JPH11151524A - Manufacture of steel tube - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method for a steel tube having high strength and high ductility capable of high efficiently producing and also coping with the many kinds-but-small lot production. SOLUTION: A strip steel 1 which is rapidly cooled in a hot rolling process is continuously formed into an opened tube 7 with a forming roll, both edge parts of the opened tube 7 are edge preheated at a temperature equal to or higher than Curie point by induction heating, and then edge heated at a temperature of >=1,300 deg.C but lower than the melting point by induction heating. After applying solid phase pressure welding with a squeeze roll 6 to obtain a base tube 8, the base tube 8 is reheated, and warm squeezing of >=5% in an outer diameter squeezing ratio is preferably applied to it at 200-700 deg.C. The treatment of heating and rapid cooling may by applied to the strip steel 1 before forming it into the opened tube 7 instead of rapid cooling treatment in the hot rolling process. A seam part is preferably cooled after forming it into the base tube 8.

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 A welded steel pipe is formed by forming a steel plate or a steel strip into a tube and welding the joint thereof, and is manufactured by various manufacturing methods from a small diameter to a large diameter. Welding (electric sewing), forge welding, and electric arc welding can be used. 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 by a forming roll to form an open tube, and then the edges of both edges of the open tube are heated by high-frequency induction heating to a temperature equal to or higher than the melting point of the steel. To produce a steel pipe by abutment welding the end faces of both edges (for example, the third edition of the Iron and Steel Handbook, Vol. III (2) 10).
56-1092).

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 edges of the open pipe above the Curie point, the second heating device further heats it above the melting point, and squeeze rolls the two edges to produce a steel pipe by impact welding. I do. In Japanese Patent Application Laid-Open No. 2-299832, a current having a frequency of 45 to 250 kHz is passed through a first heating device to preheat both etch portions, and further heated to a melting point or higher by a second heating device, and then squeezed with a squeeze roll. 2. Description of the Related Art An electric resistance welded pipe manufacturing apparatus that manufactures a steel pipe by abutment welding of both edges has been proposed.

[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 bead cutting tools are consumables, they differ depending on the pipe forming speed.However, it is necessary to change the tool every bead cutting length of 3000 to 4000 m, and the line must be stopped every 3 to 5 minutes of replacement time. You.

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 productivity was low because bead cutting became a bottleneck and high-speed pipe making was not possible. In addition, in this ERW pipe, since the open pipe is a cold pipe except that only the both edges have a melting point or higher at the time of joining, the slip between the pipe forming tool such as a hole-shaped roll and the steel strip is made. Production efficiency is poor because measures such as prevention of flaws and suppression of molding load are required.

[0007] Since it is necessary to use a hole-shaped roll matching the dimensions of the product steel pipe, it is not suitable for the production of steel pipes of small lots and many kinds. There was such a problem. On the other hand, for relatively small diameter steel pipes, there is a method for producing a forged steel pipe having extremely high productivity. In this method, a continuously supplied steel strip is heated to 1300 in a heating furnace.
After heating to about ℃, it is formed into an open pipe by forming it into a tube with a forming roll, then high-pressure air is blown to both edges of the open pipe to scale off the end face, and oxygen is blown to the end face by a welding horn. This is a method of producing a steel pipe by heating the end face to about 1400 ° C. by the heat of oxidation and then abutting both end face faces with a forging roll to perform solid-phase welding (for example, the 3rd Edition Steel Handbook No. III) Volume (2) 1056-10
92).

However, in this method of manufacturing a forged steel pipe, although the pipe forming speed is high and the productivity is high, the scale-off of the end face is not perfect, so that the scale is caught in the forged joint but the strength of the seam is reduced. It is considerably inferior to the base metal part. Since the steel strip is heated to a high temperature, scale is formed on the pipe surface and the surface skin is poor. It has disadvantages such as.

In order to solve the problems of the method for producing an electric resistance welded steel pipe and the method for producing a forged steel pipe, for example, Japanese Patent Application Laid-Open No. 63-33105 discloses that a hollow shell such as an electric resistance welded steel pipe is kept in a cold state. In this regard, there has been proposed a method of rolling and reducing the outer diameter of a steel pipe by rolling using a plurality of hole shapes formed of three rolls. However, in this method, since a hollow shell such as an electric resistance welded steel pipe is subjected to drawing rolling in a cold state, a large rolling mill capable of withstanding a large rolling load or a lubricating rolling device for preventing seizure with rolls. In addition to the need for installation, the work strain due to cold drawing rolling is superimposed on the forming strain when forming a steel strip into an open pipe, the work hardening of the material becomes remarkable, the elongation of the steel pipe decreases, and There is a problem that a heat treatment step must be added. Further, in the cold-rolling rolling, if the outer diameter is significantly reduced, there is a problem that uneven thickness and roll flaws are generated, and there is also a problem that it is difficult to largely unify the dimensions of the forming die rolls.

Further, Japanese Patent Kokoku 2-24606, heating the strip to the A less than about ₃ transformation point, then molded into an open pipe, welding the edges of the open pipe by high-frequency induction heating and squeeze roll and as a substrate tube, after which the substrate tube was raised above a ₃ transformation point, the production method of the steel pipe to a product pipe having a predetermined outer diameter tube reducing rolling devices it has been proposed. FIG. 7 is a schematic view showing a method of manufacturing the steel pipe, where 1 is a steel strip, 8 is a mother pipe,
16 is a product tube, 2 is a steel strip preheating furnace, 4 is a steel strip heating furnace, 26 is a mother pipe heating furnace, 21 is a drawing rolling device, 3 is a forming roll group (forming device), 9 is an induction coil, 6 is Squeeze roll, 11
Is a bead cutting machine.

However, in this method, the entire pipe is 800-95.
Heating to a high temperature of about 0 ° C causes new scale loss and lowers the yield.In addition to this, scale entrapment is induced during squeeze rolling, causing problems such as surface flaws and surface skin deterioration, and the installation of a heating furnace. However, there is a problem of an increase in cost such as an increase in fuel cost for heating.

[0012]

DISCLOSURE OF THE INVENTION The present invention advantageously solves the above-mentioned problems, can produce a steel pipe having high strength and high ductility without deteriorating the surface condition, has a high production efficiency, and has a small lot and a wide variety of products. An object of the present invention is to propose a method of manufacturing a steel pipe that can be used for production.

[0013]

Means for Solving the Problems The present inventors have conducted intensive studies to produce a steel pipe having high strength and high ductility. It was newly found that high ductility can be obtained by drawing. The present invention has been made based on these findings.

That is, according to the present invention, a steel strip is continuously formed with a forming roll to form an open pipe, both edges of the open pipe are heated, and abutted and joined with a squeeze roll to form a mother pipe. In the method for producing a steel pipe for drawing a pipe, the strip steel is subjected to a quenching treatment in a hot rolling step, and heating to both edges of the open pipe is performed at a temperature higher than the Curie point by induction heating. Edge preheating to heat to a temperature, and more than 1300 ° C. by induction heating, edge heating to heat to a temperature range below the melting point, the drawing process,
This is a method for producing a high-strength, high-ductility steel pipe, characterized by warm drawing performed in a temperature range of 200 to 700 ° C. In the present invention, it is preferable that the drawing is performed with an outer diameter drawing ratio of 5% or more.

In the present invention, instead of subjecting the strip to quenching in the hot rolling step, the strip may be subjected to heating and quenching before being formed into an open pipe by a forming roll. In the present invention, it is preferable that the warm drawing is performed by a multi-stand drawing rolling mill including two or more rolls. Further, in the present invention, after the mother pipe is formed, the vicinity of the mother pipe seam portion may be rolled.

Further, in the present invention, after the above-mentioned mother pipe is used,
The mother pipe seam may be cooled. Further, in the present invention, the edge heating may be performed by any one of a heating method, a tungsten inert gas welding, a laser beam, an electron beam, and a plasma beam instead of the induction heating. In the present invention, the mother tube heating for the warm drawing may be performed by induction heating.

Further, according to the present invention, the open tube
After preheating to not more than ° C., the both edge portions may be heated. Also, the present invention provides an uncoiler for discharging a steel strip,
It consists of a steel strip joining device that joins the preceding steel strip and the following steel strip, a looper that stores the steel strip, a steel strip heating and quenching device that heats and quenches the steel strip, and a forming roll group that forms and processes the steel strip. Abutment joining of a forming apparatus, or an open pipe preheating apparatus for preheating an open pipe, an edge heating induction heating apparatus having an induction heating coil, an edge heating induction heating apparatus having an induction heating coil, and an open pipe. A squeeze roll and a seam cooling device for cooling the mother pipe seam portion,
A series of steel pipe manufacturing equipment characterized by sequentially arranging a mother tube heating device for heating the mother tube to a drawing temperature and a drawing device including a plurality of drawing rolling machines for drawing and reducing the mother tube warmly. is there.

In the present invention, it is preferable that a seam rolling device including a rolling roll for rolling the vicinity of the mother pipe seam from inside and outside of the pipe is provided on the exit side of the squeeze roll.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, it is preferable that a steel strip is quenched after being rolled in a hot rolling step to form a rapidly cooled structure such as martensite or bainite. High ductility can be secured by combining such a quenched structure with subsequent warm working. Instead of quenching after rolling in the hot rolling step, the steel strip may be heated and quenched before being formed into an open pipe by a forming roll to form a quenched structure.
In this case, the steel strip unwound from the uncoiler
After heating to a temperature higher than the Ac ₃ transformation point by a heating furnace or induction heating, a quenching treatment is performed. The cooling means of the quenching process is
Fluid injection of water, gas or the like is preferred.

[0020] The chemical composition of the steel strip suitable for the present invention is the following:
And C: 0.05-0.19%, Si: 0.01-1.5%, Mn: 0.5-
3.5% as basic composition, Ni, Cr, Mo, Cu, N
Alloying elements such as b, V, Ti, and B may be added. C is
It is an element that improves the quenchability and is necessary for forming a rapidly cooled structure such as martensite and bainite. For this purpose, the content of 0.05% or more is necessary. However, if it exceeds 0.19%, the solid-phase pressure-welding property and the weldability are deteriorated.
It is preferably 0.19%.

Si is an element for improving the strength, and it is necessary to contain 0.01% or more in order to obtain the desired strength. However, if it exceeds 1.5%, the solid-phase welding property, weldability, and workability deteriorate. Therefore, the content of Si is preferably set to 0.01 to 1.5%. Mn
Is an element that improves the hardenability and is necessary for forming a rapidly cooled structure such as martensite and bainite.
For this purpose, 0.5% or more is required, but 3.5%
If Mn exceeds 0.5, the weldability and workability deteriorate, so
Preferably it is 3.5%.

In addition, Ni, Cr, M
Alloy elements such as o, Cu, Nb, V, Ti, and B can be added.
i is 2% or less, Cr is 1% or less, Mo is 2% or less, Cu is 1%
Hereinafter, it is desirable that Nb is 0.1% or less, V is 0.3% or less, Ti is 0.2% or less, and B is 0.003% or less. The strip is discharged from the uncoiler and continuously formed by a plurality of forming rolls to form an open pipe. For forming, a known processing method using a plurality of forming rolls can be suitably applied.

Prior to edge preheating, the entire open tube
It may be preheated to below ℃. The preheating is performed to reduce the temperature difference between the edge portion and the mother pipe in the vicinity thereof at the time of edge heating performed later, and to appropriately control the temperature and the temperature distribution of the edge portion at the time of solid phase pressure welding. If the preheating temperature exceeds 700 ° C, a large amount of scale is formed on the surface of the open pipe, and the surface skin of the steel pipe deteriorates. Therefore, the upper limit of the preheating temperature was set at 700 ° C. If the temperature is lower than 200 ° C., the temperature and temperature distribution near the edge portion are not appropriate.
~ 700 ° C. As the preheating method, any of a method using a heating furnace, an induction heating method using an induction coil, and a resistance heating method by energization are suitable.

Next, both edges of the open pipe are edge preheated. Edge preheating is an induction heating method using an induction heating coil. By this edge preheating, the temperature of the edge portion is set to the Curie point or higher, preferably lower than 1300 ° C. When the edge portion is heated to the Curie point or higher, the relative magnetic permeability becomes a value close to 1, the penetration depth increases, and the temperature distribution in the pressure contact surface tends to be uniform. Therefore, the edge portion is preheated to a temperature range higher than the Curie point. From the viewpoint of heating energy efficiency, it is preferable that the heating is performed at a temperature equal to or higher than the Curie point and lower than 1300 ° C., but there is no inconvenience even if the temperature is higher than 1300 ° C. However, if the temperature rises at this stage, only the corners will have a melting point or higher, and beads (surplus) will be generated at the time of joining, so high-speed pipe forming may not be possible, and edge preheating should be performed at less than 1300 ° C. preferable.

Both edges of the pre-heated open tube are further subjected to edge heating in which the solid tube is heated to a temperature range of 1300 ° C. or higher and lower than the melting point and capable of being pressed against a solid phase. The edge heating is preferably an induction heating method using an induction coil from the viewpoint of energy efficiency, but is performed by any of resistance heating by energization, tungsten inert gas welding (TIG welding), laser beam, electron beam, and plasma beam. You may. Further, these plural heating means 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 is insufficient, and the seam quality is deteriorated.
Further, if the temperature of the edge portion exceeds the melting point of the pipe material, the molten steel forms beads (surplus) inside and outside of the pipe at the time of abutment joining, so that bead cutting is required. For this reason, the edge heating is 1300 ° C. or higher and lower than the melting point, more preferably 1400 ° C. or higher and lower than the melting point.

The term "solid-phase pressure welding" as used in the present invention means a pressure welding in which bead (surplus) is suppressed and no bead cutting is required. In the present invention, the edge heating temperature is preferably in the solid phase region in order to suppress the rise of the bead (surplus), but there is no inconvenience even in the solid-liquid two-phase region below the melting point where some liquid phase exists. The open pipe whose both edges are heated to the above-mentioned solid-state pressure-contactable temperature range is abutted on both edges by a squeeze roll and solid-phase pressed.

As shown in FIGS. 5 (a) and 5 (b), depending on the ultimate temperature of the edge portion or the degree of pressure contact by the squeeze roll, the mother tube seam formed by the solid-phase pressure welding can be provided inside or outside the pipe of the seam portion. May increase the wall thickness by 5% or more of the tube wall thickness. In such a case, preferably,
It is preferable to reduce the thickness by rolling near the seam portion immediately after the welding or at an appropriate place after the welding. Rolling in the vicinity of the increased seam portion is performed, for example, from inside and outside the tube by a press-contact seam portion rolling roll 30 shown in FIG. The pressed seam roll 30 includes an outer roll 30a and an inner roll 30b, and the roll 30b is supported by a roll rod 30c.

Further, 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, the material is restrained in the vertical direction, so that the thickness increase due to the press-welding is suppressed to less than 5%, and the rolling after the press-welding is performed. It may be unnecessary.
For example, the material is restricted from inside and outside the pipe by the squeeze roll 6 and the roll 31a for restraining the inner surface of the press-contact seam shown in FIG. The roll 31a for restraining the inner surface of the press contact seam is a roll support rod 31 for restraining the inner surface of the press contact seam.
c.

Next, in the present invention, the solid state pressure-welded mother pipe is reheated, and a plurality of rolling mills are preferably used at a working temperature range of 200 to 700 ° C., preferably with an outer diameter reduction ratio of 5% or more. Drawing is performed to obtain a product tube having a predetermined outer diameter. From the viewpoint of ensuring the dimensional accuracy of the product pipe after drawing, the temperature difference in the circumferential direction of the pipe should be 50% after solid phase pressure welding and before drawing the mother pipe.
It is preferable to perform a soaking treatment at a temperature of not more than 20 ° C., preferably not more than 20 ° C. The temperature difference in the circumferential direction of the mother pipe causes a difference in deformation resistance at the time of the subsequent drawing, which tends to cause uneven thickness of the product pipe.

In the present invention, after the solid-phase pressure welding, the mother pipe is reheated in order to perform warm drawing, so that the temperature difference in the circumferential direction of the mother pipe tends to be more uniform than when no heating is performed. .
However, the temperature of the seam part edge-heated by the open pipe tends to be higher than that of other parts, and it is preferable to cool the seam part by a cooling unit before reheating. The cooling means is preferably a fluid jet of water, gas or the like.

The method of reheating the mother pipe is not particularly limited, but a heating method using a heating furnace, an induction coil, or the like is preferable, and among them, induction heating using an induction coil is preferable.
The mother tube is reheated to a drawing temperature of 200-700 ° C. The mother tube heated so that the working temperature is in a warm region of 200 to 700 ° C. is subjected to warm drawing by a drawing rolling mill.

The work strain introduced by performing the warm drawing in the warm range of 200 to 700 ° C. is combined with the prestructure of the tube material, and the ductility is significantly increased. However, if the drawing temperature is less than 200 ° C, the work hardening of the tube material is remarkable, ductility is deteriorated, the deformation resistance of the material to be rolled is high, the rolling load increases, and roll seizure flaws occur on the tube surface. I do. Also,
If the drawing temperature exceeds 700 ° C., the roughness of the tube surface increases due to scale biting flaws generated during rolling, and the surface skin deteriorates.

The drawing process is performed as shown in FIGS. 4 (a) to 4 (c).
It is preferable to carry out the reduction in a reduction rolling mill row in which a plurality of stands are provided with a reduction roll having a grooved roll structure composed of rolls to 4 rolls. The amount of drawing is preferably 5% or more in terms of outer diameter drawing ratio. When the outer diameter reduction ratio is less than 5%, the effect of improving the ductility by the reduction rolling is small.

The upper limit of the outer diameter reduction ratio is determined depending on the equipment capacity of the reduction mill. The product pipe subjected to the warm drawing is air-cooled or water-cooled and cooled to room temperature. The obtained product pipe is cut into a predetermined size by a cutting machine and is corrected by a pipe straightening device, or is straightened by a pipe straightening device and then wound into a coil.

FIGS. 1 to 3 show a row of steel pipe production facilities suitable for carrying out the present invention. In FIG. 1 (a), 1 is a steel strip, 14
Is an uncoiler that discharges the steel strip, 15 is a steel strip joining device that connects the rear end of the preceding steel strip and the tip of the following steel strip, 17
Is a looper for storing steel strips, 3 is a forming machine consisting of a group of forming rolls, 7 is an open pipe, 24 is an induction heating device for edge preheating for preheating both edges of the open pipe, and 25 is a heater for both edges of the open pipe. Induction heating device for edge heating, 6 is a squeeze roll that abuts and joins the open pipe edge, 8
Is a mother tube, 10 is a mother tube induction heating device for reheating the mother tube for drawing, 21 is a drawing rolling device for drawing the mother tube, 18
Is a product pipe cutting machine, 16 is a product pipe, 19 is a pipe straightening device, and 20 is a thermometer.

FIG. 1 (b) shows an equipment row in which a seam cooling device 12 is provided on the outlet side of the squeeze roll 6 in the equipment row of FIG. Other symbols are the same as those in FIG. FIG. 2 is a row of steel pipe manufacturing equipment provided with a steel strip heating and quenching device 22 for heating and rapidly cooling the steel strip on the exit side of the looper 17 in FIG.

FIG. 3 is a row of steel pipe manufacturing equipment provided with an open pipe preheating device 23 for preheating the open pipe on the outlet side of the forming apparatus 3 of FIG. 1 (b).

[0039]

EXAMPLES (Example 1) C: 0.17 wt%, Si: 0.20 wt%,
A steel material with a composition of Mn: 1.30 wt% and Cr: 1.0 wt% was converted to FE
A steel sheet of 2.5 mm thickness is formed by hot rolling at T800 ° C, and water-cooled immediately after the completion of rolling to form a quenched structure (martensite-based structure).
After that, a winding coil was obtained. Using the equipment row shown in FIG. 1A, the strip 1 discharged from the coil by the uncoiler 14 was used as an open pipe 7 by the forming apparatus 3.
The edges of the open pipe are preheated by the edge preheating induction heating device 24 under the conditions shown in Table 1, and edge heating is further performed by the edge heating induction heating device 25. A mm-thick mother pipe was used. The solid-pressure welded mother pipe converts the seam to a seam cooling device.
After being cooled and soaked by 12, the product was heated by the induction coil 9 and formed into a product pipe 16 of 15.0 to 42.7 mmφ × 2.3 mm by a reduction rolling device 21 equipped with 20 reduction rolling mills having a three-roll structure. The outer diameter reduction ratio of the reduction rolling at this time is 29 to
75%. The drawing rolling temperature is as shown in Table 1.

As a comparison, a steel material having the same composition was hot-rolled into a steel sheet having a thickness of 2.5 mm, wound up in a coil without water cooling, and subjected to an annealing treatment (annealing at 900 ° C.). Using this coil, a product tube was made under the same conditions as above, and a comparative example (No. A) was obtained. As a conventional example, a steel material of the same composition is hot-rolled into a 3.0 mm-thick steel sheet. 60.5mmφ
A 2.5 mm thick mother pipe was used. The beads formed at the time of joining were deleted by the bead cutting machine 11. The temperature of the mother pipe after bead cutting was 50 ° C. Thereafter, without heating, a 42.7 mmφ × 2.3 mm product pipe with an outer diameter reduction ratio of 29% was formed by a reduction rolling device 21 in which eight stands of a three-roll structure reduction rolling mill were installed.
16, which is the conventional example (No. B).

Further, a steel material having the same composition is hot-rolled into a steel sheet having a thickness of 2.5 mm, and the hot-rolled steel strip which has been formed into a coil without water cooling is heated to 1300 ° C. and forged. Outside diameter
After making a 60.5mmφ mother pipe, drawing is applied to make the outer diameter 42.7mm.
mmφ product tube, which was the conventional example (No. C). Table 1 shows the mechanical properties, the presence or absence of seizure, and the roughness of the surface skin of these product tubes. The presence or absence of seizure was visually observed, and the surface roughness was measured with a stylus-type surface roughness meter for a product pipe with a length of 15 x a circumference of 5 mm to obtain Rmax.

[0042]

[Table 1]

From Table 1, it can be seen that the examples of the present invention in the range of the present invention are high-strength, high-ductility steel pipes having a tensile strength of 700 MPa or more and an elongation of 35% or more, and have good surface texture. On the other hand, the comparative material outside the scope of the present invention has ductility, surface skin,
Strength is inferior. The comparative material A using the annealed steel strip has a low tensile strength of 630 MPa. In the conventional example in which cold drawing is performed, the elongation is as low as 14%. Further, in the example of the present invention, the load of the reduction rolling is low, there is no seizure, and the pipe forming speed is 2 times as compared with the conventional example.
Up to 5 times. (Example 2) C: 0.08 wt%, Si: 0.5 wt%, Mn: 3.0 wt%
%, Cr: 0.3 wt%, Nb: 0.02 wt%, a steel material having a composition of 2.0 mm thick was hot-rolled, and then a coil was formed. Using the equipment row shown in FIG. 2, the strip 1 discharged from the coil by the uncoiler 14 is heated to 880 ° C. through a strip heating and quenching device 22 and then water-cooled to 350 ° C. or less to form a quenched structure. Thereafter, the open pipe 7 is formed by the forming apparatus 3, and the edge preheating is performed by the edge preheating induction heating device 24 under the conditions shown in Table 3, and the edge heating induction heating device 25 is performed.
And heated in a solid phase with a squeeze roll 6 to obtain a 60.5 mmφ × 2.0 mm thick mother pipe. Thereafter, the main pipe was heated to 500 ° C. by the main pipe induction heating device 10 and a 16-roll reducing mill having a three-roll structure was installed.
According to 21, the product tube 16 was 31.8 mmφ × 1.8 mm. The drawing rolling temperature at this time was 450 to 500 ° C., and the outer diameter drawing ratio was 47%.

As shown in Table 2, the mechanical properties of this product pipe are a high-strength and high-ductility steel pipe having a yield strength of 1240 MPa, a tensile strength of 1380 MPa, an elongation of 29% and a good surface skin. Yes, and could be manufactured at a high tube forming speed.

[0045]

[Table 2]

[0046]

According to the present invention, a steel pipe having high strength and high ductility can be manufactured with high productivity without being deteriorated in the surface condition and can be rolled with a low rolling load. This makes it possible to manufacture product pipes of various sizes from a small number of mother pipes, and has a special effect of being able to cope with small lot multi-product production.

[Brief description of the drawings]

FIG. 1 is a schematic view showing one example of a steel pipe manufacturing equipment row suitable for carrying out the present invention.

FIG. 2 is a schematic diagram showing one example of a steel pipe manufacturing facility row suitable for carrying out the present invention.

FIG. 3 is a schematic diagram showing one example of a steel pipe manufacturing facility row suitable for carrying out the present invention.

FIG. 4 is an explanatory view showing a roll structure of a rolling mill.

FIG. 5 is a cross-sectional view showing one example of a cross-sectional shape of a mother pipe after solid-phase pressure welding.

FIG. 6 is a schematic partial cross-sectional side view of an equipment row suitable for carrying out the present invention.

FIG. 7 is a schematic view showing an example of a conventional steel pipe manufacturing equipment row.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Strip steel 2 Strip steel preheating furnace 3 Forming equipment 4 Strip steel heating furnace 5 Induction heating device 6 Squeeze roll 7 Open pipe 8 Main pipe 9 Induction coil 10 Main pipe induction heating apparatus 11 Bead cutting machine 12 Seam cooling apparatus 14 Uncoiler 15 Steel strip joining equipment 16 Product pipe 17 Looper 18 Cutting machine 19 Pipe straightening equipment 20 Thermometer 21 Reduction rolling equipment 22 Steel strip heating and quenching equipment 23 Open pipe preheating equipment 24 Induction heating equipment for edge preheating 25 Induction heating equipment for edge heating 26 Mother Tube heating furnace 30 Roller for seam portion of mother pipe 30a Roll for outer surface rolling of seam portion of main tube 30b Roll for inner surface rolling of seam portion of main tube 30c Roll support rod for rolling of seam portion of main tube 31a Roll for restraining inner surface of seam portion of main tube 31b Mother tube Support rod for seam inner surface restraint S Seam

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification symbol FI C21D 1/42 C21D 1/42 P 8/10 8/10 Z 9/56 101 9/56 101Z (72) Inventor Yuji Hashimoto Aichi 1-1, Kawasaki-cho, Handa-shi, Japan Kawasaki Steel Corporation Chita Works (72) Inventor Motoaki Itani 1-1-1, Kawasaki-cho, Handa-shi, Aichi Prefecture Kawasaki Steel Corporation Chita Works (72) Inventor Hiroyuki Matsui 1-1-1, Kawasaki-cho, Handa-shi, Aichi Prefecture, Chita Works, Kawasaki Steel (72) Inventor Masanori Nishimori 1-1-1, Kawasaki-cho, Handa-shi, Aichi Prefecture, Chita Works, Kawasaki Steel

Claims (10)

[Claims] 1. A steel strip is continuously formed with a forming roll to form an open pipe, both edges of the open pipe are heated, and abutted and joined with a squeeze roll to form a mother pipe. In the method for producing a steel pipe, the strip steel is subjected to a quenching treatment in a hot rolling step, and heating to both edges of the open pipe is heated to a temperature equal to or higher than the Curie point by induction heating. The edge drawing includes edge preheating, and edge heating for heating to a temperature range of 1300 ° C. or higher and lower than the melting point by induction heating, and the drawing is warm drawing performed in a temperature range of 200 to 700 ° C. Of manufacturing high strength and high ductility steel pipes. 2. The steel pipe according to claim 1, wherein, instead of the quenching in the hot rolling step of the strip, the strip is subjected to heating and quenching before being formed into an open pipe by a forming roll. Manufacturing method. 3. The method for manufacturing a steel pipe according to claim 1, wherein the warm drawing is performed by a multi-stand drawing rolling mill including two or more rolls. 4. The method for producing a steel pipe according to claim 1, further comprising rolling the vicinity of the mother pipe seam after forming the mother pipe. 5. The method of manufacturing a steel pipe according to claim 1, wherein the mother pipe seam is cooled after the mother pipe is formed. 6. The edge heating is replaced with induction heating,
6. The method according to claim 1, wherein the heating is performed by any one of a heating method, tungsten inert gas welding, a laser beam, an electron beam, and a plasma beam.
The method for producing a steel pipe according to any one of the above. 7. The heating of the mother pipe for the warm drawing is performed by:
The method for producing a steel pipe according to any one of claims 1 to 6, wherein the heating is performed by induction heating. 8. The method for manufacturing a steel pipe according to claim 1, wherein said open pipe is preheated to 700 ° C. or lower, and then said edge portions are heated. 9. An uncoiler for dispensing a strip, a strip joining apparatus for joining a preceding strip and a following strip, a looper for storing the strip, and a strip heating and quenching apparatus for heating and quenching the strip. And, a forming apparatus consisting of a group of forming rolls for forming a strip, or an open pipe preheating apparatus for preheating an open pipe, and an edge preheating apparatus having an induction heating coil,
An edge heating device having an induction heating coil, a squeeze roll that abuts and joins an open tube, a seam cooling device that cools a seam portion of a main tube, a main tube heating device that heats the main tube to a drawing temperature, and a main tube And a drawing apparatus comprising a plurality of drawing rolling mills for reducing the diameter of the steel pipe in a warm rolling sequence. 10. The steel pipe manufacturing equipment line according to claim 9, further comprising a seam rolling device including a rolling roll that rolls the vicinity of the mother pipe seam from inside and outside of the pipe on the exit side of the squeeze roll.