Title of invention: Austenitic stainless steel weld metal and welded structure
Technical field
[0001]
　The present invention relates to an austenitic stainless steel weld metal and a welded structure having the same.
Background technology
[0002]
　TP316H regulated by American Society of Mechanical Engineers (ASME) SA213 and SA213M contains Mo and has excellent corrosion resistance at high temperature, so it is widely used as a material for heat transfer tubes and heat exchangers in thermal power plants and petrochemical plants. Has been done.
[0003]
　When this TP347H is assembled as a structure, it is generally assembled by welding and used as a welded structure having weld metal. The weld metal obtained by using a commercially available welding material for Ni-based heat-resistant alloys (for example, JIS Z 3334 (2011) SNi6082) is stable and has sufficient performance in terms of creep strength and toughness. It is expensive because it contains a large amount of. On the other hand, the weld metal obtained by using a commercially available welding material for Mo-containing stainless steel (JIS Z 3321 (2010) YS16-8-2) is inexpensive and excellent in economic efficiency.
[0004]
　However, as disclosed in Non-Patent Document 1, it is widely known that an austenitic stainless steel weld metal containing Nb has high solidification cracking susceptibility during welding. Further, as disclosed in Non-Patent Document 2, when used as a welded structure at high temperature, embrittlement cracks called stress relaxation cracks or strain-induced precipitation hardening cracks occur in the welded part during use. It's easy to do. In addition to this, Patent Documents 1 to 3 disclose welding materials containing Nb.
Prior art documents
Patent literature
[0005]
Patent Document 1: Japanese Patent Application Laid-Open No. 6-142980
Patent Document 2: Japanese Patent Application Laid-Open No. 9-300996
Patent Document 3: Japanese Patent Application Laid-Open No. 2001-300763
Non-patent literature
[0006]
Non-Patent Document 1: Ogawa et al., Journal of Welding Society, Volume 50, No. 7 (1981), page 680
Non-Patent Document 2: Uchigi et al., Ishikawajima Harima Technical Report, Volume 15 (1975) No. 2, Page 209
Summary of the invention
Problems to be Solved by the Invention
[0007]
　However, the welding materials described in Patent Documents 1 to 3 and the like all contain Mo, W, Cu, etc. to increase the high-temperature strength of the obtained weld metal, but contain a large amount. , Economically inferior. Further, in both cases, impurities such as P and S are reduced to improve solidification crack resistance during welding, but cracks during use are not mentioned.
[0008]
　On the other hand, it is required to suppress weld cracking and realize excellent weld crack resistance. On the other hand, even if weld cracking is suppressed, the welded structure may be inferior in creep strength when exposed to a high temperature environment (for example, 650° C. environment). Therefore, in addition to weld crack resistance, stability in high temperature environment It is required to realize such creep strength.
[0009]
　The present invention is a weld metal constituting a structure used in equipment used at high temperatures, which is an austenitic stainless steel weld metal having excellent weld crack resistance and high creep strength, and a welded structure having the same. For the purpose of providing.
Means for solving the problem
[0010]
　The present invention has been made in order to solve the above problems, and has as its gist the following austenitic stainless steel weld metal and welded structure.
[0011]
　(1) Chemical composition in mass %,
　C: 0.05 to 0.11%,
　Si: 0.10 to 0.50%,
　Mn: 1.0 to 2.5%,
　P: 0.035% Hereinafter,
　S: 0.0030% or less,
　Co: 0.01 to 1.00%,
　Ni: 9.0 to 11.5%,
　Cr: 17.0 to 21.0%,
　Nb: 0.60 to 0 .90%,
　Ta: 0.001 to 0.100%,
　N: 0.01 to 0.15%,
　Al: 0.030% or less,
　O: 0.020% or less,
　V: 0 to 0.10% ,
　Ti:0 to 0.10%,
　W:0 to 0.50%,
　Mo:0 to 0.50%,
　Cu:0 to 0.50%,
　B:0 to 0.005%,
　Ca:0 to 0.010%,
　Mg:0 to 0.010%,
　REM:0 to 0.10%,
　balance: Fe and impurities, which
　satisfy the following formula (i) :
　Austenitic stainless steel weld metal.
　　Nb-7.8×C≦0.25 (i)
　However, the element symbol in the above formula represents the content (mass %) of each element contained in the steel.
[0012]
　(2) The chemical composition is% by mass,
　V: 0.01 to 0.10%,
　Ti: 0.01 to 0.10%,
　W: 0.01 to 0.50%,
　Mo: 0.01 To 0.50%,
　Cu: 0.01 to 0.50%,
　B: 0.0002 to 0.005%,
　Ca: 0.0005 to 0.010%,
　Mg: 0.0005 to 0.010%, And
　REM: 0.0005 to 0.10%,
　the austenitic stainless steel weld metal according to (1) above.
[0013]
　(3) A welded structure having the austenitic stainless steel weld metal according to (1) or (2) above.
Effect of the invention
[0014]
　According to the present invention, an austenitic stainless steel weld metal having a weld creep resistance and a high creep strength, which constitutes a structure used in equipment used at high temperatures, and a weld metal having the same A structure can be obtained.
Brief description of the drawings
[0015]
FIG. 1 is a schematic cross-sectional view showing the shape of a grooved plate material in Examples.
FIG. 2 is a schematic cross-sectional view showing the shape of a grooved plate material in Examples.
MODE FOR CARRYING OUT THE INVENTION
[0016]
　The present inventors conducted a detailed investigation in order to achieve both excellent weld crack resistance and stable creep strength as a structure. As a result, the following findings have been obtained.
[0017]
　As a result of investigating the cracking phenomenon which occurred in the as-welded Nb-containing austenitic stainless steel weld metal, the following two points were found.
[0018]
　(A) The cracks generated in the as-welded weld metal occurred at the association of columnar crystals, and the fractured surface had a smooth property suggesting that the liquid phase remained. Further, a remarkable concentration of Nb was observed in the portion where the liquid phase was estimated to remain. On the other hand, in the weld metal in which cracking did not occur, lamellar NbC was observed at the association of columnar crystals.
[0019]
　(B) Cracks occurring in the weld metal after use at high temperature occurred at the columnar crystal boundaries of the weld metal, the fracture surface exhibited poor ductility, and S enrichment was detected. Further, a large amount of fine Nb carbide or Nb carbonitride was precipitated in the columnar crystal.
[0020]
　From this, the former is so-called solidification cracking, which is caused by the solidification segregation of Nb during the solidification of the weld metal, and the melting point of the residual liquid phase is lowered, so that the liquid film is formed in the association portion of the columnar crystals for a long time. It was present and it was considered that the portion was a crack caused by opening due to thermal stress. In the weld metal in which cracking did not occur, eutectic solidification of NbC and the matrix occurred due to the form of NbC, and the liquid phase disappeared in a short time, so it was speculated that solidification cracking did not occur.
[0021]
　Further, the latter is stress relaxation cracking, in which a large amount of Nb carbide, Nb nitride, or Nb carbonitride precipitates during use at high temperature, which makes it difficult for the inside of the grain to be deformed, resulting in welding residual stress. It was considered that the creep deformation that occurred during the opening of the was concentrated at the columnar crystal boundaries and cracks were formed by opening. It is considered that S segregates into columnar crystals during welding or during use at high temperature and reduces the binding force thereof, so that cracks tend to occur when the S content increases.
[0022]
　As a result of repeated studies, in order to prevent cracking and obtain high creep strength in the austenitic stainless steel weld metal having the composition targeted by the present invention, the Nb content is 0.60 to 0. It has been found that it is necessary to set the range to 90%, the Nb-7.8×C to 0.25 or less, and the S content to 0.0030% or less. In addition, it has been found that it is necessary to contain Co in a predetermined amount or more in order to sufficiently obtain the effect of reducing the weld crack susceptibility.
[0023]
　The present invention has been made based on the above findings. Hereinafter, each requirement of the present invention will be described in detail.
[0024]
　(A) Chemical composition The
　reasons for limiting each element are as follows. In addition, in the following description, "%" regarding the content means "mass %".
[0025]
　C: 0.05 to 0.11%
　C stabilizes the austenite phase and combines with Nb to form fine carbides, which improves the creep strength during high temperature use. Further, C combines with Nb in the final solidification process during welding to cause eutectic solidification of NbC and the matrix, and the liquid phase disappears early to prevent solidification cracking. However, when C is contained in excess, a large amount of carbide is precipitated in the early stage of use at high temperature, which promotes stress relaxation cracking. Therefore, the C content is 0.05 to 0.11%. The C content is preferably 0.06% or more, and preferably 0.10% or less.
[0026]
　Si: 0.10 to 0.50%
　Si is an element that has a deoxidizing effect and is necessary to secure corrosion resistance and oxidation resistance at high temperatures. However, when Si is contained excessively, the stability of the austenite phase is lowered, and the creep strength is lowered. Therefore, the Si content is set to 0.10 to 0.50%. The Si content is preferably 0.15% or more, more preferably 0.20% or more. Further, the Si content is preferably 0.45% or less, and more preferably 0.40% or less.
[0027]
　Mn: 1.0 to 2.5%
　Mn is an element having a deoxidizing action, like Si. It also stabilizes the austenite phase and contributes to the improvement of creep strength. However, when the Mn content becomes excessive, the creep ductility decreases. Therefore, the Mn content is set to 1.0 to 2.5%. The Mn content is preferably 1.1% or more, more preferably 1.2% or more. The Mn content is preferably 2.2% or less, more preferably 2.0% or less.
[0028]
　P: 0.035% or less
　P is an element which is contained as an impurity and is solidified and segregated during welding to lower the melting point of the remaining liquid phase and enhance solidification cracking susceptibility. Furthermore, creep ductility is also reduced. Therefore, the upper limit of P content is set to 0.035% or less. The P content is preferably 0.032% or less, more preferably 0.030% or less. It is preferable to reduce the P content as much as possible, that is, the P content may be 0%, but the extreme reduction causes an increase in cost at the time of manufacturing the material. Therefore, the P content is preferably 0.0005% or more, more preferably 0.0008% or more.
[0029]
　S: 0.0030% or less
　S is contained as an impurity like P, and solidifies and segregates during welding to lower the melting point of the residual liquid phase and enhance solidification cracking susceptibility. Further, after solidification, the thermal cycle of the subsequent pass segregates the grain boundaries to increase the ductility-decay crack susceptibility. Therefore, the upper limit of S content is set to 0.0030% or less. The S content is preferably less than 0.0025%, more preferably 0.0020% or less. It is preferable to reduce the S content as much as possible, that is, the S content may be 0%, but the extreme reduction causes an increase in cost at the time of manufacturing the material. Therefore, the S content is preferably 0.0001% or more, and more preferably 0.0002% or more.
[0030]
　Co: 0.01 to 1.00%
　Co is an element that enhances the stability of the austenite phase and contributes to the improvement of creep strength. Further, as compared with Ni and Mn, the effects on segregation energies of P and S are small, and the effects of reducing solidification segregation and reducing weld crack susceptibility can be expected. However, since Co is an expensive element, excessive inclusion causes an increase in the manufacturing cost of the material. Therefore, the Co content is set to 0.01 to 1.00%. The Co content is preferably 0.015% or more, more preferably 0.02% or more. Further, the Co content is preferably 0.90% or less, and more preferably 0.80% or less.
[0031]
　Ni: 9.0 to 11.5%
　Ni is an essential element for ensuring the stability of the austenite phase during long-term use. However, Ni is an expensive element, and a large amount of Ni causes an increase in the manufacturing cost of the material. Therefore, the Ni content is set to 9.0 to 11.5%. The Ni content is preferably 9.2% or more, more preferably 9.5% or more. Further, the Ni content is preferably 11.2% or less, and more preferably 11.0% or less.
[0032]
　Cr: 17.0 to 21.0%
　Cr is an essential element for ensuring oxidation resistance and corrosion resistance at high temperatures. Also, it contributes to secure the creep strength by forming fine carbide. However, a large content lowers the stability of the austenite phase and, conversely, impairs the creep strength. Therefore, the Cr content is set to 17.0 to 21.0%. The Cr content is preferably 17.2% or more, and more preferably 17.5% or more. Further, the Cr content is preferably 20.8% or less, more preferably 20.5% or less.
[0033]
　Nb: 0.60 to 0.90%
　Nb is combined with C and/or N and precipitates in the grains as fine carbides, nitrides or carbonitrides to improve creep strength and tensile strength at high temperature. Is an element that contributes to. However, if it is contained in excess, a large amount of carbonitride is precipitated, which causes an increase in stress relaxation cracking susceptibility. Further, it solidifies in the solidification process of the weld metal, lowers the melting point of the liquid phase, and increases solidification cracking susceptibility. Therefore, the Nb content is set to 0.60 to 0.90%. The Nb content is preferably 0.65% or more, and preferably 0.85% or less.
[0034]
　Ta: 0.001 to 0.100%
　Like Nb, Ta is combined with C and/or N and precipitates as fine carbides, nitrides or carbonitrides in the grains, and has high creep strength and tensile strength at high temperature. It is an element that contributes to the improvement of strength. In addition, by substituting with Nb and forming a solid solution in nitride or carbonitride, it has an effect of delaying the initiation of precipitation and reducing stress relaxation cracking. However, if it is contained excessively, the stress relaxation cracking susceptibility is increased. Therefore, the Ta content is set to 0.001 to 0.100%. The Ta content is preferably 0.002% or more, and more preferably 0.005% or more in order to sufficiently delay the initiation of precipitation and reduce the stress relaxation cracking susceptibility. preferable. The Ta content is preferably 0.090% or less, more preferably 0.080% or less.
[0035]
　N: 0.01 to 0.15%
　N stabilizes the austenite phase, and forms a solid solution or precipitates as a nitride to contribute to the improvement of high temperature strength. However, if it is contained excessively, a large amount of precipitates are generated, leading to a decrease in ductility. Therefore, the N content is set to 0.01 to 0.15%. The N content is preferably 0.02% or more, more preferably 0.03% or more. Further, the N content is preferably 0.14% or less, and more preferably 0.12% or less.
[0036]
　Al: 0.030% or less When
　Al is contained in a large amount, the cleanability deteriorates and the ductility decreases. Therefore, the Al content is 0.030% or less. The Al content is preferably 0.025% or less, more preferably 0.020% or less. It is not necessary to set a lower limit on the Al content, that is, the Al content may be 0%, but an extreme reduction leads to an increase in the manufacturing cost of the material. Therefore, the Al content is preferably 0.0005% or more, more preferably 0.001% or more.
[0037]
　O: 0.020% or less
　O (oxygen) is included as an impurity. If the content is excessive, toughness and ductility are deteriorated. Therefore, the O content is 0.020% or less. The O content is preferably 0.018% or less, more preferably 0.015% or less. Note that it is not necessary to set a lower limit for the O content, that is, the O content may be 0%, but an extreme reduction causes an increase in the manufacturing cost of the material. Therefore, the O content is preferably 0.0005% or more, more preferably 0.0008% or more.
[0038]
　As described above, Nb causes solidification segregation during welding, lowers the melting point of the liquid phase, and increases solidification cracking susceptibility. In order to prevent this, it is effective to cause eutectic solidification of NbC and the matrix in the solidification process to eliminate the liquid phase early. In order to prevent solidification cracking by utilizing this effect, it is necessary that not only the Nb content falls within the above range but also the following formula (i) is satisfied. The value on the right side of the formula (i) is preferably 0.23, and more preferably 0.20. It is not necessary to set a lower limit on the value on the left side of the formula (i), but it is obvious that the value is −0.258 or more from the range of the content of each element.
　　Nb-7.8×C≦0.25 (i)
　However, the element symbol in the above formula represents the content (mass %) of each element contained in the steel.
[0039]
　In the chemical composition of the weld metal of the present invention, in addition to the above elements, one or more selected from V, Ti, W, Mo, Cu, B, Ca, Mg and REM is further contained within the range shown below. You may let me. The reasons for limiting each element will be described.
[0040]
　V: 0 to 0.10%
　V combines with C and/or N to form fine carbides, nitrides or carbonitrides, and contributes to creep strength. Therefore, V may be contained if necessary. .. However, when it is contained in excess, a large amount of carbonitride is precipitated, which causes deterioration of stress relaxation crack resistance. Therefore, the V content is 0.10% or less. The V content is preferably 0.09% or less, more preferably 0.08% or less. When it is desired to obtain the above effects, the V content is preferably 0.01% or more, more preferably 0.02% or more.
[0041]
　Ti: 0 to 0.10%
　Similar to V, Ti is combined with C and/or N to form fine carbides, nitrides or carbonitrides, and contributes to creep strength. You may. However, if it is contained excessively, a large amount of carbonitride precipitates, resulting in deterioration of stress relaxation crack resistance. Therefore, the Ti content is 0.10% or less. The Ti content is preferably 0.08% or less, more preferably 0.06% or less. In order to obtain the above effects, the Ti content is preferably 0.01% or more, more preferably 0.02% or more.
[0042]
　W: 0 to 0.50%
　W is an element that forms a solid solution in the matrix and contributes to the improvement of creep strength and tensile strength at high temperature, and thus may be contained if necessary. However, if it is contained excessively, the stability of the austenite phase is lowered, and the creep strength is rather lowered. Therefore, the W content is 0.50% or less. The W content is preferably 0.40% or less, more preferably 0.30% or less. In order to obtain the above effect, the W content is preferably 0.01% or more, more preferably 0.02% or more.
[0043]
　Mo: 0 to 0.50%
　Like W, Mo is an element that forms a solid solution in the matrix and contributes to the improvement of creep strength and tensile strength at high temperatures, so it may be contained if necessary. However, if it is contained excessively, the stability of the austenite phase is lowered and the creep strength is impaired. Furthermore, since Mo is an expensive element, excessive inclusion causes an increase in the manufacturing cost of the material. Therefore, the Mo content is 0.50% or less. The Mo content is preferably 0.40% or less, more preferably 0.30% or less. In order to obtain the above effect, the Mo content is preferably 0.01% or more, more preferably 0.02% or more.
[0044]
　Cu: 0 to 0.50%
　Cu is an element that enhances the stability of the austenite phase and contributes to the improvement of creep strength, so Cu may be contained if necessary. However, if it is contained excessively, ductility is lowered. Therefore, the Cu content is 0.50% or less. The Cu content is preferably 0.40% or less, more preferably 0.30% or less. In order to obtain the above effect, the Cu content is preferably 0.01% or more, more preferably 0.02% or more.
[0045]
　B: 0 to 0.005%
　B is also constant in that the grain boundary carbides are finely dispersed to improve the creep strength, and segregate at the grain boundaries to strengthen the grain boundaries to reduce the ductility-decay cracking susceptibility. Therefore, it may be contained if necessary. However, when it is contained excessively, the solidification cracking susceptibility is increased. Therefore, the B content is 0.005% or less. The B content is preferably 0.004% or less, and more preferably 0.003% or less. When it is desired to obtain the above effects, the B content is preferably 0.0002% or more, more preferably 0.0005% or more.
[0046]
　Ca: 0 to 0.010% Since
　Ca has an effect of improving hot deformability, it may be contained if necessary. However, if it is contained in excess, it binds to oxygen, significantly deteriorating the detergency and conversely deteriorating the hot deformability. Therefore, the Ca content is 0.010% or less. The Ca content is preferably 0.008% or less, more preferably 0.005% or less. When it is desired to obtain the above effects, the Ca content is preferably 0.0005% or more, more preferably 0.001% or more.
[0047]
　Mg: 0 to 0.010%
　Similar to Ca, Mg has an effect of improving hot deformability, and thus may be contained if necessary. However, if it is contained in excess, it binds to oxygen and significantly deteriorates the detergency, and rather deteriorates the hot deformability. Therefore, the Mg content is 0.010% or less. The Mg content is preferably 0.008% or less, more preferably 0.005% or less. In order to obtain the above effect, the Mg content is preferably 0.0005% or more, more preferably 0.001% or more.
[0048]
　REM: 0 to 0.10%
　Similar to Ca and Mg, REM has an effect of improving hot deformability, and thus may be contained if necessary. However, if it is contained in excess, it binds to oxygen, significantly deteriorating the cleanliness and conversely deteriorating the hot deformability. Therefore, the REM content is 0.10% or less. The REM content is preferably 0.08% or less, more preferably 0.06% or less. In order to obtain the above effects, the REM content is preferably 0.0005% or more, more preferably 0.001% or more.
[0049]
　Here, REM refers to a total of 17 elements of Sc, Y and lanthanoid, and the content of the REM means the total content of these elements.
[0050]
　In the chemical composition of the weld metal of the present invention, the balance is Fe and impurities. Here, the "impurity" is a component that is mixed in by raw materials such as ore and scrap when manufacturing steel industrially, and various factors of the manufacturing process, and is allowed within a range that does not adversely affect the present invention. Means something.
[0051]
　(B) Manufacturing Method
　The austenitic stainless steel weld metal according to the present invention is produced by welding a base material of austenitic stainless steel. In addition, when welding the base material, the austenitic stainless steel weld metal may be produced by using a welding material (a filler material).
[0052]
　The welding method for obtaining the austenitic stainless steel weld metal according to the present invention is not particularly limited, but examples thereof include TIG welding, MIG welding, covered arc welding, submerged arc welding, and laser welding.
[0053]
　As a method of producing an austenitic stainless steel weld metal so as to satisfy the above chemical composition, a method of controlling by adjusting the chemical composition of the base material of the austenitic stainless steel to be used, and further a welding material (filler material) When used, a method of controlling by also adjusting the chemical composition of the welding material can be mentioned.
[0054]
　For example, as the base material and welding material (filler material) of the austenitic stainless steel to be used, only the material satisfying the above chemical composition may be used so that the obtained weld metal may satisfy the above chemical composition. Further, by using a material that does not satisfy the above chemical composition as at least one of the base material and the welding material (filler material) of austenitic stainless steel, the weld metal obtained by adjusting the balance between the two compositions May be prepared so as to satisfy the above chemical composition.
[0055]
　The preferable composition of the austenitic stainless steel base material is not particularly limited. For example, the chemical composition of the base material is, in mass %, C: 0.04 to 0.12%, Si: 0.20 to 0.50%, Mn: 1.0 to 2.0%, P: 0. 045% or less, S: 0.0020% or less, Co: 0.02 to 0.80%, Ni: 9.0 to 12.0%, Cr: 16.5 to 18.5%, Nb: 0.50. To 0.90%, Ta: 0.001 to 0.100%, N: 0.01 to 0.13%, Al: 0.030% or less, O: 0.020% or less, V: 0 to 0. 10%, Ti:0 to 0.10%, W:0 to 0.60%, Mo:0 to 0.60%, Cu:0 to 0.60%, B:0 to 0.005%, Ca: It is preferable that 0 to 0.010%, Mg: 0 to 0.010%, REM: 0 to 0.10%, and the balance: Fe and impurities.
[0056]
　The chemical composition of the base material is, in mass %, V: 0.01 to 0.10%, Ti: 0.01 to 0.10%, W: 0.01 to 0.60%, Mo: 0.01. To 0.60%, Cu: 0.01 to 0.60%, B: 0.0002 to 0.005%, Ca: 0.0005 to 0.010%, Mg: 0.0005 to 0.010%, Also, one or more selected from REM: 0.0005 to 0.10% may be contained.
[0057]
　The method for producing the base material and welding material (filler material) of the above austenitic stainless steel is not particularly limited, but for the steel whose chemical composition is adjusted, hot forging, heat It can be manufactured by sequentially performing hot rolling, heat treatment, and machining.
[0058]
　(C) Welded structure The welded structure according to the
　present invention is a structure having the above-described austenitic stainless steel weld metal. For example, a welded structure is composed of a weld metal and a base material. The base material is made of a metal and is preferably a steel material, more preferably stainless steel, and further preferably an austenitic stainless steel. The specific shape of the welded structure and the specific mode (welding posture) of welding for obtaining the welded structure are not particularly limited.
[0059]
　Hereinafter, the present invention will be described more specifically by way of examples, but the present invention is not limited to these examples.
Example 1
[0060]
　A plate material (base material) having a plate thickness of 15 mm, a width of 50 mm, and a length of 100 mm was formed from an ingot obtained by melting and casting steel having the chemical composition shown in Table 1 by hot forging, hot rolling, heat treatment and machining. A plate material having a plate thickness of 4 mm, a width of 200 mm and a length of 500 mm was produced. Further, using the above plate material having a plate thickness of 4 mm, a cut filler having a 2 mm square and a length of 500 mm was produced by machining. Using these, various performance evaluation tests shown below were performed.
[0061]
[table 1]

[0062]
　
　A groove in the shape shown in FIG. 1 was applied to the end portion in the longitudinal direction of the base material. After that, two base materials having a groove formed therein were butted against each other and restrained at their four circumferences on a commercially available steel plate which was grooved so as not to interfere with the back bead. The commercially available steel plate was a steel plate specified in JIS G 3160 (2008) of SM400B, and had a thickness of 30 mm, a width of 150 mm, and a length of 200 mm. In addition, the above-mentioned constraint welding was performed using a covered arc welding rod ENi6625 specified in JIS Z 3224 (2010).
[0063]
　Then, laminated welding was performed by TIG welding in the groove. The above-mentioned lamination welding was performed using a cut filler obtained from the same plate material as each base material as a filler material. The heat input was 9 to 15 kJ/cm, and three welded joints were prepared for each base material. Then, one of the welded joints produced from each base material was left as-welded, and the other was subjected to an aging heat treatment at 650° C. for 500 hours. For each of the welded joints, test pieces were collected from 5 locations. The cross section of the collected test piece was mirror-polished and then corroded, and observed by an optical microscope to examine the presence or absence of cracks in the weld metal. Then, in all of the five test pieces, a welded joint having no crack was judged as "pass", and a welded joint in which crack was observed was judged as "fail". Since the base material and the cut filler have the same composition, the chemical composition in Table 1 is synonymous with the chemical composition of the weld metal.
[0064]
　
　Furthermore, a round bar creep rupture test piece was sampled from the remaining one of the welded joints that passed the evaluation of weld cracking resistance so that the weld metal was at the center of the parallel portion, A creep rupture test was performed under the conditions of 650° C. and 216 MPa at which the target rupture time of the base material was about 1000 hours. Then, the case where the breaking time was 90% or more of the target breaking time of the base material was defined as “pass”.
[0065]
　The results are summarized in Table 2.
[0066]
[Table 2]

[0067]
　As can be seen from Table 2, Test Nos. using Steels A to F satisfying the requirements of the present invention as both the base metal and the filler metal. In Nos. 1 to 6, sufficient solidification crack resistance and stress relaxation crack resistance were exhibited during welding and aging at high temperature, and the creep strength was excellent.
[0068]
　On the other hand, since the S content of Steel G, which is a comparative example, is out of the regulation, the test No. In No. 7, cracking considered to be stress relaxation cracking occurred in the weld metal due to aging at high temperature. Further, since Steel H exceeded the upper limit of the formula (i), the test No. In No. 8, solidification cracking occurred as a result of the melting point of the liquid phase lowering due to free Nb during solidification of the weld metal. Also, in the cross-section observation after high temperature aging, cracks that were considered to be solidification cracks that occurred during welding were observed.
[0069]
　Steel I has a Nb content lower than the lower limit value. In No. 9, cracking did not occur during welding and aging at high temperature, but the required creep strength was not obtained. Further, in Steel J, since the Nb content exceeded the upper limit value, a large amount of precipitate was generated, and cracks considered to be stress relaxation cracks occurred in the weld metal due to aging at high temperature.
Example 2
[0070]
　A plate material (base material) having a plate thickness of 25 mm, a width of 50 mm, and a length of 100 mm was produced from the residual material of the ingots of the steels A to F used in Example 1 by hot forging, hot rolling, heat treatment, and machining. .. Using this, various performance evaluation tests shown below were performed.
[0071]
　
　A groove in the shape shown in Fig. 2 was applied to the longitudinal end of the base material. After that, two base materials having a groove formed therein were butted against each other, and four circumferences were restrained and welded onto a commercially available steel plate which was grooved so as not to interfere with the back bead. The commercially available steel plate was a steel plate specified in JIS G 3160 (2008) of SM400B and had a thickness of 40 mm, a width of 150 mm and a length of 200 mm. In addition, the above-mentioned constraint welding was performed using a covered arc welding rod ENi6625 specified in JIS Z 3224 (2010).
[0072]
　Then, laminated welding was performed by TIG welding in the groove. The above-mentioned lamination welding was performed using a cut filler obtained from the same plate material as each base material as a filler material. The heat input was 9 to 18 kJ/cm, and two welded joints were produced for each base material. Then, one of the welded joints produced from each base material was left as-welded, and the other one was subjected to aging heat treatment at 650° C. for 500 hours. For each of the welded joints, test pieces were collected from 5 locations. The cross section of the collected test piece was mirror-polished and then corroded, and observed by an optical microscope to examine the presence or absence of cracks in the weld metal. A welded joint with no cracks in all five samples was evaluated as “good”, and a welded joint in which cracks were observed in only one sample was evaluated as “acceptable” with “passed” and cracks were found in two or more samples. The welded joint was judged to be "failed".
[0073]
　The results are summarized in Table 3.
[0074]
[Table 3]

[0075]
　As can be seen from Table 3, Test Nos. in which Steels A to F satisfying the requirements of the present invention were used as both the base metal and the filler metal. In Nos. 11 to 16, even under severe restraint conditions in which the plate thickness was increased, sufficient solidification crack resistance and stress relaxation crack resistance were exhibited during welding and aging at high temperature. However, the test No. In No. 12, although it was judged as acceptable, the Ta content was as small as 0.001%, so that very slight stress relaxation cracking occurred in one cross section.
Example 3
[0076]
　A plate material (base material) having a plate thickness of 15 mm, a width of 50 mm, and a length of 100 mm is formed by hot forging, hot rolling, heat treatment and machining from an ingot obtained by melting and casting steel having the chemical composition shown in Table 4. It was made. Using this, various performance evaluation tests shown below were performed.
[0077]
[Table 4]

[0078]
　
　A groove in the shape shown in FIG. 1 was applied to the end portion in the longitudinal direction of the base material. After that, two base materials having a groove formed therein were butted against each other and restrained at their four circumferences on a commercially available steel plate which was grooved so as not to interfere with the back bead. The commercially available steel plate was a steel plate specified in JIS G 3160 (2008) of SM400B, and had a thickness of 30 mm, a width of 150 mm, and a length of 200 mm. In addition, the above-mentioned constraint welding was performed using a covered arc welding rod ENi6625 specified in JIS Z 3224 (2010).
[0079]
　Then, laminated welding was performed by TIG welding in the groove. The above-mentioned lamination welding was performed using a cut filler obtained from a plate material of steel A as a filler material. The heat input was 9 to 15 kJ/cm, and three welded joints were prepared for each base material. Then, one of the welded joints made from each base material was left as-welded, and chips were collected from the weld metal for chemical analysis. The remaining one body was aged at 650° C. for 500 hours.
[0080]
　For each of the welded joints, test pieces were collected from 5 locations. The cross section of the collected test piece was mirror-polished and then corroded, and observed by an optical microscope to examine the presence or absence of cracks in the weld metal. Then, in all of the five test pieces, a welded joint having no crack was judged as "pass", and a welded joint in which crack was observed was judged as "fail".
[0081]
　
　Further, a round bar creep rupture test piece was sampled from the remaining one body of the welded joint so that the weld metal was at the center of the parallel portion, and the target rupture time of the base metal was about 1000 hours 650. A creep rupture test was conducted under the conditions of 216° C. and 216 MPa. Then, the case where the breaking time was 90% or more of the target breaking time of the base material was defined as “pass”.
[0082]
　The results are summarized in Tables 5 and 6.
[0083]
[Table 5]

[0084]
[Table 6]

[0085]
　As can be seen from Tables 5 and 6, the test No. in which the chemical composition of the weld metal satisfies the requirements of the present invention. In Nos. 17 to 19, sufficient solidification crack resistance and stress relaxation crack resistance were exhibited during welding and aging at high temperature, and the creep strength was excellent.
[0086]
　As described above, it is understood that sufficient solidification crack resistance, stress relaxation crack resistance, and excellent creep strength can be obtained only when the requirements of the present invention are satisfied.
Industrial availability
[0087]
　According to the present invention, an austenitic stainless steel weld metal having a weld creep resistance and a high creep strength, which constitutes a structure used in equipment used at high temperatures, and a weld metal having the same A structure can be obtained.
The scope of the claims
[Claim 1]
　The chemical composition is% by mass,
　C: 0.05 to 0.11%,
　Si: 0.10 to 0.50%,
　Mn: 1.0 to 2.5%,
　P: 0.035% or less,
　S : 0.0030% or less,
　Co: 0.01 to 1.00%,
　Ni: 9.0 to 11.5%,
　Cr: 17.0 to 21.0%,
　Nb: 0.60 to 0.90% ,
　Ta: 0.001 to 0.100%,
　N: 0.01 to 0.15%,
　Al: 0.030% or less,
　O: 0.020% or less,
　V: 0 to 0.10%,
　Ti: 0 to 0.10%,
　W: 0 to 0.50%,
　Mo: 0 to 0.50%,
　Cu: 0 to 0.50%,
　B: 0 to 0.005%,
　Ca: 0 to 0.010 %,
　Mg: 0 to 0.010%,
　REM: 0 to 0.10%,
　balance: Fe and impurities, which
　satisfy the following formula (i) :
　Austenitic stainless steel weld metal.
　　Nb-7.8×C≦0.25 (i)
　However, the element symbol in the above formula represents the content (mass %) of each element contained in the steel.
[Claim 2]
　The chemical composition is% by mass,
　V: 0.01 to 0.10%,
　Ti: 0.01 to 0.10%,
　W: 0.01 to 0.50%,
　Mo: 0.01 to 0. 50%,
　Cu: 0.01 to 0.50%,
　B: 0.0002 to 0.005%,
　Ca: 0.0005 to 0.010%,
　Mg: 0.0005 to 0.010%, and
　REM : 0.0005 to 0.10%,
　the austenitic stainless steel weld metal according to claim 1.
[Claim 3]
　A welded structure comprising the austenitic stainless steel weld metal according to claim 1 or 2.