JPS6343457B2 - - Google Patents

Description

[Detailed description of the invention]

[Technical Field of the Invention] The present invention relates to a nickel-iron based alloy, and more particularly to an age hardenable low expansion alloy used for heat resistance. [Background of the invention] Conventionally, the technology is 4×10 ^-6 /〓(7.2×10 ^-6 /
℃), 5×10 ^-6 /〓 (9×10 ^-6 /℃) or about 5.5
×10 ^{-6 /} 〓 (9.9
Mention was made of age-hardenable nickel-iron alloys, including nickel-iron-cobalt alloys, which have low coefficients of thermal expansion and high inflection temperatures, such as an inflection temperature (IT) of 0.5 °C. For example, in the paper by HLEiselstein and JKBell, “New Ni
-New Ni-Fe-Co Alloys Provide Constant Modulus and High Temperature Strength
Constant Modulus＋High Temperature
Materials in Design Engineering, November 1965. Although the desired expansion properties and good strength properties were obtained, 1000〓
(538℃), 1150〓 (621℃) or 1200〓 (649℃)
At high temperatures such as Physical Metallurgy and
Properties of a New Controlled―
Expansion Superalloy)”, JOM, July 1975,
And to overcome such difficulties, certain limited heat treatment processes and microstructural states, especially avoiding recrystallization, are proposed in this paper and in U.S. Pat.
It was proposed in the specification of No. 3705827. Furthermore, the development of specific compositions is mentioned in US Pat. No. 4,006,011 and US Pat. No. 7,035,28, 1976, 7, 8. Commercial production of machines, engines and other equipment still requires extensive processing flexibility, such as forging,
It is important to have a wide range of temperatures for brazing and other processing, and to obtain the desired low COE and high IT values, and to the best of the inventor's knowledge there have been no attempts to date to specifically achieve the required expansion and heat resistance properties. Not all requirements for possible alloy compositions have been met. SUMMARY OF THE INVENTION Particularly limited alloy compositions have now been discovered that are particularly useful in providing products with desirable thermal expansion properties and the ability to withstand stress concentrations in heated structures. It is an object of the present invention to provide a low expansion alloy for use at high temperatures in engines, machines and other structures. Other objects and advantages of the invention will be apparent from the following disclosure. The present invention consists of 1.5% alloy by weight of 34% to 55.3% nickel, up to 25.2% cobalt, 1% to 2% titanium, metals from the group of niobium and tantalum, and 1/2 of the weight (%) of niobium and tantalum. ~5.5%, up to 2% manganese and up to 6.2% chromium, the sum of manganese and chromium not exceeding 6.2%, and the balance substantially containing iron, preferably with the presence of aluminum included as an unavoidable impurity. limited to amounts less than 0.1%, such as 0.08%, 0.05% or 0.008%, and at least in the age hardened state.
Thermal expansion inflection temperature of 650〓 (343 °C), expansion coefficient of 5.5 × 10 ^-6 /〓 (9.9 × ^{10 -6} / °C) or less when heated to inflection temperature, at least 110 ksi (7734
An age hardenable alloy having a room temperature yield strength (0.2% offset) of Kg/cm ² ) is contemplated. Generally, in many embodiments the iron content is about 20
In the range of ~55%. The presence of a significant amount of cobalt, for example about 10% or more, is often characteristic, especially when correlated to nickel giving a nickel content plus cobalt content of about 51-53%. For example, it is desirable to increase the inflection temperature. Associated elements such as deoxidizers and malleants, scavengers, and acceptable impurities are approximately 0.01% calcium, 0.01% magnesium, 0.03% boron,
Amounts such as 0.1% zirconium, 0.5% silicon, and up to about 1% each of copper, molybdenum, and tungsten may be used. Sulfur and phosphorus are undesirable and are usually limited to no more than about 0.015% individually. In commercial embodiments of alloys, the tantalum present often does not exceed 10% of the niobium content, in which case the difference between niobium and tantalum can be considered insignificant and the alloy can easily contain niobium or tantalum. It can be shown that the total content of niobium and tantalum is 1.5 to 5.5%. However, if desired, the alloy can have up to 11% tantalum. The age hardened state is about 1350~1100〓(732~
Annealing before aging is recommended. Expansion coefficient, which is a general property of age-hardened alloys,
A useful guideline for ensuring inflection temperature and yield strength is to have specific composition proportions (within the percentage range of the present invention) according to the following relationships, respectively: A - (%Ni) + 0.84 (%Co) - 1.7 (%Ti + %Al) +
0.42 (%Mn + %Cr) is at most 51.5 B - (%Ni) + 1.1 (%Co) - 1.0 (%Ti) - 1.8 (%Mn
+%Cr)−0.33(%Nb+1/2Ta) is at least
44.4 C - (%Nb + 1/2%Ta) (%Ti) - 0.33 (%Cr) is at least 2.7 Considering the relationships A, B and C, the iron content in the alloy composition according to them is up to 51.2%. and for example tantalum 11% iron at least
21% or 5.5% niobium with substantially no tantalum and at least 26.5% iron. For particularly good expansion and strength properties,
The composition is nickel 35-39%, cobalt 12-16%, titanium 1.2-1.8%, metals of the group of niobium and tantalum,
an amount such that the sum of niobium and 1/2 of the weight of tantalum is 3.7 to 4.8 of the alloy, up to 1% each of the elements manganese and chromium, up to 0.012% boron, preferably 0.003 to 0.012% boron, and the remainder substantial It is advantageous to control the iron content and limit the aluminum content as an unavoidable impurity to a low proportion, such as less than 0.1%. 4.5×10 ^-6 /〓(8.1×
10 ^-6 /℃), at least
Inflection temperature of 780〓(415℃) and at least 13000psi
In order to provide an alloy with a room temperature yield strength of (9100 Kg/cm ² ), it is necessary to have a composition ratio in which relational expression A is at most 47.5, relational expression B is at least 48.8, and relational expression C is at least 4.8. It's advantageous. Although less precise, according to relations A and B, melting control for certain advantageous embodiments is simplified to control the sum of nickel and cobalt to 51-53%, and %Ti and %Mn+%Cr, respectively. Approximately 1.5
% and about 0.3%, and good results are often achieved. In certain instances where dilatometers or other true dilatation measurements are not available to characterize the properties of the alloy, the present invention provides thermal expansion properties in the range of COE (10 ^-6 /〓, or parts per million per degree). unit thermal expansion coefficient)
It is calculated from the composition percentage using the following relational expression for This relationship is the following COE and IT equation: COE = 0.248 (%Ni) + 0.209 (%Co) -0.427 (%Al + %Ti) +0.104 (%Mn + %Cr) - -7.39 IT =26.9 (%Ni) + 29.6 (%Co) -57.2 (%Al) -28.2 (%Ti) -47.0 (%Mn + %Cr) -8.90 (%Nb + 1/2% Ta) -509 The above COE is from room temperature The average COE for a range of temperatures up to the inflection temperature is given by the IT equation above, which is based on statistical analysis of dilatometer measurements for a large number of alloys within and moderately outside the range of the present invention. The success of the present invention in providing alloys for products and other articles that must withstand stress-dependent cracking effects when used at high temperatures, such as components of turbine engines, is later confirmed by test results. Since hot air is the operating environment for most of the articles, the ability or lack thereof to withstand stress-dependent cracking can be determined by testing the alloy specimen in air at high temperatures for long periods of stress, e.g. 1000-1200〓 (538-649° C.) as indicated by the results of a notch-break test or a stress-crack test in a heated air chamber at temperatures such as (538-649° C.). A type of stress indicated as a SAGBO (Stress Accelerated Grain Boundary Oxidation) test in which a strip specimen is held under stress in a warped or bent shape by a device placed in a furnace and examined visually.
It is understood that cracking tests provide important evidence of stress-cracking characteristics. This is because in many instances metal separation, such as crack formation and growth, has been observed to occur at grain boundary oxidation sites, and it is understood that the external surface of the bowed beam is a stress concentration area. The alloy can be produced by melting practices known for producing high quality nickel-iron alloys. Induction melting by air melting practice and vacuum melting practice was found to be satisfactory. Other melting practices can be used if desired, such as electric flux melting or vacuum arc melting or remelting. The alloy has good malleability for hot working as well as for cold working. Furthermore, warm working followed by recrystallization annealing with controlled alloy compositions according to the present invention provides satisfactory results including good notch-to-break strength properties. Here, warm working is carried out at a high temperature within several hundred degrees below the alloy recrystallization temperature, close to hot temperature, for example, 30 to 300 degrees (-1 to 149 degrees Celsius) below the recrystallization temperature of the alloy to be processed. Indicates special cold working. The recrystallized product of the alloy has an equiaxed grain structure which is advantageous for obtaining isotropic strength and other properties. Among its many advantages, alloys that are satisfactory for warm working methods allow the alloy to continue forging, rolling or other processing while cooling the processing from the hot working range through the recrystallization temperature for reheating. This is advantageous to capacity and economy in commercial production as the lost time and expense of interrupting processing for reheating is avoided. Hot processing of alloy ingots is 2100〓(1149
℃), can be continued down to the warm working range, and, if desired, can continue processing the hot worked alloy while cooling the alloy into the warm working range. Reheating for crystalline annealing of warm worked alloys will, of course, generally be about
The heating is carried out at a temperature of 1,700 to 1,900°C/927 to 1,038°C for about 1 to 1/4 hours. Annealing at 1700°C (927°C) for 1 hour or 1900°C (1038°C) for 1/4 hour, or any suitable annealing in between, is desirable to create a fine-grained structure in the bar stock, but in thin strips the grains are more It will quickly become coarse particles. Although a fine-grained structure is advantageous in ensuring good stress-cracking resistance (including notch-breaking strength) and high room temperature, in some embodiments the alloy can be used in both coarse-grained and fine-grained states. Good stress resistance
It has breakability. For the products of this invention, the grain structure as recrystallized fine grains has an average grain size up to approximately ASTM No. 5, often ASTM No. 5 to No. 8, and the grain structure as recrystallized coarse grains is approximately ASTM
No. 4, 5 or larger, often ASTM No.
It has an average particle size of 2 to No. 4. Recrystallization annealing at temperatures of at least 1700°C (927°C) also helps to bring the alloy into a homogeneous solid solution state, and in preparation for aging, most if not all of the γ′-forming elements are in solution. become. (Annealing is not carbide solution annealing.) Subsequent water cooling after annealing is desirable to maintain the solution state until the next processing step, but in some cases slower cooling, e.g. Air cooling would be sufficient. The alloy is strengthened by aging at a temperature of about 1150-1350°C (621-732°C) for about 8 hours or longer. Preferably hot worked alloys are made without or without warm working or cold working;
It is placed in a solid solution state before aging, however, in some cases good results can be obtained without complete solution treatment. Particularly good aging treatment is achieved by successively holding for 8 hours at 1325〓 (718℃) and then 100〓/hr up to 1150〓 (621℃).
8 hours hold at 1150°C (621°C), followed by cooling in air or in the oven to room temperature. Intermediate treatment at 1350-1550〓 (732-843°C) may be recommended to favor fracture ductility or SAGBO life. In general, age-hardened products in both fine-grained and coarse-grained states are at least
It has a yield strength of 110 ksi (7734 Kg/cm ² ) and a tensile elongation at room temperature of about 10% or greater. EXAMPLES In order that the present invention may be better understood by those skilled in the art, the following examples are provided. Example: approximately 36% nickel, 17% cobalt, 3% niobium
and iron-based alloy containing 1.5% titanium (alloy 1)
A vacuum induction melt was prepared and vacuum cast into an ingot mold. Small amounts of boron and calcium were added to the melt before tapping. The results of the chemical analysis of Alloy 1 are shown in the table. Ingot metal was hot rolled to 1/4 inch (0.64 cm) thick and then cold rolled to 0.06 inch (0.15 cm) sheets. Then 3/4 x 4 inches (7.62/10.2 x 10.2 cm) and 3/8 x
A 4 inch (7.62/20.32 x 10.2 cm) test blank was cut and heated at 1900㎓ (1038℃) for 0.25 hours.
After cooling the water, heat and hold at 1325〓 (718℃) for 8 hours, and reduce the temperature from 1325〓 (718℃) to 1150〓.
100〓/hr furnace cooling to (621℃), 1150〓 (621℃)
The heat treatment was carried out by annealing with holding and air cooling for 8 hours, followed by aging. The strip recrystallized to approximately ASTM 4.5 or 4-5 coarse grain structure. Measurements of 0.2% offset yield strength (YS), ultimate tensile strength (UTS), elongation (E1), and area shrinkage (RA) at room temperature (RT) and 1000° (538°C) were carried out transversely (perpendicularly) to the rolling direction. ), and the results are shown in the table.
The room temperature yield strength of 127.5 ksi (8964 Kg/cm ² ) and elongation of 14% demonstrate very good mechanical properties at room temperature. High temperature stress resistance - for evaluating cracking strength
3/8″ aged horizontal specimen for SAGBO test
(0.95 cm) blanks were surface ground to 320 grit, accurately measured for thickness, and compensated for expansion of the test equipment for the selected test stress in accordance with ASTM Bent Beam Stress - Preparation and Use of Corrosion Test Specimens. Recommended Practice for Preparation and
Use of Bent・Beam Stress Corrosion
Specimens)” G39-72 to calculate the required length,
It was prepared by cutting it to the required length. The ends of the specimens were ground into chisel blades to provide point contact on the specimen holder. A specimen of Alloy 1 thus prepared was placed in the testing apparatus and 1000
150ksi (10546Kg/
The load was applied by tightening the device bolts sufficiently to create a stress of cm ² ). The specimen held in the device was heated to 1000㎓ (538℃) in a box furnace with an observation window.
The specimens were visually inspected from time to time, for example at 4 or 24 hour intervals, and remained unchanged under load for 294 hours, but failed by cracking during the next hour. Therefore, 150 ksi at 1000〓 (538℃)
It had a life of 294 hours at a stress of (10546 Kg/cm ² ). This 294-hour result was obtained from a sheet that was cold-rolled transversely to the length of the specimen.
It is understood that this shows that the composition of Alloy 1 has very good stress-cracking resistance. Also, even though annealing at 1900㎓ (1038℃) for 0.25 hours is advantageous for isotropy, testing on specimens taken horizontally to rolling is better than testing specimens taken parallel to rolling. is considered to be an even harsher criterion. The results of chemical analysis for other examples of the invention are shown in the table along with the results for Alloy 1. Also shown in the table are the results of chemical analyzes of other alloys different from the present invention, designated as Alloys A to G. Table A shows therein the values of relational expressions A, B, and C, as well as the values of the COE and IT characteristics calculated by the expressions. Furthermore, the table shows the evaluated mechanical properties of examples of the invention and of alloys different from the invention. In the table, under the heading SAGBO, TL (Life Time) indicates the longest time the specimen was examined before failure occurred, and TC (Crack Time)) indicates the first time the specimen was observed to have failed. Show time. Therefore, the SAGBO lifetime is the time between TL and TC.

【table】

【table】

【table】

[Table] (Dilatometer measurement values)
*1: In the case of Celsius, it is (× ^10-6 ×9/5/℃).
*2: Celsius is converted by 5/9 (〓-32).

[Table] 1200〓(649℃) Notch - Fracture characteristics and room temperature and
Test specimens for evaluating the short-term tensile properties at 1200°C (649°C) were taken from 9/16 inch (22.86/40.64 cm) square forgings of Alloy 4 and Alloys C to F, and the results are shown in the table. These alloys were vacuum induction melted, forged into ingots, and then forged. The forging process is to process the ingot in 1/4" (2.54/10.16cm) steps and reheat the ingot to 2050° (1121°C) as necessary to 11/16"
(27.94/40.64cm) hammer forged into a square piece, cooled on the hammer to about 1600〓 (871℃), then 9/16″
(22.86/40.64cm) was to be finished forged into a square piece and ordered. As shown in the table, the particle size in the specimen after heat treatment was about ASTM 7-9. The results in the table are strength, ductility, stress concentration area,
2 is an illustration of the effect of limiting aluminum to no more than 0.2% in order to obtain the desired good combination of fracture resistance in, for example, notches. Also, when the table and the results in the table are related to the analytical values in the table, it is clear that long-term fracture resistance is effective when limiting aluminum. Among others, it may be noted that Alloy 2 is illustrative of the fact that considerable longevity can be obtained when a small amount of aluminum is present together with a small amount of chromium, and a small amount such as about 0.3% or 0.5% chromium. It is expected that when chromium is present it may be recommended to include a small amount of aluminum such as about 0.05% to ensure long life; This is because it occurred in one alloy that analysis showed contained.

[Table] The alloy of the present invention was evaluated for weldability using the Varestraint test method.
A low expansion nickel-cobalt-iron alloy, exemplified herein as Alloy G, has been shown to have improved weld cracking resistance compared to commercial variants. Alloy G having the analytical values in the table was processed by commercial production practice to vacuum induction melting heat of Eiselstein & Bell alloys.
The results of the Balestrain test of alloys 7, 8 and G specimens in the hot rolled condition are shown in the table. Rolled condition and 1900〓(1038℃)/0.25hr
Alloys 7 and 8 in annealed and aged condition
Evaluation of the electron beam welding method shows that the weldability is as good as that of typical market alloys, and that the weldability between the rolled and heat-treated states (both approximately
ASTM particle size #5) showed slight differences. Alloy 7 appears to be the most resistant to subbead cracking in a small number of e-beam tests, and in metallographic examination of flexural test results for Alloy 12 in the rolled and heat treated conditions, it actually No evidence of cracking was observed.

[Table] The alloy has good processing suitability for rolling and forging in hot, warm and cold conditions and also has good machinability. The alloy has good brazeability for joining articles of the alloy, including wrought products such as sheets and strips, to other articles of the same or different alloys. Certain desirable characteristics of the alloy include good strength properties and good strength properties in cold (or warm) worked parts that are subsequently heated to elevated temperatures, e.g. 1900°C (1038°C) for brazing or other requirements. Includes the ability to impart ductile properties. The present invention applies to articles for turbine engines and others, and for room temperature and temperatures of approximately 600° (316°C) and 1000° (538°C).
It can be applied to the manufacture of structures that are subjected to stress during heating and cooling to temperatures such as 1200° C. (649° C.), such as seals, brackets, flanges, shafts, bolts and casings used in gas turbines. Although the invention has been described with reference to preferred embodiments, it is to be understood that modifications and changes can be made therein without departing from the spirit and scope of the invention, as will be readily apparent to those skilled in the art.
Such modifications and changes are considered to be within the power and scope of this invention and the claims.

Claims (1)

[Claims] 1. In an age hardenable alloy, selected from the group consisting of 34 to 55.3% nickel, up to 25.2% cobalt, 1 to 2% titanium, 1.5 to 11% niobium, tantalum and mixtures thereof. containing up to 2% manganese and up to 6.2% chromium, where the sum of manganese and chromium is 6.2% of the alloy. %
and the remainder consists essentially of iron, and in the age-hardened state has a thermal expansion inflection point of at least 650〓 (343°C) and an expansion coefficient of 5.5 × 10 ^-6 /
An age hardening alloy characterized by a yield strength of at least 110000 psi (7334 Kg/cm ² ) at room temperature below (9.9×10 ^-6 /°C). 2 35-39% nickel, 12-16% cobalt,
Contains 1.2-1.8% titanium, 3.7-4.8% niobium + 1/2 tantalum, up to 1% manganese, up to 1% chromium, and in the age-hardened condition has an inflection temperature of at least 780〓 (415℃). ), expansion coefficient 4.5×
10 ^-6 /〓 (8.1 x ^{10 -6} /°C) or less and a yield strength of at least 130000 psi (9100 Kg/cm ² ) at room temperature.