MIL-DTL-13924D
6.3.2 Processing. Contractors may employ one of a number of trade name black
finishing oxidizing materials or prepared chemical mixtures to apply the black oxide
coating. The processing details should conform to MIL-HDBK-205, "Phosphatizing and
Black Oxide Coating of Ferrous Metals", or as recommended by the material supplier.
Class 2 is used to process the 4XX series corrosion resisting steels, class 3 is
used for 3XX and 4XX series, and class 4 is used to process those 300 series
corrosion resisting steels which can meet the special salt spray test criteria and
for those 4XX series corrosion resisting steels which do not have any special salt
spray test criteria. Table I provides an outline of the various processes.
6.3.3 Cast and malleable irons, and certain 400 series corrosion resistant
steels. Cast and malleable irons and 400 series corrosion resistant steels of the
martensitic type can also be effectively treated in Class 4 proprietary baths, but
will not meet the salt spray requirement of austenitic 300 series corrosion
resistant steels.
6.3.4 Class 4 coatings. Corrosion resisting steels of minimum composition
l7Cr-7Ni can be effectively blackened by this process.
6.3.5 Rinsing. In order to obtain effective removal of blackening solution and
ensure thorough rinsing, a combination of spray rinses with tank rinses or a
properly operated double counterflow rinse operation may be advantageous. Use of
such a system may help reduce the amount of water required to obtain a desired
rinsing criterion and facilitate meeting the EPA standard.
6.3.6 Ozone depleting chemicals. Classes I and II ozone depleting chemicals
should be avoided when cleaning the basis metal.
6.3.7 Hazardous materials. The DoD has put together a list of hazardous or
environmentally damaging substances in a document called the SD-14. These chemicals
should be avoided whenever another finish can be substituted for the finish
specified herein.
6.4
Subject term (key word) listing.
Chromic acid dip
Chromium compounds
Embrittlement relief
Oxalic acid spot test
Preservative
Salt spray
Smut test
6.5 Changes from previous issue. Marginal notations are not used in this
revision to identify changes with respect to the previous issue due to the
extensiveness of the changes.
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