JP3170720B2 - Dissimilar material welding method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a butt welding method for dissimilar joints, and more particularly to a method for welding dissimilar materials suitable for preventing occurrence of welding defects.

[0002]

2. Description of the Related Art As shown in FIG. 2, a secondary superheater coil 27, a tertiary superheater coil 28, and a reheater coil 29 of a boiler are used.
Are composed of a plurality of small-diameter pipes arranged in parallel at regular intervals. Even with the same coil, the design temperature differs depending on the location.

[0003] Each part is made of a material having properties suitable for use conditions, and heat-resistant ferritic steel pipes 22, 23, 26, such as Cr-Mo steel or Mo steel, or stainless steel pipes having excellent high-temperature strength at the coil outlet side where the temperature is high. 21, 24, 25
Is dissimilar material welded. Butt weld 3 of these steel pipes
0 indicates welding of steel types that differ in chemical composition and physical properties (coefficient of thermal expansion, thermal conductivity, etc.), mechanical properties (tensile strength, creep rupture strength, etc.) and metallography. There is a problem in the cracking of the weld, securing the performance of the welded joint, etc.
Careful consideration must be given to the selection of welding conditions, groove shape, etc.

An example of a welding method effective for preventing welding cracks is to minimize the dilution of the base material, particularly Cr-Mo steel, as factors such as welding conditions (current, voltage, welding speed, etc.) There is a tip shape.

FIGS. 3 and 4 show a conventional groove shape when welding different materials of Cr-Mo steel and stainless steel by an automatic TIG (Tungsten Inert Gas) welding method, and FIG. The length 33 and the groove length 34 of the Cr-Mo steel pipe 32 are the same length, the groove angle 5 is the same angle, the root gap 37 is 0, and the mutual root surfaces 3 are set.
6 is a direct match. FIG. 4 shows that the groove length 33 of the stainless steel tube 31 and the groove length 34 of the Cr—Mo steel tube 32 are the same length, and a root gap 37 is provided between the mutual root surfaces 36 so that the high Ni The base alloy- based insert ring 41 is inserted. 3 and 4,
All-layer automatic TIG by feeding high Ni-base alloy welding wire
Welding is performed.

[0006]

However, in the above prior art as shown in FIG. 3, the dilution of the Cr-Mo steel pipe-side base metal is large, and as shown in Table 1, a high Ni-based alloy- based welding wire having a diameter of 1. When the wire feed rate is 2 mm and the wire feed rate is 700 mm / min or less, cracks may occur in the first layer weld metal. To prevent the cracks from occurring, the wire feed rate is set to 800 mm / m.
in or more, and it is necessary to control the wire feed amount during welding.

[0007]

[Table 1]

Further, the welding method based on the groove shape shown in FIG. 4 is not described. No cracking occurs even when the welding wire feed rate is 400 mm / min. If there is a deviation, new defects (such as poor penetration and defective bead shape) are likely to occur, and the ring setting is inefficient because manual tack welding by manual TIG welding is required. There are problems such as requiring a large cost.

An object of the present invention is to provide a ferromagnetic material such as Cr-Mo steel.
And Ito heat-resistant steel, depressive give a dilution of ferritic heat-resistant steel in dissimilar welding between austenitic heat-resistant steel, cracking of weld metal is to prevent the occurrence of welding defects such as penetration observed defects.

[0010]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a welding method for a dissimilar material in which a groove is formed on both sides and a dissimilar material is butt-welded. Achieved by setting close to one ,
Specifically, ferritic heat-resistant steel and austenitic
Butt welding by forming extension of groove route on both sides of hot steel
The root surface of the groove in the welding of different materials
Position closer to the ferritic heat-resistant steel side than the groove center line.
The length of the groove root extension of the heat-resistant ferritic steel
Is the length of the groove extension of the austenitic heat-resistant steel
Using a high Ni-based alloy as the welding material,
This is achieved by the features of welding.

[0011] The above object is achieved, the deposition rate of the weld material <br/> of the high Ni-based alloys is accomplished by to Rukoto and 3.5 g / min or more.

The above object is achieved by that the welding is a full penetration groove welding. The above-mentioned object is attained when the component amount in the first layer weld metal is Ni: 38.4% or more,
It is achieved by making it 44.0% or less.

[0013]

In the welding of dissimilar materials, the dilution of the base material becomes a problem in order to prevent welding cracks, and the shape of the groove root portion melted by the welding arc during the first layer welding greatly affects the dilution ratio. Therefore, by setting the matching position of the groove root surface of the different material welding of the stainless steel pipe and the Cr-Mo steel pipe to the Cr-Mo steel pipe side from the groove center line,
The dilution ratio of Mo steel is suppressed, the formation of a martensite structure that easily causes welding cracks is prevented, and a stable austenite structure that is hard to crack is obtained.

Further, as shown in Table 1 above, the matching position of the groove root surface is set closer to the ferritic heat-resistant steel side than the groove center line, and the matching position of the groove shape and groove root surface of the present invention is set. Compared with the groove shape of the conventional example having the groove center line, the condition for obtaining the Ni content to prevent the occurrence of the first layer welding cracking was as follows.
mm / min, wire feed rate 900 with conventional groove shape
mm / min, and the groove shape of the present invention enables welding with a small wire feed rate. Therefore, if the groove shape according to the present invention is adopted, the range of welding conditions is significantly widened, and there is no need to employ an insert ring, so that economical and stable quality can be obtained.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings.

The superheater coil, the reheater coil, and the like constituting the power generation boiler are constituted by a plurality of small-diameter tubes arranged in parallel at regular intervals, and the design temperature varies depending on the location even with the same coil. A case arises. Therefore, each part requires a joint made of a dissimilar metal depending on the use conditions.
Particularly on the coil outlet side, there are locally different types of joints of a Cr-Mo steel pipe and an austenitic stainless steel pipe.

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

The groove shape is a groove angle 5 formed at a predetermined angle on the stainless steel pipe 1 which is one base material of the dissimilar joint.
A groove root length 3 extending from the base metal, a groove root surface 6 formed at the end of the groove root, and a Cr-Mo steel pipe 2 which is the other base metal of the heterogeneous joint formed at a predetermined angle. The groove angle 5, the groove route length 4 extended from the base material, and the groove route surface 6 formed at the end of the groove route are opposed to each other via a route gap 7. Groove root length 3 of stainless steel pipe 1 and groove root length 4 of Cr-Mo steel pipe 2
Differently, the position of the groove root surface 6 is set closer to the Cr-Mo steel pipe 2 side than the groove center line. The root gap 7 is set to 0, the root surfaces 6 are directly abutted with each other, and a TIG (not shown) installed on the groove center line is provided.
The arcs of the tungsten electrodes of the welding torch melt the mutual base metal and are welded by the addition of a welding wire. At this time, an appropriate offset from the center line of the groove at the matching position of the groove route surface is 1 to 5 mm, and an excessively large offset may cause poor penetration of the joint portion and is inefficient. Also, if the offset is too small, the effect of the present invention cannot be obtained. According to the groove shape of this embodiment, Cr-Mo
The dilution ratio of steel is suppressed, the formation of a martensitic structure that is easily cracked is prevented, and a stable austenite structure that is hard to crack is obtained. When the groove root length 3 of the stainless steel pipe 1 is 3.5 mm and the groove root length 4 of the Cr—Mo steel pipe 2 is 1.5 mm, a high Ni-based alloy wire is used as a welding material, and the wire feed rate is set. 2. Welding amount at 400 mm / min.
When the rate is 5 g / min or more, cracks do not occur in the initial layer weld metal, and the component of the initial layer weld metal is Ni: 43.8 wt.
%, Fe: 38.7 wt%.

The method for welding dissimilar materials according to the present invention is not limited to boiler tubes, but may be any combination of steel types with all kinds of dissimilar metals, such as large diameter pipes and shell plates, petroleum refinery plants other than boiler plants, and petrochemical plants. Applicable to welding joints.

As described above, the method for welding dissimilar joints using the groove shape according to the present embodiment can suppress the dilution of the Cr-Mo steel base material, and thus has the effect of preventing the occurrence of cracks in the first-layer weld metal. Further, the limit value of the crack occurrence in the prior art is 800 mm / min of wire feed, but in the groove shape of the present embodiment, the wire feed is 400 mm / min or more,
Welding under a wide range of conditions improves workability. Further, since the insert ring is not used, the groove aligning operation can be automated, the time for temporary attaching operation is not required, the cost for manufacturing the ring is eliminated, and an economical and high-quality weld can be obtained.

[0021]

According to the present invention, a ferritic heat-resistant steel and
When welding different materials with austenitic heat-resistant steels, ferritic
For example suppress the dilution of the system heat-resistant steel, cracking of weld metal, the effect of preventing the occurrence of defects such as penetration observed defects is obtained.

[Brief description of the drawings]

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

FIG. 2 is an explanatory view of a position of welding a different material of a general boiler coil.

FIG. 3 is a sectional view showing a groove shape according to the related art.

FIG. 4 is a sectional view showing a groove shape using a conventional insert ring.

[Explanation of symbols]

 Reference Signs List 1 stainless steel pipe 2 Cr-Mo steel pipe 3 groove length of groove of stainless steel pipe 4 groove length of groove of Cr-Mo steel pipe 5 groove angle 6 groove root surface 7 root gap

Continued on the front page (72) Inventor Masafumi Kobun 6-9 Takara-cho, Kure-shi, Hiroshima Pref. Inside the Kure Factory (72) Inventor Koji Tamura 3-36 Takara-cho, Kure-shi, Hiroshima Babcock-Nikko Kure Research Institute (56) References JP-A-59-166382 (JP, A) JP-A-61-108477 (JP, A) JP-A-63-13679 (JP, A) JP-A-51-126350 (JP, A) A) Japanese Utility Model Hei 1-151995 (JP, U) Japanese Utility Model Sho 59-165790 (JP, U) (58) Field surveyed (Int. Cl. ⁷ , DB name) B23K 9/23

Claims (4)

(57) [Claims] 1. A heat-resistant ferritic steel and an austenitic steel
Butt welding is performed by forming an extension of the groove route on both heat resistant steels.
In the method of welding dissimilar materials in contact with each other,
The ferrite heat-resistant steel
Set close to the side, the groove route of heat resistant ferritic steel
Extend the extension length to the groove length of austenitic heat-resistant steel.
Shorter than the length of the long part, using a high Ni-based alloy as the welding material
A welding method for dissimilar materials, characterized by performing TIG welding. 2. A dissimilar welding method, characterized in that the deposition rate of the welding material of the high Ni-based alloy was 3.5 g / min or more. 3. The method for welding dissimilar materials according to claim 1, wherein the welding is a full penetration groove welding. 4. The method according to claim 1, wherein the amount of the component in the first layer weld metal is Ni: 38.
The method for welding dissimilar materials according to claim 1 or 2, wherein the content is 4% or more and Fe is 44.0% or less.