Method for setting final blowing temperature of converter

Abstract

To improve prediction accuracy of temperature drop of molten steel in a steel refining process, thereby reducing variation in prediction error, and to provide a method for determining a final blowing temperature (end-blowing temperature) of a converter with improved prediction accuracy.SOLUTION: A method includes: predicting temperature drop of molten steel from an end of blowing to a subsequent process reference time for each temperature-influencing factor using a predetermined influence function for each temperature-influencing factor, and calculating the predicted temperature drop value; when determining a final blowing temperature by adding the predicted temperature drop value to the temperature on the subsequent process reference time, for deoxidizer input as one of the temperature-influencing factors, comparing an input amount of the deoxidizer with a predetermined threshold for each deoxidizer to determine a group of deoxidation form; calculating in advance a temperature influence function for the temperature drop of molten steel for each determined group of deoxidation form; including the input amount of deoxidizer and an amount of free oxygen at the end of blowing of molten steel in the temperature-influencing factor on deoxidation; and calculating the predicted temperature drop value of molten steel based on the temperature-influencing factor and the temperature influence function according to the group of deoxidation form to determine the final blowing temperature of a converter.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a method for setting the blowing end temperature of a converter in a steel refining process. [Background technology]

[0002] The steelmaking process consists of a refining process and a casting process. The refining process is a process in which pig iron obtained in a blast furnace is adjusted to a specified composition and temperature to produce molten steel. In the refining process, the steel is usually blown in a converter to roughly adjust the main components such as carbon, and the components and temperature are finally adjusted in secondary refining. The molten steel with the specified composition is then continuously cast in the casting process to obtain steel slabs.

[0003] In the refining process, the blow end temperature (end-point temperature) in a converter is determined by predicting the temperature drop of molten steel so that the temperatures required for the subsequent processes of secondary refining and continuous casting are obtained. Examples of methods for predicting the blow end temperature in a converter are described in Patent Document 1 and Patent Document 2.

[0004] Patent Document 1 describes an approach to improve the accuracy of prediction of temperature drop during tapping by using a multiple regression model classified by the presence or absence of Al deoxidization. Patent Document 2 describes a method of predicting the temperature drop of molten steel due to heat storage in the ladle by heat transfer calculation, and setting the converter blowing end temperature by taking into account the variation in error in the prediction of the temperature drop when the same secondary refining equipment is used. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2013-112871 A [Patent Document 2] JP 2016-180127 A Summary of the Invention [Problem to be solved by the invention]

[0006] The blowing end temperature (end-point temperature) of the converter needs to be set in consideration of the temperature required for the subsequent processes such as secondary refining and continuous casting, and the temperature drop after the end of blowing in the converter. On the other hand, the blowing end temperature of the converter is required to be as low as possible from the viewpoints of reaction efficiency during blowing, refractory wear of the converter, energy saving, carbon neutrality, etc. In reality, when comparing the temperature drop predicted by the prediction methods described in Patent Documents 1 and 2 with the actual temperature drop, there is still a large error variance. Therefore, there is room to improve the prediction accuracy of the temperature drop of molten steel in the refining process and reduce the error variance.

[0007] In order to meet such demands, an object of the present invention is to improve the prediction accuracy of the temperature drop of molten steel in the steel refining process and to reduce the variation in prediction error, and to provide a method for setting the blowing end temperature (end-point temperature) of a converter with improved prediction accuracy. [Means for solving the problem]

[0008] The present inventors have conducted extensive research to achieve the above object and have obtained the following findings.

[0009] (a) The following three factors are considered to contribute to the temperature drop of molten steel after the end of blowing in a converter. (A) Heat of chemical reaction when oxygen in molten steel is deoxidized by deoxidizing materials such as Al and Si (a) Heat of dissolution of ferroalloys added for component adjustment and cooling (c) Heat dissipation that transfers to the refractory material in contact with the molten steel or to the atmosphere Among these, the heat of chemical reaction accompanying deoxidation (a) is relatively large, and has a large impact on the accuracy of temperature drop prediction. In addition, the reaction heat varies depending on the state of deoxidation, so it has a large impact on the accuracy of temperature drop prediction. Therefore, the study focused on the temperature drop caused by the heat of chemical reaction due to deoxidation.

[0010] (b) In the conventional prediction of the effect of deoxidation on temperature drop, for example, in Patent Document 1, the temperature drop is predicted by determining the effect coefficient on temperature drop for each of three cases: no Al addition, Al deoxidized without Si addition, and Al deoxidized with Si addition. However, when the inventors analyzed the variation in the predicted value of temperature drop, they found that the heat generation amount per added amount of Al and Si cannot be accurately estimated only by the presence or absence of Al addition. Since the deoxidation reaction depends on the amount of free oxygen in the molten steel at the end of blowing in the converter, they found that the accuracy of the temperature drop prediction can be improved by predicting the temperature drop taking into account the amount of free oxygen in the molten steel at the end of blowing in the converter.

[0011] (c) The effect on the temperature drop of molten steel differs depending on whether the deoxidizer such as Al undergoes a deoxidizing (oxidizing) reaction or simply dissolves. Therefore, it is important to determine whether the amount of deoxidizer added is insufficient or excessive compared to the amount of free oxygen (hereinafter referred to as the deoxidization form). In conventional technology, there is no clear criterion for this, which is thought to be one of the causes of the large variation in temperature drop predictions. Therefore, we have been studying the criterion for determining the deoxidization form. If the amount of deoxidizer added is small relative to the amount of free oxygen, the entire amount will be consumed for deoxidation, leaving excess free oxygen, i.e., the material will be left in an undeoxidized state. On the other hand, if the amount of deoxidizer added is large compared to the amount of free oxygen, a part of the added deoxidizer (up to an amount corresponding to the free oxygen) will be consumed for deoxidation, and the remainder will dissolve in the molten steel. When an excessive amount of deoxidizer is added compared to the amount of free oxygen, for example, if the deoxidizer is Al, it is an Al-killed state, and if the deoxidizer is Si, it is a Si-killed state. Also, if the deoxidizers are Al and Si, for example, a part of both deoxidizers will be consumed for deoxidation, and the remainder will dissolve in the molten steel, which is an Al-Si killed state.

[0012] That is, the deoxidation state is classified into groups according to the amount of free oxygen, either undeoxidized (a state in which the added deoxidizer is consumed for deoxidation and a significant amount of free oxygen remains) or deoxidized (a state in which part of the added deoxidizer is consumed for deoxidation). For example, when there are two types of deoxidizers, they are classified into two groups for each deoxidizer, resulting in four groups. When the deoxidizers are Al and Si, they are classified into four groups of deoxidization states: undeoxidized, Al killed (a state in which part of the added Al is consumed for deoxidation), Si killed (a state in which part of the added Si is consumed for deoxidation), and Al-Si killed (a state in which part of Al and Si are consumed for deoxidation).

[0013] (d) The effect of deoxidizers such as Al on the temperature drop of molten steel varies depending on whether they undergo a deoxidation (oxidation) reaction or simply dissolve. However, reactions in molten steel are complex, and it is difficult to stoichiometrically separate deoxidation reactions and dissolution reactions from the amount of free oxygen and the amount of deoxidizer added, and calculate for each individual charge. Therefore, the inventors have found that it is effective to set a threshold value (deoxidation threshold value) for the amount of deoxidizer added, and to statistically obtain an influence function (temperature influence function) that is a relationship between the temperature drop record and multiple influencing factors for each group, and use the function to estimate the temperature drop, taking into consideration that the amount of heat generated per amount of deoxidizer added is large when the amount of deoxidizer added is equal to or less than each threshold, and that the amount of heat generated per amount of deoxidizer added is small when the amount of deoxidizer added exceeds the threshold value, since a part of the surplus deoxidizer dissolves in the molten steel.

[0014] The threshold value may be set according to the actual amount of free oxygen. However, it is difficult to apply the threshold value in real time to actual operation. Therefore, the inventors have found that the threshold value can be applied in real time to actual operation by setting the threshold value to a constant calculated from the distribution of the amount of free oxygen in past operation data.

[0015] (e) Regarding temperature influencing factors other than deoxidation, basically, it is not related to the grouping of the deoxidation type, and it is advisable to obtain a temperature drop prediction value by an influence function common to the group of deoxidation types obtained in advance for each temperature influencing factor.Finally, it is advisable to obtain the temperature drop of the molten steel by adding the temperature drop prediction value obtained for each deoxidation type to the temperature drop prediction value for each temperature influencing factor other than deoxidation.

[0016] The present invention has been made based on these findings, and the gist of the present invention is as follows.

[0017] [1] A steelmaking process including a blowing process for blowing molten steel in a converter, a tapping process for adjusting main components by adding a deoxidizer or the like for deoxidization while tapping the molten steel from the converter to a transport vessel such as a molten steel ladle after the blowing process, a secondary refining process for adjusting components of the molten steel as a process following the tapping process, and a casting process for continuously casting the molten steel, in order to secure a downstream process reference time temperature, which is the temperature of the molten steel required at a downstream process reference time, which is an arbitrary reference time in the downstream process, a temperature drop of the molten steel from the end of the blowing (end of blowing) to the reference time of the downstream process is predicted for each temperature influencing factor by a temperature influencing function previously obtained for each temperature influencing factor, a predicted temperature drop value of the molten steel is obtained, and the end temperature of the blowing is set by adding the predicted temperature drop value of the molten steel to the downstream process reference time temperature; Regarding the deoxidation, The amount of the deoxidizer is compared with a deoxidation threshold value that is predetermined for each of the deoxidizers to determine a group of deoxidation forms; determining in advance the temperature influence function with respect to a temperature drop of the molten steel for each group of the deoxidization forms; The method for setting the blowing end temperature of a converter includes, as the temperature influencing factors, an amount of the deoxidizing material added and an amount of free oxygen at the end of the blowing of the molten steel, and includes determining a predicted value of the temperature drop of the molten steel from the temperature influencing factors corresponding to the group of deoxidization forms and the temperature influence function. [2] The method for setting the blowing end temperature of a converter according to [1] above, wherein the deoxidizing material is either one or both of Al and Si. [3] When the deoxidizing material is Al, the deoxidizing threshold value of Al is 1.5 kg / t or less per ton of molten steel; The deoxidation threshold value of Si, which is the deoxidation threshold value when the deoxidizing material is Si, is 1.0 kg / t or less per ton of molten steel; The method for setting the blowing end temperature of a converter according to the above [2]. [4] The amount of free oxygen in the molten steel at the end of the blowing is The measured value at the end of the blowing, a predicted value obtained from the C concentration estimated value (CD value) based on the cooling and solidification temperature at the end of the blowing and the temperature of the molten steel; A predicted value obtained from an estimated [C] concentration (CD value) based on the cooling and solidification temperature during the blowing, the temperature of the molten steel, and the blowing conditions, and a predicted value obtained from the measured values ​​during the blowing and the blowing conditions; The method for setting the blowing end temperature of a converter according to any one of the above items [1] to [3]. [5] The method for setting the blowing end temperature of a converter according to any one of the items [1] to [4], further comprising: determining in advance, for the temperature influence factors other than the deoxidation, a part or all of the temperature influence functions for each of the temperature influence factors as the temperature influence functions related to the temperature influence factors common to the group of deoxidation forms. [6] The method for setting the blowing end temperature of a converter described in [5] above includes first calculating the temperature drop predicted value by the temperature influence function related to the temperature influence factor common to the group of deoxidation forms, and setting the blowing end temperature by adding the temperature drop predicted value by the temperature influence function of the temperature influence factor set for each group of deoxidation forms. [7] The method for setting the blowing end temperature of a converter according to [5] or [6], wherein when calculating the temperature influence function related to the deoxidation grouped by the deoxidation type group, a correlation is calculated between the remainder of the temperature drop obtained by subtracting the predicted value of the temperature drop due to the temperature influence factor related to the temperature influence factor common to the deoxidation type group from the actual value of the temperature drop, and the temperature influence factor given to each of the deoxidation type groups. Effect of the Invention

[0018] According to the present invention, it is possible to predict the temperature drop of molten steel in the steel refining process with little variation. As a result, when determining the blowing end temperature of a converter, there is little error, and the blowing end temperature can be set without being unnecessarily high. This contributes greatly from the viewpoints of energy saving and carbon neutrality. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] The method for setting the blowing end temperature of a converter according to the present invention will be described based on one embodiment of the present invention (hereinafter, simply referred to as the present invention). The present invention is not limited to this embodiment.

[0020] [Steel manufacturing process] The steelmaking process includes the blowing process, in which molten steel is blown in a converter to adjust its composition, the tapping process, in which the molten steel after blowing is tapped from the converter into a transport vessel such as a molten steel ladle while adding deoxidizers to adjust its main composition, the secondary refining process, in which the molten steel composition is further adjusted, and the casting process, in which the molten steel after composition adjustment is solidified to obtain slabs, billets, or ingots. The blowing process and the tapping process are collectively called the converter process. The secondary refining process includes, for example, degassing treatment such as RH or DH, and desulfurization treatment. The converter process and the secondary refining process are collectively called the refining process. The casting process includes the continuous casting process in which continuous casting is performed, and the ingot-making process in which ingots are cast. All processing in the steelmaking process after the blowing process in the converter is referred to here as the post-process. In other words, the downstream processes include not only the tapping process, secondary refining, and continuous casting, but also the transfer of molten steel to the secondary refining equipment after the end of converter blowing, the transfer of molten steel from the secondary refining equipment to the continuous casting equipment, and waiting in the ladle.

[0021] [Post-process standard temperature] The downstream process reference time refers to any reference time (point in time) in the downstream process. The downstream process reference time is selected arbitrarily and is not limited to a specific point in time. For example, the start time of secondary refining or the start time of continuous casting is easy to select.

[0022] The downstream process reference temperature refers to the temperature of molten steel required at the selected downstream process reference time. The molten steel temperature required at the downstream process reference time varies depending on the composition of the molten steel and the subsequent processing. It is the temperature of molten steel required for operation at the downstream process reference time in manufacturing the final product. For example, in a continuous casting device, the molten steel stays in the tundish during the continuous casting time, and the molten steel temperature at the start of continuous casting is an important requirement so that it does not solidify during the stay. Therefore, for example, if the start of continuous casting is set as the downstream process reference time and the molten steel temperature at that time needs to be 1600°C, the downstream process reference temperature is 1600°C.

[0023] [Temperature drop prediction] The end-of-blowing temperature of a converter is required to be as low as possible from the viewpoint of energy saving and carbon neutrality. On the other hand, it is required to ensure the reference temperature of the downstream process as the molten steel temperature at the reference time of the downstream process. Therefore, the temperature drop of the molten steel from the end of blowing in the converter to the reference time of the downstream process is predicted, and the predicted temperature drop value is added to the reference time temperature of the downstream process to determine the end-of-blowing temperature of the converter. Since the predicted temperature drop value contains an error, the predicted temperature drop value is often used as the median value, and the temperature obtained by adding the variation to it is used as the end-of-blowing temperature of the converter. Therefore, improving the accuracy of the temperature drop prediction is very important.

[0024] As mentioned above, the following three factors are considered to be the main factors that contribute to the temperature drop of molten steel after the end of blowing in a converter. Of these, (A) is the largest, and its contribution to the temperature drop of molten steel is larger than the other two. (A) The heat of chemical reaction of the deoxidizing material, which removes oxygen from molten steel (a) Heat of dissolution of ferroalloys added for component adjustment and cooling (c) Heat dissipation that transfers to the refractory material in contact with the molten steel or to the atmosphere

[0025] The temperature drop prediction of molten steel is performed by predicting the temperature drop for each temperature influencing factor using a temperature influence function previously obtained for each temperature influencing factor from the end of blowing to the reference time of the subsequent process, and then adding these up to obtain a predicted temperature drop value of molten steel. There are no particular limitations on the method of determining the influence function. For example, for each temperature influence factor, a correlation coefficient with the temperature drop may be determined by multiple regression analysis, and the influence function may be determined from the coefficient (which may also be called a temperature influence coefficient or an influence coefficient). In this case, the influence function is a linear function, so although it has a constant term, the influence function may be read as an influence coefficient in the following explanation. The influence function may be a linear function, or may be a multi-order function such as a quadratic function or a cubic function.

[0026] Also, past operational data may be learned by so-called machine learning such as neural network to derive an influence function for temperature drop for each temperature influence factor. Other advanced analysis models such as random forest, support vector machine, and XGboost may also be applied. The method to be applied should be appropriately selected based on the load state of the computer used for analysis and operation control, the CPU performance, etc.

[0027] [Prediction of temperature drop due to deoxidation reaction] Deoxidation is treated as follows. Deoxidation in molten steel progresses when the deoxidizer in the molten steel reacts with oxygen (free oxygen) in the molten steel to become an oxide. That is, the amount of deoxidizer and the amount of oxygen (free oxygen amount) in the molten steel are related. Conventionally, the influence coefficient was calculated by multiple regression analysis or the like, assuming that the amount of deoxidizer (e.g., Al or Si) contributed uniformly to the temperature drop (or temperature rise) regardless of the amount of free oxygen, which is considered to have deteriorated the accuracy. For example, even if the amount of Al or Si is excessively increased compared to the amount of free oxygen in the molten steel, the excess deoxidizer simply dissolves in the molten steel and no heat is generated due to the deoxidation reaction. Conventionally, the temperature drop was predicted assuming that the deoxidation reaction occurred even in such a case. Therefore, in the present invention, the amount of deoxidizer and the amount of free oxygen are used as temperature drop influence factors, and the temperature drop of the molten steel is predicted by statistically calculating the temperature drop influence coefficient of the amount of deoxidizer and the amount of free oxygen for each state of deoxidation in advance.

[0028] [Determination of deoxidized form group] The effect on the temperature drop of molten steel differs depending on whether the deoxidizing material such as Al undergoes a deoxidizing (oxidizing) reaction or simply dissolves. Therefore, it is important to determine whether the steel is in a deoxidized state (deoxidation form). With conventional technology, there were no clear criteria for this determination, and data on non-deoxidized states was mixed in with data on deoxidized states. This is thought to be one of the causes of the large variation in temperature drop predictions. Therefore, we have been studying criteria for determining the deoxidation form. If the amount of deoxidizer added is small compared to the amount of free oxygen, the entire amount will be consumed for deoxidation, and excess free oxygen will remain, i.e., the material will be left in an undeoxidized state.

[0029] On the other hand, if the amount of deoxidizer added is large compared to the amount of free oxygen, part of the added deoxidizer (up to an amount corresponding to the free oxygen) will be consumed for deoxidation, and the remainder will dissolve in the molten steel without contributing to deoxidation. For example, if the deoxidizer is Al, it will be in an Al-killed state, and if it is Si, it will be in a Si-killed state. Also, if the deoxidizers are Al and Si, for example, a part of both will be consumed for deoxidation, and the remainder will dissolve in the molten steel, which is called an Al-Si killed state.

[0030] That is, the deoxidation state is classified into groups according to the amount of free oxygen, depending on whether it is undeoxidized (a state in which the input deoxidizer is consumed for deoxidation and excess free oxygen remains) or deoxidized (a state in which part of the input deoxidizer is consumed for deoxidation and the excess deoxidizer dissolves in the molten steel). For example, when the deoxidizer is two elements, it is classified into two groups for each deoxidizer, resulting in four groups. For example, when the deoxidizer is Al and Si, it is classified into four groups of deoxidization states: undeoxidized, Al killed (a state in which part of the input Al is consumed for deoxidation), Si killed (a state in which part of the input Si is consumed for deoxidation), and Al-Si killed (a state in which part of Al and Si are consumed for deoxidation).

[0031] [Deoxidation threshold] The effect of deoxidizers such as Al on the temperature drop of molten steel varies depending on whether they undergo a deoxidation (oxidation) reaction or simply dissolve. However, reactions in molten steel are complex, and it is difficult to stoichiometrically distinguish between deoxidation and dissolution reactions based on the amount of free oxygen and the amount of deoxidizer added, and to calculate for each individual charge. Therefore, the inventors have found that it is effective to set a threshold value (deoxidation threshold value) for the amount of deoxidizer added for each deoxidizer, and assume that when the amount of deoxidizer added is less than the respective deoxidation threshold value, almost the entire amount is consumed for deoxidation, and when the amount is equal to or greater than the deoxidation threshold value, the surplus deoxidizer dissolves in the molten steel, and to statistically obtain the relationship between the temperature drop performance and multiple influencing factors for each group and use the result for estimating the temperature drop.

[0032] The deoxidation threshold may be set according to the amount of free oxygen. However, it is difficult to apply this to actual operation in real time. Therefore, the present inventors have found that the deoxidation threshold can be applied to actual operation in real time by setting it to a constant value obtained from past operation data or the like.

[0033] For example, a case where Al and Si are used as deoxidizers will be described. If most of the free oxygen amount at the end of blowing in normal operation is within a certain range, the Al deoxidation threshold and the Si deoxidation threshold are calculated assuming this, and the deoxidation type group may be determined only by comparing with the Al input amount and the Si input amount. The Al deoxidation threshold should be a positive value of 1.5 kg / t molten steel or less, and the Si deoxidation threshold should be a positive value of 1.0 kg / t molten steel or less. In other words, when the Al input amount is greater than the Al deoxidation threshold, it is determined that the Al killed state exists, and when the Si input amount is greater than the Si deoxidation threshold, it is determined that the Si killed state exists. The Al deoxidation threshold and the Si deoxidation threshold are expressed in basic units ((units indicating the amount of Al or Si (kg) per ton of molten steel, expressed as kg / t)) like the Al input amount and the Si input amount.

[0034] The Al deoxidation threshold may be set taking into consideration actual operation and past performance, and may be a positive value of 1.5 kg / t or less of molten steel, such as 1.5 kg / t, 1.3 kg / t, 1.2 kg / t, 1.1 kg / t, 1.0 kg / t, 0.9 kg / t, 0.8 kg / t, 0.7 kg / t, 0.6 kg / t, 0.5 kg / t, 0.4 kg / t, 0.3 kg / t, or 0.2 kg / t.

[0035] Similarly, the Si deoxidation threshold value may be set taking into consideration actual operation and past performance, and may be a positive value equal to or less than 1.0 kg / t of molten steel, such as 1.0 kg / t, 0.9 kg / t, 0.8 kg / t, 0.7 kg / t, 0.6 kg / t, 0.5 kg / t, 0.4 kg / t, 0.3 kg / t, or 0.2 kg / t.

[0036] In addition, for example, a logic for classifying the deoxidation form based on the amount of Al charged, the amount of Si charged, and the amount of free oxygen in the molten steel according to equilibrium theory may be constructed and applied to make a judgment. Also, the deoxidation form may be grouped according to a predetermined technical standard steel type group, etc.

[0037] [Predicted free oxygen] The amount of free oxygen in molten steel at the end of blowing in a converter is (a) Measurement value measured by a free oxygen sensor or the like at the end of blowing, (a) The carbon (C) concentration estimated by the cooling and solidification temperature at the end of blowing (CD value) and the predicted value obtained from the temperature of the molten steel, (c) The predicted value obtained from the estimated C concentration (CD value) based on the cooling and solidification temperature during blowing, the molten steel temperature, and the blowing conditions (especially the blowing conditions after the temperature measurement), and (D) A predicted value obtained from the measurement value measured by the free oxygen sensor during the blowing and the blowing conditions (particularly the blowing conditions after the free oxygen measurement), It is best to choose one of the following.

[0038] [Example of prediction of temperature drop caused by Al deoxidation and Si deoxidation] A method for predicting the temperature drop of molten steel due to a deoxidizer will be specifically described below using the deoxidizer, Al, and Si as an example.

[0039] For each group of deoxidation types, the temperature influence functions on the temperature drop of the amounts of Al and Si added to the molten steel during the tapping process are calculated in advance, and the temperature drop of the molten steel affected by Al deoxidation and Si deoxidation can be predicted from the amounts of Al and Si actually added during the blowing process and their respective temperature influence functions.

[0040] There is no particular limitation on the method of obtaining the temperature influence function. For example, it is advisable to obtain the correlation between the amount of Al or Si input for each deoxidation form and the temperature drop by multiple regression analysis, and obtain the temperature influence function from the correlation. Also, it is possible to learn past operation data by so-called machine learning such as a neural network, and derive the temperature influence function of the amount of Al input and the amount of Si input on the temperature drop for each deoxidation form. In addition, it is possible to apply an advanced analysis model such as a random forest, a support vector machine, or XGboost. It is advisable to appropriately select which method to apply depending on the load state of a computer used for analysis and operation control, the performance of the CPU, and the like.

[0041] The temperature influence function may be expressed as a linear function of the correlation between the temperature drop and the amount of Al or Si input, or the amount of free oxygen, as temperature influence factors, and the coefficient and constant of the correlation. For example, when the vertical axis is the temperature drop and the horizontal axis is the amount of Al input (unit consumption) and the relationship between the two is expressed as a linear function, the slope of the graph is the coefficient (influence coefficient) of the amount of Al input, and the intercept with the vertical axis is the constant. Similarly, the influence coefficient and constant of the amount of Si input can be obtained from the relationship between the temperature drop and the amount of Si input. The same is true for the amount of free oxygen. For each group of deoxidation forms, the influence coefficients and constants of the amount of Al input, the amount of Si input, and the amount of free oxygen are obtained in advance, the group of deoxidation forms is determined from the actual amount of Al input, the amount of Si input, and the amount of free oxygen, and the amounts of Al and Si input and the amount of free oxygen are multiplied by their influence coefficients according to the group of deoxidation forms, and a constant is added to the result, and the predicted temperature drop values ​​obtained for both Al and Si and for each of the free oxygen are added to predict the temperature drop due to the deoxidation reaction.

[0042] The temperature influence function explained above is an example in which the amount of Al or Si input, the amount of free oxygen, and the temperature drop are analyzed as a linear function, but the influence function used in the analysis is not limited to a linear function. For example, the analysis may be performed using a multi-order function such as a quadratic function or a cubic function.

[0043] [Influence functions previously determined for each temperature influence factor other than deoxidation] For temperature influence factors other than deoxidation, basically, similar to the deoxidizing elements (Al and Si in the above example), the temperature influence function for each temperature influence factor is obtained in advance, and the method of obtaining the temperature influence function is not particularly limited. As in the example of the deoxidizing elements, for example, it is advisable to obtain the correlation between the temperature influence factor for each deoxidization form and the temperature drop by multiple regression analysis, and obtain the temperature influence function from that relationship. For example, if the temperature influence function is a linear function of the temperature influence factors, it is advisable to obtain the coefficient (temperature influence coefficient) and constant in advance. The temperature influence function is not limited to a linear function of the temperature influence factors, and may be a multi-order function.

[0044] On the other hand, since temperature influence factors other than deoxidation are often not related to the group of deoxidation type, it is advisable to make some or all of the temperature influence functions of those temperature influence factors into temperature influence functions common to the group of deoxidation type, and obtain the predicted temperature drop value for the temperature influence factors other than deoxidation in advance. Finally, the temperature drop of the molten steel can be obtained by adding the predicted temperature drop value obtained for each group of deoxidation type and the predicted temperature drop value for each temperature influence factor other than deoxidation.

[0045] Examples of temperature influencing factors other than deoxidation include the amount of alloy material charged in the tapping process, and also the heat dissipation that moves to refractories or the atmosphere, which cannot be expressed in terms of time, such as the "heat storage amount in the ladle." In this way, the temperature influencing factors may be appropriately set according to the conditions at the operating site.

[0046] [Prediction of temperature drop due to ferroalloys] Next, the prediction of temperature drop due to the heat of dissolution of ferroalloy added for component adjustment and cooling will be explained. The influence of the heat of dissolution of ferroalloy added is relatively small compared to the deoxidation reaction. Therefore, the conventional method of predicting temperature drop may be applied.

[0047] However, in the conventional method, coefficients for calculating the influence of alloying elements and coolants, which are usually added in small amounts, are obtained by multiple regression analysis, so when manufacturing a small amount of a steel type that adds a large amount of a specific alloying element, or when manufacturing a steel type that adds an alloying element with a small amount of actual data, the prediction accuracy can be significantly reduced because the influence coefficients obtained by multiple regression analysis are used to extrapolate from the data population analyzed by multiple regression analysis. Therefore, we investigated ways to improve the prediction accuracy of temperature drop.

[0048] For ferroalloys and coolants that have a small contribution to the deoxidation reaction, prediction accuracy can be improved by determining the influence function of the heat of dissolution of each material in advance through thermodynamic calculations. For example, it is advisable to determine the heat of dissolution per unit of consumption for each type of ferroalloy material through thermodynamic calculations and then determine the influence function for temperature drop. The material type here should be determined according to the classification of ferroalloys for operational management, such as ferromanganese (FeMn).

[0049] [Prediction of temperature drop due to heat dissipation through refractories and the atmosphere] This section explains the heat dissipation that transfers from the molten steel to the refractory material in contact with it or to the atmosphere. The influence of the heat dissipation that moves to the refractory or the atmosphere is smaller than the deoxidation reaction, as is the heat of dissolution of the ferroalloy. Therefore, the improvement of the accuracy of the temperature drop prediction due to the heat dissipation does not have a significant effect on the overall temperature drop prediction. Therefore, although the conventional temperature drop prediction method may be applied, we considered improving the accuracy of the temperature drop prediction.

[0050] The heat dissipated to the refractory and the atmosphere basically depends on the operation time. Therefore, it is possible to obtain the predicted temperature drop value by analyzing each process and the elapsed time between processes and calculating the influence coefficient for each process on the drop in the temperature of the molten steel. However, since it is also affected by the state of the equipment and the environment, it is better to predict the temperature drop by calculating the influence coefficient for the operation time based on the past performance of the same equipment. Specific temperature influence factors include, for example, an index showing the operation history of the ladle (some of the following: the time when it was in the full ladle, empty ladle, or ladle heating state, the number of times it was used, the temperature of the molten steel received, etc.), an index showing the operation history of the converter (some of the following: the time when it was empty, the number of times the furnace was used (the number of times the ladle or processing furnace was used), the number of times the tapping hole was used (the number of times the tapping hole of the ladle was used), the tapping temperature, etc.), and the time information between the end-of-blow measurement and the reference point of the subsequent process (the time information of each process, the time information of the movement of the molten steel between each process).

[0051] The analytical method for determining the influence function of each temperature influence factor is not particularly limited, and multiple regression analysis, machine learning analysis, or the like can be applied.

[0052] In the above-described prediction of temperature drop due to the dissolution heat of ferroalloy and the prediction of temperature drop due to the diffused heat moving to the refractory material, the influence coefficient is an example of the case where each temperature influence factor and the temperature drop are analyzed as a linear function, as in the prediction of temperature drop due to the deoxidization reaction. The function used for the analysis is not limited to a linear function. For example, the analysis may be performed using a multi-order function such as a quadratic function or a cubic function.

[0053] For the temperature influencing factors common to the groups of deoxidation types, an operation plan is prepared in advance, and in many cases, the values ​​are determined by the end of blowing. Therefore, from the viewpoint of quickly obtaining a temperature drop prediction, it is preferable to perform a temperature drop prediction due to the temperature influencing factors common to these groups of deoxidation types before a temperature drop prediction due to deoxidation. It is preferable to obtain a temperature drop prediction value for the temperature influencing factors common to the groups of deoxidation types before the start of blowing. In this way, the calculation time for the temperature drop prediction can be shortened, and it can be applied to actual operation in real time.

[0054] In addition, when determining the temperature influence functions grouped by the deoxidation type groups, it is advisable to determine the correlation between the remainder of the temperature drop, obtained by subtracting the predicted value of the temperature drop due to the temperature influence factors common to the deoxidation type groups from the actual value of the temperature drop, and the temperature influence factors related to deoxidation (e.g., the amount of deoxidizer input) given to each deoxidation type group. By doing so, the temperature influence function for each deoxidation type group can be updated and fed back each time one operation is completed, and applied to the next operation, thereby further improving the accuracy of the temperature drop prediction. EXAMPLES

[0055] In a steel refining process that is actually performed using a converter, secondary refining, and continuous casting, the present invention was applied based on actual operation data to predict the temperature at the end of blowing in the converter, and the prediction was compared with the actual temperature drop. Post-process reference time: The time when molten steel is poured into the secondary refining equipment (RH) Post-process reference temperature: The temperature of molten steel at the start of processing in the secondary refining equipment (RH) (1600°C)

[0056] Since the actual free oxygen amount at the end of blowing in the converter used in this embodiment was 600 ppm to 1200 ppm, the Al deoxidation threshold value and the Si deoxidation threshold value shown below were set and the deoxidation type groups were determined. Al deoxidation threshold: 0.5kg / ton of molten steel -Si deoxidation threshold: 0.3kg / ton of molten steel In other words, the deoxidation type groups are classified as follows based on the amount of Al input, which is the sum of the Al consumption rate (kg / ts) (ΣAl) input during the steel tapping process, and the amount of Si input, which is the sum of the Si consumption rate (kg / ts) (ΣSi) input: When ΣAl<0.5, ΣSi<0.3: Not deoxidized When ΣAl<0.5, ΣSi≧0.3: Si kill When ΣAl≧0.5, ΣSi<0.3: Al killed When ΣAl≧0.5, ΣSi≧0.3: Al-Si killed

[0057] The influence function of the Al input amount, Si input amount, and free oxygen content (OXP), which are temperature influence factors on deoxidation, was set as a linear function, and the influence coefficient and constant, which are the slope of the linear function, were obtained by multiple regression analysis from the results of 20 cases for each of the above-mentioned groups of deoxidation forms.

[0058] Regarding the heat of dissolution of ferroalloys, which is a temperature influencing factor other than deoxidation, the ferroalloys to be charged were classified as follows: Ferromanganese (FeMn) Low phosphorus ferromanganese (LPMn) Silicomanganese (SiMn) Ferrochrome (FeCr) CaO The above are merely examples of the classification of ferroalloys, and the present invention is not limited to these.

[0059] Other temperature influencing factors considered were: -Tapping time (the time it takes for molten steel to be tapped from the tap hole of a ladle, etc.) Empty furnace time ·Ladle heat storage amount It should be noted that the above are merely examples of classifications of temperature-affecting factors accompanying processing, etc., and the present invention is not limited to these.

[0060] Influence functions for the heat of dissolution and heat dissipation of ferroalloy, which are temperature influence factors other than deoxidation (common to all deoxidation groups), were obtained in advance as linear functions using multiple regression analysis, etc. The influence coefficients (slope of linear functions) of each temperature influence factor are shown in Table 1. The influence coefficients of the Al input amount, Si input amount, and free oxygen amount vary greatly depending on the deoxidation type group.

[0061] Table 2 shows the coefficients of temperature influence factors when applying a conventional method in which deoxidation types are classified into groups based on whether or not Al and Si are added as deoxidizers without considering free oxygen, as a conventional example. Using data from the same operation, the distribution of the error (predicted value minus actual value) between the temperature drop predicted value and the temperature drop actual value was obtained for the operation in which the present invention was applied (Example) and the operation in which the conventional technology was applied (Conventional Example), and the average and standard deviation of the error for each deoxidation type group are summarized in Table 3.

[0062] In addition, since there were few cases of undeoxidized steel in actual operation, from the viewpoint of accuracy, the comparison between the present invention example and the conventional example was evaluated based on the data of the temperature drop prediction in the Al-killed, Si-killed, and Al-Si-killed steels, excluding the cases of undeoxidized steel.

[0063] As can be seen from Table 3, it was confirmed that the variation (standard deviation) of the error was smaller in the inventive example than in the conventional example. Looking at the reduction rate of the variation (standard deviation) by group, it was reduced to 62% for Si-killed, 56% for Al-killed, and 75% for Al-Si-killed, and it was confirmed that the accuracy was greatly improved. On the other hand, the non-deoxidized group was 92%, which was smaller than the other groups and there was not much change in accuracy. This shows that the temperature drop prediction accuracy was improved because the temperature influence function was calculated excluding the case where a small amount of deoxidizing material (Al or Si) was added relative to the amount of free oxygen at the end of converter blowing (i.e., the case where the material was not deoxidized). In other words, in the conventional method, there were cases where the material was judged to be Al-killed or Si-killed, but in fact it was not deoxidized. It is considered that the application of the present invention enabled a judgment closer to the actual situation, and therefore the accuracy was improved.

[0064] The reductions in the error variation (standard deviation) are 4.8°C, 4.4°C, and 2.7°C for the Al-killed, Si-killed, and Al-Si-killed, respectively. In operation, the blowing end temperature of the converter is often reduced by 1 to 2 times the obtained standard deviation (σ) (so-called 1 to 2σ) considering that the temperature can be adjusted by the heat-up treatment in the secondary refining or by the cold material input. It was confirmed that the blowing end temperature can be reduced by 3 to 10°C in operation. In addition, this makes it possible to reduce excessive heating in the converter blowing process and additional heat-up treatment in the secondary refining process. Excessive additional heat-up treatment must be avoided because it has adverse effects such as refractory wear, inclusion quality deterioration, and cycle time deterioration in the secondary refining process. Even with this in mind, it was confirmed that the effect of the present invention is great.

[0065] [Table 1]

[0066] [Table 2] In addition, a hyphen (-) in the table indicates a case where there was no record of use due to a lack of data, and therefore no impact coefficient could be obtained.

[0067] [Table 3] [Industrial Applicability]

[0068] The present invention can be utilized in the steel industry.

Claims

1. A steelmaking process including a blowing process for blowing molten steel in a converter, a tapping process for adjusting main components by adding a deoxidizer or the like for deoxidization while tapping the molten steel from the converter to a transport vessel such as a molten steel ladle after the blowing process, a secondary refining process for adjusting components of the molten steel as a process subsequent to the tapping process, and a casting process for continuously casting the molten steel, in order to ensure a downstream process reference time temperature, which is the temperature of the molten steel required at a downstream process reference time that is an arbitrary reference time in the downstream process, a temperature drop of the molten steel from the end of the blowing to the reference time of the downstream process is predicted using a temperature influence function previously obtained for each temperature influence factor to obtain a predicted temperature drop value of the molten steel, and the end temperature of the blowing is set by adding the predicted temperature drop value to the downstream process reference time temperature; Regarding the deoxidation, The amount of the deoxidizer is compared with a deoxidation threshold value that is predetermined for each of the deoxidizers to determine a group of deoxidation forms; determining in advance the temperature influence function with respect to a temperature drop of the molten steel for each group of the deoxidization forms; the temperature influencing factors include an input amount of the deoxidizer and an amount of free oxygen at the end of the blowing of the molten steel, determining the predicted temperature drop value of the molten steel from the temperature influence factor and the temperature influence function according to the group of deoxidation type.

2. 2. The method for setting the blowing end temperature of a converter according to claim 1, wherein the deoxidizer is either one or both of Al and Si.

3. The deoxidization threshold value when the deoxidizing material is Al is 1.5 kg / t or less in terms of basic unit per ton of molten steel, The deoxidation threshold value, which is a Si deoxidation threshold value when the deoxidizing material is Si, is 1.0 kg / t or less in terms of basic unit per ton of molten steel, The method for setting the blowing end temperature of a converter according to claim 2,

4. The amount of free oxygen in the molten steel at the end of the blowing is The measured value at the end of the blowing, a predicted value obtained from an estimated C concentration (CD value) based on the cooling and solidification temperature at the end of the blowing and the temperature of the molten steel; A predicted value obtained from an estimated C concentration (CD value) based on the cooling and solidification temperature during the blowing, the temperature of the molten steel, and the blowing conditions; and a predicted value obtained from the measured values ​​during the blowing and the blowing conditions; Either one of The method for setting the blowing end temperature of a converter according to any one of claims 1 to 3.

5. The method for setting the blowing end temperature of a converter according to any one of claims 1 to 3, characterized in that, for the temperature influence factors other than the deoxidation, some or all of the temperature influence functions for each of the temperature influence factors are obtained in advance as the temperature influence functions related to the temperature influence factors common to the group of deoxidation forms.

6. The method for setting the blowing end temperature of a converter as described in claim 4, characterized in that, for the temperature influence factors other than the deoxidation, some or all of the temperature influence functions for each of the temperature influence factors are previously obtained as the temperature influence functions related to the temperature influence factors common to the group of deoxidation forms.

7. 6. The method for setting the blowing end temperature of a converter as claimed in claim 5, further comprising: first determining the predicted temperature drop value by the temperature influence function related to the temperature influence factor common to the groups of deoxidation forms, and setting the blowing end temperature by adding the predicted temperature drop value by the temperature influence function of the temperature influence factor set for each group of deoxidation forms.

8. 7. The method for setting the blowing end temperature of a converter according to claim 6, further comprising: first determining the predicted temperature drop value by the temperature influence function related to the temperature influence factor common to the groups of deoxidation forms, and setting the blowing end temperature by adding the predicted temperature drop value by the temperature influence function of the temperature influence factor set for each group of deoxidation forms.

9. 6. The method for setting the blowing end temperature of a converter as claimed in claim 5, further comprising, when calculating the temperature influence function related to the deoxidation grouped by the deoxidation type group, calculating a correlation between the remainder of the temperature drop obtained by subtracting the predicted value of the temperature drop due to the temperature influence factor related to the temperature influence factor common to the deoxidation type group from the actual value of the temperature drop, and the temperature influence factor given to each of the deoxidation type groups.

10. 8. The method for setting the blowing end temperature of a converter as claimed in claim 7, further comprising the step of: when determining the temperature influence function related to the deoxidation grouped by the deoxidation type group, determining a correlation between the remainder of the temperature drop obtained by subtracting the predicted value of the temperature drop due to the temperature influence factor related to the temperature influence factor common to the deoxidation type group from the actual value of the temperature drop, and the temperature influence factor given to each of the deoxidation type groups.

11. 7. The method for setting the blowing end temperature of a converter as claimed in claim 6, further comprising the step of: when determining the temperature influence function related to the deoxidation grouped by the deoxidation type group, determining a correlation between the remainder of the temperature drop obtained by subtracting the predicted value of the temperature drop due to the temperature influence factor related to the temperature influence factor common to the deoxidation type group from the actual value of the temperature drop, and the temperature influence factor given to each of the deoxidation type groups.

12. 9. The method for setting the blowing end temperature of a converter as claimed in claim 8, further comprising, when determining the temperature influence function related to the deoxidation grouped by the deoxidation type group, determining a correlation between the remainder of the temperature drop obtained by subtracting the predicted value of the temperature drop due to the temperature influence factor related to the temperature influence factor common to the deoxidation type groups from the actual value of the temperature drop, and the temperature influence factor given to each of the deoxidation type groups.

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