Ladle temperature control method in thin slab casting process

Abstract

The invention discloses a ladle temperature control method in a thin slab casting process, and belongs to the field of steel production, the control method comprises the following steps: (1) steel ladle grading setting: the ladle is an A-grade ladle when the idle stop time is less than 180min, the ladle is a B-grade ladle when the idle stop time is 180-240min, the ladle is a C-grade ladle when the idle stop time is greater than 240min, and a cold repair ladle is a new online ladle as a D-grade ladle; (2) converter stage: carrying out temperature control according to steel ladle grading; and (3) an LF refining stage: controlling the refining period and the desulfurization temperature according to steel ladle grading until the steel grade is higher than the liquidus temperature. Compared with the prior art, the power consumption of the refining furnace is reduced to the maximum extent by controlling the steel ladles in a grading manner and making the converter and refining through the process operation of different grades of steel ladle temperatures, and meanwhile, the temperature stability control of the tundish is improved.

Description

Technical Field

[0001] The invention relates to a steel production method, in particular to a tundish temperature control method suitable for a thin slab casting process. Background Art

[0002] Continuous casting production requires a stable molten steel temperature and a certain degree of superheat in the tundish. It takes more than an hour from the addition of molten iron into the steelmaking converter to the completion of continuous casting. The path that each furnace of molten steel goes through has many changes. Each steel grade also has different requirements for the composition of molten steel and the addition of raw and auxiliary materials. Therefore, the molten steel temperature in each link of continuous casting production is dynamic, and the target temperature of each link also needs to be dynamically adjusted.

[0003] Technical personnel in this field have done a lot of work on the temperature control of the tundish. For example, in "A temperature control system and control method for molten steel process in steelmaking based on self-learning" (CN201810957032.9), the system includes a workstation exit temperature calculation system, an L3 plan reception performance upload system, a workstation target temperature control system and a molten steel temperature forecasting device. The system calculates the exit temperatures of the combined converter, argon blowing station, refining furnace and vacuum treatment furnace, as well as the target temperature of the continuous casting tundish. The workstation adjustment coefficient self-learning function of the workstation target temperature control system can automatically learn the parameter values ​​that need to be adjusted in different situations due to deviations between the plan and the actual situation based on historical data to adapt to the dynamic changes in the molten steel temperature.

[0004] However, in actual production, the steel liquid plan pre-scheduling adopts a fixed casting cycle, which has a large deviation from the actual situation, resulting in the inability to accurately connect the target temperature calculation and actual control, and unable to guide production well. The thin slab casting process requires that the temperature control range of the tundish is only ±5℃, the qualified rate of the tundish temperature is 90%, and the power consumption of the refining furnace reaches 42Kwh / t. The tundish temperature is too high, resulting in a speed reduction, causing the final rolling temperature to be inconsistent with the modified specifications. The tundish temperature is too low, resulting in excess steel in the molten steel casting. Therefore, this process often requires close coordination between the refining site operators, the continuous casting central control personnel, and the production scheduling personnel to manually determine the target steel liquid outlet temperature, and then decide whether to leave the station. Sometimes, in order to ensure the smooth progress of continuous casting, it is necessary to leave the station and send it to the continuous casting platform under the condition that the molten steel temperature is not met, which will have a certain impact on the quality of the ingot and the production rhythm, and may even cause production accidents such as broken casting and steel leakage. The main reason for the above problems is that the equipment status such as the ladle usage status and the steel outlet status is abnormal, resulting in the molten steel temperature being too high or too low, which cannot meet the normal casting of continuous casting.

[0005] Therefore, there is an urgent need for a new solution to solve this technical problem, to tackle the temperature control technology in the refining stage, to improve the qualified rate of the middle package temperature, and to minimize the refining power consumption. Summary of the invention

[0006] The technical task of the present invention is to address the deficiencies of the above-mentioned prior art and provide a ladle temperature control method for a thin slab casting process. In the refining stage, the ladle condition and idle time are graded and controlled, and the optimal desulfurization stirring temperature is set to ensure the heat storage of the ladle while minimizing the power consumption cost of the LF furnace to achieve stable casting of thin slabs.

[0007] The technical solution of the present invention to solve the technical problem is: a method for controlling the temperature of a ladle in a thin slab casting process, characterized in that the control method comprises:

[0008] (1) Ladle classification setting: A-grade ladles are those with idle time less than 180 minutes, B-grade ladles are those with idle time between 180 and 240 minutes, C-grade ladles are those with idle time greater than 240 minutes, and D-grade ladles are those with cold repair and new ladle.

[0009] (2) Converter stage: Temperature control according to ladle classification:

[0010] Grade A ladle, converter steel temperature 1590℃-1610℃;

[0011] Grade B ladle, converter steel temperature 1610℃-1620℃;

[0012] C-grade ladle, converter steel temperature 1620℃-1630℃;

[0013] D-grade ladle, converter steel temperature ≥ 1630℃;

[0014] (3) LF refining stage, controlled by ladle classification:

[0015] A and B grade ladle: refining cycle is controlled at 50-60min, desulfurization temperature is controlled at 40-60℃ higher than liquidus temperature of steel grade, and large stirring is controlled in two times;

[0016] C and D grade ladles: refining cycle is controlled at 5-70min, desulfurization temperature is controlled at 50-80℃ higher than liquidus temperature of steel grade, and controlled by three large stirrings.

[0017] Furthermore, in the converter stage: the ladle bottom blowing argon flow rate and steel release time are carried out according to the ladle classification process:

[0018] A-grade ladle, converter discharge temperature 1590℃-161℃, ladle bottom blowing argon flow rate during discharge process is set to 30-50m 3 / h, the steel-releasing time is controlled at 6-7 minutes, and after the steel-releasing is completed, the ladle is stirred for 2-3 minutes with argon bypass;

[0019] B-grade ladle, converter discharge temperature 1610℃-1620℃, ladle bottom blowing argon flow rate during discharge process is set to 40-60m 3 / h, the steel-releasing time is controlled at 5-6 minutes, and after the steel-releasing is completed, the ladle is bypassed with argon gas and stirred for 2-3 minutes;

[0020] C-grade ladle, converter discharge temperature 1620℃-1630℃, ladle bottom blowing argon flow rate during discharge process is set to 50-70m 3 / h, the steel release time is controlled at 5-6 minutes, and the argon flow rate of the ladle is 60-80m 3 / h for 3-5 minutes;

[0021] D-grade ladle, converter discharge temperature ≥ 1630℃, ladle bottom blowing argon flow rate during discharge process is set to 60-80m 3 / h, steel release time is controlled to be ≤5 minutes, after steel release, the argon gas flow rate of the ladle bottom is 60-80m 3 / h for 3-5 minutes;

[0022] Furthermore, the specific parameters for the two large stirring control of grade A and B ladles are:

[0023] The first large stirring, the temperature is 60-70℃ higher than the liquidus temperature, the large stirring time is 6-7min, after the large stirring time is completed, the ladle argon is adjusted to 40-50m 3 / h, temperature measurement operation, when the temperature rises to 50-60℃ higher than the liquidus temperature, the second large stirring is carried out;

[0024] The second large stirring, the temperature is 50-60℃ higher than the liquidus temperature, the large stirring time is 3-5min, after the large stirring time is completed, the argon gas in the ladle is adjusted to 30-40m 3 / h, temperature measurement operation, according to the temperature rise to above the liquidus temperature 30-40 ℃.

[0025] Furthermore, the specific parameters for the three-stage large stirring control of C and D grade ladles are:

[0026] The first bypass stirring temperature is 70-80℃ higher than the liquidus line, the stirring time is 8min, and after the stirring time is over, the argon gas in the ladle is adjusted to 50-60m 3 / h, temperature measurement operation, when the temperature rises to 60-70℃ above the liquidus temperature, the second large stirring is carried out;

[0027] The second large stirring, the temperature is 60-70℃ higher than the liquidus temperature, the large stirring time is 5min, after the large stirring time is completed, the argon gas in the ladle is adjusted to 40-50m 3 / h, temperature measurement operation, when the temperature rises to 50-60℃ higher than the liquidus temperature, the third large stirring is carried out;

[0028] The third large stirring, the temperature is 50-60℃ higher than the liquidus temperature, the large stirring time is 3min, after the large stirring time is completed, the argon gas in the ladle is adjusted to 30-40m 3 / h, temperature measurement operation, according to the temperature rise to above the liquidus temperature 30-40 ℃.

[0029] Compared with the prior art, the present invention has the following outstanding beneficial effects:

[0030] 1. The present invention controls the ladle by grade, formulates the temperature process operation of the converter and refining by different grades of ladles, reduces the power consumption of the refining furnace to the maximum extent, and improves the stable control of the middle ladle temperature;

[0031] 2. The converter adopts different steel discharge temperatures and ladle soft blowing operations according to the different grades of ladle conditions, so as to fully preheat the ladle refractory materials, maximize the refining station temperature and reduce power consumption, and reduce the converter terminal temperature control pressure to prevent over-blowing and erosion of the furnace lining refractory materials;

[0032] 3. The refining furnace uses the desulfurization and large stirring conditions to improve the heat storage of the ladle, increase the qualified rate of the middle ladle temperature, and minimize the refining power consumption. DETAILED DESCRIPTION

[0033] The present invention is further described below in conjunction with specific implementation modes.

[0034] For the purpose of the following detailed description, it should be understood that the present invention may take various alternative variations and step sequences unless explicitly indicated to the contrary. In addition, except in any operating examples or where otherwise indicated, all numbers expressing, for example, the amounts of ingredients used in the specification and claims should be understood in all cases as modified by the term "about". At the very least, and without attempting to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter should at least be interpreted in terms of the number of reported significant digits and by applying ordinary rounding techniques.

[0035] Notwithstanding that the numerical ranges and parameters setting forth the broad scope of the invention are approximations, the numerical values ​​set forth in the specific examples are reported as precisely as possible. Any numerical value, however, inherently contains certain errors necessarily resulting from the standard deviation found in their respective testing measurements.

[0036] It should also be understood that any numerical range stated herein is intended to include all subranges subsumed therein. For example, a range of "1 to 10" is intended to include all subranges between (and including) the stated minimum value of 1 and the stated maximum value of 10, that is, having a minimum value equal to or greater than 1 and a maximum value equal to or less than 10.

[0037] In this application, unless otherwise specifically stated, the use of the singular includes the plural and the plural includes the singular. In addition, in this application, unless otherwise specifically stated, the use of "or" means "and / or", even if "and / or" may be explicitly used in some cases. Further, in this application, unless otherwise specifically stated, the use of "a" or "an" means "at least one / kind". For example, "a" first material, "a" coating composition, etc. refer to one or more items in any of these items.

[0038] Continuous casting production requires stable molten steel temperature and tundish superheat. The molten steel temperature in each link of continuous casting production is dynamic, and the target temperature of each link must also be adjusted dynamically. The system target temperature calculation must match the actual production, but currently there are abnormal equipment conditions such as ladle usage status and tapping conditions, which cause the outlet molten steel temperature to be too high or too low, which cannot meet the normal casting of continuous casting.

[0039] The invention relates to a method for controlling the temperature of a ladle in a thin slab casting process.

[0040] 1. Ladle classification setting

[0041] Firstly, a graded control system is formulated for the condition of each ladle and its idle time. The graded setting method is as follows: for normal turnover ladles, the idle time is calculated from the time the ladle is placed after continuous casting. The ladles are divided into grades according to the length of the idle time. The idle time is <180min for Grade A ladles, 180-240min for Grade B ladles, >240min for Grade C ladles, and the cold-repaired ladles and the newly-put-on-line ladles are Grade D ladles.

[0042] 2. Converter stage

[0043] Temperature control by ladle classification:

[0044] A-grade ladle, converter discharge temperature 1590℃-161℃, ladle bottom blowing argon flow rate during discharge process is set to 30-50m 3 / h, the steel-releasing time is controlled at 6-7 minutes, and after the steel-releasing is completed, the ladle is stirred for 2-3 minutes with argon bypass;

[0045] B-grade ladle, converter discharge temperature 1610℃-1620℃, ladle bottom blowing argon flow rate during discharge process is set to 40-60m 3 / h, the steel-releasing time is controlled at 5-6 minutes, and after the steel-releasing is completed, the ladle is bypassed with argon gas and stirred for 2-3 minutes;

[0046] C-grade ladle, converter discharge temperature 1620℃-1630℃, ladle bottom blowing argon flow rate during discharge process is set to 50-70m 3 / h, the steel release time is controlled at 5-6 minutes, and the argon flow rate of the ladle is 60-80m 3 / h for 3-5 minutes;

[0047] D-grade ladle, converter discharge temperature ≥ 1630℃, ladle bottom blowing argon flow rate during discharge process is set to 60-80m 3 / h, steel release time is controlled to be ≤5 minutes, after steel release, the argon gas flow rate of the ladle bottom is 60-80m 3 / h for 3-5 minutes;

[0048] According to different ladle conditions, different steel discharge temperatures and ladle soft blowing operations are adopted to fully preheat the ladle refractory materials, while maximizing the refining station temperature to reduce power consumption, while reducing the converter terminal temperature control pressure to prevent over-blowing from causing erosion of the furnace lining refractory materials.

[0049] 3.LF refining stage

[0050] Based on the existing LF refining process, the following adjustments were made according to ladle classification:

[0051] (1) Grade A and B ladle:

[0052] The refining cycle is controlled at 50-60 minutes, the desulfurization temperature is controlled at 40-60℃ higher than the liquidus temperature of the steel grade, and the stirring is controlled in two steps:

[0053] The first large stirring, the temperature is 60-70℃ higher than the liquidus temperature, the large stirring time is 6-7min, after the large stirring time is completed, the ladle argon is adjusted to 40-50m 3 / h, measure the temperature, and when the temperature rises to 50-60℃ above the liquidus temperature, perform the second large stirring.

[0054] The second large stirring, the temperature is 50-60℃ higher than the liquidus temperature, the large stirring time is 3-5min, after the large stirring time is completed, the argon gas in the ladle is adjusted to 30-40m 3 / h, temperature measurement operation, when the temperature rises to 30-40℃ higher than the liquidus temperature, the ladle has sufficient heat storage, and the temperature drop rate of the molten steel is 0.7-1.0℃ / min.

[0055] (2) C and D grade ladle

[0056] The refining cycle is controlled at 5-70min, the desulfurization temperature is controlled at 50-80℃ higher than the liquidus temperature of the steel grade, and the stirring is controlled in three steps:

[0057] The first bypass stirring temperature is 70-80℃ higher than the liquidus line, the stirring time is 8min, and after the stirring time is over, the argon gas in the ladle is adjusted to 50-60m 3 / h, temperature measurement operation, when the temperature rises to 60-70℃ above the liquidus temperature, the second large stirring is carried out;

[0058] The second large stirring, the temperature is 60-70℃ higher than the liquidus temperature, the large stirring time is 5min, after the large stirring time is completed, the argon gas in the ladle is adjusted to 40-50m 3 / h, measure the temperature, and when the temperature rises to 50-60℃ above the liquidus temperature, perform the third large stirring.

[0059] The third large stirring, the temperature is 50-60℃ higher than the liquidus temperature, the large stirring time is 3min, after the large stirring time is completed, the argon gas in the ladle is adjusted to 30-40m 3 / h, temperature measurement operation, when the temperature rises to 30-40℃ higher than the liquidus temperature, the ladle has sufficient heat storage, and the temperature drop rate of the molten steel is 0.7-1.0℃ / min.

[0060] After the above ladle argon stirring operation, the outlet temperature of the refining furnace is controlled at a superheat of 25-35℃, and the temperature of the middle ladle is stabilized at a superheat of 15-25℃.

[0061] In order to better compare the method of the present application with the prior art, a comparative test was conducted. There was no statistical difference in the distribution of ladle conditions and idle time between the control group and the experimental group.

[0062] The control group, 50 furnaces, did not set the ladle classification, the control methods of the converter stage and the LF refining stage were all the B-grade ladle control methods in this application.

[0063] For the experimental group, 50 furnaces, the control methods of ladle classification, converter stage and LF refining stage were set from above.

[0064] There was no statistical difference in the distribution of ladle condition and idle time between the control group and the experimental group.

[0065] The experimental results show that, with the tundish temperature control range of ±5℃ as the qualified standard, the qualified rate of the tundish temperature in the control group is 90%, and the average power consumption of the refining furnace is 42.22Kwh / t; the qualified rate of the tundish temperature in the experimental group is 96%, and the average power consumption of the refining furnace is 38.17Kwh / t.

[0066] It can be seen from the above results that the present invention controls the ladles by grade and formulates temperature process operations of converters and refining ladles of different grades according to the conditions of ladles of different grades, thereby minimizing the power consumption of the refining furnace and improving the stable control of the temperature of the middle ladle, thereby providing good conditions for thin slab casting.

[0067] It should be noted that the specific embodiments of the present invention have been described in detail. For those skilled in the art, various obvious changes to the present invention without departing from the spirit and scope of the present invention are within the protection scope of the present invention.

Claims

1. A method for controlling the temperature of a ladle in a thin slab casting process, characterized in that: Control methods include: (1) Ladle classification setting: A-grade ladles are those with idle time less than 180 minutes, B-grade ladles are those with idle time between 180 and 240 minutes, C-grade ladles are those with idle time greater than 240 minutes, and D-grade ladles are those with cold repair and new ladle. (2) Converter stage: Temperature control according to ladle classification: Grade A ladle, converter steel temperature 1590℃-1610℃; Grade B ladle, converter steel temperature 1610℃-1620℃; C-grade ladle, converter steel temperature 1620℃-1630℃; D-grade ladle, converter steel temperature ≥ 1630℃; (3) LF refining stage, controlled by ladle classification: A and B grade ladle: refining cycle is controlled at 50-60min, desulfurization temperature is controlled at 40-60℃ higher than liquidus temperature of steel grade, and large stirring is controlled in two times; C and D grade ladles: refining cycle is controlled at 5-70min, desulfurization temperature is controlled at 50-80℃ higher than liquidus temperature of steel grade, and controlled by three large stirrings.

2. The method for controlling the temperature of the ladle in the thin slab casting process according to claim 1, characterized in that: Converter stage: steel discharge process is carried out according to ladle classification. Argon gas flow rate and steel discharge time at the bottom of the ladle: A-grade ladle, converter discharge temperature 1590℃-161℃, ladle bottom blowing argon flow rate during discharge process is set to 30-50m 3 / h, the steel-releasing time is controlled at 6-7 minutes, and after the steel-releasing is completed, the ladle is stirred for 2-3 minutes with argon bypass; B-grade ladle, converter discharge temperature 1610℃-1620℃, ladle bottom blowing argon flow rate during discharge process is set to 40-60m 3 / h, the steel-releasing time is controlled at 5-6 minutes, and after the steel-releasing is completed, the ladle is bypassed with argon gas and stirred for 2-3 minutes; C-grade ladle, converter discharge temperature 1620℃-1630℃, ladle bottom blowing argon flow rate during discharge process is set to 50-70m 3 / h, the steel release time is controlled at 5-6 minutes, and the argon flow rate of the ladle is 60-80m 3 / h for 3-5 minutes; D-grade ladle, converter discharge temperature ≥ 1630℃, ladle bottom blowing argon flow rate during discharge process is set to 60-80m 3 / h, steel release time is controlled to be ≤5 minutes, after steel release, the argon gas flow rate of the ladle bottom is 60-80m 3 / h for 3-5min.

3. The method for controlling the temperature of the ladle in the thin slab casting process according to claim 1, characterized in that: The specific parameters for the two-stage large stirring control of A and B grade ladles are: The first large stirring, the temperature is 60-70℃ higher than the liquidus temperature, the large stirring time is 6-7min, after the large stirring time is completed, the ladle argon is adjusted to 40-50m 3 / h, temperature measurement operation, when the temperature rises to 50-60℃ higher than the liquidus temperature, the second large stirring is carried out; The second large stirring, the temperature is 50-60℃ higher than the liquidus temperature, the large stirring time is 3-5min, after the large stirring time is completed, the argon gas in the ladle is adjusted to 30-40m 3 / h, temperature measurement operation, according to the temperature rise to above the liquidus temperature 30-40 ℃.

4. The method for controlling the temperature of the ladle in the thin slab casting process according to claim 1, characterized in that: The specific parameters for the three-stage large stirring control of C and D grade ladles are: The first bypass stirring temperature is 70-80℃ higher than the liquidus line, the stirring time is 8min, and after the stirring time is over, the argon gas in the ladle is adjusted to 50-60m 3 / h, temperature measurement operation, when the temperature rises to 60-70℃ above the liquidus temperature, the second large stirring is carried out; The second large stirring, the temperature is 60-70℃ higher than the liquidus temperature, the large stirring time is 5min, after the large stirring time is completed, the argon gas in the ladle is adjusted to 40-50m 3 / h, temperature measurement operation, when the temperature rises to 50-60℃ higher than the liquidus temperature, the third large stirring is carried out; The third large stirring, the temperature is 50-60℃ higher than the liquidus temperature, the large stirring time is 3min, after the large stirring time is completed, the argon gas in the ladle is adjusted to 30-40m 3 / h, temperature measurement operation, according to the temperature rise to above the liquidus temperature 30-40 ℃.