Classifications

• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22F—CHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
  • C22F1/00—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
  • C22F1/10—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working of nickel or cobalt or alloys based thereon

Definitions

• ABSTRACT Heat treating process enables obtaining desired combinations of strength, ductility and fabricability characteristics in heat resistant age-hardenable alloys having precipitation-hardening amounts of columbium, titanium and/or tantalum in a nickel-containing ma trlx.
• the present invention relates to age-hardenable nickel alloys and more particularly to heat treatment of nickel alloys, including nickel-iron-chromium alloys strengthened with columbium and titanium.
• heat treatments comprising annealing or solution treating at high temperatures such as l,700F. or 2,100F. or higher, cooling rapidly down from the solution temperature to room temperature, e.g., air cooling or water quenching, and thereafter reheating at lower temperatures of around l,lF. to l,400F. to precipitation harden the alloys.
• Precipitation-strengthened alloys containing chromium are often used for components of gas turbines, e.g., turbine blades and turbine rotor discs.
• gas turbines e.g., turbine blades and turbine rotor discs.
• nickel-ironchromium age-hardenable alloys is described in US. Pat. No. 3,663,213.
• Improvements in the processing of known alloys are particularly desired for obtaining specially needed combinations of such important metallurgical characteristics and for facilitating production of desired articles and structures with use of presently available alloys. And, of course, process improvements in the present can become highly beneficial for enhancing the characteristics of future alloys.
• the present invention comtemplates a process for heat treating an age-hardenable heat-resistant nickel alloy containing precipitable amounts of gamma-prime forming metal selected from the group consisting of columbium, titanium and tantalum comprising: heating the alloy at a temperature in the gamma-prime solid solution range of the alloy and obtaining the alloy in'the solid solution condition having precipitable amounts of the gamma-prime forming metal in solid solution; cooling the alloy down to the gamma-prime solvus temperature; then slowly cooling the alloy uniformly at a controlled cooling rate not greater than 500F. per hour, e.g., about 20F. per hour to 500F.
• the gamma-prime solvus temperature down to at least about L00F. below the gamma-prime solvus temperature, thus into precipitation temperature range of the alloy; heat treating the slow-cooled alloy at an upper temperature in the precipitation range to precipitate coarse particles of gamma-prime at (in the vicinity of) the grain boundaries of the alloy and dispersed uniformly within the grains while retaining a portion of the gamma-prime forming metal in solution; thereafter heat treating the alloy at a lower temperature in the precipitation hardening range to precipitate fine particles of gamma-prime dispersed uniformly within the grains; and then cooling the alloy to room temperature, thereby providing a precipitation hardened alloy having coarse particles of gamma-prime at the grain boundaries and having coarse gamma-prime particles and fine gamma-prime particles dispersed uniformly within the grains.
• the process may also precipitate the delta and eta equilibrium phases (Ni Cb and Ni -,Ti) in the
• the slow cooling rate should be controlled sufficiently to avoid having the alloy at high elevated temperature for excessively long periods of time that would result in detrimental grain growth or excessive overaging. And, of course, production economy negates extending the heat-treatment time beyond benefit. Accordingly, for most purposes the slow-cooling rate should be at least about 20F. per hour (F/Hr) and is advantageously at least 50F/Hr.
• the age-hardenable heat-resistant nickel alloys treated in the process of the. invention comprise, by weight, at least 2% metal from the group consisting of columbium, titanium and one-half the wt; of any tantalum, at least about 25% nickel, up to 60% iron with a total of at least 50% nickel-plus-iron, and are characterized by a solidus temperature of at least about 2,300F.
• Nickel is required for providing, inter alia, stability to the microstructure, including a stable austenite matrix; if the alloy does not contain sufficient nickel, detrimental phases, e.g., sigma, may be formed.
• Substantial amounts of chromium, e.g., 8% or advantageously 12% or more for corrosion resistance, can be present in the alloy.
• the process includes heat treatment of age-hardenable nickel-iron-chromium alloys, e.g., heat resistant alloys containing about 40% nickel, 40% iron, 15% chromium, 3% columbium, 1.7% titanium and 0.3% aluminum.
• the gamma-prime of the particles precipitated in the heat treatment is the Ni (Cb,Ta,Ti)' gamma-prime precipitate, which may also comprise other elements such as aluminum, e.g., Ni (Cb,Ti,Al).
• the solution temperatures are sufficiently high for enabling precipitable amounts of columbium, tantalum and/or titanium to enter into solid solution in practical solution treating times, e.g. /2 hour or 8 hours. Some columbium or titanium or other elements may be retained, possibly as carbides, without solution. Most of the solution temperatures are in a range of about 1,600F. to l,950F.
• the solution treatment is at 1,625F. to 1,700F. when the columbium-plus-titanium-plus-Vz tantalum content is 4% to 5.5% and is at 1,700F. to 1,800F. when the columbium-plus-titanium-plus-V2 tantalum content is 5.7% to 6.7%, and the time is sufficient to obtain a homogenous gamma phase solution, e.g., one-half hour or more.
• percentage summations of tantalum plus other gamma-prime forming elements, the weight percentage of tantalum present is multiplied by one-half (in view of the relatively high atomic weight of tantalum).
• the precipitation-hardening temperature range spans the temperature at which, for most commercial practices, strengthening precipitates of the gamma prime can be precipitated in the alloy, e.g., 4 hours to 48 hours at l,lF. to 1,800F.
• the coarse particles are precipitated in the upper one-third of the range and the fine particles are precipitated in the lower half of the range.
• the upper precipitation may be accomplished, and the coarse particles precipitated, by slow cooling through the precipitation range, provided that sufficient dissolved gamma-prime is retained for subsequently precipitating the fine particles.
• the present process precipitates essentially all of the dissolved columbium, titanium and tantalum, with at least about (by volume) of the gamma-prime in the coarse particle form and at least about 20% of the gamma-prime in the fine particle form.
• the process provides advantages of microstructural stability.
• Forms of the gamma-prime particles include plate-like, globular, and cubic shapes.
• the coarse particle sizes can be from about 0.04 to 1 micron and the fine particle sizes can be up to 0.1 micron, depending upon alloy composition. In the same alloy, the coarse particles are at least twice, usually five or ten times, the size of the fine particles.
• the alloy is cooled slowly from the solid solution'temperature down through the precipitation range and thereafter reheated for one or more treatments in the precipitation range to complete the gamma-prime precipitation.
• nickel-iron-chromium alloys containing 4% to 5.3% columbium-plus-titanium are cooled slowly, at rates in the range of 50F/Hr to 500F/Hr, from solid solution temperatures in the range of 1,625F. to 1,950F., down to l,l0OF. or lower and thereafter reheated at least once in the range of 1,100F. to 1,625F. to finish precipitation.
• An important feature of the invention is the provision of special embodiments whereby special benefits are achieved with heat treatments according to advantageously restricted ranges.
• advantageously long stress-rupture life in combination with good short-time tensile strength and ductility and good fabricability for welding or brazing are achieved with a triple-stage heat treatment of an age-hardenable nickel-iron-chromium alloy containing titanium, columbium, and aluminum according to a triple-stage treatment comprising: heating to a solid solution condition at least about 1,750F.
• slow-cooling at a rate of about 50F/Hr to 500F/Hr from the solid solution temperature to below the precipitation hardening range e.g., slow-cooling to 1,10'OF., and then cooling to room temperature at any desired rate, e.g., air cooling
• Another embodiment which is referred to herein as a twostage treatment, achieves good stress-rupture life and tensile strength and advantageously high ductility and also has advantages of production economy and fabricability with heat treatment of an age-hardenable nickel-iron-chromium alloy containing titanium, columbium and aluminum comprising: heating to a solid solution condition at a temperature of about ],675F. or higher; slow-cooling at a rate of 250F/Hr to 350F/l-lr from the solid solution temperature down through the precipitation-hardening range, e.g., down to l,100F., and then down to room temperature at any desired rate; and reheating to a precipitation temperature of about l,275 F. to l,425F.
• the heat treatment of the invention is generally applicable for improving the metallurgical characteristics, or obtaining at least acceptable strength and ductility characteristics while avoiding detrimental effects of more rapid cooling from solution temperature, e.g., embrittlement, cracking, warping or other structural distortion, in processing of agehardenable nickel alloys containing at least about 25% nickel, up to 60% iron, with a total of at least 50% nickel-plus-iron, up to 6.5% columbium and up to 5% titanium, up to 6% tantalum, with a total of at least 2% columbium-plus-titanium-plus-b-tantalum, up to 6.5% aluminum, provided the total of columbium, titanium, tantalum and aluminum does not exceed 10%, up to 2% vanadium, up to 25% chromium, advantageously 12% to 25% chromium, up to 30% cobalt, up to molybdenum or tungsten or mixtures thereof and up to 0.2% each of boron, zirconium and carbon.
• EXAMPLE I A nickel-iron alloy that had been hot rolled to ninesixteenths inch diameter bar was obtained in the hotrolled condition. Analyzed chemical composition of the alloy (Alloy 1) was 41.92% nickel, 16.28% chromium, 2.96% columbium, 1.90% titanium, 0.33% aluminum, 0.03% carbon, 0.003% boron, 0.14% manganese, 0.04% silicon, 0.01% copper, 0.001% sulfur and balance iron. (Percentage amounts of columbium referred to herein may include small incidental amounts of tantalum.) A specimen (Specimen 1) of the bar of alloy 1 in the hot-rolled condition was heated to the solid-solution condition by heating one hour at 1,800F. and was then slowly cooled directly from the 1,800F.
• specimen 1 was precipitation heat treated at 1,325F. for 8 hours, furnace cooled at a rate of 100F/1-1r to 1,150F., for 8 Hrs. and then air cooled to room temperature.
• Metallurgical examination of the thus heattreated specimen 1 showed the heat treatment had precipitated gamma-prime as coarse particles of about 3 (UTS), tensile elongation as percent along 10inch gage length (E1) and reduction of area across .252 inch EXAMPLE 11 l0-solution temperature to 1,100F.
• Table l Also shown in Table l are the results of comparable testing of the same alloy composition when treated by two different heat treatments, A and B, that are contrary to the invention.
• Two other specimens, A and B, of the nine-sixteenth-inch diameter hot rolled bar stock of alloy 1 were heat treated by solution treating one hour at 1,800F. and air cooling to room temperature (which caused an average cooling rate of about 22,250F. per hour between 1,800F. and 1,100F). Then, in treatment A the air-cooledalloy was further treated according to the precipitation heat treatment that followed the slow cooling of Specimen 1 in Example 1, and in treatment B the air-cooled alloy was fur-' ther treated according to the intermediate and precipitati on treatments that followed the slow cooling of the specimens in Example 11.,
• RA diameter gate section
• stress-rupture test results of life in hours, elongation and reduction of area are set forth in the following Table 1.
• Stress-rupture test result were obtai e d w it h a rn ooth section diameter characteristics.
• this example wherein the rate of cooling from solid solution was controlled within a range of 250F/Hr to 350F/Hr provides a good combination of tensile strength, stress-rupture strength and ductility and offers the production economy of the shorter two-stage treatment.
• Treatment II it is evident that superior stress-rupture life along with desirable levels of tensile strength and ductility was obtained with the three-stage treatment, especially with cooling rates of 100F/Hr to 200F/Hr.
• the invention has been exemplified herein with the specific composition of alloy 1, it is contemplated that the heat treatment be performed with many other alloys having compositions within ranges herein provided and be beneficial for obtaining improved metallurgical characteristics, particularly including advantageously good ductility, and also enhanced stressrupture life and other desirable characteristics mentioned hereinbefore.
• the invention is considered applicable in heat treatment of alloys 2 to 21 'having the nominal compositions set forth, below the nominal composition of alloy 1, in the following Table ll.
• a process of heat treating an age-hardenable heatresistant nickel alloy consisting essentially of at least about 25% nickel and up to 60% iron, with a total of at least 50% nickel-plus-iron, and precipitable amounts of gamma-prime forming metal selected from the group consisting of up to 6.5% columbium, up to titanium and up to 6% tantalum and mixtures thereof with a total of at least 2% columbium-plus-titanium-plus-Vz tantalum up to 6.5% aluminum, the total of the columbium content plus the titanium content plus the aluminum content plus one-half the tantalum content does not exceed up to 2% vanadium, up to chromium, up to cobalt, up to 10% molybdenum, tungsten or mixtures thereof, up to 0.2% boron, up to 0.2% zirconium and up to 0.2% carbon and characterized by a solidus temperature of at least about 2,300F., a gamma-prime solvus temperature of at least 1600F. and a gamm
• the present invention is particularly applicable in the gamma-prime forming metal in Solid Sol t o b. production of nickel-iron alloy products and articles cooling the alloy from the solid solution temperafor use where strength and ductility are required in ture down to the gamma-prime solvus temperature; structures, includng welded structures, engines and c. then slowly cooling the alloy uniformly at a conother machines, and in articles, including components trolled cooling rate of at least about 20F. per hour of machines, e.g., gas turbine blades, and is specially and not greater than 500F.
• the invention is useful in the protemperature in the precipitation range to precipiduction of turbine shafts and cases, diffuser cases, comtate coarse patches of gamma-prime in the vicinity pressor discs and shafts and fasteners.
• a process as set forth in claim 2 wherein the slowcooling rate is in the range of 100F. per hour to 200F. per hour.
• the solid solution temperature is at least about 1,675F.
• the alloy is slow cooled from the solid solution temperature down through the precipitation hardening temperature at a rate in the range of 250F. per hour to 350F. per hour and is thereafter further heat treated by reheating at about 1,275F. to l,425F. for about I to 24 hours, then cooling at a rate of about 20F. per hour to 200F. per hour to a range of about l,lO0F. to 1,200F. and holding at about l,l00F. for at least 5 hours.
• the alloy contains about 39% to 44% nickel, 14.5% to 17.5% chromium, 1.5% to 2% titanium, 2.5% to3.3% columbium, 0.05% to 0.4% aluminum, up to 0.06% carbon, up to 0.35% manganese, up to 0.35% silicon, up to 0.006% boron and balance essentially iron.
• Line 57 (line 35 of claim. 1) f r "or read --and--.

Landscapes

• Chemical & Material Sciences (AREA)
• Physics & Mathematics (AREA)
• Thermal Sciences (AREA)
• Crystallography & Structural Chemistry (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Turbine Rotor Nozzle Sealing (AREA)
• Heat Treatment Of Nonferrous Metals Or Alloys (AREA)
• Heat Treatments In General, Especially Conveying And Cooling (AREA)

Priority Applications (3)

Applications Claiming Priority (1)

Publications (1)

Family

ID=23531957

Family Applications (1)

Country Status (3)

Cited By (42)

Families Citing this family (7)

Citations (8)

• 1973
  • 1973-08-13 US US387944A patent/US3871928A/en not_active Expired - Lifetime
• 1974
  • 1974-03-20 CA CA195,530A patent/CA1014834A/en not_active Expired
  • 1974-05-08 JP JP49051072A patent/JPS5039620A/ja active Pending

Patent Citations (8)

Also Published As

Similar Documents