JPH0741813A - Refining method in converter - Google Patents

Abstract

PURPOSE:To provide a method, in which a desiliconizing and dephosphorizing pretreatment refining and a decarburizing refining or a decarburizing and Mn ore reduction refining of molten iron are efficiently and stably executed with a same converter. CONSTITUTION:In the refining method for producing molten steel from the molten iron with the same converter, slag discharging quantity is weighed after executing the desiliconizing and dephosphorizing refining. The remaining slag quantity in the furnace obtd. from the difference between the produced slag quantity by the desiliconizing and dephosphorizing refining obtd. by calculating and the actual slag discharged quantity is used to the calculation obtaining flux quantity and coolant quantity to be added at the time of successively executing the decarburizing refining or the decarburizing 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 refining method for producing molten steel from hot metal by carrying out desiliconization, dephosphorization pretreatment refining and decarburization and Mn ore reduction refining using a converter in the same converter. It is a thing.

[0002]

2. Description of the Related Art In order to hit the decarburization refining reaction of a converter and blow-off temperatures [% C] and [% Mn] at the end of converter refining, the following methods are conventionally known. . (A) It is a method generally known from the past,
Before the smelting, a solvent such as quick lime and fluorite and a coolant such as iron ore, Mn ore and scrap, which was calculated based on the smelting conditions as static calculation, were added, and the sublance was applied within a certain fixed time. Measure the molten steel temperature [% C] during refining by
A dynamic control method for correcting the molten steel carbon amount (for example, also described in the following (B) document).

(B) Iron and Steel Vol. 76 (1990)
As shown in No. 11 P192, a method of controlling from the exhaust gas information during converter refining (a mass spectrometer is installed in the converter OG equipment, and CO, CO ₂ , O ₂ analysis results in the exhaust gas are used. , Balance carbon and oxygen in the furnace,
The amount of oxygen contained in the molten steel and slag is estimated, and (T.Fe) in the slag and the molten steel temperature are continuously estimated from the above information at the end of blowing and the dephosphorization equilibrium formula, slag balance formula, phosphorus balance formula Method to estimate the end temperature of molten steel, phosphorus, carbon content from.

(C) Iron and Steel Vol. 76 (1990)
No. 11, p. 200, the converter is operated by measuring the emission spectrum from the fire point using the fire point formed during oxygen blowing in the converter operation as a light source for direct emission analysis of molten steel. Method for directly analyzing the Mn concentration in water.

[0005]

The conventional converter refining control techniques (A), (B), and (C) are based on a process for carrying out decarburization refining or decarburization refining and Mn ore reduction refining in a converter. It is a technology developed as, in the same converter as the present invention, hot metal preliminary desiliconization, dephosphorization treatment and decarburization refining or hot metal preliminary desiliconization, dephosphorization treatment and decarburization refining and Mn ore reduction refining Not a process to implement. Therefore, it was not necessary to accurately grasp the residual slag in the converter from the needs of refining control technology.

[0006] In the above technique (A), since the information on the slag composition in the furnace is not taken into consideration at all, especially in the refining in which a large amount of Mn ore is used in the converter in recent years, the variation of blown Mn is large and the Mn added after refining is increased. Problems such as prolongation of iron alloy weighing time and removal of Mn component have occurred. Above (B)
In the technology, a concept considering slag composition and amount is introduced in refining control, but slag cannot be estimated about the end point Mn based on estimation calculation.

Further, in the technique of (C) above, M in molten steel is
Only the n concentration is known, the reduction smelting of Mn ore cannot be controlled, and the purpose of improving the smelting refining method online cannot be achieved. In view of the above situation, the present invention is a process for performing hot metal preliminary desiliconization, dephosphorization treatment and decarburization refining or hot metal preliminary desiliconization, dephosphorization treatment and decarburization refining and Mn ore reduction refining in the same converter. The purpose of the present invention is to provide a method for accurately grasping the residual slag in the converter.

[0008]

According to the present invention, hot metal desiliconization and dephosphorization refining are performed in the same converter, and slag generated in the refining is discharged, followed by decarburization or decarburization and Mn ore reduction. In the molten iron converter refining method for refining, when the slag is discharged, the discharged slag amount is weighed, the calculated desiliconization, the dephosphorization refining generated slag amount and the weighed slag amount. Obtain the amount of slag remaining in the furnace from the difference,
The amount of residual solvent slag thus obtained is used to calculate the amount of solvent such as CaO and fluorite that should be added in the subsequent decarburization or decarburization and Mn ore reduction refining and the amount of coolant such as Mn ore and scrap. The gist is a converter refining method characterized by being used.

[0009]

In the refining process in the converter, which is the premise of the present invention, refining proceeds in four steps in the same converter as the flow sheet shown in FIG. As shown in FIG. 1, the slag after the step 4 is deoxidized with carbonaceous material (C source) or the like, and the whole amount or a part thereof is left in the converter. Next, in step 1, the hot metal is charged in the presence of the slag, and desiliconization and dephosphorization refining are performed. At that time, a dephosphorizing agent such as CaO or a cooling agent such as iron ore is added to the converter. In order to obtain a particularly stable low phosphorus hot metal, the basicity (% CaO /% SiO _{2 in} slag) in step 1 should be 1.0
In order to control in the range of ˜2.0 (target 1.5), the amount of slag in the pre-charge (after slag deoxidation) must be measured as accurately as possible to determine the amount of added CaO. Also, when decarburizing / Mn reduction refining is performed in step 3 after the slag is removed in step 2, in order to obtain a stable and constant Mn reduction efficiency,
It is desirable to control the basicity in the slag within the range of 3.0 to 4.0 (target 3.5). Therefore, it is necessary to accurately grasp the amount of slag remaining in the converter after the slag is discharged in the step 2 as accurately as in the step 1.

In the above-mentioned process, the amount of slag in each step mainly depends on the additive solvent (CaO, CaF ₂
Etc.) and the amount discharged to the outside of the process system can be accurately estimated. Therefore, in the present invention, the amount of slag discharged to the outside of the process system, particularly the amount of slag discharged in step 2, is actually weighed, and the refining control is performed while grasping the slag balance of the entire system for each charge.

Specifically, as shown in FIG. 2, the slag pan container under the converter furnace is moved to a scale by a trolley to measure the slag discharge amount, or a trolley with a scale is used to discharge the slag just after the slag. The actual amount is actually measured and the residual slag in the furnace is calculated by the following formula (1). Amount of slag generated in the furnace during dephosphorization refining-Amount of actual slag-α = Amount of residual slag in the furnace ……… (1) The amount of slag generated in the furnace here is mainly for limestone and firefly stone during refining. It is determined from the amounts of additive solvent and coolant such as iron ore, as well as the amount of erosion of the converter refractory and the remaining amount of precharge refining slag. Α is the amount of hot metal that flows out at the same time as slag discharge. This amount of hot metal is IT in the slag
Image processing of video by a V surveillance camera or a predetermined amount which is empirically known in advance may be used. Although a method of visually measuring the discharged slag is also envisioned here, this method has individual differences, and the discharged slag amount cannot be accurately measured due to a foaming phenomenon of the discharged slag and the like.

According to the present invention, the amount of discharged slag can be accurately and quickly weighed. This improves the estimation accuracy of the residual slag amount in the converter and is reflected in the decarburization refining after slag and the Mn blowing calculation, and the blowout temperature, [% C], [% Mn] hit rate The Mn reduction efficiency is greatly affected by the remaining amount of slag. However, since the present invention provides a highly accurate slag residual amount, it is necessary to add an appropriate amount of CaO according to the residual slag amount so that the basicity (= CaO / SiO ₂ ) during Mn reduction refining becomes constant. It becomes possible and a stable Mn reduction yield is obtained.

[0013]

Example: Temperature of 1510 ° C., C =, tapped from a blast furnace
4.8%, Si = 0.41%, Mn = 0.34%, P =
270t of hot metal of 0.102% and S = 0.018% was received by a torpedo car, and CaO = 1.65t Al was used as desulfurization flux at the desulfurization refining station.
Dross = 0.14 t was blown into the molten iron for about 12 minutes by a dip tube lance to carry out desulfurization refining. as a result,
Temperature 1360 ° C., C = 4.6%, Si = 0.40%, M
n = 0.35%, P = 0.100%, S = 0.008%
The low sulfur hot metal of

The obtained hot metal was transported to a converter factory and the whole amount was charged into a converter having nozzles at the bottom and the belly. N ₂ and CO ₂ gas can be blown from the nozzle. In this converter type pretreatment refining furnace, the total amount of the hot metal 27
0t and 16.2t of scrap were charged, and N ₂ = 550 Nm ³ / Hr · book from the bottom blowing nozzle, and N ₂ = 300 Nm ³ / Hr · book from the furnace abdominal nozzle, total of 2.0.
Gas blowing of 00 Nm ³ was carried out. From the top of the converter,
Agglomeration CaO 4.8t and fluorspar (CaF ₂ ) 0.6t were precharged with the aim of the calculated basicity of 2.0, and at the same time, from the main oxygen blowing lance, O ₂ = 20,000 Nm ³ / Hr Then, dephosphorization refining was carried out. Approximately 3 minutes after the start of blowing, change the distance between lance molten iron surfaces from 2.2 m to 3.0 m,
Continued blowing. As a result of stopping blowing 9 minutes after the start of blowing,
Temperature = 1350 ° C., C = 3.6%, Si = 0.02%,
Mn = 0.06%, P = 0.021%, S = 0.008
% Low phosphorus and low sulfur hot metal was obtained.

Immediately after stopping the blowing, the tilting of the furnace was started and the bottom blowing
CO and gas in the furnace₂Gas, and the gas flow rate is bottom blown
Cheat = 600Nm³/ Hr · book, furnace belly nozzle = 300
Nm ³/ Hr ・ Blow-in was started under the condition of book, and the waste was started.
The waste treatment was completed 4.5 minutes after the start of tilting. Waste
As a result of weighing immediately after the completion of the treatment, the amount of slag was 14.5 t (melting
The amount of pig iron α: 0.2t is excluded), and the amount of slag generated by calculation is 1
6.5t (4.5t of residual slag from the previous charge,
CaO balance and SiO₂Find from average of balance
The amount of waste slag produced is 12.0 t) and the slag ratio is 88%.
Therefore, the amount of residual slag in the converter was calculated to be 2t.

The weighing result is immediately input to the decarburization refining and Mn reduction refining calculation in the next step by the slag amount balance calculation formula in the process container, and the basicity 3.5 is set to obtain the Mn ore reduction yield of 60% or more. CaO = for the purpose of securing
900 kg, Mn ore = 3.1t was added, and ₂ from O ₂ = 50,000 Nm ³ / Hr from the main oxygen blowing lance.
Blow-eye blowing has started. The bottom blown gas and the furnace abdominal part gas are CO ₂ gas, and the gas flow rate is the bottom blown nozzle = 600 Nm.
Refining was performed for about 14 minutes at ³ / Hr · book, furnace abdominal nozzle = 300 Nm ³ / Hr. As a result, at the second blow stop, temperature = 1653 ° C., C = 0.16%, Si = tr. Mn =
It was possible to smelt 0.40%, P = 0.010%, S = 0.007% medium carbon low phosphorus steel, and the Mn ore reduction efficiency of the second blow was estimated to be 62%.

The amount of slag in the furnace after the second blow is 4.8.
It was calculated as t, and 1t was discharged to the molten steel pot during tapping, and 3.8t of the remaining slag was left in the furnace, and the hot metal of the next charge was received to perform dephosphorization refining. Desiliconization on the next charge,
After dephosphorization and refining, slag work is performed, slag is weighed at that time, decarburization and accurate calculation of CaO amount added to Mn ore reduction and refining are performed, and stable Mn ore reduction yield of 60% or more is obtained. I was able to.

[0018]

INDUSTRIAL APPLICABILITY As described above, in the converter refining method in which decarburization, dephosphorization and slag removal are performed in the same converter, decarburization and Mn ore reduction refining are carried out in accordance with the present invention. Stable Mn ore reduction yield, molten steel by directly weighing each amount and reflecting the obtained value directly to each compound charge in the blending calculation of the solvent and coolant during decarburization and Mn ore reduction refining in the next process It is possible to obtain the temperature and the carbon content.

[Brief description of drawings]

1 is a flow sheet of a refining process in a converter which is a premise of the present invention.

FIG. 2 is a schematic view showing an embodiment of the present invention.

[Explanation of symbols]

 1 Converter 2 Molten Steel 3 Slag 4 Slag Pan 5 Conveyor Cart 6 Weigher

Claims (1)

[Claims] 1. A converter for refining molten pig iron, in which the hot metal is subjected to desiliconization and dephosphorization refining in the same converter, and slag generated in the refining is discharged, followed by decarburization or decarburization and Mn ore reduction refining. In the method, at the time of discharging the slag, the discharged slag amount is weighed, the calculated desiliconization, the residual slag amount in the furnace from the difference between the generated slag amount by dephosphorization refining and the weighed slag amount. Then, the amount of residual slag in the furnace thus obtained is used for decarburization or decarburization and Mn
A converter refining method, which is used for calculation of an amount of a solvent such as CaO and fluorite to be added in ore reduction refining and an amount of a coolant such as Mn ore and scrap.