JPS58205687A - Method and torch for welding austenitic stainless steel - Google Patents

Abstract

PURPOSE:To obtain a welded part of austenitic stainless steel having no deterioration in corrosion resistance and a high reliability at a low cost, by cooling the welding metallic part and its vicinity which reach a heating temperature within an appropriate temperature range by jetting a refrigerant. CONSTITUTION:A cooling pipe 14 equipped with an ejecting nozzle 16 is fitted to the main body of a welding torch 1 fitted with a nozzle cup 3 equipped with a shield gas supplying pipe 2, wire tip 6 which feeds a consumable electrode wire 7, cooling jacket 9, etc., through a fittings 13, and then, a wire brush 18 which blocks cooling water is also fitted to the main body through a holding member 19. When a parent metal 20 of austenitic stainless steel is welded by generating arcs 23 in a shield gas atmosphere 22 with the above mentioned welding torch 1 and forming a molten pool 24, cooling water 17 supplied from a hose 15 is ejected upon the welding metal 21 thus formed and its vicinity which reach a temperature range of 850-1,200 deg.C and the welding metal 21 and its vicinity are quenched. Thus the austenitic stainless steel is prevented from becoming more sensitive and the corrosion resistance is also prevented from deteriorating.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to a welding method for austenitic stainless steel used in a corrosive environment, and in particular to a method for suppressing austenitic stainless steel from becoming sensitized during welding. The present invention also relates to a welding method for austenitic stainless steel that provides a welded austenitic stainless steel structure having excellent corrosion resistance, and a welding torch therefor.

[Technical background of the invention and its problems] Austenitic stainless copper has excellent corrosion resistance and is therefore widely used in various equipment, parts, and structures used in corrosive environments. .

However, austenitic stainless steel has the drawback of increasing susceptibility to localized corrosion such as intergranular corrosion or stress corrosion stamping (sec) due to welding required during assembly or manufacturing of structures.

That is, its excellent corrosion resistance deteriorates when subjected to heat from welding.

The mechanism of this corrosion resistance deterioration has been investigated by many researchers, and it has been revealed that the mechanism is as follows.

That is, it is well known that welding is a method of joining two base materials to be welded by melting and solidifying the welding material together with a part of the base metal by heat generated by an arc or the like.

At this time, a portion of the base material melts due to the heat of the arc, so it is heated to a temperature above its melting point, and then gradually cooled and solidified, and then further cooled to ambient temperature (room temperature).

Further, even in the case of a base material that does not melt, the maximum heating temperature near the fusion zone is heated to just below the melting temperature, and this maximum heating temperature decreases as the distance from the fusion zone increases.

However, austenitic stainless copper has a temperature of about 500℃.
When heated from 30 to 850° C. for a certain period of time, chromium carbide is precipitated at the grain boundaries.

The chromium concentration in the chromium carbide is lower than the chromium 11iI in the base metal.
IF! Since the chromium concentration is 1 times larger than t, the chromium concentration 1k near the precipitated carbide becomes a source and becomes lower than 13%, which is necessary to maintain corrosion resistance, and the corrosion resistance of this part deteriorates.

This is called visual acuity.

This sensitization is due to the inherent melting properties of ordinary austenitic stainless steel, and sensitization due to welding is unavoidable.

If the usage environment is highly corrosive, or if the structure requires a very high level of reliability, special stainless steel with an extremely low content of carbon that forms chromium carbide may be used, or , in a heat treatment furnace after welding,
Corrosion resistance due to +iiJ sensitization is achieved by carrying out solution heat treatment (heat treatment in which the precipitated chromium carbide is held at a temperature at which it dissolves into solid solution for a certain period of time to make the chromium carbide dissolve into solid solution again, and then rapidly cooled to prevent the chromium carbide from precipitating). prevents deterioration.

However, in the case of the 1llllI row, not only the material cost becomes the market price, but also the lower the carbon content of the lid, the lower the strength of the material, so there is a drawback that the design needs to be changed.

In the latter case, the number of balls produced increases and the heat treatment is required, and in the case of large equipment or structures, solution heat treatment is actually ineffective. .

[Purpose of the invention]

The present invention was made in order to eliminate each of the above-mentioned drawbacks, and is capable of welding austenitic stainless copper while suppressing sensitization, without deterioration of corrosion resistance, and with A (J-axis property and inexpensive austenite). It is another object of the present invention to provide a method for welding austenitic stainless steel and a welding torch for the welding process, by which a rigid stainless steel structure can be obtained.

[Summary of the invention]

That is, in the present invention, when welding austenitic stainless copper, the welded portion 11 is welded after the welded portion has solidified.
When the vicinity of the &4 part and the gold part is heated to a temperature range of 850°C to 1200°C, the weld metal part and the vicinity of the gold r14 part are rapidly cooled with running water. This is a welding method.

Further, in order to achieve the welding method described in (1), the present invention provides a cooling water spouting nozzle on the welding torch body along the bath contact direction, and the cooling water spouting nozzle is provided between the welding torch body (nll) and the separately described cooling water spouting nozzle. The present invention consists in using a welding tope characterized by the provision of a wire brush that shields water.

Immediately after the molten metal formed during welding solidifies using the above welding method and welding torch, the weld metal and surrounding base metal are rapidly cooled by the cooling water jetted from the jet nozzle provided on the welding torch, resulting in the welding area. sensitization is suppressed. , [Embodiments of the Invention] Hereinafter, embodiments of the welding method and welding)-f according to the present invention will be described in detail with reference to the drawings. FIG. 1 shows MIG welding as an example of the welding torch according to the present invention. It is a longitudinal cross-sectional view showing an example that is commonly used as a torch.

That is, the upper side II of the hollow cylindrical welding torch main body 1! 1
A 71 cup 6 is connected to the lower end of the main body 1.

Further, a half plate 4 is provided at the -F end 1 of the main body 1, a sleeve 5 is inserted through the center of the flat plate 4, and a wire tip 6 is connected to the lower part of the sleeve 5.

A consumable electrode wire 7 is inserted into this sleeve 5 .

Outside of sleeve 5! It is surrounded by a jacket 9 forming a cooling water channel 8 on one side, and the upper part of the jacket 9 communicates with an inflow hole 10 and an outflow hole 11 connected to the flat plate 4 for cooling water.

A flexible pipe for supplying cooling water is connected to the upper surface of the flat plate 4.

On the other hand, the cooling pipe 14 is attached to the main body 1 by means of a fitting 16.
A cooling water supply hose 15 is connected to the upper part of the cooling pipe 14, and a jet nozzle 16 is connected to the lower part of the cooling pipe 14.

Furthermore, along the discharge direction of the cooling water 17 from the jet nozzle 16)C
A nozzle 18 having an elasticity of 14'f is connected to the F part of the cooling part 14 via a holding μm9.

Bla &, /1δ is ta 41K P)j to prevent water from scattering into the molten pool 247, and to prevent incomplete unruding due to the generation of turbulence in the shielding gas due to the jetting of cooling water. It's no good.

The nozzle 16 is configured such that the jetting flow rate and jetting angle of the cooling water can be adjusted.

Here, an example of bath-welding the weld metal 21 to the base metal 2o using the welding torch will be described.

The base material 20 is made of austenitic stainless steel.

A welding voltage is applied between the wire 7 and the matrix 20, and shielding gas is introduced from the supply pipe 2 to create a red gas atmosphere 22.
An arc 23 is generated in the welding process, and an arc 26 is generated through the welding flow.
The wire 7 is melted by the heat generated, forming a molten pool 24, and welding is performed.

The wire 7 is also called a consumable electrode, and is supplied so that the length of the arc 26 is constant because it melts and is consumed.

The fixture 13 holds the cooling pipe 14 and adjusts the relative position and angle between the welding torch body 1 and the cooling pipe 14.

In this fixture 16, the size of the molten pool 24 of the weld metal changes depending on the welding speed, welding current, and voltage.
Because the distance to the point where the temperature range changes, the point where the cooling water hits the weld metal is always between 850℃ and 120℃
In the temperature range of 0℃.

It is for matching.

Welding is carried out under normal welding conditions, but as the welding progresses, the solidified part of the molten metal is continuously ejected from the jet nozzle 1.
It is necessary to rapidly cool it with water spouted from 6.

The position where the jet nozzle 16 rapidly cools is shown in FIG.
'4r: When forming and cooling naturally, the temperature must be in the range of 1200°C to 850°C, 2 This is 12
If it is rapidly cooled at a temperature exceeding 00°C, it is likely to cause cracks, and if it is below 850°C, the temperature at which stainless steel becomes sensitized is approximately 550°C to 850°C, so the effect of suppressing sensitization due to rapid cooling is insufficient. It is.

Figure 2 shows the position where the water jets out suddenly and the cooling curve.

The metal molten in the molten pool 24 solidifies at the solidification end point 26, and the molten metal 25 cools naturally in the conventional welding method, and the cooling curve becomes as shown in a.

Here, the temperature of the weld bead 25 is from 850°C to 1200°C.
Rapid cooling is performed using the jetted cooling water in the area indicated by mark 4127 in the cabinet.

As an example, a cooling curve when cooling is performed at the position 28 is shown in b.

The distance from the solidification end point on the bead at which the temperature reaches 550°C and 850°C in the case of natural cooling shown in cooling curve a and in the case of rapid cooling shown in cooling curve b is respectively 11. 8 and gb +8.

At this point, the base metal of stainless steel and the weld zone become sensitive5.
The range of exposure to temperatures from 50°C to 850°C is i-t in the case of conventional natural cooling, and l'b -1b in the case of rapid cooling of the present invention, which takes longer than the conventional natural cooling method. .

On the other hand, since the welding speed, that is, the moving speed of the molten pool is constant, the time of exposure to temperatures from 850° C. to 550° C. is shortened in the case of rapid cooling according to the method of the present invention.

This is to suppress sensitization based on the same principle as quenching with water during solution heat treatment to re-dissolve precipitated chromium carbides.

Next, the effect of suppressing sensitization by the welding method of the present invention will be explained by giving an example.

In order to compare the effects of the conventional welding method and the welding method of the present invention on the sensitization of austenitic stainless steel, SU3304m with a plate thickness of 13si+ was prepared using both welding methods.
A butt-welded joint of plates was fabricated, and test pieces were taken from this and intergranular corrosion tests were conducted.

Seven test pieces were taken from the positions shown in FIG. 6 for each of the welded joints manufactured by the conventional welding method and the welded joints manufactured by the method of the present invention.

Here, a test piece t■ was taken from a welded joint made by a conventional welding method.

■■For both tests, 7 each, total of 14, JISGO5
The Strauss test specified in 71 was conducted to investigate intergranular corrosion susceptibility.

In FIG. 3, the test piece 30 is a base material (5US304
) 20 and the boundary between the weld metal 31 (melting line) 32 to 5
Samples were taken from the position marked (2) at the center of the test piece 30.

The dimensions of the test piece SO are 500 (length) x IQIg (width) x
2 wa (thickness).

After completing the Strauss test, bend the test piece in the longitudinal direction with a radius of 5
0 III, the specimen was further divided into two parts in the longitudinal direction, and the cross section was observed with an optical microscope to measure the intergranular corrosion depth.

The results are shown in the table below.

Table 2 Intergranular Corrosion Depth (c) Is the intergranular corrosion depth of Test B sampled from the welded joint produced by the welding method of the present invention overwhelmingly smaller than that of Test specimen A produced by the conventional welding method? , or zero, and test A is judged to be significantly sensitized, whereas test piece B is hardly sensitized, indicating that the welding method of the present invention significantly sensitizes austenitic stainless steel by welding. It was confirmed that it was well suppressed.

In the above embodiment, MIG welding is taken as an example, and during welding, the weld metal changes from 850°C to 12°C at the solidifier welding part and its vicinity.
Next, a welding method for rapidly cooling a part in the range of 00°C was explained.

The present invention is not limited to the above-mentioned embodiments, and the present invention is not limited to the above-mentioned embodiments.In the cooling process after welding, the temperature range in which austenitic stainless steel becomes sensitive is rapidly cooled, so that short β, ? Since the basic principle is to pass the TIG
In the case of welding, the same moving parts as described in (1)-- can be obtained by rapidly cooling in the same manner as in the case of MIG welding.

In addition, when manufacturing ausbunite thread stainless steel structures by welding, multi-layer welding is usually used.
At this time (I), in addition to performing all the welding by the welding method of the present invention, in particular, in the case of a structure made of thick plates, the front surface or both sides of the surface, which are in direct contact with the corrosive environment during use, are It is also effective to apply the welding method of the present invention only to the final layer of the structure in order to increase the reliability of the structure.

〔Effect of the invention〕

As described above, in the welding method for austenitic stainless steel threads, the weld metal is rapidly cooled with running water when the weld metal is in the temperature range of 1200°C to 850°C during solidification and cooling, thereby reducing the effect of welding heat on the austenitic stainless steel thread. This can significantly improve the reliability of austenitic stainless steel welded structures in corrosive environments.

[Brief explanation of drawings]

Fig. 1 is a vertical cross-sectional view showing an embodiment of the bath welding tow according to the present invention, and Fig. 2 is a comparison of the cooling position and cooling characteristics of the welded part according to the invention and conventional welding method 1. The curve diagram shown in correspondence with the figure, and FIG. 6, are cross-sectional views showing the sampling positions of intergranular corrosion test pieces according to the present invention and the conventional welding method. 1... Welding torch body 2... Shield gas supply pipe 3...
・ Nozzle cup 4 ... Flat plate 5 ... Sleeve 6 ... Wire tip 7 ... Consumable electrode wire 8 ... Cooling channel 9 ... ...Jacket 10 ...Inflow hole 11 ...Outflow hole 12 ... Snake blind 16 ...... Accommodation I/J tool 14 ・
... Cooling pipe 15 ... Cooling water supply, j, -s 16 ...
... 11 Output nozzle 17 ... Cooling water 18 ... Brush 19 ... Holder 20 ... Base material 21 ... Welding Metal 22... Shield gas atmosphere 23...
... Arc 24 ...... Welding part 25 ...... Bead 60 ...... Test piece 61 ...... Weld metal 32 ...... Melting line agent Patent Attorney Sa Suyama - Figure 1 Figure 2 Figure 3

Claims (1)

[Claims] 1. When welding austenitic stainless steel, the weld metal solidifies when the weld metal part and the vicinity of the metal part are heated to a temperature range of 850° to 1200°C. A method for welding austenitic stainless steel, the method comprising cooling the weld metal part and the vicinity of the metal part. 2. The method of welding austenitic stainless steel copper according to claim 1, which comprises welding the final dovetail multi-111Ii welding joint on the front side or the front side and back side of the austenitic stainless steel structure. . 3. The method for welding austenitic stainless steel according to claim 1, wherein the weld metal part and the metal part are rapidly cooled by running water. 4. Welding characterized in that a refrigerant jetting nozzle is provided on the welding torch main body along the welding direction side, and a wire plan for shielding the refrigerant is provided between the welding torch main body and the refrigerant jetting nozzle described in Art. Torch. 5. A special feature that uses cooling water as the refrigerant!
Welding torch described in lead enclosure No. 4xA of claim F.