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sample tested for 100 hr at 1500°F.
As a check on these results, small
specimens of the pure braze metal
were immersed in the metal baths.
The sample tested in sodium had a
weight loss of over SOX, and the
sample tested in lithium completely
dissolved.
Figure 12.8 is a photomicrograph
of a type 316 stainless steel brazed
with the Cr-Si-Ni-Mn alloy and tested
in sodium for 100 hr at 1500°F. No
attack is exhibited, but the cracking
tendencies of this brazing alloy are
shown very clearly. It was noted that
the cracking of the Cr-Si-Ni-Mn and
Cr-Ni-Si alloys was more severe when
alloyed with stainless steel than when
a1 loyed with Inconel.
Tensile Strength of Brazed Joints.
Results of the room -temperature ten -
sile strength tests of Inconel butt-
joints brazed with Nicrobraz alloy
seem to indicate that a short brazing
time of 10 min or less leads to the
PERIOD ENDING DECEMBER 310, 1952
production of weak joints. Samples
held at the brazing temperature for
20 min seem LO produce stronger joints.
Figure 12.9 i s a photomicrograph of
the room -temperature fracture of a
joint held at the brazing t,emperature
for 5 minutes. Some Nicrobraz can be
seen in this photograph, but no brittle
fracture is evident. Although the
specimen that was held for 20 min at
the brazing temperature broke near the
brazed joint, no evidence of Nicrobraz
alloy could be found upon metallo-
graphic sectioning. The greater
alloying of the braze and the base
metal is a result of the increased
diffusion occurring at this longer
time. The increase in tensile strength
of the second bar probably results
from t h i s a1 1 oy ing I
The average of four room-temperature
tensile tests on joints brazed
at short times was 38,300 psi. A
joint brazed for 20 min at the brazing
temperature fractured at 81,100 psi.
Fig. 12.8. Type 316 Stainless Steel Brazed with 16.5% Cr-la. 0% Si-2. 55%
Wn-ll.O$ N i After 100 hr at lSOO°F in sodium. Etched with aqua regia. 150X.
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