JPH0732034A - Manufacture of butt-welded steel tube - Google Patents

Abstract

PURPOSE:To attain the manufacture of a butt-welded tube that is superior in the quality of an abutting part. CONSTITUTION:In the manufacture of a butt-welded tube in which a steel strip with a prescribed width is butt-welded after the strip is heated and hot-formed, this manufacture is superior in the quality of an abutting part such that a part to be butt-welded is heated by irradiation with a laser beam from the upstream side before a butt-welding is performed. In this way, a steel tube with a stable quality in the abutting part and with a capability for a strict working is manufactured while a high efficiency and a high productivity are maintained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a forged tube having excellent abutting portion quality.

[0002]

2. Description of the Related Art Generally, a forged tube is, as shown in FIG. 3, a steel strip having a predetermined width, which is continuously inserted into a heating furnace, at about 1200.degree.
After heating to ˜1300 ° C., it is molded by a molding stand, and oxygen blow is performed just before forging to perform forge welding. After that, squeeze with a stretch reducer to make the outer diameter wall thickness. This method is the most efficient and highly productive method for producing steel pipes and is generally widely used. However, it requires a lot of energy for heating to a high temperature. −
As described in Japanese Patent No. 122188, there is a method in which after low-temperature heating, only edge edges are subjected to high-frequency heating, and then oxygen blow is carried out immediately before forging. Further, in order to improve the quality of the abutting portion, high frequency resistance welding is performed at a relatively low temperature as disclosed in JP-A-58-9714 or JP-A-60-15082, and then the bead is used. There is a method of performing removal cutting, heating again to about 900 ° C to 1100 ° C, and then squeezing with a stretch reducer.

[0003]

Generally, in the method of manufacturing a forged pipe, the scale adhering to the edge is removed by oxygen blowing immediately before forging, and the edge is heated by oxidation heat for forge welding. According to this method, the quality of the abutting portion is unstable, and a streak-shaped recess (or simply called a streak) 1 as shown in FIG. 4 may continuously occur on the outer surface of the abutting portion. The streak-shaped dent significantly impedes workability. This problem also occurs in the same manner as long as oxygen blowing is performed by a method in which after the low temperature heating, only the edge portion is subjected to high frequency heating, and then oxygen blowing is performed immediately before forging welding.

In order to solve this problem, there is a method in which high-frequency resistance welding is carried out at a relatively low temperature, bead removal cutting is carried out, heating is carried out again at about 900 ° C. to 1100 ° C., and then squeezing is performed by a stretch reducer. In this method, high-frequency resistance welding is very good at high quality welding, but as a result, beads are formed, which causes a new problem that it must be removed by cutting at high temperature. , Greatly impairs efficiency and productivity. The present invention is intended to solve the above problems in the conventional manufacturing method, and an object thereof is to provide a method for manufacturing a forged welded tube in which excellent abutting portion quality is obtained and streaking does not occur. .

[0005]

Means for Solving the Problems That is, the present invention is a method for manufacturing a forged tube in which a steel strip having a predetermined width is heated and hot-formed, and then forged and welded. This is a method for manufacturing a forged steel pipe having excellent abutting portion quality, which comprises heating the forged portion by irradiation and then forging.

The present invention will be described in detail below. FIG. 1 shows the manufacturing process of the present invention. In the conventional process, a steel strip having a predetermined width is continuously inserted into a heating furnace as shown in FIG.
After heating to ℃ ~ 1300 ℃, it is molded in a molding stand, oxygen blow is performed just before forging and forging is performed. After that, squeeze with a stretch reducer to make the outer diameter wall thickness. In this method, as described above, the abutting part quality is unstable, and
A streak-like depression is continuously generated on the outer surface.

In the present invention shown in FIG. 1, a steel strip having a predetermined width is continuously inserted into a heating furnace, heated to about 1100 ° C. to 1300 ° C., and then formed by a forming stand. After that, the forged portion is heated by irradiating the forged portion with a laser during the forging welding.
As a laser irradiation method, for example, as shown in FIG. 4, a laser beam 4 is irradiated from a laser irradiation device 3 arranged on the upstream side toward an abutting portion. At this time, if it is difficult to hit the entire surface in the thickness direction with one beam due to the capacity of the laser generator, several beams are emitted. In any case, it is important to uniformly irradiate the laser beam in the thickness direction of the abutting portion and heat it uniformly. After heating by laser irradiation, it is forged by a forging roll 3 and then squeezed by a stretch reducer to have a predetermined outer wall thickness.

The cause of the streak is as shown in FIG.
This is because the outer surface edge portion 9 is oxidized, melted, and disappears by oxygen blowing 7 from the outer surface during the forge welding, and remains as a continuous streak-shaped recess after the forge welding. However, unlike the oxygen blow in the case of laser irradiation, the edge part melts and disappears in order to uniformly irradiate in the thickness direction of the abutting part and to heat it uniformly, not from the outer surface, but continuous stripes after forging welding. It does not remain as a dent.

Further, in the conventional oxygen blow, since the oxide is heated by the heat of oxidation, the oxide is likely to be caught in the abutting portion, and the quality of the abutting portion is not stable. However, laser irradiation does not generate oxides, resulting in stable abutting part quality.

Another purpose of oxygen blowing is to remove the scale adhering to the edge. However, when the scale removal is insufficient only by laser irradiation, the edge does not melt and the edge is not melted. Oxygen may be blown to the extent that the adhered scale is removed. In other words, if only the scale attached to the edge is removed, a very small amount is possible as compared with the conventional oxygen blow, and the edge is not melted.

[0011]

EXAMPLES Table 1 compares the conventional method and the method of the present invention with a size of φ42.7 × t4.0. No. The conventional method of No. 1 is by oxygen blowing, No. The conventional method of No. 2 is a method by high frequency induction heating + oxygen blow, but in both cases, the quality of the abutting part is not stable, streaks are generated, and the component cannot be manufactured unless the content is 0.1% C or less. . No. Three
With the conventional method of ERW welding, stable abutting part quality was obtained, streaks did not occur, and it was possible to manufacture up to 0.5% C, but the line was frequently stopped due to bead cutting adjustment. , Productivity dropped significantly. Compared to these conventional methods,
No. 4 and No. In the method of the present invention of No. 5, the quality of the abutting portion is stable, no streak is generated, and it is not necessary to stop the line on the way, so that the productivity is high.

[0012]

[Table 1]

[0013]

When a forged tube is manufactured by the conventional manufacturing method, the quality of the abutting portion is unstable, and the outer surface of the abutting portion is continuously formed with streak-like recesses to bend and expand the pipe. It could not be used for applications that require severe processing. By applying the method of the present invention, it has become possible to manufacture a steel pipe which is stable in abutting part quality and can be severely processed while maintaining high efficiency and high productivity. Also, since heating is performed by laser irradiation, highly accurate heating control is possible, and
There is little scale generation, and the range of components that can be forged, that is, the manufacturable range, expands.

[Brief description of drawings]

FIG. 1 is a diagram showing a manufacturing process of the present invention.

FIG. 2 is an explanatory diagram showing an example of a laser irradiation method of the present invention.

FIG. 3 is a diagram showing a conventional manufacturing process.

FIG. 4 is a diagram showing a state of streaks occurring in the forged tube.

FIG. 5 is a view showing a melting state of an edge by oxygen blowing.

[Explanation of symbols]

 1 streak-shaped recess 2, 6, 8 tube 3 laser irradiation device 4 laser beam 5 forging roll 7 oxygen blow 9 outer surface streak part

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Nobuo Mizuhashi 20-1 Shintomi, Futtsu-shi, Chiba Nippon Steel Corporation Corporate Technology Development Division

Claims (1)

[Claims] 1. In a method for producing a forged welded tube in which a steel strip having a predetermined width is heated to perform hot forming and then forged, the forged portion is heated by irradiating a laser from the upstream side of the forged portion during forging. A method for producing a forged steel pipe having excellent abutting part quality, which is characterized by performing forging afterwards.