JP2018003084A - Method for predicting the temperature of steel material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for predicting the temperature of a steel material capable of predicting the temperature of a steel material in a heating furnace at high precision even in the case the total combustion amount of burners is changed.SOLUTION: Provided is a method for predicting a steel material in a heating furnace provided with a plurality of burners arranged in such a manner that the central axis of a crater is made horizontal and also is made into a vertical direction to the carrying direction of the steel material, including: a step of acquiring the standard total heat absorptivity of the steel material at each position in the furnace length direction in the heating furnace when the total combustion amount of the burners being a prescribed one; a step of acquiring the corrected total heat absorptivity obtained by correcting the standard total heat absorptivity based on the total combustion amount of the burners; and a step of predicting the temperature of the steel material at each position in the furnace length direction in the heating furnace based on the corrected total heat absorptivity, and it is characterized in that the correction is performed using the carrying direction distance between the steel material and the burners.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a temperature prediction method for steel materials.

  For example, when a steel material is heated in a continuous heating furnace or the like, the steel material temperature history in the heating furnace greatly affects the quality of the steel material. If the deviation from the target temperature history is large, a phenomenon called decarburization may occur and desired mechanical characteristics may not be obtained. Therefore, in order to ensure the quality of the product, the operator needs to appropriately control the temperature history of the steel material in the heating furnace.

  In order for the operator to appropriately control the temperature history, it is necessary to accurately predict the temperature of the steel material. On the other hand, it is necessary to suppress the time and cost of temperature prediction from the viewpoint of productivity. Therefore, a method has been proposed in which the overall heat absorption rate (heat transfer efficiency from the furnace to the steel material) is obtained in advance, and the temperature of the steel material is predicted by correcting the overall heat absorption rate with a correction term (Japanese Patent Application Laid-Open No. 2005-318867). No. 2015-40333).

  However, in the heating furnace, the number of burners burned varies depending on the operating conditions. For example, when the heating temperature of the steel material is high, the burner combustion number is increased, and when the in-furnace time of the steel material is lengthened, the burner combustion number is reduced to adjust the extraction temperature of the heating furnace. When the burner combustion number (total combustion amount) changes in this way, the overall heat absorption rate changes greatly. On the other hand, in the conventional technique such as the above method, the response to the change in the total combustion amount of the burner is not considered, and there is a problem that the prediction accuracy is greatly reduced when the burner combustion number or the like is changed. .

Japanese Patent Laying-Open No. 2015-40333

  In view of the above inconveniences, an object of the present invention is to provide a steel material temperature prediction method capable of accurately predicting a steel material temperature in a heating furnace.

  The invention made to solve the above problems is a method for predicting the temperature of a steel material in a heating furnace comprising a plurality of burners arranged so that the central axis of the crater is horizontal and perpendicular to the conveying direction of the steel material. Obtaining a standard overall heat absorption rate of the steel material at each position in the furnace length direction in the heating furnace when the total combustion amount of the burner is predetermined, and the reference overall heat absorption based on the total combustion amount of the burner A step of obtaining a corrected overall heat absorption rate with the rate corrected, and a step of predicting the temperature of the steel material at each position in the furnace length direction in the heating furnace based on the corrected overall heat absorption rate. And using the distance in the conveying direction with the burner.

  The method for predicting the temperature of the steel material is for the case where the total burnup amount of the burner is changed by correcting the standard overall heat absorption rate at a certain burner total burnup amount using the distance in the conveyance direction between the steel material and the burner. In addition, the steel temperature can be predicted with relatively high accuracy without increasing the calculation load.

  The steel material temperature prediction method of the present invention can accurately predict the steel material temperature in the heating furnace even when the total combustion amount of the burner changes.

It is a flowchart which shows the procedure of the temperature prediction method of the steel material of one Embodiment of this invention. It is a top view explaining arrangement | positioning of the burner in a heating furnace, (a) is the top view seen from the downward direction of a conveyance surface, (b) is the top view seen from the upper direction of the conveyance surface. It is a side view explaining arrangement | positioning of the burner in a heating furnace. It is a graph which compares the measured temperature of steel materials in the parameter determination stage in an Example, and predicted temperature. It is a graph showing the correction coefficient calculated | required in the Example. It is a graph showing the standard overall heat absorption rate calculated | required in the Example, and a correction | amendment overall heat absorption rate. The left column is a graph comparing the measured temperature and the predicted temperature of the steel material in the example, and the right column is a graph showing the deviation between the measured temperature and the predicted temperature in the example.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings as appropriate.

[Method for predicting steel temperature]
The steel material temperature prediction method is a temperature prediction method for a steel material in a heating furnace including a plurality of burners arranged such that the central axis of the crater is horizontal and perpendicular to the steel material conveyance direction. As shown in FIG. 1, the steel material temperature prediction method includes an initial condition setting step S1 for setting initial conditions, and a steel material at each position in the furnace length direction in the heating furnace when the total combustion amount of the burner is predetermined. The reference overall heat absorption rate acquisition step S2 for obtaining the reference overall heat absorption rate, and the corrected overall heat absorption rate acquisition step S3 for obtaining the corrected overall heat absorption rate obtained by correcting the reference overall heat absorption rate based on the total combustion amount of the burner And a temperature prediction step S4 for predicting the temperature of the steel material at each position in the furnace length direction in the heating furnace based on the corrected overall heat absorption rate.

  The temperature prediction method for the steel material can be applied to a known heating furnace including the plurality of burners. Specifically, for example, as shown in FIGS. 2 and 3, a plurality of craters face the upper side and / or the lower side of the conveying surface 10 of the steel material A in the direction perpendicular to the conveying direction (arrow direction in the drawing) of the steel material A. A heating furnace provided with a pair of so-called side burners is used. In addition, the conveyance surface 10 is a surface which conveys the steel material A by a walking beam. 2 and 3, two pairs of burners 1a are disposed below the conveyance surface 10 and downstream in the conveyance direction, and a pair of burners 1b are disposed above the conveyance surface 10 and downstream in the conveyance direction. The number and position of the burners are not limited to this. In addition, the heating furnace may have a configuration in which the configuration shown in FIGS. 2 and 3 is used as one heating zone and a plurality of heating zones are used.

  The intervals in the conveyance direction of the plurality of pairs of burners can be appropriately designed. Further, as the burner, for example, an axial flow burner can be used.

  The shape of the steel material targeted by the temperature prediction method of the steel material is not particularly limited, and can be applied to steel bars, steel plates, and the like. Moreover, the heating furnace used with the temperature prediction method of the said steel material can be used in combination with another heating furnace. In addition, the final heating temperature of steel materials is 1000 degreeC or more and 1200 degrees C or less, for example.

<Initial condition setting process>
In the initial condition setting step S1, the heating condition of the steel material is mainly set. Specifically, the type of steel material, the initial heating temperature, the in-furnace time, the temperature in the heating furnace, and the like are set.

<Standard overall heat absorption rate acquisition process>
In the reference overall heat absorption rate acquisition step S2, the overall heat absorption rate (reference overall heat absorption rate) that serves as a reference for the steel material when the total combustion amount of the burner is a predetermined amount (reference value) is determined in the furnace length direction in the heating furnace. Get for each position.

  This standard overall heat absorption rate may be obtained by actually measuring the temperature when the steel material is actually heated at a predetermined combustion amount in a heating furnace and calculating from this measurement value. The reference overall heat absorption rate corresponding to the initial condition may be selected from the table and obtained.

Here, the overall heat absorption rate φ _CG (d) at the conveyance direction position d in the heating furnace is a coefficient in the relationship of the following formula (1).

In the above formula (1), q [W / m ² ] is the heat flux to the steel material, δ [W / m ² / K ⁴ ] is the Stefan-Boltzmann constant, T _f [K] is the furnace temperature, and T _s [K ] Is the steel surface temperature.

When the standard overall heat absorption rate is obtained from the actual measured value of the steel surface temperature, the temperature can be measured, for example, with a thermocouple. Using the obtained steel material temperature, furnace temperature, heat input, and the like, the overall heat absorption rate φ _CG is calculated from the equation (1), and set as the reference overall heat absorption rate.

  Here, the total combustion amount of the burner is represented by the product of the number of burners burned (hereinafter also referred to as “burner combustion number”) and the combustion load per burner. When the flame extends in the same direction as the longitudinal direction of the steel material, the change in the combustion load per piece is small, and the total amount of combustion can be regarded as being proportional to the number of burners burned. In addition, even when the change of the combustion load per one is large, if the overall heat absorption rate is given according to the combustion load, it can be handled in the same manner, and such a case is also within the intended range of the present invention. . Therefore, by controlling using the burner combustion number, that is, by obtaining the reference overall heat absorption rate when the burner combustion number is a predetermined (reference value), the control of the temperature prediction method of the steel material is facilitated. be able to. The burner combustion number (predetermined combustion number) in the reference overall heat absorption rate is not limited, but the number of combustions is preferably 1 or more from the viewpoint of easily and reliably correcting the overall heat absorption rate described later. In particular, when multiple pairs of opposed burners are used as shown in FIGS. 2 and 3, it is preferable to collectively control the on / off of combustion of the paired burners. It is good to decide.

<Correction general heat absorption rate acquisition process>
In the corrected overall heat absorption rate acquisition step S3, the obtained reference overall heat absorption rate is corrected in accordance with the current total burner combustion amount, thereby correcting the overall overall heat absorption rate (corrected) corresponding to the current burner combustion state. Obtain the overall heat absorption rate. As described above, when the combustion amount of one burner is constant, correction based on the number of combustions of the burner may be performed.

  Here, when a steel material approaches a burner, the influence of a burner flame becomes large and the amount of heat input to the steel material increases. On the other hand, when the steel material is separated from the burner, the heat input to the steel material decreases. Therefore, the accuracy of temperature prediction can be improved by correcting the overall heat absorption rate based on the distance between the burning burner and the steel material. Therefore, in the corrected overall heat absorption rate acquisition step, a corrected overall heat absorption rate in which the reference overall heat absorption rate is corrected in consideration of the conveyance direction distance between the steel material and the burner is acquired.

  The corrected overall heat absorption rate may be obtained by correcting the reference overall heat absorption rate by calculation in the procedure described later, or the burner total combustion amount (combustion number) is calculated from the previously calculated corrected overall heat absorption rate table. A corresponding corrected overall heat absorption rate may be selected and obtained.

  As an example of the procedure for obtaining the corrected overall heat absorption rate by correcting the reference overall heat absorption rate by calculation, the method of multiplying the reference overall heat absorption rate by a correction coefficient determined by the distance in the conveyance direction between the steel and the burner is preferably used. it can. More specifically, for example, a correction coefficient F (d) at the conveyance direction position d in the heating furnace represented by the following formula (2) is obtained.

In the above formula (2), n is the number of burner pairs during combustion. b ⁱ is the position in the conveying direction of the i-th burner pair during combustion in the heating furnace. K ⁱ is a coefficient set for each i-th burner pair. C ₁ , C ₂ , C ₃ , and C ₄ are coefficients. K ⁱ and C ₁ , C ₂ , C ₃ , and C ₄ are constants determined in advance so that the deviation between the actually measured value and the predicted value becomes small by actually measuring the steel material temperature. Specifically, these parameters can be determined by conducting a temperature measurement experiment on steel under a certain burner combustion condition different from the case where the reference overall heat absorption rate is calculated, and utilizing the temperature measurement result. K ⁱ can be 1 when the number n of burner pairs during combustion is 1.

Based on the correction coefficient F (d) obtained by the equation (2), the corrected overall heat absorption rate φ _CG ^NEW (d) at the conveyance direction position d in the heating furnace is calculated by the following equation (3).

In the above formula (3), φ _CG ^ST (d) is the reference overall heat absorption rate acquired in the reference overall heat absorption rate acquisition step S2.

<Temperature prediction process>
In the temperature prediction step S4, the temperature of the steel material at the transport direction position d in the heating furnace is predicted based on the corrected overall heat absorption rate acquired in the corrected overall heat absorption rate acquisition step S3.

  As a temperature prediction method, a known two-dimensional heat conduction equation is used, and the temperature distribution from the surface to the inside of the steel material at the transport direction position d using the conditions set in the above equation (1) and the initial condition setting step S1 as boundary conditions. Ask for. The two-dimensional heat conduction equation is represented by the following formula (4).

In the above formula (4), ρ [g / m ³ ] is the density of the steel material, c [J / g / K] is the specific heat of the steel material, T [K] is the temperature of the steel material [K], and δt is the minute time [s. ], [Delta] x, [delta] y are micro sections [m], [lambda] x, [lambda] y [W / m / K] are the thermal conductivities in the x direction or y direction.

  In addition, it is preferable to obtain | require a correction | amendment general heat absorption rate for every site | part of steel materials. For example, when the steel material is heated in the heating furnace shown in FIGS. 2 and 3, it is preferable to obtain the corrected overall heat absorption rate separately on the upper surface, the lower surface and the side surface of the steel material.

  By performing such temperature prediction at each of the conveyance direction positions d at a plurality of points of the steel material, it is possible to obtain a temperature change prediction of the steel material in the heating furnace.

  Since the steel material temperature prediction method can predict the steel material temperature in the heating furnace with relatively high accuracy, the steel material heating method having a step of controlling the temperature history based on the predicted temperature of the steel material, or this heating method is used. It can be suitably applied to a method for manufacturing a steel material.

[advantage]
The temperature prediction method for the steel material is based on the case where the burner total combustion amount has changed by correcting the reference overall heat absorption rate when the total burner combustion amount is predetermined using the distance in the conveyance direction between the steel material and the burner. In addition, the steel temperature can be predicted with relatively high accuracy without increasing the calculation load.

[Other Embodiments]
The method for predicting the temperature of the steel material of the present invention is not limited to the above embodiment. For example, the temperature prediction method for the steel material may include steps other than those described above as necessary.

  EXAMPLES Hereinafter, although this invention is explained in full detail based on an Example, this invention is not interpreted limitedly based on description of this Example.

  2 and 3 for a steel material having a thickness (dimension in the direction perpendicular to the conveyance surface) 155 mm, width (dimension in the conveyance direction) 155 mm, and a certain length (dimension in the conveyance direction and the direction perpendicular to the conveyance surface). The heating furnace was used in a state where only one pair of burners on the extraction side (exit side) was burned out of the two pairs of lower burners 1a. Under this condition, the steel material being heated was subjected to temperature prediction at three points of 25 mm (A), 77.5 mm (B), and 130 mm (C) from the upper surface, and temperature measurement.

  Specifically, first, as the reference overall heat absorption rate, the overall heat absorption rate of the upper surface and the lower surface in the central portion in the length direction of the steel material from the measured temperature of the steel material in a state where all the burners of FIGS. 2 and 3 are burned. Was calculated.

  Next, the parameters in the above formula (2) were determined as follows. In the following, the conveyance direction position (coordinates) d in the heating furnace is set to 0 to 1.00.

First, the deviation between the measured temperature of the steel material at the burner combustion number different from that in the case of calculating the standard overall heat absorption rate, particularly the estimated temperature of the steel material near the burner and the predicted temperature using the corrected overall heat absorption rate is 0 ° C. K ⁱ and C ₁ , C ₂ , C ₃ , and C ₄ in the above formula (2) were determined so as to approach. Specifically, among the burners of FIGS. 2 and 3, the steel material temperature measurement was performed in a state where only the lower two burners were burned without burning the upper burner. For this temperature measurement result, K ⁱ and C ₁ , C ₂ , C ₃ , C ₄ in Equation (2) are changed to K ¹ = 1, C ₁ = 1, C ₂ = 0.05, C ₃ = 1, C _By setting ₄ = 2, as shown in FIG. 4, it was possible to adjust the deviation between the measured temperature and the predicted temperature of the steel material to approach 0 ° C. at a point 25 mm from the upper surface.

  In addition, since the conveyance direction position (coordinates) of the upper burner is 0.96, and the burner has one pair of combustion numbers, b = 0.96 and n = 1 are given in the above equation (2). .

Using a similar method to that described above in that the top surface of 130 mm, to adjust so that the deviation of the measured temperature of the steel material and the predicted temperature approaches 0 ° C., K ⁱ and C ₁ in Formula (2) in the lower surface, C ₂ , C ₃ , C ₄ were determined as K ¹ = 1, C ₁ = 1, C ₂ = 0.05, C ₃ = 1, C ₄ = 2.

  In addition, since the conveyance direction position (coordinates) of the lower burner not performing combustion is 0.80, and only the lower burner on the extraction side is burned, in equation (2), b = 0.80, n = 1.

Next, the correction coefficient F (d) of the upper surface and the lower surface in a state where only one pair of burners on the extraction side in the lower two pairs of burners 1a among the two pairs of burners of FIGS. ⁱ and _{C 1, C 2, C 3} , C 4 and n, using the value of b respectively determined by the above formula (2). This correction coefficient is shown in FIG. Further, the corrected overall heat absorption rate was calculated by the above formula (3). The obtained corrected overall heat absorption rate and reference overall heat absorption rate are shown together in FIG.

  Finally, the temperature at the three points was predicted using the above equation (4) using the corrected overall heat absorption rate, and compared with the actually measured value. In addition, the overall heat absorption rate of the steel material side surface was an average value of the overall heat absorption rate of the upper surface and the lower surface. The result is shown in FIG. “Example” in FIG. 7 is a temperature prediction using the corrected overall heat absorption rate, and “Comparative example” is a temperature prediction using the reference overall heat absorption rate as it is. In addition, Table 1 shows the results of determining the area ratio within 20 ° C. between the measured value and the predicted value for each of the three points.

  From the results of FIG. 7 and Table 1, by correcting the reference overall heat absorption rate using the transport direction distance between the steel material and the burning burner, the deviation from the actual measurement value can be reduced, and the prediction accuracy can be greatly improved. Recognize.

  Since the steel material temperature prediction method can accurately predict the steel material temperature in the heating furnace even when the total combustion amount of the burner is changed, it can be suitably applied to the production of various steel materials that involve a heating process.

1a, 1b Burner 10 Conveying surface A Steel S1 Initial condition setting step S2 Standard overall heat absorption rate acquisition step S3 Correction overall heat absorption rate acquisition step S4 Temperature prediction step

Claims (1)

A method for predicting the temperature of a steel material in a heating furnace comprising a plurality of burners arranged such that the central axis of the crater is horizontal and perpendicular to the conveying direction of the steel material,
Obtaining a standard overall heat absorption rate of the steel at each position in the furnace length direction in the heating furnace when the total combustion amount of the burner is predetermined;
Obtaining a corrected overall heat absorption rate obtained by correcting the reference overall heat absorption rate based on the total combustion amount of the burner;
A step of predicting the temperature of the steel material at each position in the furnace length direction in the furnace based on the corrected overall heat absorption rate,
A method for predicting a temperature of a steel material, wherein the correction is performed using a conveyance direction distance between the steel material and the burner.

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