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MIL-DTL-13924 Coating, Oxide, Black, For Ferrous MetalsThis specification covers black oxide coatings applied to ferrous metals \(wrought iron, carbon, low alloy, and corrosion resistant steels\). Black oxide coatings, with or without a supplementary preservative treatment, may be used where a black surface is required. Only very limited corrosion protection, under mildly corrosive conditions, is obtained as a result of black oxide coating.

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MIL-DTL-13924D

TABLE I.

Materials and processing procedures.

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Process and

Approximate

Applicability to

possible

processing

immersion

Class

ferrous metals

chemicals

temperature

time

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Carbon steels,

Alkaline

1 or 2

5 to 60 min.

low alloy steels,

oxidizing,

tanks

wrought irons,

NaOH,

boiling at

285 - 305�F

cast and malleable

NaNO3,

(141 - 152�C)

irons

water

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250�F � 10�F

Certain corrosion

Alkaline

30 to 45 min.

(121�C � 5�C)

resistant steel

chromate

alloys which are

NaOH, NaNO3,

Na2Cr207 1/,

tempered at

less than 482�C

Water

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For corrosion

Fused salt

Molten bath

30 min.

750 - 850�F

resistant steel

oxidizing

(399 - 454�C)

Na2Cr207 1/

alloys which

are tempered at

and/or

900�F (482�C)

K2Cr207 1/

or higher

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250 - 265�F

For corrosion

Alkaline

15 to 30 min.

(121 - 130�C)

resistant

oxidizing,

steel alloys

proprietary

compounds

plus water

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Chromium compounds.