JPH08238572A - Narrow gap tig welding method of 9% ni steel to be welded - Google Patents

Abstract

PURPOSE: To improve efficiency by using narrow gap so as to execute TIG welding of Ni steel to be welded without generating lack of fusion and defect of bead shape. CONSTITUTION: 9% Ni steel material to be welded having narrow gap of <=30 deg. groove angle is subjected to TIG arc welding by using a filler wire for welding having a chemical composition of the base Ni, <=0.005wt.% S and the shield gas for arc environment which is the gaseous mixture of Ar gas and He gas having 25-95% He gas mixing ratio.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a TIG arc welding method applied to welding construction of a large structure made of 9% Ni steel such as LNG (liquefied natural gas) tank, and 9% Ni having a narrow groove. The present invention relates to a narrow groove TIG arc welding method for a welded material made of 9% Ni steel, which enables welding of a welded material made of steel without causing fusion failure.

[0002]

2. Description of the Related Art Recently, TIG arc welding using an automatic welding device is often used for welding a material to be welded made of 9% Ni steel when assembling an LNG tank made of 9% Ni steel. The chemical content is Ni-based and the S content is 0.00 to improve crack resistance.
A filler wire for welding of 5% by weight or less is used, Ar gas is used as a shield gas in an arc atmosphere, and a V-shaped groove whose groove angle exceeds 30 ° (in the case of welding from both sides, an X-shaped groove) Then, TIG arc welding is performed. In TIG arc welding in the assembly of large-scale structures such as 9% Ni steel LNG tank, the mechanical properties and crack resistance of the TIG arc weld metal are excellent, and the bead appearance is good, so welding There is an advantage that it is not necessary to grind and perform bead shaping later. On the other hand, however, compared to other welding methods such as submerged arc welding, the penetration of the base metal is shallow, so welding defects such as poor fusion may occur, and the welding amount cannot be increased so much that the efficiency is high. It was bad. On the other hand, as LNG tanks become larger and the applicable plate thickness tends to increase,
The demand for improved efficiency is increasing.

Therefore, U type (double U in the case of double-sided welding)
Shape) or V-shape, it is desired to improve the efficiency by narrowing the groove angle of the groove and decreasing the groove cross-sectional area. When attempting to perform TIG arc welding on a material to be welded made of steel, fusion defects are likely to occur and it is difficult to narrow the groove for the reason described below.

That is, as a filler wire for welding 9% Ni steel, a Ni-based filler wire such as a Hastelloy alloy or an Inconel alloy is usually used. Such a Ni-based filler wire for welding has a low melting point (usually about 1300 ° C., and an Fe-based filler wire of 1500).
C., about 1400 ° C. even for austenitic stainless steel), and the molten metal easily drips in a horizontal welding position. Further, the bead is not well compatible with the 9% Ni steel and the filler wire for welding based on Ni. Therefore, particularly in the lateral welding posture, the groove angle is set to 3 as shown in FIG.
When the angle was 0 ° or less, poor fusion occurred in the lower groove wall portion. Further, in order to improve crack resistance, the S content is 0.00
When a filler wire for welding of 5% by weight or less is used, the penetration tends to be shallow and the bead spread is small compared to a filler having a high S content. Therefore, conventionally, a 9% Ni steel having a narrow groove with a groove angle of 30 ° or less using a filler wire for welding having a chemical composition of Ni base and an S content of 0.005 wt% or less. When attempting TIG arc welding of the material to be welded, fusion failure occurred and it was difficult to narrow the gap.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and its purpose is to:
When using TIG arc welding to weld large structures made of 9% Ni steel such as LNG tanks, the chemical composition is Ni.
The content of S is 0.
Using a filler wire of 005 wt% or less, a 9% Ni steel welded material having a narrow groove with a groove angle of 30 ° or less can be TIG arc welded without causing defective fusion or defective bead shape. Accordingly, it is an object of the present invention to provide a narrow groove TIG arc welding method for a material to be welded made of 9% Ni steel, which can improve the efficiency by narrowing the groove.

[0006]

The invention according to claim 1 is
A narrow groove with a groove angle of 30 ° or less is provided on a material to be welded made of 9% Ni steel, the chemical component is Ni as a base, and the content of S is 0.
A filler gas for welding of 005 wt% or less is used, and a shield gas of a mixed gas of Ar gas and He gas with a He gas mixing ratio of 25 to 95% is used as the shield gas of the arc atmosphere to achieve the narrow groove. 9% characterized by performing TIG arc welding of the 9% Ni steel welded material
It is a narrow groove TIG arc welding method for a Ni steel welded material.

According to a second aspect of the invention, in the invention according to the first aspect, the narrow groove is for a lateral welding posture, and the narrow groove of a welded material made of 9% Ni steel is used. This is a TIG arc welding method.

[0008]

The narrow groove TIG arc welding method according to the present invention is preferably applied to a material to be welded made of 9% Ni steel having a plate thickness of 16 mm or more in order to improve the efficiency by narrowing the groove. The filler wire for welding is based on Ni as a chemical component and contains 0.005% by weight or less of S for improving crack resistance. From the viewpoint of improving the crack resistance, the more preferable range of the S content is 0.002% by weight or less.

In the narrow groove TIG arc welding method according to the present invention, the shielding gas of the arc atmosphere is replaced with a conventional Ar gas alone, and a mixed gas of Ar gas and He gas having a He gas mixing ratio of 25 to 95%. Even if a filler wire for welding having a Ni content of 0.005% by weight or less is used by using the shielding gas as described above, as shown in FIG. The penetration into the material (base material) can be deep and the bead width can be increased. As a result, even in a U-shaped or V-shaped narrow groove with a groove angle of 30 ° or less, the groove wall portion can be sufficiently melted to obtain a welded portion having no fusion defect.

The reason why the above-mentioned penetration is deep and the bead width is widened is considered as follows. It is known that the atmosphere of He gas has a higher potential gradient than that of Ar gas. Therefore, when the arc length is the same, the arc voltage of Ar-He gas (mixed gas of Ar gas and He gas) It is higher than that of Ar gas alone. Therefore, the heat input for welding can be increased, and the penetration increases as compared with the case of Ar gas alone. Further, it is considered that the He gas is lighter than the Ar gas, but the arc column in the Ar gas is thin and clear up to the base material, whereas Ar-
The arc column in He gas tends to expand and become unclear as it approaches the base material. Therefore, it is considered that the bead width is expanded as compared with the case of Ar gas alone.

As described above, the He gas mixture ratio (volume ratio) is preferably in the range of 25 to 95%. If the He gas mixing ratio is less than 25%, the effect due to the addition of He gas is not sufficiently exerted, and fusion defects cannot be eliminated in a narrow groove with a groove angle of 30 ° or less. In addition, the He gas mixing ratio is 9
If it exceeds 5%, the spread of the bead width becomes larger, but it is not constant, and the bead width becomes uneven, resulting in a defective bead shape. Note that a more preferable range of the He gas mixing ratio is 35 to 80 from the viewpoint that the above-mentioned effect by the He gas addition can be made more reliable without causing a bead shape defect.
%.

In high current TIG arc welding, a so-called double shield is often applied. With this double shield,
It is almost meaningless to use Ar-He gas instead of Ar gas for the outer shield, and Ar-He gas of the composition of the present invention may be used for the inner shield that supplies the shield gas to the arc atmosphere.

In the narrow groove TIG arc welding method according to the present invention, as shown in FIG. 5, the welding filler wire FW is fed from the rear side (anti-welding direction side) of the tungsten electrode E supported by the welding torch T. It is preferable that the bead width be widened to help eliminate defective fusion. This is considered to be because when the filler wire is fed from the front side (welding direction side) of the tungsten electrode, the tip of the molten pool is deprived of heat to melt the filler wire and is difficult to spread. However, with respect to the feeding direction of the filler wire for welding, if the filler wire is fed from the rear side, it is difficult to see the insertion state of the filler wire and the area in which the filler wire can be inserted becomes narrower. Therefore, it may be appropriately selected depending on the situation.

In the narrow groove TIG arc welding method according to the present invention, particularly in the lateral welding, the lower groove wall portion is sufficiently melted to obtain a weld portion without fusion failure, and the conventional molten metal sags. Poor fusion of the lower groove wall portion can be eliminated, and the effect can be sufficiently exerted.

Further, the narrow groove TIG arc welding method according to the present invention has a groove angle of 15 ° particularly in a U-shaped groove.
In the following, multi-layer welding of one layer and one pass becomes possible, so that the effect is exhibited well. 9% Ni steel LN
In the case of G tank construction, welding is often performed from both sides in order to suppress the effect of welding distortion. At this time, by using the copper backing material BP as shown in FIG. 6, the back surface can be constructed efficiently without any hanging treatment. It should be noted that double-sided welding without using the backing material is possible by providing a back shield with Ar gas or the like instead of the copper backing material.

Further, in the U-shaped narrow groove, multi-layer welding of one layer and one pass becomes possible, which facilitates automation of welding. That is, in the multi-layer welding of one layer and one pass, as shown in FIG. 7, the target position of the tungsten electrode may always be the center C of the groove. Therefore, when welding is performed while monitoring the target position of the tungsten electrode with an ITV camera or the like, or when the welding torch (tungsten electrode) position is taught in advance along the welding line before welding, and further in FIG. As shown, even when welding is performed while irradiating the groove with laser slit light LSB to detect the groove, it is sufficient to control the position so that the tungsten electrode is located at the center of the groove, which facilitates automation of welding.

[0017]

Embodiments of the present invention will be described below.
Narrow groove TIG arc welding according to the example of the present invention and the comparative example was performed under the welding conditions described below, and the presence or absence of welding defects was examined.

Standard welding conditions are welding position: sideways, base material: 9% Ni steel (JIS G 3127 SL9N59).
0 equivalent), plate thickness 40 mm, welding length 1 m, groove: U-shaped groove, groove angle 14 ° (see FIG. 1), welding filler wire: high Ni-based wire (JIS Z3323 YGT9N)
i-2 equivalent), diameter 1.2 mm (see Table 1), current:
350 A (average value of each pass), voltage: 12 V (average value of each pass), welding speed: 15 cm / min (average value of each pass), welding filler wire feed rate: 30 g / min, welding filler wire feeding direction : Electrode rear side (anti-welding direction side)
Since, Table 1 shows the chemical composition (unit weight%) of the filler wire for welding.

[0019]

[Table 1]

Table 2 shows the shield gas composition of the arc atmosphere,
Welding results are also shown together with the S content of the filler wire for welding.

[0021]

[Table 2]

As can be seen from Table 2, according to the embodiment of the present invention, for the welding, the chemical composition is Ni base and the content of S is 0.005 wt% or less for improving the crack resistance. Using filler wire, it is possible to perform TIG arc welding of a welded material made of 9% Ni steel having a narrow groove with a groove angle of 30 ° or less without causing defective fusion or defective bead shape. It is possible to improve efficiency.

[0023]

As described above, according to the narrow groove TIG arc welding method for the material to be welded made of 9% Ni steel according to the first and second aspects of the invention, the shielding gas of the arc atmosphere is A
Since a mixed gas of r gas and He gas mixed at a predetermined ratio is used, the chemical composition is Ni-based and the S content is 0.00 to improve crack resistance.
It is possible to perform TIG arc welding of a 9% Ni steel welded material having a narrow groove with a groove angle of 30 ° or less using a filler wire for welding of 5% by weight or less without causing fusion failure or bead shape failure. Therefore, the efficiency can be improved by narrowing the groove.

[Brief description of drawings]

FIG. 1 is a diagram showing an example of a groove shape according to an embodiment of the present invention.

FIG. 2 is a diagram showing another example of the groove shape in the embodiment of the present invention.

FIG. 3 is a diagram showing still another example of the groove shape in the embodiment of the present invention.

FIG. 4 is a diagram for explaining a penetration shape according to the method of the present invention.

FIG. 5 is a view for explaining a feed direction of a filler wire for welding.

FIG. 6 is a view showing a copper backing material used in double-sided welding.

FIG. 7 is a diagram for explaining a target position of a tungsten electrode in multi-layer welding of one layer and one pass.

FIG. 8 is a diagram showing a manner of groove detection using laser slit light.

FIG. 9 is a diagram for explaining a fusion failure that occurs in horizontal welding.

[Explanation of symbols]

W ... 9% Ni steel welded material W1 ... 9% Ni steel upper welded material W2 ... 9% Ni steel lower welded material N ... Penetration part E ... Tungsten electrode FW ... Welding filler wire T ... Welding Torch BP ... Copper backing material C ... Groove center line LSB ... Laser slit light

Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display location B23K 9/23 8315-4E B23K 9/23 C 35/30 320 35/30 320A

Claims (2)

[Claims] 1. A groove angle of 30 ° is applied to a material to be welded made of 9% Ni steel.
The following narrow groove is provided, the chemical composition is Ni-based, and S
The filler wire for welding whose content of 0.005 wt% or less is used, and Ar is used as a shield gas in the arc atmosphere.
Gas and He gas mixed gas having a He gas mixing ratio of 25
A narrow groove TIG arc welding method for a 9% Ni steel welded material, which comprises performing TIG arc welding of the 9% Ni steel welded material having the narrow groove using a shield gas of 95%. 2. The narrow groove TIG arc welding method for a material to be welded made of 9% Ni steel according to claim 1, wherein the narrow groove is for a horizontal welding posture.