treatment is charged into a pretreatment furnace, and the surface of the hot metal in the pretreatment furnace is covered with dephosphorization flux, and at the same time, top-blowing of oxygen and desiliconization are performed. When performing desiliconization and dephosphorization of hot metal by adding flux injection, the stirring power value [■ (unit: watt/1 ton of hot metal)] determined by the following formula during the desiliconization reaction acceleration period is 650 or more and 1100 or more. Adjust the injection gas blowing conditions as follows, and then adjust the injection gas blowing conditions so that the power value (■) is 300 or more and less than 650, and then perform injection gas alone or flux injection. A method for desiliconization and dephosphorization of hot metal, characterized by carrying out the following steps. ■=(0.0062・Q・Tl)/(Ml)×{ln(
1+0.000968ρl・Z)+(1-(To)/(
Tl))} However, Q: Carrier gas flow rate (l/min) Tl: Hot metal temperature (°K) Ml: Hot metal density (gr/cm^3) Z: Injection lance immersion depth (cm) To: Carrier gas temperature ( °K)