What Does Deep Cryogenic Treatment Do?
Deep Cryogenic Treatment (DCT) is not:
DCT is not a coating.
DCT is not a substitute for heat-treating.
DCT not a hardening process.
DCT is not a fix for bad heat-treating.
DCT is not a cure all.
DCT is a thermal process that
DCT affects the entire volume of the part. Cryogenic processing does not go away when the part is machined or sharpened. It affects every atom of the structure. This process works to enhance plating and many coatings
:Used in conjunction with proper heat-treating, it produces a better, more stable part.
: Although it will cause retained austenite to transform to martensite, so will cold treating at -140ºF. It will not cure the other ills of bad heat treat.
Cryogenic processing makes changes to the crystal structure of materials. The major results of these changes are to enhance the abrasion resistance and fatigue resistance of the materials. The changes we know about are:
- Change of Retained Austenite to Martensite in Hardened Steels.
- Reduction of Residual Stress.
- Precipitation of Fine Eta Carbides in Steel.
- Reduction in point defects.
- Re distribution of alloying elements.
- Making the crystal lattice structure more orderly.
The change of retained austenite to martensite happens in steel and cast iron only. It is the same with the precipitation of fine carbides. Many metallurgists will tell you outright that changing austenite to martensite is the only thing that cryogenic processing does. That is very wrong.
We know that there must be more than this. Why? Because cryogenic processing has been shown to work on materials other than steel. Brake rotors are made of cast iron that is pearlitic in structure. There is no retained austenite but scientific tests show an increase in life of up to seven times. Most metals will respond to cryogenic processing. Some plastics do. There is a lot of evidence that crystals such as diamonds, cubic boron nitride, and aluminum oxide also respond.
The Austenite to Martensite Myths
Let's tackle the myths that the only thing DCT can do is convert retained austenite to martensite and that is why DCT is effective. Yes, cold temperatures will cause retained austenite to convert to martensite in steel and cast irons that have been hardened. And that will cause those metals to harden somewhat and become more wear resistant. What are austenite and martensite? They are two of the ways that carbon and iron relate to themselves in steel and cast iron (which are collectively referred to a ferrous metals). There are other ways such as bainite, pearlite, and cementite. (Don't worry about those.) The key here is that DCT can increase wear resistance in other metals and in ferrous metals that have no austenite or martensite. Brake rotors exhibit tremendous wear resistance increases from DCT. Their structure is pearlitic, there is no martensite or austenite.
Some Basic Metallurgy
Metals are crystalline in structure. That means that the atoms of the metal line up in an orderly fashion. A theoretical crystal structure is pictured at the left. Notice how perfect it is. This rarely happens in the real world.
A real world crystal structure is pictured at the right. The yellow dots are the atoms. Note that the alignment of all the atoms is not perfect. There are discontinuities and changes in spacing. A theory proposed by Dr. Mark Eberhardt at the Colorado School of Mines states that there is a discreet distance between atoms where the energy in the metallic bond is minimum.
We know that when we reduce the temperature of an object the atoms in the object come closer together and we take energy out of the object. We have a theory that when we warm the object back up that some of the misplaced atoms in the crystal structure relocate to the proper spacing. This produces a more perfect crystal we’ve discussed this theory with metallurgists and scientists. Nobody has said we are crazy yet.
Other effects are that as you cool crystals down point defects such as vacancies, substitutional impurities, and interstitial atoms tend to be driven out. There are equations as to the concentrations that will be left. The other problem is if you cool the matrix too quickly these defects tend to stay. This is all taught in primary metallurgical courses.
Still other effects are the formation of compounds such as carbides as the carbide forming elements such as cobalt, chrome, titanium and such are moved around in the matrix by the cold.
The point is that there is a lot of things happening in a 'solid' piece of metal. Some of it can be driven by lowering the temperature. If you don't believe it take an elementary metallurgy course.
Picture aboveis courtesy of and used with the permission of Birmingham University’s Nonascale Physics Research Lab. We wish to thank Professor Richard Palmer for allowing us the use of the picture.
Their explanation for the picture is:
Copyright, Nanoscale Physics
University of Birmingham
“Atomic Love, in three Dimensions
Made of pure palladium, is only 8 nanometers in size; you can even see the atoms. Clusters of palladium bonded together on the surface of carbon and spontaneously arranged themselves into the world’s smallest heart.”