JPH10296458A - Manufacture of welded steel tube - Google Patents

Abstract

PROBLEM TO BE SOLVED: To unnecessitate bead cutting by executing edge preheating for heating both edge parts of an open tube to unmelting temp. region not lower than Curie point by induction heating, heating them to a melting temp. region, butt- joining them with squeeze rolls and making the area of weld bead discharged to the outside and inside of the tube not higher than a specified value. SOLUTION: Band steel is preheated to 400-650 deg.C. The band steel is formed with forming rolls and made into an open tube. Edge pre-heating is executed by heating both edge parts from the edge faces to about 5 mm to the temp. region of 600-1000 deg.C by induction heating. The edge preheating is executed under the atmosphere of oxygen content lower than that of the air or under the atmosphere whose dew point is <=-10 deg.C. Air cooling is executed for >=0.5 sec. The edge parts are heated to the melting temp. region of the melting point to the melting point +50 deg.C by high-frequency induction heating of <=400 kHz. The edge parts are butt-joined with the squeeze rolls and the are (mm<2> ) of the weld bead discharged to the outside and inside of the tube is defined as <=0.1 ×thickness (mm).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for manufacturing an electric resistance welded steel pipe.

[0002]

2. Description of the Related Art Welded steel pipes are formed by forming a steel plate or a steel strip into a tube and welding the seams thereof, and are made by various manufacturing methods from a small diameter to a large diameter.
Examples include electric resistance welding (electric resistance welding), forge welding, and electric arc welding. For small to medium diameter steel pipes, an electric resistance welding method using high frequency current (electric resistance welded steel pipe, electric resistance welded pipe) is mainly used. In this method, a steel strip is continuously supplied and formed into a tubular shape with a forming roll into an open tube,
Subsequently, a high-frequency current is used to heat both end portions of the open tube to a temperature equal to or higher than the melting point of steel, and then the two end portions are butted and welded with a squeeze roll to produce a steel pipe (for example, the 3rd Edition Steel Handbook) Volume III (2), pp. 1056-1092).

In the above-described method of manufacturing an electric resistance welded tube utilizing high-frequency current, since the end surfaces of both edges of the open tube are heated to the melting point of steel or more, molten steel flows under the influence of electromagnetic force,
There is a problem in that the generated oxide is caught in the abutting welded portion and welding defects such as a penetrator or the like, or the molten steel is easily scattered (flash). To cope with this problem, for example, Japanese Patent Application Laid-Open No. 2-299782 proposes a method for manufacturing an electric resistance welded steel pipe having two heating devices. The first heating device heats the temperature of both edges of the open pipe above the Curie point, the second heating device further heats it above the melting point, and squeezes rolls to weld both edges to produce steel pipe I do. Also, in Japanese Patent Application Laid-Open No. 2-299832, a current having a frequency of 45 to 250 kHz is passed by a first heating device to preheat both side edges, and further heated to a melting point or higher by a second heating device and squeezed by a squeeze roll. There has been proposed an electric resistance welded pipe manufacturing apparatus which manufactures a steel pipe by abutting both edges.

However, these ERW pipe manufacturing techniques are effective for relatively thin ERW pipes having a wall thickness of 4.5 mm or less, but are relatively thick ERW pipes having a wall thickness exceeding this. However, it was still insufficient to obtain stable seam quality under welding conditions that can suppress the generation of flash. In addition, although these methods suggest that the edges are heated uniformly, both edges are heated above the melting point of the steel, so the molten steel is discharged to the inner and outer surfaces of the pipe during abutment welding. And a bead is formed. This bead contains a large amount of generated slag, and therefore, it is necessary to remove the weld bead on the inner and outer surfaces of the pipe after the impact welding, and most of the bead is removed by cutting with a bead cutting tool.

[0005] For these reasons, in these methods, adjustment of the cutting amount of the bead cutting tool causes loss of material and time. Since the bead cutting tool is a consumable, it needs to be changed every 3000-4000m bead cutting length, depending on the pipe forming speed. Therefore, it is necessary to change the bite for 3-5 minutes every hour. Forced to stop the line.

In particular, in high-speed pipe forming in which the pipe forming speed exceeds 100 m / min, the life of the bead cutting tool is short and the frequency of replacement is high. There was a problem that bead cutting became a bottleneck and high-speed pipe making was not possible, resulting in low productivity.

[0007]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems and provides a method for producing an electric resistance welded steel pipe capable of producing a steel pipe having excellent seam quality and surface skin with high productivity. The purpose is to:

[0008]

[Means for Solving the Problems] In order to produce pipes at high speed,
It was essential to eliminate the need for bead cutting, and we worked diligently to achieve a completely contradictory problem of melting the edges and forming beads to obtain excellent seam quality. As a result, the present inventors suppressed the rapid cooling of the seam portion after the abutment joint,
It has been found that the heating temperature of the edge portion for bead formation can be reduced, the amount of bead formation is reduced, and bead cutting becomes unnecessary.

The present invention has been made based on the above findings. That is, the present invention relates to a method for manufacturing an electric resistance welded steel pipe in which a steel strip is continuously formed by a forming roll to form an open pipe, and both edges of the open pipe are heated and melted, and abutted and joined with a squeeze roll. After preheating the steel strip into an open pipe, both edges of the open pipe are subjected to an edge preheating for heating to a non-melting temperature region above the Curie point by induction heating, and further, an end face of the edge is heated by induction heating. Seam quality characterized by the area heating (mm ² ) of 0.1 × sheet thickness or less, which is subjected to edge heating for heating to a melting temperature range and abutted and joined with the squeeze roll, and discharged into and out of the pipe. This is a method for manufacturing an electric resistance welded steel pipe having an excellent surface skin.

In the present invention, it is preferable that the preheating of the steel strip is performed at a temperature of 800 ° C. or less, and the edge preheating is performed by medium / low frequency induction heating or further by high frequency induction heating. Further, the edge heating is preferably performed by high-frequency induction heating. Further, the air cooling time is 0.5 s between the edge preheating and the edge heating.
It is preferable to take ec or more.

Further, it is preferable that the edge preheating, the edge heating, and the abutment bonding are performed in an oxygen concentration atmosphere lower than the atmosphere or an atmosphere having a dew point of -10 ° C. or less. After the abutting bonding, the time t _k which joint is held above 1300 ° C. (sec) is, 0.03sec more or the following formula _{(1) t k ≧ a ·} exp {-b · [O _2] ^c} ... ... (1) (where, O ₂ : oxygen concentration in the atmosphere (vol%), a =
0.079, b = 1.5, c = -0.14).

Further, in the present invention, at the time of the abutment joining, the seam portion pipe material may be restrained from inside and outside of the tube to suppress the increase in the thickness of the seam portion. Further, in the present invention, after the abutment joining, the vicinity of the seam portion may be rolled.

[0013]

DETAILED DESCRIPTION OF THE INVENTION In the present invention, a strip is preheated prior to forming the strip. Preheating is to reduce the temperature difference between the edge part and the mother tube near it during edge heating performed later, to suppress rapid cooling of the seam part after abutment joining, and to ensure excellent seam quality. Do.

As the preheating, any of a method using a heating furnace, an induction heating method using an induction coil, and a resistance heating method by energization can be suitably applied. The preheating of the steel strip shall be within the temperature range of 800 ° C or less. Preheating at a temperature higher than 800 ° C causes a large amount of scale to be generated on the surface of the steel strip, and deteriorates both the seam quality and the surface skin of the steel pipe. If the preheating temperature is less than 400 ° C., heat diffusion from the edge portion to the mother pipe side during edge heating increases, and the seam portion after the abutment joining is rapidly cooled. On the other hand, if the preheating temperature exceeds 650 ° C., scale on the surface of the steel strip is likely to be formed, and therefore, it is preferable that the preheating temperature be in a temperature range of 400 to 650 ° C.

The preheated steel strip is continuously formed by a forming roll into an open pipe. For molding, a known method using a molding roll can be suitably applied. Then, preheat both edges of the open tube. Edge preheating is performed by an induction heating method. The edge preheating is preferably performed by medium / low frequency induction heating or further high frequency induction heating.

In the present invention, the low frequency means a frequency band of 10 kHz or less, the medium frequency means a frequency band of more than 10 kHz and 100 kHz or less, and the high frequency means a frequency band of more than 100 kHz. By this edge preheating, the temperature of the edge portion is set to an unmelted temperature range equal to or higher than the Curie point. The temperature is preferably in the range of 800 to 1300 ° C. It is preferable from the viewpoint of seam quality that the edge portion of the open pipe is set at a temperature of 600 ° C. or more and 1000 ° C. or less from the end face to about 5 mm during the edge preheating.

From the temperature dependence of the relative magnetic permeability of the steel shown in FIG. 7, when the steel is heated above the Curie point, the steel undergoes a magnetic transformation from a ferromagnetic material to a paramagnetic material, and the relative magnetic permeability (vs. vacuum ratio) becomes 1 It is a value close to. On the other hand, the penetration depth S of the induced current is given by the following equation (2). S = α {ρ / (μ _rf )} ^1/2 (2) where, S: penetration depth (m), ρ: resistivity (Ω · m),
μ _r: relative permeability, f: Frequency (kHz), α: a constant.

Therefore, when the edge portion is heated to a temperature higher than the Curie point, the penetration depth S increases, and the temperature distribution in the surface to be joined becomes uniform. However, if the temperature is suddenly raised to a temperature range higher than the melting point at this stage, the temperature difference between the corner portion and the flat portion becomes too large, and beads (surplus) are generated at the time of joining, so that high-speed pipe forming cannot be performed. Therefore, the edge portion is once preheated to an unmelted temperature region higher than the Curie point.

The frequency used for induction heating at the time of edge preheating is preferably a medium frequency or a low frequency (medium / low frequency) in order to equalize the temperature difference between the flat portion and the corner portion. . In addition, if the induction heating is performed at a high frequency after the induction heating is performed at the medium / low frequency, the temperature distribution near the edge portion becomes a desirable state (wide heating width).

In the present invention, the heating method for edge preheating has been described on the premise of induction heating. However, if an effect equivalent to that of the present invention is expected, a laser beam or an electron beam may be used instead of the induction heating method. Alternatively, a local heat input method using a plasma beam or the like may be used. The edge preheating may be performed in the atmosphere or in an atmosphere in which the oxygen concentration is lower than that in the atmosphere (in a shield atmosphere), but preferably in a shield atmosphere from the viewpoint of seam quality. The edge preheating is preferably performed in an atmosphere having a dew point of −10 ° C. or less.

Both edge portions of the open tube subjected to the edge preheating are further subjected to edge heating for heating to a melting temperature range not lower than the melting point. In the present invention, it is preferable that the air cooling time between the edge preheating and the edge heating is 0.5 seconds or more. As a result, the amount of heat introduced by the edge preheating is diffused, so that the temperature in the end face becomes more uniform.In addition, the temperature at a position away from the end face also increases, and the temperature distribution at the junction is further improved, and the seam quality is improved. Is further stabilized.

The heating method of the edge heating is high-frequency induction heating with a frequency of 400 kHz or less by an induction coil from the viewpoint of energy efficiency. For the edge heating, it is preferable to dispose an appropriate size of the impeder in the open tube from the viewpoint of the heating efficiency, but the edge heating can be performed even when the size of the impeder is reduced or the impeder is not arranged. In this case, the tube body other than the edge portion is also easily heated.

The temperature of the end face of each edge of the open tube is controlled by adjusting the output of the induction heating coil. In the edge heating, the temperature of the edge end face is higher than the melting point, preferably
50 ° C or less. In the edge heating, the temperature of the edge end surface is set to the melting point or higher, but in the present invention, the width of the melting zone near the edge end surface is reduced by suppressing the end surface temperature to the melting point + 50 ° C. or lower by high-frequency induction heating at a frequency of 400 kHz or less. it can. Thereby, the size of the bead formed at the time of the abutment joining is small, and the area K (mm ² ) of the formed bead is 0.1%.
× t (plate thickness: mm) or less.

The temperature distribution in the circumferential direction of the pipe from the edge end surface is moderated by the edge preheating, the temperature difference from the base material can be reduced, and the heat affected zone (HAZ) in the vicinity of the seam at the time of edge heating becomes large. The subsequent cooling rate of the seam portion is reduced, and the seam portion strength is increased even if the beads formed at the time of the abutment joining are small. Edge preheating, in the induction heating in edge heating, the size of the bead formed by the heat coefficient η13 below, an area (mm ²⁾ 0.
It can be 1 × t (plate thickness: mm) or less.

Here, the heat coefficient η is calculated by the following equation. η = input power (kVA) / {pipe production speed (m / min) x plate thickness (mm)} ... (3) Open pipes whose both end surfaces are heated to the melting temperature range are squeezed with both edges. The parts are butted and joined. As shown in FIG. 3 (a), the abutment joining is performed by installing a squeeze roll at a position where the squeeze roll comes into contact with the outer surface of the joint tube, and as shown in FIG. A method of installing the apparatus at a position where it does not contact the outer surface and FIG. 3
As shown in (c), there is a method in which a squeeze roll is installed on the outer surface side and a roll or the like is installed on the inner surface side in contact with the joining portion, but in any case, no inconvenience occurs.

The edge heating and the abutment bonding may be performed in the air or in an atmosphere in which the oxygen concentration is lower than that in the air (in a shield atmosphere), but preferably in a shield atmosphere from the viewpoint of seam quality. In addition, the edge heating and the abutment bonding are preferably performed in an atmosphere having a dew point of −10 ° C. or less from the viewpoint of seam quality. The present inventors have, after abutting joint, joint by a time t _k which is held above 1300 ° C., the seam quality of a steel pipe was found to vary. And t _k on the seam quality (flat height ratio h / D), the relationship between the oxygen concentration shown in Fig. From FIG. 2, in accordance with t _k becomes longer,
It can be seen that the seam quality has been improved. Further, in accordance with the oxygen concentration in the atmosphere is reduced, in order to obtain the same seam quality t _k it is understood that it may be shortened.

This time t _k (sec) is 0.03 when the edge preheating, the edge heating, and the butting are performed in the atmosphere.
It is preferable to set it to sec or more. On the other hand, if the edge preheating, edge heating, solid phase pressure is carried out in a low oxygen concentration atmosphere (in a sealed atmosphere) than atmospheric, t _k is preferably the time that satisfies the following equation (1) . t _k ≧ a · exp {−b · [O ₂ ] ^c } (1) where, O ₂ : oxygen concentration in the atmosphere (vol%), a,
b, c: constants, a = 0.079, b = 1.5 for low carbon steel
, C = −0.14. More preferably, a = 0.23, b
= 1.4 and c = -0.17.

[0028] The time t _k is an open pipe both edges of the heating temperature and the Curie point or more heating width during edge preheating,
Furthermore, it controls the heating temperature of the end faces of both edges during edge heating, adjusts the temperature distribution in the pipe circumferential direction from the end faces of both edges to the center of the pipe during joining, and reduces the cooling rate of the seam after joining. Control by adjusting. In the seam portion formed by the abutment bonding, the squeeze roll is brought into contact with the outer surface of the bonding portion, the temperature reached at the edge portion or the degree of the drawing in the circumferential direction of the pipe by the squeeze roll, FIG.
As shown in (b), a wall thickness of 5% or more of the pipe wall thickness may be formed inside or outside the pipe or inside the pipe at the seam portion. In such a case, it is preferable to reduce the thickness of the vicinity of the increased seam portion by rolling at an appropriate place after the abutment joining. Rolling in the vicinity of the increased seam portion is performed, for example, from inside and outside the pipe by a seam portion rolling roll 10 shown in FIG. The pressure-welded seam portion rolling roll 10 includes an outer surface rolling roll 10a and an inner surface rolling roll 10b, and 10b is supported by a pressure-welded seam portion rolling roll support rod 10c.

Further, by adopting a method in which a roll or the like is brought into contact with the inner and outer surfaces of the joint pipe in the above-mentioned abutting joining method, the material is constrained in the vertical direction, and the increase in wall thickness by pressure welding is reduced by 5%.
It is also possible to suppress the rolling after the abutment joining to less than the above. For example, the squeeze roll 6 shown in FIG.
The material is constrained from inside and outside the pipe by the joint inner surface constraining roll 11a and the increase in wall thickness due to the abutting joint is suppressed. The roll 11a for restraining the inner surface of the joint is a roll support rod 1 for restraining the inner surface of the joint.
1b.

As described above, according to the present invention, both edges of the open pipe can be stably maintained in the melting temperature range,
The size of the bead formed by discharging the molten steel by the squeeze roll butting can be controlled to be small, it is not necessary to perform bead cutting, it enables high-speed pipe forming, and has excellent seam quality and surface skin ERW steel pipes can be manufactured with high productivity.

[0031]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An equipment row suitable for carrying out the present invention shown in FIG. 1 was used. After a strip steel 1 having a thickness of 3.5 mm was continuously preheated at a temperature of 400 to 650 ° C. in a preheating furnace 2, it was continuously formed by a forming roll group 3 to obtain an open pipe 7. The squeeze roll 6 is placed at a position where the both ends of the open pipe are preheated by the edge preheating induction coil 4 under the conditions shown in Table 1 and further edge heated by the edge heating induction heating coil 5 to abut against the seam. Butt joint, pipe size: 6
0.5mmφ × 3.5mmt, standard: STKM11A steel pipe 8 was used.
The bead shape, seam quality, and surface skin of the manufactured steel pipe 8 were investigated, and the results are shown in Table 1. The seam quality was evaluated based on the flat height ratio (h / D, h: flat height mm,
D: Outer diameter of steel pipe mm). The surface roughness of the steel pipe was evaluated based on the surface roughness Rmax (μm). For some steel pipes, edge preheating, edge heating and abutment joining were performed in a shield atmosphere.

The bead shape and dimensions were measured with a laser distance meter. FIG. 6 schematically shows an example of a bead shape. (a) is an example of the present invention, and (b) is an example of a conventional electric resistance welded tube (conventional example). Table 1 shows the results.

[0033]

[Table 1]

In the test examples Nos. 1 to 5 and No. 10, the bead area was 0.35 mm ² or less and the flat height ratio was 0.3 or less.
The surface roughness was less than Rmax 10 μm, and high-speed pipe making was possible without the need for bead cutting. The conventional ERW pipe (Test No. 6) had a bead area of 0.8 mm ² and required bead cutting.

Test No. 7 had no strip steel preheating, and test No. 8
Indicates that the edge preheating temperature is low.
Temperature was too high and the heat input was too large,
0.35mm ^TwoExceeded. In Test Nos. 1 and 2 of the present invention, the pressure
A 0.5 to 1.5 mm thickening was found on the inner surface of the pipe at the seam
However, the area near the welded seam is rolled from inside and outside the pipe with rolling rolls
And reduced the thickness to within 0.2mm, within the specification range for steel pipe dimensions.
Was.

In Tests No. 3 and No. 4, the squeeze roll was brought into contact with the outer surface of the tube and the rolling roll was brought into contact with the inner surface of the tube at the pressed position to restrain the material in the vertical direction. When the wall thickness increased to 0.1 mm or less, the specification was within the specification range of the steel pipe dimensions, and rolling after pressure welding was unnecessary. In Test No. 5 of the present invention, the dew point in the atmosphere during edge heating and solid-phase pressure welding was controlled to -20 ° C. As a result, the flat height ratio is smaller than that in Test No. 4 in which dew point control in the atmosphere was not performed.

The productivity of the example of the present invention is as high as 30 tons / hr, and the productivity of the conventional ERW pipe for bead cutting is 15 tons / hr, but the productivity is remarkably improved.

[0038]

According to the present invention, a remarkable effect that both edges of an open pipe can be stably held in a melting temperature range and a steel pipe having excellent seam quality and surface skin can be manufactured with high productivity. Play.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing one example of a steel pipe manufacturing facility line suitable for carrying out the present invention.

2 is a graph showing the relationship between the oxygen concentration in the time t _k and the atmosphere is maintained above 1300 ° C. After butt joint on the seam quality.

FIG. 3 is a cross-sectional view showing a positional relationship between a squeeze roll, a seam portion inner surface restraining roll, and a joining portion during abutment joining.

FIG. 4 is a schematic partial cross-sectional side view of an equipment row suitable for carrying out the present invention.

FIG. 5 is a characteristic diagram showing temperature dependence of relative magnetic permeability of steel.

FIG. 6 is a conceptual diagram of a bead shape.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Strip steel 2 Preheating furnace 3 Forming roll group 4 Induction heating coil for edge preheating 5 Induction heating coil for edge heating 6 Squeeze roll 7 Open pipe 8 Steel pipe 9 Seam part 10 Seam part roll 10a Seam part outer surface roll 10b Seam Roll for internal rolling 10c Roll supporting rod for rolling seam 11a Roll for restricting internal surface of seam 11b Roll supporting rod for restricting internal surface of seam 12 Bead 13 HAZ

Continuation of the front page (51) Int.Cl. ⁶ Identification code FI H05B 6/10 371 H05B 6/10 371 (72) Inventor Motoaki Itaichi 1-1, Kawasaki-cho, Handa-shi, Aichi Kawasaki Steel Corporation Chita Manufacturing Co., Ltd. In-house (72) Inventor Akira Ito 1-1-1 Kawasaki-cho, Handa-shi, Aichi Prefecture Kawasaki Steel Corporation Chita Works (72) Inventor Toshio Onishi 1-1-1 Kawasaki-cho, Handa-city, Aichi Prefecture Kawasaki Steel Corporation Chita Manufacturing Co., Ltd. In-house (72) Inventor Nobuki Tanaka 1-1-1 Kawasaki-cho, Handa-shi, Aichi Kawasaki Steel Corporation Chita Works

Claims (11)

[Claims] 1. A method for producing an electric resistance welded steel pipe, wherein a steel strip is continuously formed by a forming roll to form an open pipe, and both edges of the open pipe are heated and melted, and are joined by a squeeze roll. The steel strip is preheated to form an open pipe, and both edges of the open pipe are subjected to edge preheating for heating to a non-melting temperature region equal to or higher than the Curie point by induction heating. Edge heating for heating to the temperature range is performed, and the squeeze roll is used to abut and join, and the area of the weld bead discharged into and out of the pipe (m
m ² ) is 0.1 × (sheet thickness) or less, a method for producing an electric resistance welded steel pipe excellent in seam quality and surface skin. 2. The method according to claim 1, wherein the preheating of the steel strip is performed at a temperature of 800 ° C. or less. 3. The method for producing an electric resistance welded steel pipe according to claim 1, wherein the edge preheating is performed by medium / low frequency induction heating or further by high frequency induction heating. 4. The method according to claim 1, wherein the edge heating is performed by high-frequency induction heating. 5. An air cooling time of 0.5 sec or more between the edge preheating and the edge heating.
5. The method for producing an electric resistance welded steel pipe according to any one of claims 4 to 4. 6. The method for manufacturing an electric resistance welded steel pipe according to claim 1, wherein the edge preheating is performed in an oxygen concentration atmosphere lower than the atmosphere. 7. The edge heating and the abutment bonding may include:
The method for producing an electric resistance welded steel pipe according to any one of claims 1 to 6, wherein the method is performed in an oxygen concentration atmosphere lower than the atmosphere. 8. The electric resistance welded steel pipe according to claim 1, wherein the edge preheating, the edge heating, and the abutment joining are performed in an atmosphere having a dew point of −10 ° C. or less. Production method. 9. After the butt joint, the time t _k which joint is held above 1300 ° C. (sec), characterized in that a t _k satisfying the above 0.03sec or below (1) A method for producing an electric resistance welded steel pipe according to any one of claims 1 to 8. Note that t _k ≧ a · exp ｛−b · [O ₂ ] ^c ｝ (1) where, O ₂ : oxygen concentration in the atmosphere (vol%), a = 0.
079, b = 1.5, c = -0.14. 10. The method for producing an electric resistance welded steel pipe according to claim 1, wherein the seam portion pipe material is restrained from the inner and outer surfaces of the abutment joint and the inner and outer surfaces of the tube to suppress the increase in the thickness of the seam portion. 11. The method for manufacturing an electric resistance welded steel pipe according to claim 1, wherein a portion near a seam is rolled after the abutment joining.