Blue is a kind of material protection technology, which heats steel in air or directly immerses it in concentrated oxidation solution to produce extremely thin oxide film on its surface, also known as blackening.
There are two common methods for blackening treatment: traditional alkaline heating blackening and later room temperature blackening. However, the blackening process at room temperature is not very effective for low carbon steel. There is another difference between basic blackening and secondary blackening.
The main components of blackening liquid are sodium hydroxide and sodium nitrite. When blackening, the temperature difference is not big, and a good surface can be obtained between 135- 155℃, but it takes a little long.
principle
In order to improve the anti-rust ability of steel parts, the surface of steel parts is oxidized into dense and smooth ferroferric oxide with strong oxidant. This thin layer of ferroferric oxide can effectively protect the inside of steel parts from oxidation. Ferroferric oxide oxidized at high temperature (about 550℃) is sky blue, so it is called bluing treatment.
Ferroferric oxide formed at low temperature (about 350℃) is dark black, so it is called blackening treatment. In weapons manufacturing, bluing treatment is commonly used; In industrial production, blackening treatment is widely used.
Whether the steel surface can be oxidized into dense and smooth ferroferric oxide depends on the choice of a strong oxidant. The strong oxidant consists of sodium hydroxide, sodium nitrite and trisodium phosphate. When it turns blue, treat steel parts with their melts; When blackening, treat steel parts with their aqueous solution.