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Cryogenic Treatment - Is It For You?
(December 01, 2016)
Articles describing Cryogenic Treatment.
http://www.customdesignperformance.com/ecatalog/cryo.html
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!
http://www.300below.com/motorsports/
CRYOGENICALLY TREATED RACING ENGINES AND PARTS PERFORM BETTER UNDER HIGH STRESS CONDITIONS
300 Below Inc. is changing the face of Motorsports by applying the deep cryogenic tempering and treatment process to increases engine performance, reduce wear and improve longevity. This one-time irreversible treatment improves the entire structure, not just the surface, and gives your engine the stability once found only in seasoned engines
Our process increases engine performance and engine lifespan through rearrangement of an engine’s molecular structure after utilizing our proprietary computer-controlled freezing process. Cryogenic tempering occurs after creating a significant increase in abrasive wear resistance and overall durability for an engine, resulting in improved tensile strength, toughness and stability within the metals. This helps release internal residual stresses, which were created when the engine was manufactured. Overall, our clients in the motorsports industry use cryogenic processing for stress relief, dimensional stabilization, increased wear resistance and durability for their engines and other high performance parts associated with the chassis. We help to create faster engines and offer our clients a significant competitive edge when racing against competitors with non-treated engines.
In short, the racing teams who have not yet discovered our cryogenic process find themselves at a significant disadvantage when racing against our teams who employ superior research and technology in their day-to-day operations. If you’ve seen racing on TV, it’s likely you’ve seen cryogenics in action. Racing teams in NASCAR, Indy 500, Tractor Pulling, and several other circuits call on 300 Below to give them the upper hand. Through our current non-disclosure agreements, we pledge to maintain secrecy for our clients and do not actively pursue their direct competition. If approached by a competitor, however, we maintain a policy that we will not discriminate against additional business. In keeping with this practice, and in the spirit of good sportsmanship, we will not reveal any secrets learned while working with past teams that could hurt their ongoing research and development efforts in racing.
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