JPS61139614A - Manufacture of steel - Google Patents

Abstract

PURPOSE:To reduce the number of stages and the size of equipment and to improve the yield and the efficiency of desulfurization by combining three stages including a stage for producing molten metal contg. a prescribed percentage of C and salg contg. a prescribed percentage of iron oxide in a converter type reactor enabling top and bottom blowing. CONSTITUTION:Ore contg. iron oxide and a carbonaceous material are used as starting materials. The ore may be half reduced beforehand. In the 1st stage, the starting materials are charged into a converter type reactor (melt reducing furnace) 22 enabling to and bottom blowing of oxygen to produce molten metal 27 contg. >=3.1%C and slag 28 contg. <=2% iron oxide. In the 2nd stage, part of the produced slag 28 is discharged from the reactor 22. In the 3rd stage, the molten metal 27 is decarburized to reduce the C content to <1.8%.

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a method for mass-producing molten steel using iron ore as a raw material, which can replace the conventional blast furnace-converter method. (Prior Art) The blast furnace-converter process, which is the main body of the conventional mass-produced steel manufacturing method, is shown in FIG. 1a. In recent years, various improvements have been made to this method, making it an excellent method for mass-producing molten steel with high purity. However, the problem is that it requires a large amount of equipment and requires a large amount of capital investment. Here are some things you need to know. One way to improve this is shown in Figure 1.
This is a conventionally proposed iron smelting reduction method. (For example, S. Eketorp and O. Wljk
: Injection metallurgy, at
the royal in+5 posture of t
technology. 5tockholrn, International
Conf, on InjectionMetall
urgy, Lu1ea, June 9-10 (1
977) + Patent Application No. 59-184056) In other words, the aim is to omit the sintering and coking steps by directly charging ore and coal into a top-bottom blowing converter type smelting reduction furnace and performing reduction. be. However, in general, the current blast furnace
It has the following disadvantages compared to the converter method. (1) The (T, Fe) of the slag discharged outside the system is high;
・The iron yield is lower than that of the blast furnace method. (iD) Due to the high (T, Fe) of the slag, the desulfurization ability of the slag is small, and the [,S] level of the molten metal becomes high. On the other hand, if the molten metal [C]% is high (e.g. [C) > 3%), the process after tapping will be
There is little that can be omitted, only adding to the burden of desulfurization. Therefore, from the point of view of molten steel production cost, Figure 1-b
It can be said that the improvement effect of this method is small compared to the conventional method. (Problems to be Solved by the Invention) The present invention reduces the number of steps and required equipment for the current blast furnace-converter method, and also rationally solves the problems of iron retention, desulfurization, and dephosphorization, and achieves mass production. The objective is to provide a steel manufacturing method that enables the production of molten steel at low cost. (Means for solving the problems) The object of the present invention is achieved as follows. That is,
In order to obtain molten steel by performing oxidation and reduction reactions using a compound or its semi-reduced product and carbonaceous materials as raw materials in a rolling reaction vessel in which oxygen can be blown from the top and bottom, as shown in Figure 1-C, In the first step, molten metal with [C]≧3.1 and slag with an iron oxide content of 2 or less are made, and in the second step, a part of the generated slag is discharged outside the system, thereby reducing the iron content. To reduce the amount of water and at the same time efficiently perform desulfurization. Then, by blowing acid, [C] was lowered to below 1.8,
It promotes dephosphorization of molten metal and reduces the burden of decarburization in subsequent processes. In other words, the first step is to reduce the iron content and desulfurize the slag by strong reduction smelting in the coexistence of sufficient free carbon material in a top-bottom blowing converter type smelting reduction furnace.
In the second step, most of the slag containing sulfur is removed from the slag.
) After the molten steel is transferred to a ladle, secondary dephosphorization, desulfurization, and Decarburization, vacuum treatment,
By performing reduction refining, the number of steps is significantly reduced compared to the conventional blast furnace-converter method, and the method does not reduce impurity removal ability. (Function) An example of equipment used to carry out the present invention is shown in FIG. 2. In FIG. 2, 22 is a melting reduction furnace, which is a top-bottom blowing converter type reaction vessel. The melting reduction furnace 22 has a bottom blowing tuyere 2
3 and a top blow lance 24, which can blow oxygen or oxygen-containing gas from the top and bottom. 25 is a hood, and 26 is a hopper, which supplies carbon material and flux into the melting reduction furnace υ. 27
is a molten metal, and 28 is a slag. 30 is a carbon material, for example coke. Reference numeral 31 denotes a bubble, and 32 a raw material charging device, by which a raw material such as iron ore is charged into the smelting reduction furnace 22. The smelting reduction furnace 22 is used for raw materials containing iron oxide such as iron ore or its pre-reduced product, carbonaceous materials such as coal and coke,
Fluxes such as lime are supplied, melted, and the remaining iron oxides undergo a reduction reaction, followed by decarburization to finally obtain Fe-C molten steel. It is a device. The reason why the slag is turned into a smoky form is that it is convenient for achieving strong stirring of the slag, which is essential for the progress of the reaction. Tuyere 23 for blowing gas containing oxygen from the bottom
(There may be a plurality of these) A top blow lance 24 is attached for blowing oxygen into the furnace from above. The function of the bottom blowing tuyere is to adjust the temperature of the metal by blowing oxygen-containing gas into the metal, and as a result, achieve strong stirring of the slag through stirring of the metal. The purpose of decarburization is to adjust the carbon content of the product. If it is only stirring, use Ar throughout the entire period.
However, in this case, in view of the gas cost required for stirring and the loss of sensible heat carried out of the system, it is recommended to at least use oxygen to avoid having a negative effect on the reduction reaction. It is advantageous to use a gas containing In order to blow oxygen-containing gas into the metal, for example, a double pipe siding is used, and a small amount of hydrocarbon or cooling gas such as Ar + N2 is blown from the outer pipe to protect the tuyere from melting. In addition, during the time when oxygen injection has a negative effect, the oxygen gas is
Switch to an inert gas such as r*N2. Oxygen supply from the top blowing lance is the main means of controlling exothermic conditions and decarburization reactions in the smelting reduction furnace. The nozzle shape is determined by the amount of oxygen to be supplied, the size of the furnace, exhaust gas conditions, etc. The trench is designed so that the distance between the lance tip and the slag surface can be adjusted according to operating conditions. The best refractory for the smelting reduction furnace is magnesia carbon brick for the lower half of the furnace (the part that is mostly used for slag and metal). The upper half of the furnace (co-co2
Similarly, magnesia carbon bricks or Hachrome Madanesia bricks are suitable for the parts of the system exposed to high-temperature gas atmospheres. The operating method using the above equipment is as follows. When starting up a smelting reduction furnace, F obtained from other melting furnaces should be used.
Either e-C type molten metal is charged, or coke and mold pig iron or scrap are charged and acid is blown to melt the metal and make a seed metal. From the second heat onward, the operation continues in such a way that, for example, 1/3 of the metal produced in the previous heat is left as seed water. In the first step, while top blowing and bottom blowing are performed, raw materials containing iron oxide such as ore containing iron oxide or its pre-reduced product, coal or carbonaceous material such as coke, and lime are placed in the furnace. Add flux such as to melt them and perform a reduction reaction of the remaining iron oxide,
-C-based molten metal and slag with low FeO content and high desulfurization ability are produced. Powdered ore or its prereduced product is sprayed or blown into the melt layer as powder through a top blowing lance or through a bottom blowing lance. Alternatively, the powdered material can be processed using an appropriate method (-1
! It is made into lumps by briquetting, briquetting, or other simple compression methods, and then put into a furnace from above. The carbon material used is one that is inexpensively available, such as coal or coke. In the case of lumps, it may be charged from above the melting reduction furnace, but in the case of powder, it is blown into the molten layer through a top blowing lance or through a bottom blowing tuyere. Also, together with powder ore or separately,
It may be agglomerated and put into a melting reduction furnace. Flux is added to obtain a desired slag amount and slag composition as described below. Raw materials such as lime, dolomite, and silica stone, or slags generated in other processes can be used. The behavior of the C-group of the Fe--C-based molten metal produced during melt reduction depends on the balance between the carbon supply rate to the molten metal and the decarburization rate by blowing acid. [In order to maintain a high C″1%, increase the amount of carbonaceous material present in the slag, increase the amount of carbonaceous material blown into the molten metal, and reduce the amount of oxygen or iron oxide blown into the molten metal. This can be achieved by one or a combination of two or more of the following: When slag forms during melt reduction, heat transfer from the atmosphere to the melt is inhibited, resulting in poor thermal efficiency. In order to prevent slag forming, the C% of the molten metal should be 3.1 or more, particularly preferably 3.1.
It is necessary that the molten slag is maintained at 5 or more, and that free carbonaceous material coexists in the molten slag. Further, as for the slag component, it is desirable that CaO/S i 02 be 1.2 or more, particularly preferably 1.4 or more. FIG. 3 shows the relationship between the iron oxide content of the slag (calculated as FeO) and the desulfurization ability of the slag ((S), expressed as 4sl). It can be seen that in order to increase the desulfurization ability of the slag, it is desirable that the iron oxide content of the slag be 20 parts or less, particularly 12 parts or less. The iron oxide content of the slag is determined by the reduction rate determined by the combination of the t1ψ iron supply rate to the molten slag, the molten metal temperature, the carbon material supply rate, the molten metal [C″l ratio, the blowing acid rate, etc.], and the reduction rate of the metal. It is determined by the reoxidation rate, etc.The reoxidation rate of metal is determined by the amount of oxygen blown into the metal bath, the amount of metal [
C%] (see FIG. 4) and the amount of slag produced. When the amount of slag is 200 kg/l-metal or more, particularly preferably 250 kg/l-metal or more, the metal is stably covered by the slag phase even with strong bottom-blowing stirring, so that it does not come into direct contact with the atmosphere in the furnace. This can substantially prevent re-oxidation phenomena caused by In order to increase the desulfurization ability of slag, at least the iron oxide content in slag before slag is set to 2.0% or less as described above.
If possible, the kernel should be 1.2% or less, which means 200 kg/l.
- In the coexistence of slag containing more than metal, (a) raw materials containing iron oxide should not be introduced into the smelting reduction furnace within 5 minutes before slag removal, (b) bottom blowing should not be performed within 5 minutes before slag removal. Switch the gas from an oxidizing gas to a non-oxidizing gas (e.g. Ar, 'N2, etc.), but prevent re-oxidation of the metal bath by mixing and supplying a carbonaceous material that combines with oxygen gas to form CO. This can be achieved by one or a combination of two or more of the following: (c) coexisting carbonaceous material in an amount of 3% or more of the weight of the produced slag in the smelting reduction furnace, and maintaining an excessive carbonaceous state. Under the strong stirring conditions of top and bottom blowing as in the present invention, the temperature difference between the molten metal and the slag is within ±20°C, and there is almost no difference. The operating temperature is in the range from 1400 to 1600°C, particularly preferably from 1450 to 1550°C. A higher temperature is more desirable from the point of view of reduction reaction rate, but a lower temperature is more desirable from the point of view of thermal efficiency and refractory unit consumption. The compromise point for both is within the above temperature range. While keeping the [C] of the metal at 3.0% or more, the iron oxide content in the slag (calculated as FeO) can be reduced to 2.0 or less, achieving high iron yield and high efficiency desulfurization. , the furnace is tilted and a part of the slag is discharged as a second step. The purpose of slag discharge is to prevent metal re-oxidation and to achieve 1/2 of the large amount of slag needed for high iron yield and high efficiency desulfurization.
As described above, it is preferable to discharge 3/4 culm to create slag conditions favorable for decarburization and dephosphorization in the third step. It should be noted that the carbonaceous material remaining in the furnace FKJ during slag discharge floats to the surface of the slag. This carbonaceous material can be effectively used as a heat source in the next process, so by using a simple skinmer etc. during the slag discharge, only the slab of the three-layer structure of carbonaceous material - slag - metal is discharged, and the carbonaceous material is It is preferable to leave it in the furnace. A slag-forming agent such as lime and, if necessary, scrap, iron ore or a semi-reduced product thereof are added to the smelting reduction furnace after slag removal, and top-bottom acid blowing is performed. Adding sludge-forming agents such as lime is
To improve the dephosphorization ability of the slag at the end of the third step, to prevent slag foaming during the third step treatment, and to suppress the increase in (T, Fe) of the slag at the end of the third step to reduce iron yield. This is to prevent Ca O/S 10
2 is 2.5 or more, particularly preferably 3.0 to 4.5. On the other hand, the addition of scrap, iron ore, or its semi-reduced products is to adjust the temperature in response to the rise in metal temperature due to the combustion of residual carbonaceous materials and metal decarburization, and the choice is made depending on the raw material situation at the time. It is possible. The second step is performed until the [C] content of the metal becomes less than 1.8%. If [C] is less than 1.8 inches, it is difficult to improve the dephosphorizing ability of the slag, as shown in FIG. Although it is possible to tap the metal by lowering the [C] to the required composition of steel, it is possible to tap the metal once at a [C] of 1.8 to 0.09% and then adjust the ladle thickness as necessary. It is desirable to refine the molten steel to a predetermined composition through processing. The reason is as follows. (i) If [C] is low, the melting point and the range of heat increase due to subsequent decarburization are small, so the temperature at the time of tapping must be increased. As a result, a relationship as shown in FIG. 5 is established between molten steel [:C]% and slag dephosphorization ability. Therefore, from the viewpoint of promoting dephosphorization, it is desirable that CCI>o, 7es. (:i) Figure 6 shows the relationship between [01% at the time of steel tapping and the de-N ratio at the time of decarburization in the ladle after tapping. [C]>0.
It can be seen that when steel is tapped at 7%, sufficient denitrification can be achieved in the subsequent decarburization process, so there is no need to consider the N level in the smelting reduction furnace. That is, it is understood that it is also possible to use inexpensive N2 gas as the bottom blowing gas. In addition, de-N
The decarburization conditions for sufficient decarburization are C > 0.
Since the decarburization width at 2% is determined by Δ[C1%, if 0% of the finished molten steel is high, the [C]% of the molten steel tapped from the smelting reduction furnace needs to slide. In addition,[:
C]>0.2%, the molten steel

[0] Since the ratio is low, nitrogen absorption from the atmosphere is likely to occur. If sufficient denitrification occurs in the ladle decarburization after tapping, there is no need to consider this nitrification during tapping, but if the width of decarburization after tapping is not sufficient, the effect will be This makes it difficult to manufacture low-nitrogen steel. From this point of view, it is desirable that 0% at the time of tapping is 0.7% or more when the steel exceeds 0.2 inches. In addition, when steel is tapped under the above conditions, secondary dephosphorization and desulfurization treatment can be carried out by adding, for example, a Cab-Na2Co3-CaF2 flux, if necessary. In this invention, steel is tapped at a higher [C] than in normal converter operation, and ladle processing can also be performed at a lower temperature, so N
There is an advantage that high temperature treatment can increase the content of components such as a2CO3 or CaF2, which have a large vCrt refining effect, but which have a large effect on damage to refractories. After this ladle self-desorption P and S removal treatment, the slag is removed by, for example, a vacuum slag suction method, and the phosphorus in the slag is removed. Most of the sulfur is removed from the system, followed by decarburization. Finished molten steel can be obtained by performing vacuum treatment and component adjustment. C generated during melting, reduction and decarburization from the smelting reduction furnace
Exhaust gas containing o-co2 (preliminary reduction of waste ore. It can be used for scrap preheating, etc., and can also be supplied outside the system as fuel gas. Obtaining the necessary steel production! and gas production amount is achieved by blowing acid speed. , melting (the latter is determined by the charging conditions of the carbon material into the smelting-reduction furnace), and the degree of CO2 removal treatment of the exhaust gas. (Example) <1st step> As shown in Figure 2, acid blowing capacity 30.000 Nm”/
30 tons of hot metal was charged into a top-bottom blowing converter of 300 hr, and while top-bottom blowing acid was applied to it, 70% pre-reduced iron ore briquettes and coke were charged and melted and reduced. The immediately preceding metal composition, temperature, and slag composition are as follows. <Second Step> Approximately 3/4 of the generated slag is discharged. <3rd step> After adding 5.2 tons of lime and 15 tons of scrap, top blow 022700 ON? y+3/hr, bottom blowing 02200
0 Nm3/hr, Prot9n 50 Nm3/hr
Decarburization was performed for 10 minutes. The composition, temperature, and slag composition of the metal just before tapping are as follows. [wt%] [Wt Section] During tapping, Ca050%-Car220% in the ladle,
A slag of 30% FeO was added at a rate of 5 kg. The obtained dephosphorization rate was 70%, and the desulfurization rate was 30%. After removing the slag by vacuum suction method, C: 0.2 under atmospheric pressure
It was decarburized up to the point where it was removed, and then it was decarburized under reduced pressure. The components and temperature of the obtained molten steel are as follows. (Effects of the Invention) As described above, this invention has the advantage of improving the conventional iron smelting reduction method (IQ
), it can replace the conventional blast furnace-converter process as a method of obtaining molten steel from ore. Although the case where only iron ore is used as the ore has been described, alloys can be created by blending predetermined amounts of iron-manganese ore, chromium-iron ore, etc. It is also possible to produce molten steel.

[Brief explanation of the drawing]

Figure 1 is a diagram conceptually showing the process (c) of the present invention in comparison with (a) the conventional blast furnace-converter process and (b) the conventional smelting reduction process, and Figure 2 shows the process of implementing the present invention. Fig. 3 is a diagram showing the relationship between the iron oxide content of slag and the sulfur distribution ratio (s)/[S] between slag and metal, and Fig. 4 is an explanatory diagram showing an example of equipment used for Figure 5 shows the relationship between [C%] of slag and the iron oxide content of slag.
Figure 6 shows the relationship between [C'3%] at the time of tapping and the de-N rate during decarburization in the ladle after tapping. It is a diagram.

Claims (1)

[Scope of Claims] A converter-like reaction vessel capable of blowing oxygen from the top to the bottom, in which oxidation,
When performing a reduction reaction to obtain molten steel, [C]≧3.
1% molten metal and iron oxide content: 1st step to make slag with less than 2.0%, 2nd step to discharge part of the slag out of the system, and decarburize the molten metal to [C]<1 .8% steel manufacturing method.