JP5703177B2 - Ni-base alloy for welding and filler metal - Google Patents

Description

  Embodiments of the present invention relate to a Ni-based alloy for welding and a filler material produced using the same.

  In recent years, in steam turbines, the temperature of steam has been increased, and accordingly, improvement in heat resistance strength has been demanded for materials constituting the steam turbine. In particular, in an A-USC (advanced ultra super critical pressure) steam turbine that is currently under development, a steam temperature exceeding 700 ° C. or close to that is assumed. For this reason, application of a Ni-based alloy is being studied because it exceeds the usable temperature of heat-resistant low alloy steel such as conventional CrMoV steel.

  As this Ni-based alloy, for example, application of a 600 series alloy or the like is being studied. Examples of the turbine rotor material of the steam turbine include 617 alloy and TOS1X (manufactured by Toshiba). Further, as a representative filler material used when welding the components constituting the turbine rotor, for example, a filler material made of a 617 alloy is used.

Proceedings of the 2008 Thermal Power and Nuclear Power Generation Conference p98-104 JP 2009-22899 A

  However, in contrast to Ni-based alloys such as TOS1X with improved strength characteristics at high temperatures, conventional 617 alloy filler materials have problems such as insufficient maintenance of high temperature strength. Therefore, there is a demand for a Ni-base alloy filler material with improved strength characteristics at high temperatures, which has excellent high-temperature strength without increasing crack sensitivity.

  The problem to be solved by the present invention is to provide a Ni-base alloy for welding and a filler metal having excellent high-temperature strength characteristics, weldability and manufacturability.

  The Ni-based alloy for welding of the embodiment is in mass%, C: 0.01 to 0.15, Cr: 15 to 25, Co: 9 to 15, Mo: 8 to 12, Al: 0.3 to 1. 8, Ti: 0.5-3, Ta: 0.05-1.5, Nb: 0.4 or less, Si: 0.01-0.5, Mn: 0.5 or less, the balance is Ni And inevitable impurities.

  In the present invention, it is possible to provide a welding Ni-base alloy and a filler material that are excellent in high-temperature strength characteristics, weldability and manufacturability.

  Embodiments of the present invention will be described below.

  The Ni-base alloy for welding in the embodiment is composed of the following composition component ranges. In the following description, “%” representing a composition component is “% by mass” unless otherwise specified.

  (M1) C: 0.01 to 0.15%, Cr: 15 to 25%, Co: 9 to 15%, Mo: 8 to 12%, Al: 0.3 to 1.8%, Ti: 0.00. 5 to 3%, Ta: 0.05 to 1.5%, Nb: 0.4% or less, Si: 0.01 to 0.5%, Mn: 0.5% or less, with the balance being Ni and Ni-based alloy consisting of inevitable impurities.

  (M2) C: 0.01 to 0.15%, Cr: 15 to 25%, Co: 9 to 15%, Mo: 8 to 12%, Al: 0.3 to 1.8%, Ti: 0.00. 5 to 3%, Ta: 0.05 to 1.5%, Nb: 0.4% or less, Si: 0.01 to 0.5%, B: 0.001 to 0.006%, the balance Ni-based alloy consisting of Ni and inevitable impurities.

  (M3) C: 0.01 to 0.15%, Cr: 15 to 25%, Co: 9 to 15%, Mo: 8 to 12%, Al: 0.3 to 1.8%, Ti: 0.00. A Ni-based alloy containing 5 to 3%, Ta: 0.05 to 1.5%, Si: 0.01 to 0.5%, W: 5% or less, with the balance being Ni and inevitable impurities.

  Moreover, P, S, Cu, Fe etc. are mentioned as an unavoidable impurity in Ni base alloy of said (M1)-(M3) mentioned above, for example.

  The Ni-based alloy having the composition range described above can be used, for example, as a filler material for welding. For example, it can be used as a filler material when welding turbine rotor constituent members made of a Ni-based alloy. Moreover, it can use as a filler material at the time of welding the turbine rotor structural member which consists of Ni-base alloys, and the turbine rotor structural member which consists of low alloy steel (for example, CrMoV steel and 12Cr steel). This filler material is used for TIG welding and the like.

  Examples of the turbine rotor that is welded using the above-described filler material include a turbine rotor that can be used in a high-temperature steam environment that exceeds or is close to 700 ° C. In addition, the component parts welded using this filler material are not restricted to the component parts of a turbine rotor, For example, the other component parts used in the high temperature steam environment over 700 degreeC or near it It may be.

  Moreover, the Ni-based alloy having the above compositional component range is excellent in high-temperature strength characteristics, weldability and manufacturability. The filler metal produced using this Ni-based alloy is also excellent in high temperature strength characteristics, weldability and manufacturability.

  Next, the reason for limiting each composition component range in the welding Ni-based alloy in the above-described embodiment will be described.

(1) C (carbon)
C is useful as a constituent element of the M ₂₃ C ₆ type carbide that is the strengthening phase, and has an effect of suppressing grain coarsening due to the peening effect. If the C content is less than 0.01%, a sufficient amount of precipitation of carbide cannot be secured, and thus the above-described effects cannot be exhibited. On the other hand, if the C content exceeds 0.15%, the productivity decreases. Therefore, the C content is determined to be 0.01 to 0.15%. Further, the C content is more preferably 0.01 to 0.06%.

(2) Cr (chromium)
Cr is an essential element for increasing the oxidation resistance, corrosion resistance and mechanical strength of the Ni-based alloy. When the Cr content is less than 15%, the oxidation resistance decreases. On the other hand, if the Cr content exceeds 25%, the mechanical strength decreases due to the precipitation of the σ phase, which is a harmful phase. Therefore, the Cr content is determined to be 15 to 25%. The Cr content is more preferably 15 to 21%.

(3) Co (cobalt)
Co is a solid solution strengthening element that improves the mechanical strength of the parent phase by forming a solid solution in the Ni parent phase. When the Co content is less than 9%, the mechanical strength decreases. On the other hand, when the Co content exceeds 15%, the hot workability decreases. Therefore, the Co content is determined to be 9 to 15%. The Co content is more preferably 9 to 13%.

(4) Mo (molybdenum)
Mo is a solid solution strengthening element that improves the mechanical strength of the parent phase by dissolving in the Ni parent phase. When the Mo content is less than 8%, the above effects are not exhibited. On the other hand, if the Mo content exceeds 12%, the mechanical strength is reduced by σ phase precipitation. Therefore, the Mo content is determined to be 8 to 12%. The Mo content is more preferably 8 to 10%.

(5) Al (aluminum)
Al forms a γ ′ (Ni ₃ Al) phase together with Ni, and improves the mechanical strength of the Ni-based alloy by precipitation. When the Al content is less than 0.3%, the solid matrix is completely dissolved in the Ni matrix, so that the effect of the γ ′ (Ni ₃ Al) phase cannot be obtained. On the other hand, if the Al content exceeds 1.8%, σ phase precipitation is promoted and the mechanical strength is lowered. Furthermore, the solid solution temperature increases due to the formation of the γ ′ (Ni ₃ Al) phase, and the hot workability decreases. Therefore, the Al content is determined to be 0.3 to 1.8%. The Al content is more preferably 0.9 to 1.7%.

(6) Ti (titanium)
Ti forms a γ ′ (Ni ₃ Ti) phase together with Ni, and improves the mechanical strength of the Ni-based alloy by precipitation. When the Ti content is less than 0.5%, the above-described effects are not exhibited. On the other hand, if the Ti content exceeds 3%, σ phase precipitation is caused and hot workability is lowered. Therefore, the Ti content is determined to be 0.5 to 3%. The Ti content is more preferably 0.5 to 2%.

(7) Ta (tantalum)
Ta can be dissolved in the γ ′ (Ni ₃ (Al, Ti)) phase to strengthen the γ ′ phase and stabilize the γ ′ phase. When the Ta content is less than 0.05%, the above-described effects are not exhibited. On the other hand, when the content of Ta exceeds 1.5%, weldability and hot workability are deteriorated. Therefore, the Ta content is determined to be 0.05 to 1.5%. Further, the Ta content is more preferably 0.05 to 0.1%.

(8) Nb (Niobium)
Nb, like Ta, solidifies into the γ ′ (Ni ₃ (Al, Ti)) phase to strengthen and stabilize the γ ′ phase. If the Nb content exceeds 0.4%, the liquefaction cracking sensitivity increases. Therefore, the Nb content is set to 0.4% or less. The Nb content is more preferably 0.2 to 0.3%. Here, in order to acquire the said effect of Nb, Nb is contained at least 0.2% or more.

(9) Si (silicon)
Si has the effect of improving the hot water flow. When the Si content is less than 0.01%, this effect cannot be obtained. On the other hand, when the Si content exceeds 0.5%, the weldability is lowered. Therefore, the Si content is determined to be 0.01 to 0.5%. Further, it is more preferable that the Si content is 0.01 to 0.25%.

(10) Mn (manganese)
Mn becomes S (sulfur) and MnS resulting from brittleness, and has the effect of preventing brittleness and improving the flow of hot water. On the other hand, if the Mn content exceeds 0.5%, the weldability is lowered. Therefore, the Mn content is set to 0.5% or less. Further, the Mn content is more preferably 0.15 to 0.4%. Here, in order to acquire the said effect of Mn, Mn is contained at least 0.1% or more.

(11) B (Boron)
B has the effect of segregating at grain boundaries and improving the high-temperature strength. When the B content is less than 0.001%, the above-described effects are not exhibited. On the other hand, if the B content exceeds 0.006%, grain boundary embrittlement is caused and weldability is lowered. Therefore, the B content is determined to be 0.001 to 0.006%. The B content is more preferably 0.002 to 0.005%.

(12) W (tungsten)
W, like Mo, is a solid solution strengthening element that dissolves in the Ni matrix and improves the mechanical strength of the matrix. When the W content exceeds 5%, the σ phase precipitation becomes significant and the productivity decreases. Therefore, the W content is set to 5% or less. Moreover, it is more preferable that the W content is 4 to 4.8%. Here, in order to acquire the said effect of W, W contains at least 4% or more.

(13) P (phosphorus), S (sulfur), Cu (copper) and Fe (iron)
P, S, Cu and Fe are classified as inevitable impurities in the welding Ni-based alloy in the embodiment. It is desirable that the residual content of these inevitable impurities is as close to 0% as possible. Of these inevitable impurities, at least P is preferably suppressed to 0.03% or less, and S is suppressed to 0.015% or less.

  P and S lower the melting point and form a low-melting eutectic with Ni, so that the cracking sensitivity is increased. Therefore, it is desirable that the P content is 0.03% or less and the S content is 0.015% or less, and the respective residual contents are as close to 0% as possible.

  In addition, when the content rate of P or S exceeds the said range, a dephosphorization process or a desulfurization process is performed and it is set as the content rate in the said range.

  Here, the Ni-based alloy for welding in the embodiment and the method for producing the filler material produced using the Ni-based alloy for welding will be described.

  The welding Ni-based alloy in the embodiment is produced by vacuum induction melting (VIM) of the constituent components constituting the welding Ni-based alloy and injecting the molten metal into a predetermined mold to form an ingot. Is done.

  Further, the filler material of the embodiment forms the ingot by vacuum induction melting (VIM) the composition components constituting the Ni-based alloy for welding in the embodiment and injecting the molten metal into a predetermined mold. A member obtained by machining the ingot is drawn to produce a wire shape.

(Evaluation of high temperature strength characteristics, weldability and manufacturability)
Here, it will be described that the Ni-based alloy in the chemical composition range of the embodiment has excellent high-temperature strength characteristics, weldability and manufacturability. Table 1 shows the chemical compositions of Sample 1 to Sample 10 used for evaluation of high temperature strength characteristics, weldability and manufacturability.

  Samples 1 to 3 are Ni-based alloys in the chemical composition range of the embodiment, and Samples 4 to 10 are Ni-based alloys whose compositions are not in the chemical composition range of the embodiment. It is. Further, the Ni-based alloy in the chemical composition range of the embodiment used here contains P, S, and Fe as unavoidable impurities.

  In samples 1 to 10, the high-temperature strength characteristics were evaluated by a tensile strength test and a creep rupture test.

  The test pieces used for the tensile strength test were prepared by melting the Ni-based alloys of Sample 1 to Sample 10 having the chemical composition shown in Table 1 in a vacuum induction melting furnace to produce an ingot. A size test piece was prepared.

  In the tensile strength test, a test piece of each sample is subjected to a tensile strength test according to JIS Z 2241 (metal material tensile test method) at a temperature of room temperature (23 ° C.), and 0.2% proof stress is obtained. It was measured.

  The test piece used for the creep rupture test is prepared by preparing two flat plates made of TOS1X having a thickness of 15 mm, a width of 60 mm, and a length of 200 mm. A butt joint was produced by TIG welding.

  Here, as the filler material, the Ni-based alloys of Sample 1 to Sample 10 having the chemical compositions shown in Table 1 were respectively melted in a vacuum induction melting furnace to produce a steel ingot, and this steel ingot was hot forged. Then, a member having a predetermined size was formed, and this was rolled into a wire shape having a diameter of 1 mm.

  In the creep rupture test, the creep rupture strength at a temperature of 800 ° C. and a stress of 140 MPa was measured according to JIS Z 2271 with respect to a test piece of each sample.

  In addition, the weldability of each sample was evaluated. Two flat plates having a thickness of 15 mm, a width of 60 mm, and a length of 200 mm were prepared as a base material, a groove was formed at each joint, and TIG welding was performed using a filler material.

  Weldability was evaluated for cracks in the welded portion by appearance observation after welding, dye penetration test, X-ray transmission test, cross-sectional micro observation and macro observation, and side bending test.

  In addition, manufacturability was evaluated for each sample. This manufacturability refers to manufacturability at the time of producing a wire as a filler material. The evaluation of manufacturability was performed by observing the surface and cross section of the filler material completed by rolling the wire rod with an optical microscope and confirming the presence or absence of cracks.

  The test results described above are shown in Table 2. In the results of the weldability evaluation shown in Table 2, when the welded part is not cracked and is sound, it is indicated by “◯”, and when a crack is confirmed, it is indicated by “x”. Moreover, in the result of the evaluation of manufacturability, when the crack is not confirmed and is sound, it is indicated by “◯”, and when the crack is confirmed, it is indicated by “x”.

  Samples 1 to 3 were found to have a creep rupture strength (rupture time) of about 1.5 to 2.5 times that of Sample 4 which is a material corresponding to the 617 alloy. This creep rupture strength is equivalent to the creep rupture strength in TOS1X reinforced with 617 alloy as a base. Samples 1 to 3 were also found to be superior in high temperature strength characteristics (tensile strength and creep rupture strength), weldability and manufacturability.

  On the other hand, Samples 4 to 10 according to the comparative example did not give excellent results in all of the high-temperature strength characteristics, weldability, and manufacturability.

  Although several embodiments of the present invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

Claims (5)

  In mass%, C: 0.01 to 0.15, Cr: 15 to 25, Co: 9 to 15, Mo: 8 to 12, Al: 0.3 to 1.8, Ti: 0.5 to 3, Ta: 0.05 to 1.5, Nb: 0.4 or less, Si: 0.01 to 0.5, Mn: 0.5 or less, and the balance is made of Ni and inevitable impurities Ni-base alloy for welding.   In mass%, C: 0.01 to 0.15, Cr: 15 to 25, Co: 9 to 15, Mo: 8 to 12, Al: 0.3 to 1.8, Ti: 0.5 to 3, Ta: 0.05 to 1.5, Nb: 0.4 or less, Si: 0.01 to 0.5, B: 0.001 to 0.006, with the balance being Ni and inevitable impurities A Ni-based alloy for welding characterized by   In mass%, C: 0.01 to 0.15, Cr: 15 to 25, Co: 9 to 15, Mo: 8 to 12, Al: 0.3 to 1.8, Ti: 0.5 to 3, A Ni-based alloy for welding which contains Ta: 0.05 to 1.5, Si: 0.01 to 0.5, W: 5 or less, and the balance is made of Ni and inevitable impurities.   4. The Ni base for welding according to claim 1, wherein, among the inevitable impurities, at least P is suppressed to 0.03% by mass or less and S is controlled to 0.015% by mass or less. alloy.   A filler metal produced by using the welding Ni-based alloy according to any one of claims 1 to 4.