Steel burnishing

2024 Author: Howard Calhoun | [email protected]. Last modified: 2023-12-17 10:16

Steel burnishing is a chemical process used to obtain a thin protective film of Fe3O4 iron oxides 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 "blue" in the general case, regardless of color - "oxidation". The resulting film passivates the surface and protects the part from atmospheric corrosion and other aggressive environments.

Before bluing 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. Pickling is needed to remove all excess oxides from the surface, leaving bare metal.

The easiest way is to burnish 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 stain,and do not overheat the part, as it can deform or release. Many people make the mistake of dipping a heated part into oil, this is wrong. It is necessary just the opposite: first smear, then heat. Any oil is used, from sunflower to transmission or machine oil. Such burnishing of steel has a low coating strength. It is suitable only for decorative and protective purposes.

Bluing steel using ferrous sulfate, ferric chloride and nitric acid

To do this, you need to dissolve 15 g of iron, 30 g of vitriol and 10 g of acid per liter of water. A rusty coating will form on the product dipped into the solution, it must be periodically removed with a brush and continued to be dipped until the desired color of the oxide film is obtained. Now almost every city has a shop selling chemicals, so getting them is relatively easy.

Burning of steel using chromic (potassium bichromate). To do this, 200 grams of chrompic is diluted per liter of water and the item is immersed in the solution for 20-30 minutes. After being removed from the solution, it must be dried at a high temperature (in an oven or over coals). Repeat the process until a uniform blue-black color is obtained. Then wipe the part with an oiled rag. Chrompeak is a very common reagent used in the leather industry.

For bluing gun barrels, mix with heating 1 weight part of antimony trichloride with 3 parts of olive oil. 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, bluing steel at home is a completely feasible and uncomplicated process. It can be applied to any steel products in cases where other methods of corrosion protection, such as painting, are not applicable.