JPH028016B2 - - Google Patents

Abstract

Nickel-chromium-cobalt base casting alloys having compositions within the range (in percent by weight) Cr 20-23%, Co 17-23%, W 1-2.5%, Mo 0-0.5%, Nb 0.4-1.2%, Ta 0.6-1.4%, Ti 2,95-3.85%, Al 1.6-2.8%, Hf 0.3-1.3%, Zr 0.005-1%, B 0.001-1%, C 0.01-0.25%, balance Ni and impurities, wherein the contents of Nb, Hf, Ti and Al are further specifically correlated, exhibit at high temperatures a combination of good resistance to corrosion and very high creep-rupture lives, particularly when directionally solidified. The alloys are useful as materials for cast blades and vanes for gas turbines for marine and land-based service.

Description

[Detailed description of the invention]

This invention relates to an improved castable nickel-chromium-cobalt based alloy. Nickel-chromium-based alloys and nickel-chromium-cobalt-based alloys containing titanium and aluminum exhibit high creep rupture strength at elevated temperatures and, with appropriate heat treatment, can be used to induce high stresses at elevated temperatures. Widely applied. Examples of this include, for example, rotor blades and vanes of gas turbine engines. However, the use of impure fuels such as diesel oil in land-based or offshore thrust turbines poses the problem of adverse sulfur effects. Serious corrosion problems also occur at sea and in other chloride-containing atmospheres. Many gas turbine and other components, especially those with complex designs, are best made by investment casting. Therefore, the alloy is cast to form and, in the cast state, has (1) great strength at elevated temperatures, (2) corrosion resistance in sulfur-containing and chloride-containing atmospheres, and (3) Structural stability, ie, no sigma phase is required after being stretched and used at elevated temperatures. GB 1367661 has already disclosed and claimed an alloy exhibiting all of the above properties. This alloy contains 0.02-0.25% carbon; 20
~25% chromium; 5-25% cobalt; %W+
Molybdenum (up to 3.5%) or tungsten (up to 5%) or both in an amount such that 0.5 (%Mo) satisfies 0.5-5%; the sum of aluminum content and titanium content is 4-7%, and titanium relative to aluminum under the condition that the ratio of is 0.75:1 to 4:1.
1.7-5% titanium and 1-4% aluminum; 0.5-3% tantalum; 0-3% niobium;
Under the condition that %Zr+0.5 (%Hf) is 0.01~1%
0.005-1.0% zirconium and 0-1.99% hafnium; 0.001-0.05% boron; and 0
Contains ~0.2% yttrium or lanthanum or lanthanum or both (0 to 0.2% in total if both are included), with the balance being at least 30% nickel excluding impurities. All percentages and comparisons in this composition range and elsewhere in this specification and claims are by weight. One alloy according to this specification is commercially available under the designation 1N-939 and has the following nominal composition: C: 0.15%, Cr: 22.5%, Co: 19%, W: 2
%, Ti: 3.7%, Al: 1.9%, Ta: 1.4%, Nb:
1.0%, Zr: 0.1%, B: 0.01%, Ni: remainder Solution treatment at 1150°C for 4 hours, air cooling and 850°C
After a heat treatment consisting of aging for 16 hours at
−939 equiaxed castings (made by vacuum melting followed by remelting and casting under vacuum) typically
It has a creep rupture period of approximately 1250 hours at a temperature of 870°C under a stress of 185N/mm ² (19Kgf/mm ² ), which is approximately 850 hours at the same temperature and under a higher stress of 200N/mm ² . corresponds to Directional solidification of the alloy to produce a columnar crystal structure increases the creep rupture period to approximately 1170 at 200 N/mm ² and 870° C. when stressed along the main crystal axis. GB 1367661 gives creep rupture test results for two alloy compositions, with and without hafnium addition. Comparison of results with and without hafnium shows that the presence of 0.75% hafnium produces some increase in elongation at break, but has no or little effect on creep rupture time. Nickel, chromium, cobalt, tungsten,
Titanium, aluminum, in a range of alloy compositions including tantalum, carbon, boron and zirconium.
The present invention is based on the discovery that a specific correlation of the niobium and hafnium contents substantially lengthens the creep rupture period of castings of the alloy, especially in the directionally solidified state. According to the invention, the nickel-chromium-cobalt alloy comprises 20-23% chromium, 17-23% cobalt, 1-2.5% tungsten, 0.4-1.2% niobium, 0.6-1.4% tantalum, 2.95% ~3.85% titanium, 1.6~2.8% aluminum, 0.3~1.3% hafnium, 0.005~1% zirconium, 0.002~
Contains 0.02% boron and 0.05-0.2% carbon, the balance is nickel excluding impurities, and the content of niobium, hafnium, titanium and aluminum (in weight % in the alloy) is 28327 (%Nb) + 804 (% Hf) +36956 (%Ti) +115057
(%Al) −6676(%Nb) ² −564 (%Hf) ² −4847(%Ti) ² −54349(Al) ² +8392(Al
) ³ −5255 [(%Nb) x (%Ti)] ≧153123. The value on the left side of this equation is herein referred to as the correlation factor, and preferably it is at least 153,223. Generally, the zirconium content is preferably in a narrower range, which is 0.005-0.15% zirconium. It should be noted that in the present invention small amounts of carbon and boron may be present in single crystal castings, where their contribution to grain boundary strengthening is not required. Within the preferred composition range, the alloy of the invention exhibits a creep rupture period of over 1600 hours at 200 N/mm ² and 870° C. in the directionally solidified state and after solution treatment and aging. The effect of the required correlation of hafnium and aluminum in defining the titanium and niobium contents is shown in FIG. 1 for an alloy containing 0.7% hafnium and 2% aluminum. In the figure, alloys of composition corresponding to points within the area defined by the ellipse have a correlation factor of at least 153,223. Apart from the components mentioned above, impurities that may be present include small amounts of silicon, manganese and iron, which should be kept as low as possible. The silicon content is less than 1%, preferably
It is less than 0.5%, more preferably less than 0.2%. Silicon impairs corrosion resistance. Manganese is less than 1% and preferably less than 0.2%. The iron content can be as high as 3%, but is preferably less than 0.5%. Traces of nitrogen and sulfur may be present but preferably they are 0.005%
less than The preferred alloy of the present invention is Cr:22
%, Co: 19%, W: 2%, Ta: 1.1%, Ti: 3.4
%, Nb: 0.8%, Hf: 0.7%, Al: 2%, C:
0.15%, Zr: 0.1%, B: 0.01% and balance Ni
and impurities. The correlation factor calculated for this composition is 153855
It is. The alloy is made by vacuum melting followed by vacuum smelting (e.g., held under vacuum for 15 to 1 hour). In remelting the alloy to produce a casting, the casting stake or other primary shape is remelted and cast under vacuum. The alloy has good castability and is particularly suitable for producing articles or parts shaped by casting. In order to obtain optimum properties, in particular creep rupture duration, thermal fatigue resistance, ductility, the casting is preferably directionally solidified to obtain a columnar crystal structure. However, the present invention clearly includes molded castings made from alloys of both substantially equiaxed and columnar crystal structures. Such castings include gas turbine engine components (eg, gas turbine stators or rotors with or without air cooling passages) and integrated blade turbine rotor disks. Directional coagulation
Solidification is done by conventional methods used for high temperature alloys. In order to develop desirable creep rupture properties, it is necessary to subject the cast product to heat treatment including solution treatment and aging. The solution treatment preferably includes:
It consists of heating at 1120-1200℃ for 2-24 hours,
Then, it is aged for 2 to 24 hours at a temperature range of 1020 to 650°C. Aging is carried out in one stage or in two stages (for example, 1020-870℃ for 2-12 hours, then 860-650℃
℃ for 6-48 hours). The preferred heat treatment is (1)
4 hours/1160°C + 10 hours/843°C (single aging) or (2) 8 hours/1160°C + 4 hours/900°C + 16 hours/760°C (double aging). The alloy is air cooled between each stage of heat treatment. A series of alloys having the compositions shown in Table 1 were tested to demonstrate the importance of maintaining alloy compositions and correlation factors within the inventive range. Among them, alloys Nos. 1-3 are according to the invention, while alloys Nos. A-E are not. All alloys were melted and cast in vacuum and then cast using a refractory or exothermic mold with a cooled substrate to form a casting with a cylindrical crystal structure. The castings were heat treated as shown in Table 2 and standard creep rupture test specimens were standardized and manufactured such that all test specimens had a cylindrical crystal structure extending in the direction of their axis. Next, the test piece was placed under a stress of 200N/ ^mm2 .
A creep rupture test was carried out at 870°C and the results are shown in Table 2. Table 2 also includes correlation factors calculated from the alloy composition. The test results show that alloys Nos. 1-3 of the present invention are substantially superior to the creep rupture times of alloys Nos. A-E. Here, alloy No.E is IN-939
It is.

【table】

【table】

[Table] Heat corrosion resistance test: C: 0.15%, Cr: 22.0%,
Co: 19.0%, W: 2.0%, Nb: 0.8%, Ta: 1.1
%, Hf: 0.7%, Ti: 3.6%, Al: 2.0%, Zr:
An alloy of the present invention (alloy No. 4) and a sample of IN-939 (alloy No. E) having a composition of 0.10% B, 0.01% B, and the balance nickel were also tested. Cylindrical specimens machined from heat-treated castings of the alloy were exposed to an air:fuel ratio of 30:1 in a marine diesel fuel burner. Diterciabutyl sulfide was added to raise the sulfur content of the fuel to 2%, and then ASTM sea salt was added to the hot gas stream to give an air concentration of 10 ppm. The samples were heated to 704°C and thermal cycled to room temperature by using forced air cooling every 24 hours. The penetration depth of corrosion from the sample surface was measured, and the following results were obtained. Alloy No. Average penetration depth (μm) 4 2.5, 7.5, 7.5, 5.0 (number of samples: 4) F 38 Although initially aimed at casting products, the alloy is also useful in rough form. be. These states are for single crystal castings (single
crystal castings), for example monocrystalline gas turbine blades or vanes. If heat treatment is performed in vacuum, each stage of heating may be followed by rapid cooling by gas fan quenching.

[Brief explanation of drawings]

FIG. 1 is a graph showing the specification of Ti and Al contents in the case of 0.7% Hf and 2% Al.

Claims (1)

[Claims] 1. By weight, 20-23% chromium, 17-23% cobalt, 1-2.5% tungsten, 0.4-1.2% niobium, 0.6-1.4% tantalum, 2.95-3.85% Titanium, 1.6-2.8% aluminum, 0.3-1.3% hafnium, 0.005-1% zirconium, 0.002
Contains ~0.02% boron and 0.05-0.20% carbon, the balance is nickel except for impurities, and the content of niobium, hafnium, titanium and aluminum is 28327 (%Nb) + 804 (%Hf) + 36956 (%Ti) +115057
(%Al) −6676 (%Nb) ² −564 (%Hf) ² −4847 (%Ti) ² −54349 (%Al) ² +8392 (%Al) ³ −
5255 A nickel-chromium-cobalt-based alloy for casting, characterized in that it satisfies the relational expression expressed by [(%Nb)×(%Ti)]≧153123. 2 Zirconium content is 0.005-0.15% by weight
A nickel-chromium-cobalt-based alloy for casting according to claim 1. 3. The nickel-chromium-cobalt-based alloy for casting according to claim 1 or 2, wherein the value of the left side of the relational expression is at least 153223. 4 By weight, 22% chromium, 19% cobalt, 2
% tungsten, 1.1% tantalum, 3.4% titanium, 0.8% niobium, 0.7% hafnium, 2%
The nickel-chromium-cobalt-based alloy for casting according to claim 1, which contains aluminum, 0.15% carbon, 0.1% zirconium, and 0.01% boron, with the balance being nickel excluding impurities.