FF-S-85D
4.4.4
Metallographic tests.
4.4.4.1 Decarburization. To test for decarburization (see 3.5.1), the threaded
part shall be sectioned longitudinally through the axis and polished in such a
manner that rounding of the thread edges is held to a minimum. The section shall
be etched with the usual metallographic etchants (such as nital) and examined with
a metallographic microscope. Measurements shall be made from the crest of the
thread to the end of the decarburized zone. Such distance shall not exceed that
indicated in figure 1 (see 6.4). Measurements shall be made with a fixed-scale
micrometer eye-piece, or the image of the threading may be thrown on the ground
glass of the camera and measurements made with a pair of dividers and a scale.
This does not apply to austenitic grades of stainless steel.
4.4.4.2 Grain size of copper alloys. Determination of grain size of copper
alloy shall be made in accordance with ASTM E112.
4.4.5 Protective coating test. Protective coating and plating tests shall be
conducted in accordance with the applicable specifications shown in 3.4.3 through
3.4.7.
4.6 Passivation test.
Passivation test shall be conducted in accordance with
SAE-AMS-QQ-P-35.
4.4.7 Hydrogen embrittlement. The contractor shall furnish the Government
certification that electroplated or phosphate coated alloy steel screws have been
subjected to the hydrogen embrittlement relief treatment specified in 3.4.8. When
specified (see 6.2), electroplated or phosphate coated screws shall be subjected
to the embrittlement relief test specified in the applicable plating or coating
specification.
4.4.8 Magnetic permeability. Austenitic corrosion resisting steel cap screws,
subjected to visual and dimensional examination, shall also be tested to determine
magnetic permeability (see 3.1.4.1) in accordance with ASTM A342.
4.4.9 Discontinuities. Magnetic particle inspection performed in accordance
with ASTM E1444 or liquid penetrant inspectin performed in accordance with ASTM
E1417 shall be used to determine the presence of cracks and discontinuities such
as laps, seams, and inclusions. Magnetic particle or penetrant indications alone
shall not be cause for rejection, and such screws may be sectioned and
discontinuities measured microscopically under 10X magnification to determine
conformance to the requirements of 3.9. The inspection shall be performed on
unfinished cap screws, free of lubrication and subsequent to any processing
operation which could adversely affect the cap screws.
4.4.9.1 Tool marks. Tool marks on the bearing surface are permissible
discontinuities providing that the surface roughness does not exceed 125
microinches, determined as the arithmetic average deviation from the mean surface.
Tool marks on other surfaces are permissible discontinuities and shall not be
cause for rejection of otherwise acceptable screws.
4.4.9.2 Voids. Voids on the bearing surface of the screws are permissible
discontinuities providing that no void has a depth greater than 0.010 inch and
that the combined area of all voids does not exceed 5 percent of the specified
minimum area of the bearing surface.
4.4.9.3 Folds. Folds located in internal corners at or below the bearing
surface, e.g. in the fillet at the junction of head and shank, are not permitted.
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