This solution further converts the iron on a metal surface into magnetite. It gets a black coating on the metallic surface. Metals you can black oxide include all the Ferrous Steel.
Consequently, the finish may not peal, chip, or flake off. It is possible to remove them chemically or mechanically, applying black oxide finishes to metal parts involves dipping them in alkaline solutions.
Standards Followed In FMC
MIL-DTL-13924 (Class 1 & Class 4)- Black Oxide Coating for Ferrous Metals