Based on the operating temperature and the chemical solvent used, black oxide is generally divided into the following types:
Hot black oxide
The hot black oxide process operates at 140℃- 155℃. Immerse the metal workpiece in strong alkaline solutions such as NaOH and NaNO₂ to form a deep black and wear-resistant film on its surface.
This type is more suitable for high-performance tools and key precision parts.
Mid-temperature black oxide
The mid-temperature black oxide needs 90℃-120℃. Use modified alkaline solutions, which can react effectively at a lower temperature, to transform the workpiece surface into a black oxide film.
This type is safer and energy-efficient, while the coating performance is close to that of hot black oxide.
Cold black oxide
Unlike the above methods, cold black oxide utilizes acidic or neutral solutions (such as selenate and copper salts) to deposit black Cu2Se compounds.
This type may not be as perfect in performance, but it is fast and cost-effective, making it ideal for decorative pieces or indoor hardware.
