JPH073320A - Converter refining method - Google Patents

Abstract

(57) [Summary] [Object] The present invention provides a method for efficiently and stably carrying out desiliconization, dephosphorization, decarburization and Mn ore reduction refining of hot metal in the same converter. A refining method for producing molten steel from hot metal in the same converter by using a converter having a bottom-blowing nozzle and a side-blowing nozzle, wherein degassing is performed while blowing gas from both the bottom-blowing and side-blowing nozzles. Silica and dephosphorization treatment, slag discharge,
A converter refining method comprising sequentially performing decarburization and Mn ore reduction refining.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing molten steel from hot metal by carrying out desiliconization, dephosphorization pretreatment refining and decarburization, and Mn ore reduction refining in the same converter.

[0002]

2. Description of the Related Art Conventionally, as a refining method including a hot metal pretreatment using a converter, the following method is known. (A) Chemical Engineering Vol. 56, No. 6 (1992) P26
As shown in ~ 28, after carrying out de-Si refining in the casting floor of the blast furnace, de-S refining is carried out in a container for carrying hot metal, and after carrying and charging to converter-1, de-P refining is carried out. carry out. After that, after the hot metal and the slag are completely separated by tapping and slag, only the hot metal is transferred to a dedicated pot, while the slag remaining in the converter after de-Ping is discharged to another dedicated slag receiving container. De-P refined hot metal is transported and loaded into converter-2 in a container for carrying hot metal, and then depends on decarburization refining and its heat margin (excess heat on heat balance causes cooling of scrap etc.) (There is room for addition of materials, etc.), and reduction refining of Mn ore is carried out. In this process, stirring power is applied for the purpose of improving refining efficiency, and nitrogen, Ar and CO are supplied to each of the converters-1 and 2 during refining.
_{2 A} nozzle for blowing gas is provided at the bottom of the reaction vessel. The purpose of this nozzle is to promote the reaction of the converter slag, iron oxide, CaO, fluorspar and [P] in the hot metal that are added during de-P refining in converter-1, and in converter-2, It promotes the smelting reduction reaction of Mn ore.

(B) 100th Steelmaking Section Steel 100-Own
Kobe Steel, Ltd. "Technology for hot metal pretreatment for converter heat compensation" March 1st, 1991, and Japanese Patent Publication 1-4
As disclosed in Japanese Patent No. 1681, as in the case of (A), after carrying out de-Si refining in the casting floor of the blast furnace, it is directly conveyed to the converter-1 in a container for carrying hot metal and charged. The molten pig iron charged in the converter-1 is subjected to de-P refining and then de-S refinement is performed by blowing the de-S material together with the carrier gas into the molten pig iron without forcibly removing the slag. Then, after the hot metal and the slag are completely separated by the tap slag, only the hot metal is transferred to a special pan, and the slag remaining in the converter after de-Ping and de-S is discharged into a special slag pan container. De-P and de-S refined, low P,
The low-S hot metal is transported to and loaded into the converter-2 in a container for hot metal transport, and then de-C refined. Although the converter-1 is not equipped with a bottom blowing nozzle for stirring, the carrier gas at the time of adding the S-depleting agent in the injection lance promotes the mixing of the hot metal and the refining flux and the increase of the reaction efficiency. Further, in the converter-2, for the purpose of promoting decarbonization refining reaction efficiency, Ar, N
₂ Gas is blown into the furnace from the nozzle at the bottom of the converter as in the case of (A) above.

(C) LD Committee 10th Anniversary Anniversary Collection Japan BOT Group LD Committee (S44) As shown in P235, in the first blow in the converter, the soft blow refining is used for de-P refining. This is a method of discharging P-depleted slag in a range where the hot metal does not flow out from the furnace port after P-depletion, and continuously performing C-refining after the discharge. In this document, there is no report that the bottom blowing nozzle and the side blowing nozzle are installed in the converter to improve refining efficiency and slag removal property.

FIG. 6 shows the steps of the above methods (A), (B), and (C) in schematic form.

[0006]

The methods (A) and (B) described above use converters 1, 2 and 2 converters to prepare hot metal preliminary de-P, de-S refining and de-C refining, and Mn. It was separated from ore reduction and refining. The reason for separating into two furnaces in these processes is to avoid blowing in a converter contaminated with phosphoric acid or phosphoric acid and slag having a high S content after de-P refining, and avoiding a decrease in steelmaking capacity in one furnace continuous refining. there were. Therefore, in the conventional method, in particular, with respect to the above, a tapping process and a slag removal process are provided, the hot metal is once tapped out of the furnace, and the separation efficiency of slag and hot metal is increased
In addition, the molten iron was smelted in another converter without the above slag contamination and molten steel was obtained from the molten iron. However, in this method, the loss of sensible heat of hot metal during transfer and transportation of hot metal is large, and since each converter is operated intermittently in order to operate two converters at the same time, further heat loss is promoted. It had been. Therefore, the heat allowance in the primary refining process from the pretreatment to the converter refining is lowered, and the adverse effects such as the reduction of the scrap melting ratio and the reduction amount of Mn ore occur. 2 bottom blowing nozzles
Since it was installed and used in the furnace, there were also disadvantages such as nozzle and nozzle cooling gas during standby.

In the above method (C), in order to improve the slag slag ratio after P removal, the soft blow (the stirring force of the hot metal in the converter is reduced intentionally, and the mass transfer rate control of [C] in the hot metal is controlled. Refining to maintain the fluidity of the slag, because iron loss increases because the slag concentration (% T.Fe) concentration is secured at about 15% or more so that the slag is easily formed. As a result of increasing the refining temperature so that the blowing stop temperature is 1400 ° C or higher, wear and melting loss of the refractory of the inclined part of the converter increase, and the P removal efficiency decreases due to high temperature blow stop. Since CaO / SiO ₂ is secured at 3.0 or more, the flux cost increases. In the slag slag, since the slag is forcibly discharged without adding any means such as gas blowing, the slag and the loss of hot metal also increase. Refractory material in terms of cost Basis to be high load,
The continuous double slag method was difficult.

The present invention has been made in order to solve the above-mentioned problems of the prior art. From the hot metal that can efficiently perform desiliconization, dephosphorization pretreatment refining and decarburization, and Mn ore reduction refining in the same converter. A method for producing molten steel is provided.

[0009]

The present invention is a refining method for producing molten steel from hot metal in the same converter using a converter having a bottom blowing nozzle and a side blowing nozzle. A gist of a converter refining method is characterized in that the following steps (a), (b) and (c) are sequentially performed while gas is blown from both blowing nozzles. (A) A step of desiliconizing and dephosphorizing the hot metal in a state where both the nozzles are in the hot metal (b) The converter is tilted so that the side blowing nozzle is at the bottom, and at least the side blowing nozzle is in the hot metal. With
(A) A step of discharging the slag generated in the step from the furnace opening. (C) A step of returning the converter posture to the original state and decarburizing the hot metal and smelting and refining the Mn ore with both nozzles in the hot metal.

[0010]

In carrying out the present invention, the hot metal de-P treatment and refining of slag after the de-P treatment in the converter of one furnace are improved, and the de-C refining and the Mn ore reduction refining after the slag are efficiently carried out. To achieve this, gas blowing nozzles are installed at the bottom and in the belly of the converter according to the invention. Thus, in the refining state where the converter is maintained vertically and oxygen is blown upward from the oxygen blowing lance at the upper part of the converter (Fig. 1- (A)), gas is introduced into the hot metal through the nozzle installed at the bottom. The flux added for refining was carried out by injecting gas to avoid the rate-controlling of the material movement on the hot metal side of the refining target substances such as P and Si on the hot metal side, and at the same time, performing gas injection from the nozzle installed in the furnace belly. The nozzle is used for the purpose of promoting the mixing and reaction of the hot metal and the hot metal. After de-Ping and de-Si refining, when tilting the converter to discharge slag from the converter furnace port (Fig. 1-
(B)), the nozzle installed at the bottom of the furnace has a furnace tilt angle of 90.
While it is coming out of the hot metal and slag immersion position on the way to 0 °, the forming of the slag is promoted by the fine bubbles generated by the gas blown through the nozzle until it comes off, and it has the effect of facilitating the removal of slag. At the same time, the nozzles installed in the furnace belly are in a state where all the nozzles are always immersed in the hot metal and slag even after being tilted 90 ° after the blowing.
It is used for the purpose of promoting the discharge of slag from the furnace opening by forming the slag in the forming state by the gas floating through the hot metal. Therefore, as an apparatus for carrying out the present invention, a nozzle installed in the furnace bottom portion and the furnace belly portion is used for promoting refining efficiency and improving slag discharge efficiency from the furnace mouth of the converter. Use a processing furnace. By using such a furnace, it becomes possible to carry out a de-P refining in one furnace and a continuous de-carbonization after slag and a Mn ore reduction refining process.

A detailed description will be given below. FIG. 2 shows the process of the present invention and the functions of the bottom blowing nozzle and the furnace abdominal nozzle at each refining time. In the process of the present invention, the hot metal tapped from the blast furnace is de-S refined outside the converter in advance, and the de-S refining inside the converter is not required. The hot metal charged in the converter is de-Si and de-P refined. At that time, iron oxide, converter dust, CaO, C from the top of the furnace are used as de-Si and de-P flux.
Since aF ₂ is added and the blow-off temperature after de-P refining is determined in advance, the surplus heat in terms of heat balance is adjusted by adding a coolant such as iron ore or scrap. At this time, a stirring gas such as Ar, nitrogen, or CO ₂ gas is blown through the bottom blowing nozzle and the furnace abdominal nozzle to accelerate the melting of the flux and the reaction between the slag and the metal. The bottom-blown gas is effective for supplying [Si] or [P] in the hot metal to the molten slag surface on the hot metal at an appropriate rate,
The mass transfer rate limiting at the time of Si removal and P reaction is avoided.
Further, the gas blown from the furnace abdomen particularly contributes to the stirring and mixing of the hot metal and the slag interface, and qualitatively improves the de-Si and de-P reaction rate control (including the mass transfer rate control of the reaction interface).

FIG. 3 shows P distribution at the time of de-P refining depending on whether or not gas is blown into each part. The de-P distribution when gas is blown from both the bottom and the abdomen of the furnace is the highest and the efficiency is high. It shows that de-P refining can be performed. After de-P refining, slag is discharged from the converter furnace mouth. The tilting of the converter starts, and the slag outflow starts at about 65 ° (clockwise tilt angle with respect to the vertical axis of the converter), but both nozzles of the bottom blowing nozzle and the furnace abdomen nozzle are initially in the hot metal and slag. Since the slag foaming height is large and the number of bubbles is large, the slag foams violently and the outflow amount of slag increases as the tilt angle increases (65 ° → 75 °). When the tilt angle is 75 ° or more, the bottom blowing nozzle is outside the hot metal, and the slag foaming is promoted by the nozzle in the furnace belly. The tilt angle of the converter shown here depends, of course, on the furnace shape, old and new converters, and the amount of slag and hot metal, but no matter what the conditions are, the nozzle installed at the bottom of the furnace has a certain angle with the tilt of the converter. At the outside of the hot metal. In particular, at the end of slag discharge, the slag discharge rate tends to decrease remarkably due to the solidification of the slag surface and the decrease in the foaming height.
At that time, by increasing the amount of gas from the furnace abdomen, it is possible to suppress the decrease in the slag slag speed.

FIG. 4 shows the influence of the bottom blowing nozzle and the furnace abdominal nozzle on the slag slag ratio after P removal. By installing the nozzles at both the furnace bottom and the furnace belly and discharging the slag, the dispersion of the slag ratio is small, and a slag ratio of 90% or more can be stably obtained. Although the effect of the gas blowing method on the P removal rate and the slag slag removal rate is the same, further, when the P removal rate is high, the concentration of phosphoric acid in the slag increases and the surface tension of the slag decreases, resulting in a decrease in slag. It is presumed that the life extension effect of foaming (foam) contributes to improve the slag scavenging property.

Further, FIG. 5 shows the effect of the Mn ore reduction refining efficiency during decarbonization refining and the effect of the gas blowing method in the second blow after the slag removal. Similar to the de-P distribution, when gas was blown from the furnace belly at the same time as the nozzle at the bottom of the converter, the reduction efficiency was shown to be highest as the Mn ore reduction efficiency was higher and the total gas amount was higher. .

[0015]

Example: Temperature of 1510 ° C., C =, tapped from a blast furnace
4.8%, Si = 0.41%, Mn = 0.34%, P =
298 t of hot metal of 0.102% and S = 0.018% was received in a transport container called a torpedo car, and CaO =
6.1 kg / t and Al dross = 0.51 kg / t were blown into the hot metal by a dip tube lance for about 12 minutes to perform de-S refining. As a result, the temperature was 1360 ° C. and C = 4.6.
%, Si = 0.40%, Mn = 0.35%, P = 0.1
A low S hot metal having a S content of 00% and S = 0.008% was obtained.

The molten pig iron was transferred to a converter plant, and the whole amount was charged into a converter having two bottom blowing nozzles at the bottom of the furnace and three nozzles at the belly of the furnace. The bottom blowing nozzle is a thin tube collecting nozzle type that can blow up to 600 Nm ³ / Hr · book of N ₂ and CO ₂ gas, and the furnace abdominal nozzle is the same thin tube collecting nozzle type as the bottom part, that is, 400 Nm ³ maximum. / H
N _2, CO ₂ of r · present, it is possible to blow compressed air.

Two pieces of the hot metal are placed in the converter type pretreatment refining furnace.
I loaded 98t. N from bottom blowing nozzle₂= 550 Nm
³/ Hr ・ Book Also, from the furnace belly nozzle, N₂= 300
Nm ³/ Hr / book total of 2,000 Nm³Gas blowing
Only carried out. From the upper part of the converter, block CaO = 18 kg /
t, iron ore = 23 kg / t, fluorite (CaF₂) =
4.0 kg / t was pre-charged and at the same time the main oxygen blow run
Than su₂= 20,000 Nm³De-P under the condition of / Hr
Performed refining. About 3 minutes from the start of blowing Lance-hot metal surface
Changed the distance from 2.2m to 3.0m and continued blowing
It was As a result of blowing off 9 minutes after the start of blowing, the temperature was 135.
0 ° C. C = 3.6%, Si = 0.02%, Mn = 0.0
6%, P = 0.021%, S = 0.008%, low P, low
Si hot metal was obtained.

Immediately after the blowing is stopped, the furnace tilting is started, and the bottom blowing gas amount is 600 Nm ³ / Hr · book and the nozzle 30 in the furnace abdomen.
The slag was started as 0 Nm ³ / Hr CO ₂ gas.
The in-furnace slag starts to flow out at a tilt angle of 71 ° and reaches 75 °
Confirm that the bottom blowing nozzle has come out of the hot metal with a pressure gauge, and then continuously perform furnace tilting and slag treatment, and slag at a tilting angle of 91 ° 4.5 minutes after tilting starts. The process is complete. The completion was judged by visual observation because a part of the molten pig iron outflow was observed. Immediately after returning the converter to the vertical state and measuring the temperature, the amount of temperature drop in the slag at 1335 ° C was 15 ° C. Further, the amount of outflowing slag in the slag pan after the slag was weighed was 10.2 t, and the slag ratio was 91.
It was 7%.

After the furnace is upright, the hot metal in the furnace is CaO 7 kg / t.
And 11 kg / t of Mn ore were added, and the second blow blowing was started from the main oxygen blowing lance at O ₂ = 50,000 Nm ³ / Hr. The bottom blown gas and the furnace abdominal part gas are CO ₂ gas, and the gas flow rate is bottom blown nozzle = 600 Nm ³ / H
r · book, furnace abdominal nozzle = 300 Nm ³ / Hr for about 14 minutes. As a result, at the second blow stop, temperature = 1
653 ° C., C = 0.16%, Si = tr, Mn = 0.4
0%, P = 0.010%, S = 0.007% Medium coal low P
The steel could be melted and the Mn ore reduction efficiency of the second blow was estimated to be 62%.

After the molten steel is tapped, RH which is a degassing facility is used.
And a BL slab for a healthy steel bar could be manufactured by casting with a 350 × 560 mm large-section BL continuous casting machine.

[0021]

As described above, according to the present invention,
With one furnace, it became possible to stably carry out de-P, de-Si treatment refining and intermediate slag, and further de-C and Mn ore reduction refining with high refining efficiency. In addition, the present invention is intended to significantly expand the functions and efficiency of the one-furnace method, which is the method of the prior art (C), and to stabilize the one-furnace hot metal pretreatment method, so-called double slag refining technology. In addition, the cost is low and it is possible to apply the entire amount to the hot metal, which is extremely beneficial in the industry.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of the present invention.

FIG. 2 is a diagram showing the functions of the steelmaking process and the gas blowing nozzle of the present invention.

FIG. 3 is a diagram showing a blowing method in a converter and P distribution after deP refining.

FIG. 4 is a diagram showing an effect of gas blowing on a slag slag removal rate.

FIG. 5 is a diagram showing the effect of gas blowing on the Mn ore reduction rate.

FIG. 6 is a diagram showing an example of a refining method including a hot metal pretreatment using a conventional converter.

Claims (1)

[Claims] 1. A refining method for producing molten steel from molten pig iron in the same converter using a converter having a bottom blowing nozzle and a side blowing nozzle, wherein gas is blown from both the bottom blowing nozzle and the side blowing nozzle. Meanwhile, a converter refining method characterized by sequentially performing the following steps (a), (b) and (c). (A) A step of desiliconizing and dephosphorizing the hot metal in a state where both the nozzles are in the hot metal (b) The converter is tilted so that the side blowing nozzle is at the bottom, and at least the side blowing nozzle is in the hot metal. With
(A) A step of discharging the slag generated in the step from the furnace opening. (C) A step of returning the converter posture to the original state and decarburizing the hot metal and smelting and refining the Mn ore with both nozzles in the hot metal.