JP2003013133A - Method and device for heat-treating thick steel plate - Google Patents

Abstract

(57) Abstract: The present invention relates to a heat treatment of a steel plate accelerated and cooled after hot rolling, capable of efficiently heat-treating a large amount of a steel plate having a small residual stress in a large amount online. An object of the present invention is to provide a method and an apparatus for heat treatment of a steel sheet. The steel plate after hot rolling is accelerated cooled by a cooling device provided on the outlet side of the hot rolling mill, and then heat-treated by an induction heating device provided on the outlet side of the cooling device. Heat treatment method for thick steel plate.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus suitable for continuously heating and heat treating a thick steel plate.

[0002]

2. Description of the Related Art Thick steel plates are manufactured by rolling a slab heated to a predetermined temperature in a heating furnace with a hot rolling mill, cooling it to room temperature, and then cutting it into predetermined dimensions. In recent years, in order to increase the strength and toughness of thick steel sheets, a cooling device is provided on the outlet side of the hot rolling mill to accelerate and cool the thick steel sheets rolled by the hot rolling mill.

Since the temperature of the accelerated cooled steel plate is not necessarily uniform, a uniform shape can be obtained even if hot correction is subsequently performed with a hot leveler or the like which is conventionally provided on the assumption of accelerated cooling. Hateful. Further, even if the shape is improved, it is difficult to eliminate the residual stress due to the uneven thermal stress inside the steel sheet.

[0004] Although the accelerated cooled thick steel plate is often subjected to tempering heat treatment after that, since this heat treatment is usually processed by a heat treatment furnace installed off-line,
This is not an efficient manufacturing method because the transportation process becomes complicated and the processing man-hours require time to mass-produce.

The following is a description of a conventional technique relating to heat treatment of thick steel plates.

Japanese Unexamined Patent Publication (Kokai) No. 4-358022 discloses that a heating apparatus installed on the same line as a rolling mill and an accelerated cooling apparatus performs tempering treatment by rapid heating. In tempering, the temperature rising rate to a predetermined tempering temperature of 450 ° C or higher and _Ac1 point or lower is 1 ° C / sec or more, the tempering temperature is not maintained, and the subsequent cooling rate is 0.05 ° C / sec or more 20 ° C It is limited to cool at less than 1 second. This treatment aims to improve work efficiency and toughen the steel sheet,
As the heating method, electric heating, dielectric heating, infrared radiation heating, or the like is used.

In Japanese Unexamined Patent Publication No. 6-254615, a hot straightening machine, a cooling device and a heat retaining device are arranged in this order, and the steel plate is kept at a constant temperature by the heat retaining device to make the temperature distribution on the inner surface of the steel plate uniform. This shows a configuration for manufacturing a steel sheet having an excellent shape.

[0008]

However, the above-mentioned conventional technique has the following problems.

The method disclosed in Japanese Patent Laid-Open No. 4-358022 does not show any specific equipment layout and heating method in actual manufacturing. If the facilities are arranged on the same line as in the embodiment, there is a problem that the rolling efficiency and the heat treatment efficiency are unbalanced. Also, 40-
The heat treatment of a steel sheet having a total length of 50 m requires a large-scale facility corresponding to it, and it is practically difficult to install such a facility. Further, after the heat treatment, a cooling device is required again, which makes the production of steel sheet costly.

In the method of Japanese Patent Laid-Open No. 6-254615, there is no description of the details of the heat retaining device, and there is a problem in processing efficiency and ability to keep the temperature online.
Processing on the same line is practically impossible.

As described above, it is desirable to provide a heat treatment furnace on-line in order to heat-treat a large amount of rolled and accelerated cooled thick steel plates efficiently. There is a problem and no technology has been developed to solve it.

The present invention has been made in order to solve the above problems, and in the heat treatment of a thick steel sheet that has been hot-rolled and then accelerated-cooled, online, efficiently, in a large amount and with little residual stress. An object of the present invention is to provide a heat treatment method and an apparatus for thick steel plates, which can heat treat steel plates.

[0013]

The method and apparatus for heat treatment of thick steel plate of the present invention have the following features.

(1) After carrying out accelerated cooling of a thick steel sheet after hot rolling by a cooling device provided on the outlet side of the hot rolling mill, heat treatment is performed by an induction heating device provided on the outlet side of the cooling device. Characteristic method for heat treatment of thick steel plate.

(2) The heat treatment method for a thick steel plate as described in (1) above, wherein the induction heating device is a solenoid type induction heating device.

(3) The heat treatment method for a thick steel sheet according to the above (1) or (2), characterized in that the thick steel sheet is heat-treated by an induction heating device and then hot-corrected by a hot leveler.

(4) The heat treatment method for a thick steel sheet according to any one of the above (1) to (3), wherein the tempering heat treatment is performed by the heat treatment of the thick steel sheet by the induction heating device.

(5) Any one of the above (1) to (4), characterized in that the temperature distribution of the thick steel plate after accelerated cooling is measured and the heating condition of the induction heating device is set based on the measurement result. The method for heat treating a thick steel sheet according to.

(6) The induction heating apparatus is a transverse induction heating apparatus, characterized in that the temperature distribution of the thick steel sheet after accelerated cooling is measured, and the thick steel sheet is locally heat-treated based on the measurement result. The method for heat treating a thick steel plate according to (5) above.

(7) A device for continuously heat-treating a thick steel plate after hot rolling on the same line, which comprises a cooling device for accelerated cooling from the upstream of the continuous line, and an accelerated cooling by the cooling device. A heat treatment apparatus for a thick steel plate, comprising: an induction heating device for heat treating the thick steel plate; and a hot leveler for hot straightening the thick steel plate heat-treated by the induction heating device.

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is an explanatory view showing an embodiment of an apparatus for manufacturing a thick steel plate used for carrying out the heat treatment method for a thick steel plate according to the present invention.

The apparatus for manufacturing a thick steel plate of this embodiment comprises a rolling mill 1 from the upstream of the continuous line, a cooling device 2 for accelerated cooling of the thick steel plate 5 to the exit side of the rolling mill 1, and an accelerated cooling by the cooling device 2. An induction heating device 3 for heat-treating the thick steel plate 5 thus prepared and a hot leveler 4 for hot-correcting the thick steel plate 5 heat-treated by the induction heating device 3 are provided.

The cooling device 2 is a device for accelerating and cooling a thick steel plate by a water spray or a jet flow, and an ordinary device such as roller quench or pressure quench can be used.

The hot leveler 4 is not particularly limited as long as it can correct the strain after rolling and accelerated cooling, and a normal hot straightening machine can be used.

The induction heating device 3 is used as a tempering furnace after accelerated cooling by the cooling device 2, and heat treatment of the material,
It is used for the purpose of reducing residual stress. An induction heating device capable of rapid heating is used in order to efficiently heat-process a large amount of thick steel plates manufactured by a cooling device online.

The induction heating device is preferably a solenoid type induction heating device. Since the solenoid-type induction heating device can give the steel material surface layer a different heat history than the inside of the steel material, the hardness of the steel material in the thickness direction, such as softening of the steel material surface layer only, and the heating rate of the surface layer part higher than the center part This is because it is possible to rapidly heat the steel with the effect of reducing the residual stress of the steel material.

Next, the operation and action of the thick steel plate manufacturing apparatus of the above embodiment will be described.

The thick steel plate 5 which has been accelerated and cooled by the cooling device 2 after being rolled by the rolling mill 1 is rapidly heated by the induction heating device 3 and tempered. After the heat treatment by the induction heating device 3, the thick steel plate 5 is hot-corrected by the hot leveler 4, so that the heat-treated steel plate can be efficiently manufactured online. Since it is an induction heating device that heats a steel sheet through it, the equipment can be made compact, can be installed between the existing accelerated cooling equipment and the hot leveler, and can be installed inexpensively. Furthermore, after heat treatment, it can be cut as it is on the shear line, and the manufacturing period can be greatly shortened.

Table 1 shows an example of specifications of a solenoid type induction heating apparatus used for carrying out the heat treatment method for thick steel plates for the purpose of tempering the material of the present invention. According to Table 1, the number of inductors is 6, and the frequency of each inductor is 1000 Hz. The maximum input power is set to 5100 KW by the inductor 2 through which the thick steel plate passes second.

The coil length of each inductor of the present solenoid type induction heating apparatus is 0.8 m, the distance between the inductors is 1.6 m, and the equipment length is 14.4 m. Since the equipment length is short in this way, the equipment is compact and can be installed between the existing accelerated cooling equipment and the hot leveler. The heating capacity is, for example, 25 mm in thickness and 645 ° C at the center of thickness.
When heating is performed for 10 seconds and soaking for 20 seconds, the tempering processing time is 3 minutes.

As described above, a space is provided between the inductors and intermittent heating is performed to enable rapid and uniform heating. By soaking the steel sheet, the heat stress of the surface layer of the steel sheet is small, the strain is small, and as a result, a steel sheet with low residual stress can be manufactured.

[0032]

[Table 1]

Next, a method for heat treatment of a thick steel sheet in which it is preferable to measure the temperature distribution of the thick steel sheet after accelerated cooling and set the heating conditions of the induction heating device based on the measurement result will be described.

In the embodiment of FIG. 1, for example, a radiation thermometer is installed on the outlet side of the cooling device to measure the temperature distribution of the thick steel plate after accelerated cooling. The residual stress is estimated from this temperature distribution, and the heating conditions for the induction heating device are set. When the residual stress seems to be lower than the temperature distribution, it is possible to increase the efficiency by, for example, increasing the conveying speed in the induction heating device, or perform hot correction with a hot leveler without heat treatment with the induction heating device. It is also possible.

In the present invention, a solenoid type is used as the induction heating device, but when the temperature distribution of the thick steel plate after accelerated cooling is measured and the width direction of the thick steel plate is locally heated based on the measurement result, A transverse type induction heating device may be used together.

[0036]

(Embodiment 1) In the embodiment of the present invention, the apparatus as shown in FIG. 1 is used to perform reverse rolling by finish rolling mill 1 and finish rolling, and then cooling stop temperature 550 ° C. by cooling device 2.
The thick steel plate 5 that has been accelerated to be cooled is subjected to a tempering heat treatment for the purpose of reducing the residual stress so that the surface temperature of the thick steel plate becomes the tempering temperature of 650 ° C. by the solenoid type induction heating device 3, and then the hot leveler 4 heats it. I just corrected it. Here, the hot leveler is a straightening machine in which a total of 5 rolls including 3 upper rolls and 2 lower rolls are arranged, and it is possible to correct the shape defect of the thick steel plate caused by the repeated bending such as warpage during rolling or accelerated cooling. it can. After hot straightening with a hot leveler 4, the thick steel plate was cut into strips, and the amount of camber of the thick steel plate after stripping due to residual stress was measured. The results are shown in Table 2 together with steel plate dimensions and flatness after hot leveler straightening.
It was shown to.

As a comparative example, a material having the same size as that of the embodiment is reverse-rolled and finish-rolled by a finish rolling mill 1 using a device as shown in FIG. 1, and then cooling is stopped by a cooling device 2. The thick steel plate 5 accelerated and cooled to a temperature of 550 ° C. was hot-corrected by the hot leveler 4 without being heat-treated by the solenoid-type induction heating device 3. The thick steel plate was cut into strips, and the amount of camber of the thick steel plate after stripping due to residual stress was measured. The results are also shown in Table 2 together with the steel plate dimensions and the flatness after the hot leveler straightening.

[0038]

[Table 2]

According to Table 2, when the tempering heat treatment for the purpose of reducing the residual stress is carried out, the camber amount after cutting the thick steel plate is 1.5 mm and the flatness after the hot leveler straightening is 2 mm. On the other hand, in the case of the comparative example in which the tempering heat treatment for the purpose of reducing the residual stress was not carried out, the camber amount after cutting the thick steel plate was 35 mm and the flatness after straightening the hot leveler was 16 mm. It can be seen that, by carrying out the tempering heat treatment, the residual stress is reduced, and a steel sheet having excellent striped camber characteristics and flatness can be efficiently produced online. (Example 2) In the example of the present invention, using a device as shown in FIG. 1, after reverse rolling by finish rolling mill 1 and finish rolling, the thickness accelerated accelerated by cooling device 2 to a cooling stop temperature of 230 ° C. The steel sheet 5 is subjected to a tempering heat treatment for the purpose of tempering the material using a solenoid type induction heating device 3 so that the center temperature of the thick steel sheet becomes a tempering temperature of 645 ° C., and then hot working is performed by a hot leveler 4. I corrected it. Here, the hot leveler is a straightening machine in which a total of 5 rolls including 3 upper rolls and 2 lower rolls are arranged, and it is possible to correct the shape defect of the thick steel plate caused by the repeated bending such as warpage during rolling or accelerated cooling. it can. After hot-correcting with the hot leveler 4, the thick steel plate was inspected for material and its material characteristic value was measured. The results are shown in Table 3.

As a comparative example, a material having the same size as that of the invention example is reverse-rolled by the finish rolling mill 1 to finish rolling using the apparatus shown in FIG. 1, and then the cooling is stopped by the cooling device 2. The thick steel plate 5 accelerated and cooled to a temperature of 230 ° C. is tempered at a tempering temperature of 645 ° C. at a tempering temperature of the thick steel plate using the conventional off-line gas combustion furnace instead of the solenoid induction heating device 3. A heat treatment for tempering was carried out for the purpose of hot-straightening with a hot leveler 4. This thick steel plate was subjected to a material inspection to measure its material characteristic values. The results are also shown in Table 3.

[0041]

[Table 3]

According to Table 3, in both the present invention example and the comparative example, the material characteristic values after tempering heat treatment for the purpose of tempering the material are as follows: YS = 550 MPa for yield strength YS and TS = 640 MPa for tensile strength TS. Was exactly the same as. However, in the example of the present invention, while the rolling-heat treatment-manufacturing time until product cutting completion in the shear line was several hours,
In the comparative example, the manufacturing time required several days due to transportation to the heat treatment furnace, waiting in order depending on the temperature of the heat treatment furnace, transportation to the shear line, and the like. That is, by carrying out the tempering heat treatment using the solenoid type induction heating apparatus of the present invention, a material equivalent to a normal off-line gas combustion furnace temper material was obtained in a short time. Here, in the induction heating device used in the example of the present invention, since the heating temperature can be set to an arbitrary temperature for each thick steel plate, naturally there is no waiting depending on the temperature of the heat treatment.

[0043]

As described above, according to the present invention, the purpose of the present invention is to reduce the residual stress of thick steel plates online in an efficient and large amount in the heat treatment of the thick steel plates that have been accelerated and cooled after hot rolling. It is possible to perform tempering heat treatment and tempering heat treatment for the purpose of tempering the material.

[Brief description of drawings]

FIG. 1 is an explanatory view showing an embodiment of an apparatus for manufacturing a thick steel plate for carrying out a heat treatment method for a thick steel plate of the present invention.

[Explanation of symbols]

1 Finishing mill 2 Cooling device 3 induction heating device 4 hot levelers 5 thick steel plate

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Hiroshi Sekine             1-2-1, Marunouchi, Chiyoda-ku, Tokyo             Main Steel Pipe Co., Ltd. (72) Inventor Akio Fujibayashi             1-2-1, Marunouchi, Chiyoda-ku, Tokyo             Main Steel Pipe Co., Ltd.

Claims (7)

[Claims] 1. A hot rolled steel sheet is accelerated and cooled by a cooling device provided on the outlet side of the hot rolling mill, and then heat treated by an induction heating device provided on the outlet side of the cooling device. Heat treatment method for thick steel plate. 2. The heat treatment method for a thick steel plate according to claim 1, wherein the induction heating device is a solenoid type induction heating device. 3. The heat treatment method for a thick steel plate according to claim 1, wherein the thick steel plate is heat-treated by an induction heating device and then hot-corrected by a hot leveler. 4. The heat treatment method for a thick steel plate according to claim 1, wherein the tempering heat treatment is performed by the heat treatment of the thick steel plate by an induction heating device. 5. The thickness according to claim 1, wherein the temperature distribution of the thick steel plate after accelerated cooling is measured, and the heating condition of the induction heating device is set based on the measurement result. Steel plate heat treatment method. 6. The induction heating apparatus is a transverse type induction heating apparatus, wherein the temperature distribution of the thick steel sheet after accelerated cooling is measured, and the thick steel sheet is locally heat-treated based on the measurement result. The heat treatment method for a thick steel plate according to claim 5. 7. A device for continuously heat-treating a thick steel sheet after hot rolling on the same line, comprising a cooling device for accelerated cooling from the upstream of the continuous line, and an accelerated cooling by the cooling device. A heat treatment apparatus for a thick steel plate, comprising: an induction heating device for heat treating the thick steel plate; and a hot leveler for hot-correcting the thick steel plate heat-treated by the induction heating device.