Why do some mechanical parts go through blackening process instead of heat treatment?

The traditional blackening treatment is oil quenching after the workpiece is heated, so that an oxide film, namely ferroferric oxide, is formed on the metal surface, thereby preventing the internal oxidation of the metal and achieving the purpose of rust prevention. ? Heat treatment is troublesome and difficult to complete.

In recent years, a new blackening process has been developed, which uses oxidizing chemicals such as phosphate to oxidize and blacken the surface of the workpiece, and its characteristic is that it does not need high temperature heating. Generally speaking, this is the temperature at which water boils. This method is called boiling black. Most of them refer to quenching and tempering processes, including heat treatment processes such as quenching and tempering and isothermal quenching; Normalization is sometimes used as the final heat treatment process to refine grains and adjust the internal structure of steel.

Heat treatment refers to the metal hot working process in which materials are heated, insulated and cooled in solid state to obtain the expected structure and properties.