JP4864337B2 - Control method of walking beam type heating furnace - Google Patents

Description

  The present invention relates to a method for controlling a walking beam furnace.

Conventionally, there has been a problem that the billet is warped during rolling in the billet rolling line. This warpage is caused by various asymmetries in the thickness direction of the steel slab, but among them, the major cause is the temperature difference in the thickness direction of the steel slab. When there is a temperature difference in the thickness direction of the billet, when rolling the billet, if the γ phase (austenite phase) and the α phase (ferrite phase) coexist at the Ar ₃ transformation point, the thickness direction of the billet A difference occurs in the deformation resistance and the steel piece is warped. For example, when a slab is heated in a walking beam type furnace before rolling, the steel slab is moved using a stationary skid and a mobile skid, so that the bottom surface temperature of the slab in contact with the skid is In some cases, the temperature of the upper surface of the substrate becomes lower and warpage occurs.

  In order to solve the above-mentioned problem, in Patent Document 1, first, an average temperature of the steel slabs in the heating furnace calculated from the value of the lower furnace temperature and the like is obtained. The average temperature is used to bring the temperature difference between the upper and lower surfaces of the steel slab closer to a predetermined value, thereby eliminating the temperature difference between the upper and lower surfaces of the steel slab and preventing warpage.

Also, in Patent Document 2, the expected extraction temperature at the time of extraction of the material to be heated in the heating furnace, the expected front / back temperature difference, etc. are obtained from the value of the lower furnace temperature, etc., and these values are used to determine the upper and lower surfaces of the steel slab. The temperature difference is eliminated to prevent warping.
JP-A-62-174325 JP-A-5-255762

  However, in the above-mentioned Patent Document 1, since the output of the heating furnace is controlled using the average temperature of the steel slab calculated from the value of the lower furnace temperature, there is a possibility that a large error occurs in the set temperature of the heating furnace. . Usually, when the temperature of the lower furnace is measured, the temperature of the lower atmosphere in the furnace is measured using a temperature sensor provided in the lower part of the furnace side wall of the heating furnace. The atmosphere in the lower part of the furnace measured by this temperature sensor is strongly influenced by the end of the steel slab near the furnace side wall and the skid provided in the lower part of the furnace. In other words, the temperature of the lower atmosphere in the furnace measured is affected by disturbances caused by fluctuations in the end of the slab due to the difference in the slab length of each slab, movement of the skid for moving the slab, etc. Strongly received. Therefore, the average slab temperature and the upper and lower surface temperature difference calculated based on the temperature in the lower atmosphere of the furnace are prone to errors, and the temperature control of the heating furnace is performed based on the average temperature and upper and lower surface temperature difference. Becomes unstable.

  Also in the said patent document 2, after calculating the internal temperature distribution at the time of extraction of a to-be-heated material based on the value of a lower furnace temperature, the preset furnace temperature for output control is calculated | required. Accordingly, in this case as well, an error occurs in the internal temperature distribution calculated based on the lower furnace temperature and the set furnace temperature, and the furnace temperature control becomes unstable.

  The present invention has been made in view of the above problems, and provides a walking beam heating furnace control method that enables stable control with few errors when controlling the temperature of a walking beam heating furnace. That is the purpose.

In order to solve the above-described problems, according to the present invention, in a walking beam type heating furnace in which a steel piece in a furnace is moved by a skid in a predetermined direction and heated by heating devices provided at an upper part and a lower part in the furnace. , Measuring the temperature of the upper atmosphere in the furnace above the steel slab, and calculating the upper surface temperature of the steel slab at a position where the skid is not disposed vertically below, based on the temperature of the upper atmosphere in the furnace, Adjusting the output of the heating device in the upper part of the furnace so that the upper surface temperature approaches the target upper surface temperature, and measuring the temperature of the lower atmosphere in the furnace below the steel slab, Calculating the bottom surface temperature of the steel slab at a position in contact with the skid based on the temperature, and adjusting the output of the heating device at the lower part in the furnace so that the bottom surface temperature of the steel slab approaches the target bottom surface temperature Have a said steel strip comprises 0.01% of C in mass%, the Ar ₃ transformation temperature of the steel strip as _{T Ar @ 3} ° C., the target upper surface temperature X ° C. and the target bottom surface temperature (X-Y ) ° C. is set so as to satisfy 0 <Y <X− (T _Ar3 +60) . A method of controlling a walking beam heating furnace is provided.

Further, in the above control method, when measuring the temperature of the upper atmosphere in the furnace, the temperature is near the center in the width direction of the heating furnace and above the position where the skid is not arranged vertically below. When the temperature of the upper atmosphere in the furnace is measured and the temperature of the lower atmosphere in the furnace is measured, the temperature of the lower atmosphere in the furnace near the inner wall of the furnace may be measured.

  According to the present invention, stable control with few errors can be performed when controlling the temperature of a walking beam type heating furnace.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. In the present specification and drawings, elements having substantially the same functional configuration are denoted by the same reference numerals, and redundant description is omitted.

  FIG. 1 is an explanatory diagram of a walking beam heating furnace 1 to which a walking beam heating furnace control method according to an embodiment of the present invention is applied. The heating furnace 1 heats a steel slab 10 before rolling to a predetermined temperature. As shown in FIG. 1, the heating furnace 1 includes a pre-tropical zone 12, a heating zone 13, and a soaking zone 14 in order along the conveying direction of the steel slab 10 (longitudinal direction Y of the heating furnace 1 in FIG. 1). . FIG. 2 is a plan view of the heating furnace 1. As shown in FIGS. 1 and 2, a plurality of elongated fixed skids 15 and movable skids 16 are provided inside the heating furnace 1. The fixed skid 15 and the movable skid 16 are arranged in parallel along the longitudinal direction Y of the heating furnace 1 as viewed from above. The fixed skid 15 and the movable skid 16 are alternately arranged in the width direction X orthogonal to the longitudinal direction Y of the heating furnace 1. The fixed skid 15 is fixed to the heating furnace 1. As shown by arrows 17a, 17b, 17c and 17d in FIG. 1, the mobile skid 16 can perform periodic motion in a vertical plane while maintaining parallelism with the ground. The steel piece 10 is placed on the upper surfaces of the fixed skid 15 and the movable skid 16 so that the long side direction is in the width direction X. As will be described below, the steel slab 10 is moved in the longitudinal direction Y by the periodic movement of the movable skid 16.

  The periodic motion of the mobile skid 16 will be described. Both the fixed skid 15 and the mobile skid 16 always maintain their upper surfaces parallel to the ground. First, as a first state, the movable skid 16 is at a lower position than the fixed skid 15, and a plurality of steel pieces 10 are placed on the fixed skid 15. When the movable skid 16 is lifted and the position becomes higher than the fixed skid 15 from the state as indicated by an arrow 17 a, the steel piece 10 placed on the fixed skid 15 is placed on the upper surface of the movable skid 16. Lifted by. That is, the steel slab 10 is supported by the ascending movable skid 16. Then, as indicated by the arrow 17b, the moving skid 16 advances in the longitudinal direction Y of the heating furnace 1 together with the steel piece 10, and then descends as indicated by the arrow 17c. When the movable skid 16 descends and the position becomes lower than the fixed skid 15, the steel piece 10 supported on the movable skid 16 is placed on the upper surface of the fixed skid 15. Accordingly, the steel piece 10 is placed again on the fixed skid 15 at a position advanced in the longitudinal direction Y from the initial position. Thereafter, the moving skid 16 moves backward and returns to the initial position as indicated by an arrow 17d. Hereinafter, the steel piece 10 advances in the longitudinal direction Y in the heating furnace 1 by repeating this motion.

  Returning to FIG. 1, a plurality of thermocouples 18 a as longitudinal temperature sensors for measuring the temperature of the atmosphere in the upper part of the furnace are provided in the upper part of the pre-tropical zone 12 and the heating zone 13 of the walking beam type heating furnace 1. It is provided along the direction Y. Similarly, a plurality of thermocouples 18b are provided in the upper part of the soaking zone 14 of the heating furnace 1 as temperature sensors for measuring the temperature of the atmosphere in the upper part of the furnace. A plurality of thermocouples 19 a are provided along the longitudinal direction Y as temperature sensors for measuring the temperature of the atmosphere in the lower part of the furnace in the pre-tropical zone 12 of the heating furnace 1 and the heating zone 13. Yes. Similarly, a plurality of thermocouples 19b are provided in the lower part of the soaking zone 14 of the heating furnace 1 as temperature sensors for measuring the temperature of the atmosphere in the lower part of the furnace.

  FIG. 3 is a plan view showing the detailed arrangement of the thermocouples 18a and 18b in the upper part of the furnace and the thermocouples 19a and 19b in the lower part of the furnace. As shown in FIG. 3, the thermocouples 18 a and 18 b are provided in the upper part of the furnace, that is, on the ceiling of the furnace body 11. The position is a position in the vicinity of the center of the heating furnace 1 where neither the fixed skid 15 nor the movable skid 16 is disposed vertically below.

  As shown in FIG. 3, the thermocouple 19 a provided in the lower part of the furnace is disposed on the inner wall of the heating furnace 1. By arranging the thermocouple 19a in the lower part of the furnace in the lower part of the side wall of the heating furnace 1 in this way, when measuring the temperature of the atmosphere in the lower part of the furnace, the steel slab 10, the fixed skid 15, the movable skid 16, etc. It is possible to reduce the adverse effects such as debris and dust caused by. That is, it becomes possible to measure the temperature of the lower atmosphere in the furnace more stably.

  Further, a plurality of burners 20 a are provided along the longitudinal direction Y as heating devices for heating the steel slab 10 in the pre-tropical zone 12 of the heating furnace 1 and the upper part of the heating zone 13 in the furnace. Similarly, a burner 20b is provided as a heating device also in the upper part of the soaking zone 14 of the heating furnace 1. Further, a plurality of burners 21 a are provided along the longitudinal direction Y as a heating device in the pre-tropical zone 12 of the heating furnace 1 and the lower part of the heating zone 13 in the furnace. Similarly, a burner 21b is provided as a heating device in the lower part of the soaking zone 14 of the heating furnace 1 as well.

  Further, as shown in FIG. 1, the temperature control device 22 of the heating furnace 1 includes a thermocouple 18 b in the upper part of the soaking zone 14, a thermocouple 19 b in the lower part of the soaking zone 14, and a soaking zone 14 furnace. The inner upper burner 20b is connected to the soaking zone 14 lower burner 21b.

  The temperature controller 22 calculates the upper surface temperature of the steel slab 10 based on the temperature of the upper atmosphere in the furnace measured by the thermocouple 18b at the upper part of the furnace, and the upper surface temperature of the steel slab 10 heats the steel slab 10. The fuel and air amount of the burner 20b in the upper part of the furnace can be adjusted so as to approach the target upper surface temperature of the steel slab 10 when extracting from the furnace 1.

The temperature control unit 22 calculates the lower surface temperature of the steel strip 10 based on the temperature of the thermocouple furnace bottom atmosphere measured by 19b in the furnace bottom portion of the heating furnace 1 in the soaking zone 14, the steel strip 10 so that the bottom surface temperature of the steel plate 10 approaches the target bottom surface temperature of the steel piece 10 when the steel piece 10 is extracted from the heating furnace 1. Can be adjusted.

  Next, a control method performed in the above-described walking beam type heating furnace will be described.

  The steel slab 10 stays in the heating furnace 1 for 3 hours to 3 and a half hours, for example. The steel piece 10 is carried in from the pre-tropical zone 12 in the walking beam type heating furnace 1 shown in FIG. At this time, the temperature of the pre-tropical zone 12 is set to, for example, about 1100 to 1200 ° C. In addition, since the upper surface temperature of the steel slab 10 will be easily influenced by the lower surface temperature of the steel slab 10 if the thickness of the steel slab 10 is too thin, for example, 150 mm or more is preferable. Further, if the width of the steel slab 10 is too small, for example, the upper surface temperature of the steel slab 10 is likely to be affected by the end temperature of the steel slab 10, so that the thickness of the steel slab 10 is preferably four times or more. As described above, the slab 10 is moved in the longitudinal direction Y of the heating furnace 1 by the fixed skid 15 and the movable skid 16 (hereinafter collectively referred to as skids 15 and 16) in the pre-tropical zone 12. However, it is preheated by the burners 20a and 21a. In the pre-tropical zone 12, the steel slab 10 is heated to, for example, about 900 to 1000 ° C.

  Next, the steel piece 10 is moved to the heating zone 13 by the skids 15 and 16. The heating zone 13 at this time is set to a temperature of about 1100 ° C., for example. The steel piece 10 is heated by the burners 20 a and 21 a while being moved in the longitudinal direction Y of the heating furnace 1 by the skids 15 and 16 in the heating zone 13. In the heating zone 13, the steel piece 10 is heated to about 1100 ° C., for example.

Next, the billet 10 is moved within the soaking zone 14 by skids 15 and 16. Soaking zone 14 at this time is, for example, set to a temperature of about 1050 ° C., the steel strip 10 is heated around for example 1100 ° C.. If the slab 10 stays in the soaking zone 14 exceeds 60 minutes, the upper surface temperature of the slab 10 may be affected by the lower surface temperature of the slab 10, so it is preferable to set it to 60 minutes or less. . In the soaking zone 14, if the temperature difference between the temperature in the furnace upper atmosphere above the slab 10 and the temperature in the furnace lower atmosphere below the slab 10 exceeds 50 ° C., the temperature in the soaking zone 14 Since the balance may become non-uniform, it is preferable to set the temperature to 50 ° C. or lower.

  In the soaking zone 14, the temperature of the upper atmosphere in the furnace above the steel slab 10 is measured by the temperature control device 22 using the thermocouple 18 b in the upper soaking zone of the soaking zone 14. FIG. 4 is a cross-sectional view of the soaking zone 14 including the thermocouples 18b and 19b. As shown in FIGS. 3 and 4, the thermocouple 18 b in the upper part of the furnace of the soaking zone 14 is located near the center in the width direction X of the heating furnace 1, and either the skid 15 or 16 is arranged vertically downward. There is no position. By these thermocouples 18b, the temperature of the upper atmosphere in the furnace above the steel slab 10 is measured. Since neither the skid 15 nor 16 is disposed vertically below the upper atmosphere in the furnace, the temperature of the upper atmosphere in the furnace is stabilized by reducing the influence of thermal disturbance caused by the skids 15 and 16. Value.

  Next, the upper surface temperature of the steel slab 10 at the position A (shown in FIG. 4) where neither the skid 15 nor 16 is disposed vertically below the temperature control device 22 based on the measured temperature of the upper atmosphere in the furnace. Is calculated. In this calculation, for example, a calculation method using a difference described in “Steel Handbook 3rd Edition, Volume III, pages 8 to 15” may be used. Or you may utilize the calculation method by the control volume method etc. which are described in the formula 1-formula 3 of Unexamined-Japanese-Patent No. 5-255762, for example. Usually, the upper surface temperature of the steel slab 10 such as the position B or C where the skid 15 or 16 is disposed vertically below is very unstable because it is affected by thermal disturbance caused by the skid 15 or 16. Therefore, in the present application, by measuring the upper surface temperature of the steel slab 10 at the position A where neither the skid 15 nor 16 is vertically arranged, the error included in the measured value of the upper surface temperature of the steel slab 10 is reduced. it can.

  Next, the fuel, air amount, etc. of the burner 20b in the soaking zone 14 are adjusted by the temperature control device 22 so that the upper surface temperature of the steel piece 10 calculated as described above becomes the target upper surface temperature. This target upper surface temperature is obtained from a preset billet extraction temperature.

  Moreover, the temperature of the lower atmosphere in the furnace below the steel slab 10 is measured by the temperature control device 22 using the thermocouple 19b provided on the inner wall of the furnace in the soaking zone 14. Based on the measured temperature of the lower atmosphere in the furnace, the lower surface temperature of the steel piece 10 at the position D in contact with the skid 15 or 16 shown in FIG. 4 is calculated. In this calculation, for example, a calculation method using a difference described in “Steel Handbook 3rd Edition, Volume III, pages 8 to 15” may be used. Or you may utilize the calculation method by the control volume method etc. which are described in the formula 1-formula 3 of Unexamined-Japanese-Patent No. 5-255762, for example. Further, the temperature control device 22 adjusts the fuel and air amount of the burner 21b in the soaking zone 14 so that the lower surface temperature of the steel slab 10 calculated as described above becomes a preset target lower surface temperature. The

  In the above embodiment, the output of the heating device in the upper part of the furnace is adjusted based on the upper surface temperature of the steel piece at a position where neither the skid 15 nor 16 is arranged vertically below. It is possible to bring the upper surface temperature of the piece 10 closer to the target upper surface temperature that is more accurate and less error-prone.

  Furthermore, in the above embodiment, since the temperature of the upper atmosphere in the furnace above the position where neither the skid 15 or 16 is vertically arranged is measured, the influence of disturbance is less. It is possible to measure the temperature of the upper atmosphere in the furnace with little error.

Here, as described above, when the upper surface temperature and the lower surface temperature of the steel slab 10 are controlled, it is examined under what conditions it is optimal to perform the control. In order to solve the problem of warping during rolling of the steel slab 10, it is necessary to consider the Ar ₃ transformation temperature of the steel slab 10. When the steel slab 10 is heated and cooled before rolling, the steel slab 10 changes from the γ phase (austenite phase) to the α phase (ferrite phase) at the Ar ₃ transformation point. Therefore, when the temperature of the steel strip 10 is near Ar ₃ transformation temperature, the temperature becomes billet portion γ phase above the Ar ₃ transformation temperature, the steel strip portion temperature is below the Ar ₃ transformation temperature is α-phase . In general, the γ phase has a large deformation resistance, and the α phase has a small deformation resistance. Therefore, when the steel slab 10 is rolled at a temperature in the vicinity of the Ar ₃ transformation temperature, the relationship between the temperature in the thickness direction of the steel slab 10 and the deformation resistance changes due to phase transformation, and the problem of warpage becomes complicated. Therefore, in the present application, when the steel slab 10 containing 0.01% or less by mass% is controlled in the heating furnace 1, the target bottom surface temperature is set to be 60 ° C. or more higher than the Ar ₃ transformation temperature of the steel slab 10. Set.

When the steel slab contains 0.01% or less by mass% of C, the Ar ₃ transformation temperature of the steel slab is T _Ar3 ° C., the target upper surface temperature is X ° C. and the target lower surface temperature is (XY ) _.Degree . C. is set so as to satisfy 0 <Y <X- (T _Ar3 +60). By doing so, it has been experimentally found that the amount of warpage of the steel slab 10 is most preferably reduced.

  As mentioned above, although preferred embodiment of this invention was described referring an accompanying drawing, this invention is not limited to the example which concerns. It is obvious for those skilled in the art that various changes or modifications can be conceived within the scope of the technical idea described in the claims. It is understood that it belongs to.

  For example, in the above-described embodiment, the case where a thermocouple is used as the temperature sensor has been described. However, the temperature sensor uses a metal thermometer, uses an ultrasonic wave, uses an optical fiber, uses nuclear quadrupole resonance. , Those using nuclear magnetic resonance, those using electron spin resonance, those using microwaves, those using infrared rays, those using a gas thermometer, glass double tube thermometers It may be the one used.

  With respect to the steel plate 10 of IF steel whose values in mass% are as shown in Table 1, specific conditions for minimizing warpage were obtained by experiments.

Here, the steel piece 10 has a thickness of 250 mm, a width of 1250 mm, and a length of 8000 mm. The Ar ₃ transformation temperature of the billet 10 is 900 ° C. Moreover, the time for which the steel slab 10 exists in the heating furnace 1 is 180 minutes, and the time for which it exists in the soaking zone 14 is 30 minutes. Under such conditions, the target upper surface temperature of the steel slab 10 in the soaking zone 14 and the temperature difference between the upper and lower surfaces of the steel slab 10 (that is, no skid 15 or 16 is arranged vertically below as shown in FIG. 4). Heat control by adjusting the temperature to the various values from the upper surface temperature of the slab 10 at position A minus the lower surface temperature of the slab 10 at position D shown in FIG. Then, the amount of warpage was measured by rough rolling. The measurement results are shown with the target upper surface temperature of the steel slab 10 in the soaking zone 14 in the heating furnace 1 as the horizontal axis and the upper and lower surface temperature difference of the steel slab 10 as the vertical axis. It is. As shown in FIG. 5, the warpage amount as a result of rough rolling after heating control under each condition is indicated by different marks depending on the values.

When the condition between the target upper surface temperature of the steel slab 10 and the temperature difference between the upper and lower surfaces of the steel slab 10 corresponds to a region above the straight line L1 shown in FIG. 5, the amount of warpage during rough rolling was 400 mm or more. If the condition between the target upper surface temperature of the steel slab 10 and the temperature difference between the upper and lower surfaces of the steel slab 10 falls below the straight line L1 shown in FIG. 5 and above the straight line L2 shown in FIG. The amount became 300-400 mm. When the condition between the target upper surface temperature of the steel slab 10 and the temperature difference between the upper and lower surfaces of the steel slab 10 corresponds to a region below the straight line L2 shown in FIG. 5 and above L3 shown in FIG. Became 200-300 mm. When the condition between the target top surface temperature of the steel slab 10 and the temperature difference between the top and bottom surfaces of the steel slab 10 corresponds to a region below the straight line L3 shown in FIG. 5 and above L4 shown in FIG. Became 100-200 mm. Furthermore, when the condition between the target upper surface temperature of the steel slab 10 and the temperature difference between the upper and lower surfaces of the steel slab 10 corresponds to a region below the straight line L4 shown in FIG. 5, the amount of warpage during rough rolling is less than 100 mm. It was. Therefore, in order to suppress the warpage amount to 200 mm or less, it is necessary to set both conditions so that the target upper surface temperature and the upper and lower surface temperature difference conditions of the steel slab 10 correspond to the region below the straight line L3 shown in FIG. is there. Here, the straight line L3 shown in FIG. 5 can be expressed as Y = X-960 when the target upper surface temperature of the steel slab 10 is X ° C. and the target lower surface temperature of the steel slab 10 is (XY) ° C. Therefore, if the temperature of the soaking zone 14 in the heating furnace 1 is controlled so that the target upper surface temperature X of the slab 10 and the upper and lower surface temperature difference Y of the slab 10 satisfy 0 <Y <X-960, the amount of warpage is minimized. It becomes possible to limit to the limit. Further, _assuming that the Ar ₃ transformation temperature is T _Ar3 , since T _Ar3 = 900 ° C., the above formula can be generalized as 0 <Y <X− (T _Ar3 +60). That is, _assuming that the Ar ₃ transformation temperature of the steel slab is T _Ar3 ° C, the target upper surface temperature is X ° C, and the target lower surface temperature is (XY) ° C, 0 <Y <X− (T _Ar3 +60) If controlled within the range, the amount of warp of the steel slab 10 can be minimized.

  According to the present invention, it is possible to control a walking beam type heating furnace.

It is side surface sectional drawing of the walking beam type heating furnace to which the control method of the walking beam type heating furnace which concerns on embodiment of this invention is applied. It is a top view of the walking beam type heating furnace which concerns on embodiment of this invention. It is a top view which shows the detailed arrangement | positioning condition of the thermocouple of the inside of a soaking tropics furnace, and the thermocouple of the soaking tropics inside a furnace. It is sectional drawing of a soaking zone containing a thermocouple and. When heating control is performed in the soaking zone in the heating furnace, the target upper surface temperature of the steel slab is plotted on the horizontal axis and the temperature difference between the upper and lower surfaces of the steel slab is plotted on the vertical axis, and then the amount of warpage resulting from rough rolling varies depending on the value. It is the figure displayed with the mark.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Walking beam type heating furnace 10 Billet 11 Heating furnace body 12 Pre-tropical zone 13 Heating zone 14 Soaking zone 15 Fixed skid 16 Mobile skid 18a, 18b, 19a, 19b Thermocouple 20a, 20b, 21a, 21b Burner 22 Temperature controller L1, L2, L3, L4 A straight line that determines the region in FIG.

Claims (2)

In a walking beam type heating furnace in which a steel piece in a furnace is moved by a skid in a predetermined direction and heated by heating devices provided at the upper and lower parts of the furnace,
The temperature of the upper atmosphere in the furnace above the steel slab is measured, and based on the temperature of the upper atmosphere in the furnace, the upper surface temperature of the steel slab at a position where the skid is not disposed vertically below is calculated, Adjusting the output of the heating device in the upper part of the furnace to bring the upper surface temperature closer to the target upper surface temperature;
Measure the temperature of the lower atmosphere in the furnace below the steel slab, calculate the lower surface temperature of the steel slab at the position in contact with the skid based on the temperature of the lower atmosphere in the furnace, Adjusting the output of the heating device at the lower part of the furnace so that the temperature approaches the target bottom surface temperature,
The steel slab contains 0.01% by mass or less of C and the Ar ₃ transformation temperature of the steel slab is T _Ar3 ° C. The target upper surface temperature X ° C and the target lower surface temperature (XY) ° C are , 0 <Y <X− (T _Ar3 +60). A method for controlling a walking beam type heating furnace. When measuring the temperature of the upper atmosphere in the furnace, the temperature of the upper atmosphere in the furnace near the center in the width direction of the heating furnace and above the position where the skid is not arranged vertically below the furnace. Measure,
2. The walking beam heating furnace according to claim 1, wherein when the temperature of the lower atmosphere in the furnace is measured, the temperature of the lower atmosphere in the furnace near the inner wall of the furnace is measured. Control method.

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