JPH0437136B2 - - Google Patents

Description

[Detailed description of the invention]

<Industrial Application Field> The present invention provides a method for dephosphorizing hot metal (hereinafter referred to as dephosphorization) that can dissolve a large amount of steelmaking auxiliary raw material scrap without adversely affecting the product composition. It is about the method. <Conventional technology> In response to the increasing quality requirements for various steel materials in recent years, efforts have been made to produce low-P steel at low cost and to rationalize costs as a total steel manufacturing system (reducing the total amount of slag-forming agent used, converter With the aim of reducing ferromanganese by melting and reducing Mn ore in steelmaking, hot metal dephosphorization treatment, which removes phosphor from hot metal before steelmaking, has been actively adopted. The following methods are representative of the hot metal dephosphorization treatment methods that have been proposed so far. (A) A method in which quicklime-based flux or soda ash is injected into hot metal in a torpedo. (B) A method in which quicklime-based flux is injected or blasted onto hot metal in a ladle. (C) A method in which quicklime-based flux is blasted onto the hot metal in the blast furnace casthouse trough. (D) A method of blowing using a quicklime-based flux using an upper and lower blowing converter [Tetsu to Hagane, (1987),
S276 pages]. (E) A method of blowing using an upper and lower blowing converter and using the converter slag (produced in the decarbonization furnace) as the main component of the dephosphorizing agent [Patent Application No. 132517/1982]. On the other hand, there has recently been a tendency for scrap to increase with the accumulation of social capital, and for this reason, increasing the amount of scrap used as an auxiliary raw material for steelmaking has become an important issue. However, hot metal pretreatment, such as torpedo dephosphorization,
If this is done, the temperature after deP treatment will drop to about 1250°C. Furthermore, when hot metal is generally dephosphorized, there is almost no [Si] in the dephosphorized hot metal, and the hot metal [C] concentration also partially decreases (dephosphorized pig iron [C] concentration ≒ 4% by weight). , decarbonization in the next step
The heat source in the furnace tends to be insufficient. For this reason, it has been pointed out that there is a problem that the amount of scrap that can be added is smaller than when hot metal dephosphorization is not performed.
For this reason, attempts have been made to increase the usable amount of scrap by adding carbonaceous materials (coke, etc.) into the converter during converter blowing and utilizing the combustion heat. In this case, S from the added carbon material
There was a problem in that the [S] concentration in the obtained molten steel was increased because the molten steel was picked up. Therefore, it has become necessary to develop a method that allows the use of scrap when depurating hot metal. However, in the hot metal dephosphorization methods described in (A), (B), and (C) above, scrap melting is impossible because the torpedo, ladle, and blast furnace cast bed are not designed to add scrap. Even if an attempt was made to forcibly introduce scrap during depuration of hot metal using this method, the scrap would not dissolve because the stirring of the hot metal was weak. On the other hand, the hot metal removal P shown in (D) and (E) above
In the case of the method, it is used in a converter, and the hot metal can be stirred by blowing gas from the bottom of the furnace, so it is possible to melt the scrap. In fact, the above-mentioned “iron and steel,
(1987), p. S276'' also indicates that it is possible to melt scrap by adopting a method of overturning the furnace to increase the stirring effect during processing. However, even in the case of the hot metal dephosphorization method shown in (D) above, the dissolvable amount of the input scrap is [Si] in the hot metal and [C] in the hot metal that is partially burned at the same time (dephosphorization
[C] decrease during processing: Δ[C] = about 0.7% by weight)
It was only possible to utilize the heat of combustion. Moreover, in method (D) above, the heat source for scrap melting is mainly found in the hot metal [Si].
In order to make deP more advantageous, it is not assumed that Si is removed in advance, and therefore the amount of quicklime used is reduced by ``conventional method of blowing hot metal without pre-deP into steel as usual in a converter''. Therefore, the benefits of hot metal pretreatment cannot be expected to be that great. <Problems to be Solved by the Invention> Under these circumstances, the purpose of the present invention is to reduce the increase in [S] concentration, decrease in temperature, etc. without impairing the benefits of pre-dephosphorizing hot metal. It is an object of the present invention to provide a method for dephosphorizing hot metal that can add and dissolve a large proportion of scrap without causing any inconvenience. <Means for Solving the Problems> In order to achieve the above object, the present inventors conducted research from various viewpoints and came to obtain the following knowledge. (a) The method proposed in the above-mentioned Japanese Patent Application No. 132517/1983 (one of the two upper and lower blowing converters is replaced with a dephosphorizing furnace,
The other is a carbon removal furnace, and a refining material mainly composed of converter slag generated in the carbon removal furnace is added to the hot metal injected into the carbon removal furnace, and the hot metal is removed by oxygen blowing while bottom-blowing gas is stirred. After performing P, the resulting dephosphorized hot metal is decarbonized and finished dephosphorous in a decarbonizing furnace)
As in the deP treatment process in
When blowing is carried out by adding carbonaceous materials such as coke as a heat source along with scrap, it is possible to avoid subsequent converter blowing (decarbonization), which was previously attempted.
Unlike "scrap melting," which is performed by adding carbonaceous materials together with scrap during furnace blowing, there is sufficient S, which tends to infiltrate from the carbonaceous materials into the hot metal.
S is captured in the slag and removed, and even though a sufficient amount of scrap is dissolved by the combustion heat of the input carbonaceous material, the [S] concentration after deP tends to rise significantly. Don't show it. (b) However, when scrap melting is performed by heating with carbonaceous materials such as coke and top-blown oxygen during hot metal dephosphorization, the iron oxide content in the dephosphorization slag is reduced due to the presence of carbonaceous materials. However, this problem was solved by adding only a part of the dephosphorizing agent at the beginning of oxygen blowing after adding scrap and carbonaceous material, and during the scrap dissolution stage. When the above-mentioned process is completed, the amount of oxygen top blowing is reduced to the normal amount in the "Hot metal dephosphorization method using a double blowing converter" as shown in the above-mentioned patent application No. 132517/1986, etc., and the amount of dephosphorization agent is reduced. When the remaining part is added and dephosphorization is performed for a predetermined period of time (about 10 to 15 minutes) in this state, iron oxide (T. Fe) de-P
It is secured to an advantageous level and good P removal progresses, so it is sufficiently wiped out. This invention was made based on the above knowledge, and is based on the following: ``Dephosphorizing agent is added to hot metal poured into a converter-type furnace with both upper and lower blowing functions, and oxygen gas is removed while bottom blowing gas is stirred. To dephosphorize hot metal by top-blowing, first add a portion of the desulfurization agent, scrap and carbonaceous material to the hot metal, top-blow oxygen to dissolve the scrap, and then remove the remaining desulfurization agent. It is characterized by the fact that the amount of scrap dissolved during hot metal dephosphorization treatment can be improved by adding it, without causing any inconvenience such as an increase in the amount of impurities. The "converter type furnace with both upper and lower blowing functions" referred to here is basically an LD converter, which blows Ar, N ₂ , CO ₂ , CO or O ₂ gas from the bottom of the furnace.
A typical example is a so-called "compound blowing converter" in which supplementary stirring is provided by blowing at a rate of about 0.03 to 0.30 Nm ³ /min·t. In addition, although the dephosphorizing agent is not particularly specified, from the viewpoint of reducing slag and reducing the total cost of steelmaking, it is recommended to
Low P ₂ O ₅ generated in the furnace (e.g. 1% by weight or less)
A ``converter slag-iron oxide-fluorspar system'' or a ``converter slag-manganese ore-fluorspar system'' in which the basic component is ``converter slag'' are good, and quicklime may be added thereto.
Of course, as mentioned above, the quicklime-iron oxide-fluorite system, which is commonly used for hot metal dephosphorization in a torpedo or ladle, may be used. However, since the latter flux has poor sludge-forming properties compared to the converter slag-based dephosphorization agent, it may be necessary to take measures to promote sludge-forming, such as collapsing the furnace during the process. The amount of dephosphorizing agent to be used is approximately 50 kg/t, which is mainly composed of converter slag, but the basicity of the slag (CaO/SiO ₂ ) should be 2 or more, preferably 2.5 to 3.0.
It is preferable to set the above value from the viewpoint of eliminating S. This is because, as mentioned above, when carrying out the method of the present invention, S tends to infiltrate into the hot metal from carbonaceous materials such as coke, but in order to prevent the [S] level after deP from becoming high, it is necessary to This is because removal of S by P slag becomes important. There are no particular restrictions on the shape, particle size, etc. of the dephosphorizing agent; for example, there is no need to transform a granular agent into a powder. Coke is commonly used as a carbonaceous agent, but the type is not particularly important as long as it can be used as a fuel. Of course, it is preferable to use coke with low S content, but during deP treatment, deS
Since this also progresses, a regular product with an S content of about 0.5% by weight is sufficient. However, when the S content of the carbonaceous material is high, as mentioned above, it is preferable to adjust the basicity of the slag to 2.5 to 3.0 or more. The amount of carbon material added varies depending on the hot metal temperature before treatment, the target temperature after treatment, and the amount of scrap used, but it is 1% coke per 1% increase in scrap ratio.
~3Kg/t is a rough guideline. In the case of coke, a standard carbon material particle size of about 1 to 100 mm is sufficient, but from the viewpoint of increasing coke usage efficiency and not lowering the [C] of hot metal,
It is preferable to make the particle size as small as possible without scattering. The amount of scrap used varies depending on the time given to the P removal process, but the scrap ratio increment is usually about 10% or less. Of course, it is basically possible to have more than this. As for the shape of the added scrap, it is preferable to use scraps that are as light as possible, such as trimmer scraps, since the scraps are added at the hot metal pretreatment stage and are melted at low temperatures. Furthermore, if the size of the scrap is large, it is important to increase the stirring at the bottom of the furnace as much as possible to promote the dissolution of the scrap. How to add scraps:
Hot metal may be charged before pouring into the converter, or after pouring, it may be charged together with a portion of the dephosphorizing agent and coke in a scrap chute. Next, details of the hot metal dephosphorization process according to the present invention,
This will be explained along with its effect. <Function> In the hot metal dephosphorization treatment according to the present invention, a part of the dephosphorization agent, scrap, and coke are added at the initial stage, and the scrap is usually heated and melted using top-blown oxygen. After the scrap dissolution is completed, the remaining dephosphorizing agent is added to dephosphorize.
Entering the refining period. FIG. 1 shows an example of the above-mentioned method of the present invention, with the amounts of dephosphorization agent and carbonaceous material added, and the amount of top-blown oxygen added (in the case of a scrap ratio increment of about 5%).
FIG. 2 similarly shows another example, and the characteristics of the scrap dissolution period and the de-P phase will be described below. Scrap melting stage In the scrap melting stage, if the scrap is simply melted by heating, it is sufficient to add scrap and coke and top-blow oxygen, but even in this case, there is no slag present. (a) The Fe yield decreases due to spitting (scattering of iron particles with a diameter of 1 mm or less) and an increase in fume loss; (b) [Si] in the hot metal is oxidized, and the resulting acidic SiO ₂ dissolves in the basic refractory. (c) Top-blown oxygen tends to cause combustion of not only coke but also [C] in the hot metal, reducing the [C] in the hot metal (i.e., if slag is present, coke is generally deposited on top of the slag). This results in inconveniences such as floating particles, which can be made more flammable by soft blowing with oxygen gas. Therefore, a cover slug is necessary. If part or most of the dephosphorizing agent is added to form this cover slag, this will turn into slag during the scrap dissolution stage, so the next dephosphorizing agent will be removed.
Make it advantageous to withdraw from P during the period. The amount of top-blown oxygen during scrap melting is generally about the same as during decarbonization blowing (2 to 4 Nm ³ /min・t).
That's fine. However, in order to reduce the reduction in [C] in the hot metal and mainly burn coke, it is also preferable to reduce the oxygen gas blowing speed somewhat in addition to soft blowing of oxygen gas, which will be described later. This is because when the oxygen gas blowing speed is reduced,
“Carburizing by coke” tends to be delayed compared to “reduction of [C] in hot metal due to oxygen gas (decarbonization)”
This is to save time. As for the blowing conditions, it is important to make the blowing as soft as possible so that the coke grains in the slag burn more easily than in the hot metal [C]. This also allows for effective secondary combustion (burned and generated
This is a phenomenon in which CO gas is further combusted into CO ₂ by top-blown oxygen, and the heat of combustion at this time can also be used advantageously). This secondary combustion is more likely to occur at lower temperatures, such as during hot metal deP, and since the refractory in the furnace is also at a lower temperature than during decarbonization main blowing or general converter blowing, refractory melting may occur. It does not cause the problem mentioned above. When carrying out the above soft blowing, the design of the lance nozzle must be devised or the distance between the lance and the hot water surface must be increased so that L/L ₀ (L: Depth of depression in the metal bath due to O ₂ jet, L ₀ : Metal It is desirable to blow so that the ratio (bath depth) is 0.1 or less. The ratio of coke to top-blown oxygen at this time is determined by the stoichiometric amount of oxygen required to burn the coke. However, it goes without saying that it is necessary to consider the amount of oxygen required for secondary combustion. The time required for deP processing is 1% increment of scrap ratio.
It takes about 1 minute for 5% scrap, and about 5 minutes for 5% scrap. DeP phase What is important in the deP phase is to be careful not to put the slag formed during the scrap dissolution phase into a situation where the amount of iron oxide is so low that deP becomes disadvantageous. For this reason, it is important to add iron oxide or Mn ore to increase the oxidizing power of the slag during the deP phase. The amount of top-blown oxygen during the dephosphorization phase is 0.5Nm ³ /min・t
A small amount is sufficient. The time required for the deP phase is usually 5 to 15 minutes. Here, when taking the P removal rate into consideration, it is important to suppress the hot metal temperature during the P removal period to 1400°C or less. This is because when the hot metal temperature exceeds 1400℃, the iron oxide in the dephosphorization slag is reduced by [C] in the hot metal (T.Fe in the slag needs to be 2% or more), worsening dephosphorization. be. However, the [Si] concentration in the raw hot metal before performing the hot metal dephosphorization treatment according to the present invention may be about that of ordinary blast furnace pig iron (0.2 to 0.6% by weight), but from the viewpoint of the dephosphorization rate, [Si] ]<0.3% by weight is desirable. For this purpose, it is also important to remove Si in advance in a blast furnace casthouse or torpedo. Next, the present invention will be specifically explained with reference to Examples. <Example> Example 1 11 tons of trimmer scraps were charged into an upper and lower double blowing combined blowing converter used as a deP furnace, and then the hot metal shown in the upper row of Table 1 was subjected to deS and deSi treatment in a torpedo.
160 tons of iron was poured. Next, the converter slag generated in the same type of carbon removal furnace is cooled and solidified and crushed into particles with a particle size of 30 mm or less: 25
Kg/t, iron ore of similar particle size: 5 Kg/t and fluorite: 8 Kg/t, and coke grains were added to 11 kg/t.
Kg/t added, distance between top blowing lance and melt surface: 3m
Then, oxygen gas was blown upward for 4 minutes at an oxygen flow rate of 3 Nm ³ /min·t to dissolve heated scrap (trimmer debris). The middle row of Table 1 shows the composition of hot metal after scrap melting.

[Table] After the scrap has melted down, the distance between the lance and the hot water surface is set to 2m, and the amount of oxygen supplied is set to 0.5N.
m ³ /min·t, 5 kg/t of iron ore was added, and blowing (deP treatment) was carried out for 10 minutes. As a result, hot metal having the composition shown in the lower row of Table 1 was obtained with an increase in scrap ratio of 5% compared to the conventional method (comparative method) described later. From this table 1,
Hot metal dephosphorization with less [S] build-up under good dephosphorization rate
You can confirm that the process has been completed. Considering also the scrap melting ability in the decarbonization furnace after this treatment, the scrap melting ability (hot metal temperature) of the hot metal obtained by applying this treatment method is the same as that without dephosphorization. I can see that there is no difference between this and that. The refining conditions of the deP furnace used were as follows. Top-blown _O2 lance nozzle: 3-hole Laval, stirring gas blown into the bottom of the furnace: CO ₂ gas, stirring gas amount: 0.2Nm ³ /min・t. Example 2 Converter slag as a dephosphorizing agent during the scrap dissolution stage: 15
Scrap melting was carried out under the same conditions as in Example 1 except that 4 kg/t of fluorite and 4 kg/t of fluorite were added (of course, 11 kg/t of coke grains were added as a carbon material), and then 2m between lance and hot water surface
At the same time, the amount of oxygen fed was reduced to 0.5Nm ³ /min・t, and converter slag: 10Kg/t, quicklime: 5Kg/t.
t, Mn ore: 5Kg/t and fluorite: 4Kg/t
was added and blowing was carried out for 8 minutes (deP treatment), then 5 kg/t of Mn ore was added and extended blowing (deP treatment) was carried out for 2 minutes to complete the hot metal deP treatment. . As a result, as in Example 1, sufficiently satisfactory scrap melting could be carried out, and hot metal having the composition shown in Table 2 could be obtained.

[Table] As is clear from the results shown in Table 2 above, this treatment enables hot metal dephosphorization accompanied by scrap dissolution with a good dephosphorization rate, and also effectively increases the hot metal [Mn] concentration. I know that I was able to do it. Comparative Example 1 A top and bottom double blowing combined blowing converter under the same conditions as in Example 1 was used, and trimmer scrap was charged therein.
160 tons of hot metal having the composition shown in the upper row of Table 3, which had been subjected to S and Si removal treatment in a torpedo, was poured, and the same converter slag as in Example 1: 25 kg/t, iron ore: 10 kg/t.
t and fluorite: 8 kg/t, distance between top blowing lance and hot water surface: 2 m, oxygen supply amount: 0.5 Nm ³ /min・
At t, dephosphorization blowing was continued for 10 minutes to obtain hot metal having the composition shown in the lower row of Table 3.

[Table] In this case, only 3 tons of scrap trimmer waste could be charged due to the heat source. From Table 3 above, it is clear that hot metal is dephosphorized with a good dephosphorization rate.
Although it can be confirmed that the treatment was successful, this treatment was only able to dissolve scraps at a scrap ratio of 2%. Comparative Example 2 Hot metal dephosphorization was carried out under the same conditions as in Example 1 except that all of the dephosphorizing agent was added during the scrap melting period, and the results shown in Table 4 were obtained.

[Table] As is clear from the results in Table 4 above, if a dephosphorizing agent is added only during the scrap dissolution period and no new dephosphorizing agent is added during the subsequent dephosphorizing period, a sufficient ratio It can be seen that although scrap dissolution is possible, the dephosphorization rate deteriorates. <Summary of Effects> As explained above, according to the present invention, it is possible to perform scrap melting without requiring complicated operations at a large scrap usage ratio, and without having to suffer from adverse effects on the P removal rate or other adverse effects. Therefore, it is possible to provide a hot metal dephosphorization treatment method that is not available in the past, and extremely useful effects can be brought about industrially.

[Brief explanation of drawings]

FIG. 1 illustrates an example of the method of the present invention, with the addition amounts of the dephosphorizing agent and carbonaceous material and the amount of top-blown oxygen added. FIG. 2 shows another example of the method of the present invention.

Claims (1)

[Claims] 1. When dephosphorizing the hot metal by adding a dephosphorizing agent to the hot metal poured into a converter-type furnace having both top and bottom blowing functions and blowing oxygen gas upward while stirring the bottom blowing gas, first the dephosphorization is performed. A hot metal dephosphorization method involving scrap melting, characterized in that a part of the phosphorifying agent, scrap and carbon material are added to the hot metal, oxygen is top blown to melt the scrap, and then the remaining dephosphorizing agent is added. .