Classifications

• • 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
  • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
  • C21D9/46—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals
• • 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
• • 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

Definitions

• the present invention relates to a process for manufacturing a zirconium alloy strip for nuclear use "Zircaloy 2" (specification ASTM B52, grades R 60802 and R 60812) or "Zircaloy 4" (same specification, grades R 60804 and R 60814 ), resulting for this strip in a "restored” state corresponding to a compromise of mechanical strength and ductility.
• “restored” state one indicates here a heat treated state without there being complete recrystallization as in an annealed state, in which the stresses due to hardening are partly at least relaxed.
• the present invention also relates to the strip obtained.
• Zircaloy 2 or 4 strip of thickness typically between 0.3 and 0.9 mm, having both: a good elastic limit at the operating temperature, and good ductility at room temperature (20 ° C) identified by the elongation distributed in the long direction and also in the transverse direction of the strip - so as to behave well vis-à-vis conformations of this manufacture of grids.
• distributed elongation is the maximum elongation of a test piece during a tensile test, before the necking begins.
• the characteristics thus sought for this strip are typically: E 0.2 to 315 ° C ⁇ 250 MPa A% distributed long direction ⁇ 4 and if possible ⁇ 5 A% distributed across ⁇ 4 and if possible ⁇ 5.
• the invention relates to a strip of Zircaloy 2 or Zircaloy 4, typically having: - an oxygen content of between 900 and 1600 ppm, - And a carbon content preferably between 50 and 160 ppm.
• the deformation rates (%) corresponding to each rolling or rolling sequence are calculated according to the formula: (1 - final thickness / initial thickness) x 100.
• the intermediate deformation rates and the intermediate annealing conditions are chosen so that, after each of these intermediate anneals, a just recrystallized state is obtained, while avoiding grain enlargement, which makes it possible to obtain an extremely equiaxed grain. end by annealing.
• the rate of deformation and the conditions of final heat treatment are themselves chosen, and these are particularly important points, so that this treatment results in partial recrystallization of the strip.
• Micrographically the strip then comprises very fine grains obtained by the last intermediate annealing and elongated by the last rolling, grains which often have a length of between 10 and 20 microns.
• Electron microscope examinations show that in these elongated grains there are locally sub-grains a few microns in diameter which are fully recrystallized, while the surrounding matrix has remained hardened.
• the fully recrystallized subgrains represent a volume of between 20 and 40% of the total.
• the final heat treatment is preferably carried out at the runway between 600 and 625 ° C., the constant speed of the strip ensuring maintenance of 2 to 5 min at the processing temperature. And, more preferably, independently of, or in combination with the previous measurement, the strip is laminated between the last intermediate annealing and the final heat treatment with a deformation rate of 35 to 45%.
• the deformations and the two preceding intermediate anneals also play a role in obtaining and improving the surprising compromise in the characteristics of the strip of the invention.
• the adjustment of these intermediate anneals is then particularly desirable (obtaining states that are just recrystallized at 100%), and it is preferable to tighten the conditions of duration and temperature. ture of these last two intermediate anneals: each then comprising for the strip a stay of 1 to 3 min between 680 and 720 ° C, whether this is the general case or the process already improved at the level of the final heat treatment or final strain rate.
• An optimum consists in making the last two intermediate anneals as well as the final heat treatment at the constant speed parade, each of these two intermediate anneals is then preferably carried out between 680 and 720 ° C with a scrolling speed ensuring a maintenance of 1 3 min at processing temperature.
• the final heat treatment is thus preferably carried out in the procession, under a protective atmosphere or possibly in air, and it is then followed either by a pickling, or by a slight brightening of the surface itself followed by a pickling.
• the protective gas is preferably under slight overpressure in the heating chamber, and at the exit of this heating chamber, the strip enters an airlock or a cooling chamber where it is cooled below 300 ° C by blowing cold inert gas .
• the subject of the invention is also the strip of the invention which, with its composition and its particular mechanical characteristics, is distinguished in particular from the strips previously known by a particularly fine grain, this grain being in cross section finer than the ASTM index. "11" with partial recrystallization affecting 20 to 40% of the volume.
• Zircaloy 4 strip (nominal composition: Sn 1.5% - Fe 0.2% - Cr 0.1% - Zr the balance), coming from a flow X of oxygen content 1290 ppm and carbon content 90 ppm, laminated to thickness 0.44 mm.
• the final deformation rate was 43% and the final heat treatment was done in static under vacuum as it was then usual at 460 ° C for 24 h, the intermediate anneals themselves being 3 to 4 h at 650/700 ° C.
• the heat-treated samples have a recrystallized grain deformed in the long direction, corresponding on cross section to the ASTM index "10".
• the parade heat treatments were carried out in an oven operating with a protective argon atmosphere.
• the running speed of the strip was chosen so as to obtain the desired temperature residence time for each portion of the strip treated.
• Each of the three intermediate anneals at the parade gives for the strip, according to examinations carried out with the electron microscope, a just state recrystallized with very fine grain.
• the size of the fine grain recrystallized at the last intermediate annealing measured on cross section is from “11" to "11.5" ASTM.
• the final recrystallization, appreciated with the electron microscope, is very fine and affects 20 to 40% of the volume.
• f T and f L show that the anisotropy remains relatively low, which is favorable for the behavior in the reactor, the deformations of the grids then being less troublesome (less distortions in service).
• the strip obtained thus achieves a good compromise between aptitude for stamping and isotropy of texture.
• this strip is too stiff (E 0.2 strong cross) and difficult to conform (see also A% distributed across).
• the size of the fine grain recrystallized during the last intermediate annealing is the same as in the 2nd series of tests (only the final heat treatment differs).
• the final recrystallization affects 20 to 40% of the volume.
• This strip is a little less stiff and a little easier to conform than that of the 2nd series of tests.
• the method of the invention therefore allows precise quality adjustments, with particularly reproducible results in the case of parade treatments.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Organic Chemistry (AREA)
• Metallurgy (AREA)
• Materials Engineering (AREA)
• Crystallography & Structural Chemistry (AREA)
• Physics & Mathematics (AREA)
• Thermal Sciences (AREA)
• Heat Treatment Of Sheet Steel (AREA)
• Inorganic Compounds Of Heavy Metals (AREA)
• Battery Electrode And Active Subsutance (AREA)
• Heat Treatment Of Strip Materials And Filament Materials (AREA)
• Metal Rolling (AREA)

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Citations (4)

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• 1986
  • 1986-05-21 FR FR8607760A patent/FR2599049B1/fr not_active Expired
• 1987
  • 1987-05-18 DE DE8787420129T patent/DE3761023D1/de not_active Expired
  • 1987-05-18 US US07/050,569 patent/US4775428A/en not_active Expired - Fee Related
  • 1987-05-18 ES ES87420129T patent/ES2011818B3/es not_active Expired - Lifetime
  • 1987-05-18 EP EP87420129A patent/EP0246986B1/de not_active Expired
  • 1987-05-19 KR KR1019870004958A patent/KR920000526B1/ko not_active Expired
  • 1987-05-20 JP JP62123630A patent/JPS6324048A/ja active Granted
• 1988
  • 1988-03-15 US US07/168,451 patent/US4881992A/en not_active Expired - Fee Related

Patent Citations (4)

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