JPH06304648A - High precision stretch reducer base tube and manufacture thereof - Google Patents

Abstract

PURPOSE:To specify a stretch reducer base tube for the purpose of preventing the cracks of a product due to flaws on the inner surface of a stretch reducer tube. CONSTITUTION:The rising angle of a metal flow is specified at 40 degrees or less, and ERW+ laser is taken as its manufacture. Consequently, by setting the rising angle of the metal flow at 40 degrees or less, the quantity for reducing thickness of the inner surface at the time of a stretch reducer is reduced to a large extent. Thus, notches and cracks are eliminated which are caused by the reduced thickness of the inner surface generated during a process such as forging to a product.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mother tube stretched by a stretch reducer and its manufacture. In particular, it relates to manufacturing when the mother tube is a welded tube.

[0002]

2. Description of the Related Art In recent years, in order to improve the production efficiency of steel pipes and to manufacture thick pipes, the pipes are often stretched by a stretch reducer. These stretch reducer mother tubes
ERW tubes are often used. FIG. 1 shows a schematic diagram of the welding process of an electric resistance welded pipe. This ERW mother pipe requires a large upset to discharge oxides and the like from the abutting part, and the strength of the surroundings is reduced by the welding heat, so the metal flow near the welding part rises ( (Fig. 2). The molten metal protruding to the surface after upsetting is smoothly removed from both the inner surface and the outer surface, but the metal shrinkage that occurs during the stretch reducer process due to this metal flow rising portion becomes a notch on the inner surface of the product pipe.

[0003]

In the stretch reducer pipe using the stretch reducer mother pipe according to the prior art, the shrinkage of the stretch reducer pipe that occurs in the vicinity of the welded portion of the mother pipe becomes an inner surface notch of the product pipe, resulting in product performance. Lower. Since it is used as a structural material, the cross-section is drawn by forging, etc., but at this time cracks originate from the inner surface notch (Fig. 3).

It is an object of the present invention to provide a stretch reducer mother tube and a method for manufacturing the same, which prevent the product from cracking due to an inner surface flaw of the stretch reducer tube.

[0005]

The gist of the present invention is as follows. (1) When the mother pipe stretched by the stretch reducer is a welded pipe, the rising angle of the metal flow at the welded portion is 40.
Stretch reducer mother tube characterized by sub-degree. (2) When the mother tube stretched by the stretch reducer is a welded tube, a high frequency heat source and a laser heat source are used together, (1) The method for producing a stretch reducer mother tube.

[0006]

According to the present invention, the rise of the metal flow is set to 40 degrees or less as described above. The rising angle θ of the metal flow is defined by the angle between the tube surface and the metal flow, as shown in FIG. It was found that when the rising angle of the metal flow is large, the deformation characteristic of the metal flow is different from that of the base material parallel to the peripheral surface of the pipe during circumferential compressive deformation at the time of stretch reducer, and this results in thinning. It was Therefore, the rising angle of the metal flow is reduced to 40 degrees or less to prevent the shrinkage of the meat during the stretch reducer. At the time of high-frequency heating, the rising of the metal flow causes the current to concentrate and heat at the corners of the plate end faces, so the amount of melting at the corners is greater than at the center of the plate thickness, and the unmelted end face is not flat and the plate thickness is high. This is caused by the convexity at the center (Fig. 4), and in order to prevent this, the amount of melting is made uniform in the plate thickness direction by a heat source other than high frequency (Fig. 5).
do it.

To reduce the rising angle of the metal flow,
This can be achieved by lowering the upset by using a high-frequency heat source and a laser heat source having a high energy density together when manufacturing the stretch reducer mother tube. This method can be used effectively not only with the cold stretch reducer but also with the hot stretch reducer because the metal flow band structure does not disappear during heating.

[0008]

EXAMPLES Next, examples of the present invention will be described. Table 1
Indicates an outer diameter of 89.1 mm and a plate thickness of 4.8 mm at a welding speed of 25 m / min.
When welding the pipes of and manufacturing the stretch reducer mother pipe,
High-frequency induction heating 300kVA Welding alone, the rising angle of the metal flow of the mother tube and carbon dioxide laser 1
The figure shows the metal flow rise angle of the mother tube when 0 kW is input and high-frequency heating is reduced to 200 kVA. As shown in Table 1, in the case of high frequency heating alone, the rising angle of the metal flow is as large as 64 degrees, whereas in the case of laser compound welding, the rising angle of the metal flow is 36 degrees and 40 degrees or less. FIG. 6 shows the relationship between the metal flow rising angle and the product meat shrinkage depth, including the case of only ordinary high frequency induction heating. It can be seen that when the rising angle of the metal flow is 40 degrees or less, the shrinkage of meat is sharply reduced.

[0009]

[Table 1]

[0010]

As described in detail above, by adopting the method of the present invention, it is possible to prevent the stretch reducer pipe from being thinned. As a result, the dimensional accuracy and processing limit of the product can be improved. In addition, when used for piping or the like, it is possible to reduce geometrical and organizational discontinuities and improve corrosion resistance.

[Brief description of drawings]

FIG. 1 is a schematic diagram of a welding process of an electric resistance welded pipe. The upset amount is defined by the difference in circumferential length before and after welding.

FIG. 2 is a diagram showing a state of metal flow in the vicinity of a welded portion and a definition of a rising angle of the metal flow.

FIG. 3 is a schematic view showing a shrinkage of a stretch reducer pipe and an inner notch of the pipe manufactured from the stretch reducer pipe having the shrinkage.

FIG. 4 is a schematic diagram showing a melting state of a plate end surface by high frequency heating.

FIG. 5 is a schematic diagram showing the uniformization of the melting state of the plate end surface by the combination of high-frequency heating and laser heating.

FIG. 6 is a graph showing the relationship between the rising angle of the metal flow and the shrinkage of the stretch reducer pipe.

Claims (2)

[Claims] 1. A stretch reducer mother pipe, wherein when the mother pipe stretched by the stretch reducer is a welded pipe, the rising angle of the metal flow at the welded portion is 40 degrees or less. 2. The method for producing a stretch reducer mother tube according to claim 1, wherein when the mother tube stretched by the stretch reducer is a welded tube, a high frequency heat source and a laser heat source are used together.