ADVANCED HIGH TEMPERATURE CORROSION RESISTANT ALLOY

Abstract: A nickel-base alloy consisting of, in weight percent, 42 to 58 nickel, 21 to 28 chromium, 12 to 18 cobalt, 4 to 9.5 molybdenum, 2 to 3.5 aluminum, 0.05 to 2 titanium, at least one microalloying agent selected from the group consisting of 0.005 to 0.1 yttrium and 0.01 to 0.6 zirconium, 0.01 to 0.15 carbon, 0 to 0.01 boron, 0 to 4 iron, 0 to 1 manganese, 0 to 1 silicon, 0 to 1 hafnium, 0 to 0.4 niobium, 0 to 0.1 nitrogen, incidental impurities and deoxidizers.

Description: ADVANCED HIGH TEMPERATURE CORROSION RESISTANT ALLOY FIELD OF THE INVENTION This invention relates to the field of nickel-base alloys possessing resistance to high temperature corrosive environments. BACKGROUND OF THE INVENTION Nickel-base high temperature alloys serve in numerous applications, such as, regenerators, recuperators, combustors and other gas turbine components, muffles and furnace internals, retorts and other chemical process equipment and transfer piping, boiler tubing, piping and water ail aprons and waste incineration hardware. Alloys for these applications must possess outstanding corrosion resistance to meet the long life requirements becoming critical in new facility design and operation. While virtually all major industrial equipment is exposed to air on one surface or at one part of the unit, the internal surfaces can be exposed to very aggressive carburizing, oxidizing, suifidizing, nitriding, or combinations of these corrodents. Consequently, maximum corrosion resistance to the broadest possible range of aggressive high temperature environments, is a long-sought aim of the metallurgical industry. Traditionally, these alloys reiy on precipitation hardening from a comoinaπon of-/' [Ni 3 (Al, Ti)], γ " [Nι 3 (Nb. Al. Ti)], carbide precipitation and solid solution strengthening to give the alloy strength The γ' and γ " phases precipitate as stable lπtermetallics that are essentially coherent with the austemtic-fcc aiπx This comoination of precipitates signrπcandy enhances the high temperarure mechanical properties of the alloy It is an object of this invention to provide an alloy that possesses resistance to carbuπzmg, oxidizing, nitπdiπg and suifidizing environments It is a further object of this invention to provide an alloy with sufficient phase stability and mechanical integrity for demanding, high temDerature applications SUMMARY OF THE INVENTION A nickel-base alloy consisting of, in weight percent. 42 to 58 nickel, 21 to 28 chromium, 12 to 18 cobalt, 4 to 9 5 molybdenum, 2 to 3 5 aluminum. 0 05 to 2 titanium, at least one microalloymg agent selected from the group consisting of 0 005 to 0 1 yttπum for carbuπzauon resistance and 0 01 to 0 6 zirconium for sulfidation resistance, 0 01 to 0 15 carbon. 0 to 0.01 boron, 0 to 4 iron, 0 to 1 manganese. 0 to 1 silicon. 0 to 1 hafnium. 0 to 0 4 niobium, 0 to 0 1 nitrogen, incidental impurities and deoxidizers DESCRIPTION OF PREFERRED EMBODIMENT A high temperature, high strength alloy characterized, in part, by a unique combination of microalloymg elements to achieve extremely high levels of corrosion resistance in a broad spectrum of aggressive environments A nickel base of 42 to 58 weight percent provides an austenitic matπx for the alloy (This specification expresses all alloy compositions in weight percent.) An addition of 12 to 18 weight percent cobalt enhances the corrosion resistance of the alloy and contributes solid solution strengthenine to the matrix. This matπx has sufficient corrosion resistance to tolerate up to 4 weight percent iron, up to 1 weight percent manganese and up to 1 weight percent silicon without a substantial decrease in corrosion resistance. Allowing iron, manganese and silicon into the alloy facilitates the recycling of nickel-base alloys Furthermore, manganese mav benefit the alloy by tying up trace amounts of sulfur In addition, the allov mav contain incidental impuπues such as oxygen, suifiir, phosπhorus ana sucn as caicium magnesium and cεπu An addition of 21 to 28 weignt percent chromium impairs oxidation resistance to the alloy Chromium levels less than 21 weight percent are inadequate for oxidation resistance, levels above 28 weight percent can produce detπmental chromium-containing precipitates An addiπon of 4 to 10 weight percent molybdenum contπbutes to stress corrosion cracking resistance and contπbutes some solid solution strengthening to the matπx Aluminum m an amount ranging from 2 to 3 5 weight percent contπbutes to oxidation resistance and can precipitate as γ' phase to strengthen the matπx at intermediate temperatures Most advantageously, the matπx should contain at least 2 75 weignt percent aluminum for excellent oxidation resistance For sulfidation resistance, it is cmical that the alloy contain a minimum of 0 01 weight percent zirconium to stabilize the scale against inward migration of sulfur through its protective scale layer Zirconium addiUons above 0 6 weight percent adversely impact the alloy's fabπcabihty Advantageously, an addition of at least 0 005 weight percent yttπum improves both oxidation and nitπdatioπ resistance of the alloy and is cπtical to establish carbuπzauon resistance Yttπum levels above 0 1 increase the cost and decrease the hot workability of the alloy Only when optimum levels of chromium, aluminum and cπtical microalloymg levels of yttπum and zirconium are present in the alloy will outstanding corrosion resistance be achieved in the complete spectrum of carbuπzmg, oxidizing, nitπding and suifidizing environments. However, where only carbuπzing and oxidizing corrosion resistance is required, the microalloymg with zirconium can be omitted from the composition Where only suifidizing and oxidizing corrosion resistance is required, yttπum can be omitted from the composition Maximum overall coπosioπ resistance is achieved by a combination containing at least 2 75 weight percent aluminum, 0 01 weight percent zirconium and 0 01 weight percent yttπum The optional elements of 0 to 1 weight percent hafnium and 0 to 0 1 weight percent nitrogen stabilize the oxide scale to contπbute toward oxidation resistance Hafnium in the amount of at least 0 01 weight percent and nitrogen in the amount of at least 0 01 weight percent each serve to increase oxidation resistance Excess hafrnum or nitrogen levels deteπorate the mechanical properties of the alloy An addition of 0 05 to 2 weight percent titanium will act like the aluminum addition ana contπbutes to the alloy ' s high temperature mecnaπicai propemes by precipitatmg as γ' phase Most advantageously, γ' phase consists of 8 to 20 weight percent of the alloy Maintaining niobium at less than 0 4 percent enhances the allov's stabi tv bv limiting the amount of metastable γ" precipitated. Most advantageously, -/" consists of less than 2 weight percent of the alloy An addition of at least 0 01 percent caroon strengthens the matπx But carbon levels above 0 15 weight percent can precipitate detπmeπtai carbides Optionally, a boron addition of at least 0 0001 weight percent boron enhances the hot workability of the alloy Boron additions aoove 0 01 weight percent form excess precipitates at the gram boundaπes A combination of cobalt, molybdenum and chromium with microalloymg additions of titanium and zirconium achieve the unexpected corrosion resistance for multiple environments The overall compositional range is defined as "about" the following ranges TABLE 1 'Contains at least one of yttπum for carbuπzauon resistance or zirconium for sulfidation resistance. Alloys 1 to 9 of Table 2 represent heats of the invention; Alloys A to D represent comparative heats. MECHANICAL PROPERTIES Components constructed from the alloy possess the strength necessarv for mechanical integrity and the required stability necessary to retain structural intezrity for high temperamre corrosion applications. Alloy 13 is typical of the alloy ' s strength properties. The composition was vacuum melted and cast as a 25 kilogram heat. Part of the heat was soaked at 1204°C and hot worked to 7.6 mm x 127 mm x length slab with intermediate anneals at 1 I77°C/20 minutes/air cooled and then cold rolled to 0.158 mm x 127 mm x length. A second portion of the heat was hot bar rolled from a 1204°C furnace preheat to 22.2 mm diameter bar with a final anneal at 1177°C/20 minutes/air cooled. Table 3 presents the tensile properties of alloy 13 for selected temperatures to 982°C. Stress rupture strength data for the screening test condition of 982°C/41 A MPa are siven in Table 4. The effect of aging at 760°C/100 hours on room temperature tensile strength and Charpy impact strength are presented in Table 5. Table 5 EIFect of Aging on RT Tensile Properties of Selected Allovs 1I77°01 Hour/Air Cool ASTM 0.2 % Yield Ultimate Charpy Grain Size Strength Tensile Elongation Impact Allov Number (MPa) (MPa) (%) Strength (J) 606 1072 31.4 80 528 894 52.9 228 565 939 49 278 After Aging at 760°C/100 Hours/Air Cool 810 1239 21 4 45 669 1074 25 7 31 D 681 1089 30 7 29 OXIDATION RESISTANCE High temperature alloys, a pπoπ, must possess outstanding oxidation resistance Retorts, muffles, piping and reactors, all too often, while internally containing a hot reactive process stream are exposed externally to air and, consequently, oxidation Manv process streams are oxidizing in nature as weil, damaging the internals of gas turbines, boilers and power generation components The oxidation resistance of the range of composraoπs of this patent application is exemplified by the oxidation data of Tables 6 and 7 The testing was done using 0 76 mm diameter x 19 1 mm length pins in an electπcallv heated horizontal tube furnace using an air atmosphere plus 5 percent water va D or bv weight. The specimens were cycled to RT at least weekly for weighing The mass change (mg/cm : ) data versus time to 5,000 hours at 1100°C are given in Table 6 and for times to 5,784 hours at 1200°C in Table 7 Clearly aluminum contπbutes significaπtlv to oxidation resistance in this range of compositions Compare Alloys A and B with the compositions of this patent applicaϋon at 1100°C Note the progressive increase oxidation resistance at 1200°C with the increase in aluminum content and the further enhancement afforded bv the microalloymg in alloys 7 and 8 Scale tegπty at 1 100°C has been enhanced as shown by the positive mass changes (no apparent loss of chromium by evaporation or spallation) by the additions 190 ppm yttπum, 420 ppm zirconium and 420 ppm hafinum of Alloy 2, by the additions of 320 ppm yttπum. 2100 ppm zirconium and 320 ppm nitrogen of Allov 5 and by the addition of 270 ppm yttπum to alloy 13 This enhancement is maintained at 1200°C as depicted in Table 7 CARBURIZATION RESISTANCE Carbuπzation resistance is of paramount importance for certain high temperature equipment, such as, heat treating and smteπng furnace muffles and internal hardware, selected chemical reactors and their process stream containment apparatus and power generation components. These atmospheres can range from purely carboneous (reducing) to highly oxidizmg (as seen in gas turbme engmes). Ideally, a corrosion resistant, high temperature alloy should be able to perform equally well under both reducing and oxidizing carburizing conditions Alloys of the compositional range of this application possess excellent carbuπzation resistance under both extremes of oxygen potential These tests were conducted in eiecτπcaily heated muilite tube furnaces in which the atmospheres were 10 generated from bottled gases which were electronically metered through the capped furnace tubes. The atmospheres, pπor to reacting with the test specimens, were passed over reformer catalysts (Girdler G56 or G90) to achieve equilibπum of the atmosphere The flow of the atmospheres through the furnace was approximately 150 cc/mmute SULFIDATION RESISTANCE Sulfidatioπ resistance can be cπtical for hardware components exposed to certain chemical process streams, gas turbine combustion and exhaust streams, coal combustion 20 and waste mcineration environments Scale penetration by sulfur can lead to nickel sulfide formation. This low melting point compound can cause rapid disintegration of nickel- coπtaiπmg alloys. It was discovered that alloys containing a minimum of about 0 015% (150 ppm) zirconium are unexpectedly extremely resistant to sulfidation as exemplified by the data of Table 9 Alloy A expeπences rapid liquid phase degradation in H : - 45%CO: - • >« 1% R> at 816°C in approximately 30 hours The remaining aliovs showed gradual improvement as the zircomum content was raised but became dramatically resistant to sulfϊdaoon above about 0 015% (150 ppm) zircomum. Examination of the compositions tested suggest that yttπum plays a minor positive role in enhancing suifidatioπ resistance, but is unable to dramatically effect sulfidation resistance Alloys containing more than 0.015 weight percent (150 ppm) zircomum have been testeα in the above environment for nearly 1.5 years (12,288 hours) without failure. NITRIDATION RESISTANCE The zirconium-containing alloy also has outstanding resistance to πitπdation as measured m pure ammonia at 1100°C. Data to 1056 hours are presented in Table 10 These data show that alloy B (low in aluminum) alloys containing 3 weight percent aluminum but no zirconium or yttπum (such as alloy C) and alloys containing only yttπum (such as alloy 13) possess good but not outstanding resistance to nitπdation Alloys 3 and 8, containing at least 2 75 weight percent aluminum and greater than 0 01 weight percent (100 ppm) each of zirconium and yttπum, possess outstanding resistance to nitπdation This alloy range has maximum corrosion resistance to a broad range of aggressive high temperature environments. The alloy's properties are suitable for multiple high temperature corrosion applications, such as, regenerators, recuperators, combustors and other gas turbine components, muffles and furnace internals, retorts and other chemical process equipment and transfer piping, boiler tubing, piping and wateπvall aprons and waste incineration hardware. Furthermore, a combination of γ', carbide precipitation and solid solution hardening provides a stable structure with the requisite strength for these high temperature corrosion applications. In accordance with the provisions of the statute, the specification illustrates and describes specific embodiments of the invention. Those skilled -in the an will understand that changes may be made in the form of the invention covered by the claims that certain features of the invention may sometimes be used to advantage without a corresponding use of the other features.

Claims: We claim: 1. A nickel-base alloy consisting of in weight percent, about 42 to 58 nickel, about 21 to 28 chromium, about 12 to 18 cobalt, about 4 to 9.5 molybdenum, about 2 to 3.5 aluminum, about 0.05 to 2 titanium, at least one microalloying agent selected from the group consisting of about 0.005 to 0.1 yttrium and about 0.01 to 0.6 zirconium, about 0.01 to 0.15 carbon, about 0 to 0.01 boron, about 0 to 4 iron, about 0 to 1 manganese, about 0 to 1 silicon, about 0 to 1 hafnium, about 0 to 0.4 niobium, about 0 to 0.1 nitrogen, incidental impurities and deoxidizers. 2. The nickel-base alloy of claim 1 containing about 8 to 20 weight percent -/' phase. 3. The nickel-base alloy of claim 1 containing less than about 2 weight percent y " phase. 4. The alloy of claim 1 including about 43 to 57 nickel, about 21.5 to 27 chromium, about 12.5 to 17.5 cobalt and about 4.5 to 9 molybdenum. 5. The alloy of claim 1 including about 2.25 to 3.5 aluminum and about 0.06 to 1.6 titanium. 6. The alloy of claim 1 including about 0.01 to 0.5 zirconium, about 0.01 to 0.14 carbon and about 0.0001 to 0.01 boron. 7. A nickel-base alloy consisting of in weight percent, about 43 to 57 nickel. about 21.5 to 27 chromium, about 12.5 to 17.5 cobalt, about 4.5 to 9 molybdenum, about 2.25 to 3.5 aluminum, about 0.06 to 1.6 titanium, at least one microalloying agent selected from the group consisting of about 0.01 to 0.08 yttrium and about 0.01 to 0.5 zirconium, about 0.01 to 0.14 carbon, about 0.0001 to 0.01 boron, about 0 to 3 iron, about 0 to 0.8 manganese, about 0.01 to 1 silicon, about 0.01 to 0.8 hafnium, about 0.00001 to 0.08 nitrogen, incidental impurities and deoxidizers. 8. The nickel-base alloy of claim 7 containing about 8 to 20 weight percent γ' phase. 9. The nickel-base alloy of claim 7 containing less than about 2 weight percent γ " phase. 10. The alloy of claim 7 including about 44 to 56 nickel about 22 to 27 chromium, about 13 to 17 cobalt and about 5 to 8.5 molybdenum. 11. The alloy of ciaim 7 including about 2.5 to 3.5 aluminum and about 0.08 to 1.2 titanium. 12. The alloy of ciaim 7 including about 0.02 to 0.5 zirconium, about 0.01 to 0.12 carbon and 0.01 to 0.009 boron. 13. A nickel-base alloy consisting of in weight percent, about 44 to 50 nickel, about 22 to 27 chromium, about 13 to 17 cobalt, about 5 to 8.5 molybdenum, about 2.5 to 3.5 aluminum, about 0.08 to 1.2 titanium, about 0.01 to 0.07 yttrium, about 0.02 to 0.5 zirconium, about 0.01 to 0.12 carbon, about 0.001 to 0.009 boron, about 0.1 to 2.5 iron, about 0 to 0.6 manganese, about 0.02 to 0.5 silicon, about 0 to 0.7 hafnium, about 0.0001 to 0.05 nitrogen, incidental impurities and deoxidizers. 14. The nickel-base alloy of claim 13 containing about 8 to 20 weight percent γ 1 phase. 15. The nickel-base alloy of ciaim 13 containing less than about 2 weight percent γ " phase. 16. The alloy of claim 13 including about 45 to 55 nickel, about 22 to 26 chromium, about 14 to 16 cobalt and 5 to 8 molybdenum. 17. The alloy of claim 13 including about 2.75 to 3.5 aluminum and about 0. to 1 titanium. 18 The alloy of ciaim 13 including about 0 01 to 0.06 yttπum. about 0 02 to 0 4 zirconium, about 0.02 to 0 I carbon and about 0.003 to 0 008 boron 19. The nickel base alloy of claim 13 containing about 2.75 to 3.5 aluminum. about 0.003 to 0.008 boron, about 0.02 to 0.1 carbon, about 14 to 16 cobalt, about 22 to 26 chromium, about 0.5 to 2 iron, about 0 to 0.5 hafnium, about 5 to 8 molybdenum, about 0.01 to 0.05 nitrogen, about 0 to 0.2 niobium, about 45 to 55 nickel, about 0.05 to 0 4 silicon, about 0 1 to 1 titanium, about 0 01 to 0.06 yttπum and about 0 02 to 0 4 zirconium.

Inventors: SMITH GAYLORD DARRELL, TASSEN CURTIS STEVEN, SMITH, GAYLORD, DARRELL, TASSEN, CURTIS, STEVEN
Applicants: INCO ALLOYS INT, INCO ALLOYS INTERNATIONAL, INC.
Application year: 1999
Main classification: C22C19
IPC codes: C22C19