Types of Black Oxide

3 types different processes

Black oxidation is a method used to cure metal surfaces. It protects against corrosion, increases surface hardness, and enhances attractiveness by producing an oxide coating on the metal surface. Depending on the treatment temperature, the black oxidation process may be classified into three types:

1. Hot black oxidation process

Hot black oxidation is a treatment process carried out at a higher temperature (usually between 135°C and 150°C). The metal workpiece is heated in an alkaline salt solution, causing the metal surface to react with oxygen to form a black iron oxide (Fe₃O₄) coating.

Hot black oxidation can provide good corrosion protection and high surface hardness, and the oxide film is thicker and has better wear resistance. This process is widely used in the treatment of steel parts. It is often used in industrial machinery parts, tools, and parts that need to increase wear resistance.

2. Medium temperature black oxidation process

Medium temperature black oxidation is usually carried out in the temperature range of 107°C to 135°C. It is a process between hot black oxidation and cold black oxidation, with a relatively low treatment temperature, suitable for some heat-sensitive metal materials.

This method can be carried out at a lower temperature, reducing the thermal stress on the workpiece, while also providing good protection and appearance quality. It is usually used for parts that require high dimensional accuracy and cannot withstand high temperature treatment, such as precision instruments and certain alloy materials.

3. Cold black oxidation process

Cold black oxidation is carried out at room temperature or near room temperature, and the surface oxide film is usually formed by immersion in a chemical solution. The process is usually simple and suitable for small batches or workpieces with low appearance requirements.

Because it is operated at room temperature, cold black oxidation has the least effect on the metal and will not cause material deformation or change its mechanical properties. At the same time, it is easy to operate and has low cost. It is mainly used for parts with low corrosion resistance requirements or occasions for rapid processing, such as hand tools, fasteners, and some low-stress decorative applications.

The kind of black oxidation treatment is often chosen based on the workpiece's material qualities, the operating environment, and cost and process concerns. Hot black oxidation is appropriate for situations that demand great wear and corrosion resistance, medium-temperature black oxidation is appropriate for components with high accuracy, and cool black oxidation is utilized for applications with minimal economic and process requirements.