ORNL-TM-1997.txt

 

   

f""_-OAK RIDGE 'NATIONAL LABORATORY
e =" operated by - - DRI
,,.,_—:.f,;;_unmu CARBIDE CORPORATION - S
. NUCLEAR DIVISION .

 
  

' 'i‘ 15 S for the
U S f A'I'OMIC ENERGY COMMISSION B
| ’ ORNL m--1997

 

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AN EVALUAT[ON OF THE MOLTEN SALT REACTOR EXPERIMENT
o HASTELLOY N SURVEILLANCE SPECIMENS FIRST GROUP

H E MCCoy, Jr "

      

- “0"‘:5 Tl-us document “confains. mfofmcrtlon of o prehmmary nature - <. , B
- ond was prepared pnmnnly for internol use at the Ook Ridge Notional - R LT ¥
- Laboratory. It is subject to revision or- correchon ond thereforc does o ' T
s not represent a fmalreporL SRS el e e s , S 1

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- or controctor of the Commission, or omployo. of such contractor prepares, disseminates, or

 

LEGAL NOTICE

This report was prepored as an account of Government sponsored work. Neither the United States, o ' T

not the Commission, nor any person acting on behalf of the Commission: )

A. Mokes any warranty or representation, -xprcsud or implied, with rospoct to the accuracy, ST
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or his employment with such contractor, - ’ Lol

 

 

 

 

 

 

 

 

 

 

 

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:L V N' ‘:n

ORNL-TM-1997

~ Contract No. W-7405-eng-26

METALS AND CERAMICS DIVISION

 

G
¥
AN EVATUATION OF THE MOLTEN SALT REACTOR EXPERIMENT
HASTELIOY N SURVEILIANCE SPECIMENS — FIRST GROUP

7 ‘H. E. McCoy, Jr.
o LEGAL NOTICE
. i This report was prepared as an account of Government sponsored work. Neither the United
P‘?’:.: ;- Btates, nor the Commission, nor any person acting on behalf of the Commission: ’

=2

: A. Makes any warranty or representation, expresPod or implied, with respect to the accu-
; racy, completeness, or usefulness of the information contained in this report, or that the use
of any information, apparatus, method, or process disclosed in this report may not infrings
" privately owned rights;: or _ . ) )
B. Assumes any liabilities with respect to the ude of, or for damages resulting from the
" use of any information, apparatus, method, or process disclosed in this report. .
; As ussd in the sbove, “‘person acting on behalf of the Commissfon® includes any em-
i ployee or contractor of the Commission, or employée of such eontractor, to the extent that
. such empioyee or contractor of the Commission, ofl_ employee of such contractor prepares,
| disseminates, or provides access to, any latonmflol'; pursuant to his employment or contract
. with the Commission, or his employment with such contractor.

4]£: 

o

. NOVEMBER 1967

OAK RIDGE NATIONAL LABORATORY
Qak Ridge, Tennessee
. operated by
UNION CARBIDE CORPORATION

 

. . for the
gia : : b U.S. ATOMIC ENERGY COMMISSION

- t‘—\fl

fi?STRTB‘EMON\OF THIS DOCUMENT IS UNCIMITED,

 
 

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AbStract . o « « o 4 4 oo
Introduction . . . . . . .
Experimental Details . .

Surveillance'Assembly
Moterials . . . . .

Test Specimens . . . .

Irradiation Conditions .

Testing Techniques .
Test Results . . . . .

’

Discussion of Results . .
Summary and Conclusions

Acknowledgments . . . . .

iii

'CONTENTS

 

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AN EVALUATION OF THE MOLTEN SALT REACTOR EXPERIMENT
HASTELIOY N SURVEILIANCE SPECIMENS — FIRST GROUP

H. E. McCoy, Jr.

ABSTRACT

., We have tested the first group of surveillance specimens
from the Molten Salt Reactor Experiment core. They were
removed after 7823 Mwhr of reactor operation during which
the specimens were held at 645 * 10°C for 4800 hr and
accumulated & thermal dose of 1.3 X 102 neutrons/cm?.

The high-temperature ductility was reduced but the reduction
was similar to that observed for these materlals when -
irradiated in the Osk Ridge Reactor in a helium environment.
The low-temperature ductility was reduced, and this is

thought to be due to the formation of intergranular MgC.

The specimens showed no evidence of corrosion; however, a
carbon-rich layer, 1 to 2 mils in depth, was noted where

the Hastelloy N and graphite were in contact. The mechanical
properties of the Hastelloy N appear adequate for the

continued satisfactory operation of the MSRE.

Test results are presented for the effects of several
variebles on the tensile ductlllty of irradiated and
unirradiated Hastelloy N. These variables included test
temperature, strain rate, and prestraining..

 

| INTRODUCTION -'

The Molten Salt Reactor Experiment is a single reglon reactor that

- is fueled by a molten fluorlde salt (65 LiF, 29.1 BeF,, 5 ZrF4,

0.9 UF4 mole %), moderated by unclad grephlte, and contalned by Hastelloy N

"(N1—16 Mo~7 Cr—4 Fe—O 05 C, wt %) The details of the reactor design and

rconstructlon can be found elsewhere 1 We knew that the neutron envmronment

would produce some changes 1n the two structural materlals —-graphlte and

'l Hastelloy N. Although we were very confldent of the compatlblllty of these

.

 

1R. C Robertson, MSRE De51gn and Operations Report, Pt l Description
of Reactor De51gg, ORNL-TM-728 (January 1965).

 
 

materials with the fluoride salt, we needed to keep ébreast of the possible
development of corrosion prdblefis within the reactor itself. For thése
reasons;‘we developed a surveillance program that would allow us to follow
the property changes of graphite and Hastelloy N specimens as the reactor
operated. ) | . |

The reactor went critical on Jufie 1, 1965, and after numerous
small problems were solved, assumed normal operation on May 1966. The
present grbup of surveillance specimens was in the reactof from
September 8, 1965, to July 28, 1966, and was removed after 7823 Mwhr of
operation (designated "first grpup"). This report covers the tests that

were run on the Hastelloy N specimens that were removed.
EXPERIMENTAYL DETAIIS

Surveillance Assembly °

The core surveillancé assembly was designed by W. H. Cook and others,

and the details have been reported previously.2 The facility is shown

- pictorially and schematically in Fig. 1. The specimens are arranged in
three stringers. Each stringer is about 62 in. long and consists of two
Hastelloy N rods and a graphite section made up of various pieces that are
joined by pinning and tongue-and-groove Joints. The Hastelloy N rod has
periodic reduced sections 1 1/8 in. iong X 1/8 in. in diemeter and can be
cut into small tensile specimens after it is removed from the reactor.
Three stringers are joined together so that they can be separated in a hot
cell and reassembled with one or more new stringers for reinsertion into
the reactor. The assembléd stringers fit into a‘perforatedJHastellqy N
basket that is inserted into an axial position about 3.6 in. from the core
center line. |

-

 

2W. H. Cook, MSR Program Semiann. Progr. Rept. Aug. 31, 1965,
ORNL-3872, p. 87. , L .

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PHOTO 81674

 

GUIDE PIN
ASSEMBLY

SPACER AND
BASKET LOCK

      
 
 
 

- | ~ UPPER GUIDE
INOR-8 ROD OF TENSILE SPECIMENS-

 
  
   
 
  
 
  

' GRAPHITE (CGB) SPECIMENS
| ' BINDING STRAP=
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- VFLUX MONITORS TUBE

   
      
 
   
     

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CONTROL ROD
GUIDE TUBE
GUIDE BAR

  
    
    
    
 
   
  
 

 
 

 
 

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0.200-in. R
. | | 0400 in.
(6 ~ SURVEILLANCE SPECIMENS’

   
    

2in. TYPICAL
) L | | | () R=RemowaBLE STRINGER

Fig. 1. MSRE Surveillance Fixture.

 

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When the basket was remofed on July 28, 1966, some of the specimens
were bent and the entire assembly had to be replaced. 3 Sllght modlflcatlons
in the design were made, and the assembly was removed recently and found
to be in excellent condltlon.4 ,

A coqtrol facility is associated with the surveillance program. It
utilizes a "Puel salt" containing depleted uranium in a static pot that is
heated eiectriéally. The temperatflre is controlled by the MSRE computer so
that the‘temperature matches that of the reactor. Thus, these specimens
are eprsed to conditions the same as thbse in the féagtor except for the
static selt and the sbsence of a neutron flux. | | |

There is another surveillance facility for Hastelloy N located outside
the core in a vertical position about 4.5 in. from the vessel These
- specimens are exposed to the cell env1ronment (N + 2-5% 02) . They,were

not removed durlng ‘the flrst group.

. Materials

Two heats of Hastelloy N were fised in this program: heats 5081 and
5085. Both of these heats were air-melted by Stellite Division of fihion
Carbide Corporation, and their chemical analyses are given in Table 1.
Heat 5085 was used for making the cylindrical portion of the core vessel,

and heat 5081 was used for various parts inside the reactor.

Test Specimens

The specimens were put into the reactor as rods 62 in. long by
1/4 in. in diameter with reduced sections 1/8 in. in diameter by
1 1/8 in. long. The long rod was made in sevefi pieces and welded together
to obtain the 62-in.-long rod. After removal from the reactor, the rod \
was sawed into small specimens with a gage section 1 1/8 in. long by
1/8 in. in diemeter. Each rod is designated by a letter and the individual

 

3. H. Cook, MSR Program Semiann. Progr. Rept. Aug. 31, 1966,
ORNL-4037, p. 97.

“W. H. Cook, "Molten Salt Reactor Program," Metals and Ceramics Div.
Ann. Progr. Rept. June 30, 1967, 0RNIr4l7O Chap. 34 (in press).

 
 

 

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Table 1. Chemical Analysis of Surveillance Heats
Content, wt %
Element - ' - :
Heat 5085 Heat 5081

Cr 6.2 | 6.1
Fe 3.3 3.4
Mo 16.3 | 16.4
c 0.054 | 0.059
Si - 0.58 7 0.52
Co 0.15 | 0.10
W 0.07 o 0.07
Mn 0.67 0.65
v 0.20 | 0.20
P 0.013 © 0.012
S 0.004 0,002
Al 0.02 - 0.05
T4 <0.01 | <0.01
Cu 0.0 . 0.01
B ~ 0.0038 | ~ 0.0050

bal . bal

 

 
 

 

 

6

specimens are numbered beginning at the bottom of the rod and ihcreasing
to 27 at the top. ' | | ‘

The rods in the first group were bent, and it was necessary to examine
.each specimen with an optical comparator to determine whether it was
suitable ‘Por use. If the total indicated runout of the gage section was
greater than 0.002 in., the spécifien'was not used. The best specimens
fiere'fised for the higher temfierature tests where the_expected strains were
smallest. The results from a brittle material are affected more seriofisly
by specimen alignment-than are those from a ductile material.

The materials were received in the mill annealed condition (1 hr at
1177°C). They were giveh a further anneal of 2 hr at 900°C prior to |

insertion into the reactor and the control facility.

Trradiation Conditions

The épecimens from the first group were in the reactor from
Septenber 8, 1965, to July 28, 1966.; The réactor had operated 0.0066 Mwhr
when the specimens were inserted and 7823 Mwhr when they were removed.
They were at temperature for 4800 hr with the temperature range being
645 * 10°C. However, the material was only exfiosed to salt for 2796 hr,
The flux was measured by H. B. Piper’® using stainless steel wires that
were attached to the surveillance specimens. The thermal and fast £lux
profiles are shown in Figs. 2 and 3 along with the axial location of each
specimen. The peak thermal dose, based on the 5900(n,7)6°Co transmtation,
was 1.3 X 1020 neutrons/cm® and the fast dose (>1.22 Mev), based on the
58Ni(n,p)5800 transmutation, was 3 X 101° néutrons/cmz. The croSs-sectionr
used for the 5°Co(n,7)8°Co transmutation was 22.25 barns, and that for

the 78Ni(n,p)38Co transmutation was 0.1262 barns.

 

SH. B. Piper, private commnication.

 

 
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ORNL—DWG 67-7932"

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Speclmens - First Group.

 

 

 

ORNL-DWG 67-7933

 

(x10'3)

MTL
& Fe

 

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- 0.4

02

Fig. 3.
F_irst Group.

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r - A 1 i 1 1
NEUTRON
- ENERGY _REACTION

>2.02 MeV  %¥Fe(n, p)%%mn
> 1.22 MeV  38Ni(n, p)%8Co
>2.02 MeV  3¥Fe(n, p)%Mn

EXPOSURE - 7823 MW-hr

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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2 3 4 5 6 7 B -9 10 1t 42 13 14 15 16 17 18 19 20 21 22 23 24 28 26 27
| | | " | LOCATION OF SURVEILLANCE SPECIMENS | | | j
0 4 8 12 20 24 28 32 36 40 44 48 B2 56 60

Measurements of the Fast Flux for the MSRE Core Specimens —

inches

’

(x10'3) T T T 1 T 1
NEUTRON R
6 . MTL_ENERGY . REACTION
AFe <0876 v °Feln,)°Fe
©SS <0.876 eV 5900(n7)6°Co -
5 G SS <0876 ev- Fe(n.r) Fe
7 8 i EXPOSURE — 7823 MW —hr
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g 3 s u- H 0 & ®
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= B
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' 1 2 3 4.5 6 7 8 8 10 1 12 43 14 5 16 {7 18 19 20 21 22 23 24 25 26 27
’; ooHHHMHH HH H R R R R O
| | | | LOCATION OF SURVEILLANCE SPECIMENS | | |
0 1 i i 1 1 I 1 L
0 4 8 12 16 20 24 28 32 36 40 44 48 52 56 60
. inches
Fig. 2. Measurements of the Thermal Flux for the MSRE Core

 
 

“Testing Techniques

~The laboratory_creep-rupture tests were run in conventional creep
machines of the dead load and lever arm types. The strain was measured by
a dial indicator that showed fhe total movement of the specimen and part
of the load traifl. The zero strain measurement was taken immediate1y after
the loéa was applied. The temperature accuracy was 0.75%, the guaranteed
accuracy of the Chromel-P-Alumel fhermocouples used.

The postirradiation creep-rupture tests were run in lever arm>ma¢hiqes
that were located in hot cells. The strain was measured by an extensometer
with rqu attached to the upper and lower specimen grips. The relative

movement of these two fods was measured by a linear differential trans-

- former, and the transformer signal was recorded. The accuracy of the strain

measurements is difficult to determine. The extefisogeter'(mechaniCal and
electrical portions) produced.meaSurements that could be read to about
+0.02% strain; however, other factors (temperature changes in-the.cell,
mechanical vibrations, etc.) probably combined‘to give an overall accuracy
of $0,1% strain. This is considerably better than the specimen-to-specimen
reproducibility that one would expect for relatively brittle materials.
The temperature measuring and control system was the same as fihat u§ed in -
the laboratory with;only one exception. In the laboratory, the control
system was stabilized at the desired temperature by use of a recbrder with
an expanded scale. In the tests in the hot cells, the control point was
established by setting the controller without the aid of the expanded-scale
recorder. This efror and the thermocouple accuracy combine to give a
temperature uncertainty of about +1%, | |

The tensile tests were run on Instroanniversal TESting Machines. The
strain méasurements were taken from the crosshead travel.

The test environment was air in all cases. Métallographic examinétion
showed that the depth of oxidation was small (<0.002 in.), and hence we
feel that the envifonment did not appreciably influence the test results.

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. temperature are shown in Fig. 4 for strain rates of 0.05 and 0.002 min~l.

 

Test Results

Slnce the - survelllance assembly was -bent, it was necessary to remove
all the spec1mens in the flrst group, and we had about 50 specimens of
each heat after the bent ones were dlscarded Thus, we had enough specimens
to run the desired tests for surveillance purposes and enough to lock at
some further varisbles that are of value in understanding'the behavior of -
irradiated HasteliOy N. We shall present-all the results that were obtained
even though much of this 1nformat10n has 11ttle direct bearing on the safe
operation of the MSRE Slnce the rupture ductility is of prlmary impor-
tance, we shall be most concerned with this property

‘The results of tensile tests on the control specimens of heat 5081
are given in Table 2. The total elongations at fracture as a function of

-1

This material exhibits therdUCtility minirum that is characteristic of
nickel-base alloys. The temperature of the minimum ductility seems to
decrease.withvdecreasing strain rate, Several of the specimens were run
at various strain rates over the range of 2 to 0.002 min~%. The results
of these tests are also given in Table 2, and the fracture elongations are
given in Fig. 5. The fracture elongation is very sen51t1ve to strain rate
at 650°C, but relatlvely insensitive at hlgher and lower temperatures

The results of the tests on the survelllance spec1mens from heat 5081
are summarized in Table 3,  The elongation at fracture is plotted as a
function of tempersture in Fig. 6. The irradiated material is characterized
by a sharp drop in ductility_with'increasinghtemperatureabove about_500°C:

The ductility continues to decrease with increasing temperature rather than

jexhlbltlng a. ductlllty mlnlmum like the unirradiated material (Fig. 4).

The ductility is lower at a straln rate of 0.002 min~l than at 0.05 min~ %,

but the dlfference decreases w1th 1ncrea31ng temperature This point is

_ demonstrated qulte well 1n Flg 7 where the dependence of the ductlllty on -

strain rate is shown for several temperatures

We have lodked 1nd1v1dually at the propertles of the survelllance and

- control speclmens of heat 5081 let us now compare these propertles The

ratlos of the property for the 1rrad1ated materlal to that of the

unlrradlated material are compared in Flg 8 as a functlon of temperature.

 
)

‘Teble 2. Results of Tensile Tests on MSRE Surveillance Control Specimens

 

 

 

 

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Al

Heat 5081
Specimen Test Strain Stress (psi) Elongation gfi) 'Reduction True Fracture
Number Temperature Rate Tield Ultimate Uniform  Total in Area Strain
(°c) (min=1) (%) (%)

AC~8 25 0.05 47,700 118,700 55,9  57.6 48.8 67.4
AC-11 200 0.05 40, 200 ¥07,100 53.3 54,6 42,0 58.9
0e-27 400 2 41,400 94,500 50.4  53.6 42,4 55,7
CC=25 400 0.2 36,300 97,900 52,2 53.8 42."7 56.0
AC-22 400 0.05 36,700 100,600 51.0. 52.0 48,7 66.8
- CC-24 400 . 0.02 37,800 99,900 51,7 56.0 41.7 54.4
CC-23 400 0.005 34,700 97,400 55.4 56.3 44,0 '58.6
BC-8 400 0.002 37,100 ' 52.9 55,2 46,7 63.0
CC-21 500 2 36,200 93,200 52.0 56.0 48,8 67.4
CC-19 500 2 35,200 92,700 52.4 56.0 42,6 55.8
CC-29 500 0.5 52,600 105,400 45,8 49.4 40.5 52.0

- CC=-17 500 0.02 34,900 97,600 55.5 56.6 46.2 62.5
CC-16 500 0.005 34,700 92,500 54.4 55,4 - - 40.3 51.6
AC=24 500 0.002 35,000 97,700 44,9 45,3 33.6 41.0
BC-9 500 0.002 36,200 95,300 - 46,2 - 47.0 - 38.1 48.2
AC-20 550 0.05 . 35,900 93,300 49.7  51.1 . 40.3 51.8
AC-25 550 0.002 37,300 80,300 22.8 23.7 23.0 26,2
AC-18 600 0.05 34,900 81,200 - 31.8 32.3 31.0 37.2
AC-29 600 0.002 37,400 71,400 21.2 21.7 19.9 22.4

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' Table 2 (continued)

 

Specimen - Test -+~ Btraln’ Stress (psi) | Elongation'gfil Reduction True Fracture.

 

 

Number Temperature = Rate YIeId  Ultimate Uniform Total in Area Strain-

@ (mal - (%) %)
BC-10 650 -2 36,300 88, 500 51.5 52.4 - 36.9 46,3
cc-8 - 650 C 2. 42,400 85,200 bbb 46.8 37.2 46.5
AC-4 . 650 0.5 32,900 81,500 - 37.1 39.0 28.8 34.0
AC-10 | 650 0.2 36,300 78,200 28.5 29.3 - 23.4 26.4
CAC-27 . 650 - 0.05 32,400 68,400 23.8 24 .6 - 23.1 26.2
CAC-7 850 . 0.02 34,400 65,200 6.8  17.7 19.0 211

AC-5 650 0,005 33,900 68,400 22.6 23.1 4.4 28.0
AC-17 T 650 0.002 33,600 66,700 22.8  23.2 21.6 21.4
Ac-28. 700 0.05 39,500 68,400 18.8 19.8 ©25.8 14,9
AC-16 . 700 - 0.002 32,400 63,100 20.0 29.3 3.5 21.7

cc-2- | 760 2 41,600 76,600 - 36.8 - 40.8 4.4 28.0"
cCc-9 - 760 0.5 30, 800 72,700 37.1 40.2 30.7 36.9
- CC-5 - 760 0.2 32,100 71,900 33.3 38,9 21.9 4.7
AC-12 _ - 760 0.05 29,900 64,500 25.1 41.6 35.0 43,1
CC-4 760 -0.02 . 32,400 63, 800 20.0 . 43.8 42.4 .55.3
cc-3 760 0.005 32,700 54,500 12.7 39.2 41.0 52.9
AC-14 760 - 0,002 32,600 47,200 9.4 . 39.5 42,7 56.0
cc-15 850 2 33,200 66,300 30.0  48.0 46.3 62.5
CcC-14 850 0.5 . 28,900 60,600 23.2 49,2 43.9 58.2
cc-12 - 850 0.2 29,600 54,100 16.3 51.4 - 50.8 71.1
- AC-6 . 850 0.05 28,300 43,400 11.2 53.2 49.8 69.0
CC-11 - 850 0.02 30,000 40,400 7.8 43.6 48.7 67.0
CcCc-10 850 0.005 29,200 30,600 2.0 btv, b 50.9 71.6
AC-15 850 0.002 26,400 26,400 ‘1.5 45,0 43.9 58.3

 

 

 

 

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TEST TEMPERATURE, °C

Fig. 4. Tensile Ductilities of MSRE Surveillance Control Specimens,
Heat 5081. ' |

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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STRAIN RATE, MiN~!

Fig. 5. Influence of Strain Rate on the Ductlllty of MSRE
Surveillance Control Spec1mens , Heat 5081

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) -'j_Téble 3. Resul‘cs of Tensile Tests on MSRE Surveillance Specimens
: Heat 5081 '
'Specinien Test Strain Stress (psi) Elongation Reduction True Fracture

Number Temperature Rate -~ eld - Ultimate Uniform  Total in Area Strain
(°c) (min~1) (%) (%)

D-16 25 0.05 51,100 105;500 38.5  38.7 31.3 37.0
D-19 .25 0.05 54,100 109,000 42.6 42.6. 25.9 30.0
D15 200 0.05 42,700 99,600 49.0  49.4 33.3 40.7
F-2 400 2 41,200 91,400 49.2  51.6 34,4 42.0
F-1 . 400 0.5 43,700 88,300 33.2 33.9 32,5 39.5
E-15 400 0.5 39,900 93,800 48.3 49.1 33.9 41.5
F-7 400 0.2 38,300 92,200 49.4  51.0 37.2 46,9
D-24 400 0.05 37,100 94,100 49.3 50,9 33.3 40.7
Fu23 400 0.02 37,800 - 91,700 45.8 46.1 36.0 44,7
 F-10 400 0.005 38,806 93,300 49.9 50. 4 37.7 47.7
 F-19 400 - 0.002 39,100 92,500 47,1 477 32.3 38.9
(F-5 450 0.002 38,200 86,900 37.8  38.6 25.8 30.1
F-8 500 2 44,000 85,600 b 46.0 31.6 - 38.2
F-20 500 0.5 36,400 87,000 43.1 441 36.2 45,2
E-6 500 0.2 37,300 86,500 47.8 48,5 32.1 38.7
 D-9 500 0.05 38,600 90,200 50.6 51.0 31.9 38.7
 E-25 500 0.02 36,600 83,600 37.0  37.5 30.2 35.8
E-12 500 10.005 38,000 76,800 23.3  24.1 24,2 27.8
F-13 500 1 0.002" 38,800 75,800 2.4 23,1 21.9 24..9

. B9 500 10.002 38,000 84,800 31.0  32.1 29.8 35.4
D-25 550 0.05 135,400 77,800 3.6  32.1  26.1 30.3
F-27 550 0.002 42,200 62,700 11.8  13.8 3.34 6.5
E-23 600 0.05 35,200 74,800 25.6  26.4 31.8 38.2
E-24 600 0.002 36,100 62,100 15.0  15.8 16,7 18.3

 

£T

 
 

Table 3 (continued)

 

Specimen Test Strein Stress (psi) - Elongation (%) Reduction True Fracture

 

 

Number Temperature Rate Yield Ultimate Uniform  Total in Area Strain
| (°0) (min=1) | | () | (%)

7-18 650 2 36,700 61,100 20.8 24,0 21.8 - 24,4 .
F=-6 650 0.5 33,400 63,900 18,2 18.9 15.4 16.9
F=26 650 0.5 30,500 34,900 2.6 3.7 2.9 2l.5
F-3 650 0.5 34,300 75,600 34.0 35.3 29.1 58.4
E-3 650 0.2 37,200 64, 200 14.9 15.8 ! 22.5 25.4
B-7 - o 650 0.05 34,600 57,200 13.8 14.3 13,9 14.8
E-13 650 0.02 33,800 53,600 1.1 12.9 17.6 19.1
E-19 650 0.005 34,600 53,000 10.8  11.3 14.6 15.9
BE-14 | 650 0,002 34,400 48,400 8.2 9.0 11,6 12.2
E-22 700 0.05 31,700 53,900 13.8 14.2 12.9 . 13.9
E-2 700 0.002 33,800 44,000 4.8 5.5 6.7 6.9
=22 760 2 36,100 57,600 18.8 22.0 14.7 15.9
D-8 760 0.5 31,000 49,100 12.0 12.9 11.0 11,5
D-13 760 0.2 31,300 49,400 11.9 12.4 - 10.2 10.5
E-8 760 0.05 31,400 43,200 6.7 7.4 6.2 6.1
D-10 760 0.02 32,000 42,200 5.2 5.7 4.6 4.6
D-27 760 0.005 . 36,500 40,600 4,0 4.3 2.6 2.6
E-20 760 0.002 32,100 36,700 1.9 3.9 3.5 3.6
. E~4 _ 850 2 4. 8.4 8.7 9.0
E-27 -850 0.5 32,700 39,100 3.5 4.6 5.4 5.5
E-1 , 850 0.2 33,600 38,600 3.0 . 3.8 1.6 0.8
Fa17" 850 0.05 30,700 32,400 1.8 2.3 2.3 2.4
D-14 - 850 0.02 30,600 30,700 - 1.2 2.0 . 1.7 0.9
D-23 850 0.005 20,200 20,200 0.7 2.0 0.3 0.2
E-21 850 0.002 21,800 21, 800 0.7 2.1 0.7  0.3

 

71

 

 
 

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15
€0 , ORNL-DW'!G 67-2447
i ¢ €x.05mN™!
0 €=,002 MIN!
30
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£ AN -
- N \
L N
o 7‘\ e 9 : .
10 N A
. N _
: o .-..g___h;
0 ' . 1 1 0y 11 1 i
o 100 200 300 400 500 600 700 800 500
- - TEST TEWP, °C : |
Fig. 6. Tensile Ductility of MSRE Surveillance Specimens, Heat 5081.
ORNL-DWG 67-3961R
) |
—o—400°C
50 \ 0 o ‘]’—f f
A | |
g 40 7
0 ] T
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5 | ] |~ 760
k20 : - - ' ; =TT 7"
'o -L-—'-—"‘”’_Jf_"— ! "', - "7 . .
' | o ,‘if"f ‘Jk —%fl |_—Y850°C
- 0001 ,.001__ o | o 0
e o - STRAIN RATE (min~ ) o
Fig. 7. Influence of Straln Rate on the Ductlllty of Hastelloy N

(Heat 5081) — MSRE Surveillance Specn.mens.

 

 
 

16

ORNL-DWG 67-2458A

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

12
1.0 =2 { — . . . .
~ -1 A
T 4T~
2lE o8 zZ & ‘\,
wl 77 \ ~— A
§ g 7 \ N ————
a z ~ u \\ ‘
BiE o .
1i\5 N
g3 e YIELD STRESS | \
EZ o4 4 ULTIMATE STRESS - N
= & TOTAL ELONGATION \
‘ é=0.05 min ! ' \
N
_ S
0 : s
0 100 200 300 400 500 . 600 700 80O 900 4000

. TEST TEMPERATURE (°C)

- Fig. 8. Comparative Tensile Properties of Irradiated and Unirradiated
MSRE Surveillance Specimens, Heat 5081. : |

The yield stress is unaffected by irradiation. The ultimate stress is
reduced approximately 8% up to about 600°C where the rédfiction becomes
greater with increasing temperaturé.

The total elongation at fracture for the irradisted material is lower
by about 30% at room temperature, but recovers to be almost equivalent at
400°C, As the temperature is increased sbove 400°C, the ductility of the -
irradiated materiai-drqps to where it is only about 4% of thatAof_the
unirradiated specimens. The strain rate versus temperature data are
‘treated in a similar way in Fig. 9. At 400°C the surveillance and control
specimens have about the same ductility with only a slight decrease in the
ratio with decreasing strain rate. - At 500°C there is a Sharp drop in the

ratio at a strain rate of about 0.05 min~?!.

This sharp change in stréin
rate sensitivity is probably due to the transition from transgranular to
intergranular fracture. The rati@ is a bit confusing at 650°C; its rise
vith‘decreasing strain rate is due to the fact that the‘ducfility of the
.control specimens decreases more rapidly with decreasing étrain rate than
~ that of the surveillance specimens. At 760 and 850°C the ratio becomes

quite small and its dependence on strain rate becomes ;eés.'

-

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) TOTAL ELONGATION

 

17

ORNL-DWG 67-24
TEST TEMP.
© 400 °c () 760 °C

A 500 "c v 850 °C
B 650 *C

 

IRRADIATED
UNIRRADIATED
s

—

00! oo S A ' { 10
' STRAIN RATE, MIN.™! ’

Fig. 9. Comparatlve Ductilltles of MSRE Surveillance Specimens as a
Function of Straln Rate, Heat 5081 :

The results of the teh'sile tests .on the control speoimens of heat 5085
are given in Table 4. The total elongation at fracture is plotted in
Fig. 10 as a. ffinction of the test te@erature. The characteristic ductility
minimum is obtained, but the temperature of the minimm ductility does not
appear to be rsensitive to strain rate. '

The results of the ten51le tests on the survell_'l.ance specimens from

heat 5085 are given in Table 5. The ‘f'racture elongation is plotted as &

functlon of test temperature in Flg. 11. The ductlllty drops prec1p1tously
above 500°C with the elongatlon belng lower at the lower strain rate '

The ratio of the irradiated property to that of the unirradiated

'property for heat 5085 is shown 1n Fig. 12 as a functlon of temperature.

The yield and ultimate stresses of this heat are :mfluenced about the same

by irradiation as those pf heat 5081 (Fig. 8). 'The elongatlon at low

', temperatures is not reduced as much by 1rrad1at10n, but :Lt does not recover

- as the test temperature is’ :mcreased

 
Table 4. Results of Tensile Tests on MSRE Surveillance Control Specimens

 

 

 

 

Heat 5085
Specimen Test Strain Stress (psi) . "~ Elongation (%) Reduction True Fracture

Number Temperature Rate Yield Ultimate Uniform Total in Ares Strain
(°c) (min=3) | - (%) (%)
DC=-24 25 0.05 46,200 109,200 40.0 40.0 28.61 33,8
FC=3 ' 25 0.05 45,500 111,200 46,8 46,8 31.45 39.5
DC-20 200 0.05 39,100 105,200 48.6 49.8 36.69 46.1
DC=-23 400 0.05 34, 800 95, 800 47,6 48.8 39.01 - 49,6
DC-19 500 0.05 33,600 94,300 48.8 49,3 41.48 54.1
DC0-26 500 0.002 33,400 = 91,700 43.3 44,3 37.78 47.7
DC-18 , 550 0.05 33,700 89, 200 47.0 47.5 35.19 43,4
DC=-13 550 0.002 32,500 74,000 26,5 _7.5 26.1 30.2
FC=2 550 0,002 33,600 77,900  30.3 31.0 33,98 41.6
DC-17 600 0.05 32,200 78,300 33.8 - 34.6 32.60 37.8

DC-16 600 0.002 32,100 69,600 . 26.5 27.3 25.55 _ 29.6 -
- DC=-14 650 0.05 31,800 70,100 25,8 26.8 29,97 35.9
DC-25 650 0.002 31,500 62,500 22.8 24.3 27.15 31.8
DC=-5 700 0.05 29,200 64,000 28.4 29.5 28.14 33.2
DC-10 700 : 0.002 30,900 62,100 22.3 28.3 24.04 27.5
- DC=-3 - 760 0.05 28,100 60, 800 27.0 33.0 32.16 38.7
DC-9 760 0.002 . 28,900 51,500 11.0 35.1 - 36.07 44,8
DC-22 850 -0.G5 25,700 " 45,100 11.5 38.8 47.23 64.1
1.4 39.2 43,76 55,7

DC-8 - 850" - 0.002 27,900 28,400

 

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ORNL-DWG 67-2444

 

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- 100

- Fig, 10.

200 300

400

300

600

TEST TEMP, °C

700

800

200

Tensile Ductilities of MSRE Surveillance Control Specimens, Heat 5085,

 

 

1000

 
 

 

-

Table 5. ‘Results-bf Tensile Tests on MSRE Survelllance Specimens

 

 

 

 

Heat 5085
Specimen Test Strain Stress (psi) Elongstion (%) Reduction  True Fracture
fifi;b ° Temperature  Rate . . in Area Strain
er (°c) (min"1)  Yield Ultimate  Uniform Total (%) (%) -
c-27 25 2 62,300 101,500 25,6 28.4 17.1 19.0
A-25 25 0.5 50,200 95,600 26.7 27.3 19.7 22,0
A-16 25 0,05 48,100 100,300 34,3 . 34.5 1 26.0 30.1
A-15 200 0.05 39,500 94,100 37.8 38.6 28.2 33,3
A-26 400 0.05 35,700 87,300 35.0 36.0 = 26.3 30.6
A-9 500 0.05 34,900 87,900 42.2 42.8 - 33.9 40,0
B-23 500 0,002 34,000 171,600 21.9 23.1 27.9 32.6
B-1 550 0.05 42,000 174,000 19.6 ~ 20.0 18.7 1 20.9
B-5 550 0.002 33,700 55,100 10.4. 12.7 14.7 15.9
B-26 600 0.05 32,500 62,000 18.2 19.6 21,7 24.5
B-4 600 - 0.002 32,300 52,000 11.1 12.0 12.5 13.5
B-19 650 0.05 32,000 52,800 12.6 13.7 13.9 15.0
B-6 650 0.002 32,100 42,900 6.5 9.4 7.9 8.1
c-20" 700 0.05 29,900 43,600 9.3  12.3 5.6 9.4
c-1 700 0,002 37,800 43,100 2.4 2.8 5.9 5.9
B-2 760 0.05 28,900 41,100 8.0 8.5 10.0 10.5
c-21 760 0.002 28,010 33,700 2.4 3.5 2.3 . 2.0
B-20 850 0.05 27,900 . 31,400 2.5 3.8 0.65 0.20
c-8 850 0.002 20,600 20,600 0.8 1.8 1.3 0.60

 

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o 1 1 1 I : { 1 1 1 -"?-— 1
o 100 200 - 300 400 500 €00 700 800 900 1000
: TEST TEMP, °C .

Fig. 11. Tensile Ductilities of MSRE Surveillance Specimens, Heat 5085.

ORNL-OWG 67-2459A

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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O ~ 400 200 300 400 500 600 700 800 900
TEST TEMPERATURE (°C)

Fig., 12. Comparatlve Tens:l,le Propertles of Irradlated. and
Unlrradlated MSRE . Survelllance Specimens, Heat 5085.

1000

 
22

The elongations at failure for the two heats of material are compared

in Figs. 13 and 14. At a strain rate of 0.05 min~* (Fig. 13) there are
several minor variations in the ductilities of the control specimené. The
main difference is that the ductility of heat 5085 is consistently lower
up to about 500°C. Both heats of the surveillance specimens -exhibit a

-reduction in ductility at a test temperature'of-25°C; howe#er, the

reduction is greater for heat 5085, The duectility of heat 5081 recovers
some with increasing test temperature, but heat 5085 maintains its reduced
ductility. Above about 500°C the ductility of the controls drops rapidly,
but the ducfility of the irradiated surveillance specimenS'decreases more.
rapidly. Both heats have very similar ductilities at températures;above
600°C. - The ductilities of the two heatS'afi a strain rate of 0,002 min~t
are compared in Fig. 14. The control specimens of both heats éxhibited

very similar ductilities, the characteristic ductility minimum being

exhibited. The irradiated surveillance specimens have much lower

ductilities, but the values are very similar for the two heats.

ORNL-DWG 67-2452

 

T0
CONTROL IRRADIATED
. A  © 808l
A ® 5085
€0 €= .05 MIN"!

 

 

 

 

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0 i i 4 ! 1 1 1 1 1 1

0 . IOO 200 300 400 $00 €00 700 800 900 1000

TEST TEMP, “C

 

 

 

 

 

 

 

 

 

 

 

 

Fig. 13. Comparatlve Tensile Ductilities of MSRE Survelllance
Specimens and Their Controls at a Strain Rate of 0,05 min~?1,

§!

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23

ORNL-DWG 67-2453A

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

60
50 ———
5. ._ ,/
8 | | al
g CONTROL IRRADIATED
§3° —— a o 508t
w 4 e 5085
- . L -
'<_( 20 é = 0.002 min
o
'—
10
0..______0__.
0O 100 200 300 400 500 600 700 800 900 1000

TEST TEMPERATURE {°C)

| Flg 14 Comparatlve Ten81le Ductilities of MSRE Surveillance
Specimens and The1r Controls at a Strain Rate of O. 002 min~ Y,

We took a brief look at how the tensile properties of the material
varied as a function of heat treatment in the finirradiated state. The
propertles of heat 5081 in several metallurglcal conditions are given in
Table 6. The anneal for 2 hr at 900°C generally decreased the strength
and 1ncreased the rupture. straln over that of the as-received materlal

One exception to this behavlor is an ;nerease in ultimate stress at 650°C

~due to the 2 hr anneal at 900°C. The exposure to molten salt at 650°C

 for 4800 hr caused a decrease in the ductility and slight variations in

the strength. The tensile properties of heat 5085 in the unirradiated

eondition'arergiven in T&ble77.s The properties of;this,heat are not

. significantly different'in the'asereceived condition and after annealing
-2 hr at 900°C. The exposure to ‘molten salt at 650°C caused a general
‘ 'decrease of 10 to 20% in the rupture ductlllty, but the strength was not
- affected s1gn1flcantky

The postlrradlatlon tens1le propertles of several heats of MSRE
material are compared_1n Tsble 8. The first two sets ‘of data for

heat 5065 show that the postirradiation properties were hot affected by

 
 

 

 

Table 6, Tensile Properties of Uhirradiated Hastelloy N
Heat 5081

 

. Specimen Test Strain Stress (psi) .~ Elongation (%) Reduction

 

Number Temperature Rate YIeld  ULtimate DaiTorm Total in Area
| (°c) (min~1) | ' (%)
. As-recelved ' |
5006 25 - 0.05 77,400 130,600 44,9 46,9 48,0
- 5005 500 ' 0.05 38,200 103,300 53.3 55.3 34,0
5004 500 0.002 40,000 103,200 51.2 - 52.6 - 41.5
5008 650 0.05 - 39,100 73,400 18.0 19.8 - 19.1
5007 650 0.002 38,200 65,100 14.4 15,2 15.8
' Annealed 2 hr at 900°C
- 4300 25 | 0.05 - 52,600 125,300 - 56.7 59.5 @ . 50.5
4303 ' 500 0.05 32,000 100,300 57.8 60.7 by 4
4301 650 - 0.05 32,200 81,800 31.7  33.9 29.9
4302 650 | 0.002 32,900 74,900 29.0 29.5 31.8
| " Annealed 2 hr at 900°C plus 4800 hr in MSRE salt at 650°C '

AC-8 25 z 0.05 - 47,700 118,700 55.9  57.6 48.8
AC-19 500 0.05 35,800 97,800 53.6 . 56.6 ) 46,2
BC-9 500 - 0.002 36,200 95,300 46.2 47.0 " 38.1
21.6

7e

 

 

AC-17 . 650 | 0.002 . 33,600 66,700 22.8. 23.2

 
 

 

,Table 7. Ten81le Properties of Uhirradiated Hastelloy N

 

 

 

 

Heat 5085
Specimen - Test : Strain Stress (psi) Elongation (%) . Reduction
Number ~  Temperature Rate Yield Ultimate = UnliTorm  Total in Ares
(°c) (min™?) | - G
o L | Asépeceived | |
7% 25 0.05 52,200 116,400 51.3 52,5 56.3
77 427 0,05 30,700 102,900 57.6 - 59.4 49.9
284 600 0,02 32,200 85,100  46.6 = 47.6 40,4
78 650 . . 0.05 28,700  €0,700 - 35.5  36.7 33.2
285 650 - 0.02 31,900 65,000 . 25.8  31.8 27.2
283 650° 10.002 30,500 64,300 - . 22.6 - 24.1 28.8
79 - 760 ©0.05 32,100 - 61,500 24.7 27.0 31.9
80 . 871 - 0.05- 30,700 42,300 2.0 31.8 33.4
81 . 982 0.05 23,100 23,100 1.8 40.2 43.9
- ' o _ 1  | Annesled 2 hr at 900°C
4295 : 25 0.05 51,500 120,800 = 52.3 53.1 42,2
4298 “ 500 0.05 32,600 94, 800 - 51.2 54.1 40,9
4299 A 500' 0,002 33,500 100,200 52.0 . 53.3 41.7
4296 - 650 0.05 29,600 75, 800 31.7 33.7 34,6
e Annealed 2 hr at 900°C plus 4800 hr in MSRE salt at 650°C
FC-3 - 25 0.05 45,5000 111,200 46,8 46,8 3L.5
DC-19 500 - 0.05 33,600 94 300 48.8 49,3 4.5
DC-26 S 500 - 0.002 33,400 91,700 43.3 44,3 37.8
DC-14 - 650 " 0.05 31,800 70,100 25,8  26.8 30.0
24,3 27.2

DC-25 650 10.002 31,500 62,500 22.8

 

 

 

A

) "

 
Table 8, Postirradiation Tensile Prc:aper'ciesataL of Several Heats of MSRE Hastelloy N

 

 

 

Specimen ' Heat Irradiation Thermal Test Strain Btresa (psi) Elongation ;fié Reduction
Rumber Number = Roron Level Temperature Tose Temperature Rate TeId UltImete Uniform Tot in Area
' (rpm) (*c) (neutrons/cn?) (°c) (min-1) (%)
x 1020
4 Experiment ORR-149
5702 5065 20 43 8.5 25 0.05 102,900 135,100 31.5 35.5 52.0
‘ 57lb 5065 20 43 8.5 200 0.05 82,300 119,600 36.1 39,2 54.8
572b 5065 20 43 8.5 650 0.05 44,600 76,900 26.3 27.3 24,5 ,
574b 5065 20 43 8.5 650 0.002 ,800 57,400 12.2 13,1 21.9
573, 5065 20 43 8.5 871 - 0.05 33,500 36,400 1.7 1.8 3.25
575c 5065 20 43 8.5 8N 0.002 23,200 23,400 0.9 1.8 6.07
531c 5065 20 43 8.5 25 0.05 101,500 132,200 30.0 - 33.6 55,2
582c 5065 20 43 8.5 200 0.05 78,600 118,300 7.3 39.8 45.9
583c 5065 20 43 8.5 650 0.05 - 35,100 77,700 25.3 25,8 22.6
585c 5065 20 43 8.5 &30 0.002 38,100 66,200 13.7 14.3 i7.3
584:: 5065 20 43 8.5 87 0.05 37,100 38,500 1.7 1.9 2,94
586 5065 20 43 8.5 . 871 0.002 25,900 25,900 0.8 1.6 5.26
Experiment ORR-155 :
2289: 5067 20 500700 1.4 ' 25 0.05 59,000 123,700 49.4 51,2 45,4
2290b 5067 20 500-700 1.4 650 0.05 38,400 66,800 14.0 14.0 20.5
25.’9].b 5067 20 500700 1.4 650 0.002 36,400 59,900 9.6 9.6 16.0
2285.b 5085 38 500700 1.4 25 0.05 46,300 110,600 41.1 41.2 40.3
22867 5085 38 500~700 1.4 650 0.05 30,800 64,400 18.0 21,2 19.1
2287.b 5085 ag 500~700 1.4 650 0.002: 30,200 51,800 9.3 . 9.9 15.4
1857 5065 20 500700 1.4 25 0.05 50,100 117,000 54,4 56.1 53.2
185 5065 20 500-700 1.4 650 0.05 37,400 62,100 12.3 12.4 17.2
1859 5065 20 500700 1.4 650 - 0.002 34,800 49,100 6.4 6.5 15.3
Experiment ETR-41-31 _
1273P 5065 20 600 £ 100 - 3.5 550 0.002 . 49,100 = 68,600 9.1 9.4 14,7
1276P 5065 20 600 + 100 3.5 600 0.002 42,200 56,300 8.2 8.5 11.7
1270b‘ 5065 - 20 600 ¢ 100 3.5 650 0.05 41,200 59,000 10.8 11.3 14.7
1271 5065 20 600 % 100 3.5 650" 0.002 42,600 51,800 5.9 6.1 10,2
1274 5065 20 600 £ 100 3,5 760 0.002 41,900 46,000 2.8 2.8 5.6
Experiment ETR-41-30 _ .
383P 5065 20 <150 5 650 0.05 46,700 76,200 21.6 22,2 28.8
380P 5065 20 <150 5 650 0.002 37,700 53,300 9.3 10,0 10,1
3849 5065 20 <150 5 650 0.002 40,000 57,500  1.l.4  11.6 17.5
Experiment M3SRE
p-142 5081 50 650 1.3 ' 25 0.05 51,100 105,500 8.5 38,7 31,3
E-7 5081 50 650 . 1.3 650 0.05 34,600 57,200 - 13.8 14,3 13.9
3-143 5081 50 650 1.3 650 0.002 34,400 48,400 8.2 9.0 11.6
A—16d 5085 ag 650 1.3 ' 25 0.05 48,100 100,300 . 34,3 34.5 26.0
B-lg 5085 38 630 1.3 650 0.05 32,000 52,800 12,6 13,7 13.9
B-6 - 5085 38 650 : 1.3 650 0,002 32,100 42,900 6.5 9.4 7.9
®Irradiated in a helium environment except for specimens from MRE. | ®Annesled 8 hr at 871°C.
Pis received, ‘ dnnealed 2 hr at 900°C,

92

 

 
 

Mm

"

"

 

27

whether the material was irradiated in the as-received condition or

- whether it was annealed 8 hr at 871°C. These specimens were irradiated at
1 43°C, and the ductilities at 25°C (0.05 min~!) and 650°C (0.002 min™") were

34 to 36 and 13 to 14%, respectively. When irradiated at an elevated
temperature, this same heat had elongations at 650°C (0.002 min~') of

6.5 and 6.1%. Heats 5067 and 5085 'showed somewhat better ductilities at

650°C (0.002 min~1) with values of 9 to 10% being.obtained for irradiations
at~élevated temperatures. The ductilities of the two surveillance heats

at 650°C agree closély-with those observed previously for héats-5085

and 5067. However, the room temperature ductilities are lower than those
observed for any heat of material irradiated at an elevated temperature,
Heat 5081 was included in another experiment in the Oak Ridge Research
Reactor, © and the results are compared with those for the MSRE surveillance
specimens’in Fig.'lS; These results indicate that the properties of the

material are unaffected by the salt environment.

 

64y, R. Martin and J. R. Weir, "Effect of Elevated Temperature
Irradiation on the Strength and Ductility of the Nickel-Base Alloy,
Hastelloy N," Nucl. Appl. 1(2), 16067 (1965).

ORNL-DWG 67-3531

 

o

 

 

 

 

 

 

 

 

 

 

 

 

g ] T | |
Z - &=0002 min™ '
g ®  THIS STUDY, ¢, =13 %107, | .
o 08 7=650°C ’ |
g ¢? A ORNL-TM-005, ¢, =9x10°%m,
4 T=700°C
<I : .
‘—
I-O- 06 *
8 .
wi
g &
5 04 v
x
@
2 \
- f

\
8 o2
£
o ®
n<: . a e
g o _ _ 4

~ 400 500 800 - 700 800 900 1000

- TEST 'TEMPERATURE (°C)

Fig. 15. -Cofiparative EffédtS'of Irradiation in MSRE and ORR on the
Ductility of Hastelloy N, Heat 5081.

 
 

 

 

28

We also ran several crgep-rupture fiests on the irradiated métepials
to evaluate their properties under creep conditions. For compariéon, the
resfilts of several creep-rupture tests on unirradiated heat 5081 are given
in Table 9. Of the two heat treatments investigated, 2 hr at 900°C and
the surveillance control treatment, the latter resulted in slightly lower |
rupture strains. The creep-rupture data are plotted in Fig. 16, and the
' MSRE surveillance control specimens exhibit a slightly reduced-rupture
life. However, the minimum creep rate is the same after the two heat
treatments (Fig. 17). | |

Table 9. ‘Creep-Rupture Properties of Unirradiated Hastelloy N at 650°C

 

 

Heat 5081
Pest Stress Bugture : Ruptu;e ‘R§duction ‘,Minimum Creep

Numbey (psi) Life Strain in Area Rate

(hr) (%) - (P) (%/hr)

Anneéled 2 hr at 900°C |
6159 70,000 5.1 35.0 12.8. C 2.1
6155 55,000 71.8 33.9 29.2 . 0.26
6156 47,000 76.0 12.4 27.0 0.091
6157 40,000 - 648.3 42.5 25.2 0.032
6158 32,400 2133.3 46.8 20.1 0.012
6160° 27,000 2349.0  10.2 3.7 0.0047

Annealed 2 hr at 900°C plus 4800 hr at 650°C in MSRE salt

6077 55,000 40.7 24.3 21.9 0.25
6075 47,000 147.9 27.2 21.9 0.098
6076 40,000 321.0 31.1 26.7 0.061
6071 32,400 848.0 16.5 16.1 0.014

 

®Discontinued prior to failure.

‘¥
 

#

o

29

ORNL~-DWG 67-T7934

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

70 4 -~ TTT T T TT1
| \il\ | PRETEST ANNEAL
a 2hr AT 900°C
60 < O MSRE CONTROLS
NN
NURL

50 NN
: A o \
2 \K\\

nt

§ 40 N DN g
= N N
§ \\h\\
xr 30 N
o N

20

10

0 O 4 2 3
10 10 10 10 04

RUPTURE LIFE (hr)

Fig. 16. Creep-Rupture Properties of Hastelloy N at 650°C, Heat 5081.

ORNL -DWG 67-7935

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

70
A
. . ' /’/
60 _ A
' \ L
50 A
: ' j!‘.‘/
= L1
8 LA
g 40 T2 T%
3 30 / '
o A aE PRETEST ANNEAL.
20 ' - _ & 2hr AT 900°C |
o MSRE CONTROLS |
10

_ MINIMUM CREEP RATE (%/hr)

Fig' 7. Minimm Creép' Rate of Has'il'.e:iloy N at 65IO°C;,.. Heat 5081r

 
 

30

The creep-rupture properties of heat 5085 were investigated in three
conditions — as-received, annealed 2 hr at'QOOéc, and 2 hr at 900°C plus
4800 hr in molten salt (Table 10). The rupture strain of the as-received
material is improved by annealing at 900°C, but the long aging treatment

at 650°C brings about & slight reduction in the fracture ductility.

 

Figure 18 compares the rupture life after the various heat treatments.

Thé pattern is the same as that for the du¢tility with the minimum strengthr
being observed for the as-received material and the maximum for the materiai
annealed 2 hr at 900°C. However, the minimum creep rate was unaffected by-

heat treatment (Fig. 19).

 

 

 

Table 10. Creep-Rupture Properties of Unirradiated Hastelloy N at 650°C
- : Heat 5085
g Rupture - Rupture Reduction Minimuum Creefi
Nfi;fi; Si(’r:ii Life Strain in Area '  Rate
F @r)  (® () (%/nr)
As-received |
3792 70,000 0.4 - 28.0 21.9 9.0
3710 55,000 10.8 10.9 13.3 0.27
3781 47,000 . 48.6 12.5 14.6 0.086
3713 40,000 179.5 10.9 5.6 0.024
3714 40,000 215.7 14.0 5.6 0.024
3975 30,000 672.6 6.3 6.4% 0.006
3795 30,000 1030.0 9.4 7.1 0.006
Annealed 2 hr at 900°C
6153 70,000 4.1 32.6 30.7 2.1
6149 - 55,000 49.5 22.6 30.8 0.26
6150 47,000 246.8 38.5 28.9 0.084
- 6151 40,000 725.1 37.6 18.4 0.029
6152a 32,400 2386.0 37.7 19.9 0.009
6154 27,000 2445.0 2.0 4.0 0.0035
. Annealed 2 hr at 900°C plus 4800 hr at 650°C in MSRE salt
6074 55,000 20.5 20.8 21.9 © 0.30
6073 - 47,000 124.6 31.2 - 22.9 0.080.
6072 40,000 513.3 22.3 19.7 0.029
6070 32,400 2054.6 26.7 16.7 0.0082

 

" ®piscontinued prior to Failure.
 

 

31

ORNL-DWG 67-7936

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

70 - QT T T T 1 -
NG| PRETEST ANNEAL
\ : . © AS'RECEIVED
60 : : - b HH— a2 hr AT900°C
N \4 {1l oMSRE CONTROLS
NN
. \\ \\\ . !
50 P, \ ™~ N \\
& N TN
o \ NI
8 40 R TTRY
- N
= NN
» \\
& 30 R
v .
oy
20
10
0 4
10! . 10° 10 107 103 104

RUPTURE TIME (hr)

Fig. 18. Creep-Rupture Properties of Hastelloy N at 650°C, Heat 5085.

ORNL—-DWG 67-T937

70 — . /
. 5 b

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

60 - —t ~
7 . /&J ’
50 - /
~ | U s .
2 P//’ PRETEST ANNEAL
8 40 T ' o AS RECEIVED
e - / - & 2hr AT 900°C
» 2 ] HE . 8 MSRE CONTROLS
“-30 b’ : : - |
& o7
o )
.20 —
10
010*3 1072 ' 10! 100 10!

" MINIMUM CREEP RATE (% /hr)

Fig. 19. Minimm Creep Rate of Hastelloy N at 650°C, Heat 5085.

 
 

 

32

_ The results of the tests on the surveillance specimens are given

in Table 11. The properties (ductility and strength) of heat 5081 are
superior to those of heat 5085, However, a comparison of these data with
those for the control specimens in Tables 9 and 10 shows that irradiation
has significantly reduced the rupture life and ductility of both heats.
~ The rfipture lives are compared in Fig. 20 for both heats—of'méterial in
the irradiated and unirradiated éohditions. The effect of irradiation is
greater as the stress level increases. The minimum creep rates of the
two heats of material in the irradiated end unirradiated conditioné are
compared in Fig. 21. This parameter'appears t0 be independent of the
varisbles being studied with the possible exception of the irradiated
specimens exhibiting a higher strain rate at the 47,000-psi stress level.

Mable 11. Postirradiation Creep-Rupture Properties of
MSRE Surveillance Specimens at 650°C '

 

Rupture Rupture Reduction Minimum Creep

 

Test Heat  Stress 3 :

. Life Strain in Ares Rate
Number  Number (psi) (hr) (4) (%) C (d/nr)
R-230 5085 47,000 0.8 1.45 10.0 - 0.81
R-266 5085 40,000 24.2 1.57 9.7 0.031
R-267 = 5085 32,400  148.2 1.05 6.5 0.006
R-250 5085 27,000  25.2 1.86 2.2 - 0.004
R-229 5081 47,000 8.7 2.28 9.2 0.20
R-231 5081 40,000 - 98.7 .2.65 5.8 0.017
R-226 5081 32,400  474.0 3.78 4.0 0.0059
R-233 5081 27,000 2137.1 4.25 - 0.58 0.0009

 

®annealed 2 hr at 900°C prior to irradiationm.
 

 

»

.

33

ORNL-DWG 67-7938

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

70
60
%
' 1l 2?3%
50 Pry
M T~ %225 '
% : B S~ ’
§ i T~ la | TN 4 9
40 R § L
, , ~. %
g‘ . . \\\ .\\ éé%é;;
0 | THa e *fé A
@ N4 4 %
g 30 ‘ S = 772k
5 ' 4
5081 5085
20 — CONTROL o a
SURVEILLANCE e &
40
o | |
10" 10° | 10 0?2 10° 10*

RUPTURE TIME (hr)

Fig. 20. Comparatlve Creep-Rupture Propertles of Sumre:.llance and
Control Specimens at 650°

ORNL-DWG 67-793%9

 

70

 

60 |- _ . i

 

>
o

 

H
o

 

STRESS (1000psi)
o
o
N

 

 

 

 

 

 

 

 

 

n
o

: 5084 5085
CONTROL . o A

SURVEILLANCE ' oA

 

S

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

o | ;
ot . w0 10” cano 0 el
MINIMUM CREEP RATE (%/hr) T

Fig. 21 Comparatlve Creep Rates for Survelllance and Control
Specimens at 650°C.

 
 

 

 

34

The results of the creepfrupture‘tests on the surveillance épecimens
were compared with data which we had cbtained on the "MSRE materials"” in
other irradiation experiments in the ORR. The results usedrin this
comparison are given in Tabie 12. The creep-rupture lives are compared inf
Fig. 22. The data for heafi 5085 agree quite wéll with those Obtained‘
previously in the ORR for this same heat and several other MSRE heats.
However, the results for heat 5081 are slightly superior. The fracture
strains for the various heats of irradiated méterial are compared in Fig. 23.
The data indicate a minimm ductility for & rupture life of 1 to 10 hr with
ductility increasing with increasing rupture life. A lower ductility of
heat 5085 after irradiation in the MSRE is also indicated, although the
data scatter will not permit this as an unequivocal conclusion. The
superior ductility of heat 5081 and the least ductility of heat 5065 (heat
uséd for the top and bottom heads of MSRE) are clearly‘illustrated.

_ Since transients may occur in which the material is'straihed at some |
temperature other than the operating temperature (650°C), we ran a series
of tests fo determine what effect such transients could have on the
fracture strain at 650°C. The results of these tests afe givefi in Table 13.
The specimens were strained at other temperatures and then quickly cooled
‘or heated to 650°C and tested to failure. .EVen though the‘prestraining
treatments carried the specimens as far as 37% of the strain to failure,

the strain at 650°C was not decreased. In fact, the prestraining at

760 and 850°C seemed to improve the ability of the material to stfain at
650°C. o |

Several. of the specimens were examined metallographically after
testing. Figure 24 shows the microétructure of a control specimen from
heat 5081 that was tested at 25°C. 'The‘specimen has undergone extensive
'deformation, and the fracture is typical of a transgranular shear-type
failure. There is no evidence of intergranular cracking. 'In contrast,
the irradiated specimen from the same heat, shown in Fig. 25, failed
ihtergranularly with less strain and considerable infergranular cracking.
At 650°C the failure of the‘control;specimen was predominantly
intergranular (Fig. 26). Thé failure of the surveillance specimen was
also intergranular at 650°C with no microstructural evidence of plastic
deformation (Fig. 27). | |

-
 

Table‘l2. 'Postirradiation Creep-Rupture Properties of Irradiasted® Hastelloy N at 650°C

 

‘Experiment

Rupture

 

Test Thermal Rupture Minimum Creep
Number Dose . Number Stress Life Strain Rate
(neutrons/en?) (pst) () () (/1)
% 10?0 . | |
B Heat 5065
R-15 3.0 ORR-138 39, 800 2.8  0.59 0.086
R-13 3.0 ORR-138 32,400 ‘62,6 2.23 0.011
R-35 3.0 - ORR-138 27,000 - 765.8 1.75 0.0019
‘R=12 ~ 3,0+ ORR-138 - 21,500 - 1907.8 - 2.28 0.0010
R-159 5.2 ORR-148 40,000 28.6 - 0.98 0.028
. R-167 - 5.2 ORR-~148 40,000 -13.0 -~ 0.46 0.018
R-65 5.2 ORR-148 35,000 17.7 0.60 0.016
R-168 5.2 ORR-148 30,000 117.0 0.66 0.0049
R-215 1.4 ORR-155 32,400 135.7 1,45 0.0083
Heat 5067
‘R-214 1.4 ORR-155 32,400 36L.4 2:78 ' 0.0056
- Heat 5085,
R-14 - 2.0 - ORR-140 39, 800 6.7 1,90 0.25
R-11 2.0 ORR-140 32,400 49.3 1.61 0.0098
R-41 2.0 ORR-140 27,000 102.8 - 2.88 0.0023
R-10 - 2.0 ORR-140 21,500 2625.8 3.70 0.0009
R-206 1.4 ORR-155 32,400 _247.6 1.48 - 0.0055

 

®rradiation environment: He—l vol % 0p- All specimens in the as-received condition.

Gt

 

 

 
36

ORNL-DWG 6T7-T940 u

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

70 , R
T llll
TYPICAL UNIRRADIATED
60
\\\
™\
N
50 I
[ .
= h_'~'---_.._.~ \
Q -:____
§ 40 ) -»-]~-=0<\\- L .
=4 AVERAGE IRRADIATED DATA o N R \\
@ 30 L Aol‘qu AN
E . 7 s . ‘\\t\. \.
MSRE ORR _ \\ ) ,
o 5065 N |
20 A 5067 - A
u o - 5085 Y
+ 5081
© r
' ° 107! 10° o 102 o 0%

RUPTURE TIME (hr)

Fig. 22. Comparatlve Stress-Rupture Properties for Material Irradiated
in the MSRE and the ORR at 650°C. ,

ORNL-DWG 67-794

 

 

 

 

 

 

 

 

 

 

vy

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

6 MSRE ORR : :
& 5085
° 5065
9 . 0 508
® o 5067
"
Za
= ¢ A
o
w 3
a
2 L 0 o
g 3 o
o 2 " " i
4 Al 14 o | &
1
1 o o o
! o
0
10! 10° Tk 10 103 1ot

RUPTURE TIME (hr)

Fig. 23. Comparative Rupture Strains for Irradiated Hastelloy
at 650°C.
 

 

 

> 4 (

‘Tgble 13.

 

 

Effects of Prestralnlng on theaTens.1le Propertles of Hastelloy N
- Heat 5081 -
' L B o | o o - "Fraction" of |
Specimen . Pretreatment Stress (psi) . ElongationP (%) Reduction True . - Rupture Strain at -
Number o Yield  —UItimate ' Uniform Total in Area = Strain _Pres'traininéf[‘emperature
| e (% )
E-19 None 34,600 53,000 . 10.8  11.3 = 14.6 15.9
| E-14 j_mone B 34,400 48,400 8.2 9.0 1.6 12.2 | -
F-11 'S'brained 5% at 4—00° 45,900 | 54;'700 - 8.0 ©10.0 | 8.2 . 8.2 S 10
F-25 Strained 5% at 500°C 47,700 58,300  10.9  1L.5 4.2 15.4 20
F-24 Strained 5% at 600°C 47,900 58,500  10.4  11.3 1.0 11.3 32 “
D-11  Strained 2% at 700°C 40,200 54,000 9.7 10,6 4.2 5.4 . 37
pd lStrained 1% at 760°C 35,500 56,400  11.9  12.6 15.5 16.9 26
F-16 Strained 0.5% at 850°C 35,700 59,800  15.2 © 15.9 13.5 147 24

 

a'Rl:t;ptu:c‘ed at 650°C:

Strain rate = 0.002 min-1,

bPres'ti'aining .;iarried out at a strain rate of 0,002 min-1,

TIneciudes ofily the strain at 650°C.

 

LE

 

 
 

 

i

 

 

 

Y-78243

 

0.025 INCHES
N 100X

 

[

 

 

 

-

 

 

 

 

 

M 100X

 

 

Fig. 24. Photomicrographs of Control Spec:unen AC-8 from Heat 5081
Tested at 25°C and at a Strain Rate of 0.05 min~!. (a) Fracture. (b) Edge
of spe01men about 1/4 1n. from fracture. Etchant: glyceria regia.

: /

t

~%
 

 

»

 

39 o

R-34227

 

 

0.035 INCHES
I 100X

|

 

 

=

 

0.035 INCHES
S 100X

i

 

 

 

(b)

Fig. 25. Photomicrographé of Surveillance Specimen D-16 from
Heat 5081 Tested at 25°C and at a Strain Rate of 0.05 min~1, (a) Fracture.
(b) Edge of specimen,,about_—.l/4-ir_;_. from fracture. Etchant: glyceria regia.

 
 

 

 

 

 

 

|

i Y-78248

 

[

 

 

 

 

0.023INTHES
M 100X

 

 

[

 

 

 

 

 

 

Fig. 26. Photomicrograph of the Fracture of Control Specimen AC-17
from Heat 5081 Tested at 650°C and at a Strain Rate of 0.002 min™*.
Etchant: glyceria regia. ' - | - .

R-34235 ||’

 

 

0.035 INCHES
I~ 100X

 

 

[

 

 

 

Fig. 27. Fracture of Surveillance Specimen E-14 from Heat 5081 Testéd
at 650°C and at a Strain Rate of 0.002 min~!. BEtchant: glyceria regia.

1

o

 
 

-

 

41

The fallure of the control material from.heat 5085 was found to be
predomlnantly 1ntergranular (F1g 28). However, the elongated grains
attest to the large amount of stra1n that has occurred The large
preclpltates have been identified as MgC, and they normally fracture when
strained'at”temperatUres less than about 500°C. The surveillance specimen
from heat. 5085 tested at 25°c is shown in Fig. 29. The failure is largely
1ntergranular w1th numerous 1ntergranular cracks in the microstructure.

The . edge of the spec1men (Flg 29b) is quite clean with no evidence of
corrosion or materlal depos1tlon However, the part of the specimen that
touched the. graphlte in the surveillance sssembly was found to have a
reactlon product,near the surface varying from 1 to 2 mils in depth (Fig. 30).

This'productAwaSVnot distributed uniformly around the specimen and varied

'inuformffrofifa lamellar to a rope-like intergranular product. At 650°C the

fallure of the control specimen was predominantly 1ntergranular (Fig. 31).
The surface reactlon praduct observed in specimens from the reactor where

they were in contact with the graphlte was also noted in the control )

specimens (Fig. +32). Although the mlcrographs that have been shown are

for heat 5085 the surface reaction was also noted in heat 5081. Electron
microprobe examination showed that this layer contained’ from |
0.3 to 1.5 wt % C, indicating that there was some transfer of carbon from
the graphite to the Hastelloy N where the two materials were in contact.
Flgure 33 shows the ‘fracture of the surveillance speclmen from heat 5085
that was tested at 650°C. The fallure 1s predomlnantly intergranular with
no metallographlc evidence of plast1c deformation. -

Extraction repllcas.weregmade on the surveillance and control specimens.

'This'technique involves depositing carbon'on a polished surface of the

specimen and then dlssolv1ng electrolytlcally the matrlx in a solution of

10% HC1 1n ethanol untll the carbon falls free. The prec1pitates are not

, attacked by the solutlon, and they are held by the carbon _After suitable

washlng and drylng, the repllca can be examlned in the electron mlcroscope.

‘Transmission electron micrographs can be made as well as’ selected area

-_diffraction patterns for phase'identification.- An - extractlon replicsa of

a control specimen from heat 5081 is shown in F1g 34. The predomlnant

Ifeature is the relatlvely large preclpltates that have been 1dent1f1ed

 
 

 

l..

 

0.025 INCHES
N 100X

3

 

 

 

1=

 

 

 

) INUHED

a
~

U
N 00X

Jes

 

 

 

 

 

 

 

.~ PFig. 28. Photomicrographs of Control Specimen DC-24 from Heat 5085
Tested ‘at 25°C and at a Strain Rate of 0.05 min~*. (a) Fracture. (b) Edge
of gpecimen sbout 1/4 in. from fracture. Etchant: glyceria regia.

 
 

 

 

 

 

 

43

 

0.035 INCHES
i 100X

Jen

 

 

 

  

0.035 INCHES
i 100X

 

Jew

 

 

- -

- Fig. 29. Photomicrographs of Surveillance Specimen A-16 from Heat 5085
Tested at 25°C and at a Strain Rate of 0.05 min~1, (a) Fracture. (b) Edge
of specimen about 1/4 in. from fracture. Etchant: glyceria regia.

 

 
 

 

 

 

i
1
i
1
i

  
  

  

NS

 

0Q.035 INCHES
N 100X

o

 

 

Ira

 

0.007 INCHES
S00X

 

 

A e 9T

 

Fig. 30. Cross Section of the Buttonhead of Surveillance Specimen A-16
from Heat 5085 Tested at 25°C. (a) 100 x. (b) 500 X.

%

g

uh

 
 

 

 

 

 

 

 

 

 

. T
1
a2
olz
O
] i
o
-~ ) 1
t
's.
! alz
O’—
: 5
o
. - - Fig. 31. Photomik:régrap’hs of Control 'Spec'.imen DC-25 from Heat 5085
Tested at 650°C and at a Strain Rate of 0,002 mi_nfl. (a) Fracture.
~ (b) Edge of specimen about 1/4 in. from fracture. Etchant: glyceria regia.

 
 

 

 

 

 

 

 

46

 

 

 

 

 

 

 

 

 

 

0.02% INCHES
I 100X

T

 

 

I..

I3

 

0.007 IMN4LHES
2 500x To

'

 

 

Fig. 32. Photomicrographs of the Cross Section of the Buttonhead of

Spec_imen DC-25.

(a) 100 x..

(b) 500 X. Etchant: glyceria regia.

 
= S3IHONI G500 -

 

 

 

 
  

glyceria regia.

 

6 from Heat 5085 Tested

Btchant

 

ecimen B

 

 

illance Sp

e

 

 

Rate of 0,002 min~?1.

 
 

Fracture of S

33
at 650°C and at a Strain

. S S

 

Fig

3T

 

 

 

 

Extraction Replica from Control Specimen, Heat 5081.

Fig. 34.
 

 

 

48

as MgC. 'A(replica is showh ihfFig; 35 for a surveillance specimgn“from

heat 5081. The large MgC particles-ére present,,but'tfiere is a lot of

fine intergranular precipitate that has aiso-been_identified as MgC.

The irradiation appears to enhance the formation of the fine intergranfilar

precipitate.

~ . Y-79402

G c 5 . »

 

Fig. 35. 'Extracfiion Replica From Surveillance Specimen, Heat 5081.

W

iyt

 
 

)

 

49

DISCUSSION OF RESULTS

Because of the large amount'of datse presented, we will briefly
recapitulate the most important observations. ) ‘

1. The control spec1mens from both heats of Hastelloy N exhibited
the characterlstlc ductlllty minimum in the tenperature range of 600 to
700°C. The ductlllty at varlous temperatures was reasonably insensitive
to straln rate except near 650°C where the ductlllty decreased with
decreasing straln rate.

2. After 1rradiat10n the tensile ductlllty was reduced s1gn1f1cantly.

Thereuwas,an unexpected reductlon in the room temperature ductility with

- fracture strains in the range cf 35 to 40% being observed. Intergranular

fractures were obtained at room temperature in heat 5085. The fracture
straln generally became lower as the test temperature was increased and
the strain rate decreased.

3. At elevated temperatures (400—850°C) the fracture strains were
equivalent for the two heats of surve;llance specimens and were found to
be the same as those observed preriously in other experiments where
molten salt was not present,: | o |

4., Creep-rupture tests run on unirradiated.specimens indicated that
the pretest-anneal of 2'hr_at:900°C improved the_rupture strength and

ductility over that of the material in the as-received condition. Thus,

~ the stress-relieving anneals at 871°C used in fabrlcatlng the MSRE
'1mproved the base prcperties.r However, the long exposure of the control
,,speclmens at 650°C (operating temperature of the MSRE) caused sllght

jreductlons in rupture strength and ductility.

- 5, The creep-rupture llfe of the surveillance speCimens"was less

than that of the control specimens, the effect being greater ‘at.the

“higher stress levels ' Heat 5085 was. affected much ‘as we had Observed
: 'prev1ously in other experlments on th1s same heat and other MSRE heats
- Heat 5081 exh1b1ted & s1gn1ficant but smaller effect

_6.l The - creep-rupture ductlllty of 1rrad1ated Hastelloy N goes

.through a mlnimum'value for a rupture life of from 1 to 10 ‘hr. ‘The : -

fracture strain increases as the. rupture llfe 1ncreases (or'the stress

level decreases). ‘Heat 5081 exhiblted apprec1ably hlgher fracture stralns

 
 

 

 

50

than did heat 5085. Heat 5065 (material used for the top and bottom

~ heads of the MSRE) exhibited the lowest ductility of any heat examined
to date. | '

| 7. A series of tensile tests indicated that prestraining at
temperatures over the range of 400 to 850°C did not appreciabiy lower
the fracture strain of the material when tested. to failure at 650°C.

8. Neither the control nor the surveillance specimens showed any
evidence of corrosion. However, there was a surface product from
0. 001 to 0.002 in. in depth that formed where the Hastelloy N and graphite
were in contact. Microprobe studies indicate that this layer is hlgh in
carbon, and hence the reaction product is probably a metal carblde

9. Extraction replicas indicated that more 1ntergranular preclpltate
formed in the surveillance speclmens then in the controls. Thus,
irradiation must enhance the nucleation and growth of the precipitate |
(identified as MgC). | ’

The chenges in the unirradiated properties of these heats of
Hastelloy N have been demonstrated previously.7 However, these changés
are relatively small, and the properties do not appear to be deteriorating
enough for concern. They are prdbably due to the solution and
reprecipitation of MgC. |

The effects of irradiation on Hastelloy N are drastic, but pretty
much as expected. Previous work had shown a reduction 1n the rupture
ductility in postirradiation tensile and creep—rupture'tegts afi elevated
'temperatures.sfg These effects are attribfited to the helium produced by
the 1B(n,) transmutation. Many of the details of the role of helium

in metals have been reviewed by Harries,?® and we have applied these

 

7H. E. McCoy, Influence of Several Metallurgical Varisbles on the
Tensile Properties. of Hastelloy N, ORNL-3661 (August 1964).

8y, R. Martin and J. R. Weir, "Effect of Elevated Temperature
Irradiation on the Strength and Ductility of the Nickel-Base Alloy,
Hastelloy N," Nucl. Appl. 1(2), 160-67 (1965).

® W. R. Martin and J. R. Weir, "Postirradiation Creep and Stress-
Rupture of Hastelloy N," Nucl. Appl. 3(3), 167 (1967).

- 10p, R. Harries, "Neutron Irradietion Embrittlement of Austenitic
 Stainless Steels and Nickel-Base Alloys," J Brit. Nucl. Energy Soc.
5, 74 (1966). |

4

 
 

o

 

51
ideas to Hastelloy N in two-recent papers,tlr12 Hence, we shall not
discuss the mechanism whereby helium alters the propefties. There are
some guestions concerning the comparison of thermal flux measurements
for the MSRE and ORR. However, about 30 to 40% of the 1B was transmuted
in the surveillance specimens with a resulting atomic fraction of helium
of about 1 x 1073, " We feel that, at least at low strain rates, the
deterioration of properties saturates at helium levels an order of magnltude
lower. Hence, the exact helium level is rather academlc, and the high-
temperature properties have probably stabilized unless continued exposure
at 650°C causes metallurgical changes that are detrimental. The drop in
ductility at low temperatures is somewhat surprising and.bears watching.
However, the ductility levels are stlll quite reasonable.

The mechanical properties appear ‘unaffécted by the salt., This is
evidenced by the excellent agreement between the results of tests on
materials irradisted in the MSRE and the ORR (helium environment). The
small amount of carburization that occurred in the'HastellOy N which was
in contact with graphlte was not surprlslng and did not extend to alarming
depths. . |

The very low stress levels in the MSRE during normal operation,®?
coupled with the experimental dbservatlon that the deterioration of the

creep-rupture properties (rupture life and ductlllty) due to irradiation

 becomes smaller at low stresses, indicate that transient conditions offer

the greatest risk of failure. Thus, with reasonable care in operation, it

does not appear- at this time that the life of the MBRE'Wlll be limited by

-radiation damage to the Hastelloy N.

 

1y, E. MbCoy, Jr., and J. R Welr, Jr., In- and Ex-Reactor Stress-
Rupture Properties of Hastelloy N Tubing, ORNL-TM-1906 (September 1967).

12y, E. McCoy, Jr., and J. R. Weir, Jr., Effects of Irradiation on

.-the Mechanical Properties of Two Vacuum-Melted HEats of Hastelloy N,

(to be published). _
13R. B. Briggs, private cqmmuhication.

 
 

 

SUMMARY AND CONCLUSIONS

We have tested the first group of eurveillance specimens from the
MSRE core. They were removed after 7800 Mwhr of operation during whlch
the specimens were held at 645 * 10°C for 4800 hr and accumulated a
thermal dose of 1.3 x 1020 neutrons/cm .. Specimens were exposed to
molten salt to duplicate the thermal history of the surveillance specimens.
Two heats of materlal 5081 and 5085, were used w1th both showing similar
~deterioration of tensile ductility at elevated temperatures. However,
heat 5085 (cylindrical core vessel) exhibited a greater loss of creep- -
rupture strength and ductility. The property changes were quite similar
to those that had been observed for theee same materials after irradiation
in the ORR where the environment was helium. There was a,signifieant
reduction in the low-temperature ductility, but fraeture strains of
35 to 40% were still obtained. This change in properties is prdbably
due to the formation of 1ntergranular MgC.

" We noted the formation of a carbon-rich layer on the Hastelloy N
where it was in contact with graphite. This layer was only 1 to 2 mils
deep and probably would have little effect on the mechanical prqpertiee
of thick sections. Sacrificial metal shims were placed in the MSRE
-where the graphite end Hastelloy N were in contact, so the noted

fer

carburization should present no problems in the MSRE.

The mechanical properties of the Hastelloy N appear to be quite
adequate for the normal operating conditions of the MSRE. However,
transients should be prevented that expoée the material to high stresses

- - {
or straims.

ACKNOWLEDGMENTS

The author is indebted to numerous persons for assistance in this

study.

W. H. Cook and A. Taboada —-De51gn of surveillance assembly and 1nsert10n
of specimens.

W. H. Cook and H. B. Piper — Flux measurements. | kaj
J. R. Weir, Jr., and W. H. Cock — Review of manuscript.

te

 
 

P ]

g

 

53

‘R. E. Gehlbach — Prepared the extraction replicas

E. J. Lawrence and J. L Griffith — Assembled surveillance and control
spec1mens in fixture.

P Haubenreich and MSRE Qperatlon Staff — Exercised extreme care in insert-
ing and removing the surveillance
specimens.

E. M, King and Hot Cell Operation Staff — Developed technlques for cutting
long rods into individual
" specimens, determined specimen
straightness, and offered assis-
tance in running creep and tensile
tests.

B. C. Wlllams, B. McNabb, N. O. Pleasant — Ran tensile and creep tests on

survelllance and control
specimens.

E. M, Thomas, V. G. Lane, and J. Feltner — Processed test data.
H. R. Tinch and E. lLee —'Métallography on control and surveillance specimens.

‘Metals and Ceramics Reports Office — Preparation of manuscript.

Graphic Arts — Preparation of drawings.

 
 

 
 

 

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