JPH07323333A - Manufacture of resistance welded tube - Google Patents

Abstract

PURPOSE:To manufacture a resistance welded tube free from buckling by heating the region where the buckled part generated in the vicinity of the edge is contained to the temperature immediately above the AC3 transformation point, and immediately executing the 7 thereto. CONSTITUTION:A strip 1 is successively finished to the cylindrical shape by a break-down roll 2 or the like, and finished to an open tube 1A of the prescribed dimension by a fin-pass roll 6. Alter the welding by a welding machine 7, both edges are pressed against each other by a squeeze roll 8 to make a tube stock 1B. The weld seam part W of the stock tube 1B is heat treated by a heat treating equipment 9, and in this heat treatment process, the heating is achieved at the temperature immediately above the AC3 transformation point over the region capable of completely covering the buckled part in the vicinity of the edge of the open tube 1A generated by the pressing of the squeeze roll 8. Immediately after the heating, the reduction is applied to the longitudinal region R to be heated using caliber rolls 12a, 12b of a reducing equipment 12, and the vicinity of the weld seam part W is re-formed to manufacture the resistance welded tube free from the buckling on the surface.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing an electric resistance welded steel pipe, and is particularly suitable for improving a small recess formed on the outer surface side near an edge when fin-pass forming a large diameter thin wall electric resistance welded steel pipe. The present invention relates to a method for manufacturing an electric resistance welded steel pipe.

[0002]

2. Description of the Related Art Conventionally, when manufacturing a large diameter electric resistance welded steel pipe,
For example, the process is generally performed as shown in FIG. That is, the strip 1 is sequentially formed into a cylindrical shape by a breakdown roll 2, an edge forming roll 3, an outside cage roll 4, and an inside cage roll 5, and then a fin pass roll 6 which is a finish forming roll.
Is finish-molded into an open pipe 1A having a predetermined size. Then, after welding with a welding machine 7, both edges are crimped with a squeeze roll 8 to form a raw tube 1B, and then a heat treatment device 9
The welded seam W is subjected to heat treatment by means of the sizer 10 and finished to a predetermined outer diameter by the sizer to obtain a product.

By the way, t / D (t: wall thickness, D: outer diameter)
When forming a large-diameter thin-walled electric resistance welded steel pipe having a small size with the fin pass roll 6, the outer surface of the fin pass roll 6 is often attached to the outer surface side near the edge.
A recessed defect (hereinafter referred to as buckling) 11 having a depth d as shown in FIG. When this buckling 11 occurs, it causes an edge wave and impairs the shape of the welded portion, which adversely affects the quality and yield.

As a measure for preventing the occurrence of such buckling 11, for example, as disclosed in Japanese Patent Laid-Open No. 57-149016, fin pass reduction is performed up to the limit where an edge wave in the pipe longitudinal direction does not occur. There is a way to reduce it.

[0005]

However, the conventional method of Japanese Patent Laid-Open No. 57-149016 described above has a drawback in that buckling cannot be completely eliminated even if the best molding conditions are selected. That is, the present inventors
As a result of experimenting with various t / D using various materials, as shown in Fig. 5, when t / D is less than 1.3% for 590N material and t / D is less than 1.1% for 400N material. ,
It was found that buckling 11 with a depth d of 0.1 mm or more occurs.

The present invention has solved the above-mentioned problems of the prior art, and an object of the present invention is to provide a method for producing an electric resistance welded steel pipe which does not buckle in the final product.

[0007]

DISCLOSURE OF THE INVENTION According to the present invention, when manufacturing a large-diameter thin-walled electric resistance welded steel pipe, in a heat treatment step of a weld seam portion after forming welding, a region including a buckling portion generated near an edge is included. Was heated to a temperature just above the A _C3 transformation point, and immediately thereafter, a reduction was applied to the region, thereby achieving the above object.

[0008]

[Operation] According to the present invention, since the region including the buckling portion generated near the edge is heated to a temperature just above the A _C3 transformation point, the rolling is immediately applied to the region, so that the buckling is completely completed. It can be lost in The reason why the heating temperature was just above A _C3 transformation point, softening temperature by austenitizing in the case of ordinary steel plate is the A _C3 transformation point or higher, it drops abruptly high temperature deformation resistance in the A _C3 transformation point It focuses on. When heated to a temperature higher than the A _C3 transformation point, the austenite grains become coarse and brittle, so the upper limit is practically at most + 50 ° C in consideration of the accuracy of temperature control of the heat treatment apparatus.

[0009]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a schematic view showing an electric resistance welded steel pipe production line used for carrying out the present invention. The difference from the conventional example is that a rolling down device 12 consisting of a pair of upper and lower caliber rolls is provided between a heat treatment device 9 and a sizer 10. It is arranged.

As shown in FIG. 1, the strip 1 includes a breakdown roll 2, an edge forming roll 3, an outside cage roll 4, and an inside cage roll 5.
Is sequentially formed into a cylindrical shape by a fin-pass roll 6 and finish-formed into an open pipe 1A having a predetermined size.
After being welded at 1, both edges are crimped by the squeeze roll 8 to form the raw tube 1B.

Then, after that, the weld seam W of the blank tube 1B is formed.
Is heat-treated by the heat treatment device 9. In this heat treatment step, the region directly above the _AC3 transformation point is covered over a region capable of completely covering the buckling site near the edge of the open pipe 1A generated by the pressure contact of the squeeze roll 7. Heat at temperature. At this time, the vicinity of the weld seam portion W is brought into a lengthy state called peaking by heating.

Immediately after heating, as shown in FIG. 2, the vertically long heating region R is subjected to reduction using the caliber rolls 12a and 12b of the reduction device 12 to reshape the vicinity of the weld seam portion W. The degree of this reduction is, for example, 0.05 to 0.25.
It is suitable to set it in a light range such as%. Outer diameter D is 60
API X6 with 9.4 mmφ and wall thickness t of 6.4 mm (t / D = 1.05%)
When manufacturing 0-standard large-diameter thin ERW steel pipe, after heat-treating at a temperature of 920 ° C for 30 mm centered on the weld seam W,
Immediately, when a reduction of 3 mm was applied with caliber roll, an extremely smooth ERW steel pipe without buckling on the surface could be produced. This makes it possible to completely eliminate buckling even in high-grade materials such as 590N.

[0013]

As described above, according to the present invention,
Since the region including the buckling part generated near the edge in the heat treatment process after forming and welding is completely heated at a temperature just above the _AC3 transformation point and immediately after that, it is pressed down. Regardless of this, it is possible to manufacture ERW steel pipes with extremely smooth surfaces, which contributes to the improvement of product quality and yield.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing an electric resistance welded steel pipe production line used for carrying out the present invention.

FIG. 2 is a front view showing the operation of the rolling-down device.

FIG. 3 is a schematic view showing a conventional example of an electric resistance welded steel pipe production line.

FIG. 4 is an explanatory diagram of a buckling phenomenon.

FIG. 5 is a characteristic diagram showing an example of a relationship between t / D and buckling depth.

[Explanation of symbols]

 1 Strip 1A Open Pipe 1B Element Pipe 6 Fin Pass Roll 7 Squeeze Roll 8 Welding Machine 9 Heat Treatment Equipment 10 Sizer 11 Cavity (Buckling) 12 Rolling Down Equipment 12a, 12b Caliber Roll W Weld Seam

Claims (1)

[Claims] 1. When manufacturing a large-diameter thin-wall ERW steel pipe,
In the heat treatment process of the weld seam after forming welding, the region including the buckling region generated near the edge is heated to a temperature just above the _AC3 transformation point, and immediately thereafter, a reduction is applied to the region. Manufacturing method of sewn steel pipe.