JPH0472007A - Production of molten steel - Google Patents

Abstract

PURPOSE:To attain energy saving as well as remarkable reduction in fixed costs and equipment costs by successively repeating a stage of charging molten pig iron into a converter, a stage of flux addition to exert dephosphorization and desulfurizing refining, a stage of slag removal, a stage of decarburization, and a stage of tapping, leaving slag. CONSTITUTION:At the time of producing a molten steel by refining blast furnace molten pig iron, first the molten pig iron is charged into a converter as a first stage, and then, as a second stage, the addition of flux by means of any of throwing, spraying, and blowing or a combination of more than two among the above and the top blowing of oxygen are carried out to perform dephosphorization and desulfurizing refining and reduce P content and S content to the prescribed values, respectively. Subsequently, as a third stage, the converter is tilted and the formed slag is slagged off, and, as a fourth stage, decarburization is exerted until the prescribed C content is reached by means of flux addition and O2 blowing. Finally, tapping is performed while leaving the slag formed in the fourth stage as a fifth stage. Then, the first stage is restored again, and the above-mentioned five stages are repeatedly carried out.

Description

[Detailed Description of the Invention] [Industrial Field of Application] The present invention uses blast furnace hot metal to efficiently remove P in a converter.
, relates to a method for de-S and decarburization refining.

[Prior Art] Conventionally, the common method was to charge blast furnace hot metal into a converter, add a flux mainly composed of quicklime, and melt steel by 02 blowing. After that, in order to increase the reaction efficiency of deP and S removal, the hot metal before charging into the converter is subjected to deS, deSi, and deP treatment (hereinafter referred to as hot metal pretreatment). A method of conducting a reaction has become commonly used.

In addition, in response to the increasing demand for ultra-low carbon steel in recent years, converter
It has become common to decarburize to 00 ppm to 200 ppm [C], and after tapping the steel, decarburize in the [C] region of 50 ppm or less in a secondary refining furnace such as RH or DH.

The present invention consolidates these multi-step refining functions into a converter, greatly reducing the energy loss of hot metal, and
This method makes it possible to significantly reduce the fixed costs (equipment costs, labor costs) of the processes before and after the converter.

[Problems to be Solved by the Invention] According to the conventional multi-stage refining method described above, a large amount of equipment investment and operating personnel were required for each refining process, resulting in a large fixed cost burden.

In addition, since each process in the reaction vessel is sequentially passed through, the amount of materials (refractories, etc.) used in each process increases.Furthermore, it takes a long time from tapping the blast furnace to the final molten steel, which dissipates energy. The loss was also excessive, and the total refining cost was also large.

In order to solve these problems, the present invention aims to incorporate the refining functions of (1) or (2) and (3) into the converter process among the current refining processes, namely (1) hot metal pretreatment process, (2) converter process, and (0) secondary refining process. It is a technology of aggregation.

[Means for Solving the Problems] The present invention has solved the above-mentioned problems, and the gist thereof is 1. When refining hot metal in a blast furnace to produce molten steel, as a first step, the hot metal is transferred to a converter. As the second step, charging,
Flux is added by one method or a combination of two or more methods, such as spraying or blowing, and oxygen top blowing is performed to remove P and S, thereby achieving a predetermined P content and S content. In the third step, the converter is turned over to remove the slag produced in the second step, and in the fourth
The process involves flux addition and 02 blowing to achieve a specified C.
decarburization to the content, and as a fifth step, tap the steel while leaving the slag produced in the fourth step in the converter, return to the first step again, and repeat the fifth step. Characteristic molten steel manufacturing method.

2. The method for manufacturing molten steel according to item 1 above, wherein in the third step, inert gas is blown into the furnace through a plurality of tuyeres provided in the furnace belly to form and discharge the slag.

3. The method for producing molten steel according to item 2 above, characterized in that each of the plurality of tuyeres is a spiral tuyere to make the bubbles finer.

4. In the fourth step, stop oxygen blowing in the range of 0.03 to 0.20% [C], and add 0 to 3% of 02 from the bottom blowing tuyere.
The method for producing molten steel according to item 1 above, characterized in that ultra-low carbon steel is produced by blowing Ar gas containing 0% to decarburize to 50 ppm [C] or less.

A specific method of the present invention that combines the hot metal pretreatment process and the decarburization process will be described below with reference to FIG.

Equipped with one or more bottom blowing tuyeres for injecting flux for removing P and S into the furnace bottom, and multiple tuyeres for injecting gas for slag forming into the furnace belly facing the tapping hole. Hot metal is charged into a top-bottom blowing converter, and a flux based on quicklime powder is blown into the bottom-blowing tuyeres using N2 as a carrier gas. At this time, the dephosphorization reaction rate can be increased by mixing iron oxide powder with quicklime powder, or by making the tuyeres have a triple tube structure and blowing O2 gas through the same tuyeres. On the other hand, by blowing 02 gas from the top blowing lance, adding flux from above, blowing, spraying, etc., and controlling the [FeO%] of the generated slag to 3 to 8%, P removal is possible. promote.

When the p and S contents have decreased to a predetermined level, the furnace is moved to the opposite side (
Tilt to the slag discharge side) to allow only the slag to flow and be discharged. At this time,
For example, as shown in Figure 3, inert gas such as N2 gas or A gas is injected through multiple tuyeres installed in the furnace belly on the slag side to promote slag forming, resulting in more efficient exhaust. You can make the slag work.

At that time, as shown in Figure 4, inside this furnace injection tuyere,
By constructing a spiral conductor belt to make the discharge gas flow spiral, the discharge gas receives the lateral shear force from the molten iron and becomes more finely dispersed than the bubbles that occur when blowing through a straight tuyere. That's good. These microbubbles reduce ripples on the top surface of the hot metal and contribute to the uniform formation of the slag layer, so the loss of hot metal flowing out is minimized and effective slag removal can be carried out in a short time. It becomes like this.

Next, as soon as the sludge has been removed, the furnace is erected, and a small amount of auxiliary materials (quicklime for protecting large objects and preventing back-up, dolomite,
(iron ore, etc.) and performs normal top-bottom blowing decarburization refining. After blowing up, the molten steel is tapped, but the slag remains in the furnace and is used as pre-treated hot metal for the next charge.

Furthermore, since this slag is generated for relatively high temperature, low P molten steel during decarburization refining, it has sufficient refining ability even if it is reused for low temperature, high P molten metal. .

In this way, after charging the next charge of hot metal, the same steps of hot metal pretreatment, slag removal, and coal brining as described above are repeated.
Refining, which was conventionally done in two steps, can be consolidated into one converter step.

Furthermore, with the increase in demand for automobile outer panels in recent years, the production of ultra-low carbon steel (≦soppm [C]) has increased, and in response to this, ultra-low carbon steel (300 to 10 ppm [C] ) is being decarburized.

As shown in Figure 2, by sharing most of the load with the converter, it becomes possible to omit the vacuum treatment step, use light treatment, or use the easy decarburization method using the furnace outer tube. , it is possible to significantly reduce equipment and operating costs required for vacuum processing.

In order to perform this ultra-low composition decarburization in a converter, the top and bottom blowing decarburization must be completed at 2000 to 300 ppm [C], the bottom blowing gas should be immediately switched to Ar-02 gas, and the decarburization should be carried out by bottom blowing rinsing. Continue charcoal. At this time, the -02 gas is preferably a mixed gas of 0 to 30% 02, and it is more effective to lower the mixing ratio as the [C] decreases.

Moreover, decarburization can be further promoted by spraying Ar using a top-blown oxygen lance during this rinsing.

When producing ultra-low carbon steel, the steel is tapped after the above refining is completed, and hot metal is charged again with the slag left in the furnace, and the hot metal is pretreated.
Exhaust, decarburize, and refine the next charge.

[Function] The technical points of each step in the present invention are listed below.

Regarding the hot metal entertainer process and the hot metal pretreatment process, the following two points are important.

That is, firstly, by reusing the decarburized slag from the previous charge that has the ability to dephosphorize and silken, it is possible to: 1) promote slag formation, 2) reduce the flux consumption rate, and 2) effectively recover the sensible heat of the slag. This means that two effects can be obtained.

Secondly, by injecting (blowing) flux using the bottom blowing tuyere, we can simultaneously remove P and
All you need to do is remove S. If hot metal removal S is performed in advance, flux injection is not particularly necessary, and P can be removed by upward injection of flux and 02 top blowing.

Next, the key point in the slag removal process is to blow inert gas through multiple tuyeres installed in the furnace belly to disperse air bubbles finely, without causing large fluctuations to the surface of the iron bath. The key point is that it is possible to form the slag and perform smooth fluid drainage while minimizing iron loss.

In the decarburization process, high-speed decarburization is performed by adding enough flux to protect the refractories.

In addition, in the decarburization process with low carbon dioxide, there are two points below.

That is, firstly, by generating Ar bubbles in the air, a chemical vacuum state is created to promote the [C] + [ol-co reaction at the gas/liquid sea surface. In this case, 02 is mixed into the reactor as an 02 supply source, but if an excess of [0] is produced, an excess of [0] will be present at the reaction site and CO production will be inhibited.

Therefore, bottom blowing is performed with the mixing ratio of 02 being 0 to 30%.

Second, in order to promote the diffusion of the generated CO into the gas phase, Ar can be blown from the top blowing lance to accelerate the decarburization reaction rate.

The final steel tapping process uses the same tapping method as in conventional converter operation, and is unique in that the slag is not disposed of for reuse.

[Example 1] First, as shown in FIG. 1, Examples 1 and 2 are cases in which a type of refining that combines a hot metal pretreatment process and a decarburization process is performed.

Among these, Example 1 is a case where a 320 ton converter was used, 417 tons of scrap was charged before the hot metal making process, and flux addition in the hot metal pretreatment process was performed both by top charging and bottom blowing. The operating conditions and results are shown in Table 1. At this time, CaF2 was added by bottom blowing, and the total processing time was 37 minutes.

In addition, in Example 2, light S removal treatment was carried out in advance using a torpedo car, 307 tons of scrap was introduced in front of the hot metal maker using a 300 ton converter, and flux was only added upward in the hot metal pretreatment process. This is an example of the simplified method performed in . The operating conditions and results are shown in Table 2. The total processing time in this case was 39 minutes.

Next, as shown in Figure 2, the hot metal pretreatment process, the decarburization process,
Example 3 is a case in which a type of refining is performed in which the three steps of the decarburization step and the extremely low-density zone decarburization step are integrated.

Here, a 320 ton converter is used, only hot metal from the blast furnace is used without using scrap, and flux is added in both top injection and bottom blowing in the hot metal pretreatment process.Operating conditions and The results are shown in Table 3. The total processing time in this case is 41 minutes, and [C] during tapping is 0.0031%, or 31 ppm.
It became.

The processing time for one cycle is 37~ for each of the three cases above.
The total time was 41 minutes, which was within the required cycle time for continuous casting in the continuous casting process, so there was no influence on subsequent processes. Moreover, there were no problems in terms of ingredients, and the present invention was found to be effective.

[Effects of the Invention] There are the following three advantages when the hot metal pretreatment process is consolidated as in Example 1.2.

First of all, it is possible to reduce the amount of materials used for hot metal pretreatment, that is, the basic unit. For example, compared to the conventional method, the basic unit of refractories is reduced by 0.4 kg/T, and the basic unit of CaO is reduced by 4 kg/T.

Second, fixed costs for hot metal pretreatment, that is, equipment costs and personnel costs, can be significantly reduced. Regarding personnel costs, for example, it is expected that there will be a reduction of 12 people compared to the past.

Thirdly, thermal energy loss due to dissipation can be reduced, approximately 16,000 per m t141 Ton.
There is no need to dissipate kcal energy. Along with this, the production melting rate will increase, making it possible to increase the scrap blending ratio by approximately 5%, or reduce the amount of iron ore input to molten steel IT.
It becomes possible to increase the weight by about 20 kg per turn, and it is possible to improve the yield by about 15%.

Next, as in Example 3, the advantages of integrating the secondary refining process in addition to the hot metal pretreatment process and decarburization process are as follows:
In addition to the advantages of aggregation in the case of Example 1.2 above, the following two advantages are added.

First, variable costs for secondary refining such as R)l treatment, such as steam, refractories, and various materials, can be reduced.

In addition, thermal energy loss due to dissipation is further reduced,
Energy saving of approximately 70 (10 kcaM) is expected for I Ton of molten steel.This will further increase the yield by approximately 0.7
%.

As described above, by implementing the present invention, significant reductions in fixed and variable costs and significant energy savings can be achieved.

[Brief explanation of the drawing]

Figure 1 is a process conceptual diagram showing a refining method in which the hot metal pretreatment process and the decarburization process are integrated into a converter, and deP, S, and decarburization are performed in the same converter; Figure 2 is the hot metal pretreatment process; decarburization process,
The ultra-low carbonation decarburization process in RH and RH is integrated into a converter, and
, a process conceptual diagram showing a refining method that performs S decarburization, decarburization, and ultra-low carbon decarburization all in the same converter. Figure 3 shows the slag forming installed in the furnace belly used when slag from hot metal prediction treatment is discharged. FIG. 4 is a diagram illustrating an example of the arrangement of control tuyeres, and FIG. 4 is a diagram illustrating the shape of a spiral tuyere installed in the belly tuyere to generate fine bubbles. Other 4 people Molten iron charging Molten iron pretreatment 0° Decarburized slag (or Todo Decarburized steel in low-coal area

Claims (1)

[Claims] 1. When refining hot metal in a blast furnace to produce molten steel, the first step is to charge the hot metal into a converter, and the second step is any one of charging, blowing, and blowing. Flux addition by one method or a combination of two or more methods and oxygen top blowing are performed to perform deP and deS refining to reduce the P content and S content to predetermined values, and as a third step, The converter is turned over, the slag generated in the second step is slaged out, the fourth step is decarburization to a predetermined C content by adding flux and O_2 blowing, and the fifth step is the fourth step. A method for manufacturing molten steel, characterized in that the slag produced in step 1 is tapped while remaining in the converter, the process returns to the first step, and the fifth step is repeated. 2. Claim 1, characterized in that in the third step, inert gas is blown into the furnace through a plurality of tuyeres provided in the furnace belly to form and discharge the slag.
The molten steel manufacturing method described. 3. The molten steel manufacturing method according to claim 2, wherein each of the plurality of tuyere is a spiral tuyere to make the bubbles fine. 4 In the fourth step, oxygen blowing is stopped in the range of 0.03 to 0.20% [C], and O_2 is introduced from the bottom blowing tuyere to 0 to 0.
2. The method for producing molten steel according to claim 1, wherein the molten steel is decarburized to 50 ppm [C] or less by spraying Ar gas containing 30% to produce ultra-low carbon steel.