Patent Number: 056489951
Section: description

DESCRIPTION OF PREFERRED EMBODIMENTS EXAMPLE 1 Intermediate treatments: 2 hours at 580.degree. C. PA1 Final treatment: 2 hours at 580.degree. C. PA1 Intermediate treatments: 2 hours at 700.degree. C. PA1 Final treatment: 2 hours at 580.degree. C. PA1 Intermediate treatments: 2 hours at 700.degree. C. PA1 Final treatment: 2 hours at 700.degree. C. PA1 Example 1: 48 mg/dm.sup.2 PA1 Example 2: 57 mg/dm.sup.2 PA1 Example 3: 63 mg/dm.sup.2 PA1 quenching in water after heating for 1 hour at 1050.degree. C.; PA1 machining a billet having an outside diameter of 168 mm and an inside diameter of 48 mm; PA1 extrusion after induction heating to 650.degree. C. to obtain an outside diameter of 80 mm and an inside diameter of 48 mm; PA1 rolling tubes in five cycles, including intermediate heat treatments for 2 hours at 580.degree. C.; and PA1 final heat treatments for 2 hours at 580.degree. C. PA1 Zr: 1% Nb, 150 ppm Fe, recrystallized: 0.5; PA1 "Zircaloy 4" recrystallized from a composition that is optimal from the creep point of view: .ltoreq.1.0%. EXAMPLE 2 EXAMPLE 3 The mass increases during autoclave testing were as follows: The samples in all three examples had an iron content of 150 ppm. It was observed that the alloy presented a "memory" phenomenon such that the effect of a single treatment at above 620.degree. C. applied to the alloy later than the first pass was never completely "forgotten". In general, the intermediate heat treatments should be performed at a set temperature lying in the range 565.degree. C. to 605.degree. C.; a temperature greater than 580.degree. C. for the intermediate treatments and a temperature of about 580.degree. C. for the final treatment have been found to be particularly satisfactory for most compositions. A tube can be manufactured from an extruded blank in particular by performing four or five passes separated by heat treatments in the range 560.degree. C. to 620.degree. C., and advantageously close to 620.degree. C. An oxygen content of about 1200 ppm has been found satisfactory to obtain a favorable effect on the resistance to creep in a recrystallized alloy. The invention also proposes a sheathing or guidance tube for a fuel assembly for a nuclear reactor that is cooled and moderated by pressurized water, the tube being made of a zirconium-based alloy in the fully recrystallized state, having 50 ppm to 250 ppm iron, 0.8% to 1.3% by weight niobium, 1000 ppm to 1600 ppm oxygen, less than 200 ppm carbon, less than 120 ppm silicon, the balance being zirconium, excepting unavoidable impurities. When the alloy made in this way is examined, it can be seen that there are no alignments of .beta. Zr precipitates, which are harmful from the corrosion point of view. Comparative tests have been performed on alloys having niobium contents lying in the range 0.86% to 1.3% and iron contents lying in the range 100 ppm to 150 ppm. A representative manufacturing range, starting from a forged bar having a diameter of 177 mm, is as follows: Tests showed generalized corrosion resistance in a high temperature aqueous medium representative of conditions in a high pressure water reactor comparable to those of known Zr-Nb alloys having a high niobium content; they also showed hot creep strength much better than that of known alloys and very comparable to that of the best "Zircaloy 4" alloys: thus, after 240 hours at 400.degree. C. under 130 MPa, the following creepage diameter deformations were measured: