Cryogenic Treatment - Is It For You?
First, Deep Cryogenic Treatment is an extended process that very gradually "freezes" or removes heat from the
items being treated. Typically, the parts are brought down to 300 degrees below zero (F) in a very slow ramp
and then held at that temperature for an extended dwell (24 hours), before being returned to ambient temperature.
The last step is a post temper to +300/ +350 degrees F. The entire process takes 48 to 72 hours.
The technology has its roots in research conducted by NASA in the 60's as early space engineers tried to
understand what happened to metals subject to the extreme temperatures of space.
Having said that, Swiss watchmakers and German machinists recognized from experience that metal properties
were enhanced when allowed to "season" over a cold winter - sometimes packed in snow and placed in caves.
The metals were stabilized and less prone to distortion when machined, enabling critical tolerances in precision
components to be held more tightly.
Today's cryogenic treatment is a further advancement of this metals-aging "secret" practiced by these old craftsmen.
Based on before and after analysis, we know that deep cryogenic treatment provides for three documented mechanisms
that transforms metals. First, in heat treated steels, we know that retained austenite is transformed to
martensite, creating a more uniform grain structure and homogenous steel. This provides for a tougher and more
durable material as the voids and weaknesses of an irregular grain (or crystal) structure are eliminated.
It is also believed that it is this mechanism that provides for better thermal properties -- better heat
dissipation -- in cryogenically treated steels. Additionally, it is this mechanism that leads to friction
reducing qualities in metals, especially when final machining, polishing, grinding and honing are done AFTER
cryotreatment. It is also why cryogenically treated steels show more uniform hardness than non-treated steels.
(It is technically inaccurate to say that cryo treatment increases hardness. Testing, before and after, shows
little - if any - change to hardness. What has been documented, though, is that hardness is more uniform across
the part.)
The second mechanism relates to modification in the carbon microstructure of cryogenically treated steels.
Before and after micrographs show the formation of carbides within the steels. The technical description of this
is called "the precipitation of eta-carbides". At the National meeting of the Heat Treating Society of ASM held
in Pittsburgh this fall, some new dramatic SEM images were presented by Zbigiew Zurecki, a metallurgist from Air
Products showing the vast increase in such carbides after cryogenic treatment. This follows on earlier work
documenting the mechanism by Dr. Randall Barron of Louisiana Tech and a team of Japanese researchers who published
a paper for ISIJ in the mid 1990's.
This mechanism is what contributes to the dramatic increase in wear resistance of cryogenically treated steels.
Steel is, at its most basic formulation, iron (Fe), a metal, and carbon (C), a non-metal. The carbon is dissolved
chemically into the iron and is what provides wear resistance. In other words, high carbon content equates to
high wear resistance. (The most amount of carbon that can be dissolved chemically is about 6% and a "high carbon"
tool steel like A2 has about 1% carbon.) So just a little bit of carbon (diamond) goes a long way in promoting
wear resistance.
Hence, this tweaking to the carbon microstructure, through the precipitation of eta-carbides, has dramatic
impact on the wear resistance of cryogenically treated steels and cast irons (brake rotors, for instance. Note
that cast irons - rotors - are even higher in carbon content, 2% to 3%, for instance). That's why parts that
are cryogenically treated typically wear 2X to 3X longer than untreated steels.
The third mechanism relates to stress relief. It is based on Einstein's (and Bose's) observation that matter is
at its most relaxed state when it has the least amount of molecular activity of kinetic energy. When we freeze
the components, we are actually removing heat, or reducing the molecular activity in the metal. This relaxes
the metal and reduces residual stresses in the metal. It is these stresses that propagate when the part is put
into service and causes failure due to fatigue. Hence, by reducing residual stresses, you greatly reduce failure
due to cracking or what people term "metal fatigue".
This “myriad of mechanisms” brings practical benefit to a variety of engine components and other automotive parts.
With better thermal properties and reduced stresses, distortion of parts is greatly reduced or eliminated.
Therefore, "blow by" associated with distortion of pistons and cylinder walls is greatly reduced. In addition,
blocks that are honed after cryogenic treatment will enjoy the benefit of "microsmoothing" from the more uniform
grain structure. This means less drag and a reduced coefficient of friction. So by cryo-treating the pistons and
block BEFORE final machining, (hone, grind and/or polish,) you will create more HP and torque (as measured on a
DYNO) with a cryo-treated engine than the non-treated engine. (Typically up to 5% more).
After cryogenic treatment, brake rotors do not distort (warp or twist) and therefore brake fade and chatter are
eliminated. In addition, rotors typically perform in service at least twice as long and more typically three
times longer.
Cranks and pistons can be machined after treatment to a more critical tolerance because part walk or creep is
greatly reduced. That is because residual stresses are impacted during machining and their removal actually
causes the part to "walk" or "creep". In addition, they will wear much better and hold their desired tolerance
much longer due to the enhanced wear resistance properties. Likewise, gears benefit because of their unique
fabrication.
Gears are subject to great torque stress requiring ductility internally, and high wear demands on the surface
resulting from the steel-on-steel meshing of the components. Add to that their complex geometry and you have a
sophisticated - and complex- metallurgical environment. Many gears are case hardened to provide a high carbon
content on the skin to promote wear resistance while not inducing brittleness (caused by higher carbon content)
in their interior. Their shape, coupled with the associated machining, produces a stress rich environment that
is easily exploited by the action of the gear box. So you can see how cryogenic treatment is beneficial to gears.
Stresses are relieved, reducing failures associated with their propagation into cracks, while carbon
microstructure is enhanced to provide a more wear resistant outer layer. A real win-win application!
Cost
We at Custom Design Performance price the individual components of an engine affordably. Our individual
component prices for our Nitrofreeze(TM) cryogenic Treatment ranges from $2.50 per spark plug , $10 for a
connecting rod or piston w/ rings, to $600 for an entire engine (including block). (A V8 block alone is $300.)
So you can see that is quite affordable. Racers are amazed to see how parts are almost like new when they break
their engines down after a season of racing.
Also, engines and transmissions should be broken down prior to treatment. I do not recommend treating a
transmission case, although it can be done.
Aluminum parts benefit also, certainly from stress relief, as well as other enhancements from the mechanical
compression they see from the extended freeze at -300 F.
Turbo compressor and exhaust turbine housings respond very well to treatment.
Please call Ken or Tim at Custom Design Performance, 860-228-3449, to see how this could benefit your race program.
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