Q. What happens during deep cryogenic tempering?
A. During the process of deep cryogenic tempering austenite is transformed into martensite, which is then tempered to change into tempered martensite. In addition, small complex carbides called eta carbides are precipitated out. 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 -250°F (-157°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 -250°F (-157°C) using gas is also controlled for a slow easy transition to -250°F (-157°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. 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 Cryotron does, we are assured of zero moisture problems. Water cannot exist in a liquid nitrogen atmosphere. Water is completely driven off. Processing with dry gas as nearly all our competitors do, create terrible water 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 will plasticize 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 well.
Contact us: Info at cryotron.com or phone us (Edmonton, AB) 1-780-405-2515 or (Houston, TX) 1-832-690-2717.