JP6627373B2 - Austenitic stainless steel - Google Patents

Description

  The present invention relates to stainless steel, and more preferably to an austenitic stainless steel used for hydrogen equipment such as high-pressure hydrogen gas equipment and liquid hydrogen storage tanks.

  In recent years, research for practical use of transportation equipment using hydrogen as an energy alternative to fossil fuel has been advanced. For practical use, it is necessary to prepare an environment (hereinafter, also referred to as hydrogen equipment) that can store and transport hydrogen at high pressure. The hydrogen equipment is, for example, a device for high-pressure hydrogen gas, a liquid hydrogen storage tank, or the like. Materials used for such equipment are required to have resistance to embrittlement in a hydrogen environment.

  WO 2004/083476 (Patent Document 1), WO 2004/083377 (Patent Document 2), WO 2004/110695 (Patent Document 3), and WO 2012/132992 (Patent Document 4). ) Proposes an austenitic stainless steel for high strength. In these patent documents, the solubility of N is increased by increasing the Mn content of stainless steel, and the solid solution strengthening of N, the precipitation strengthening of nitride, and the strengthening of nitride are performed by containing V and Nb. Reinforcement by crystal grain refinement by pinning hardening.

  When using the austenitic stainless steel having a high N content in a hydrogen facility, it is required that the steel can be assembled by welding. Patent Document 3, Japanese Patent Application Laid-Open No. 5-192785 (Patent Document 5), and Japanese Patent Application Laid-Open No. 2010-227949 (Patent Document 6) contain Al, Ti, and Nb and perform heat treatment after welding. , A filler metal (weld metal) capable of obtaining a tensile strength exceeding 800 MPa has been proposed. Further, in WO2013 / 005707 (Patent Document 7), the N content of the filler metal, the shielding gas at the time of welding and the area of the molten pool are controlled to increase the N content of the weld metal. There has been proposed a welded joint capable of increasing strength without performing post-weld heat treatment. Further, Japanese Patent Application Laid-Open No. 9-137255 (Patent Document 8) proposes a steel in which welding workability is improved by adjusting the oxygen content according to the Al content in the austenitic steel material.

WO 2004/083476 International Publication No. WO 2004/083377 WO 2004/110695 WO 2012/132992 JP-A-5-192785 JP 2010-227949 A WO 2013/0057070 JP-A-9-137255

  By the way, when a steel material is used in an actual hydrogen facility (building), it may be difficult to use a filler material depending on a use site such as a thin member. In this case, steel materials are butt-welded by gas tungsten arc welding without using a filler material. At the time of butt welding, if the penetration depth is insufficient, the unmelted butt surface remains as a defect. In this case, the required strength cannot be obtained in the welded joint.

  In order to suppress the unmelted butted surface, the welding heat input may be increased. However, in this case, the melted portion becomes large, undercuts and burn-through occur, and the soundness of the welded joint is rather deteriorated.

  Patent Documents 1 to 7 do not disclose or suggest this problem. Patent Document 8 describes that the bead width uniformity and the back bead forming ability can be improved with respect to this problem. However, Al has a strong affinity for N. Therefore, even if the technology of Patent Literature 8 is applied to a stainless steel containing N positively, the effect on this problem may not be obtained.

  An object of the present invention is to provide an austenitic stainless steel having excellent weldability even when welding is performed without using a filler material, specifically, a deep penetration depth can be obtained. It is.

The austenitic stainless steel according to the present embodiment is, by mass%, C: 0.005 to 0.07%, Si: 0.1 to 1.2%, Mn: 2.5 to 10%, Ni: 9 to 14 %, Cr: 19 to 24%, Mo: 1 to 4%, Nb: 0 to 0.4%, N: 0.20 to 0.50%, Al: 0.05% or less, and Se, Te, One or more selected from the group consisting of Bi, Sn, Zn and Pb are contained in a content satisfying the formula (1) in total, and the balance is made up of Fe and impurities. And O are respectively P: 0.03% or less, S: 0.01% or less, and O: 0.02% or less.
0.0300 ≧ (Se + Te + Bi) +2 (Sn + Zn + Pb) ≧ 0.0010 (1)
Here, the content (% by mass) of the corresponding element is substituted for each element symbol in the formula (1).

  The austenitic stainless steel according to the present embodiment has excellent welding workability when welding without using a filler metal.

FIG. 1 is a side view of a steel plate before butt welding according to the embodiment.

  The present inventors have conducted investigations and studies to solve the above problems. As a result, the present inventors have obtained the following findings.

  In mass%, C: 0.005 to 0.07%, Si: 0.1 to 1.2%, Mn: 2.5 to 10%, Ni: 9 to 14%, Cr: 19 to 24%, Mo : 1 to 4%, Nb: 0 to 0.4%, N: 0.20 to 0.50%, Al: 0.05% or less To obtain a sufficient penetration depth in austenitic stainless steel. It is effective to contain one or more selected from the group consisting of Se, Te, Bi, Sn, Zn and Pb. Hereinafter, Se, Te, Bi, Sn, Zn, and Pb are referred to as “specific element group”.

  The following items can be considered as reasons why the specific element group enhances the welding workability. Se, Te and Bi in the specific element group (Se, Te, Bi, Sn, Zn and Pb) act as surface active elements. Se, Te, and Bi enhance the inward convection in the molten pool, even when contained in trace amounts. Therefore, the heat from the arc is easily transported in the depth direction during welding, and the penetration depth increases.

  Of the specific element group, Sn, Zn and Pb evaporate from the surface of the molten pool during welding to form an arc conduction path. Therefore, the current density of the arc increases, and the penetration depth increases.

In order to obtain a sufficient penetration depth by containing the specific element group, at least one or more of the specific element group may be contained in an appropriate range. On the other hand, if the total content of the specific element group is too high, weld cracking susceptibility during welding increases, and the ductility of the weld metal decreases. If the total content of the specific element group satisfies the expression (1), a sufficient penetration depth can be obtained while maintaining the ductility of the weld metal, and the weldability is improved.
0.0300 ≧ (Se + Te + Bi) +2 (Sn + Zn + Pb) ≧ 0.0010 (1)
Here, the content (% by mass) of the corresponding element is substituted for each element symbol in the formula (1).

The austenitic stainless steel of the present embodiment completed on the basis of the above findings has, by mass%, C: 0.005 to 0.07%, Si: 0.1 to 1.2%, and Mn: 2.5 to 10%, Ni: 9 to 14%, Cr: 19 to 24%, Mo: 1 to 4%, Nb: 0 to 0.4%, N: 0.20 to 0.50%, Al: 0.05% In the following, one or more selected from the group consisting of Se, Te, Bi, Sn, Zn and Pb are contained in a content satisfying the formula (1) in total, and the balance consists of Fe and impurities. . Among the impurities, P, S, and O are P: 0.03% or less, S: 0.01% or less, and O: 0.02% or less, respectively.
0.0300 ≧ (Se + Te + Bi) +2 (Sn + Zn + Pb) ≧ 0.0010 (1)
Here, the content (% by mass) of the corresponding element is substituted for each element symbol in the formula (1).

  The austenitic stainless steel of the present embodiment has excellent welding workability, specifically, a deep penetration depth when welding is performed without using a filler material. The austenitic stainless steel according to the present embodiment can be used as a high-pressure hydrogen gas equipment even if a weld metal that satisfies the required performance such as hydrogen embrittlement resistance and strength is obtained. Needless to say, it can be used as.

  The austenitic stainless steel further substitutes for a part of Fe and, in mass%, Cu: 3% or less, Co: 3% or less, V: 0.5% or less, Ti: 0.5% or less, B: One or more selected from the group consisting of 0.01% or less, Ca: 0.05% or less, Mg: 0.05% or less, and rare earth elements: 0.5% or less Good.

  Preferably, the austenitic stainless steel has a tensile strength at room temperature of 690 MPa or more.

Preferably, the austenitic stainless steel is used for equipment for storing or transporting high-pressure hydrogen gas and liquid hydrogen.
The austenitic stainless steel may be welded without using a filler metal.

  Hereinafter, the austenitic stainless steel according to the present embodiment will be described in detail. In the following description, “%” of the content of each component element means “% by mass”.

[Chemical composition]
The chemical composition of the austenitic stainless steel according to the present embodiment contains the following elements.

C: 0.005 to 0.07%
Carbon (C) stabilizes the austenitic structure. If the C content is too low, this effect cannot be obtained. On the other hand, if the C content is too high, carbides are formed at the grain boundaries due to heating during welding, and the corrosion resistance of the heat affected zone is reduced. Therefore, the C content is 0.005 to 0.07%. A preferred lower limit of the C content is 0.01%, and more preferably 0.02%. A preferred upper limit of the C content is 0.06%, and more preferably 0.05%.

Si: 0.1 to 1.2%
Silicon (Si) deoxidizes steel. Si further increases the corrosion resistance of the steel. If the Si content is too low, this effect cannot be obtained. On the other hand, if the Si content is too high, the stability of the austenite structure decreases, and the ductility decreases. Furthermore, in the case of welding without using a filler material, the susceptibility of the weld metal to solidification cracking increases. Therefore, the Si content is 0.1 to 1.2%. A preferred lower limit of the Si content is 0.15%, and more preferably 0.2%. The preferred upper limit of the Si content is 1.1%, and more preferably 1.0%.

Mn: 2.5 to 10%
Manganese (Mn) deoxidizes steel and stabilizes the austenitic structure. Mn further increases the solubility of N in the molten metal during the production of the base material and during welding, thereby increasing the strength. Mn further increases the current density of the arc and increases the penetration depth. If the Mn content is too low, these effects cannot be obtained. On the other hand, if the Mn content is too high, the ductility decreases. Therefore, the Mn content is 2.5 to 10%. A preferred lower limit of the Mn content is 2.8%, more preferably 3.0%. The preferred upper limit of the Mn content is 8%, and more preferably 6.5%.

Ni: 9 to 14%
Nickel (Ni) stabilizes the austenitic structure. Ni further increases stacking fault energy and reduces susceptibility to embrittlement in a hydrogen environment. If the Ni content is too low, these effects cannot be obtained. On the other hand, if the Ni content is too high, the production cost increases. If the Ni content is too high, the solubility of N in the molten metal decreases during the production of the base material or during welding, and the strength of the steel decreases. Therefore, the Ni content is 9 to 14%. A preferred lower limit of the Ni content is 9.5%, more preferably 10%. A preferred upper limit of the Ni content is 13.5%, and more preferably 13%.

Cr: 19 to 24%
Chromium (Cr) enhances the corrosion resistance of steel under the use environment. Cr further increases the solubility of N in the molten metal during the production of the base material and during welding, and increases the strength of steel by forming carbides. If the Cr content is too low, these effects cannot be obtained. On the other hand, if the Cr content is too high, the austenite structure becomes unstable, and further, carbides are excessively generated and the steel is embrittled. Therefore, the Cr content is 19 to 24%. A preferred lower limit of the Cr content is 19%, more preferably 19.5%, and still more preferably 20%. A preferred upper limit of the Cr content is 23.5%, and more preferably 23%.

Mo: 1-4%
Molybdenum (Mo) increases the corrosion resistance of steel in a hydrogen environment and increases the strength of the steel. If the Mo content is too low, these effects cannot be obtained. On the other hand, if the Mo content is too high, the production cost increases, and the austenite structure becomes unstable. Therefore, the Mo content is 1 to 4%. A preferred lower limit of the Mo content is 1.2%, and more preferably 1.5%. The preferable upper limit of the Mo content is 3.8%, and more preferably 3.5%.

Nb: 0 to 0.4%
Nb is an optional element and may not be contained. When contained, Nb forms a solid solution in the steel or precipitates as carbonitride to increase the strength of the steel. These effects can be obtained if Nb is contained at all. However, if the Nb content is too high, the susceptibility of the weld metal to solidification cracking is increased and the ductility of the weld metal is reduced during welding without using a filler metal. Therefore, the Nb content is 0 to 0.4%. A preferred lower limit of the Nb content is 0.10%, and more preferably 0.12%. A preferred upper limit of the Nb content is 0.38%, and more preferably 0.35%.

N: 0.20 to 0.50%
Nitrogen (N) increases the strength of the steel by forming a solid solution in the steel or forming fine nitrides. N further stabilizes the austenitic structure. If the N content is too low, these effects cannot be obtained. On the other hand, if the N content is too high, the hot workability decreases during the production of the base material, and blow holes and pits are formed in the weld metal during welding. Therefore, the N content is 0.20 to 0.50%. A preferred lower limit of the N content is 0.22%, more preferably 0.25%. The preferable upper limit of the N content is 0.48%, and more preferably 0.45%.

Al: 0.05% or less Aluminum (Al) deoxidizes steel like Si. On the other hand, if the Al content is too high, the penetration depth during welding will be shallow. Therefore, the Al content is 0.05% or less. The lower limit of the Al content is not particularly limited. However, considering the steelmaking cost, the preferred lower limit of the Al content is 0.0005% or more, and more preferably 0.001%. A preferred upper limit of the Al content is 0.04%, and more preferably 0.03%.

Specific element group (Se, Te, Bi, Sn, Zn and Pb): the total content satisfies the formula (1).
0.0300 ≧ (Se + Te + Bi) +2 (Sn + Zn + Pb) ≧ 0.0010 (1)
Each of the specific elements increases the penetration depth. Specifically, Se, Te, and Bi all affect the temperature dependence of the surface tension of the molten metal and increase the penetration depth. Sn, Zn, and Pb all increase the penetration depth by evaporating from the molten pool and increasing the current density of the arc. When F1 = (Se + Te + Bi) +2 (Sn + Zn + Pb), if the total content of one or more selected from the specific element group is F1 of 0.0010 (%) or more, the penetration depth is Increase sufficiently. On the other hand, if the content of the specific element group is too high, specifically, if F1 exceeds 0.0300 (%), solidification cracks occur in the molten metal during welding. Therefore, F1 is 0.0010 to 0.0300. A preferred lower limit of F1 is 0.0015, and more preferably 0.0020. The preferred upper limit of F1 is 0.0250, and more preferably 0.0200.

  The austenitic stainless steel according to the present embodiment contains the above elements, and the balance consists of Fe and impurities. The term “impurities” as used herein means components that are mixed due to raw materials such as ores and scraps and other factors when industrially producing steel materials. Among the impurities, the contents of P, S and O are as follows, respectively.

P: 0.03% or less Phosphorus (P) is an impurity. P lowers the hot workability of the base material during production. P further increases the susceptibility of the weld metal to solidification cracking when welding without filler metal. Therefore, the P content is 0.03% or less. The preferred P content is 0.025% or less, more preferably 0.02% or less. The P content is preferably as low as possible.

S: 0.01% or less Sulfur (S) is an impurity. S lowers the hot workability of the base material during manufacturing. S further increases the susceptibility of the weld metal to solidification cracking when welding without a filler metal. Therefore, the S content is 0.01% or less. The preferred S content is 0.008% or less, more preferably 0.005% or less. The S content is preferably as low as possible.

O: 0.02% or less Oxygen (O) is an impurity. O reduces the hot workability of the base material during production. O further reduces the cleanliness of the steel and reduces the ductility. Therefore, the O content is 0.02% or less. The preferred O content is 0.015% or less, and more preferably 0.01% or less. The lower limit of the O content need not be particularly set. However, considering the production cost and the fact that O acts as a surface active element and has a considerable effect of increasing the penetration depth, the preferable lower limit of the O content is 0.001%, and more preferably 0%. 0.002%.

  The austenitic stainless steel of the present embodiment further includes one or two selected from the group consisting of Cu, Co, V, Ti, B, Ca, Mg, and a rare earth element (REM) instead of a part of Fe. The above may be contained.

Cu: 0-3%
Copper (Cu) is an optional element and need not be contained. When contained, Cu stabilizes the austenitic structure. This effect can be obtained to some extent if Cu is contained at all. However, if the Cu content is too high, when welding is performed without using a filler metal, the solidification cracking susceptibility of the weld metal increases. Therefore, the Cu content is 0 to 3%. The preferable lower limit of the Cu content is 0.005%, more preferably 0.008%, and further preferably 0.01%. The preferred upper limit of the Cu content is 2.5%, and more preferably 2.0%.

Co: 0-3%
Cobalt (Co) is an optional element and need not be contained. When contained, Co stabilizes the austenitic structure, similar to Cu. This effect can be obtained to some extent if Co is contained even a little. However, if the Co content is too high, the ductility of the weld metal decreases. Therefore, the Co content is 0 to 3%. A preferred lower limit of the Co content is 0.005%, more preferably 0.008%, and still more preferably 0.01%. A preferred upper limit of the Co content is 2.5%, and more preferably 2.0%.

V: 0 to 0.5%
Vanadium (V) is an optional element and may not be contained. When contained, V, like Nb, forms a solid solution in steel or precipitates as carbonitride to increase the strength of the steel. This effect can be obtained to some extent if V is contained at all. However, if the V content is too high, a large amount of carbonitride precipitates and ductility decreases. Therefore, the V content is 0 to 0.5%. A preferred lower limit of the V content is 0.001%, more preferably 0.005%, and still more preferably 0.01%. A preferred upper limit of the V content is 0.45%, and more preferably 0.40%.

Ti: 0 to 0.5%
Titanium (Ti) is an optional element and need not be contained. When contained, Ti, like V and Nb, forms a solid solution in steel or precipitates as carbonitride to increase the strength of the steel. If a small amount of Ti is contained, this effect can be obtained to some extent. However, if the Ti content is too high, a large amount of carbonitride precipitates and ductility decreases. Therefore, the Ti content is 0 to 0.5%. A preferable lower limit of the Ti content is 0.001%, more preferably 0.003%, and further preferably 0.005%. The preferable upper limit of the Ti content is 0.45% or less, more preferably 0.40% or less.

B: 0 to 0.01%
Boron (B) is an optional element and need not be contained. When B is contained, B segregates at the grain boundary to increase the grain boundary fixing force, thereby increasing the strength of the steel. B further suppresses the embrittlement of steel in a hydrogen environment. The above effect can be obtained to some extent if B is contained at all. However, when the B content is too high, the susceptibility of the weld metal to solidification cracking increases when welding is performed without using a filler material. Therefore, the B content is 0 to 0.01%. A preferred lower limit of the B content is 0.0001%, more preferably 0.0002%, and still more preferably 0.0005%. The preferable upper limit of the B content is 0.008%, and more preferably 0.005%.

Ca: 0 to 0.05%
Calcium (Ca) is an optional element and may not be contained. When included, Ca enhances the hot workability of the steel. This effect can be obtained to some extent if Ca is contained at all. However, if the Ca content is too high, Ca bonds to O and the cleanliness of the steel decreases, and the hot workability rather decreases. Therefore, the Ca content is 0 to 0.05%. A preferred lower limit of the Ca content is 0.0001%, more preferably 0.0005%, and still more preferably 0.001%. The preferable upper limit of the Ca content is 0.03% or less, and more preferably 0.01%.

Mg: 0 to 0.05%
Magnesium (Mg) is an optional element and need not be contained. When included, Mg enhances the hot workability of the steel, similar to Ca. This effect can be obtained to some extent if Mg is contained at all. However, if the Mg content is too high, Mg bonds with O and the cleanliness of the steel is reduced, and the hot workability of the steel is rather reduced. Therefore, the Mg content is 0 to 0.05%. A preferable lower limit of the Mg content is 0.0001%, more preferably 0.0005%, and further preferably 0.001%. The preferred upper limit of the Mg content is 0.03%, and more preferably 0.01%.

Rare earth element (REM): 0 to 0.5%
The rare earth element (REM) is an optional element and may not be contained. When contained, REM has a strong affinity for S and enhances hot workability of steel. This effect can be obtained to some extent if REM is contained at all. However, if the REM content is too high, the REM bonds with O, thereby reducing the cleanliness of the steel and, on the contrary, reducing the hot workability of the steel. Therefore, the REM content is 0-0.5%. A preferable lower limit of the REM content is 0.001%, more preferably 0.002%, and further preferably 0.005%. A preferred upper limit of the REM content is 0.3%, more preferably 0.1%.

  “REM” as used herein is a general term for a total of 17 elements of Sc, Y and lanthanoid, and the REM content means the total content of one or more elements of REM. REM is generally contained in misch metal. Therefore, for example, misch metal may be added to molten steel so that the content of REM in the steel falls within the above range.

[Production method]
An example of the method for manufacturing an austenitic stainless steel according to the present embodiment will be described. A molten steel having the above chemical composition is manufactured. For example, the molten steel is manufactured using an electric furnace, an AOD (Argon Oxygen Decarburization) furnace, and a VOD (Vacuum Oxygen Decarburization) furnace.

  An ingot is manufactured from the manufactured molten steel by an ingot-making method. The ingot is hot worked (hot forging, hot rolling, etc.) to produce steel materials such as slabs, blooms and billets. Steel materials such as slabs, blooms, and billets may be manufactured from the manufactured molten steel by a continuous casting method.

  The manufactured steel material is hot worked to produce an austenitic stainless steel material. For example, a steel material is hot-rolled to produce a steel plate, a bar, and a wire. Also, an austenitic stainless steel pipe is manufactured by hot extrusion, hot piercing and rolling, or the like. As described above, the specific method of the hot working is not particularly limited, and the hot working may be performed according to the shape of the final product.

  Cold working may be performed on the austenitic stainless steel material after hot working. When the austenitic stainless steel material is a steel pipe, the cold working is, for example, cold drawing. When the austenitic stainless steel material is a steel plate, cold rolling or the like is used.

  Heat treatment (solution treatment) may be performed after hot working or after cold working. The heat treatment may be performed plural times.

  The austenitic stainless steel manufactured by the above manufacturing method has a tensile strength of 690 MPa or more. Furthermore, this austenitic stainless steel shows excellent welding workability. Specifically, when welding is performed without using a filler material, a sufficient penetration depth can be obtained.

  Molten steel having the chemical compositions of steel types A to J shown in Tables 1A and 1B was produced.

  Ingots were manufactured by casting molten steel. The ingot was subjected to hot forging, hot rolling, heat treatment, and machining to produce a steel plate having a thickness of 2 mm, a width of 50 mm, and a length of 100 mm.

  The groove shape of the two steel plates of each test number was the I shape shown in FIG. Numerical values in FIG. 1 indicate dimensions (parentheses indicate units). By the gas tungsten arc welding method, butt welding was performed on the steel sheets of FIG. 1 at a heat input of 5 kJ / cm without using a filler material, and welded joints of test numbers 1 to 10 shown in Table 2 were manufactured. . The welding conditions were the same for all test numbers.

[Welding workability test]
The welded portion of the manufactured welded joint was visually observed. By observing the back surface of the welded joint, if no back bead was formed, it was determined that a sufficient penetration depth was not obtained, and it was determined as "impossible". When the back bead was observed but the back bead width was less than 1 mm, it was judged as "good". Those with a back bead of 1 mm or more were judged as "excellent". In the case of “good” and “excellent”, it was determined that a sufficient penetration depth was obtained. Furthermore, in welded joints having a penetration depth of “good” and “excellent”, the presence or absence of defects in the welded portions was visually observed. When no welding defects such as cracks and burn-through were observed, it was judged as “excellent”. When a welding defect was observed, it was judged as “impossible”.

[Tensile test]
A tensile test was performed on the welded joint determined to be “good” or “excellent” in the weldability test. Specifically, a plate-shaped tensile test piece having a weld metal at the center of the parallel portion was prepared. A tensile test was performed on the test piece at normal temperature. When the tensile strength TS (MPa) was 690 MPa or more, which is the required strength of the base material, it was judged as “good”, and when it exceeded 800 MPa, it was judged as “excellent”. When the tensile strength TS was less than 690 MPa, it was judged as "impossible".

  Further, a plate-shaped tensile test piece was prepared for the base material of each test number, and a tensile test was performed under the same conditions as the tensile test for the welded joint. As a result, each of the base materials of the test numbers had a tensile strength of 690 MPa or more.

[Low strain rate tensile test (SSRT)]
A low strain rate tensile test (SSRT) was performed on the welded joint determined as “good” or “excellent” in the tensile test in order to evaluate the embrittlement resistance under a high-pressure hydrogen environment. Specifically, a stepped plate-like low strain rate tensile test piece having a weld metal at the center of the parallel portion was sampled. A low strain rate tensile test was performed on the test piece in the atmosphere and under a high-pressure hydrogen environment of 45 MPa. Note that the strain rate was 3 × 10 ⁻⁵ / s. In the low strain rate tensile test, a specimen in which the ratio of the fracture drawing in a high-pressure hydrogen environment to the fracture drawing in the air was 90% or more was regarded as “pass”.

[Test results]
Table 2 shows the test results.

  "-" In Table 2 indicates that the test was not performed. Referring to Table 2, in Test Nos. 1 to 6, the chemical composition was appropriate, and F1 satisfied Expression (1). Therefore, it had excellent welding workability to obtain a sufficient penetration depth, and the tensile strength of the welded joint was 690 MPa or more, which is the required strength of the base material. Furthermore, it exhibited excellent hydrogen embrittlement resistance.

  On the other hand, in Test No. 7, F1 exceeded the upper limit of Expression (1). Therefore, although a sufficient penetration depth was obtained, a welding crack considered to be a solidification crack occurred at the center of the weld bead.

  In Test Nos. 8 and 9, F1 was less than the lower limit of Expression (1). For this reason, the penetration depth was not sufficient and the back bead was not formed. That is, in Test Nos. 8 and 9, welding workability was low.

  In test number 10, the N content was too low. Therefore, the tensile strength was lower than the required tensile strength of 690 MPa.

  The embodiments of the present invention have been described above. However, the above-described embodiment is merely an example for implementing the present invention. Therefore, the present invention is not limited to the above-described embodiment, and can be implemented by appropriately modifying the above-described embodiment without departing from the spirit thereof.

  The austenitic stainless steel of the present embodiment has excellent welding workability, specifically, a deep penetration depth when welding is performed without using a filler material. Therefore, it is particularly suitable as a steel material for equipment for high-pressure hydrogen gas use such as storage and transportation of high-pressure hydrogen gas.

Claims (5)

In mass%,
C: 0.005 to 0.07%,
Si: 0.1 to 1.2%,
Mn: 2.5 to 10%,
Ni: 9 to 14%,
Cr: 19 to 24%,
Mo: 1 to 4%,
Nb: 0 to 0.4%,
N: 0.20 to 0.50%,
Al: 0.05% or less, and
One or more selected from the group consisting of Se, Te, Bi, Sn, Zn and Pb in a content satisfying the formula (1) in total;
The balance consists of Fe and impurities,
Among the impurities, P, S and O are respectively
P: 0.03% or less,
S: 0.01% or less, and
O: austenitic stainless steel of not more than 0.02%.
0.0300 ≧ (Se + Te + Bi) +2 (Sn + Zn + Pb) ≧ 0.0010 (1)
Here, the content (% by mass) of the corresponding element is substituted for each element symbol in the formula (1). The austenitic stainless steel according to claim 1, further comprising:
Instead of part of Fe, in mass%,
Cu: 3% or less,
Co: 3% or less,
V: 0.5% or less,
Ti: 0.5% or less,
B: 0.01% or less,
Ca: 0.05% or less,
Mg: 0.05% or less, and
Austenitic stainless steel containing one or more rare earth elements selected from the group consisting of 0.5% or less.   The austenitic stainless steel according to claim 1 or 2, wherein the tensile strength at room temperature is 690 MPa or more. Austenitic stainless steel according to any one of claims 1 to 3, wherein
It is used to store or transport equipment of the high-pressure hydrogen gas及beauty liquid body hydrogen, austenitic stainless steel. Austenitic stainless steel according to any one of claims 1 to 4, wherein
Austenitic stainless steel welded by gas tungsten arc welding without using filler metal.

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