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
  • C22C19/055—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
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
  • C21D1/74—Methods of treatment in inert gas, controlled atmosphere, vacuum or pulverulent material
  • C21D1/76—Adjusting the composition of the atmosphere
• • 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
  • C22C1/06—Making non-ferrous alloys with the use of special agents for refining or deoxidising
• • 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
  • C22C19/058—Alloys based on nickel or cobalt based on nickel with chromium without Mo and W
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C8/00—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
  • C23C8/06—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases
  • C23C8/08—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases only one element being applied
  • C23C8/10—Oxidising
  • C23C8/16—Oxidising using oxygen-containing compounds, e.g. water, carbon dioxide

Definitions

• the present invention relates to a method of producing a Ni-based alloy, which elutes little Ni even when used in a high-temperature water environment for a long period, and particularly relates to a method of producing the Ni-based alloy suitable for use in a member for a nuclear power plant.
• a Ni-based alloy is used for various kinds of members due to its superior mechanical properties. Particularly, for the member in a nuclear reactor, which is exposed to high-temperature water, the Ni-based alloy superior in corrosion resistance is used. For instance, for a steam generator of a pressurized water reactor (PWR), a 60%Ni-30%Cr-10%Fe alloy is used.
• PWR pressurized water reactor
• Ni-based alloy is superior in corrosion resistance and has a low corrosion rate. However, when used for a long period, a very small amount of Ni elutes from the alloy.
• Eluted Ni is carried to a reactor core part along with circulating furnace water and is irradiated with neutrons in the proximity of the fuel. Then, the irradiated Ni with neutrons is converted to radioactive Co through a nuclear reaction. Radioactive Co has a very long half-life, and incessantly emits radioactive rays for a long term. Therefore, as the elution amount of Ni increases, the exposed dose of an operator conducting a periodic inspection increases.
• the reduction of the exposed dose is a very important subject for using a light water reactor for a long period. Accordingly, the countermeasures have been taken until now in order to prevent Ni from eluting from a Ni-based alloy, through improving the corrosion resistance of materials and controlling the water quality of the nuclear reactor water.
• the Patent Document 1 discloses a method for improving uniform corrosion resistance of a heat exchanger tube made of a Ni-based alloy, by annealing it in an atmosphere having the degree of vacuum of 10 -2 to 10 -4 Torr at 400 to 750°C, and forming an oxide film mainly containing chromium oxide on the surface of it.
• the Patent Document 2 discloses a method of manufacturing a member for a nuclear power plant by solution-treating a Ni-based precipitation-strengthened alloy, and then heat-treating it in an oxidizing atmosphere of air with 10 -3 Torr to ambient pressure, while combining the treatment with at least one part of aging treatment and oxide film-forming treatment.
• the Patent Document 3 discloses a method of producing a Ni-based alloy product through heat-treating a Ni-based alloy product in an atmosphere of hydrogen or a mixed gas of hydrogen with argon, having a dew point of -60 to +20°C.
• Patent Document 4 discloses a method for forming a chromium enriched layer on an alloy workpiece containing Ni and Cr by exposing the work-piece with a gaseous mixture consisting of water vapor and at least one of non-oxidizing gases.
• Patent Document 1 JP S64-55366A
• Patent Document 2 JP H08-29571A
• Patent Document 3 JP 2002-121630A
• Patent Document 4 JP 2002-322553A
• the film formed by the method disclosed in the Patent Document 1 has such insufficient thickness that it tends to be damaged during service for a long period, and may lose the effect of preventing the elution.
• the method disclosed in the Patent Document 2 has such a problem that oxidized Ni is easily taken into a film and the Ni elutes during use.
• Methods for forming an oxide film by controlling the amount of water vapor (a dew point) such as the methods disclosed in the Patent Documents 3 and 4 have difficulty in forming the oxide film consistent from the inlet side to the outlet side of water vapor. This is for the following reason.
• the growth rate of the oxide film is limited not only by oxygen potential but also by the diffusibility of an oxidizing gas to the surface of a material to be treated through a concentration boundary layer.
• the concentration boundary layer means a boundary layer having a concentration gradient of a gas, from the surface of the material to a portion apart from the surface (for instance, the vicinity of the medial axis inside of the tube).
• the diffusibility is affected by physical properties such as diffusion coefficient and coefficient of kinematic viscosity of a gas, and oxidation treatment conditions such as the concentration and flow rate of the gas.
• Water vapor (H 2 O) has the higher diffusibility than other oxidizing gases such as CO 2 have, hence it is hard to form the oxide film consistent from the inlet side to outlet side on the tube by the oxidation treatment in a water vapor atmosphere.
• the present invention was accomplished for the purpose of solving these problems, and is directed at providing a method of producing a Ni-based alloy having a uniform oxide film comprising chromium oxide inexpensively formed on the surface.
• the present invention is summarized into the method of producing a Ni-based alloy described in the following items (1) to (14).
• oxide film comprising chromium oxides means an oxide film mainly containing Cr 2 O 3 , but may contain oxides other than Cr 2 O 3 , such as MnCr 2 O 4 , TiO 2 , Al 2 O 3 and SiO 2 .
• the alloy may have other oxides layer formed as the upper layer (the outside layer) and/or the lower layer (the inside layer) of the chromium oxide layer.
• Ni based alloy can form chromium oxide on the surface of a Ni-based alloy inexpensively and uniformly. Therefore, manufactured Ni-based alloy elutes very little Ni even when used in high-temperature water such as in a nuclear power plant for a long time. Accordingly, the Ni-based alloy is most suitable for a member for a nuclear power plant, such as steam generator tubing, and a spacer spring, a coil spring, a finger spring, a channel fastener and a nozzle stub for a lid used in high-temperature water.
• a member for a nuclear power plant such as steam generator tubing, and a spacer spring, a coil spring, a finger spring, a channel fastener and a nozzle stub for a lid used in high-temperature water.
• a Ni-based alloy is subjected to a heat treatment in the atmosphere consisting of carbon dioxide gas or the atmosphere consisting of 0.0001 vol.% or more carbon dioxide gas and 99.9999 vol.% or less non-oxidizing gas in order to form an oxide film composed of chromium oxide on the surface of the alloy.
• the present invention is characterized by a heating atmosphere containing carbon dioxides of 0.0001 vol.% or more for forming an oxide film comprising chromium oxide on the surface of the Ni-based alloy through the oxidative effect.
• the atmosphere contains less than 0.0001 vol.% carbon dioxide, the oxide film comprising chromium oxide may be insufficiently formed.
• concentration of carbon dioxide contained in an atmosphere for heat treatment there is no particular upper limit on the concentration of carbon dioxide contained in an atmosphere for heat treatment and it could be 100 vol.%. However, from the viewpoint of manufacturing cost reduction, it is preferable that non-oxidizing gas, to be described in later paragraphs, is added in an atmosphere for heat treatment in order to set the concentration of carbon dioxide to be 50 vol.% or less, and more preferably 10 vol.% or less.
• Carbon dioxide gas in a high-temperature atmosphere has an effect of forming an oxide film comprising chromium oxide on the surface of a Ni-based alloy. More specifically, in an atmosphere comprising carbon dioxides, as shown in the following reaction formula, CO 2 adsorbs to a Ni-based alloy, and then a Ni-based alloy directly takes O (oxygen) therein from CO 2 to form chromium oxide.
• Patent Documents 3 and 4 disclose a method for forming an oxide film by heating a Ni alloy under a water vapor atmosphere, the method has difficulty in forming an oxide film consistent from the inlet side to the outlet side of water vapor.
• a merit of using carbon dioxide gas includes that it can produce a desired oxidation atmosphere more inexpensively than a method of controlling the concentration of water with a conventional dew point controller.
• An atmosphere for heat treatment may contain 99. 9999 vol. % or less non-oxidizing gases, that do not promote Cr oxide, in addition to carbon dioxide gas.
• gases involve hydrogen gas, rare gas (Group 18 gases, e.g. Ar, He and so on), carbon monoxide gas, nitrogen gas and hydrocarbon gas.
• rare gas Group 18 gases, e.g. Ar, He and so on
• carbon monoxide gas, nitrogen gas and hydrocarbon gas may cause carburisation or nitriding when they are contained in an atmosphere for heat treatment. Therefore, it is preferable to use at least either or both of hydrogen gas and rare gas.
• the concentration of the carbon dioxide gas can be appropriately controlled.
• An atmosphere for heat treatment may contain 5 vol.% or less of one or more oxidizing gases (e.g. oxygen) that cause the oxidation of a Ni-based alloy in addition to carbon dioxide gas, or carbon dioxide gas and non-oxidizing gas.
• oxidizing gases e.g. oxygen
• Hydrogen gas is industrially often used as an atmospheric gas for heat treatment, so that the use of it for diluting carbon dioxides can reduce a manufacturing cost. Therefore, it is most preferable to perform heat treatment under the atmosphere of the mixed gas consisting of carbon dioxides and hydrogen gas.
• Heating temperature 500 to 1,250°C
• a heating temperature has only to be in a range for producing the appropriate thickness and composition of an oxide film on a surface of the alloy being heated, and imparting the appropriate strength to the alloy itself.
• the heating temperature is lower than 500°C, the oxidation of chromium can be insufficient, but when exceeding 1,250°C, the strength of the Ni-based alloy may not be ensured. Consequently, the heating temperature is preferably in a range of 500 to 1,250°C. Heating time: 10 seconds to 35 hours
• a heating time has only to be set into a range capable of giving an alloy the appropriate thickness and composition of an oxide film. More specifically, the alloy is preferably heated for 10 seconds or longer in order to form the oxide film mainly containing chromium oxide, but the oxide film does not grow any more by heating for longer than 35 hours. Consequently, the heating time is preferably in a range of 10 seconds to 35 hours.
• a heating temperature is set in a range from 1, 000 to 1,200°C for instance, a heating time may be in a range of 10 seconds to 60 minutes.
• the thickness and composition of an oxide film can be adjusted.
• Ni-based alloy used in a producing method of the present invention comprises, by mass%, 0.15% or less C, 1.00% or less Si, 2.0% or less Mn, 0.030% or less P, 0.030% or less S, 10.0-40.0% Cr, 15.0% or less Fe, 0.5% or less Ti, 0.50% or less Cu, 2.00% or less Al and the balance Ni and impurities.
• Reasons for limiting each element are as follows.
• “%” on content means “mass%” in the following discussion.
• C content exceeding 0.15% may cause the lowering of stress corrosion cracking resistance. Accordingly, when C is added, the content is preferably controlled to 0.15% or less, and further preferably to 0.06% or less. C has an effect of increasing the strength of grain boundaries in an alloy. In order to acquire the effect, the content of C is preferably 0.01% or more. Si: 1.00% or less
• Si is used as a deoxidizing material in refining process and remains as an impurity in an alloy.
• the content needs to be limited to 1.00% or less.
• Si content exceeds 0.50%, the cleanliness factor of the alloy can be decreased. Accordingly, Si content is preferably limited to 0.50% or less.
• Mn 2.0% or less
• Mn content exceeding 2.0% lowers the corrosion resistance of an alloy. Accordingly, the content is preferably controlled to 2.0% or less. Mn has a lower free energy of formation for the oxide than Cr, hence, Mn is precipitated as MnCr 2 O 4 by heating.
• Cr 2 O 3 normally forms in the vicinity of a base metal by heating with precedence, and MnCr 2 O 4 forms as an upper layer on the outside of it because Mn has comparatively high rate of diffusion. If MnCr 2 O 4 layer exists, it protects a Cr 2 O 3 layer in a use environment, and even when the Cr 2 O 3 layer is disrupted by some reason, MnCr 2 O 4 promotes the restoration of the Cr 2 O 3 layer. Such an effect becomes remarkable when Mn content is more than 0.1%. Consequently, desirable Mn content is 0.1 to 2.0%, and further desirably is 0.1 to 1.0%. P: 0.030% or less
• P is an element existing as an impurity in an alloy. P content exceeding 0.030% may exert an adverse effect on corrosion resistance. Accordingly, P content is preferably limited to 0.030% or less. S: 0.030% or less
• S is an element existing as an impurity in the alloy. When the content exceeds 0.030%, S may exert adverse effect on corrosion resistance. Accordingly, S content is preferably limited to 0.030% or less. Cr: 10.0 to 40.0%
• Cr is a necessary element for forming an oxide film comprising chromium oxide.
• the content is preferably 10.0% or more.
• Cr content exceeding 40.0% may deteriorate the corrosion resistance of the alloy, because Ni content becomes relatively low.
• Cr content is preferably 10.0 to 40.0%.
• the alloy has superior corrosion resistance in a chloride-containing environment, and when Cr content is 27.0% to 31.0%, the corrosion resistance not only in a chloride-containing environment, but also in high-temperature pure water and an alkaline environment becomes superior.
• Fe 15.0% or less
• Fe content When Fe content is more than 15.0%, it may impair the corrosion resistance of the Ni-based alloy, and therefore Fe content should be set at 15.0% or less.
• Fe is an element that is dissolved in Ni and is usable as a substitute for a part of expensive Ni, so that 4.0% or more Fe is desirably contained.
• the content of Fe can be decided in terms of the balance between Ni and Cr. When Cr content is 14.0 to 17.0%, preferable Fe content is 6.0 to 10.0%, and when Cr content is 27.0 to 31.0%, preferable Fe content is 7.0 to 11.0%. Ti: 0.5% or less
• Ti content exceeding 0.5% may reduce cleanliness of an alloy. Accordingly, the content is desirably controlled to be 0.5% or less, and further desirably to 0.4% or less. However, from the viewpoint of improving the workability of the alloy and inhibiting grain growth in welding, 0.1% or more Ti is preferably contained.
• Cu is an element existing as an impurity in the alloy. If the content exceeds 0.50%, the corrosion resistance of the alloy can be lowered. Accordingly, Cu content is desirably limited to 0.50% or less. Al: 2.00% or less
• Al is used as a deoxidizing material in refining process and remains as an impurity in an alloy. Remaining Al forms an oxide-based inclusion in the alloy, reduces the cleanliness of the alloy, and may exert an adverse effect on the corrosion resistance and mechanical properties of the alloy. Accordingly, Al content is desirably limited to 2.00% or less.
• Ni-based alloy has only to include the above-described elements and the balance Ni and impurities, however one or more elements among Nb, Ta and Mo may be added in appropriate amount in order to improve characteristics such as corrosion resistance and strength.
• Nb and/or Ta 3.15-4.15% each element alone or in total
• Nb and Ta are effective for improving the strength of the alloy, because they easily form carbides. In addition, they have an effect of fixing C in the alloy, hence they inhibit a shortage of Cr in grain boundaries and improve the corrosion resistance of grain boundaries. Accordingly, one or both of these elements are desired to be contained. The effect becomes remarkable, when the content of either element is 3.15% or more in the case of the alloy containing either one, or when the total content of these is 3.15% or more in the case of the alloy containing both.
• the excessive content of Nb and/or Ta may impair hot workability and cold workability, and may increase susceptibility to heating embrittlement.
• the content of either element in the case of the alloy containing either one, or the total content of these in the case of the alloy containing both, is preferably controlled to 4.15% or less. Consequently, the content of one element or both elements of Nb and Ta is desirably controlled to 3.15 to 4.15%.
• Mo is effective in improving pitting corrosion resistance, so that it may be contained as needed.
• the above described effect becomes remarkable when the content is 8% or more, but when it exceeds 10%, intermetallic compounds precipitate and may lower corrosion resistance. Accordingly, the content of Mo, when added, is desirably controlled to 8 to 10%.
• Ni-based alloys are typically two kinds described below.
• the alloy (a) includes Cr of 14.0 to 17.0% and Ni of about 75% and has superior corrosion resistance in a chloride-containing environment.
• Fe content is desirably controlled to 6.0 to 10.0%, from the viewpoint of a balance between the contents of Ni and Cr.
• the alloy (b) includes 27.0 to 31.0% Cr and about 60% Ni, therefore, it has superior corrosion resistance not only in a chloride-containing environment, but also in high-temperature pure water and an alkaline environment.
• Fe content is desirably controlled to 7.0-11.0% from the viewpoint of a balance between the contents of Ni and Cr.
• a tube was manufactured into the dimension with a diameter of 20 mm a wall thickness of 1.5 mm and a length of 20 m with the use of an alloy-A shown in Table 1, and a tube was manufactured into the dimension with a diameter of 20 mm, a wall thickness of 1.5 mm and a length of 10 m with the use of alloys B to G shown in Table 1. Then, the tubes were continuously heat-treated under the conditions shown in table 2.
• oxide films formed in the conditions shown in No. 1 and 2 with the use of CO 2 as an oxidizing gas showed as small dispersions as 0.05 and 0.17
• the oxide film formed in a condition shown in No. 27 with the use of H 2 O showed the dispersion of 3.00, which was quite large compared to the case with the use of CO 2 .
• Other examples treated by the producing method of the present invention showed the dispersions evaluated as O, whereas examples treated by a comparative method using H 2 O showed large dispersions.
• the method according to the present invention can inexpensively form uniform chromium oxide on the surface of a Ni-based alloy, Therefore, it can manufacture a Ni-based alloy which elutes extremely little Ni even when used in a high-temperature water environment such as in a nuclear power plant, for a long time. Accordingly, the Ni-based alloy is most suitable for members of a nuclear power plant, such as steam generator tubing, and a spacer spring, a coil spring, a finger spring, a channel fastener and a nozzle stub for a lid used in high-temperature water.

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• 2004
  • 2004-10-13 JP JP2004298835A patent/JP4304499B2/ja not_active Expired - Fee Related
• 2005
  • 2005-09-22 CA CA002520700A patent/CA2520700C/en not_active Expired - Fee Related
  • 2005-10-06 KR KR1020050093768A patent/KR100765015B1/ko active IP Right Grant
  • 2005-10-12 CN CNB2005101136974A patent/CN100519820C/zh not_active Expired - Fee Related
  • 2005-10-13 EP EP05256349.1A patent/EP1647609B1/de not_active Expired - Fee Related

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