The 1350 F stress-rupture properties of two wrought alloys and three cast alloys Page: 6 of 24
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NACA TN No. 1380
SNo comparison on a similar treatment basis is possible for wrought
alloy NR-82 (6059 modified-low carbon), because the unmodified 6059 al-
loy has not been tested in the wrought condition. It does. have lower
strength than cast standard 6059. However., castings usually have *
higher rupture strengths at 13500 F than wrought materials..
The cast alloys had similar rupture strengths. Variations in
rupture times from-those predicted by the rupture curve, which were
possibly due to varying crystal orientation between specimens, make it
impossible to attribute the slight strength differences observed to
chemical composition.
The strengths of these three alloys are of the same order of mag-
nitude as that of-the best cast- cobalt-chromium-nickel base alloy.
(422-19) p~revibusly tested at 1350C P. They have much lower strength,
however, than cast 60Cr-25Fe--15Mo which is one of the highest-strength
alloys known,
Time-elongation curves from the rupture tests on.the two. wrought
alloys showedd that the alloy with lower ductility, NR-82 (6059 modifieA-
low 6arbQ), had a iower deformation rate than did alloy iNR-84 (N-155"
modified-16w carbon). This was true also for the lowest-ductility cast
alloy NR-90 compared with NR-.71 and IR-87. Attention is called to. the..-
fact that the specimen of alloy NR-71 (X-40) under 32,500 psi had ex-
cessively high elongation. The fracture of this specimen was of the
single-crystal type, namely, an oval-shaped formation of the crystal
adjacent to the fracture. This -explaits the high ductility.
Metallographic examination of the longest-time rupture-test spec-
imens revealed a matrix filled with fine particles of excess
constituent. This is the usual appearance of long-time rupture-test
specimens of alloys of this type, the fine particles precipitating
during the test and increasing the hardness of the material. This
precipitation is considered to be an influential factor in the develop-
ment of the outstanding properties of these materials.
A correlation, which shows the variation in rupture strength with
temperature, 'obtained from the research program at 15000, 16000, and
20000 ' (references 1, 2, and 4) with the NACA data at 13500 17000,
and 1800 F, is shown in figure 4 for the five alloys studied. Ac-
tually the only alloy for which rupture strengths are avagable over
the.complete temperature range is NR-T1 (X-40). On the basis of the
data available, the other two cast alloys with strengths of the same
order of magnitude would be expected to vary in strength with tem-
perature to about the same extent as YRL-71. Alloy NR-71, incidentally,
was the strongest of a group of cast alloys tested..at 17000 and 18000
F. (See reference 4.) The two wrought alloys, NR-82 apd NR-84, had
practically identical rupture strengths at both 13500 and 15000 F.
Higher-temperature data have not been determined on these two alloys.5
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Reynolds, E. E.; Freeman, J. W. & White, A. E. The 1350 F stress-rupture properties of two wrought alloys and three cast alloys, report, November 1947; (https://digital.library.unt.edu/ark:/67531/metadc55436/m1/6/: accessed July 17, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.