JPH01237080A - Manufacture of resistance welded steel tube - Google Patents

Abstract

PURPOSE:To obtain the title resistance welded steel tube having a seam part with few weld defects by manufacturing the tube while adding flux to both side edges in the course getting to squeeze rolls from the feeding position of a tube stock formed by bending a steel strip. CONSTITUTION:The streel strip fed continuously is bent so that both side edges Sa and Sb in its width direction are opposed mutually and formed to the tube stock. A nozzle 4 to add the flux to both side edges Sa and Sb in the course up to a V convergent point, O1 from a feeding part 1 is then arranged and the flux is supplied by the prescribed quantity from a flux adding device 5.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a method of manufacturing a T4 sewn steel pipe, and particularly to a manufacturing method suitable for preventing the occurrence of weld defects during electric resistance welding.

<Conventional technology> General use of ERW steel pipes! ! 8! In the I5a process, as schematically shown in FIG. 3, the steel strip S, which has been curved into a C-shaped cross section by forming rolls (not shown) with opposite side edges, is formed into a work coil or a contact, for example. After passing through the power supply position of the chip etc., its both side edges S a , S b
is fed into the squeeze roll 2 while being heated, and side pressure is applied in the squeeze roll 2 to form a so-called V shape, and both side edges Sa and S are in a molten state.
The steel pipes P are manufactured by abutting and contacting each other.

Immediately before reaching the center position 0□ of the squeeze roll 2 from the power supply part 1, a welding current of 10 is applied toward the intersection position of the ■shape, that is, ■convergence point 0, where both side edges Sa and Sb contact each other.
However, due to the skin effect and proximity effect, one side edge S
While flowing from a to the dotted line path and reaching the other side edge sb, this welding current 10 causes the both side edges Sa
, Sb are heated and melted and butt welded.

<Problems to be Solved by the Invention> However, if the above manufacturing method is used to produce materials with high surface tension and viscosity, such as steel and stainless steel, for example When butt welding steel types that are susceptible to Sa 8 steel, the molten steel generated on the side edges is difficult to be pushed out, and as shown in an enlarged view in Fig. 4, the molten steel 3 aggregates and forms on both side edges Sa. , Sb is short-circuited, and as shown by the dotted line path, most of the welding part tXio is shunted, and sufficient heat is not given to the V convergence point OI, which is the true welding point, resulting in a so-called cold welding defect. This causes welding defects.

Further, the molten steel 3 short-circuited between the side edge portions Sa and Sb is sparked and fused by this shunt current, causing spatter to occur.

Furthermore, since molten steel is difficult to be pushed out during butt welding, oxidized molten steel is removed! 1il (oxide) remains in the weld and causes so-called Venetrator defects.

In order to improve this problem, by increasing the angle of the V-shape formed by both side edges Sa and Sb from the power supply part 1 to the V convergence point OI, short circuits at both side edges of molten steel are avoided. In some cases, measures have been taken to reduce the phenomenon, but although these methods have some effect, they are not sufficient countermeasures.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a welding method for electric resistance welded steel pipes suitable for preventing welding defects and spatter caused by molten steel.

Ku! ! Means for Solving Problem I> The present inventor has found that for steel types such as stainless steel, where the surface tension and viscosity of molten steel are large, it is effective to add a flux with a low basicity to the heated part of the shape. The present invention was completed based on this finding.

That is, in the present invention, a continuously fed steel strip is formed into a blank pipe by curving the steel strip so that both edges in the width direction face each other, and then a welding current is applied to the both edges. A method for manufacturing an electric resistance welded steel pipe in which the pipe is butt welded while being heated and melted, characterized by forming the pipe while adding flux to the both side edges from the power supply position to the squeeze roll. This is a method for manufacturing ERW steel pipes.

The specific configuration of the present invention will be explained below with reference to the drawings.

FIG. 1 is a plan view schematically showing an embodiment of the method of the present invention. In FIG. 6, the same members as those in the conventional example are given the same reference numerals and explanations are omitted.

As shown in the figure, a nozzle 4 for adding flux to both side edges Sa and Sb is arranged between the power feeding position and the V convergence point o1, and the flux is supplied from a flux adding device 5.

The material of this nozzle 4 is preferably heat resistant enough to withstand the high temperature of the molten steel 3 and has insulating properties, such as ceramics.

Such a device is configured to add a predetermined amount of flux to both side edges Sa and Sb of the shaver during electric resistance welding.

Note that if the flux added to both side edges Sa and Sb of the shape is left as is, it will scatter and accumulate around the squeeze roll 2, which is unfavorable in terms of environmental hygiene, and it will also get caught in the squeeze roll 2. It is desirable to provide a flux removal device since this may cause dents in the steel pipe P.

<For production> The operation of the present invention will be explained below.

Generally, basicity of flux (hereinafter simply referred to as B).

) is expressed by the following formula (1).

B L -6,31N 5iJ-4,97N Ti1t
-0,2N/UtOs + 4.8 NMn0+4.
0 NMgO+6.05(NCaO+NCaFz)・-
・−・・−・−・−・−・・・・−・・・・−・・
・・・－・・・・・・・・・・・・－・・・(1) Here, N: molar fraction The present inventor conducted the following research in order to investigate the relationship between B of flux and welding defect incidence rate. We conducted an experiment.

Using a flux with a BL of -0.8 to 5.0, apply approximately 500 g/sin of flux to one part of the shoe during electric resistance welding.
Add each layer to a plate thickness of 3I! 11 5jlS304 belts were butt welded at a tube making speed of 30 m/m111. The relationship between the B value of the flux and the incidence of welding defects at that time is shown in FIG. Here, the welding defect occurrence rate is the number of welding defects occurring as a percentage of the number of pipes produced.

As can be seen from the figure, when the BL value exceeds 2.0, a short circuit phenomenon occurs on both side edges of the molten steel and welding defects are likely to occur.This is because the viscosity 9 surface tension of the molten steel of 5OS304 is large. This is thought to be due to agglomeration of molten steel, indicating that the addition of flux has no effect. Also, the BL value is -
The welding defect occurrence rate in the range of 0.5 to 2.0 is 0.1% or less, and no short circuit phenomenon occurs at both side edges. This is considered to be because the addition of flux lowered the viscous 2 surface tension of the molten steel. Furthermore, B, the value is -
If it is less than 0.5, the oxygen concentration in the weld metal part becomes high, the material quality of the weld seam part deteriorates, and the weld defect occurrence rate increases.

Therefore, in order to prevent welding defects from occurring and to prevent deterioration of the material of the weld seam, it is necessary to set BL (+ff to −0,
It needs to be within the range of 5 to 2.0.

Table 1 shows an example of a suitable representative composition of the flux to be added that satisfies the above appropriate range.

Table 1 (% by weight) Next, the appropriate addition tX (g) of flux may be given by the following equation (2).

X-f Ca, t, EF, IP, V, θ) ---
(2) Here, α: Coefficient L determined by steel type: Plate thickness (ff11) EP Nibrate voltage (V) ■? ; Plate current (A) V ; Pipe forming speed (m/min) θ : ■Shape angle (@) The guideline for flux addition fiX is: The amount should be approximately 175% of the melted weight of Sb. For example, 5OS304
When welding a 3 m thick steel plate at a speed of 30 m/win, the amount of flux added is preferably about 500 g/sin.

Although solid flux is effective, it is preferable to use molten flux because it has the effect of accelerating the reaction rate with molten steel. .

Also, as the pipe-making speed increases, the reaction time between flux and molten steel becomes shorter (which tends to reduce the effect of flux addition. Therefore, the pipe-making speed is 100 m/win).
It is preferable to do the following.

<Example> Examples of the present invention will be described below.

Using the flux of the components shown in Table 1 above, 5llS
Electric resistance welded steel pipes were manufactured using two steel types, 304 and 5US410, in two sizes shown in Table 2. Note that the BL value of the flux used here was -0,2.

For comparison, a conventional method without using flux was also used to form pipes. The status of the welding defect occurrence rate due to these
It is also shown in the table.

As is clear from this table, welding defects such as penetrators and cold welding defects occurred frequently in the conventional method, but
Table 1: According to the method of the present invention, electric resistance welded steel pipes with almost no welding defects (and having sound seams) were produced for all steel types, 5US304.5US410.

<Effects of the Invention> As explained above, according to the present invention, ■Flux is added to both side edges of the shape, so it is possible to extremely produce an electric resistance welded steel pipe having a healthy beam part with few welding defects. It is possible to manufacture stably.

[Brief explanation of the drawing]

Figure 1 is a plan view schematically showing an example of the method of the present invention, Figure 2 is a characteristic diagram showing the relationship between flux basicity and welding defect incidence rate, and Figure 3 is a schematic diagram of a conventional example. FIG. 4 is a plan view showing an enlarged main part. ■...Power supply part, 2...Squeeze roll. 3...78 steel, 4...nozzle. 5...Flux addition device. S...Steel plate, P...Steel pipe (ERW steel pipe)
. Sa, Sb... side edge, io... welding current. Patent applicant: Kawasaki Steel Corporation Figure 1 Figure 2 Basicity of flux (at)

Claims (1)

[Claims] The continuously fed steel strip is curved so that both edges in the width direction face each other and formed into a blank tube, and then a welding current is applied to both edges to heat and melt them while abutting them. A method for manufacturing an electric resistance welded steel pipe to be welded, characterized in that the pipe is formed while adding flux to both side edges from a power supply position to a squeeze roll.