COLLEGE OF ENGINEERING Department of Chemical and Metallurgical Engineering HIGH TEMPERATURE PROPERTIES OF Z4Cr-I Mo AND TYPE 316 STEELS IN AIR AND IN HELIUM BEFORE AND AFTER EXPOSURE TO LIQUID SODIUM P. D, Goodell T M. Cullen,'J6 W. Freemin. i..~"Fina 1 Report:l " - ORA Proje-ct.:48 70., ~. ~ ^.~.". -. " MSA Research Corporation Gallery, Pennsylvania administered through: OFFICE OF RESEARCH ADMINISTRATION ANN ARB OR March 15, 1966

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TABLE OF CONTENTS Page LIST TABLES........ ii LIST OF FIGUR S iii INTRODUCTION..... a EXPERIMENTAL MATERIA 6......... 2 EXPERIMENTAL PROCEDURES 3 Air Tests....... 4 Helium Tests..... 0. 4 RESULTS AND DISC USSION......... 5 Type 316 Stainless Steel........ 5 Tensile Properties...... 6 Creep and Rupture Properties.. 7 4Cr-I Mo Steel. 0.. 9 Tensile Properties $ 0 a 0 a 0 9 Creep and Rupture Properties I. 0 10 GENERAL DISCUSSION..... a a 15 C ONCLUSINS 0 0.... 0 x. 0. 17 R EFERENCES.......... 18 TABLES 0 0 0 0..... 0. 19 FIGUR ES 0......... 30 i

Table Page I Results of Tensile Tests on Type 316 Stainless Steel Sheet Specimens.... 19 II Averages of Tensile Data for Type 316 Steel. 21 TII Results of Stress-Rupture Tests at 1200'F on Type 316 Stainless Steel... <. 22 IV Summary of Creep Test Results at 12003F on Original Type 316 Steel... 24 V Results of Tensile Tests on 24Cr-lMo Steel.. 25 Vi Averages of Tensile Data for 2Z4Cr-lMo Steel... Z7 VII Results of Creep Tests at O1100F on 214Cr-IMo Steel.. 28 VIII Results of Stress-Rupture Tests at 1100~F on 2l4Cr-lJMo Steel 29 ii

Figure Page I Stress-rupture time relationship for Type 316 austenitic steel tested at 1200 F in air and helium with no prior exposure 30 2 Stress versus minimum creep rate relationship for Type 316 austenitic steel tested at 1200 F in air and helium with no prior exposure 31 3 Stress-rupture time and minimum creep rate relationships for Type 316 austenitic steel tested at 1200 F in air and helium after exposure at 1200F for 4000 hours in various environments 32 4 Stress-rupture time relationships for Type 316 austenitic steel tested at 1200'F in air and helium after various exposures. 33 5 tStress-rupture time and minimun creep rate relationships for 24SCr-lMo steel tested at lt100F in air and helium with no prior exposure 34 6 SStress-rupture time and minimum creep rate relationships for 240Cr-IMo steel tested at 1100OF in air and helium after exposure at 1100 F for 4000 hours in various environ-.ments 35 iii

INTRODUCTION The proposed use of liquid sodium as a coolant and heat transfer medium in nuclear reactors has caused concern regarding the possible effects of the sodium environment on the mechanical properties of the materials with which it is in contact. The operating temperatures of such reactors will be sufficiently high so that the creep-rupture properties of the construction materials may be a limiting design criterion. Creep-rupture properties under some circumstances may be markedly affected by environment. As an. example it could be possible for liquid sodium at the operating temperatures of the reactor to contribute to mass transfer reactions which affect the elevated temperature properties of the materials with which it is in contacts MSA Research Corporation has operated two sodium loops in which creep-rupture tests have been conducted for the Atomic Energy Commission, In one loop, 2/4Cr-IMo steel specimens were tested in sodium at 1100FT In the second, Type 316 (18~8+Mo) stainless steel specimens were tested at 1200F, The sodium in the loops was reactor grade with helium used as the cover gas. Other samples of these two steels were exposed at the same temperatures, unstressed, for 4000 hours in different environments and then removed for various tests. The exposure environments were: sodium containing 20-30 ppm oxygen (hereafter referred to as lowoxygen sodium), sodium containing 200-300 ppm oxygen (high-oxygen sodium), sodium saturated with carbon, and helium, The helium exposures were included to evaluate the effect of the thermal history of the material on. the properties, independent of the influence of sodiumi Under a sub-contract with MSA Research Corporation the University of Michigan conducted comparative tensile, creep and/or rupture tests on both unexposed and exposed samples of the 214Cr-IMo and Type 316 steels This report presents a summary of the results of the testing program carried out at the University of Michigan. Some of the data presented 1

herein were oriJginally presented in an interim report (Ref~ 1). These data, particularly from the original material, were described quite extensively in the interim report.. Discussion of these data has been somewhat abbreviated in this report as well as discussion of the details of the experimental procedures EXPERIMENTAL MATERIALS The 2/4Cr-lMo steel specimens were made from 0, 080-0, 085-inch thick sheets. The sheets had been reduced by cold rolling by the U. S Steel Corporation Research Laboratory, Monroeville, Pennsylvania, from annealed /4-inch x 4-inch blanks purchased from the McInnes Steel CompanyAfter cold rolling the sheet was heated in an inert atmosphere at 400 F per hour to 1575~F, held one hour and cooled at 80~F per hour to 13300F and then cooled at 350'F per hour to 600tF followed by air cooling to room temperature. The resulting Rockwell hardness was Rb 73-75. The chemical composition was as follows: C Mn P S Si Cr Mo %o) (o) ) (% T) (o) (%To (%o) Suppliers Analysis 0.097 0 56 0.007 0.022 0.33 2. 17 1.01 Check Analysis by Allegheny 0 086 0 64 0.010 0 024 0. 33 2 19 0.99 Ludlum Steel Corporation The Type 316 stainless steel had been purchased to ASTM Specification A240-54 from William M, Orr Company Inc, Pittsburgh, Pennsylvania, in the form of 16 gage sheet 48 inches wide by 96 inches long. It had been fully annealed and had a grain size of ASTM 5-7 and a Rockwell hardness -f Rb832 The chemical composition was as follows: C Mn Si P S Cr Ni Mo (Qo) (%0)'%o) (%} (%o) (TO) (%) (T%) Suppliers Analysis 0 045 1.94 0 45 0.019 0,012 18.00 12 84 2 33 Check Analysis 0.047 2. 02 0 46 0,020 0 014 18 24 12 57 2. 19

Specimen blanks were cut from the sheets in the direction of rolling. The blanks were milled to within 0. 002 -nch of the final dimensions. The fina.l 0 002-inch was removed by wet grinding in small increments to a finish of 32 RMS or better, It is important to note that the flat surfaces were machined as well as the edges, Both original specimens and specim-ens which had been exposed to sodium for 4000 hours were supplied by MSA Research Corporation. Part of the specimens exposed to sodium for 4000 hours were washed to remove sodium and part were left unwashed by MSA Research Corporation before they were forwarded for testing, After exposure the "unwashed" specimens were sealed in plastic bags under a helium gas cover, The "washedT specimens were cleaned with alcohol., then with distilled water, and finally with alcohol again before being sealed in plastic bags under helium. These bags were placed in a desiccant jar which was then purged. with helium and sealed. EXPERIMENTAL PROCEDURES The MSA Research Corporation supplied specimens in the various conditions of exposure with 1-inch gage length for rupture and creep-rupture tests and with 2-inch gage lengths for tensile and creep tests. Tensile tests were conducted in a 60, 0-lb. hydraulic testing machine. The load was applied in increments of 50 lbs. until the yield point was exceeded and then the test was completed at a constant head of speed of 0~ 01inch per minute. Strain readings'were taken for each increment of load and a stress-strain curve was plotted to establish the 0 2 percent offset yield strength. For the high temperature tests in air the specimen was mounted in an electric resistance furnace. The specin en was brought to temperature in about four hours after which the test was conducted. The tests in helium were conducted in the same manner except that the specimens were mounted in a chamnber which was out-gassed and charged with 3

helium. This procedure will be described later in the report. Air Tests The rupture tests in air were conducted in simple-beam creep-rupture units' The specimens were mounted in the automatcally-controlled electric furnace and brought to temperature and equalized in about 4 hours' The load was then applied to the specimen. The time for rupture was automatically recorded. The creep tests were conducted in the same manner except that a modified Martens-type optical extensometer was attached to each of the specimens. After the initial loading of a specimen its creep extension was measured every 24 hours. All tests were conducted in accordance with ASTM Recommended Practices E21-58T and E139-58T. Helium Tests The chamber used for the tests in helium was an inverted'vT"-shaped retort constructed of Type 304 stainless steel tube, The actual construction of the retort is described in Ref. l1 Pull rods extended into the chamber through vacuum-tight seals, transmitting the load to the specimen. The extensometer was totally enclosed in the chamber and was read and adjusted from outside the chamber. The furnace and its controls were outside the retort, The procedure used to minimize oxidation during creep and rupture testing can be summarized as follows: l. The chamber was evacuated to a pressure of less than 5 microns of mercury and flushed 3 times with helium. 2, With the chamber at 5 microns pressure or less, the furnace temperature was raised to 650"F in about 6 hours and was maintained at that temperature for about 6 hours. Heating tape was used to warm those parts of the chamber not heated by the furnace, This prolonged heating at 650o greatly facilitated outgassing of the chamber and reduced oxidation during testing.A closed system pressure rise of less than 3 microns per minute at a pressure of less than 5 microns was taken as 4

an indication than no leaks were present. 3. The temperature of the specimen was raised tothe test temperature while the specimen was held in the vacuum overnight. 4a When the closed system leak rate was less than 3 microns per minute, the chamber was closed and helium was admitted to the specimen chamber and pumped out several times' The chamber was then filled with helium,':, at 3 psig, final temperature adjustments.made and the test started. The same type of retort and experimental procedures were used for the tensile tests conducted in helium. RESULTS AND DISCUSSION The data obtained for the Type 316 stainless steel and the 24Cr-lMo steel are presented and discussed in separate sections' Type 316 Stainless Steel Tensile tests at room temperature and at 1200F, creep tests and rupture tests at 1ZOOF were used to evaluate the properties of the original material in air and in helium. The results of these tests were discussed in. detail in the Interim Report (Ref. 1). In the present report the data from the tests on the original material have been repeated to provide a base with which to compare the properties of the alloy after exposure to the various environments. Samples of Type 316 steel were exposed at MSA Research Corporation for 4000 hours at 1200"F in low-oxygen sodium (20-30 ppm oxygen), highoxygen sodium (200-300 ppm oxygen), carbon saturated sodium and heliumn: - The helium used was obtained from the Bureau of.Mines. It was passed through a NaK purifier to a copper tube ma-nifold which distributed the helium to the units, The NaK purifier was supplied by the MSA Research Corporation,

These samples were then subjected to tensile and creep-rupture tests. Tests were performed on both unwashed exposed specimens and exposed specimens which had been washed free of any adherent sodium, Tensile roperties The results of the tensile tests on the Type 316 austenitic steel are given in Table I; the averages of duplicate tests have been computed and are given in Table II These data indicate that the tensile and yield strengths of the original material tested at room temperature in heLium are slightly above the average for commercial material, tested in air. It seems very unlikely, however, that the helium atmosphere could have influenced the room temperature test results. The unexposed specimens tensile tested at 1200FZOO showed strength properties corresponding to the average expected values for this grade of steel. The yield strengths for the tests in air and in helium were identical, while the tensile strengths of the specimens tested in air were slightly higher than those of the specimens tested in helium at 12000QF With the exception of the material exposed in high-carbon sodium for 4000 hours at 1200F, the prolonged exposures in varying environments had no significant influence on either the room temperature or the.Z00'F tensile properties of the Type 316 steel. In the case of the material exposed in the high-carbon sodium, the room temperature tensile strength was reduced to an average of 69,980 psi (from 89,000 psi for unexposed material) and the yield strength increased to 57, 830 psi (from 47, 550 psi) the elongation decreased to an average of 1.6 percent and the reduction of area to 6 4 percent (fron 65 and 59 percent respectively), At 1200~F the tensile strength was increased by the high-carbon sodium exposure to an average of 57,040 psi (from 47, 790 psi) and the yield strength increased to 40, 290 psi (from 25, 930 psi); the elongation and reduction of area after the exposure averaged 2. 1 percent and 3., 1 perce nt respectively. 6

Creep and Rupture Properties Or.igin.l m1 -nat:eria]. - The creep and rupture data for the original, unexposed Type 316 st eel is summrnarized in Tables I and IV and in Figures I and 2, These data include specim. ens tested in air and in helium, As was observed in. the previous report (Ref. 1), there was no detectable difference in rupture strength between the specimens tested in the two environments and there was relatively little scatter in the data. The creep tests at low stress levels exhibited slightly higher minimum creep rates for specimens tested in heliurm. t than in air, These differences, how-ever, are not large enough to be considered significant. Lovw-oxygen sodium exposure.a - The data from specimens exposed 4000 hours in low-oxygen sodium and rupture tested in helium exhibited somewhat greater scatter than the specimens tested in air; see Figures 3 and 4a, Both the helium and the dai rupture data for the Tmaterial in this condition of exposure fell within the scatter band of the rupture data for the unexposed material', High-oxygen sd.ium exposure. - The creep-rupture data for the Type 316 tnateri-al exposed 4000 hours at 1200 F in high-oxygen sodium are given in part C of Table IXc and are also shown in Figures 3 and 4b, The rupture data for the material in this condition of exposure tested in helium also fell within the scatter band of the unexposed material. The slope, however, of the rupture curve see Fig,, 4b) was somewhat flatter than that of the unexposed material so that the rupture time at the lowest stress was on the high side of the unexposed rupture band. The results from the material tested in air appear t to fall on a line parallel to but below the band of rupture strengths of unexposed material. The possible loss of carbon from the material du ring the exp suue to high-oxygen sodium could possibly account for somewhat lower properties in the exposed specimens than in the unexposed, If carbon losses, howeve r, were responsible for the reduced strength, a. simila.r reduction of rupture strength should have 7

been noted i.-9 the resu..ts3 of tests co)nducted in heliurm. The relation between rupture properties in air and helium also existed for the creep rates. The creep rates of specinmens tested in helium. corresponded to those of unexposed material, butI those of specimens tested in air were some-what highero The latter correspond to the creep rates of the material. exposed 4000 hours in helium a.t 1200 F and creep-rupture tested in air at 1200 Fo High-carbon sodium exposure, - The material exposed to carbon satura.ted sodium exhibited srnmilar rupature prooperties when subsequ.ently tested in air and. iJn helium:R(see Ta.ble:il:I part D and Figures 3 and 4c. At low stress levels the rupture times -were greater than those of the unexposed material, The mininmum creep rates from. these tests were an order of mragnitude lower th.an th.oe of the unexposed m.ateriaal; the heliumr tests exhibiting somewhat lower rates than the air tests, The rupture ductility and elongation'see Ta.ble 1II p-part D) for the specimers tested after this exposur We were very i:l The behavior of the speciLrmens after exposure to high-carbon sodium can apparently be acc-o nuted. fo- on the basis of the greatly increased, carbo:n conten{t of the mt.na teuria:l resu ltisng fromr exposureO Helium exposure. - The rupture data for the Type 316 m.aterial exposed 4000 hours in helium a t 1.200 F and tested. in air at 1200 "0F fell within the scatter band for unexposed mater.ia.l. The ruptture data fell on a straight line, the slope of w:hich was slightly less than that of the unexposed miaterial (Figures 3 and 4d)o The rninirimum creep rates of the alloy tested in air at 1200 PTF after exposure to helium were somewhat greater than those of the unexposed materials.No subsequent c:reepe-ruptuere tests were run in helium on the steel in this condi-tiono 8

2' (4Cr-IMo Steel. Tensile tests at room temperature and at 1100F, creep tests and rupture tests at ll001F were used to evaluate the properties of the original material in air and heu heum The results of these tests were discussed in detail in the Interim Report (Ref. )i Some of these data and the discussion thereof have been repeated in this report to provide a base with which to compare the properties of the material exposed undervarious conditions. Samples of the 2/4Cr-lMo steel were exposed at MSA Research Corporation for 4000 hours at 1100PF in low-oxygen sodium (20-30 ppm oxygen), high-oxygen sodium (Z00-300 ppm oxygen) and in helium. Some of the exposed specimens, in both the washed and unwashed conditions, were tensile tested in helium at room temperature and at 1I00F,O a Other exposed specimens were creep-rupture tested in helium at 1100 F and still other specimens which had been exp.osed in. low-oxygen sodium were rupture tested. in air Tensile Propertie s The results of the tensile tests on the 2'4Cr-lMo steel are given in Table V; the averages of duplicate tests have been computed and are given in Table Vi These data indicate that the tensile and yield strengths of the original material tested in air at 1 100 were within but on the high side of the range for commercial ZG/4Cr-IMo steel: the ductility data for these tests were within but on the low side of the usual range of commercial material, The tensile strength of specimens of origina. material tested in helium at 11001F were significantly lower than those tested in air, Their yield strengths, however, were only slightly lower, Following the 4000 hour exposureS at l 100F in various environments, the strength of the 2'4Cr-lMo steel at 11001F w:as much lower than that of the original material wvhen tested either in air or in helium (see Tables V and VI). The material exposed in low-oxygen sodium and that exposed in helium exhibited v'ery similar properties; the former ha-ving a tensile 9

strength in helium at lOO 10F of 26, 150 psi and a yield strength of 17 100 psi, the la.tter having values of 253 730 psi and 16 770 psi respectively. After the exposure to high-oxygen sodium, the tensile and yield strengths were 21, 710 psi and 16, 000 psi. The corresponding values of tensile and yield strength of the original material tested in helium were 38, 550 and 23 700 psi respectively, The similarity of t data for the o ematerial exposed in low-oxygen sodiu and in heli.m suggests that the difference in tensile properties between the material in these conditions and the original unexposed material was probably due to thermally-induced structural changes and not to the environments The lower level of the tensile data for the material exposed in high-oxygen sodium in comparison to the material subjected to the other exposures, can probably be attributed to decarburization during exposure. Creep and Rupture Properties Original materal - The creep and rupture data for the orsiginal urnexposed 2'iCr-lMo steel are summarsized in Tables VII and VIIf, The stress versus rupture time and versus minimum creep rate curves ae plotted in Figure 5s These figures include data fro both air and helium tests. The l1 OOF rupture tests in air on t o riginal material exhibited relatively little scatter. While the extrapolated 100, 000 hour rupture strength at li00PF was low, it was within the expected range for this mnateriat The data from rupture tests in helium were erratic but the average rupture curve for the helium tests was consistent with at of the original material tested in air at g00"Fe There doe not appar to be any justification for draig separate rupture curves for the two test conditions,, The cause for the observed scatter in the results from the helium tests has not been determined., The following comments, which are essentially the same as those contained in Ref. 1, are offered concerning the, scatter of the results* I. No other series of tests of either steel in any condition of expo'ure exhibited this amount of data scatter. This fact indicates hat the testing procedures and conditions alone were not responsible for the observed scatter., 2, Specimen 2DASX5, which ruptured vvery prexlaturely in 624 hours under 10, 500 psi, fra.ctured at a scribe mark used as a gage mark~ This 10

suggests that the 2/4Cr-IMo steel may be sensitive to stress concentrations when tested in helium, No obvious relationship between rupture time and surface condition was found in any of the other tests, 3 h The use of the helium. atmosphere did not prevent oxidation, The extent of oxidation encountered in the creep and rupture tests in helium at 11000F varied among the specimens from a slight discoloration to appreciable oxide (never as great, however, as encountered in the tests in air), There appears to be no relation between the degree of oxidation and the scatter in the data, of the tests run in helium. It may also be noted that the latter comment and the similarity between the average rupture properties i.n air and in helium indicate that the oxidation which occurred during the tests in air was not very influential toward the rupture characteristicss of the mater:.al. At the time that the above tests were run, creep measurements were not being made during the rupture testing, so these data are not available for evaluation~ Low stress creep tests of about 4000 hours duration were run on the original materiali at liOO0F in a.ir and in helium. The stress dependence of the minimum creep rates of these tests is shown in the lower part of Figure 5~ The stress dependence of the minimum creep rate (i_ e. the slope of the stress verss e minimum creep ra.te curve in this figure) of the tests in air was as expected for this material. The slope of the curve for the tests in helium, how'ever, wa.s flatter than that of the tests in air and at the two lowest- stresses the minimum creep rates in heliu m were less than those measured in the air tests. This is someewhat. unusual in that it has been generally considered that an -inert atmosphere lowers creep strength. It was noted in Ref. I in connection with these data that the tests in helium at 6000 and 7000 psi exhibited an early onset of third-stage creep which was not found in the similar tests in airO Considering the limited amount of creep data and the uncertai nty of the properties reflected by the erratic rupture data, the early onset of increasing creep rate is the strongI1

est suggestion of an effect which may be attributable to the helium atmosph.e re Helium exposure. - The data from the specimens exposed 4000 hours in helium a't I 1.00F and then creep-ruptuae tested in helium at I l00F are given in Table VIII and plotted in Figure 6, Note that in contrast to the original material. these data exhibit very little scatter, The significant feature of these data is the reduction in short-time strength as a result of the 4000 hour exposure, This behavior has been found to be typical of 2z /Cr- Mo steel., It is thought that the prolonged heating of this alloy at 11000F caused structural changes to occur. These microstructural changes caused the short-time rupture properties of the exposed material to be much lower than characteristic of unexposed virgin material As would have been expected, however, the long-time properties of the exposed specimens were similar to the long-ti-me properties of the unexposed specirnens, Since most of the microstructural changes occur in a few thousand hours at 1100F and are essentially the same in either low stress or unstressed exposure, their influence on rupture properties should be greatly reduced after these relatively short-tim periods. The result of this type of'behavior is that while the short-timne rupture strength can be drastically reduced, the long-time rupture strength may not be significantly changed by the prior exposure. This is precisely the behavior exhibit.ed. in Figure 6 for the material exposed in helium for 4000 houars prior to creep-rupture testing. Note Tthat at about 2500 hours the extrapolated rupture curves for the original material and the material prior-exposed in helium, appear to intersect,, After about 2500 hours the prior-exposed material is assaumned to be a-s strong as the original material, The creep data for the helium exposed material is such that the minimum creep rates are somewhat lower than either those of the unexposed material or of the material exposed in high-oxygen sodium, The stress dependence of the minimum creep rate of the -material subjected to the 12

helium exposure and tested in helium appears to be the same as that of the unex posed material tested in helium and the material exposed in highoxygen sodium tested in helium. Low- and high-oxygen sodium e:xposture - The creep and/or rupture data fr -.om the specimens exposedi 4000 hours in laow and high-o' xygen sodium at l00~F' are given in Table V.It and plotted in Figure 6o The rupture data at 0ll0'F fromt the tests in ar and in helium on the material subject to the low-oxygen sodium exposure are almost identical and exhibited virtually no scatter, The rupture curve fitted to this data fell below that of the original material and had a. flatter slope. There were no rupture tests run in air on the material exposed in high-oxygen sodium; the rupture data from tests in helium on this material laid somewhat below the rupture d.ata from the material exposed in low-oxygen sodium and the slope of the curve was even less steep thanu. that of the mate.rial after the low-oxygen exposure. There was also no scatter in the data.from the material exposed in high-oxygen sodium. As a consequence of the difference in the slopes of the rupture curves of the original and the exposed materials, extrapolation of the curves indicate that the curves of the exposed material wOuld i.ntersect that of the original material; the material exposed in low-oxygen sodiun at about 35, 000 hours and the ma.terial exposed in. high-oxygen sodium at about 15, 000 hours' Assuming that such extrapolations are valid, as well as the extrapolation of the rupture curve of the original mnaterial, the exposed material would be at lea-st as strong as th-e original at times greater than those indicated by the intersection of the two curves, This general type of behavior, as mnentioned previously, is not unusual in 2'4Cr-iMo steel. it results from thermally-induced structural changes accomnpanying the prolonged h.eating of the steel at 1100'1F These structural changes usually reduce the short-ti-me strength but not the long-time strength relative to unexposed rmatetrial. Consequently, to evaluate the in.fluence of t.e sodrli environment t. which the material was exposed, 13

the test results imust be compared not to the ori.ginal material but to the nma te ri a e xpsed 4000 hours at 1iOOF in helium. The latter, it is assumed, has undergone the same thermally-induced structura.l changes as the material exposed in the sodium. environments. The following features are evident in the stress-rupture curves of Figure 6. l~ At short times the rupture behaviors of the material exposed in helium and in low-oxygen sodium appear to be very simi9ar; this is also supported by the 1100'F tensile tests on these materials, 2, At short times there was a signific:ant difference in rupture strength between the material exposed in low-oxygen ssodiu:n and tha.t exposed in high-oxygen sodium,, This same trend'was noted in the results of tensile tests on the alloy in these conditions of exposure. 3. At long times only slight dfferences were noted in the rupture strengths of the steel subjected'to the two sodium exposures. 4~ There was a divergence of the rupture curves of the material exposed to low-oxygen sodium and that exposed in helium, At long time periods the rupture strength of the miaterial exposed to helium was significantly higher than that of the alloy exposed to low-oxygen sodium for 4000 hours' The differences between the material.s subject to the two sodium exposures imay be due to d.ecarburization of the steel during the high-oxygen sodiumn exposurte Carbon analysis performed by MSA Research Corporation on expo sed specimens indicated that the mat:erial had been decarburized during both exposures, the high-oxygen sodium resulting in somewhat greater deca.rburiza.tion tha-.n the low-oxygen sodium environments The differences between the test results shown in Figure 6 for the materials subjected to the three types of exposure suggest that the sodium environment with which the material was in contact during the exposure did contribute to a change in properties larger than that associated with the rmally-induced structural. changes.a.lone. 14

GENERAL DISC USSION Mic:rostructura.l Instability Most comrnerc"ially -produced ma.terials used in elevated temperature applications are microstructurally unstableb. The degree of the structural instability is reflected in the slope of the rupture curve, since the processes through which creep acts on an alloy to cause rupture are inter-related with the processes through. which the microstructlire acts to attain its stable state. In most cases the higher the degree of ins'tability in the microstructure, the greater the slope of the rupture curves Unstressed exposure for 4000 hours at ll0 F in the case of 2L4Cr-IMo steel and 1200 Q in the ca.se of'ype 316 stainless steel should have caused each alloy to approach a stable st.ate. Type 316 stainless steel, however, in the fully annealed cond.ition, is a rather stable a. loy. For this reason only minor structural changes would, be a.nticipated during 4000 hours at 1200 F, Examina:tion of Figure 4 showvs that witlh one exception the rupture properti.es of the steel. i.Ln ei.ther air or heli um after 4000 hours of exposure in high-oxygen s odium, lo w- ygen sod.ium r helium were within the range expected of unexposed -material; the slopes of the riupture curves of the steel, after the different exposures owere s:lightly flatter than that of the unexposed Amaterial, indicating tha t the microstructture did change somewhat during the prolonged exposure. The effect of the approach of:mic-1r-ostructural stabi-'lity duri-ng exposure was mutch more apparent in the results from the.1/4C-. IMo steel than in the Type 316 steel data. Figu.ure 6 shows a co.mparison of the average properties of the urnexposed all.oy with rupture properti:es' after 4000 hours exp-sure at 1100"F in different environments. In. every cease exposure drasti.cally reduc ed short-t-ime rupture properties a.nd caused the alloy to exhibit a much flatter rupture curve than typical of new material. Such behavior is characteristic of the influence of long-timne lo-stwress service on the rupture properties of this type of alloy (Ref. 2). 15

Exposure Envinronirnent In order to evalhra.te the irfl.ue-ace of sodiu.m environment during exposure on the subsequent properties of the two steels, the properties have to be compared with the alloy properties after helium exposure This comparison is necessary in order to elimina/te any influence of thermally-i.nduced. icrostructural changes on properties. Such changes should only be a function of time and temperature and should be independent of environments Exposure of Type 316 stainless steel in low — or high-oxygen sodium had very little influence orn subsequent tensile or creep-rupture properties of the alloy. Exposure to high-carbon sodium, however, did markedly affect the properties of the steel. While rupture strength was relatively unaffected by this exposure, creep resistance was improved significantly~ Rupture and tensile ductility was reduced to a very low level. Tensile properties were also influenced greatly by the exposure.At room temperature the strength was reeduced but at 1200%'F it was raised, All these effects are most probably related to carbon pick-up by the steel duriSng the exposure to carbonsaturated sodium. The tensile properties of 2/4Cr-IMe steel exposed to low-oxygen sodium. were similar to the properties exh.ibted by the heliurn-exposed material, Exposure to high-oxygen sodium presruLa-bly decarburized the alloy and thereby lowered its tensile strength properties So.me decarburizattion may also have occurred during exposure to the low-oxygen sodium, since the rupture properties of the steel after this exposu-re were somewhat lower than those of the steel after exposure to helium at 1IOO 10 The rupture properti.es of the specimens exposed to high-oxygen sodium were even lower, due to the still greater degree of decarrization n all cases the tensile and rupture ductility were quite high, indicating little influence of exposure conditions on this property. 16

CONCLUSIONS The conclusions drawn:fron this research on the influence of exposure to different sodiun env'ironments can be summarized as fAtllows: l~ Thermally-induced microstructural changes occurr'.In duirng 4000 hours of exposure at: 1.200"F for Type 316 stainlesvs steel and at 11O00F for 214Cr,-IMo steel caused a reduction in the subsequent short-time strength of each alloy and a. flattening of the stress-rupture curve. 2, The degree of reduction of short-time strength properties wais much greater in 2/4Cr-lMo steel than in Type 316, due to its greater microstructural instability. 3, Exposure to low- or high-oxygen sodium d.id.d not have any greater influence on the properties of Type 316 steel. tha.n did exposure to helium. 4. Exposure to high-carbon sodium i mproved the creep resistance but lowered the rupture ductility of Type 316 steel, 5. Lw-o xygen sodium exposure had relatively little influence on the properties of 2/4Cr- lMo steel, 6. Exposure to high-oxygen sodium reduced the strength of 2'4Cr-IlMo steel t due to decarbu rization of the alloy..7

R EF FERENCES IK Lee, B. Wc, and Freeman, J W;. High Temperature Properties of Z/4Cr-IMo and Type 316 Steels in Air and in Helium Before and After Exposure to Molten Sodium; Interim Report 048701 ~F to the MSA Research Corporation, October 1963, 2, Cullen, T. M., Rohrig, 9l A., and Freenmaan J. W: Creep-Rupture Properties of 1. 25Cr-0 5Mo Steel After Service at 1000F; ASME Paper 65-WVA/Met-3, Presented at ASME Winter Annual Meeting, Chicago, Illinois, November 1965. 18

Results of 1tensile Tests on Type 316 Stainless Steel Sheet Specimens Tensile 0, 2% Yield Reduction Specimen Temp. Test Strength Strength Elongation of Area No, / Code (OF) Atmosphere (psi) (ppsi ); _%) A) Original Material 271//3BHX 10 Room IHelium 89,500 49,700 6 559 272/?3BHX 11 Room Helium 88,500 49,400 66 59 3BHX 1 1200 Helium 47 200 26,600 46 58 3BHX 2 1200 Helium 47,500 25,900 52 54 3BHX 3 1200 Helium 48,600 25 300 44 53 3BAX 1 1200 Ar 51,200 26,300 47 44 3BAX 3 1200 Air 50,250 25,550 41 48 3BAX 4 1200 Air 49,400~ 26, 100 43 4-7 B) Material exposed 4000 hours in low oxygen sodium at 1200'F 8/3BHX 4 Room Helium 93,200 44, 600 47 46 87/3BHX 5 Room Helium 92, 000 43, 750 48 50 88/3BHX 6 Room Helium 92, 50 42000 46 89/3BHX 7 Room Helium 91, 400 43,700 49 52 90/3BHX 8 Room Helium 92,500 43,900 49 52 91 /3BHX 9 Room Helimum 95,500 4,0 4500 5213BHL1C 1200 Helium 48,850 24,500 39 46 53/3BHL2O C 120 Helu 60 46,90 24,800 52 52 54/3BHL3C 1200 Hel ium 50,000 26, 200 41 46 55,/3BHLIUb 1200 hliam 49. 100 26,750 41 56 56/'3BHL2U 1200 Heulm 46,400 2H5, 00 46, 55 b 57/37BHL3U 120) Heli um 49, 900 25,650 46 51 C;, Material exposed 4000 hours in high oxygen sodium 470 Room Air 85,200 40,600 3 324 471 Room Air 85, 900 41, 250 48 34 474 Room Air 84,900 39 75 0 39 34 473 Room Air 85,000 39, 750 38 30 474 Room Air 85,600 41, 250 42 32 475 Room Air 82,900 41,600 40 32 cont:inued.... 19

Tensile 0. 2% Yield Reduction Specimen T emp. Test Strength Strength Elongation of Area No / Code ( F) Atmosphere (psi (psi) ('%) (To) C) Material exposed 4000 hours in high oxygen sodium (continued) 476 1200 Helium 46, 700 24 400 27 46 477 1Z00 Helium 47, 800 24 000 31 42 509 1200 Helium- 49, 100 24, 00 25 46 a 473 100. Helium 49 500 23, 300 25 38 479. 1200 Heliunm 49 250 25,000 24 26 480 1200 Helium 48,500 24 600 21 36 D) Material exposed 4000 hours in high carbon sodium 360 Room Air 67,806 53, 750 <1 <1 361 Room Air 66, 500 57, 500 1.0 5. 5 364 Room Air 78, 100 572 250 24 7 4 369 Room Air 68,800 57, 750 20 8.5 378 Room Air 68 400 62,25 12 9. 2 379 Room Air 69 000 58,500 2.2 7 0 366 1200 Helium 57,300 39 700 2 1 2. 1 367 1200 Helium 54, 300 40, 500 1 7 4.3 368 1200 Helium 57, 000 40, 300 2 7 4. 5 362a 1200 Helium 59,000 38,000 2 3 1 5 363 1200 Helium 56,375 41,250 1 7 3 6 365a 1200 Helium. 58, 250 42,000 2 0 2 6 E) Material exposed 4000 hours in helium at: 120F 353 Room Air 81, 100 40, 250 53 57 354 Room Air 86,400 38,600 59 56 355 Room Air 87, 500 41,250 49 39 511 Room Air 87 000 38, 500 55 54 512 Room Air 87, 700 29, 300 53 56 512 Roon Air 87, 200 40,500 53 58 356 1200 Helium 48, 100 23, 600 14 62 357 i200 Helium 46,400 23, 400 31 67 358 1200 Helium 46, 100 23, 500 25 62 514 1200 Helium 48,000 23, 500 23 48 515 1200 Helium 54, 250 27,600 24 47 516 1200 eliu 65,000 27,750 26 50 a - Unwashed Specimens 20

TABLE.II Averages of Tensile Data for Type 316 Steel Tensile 0. 2% Yield Reduction Prior Temp. Test Strength Strength Elongation of Area Exposure (F) Atmosphee e p (si) (p i (%) (%o) None Room Helium 89,000 49 550 66 59 None 1200 Helium 47,790 25,930 47 55 None 1200 Air 53,620 25,980 44 46 Lo-O -Na Room Helium 92,850 43,925 48 47 Lo-Oz -Na 1200 Helium 48,580 25,170 44 48 Lo-02z -Na 1200 Helium 48,470 25,870 44 54 Hi —O -Na Room Air 84, 920 40,700 40 32 HiO ~ -Na 1200 Helium 47,870 24,200 28 45 Hi -.2 -Naa 1200 Helium 49,080 24,300 23 33 Hi - C -Na Room. Air 69 980 57,830 1.6 6.4 Hi C -Na 1200 Helium 56,200 40,170 2.2 3.6 Hi-C -Naa 1200 Helium 57,880 40,420 2.0 2.6 Helium Room Air 86, 150 38,070 55 57 Helium 1200 Helium 51,310 24,890 24 56 Average Properties of Commercially Produced Type 316 Steel: None Room Air 81,000 39,000 45 55 None 1200 Air 50,000 22,000 39 52 a Unwashed specimen 21

TABLE III Results of Stress-Rupture Tests at 1200 TF on Type 316 Stainless Steel Rupture Reduction Min. Creep Sp<ecimen Test Stress Timre Elongation of Area Rate Ne O.,, todse mosphere (pi) (hours) {%) (% (/(hr ) A) Original Material 97/3C0AX 10 Air 27, 500 173.6 61 45 3GAX 2 Air 27, 500 152 8 58 49 98/3CAX 9 Air 27,500 146. 5 52 46 3GA X 3 Air 27,500 143 0 63 50-60 0 12 3DAX 4 Air 24,000 476 2 40 38 0 034 94/3CAX 6 Air 24 000 4 6 3 60 43 95/3CAX 7 Air 24,000 449 7 44 39 3CAX I Air 22,000 863 5 33 31 96/3CAX 8 Air 21,500 1000 6 33 28 93/3CAX 5 Air 21,500 971 0 35 38 3DAX 3 Air 20,500 1387.8 35 29 3DAX 1 Air 18,500 2363 0 34 29 3DAX 2 Air 17,750 1969. 5 39 20 3AAX 4 Air, 17,750 3695. 1 18 18 3CAX 4 Helium 27,500 166.3 63 46 3CHX 2 Helium 27, 500 152 8 53 49 3CHX 3 Helium 24,000 697 7 48 49 3DHX 3 Helium 24,000 483. 65.54 3CSHX Helium g. 21,500 894 3 56 47 3DHX I Helium 20,000 1509 5. 34 37 3DHX 2 Helium 18,000 261 99 44 32 104/3DHX 4 Helium 17,750 3068. 1 40 67 B) Material exposed 4000 hours in low-oxygen sodium at 1 200 F 3EAL 1 Air 27,500 144 6Z 46 3EAL 2 Air 24,000 574 4 44 3EAL 3 Air 21,500 985.Z 59 42 3EHL I Helium 27,500 5 57.6 57 52 3EHL 2 Heliumr 24 000 675.0 48 44 3EHL 3 Heelium 21,500 822 2 49 42 continued.... 22

Rupture Reduction Min. Creep Spe cimen Test Stress Timne Elongation of Area Rate No /Code Atmosphere (psi) (hours (%) (o) (o/hr.) C) Material exposed 4000 hours in high-oxygen sodium at 1200 Z F 491 Air 27 500 876 36 64 0. 151 490 Air 2500 575. 3 29 29 00 029 489 Air 18,500 1269, 4 23 27 0. 0088 492 Helium 24, 000 369. 8 32 37 0, 032 494 Helium 2, 500 736 42 48 0. 019 493 Helium 20,000 1915 42 4 0 0055 D) Material exposed 4000 hours in high-carbon sodium at 1200 F 380 Air 27,500 163.5 14 6 13 0 0.017 381 Air 22,500 940, 6 6.0 9. 1 0.0037 382 Air 21,000 16011,a 559 5 4 0,0015 481 Helium 27,500 167 7 7 75 13. 0 0.0094 482 Helium 23,000 924 4,5 15. 50 0 0012 483 Helium 20, 500 3396 11. 0 17.5 0 00067 E) Material exposed 4000 hours in helium at 1200'F 496 Air 27,500 102. 1 66 79 0. 0239 469 Air 25,000 300.5a 55 56 0.074 506 Air 23,000 542 70 92 0.034 370 Air 21,500 1003 8 51 56 00248 507 Air 20,500 1076 71 69 0 019 468 Air 20,000 1543 7 34 52 0. 013 a - Specimen broke in gage mark or fillet b - Test interrrupted at 2097 hours c - Test brought up to temperature twice before test could be run 23

TABLE IV Su.mmary of Creep Test Results at 1200F on Original Type 316 Steel. Specimen Stress Minimum Creep Rate Discontinued Code Atmosphere (psi) o%/000 hours after: (hrs.) 3AAX3 Air 11, 500 0, 040 3987 3BAXZ Air 12, 500 0, 143 4243 3AAX2 Air 13, 000 0. 215 3693 3AHX3 Helium 10, 500 0, 08 3AHiXZ Helium 11,000 0. 18 3AHtXi Helium 12,000 0 23 4008 24

TABLE V Results of Tensile Tests on 214Cr-lMo Steel Tensile 0. 2% Yield Reduction Specir ren Temp. Test Strength Strength Elongation of Area No,. /Code (OF) Atmosphere (psi) (psi) (%0) (%) A) Original Material 2BAXI 1100 Air 56, 800 28, 800 32 57 2BAX4 1100 Air 49, 170 25,800 28 64 2AAX4 1100 Air 59,400 29,370 32 62 2BHX3 1100 Helium 39,700 25, 000 26 63 2BSHX4 1100 Helium 38,120 22,600 31 44 3BHX5 1100 Helium 37,820 23,500 41 74 B) Material exposed 4000 hours in low-oxygen sodium at 1100l F 208 1100 Helium 26,620 17,200 45 54 209 1100 Heliun 25,230 46 55 210 1100 Helium 26,580 16,800 47 41 206 1100 Helium 26,160 17,300 41 50 211 1100 Helium 25,800 16,150 40 65 242 1100 Helium 26,410 17 950 42 56'43 1100 Helium 29,200 19,400 38 57 C) Material exposed 4000 hours inn high-oxygen sodium at ll00F 331 Room Helium 61,600 28,600 23 56 332 Room Helium 69,280 25,800 33 66 333 Room Helium 57,910 24,400 28 63 334 Room Helium 59,550 28,300 21 61 335 Room IHelium 59,700 27,300 28 60 337 Room Helium 60,520 27,300 32 64 324 1100 Helium 23,800 18,300 46 66 325 1100 Helium 20,600 14,700 38 61 326 1100 Helium 20,740 15,000 39 54 328 1100 Helium 23,400 14,500 37 64 329a 1100 Helium 22,300 - 36 64 330a 1100 Helium 2, 000 13, 200 37 64 continued... 25

Tensile 0. 2% Yield Reduction Speci.men Temlp. Test Strength Strength Elongation of Area No. / Code (CF) Atmosphere (psi) (si) (%) () D) Material exposed 4000 hours in helium at l100'T 436 Room Helium 67, 300 29, 700 28 57 437 Room Helium 64,500 26,900 23 65 438 Room Helium 66,200 29,700 28 62 433 1100 Helium 20, 800 13, 500 33 81 434 1100 Helium 28, 200 18, 000 30 63 435 1100 Heliun 28, 200 18,800 47 76 a - Unwashed specim.en 26

TAB LE VI Averages of Tensile Data for 2gCr-IMo Steel Tensile 0. 2% Yield Reduction Prior TempT Test Strength Strength Elongation of Area Exposure (~FP) Atmosphere (psi) (psi) (%o) (%) None 1100 Air 5, 0 27,990 31 61 None 1100 Helium 38, 550 23 700 32 60 Lo-02 -Na 1100 Helium 26,150 17,100 45 50 Lo-02 -Na 1100 Helium 27, 140 17,833 40 59 Hi 02 -Na Room Helium 61,430 26,950 27 62 Hi- 02 -Na 1100 Helium 21,710 16,000 41 61 Hi -02zNaa 1100 Helium 22,570 13,850 37 64 Heliuml Room Helium 66,000 28,770 27 61 -elium 1100 Helium 25,730 16,770 37 73 Average Properties of Commercially Produced 21?4Cr- I Mo Steel: None Room Air 73,000 42,000 35 50 None 1100 Air 42,000 27,000 44 88 a - Unwa-shed specimens 27

TABLE VII Results of Creep Tests at 1100F on 21/4Cr-iMo Steel Specimen Stress Minimum Creep Rate Discontinued Code Atmosphere (psi) %/1000 hours after: (hrse) 2,AAXI Air 5, 500 0. 076 4003 2A AXZ Air 6,000 0 12 4010 2BAXZ Air 8, 000 0. 36 3957 2AHXZ Helium 5, 500 0. 023 2AHXI Helium 6, 000 0 0'75 4009 2AHX3 Helium 7,000 0. 28 28

TABSLE VII Resultes of Stress-Rupture Tests at 1100 F on Z'4Cr-1Mo Steel Rupture Reduction Mmin Creep Specimen Test Stress Time Elongation of Area Rate No, /CQode Atmosphere (psi) (hour ) (%) (%) (%o/hra) A) Original Material 2CAX 4 Air 20, 000 90. 8 64 58 2CAX 2 Air 17,500 139.2 42 36 2CAX 3 Air 15,000 302 3 41 32 2CAX Air 12, 000 1390 5 23 15 2CHX I Helium 20,000 108 0 55 55 2CHX 3 Helium 20, 000 86. 5 56 40 2DHX I Helium 16, 500 246. 6 47 41 2DHX 3 Helium 16, 500 98, 4 47 54 2DAX I Helium 14, 500 303 8 36 41 2DAX 2 Helium 14, 000 479 2 28 - 2DAX 4 Helium 12,500 1545. 0 29 27 219/ZDAX 5 Helium 10,500 624 0a 22 27 2Z0/G2CHX 4 Helium 10, 500 1398.0 27 28 B) Material exposed 4000 hours in low-oxygen sodium at 1100OF 2. 5 Air 14, 000 74 3 26 21.4 Air 12, 500 195 2 44 213 Air 10, 000 1205 0 16 11 2EHL I Helium 14 000 78.8 36 31 ZEHlL 2 Helium 12,500 180. 4 31 21 EHL 3 Helium 10,000 1078. 4 27 27 C) Material exposed 4000 hours in high-oxygen sodium at 1100F 222 He lium 13,720 8 041 45 0 61 188 Helium 12,000 68. 3 32 29 0. 0487 223 Helium 10,000 780. 8 13 18 0. 00816 D) Material ePused 4000 hours in Helium at 1100'F 257 Helium 13,000 312 1a 31 48 0.031 344 Helium 11,500 961. 5 37 39 0 0086 258 Helium 10,800 2374 33 32 0. 0031 a - Specimen broke in gage mark or fillet b - Heavily oxidized c - Oxidized d - stimated from shoulder to shoulder length of specimen 29

Solid Points - Tested in Air at 1200 F~ f. Open Points - Tested in Helium at 1200F O -3CAX9 60 -- -----— ~ - ~ 3DAX4 - |^ /^ g | | gr ~3CHXZ 3/ X, f 3 0 Y 4|!1| t // 5 z ^rA^ /a j ^/ 3CAX7 I 0 8 i -.. // ~ ~TIoXJ ~ ZC I - r3CAXI C// 3 DAX 1U5 k~/ 3CAX /3CAX3 3CXDHX3/ 3DA / /D I I -- f | 3CA.3~/ 3~/3 3CA....X5 3DHX2 /./.. 100 200 300 400 600 800 1000 2000 3000 Rupture Life - Hours Figure 1. Stress-rupture time relationship for Type 316 austenitic steel tested at 1200F in air and helium with no prior exposure,

Solid Points.ested n Air at I200"F, Open Points -Tested in Helium at 1200F. s.:,.~.....'-...-,:.:..:..::.:................:.:.:...:.......:~.:.............._~__,.. s:'' t: o' " ~:: t jy:' If F I 7777 —^^', /-/ - as 3.... I I I I G,. t -. 0.00 0.00 1.0 OCA A 32I~ t Miinsunn Creep Rate /o/ our igure r. Stress versus minum creep rate reationshiip for Type 316 amstenitic steel tested at 12f00F in air and hel um with no prior exposure

I I I I ~~~~~~~~~Band. of Proprtie s f orlil I"~~ ~ ~~~~~~~~~~~~~~ I I Unxoed aMater'-2,ia~~.i l!II 15 i 40 ~ XPSR I —"-~ ~L L~ ~~... ~~~ 1 -33 ~ ~ -. — 52 ^f I A Low Oz 4Na 7 A -^-. —- \l 6 0S I CHh-O02Na i- 1 1 1~ ~ II-h 0 HNeC-N, 3EHILI 49 1 /3EA L // f i~~~~~~~~~~~~~~~~~~~4 7 420 He", =' 6 3- "^16 —... iAi/ - I~~~~~~~~... I II i^',,^ /EH3 / l ~ —'"S.I?,NVIRONMENT l ll II I S ~i:A ) / fi I -Rutur Low Ozie,. - Hours I 48~1 / —/r —- 4-~ ll j I I 3- 000 H. im S1 111 i ~Uinexposed Material "I I ~ ~ ~~ ~~~~~~~~~~ Io / ll _ ~.,,lqz- /1 __:sP................ /-380-....:i~~~~~~~~~/i 1 1 ~483 - - -----— 481 /94 7 {^ 1 40l/ ^82 I I;C lo ~ // J -~~ ~ -V~ / 4 86 ^ / 9/ ~ ~' / ^ /7 8 K49 /1 / - -~/ /1 ^~ ~~ Dt / I - -r ^ / _ ________ i__ / —-' -''..... jR8489 490 506 482 ~ ~ ~ ~ ~ ~ ~ 6 48r 40 / / 6 i0001 0.01 0 0.4 Minimurnm Creep Rate - %/Hour Figure 3. Stress-rupture time and minimum creep rate relationships for Type 316 austenitic steel tested at 1200 0P In air and helium after exposure at 12000F for 4000 hours in various environments.

$ 1 1. -— ~:: z _ t A,. 30I I I I 2: P } Band of Properties for IU) 1' Unexposed Maaterial 0 {I I _jPre-exposed 4000 hours ~I; l L L /1 ~ | ~in Low-Oxygen Sodium 40i - _ _ 1. L-.... aU 2 0 ~ ----------- - ---- - -- - - -- - ----- — ~- ------ - - -4. \ _ ) I Solid Points - Tested in Air at iZ006F Open Points - Tested in a-Heliumn at 100 F Pre-exposed 4000 hours I I I in HFigh-Oxygen Sodium 40.. 30 ( 0 0 -- Pre-eposed 4000 hours in Hligh-Carbon Sodiun t30 (5......-. 3..,~~~~~I 1'Pre-exposed 4000 hours I~0~~~~~ ~|~~~ in Hin Sdeium60 80 100 200 300 400 600 800 1000 2000 3000 Ru.ptur ie ele Hours Figure 4. Stress -rupt:ure time relationshlips ior Type 316 austenitic steel tested a.'t i.Z^00 i.n a.ir a8nd he.lium after various exposlures 33

.140 r - -- - I I II r2 ~1ZCAX4 30 Specimnen.ZDAut broke I /CHX ZDHX 1 _ | _ _ gag mark, _ / / g e/ CAXa I CAX G - ----- ---------------- --- 1 1 0 / 7 ^151 { I// /^B"^^-Z I=A //I 0 i0^"""~"" --------— ~~~ —-~~~j —-- j>**zo 2*z.-,,tCAX2~.,. I.: 2DAX5 —---— _ —----— ^'~1-j 1100 200 300 400 600 800 1000 2000 3 74,. 15 Solid Points - Tested in Air at1 llOO0'. j Open Points - Tested in Helium at 10 lOO I $t O -I B_ f "QQ'2 1 7 1_ AX | X _ZAH _XI / ~~ I _ r> h'V"1 ____/ / ^~-<.&^.^^^.~^' 0. 00001 0.0001 0.001 Mininumr Creep Rate - %/ Hour Fig 5 Stress-pture 5time and minimum creep rate relationships for 2V4Cr-1Mo steel tested at 1100l F in air and helium with no prior exposure.

40 1 / ~~~~~~~Average Properte o 30 l-Unexposed Mat ria1 25 15 iIk /~ / 0 YPOSJR 2 EXP OSUR' E 30NVIRONMFNI 188 2 2 3 Solid PHigh- i,-Na 100 200 300 400 600 800 1000 20 30 TEST ~~~~~Ruptuire ILife - H-ours Solid P8ointks -Air 2E5 Open Points - H____elium_ _ 20...... ~~~~~~~344 ------ 258 55/I I [ 8~~~~~~~~~~~~~ Unexposed Materiai 223 88 6 (~~See Pig. 5) ____ 0. 001 0.01 0. 1 Min-Jimumn Creep Rate - To/Hou'r Figure 6. Stress-rupture time and minimum creep rate relationships for 2V40r- I Mo steel tested at 11000F in air and helium after exposure at 1 1000F for 4000 hours in various environments.

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