DK141763B - Zirconium alloy containing niobium, tin, iron and chromium and / or molybdenum. - Google Patents

Description

(11) PUBLICATION REPORT 1 41763 DENMARK («11 Intel.» C 22 C 16/00 § (21) Application No 3640/74 (22) Filed on 8 Jul 1974 (23) Running day 8 Jul 1974 (44) ) The application presented and the letter of presentation published on 9 · Jhn * '9 ου DIRECTORATE FOR _ PATENT AND TRADEMARKET <3 °) Priority book from the

Jul 9 1973, 2801/73, NO

(71) AB ATOMENERGI, Studsvik, 611 01 Nykoeping, SEE: ATOMENERGY COMMISSION, Strandgade 29, Copenhagen K, DK: INSTITUTE OF ATOMENERGY, PO Box 40, 2007 Kjeller, NO: UNITED KINGDOM-ATOMIC ENERGY AUTHORITY, 11, Char * les II Street , Loncfon SW 1, GB: VALTION TEKNILLINEN TUTKIMUSKESKUS, Loennrotln Katu 37, 00180 Helsinki 18, FI.

(72) Inventor: Liv Lunde, Askeladdveien 12, 1482 Nlttedal, NO: Gustaf Oes.t = berg, Karlavaegen 46, Stockholm, SE: Erich Tolksdorf, Rhoen Stresse 49, 6051 Nieder-Roden-Rollwold, DE: Raymond Cecil Asher, Woodcutts, Hermi * take Road, Cold Ash, Newbury, Berks, GB: Gerard Slattery, "Winterings, No. Preston PR4 ORI, GB: Frank William Trowse, 1" 2, Lea Road, Lea, ire * ston, GB: Christopher Tyzack, 19, GorseFank Road, Hale Barns, Chesbi = re, GB.

(74) Plenipotentiary in the proceedings:

Hofman-Bang & Boutard Engineering Company.

(δ4) Zirconium alloy containing niobium, tin, iron and chromium and / or molybdenum.

The invention relates to a corrosion resistant zirconium alloy containing niobium, tin, iron and chromium and / or molybdenum.

Zirconium alloys have been widely used for encapsulation for nuclear fuel, pressure pipes and other components within the reactor core due to their low neutron cross-section combined with satisfactory corrosion and mechanical properties.

In commercial water-cooled nuclear reactors, zirconium tin alloys preferably have "Zircaloy 2" (1.50% Sn, 0.15% Fe, 0.10% Cr and 0.05% Ni, the remainder Zr) and "Zircaloy 4" (1.50% Sn, 0.22% Fe, 0.10% Cr and at most 0.007% Ni, the remainder Zr) have been used extensively.

(All percentages given in this specification are by weight).

At a temperature below 300 ° C and without radioactive radiation, these alloys have the lowest corrosion rate reported for zirconium alloys, but their corrosion rate increases rapidly at higher temperatures. Under the combined influence of oxygen and radioactive radiation, the corrosion rate can be significantly increased.

A number of alloys with much better corrosion resistance at higher temperatures than "Zircaloy 2 and 4" are already known. All of these alloys, consisting essentially of Zr, Cr and Fe, have the disadvantage of having much higher corrosion rates than "Zircaloy 2 and 4" at low temperatures. For most of the alloys, the corrosion resistance depends on a complicated heat treatment which increases the price of the finished product so that they cannot be exploited commercially on a large scale.

Zirconium alloy with 1.0% Nb has been widely used for enclosure tubes in the USSR, and zirconium alloy with 2.5% Nb is used. used for pressure pipes for reactors in many countries. These alloys have a corrosion rate higher than "Zircaloy" without irradiation, especially in environments containing oxygen. The usual difficulty with these alloys is that their corrosion behavior is highly dependent on proper heat treatment. This problem is particularly pronounced in connection with welds.

Zirconium-niobium-tin alloys are also known. Among these alloys, one has the most experience with "Ozhenite 0.5", (0.2% Sn, 0.1% Fe, 0.1% Ni and 0.1% Nb, the remainder Zr) and zirconium alloy with 3% Nb and 1% Sn. The combination of Nb and Sn appears to provide alloys with good corrosion resistance over a larger temperature range, since Sn ensures low temperature resistance by counteracting the detrimental effect of nitrogen. The 3% Nb alloy has the same disadvantages as the above-mentioned Nb alloys, while "Ozhenite 0.5" has the disadvantage of having lower strength.

From Swedish Patent Specification No. 319,309, a zirconium alloy containing 0.5-5% by weight of niobium, 0.005-1% by weight of beryllium and possibly one or more of the substances tin, copper, iron, chromium, molybdenum, vanadium, tungsten is known. , tantalum, nickel, yttrium, antimony and tellurium, as well as the rest zirconium (except impurities), whereby the amount of components other than zirconium in the alloy constitutes a maximum of 10% by weight. This alloy has a relatively high niobium content, and therefore pure niobium tends to precipitate from the solid zirconium / niobium phase in the alloy. This makes the heat treatment of the alloy more difficult and the welding properties of the alloy deteriorate.

The zirconium alloy of the present invention is characterized in that it consists of 0.25-1.50 wt% niobium, 0.025-0.20 wt% tin, 0.02-1.00 wt% of chromium and molybdenum and the remainder zirconium, the total sum of niobium, chromium and molybdenum being between 0.7 and 1.8% by weight.

By adding alloys of Zr-Nb-Sn small amounts of chromium and molybdenum improved corrosion resistance and lower heat treatment sensitivity were achieved. The special features of the new alloy are: - Corrosion resistance comparable to "Zircaloy 2 and 4" at low temperature and at high temperature comparable to the best resistant zirconium alloys.

- Corrosion rate which is not accelerated by the combined influence of oxygen and radioactive radiation.

- Good corrosion resistance and mechanical properties that do not depend on complicated and expensive heat treatments.

The use of Sn ensures the resistance at low temperature, and the other alloying additions ensure the resistance at high temperature. Experiments have shown that good corrosion resistance is dependent on a fine and evenly distributed secondary phase. The alloys of the invention achieve the distribution of the secondary phase by normal fabrication routines, with quenching and aging steps being required only at the workpiece stage.

Another advantage is that the secretions prevent grain growth by prolonged heating over recrystallization temperature. This effect arises from fixation of the grain structure due to the precipitation.

4 141763

By extensive trials and tests, the applicants have determined that, with zirconium alloys with alloying constituents within the limits set forth in the patent claim, a significant simplification of the alloy thermal treatment is surprisingly achieved. Thus, a troublesome quenching that has previously been necessary for niobium-containing zirconium alloys has been possible to avoid without reducing the alloy's corrosion resistance and mechanical strength properties. This is of particular importance in the manufacture of very large reactor components which can be of such length that effective quenching is hardly possible ·, in any case not on an industrial scale.

Chromium and molybdenum can replace each other over a wide mixing range. Iron is almost always present as an inevitable contaminant in zirconium alloys. Preferably, the alloys should contain at least 0.02% Fe.

Five alloys which constitute preferred embodiments are the alloys listed below "Scanuk 2, 3, 4, 5 and 6".

e

Alloy Nb Sn Cr Mo Fe 2 0.92-0.94 0.06-0.09 200 ppm 45 ppm 0.04 3 1.10-1.13 0.05-0.06 0.41-0.54 40 ppm 0.04-0.05 4 0.49-0.54 0.05-0.07 0.45-0.50 40 ppm 0.03-0.04 0.47-0.51 0, 04-0.05 100 ppm 0.27-0.28 0.03-0.04 6 0.56-0.61 0.05-0.06 0.32 0.22 0.04

Results of corrosion tests for these alloys and some prior art alloys are shown in Tables 1-6.

The corrosion tests show that preferred alloys should contain 0.45-1.2% by weight niobium, 0.04-0.1% by weight tin, 0.25-0.60% by weight of the sum of chromium and molybdenum and 0 , 02-0.05% by weight of iron, the total sum of niobium, chromium and molybdenum being between 0.7 and 1.8% by weight.

Corrosion tests have been performed in autoclaves and test circuits under conditions as specified in the tables below. The alloys have been tested as thin sheets and tubes. It will be appreciated that the new alloys are noted to have a corrosion rate comparable to the corrosion rate of "Zirca-loy 2" at low temperatures and that they have a much better corrosion rate at high temperatures.

It can be seen from Table 5 that the hydrogen uptake of the alloys over the entire temperature range 290-500 ° C is significantly lower than that of "Zircaloy 2".

The alloys have been tested at 240 ° C in the Halden reactor, and as can be seen from Table 6, the good corrosion behavior at low temperatures is also maintained under radioactive irradiation. Other improved alloys such as Zr-Cr-Fe and "Ozhenite 0.5" have a much higher corrosion rate.

Table 7 shows a comparison of the grain size of the different alloys at different temperatures together with "Zirca-Loi 2". The results clearly show the current resistance of grain alloys to grain growth compared to "Zircaloy 2" at the same temperature.

During fabrication, all alloys were cast into blocks of 15 cm diameter and heat treated at 1000-1050 ° C for 1 hour. The block was hammered to 20 cm diameter at a temperature of 950 ° C with subsequent heat treatment at 1000-1050 ° C for 1 hour. The blank was then forged to 14 cm diameter at a temperature of 950 ° C and again heat-treated at 1000-1050 ° C for 2 hours before a subsequent quench in water. Samples for chemical analyzes, metallographic examination of grain size and distribution of intermetallic particles were taken from the end and middle of the blanks. The blanks were machined to remove incandescent shells. The further treatment varied, depending on whether bolts, plates or tubes were to be made.

1. For making bolts, the material was heat treated at 750 ° C and hot rolled to the desired dimension with intermediate heat treatments at 750 ° C. The bolt was then subjected to centerless grinding, stained and cast for 1 hour at 675 ° C.

2. For making sheets, the material was heat treated at 750 ° C and forged by medium annealing to 750 ° C. The final thickness was obtained by cold rolling with intermediate annealing at 675 ° C.

The final roll-out provided a 60% thickness reduction without further heat treatment.

3. For the manufacture of pipes, the workpiece was machined, coated with copper, heat-treated at 750 ° C and extruded. The copper was removed by acid machining, and the tubes were cast at 675 ° C. The tubes were rolled to the desired dimension in a medium annealing pilgrimage plant made at 675 ° C. The final tube reduction gave an area reduction of 70% and the tubes were given a final heat treatment. 4 hours at 600 ° C. The tubes were sanded externally and sand blasted inside.

TABLE 1 Weight gain for various alloys tested in degassed water at 290 ° C. 74 kg / cm2 p Weight gain - mg / dm

Alloy 168 504 1176 1848 2856 3452 Hours Hours Hours Hours Hours "Soanuk 2" 8.2 10.5 13.7 16.4 18.9 20.5 3 8.4 11.4 14.8 17.6 20 4 22.3 4 8.2 9.9 12.2 14.0 15.7 16.9: - 5 8.8 11.6 13.9 16.1 18.3 19.4 6 9.2 13.7 16.1 18.0 19.7 20.7

Zr-2 plate 9.9 12.2 14.9 15.5 16.7 17.3 iS plate? M «1 13-2 16> 3 22'4 24'3" Pressure Tube 9.5 13.2 16.0 19.2 21.5 22.9 7 141763 TABLE 2 Weight gain for various alloys tested in water with 7 ppm oxygen at 290 ° C, 91 kg / cm2 2 Weight gain - mg / dm

Alloy 168 528 1200 hours hours hours "Scanuk 2" 13.2 21.3 29.0 3 11.6 23.2 30.8 in 4 8.6 15.4 16.4 5 10.1 13.0 16, 4 6 12.1 19.4 21.0

Zr plate 11.9 14.3 16.4; plate1 / 2% Nb "16'8 28'4 56.6" pressure tube 15.7 24.3 33.1 ......

TABLE 3 Weight gain for different alloys

r \ O

tested in steam at 400 C, 70 kg / cm 2 Weight gain - mg / dm

Alloy 33 72 ~~ 72 336 624 1248 1752 2424 Hours Hours Hours Hours Hours ', fScanuk 2 "24.0 44.7 57.1 66 ·,' 8 84.4 101.0; 3 23.0 46.0 62.9 80.7 112.8 151.2 4 22.2 34.0 45.1 52.6 68.5 93.2 j 5 28.4 40.6 51.9 61.7 77.9 103, 4 6 27.5 50.4 60.5 69.0 89.2 113.6 i

Zr-2 plate 25.4 38.1 53.8 61.5 78.6 93.9 j

NblplJd? 38'5 75> 0 99 »3 132» ° 192'2 260'8 '"Pressure Tube 29.6 48.9 62.3 70.5 90.4 120.5 i 8 141763 TABLE 4 Weight gain for various alloys tested in steam at 500 ° C, 70 kg / cm2 Weight gain - mg / dm

Alloy - 72 168 336 672 1008 Hours Hours Hours Hours "Scanuk 2" 80.6 135 229 447 644.7 3 92.3 149 294 539 751.7 4 64.8 109 233 420 597.9 5 76.5 133 234 416 569.4 6 90.1 153 293 518 734.3

Zr-2 plate 5797 disintegrated

Nb Platform 111 207 457 776 1050 · 6 "Pressure Tube 84.4 132 334 556 742.7 TABLE 5 Weight gain for alloys tested for 331 days under 12 irradiation at a neutron flux of 10 neutron / cm * sec in water _ at 240 ° C__ Weight- Range Number of Appearances

Alloy increase mg / dm ^ samples "Scanuk 2" 62.1 58.0-64.2 4 Black, glistening 3 53.4 51.9-54.3 4 "» 4 55.9 51.0-58.0 4 Black, some matt 5 76.5 72.8-79.0 3 "" "6 69.8 63.0-79.0 4 Black, glossy (66.6) (63.0-69.1) ( 3)

Zr-2.5% Nb 58.1 51.9-63.0 3 Gray, matt "Ozhenite 143.4 135.8-150.6 3 Black, glistening 0.5"

Zr-Cr-Fe 130.9; 128.4-133.3 3 Black

Zr-2 54.3! 53.1-55.6 3 Black, shiny 141763 9 TABLE 6

Hydrogen uptake under various furnace-irrip conditions

^ —I ————— I I I II I j "'........ I' '" 1 "1 —I. P

i. Degassed water 9 Vapor 9 Vapor Q

2goo? 4 kg / cm ^ 400o 70 kg / cm ^ 500o c> 70 kg / cm ^ 2856 hours 2682 hours 1008 hours

Alloy mgH2 / dm2% H2 mgH2 / dm2% H2 mgH2 / dm2% H2 "Scanuk 2" 0.23. 9.7 3.02 21.3 28.81 36.8 3 0.23 9.7 4.74 21.7 52.11 57.4 4 0.20 10.7 3.98 31.6 32.19 43.4 5 0.28 11.7 4.39 28.7 37.57 55.6 6 0.29 11.8 6.29 38.9 53.02 56.9

Zr-2 plate 0.88 41.9 5.37 40.7 disintegrated plate590 ^ ° '38 l4' ° 7'75 20'7 ^ 36 37.3 "pressure tube 0.30 11.0 3.43 20.1 34.20 38.1 TABLE 7

Grain size dependence on annealing temperature

alloy

Time Temperature "Scanuk" Scanuk "Scanuk" Scanuk "Scanuk 7 P (hours) (° C) 2" 3 "4" 5 "6"

Average grain size in 550 4.1 3.8 3.8 3.7 3.9 4.9 600 4.7 4.2 3.9 4.1 4.4 5.8 24 650 5.3 4.4 4 , 3 4.5 5.1 7.3 700 7.4 5.1 5.0 5.8 5.9 9.2 760 9.0 6.3 6.5 6.7 6.6 11.9