JP2001009589A - Austenitic/ferrite two phase stainless steel welding material, and high chromium steel welding method using it - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a welding material and a welding method which do not cause delayed crack even in welding without preheating or post heat treatment. SOLUTION: This invention relates to a two phase stainless steel welding material to weld a stainless steel including 0.03 wt.% or less C and 727 wt.% Cr, where the product of hydrogen content (Hw, ppm) in the steel of the welding material and the ferrite volume (ω, volume %) of the deposit metal of the welding material is 135 or less. Also, a gas shield arc welding method is provided, wherein the product of the ferrite volume (δw, volume %) of the welding metal part and Hw is adjusted to be 154 or less using the welding material. It is preferable that the welding material includes 0.08% or less C, 1.0% or less Si, 2.5% or less Mn, 0.03% or less P, 0.02% or less S, 18-27% Cr, 5-11% Ni, 4% or less Mo, 2.5% or less W, 0.35% or less N, and the balance of Fe and inevitable impurities.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a high Cr stainless steel having high strength and high corrosion resistance, that is, 0.03% by weight of C.
When welding a steel containing Cr of 7 to 27% by weight (hereinafter, the weight% indicating the content of the chemical composition is simply referred to as “%”), a pre-heat treatment of the base material and a heat treatment after the welding are performed. The present invention relates to an austenitic / ferritic duplex stainless steel welding material free from weld cracking, especially delayed cracking occurring after welding, and a method for welding high Cr stainless steel using the same.

[0002]

2. Description of the Related Art In recent years, with the harsh development conditions of oil fields,
As oil well pipes and steel pipes for line pipes used there,
Austenitic-ferritic duplex stainless steel or 13% Cr martensitic stainless steel having good corrosion resistance and strength has come to be used. In particular, the latter, 13% Cr martensitic stainless steel, can be welded without preheating before welding and heat treatment immediately after welding (hereinafter referred to as post heat treatment) by lowering C and other improvements. Was.

For example, it is highly desirable that welding can be performed at the site of line pipe laying without preheating or post-heating. However, recently, cracks (delayed cracks) that occur after a lapse of a certain time after welding have been found in joints of the above steel types welded without heat treatment.

[0004] The phenomenon of delayed cracking (delayed fracture) in high-strength steel has been known for a long time. This phenomenon is considered to be due to hydrogen embrittlement due to diffusible hydrogen. In particular, in the welded joint portion, a portion having a high welding residual stress in a fusion line (hereinafter, referred to as a bond) and a welding heat-affected zone (hereinafter, referred to as a HAZ), which is a boundary portion between a weld metal and a base metal, is formed as a trap site for diffusible hydrogen. As a result, delayed cracking is likely to occur.

In order to prevent delayed cracking of the weld joint,
Conventionally, the weather at the time of welding construction is selected (for example, welding work is stopped during rainfall), baking of the welding material is performed immediately before welding to remove moisture, and moisture and oil at the welding groove are removed. Further, measures to prevent the intrusion of hydrogen into the weld metal, such as employing a gas shielded arc welding method such as TIG or MIG welding using a bare welding rod or wire having a low hydrogen potential, are taken.

In addition to these, a method of reducing the cooling rate of the weld metal by pre-heat treatment to promote the diffusion of hydrogen from the weld metal, and performing heat treatment immediately after welding to dehydrogenate the weld metal. In addition, measures such as a method of preventing hydrogen accumulation at a trap site are also effective.

However, in order to completely prevent the occurrence of delayed cracking in the welding of the high Cr stainless steel,
Measures are not enough. Further, the heat treatment of (1) and (2) is not preferable in the welding of a base material, which has an advantage that such heat treatment is not necessary.

[0008] If welding of these high Cr stainless steels is performed using a welding material of stainless steel such as Y309L specified in JIS, or an austenitic Ni-base superalloy such as YNiCr-3, preheating may be performed. Also, the occurrence of delayed cracking can be prevented without performing post heat treatment. The reason for this is that the weld metal formed from these welding materials has a face-centered cubic austenitic structure, which has a large solid solubility limit of hydrogen and a low diffusion coefficient of hydrogen, This is considered to be because hydrogen hardly diffuses into the bond or the HAZ from the metal. However, the austenitic welding material as described above has a disadvantage that the strength is relatively low and only an undermatching welded joint can be obtained as compared with the high Cr stainless steel base material.

[0009]

In order to increase the strength of a welded joint, a duplex stainless steel welding material having both corrosion resistance, toughness and strength may be used. However, this is because the amount ratio of the austenite phase is as small as about 1/2 compared with the austenitic welding material described above, and as described above, the effect of preventing diffusion of hydrogen to the bond or HAZ of the austenitic structure is reduced by half, and after welding, May cause cracking.

A first object of the present invention is to provide a welding material for high-strength, high-corrosion-resistant, low-C, high-Cr stainless steel, which can produce delayed cracks even when welded without preheating and post-heat treatment. An object of the present invention is to provide an austenitic / ferritic duplex stainless steel welding material.

A second object of the present invention is to provide a welding method for obtaining a high Cr stainless steel welded joint which does not cause delayed cracking by using the above welding material without performing preheating and post heat treatment. is there.

[0012]

SUMMARY OF THE INVENTION The present inventors have developed a low C, high
Using a duplex stainless steel solid wire, a base stainless steel of Cr stainless steel was subjected to TIG welding without pre-heat treatment, and the form of delayed crack generation was investigated without heat treatment immediately after welding.

As a result, by setting the hydrogen content in the steel of the welding material (wire) in an appropriate range according to the amount of ferrite (volume%) in the weld metal or the weld metal portion, the occurrence of delayed cracking in the welded joint is prevented. We have found that we can do this and completed the present invention.

The gist of the present invention is a welding material of the following (1) and a welding method of the following (2) using the welding material.

(1) By weight%, C: 0.03% or less, Cr: 7 to 2%
A welding material for gas shielded arc welding of stainless steel containing 7%, the hydrogen content in steel (Hw, ppm) of the welding material and the amount of ferrite (δd, where δd ≧ 30% by volume)
Austenitic / ferritic duplex stainless steel welding material that satisfies the formula.

Hw × δd ≦ 135 (1) C: 0.08% or less, Si: 1.0% or less, M
n: 2.5% or less, P: 0.03% or less, S: 0.02% or less, Cr:
It is desirable that the composition contains 18 to 27%, Ni: 5 to 11%, Mo: 4% or less, W: 2.5% or less, and N: 0.35% or less, with the balance being Fe and unavoidable impurities.

(2) By weight%, C: 0.03% or less, Cr: 7 to 2%
Stainless steel containing 7%, C: 0.08% or less, Si: 1.0%
Mn: 2.5% or less, P: 0.03% or less, S: 0.02% or less, Cr: 18 to 27%, Ni: 5 to 11%, Mo: 4% or less, W:
Using a welding material containing 2.5% or less and N: 0.35% or less, with the balance being Fe and unavoidable impurities, the ferrite content (δ
w, where δw ≧ 30% by volume) and the product of the hydrogen content in steel (Hw, ppm) of the welding material are adjusted so as to satisfy the following equation (2). Gas shielded arc welding method for stainless steel.

Hw × δw ≦ 154 (2) The material to be welded (base metal) to be welded by using the welding material of the present invention is “by weight, C: 0.03% or less, Cr: Stainless steel containing 7-27% ". The base steel is roughly classified into a martensitic stainless steel and an austenitic / ferritic duplex stainless steel.

The former representative steel has a Cr content of about 10.5 to 14%.
There is a so-called super martensitic steel containing about 2 to 6% of Ni and about 2.5% or less of Mo. Note that 50
Some steels contain ferrite of not more than about% by volume and should be strictly called martensitic / ferritic steels.

Typical of the latter is JIS SUS329J3
L, SUS329J4L duplex stainless steel, and JIS SUS
There is a so-called super duplex stainless steel in which the contents of N and Mo are increased in 329J4L and an alloy such as W is added to further increase the corrosion resistance. For example, Japanese Patent Application Laid-Open No. 8-260101 proposes an improved material of this type of steel.

Any of the above base steels has high strength and excellent corrosion resistance, and is suitable as a material for oil wells such as line pipes exposed to a corrosive environment containing hydrogen sulfide and carbon dioxide.

[0022]

BEST MODE FOR CARRYING OUT THE INVENTION The present inventors pre-heat treated the above-mentioned martensitic stainless steel (reference B1 in Table 1 below) using a duplex stainless steel solid wire (reference W5 in Table 1 below). TIG welding without applying
When left for 168 hours without heat treatment immediately after welding, delayed cracking was observed.

The delayed crack in the weld joint is a crack caused by hydrogen. The cracks are associated with the material factors of the weld metal and the base steel, and the residual stress generated after welding. Particularly significant is the diffusible hydrogen in the weld metal that enters during welding.

Then, when the hydrogen content in the steel and the diffusible hydrogen content in the weld metal of the above duplex stainless steel solid wire were measured, the hydrogen content in the steel was 6.6 ppm, and the diffusible hydrogen content was 1.99 ml / d. It was 100gr. This was a much higher level than the amount of diffusible hydrogen detected using a conventional austenitic stainless steel wire, which was undetectable. This is for the following reason.

The microstructure of the weld metal formed from the duplex stainless steel welding material naturally exhibits a two-phase structure consisting of a ferrite phase and an austenite phase. For more information,
This two-phase structure is a structure in which an austenite phase generated by solid phase transformation is dispersed in a base of a ferrite phase. Therefore, the diffusion form of hydrogen in duplex stainless steel is
Since it is largely governed by the properties of the mother ground (ferrite phase), it becomes closer to the diffusion form of ferritic stainless steel rather than austenitic stainless steel. That is, in the weld metal portion of the duplex stainless steel, diffusion and migration of hydrogen occur as in the case of the ferrite single phase steel.

As described above, since the solid solubility limit of hydrogen in the austenite phase is large and its diffusion coefficient is small,
Diffusible hydrogen that causes delayed cracking is mainly derived from hydrogen present in the ferrite phase. If the hydrogen potential in the ferrite phase is high, bond or HAZ
It is thought that hydrogen diffuses and accumulates at the trap site (stress concentration portion) of the, causing delayed cracking.

However, the duplex stainless steel wire, like the austenitic steel wire, is subjected to a solution heat treatment at about 1100 ° C. (generally referred to as bright annealing) in order to remove strain generated during wire drawing and to improve the structure. ) Is applied. This heat treatment is performed in a reducing gas atmosphere to prevent oxidation of the wire.
For example, it is carried out in an ammonia decomposition gas (gas of about 75% by volume of hydrogen and about 25% by volume of nitrogen) or a pure hydrogen gas atmosphere. Hydrogen in this atmospheric gas enters the wire during the heat treatment. For this reason, the wire absorbs more hydrogen as the number of bright annealing increases, and as the diameter decreases,
Dissolved hydrogen amount (hydrogen content in steel) increases. Thus, similar to the austenitic steel wire, the conventional duplex stainless steel wire was confirmed to have substantially the same amount of dissolved hydrogen (hydrogen content in steel), but to have a high diffusible hydrogen content.

The present inventor conducted a test shown in Examples described later to quantify the relationship between the hydrogen content in steel of the welding material and the diffusible hydrogen in the weld metal and the relationship between these and delayed cracking. Was.

FIG. 1 shows the relationship between the ratio of the amount of diffusible hydrogen in the weld metal to the hydrogen content in the steel of the welding material and the amount of ferrite in the weld metal. This figure shows the ratio (Hd / Hd) between the diffusible hydrogen (Hd) in the weld metal and the hydrogen content in steel (Hw) of the welding material from the results in Table 3 obtained in Examples described later.
Hw) is plotted on the vertical axis, and the amount of ferrite (δw) in the weld metal is plotted on the horizontal axis. From this figure, the diffusible hydrogen amount (Hd) of the weld metal and the hydrogen content in steel of the welding material (Hw)
(Hd / Hw) is the amount of ferrite (δ
w) increases almost linearly with respect to
The relationship of the equation (a) was obtained.

Hd = Hw × 0.0046 × δw (ppm) (a) Next, a y-type weld crack test using the same 13Cr-based high-strength martensitic stainless steel and duplex stainless steel as base materials ( From the results of JIS Z3158), the effects of the amount of ferrite in the weld metal, the amount of diffusible hydrogen, and the hydrogen content of steel in the welding material on delayed welding cracking were examined.

FIG. 2 is a graph showing the effect of the amount of ferrite in the weld metal and the hydrogen content in steel of the welding material on the delayed welding crack. In the figures, ○ and ● indicate the case where a 13Cr-based high-strength martensitic stainless steel is used as a welding base material, and □ and □ indicate the case where a duplex stainless steel is used as a welding base material. The marks ○ and □ indicate that no crack was observed in the y-shaped weld crack test, and the marks も の and Δ indicate that cracks were observed in the y-shaped weld crack test. As apparent from FIG. 2, those in which cracks were observed and those in which no cracks were observed can be stratified by the curve A. This curve A
As a result of various attempts to specify the following, a relationship graph between the reciprocal (1 / δw) of the amount of ferrite δw of the weld metal portion (1 / δw) and the hydrogen content Hw in the welding material as shown in FIG. It was found that stratification can be performed by the straight line in the equation (b).

1 / δw = Hw / 154 (b) By transforming the equation (b), the following equation (2) is obtained.

Hw × δw ≦ 154 (2) That is, if the product of the ferrite amount δw of the weld metal portion and the hydrogen content Hw in steel of the welding material is smaller than 154, delayed cracking after welding is performed. It can be seen that can be prevented.

Strictly speaking, the weld metal formed using the above welding material must have a two-phase structure in which the amount of ferrite is 30% by volume or more. If the amount of ferrite is less than 30% by volume, it belongs to the broad category of austenitic stainless steel such as JIS Y309MoL, and the high strength advantage of duplex stainless steel is lost. The upper limit of the amount of ferrite is preferably about 75% by volume.

The amount of ferrite in the weld metal is calculated by calculating Ni equivalent and Cr equivalent from the chemical composition of the welding material.
py diagram (ASME Sec.II Part C SFA 5.9 Appendix Fig.A
From 2) can be roughly predicted. However, if the welding material contains components that are not included in the equations for Ni equivalent and Cr equivalent used in these figures, it is difficult to predict the same. Also,
The cooling rate depending on the welding conditions also has a large effect on the amount of ferrite. Therefore, the exact amount of ferrite in the weld metal is
It is desirable to actually measure by a method using a microstructure specified in JIS Z3119. Depending on the ferrite content ratio,
In order to satisfy the above formula (2), the hydrogen content in steel of the welding material H
Adjust w.

The reduction of the hydrogen content in steel of the welding material can be achieved, for example, by performing the final bright annealing using a vacuum heating furnace instead of the conventional heating in an ammonia decomposition gas atmosphere or pure hydrogen gas. . In addition, welding material (wire)
Adhered water evaporates due to the heat generated by the wire during the welding operation, and thus hardly affects the hydrogen content in the steel. However, it is, of course, desirable to prevent moisture in the wire and to prevent wetting during welding.

Further, the relationship between the amount of ferrite δd of the deposited metal and the hydrogen content Hw in the steel, which should be originally provided by the welding material for satisfying the expression (2), was examined. As shown in FIG. 4 and FIG. Δd and H
The smaller the product of the amount of w, the better, and it is necessary to secure at least 135 or less.

Hw × δd ≦ 135 (1) Next, a desirable composition of the welding material will be described.

C: C is an element that stabilizes the austenite phase, like N described later. However, if the content exceeds 0.08%, carbides are liable to precipitate, and the pitting corrosion resistance of the weld metal part is reduced. Therefore, C content is 0.08%
The following is desirable. More desirable is 0.03% or less.

Si: Si is used as a deoxidizing element when melting a welding material. However, during welding, the intermetallic compound (σ
Phase) and reduce the toughness of the weld metal. Therefore, the upper limit is preferably set to 1.0%. The lower limit may be the impurity level, but it should be 0.
1% or more is desirable.

Mn: Mn is used as a deoxidizing element when smelting a welding material, and combines with S to improve hot workability.
It is an element that further increases the solubility of N. But Mn
If the content exceeds 2.5%, the pitting corrosion resistance of the weld metal part is reduced. Therefore, its content is desirably 2.5% or less.
Note that the lower limit is desirably 0.2% or more to ensure the effect of deoxidation.

P: P is an impurity element that is inevitably mixed during the melting of the welding material. If the content exceeds 0.03%, the pitting corrosion resistance and toughness of the weld metal are significantly reduced, so the content should be 0.03% or less.

S: Like P, S is an element that is inevitably mixed during melting of the welding material, and the smaller the better, the better. S lowers the hot workability of steel, making it difficult to roll into a wire, and becomes a sulfide to become a starting point of pitting corrosion.
Impairs the pitting corrosion resistance of the weld metal. Therefore, its content is 0.
Should be no more than 02%.

Ni: Ni stabilizes the austenite phase,
It is an important element that adjusts the balance between the austenite phase and the ferrite phase of the weld metal. However, its content is 5
%, The ferrite phase becomes 75% or more, and an appropriate phase balance cannot be obtained. However, when the Ni content exceeds 11%, precipitation of the σ phase is promoted during welding, and the toughness is reduced.
Therefore, its content is preferably in the range of 5 to 11%.

Cr: Cr is an element that enhances corrosion resistance. If the content is less than 18%, the same corrosion resistance of the weld metal as the base metal cannot be obtained. However, excessive Cr promotes precipitation of an intermetallic compound (such as the σ phase), and lowers workability in wire processing. In addition, a σ phase is precipitated in a weld metal part at the time of welding to reduce toughness. Therefore, its content is desirably in the range of 18 to 27%.

Mo: Mo, like Cr, is an element that improves the pitting corrosion resistance of the weld metal. However, the Mo content is 4.0%
If it exceeds 3, the effect of facilitating the precipitation of the intermetallic compound is strong like Cr, which causes embrittlement of the raw material during production and makes wire processing difficult. Further, at the time of welding, precipitation of the σ phase is promoted in the weld metal portion, and the joint portion is embrittled. Therefore, its content is desirably 4% or less. Especially when added to enhance pitting corrosion resistance and crevice corrosion resistance, the content is 2.
It is desirable to set it to 0 to 4.0%.

W: Like Mo, W is an element that improves the corrosion resistance of the weld metal, especially the resistance to pitting and crevice corrosion, and is a stable oxide that does not reduce pitting resistance even in a low pH environment. To form Further, like Cr, Mo, and N, it is an element that improves pitting corrosion resistance.
The effect of promoting the precipitation of the phase is relatively small. That is, Cr,
The pitting corrosion resistance can be improved by reducing the content of Mo. Therefore, W can be added as needed, and when added, its content is desirably 1.5% or more. However, even if the content exceeds 2.5%, the effect saturates.

N (nitrogen): N forms austenite and improves pitting resistance. When the ferrite-forming elements Cr and Mo are contained in a large amount as in the welding material of the present invention, the N content is set to 0.12 to make the balance between the ferrite phase and the austenite phase of the weld metal part appropriate. % Is desirable. N is Cr, Mo
And W, improve pitting resistance. But 0.35
%, Blowhole defects occur in the weld metal. Moreover, the toughness and corrosion resistance of the weld metal part are degraded due to the formation of nitrides due to the heat effect during welding. Therefore,
The upper limit for the N content should be 0.35%.

[0049]

EXAMPLE A y-type weld crack test plate (sheet thickness: 13 mm) according to JIS Z3158, using 13Cr-based high-strength martensitic stainless steel and duplex stainless steel (both API-X80 grade) shown in Table 1. 25 mm, root gap: 2 mm). Further, as shown in Table 2, an austenitic / ferritic duplex stainless steel wire (diameter = 1.2 mm) in which the amount of hydrogen was changed was automatically fed, and a 1-pass bead was welded by a TIG welding method.

To increase the hydrogen content in the steel of the wire, the wire was subjected to a solution heat treatment in a hydrogen gas atmosphere, and to reduce the hydrogen content in the steel, a dehydrogenation heat treatment was performed in a vacuum atmosphere. . The hydrogen content in the steel of the wire is measured by washing the wire in advance with an organic solvent such as acetone, heating the wire in an inert gas, and detecting the hydrogen released at that time using gas chromatography (inactive gas). (Extraction / dissolution in gas-column decomposition-heat conduction method). What is measured in this way is the total amount of hydrogen dissolved in the wire (hydrogen content in steel). Further, a weld metal was formed on the surface of the austenitic / ferritic duplex stainless steel using the respective wires, and the amount of ferrite was measured from the microscopic structure.

[0051]

[Table 1]

[0052]

[Table 2]

The welding was performed without any pre-heat treatment and immediately after heat treatment, and the welding conditions were set as follows.

Welding current: 180 A, arc voltage: 14 V, welding speed: 10 cm / min, wire feeding speed: 8 g / min, atmosphere: temperature: 20 ° C., relative humidity: 60 %.

Shield gas (including back shield)
Used first-class argon gas specified in JIS K 1105.
The gas flow rate of the welding torch was 10 l / min, and the gas flow rate of the back shield was 5 l / min.

The diffusible hydrogen content (Hd), ferrite content (δw) and delayed cracking of the weld metal were examined from the obtained welds.

[0057]

[Table 3]

The amount of diffusible hydrogen (Hd) was measured by a gas chromatography method specified in JIS Z3118.

Ferrite amount δw of weld metal (volume%)
Was actually measured from the microstructure.

For evaluation of delayed cracking, the specimen after welding was held at room temperature for 168 hours, and then cracks in the cross section were observed. The case where cracks were not recognized was indicated as pass (none), and the case where cracks were recognized was rejected (presence).

From Table 3, the test numbers 1 to 9 of the examples of the present invention show that the product (Hw × δw) of the hydrogen content Hw (ppm) in steel of the welding material and the ferrite content δw (volume%) of the welding metal part is obtained. Left side of equation (154)
Below, no delayed cracking was observed.

On the other hand, the test numbers 10 to 15 of the comparative examples
The product (Hw × δw) of the hydrogen content Hw (ppm) in steel of the welding material and the ferrite content δw (volume%) of the weld metal exceeds 154, and delayed cracking is observed in the base metal HAZ or the bond. Was. This is because the amount of diffusible hydrogen in the weld metal has increased.

[0063]

According to the welding material of the present invention, the hydrogen content in steel is set to a value equal to or less than an allowable upper limit calculated according to the ferrite content of the deposited metal (the product of the hydrogen content in steel of the welding material and the ferrite content). Is 135 or less). By using this welding material, it is possible to prevent the occurrence of delayed cracking in gas shielded arc welding of high-strength, high-corrosion-resistant, high-Cr stainless steel without performing pre-heating and heat treatment immediately after.
Further, since the welding method of the present invention uses a welding material in which the hydrogen content in steel is adjusted according to the amount of ferrite in the weld metal, the occurrence of delayed cracking can be prevented without performing a pre-heat treatment and a heat treatment immediately after.

As a result, the welding method of the present invention can be effectively used for on-site welding of oil country tubular goods and line pipes, for which pre-heat treatment and immediate heat treatment are difficult.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between the ratio of the amount of diffusible hydrogen in a weld metal to the hydrogen content in steel of a welding material and the amount of ferrite in a weld metal.

FIG. 2 is a view showing the effect of the amount of ferrite in a weld metal part and the hydrogen content in steel of a welding material on welding delayed cracking.

FIG. 3 is a graph showing the relationship between the reciprocal of the amount of ferrite in a weld metal part and the hydrogen content in steel of a welding material.

FIG. 4 is a view showing the effect of the amount of ferrite of a deposited metal and the content of hydrogen in steel of a welding material on delayed welding cracking.

FIG. 5 is a graph showing the relationship between the reciprocal of the amount of ferrite in a deposited metal and the hydrogen content in steel of a welding material.

Claims (3)

[Claims] (1) C: 0.03% or less, Cr: 7 to 27% by weight%
Is a welding material for gas-shielded arc welding of stainless steel containing: (a) a hydrogen content (Hw, ppm) in steel of the welding material; and (b) a ferrite amount of a deposited metal of the welding material (δd, where δd ≧ Austenitic-ferritic duplex stainless steel welding material characterized in that the product of the austenitic and ferritic duplex stainless steels satisfies the following formula (1). Hw × δd ≦ 135 ・ ・ ・ ・ ・ (1) 2. The chemical composition in weight%, C: 0.08% or less, S
i: 1.0% or less, Mn: 2.5% or less, P: 0.03% or less, S:
0.02% or less, Cr: 18 to 27%, Ni: 5 to 11%, Mo: 4% or less, W: 2.5% or less, N: 0.35% or less, balance Fe and inevitable impurities Item 4. An austenitic / ferritic duplex stainless steel welding material according to item 1. 3. In% by weight, C: 0.03% or less, Cr: 7 to 27%
Gas-assisted arc welding of stainless steel containing iron, C: 0.08% or less, Si: 1.0% or less, Mn: 2.5%
Below, P: 0.03% or less, S: 0.02% or less, Cr: 18 to 27
%, Ni: 5 to 11%, Mo: 4% or less, W: 2.5% or less,
N: A welding material containing 0.35% or less, with the balance being Fe and unavoidable impurities, and the amount of ferrite (δw, where δw,
≧ 30% by volume) and the hydrogen content (Hw, p
pm) is adjusted so as to satisfy the following equation (2). Hw × δw ≦ 154 (2)