JP2006175514A - Electric resistance welded tube having reduced defect in weld zone and its production method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electric resistance welded tube having reduced defects in the weld zone, and to provide its production method. <P>SOLUTION: A steel strip mainly comprising iron and an ordinary alloy elements used for a steel material with inevitable impurities is subjected to electric resistance welding under the welding condition where the thickness of an oxide film in the edge faces of the steel sheet to form into a welding face in the range from a welding point to 15 mm before the welding point reaches ≤40 nm expressed in terms of SiO<SB>2</SB>, the thickness of the oxide film is obtained by a fluorescent X-ray spectroscopy measuring method, and the concentration of oxygen in an atmosphere at the time of the welding is controlled to ≤60 ppm. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an electric resistance welded pipe and a method for manufacturing the same, and more particularly to a pipe with few weld defects.

  Steel pipes are used for various purposes such as pipelines, machine structural members, heat exchangers, automotive parts, and various plants. Seamless steel pipes and welds manufactured by various methods according to their use or size. Steel pipe is used.

  Among them, a steel strip is continuously formed into a tubular shape to form a tubular body (open pipe), and both opposing edge portions are heated by high-frequency heating or resistance heating and welded to be electroformed. Steel pipes have a high dimensional accuracy, can be manufactured more efficiently than other manufacturing methods, and have been manufactured and used in large quantities since they are relatively inexpensive.

  However, when using ERW pipes in fields where high material properties and high reliability are required, there are many oxide inclusions in the weld and cause cracking. Become.

  The reason why there are more oxide inclusions in the welded parts of ERW steel pipes compared to other welded steel pipes is that ERW welding is an intermediate welding method between fusion welding such as arc welding and pressure welding. This is because a clear molten pool is not formed in the portion, and a considerable amount of oxide formed by oxidation during welding is difficult to be removed from the inside of the steel.

  A weld with a high oxygen content deteriorates mechanical properties and causes cracking. For this reason, various methods, such as shielding the weld with a non-oxidizing gas and performing electric resistance welding, upsetting the steel strip to a tubular body during welding, and discharging inclusions as much as possible to the outside It has been proposed to reduce the oxygen content of the weld.

  Patent Document 1 discloses a method in which the joint end is shielded with a non-oxidizing gas and electro-welding welding is performed, the upset amount is regulated with respect to the welded pipe wall thickness, and the oxygen amount and inclusions in the welded portion are reduced. It is disclosed.

  Nitrogen and argon are used as a non-oxidizing atmosphere, and a seal box is provided to keep the welded portion non-oxidizing to suppress the formation of oxides. Further, poor bonding and non-metallic inclusions appear on the surface of the welded portion. It is characterized in that upset is performed so as to prevent cracking of inclusions in the welded portion.

  In Patent Document 2, the oxygen content of the welded portion is set to 200 ppm or less, but the edge portion with which the tubular body is attached is preheated within a specific temperature range, irradiated with a laser beam, and welded after melting. In addition, the oxide occupying most of the oxygen content of the steel is discharged to the outside of the steel pipe.

Patent Document 3 shields the weld with a non-oxidizing gas such as nitrogen or argon, irradiates the welded part during high-frequency heating with a laser beam or a plasma arc, and raises the pressure-contacted part to a higher temperature. It is characterized by facilitating discharge and effectively preventing welding defects.
JP 63-241116 A JP-A-9-194998 JP-A-5-23867

  However, the method of shielding the weld with a non-oxidizing gas does not clearly show the relationship between the shielding situation and the effect of preventing the formation of oxides, and the weld is heated with a laser beam or the like to discharge oxides by upset. Even if it is easy, inclusions are not completely eliminated, and a considerable amount of inclusions remain, increasing the amount of oxygen in the steel. Therefore, the mechanical properties such as strength and toughness of the welded part are the base material. The ERW welded steel pipe, which is inferior to the parts, has been considered impossible to manufacture in the past, and this has been a major cause of limited applications.

  Therefore, the present invention clarifies a quantitative guideline indicating a shield state where a sound weld is obtained, and the mechanical properties such as the weld and the strength and toughness are not inferior to those of the base material, and the application is limited. An object of the present invention is to provide an electric resistance welded steel pipe and a manufacturing method thereof.

As for the cause of the mechanical properties of ERW welds being inferior to that of the base metal part, the present inventors pointed out the oxygen content of the weld, the amount of inclusions, the heat history of the weld, and the metal flow in the vicinity of the weld. From these researches, we found that the effects of oxygen and inclusions in one weld were particularly significant, and repeated research. The present invention has been made based on further findings based on the obtained knowledge.
1. An electric resistance welded steel pipe having few weld defects, wherein the oxide film on the edge surface of the steel sheet, which is a weld surface in the range from the weld point to 15 mm before the weld point, is manufactured under welding conditions in which the SiO ₂ equivalent is 40 nm or less. Production method.
2. 2. The method for producing an electric-welded steel pipe with few weld defects, wherein the thickness of the oxide film is determined by a fluorescent X-ray analysis measurement method.
3. 3. The method for manufacturing an electric resistance welded steel pipe according to 1 or 2, wherein the welding condition is adjusted by adjusting the oxygen concentration in the atmosphere during welding to 60 ppm or less.

  According to the present invention, the amount of oxygen in the welded portion is greatly reduced, the number of defects consisting of oxide inclusions is small, and the electric resistance welded steel pipe provided with a welded portion having mechanical properties comparable to the base metal portion. Is very useful in industry.

In the present invention, when electro-welding welding is performed, the oxide film thickness on the edge surface of the steel sheet, which is a weld surface ranging from the welding point to 15 mm before the welding point, is 40 nm in terms of SiO ₂ in fluorescent X-ray analysis measurement (FX measurement). The welding is performed under the following welding conditions.

  FIG. 1 is a schematic explanatory view showing an example of a pipe making facility for carrying out the present invention. In the figure, 1 is a tubular body that is electro-welded and becomes an electric-welded steel pipe, 2 is a shield device, 3 is a work coil, and 4 is a squeeze. The roll 5 is an edge portion of the tubular body 1, and a is a welding point formed by the edge portion 5 of the tubular body 1 striking first.

  In the illustrated pipe making equipment, a steel strip is formed into a tubular body 1 by a multi-stage roll (not shown), and a portion where the edge portion 5 of the tubular body 1 is abutted in the shield device 2 is heated and melted by a work coil 3. Thereafter, the squeeze roll 4 is used for upsetting to produce an ERW steel pipe.

In the present invention, the edge surface of the steel sheet that becomes the weld surface in the range from the welding point a when the tubular body 1 is heated and melted by the work coil 3 in the shield device 2 to the front side 15 mm where the welding point a is formed. The oxide film thickness is defined as 40 nm or less in terms of SiO ₂ by FX measurement.

  The thickness of the oxide film is measured when the edge portion 5 of the tubular body 1 is abutted and heated and melted, and the edge portion 5 is 15 mm in length from the weld point a of the tubular body 1 that is stopped to the front side of the weld point a. A test piece for measuring the cut oxide film thickness is measured, and the edge surface of the edge portion 5 is measured for the entire length of the test piece by measuring the oxide film with a fluorescent X-ray analysis measuring device (FX device).

  FIG. 2 shows a schematic diagram of the FX apparatus. X-rays applied to the sample 12 from the X-ray source 11 generate fluorescent X-rays from the sample 12. The spectroscopic crystal 13 separates the fluorescent X-rays, and the sample 14 is identified by the detector 14.

The measurement conditions are tube voltage 30 kV, tube current 100 mA, beam diameter 1 mmΦ, and the intensity of repeated measurements of oxygen Kα rays 20 times with an integration time of 10 sec, converted to SiO ₂ film thickness using SiO ₂ (96 nm) / Si as a standard sample. However, it is not specified in the present invention.

  The length of the edge portion 5 for measuring the thickness of the oxide film is within 15 mm before the welding point a from the welding point a where the thickness of the oxide film changes depending on the shielding conditions. The thickness of the oxide film within the above range is The maximum thickness is 40 nm or less, which is observed in the case of manufacturing conditions where a good weld is obtained.

  3 and 4 are diagrams showing the relationship between the thickness of the oxide film on the edge surface of the edge portion 5 and the distance from the welding point a. FIG. 3 shows a large amount of oxide inclusions observed in the weld after welding. FIG. 4 shows the results of a test piece collected by stopping the tubular body being manufactured under the same conditions as those described above, and FIG. 4 is being manufactured using the same conditions as the welding conditions under which a good weld was obtained. The result performed about the test piece extract | collected from this tubular body is shown.

From FIG. 3, in the case of welding conditions in which a large amount of oxide inclusions are observed in the welded portion, the oxide film thickness rapidly increases within 15 mm from the weld point, and the oxide film thickness is 10 mm before the weld point (in terms of SiO ₂ ). The thickest part of is measured.

Moreover, in the case of the welding conditions in which a better weld is obtained than in FIG. 4, the oxide film thickness (in terms of SiO ₂ ) is 40 nm or less even at 10 mm before the welding point.

The oxygen concentration in the atmosphere is 78 ppm or more under the welding conditions for obtaining the weld of FIG. 3, the oxygen concentration in the atmosphere is 60 ppm or less for the welding conditions for obtaining the weld of FIG. 4, and the number of oxide inclusions in the weld is The number of welds shown in FIG. 3 was 10 or more, and the number of welds shown in FIG. 4 was less than 10. The number of oxide inclusions was measured for the welded part immediately before being stopped, and the number of oxide inclusions having a particle size of 3 μm or more in an observation area of 4 mm ² was used.

The welding conditions for the ERW steel pipe according to the present invention were determined in advance, and the oxidation at the edge surface of the steel sheet, which is a welded surface in the range from the welding point to 15 mm before the welding point by stopping the tubular body being manufactured. In the FX measurement, the film thickness is set to a condition of 40 nm or less in terms of SiO ₂ , and the oxygen concentration in the atmosphere is preferably 60 ppm or less from the results described above.

  In the present invention, the material of the ERW steel pipe may be steel as long as the chemical composition is not specified. The present invention can be applied to an ERW pipe made of steel mainly composed of ordinary alloy elements and unavoidable impurities used for iron and steel materials.

  The effects of the present invention will be described in detail with reference to examples. Using steel strips of various compositions as test materials, ERW steel pipes were manufactured using the manufacturing apparatus shown in FIG. The ERW steel pipe was stopped during production, and a 15 mm portion before the welding point was cut out from the welding point, and the thickness of the oxide film on the edge surface was measured. The number of oxides was measured for the welded part immediately before it was stopped. All measurements were performed under the conditions described above.

The manufacturing conditions were selected such that the thickness of the oxide film on the edge surface of the steel sheet, which is the weld surface in the range from the weld point to 15 mm before the weld point, was obtained in terms of SiO ₂ and had various thicknesses. Table 1 shows the component composition of the test material, and Table 2 shows the production conditions, oxide film, and oxide inclusions.

Specimen No. Nos. 1 to 8 are all Si-Mn steels. 1-4 are examples of the present invention in which the oxide film thickness on the edge surface 15 mm before the welding point from the welding point is 40 nm or less in terms of SiO ₂ , and the number of oxide inclusions in the welded portion is 10 or less, which is sound welding. Part was obtained.

On the other hand, no. 5 to 8 are comparative examples having an oxide film thickness of 120 nm or more in terms of SiO ₂ , and the number of oxide inclusions in the welded portion was 10 or more.

  The oxygen concentration in the present invention example was 60 ppm or less, and the oxygen concentration in the comparative example was 78 ppm or more.

The figure which shows an example of the manufacturing apparatus of an electric resistance steel pipe. The figure explaining the measuring method by a FX apparatus. The figure which shows the relationship between the thickness from the thickness (the oxygen concentration of 78 ppm or more) of an oxide film in an edge part, and a welding point. The figure which shows the relationship between the thickness from the oxide film thickness (oxygen concentration of 60 ppm or less) in an edge part, and a welding point.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Tubular body 2 Shielding device 3 Work coil 4 Squeeze roll 5 Edge part a Welding point 11 X-ray source 12 Sample 13 Spectroscopic crystal 14 Detector

Claims (3)

An electric resistance welded steel pipe having few weld defects, wherein the oxide film on the edge surface of the steel sheet, which is a weld surface in the range from the weld point to 15 mm before the weld point, is manufactured under welding conditions in which the SiO ₂ equivalent is 40 nm or less. Production method.   2. The method for producing an electric-welded steel pipe with few weld defects according to claim 1, wherein the thickness of the oxide film is determined by a fluorescent X-ray analysis measurement method. 3. The method for producing an electric resistance welded steel pipe according to claim 1, wherein an oxygen concentration in an atmosphere during welding is 60 ppm or less as an adjustment method of the welding conditions.

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