Black Oxide Coating
Hot alkaline black oxide converts steel surfaces to magnetite (Fe₃O₄) — a classic finish for tooling, fasteners, and mechanical assemblies where a matte black appearance and mild corrosion protection are needed with virtually no dimensional growth.
Process Overview
Minimal Growth
Typically <5 μm — ideal for threaded fasteners and precision fits without masking.
Oil & Wax Seal
Post-treatment oil or wax dip improves corrosion resistance for indoor and handled parts.
Batch Processing
Efficient lot processing for brackets, screws, and small mechanical components.
Specifications
| Parameter | Specification |
|---|---|
| Process | Hot black oxide (285°F alkaline bath) |
| Coating Growth | <5 μm typical |
| Materials | Low and medium carbon steel, alloy steel |
| Standards | MIL-DTL-13924, AMS 2485 |
| Post-Treatment | Water-displacing oil or wax optional |
Compatible Materials
- Carbon steel 1018 / 1045
- Alloy steel 4140
- Tool steel (select grades)
- Stainless (limited — passivation preferred)
Applications
- Socket head cap screws
- Tooling and fixtures
- Firearm components (where permitted)
- Machine brackets
- Optical instrument hardware
Frequently Asked Questions
Black oxide vs phosphate?
Black oxide is primarily cosmetic with mild corrosion resistance when oiled. Zinc phosphate is a heavier pretreatment for paint or oil retention on structural parts.
Is black oxide suitable outdoors?
Limited — without sealant it rusts outdoors. For exterior exposure, consider zinc plating, powder coat, or e-coat instead.
Can stainless steel be black oxided?
Hot black oxide is for ferrous alloys. Stainless typically uses passivation or specialty PVD/blackening — we recommend alternatives per grade.
Need Black Oxide on Your Parts?
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