& -~ OAK RIDGE NATIONAL LABORATORY operated by UNION CARBIDE CORPORATION for the U.S. ATOMIC ENERGY COMMISSION ORNL- TM- 2858 ™ : ""‘ TENSILE PROPERTIES OF HASTELLOY N WELDED AFTER IRRADIATION 3 H. E. McCoy, R. W. Gunkel, and G. M. Slaughter THIS DOCUMENT CONFIRMED A8 - UNCLASSIFIED . o 3963 . b AW NOTICE This document contains information of a preliminary nature P «J 1 ond was prepared primarily for internal use at the Oak Ridge National Laboratery. It is subject to revision or correction and therefore does not represent a final report. DISTRIBUTION OF THIS DOCUMENT IS UNLIMITED LEGAL NOTICE - This report was prepared as an account of Government sponsored work. Neither the United States, nor the Commission, nor any person acting on behalf of the Commission: A. 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Assumes any liabilities with respect to the use of, or for damages resulting from the use of any information, apparatus, method, or process disclosed in this report, As used in the above, ‘‘person acting on behalf of the Commission” includes any employee or contractor of the Commission, or employee of such contractor, to the extent that such employee or contractor of the Commission, or employee of such contractor prepores, disseminates, or provides access to, any information pursuant to his employment or contract with the Commission, or his employment with such contractor. r“‘ ORNL-TM-2858 .} Contract No. W-7405-eng-26 METALS AND CERAMICS DIVISION TENSILE PROPERTIES OF HASTELLOY N WELDED AFTER IRRADIATION H. E. McCoy, R. W. Gunkel, and G. M. Slaughter LEGAL NOTICE——=—— This nmnmmplrodnanmto! Qovernment sponsorsd work. Neluwrfia‘l']nlhd States, mhmmmmmprmwmmmuuhmmmm : S A,Ihlu--nymnnty or representution, éxpressed or lnplud with ulpaeththnpecu . | TREY, P of the d in this report, or that the uss - } of any tnformatioa, -nnnhu. method, o process disciosed tn this report may not Infrlnga privately owned rights; or B. Assumes any liabilitics with reapsct to the uss of, of for damages resulting lru-flle use of aay information, apparstus, mthud.ormcen disclosed in thin npurl. . As used in the shove, “wlmmflngnhhnflolflncommlm Ilehdumon kil ployuor of the or amployes of such 0 the oxten} that - such or ¢ of the isslon, or ssaployes of such disseminates, or provides acceas to, any information mrnmto uis smployment or edtrnt - with the or his émpl nt with such contr. - 7 ~ APRIL 1970 OAK RIDGE NATIONAL LABORATORY . Oak'Ridge, Tennessee r ‘operated by > UNION CARBIDE CORPORATION LY co : o for the &afi ' U.S. ATOMIC ENERGY CQMMISSIQN DISTRIBUTION OF THIS DOCUMENT IS UNL « ) o . O A A AR 144 9 Abstract . 40 I . ® . . Introduction C e e . Emperimental Details . Experimental Results coee ‘Discussion -of Results ~ Summary . .. .. . L Acknowledgments . . . J Y w + b 3 . TENSILE PROPERTIES OF_HASTELLOY N WELDED AFTER IRRADIATION - H. E. McCoy, R. W. Gunkel, and G. M. Slaughter - ABSTRACT Fu31on welds. affecting 75% of the cross section were made in small tensile samples (0.125 in. in diameter) of Hastelloy N irradiated to thermal fluences up to .9.4 X 1029 neutrons/em?®. All of the unirradiated samples and 67% of the irradiated samples were satisfactorily welded using a specialized technique developed for this program. Surface contamination is suspected to be the cause of the unsuccessful welds in the irradiated samples. The welded irradiated samples generally had as good tensile properties ‘at 25 and 650°C as the irradiated base metal. The weld metal deformed appreciably at 650°C and made a significant contribution to the overall fracture strain. The fracture location in the irradiated samples tested at 650°C shifted from the weld metal to the base metal following the post- weld anneal of 8 hr at 870°C. The porosity which was observed near the fusion line of the irradiated samples probably results from transmuted helium bubbles, but this did not seem to affect the location of the fracture. o INTRODUCTION - The maintenance and repair of nuclear systems will frequently involve cutting and reweldlng plpes and components that have been irra- :diated. The prospect of these repairs raises the obv1ous questions of how such welds .can be ‘made and.what are their mechanical properties. V:It is this latter question that will be discussed in the present report. ~ This report will also deal-speclflcally with molten-salt reactors where '__the addltlonal problem exists of removing residual fluoride salt or ‘corrosion products.' However, ‘cleanliness will likely be: a paramount problen in meking remote welds in any reactor system. The alloy studied is Hastelloy N, & nickel-based material developed specifically for use in molten-salt reactors.?! The'irradiated material studied had been exposed to the core of the Mblten—Salt Reactor Experi- ment for long periods of time as & surveillance material for the reactor vessel. The welds made in this study were simple gas tungStensarc fusion welds that melted about 75% of the cross-sectional area of a miniature (0.125 in. in diameter) tensile sample. Thus, the welds were made with very low heat input and minimal restraint .and the results can be used only qualltatlvely EXPERIMENTAL DETATILS The heats of material involved in this study were air-melted and " the chemical compositions are given in Table 1. These heats were used in fabricating the MSRE vessel; heat.5065 for the top and bottom heads and heat 5085 for the cylindrical shell. Samples of these heats were placed in the various surveillance facil- ities of the MSRE.2~* These samples have the general eonfiguration of a long rod 1/4 in. in diameter with periodic reduced sections 1 1/8 in. long and 1/8 in. in diameter. After the desired exposure, these rods can be segmented to obtain small tensile samples. The core surveillance assembly is located axially about 3.6 in. from the core center line where the ther- mal flux (< 0.876 Mev) is 4.1 x 10*2 neutrons cm™2? sec™! and the fast flux (> 1.22 Mev) is 1.0 x 1012 neutrons cm™? sec™!. The environment is a I¥. D. Manly et al., "Metallurgical Problems in Molten Fluoride Systems," pp. 164-179 in Progr. Nucl. Energy Ser. IV 2, Pergamon, Oxford, 1960. °W. H. Cook, Molten-Salt Reactor Program Semiann. Progr. Rept;‘ Aug. 31, 1965, ORNL-3872, pp. 87-92. 3H. E. McCoy, An Evaluation of the Molten-Salt Reactor Experi- ment Hastelloy N Surveillance Specimens — First Group, ORNL~-TM-1997 - (November 1967). “H. E. McCoy, An Evaluation of the Molten-Salt Reactor Experi- - ment Hastelloy N Surveillance Speclmens — Second Group, ORNI~TM-2359 (February 1969). 2 A i Ay Table 1. Chemical Analysis of Surveillance Heats Content, wt % Element Heat 5065 . Heat 5085 Cr 7.2 7.3 Fe -3.9 - 3.5 Mo 16.5 16.7 C 0.065 0.052 Si 0.60 . 0.58 - Co .0.08 0.15 W 0.04 0.07 Mn - 0.55 0.67 v 0.22 - 0.20 P 0.004 - 0.0043 S 0.007 0.004 Al 0.01 0.02 Ti 0.01 < 0.01 Cu 0.01 0.01 B (ppm) - 4, 37, 38 20, 10 0 0.0016 0.0093 N 0.011 0.013 molten fluoride salt 65 L1F 29 l Bng, 5 ZrF;, 0.9 UF,; (mole %), at - 650°C. There is a control fac1lity in which the samples are exposed to static "fuel salt" contalnlng depleted uranium. The temperature follows that of the MSRE. A second surveillance facility is located outside the core in a vertical position”aboutlé 5 in. from the vessel. The tempera- ture is also 650°C at this location and the thermal flux (< .0.876 Mev) is 1.0 X 101! peutrons em~2 sec~! and the fast flux (> 1.22 Mev) is “1.6 X 1011 neutrons cm™ =2 sec 1. The environment is nitrogen with 2 to - 5% 05, and the Hastelloy N samples have a thin oxide film after exposure. - In order to make fusion welds (no filler metal added) on the irra- dlated tensile specmmens, it was necessary to design a special welding ~ fixture that could be 0perated remotely in a hot cell. We aimed for a ~ reasonable assurance of good penetration (high percentage of cross sec- tlon of specimen to be;weld metal),without spec;men distortlon, Figure 1 is a photograph of the welding fixture assembled for use in ‘the hot cell. As cen be seen, the fixture consists of a rigid stand, motor-driven chuck,rspecimen'support, and a gas tungsten-arc welding Fig. 1. Welding Equipment Developed for Making Remote Welds. torch. The upper support has an internal curved surface that contacts the fillet radius of the tensile sample and keeps the sample aligned -Quring welding. The torch was connected to a programmed welding power supply located outside the-hot cell. The welding cbnditionS'were adjusted to obtain penetration'of about 75% of the sample cross section. All samples were abraded with 240-grit emery paper and cleaned with acetone before welding. - We did the final abrasion on each sample with a clean piece of emery paper in an effort to minimize contamination. '_ The tensile tests were run on Instron Universal testing machines. Thé strain measurements were taken from the crosshead travel. The test environment wes air in each case. n o »n ” o EXPERIMENTAL RESULTS We welded 25 unirradiated samples both in the hot cell and in the laboratory and all welds visually appeared sound. We welded 15 irra- diated samples; three welds were completely unsatisfactory and two - others were very questioneble due to surface cracks. . Thus, 67% of the welded irradiated specimens were found to be sound by visual examina- tion. The bad welds ocourred randomly, and we suspected that cleanli- | ness was our main problem.in obtaining sound welds. | | The results of tenSile!fiests on base-metal samples are given in Table 2, and those for the'#elded samples are given(in Table 3. Numer- ous variables are included, and care must be used in making comparisons. .The changes in strength are ' not thought to be signlficant and we shall dlscuss in some . detail only the changes in the fracture characteristics. A comparlson of Groups 3, 4, and 5 in Table 2 shows that the _ fracture strain of the unlrradlated base metal decreases with aging at 650°C. (Corrosion is very sllght in the samples and the property changes are ettrlbuted ent;rely to thermal aging.?3s 4) The property Vchanges'are greater for heat 5085 than for heat 5065."Groups 1 and 2, ‘Table 2, show that irradiation reduces the fracture strain with the magnitude of the change increasing with 1ncrea51ng fluence. The reduc- - tion in fracture strain in tests at 25°C is thought to be due to carbide precipitation, and samples 7982 and 7976, Growp 2, Table 2, lend sup- port to this hypothesis. The fracture strain at 25°C was only 32.8% in the as-irradiated conditlon, but improved to 48.3% after an anneal of - 8 hr at 870°C. The reduction in the fracture strain at 650°C due to irradlation is even more dramatlc. We attribute this reductlon in " fracture strain to the productlon of helium in the metal by the '1°B(n,a)7L1 transmutation and have found that postlrradiation annealing - .does not 1mprove the proPerties at elevated temperatures.5 Comparison of the data for Group 3 in Tables 2 and 3 shows that weld- ~ ing decreases the fracture straln in the unirradiasted condltlon and that " 5MSR Program Semionn. Progr. Rept. Feb. 28, 1966, ORNL-2936, p. 117. Table 2. Tensile Properties of Base-Metal Samples 5065 O 73,300 . Test Strain ' | ‘ Reduction Heat Sample ___ Btress, psi Elongation, % Number TSV Number Temffg?t“re (miee1) . Yield Ultimate Uniform Total 1n(%§ea Group 1 | 5065 a 7915 25 0.05 - 51,700 109,300 4.4 41,5 34.1 5065 a 7913 650 0.002 40,400 46,300 3.2 3.4 6.0 5085 & 7888 25 0.05 52,300 95,000 28.7 28.9 20.0 5085 a 7886 650 0.002 35,000 42,400 4.5 5.0 S 13.1 | . Group 2 5065 b 7940 25 0.05 49,000 118,800 57.8 59.7 38.4 5065 b 7947 650 0.002 34,100 55,500 12.2 12,5 16.1 5085 b 7976, 25 0.05 46,500 99,100 32.8 32.8 24,5 5085 b 7982 25 0.05 46,700 119,000 48.2 48.3 34.2 5085 b 7965 650 0.002 31,300 49,900 1.1 11.6 18.6 Group 3,' o | S o 5065 d 1843 25 0.05 64,000 124,600 52.0 55.5 52,1 5065 d 280 650 0.002 46,300 75,400 22.8 24.0 28,1 5085 d 4295 25 0.05 51,500 120,800 52.3 53.1 42.2 5085 d 10,083 650 0.002 - 32,200 70,600 32.8 34.5 27.5 | | Group 4 . | 5085 e FC-3 25 0.05 45,500 111,200 46.8 46.8 31.5 5085 e DC-25 650 0.002 31,500 62,500 22.8 24.3 27.2 Group 5 o 5065 f 10,215 25 0.05 60,900 126,700 46.5 47.4 39,3 £ 10,216 650 ©0.002 44,200 16.0 16.5 16.8 ( oy » - ”» X ) »n : _ Table 2 (continued) Heat " sample Test Strain = Stress . Elongatio Reduction Nunber History Nzggei - Temperature Rate - > PS% € n, % in Ares | | (°c) (min=1) Yield * Ultimate Uniform Total (%) | | | - Group 5 (continued) 5085 £ 10,166 25 0.05 53,900 115,900 38.4 38, 29,7 5085 £ 10,190 650 0.002 37,700 64,700 17.4 18.0 19.7 T osed to fuel salt 1n the core of the MSRE for 15, 289 hr at 650°C to & thermal fluence of | 9 4 X 10<° neutrons/cm?.\‘ , . | osed to MSRE’ cell environment of N2—2 to 5% 02 for 20 789 hr at 650°C to a thermal fluence of _2 6 X ?gg neutrons/cm i Cgiven a postirradiation anneal of 8 hr at 870° C. dUhlrradlated, ennealed 2 hr at 900°C | ®Unirradiated, annealed 2 hr at 900°C, exposed to static barren "fuel" salt for 4800 hr at 650°C. fUnirradla.ted, annealed 2 hr at 900°C, exposed to static barren "fuel" salt for 15,289 hr at 650°C. Table 3. Tensile Properties of Welded Samples Test 10,087 B gy Somple POIV maper. SRR Stress, gl Hongation, 4 Reduction Lecation Number Number Anneal a?g€§ (min=1) Yield Ultimate Uniform Total (%) Failure Grbgg 1 5065 8 7899 b 25 0.05 56,600 92,200 15.2 15.4 16.0 e 5065 a 7898 b 650 0.002 40,700 55,200 7.5 7.6 8.6 a 5085 a 7872 b 25 0.05 52,900 105,700 @ 33.3 33.6 25,2 d,e 5085 a 7870 none 650 0.002 36,900 45,400 L4 5.4 9.5 d,e 5085 a 7871 b . 650 0.002 38,000 52,300 7.5 9.3 2.4 d Group 2 N _ 5065 £ 7959 b 25 0.05 52,700 55,300 2.5 4.3 19.6 e 5065 . f 7957 none 650 0.002 35,400 48,800 6.1 6.8 19.2 c 5065 £ 7958 b 650 0.002 32,700 55,100 10.9 11.3 10.8 d 5085 £ 7992 none 25 0.05 48,600 104,200 40,2 40.4 33.2 d 5085 £ 7990 b 25 0.05 47,300 112,800 40.5 40.8 26.8 d,e 5085 f 799% none 650 0.002 33,100 55,700 12.2 12.9 13.1 c 5085 £ 7991 b 650 0.002 32,700 62,300 18.2 18.6 13.9 d : Group 3 5065 g 4158 b 25 - 0.05 63,700 138,700 43.2 43.4 30.3 c 5065 g 4155 - none 650 0.002 37,500 59,300 9.7 10.4 15.6 c 5065 g 4162 b 650 '0.002 43,200 80,300 19.5 . 20.1 16.0 c 5085 g 10,086 b 25 0.05 49,800 105,900 29.9 30.0 15.7 c 5085 g 10,085 none 650 0.002 35,400 61,500 - 12.7 13.7 10.7 c 5085 g b 650 0.002 30,400 70,600 33.3 34.5 18.0 c vt »n . o« » _ " Table 3 (continued) Test Heat .Hi i Sample :Poig- Temper- S;?:in Stress, psi . Elongation, % R:duz;ion Loca;ion Number TSTOTY wumber €24 ature R8YC o Yield Ultimate Uniform Total in Area of Anneal (o) (min=1) : (%) . Failure . \ - | o Group 4 5085 = h 10,082 none 25 0.05 53,200 121,600 57.0 60.8 8.1 4 5085 = h 10,081 = none 650 0.002 29,400 56,100 14.5 = 15.5 14.0 c 5085 ji'“-- ‘;9’0‘10 ~ mome’ 650 0.002 33,700 55,700 10.1 10.7 . 12.8 e 0 osed to fuel salt in core of MSRE for 15, 289 hr at 650°C to a thermal fluence of 9.4 X lO o neutrons/cm., welded in cell. Elght hours at 870°C. :cweld metal. %Base metal. Exceptlons to the general fracture trend. xgosed to MSRE cell environment of No—2 to 5% 0 for 20,789 hr at 650°C to a thermal fluence of 2.6 X neutrons/cm?; welded in cell. . gUhirradiated,.welded outside cell. hunirradiated, welded in cell. iExposed to static barren "fuel" salt for 4800 hr at 650°C; welded in cell. 10 the fractures were located in the weld metal for the conditions investi- gated. Group 4, Table 3, involves unirradiated semples welded in the “hot cell. sample 10,081 is a duplicate of 10,085 prepared outside thg hot cell and attests to the reproducibility of the welding technique. Sample 10,082 was not given & postweld anneal before testing at 25°C as was sample 10,086 and the location of fracture changed from the weld metal to the base metal. Sample 9010, Group 5,‘Tablé 3, had been exposed to fluoride salt for 4800 hr at 650°C, and its good properties show that no basic problem prevents welding components that have been exposed to salts. ; The samples in Groups 1 and 2, Table 3, were welded after irradia- ~tion. These samples generally have lower fracture strains than their unirradiated counterparts shown in Groups 3, 4, and 5, Table 3. The fracture strains for heat 5085 tested at 25°C are an exception, since they are about equal for unirradiated and irradiated'fields. The frac- ture strains for safiples from heat 5065 which were irradisted, welded, and tested at 25°C are quite low (samples 7899 and 7959, Groups 1 and 2, Table 3). | o A comparison of the properties of the irradiatedrbase metal, Groups 1 and 2, Table 2, with those of the samples irradiated and welded, Groups 1 and 2, Table 3, shows that the welds generally have as high a fracture strain as did irradiated base metal. The poor proper- ties of heat 5065 at 25°C after welding are again an exception to this generalization. The fracture strain of samples irradiated, welded, annealed 8 hr at 870°C, and tested at 650°C is higher than for the comparable irradisted base metal sample. Note that the fracture loca- tion in the irradiated sample shifts from the weld metal to the base metal following the postweld anneal of 8 hr dt 870°C. This is in con- trast to the unirradiated welds where fracture occurred in the weld metal of both as-welded and postweld annealed samples. Several of the samples were examined metallographically. The frac-l ture of an unirradiated welded sample is shown in Fig. 2. This sample was tested at 25°C without postweld annealing, and fracture occurred in the base metal. The weld area has a larger dismeter, indicating that » =3 vy R-47562 (2) R-47563 (b) i Fig. 2. Photomicrographs of Sample 10,082. Heat 5085, Unirradiated, " welded in the hot cell and tested at 25°C. Fracture occurred in the base metal. (a) As polished. (b) Etchant: glyceria regia. 35X. 12 it is stronger than the base metal under these test conditions. The fracture of an unirradiatéd weld sample is shown in Fig. 3. The frac- ture is across the weld zone and the base metal fracture has both trans- and intergrdnular sections. There is also some porosity in the weld metal. The fracture of an wnirradiated welded sample tested at 650°C is shown in Fig. 4. .This sample had been exposed to molten salt for 4800 hr at 650°C, and the weld looks very sound with only a little porbsity. The intercellular cracks in the weld metal indicate that the weld metal did deform. - | | The fracture of an irradiated sample that fractured as it was removed from the welding fixture is shown in Fig. 5. There is some porosity near the fusion line and some within the weld metal. The microstructure of another Sample that was welded after irradiation is shown in Fig. 6. This sample was tested at 650°C, and fhe fracture was intergranular and located in the base metal. Again, there is:a‘large amnfint of porosity near the fusion line and in the weld metal. Much of the porosity near the fusion line is associated with the carbide stringers that are'presént. Because of the similsr chemical behavidr of carbon and boron, it is quite reasonable to suspect that these stringers of carbides would also be enrlched in boron. Transmission electron microscopy of this materisl shows that hellum.fiubbles afe present in this material (Fig. 7), and the heating may allow enough diffusion to occur near the fusion line for the bubbles to agglpmerate. DISCUSSION OF RESULTS ' These tests have shown that the fracture strain of Hastelloy N in tensile tests at 25 and 650°C decreases with long exposure at 650°C. Neutron irradiation causes an even more dramatic decrease in the frac- ture strain. We fused about 75% of the cross section of both unirra- . diated and irradiated samples. Welding alone caused rather large -‘fdecreases in the fracture straln of unlrradlated samples. These sam- -'ples responded much as we had noted earlier in another study 1nvolv1ng SH. E. McCoy and D. A. Canonico, "Preirradiation and Postlrradlatlon Mechanical Properties of Hastelloy N'Welds," Welding J. (N.Y.) 48(5), 203-5—211-s (May 1969). . O i i i i ] i i i 3 i ! ! i ! R=-47559 > 3 . Fig. 3. Photomicrograph of Sample 10,081. Heat 5085, Unirradiated, Welded in Hot Cell, Tested at 650°C. Fracture occurred in the weld metal. ; (a) As polished. (b) Etchant: glyceria regia. 35X. B Fig. 4. Photomicrograph of Sample 9010. Heat 5085, exposed to static barren "fuel" salt for 4800 hr at 650°C, welded in hot cell, tested at 650°C. Fracture occurred in the weld metal. (a) As polished. (b) Etchant: glyceria regia. 35X. iy O R-45450 R=-45449 - (b Fig. 15,289 hr in fuel salt in the MSRE at 650°C. o - 9.4 X 10%° neutrons/em?, welded in hot cell, and broke while removing 5. 'Phot'oniicrdgraphs of Semple 7897. Heat 5065 s irré_udia.ted for Thermal fluence was ) from weld fixture. (a) As polished, (b) etchant: aqua regia. -35X. ™ - Fig. 6. Photomicrographs of Sample 7870. Heat 5085, irradiated for 15,289 hr in fuel salt in the MSRE at 650°C to a thermal fluence ‘of 9.4 X 10?9 neutrons/cm?, welded in a hot cell, and tested at 650°C. Fracture occurred in the base metal. (a) As polished, (b) etchant: aqua regia. -35X. . O "‘\ YE-9913 Fig. 7. Transmission Electron Micrograph of Hastelloy N (Heat 5085) Irradiated in the MSRE to & Thermal Fluence of 9.4 X 102° neutrons/em? at 650°C. 25,000X, welds in large plates of*Hastelloy‘N. Some of the irradiated samples were welded and these were fbund,to have fracture strains at least as high as those observed for the irradiated base metal. (Heat 5065 tested et 25°C is an'exception gnd'itsiductility was very low after welding.) Our previous work had'infidlved some samples that_were‘fielded and then irradiated.” Most of our samples that were welded after irradiation had higher fracture strains at 650°C than the samples in our previous _study'thét Were'welded'befbfé'irfadiation. This is probably due to the drastic redlstrlbution of hellum.that occurs when the metal is fused. ‘Most of the helium_shouldfibe'lcst;from the weld metal,-and-this exhibits 7H. E. McCoy and D. A. Canonico, "Preirradiation and Postirradiation Mechanical Properties of Hastelloy N Welds," Welding J. (N.Y.) 48(5), 203- s—211-s (May 1969). .18 ‘more ductility at high temperatures than the irradiated base metal vwhere the helium is thought to be associated with grain boundaries. Thus;_the weld metal will strain'and make a significant contribution to the total strain. | N - A rather consistent pattern evolves for the location of the frac- ture in welded samples. In both irradiated and unirradiated samples tested at 25°C, the fracture occurs in the base metal in as-welded samples and shifts to the weld metal aftef a postweld heat treatment. -of 8 hr at 870°C. The weld metal in the as-deposited form is stronger at 25°C (Fig. 2) and does not deform as much as the base metal.i After annealing, the weld metal softens and fracture occurs in the weld metal. This observation does not indicate anything about the relative ductili- ties of the weld and base metals, since the sample geometry allows the zweakef-matérial to deform without any deformation occurring in the stronger material. Thus, the as-deposited weld metal is strong at 25°C, but may be extremely brittle. At 650°C unirradiated welded samples failed in the weld metal in the as-welded and heat-treated conditions. The irradiated samples failed in the weld metal when tested in the as- welded condition and the fracture shifted to the base metal after annéaliné for 8 hr at 870°C. Mbtallogr&phié studies indicate that the weld metal and the base metal both deform when tested at 650°C. Thus, the location of the fracture is likely governed by crack'propagation. - Cracks can propagate in unirradiated welds more easily in the weld metal than in the base metal and fracture occurs in the weld metal. Cracks seem to propagate very‘easily through irradiated base metal and the postweld annealed weld metal has better resistance to crack propaga- tion. Thus, irradiated welded samples fail in the weld metal in the as- welded condition and in the base metal after annealing. Two metallographic features in the irradiated welds deserve some comment; the porosity in the weld metal and the porosity near the fusion line (Figs. 5 and 6). The voids in the weld metal are thought to be related to superficial surface films on the samples before welding or are characteristics of the particular heats of material involved. O, . L ¥k 19 The porosity near the fusion lines is associated preferentially - with the carbide stringers; We have noted that these stringers are high in silicongssand that'melting starts in these areas when the alloy is heated to about 1400°C (ref. 9). Thus, the supposition that these void areas result.from localized melting would seem reasonable were it not for the observation thatIUhirradiated welded samples do not contain this porosity (Figs. 2, 3, and 4). The possibility that they are large agglomerates of helium that form during welding must at least be con- - sidered. A shell of material 0.037 cm (~ 0.015 in.) thick around the - fusion zone would contain about 0.2 em? of transmuted helium at atmospheric pressure and 1400°C, If this helium were distributed as small bubbles 0.005 em (~ 0.002 in.) in diameter, there would be about 2 X 10® bubbles presen£ in this small volume. Thus, it seems likely that the porosity near the ffision line is actually helium bubbles. There is no evidence that elther type of porosity influenced the loca- tion of the fracture. SUMMARY Our studles have shown that fu81on'welds can be made in irradiated Hastelloy N after exposure to fluorlde salts. - The rather meager statis- tics indicate that acceptable welds are_not obtained as frequently in the irradisted material as in the unirradiated samples. ~ Samples that had been irradiated and welded were found generally %o have as good tensile fracture strain at 25 and 650°C as the base lfietal Welded samples that were glven a postweld anneal of 8 hr at | 870°C'were even more ductile than the jrradiated base metal At 25°C "bothunlrradlated and;irradlatedfwelds failed in the base metal in the as-welded condition snd in the weld metal after annealing 8 hr at 870°C. 8R. E. Gehlbach and H. E. McCoy, Jr., "Phase Instability in L Hastelloy N," pp. 346~366 in-International Symposium on Structural . Stability in Superalloys, Seven Springs, Pennsylvania, September 4—6, 1968, Vol. II. Available from Dr. John Radavich, AIME ngh-Temperature Alloys Commlttee, Micromet Laboratories, West Lafayette, Indiana. °H. E. McCoy, ‘Influence of Several Metallurgical Variables on the Tensile Properties of Hastelloy N, ORNL-3661 (August 1964). 20 At a test temperature of 650°C, the unirradiated welds failed in the weld metal in the as-welded and heat-treated condition. The samples' irradiated and welded failed in the weld metal in the as-welded condi- tion and in the base metal after annealing. The weld metal in all samples contained minor porOS1ty that likely reflects the welding characteristics of this alloy under the welding parameters that we used. The irradiated samples had a large amount of pbrosity associated with the carbide 'stringers near the fusion line. We feel‘that.this porosity resulted from the agglomeration of small transmutation-produced helium bubbles during the welding. The data are not sufficient to draw a meaningful conclusion about the weldability of irradiated reactor components of Hastelloy Nj the samples were too small, the heat inpfit too low, and the degree of restraint too low. The observatidn that the fused weld metal will deform readily at 650°C is encouraging since this indicates that the weld metal might deform small amounts to relieve stresses between rela- tively large and brittle éomponents or pipe segments. The observed porosity near the fusion line means that this area will be weakened. Welds in large sections will be required to determine whether the com- posite joint of weld metal and fusion zone has acceptable properties. - ACKNOWLEDGMENTS The-authofs are grateful to technicians‘T.-E. Scott for making the welds and to B. C. Williams for running the tensile tests. The metal- lographic work was done by E. Lee and S. E. Spencer. The transmission electron microscopy was done by R. E. Gehlbach. We are also grateful to J. R. Weir for his interest in this work and for reviewing the manuscript. The manuscipt was prepared by the Metals and Ceramics Division Reports Office. O & 1-3. 4=5. 6—25. 26. 27. 28. 29. 30. 31. 32. 33, 3. 35, 36. 37, 38, 39. 40, 41, 42. 43. 4. 45, 46. 47, 48. 49, 500 . 51. 52. 53. 544 55. 56. 57. 58. 59, - 60, 61. 62. 63. . 65. ' 66. 21 - INTERNAL DISTRIBUTION Central Research Library - ORNL Y-12 Technical Library Document Reference Section Laboratory Records Laboratory Records, ORNL RC ORNL Patent Office. R. G. R. Je R. W. C. J. S. C. c. H. M. Se. M. M. C. E. D. R. F. J. E.. Blumberg .. R. E. B. C. H. C. .G. J. M. R. H‘ G. 0. S. D. J. K. Adams - M. Adamson, Jr. G. Affel - . Anderson Apple Atkinson Baes Baker Ball Bamberger Barton . Bauman Bautista Beall J. Bell Bender E. Bettis - S. Bettis S. Billington E. Blanco - F. Blankenship - 0. Blomeke : E. Bloom REOMEERAEEN b G. Bohlmann -~ - S. Borie o J. Borkowski - I, Bowers M. Boyd - E. Boyd = Braunstein A. Bredig = ] B. Briggs =~ R. Bronstein D. Brunton - . - W. Burke Cantor B W. Cardwell H. Carswell, Jr. 67. 68, 69. - 70. 71. 2. 73. e, 5. 76. 77. 78. 79. 80. 8l. 82. 83. 84. 85. gé. 87. 88. 89. 20. 91. 92. 93. 9%. 95. %96. 97, 98. 99. 100. 101. 1020 . 103. 104. 105. 106. 108. 109. 110. 111, L. S w. G. Je - 0. J. C. F. H. 'Ln I. E. ‘B. M. J. H. D. Nancy C. - E. K. W. J B. Je F. D. Je J. D. R. Je J. F. W. L. V. H. W. T. ORNL-TM-2858 Carter ‘Cathers Caton Cavin Chandler Claffey Clark Cochran Cole .Collins Compere Cook Cook Cooke Corbin . Cox L. L.. R. E. M. G. J. H. R. J. A. . S, . P. . R. P. . I. -Ee M. P. '. K. A. - N c. K. . H. . B. . E. H. Crowley Culler - Cuneo Cunningham Dale - Davis DeBakker DeVan DiStefano Ditto Doss Dworkin Eatherly Engel Epler Federer ‘Ferguson Ferris Fraas Franzreb "Friedman - . Fry - :71 . H Frye, Jr. Fuller . ‘Furlong Gabbard . Gallaher ‘Gehlbach Gibbons 13-2.'— L‘. 114. W. 115. A. 116. R. 117. J. 118. R. 119. T. 120. B. 121. P. 122. D. 123. W. 124, C. -~ 125. P. 126. F. 127. R 128. 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Lane 22 165. 166. 167. 168. 169. 170. 171.. 172. 173. 174, 175. 176. 177. 178. 179-183. 184. 185. 186. 188. 189. 120. 191. 192. 193. 194, 195, 196. 197. 198. 199, 200. 201. 202. 203. 204. 205. 206. 207. 208. 209. 210. 211, 212. 213. 214. 215. 216. 217. 218. 219. Lin Lindauer Long, Jr. Lotts Lundin Lyon K. Macklin G. MacPherson SHEDwn . E. MacPherson . C. Mailen ' L. Manmning D. Martin R. Martin W. McClung . E. McCoy . . L. ) : K. McGlothlan McElroy J. McHargue A. Mclain E. McNeese . R. McWherter . J. Metz . S. Meyer . L. Moore A. Mossman . M. Moulton R. Mueller Myers Nichol Nichols Nicholson Noggle Oakes M. Ohr Patriarca Perry Pickel Piper Pollock Prince Ragan Redford Redman . Richardson Richardson QupuEr - RPrrREEER . D. Robbins . C. Robertson A. Romberger . W. Rosenthal . G. Ross . 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