On the Problem of Stress Corrosion Page: 3 of 23
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NAGA Th No. 1090
thus,:found. the existence of a limiting stress below which no
stress corrosion occurs. By predef6oriatio the limiting
stress may be displaced more and more toward lower stresses
and practically be made to vanish. Plastic deformation with-
out elastic stress does not increase the corrosion sensitivity
of the material. The absence of stress corrosion for the cast
alloys AZF and AZG is to be ascribed to the special posi-
tion of the limiting stress above the plastic limit of these
alloys.
4. As a cause of the stress corrosion, sensitivity or the
intercrystalline corrosion in the majority of alloys may be
considered the high dispersiveness of the precipitated phase
with at least partial microscopically inhbmogeneous precipi-
tation. A brief discussion of the most recent state of knowl-
edge of the precipitation processes is therefore given.
DETERMINATION OF THE STRESS CORROSION SENSITIVITY
BY MEANS OF POLISHED SPECIMEN TESTING
The microscopic examination method is a practical test
method for the rapid and simple determination of whether and
to what extent a substance tends to stress corrosion. (See
reference 1.) The great advantage of simplicity of the pro-
cedure, which may be here assumed as familiar, is offset by
certain disadvantages : namely,
1. The inaccurate knowledge of the magnitude of the elas-
tic stress
2. The gradual reduction of the elastic stress
The magnitude of the elastic stress generally affects the
behavior toward stress corrosion only quantitatively - that is,
the failure of the specimen occurs earlier with increasing
stress. In the case of certain alloys there exists, however,
a so-called "limiting stress" (see fig. 14) below which no
stress corrosion occurs. In these cases, therefore, the stress
should not go below a certain minimum value. This requirement
is initially always satisfied, as will be shown, for all test
specimens. However, the gradual reduction of the stress may
give an increased life of the specimen and even deceive as to
the freedom from corrosion stress if the stress is below the
limiting stress,ElW
2
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Graf, L. On the Problem of Stress Corrosion, report, July 1946; (https://digital.library.unt.edu/ark:/67531/metadc64372/m1/3/: accessed April 25, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.