CA1163120A - Low in reactor creep zr-base alloy tubes - Google Patents
Low in reactor creep zr-base alloy tubesInfo
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- CA1163120A CA1163120A CA000355707A CA355707A CA1163120A CA 1163120 A CA1163120 A CA 1163120A CA 000355707 A CA000355707 A CA 000355707A CA 355707 A CA355707 A CA 355707A CA 1163120 A CA1163120 A CA 1163120A
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- 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
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- Materials Engineering (AREA)
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- Metallurgy (AREA)
- Organic Chemistry (AREA)
- Heat Treatment Of Steel (AREA)
- Heat Treatment Of Nonferrous Metals Or Alloys (AREA)
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Abstract
ABSTRACT
A process for fabricating tubes from a quaternary 3.5% Sn, 1%Mo, 1% Nb balance Zr alloy by hot extrusion, cold working and heat treatment so that the tubes have small grains that have low dislocation densitics. The tubes are superior to the standard cold worked Zr-2.5wt% Nb tubes because during service in CANDU-PHW reactors they (a) have lower axial elonga-tion and diametral expansion and (b) the hydrides are less susceptible to reorientation from the circumferential-axial plane into the radial-axial plane.
A process for fabricating tubes from a quaternary 3.5% Sn, 1%Mo, 1% Nb balance Zr alloy by hot extrusion, cold working and heat treatment so that the tubes have small grains that have low dislocation densitics. The tubes are superior to the standard cold worked Zr-2.5wt% Nb tubes because during service in CANDU-PHW reactors they (a) have lower axial elonga-tion and diametral expansion and (b) the hydrides are less susceptible to reorientation from the circumferential-axial plane into the radial-axial plane.
Description
1 :~ 63:1~0 This invention relates to zirconium alloy tubes especially Eor use in nuclear power reactors. More parti-cularly this invention relates to quaternary 3.5% Sn, 1% Mo, 1% Nb, balance Zr alloy tubes which have been extruded, cold worked and heat treated to lower their dislocation density.
In one preferred embodiment ~he alloys are cold worked less than 5~ and stress relieved to produce a low dislocation den-sity and in another embodiment the alloys are cold worked up to about 50~ and annealed to produce a very low dislocation density and also small equiaxed a grains.
Conventionally, pressure tubes for CANDU-PHW type nuclear reactors (Canada-Deuterium-Uranium-Pressurized Heavy Water) are fabricated by extrusion of Zr-2.5 wt.~Nb billets, followed by cold working and age hardening. Other Zr alloys can also be used for tubinq in CANDU-PHW tYPe reactors, such as Zircaloy-2~ and quaternary alloys containing 3.5~ Sn, 1% Mo, 1~ Nb, balance Zr, which provide high strength, low neutron capture cross section and reasonable corrosion resistance.
The heat treatment of the quaternary alloys above is described in the literature, and attention is particularly directed to U.S. Patent 4,065,32~ to Brian A. Cheadle, issued December 27, 1977 which describes a process for heat treating the quaternary alloys noted above and hereinafter referred to as EXCEL alloys, to produce a duplex micro-structure comprising primary a-phase and a complex acicular grain boundary phase. The object of the invention described in the aEoresaid U.S. patent is to provide an alloy having the maximum possible strength which i9 achieved by cold working to about 25% followed by age hardening but at the expense of increasing the dislocation density as well.
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7 ~ ~31~0 Although such heat treated -tubes have relatively good out-of-reactor creep strength, their in-reactor creep strength is adversely affected by the high dislocation density.
Unless otherwise stated all alloy percentages in this specification are percentages by weight.
In CANDU reactors it is desirable for the pressure tubes to have as low axial elongation and diametral expansion as possible during service. While it is possible to reduce elongation and expansion levels in conventional 30% cold worked Zr-2.5~ Nb pressure tubes by lowering their dislocation density and making their grains more equiaxed, this, however, also results in a lowering of the tensile strength which would then necessitate increasing the wall thickness with a consequent reduction in reactor efficiency. It is, therefore, necessary to consider the use of one of the alternative alloys referred to above. EXCEL is a stronger and more creep resistant alloy both in and out of reactor than Zr-2.5% Nb, and it has been found that pressure tubes having similar strength to 30% cold worked Zr-2.5~ Nb tubes can be fabricated with less than 5% cold work followed by stress relieving at a temperature in the range 650-800K. Similarly it has been found that low dislocation density EXCEL alloys can also be produced by cold working up to about 50% followed by annealing at a selected temperature in the range 900-1100K.
Thus it is an object of the present invention to provide a process -for heat treating and cold working EXCEL alloys, such that they have a minimum ultimate tensile strength of 479 MPa, and during service equivalent to 30 years in a CANDU-PHW 600 MW
reactor they have a maximum axial elongation of about l.5%, and ~ 3B3~0 a maximum diametral expansion of 2.5%.
It is another object of this invention to provide a heat treated and cold worked product consisting essentially of Sn 2.5-4.0~, Mo 0.5-1.5%, Nb 0. 5~1.5~, 0 800-1300 ppm, balance Zr and incidental impurities, said product having a minimum ultimate tensile strength of 479 MPa, a maximum axial elonga-tion less than 1.5~ and a maximum diametral expansion less than 2.5~ under conditions equivalent to 30 years service ïn a CANDU-PHW 600 MW reactor.
For the purposes of the present specification a 600 MW
CANDU-PHW reactor is considered to operate at a temperature of 565K, with a peak neutron flux of 3.85 x 1017 n/(m2.s) and at a mean coolant pressure of 10.6 MPa.
Thus, by one aspect of this invention there is provided a method of fabricating an extruded product from an alloy con-sisting essentially of Sn 2.5-4%, Mo 0.5-1.5%, Nb 0.5-1.5%, 0 800-1300 ppm balance Zr and incidental impurities wherein a billet of said alloy is preheated in the temperature range gO0-~ 1200K and extruded into said produc-t, and said extruded product is cold worked, by an amount up to about 50%, and heat treated at a selected temperature in the range 650-1100K, so as to have a dislocation density of less than about 5 x 1014 m 2 a minimum U.T.S. of 479 MPa, a maxlmum axial elongation less than 1.5~ and a maximum diametral expansion less than 2.5% under conditions equivalent to 30 years service in a CANDU-P~IW 600 M~
reactor.
By another aspect of this invention there is provided a heat treated and cold worked alloy for use in nuclear , `t~' ':' ,~
3~2~
reactor tubes and other extruded products and consisting essentially of Sn 2.5-4.0~/ Mo 0.5-1.5%, Nb 0.5-1.5% 0 ~00-1300 ppm, balance Zr and incidental impurities, having a minimum ultimate tensile strength of 479 MPa, a maximum in-service axial elongation of 1.5% and preferably in the range 0.5-0.8%, a maximum in-service diametral expansion of 2.5~ and preferably in the range 1.1 to 1.4~ and an equiaxed grain structure.
The invention will be described in more detail herein-after with reference to the accompanying drawings in which:
Figure 1 is a flow chart of a general fabrication route for alloys of the present invention;
Figure 2 is a flow chart of a specific fabrication route for alloys according to one aspect of the present invention;
Figure 3ta) is a transmission electron micrograph at 11,500X of extruded tubes cold worked less than 5% and stress relieved at 700K, of the present invention;
Figure 3(b) is a transmission electron micrograph at 11,500X of tubes cold worked greater than 5% and annealed at 1075 K, of the present invention;
Figure 4 is an average (0002) pole figure for seven tubes of the present invention; and Figure 5 is a ~eries of optical micrographs showing the effect of stress on the orientation of zirconium hydrides in E~CEL and Zr-2.5 wt.~ Nb tubes.
In power reactors that use internally pressurized tubes two important mechanical property requirements are tensile strength and dimensional stability during service. Dimensional ~ :~ 63 1 2~) stability is a function of both creep and growth (dimensiona]
change during irradiation without an applied stress). In zircon-ium tubes the ratio of creep in the axial and circumferential directions is a function of their crys-tallographic texture and the ratio of their growth in the axial and circumferential directions i5 a function of both crys-tallographic texture and the shape of the a grains. The crystallographic -texture of extruded and cold drawn tubes is largely a function of the extrusion conditions - temperature, die shape, strain rate, billet micro-structure and extrusion ratio. It has been found that the ratio of di`ametral expansion to axial elongation of a tube duriny service in a power reactor can be controlled by selecting the appropriate extrusion conditions.
The longitudinal tensile strength of 30% cold worked Zr-2.5 weight % Nb pressure tubes is due to their combination of high dislocation density, very small a grain thickness (0.3 x 10 3mm) and a duplex microstructure of a grains and grain boundary network of ~-phase. However, the in-reactor creep of of these tubes is adversely affected by their dislocation density and their in-reactor axial elongation due -to growth is adversely -affected by both their dislocatlon densit~and their very long elongated a grains (0.3 x 10 3mm thick x lOmm long)~ EXCEL is a stronger material than Zr-2.5 wt.% Nb. There~ore EXCEL tubes can be fabricated that are as strong or stronger than 30% cold worked Zr-2.5 wt.% Nb tubes, but have lower dislocation densities and/or more equiaxed ~ grains. These tubes have considerably better dimensional stability during service in pGwer reactors.
The tensile strength of these EXCEL tubes is largely a function of their dislocation density and grain size. Tubes ~ ~3~O
cold worked a minimum after extrusion and stress relieved will have thin elonyated a grains (Figure 3a). Their longitudinal tensile strengths can be up to 600 MPa at 575K depending on the stress relieving temperature. If the tubes are annealed after cold working to produce equiaxed recrystallized a grains (Figure 3b) then the size of the grains depends on -the amount of cold work and the annealing heat treatment.
Fabrication of Experimental Tubes A double arc melted ingot of EXCEL alloy was forged to 215mm diameter bar and machined to form seven hollow billets numbered 248-254. The billets were clad in steel and copper and preheated to about 1130K for approximately 5 hours and then extruded into tubes at a ratio of 13.5:1. The cladding was removed by dissolution in ni-tric acid, the inside of the tubes were sand blasted and the outside centerless ground. One end of each of the tubes was flame annealed, air cooled and pushed onto a die to point the end. A conversion coating was then applied and the tubes cold drawn between 2 and 5% as shown in Table 2. The chemical composition of the tubes is recorded in Table 1. The cold worked tubes were then sand blasted inside and centerless ground on the outside.
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TABLE 1: The Chemical Analysis of -the EXCEL Tubes ._ _ __ .. _____ _ . I
Tube Element Number Sn wt% Mo wt% Nb wt% O ppm H ppm .. _ _~ ._ 248 F 3.32 0.81 0~83 1157 34 248 B 3.08 0.77 0.79 1203 48 249 F 3.31 0.81 0.80 1142 30 249 B 3.29 0.82 0.81 1089 26 250 F 3.23 0.79 0.82 1142 36 250 B 3.31 0.82 0.82 1131 26 251 F 3.32 0.79 0.83 1149 , 34 251 B 3.42 0.80 0.81 1134 28 252 F 3.46 0.83 0.80 1142 29 252 B 3.29 0.75 0.79 1119 25 253 E' 3.39 0.78 0.84 1149 32 253 B 3.31 0.80 0.70 1116 18 254 F 3.38 0.78 0.82 1118 54 254 B 3.47 0.81 0.80 1115 34 .. _._ _ _ _ MEAN 3.33 0.80 0 80 1136 34 F is the front end of the tube and comes out of the extrusion press first.
B is the back end of the tube and comes out of the extrusion press ]as-t.
~ 3 63 1 ~
TA~LE 2: Extrusi~ C~ld Dr~wing Data for the EXCEL Pressure Tubes .. _.. _ ..._, ,_ . . .
Billet Total Furnace Pressure I.ength of % Cold Number Preheat Time to Start Tube Extruded Draw ps i m __ . _ . _ ._ . . . _ .. .__ ~
248 5 hours 52 minutes 1800 7.5 2.83 249 5 hours 56 minutes 2000 5.8 3.71 250 6 hours 3 minutes 1750 7~3 3.16 251 7 hours 22 minutes 1700 7.5 2.77 10 252 7 hours 17 minutes 1800 7.4 4.36 253 6 hours 48 minutes 2300 4.3 2.90 254 7 hours 10 minutes 160- .. _.. __ ~.. .. .__. 2.89 Two tubes, 249 and 251 were annealed in a vertical vacuum furnace for 30 minutes at 1023K to produce an equiaxed alpha grain s-tructure. An equiaxed alpha grain structure should produce a lower ln-reactor axial elongation rate at the expense . . - of a slightly lower tensile strength.
. ~ -- Sections o~ tube 248:were cold worked up to 40% and :~
-then annealed for 30 minutes at a selected temperature in the ::
range 1025-1075K.
All the tubes were finally stress relieved in an auto-clave for 24 hours at 675K.
The general fabrication route is shown in Figure 1 and the particular steps for these seven tubes are shown in Figure 2.
3~ 2~
TABLE 3: a Grain Size and Dislocation Density -of the EXCEL Pressure ~ubes Tube % Cold Grain Size mmxlO 3 Disloca-Number Drawn Front eod Back end Aver. D n~i 250 3.7 0.15 0.48 0.62 8.4 x 252 3.2 0.81 0.46 0.6 253 2.8 0.76 0.39 0.5 254 4.4 0.70 0.5~ 0.62 Mean 0.76 0.51 0.64 _ __ 24~ 2.9 0.80 1.4 x 251 2.9 0.74 l~l~
Cold worked 5-9 x Zr-2.5% Nb 0.4 0.2 0.3 1~14 tubes - _ PROPERTIES OF THE EXPERIMENTAL TUBES
- Microstructure and Texture .
- - Grain sizè and shape are important parameters in -the .
tensile strength and in-reactor dimensional stability of zirconium alloy pressure tubes. The microstructures were examined by thin film electron microscopy. The results, Figure 3a and Table 3, show that the microstructure of the cold worked tubes consists of elonga-ted a grains, a thin grain boundary network of ~-phase, and a few localized areas of martensitic a'. The a grain thicknesses were larger than typical cold worked ~r-2.5% Nb pressure tubes, Table 3. The two annealed tubes~ 249 and 251 had larger relatively equiaxed a grains, Figure 3b, with the ~phase concentrated a-t grain ~ ~i33~
corners. The five cold worked and stress relieved tubes had much higher average dislocation density than the annealed tubes, as seen in Table 3. The texture of the annealed and cold worked tubes was similar and an average (0002) pole ~igure for the seven tubes is shown in Figure 4.
The effect of varying amounts of cold work and anneal-ing temperature on the a grain thickness of an extruded tube is shown in Table 4 (below). The smallest grain thickness was obtained with 30% cold work followed by annealing for 30 minutes 10at 1025K.
TABLE 4: The Effect of Cold Work and Annealing Heat Treatment on the Grain slze of Extruded EXCEL Tube 248 Thlckness of a Grain, mm x 10 ~
% Cold Work 30 minu-tes at30 minutes at ...
0 0.80 0.80 0.79 1.08 0.72 _ 0.59 0.98 0.53 0.97 1.11 1.72 ; 20Tensile Strength The longitudinal and transverse tensile strengths of the tubes are shown in Table 5. The cold-worked and stress relieved tubes were considerably stronger than the annealed tubes due to their smaller grain thickness and higher disloca-tion densityO The annealed tubes met -the minimum specifications : for 30~ cold-worked Zr-2.5 wt~ Nb pressure tubes.
Hydride Orientation As fabricated the hydrides were oriented in -the radial-axial plane. The effect of hoop stress on the orientation of .
3 ~ 2 ~
the hydrides that precipitate during cooling from 575K is shown in Fiyure S. To precipi-tate hydrides in the radial-axial plane required a hoop stress of 827 MPa.
TABLE 5: Tensile Properties of the EXCEL Pressure Tubes and Typical Tens.ile Properties of 30% Cold-Worked -Zr-2._~ Nb Pressure Tubes Alloy Tube Test Test 0.2~ Yield UTS
Condi- Tempera- Direc- Stress MPa MPa Elonga-tion ture K tion _ tion 5% T 620 645 13 cold drawn 300 L 736 845 12 EXCEL _ an- 575 T 490 555 13 _ nealed 300 T 615 745 17 Zr- co%ld 575 L 580 56200o 152 Nb drawn 3 0 0 T 640 810 15 L is longitudinal T is transverse COMPARISON WITH ST~NDARD Zr-2.5% Nb ALLOY ~RES5VRE TUBES
Tensile Strength Cold worked Zr-2.5% Nb is the reference pressure tube material for CANDU-PHW reactors. EXCEL alloys having chemical compositions in the range 2.5-4.0% Sn, 0.5-1.5% Mo, 0.5-1.5% Nb, 800-1300 ppm O, balance Zr plus incidental impurities, have been found to have higher strengthG than the Zr-2.5% Nb alloys and good in-reactor creep resistance.
In all metallurgical conditions EXCEL alloys are stronger than Zr-2.5% Nb but when heat treated to produce the ~, - 11 -~ t ~3~2~
required high strengths for use in a reactor the ductility is relatively low as shown in Table 6.
TABLE 6: T} Tensile Properties of Zr-2.5% Nb and EXCEL alloy at 575K
Alloy Conditlon 0.2% YS UTS Total MPa K psi MPa K psi Elongation _ Zr-2.5% Nb Annealed 207 30 28040 30 EXCEL Annealed 338 40 46065 20 Zr-2.5% Nb 20% cold worked 365 53 40659 11 EXCEL 20% cold worked 517 75 57984 11 Zr-2.5% Nb Heat treated 579 84 644935 15 EXCEL Heat _ _ __ treated 620 115 860130 1_ _ ___ _ _ Typical tensile properties of cold worked Zr-2.5%
Nb pressure tubes and EXCEL pressure tubes in the extruded condition and also cold drawn about 3%, 10%, and 15% are shown below in Table 7.
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TABLE 7: Typical Te_sile Proper-ties of Cold Worked Zr 2.5% Nb and EXCEL Alloy Pressure Tubes at 57SK
.... _ Alloy Condition Test 0.2%
. Direc- Yield tion Stress UTS
Kpsi MPa Kpsi MPa %EL %RA
......... _ __ Zr-2.5% ex-truded and : Nb cold drawn L 50 379 71 48918 50 28% T 79 544 88 60612 75 extruded L 5~ 400 75 51715 47 extruded and cold drawn L 60 413 83 57214 48 EXCEL ~ 3% T _ 99 682 _ 60 Alloy ex-truded and cold drawn L 73 503 87 59915 46 ~10% T _ 90 620 _ 59 extruded and cold drawn L 75 517 90 62013 40 15~ T 96 661 _ 58 L is longitudinal T is transverse ; 20 ~ CEL alloy tubes in the extruded condition are shown to be stronger than conventional 30% cold drawn Zr-2.5% Nb tubes :~ but cold drawing of the EXCEL tubes 15% does not increase their strength very much.
Pressu_e Tube Safety The design stress of reactor pressure tubes is only one third of the minimum ultimate tensile strength in the unirradiated condïtion at the design -temperature so that it is inconceivable for failure to occur by tensile rupture, in view of the pressure warning and relief systems in a power reactor. IE
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the pressure tube should sustain a deEect o~ sufficient severity, however, its rup-ture strength will be reduced to the level of the design or operating stress, and the tube would break. The most severe defect is a sharp longitudinal -through wall crack, because the maximum (hoop) tensile stress acts to open and extend the crack. An important parameter in the ability oE tubes to tolerate longitudinal defects is the presence o~
zirconium hydrides. The tolerance of pressure tubes to such deEects depends on such factors as neutron irradiation, test tempera-ture and hydrogen concentration. Test results show both Zr-2.5~ Nb and EXCEL tubes have similar tolerances with respect to neutron irradiation, test temperature, and hydrogen concen-tration although the effects of hydrogen will be described in more detail hereinafter. Normally it is expected that pressure tube alloys will fracture in a completely ductile manner with large local plasticity and that a tube will leak coolant before it actually breaks.
CANDU PHW reactors are normally operated with a reduc-ing coolant chemistry which is maintained by adding hydrogen to the water. During service the pressure tubes corrode in the heavy water coolant and some of the deuterium is picked up by the tube. Hydrogen and deuterium have a very low solubility in zirconium alloys and form zirconium hydride or zirconium deuteride platelets which are brittle. As-fabricated pressure tubes only contain 10-15 ppm hydrogen and no hydride platelets are present at reactor operating temperatures ~530-575K). However towards the end of their service life (`15 years) they are predicted to contain 30-50 ppm hydrogen (60-100 ppm deuterium~ and hydride p]atelets could be present at the operating temperatures. 1'he ~.
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orientation of the hydride platelets is a function of crystallo-graphic texture and stress. Although EXCEL alloys tend to corrode marginally faster under these conditions than do Zr-2.5% Nb alloys, the hydrogen pick-up (hydriding) rate is about the same.
Hydrogen pick-up is particularly significant because it is known that failures, due to delayed hydrogen cracking, can occur at stresses below the ultimate tensile strength of the alloy if such stresses are present for long periods of time as would be the case in-reactor. Crack propagation i5 quite slow and the fracture surfaces are characterized by areas of flat cleavage compared to the dimpled surface of a ductile fracture.
These flat fracture areas corresponding to failure either through hydride platele-ts or at the hydride/matrix interface. For de-layed hydrogen cracking to occur, hydrogen concentration in the alloy must exceed the terminal solid solubility at the test/
operating temperature. Important parameters for crack initiation and propagation include (a) stress or stress intensity at a notch; (b) hydrogen concentration and hydride orientation and (c) temperature.
Crack initiation at the inside surface of cold worked Zr-2.5~ Nb pressure tubes has been studied using cantilever beam specimens. Specimens from the transverse direction were loaded in cantilever beam test rigs so that the maximum outer :~ :
fiber tensile stress was imposed on the inside surface of the tube in the circumferential direction. The -test results, Table 8, show that the probability of crack initiation increases with stress and at 350K also increases with hydrogen concentration.
Similar tests have been performed on EXCEL alloys and the results, summarized in Table 9, show that crack initiation by delayed ~ r ~s~ - 15 -63 ~ ~
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hydrogen cracking is more difficult to initiate in EXCEL
pressure tubes than in Zr-2.5~ Nb pressure tubes.
In cold worked Zr-2.5% Nb and EXCEL alloy pressure tube materials the hydrides in unstressed material lie in cir-cumferential planes, and have very little effect on the tolerance of the tubes to longitudinal defects. Howe~er if the hydrides precipitate under a hoop stress as during a reactor shut down, above a critical stress the hydrides precipitate in the radial-axial plane and severely reduce the tolerance of the tubes to longitudinal defects. When the Zr-2.5% Nb material is thermally cycled to 575K under a circumferential tensile stress, then some of the hydrides become reoriented to the radial plane. As the zirconium hydrides are less ductile than a zirconium, hydrides perpendicular to a tensile stress lower the ductility. It will be noted that even relatively low stress levels of the order of 200 MPa causes reorientation of mos-t of the hydrides into the radial axial plane. The results of thermally cycling EXCEL
alloys to 575 K at similar stress levels are also shown and it will be observed that the hydrides in the EXCEL tubes are very much more resistant to reorienting in the radial direction, which ., is a very desirable property. Therefore EXCEL tubes should be more tolerant to longitudinal defects than Zr-2.5% Nb tubes.
In summary, therefore, the axial elongation and diametral expansion of current 30% cold worked Zr-2.5% Nb pressure tubes could be reduced by lowering their dislocation density and making their grains more equiaxed. This would, however, also lower the tensile strength below specifications.
EXCEL a]loys are stronger and more creep resistant than Zr-2.5 Nb. This enables EXCEL pressure tubes to be made that have .
63~2~
similar strength to 30~ cold worked Zr-2.5% Nb tubes yet only be cold worked ~5%. This dislocation density of EXCEL alloys can be further lowered by annealing to produce a more equiaxed grain structure as shown in Figure 3b. The predicted dimen-sional changes for EXCEL tubes after 30 years service in a C~NDU-PHW 600 MW reac-tor are shown in Table 10. The 5% cold-worked tubes were much s-tronger than the current requirements for CANDU-PHW reactors (minimum longitudinal UTS at 575K, 479 MPa). If these tubes were stress relieved at a higher tempera-ture to reduce their longitudinal strength at 575K to 500 ~Pa, then their dimensional changes would be much less as shown in Table 10. Similarly, if the extrusion ratio used ~or these tubes was reduced from 13.5:1 to 11:1 then the texture would be changed and the axial elongation could be further reduced.
TABI,ElQ: Predicted Dimensional Performance of the EXCEL
Pressure Tubes in 600 MW CANDU-PHW Reactors .... __ , Dimensional Change for : Central Channel after Alloy Tube Type 30 Years % Axial % Diametral Elongation Expansion _ _ extruded 13.5:1 5% cold worked stress relieved 675K 2.2 1.8 extruded 13.5:1 5% cold worked stress relieved ~700K 1.4 2.2 extruded 11:1 EXCEL 5% cold worked stress relieved >700K 1.0 2.0 extruded 13.5:1, cold worked, annealed 0.8 1.1 extruded at 11:1 cold worked, annealed 0.5 1.4 _ _ . ..... ... ...
Zr-2.5% Nb 30% cold worked 2.5 3.9
In one preferred embodiment ~he alloys are cold worked less than 5~ and stress relieved to produce a low dislocation den-sity and in another embodiment the alloys are cold worked up to about 50~ and annealed to produce a very low dislocation density and also small equiaxed a grains.
Conventionally, pressure tubes for CANDU-PHW type nuclear reactors (Canada-Deuterium-Uranium-Pressurized Heavy Water) are fabricated by extrusion of Zr-2.5 wt.~Nb billets, followed by cold working and age hardening. Other Zr alloys can also be used for tubinq in CANDU-PHW tYPe reactors, such as Zircaloy-2~ and quaternary alloys containing 3.5~ Sn, 1% Mo, 1~ Nb, balance Zr, which provide high strength, low neutron capture cross section and reasonable corrosion resistance.
The heat treatment of the quaternary alloys above is described in the literature, and attention is particularly directed to U.S. Patent 4,065,32~ to Brian A. Cheadle, issued December 27, 1977 which describes a process for heat treating the quaternary alloys noted above and hereinafter referred to as EXCEL alloys, to produce a duplex micro-structure comprising primary a-phase and a complex acicular grain boundary phase. The object of the invention described in the aEoresaid U.S. patent is to provide an alloy having the maximum possible strength which i9 achieved by cold working to about 25% followed by age hardening but at the expense of increasing the dislocation density as well.
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7 ~ ~31~0 Although such heat treated -tubes have relatively good out-of-reactor creep strength, their in-reactor creep strength is adversely affected by the high dislocation density.
Unless otherwise stated all alloy percentages in this specification are percentages by weight.
In CANDU reactors it is desirable for the pressure tubes to have as low axial elongation and diametral expansion as possible during service. While it is possible to reduce elongation and expansion levels in conventional 30% cold worked Zr-2.5~ Nb pressure tubes by lowering their dislocation density and making their grains more equiaxed, this, however, also results in a lowering of the tensile strength which would then necessitate increasing the wall thickness with a consequent reduction in reactor efficiency. It is, therefore, necessary to consider the use of one of the alternative alloys referred to above. EXCEL is a stronger and more creep resistant alloy both in and out of reactor than Zr-2.5% Nb, and it has been found that pressure tubes having similar strength to 30% cold worked Zr-2.5~ Nb tubes can be fabricated with less than 5% cold work followed by stress relieving at a temperature in the range 650-800K. Similarly it has been found that low dislocation density EXCEL alloys can also be produced by cold working up to about 50% followed by annealing at a selected temperature in the range 900-1100K.
Thus it is an object of the present invention to provide a process -for heat treating and cold working EXCEL alloys, such that they have a minimum ultimate tensile strength of 479 MPa, and during service equivalent to 30 years in a CANDU-PHW 600 MW
reactor they have a maximum axial elongation of about l.5%, and ~ 3B3~0 a maximum diametral expansion of 2.5%.
It is another object of this invention to provide a heat treated and cold worked product consisting essentially of Sn 2.5-4.0~, Mo 0.5-1.5%, Nb 0. 5~1.5~, 0 800-1300 ppm, balance Zr and incidental impurities, said product having a minimum ultimate tensile strength of 479 MPa, a maximum axial elonga-tion less than 1.5~ and a maximum diametral expansion less than 2.5~ under conditions equivalent to 30 years service ïn a CANDU-PHW 600 MW reactor.
For the purposes of the present specification a 600 MW
CANDU-PHW reactor is considered to operate at a temperature of 565K, with a peak neutron flux of 3.85 x 1017 n/(m2.s) and at a mean coolant pressure of 10.6 MPa.
Thus, by one aspect of this invention there is provided a method of fabricating an extruded product from an alloy con-sisting essentially of Sn 2.5-4%, Mo 0.5-1.5%, Nb 0.5-1.5%, 0 800-1300 ppm balance Zr and incidental impurities wherein a billet of said alloy is preheated in the temperature range gO0-~ 1200K and extruded into said produc-t, and said extruded product is cold worked, by an amount up to about 50%, and heat treated at a selected temperature in the range 650-1100K, so as to have a dislocation density of less than about 5 x 1014 m 2 a minimum U.T.S. of 479 MPa, a maxlmum axial elongation less than 1.5~ and a maximum diametral expansion less than 2.5% under conditions equivalent to 30 years service in a CANDU-P~IW 600 M~
reactor.
By another aspect of this invention there is provided a heat treated and cold worked alloy for use in nuclear , `t~' ':' ,~
3~2~
reactor tubes and other extruded products and consisting essentially of Sn 2.5-4.0~/ Mo 0.5-1.5%, Nb 0.5-1.5% 0 ~00-1300 ppm, balance Zr and incidental impurities, having a minimum ultimate tensile strength of 479 MPa, a maximum in-service axial elongation of 1.5% and preferably in the range 0.5-0.8%, a maximum in-service diametral expansion of 2.5~ and preferably in the range 1.1 to 1.4~ and an equiaxed grain structure.
The invention will be described in more detail herein-after with reference to the accompanying drawings in which:
Figure 1 is a flow chart of a general fabrication route for alloys of the present invention;
Figure 2 is a flow chart of a specific fabrication route for alloys according to one aspect of the present invention;
Figure 3ta) is a transmission electron micrograph at 11,500X of extruded tubes cold worked less than 5% and stress relieved at 700K, of the present invention;
Figure 3(b) is a transmission electron micrograph at 11,500X of tubes cold worked greater than 5% and annealed at 1075 K, of the present invention;
Figure 4 is an average (0002) pole figure for seven tubes of the present invention; and Figure 5 is a ~eries of optical micrographs showing the effect of stress on the orientation of zirconium hydrides in E~CEL and Zr-2.5 wt.~ Nb tubes.
In power reactors that use internally pressurized tubes two important mechanical property requirements are tensile strength and dimensional stability during service. Dimensional ~ :~ 63 1 2~) stability is a function of both creep and growth (dimensiona]
change during irradiation without an applied stress). In zircon-ium tubes the ratio of creep in the axial and circumferential directions is a function of their crys-tallographic texture and the ratio of their growth in the axial and circumferential directions i5 a function of both crys-tallographic texture and the shape of the a grains. The crystallographic -texture of extruded and cold drawn tubes is largely a function of the extrusion conditions - temperature, die shape, strain rate, billet micro-structure and extrusion ratio. It has been found that the ratio of di`ametral expansion to axial elongation of a tube duriny service in a power reactor can be controlled by selecting the appropriate extrusion conditions.
The longitudinal tensile strength of 30% cold worked Zr-2.5 weight % Nb pressure tubes is due to their combination of high dislocation density, very small a grain thickness (0.3 x 10 3mm) and a duplex microstructure of a grains and grain boundary network of ~-phase. However, the in-reactor creep of of these tubes is adversely affected by their dislocation density and their in-reactor axial elongation due -to growth is adversely -affected by both their dislocatlon densit~and their very long elongated a grains (0.3 x 10 3mm thick x lOmm long)~ EXCEL is a stronger material than Zr-2.5 wt.% Nb. There~ore EXCEL tubes can be fabricated that are as strong or stronger than 30% cold worked Zr-2.5 wt.% Nb tubes, but have lower dislocation densities and/or more equiaxed ~ grains. These tubes have considerably better dimensional stability during service in pGwer reactors.
The tensile strength of these EXCEL tubes is largely a function of their dislocation density and grain size. Tubes ~ ~3~O
cold worked a minimum after extrusion and stress relieved will have thin elonyated a grains (Figure 3a). Their longitudinal tensile strengths can be up to 600 MPa at 575K depending on the stress relieving temperature. If the tubes are annealed after cold working to produce equiaxed recrystallized a grains (Figure 3b) then the size of the grains depends on -the amount of cold work and the annealing heat treatment.
Fabrication of Experimental Tubes A double arc melted ingot of EXCEL alloy was forged to 215mm diameter bar and machined to form seven hollow billets numbered 248-254. The billets were clad in steel and copper and preheated to about 1130K for approximately 5 hours and then extruded into tubes at a ratio of 13.5:1. The cladding was removed by dissolution in ni-tric acid, the inside of the tubes were sand blasted and the outside centerless ground. One end of each of the tubes was flame annealed, air cooled and pushed onto a die to point the end. A conversion coating was then applied and the tubes cold drawn between 2 and 5% as shown in Table 2. The chemical composition of the tubes is recorded in Table 1. The cold worked tubes were then sand blasted inside and centerless ground on the outside.
~ ~ ~3~ ~
TABLE 1: The Chemical Analysis of -the EXCEL Tubes ._ _ __ .. _____ _ . I
Tube Element Number Sn wt% Mo wt% Nb wt% O ppm H ppm .. _ _~ ._ 248 F 3.32 0.81 0~83 1157 34 248 B 3.08 0.77 0.79 1203 48 249 F 3.31 0.81 0.80 1142 30 249 B 3.29 0.82 0.81 1089 26 250 F 3.23 0.79 0.82 1142 36 250 B 3.31 0.82 0.82 1131 26 251 F 3.32 0.79 0.83 1149 , 34 251 B 3.42 0.80 0.81 1134 28 252 F 3.46 0.83 0.80 1142 29 252 B 3.29 0.75 0.79 1119 25 253 E' 3.39 0.78 0.84 1149 32 253 B 3.31 0.80 0.70 1116 18 254 F 3.38 0.78 0.82 1118 54 254 B 3.47 0.81 0.80 1115 34 .. _._ _ _ _ MEAN 3.33 0.80 0 80 1136 34 F is the front end of the tube and comes out of the extrusion press first.
B is the back end of the tube and comes out of the extrusion press ]as-t.
~ 3 63 1 ~
TA~LE 2: Extrusi~ C~ld Dr~wing Data for the EXCEL Pressure Tubes .. _.. _ ..._, ,_ . . .
Billet Total Furnace Pressure I.ength of % Cold Number Preheat Time to Start Tube Extruded Draw ps i m __ . _ . _ ._ . . . _ .. .__ ~
248 5 hours 52 minutes 1800 7.5 2.83 249 5 hours 56 minutes 2000 5.8 3.71 250 6 hours 3 minutes 1750 7~3 3.16 251 7 hours 22 minutes 1700 7.5 2.77 10 252 7 hours 17 minutes 1800 7.4 4.36 253 6 hours 48 minutes 2300 4.3 2.90 254 7 hours 10 minutes 160- .. _.. __ ~.. .. .__. 2.89 Two tubes, 249 and 251 were annealed in a vertical vacuum furnace for 30 minutes at 1023K to produce an equiaxed alpha grain s-tructure. An equiaxed alpha grain structure should produce a lower ln-reactor axial elongation rate at the expense . . - of a slightly lower tensile strength.
. ~ -- Sections o~ tube 248:were cold worked up to 40% and :~
-then annealed for 30 minutes at a selected temperature in the ::
range 1025-1075K.
All the tubes were finally stress relieved in an auto-clave for 24 hours at 675K.
The general fabrication route is shown in Figure 1 and the particular steps for these seven tubes are shown in Figure 2.
3~ 2~
TABLE 3: a Grain Size and Dislocation Density -of the EXCEL Pressure ~ubes Tube % Cold Grain Size mmxlO 3 Disloca-Number Drawn Front eod Back end Aver. D n~i 250 3.7 0.15 0.48 0.62 8.4 x 252 3.2 0.81 0.46 0.6 253 2.8 0.76 0.39 0.5 254 4.4 0.70 0.5~ 0.62 Mean 0.76 0.51 0.64 _ __ 24~ 2.9 0.80 1.4 x 251 2.9 0.74 l~l~
Cold worked 5-9 x Zr-2.5% Nb 0.4 0.2 0.3 1~14 tubes - _ PROPERTIES OF THE EXPERIMENTAL TUBES
- Microstructure and Texture .
- - Grain sizè and shape are important parameters in -the .
tensile strength and in-reactor dimensional stability of zirconium alloy pressure tubes. The microstructures were examined by thin film electron microscopy. The results, Figure 3a and Table 3, show that the microstructure of the cold worked tubes consists of elonga-ted a grains, a thin grain boundary network of ~-phase, and a few localized areas of martensitic a'. The a grain thicknesses were larger than typical cold worked ~r-2.5% Nb pressure tubes, Table 3. The two annealed tubes~ 249 and 251 had larger relatively equiaxed a grains, Figure 3b, with the ~phase concentrated a-t grain ~ ~i33~
corners. The five cold worked and stress relieved tubes had much higher average dislocation density than the annealed tubes, as seen in Table 3. The texture of the annealed and cold worked tubes was similar and an average (0002) pole ~igure for the seven tubes is shown in Figure 4.
The effect of varying amounts of cold work and anneal-ing temperature on the a grain thickness of an extruded tube is shown in Table 4 (below). The smallest grain thickness was obtained with 30% cold work followed by annealing for 30 minutes 10at 1025K.
TABLE 4: The Effect of Cold Work and Annealing Heat Treatment on the Grain slze of Extruded EXCEL Tube 248 Thlckness of a Grain, mm x 10 ~
% Cold Work 30 minu-tes at30 minutes at ...
0 0.80 0.80 0.79 1.08 0.72 _ 0.59 0.98 0.53 0.97 1.11 1.72 ; 20Tensile Strength The longitudinal and transverse tensile strengths of the tubes are shown in Table 5. The cold-worked and stress relieved tubes were considerably stronger than the annealed tubes due to their smaller grain thickness and higher disloca-tion densityO The annealed tubes met -the minimum specifications : for 30~ cold-worked Zr-2.5 wt~ Nb pressure tubes.
Hydride Orientation As fabricated the hydrides were oriented in -the radial-axial plane. The effect of hoop stress on the orientation of .
3 ~ 2 ~
the hydrides that precipitate during cooling from 575K is shown in Fiyure S. To precipi-tate hydrides in the radial-axial plane required a hoop stress of 827 MPa.
TABLE 5: Tensile Properties of the EXCEL Pressure Tubes and Typical Tens.ile Properties of 30% Cold-Worked -Zr-2._~ Nb Pressure Tubes Alloy Tube Test Test 0.2~ Yield UTS
Condi- Tempera- Direc- Stress MPa MPa Elonga-tion ture K tion _ tion 5% T 620 645 13 cold drawn 300 L 736 845 12 EXCEL _ an- 575 T 490 555 13 _ nealed 300 T 615 745 17 Zr- co%ld 575 L 580 56200o 152 Nb drawn 3 0 0 T 640 810 15 L is longitudinal T is transverse COMPARISON WITH ST~NDARD Zr-2.5% Nb ALLOY ~RES5VRE TUBES
Tensile Strength Cold worked Zr-2.5% Nb is the reference pressure tube material for CANDU-PHW reactors. EXCEL alloys having chemical compositions in the range 2.5-4.0% Sn, 0.5-1.5% Mo, 0.5-1.5% Nb, 800-1300 ppm O, balance Zr plus incidental impurities, have been found to have higher strengthG than the Zr-2.5% Nb alloys and good in-reactor creep resistance.
In all metallurgical conditions EXCEL alloys are stronger than Zr-2.5% Nb but when heat treated to produce the ~, - 11 -~ t ~3~2~
required high strengths for use in a reactor the ductility is relatively low as shown in Table 6.
TABLE 6: T} Tensile Properties of Zr-2.5% Nb and EXCEL alloy at 575K
Alloy Conditlon 0.2% YS UTS Total MPa K psi MPa K psi Elongation _ Zr-2.5% Nb Annealed 207 30 28040 30 EXCEL Annealed 338 40 46065 20 Zr-2.5% Nb 20% cold worked 365 53 40659 11 EXCEL 20% cold worked 517 75 57984 11 Zr-2.5% Nb Heat treated 579 84 644935 15 EXCEL Heat _ _ __ treated 620 115 860130 1_ _ ___ _ _ Typical tensile properties of cold worked Zr-2.5%
Nb pressure tubes and EXCEL pressure tubes in the extruded condition and also cold drawn about 3%, 10%, and 15% are shown below in Table 7.
~ 12 -J :~ 63:~2~
TABLE 7: Typical Te_sile Proper-ties of Cold Worked Zr 2.5% Nb and EXCEL Alloy Pressure Tubes at 57SK
.... _ Alloy Condition Test 0.2%
. Direc- Yield tion Stress UTS
Kpsi MPa Kpsi MPa %EL %RA
......... _ __ Zr-2.5% ex-truded and : Nb cold drawn L 50 379 71 48918 50 28% T 79 544 88 60612 75 extruded L 5~ 400 75 51715 47 extruded and cold drawn L 60 413 83 57214 48 EXCEL ~ 3% T _ 99 682 _ 60 Alloy ex-truded and cold drawn L 73 503 87 59915 46 ~10% T _ 90 620 _ 59 extruded and cold drawn L 75 517 90 62013 40 15~ T 96 661 _ 58 L is longitudinal T is transverse ; 20 ~ CEL alloy tubes in the extruded condition are shown to be stronger than conventional 30% cold drawn Zr-2.5% Nb tubes :~ but cold drawing of the EXCEL tubes 15% does not increase their strength very much.
Pressu_e Tube Safety The design stress of reactor pressure tubes is only one third of the minimum ultimate tensile strength in the unirradiated condïtion at the design -temperature so that it is inconceivable for failure to occur by tensile rupture, in view of the pressure warning and relief systems in a power reactor. IE
~ ~ ~3 ~ 2~
the pressure tube should sustain a deEect o~ sufficient severity, however, its rup-ture strength will be reduced to the level of the design or operating stress, and the tube would break. The most severe defect is a sharp longitudinal -through wall crack, because the maximum (hoop) tensile stress acts to open and extend the crack. An important parameter in the ability oE tubes to tolerate longitudinal defects is the presence o~
zirconium hydrides. The tolerance of pressure tubes to such deEects depends on such factors as neutron irradiation, test tempera-ture and hydrogen concentration. Test results show both Zr-2.5~ Nb and EXCEL tubes have similar tolerances with respect to neutron irradiation, test temperature, and hydrogen concen-tration although the effects of hydrogen will be described in more detail hereinafter. Normally it is expected that pressure tube alloys will fracture in a completely ductile manner with large local plasticity and that a tube will leak coolant before it actually breaks.
CANDU PHW reactors are normally operated with a reduc-ing coolant chemistry which is maintained by adding hydrogen to the water. During service the pressure tubes corrode in the heavy water coolant and some of the deuterium is picked up by the tube. Hydrogen and deuterium have a very low solubility in zirconium alloys and form zirconium hydride or zirconium deuteride platelets which are brittle. As-fabricated pressure tubes only contain 10-15 ppm hydrogen and no hydride platelets are present at reactor operating temperatures ~530-575K). However towards the end of their service life (`15 years) they are predicted to contain 30-50 ppm hydrogen (60-100 ppm deuterium~ and hydride p]atelets could be present at the operating temperatures. 1'he ~.
_ 14 -~.~., .
~ ~ ~312~
orientation of the hydride platelets is a function of crystallo-graphic texture and stress. Although EXCEL alloys tend to corrode marginally faster under these conditions than do Zr-2.5% Nb alloys, the hydrogen pick-up (hydriding) rate is about the same.
Hydrogen pick-up is particularly significant because it is known that failures, due to delayed hydrogen cracking, can occur at stresses below the ultimate tensile strength of the alloy if such stresses are present for long periods of time as would be the case in-reactor. Crack propagation i5 quite slow and the fracture surfaces are characterized by areas of flat cleavage compared to the dimpled surface of a ductile fracture.
These flat fracture areas corresponding to failure either through hydride platele-ts or at the hydride/matrix interface. For de-layed hydrogen cracking to occur, hydrogen concentration in the alloy must exceed the terminal solid solubility at the test/
operating temperature. Important parameters for crack initiation and propagation include (a) stress or stress intensity at a notch; (b) hydrogen concentration and hydride orientation and (c) temperature.
Crack initiation at the inside surface of cold worked Zr-2.5~ Nb pressure tubes has been studied using cantilever beam specimens. Specimens from the transverse direction were loaded in cantilever beam test rigs so that the maximum outer :~ :
fiber tensile stress was imposed on the inside surface of the tube in the circumferential direction. The -test results, Table 8, show that the probability of crack initiation increases with stress and at 350K also increases with hydrogen concentration.
Similar tests have been performed on EXCEL alloys and the results, summarized in Table 9, show that crack initiation by delayed ~ r ~s~ - 15 -63 ~ ~
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hydrogen cracking is more difficult to initiate in EXCEL
pressure tubes than in Zr-2.5~ Nb pressure tubes.
In cold worked Zr-2.5% Nb and EXCEL alloy pressure tube materials the hydrides in unstressed material lie in cir-cumferential planes, and have very little effect on the tolerance of the tubes to longitudinal defects. Howe~er if the hydrides precipitate under a hoop stress as during a reactor shut down, above a critical stress the hydrides precipitate in the radial-axial plane and severely reduce the tolerance of the tubes to longitudinal defects. When the Zr-2.5% Nb material is thermally cycled to 575K under a circumferential tensile stress, then some of the hydrides become reoriented to the radial plane. As the zirconium hydrides are less ductile than a zirconium, hydrides perpendicular to a tensile stress lower the ductility. It will be noted that even relatively low stress levels of the order of 200 MPa causes reorientation of mos-t of the hydrides into the radial axial plane. The results of thermally cycling EXCEL
alloys to 575 K at similar stress levels are also shown and it will be observed that the hydrides in the EXCEL tubes are very much more resistant to reorienting in the radial direction, which ., is a very desirable property. Therefore EXCEL tubes should be more tolerant to longitudinal defects than Zr-2.5% Nb tubes.
In summary, therefore, the axial elongation and diametral expansion of current 30% cold worked Zr-2.5% Nb pressure tubes could be reduced by lowering their dislocation density and making their grains more equiaxed. This would, however, also lower the tensile strength below specifications.
EXCEL a]loys are stronger and more creep resistant than Zr-2.5 Nb. This enables EXCEL pressure tubes to be made that have .
63~2~
similar strength to 30~ cold worked Zr-2.5% Nb tubes yet only be cold worked ~5%. This dislocation density of EXCEL alloys can be further lowered by annealing to produce a more equiaxed grain structure as shown in Figure 3b. The predicted dimen-sional changes for EXCEL tubes after 30 years service in a C~NDU-PHW 600 MW reac-tor are shown in Table 10. The 5% cold-worked tubes were much s-tronger than the current requirements for CANDU-PHW reactors (minimum longitudinal UTS at 575K, 479 MPa). If these tubes were stress relieved at a higher tempera-ture to reduce their longitudinal strength at 575K to 500 ~Pa, then their dimensional changes would be much less as shown in Table 10. Similarly, if the extrusion ratio used ~or these tubes was reduced from 13.5:1 to 11:1 then the texture would be changed and the axial elongation could be further reduced.
TABI,ElQ: Predicted Dimensional Performance of the EXCEL
Pressure Tubes in 600 MW CANDU-PHW Reactors .... __ , Dimensional Change for : Central Channel after Alloy Tube Type 30 Years % Axial % Diametral Elongation Expansion _ _ extruded 13.5:1 5% cold worked stress relieved 675K 2.2 1.8 extruded 13.5:1 5% cold worked stress relieved ~700K 1.4 2.2 extruded 11:1 EXCEL 5% cold worked stress relieved >700K 1.0 2.0 extruded 13.5:1, cold worked, annealed 0.8 1.1 extruded at 11:1 cold worked, annealed 0.5 1.4 _ _ . ..... ... ...
Zr-2.5% Nb 30% cold worked 2.5 3.9
Claims (12)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A method of fabricating an extruded product from an alloy consisting essentially of Sn 2.5-4wt%, Mo 0.5-1.5w%, Nb 0.5-1.5wt%, O 800-1300 ppm, balance Zr and incidental impurities wherein a billet of said alloy is preheated in the temperature range 900-1200°K and extruded into said product at an extrusion ratio between 4:1 and 15:1 and said extruded product is cold worked by an amount up to about 50%
and heat treated at a selected temperature in the range 650-1100°K, the amount of cold working and heat treatment temperature being selected so as to produce a product having a fine grain size, a crystallographic texture with a predominance of basal plane normals in the radial trans-verse plane, a dislocation density of less than about 5 x 1014 m-2 a minimum U.T.S. of 479 MPa, a maximum axial elongation less than 1.5% and a maximum diametral expansion less than 2.5% under conditions equivalent to 30 years service in a CANDU-PHW 600 MW reactor.
and heat treated at a selected temperature in the range 650-1100°K, the amount of cold working and heat treatment temperature being selected so as to produce a product having a fine grain size, a crystallographic texture with a predominance of basal plane normals in the radial trans-verse plane, a dislocation density of less than about 5 x 1014 m-2 a minimum U.T.S. of 479 MPa, a maximum axial elongation less than 1.5% and a maximum diametral expansion less than 2.5% under conditions equivalent to 30 years service in a CANDU-PHW 600 MW reactor.
2. A method of fabricating an extruded alloy product as claimed in claim 1 wherein said extruded product is cold worked less than 5% and stress relieved at a temperature in the range 650-800°K.
3. A method of fabricating an extruded alloy product as claimed in claim 1 wherein said extruded product is cold worked 10-40% and annealed at a selected temperature in the range 950-1100°K.
4. A method of fabricating an extruded alloy product as claimed in claim 2 wherein said stress relieving temperature is selected so as to provide a product having an in-service axial elongation in the range 1.0-1.4% and an in-service diametral expansion in the range 1.8-2.2%.
5. A method of fabricating an extruded alloy product as claimed in claim 3 wherein said cold working and said annealing temperature are selected to provide a product having an in-service axial elongation in the range 0.3-0.8%, an in-service diametral expansion in the range 1.1-1.4%, and an equiaxed grain structure.
6. A method of fabricating an extruded alloy product as claimed in claim 1, 2 or 3 wherein said extrusion is effected at a ratio between 6:1 and 11:1.
7. A method of fabricating an extruded alloy product as claimed in claim 1, 2 or 3 wherein said cold working step comprises cold drawing.
8. A method of fabricating an extruded alloy product as claimed in claim 3 or 5 wherein said annealing is effected at about 1023°K for about 30 minutes.
9. A heat treated and cold worked alloy product consisting essentially of Sn 2.5-4.0wt%, Mo 0.5-1.5wt%, Nb 0.5 1.5wt%, O 800-1300 ppm, balance Zr and incidental impurities, having a fine grain size, a crystallographic texture with a pre-dominance of basal plane normals in the radial transverse plane, a dislocation density of less than about 5 x 1014 m-2, a minimum ultimate tensile strength of 479 MPa, a maximum in-service axial elongation of less than 1.5% and a maximum in-service diametral expansion of less than 2.5% under conditions equivalent to 30 years service in a CANDU-PHW
600 MW reactor.
600 MW reactor.
10. A heat treated and cold worked alloy product as claimed in claim 9 in the form of an extruded and cold worked tube for use in a nuclear reactor.
11. A heat treated and cold worked alloy product as claimed in claim 9 or 10 having an in-service axial elongation in the range 1.0-1.4% and an in-service diametral expansion in the range 1.8-2.2%.
12. A heat treated and cold worked alloy product as claimed in claim 9 or 10 having an in-service axial elongation in the range 0.3-0.8%, an in-service diametral expansion in the range 1.1-1.4% and an equiaxed grain structure.
Priority Applications (8)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000355707A CA1163120A (en) | 1980-07-08 | 1980-07-08 | Low in reactor creep zr-base alloy tubes |
| GB8120617A GB2079317B (en) | 1980-07-08 | 1981-07-03 | Zr base alloy tubes providing low inreactor creep |
| RO81104795A RO83384A (en) | 1980-07-08 | 1981-07-06 | METHOD FOR MANUFACTURING ZIRCONIUM ALLOY TUBES |
| JP56105159A JPS5794542A (en) | 1980-07-08 | 1981-07-07 | Alloy product and production thereof |
| SE8104233A SE8104233L (en) | 1980-07-08 | 1981-07-07 | ZR alloy tubes with low reactor creep |
| IT22790/81A IT1137284B (en) | 1980-07-08 | 1981-07-07 | PROCEDURE FOR MANUFACTURING ZIRCONIUM ALLOY PIPES INTENDED FOR USE IN REACTORS AND NUCLEAR ENERGY |
| KR1019810002464A KR830006454A (en) | 1980-07-08 | 1981-07-07 | Low-Crip Zr-Base Alloy Tubes for Reactors |
| FR8113581A FR2486541A1 (en) | 1980-07-08 | 1981-07-08 | LOW-FLOWING ZIRCONIUM ALLOY TUBES FOR NUCLEAR REACTORS, AND METHOD FOR MANUFACTURING THE SAME |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000355707A CA1163120A (en) | 1980-07-08 | 1980-07-08 | Low in reactor creep zr-base alloy tubes |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1163120A true CA1163120A (en) | 1984-03-06 |
Family
ID=4117371
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000355707A Expired CA1163120A (en) | 1980-07-08 | 1980-07-08 | Low in reactor creep zr-base alloy tubes |
Country Status (8)
| Country | Link |
|---|---|
| JP (1) | JPS5794542A (en) |
| KR (1) | KR830006454A (en) |
| CA (1) | CA1163120A (en) |
| FR (1) | FR2486541A1 (en) |
| GB (1) | GB2079317B (en) |
| IT (1) | IT1137284B (en) |
| RO (1) | RO83384A (en) |
| SE (1) | SE8104233L (en) |
Families Citing this family (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4649023A (en) * | 1985-01-22 | 1987-03-10 | Westinghouse Electric Corp. | Process for fabricating a zirconium-niobium alloy and articles resulting therefrom |
| DE3663372D1 (en) * | 1985-03-12 | 1989-06-22 | Santrade Ltd | Method of manufacturing tubes of zirconium alloys with improved corrosion resistance for thermal nuclear reactors |
| CN105808910B (en) * | 2014-12-30 | 2018-11-02 | 中核核电运行管理有限公司 | Irradiation Method for Calculating Deformation of the zirconium niobium pressure pipe in CANDU reactors |
Family Cites Families (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CA1014833A (en) * | 1974-07-12 | 1977-08-02 | Stuart R. Macewen | Zirconium base alloy and method of production |
| CA1027781A (en) * | 1975-05-06 | 1978-03-14 | Brian A. Cheadle | High strength sn-mo-nb-zr alloy tubes and method of making same |
-
1980
- 1980-07-08 CA CA000355707A patent/CA1163120A/en not_active Expired
-
1981
- 1981-07-03 GB GB8120617A patent/GB2079317B/en not_active Expired
- 1981-07-06 RO RO81104795A patent/RO83384A/en unknown
- 1981-07-07 SE SE8104233A patent/SE8104233L/en not_active Application Discontinuation
- 1981-07-07 KR KR1019810002464A patent/KR830006454A/en unknown
- 1981-07-07 JP JP56105159A patent/JPS5794542A/en active Pending
- 1981-07-07 IT IT22790/81A patent/IT1137284B/en active
- 1981-07-08 FR FR8113581A patent/FR2486541A1/en active Granted
Also Published As
| Publication number | Publication date |
|---|---|
| IT1137284B (en) | 1986-09-03 |
| FR2486541B1 (en) | 1984-09-14 |
| GB2079317B (en) | 1984-11-07 |
| JPS5794542A (en) | 1982-06-12 |
| IT8122790A0 (en) | 1981-07-07 |
| GB2079317A (en) | 1982-01-20 |
| FR2486541A1 (en) | 1982-01-15 |
| RO83384A (en) | 1984-08-17 |
| SE8104233L (en) | 1982-01-09 |
| RO83384B (en) | 1984-04-30 |
| KR830006454A (en) | 1983-09-24 |
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