Corrosion Protection – Depending on the post-treatment applied, black oxide coating can give corrosion resistance equivalent to 144 hrs of salt spray exposure. Other applications are designed to provide extended shelf life for stored parts prior to their use or to prepare them for further surface treatment (painting).
Dimensional Stability – Black oxide adds no more than 5 to 10 millionths of an inch to the dimension of a part (it also penetrates to an approximate depth of 5 to 10 millionths). For all intents and purposes, the as-formed dimensions do not change (as they do when painted or plated). This provides corrosion protection for critical-size parts.
Anti-galling – where break-in of mating parts is necessary, the anti-galling surface lets the outer lubricating layer be sacrificed during initial contact and abrasion while work-hardened surfaces are formed. The black oxide itself has a hardness of 5.5 on the Mohs’ Scale.
Reduced Light Glare – Moving machine parts, hand tools, and surgical instruments coated with black oxide reflect less light and reduce eye fatigue when used under bright lights.
Pre-treatment for Paint – Black oxide greatly improves the adhesion qualities of the metal, allowing paint and other finishes to hold better, last longer. It also minimizes paint chipping and flaking.
No Embrittlement – Unlike painted or plated parts which are oftentimes acid etched, no hydrogen embrittlement accompanies black oxiding. (However, if parts are already scaled or rusted, they may require pickling prior to black oxide and some embrittlement may occur.) Baking of the parts within four hours after black oxide application will relieve this problem. On extremely hard parts, 55 Rockwell C or above, and very thin springs, there is a possibility of "caustic" embrittlement. This condition can be minimized by careful control of the black oxide cycle time.
