JP5170297B1 - Welding material for Ni-base heat-resistant alloy, weld metal and welded joint using the same - Google Patents

Abstract

Welding material for Ni-base heat-resistant alloys having excellent hot cracking resistance during welding, and weld metal having hot cracking resistance during welding, stress relaxation cracking resistance during long-term use at high temperature, and good creep strength And providing welded joints.
(1) C: 0.06 to 0.18%, Si ≦ 0.5%, Mn ≦ 1.5%, Ni: 45 to 55%, Cr: 25 to 35%, W: 7. 0 to 13.0%, Ti: more than 0.2 to 1.5%, Al <0.1% and N: 0.002 to 0.20%, with the balance being Fe and impurities, A welding material for a Ni-base heat-resistant alloy having a chemical composition of O ≦ 0.02%, P ≦ 0.008% and S ≦ 0.005%. This welding material may include Nb ≦ 1.0% instead of a part of Fe. (2) A weld metal using the above-mentioned welding material for Ni-base heat-resistant alloys. (3) A welded joint comprising the weld metal and a base material of a Ni-base heat-resistant alloy excellent in high temperature strength.
[Selection figure] None

Description

  The present invention relates to a welding material for a Ni-base heat-resistant alloy, a weld metal and a welded joint using the same. More specifically, the present invention relates to a welding material suitable for welding a Ni-based heat-resistant alloy used in equipment used at high temperatures such as a power generation boiler, and a weld metal and a welded joint obtained by using the welding material.

  In recent years, high-temperature and high-pressure operating conditions have been promoted on a global scale for power generation boilers and the like from the viewpoint of reducing environmental impact, and the materials used therefor are required to have superior high-temperature strength. Yes.

  As a material satisfying such requirements, for example, there is a Ni-based heat-resistant alloy specified in UNS N06617. Patent Documents 1 to 5 disclose various Ni-based alloys. These all define various alloy element ranges in order to satisfy the required performance as a base material.

  When these Ni-base heat resistant alloys are used as structures, they are generally assembled by welding.

  However, when the Ni-base alloy base material is used as it is as a welding material when assembling by welding, there is a case where high-temperature cracking susceptibility during welding in the weld metal is increased. Therefore, instead of using a Ni-based alloy base material having a wide composition range as it is as a welding material, it is necessary to use an alloy with a more strictly controlled component range to prevent the above-mentioned hot cracking. is there. The “hot cracking during welding” includes “solidification cracking” and “ductility-reducing cracking”.

  On the other hand, AWS A5.14-2005 ER NiCrCoMo-1 is known as a welding material for Ni-base heat-resistant alloys used when assembling by welding.

  Further, various welding materials for Ni-based alloys are proposed in Patent Documents 6 to 8.

  Patent Document 6 discloses a welding material used for welding an oxide dispersion strengthened alloy having high strength and a heat-resistant alloy, and by actively containing a solid solution strengthening element such as Mo and Nb, There has been proposed a welding material for oxide dispersion-strengthened alloys that has improved strength.

  Patent Document 7 proposes a welding material for a Ni-based alloy, which has been strengthened by utilizing the solid solution strengthening by Mo and W and the precipitation strengthening effect by Al and Ti.

  Patent Document 8 proposes a welding material for a Ni-based alloy that contains Nb and W to achieve both solidification cracking during welding and creep strength.

  By the way, a welded structure using the Ni-base heat-resistant alloy and the welding material for the Ni-base heat-resistant alloy is used at a high temperature. However, when it is used at a high temperature for a long time, cracks may occur in the welded portion. Concerned.

  For example, Non-Patent Document 1 points out that intergranular cracking occurs during post-weld heat treatment in a welding heat-affected zone (hereinafter referred to as “HAZ”) of a Ni-base heat-resistant alloy. In addition to precipitation, it is suggested that S grain boundary segregation affects.

  Non-Patent Document 2 discusses measures for preventing intergranular cracking in HAZ during long-time heating of 18Cr-8Ni-Nb austenitic heat-resistant steel welds. And the countermeasure from the welding process surface that reduction of the welding residual stress by application of appropriate post-heat treatment is effective in preventing grain boundary cracking in HAZ has been proposed.

  As described above, when a Ni-based heat-resistant alloy is used for a long time, the phenomenon of cracking in HAZ has been known for a long time. However, in recent years, various alloy elements have been included to increase the strength of materials. In addition, the occurrence of cracks during long-time heating tends to become apparent in weld metal.

  However, regarding cracks occurring in the welded part during long-time use, the mechanism has not yet been fully elucidated, and furthermore, countermeasures against cracking, particularly cracks from the material surface of the weld metal have not been established.

  Therefore, the weld metal obtained using AWS A5.14-2005 ER NiCrCoMo-1 known as a welding material for the above-mentioned Ni-base heat-resistant alloy is cracked during use for a long time (hereinafter referred to as “stress relaxation cracking”). Is still a problem.

  In the above-mentioned Patent Document 6 and Patent Document 7, stress relaxation cracking is not considered at all. For this reason, the weld metal obtained using the welding material proposed by the said patent document 6 and the patent document 7 also has a subject with respect to a stress relaxation crack. In addition, when the welding materials proposed in Patent Document 6 and Patent Document 7 contain a large amount of Ti and / or Al, there is also a problem that workability during welding is poor.

  On the other hand, since the welding material proposed by the present inventors in Patent Document 8 has a small Ti content, there is room for improvement in terms of securing better creep strength.

Japanese Unexamined Patent Publication No. 63-050440 JP-A-9-157779 JP 2004-3000 A International Publication No. 2009/154161 JP 2010-150593 A Japanese Patent Laid-Open No. 10-193174 International Publication No. 2010/013565 JP 2008-207242 A

Igawa et al .: Journal of the Japan Welding Society, Vol. 47 (1978) No. 10, p. 679 Uchigi et al .: Ishikawajima-Harima Technical Report, Volume 15 (1975) No. 2, p. 209

  The present invention has been made in view of the above situation, and provides a welding material for a Ni-base heat resistant alloy having excellent hot cracking resistance at the time of welding, and hot cracking resistance during welding using the same. It is an object of the present invention to provide a weld metal having stress relaxation crack resistance and good creep strength during long-time use. Furthermore, it is also an object of the present invention to provide a welded joint comprising a weld metal using this weld material and a base material of a Ni-base heat-resistant alloy excellent in high temperature strength.

  In order to solve the above-described problems, the present inventors first conducted a detailed investigation on stress relaxation cracks generated in a weld metal during long-time use at high temperatures. As a result, the following items (a) to (c) became clear.

  (A) Stress relaxation cracks occur at the columnar crystal boundaries of the weld metal.

  (B) The fracture surface is poor in ductility, and P and S are concentrated on the fracture surface.

  (C) In the microstructure near the cracked portion, a large amount of fine intermetallic compounds are precipitated in the crystal grains.

  From the above findings (a) to (c), the present inventors have reached the following conclusions (d) to (f).

  (D) Stress relaxation cracking is caused by welding residual stress and external stress acting on grain boundaries that have weakened due to segregation of P and S during solidification during welding and subsequent heating at high temperatures. It is an opening.

  (E) When a large amount of intermetallic compounds and / or carbonitrides are finely precipitated in the grains, the deformability in the grains decreases, and stress concentration occurs at the grain interfaces, resulting in weak grain boundaries. Cracks are likely to occur due to the superimposing action.

  (F) The above mechanism is suggested in Non-Patent Document 1 for similar cracks in HAZ. Non-Patent Document 1 shows that the reduction of S that weakens the grain boundaries or the inclusion of Ca and Mg to fix S is effective in preventing the cracking. However, the weld metal is generally used in an as-solidified structure, and the phenomenon is expected to be different from HAZ based on a tempered base material such as heat treatment. It is unlikely that the proposed HAZ crack countermeasures can be applied to stress relaxation cracks as they are. Specifically, since Ca and Mg proposed in Non-Patent Document 1 have a very strong affinity for oxygen, oxides are easily formed during welding, and the yield to the weld metal after welding is welded. Under the influence of conditions, it is difficult to obtain the effect stably. Furthermore, since extreme reduction of impurity elements, particularly P, causes a significant increase in steelmaking costs, it is difficult to apply to industrial products that are mass-produced.

  Therefore, the present inventors conducted further detailed studies in order to prevent stress relaxation cracking. As a result, it was found that the following (g) and (h) can reduce the sensitivity to stress relaxation cracking.

  (G) Regulating the contents of S and P in the weld metal that segregates at the grain boundaries and weakens the grain boundaries within a specific range.

  (H) To restrict the contents of elements, specifically Ti and Al, which are finely precipitated as intermetallic compounds and / or carbonitrides and cause an increase in intragranular deformation resistance within a specific range.

  However, even if the measures (g) and (h) are taken, stress relaxation cracks have not been completely prevented. In addition, it has been found that the desired good creep strength cannot be obtained because the precipitation strengthening effect cannot be fully utilized.

  Therefore, as a result of further investigation by the present inventors, by containing a high concentration of W and Cr, specifically, 7.0 to 13.0% W and 25 to 35% by mass%. It has been found that the inclusion of Cr in this manner makes it possible to achieve both the prevention of stress relaxation cracking and the securing of a desired good creep strength. The reason is considered to be due to the following (i) and (j).

  (I) Increasing the W and Cr contents indirectly reduces the segregation energy of grain boundaries of S and P that have been used at high temperatures for a long time, and reduces the concentration of S and P at the grain boundaries. Suppresses weakening of grain boundaries.

  (J) W contributes to the improvement of creep strength as a solid solution strengthening element, but in this case, the decrease in intra-grain deformability is smaller than when fine intermetallic compounds and carbonitrides precipitate.

  (K) Cr precipitates as an α-Cr phase and contributes to the improvement of creep strength. However, when this α-Cr phase precipitates, the deterioration of intra-grain deformability is small as compared with the case where fine intermetallic compounds and carbonitrides precipitate.

  However, when the above-mentioned high concentrations of W and Cr are contained, it is clear that stress relaxation cracking that occurs in the weld metal during long-time use at high temperatures can be prevented, but the susceptibility to solidification cracking during welding increases conversely. became.

  Therefore, the present inventors have further studied to prevent solidification cracking during welding. As a result, the following knowledge (1) was obtained.

  (L) By controlling the C content within a specific range, specifically, 0.06 to 0.18% by mass, it is possible to prevent solidification cracking during welding. it can.

  The reason is considered to be due to the following (m) from the observation result of the structure of the weld metal.

(M) When Cr is contained in an amount of 25 to 35% by mass, if the C content is controlled within the above range, C is mainly combined with Cr during the solidification process of the weld metal, and (Cr, M) Eutectic solidification of ₂₃ C ₆ and austenite occurs. As a result, the disappearance of the liquid phase during solidification is accelerated, so that solidification cracking during welding can be prevented.

  In addition, it was confirmed that the management of the C and Cr contents within the appropriate range is effective for preventing ductile deterioration cracks during welding.

  The reason is considered to be due to the following (n) from the observation result of the structure of the weld metal.

(N) (Cr, M) ₂₃ C ₆ produced by the combination of C and Cr in the solidification process of the weld metal exists at the columnar crystal boundary in a lamellar shape. As a result, the final solidification interface, which is a segregation site of impurity elements, is increased, and the above carbides (that is, (Cr, M) ₂₃ C ₆ ) suppresses the sliding of grain boundaries and prevents ductile deterioration cracks during welding. can do.

  In addition, the present inventors also examined welding workability during welding. As a result, it came to think as follows (o).

  (O) Deterioration of welding workability occurs because the subsequent pass cannot sufficiently melt the high melting point oxide scale containing a large amount of Al produced on the surface of the weld bead of the previous layer.

  Therefore, the present inventors further studied improvement of welding workability. As a result, the following knowledge (p) was obtained.

  (P) Oxidation scale generated on the surface of the weld bead when the welding material is in mass%, Ti is more than 0.2% and not more than 1.5%, and Al is less than 0.1%. Can be changed from one containing a large amount of Al to one containing mainly Ti, so that the welding workability is improved. In addition, the fine precipitation strengthening action by the intermetallic compound of Ti and Al and Ti carbonitride can be ensured within a range that does not adversely affect the stress relaxation cracking.

  From the above, the welding material for Ni-base heat-resistant alloy is based on an alloy of Cr: 25-35% and Ni: 45-55% in mass%, C: 0.06-0.18%, W : 7.0 to 13.0%, Ti: more than 0.2% and 1.5% or less, and Al: less than 0.1%, excellent welding workability during welding and hot cracking resistance In other words, it has been found that it is possible to secure the desired stress relaxation cracking resistance and desired good creep strength during long-term use at high temperatures.

  And using this welding material for Ni-base heat-resistant alloy, it was excellent in high temperature crack resistance, high temperature crack resistance during welding, stress relaxation crack resistance during long time use at high temperature and good creep strength, and high temperature strength A welded joint made of a Ni-base heat-resistant alloy base material can be obtained.

  When obtaining a welded joint using this welding material, the Ni base excellent in high-temperature strength including Ni: 45-55%, Cr: 25-35% and W: 3.5-8.5% in mass%. It is preferable to use a heat-resistant alloy as a base material because excellent creep strength can be secured even in the base material. The Ni-base heat-resistant alloy having excellent high-temperature strength used as the base material may be a Ni-base heat-resistant alloy having the same chemical composition as the welding material according to the present invention, or may be different.

  In addition, as said base material, it is the mass%, C: 0.04-0.12%, Si: 0.5% or less, Mn: 1.5% or less, P: 0.03% or less, S: 0.01% or less, Ni: 45-55%, Cr: 25-35%, W: 3.5-8.5%, Ti: 0.05-1.0%, Zr: 0.005-0. A Ni-based heat-resistant alloy containing 05%, N: 0.02% or less, B: 0.005% or less, and Al: 0.05-0.3%, with the balance being Fe and impurities and having excellent high-temperature strength It is preferable to use it.

  The “impurities” in the “Fe and impurities” as the balance are various materials in the manufacturing process including raw materials such as ore or scrap when industrially manufacturing welding materials and / or heat-resistant alloys. Refers to something that gets mixed in by factors.

  The present invention has been completed based on the above findings, and the gist of the present invention is a welding material shown in the following (1) and (2), a weld metal shown in (3), and (4) to (6). It is in the welded joint shown in

  (1) By mass%, C: 0.06-0.18%, Si: 0.5% or less, Mn: 1.5% or less, Ni: 45-55%, Cr: 25-35%, W: 7.0 to 13.0%, Ti: more than 0.2% and 1.5% or less, Al: less than 0.1% and N: 0.002 to 0.20%, the balance being Fe and impurities Ni, characterized in that O, P and S in the impurities have chemical compositions of O: 0.02% or less, P: 0.008% or less and S: 0.005% or less, respectively Welding material for heat-resistant alloys.

  (2) The welding material for a Ni-base heat-resistant alloy as described in (1) above, having a chemical composition containing Nb: 1.0% or less in mass% instead of part of Fe.

  (3) A weld metal using the welding material for a Ni-base heat-resistant alloy as described in (1) or (2) above.

  (4) A welded joint comprising the weld metal according to (3) and a base material of a Ni-base heat-resistant alloy excellent in high-temperature strength.

  (5) The base material of the Ni-base heat-resistant alloy having excellent high-temperature strength contains, by mass%, W: 3.5 to 8.5%, Ni: 45 to 55%, and Cr: 25 to 35%. The weld joint according to (4) above, which is characterized.

  (6) The base material of the Ni-based heat-resistant alloy having excellent high-temperature strength 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: 45-55%, Cr: 25-35%, W: 3.5-8.5%, Ti: 0.05-1.0%, Zr: 0.005 to 0.05%, N: 0.02% or less, B: 0.005% or less, and Al: 0.05 to 0.3%, the balance being made of Fe and impurities The weld joint according to (4) above, which is characterized.

  According to the present invention, it is possible to provide a welding material for a Ni-base heat-resistant alloy having excellent welding workability and high-temperature cracking resistance at the time of welding. Thus, it is possible to provide a weld metal having stress relaxation cracking resistance and good creep strength during long-time use. Furthermore, using this welding material, a high temperature cracking resistance during welding, a stress relaxation cracking resistance during long-time use at high temperatures, and a base of a Ni-base heat-resistant alloy excellent in high-temperature strength and a weld metal having good creep strength. A welded joint made of a material can be provided.

  In the present invention, the reason for limiting the chemical composition of the Ni-base heat-resistant alloy welding material is as follows. In the following description, “%” display of the content of each element means “mass%”.

C: 0.06 to 0.18%
C is an austenite-forming element and is an element effective for enhancing the stability of the austenite structure when used at high temperatures. Furthermore, C is an important element for preventing hot cracking during welding in the present invention. That is, C mainly binds to Cr in the solidification process to generate eutectic carbide, thereby facilitating the disappearance of the liquid phase, and the structure of the final solidified part is a lamella of (Cr, M) ₂₃ C ₆ and austenite. A tissue is used. As a result, the remaining form of the liquid phase changes from a planar shape to a point shape, and stress concentration on a specific surface is suppressed, so that solidification cracking can be prevented. Furthermore, C increases the final solidification interface area that becomes a segregation site of impurities, and thus contributes to the prevention of ductile deterioration cracking during welding and the reduction of the sensitivity of stress relaxation cracking during high temperature use. In order to obtain the above effects sufficiently within the range of the Cr content of the present invention described later, it is necessary to contain C by 0.06% or more. However, when C is contained excessively, excess C that does not become carbide during solidification is finely precipitated as carbide during high temperature use, and on the contrary, the stress relaxation cracking sensitivity is increased. Therefore, the C content is 0.06 to 0.18%. A desirable lower limit of the C content is 0.07%, and a desirable upper limit is 0.15%.

Si: 0.5% or less Si is contained as a deoxidizer, but segregates at the columnar grain boundaries during solidification of the weld metal, lowers the melting point of the liquid phase, and increases the susceptibility to solidification cracking. Therefore, the Si content needs to be 0.5% or less. The Si content is preferably 0.3% or less. However, excessive reduction of the Si content does not provide a sufficient deoxidation effect, lowers the cleanliness of the alloy, and increases the manufacturing cost. Therefore, the lower limit of the Si content is not particularly set, but is desirably 0.01%. If at least 0.01% of Si is contained, a deoxidizing effect can be obtained. A more desirable lower limit of the Si content is 0.02%.

Mn: 1.5% or less Mn is contained as a deoxidizer in the same manner as Si. However, when Mn is excessively contained, embrittlement is caused, so the Mn content needs to be 1.5% or less. The Mn content is preferably 1.2% or less. Although there is no particular lower limit for the Mn content, it is preferably 0.01%. If at least 0.01% of Mn is contained, a deoxidizing effect can be obtained. A more desirable lower limit of the Mn content is 0.02%.

Ni: 45-55%
Ni is an effective element for obtaining an austenite structure, and is an essential element for ensuring the structure stability during long-time use and obtaining sufficient creep strength. In order to obtain the effect, a Ni content of 45% or more is necessary. However, Ni is an expensive element, and a large content of Ni exceeding 55% causes an increase in cost. Therefore, the Ni content is 45 to 55%. A desirable lower limit of the Ni content is 45.5%, and a desirable upper limit is 54.5%. The more desirable lower limit of the Ni content is 46%, and the more desirable upper limit is 54%.

Cr: 25 to 35%
Cr is an essential element for securing oxidation resistance and corrosion resistance at high temperatures. Moreover, Cr precipitates as an α-Cr phase during long-time use, and contributes to the creep strength. In addition, Cr is combined with C in an appropriate range to combine with C in the solidification process to generate eutectic carbide, and prevent solidification cracking and ductile deterioration cracking during welding, It reduces the segregation energy of P during high temperature use, and indirectly contributes to the reduction of stress relaxation crack sensitivity. In order to obtain these effects, it is necessary to contain 25% or more of Cr. However, when the Cr content is excessive and exceeds 35%, the stability of the structure at a high temperature deteriorates and the creep strength is reduced. For this reason, the content of Cr is set to 25 to 35%. A desirable lower limit of the Cr content is 25.5%, and a desirable upper limit is 34.5%. A more desirable lower limit of the Cr content is 26%, and a more desirable upper limit is 34%.

W: 7.0 to 13.0%
W is an element that contributes greatly to the improvement of creep strength at a high temperature exceeding 700 ° C. by dissolving in the matrix. In addition, W lowers the grain boundary segregation energy of S and suppresses the weakening of the grain boundary by reducing the concentration of S at the grain boundary during high temperature use, and indirectly prevents stress relaxation cracking. Contribute to. In order to ensure such effects sufficiently and to achieve both stress relaxation crack resistance and creep strength during use at high temperatures, a W content of 7.0% or more in relation to other elements constituting the present invention. is necessary. However, even if W is excessively contained, the effect is saturated, and on the contrary, toughness and creep strength are lowered. Furthermore, W is an expensive element, and the inclusion of a large amount of W exceeding 13.0% causes an increase in cost. Therefore, the W content is 7.0 to 13.0%. A desirable lower limit of the W content is 7.2%, and a desirable upper limit is 11.5%. A more desirable lower limit of the W content is 7.5%, and a more desirable upper limit is 9.5%.

Ti: more than 0.2% and 1.5% or less Ti binds to Ni and precipitates as an intermetallic compound, or carbon and nitrogen, and precipitates as a carbonitride, and creep strength at high temperature It contributes to the improvement. Furthermore, in the Al content range of the present invention, the oxide scale generated on the surface of the weld bead is mainly Ti, thereby improving welding workability and suppressing the occurrence of welding defects. In order to obtain such an effect, a Ti content exceeding 0.2% is necessary in relation to other elements constituting the present invention. However, if the Ti content is excessive and exceeds 1.5%, the intermetallic compound is excessively precipitated and the deformation resistance in the grains is remarkably increased, so that the stress relaxation cracking susceptibility during high temperature use is increased. To do. Therefore, the Ti content exceeds 0.2% and is 1.5%. A desirable lower limit of the Ti content is 0.3%, and a desirable upper limit is 1.4%.

Al: less than 0.1% Al, like Ti, binds to Ni and precipitates finely as an intermetallic compound, contributing to the improvement of creep strength at high temperatures. However, when the Al content becomes excessive and becomes 0.1% or more, an oxide scale mainly composed of Al having a high melting point is generated on the surface of the weld bead, and the welding workability is deteriorated. In addition, the increase in stress relaxation cracking susceptibility during high temperature use due to the precipitation of intermetallic compounds is not a little. Therefore, the Al content is less than 0.1%. A desirable upper limit of the Al content is 0.05%. The lower limit of the Al content is not particularly set, but an extreme reduction leads to an increase in cost, so it is preferably 0.0002%. If at least Al is contained in 0.0002%, an effect of improving the creep strength can be obtained. A more desirable lower limit of the Al content is 0.0005%.

N: 0.002 to 0.20%
N is an austenite generating element and is an element effective for enhancing the stability of the austenite structure at the time of high temperature use. Further, N is also an element that dissolves in the matrix and precipitates as a nitride and contributes to an improvement in tensile strength and creep strength. In order to acquire said effect, N content of 0.002% or more is required. However, if the N content is excessive and exceeds 0.20%, a large amount of nitride precipitates during long-time use, and the deformation resistance in the grains is remarkably increased, and stress relaxation cracking susceptibility during high-temperature use is increased. While increasing, it causes a blowhole generation at the time of welding. Therefore, the N content is 0.002 to 0.20%. The lower limit of the N content is desirably more than 0.03%, and a more desirable lower limit is 0.035%. A desirable upper limit of the N content is 0.18%.

  One of the welding materials for the Ni-base heat-resistant alloy of the present invention contains the elements C to N described above, the balance is made of Fe and impurities, and the contents of O, P and S in the impurities are respectively It has a chemical composition limited to the stated range.

O: 0.02% or less O (oxygen) exists as an impurity, but when it is contained in a large amount, it degrades the workability of the welding material and the ductility of the weld metal. Therefore, the content of O needs to be 0.02% or less. The O content is preferably 0.015% or less.

P: 0.008% or less P is contained as an impurity, lowers the melting point of the final solidified portion during solidification of the weld metal, remarkably increases solidification cracking susceptibility, and causes intergranular embrittlement during high-temperature use, resulting in resistance to resistance. It is an element that causes a decrease in stress relaxation cracking property. Therefore, the P content needs to be 0.008% or less. The P content is preferably 0.006% or less.

S: 0.005% or less S, like P, is an element that is contained as an impurity, lowers the melting point of the final solidified portion during solidification of the weld metal, and increases the susceptibility to solidification cracking. Furthermore, S is an element that segregates and concentrates at the grain boundaries during high temperature use, and significantly increases the stress relaxation cracking susceptibility. Therefore, the S content needs to be 0.005% or less. The S content is preferably 0.003% or less.

  Another one of the welding materials for Ni-base heat-resistant alloys of the present invention has a chemical composition containing 1.0% or less of Nb in place of a part of Fe in the “Fe and impurities” as the balance. is there.

  Hereinafter, the effect of Nb which is an arbitrary element and the reason for limiting the content will be described.

Nb: 1.0% or less Nb is an element that precipitates in the grains as a fine intermetallic compound or / and carbonitride like Ti, and contributes to the improvement of creep strength at high temperatures. For this reason, you may contain Nb as needed. However, if the Nb content is excessive and exceeds 1.0%, a large amount of these precipitates are caused, the deformation resistance in the grains is remarkably increased, and the stress relaxation cracking susceptibility during high temperature use is increased. Therefore, the amount of Nb in the case of inclusion is set to 1.0% or less. When Nb is contained, the Nb content is desirably 0.9% or less.

  On the other hand, in order to stably obtain the effect of Nb described above, the amount of Nb in the case of inclusion is preferably 0.005% or more, and more preferably 0.01% or more.

  As described above, the chemical composition of the Ni-base heat-resistant alloy welding material according to the present invention has been described in detail. This welding material has excellent welding workability and high-temperature cracking resistance during welding. And using this welding material, the weld metal which has the high temperature cracking resistance in welding, the stress relaxation cracking resistance in use for a long time at high temperature, and favorable creep strength can be obtained. Furthermore, using this welding material, a high temperature cracking resistance during welding, a stress relaxation cracking resistance during long-time use at high temperatures, and a base of a Ni-base heat-resistant alloy excellent in high-temperature strength and a weld metal having good creep strength. A welded joint made of a material can be obtained.

  In addition, when obtaining a welded joint using the welding material for Ni-base heat-resistant alloys according to the present invention, W: 3.5 to 8.5%, Ni: 45 to 55%, and Cr: 25 to 30% are contained. It is preferable to use a Ni-base heat-resistant alloy excellent in high-temperature strength as a base material because the base material also has excellent ductility and creep strength in a high-temperature region of 700 ° C. or higher. The Ni-base heat-resistant alloy having excellent high-temperature strength used as the base material may be a Ni-base heat-resistant alloy having the same chemical composition as the Ni-base heat-resistant alloy welding material according to the present invention, or may be different.

  Here, when using a Ni-base heat-resistant alloy excellent in high-temperature strength as a base material, the base material is W: 3.5 to 8.5%, Ni: 45 to 55%, and Cr: 25 to 35%. The reason why it is preferable to contain the material will be described in detail.

W: 3.5-8.5%
W is an element which contributes to the improvement of the creep strength at a high temperature exceeding 700 ° C. by dissolving in the matrix as in the weld metal. Unlike the weld metal that is used as it is in the solid state, the base material is homogenized by heat treatment, and the effect is more easily obtained. For this reason, it is preferable that a base material contains W and the quantity should just be 3.5% or more. However, W is an expensive element and causes an increase in cost. Therefore, when W is contained, the amount is desirably 8.5% or less. A more desirable lower limit of the W content in the base material is 3.8%, and a more desirable upper limit is 8.2%.

Ni: 45-55%
Ni is an element effective for obtaining an austenite structure, as in the case of a weld metal, and is an element effective for ensuring sufficient structure strength during long-time use and obtaining sufficient creep strength. In order to obtain the effect, the base material preferably contains Ni, and the amount thereof is preferably 45% or more as in the case of the weld metal. On the other hand, Ni is an expensive element and causes an increase in cost. Therefore, when Ni is contained, the amount is desirably 55% or less. The more desirable lower limit of the Ni content in the base material is 45.5%, and the more desirable upper limit is 54.5%. The more desirable lower limit of the Ni content in the base material is 46%, and the more desirable upper limit is 54%.

Cr: 25 to 35%
Cr is an effective element for ensuring the oxidation resistance, corrosion resistance, and creep strength of the base metal at a high temperature, as in the case of a weld metal. In order to obtain these effects, the base material preferably contains Cr, and the amount thereof is preferably 25% or more as in the weld metal. However, when the Cr content is excessive, the stability of the structure at high temperatures is deteriorated and the creep strength is lowered. For this reason, when it contains Cr, it is desirable that the quantity shall be 35% or less. A more desirable lower limit of the Cr content in the base material is 25.5%, and a more desirable upper limit is 34.5%. A more desirable lower limit of the Cr content in the base material is 26%, and a more desirable upper limit is 34%.

  It is more preferable that the base material of the Ni-base heat-resistant alloy having excellent high temperature strength contains the elements described below in addition to W, Ni and Cr in the above ranges, with the balance being Fe and impurities.

C: 0.04 to 0.12%
C is an austenite-forming element, as in the weld metal, and is an element effective for enhancing the stability of the austenite structure when used at high temperatures. Unlike a weld metal that is used as it is, the base metal is homogenized by heat treatment, and its effect is more easily obtained, and no measures for preventing weld cracks are required. For this reason, it is preferable that the base material contains C, and the amount may be 0.04% or more. However, if the C content is excessive, coarse carbides are generated during use at high temperatures, which in turn leads to a decrease in creep strength. Therefore, when C is contained, the amount is desirably 0.12% or less. A more desirable lower limit of the C content in the base material is 0.05%, and a more desirable upper limit is 0.10%.

Si: 0.5% or less Si has a deoxidizing action. Although the base material does not require measures for preventing weld cracks as described above, the toughness is lowered when the Si content is excessive and exceeds 0.5%. Therefore, when the base material contains Si, the amount is desirably 0.5% or less. The Si content in the base material is more preferably 0.4% or less. However, excessive reduction of the Si content does not provide a sufficient deoxidation effect, lowers the cleanliness of the alloy, and increases the manufacturing cost. Therefore, the lower limit of the Si content in the base material is not particularly set, but is desirably 0.01%. If at least 0.01% of Si is contained, a deoxidizing effect can be obtained. A more desirable lower limit of the Si content is 0.02%.

Mn: 1.5% or less Mn has a deoxidizing action like Si. However, when the Mn content is excessive, embrittlement is caused. For this reason, when the base material contains Mn, the amount is desirably 1.5% or less, and more preferably 1.2% or less. The lower limit of the Mn content in the base material is not particularly set, but is desirably 0.01%. If at least 0.01% of Mn is contained, a deoxidizing effect can be obtained. A more desirable lower limit of the Mn content is 0.02%.

P: 0.03% or less P is contained as an impurity, and when the content of P is excessive, the creep ductility is reduced. Unlike the case of a weld metal, the base material does not require measures for preventing weld cracking, and the extreme reduction of the P content causes a significant increase in steelmaking costs. For this reason, it is desirable that the P content in the base material be 0.03% or less, and more preferably 0.02% or less.

S: 0.01% or less S, like P, is contained as an impurity, and when the S content is excessive, the creep ductility is reduced. Unlike the case of a weld metal, the base material does not require measures for preventing weld cracking, and the extreme reduction of the S content causes a significant increase in steelmaking costs. For this reason, the S content in the base material is preferably 0.01% or less, and more preferably 0.008% or less.

Ti: 0.05-1.0%
Ti is an element that precipitates in the grains as a fine intermetallic compound and carbonitride, and contributes to the improvement of creep strength at high temperatures. For this reason, the base material preferably contains Ti, and the amount is preferably 0.05% or more. However, when the Ti content is excessive, a large amount of intermetallic compounds and carbonitrides are produced, leading to a decrease in toughness. Therefore, when Ti is contained, the amount is desirably 1.0% or less. A more desirable lower limit of the Ti content in the base material is 0.10%, and a more desirable upper limit is 0.95%.

Zr: 0.005 to 0.05%
Zr dissolves in austenite as a matrix and improves strength at high temperatures. Unlike the weld metal, the base material does not melt. For this reason, in the base material, the above-mentioned effect of active Zr, which is combined with O in the weld metal and becomes slag, can be fully utilized. Therefore, the base material preferably contains Zr, and the amount is preferably 0.005% or more. However, when the Zr content is excessive, creep ductility is reduced. Therefore, when Zr is contained, the amount is desirably 0.05% or less. A more desirable lower limit of the Zr content in the base material is 0.01%, and a more desirable upper limit is 0.04%.

N: 0.02% or less N is an element effective for stabilizing the austenite phase, and is an element effective for increasing the tensile strength by solid solution in the matrix. On the other hand, the hot workability is remarkably increased. It will decrease. For this reason, in the base material, it is preferable to strictly manage the upper limit of the N content as compared with the weld metal, and it is preferable to set the content to 0.02% or less. A more desirable upper limit of the N content in the base material is 0.01%. In addition, although the minimum of N content in a base material is not provided in particular, the minimum from the point of stability of an austenite phase is 0.0005%.

B: 0.005% or less B is an element effective for improving the creep strength by segregating at grain boundaries during use at high temperatures to strengthen the grain boundaries and finely dispersing grain boundary carbides. is there. For this reason, it is preferable that the base material contains B. However, if the B content is excessive, the HAZ liquefaction cracking sensitivity is increased. Therefore, when B is contained, the amount is preferably 0.005% or less. In addition, although the minimum of B content in a base material is not provided especially, it is 0.0002% desirably.

Al: 0.05-0.3%
Al is an element that combines with Ni and precipitates finely as a fine intermetallic compound and contributes to the improvement of creep strength at high temperatures. For base materials that are not directly related to welding workability, You may actively use it. Therefore, the base material preferably contains Al, and the amount is preferably 0.05% or more. However, when the Al content is excessive, intermetallic compounds are excessively precipitated, resulting in a decrease in toughness. Therefore, when Al is contained, the amount is desirably 0.3% or less. A more desirable lower limit of the Al content in the base material is 0.06%, and a more desirable upper limit is 0.25%.

  EXAMPLES Hereinafter, although an Example demonstrates this invention more concretely, this invention is not limited to these Examples.

  A plate material having a thickness of 12 mm, a width of 50 mm, and a length of 100 mm is welded from an ingot in which a material having the chemical composition shown in Table 1 is melted and cast in a laboratory by hot forging, hot rolling, heat treatment and machining. It was produced as a material.

  Furthermore, from an ingot in which the materials A to L having chemical compositions shown in Table 2 were melted and cast in the laboratory, an outer diameter of 1.2 mm and a length of 1000 mm were obtained by hot forging, hot rolling and machining. A welding material (welding wire) was produced.

  After processing a V groove with an angle of 30 ° and a root thickness of 1 mm in the longitudinal direction of the above-mentioned plate material for welded base material, it is specified in SM400B JIS G 3106 (2008) having a thickness of 25 mm, a width of 200 mm and a length of 200 mm. On the commercially available steel plate, four rounds were restrained and welded using “E Ni 6625” defined in JIS Z 3224 (2010) as a coated arc welding rod.

  Thereafter, multilayer welding was performed in the groove by TIG welding with a heat input of 9 to 15 kJ / cm using the above-described welding materials of A to L, and two welded joints were produced for each symbol of the welding material. .

  The welded joints were subjected to the next test after being subjected to an aging heat treatment of 700 ° C. × 500 hours, with one welded as-welded for each symbol.

  That is, for each symbol, the cross-section of the sample taken from each of the five welded joints as welded and the welded joint subjected to aging heat treatment is mirror-polished and corroded, then examined by an optical microscope, and fused in the weld metal. The presence or absence of defects and the presence or absence of cracks were investigated. In addition, the welded joint which does not have a crack in all the five samples examined with the optical microscope was set as "pass". In addition, the welding workability was evaluated as “good” when there was no poor fusion.

  Further, as a result of the microscopic examination, a round bar creep rupture test piece was collected from the welded joint as-welded in which no fusion failure or cracking was found in the weld metal so that the weld metal was at the center of the parallel part. The creep rupture test was conducted under the conditions of 700 ° C. and 167 MPa, in which the target rupture time was 1000 hours or more. A creep rupture time of 1000 hours or more, which is the target rupture time of the base plate, was regarded as “pass”.

  Table 3 shows the results of the above tests.

  “◯” in the “crack observation result” column of Table 3 indicates that the welded joint is “accepted” in which all five samples are not cracked by an optical microscope. On the other hand, “x” indicates that cracking was observed in at least one of the five samples by inspection with an optical microscope.

  In addition, “◯” in the “Welding workability result” column of Table 3 indicates that the welded joint has good fusion workability and no fusion failure in all five samples by optical microscope inspection. Show. On the other hand, “x” indicates that fusion failure was observed in at least one of the five samples by optical microscopy.

  Furthermore, “◯” in the “Creep rupture test result” column indicates that the creep rupture time is a “pass” welded joint that has cleared 1000 hours or more, which is the target rupture time of the base plate. On the other hand, “x” indicates that the creep rupture time did not reach 1000 hours. “-” Of the welding material code J indicates that the creep rupture test was not performed because a fusion failure was observed in the weld metal of the sample taken from the welded joint as welded. Similarly, “−” of the welding material code L indicates that the crack rupture test was not performed because cracks were observed in the weld metal of the sample taken from the welded joint as welded.

  From Table 3, the welding materials of the symbols A to G whose chemical compositions are within the range defined by the present invention are excellent in welding workability, and the weld metal of the welded joint welded using these has no fusion failure and is subjected to aging heat treatment. It is clear that neither stress relaxation cracks in the inside nor high temperature cracks in welding occur, and that the creep strength is high.

  On the other hand, in the welded joint welded using the welding material with the symbol H exceeding the upper limit specified in the present invention, the fine intermetallic compound is generated excessively in the grains, and the deformation in the grains Due to the high resistance, stress relaxation cracking occurred during aging heat treatment.

  Since the weld joint welded using the welding material of the symbol I whose Ti content is lower than the lower limit prescribed in the present invention did not generate cracks, an intermetallic compound necessary for securing the strength was not generated. The rupture time did not reach 1000 hours, and the creep strength was not satisfied.

  Welded joints welded using a welding material with a symbol J whose Al content is outside the range defined in the present invention have poor fusion workability and poor welding workability, and fine intermetallic compounds are included in the grains. The stress relaxation cracks occurred during the aging heat treatment because of excessive deformation in the grains and high deformation resistance in the grains.

  A welded joint welded with a welding material with a sign K outside the range specified in the present invention for the W content did not generate cracks, but did not reach 1000 hours and did not satisfy the creep strength. .

A welded joint welded with a welding material with a symbol L, which has a low C content of 0.02% and is outside the range specified in the present invention, can produce (Cr, M) ₂₃ C ₆ sufficient for the final solidified part. As a result, solidification cracking occurred.

  As described above, when using a welding material having a chemical composition within the range specified in the present invention, resistance to hot cracking during welding, resistance to stress relaxation cracking during long-term use at high temperatures, and good creep strength. It turns out that it becomes a weld metal which has.

  According to the present invention, it is possible to provide a welding material for a Ni-base heat-resistant alloy having excellent welding workability and high-temperature cracking resistance at the time of welding. Thus, it is possible to provide a weld metal having stress relaxation cracking resistance and good creep strength during long-time use. Furthermore, using this welding material, a high temperature cracking resistance during welding, a stress relaxation cracking resistance during long-time use at high temperatures, and a base of a Ni-base heat-resistant alloy excellent in high-temperature strength and a weld metal having good creep strength. A welded joint made of a material can be provided.

Claims (6)

  In mass%, C: 0.06-0.18%, Si: 0.5% or less, Mn: 1.5% or less, Ni: 45-55%, Cr: 25-35%, W: 7.0 -13.0%, Ti: more than 0.2% and 1.5% or less, Al: less than 0.1% and N: 0.002-0.20%, the balance consisting of Fe and impurities, O, P, and S in impurities have chemical compositions of O: 0.02% or less, P: 0.008% or less, and S: 0.005% or less, respectively, for a Ni-based heat-resistant alloy Welding material.   The welding material for a Ni-base heat-resistant alloy according to claim 1, having a chemical composition containing Nb: 1.0% or less in mass% instead of a part of Fe.   A weld metal using the welding material for a Ni-base heat-resistant alloy according to claim 1 or 2.   A welded joint comprising the weld metal according to claim 3 and a base material of a Ni-base heat-resistant alloy excellent in high-temperature strength.   The base material of the Ni-base heat-resistant alloy having excellent high-temperature strength is characterized by containing W: 3.5 to 8.5%, Ni: 45 to 55%, and Cr: 25 to 35% in mass%. The welded joint according to claim 4.   The base material of the Ni-base heat-resistant alloy having excellent high-temperature strength is mass%, C: 0.04 to 0.12%, Si: 0.5% or less, Mn: 1.5% or less, P: 0.03 %: S: 0.01% or less, Ni: 45-55%, Cr: 25-35%, W: 3.5-8.5%, Ti: 0.05-1.0%, Zr: 0 0.005 to 0.05%, N: 0.02% or less, B: 0.005% or less, and Al: 0.05 to 0.3%, the balance being Fe and impurities The welded joint according to claim 4.