JPH09108729A - Production of forge welded steel tube excellent in quality - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a production method of a forge welded steel tube excellent in quality. SOLUTION: In this production method of a forge welded tube where forge welding is executed while blowing of oxygen after a steel strip of a prescribed width is heated and hot-formed, the relation of the diameter of bottom DH of a forge welding roll arranged just after tube like forming and oxygen blowing and the average outer diameter of tube DT during passing through the forge welding roll is set to 0.5DT<=DH<=0.7DT. The forge welding steel tube with the excellent quality of the butt part can be produced.

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 forged steel pipe having excellent abutting portion quality.

[0002]

2. Description of the Related Art Generally, a forged welded tube is manufactured by inserting a steel strip having a predetermined width into a heating furnace continuously as shown in FIG.
After heating to ˜1350 ° 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 manufacturing steel pipes and is generally widely used. However, in this method, a large amount of energy is required for heating to a high temperature, and a scale is generated at the edge of the steel strip to be bitten into the forged abutting portion as it is. Therefore, it is described in JP-A-58-122188. As described above, there has been proposed a method in which after the low temperature heating, only the edge portion is subjected to high frequency heating, and then oxygen blow is performed just before the forging welding. Further, in order to improve the quality of the abutting portion, as described in Japanese Patent Laid-Open No. 60-15082, high frequency resistance welding is performed at a relatively low temperature, then bead removal cutting is performed, and again about 900 ° C. ~ 1100
There is a method of squeezing with a stretch reducer after heating to ℃.

[0003]

Generally, in a method for manufacturing a forged steel pipe, oxygen blow is carried out immediately before forging.
The oxygen blow has two purposes of removing the scale attached to the edge and heating the edge by the heat of oxidation and removing the scale generated at that time. However, the former adhered scale is a scale that is generated when the steel strip is heated and a scale that is adhered from others at that time, but it is very difficult to remove the adhered scale from the edge. Therefore, a problem arises in that the scale is caught in the forged butting portion during forging.

In order to solve this problem, there has been devised a method of heating the steel strip to a relatively low temperature to suppress the generation of scale and adding high frequency induction heating to the vicinity of the forged butting portion after heating. However, since this method uses high-frequency resistance welding, the heating width is wide, and swelling occurs during forge welding, that is, a bead is generated, and it is necessary to perform bead removal cutting after that, and the forged portion and other parts are Due to the difference in temperature, uneven thickness will occur when squeezing with a stretch reducer. So again about 900
It must be squeezed with a stretch reducer after heating to ℃ ~ 1100 ℃. Due to these new problems, efficiency and productivity are greatly impaired. The present invention solves the problems in the method for manufacturing a forged steel pipe as described above, and provides a method for manufacturing a forged steel pipe having excellent abutting portion quality.

[0005]

In order to achieve the above object, the present invention provides a method for producing a forged tube in which a steel strip having a predetermined width is heated and hot formed, and then forged while oxygen blowing. In the above, forging is performed so that the relationship between the bottom diameter DH of the forging roll placed immediately after oxygen blowing and the tube average outer diameter DT when passing through the forging roll is 0.5DT ≦ DH ≦ 0.7DT. This is a method for producing a forged steel pipe having excellent abutting portion quality.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail.
FIG. 1 shows a manufacturing process of the present invention. The method of the present invention is illustrated in FIG.
As shown in Fig. 5, a steel strip having a predetermined width is continuously inserted into a heating furnace, heated to about 1200 ° C to 1350 ° C, molded by a molding stand, and oxygen blown immediately before forging. It is the same. Then, as in the conventional method, it is forged by the forged roll as it is, but since the scale often remains in the forged abutting portion, the method of the present invention,
As shown in FIG. 3, the bottom diameter DH of the forging roll is changed by the average DT of the pipe when passing through the forging roll. That is, DH ≦ 0.7DT.

Here, the principle of forge welding will be described. FIG.
As shown in, after heating the skelp to about 1200 ° C to 1350 ° C, the skelp is molded by a molding stand, and then, for forge welding, a large amount of scale 2 is attached to the abutting edge surface of the skelp 1 immediately after the molding, You can't train as it is.
Therefore, oxygen blow 3 is performed immediately before forging. In oxygen blowing, first, the temperature of the abutting edge surface is raised to 1380 ° C. or higher by an oxidation exothermic reaction with steel, the scale 2 is melted, and further blown off by the blowing effect. This allows the abutting edge surface to be cleaned and forge welding to be possible.

In practice, however, as shown in FIG. 4, it is necessary to carry out oxygen blow 5 immediately before forging, but the edge surface is covered with the forging roll 6 and sufficient oxygen is applied to the forging contact 7 as described above. Since the blow cannot be performed and the effect of oxygen blow cannot be exhibited, the scale remains in the forged abutting portion, and the quality of the abutting portion is significantly deteriorated.

Therefore, as shown in FIG. 5, the diameter DH of the bottom of the forging roll is made small so that oxygen blowing can be sufficiently exerted. On the other hand, the forged roll is a very important roll for forming. If it is too small, it becomes impossible to form and edge buckling occurs between the forming roll and the forging roll. For this reason, 0.5DT ≦ D
It must be H. Also, from the effect of oxygen blow, D
It must be H ≦ 0.7DT. Here, DH is the bottom diameter of the forging roll, and DT is the average diameter of the pipe when passing through the forging roll. This is different from the actual pipe diameter because the stretch reducer reduces the pipe diameter thereafter.
Further, the reason why the average diameter is set is that the outer diameter in each direction needs to be averaged because it is not a perfect circle when passing through the forging roll. By making the forging roll as small as possible in this manner, oxygen blowing can sufficiently exert its effect, and a forged steel pipe having excellent abutting portion quality can be manufactured.

[0010]

EXAMPLE A method for manufacturing a forged welded steel pipe having a diameter of 42.7 xt 4.0 (mm), the conventional method and the method of the present invention,
Compared to Table 1. In the conventional method, the bottom diameter D of the forging roll is
Although H = DT, Table 1 shows the results in the case of this conventional method, the method of the present invention, and the case of forging under the conditions such as the case where the forged roll bottom diameter is small. According to the method of the present invention, there is almost no scale bite in the forged abutting portion, the flatness does not decrease, and excellent abutting portion quality can be secured.

[0011]

[Table 1]

[0012]

INDUSTRIAL APPLICABILITY Generally, in a method for manufacturing a forged steel pipe,
The adhesion scale before forging is the scale that occurs when heating the steel strip and the scale that adheres from others at that time.
In both cases, it is very difficult to remove the material attached to the edge. Therefore, a problem arises in that the scale is caught in the forged butting portion during forging. This problem cannot be solved by the conventional method, which causes the deterioration of the quality of the forged butting portion.

The present invention solves the problems in the method for manufacturing a forged steel pipe as described above, and provides a forged steel pipe having excellent abutting portion quality.

[Brief description of the drawings]

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

FIG. 2 is a diagram showing a manufacturing process of a conventional method.

3 (a) and 3 (b) are views for explaining the effect of oxygen blowing.

FIG. 4 is a diagram illustrating a situation of oxygen blow.

FIG. 5 is a view showing the shape of a forged roll.

[Explanation of symbols]

 1 Edge surface 2 Scale 3 Oxygen blow 4 Tube 5 Oxygen blow 6 Forge roll 7 Forge contact

Front page continuation (72) Inventor Shinya Sakamoto 1 Kimitsu, Kimitsu-shi, Chiba Nippon Steel Corp. Inside Kimitsu Steel Co., Ltd.

Claims (1)

[Claims] 1. In a method for producing a forged tube in which a steel strip having a predetermined width is heated and hot formed, and then forged while oxygen is blown, the bottom of the forging roll is formed into a tubular shape and placed immediately after oxygen blowing. Of the forged steel pipe with excellent abutting portion quality, which is characterized in that the relationship between the diameter DH of the pipe and the average outer diameter DT of the pipe after passing through the forging roll is 0.5DT ≦ DH ≦ 0.7DT. Production method.