Classifications

• • 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
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
  • C22C38/48—Ferrous alloys, e.g. steel alloys containing chromium with nickel with niobium or tantalum
• • 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
• • 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
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
  • C22C38/44—Ferrous alloys, e.g. steel alloys containing chromium with nickel with molybdenum or tungsten

Definitions

• the present invention relates to high temperature alloys and, more particularly, to nickel-iron-chromium alloys of novel composition which, because of their high tensile and stress-rupture strengths, good tensile ductility and corrosion resistance, and an unique ability to provide improved high temperature stability upon exposure to elevated temperatures over extended periods, are particularly suited for use as superheater tubes in steam power stations, heat exchangers or for other high temperature applications.
• high temperature alloys of the nickel-iron-chromium type are useful for a variety of commercial applications since they manifest a desired combination of metallurgical properties, including good stress-rupture characteristics, tensile ductility, corrosion resistance, etc. It is also well known that certain high temperature applications require alloys which exhibit one or more specific characteristics to an outstanding degree. For example, alloys used in steam power applications, e.g., super-heater tubes, heat exchangers and the like, must be particularly characterized by stability and freedom from embrittlement over long periods at high temperature. Steam temperatures in the neighborhood of 1000 F. to 1100 F., e.g., 1050 F., are in current use and stainless steels such as AISI 304 and 316, among other materials, have proven satisfactory.
• alloys suitable for this purpose should manifest the ability to absorb at least 50 foot-pounds of impact energy at room temperature after exposure at 1200 F. for about 1000 hours and at least 20 foot-pounds of impact energy at room temperature after exposure at 1200 F. for about 10,000 hours.
• the material to be used for such applications were also capable of withstanding 40,000 pounds per square inch (p.s.i.) stress for at least 1000 hours at 1200 F. Accordingly, there is a need to provide new alloys of relatively low cost capable of meeting the above objectives, but, in so doing, other mechanical characteristics must not be sacrificed.
• nickel-iron-chromium alloys containing special and correlated amounts of columbium, tungsten, molybdenum, titanium, aluminum and carbon provide outstanding long term stability while concurrently exhibiting good tensile ductility, stress-rupture life, corrosion resistance, etc.
• alloys within the invention Upon exposure to temperaice tures of the order of 1200 F. for at least 1000 hours alloys within the invention not only possess Charpy V-notch impact strengths of at least 50 foot-pounds but many alloys exhibit impact strengths of up to 100 footpounds or more.
• An object of this invention is to provide novel nickeliron-chromium alloys possessing a highly satisfactory combination of high strength, toughness, ductility and corrosion resistance after exposure to high temperatures for extended periods.
• Another object is to provide nickel-chromium-iron alloys possessing long term stability as evidenced by Charpy V-notch impact strengths greater than 50 foot-pounds and preferably in excess of 75 foot-pounds after exposure to elevated temperatures for prolonged periods.
• Another object is to provide nickel-iron-chromium alloys especially adapted to high temperature use as, for example, superheater tubing in steam power stations, heat exchangers and the like.
• alloys contemplated herein characterized by long term stability upon exposure to high temperature for extended periods contain (in percent by weight) about 34% to 40% nickel, about 15% to about 19% chromium, about 0.25% to 2% columbium, at least one metal selected from the group consisting of tungsten and molybdenum in an amount of up to 3.5% each, the sum of the columbium, tungsten and molybdenum being at least 1.25%, advantageously at least 2%, and not greater than about 6%, up to about 0.75% titanium, up to about 0.75% aluminum and, advantageously, from 0.35% to about 0.75 titanium or aluminum or both, up to about 0.08% carbon, up to about 0.015% boron, up to about 0.75%, e.g., up to 0.3%, silicon, up to about 4%, e.g., up to 1%, manganese, and the balance essentially iron.
• the aforedescribed alloys should contain from 0.5% to 1.5% columbium and at least 2.5% of metal from the group consisting of tungsten and molybdenum. It is to advantage that both tungsten and molybenum are present in amounts of at least 0.5 and up to 3% each.
• the nickel content not fall below about 34% in order to minimize or preclude formation of sigma phase, a phase which detracts from strength, toughness and stress-rupture properties.
• the other constituents i.e., chromium, columbium, tungsten, molybdenum, etc., which are useful as strengtheners must be balanced with suflicient nickel, beneficially at least 36% nickel, to avoid poor stability after long time exposure at intermediate temperatures, say, 1200 F. to 1400 P.
• nickel contents above 40% raise the cost of the alloy without appreciably increasing the strength, toughness or ductility.
• a total of at least 1.25%, preferably 2%, of columbium, tungsten and molybdenum is necessary for sufiicient yield and stress-rupture strengths.
• tungsten and molybdenum should be copresent and in this regard the more advantageous alloys contain from 1% to 3% of each.
• the upper limit of tungsten or molybdenum or any combination thereof should not exceed 3.5%, while columbium should not be present in amounts in excess of 2% and preferably not above 1.5%.
• columbium plus tungsten plus molybdenum not exceeding 5.5% or 5.25% markedly contributes to retention of a high level of toughness.
• columbium contains up to about 10% tantalum, the values reported for columbium include up to about 10% thereof as tantalum.
• the alloys contain at least 0.35% of each of the constituents titanium and aluminum in order to achieve both good room and elevated temperature strength characteristics.
• the presence of titanium or aluminum in amounts less than 0.35% decreases strength and stress-rupture life. If titanium or aluminum are present in amounts much above 0.75%, toughness is decreased although stress-rupture properties are enhanced.
• a total of from 0.35 to 1% of titanium and aluminum provides for an excellent combination of strength and toughness.
• Carbon should not exceed about 0.08% because of the tendency of the strengthening elements, chromium, tungsten, molybdenum and columbium, to form carbides which adversely affect stress-rupture strength and corrosion resistance. More specifically, with a total columbium plus tungsten plus molybdenum content of about 1.25% to 2.5%, the carbon content advantageously should not exceed about 0.03%. When this sum is from about 2.5% to about 3.5%, carbon can be increased up to 0.06% and when this correlation exceeds 3.5%, from 0.06% to 0.08% can be tolerated; however, it is much preferred to keep the carbon at a level not greater than 0.03%.
• a most advantageous alloy range in achieving optimum results in accordance with the invention is as follows: about 36% to about 39% nickel, about 16% to about 18% chromium, about 1% to 2% tungsten, about 1% to 2% molybdenum, about 0.7% to about 1% columbium, about 0.35% to 0.5% titanium, about 0.35% to 0.5% aluminum, carbon in an amount up to about 0.06%, up to 0.01% boron, e.g., from 0.005% to 0.01% boron, up to 0.3% silicon, up to 0.4% manganese, and the balance essentially iron.
• These alloys show marked ability to retain corrosion resistance, high strength, toughness and ductility after high temperature exposure for prolonged periods of time. Because of such characteristics, the alloys are eminently suitable for superheater tubes. Moreover, these alloys are easily fabricated by conventional methods.
• Alloys 1 through 4 (within the invention) and Alloys A and B (outside the invention) were vacuum melted (except No. 4 which was air melted), and were then cast into 30 pound ingots, the ingots being then soaked one hour at 2150 -F. and thereafter forged to 1 /2 inch square billets. The billets were then cut into quarters (to minimize the effect of segregation) to produce inch square bars which were annealed at 2000 F. for one hour and then cold rolled to /3 inch square pieces.
• Treatment I solution annealing at 1800 F. for about one hour followed by air cooling
• Treatment 11 solution heating at 1800 F. for about one hour, air cooling, and then exposing the alloys for 1000 hours at 1200 F. followed by air cooling.
• Trcatoflset U.T.S., Elong., R.A., C.V.N., Alloy mcnt p.s.i. p.s.i. percent percent ft.lbs.
• the alloys of the present invention are characterized by substantial freedom from severe embrittlement upon long time exposure to elevated temperatures, they are particularly suitable as superheater tubes, heat exchangers, components, etc.
• a nickel-chromium-iron alloy having an impact strength of at least 50 ft.-lbs. after exposure to a temperature of 1200 F. for about 1000 hours and a 1000 hour stress rupture strength of at least 40,000 p.s.i. at 1200 F.
• said alloy consisting essentially of about 34% to about 40% nickel, about to 19% chromium, about 0.5% to 2 %columbium, about 0.5% to 3% of tungsten, about 0.5% to 3% molybdenum, the sum of the columbium, tungsten and molybdenum being at least about 2.5% and not greater than about 6%, titanium and aluminum each being present in an amount up to 0.75% with the total percentage of titanium and aluminum being at least 0.35 up to about 0.06% carbon, up to about 0.015% boron, up to about 0.75% silicon, up to about 4% manganese, and the balance essentially iron.
• a novel nickel-chromium-iron alloy adapted for elevated temperature use having an impact strength of at least 50 ft.-lbs. after exposure to a temperature of 1200 F. for about 1000 hours and a 1000 hour stress rupture strength of at least 40,000 p.s.i. at 1200 F. and consisting essentially of about 34% to about 40% nickel, about 15 to 19% chromium, about 0.25% to 2% columbium, at least one metal from the group consisting of tungsten and molybdenum in an amount up to 3.5% tungsten and up to 3.5% molybdenum, the sum of the columbium,
• tungsten and molybdenum being at least 2.5% but not greater than about 6%
• titanium and aluminum each being present in an amount up to 0.75 with the total percentage of titanium and aluminum being at least 0.35 up to about 0.06% carbon, up to about 0.015% boron, up to 0.75% silicon, up to about 4% manganese, and the balance essentially iron.
• the alloy as set forth in claim 5 which consists essentially of 34% to 39% nickel, 15 to 19% chromium, at least 0.5% and up to 1.5% columbium, and from 1% to 3% molybdenum, the sum of the columbium plus molybdenum not exceeding 3.5%.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Heat Treatment Of Steel (AREA)

Priority Applications (9)

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Publications (1)

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Cited By (6)

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• 1966
  • 1966-07-14 US US565083A patent/US3592632A/en not_active Expired - Lifetime
• 1967
  • 1967-07-04 GB GB30801/67A patent/GB1135003A/en not_active Expired
  • 1967-07-11 AT AT647867A patent/AT276787B/de not_active IP Right Cessation
  • 1967-07-12 DE DE1608170A patent/DE1608170C3/de not_active Expired
  • 1967-07-13 SE SE10509/67A patent/SE351240B/xx unknown
  • 1967-07-13 ES ES342990A patent/ES342990A1/es not_active Expired
  • 1967-07-13 FR FR114401A patent/FR1531171A/fr not_active Expired
  • 1967-07-14 BE BE701379D patent/BE701379A/xx unknown
  • 1967-07-14 CH CH1009367A patent/CH477556A/fr not_active IP Right Cessation

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