JPH0696196B2 - Welding method for nickel-base alloy materials - Google Patents

Description

TECHNICAL FIELD The present invention relates to a welding method for nickel-based alloy materials and the like, and particularly to stress corrosion cracking due to a sensitized region that tends to remain near the groove of the base metal. The present invention relates to a welding method suitable for suppressing generation and growth.

“Conventional Technology and Its Problems” Generally, nickel-based alloy materials having excellent heat resistance and corrosion resistance are often used for structural materials, devices, parts and the like of nuclear power plants, chemical plants and the like.

By the way, the nickel-based alloy material has a problem that, when a welded joint is formed, stress corrosion and intergranular corrosion easily occur near the welded portion.

Nickel-based alloy material, for example, Inconel material, when explaining a conventional example of a general welding method in stainless steel,
As shown in FIG. 3, the base material 1
Multi-layered welding beads 4 are sequentially stacked on the groove 3 of 2,
It ends the bead with ... x, y, z.

However, as described above, the nickel-based alloy material is repeatedly subjected to welding heat, so that
A heat-affected zone Y is generated in which a part of the tissue is deteriorated. According to the research conducted by the inventors, the heat-affected zone Y is shown in FIGS. 4 (i) (ii) (ii) when nickel-based alloy materials such as Inconel 600 and austenitic stainless steel are welded.
As shown in i) ..., the solid solution region of the chrome carbide moves through the semi-solid solution region according to the heating amount to the precipitation region where the chrome carbide is deposited. If they are sequentially formed as shown by the arrow in the drawing and are terminated by z, a semi-solubilized region is left in a part of the heat-affected zone Y located near the bead z, and the semi-solidified region is
It is considered that the sensitization region X is likely to cause the stress corrosion and the intergranular corrosion.

Further, the sensitization region X depends on the degree of welding heat input, but the heat-affected zone Y, which is the generation source thereof, exists in the thickness direction of the base materials 1 and 2 as shown in FIG. Therefore, depending on the welding conditions, there is a possibility that the sensitized region X is continuously formed in the thickness direction. Therefore, the base materials 1 and 2
If the corrosive fluid is in contact with the surface of the base material and the surface is under tensile stress,
There is a problem that stress corrosion cracking gradually progresses so as to connect the sensitized regions X in the thickness direction 2.

"Means for Solving Problems" The present invention has been made to effectively solve such problems, and a multilayer weld bead is sequentially stacked on a groove of a base material made of a nickel-based alloy. The welding bead forming the final layer is formed so as to be wider than the width of the groove, and the welding bead forming the final layer is formed in the center from a position separated on both sides from the width of the groove. The heat-affected zone in the vicinity of the surface of the nickel-based base material is deviated from the growth direction of stress corrosion cracking or the like due to tensile stress by sequentially stacking the heat-affected zones toward the portions.

[Example] Hereinafter, an example of a method for welding a nickel-based alloy material or the like according to the present invention will be described with reference to FIG.
3 is similar to the example shown in FIG. 3 in that the welding of the multi-layered weld beads 4 is sequentially performed, but the final layer of the weld beads 4 is formed to be wider than the width of the groove 3. 1 and the arrows (a) and (b) in FIG. 1, a welding bead 4 is formed from a position separated from the both sides of the groove 3 to the left and right toward the center of the groove 3. There is a big difference with the point,
Further, a bead recess 5 is formed in advance on the front surface side so that the final layer of the weld bead 4 does not largely project from the surface of the base materials 1 and 2.

That is, in FIG. 1, the welding beads 4 are sequentially stacked,
When the beads are formed up to x, y, z, due to the welding heat,
Inside the base materials 1 and 2, the heat-affected zone Y along the side of the groove 3
Occurs, and particularly the heat-affected zone Y near the bead z.
, There is a possibility that the solution-solubilized region may be left in a state of being moved to the semi-solution-solubilized region, that is, the sensitization region X. Therefore, as shown by arrows (a) and (b) in FIG. 1, a, b, c, ... And i, j, k ,. Then, the sensitized area X receives a heating history and shifts as shown in (i), (ii), and (iii) of FIG. 4 described above, and the entire area of the heat-affected zone Y of FIG. 1 is sensitized. It can be separated from X. Further, the welding conditions in this case are as follows: "Processing method for Inconel welded joint" proposed by the present inventors, Japanese Patent Application No. 58-20307 (Japanese Patent Laid-Open No. 59-14778).
(Gazette No. 1).

In the example of FIG. 1, as indicated by arrows (a) and (b),
Since the beads are formed by stacking the beads toward the center from the left and right positions on both sides of the groove 3, the heat-affected zone Z is generated also in the lower portion of the bead recess 5, and the bead is formed. a, i
There is a possibility that the sensitized zone X is formed in the vicinity of the above because the welding heat input decreases.

However, the tensile stress applied to the base materials 1 and 2 is in the direction along the surface thereof (for example, in the case of a pipe, the pipe axial direction and the circumferential direction), and is ignored in the thickness direction. Therefore, even if the sensitized region X is present at a position separated from the groove 3, the direction of tensile stress is along the surface, and therefore the direction in which stress corrosion cracking or the like grows due to tensile stress is As described above, the thickness direction is deviated from the direction of the heat-affected zone Z and is substantially orthogonal to each other, so that the sensitized regions X are connected one after another and a defect portion grows. It is possible to prevent the occurrence of.

Next, another embodiment in which the welding method for the nickel-based alloy material or the like of the present invention is applied to the bottom of a reactor pressure vessel will be described with reference to FIG. In FIG. 2, reference numeral 6 is a lower mirror portion of the reactor pressure vessel, reference numeral 7 is a stub tube, reference numeral 8 is a clad layer covering the inner surface of the lower mirror portion 6, and reference numeral 9 is weld metal. Also in the case of this example, the bead recess 5 is formed above the opening of the groove 3 to sequentially stack the multi-layered weld beads and to form the weld bead forming the final layer thereof. By sequentially stacking the weld metal 9 toward the central portion, the sensitized area is removed from the weld metal 9 and stress corrosion cracking of the stub tube 7 in the thickness direction of the pipe wall is prevented. It suppresses growth. In the case of this example, a fluid, that is,
Reactor cooling water is filled.

In FIGS. 1 and 2, the bead depression 5 is formed, and then the final-layer weld bead is stacked.
The bead recess 5 may be omitted, and the final layer of the weld bead may be directly stacked on the surface of the base material.

"Effects of the Invention" As described above, the welding method for nickel-based alloy materials and the like of the present invention has the following excellent effects.

Multi-layered weld beads are sequentially stacked on the groove of the base metal, and the weld bead forming the final layer is formed wider than the width of the groove. Even if a sensitized region is generated in the portion, it can be removed, sensitivity to stress corrosion and intergranular corrosion can be reduced, and strength of a welded joint portion such as a nickel-based alloy material can be improved.

By forming the weld beads that make up the final layer by sequentially stacking them from the positions separated from the groove width on both sides toward the center, the direction of the heat-affected zone near the surface of the nickel-based base metal is pulled. It is possible to increase the stability of the welded joint by removing it from the growth direction of stress corrosion cracking due to stress.

Since the weld beads in the final layer are piled up widely, it is possible to remove the sensitized area of the heat affected zone at the same time as the welding is completed, and to prevent growth such as stress corrosion inclusion and to improve workability. Can be improved.

[Brief description of drawings]

FIG. 1 is an explanatory view of a welding bead forming step in an embodiment of a welding method for an Inconel material or the like of the present invention, and FIG. 2 is a welding bead formation in another embodiment to which the welding method for an Inconel material or the like of the present invention is applied. FIG. 3 is an explanatory diagram of a process, FIG. 3 is an explanatory diagram of a welding bead forming process of a conventional example of a welding method, and FIG. 1 ... Base material, 2 ... Base material, 3 ... Groove, 4 ... Weld bead, 5 ... Bead recess, 6 ... Lower mirror section, 7 ... Stub tube, 8 ... Clad layer , 9 …… Weld metal, X ……
Sensitization zone, Y ... Heat affected zone, Z ... Heat affected zone.

Claims (2)

[Claims] 1. A multi-layered weld bead is sequentially stacked on a groove of a base material made of a nickel-based alloy, and a weld bead constituting a final layer is formed wider than the groove. Welding method for nickel-based alloy materials, etc. 2. A multi-layered weld bead is sequentially stacked on the groove of a base material made of a nickel-based alloy, and the weld beads constituting the final layer are separated from both sides of the groove width. A method for welding a nickel-base alloy material or the like, characterized in that the nickel-base alloy material and the like are formed by sequentially stacking toward the center.