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

Definitions

• Another object of this invention is to provide a superior oxidation-resistant cobalt-base alloy in the form of wrought products.
• a further object of this invention is to provide cobaltbase alloys that have an optimum combination of high strength and resistance to embrittlement and oxidation.
• COnsistS essentially of about: 18 to 25 percent chromium, 11 to 15 percent tungsten, 1 6 to 25 percent nickel, 0.05 to 0.5 percent carbon, 0.001 to 0.025 percent boron balance cobalt and incidental impurities.
• the alloy of this invention may contain the usual impurities found in commercial alloys of this class, i.e. up to, about percent iron, about 1.5 percent molybdenum, about 1 percent manganese, about 0.75 percent silicon; and about 0.15 percent total phosphorous, sulfur, hydrogen, oxygen, and nitrogen. Table 1 shows alloy ranges and specific compositions in accordance with the present invention.
• alloys often called superalloys are especially suitable for service at high temperature except that they tend to embrittle after prolonged use at temperatures above about 1400" F.
• each alloy has certain outstanding individual characteristics, none by itself has the advantage of combined optimum characteristics of high strength, oxidation resistance and resistance to embrittlement.
• Alloy 1 is known to have outstanding, high temperature strength but its oxidation resistance is lower than that of Alloy 2.
• Alloy 2 has outstanding oxidation resistance but its high temperature strength is lower than that of Alloy 1. Up to the present such limitations had to be tolerated in the application of these superalloys.
• alloys of this invention provide an optimum combination of all the advantageous properties generally associated with this class of superalloys. As shown hereinbelow, the alloys of this invention have strengths equal to or higher than Alloy 1 and also have oxidation resistance characteristics approaching that of Alloy 2.
• chromium within the ranges shown in Table 1, provides oxidation resistance and contributes to high temperature strength; chromium contents below the indicated range are not sufiicient to provide adequate oxidation resistance while chromium contents above the indicated range tend to yield alloys of decreased dutility at room temperature.
• Tungsten is present in the alloy, within the indicated ranges, as a carbide former and in a solid solution matrix to provide high strength.
• Molybdenum is not substitutable for tungsten in the alloy of this invention, although molybdenum may be present as an unavoidable impurity up to not more than 1.5 percent by weight in the total alloy as previously noted.
• Carcon is required in the alloy within the range as indicated in Table 1 as a solid solution strengthening element and as a carbide former to provide high strength and nickel must be present in the alloy within the indicated ranges to provide adequate post aging ductility, oxidation resistance, and high temperature strength. Alloys containing less than 15.5 percent nickel tend to embrittle after prolonged use at temperatures between about 1400 F. and 1900 F.
• Manganese may be present in the alloy in amounts not loys 1 and 2, in addition Table 6 shows that the alloys of this invention have much better oxidation resistance than alloy 1 of the prior art.
• the oxidation tests of Table 6 were identical for all alloys tested. All oxidation test samples were nominally 0.07-inch thick sheet, 0.75-inch square and were uniformly polished to a 120-grit finish. One group of samples was exposed at 2000 F. for 100 hours continuously while another group was intermittently exposed at 2000 F. for eight 3-hour periods and four 19-hour periods for a total of 100 hours as indicated in Table 6. The oxidation rates were determined and are shown on the basis of mils penetration per year (m.p.y.). It is significant that the oxidation rates of the alloys of this invention closely approach those of alloy 2 which is generally recognized as the superior wrought oxidation-resistant alloy presently available in the metals industry.
• Incidental impurities in amounts normally found in alloys of this type may be tolerated as previously mentioned while zirconium, columbium, titanium and tantalum, often added in alloys of this class, are not required in the alloys of this invention.
• the combined total content in the final alloy of zirconium, columbium, titanium and tantalum must not exceed over one percent by weight, as impurities and residuals of prior processing steps, in order that the desired combination of properties be obtained.
• alloys were prepared by a process commonly used in alloys of this class; however, other consolidating techniques could be used.
• the alloy compositions were melted in an induction furnace, cast into ingots, forged and rolled into 0.063-inch thick sheet for testing purposes. Prior to testing, the alloys were annealed at 2150 F. for 15 minutes and fan cooled.
• Compositions of alloys prepared and tested are given in Table 3.
• the alloys of this invention described in Table 3 are in the range of about 19-20% Ni, 11-14% W, 19-22% Cr and 0.l-0.3% C. and will be seen to have an excellent combination of industrially useful properties. All of the alloys of Table 3, except alloy B, are in accordance with this invention. Tensile test results of these alloys, and prior are alloys, are shown in Table 4 while creep and stress-rupture test results are shown in Table 5.
• the alloys of this invention are seen to be superior, or at least comparable to, both alloys 1 and 2 of the prior art.
• the average tensile strengths of the alloys of this invention are about 1.5 times the strengths of al- TABLE 4.AVERAGE TENSILE PROPERTIES OF ALLOYS TESTED Yield Ultimate Strength Tensile Elongation, 0.2% Strength, Percent Offset, 1,000 1,000 p s l p.s.i.
• a cobalt base alloy characterized by high temperah, oxidation resistance and resistance to em- DATA [.063-inch thick sheet] Load at Cup Depth, Cup Depth,
• the two alloys are simi brittlement after exposure to elevated temperatures, said alloy consisting essentially of about:

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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)
• Heat Treatment Of Strip Materials And Filament Materials (AREA)
• Powder Metallurgy (AREA)
• Manufacture Of Alloys Or Alloy Compounds (AREA)

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Cited By (7)

Citations (4)

• 1966
  • 1966-07-07 US US563371A patent/US3416916A/en not_active Expired - Lifetime
• 1967
  • 1967-06-30 DE DE1558676A patent/DE1558676B2/de active Granted
  • 1967-06-30 SE SE10027/67*A patent/SE342474B/xx unknown
  • 1967-07-03 GB GB30501/67A patent/GB1137019A/en not_active Expired

Patent Citations (4)

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