Bluing, also known as blackening, is a metal surface treatment process mainly used for steel materials. Bluing is to place steel parts in a solution containing an oxidant, such as molten salts of sodium nitrite and sodium nitrate, or in high-temperature hot air and superheated steam above 500°C. A more common practice is to heat in concentrated caustic soda with sodium nitrite. After this treatment, a layer of oxide film mainly composed of magnetic iron oxide will be formed on the metal surface, with a thickness of about 0.5 to 1.5 microns.
The process flow of bluing usually includes degreasing, cleaning, pickling, oxidation, re-cleaning, saponification, hot water boiling, and final inspection. Since the size and finish of the workpiece after bluing are not greatly affected, this process is often used in precision instruments, optical instruments, tools, hardness blocks, and standard parts in the machinery industry.
At Turnkey, the products after bluing will also be properly maintained and cared for, such as oiling and waxing, so the corrosion resistance and friction resistance are at the leading level in the industry.
