KR20160118980A - METHOD FOR PRODUCING Ni-BASED HEAT-RESISTANT ALLOY WELDING JOINT AND WELDING JOINT OBTAINED BY USING THE SAME - Google Patents

Abstract

A method for manufacturing a welding joint made of a Ni-based heat-resistant alloy includes welding an alloy base material comprising: 0.03-0.12 wt% of C; 1.0 wt% or less of Si; 1.0 wt% or less of Mn; 0.015 wt% or less of P; 0.005 wt% or less of S; 8.0-25.0 wt% of Co; 18.0-27.0 wt% of Cr; 0.1-2.5 wt% of Ti; 0.2-2.0 wt% of Al; 0.0001-0.01 wt% of B; 0.001-0.5 wt% of REM; 0.02 wt% or less of N; 0.01 wt% or less of O; 0-0.05 wt% of Ca; 0-0.05 wt% of Mg; 0-15.0 wt% of Fe; 0-12.0 wt% of Mo; 0-10.0 wt% of W; 0-4.0 wt% of Cu; 0-2.5 wt% of Nb; 0-0.5 wt% of V; and the remainder consisting of Ni and impurities. In the method, the alloy base material is used under a condition that a heating maintaining temperature T_A(C) and a heating maintaining time t_A(h) satisfy the formulas: [600 <= TA <= 850] and [1700 <= TA (1.0 + logtA)]. The alloy base material is thermally treated under a condition that a thermal treatment maintaining temperature T_P(C) and a thermal treatment maintaining time t_P(h) satisfy the formulas: [1050 <= T_P <= 1250] and [-0.1 (T_P / 50 - 30) <= t_P <= -0.1 (T_P / 10 - 145)].

Description

TECHNICAL FIELD [0001] The present invention relates to a method of manufacturing a welded joint of a Ni-base heat-resistant alloy, and a welded joint obtained by using the same. BACKGROUND ART [0002]

TECHNICAL FIELD The present invention relates to a method of manufacturing a welded joint of a Ni-base heat resistant alloy and a welded joint obtained using the same. Particularly, the present invention relates to a method for 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 shaft of a boiler for thermal power generation or a reheated steam pipe, and a welded joint obtained using the same.

Recently, from the viewpoint of environmental burden reduction, high-temperature and high-pressure operation of operating conditions have been progressing on a world scale in boilers for thermal power generation, and austenitic heat-resistant alloys or Ni- Temperature strength and corrosion resistance.

In addition, it has been required to increase the strength of various members such as the main steam furnace in which the ferritic heat-resistant steel was used or the member of the bottom heat such as the reheated steam tube, and the application of the high strength austenitic heat- .

Under these technical backgrounds, for example, International Patent Publication No. 2009/154161 (Patent Document 1) discloses an austenitic heat-resistant alloy having enhanced creep rupture strength by utilizing Cr, Ti and Zr. In addition, International Publication No. WO03038826 (Patent Document 2) discloses that Ni and Fe which increase the creep rupture strength by incorporating a large amount of W and utilizing precipitation strengthening by solid solution and γ ' Heat-resistant alloys are disclosed. Further, Japanese Patent Laid-Open Publication No. 2013-49902 (Patent Document 3) discloses a Ni-based heat-resistant alloy in which the precipitation amount of Cr determined by quantitative analysis of extracted residues is specified and the toughness is increased in addition to the creep rupture strength .

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

Therefore, in International Publication No. 2011/071054 (Patent Document 4), the contents of Al, Ti, and Nb, and P, Cr, and B are specified within a predetermined range to improve the liquefying crack resistance at the time of welding Austenitic heat-resistant alloys have been proposed. Further, Japanese Patent Application Laid-Open No. 2010-150593 (Patent Document 5) discloses a method of using Mo and W to increase the creep strength, to prescribe the content of impurity element and Ti and Al, There is proposed an austenitic heat-resistant alloy improved in liquefaction cracking and stress relaxation and cracking resistance at the time of use. Japanese Patent Application Laid-Open No. 2013-36086 (Patent Document 6) discloses a method of increasing the creep strength by using γ 'phase by containing Al and Ti, and adjusting the content of Nd and O according to the grain size, There has been proposed a Ni-base heat-resistant alloy improved in creep ductility after use at a high temperature for a long time and improved in stress relaxation and cracking resistance during repair welding.

International Publication No. 2009/154161 International Publication No. 2010/038826 Japanese Patent Application Laid-Open No. 2013-49902 International Publication No. 2011/071054 Japanese Patent Application Laid-Open No. 2010-150593 Japanese Patent Application Laid-Open No. 2013-36086

When these austenitic heat-resistant alloys and Ni-based heat-resistant alloys are applied to the members of the rear fuselage such as the main steam furnace or the reheated steam tube and assembled by welding, it is possible to reliably prevent liquefaction cracking during welding and stress relaxation cracks during use .

However, in the structure of the Ni-based heat resistant alloy used at these high temperatures, it is sometimes necessary to repair a part of the structure by welding due to partial deterioration due to aged deterioration. When welding is performed using the Ni-based heat resistant alloy used at these high temperatures, it has been newly found that cracks may occur in the weld heat affected zone. In addition, the welding cracks to be targeted in Patent Document 6 are not aimed at solving the problems of the present invention, because they are intended for heat treatment after repair welding and cracks occurring at high temperature use.

The present invention has been made in view of the above phenomenon, and a method for manufacturing a welded joint of a Ni-base heat-resistant alloy by using a Ni-base heat-resistant alloy used for a long time as a high temperature member such as a main engine of a boiler for thermal power generation, And to provide a welded joint obtained by using the welded joint.

In order to solve the above problems, the inventors of the present invention firstly investigated the crack generation phenomenon of the weld heat affected zone in a welded joint using a Ni-based heat resistant alloy containing a large amount of Al and Ti exposed at a high temperature for a long time Investigation was conducted. As a result, the following <1> to <3> were confirmed.

<1> It has been found that the cracks in the weld heat affected zone tend to occur together with an increase in temperature and time when used at a high temperature, and tend to occur when a certain condition is exceeded. Specifically, when the heating and holding temperature T _A at the time of use is 600 to 850 ° C and the parameter (hereinafter also referred to as P _A ) determined from the heating holding temperature T _A and the heating holding time t _{A at the} time of use is 1700 or more, Cracks tend to occur in the weld heat affected zone. However, P _A = T _A × (1.0 + log t _A ).

<2> Cracks in the weld heat affected zone occurred at a position hundreds of μm away from the melting boundary. As a result of observing the fracture surface of the crack, no evidence of melting was recognized, and the fracture surface lacking in ductility was exhibited. Also, concentrated S and P were detected on the crack wavefront.

Further, as a result of the observation of the structure of the weld heat affected zone, the particles of the weld heat affected zone, which are several hundreds of micrometers away from the melt boundary where cracks occurred, contain fine M ₂₃ C ₆ carbides and metals A large amount of hepatic compound phase (γ 'phase) was observed.

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

That is, with the long-term use at a high temperature, the M ₂₃ C ₆ carbide and the intermetallic compound phase are finely precipitated in the crystal grains of the Ni-based heat resistant alloy. However, when the use temperature is high, the precipitation occurs in a short time, . During use, grain boundary segregation of S and P, which are impurity elements, also occurs.

In this way, when the Ni-based heat-resistant alloy in which the precipitate phase exists in the grain and the impurities are segregated in the grain boundary is welded, the precipitate in the grain is again solidified because the maximum temperature is reached at the weld heat affected zone near the melting boundary , The grain boundary segregation is solved. However, at the weld heat affected zone slightly distant from the melting boundary, the maximum reaching temperature is low, so that the reuse of the precipitates in the grain and the resolution of grain boundary segregation do not occur. Here, during welding, thermal stress is generated in the weld heat affected zone by the expansion and contraction due to welding. Therefore, in a region where a large amount of precipitate exists in the particle, that is, in a weld heat affected zone slightly distant from the melting boundary, the deformation resistance in the particle is high and the inside of the particle can not be deformed, and deformation due to thermal stress is concentrated do. Further, impurity elements such as S and P are segregated in a large amount in the grain boundary, and embrittlement occurs. As a result, it is thought that it is not able to withstand the deformation, and the grain boundary is opened and cracked.

As a result of repeating the examination of examples, it has become clear that the following method is effective for preventing this. That is, in order to prevent cracking during welding, it has been found that it is effective to alleviate intergranular segregation of impurities in addition to reuse of the precipitates when excessive precipitation occurs in the particles during use at a high temperature.

Concretely, those shown in the following [1] and [2] were found.

[1] In the Ni-based heat resistant alloy, also referred to as a heating and holding temperature of use T _A is 600 ~ 850 ℃ and, also, maintaining the heating of the use temperature T _A and the heating holding time t parameters (hereinafter, P _A, which is defined from the _A .) Is 1700 or more, it is effective to perform heat treatment before welding. However, P _A = T _A × (1.0 + log t _A ).

[2] It is effective that the heat treatment to be carried out before welding is such that the heat treatment holding temperature T _P is 1050 to 1250 ° C and the heat treatment holding time t _P is [-0.1 × (T _P / 50-30)] or more. However, if the heat treatment holding time t _P exceeds [-0.1 x (T _P / 10-145)], the effect is not so much but rather adversely affects.

The present invention is based on the above-described findings, and a method of manufacturing a welded joint of a Ni-based heat resistant alloy and a welded joint obtained using the same.

(1) the chemical composition, in mass%

C: 0.03 to 0.12%,

Si: 1.0% or less,

Mn: 1.0% or less,

P: not more than 0.015%

S: 0.005% or less,

Co: 8.0 to 25.0%

Cr: 18.0 to 27.0%

Ti: 0.1 to 2.5%

0.2 to 2.0% of Al,

B: 0.0001 to 0.01%

REM: 0.001-0.5%,

N: 0.02% or less,

O: 0.01% or less,

Ca: 0 to 0.05%,

Mg: 0 to 0.05%,

Fe: 0 to 15.0%

Mo: 0 to 12.0%,

W: 0 to 10.0%,

Cu: 0 to 4.0%,

Nb: 0 to 2.5%,

V: 0 to 0.5%,

The remainder is Ni and impurities,

The alloy base material used under the conditions satisfying the following expressions (i) and (ii)

Heat-treatment is performed under the conditions satisfying the following expressions (iii) and (iv), and then the weld is welded.

600? T? _A? 850 (i)

_{1700≤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)

The meanings of the symbols in the above formula are as follows.

T _A : Heating holding temperature (° C)

t _A : Heating holding time at the time of use (h)

T _P : Heat treatment holding temperature (캜)

t _P : heat treatment holding time (h)

(2) the chemical composition of the alloy base material is, in mass%

Ca: 0.0001 to 0.05%

Mg: 0.0001 to 0.05%

Fe: 0.01 to 15.0%

Mo: 0.01 to 12.0%

W: 0.01 to 10.0%

0.01 to 4.0% of Cu,

0.01 to 2.5% Nb, and

V: 0.01 to 0.5%,

(1), wherein the heat-resistant welded joint comprises at least one member selected from the group consisting of Ni, Ti, and Ni.

(3) The method for producing a welded joint of a Ni-base heat-resistant alloy as described in (1) above, wherein the average cooling rate up to 500 캜 in the cooling process in the heat treatment is not less than 50 캜 / h.

(4) The process for producing a welded joint of a Ni-base heat-resistant alloy as described in (2) above, wherein the average cooling rate up to 500 캜 in the cooling process in the heat treatment is not less than 50 캜 / h.

(5) The method for manufacturing a welded joint of a Ni-base heat-resisting alloy as described in any one of (1) to (4), wherein the heat treatment is performed in a range of at least 30 mm from the welded portion.

(6) The composition according to any one of

C: 0.06 to 0.15%

Si: 1.0% or less,

Mn: 1.0% or less,

P: 0.01% or less,

S: 0.005% or less,

Co: 8.0 to 25.0%

Cr: 18.0 to 27.0%

Ti: 0.1 to 2.5%

0.2 to 2.0% of Al,

Mo: 0 to 12.0%,

W: 0 to 10.0%,

Nb: 0 to 2.5%,

B: 0 to 0.005%,

Fe: 0 to 15.0%

N: 0.02% or less,

O: 0.01% or less,

A method for manufacturing a welded joint of a Ni-base heat-resistant alloy as set forth in any one of (1) to (4), wherein the weld is performed using a welding material which is Ni and impurities.

(7) The composition according to any one of (1) to

C: 0.06 to 0.15%

Si: 1.0% or less,

Mn: 1.0% or less,

P: 0.01% or less,

S: 0.005% or less,

Co: 8.0 to 25.0%

Cr: 18.0 to 27.0%

Ti: 0.1 to 2.5%

0.2 to 2.0% of Al,

Mo: 0 to 12.0%,

W: 0 to 10.0%,

Nb: 0 to 2.5%,

B: 0 to 0.005%,

Fe: 0 to 15.0%

N: 0.02% or less,

O: 0.01% or less,

The remainder is a method for manufacturing a welded joint of a Ni-base heat-resisting alloy according to (5), wherein the weld is performed using a welding material which is Ni and impurities.

(8) A welded joint of a heat-resistant Ni-base alloy obtained by the manufacturing method according to any one of (1) to (7).

According to the manufacturing method of the present invention, a Ni-base heat-resistant alloy welded joint can be stably obtained by using a Ni-based heat-resistant alloy which has been used for a long period of time as a high temperature member such as a main combustion engine or a reheat steam pipe of a boiler for thermal power generation.

Hereinafter, each of the requirements of the present invention will be described in detail. In the following description, "%" with respect to the content means "% by mass".

1. Chemical composition of base alloy

The reason for limiting each element contained in the alloy base material used in the production of the welded joint of the Ni-base heat-resistant alloy according to the present invention is as follows.

C: 0.03 to 0.12%

C is an element having an effect of stabilizing the texture and forming fine carbides and improving the creep strength during high temperature use. In order to sufficiently obtain this effect, the C content needs to be 0.03% or more. However, if the C content is excessive, the carbides become coarse and precipitate in a large amount, so that the creep strength is lowered. Furthermore, the ductility is deteriorated and the weldability of the material used for a long time is deteriorated. Therefore, the C content is 0.12% or less. The C content is preferably 0.04% or more, more preferably 0.06% or more. The C content is preferably 0.11% or less, and more preferably 0.10% or less.

Si: 1.0% or less

Si is an element effective for deoxidation and improvement in corrosion resistance and oxidation resistance at a high temperature. However, when Si is contained excessively, the stability of the structure is deteriorated and the toughness and the creep strength are lowered. Therefore, the Si content should be 1.0% or less. The Si content is preferably 0.8% or less, more preferably 0.6% or less.

Although it is not necessary to set a lower limit specifically for the Si content, if it is extremely reduced, the deoxidation effect can not be sufficiently obtained, the cleanliness of the alloy deteriorates, the effect of improving the corrosion resistance and oxidation resistance at high temperatures becomes difficult to obtain, Costs also rise significantly. Therefore, the Si content is preferably 0.01% or more, more preferably 0.03% or more.

Mn: 1.0% or less

Mn, like Si, is an element having a deoxidizing action. Mn also contributes to the stabilization of the structure. However, if the Mn content is excessive, brittleness is caused, and toughness and creep ductility also decrease. Therefore, the Mn content is set to 1.0% or less. The Mn content is preferably 0.8% or less, more preferably 0.6% or less.

It is not necessary to set a lower limit particularly for the Mn content. However, if the Mn content is extremely reduced, the deoxidation effect can not be sufficiently obtained and the cleanliness of the alloy deteriorates. In addition, the effect of stabilizing the structure is hardly obtained, . Therefore, the Mn content is preferably 0.01% or more, more preferably 0.02% or more.

P: not more than 0.015%

P is contained as an impurity in an alloy, and when contained in a large amount, P is an element which not only deteriorates hot workability but also significantly increases susceptibility to liquefaction cracking during welding. Further, the alloy is segregated in the grain boundaries during use at a high temperature, and the weldability of the material used for a long time is lowered. Therefore, the content of P is 0.015% or less. The P content is preferably 0.012% or less, and more preferably 0.010% or less.

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

S: not more than 0.005%

S, like P, is contained as an impurity in an alloy, and when contained in a large amount, S is an element that lowers hot workability and increases the susceptibility to liquefied cracks during welding. Further, when used at high temperature for a long time, it is segregated at the grain boundary, and the weldability of the material used for a long time is lowered. Therefore, the S content should be 0.005% or less. The S content is preferably 0.004% or less, and more preferably 0.003% or less.

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

Co: 8.0 to 25.0%

Co is an element having an action to improve the creep strength. In order to sufficiently obtain this effect, the Co content needs to be not less than 8.0%. However, since Co is a very expensive element, excessive inclusion causes a great increase in cost. Therefore, the Co content should be 25.0% or less. The Co content is preferably 8.5% or more, and more preferably 9.0% or more. The Co content is preferably 23.5% or less, and more preferably 22.0% or less.

Cr: 18.0 to 27.0%

Cr is an essential element for ensuring oxidation resistance and corrosion resistance at high temperatures. Cr also forms a fine carbide and contributes to securing the creep strength. In order to obtain the above effect, it is necessary to set the Cr content to 18.0% or more. However, when the Cr content is excessive, the structure stability at high temperature is lowered, and a large amount of carbides is produced, thereby deteriorating the weldability of the material used for a long time. Therefore, the Cr content should be 27.0% or less. The Cr content is preferably 18.5% or more, more preferably 19.0% or more. The Cr content is preferably 26.5% or less, more preferably 26.0% or less.

Ti: 0.1 to 2.5%

Ti binds with Ni to precipitate into fine intermetallic compound phases and contribute to improvement of creep strength and tensile strength at high temperatures. In order to sufficiently obtain the effect, it is necessary to set the Ti content to 0.1% or more. However, when the Ti content is excessive, a large amount of the intermetallic compound phase precipitates, resulting in creep ductility and deterioration of toughness. Moreover, the ductility is lowered and the weldability of the material used for a long time is lowered. Therefore, the Ti content should be 2.5% or less. The Ti content is preferably 0.15% or more, more preferably 0.2% or more. The Ti content is preferably 2.4% or less, and more preferably 2.3% or less.

Al: 0.2 to 2.0%

Al, like Ti, is an element that binds with Ni to precipitate as a fine intermetallic compound phase and contributes to improvement of creep strength and tensile strength at high temperatures. In order to sufficiently obtain the effect, it is necessary to set the Al content to 0.2% or more. However, when the content of Al is excessive, an intermetallic compound phase is formed in a large amount, resulting in deterioration of toughness and ductility, as well as deterioration of weldability in materials used for a long time. Therefore, the Al content should be 2.0% or less. The Al content is preferably 0.25% or more, more preferably 0.3% or more. The Al content is preferably 1.8% or less, and more preferably 1.6% or less.

B: 0.0001 to 0.01%

B is an element effective for improving the creep strength by finely dispersing the intergranular carbides and strengthening the grain boundaries in the grain boundaries. In order to obtain this effect, the B content needs to be 0.0001% or more. However, when the content of B is excessive, B is segregated in a large amount in the heat affected zone in the vicinity of the melting boundary due to the welding heat cycle during welding, so that the melting point of the grain boundaries is lowered and the susceptibility to liquefaction cracking increases. Therefore, the B content is set to 0.01% or less. The B content is preferably 0.0005% or more, more preferably 0.001% or more. The B content is preferably 0.008% or less, and more preferably 0.006% or less.

REM: 0.001-0.5%

REM has strong affinity with S and has an effect of improving hot workability, and is an effective element for reducing the susceptibility to liquefied cracks during welding. In addition, grain segregation of S in high-temperature use is reduced, contributing to reduction of weldability deterioration in materials used for a long time. In order to obtain this effect, it is necessary to set the REM content to 0.001% or more. However, when the REM content is excessive, it is combined with O to remarkably reduce the cleanliness and deteriorate the hot workability. Therefore, the REM content is set to 0.5% or less. The REM content is preferably 0.002% or more, and more preferably 0.005% or more. The REM content is preferably 0.4% or less, and more preferably 0.3% or less.

The term &quot; REM &quot; means a total of 17 elements of Sc, Y and lanthanoid, and the content of REM indicates the total content of at least one element among the REMs. The REM is generally contained in mis-metal. For this reason, for example, it may be added in the form of micrometal so that the amount of REM is in the above range.

N: 0.02% or less

N is an element effective for stabilizing the structure, but if it is contained excessively, a large amount of fine nitrides precipitate in the particles during use at high temperatures, resulting in creep ductility and deterioration of toughness. Further, the weldability of the material used for a long time is lowered. Therefore, the content of N is 0.02% or less. The content of N is preferably 0.018% or less, and more preferably 0.015% or less.

Further, it is not necessary to set a lower limit particularly for the N content, but if it is extremely reduced, the effect of stabilizing the structure becomes difficult to obtain, and the manufacturing cost also increases greatly. Therefore, the N content is preferably 0.0005% or more, and more preferably 0.0008% or more.

O: not more than 0.01%

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

In addition, it is not necessary to set a lower limit specifically for the O content, but extreme reduction leads to 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%

Ca is an element having an action to improve hot workability. It is also possible to reduce the grain segregation of S during high-temperature use and contribute to alleviating the deterioration in weldability of a material used for a long period of time. However, when the Ca content is excessive, it is combined with O to remarkably lower the cleanliness and deteriorate the hot workability. Therefore, when Ca is contained, the content thereof is made 0.05% or less. The Ca content is preferably 0.03% or less.

Further, when it is desired 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%

Mg, like Ca, is an element having an effect of improving hot workability. It is also possible to reduce the grain segregation of S during high-temperature use and contribute to alleviating the deterioration in weldability of a material used for a long period of time. However, when the Mg content is excessive, it is combined with O to remarkably lower the cleanliness and deteriorate the hot workability. Therefore, when Mg is contained, the content thereof is set to 0.05% or less. The Mg content is preferably 0.03% or less.

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

Fe: 0 to 15.0%

Fe may be contained because it is an element having an effect of improving the hot workability when a trace amount of Ni is contained in the Ni-based alloy. However, when the Fe content is excessive, the thermal expansion coefficient of the alloy becomes large, and the steam oxidation resistance also deteriorates. Therefore, when Fe is contained, the content thereof is set to 15.0% or less. The Fe content is preferably 10.0% or less, and more preferably 1.0% or less.

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

The above-mentioned Ca, Mg and Fe all have an effect of improving hot workability, so that any one of them, or a combination of two or more thereof, can be contained. The total amount when these elements are mixed and contained is preferably 15.1% or less.

Mo: 0 to 12.0%

Mo may be contained as a matrix because it is an element having a function of improving the creep strength and tensile strength at a high temperature by being employed as a matrix. However, even if Mo is added excessively, the effect is saturated, and the creep strength may be lowered in some cases. Further, since it is an expensive element, excessive use of the element causes an increase in cost. Therefore, when Mo is contained, its content is set to 12.0% or less. The MO content is preferably 10.0% or less.

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

W: 0 to 10.0%

Like Mo, W may be incorporated as a matrix because it is an element having a function of improving the creep strength and tensile strength at a high temperature by being solidified as a matrix. However, even if W is contained excessively, the effect is saturated. In addition, since it is an expensive element, if it is contained in excess, it causes an increase in cost. Therefore, when W is contained, the content thereof is set to 10.0% or less. The W content is preferably 8.0% or less, and more preferably 5.0% or less.

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

Cu: 0 to 4.0%

Cu is an element having an action to improve the creep strength. In other words, Cu, like Co, is an element that enhances the structure stability of a Ni-based heat resistant alloy and is an element having an effect of improving the creep strength. However, if the Cu content is excessive, the hot workability is deteriorated. Therefore, when Cu is contained, the content thereof is 4.0% or less. The Cu content is preferably 3.0% or less, and more preferably 1.0% or less.

In order to obtain the above effect, the Cu content is preferably 0.01% or more, and more preferably 0.03% or more.

Nb: 0 to 2.5%

Nb may be added because it binds with C or N to precipitate into fine carbides or carbonitrides in the particles or to form an intermetallic compound phase by binding with Ni and to contribute to improvement of creep strength at high temperatures. However, if the Nb content is excessively large, it precipitates as carbides and carbonitrides in a large amount, causing creep ductility and toughness to deteriorate, and deteriorating weldability in materials used for a long time. Therefore, when Nb is contained, its content is set to 2.5% or less. The Nb content is preferably 2.3% or less.

Further, when it is desired to obtain the above effect, the Nb content is preferably 0.01% or more, and more preferably 0.02% or more.

V: 0 to 0.5%

V is an element having an action to improve the creep strength. That is, V may be added because it has a function of forming a fine carbide or carbonitride by bonding with C or N and improving the creep strength. However, if the V content is excessive, a large amount of carbides or carbonitrides are precipitated to cause creep ductility to deteriorate, and the weldability of the material used for a long time is lowered. Therefore, when V is contained, its content is made 0.5% or less. The V content is preferably 0.4% or less.

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

Since Mo, W, Cu, Nb and V each have an effect of improving the creep strength, any one of them, or a combination of two or more of them, can be contained. The total amount when these elements are mixed and contained is preferably 7% or less.

The alloy base material used for manufacturing the welded joint of the Ni-base heat-resisting alloy according to the present invention has the above-mentioned respective elements, and the remainder has the chemical composition consisting of Ni and impurities.

The term &quot; impurity &quot; refers to the incorporation from an ore or scrap or a manufacturing environment as a raw material when the Ni-based heat resistant alloy member is industrially manufactured.

2. Terms of use of alloy base materials

The alloy base material used for manufacturing the Ni-based heat resistant alloy welded joint of the present invention is such that the heating holding temperature T _A at the time of use satisfies the following formula (i) and the heating holding temperature T _A and the heating holding time t _A (Hereinafter also referred to as &quot; P _A &quot;) is used as a condition satisfying the following formula (ii).

Heating and holding the temperature of use _{T A (℃): 600≤T A} ≤850 ··· (i)

_{P A: 1700≤T A × (1.0} + logt A) ··· (ii)

When the alloy base material used for manufacturing the welded joint of the Ni-base heat-resistant alloy of the present invention is heated to 600 to 850 캜, the M ₂₃ C ₆ carbide and the intermetallic compound phase γ 'phase are finely precipitated. In addition, grain boundary segregation of S and P occurs at the same time. If the amount of carbide and intermetallic compound precipitated in the grain and the amount of segregation of impurities in the grain boundary exceeds a predetermined amount, the deformation resistance in the grain becomes large and the grain boundary becomes weak. Therefore, Cracks occur. When the P _A is 1700 or more, the alloy base material used in the production of the welded joint of the Ni-base heat-resistant alloy of the present invention is remarkably increased in resistance to deformation due to precipitation and weakening of grain boundaries due to segregation. It is necessary to perform heat treatment.

3. Heat treatment conditions

In the method for manufacturing a welded joint of a Ni-base heat-resistant alloy of the present invention, the alloy base material is subjected to heat treatment before welding. Since the heat treatment prevents weld cracking, it is necessary to perform the heat treatment holding temperature T _P and the heat treatment holding time t _{P on the condition} that the following expressions (iii) and (iv) are satisfied.

Heat treatment holding temperature _{T P (℃): 1050≤T P} ≤1250 ··· (iii)

In order to prevent weld cracking, it is effective to heat the carbide and intermetallic compound phase excessively precipitated in the particles during use at a high temperature by heat treatment, and alleviate the impurity element segregated in the grain boundary. For this purpose, it is necessary to set the heat treatment holding temperature T _P to at least 1050 ° C or more. However, when the heat treatment holding temperature T _P exceeds 1250 占 폚, local melting of grain boundaries is started. Therefore, the heat treatment holding temperature T _P is set to 1250 ° C or lower. Further, as will be described later, in the heat treatment, it is necessary to control the heat treatment holding time t _P in a predetermined range in accordance with the heat treatment holding temperature T _P. The heat treatment holding temperature T _P is preferably 1080 ° C or higher, and more preferably 1100 ° C or higher. The heat treatment holding temperature T _P is preferably 1230 캜 or lower, and more preferably 1200 캜 or lower.

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 welding cracking, the heat treatment is effective, but the heat treatment holding time t _P is required to be -0.1 x (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 reuse of the precipitate to the base and the diffusion of the alloying element to attain the reduction of grain boundary segregation becomes insufficient. However, when the heat treatment holding time t _P exceeds -0.1 x (T _P / 10-145), coarsening of the crystal grain diameter becomes remarkable and liquefaction cracks tend to occur in the vicinity of the melting wire at the time of welding. Therefore, the heat treatment holding time t _P is required to be -0.1 x (T _P / 10-145) or less.

Further, in the heat treatment, in the course of the cooling, the average cooling rate up to 500 占 폚 is preferably 50 占 폚 / h or higher. This is because when the average cooling rate is lower than 50 캜 / h, the carbide and intermetallic compound phases are precipitated again in the course of cooling and grain segregation of impurities occurs in some cases.

It is preferable that the heat treatment is performed in a range of at least 30 mm from the welded portion. This is because the distortion caused by the thermal stress generated during welding becomes large in this region.

4. Chemical composition of welding material

The reason for limiting each element contained in the welding material used for manufacturing the welded joint of the Ni-base heat-resistant alloy according to the present invention is as follows.

C: 0.06 to 0.15%

C is an element having an effect of improving the phase stability in the weld metal after welding, forming a fine carbide and improving the creep strength during use at high temperatures. In addition, by forming Cr and a process carbide during welding solidification, it contributes to reduction of the susceptibility to solidification cracking. 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 carbide precipitates, and therefore, the creep strength and ductility are deteriorated. Therefore, the C content should be 0.15% or less. The C content is preferably 0.07% or more, more preferably 0.08% or more. The C content is preferably 0.14% or less, and more preferably 0.12% or less.

Si: 1.0% or less

Si is effective for deoxidation at the time of production of a welding material and is effective for improving corrosion resistance and oxidation resistance at a high temperature of the welding metal after welding. However, when Si is contained excessively, the phase stability is lowered, and toughness and creep strength are lowered. Therefore, the Si content should be 1.0% or less. The Si content is preferably 0.8% or less, more preferably 0.6% or less.

Although it is not necessary to set a lower limit specifically for the Si content, if it is extremely reduced, the deoxidation effect can not be sufficiently obtained, the cleanliness of the alloy deteriorates, the effect of improving the corrosion resistance and oxidation resistance at high temperatures becomes difficult to obtain, Costs also rise significantly. Therefore, the Si content is preferably 0.01% or more, more preferably 0.03% or more.

Mn: 1.0% or less

Mn, like Si, is an element effective for deoxidation in the production of a welding material. Mn also contributes to improvement of phase stability in the weld metal after welding. However, if the Mn content is excessive, brittleness is caused. Therefore, the Mn content is set to 1.0% or less. The content of Mn is preferably 0.8% or less, and more preferably 0.6% or less.

In addition, it is not necessary to set a lower limit particularly for the Mn content. However, if the Mn content is extremely reduced, the deoxidation effect can not be sufficiently obtained, the cleanliness of the alloy deteriorates, the effect of improving the phase stability becomes difficult to obtain, do. Therefore, the Mn content is preferably 0.01% or more, more preferably 0.02% or more.

P: not more than 0.01%

P is an element that is included in the welding material as an impurity and increases the susceptibility to solidification cracking during welding. Further, the creep ductility of the weld metal after a long use at a high temperature is lowered. Therefore, the P content should be 0.01% or less. The P content is preferably 0.008% or less, and more preferably 0.006% or less.

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

S: not more than 0.005%

S, like P, is contained as an impurity in the welding material, and if it is contained in a large amount, the hot workability and weldability are remarkably lowered. Further, when S is used for a long time at a high temperature, S segregates in the main phase grain boundaries in the weld metal, resulting in embrittlement and enhances stress relaxation crack susceptibility. Therefore, the S content should be 0.005% or less. The S content is preferably 0.004% or less, and more preferably 0.003% or less.

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

Co: 8.0 to 25.0%

Co, like Ni, enhances the stability of the structure and contributes to improvement of the creep strength. In order to sufficiently obtain this effect, the Co content needs to be not less than 8.0%. However, since Co is a very expensive element, an excessive amount of Co also causes a significant increase in cost. Therefore, the Co content should be 25.0% or less. The Co content is preferably 8.5% or more, and more preferably 9.0% or more. The Co content is preferably 23.5% or less, and more preferably 22.0% or less.

Cr: 18.0 to 27.0%

Cr is an effective element for ensuring oxidation resistance and corrosion resistance at a high temperature of a weld metal. Cr also forms a fine carbide and contributes to securing the creep strength. Further, by forming C and a process carbide during welding solidification, it contributes to reduction of the susceptibility to solidification cracking. In order to obtain these effects, the Cr content needs to be 18.0% or more. However, when the Cr content exceeds 27.0%, the phase stability at high temperature is deteriorated and the creep strength is lowered. Therefore, the Cr content should be 27.0% or less. The Cr content is preferably 18.5% or more, more preferably 19.0% or more. The Cr content is preferably 26.5% or less, more preferably 26.0% or less.

Ti: 0.1 to 2.5%

Ti precipitates as a fine intermetallic compound phase and contributes to improvement of creep strength and tensile strength at high temperatures. In order to sufficiently obtain the effect, it is necessary to set the Ti content to 0.1% or more. However, if the Ti content is excessive, a large amount of intermetallic compound phase precipitates, resulting in lowering creep ductility and toughness. Therefore, the Ti content should be 2.5% or less. The Ti content is preferably 0.15% or more, more preferably 0.2% or more. The Ti content is preferably 2.4% or less, and more preferably 2.3% or less.

Al: 0.2 to 2.0%

Al, as well as Ti, also precipitates as a fine intermetallic compound phase in a weld metal, and contributes to improvement of creep strength and tensile strength at high temperatures. In order to sufficiently obtain the effect, it is necessary to set the Al content to 0.2% or more. However, when the Al content is excessive, a large amount of the intermetallic compound phase precipitates, resulting in lowering creep ductility and toughness. Therefore, the Al content should be 2.0% or less. The Al content is preferably 0.25% or more, more preferably 0.3% or more. The Al content is preferably 1.8% or less, and more preferably 1.6% or less.

Mo: 0 to 12.0%

Mo may also be contained in the weld metal because it is an element having an effect of improving the creep strength and tensile strength at high temperature by being solidified as a matrix. However, even if Mo is added excessively, the effect is saturated, and the creep strength may be lowered in some cases. Further, since it is an expensive element, excessive use of the element causes an increase in cost. Therefore, when Mo is contained, its content is set to 12.0% or less. The MO content is preferably 11.0% or less, and more preferably 10.0% or less.

In order to obtain the above effect, the MO content is preferably 0.01% or more, and more preferably 0.03% or more.

W: 0 to 10.0%

W may be contained in the weld metal because it is an element having a function of improving the creep strength and tensile strength at high temperature by being solidified in a matrix as in the case of Mo. However, even if W is excessively contained, the effect is saturated and the creep strength may be lowered in some cases. In addition, since it is an expensive element, if it is contained in excess, it causes an increase in cost. Therefore, when W is contained, the content thereof is set to 10.0% or less. The W content is preferably 9.0% or less, and more preferably 8.0% or less.

In order to obtain the above effect, the W content is preferably 0.01% or more, and more preferably 0.03% or more.

Nb: 0 to 2.5%

Nb is also bonded to C or N in the weld metal to precipitate into fine grains as fine carbides or carbonitrides or to bind with Ni to form an intermetallic compound phase and to contribute to improvement of creep strength at high temperatures do. However, when the Nb content is excessive, a large amount of carbides and carbonitrides are precipitated to cause creep ductility and toughness to deteriorate. Therefore, when Nb is contained, its content is set to 2.5% or less. The Nb content is preferably 2.3% or less, and more preferably 2.0% or less.

Further, when it is desired to obtain the above effect, the Nb content is preferably 0.01% or more, and more preferably 0.02% or more.

B: 0 to 0.005%

B may be contained because it is an element effective for improving the creep strength of the weld metal. However, if the B content is excessive, the susceptibility to coagulation cracking during welding becomes remarkably high. Therefore, the B content should be 0.005% or less. The B content is preferably 0.004% or less, more preferably 0.003% or less.

Further, when it is desired to obtain the above effect, the B content is preferably 0.0001% or more, and more preferably 0.0005% or more.

Fe: 0 to 15.0%

Since Fe is an element having an effect of improving the hot workability, even if a trace amount of Fe is contained in the Ni-based alloy, the Fe may be contained in the welding material and the effect thereof may be utilized. However, if the Fe content is excessive, the thermal expansion coefficient of the weld metal becomes large, and the steam oxidation resistance also deteriorates. Therefore, when Fe is contained, the content thereof is set to 15.0% or less. The Fe content is preferably 10.0% or less, and more preferably 8.0% or less.

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

N: 0.02% or less

N is an element contributing to securing the tensile strength by solidifying the weld metal, improving the creep strength, and solidifying it by employment. However, if it is contained in excess, a large amount of fine nitrides precipitate in the particles during use at a high temperature, resulting in creep ductility and deterioration of toughness. Therefore, the N content should be 0.02% or less. The N content is preferably 0.018% or less, and more preferably 0.015% or less.

In addition, it is not necessary to set a lower limit specifically for the content of N, but if it is extremely reduced, the effect of improving the phase stability becomes difficult to obtain, and the manufacturing cost also increases greatly. Therefore, the N content is preferably 0.0005% or more, and more preferably 0.0008% or more.

O: not more than 0.01%

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

In addition, it is not necessary to set a lower limit specifically for the O content, but extreme reduction leads to 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 in the production of the welded joint of the Ni-base heat-resisting alloy according to the present invention has the above-mentioned respective elements, and the remainder has the chemical composition of Ni and impurities.

5. Others

In the method for manufacturing a welded joint of a Ni-base heat-resistant alloy 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, coated arc welding, or the like can be used.

There is no particular limitation on the shape or dimensions of the alloy base material and the welding material used in the production of the welded joint of the Ni-base heat-resistant alloy according to the present invention. However, the manufacturing method according to the present invention exerts an effect particularly 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 in more detail by way of examples, but the present invention is not limited to these examples.

[Example]

An alloy having the chemical composition shown in Table 1 was dissolved to prepare an ingot. The ingot was formed by hot forging and then subjected to solution heat treatment to produce Ni-based heat resistant alloy plates A to E each having a thickness of 30 mm, a width of 50 mm and a length of 100 mm.

[Table 1]

In addition, ingots were produced by dissolving an alloy having the chemical composition shown in Table 2, followed by hot forging, hot rolling and machining to produce welding materials W to Z having an outer diameter of 1.2 mm.

[Table 2]

In order to simulate the use at a high temperature, a Ni-base heat-resistant alloy plate was heated at a heating holding temperature and a heating holding time shown in Table 3. Thereafter, heat treatments were carried out at the heat treatment holding temperature, the heat treatment holding time and the average cooling rate shown in Table 3, except for the weld joints of Test Nos. A3 and A23.

[Table 3]

V improvement was performed in the longitudinal direction of the above-described alloy plate with an improvement angle of 30 DEG and a root thickness of 1 mm. Thereafter, a covered arc welding electrode DNiCrFe-3 specified in JIS Z 3224 (1999) was applied to an SM400B steel plate specified in JIS G 3160 (2008) having a thickness of 50 mm, a width of 200 mm and a length of 200 mm, The welded joint was welded.

Thereafter, the above-described welding material was used to perform lamination welding at an intake heat of 10 to 15 kJ / cm in the improvement by TIG welding to produce a welded joint.

(Crack Observation Test)

The cross sections of the samples taken from the five places of the obtained weld joint were polished by mirror polishing and subjected to bacterial inspections by an optical microscope to investigate the presence or absence of cracks in the weld heat affected zone. A welded joint in which no cracks were recognized in all of the five samples was evaluated as &quot;? &Quot;, and a welded joint in which cracks were recognized in one to three samples as &quot;? &Quot; In addition, a weld joint in which cracks were recognized in four or more samples was evaluated as &quot; X &quot; The results are shown in Table 3.

As can be seen from the results of Table 3, the test conditions A1, A2, A5 to A7, A9 to A15, A17, A18, A20 to A22, A24 to A28, B1, C2 to C6 , D1 and E1 weld joints, the result of the cracking test was satisfactory, and even if the thickness was 30 mm, a sound weld joint was obtained.

On the contrary, in the weld joints of Test Nos. A3 and A23, since the alloy plate was not subjected to the heat treatment, cracks occurred in the weld heat affected zone.

In the weld joint of Test No. A4, the heat treatment holding temperature before welding was as low as 1000 占 폚, so that the deformation resistance in the grain was high and the resolution of grain boundary segregation was also insufficient. As a result, welding cracks occurred at a position slightly distant from the fusion line at the time of welding.

The welding joint of Test No. A19 has a high heat treatment holding temperature of 1300 deg. C, so local melting of the grain boundary occurs and the weld portion is opened and cracks occur at the time of welding.

The weld joints of Test Nos. A8 and C1 have a heat treatment holding time that is lower than the range specified in the present invention. Therefore, it is difficult to reuse the precipitates and to solve grain boundary segregation, Has occurred.

The welding joints of Test Nos. A16 and C7 exceeded the range defined by the present invention because of the heat treatment holding time, so that crystal grains were remarkably coarsened and liquefaction cracks occurred in the portions adjacent to the fusion lines at the time of welding.

Further, in the welded joint of Test No. A10, since the average cooling rate in the heat treatment was less than 50 占 폚 / h, precipitation of precipitates and grain boundary segregation occurred during cooling. Therefore, although the results of the cracking test were acceptable, cracks occurred in the weld heat affected zone in the three samples.

According to the manufacturing method of the present invention, it is possible to stably obtain a welded joint of a Ni-base heat-resisting alloy by using a Ni-base heat-resistant alloy which has been used for a long time as a high temperature member such as a main combustion engine or a reheated steam pipe of a boiler for thermal power generation.

Claims (11)

Chemical composition, in% by mass,
C: 0.03 to 0.12%,
Si: 1.0% or less,
Mn: 1.0% or less,
P: not more than 0.015%
S: 0.005% or less,
Co: 8.0 to 25.0%
Cr: 18.0 to 27.0%
Ti: 0.1 to 2.5%
0.2 to 2.0% of Al,
B: 0.0001 to 0.01%
REM: 0.001-0.5%,
N: 0.02% or less,
O: 0.01% or less,
Ca: 0 to 0.05%,
Mg: 0 to 0.05%,
Fe: 0 to 15.0%
Mo: 0 to 12.0%,
W: 0 to 10.0%,
Cu: 0 to 4.0%,
Nb: 0 to 2.5%,
V: 0 to 0.5%,
The remainder is Ni and impurities,
The alloy base material used under the conditions satisfying the following expressions (i) and (ii)
Heat-treatment is performed under the conditions satisfying the following expressions (iii) and (iv), and then the weld is welded.
600? T? _A? 850 (i)
_{1700≤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)
The meanings of the symbols in the above formula are as follows.
T _A : Heating holding temperature (° C)
t _A : Heating holding time at the time of use (h)
T _P : Heat treatment holding temperature (캜)
t _P : heat treatment holding time (h) The method according to claim 1,
Wherein the chemical composition of the alloy base material is, by mass%
Ca: 0.0001 to 0.05%
Mg: 0.0001 to 0.05%
Fe: 0.01 to 15.0%
Mo: 0.01 to 12.0%
W: 0.01 to 10.0%
0.01 to 4.0% of Cu,
0.01 to 2.5% Nb, and
V: 0.01 to 0.5%,
Based alloy welded joint according to any one of claims 1 to 3, The method according to claim 1,
Wherein the average cooling rate up to 500 캜 in the cooling process is 50 캜 / h or more in the heat treatment. The method of claim 2,
Wherein the average cooling rate up to 500 캜 in the cooling process is 50 캜 / h or more in the heat treatment. The method according to any one of claims 1 to 4,
Wherein the heat treatment is performed at least within a range of 30 mm from the welded portion. The method according to any one of claims 1 to 4,
Chemical composition, in% by mass,
C: 0.06 to 0.15%
Si: 1.0% or less,
Mn: 1.0% or less,
P: 0.01% or less,
S: 0.005% or less,
Co: 8.0 to 25.0%
Cr: 18.0 to 27.0%
Ti: 0.1 to 2.5%
0.2 to 2.0% of Al,
Mo: 0 to 12.0%,
W: 0 to 10.0%,
Nb: 0 to 2.5%,
B: 0 to 0.005%,
Fe: 0 to 15.0%
N: 0.02% or less,
O: 0.01% or less,
The remainder is a method of manufacturing a welded joint of a Ni-base heat-resistant alloy to be welded using a welding material which is Ni and impurities. The method of claim 5,
Chemical composition, in% by mass,
C: 0.06 to 0.15%
Si: 1.0% or less,
Mn: 1.0% or less,
P: 0.01% or less,
S: 0.005% or less,
Co: 8.0 to 25.0%
Cr: 18.0 to 27.0%
Ti: 0.1 to 2.5%
0.2 to 2.0% of Al,
Mo: 0 to 12.0%,
W: 0 to 10.0%,
Nb: 0 to 2.5%,
B: 0 to 0.005%,
Fe: 0 to 15.0%
N: 0.02% or less,
O: 0.01% or less,
The remainder is a method of manufacturing a welded joint of a Ni-base heat-resistant alloy to be welded using a welding material which is Ni and impurities. A welded joint of a heat-resistant Ni-base alloy obtained by using the manufacturing method according to any one of claims 1 to 4. A welded joint of a heat-resistant Ni-base alloy obtained by using the manufacturing method according to claim 5. A welded joint of a heat-resistant Ni-base alloy obtained by using the manufacturing method according to claim 6. A welded joint of a heat-resistant Ni-base alloy obtained by the manufacturing method according to claim 7.