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
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/10—Ferrous alloys, e.g. steel alloys containing cobalt

Definitions

• This invention relates to an improved alloy useful in electrical applications because of its magnetic properties. More particularly, the invention concerns an improved version of the cobalt, vanadium, iron alloy known commercially as, Vanadium Permendur. This alloy contains 47.5 to 50.5 cobalt, 1.7 to 2.1% vanadium and the balance essentially iron.
• the vanadium, cobalt and iron-containing alloy is finding increasing use as a rotor and stator material in electrical generators for aircraft because of its high magnetic flux carrying capacity which makes it possible to achieve a considerable reduction in weight of the units in which components of the alloy are employed.
• the material As a result of the high operating speeds, i.e., 8,000 to 20,000 rpm. of these generators, it is also important that the material have high mechanical strength as well.
• specific requirements may vary, some applications require a minimum .2% ofiset yield strength of 70,000 p.s.i. coupled with the minimum tensile elongation of 5% and relatively little deterioration in magnetic properties.
• the presently commercial version of this alloy develops a yield strength of only approximately 55,000 p.s.i. when annealed for four hours at 1385 F., which is a standard pilot test procedure.
• the present invention provides a composition which possesses significantly improved strength while retaining satisfactory magnetic properties.
• an alloy consisting essentially of 47.5 to 50.5% cobalt, 1.7 to 2.1% vanadium, a controlled carbon content of 0.025 to 0.1%, preferably 0.03 to 0.08%, and the balance essentially iron.
• Larninations or strips made of alloys in accordance with the invention possess increased yield strength and relative insensitivity to normal variations in annealing conditions, i.e., temperature and time at temperature, and good ductility as well.
• alloys in accordance with the invention may be made which possess a minimum yield strength of 70,000 p.s.i. while retaining satisfactory magnetic properties.
• Vanadium Permendur contains less than 0.02% carbon and usually less than 0.01% carbon. I have found that when the carbon is increased to the range of 0.025 to 0.1%, the yield strength of the alloy is materially improved. Oarbon contents above about 0.1% result in relatively little additional refinement of recrystallized grain size and, hence, relatively little strength increase. The additional carbide particles formed by increasing the carbon concentration to greater than 0.1% have a disproportionately harmful etfect on magnetic properties particularly the alternating current properties. As the examples below indicate, in the fully recrystallized condition, the yield strength for Co-V-C-Fe alloys increases only slightly with increasing carbon content up to a threshold concentration of about .020% carbon.
• Yield strength then increases very rapidly with increasing carbon content up to a concentration in the range .025.030% carbon. As carbon is increased above this level yield strength again increases rather gradually.
• the yield strength level attained in the range .025.030% carbon is approximately 70,000 p.s.i.
• Alloys of the composition described in Table I were prepared in ingot form and reheated to 2250 F., thereafter hot rolled to 0.080-inch thickness.
• the resulting hot rolled strip was annealed at 1450 F. and brine quenched to render it suificiently ductile for cold rolling. It was determined metallographically that. the grain size of the quenched 0.080-inch strip containing 0.028% or more carbon was distinctly finer than that of the 0.0045 carbon material.
• sample sections of the annealed and quenched 0.080inch strip from each of the four heats were cold rolled to 0.014" and 0.010" respectively, without intermediate heat treatment. This processing duplicated as nearly as possible the practices used in the commercial production of Vanadium Permendur.
• Ring samples (1'' ID. X 1 /2" 0.1).) and tensile test specimens were prepared from the cold rolled experimental strip and similarly from the 0.014" and 0.010" strip, representing commercially available Vanadium Permendur (the latter designated heat 73205 and 82228 respectively).
• the 0.014" test samples were batch annealed (stacked laminations and tensile specimens in a welded box) at various temperatures in the range 1300 to 1550 F. and for various times in dry hydrogen (dew point of hydrogen supply was F. or dryer).
• the 0.010 samples were continuously annealed, singly and without stacking, in a belt furnace for 10 minutes at 1400 F., 1450 F. and 1500 F. in dry hydrogen atmosphere having a dew point of about 20 F.
• Tables II and III illustrate that, in the fully recrystallized condition, the materials containing 0.028% or more carbon have satisfactory and acceptable magnetic properties but at substantially higher strength levels than the materials containing less than 0.028% carbon. Similar structures and properties can be developed in short time heat treatments (10 minutes at temperature) by continuous annealing.
• a useful increase in the yield strength of Vanadium Permendur can be obtained by a deliberate increase in the carbon content of the alloy.
• An increase in carbon concentration to higher than normal levels, i.e., greater than 0.020% carbon results in the formation during processing of second phase particles, presumed to be vanadium carbides, which are then present in sufficient number to decrease significantly the recrystallized grain size developed during the annealing of cold rolled Vanadium Permendur strip or laminations and which efiectively limit grain growth following recrystallization.
• the action of the second phase particles is such that the development of a stable fine-grained recrystallized structure is relatively insensitive to variations in annealing time and temperature.
• the second phase particles and the associate fine grain size act in combination to produce yield strengths which are substantially higher than those developed in the normal alloy by the same annealing conditions.
• the ductility of the recrystallized fine-grained structure as measured by elongation in a tensile test, is acceptable but somewhat lower than that of the normal alloy.
• the presence of second phase particles causes some deterioration in magnetic properties, the associated fine-grained structure is magnetically satisfactory.
• An important advantage of the invention is that the yield strength improvement associated with increased carbon concentration in Vanadium Permendur is attained in fully recrystallized structures in which grain growth following recrystallization is relatively limited. These characteristics greatly increase the range of annealing conditions which can be employed to realize the strength improvements. It is difficult to attain a strength increase in the conventional alloy by establishing a partially recrystallized or barely recrystallized structure, particularly with a batch heat treatment. In contrast, the fully recrystallized grain structure is relatively stable and, therefore, the yield strength of the higher carbon alloys, e.g., 0.055% carbon alloy, Heat 3837, remains high.
• the higher carbon alloys e.g., 0.055% carbon alloy, Heat 3837
• a low carbon aly (Heat 3835, .0045%C) and the normal commercial alloy (Heats 73205 and 82228) develop lower strengths in the fully recrystallized condition and show a greater tendency toward grain growth and loss of strength with increasing annealing temperature and time.
• the similarity of the yield strengths and magnetic properties developed by batch heat treatments (Table I) and by continuous annealing (Table II) further indicate the latitude in annealing conditions which may be employed to develop the strength improvements which are characteristic of alloys having controlled critical amounts of carbon in accordance with the invention.
• An improved cold worked and subsequently fully recrystallized alloy consisting essentially of 47.5 to 50.5% cobalt, 1.7 to 2.1% vanadium, the balance essentially iron and containing 0.025 to 0.10% carbon and having a yield strength of at least 70,000 p.s.i.'
• An improved alloy according to claim 1 having 0.03 to 0.08% carbon.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Soft Magnetic Materials (AREA)
• Hard Magnetic Materials (AREA)

Applications Claiming Priority (1)

Publications (1)

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ID=21947199

Family Applications (1)

Country Status (7)

Cited By (11)

• 1970
  • 1970-06-17 US US47126A patent/US3695944A/en not_active Expired - Lifetime
• 1971
  • 1971-06-08 CA CA115,052A patent/CA940344A/en not_active Expired
  • 1971-06-16 GB GB2813271A patent/GB1330543A/en not_active Expired
  • 1971-06-16 DE DE19712129930 patent/DE2129930A1/de active Pending
  • 1971-06-16 NL NL7108258A patent/NL7108258A/xx unknown
  • 1971-06-17 FR FR7122077A patent/FR2099174A5/fr not_active Expired
  • 1971-06-17 BE BE768665A patent/BE768665A/xx unknown

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