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[Applied Cryogenics]

 

What is Cryogenic Treatment?

 

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[What can you expect?]

Why ACI?

What can you expect?

 

Stable, stress relieved materials with improved wear resistance. This can be extremely beneficial in many areas, for example in the stamping die and mould industry. If dies or moulds are processed after heat treatment but before finish grinding assembly (to avoid growth interference or tolerance violation), and then, once in production, given a quick cryogenic re-processing every 3-4 months or so, it will relieve any long-term build up of compressive stresses, and as a result tools and moulds will last much longer than untreated tools, with a 400% increase in life being fairly typical.

Aluminium and non-ferrous metals cryo-treated not only gain immense stability under the most demanding machining work, but they also gain better machinability after processing, which a real aid in tight tolerance work.

Cold processes have been used for years to stabilize fixtures and tooling. The process will relieve stresses and that will help to machine parts to the proper size and shape. Cryogenic processing establishes a very stable piece of metal that remains distortion free. The process will also stabilize some plastics.

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.
In general, the process seems to refine the crystal structure of metals and crystalline plastics. Although there has not been definitive research on the subject, the theory is that it crystal structures are not perfect. Some research shows that there are around 10 vacancies per cubic inch of metal in the crystal lattice. Also, some atoms are not ideally located in respect to their nearest neighbors. We believe that cryogenic processing makes the crystal more perfect and therefore stronger.

In Ferrous metals, it converts retained austenite to martensite and promotes the precipitation of very fine carbides.


It has been known for many years that cold will cause retained austenite to change to martensite. This can be verified through publications such as Machinery's Handbook, ASM's Metals Handbook and more. Even the best heat treating facility will leave somewhere between ten and twenty percent retained austenite in ferrous metals. Because austenite and martensite have different size crystal structures, there will be stresses built in to the crystal structure where the two co-exist. Cryogenic processing eliminates these stresses by converting most of the retained austenite to martensite. This also creates a possible problem. If there is a lot of retained austenite in a part, the part will grow due to the transformation. This is because the austenitic crystals are about 4% smaller than the martensitic crystals due to their different crystal structure.

 

 

 

 

The process also promotes the precipitation of small carbide particles in tool steels and steels with proper alloying metals. A study in Rumania found the process increased the countable small carbides from 33,000 per mm3 to 80,000 per mm3. The fine carbides act as hard areas with a low coefficient of friction in the metal that greatly adds to the wear resistance of the metals. A Japanese study (Role of Eta-carbide Precipitations in the Wear Resistance Improvements of Fe-12Cr-MO-V-1.4C Tool Steel by Cryogenic Treatment; Meng, Tagashira, et al, 1993) concludes the precipitation of fine carbides has more influence on the wear resistance increase than does the removal of the retained austenite.


Note that the hardness of a piece of metal becomes more even during the process. When multiple hardness readings are taken before and after the process, the standard deviation of those readings will drop a significant amount.

 

Improvement in wear resistance after cryogenic treatment

 

The table below indicates improvement in wear resistance in various steels. These tests carried out by Dr. Randall F. Barron at the University of Lousiana, USA, show significant improvement in wear characteristics of certain metals.

 

D-2 High Carbon / Chromium Die Steel

817%

S-7 Silicon Tool Steel

503%

52100 Standard Steel

420%

0-1 Oil Hardening Cold Work Die Steel

418%

A-10 Graphite Tool Steel

264%

M-1 Molybdenum High Speed Steel

225%

H-13 Chromium / Moly Hot Die Steel

209%

M-2 Tungsten / Moly High Speed Steel

203%

T-1 Tungsten High Speed Tool Steel

176%

CPM-10V Alloy Steel

131%

P-20 Mold Steel

130%

 

 

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