JP4835771B1 - 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 alloy 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.
SOLUTION: (1) C: 0.06-0.18%, Si ≦ 0.5%, Mn ≦ 1.5%, Ni: 46-56%, Co: 10-15%, Cr: 20-25%, Mo: more than 10.0% ~ 14.0%, Ti: 0.01 ~ 0.5%, Al: 0.1 ~ 1.0% and N ≦ 0.006%, the balance is Fe and impurities, O ≦ 0.02%, P ≦ 0.008% and S ≦ 0.005% as impurities A welding material for Ni-base heat-resistant alloys having a chemical composition of The welding material may include Nd ≦ 0.1%. (2) A weld metal using the above-mentioned welding material for Ni-base heat-resistant alloys. (3) A welded joint comprising the above 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 a requirement, for example, there is a Ni-base heat-resistant alloy specified in UNS06617. 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. The “hot cracking at the time of 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 high-strength oxide dispersion strengthened alloys and heat-resistant alloys. By actively containing solid solution strengthening elements such as Mo and Nb, strength is increased. An improved oxide dispersion strengthened alloy welding material has been proposed. Patent Document 7 and Patent Document 8 propose a welding material for Ni-based alloys, which has been strengthened by utilizing the solid solution strengthening effect by Mo and W and the precipitation strengthening effect by Al and Ti.

  By the way, although the 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, there is a problem that cracks occur at the welded portion when used at a high temperature for a long time.

  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, a weld metal obtained using the above-mentioned welding material for Ni-base heat-resistant alloys (AWS A5.14-2005 ER NiCrCoMo-1) is a crack generated during long-term use (hereinafter referred to as “stress relaxation crack”). Is still a challenge. In the above-mentioned Patent Documents 6 to 8, stress relaxation cracking is not considered at all. For this reason, the weld metal obtained using the welding material proposed by patent documents 6-8 also has a subject with respect to a stress relaxation crack.

Japanese Patent Application Laid-Open No. 2-1077736 Japanese Unexamined Patent Publication No. 63-050440 Japanese Unexamined Patent Publication No. 7-150277 JP-A-9-157779 JP 2001-073053 A Japanese Patent Laid-Open No. 10-193174 WO2010-013565 WO2007-119847

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 compound is finely precipitated in the grains, the deformability in the grains is lowered, and stress concentration occurs at the grain interface, resulting in a superimposing action with the weakening of the grain boundaries. , Cracking is likely to occur.

  (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) The element that precipitates as an intermetallic compound and causes an increase in intragranular deformation resistance, specifically, the content of Al is regulated 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 studies by the present inventors, it has been found that the inclusion of a high concentration of Mo 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) Mo combines with P segregated at grain boundaries at a high temperature to reduce grain boundary embrittlement due to P.

  (J) Mo contributes to the improvement of creep strength as a solid solution strengthening element. In this case, the decrease in intra-grain deformability is small compared to the case where a fine intermetallic compound precipitates.

  However, it has been clarified that, when a high concentration of Mo is contained, the susceptibility to solidification cracking during welding increases conversely, although stress relaxation cracking generated in the weld metal during long-time use at high temperatures can be prevented.

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

  (K) By controlling the content of Cr and C within a specific range, specifically, when the content of Cr is 20 to 25% and the content of C is 0.06 to 0.18. By setting it as%, solidification cracking during welding can be prevented.

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

(L) When the contents of C and Cr are controlled within a specific range, C is mainly combined with Cr in the solidification process of the weld metal, and eutectic solidification of (Cr, M) ₂₃ C ₆ and austenite is caused. Arise. 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.

  From the above, the welding material for the Ni-base heat-resistant alloy is based on an alloy of Cr: 20-25% and Ni: 46-56% in mass%, C: 0.06-0.18%, Mo : By containing more than 10.0% and not more than 14% and Al: 0.1 to 1.0%, resistance to hot cracking during welding, resistance to stress relaxation cracking during long-term use at high temperature, and desired It was found that good creep strength can be secured.

  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: 46 to 56%, Cr: 20 to 25% and Mo: 7.0 to 10.0% 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: 1.0% or less, Mn: 1.5% or less, P: 0.03% or less, S: 0.01% or less, Ni: 46 to 56%, Co: 10 to 15%, Cr: 20 to 25%, Mo: 7.0 to 10.0%, W: 0.5% or less, Ti: 0.00. 1 to 0.5%, N: 0.01% or less, B: 0.005% or less, Al: 0.8 to 1.8% and Nd: 0.005 to 0.1%, the balance being It is preferable to use a Ni-base heat-resistant alloy composed of Fe and impurities and excellent in high temperature strength.

  In addition, “impurities” in the “Fe and impurities” as the balance are due to various factors in the manufacturing process including raw materials such as ore or scrap when industrially manufacturing welding materials and heat-resistant alloys. It refers to what gets mixed.

  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: 46-56%, Co: 10-15%, Cr: 20 to 25%, Mo: more than 10.0% to 14.0% or less, Ti: 0.01 to 0.5%, Al: 0.1 to 1.0%, and N: 0.006% or less And the balance consists of Fe and impurities, and O, P and S as impurities have chemical compositions of O: 0.02% or less, P: 0.008% or less and S: 0.005 or less, respectively. A welding material for Ni-base heat-resistant alloys, which is characterized.

  (2) The welding material for a Ni-base heat-resistant alloy according to (1) above, which has a chemical composition containing Nd: 0.1% 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, in mass%, Mo: 7.0 to 10.0%, Ni: 46 to 56%, and Cr: 20 to 25%. 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: 1.0% or less, Mn: 1.5% or less, P: 0.03% or less, S: 0.01% or less, Ni: 46-56%, Co: 10-15%, Cr: 20-25%, Mo: 7.0-10.0%, Ti: 0.0. 1 to 0.5%, N: 0.01% or less, B: 0.005% or less, Al: 0.8 to 1.8% and Nd: 0.005 to 0.1%, the balance being It consists of Fe and an impurity, The weld joint as described in said (4) characterized by the above-mentioned.

  According to the present invention, it is possible to provide a welding material for a Ni-base heat resistant alloy having excellent hot cracking resistance during welding, and using it, hot cracking resistance during welding and use at high temperatures for a long time. It is possible to provide a weld metal having moderate stress relaxation cracking resistance and good creep strength. 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 steel, 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%. The above effect can be obtained if at least 0.01% of Mn is contained. A more desirable lower limit of the Mn content is 0.02%.

Ni: 46-56%
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 46% or more is necessary. However, Ni is an expensive element, and a large amount of Ni exceeding 56% causes an increase in cost. Therefore, the Ni content is set to 46 to 56%. A desirable lower limit of the Ni content is 46.5%, and a desirable upper limit is 55.5%. A more desirable lower limit of the Ni content is 47%, and a more desirable upper limit is 55%.

Co: 10-15%
Co, like Ni, is an element effective for obtaining an austenite structure, and contributes to creep strength by increasing phase stability. In order to sufficiently obtain the effect, a Co content of 10% or more is necessary. However, Co is an extremely expensive element, and a large content of Co exceeding 15% causes an increase in cost. Therefore, the Co content is 10 to 15%. A desirable lower limit of the Co content is 10.5%, and a desirable upper limit is 14.5%.

Cr: 20-25%
Cr is an essential element for securing oxidation resistance and corrosion resistance at high temperatures. Cr combines with C in the solidification process to produce eutectic carbide, prevents solidification cracking and ductile degradation cracking during welding, and also has the effect of reducing stress relaxation cracking susceptibility during high temperature use. In order to obtain these effects, it is necessary to contain 20% or more of Cr. However, if the Cr content is excessive and exceeds 25%, the stability of the structure at high temperatures deteriorates, leading to a decrease in creep strength. For this reason, content of Cr shall be 20-25%. A desirable lower limit of the Cr content is 20.5%, and a desirable upper limit is 24.5%. The more desirable lower limit of the Cr content is 21%, and the more desirable upper limit is 24%.

Mo: more than 10.0% and not more than 14.0% Mo is an element that contributes greatly to the improvement of creep strength at a high temperature exceeding 700 ° C. by dissolving in the matrix. Further, Mo has a strong affinity with P, and by bonding, it reduces grain boundary embrittlement due to heat treatment after welding and P during high temperature use, and contributes to prevention of stress relaxation cracking. In order to ensure such effects sufficiently to achieve both stress relaxation crack resistance and creep strength during high temperature use, the Mo content exceeds 10.0% in relation to other elements constituting the present invention. is required. However, even if Mo is excessively contained, the effect is saturated, and on the contrary, toughness and creep strength are lowered. Furthermore, Mo is an expensive element, and a large amount of Mo exceeding 14.0% causes an increase in cost. Furthermore, the inclusion of a large amount of Mo exceeding 14.0% also increases the susceptibility to solidification cracking. Therefore, the Mo content is more than 10.0% and not more than 14.0%. A desirable lower limit of the Mo content is 10.5%, and a desirable upper limit is 13.8%. A more desirable lower limit of the Mo content is 11.0%, and a more desirable upper limit is 13.5%.

Ti: 0.01 to 0.5%
Ti combines with Ni and precipitates finely as an intermetallic compound, thereby contributing to the improvement of creep strength at high temperatures. In order to obtain the effect, a Ti content of 0.01% or more is necessary in relation to other elements constituting the present invention. However, if the Ti content is excessive and exceeds 0.5%, excessive precipitation of intermetallic compounds is caused, 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 is set to 0.01 to 0.5%. A desirable lower limit of the Ti content is 0.1%, and a desirable upper limit is 0.4%.

Al: 0.1 to 1.0%
Al, like Ti, binds to Ni, precipitates finely as an intermetallic compound, and contributes to the improvement of creep strength at high temperatures. In order to obtain the effect, an Al content of 0.1% or more is necessary in relation to other elements constituting the present invention. However, if the Al content is excessive and exceeds 1.0%, 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 content of Al is set to 0.1 to 1.0%. A desirable lower limit of the Al content is 0.2%, and a desirable upper limit is 0.9%. A more desirable lower limit of the Al content is 0.3%, and a more desirable upper limit is 0.8%.

N: 0.006% or less N is an element effective for stabilizing the austenite phase, but in the Cr content range of the present invention, if the N content becomes excessive and exceeds 0.006%, During use at a high temperature, a large amount of fine nitride precipitates in the grains, resulting in a decrease in creep ductility and toughness. Therefore, the N content is 0.006% or less. A desirable upper limit of the N content is 0.005%. Although the lower limit of the N content is not particularly set, an extreme decrease leads to an increase in manufacturing cost. For this reason, the desirable lower limit of the N content is 0.0005%.

  One of the welding materials for a 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 as impurities are respectively It has a chemical composition limited to the stated range.

O: 0.02% or less O 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, it 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 0.1% or less of Nd in place of a part of Fe in the remaining “Fe and impurities”. is there.

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

Nd: 0.1% or less Nd has a strong affinity with P and forms a compound, and also combines with S and O to form a compound, suppresses weakening of grain boundaries by P and S, and stress relaxation cracking resistance It is an element that contributes to improving the properties. For this reason, you may contain Nd as needed. However, if the content of Nd becomes excessive and exceeds 0.1%, the above effect is saturated, and a large amount of carbide precipitates in the grains, which increases the stress relaxation cracking sensitivity. Therefore, the amount of Nd in the case of inclusion is set to 0.1% or less. In the case of inclusion, the amount of Nd is preferably 0.08% or less.

  On the other hand, in order to stably obtain the above-described effect of Nd, the amount of Nd when contained 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, but this welding material has excellent hot 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, Mo: 7.0 to 10.0%, Ni: 46 to 56%, and Cr: 20 to 25% 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 Mo: 7.0 to 10.0%, Ni: 40 to 50%, and Cr: 20 to 25%. The reason why it is preferable to contain the material will be described in detail.

Mo: 7.0 to 10.0%
As in the weld metal, Mo is an element that contributes greatly to the improvement of creep strength at a high temperature exceeding 700 ° C. by dissolving in the matrix. 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 Mo, and the amount should just be 7.0% or more. However, Mo is an expensive element and causes an increase in cost. Therefore, when Mo is contained, the amount is desirably 10.0% or less. The more desirable lower limit of the Mo content in the base material is 7.5%, and the more desirable upper limit is 9.8%. A more desirable lower limit of the Mo content in the base material is 8.0%, and a more desirable upper limit is 9.5%.

Ni: 46-56%
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 46% or more as in 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 56% or less. The more desirable lower limit of the Ni content in the base material is 46.5%, and the more desirable upper limit is 55.5%. The more desirable lower limit of the Ni content in the base material is 47%, and the more desirable upper limit is 55%.

Cr: 20-25%
Cr is an effective element for ensuring the oxidation resistance and corrosion resistance of the base metal at high temperatures, as in the case of weld metal. In order to obtain the same effect as the weld metal, the base material preferably contains Cr, and the amount thereof is preferably 20% or more. 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 amount be 25% or less. A more desirable lower limit of the Cr content in the base material is 20.5%, and a more desirable upper limit is 24.5%. A more desirable lower limit of the Cr content in the base material is 21%, and a more desirable upper limit is 24%.

  It is more preferable that the base material of the Ni-base heat-resistant alloy having excellent high-temperature strength contains the following amounts of elements in addition to the above ranges of Mo, Ni and Cr, 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: 1.0% or less Si has a deoxidizing action. Although the base material does not require measures for preventing weld cracking as described above, the toughness is lowered when the Si content is excessive and exceeds 1.0%. Therefore, when the base material contains Si, the amount is desirably 1.0% or less. The Si content in the base material is more preferably 0.8% or less. However, excessive reduction of the Si content does not provide a sufficient deoxidation effect, lowers the cleanliness of the steel, 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.

Co: 10-15%
Co is an element that is effective for obtaining an austenite structure as in the case of a weld metal, and is an element that ensures the structure stability during long-time use and contributes to the improvement of creep strength. For this reason, it is preferable that the base material contains Co, and the amount may be 10% or more. However, Co is an extremely expensive element, and a large content of Co exceeding 15% causes an increase in cost. Therefore, when it contains Co, it is desirable that the amount be 0.15% or less. A more desirable lower limit of the Co content in the base material is 10.5%, and a more desirable upper limit is 14.5%.

Ti: 0.1 to 0.5%
Ti is an element that precipitates in the grains as fine intermetallic compounds and carbonitrides and contributes to the improvement of creep strength at high temperatures, and has a lower stress relaxation cracking susceptibility than weld metal during high temperature use Then, it may be actively used to increase the strength. For this reason, the base material preferably contains Ti, and the amount thereof is preferably 0.1% or more. However, when the Ti content is excessive, a large amount of carbonitride is generated, resulting in a decrease in toughness. Therefore, when Ti is contained, the amount is desirably 0.5% or less. A more desirable lower limit of the Ti content in the base material is 0.15%, and a more desirable upper limit is 0.45%.

N: 0.01% or less N is an element effective for stabilizing the austenite phase, but when the content is large, a large amount of carbonitride precipitates during use, and ductility and toughness Incurs a decline. However, since the base material is finer than the weld metal used as welded, and the degree of influence is small, the content of N may be 0.01% or less in the base material. A more desirable upper limit of the N content in the base material is 0.008%.

B: 0.005% or less B is an element effective for improving the creep strength by segregating at the grain boundary during use at a high temperature to strengthen the grain boundary and finely dispersing the grain boundary carbide. 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. A desirable lower limit of the B content in the base material is 0.0002%.

Al: 0.8 to 1.8%
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. The material may be actively used to increase the strength. For this reason, the base material preferably contains Al, and the amount is preferably 0.8% 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 1.8% or less. A more desirable lower limit of the Al content in the base material is 0.9%, and a more desirable upper limit is 1.6%.

Nd: 0.005 to 0.1%
Nd has a strong affinity for P, S, and O, and is effective in improving the manufacturability of the base material. In addition, Nd is an element effective in reducing the susceptibility to liquefaction cracking of HAZ. For this reason, the base material preferably contains Nd, and the amount is preferably 0.005% or more. However, when the content of Nd becomes excessive, in addition to saturation of the above effect, a large amount of carbide precipitates in the grains and lowers toughness. Therefore, when Nd is contained, the amount is desirably 0.1% or less. A more desirable lower limit of the Nd content in the base material is 0.01%, and a more desirable upper limit is 0.08%.

  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 the ingot in which the materials of reference numerals 1 to 6 having the chemical composition shown in Table 2 were melted and cast in the laboratory, the outer diameter was 1.2 mm and the length was 1000 mm 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 a commercially available steel plate, four rounds were restrained and welded using “DNiCrFe-3” defined in JIS Z3224 (1999) as a coated arc welding rod.

  Thereafter, multilayer welding was performed in the groove by TIG welding at a heat input of 9 to 15 kJ / cm using the welding materials of the above-described symbols 1 to 6, 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 code, the cross section of the sample taken from each of the five welded joints and welded joints subjected to aging heat treatment was mirror-polished and corroded, then examined with an optical microscope, and cracked in the weld metal. The presence or absence of was 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".

  Furthermore, as a result of microscopic examination, a round bar creep rupture test specimen was collected from the welded joint with no weld metal cracked so that the weld metal was at the center of the parallel part, and the target fracture of the base metal plate was taken. The creep rupture test was conducted under the conditions of 700 ° C. and 196 MPa for which the time was 1000 hours or more. In addition, the thing whose creep rupture time exceeded 1000 hours which is the target rupture time of a base material board material was set as the 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.

  Further, “◯” in the “Creep rupture test result” column indicates that the welded joint has a “pass” in which the creep rupture time exceeds 1000 hours, which is the target rupture time of the base metal plate. On the other hand, “x” indicates that the creep rupture time did not reach 1000 hours. “−” Of welding material code 6 indicates that the creep 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 weld metal of welded joints welded with the welding materials of reference numerals 1 to 3 whose chemical composition is in the range specified in the present invention, both stress relaxation cracks during aging heat treatment and hot cracks during welding occur. It is clear that it has a high creep strength.

  On the other hand, welded joints welded using the welding materials of reference numerals 4 and 6 whose chemical composition deviates from the range specified in the present invention are stress relaxation cracks during aging heat treatment and hot cracks during welding. Either occurrence was observed. Moreover, the weld joint welded with the welding material of the code | symbol 5 from which the chemical composition remove | deviated from the range prescribed | regulated by this invention had low creep strength.

  That is, in the welded joint welded using the welding material of reference numeral 4 whose Al content is outside the range specified in the present invention, fine intermetallic compounds are excessively generated in the grains, and the deformation resistance in the grains is high. Therefore, stress relaxation cracks occurred during the aging heat treatment.

A welded joint welded with a welding material having a low C content of 0.03% and 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.

  The welded joint welded with the welding material of reference numeral 5 whose Mo content is outside the range defined in the present invention did not generate cracks but did not reach 1000 hours and did not satisfy the creep strength. .

  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 hot cracking resistance during welding, and using it, hot cracking resistance during welding and use at high temperatures for a long time. It is possible to provide a weld metal having moderate stress relaxation cracking resistance and good creep strength. 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: 46-56%, Co: 10-15%, Cr: 20-25 %, Mo: more than 10.0% and not more than 14.0%, Ti: 0.01 to 0.5%, Al: 0.1 to 1.0% and N: 0.006% or less, the balance Is composed of Fe and impurities, and O, P, and S as impurities have chemical compositions of O: 0.02% or less, P: 0.008% or less, and S: 0.005 or less, respectively. , Welding materials for Ni-base heat-resistant alloys.   The welding material for a Ni-base heat-resistant alloy according to claim 1, wherein the welding material has a chemical composition containing Nd: 0.1% 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 excellent in high temperature strength is characterized by containing Mo: 7.0 to 10.0%, Ni: 46 to 56%, and Cr: 20 to 25% by 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: 1.0% or less, Mn: 1.5% or less, P: 0.03 %: S: 0.01% or less, Ni: 46-56%, Co: 10-15%, Cr: 20-25%, Mo: 7.0-10.0%, Ti: 0.1-0 0.5%, N: 0.01% or less, B: 0.005% or less, Al: 0.8 to 1.8% and Nd: 0.005 to 0.1%, the balance being Fe and impurities The weld joint according to claim 4, comprising: