WO2016129666A1 - Method for manufacturing austenitic heat-resistant alloy welded joint, and welded joint obtained using same - Google Patents

Abstract

A method for manufacturing an austenitic heat-resistant alloy welded joint, said method comprising welding an alloy base material after heat-treating said alloy base material under conditions at which a heat-treatment holding temperature T_P (°C) and a heat-treatment holding time t_P (h) satisfy [1050≤T_P≤1300] and [-0.1×(T_P/50-30)≤t_P≤-0.1×(T_P/10-145)], said alloy base material being used under conditions at which a heat-treatment holding temperature T_A (°C) during use and a heat-treatment holding time t_A (h) during use satisfy [600≤T_A≤850] and [2100≤T_A×(1.0+logt_A)], and having a chemical composition comprising, in mass%, 0.04-0.12% of C, 1.0% or less of Si, 2.0% or less of Mn, 0.03% or less of P, 0.01% or less of S, 42.0-54.0% of Ni, 20.0-33.0% of Cr, 3.0-10.0% of W, 0.05-1.0% of Ti, 0.3% or less of Al, 0.0001-0.01% of B, 0.02% or less of N, 0.01% or less of O, 0-0.05% of Ca, 0-0.05% of Mg, 0-0.5% of REM, 0-1.0% of Co, 0-4.0% of Cu, 0-1.0% of Mo, 0-0.5% of V, 0-0.5% of Nb, and 0-0.05% of Zr, with the remainder comprising Fe and impurities.

Description

Method for producing austenitic heat-resistant alloy welded joint and welded joint obtained using the same

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

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

In addition, various members including thick members such as main steam pipes and reheat steam pipes, which conventionally used ferritic heat resistant steel, are required to have high strength, and high strength austenitic heat resistant Application of alloys or Ni-base heat-resistant alloys is being studied.

Under such technical background, for example, Patent Document 1 discloses a Ni-based alloy product that improves the hot workability by using W to increase the high-temperature strength and defining the effective B amount. Has been. Further, Patent Document 2 discloses an austenitic heat-resistant alloy having enhanced creep rupture strength by utilizing Cr, Ti and Zr. Patent Document 3 discloses a Ni-based heat-resistant alloy that contains a large amount of W and uses Al and Ti to increase the creep rupture strength by solid solution strengthening and precipitation strengthening by the γ ′ phase.

When these austenitic heat-resistant alloys or Ni-base heat-resistant alloys are used as structures, 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. In particular, there is a problem that so-called stress relaxation cracks occur when used in a high temperature environment for a long time. The stress relaxation crack is a crack generated in the process in which the residual stress generated by welding is relaxed.

Therefore, Patent Document 4 discloses an austenitic heat-resistant alloy that uses Al, Ti, and Nb to increase the creep strength, and at the same time, manages the contents of P and B and increases the liquefaction cracking resistance by containing Nd. Has been. Patent Document 5 also uses Mo and W to increase the creep strength and regulate the content of impurity elements, and Ti and Al, and resistance to liquefaction cracking during welding and stress relaxation cracking during use. An austenitic heat-resistant alloy with improved properties is disclosed.

Japanese Patent No. 4631986 International Publication No. 2009/154161 International Publication No. 2010/038826 International Publication No. 2011/071054 JP 2010-150593 A

When the austenitic heat-resistant alloy disclosed in Patent Documents 4 and 5 is applied to a thick member such as a main steam pipe or a reheat steam pipe, and assembled by welding, it is sure to cause liquefaction cracking during welding and during use. Stress relaxation cracking can be prevented.

However, the austenitic heat-resistant alloy structures used at these high temperatures may need to be partially repaired by welding due to partial damage due to aging. It was newly found that when welding is performed using these austenitic heat-resistant alloys used at high temperatures, cracks may occur in the weld heat-affected zone.

The present invention has been made in view of the above situation, and uses an austenitic heat-resistant alloy welded joint using an austenitic heat-resistant alloy that has been used for a long time as a high-temperature member such as a main steam pipe or a reheat steam pipe of a boiler for thermal power generation. An object of the present invention is to provide a method for producing a welded joint and a welded joint obtained by using the method.

In order to solve the above-mentioned problems, the present inventors first conducted a detailed investigation on a crack occurrence phenomenon in a weld heat-affected zone of a welded joint using an austenitic heat-resistant alloy exposed to a high temperature for a long time. As a result, the following <1> to <3> were confirmed.

<1> It was found that cracks in the weld heat affected zone tend to occur with increasing temperature and time when used at high temperatures, and tend to occur when exceeding certain conditions. Specifically, if the heating retention temperature _{T A} at the time of use is 600 ~ 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.)} 2100 It turned out that it exists in the tendency which the crack of a welding heat affected zone tends to arise as it is the above. However, 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. And as a result of observing the crack fracture surface, no melt mark was observed, and a fracture surface with poor ductility was exhibited. Further, concentrated S and P were detected on the fracture surface.

<3> Further, as a result of the observation of the structure of the weld heat affected zone, in the grains of the weld heat affected zone that is several hundred μm away from the melting boundary where cracks occurred, it is finer than the weld heat affected zone near the melt line. Many precipitates were observed.

From these results, it was estimated that the cracks that occurred in the heat affected zone when welding was performed using an austenitic heat-resistant alloy that was used at high temperatures for a long period of time, occurred due to the following mechanism.

That is, with long-term use at high temperatures, precipitates precipitate finely in the crystal grains of the austenitic heat-resistant alloy. However, the higher the use temperature, the shorter the precipitation time, and the longer the use time, the greater the amount. Further, during use, grain boundary segregation of impurity elements S and P also occurs.

In this way, when the austenitic heat-resistant alloy in which the precipitation phase is present in the grains and the impurities are segregated at the grain boundaries is welded, the maximum ultimate temperature is high in the weld heat affected zone near the melting boundary. It dissolves again in the parent phase, and the grain boundary segregation is eliminated. However, in the weld heat-affected zone a little away from the melting boundary, the maximum temperature reached is low, so re-solution of intragranular precipitates and elimination of grain boundary segregation do not occur. Here, at the time of welding, thermal stress is generated in the weld heat affected zone due to expansion and contraction accompanying welding. For this reason, in a region where a large amount of precipitated phase exists in the grain, that is, in the weld heat affected zone slightly away from the melting boundary, the deformation resistance in the grain is high, the grain cannot be deformed, and the deformation due to thermal stress occurs at the grain boundary. concentrate. In addition, a large amount of impurity elements such as S and P are segregated at the grain boundaries, resulting in embrittlement. As a result, it is considered that the grain boundary opened due to inability to withstand deformation and led to cracking.

And, as a result of repeated intensive studies, it became clear that the following methods are effective in preventing this. In other words, in order to prevent cracking during welding, when precipitation occurs excessively in the grains during use at high temperatures, the precipitates are re-dissolved and the grain boundary segregation of impurities is reduced. Was found to be effective.

Specifically, the following [1] and [2] were found.

[1] In austenitic heat resistant alloy, the heating retention temperature _{T A} at the time of use is the 600 ~ 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 2100 or more, it is effective to perform heat treatment before welding. However, P _A = T _A × (1.0 + logt _A ).

[2] The heat treatment applied before welding is effective when the heat treatment holding temperature _TP is 1050 to 1300 ° C. and the heat treatment holding time t _P is [−0.1 × (T _P / 50-30)] or more. It is. However, if the heat treatment holding time t _P exceeds [−0.1 × (T _P / 10-145)], there is an adverse effect rather than no effect.

The present invention has been made on the basis of the above knowledge, and the gist thereof is a manufacturing method of the following austenitic heat-resistant alloy welded joint and a welded joint obtained by using the same.

(1) An alloy base material used under conditions satisfying the following formulas (i) and (ii)
A method for producing an austenitic heat-resistant alloy welded joint, wherein heat treatment is performed under conditions satisfying the following formulas (iii) and (iv) and then welding is performed.
600 ≦ T _A ≦ 850 (i)
2100 ≦ T _A × (1.0 + logt _A ) (ii)
1050 ≦ T _P ≦ 1300 (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 during use (° C.)
t _A : Heating holding time during use (h)
T _P : heat treatment holding temperature (° C.)
t _P : heat treatment holding time (h)

(2) The chemical composition of the alloy base material is mass%,
C: 0.04 to 0.12%,
Si: 1.0% or less,
Mn: 2.0% or less,
P: 0.03% or less,
S: 0.01% or less,
Ni: 42.0-54.0%,
Cr: 20.0-33.0%,
W: 3.0-10.0%,
Ti: 0.05 to 1.0%,
Al: 0.3% or less,
B: 0.0001 to 0.01%,
N: 0.02% or less,
O: 0.01% or less,
Ca: 0 to 0.05%,
Mg: 0 to 0.05%,
REM: 0 to 0.5%
Co: 0 to 1.0%,
Cu: 0 to 4.0%,
Mo: 0 to 1.0%,
V: 0 to 0.5%
Nb: 0 to 0.5%,
Zr: 0 to 0.05%,
The balance: The method for producing an austenitic heat-resistant alloy welded joint according to (1), which is Fe and impurities.

(3) The chemical composition is mass%,
C: 0.04 to 0.12%,
Si: 1.0% or less,
Mn: 2.0% or less,
P: 0.03% or less,
S: 0.01% or less,
Ni: 42.0 to 48.0%,
Cr: 20.0-26.0%,
W: 4.0-10.0%,
Ti: 0.05 to 0.15%,
Nb: 0.1 to 0.4%,
Al: 0.3% or less,
B: 0.0001 to 0.01%,
N: 0.02% or less,
O: 0.01% or less,
Ca: 0 to 0.05%,
Mg: 0 to 0.05%,
REM: 0 to 0.1%,
Co: 0 to 1.0%,
Cu: 0 to 4.0%,
Mo: 0 to 1.0%,
V: 0 to 0.5%
Balance: Fe and impurities, and
An alloy base material used under the conditions satisfying the following formulas (i) and (ii):
A method for producing an austenitic heat-resistant alloy welded joint, wherein heat treatment is performed under conditions satisfying the following formulas (iii) and (iv) and then welding is performed.
600 ≦ T _A ≦ 850 (i)
2800 ≦ T _A × (1.0 + logt _A ) (ii)
1050 ≦ T _P ≦ 1300 (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 during use (° C.)
t _A : Heating holding time during use (h)
T _P : heat treatment holding temperature (° C.)
t _P : heat treatment holding time (h)

(4) The chemical composition of the alloy base material is mass%,
Ca: 0.0001 to 0.05%,
Mg: 0.0001 to 0.05%,
REM: 0.0005 to 0.1%,
Co: 0.01 to 1.0%,
Cu: 0.01 to 4.0%,
Mo: 0.01 to 1.0%, and V: 0.01 to 0.5%,
The manufacturing method of the austenitic heat-resistant-alloy weld joint as described in said (2) or (3) containing 1 or more types selected from these.

(5) The chemical composition is mass%,
C: 0.04 to 0.12%,
Si: 0.5% or less,
Mn: 1.5% or less,
P: 0.03% or less,
S: 0.01% or less,
Ni: 46.0-54.0%,
Cr: 27.0-33.0%,
W: 3.0-9.0%,
Ti: 0.05 to 1.0%,
Zr: 0.005 to 0.05%,
Al: 0.05-0.3%
B: 0.0001 to 0.005%,
N: 0.02% or less,
O: 0.01% or less,
Ca: 0 to 0.05%,
Mg: 0 to 0.05%,
REM: 0 to 0.5%
Co: 0 to 1.0%,
Cu: 0 to 4.0%,
Mo: 0 to 1.0%,
V: 0 to 0.5%
Nb: 0 to 0.5%,
Balance: Fe and impurities, and
An alloy base material used under the conditions satisfying the following formulas (i) and (ii):
A method for producing an austenitic heat-resistant alloy welded joint, wherein heat treatment is performed under conditions satisfying the following formulas (iii) and (iv) and then welding is performed.
600 ≦ T _A ≦ 850 (i)
2100 ≦ T _A × (1.0 + logt _A ) (ii)
1050 ≦ T _P ≦ 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 during use (° C.)
t _A : Heating holding time during use (h)
T _P : heat treatment holding temperature (° C.)
t _P : heat treatment holding time (h)

(6) The chemical composition of the alloy base material is mass%,
Ca: 0.0001 to 0.05%,
Mg: 0.0001 to 0.05%,
REM: 0.0005 to 0.5%,
Co: 0.01 to 1.0%,
Cu: 0.01 to 4.0%,
Mo: 0.01 to 1.0%,
V: 0.01 to 0.5%, and Nb: 0.01 to 0.5%,
The manufacturing method of the austenitic heat-resistant-alloy weld joint as described in said (2) or (5) containing 1 or more types selected from these.

(7) In the said heat processing, the manufacturing method of the austenitic heat-resistant alloy welded joint in any one of said (1) to (6) whose average cooling rate to 500 degreeC in a cooling process is 50 degrees C / h or more. .

(8) The method for manufacturing an austenitic heat-resistant alloy welded joint according to any one of (1) to (7), wherein the heat treatment is performed at least in a range within 30 mm from the welded portion.

(9) The chemical composition is mass%,
C: 0.06 to 0.18%,
Si: 1.0% or less,
Mn: 2.0% or less,
P: 0.03% or less,
S: 0.01% or less,
Ni: 40.0-60.0%,
Cr: 20.0-33.0%,
One or more selected from Mo and W: Total 6.0 to 13.0%
Ti: 0.05 to 1.5%,
Co: 0 to 15.0%
Nb: 0 to 0.5%,
Al: 1.5% or less,
B: 0 to 0.005%,
N: 0.18% or less,
O: 0.01% or less,
The balance: The method for producing an austenitic heat-resistant alloy welded joint according to any one of (1) to (8), wherein welding is performed using a welding material that is Fe and impurities.

(10) An austenitic heat-resistant alloy welded joint obtained by using the production method according to any one of (1) to (9) above.

According to the production method of the present invention, an austenitic heat-resistant alloy welded joint is stably used by using an austenitic heat-resistant alloy that has been used for a long time as a high-temperature member such as a main steam pipe or a reheat steam pipe of a boiler for thermal power generation. Obtainable.

Hereinafter, each requirement of the present invention will be described in detail. In the following description, “%” for the content means “% by 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 austenitic heat-resistant alloy welded joint according to the present invention are as follows.

C: 0.04 to 0.12%
C is an element having the effect of stabilizing austenite, forming fine carbides, and improving the creep strength during use at high temperatures. In order to sufficiently obtain this effect, a C content of 0.04% or more is necessary. However, if the C content is excessive, the carbide becomes coarse and precipitates in a large amount, so that the contribution to the creep strength is saturated. Not only that, it reduces ductility and reduces weldability in materials that have been used for a long time. Therefore, the C content is 0.12% or less. The C content is preferably 0.05% or more, and more preferably 0.06% or more. Further, the C content is preferably 0.11% or less, and more preferably 0.08% or less.

Si: 1.0% or less Si is an element that has a deoxidizing action and is effective in improving corrosion resistance and oxidation resistance at high temperatures. However, when Si is contained excessively, the stability of austenite is lowered, leading to a decrease in toughness and creep strength. Therefore, an upper limit is set for the Si content to 1.0% or less. The Si content is preferably 0.8% or less, more preferably 0.5% or less, and further preferably 0.3% or less.

In addition, it is not necessary to set a lower limit in particular for the Si content, but if it is extremely reduced, the deoxidation effect cannot be obtained sufficiently and the cleanliness of the alloy is deteriorated, and the effect of improving the corrosion resistance and oxidation resistance at high temperatures. Is difficult to obtain, and the manufacturing cost is greatly increased. Therefore, the Si content is preferably 0.02% or more, and more preferably 0.05% or more.

Mn: 2.0% or less Mn, like Si, is an element having a deoxidizing action. Mn also contributes to stabilization of austenite. However, when the Mn content is excessive, embrittlement is caused, and the toughness and creep ductility are also reduced. Therefore, an upper limit is set for the Mn content to 2.0% or less. The Mn content is preferably 1.8% or less, more preferably 1.5% or less, and even more preferably 1.3% or less.

In addition, it is not necessary to provide a lower limit for the Mn content, but if it is extremely reduced, the deoxidation effect cannot be sufficiently obtained, the cleanliness of the alloy is deteriorated, and the austenite stabilizing effect is difficult to obtain. Manufacturing costs also increase significantly. Therefore, the Mn content is preferably 0.02% or more, and more preferably 0.05% or more.

P: 0.03% or less P is an element contained in the alloy as an impurity and segregates at the grain boundary of the weld heat-affected zone during welding to increase liquefaction cracking sensitivity. Furthermore, when segregated at the grain boundaries when used for a long time at high temperature, the creep ductility is lowered, and the weldability is lowered in the material used for a long time. Therefore, an upper limit is set for the P content to 0.03% or less. The P content is preferably 0.025% or less, and more preferably 0.02% or less.

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

S: 0.01% or less S is an element which is contained in the alloy as an impurity like P and segregates at the grain boundary of the weld heat-affected zone during welding to increase liquefaction cracking sensitivity. Furthermore, when used for a long time at a high temperature, it segregates at the grain boundary and causes embrittlement, and the weldability is lowered in the material used for a long time. Therefore, an upper limit is set for the S content to 0.01% or less. The S content is preferably 0.008% or less, and more preferably 0.005% or less.

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

Ni: 42.0-54.0%
Ni is an effective element for obtaining austenite, and is an essential element for ensuring the structural stability when used for a long time at a high temperature. In order to obtain a sufficient effect within the range of the Cr content of the present invention, a Ni content of 42.0% or more is necessary. However, Ni is an expensive element, and if it is contained in a large amount, the cost increases. Therefore, an upper limit is provided so that the Ni content is 54.0% or less. The Ni content is preferably 42.5% or more, and more preferably 43.0% or more. Further, the Ni content is preferably 53.0% or less, and more preferably 52.0% or less.

Cr: 20.0-33.0%
Cr is an essential element for securing oxidation resistance and corrosion resistance at high temperatures. Further, Cr contributes to ensuring creep strength by forming fine carbides or further Cr-enriched phases. In order to obtain the above effects within the range of the Ni content of the present invention, a Cr content of 20.0% or more is necessary. However, if the Cr content exceeds 33.0%, the stability of austenite at high temperatures deteriorates and the creep strength decreases. In addition, a large amount of carbide or further Cr-enriched phase is precipitated, the deformation resistance is increased, and the weldability is lowered in a material used for a long time. Therefore, the Cr content is 33.0% or less. The Cr content is preferably 20.5% or more, and more preferably 21.0% or more. Further, the Cr content is preferably 32.5% or less, and more preferably 32.0% or less.

W: 3.0-10.0%
W is an element that contributes greatly to the improvement of creep strength and tensile strength at high temperatures by forming a solid solution in the matrix or forming a fine intermetallic compound phase. In order to obtain this effect sufficiently, a W content of 3.0% or more is necessary. However, even if W is excessively contained, the effect is saturated, and the creep strength is decreased. Furthermore, precipitation of a large amount of intermetallic compounds may be caused, the deformation resistance may be increased, and the weldability may be lowered in a material used for a long time. Moreover, since it is an expensive element, when it contains excessively, an increase in cost will be caused. Therefore, an upper limit is provided so that the W content is 10.0% or less.

The W content is preferably 3.5% or more, more preferably 4.0% or more, further preferably 4.5% or more, and particularly preferably 5.0% or more. preferable. Further, the W content is preferably 9.5% or less, more preferably 9.0% or less, further preferably 8.5% or less, and 8.0% or less. Is particularly preferred.

Ti: 0.05 to 1.0%
Ti precipitates in the grains as a fine carbonitride or intermetallic compound phase, and contributes to the improvement of creep strength and tensile strength at high temperatures. In order to sufficiently obtain the effect, a Ti content of 0.05% or more is necessary. However, if the Ti content is excessive, a large amount of carbonitride precipitates, leading to a decrease in creep ductility and toughness, and a decrease in weldability in materials used for a long time. Therefore, an upper limit is set so that the Ti content is 1.0% or less. The Ti content is preferably 0.06% or more, and more preferably 0.07% or more. Further, the Ti content is preferably 0.9% or less, and more preferably 0.8% or less.

Al: 0.3% or less Al is an element that has a deoxidizing action, precipitates as an intermetallic compound phase during use, and contributes to an improvement in creep strength. However, when the Al content is excessive, the cleanliness of the alloy is remarkably deteriorated and the hot workability and ductility are lowered. Therefore, an upper limit is set so that the Al content is 0.3% or less. The Al content is preferably 0.2% or less, and more preferably 0.1% or less.

Although there is no particular need to set a lower limit for the Al content, if it is extremely reduced, the deoxidation effect cannot be obtained sufficiently, the cleanliness of the alloy deteriorates, and the manufacturing cost increases greatly. Therefore, the Al content is preferably 0.0005% or more, and more preferably 0.001% or more. Further, when it is desired to obtain the effect of improving the creep strength, the Al content is preferably 0.05% or more, more preferably 0.06% or more, and 0.07% or more. Further preferred.

B: 0.0001 to 0.01%
B is an element effective for improving the creep strength by finely dispersing grain boundary carbides and segregating at the grain boundaries to strengthen the grain boundaries. In order to obtain this effect, the B content needs to be 0.0001% or more. However, if the B content 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 liquefaction cracking sensitivity is increased. Therefore, an upper limit is provided so that the B content is 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.

N: 0.02% or less N is an element effective for stabilizing austenite, but if it is contained in excess, a large amount of fine nitride precipitates in the grains during use at high temperatures, Decreases creep ductility and toughness. Furthermore, the weldability of the material used for a long time is lowered. Therefore, an upper limit is set for the N content to 0.02% or less. The N content is preferably 0.018% or less, and more preferably 0.015% or less.

Although there is no particular need to set a lower limit for the N content, it is difficult to obtain the effect of stabilizing austenite and the manufacturing cost is greatly increased if it is extremely reduced. 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, hot workability is lowered, and further, toughness and ductility are deteriorated. For this reason, an upper limit is set for the O content to 0.01% or less. The content of O is preferably 0.008% or less, and more preferably 0.005% or less.

Although there is no particular need to set a lower limit for the O content, an extreme reduction causes an increase in manufacturing cost. Therefore, the O content is preferably 0.0005% or more, and more preferably 0.0008% or more.

Ca: 0 to 0.05%
Since Ca is an element having an effect of improving hot workability, Ca may be contained. However, when the content of Ca is excessive, it combines with O to significantly reduce cleanliness, and on the other hand, deteriorate hot workability. Therefore, when Ca is contained, its content is set to 0.05% or less. The Ca content is preferably 0.03% or less.

In order to obtain the above effect, the Ca content is preferably 0.0001% or more, and more preferably 0.0005% or more.

Mg: 0 to 0.05%
Since Mg is an element having an effect of improving hot workability like Ca, it may be contained. However, if the Mg content is excessive, it combines with O to significantly reduce cleanliness, and on the contrary, deteriorate hot workability. Therefore, when it contains Mg, the content shall be 0.05% or less. The Mg content is preferably 0.03% or less.

In addition, when obtaining said effect, it is preferable to make Mg content 0.0001% or more, and it is more preferable to set it as 0.0005% or more.

REM: 0 to 0.5%
REM is an element that has a strong affinity with S and has an effect of improving hot workability, and therefore may be contained. However, when the content of REM becomes excessive, it combines with O to significantly reduce cleanliness and, on the contrary, deteriorate hot workability. Therefore, when it contains REM, the content shall be 0.5% or less. The REM content is preferably 0.2% or less, more preferably 0.1% or less, and further preferably 0.06% or less.

In addition, when obtaining said effect, it is preferable to make REM content into 0.0005% or more, and it is more preferable to set it as 0.001% or more.

Note that “REM” is a generic name for a total of 17 elements of Sc, Y and lanthanoid, and the content of REM refers to the total content of one or more elements of REM. Further, REM is generally contained in Misch metal. For this reason, for example, it may be added in the form of misch metal and contained so that the amount of REM falls within the above range.

The above Ca, Mg, and REM all have an effect of improving the hot workability, and therefore can be contained alone or in combination of two or more thereof. The total amount when these elements are contained in combination is preferably 0.5% or less.

Co: 0 to 1.0%
Co, like Ni, is an effective element for obtaining austenite, and contributes to the improvement of creep strength by increasing phase stability, so it may be contained. However, since Co is an extremely expensive element, excessive content of Co causes a significant cost increase. Therefore, when Co is contained, the content is made 1.0% or less. The Co content is preferably 0.8% or less, and more preferably 0.4% or less.

In addition, when obtaining said effect, it is preferable to make Co content 0.01% or more, and it is more preferable to set it as 0.03% or more.

Cu: 0 to 4.0%
Cu is an element having an action of improving creep strength. That is, Cu, like Ni and Co, is an effective element for obtaining austenite, and contributes to the improvement of creep strength by increasing phase stability. For this reason, you may contain Cu. However, when Cu is contained excessively, the hot workability is lowered. Therefore, when it contains Cu, the content shall be 4.0% or less. The Cu content is preferably 3.0% or less, and more preferably 1.0% or less.

In addition, when obtaining said effect, it is preferable to make Cu content 0.01% or more, and it is more preferable to set it as 0.03% or more.

Mo: 0 to 1.0%
Mo is an element having an effect of improving the creep strength. That is, since Mo has a function of improving the creep strength at a high temperature by dissolving in the matrix, it may be contained. However, when Mo is contained excessively, the stability of austenite is lowered, and instead the creep strength is lowered. Therefore, when it contains Mo, the content shall be 1.0% or less. The Mo content is preferably 0.8% or less, and more preferably 0.5% or less.

In addition, when obtaining 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.

V: 0 to 0.5%
V is an element having an effect of improving the creep strength. That is, V combines with C or N to form fine carbides or carbonitrides, and has the effect of improving creep strength, so may be included. However, when V is contained excessively, it precipitates in a large amount as a carbide or carbonitride, leading to 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 set to 0.5% or less. The V content is preferably 0.4% or less, and more preferably 0.2% or less.

In addition, when obtaining said effect, it is preferable to make content of V into 0.01% or more, and it is more preferable to set it as 0.02% or more.

Nb: 0 to 0.5%
Nb, like Ti and V, may combine with C or N to precipitate in the grains as fine carbides or carbonitrides and contribute to the improvement of creep strength at high temperatures, so may be included. However, when the Nb content is excessive, a large amount of carbides and carbonitrides are precipitated, resulting in a decrease in creep ductility and toughness, and a decrease in weldability in materials used for a long time. Therefore, an upper limit is provided so that the Nb content is 0.5% or less. The Nb content is preferably 0.4% or less, more preferably 0.38% or less, and further preferably 0.35% or less.

In order to obtain the above effect, the Nb content is preferably 0.01% or more, more preferably 0.02% or more, and even more preferably 0.05% or more. .

The above Co, Cu, Mo, V, and Nb all have the effect of improving the creep strength, and therefore, any one of them or a combination of two or more thereof can be contained. The total amount when these elements are contained in combination is preferably 6.0% or less.

Zr: 0 to 0.05%
Zr, like Ti, dissolves in the matrix and improves the creep strength at high temperatures. Zr has a strong affinity for S, and the fixation of S improves the creep ductility. However, when the Zr content is excessive, creep ductility is reduced. Therefore, an upper limit is provided so that the Zr content is 0.05% or less. The Zr content is preferably 0.04% or less, and more preferably 0.03% or less.

In addition, when obtaining said effect, it is preferable that Zr content is 0.005% or more, It is more preferable that it is 0.008% or more, It is further more preferable that it is 0.01% or more. .

The alloy base material used for manufacturing the austenitic heat-resistant alloy welded joint according to the present invention has a chemical composition containing the above-described elements, with the balance being Fe and impurities.

In addition, “impurities” refer to materials mixed from ores, scraps, or production environments as raw materials when an alloy is industrially produced.

The following two types are typical as the composition of the alloy base material.

(A) The chemical composition is mass%, C: 0.04 to 0.12%, Si: 1.0% or less, Mn: 2.0% or less, P: 0.03% or less, S: 0.00. 01% or less, Ni: 42.0 to 48.0%, Cr: 20.0 to 26.0%, W: 4.0 to 10.0%, Ti: 0.05 to 0.15%, Nb: 0.1-0.4%, Al: 0.3% or less, B: 0.0001-0.01%, N: 0.02% or less, O: 0.01% or less, Ca: 0-0. 05%, Mg: 0 to 0.05%, REM: 0 to 0.1%, Co: 0 to 1.0%, Cu: 0 to 4.0%, Mo: 0 to 1.0%, V: 0 to 0.5%, balance: alloy base material which is Fe and impurities.

(B) The chemical composition is mass%, C: 0.04 to 0.12%, Si: 0.5% or less, Mn: 1.5% or less, P: 0.03% or less, S: 0.00. 01% or less, Ni: 46.0-54.0%, Cr: 27.0-33.0%, W: 3.0-9.0%, Ti: 0.05-1.0%, Zr: 0.005 to 0.05%, Al: 0.05 to 0.3%, B: 0.0001 to 0.005%, N: 0.02% or less, O: 0.01% or less, Ca: 0 -0.05%, Mg: 0-0.05%, REM: 0-0.5%, Co: 0-1.0%, Cu: 0-4.0%, Mo: 0-1.0% V: 0 to 0.5%, Nb: 0 to 0.5%, balance: Fe and an alloy base material containing impurities.

In the chemical composition (a), the Si content is preferably 0.6% or less. The Ni content is preferably 48.0% or less, more preferably 47.5% or less, and even more preferably 47.0% or less. Further, the Cr content is preferably 25.5% or less, and more preferably 25.0% or less. Furthermore, the Ti content is preferably 0.14% or less, and more preferably 0.13% or less. And Nb content is preferably 0.12% or more, and more preferably 0.15% or more.

In the chemical composition (b), the Mn content is preferably 1.1% or less. The Ni content is preferably 46.0% or more, more preferably 47.0% or more, and further preferably 48.0% or more. The Cr content is preferably 27.5% or more, and more preferably 28.0% or more. Furthermore, the Nb content is preferably 0.2% or less.

2. Alloy matrix used in the production of austenitic 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.) during use: 600 ≦ T _A ≦ 850 (i)
P _A : 2100 ≦ T _A × (1.0 + logt _A ) (ii)
When the alloy base material used for manufacturing the austenitic heat-resistant alloy welded joint of the present invention is heated to 600 to 850 ° C., precipitates are finely precipitated in the crystal grains. In particular, when the alloy base material has the chemical composition described in (a) above, a Laves phase that is M ₂₃ C ₆ carbide and an intermetallic compound precipitates, and the chemical composition described in (b) above is obtained. In the case where it has, the bcc phase enriched with M ₂₃ C ₆ carbide and Cr tends to precipitate.

Further, S and P grain boundary segregation also occur at the same time. When the amount of precipitates precipitated in the grains and the amount of grain boundary segregation of impurities exceeds a predetermined amount, the deformation resistance within the grains increases and the grain boundaries weaken. When welding, welding cracks occur. Alloy matrix used in the production of austenitic heat resistant alloy welded joint according to the present invention, when P _A is 2100 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 perform heat treatment before. Incidentally, when the alloy matrix having a chemical composition described in (a) above, when P _A is equal to or greater than 2800, may be subjected to heat treatment prior to welding.

3. Heat Treatment Conditions In the method for producing an austenitic heat-resistant alloy welded joint according to the present invention, heat treatment is performed before welding the alloy base material. In order to prevent weld cracking, the heat treatment needs to be performed under the condition that the heat treatment holding temperature T _P and the heat treatment holding time t _P satisfy the following formulas (iii) and (iv).

Heat treatment holding temperature T _P (° C.): 1050 ≦ T _P ≦ 1300 (iii)
In order to prevent weld cracking, it is effective to reduce the impurity elements segregated at the grain boundaries while heat-treating the precipitates excessively precipitated in the grains during use at high temperatures again in the base. is there. 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 1300 ° C., local melting of the grain boundary is started. Therefore, the heat treatment holding temperature _TP is set to 1300 ° C. or lower.

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 1280 ° C. or less, more preferably 1250 ° C. or less. In particular, when the alloy matrix having a chemical composition as described in (b) above is preferably a heat treatment holding temperature T _P is 1250 ° C. or less, more preferably 1230 ° C. or less, 1200 ° C. or less More preferably.

Heat treatment holding time _{t P (h): - 0.1} × (T P / 50-30) ≦ t P ≦ -0.1 × (T P / 10-145) ··· (iv)
In order to prevent weld cracking, heat treatment is effective, but the heat treatment holding time t _P needs to be −0.1 × (T _P / 50-30) or more. This is because if the heat treatment holding time t _P is less than this value, the time required for the diffusion of the alloy element to achieve re-dissolution of precipitates in the matrix and reduction of grain boundary segregation becomes insufficient. . However, when the heat treatment holding time t _P exceeds −0.1 × (T _P / 10-145), the crystal grain size becomes extremely large, and liquefaction cracks are likely to occur near the melting line during welding. 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 cooling process, the average cooling rate up to 500 ° C. is preferably 50 ° C./h or more. This is because when the average cooling rate is less than 50 ° C./h, carbides and the like are precipitated again in the grains in the course of cooling, and grain boundary segregation of impurities may occur.

Further, it is preferable to perform the heat treatment at least in a range within 30 mm from the welded portion. This is because strain generated by thermal stress generated during welding becomes large in this region.

4). Chemical composition of welding material There is no particular limitation on the chemical composition of the welding material used for manufacturing the austenitic heat-resistant alloy welded joint according to the present invention. However, it is preferable to use a welding material having a chemical composition in the range shown below. The reasons for limiting each element are as follows.

C: 0.06 to 0.18%
C is an element that has the effect of stabilizing the austenite in the weld metal after welding, forming fine carbides, and improving the creep strength during use at high temperatures. Furthermore, by forming eutectic carbide with Cr during welding solidification, it contributes to reduction of solidification cracking sensitivity. In order to sufficiently obtain this effect, a C content of 0.06% or more is necessary. However, if the C content is excessive, a large amount of carbide precipitates, so that the creep strength and ductility are reduced. Therefore, the C content is 0.18% or less. The C content is preferably 0.07% or more, and more preferably 0.08% or more. Further, the C content is preferably 0.16% or less, and more preferably 0.14% or less.

Si: 1.0% or less Si is an element that is effective for deoxidation at the time of manufacturing a welding material and is effective for improving the corrosion resistance and oxidation resistance of the weld metal after welding at a high temperature. However, when Si is contained excessively, the stability of austenite is lowered, leading to a decrease in toughness and creep strength. Therefore, an upper limit is set for the Si content to 1.0% or less. The Si content is preferably 0.8% or less, and more preferably 0.6% or less.

In addition, it is not necessary to set a lower limit in particular for the Si content, but if it is extremely reduced, the deoxidation effect cannot be obtained sufficiently and the cleanliness of the alloy is deteriorated, and the effect of improving the corrosion resistance and oxidation resistance at high temperatures. Is difficult to obtain, and the manufacturing cost is greatly increased. Therefore, the Si content is preferably 0.02% or more, and more preferably 0.05% or more.

Mn: 2.0% or less Mn, like Si, is an element effective for deoxidation during the production of a welding material. Mn also contributes to stabilization of austenite in the weld metal after welding. However, when the Mn content is excessive, embrittlement is caused, and the toughness and creep ductility are also reduced. Therefore, an upper limit is set for the Mn content to 2.0% or less. The Mn content is preferably 1.8% or less, and more preferably 1.5% or less.

In addition, it is not necessary to provide a lower limit for the Mn content, but if it is extremely reduced, the deoxidation effect cannot be sufficiently obtained, the cleanliness of the alloy is deteriorated, and the austenite stabilizing effect is difficult to obtain. Manufacturing costs also increase significantly. Therefore, the Mn content is preferably 0.02% or more, and more preferably 0.05% or more.

P: 0.03% or less P is an element that is contained in the welding material as an impurity and increases the susceptibility to solidification cracking during welding. Furthermore, the creep ductility of the weld metal after long time use at high temperature is reduced. Therefore, an upper limit is set for the P content to 0.03% or less. The P content is preferably 0.025% or less, and more preferably 0.02% or less.

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

S: 0.01% or less S is an element that is contained in the welding material as an impurity as in the case of P and increases the susceptibility to solidification cracking during welding. Furthermore, S segregates at columnar grain boundaries during use for a long time in weld metal, leading to embrittlement and increasing stress relaxation crack sensitivity. Therefore, an upper limit is set for the S content to 0.01% or less. The S content is preferably 0.008% or less, and more preferably 0.005% or less.

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

Ni: 40.0-60.0%
Ni is an element effective for stabilizing austenite in the weld metal after welding, and is an essential element for ensuring the creep strength when used for a long time. In order to obtain the effect, the Ni content of the welding material needs to be 40.0% or more. However, Ni is an expensive element, and even in a welding material manufactured in a small scale, if a large amount is contained, the cost increases. Therefore, an upper limit is provided so that the Ni content is 60.0% or less. The Ni content is preferably 40.5% or more, and more preferably 41.0% or more. Further, the Ni content is preferably 59.5% or less, and more preferably 59.0% or less.

Cr: 20.0-33.0%
Cr is an effective element for ensuring oxidation resistance and corrosion resistance at high temperatures of the weld metal after welding. Further, Cr contributes to ensuring the creep strength by forming a fine carbide or a bcc phase enriched with Cr. Furthermore, forming eutectic carbide with C during welding also contributes to a reduction in solidification cracking susceptibility. In order to obtain these effects, a Cr content of 20% or more is necessary. However, when the Cr content exceeds 33.0%, the stability of austenite at high temperatures deteriorates in the Ni content range of 40 to 60%, leading to a decrease in creep strength. Therefore, the Cr content is 33.0% or less.

The Cr content is preferably 20.5% or more, and more preferably 21.0% or more. Further, the Cr content is preferably 32.5% or less, and more preferably 32.0% or less. When the alloy base material has the chemical composition described in (a) above, the Cr content is preferably 26.0% or less, and more preferably 25.5% or less. More preferably, it is 25.0% or less.

One or more selected from Mo and W: Total 6.0 to 13.0%
Mo and W are elements that make a solid solution in the matrix in the weld metal or form a fine intermetallic compound phase and greatly contribute to the improvement of the creep strength and tensile strength at high temperatures. In order to sufficiently obtain this effect, it is necessary to contain at least 6.0% in total of at least one selected from Mo and W. However, even if these elements are contained excessively, the effect is saturated, and on the contrary, the creep strength is lowered. Furthermore, since Mo and W are expensive elements, an excessive amount causes an increase in cost. Therefore, an upper limit is provided so that the total content of one or more selected from Mo and W is 13.0% or less. The total content is preferably 6.5% or more, and more preferably 7.0% or more. Further, the total content is preferably 12.5% or less, and more preferably 12.0% or less.

Ti: 0.05 to 0.6%
Ti is an element that precipitates in the grains as a fine carbonitride in the weld metal and further as an intermetallic compound phase with Ni, and contributes to an improvement in creep strength and tensile strength at high temperatures. In order to sufficiently obtain the effect, the Ti content needs to be 0.05% or more. However, when the Ti content is excessive, a large amount of carbonitride precipitates, resulting in a decrease in creep ductility and toughness. Therefore, an upper limit is set so that the Ti content is 1.5% or less.

The Ti content is preferably 0.06% or more, and more preferably 0.07% or more. Moreover, it is preferable that Ti content is 1.3% or less, and it is more preferable that it is 1.1% or less. When the alloy base material has the chemical composition described in (a) above, the Ti content is preferably 0.6% or less, more preferably 0.58% or less, More preferably, it is 0.55% or less.

Co: 0 to 15.0%
Co, like Ni, is an effective element for obtaining austenite, and contributes to the improvement of creep strength by increasing phase stability, so it may be contained. However, since Co is an extremely expensive element, even if it is a welding material, excessive content causes a significant cost increase. Therefore, when Co is contained, the content is made 15.0% or less. The Co content is preferably 14.0% or less, and more preferably 13.0% or less.

In addition, when obtaining said effect, it is preferable to make Co content 0.01% or more, and it is more preferable to set it as 0.03% or more.

Nb: 0 to 0.5%
Nb, like Ti, is combined with C or N and precipitates in the grains as fine carbides or carbonitrides, and contributes to the improvement of creep strength at high temperatures. Therefore, Nb may be contained. However, when the Nb content is excessive, a large amount of carbide or carbonitride precipitates, resulting in a decrease in creep ductility and toughness. Therefore, when Nb is contained, the content is set to 0.5% or less. The Nb content is preferably 0.48% or less, and more preferably 0.45% or less.

In addition, when obtaining said effect, it is preferable to make Nb content 0.01% or more, and it is more preferable to set it as 0.03% or more.

Al: 1.5% or less Al is an element effective for deoxidation at the time of manufacturing a welding material. Moreover, a fine intermetallic compound phase is formed in the weld metal, which contributes to the improvement of creep strength. However, if the Al content is excessive, the cleanliness of the alloy is remarkably deteriorated, and the hot workability and ductility of the welding material are lowered, so that the productivity is lowered. In addition, a large amount of intermetallic phase is formed in the weld metal, and the stress relaxation cracking susceptibility when used at a high temperature for a long time is remarkably increased. Therefore, an upper limit is set so that the Al content is 1.5% or less. The Al content is preferably 1.4% or less, and more preferably 1.3% or less.

Although there is no particular need to set a lower limit for the Al content, if it is extremely reduced, the deoxidation effect cannot be sufficiently obtained, the cleanliness of the alloy is deteriorated, and the manufacturing cost is greatly increased. Therefore, the Al content is preferably 0.0005% or more, and more preferably 0.001% 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, if the B content is excessive, the susceptibility to solidification cracking during welding is significantly increased. Therefore, an upper limit is provided so that the B content is 0.005% or less. The B content is preferably 0.004% or less, and more preferably 0.003% or less.

In addition, when obtaining said effect, it is preferable to make B content 0.0001% or more, and it is more preferable to set it as 0.0005% or more.

N: 0.18% or less N is an element that stabilizes austenite in the weld metal, improves creep strength, and contributes to securing tensile strength by solid solution. However, if it is contained excessively, a large amount of fine nitride precipitates in the grains during use at high temperatures, leading to a decrease in creep ductility and toughness. Therefore, an upper limit is set for the N content to 0.18% or less. The N content is preferably 0.16% or less, and more preferably 0.14% or less.

Although there is no particular need to set a lower limit for the N content, it is difficult to obtain the effect of stabilizing austenite and the manufacturing cost is greatly increased if it is extremely reduced. 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, hot workability is deteriorated and productivity is deteriorated. For this reason, an upper limit is set for the O content to 0.01% or less. The content of O is preferably 0.008% or less, and more preferably 0.005% or less.

Although there is no particular need to set a lower limit for the O content, an extreme reduction causes an increase in manufacturing cost. Therefore, the O content is preferably 0.0005% or more, and more preferably 0.0008% or more.

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

5. Others In the method for producing an austenitic heat-resistant alloy welded joint according to the present invention, the alloy base material is subjected to heat treatment and then welded. The welding method is not particularly limited, and for example, gas tungsten arc welding, gas metal arc welding, covered arc welding, or the like can be used.

The shape or dimensions of the alloy base material and the welding material used for manufacturing the austenitic heat-resistant alloy welded joint according to the present invention are not particularly limited. 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.

Hereinafter, the present invention will be described more specifically by way of examples. However, 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 above ingot, solution heat treatment was performed to produce an austenitic heat-resistant alloy plate having a thickness of 30 mm, a width of 50 mm, and a length of 100 mm.

 

 

Furthermore, an alloy having the chemical composition shown in Table 2 was melted to produce an ingot, and then a welding material having an outer diameter of 1.2 mm was produced by hot forging, hot rolling and machining.

 

 

In order to simulate use at a high temperature, the austenitic heat-resistant alloy plate 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 A22, heat treatment was performed at the heat treatment holding temperature, the heat treatment holding time and the average cooling rate shown in Table 3.

 

 

A V groove having a groove angle of 30 ° and a root thickness of 1 mm was processed in the longitudinal direction of the alloy plate described above. After that, on the SM400B steel plate specified in JIS G3160 (2008) having a thickness of 50 mm, a width of 200 mm, and a length of 200 mm, four rounds were restrained and welded using the covered arc welding rod DNiCrFe-3 specified in JIS Z3224 (1999). .

After that, using the above-described welding materials, lamination welding was performed in the groove with heat input of 12 to 18 kJ / cm by TIG welding to produce a welded joint.

(Crack observation test)
The cross section of the sample taken from five places of the obtained welded joint was mirror-polished and corroded, and examined with an optical microscope to investigate the presence or absence of cracks in the weld heat affected zone. Of the five samples, “○” indicates a welded joint in which no cracks were observed in all samples, and “△” indicates a welded joint in which cracks were observed in one or two samples. Judged. Moreover, the welded joint in which the crack was recognized by all five samples was set to "x", and it determined with "failed."

As can be seen from the results in Table 3, the test numbers A1, A2, A5 to A8, A10 to A16, A18, A20, A21, A23 to A26, B2 to B6, C1 and D1 satisfy the heat treatment conditions of the present invention. It can be seen that the welded joint of No. 1 passed the result of the crack observation test, and even if the thickness was 30 mm, a sound welded joint was obtained.

In contrast, the weld joints of test numbers A3 and A22 were cracked in the weld heat affected zone because the alloy plate was not heat treated.

The weld joint of test number A4 had a low heat treatment holding temperature of 1000 ° C. before welding, so that the re-dissolution of precipitates was insufficient, so the deformation resistance within the grains was high, and the grain boundaries The resolution of segregation was insufficient. Therefore, a weld crack occurred at a position slightly away from the melting line during welding.

The weld joint of test number A19 had a heat treatment holding temperature as high as 1350 ° C., so local melting of the grain boundary occurred, and the part opened during cracking and cracking occurred.

In the welded joints of test numbers A9 and B1, the heat treatment holding time was less than the range specified in the present invention, so the re-dissolution of precipitates and the elimination of segregation at the grain boundaries were insufficient, and a little away from the melting line during welding. A weld crack occurred at the position.

In the welded joints of Test Nos. A17 and B7, the heat treatment retention time exceeded the range specified in the present invention, so that the crystal grains were significantly coarsened, and liquefaction cracks occurred in the portion adjacent to the melt line during welding.

In the welded joint of test number A11, the average cooling rate in the heat treatment was lower than 50 ° C./h, so that reprecipitation of precipitates and grain boundary segregation occurred during cooling. Therefore, although the result of the crack observation test was acceptable, a crack occurred in the weld heat affected zone in one sample.

An alloy having the chemical composition shown in Table 4 was melted to produce an ingot. After forming by hot forging using the above ingot, solution heat treatment was performed to produce an austenitic heat-resistant alloy plate having a thickness of 30 mm, a width of 50 mm, and a length of 100 mm.

 

 

Furthermore, an alloy having the chemical composition shown in Table 5 was melted to produce an ingot, and then a welding material having an outer diameter of 1.2 mm was produced by hot forging, hot rolling and machining.

 

 

In order to simulate use at a high temperature, the austenitic heat-resistant alloy plate was heated at the heating holding temperature and heating holding time shown in Table 6. Thereafter, except for the welded joints of test numbers AA3 and AA22, heat treatment was performed at the heat treatment holding temperature, the heat treatment holding time and the average cooling rate shown in Table 6.

 

 

A V groove having a groove angle of 30 ° and a root thickness of 1 mm was processed in the longitudinal direction of the alloy plate described above. After that, on the SM400B steel plate specified in JIS G3160 (2008) having a thickness of 50 mm, a width of 200 mm, and a length of 200 mm, four rounds were restrained and welded using the covered arc welding rod DNiCrFe-3 specified in JIS Z3224 (1999). .

After that, using the above-described welding materials, lamination welding was performed in the groove with heat input of 12 to 18 kJ / cm by TIG welding to produce a welded joint. And the crack observation test was done by the method similar to Example 1 about the obtained welded joint.

As can be seen from the results in Table 6, the test numbers AA1, AA2, AA5 to AA7, AA9 to AA14, AA16, AA17, AA19 to AA21, AA23 to AA26, BB2 to BB5, CC1 satisfying the provisions of the present invention. As for the welded joint of DD1 and DD1, it can be seen that a sound welded joint was obtained even if the result of the crack observation test was acceptable and the thickness was 30 mm.

In contrast, the weld joints of test numbers AA3 and AA22 were cracked in the weld heat affected zone because the alloy plate was not heat-treated.

The weld joint of test number AA4 had a low heat treatment holding temperature of 1000 ° C. before welding, so that the re-dissolution of precipitates was insufficient, so the deformation resistance in the grains was high, and the grain boundary The resolution of segregation was insufficient. Therefore, a weld crack occurred at a position slightly away from the melting line during welding.

The weld joint of test number AA18 had a heat treatment holding temperature as high as 1320 ° C., so local melting of the grain boundary occurred, and the part opened during welding and cracking occurred.

In the welded joints of test numbers AA8 and BB1, the heat treatment holding time was less than the range specified in the present invention, so that re-dissolution of precipitates and elimination of grain boundary segregation were insufficient, and a little away from the melting line during welding. A weld crack occurred at the position.

In the welded joints of test numbers AA15 and BB6, the heat treatment holding time exceeded the range specified in the present invention, so that the crystal grains were significantly coarsened, and liquefaction cracks occurred in the portion adjacent to the melt line during welding.

In the welded joint with test number AA10, the average cooling rate in the heat treatment was lower than 50 ° C./h, so that reprecipitation of precipitates and grain boundary segregation occurred during cooling. Therefore, although the result of the crack observation test was acceptable, a crack occurred in the weld heat affected zone in one sample.

According to the production method of the present invention, an austenitic heat-resistant alloy welded joint is stably used by using an austenitic heat-resistant alloy that has been used for a long time as a high-temperature member such as a main steam pipe or a reheat steam pipe of a boiler for thermal power generation. Obtainable.

Claims (10)

An alloy base material used under the conditions satisfying the following formulas (i) and (ii):
A method for producing an austenitic heat-resistant alloy welded joint, wherein heat treatment is performed under conditions satisfying the following formulas (iii) and (iv) and then welding is performed.
600 ≦ T _A ≦ 850 (i)
2100 ≦ T _A × (1.0 + logt _A ) (ii)
1050 ≦ T _P ≦ 1300 (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 during use (° C.)
t _A : Heating holding time during use (h)
T _P : heat treatment holding temperature (° C.)
t _P : heat treatment holding time (h) The chemical composition of the alloy base material is mass%,
C: 0.04 to 0.12%,
Si: 1.0% or less,
Mn: 2.0% or less,
P: 0.03% or less,
S: 0.01% or less,
Ni: 42.0-54.0%,
Cr: 20.0-33.0%,
W: 3.0-10.0%,
Ti: 0.05 to 1.0%,
Al: 0.3% or less,
B: 0.0001 to 0.01%,
N: 0.02% or less,
O: 0.01% or less,
Ca: 0 to 0.05%,
Mg: 0 to 0.05%,
REM: 0 to 0.5%
Co: 0 to 1.0%,
Cu: 0 to 4.0%,
Mo: 0 to 1.0%,
V: 0 to 0.5%
Nb: 0 to 0.5%,
Zr: 0 to 0.05%,
The balance: The method for producing an austenitic heat-resistant alloy welded joint according to claim 1, which is Fe and impurities. Chemical composition is mass%,
C: 0.04 to 0.12%,
Si: 1.0% or less,
Mn: 2.0% or less,
P: 0.03% or less,
S: 0.01% or less,
Ni: 42.0 to 48.0%,
Cr: 20.0-26.0%,
W: 4.0-10.0%,
Ti: 0.05 to 0.15%,
Nb: 0.1 to 0.4%,
Al: 0.3% or less,
B: 0.0001 to 0.01%,
N: 0.02% or less,
O: 0.01% or less,
Ca: 0 to 0.05%,
Mg: 0 to 0.05%,
REM: 0 to 0.1%,
Co: 0 to 1.0%,
Cu: 0 to 4.0%,
Mo: 0 to 1.0%,
V: 0 to 0.5%
Balance: Fe and impurities, and
An alloy base material used under the conditions satisfying the following formulas (i) and (ii):
A method for producing an austenitic heat-resistant alloy welded joint, wherein heat treatment is performed under conditions satisfying the following formulas (iii) and (iv) and then welding is performed.
600 ≦ T _A ≦ 850 (i)
2800 ≦ T _A × (1.0 + logt _A ) (ii)
1050 ≦ T _P ≦ 1300 (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 during use (° C.)
t _A : Heating holding time during use (h)
T _P : heat treatment holding temperature (° C.)
t _P : heat treatment holding time (h) The chemical composition of the alloy base material is mass%,
Ca: 0.0001 to 0.05%,
Mg: 0.0001 to 0.05%,
REM: 0.0005 to 0.1%,
Co: 0.01 to 1.0%,
Cu: 0.01 to 4.0%,
Mo: 0.01 to 1.0%, and V: 0.01 to 0.5%,
The manufacturing method of the austenitic heat-resistant alloy welded joint of Claim 2 or Claim 3 containing 1 or more types selected from these. Chemical composition is mass%,
C: 0.04 to 0.12%,
Si: 0.5% or less,
Mn: 1.5% or less,
P: 0.03% or less,
S: 0.01% or less,
Ni: 46.0-54.0%,
Cr: 27.0-33.0%,
W: 3.0-9.0%,
Ti: 0.05 to 1.0%,
Zr: 0.005 to 0.05%,
Al: 0.05-0.3%
B: 0.0001 to 0.005%,
N: 0.02% or less,
O: 0.01% or less,
Ca: 0 to 0.05%,
Mg: 0 to 0.05%,
REM: 0 to 0.5%
Co: 0 to 1.0%,
Cu: 0 to 4.0%,
Mo: 0 to 1.0%,
V: 0 to 0.5%
Nb: 0 to 0.5%,
Balance: Fe and impurities, and
An alloy base material used under the conditions satisfying the following formulas (i) and (ii):
A method for producing an austenitic heat-resistant alloy welded joint, wherein heat treatment is performed under conditions satisfying the following formulas (iii) and (iv) and then welding is performed.
600 ≦ T _A ≦ 850 (i)
2100 ≦ T _A × (1.0 + logt _A ) (ii)
1050 ≦ T _P ≦ 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 during use (° C.)
t _A : Heating holding time during use (h)
T _P : heat treatment holding temperature (° C.)
t _P : heat treatment holding time (h) The chemical composition of the alloy base material is mass%,
Ca: 0.0001 to 0.05%,
Mg: 0.0001 to 0.05%,
REM: 0.0005 to 0.5%,
Co: 0.01 to 1.0%,
Cu: 0.01 to 4.0%,
Mo: 0.01 to 1.0%,
V: 0.01 to 0.5%, and Nb: 0.01 to 0.5%,
The manufacturing method of the austenitic heat-resistant-alloy weld joint of Claim 2 or Claim 5 containing 1 or more types selected from these. In the heat treatment, the method for producing an austenitic heat-resistant alloy welded joint according to any one of claims 1 to 6, wherein an average cooling rate to 500 ° C in the cooling process is 50 ° C / h or more. The method for manufacturing an austenitic heat-resistant alloy welded joint according to any one of claims 1 to 7, wherein the heat treatment is performed at least in a range within 30 mm from a welded portion. Chemical composition is mass%,
C: 0.06 to 0.18%,
Si: 1.0% or less,
Mn: 2.0% or less,
P: 0.03% or less,
S: 0.01% or less,
Ni: 40.0-60.0%,
Cr: 20.0-33.0%,
One or more selected from Mo and W: Total 6.0 to 13.0%
Ti: 0.05 to 1.5%,
Co: 0 to 15.0%
Nb: 0 to 0.5%,
Al: 1.5% or less,
B: 0 to 0.005%,
N: 0.18% or less,
O: 0.01% or less,
The balance: The method for producing an austenitic heat-resistant alloy welded joint according to any one of claims 1 to 8, wherein welding is performed using a welding material that is Fe and impurities. An austenitic heat-resistant alloy welded joint obtained by using the production method according to any one of claims 1 to 9.