Blackening
What is the blackening of steel parts in chemical surface treatment?
In chemical surface treatment, blackening of steel parts is a method of oxidizing the surface of steel parts to make them appear black or dark gray. This surface treatment method is usually called steel oxidation black, which can improve the decorative and corrosion resistance of the steel surface, as well as provide some protection.
There are generally a variety of oxidizers for steel blackening, such as copper chloride, nitric acid, alkaline oxidizing solution, etc. Different oxidizers can produce different effects and colors, and different treatment methods and process parameters can be selected as needed.
In conclusion, blackening of steel parts is a surface treatment method that forms a black oxide film by chemical reaction between the surface of steel parts and oxidizing agents. It can improve the decorative and corrosion resistance of the surface of steel parts, and is often used to make decorative items, handicrafts and mechanical parts, etc.
Applicable blackened materials
| 45 Steel | 40Cr | Cr12 |
| 3Cr13 | GCr15 | Q235 (A3 steel) |
| Spring steel-65Mn | Die steel-SKD11 |
Steps for blackening of steel parts?
The following are the general operation steps for blackening of steel parts.
Pretreatment: cleaning and removing surface dirt and oxide layer. Mechanical cleaning, acid washing, electrolytic descaling can be used. If the surface is not clean, the effect of oxidation blackening will become poor.
Oxidation treatment: The pretreated steel parts are put into oxidizing solution for oxidation treatment. The commonly used oxidizing agents are nitric acid, copper chloride, copper acid, hydrogen chloride, etc. The oxidizing solution can be saturated solution or dilute solution.
Cleaning: Remove the treated steel parts from the oxidizing solution and rinse them off with water. It is better to carry out multiple cleaning to ensure clean cleaning.
Neutralization: The steel parts are placed in a neutralizing solution to remove the oxidant residue and prevent the oxide film from growing. The neutralizing solution is usually alkaline.
Re-cleaning: The treated steel parts are removed from the neutralizing solution and rinsed with water.
Drying: The steel parts are dried or dried using a dryer to ensure that the surface is free of moisture.
It should be noted that during the operation, attention should be paid to safety, such as wearing personal protective equipment like protective gloves and goggles, to avoid splashing the oxidizing solution on the body or skin. Meanwhile, the process parameters should be strictly controlled to avoid quality problems.
What are the common problems and solutions for the blackening of steel parts?
The following common problems may occur in the process of blackening of steel parts.
Uneven blackening effect: spots or inconsistent colors appear on the surface of steel parts. This may be due to uneven concentration of some components in the oxidizing solution or uneven treatment of the steel surface. The solution is to strengthen the mixing of the oxidizing solution or to treat the steel parts several times to ensure the surface color is uniform.
Improper color: The color of the steel surface after blackening is different from the required color. This may be due to incorrect composition or concentration in the oxidizing solution, or incorrect treatment time or temperature. The solution is to adjust the composition or concentration of the oxidizing solution and strictly control the treatment time and temperature.
Poor rust prevention performance: After the surface of steel parts is blackened, there may be poor rust prevention performance. This may be due to the fact that the oxide or residual oxidizing solution is not completely removed from the surface of the steel parts during the treatment process, resulting in poor quality of the oxide film. The solution is to strengthen the cleaning and neutralization treatment during the treatment process to ensure that the surface of the steel parts is dry and clean.
Cracks on the metal surface: This may be due to high processing temperature or long processing time, resulting in deformation or cracks on the steel surface. The solution is to reduce the treatment temperature or shorten the treatment time and strictly control the treatment conditions.
It should be noted that during the operation, attention should be paid to safety, such as wearing personal protective equipment like protective gloves and goggles to avoid splashing the oxidizing liquid on the body or skin. Meanwhile, the process parameters should be strictly controlled to avoid quality problems.
