JPH11147193A - Partial stress relieving method for weld zone - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a partial stress relieving method for a weld zone by which residual tensile stresses partially produced in a weld zone are easily relieved in the same process. SOLUTION: A bracket 2 is fillet welded to a base metal 1, and a surface of the base metal 1 a distance L away from a toe of a formed bead part 3 is partially heated by arc welding or other way using the same electrode 5 as an electrode used for a fillet weld between the base metal 1 and the bracket 2, in the same process of this fillet welding, namely, at the same time as the fillet welding between the base metal 1 and the bracket 2 is performed, or, after this fillet welding. The residual tensile stresses caused by the fillet welding on the base metal 1 are compensated and relieved by applying a residual compressive stress produced by partial heating.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for relieving stress in a welded area, and more particularly to a method for relieving residual stress generated by heat during welding.

[0002]

2. Description of the Related Art Generally, in welding, a base metal and a welding metal such as a welding rod are melted by thermal energy such as an arc, and the melted portions solidify to join the base metals together. is there. The weld zone is a heat-affected zone that continues from the quenched bead after being exposed to a temperature close to melting, although not being melted, from the bead that solidified by melting the metal with heat energy such as arc, Changes from the bead portion, which is hardly affected by the welding heat, to the base metal material portion. The base material repeats expansion due to heating until melting and shrinkage due to cooling until solidification, and the expansion and shrinkage changes are local ones that occur only near the welding site. Become. For this reason, expansion and contraction changes cannot occur freely, and residual stress and the like occur.

[0003] Taking fillet welding as an example, generally, as shown by a solid line W in Fig. 2, in the direction orthogonal to the welding line, the vicinity of the bead portion 3 (see Fig. 1) becomes tensile stress,
The distance from the bead portion 3 changes to a compressive stress. The brittle fracture strength or the fatigue fracture strength of the welded portion where such a residual stress W is generated is reduced, and particularly when a repeated load is applied, a fatigue crack or the like is generated at the portion where the tensile stress is generated (C in FIG. 1). Will occur.

[0004] Therefore, in order to remove such residual stress W, post-weld heat treatment such as stress relief annealing or shot peening has been conventionally performed. The stress relief annealing method is a method in which at least the welded portions of both base metals joined by welding are put in a furnace or the like, and held at a predetermined temperature for a sufficiently long time, and then the residual stress is released and relaxed by gradually cooling. It is. The heating conditions vary depending on the material of the base material. For example, in the case of mild steel, the heating temperature is 600 to 650.
The degree is about 60 minutes per sheet thickness of 25 mm.
In addition, shot peening is a method of causing steel grains and the like to collide with the vicinity of a welded portion. The shot peened generates a compressive residual stress (WPC in FIG. 2) on the surface of the welded portion where the tensile residual stress W of the base metal occurs, and also causes work hardening. Is caused. The compressive residual stress generated by shot peening acts to offset the tensile residual stress generated by welding heat.

On the other hand, another conventional technique is disclosed in
Japanese Unexamined Patent Publication No. 78575/75 discloses a method for preventing brittle fracture. In this type, a tough tough ring is welded to the base metal so as to surround the area where a brittle crack is likely to occur, and the ring prevents the propagation of the crack to the outside of the ring. Thus, the thickness of the portion of the base member in the ring member is increased, and the high toughness of the ring member causes propagation of cracks generated in the base material inside the ring member to the outside of the ring member. Is described, and as a result, the propagation of the brittle crack is locally limited and the base material itself is prevented from being broken, and the like. line). In addition, the propagation of brittle cracks is prevented only around the nozzle (the other base material), preventing total destruction, and a material having a higher thermal expansion coefficient and higher toughness than the base material as the material of the annular material. When the is selected, the residual stress after welding or after annealing is compressed in the circumferential direction by the base metal under the circular material, and the thickness of the circular material part and the high toughness of the circular material cause the residual stress in the circular material. Is described as being prevented from propagating to the outside of the ring material (page 11, upper right column, line 11 to column 20, line 20). Further, this document also describes that the nozzle is welded to a reinforcing plate and the reinforcing plate is welded to a base material.

[0006]

However, in the above-described stress relief annealing method, the residual stress of the entire base metal to which the welding member is welded is released and alleviated, but in order to perform this stress relief annealing. However, there is a problem that a time for heating in the furnace and a time for slow cooling are required. In addition, equipment other than welding is required, such as a large furnace for performing stress relief annealing.In addition to this, it is necessary to perform stress relief annealing in a separate process from welding. However, there is a problem that it takes time, labor, equipment costs, and the like. In addition, in the above-described shot peening, the time for heating and slow cooling as in the stress relief annealing method is not required, but again, equipment for performing shot peening separate from welding is required,
Further, it is necessary to perform shot peening in a step different from welding, so that the number of steps is increased, and there is a problem that time, labor, equipment cost, and the like are required.

On the other hand, in the method for preventing brittle fracture disclosed in JP-A-61-78575, the thickness of the base material is increased by welding a high-toughness annular member and a reinforcing plate to the base material. It is based on a technical idea and presupposes that a brittle crack is not propagated, that is, a brittle crack is generated, and is not based on a technical idea that relieves the residual stress that causes the brittle crack. When a ring material having a higher coefficient of thermal expansion and higher toughness than the base material is selected, the residual stress of the base material below the ring material after welding or after annealing is reduced by the ring material. It was compressed in the circumferential direction, and required a high toughness annular material as an essential component. Therefore, in addition to the base material and the nozzle, it is necessary to separately prepare an annular material, and when the surface of the base material for welding the annular material is a curved surface, the annular shape is determined according to the curved surface. There was a problem that the material had to be formed.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problems in an advantageous manner, and it is intended to relieve a partial stress in a welded portion in which a tensile residual stress partially generated in the welded portion can be easily reduced in the same process. The aim is to provide a method.

[0009]

According to a first aspect of the present invention, there is provided a method for relieving partial stress at a welded portion, wherein the base material is joined to each other by welding, and the residual tensile stress is reduced by the welding. The present invention is characterized in that partial heating for generating a compressive residual stress is performed at a position where the heat is generated.

According to a second aspect of the present invention, there is provided a method for relieving partial stress in a welded portion, wherein the partial heating is performed by welding in order to achieve the above object. It is.

According to the first aspect of the present invention, when the base materials are welded to each other, they are heated by welding heat, thermally expanded, and then cooled, whereby tensile and compressive residual stresses are partially generated. In order to generate a compressive residual stress at a location where a tensile residual stress has been generated by welding for joining materials together, a location away from the welding location by a predetermined distance is partially heated. The partial tensile residual stress generated by the welding for joining the base materials to each other is offset by the compressive stress generated by the partial heating at a location away from the welding site by a predetermined distance, and is alleviated.

According to the second aspect of the present invention, the partial heating is performed in the same step as the step of joining the base materials to each other by the same or other welding equipment used for joining the base materials to each other.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of a method for relieving partial stress in a welding portion according to the present invention will be described in detail with reference to FIGS. In the present embodiment, a case where the other base material 2 (hereinafter, referred to as a bracket 2) in the form of a bracket is fillet-welded to one base material 1 as a welding portion will be described. In the drawings, the same reference numerals denote the same or corresponding parts.

The outline of the method for alleviating the partial stress at the welding portion according to the present invention is as follows. After the base material 1 and the bracket 2 are welded, partial heating is performed to generate a compressive residual stress at a position where a tensile residual stress is generated by this welding. Further, the partial heating is performed by a welding facility used when the base material 1 and the bracket 2 are welded.

The tip of the bracket 2 abuts against the surface of the base material 1 and is joined by, for example, arc welding. When the welding is performed, a bead portion 3 is formed together with the surface of the base material 1 and the bracket 2 and a filler material such as a welding rod or a wire is melted and overlaid. The base material 1 is locally heated and expanded only by the heat of an arc or the like near the portion where the welding is being performed, and then rapidly cooled to form a bead portion 3 on which a filler material such as a welding rod is loaded. A heat affected zone is formed in parallel. And bead part 3 of base material 1
As shown by the solid line W in FIG. 2, a residual stress generated in a direction orthogonal to
The tensile stress gradually decreases as the distance from the bead portion 3 increases, and in this embodiment, the compressive stress is changed from the tensile stress to the reverse at a position exceeding 3 mm from the side edge of the bead portion.

Therefore, in the present invention, as shown in FIG.
Base material 1 at a distance L from the side edge of bead portion 3
At the same time as or after the fillet welding of the bracket 2 to the base material 1, the same welding rod 5 as the fillet welding of the bracket 2 to the base material 1 Partial heating by arc welding or other welding techniques. Base material 1 partially heated
Is locally heated and expanded like fillet welding, and then rapidly cooled to form a heat affected zone. In this embodiment, when about 5 mm from the side edge of the bead portion 3 is arc welded so that the temperature becomes about 420 degrees,
Tensile and compressive residual stress was generated as shown by a dashed line H in FIG. The residual stress H generates a tensile stress with a peak at about 5 mm from the side edge of the partially heated bead portion, and this tensile residual stress becomes a compressive stress at a point about 3 mm from the side edge of the bead portion. Has changed. The compressive stress increases, as it approaches the bead, contrary to the tensile residual stress caused by the fillet welding. As a result of the addition of the residual stress H due to partial heating to the residual stress W due to the fillet welding, as shown by the broken line R in FIG. Has been relaxed.

The bead portion 3 shown by a broken line R in FIG.
The slight residual tensile residual stress from about 1 mm to about 6 mm can be further improved by adjusting the location of the partial heating (distance L in FIG. 1) and its temperature. The position of the partial heating and the range thereof are not limited to this embodiment, and the residual heat is pulled from a position 3 mm from the side edge of the bead portion 3 by welding for joining the base materials 1 and 2 to each other. It can be appropriately changed to a position where a compressive residual stress (H in FIG. 2) can be generated at a position where the stress (W in FIG. 2) is generated. The partial heating temperature can generate a compressive residual stress (H in FIG. 2) at a position where a tensile residual stress (W in FIG. 2) is generated by welding for joining the base materials 1 and 2 to each other. At a temperature, it can be from 380 degrees to the A ₁ transformation point. Further, the means for partial heating is not limited to arc welding using a filler material such as a welding rod 5, but may be gas welding using a torch, TIG welding, MIG welding, MAG welding, or the like. Any material can be used as long as it can be partially heated to generate a compressive residual stress at a position where a tensile residual stress has been generated by welding for joining the two. Furthermore, in the present invention, the tensile residual stress is offset by generating a compressive residual stress at a position where a tensile residual stress has been generated by welding for joining the base materials 1 and 2 to each other. Is not always necessary, but it is also possible to increase the thickness of the bead portion to increase the strength of the base material itself.

[0018]

According to the first aspect of the present invention, after the base materials are joined to each other by welding, partial heating for generating a compressive residual stress at a position where a tensile residual stress is generated by the welding is performed. The tensile residual stress generated partially when the base materials are welded to each other is offset by the compressive residual stress generated by partial heating, and is alleviated, and the stress generated partially in the welded area is easily alleviated. The present invention can provide a method for relieving partial stress at a welded portion that can be performed.

According to the second aspect of the present invention, the first aspect is provided.
In the invention according to the above, by performing the partial heating by welding, the same welding equipment used to join the base material to each other or other welding equipment, in the same step as the step of joining the base material to each other, It is possible to provide a method for relieving partial stress in a welded portion, in which heating can be performed and stress generated partially in the welded portion can be easily reduced in the same process.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing a base metal and a fillet-welded bracket on which a method for partial stress relaxation of a welding portion according to the present invention is performed.

FIG. 2 shows the residual stress generated when the base materials are welded to each other, the residual stress generated when performing the partial heating according to the present invention, and the residual stress generated when the base materials are welded to each other by the partial heating according to the present invention. 5 is a graph showing a result of relaxation of residual stress and a compressive residual stress generated when shot peening is performed.

[Description of sign]

DESCRIPTION OF SYMBOLS 1 Base material 2 Bracket (other base material) 3 Overlaid weld metal 5 Welding rod W Residual stress generated when base materials are welded to each other H Residual stress generated when performing partial heating according to the present invention R Residual stress resulting from partial heating WPC Compressive residual stress due to shot peening

Claims (2)

[Claims] After the base materials are joined to each other by welding,
A partial stress relieving method for a welded portion, comprising performing partial heating for generating a compressive residual stress at a position where a tensile residual stress is generated by the welding. 2. The method according to claim 1, wherein the partial heating is performed by welding.