Q. What happens during deep cryogenic treatment?
A. During the process of deep cryogenic treatment austenite is transformed into martensite, which is then tempered to change into
tempered martensite. In addition, small complex carbides called eta carbides are precipitated throughout. This greatly reduces residual stress and promotes "micro-smoothing" of the surface.
Q. Does using liquid Nitrogen cause any type of thermal shock?
A. No. We use dry Nitrogen to bring the parts down to roughly -290°F (-180°C). It isn’t until the parts are fully chilled with the dry
gas that we allow the liquid (wet) process to take place. That protects the parts from thermal shock completely. The ramp down to -290°F (-180°C) using gas is also controlled for a slow easy
transition to -290°F (-180°C). Nothing in our process ever sees an abrupt thermal shock.
Q. Will my materials become more brittle? Will the material become damaged?
A. No. The strength of the material is actually increased after the process. The molecular structure is "filled in" increasing the
strength of the material by up to 400%! Also, the material will not be damaged and it will retain its shape.
Q. Why do you use the dual process (gas and liquid), as opposed to just gas?
A. We use a combination of dry and wet processing which produces the following:
1) Total uniform transformation. Temperature in parts in our processor does not vary a
degree during the soak. Compared to using a dry process only which is completely unpredictable and can vary up to 20 degrees!. Which in turn relates to poor transformation in portions of the load.
Because of this, many processor manufacturers put fans in their units, but there is not one of them that would be effective to mix the gas at -300°F (-184°C). Totally impossible in an empty chamber
and loading it just makes it worse.
2) Dry processing cannot get to and maintain -320°F (-196°C). Liquid nitrogen is -320°F
(-196°C) in liquid form and right at the flash point as it evaporates. Gas processing struggles to attain and maintain -300°F (-184°C) and often slips below -260°F (-162°C), this being the critical
temperature point junction in performing transition.
3) By using the wet process as National Cryogenics does, we are assured of zero moisture
problems. Water cannot exist in a liquid nitrogen atmosphere. Moisture is completely driven off. Processing with dry gas as nearly all our competitors do, create terrible moisture problems and with
it comes rusting and oxidation. Using liberal lubrication on the parts keeps them from rusting but when tempered causes a blue noxious smoke which is bad for your lungs. Plus the parts get this dry
brown crusted coating from the burnt oil. Ugly stuff and customers don’t want their parts covered with burnt oil.
Q. What exactly does soak mean, since it is used in both cryogenic and heat treating terms?
A. Soak does not refer to being in liquid as one would think. It means “when a metal is soaked at a given temperature”. Soak, in our
instance, would mean from the time the material is first immersed in LN2 until the time the last drop of LN2 has flashed off the bottom of the tank.
Q. Can I treat bearings without worrying about anything?
A. No. If the bearings are already packed with grease, you must remove the grease before cryogenically processing as it may harden the
grease. You should also make sure to remove grease for tempering (unless high temperature grease is used). Also you do not want to process a high grade bearing. A grade 5 or 7 bearing is selected for
tight tolerance and the grain growth may bind the bearing up and prevent turning if there happens to be a large degree of retained austenite. Standard low grade bearings do very