Steel burnishing is a chemical process used to produce a thin protective film of iron oxides Fe3O4 on the surface of a steel part. The name was given due to the characteristic color of the part after processing (blue-black, raven wing), it also has the names “blackening” or “blueing” in the general case, regardless of the color - “oxidation”. The resulting film passivates the surface and protects the part from atmospheric corrosion and other aggressive environments.
Before burnishing steel, the part is pre-prepared, mechanically cleaned of rust, polished, degreased and pickled in an acid solution. You can degrease with a solvent or alcohol. Etching is needed to remove all excess oxides from the surface and leave bare metal.
The easiest way is to burn steel with oil. There are different methods, but the meaning is simple: a thin layer of oil is applied to the part, after which it must be heated to 300-350 ° C. Burning oil leaves an oxide film on the surface. From the first time, a uniform coating is not obtained, so the process is repeated until the desired result is achieved. It is important to achieve uniform heating, otherwise the film will go stained, and not overheat the part, since it can deform or release. Many make a mistake and lower the heated part in oil, this is wrong. It is necessary exactly the opposite: first smear, then warm. Any oil is used, from sunflower to transmission or machine. Such steel burnishing has a low coating strength. It is suitable only for decorative and protective purposes.
Steel Burning Using
Iron Vitriol, Iron Chloride, and Nitric Acid
For this, 15 g of iron, 30 g of vitriol and 10 g of acid must be dissolved per liter of water. A rusty coating will form on the product dropped into the solution, it must be periodically removed with a brush and continued to dip until the desired color of the oxide film is obtained. Now in almost every city there is a store selling chemical reagents, so getting them is relatively easy.
Steel burnishing using chrompeak (potassium dichromate). For this, 200 grams of chrompeak are diluted per liter of water and the component is immersed in the solution for 20-30 minutes. After extraction from the solution, it must be dried at high temperature (in the oven or over charcoal). Repeat the process until a uniform blue-black color is obtained. Then wipe the part with oiled rags. Chrompeak is a very common reagent; it is used in the leather industry.
To burn gun trunks, 1 part by weight of antimony trichloride is mixed with 3 parts of olive oil when heated. Then the mixture is applied to the part and left for a day. The process is repeated 10-12 times, after which the barrel is washed, dried and polished. The color is greenish brown.
As can be seen from the above, steel burnishing at home is a completely feasible and uncomplicated process. It can be used for any steel products in cases where other
corrosion protection methods
, such as painting, are not applicable.