JP6519007B2 - Method of manufacturing Ni-based heat resistant alloy welded joint - Google Patents

Description

  The present invention relates to a method of manufacturing a Ni-based heat-resistant alloy welded joint and a welded joint obtained using the same. In particular, the present invention relates to a method of manufacturing a welded joint using a Ni-based heat resistant alloy used for a long time as a high temperature member such as a main steam pipe or a reheat steam pipe of a thermal power generation boiler, and a welded joint obtained using the same .

  In recent years, high-temperature and high-pressure operating conditions have been promoted on a global scale in boilers for thermal power generation and the like from the viewpoint of reducing environmental impact, and austenitic heat-resistant alloys or used as materials for superheater tubes or reheater tubes Ni-based heat-resistant alloys are required to have better high-temperature strength and corrosion resistance.

  Furthermore, high strength is also required for various members such as thick members such as main steam pipes or reheat steam pipes in which ferrite heat resistant steels have been conventionally used, and high strength austenitic heat resistant alloys Or application of a Ni-based heat-resistant alloy is being considered.

  Under such technical background, for example, WO 2009/154161 (Patent Document 1) discloses an austenitic heat resistant alloy having enhanced creep rupture strength by utilizing Cr, Ti and Zr. There is. In addition, in International Publication No. 2010/038826 (Patent Document 2), Ni containing a large amount of W, utilizing Al and Ti, and enhancing creep rupture strength by solid solution strengthening and precipitation strengthening by γ 'phase is used. A base heat resistant alloy is disclosed. Furthermore, a Ni-based heat-resistant alloy is disclosed in JP-A 2013-49902 (Patent Document 3), which specifies the precipitation amount of Cr determined by quantitative analysis of the extraction residue and enhances toughness in addition to creep rupture strength. ing.

  When these austenitic heat-resistant alloys or Ni-based heat-resistant alloys are used as a structure, they are generally assembled by welding. At that time, it is known that various cracks are likely to occur in the welded portion mainly due to metallurgical factors.

  Therefore, the contents of Al, Ti and Nb, and P, Cr and B are specified in a predetermined range in International Publication No. 2011/071 054 (Patent Document 4), and the liquid cracking resistance during welding is improved. Austenitic heat resistant alloys have been proposed. Moreover, while using Mo and W to raise creep strength in Unexamined-Japanese-Patent No. 2010-150593 (patent document 5), the content of an impurity element and Ti and Al is prescribed, and liquefaction resistance at the time of welding is specified. Austenitic heat resistant alloys have been proposed which have improved cracking and stress relaxation cracking resistance during use. Furthermore, in JP 2013-36086 A (Patent Document 6), the creep strength is enhanced by containing Al and Ti to utilize the γ ′ phase, and the contents of Nd and O according to the crystal grain size A Ni-based heat-resistant alloy has been proposed in which the creep ductility is improved after long-term use at high temperature and the stress relaxation cracking resistance during repair welding is improved by adjusting.

WO 2009/154161 International Publication No. 2010/038826 JP, 2013-49902, A International Publication No. 2011/071054 JP, 2010-150593, A JP, 2013-36086, A

  When these austenitic heat-resistant alloys and Ni-based heat-resistant alloys are applied to thick-walled members such as main steam pipes or reheated steam pipes and assembled by welding, it is true that liquefied cracking at welding and stress relaxation cracking at the time of use It could be confirmed that it could be prevented.

  However, the structure of the Ni-based heat-resistant alloy used at these high temperatures may require welding repair of a part of the structure due to partial damage accompanying aging. And when it welds using Ni base heat-resistant alloys used at these high temperatures, it became clear newly that a crack might arise in a welding heat affected zone. In addition, since the welding crack made into the object by patent document 6 is aimed at the heat treatment after repair welding, and the crack which arises during high temperature use, it can not solve the subject of the present invention.

  The present invention was made in view of the above-mentioned present situation, and a Ni-based heat-resistant alloy welded joint using a Ni-based heat-resistant alloy used for a long time as a high temperature member such as a main steam pipe or reheat steam pipe of a boiler for thermal power generation. It is an object of the present invention to provide a method of manufacturing a welded joint and a welded joint obtained using it.

  In order to solve the above-mentioned problems, the present inventors first of all, a crack generation phenomenon of a weld heat affected zone in a welded joint using a Ni-based heat-resistant alloy containing a large amount of Al and Ti exposed to a high temperature for a long time We conducted a detailed survey on As a result, the following <1> to <3> were confirmed.

(1) It has been found that cracking of the weld heat affected zone tends to occur with the increase of temperature and time when used at high temperature, and tends to occur more than certain conditions. Specifically, if the heating retention temperature _{T A} at the time of use is 600 to 850 ° C., the parameters determined from the heating retention temperature _{T A} and the heating retention time when using _{t A} (hereinafter also referred to as _{P A.)} 1700 It turned out that it exists in the tendency which the crack of a welding heat affected zone tends to produce as it is more than. _However, it is _{P A = T A × (1.0} + logt A).

<2> Cracking of the weld heat affected zone occurred at a position several hundred μm away from the melting boundary. As a result of observation of the fractured surface, no melting mark was observed, and the fractured surface with poor ductility was exhibited. Furthermore, concentrated S and P were detected on the fracture surface.

<3> Furthermore, as a result of the structure observation of the weld heat affected zone, within the grains of the weld heat affected zone several hundred μm away from the melting boundary where the crack has occurred, finer in the grain of the weld heat affected zone near the melting line. Many M ₂₃ C ₆ carbides and intermetallic compound phases (γ ′ phases) were observed.

  From these results, it is presumed that the crack generated in the weld heat affected zone when welded using a Ni-based heat resistant alloy used for a long time at high temperature is generated by the following mechanism.

That is, with long-term use at high temperature, M ₂₃ C ₆ carbides and intermetallic compound phases finely precipitate in the crystal grains of the Ni-based heat-resistant alloy, but they are precipitated in a short time as the use temperature increases. As it gets longer, the amount increases. Furthermore, during use, grain boundary segregation of the impurity elements S and P is also generated.

  As described above, when welding a Ni-based heat-resistant alloy in which precipitation phases exist in the grains and impurities segregate at grain boundaries, the highest reached temperature is high in the welding heat affected zone near the melting boundary, so As well as solid solution in the matrix again, grain boundary segregation is eliminated. However, in the weld heat-affected zone slightly away from the melting boundary, the maximum reached temperature is low, so that the dissolution of intragranular precipitates and elimination of grain boundary segregation do not occur. Here, at the time of welding, thermal stress is generated in the welding heat affected zone due to expansion and contraction associated with welding. Therefore, in the region where a large amount of precipitated phase exists in the grain, that is, in the welding heat-affected zone slightly away from the melting boundary, deformation resistance in the grain is high, the grain can not be deformed, and deformation due to thermal stress concentrate. In addition, a large amount of impurity elements such as S and P are segregated in the grain boundaries to cause embrittlement. As a result, it is considered that the grain boundaries can not withstand deformation and the grain boundaries are opened, leading to cracking.

  And as a result of repeating earnest examination, in order to prevent this, it became clear that the following method is effective. That is, in order to prevent cracking at the time of welding, when precipitates are generated in the grains excessively during use at high temperature, the precipitates are dissolved again and the grain boundary segregation of impurities is reduced. Was found to be effective.

  Specifically, it was found that it is shown in the following [1] and [2].

In [1] Ni-base heat-resistant alloy, the heating retention temperature _{T A} at the time of use is 600 to 850 ° C., and parameters determined by the heating retention temperature _{T A} and the heating retention time when using _{t A} (hereinafter, both _{P A} When it is more than 1700, it is effective to perform heat treatment before welding. _However, it is _{P A = T A × (1.0} + logt A).

[2] a heat treatment is subjected before welding, heat treatment holding temperature _{T P} is from 1,050 to 1,250 ° C., effective to heat treatment holding time _{t P} is _{[-0.1 × (T P / 50-30} )] or It is. However, if the heat treatment holding time t _P exceeds [−0.1 × (T _p / 10−145)], the heat treatment holding time t _P adversely affects rather than being ineffective.

  The present invention is made on the basis of the above-mentioned findings, and the gist of the following method for producing a Ni-based heat-resistant alloy welded joint and a welded joint obtained using the same.

(1) Chemical composition is in mass%,
C: 0.03 to 0.12%,
Si: 1% or less,
Mn: 1% or less,
P: 0.015% or less,
S: 0.005% or less,
Co: 8 to 25%,
Cr: 18 to 27%,
Ti: 0.1 to 2.5%,
Al: 0.2 to 2.0%,
B: 0.0001 to 0.01%,
REM: 0.001 to 0.5%,
N: 0.02% or less,
O: 0.01% or less,
Ca: 0 to 0.05%,
Mg: 0 to 0.05%,
Fe: 0 to 15%,
Mo: 0 to 12%,
W: 0 to 10%
Cu: 0 to 4%,
Nb: 0 to 2.5%
V: 0 to 0.5%, as well as
Remainder: Ni and impurities, and
An alloy base material used under the conditions satisfying the following formulas (i) and (ii)
The manufacturing method of Ni base heat-resistant-alloy weld joint which welds, after heat-processing on the conditions which satisfy following formula (iii) and (iv) formula.
600 ≦ T _A ≦ 850 (i)
1700 ≦ T _A × (1.0 + log t _A ) (ii)
1050 ≦ _TP ≦ 1250 (iii)
−0.1 × (T _P / 50−30) ≦ t _P ≦ −0.1 × (T _P / 10−145) (iv)
However, the meaning of each symbol in the above formula is as follows.
T _A : Heating holding temperature (° C) during use
t _A : Heat holding time during use (h)
T _P : Heat treatment holding temperature (° C)
t _P : Heat treatment holding time (h)

(2) The Ni-based heat-resistant alloy welded joint according to the above (1), wherein the chemical composition of the alloy base material contains, in mass%, at least one selected from the following first group and second group Production method.
First group Ca: 0.0001 to 0.05%, Mg: 0.0001 to 0.05%, Fe: 0.01 to 15%
Second group Mo: 0.01 to 12%, W: 0.01 to 10%, Cu: 0.01 to 4%, Nb: 0.01 to 2.5%, V: 0.01 to 0.5 %

  (3) In the heat treatment, the method for producing a Ni-based heat-resistant alloy welded joint according to (1) or (2), wherein the average cooling rate to 500 ° C. in the cooling process is 50 ° C./h or more.

  (4) The method for producing a Ni-based heat-resistant alloy welded joint according to any one of (1) to (3), wherein the heat treatment is performed at least within a range of 30 mm from the welded portion.

(5) Chemical composition is in mass%,
C: 0.06 to 0.15%,
Si: 1% or less,
Mn: 1% or less,
P: 0.01% or less,
S: 0.005% or less,
Co: 8 to 25%,
Cr: 18 to 27%,
Ti: 0.1 to 2.5%,
Al: 0.2 to 2.0%,
Mo: 0 to 12%,
W: 0 to 10%
Nb: 0 to 2.5%
B: 0 to 0.005%,
Fe: 0 to 15%,
N: 0.02% or less,
O: 0.01% or less, and
Remainder: The method for producing a Ni-based heat-resistant alloy welded joint according to any one of (1) to (4), wherein welding is performed using a welding material which is Ni and impurities.

  (6) A Ni-based heat-resistant alloy welded joint obtained by using the manufacturing method according to any one of (1) to (5).

  According to the manufacturing method of the present invention, a Ni-based heat-resistant alloy welded joint can be stabilized using a Ni-based heat-resistant alloy used for a long time as a high temperature member such as a main steam pipe or reheat steam pipe of a thermal power generation boiler. You can get it.

  Hereinafter, each requirement of the present invention will be described in detail. In the following description, “%” of the content means “mass%”.

1. Chemical composition of alloy base material The reasons for limitation of each element contained in the alloy base material used for manufacturing the Ni-based heat-resistant alloy welded joint according to the present invention are as follows.

C: 0.03 to 0.12%
C is an element having the function of stabilizing the structure, forming a fine carbide, and having the effect of improving the creep strength during high temperature use. In order to obtain this effect sufficiently, the C content needs to be 0.03% or more. However, if the C content is excessive, the carbides become coarse and precipitate in large amounts, thereby reducing the creep strength. In addition, it lowers the ductility and degrades weldability in materials used for a long time. Therefore, the C content is 0.12% or less. The C content is preferably 0.04% or more, more preferably 0.06% or more. Further, the C content is preferably 0.11% or less, more preferably 0.10% or less.

Si: 1% or less Si has a deoxidizing action and is an element effective for improving corrosion resistance and oxidation resistance at high temperatures. However, when Si is contained in excess, the stability of the structure is reduced, leading to a decrease in toughness and creep strength. Therefore, the Si content is 1% or less. The Si content is preferably 0.8% or less, more preferably 0.6% or less.

  It is not necessary to set a lower limit on the Si content, but if it is extremely reduced, the deoxidizing effect is not sufficiently obtained and the cleanliness of the alloy deteriorates, and the corrosion resistance and oxidation resistance improvement effects at high temperatures It becomes difficult to obtain, and the manufacturing cost also rises greatly. Therefore, the Si content is preferably 0.01% or more, and more preferably 0.03% or more.

Mn: 1% or less Mn, like Si, is an element having a deoxidizing action. Mn also contributes to the stabilization of the tissue. However, when the Mn content is excessive, embrittlement occurs, and furthermore, toughness and creep ductility also decrease. Therefore, the Mn content is 1% or less. The Mn content is preferably 0.8% or less, more preferably 0.6% or less.

  The lower limit of the Mn content is not particularly required. However, if the Mn content is extremely reduced, the deoxidizing effect can not be sufficiently obtained, the cleanliness of the alloy is deteriorated, and the structure stabilizing effect becomes difficult to obtain. Manufacturing costs also rise sharply. Therefore, the Mn content is preferably 0.01% or more, and more preferably 0.02% or more.

P: 0.015% or less P is an element contained in the alloy as an impurity, and when it is contained in a large amount, it is an element that significantly reduces the hot workability and also increases the susceptibility to liquefied cracking during welding. In addition, they segregate to grain boundaries during use at high temperatures and reduce weldability in materials used for extended periods of time. Therefore, the P content is 0.015% or less. The P content is preferably 0.012% or less, more preferably 0.010% or less.

  In addition, although it is preferable to reduce P content as much as possible, extreme reduction causes increase of manufacturing cost. Therefore, the P content is preferably 0.0005% or more, and more preferably 0.0008% or more.

S: 0.005% or less S, like P, is an element contained in the alloy as an impurity as well as P, and when it is contained in a large amount, it is an element that reduces the hot workability and increases the susceptibility to liquefied cracking during welding. Furthermore, when used for a long time at high temperature, it segregates in grain boundaries, and reduces the weldability in materials used for a long time. Therefore, the S content is made 0.005% or less. The S content is preferably 0.004% or less, more preferably 0.003% or less.

  In addition, although it is preferable to reduce S content as much as possible, extreme reduction causes increase of manufacturing cost. Therefore, the S content is preferably 0.0001% or more, and more preferably 0.0002% or more.

Co: 8 to 25%
Co is an element having an effect of improving creep strength. In order to obtain this effect sufficiently, the Co content needs to be 8% or more. However, since Co is a very expensive element, the excess content causes a significant cost increase. Therefore, the Co content is 25% or less. The Co content is preferably 8.5% or more, and more preferably 9% or more. Further, the Co content is preferably 23.5% or less, more preferably 22% or less.

Cr: 18 to 27%
Cr is an essential element for securing oxidation resistance and corrosion resistance at high temperatures. Further, Cr forms fine carbides and contributes to securing creep strength. In order to obtain the above effect, the Cr content needs to be 18% or more. However, when the Cr content is excessive, the structure stability at high temperature is reduced, and a large amount of carbides are formed to reduce weldability in a material used for a long time. Therefore, the Cr content is 27% or less. The Cr content is preferably 18.5% or more, more preferably 19% or more. Further, the Cr content is preferably 26.5% or less, more preferably 26% or less.

Ti: 0.1 to 2.5%
Ti combines with Ni and precipitates in the grains as a fine intermetallic compound phase, and contributes to the improvement of creep strength and tensile strength at high temperatures. In order to sufficiently obtain the effect, the Ti content needs to be 0.1% or more. However, when the Ti content is excessive, a large amount of intermetallic compound phase precipitates, resulting in a decrease in creep ductility and toughness. In addition, the ductility is reduced, which reduces the weldability in materials used for a long time. Therefore, the Ti content is 2.5% or less. The Ti content is preferably 0.15% or more, more preferably 0.2% or more. Moreover, it is preferable that it is 2.4% or less, and, as for Ti content, it is more preferable that it is 2.3% or less.

Al: 0.2 to 2.0%
Al, like Ti, is an element that combines with Ni and precipitates as a fine intermetallic compound phase and contributes to the improvement of creep strength and tensile strength at high temperatures. In order to obtain the effect sufficiently, the Al content needs to be 0.2% or more. However, when the content of Al is excessive, a large amount of intermetallic compound phase is generated, which in turn causes a decrease in toughness and ductility, and also reduces weldability in a material used for a long time. Therefore, the Al content is 2.0% or less. The Al content is preferably 0.25% or more, and more preferably 0.3% or more. The Al content is preferably 1.8% or less, more preferably 1.6% or less.

B: 0.0001 to 0.01%
B is an element effective to segregate at grain boundaries and strengthen grain boundaries while improving creep strength by finely dispersing grain boundary carbides. In order to obtain this effect, the B content needs to be 0.0001% or more. However, when the content of B is excessive, a large amount of B is segregated in the heat affected zone near the melting boundary due to the welding heat cycle during welding, the melting point of the grain boundary is lowered, and the liquation cracking sensitivity is increased. Therefore, the B content is made 0.01% or less. The B content is preferably 0.0005% or more, and more preferably 0.001% or more. Further, the B content is preferably 0.008% or less, and more preferably 0.006% or less.

REM: 0.001 to 0.5%
REM has a strong affinity with S, has an effect of improving hot workability, and is an element effective for reducing the susceptibility to liquefied cracking during welding. Furthermore, it reduces grain boundary segregation of S during high temperature use, and also contributes to the reduction of the decrease in weldability in materials used for a long time. In order to obtain this effect, the REM content needs to be 0.001% or more. However, when the REM content is excessive, it combines with O to significantly reduce the cleanliness and rather degrade the hot workability. Therefore, the REM content is 0.5% or less. The REM content is preferably 0.002% or more, more preferably 0.005% or more. Further, the REM content is preferably 0.4% or less, more preferably 0.3% or less.

  In addition, "REM" is a general term for 17 elements in total of Sc, Y and a lanthanoid, and the content of REM indicates the total content of one or more elements of REM. In addition, REM is generally contained in misch metal. Therefore, for example, it may be added in the form of misch metal, and the amount of REM may be contained so as to fall within the above range.

N: 0.02% or less N is an element effective to stabilize the structure, but when it is contained in excess, a large amount of fine nitrides are precipitated in the grains during use at high temperatures, It leads to a decrease in creep ductility and toughness. Furthermore, the weldability of the material used for a long time is reduced. Therefore, the content of N is 0.02% or less. The content of N is preferably 0.018% or less, more preferably 0.015% or less.

  Although it is not necessary to set a lower limit in particular for the N content, if it is extremely reduced, it will be difficult to obtain the effect of stabilizing the structure, and the manufacturing cost will also be greatly increased. Therefore, the N content is preferably 0.0005% or more, and more preferably 0.0008% or more.

O: 0.01% or less O (oxygen) is contained as an impurity in the alloy, and when its content is excessive, the hot workability is reduced, and the toughness and the ductility are further deteriorated. Therefore, the O content is 0.01% or less. The O content is preferably 0.008% or less, more preferably 0.005% or less.

  In addition, although it is not necessary to set a minimum in particular about O content, extreme reduction causes a rise of manufacturing cost. Therefore, the O content is preferably 0.0005% or more, and more preferably 0.0008% or more.

Ca: 0 to 0.05%
Ca is an element having an effect of improving hot workability. Furthermore, since it is an element which reduces grain boundary segregation of S during high temperature use and contributes to the reduction of a decrease in weldability in a material used for a long time, it may be contained. However, when the Ca content is excessive, it combines with O to significantly reduce the cleanliness and rather deteriorate the hot workability. Therefore, when Ca is contained, the content is made 0.05% or less. The Ca content is preferably 0.03% or less.

  In addition, in order to acquire the said effect, it is preferable to make Ca content into 0.0001% or more, and it is more preferable to set it as 0.0005% or more.

Mg: 0 to 0.05%
Mg, like Ca, is an element having the effect of improving hot workability. Furthermore, since it is an element which reduces grain boundary segregation of S during high temperature use and contributes to the reduction of a decrease in weldability in a material used for a long time, it may be contained. However, when the Mg content is excessive, it combines with O to significantly reduce the cleanliness and rather deteriorate the hot workability. Therefore, when it contains Mg, the content is made into 0.05% or less. The Mg content is preferably 0.03% or less.

  In addition, in order to acquire the said effect, it is preferable to make Mg content into 0.0001% or more, and it is more preferable to set it as 0.0005% or more.

Fe: 0 to 15%
Fe may be contained because it is an element having the effect of improving the hot workability when it is contained in a small amount in a Ni-based alloy. However, when the Fe content is excessive, the thermal expansion coefficient of the alloy increases and the water vapor oxidation resistance also deteriorates. Therefore, when Fe is contained, the content is made 15% or less. The Fe content is preferably 10% or less, more preferably 1% or less.

  In addition, in order to acquire the said effect, it is preferable to make Fe content into 0.01% or more, and it is more preferable to set it as 0.02% or more.

  Since all of the above-described Ca, Mg and Fe have the effect of improving the hot workability, they can be contained alone or in combination of two or more. It is preferable that the total amount in the case of containing these elements in combination is 15.1% or less.

Mo: 0 to 12%
Mo may be contained because it is an element having a function of solid-solving in the matrix to improve creep strength and tensile strength at high temperature. However, even if Mo is excessively contained, the effect is saturated and the creep strength may be reduced. Furthermore, since it is an expensive element, containing excessively increases cost. Therefore, when it contains Mo, the content is made 12% or less. The Mo content is preferably 10% or less.

  In addition, in order to acquire the said effect, it is preferable to make Mo content into 0.01% or more, and it is more preferable to set it as 0.05% or more.

W: 0 to 10%
Like Mo, W may be contained because it is an element having a function of dissolving in the matrix and improving creep strength and tensile strength at high temperatures. However, even if W is contained excessively, the effect is saturated. Moreover, since it is an expensive element, when it contains excessively, the cost will increase. Therefore, when W is contained, the content is made 10% or less. The W content is preferably 8% or less, more preferably 5% or less.

  In addition, in order to acquire the said effect, it is preferable to make W content into 0.01% or more, and it is more preferable to set it as 0.05% or more.

Cu: 0 to 4%
Cu is an element having an effect of improving creep strength. That is, Cu, like Co, is an element that enhances the structural stability in a Ni-based heat-resistant alloy, and is an element that has the effect of improving the creep strength, so Cu may be contained. However, when the Cu content is excessive, the hot workability is reduced. Therefore, when Cu is contained, the content is made 4% or less. The Cu content is preferably 3% or less, more preferably 1% or less.

  When the above effect is to be obtained, the Cu content is preferably 0.01% or more, and more preferably 0.03% or more.

Nb: 0 to 2.5%
Nb is contained because it combines with C or N to precipitate in the grains as fine carbides or carbonitrides, or combines with Ni to form an intermetallic compound phase, and contributes to the improvement of creep strength at high temperatures. You may However, when the Nb content is excessive, a large amount of precipitates as carbides and carbonitrides is caused, which leads to a decrease in creep ductility and toughness, and a decrease in weldability in materials used for a long time. Therefore, when Nb is contained, the content is made 2.5% or less. The Nb content is preferably 2.3% or less.

  In addition, in order to acquire the said effect, it is preferable to make Nb content into 0.01% or more, and it is more preferable to set it as 0.02% or more.

V: 0 to 0.5%
V is an element having an effect of improving creep strength. That is, V may be contained because it combines with C or N to form fine carbides or carbonitrides and has an effect of improving creep strength. However, when the V content is excessive, a large amount of carbides or carbonitrides precipitates, which causes a decrease in creep ductility and a decrease in weldability in a material used for a long time. Therefore, when V is contained, the content is made 0.5% or less. The V content is preferably 0.4% or less.

  In addition, in order to acquire the said effect, it is preferable to make V content into 0.01% or more, and it is more preferable to set it as 0.02% or more.

  Since all of Mo, W, Cu, Nb and V have the effect of improving creep strength, they can be contained alone or in combination of two or more. It is preferable that the total amount in the case of containing these elements in combination is 7% or less.

  The alloy base material used to manufacture the Ni-based heat-resistant alloy welded joint according to the present invention has a chemical composition including the above-described elements, with the balance being Ni and impurities.

  The term "impurity" refers to what is mixed from ore as a raw material, scrap, manufacturing environment or the like when industrially manufacturing a Ni-based heat-resistant alloy member.

2. Alloy base material used in the manufacture of Ni-base heat-resistant alloy welded joint use conditions invention alloy base material, satisfy the heating and holding temperature T _A is below formula (i) in use, and the heating retention time of use temperature T _a and parameters determined from the heating retention time t _a (hereinafter also referred to as P _a.) is that used in the conditions satisfying the following (ii) expression.

Heating holding temperature T _A (° C.) at the time of use: 600 ≦ T _A ≦ 850 (i)
P _A : 1700 ≦ T _A × (1.0 + log t _A ) (ii)
The alloy base material used to manufacture the Ni-based heat-resistant alloy weld joint according to the present invention, when heated to 600 to 850 ° C., has a fine M ₂₃ C ₆ carbide and intermetallic compound phase γ 'phase in the crystal grains To precipitate. Also, grain boundary segregation of S and P occurs simultaneously. If the amount of carbide and intermetallic compound phase precipitating in the grains and the amount of grain boundary segregation of impurities exceed a predetermined amount, deformation resistance within grains increases and grain boundaries weaken, so long time Welding cracks occur when the used material is welded. Alloy base material used in the manufacture of Ni-base heat-resistant alloy welded joints of the present invention, when P _A is 1700 or more, since the weakening of grain boundaries by increasing the segregation of grain deformation resistance due to precipitation becomes significant, welding It is necessary to apply a heat treatment before.

3. Heat Treatment Conditions In the method for producing a Ni-based heat-resistant alloy welded joint of the present invention, heat treatment is performed before welding the alloy base material. The heat treatment, to prevent weld cracking, thermal treatment holding temperature T _P and the heat treatment holding time t _P is required to perform under the condition that satisfies (iii) below formula and (iv) expression.

Heat treatment holding temperature T _p (° C.): 1050 ≦ T _p ≦ 1250 (iii)
In order to prevent weld cracking, by heat treatment, carbides and intermetallic compound phases precipitated in the grains excessively during use at high temperatures are dissolved again in the matrix, and impurity elements segregated at grain boundaries are reduced. Is effective. For this purpose, there should be at least 1050 ° C. The heat treatment holding temperature T _P. However, when the heat treatment holding temperature T _P exceeds 1250 ° C., local melting of the grain boundary is started. Therefore, the heat treatment holding temperature _TP is set to 1250 ° C. or less. Furthermore, as described later, in the thermal treatment, depending on the heat treatment holding temperature T _P, it is necessary to manage the heat treatment holding time t _P within a predetermined range. Heat treatment holding temperature _{T P} is preferably at 1080 ° C. or higher, more preferably 1100 ° C. or higher. The heat treatment holding temperature _{T P} is preferably 1230 ° C. or less, more preferably 1200 ° C. or less.

Heat treatment holding time _{t P (h): - 0.1} × (T P / 50-30) ≦ t P ≦ -0.1 × (T P / 10-145) ··· (iv)
Although heat treatment is effective to prevent weld cracking, the heat treatment holding time t _P needs to be -0.1 × (T _p / 50-30) or more. This is because when the heat treatment holding time t _P is below this value, the time required for the diffusion of alloying elements to achieve the re-dissolution of precipitates to the matrix and the reduction of grain boundary segregation will be insufficient. . However, when the heat treatment holding time t _P exceeds −0.1 × (T _p / 10−145), coarsening of the crystal grain size becomes remarkable, and in the case of welding, liquefied cracking tends to occur near the melting line. Therefore, the heat treatment holding time t _P needs to be −0.1 × (T _P / 10 −145) or less.

  In the heat treatment, in the process of cooling, the average cooling rate to 500 ° C. is preferably 50 ° C./h or more. The reason is that if the average cooling rate is less than 50 ° C./h, grain boundaries of impurities may occur at the same time as carbide and intermetallic compound phases are again precipitated in the grains during the cooling process.

  The heat treatment is preferably performed at least within 30 mm from the portion to be welded. This is because the strain caused by the thermal stress generated during welding is increased in this region.

4. Chemical composition of welding material The reasons for limitation of each element contained in the welding material used for manufacturing the Ni-based heat-resistant alloy welded joint according to the present invention are as follows.

C: 0.06 to 0.15%
C is an element which has the effect of forming fine carbides and improving the creep strength during high temperature use, while enhancing the phase stability in the weld metal after welding. Furthermore, the formation of eutectic carbides with Cr during welding solidification contributes to the reduction of solidification cracking sensitivity. In order to sufficiently obtain this effect, the C content needs to be 0.06% or more. However, if the C content is excessive, a large amount of carbides precipitate, which in turn lowers the creep strength and the ductility. Therefore, the C content is made 0.15% or less. The C content is preferably 0.07% or more, more preferably 0.08% or more. Further, the C content is preferably 0.14% or less, and more preferably 0.12% or less.

Si: 1% or less Si is an element effective for deoxidation at the time of production of a welding material and is also effective for improving the corrosion resistance and oxidation resistance at high temperatures of the weld metal after welding. However, when Si is contained in excess, the phase stability decreases, resulting in a decrease in toughness and creep strength. Therefore, the Si content is 1% or less. The Si content is preferably 0.8% or less, more preferably 0.6% or less.

  It is not necessary to set a lower limit on the Si content, but if it is extremely reduced, the deoxidizing effect is not sufficiently obtained and the cleanliness of the alloy deteriorates, and the corrosion resistance and oxidation resistance improvement effects at high temperatures It becomes difficult to obtain, and the manufacturing cost also rises greatly. Therefore, the Si content is preferably 0.01% or more, and more preferably 0.03% or more.

Mn: 1% or less Mn, like Si, is an element effective for deoxidation at the time of production of a welding material. Mn also contributes to the improvement of the phase stability in the weld metal after welding. However, excessive Mn content causes embrittlement. Therefore, the Mn content is 1% or less. The content of Mn is preferably 0.8% or less, more preferably 0.6% or less.

  The lower limit of the Mn content is not particularly required, but if the Mn content is extremely reduced, the deoxidizing effect can not be sufficiently obtained, the cleanliness of the alloy is deteriorated, and the effect of improving the phase stability becomes difficult to obtain. Furthermore, the manufacturing cost is also greatly increased. Therefore, the Mn content is preferably 0.01% or more, and more preferably 0.02% or more.

P: 0.01% or less P is an element contained in the welding material as an impurity to enhance solidification cracking sensitivity during welding. Furthermore, it reduces the creep ductility of the weld metal after prolonged use at high temperatures. Therefore, the P content is 0.01% or less. The P content is preferably 0.008% or less, more preferably 0.006% or less.

  In addition, although it is preferable to reduce P content as much as possible, extreme reduction causes increase of manufacturing cost. Therefore, the P content is preferably 0.0005% or more, and more preferably 0.0008% or more.

S: 0.005% or less S, like P, is contained as an impurity in the welding material, and when it is contained in a large amount, it significantly reduces the hot workability and weldability. Furthermore, when used at a high temperature for a long time, S segregates in columnar grain boundaries in the weld metal, causing embrittlement and enhancing stress relaxation cracking sensitivity. Therefore, the S content is made 0.005% or less. The S content is preferably 0.004% or less, more preferably 0.003% or less.

  In addition, although it is preferable to reduce S content as much as possible, extreme reduction causes increase of manufacturing cost. Therefore, the S content is preferably 0.0001% or more, and more preferably 0.0002% or more.

Co: 8 to 25%
Co, like Ni, improves the stability of the structure and contributes to the improvement of creep strength. In order to obtain this effect sufficiently, the Co content needs to be 8% or more. However, since Co is a very expensive element, excessive inclusion in the welding material also causes a significant increase in cost. Therefore, the Co content is 25% or less. The Co content is preferably 8.5% or more, and more preferably 9% or more. Further, the Co content is preferably 23.5% or less, more preferably 22% or less.

Cr: 18 to 27%
Cr is an effective element for securing the oxidation resistance and corrosion resistance of the weld metal at high temperatures. Further, Cr forms fine carbides and contributes to securing creep strength. Furthermore, forming eutectic carbide with C during weld solidification also contributes to the reduction of solidification cracking sensitivity. In order to obtain these effects, the Cr content needs to be 18% or more. However, if the Cr content exceeds 27%, the phase stability at high temperatures is degraded, which leads to a decrease in creep strength. Therefore, the Cr content is 27% or less. The Cr content is preferably 18.5% or more, more preferably 19% or more. Further, the Cr content is preferably 26.5% or less, more preferably 26% or less.

Ti: 0.1 to 2.5%
Ti is an element which precipitates as a fine intermetallic compound phase and contributes to the improvement of creep strength and tensile strength at high temperature. In order to sufficiently obtain the effect, the Ti content needs to be 0.1% or more. However, when the Ti content is excessive, a large amount of intermetallic compound phase precipitates, which in turn causes a decrease in creep ductility and toughness. Therefore, the Ti content is 2.5% or less. The Ti content is preferably 0.15% or more, more preferably 0.2% or more. Moreover, it is preferable that it is 2.4% or less, and, as for Ti content, it is more preferable that it is 2.3% or less.

Al: 0.2 to 2.0%
Al is an element which precipitates as a fine intermetallic compound phase similarly to Ti in a weld metal and contributes to the improvement of creep strength and tensile strength at high temperature. In order to obtain the effect sufficiently, the Al content needs to be 0.2% or more. However, when the Al content is excessive, a large amount of intermetallic compound phase precipitates, which in turn causes a decrease in creep ductility and toughness. Therefore, the Al content is 2.0% or less. The Al content is preferably 0.25% or more, and more preferably 0.3% or more. The Al content is preferably 1.8% or less, more preferably 1.6% or less.

Mo: 0 to 12%
Mo may also be contained because it is an element that has the function of improving the creep strength and tensile strength at high temperatures by dissolving in the matrix also in the weld metal. However, even if Mo is excessively contained, the effect is saturated and the creep strength may be reduced. Furthermore, since it is an expensive element, containing excessively increases cost. Therefore, when it contains Mo, the content is made 12% or less. The Mo content is preferably 11% or less, more preferably 10% or less.

  In addition, in order to acquire the said effect, it is preferable to make Mo content into 0.01% or more, and it is more preferable to set it as 0.03% or more.

W: 0 to 10%
W is also contained in the weld metal as in the case of Mo, since it is an element having a function of improving the creep strength and the tensile strength at high temperature by dissolving in the matrix and improving the creep strength and the tensile strength. However, even if W is excessively contained, the effect may be saturated and the creep strength may be reduced. Moreover, since it is an expensive element, when it contains excessively, the cost will increase. Therefore, when W is contained, the content is made 10% or less. The W content is preferably 9% or less, more preferably 8% or less.

  In addition, in order to acquire the said effect, it is preferable to make W content into 0.01% or more, and it is more preferable to set it as 0.03% or more.

Nb: 0 to 2.5%
Nb combines with C or N in the weld metal and precipitates in the grains as fine carbides or carbonitrides, or combines with Ni to form an intermetallic compound phase, contributing to the improvement of creep strength at high temperatures In order to do so, it may be contained. However, when the Nb content is excessive, a large amount precipitates as carbides and carbonitrides, resulting in a decrease in creep ductility and toughness. Therefore, when Nb is contained, the content is made 2.5% or less. The Nb content is preferably 2.3% or less, more preferably 2% or less.

  In addition, in order to acquire the said effect, it is preferable to make Nb content into 0.01% or more, and it is more preferable to set it as 0.02% or more.

B: 0 to 0.005%
Since B is an element effective for improving the creep strength of the weld metal, it may be contained. However, when the B content is excessive, the solidification cracking susceptibility during welding becomes extremely high. Therefore, the B content is made 0.005% or less. The B content is preferably 0.004% or less, more preferably 0.003% or less.

  In addition, in order to acquire the said effect, it is preferable to make B content into 0.0001% or more, and it is more preferable to set it as 0.0005% or more.

Fe: 0 to 15%
Since Fe is an element having the effect of improving the hot workability when it is contained in a Ni-based alloy even in a very small amount, it may be contained also in the welding material and the effect may be utilized. However, when the Fe content is excessive, the thermal expansion coefficient of the weld metal increases and the water vapor oxidation resistance also deteriorates. Therefore, when Fe is contained, the content is made 15% or less. The Fe content is preferably 10% or less, more preferably 8% or less.

  In addition, in order to acquire the said effect, it is preferable to make Fe content into 0.01% or more, and it is more preferable to set it as 0.02% or more.

N: 0.02% or less N is an element that stabilizes the structure in the weld metal, improves the creep strength, and forms a solid solution to contribute to securing the tensile strength. However, when contained in excess, a large amount of fine nitrides precipitate in the grains during use at high temperatures, resulting in a decrease in creep ductility and toughness. Therefore, the N content is 0.02% or less. The N content is preferably 0.018% or less, more preferably 0.015% or less.

  Although it is not necessary to set a lower limit in particular for the content of N, if it is extremely reduced, it will be difficult to obtain the effect of improving the phase stability, and the manufacturing cost will also increase greatly. Therefore, the N content is preferably 0.0005% or more, and more preferably 0.0008% or more.

O: 0.01% or less O (oxygen) is contained as an impurity in the welding material, and when its content is excessive, the hot workability is reduced and the productivity is deteriorated. Therefore, the O content is 0.01% or less. The O content is preferably 0.008% or less, more preferably 0.005% or less.

  In addition, although it is not necessary to set a minimum in particular about O content, extreme reduction causes a rise of manufacturing cost. Therefore, the O content is preferably 0.0005% or more, and more preferably 0.0008% or more.

  The welding material used to manufacture the Ni-based heat-resistant alloy welded joint according to the present invention has a chemical composition containing the above-described elements, with the balance being Ni and impurities.

5. Others In the method of manufacturing a Ni-based heat-resistant alloy welded joint of the present invention, the alloy base material is heat-treated and then welded. The welding method is not particularly limited, and, for example, gas tungsten arc welding, gas metal arc welding, coated arc welding and the like can be used.

  There are no particular restrictions on the shape or size of the alloy base material and welding material used to manufacture the Ni-based heat-resistant alloy welded joint according to the present invention. However, the manufacturing method according to the present invention is particularly effective when an alloy base material having a thickness of 30 mm or more is used. Therefore, the thickness of the alloy base material is preferably 30 mm or more.

  EXAMPLES Hereinafter, the present invention will be more specifically described by way of examples, but the present invention is not limited to these examples.

  An alloy having the chemical composition shown in Table 1 was melted to produce an ingot. After forming by hot forging using the ingot, solution heat treatment was performed to prepare Ni-based heat-resistant alloy sheets A to 30 each having a thickness of 30 mm, a width of 50 mm, and a length of 100 mm.

  Furthermore, after melt | dissolving the alloy which has a chemical composition shown in Table 2, and producing an ingot, welding material WZ with an outer diameter of 1.2 mm was produced by hot forging, hot rolling, and machining.

  In order to simulate the use at high temperature, the Ni-based heat-resistant alloy sheet was heated at the heating holding temperature and heating holding time shown in Table 3. Thereafter, except for the weld joints of test numbers A3 and A23, heat treatment was performed at the heat treatment holding temperature, heat treatment holding time, and average cooling rate shown in Table 3.

  In the longitudinal direction of the alloy sheet described above, a V-groove having a groove angle of 30 ° and a root thickness of 1 mm was machined. After that, on the SM400B steel plate prescribed in JIS G3160 (2008) with a thickness of 50 mm, width 200 mm and length 200 mm, four sides were subjected to restraint welding using a coated arc welding rod DNiCrFe-3 prescribed in JIS Z3224 (1999) .

  Thereafter, using the above-described welding material, lamination welding was performed at a heat input of 10 to 15 kJ / cm in the groove by TIG welding to produce a welded joint.

(Crack observation test)
The cross section of the sample collected from five places of the obtained weld joint was mirror-polished and corroded, and the mirror was subjected to an optical microscope to investigate the presence or absence of cracks in the weld heat affected zone. And, of five samples, weld joints in which no cracks were found in all samples are "○", weld joints in which cracks were recognized in one to three samples are "Δ", and "pass" It was judged. Moreover, the weld joint in which the crack was recognized by four or more samples was made into "x", and it was determined as "reject." The results are shown in Table 3.

  As can be seen from the results in Table 3, the test numbers A1, A2, A5 to A7, A9 to A15, A17, A18, A20 to A22, A24 to A28, B1, C2 to C6 in which the heat treatment conditions satisfy the definition of the present invention. It can be seen that, in the welded joints D1, D1 and E1, the results of the crack observation test passed, and a sound welded joint was obtained even when the thickness was 30 mm.

  On the other hand, in the welded joints of Test Nos. A3 and A23, since the heat treatment was not performed on the alloy plate, cracking occurred in the welding heat affected zone.

  In the welded joint of test No. A4, since the heat treatment holding temperature applied before welding was as low as 1000 ° C., the re-solid solution of the precipitate is insufficient, so the deformation resistance in the grain is high and the grain boundary Elimination of segregation was also insufficient. Therefore, weld cracking occurred at a position slightly away from the melting line during welding.

  In the welded joint of Test No. A19, the heat treatment holding temperature was as high as 1300 ° C., so local melting of grain boundaries occurred, and that part was opened during welding, and a crack occurred.

  In the welded joints of test numbers A8 and C1, since the heat treatment holding time was below the range specified in the present invention, the solution of precipitates and elimination of grain boundary segregation were insufficient, and they were slightly separated from the melting line during welding. Cracking occurred at the same position.

  In the welded joints of Test Nos. A16 and C7, since the heat treatment holding time exceeded the range specified in the present invention, the coarsening of the crystal grains was remarkable, and at the time of welding, liquefied cracking occurred in the portion adjacent to the melting line.

  Further, in the welded joint of test No. A10, since the average cooling rate in the heat treatment was lower than 50 ° C./h, precipitation of precipitates and grain boundary segregation occurred during cooling. Therefore, although the result of the crack observation test passed, cracks occurred in the weld heat affected zone in the three samples.

  According to the manufacturing method of the present invention, a Ni-based heat-resistant alloy welded joint can be stabilized using a Ni-based heat-resistant alloy used for a long time as a high temperature member such as a main steam pipe or reheat steam pipe of a thermal power generation boiler. You can get it.

Claims (5)

The chemical composition is in mass%,
C: 0.03 to 0.12%,
Si: 1% or less,
Mn: 1% or less,
P: 0.015% or less,
S: 0.005% or less,
Co: 8 to 25%,
Cr: 18 to 27%,
Ti: 0.1 to 2.5%,
Al: 0.2 to 2.0%,
B: 0.0001 to 0.01%,
REM: 0.001 to 0.5%,
N: 0.02% or less,
O: 0.01% or less,
Ca: 0 to 0.05%,
Mg: 0 to 0.05%,
Fe: 0 to 15%,
Mo: 0 to 12%,
W: 0 to 10%
Cu: 0 to 4%,
Nb: 0 to 2.5%
V: 0 to 0.5%, as well as
Remainder: Ni and impurities, and
An alloy base material used under the conditions satisfying the following formulas (i) and (ii)
The manufacturing method of Ni base heat-resistant-alloy weld joint which welds, after heat-processing on the conditions which satisfy following formula (iii) and (iv) formula.
600 ≦ TA ≦ 850 (i)
1700 ≦ TA × (1.0 + logtA) (ii)
1050 ≦ TP ≦ 1250 (iii)
−0.1 × (TP / 50-30) ≦ tP ≦ −0.1 × (TP / 10-145) (iv)
However, the meaning of each symbol in the above formula is as follows.
TA: Heating holding temperature (° C) during use
tA: Heat holding time during use (h)
TP: Heat treatment holding temperature (° C)
tP: Heat treatment holding time (h) The method for producing a Ni-based heat-resistant alloy welded joint according to claim 1, wherein the chemical composition of the alloy base material contains, in mass%, one or more selected from the following first group and second group.
First group Ca: 0.0001 to 0.05%, Mg: 0.0001 to 0.05%, Fe: 0.01 to 15%
Second group Mo: 0.01 to 12%, W: 0.01 to 10%, Cu: 0.01 to 4%, Nb: 0.01 to 2.5%, V: 0.01 to 0.5 %   The method for producing a Ni-based heat-resistant alloy weld joint according to claim 1 or 2, wherein in the heat treatment, the average cooling rate to 500 ° C in the cooling process is 50 ° C / h or more.   The method for manufacturing a Ni-based heat-resistant alloy welded joint according to any one of claims 1 to 3, wherein the heat treatment is performed at least within a range of at least 30 mm from a portion to be welded. The chemical composition is in mass%,
C: 0.06 to 0.15%,
Si: 1% or less,
Mn: 1% or less,
P: 0.01% or less,
S: 0.005% or less,
Co: 8 to 25%,
Cr: 18 to 27%,
Ti: 0.1 to 2.5%,
Al: 0.2 to 2.0%,
Mo: 0 to 12%,
W: 0 to 10%
Nb: 0 to 2.5%
B: 0 to 0.005%,
Fe: 0 to 15%,
N: 0.02% or less,
O: 0.01% or less, and
The manufacturing method of the Ni-based heat-resistant alloy welded joint according to any one of claims 1 to 4, wherein the remaining part is welded using a welding material which is Ni and impurities.