JPS62109908A - Desiliconizing, dephosphorizing and desulfurizing method for molten iron - Google Patents

Abstract

PURPOSE:To simultaneously progress desulfurization and dephosphorization after desiliconization by coating a flux compounded with CaO and slag formability improving material on the surface of a molten iron from the initial period of a preliminary treatment for the molten iron and successively blowing a ferrous flux and alkaline flux thereto. CONSTITUTION:The flux essentially consisting of CaO and compounded with the slag formability improving material such as Mn ore is coated and imposed on the surface of the molten iron from the initial period of the preliminary treatment for the molten iron. The flux powder essentially consisting of iron oxide is blown by using a carrier gas simultaneously with top blowing of oxygen or addition of a solid oxygen source to execute the desiliconization treatment. The iron oxide flux is changed to the alkaline flux powder such as Na2CO3 for desulfurization and the supply of the oxygen is continued upon lapse of the desiliconization period to execute the desulfurization and dephosphorization reaction at the same instant. The entire stage of the desiliconization, desulfurization and dephosphorization is completed in a short period and the respective target values are attained with high accuracy by the above- mentioned method.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for removing silicon, phosphorus and sulfur from hot metal in one vessel within a short time, and in particular, for carrying out ladle treatment. This invention relates to a method for removing the above three elements by combining the coating of flux on the surface of hot metal and the injection of flux powder into the deep part of hot metal.

[Prior Art] Pre-treatment of hot metal is carried out mainly for the purpose 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 perfected in which the converter is exclusively used for decarburization and the associated rise in molten steel temperature.

The present applicant has also been conducting basic research and practical research on hot metal pretreatment technology, for example, in JP-A-58-160.
No. 06 is disclosed. The disclosed method involves blowing flux powder consisting of Cab, iron oxide, and a solvent (further reaction accelerator if necessary) deep into hot metal using a carrier gas (
This is a method that uses oxygen top blowing (hereinafter simply referred to as injection), and is low even in actual reactor rails.
We have succeeded in obtaining j8 El.

[Problems to be Solved by the Invention] The present inventors are conducting research to further improve the above method, and even if the amount of flux used is reduced, desiliconization and desiliconization can be achieved at the same level or greater than the above. We aim to establish a pretreatment method that can achieve high dephosphorization efficiency and desulfurization efficiency, and can also provide moderate operational advantages.

That is, all the fluxes used in the above disclosed method are in powder form, and are all supplied by injection method. Therefore, the production cost of flux is not only expensive, but also when there is a lot of 31 in the hot metal, it is necessary to adjust the basicity of the slag, so a large amount of flux has to be input, which further increases the cost. This problem is included. 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. This will lead to a new problem of having to struggle with heat compensation in the converter.

The inventors of the present invention were concerned about the above-mentioned situation, and the so-called casting bed desiliconization was omitted or carried out to a minor extent, so that the hot metal was supplied to the preliminary treatment equipment with a large amount of Si. However, the above-mentioned disadvantages do not occur, and if the amount of -Sl is the same, the total amount of flux used can be reduced, contributing to cost reduction, and it is possible to shorten the total processing time and suppress decarburization. Various studies have been conducted with the aim of establishing new pretreatment methods. As a result, a flux containing CaO as a main component and a slag slag-improving material is coated on the surface of the hot metal from the initial stage of hot metal pretreatment, and a flux powder containing iron oxide as a main component is applied to the surface of the hot metal using a carrier gas. We have established a hot metal pretreatment technology that removes silicon and phosphorus by blowing oxygen onto the surface of the hot metal while blowing it into the hot metal, and have already filed a patent application (Patent Application No. 6O-4154).
2).

By the application method, desiliconization and dephosphorization proceed efficiently,
In particular, even in cases where blast furnace casthouse desiliconization is not carried out or only lightly carried out, sufficient desiliconization can be carried out. This is because CaO has the ability to remove silicon. By the way, it is known that when 31 and P7+) coexist in hot metal, even if desiliconization and dephosphorization are attempted to proceed simultaneously, substantial dephosphorization will not start unless desiliconization has progressed to some extent. , CaO is a self-application method.
Because they are used in combination, desiliconization progresses relatively quickly, and desiliconization can be further accelerated by increasing the stirring power or increasing the oxygen supply rate, so the dephosphorization reaction starts relatively early after the start of treatment. Processing time will never be long.

Furthermore, since the above-mentioned CaO also has a desulfurization ability, the desulfurization reaction proceeds to some extent simultaneously with dephosphorization. However, the desulfurization that progresses here is not so remarkable, and in order to obtain an effect worthy of the name desulfurization, it is necessary to add another full-scale desulfurization treatment after the completion of the dephosphorization reaction. In other words, although the above-mentioned invention has the advantage of being able to quickly complete desiliconization and dephosphorization in the same container, it requires an independent desulfurization reaction treatment period to complete the entire process. It will take quite a long time to do so. Therefore, with the expectation that it would be possible to shorten the total processing time if dephosphorization and desulfurization could be performed simultaneously, dephosphorization was carried out using a flux that has both dephosphorization and desulfurization functions (for example, CaO-based flags). We also examined the possibility of simultaneously performing desulfurization and desulfurization. However, in this case, it is difficult to simultaneously set the target contents of P and S.
There was a problem in that if the content was tried to be adjusted to the target value, excessive dephosphorization would occur.

Concerned about these circumstances, the present inventors conducted research to establish a method that allows desulfurization to proceed at the same time as dephosphorization, while also accurately setting target values for both S and P. By improving the invention of the above-mentioned Japanese Patent Application No. 60-41542, we provide a method that can complete all steps of desiliconization, desulfurization, and desulfurization within a short time, and can set each target value with high precision. It was very successful.

[Means for Solving the Problems] The main point of the present invention is to coat the surface of hot metal with a flux composed of CaO as a main component and a slag slag-improving material from the initial stage of hot metal pretreatment, and to oxidize it. Flux powder whose main component is iron is blown into the hot metal using a carrier gas, while oxygen is blown onto the surface of the hot metal or a solid oxygen source is added. After the desiliconization period has passed, the blown flux powder is converted into alkaline desulfurization flux. It exists in the point that desulfurization is carried out by changing to powder, blowing into the hot metal with a carrier gas, blowing oxygen to the surface of the hot metal, or adding a solid oxygen source, and simultaneously carrying out the dephosphorization reaction. It is something.

[Function] As clarified by the above points, in the present invention, the fluff soot injection is not carried out alone, but the top addition of flux (a technique in which flux is coated and placed on the surface of hot metal, hereinafter simply referred to as top addition or flux top The first feature is that the injection flux is changed while also using
In addition, the above-mentioned problem has been solved by providing certain conditions for the injection flux and the top addition flux, respectively, and allowing these constituent elements to act synergistically.

The flux for addition to the upper part used in the present invention is mainly composed of CaO, and the CaO is not limited to high-purity ones (98% like lump lime) but also low-purity ones (such as those in converter furnaces). It is also possible to use slag, which has a concentration of around 50%. The latter converter slag contains 1/3 to 1/4 5i02, so it has the disadvantage that the amount used is slightly higher,
In addition to cost reduction, this method is advantageous in terms of temperature reduction and improvement in dephosphorization efficiency due to T-Fe.

CaO selected as the main component is a useful component as a dephosphorizing agent, and the present invention aims to strengthen the dephosphorizing effect by the flux added at the top. As mentioned above, the desiliconization effect and the desulfurization effect by CaO are exerted in parallel, so by using the flux added at the top, desiliconization, desulfurization, and dephosphorization proceed throughout the entire treatment period. However, for full-scale desiliconization, we should rely on the action of the desiliconization injection flux that mainly contains iron oxide, which will be described later, and for full-scale desulfurization, we should rely on the alkaline-based desulfurization injection flux that will be described later.

By the way, CaO has a drawback of having a high melting point and lacking in slag forming property, so the present invention adopts a configuration in which a slag slag forming property improving material is blended. M as a sludge-improving material
Low melting point components such as n-ore and calcium fluoride are used.

That is, the top-added flux of the present invention has CaO and a slag slag property improving agent as essential components, and the cooperative action of these forms a highly fluid slag and promotes the dephosphorization reaction at the slag-metal interface. 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.

In view of the fact that the dephosphorization reaction in the hot metal pretreatment proceeds from the beginning of the hot metal pretreatment, it is desirable to place the above-mentioned top-added flux on the surface of the hot metal from the initial stage of the hot metal pretreatment. The initial stage here refers to the first 3 to 5 minutes.
It is best to consider the time limit to be within minutes. Although it has been stated that the dephosphorization reaction progresses throughout the treatment process, the progress of the desiliconization reaction is remarkable for a while after the start of the treatment, and during this period the dephosphorization reaction only progresses slowly. This part can be positioned as the desiliconization stage. As this desiliconization reaction progresses, an environment suitable for the dephosphorization reaction is formed, and after the desiliconization has progressed to a considerable level (for example, below 0.10%), full-scale dephosphorization begins. The reaction begins.

Next, regarding the injection flux, as mentioned above, the main purpose of the dephosphorization reaction is almost achieved by the action of the flux added at the top. Therefore, the injection flux used in the present invention is one that exclusively contributes to desiliconization and one that exclusively contributes to desulfurization.

First, as the injection flux for desiliconization, one whose main component is iron oxide (including mill scale and iron ore, hereinafter the same) is used. Since iron oxide has a low melting point and exhibits sufficient slag-forming properties, there is no need to include a sludge-improving agent such as CaF2, and the injection flux is also expected to contribute to the dephosphorization reaction. In this case, some amount of CaO may be added to the flux. Therefore, in such cases, it is recommended to add some sludge-promoting material.

When the flux for desiliconization is injected in this way, the flux becomes slag and floats in the mtc, and in this floating process, the desiliconization reaction is carried out, and the flux added at the top promotes the dephosphorization reaction at the slag-metal interface. However, during the desiliconization stage, injection flux and top addition flux are used together, so a considerable amount of slag is present from the initial stage of hot metal pretreatment. Since it is necessary to allow the dephosphorization reaction to proceed under such conditions, the slag must exhibit sufficient fluidity. In other words, if the fluidity of the slag is low, it not only inhibits the progress of the slag-metal interface reaction, but also causes formation (especially noticeable during the desiliconization stage) due to the rise of carrier gas bubbles blown into the slag. is harmful to operational safety. From this point of view, the amount of CaO added is increased and the basicity (CaO/Si
O2) is recommended to be at least 1.0, preferably at least 1.5. Further, under the condition that the basicity is 1.5 or more, the dephosphorization ability is guaranteed. On the other hand, basicity is 4
If it exceeds 5, there are problems such as poor slag formation due to an increase in the melting point, a risk of slopping due to an increase in the amount of slag, or high costs due to an increase in Ca₂ consumption. Incidentally, the amount of silicon in the vortex is considerably reduced even though the injection of the desiliconizing flux is continued for 3 to 5 minutes, and the desiliconizing reaction shifts from oxygen rate-limiting to silicon amount-limiting, so the injection of the desiliconizing flux is stopped at this point. However, the desiliconization reaction continues to progress due to the desiliconization effect of the dephosphorization flux and the top blowing of oxygen. That is, in the desiliconization/deloading stage of the present invention, under the above-mentioned flux conditions (including flux for injection), upper blowing of oxygen (particularly wide-area blowing (one shot) to the entire surface of the upper flux is used), Improving the oxygen potential by top-blowing oxygen is considered to be an essential requirement for the progress of the desiliconization and dephosphorization reactions.Instead of top-blowing oxygen, a solid oxygen source (such as scale or manganese ore) may be sprinkled. For convenience, the explanation in this specification takes up top blowing of oxygen gas as a representative example.Whether top blowing oxygen or dispersing a solid oxygen source, is it possible to supply it evenly to the entire surface of the hot metal? Needless to say, it's a good thing.

Either the initial dephosphorization centering on desiliconization is performed as described above, or in the prior invention mentioned above, the injection of the desiliconizing flux is completed when the desiliconization stage is completed, and after that, We focus exclusively on stirring hot metal by gas bubbling (an operation that increases the opportunity for dephosphorization by moving the hot metal deep in the vessel to the slag-metal interface) and top-blowing oxygen (promoting the dephosphorization reaction by improving the oxygen potential). The idea was to perform dephosphorization (including some desiliconization as mentioned above) and then move on to desulfurization after the dephosphorization was completed. The disadvantages of this method are as described above, and in the present invention, once the desiliconization period has been completed, the injection flux is switched to an alkaline desulfurization flux, and this desulfurization flux is injected into the injection gas (generally an inert gas such as nitrogen). and blow into the hot metal. This flux is also turned into slag and floats in the hot metal, and the desulfurization reaction progresses during this floating process. The same was true for desiliconization fluxes, but since desiliconization and desulfurization proceed during the flux floating process, these fluxes should be injected through a porous nozzle so that they are spread as widely as possible. . That is, in desiliconization and dephosphorization, the desiliconization reaction tends to take precedence, but in dephosphorization and desulfurization, both reactions proceed simultaneously and at different sites. Desulfurization fluxes used in the present invention include Na2 CO3, Ni2 CO3, and Li2 CO3.

Alkaline fluxes such as CaCO3, Ca(OH)2, CaO, etc. are used. Among these, especially Na2C
O3 is also useful as a dephosphorizing agent and has the advantage of low resulfurization, making it the most widely used. Regarding resulfurization, another consideration is required.If the previously mentioned wide-area diffusion of the injection flux into the hot metal and wide-area spraying of top-blown oxygen are not observed, in other words, the injected desulfurization flux is not diffused and may be dispersed at a specific location. If the desulfurization slag floats to the surface and intensively blows oxygen toward the floating position, there is a danger that oxygen will be supplied excessively to the desulfurization slag and resulfurization will occur due to reoxidation of sulfides.

In order to perform such simultaneous dephosphorization and desulfurization, the following conflicting demands must be overcome.

(b) For dephosphorization, the lower the temperature at which the oxygen activity increases, the better.

(b) For desulfurization, the lower the oxygen activity and the higher the temperature, the better.

At that point, the flux added to the upper part of the CaO system and Na2 (:'0
In an environment where 3-system injection flux is used in combination, there is an oxygen potential region (the following formula) that can satisfy the dephosphorization rate and desulfurization rate at the same time, and if controlled within this region, dephosphorization and desulfurization can be performed simultaneously and efficiently. It is possible to make good progress.

10-13≦Oxygen potential≦l0-8 [Example Example 1 and Comparative Example 1 The target was hot metal that had been preliminarily desiliconized in a blast furnace casthouse, and lump quicklime (to, 2bg/T), scale (2, 8k
An upper flux consisting of Mn ore (s, akg/T) and Mn ore (s, akg/T) is sprinkled on the surface of the hot metal and 5.6Nrn'
/T oxygen top blower and scale (7,8 kg/T) injection (carrier gas is nitrogen) were started at the same time. In both Example 1 and Comparative Example 1, flux injection was stopped after 3 minutes, but in Example 1, oxygen top blowing and Na 2 CO 3 (5.1 kg/T) injection were continued for 6 minutes (total processing time: In Comparative Example 1, after 6 minutes of bubbling with oxygen top blowing and nitrogen gas alone, the oxygen top blow was stopped and Na 2 CO3 (5.1 kg/T) was injected at 4.5 minutes. (total processing time: 13.5 minutes)
minutes). The hot metal components and temperature are as shown in Table 1, and the effects of desiliconization, dephosphorization, and desulfurization are the same, and Example 1 can shorten the treatment time by as much as 4.5 minutes (33%). The amount of temperature drop is small and the amount of decarburization is also small.

Example 2 and Comparative Example 2 ``Lump quicklime (17.2 kg/T) and scale (5.8 kg
g/T) and Mn ore/6.7 kg/T), and at the same time, 6.2 Nm'/T of oxygen was blown over and scale (9.7 kg/T) was injected (the carrier gas was nitrogen). ) were started at the same time.

In Example 2, Na2 CO3 (5
, 1 kg/T) injection (for 7 minutes) (oxygen top blowing was also used) and the treatment was carried out for a total of 10 minutes. Comparative Example 2, like Comparative Example 1, switched to oxygen top blowing and gas bubbling after 3 minutes, and after another 7 minutes (10 minutes if calculated from the beginning), oxygen top blowing was stopped and N a 2 CO
3 (5,1kg/T) injection (4,5 minutes)
(total processing time + 14.5 minutes). The results are shown in Table 1, and the practical example 2 has a machining time of 4.
The time was reduced by 5 minutes (31%), and as a result, the amount of temperature drop was small and the amount of decarburization was also small. Furthermore, the desiliconization, dephosphorization, and desulfurization effects are completely inferior -4? [Effects of the Invention] As described above, the present invention eliminates the need to desiliconize the blast furnace cast bed, so loss of valuable components such as Fe and Mn is suppressed, and heat loss (due to desiliconization slag and refractories) is suppressed. heat loss) is also low. and CaO
Since inexpensive lump lime or converter slag can be used as a source, the flux consumption rate is low, and both the desiliconization and dephosphorization reactions proceed quickly. Furthermore, since a dedicated furnace with a high freeboard can be used, slopping is prevented and operational safety is ensured.

January 30, 1986 Director-General of the Patent Office Tomo Utsumi Michibe 1 ``g Display Showa E Patent Application No. 249666
7''-゛-- 2. Name of the invention Method for desiliconization, dephosphorization, and desulfurization of hot metal 3. Relationship with the case of the person making the amendment Patent applicant 4. Address of the agent: 7-3 Ikejima, 2-chome, Kita-ku, Osaka. No coffee 4075, date of amendment order Showa month, day (shipment date) 6, subject of amendment

Claims (1)

[Claims] A flux containing CaO as a main component and a slag slag-improving material is coated on the surface of the hot metal from the initial stage of hot metal pretreatment, and a flux powder containing iron oxide as a main component is added to the hot metal using a carrier gas. Oxygen is blown or a solid oxygen source is added to the surface of the hot metal while blowing into the hot metal, and after the desiliconization period, the blowing flux powder is changed to an alkaline desulfurization flux powder, and the hot metal is blown into the hot metal using a carrier gas. 1. A method for desiliconization, dephosphorization, and desulfurization of hot metal, characterized in that desulfurization is carried out by continuing oxygen blowing or addition of a solid oxygen source to the surface of the hot metal, and a dephosphorization reaction is simultaneously carried out.