JP2003001423A - Method for producing welded joint - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a welded joint which has an excellent bead shape using a consumable electrode type gas-shieled arc welding method by which the falling of molten metal can be prevented in all position welding. SOLUTION: Welding is performed in such a manner that a steel wire containing 0.010 to 0.300 mass% rare earth elements and <=0.01 mass% O is used as a consumable electrode, an inert gas is used as a shielding gas, and weld heat input is controlled to 5.0 to 25.0 kJ/cm, so that the falling of molten metal can be prevented, a welded joint having an excellent bead shape can be produced, and high efficiency welding is made possible.

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 welded joint by a consumable electrode type gas shield arc welding method,
In particular, it relates to prevention of molten metal sagging and improvement of bead shape in lateral welding, vertical welding, and upward welding.

[0002]

2. Description of the Related Art A consumable electrode type gas shielded arc welding method is a method of welding metal by arc melting a consumable electrode (welding wire) continuously supplied and a material to be welded (base material) in a shield gas atmosphere. According to the shielding gas type, it is classified into MAG welding and MIG welding. MAG welding is arc welding using carbon dioxide (100% CO ₂ ), or an oxidative (active) gas such as carbon dioxide or a mixed gas of oxygen and argon, and it is possible to use an inexpensive gas. It is used in various welding construction fields such as shipbuilding, bridges, construction, storage tanks, piping, and penstock. on the other hand,
MIG welding is arc welding using an inert gas such as argon or helium, but from the viewpoint of arc stability, a mixture of a small amount of such an inert gas as carbon dioxide gas or oxygen gas is used. Often.

In the consumable electrode type gas shielded arc welding method using a shield gas in which an active gas such as carbon dioxide gas or oxygen gas is mixed, O is mixed in the molten metal from carbon dioxide gas or oxygen gas in the shield gas. However, there is a problem that the viscosity of the molten metal decreases. Therefore, when manufacturing a welded joint by the consumable electrode type gas shielded arc welding method that uses a shield gas mixed with an active gas such as carbon dioxide or oxygen gas, when welding in a position other than downward, such as sideways, vertical, or upward In addition, if the welding is performed under a welding condition of a large current and a high deposition rate, drooling of molten metal and defective bead shape frequently occur.

Therefore, by using the consumable electrode type gas shield arc welding method in which a shield gas mixed with an active gas such as carbon dioxide gas or oxygen gas is used, welding work including postures other than the downward posture (sideways, upright, upward) is performed. When performing, it had to be performed under the welding conditions of low current and low deposition rate. On the other hand, even in the consumable electrode type gas shield arc welding method (MAG welding) that uses active gas as the shield gas, by using the flux-cored wire as the welding wire, the slag layer having a lower melting point than the molten metal is outside the molten metal. Since the molten metal is formed on the substrate, it is possible to obtain a relatively good bead shape even under welding conditions of high current and high deposition rate. However, when performing laminated welding, slag removal work for removing slag between welding passes is required. The slag removing work between the passes may require a large number of man-hours, which becomes a factor to reduce the efficiency of the entire welding work.

Further, the consumable electrode type gas shielded arc welding method using a flux-cored wire is difficult to apply to welding using a narrow angle groove (narrow groove welding) from the viewpoint of slag removability, There is no choice but to use a wide angle groove. Welding using a wide angle groove requires a large amount of welding, which is disadvantageous from the viewpoint of welding efficiency.

On the other hand, in Japanese Unexamined Patent Publication No. 8-243783, C: 0.
15% by weight or less, Si: 0.3-1.10% by weight, Mn: 0.9-2.6
%, P: 0.030% by weight or less, S: 0.007 to 0.022% by weight, a balance of Fe and unavoidable impurities, and a shield gas arc welding wire having a diameter of 2.0 mm or less is proposed. The welding wire described in JP-A-8-243783 is inevitably applied to all-position welding, for example, in welding work such as circumferential welding of fixed pipes, the welding bead from the upward position to the upward position. It is said that a good bead shape can be obtained by avoiding sagging and uneven thickness.

[0007]

SUMMARY OF THE INVENTION
The welding wire described in Japanese Patent No. 8-243783 has a problem that the usable current range is as low as 125 to 150 A and cannot be applied to high efficiency welding using a high current. The present invention is
It was made in view of the problems of the conventional art as described above, and is suitable for use in consumable electrode type gas shielded arc welding, at least in sideways, upright, and in all the postures including one of the upwards, melting To propose a method for manufacturing a welded joint with an excellent bead shape using the consumable electrode gas shield arc method, which can prevent metal dripping, obtain a good bead shape, and enable high-efficiency welding work. With the goal. It should be noted that the term “all postures” as used in the present invention means a downward posture, a lateral posture, a vertical posture, and an upward posture.

[0008]

The inventors of the present invention have turned sideways,
In order to obtain a good weld bead shape in all-position welding including vertical and upward welding, it is necessary to keep the amount of O in the molten metal at a low level and keep the viscosity of the molten metal high in order to obtain a good weld bead shape. We considered that it is advantageous to use a shield gas that does not mix carbon dioxide gas (CO ₂ ) or oxygen gas (O ₂ ) in the gas and that contains only an inert gas. However, if CO ₂ or O ₂ is not mixed with the shielding gas, the oxide film that will become the cathode spot will not be formed on the surface of the molten metal, and the arc will become unstable, making welding practically impossible, or Was significantly reduced and the bead shape was deteriorated.

In order to solve such a problem, the inventors of the present invention have contained an appropriate amount of rare earth element and have an oxygen (O) content of not more than an appropriate value even if the shield gas is welded only with an inert gas. It was found that by using the reduced steel wire as a consumable electrode, it is possible to weld with a stable arc. Also, by using a steel wire containing an appropriate amount of rare earth elements and reducing the O content, and by using an inert gas as a shielding gas, it is possible to prevent O from being mixed into the molten metal and maintain the viscosity of the molten metal high. It was found that a welded joint having a good bead shape can be manufactured even if welding is performed including at least one of the lateral, vertical, and upward postures under high current and high welding speed conditions.

The present invention has been completed based on the above findings. That is, the gist of the present invention is as follows. (1) Steel wire containing 0.010 to 0.300% by mass of rare earth elements and 0.01% by mass or less of O as a consumable electrode when welding steel materials by using the consumable electrode gas shield arc welding method to manufacture a welded joint. A method for manufacturing a welded joint with an excellent bead shape, which comprises welding with an inert gas as a shield gas and a welding heat input of 5.0 to 25.0 kJ / cm. (2) In (1), the welding is performed in a horizontal direction, a vertical direction,
A method for manufacturing a welded joint excellent in bead shape, which is welding performed in a posture including at least one of the upward postures. (3) The method for manufacturing a welded joint according to (1) or (2), wherein the welding is circumferential welding.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The steel wire for welding used in the present invention is a steel wire containing 0.010 to 0.300 mass% of rare earth element (hereinafter referred to as REM) and 0.01 mass% or less of O. First, the reasons for limiting the composition of the steel wire for welding used in the present invention will be described. The mass% in the composition is simply expressed as%.

REM: 0.010 to 0.300% REM stabilizes the arc by forming a cathode spot on the surface of the molten metal when consumable electrode type gas shielded arc welding (MIG welding) is performed with the shield gas as an inert gas. Have an effect. If the REM content is less than 0.010%, the effect of stabilizing the arc cannot be obtained. On the other hand, if the content exceeds 0.300%, the inclusions in the weld metal increase and the weld metal properties deteriorate, and the risk of production defects such as steel ingot cracks and wire drawing defects during wire production increases. Therefore, in the present invention, REM is limited to the range of 0.010 to 0.300%. From the viewpoint of achieving a high level of both arc stability, welded joint characteristics, and manufacturing yield during wire manufacturing, REM is preferably in the range of 0.030 to 0.200%.

REM is Sc, Y or atomic number 57
It is a general term for elements (La) to atomic number 71 (Lu), and in the present invention, one or more of these elements can be used. From the viewpoint of easy availability, it is preferably La or Ce. When two or more elements are mixed and used, it goes without saying that the total content of REM is within the range of 0.010 to 0.300%.

O: 0.01% or less O reduces the viscosity of the molten metal, causes sagging of the molten metal and defective bead formation during upward, sideways, and vertical position welding, and reduces welding quality and welding efficiency. For this reason, it is preferable to reduce the O content in the molten metal as much as possible. However, when the shielding gas is an inert gas atmosphere, if the O content in the welding steel wire is 0.01% or less, melting A significant decrease in the viscosity of the metal is avoided. Therefore, in the present invention, the O content of the welding steel wire is
Limited to 0.01% or less. From the viewpoint of obtaining a good bead-shaped welded joint even under welding conditions of high current and high welding speed, 0.005% or less is preferable.
The O content is preferably 0.0005% or more from the viewpoint of reducing the economical load of reducing the O content during wire production.

In the steel wire used in the present invention, it is not necessary to specify the content of the constituent elements other than REM and O, and the content of the other constituent elements depends on the application (type of steel material to be welded). It may be determined accordingly. When the steel to be welded is ordinary steel such as mild steel or high-strength steel, the content of other constituent elements such as C, Si, Mn other than REM and O depends on the strength of the steel to be welded, for example, JIS YGW11 specified in Z3312
The range can be based on the composition of ~ YGW24.

For example, when the steel to be welded is mild steel or high strength steel, REM: 0.010 to 0.300%,
O: 0.01% or less, C: 0.15% or less, Si:
1.00% or less, Mn: 2.50% or less, P: 0.025% or less, S:
Contains 0.025% or less, or further contains one or more of Cu: 0.50% or less, Ni: 0.80% or less, Mo: 0.40% or less, Al: 0.05% or less, and the balance Fe and unavoidable impurities. The composition is preferably composed of

When the steel material to be welded is stainless steel, the content of other constituent elements such as C, Si, Mn other than REM and O depends on the type of steel material to be welded, for example JIS Z3321. Specified, Y308, Y309, Y310, Y312, Y316, Y317, Y321, Y34
The range can be based on the composition of 7, Y410, Y430, etc. For example, if the steel to be welded is martensitic stainless steel, REM: 0.010 to 0.30
0%, O: 0.01% or less, C: 0.15% or less, Si: 1.00% or less, Mn: 2.00% or less, Cr: 11.00 to 1
Composition containing 5.00%, P: 0.025% or less, S: 0.025% or less, or Ni: 8.00% or less, Mo: 4.00% or less, one or two kinds, and the balance Fe and inevitable impurities. It is preferable that

When the steel to be welded is ferritic stainless steel, rare earth elements: 0.010 to 0.300%, O: 0.0
Including 1% or less, C: 0.15% or less, Si: 3.00%
Below, Mn: 1.00% or less, Cr: 11.00 to 30.00, P: 0.02
5% or less, or Ni: 8.00% or less, Mo: 4.00%
It is preferable to have a composition containing one or two of the following and the balance Fe and unavoidable impurities.

When the steel to be welded is austenitic stainless steel, REM: 0.010 to 0.300%, O: 0.01% or less, C: 0.15% or less, Si: 1.00% or less,
Mn: 2.50% or less, Cr: 14.50 to 30.00%, Ni: 7.50 to 1
5.00%, P: 0.025% or less, S: 0.025% or less, or Mo: 4.00% or less, balance Fe
It is preferable that the composition be composed of unavoidable impurities.

In the method for manufacturing a welded joint according to the present invention, an inert gas is used as the shield gas, but Ar, He, or a mixed gas of Ar and He is preferably used as the inert gas. When a mixed gas of Ar and He is used, the mixing ratio is preferably Ar: 80 to 30% by volume, and the balance is He, from the viewpoint of ensuring the directivity of the arc and the penetration depth. . By using the shielding gas as described above,
O of the molten metal is suppressed to a low level, and the viscosity of the molten metal can be maintained high.

The polarity at the time of performing gas shielded arc welding is preferably reverse polarity with the welding wire, which is the consumable electrode, on the positive side. Performing reverse polarity gas shielded arc welding gives a stable arc from low current to high current,
This is because the penetration becomes deeper. Also, the welding heat input is 5.0k
Below J / cm, humping beads are generated, while 25.0
If the kJ / cm is exceeded, the bead drips in the upward posture or the vertical posture, so that the welding heat input is 5.0 to 25.0 in the present invention.
It was limited to the range of kJ / cm.

According to the method for manufacturing a welded joint of the present invention, carbon steel, ordinary steel such as high-strength steel, and various stainless steels can be preferably used as the steel material to be welded. In particular, various types of piping that require all-position welding,
Circumferential welding of steel pipes required for on-site welding of pipelines, hydraulic iron pipes, etc., for example, when welding steel pipes (steel materials) in the horizontal direction, vertical direction or inclined direction, and welding the ends together. is there.

According to the method for manufacturing a welded joint of the present invention, even if welding is performed in a welding position (all-position welding) including at least one of horizontal, vertical, and upward positions, a good bead shape and high welding are obtained. You can achieve speed.

[0024]

(Example) (Example 1) Martensitic stainless steel pipe having the composition shown in Table 1 (diameter: 178 mm φ, wall thickness: 12.7 m)
m) end faces were abutted against each other, and consumable electrode type gas shield arc welding was performed under the welding conditions shown in Table 3 using steel wires having the compositions shown in Table 2 to produce welded joints (steel pipe circumferential joints). The welding was circumferential welding with the steel pipe fixed in a vertical posture and in a horizontal posture. The groove shape was a groove whose bottom surface shown in FIG. 1 was R-processed.

As the shield gas, a mixed gas of Ar and He (inert gas) was used. As a shield gas, a mixed gas of Ar and He (inert gas) with a small amount (2% by volume) of carbon dioxide (CO ₂ ) was also used in the production of some welded joints. Under the welding conditions shown in Table 3, the welding current value and the accompanying welding speed were changed. Further, the welding speed was adjusted so that the number of laminated layers was 1 to 7. The welding heat input was 4.7 to 33.3 kJ / cm. A copper backing was attached to the inner surface of the pipe to form beads on the inner surface of the pipe.

Whether the obtained welded joint can be welded,
And the bead shape was evaluated. Whether or not welding was possible was judged to be impossible if the arc was not stable or if the molten metal dripped significantly and the welding operation could not be continued. As for the bead shape, the difference in height of the bead surface was measured with a caliper at each of the four layers in the welding length direction, and the average value was used.
The case where the height difference of the bead exceeded 3 mm due to the drop of the bead was judged as bad, and the case where it was 3 mm or less was judged as good. In addition, even when the difference in height of the beads did not exceed 3 mm, the case where the difference in the height of the beads fluctuated by 2 mm or more in the longitudinal direction of the welding was also regarded as defective. A method of measuring the height difference of the beads is schematically shown in FIG.

In any of the welded joints, the amount of slag produced was extremely small, and it was not necessary to perform slag peeling work in which a metal tool such as a chisel was hit. The results obtained are shown in Table 4.

[0028]

[Table 1]

[0029]

[Table 2]

[0030]

[Table 3]

[0031]

[Table 4]

In all of the examples of the present invention (welded joints No. 1 to No. 4), even if the welding is performed in the horizontal position, even if the high welding speed welding is performed at the high welding current of 150 to 300 A, the molten metal A welded joint having a good bead shape without sagging or the like is obtained. On the other hand, in Comparative Examples outside the scope of the present invention, welding is not possible, or even if welding is possible, problems such as sagging of molten metal and humping occur in welding work and bead shape.

In welded joint No. 5, the heat input for welding fell outside the range of the method of the present invention, and the bead shape became a humping bead, so that stable welding could not be performed. In the welded joint No. 6, the welding heat input was outside the range of the method of the present invention, the bead dripping was observed, and the bead shape was poor. Further, since the welded joint No. 7 was a mixed gas containing an active gas as a shield gas and was out of the range of the method of the present invention, stable droplet transfer could not be obtained, and welding work became impossible. Welded joint No.8
Since the composition (REM content) of the welding steel wire used was outside the range of the method of the present invention, stable cathode spots were not formed and welding became impossible. In the welded joint No. 9, the composition (O content) of the welding steel wire used was outside the range of the method of the present invention, so that dripping of the molten metal was observed and the bead shape was poor. (Example 2) A carbon steel pipe having a composition of API 5L X65 grade shown in Table 5 (diameter: 610 mm φ, wall thickness: 12.7 mm) was butted, and steel wires having the composition shown in Table 6 were used. Under the welding conditions shown in Table 7, consumable electrode type gas shield arc welding was performed to produce a welded joint (steel pipe circumferential joint). The welding was carried out by using a steel tube as a fixed tube fixed in a horizontal posture, and performing circumferential welding in a downward posture, a vertical posture, and an upward posture. The groove shape is V shown in FIG.
Shaped groove.

As the shield gas, a mixed gas of Ar and He (inert gas) was used as in Example 1.
For comparison, in some of the welded joints, Ar gas (inert gas) mixed with 20% by volume of carbon dioxide gas (CO ₂ ) was used as the shield gas. Under the welding conditions shown in Table 7, the welding current value and the accompanying welding speed were changed. As a stacking method, a downward sorting method was used. Also,
The welding heat input was 3.6-32.1 kJ / cm. A copper backing was attached to the inner surface of the pipe to form beads on the inner surface of the pipe.

The welded joints thus obtained were evaluated for weldability and bead shape in the same manner as in Example 1. The evaluation method was the same as in Example 1. The results obtained are shown in Table 8.

[0036]

[Table 5]

[0037]

[Table 6]

[0038]

[Table 7]

[0039]

[Table 8]

In all of the examples of the present invention (welded joints No. 21 to No. 23), even if the welding is performed in the upright position and the upright position, high welding speed welding with a high welding current of 150 to 250 A is performed. A welded joint having a good bead shape without dripping of molten metal has been obtained. In the example of the present invention,
The generation of slag between passes was extremely small, and welding was possible without slag peeling work. As described above, according to the present invention, it is possible to efficiently perform the circumferential welding in the downward posture, the vertical posture, and the upward posture.

On the other hand, in Comparative Examples outside the scope of the present invention, there is a problem in the welding work and the bead shape such that welding is not possible or even if welding is possible, molten metal sags and humping occurs. In welded joint No. 24, the heat input for welding fell outside the range of the method of the present invention, and the bead shape became a humping bead, so stable welding could not be performed. Welded joint N
Since o.25 was a mixed gas containing an active gas as a shield gas, which was out of the range of the method of the present invention, stable droplet transfer could not be obtained and welding work became impossible. Welded joint No.28
Since the composition (O content) of the welding steel wire used was outside the range of the method of the present invention, the sagging of the molten metal was observed and the bead shape was poor.

[0042]

As described above, according to the present invention,
In all postures such as upward posture, sideways posture, and vertical posture, molten metal can be prevented from dripping and bead with good shape can be formed.Furthermore, welding at high current and high welding speed can be performed, which contributes to higher efficiency of welding work. , It becomes possible to shorten the construction period of the welded structure, and it has a great effect on the industry.

The present invention is applicable to bridges, iron structures, storage tanks,
It can be widely applied to welding construction of all structures including vertical, upward and sideways welding such as penstock, and there is no particular limitation on the groove shape.

[Brief description of drawings]

FIG. 1 (a) shows a groove shape used in Examples,
(B) is a schematic diagram which shows the measurement position of a bead shape.

FIG. 2 is a cross-sectional view showing a groove shape used in Examples.

Front page continuation (51) Int.Cl. ⁷ Identification code FI theme code (reference) B23K 35/30 320 B23K 35/30 320A F term (reference) 4E001 AA03 BB08 BB09 CC03 DA02 DA03 DA04 DA06 EA02 EA05 4E081 AA13 BA27 BB04 CA08 CA09 CA10 DA19 DA20 DA21 DA23

Claims (3)

[Claims] 1. A steel material is welded using a consumable electrode type gas shielded arc welding method to produce a welded joint, wherein a consumable electrode contains 0.010 to 0.300% by mass of rare earth element and O.
Steel wire containing less than 0.01% by mass of inert gas as the shielding gas, and the welding heat input is 5.0 to 25.0 kJ / cm.
As a method of manufacturing a welded joint excellent in bead shape, which is characterized by welding. 2. The method for producing a welded joint excellent in bead shape according to claim 1, wherein the welding is welding performed in a posture including at least one of a horizontal posture, a vertical posture and an upward posture. . 3. The method for manufacturing a welded joint according to claim 1, wherein the welding is circumferential welding.