JPH0732035A - Low cost high quality forged steel pipe manufacturing method - Google Patents

Abstract

(57) [Abstract] [Purpose] Low cost high quality forged steel pipe manufacturing method. [Structure] In a method of manufacturing a forged tube in which a steel strip having a predetermined width is heated and hot-formed, and then forged, a heating temperature is set to 8
50 ° C. to 1200 ° C., high-frequency induction heating is performed only on the edge end after hot forming, and the forged portion is heated by irradiating a laser from the upstream side of the forged portion during forging, and then forged. A method of manufacturing a forged steel pipe with excellent abutting part quality. [Effect] It has become possible to manufacture a steel pipe with stable abutting part quality and capable of severe processing at low cost while maintaining high efficiency and high productivity.

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 a low cost and high quality forged steel pipe.

[0002]

2. Description of the Related Art In general, a forged tube has a steel strip of a predetermined width continuously inserted into a heating furnace as shown in the flow chart of FIG.
After heating at 200 ° C. to 1300 ° C., it is molded by a molding stand, and oxygen is blown 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 JP-A-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 welding. 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 for manufacturing a forged steel pipe, oxygen blow immediately before forging removes scale adhering to the edge and heats the edge by oxidation heat for forge welding. In this method, the quality of the abutting part is unstable, and streak-like recesses (or simply called streaks) 1 are continuously generated on the outer surface of the abutting part of the forged tube 2 as shown in FIG. There is. The streak-shaped dent significantly impedes workability. Further, since heating is performed at a high temperature of 1200 ° C to 1300 ° C, a large amount of heating energy is required, and the surface texture is also poor. These problems are 900 ℃ ~ 11
This can be improved by heating at a low temperature at 00 ° C., high-frequency heating only at the edge portion, and then oxygen blowing immediately before forging welding, but it is difficult to eliminate streaks as long as oxygen blowing is performed.

In order to solve these problems, as mentioned above, high frequency resistance welding is carried out at a relatively low temperature, then bead removal cutting is carried out, again heated to about 900 ° C. to 1100 ° C., and then squeezed by a stretch reducer. There is. With this method, high-frequency resistance welding is performed with high quality, and the heating energy and surface texture are very good, but
As a result, a bead is generated, which causes a new problem that the bead must be removed by cutting at a high temperature, which greatly hinders efficiency and productivity. The present invention solves the problems in the conventional manufacturing method as described above, and provides a method for manufacturing a forged steel pipe having an excellent quality of the abutting portion and an excellent surface texture without streaks in the abutting portion. That is the purpose.

[0005]

That is, according to the present invention, in a method for producing a forged welded tube in which a steel strip having a predetermined width is heated and hot-formed, and then forged, the heating temperature is 850 to 1200.
After the hot forming, only the edge end is subjected to high-frequency induction heating, and the forged portion is heated by irradiating a laser from the upstream side of the forged portion at the time of forging, and then the forged portion is joined. This is a method of manufacturing a forged steel pipe with excellent quality.

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 quality of the abutting portion is unstable, streak-like depressions are continuously generated on the outer surface, a large amount of heating energy is required, and the surface texture is also poor.

According to the present invention shown in FIG. 1, a steel strip having a predetermined width is continuously inserted into a heating furnace, heated to 850 ° C. to 1200 ° C., molded by a molding stand, and then only edge edges are subjected to high frequency induction heating. After that, the forged portion is heated by irradiating the forged portion with a laser during the forging welding. At this time, the heating temperature is set to 850 ° C. or higher because the difference between the temperature of the edge after induction heating and the temperature of other pipe parts is too large below this temperature, and only the abutting part is thickened by the stretch reducer thereafter. The reason why the heating temperature is set to 1200 ° C. or lower is that the abutting part quality becomes unstable when the heating temperature exceeds this temperature.
This is because the skin is also bad.

In the method of high-frequency induction heating only the edge portion, for example, as shown in FIG. 2, a high-frequency induction coil 5 is arranged in the edge opening 4 on the upstream side of the forging roll 3 to heat it. Alternatively, as shown in FIG. 3, the edge can be heated by passing a tube having the opening 12 through the through coil 13.

The laser irradiation method is, for example, as shown in FIGS. 2 and 3, a laser irradiation device 6 arranged on the upstream side.
Laser beams 7 and 15 are emitted from 14 toward the 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,
Irradiates several beams. 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 laser irradiation heating, forging roll 3,1
Forge welding at 1 and then squeeze with a stretch reducer to a predetermined outside diameter wall thickness.

As shown in FIG. 6, the cause of the streak is that in the conventional process, the outer surface edge portion 18 is oxidized, melted and disappears by oxygen blowing from the outer surface at the time of forging, and a continuous streak-like dent is formed after the forging. It will remain as.
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 it is heated by the heat of oxidation, it is easy for the oxide 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 the oxygen blow is to remove the scale attached 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.

[0013]

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. 7, the quality of the abutting portion is stable, no stripes are generated, and it is not necessary to stop the line on the way, so that the productivity is high. However, No. 5, 6,
Even in the same steps as in the present invention, as in Nos. 8 and 9, when the heating temperature is out of the predetermined range, the surface texture is poor and stretch reducing is impossible.

[0014]

[Table 1]

[0015]

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. Moreover, a large amount of heating energy is required to heat to a high temperature. By applying the method of the present invention, it has become possible to manufacture a steel pipe with stable abutting part quality and capable of severe processing, while maintaining high efficiency and high productivity, and at low cost.

[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 the high frequency induction heating and laser irradiation method of the present invention.

FIG. 3 is an explanatory diagram showing another example of the high-frequency heating and laser irradiation method of the present invention.

FIG. 4 is a diagram showing a conventional manufacturing process.

FIG. 5 is a diagram showing a state of streaks occurring in a forged welded tube.

FIG. 6 is an explanatory diagram showing a melted state of an edge due to oxygen blowing.

[Explanation of symbols]

 1 streak dent 2,8,16,19 tube 3,11 forged roll 4,12 opening 5 high frequency induction coil 6,14 laser irradiation device 7,15 laser beam 9,10 forming roll 13 high frequency induction coil (through coil) 17 Oxygen blow 18 External stripe

 ─────────────────────────────────────────────────── ─── 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. A method for producing a forged tube in which a steel strip having a predetermined width is heated and hot-formed and then forged and welded, the heating temperature is set to 850 ° C. to 1200 ° C., and only the edge portion after hot-forming is applied. After performing high-frequency induction heating and heating the forged part by irradiating a laser from the upstream side of the forged part during forging,
A method for manufacturing a forged steel pipe having excellent abutting portion quality, which is characterized by forging.