JPH10152714A - Method for refining molten iron - Google Patents

Abstract

PROBLEM TO BE SOLVED: To drastically reduce the consumption of flux and the producing quantity of slag by discharging the slag after treating desiliconization by adjusting the supplying quantity of material containing CaO to a specific quantity, and executing dephosphorizing treatment. SOLUTION: Molten iron 2 is received into a refining furnace 1. The refining furnace 1 is erected, and the desiliconizing treatment is executed by injecting the flux from a tuyere 4 and blowing oxygen from a top-blown lance 7. The furnace is tilted and the slag 8 with the desiliconization is discharged from the furnace hole. The furnace is erected and the dephosphorizing treatment is executed by injecting the flux and blowing the gaseous oxygen. The molten iron 2 treated to the desiliconization and the dephosphorization is discharged into a molten iron ladle 10 from a molten iron tapping hole 9. Then, the desiliconizing treatment is executed by adjusting the supplying quantity of the material containing CaO so that the wt. ratio of (Cab)/(SiO2 ) in the slag at the time of completing the dissiliconizing treatment comes in the range of 0.3-1.3. By this method, the desiliconizing treatment and thereafter, intermediate slag-off can smoothly be executed in a converter type refining furnace.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for preliminarily refining molten metal, and more particularly to a method for efficiently refining molten metal that has not been subjected to Si removal in advance.

[0002]

2. Description of the Related Art In recent years, the development of various hot metal pretreatment methods has been advanced, and Si, P, S, etc. in hot metal charged into a converter has been reduced to a predetermined level. Is being completed.

[0003] Among the hot metal pretreatments, the de-P treatment involves the basicity of slag (CaO) / (SiO ₂ ) from the viewpoint of de-P equilibrium.
Is required to be a predetermined value, for example, 2 to 3 or more. When the Si concentration in the hot metal is high, the amount of the CaO-containing substance used and the amount of generated slag increase, which is not economical.

[0004] As a method for solving such a problem, hot metal separated from de-Si slag by performing a de-Si treatment in a cast floor gutter of a blast furnace is received in a hot-metal transport container such as a torpedo car, a hot metal ladle or the like, and is sent to a predetermined station. A method of transporting and removing P, or removing hot metal in a hot metal transfer vessel at a predetermined station
After the treatment, a method of tilting the transfer container to discharge the Si-removed slag and thereafter performing the P-removing treatment has been put to practical use.

[0005] However, in the method (1), the cast floor gutter is considerably worn, and the maintenance thereof requires considerable cost and labor. In the method (2), there is a problem that the refractory of the vessel is worn and the heat loss is increased due to prolonged processing time. Become. In addition, both of Si and C in the hot metal
There is a problem that it is difficult to effectively use the combustion heat of the steel for melting the scrap.

On the other hand, a dedicated preliminary refining furnace is provided, and flux is injected from the bottom of the furnace or deep into the bath, and oxygen gas is blown from the upper part of the furnace to hot metal to remove sulfur.
i. A method of performing the P removal treatment is disclosed in, for example, JP-A-62-109911 and JP-B-6-60339.

According to this method, the supply rates of flux and oxygen gas are increased to shorten the time of de-Si and de-P treatments, and the scrap is added to a refining furnace so that the heat of combustion of Si and C is used for melting the scrap. There is an advantage that it can be used effectively.

[0008] On the other hand, however, since a large amount of blown gas and high-speed top-blown oxygen jet cause the splash of hot metal and slag to increase, a refining furnace in the form of a converter with a large hollow tower inevitably is used. There is no choice but to make tilting waste of the furnace difficult, and in general, intermediate waste after Si removal treatment is not performed.

Therefore, when the Si concentration in the hot metal is high, there is a problem that the amount of flux and slag required for the de-P treatment increases, which is not economical. Is also not disclosed.

[0010]

SUMMARY OF THE INVENTION The present invention relates to a method for removing molten Si which has not been subjected to Si removal at a high speed in a so-called converter type refining furnace at a high speed. It is intended to reduce the amount of CaO flux used in the de-P treatment.

In particular, regarding the intermediate waste after the de-Si treatment in a converter type refining furnace, the amount of the de-Si slag is small, and it is difficult to use a slag remover, etc. In order to secure the rate,
The fluidity of the slag becomes a problem.

[0012] When the furnace is tilted for waste, the gas blown from the furnace bottom blows up hot metal droplets and oscillates in the bath, resulting in a decrease in the yield of hot metal.

In general, de-Si slag is easy to form, and there is a problem that the formed slag adheres to the upper wall of the furnace and is difficult to remove. Therefore, it is important to prevent the forming during the de-Si processing. Become.

In order to solve the above-mentioned problems, the present invention is suitable for the composition of the de-Si slag, the Si concentration at the end of the de-Si treatment, and the arrangement of the tuyere for blowing powder or gas from the bottom of the furnace. The purpose is to present appropriate conditions.

[0015]

The gist of the present invention for solving the above-mentioned problems is as follows: (1) Means for injecting powder and / or gas into the hot metal from the bottom of the furnace and hot metal from the upper part of the furnace. Removal of hot metal using a refining furnace having means for blowing oxygen gas
i. When performing the de-P treatment, first, the supply amount of the CaO-containing substance is adjusted such that the (CaO) / (SiO ₂ ) weight ratio of the slag at the end of the de-Si treatment is in the range of 0.3 to 1.3. This is a method for refining molten iron, which comprises performing a de-Si treatment and then tilting the furnace to discharge slag generated in the furnace from a furnace port, and then performing a de-P treatment.

(2) In addition, all the tuyeres for blowing powder and / or gas at the bottom of the furnace are located above the molten hot metal surface in the tilted refining furnace at the end of the waste after the Si removal treatment. The refining method for molten iron according to the above (1), wherein a refining furnace arranged to perform the refining is used.

(3) The method for refining hot metal according to the above (1) or (2), wherein the Si concentration in the hot metal at the end of the Si removal treatment is 0.05% by weight or more. is there.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is an explanatory view showing an example of a refining furnace used in the present invention and working steps of a refining method of the present invention. Hot metal 2 and scrap 3 as required are charged into a converter type refining furnace 1, and powder and / or gas is blown into the hot metal from a tuyere 4 provided at the furnace bottom.

In the example of FIG. 1, the powder in the blow tank 5
(For example, a CaO-containing substance or iron oxide) is blown by N ₂ gas. Oxygen gas is blown onto the hot metal from an upper blowing lance 7 inserted from the upper part of the furnace, and a CaO-containing substance and iron oxide are supplied from a hopper 6 on the furnace as required.

As shown in FIG. 1, the working process of the hot metal refining method of the present invention is generally a process of receiving hot metal 2 in a refining furnace 1, the furnace is erected, and flux is introduced from a tuyere 4 at the bottom of the furnace. Injection and de-Si treatment by blowing oxygen from the top blowing lance 7, Intermediate waste disposal step of tilting the furnace to discharge the de-Si slag 8 from the furnace port, Flux injection and oxygen gas And a tapping step of discharging the hot metal 2 subjected to the Si removal and the P removal from the tap hole 9 to the hot metal pot 10 by spraying the molten iron.

The hot metal refined by the method of the present invention is substantially not subjected to Si removal treatment and usually contains about 0.3% or more of Si. Si is removed to, for example, about 0.05 to 0.10% by the de-Si treatment, but the (CaO) / (SiO ₂ ) weight ratio of the slag at the end of the de-Si treatment is 0.3.
The supply amount of the CaO-containing substance is adjusted so as to fall within the range of ~ 1.3.

(CaO) / (SiO ₂ ) at the end of the de-Si treatment
Is limited to the range of 0.3 to 1.3 in order to secure the fluidity of the Si-removed slag 8 when the furnace is tilted and the intermediate waste is discharged. De-Si slag is CaO, SiO ₂ , Fe
_x O, MnO, etc. as a main component, usually 15-30% Fe _x
Contains O and 10-15% MnO.

The inventors of the present invention have found that in such a slag system, if (CaO) / (SiO ₂ ) is in the range of 0.3 to 1.3, the slag is sufficient even at a hot metal temperature of, for example, about 1300 ° C. It shows fluidity, but when (CaO) / (SiO ₂ ) is out of this range, it has been found that fluidity is significantly reduced.

Actually, as shown in a later example, the rate of waste from the furnace port due to the tilting of the furnace depends on (CaO) / (SiO ₂ ). In addition, the rate of waste is significantly reduced. Therefore, in the present invention, the (CaO / SiO ₂ ) weight ratio at the end of the Si removal treatment is 0.3 to 1.3.
It is necessary to adjust the supply amount of the CaO-containing substance in the Si removal treatment step so as to fall within the range.

At the time of intermediate waste for discharging the de-Si slag,
It is necessary to blow gas from the tuyere 4 at the furnace bottom to prevent the melt from being inserted into the tuyere. However, when the furnace is tilted, the immersion depth of the tuyere becomes shallower, and as a result, blasting of hot metal droplets and swinging of the hot metal bath surface due to the kinetic energy of the blown gas become severe. When the tuyere was below the surface of the hot metal at the end of the intermediate waste, it was found that the hot metal was mixed and discharged into the de-Si slag and the yield of the hot metal was significantly reduced.

In the present invention, in order to prevent such a decrease in the yield of hot metal, all the tuyeres for blowing powder and / or gas at the bottom of the furnace are tilted at the end of the intermediate waste, and the refining furnace is tilted. It is desirable to use a refining furnace arranged so as to be located above the surface of the molten metal in the inside.

FIG. 2 is an explanatory view showing an example of the arrangement of the tuyere at the furnace bottom in the present invention. FIG. 2 (a) shows two tuyeres 4
Are arranged at the center of the furnace bottom in parallel with the axis of the trunnion 11, and FIG. 2B shows two of the four tuyeres.
a is arranged at the center of the furnace bottom in parallel with the axis of the trunnion 11, and the other two tuyeres 4b are arranged so as to be offset from the central axis of the trunnion toward the tap hole 9 side (opposite the waste side). Here is an example.

When pre-treating hot metal in a converter type refining furnace, a so-called heavy charging operation, in which the amount of hot metal charged per unit internal volume of the furnace is larger than in the decarburization blowing of the converter, may be performed. Many. However, even in the case of heavy charging operation, the hot metal surface at the end of the tailing is usually lower than the center of the furnace bottom. It can be kept above the surface of the bath.

In the refining method of the present invention, as shown in FIG. 2, it is preferable that the tuyere arrangement is such that all the bottom-blowing tuyeres are located at the center of the furnace bottom or on the side of the tap hole 9 therefrom. Since the relationship between the position of the spout and the molten metal surface at the end of the slag differs depending on the shape of the furnace and the amount of the hot metal charged, it is not necessary to limit the arrangement to the tuyere as shown in FIG.

In the hot metal refining method of the present invention, it is desirable that the Si concentration in the hot metal at the end of the Si removal treatment is 0.05% by weight or more. As will be shown in the examples below, when the Si concentration at the end of the de-Si treatment is less than 0.05% by weight, the slag undergoes severe forming at the end of the de-Si treatment, and this slag overflows outside the furnace. Lapping was observed to occur.

In the de-Si treatment, when the Si concentration at the end of the de-Si treatment is less than 0.05%, the reason why the slopping occurs is that when the Si content is 0.05% or less, the de-Si rate is remarkably reduced, The supplied oxygen is consumed for de-C and C
It is presumed that the amount of O bubbles generated increases. That is, since the de-Si slag has a relatively high viscosity, it is considered that when the amount of generated CO bubbles increases, the CO bubbles cannot be completely removed from the slag and forming occurs.

In the present invention, the conditions for the de-P treatment are not particularly limited, and the ordinary de-P treatment conditions for the hot metal subjected to the Si removal can be applied. FIG. 1 shows an example in which the hot metal is discharged to the hot metal ladle 10 after the de-P treatment, but the de-P treatment and the de-C treatment can be performed simultaneously in the same refining furnace.

[0033]

EXAMPLE The hot metal refining method of the present invention was carried out using an 8t test converter. The hot metal used was Si 0.5-0.6
%, And about 0.1% of P. The hot metal 8t was charged into the converter, the top blown O ₂ flow rate was set to 800 Nm ³ / h, and the bottom blow tuyere was a single tube nozzle having an inner diameter of 9 mm. Use one, bottom blow N
_{2. The} tests shown in the following examples were performed under a constant flow rate of 100 Nm ³ / h.

Example 1 Slag basicity (CaO) / (Si
O ₂ ) was changed in the range of 0.2 to 1.8, and after the de-Si treatment, the furnace was tilted to allow spontaneous discharge, and the relationship between the basicity and the discharge rate was investigated. As the flux, granular quick lime was charged at once or dividedly from the upper part of the furnace, and the input amount was changed to adjust the slag basicity after the removal of Si. The waste rate was obtained from the ratio of the weighed value of the discharged slag and the amount of generated slag calculated by the material balance. FIG. 3 shows the results of the investigation.

As shown in FIG. 3, at the end of the de-Si treatment,
When the weight ratio of (CaO) / (SiO ₂ ) was in the range of 0.3 to 1.3, a waste ratio close to 80% was obtained, but outside this range, the waste ratio was significantly reduced.

Example 2 The occurrence of sloping during the de-Si treatment was investigated by changing the Si concentration at the end of the de-Si treatment in the range of 0.02 to 0.10%. The flux is the same as above, and the granular quicklime is charged all at once from the top of the furnace, and the (CaO) /
The dosage was adjusted so that (SiO ₂ ) was approximately 0.5. Table 1 shows the survey results. The determination of the presence or absence of occurrence of slopping was made by visual observation. In each case, the treatment was performed under the same conditions of 2 to 3 heats, and the reproducibility of the results was confirmed.

As can be seen from Table 1, it was confirmed that when the Si concentration at the end of the Si removal treatment was less than 0.05% by weight, slopping occurred.

[0038]

[Table 1]

Example 3 At the end of the waste after the Si removal treatment, the case where the bottom blown tuyere is located above the hot metal surface (case A) and the case where the tuyere is located below the hot metal surface (case A) With respect to B), a test was conducted in which the waste was removed after the de-Si treatment for each of 15 charges, and the amount of iron loss in the removed de-Si slag in both cases was compared.

As shown in FIG. 4 (a), case A has a tuyere placed at the center of the hearth having a hearth diameter D of 1500 mm, and case B has a distance l from the center of the hearth of 400 mm. In this case, the tuyere is arranged on the waste side. In each case, (CaO) / (SiO ₂ ) of the slag after the Si removal treatment
Was about 0.5. FIG. 4B shows the result of the investigation.

As can be seen from FIG. 4, in case A where the tuyere was above the surface of the hot metal at the end of the tailing, the average iron loss was as small as 16 kg / ch. On the other hand, in case B where the tuyere was below the surface of the hot metal, the iron loss amounted to 81 kg / ch on average.
From these results, it was confirmed that the effect of the present invention of disposing the bottom-blowing tuyere so as to be located above the molten metal surface at the end of the slag discharge.

Example 4 The amount of P in the hot metal was reduced from 0.10% to 0.015% with and without intermediate waste after the Si removal treatment.
The amount of quicklime required to do so was compared.

In the embodiment in which the intermediate waste was removed, quick lime was used at a rate of 5 kg / t during the Si removal treatment to remove up to 0.1% of Si.
After the treatment, the furnace was tilted to discharge the Si-removed slag.
The waste rate is about 80%, and the (CaO) / (Si
O ₂ ) was about 0.5. Thereafter, the furnace was allowed to stand upright, and quicklime was added to remove P until the P became 0.015%. The amount of quicklime used in the removal of P was 7 kg / t.

On the other hand, in the comparative example in which the intermediate waste was not used, the total amount of quicklime used in the de-Si treatment and the P removal treatment (P removal to 0.015%) was 22 kg / t ((CaO after the P removal treatment). )
/ (SiO ₂ ) was about 1.7), and it was confirmed that the amount of quicklime used could be significantly reduced by the method of the present invention for performing intermediate waste.

[0045]

According to the method of the present invention, it is possible to smoothly perform the de-Si treatment and the subsequent intermediate waste in a converter type refining furnace, and a conventional refining method for simultaneously performing the de-Si treatment and the P removal treatment. Compared with the above, it has become possible to greatly reduce the amount of flux used and the amount of slag generated.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing an example of a refining furnace used in the present invention and working steps of a refining method of the present invention.

FIG. 2 is an explanatory view showing an example of tuyere arrangement at a furnace bottom in the present invention.

FIG. 3 shows (CaO) /
Diagram showing the relationship (SiO ₂₎ and Haikasu rate.

FIG. 4 is a diagram showing the relationship between the position of the tuyere and the amount of iron loss into the discharged slag in this embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Refining furnace 2 Hot metal 3 Scrap 4, 4a, 4b Tuyere 5 Blow tank 6 Hopper 7 Top blowing lance 8 De-Si slag 9 Tap hole 10 Hot metal pot 11 Trunnion

Continued on the front page (72) Inventor Toshio Ogino 5-3 Tokai-cho, Tokai City, Aichi Prefecture Inside Nippon Steel Corporation Nagoya Works (72) Inventor Koichi Matsumoto 5-3 Tokai-cho, Tokai City, Aichi Prefecture Made in New Japan Nagoya Works, Steel Corporation (72) Inventor Susumu Mitsukawa 5-3 Tokai-cho, Tokai City, Aichi Prefecture Inside Nagoya Works, Nippon Steel Corporation

Claims (3)

[Claims] 1. A process for removing Si and P from molten iron using a refining furnace having means for injecting powder and / or gas into the hot metal from the bottom of the furnace and means for blowing oxygen gas from the upper part of the furnace to the hot metal. In carrying out, first, the (CaO) / (SiO ₂ ) weight ratio of the slag at the end of the de-Si treatment is 0.3 to 0.3%.
After performing the de-Si treatment by adjusting the supply amount of the CaO-containing substance so as to fall within the range of 1.3, the furnace is tilted to discharge the slag generated in the furnace from the furnace port, and then the de-P treatment is performed. A method for refining hot metal, which is performed. 2. When all the tuyeres for blowing powder and / or gas in the furnace bottom are discharged at the end of the waste after the Si removal treatment,
2. A smelting furnace arranged so as to be positioned above a surface of molten metal in a tilted smelting furnace.
The refining method of the hot metal described. 3. The hot metal refining method according to claim 1, wherein the Si concentration in the hot metal at the end of the Si removal treatment is 0.05% by weight or more.