JPH04323324A - Method for controlling temperature of steel sheet in continuous heating furnace - Google Patents

Abstract

PURPOSE:To establish accurate temp. controlling method in the case of executing continuous heating treatment in a continuous heating furnace after joining steel sheets having different conditions in dimension, aimed sheet temp., material quality, etc. CONSTITUTION:A sheet temp. resposive curve from the preceding material to the following material so as to satisfy the preset sheet temp. control standard and sheet passing velocity, furnace temp. and these setting changing timing for thin prupose, are precalculated, but all the same, in the case where out of the torelance in the sheet temp. develops, according to (a) the case where the out of torelance only to the preceding material side develops, (b) the case where the out of the torelance only to the following material side develops, and (c) the case where the out of torelance to both of the preceding material side and the following material side develops, the sheet temp. control model compensating this with the sheet passing velocity is added, and the sheet passing velocity is continuously, incliningly and slowly changed before and after changing the setting to restrain the out of torelance in the sheet temp.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] This invention is applicable to, for example, "plate thickness", "
Various steel plates with different widths, materials, or target temperatures at the outlet of the heating furnace are welded to form a continuous steel plate, which is then passed continuously into the furnace for heat treatment. Concerning “temperature control method of steel plate”.

0002

[Prior art and its problems] In general, cold rolled steel sheets are subjected to various heat treatments that combine heating, soaking, cooling, etc. in order to impart the required properties. From this point of view, it is normally done continuously and at high speed.

However, in recent years, steel plates processed in continuous heat treatment furnaces (continuous annealing furnaces) have been manufactured using coils with different plate thicknesses, plate widths, materials, etc., reflecting the increasing demand for a wide variety of products and small lots. The number of continuous welded parts is rapidly increasing, and it is therefore necessary to frequently change the furnace temperature setting of the heat treatment furnace.

By the way, as a heating method for a heating furnace, an indirect heating method using a radiant tube or the like is widely adopted from the viewpoint of preventing oxidation of the steel plate.
There is a drawback that the followability of the actual furnace temperature value when changing the furnace temperature setting value is extremely low. For example, JP-A-57-3564
As exemplified by the operation using the heating device proposed as No. 0, in continuous heat treatment of steel plates that is performed after welding different steel plates together, the steel plate temperature increases before and after the welding point of the steel plate entering the heating furnace. In this case, the "amount of change in the furnace temperature set value" and the "timing of displacement" are calculated in advance according to operational conditions, and the furnace temperature is adjusted based on the calculation results. The set value is changed.

[0005] FIG. 4 shows an example of controlling the temperature of a steel plate using the above device, and explains the control method in a welded section of “steel plates that have the same width, material, and target temperature, but differ only in thickness.” However, as shown in FIG. 4, the set value of the furnace temperature is set as indicated by a broken line in order to correspond to changes in plate thickness.

However, the actual value of the furnace temperature follows a change course as shown by the solid line due to poor followability. Therefore, the steel plate temperature results in a region shown by hatching before and after the welding point that deviates from the target temperature. If the steel sheet temperature deviates from the target temperature in this way, the steel sheet will be "under-baked" or "over-baked" and the yield as a product will be reduced.

Therefore, in order to eliminate such "deviation from the target temperature", in addition to the above-mentioned "change of the furnace temperature setting value", "
A method was proposed in JP-A No. 61-190026 in which the steel sheet temperature at the outlet of the heating furnace (hereinafter simply referred to as "sheet temperature") In addition to providing a plate temperature control model that dynamically expresses the relationship between furnace temperature, fuel flow rate, plate thickness, plate width, and strip threading speed, it also allows for future changes in plate thickness, plate width, or target plate temperature values (
(hereinafter referred to as "set change"), this model is used to calculate the "optimum transition trajectory of sheet temperature,""optimum amount of change in sheet threading speed," and "optimum timing to start speed change," and based on the results, The key point is to implement "control that includes changing the threading speed only once and discontinuously."

However, Japanese Patent Application Laid-Open No. 61-190026
Even with the above-mentioned method proposed in No. 1, if the amount of change in plate thickness, plate width, or target plate temperature value at the time of set change is large, even if the optimum transition trajectory of plate temperature is achieved, the plate may not be properly adjusted over a relatively long period. The problem of temperature deviating from the target value could not be completely resolved. Also,
The present applicant previously published Japanese Patent Application No. 2-79194 entitled ``In the field of process control, heat balance theory
We created a model that dynamically expresses the relationship between strip temperature, furnace temperature, strip thickness, strip width, and strip threading speed, and determined the strip threading speed based on the strip threading speed command value and furnace temperature command value obtained by this model. proposed a method for controlling the furnace temperature (hereinafter referred to as "Method A"). The above model makes it possible to determine in advance the optimal transition trajectory of sheet temperature (optimal trajectory in the case of discontinuous speed changes), the amount of change in sheet threading speed, and the speed change start timing at the time of future set changes. At the same time, deviation of the plate temperature from the target value as shown in FIG. 5 can also be predicted. In other words, t1: Furnace temperature set value change time, t2: Time when the furnace temperature reaches a steady state, t3: Speed change timing, t
4: Time at which the plate thickness changes at the outlet of the heating furnace, h1: Thickness of the preceding material, h2: Thickness of the succeeding material, TF1: Furnace temperature set value in the steady state of the preceding material, TF2: Furnace temperature in the steady state of the succeeding material Set value, v1: Threading speed in the steady state of the preceding material, v2: Threading speed in the steady state of the succeeding material, ΔT1
ΔT (ΔT1, ΔT2) in Fig. 5, which is expressed as the target deviation width of the plate temperature at the tail end of the leading material, ΔT2: The width of the deviation from the target plate temperature at the leading edge of the trailing material (ΔT1, ΔT2) can be predicted. Assuming that the plate width w is the same, if the plate temperature deviates above the target value, ΔT > 0, and if it deviates downward, ΔT < 0.
).

[0009] Furthermore, the present applicant has discovered that even with the above-mentioned "Method A", the optimal transition trajectory of the plate temperature at the time of set change deviates from the target deviation tolerance range (hereinafter referred to as "tolerance") (hereinafter referred to as "plate temperature deviation"). As a method of controlling sheet temperature when the sheet temperature is expected to change (hereinafter referred to as (referred to as "Method B")" (Japanese Patent Application No. 185864/1999).

[00010] In this method, first, the optimal transition trajectory of the sheet temperature, the amount of change in the sheet-threading speed, and the start timing of the change in the sheet-threading speed are determined in advance by the above-mentioned ``Method A'' (the optimal transition trajectory is determined at this stage at a discontinuous speed). (This refers to the optimal trajectory when changes are made) and at the same time predicts the deviation of the plate temperature from the target value. Next, the influence coefficient of the speed of the preceding material and the furnace temperature (hereinafter,
ε1 (simply referred to as the "influence coefficient") was slightly changed by the threading speed ∂v1 from the steady state of the preceding material (furnace temperature TFe, threading speed v1, and sheet temperature constant at Ts1). When the temperature change is ∂Ts1, ε1 = ∂Ts1/∂v1 is defined, and the value of this influence coefficient ε1 is calculated using a known model. Similarly, the influence coefficient ε2 of the trailing material is expressed as ε2 = ∂T
Define s2/∂v2 and calculate using the same procedure. However, TFe=αT
F1+(1-α)Ts2, 0≦α≦1, α
is determined by the equipment and operating conditions of the heating furnace.

[00011] As shown in FIG.
The sheet threading speed shown in is corrected as follows. (1) At time t≦t4, the threading speed v=v1,
(2) At t=t4 -Δt, v=v1 -βΔT
1/ε1, (3) At t1 < t < t4 - Δt, (4) At t=t4, v=v2 - β
ΔT2/ε2, (5) When t4 <t<t2, (2) When t=t2, v=v2. That is, the previously proposed "Method B" is a method of controlling the threading speed and furnace temperature based on the threading speed command value obtained here and the furnace temperature command value obtained by the "Method A". .

[00012] However, through subsequent studies, it has been recognized that the method B previously proposed by the present applicant also has the following problems. In other words, in general, there is a difference in grade between the preceding material and the following material, and even if they have the same sheet temperature deviation length, for example, deviation on the preceding material side is a big problem in terms of product properties, but deviation on the succeeding material side. may be a relatively small problem, or vice versa. Also, even if the plate temperature deviation length is the same, deviation on the low-temperature side (under-heating the steel plate) is a major problem in terms of product properties, but high-temperature deviation (over-heating the steel plate) is relatively less of a problem. This is well known. However, in "Method B" proposed earlier, such a difference is not recognized, so instead of reducing the disc temperature deviation on the side with fewer problems, it increases the disc temperature deviation on the side with more problems, and as a result, In this case, a plate temperature trajectory that is less preferable than in the case of "Method A" may occur.

[00013] Such problems tend to occur under the following conditions. That is, a problem arises when, for example, the succeeding material is of a higher grade than the preceding material and the following material is not allowed to deviate in plate temperature. In such a case, the above "Method A"
If the above-mentioned "Method B" is applied, no plate temperature deviation will occur on the trailing material side as shown in Fig. 7.
As shown in Fig. 8, the overall plate temperature deviation length is L1.
Although the temperature decreases from L2 to L2, there is a tendency for plate temperature deviations shown by hatching to occur on the trailing material side.

[00014] In view of the above, an object of the present invention is to accurately cope with the case where it is expected that the optimal transition trajectory of the plate temperature at the time of set change will cause the plate temperature to deviate. The objective was to establish a ``plate temperature control method in a continuous heating furnace'' that would shorten the plate temperature deviation on both the leading and trailing material sides.

00015

[Means for Solving the Problems] The present invention was completed through numerous experiments and studies conducted by the present inventors in order to achieve the above object. When continuously heating "continuous steel plates," the trajectory of the steel plate temperature up to the exit of the continuous heating furnace is predicted in advance, and the furnace temperature and strip threading speed are manipulated if the predicted steel plate temperature at the exit of the heating furnace deviates from the target value. In the sheet temperature control method that compensates for this by preset control based on the amount of material, first, the length of the sheet temperature deviation between the preceding material and the succeeding material satisfies the predetermined sheet temperature control standard. We have calculated the plate temperature response curve for the plate temperature response curve, the plate threading speed, furnace temperature, and the timing of changing these settings to achieve this, and if the plate temperature still occurs, “
When decelerating, the plate temperature is higher on the preceding material side and the plate temperature is off. When speeding up, the preceding material side is lower and the plate temperature is lower than the plate temperature. Continuous and sloping changes are made at a small change rate, and on the other hand, when increasing the plate temperature on the trailing material side when increasing speed, and when decreasing the plate temperature on the trailing material side during deceleration, If this occurs, the sheet threading speed should be changed to a value greater than the required speed change width at the speed change timing determined by the predictive calculation, and then returned to the necessary change value continuously and in an inclined manner. The major feature is that by implementing this method, it is possible to suppress the temperature deviation of the steel plate in a continuous heating furnace and to perform accurate temperature control.

That is, the present invention predicts the amount of deviation from the target value when the optimum transition trajectory of the plate temperature at the time of changing the set of the continuous heating furnace is expected to cause the plate temperature to deviate from the target value, and This relates to a sheet temperature control method that continuously controls the sheet threading speed with a preset setting so that the sheet temperature deviation on the trailing material side is shortened. "Welding point detector", "Speed detector to detect the threading speed of the steel plate", "Furnace temperature detector to detect the temperature of the heating furnace", and "Plate temperature detector to detect the temperature of the steel plate at the outlet of the heating furnace" A "detector group" equipped with a "detector group" and a "tracking means" that tracks the welding point of the steel plate according to the output signals from the welding point detector and speed detector mentioned above, and a "tracking means" that tracks the welding point of the steel plate in accordance with the output signals from the welding point detector and speed detector, and the optimum transition of the plate temperature when replacing the set in the future. A well-known "sheet temperature control model" that calculates the trajectory, the amount of change in the sheet threading speed, and the speed change timing is used, and the sheet temperature is predicted to deviate from the target from the above sheet temperature trajectory, and the sheet threading speed is continuously changed to correct this. A control device including a "sheet temperature control model" for compensation and a "speed control means" for controlling the sheet passing speed to a value calculated by the model can be applied. The control procedure at that time is as follows.

[0017] First, the optimal transition trajectory of the sheet temperature, the amount of change in the sheet threading speed, and the speed change start timing are obtained in advance using the above-mentioned ``Method A''. At the same time, deviations of the plate temperature from the target value are also predicted. In addition, "Method A"
The sheet temperature transition trajectory determined by is optimized assuming that the sheet passing speed is discontinuously changed only once at the time of changing the set.

If plate temperature deviation still occurs even with this method, it is classified into the following three cases. Case 1: Temperature deviation occurs only on the leading material side; Case 2: Temperature deviation occurs only on the trailing material side; Case 2: Board temperature drops on both the leading material side and the trailing material side. Temperature loss occurs.

Therefore, we added a plate temperature control model to each of the above three cases to compensate for the plate temperature deviation by the plate passing speed, and changed the plate passing rate continuously and in an inclined manner before and after the set change. As a result, both the sheet temperature deviation on the preceding material side and the sheet temperature deviation on the succeeding material side with respect to the sheet temperature transition trajectory obtained by "Method A" are reduced.

[00020] Here, the above three cases in which plate temperature deviation occurs will be explained in more detail. Case 1 (When sheet temperature deviation occurs only on the preceding material side) The situation shown in FIG. 7 is an example of this case. In such a case, changing the sheet threading speed is The welding point between the leading material and the trailing material passes through the heating furnace outlet.
Make sure to finish making changes a minute in advance. By adopting such a method, it is possible to reduce the length of sheet temperature deviation on the preceding material side without causing new sheet temperature deviation in the succeeding material. Note that the pre-welding point speed holding time Δt1 may be set to a value determined by experiment to determine the shortest time at which new sheet temperature deviation does not occur in the trailing material.

Specifically, the speed is changed as shown in the following equation. (1) At time t≦t3, the threading speed v=v1,
(2) If t≧t4 −Δt1, v=v2, (
3) If t3 ≦t≦t4 −Δt1,

The plate temperature control state when such speed compensation is applied is as shown in FIG. However, this speed compensation is not applied in the following cases. 1) When t4 −Δt1 ≦t3. That is, when the speed change timing is close to "the time when the welding point passes the heating chamber outlet" or later. 2) (v2 −v1) and ΔT1 have the same sign (+
or -). For example, normally the strip threading speed is lowered under conditions that lower the strip temperature, but the opposite may be true depending on the furnace temperature setting. If the speed compensation described above is performed in such a case, the plate temperature deviation will further increase. However, in these cases, it is known that the plate temperature deviation is originally short, so there is little problem even if this speed compensation is not applied.

Case 2 (case where plate temperature deviation occurs only on the trailing material side) The state shown in FIG. 9 is an example of this case (
The symbol t5 in the diagram indicates the time when the strip temperature ends.) In such a case, instead of changing the threading speed discontinuously, the speed should be changed once to a value larger than the required speed change range. , and then the speed is returned to the required speed in a continuous and ramped manner. By such a method, the length of the plate temperature deviation on the trailing material side can be effectively reduced.

Specifically, the sheet threading speed is changed as shown in the following equation. (1) At time t≦t3, the threading speed v=v1,
(2) At t=t3 +Δt2, v=v2 +Δ
v, (where Δv=-k(ΔT2)/ε2, ε2 is the influence coefficient of the following material.v2 +Δv is the steel plate size, plate temperature target, and speed for each steel type determined from the viewpoint of operational stability. If the range exceeds the upper and lower speed limits, reduce the absolute value of Δv and adjust so that v2 +Δv falls within the range of the upper and lower speed limits.) (3) t3 ≦t≦t3 +Δt2, (4) t3 +Δt2 <t<t5, (5) t≧t5, v=v2.

The plate temperature control state when such speed compensation is applied is as shown in FIG. However, in this case, in order to prevent plate temperature deviation from occurring on the preceding material side, plate temperature deviation occurs only on the succeeding material side, so the speed change timing is performed near or after the welding point. Therefore, even if this compensation is performed, no new plate temperature deviation will occur on the preceding material side.

[00026] Case 3 (when the plate temperature drops on both the preceding material side and the succeeding material side) In this case, in the same way as in "Case 2", the plate temperature on the preceding material side is removed. It is possible to reduce the plate temperature deviation length on the next material side without increasing it. Next, the present invention will be described in more detail based on explanatory drawings of examples.

[00027]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a schematic diagram showing the configuration of a "temperature control device for steel plates in a continuous heating furnace" according to the present invention. In FIG. 1, the reference numeral (1) indicates a continuous annealing furnace heating zone equipped with a hearth roll (2) for transferring a steel plate (s) thereinto. The flow rate of fuel supplied to the continuous annealing furnace heating zone (1) is controlled by the furnace temperature control device (5).
This is performed via a fuel flow rate control device (4) based on a signal from a furnace temperature detector (3) provided inside the continuous annealing furnace heating zone (1).

A plate temperature detector (6) is provided on the exit side of the continuous annealing furnace heating zone (1). In addition, a drive motor (7) is installed on the entrance side of the continuous annealing furnace heating zone (1).
A pair of upper and lower bridle rolls (8) driven by a motor are provided, and the speed of this drive motor (7) is controlled by a speed control device (9).

A welding point detector (10) is provided on the entry side of the bridle roll (8), and a welding point position signal is input to a tracking device (12). The welding point position tracking device (12), speed control device (9), furnace temperature control device (5), plate temperature control device 1 (
13) are connected to each other, and the speed control device (9
), Furnace temperature control device (5), Plate temperature control device 1 (13)
each receives information on the welding point position from the tracking device (12).

[00030] In addition to the tracking device (12), the plate temperature control device 1 (13) also includes a steel plate specification setting device (
Information on the plate thickness, plate width, material, target plate temperature, and tolerance in the continuous annealing furnace heating zone (1) of the succeeding material is received from the furnace temperature detector (3). 1) The internal furnace temperature is received from the plate temperature detector (6), which receives the temperature of the steel plate (s) at the exit side of the continuous annealing furnace heating zone (1).

[00031] The plate temperature control device 1 (13) uses "Method A"
The optimum transition trajectory of the plate temperature is predicted by the method, and the set value of the furnace temperature and its change timing, the set value of the sheet threading speed and its change timing, and the predicted optimum change trajectory of the plate temperature are determined. The furnace temperature setting value determined here and its change timing are sent to the furnace temperature control device (5), and the furnace temperature control device receives the welding point position from the tracking device (12) in accordance with the furnace temperature setting change timing. At the point when the furnace temperature has passed the point where the furnace temperature is set, the furnace temperature setting value is used as the furnace temperature setting value of the succeeding material, and the fuel flow device (4) is set so that the furnace temperature setting value and the furnace temperature measured by the furnace temperature detector (3) match. ) to control the fuel flow rate supplied to the furnace. Further, the sheet temperature control device 1 (13) transmits the sheet passing speed set value, its change timing, and the predicted optimum transition trajectory of the temperature to the control device selection device (15).

The control device selection device (15) selects the sheet temperature control device 2a (16a) if the sheet temperature deviation occurs only on the preceding material side in the received predicted optimal trajectory of sheet temperature. Conversely, if the plate temperature deviation occurs only on the trailing material side in the received predicted optimal trajectory, the plate temperature control device 2
b (16b). If the plate temperature deviation occurs on both the preceding material side and the succeeding material side in the predicted optimum trajectory of the received plate temperature, the plate temperature control device 2c (16c) is selected.

Next, the control device selection device (15) transmits the sheet threading speed set value, its change timing, and the predicted optimum transition trajectory of the sheet temperature to the selected control device. and,
Each selected control device receives the result of calculating the changing trajectory of the sheet threading speed according to the method related to the present invention described above, and transmits the received changing trajectory of the sheet threading speed to the speed control device (9). Send. The speed control device (9) is
The sheet threading speed is controlled by controlling the speed of the drive motor (7) based on the changing trajectory of the sheet threading speed and the welding point position information received from the tracking device (12).

Next, a control process based on the temperature control device having the above configuration will be explained. First, the plate temperature control device 1 (13) is caused to find an optimal transition trajectory according to "Method A". However, since the sheet temperature transition trajectory predicted by the sheet temperature control device 1 (13) only changes the sheet passing speed discontinuously, the sheet temperature deviates over a long range as shown in Figures 7 and 9. There is. In addition, in the case shown in Fig. 7, if control is performed using the above-mentioned "Method B" in order to reduce the length of sheet temperature deviation, sheet temperature deviation will occur in the trailing material on the high grade side as shown in Fig. 8. There is a problem that occurs in

Therefore, according to the present invention, the plate temperature control device 2a (16a) and plate temperature control device 2b (16a) are newly added.
b) The plate temperature control device 2c (16c) and the control device selection device (15) calculate the target plate temperature deviation width from the predicted plate temperature transition trajectory, and thread the plate using the method according to the present invention described above. Determine the speed setting. The speed setting value determined in this way is sent to the speed control device (9), which controls the drive roll so that the sheet passing speed becomes the above-mentioned setting value.

If the temperature control device adopts a configuration in which the output of the plate temperature control device 1 (13) is directly transmitted to the speed control device (9) (configuration of ``Method A''), In cases where there is an inconvenient result as shown in 9.
Plate temperature control device 2a (16a), plate temperature control device 2b (16
b) By adding a plate temperature control device 2c (16c) and a control device selection device (15) and implementing control according to the present invention, results as shown in FIG. 2 or 3 can be obtained, respectively. , it becomes possible to reduce the board temperature deviation length as much as possible on both the leading material side and the trailing material side.

However, the path of the steel plate in the heating furnace has a finite length, and it is impossible to eliminate the deviation of the plate temperature from the target due to the thermal inertia of the hearth roll in the furnace. If the sheet temperature control method according to the invention is applied, sheet temperature deviations on both the leading material side and the trailing material side will be significantly reduced.

[00038]

[Summary of Effects] As explained above, according to the present invention,
During continuous heat treatment of strips made by welding dissimilar steel plates,
It has extremely useful effects industrially, such as being able to significantly reduce deviations from the target temperature that occur over a long range before and after the welding point, and making it possible to manufacture high-quality steel plates at a high yield. brought about.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing a configuration example of a temperature control device for a steel plate according to the present invention in a continuous heating furnace.

FIG. 2 is a graph showing the concept of the continuous heating furnace temperature control method and the control state of the steel plate temperature according to the present invention.

FIG. 3 is a graph showing the concept of the continuous heating furnace temperature control method and the control state of the steel plate temperature according to the present invention.

FIG. 4 is a graph showing an example of a control state of steel plate temperature according to a conventional method.

FIG. 5 is a graph showing an example of a steel plate temperature control state according to a conventional method.

FIG. 6 is a graph showing an example of a steel plate temperature control state according to a conventional method.

FIG. 7 is a graph showing an example of a steel plate temperature control state according to a conventional method.

FIG. 8 is a graph showing an example of a steel plate temperature control state according to a conventional method.

FIG. 9 is a graph showing an example of a steel plate temperature control state according to a conventional method.

[Explanation of symbols]

1 Continuous annealing furnace heating zone 2 Hearth roll 3 Furnace temperature detector 4 Fuel flow control device 5 Furnace temperature control device 6 Plate temperature detector 7 Drive motor 8 Bridle roll 9 Speed control device 10 Welding point detection device 11 Threading speed detector 12 Tracking device 13 Sheet temperature control device 1 14 Steel plate specification setting device 15 Sheet temperature control device selection device 16a Sheet temperature control device 2a 16b Sheet temperature control device 2b 16c Sheet temperature control device 2c s Steel plate t1 Furnace Temperature setting value change time t2 Time when the furnace temperature reaches a steady value t3 Speed change timing (however, when the speed is not changed, t3 = t4) t4 Time h1 when the welding point passes the heating furnace outlet
Preceding material plate thickness h2 Following material plate thickness

Claims (1)

[Claims] [Claim 1] When continuously heating a "continuous steel plate" made by welding different types of steel plates, the transition trajectory of the steel plate temperature up to the exit of the continuous heating furnace is predicted in advance, and the predicted steel plate temperature at the exit of the heating furnace is In the plate temperature control method, which compensates for deviations from the target values by preset control using the furnace temperature and sheet threading speed as manipulated variables, first, the length of the plate temperature deviation of the preceding material and the following material is determined in advance. We predict and calculate the plate temperature response curve from the preceding material to the succeeding material that satisfies the plate temperature control standards, and the plate threading speed, furnace temperature, and timing of changing these settings to achieve this, and still maintain the plate temperature tolerance. If this results in stripping, the threading speed should be changed in the following cases: ``When decelerating, the preceding material side is higher and the sheet temperature tolerance deviation occurs'' and ``When speeding up, the preceding material side is lower, and sheet temperature tolerance deviation occurs''. is changed continuously and in an inclined manner at a change rate smaller than the maximum change rate allowed in advance, and on the other hand, "when increasing speed on the trailing material side and causing sheet temperature tolerance deviation" In addition, if "a deviation from the lower sheet temperature tolerance occurs on the trailing material side during deceleration," the sheet threading speed should be changed once to a value greater than the required speed change width at the speed change timing determined by the above prediction calculation. 1. A method for controlling the temperature of a steel plate in a continuous heating furnace, characterized by carrying out an operation of continuously and slopingly returning the temperature to the required change value.