Molten neutral salt, Durferrit GS540/R2 by Degussa, covers the works throughout heating works up and protects against decarburization and scaling. Taking out the works out of salt, thin film of salt is covering surface of work pieces, pre-venting decarburization and scaling. The film is easily pealed out in quenching media not disturbing rapid cooling. As the heat mass of the salt bath is huge, work pieces can be heated and equalized 3 times as quick as other furnace, and suitable for both small and mass production. The salt bath is daily quality controlled by deslugging and checking decarburization using some high carbon steel wire.
Through quenching, both thermal and transformation stresses arise by temperature difference between surface and core of complicated work piece. Those stresses might cause crack or distortion of work piece.
In order to prevent these ploblems, the work piece has to stop cooling at just above the transformation start temperature (MS), and then slow cooled. This process is called as "time quenching".
	Explanation of time quenching
Austempering
Astempering is the special hardening process by  which the work pieces are quenched into hot  salt  bath and  hold  for  hours to transform(isothermal transform) in order to conform Bainite structure. The Bainite structure has excellent high ductility and toughness compares with those of tempered Martensite by conventional quenching and tempering. The table 1 below show an example  of   mechanical   properties  obtained   by  three   different  process.  This  process is advantageous for minimizing deformation and dimentional changes by hardening.
Table 1. Mechanical properties by 3 different hardening process
The relationship between hardness and austempering temperature in case of SK5.