Parts are loaded into a sealed ultra-insulated chamber where a computer controls the introduction of liquid nitrogen (LN2) at a rate that allows cooling the chamber to a rate of 1 degree per minute.  The cooling is achieved by evaporation, not immersing parts in the LN2, it is a dry process.   This slow rate prevents any dimensional distortion or temperature induced stress.  Once at -300F below zero, this temperature is maintained for a period of 15 to 25 hours.  During this time, the microstructure grain change occurs, changing austenitic grain (soft) to martensitic grain (harder).  Some say this process “realigns” the grain structure or makes the grain structure smaller.  In truth, both are happening with this microstructure grain change.  

Once this dwell at temperature has been accomplished, the processor then starts to heat the chamber, once again at 1 degree per minute, to a temperature of 300F above zero.  The chamber is held at this temperature for several hours, this temper cycle is what finalizes the grain structure conversion.

The end result is a base material that is not appreciably harder but has greater durability and wear resistance.  Since this is a thru the grain structure transformation, if the material wears or requires sharpening, the treatment is not removed and remains effective throughout the life of the component.