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Fig. 18.5. Hasvellcy N (Titanium Modified, Heat 66-
548) Annealed 1 hr at 215OoF, Aged 30 min at About
1200" F.
Typi caI precipi tote morphologies determined
by extraction replica technique.
been included. It can be seen in Fig. 18.73 that
the Hastelloy N modified by reducing the molyb-
denum content (No. 168) is superior to the corn-
mercial inaterial (INSRE grade Hastelloy N). The
addition of 0.5% Zr to the modified alloy lowers
the ZDT by 225°F. As is shown in Fig. 18.7b,
223
Table 18.2. The Zero Ductility Temperature
of the Base Materials Studied
Identification Composition (wt X)
1 Wuinber Ni Mo Cr Fe Zr ("F)
K educ ti on
ZDT in AreaB
(a)
IGR ha1 12 7 2350 22
169 bal 12 7 0.1 2350 21
170 bal 12 7 0.3 2125 20
171 bal 12 7 0.5 2125 32
172 bal 12 7 0.7 2120 5
lllSRE grade bal 16 4 2300 3
Hastelloy N
aMeasured at 50°F below ZDT.
the recovery of all four of these alloys is quite
good. Excellent recovery is exhibited by alloy
174. Its recovery of ductility was nearly instan-
taneous and to a rather high level; however, from
the standpoint of weldability, its low ZDT is not
acceptable.
Further efforts will be made to develop a zir-
conium-bearing alloy with a higher ZDT. If we
can find a combination of alloying elements that
will raise the ZDT and retain the good recovery
characteristics, we shall proceed further with the
development of this alloy system.
18.5. RESIDUAL STRESS MEASUREMENTS
IN HASTELLOY N WELDS
A. G. Cepolina
Welding inherently leads to large residual
stresses. These stresses can lead to dimensional
changes and can even be large enough to cause
cracks in the weldment. For these reasons we
have initiated a study to investigate the stress
distribution in and near welds in Hastelloy N.
A technique was developed which allowed con-
tinuous reading of the stress values, thus making
it possible to know, with sufficient precision, the
stress gradient adjacent to the weld axis. For
this study, a 12-in.-diam, '/,-in.-thick piece of
Hastelloy N base metal was used. Two circular
bead-on-plate welds were simultaneously made,
one on each side of the plate. 'The diameter of the