Precision Black Oxide
Services
Protect your precision machined parts without altering tolerances. Our hot black oxide conversion coatings deliver a sleek black aesthetic, reduce glare, and provide mild corrosion resistance.
What is Black Oxide?
Black oxide is a chemical conversion coating. Rather than applying a material over the surface (like paint or plating), the part is immersed in a heated alkaline solution. This causes a chemical reaction that converts the iron on the surface into magnetite (Fe3O4), leaving a deep black, integral finish.
Zero Dimensional Change
Unlike plating, black oxide adds virtually no thickness (less than 5 to 10 millionths of an inch). Your precision tolerances and tight fits remain completely unaffected.
Reduced Light Glare
The matte or semi-gloss black finish minimizes light reflection, making it the standard choice for optical equipment, firearms, and surgical instruments.
Anti-Galling Properties
The porous nature of the black oxide layer holds oil and lubricants exceptionally well, reducing friction and preventing galling during assembly or dynamic movement.
Mild Corrosion Protection
When combined with post-treatment oils or waxes, black oxide provides an effective barrier against rust for parts used in indoor or low-humidity environments.
Specifications & Post-Treatments
Huade Precision strictly adheres to military standards (MIL-DTL-13924). Because bare black oxide offers minimal rust protection on its own, specifying the correct post-treatment seal is essential.
Technical Specifications
- Standard MIL-DTL-13924 (Class 1, 2, 3, 4)
- Thickness 0.000005” to 0.000010” (Negligible)
- Process Temp 285°F (140.5°C) for Hot Black Oxide
- Electrical Maintains ~1% conductivity of base metal
Crucial Post-Treatments
Oil Finish (Standard)
The most common seal. Leaves the part slightly oily to the touch, providing a glossy black appearance and reliable indoor corrosion protection.
Wax Finish
Dries to a harder, matte finish. It doesn't rub off like oil and offers slightly better corrosion resistance, but parts may feel slightly sticky.
Lacquer / Clear Coat
Provides the highest level of protection. Dries completely hard to a glossy or semi-gloss finish. Note: This will add a slight measurable thickness to the part.
Metals for Black Oxide
Carbon & Alloy Steels
The most standard application (MIL-DTL-13924 Class 1). Yields the deepest, richest black color. Works exceptionally well on low-carbon steels, high-carbon steels, and cast iron.
Stainless Steels
Requires a specialized, higher-temperature process (MIL-DTL-13924 Class 4). Perfect for surgical tools and fasteners that need anti-galling properties without losing stainless qualities.
Copper & Brass
Achieves a highly aesthetic black finish. Often used in decorative applications, optical instruments, and architectural hardware to reduce reflectivity.
* Note: Aluminum cannot be black oxided. If you need black aluminum, please visit our Black Anodizing page.
Design & DFM Guidelines
Black oxide is arguably the most engineer-friendly surface finish because it completely eliminates the need to recalculate CAD dimensions for coatings.
No Masking Required
Because there is no dimensional buildup, you do not need to mask fine internal threads, bearing bores, or tight slip-fits. The entire part can be uniformly submerged.
This significantly reduces the manual labor and cost compared to painting, powder coating, or hardcoat anodizing where meticulous masking is mandatory.
Aesthetic Dependence
Black oxide does not fill in scratches or machining marks. The final appearance relies entirely on the pre-existing surface finish.
- Polished Parts: Will yield a glossy, highly reflective black finish.
- Bead Blasted Parts: Will yield a flat, non-reflective matte black finish (ideal for optical parts).
Black Oxide FAQs
Common questions regarding our black oxide conversion process for CNC machined parts.
Is Black Oxide rust-proof?
By itself, black oxide offers very limited corrosion resistance. Its true rust-preventative power comes from the post-treatment (oil or wax) which absorbs into the porous oxide layer. For outdoor or marine applications, Zinc Plating or Powder Coating is highly recommended over black oxide.
Will the black finish rub off?
No. Because black oxide is a chemical conversion of the base metal (not a deposited coating), it will not chip, flake, peel, or rub off. It can only be removed mechanically by scratching or removing the actual steel surface.
Does it affect the conductivity of my part?
Black oxide retains about 1% of the base metal's electrical conductivity. While it is not a perfect insulator, it also cannot be used as a reliable electrical ground without removing the finish in the contact area.
Quote Machining & Black Oxide
Get a turnkey manufacturing solution. Upload your 3D CAD files today, and specify "Black Oxide with Oil Seal" for your steel components.