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
  • C22C19/03—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
  • C22C19/057—Alloys based on nickel or cobalt based on nickel with chromium and Mo or W with the maximum Cr content being less 10%
• • 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

Definitions

• the present invention relates to a low thermal expansion Ni superalloy, and more particularly to a low thermal expansion Ni superalloy having high strength and excellent corrosion-resistance and oxidation-resistance.
• the bolt material for high temperature which is used for a pressure vessel member which is heated to the high temperature, such as a chamber of a steam turbine and gas turbine is made of 12 Cr ferritic steel (containing C: 0.12%, Si: 0.04%, Mn: 0.7%, P: 0.1%, Ni: 0.4%, Cr: 10.5%, Mo: 0.5%, Cu: 0.03%, V: 0.2%, W: 1.7%, Nb: 0.1% and Fe: remaining percent) or austenitic heat-resistant alloy (Nimonic alloy 80A including Cr: 10.5%, Mn: 0.4%, Al: 1.4%, Ti: 2.4%, Si: 0.3%, C: 0.06%, Zr: 0.06%, B: 0.003%, Ni: remaining percent, and Refrataloy 26 including Cr: 18%, Co: 20%, Mo: 3%, Ti: 2.6%, Fe: 16%, C: 0.05%, Ni: remaining percent).
• 12 Cr ferritic steel containing C: 0.12%, Si: 0.04%, Mn: 0.7%, P: 0.1%,
• austenitic heat-resistance ally is also problematic as a material used at higher temperatures.
• JP-A-9-157779 discloses a low thermal expansion Ni-base super heat-resistant alloy with excellent corrosion-resistance and oxidation-resistance containing, by weight %, C of 0.2% or less, Si of 1% or less, Mn of 1% or less, Cr of 10 to 24%, one or more kinds of Mo and W of Mo+1 ⁇ 2 W of 5 to 17%, Al of 0.5 to 2%, Ti of 1 to 3%, Fe of 10% or less, B of 0.02 or less and Zr of 0.2% or less, and as necessary Co of 5% or less and Nb of 1.0% or less and remainder of Ni and inevitable impurities.
• JP-A-8-85838 also discloses a similar alloy.
• a previously known example of alloys having a low linear expansion coefficient is Inconel 783 of an Invar alloy (containing Cr: 3.21%, Mn: 0.08%, Al: 5.4%, Ti: 0.2%, Si: 0.07%, C: 0.03%, B: 0.003%, Fe: 24.5%, Ni: 28.2% and Co: 35.3% . . . Comparative Example No. 2) which has been developed as the material for a jet engine.
• This alloy has a low linear expansion coefficient in a ferromagnetic state with the Curie point adjusted in the balance of Fe—Ni—Co. However, this alloy does not have corrosion-resistance enough to be used for the steam turbine.
• the inventors of the invention have eagerly investigated the low linear expansion Ni-base superalloy.
• the inventors found that as regards Mo, W and Re, when the value represented by Mo+1 ⁇ 2 (W+Re) is 10 or more, the target thermal expansion coefficient can be obtained; in order to increase the thermal expansion coefficient in this case, Cr should be 20% or less; the thermal expansion coefficient further lowers where the value of Mo+1 ⁇ 2 (W+Re) exceeds 17 and Cr is lower than 10%; and even if Cr is lower than that of a conventional Ni-base heat-resistant alloy, a problem of steam oxidation does not occur, and have accomplished the invention on the basis of these findings.
• a low thermal expansion Ni-base superalloy of the present invention comprises, by weight % (hereinafter the same as long as not particularly defined), C: 0.15% or less; Si: 1% or less; Mn: 1% or less; Cr: 5 to 20%; at least one of Mo, W and Re of Mo+1 ⁇ 2 (W+Re) of 10 to 25%; Al: 0.2 to 2%; Ti: 0.5 to 4.5%; Fe of 10% or less; at least one of B: 0.02% and Zr: 0.2% or less; a remainder of Ni and inevitable impurities; wherein the atomic % of Al+Ti is 2.5 to 7.0.
• the amount of Cr is from 5 to 10 (exclusive) %; wherein the amount of at least one of Mo, W and Re of Mo+1 ⁇ 2 (W+Re) is from 17 (exclusive) to 25%; the amount of Al is from 0.2 to 0.4 (exclusive) %; and/or the amount of Ti is from 3.5 (exclusive) to 4.5%.
• the low thermal expansion Ni-base superalloy may further comprises at least one of Nb and Ta in Nb+1 ⁇ 2 Ta: 1.5% or less; wherein the atomic % of Al+Ti+Nb+Ta is 2.5 to 7.0.
• a part of Ni may be replaced by Co of 5% or less.
• an average expansion coefficient at a temperature from room temperature to 700° C. is 14.0 ⁇ 10 ⁇ 6 /° C. or less.
• Element C is contained to create carbide in combination with Ti, Nb, Cr and Mo, enhance the high temperature strength and prevent the size of the crystal grain from increasing.
• the contents of C exceeding 0.15% decreases the property of hot working so that it is 0.15% or less and preferably 0.10% or less.
• Element Si is added as deoxidant and contained to increase the oxidation resistance.
• the contents of Si exceeding 1% reduces ductility so that it is 1% or less, preferably 0.5% or less.
• Element Mn is added as deoxidant like Si.
• the contents of Mn exceeding 1% deteriorates the high temperature oxidation characteristic and also promotes precipitation of ⁇ phase (Ni, Ti) spoiling the ductility so that it is 1% or less, preferably 0.5% or less.
• Cr is contained to improve the high temperature resistance and corrosion resistance through solid solution in the austenite phase. In order to maintain the sufficient high temperature oxidation resistance and corrosion resistance, although more contents of Cr is desired, it increases the thermal expansion coefficient so that it desired to be less from the standpoint of view of the thermal expansion.
• the contents of Cr In order to obtain a target thermal expansion coefficient in the vicinity of 650 to 700° C. which is a using temperature intented by the invention, the contents of Cr of 5 to 20% is desired. In order to obtain a lower thermal expansion coefficient, the contents of Cr is preferably 5 to 15%, and further lower thermal expansion coefficient. the contents of Cr is preferably 5 to 10 (exclusive) %.
• Elements Mo, W and Re are contained in order to increase the high temperature strength through strengthening of solid solution in the austenite phase and reduce the thermal expansion coefficient.
• the total of one or more kinds of Mo+1 ⁇ 2 (W+Re) is at least 10% or more. The total of them exceeding 25% reduces the property of hot working and precipitates the embrittling phase to reduce the ductility so that the contents of Mo+1 ⁇ 2 (W+Re) is set at 10 to 25%.
• the contents of Mo+1 ⁇ 2 (W+Re) is preferably 17 (exclusive) to 25%.
• Element Ti is contained to strengthen the ⁇ ′ phase formed in combination with Ni, reduce the thermal expansion coefficient and promote the effect of aging precipitation in the ⁇ ′ phase. In order to provide such an effect, the contents of 0.5% or more must be contained. However, the contents of 4.5% or more precipitates the ⁇ phase (Ni, Ti) of the embrittling phase to reduce ductility so that it is set at 0.5 to 4.5%. In order to obtain the sufficient strength and low thermal expansion coefficient at the using temperature of 700° C. intended by the invention, the contents of Ti preferably exceeds 3.5% and 4.5% or less.
• Element Al is the most important element to create the ⁇ ′ phase in combination with Ni and strengthen by it's the precipitation.
• the contents of less than 0.2% provides insufficient precipitation of the ⁇ ′ phase.
• a large quantity of Ti, Nb and Ta makes the ⁇ ′ phase unstable and precipitates ⁇ phase and phase to cause embrittlement.
• the contents of 2.0% or more deteriorates the property of hot working and makes it impossible to forge a component. Therefore, the contents is set at 0.2 to 2.0% and preferably 0.2 to 0.4 (exclusive) %.
• Element Fe is an impurities contained when inexpensive scrap or inexpensive mother alloy containing W, Mo, etc. is used in order to reduce the cost of the alloy.
• the element Fe decrease the high temperature strength and increase the thermal expansion coefficient.
• the content of 10% or less slightly influences the high temperature strength so that it is set at 10% or less.
• it is 5% or less, and more preferably, it is 2% or less.
• Elements B and Zr segregates in a crystal grain boundary to increase the creep strength.
• the element B can suppress the precipitation of ⁇ -phase in the alloy containing a larger quantity of Ti.
• These elements B and Zr are contained to provide such an effect. Excessive content of these elements deteriorates the property of hot working and excessive Zr spoils the creep characteristic. For these reasons, the content of B is set at 0.02% and that of Zr is set at 0.2% or less.
• Element Co is contained to increase the high temperature strength in solid solution in the alloy.
• the effect is relatively low as compared with the other elements and expensive. For this reason, the content thereof is set at 5% or less.
• Nb+1 ⁇ 2 Ta 1.5% or Less
• Elements Nb and Ta can form the ⁇ ′ phase (Ni 3 (Al, Nb, Ta) which is a precipitation strengthening phase of Ni-base superalloy and have the effects of strengthening the ⁇ ′ phase and preventing the coarsening of ⁇ ′ phase. These elements are contained to provide such an effect. Excessive content thereof precipitates the ⁇ phase (Ni 3 (Nb, Ta) to lower ductility. For this reason, the content of Nb+1 ⁇ 2 Ta is set at 1.5%. The desired range is 1.0% or less.
• Element Ni is an main element to create austenite which serves as matrix, and can increase heat-resistance and corrosion-resistance.
• Ni forms the ⁇ ′ phase which is a precipitation strengthening phase.
• Al+Ti 2.5 to 7.0% by atomic %
• Al+Ti+Nb+Ta 2.5 to 7.0% by Atomic %
• Elements Al, Ti, Nb and Ta are constituents of the ⁇ ′ phase. Therefore, where there is sufficient quantity of Ni, the volume fraction of the precipitated ⁇ ′ phase is proportional to the total of the atomic percent of these elements. Further, the high temperature strength is proportional to the volume fraction of the ⁇ ′ phase so that it increases with the total of these elements. Therefore, the content thereof of 2.5% or more is required to acquire the sufficient strength. However, the contents thereof exceeding 7.0% excessively increases the volume fraction of the ⁇ ′ phase to deteriorate the property of hot working remarkably. For this reason, the content thereof is set at 2.5 to 7.0% by atomic %, preferably 3.5 to 6.0%.
• the property of the low thermal expansion Ni-base superalloy according to the invention will not be deteriorated as long as Mg: 0.03% or less, Ca: 0.03% or less, P: 0.05% or less, S: 0.001% or less, and Cu: 2% or less.
• the low thermal expansion Ni-base superalloy according to the invention can be prepared by the same method as a conventional method for preparing Ni-base superalloy.
• the heat treatment after solid-solution heat treatment not less than 950° C., is effective in a single step aging (700 to 850° C.) and a two-step aging (first step: 800 to 900° C., second step: 700 to 800° C.).
• the alloy having the compositions as shown in Table 1 was molten in a vacuum induction furnace having a capacity of 50 kg and its ingot having 50 kg was cast. The surface of an ingot of the ingot was cut away and the ingot was heat-treated for 15 hr at 1150° C. as a homogenizing treatment. Thereafter, the ingot was forged into rods each having 60 mm square. The forged rods were heated for 2 hr at 1100° C., and thereafter water-cooled for its solid solution. The rods were hardening-treatment aged for 16 hr at 750° C. Sample pieces cut out from the rods were subjected to various tests. Thus, the test results as shown in Table 2 were obtained.
• the thermal expansion coefficient using quartz as a standard sample, the average thermal expansion coefficient from room temperature to 70° C. was measured by a dilatometer available from RIGAKU DENSI CO. LTD. The measurement was carried out under the condition of a temperature rising speed of 5° C./min on the basis of a differential dilatometry. The sample used has a size of ⁇ 5 ⁇ L19.
• the high temperature tensile test was carried out for a tensile specimen with ridges having a parallel portion of 6 mm in diameter at 700° C. on the basis of the JIS high temperature tensile test method.
• the creep rupture test was carried out for a specimen with a parallel portion having 6.4 mm in diameter at 700° C. under load stress of 343 MPa.
• comparative example No. 1 which is 12 Cr ferritic steel, has a low average thermal expansion coefficient of 12.4 ⁇ 10 ⁇ 6 /° C. However, it's high temperature tensile strength is lower than the samples according to the invention.
• Comparative examples Nos. 4 and 5, which are Inconel 783 and Incoloy 909 have average thermal expansion coefficients which are equal or lower than those of the samples according to the invention, but have worse steam oxidation characteristics than those according to the invention.
• Comparative example No. 8 which is an alloy containing more Cr and a smaller value of Mo+1 ⁇ 2 (W+Re) than those of the samples according to the invention, has a larger average thermal expansion coefficient of 14.1 ⁇ 10 ⁇ 6 /° C. than those of the samples according to the invention.
• Comparative example No. 9 which is an alloy having a larger value of Mo+1 ⁇ 2 (W+Re), has worse forgeability. This alloy produced a crack during the forging and could not evaluated thereafter.
• Comparative example No. 10 which is lower in the total of Al+Ti than in the invention and insufficient in the precipitation amount of ⁇ ′ phase, has a smaller high-temperature strength than those of the samples according to the invention.
• the low thermal expansion Ni-base superalloy according to the invention which has the compositions as shown, has the average thermal expansion coefficient of 14.0 ⁇ 10 ⁇ 6 /° C. which is approximately equal to that of 12 Cr ferritic steel, and also has the creep rupture life of 791 to 2880 hr and weight gain of steam oxidation of 0.05 to0.21 mg/cm 2 .
• the Ni-base superalloy according to the invention has an excellent effects of the high temperature strength and corrosion/oxidation resistance where are approximately equal to those of the austenite heat-resistant alloy.
• the low thermal expansion Ni-base superalloy can be applied to the bolt, blade and disk of a steam turbine, gas turbine and jet engine, and also applied to a boiler tube of a heating machine and pressurizing machine, thereby giving an excellent effect of improving the reliability of a thermal power plant.

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• Chemical & Material Sciences (AREA)
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• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Physics & Mathematics (AREA)
• Thermal Sciences (AREA)
• Crystallography & Structural Chemistry (AREA)
• Turbine Rotor Nozzle Sealing (AREA)
• Manufacture And Refinement Of Metals (AREA)
• Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)
• Chemically Coating (AREA)

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• 1999
  • 1999-03-03 JP JP05605999A patent/JP3781402B2/ja not_active Expired - Fee Related
• 2000
  • 2000-03-02 US US09/517,305 patent/US20020015656A1/en not_active Abandoned
  • 2000-03-03 AT AT00104667T patent/ATE296901T1/de active
  • 2000-03-03 EP EP00104667A patent/EP1035225B1/de not_active Expired - Lifetime
  • 2000-03-03 DE DE60020424T patent/DE60020424T8/de active Active

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