Surface Finish · Chemical Treatments
Black Oxide
Black with zero dimensional change: the gauge-and-tool finish for precision steel.
Process specifications
| Parameter | Value |
|---|---|
| Process group | Chemical Treatments |
| Coating thickness | 1–2 µm |
| Tolerance impact | Negligible (<2 µm) — a gauge pin measured before black oxide measures the same after. Safe on finished precision features without compensation. |
| Corrosion rating | 24–96 h salt spray with oil or wax seal — mild, indoor-grade protection only. |
| Appearance | Satin black with low glare; preserves the underlying machined texture. |
⚠ Not suitable for
Bare outdoor or humid service — corrosion protection is very weak (24–96 h salt spray vs 96–200 h for chromated zinc); treat it as cosmetic-plus-oil only. Not applicable to aluminum or titanium; not a wear coating (the oxide is microns thin and offers no abrasion resistance).
Typical applications
- Gauge pins, fixtures and inspection tooling
- Fasteners and dowel pins
- Optical mounts and glare-sensitive hardware
- Machine elements running in oil
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