Classifications

• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C19/00—Alloys based on nickel or cobalt
  • C22C19/07—Alloys based on nickel or cobalt based on cobalt
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
  • C22B9/00—General processes of refining or remelting of metals; Apparatus for electroslag or arc remelting of metals
  • C22B9/003—General processes of refining or remelting of metals; Apparatus for electroslag or arc remelting of metals by induction
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
  • C22B9/00—General processes of refining or remelting of metals; Apparatus for electroslag or arc remelting of metals
  • C22B9/006—General processes of refining or remelting of metals; Apparatus for electroslag or arc remelting of metals with use of an inert protective material including the use of an inert gas
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
  • C22B9/00—General processes of refining or remelting of metals; Apparatus for electroslag or arc remelting of metals
  • C22B9/04—Refining by applying a vacuum
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
  • C22B9/00—General processes of refining or remelting of metals; Apparatus for electroslag or arc remelting of metals
  • C22B9/16—Remelting metals
  • C22B9/18—Electroslag remelting
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
  • C22B9/00—General processes of refining or remelting of metals; Apparatus for electroslag or arc remelting of metals
  • C22B9/16—Remelting metals
  • C22B9/20—Arc remelting
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C1/00—Making non-ferrous alloys
  • C22C1/02—Making non-ferrous alloys by melting
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C1/00—Making non-ferrous alloys
  • C22C1/02—Making non-ferrous alloys by melting
  • C22C1/023—Alloys based on nickel
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C19/00—Alloys based on nickel or cobalt
  • C22C19/03—Alloys based on nickel or cobalt based on nickel
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C19/00—Alloys based on nickel or cobalt
  • C22C19/03—Alloys based on nickel or cobalt based on nickel
  • C22C19/05—Alloys based on nickel or cobalt based on nickel with chromium
  • C22C19/051—Alloys based on nickel or cobalt based on nickel with chromium and Mo or W
  • C22C19/055—Alloys based on nickel or cobalt based on nickel with chromium and Mo or W with the maximum Cr content being at least 20% but less than 30%
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C19/00—Alloys based on nickel or cobalt
  • C22C19/03—Alloys based on nickel or cobalt based on nickel
  • C22C19/05—Alloys based on nickel or cobalt based on nickel with chromium
  • C22C19/051—Alloys based on nickel or cobalt based on nickel with chromium and Mo or W
  • C22C19/056—Alloys based on nickel or cobalt based on nickel with chromium and Mo or W with the maximum Cr content being at least 10% but less than 20%
• • 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
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
  • Y02P10/00—Technologies related to metal processing
  • Y02P10/25—Process efficiency

Definitions

• the present disclosure relates to multi-step methods for melting and refining superalloys and other alloys.
• the present disclosure also is directed to alloys prepared and refined using the multi-step melting and refining methods described herein, as well as to mill products and manufactured products including the alloys. DESCRIPTION OF THE BACKGROUND OF THE TECHNOLOGY
• a method of melting and refining an alloy comprises a vacuum induction melting (VIM) step, an electroslag remelting (ESR) step, and first and second vacuum arc remelting (VAR) steps.
• VIM vacuum induction melting
• ESR electroslag remelting
• VAR vacuum arc remelting
• At least a portion of the electroslag remelted ingot is vacuum arc remelted in a first vacuum arc remelted operation to provide a vacuum arc remelted ingot. At least a portion of the vacuum arc remelted ingot is vacuum arc remelted in a second vacuum arc remelting operation to provide an ingot of double vacuum arc remelted alloy.
• a method of melting and refining an alloy comprises: vacuum induction melting starting materials to provide a vacuum induction melted alloy; electroslag remelting at least a portion of the vacuum induction melted alloy to provide an electroslag remelted alloy; vacuum arc remelting at least a portion of the electroslag remelted alloy to provide a singly vacuum arc remelted alloy; and vacuum arc remelting at least a portion of the singly vacuum arc remelted alloy to provide a doubly vacuum arc remelted alloy.
• the vacuum induction melted alloy comprises primarily one of vanadium, chromium, manganese, iron, cobalt, nickel, copper, niobium, molybdenum, technetium, ruthenium, rhodium, palladium, silver, tantalum, tungsten, rhenium, osmium, iridium, platinum, and gold.
• a method of melting and refining an alloy comprises: vacuum induction melting starting materials to provide an alloy; electroslag remelting at least a portion of the alloy to provide a first ingot; vacuum arc remelting at least a portion of the first ingot to provide a second ingot; and vacuum arc remelting at least a portion of the second ingot.
• the alloy comprises primarily one of vanadium, chromium, manganese, iron, cobalt, nickel, copper, niobium,
• Figure 1 is a graph illustrating oxide area per unit mass for electron beam button melt testing on Alloy 718 using VIM only and sequences of VIM-ESR and VIM-ESR-VAR (triple melt);
• Figure 2 is a graph illustrating oxide quantity (ppm) for button melt testing on Alloy 718 for VIM only, VIM-ESR, and VIM-VAR routes;
• Figure 3 is a flow diagram of a non-limiting embodiment of a method of melting and refining an alloy according to the present disclosure.
• VIM vacuum induction melting
• ESR electroslag remelting
• An alternate melting and refining method used to produce nickel base superalloy for turbine components consists of steps of vacuum induction melting (VIM), followed by electroslag remelting (ESR), and then followed by vacuum arc remelting (VAR).
• VIM + ESR + VAR processing route is commonly referred in the industry as the triple-melt process.
• the triple melt process combines a VIM operation for basic melting and refining of the charge materials, an ESR operation that reduces oxide inclusions, and a final VAR operation to minimize segregation of alloying elements.
• VIM-ESR, VIM-VAR, and VIM-ESR-VAR triple melt sequences in refining the nickel base superalloy Alloy 718 (UNS N07718) can be seen in the Figures 1 and 2, which appear in Moyer et al., "Advances in Triple Melting Superalloys” (1994).
• Figure 1 plots the oxide area per unit mass for electron beam button melt testing on Alloy 718 using VIM only and sequences of VIM-ESR and VIM-ESR-VAR (triple melt).
• Figure 1 shows a reduction in oxide content of over 50% for a triple melt sequence relative to a VIM-ESR sequence.
• Figure 2 plots oxide quantity (ppm) for button melt testing on Alloy 718 for VIM only, VIM-ESR, and VIM- VAR routes, and shows that an ESR operation is signficantly more effective than VAR at reducing oxide inclusion incidence in Alloy 718.
• These oxide segregates can render the alloy unsuitable for fabrication into turbine disk components and other high performance parts.
• the segregates form an interface in the alloy that can be detected during ultrasonic inspection after billet conversion.
• the segregates may carry into the final part and be a cause for rejection of a component during final part inspection. The deficient billet or finished part is then scrapped, reducing yield and increasing production costs.
• VIM + VAR + VAR In the production of certain steel alloys requiring extremely high cleanliness, a melting and refining process with the sequence VIM + VAR + VAR has been used. When remelting steel alloys, the alloys' high melting point results in a relatively deep melt pool on the top of the forming VAR ingot. This allows the molten material additional residence time, permitting oxide inclusions to float to the surface as a result of the density difference with the base alloy.
• a VIM + VAR + VAR sequence has not been adapted for use with nickel base superalloys. Nickel base superalloys generally have a shallower melt pool during VAR melting when compared to steel alloys.
• An objective of the present invention is to reduce the incidence of residual oxides, as well as carbide and carbonitride agglomerations associated with, for example, crucible contaminants in nickel base superalloys.
• titanium melt process utilizes a welded electrode of sponge material and scrap material.
• This primary electrode can contain nitrides which readily form with titanium or melt contaminants such as TiN tool bits used in machining. Since the primary melt step in titanium production is typically a VAR operation of this composite electrode, such inclusions can be trapped in the solidifying pool. The multiple melt steps are utilized to progressively dissolve any retained material during the progressive operation.
• titanium readily accepts oxides into solution and it can be utilized as an alloy strengthener in many cases.
• the original melt is a vacuum induction melt in which nitrides would be put into solution during the primary melt operation. Oxides typically form a slag or can be entrained in the melt stream during pouring. Therefore, the remelt operations in the production of nickel base alloys are directed at physically removing oxides rather than putting them in solution.
• a nickel base alloy is provided by an improved melting and refining sequence including a VIM operation followed by an ESR operation, and then followed by two sequential VAR operations.
• Figure 3 is a flow diagram schematically illustrating this sequence.
• the sequence may be referenced by the shorthand VIM + ESR + VAR + VAR, and may be referred to as a "quadruple melt” process herein, terminology that fundamentally contrasts it with a triple melt sequence, as well as with double melt sequences.
• the terminal (final) vacuum arc remelt operation of the quadruple melt process may further reduce the incidence of oxide, carbide, and carbonitride segregates in the alloy.
• Nickel base superalloys for example, made using the quadruple melt sequence according to the present disclosure have been observed to exhibit a reduced incidence of oxide, carbide, and carbonitride segregates, and may be used in critical components such as, for example, turbine disk components.
• the final VAR melt operation of the quadruple melt sequence provides a means to remove clusters of secondary phases such as oxides, and clusters of carbides and carbonitrides that can become entrapped in an ingot product during prior melt operations.
• the oxides and secondary phase clusters typically are small and infrequent.
• Utilizing an ingot prepared by a VIM + ESR + VAR sequence as an electrode for the terminal VAR operation provides a relatively metallurgically clean starting stock which is further refined during the terminal VAR operation.
• the terminal VAR operation may be conducted so that the content of elements having a relatively low vapor pressure is controlled.
• Such elements include, for example, magnesium, and potentially other elements that may provide the alloy with material properties important both in subsequent forming operations and in final applications.
• the quadruple melt process according to the present disclosure may improve the final integrity of the product and may refine alloy chemistry, without
• FIG. 3 illustrates a non-limiting embodiment 100 of a quadruple melt sequence.
• the VIM operation 102 of the quadruple melt sequence 100 involves induction melting charge materials to provide a partially refined alloy that may be used as an electrode for the following ESR operation.
• the VIM operation may be conducted in a conventional manner as known to those having ordinary skill to produce as-cast electrodes within required alloy specification ranges and having sufficient structural integrity to permit a stable remelt operation.
• the VIM operation uses induction coils to melt the raw material charge inside a refractory lined crucible.
• the charge materials may include, for example and without limitation, both prime material, such as relatively high purity (e.g., 99+%) elemental materials produced by refining an ore body, and recycled material such as machined turning revert cleansed of residual cutting fluid.
• the raw materials are selected and combined in proportions to ensure the resulting heat adheres to the desired alloy specification.
• the VIM operation is typically conducted under a vacuum lower than 100 microns or under a partial inert gas atmosphere when the alloy specification includes low vapor pressure elemental requirements.
• the VIM process concludes with a pouring operation in which the electrodes may be bottom poured through a central sprue and runner system or each electrode may be top poured individually.
• operations typically include a stripping operation to extract the electrode from the mold after solidification and may include a surface grinding operation depending on the subsequent remelt method employed.
• the ESR operation 104 of the quadruple melt sequence 100 involves electroslag remelting an electrode of the alloy prepared in the VIM operation 102.
• the ESR operation may be generally conducted in a
• the VIM electrode may require grinding before the ESR operation to remove loose surface scale if present.
• the alloy electrode may be welded to a non-consumable stub that includes a mating surface capable of transmitting, for example, at least 20 kW of electrical energy from the ESR furnace.
• the ESR process passes current through flux to melt the flux.
• the flux may be, for example, a CaF 2 -based flux that also includes significant CaO (10-40 wt%) and AI 2 O 3 (10-40 wt%) components.
• Additional oxides may be included in the flux in smaller concentrations to ensure flux chemistry compatibility with the remelting electrode and to minimize any gain or loss of reactive elements to the flux.
• Other oxides that may be employed in the flux include La 2 03, MgO, SiO 2 , TiO 2 , and ZrO 2 .
• the electrode is immersed in the molten ESR flux, which transfers sufficient heat to melt the electrode tip.
• the immersion depth of the electrode into the flux is typically 6-12 mm and is controlled in a conventional manner, for example, through either a resistance swing or voltage swing automatic control loop.
• the control loop may measure the offset of the resistance or voltage swing from the set point and adjust the electrode position in the proper direction to maintain the desired set point corresponding to the immersion depth.
• the ESR second control loop either melts at a constant current set point or utilizes load cells to measure a melt rate per unit time. If employing melt rate control, the applied current may be adjusted to maintain the desired melt rate set point.
• the first VAR operation 106 of the quadruple melt sequence 100 involves vacuum arc remelting an electrode of the alloy prepared in the ESR operation 104.
• the first VAR operation 106 may be generally conducted in a conventional manner as known to those having ordinary skill.
• the VAR electrode may require grinding to remove ESR flux entrapped in the extreme surface layer.
• the electrode may be welded to a non- consumable stub that includes a mating surface capable of transmitting, for example, at least 15 kW of electrical energy from the VAR furnace.
• the VAR process passes current between the electrode and the resulting molten ingot forming directly below.
• the startup of the process passes current directly to a baseplate, such as, for example, a water-cooled copper baseplate.
• the copper baseplate does not melt because its high thermal conductivity rapidly transmits the resulting heat energy into the cooling water, so that the baseplate temperature does not exceed the melting temperature of copper.
• the VAR process typically maintains a relatively constant and conventional standoff distance (arc gap) of, for example, 6-12 mm between the electrode tip and the molten ingot top.
• a standoff distance control loop automatically measures voltage and adjusts the electrode position in the proper direction to maintain a set point corresponding to the desired standoff distance.
• a VAR second control loop either melts at a constant current set point or utilizes load cells to measure a melt rate per unit time.
• the second VAR operation 108 of the quadruple melt sequence 100 involves vacuum arc remelting an electrode of the alloy prepared in the first VAR operation 106.
• the second VAR operation 108 may be generally conducted in a conventional manner as known to those having ordinary skill.
• the second VAR operation is conducted in the same manner as the first VAR operation. Surface grinding of the first VAR ingot may be required to remove oxides present on and near the surface that accumulated during the first VAR operation.
• the same control loops and methodology are applied to the second VAR step to control standoff and melting current and/or melting rate.
• the alloy composition dictates the segregation tendency, which in turn restricts the solidification conditions required to avoid the presence of deleterious phases.
• Deleterious phases may include, for example, zones of an abnormally high fraction of carbide precipitation and/or precipitation of topologically close packed (TCP) phases which generally act as stress concentrators that reduce the local ductility of the material.
• TCP topologically close packed
• the combination of arc gap and melt rate may be controlled within minimum and maximum ranges, which are alloy composition dependent, to control the solidification rate within a range to produce a structure without an excessive fraction of deleterious phases.
• an inert gas may be introduced into the gap between the copper crucible and the VAR ingot that occurs due to shrinkage associated with the solidification and cooling of the VAR ingot.
• the thermal conductivity of the inert gas may be orders of magnitude higher than the thermal conductivity of the vacuum that would otherwise exist in the gap.
• the present quadruple melt method may be used with any alloys whose base element or primary constituent is any of vanadium, chromium, manganese, iron, cobalt, nickel, copper, niobium, molybdenum, technetium, ruthenium, rhodium, palladium, silver, tantalum, tungsten, rhenium, osmium, iridium, platinum, and gold.
• an element is the "primary constituent" of an alloy if the element's weight percentage exceeds that of each other element in the alloy.
• a non-limiting list of specific commercially significant alloys that may be processed using the quadruple melt method of the present disclosure include: nickel base alloys and superalloys, including, for example, Alloy 718 (UNS N07718), Alloy 720 (UNS
• Rene 65 alloy cobalt base alloys and superalloys, including, for example, L605 alloy (UNS R30605); nickel-cobalt base alloys, including, for example, MP35N alloy (UNS R30035); and nickel-chromium-molybdenum alloys, including, for example, C-22 alloy (UNS N06022).
• L605 alloy UNS R30605
• nickel-cobalt base alloys including, for example, MP35N alloy (UNS R30035)
• nickel-chromium-molybdenum alloys including, for example, C-22 alloy (UNS N06022).
• the composition of each of those alloys is well known and is provided in the following table (the alloys also may include incidental impurities).
• Embodiments of the method according to the present disclosure may improve alloy cleanliness, leading to an increase in property performance where microstructural discontinuities are detrimental.
• the resistance to fatigue failure is an example of a mechanical property that will benefit from improved alloy cleanliness.
• Improved alloy cleanliness may improve fatigue properties by enhancing the resistance to crack initiation and/or the propagation of existing cracks.
• Corrosion is another property whose performance may be enhanced by a lower rate of
• microstructural discontinuities The commercial 718, 720, and Rene 65 alloys are currently processed by the triple melt method of VIM + ESR + VAR to provide material in, for example, aerospace turbine engine cores as engine disks.
• the present inventors believe that the fatigue performance of these alloys may be enhanced if processed according to the method of the present disclosure, enabling a longer service life of engine components made of the alloys, or permitting a lighter weight part while maintaining the current service life.
• Alloys such as C-22 alloy and MP35N alloy are often utilized in extreme corrosion environments in which enhanced alloy cleanliness could improve alloy performance. This is particularly so for pitting corrosion performance, where a microstructural discontinuity can initiate the corrosion reaction.
• the method involves a VIM + ESR + VAR + VAR sequence.
• the initial VIM step preferably is conducted in a conventional manner under a vacuum level less than 100 microns of pressure to allow for no more than minimal atmospheric contamination, inhibiting or preventing the excessive pickup of nitrogen.
• Electrodes produced in the VIM step are ground to reduce surface oxide content.
• An ESR operation using the electrodes is conducted in a conventional manner to provide a melt rate range of 6-20 pounds per minute.
• the ingot produced in the ESR step is conditioned by grinding to remove the ESR flux from the ingot's surface, before proceeding to a first VAR step.
• the first VAR step preferably is ideally conducted with a vacuum level less than 20 microns of pressure to allow for only minimal atmospheric contamination, an arc gap in the 6-12 mm range, and a melt rate in the 6-20 pounds per minute range.
• the first VAR ingot produced in this step may be conditioned by grinding to remove the ingot's surface layer, which contains higher oxide content than the ingot interior.
• the first VAR ingot is used as the electrode for a second VAR step.
• the second VAR step preferably is conducted with a vacuum level less than 20 microns of pressure to allow for only minimal atmospheric contamination, an arc gap in the 6-12 mm range, and a melt rate in the 6-20 pounds per minute range.
• a larger diameter ingot for example, 2-4 inches larger in diameter than the
• Alloy 718 may be produced by the method so as to provide a 14 inch VIM ingot, a 17 inch ESR ingot, a 20 inch VAR (first VAR step) ingot, and then a 22 inch VAR (second VAR step) ingot.
• Alloy 718 may be produced by one non-limiting embodiment of the method so as to provide a 36 inch VIM ingot, a 40 inch ESR ingot, then an
• the method involves a VIM + ESR + VAR + VAR sequence.
• the initial VIM step preferably is conducted in a conventional manner under a vacuum level less than 100 microns of pressure to allow for no more than minimal atmospheric contamination, inhibiting or preventing the excessive pickup of nitrogen.
• the electrodes produced in the VIM step may be ground to reduce surface oxide content.
• ESR is conducted in a conventional manner with the electrodes produced from the VIM operation using a melt rate range of 6-20 pounds per minute.
• the ingot produced in the ESR step is conditioned by grinding to remove ESR flux from the ingot's surface, and the ingot is then subjected to a first VAR step.
• the first VAR step preferably is conducted with a vacuum level less than 20 microns of pressure to allow for only minimal atmospheric contamination, an arc gap in the 6-12 mm range, and a melt rate in the 6-20 pounds per minute range.
• the first VAR ingot may be conditioned by grinding to remove the ingot's higher oxide surface layer, and the ingot is then used as the electrode for a second VAR step.
• the second VAR step preferably is conducted with a vacuum level less than 20 microns of pressure to allow for only minimal atmospheric contamination, an arc gap in the 6-12 mm range, and a melt rate in the 6-9 pounds per minute range (Alloy 720 has a higher segregation tendency than Alloy 718).
• a larger diameter ingot (for example, 2-4 inches larger in diameter than the preceding ingot) is produced in each successive stage of the VIM + ESR + VAR + VAR sequence to maximize industrial efficiency, but a forgeback may be used between stages when necessary to accommodate equipment limitations.
• the forgeback will homogenize the prior ingot at, for example, 2175°F (1190°C) for a minimum of 24 hours, before forging to an appropriate smaller diameter.
• Alloy 720 may be produced by the method so as to provide an 18 inch VIM ingot, a 20 inch ESR ingot, a 22 inch VAR (first VAR step) ingot, and then a 24 inch VAR (second VAR step) ingot.
• Alloy 720 may be produced by the method so as to provide a 24 inch VIM ingot, a 26 inch ESR ingot, then an
• the method involves a VIM + ESR + VAR + VAR sequence.
• the initial VIM step preferably is conducted in a conventional manner under a vacuum level less than 100 microns of pressure to allow for no more than minimal atmospheric contamination, inhibiting or preventing the excessive pickup of nitrogen, and the electrodes produced in the VIM step are ground to reduce surface oxide content.
• the electrodes produced in the VIM step are subjected to ESR using a melt rate range of 6-20 pounds per minute.
• the ingot produced in the ESR step is surface ground to remove ESR flux from the ingot's surface, and the ingot is then subjected to a first VAR step.
• the first VAR step preferably is conducted with a vacuum level less than 20 microns of pressure to limit atmospheric contamination, an arc gap in the 6-12 mm range, and a melt rate in the 6-20 pounds per minute range.
• the first VAR ingot may be conditioned by grinding to remove the ingot's higher oxide surface layer, and the ingot is used as the electrode for a second VAR step, which preferably is conducted with a vacuum level less than 20 microns of pressure to allow for only minimal atmospheric
• a larger diameter ingot (for example, 2-4 inches larger in diameter than the preceding ingot) is produced in each successive stage of the VIM + ESR + VAR + VAR sequence to maximize industrial efficiency, but a forgeback may be used between stages when necessary to accommodate equipment limitations.
• the forgeback will homogenize the prior ingot at, for example, 2175°F (1 190°C) for a minimum of 24 hours before forging to an appropriate smaller diameter.
• MP35N alloy may be produced by the method so as to provide an 18 inch VIM ingot, a 20 inch ESR ingot, a 22 inch VAR (first VAR step) ingot, and then a 24 inch VAR (second VAR step) ingot.

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