[0001]The present invention relates to an austenitic heat resistant alloy and welded joints using the same.
BACKGROUND
[0002]Recently, new construction of ultra-supercritical boiler with improved temperature and pressure of the steam for high efficiency have been developed throughout the world. Such use conditions of the device in a high temperature environment is remarkably severer, to the request performance materials used with it have become stricter. For example, in the field of boilers for thermal power generation, the steam temperature is above 650 ° C., high creep strength is required.
[0003]
　Further, welding in order to use the material as a structural member or the like is essential, so that the high creep strength at the weld portion is required. Therefore, by containing optimum amounts of various alloying elements, austenitic stainless steel having improved creep strength it has been invented.
[0004]
　With respect to the stringent requirements, Patent Document 1, high strength austenitic stainless heat resistant steels excellent in embrittlement cracking resistance of weld during high temperature use to be used in high temperature devices such as power boiler is disclosed .
CITATION
Patent Document
[0005]
Patent Document 1: International Publication No. WO 2009/044796
Summary of the Invention
Problems that the Invention is to Solve
[0006]
　In Patent Document 1, P, S, Sn, Sb, Pb, as well as reducing the content of Zn and As, Nb, V, by adjusting Ti, and the content of N in the specific range, the weld heat affected part (HAZ) less susceptibility to cracking in, it is possible to obtain a high strength austenitic stainless heat resistant steels excellent in embrittlement cracking resistance of weld.
[0007]
　However, in the technique described in Patent Document 1, although there have been detailed studies regarding cracks in HAZ, not been studied with respect to cracks in the weld metal, there remains room for improvement.
[0008]
　The present invention solves the above problems, the weld metal low crack susceptibility, and aims to provide a suitable austenitic heat resistant alloy for making welded joints having excellent creep strength.
Means for Solving the Problems
[0009]
　The present invention has been made to solve the above problems, and the gist of welded joints using austenitic heat resistant alloy and its following.
[0010]
　(1) chemical composition, in
　mass%, C: 0.04 ~
　0.18%, Si: 1.5% or
　less, Mn: 2.0% or
　less, P: 0.020% or
　less, S: 0. 030% or
　less, Cu: 0.10% or
　less,
　Ni: 20.0 ~
　30.0%, Cr: 21.0 ~ 24.0%, Mo: 1.0
　~ 2.0%, Nb: 0.10
　0.40% ~, Ti: 0.20% or
　less, Al: 0.05% or
　less,
　N: 0.10 ~ 0.35%, B: 0.0015 ~ 0.005%,
　the balance of Fe and impurities There,
　it satisfies the following equation (i),
　austenitic heat resistant alloy.
　P + 6B ≦ 0.040 ··· (i )
　wherein each element symbol in the formulas represents the content of each element contained in the alloy (mass%).
[0011]
　(2) A heat-resistant alloy used to make the weld joint using the welding material,
　the chemical composition of the weld material, by
　mass%, C: 0.01 ~
　0.18%, Si: 1 .5% or
　less, Mn: 2.0% or
　less, P: 0.020% or
　less, S: 0.030% or
　less, Cu: 0.15% or
　less, Cr: 20.0 ~
　25.0%, Mo: 10.0% or less,
　Nb: 4.0% or
　less, Ti: 0.50% or
　less, Co: 15.0% or
　less, Al: 2.0% or
　less, B: 0.005% or
　less, Fe: 30. 0% or less,
　the balance is Ni and impurities,
　austenitic heat resistant alloy according to the above (1).
[0012]
　(3) and the base metal made of austenitic heat resistant alloy according to the above (1),
　by
　mass%, C: 0.01 ~
　0.18%, Si: 1.5% or
　less, Mn: 2.0%
　hereinafter, P: 0.020% or
　less, S: 0.030% or
　less, Cu: 0.15% or
　less,
　Ni: 20.0 ~ 90.0%, Cr: 21.0 ~ 24.0%,
　Mo:
　~ 10.0% 1.0, Nb: 0.01
　~ 4.0%, Ti: 0.20% or
　less, Co: 15.0% or
　less, Al: 2.0% or
　less, N: 0.01 ~
　0.35%, B: 0.005% or less,
　the balance is Fe and impurities,
　including a weld metal having a chemical composition satisfying the (ii) the following equation,
　welded joint of austenitic heat resistant alloy.
　P + 6B ≦ 0.030 ··· (ii )
　wherein each element symbol in the formulas represents the content of each element contained in the weld metal portion (mass%).
Effect of the invention
[0013]
　According to the present invention, cracking susceptibility of the weld metal is low and it is possible to obtain a suitable austenitic heat resistant alloy for making welded joints having excellent creep strength.
DESCRIPTION OF THE INVENTION
[0014]
　It will be described in detail below each requirement of the present invention.
[0015]
　1. Heat the chemical composition of the alloy (base material)
　reasons for limiting each element are as follows. Incidentally, "%" for the content in the following description means "mass%".
[0016]
　C: 0.04 ~ 0.18%
　C, as well as has the effect of stabilizing the austenitic phase, with forms fine intragranular carbonitrides N, an element which contributes to the improvement of high-temperature strength. However, to generate the coarse carbides during use at high temperatures when the content of C is excessive, the corrosion resistance decreases with lowering the creep strength. Therefore, C content is from 0.04 to 0.18%. C content is preferably 0.05% or more is preferably not more than 0.13%.
[0017]
　Si: 1.5% or less
　Si has a deoxidizing effect, also, the corrosion resistance at high temperatures, is an element effective oxidation resistance. However, when the content is excessive, reduce the stability of the austenite phase, it leads to a decrease in creep strength and toughness. Therefore, Si content is 1.5% or less. Si content is preferably but 1.0% or less, and more preferably 0.8% or less.
[0018]
　It is not necessary to particularly specify any lower limit in the Si content, the extreme lowering, with deoxidizing effect degrades the cleanliness of the steel is not sufficiently obtained, leading to increase in manufacturing cost. Therefore, Si content is preferably 0.02% or more.
[0019]
　Mn: 2.0% or less
　Mn has a deoxidizing effect similar to the Si. Mn also contributes to stabilization of austenite phase. However, when the content is excessive, lead to embrittlement, causing a decrease in creep ductility and toughness. Therefore, Mn content is 2.0% or less. Mn content is preferably 1.5% or less.
[0020]
　It is not necessary to particularly specify any lower limit in the Mn content, the extreme lowering, with deoxidizing effect degrades the cleanliness of the steel is not sufficiently obtained, leading to increase in manufacturing cost. Therefore, Mn content is preferably 0.02% or more.
[0021]
　P: 0.020% or less
　S: 0.030% or less
　P and S are elements included as an impurity in the alloy. Both of these elements lowers the melting point of the final solidified portion during solidification of the weld metal, with significantly increase the solidification cracking susceptibility, leads to a decrease in stress relaxation cracking resistance causing grain boundary embrittlement during use at high temperatures it is an element. Thus, each content, P: 0.020% or less and S: is limited to 0.030% or less.
[0022]
　Cu: 0.10% or less
　Cu is an excessive contained, an element leading to embrittlement. Therefore, Cu content is desirably reduced as much as possible, and 0.10% or less. Cu content is preferably less than 0.05%, more preferably less than 0.01%.
[0023]
　Ni: 20.0 ~ 30.0% Ni
　is an element effective for obtaining an austenitic structure, to ensure structural stability of long-term use at an indispensable element in order to obtain the desired creep strength is there. In order to obtain a sufficient effect of the range of Cr content specified by the present invention is required to contain more than 20.0%. On the other hand, since Ni is an expensive element, if its content exceeds 30.0%, causing an increase in cost. Therefore, Ni content is 20.0 to 30.0%. Ni content is preferably 22.0% or more is preferably not more than 28.0%.
[0024]
　Cr: 21.0 ~
　24.0% Cr is an essential element for ensuring the oxidation resistance and corrosion resistance at high temperatures. To obtain the effect, it is necessary to contain more than 21.0 percent. However, the content thereof is excessive, in particular, when it exceeds 24.0% by reducing the stability of the austenite phase at high temperatures, leading to reduction in creep strength. Therefore, Cr content is 21.0 to 24.0%. Cr content is preferably 21.5% or more is preferably not more than 23.5%.
[0025]
　Mo: 1.0 ~
　2.0% Mo, the improvement of high-temperature strength by solid solution in the matrix, an element which contributes to the improvement of creep strength at inter alia a high temperature. However, the stability of the austenite phase when the Mo content is excessive decreases, thereby rather lower the creep strength. Further, there is a possibility to increase the weld metal cracking susceptibility. Therefore, Mo content is 1.0 to 2.0%. Mo content is preferably at 1.2% or more, and preferably not more than 1.8%.
[0026]
　Nb: 0.10 ~
　0.40% Nb is finely precipitated in the grains as carbonitrides, an element which contributes to the improvement of creep strength at high temperatures. However, when the Nb content is excessive, and carbonitride rapidly coarsened during use at high temperatures, leading to extreme reduction in creep strength and toughness. Further, there is a possibility to increase the weld metal cracking susceptibility. Therefore, Nb content is from 0.10 to 0.40%. Nb content is preferably 0.15% or more is preferably not more than 0.35%.
[0027]
　Ti: 0.20% or less
　Ti is finely precipitated in the grains as carbonitrides, but an element contributing to the improvement of creep strength at high temperatures, when the content is excessive, during use at high temperatures carbonitrides rapidly coarsened, not only leads to extreme reduction in creep strength and toughness, leading to significant increase in liquation cracking susceptibility during welding. Therefore, Ti content is 0.20% or less.
[0028]
　Al: 0.05% or less
　Al has the deoxidation, addition of a large amount impairs significantly the cleanliness and deteriorates the workability and ductility. Therefore, Al content is 0.05% or less. The lower limit of the Al content is not particularly provided but is preferably 0.0005% or more.
[0029]
　N: 0.10 ~ 0.35% N
　is an austenite stabilizing element, as well as a solid solution in the matrix, similarly forms fine intragranular carbonitrides and C, and to ensure creep strength at high temperatures an element which contributes. In addition, an element effective in improving the corrosion resistance of. However, when N content becomes excessive, nitrides large amount deposited, in addition to reducing the creep ductility, reduce the hot workability, which causes surface defects of the base material. Therefore, N content is 0.10 to 0.35%. N content is preferably at 0.15% or more, and preferably 0.30% or less.
[0030]
　B: 0.0015 ~ 0.005%
　B, by finely dispersing a grain boundary carbides as well as segregation in grain boundaries, an element which contributes to grain boundary strengthening. However, when the B content is excessive, during solidification of the weld metal lowers the melting point of the final solidified portion, with significantly increase the solidification cracking susceptibility, the stress relaxation cracking resistance causing grain boundary embrittlement during use at high temperatures It leads to a decrease. Therefore, B content is from 0.0015 to 0.005%. B content is preferably at 0.002% or more, preferably not more than 0.0045%.
[0031]
　In the chemical composition of the austenitic heat resistant alloys of the present invention, the balance being Fe and impurities. Here, the "impurities", when producing the alloy industrially, ores, raw material scraps, a component mixed by various factors of the manufacturing process, is allowed to the extent that the present invention does not adversely affect means shall.
[0032]
　P + 6B ≦ 0.040 ··· (i )
　wherein each element symbol in the formulas represents the content of each element contained in the alloy (mass%).
　Even within the chemical composition of the above alloy, there is a case where cracking occurs in the weld metal. However, the content of the relationship between P and B, by satisfying the above formula (i), it is possible to suppress the first layer solidification cracking and reheat cracking in the weld metal.
[0033]
　2. Chemical composition of the weld material
　for the composition of the weld material to be used in welding the base material, is not provided particularly limited, it preferably has a chemical composition described below.
[0034]
　C: 0.01 ~ 0.18%
　C is an austenite forming element, it is an element effective for enhancing the stability of the austenitic structure at high temperatures used. Furthermore C increases the resistance to hot cracking during welding. Specifically, C is primarily to form a combine with Cr eutectic carbides in the solidification process during welding. Thus the loss of liquid phase earlier, the final solidified portion of the tissue (Cr, M) 23 C 6 to lamellar structure of the austenite. As a result, the residual form of the liquid phase along with changes from planar to the point shape, stress concentration at a particular surface is suppressed, solidification cracking is inhibited. Furthermore C, since increasing the final solidification interfacial area as the impurity segregation sites contributes to susceptibility reduction of the stress relaxation cracking in preventing ductility dip cracking during welding and high temperature service.
[0035]
　In the range of Cr content, which will be described later, for the above-described effect may sufficiently, the C content should be 0.01% or more. However, if excessively contained C, excess C that do not carbide fine precipitated as carbides during use at high temperatures, thereby adversely increasing the stress relaxation cracking susceptibility during solidification. Therefore, the content of C is set to 0.01 to 0.18%. C content is preferably 0.02% or more, more preferably 0.06% or more. Also, C content is preferably 0.15% or less.
[0036]
　Si: 1.5% or less
　Si is contained as a deoxidizing agent, segregates in columnar Akiratsubu boundaries during solidification of the weld metal lowers the melting point of the liquid phase, increases the solidification cracking susceptibility. Therefore, Si content should be 1.5% or less. It is not necessary to particularly specify any lower limit in the Si content, the extreme lowering, with deoxidizing effect degrades the cleanliness of the steel is not sufficiently obtained, leading to increase in manufacturing cost. Therefore, Si content is preferably 0.02% or more.
[0037]
　Mn: 2.0% or less
　Mn, like Si, is contained as a deoxidizing agent. Mn is suppressed scattering of N from in the arc atmosphere by lowering the activity of N in the weld metal, also contribute to securing the strength. However, because it causes embrittlement if excessive containing Mn, the content of Mn should be 2.0% or less. The content of Mn is preferably 1.5% or less.
[0038]
　It is not necessary to particularly specify any lower limit in the Mn content, the extreme lowering, with deoxidizing effect degrades the cleanliness of the steel is not sufficiently obtained, leading to increase in manufacturing cost. Therefore, Mn content is preferably 0.02% or more.
[0039]
　P: 0.020% or less
　S: 0.030% or less
　P and S are contained as an impurity, lowers the melting point of the final solidified portion during solidification of the weld metal, significantly increase the solidification cracking susceptibility. Therefore, P content is 0.020% or less, S content should be as 0.030% or less. P content 0.015% is less, S content is preferably not more than 0.020% or.
[0040]
　Cu: 0.15% or less
　Cu is an excessive contained, an element leading to embrittlement. Therefore, Cu content is desirably reduced as much as possible, and 0.15% or less. Cu content is preferably 0.10% or less.
[0041]
　Cr: 20.0 ~
　25.0% Cr is an essential element for ensuring the oxidation resistance and corrosion resistance at high temperatures. Cr combines with C in the solidification process, to produce a eutectic carbides, thereby preventing the solidification cracking and ductility dip cracking during welding, also has the action of reducing the stress relaxation cracking susceptibility during high temperature use. In order to obtain these effects, it is necessary that the Cr content is 20.0% or more. However, if the Cr content exceeds 25.0% becomes excessive, stability of the tissue at a high temperature is deteriorated, leading to reduction in creep strength. Therefore, Cr content is 20.0 to 25.0%. Cr content is preferably at 20.5% or more, and preferably not more than 24.5 percent.
[0042]
　Mo: 10.0% or less
　Mo is the improvement of high-temperature strength by solid solution in the matrix, an element which contributes to the improvement of creep strength at inter alia a high temperature. However, local corrosion at high temperature along with the stability of the austenite phase when the Mo content is excessive drops increases. Therefore, Mo content is at most 10.0%. Mo content is preferably not more than 9.5%. The lower limit need not be particularly specified, it is 0%. However, when it is desired to obtain the effects described above, Mo content is preferably at least 0.5%, more preferably at least Mo content in the matrix.
[0043]
　Nb: 4.0% or less
　Nb is finely precipitated in the grains as carbonitrides, an element which contributes to the improvement of creep strength at high temperatures. However, when the Nb content is excessive, and carbonitride rapidly coarsened during use at high temperatures, leading to extreme reduction in creep strength and toughness. Further, there is a possibility to increase the weld metal cracking susceptibility. Therefore, Nb content is 4.0%. Nb content is preferably 3.5% or less. The lower limit need not be particularly specified, it is 0%. However, when it is desired to obtain the above effect is preferably Nb content is 0.1% or more, and more preferably 0.5% or more.
[0044]
　Ti: 0.50% or less
　Ti is finely precipitated in the grains as carbonitrides, but an element contributing to the improvement of creep strength at high temperatures, when the content is excessive, during use at high temperatures carbonitrides rapidly coarsened, not only leads to extreme reduction in creep strength and toughness, leading to significant increase in liquation cracking susceptibility during welding. Therefore, Ti content is preferably to reduce, and 0.50% or less.
[0045]
　Co: 15.0% or less
　Co, like Ni and Cu, is an austenite forming element, which contributes to the improvement of creep strength by increasing the stability of the austenitic structure. However, Co is because it is a very expensive element, an excessive content leads to significant cost increase. Therefore, Co content is at most 15.0%. Co content is preferably not more than 14.0%. The lower limit need not be particularly specified, it is 0%. However, when it is desired to obtain the effects described above, Co content is preferably 0.5% or more.
[0046]
　Al: 2.0% or less
　Al is an element having a deoxidizing action. However, addition of a large amount impairs significantly the cleanliness and deteriorates the workability and ductility. Therefore, Al content is 2.0% or less. The lower limit need not be particularly specified, it is 0%. However, when it is desired to obtain the effects described above, Al content is preferably 0.5% or more.
[0047]
　B: 0.005% or less
　B segregates in grain boundaries during the use at high temperatures, it is an element effective for improving the creep strength by finely dispersing the grain boundary carbides to strengthen the grain boundaries. Therefore, it may contain a B in order to obtain this effect. However, excessive content of B increases the solidification cracking susceptibility of the gas shielded arc welding. Therefore, B content is 0.005% or less. B content is preferably not more than 0.0045%. The lower limit need not be particularly specified, it is 0%. However, when it is desired to obtain the effects described above, B content is preferably 0.002% or more.
[0048]
　Fe: 30.0% or less
　Fe is effective to obtain the austenitic structure, to ensure structural stability of the long period of use time, is an essential element in order to obtain the desired creep strength. However, in order to ensure the Ni content, Fe content is at most 30.0%. Fe content is preferably not more than 20.0%.
[0049]
　In the chemical composition of the welding material, the balance being Ni and impurities. Here, the "impurities", when producing the alloy industrially, ores, raw material scraps, a component mixed by various factors of the manufacturing process, is allowed to the extent that the present invention does not adversely affect means shall.
[0050]
　3. Chemical composition of the weld metal
　chemical composition of the weld metal formed by using the base material and welding material having a chemical composition described above, is determined by the flow ratio between the base metal and the welding material. Therefore, the welded joint of the present invention, the weld metal portion, in mass%, C: 0.01 ~ 0.18% , Si: 1.5% or less, Mn: 2.0% or less, P: 0.020 % or less, S: 0.030% or less, Cu: 0.15% or less, Ni: 20.0 ~ 90.0%, Cr: 21.0 ~ 24.0%, Mo: 1.0 ~ 10.0 %, Nb: 0.01 ~ 4.0% , Ti: 0.20% or less, Co: 15.0% or less, Al: 2.0% or less, N: 0.01 ~ 0.35%, B: 0.005% or less, and the balance: an Fe and impurities, it is preferred to have a chemical composition satisfying the following (ii) expression.
[0051]
　Among the above, it is preferable C content is 0.02% or more is preferably not more than 0.15%. Si content is preferably 0.02% or more is preferably 1.0% or less. Mn content is preferably at 0.02% or more, and preferably 1.5% or less. P content 0.015% is less, S content is preferably not more than 0.020% or. Cu content is preferably less than 0.10%.
[0052]
　Further, it is preferable Ni content is 30.0% or more, but preferably not more than 80.0%, more preferably not more than 70.0, further not more than 60.0% preferable. Cr content is preferably at 21.2% or more, and preferably not more than 23.5%. Mo content is preferably 2.0% or more is preferably not more than 9.5%. Nb content is preferably 0.10% or more is preferably not more than 3.5%.
[0053]
　Furthermore, Co content is preferably at least 0.5%, and preferably not more than 14.0%. Al content is preferably at least 0.01%, and preferably 1.5% or less. N content is preferably at 0.02% or more, and preferably not more than 0.15%. B content is preferably at not less than 0.0002%, preferably not more than 0.0045%.
[0054]
　P + 6B ≦ 0.030 ··· (ii )
　wherein each element symbol in the formulas represents the content of each element contained in the weld metal portion (mass%).
　In particular, the P and B in the weld metal portion, by satisfying the above (ii) expression, it is possible to suppress the first layer solidification cracking and reheat cracking in the weld metal.
[0055]
　The following examples illustrate the present invention more specifically, the present invention is not limited to these examples.
Example
[0056]
　By dissolving an alloy having a chemical composition shown in Table 1, hot forging, and hot rolling and cold rolling, were subjected to a solution heat treatment at 1230 ° C.. Thereafter, JIS Z 3001-1 thickness 15mm which U beveling is performed to the number 14349 root radius r = 0.5 mm, root face b = 1.2 mm, and the included angle theta = 40 ° of the (2013) to prepare a width 120 mm, restraint weld cracking test specimens length 200 mm.
[0057]
　With each restraint weld cracking test specimens obtained as described above, with reference to JIS Z 3224 (2010) to the provisions ENi6182 as covered electrode, thickness 25 mm, width 200 mm, length 300 mm JIS to G 3106 (2008) on a commercial steel of defined SM400C, it was constrained welded four sides.
[0058]
[Table 1]

[0059]
　Thereafter, the inside of GMA was performed first layer TIG welding using a spool welding material diameter 1.2mm, having the chemical compositions shown in Table 2. Heat input 9 ~ 12kJ / cm, feed rate of the welding material is a condition of 150 mm / min. Then, leaving about half the root pass weld, it was laminated welding the remainder under the conditions of heat input 9 ~ 12kJ / cm. At that time, the interpass temperature was controlled to 0.99 ° C. or less. Then, to measure the composition of the weld metal by quantified EPMA analysis of the central portion of the weld metal. The results are shown in Table 3.
[0060]
[Table 2]

[0061]
[table 3]

[0062]
　After the above welding procedure, each test specimen, the cross-sectional microstructure observation test pieces of the joint, the welded portion only initial layer, and two each were taken from the lamination welding portion. Then, chromic acid electrolytic corrosion after mirror polishing the cross section, the occurrence of cracks was observed as 500-fold magnification using an optical microscope. Solidification cracking to cracking was observed in the welded portion only initial layer, cracks in the laminated welded portions when observed was determined to be reheat cracking. Then, the case where solidification cracking or reheat cracking was observed from all of the test piece "○", and the case where the observed from at least one specimen as "×".
[0063]
　Next, the weld metal portion, so as to be positioned at the center of the parallel portion diameter 6 mm, length 10 mm, cut out round bar creep test specimens stepped was performed creep rupture tests. Then, assuming the actual use environment, was a case where the break time during the stress load of 200MPa is more than 1,000 hours at 650 ℃ as "○", "×" the case is less than 1,000 hours.
[0064]
　The results are shown in Table 4.
[0065]
[Table 4]

[0066]
　If using a base material which satisfies the requirements of the present invention, solidification cracking in the weld metal, without generating both of reheat cracking, it resulted in showing a better creep strength. In contrast, the value of P + 6B of the base material exceeds 0.040, the test value of P + 6B exceeds 0.030 in the welded metal portion due thereto No. In 7, 8, 10 and 11, reheat cracking was observed. In addition, among them the value of P + 6B of the base material has exceeded the 0.050 test No. In 7 and 11, the initial layer solidification cracking was observed. Then, the alloy C content is out of the specified No. Test using a 8 No. 9, as well as Ni, Cr, departing content of Mo and Nb from specified alloy No. Test using a 11 No. In 12, it resulted in the creep strength of the welded joint inferior.
Industrial Applicability
[0067]
　According to the present invention, cracking susceptibility of the weld metal is low and it is possible to obtain a suitable austenitic heat resistant alloy for making welded joints having excellent creep strength. Therefore, the austenitic heat resistant alloy of the present invention can be suitably used as a device material such as a boiler that is used in a high temperature environment.

WE CLAIM

Chemical composition, in
　mass%, C: 0.04 ~
　0.18%, Si: 1.5% or
　less, Mn: 2.0% or
　less, P: 0.020% or
　less, S: 0.030% or less ,
　Cu: 0.10% or
　less,
　Ni: 20.0
　~ 30.0%, Cr: 21.0 ~ 24.0%, Mo:
　1.0 ~ 2.0%, Nb: 0.10 ~ 0.
　40%, Ti: 0.20% or
　less, Al: 0.05% or
　less,
　N: 0.10 ~ 0.35%, B: 0.0015 ~ 0.005%,
　the balance is Fe and impurities,
　the following of (i) satisfies the formula,
　austenitic heat resistant alloy.
　P + 6B ≦ 0.040 ··· (i )
　wherein each element symbol in the formulas represents the content of each element contained in the alloy (mass%).
[Requested item 2]
　A heat-resistant alloy used to using the welding material to prepare a welded joint,
　the chemical composition of the weld material, by
　mass%, C: 0.01
　~ 0.18%, Si: 1.5%
　hereinafter, Mn: 2.0% or
　less, P: 0.020% or
　less, S: 0.030% or
　less, Cu: 0.15% or
　less, Cr: 20.0
　~ 25.0%, Mo: 10.0 % or less,
　Nb: 4.0% or
　less, Ti: 0.50% or
　less, Co: 15.0% or
　less, Al: 2.0% or
　less, B: 0.005% or
　less, Fe: 30.0% or less ,
　the balance is Ni and impurities,
　austenitic heat resistant alloy according to claim 1.
[Requested item 3]
　A base metal made of austenitic heat resistant alloy according to claim 1,
　in
　mass%, C: 0.01 ~
　0.18%, Si: 1.5% or
　less, Mn: 2.0% or
　less, P: 0.020% or
　less, S: 0.030% or
　less, Cu: 0.15% or
　less,
　Ni: 20.0 ~ 90.0%, Cr: 21.0
　~ 24.0%, Mo: 1.0 ~
　% 10.0, Nb: 0.01
　~ 4.0%, Ti: 0.20% or
　less, Co: 15.0% or
　less, Al: 2.0% or
　less, N: 0.01 ~ 0.35% ,
　B: 0.005% or less,
　the balance is Fe and impurities,
　including a weld metal having a chemical composition satisfying the (ii) the following equation,
　welded joint of austenitic heat resistant alloy.
　P + 6B ≦ 0.030 ··· (ii )
　wherein each element symbol in the formulas represents the content of each element contained in the weld metal portion (mass%).