Curved springs are widely used in daily life. To prevent rusting or damage to the spring, we should use chemical reactions to form a dense protective film on the surface of the spring. For the protection of spring surfaces, we usually use oxidation treatment and phosphating treatment. So how is oxidation treatment carried out?
Oxidation treatment and phosphating treatment have low cost and high production efficiency. Generally, manufacturers use oxidation treatment as an anti-corrosion treatment. The oxidation treatment of steel is also known as bluing, blackening, or boiling black. After oxidation treatment, protective magnetic iron oxide is generated on the surface of the spring, which is generally blue or black in color, and sometimes black brown in color. Its color is determined by the surface state of the spring, the chemical composition of the spring material, and the oxidation treatment process.

The methods of oxidation treatment include salty oxidation, alkali free oxidation, and electrolytic oxidation. The alkaline oxidation method is commonly used. The alkaline oxidation method involves immersing a spring in a sodium hydroxide solution containing an oxidizing agent at a temperature of around 140 ° C for a certain period of time. The oxidizing agent and sodium hydroxide react with iron to produce sodium ferrocyanide and sodium ferrite, which then react with each other to produce magnetic iron oxide. The thickness of the oxide film layer is about 0.6~2 μ m. Although oxide film can improve the corrosion resistance of springs, its protective ability is poor due to its thin film and pores, and it can only be used for springs working in media with low corrosiveness. The level of its anti-corrosion performance depends on the density and thickness of the oxide film, which in turn determines factors such as the concentration of sodium hydroxide and oxidant used in the oxidation treatment, as well as the temperature of the solution.

In order to improve the corrosion resistance and lubrication ability of the oxide film, it is necessary to strengthen the treatment before and after oxidation treatment. Before oxidation treatment, the surface of the spring must be thoroughly cleaned of rust, oxide scale, oil stains, salt residue from heat treatment, and surface contact layer. After oxidation treatment, the spring is usually filled with soap solution or dichromate, then washed, blown dry or dried with running warm water, and finally replaced with rust proof oil with a water film or soaked with mechanical oil at a certain temperature for oil treatment. Oxidation treatment can corrode the surface grain boundaries of certain hot-rolled spring materials, which can reduce fatigue strength to a certain extent. Therefore, caution should be taken when using oxidation treatment.
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