finish for macroetching and be etched according to ASTM E 340. The
QQ-N-286G
macroetched surface shall be visually examined (unaided visual or low power, up to 10X magnification). One grain size specimen shall be taken from the coarsest grained area and one from the finest grained area of the macroetched surface. The selected grain size specimens shall be prepared and inspected in accordance with ASTM E 112. The inspected surface of the specimen shall be perpendicular to the major direction of working.
4.3.6 Slow strain rate tensile test procedure. The slow strain rate tensile test will determine if a lot of metal is susceptible to intergranular cracking. The slow strain rate test specimens shall be heat treated using the final heat treatment procedure used on the lot before being placed into service. Any lot that has been rejected shall not be submitted for
acceptance.
4.3.6.1 Heat treatment of slow strain rate test specimens. Specimens representing lots of material sold in the annealed condition shall be heat treated as specified (see 6.2). Lots of material that are aged or re-solution annealed and aged with a heat treating procedure that is not equivalent, per
4.3.6.1.1, to the procedure used on the slow strain rate tensile test shall be re-tested using specimens taken from the material after the final heat treatment.
4.3.6.1.1 Slow strain rate tensile test specimen heat treatment. For the purpose of sampling slow strain rate tensile tests in accordance with 4.2.1.3 two heat treatments shall be considered to be equivalent if the following conditions hold:
A) If the material is solution annealed, the solution annealing temperatures are between 1600 and 1900 F or, if above 1900°F, are within 50 F of each other.
B) The age hardening temperatures for the highest temperature age hardening step are within 50 F of each other. Variations in the aging time and the cooling method under 1000 F are allowed.
C) Variations in aging times, variations in aging temperatures
other than the highest-temperature aging step, and variations in
cooling rates between aging steps, and after the last aging
step, do not affect the definition of equivalence, for purposes
of determining slow strain rate test sampling frequency.
4.3.6.2 Slow strain rate tensile test. Each specimen selected in accordance with 4.2.2.2 shall be machined to the dimensions of the specimen of ASTM E 602 except that the notch root radius shall be 0.002±0.0005 inches.
The tensile tests shall be conducted in accordance with ASTM ES at a
temperature of 700 F. The displacement rate for two of the three specimens shall not exceed 0.001 in./in. Of the distance between the grips per minute. The third specimen shall be tested at a displacement rate between 0.05 and
0.5 in./in. Of the distance between the grips per minute. Alternatively, if
an extensometer is used to measure displacement, the displacement rate for two
of the specimens shall not exceed 0.001 in./in./min. and it shall be between
0.05 and 0.5 in./in./min. for the third specimen. Loading below 50 percent of
the minimum yield strength of the material can be conducted at any rate under
100,000 psi/minute.
4.3.6.3 Grain size determination. The average grain size of the half of the slow strain rate tensile specimen not used for fracture surface analysis in accordance with 4.3.6.4 shall be determined as specified in ASTM E 112. The grain size shall be measured such that the average grain size in
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