Patent Number: 058870458
Section: description

Other characteristics will become more clear from the description of particular embodiments. The following compositions found of interest: ______________________________________ COMPOSITIONS I II III ______________________________________ Tin 1.3 1.3 1.3 Iron 0.6 0.6 0.6 Vanadium 0.3 0.25 0 Chromium 0 0 0.25 Oxygen 0.12 0.14 0.14 Carbon 140 140 140 Silicon 90 90 90 ______________________________________ the other components being zirconium and impurities. The starting alloy was in the form of an ingot. It was formed into a bar by forging or rolling and, after heating to the .beta. phase, was water quenched at a controlled rate to bring it into the .alpha. region, for example at a cooling rate in the range 5.degree. C. per second to 30.degree. C. per second until the temperature was less than about 800.degree. C. After quenching, annealing was effected at a temperature of less than 800.degree. C. to prevent transformation of the .alpha. phase into the .beta. phase. Extrusion was carried out after machining a tubular billet and heating to between 600.degree. C. and 700.degree. C. The drawn blank, after undergoing any required annealing at a temperature of less than 800.degree. C., then underwent the required number of successive cold rolling steps to bring it to the required thickness, with intermediate annealing steps carried out in argon, each for one to three hours, to produce a suitable .SIGMA.A. In practice, four or five rolling steps were generally carried out to produce solid cladding tubes of conventional diameter and thickness. Finally, a final annealing step was carried out in an inert atmosphere, at about 485.degree. C. for one to three hours if a stress-relieved structure was required, or at about 580.degree. C. for about two hours if a recrystallized structure was required. The tests were carried out on samples to compare the alloys of the invention containing different tin contents with Zircaloy-4 type alloys. Generalized Corrosion Tests were carried out on recrystallized samples in an autoclave, in water and steam. The results are shown in Table I below. TABLE I ______________________________________ Weight gain .DELTA.P (mg/dm.sup.2) Water Steam ALLOY 350.degree. C. - 210 days 400.degree. C. - 30 days ______________________________________ 1 Zr 0.6 Fe; 0.3 V 29.2 26.4-38.5 2 Zr 0.6 Fe; 0.3 V; 0.5 Sn 31 27.5 3 Zr 0.6 Fe; 0.3 V; 1.0 Sn 32.2 30.4 4 Zr 0.6 Fe; 0.3 V; 1.5 Sn 32 30.9 (invention) 5 Zircaloy 4 43.9-47.2 32 ______________________________________ The results obtained, in particular for alloy 4 which was in accordance with the invention, show that an increase in the tin content from 0 to 1.5% had no effect on generalized corrosion resistance in water and steam. Corrosion in a Lithium Medium and Creep Resistance The influence of tin content on the corrosion resistance of Zircaloy 4 type alloys in a medium containing lithium hydroxide was studied in water containing 70 ppm of lithium at 360.degree. C. The results are shown in Table II. TABLE 2 ______________________________________ % Sn in Weight gain .DELTA.P (mg/dm.sup.2) alloy 50 days 100 days 150 days ______________________________________ 1.5 48 78 112 1.3 51 85 148 0.5 35 72 740 ______________________________________ The highly favorable influence of a high tin content (between 1.2% and 1.5%) on the corrosion resistance in a lithium hydroxide medium was observed in alloys in accordance with the invention. A high tin content was also shown to be favorable to the creep resistance of this alloy. Measurements of diametral creep .epsilon..sub.D at 400.degree. C. over 240 hours at a pressure of 130 MPa gave the following values for a stress-relieved alloy: ______________________________________ Sn content (%) .epsilon..sub.D (%) ______________________________________ 1.5 (invention) 1.5 1.3 (invention) 2 0.5 4.2 ______________________________________ The results obtained show a quasi-linear relationship between the Sn content and the creep characteristics.