MIL-DTL-16232G
c. Spray rinsing may be utilized provided the same end-product quality is maintained.
d. Immediately following the water rinse, all items (except class 4) shall be treated in a
chromic acid rinse (see 3.2.5).
3.2.5 Chromic acid rinse. (Classes 1, 2 and 3). The chromic acid rinse of classes 1, 2, and 3
shall be performed in accordance with the following:
a. The final rinse shall be hot 63 to 93oC (150 to 200oF) chromic acid or chromic
phosphoric acid solution: approximately 300 grams chromic acid flake in 1000 liters (L) of water.
b. The final rinse shall be maintained at a pH of 2 to 4 by the addition of flake chromic
acid or mixtures of chromic and phosphoric acids. The pH of the final rinse shall be checked at
least every 8 hours.
c. The final rinse shall be checked by a standard free and total acid titration or pH reading
as often as is necessary to assure that the bath remains within the limits set at all times during
which it is in operation.
d. All rinses should be discarded whenever they become contaminated. The final rinse
shall be checked at least every 8 hours and shall be discarded when the total acid reading rises
to more than 7 times the free acid reading.
e. The item should remain in each rinse for a minimum of 60 seconds.
f. Following the chromic acid rinse, the item shall be thoroughly dried before application of
a supplementary treatment, as applicable.
3.3 Stress Relief. Unless otherwise specified (see 6.2), parts with a surface or through
hardness of Rockwell C 39 or greater shall be given a stress relief treatment. This includes
carburized, induction hardened, flame hardened, etc. treatments. Also, any part that is ground,
cold formed, cold straightened, etc., that may induce residual tensile stresses after machining or
heat treatment shall be given a stress relief treatment. The stress relief treatment shall consist of
a heat treatment at 177 to 204°C (350 to 400°F) for a minimum of one hour for every inch of
thickness but not less than one half hour for thicknesses less than one-half inch. Optional heat
treatment for carburized parts is 104 to 155oC (225 to 275o F) for 8 hours.
3.4 Hydrogen embrittlment relief heat treatment.
3.4.1 After coating. Unless otherwise specified (see 6.2), parts (including carburized parts)
having the hardness values shown in Table I shall be given a hydrogen embrittlement relief heat
treatment after coating per Table I without any parts developing cracks.
3.4.2 After baking. Unless otherwise specified (see 6.2), all lots of parts or materials for
which baking is required shall be tested for hydrogen embrittlement.
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