JP2009263711A - Heat treatment apparatus for welding area of electro-resistance welded tube - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problems of the conventional technique that the equipment length of a heat treatment apparatus increases, and an enormous running cost is necessitated, resulting in nonefficient electro-resistance welded tube manufacture. <P>SOLUTION: The heat treatment apparatus for subjecting a welding area of the electro-resistance welded tube constituted by welding unwelded seam part 21 of an open tube 20 by an electro-resistance welding equipment 1 to heat treatment on an outlet side of an electro-resistance welding equipment, is provided with an external surface side induction heating means 2 having a plurality of induction heating stands 13 arranged on an external surface side of the tube in a material passage direction, and an internal surface side induction heating means 3 having a plurality of magnetic flux generation units 4 held with bars 6 on an internal surface side of the tube and arranged in a material passage direction. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a heat treatment apparatus for an electric resistance welded portion, and more particularly, to a heat treatment apparatus for an electric resistance welded portion used for performing heat treatment for improving the toughness of the electric resistance welded portion.

  Usually, the ERW pipe is formed into an open pipe by a roll forming device while continuously passing the hot-rolled strip, and then the unwelded seam portion of the open pipe (the circumferential ends of the open pipe, It is manufactured by welding to a pipe by a method in which the belt is heated to the melting point or higher by an electric seam welder, and the heated unwelded seam part is abutted and crimped. Is done. The electric seam welding apparatus has a melting and heating means (induction coil or the like) that causes high-frequency current to flow through an unwelded seam portion to concentrate Joule heat, and a squeeze roll that abuts and presses the heated and melted unwelded seam portion. Since the welded part formed by welding the unwelded seam part with an electric seam welding device and its surroundings were rapidly heated and cooled rapidly during this welding, the structure, hardness, The components and the like are in a non-uniform state as welded, and workability, toughness, corrosion resistance and the like are reduced.

Therefore, it is necessary to heat-treat the welded part and the welded heat-affected part around the welded part (collectively, an electric-welded pipe welded part) in order to make the workability, toughness, corrosion resistance, and the like comparable to the base material. An induction heating type heat treatment apparatus is installed on the exit side of the roll, and is used to heat treat the welded portion immediately after welding.
Conventionally, this heat treatment apparatus generally has a plurality of induction heating stands arranged in series along the material direction on the outer surface side of the welded portion of the ERW pipe welded portion, and generates a magnetic flux by these induction heating stands, so that the ERW pipe welding is performed. An induced current is generated in the part, and heat treatment is performed by the resistance heat.

  Therefore, in the conventional heat treatment apparatus, since heating is performed only from the outer surface side of the pipe, it is difficult to heat the entire thickness, particularly thick materials, and the temperature is inevitably increased between the outer surface side of the pipe and the inner surface side of the pipe. There was a difference. This temperature difference increases as the wall thickness of the pipe increases. When the pipe wall becomes thicker, either the pipe outer surface temperature or the pipe inner surface temperature deviates from the target temperature, which often causes a problem. For example, when manufacturing ERW pipes for thick and high toughness line pipes, if the induced current on the pipe outer surface side is increased in order to improve the toughness by sufficiently normalizing the pipe inner surface side, the pipe outer surface temperature becomes the target temperature. And a coarse bainite structure is generated, the hardness increases and the toughness further decreases. On the other hand, if the induced current on the tube outer surface side is reduced so that a coarse bainite structure is not generated, an untransformed structure remains as welded on the tube inner surface side, and the target toughness is hardly obtained.

  Therefore, in order to cope with these problems, a means for reducing the temperature difference between the tube outer surface side and the tube inner surface side by securing a sufficient heat transfer time after induction heating has been adopted. That is, measures are taken such as installing a long facility in which a large number of the stands are arranged in series and gradually heating them. However, if the equipment length becomes long (the number of stands increases), not only the capital investment cost but also the input power increases and a great running cost is required. There is also a problem that the non-uniform portion increases and the yield of the material is greatly reduced.

As means for solving these problems, as shown in Patent Document 1 and Patent Document 2, a method of heating to a specific target temperature exceeding the Ac ₃ transformation point, cooling once, and further heating is known.
JP 59-129729 A JP-A-6-220547

However, in the conventional techniques shown in Patent Document 1 and Patent Document 2, a heating pattern up to a specific target temperature exceeding the Ac ₃ transformation point is not particularly defined, and since cooling is performed during heating, As before the proposal, the equipment length of the heat treatment apparatus becomes long, and a large running cost is required due to a large amount of input power, which causes a problem of inefficient manufacture of the ERW pipe.

The present invention has been made to solve the above problems, and the gist of the present invention is as follows.
(Claim 1)
While the strip material is continuously passed, the above-mentioned ERW welding device is applied to an ERW welded portion formed by roll forming an open tube and welding an unwelded seam portion of the open tube with an ERW welding device. A heat treatment apparatus for an electric-welded pipe welded portion that performs heat treatment on the outlet side of the pipe, and includes an outer surface-side induction heating means in which a plurality of induction heating stands are arranged in the material direction on the tube outer surface side, and a magnetic flux generation unit on the tube inner surface side A heat treatment apparatus for an electric-welded pipe welded portion, comprising: an inner surface-side induction heating means that is held in a bar and is arranged in the material passing direction.
(Claim 2)
The induction heating stand and the magnetic flux generation units are arranged in the same number, and the induction heating stand and the magnetic flux generation units that are arranged in the same order in the material passing direction are arranged at substantially the same material passing position. Item 2. An apparatus for heat-treating an electric-welded pipe weld according to Item 1.

  According to the present invention, it is possible to heat-treat an ERW welded portion with a small number of stands, and it is possible to efficiently manufacture an ERW tube that is excellent in the toughness of the welded portion.

  Conventionally, in the production line of the ERW pipe, the heat treatment apparatus on the outlet side of the ERW welding apparatus has to be a long facility, and it has been a problem that a great running cost is required. This is because the heating means of the conventional heat treatment apparatus is installed only on the outer surface side of the tube and is heated only from the outer surface side of the tube, so it is difficult to uniformly heat the entire thickness, and inevitably the inner and outer surfaces of the tube The temperature difference increases as the wall thickness increases, and when the wall thickness increases, one of the inner and outer surfaces of the pipe is easily removed from the target temperature. It was necessary to increase the inner surface temperature by conducting heat and gradually increasing the heating time.

Therefore, the inventors focused on the heating means, and as a result of examination, in order to prevent insufficient heating on the tube inner surface side without overheating the tube outer surface side even if the equipment is short, It has been found that it is effective to install induction heating means not only on the outer surface side but also on the inner surface side of the tube and use them to heat the ERW pipe welded part.
That is, with the conventional heating means only on the tube outer surface side, when heating to the target Ac ₃ transformation point + α temperature range, the tube inner surface side even when the tube outer surface side reaches the target temperature, especially as the wall thickness increases. In many cases, the temperature of did not reach the target temperature. For this reason, the length of the induction heating means installed on the outer surface side of the pipe must be lengthened and gradually heated while utilizing heat conduction, and inefficient ERW pipe manufacturing has been performed.

Therefore, as an apparatus for efficient heating, if induction heating means is installed not only on the tube outer surface side but also on the tube inner surface side and heated from both the tube outer surface side and the tube inner surface side, even if the wall thickness is thick, about It is only necessary to heat 1/2, and it can be efficiently heated.
The induction heating means on the tube outer surface side (outer surface induction heating means) can be configured using a conventional induction heating stand, but in the present invention, the number of the stands can be reduced as compared with the conventional one.

  The pipe inner surface side induction heating means (inner surface side induction heating means) is configured by holding a plurality of magnetic flux generating units on the inner surface side of the pipe with a bar and arranging them in the material passing direction. As long as the magnetic flux generation unit functions as a magnetic flux generation source that can be inserted into the inner surface of the tube and can efficiently generate an induced current on the inner surface of the welded portion of the ERW tube, The material, structure, shape, and dimensions are not particularly limited.

  In addition, in order to efficiently control the temperature with high accuracy, the induction heating stand and the magnetic flux generation unit have the same number of the induction heating stands and the magnetic flux generation units, and the arrangement order in the material passing direction is the same order. May be arranged at substantially the same position in the material passing direction. This is because it becomes easy to control the magnetic flux density for controlling the temperature.

Hereinafter, a description will be given based on examples.
(Example of the present invention)
FIG. 1 is a schematic diagram showing an example of the present invention. The electric seam welding apparatus 1 crimps the induction coil 10 that heats the unwelded seam portion 21 of the open pipe 20 that is continuously passed through to the melting point or higher, and the heated unwelded seam portion 21 so as to crimp the electric welded pipe. A squeeze roll 11 is formed to form a weld. Note that the open pipe 20 is formed by roll forming with a continuous roll material passing through an upstream roll forming apparatus (not shown). On the exit side of this electric seam welding apparatus 1, and preferably on the exit side of the cutting bit 12 for welding bead cutting, as shown in the drawing, a heat treatment apparatus for an electric resistance welded portion as an example of the present invention is installed. Yes. This heat treatment apparatus has an outer surface side induction heating means 2 in which four induction heating stands 13 are arranged in the material direction on the outer surface side of the tube, and a magnetic flux generating unit 4 held by a bar 6 on the inner surface side of the tube. And 4 units of inner surface side induction heating means 3. The bar 6 is a hollow bar, and an energizing plate 8 for energizing the magnetic flux generating unit 4 on the inner surface side of the tube is inserted into the hollow bar, and the energizing plate 8 passes through the mutual facing gap of the unwelded seam portion 21. Then, it is connected to the power supply means 7 placed on the outer surface side of the pipe, and power is supplied from this power supply means 7. Therefore, it is possible to supply power from the power supply means 7 on the outer surface side of the tube to the magnetic flux generation unit 4 on the inner surface side of the tube via the energizing plate 8.

Furthermore, as a preferred embodiment, the same number of induction heating stands 13 and magnetic flux generation units 4 having the same passing direction position are arranged at substantially the same passing direction position.
Further, a thermometer 9 is arranged on the exit side of each induction heating stand 13 of the outer surface side induction heating means 2 and each magnetic flux generation unit 4 of the inner surface side induction heating means 3, and each induction based on the measured value of each thermometer 9. It is possible to control the temperature on both the outer surface side and the inner surface side of the welded portion of the ERW pipe by adjusting the amount of power supplied to the heating stand 13 and / or each magnetic flux generation unit 4.

Flattening with a leveler while passing a strip of steel (Ac ₃ transformation point is 860 ° C.) containing 0.05% C-0.2% Si-1.4% Mn by mass% Following straightening, it is formed into an open tube with a roll forming device, and the unwelded seam of the open tube is welded with an electric resistance welding device to form an electric resistance tube with an outer diameter of 600 mm and a wall thickness of 19.1 mm. 1 was heat-treated using the heat treatment apparatus shown in FIG. The following test was performed on the welded portion of the electric resistance welded tube after the heat treatment.
1) Structure test: The structure of the thick section was examined with an optical microscope.
2) Charpy test: An impact test piece (V-notch test piece) was collected in accordance with JIS Z 2242. The test specimens were collected at 10 locations in the pipe longitudinal direction, with the test specimen length direction parallel to the pipe circumferential tangent direction, and the test specimen notch position as the width of the ERW pipe welded portion (extended range in the pipe circumferential direction). ) The sample was taken from the thickness center part of the welded part of the ERW pipe according to the center position. Using these test pieces, a Charpy impact test was performed at a test temperature of −46 ° C. in accordance with the provisions of JIS Z 2242, and the absorbed energy and the brittle fracture surface ratio were determined.
(Conventional example)
The heat treatment apparatus of the conventional example is configured by deleting the inner surface side induction heating means 3 and increasing the number of stands of the outer surface side induction heating means 2 from 4 to 7 in the heat treatment apparatus of FIG.

The same strip material as used in the present invention example was made into an ERW pipe of the same size in the same process until ERW welding, and subsequently the ERW pipe welded portion was used using the heat treatment apparatus of the conventional example. Was heat treated. The same test as in the example of the present invention was performed on the welded portion after the heat treatment.
According to the results of the structure test, in the ERW pipe according to the present invention, a substantially uniform ferrite-pearlite structure is observed over the entire thickness cross section of the ERW weld zone, and the target temperature exceeding the Ac ₃ transformation point is sufficiently reached. It showed that it was normalized. On the other hand, in the electric-resistance-welded pipe according to the conventional example, is organized to indicate that barely reaches the inner surface side to the target temperature of the Ac ₃ transformation point than is observed, the development of coarse bainite structures to reduce the toughness in Kangaimen side observation It was done.

  The results of the Charpy test are shown in Table 1. From Table 1, in the ERW pipe according to the example of the present invention, although the number of stands of the heat treatment device for the ERW pipe welded portion is small, the absorbed energy of the welded portion is high, the brittle fracture surface ratio is small, and the toughness is good. And the reliability of the product is high. On the other hand, in the case of the ERW pipe according to the conventional example, although the number of the heat treatment devices for the ERW welded part is large, the absorbed energy of the welded part is low, the brittle fracture surface ratio is large, and the toughness is reduced. Poor reliability.

It is a schematic diagram which shows one example of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Electric resistance welding apparatus 2 Outer surface side induction heating means 3 Inner surface side induction heating means 4 Magnetic flux generation unit 5 Electric resistance pipe 6 Bar 7 Power supply means 8 Current supply plate 9 Thermometer
10 induction coil
11 Squeeze Roll
12 Cutting tool
13 Induction heating stand
20 open tube
21 Unwelded seam

Claims (2)

  While the strip material is continuously passed, the above-mentioned ERW welding device is applied to an ERW welded portion formed by roll forming an open tube and welding an unwelded seam portion of the open tube with an ERW welding device. A heat treatment apparatus for an electric-welded pipe welded portion that performs heat treatment on the outlet side of the pipe, and includes an outer surface-side induction heating means in which a plurality of induction heating stands are arranged in the material direction on the tube outer surface side, and a magnetic flux generation unit on the tube inner surface side A heat treatment apparatus for an electric resistance welded portion having an inner surface side induction heating means which is held by a bar and is arranged in the material passing direction.   The induction heating stand and the magnetic flux generation units are arranged in the same number, and the induction heating stand and the magnetic flux generation units that are arranged in the same order in the material passing direction are arranged at substantially the same material passing position. Item 2. An apparatus for heat-treating an electric-welded pipe weld according to Item 1.

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