JPS622603B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for melting high carbon steel using a top-blowing and bottom-blowing converter equipped with an oxygen top-blowing lance and a gas-injection tuyere at the bottom of the furnace. Generally, the degree of oxidation of slag in converter blowing (the total amount of iron in the slag, expressed as T, Fe) and the amount of carbon in molten steel are in an inversely proportional relationship. Conventionally, when melting low-carbon steel with a carbon content of 0.1% or less in a top-blown converter, the degree of oxidation of the slag increases to promote decarburization, and the melting can be performed under favorable conditions for dephosphorization. It was rarely a problem. On the other hand, in the production of high-carbon steel with a carbon content of 0.4% or more, dephosphorization is extremely difficult because the degree of oxidation of the slag is low. Therefore, when melting high carbon steel in a top-blown converter, a method is adopted in which the top-blowing lance is raised to perform soft blowing, increasing the degree of oxidation of the slag and promoting dephosphorization while suppressing decarburization. has been done. In this conventional method, oxygen from the top blowing lance is supplied through the slag layer, and the kinetic energy of the oxygen jet does not sufficiently stir the steel bath, so the slag becomes overoxidized. Equilibrium with the steel bath is easily lost, causing abnormal reactions such as sloping and boiling, which often impede blowing. The present invention was made with the aim of solving the problems in top-blown converters according to the prior art, and in order to compensate for the lack of steel bath stirring power in top-blown converters, impellers are provided at the bottom of the converter. We focused on injecting inert gas or oxygen gas (hereinafter referred to as stirring gas) directly into the steel bath through the mouth to strengthen the stirring power, and on the other hand, taking advantage of the effect of top blowing to adjust the oxidation degree of the slag. It was done by By the way, so-called dynamic control, which measures the carbon content and molten steel temperature in the steel bath using a sub-lance and estimates and corrects the end point from the results, is widespread in top-blown converters. This dynamic control was applied to the melting of high carbon steel using a converter combined with bottom blowing, and various blowing methods were attempted, but not only were there problems with the accuracy of the end point carbon content and temperature, but also problems such as slopping and Phosphorus could not be adequately controlled. Therefore, we standardized the blowing method for high carbon steel by taking into account initial blowing conditions, such as hot metal composition, temperature, and hot metal ratio, and created a blowing model. height,
We tried adjusting the top-blowing oxygen flow rate and bottom-blowing stirring gas flow rate, and adding auxiliary raw materials, and were able to achieve considerable results. However, depending on the hot metal conditions and furnace operating conditions, it may not be possible to carry out the desired blowing process.
It is desirable to control the end point carbon concentration and molten steel temperature with even higher accuracy, and as mentioned above, especially in the production of high carbon steel, it is necessary to control phosphorus to an acceptable value without causing troubles such as slopping. It's important,
To this end, detection of slag formation during the blowing process becomes a major issue. Conventionally, in-furnace acoustic measurement has been known as a means of detecting the slag condition, but the information is indirect and insufficient, and it also has the disadvantage of being exposed to adverse environments such as high temperatures and dust. Similarly, methods based on converter exhaust gas analysis provide indirect information and cannot be expected to be fully utilized due to the time delay in reacting in the reactor. The present inventors attached a vibration accelerometer to the oxygen lance in a top-blowing converter as a means of detecting the slag formation state, and measured the acceleration of the oxygen lance movement caused by the movement of the slag during blowing. We have developed a method to understand the progress of this process and have achieved results. Therefore, we attempted a method of melting high carbon steel by incorporating this detection means into blowing according to the program of a top-bottom blowing converter, and developed the present invention. An object of the present invention is to provide a high carbon steel melting method that solves the problems of the conventional top-blown converter as described above. The above object can be achieved by a melting method using a combined converter. Next, the method for producing high carbon steel of the present invention will be explained in detail. When melting high carbon steel using a top-blown and bottom-blowing converter, the present invention first creates a standardized model for blowing, and according to this model, the height of the top-blowing lance, the top-blowing oxygen flow rate, the bottom-blowing We set up a top blowing and bottom blowing program, including the amount of stirring gas blown from the blowing tuyere and the amount of auxiliary materials input.
Perform blowing training using this program. The technical concept is to detect changes in the slag condition during the progress of the program blowing using a vibration acceleration detector inserted into the furnace, and to modify the top blowing bottom blowing program based on this detection. It is based on Now, blowing in the top-blowing and bottom-blowing converter is carried out according to the work procedure shown in the flow sheet of FIG. That is, after charging 1 of hot metal to the converter and pre-charging 2 of auxiliary materials, blowing starts 3 upon completion of preparation for blowing, and then during the blowing process, the height of the top blowing lance and the top blowing oxygen are adjusted. Settings and changes 4 such as the flow rate, bottom blowing gas flow rate, and supply of auxiliary materials are performed, and the blowing is completed 5. Subsequently, temperature measurement/sampling 6 is performed, and if the desired target value is obtained, steel is tapped 7. In the present invention, first, a top-bottom blowing program for producing high carbon steel as a first step is set in accordance with the basic model shown in FIG. In other words, the conditions for top-blowing oxygen injection during the blowing process are such that until 60 to 80% of the entire blowing process has progressed, the oxygen jet penetration ratio from the top-blowing lance is L/L ₀ (L ₀ is the ratio of oxygen to the steel in a static steel bath). The height of the top blowing lance and the amount of top blowing oxygen are programmed so that the bath depth (L is the depth of the depression near the steel bath hot point caused by the oxygen jet (see Figure 3)) is in the range of 0.6 to 0.7. Set. On the other hand, the amount of stirring gas blown from the bottom blowing tuyere is
Similarly, until 60 to 80% of the entire blowing process has progressed, the program is set for the amount of injection from the bottom blowing tuyere to match the range equivalent to 50 to 70% of the predetermined maximum amount of gas injection for stirring. do. In addition, for blowing after 60 to 80% of the entire blowing process has passed, the top blow lance should be set so that the oxygen jet penetration ratio L/L ₀ from the top blow lance is within the range of 0.3 to 0.4. A program is set for the air flow rate and the amount of top blown acid, and a program is set for the stirring gas from the bottom tuyere at a predetermined maximum blown amount. Generally speaking, the stirring force for molten steel increases as the amount of stirring gas blown in from the bottom blowing tuyere increases, but there is a limit to the effect that this increase in stirring force has on the flow of molten steel, and the amount of gas blown in excess of that limit is naturally limited. Even if the amount of injection is increased, it becomes difficult to expect an increase in the fluidity of the molten steel. According to the inventors' operating experience in a 200-ton converter, when the number of tuyeres is about 10 to 12, ^the
It was found that min is almost the limit, so the maximum amount of gas injection for stirring in the case of high carbon steel melting was determined.
It was set to 10Nm ³ /min. Therefore, 60 years have passed since the start of blowing.
The amount of stirring gas blown is 4 to 7 Nm ³ /min during the blowing time up to 80%, and 8 to 10 Nm ³ /min after 60 to 80% of the entire blowing process. Here, the oxygen jet penetration ratio from the top blowing lance is
The relationship between L/L ₀ , lance height, and oxygen supply amount is as follows:
The top blowing lance is determined in advance from the converter specifications and the nozzle structure of the top blowing lance, and as the top blowing bottom blowing program progresses, the top blowing lance is adjusted so that the oxygen jet penetration ratio L/L ₀ falls within a predetermined range. All you have to do is set the height and amount of oxygen. By the way, as mentioned above, the conventional melting of high carbon steel using a top-blown converter had the disadvantage that it was necessary to remove phosphorization while leaving carbon behind, resulting in too soft blowing, which easily caused sloping. In the present invention, in order to solve this drawback, 60 to 80% of the entire blowing process is
Until now, the top blowing side was operated with a harder blow orientation than the conventional top blowing converter, and agitation by stirring gas injection from the bottom blowing was used to some extent (maximum blowing volume of 50 to
70%), and blowing is carried out to maintain equilibrium between the slag and the steel bath and to prevent sloping. Then, in the blowing process from 60 to 80% of the entire blowing process, in order to promote slag formation, the top blowing side is blown super soft to increase the degree of oxidation of the slag, and the bottom blowing side is given the maximum amount of stirring gas. By stirring the steel bath and maintaining a balance between the slag and the steel bath, phosphorization can be removed all at once without causing problems such as slopping. Here, for 60 to 80% of the entire blowing process, the top blowing oxygen jet penetration ratio L/L ₀ was set to 0.6 to 0.7, and the stirring gas injection amount was set to a range of 50 to 70% of the set maximum injection amount. If the oxygen jet penetration ratio is less than 0.6 and the stirring gas injection amount is less than 50%, slopping prevention will not be sufficient, and if the oxygen jet penetration ratio is more than 0.7 and the stirring gas injection amount is more than 70%, the blowing will be too hard. This is because slag formation becomes defective during the forging process. On the other hand, for the blowing process from 60 to 80% of the entire blowing process, the oxygen jet penetration ratio was set to 0.3 to 0.4, and the stirring gas injection amount was set within the range of 80 to 100% of the maximum injection amount. Soft blowing promotes slag formation and increases the degree of oxidation of the slag, and the steel bath is sufficiently stirred by blowing in sufficient stirring gas to maintain a balance with the degree of oxidation of the slag, allowing for dephosphorization without causing problems such as slopping. This is for the purpose of achieving this. As already mentioned, in the present invention, the slag formation status is detected during the progress of blowing in a top- and bottom-blowing converter using a vibration acceleration detector inserted into the furnace. It utilizes the fact that it is closely related to the movement of the top blowing lance, and for example, the acceleration of the movement of the top blowing lance is measured using a vibrator. (In some cases, a special detection rod may be inserted into the furnace and a vibrator attached to it.) The movement of the top blowing lance includes the free movement that occurs when the lance clamp is opened, and the movement of the slag. However, the frequency of free vibration is lower than that of forced vibration, for example, the former is 0.1 to 0.5 Hz, while the latter is 1 to 2 Hz. For actual control, it is necessary to select and use only the latter, taking advantage of the fact that the two frequencies are different. By integrating this acceleration waveform, the average intensity over a certain period of time is determined, and the slag formation state during the blowing process is detected. If the detected value deviates from the standard pattern regarding the integral average value of the lance vibration acceleration set in advance regarding the end point carbon concentration and phosphorus concentration, the amount of gas blowing for stirring set in the program is adjusted according to the deviation, and the blowing program is performed. Make corrections. Although the blowing program can be modified by adjusting the height of the top blowing lance or the amount of top blown acid, which is done in a conventional top blowing converter, it is most effective to adjust the amount of gas blown for stirring. It is a method. Specifically, as shown in FIG. 4, for example, a crystal oscillation accelerometer 13 is attached to the top of the top blowing lance 12 (in some cases, two accelerometers may be attached at right angles to the circumference of the lance). The horizontal direction acceleration of the lance 12 is detected, and the demodulator 14, the waveform converter 15, and the recorder 1
6. Slag production control is performed by a system consisting of a process computer 17, a bottom blowing stirring gas flow rate, a top blowing lance position, and a top blowing oxygen flow rate setting device 18. In the figure, 19 is molten steel, 20 is formed slag, 21 is a bottom blowing tuyere, and 22 is a gas pipe. The above signal-processed waveform corresponds to the slag formation condition in the furnace depending on the wave height index, so as shown in Fig. 5, the waveforms correspond to the sludge formation condition in the furnace, respectively. Determine the slag formation status and increase or decrease the bottom blow stirring gas flow rate so that the slag formation is classified as good. Each classification of the slag condition, that is, the slag level, can be determined appropriately based on the accumulation of blowing, and the setting of the wave height index for good slag formation is as follows:
Changes may be necessary depending on equipment characteristics, aging factors, etc. Examples of the present invention will be described below. High carbon steel produced by a 200 ton top-blown and bottom-blown converter (chemical composition C: 65×10 ^-2 , Si: 25×10 ^-2 , Mn: 60×
10 ^-2 , P < 15×10 ^-3 , S < ²⁰ FIG. 6 specifically shows an example of the slag control method for blowing according to the blowing program. In Figure 6, the horizontal axis is the time axis showing the blowing process as a percentage, and the vertical axis is the top blowing lance height, top blowing acid flow rate, bottom blowing stirring nitrogen gas flow rate, and blowing strength index. It is an explanatory view of a program and dregs detection. Since slag control is not required at the beginning and end of blowing, slag formation is carried out from 8 minutes after the start of blowing until 90% of the entire blowing period is scheduled to end. It was set as a control period. The blowing condition correction action was performed by taking the average of the integrated values of the wave height of the lance vibration acceleration obtained every 5 seconds over a period of 10 to 30 seconds as the slag strength index. The height of the top blowing lance shown in Figure 6 (height from the stationary steel bath surface in meters) and the top blowing acid flow rate (Nm ³ /
min) and nitrogen gas flow rate for bottom-blowing stirring (Nm ³ /
The solid line indicating the progress of the blowing process (min) indicates the established upper blowing blowing program setting value determined based on the basic blowing model in Fig. 2, whereas the dashed line indicates the progress due to the forming of the slag. It shows the operating values obtained by taking corrective action and controlling the slag based on the detection results of the horizontal acceleration acting on the top blowing lance. First, it conforms to the basic blowing model shown in Figure 2, that is, top-blown oxygen injection conditions (oxygen jet penetration ratio 0.6 to 0.7) and bottom-blown nitrogen gas injection conditions for stirring (50 to 70% of maximum injection amount). The blowing was performed by setting the height of the top blowing lance to 2.4 m, the top blowing acid flow rate to 550 Nm ³ /min, and the bottom blowing nitrogen gas flow rate to 4 Nm ³ /min (total flow rate of 10 bottom blowing tuyeres). It started. As shown in Figure 6, slag formation progresses as the blowing progresses, but the top blowing is carried out in accordance with the top blowing bottom blowing program, which is set in consideration of the oxygen jet penetration ratio being 0.6 to 0.7 at point a. The lance height was set to 2.0m, and the oxygen flow rate was set to 2.0m.
When blowing was performed at a lower rate of 500Nm ³ /min, it was detected that the sludge strength index entered the slopping danger zone at time x, so the nitrogen gas flow rate for bottom blowing stirring was reduced.
Stirring of the steel bath was strengthened by increasing from 4 Nm ³ /min to 7 Nm ³ /min, and an action was taken so that the degree of oxidation of the slag and the steel bath approached equilibrium. As a result, the sludge intensity index reached a small peak and then followed a downward trend, leaving the slopping danger zone. At time x', the nitrogen gas flow rate for bottom blowing stirring was changed from 7 Nm ³ /min to the programmed flow rate of 4 Nm. It was returned to ³ /min. Then, at point b, according to the top blowing and bottom blowing program which was determined so that the oxygen jet penetration ratio would be 0.6 to 0.7, the height of the top blowing lance was set to 1.6 m, and blowing was continued according to the program. After that, the trend continued to be slightly excessively ^{sludged ,} but it entered the slopping danger zone again, so at point When the stirring of the bath was strengthened, the sludge strength index showed a slight slopping tendency near the peak, but after reaching the peak, the sludge strength index showed a downward trend, so the nitrogen gas flow rate for stirring was reduced at time x. The blowing was continued after returning to the programmed setting amount of 4Nm ³ /min.After that, the slag strength index changed in the direction of good slag formation, so the blowing was continued to 80% of the blowing process. At point c of 80% of the refining process, the height of the top blowing lance is 1.8 m and the amount of top blowing acid is adjusted according to the blowing program.
500Nm ³ /min, nitrogen gas flow rate for bottom-blowing stirring 8Nm ³ /
Min. soft blowing was carried out, but the condition remained completely within the zone of good slag formation, and blowing could be carried out without any problems such as slopping. After this, the blowing trajectory is corrected to increase the accuracy of the steel production target by analyzing the carbon concentration of the molten steel and measuring the temperature of the molten steel using a sublance. After blow-stopping, the top-blowing and bottom-blowing converter is horizontally tilted to prevent decarburization due to stirring of the bottom-blowing stirring gas, and wait until the results of the analysis of all components of the blow-stopping molten steel are obtained. Once the desired target value is reached, steel will be tapped. As a result of the above-mentioned blowing, the results shown in the table were obtained, and the T.Fe of the slag was
This not only contributes to improved yield, but also significantly reduces slopping frequency, allowing stable operation. 【table】

[Brief explanation of the drawing]

Figure 1 is a flow sheet showing the operational procedure of the present invention, Figure 2 is a basic model of blowing, and Figure 3 shows the relationship between the depth of the steel bath when it is stationary and the steel bath when oxygen jet is blown. Figure 4 is an explanatory diagram of a system that detects changes in slag production during blowing and controls slag production, and Figure 5 is a comparison between the magnitude of the wave height index and the slag production in the converter. FIG. 6 is an explanatory diagram showing an example of a top-bottom blowing program and slag-making control based on slag formation detection. 1...Charging, 2...Pre-charging of auxiliary raw materials, 3...Blowing start, 4...Height of top blowing lance, top blowing oxygen flow rate, bottom blowing gas flow rate, setting and changing of auxiliary raw materials, 5...Blowing Finished, 6... Temperature measurement/sampling, 7... Steel tapping, 11...
Top blowing combined converter with bottom blowing, 12...Top blowing lance, 13...Crystal oscillation accelerometer, 14...Demodulator, 15...Waveform converter, 16...Recorder, 17...Process computer, 18...Top blowing oxygen flow rate setting device , 19...molten steel, 2
0...formed slag, 21...bottom blowing tuyere,
22...Gas piping.

Claims (1)

[Claims] 1. When melting high carbon steel in a top-blowing/bottom-blowing converter; during the blowing period from the start of blowing to 60 to 80% of the total blowing period, the oxygen jet penetration ratio L from the top blowing lance is /L ₀ is in the range of 0.6 to 0.7, and the amount of stirring gas blown from the bottom blowing tuyere is set to be in the range of gas injection amount corresponding to 50 to 70% of the maximum injection amount. Set the top blowing bottom blowing program and blow it; in the blowing period after 60 to 80% of the total blowing period has passed, the oxygen jet penetration ratio L/L ₀ from the top blowing lance will be 0.3. ~0.4, and the amount of stirring gas blown from the bottom blowing tuyere to the maximum blown amount.
A top blowing bottom blowing program is set and blowing is carried out according to a model in which the stirring gas blowing amount range corresponds to 80 to 100%; Changes in the slag condition as the smelting time progresses are detected by measuring the motion acceleration of the vibration acceleration detector charged in the converter, which is caused by the movement of the slag in the furnace. A method for melting high carbon steel using a converter with top-blowing and bottom-blowing, which comprises modifying the top-blowing and bottom-blowing program by adjusting the amount of stirring gas blown from the bottom-blowing tuyeres in accordance with the detection results. .