JP2010121190A - Austenitic stainless welded pipe for high-pressure hydrogen transport, and method for producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an austenitic stainless steel welded pipe which has excellent hydrogen embrittlement resistance and salt corrosion resistance at normal temperature, and is suitable for the transport of high-pressure hydrogen, e.g., under about 40 MPa without depending on the remarkable enlargement of thickness and diameter. <P>SOLUTION: The austenitic stainless steel welded pipe for high-pressure hydrogen transport has a composition comprising, by mass%, &le;0.15% C, &le;4.0% Si, &le;3.0% Mn, &le;0.10% P, &le;0.03% S, 6 to 20% Ni, 14 to 28% Cr and &le;0.25% N, and the balance Fe with inevitable impurities, wherein M value shown by expression; M=551-462(C+N)-9.2Si-8.1Mn-29(Ni+Cu)-13.7Cr-18.5Mo is controlled to &le;-100, and, D value shown by expression D=(Cr+1.5Si+0.5Nb+Mo)-(Ni+0.5Mn+30C+30N) is controlled to 6 to 10. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to an austenitic stainless steel welded pipe for transporting high-pressure hydrogen having excellent hydrogen embrittlement resistance against high-pressure hydrogen gas of 0.1 MPa or more and excellent corrosion resistance, and a method for producing the same.

  In recent years, hydrogen has attracted attention as a clean energy source due to global environmental conservation problems, and fuel cells have been actively studied for high-efficiency power generation due to the problem of fossil fuel depletion. Fuel cells are roughly classified into stationary types and portable types. In the stationary type, fossil fuel is reformed immediately before use in the stationary type, and in the portable type, hydrogen is pressurized in a high-pressure vessel, liquefied in a low-temperature vessel, occluded in a hydrogen-absorbing alloy, and cyclohexane, etc. The use of hydrogen-containing materials as a hydrogen source is becoming mainstream.

  A typical example of the portable type is a fuel cell vehicle. In order to efficiently transport stored or filled hydrogen to the battery, it is preferable to handle it at a high pressure of 1 MPa or more. In plants that handle hydrogen, thick large-diameter pipes such as Cr-Mo steel and Mn steel have been used for piping. Since these steels have low strength, it is necessary to increase the wall thickness, but they are not necessarily the most suitable materials for automotive use in terms of space saving and weight reduction.

  In order to reduce the thickness and weight of piping applied to high-pressure hydrogen gas, a material with excellent resistance to hydrogen embrittlement and high strength is required. For pipes that come into contact with high-pressure hydrogen gas, ordinary steel, ferritic stainless steel, and martensitic stainless steel with a body-centered cubic structure are not suitable because of their high hydrogen diffusion coefficient and low hydrogen solubility. , Adopting austenitic stainless steel with face-centered cubic structure is advantageous. Therefore, it has been studied to use austenitic steel, which is capable of higher strength than the Cr-Mo steel and Mn steel, and is advantageous in hydrogen embrittlement resistance, for a hydrogen storage tank. Patent Documents 1 and 2 show a technique using high Mn austenitic steel. Patent Document 3 discloses an austenitic stainless steel to which Mn, V, and N are added. Patent Document 4 discloses a technique for controlling texture. Patent Document 5 discloses a method of covering aluminum on a portion in contact with hydrogen.

International Special Publication No. 2004/83477 Pamphlet JP 2007-126688 A International Publication No. 2004/83476 Pamphlet International Special Publication No. 2004/111285 Pamphlet JP 2004-324800 A

  On the other hand, when considering automotive applications, the pipe in the part after being depressurized from the high-pressure tank may be mounted on the site of the conventional exhaust gas path. It is preferable to have sufficient durability. However, existing austenitic stainless steels with improved water brittleness resistance do not always have satisfactory properties from the viewpoint of resistance to stress corrosion cracking caused by salt damage corrosion. In addition, it is preferable to use an inexpensive welded pipe because the use of a seamless pipe having no welded portion increases the cost. In the methods of Patent Documents 1 to 5, although the manufacturing method of the pipe is not specified, since a high pressure of 70 to 120 MPa is assumed at the maximum, the method itself tends to cause an increase in cost and is further simplified. It is desired to establish a technology that imparts excellent hydrogen embrittlement resistance by a simple method.

  Many austenitic stainless steels with improved resistance to stress corrosion cracking have been developed so far, and JIS has established SUS315Jl and SUS315J2. However, the hydrogen embrittlement resistance of these austenitic stainless steels is not necessarily sufficient depending on the alloy composition according to the study by the inventors, and in particular, the hydrogen embrittlement resistance of welded pipes is not always satisfactory. I understood. For this reason, it can be said that it is difficult to directly apply these welded pipes to, for example, a vehicle-mounted member.

  The present invention provides an austenitic stainless steel welded tube excellent in hydrogen embrittlement resistance and salt corrosion resistance at room temperature, and suitable for transporting high-pressure hydrogen of, for example, about 40 MPa without relying on a large increase in diameter. It is to provide.

  As a result of various studies, the inventors have used austenitic stainless steels whose components are strictly adjusted to a specific range, and severely restricted the structure of the welded pipe, thereby suppressing the increase in cost as much as possible, and preventing hydrogen embrittlement and resistance. The present inventors have found that a welded pipe having excellent salt corrosion resistance can be provided.

That is, in the present invention, by mass%, C: 0.15% or less, Si: 4.0% or less, Mn: 3.0% or less, P: 0.10% or less, S: 0.03% or less, Ni : 6 to 20%, Cr: 14 to 28%, N: 0.25% or less, with the balance being Fe and inevitable impurities, M value represented by formula (1) is -100 or less, (2 An austenitic stainless steel welded pipe for high-pressure hydrogen transport in which the D value represented by the formula is adjusted to 6 to 10 is provided.
M = 551-462 (C + N) -9.2Si-8.1Mn-29 (Ni + Cu) -13.7Cr-18.5Mo (1)
D = (Cr + 1.5Si + 0.5Nb + Mo) − (Ni + 0.5Mn + 30C + 30N) (2).

  In the composition, those containing any of the following elements in addition to the above elements, either alone or in combination, can be employed. (I) One or more of Nb ≦ 1.0%, Ti ≦ 1.0%, Mo ≦ 4.0%, Cu ≦ 4.0%, (ii) Al ≦ 1.0%, rare earth and alkaline earth One or more metals ≦ 0.10% and B ≦ 0.010%.

  The value of the content of each element expressed in mass% is substituted for the element symbol in the above formulas (1) and (2). “Remaining substantially Fe” means that other elements are allowed to be mixed within a range not impairing the effects of the present invention, and includes “remaining part consisting of Fe and inevitable impurities”. When C, Si, Mn, and N are not added, the amount inevitably contained is substituted by mass%, and when Nb, Mo, and Cu are not added, 0 (zero) is substituted.

  Further, as a method for manufacturing the welded pipe, a manufacturing method in which an annealing heat treatment is carried out in the range of 1050 ° C. to 1150 ° C. for a soaking time of 5 minutes or less after pipe forming, and further, a surface reduction rate of 10% to 50% before performing the annealing heat treatment. A manufacturing method is provided for drawing at%.

  According to the study by the inventors, in the above-mentioned austenitic stainless steel welded pipe, when the δ ferrite phase of the weld zone is 0.5% or less in area%, the hydrogen embrittlement resistance can be remarkably improved. It becomes possible. For example, the δ ferrite phase can be easily identified by measuring using a ferrite content meter manufactured by Fischer Instruments.

  According to the present invention, the austenitic stainless steel welded pipe is used to severely limit the microstructure of the welded pipe, thereby suppressing the cost increase as much as possible and obtaining a welded pipe excellent in hydrogen embrittlement resistance and salt corrosion resistance. It became possible. This welded tube can be provided with strength suitable for transporting high-pressure hydrogen, for example, about 40 MPa without relying on a large increase in diameter and thickness, and is suitable for reducing the size and weight of high-pressure hydrogen transport sites. . It is also excellent in stress corrosion cracking susceptibility starting from salt corrosion resistance. Therefore, the present invention is expected to greatly contribute to the popularization of automobile fuel cell systems.

  As a result of detailed studies, the inventors have found that the hydrogen embrittlement resistance of the austenitic stainless steel welded pipe can be improved by severely limiting the δ ferrite phase of the weld. On the other hand, for salt damage characteristics at room temperature, it has been found that it is effective to reduce the Mn content and to contain appropriate amounts of Cr and N. Hereinafter, matters for specifying the present invention will be described in more detail.

[Δ ferrite content of welded pipe]
In the present invention, in the austenitic stainless copper adjusted to the chemical composition described later, the area% of the δ ferrite phase of the welded portion needs to be 0.5% or less. The area% can be easily obtained by measuring the volume% with the above-mentioned ferrite content meter, but a measurement error occurs in the weld. Therefore, after cutting and polishing the welded section in advance, electrolytic etching is performed with an aqueous sodium hydroxide solution to reveal the δ ferrite phase, and the area% may be obtained.

  It is possible to improve the hydrogen embrittlement resistance by reducing the area% of the δ ferrite phase having a body-centered cubic structure. However, in the chemical composition, the D value in the formula (2) is adjusted in advance. It is necessary to keep. When the D value exceeds 10, the δ ferrite phase of the weld exceeds 1.0% in area%, and the hydrogen embrittlement resistance is poor as it is. Although it is possible to reduce the δ ferrite phase by heat treatment, even when the δ ferrite phase is 0.5% or less, the σ phase may be formed, and the subsequent workability is significantly reduced. If the D value is 6 or less, the δ ferrite phase does not exist even in the as-welded state, but on the other hand, there is a possibility that hot cracking will occur during pipe making. If cracks are inherent, there is a possibility that they will break during subsequent processing, and there is a possibility that the strength will be insufficient during high-pressure hydrogen transport, causing problems.

  Note that the M value in the above equation (1) needs to be adjusted in order to prevent the formation of a work-induced martensite phase when processing a welded pipe. If the radius is the same as the diameter of the welded pipe), no martensite phase is formed, and excellent hydrogen embrittlement resistance can be maintained. In addition, since the smaller the M value, the more elements effective for corrosion resistance except for C and N are contained. As a rough guide, it is -50 or less, preferably a condition for suppressing the processing-induced martensite phase. If -100 or less is satisfied, good corrosion resistance can be secured.

[Chemical composition of steel]
The welded pipe of the present invention is made of austenitic stainless steel in which the content of component elements is adjusted as follows. “%” In steel composition means “mass%” unless otherwise specified.
C: 0.15% or less C is an austenite forming element, which is effective in increasing the strength and can be used for adjusting the D value and the M value. However, excessive addition may cause grain boundary corrosion due to sensitization depending on the heat treatment conditions, so it is contained in the above range. The C content may be controlled to 0.10% or less.

Si: 4.0% or less Si is an element that improves the resistance to stress corrosion cracking and improves the formability of steel. However, if added excessively, hot cracking is likely to occur when forming a welded pipe, and stacking faults are likely to be introduced during processing, resulting in reduced hydrogen embrittlement resistance. In addition, it becomes easier to generate the σ phase, which hinders the workability of the welded pipe. Therefore, the Si content in the steel is specified in the above range.

Mn: 3.0% or less Mn acts effectively as an austenite forming element to improve hydrogen embrittlement resistance. However, excessive addition destabilizes the passive film of steel. In addition, inclusions such as MnS are easily formed, and as a result, the occurrence of pitting corrosion, which is the starting point of stress corrosion cracking, is promoted. Therefore, the Mn content in the steel is limited to the above range so as not to adversely affect the salt corrosion resistance at room temperature. The Mn content may be controlled to 2.0% or less, or 1.0% or less.

P: 0.10% or less P has a lower P content because it promotes welding hot cracking when manufacturing a welded pipe. However, since it is difficult to remove P in the refining of stainless steel containing Cr, it is necessary to carefully select raw materials for reducing P, resulting in high cost of steel. In the present invention, if the D value is adjusted to a specified range, the P content is allowed in the above range from the viewpoint of welding hot cracking sensitivity.

S: 0.03% or less S, as described above, facilitates the formation of MnS, which tends to be the starting point of pitting corrosion, and promotes stress corrosion cracking. Moreover, in order to promote a hot crack in welding when manufacturing a welded pipe, it is preferable that the S content is low. For this reason, S content is restrict | limited to said range.

Ni: 6-20%
Ni is indispensable as an austenite forming element. When limiting the addition amount of Mn, Ni is necessary for adjusting the D value and the M value, and 6% or more is necessary. Even when the components are adjusted by forming austenite such as N or Cu, which will be described later, it is more preferable to secure a Ni content of 8% or more. On the other hand, since Ni is an expensive element, excessive addition is not preferable, and the upper limit may be controlled to 20% or 15%.

Cr: 14 to 28%
Cr is a main element constituting the passive film, and as its content increases, the occurrence of pitting corrosion is suppressed, and as a result, the stress corrosion cracking resistance is improved. On the other hand, since Cr is a ferrite-forming element, excessive addition tends to generate a δ ferrite phase or a σ phase, which hinders the hydrogen embrittlement resistance and workability of the welded pipe. The Cr content is specified in the above range so that it has sufficient pitting corrosion resistance and does not adversely affect hydrogen embrittlement resistance and workability. In order to ensure sufficient stress corrosion cracking resistance and hydrogen embrittlement resistance, the Cr content range may be controlled to 16 to 25% or 18 to 22%.

N: 0.25% or less N is an element that is effective in improving hydrogen embrittlement resistance as an austenite forming element and is extremely effective in increasing the strength of steel. However, excessive N content causes blowholes during the formation of the welded pipe and impairs the ductility of the welded pipe, so the N content is specified in the above range. In order to ensure higher ductility, the N content may be controlled to 0.20% or less.

Nb, Ti: 1.0% or less Cu, Mo: 4.0% or less Nb and Ti are powerful carbide-forming elements. By combining with C, the intergranular corrosion resistance is improved and the carbide is added. If it is finely dispersed, it will effectively increase the strength.
Mo and Cu improve the stress corrosion cracking resistance and effectively increase the strength as a solid solution strengthening element. For this reason, in this invention, 1 or more types of these elements can be added as needed.
However, if these elements are added excessively, the sensitivity to hot cracking of the weld is increased, cracks are likely to occur when the welded pipe is formed, and manufacturing costs are increased.
Therefore, when adding 1 or more types of Nb, Ti, Mo, Cu, each content shall be the said range.

Al: 1.0% or less One or more of rare earths or alkaline earth metals: 0.10% or less B: 0.010% or less Al, rare earths and alkaline earth metals form MnS that tends to start pitting corrosion. Suppress and improve stress corrosion cracking resistance. B also improves weld hot cracking and improves welded pipe manufacturability. For this reason, in this invention, 1 or more types of these elements can be added as needed. However, if these elements are added excessively, the sensitivity to hot cracking of the weld is increased, and cracks are likely to occur when the welded pipe is formed, and the manufacturing cost is increased. Therefore, when adding 1 or more types of Al, rare earths, alkaline-earth metals, and B, each content shall be the said range.

  Other alloy elements can be included as required within a range that does not impair the salt corrosion resistance of the base metal and the weld hot cracking susceptibility of the weld. Specifically, W effective for solid solution strengthening is 4.0% or less, or Zr and V effective for carbide formation are 1.0% or less, Sn effective for corrosion resistance is 0.1% or less, welding high temperature Y and Ca effective for cracking sensitivity can each contain these elements in the range of 0.1% or less.

[Manufacture of welded pipes]
The welding method of the present invention is not limited as long as the δ ferrite phase of the weld zone satisfies the area% of 0.5% or less. Generally, it is manufactured by manufacturing a steel plate material on a normal austenitic stainless steel pipe manufacturing line and then pipe-forming it by TIG welding or laser welding.

  When annealing heat treatment is performed after pipe forming, the soaking temperature should be less than 5 minutes in the range of 1050 to 1150 ° C for the purpose of removing processing strain generated in pipe forming, reducing δ ferrite phase, and suppressing the formation of σ phase. Do it. If it is less than 1050 ° C., a σ phase is likely to be generated, and if it exceeds 1150 ° C., a remarkable effect on the reduction of the δ ferrite phase does not appear. On the other hand, if the soaking time exceeds 5 minutes, the crystal grains tend to be coarsened, resulting in a decrease in strength. The heating and cooling rates during the annealing heat treatment are not particularly specified, but it is preferable to cool at a cooling rate of 100 ° C./min or more in a temperature range of 500 to 800 ° C. in order to avoid sensitization due to the formation of carbides. Although the annealing heat treatment atmosphere is not particularly specified, it is preferably performed in a reducing atmosphere in which no annealing scale is formed, for example, in a 100% hydrogen, 75% hydrogen and 25% nitrogen mixed atmosphere, or in an air annealing atmosphere. . In the case where the annealing process is performed in an air atmosphere, an oxide scale is formed. Therefore, it is preferable to subsequently perform a pickling process with a mixed acid, for example, a mixed solution of hydrofluoric acid and nitric acid in a ratio of 1: 9. .

  In this patent, when the δ ferrite phase generated during pipe forming is reduced by annealing heat treatment, it is possible to perform a drawing process with a reduction in area of 10 to 50% before the annealing heat treatment. Here, the area reduction rate represents the reduction rate of the cross-sectional area before and after drawing, and annealing heat treatment may be performed between a plurality of drawing times. If the area reduction rate in the drawing process is too small, a remarkable effect will not appear in the reduction of the δ ferrite phase, and if the area reduction rate is too large, the welded tube will break easily during the drawing process. Perform drawing.

  Steels having the chemical components shown in Table 1 were melted and hot rolled to a sheet thickness of 4.0 mm, and subjected to annealing, cold rolling, and annealing to obtain a cold rolled annealed material having a sheet thickness of 1.5 mm. Thereafter, in order to simulate the welded portion of the welded pipe, two flat plates were butt welded by TIG welding. Some of the cold-rolled annealed plates were made into a tube with a diameter of 12.7 mm by passing through a continuous tube-making line equipped with equipment for making each material steel plate into a tubular shape by roll forming and performing butt welding by TIG. Further, a part of the tube was drawn out by roll forming at a surface reduction rate of about 40% to obtain a tube having an outer diameter of 9.35 mm and a plate thickness of 1.2 mm. Welded plate and part of the tube are annealed in air and cooled with water, and then immersed in a mixed acid solution of 5% hydrofluoric acid concentration and 95% nitric acid concentration at 60 ° C for 2 minutes. Removed. Test specimens manufactured under various conditions as described above were used as test materials.

  When the metallographic structure of each test material was observed with a microscope, all of them exhibited an austenite single phase structure, and the δ ferrite phase was less than 0.1 area%. For each specimen, the area% of δ-ferrite phase, weld bendability, hydrogen embrittlement reduction rate, hydrogen embrittlement strength reduction rate, and corrosion resistance were evaluated by the following methods.

[Area% of ferrite phase]
As shown in FIG. 1, both the weld plate and the weld pipe are cut perpendicularly to the weld line, and five cross sections are cut out. After polishing, electrolytic etching is performed with a 30% aqueous sodium hydroxide solution at 6 V for 10 seconds to reveal a δ ferrite phase. When the area% of the δ ferrite phase with respect to the total area of the weld is 5% or less by visual observation, the area% is calculated by point calculation according to JIS G0565 (silver microscopic test method for nonmetallic inclusions in steel). If it is 5% or more by visual inspection, it shall be 5%.

[Bendability of welds]
The welding plate uses the vertical surface bending test piece (length 150 mm, width 40 mm, longitudinal direction parallel to the weld line) described in JISZ3122 (bend test method for butt weld joints), and JISZ2248 (metal material bending test method). 180 ° bending was carried out by the described push bending method. The case where cracks due to welding hot cracking did not occur was evaluated as ◯ (good), and the others were evaluated as x (defect). The welded pipe was evaluated for bendability by the flat test described in JISG3459 (stainless steel pipe for piping). The distance H between the flat plates in the flat test was 5 mm. The case where cracks due to welding hot cracking did not occur was evaluated as ◯ (good), and the others were evaluated as x (defect).

[Hydrogen embrittlement reduction rate]
A test piece was cut from the weld plate so that the longitudinal direction of the test piece was perpendicular to the weld line, and a parallel part length 30 mm, a width 3 mm, a shoulder radius 10 mm, and a grip part width 25 mm. The test was conducted in a normal pressure atmosphere of −40 ° C. and 40 MPa hydrogen at a crosshead speed of 0.05 mm / min. Each fracture drawing was obtained by JISZ2241 (metal material tensile test method), and the hydrogen embrittlement drawing reduction rate (%) was calculated by the following equation (3). In each test material, those with a hydrogen embrittlement drawing reduction rate of 80% or more were evaluated as ◯ (good), and those other than that were evaluated as x (defective). [Hydrogen embrittlement reduction ratio] = [Breaking restriction in high-pressure hydrogen] / [Breaking restriction in atmospheric pressure] × 100 (3)

[Hydrogen embrittlement strength reduction rate]
A 12C No. 12C test piece described in JISZ2201 (metallic material tensile test piece) was sampled from the welded tube, and a nominal tensile strain of 30% was applied in advance for the test. The evaluation was performed by a tensile test according to JISZ2241 (metal material tensile test method) in warm water at 40 ° C. and a lever type constant load test in which constant stress is applied while hydrogen charging is performed at 40 ° C. Hydrogen charging was performed in 1 N sulfuric acid at a temperature of 40 ° C. under conditions of a current density of 0.5 A / cm ² with platinum as the anode and a welded tube as the cathode. The stress applied to the welded pipe was varied and the respective fracture times were determined. The yield strength ratio under each condition was calculated by the following equation (4), and the yield strength ratio when the rupture time was 1000 hours was defined as the hydrogen embrittlement strength reduction rate, which was obtained. In each test material, those with a hydrogen embrittlement strength reduction rate of 100% or more were evaluated as ○ (good), and the others were evaluated as × (defect) [Yield ratio] = [Load stress in constant load test] / [ 0.2% yield strength] x 100 (4)

[Evaluation of corrosion resistance]
A large piece of 30 mm each from the weld plate and a small piece of 15 mm square from the cold-rolled annealed plate were cut out, overlapped, and joined by spot welding to produce a spot weld test piece having the shape shown in FIG. One cycle of “salt spray (5% sodium aqueous solution, 35 ° C. × 15 minutes) → drying (60 ° C., 30% RH × 1 hour) → wet (50 ° C., 90% RH × 3 hours)” on each test piece The salt dry / wet test was performed for 600 cycles, the large piece and the small piece were separated from the spot welded test piece after the test, and the corrosion state of each of the large piece and the small piece was visually observed. For each specimen, the number of tests was n = 3, and ○ (good) if no stress corrosion cracking was observed in both large and small pieces of the three spot weld specimens, and x (defective) ).
Table 2 summarizes the results of the welded plates, and Table 3 summarizes the results of the welded pipes.

  As can be seen from Table 2, in the austenitic stainless steel having a predetermined chemical composition, the example of the present invention in which the area% of the δ ferrite phase of the weld is 0.5% or less, the workability of the weld (bending In addition, it was excellent in stress corrosion cracking resistance in a salty and wet environment. Therefore, using these austenitic stainless steels, it is possible to construct a welded pipe for high-pressure hydrogen transport that has excellent resistance to hydrogen embrittlement and corrosion resistance (stress corrosion cracking starting from salt corrosion at room temperature). it can.

  On the other hand, No. which is a comparative example of a welded plate. Nos. 13, 16, and 18 are steel Nos. Since the M values of I, L, and N are larger than the values specified in the present invention, a work-induced martensite phase is generated during the tensile test, the hydrogen embrittlement drawing reduction rate is low, and the hydrogen embrittlement resistance is poor. . In particular, no. Nos. 13 and 18 are steel Nos. Since the M values of l and N were -50 or more, stress corrosion cracking occurred in the corrosion resistance evaluation. No. Nos. 14 and 17 are steel Nos. Since the D values of J and M were smaller than the range specified in this range, it was considered that hot cracking occurred during welding, resulting in poor bendability. No. 15 is steel No. 15; Since the D value of K is larger than the range specified in this range, a δ ferrite phase is formed in the welded portion, resulting in poor hydrogen embrittlement resistance.

  On the other hand, no. Although 26 and 27 have the chemical composition which is the object of the present invention, more δ ferrite phases were generated than the scope of the present invention. This is because the annealing heat treatment condition of the welded tube is longer (No. 26) or higher temperature (No. 27) than the range specified in the present invention, so that the δ ferrite phase increases, resulting in Inferior to hydrogen embrittlement resistance.

A diagram schematically showing the appearance of the welded pipe and the shape of the weld metal in the weld cross section The figure which showed the shape of the spot welding test piece typically

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Base material 2 Weld bead 3 Welding part cross section 4 Weld metal 5 Base material welding interface 6 Back bead 7 Pipe outer surface 8 Pipe inner surface 9 Thickness center 10 Large piece 11 Small piece 12 TIG welding part 13 Spot welding part

Claims (5)

In mass%, C: 0.15% or less, Si: 4.0% or less, Mn: 3.0% or less, P: 0.10% or less, S: 0.03% or less, Ni: 6 to 20% , Cr: 14 to 28%, N: 0.25% or less, with the balance being Fe and inevitable impurities, M value represented by formula (1) is −100 or less, and represented by formula (2) An austenitic stainless steel welded pipe having a D value adjusted to 6 to 10, wherein the δ-ferrite phase of the weld zone is adjusted to 0.5% or less in area%. Stainless steel welded pipe.
M = 551-462 (C + N) -9.2Si-8.1Mn-29 (Ni + Cu) -13.7Cr-18.5Mo (1)
D = (Cr + 1.5Si + 0.5Nb + Mo) − (Ni + 0.5Mn + 0.3Cu + 30C + 30N) (2)
Here, in the formulas (1) and (2), the content of the element is substituted by mass% for each element symbol. For Nb, Mo, Cu, 0 (zero) is substituted. When C, Si, Mn, and N are not added, the amount inevitably contained is substituted by mass%. The austenitic stainless steel for high-pressure hydrogen transport according to claim 1, comprising at least one of Nb ≦ 1.0%, Ti ≦ 1.0%, Mo: ≦ 4.0%, and Cu ≦ 4.0% by mass%. Steel welded pipe.
Here, in the formulas (1) and (2), 0 (zero) is substituted when Nb, Mo, and Cu are not added.   The austenite for high-pressure hydrogen transport according to claim 1 or 2, comprising, by mass%, Al ≤ 1.0%, at least one rare earth or alkaline earth metal ≤ 0.10%, and B ≤ 0.010%. Stainless steel welded pipe.   The method for producing an austenitic stainless steel welded pipe for high-pressure hydrogen transport according to claim 1, 2 or 3, wherein an annealing heat treatment is carried out in the range of 1050 ° C to 1150 ° C after the pipe making and a soaking time of 5 minutes or less. .   The austenitic stainless steel for high-pressure hydrogen transport according to claim 1, 2 or 3, wherein a drawing process is performed at a reduction in area of 10% to 50% before performing the annealing heat treatment according to claim 4. Manufacturing method of welded pipe.

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