Black Oxide

B L A C K   O X I D E

Black oxide is a conversion coating for ferrous materials. It is used to add mild corrosion resistance and for appearance. The coatings are frequently employed for decorative purposes and for decreasing light reflection. Black oxide coatings are often used on munition cases and gun barrels due to the decrease in light reflection. Black oxide coating of steel parts by this process lowers the coefficient of friction by providing a more oil-absorptive surface than for untreated steel and thereby lessens the tendency for galling and scoring during breaking-in periods. The treatment does not affect dimensional tolerances nor does it significantly affect fatigue strength or endurance. The process is performed with chemicals at temperatures of about 290°F making it a process requiring extra precautions.

A stress relief bake prior to application of the black oxide may be necessary and it may also be necessary to perform an embrittlement relief bake after the coating is applied. Material hardness is the major characteristic that influences the need for these operations.

A final magnetic particle inspection may be performed to detect any cracking that may have been induced by the black oxide process. This may be a limited inspection due to the nonconductive nature of the black oxide coating.

Finished parts are often oiled prior to shipment.

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