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EX TRAC TI0 N RE PLICA
222
SELECTED AREA
ELECTRON DIFFRACTION AUTO MDlO GRAPH
ELECTRON MICROPROBE OUTPUT
Fig. 18.4. Hastelloy N Containing 14C Annealed 1 hr at 24OOOF. Correlation of extraction replication, auto-
radiography, selected area electron diffraction, and microprobe analysis for effective precipitate identification.
degree of ductility (as measured by reduction in
area). 'This zero ductility temperature (ZDT) is
then set as the maximum temperature, and sub-
sequent specimens are subjected to the ZDT,
cooled at a rate which simulates that experienced
by the IIAZ, and fractured at a predetermined tem-
perature. The ductility exhibited at these tem-
peratures is compared with the on-heating duc-
tility at the same temperature. 'The criteria for
evaluating the weldability of the base metal are
its ZDT and, even more important, its ability to
recover its ductility after being exposed to the
m'r.
'The nominal analyses of the experimental alloys
studied in this program are given in 'Table 18.2.
For comparative purposes, a hot-ductility study
was conducted on an MSRE grade of Hastelloy N.
Its nominal composition is also given in Table
18.2. The zirconium levels in the experimental
alloys ranged from 0 (No. 168) to 0.7% (No. 172).
Y--8254C
The influence of the zirconium on the ZDT is
summarized in Table 18.2. Kt can be seen that
the presence of 0.3% Zr lowered the ZDT by
225°F. This is a rather significant decrease;
however, as has been pointed out earlier, the
ZDT is not the sole criterion for evaluating the
effect of zirconium. The recovery of ductility
upon cooling is equally important. The on-heating
and on-cooling results of the hotductility study
are shown in Fig. 18.6. It can be seen that alloy
168, which contained no zirconium, had both a
high ZDT and a satisfactory recovery of its duc-
tility. Alloy 169 had a ZDT identical to 158;
however, its ductility upon cooling is unsatis-
factory. Alloys 170 and 171 both had ZDT's of
appioxirnately 2150OF and both exhibited good
ductilities on cooling.
Figure 18.7 shows the results obtained from
alloys 168, 171, and 174. The results obtained
from an MSRE grade of Hastelloy N have also