Method for stably controlling superheat degree of tundish

Abstract

The invention discloses a method for stably controlling the superheat degree of a tundish. The method for stably controlling the superheat degree of the tundish comprises the steps that the grades of steel ladles are classified finely, and temperature compensation is conducted on the steel ladles of different grades and different refining durations, so that the superheat degree of the tundish can be stably controlled when the steel ladles of different types are used. According to the method provided by the invention, the steel ladles with similar states are converted into one class, and temperature compensation is carried out on different classes of steel ladles when the steel ladles are in a converter, an argon station and a refining station, so that stable control on the superheat degree of the tundish is realized.

Description

Technical Field

[0001] The invention relates to the technical field of metallurgy, in particular to a method for stably controlling the superheat of a tundish. Background Art

[0002] In the production process, the superheat of molten steel in the continuous casting tundish is of great significance to the quality of molten steel and the stable and smooth production. There are many factors affecting the control of molten steel superheat, among which the influence of the ladle state on the superheat of molten steel is particularly critical. At present, there are mainly the following problems in the control of molten steel superheat in the tundish:

[0003] (1) The hit rate of tundish temperature (superheat 15-35°C) is as low as only about 70%.

[0004] (2) Low or high temperatures are prone to occur, resulting in low-temperature dead flow or high-temperature steel leakage problems in continuous casting. Summary of the invention

[0005] The purpose of the present invention is to overcome the defects of the above-mentioned prior art and provide a method for stably controlling the superheat of the tundish.

[0006] The present invention provides a method for stably controlling the superheat of a tundish, which comprises: sub-classifying the grades of ladles, and performing temperature compensation for ladles of different grades and different refining times, so as to achieve stable control of the superheat of the tundish when using different types of ladles.

[0007] The present invention has the following beneficial effects:

[0008] The present invention provides a method for stably controlling the superheat of a tundish, which comprises: sub-classifying the grades of ladles, and performing temperature compensation for ladles of different grades and different refining times, so as to achieve stable control of the superheat of the tundish when using different types of ladles. The above method classifies ladles with similar ladles into one category, and performs temperature compensation for ladles of different categories at the converter, argon station and refining exit station, so as to achieve stable control of the superheat of the tundish. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments are briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without creative work.

[0010] Figure 1 The bar chart shows the superheat hit rate of the tundish before and after improvement. DETAILED DESCRIPTION

[0011] In order to make the purpose, technical scheme and advantages of the embodiments of the present invention clearer, the technical scheme in the embodiments of the present invention will be described clearly and completely below. If the specific conditions are not specified in the embodiments, they are carried out according to conventional conditions or conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments used is not specified, they are all conventional products that can be purchased commercially.

[0012] A method for stably controlling the superheat of a tundish provided in an embodiment of the present invention is described in detail below.

[0013] An embodiment of the present invention provides a method for stably controlling the superheat of a tundish, which includes: sub-classifying the grades of ladles, and performing temperature compensation for ladles of different grades and different refining times, so as to achieve stable control of the superheat of the tundish when using different types of ladles.

[0014] During the production process, the superheat of molten steel in the continuous casting tundish is of great significance to the quality of molten steel and the stable and smooth production. There are many factors that affect the control of molten steel superheat, among which the influence of the ladle state on the superheat of molten steel is particularly critical. However, during the use of the ladle, its usage state, such as the time from the ladle pouring steel to the time when the ladle is filled with molten steel again, the number of times the ladle is used, etc., causes different ladles to have different temperatures after pouring molten steel. If unified classification and planning are not performed, it will cause great fluctuations in the superheat of the tundish. The method provided by the present invention classifies ladles with similar ladle states into one category, performs temperature compensation on different categories of ladles at the converter, argon station and refining station, so as to achieve stable control of the superheat of the tundish.

[0015] In an optional embodiment, the standard for subdividing the ladle grades according to the time from the ladle pouring steel to the ladle being filled with molten steel again is shown in the following table:

[0016]

[0017] The main functions of the ladle include holding molten steel, transporting molten steel and refining outside the furnace. The ladle is an important equipment in the steelmaking process, which is mainly used to hold and transport molten steel and part of the slag.

[0018] The composition structure of the ladle includes the boiler steel plate shell, the refractory lining and the sliding nozzle control mechanism. When the ladle is filled with molten steel, the steel plate shell and the refractory lining have an endothermic effect on the molten steel, causing the temperature of the molten steel in the ladle to drop. The lower the temperature of the ladle shell and the refractory lining, the longer the heat absorption process of the molten steel, the greater the heat absorbed, and the faster the temperature of the molten steel drops.

[0019] The time from pouring steel to refilling molten steel in the ladle determines the temperature of the ladle shell and refractory lining. The longer the time from pouring steel to refilling molten steel, the lower the temperature of the ladle itself, and the more obvious the temperature drop of molten steel in the subsequent use process. In order to distinguish the impact of the ladle on the temperature drop of molten steel, the ladle is graded and controlled according to the time from pouring steel to refilling molten steel in the ladle in combination with the actual production and operation of the ladle.

[0020] In addition, the residual slag / steel in the ladle, i.e. "bottom of ladle", also absorbs heat for the molten steel poured into the ladle. The more bottom of ladle, the greater the heat absorption and the more obvious the temperature drop of molten steel. Therefore, the ladle cannot be simply graded based on the time from pouring steel to refilling molten steel. At the same time, the ladle bottom situation should be combined to further standardize and improve on the basis of the previous classification. Thus, the ladle classification and degrading standard of "time from pouring steel to refilling molten steel + ladle usage" is formed.

[0021] In summary, the ladle plays a vital role in the steelmaking process. It is not only a means of transportation, but also a key equipment for refining outside the furnace. It is of great significance to improve the quality and production efficiency of steel.

[0022] In an optional embodiment, the invention further comprises: the ladle is downgraded according to the usage of the ladle, and the classification standard is shown in the following table:

[0023]

[0024] In the above ladle downgrading process, the downgrading method is as follows: if the A-type ladle has a bottom weight of 0.5 to 1 ton, it will be downgraded by 2 levels to a C-type ladle; if the A-type ladle has a bottom weight of 1 to 2 tons, it will be downgraded by 3 levels to a D-type ladle; if the A-type ladle has a bottom weight of more than 2 tons, it will be downgraded by 4 levels to an E-type ladle; if the F-type ladle has a bottom weight of 1 to 2 tons, it will be downgraded by 3 levels, but the highest downgrade is H-type, then it is judged as an H-type ladle.

[0025] In an optional embodiment, the temperature compensation for different grades of ladles is shown in the following table:

[0026]

[0027] The temperature control system of the steel smelting manufacturing standard is formulated based on the Class A ladle. Compared with the Class A ladle, the subsequent ladle absorbs heat for a longer time and absorbs more heat, resulting in a greater temperature drop of the molten steel. In order to offset this part of the temperature drop of the molten steel, it is necessary to compensate (increase) the tapping temperature. In order to make the temperature compensation fully and effectively play a role, the temperature compensation is carried out in stages. First, compensation is made during the tapping of the converter. The temperature compensation of the converter tapping can quickly offset the heat absorption on the ladle surface. In the subsequent molten steel treatment process, the refractory will gradually absorb heat. If the temperature compensation is not performed in the subsequent process, the molten steel will have a significant temperature drop on the continuous casting platform and during the casting process, resulting in a low temperature in the tundish. Therefore, it is necessary to further perform temperature compensation during the subsequent refining station. The above temperature compensation system is formulated based on production tracking.

[0028] In an optional embodiment, temperature compensation for ladles with different refining times includes: compensating the converter tapping temperature by a maximum of 18°C.

[0029] In an optional embodiment, temperature compensation for ladles with different refining times also includes: when LF refining time is greater than 50 minutes, the LF refining outlet temperature compensation increases by 1 level for every additional 5 minutes; after the LF refining outlet temperature compensation increases to level A, the LF refining outlet temperature of the continuous casting furnace decreases by 1°C for every additional 5 minutes of LF refining time, the LF refining outlet temperature of the continuous casting furnace can decrease by up to 5°C, and the LF refining outlet temperature of the open casting furnace does not decrease.

[0030] In an optional embodiment, temperature compensation for ladles with different refining times includes: using a Class F ladle, the refining time must be ≥ the lower limit of the standard time + 10 minutes.

[0031] In an optional embodiment, temperature compensation for ladles with different refining times includes: G and H type ladles and ladles downgraded to G and H type ladles must be processed in a LF furnace when used for the first time.

[0032] The present invention will be further described below in conjunction with the embodiments.

[0033] Example 1

[0034] An embodiment of the present invention provides a method for stably controlling the superheat of a tundish, comprising the following steps:

[0035] 1. To produce 45 steel, the ladle used is “30 minutes from the time the ladle finishes pouring steel to the time it is filled with molten steel again”, the ladle is clean and has no bottom, and is judged to be Class A based on the condition of the ladle.

[0036] Ladle Classification Technology

[0037]

[0038]

[0039] 2. Type A tundish is used to produce 45 steel, and the LF refining time is 60 minutes. According to the temperature compensation system, the refining outlet temperature is reduced by 2°C.

[0040] Temperature compensation system

[0041]

[0042]

[0043] The result is: the superheat of the tundish is 30℃ and the superheat of the tundish is hit.

[0044] Example 2

[0045] 1. To produce 45 steel, the ladle used is "the time from the ladle pouring steel to the ladle filling with molten steel again is 30 minutes", and the ladle bottom is 1.2t. According to the condition of the ladle, the ladle is judged to be Class D.

[0046] Ladle Classification Technology

[0047]

[0048]

[0049] 2. Type A tundish is used to produce 45 steel, and the LF refining time is 50 minutes. According to the temperature compensation system, the converter steel output temperature is compensated by 8°C and the refining station outlet temperature is compensated by 3°C.

[0050] Temperature compensation system

[0051]

[0052]

[0053] The result is: the superheat of the tundish is 32℃, and the superheat of the tundish is hit.

[0054] Example 3

[0055] 1. To produce 45 steel, the ladle used is "the spare ladle after the baking time of the medium and small repair ladle is over (first use)", the ladle is clean and has no bottom, and the ladle is judged as Class G according to its condition.

[0056] Ladle Classification Technology

[0057]

[0058]

[0059] 2. The production of 45 steel uses G-type tundish, and the LF refining time is 50 minutes. According to the temperature compensation system, the converter steel output temperature is compensated by 15°C, and the refining station outlet temperature is compensated by 8°C.

[0060] Temperature compensation system

[0061]

[0062]

[0063] The result is: the superheat of the tundish is 25℃, and the superheat of the tundish hits the target.

[0064] Example 4

[0065] 1. To produce 45 steel, the ladle used is "the spare ladle after the baking time of the medium and small repair ladle is over (the second use)", the time from pouring the steel to filling the ladle with molten steel again is 80 minutes, and the ladle has no bottom. According to the condition of the ladle, it is judged to be Class E.

[0066] Ladle Classification Technology

[0067]

[0068]

[0069] 2. The production of 45 steel uses E-type tundish, and the LF refining time is 65 minutes. According to the temperature compensation system, the converter steel output temperature is compensated by 10°C, and the refining station outlet temperature is compensated by 2 (5-3)°C.

[0070] Temperature compensation system

[0071]

[0072] The result is: the superheat of the tundish is 28℃, and the superheat of the tundish is hit.

[0073] Comparative Example 1

[0074] The steps are similar to those in Example 1, except that: there is 2.5t of bottom clump in the ladle, but no downgrading management is performed on the bottom clump. The cooling and solidification of the residual slag / steel in the ladle, i.e., "bottom clump", absorbs heat for the molten steel poured into the ladle. The more bottom clumps there are, the greater the amount of heat absorbed, and the more obvious the temperature drop of the molten steel. If the bottom clump is not downgraded, and the smelting is still carried out according to the original temperature, the original heat of the molten steel is the same as in Example 1, but the heat loss in the process increases, and the temperature drop of the molten steel is greater than that in Example 1.

[0075] The result is: the superheat of the tundish is 14℃ and the superheat of the tundish is not hit.

[0076] Comparative Example 2

[0077] The steps are similar to those in Example 1, except that: a spare bag (for the second use) is used after the baking time of the medium repair bag is over, but no downgrade control is performed on the second use of the medium repair bag. The initial refractory temperature of the medium repair bag is room temperature. After being used once, the refractory of the ladle absorbs a certain amount of heat, but because the turnover is only one time and the steel filling time is short, the middle part of the refractory has not yet been "heated through" and the temperature is relatively low. There will be an obvious heat absorption process when the molten steel is filled for the second time, until the refractory is completely "heated through". If the second use of the medium repair bag is not downgraded and controlled, smelting is still carried out according to the original temperature. In this way, the original heat of the molten steel is the same as in Example 1, but the subsequent temperature drop is greater than that in Example 1.

[0078] The result is: the superheat of the tundish is 20℃ and the superheat of the tundish is hit.

[0079] Comparative Example 3

[0080] The steps are similar to those in Example 1, except that the LF refining time is 80 minutes, but no compensation control is performed on the refining time. The longer the refining time, the longer the heat absorption time of the ladle, the more heat the refractory material of the ladle absorbs, the higher the temperature of the refractory material, the better the insulation effect of the molten steel in the ladle in the subsequent process, and the smaller the temperature drop of the molten steel in the ladle. If the temperature compensation control is not performed on the molten steel refined for a long time, the smelting is still carried out according to the original temperature, so that the original molten steel heat is the same as in Example 1, but the subsequent temperature drop is smaller than that in Example 1.

[0081] The result is: the superheat of the tundish is 36℃ and the superheat of the tundish is not hit.

[0082] Comparative Example 4

[0083] The steps are similar to those in Example 1, except that a D-type tundish is used, but the converter tapping temperature compensation is 12°C and the LF refining outlet temperature compensation is 10°C, which is higher than the existing compensation temperature system. In this way, the original molten steel heat is higher than that in Example 1, but the subsequent temperature drop is the same as that in Example 1.

[0084] The result is: the superheat of the tundish is 36℃ and the superheat of the tundish is not hit.

[0085] By analyzing the results of the embodiments of the present invention and the comparative examples, it can be seen that:

[0086] (1) Ladles are graded based on the time from pouring steel to refilling with molten steel. At the same time, the ladle bottoming and initial condition are combined to form the "time from pouring steel to refilling with molten steel + ladle usage" to form a ladle grading and downgrading standard that classifies ladles with similar conditions.

[0087] (2) By making temperature corrections for different types of ladles at the converter, argon station and refining station, as well as for ladles with long refining time, the temperature of the molten steel in the ladles can be effectively stabilized under various conditions in each link, thereby improving the temperature hit rate of the tundish.

[0088] Figure 1 It is a bar graph of the superheat hit rate of the tundish before and after improvement (the scheme before improvement is the original scheme, and the scheme after improvement is the scheme provided by the embodiment of the present invention). It can be seen that after the improvement, that is, when the scheme provided by the embodiment of the present invention is used to control the stability of the tundish, the superheat hit rate of the tundish can be greatly improved regardless of whether it is ordinary steel or special steel, and when using ladles of different types and different refining times, the superheat of the tundish can be stably controlled, thereby improving the pouring efficiency and the quality of the steel.

[0089] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for stably controlling the superheat of a tundish, characterized in that: It includes: The steel ladle grades are sub-classified, and temperature compensation is performed for ladles of different grades and different refining times, so that the superheat of the tundish can be stably controlled when using different types of ladles.

2. The method according to claim 1, characterized in that The following table shows the subdivision standards for ladle grades based on the time from when the ladle is finished pouring steel to when it is filled with molten steel again:

3. The method according to claim 2, characterized in that Also includes: The following table shows the downgrading classification standards for steel ladles according to their usage:

4. The method according to claim 1, characterized in that The temperature compensation for different grades of ladles is shown in the following table:

5. The method according to claim 1, characterized in that Temperature compensation for ladles with different refining times includes: converter tapping temperature compensation up to 18°C.

6. The method according to claim 1, characterized in that Temperature compensation for ladles with different refining times also includes: when LF refining time is greater than 50 minutes, the LF refining outlet temperature compensation increases by 1 level for every additional 5 minutes; after the LF refining outlet temperature compensation increases to Level A, the LF refining outlet temperature of the continuous casting furnace decreases by 1°C for every additional 5 minutes of LF refining time, and the LF refining outlet temperature of the continuous casting furnace can decrease by up to 5°C, and the LF outlet temperature of the open casting furnace does not decrease.

7. The method according to claim 1, characterized in that Temperature compensation for ladles with different refining times includes: When using Class F ladles, the refining time must be ≥ the lower limit of the standard time + 10 minutes.

8. The method according to claim 1, characterized in that Temperature compensation is performed for ladles with different refining times, including: G and H ladles, as well as ladles downgraded to G and H ladles that must be treated in LF furnaces when used for the first time.

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