JP2002172411A - Method and apparatus for heat-treating thick steel plate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method and apparatus for heat-treating a thick steel plate capable of fixing a cooling start-up temperature and a cooling shut-down temperature, after cooling, in the longitudinal direction of the thick steel plate. SOLUTION: A heat treatment method for the thick steel plate 2 after rolling is that performing leveling through a straightening machine 3 and then, heating the steel through induction heating devices 4, 5 and lastly an accelerative cooling is executed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and apparatus for heat-treating a thick steel plate, and more particularly to a cooling stop temperature of a thick steel plate at an outlet side of a cooling device when cooling a high-temperature thick steel plate having a relatively small thickness. The present invention relates to a heat treatment method for a thick steel plate and a heat treatment facility for the heat treatment, wherein the temperature of the steel plate can be controlled accurately and a uniform temperature can be maintained from the front end to the rear end of the thick steel plate.

[0002]

2. Description of the Related Art Generally, a hot steel sheet after rolling is cooled while passing through a cooling device online. In recent years, in particular, in controlled rolling, which combines cooling and rolling, and in controlled cooling, in which steel sheets are cooled online, with high quality products, high-precision temperature control, in particular, the cooling start temperature and cooling stop temperature have a narrow It is important to control the cooling within the range and to cool the steel plate.

In the conventional method of controlling the temperature of a steel sheet, cooling water is injected from above and below while passing the steel sheet through a cooling device at a constant conveying speed, and the flow rate is controlled by adjusting the amount of the cooling water to change the cooling intensity. Or, a method of controlling the cooling stop temperature by changing the conveying speed of the steel sheet passing through the cooling device in which the cooling condition is fixed has been generally used.

[0004] As a method by flow control, for example, Japanese Patent Publication No. 7-61493 (hereinafter referred to as prior art 1)
As disclosed in Japanese Patent Application Laid-Open No. 9-10823, a method of detecting the temperature of a steel sheet conveyed in a cooling device and controlling the amount of cooling water so that the temperature difference between the upper and lower surfaces is within a specified value is disclosed.
As disclosed in Japanese Unexamined Patent Publication (hereinafter referred to as “prior art 2”), a critical flow rate at which the flow rate of the upper nozzle becomes non-uniform cooling is obtained, and the required total flow rate of the upper and lower nozzles is less than twice the critical flow rate. Then, there has been a method of setting the flow rate of one of the upper and lower nozzles to 0, or a flow rate control method of fixing the flow rate of the upper nozzle to the limit flow rate and adjusting only the flow rate of the lower nozzle.

On the other hand, as a method of controlling the transfer speed, for example, Japanese Patent Application Laid-Open No. 62-199723
As disclosed in Prior Art 3), a method of calculating a steel sheet speed change amount every time the steel sheet advances into the cooling device by an amount corresponding to the cooling zone length of the cooling device and changing the steel plate speed, JP-A-1-205581 (hereinafter referred to as “JP-A”)
As disclosed in Prior Art 4), there has been a method of cooling while accelerating the steel sheet speed.

[0006]

However, in the prior art 1 based on the flow rate control, when the cooling water amount is reduced, the cooling water amount injected from the nozzle decreases, and the cooling in the width direction and the longitudinal direction may become uneven. Was. Further, in the prior art 2,
Even if non-uniform cooling can be prevented, it is difficult to perform fine temperature control because the upper and lower control ranges are discontinuous, and distortion is likely to occur due to an increase in the difference between the upper and lower temperatures.
Further, in order to adjust the flow rate of the cooling water, a complicated control system is required for the flow control valve and its control, and the equipment cost has been enormous.

In the prior art 3 for controlling the conveying speed, the cooling speed changes stepwise, so that the temperature distribution in the longitudinal direction of the steel sheet after cooling becomes stepwise, and the material discontinuity, for example, the hardness distribution. And there is a problem that heat distortion occurs. Further, in the prior art 4, the temperature of the leading end of the steel sheet and the required cooling time at the time of entering the cooling device, the actually measured temperature at the time of the rear end of the steel plate entering the cooling device (or its predicted temperature), and the required cooling time If the temperature was not known or accurately predicted, it was difficult to determine the initial transport speed and acceleration rate, or it was difficult to accurately control the cooling stop temperature. In particular, if the measured temperature at the rear end differs from the temperature originally assumed after the stage where the initial speed and acceleration rate were determined, the target cooling stop temperature at the front end becomes Because of the discrepancy, it was not possible to change the pattern after determining the initial speed and acceleration.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and it is possible to keep the cooling start temperature constant and, after cooling, keep the cooling stop temperature constant in the longitudinal direction of the thick steel plate. To provide a heat treatment method for steel plates and a heat treatment facility for the heat treatment, particularly, heat treatment so that the cooling start temperature and the cooling stop or end temperature fall within a substantially constant temperature range from the front end to the rear end of the steel plate. It is an object of the present invention to provide a heat treatment method for a thick steel plate and a heat treatment facility for the heat treatment.

[0009]

Means for Solving the Problems A heat treatment method and heat treatment equipment for a thick steel plate according to the present invention are configured as follows. (1) A heat treatment method for a thick steel plate after rolling, in which the steel plate is leveled through a straightening machine, heated by passing through an induction heating device, and then subjected to accelerated cooling. (2) The heat treatment method for a thick steel plate according to the above (1), wherein a thermometer for measuring the temperature of the thick steel plate is provided in front of or behind the straightener to measure the temperature of the thick steel plate, and accelerated according to the temperature. The output of the induction heating device is adjusted so that the temperature in the longitudinal direction of the thick steel plate at the entrance of the cooling device becomes uniform.

(3) Heat treatment equipment for thick steel plates, in which a straightening machine, an induction heating device, and a passing-type acceleration cooling device are sequentially installed, and heat treatment is performed by continuously passing thick steel plates. (4) The heat treatment equipment for thick steel plates of the above (3), wherein thermometers are provided before and after the straightening machine so that the temperature of the thick steel plates on the entrance side of the accelerated cooling device becomes uniform according to the temperature output. A control device for controlling the output of the induction heating device was provided.

[0011]

DETAILED DESCRIPTION OF THE INVENTION In general, thick steel plates are often rolled by reverse rolling in a finishing mill. in this case,
Since the temperature effect by cooling naturally increases as the sheet thickness decreases during rolling, a temperature difference occurs in the thick steel sheet, particularly in the longitudinal direction, every time the sheet is rolled. Particularly, the temperature at the leading end and the trailing end of the thick steel plate tends to decrease.

On the other hand, the accelerated cooling method is a pass-type cooling method in which cooling is performed while passing the cooling device sequentially from the front end of the steel sheet, because the productivity is high and the equipment length is short. It is more common than the simultaneous cooling method in which a steel sheet is kept in a room and cooled all at once. In this pass-through cooling method, there is a time difference between when the front end of the steel sheet enters the cooling device and when the rear end of the steel plate is inserted into the cooling device. During this time, assuming that the temperature at the rear end gradually decreases and the steel sheet is transported and cooled at a constant transport speed,
There is a difference in the longitudinal direction of the steel sheet between the cooling start temperature of the steel plate tip and the rear end, and even if constant cooling is performed, the temperature difference between the steel plate front and rear ends at the start of cooling is almost the same. The same temperature difference occurs at the cooling stop temperature. This is due to material variations,
Particularly, the tensile strength of the steel sheet is different between the front end portion, the center portion, and the rear end portion.

Therefore, in the present invention, heating and temperature control are performed by induction heating the thick steel plate by the induction heating device so that the temperature of each part of the steel plate at the time of entering the acceleration cooling device becomes the same. At this time, in order to perform induction heating and accelerated cooling, it is necessary for the induction heating device to pass a wide range of thick steel plates without colliding with the gap between the narrow coils. In this case, there is a risk that cooling water will stay in the area that is recessed downward after cooling, and that supercooling may occur due to unevenness in local cooling. After passing through a machine, leveling is performed. Before induction heating and accelerated cooling, a flat thick steel plate is formed, and then induction heating and accelerated cooling are performed.

Next, from the leading end to the trailing end of the straightened thick steel plate, the temperature of each part passing through the induction heating device is adjusted according to the temperature of each part so as to enter the accelerated cooling device within the allowable cooling start temperature range. Further, the output of the induction heating device is changed according to the speed, and the heating is controlled so that the temperature of the thick steel plate at the entrance of the accelerated cooling device is always constant. In addition, at the end of rolling, there may be a case where there is a certain temperature deviation in the longitudinal direction of the thick steel plate. When continuously heating a thick steel plate having such a temperature deviation in the longitudinal direction through an induction heating device, the conveying speed may be controlled. Transfer speed of steel plate,
The time of intrusion into the accelerated cooling device can also be determined by calculating the amount of temperature drop of the thick steel plate by heat transfer calculation, or the amount of temperature drop during natural cooling is determined by experiment, and determined based on this, Alternatively, it may be determined.

As can be seen from the above description, the present invention
For example, a thin steel plate having a thickness of 20 mm or less or a thick steel plate having a long thickness, such as from the leading end of the thick steel plate entering the acceleration cooling device to the rear end portion of the thick steel plate entering the acceleration cooling device. This is particularly effective when the temperature at the rear end of the thick steel plate falls and deviates from the target cooling start temperature range.

[Embodiment] An embodiment of the present invention will be specifically described below. FIG. 1 is a schematic diagram showing a production line for a thick steel plate according to the present embodiment. As shown in FIG.
The steel plate 2 reverse-rolled in the above passes through a straightening machine 3, induction heating devices 4, 5 and an accelerating cooling device 6, which are linearly and continuously arranged behind the finishing mill 1, and is continuously accelerated and cooled. (Quenching process). Here, the straightening machine 3 is provided at a position of about 50 m behind the finishing mill 1, and is a straightening machine in which three upper rolls and two lower rolls are arranged, and a total of five rolls are arranged. Ear waves,
The poor formation of the thick steel plate 2 generated at the time of rolling such as middle elongation can be corrected.

The induction heating device provided next has a solenoid type induction heating device 4 capable of heating the entire cross section of the thick steel plate 2 almost uniformly, and a plate end portion which can be moved in the width direction of the plate and preferentially has a plate end. It comprises a movable transverse induction heating device 5 capable of heating, and its length is about 5 m. The output of these induction heating devices 4 and 5 is controlled by a control device 7. As shown in FIG. 2, the solenoid-type induction heating device 4 includes a coil 8 for heating the surface of the thick steel plate 2 and a power supply 9 connected thereto. A coil 10 for uniformly heating the steel plate 2 in the thickness direction and a power supply 11 connected to the coil 10 are provided. Immediately after the induction heating devices 4 and 5, an acceleration cooling device 6 having a length of 20 m is arranged.

In this heat treatment line, before the straightening machine 3, after the straightening machine 3, after the induction heating devices 4 and 5, and the acceleration cooling device 6
After the thermometers 12a, 12b, 12c, 12d
Are provided to measure the temperature in the width direction and the longitudinal direction of the thick steel plate 2. The temperature control is performed by using the temperature control model built in the computer 7 to sequentially control the thick steel plate 2.
In this method, while calculating the temperature of each part, that is, the temperature in the width direction, the longitudinal direction and the thickness direction, and correcting the calculated values based on the actual results, the temperature of each part at a certain moment is recognized on the computer. The temperature control performed here is performed so that the temperature of each part based on the results on the computer becomes substantially constant when the temperature reaches the entrance of the accelerating cooling device 6, for example, the water cooling of the straightening machine 3 is performed. The output of the apparatus, the output of the solenoid type induction heating device 4, and the position and output of the transverse type induction heating device 5 for selectively heating the plate edge in the width direction of the steel plate are controlled.

The accelerated cooling device 6 has 21 sets sandwiched vertically.
Between the upper constraining roll 13a and the lower roll 13b
The steel plate 2 is cooled online while being transported
A cooling device, wherein the pitch between each roll is 1.0 m,
The total length of the accelerated cooling device 6 is 20 m. Top between each roll
On the side of the surface and the lower surface, a market provided with a pitch of 100 mm
1m thick steel plate from spray nozzle 14^TwoPer, top
2000L / (m ^Two・ Min)
Water of twice the amount is sprayed to cool the steel plate 2.
Cooling control depends on the desired material and structure of the thick steel plate 2.
The cooling start temperature, cooling rate,
The transport speed of the thick steel plate 2 so as to satisfy the cooling stop temperature,
Calculates the required cooling time and on / off control of each cooling water supply valve
And control.

A heat treatment apparatus having this configuration was passed through a thick steel plate 2 having a width of 4000 mm, a length of 48 m, and a thickness of 15 mm immediately after finish rolling to perform heat treatment. The required cooling conditions for this thick steel plate 2 are a cooling start temperature of 830 ° C. ± 10 ° C., a cooling stop temperature of 600 ° C. ± 10 ° C., and a cooling rate of 30 ° C./s or more. Now, even if the thick steel plate 2 after the rolling is finished and rolled and immediately conveyed at the highest speed and passed through the accelerating cooling device 6, the temperature of each part of the thick steel plate 2 at the entrance of the accelerating cooling device 6 is equal to the tip temperature. Part is 830 ℃, the highest part is 12m from the tip
At the position of 860 ° C. and 780 ° C. at the rear end, there is a problem that a required cooling start temperature cannot be obtained at the rear end.

Therefore, in this embodiment, the output is controlled by using the solenoid type induction heating device 4 so that the temperature of each part of the thick steel plate 2 at the entrance of the acceleration cooling device 6 falls within the required cooling start temperature range. . At this time, the temperature of the edge portion in the plate width direction is usually lower than that of the center portion, and the transformer for selectively heating the edge portion in the width direction such that the cooling start temperature of the edge portion falls within a required temperature range. Bath type induction heating device 5
To control the width direction position and output.

Next, a temperature control method will be described. Here, for the sake of simplicity, a case where the speed of the thick steel plate 2 passing through the heat treatment apparatus is constant will be described. If heating is not performed by the induction heating devices 4 and 5 from the measured value of the thermometer 12a on the inlet side of the straightening machine 3, the temperature at the time when the heating reaches the inlet of the accelerated cooling device 6 is predicted by calculation. At this time, it is better to calculate the temperature to be measured using a temperature as close to the accelerating cooling device 6 as possible, that is, to predict using the measured value of the thermometer 12 b after the straightening machine 3. 6
When the accuracy of the temperature predicted on the entrance side is high, but the calculation cannot be completed in time, the temperatures of the respective parts at the time of reaching the acceleration cooling device 6 are sequentially calculated from the temperature on the entrance side of the straightening machine 3.

In the present embodiment, the temperature at the tip end of the thick steel plate 2 was measured to be 830 ° C. by the thermometer 12a. The temperature is lowered before being conveyed at this speed and reaching the accelerated cooling device 6. This temperature drop amount is sequentially obtained for each part of the thick steel plate 2 so that the temperature of each part when each part of the thick steel plate 2 reaches the accelerated cooling device 6 falls within the cooling start temperature 830 ° C. ± 10 ° C. of the required heat treatment condition. When the measured part reaches the induction heating devices 4 and 5, the output of the induction heating devices 4 and 5 is adjusted to perform heat compensation. By performing this operation continuously, control was performed such that the cooling start temperature of the thick steel plate 2 was within 830 ° C. ± 10 ° C.

Here, in order to compensate for the temperature, only the heating by the induction heating devices 4 and 5 has been described. However, for the portion where the temperature is high, for example, the acceleration cooling device 6 is replaced with the straightening machine 3 or the induction heating devices 4 and 5. Before and after the cooling. When the transport speed is changed, if the calculation for estimating the heat loss due to cooling down to the time of arrival at the accelerating cooling device 6 is repeated sequentially according to the speed change, the amount of heat compensation, that is, the induction heating device 4, 5 can be continuously determined.

Here, the case where the conditions of the straightening machine 3, the induction heating devices 4 and 5, and the accelerated cooling device 6 are determined when the transport speed is kept constant has been described. If the pattern is determined in advance by the calculation model described above, the output and position of the induction heating devices 4 and 5 can be obtained and controlled. By the above method and equipment, the temperature of the steel plate 2 at the entrance of the accelerated cooling device 6 is
The temperature was within the range of 830 ° C. ± 10 ° C. over the entire surface of the steel plate 2. According to the present embodiment, the thermal history of the front end portion and the rear end portion falls within the initial target cooling start temperature range of 830 ° C. ± 10 ° C. and the cooling stop temperature range of 600 ° C. ± 10 ° C. Since there is little difference in the thermal history over the whole, the variation in the material is extremely small, and the difference in hardness in the thick steel plate 2 can be suppressed to 1/3 or less as compared with the conventional speed control method or flow rate control method. As a result, there was no downgrade due to material slippage, and the product yield was greatly improved.

[0026]

As is clear from the above description, according to the present invention, the following effects can be obtained. (1) This is a method for heat treatment of a thick steel plate after rolling. After performing leveling through a straightening machine, the plate is heated by passing through an induction heating device, and then accelerated cooling is performed.
It is possible to reduce the occurrence of local variation of material and thermal strain, and to reduce the variation in temperature of the entire thick steel plate.

(2) The method for heat-treating a thick steel plate according to the above (1), wherein a thermometer for measuring the temperature of the thick steel plate is provided in front of or behind the straightening machine to measure the temperature of the thick steel plate. Accordingly, the output of the induction heating device is adjusted so that the temperature in the longitudinal direction of the thick steel plate at the entrance of the accelerated cooling device becomes uniform, so that the same effect as the above (1) can be obtained.

(3) Heat treatment equipment for thick steel plates, in which a straightening machine, an induction heating device, and a pass-type acceleration cooling device are sequentially installed, and heat treatment is performed by continuously passing thick steel plates. In an accelerated cooling device that continuously cools a thick steel plate, it is possible to manufacture a thick steel plate having a uniform cooling start temperature and a uniform cooling stop temperature. In addition, it is possible to stably produce a uniform thick steel plate with little variation in the material in the thick steel plate. Further, the product yield can be increased.

(4) The heat treatment equipment for thick steel plate according to the above (3), wherein thermometers are provided before and after the straightening machine, and the temperature of the thick steel plate on the entrance side of the acceleration cooling device is made uniform according to the temperature output. Since the control device for controlling the output of the induction heating device is provided so as to obtain the same effect as described in (3) above.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing an embodiment of the present invention.

FIG. 2 is an explanatory diagram of a main part of FIG. 1;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Finish rolling mill 2 Thick steel plate 3 Straightener 4 Induction heating device 5 Induction heating device 6 Acceleration cooling device 7 Control device 12a-12d Thermometer

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Akira Tagane, 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Inside Nihon Kokan Co., Ltd. (72) Inventor Noriyuki Suzuki 1-2-1, Marunouchi, Chiyoda-ku, Tokyo No.Nihon Kokan Co., Ltd.

Claims (4)

[Claims] 1. A method for heat-treating a steel plate after rolling, comprising:
A heat treatment method for a thick steel plate, comprising performing leveling through a straightening machine, heating by passing through an induction heating device, and then performing accelerated cooling. 2. A temperature gauge for measuring the temperature of the thick steel plate is provided in front of or behind the straightening machine to measure the temperature of the thick steel plate, and according to the temperature, the temperature in the longitudinal direction of the thick steel plate at the entrance of the accelerated cooling device. 2. The heat treatment method for a thick steel plate according to claim 1, wherein the output of the induction heating device is adjusted so as to be uniform. 3. A heat treatment equipment for a steel plate, comprising: a straightening machine;
A heat treatment equipment for thick steel plates, wherein an induction heating device and a passing-type accelerated cooling device are sequentially installed, and heat treatment is performed by continuously passing the thick steel plates. 4. A heat treatment equipment for thick steel plates, wherein thermometers are provided before and after the straightening machine, and induction heating is performed so that the temperature of the thick steel plate on the entrance side of the accelerated cooling device becomes uniform according to the temperature output. 4. The heat treatment equipment according to claim 3, further comprising a control device for controlling an output of the device.