Classifications

• • 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
  • C22F1/16—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working of other metals or alloys based thereon
  • C22F1/18—High-melting or refractory metals or alloys based thereon
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C16/00—Alloys based on zirconium
• • 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
  • C22F1/16—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working of other metals or alloys based thereon
  • C22F1/18—High-melting or refractory metals or alloys based thereon
  • C22F1/186—High-melting or refractory metals or alloys based thereon of zirconium or alloys based thereon

Definitions

• the invention relates to a method for manufacturing a zirconium alloy semi-product intended for the preparation of a flat product used for the production of fuel assembly elements.
• Fuel assemblies for nuclear reactors cooled by light water for example nuclear reactors cooled by pressurized water (PWR) and nuclear reactors cooled by boiling water (BWR) or CANDU reactor fuel includes elements consisting of a zirconium alloy having the property of having a low neutron absorption in the core of the nuclear reactor.
• PWR pressurized water
• BWR boiling water
• CANDU reactor fuel includes elements consisting of a zirconium alloy having the property of having a low neutron absorption in the core of the nuclear reactor.
• the cladding tubes of the fuel rods and the plates used for the manufacture of the spacer grids of the fuel assembly can be made of zirconium alloy, in particular al- bonding of zirconium containing tin and iron such as the alloy Zircaloy 2 or Zircaloy 4.
• the parallelepipedic housings of the fuel assemblies for BWR reactors are also generally produced from flat products made of zirconium alloy such as Zircaloy 2 or Zircaloy 4.
• alloys such as the alloy known under the trade name 5 essentially containing zirconium and niobium are also used for the manufacture of fuel assembly elements in the form of flat or tubular products.
• the zirconium alloys used for the manufacture of elements for fuel assemblies contain at least 97% of zirconium by weight, the rest of the composition which represents at most 3% by weight, with the exception of impurities due in the development of alloys, which may consist of different elements and, in particular, iron, tin or niobium.
• zirconium alloys meeting these conditions relating to their composition may be present, depending on the temperature and the heat treatments which they have undergone, in one or the other of the two allotropic forms of zirconium, that is to say say in alpha phase which is the stable phase at low temperature of zirconium, with a compact hexagonal structure or in beta phase which is the stable phase at high temperature with cubic structure.
• the zirconium alloys such as the technical alloys used for the manufacture of fuel assembly elements defined above may have a mixed alpha + beta structure.
• the starting product is generally a very large ingot obtained by casting an alloy adjusted to the chosen shade.
• an ingot having a diameter between 400 mm and 800 mm and a length between 2 m and 3 m is cast.
• the ingot then undergoes forging operations in a temperature range in which it can be in the ce, ⁇ or ⁇ + ⁇ phase (EP-0.085.552 and US-5,674,330).
• the ingot is heated, so that the alloy is in the beta phase and then a first forging step is carried out on the ingot heated in the beta phase.
• the ingot can be heated at 1050 ° C for ten hours, prior to forging.
• the product obtained by forging is quenched from the beta phase.
• a second forging step is then carried out at a temperature below 800 ° C., the alloy being in the alpha phase, in the case of Zircaloy type alloys.
• the product obtained which constitutes the semi-product of the process for producing a flat product, is a slab which can have a thickness of the order of 100 mm.
• the slab is then subjected to various hot rolling operations and then cold rolling to obtain a final flat product such as a strip with a thickness of 0.2 mm to 4 mm.
• Heat treatments of quenching and annealing are carried out between at least some of the operations for forming the final flat product.
• the transformation process which has been described comprises numerous successive treatment phases and in particular several quenchings from the beta domain to obtain the semi-finished product such as a slab, which is formed hot and the second intermediate product which is formed cold.
• the zirconium alloy product comes into contact with moist air and / or water, so that it absorbs hydrogen which is fixed in the material in the form of hydrides.
• the precipitation of hydrides generally occurs in a range of temperatures ranging from 220 ° C. to 100 ° C., during the cooling of the product and the hydrides are formed in an amount all the greater and in a coarser form than the material has absorbed more hydrogen.
• the heat or thermomechanical treatment in the temperature range from 830 ° C to 950 ° C which corresponds to a range in which the alpha and beta phases are present in the alloy is only implemented after a first forging of a beta phase ingot followed by water quenching.
• the process according to the prior patent is therefore limited as regards its applications and the results obtained with regard to the presence of hydrides in the final product.
• the object of the invention is to propose a process for manufacturing a semi-finished product of zirconium alloy containing by weight at least 97% of zirconium, intended for the production of flat products, in which an ingot of large quantities is produced.
• the semi-finished product is produced from the ingot of large dimensions, by a single forging operation at a temperature at which the zirconium alloy is in a state comprising the crystalline phases ⁇ and ⁇ of the alloy of zirconium.
• the ingot contains a volume proportion of zirconium alloy in the ⁇ phase of between 10% and 90%; the rest of the zirconium alloy of the ingot being in the ⁇ phase.
• the semi-finished product is a slab;
• the slab has a thickness of about 100 mm and it is intended for the manufacture of a flat product having a thickness between 0.2 mm and 4 mm;
• the forging of the zirconium alloy in the ⁇ and ⁇ phase is carried out at a temperature between 850 ° C and 950 ° C;
• the zirconium alloy contains at most 3% by weight in total of addition elements constituted by at least one of the elements: tin, iron, chromium, nickel, oxygen, niobium, vanadium and silicon, the rest of the alloy consisting of zirconium, with the exception of unavoidable impurities.
• the invention also relates to the use of the method for the manufacture of a slab intended for the preparation of a flat product with a thickness of between 0.2 mm and 4 mm for the production of an element for nuclear fuel assembly such as a fuel assembly spacer grid plate for a PWR reactor or a wall of a fuel assembly housing for a BWR reactor or a fuel assembly element for a CANDU reactor.
• an element for nuclear fuel assembly such as a fuel assembly spacer grid plate for a PWR reactor or a wall of a fuel assembly housing for a BWR reactor or a fuel assembly element for a CANDU reactor.
• Figure 1 is a diagram showing symbolically the different stages of a manufacturing process according to the prior art.
• Figure 2 is a schematic representation, similar to that of Figure 1, of the manufacturing method according to the invention for obtaining the semi-finished product.
• Figure 1 there is shown a cast ingot 1 which can be a large ingot whose diameter can be between 400 mm and 800 mm and the length between 2 m and 3 m which is obtained by casting an alloy of zirconium used for the manufacture of flat products for the production of fuel assembly elements.
• the zirconium alloy may for example be a Zircaloy 2 alloy containing, by weight, from 1.2 to 1.7% of tin, from 0.07 to 0.20% of iron, from 0.05 to 0, 15% chromium, 0.03 to 0.08% nickel, not more than 120 ppm silicon and 150 ppm of carbon, the rest of the alloy consisting of zirconium, with the exception of usual impurities.
• the alloy for manufacturing the flat product can also be a Zircaloy 4 containing by weight, from 1.2 to 1.7% of tin, from 0.18 to 0.24% of iron, from 0.07 to 0, 13% chromium, at most 150 ppm carbon, the rest of the alloy consisting of zirconium and impurities.
• the alloy is cast in the form of the ingot of large dimensions 1 which is then brought to a temperature above 1000 ° C. and for example at a temperature of 1050 ° C. for ten hours, so that the alloy of the ingot is entirely in stable cubic beta phase at high temperature.
• the cast ingot is then forged at a temperature situated in the beta range of the alloy and, for example, at a temperature close to 1000 ° C., in the form of a very thick flat product called slab, as represented by l step 2 in figure 1.
• the very thick slab 3 is then quenched with water or moist air, as symbolically represented by the arrows representing a third step 4 of the manufacturing process.
• the very thick slab 3 is forged at a temperature situated in the alpha range of the zirconium alloy, for example at a temperature of the order of 800 ° C. .
• a slab 3 is obtained having a thickness which can be of the order of 100 mm and which constitutes the semi-finished product from forging and subjected to hot rolling and then to cold rolling to obtain the final flat product in the form a sheet or strip with a thickness which may be between 0.2 mm and 4 mm.
• step 2 of the process The initial forging of ingot 1 in beta phase (step 2 of the process) must be followed by quenching in beta phase (step 4 of the process), since the metal which cools during forging may include an external zone.
• alpha + beta phase resulting in the formation of segregation of alphagenic elements such as tin and oxygen and betaagene elements such as iron, chromium, nickel or niobium, depending on the elements contained in the alloy.
• the quenching in beta phase involves bringing into contact with the slab 3 a quenching medium consisting of water or moist air, that is to say a medium containing hydrogen.
• Hydrogen is absorbed by the slab at the time of the heat treatment and is fixed inside the alloy in the form of hydrides.
• the method according to the invention for the manufacture of a slab intended for the production of flat products will be described with reference to FIG. 2.
• the large-sized ingot 1 made of zirconium alloy is subjected to a single forging operation 7 in the ⁇ + ⁇ phase to obtain the slab 8 substantially similar to the slab 3 obtained by the complex forging process in the ⁇ phase, quenching from the ⁇ phase and forging in the ⁇ phase.
• the method according to the invention therefore consists in replacing the first three steps 2, 4 and 5 of the method according to the prior art, that is to say step 2 of forging in beta phase (above 1000 ° C), followed by step 4 of quenching the slab 3 'from the beta phase and forging in the alpha phase at a temperature below 800 ° C, a simple step 7 of forging in the alpha + beta phase, for example in the case of Zircaloy 2 and 4 alloys, at a temperature between 850 ° C and 950 ° C and for example at a temperature of the order of 900 ° C.
• the forging temperature in the ⁇ + ⁇ phase is chosen so that the volume proportion of the ⁇ phase in the ingot alloy is between 10% and 90%, the rest of the alloy being in the ⁇ phase.
• the ingot 1 is forged so as to obtain a slab 8 the thickness of which can be of the order of 100 mm which constitutes the semi-finished product which is then subjected to the operations of hot rolling and rolling to cold as described above, separated by steps of heat treatment of quenching and annealing.
• the hydrides precipitated in the product according to the invention are also generally smaller in size than the hydrides precipitated in a flat product according to the prior art.
• the corrosion resistance and formability properties of the flat product produced from the semi-finished product obtained according to the invention are therefore substantially superior to those of a product obtained by the process according to the prior art. These advantageous and surprising results could be due to the absence of quenching at high temperature on a slab obtained by forging in the ⁇ phase.
• one of the advantages of the process according to the invention is that it considerably simplifies the process for manufacturing the semi-finished product. There is thus obtained a substantial reduction in cost and duration in the implementation of the method.
• the product is only brought to a temperature situated in the range ⁇ and ⁇ , that is to say a temperature substantially lower than the temperature for maintaining the ⁇ phase of the process according to the prior art.
• the forging of ingot 1 in the ⁇ + ⁇ phase is carried out in a temperature range from 850 ° C to 950 ° C and for example 900 ° C.
• the transition into the ⁇ + ⁇ phase of the alloy for forging the process according to the invention can lead to the formation of tin segregations .
• the forging temperature in the ⁇ + ⁇ phase may be sensitive - ment less than 900 ° C, taking into account however the malleability properties of the alloy at the forging temperature.
• the invention applies in particular to the manufacture of a flat zirconium alloy product for the production of fuel assembly elements such as plates for the production of spacer grids for nuclear reactor assemblies.
• fuel assembly elements such as plates for the production of spacer grids for nuclear reactor assemblies.
• the temperature of forging in the ⁇ and ⁇ phase depends on the composition of the zirconium alloy.
• the forging operations can be carried out using the usual means for forging in the ⁇ phase or in ⁇ phase of the process of the prior art or other means suitable for forging in the ⁇ + ⁇ phase in a single operation to obtain a slab.
• the invention applies, in general, to any product made of a technical zirconium alloy defined by the limits of compositions given above.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
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• Organic Chemistry (AREA)
• Physics & Mathematics (AREA)
• Thermal Sciences (AREA)
• Crystallography & Structural Chemistry (AREA)
• Forging (AREA)

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Citations (7)

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• 2003
  • 2003-01-13 FR FR0300316A patent/FR2849865B1/fr not_active Expired - Fee Related
• 2004
  • 2004-01-09 CN CNB200480002113XA patent/CN100529148C/zh not_active Expired - Fee Related
  • 2004-01-09 RU RU2005125715/02A patent/RU2337177C2/ru not_active IP Right Cessation
  • 2004-01-09 EP EP04701028A patent/EP1585841A1/fr not_active Withdrawn
  • 2004-01-09 KR KR1020057012999A patent/KR20050090456A/ko not_active Application Discontinuation
  • 2004-01-09 WO PCT/FR2004/000036 patent/WO2004072318A1/fr active Application Filing
  • 2004-01-09 JP JP2006502091A patent/JP2006520430A/ja active Pending
  • 2004-01-09 US US10/541,262 patent/US20060081313A1/en not_active Abandoned

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