JPH1080718A - Manufacture of steel tube - Google Patents

Abstract

PROBLEM TO BE SOLVED: To manufacture a steel tube having an excellent seam quality and a surface skin with high productivity. SOLUTION: A band steel is preheated and continuously formed by a forming roll group to obtain an open tube 7. Both edge parts of the open tube 7 is subjected to edge preheating 4 heating to Curie point or over, preferably less than 1300 deg.C by an induction heating and further subjected to the edge heating treatment to a temperature area of 1300 deg.C or over and less than a melting point by either one 5 of laser beam, electronic beam or plasma beam, then abutted on each other by a squeeze roll 6 and press-weld to obtain the steel tube. It is preferable that the time tK (sec) keeping joint part at 1300 deg.C or over after press-welding is 0.03sec or over, or the joint part is kept for the time according to an oxygen concentration in an atmosphere. Further, it is preferable that the preheating of the band steel is performed at 800 deg.C or below, the edge preheating, the edge heating, and the press-welding is performed in an atmosphere with an oxygen concentration lower than the atmosphere or in an atmosphere whose dew point is -10 deg.C or below.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for manufacturing a steel pipe, and more particularly, to a method for manufacturing a steel pipe by solid-state pressure welding.

[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 (electric resistance welded steel pipe, electric resistance welded pipe) utilizing high frequency induction heating is mainly used. In this method, a steel strip is continuously supplied, formed into a tubular shape with a forming roll to form an open pipe, and then the end faces of both edges of the open pipe are heated by high-frequency induction heating to a temperature equal to or higher than the melting point of the steel. (See, for example, the third edition of the Iron and Steel Handbook, Vol. III (2), 1056-10).
92).

In the above-described method of manufacturing an electric resistance welded tube utilizing high frequency induction heating, since the end surfaces of both edges of the open tube are heated to the melting point of the steel or higher, the molten steel flows under the influence of electromagnetic force, and the generated oxidation occurs. An object is caught in the abutment weld and welding defects such as penetrators or molten steel scatter (flash)
There is a problem that is easy to occur. For this issue,
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 side edges of the open tube to the Curie point or higher, and the second heating device further heats to the melting point or higher.
A steel pipe is manufactured by butt welding both edges with a squeeze roll. 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.

[0004] However, although these electric resistance welded pipe manufacturing techniques suggest that the edges are uniformly heated, since both edges are heated to the melting point of the steel or higher, the molten steel is hardened at the time of impact welding. Is discharged to the inner and outer surfaces of the tube to form a bead. 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 this reason, in this method, loss of material and time occurs due to adjustment of the cutting amount of the bead cutting tool. 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. on the other hand,
There is a method for manufacturing a forged steel pipe having extremely high productivity for a relatively small diameter steel pipe. In this method, a continuously supplied steel strip is heated to about 1300 ° C in a heating furnace, and then formed into a tubular shape with a forming roll to form an open pipe. After performing the scale-off, oxygen is blown to the end face by the welding horn, and the end face is heated to about 1400 ° C. by the heat of oxidation, and then the end faces of both edges are abutted by a forging roll to perform solid-state joining. This is a method for producing a steel pipe (for example, Third Edition Iron and Steel Handbook, Vol. III (2), pp. 1056-1092).

However, in this method for producing a forged steel pipe, the scale-off of the end face is not perfect, so that the scale is caught in the forged joint portion, and the strength of the seam portion is considerably inferior to that of the base material portion. For this reason, in the flattening test, the flattened height ratio h / D = 2t / D (t: plate thickness) can be achieved with an ERW steel pipe, while the flattened height ratio h / D is inferior to about 0.5 with a forged steel pipe. It will be.

[0008] Since the steel strip is heated to a high temperature, scale is formed on the pipe surface, and the surface skin is poor. The pipe making speed is 300m /
Although the productivity is high as short as min or more, the seam quality and the surface skin are poor, and there is a problem that products requiring strength reliability and surface quality such as JIS STK cannot be manufactured.

[0009]

SUMMARY OF THE INVENTION The present invention is to solve the above problems advantageously and to propose a method of manufacturing a steel pipe capable of manufacturing a steel pipe having excellent seam quality and surface skin with high productivity. Aim.

[0010]

SUMMARY OF THE INVENTION According to the present invention, a steel pipe is manufactured by continuously forming a strip from a forming roll into an open pipe, heating both edges of the open pipe, and abutting and joining with a squeeze roll. In the method, the steel strip is preheated into an open pipe, and both edges of the open pipe are subjected to an edge preheating for heating to a temperature equal to or higher than the Curie point and preferably lower than 1300 ° C. by induction heating. ,
A steel pipe with excellent seam quality and surface skin, characterized by applying edge heating to a temperature range of 1300 ° C. or higher and lower than the melting point by one of electron beam and plasma beam, and pressing with the squeeze roll. The preheating of the steel strip is preferably performed at a temperature of 800 ° C. or less. The edge preheating, the edge heating, and the pressure welding are preferably performed in an oxygen concentration atmosphere lower than the atmosphere or in an atmosphere having a dew point of −10 ° C. or less. After the pressure welding, the time t _k (sec) at which the joint is maintained at 1300 ° C. or more
) Is 0.03 sec or more or the following equation (1) t _k ≧ a · exp {−b · [O ₂ ] ^c } (1) (where, O ₂ : oxygen concentration in atmosphere (vol%), a =
0.079, b = 1.5, c = -0.14).

Further, in the present invention, at the time of the pressing, the seam portion pipe 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 pressing, the vicinity of the pressing seam portion may be rolled.

[0012]

DETAILED DESCRIPTION OF THE INVENTION In the present invention, a strip is preheated prior to forming the strip. The preheating reduces the temperature difference between the edge portion and the mother tube near the edge portion during edge heating performed later, so that the temperature and the temperature distribution of the edge portion can be easily maintained in the solid-state pressure-welding temperature range in the solid-phase pressure welding stage. Do to make.

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., the edge temperature and the temperature distribution during pressure welding cannot be maintained in the temperature range where solid-state pressure welding is possible, since there is much heat diffusion from the edge to the mother pipe side during edge heating. However, if the preheating temperature exceeds 650 ° C, scale on the surface of the steel strip is likely to be generated, and therefore, the preheating temperature is
Preferably, the temperature is in the 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. This edge preheating reduces the temperature of the edge,
The temperature is higher than the Curie point and preferably lower than 1300 ° C.

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 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 pressed becomes uniform. Therefore, the edge portion is preheated to a temperature range higher than the Curie point.
From the viewpoint of heating energy efficiency, the Curie point is 1300 or more.
It is preferable to carry out the reaction at a temperature lower than 1 ° C., but there is no inconvenience even if the temperature is higher than 1300 ° C. However, at this stage, 1300 ℃
When the temperature is raised to the above temperature range, only the corners become higher than the melting point, and beads (surplus) are generated at the time of joining, so high-speed pipe forming may not be possible, and the edge preheating is not less than the Curie point and less than 1300 ° C. It is preferable to carry out in a temperature range.

The edge preheating is most preferably performed by the induction heating method. However, the edge preheating can be performed by any method other than the induction heating method. For example, the edge preheating may be performed by a laser beam, an electron beam, a plasma beam, or the like. The edge preheating may be performed in the atmosphere or in an atmosphere having a lower oxygen concentration than the atmosphere (in a shield atmosphere), but is 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 edges of the open tube subjected to the edge preheating are further subjected to edge heating for heating to a temperature range of 1300 ° C. or higher and lower than the melting point. The heating method of edge heating is
One of a laser beam, an electron beam, and a plasma beam is used. Either heating method can similarly heat the edge portion, but among them, the laser beam method is preferred from the viewpoint of easy handling of the apparatus and heating ability.

The temperature of both ends of the open tube is adjusted by adjusting the beam output or the beam diameter, the beam scanning speed, and the like.
It is controlled by a scanning range or the like. Note that a plurality of heating means of the laser beam, the electron beam, and the plasma beam may be used in combination. In addition to these heating means, high-frequency induction heating may be used in combination.

If the temperature of the edge heating is lower than 1300 ° C., the joining at the end face of the edge portion becomes insufficient and the seam quality is deteriorated.
Further, if the temperature of the end face of the edge portion exceeds the melting point of the pipe material, the molten steel forms beads (extra-bulb) inside and outside the pipe at the time of abutment joining, so that bead cutting is required. For this reason, the edge heating is performed in a temperature range of 1300 ° C. or higher and lower than the melting point where solid-state pressure welding can be performed. The melting point is preferably 1350 ° C. or higher and lower than the melting point, more preferably 1400 ° C. or higher and lower than the melting point.

The solid-phase pressure welding referred to in the present invention means a pressure welding in which bead (surplus) swelling is suppressed and bead cutting is not required. In the present invention, the edge heating temperature is preferably the temperature in the solid phase region in order to suppress the amount of bead (surplus) rising, but may be the temperature in the solid-liquid two-phase region slightly lower than the melting point where a liquid phase exists.

The open pipe whose both edge portions are heated to the above-mentioned solid-state pressure-contactable temperature range is abutted on both edge portions by a squeeze roll, and is solid-phase pressed. As shown in FIG. 3 (a), the pressure welding is performed by setting a squeeze roll at a position where the squeeze roll is in contact with the outer surface of the pressure-welded joint pipe, and as shown in FIG. 3 (b),
As shown in FIG. 3 (c), a method in which a squeeze roll is installed at a position where the squeeze roll does not abut against the outer surface of the press-joined portion and the outer surface side is at a position where the squeeze roll is in contact with the press-joined portion. There is a method of installing and performing, but in any case, no inconvenience occurs.

The edge heating and the solid-state pressure welding may be performed in the atmosphere or in an atmosphere having a lower oxygen concentration than the atmosphere (in a shield atmosphere), but preferably in a shield atmosphere from the viewpoint of seam quality. Further, the edge heating and the solid-state pressure welding are preferably performed in an atmosphere having a dew point of −10 ° C. or less from the viewpoint of seam quality. The inventors have after pressed, by the time t _k which joint 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 2
Shown in From Figure 2, t _k in accordance becomes longer, it can be seen that the seam quality is 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 solid phase pressure welding 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.

[0025] 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,
In addition, by controlling the heating temperature of the end faces of both edges during edge heating and adjusting the temperature distribution in the pipe circumferential direction from the end faces of both edges to the center of the pipe during solid phase pressure welding, Adjust and control the seam cooling rate. 4 (a) and 4 (b), depending on whether or not the squeeze roll is in contact with the outer surface of the press-bonded portion, the temperature reached at the edge portion, or the degree of reduction in the pipe circumferential direction by the squeeze roll. As shown in b), the thickness of the pipe may be increased by 5% or more inside or outside the pipe or inside the pipe at the seam portion. In such a case, at an appropriate place after the welding,
It is preferable to reduce the thickness in the vicinity of the increased seam portion by rolling. Rolling in the vicinity of the increased seam portion is performed, for example, as shown in FIG.
Rolling is performed from inside and outside of a pipe by a press-seam rolling roll 10 shown in FIG. The roll 10 for rolling the press-seam portion includes a roll 10a for rolling the outer surface of the press-seam portion, and a roll 10b for rolling the inner surface of the press-welding seam portion.

In addition, by adopting a method in which a roll or the like is brought into contact with the inner and outer surfaces of the press-joined pipe of the press-joining method, the material is constrained in the vertical direction, and the increase in thickness due to the press-contact is 5%.
It is also possible to suppress the rolling after the pressure welding. For example, the squeeze roll 6 and the roll 11a for restraining the inner surface of the press contact seam shown in FIG. The roll 11a for restricting the inner surface of the press contact seam is supported by a roll support rod 11b for restricting the inner surface of the press contact seam.

In the welded seam formed by the solid-phase welding, the presence or absence of rolling of the welded portion depends on the degree of edge droop of the steel strip, the precision of the edge refining of the steel strip, the welding method or the degree of thickness increase by the welding. Irrespective of this, as shown in FIG. 6, a minute concave portion having a depth of about 0.2 mm called a weld line may be formed on the outer surface, which adversely affects the appearance and seam quality. In such a case, it is preferable to remove the weld line at an appropriate place after the welding to smooth the outer surface. The removal of the weld line is performed by performing processing such as cutting and polishing. Further, the removal of the weld line may be performed before or after the rolling in the case of rolling the press-welded thickened portion.

As described above, according to the present invention, both edges of the open pipe can be stably held in the temperature range in which solid pressure welding can be performed, and then, the squeeze roll is used for solid pressure welding to obtain excellent seam quality and surface quality. A steel pipe having skin can be manufactured with high productivity.

[0029]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An equipment row suitable for carrying out the present invention shown in FIG. 1 was used. A 3.5 mm-thick steel strip 1 was continuously preheated at a temperature of 400 to 650 ° C. in a preheating furnace 2 and then continuously formed by a forming roll group 3 to obtain an open pipe 7. Under the conditions shown in Table 1, edge preheating is performed at both ends of the open tube by the edge preheating induction heating coil 4 and further generated by the laser beam source 5a, and the edge heating laser beam 5 adjusted by the mirror 5c and the condenser lens 5b. The edge is heated by using a squeeze roll 6 installed at a position where it comes into contact with the pressure welding seam, and solid-state pressure welding is performed. Tube dimensions: 60.5 mmφ × 3.5 mmt, standard: STKM11
A steel pipe 8 was used. The seam quality and surface skin of the manufactured steel pipe 8 were investigated, and the results are shown in Table 1. The seam quality is evaluated by the flat height ratio (h / D, h: flat height m) of the steel pipe.
m, 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 solid-state pressure welding were performed in a shield atmosphere.

[0030]

[Table 1]

After the strip was heated to 1300 ° C., a forged pipe of 60.5 mmφ was formed by forging to obtain a conventional example (No. 11). The flat height ratio and the surface roughness Rmax of the steel pipe were measured in the same manner as in the example, and are also shown in Table 1. Test No.1, No.2, No.6, No.
In the examples of the present invention of No. 8, No. 9 and No. 12, the flatness height ratio was 0.3 or less and the surface roughness Rmax was 10 μm or less.
o.11 forged pipe has a flat height ratio of 0.56 and a surface roughness of Rmax 3
It is improved to 7.5 μm. Outside the range of the present invention, the flattened height ratio increases as in Tests No. 3, No. 4, and No. 7, and the surface roughness Rm as in Test No. 10.
ax increases. Furthermore, as shown in Test No. 5, when the end face of the edge portion melts, a margin is formed and it is necessary to perform bead cutting, so that the pipe forming speed is reduced to 100 m / min.

In Test No. 6, the edge portion was preheated to a temperature exceeding 1300 ° C., but the seam quality and surface skin were excellent.
There was no decrease in the tube forming speed. The productivity of the example of the present invention is as high as 30 ton / hr, and the productivity of the conventional ERW pipe for bead cutting is 15 ton / hr, but the productivity is remarkably improved. In Tests No. 1, No. 8 and No. 9 of the present invention example, a wall thickness of 0.5 to 1.5 mm was found on the inner surface of the welded seam portion, but the vicinity of the welded seam portion was rolled from inside and outside of the tube with rolling rolls. And 0.2m
The wall thickness was reduced to within m, which was within the specification range for steel pipe dimensions.

In Tests No. 2 and No. 12, 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. 12 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 in Test No. 9 in which dew point control in the atmosphere was not performed.

[0034]

According to the present invention, both edges of an open pipe can be stably held in a temperature range in which solid pressure welding can be performed, and a steel pipe having excellent seam quality and surface skin can be manufactured with high productivity. Has the effect of

[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.

Fig. 2 Effect of post-welding on seam quality of solid-state welded joints
00 is a graph showing the relationship between the oxygen concentration in the time t _k and the atmosphere is maintained above ° C..

FIG. 3 is a cross-sectional view showing a positional relationship between a squeeze roll, a roll for restraining the inner surface of a press-seam portion, and a press-joint portion during solid-phase press welding.

FIG. 4 is a cross-sectional view illustrating an example of a cross-sectional shape of a steel pipe after solid-phase pressure welding.

FIG. 5 is a schematic partial sectional side view of an equipment row suitable for carrying out the present invention.

FIG. 6 is a cross-sectional view showing an example of the outer shape of a press-seam portion after solid-phase press-bonding.

FIG. 7 is a characteristic diagram showing temperature dependence of relative magnetic permeability of steel.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Strip steel 2 Preheating furnace 3 Forming roll group 4 Induction heating coil for edge preheating 5 Laser beam for edge heating 5a Laser beam source 5b Condensing lens 5c Mirror 6 Squeeze roll 7 Open pipe 8 Steel pipe 9 Pressure welding seam section 10 Pressure welding seam section rolling Roll for roll 10a Roll for outer surface rolling of pressure welded seam 10b Roll for inner surface rolling of pressure welded seam 10c Roll support rod for rolling of pressure welded seam 11a Roll for restraining inner surface of pressure welded seam 11b Roll support rod for inner surface restraint of pressure welded seam 12 Outer surface of pressure welded seam Weld line

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code Agency reference number FI Technical indication B23K 28/02 B23K 28/02 37/08 37/08 C (72) Inventor Motoaki Itaya Aichi 1-1, Kawasaki-cho, Handa-shi, Chita Works, Kawasaki Steel Corp. (72) Inventor Akira, 1-1 1-1, Kawasaki-cho, Handa-shi, Aichi Prefecture, Chita Works, Kawasaki Steel Corp. (72) Inventor, Toshio Onishi Aichi Prefecture 1-1-1 Kawasaki-cho, Handa-shi Kawasaki Steel Corporation Chita Works (72) Inventor Nobuki Tanaka 1-1-1 Kawasaki-cho Handa-city Aichi Prefecture Kawasaki Steel Corporation Chita Works

Claims (9)

[Claims] 1. A method of manufacturing a steel pipe in which a steel strip is continuously formed by a forming roll to form an open pipe, both edges of the open pipe are heated, and abutted and joined by a squeeze roll. After the edge of the open tube is heated to a temperature equal to or higher than the Curie point by induction heating, an edge preheat is applied to both edges of the open tube, and then any one of a laser beam, an electron beam, and a plasma beam is used. A method for producing a steel pipe having excellent seam quality and surface texture, comprising performing edge heating for heating to a temperature range of 1300 ° C. or higher and lower than the melting point, and pressing with a squeeze roll. 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 according to claim 1, wherein the edge preheating is performed at a temperature above the Curie point of 1300.
The method for producing a steel pipe according to claim 1, wherein the steel pipe is heated to a temperature lower than ℃. 4. The method for producing a steel pipe according to claim 1, wherein the edge preheating is performed in an oxygen concentration atmosphere lower than the atmosphere. 5. The method according to claim 1, wherein the edge heating and the pressure welding are performed in an oxygen concentration atmosphere lower than the atmosphere. 6. The method according to claim 1, wherein the edge preheating, the edge heating and the pressure welding are performed in an atmosphere having a dew point of −10 ° C. or less. . 7. After the pressure, claim joint time t _k which is held above 1300 ° C. (sec), which is a t _k satisfying the above 0.03sec or below (1) 7. The method for producing a steel pipe according to 1, 2, 3, 4, 5, or 6. 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. 8. The steel pipe according to claim 1, wherein the seam portion tube material is restrained from the inner and outer surfaces of the tube at the time of the pressure welding to suppress the increase in the thickness of the seam portion. Production method. 9. The method according to claim 1, wherein after the pressing, the vicinity of the pressing seam is rolled.
Or the method for producing a steel pipe according to 8.