JP4190504B2 - Heat treatment method for formed steel pipe - Google Patents

Description

  The present invention relates to a heat treatment method for various shaped steel pipes such as steel pipes used as steel pipe columns of steel structures.

Conventionally, in order to remove residual stress by annealing (tempering) after cold working a steel sheet, for example, the cold work is heated to about 600 ° C. and then gradually cooled (for example, (See Non-Patent Document 1 and Non-Patent Document 2.)
Kumao Ebihara “Metal Handbook” published by Maruzen Co., Ltd., December 20, 1982, p. 360-365 Saburo Misawa “Introduction to New Heat Treatment Technology”, Taiga Publishing, August 15, 1980, 11. Structure and transformation of steel materials 2-3, P.I. 12, 21. General heat treatment operation 118-119

  However, according to the above-described conventional configuration, the temperature of the cold-worked material at room temperature is raised to around 600 ° C. by one heating means, so that a considerable heat treatment time is required and the processing efficiency is poor. The cost was high. In addition, when the cold-worked product is a formed steel pipe (such as a square steel pipe), it is difficult to raise the temperature uniformly in the circumferential direction and the length direction when the temperature is raised from room temperature to around 600 ° C. at once. There was a problem as a product due to severe twisting, bending and deformation.

  Accordingly, the invention according to claim 1 of the present invention can remove the residual stress and restore the toughness, and can also heat-treat the formed steel pipe that is hardly twisted, bent, or deformed at a significant cost reduction. It is intended to provide a method.

In order to achieve the above-described object, in the heat treatment method for a shaped steel pipe according to claim 1 of the present invention, a plurality of heating zones and hold zones are respectively arranged in the heat treatment portion, and these heating zones and hold zones are arranged. Is a zone length similar to each other, and is set a little longer than the tube length, and at the boundary between the heating zone and the hold zone, a partition body that allows passage of the formed steel pipe is provided, the molded shaped steel tube cold, and alternately moved sequentially into the heating zone and hold zone, with stepwise temperature rise in the heating zone group, the hold zone group was raised at the previous stage of the heating zone forming by holding in an atmosphere of the same temperature condition as the temperature of the steel pipe, achieving uniformity of heating temperature in the circumferential direction and length direction of the forming steel, the final stage hole Dozo Thereby gradually cooling the heated shaping steel pipe taken out from those that characterized.

Therefore, according to the first aspect of the present invention, the residual stress can be removed and the toughness can be recovered by heat-treating the cold-formed formed steel pipe. Further, in each heating zone in which the heat treatment is set to be slightly longer than the tube length, the amount of combustion heat can be made useless by gradually raising the temperature to the target temperature. And in each hold zone that is set a little longer than the pipe length and partitioned by the partition that allows passage of the shaped steel pipe, the atmosphere in the same temperature state as the temperature of the shaped steel pipe raised in the preceding heating zone By holding below, the heating temperature in the circumferential direction and length direction of the formed steel pipe can be made uniform.

  Further, the heat treatment method for a shaped steel pipe according to claim 2 of the present invention is characterized in that, in the configuration according to claim 1 described above, the temperature of the shaped steel pipe is increased up to 650 ° C. in the final heating zone. Is.

Therefore, according to the invention of claim 2, it is possible to prevent the crystal graining after the slow cooling and maintain the stickiness and strength.
In the heat treatment method for a shaped steel pipe according to claim 3 of the present invention, in the configuration according to claim 1 or 2, a plurality of heating zones and hold zones are respectively formed in a common furnace, The steel pipe is moved linearly.

Therefore, according to the invention of claim 3, the furnace and the conveying means can be made compact and inexpensive, and the movement control can be simplified.
Furthermore, the heat treatment method for a shaped steel pipe according to claim 4 of the present invention is characterized in that, in the configuration according to any one of claims 1 to 3, the shaped steel pipe is a square steel pipe.

  Therefore, according to the invention of claim 4, the cold-formed square steel pipe can be heat-treated to remove the residual stress and restore the toughness, and the square steel pipe that is hardly twisted, bent, or deformed is greatly reduced. It can be obtained by cost reduction.

  Moreover, the heat treatment method for a shaped steel pipe according to claim 5 of the present invention is characterized in that, in the configuration according to any one of claims 1 to 3, the shaped steel pipe is a round steel pipe. .

  Therefore, according to the invention of claim 5, by subjecting the cold-formed round steel pipe to heat treatment, the residual stress can be removed and the toughness can be restored, and the round steel pipe that is hardly twisted, bent, or deformed, It can be obtained at a significant cost reduction.

According to the first aspect of the present invention described above, it is possible to remove residual stress and restore toughness by heat-treating the cold-formed formed steel pipe, and the formed steel pipe obtained by such heat treatment is In addition, there is almost no residual stress and a high buckling strength can be obtained, and the secondary weldability can be improved, so that the proof stress and toughness can be improved while maintaining the effect of the heat treatment. Further, in each heating zone in which the heat treatment is set to be slightly longer than the tube length, the amount of combustion heat can be made useless by gradually raising the temperature to the target temperature. And in each hold zone that is set a little longer than the pipe length and partitioned by the partition that allows passage of the shaped steel pipe, the atmosphere in the same temperature state as the temperature of the shaped steel pipe raised in the preceding heating zone By holding below, it is possible to make the heating temperature uniform in the circumferential direction and length direction of the formed steel pipe, to prevent the occurrence of distortion, and thus homogeneous forming that hardly twists, bends and deforms. Steel pipes can be obtained at a significant cost reduction.

Further, according to the second aspect of the present invention described above, it is possible to prevent the grain formation after the slow cooling and maintain the stickiness and strength.
According to the third aspect of the present invention described above, the furnace and the conveying means can be configured to be compact and inexpensive, and the movement control can be simplified.

  Further, according to the fourth aspect of the present invention described above, the heat treatment of the cold-formed square steel pipe can achieve the removal of residual stress and the recovery of toughness, and hardly causes twisting, bending or deformation. A homogeneous square steel pipe can be obtained at a significant cost reduction.

  Moreover, according to the fifth aspect of the present invention described above, it is possible to remove residual stress and restore toughness by heat treatment of the cold-formed round steel pipe, and torsion, bending, and deformation almost occur. No homogeneous round steel pipe can be obtained at a significant cost reduction.

[Embodiment 1]
Below, Embodiment 1 of this invention is demonstrated based on FIGS. 1-3 as a state employ | adopted as the square-shaped square steel pipe.

  As shown in FIGS. 1 and 3, a cold-formed long and square prismatic steel pipe (an example of a formed steel pipe) 1 has an outer dimension W between regular outer surfaces and a corner having a regular outer radius of curvature R. A butt weld 2 by butt welding is formed on one flat plate portion. The square steel pipe 1 has a predetermined pipe length L.

  As shown in FIGS. 1 and 2, the square steel pipe 1 is transferred to the carry-in floor 11 and is conveyed. The square steel pipe 1 transported to the terminal end of the carry-in floor 11 is transferred to a roller conveyor (an example of a transport means) 12 and transported on a transport path 13 formed by the roller conveyor 12. A heat treatment section 21 and a cooling bed 31 are disposed in the transport path 13.

  That is, the heat treatment section 21 is a combustion heating method in which the square steel pipe 1 is put in one furnace 22, and a carry-in port and a carry-out port are formed at both ends of the furnace 22 in the front-rear direction by through holes. Opening and closing doors 23 are respectively provided at the mouth and the carry-out port. In the furnace 22, three (a plurality of) heating zones 25A, 25B, and 25C and hold zones 26A, 26B, and 26C are formed (arranged) in an intersecting manner. At that time, the heating zones 25A, 25B, and 25C and the hold zones 26A, 26B, and 26C have the same zone length L + α, and are set slightly longer (α) than the tube length L. The first heating zone 25A is opposed to the carry-in entrance, and the final hold zone 26C is opposed to the carry-out exit.

  Further, in each heating zone 25A, 25B, 25C, lower heating burners 27A, 27B, 27C are arranged on one side lower part of the furnace 22 and facing the intermediate position between the rollers of the roller conveyor 12, and Upper heating burners 28A, 28B, 28C are disposed on the other upper side of the furnace 22 and at positions facing the lower heating burners 27A, 27B, 27C in a staggered manner.

  The heating temperatures of the heating zones 25A, 25B, and 25C are managed by adjusting the heating burners 27A, 28A, 27B, 28B, 27C, and 28C. That is, the heating burners 27A and 28A corresponding to the first heating zone 25A can be adjusted and controlled to raise the temperature of the square steel pipe 1 at room temperature to around 200 ° C., and the heating corresponding to the intermediate heating zone 25B. The burners 27B and 28B can be adjusted and controlled so as to raise the temperature of the square steel pipe 1 around 200 ° C. to around 400 ° C., and the heating burners 27C and 28C corresponding to the heating zone 25C in the final stage are square steel pipes around 400 ° C. 1 can be adjusted and controlled to increase the temperature to around 600 ° C. (up to 650 ° C.).

A partition body 29 that allows the rectangular steel pipe 1 to pass is provided at the boundary between the heating zones 25A, 25B, and 25C and the hold zones 26A, 26B, and 26C . An example of the heat treatment unit 21 due 22-29 on than is constructed.

  As described above, after the cold forming, the square steel pipe 1 conveyed to the terminal portion of the carry-in floor 11 is transferred to the roller conveyor 12 and is carried into the furnace 22 of the heat treatment unit 21 by the roller conveyor 12. This square steel pipe 1 is gradually and uniformly distributed from the outer surface side by the combustion heat of each heating burner 27A, 28A, 27B, 28B, 27C, 28C while being transported linearly on the transport path 13 in a common furnace 22. Heated. At this time, the heating is alternately moved to the heating zones 25A, 25B, and 25C and the hold zones 26A, 26B, and 26C in order to raise the temperature stepwise in the heating zones 25A, 25B, and 25C, and the hold zone 26A. , 26B, and 26C, the heating zones 25A, 25B, and 25C in the preceding stage can be held in a temperature state that is raised.

  That is, the square steel pipe 1 in the normal temperature state carried into the furnace 22 is first heated so that the temperature is raised to around 200 ° C. by the heating burners 27A and 28A in the heating zone 25A at the first stage. The square steel pipe 1 heated to about 200 ° C. is moved to the first hold zone 26A and held in an atmosphere of about 200 ° C. Next, the square steel pipe 1 at around 200 ° C. is moved to the intermediate heating zone 25B, and is entirely heated so that the temperature is raised to around 400 ° C. by the heating burners 27B, 28B. The square steel pipe 1 heated to about 400 ° C. is moved to the intermediate stage hold zone 26B and held in an atmosphere of about 400 ° C. Then, the square steel pipe 1 having a temperature of about 400 ° C. is moved to the final heating zone 25C and is heated by the heating burners 27C and 28C so that the temperature is raised to about 600 ° C. The square steel pipe 1 heated to around 600 ° C. is moved to the final stage hold zone 26C and held in an atmosphere around 600 ° C.

  Thus, by heating the cold-formed square steel pipe 1 stepwise to the target temperature in each heating zone 25A, 25B, 25C, the respective heating burners 27A, 28A, 27B, 28B, 27C. , 28C can reduce the amount of combustion heat without waste. Moreover, in each hold zone 26A, 26B, 26C, the heating temperature in the circumferential direction and the length direction of the square steel pipe 1 is made uniform by holding in the temperature state where the temperature is raised in the preceding heating zones 25A, 25B, 25C. Can be realized.

  That is, the heating burners 27A and 28A in the heating zone 25A at the first stage may be the amount of combustion heat that raises the temperature of the square steel pipe 1 in the room temperature to around 200 ° C. Then, by holding the square steel pipe 1 heated to around 200 ° C. in an atmosphere at around 200 ° C. in the first stage hold zone 26A, when heating in the first stage heating zone 25A (around 200 ° C.) A slight temperature difference occurs in the circumferential direction and the length direction, and the temperature of the square steel pipe 1 heated in a non-uniform (non-uniform) shape can be made uniform during the holding, thereby preventing distortion.

  Further, the heating burners 27B and 28B in the intermediate heating zone 25B may have a combustion heat amount that raises the temperature of the square steel pipe 1 around 200 ° C. to around 400 ° C. The square steel pipe 1 heated to around 400 ° C. is held in an intermediate stage hold zone 26B in an atmosphere around 400 ° C., so that the circumferential direction during heating (around 400 ° C.) in the intermediate stage heating zone 25B In addition, a slight temperature difference occurs in the length direction, and the temperature of the square steel pipe 1 heated in a non-uniform (uneven) shape can be made uniform during the hold, thereby preventing the occurrence of distortion.

  Furthermore, the heating burners 27C and 28C in the heating zone 25C at the final stage may have a combustion heat amount for raising the temperature of the rectangular steel pipe 1 at around 400 ° C. to around 600 ° C. Then, by holding the square steel pipe 1 heated to around 600 ° C. in an atmosphere at around 600 ° C. in the final stage hold zone 26C, in the circumferential direction during heating (around 600 ° C.) in the final stage heating zone 25C. In addition, a slight temperature difference occurs in the length direction, and the temperature of the square steel pipe 1 heated in a non-uniform (uneven) shape can be made uniform during the hold, thereby preventing the occurrence of distortion.

  In addition, a plurality of heating zones 25A, 25B, and 25C and hold zones 26A, 26B, and 26C are alternately formed in a common furnace 22, and the cold-formed square steel pipe 1 is moved while moving linearly. The zones 25A, 25B, and 25C and the hold zones 26A, 26B, and 26C are alternately moved sequentially to raise the temperature stepwise in the heating zones 25A, 25B, and 25C, and in the hold zones 26A, 26B, and 26C, By holding in the temperature state raised in the heating zones 25A, 25B, and 25C in the previous stage, the furnace 22 and the conveying means can be configured in a compact and inexpensive manner, and the movement control can be simplified. The movement between zones in the furnace 22 is efficiently performed simultaneously (synchronously).

  As described above, the square steel pipe 1 held at around 600 ° C. in the hold zone 26C of the final stage can be carried out from the furnace 22 to the cooling bed 31 through the carry-out port by opening the open / close door 23. When the end of the square steel pipe 1 is completely carried out, the opening / closing door 23 at the carry-out port is closed. Thus, the heated square steel pipe 1 taken out from the hold zone 26C at the final stage is configured to be gradually cooled in the cooling bed 31.

  That is, the square steel pipe 1 taken out from the last-stage hold zone 26 </ b> C is received by the cooling bed 31. The cooling bed 31 is of a conveyor type, supports a plurality of rectangular steel pipes 1 in parallel, and conveys them in a direction transverse to the length direction. During the conveyance on the cooling bed 31, the square steel pipe 1 is gradually cooled in an air cooling manner. The conveyance of the group of square steel pipes on the cooling bed 31 is carried in a state where the adjacent square steel pipes 1 are separated from each other or in a state where the adjacent square steel pipes 1 are brought into contact with each other and clamped from both sides. As a result, the square steel pipe 1 is gradually cooled under the same atmospheric temperature, so that bending during cooling can be reduced. The square steel pipe 1 that has reached the end of the cooling bed 31 is transported to a straightening device, a front end cutting device, a rear end cutting device, a cleaning device, and a rust prevention device (not shown), and after being processed as necessary. Is stored as a product. In addition, the square steel pipe 1 heat-treated in this way is used, for example, as a steel pipe column of a steel structure.

  As described above, the heat treatment is performed on the cold-formed square steel pipe 1 to remove residual stress and restore toughness. The square steel pipe 1 obtained by such heat treatment has almost no residual stress. High buckling strength can be obtained, and secondary weldability is excellent, so that the proof stress and toughness can be improved while maintaining the effect of heat treatment. In addition, by heating the heat treatment stepwise to the target temperature and holding it at the stepped temperature rise, a homogeneous formed steel pipe that hardly twists, bends and deforms is obtained. It will be obtained at a significant cost reduction. At that time, by raising the temperature of the shaped steel pipe 1 with the upper limit of 650 ° C. in the heating zone 26C in the final stage, it is possible to prevent crystal graining after slow cooling and maintain the viscosity and strength.

  In the first embodiment described above, as the square steel pipe 1, for example, a one-seam square steel pipe by roll forming, a two-seam square steel pipe in which a pair of groove-shaped members by press forming are face-to-face welded, and a pair of rolled groove shapes are welded. A two-seam square steel pipe, a two-seam square steel pipe obtained by welding a pair of rolled chevron members facing each other, and the like are appropriately used.

  In the first embodiment described above, a square steel pipe having a regular tetragonal cross section is adopted as the square steel pipe 1, but a rectangular steel pipe having a rectangular cross section can be used as well. Furthermore, it can be similarly applied to various polygonal square steel pipes such as regular pentagons and regular hexagons.

In the first embodiment, the square steel pipe 1 is a large diameter and thick square steel pipe, a large diameter and thin square steel pipe, a small diameter and thick square steel pipe, a small diameter and thin square steel pipe, and the like. Also good. For example, a square steel pipe 1 having an outer dimension W between regular outer surfaces of 300 to 700 mm and a plate thickness of 9 to 70 mm is obtained. In this case, the outer surface curvature radius R of the corner portion is 1.0 to 3 of the plate thickness. . Sharply formed so as to be 0 times.
[Embodiment 2]
Next, Embodiment 2 of the present invention will be described with reference to FIG. 4 as a state adopted in a round steel pipe.

  That is, a long round steel pipe (an example of a formed steel pipe) 5 that has been cold-formed has a regular outer surface diameter D over its entire length, and a butt weld 6 by butt welding is provided at one place in the circumferential direction. Is formed.

This round steel pipe 5 is heat-treated in the same manner as in the first embodiment. Therefore, by heat-treating the cold-formed round steel pipe 5, it is possible to remove residual stress and restore toughness, and to produce a homogeneous round steel pipe 5 that hardly twists, bends, and deforms at a significant cost. Get down.
[Embodiment 3]
Next, a third embodiment of the present invention will be described with reference to FIG.

  In the third embodiment, the heating zones 25A, 25B, and 25C are arranged in parallel, and the hold zones 26A, 26B, and 26C are arranged corresponding to the arrangement, and the square steel pipes are arranged in the hold zones 26A and 26B. 1 (or the round steel pipe 5) is configured to be moved in the lateral direction with respect to the length direction by, for example, a conveyor-type lateral feed device 33.

That is, the square steel pipe 1 in the normal temperature state carried into the furnace 22 is first heated so that the temperature is raised to around 200 ° C. by the heating burners 27A and 28A in the heating zone 25A at the first stage. The square steel pipe 1 heated to about 200 ° C. is moved to the first hold zone 26A, and is moved to about 200 ° C. while being moved in the horizontal direction by the transverse feed device 33 in the first hold zone 26A. Hold in the atmosphere. Next, the square steel pipe 1 at around 200 ° C. is moved to the intermediate heating zone 25B, and is heated as a whole by the heating burners 27B, 28B so that the temperature is raised to around 400 ° C. The square steel pipe 1 heated to about 400 ° C. is moved to the intermediate stage hold zone 26B, and is moved in the horizontal direction by the lateral feed device 33 in the intermediate stage hold zone 26B. Is held at. Then, the square steel pipe 1 having a temperature of about 400 ° C. is moved to the final heating zone 25C and is heated by the heating burners 27C and 28C so that the temperature is raised to about 600 ° C. The square steel pipe 1 heated to about 600 ° C. is moved to the final stage hold zone 26C, and is held in the final stage hold zone 26C in an atmosphere of about 600 ° C.
[Embodiment 4]
Next, a fourth embodiment of the present invention will be described with reference to FIG.

  In the fourth embodiment, six (a plurality of) heating zones 35A, 35B, 35C, 35D, 35E, and 35F and hold zones 36A, 36B, 36C, 36D, 36E, and 36F are combined in the furnace 22 respectively. Formed (arranged). At that time, the first heating zone 35A, the first heating zone 36A, and the second heating zone 35B are arranged in a straight line, and the third heating zone 35C and the third holding zone 36C. And the fourth heating zone 35D are linearly arranged, and the fifth heating zone 35E, the fifth holding zone 36E, the final heating zone 35F, and the final holding zone 36F are linear. Has been placed. The three linear portions are arranged in parallel, and the second-stage hold zone 36B and the fourth-stage hold zone 36D are arranged corresponding to this arrangement, and the second-stage hold zone 36B and the second-stage hold zone 36B In the four-stage hold zone 36D, the square steel pipe 1 (or the round steel pipe 5) is configured to be moved in the lateral direction with respect to the length direction by, for example, a conveyor-type lateral feed device 39.

  In the fourth embodiment, the square steel pipe 1 in the normal temperature state carried into the furnace 22 is first heated so that the temperature is raised to around 100 ° C. by the heating burners 37A and 38A in the heating zone 35A at the first stage. . The square steel pipe 1 heated to about 100 ° C. is moved to the first-stage hold zone 36A, and is held in the first-stage hold zone 36A in an atmosphere of about 100 ° C. Next, the square steel pipe 1 at around 100 ° C. is moved to the second stage heating zone 35B, and is entirely heated by the heating burners 37B, 38B so as to increase the temperature to around 200 ° C. The square steel pipe 1 heated to around 200 ° C. is moved to the second stage hold zone 36B, and is moved around 200 ° C. while being moved laterally by the transverse feed device 39 in the second stage hold zone 36B. Hold in the atmosphere.

  Then, the rectangular steel pipe 1 at around 200 ° C. is moved to the third stage heating zone 35C, and is entirely heated by the heating burners 37C, 38C so that the temperature is raised to around 300 ° C. The square steel pipe 1 heated to around 300 ° C. is moved to the third stage hold zone 36C, and is held in the third stage hold zone 36C in an atmosphere around 300 ° C. Next, the square steel pipe 1 having a temperature of about 300 ° C. is moved to the fourth heating zone 35D, and is heated by the heating burners 37D and 38D so that the temperature is raised to about 400 ° C. The square steel pipe 1 heated to about 400 ° C. is moved to the fourth stage hold zone 36D, and is moved to about 400 ° C. while being moved laterally by the lateral feed device 39 in the fourth stage hold zone 36D. Hold in the atmosphere.

  Then, the square steel pipe 1 at around 400 ° C. is moved to the fifth stage heating zone 35E, and is entirely heated by the heating burners 37E, 38E so that the temperature is raised to around 500 ° C. The square steel pipe 1 heated to about 500 ° C. is moved to the fifth stage hold zone 36E, and is held in the fifth stage hold zone 36E in an atmosphere of about 500 ° C. Next, the square steel pipe 1 at around 500 ° C. is moved to the heating zone 35F at the final stage, and is entirely heated by the heating burners 37F, 38F so that the temperature is raised to around 600 ° C. The square steel pipe 1 heated to about 600 ° C. is moved to the final stage hold zone 36F, and is held in the final stage hold zone 36F under an atmosphere of about 600 ° C.

Steel, iron, etc. are employ | adopted as a raw material of the square steel pipe 1 in Embodiment 1 mentioned above and the round steel pipe 5 in Embodiment 2. FIG.
In the first embodiment and the third embodiment described above, the three heating zones 25A, 25B, 25C and the hold zones 26A, 26B, 26C are formed (arranged) in the furnace 22 in an intended manner. The temperature is raised stepwise by setting the temperature to 200 ° C., and in the fourth embodiment, six (a plurality of) heating zones 35A, 35B, 35C, 35D, 35E, and 35F are provided in the furnace 22, respectively. The hold zones 36A, 36B, 36C, 36D, 36E, and 36F are formed (arranged) in an intersecting manner, and the target temperature is raised stepwise by setting the target temperature to 100 ° C. However, the number of steps and the temperature rise are arbitrary. There is also a stepwise temperature difference.

In the first embodiment, the third embodiment, and the fourth embodiment described above, adjustment control is performed so that the temperature of the rectangular steel pipe 1 is increased to around 600 ° C. (up to 650 ° C.) in the final heating zones 25C and 35F. Although there is a get configuration, this heating zone 25C of the final stage, the square tube 1 at 35F, as the temperature is raised to a temperature below a ₃ transformation point which changes by the amount of carbon (a ₃ transformation point near) The configuration may be adjusted.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic plan view of a heat treatment step in a heat treatment method for a formed steel pipe according to a first embodiment of the present invention. It is a partially cutaway perspective view of the heat treatment process in the heat treatment method for the shaped steel pipe. It is a front view of the square steel pipe in the heat treatment method of the forming steel pipe. It is Embodiment 2 of this invention and is a front view of the round steel pipe in the heat processing method of a shaped steel pipe. It is Embodiment 3 of this invention, and is a schematic plan view of the heat treatment process in the heat treatment method of a shaped steel pipe. FIG. 9 is a schematic plan view of a heat treatment step in a heat treatment method for a formed steel pipe according to a fourth embodiment of the present invention.

Explanation of symbols

1 Square steel pipe (formed steel pipe)
5 Round steel pipe (formed steel pipe)
11 Loading floor 12 Roller conveyor (conveying means)
13 Transport path 21 Heat treatment section 22 Furnace 25A First stage heating zone 25B Middle stage heating zone 25C Last stage heating zone 26A First stage hold zone 26B Middle stage hold zone 26C Last stage hold zone 31 Cooling bed 33 Horizontal feed device 35A First stage heating zone 35B Second stage heating zone 35C Third stage heating zone 35D Fourth stage heating zone 35E Fifth stage heating zone 35F Last stage heating zone 36A First stage hold Zone 36B Second-stage hold zone 36C Third-stage hold zone 36D Fourth-stage hold zone 36E Fifth-stage hold zone 36F Final-stage hold zone 39 Cross feed device W Outer dimension R of square steel pipe 1 Square steel pipe 1 The outer surface radius of curvature L of the square steel pipe 1 L + α Zone length D The outer diameter of the round steel pipe 5

Claims (5)

In the heat treatment section, a plurality of heating zones and hold zones are arranged in an intersecting manner, and these heating zones and hold zones have the same zone length and are set slightly longer than the tube length. The partition between the heating zone and the hold zone is provided with a partition that allows passage of the formed steel pipe, and the cold-formed formed steel pipe is alternately moved to the heating zone and the hold zone in turn, In the hold zone group, the circumferential direction and length of the formed steel pipe are held by holding in an atmosphere of the same temperature as the temperature of the formed steel pipe heated in the preceding heating zone. Heat treatment method for a shaped steel pipe characterized by uniformizing the heating temperature in the direction and gradually cooling the hot-formed steel pipe taken out from the hold zone at the final stage   2. The method for heat-treating a shaped steel pipe according to claim 1, wherein the temperature of the shaped steel pipe is increased up to 650 [deg.] C. in the final heating zone.   3. The heat treatment method for a shaped steel pipe according to claim 1, wherein a plurality of heating zones and hold zones are formed in a common furnace, and the shaped steel pipe is moved linearly.   The method for heat treatment of a shaped steel pipe according to any one of claims 1 to 3, wherein the shaped steel pipe is a square steel pipe.   The method for heat treatment of a shaped steel pipe according to any one of claims 1 to 3, wherein the shaped steel pipe is a round steel pipe.

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