Process media in vacuum heat treatment. Liquid quenchants and stop-off paints – properties and application
Quenching is a very important part of the heat treatment process and its success. The heat transfer characteristics of the quenchant strongly influence the parts’ microstructure after heat treatment, the resulting mechanical properties of the quenched component but also the amount of internal stresses and distortion.
According to DIN EN 10052 quenching is defined as „Cooling a part faster than with still air“. The quenching media commonly used for heat treatment of steel and aluminium parts are water, brine, aqueous polymer solutions, quenching oils, molten salts and pressurized gases such as air, nitrogen, hydrogen and helium.
In regards to vacuum heat treatment processes the choice of the quenchant and also the choice of stop-off paint, its proper use and adaptation to the process is mandatory to make sure that the heat treated part meets the well defined requirements for safe, consistent and longtime functioning.
In this paper the main liquid quenching media and stop-off paints for vacuum heat treatment processes are presented with their physical and chemical properties and furhermore their typical applications in the car manufacturing industries.
Finally an outlook on the future development of liquid quenchants and quenching technologies is given.