JPH08155650A - Welding method of austenitic stainless steel - Google Patents

Abstract

PURPOSE: To suppress generation of precipitation of alloy component, coarsing of grain, thermal strain, residual stress so as to obtain the weld zone excellent in corrosion resistance, durability and external appearance by cooling the weld zone right after heating to high temp. with solidified solid particle of dioxide carbon in welding of austenitic stainless steel. CONSTITUTION: On the surface of a weld zone 7 in high temp. right after welding, a solidified solid particle 8 of a dioxide carbon is sprayed for cooling by a spraying machine 5. At this time, the weld zone 7 is rapidly cooled in short time by the latent heat sublimating from solid to gas. In order not to give adverse influence on welding such as the solidified solid particle 8 is directly spattered on the weld zone or air is entrapped for oxidizing weld zone, etc., the nozzle direction of the spraying machine 5 is inclined backward in the prescribed angle or a protective cover, spraying guide, etc., are mounted.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for welding austenitic stainless steel while cooling it.

[0002]

2. Description of the Related Art When welding austenitic stainless steel, if the welding site and its vicinity are maintained in a temperature range of about 500 ° C. to 800 ° C. for a long time during the cooling process due to the high welding heat of the welding site, the heat is generated. It is known that the deposited metal and carbide of the alloy component of the heat-affected zone are precipitated in the crystal grain boundary portion due to the thermal influence, and the corrosion resistance deteriorates, causing intergranular corrosion. In addition, coarsening of crystal grains and thermal strain cause deterioration in strength and generation and deformation of residual stress, which cause stress corrosion cracking, and a surface oxide film that deteriorates corrosion resistance and aesthetics is formed. Problems such as are known. Also,
It is known that the above-mentioned welding defect occurs in the initial layer and the laminated welded portion due to the influence of the welding heat of the laminated welding when performing the laminated welding after the initial layer welding.

In order to solve these problems, there is known a method of welding while welding a welded portion of austenitic stainless steel. As the method, there is a welding method in which a low temperature inert gas is directly injected from the side to be welded, that is, the front side, to the surface of the welded portion to perform welding. Further, as another method, when laminating welding after the initial layer welding, to the first layer welding portion on the back side corresponding to the laminated welding portion, while cooling by spraying or flowing a liquid refrigerant such as water. There was a welding method for welding.

[0004]

When welding austenitic stainless steel, a welding method for cooling a weld by injecting a low temperature inert gas as a welding shield gas onto the surface of the weld is a low temperature gas. Since it is cooled by utilizing the sensible heat due to the temperature change related to the specific heat, it is difficult to sufficiently cool the welded part in a short time, and sufficient corrosion resistance and durability of the welded part cannot be obtained. Also, a large amount of low-temperature gas was required because the thermal efficiency of cooling was not good.

In addition, when performing a layered welding after the first layer welding of austenitic stainless steel, a welding method of cooling the welded portion by spraying or flowing a liquid refrigerant such as water at the first layer welding portion on the back side is used. Although the sensible heat and the heat of vaporization of the liquid refrigerant are used, it is still insufficient to cool them in a short time, and it has been difficult to obtain sufficient corrosion resistance and durability of the initial layer and the laminated weld. In addition to the fact that a large amount of water or other refrigerant is required due to the poor thermal efficiency of cooling,
When welding pipes, etc., it is necessary to have a mechanism to seal liquid refrigerant such as water so that it does not leak and to circulate it evenly, and protect it so that it does not splash and get wet or hinder work. The cooling mechanism was complicated and it was difficult to handle. Further, when a liquid refrigerant such as water adheres to the surface, an oxide film is formed on the surface, which impairs corrosion resistance and aesthetics.

The present invention has been made in view of the above-mentioned problems, and when welding austenitic stainless steel,
Efficient in a short time due to large latent heat of sublimation of high temperature welds by using particles of solidified carbon dioxide (trade name, dry ice) without using liquid refrigerant such as conventional low temperature gas or water. Cooling eliminates precipitation of alloy components due to heat effect, coarsening of crystal grains, generation of thermal strain and residual stress, formation of surface oxide film, etc., resulting in a good quality weld with excellent corrosion resistance and durability. The present invention provides a welding method for austenitic stainless steel, which is easy to weld and cool.

[0007]

In the welding method for austenitic stainless steel according to the present invention, condensed solid particles of carbon dioxide are sprayed on at least one of the front and back surfaces of the welded portion immediately after welding to cool it. .

Further, the welding method for austenitic stainless steel according to the present invention is such that, when the first layer welding is followed by the layer welding, the solidified carbon dioxide is directly added to the first layer welding point on the back side corresponding to the layer welding point. Spray the particles to cool,
The welding is performed.

[0009]

In the method for welding austenitic stainless steel according to the present invention, the solidified particles of carbon dioxide are cooled by spraying condensed solid particles of carbon dioxide to at least one of the front and back surfaces of the welded portion immediately after welding, so that solid particles in the form of powder or particles are cooled. However, at the same time, they collide with the places heated to a high temperature one after another, and at the same time, they instantly change from solid to gas and take large latent heat from sublimation to cool rapidly. The solid particles directly reach the surface and instantaneously evaporate at the same time as the collision, so that new solid particles are constantly brought into contact with the surface to further enhance the cooling effect. As described above, since the cooling is efficiently performed in a short time, problems such as deterioration of corrosion resistance due to high heat of welding, occurrence of thermal distortion, and factors of stress corrosion cracking do not occur.

When the object to be welded cannot be welded or cooled from the back side such as a pipe material having a small diameter, cooling is performed by spraying condensed solid particles of carbon dioxide only from the welding side, that is, from the front side to the welded surface immediately after welding. To cool the weld in a short time. Further, when the above cooling is performed only on the back surface of the welded portion immediately after welding, the welding operation is easy because there is no simultaneous cooling operation on the welding side. Furthermore, when the above-mentioned cooling is performed simultaneously from both the front and back surfaces of the welded portion immediately after welding, not only the cooling efficiency is further improved by cooling in a short time,
Since cooling is performed from both sides, residual stress, thermal strain and plastic deformation can be further suppressed.

Further, since the present invention uses condensed solid particles of carbon dioxide which immediately sublimes from a solid to a gas as a cooling medium, it wets the welding site or the surface of the back surface like a liquid refrigerant such as water, Since it does not leak and there is no need to consider post-processing, it is easy to handle and the workability of cooling the welded part is good.

Further, the welding method for austenitic stainless steel according to the present invention is such that, when performing the laminated welding after the initial layer welding, condensed solid particles of carbon dioxide are formed on at least one of the front and back surfaces of the welded portion immediately after the laminated welding. At the same time as spraying and cooling, the solidified carbon dioxide particles are also sprayed directly to the first layer welded part on the back side corresponding to the laminated welded part. Since cooling is performed from both sides, cooling efficiency is further enhanced. In this way, even in the case of laminated welding, efficient cooling in a short time suppresses deterioration of corrosion resistance and stress corrosion cracking of the initial layer and laminated weld due to high heat of laminated welding, and cools from both sides. Therefore, the occurrence of residual stress, thermal strain, etc. can be further suppressed.

[0013]

Embodiments of the present invention will be described with reference to the drawings.
FIG. 1 shows a welding method according to the present invention. In the figure, 1 is an austenitic stainless steel material to be welded, 2 is a welding torch for TIG welding, 3 is a welding material wire, 4 is a welding machine, 7 is a weld metal immediately after the welding site and a heat-affected zone in the vicinity thereof It is a welded part including. Further, 5 is a spraying machine of carbon dioxide condensed solid particles 8 for cooling the welded portion 7, and 6 is a supply device for producing and sending carbon dioxide of the condensed solid particles.

FIG. 1 shows a state in which only the surface of the welded portion 7 immediately after one side is welded from the welding direction side, that is, the front side, when the welding from the back side such as a small-diameter pipe material is not possible. . As shown in the figure, the solidified carbon dioxide spraying machine 5 sprays the solidified carbon dioxide particles 8 onto the surface of the welded portion 7 which has been heated to a high temperature immediately after welding and is cooled. At this time, the weld 7 is rapidly cooled in a short time by the large latent heat that instantly sublimes from solid to gas.

As described above, since the welded portion 7 is efficiently cooled in a short time, the weld metal and the carbide of the alloy component of the heat-affected zone are precipitated at the grain boundary portion by the high welding heat of the welded portion, and the corrosion resistance is improved. It causes deterioration and causes intergranular corrosion.
It does not occur that strength is deteriorated or residual stress is generated due to coarsening of crystal grains or thermal strain, which cause stress corrosion cracking, or a surface oxide film that impairs corrosion resistance or aesthetics is formed.

Further, in order to prevent the condensed solid particles 8 of carbon dioxide from scattering and directly hitting the welded portion, or entraining air to oxidize the welded portion, there is no adverse effect on the welding. The direction is inclined at a predetermined angle rearward with respect to the welding proceeding direction, and a protective cover, a blowing guide, etc. are attached.

The condensed solid carbon dioxide supply device 6 includes a container 9 for storing low temperature liquefied carbon dioxide, and a carbon dioxide condensed solid particle production device 1 for condensing and solidifying the liquid for granulation.
0 and a delivery device 11 for delivering the solid particles. The condensed solid particles 8 of carbon dioxide are mixed by a mixing device 13 with a compressed low temperature gas sent from a gas container 12 storing an inert gas such as carbon dioxide gas or argon gas and mixed by a carbon dioxide spraying machine. Transport to 5.

The condensed solid particles 8 of carbon dioxide sprayed onto the weld 7 are, for example, low-temperature liquefied carbon dioxide having a specific gravity of about 1.1 and a boiling point of -78.5 ° C. Carbon condensed solid particle production device 1
At 0, the pressure is compressed and cooled to about 80 atm, and the particles are ejected from the pores and adiabatic expansion is caused to condense into a snowflake having a specific gravity of about 1.5, and the snowflake is compression-molded and manufactured. The condensed solid particles 8 of carbon dioxide are sent out to the mixing device 13 by the sending device 11, and the low temperature gas sent from the gas container 12 is used as a carrier to increase the pressure and to be transferred.

In the above embodiment, the condensed solid particles 8 of carbon dioxide were produced by the low temperature liquefied carbon dioxide sent from the container 9 by the carbon dioxide condensed solid producing apparatus 10. It is also possible to simplify the manufacturing apparatus by using carbon dioxide (trade name: dry ice) and crushing and granulating it into particles of a desired size by a crushing apparatus or the like.

The solidified particles 8 of carbon dioxide are welded to each other at the welded portion 7.
Even if the surface of the cooling part has unevenness or a narrow range, the particles can be hardened and the pressure can be increased with a strong impact so that the desired cooling spot can be accurately aimed and cooled efficiently.
For example, it is formed in the shape of coarse spheres or columns having a size of several hundreds of microns to several millimeters.

FIG. 2 shows that when the austenitic stainless steel plate materials 14 are welded, the solidified carbon particles 8 of carbon dioxide are simultaneously applied to the front and back surfaces of the welded portion immediately after the welding from both front and back surfaces.
Shows the state of being sprayed and cooled.

In the figure, 5A is a front side spraying machine and 5B is a back side spraying machine. Front side spraying machine 5A
Is to cool the welded portion 7A by spraying the solidified carbon particles 8 of carbon dioxide onto the welded portion 7A immediately after the welding, and at the same time, the spraying machine 5B on the back surface side corresponds to the welded portion 7A on the surface immediately after the welding. It is installed so that the solid particles 8 of carbon dioxide are sprayed onto the welded part 7B of FIG. As described above, when the front and back surfaces of the welded portions 7A and 7B immediately after welding are simultaneously cooled, not only the cooling efficiency can be further improved, but also residual stress, thermal strain and plastic deformation hardly occur.

Further, as a method other than those shown in FIGS. 1 and 2, when the solidified carbon dioxide particles are sprayed to cool only the back surface of the welded portion immediately after welding, the front side of the welding is simultaneously cooled. There is no work, and since the solidified particles of carbon dioxide and carbon dioxide do not scatter around the welding spot, the welding work becomes easier.

FIG. 3 shows that when welding austenitic stainless steel pipe materials 15 and 15, carbon dioxide is directly condensed from the inside of the pipe material 15 to the 17 places of the first layer welding during the laminated welding 18 after the first layer welding 17 is performed. The state where the solid particles 8 are sprayed and cooled is shown.

In the figure, 5C is a carbon dioxide condensation solid spraying machine for pipes, and 16 is a dispersion guide for guiding the carbon dioxide condensation solids particles 8 and spraying them to a predetermined cooling part for efficient cooling. After performing the first layer welding 17 on the pipe materials 15 and 15 by self-shield arc welding or TIG welding using the back shield gas on the back surface, when performing the laminated welding 18, carbon dioxide is formed on the surface of the welded portion 7C immediately after the laminated welding 18. At the same time as spraying the solidified solid particles 8 of
The solidified particles 8 of carbon dioxide are condensed from the inside of the pipe material 15 by the spraying machine 5C for the pipe and the dispersion guide 16 so as to directly cool the first layer welding 17 on the back side corresponding to the place.
The entire surface of the first layer weld 17 including the back side position directly corresponding to the laminated welded portion 7C of the pipe material 15 is sprayed and formed so as to be efficiently cooled from both the front and back sides in a short time.

As described above, even during the laminated welding 18, both the 18 laminated welding portions and the 17 first layer welding portions on the back side thereof are efficiently cooled simultaneously in a short time. The weld metal of both the layered weld 18 and the first layer weld 17 and the carbide of the alloy component of the heat-affected zone are precipitated in the grain boundary portion, which deteriorates the corrosion resistance and causes the intergranular corrosion. The deterioration of strength and the generation of residual stress due to aging and thermal strain do not cause stress corrosion cracking, and a surface oxide film that impairs corrosion resistance and aesthetics is not formed.

When the diameter of the pipe material 15 is large,
When performing the laminated welding 18 after the first layer welding 17 is performed, the solidified carbon particles 8 of carbon dioxide are sprayed onto the surface of the welded portion 7C immediately after the laminated welding 18 and at the same time, the back side corresponding to the laminated welded portion 7C is locally localized. If the outlet nozzle of the pipe spraying machine 5C is bent in one direction on the inner surface of the pipe so as to be cooled directly, and is formed so as to rotate following the progress of welding, it directly concentrates following the welding point where the temperature becomes high. Therefore, cooling efficiency and economic efficiency are further improved.

[0028]

[Effect] As described above, the welding method for austenitic stainless steel according to the present invention efficiently cools the welded portion immediately after welding heated to a high temperature in a short time by the large latent heat of sublimation of condensed solid particles of carbon dioxide. Therefore, it is possible to obtain a welded portion which is excellent in corrosion resistance, durability and aesthetics by suppressing precipitation of alloying components, coarsening of crystal grains, generation of thermal strain and residual stress due to thermal influence of welding.

Further, the condensed solid particles of carbon dioxide instantly sublimate from a solid to a gas, and therefore, unlike liquid refrigerants such as water, they do not get wet or leak and do not harm the surroundings, and are easy to handle. Therefore, good cooling workability during welding can be obtained.

Further, the welding method for austenitic stainless steel according to the present invention, as described above, corresponds to the surface of the welded portion immediately after the laminated welding and the laminated welded portion when the laminated welding is performed after the initial layer welding. On both sides of the first layer weld on the back side,
Since condensed solid particles of carbon dioxide are simultaneously sprayed and efficiently cooled directly in a short time, precipitation of alloy components and coarsening of crystal grains in the initial layer and the laminated weld due to the heat effect of laminated welding,
It is possible to obtain the initial layer and the laminated weld which are further excellent in corrosion resistance and durability by suppressing the generation of thermal strain and residual stress, the formation of surface oxide film, and the like.

[0031]

[Brief description of drawings]

FIG. 1 is an explanatory view showing a welding method according to the present invention.

FIG. 2 is an explanatory view showing a state in which a plate material is welded by simultaneously cooling both front and back sides of the welding method according to the present invention.

FIG. 3 is an explanatory view showing a state where the pipe material is cooled and welded when the laminated welding is performed after the initial layer welding of the welding method according to the present invention.

[Explanation of symbols]

1 Austenitic stainless steel 11
Delivery device 2 Welding torch 12
Gas container 3 wire 13
Mixer 4 Welder 14
Plate material 5, 5A, 5B, 5C Spraying machine 15
Pipe material 6 Supply device 16
Dispersion guide 7, 7A, 7B, 7C Welded part 17
First layer welding 8 Solid particles 18
Multilayer welding 9 Container 10 Solid particle manufacturing equipment

Claims (2)

[Claims] 1. When austenitic stainless steel is welded, condensed solid particles of carbon dioxide are sprayed on at least one of the front and back surfaces of the welded portion immediately after welding to cool the austenitic stainless steel. Welding method. 2. When carrying out layered welding after the first layer welding, condensed solid particles of carbon dioxide are directly blown to and cooled at the first layer welded portion on the back side corresponding to the layered welded portion. 1. A welding method for austenitic stainless steel according to 1.