JP2009132964A - Ni-based alloy - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a γ' precipitation-strengthening type Ni-based alloy which has improved corrosion resistance, heat treatment properties and weldability, while maintaining high strength. <P>SOLUTION: The Ni-based alloy includes, by mass, 5 to 15% Co, 13 to 15.5% Cr, 4.0 to 5.5% Al, 0.1 to 2.0% Ti, 0.1 to 1.0% Nb, 0.1 to 3.0% Ta, 0.1 to 2.0% Mo, 4.5 to 10% W, 0.1 to 2.0% Hf, 0.05 to 0.20% C, 0.001 to 0.03% B, 0.01 to 0.1% Zr and the balance Ni except unavoidable impurities. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a Ni-based alloy for a gas turbine stationary blade having excellent high-temperature corrosion resistance.

In order to increase the strength of Ni-based alloys used in industrial gas turbines and aircraft jet engines, a large amount of solid solution strengthening elements such as W, Mo, Ta and Co are added, and Al and Ti are added. It is important to add a large amount of γ′Ni ₃ (Al, Ti) phase, which is a strengthening phase.

  On the other hand, it is also important to have corrosion resistance at high temperatures, and it is desirable to add a large amount of Cr that forms a protective film.

  However, the greater the content of these alloy elements, the lower the stability of the material structure, and the problem is that a hard and brittle harmful phase such as the σ phase precipitates during long-term use. In recent years, heat turbine alloys for gas turbines have been focused on increasing the strength and added a lot of strengthening elements, but there is a strong tendency to reduce the Cr content even at the expense of corrosion resistance so that no harmful phase precipitates ( (See Patent Document 1 and Patent Document 2).

  When an alloy having a low Cr composition is used for a gas turbine moving blade and the like, it is common to improve the corrosion resistance by applying a corrosion resistant coating to the surface.

  However, the service temperature of the surface coating is about 950 ° C., and a heat-resistant material with a service temperature of 950 ° C. or higher is thinned by high-temperature corrosion even if the strength is sufficient, resulting in a decrease in material strength and damage. Is a problem.

  By adding a large amount of noble metal element such as Re, it is possible to increase the amount of Cr while suppressing the appearance of a harmful phase, but the material becomes very expensive. For this reason, development of a high-strength Ni-based alloy in which these expensive elements are reduced has been carried out (see Patent Document 3).

  Another problem with the high-strength Ni-base alloy of the γ ′ phase strengthening type is that the manufacturing process such as heat treatment and welding becomes more difficult as the strength increases. This is because the γ 'phase is stably present up to a high temperature, so that the heat treatment temperature range for dissolving the γ' phase is narrowed, and defects such as weld cracks are generated.

Japanese Patent Publication No. 1-59344 JP 2004-307999 A JP 2004-332061 A

  As described above, high-strength Ni-base alloys (hereinafter sometimes referred to as Ni-base superalloys and Ni-base heat-resistant alloys) are subject to corrosion resistance, heat resistance, weldability, etc. as the strength further increases. At present, the process characteristics are sacrificed.

  If the corrosion resistance is improved by increasing the Cr content while allowing a slight decrease in the amount of γ 'and the accompanying strength reduction, the material can be expected to have a longer life and improved reliability. This eliminates the need for coating the parts that needed to be reduced, leading to a reduction in manufacturing costs and maintenance costs.

  Moreover, it can be expected that heat treatment properties and weldability are also improved.

  An object of the present invention is to provide a Ni-based alloy having improved process characteristics such as corrosion resistance, heat treatment properties and weldability while maintaining high-temperature strength necessary for gas turbine stationary blades, particularly first-stage stationary blades.

  The inventors have conducted research on Ni-base heat-resistant alloys such as strength evaluation and thermodynamic calculation, and have led to the invention of an alloy having sufficient high-temperature strength as a gas turbine stationary blade and improved corrosion resistance, heat treatment properties and weldability. It was.

  That is, according to the present invention, Co is 5 to 15%, Cr is 13 to 15.5%, Al is 4.0 to 5.5%, Ti is 0.1 to 2.0%, and Nb is 0.00. 1 to 1.0%, Ta: 0.1 to 3.0%, Mo: 0.1 to 2.0%, W: 4.5 to 10%, Hf: 0.1 to 1.5%, C : 0.05 to 0.20%, B: 0.001 to 0.03%, Zr: 0.01 to 0.1%, the balance being made of Ni except for inevitable impurities It is a base alloy.

  The effects of these alloy elements and the reasons for limiting the alloy composition will be described below.

  Co has been found to replace Ni and dissolve in the matrix phase to improve the high-temperature strength and increase the amount of γ ′ phase precipitation at low temperatures, which also contributes to high-temperature corrosion resistance. These effects are remarkably observed in 5% or more. However, if added excessively, the γ 'phase decreases at a high temperature and precipitation strengthening weakens, and harmful phases such as σ phase and μ phase appear. The upper limit was 15%. A more preferable range is 7 to 10%.

  As described above, Cr is an element that improves the oxidation resistance and high-temperature corrosion resistance by forming a dense oxide film on the surface. In order to use for the high temperature member for gas turbines, such as a stationary blade made into object by this invention, it is necessary to contain at least 13%. However, if added in an amount of 15.5% or more, the σ phase is precipitated and the ductility and fracture toughness of the material are deteriorated. A particularly preferred range is 13.5 to 15.0%.

Al is an element that forms a γ′Ni ₃ (Al, Ti) phase, and is an indispensable element for strengthening a γ ′ phase strengthened heat-resistant alloy. If less than 4.0% is added, the amount of γ ′ phase precipitated is small and strength cannot be obtained. On the other hand, as the amount added increases, the amount of precipitation of the γ 'phase increases and the high temperature strength increases, but the weldability and high temperature ductility decrease, so the upper limit was made 5.5%.

  Ti, like Al, constitutes a γ 'phase and is an element that contributes to the improvement of high-temperature strength. The effect is exhibited by adding 0.1% or more, but in the composition range of the present invention, when it exceeds 2.0%, the tendency to form η phase and the like becomes strong and the contribution to high temperature strength becomes weak.

  Nb has a large amount of solid solution in the γ ′ phase and has an effect of stabilizing the γ ′ phase. It also has the effect of strengthening the γ 'phase itself. The effect is exhibited by addition of 0.1% or more, but in order to promote the formation of a harmful phase such as a hard and brittle Laves phase, the range is not more than 1.0%. A more preferable composition range is 0.2 to 0.8%.

  Ta, like Nb, has a great effect of stabilizing and strengthening the γ 'phase. Although the effect is exhibited by addition of 0.1% or more, the γ 'phase solid solution temperature is significantly increased. Therefore, from the viewpoint of heat treatment and weldability, the range is not more than 3.0%. A more preferable composition range is 1.0 to 2.5%.

  Mo has an effect of strengthening the base material by solid solution strengthening. The effect is seen when 0.1% or more is added, but the upper limit is set to 2.0% because there is a strong tendency to form a σ phase like Cr. A more preferable composition range is 0.2 to 1.5%.

  W also contributes to improving the strength of the parent phase by solid solution strengthening, like Mo. In order to obtain a remarkable effect, addition of 4.5% or more is necessary. However, although the tendency is smaller than that of Mo, it is also an element that forms a σ phase, so the upper limit is made 10%. A more preferable range is 5.0 to 8.5%.

  Hf stabilizes the γ ′ phase to increase the high-temperature strength and improve castability. Although these effects are observed with addition of about 0.1%, the tendency to form coarse eutectic carbides becomes stronger as the addition amount increases, so the upper limit is made 1.5%. A particularly preferable addition amount is 0.8% or less.

C dissolves in the matrix and improves the tensile strength at high temperatures, and improves the grain boundary strength by forming carbides such as MC and M ₂₃ C ₆ . These effects become remarkable from about 0.05%, but excessive addition of C causes coarse eutectic carbides and causes toughness reduction, so the upper limit is made 0.2%. Therefore, an addition amount of 0.08 to 0.16% is preferable.

  The two elements B and Zr both have the effect of strengthening the grain boundaries and improving the creep strength by adding a small amount. However, excessive addition causes precipitation of harmful phases and partial melting due to lowering of the melting point. Therefore, the appropriate ranges are B: 0.001 to 0.03, Zr: 0.01 to 0.1. .

  In the present invention, P and Q are defined as follows as parameters for evaluating the stability of the γ ′ phase.

      P = Al amount + 0.61 × Ti amount + 0.18 × Ta amount + 0.29 × Nb amount (1) Q = Al amount + 0.38 × Ti amount + 0.35 × Ta amount + 0.54 × Nb amount ((1)) 2) The amount of each element is mass%.

  P is a parameter relating to the precipitation amount of the γ ′ phase at 900 ° C. Coefficients are determined from the results of various investigations on the influence of each element per 1% by mass on the precipitation amount of the γ 'phase. By using this parameter, it is possible to estimate the amount of precipitation of the γ ′ phase at high temperatures.

  As already mentioned, the γ 'phase stabilizing elements Al, Ti, Ta, Nb increase, and the larger the value of P, the more the γ' phase increases and the strength of the alloy increases. As a material, in order to achieve a durable temperature of 950 ° C., it is desirable to select a composition in which P is 5.2 or more. As a more preferable range, a composition satisfying P ≧ 5.4 is desirable.

  On the other hand, Q is a parameter relating to the solid solution temperature of the γ ′ phase, that is, the upper limit temperature at which the strengthening phase can exist, and is similarly expressed by a function of Al, Ti, Ta, and Nb. As the value of Q increases, the solid solution temperature of the γ ′ phase increases, and heat treatment and welding become difficult.

  Since the γ 'phase solution temperature of the rotor blade alloy that can be welded and repaired in the current gas turbine is 1170 ° C, the alloy solution of the present invention should also have a temperature not exceeding 1170 ° C. For this purpose, the value of Q needs to be 6.5 or less. As a more preferable range, it is desirable that Q ≦ 6.4.

  Since P and Q are all functions of Al, Ti, Ta, and Nb, they cannot be controlled independently. By selecting a composition that satisfies the desirable ranges of P and Q at the same time, an alloy having both high temperature strength and manufacturing process characteristics such as heat treatment and welding can be obtained.

  In the Ni-based alloy of the present invention, the volume fraction of γ ′ phase precipitates at 900 ° C. is preferably 44% or more, and the solid solution temperature of the γ ′ phase is preferably 1170 ° C. or less.

  Furthermore, the composition parameter P represented by the formula (1) is preferably 5.2 ≦ P, and the composition parameter P represented by the formula (2) is preferably 6.5 ≧ Q.

  Such a Ni-based alloy is suitable for a gas turbine stationary blade, particularly, a first stage stationary blade of a gas turbine stationary blade.

  According to the present invention, it is possible to provide a Ni-based alloy having excellent oxidation resistance and having both high temperature strength, heat treatment property and weldability.

  Examples of the present invention will be described below.

  Table 1 shows the chemical composition of the alloy of the present invention and the comparative alloy subjected to the experiment in the process leading to the present invention.

  Nos. 1 to 10 are the present invention, and Nos. 11 to 20 are comparative alloys.

  10 kg of alloys having these compositions were melted by high frequency induction heating and precision cast into a cylindrical ingot having a diameter of 15 mm by the lost wax method. The ingot was subjected to solution heat treatment at 1232 ° C. for 2 hours, followed by aging heat treatment at 982 ° C. for 5 hours and 871 ° C. for 20 hours.

  All the heat treatments were performed in the atmosphere, and after the heat treatment, they were cooled to room temperature.

  Various test pieces were produced from the ingot after heat treatment by machining.

  Table 2 shows the results of a creep test performed at 982 ° C. to 137 MPa using the prepared creep test pieces (parallel portion length: 30 mm, diameter: 6 mm).

  From Table 1 and Table 2, it can be seen that the alloy of the present invention is comprehensively superior to the comparative alloy.

  1 and 2 show the creep rupture time and elongation at break of each alloy.

  In FIG. 1, the service temperature corresponding to the creep rupture time (temperature at which the stator blade material can withstand 100 MPa hours at 59 MPa without breaking) is also shown.

  It can be seen that all the alloys of the present invention having Nos. 1 to 10 have a service temperature exceeding 950 ° C.

  The No. 11 alloy of the comparative example is an alloy having a composition corresponding to that of a general polycrystalline Ni-base superalloy, and shows a very high service temperature of about 980 ° C., which is in good agreement with the previous reports. . However, since the Cr content is small, the oxidation is remarkable, and when the appearance of the test piece after the creep test is observed, a part of the oxide film is peeled off.

  Similarly, Nos. 12 and 13 were inferior in oxidation resistance characteristics to the present invention due to the small amount of Cr.

  Nos. 14 and 15 have the same amount of γ 'phase precipitation as that of the conventional material, and since the amount of Cr is the same as that of the present invention, the strength and oxidation resistance are good. Due to the rise, improvement from the conventional material cannot be expected in terms of heat treatment and weldability.

  Further, in comparison with the results of the creep rupture elongation in FIG. 2, the creep rupture elongation tends to be smaller as the alloy has a longer creep rupture time. It is also clear that the high strength alloys No. 11 to 15 have a lower elongation than the alloys of the present invention, and the elongation of 10% desired as a stator blade material is not obtained.

  No. 16-18 alloys have a low γ ′ solid solution temperature, but have a short creep rupture time and a service temperature of 950 ° C. or less, so they do not achieve the strength target of the present invention.

  Nos. 19 and 20 are examples of alloys with a large amount of Cr, but both the creep rupture time and elongation are low. As a result of investigating the sample after the test, it was confirmed that the σ phase was precipitated, and it was found that fracture occurred from this point.

  As the Cr content increases, the oxidation resistance and corrosion resistance improve, but it is necessary to adjust the Cr content within a range in which the σ phase does not precipitate from the viewpoint of strength and reliability.

  1 and 2 also show that the alloy of the present invention has a well-balanced creep property that satisfies a service temperature of 950 ° C. and a creep rupture elongation of 10% or more, and is generally superior to the comparative alloy. You can see that it is.

  In this experiment, in order to evaluate the precipitation amount of the γ ′ phase, the precipitation amount at 900 ° C. of each alloy was considered as a reference.

  FIG. 3 is a graph showing the relationship between the amount of γ ′ phase precipitation and the service temperature.

  From this result, it can be seen that the precipitation amount of the γ 'phase and the service temperature have a substantially linear relationship. In order to have a service temperature of 950 ° C. or higher as a stationary blade material of a gas turbine, it is necessary that 44% or more of the γ ′ phase is precipitated.

  FIG. 4 shows the relationship between the amount of precipitation of γ ′ phase at 900 ° C. and the parameter P.

  It can be seen that the amount of precipitation increases as the γ ′ phase stabilizing element such as Al, Ti, Ta, Nb increases and P increases. Since the comparative alloys No. 16 to 19 having P <5.2 have a γ ′ phase precipitation amount of less than 44%, the target creep resistance temperature of 950 ° C. cannot be obtained as shown in FIG. The alloys of the invention all satisfy P ≧ 5.2 and satisfy the γ ′ phase precipitation amount of 44%. The comparative alloy in the region of P ≧ 5.2 in FIG. 4 has a different Cr content range (No. 11, 12, 13, 20) and another parameter Q value.

Considering the results of FIGS. 3 and 4, in order to obtain a γ ′ phase of 44% or more in order to satisfy the service temperature of 950 ° C., an alloy composition having a P value of 5.2 or more is selected. There is a need.
More preferably, P is in the range of 5.4 or more.

  FIG. 5 is a diagram showing a correlation between the parameter Q and the γ ′ phase solid solution temperature of each alloy.

  Since the γ ′ phase is stabilized as the value of Q increases, the solid solution temperature tends to increase. In order to reduce the solid solution temperature to 1170 ° C. or lower from the viewpoint of heat treatment and weldability, the Q value must be 6.5 or lower. No. 11, 13, 14, and 15 alloys having a Q of over 6.5 have a too high solid solution temperature and are difficult to construct with the current welding technology, and the time and cost required for heat treatment such as solution heat treatment. Is not desirable. A more preferable range is a range where Q is 6.4 or less.

  The upper limit value of P is when Al, Ti, Ta, and Nb have the maximum values in the respective composition ranges.

  On the other hand, the lower limit value of Q is when these elements take the minimum value.

  However, since both P and Q are functions of the composition of Al, Ti, Ta, and Nb, the two parameters cannot be moved independently.

  FIG. 6 is a diagram in which the values of P and Q of each alloy are plotted, and there is a correlation that Q increases as P increases.

  A suitable range for both P and Q is the area shown by hatching in the figure. As shown in FIG. 6, since the alloy of the present invention focuses on increasing strength, the Ti and Ta contents are large, and many of P and Q are high, but all are included in the hatched area. Yes. This figure focuses only on the relationship between parameters P and Q, and does not consider alloy elements other than Al, Ti, Ta, and Nb. Therefore, some of the comparative alloys are in the hatched region (No. 12, 20), but these are different from the claims of the present invention in the composition of Cr.

  7 and 8 are diagrams showing the relationship between the Cr amount and P and Q, respectively.

  The amount of Cr is specified in a range where oxidation resistance and corrosion resistance can be obtained and no harmful phase is produced. By satisfying the conditions of P and Q in this range, a Ni-based heat-resistant alloy with good high-temperature strength and process characteristics can be obtained. It is done. Among the alloys shown in the comparative examples, those in the range of Cr amount are Nos. 14 to 18 alloys. 7, the alloys No. 14 and 15 satisfy both the Cr content and the P range, but it is clear that the Q range is out of FIG. 8. On the other hand, Nos. 16 to 18 satisfy the condition of Q, but do not satisfy the condition of P. The alloy of the present invention has a Cr content in this range and satisfies the conditions of P ≧ 5.2 and Q ≦ 6.5, and has an excellent balance of creep characteristics, heat treatment / weldability, and high temperature corrosion resistance, and a gas turbine stationary blade It has very suitable characteristics as a material.

  A gas turbine stationary blade having the shape shown in FIG. 9 is manufactured by precision casting using the alloy of the present invention.

  This stationary blade is a casting in which a blade portion is formed between sidewalls on the outer peripheral side, and a slit of an air passage is provided at the tip of the blade portion.

  FIG. 10 is a partially cut perspective view of the wing portion, and is provided with holes for pin fin cooling, impingement cooling, and film cooling. The obtained nozzle is subjected to solution treatment and aging treatment in a non-oxidizing atmosphere.

  The nozzle of this embodiment is most suitable for the first stage (first stage), but can be provided in the second and third stages, but the second and third stages are made of a Co-based alloy blade. A nozzle is provided.

  Both ends of the first stage nozzle are constrained, but the second and third stages are one-side restraints that are constrained on one side of the sidewall outer peripheral side. The wing width is larger in the second and third stages than in the first stage.

  In the nozzle made of the Ni-based alloy in this embodiment, the γ ′ phase is precipitated in the γ phase matrix.

  FIG. 11 is a partial cross-sectional view of a rotating portion of a gas turbine having a gas turbine nozzle.

  10 is a turbine stub shaft, 3 is a turbine blade, 13 is a turbine stacking bolt, 18 is a turbine spacer, 19 is a distance piece, 20 is a first stage nozzle, 6 is a compressor disk, 7 is a compressor blade, 16 is a compressor nozzle, 8 is Compressor stacking bolts, 9 is a compressor stub shaft, 4 is a turbine disk, 11 is a hole, and 15 is a combustor.

  The gas turbine of this embodiment has 17 stages of compressor disks 6 and two stages of turbine blades 3. The turbine blade 3 may have three stages, and the alloy of this embodiment can be applied to any of them.

  In other words, the inventors conducted detailed studies on the precipitation amount and solid solution temperature of the γ 'phase, which is the strengthening phase of the Ni-base alloy, and found that it has good oxidation resistance and corrosion resistance, and has strength characteristics and heat treatment properties. And the alloy composition range which is excellent also in weldability was clarified.

  The present embodiment provides a Ni-based alloy having improved corrosion resistance, heat treatment property and weldability while maintaining excellent high temperature strength by controlling the alloy composition within a range defined by parameters P and Q. .

  The Ni-base alloy in the present invention relates to a Ni-base heat-resistant alloy suitable as a material for high-temperature members for gas turbines, particularly a stationary blade. In particular, it can be used for a first stage stationary blade of a gas turbine.

The graph which shows the creep rupture time of each alloy. The graph which shows the creep rupture elongation of each alloy. The figure which shows the relationship between (gamma ') phase precipitation amount (900 degreeC), and durable temperature. The figure which shows the relationship between the parameter P and the amount of γ 'phase precipitation. The figure which shows the relationship between the parameter Q and (gamma) 'phase solution temperature. The figure which shows the correlation of parameter P and Q. The figure which shows the relationship between Cr amount and P of this invention alloy. The figure which shows the relationship between Cr amount and Q of this invention alloy. The figure which shows the turbine stationary blade using the Ni base alloy of this form. The figure which shows a wing | blade part. The figure which shows a gas turbine.

Explanation of symbols

3 Turbine blade 4 Turbine disk 6 Compressor disk 7 Compressor blade 8 Compressor stacking bolt 9 Compressor stub shaft 10 Turbine stub shaft 11 Hole 13 Turbine stacking bolt 15 Combustor 16 Compressor nozzle 18 Turbine spacer 19 Distant piece 20 First stage nozzle

Claims (9)

  By mass, Co: 5 to 15%, Cr: 13 to 15.5%, Al: 4.0 to 5.5%, Ti: 0.1 to 2.0%, Nb: 0.1 to 1.0 %, Ta: 0.1-3.0%, Mo: 0.1-2.0%, W: 4.5-10%, Hf: 0.1-1.5%, C: 0.05- Ni-based alloy of 0.20%, B: 0.001 to 0.03%, Zr: 0.01 to 0.1%, the balance being made of Ni except for inevitable impurities.   The Ni-based alloy according to claim 1, wherein the volume fraction of γ 'phase precipitates at 900 ° C is 44% or more.   The Ni-based alloy according to claim 1, wherein the solid solution temperature of the γ 'phase is 1170 ° C or lower.   The Ni-based alloy according to claim 1, wherein the volume fraction of γ 'phase precipitates at 900 ° C is 44% or more and the solid solution temperature of the γ' phase is 1170 ° C or less. The Ni-based alloy according to claim 1, wherein the composition parameter P expressed by the formula (1) satisfies P ≧ 5.2.
P = Al amount + 0.61 × Ti amount + 0.18 × Ta amount + 0.29 × Nb amount (1) Here, the unit of the element amount is mass%. 2. The Ni-based alloy according to claim 1, wherein the composition parameter Q represented by the formula (2) is Q ≦ 6.5. 3.
Q = Al amount + 0.38 × Ti amount + 0.35 × Ta amount + 0.54 × Nb amount (2) Here, the unit of the element amount is mass%. 2. The Ni-based alloy according to claim 1, wherein composition parameters P and Q represented by the formulas (1) and (2) are P ≧ 5.2 and Q ≦ 6.5. Base alloy.
P = Al amount + 0.61 × Ti amount + 0.18 × Ta amount + 0.29 × Nb amount (1) Q = Al amount + 0.38 × Ti amount + 0.35 × Ta amount + 0.54 × Nb amount ((1)) 2) Here, the unit of the element amount is mass%.   A gas turbine stationary blade using the Ni-based alloy according to claim 1.   A gas turbine using the gas turbine stationary blade according to claim 8.

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