JPH0280180A - Manufacture of resistance welded steel tube excellent in workability - Google Patents

Abstract

PURPOSE:To obtain the title tube having a bead shape with little variance and stable inside bead shape and to prevent the generation of breaking and cracking by forming both edge ends into a cylindrical shape by a roll of forming line. CONSTITUTION:An increased wall part is formed on both edge ends with the cylindrical shape by the roll of a fin-pass line or the side roll of a breakdown line at the time of forming. By this method, the stable inside bead shape with uniform height can be formed and at the time of working, cracking is not generated and workability is improved.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention relates to a method of manufacturing an electric hI steel pipe obtained by curving a steel band material into a tubular shape and making the abutted portions contact by /8. The present invention relates to a method for manufacturing an electric resistance welded steel pipe with an excellent cross-sectional shape and workability by controlling the shape of an inner bead that occurs when welding both edge portions of a steel material.

(Prior art) TL electric resistance welded steel pipes are manufactured by forming them into a cylindrical shape using forming rolls, and joining the cylindrical steel strips by melting and joining the longitudinally opposing joint parts using a high-frequency heating device. These days, they are used in a wide range of applications because they are cheaper to manufacture than drawn tubes.

FIG. 11 is a diagram schematically showing a general manufacturing process of an electric resistance welded steel pipe. As shown in FIG. 11, the steel strip l wound into a roll sheet is continuously fed in the direction (B) at a constant feeding speed, and then the breakdown 2 and the fin bath 3 form each multistage forming train in the forming train section. Through the passage of rolls, the flat steel strip material is sequentially formed into a cylindrical shape, and finally becomes a tubular blank pipe 47.

When the tubular blank tube 4 passes through the high-frequency heating device 5, its electromagnetic induction action heats and melts both edge portions of the cylindrical circumferential side, which are opposite sides. The edges are abutted and absented by strong pressing pressure, causing the molten metal to protrude to the inner and outer surfaces, melting and joining, and solidifying in that state. The molten metal thus discharged onto the outer and inner surfaces of the welded pipe solidifies and becomes an excess metal called a bead. The outer bead of the electric resistance welding line on the outside of the tube is cut off by an outer bead cutting hide 7 provided behind it. The inner bead on the inside of the pipe is also removed as necessary, but it is technically difficult to economically cut out the inner bead in the narrow tube of a small diameter ERW steel pipe, so generally the inner bead is removed. Used with beads attached.

TL sewn steel pipe with internal bead, which is the method of the prior art described in 8.
When we cut the weld and look at the cross section of the weld, we find that the rising part of the inner bead forms an acute angle as shown in Figure 8, or the cross-sectional shape is open at the tip of the inner bead as shown in Figure 9. It is occurring.

As described above, when using an electric resistance welded steel pipe with an internal bead, adverse effects are often observed.

For example, if the shape of the inner bead is not constant,
As shown in the figure, when bending is performed so that the welded part is on the outside, undulations occur on the bent surface.

In addition, when severe processing such as flattening is applied as shown in Fig. 12, the sharp corner of the rising inner bead shown in Fig. 8,
If the tip of the inner bead in Figure 9 is open,
This location may become a notch and cause cracks to occur.

Furthermore, in the central part of the melt welding (as shown in FIGS. 6 and 7), components such as C, Si, and Mn are lower than in the peripheral part, and a low-strength part called a white layer is generated. If torsional stress is applied in the presence of this white layer, a shear conforming force is applied to the white layer region, causing weld fracture, which reduces the reliability of the weld.

As mentioned above, Den! -1 In order to improve and stabilize the quality of steel pipes, technology is being developed to control both the inner bead shape and the white layer.

Therefore, conventional methods for controlling the inner bead shape of ERW steel pipes include various cutting methods such as the edge scarf method and edge shaping method, in which both edges are cut before forming, and the The pipe manufacturing method involves forming thickened parts on both ends of the ERW pipe material plate using tapered rolls before forming, to prevent dimensional defects and concave grooves after the inner bead is removed. A method is disclosed.

(Problem B to be Solved by the Invention) The above-mentioned electric resistance welded steel pipe is particularly required to have satisfactory mechanical properties and excellent workability.

However, the above-mentioned conventional methods, such as the edge scarf method and the edge shaping method, have the disadvantage of shortening the life of the cutting jig, and are also problematic in terms of the workability of the equipment itself, stable production of ERW steel pipes, and operation. It is difficult to ensure good quality, and the technology is not necessarily fully satisfactory.

In addition, in the prior art method of forming thickened portions on both ends using tapered rolls before forming, the thickened portions are formed in a step before the forming step, and as a result, the thickened portions are formed in the next forming step. The thickened portion is likely to be thinned, and therefore it is difficult to control the thickened portion.

Furthermore, when thickening the edges in the pre-process of the molding machine, if the center of the material is shifted, it is difficult to correct it during molding, which causes problems such as variations in workability. There is.

An object of the present invention is to provide a method of manufacturing an electric resistance welded steel pipe that can solve the problems of the conventional manufacturing method described above.

(Means for Solving the Problems) The present invention provides countermeasures based on the knowledge that poor workability of ERW steel pipes caused by conventional manufacturing methods is mainly due to the occurrence of cracks due to the shape of the inner bead. When controlling the shape of the inner bead,
In order to prevent the rising part of the inner bead from becoming an acute angle and to prevent the tip of the inner bead from opening, a thickened part is formed during the forming stage of the edge shape of the artist and jig parts to control the welding heat build-up and the amount of absent. By doing so, it is possible to perform a manufacturing method with excellent workability.

That is, the method of manufacturing an electric resistance welded steel pipe with excellent workability of the present invention is as follows:
Electric resistance welded steel pipes are manufactured by sending a steel strip in one direction, forming it into a cylindrical shape, and melting and joining both edges of the cylindrical steel strip that face each other in the longitudinal direction using high-frequency heating. In this method, the ends of the cylindrical edge portions are formed by rolls on a forming line, and the rolls on the forming line form the ends of the fin pass line on the rear side or the sides of the breakdown line on the front side. The roll is characterized by forming the ends of both cylindrical edge portions.

(Function) According to the method of the present invention, a thickened part is formed at the end of the cylindrical groove part by the roll of the fin pass line or the side roll of the breakdown line during molding, so that the height is uniform and the thickness is increased. A stable inner bead shape can be formed, and cracks do not occur during processing, resulting in excellent workability.

As shown in Fig. 11, in each of the multi-stage forming J-rules of the forming line, it is preferable that the thickening part be formed by the roll in the previous stage in the roll of the fin pass line, and in the breakdown line, If the thickened portion is formed using the front side roll that is easy to apply, the forming effect can be significantly improved.

(Example) Hereinafter, an example of the method for manufacturing an electric resistance welded steel pipe with excellent workability according to the present invention will be described with reference to FIGS. 1 to 10.

FIG. 1 is a diagram showing the relationship between the degree of reduction in which the ends of both edge portions are thickened by the roll of a fin pass line in the method of the present invention and the rate of thickness increase in the edge due to reduction.

As shown in Figure 1, the forming effect is greater when the thickness is increased by strong reduction, and the strong reduction by the front roll (Fl roll) with a large fin angle increases the thickness at the ends of both edges. It shows that it is promoted.

FIG. 2 is a diagram showing the relationship between coil width and thickness increase rate. As shown in the figure, even if the rolling reduction amount is at a normal level, the effect of increasing the thickness can be recognized when a material coil having a plate width larger than the standard is used.

Figure 3 is a diagram showing the effect of increasing the thickness of the ends of both edge portions using the side rolls of the breakdown line, which is one of the methods of the present invention.It can be improved by making the gap between the side rolls smaller than the standard. That will happen.

Table 1 shows the welding conditions of the present invention and the conventional method in which the same material was made into a pipe with a pipe diameter of 22.2 ffill and a wall thickness of 2.6 mm. 1
The metal flow in the cross section of the welded part in the method of the present invention when welded under the welding conditions shown in the table is shown.

6 and 7 are metallographic diagrams showing the metal flow in the cross section of the welded part obtained by the conventional method welded under the welding conditions shown in Table 1, and as is clear from the comparison between the two figures, It can be seen that the cross-sectional shape of the method according to the invention is significantly improved.

In the 10th session, pipe diameter: 22.2 m using the present invention method and conventional method.
FIG. 2 is a diagram showing the results of a torsion fatigue test on a pipe having a size of 2.6+n+s. As shown in No. 10 [Z], in the conventional method, fracture occurred from the bead part after 20,000 times or less, which is the limit number of times for the shear fatigue test, but as in the method of the present invention, the shape of the inner bead can be controlled. In the case of ff1l, no breakage due to internal beats was observed.

Table 1 Results of welding conditions (effects of the invention) As described above, according to the method of manufacturing an ERW steel pipe of the present invention,
Since the thickened part is formed during the forming process, it is possible to achieve a stable inner bead shape with less variation in bead shape, which eliminates breakage and cracking caused by poor inner bead shape, which was a problem with conventional technology. This is an improvement.

As a result, the reliability of the welded part is high, and it is excellent in that it is possible to stably manufacture electric tubes with a processing time of 1 F.

[Brief explanation of the drawing]

Figure 1 is a diagram showing the relationship between the rolling reduction I and the thickness increase rate of the fin pass line roll according to the method of the present invention, Figure 2 is a diagram showing the relationship between the coil width and the thickness increase rate, and Figure 3 is a diagram showing the relationship between the thickness increase rate and the roll width of the fin pass line roll according to the method of the present invention. Diagram showing the effect of thickening molding with downline sight roll,
Fig. 4 is a diagram showing the situation during forming according to the present invention, Fig. 5 is a metallographic diagram showing the meckle flow of the welded part in ERW steel/blue according to the present invention, and Figs. 6 and 7 are welded parts according to the conventional method. Metal Mi weave diagram showing metal flow, Figures 8 and 9 are diagrams showing the inner bead shape of the conventional method, Figure 10 is a diagram showing the results of the shear fatigue test, and Figure 11 is a typical diagram of ERW steel pipes. Figure 12 is a diagram showing an example of flattening process.
Figure 3 shows the situation of the bending test. 1. . . 1m material, 2. . . Breakdown, 3.
Fin bath, 4... Tubular raw tube, 5... High frequency heating device, 6... Squeeze roll, 7 External bead cutting hide, 8... Uncoiler - 1D radius. ERW steel pipe, 1] Pipe diameter, R...curve

Claims (2)

[Claims] (1) By feeding the steel strip in one direction, forming it into a cylindrical shape, and melting and joining both edges of the cylindrical steel strip that face each other in the longitudinal direction using high-frequency heating, A method for manufacturing an electric resistance welded steel pipe with excellent workability, characterized in that the ends of both cylindrical edge portions are formed by rolls on a forming line. (2) A patent claim characterized in that the rolls of the forming line are rolls of the fin pass line on the rear stage side or side rolls of the breakdown line on the front stage side, and form the ends of both cylindrical edge portions. A method for manufacturing an electric resistance welded steel pipe with excellent workability according to item 1.