JP2023050553A - Stainless steel weld joint, stainless steel welding method and automatic welding equipment - Google Patents

Abstract

An object of the present invention is to provide a welded joint of stainless steel with excellent weld quality.
A base material made of stainless steel containing ₁₈ % by mass or more of Cr and a weld metal part are provided. The relationship with _B satisfies [N] _W / [N] _B ≥ 1.00, and the number of dissimilar metals involved in the weld metal part is 1 or less per 1000 mm of the length of the weld metal part in the welding direction. , adopting welded joints.
[Selection figure] None

Description

The present invention relates to a stainless steel welded joint, a stainless steel welding method and an automatic welding apparatus.

Duplex stainless steel represented by SUS329J3L has a dual phase structure of ferrite phase and austenite phase with Cr, Ni, Mo and N as main elements, and has excellent strength and corrosion resistance. For this reason, it is applied to various fields including river infrastructure facilities, chemical plants, food manufacturing plants, water storage tanks, and seawater desalination equipment.

In addition, austenitic stainless steels such as SUS312L and SUS836L have high contents of Cr, Ni, Mo, N, etc., and therefore exhibit high corrosion resistance. Therefore, austenitic stainless steels are used in severe corrosive environments with high chloride ion concentrations such as offshore structures, chemical plants, and food tanks.

Non-consumable electrode welding methods such as TIG welding and plasma welding are used as welding methods for constructing stainless steel welded structures. Non-consumable electrode welding is inferior to consumable electrode welding in terms of welding efficiency. It is suitable for the construction of welded structures with strict quality requirements because it can form high-quality weld metal with few defects and bubble defects.

Many of the above-mentioned duplex stainless steels and austenitic stainless steels contain N as a main element. As a result, the N content of the weld metal becomes lower than that of the base metal, which may lead to deterioration of mechanical properties and corrosion resistance. In order to prevent this, there is a method of non-consumable electrode welding using a shielding gas mixed with nitrogen.

As an example of a welding method for duplex stainless steel, Patent Document 1 below discloses that when welding duplex stainless steel by a non-consumable electrode type welding method, the torch shield gas, back shield gas and after shield gas are 60 to 100. % nitrogen is described.

JP 2021-74738 A

However, when non-consumable electrode type gas-shielded arc welding is performed using a torch shield gas containing nitrogen as a main component, there is a problem that the electrode is rapidly melted and consumed. In addition, if the melted and consumed tungsten electrode is mixed with the weld metal, a welding defect such as entrainment of dissimilar metals will occur, and the quality of the welded joint will be deteriorated.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a welded joint of stainless steel with excellent weld quality. Another object of the present invention is to provide a stainless steel welding method and an automatic welding apparatus that suppress the melting consumption of the electrode and prevent the quality of the welded portion from deteriorating.

In order to solve the above problems, the present invention employs the following configuration.
[1] A base material made of stainless steel containing 18% by mass or more of Cr and a welded metal part,
The relationship between the N content [N] _W of the weld metal part and the N content [N] _B of the base metal satisfies [N] _W / [N] _B ≥ 1.00,
A welded joint of stainless steel, wherein the number of dissimilar metals involved in the welded metal portion is 1 or less per 1000 mm of the length of the welded metal portion in the welding direction.
[2] The welded joint of stainless steel according to [1], wherein the dissimilar metal is tungsten.
[3] Using a stainless steel containing 18% by mass or more of Cr as a base material, using a welding torch capable of holding an electrode and ejecting a torch shield gas, and using a welding torch without using a filler material. A method of welding by a consumable electrode gas shielded arc welding method,
The torch shield gas is a gas containing 65% by volume or more and 100% by volume or less of nitrogen,
The electrode is a tungsten electrode,
Reverse welding in which the direction of the welding torch during welding is directed in the direction opposite to the direction of welding,
A method for welding stainless steel, wherein the backward movement angle of the electrode is 5° or more and 60° or less.
[4] The method for welding stainless steel according to [3], wherein the backward movement angle of the electrode is 5° or more and 30° or less.
[5] The stainless steel welding method according to [3] or [4], wherein a pure tungsten electrode or a tungsten electrode containing oxide is used as the electrode.
[6] The stainless steel according to any one of [3] to [5], wherein the atmosphere of the welded portion after welding is an after-shield gas atmosphere containing 65% by volume or more and 100% by volume or less of nitrogen. Welding method.
[7] Any one of [3] to [6], wherein the atmosphere on the back side of the welded part during and after welding is a back shield gas atmosphere containing 65% by volume or more and 100% by volume or less of nitrogen. The method for welding stainless steel according to .
[8] An automatic welding apparatus for welding a base material made of stainless steel containing 18% by mass or more of Cr by a non-consumable electrode gas shielded arc welding method without using a filler material. hand,
a welding torch holding a tungsten electrode as an electrode and capable of ejecting a torch shield gas;
a shield gas supply unit that supplies a gas containing 65% by volume or more and 100% by volume or less of nitrogen as the torch shield gas to the welding torch,
The automatic welding device, wherein the welding torch is oriented in a direction opposite to the advancing direction of welding, and the backward movement angle of the electrode is set within a range of 5° or more and 60° or less.
[9] The automatic welding device according to [8], wherein the backward movement angle of the electrode is in the range of 5° or more and 30° or less.
[10] The automatic welding device according to [8] or [9], wherein the electrode is a pure tungsten electrode or a tungsten electrode containing oxide.
[11] A first atmosphere adjustment unit is further provided for making the atmosphere of the welded portion after welding into an after-shield gas atmosphere containing 65% by volume or more and 100% by volume or less of nitrogen, [8] to [ 10] The automatic welding device according to any one of items.
[12] A second atmosphere adjustment unit is further provided for changing the atmosphere on the back side of the welded part during and after welding to a back shield gas atmosphere containing 65% by volume or more and 100% by volume or less of nitrogen. , the automatic welding device according to any one of [8] to [11].

ADVANTAGE OF THE INVENTION According to this invention, the welded joint of stainless steel which is excellent in the quality of a weld can be provided.
Further, according to the present invention, it is possible to provide a stainless steel welding method and an automatic welding apparatus that suppress the melting consumption of the electrode and prevent the quality of the welded portion from deteriorating.

BRIEF DESCRIPTION OF THE DRAWINGS The schematic diagram which shows an example of the automatic welding apparatus which is embodiment of this invention. The schematic diagram which shows another example of the automatic welding apparatus which is embodiment of this invention. BRIEF DESCRIPTION OF THE DRAWINGS The schematic diagram explaining the welding method of the stainless steel which is embodiment of this invention. BRIEF DESCRIPTION OF THE DRAWINGS The schematic diagram explaining the welding method of the stainless steel which is embodiment of this invention.

The inventors of the present invention have investigated the cause of the rapid melting consumption of the electrode when non-consumable electrode type gas-shielded arc welding is performed using a torch shield gas containing nitrogen as a main component. In TIG welding, which is a type of non-consumable electrode gas shielded arc welding, nitrogen is known to have a higher specific heat than argon, which has been conventionally used as a shielding gas. Due to this difference in specific heat, in non-consumable electrode gas-shielded arc welding using a nitrogen-based gas, the arc becomes tighter and the energy density increases compared to the conventional case of using argon. Moreover, the flow velocity of the plasma airflow generated around the arc also increases. For this reason, it has been found that spatter tends to fly from the molten pool and a large amount of metal vapor tends to be generated. Here, in the conventional non-consumable electrode type gas-shielded arc welding, welding is performed with the welding torch standing vertically, and the electrode is positioned directly above the molten pool. For this reason, in non-consumable electrode type gas shielded arc welding using a gas containing nitrogen as the main component as the shielding gas, metal derived from spatter and metal vapor adheres to the electrode surface during welding, reducing the electron emission efficiency of the electrode. was found to decrease, resulting in an increase in the electrode temperature, leading to melting and consumption of the electrode.

Therefore, as a result of intensive studies by the present inventors, backward welding in which welding is performed while the direction of the welding torch is directed in the direction opposite to the direction of welding progress, and the backward angle of the electrode is set to 5 ° or more and 60 ° or less. It has become clear that adhesion of metal originating from spatter and metal vapor to the electrode surface is avoided, melting consumption of the electrode is reduced, dissimilar metal entrainment into the weld metal is reduced, and welding quality is improved.

Hereinafter, a stainless steel welded joint, a stainless steel welding method, and an automatic welding apparatus according to embodiments of the present invention will be described.
FIG. 1 shows an automatic welding device 1 of this embodiment. The automatic welding apparatus 1 shown in FIG. 1 includes a welding torch 2, a shield gas supply section 3 for supplying a torch shield gas to the welding torch 2, a power source (not shown), and a control section (not shown).

Further, the automatic welding apparatus 1 shown in FIG. 1 is provided with feeding means 4 for feeding the base material 11 made of stainless steel in the direction opposite to the welding direction (direction of arrow A in FIG. 1). The conveying means 4 may be a conveying roller as shown in FIG. 1, or a conveying stage on which the base material 11 is placed and movable. Further, instead of the conveying means 4 for the base material 11, driving means for moving the welding torch 2 in the welding direction (direction of arrow B in FIG. 1) may be provided. The operation of the conveying means 4 or the driving means is controlled by a control section.

The welding torch 2 is equipped with an electrode 5 and a gas nozzle 6 capable of ejecting a torch shield gas. The welding torch 2 is provided with a hollow cylindrical torch housing 21 with one end 2 a open, and an electrode 5 is held in a hollow portion 22 of the torch housing 21 . A hollow portion 22 of the torch housing 21 is used as the gas nozzle 6 . By supplying the torch shield gas from the shield gas supply unit 3 , the torch shield gas can be jetted from the tip of the welding torch 2 .

A power source (not shown) is connected to the electrode 5 . The power supply is connected to the control section, and the operation of the power supply is controlled by the control section. Electric power supplied from the power supply causes the electrode 5 to generate an arc from its tip.

The electrode 5 is a tungsten electrode. The tungsten electrode may be either a pure tungsten electrode or a tungsten electrode containing oxide, and the tungsten electrode containing oxide is preferable because it has excellent electron emission capability. Examples of oxides include lanthana (lanthanum oxide), ceria (cerium oxide), thoria (thorium oxide), and the like. The content of these oxides is in the range of 0.1 to 5% by mass.

In the automatic welding device 1, the tip of the welding torch 2 is oriented in a direction opposite to the direction in which welding proceeds (the direction of arrow B in FIG. 1). Further, the backward movement angle of the electrode 5 is set within a range of 5° or more and 60° or less. The attitude of the welding torch 2 and the backward movement angle of the electrode 5 will be described later.

A shield gas supply unit 3 supplies a torch shield gas to the welding torch 2 . As the torch shield gas, a gas containing 65% by volume or more and 100% by volume or less of nitrogen is preferable, and a mixed gas containing 65% by volume or more and less than 100% by volume of nitrogen and the balance being argon is more preferable. % or more and less than 100% by volume of nitrogen with the remainder being argon, more preferably nitrogen gas with a nitrogen content of 100% by volume. The shield gas supply unit 3 is connected to the control unit and its operation is controlled by the control unit.

The control unit automatically welds the base material 11 by the non-consumable electrode gas-shielded arc welding method by controlling the shield gas supply unit 3, the power supply, the conveying means 4, or the driving means.

Further, the automatic welding device 1 of the present embodiment may be provided with a first atmosphere adjustment section 41 and a second atmosphere adjustment section 51 as shown in FIG. Although both the first atmosphere adjustment section 41 and the second atmosphere adjustment section 51 are illustrated in FIG. 2, either the first atmosphere adjustment section 41 or the second atmosphere adjustment section 51 is provided. good too. The first atmosphere adjustment unit 41 and the second atmosphere adjustment unit 51 are connected to a control unit (not shown), and their operations are controlled by the control unit.

The first atmosphere adjustment unit 41 is composed of a first gas box 42 and a first supply unit 43 that supplies after-shield gas to the first gas box 42 . The first gas box 42 is arranged at a position covering the welded portion after welding from the surface 11a side of the base material 11 . The surface 11 a of the base material 11 is the surface facing the welding torch 2 . The first gas box 42 is a hollow box-shaped body and is open on the side of the base material 11 . By supplying the after-shield gas to the inside of the first gas box 42, the atmosphere on the surface 11a side of the welded portion after welding can be changed to the after-shield gas atmosphere. The after-shield gas is a gas containing 65% by volume or more and 100% by volume or less of nitrogen. As a result, the welded portion immediately after welding is brought into an after-shield gas atmosphere, contact of the welded portion with the outside air is avoided, and oxidation of the welded portion is reduced.

The second atmosphere adjustment section 51 is composed of a second gas box 52 and a second supply section 53 that supplies back shield gas to the second gas box 52 . The second gas box 53 is arranged at a position that covers the welded portion during and after welding from the back surface 11b side of the base material 11 . The back surface 11b of the base material 11 is the opposite surface of the front surface 11a. The second gas box 52 is a hollow box-shaped body and is open on the side of the base material 11 . By supplying the back shield gas to the inside of the second gas box 52, it is possible to change the atmosphere on the back surface 11b side of the welded portion during and after welding to a back shield gas atmosphere. The back shield gas is a gas containing 65% by volume or more and 100% by volume or less of nitrogen. Instead of the second gas box 52, a gas nozzle that blows back shield gas toward the rear surface 11b of the welded portion during and after welding may be used.

The after shield gas and the back shield gas may be a mixed gas containing 65% by volume or more and less than 100% by volume of nitrogen and the balance being argon, and containing 95% by volume or more and less than 100% by volume of nitrogen. It may be a mixed gas in which the balance is argon, or a nitrogen gas with a nitrogen content of 100% by volume.

The automatic welding apparatus 1 of the present embodiment is capable of automatic welding by mechanically or electrically controlling necessary welding parameters. Further, the automatic welding device 1 of the present embodiment is capable of fully automatic welding in which the welding operation is not interfered by the welding operator. Furthermore, the automatic welding device 1 of this embodiment is not limited to the form shown in FIG. 1 or 2, and may perform welding while controlling the welding torch 2 by a robot device.

Next, a method for welding stainless steel according to the present embodiment will be described with reference to FIGS. 1 to 4. FIG. The welding method of this embodiment can be carried out, for example, by the automatic welding device 1 shown in FIG. 1 or FIG.

The stainless steel welding method of the present embodiment uses a stainless steel containing 18% by mass or more of Cr as a base material 11, uses a welding torch 2 that holds an electrode 5 and can eject a torch shield gas, and welds. In this method, the base material 11 is welded by a non-consumable electrode gas-shielded arc welding method without using any material. Specifically, a TIG welding method can be applied as the non-consumable electrode gas-shielded arc welding method.

The base material 11 is made of stainless steel containing 18% by mass or more of Cr. Among stainless steels, stainless steels containing an austenite phase in the metal structure are particularly preferable, and more specifically, austenitic stainless steels or ferrite-austenite duplex stainless steels are preferable.

In this embodiment, the shape of the base material 11 may be a plate material, a pipe material, a bar material, a wire material, or the like, and is not particularly limited. However, since the welding method of the present embodiment performs welding without using a filler material, it is preferable that the plate thickness of the plate material, the wall thickness of the pipe material, and the diameters of the bar and wire are small. For example, in the case of a plate material, a steel plate having a thickness of 6 mm or less is preferable. Moreover, in the case of pipe material, a steel pipe having a wall thickness of 3 mm or less is preferable. In the case of rods or wires, those with a diameter of 6 mm or less are preferred.

Also, the welding method of the present embodiment may be directed to, for example, butt welding or fillet welding. In the case of butt welding, butt welding of steel plates and butt welding of ends of steel pipes can be exemplified.

Moreover, in the welding method of this embodiment, the shape of the groove need not be particularly limited.

In the welding method of this embodiment, the electrode 5 is a tungsten electrode. The tungsten electrode may be a pure tungsten electrode or a tungsten electrode containing oxide. By using a tungsten electrode having excellent electron emission efficiency as the electrode, an arc can be stably generated.

In the welding method of the present embodiment, the torch shield gas is gas containing 65% by volume or more and 100% by volume or less of nitrogen. Preferably, the torch shield gas is a mixed gas of 65% by volume or more and less than 100% by volume of nitrogen and the balance of argon, more preferably 95% by volume or more and less than 100% by volume of nitrogen and the balance of argon. More preferably, nitrogen gas with a nitrogen content of 100% by volume is used. These gases may contain impurities. A more preferable gas is pure nitrogen gas (purity of 99.995% or more (JIS K 1107:2005)) because it is easily available.

In the welding method of this embodiment, as shown in FIGS. is 5° or more and 60° or less, more preferably 5° or more and 30° or less. As shown in FIG. 4, a molten pool P is formed by an arc A emitted from the electrode 5. By performing welding with the welding torch 2 as backward welding, the electrode 5 moves toward the molten pool as the welding progresses. You will leave P. In addition, the electrode 5 is positioned obliquely above the molten pool P by tilting the electrode 5 by 5° or more in the direction in which welding proceeds. As a result, the spatter S and metal vapor V generated from the molten pool P are less likely to adhere to the surface of the electrode 5 .

If the backward angle θ of the electrode 5 is less than 5°, adhesion of spatter S and metal vapor V to the surface of the electrode 5 cannot be avoided even if backward welding is performed. Further, if the backward movement angle θ of the electrode 5 exceeds 60°, the reaching distance of the arc A from the electrode 5 to the surface 11a of the base material 11 becomes long, and sufficient heat is not transmitted to the base material 11, making welding difficult. Become. Therefore, the retreating angle θ of the electrode 5 is preferably in the range of 5 to 60°. A range of 5 to 30° is preferable.

Further, in the present embodiment, in order to further suppress the decrease in the amount of nitrogen in the weld metal, the atmosphere of the welded portion after welding is set to an after-shield gas atmosphere containing 65% by volume or more and 100% by volume or less of nitrogen. is preferred. Furthermore, the atmosphere on the back side of the weld zone during and after welding may be a back shield gas atmosphere containing 65% by volume or more and 100% by volume or less of nitrogen. It is preferable that the range of the back shield gas atmosphere or the after shield gas atmosphere includes the weld metal having a temperature of 1000° C. or higher. As a result, the release of nitrogen from the weld metal and the absorption of nitrogen from the atmosphere are brought into equilibrium, thereby suppressing the decrease in the amount of nitrogen in the weld metal.

As described above, in the welding method of the present embodiment, the torch shield gas is a gas containing 65% by volume or more and 100% by volume or less of nitrogen, thereby dissociating N ₂ in the arc and forming a single unit. Atomic nitrogen (N) is absorbed into the molten metal, increasing the N content of the weld metal. In addition, since the _N2 partial pressure in the atmosphere increases, the release of N from the outermost surface of the weld metal due to diffusion in the solid phase is suppressed in the cooling process after solidification. As the _N2 partial pressure increases, the release of N from the outermost surface of the weld metal is suppressed. As a result, it is possible to suppress the release of nitrogen from the weld metal during welding, thereby suppressing deterioration in the corrosion resistance of the weld metal. In addition, the mixed gas of 2 to 5% by volume of N ₂ and the balance of Ar, which is sometimes used for TIG welding, cannot sufficiently increase the N content of the weld metal because the N ₂ concentration is low.

On the other hand, in non-consumable electrode gas shielded arc welding using a gas containing 65% by volume or more of nitrogen as the torch shield gas, the arc is constricted and the energy density increases. Moreover, the flow velocity of the plasma airflow generated around the arc also increases. For this reason, spatter tends to fly out from the molten pool, and a large amount of metal vapor tends to be generated. When metal originating from sputtering or metal vapor adheres to the surface of the electrode 5, the electron emission efficiency of the electrode 5 decreases, the electrode temperature rises, and the electrode 5 may be melted and consumed. Therefore, in the present embodiment, backward welding is performed while setting the backward angle θ of the electrode 5 to 5° or more and 60° or less. As a result, the spatter S and the metal vapor V generated from the molten pool P are less likely to adhere to the surface of the electrode 5, and the temperature rise of the electrode is suppressed without lowering the electron emission efficiency of the electrode. is suppressed.

In addition, by setting the atmosphere of the weld metal during or after welding to a back shield gas atmosphere or after shield gas atmosphere, the release of nitrogen from the weld metal, which is in a high temperature state immediately after welding, is suppressed, and the austenite stabilizing element nitrogen becomes difficult to decrease, and deterioration of the mechanical properties and corrosion resistance of the weld metal can be suppressed.

Next, a stainless steel welded joint manufactured by the welding method of the present embodiment will be described.
The welded joint of the present embodiment includes a base material made of _stainless steel containing 18% by mass or more of Cr, and a weld metal part. The relationship with the content [N] _B satisfies [N] _W / [N] _B ≥ 1.00, and the number of dissimilar metals with a diameter of 0.5 mm or more involved in the weld metal part is One or less per 1000 mm of length in the welding direction. The dissimilar metal is tungsten.

In the welding method of this embodiment, a gas containing 65% by volume or more and 100% by volume or less of nitrogen is used as the torch shield gas. Therefore, N is prevented from evaporating from the molten metal that occurs in non-consumable electrode welding using argon as a torch shield gas, and rather N is supplied to the molten metal from the torch shield gas. As a result, the relationship between the N content [N] _W of the weld metal and the N content [N] _B of the base metal satisfies [N] _W /[N] _B ≥ 1.00. Even if there is concern about deterioration in the properties of the weld metal (for example, deterioration in strength or corrosion resistance) due to a decrease in the content, the deterioration of these properties is prevented. Further, in the welding method of the present embodiment, as described above, the melting consumption of the electrode 5 is suppressed. Therefore, in the welded joint of the present embodiment, part of the melted electrode 5 is not mixed into the weld metal. For the above reasons, the welded joint of the present embodiment can remarkably improve the quality of the weld metal.

The welded joint of the present embodiment may be a welded joint formed by butt welding, or may be a joint welded by lap welding, fillet welding, or the like. Examples of welded joints formed by butt welding include welded joints in which steel plates are butt-welded, and welded joints in which ends of steel pipes are butt-welded.

As described above, the base material 11 in the welding method and the welded joint of the present embodiment is preferably stainless steel containing 18% by mass or more of Cr, and is preferably stainless steel containing an austenite phase in the metal structure. Specifically, austenitic stainless steel or ferrite-austenitic duplex stainless steel is preferred.

Of the chemical components of the austenitic stainless steel and the ferrite-austenitic duplex stainless steel, chemical components other than Cr are not particularly limited.

In stainless steel, Cr has the effect of increasing the corrosion resistance of the passive film of stainless steel. In addition, when the composition of the torch shield gas in the non-consumable electrode gas shielded arc welding method is N ₂ : 60 to 100% by volume, the N content in the weld metal significantly increases, resulting in pore defects (blow holes, porosities) are likely to occur. Cr has the effect of increasing the solid solution amount of N in the ferrite phase, suppressing solidification microsegregation of N, and suppressing pore defects. These effects cannot be obtained sufficiently if the Cr content is less than 18%, so the Cr content is made 18% by mass or more. More preferably, it is 20% by mass or more. Although the upper limit of the Cr content is not particularly specified, it is preferably 28% by mass or less from the viewpoint of cost.

As described above, alloying elements other than Cr are not particularly limited, but duplex stainless steels to which the present embodiment can be applied include, for example, C: 0.001 to 0.030%, Si: 1.0% by mass. 5% or less, Mn: 0.1 to 6.0%, P: 0.04% or less, S: 0.0100% or less, Ni: 0.1 to 8.0%, Cr: 18 to 28%, Mo : 0.1 to 5.0%, Cu: 0.1 to 2.0%, N: 0.1 to 0.4%, and the balance being Fe and impurities. This chemical composition is merely an example, and the present embodiment is not limited thereto.

Further, the austenitic stainless steel to which the present embodiment can be applied includes, for example, Cr: 18 to 30%, Ni: 6 to 30%, Mo: 0.01 to 8%, N: 0.001 to 0.4%, the balance being Fe and impurities, and optionally C: 0.001 to 0.10%, Si: 0.1 to 4.0%, Mn: 0.1 to 8.0%, P: 0.04% or less, S: 0.01% or less, Cu: 0.01 to 4.00%.

As described above, according to the present embodiment, it is possible to provide a welded joint of stainless steel with excellent weld quality.
Further, according to the present embodiment, it is possible to provide a stainless steel welding method and an automatic welding apparatus that suppress the melting consumption of the electrode and prevent the quality of the welded portion from deteriorating.

EXAMPLES The present invention will be described in more detail below with reference to examples. The invention is not limited to these examples.

A stainless steel having the chemical composition shown in Table 1 is melted in a laboratory, hot forged, hot rolled, cold rolled, and solution heat treated to obtain a plate with a thickness of 2 mm, a width of 50 mm, and a length of 600 mm for welding. A steel plate (base material) was produced.

At the center of the width of the steel plate for welding, under the conditions shown in Table 2, a TIG welding method using a tungsten electrode without using a welding material (filler material) is performed so that the total weld length is 1000 mm. plate welded. Welding was backward welding, and the reverse angle of the electrode, the welding current and the welding speed were as shown in Table 2. The tungsten electrode was a tungsten electrode containing 2% lanthana. The spraying range of the back shield gas and the after shield gas was set to include at least the weld metal having a temperature of 1000° C. or higher.

The N content of each of the base metal and the weld metal was measured in accordance with JIS G 1228: 1997 Annex 4 (normative) inert gas fusion-thermal conductivity method (1), and the N content of the weld metal part A ratio [N] _W /[N] _B between the amount [N] _W and the N content [N] _B of the base metal was obtained.

[Electrode melting consumption]
After TIG welding was performed under the conditions shown in Table 2 so that the total welding length was 1000 mm, the tip of the electrode was observed with a microscope at a magnification of 50. When no melting deformation occurred at the tip of the electrode, it was judged that electrode consumption did not occur, and was marked with "◯". When melting deformation occurred, it was marked as “x”.

[Involvement of dissimilar metals]
The presence or absence of dissimilar metal entrapment in the weld metal was analyzed by an X-ray transmission test. A test was performed on a weld metal with a length of 1000 mm, and when there was 1 or less dissimilar metals with a diameter of 0.5 mm or more involved, it was judged that almost no entrainment occurred, and was rated as "◯". When more than one dissimilar metal with a diameter of 0.5 mm or more was involved, it was marked as "x".

Table 2 shows the results.

As shown in Table 2, in all of Invention Examples 1 to 16, the torch shield gas is a gas containing 65% by volume or more and 100% by volume or less of nitrogen, and the retreating angle of the electrode is in the range of 5° or more and 60° or less. As a result, consumption melting of the electrode was prevented, and entanglement of dissimilar metals in the weld metal portion was suppressed. In addition, in Examples 1 to 16, by using a gas containing 65% by volume or more of nitrogen as the torch shield gas, the N content [N] _W of the weld metal portion is changed from the N content [N] _B of the base metal. 1.00 times or more ([N] _W /[N] _B ≧1.00), and no deterioration in the properties of the weld metal was confirmed.

On the other hand, in Comparative Examples 17 to 20, the torch shield gas was 100% by volume nitrogen gas, and the retreating angle of the electrode was 0°, so dissimilar metals were involved due to consumption melting of the tungsten electrode, and welding defects increased. bottom.

DESCRIPTION OF SYMBOLS 1... Automatic welding apparatus, 2... Welding torch, 3... Shield gas supply part, 4... Conveying means, 5... Electrode, 6... Gas nozzle, 11... Base material, 41... First atmosphere adjustment part, 51... Second atmosphere adjustment Department.

Claims (12)

A base material made of stainless steel containing 18% by mass or more of Cr and a welded metal part,
The relationship between the N content [N] _W of the weld metal part and the N content [N] _B of the base metal satisfies [N] _W / [N] _B ≥ 1.00,
A welded joint of stainless steel, wherein the number of dissimilar metals involved in the welded metal portion is 1 or less per 1000 mm of the length of the welded metal portion in the welding direction. A stainless steel weld joint according to claim 1, wherein said dissimilar metal is tungsten. Using a stainless steel containing 18% by mass or more of Cr as a base material, using a welding torch capable of holding an electrode and ejecting torch shield gas, and using a non-consumable electrode type without using a filler material A method of welding by a gas shielded arc welding method,
The torch shield gas is a gas containing 65% by volume or more and 100% by volume or less of nitrogen,
The electrode is a tungsten electrode,
Reverse welding in which the direction of the welding torch during welding is directed in the direction opposite to the direction of welding,
A method for welding stainless steel, wherein the backward movement angle of the electrode is 5° or more and 60° or less. 4. The method of welding stainless steel according to claim 3, wherein the backward movement angle of the electrode is 5[deg.] or more and 30[deg.] or less. The method of welding stainless steel according to claim 3 or 4, wherein a pure tungsten electrode or a tungsten electrode containing oxide is used as the electrode. The stainless steel welding method according to any one of claims 3 to 5, wherein the atmosphere of the welded portion after welding is an after-shield gas atmosphere containing 65% by volume or more and 100% by volume or less of nitrogen. 7. The atmosphere of the back side of the welded part during and after welding is a back shield gas atmosphere containing 65% by volume or more and 100% by volume or less of nitrogen. Welding method of stainless steel. An automatic welding apparatus for welding a base material made of stainless steel containing 18% by mass or more of Cr by a non-consumable electrode gas shielded arc welding method without using a filler material,
a welding torch holding a tungsten electrode as an electrode and capable of ejecting a torch shield gas;
a shield gas supply unit that supplies a gas containing 65% by volume or more and 100% by volume or less of nitrogen as the torch shield gas to the welding torch,
The automatic welding device, wherein the welding torch is oriented in a direction opposite to the advancing direction of welding, and the backward movement angle of the electrode is set within a range of 5° or more and 60° or less. 9. The automatic welding device according to claim 8, wherein the backward movement angle of said electrode is in the range of 5[deg.] or more and 30[deg.] or less. The automatic welding device according to claim 8 or 9, wherein the electrode is a pure tungsten electrode or a tungsten electrode with oxide. 11. The method according to any one of claims 8 to 10, further comprising a first atmosphere adjustment unit for adjusting the atmosphere of the welded portion after welding to an after-shielding gas atmosphere containing 65% by volume or more and 100% by volume or less of nitrogen. The automatic welding device according to any one of the items. A second atmosphere adjustment unit is further provided for changing the atmosphere on the back side of the welded part during and after welding to a back shield gas atmosphere containing 65% by volume or more and 100% by volume or less of nitrogen. The automatic welding device according to any one of claims 8 to 11.

Images